Microstructural evolution and mechanical properties in steels treated by quenching & partitioning with the partitioning stage in teh intercritical range.

Ph.D. Thesis
MICROSTRUCTURAL EVOLUTION AND
MECHANICAL PROPERTIES IN STEELS
TREATED BY QUENCHING & PARTITIONING
WITH THE PARTITIONING STAGE IN THE
INTERCRITICAL RANGE
Au ho :
Eide Del Molino Du an
Bilbao, May 2022
Ad iso s:
Ja ie Jesús González Ma ínez
Ma ibel A ibas Telle ía
(cc)2022 EIDER DEL MOLINO DURAN (cc by 4.0)
Ph.D. Thesis
MICROSTRUCTURAL EVOLUTION AND
MECHANICAL PROPERTIES IN STEELS
TREATED BY QUENCHING & PARTITIONING
WITH THE PARTITIONING STAGE IN THE
INTERCRITICAL RANGE
Au ho :
Eide Del Molino Du an
Bilbao, May 2022
Ad iso s:
Ja ie Jesús González Ma ínez
Ma ibel A ibas Telle ía
Science makes people each sel lessly
o u h and objec i i y;
i eaches people o accep eali y,
wi h wonde and admi a ion,
no o men ion he deep awe and joy
ha he na u al o de o hings
b ings o he ue scien is .
Lise Mei ne

ACKNOWLEDGMENTS
Tesia idaz en hasi nin zen momen uan ez nuen inondik ino a espe o a alik zailene akoa
(zailena ez bada) hau izango zenik. Asko izan bai za e e bide luze hone an, animoak eman
e a nigan sinis u izan duzuenok e a ez nuke ino bidean u zi nahi.
En p ime luga , quie o ag adece a Tecnalia el habe me dado la opo unidad de ealiza la
esis. En especial, a mi di ec o a de esis de Tecnalia, Ma ibel A ibas, po habe pues o odo
u empeño en hace que es e iaje me ue a lo más sencillo y en iquecedo posible. Soy
incapaz de imagina me una pe sona más idónea pa a ealiza ese desempeño. Po
supues o, g acias a el es o de los compañe os y compañe as de abajo, comidas, ca és,
e c., po habe me acogido desde el p ime día como una más y habe hecho que es os años
se pasen olando. Se me hace imposible menciona os a odos y odas indi idualmen e, pe o
sí que me gus a ía da les las g acias en pa icula a Iñaki e Igo , po odo el iempo dedicado
a apoya me en el desa ollo de g an pa e expe imen al de la esis.
También quie o ag adece a la UPV/EHU la opo unidad de ealiza es a esis. A mi di ec o ,
el p o eso Ja ie Jesús González, po u aseso amien o en odos los momen os en los que
lo he necesi ado y po habe me apo ado an a expe iencia. Tampoco me gus a ía deja de
lado al p o eso José Tomás San José, po habe me o ecido u ayuda de una o ma
o almen e desin e esada desde que comencé mis es udios de Más e y has a el día de hoy.
¡Muchas g acias a los dos!
I would like o ex end my g a i ude o he Ad anced S eel P ocessing and P oduc s Resea ch
Cen e (ASPPRC) a Colo ado School o Mines. Thanks o Casey Gilliams o he ime
sac i iced, wi hou which pa o his hesis would no ha e been possible. Thanks also o
P o . John G. Spee and P o . Emmanuel De Moo because, al hough he pandemic si ua ion
has no allowed me o mee you in pe son, i has been a ue hono o discuss he esul s o
my hesis wi h expe s like you.
I would also like o hank D . A em A laza o , om A celo Mi al Maiziè es, o he supply o
he medium Mn s eels employed in his hesis and o sha ing you knowledge wi h me.
Po o o lado, ya que es a esis se ha desa ollado en el ma co de a ios p oyec os de
in es igación, que ía ala ga mis ag adecimien os a la inanciación ecibida en el p og ama
RFCS, de la Comisión Eu opea, pa a la ejecución del p oyec o HIGHQP (g an numbe :
709855) y el p og ama HAZITEK, del Gobie no Vasco, pa a la ejecución del p oyec o
CHALET (expedien e: ZL-2020/00434).
Eske ik asko ni e kuad ilako lagunei, niga ik a du a zeaga ik e a ni e ausen zia (ba ez e e
azkenengo hilabe e haue akoa) ule zeaga ik. Zuek gabe bide hau ez li za eke be dina
izango. Mila eske unibe si a eko lagunei e e, ze en, nahiz e a sak i ika u ako denbo ak
zuekin a e gu xiago ego eko auke a eman didan, oga u didazuenez, u e gu xi ba zue an
e aiki ako adiskide asuna denbo an muga ik gabe luza u dai ekeelako ( xip- xip).
Muchas g acias a mi amilia. A mi amama, po que aunque no la llamo, ni isi o an o como
debe ía (casi) siemp e iene buenas palab as pa a mí. A mi ai a, po esa mane a an peculia
que ha enido siemp e de mo i a me, que con los años he ido “en endiendo”, aunque más
de una ez me haya sacado de quicio. A mi ama, po se un pila undamen al en mi ida y
un espejo de supe ación en el que mi a me.
Azkenengo hi zak, u e haue an zeha gehien aguan a u nauen pe sona en za . Jon Ande ,
eske ik asko ni e o eka pun ua iza eaga ik. Momen u one an e a, ba ez e e, xa e an,
i iba e ba a e a zen jaki eaga ik. Inda ak ansmi i zeaga ik. Bizi izandako une
guz ienga ik e a biziko di ugunenga ik.
Guz iei, eske ik asko biho z biho zez. Muchas g acias. Thank you.
LABURPENA
E esis en zia handiagoko al zai uak so zeko eska iak, bes e p opie a e ba zuk man en zen
di en bi a ean, hala nola kon o maga i asun plas ikoa edo soldaga i asuna, E esis en zia
Handiko Al zai u Au e a uak ga a zea eska u du (AHHS, ingeleseko sigle an). Tesi hone an
ike u ako Q&P (Quenching and Pa i ioning) al zai uak AHSSen hi uga en belaunaldia en
ba uan daude. Al zai u ho ien ezauga i nagusia aus eni a a xiki u balio al u sama ak e a
ma ize ma ensi ikoa di uz ela da. Ho ek e esis en zia e a kon o maga i asun handia
ema en die e a, be az, oso in e esga iak di a au omobilak ab ika zeko.
Q&P al zai uen p ozesa zea bi e apako a amendu e miko ba en da za. Lehenengoan,
al zai ua Ms-M (hau da, ma ensi a hasie ako enpe a u a - ma ensi a amaie ako
enpe a u a) a eko enpe a u a lehene si ba e a hoz en da, mik oegi u a pa zialki
ma ensi ikoa e a aus eni ikoa so zeko. Biga enak, pa izio e apa izenekoak (al zai u
ma ensi ikoen i aoke a klasikoa gogo a az en duena), aus eni a en ka bono edukia
abe as ea du helbu u, ma ensi a en ka bono edukia (pa zialki) mu iz uz. Ho ela, ka bonoz
egonko u ako aus eni a mik oegi u an a xiki zea lo zen da, gi o enpe a u a a hoz u
ondo en.
Tesi hone an, Q&P a amendua Mn edukia du en al zai ue an aplika u da, e a be i asuna
pa izio e apa a e in e k i ikoa i dagokion enpe a u a ba ean egin dela da, ma ensi a ik
aus eni a ako ans o mazioa en enomenoa e aginez. Ho ela, a xiki ako aus eni a eduki
handiagoak lo u nahi izan di a e a, ho e az gain, aus eni a ka bonoak ez ezik,
manganesoak e e egonko u du. Al zai ua en konposizio kimikoak (manganeso e a nikel
eduki desbe dineko al zai u za ike u a) e a a amendu e mikoak ( enplake a enpe a u a
e a pa izio denbo a) bilakae a mik oegi u alean, ase aus eni ikoa en egonko zean e a
akzioa ekiko p opie a ee an du en e agina ike u da.
T a a u ako al zai uen mik oegi u a en ka ak e izazioa i eske , manganeso gehien du en
al zai ue an, a xiki u ako aus eni a eduki handiak baiez a u ahal izan di a, bai a ase
aus eni ikoko manganeso abe as ea e e. Gaine a, pa izio e apa en au eko mik oegi u ak
( enplake a enpe a u ak zehaz ua) e agin handia duela ikusi da, e a baldin ze ako ba zue an
mik oegi u a inagoa, aus eni a eduki handiagoak e a apa eko akzioa ekiko p opie a eak
lo u izan di a, akzioa ekiko e esis en zia en e a elongazio o ala en a eko p oduk uan
30 GPa% gaindi uz. Nikela gehi zea onu aga ia izan da aus eni a a xiki u gehiago e a
p oduk u ho en balio handiagoak lo zeko. T akzioa ekiko emai zak ma ensi a
3.1 Ma e ials and p ocessing ...................................................................................... 39
3.1.1 Ma e ials ........................................................................................................ 39
3.1.2 Design o he Q&P cycles based on dila ome y ........................................... 43
3.1.3 Applica ion o he Q&P hea ea men s: Fu naces and sal ba hs ............... 51
3.2 Mic os uc u al cha ac e iza ion ............................................................................ 53
3.2.1 X- ay di ac ion (XRD) .................................................................................. 53
3.2.2 Scanning Elec on Mic oscope (SEM and FE-SEM) ..................................... 54
3.2.3 Elec on Backsca e Di ac ion (EBSD) ....................................................... 55
3.2.4 T ansmission Elec on Mic oscopy (TEM) .................................................... 56
3.3 Mechanical beha io ............................................................................................. 59
3.3.1 Tensile es .................................................................................................... 59
3.3.2 In e up ed ensile es ................................................................................... 60
3.3.3 Ha dness ....................................................................................................... 60
3.3.4 T ibology: pin-on-disk (PoD) .......................................................................... 61
3.3.5 Toughness ..................................................................................................... 63
Chap e 4 Resul s and discussion .................................................................................... 67
4.1 Q&P applied o medium Mn and Ni s eels ............................................................ 67
4.1.1 Dila ome y cu es o he Q&P hea ea men s ............................................ 67
4.1.2 Mic os uc u e a e he Q&P hea ea men s............................................... 70
4.1.3 Tensile p ope ies .......................................................................................... 77
4.1.4 In e up ed ensile es esul s ....................................................................... 81
4.1.5 Analysis o he in luence o he hea ea men pa ame e s on mic os uc u e
and aus eni e s abiliza ion ............................................................................................ 82
4.1.6 Analysis o he in luence o Ni on mic os uc u e and aus eni e s abiliza ion 86
4.1.7 Theo e ical analysis o aus eni e s abiliza ion using DICTRA ....................... 87
4.1.8 Rela ionship be ween mic os uc u e and ensile p ope ies ........................ 92
4.2 Q&P applied o medium and high C s eels ........................................................... 96

4.2.1 Dila ome y s udy o selec he s eels and Q&P cycle o u he s udy ......... 96
4.2.2 Dila ome y cu es o he Q&P cycle applied in u naces and sal ba hs ..... 97
4.2.3 Mic os uc u e a e Q&P ea men ............................................................... 99
4.2.4 Ha dness ..................................................................................................... 102
4.2.5 Wea beha io ............................................................................................. 103
4.2.6 Re ained aus eni e s abili y ......................................................................... 105
4.2.7 Toughness ................................................................................................... 106
Chap e 5 Conclusions ..................................................................................................... 111
5.1 Q&P applied o medium Mn and Ni s eels .......................................................... 111
5.2 Q&P applied o medium and high C s eels ......................................................... 112
Chap e 6 Fu u e wo k ...................................................................................................... 117
6.1 Q&P applied o medium Mn and Ni s eels .......................................................... 117
6.2 Q&P applied o medium and high C s eels ......................................................... 118
Chap e 7 Bibliog aphy ..................................................................................................... 121
Publica ions ela ed o he doc o al hesis .................................................................... 137
Appendix A: Dila ome y .................................................................................................. 139
Appendix B: Rou e ollowed in he u naces and sal ba hs ........................................ 151
Appendix C: Tensile es specimens ............................................................................... 152
Appendix D: Ha dness measu emen s ........................................................................... 155
Appendix E: Cha py specimens ...................................................................................... 156
Lis o Figu es
Figu e 1. Global Fo mabili y Diag am (2021) compa ing s eng h and elonga ion o cu en
and eme ging s eel g ades. Cou esy o Wo ldAu oS eel [2]. ................................................ 4
Figu e 2. Schema ic o a ypical Q&P cycle ep esen ing he di e en mic os uc u es and C
con en o each phase wi hin he cycle, whe e α’ is ma ensi e, α’sec is seconda y ma ensi e
and γ is aus eni e. ................................................................................................................... 6
Figu e 3. To al elonga ion e sus ensile s eng h diag ams a e he applica ion o Q&P hea
ea men s showing he e ec o C and Mn addi ions [49]. .................................................. 11
Figu e 4. To al elonga ion e sus ul ima e ensile s eng h o Q&P ea ed 0.3C-Mn-1.6Si
s eels con aining a ious le els o manganese [86]. ........................................................... 13
Figu e 5. Volume ac ion o e ained aus eni e and co esponding ca bon con en a e ull
aus eniza ion, quenching o di e en empe a u es and pa i ioning a 400 °C o 100 s [108].
.............................................................................................................................................. 16
Figu e 6. Volume ac ion o e ained aus eni e a e Q&P ea men a di e en pa i ioning
empe a u es and imes [8]. .................................................................................................. 19
Figu e 7. Mic os uc u al e olu ion ha unde goes du ing Q&P cycles showing he di e en
phases and ca bon con en s o each phase expec ed a aus eniza ion, quenching
empe a u e, a he end o pa i ioning, and inal mic os uc u e. In his igu e, i is assumed
ha nei he aus eni e decomposi ion no ca bide p ecipi a ion occu ed. ........................... 20
Figu e 8. SEM mic og aphs o a ypical Q&P mic os uc u e con aining e ained aus eni e
(RA), empe ed ma ensi e (M1), seconda y ma ensi e (α’sec), and ma ensi e-aus eni e
islands (MA). Adap ed om [117]. ........................................................................................ 20
Figu e 9. Schema ic o he ypical p ocessing ou e o medium-Mn s eels, whe e α’ is
ma ensi e, α is e i e and γ is aus eni e. ............................................................................ 25
Figu e 10. Compa ison o Cha py impac ene gies a di e en empe a u es o Q&T and Q&P
ea ed specimens [194]. ...................................................................................................... 30
Figu e 11. Ligh op ical me allog aphy (LOM) images and ha dness o he ho olled
mic os uc u es. The 2Mn (a), 4Mn (b), 6Mn (c) and 6Mn2Ni (d) s eels a e ho olling, and
he 4Mn (e), 6Mn ( ) and 6Mn2Ni (g) s eels a e so annealing. ........................................ 41
Figu e 12. Theo e ical CCT cu es o 1.2990 (a), 1.2344 (b), and 300M (c) s eels ob ained
wi h JMa P o. ........................................................................................................................ 42
Figu e 13. Global iew on L78 RITA dila ome e . ................................................................ 43
Figu e 14. Dila ome y cu es ep esen ing he de e mina ion o Ac1 and Ac3 empe a u es o
he 2Mn (a) and 1.2344 (b) s eels. In (a) Ac1 was de e mined as he empe a u e wi h
maximum change in leng h jus be o e ans o ma ion s a ed and Ac3 was de e mined by he
angen me hod; in (b) bo h empe a u es we e ob ained by he angen me hod. ............. 44
Figu e 15. Dila ome y cu e o he 2Mn s eel o he de e mina ion o Ms, M and ma ensi e
ans o ma ion cu e (a) and he co esponding ma ensi ic ans o ma ion cu e showing he
de e mina ion o he empe a u e co esponding o a ans o ma ion o 75% ma ensi e (b).
.............................................................................................................................................. 46
Figu e 16. Dila ome y cu e showing he ob en ion o TART o he 6Mn2Ni s eel ehea ing
om QT25. ............................................................................................................................ 48
Figu e 17. Schema ic o he Q&P cycles ca ied ou in his wo k o medium Mn s eels. ... 49
Figu e 18. Schema ic o he Q&P cycles ca ied ou in his wo k o medium and high C s eels.
.............................................................................................................................................. 50
Figu e 19. Shee o he 2Mn s eel p epa ed o ca y ou Q&P he mal ea men in u naces
and sal ba hs wi h one he mocouple welded in he cen e and o he in he edge. The
dimensions o he showed shee we e 250 mm leng h, 50 mm wide, and 1.5 mm hick. ... 51
Figu e 20. Cylinde o he 300M s eel employed o ca y ou he Q&P he mal ea men in
u naces and sal ba hs ep esen ing he posi ion o he he mocouples. ........................... 52
Figu e 21. Schema ic ep esen a ion o he ou e ollowed o ca ied ou Q&P he mal cycles
in he u naces and sal ba hs. Blue and ed labels and a ows ep esen s cooling and hea ing
s ages, espec i ely. ............................................................................................................. 52
Figu e 22. Schema ic ep esen a ion o B agg di ac ion o c ys allog aphic planes. ........ 53
Figu e 23. Funnel whe e samples we e glued o be polished. ............................................ 57
Figu e 24. Hand d ill employed o ake ou 3 mm diame e discs om he samples hinned
down o 100 μm. ................................................................................................................... 57
Figu e 25. Sample holde o he elec oly ic ba h and elec opolishing equipmen . ........... 58
Figu e 26. In ensi y-Vol age cu e. ...................................................................................... 58
Figu e 27. Dimensions o he ensile specimens. All measu emen s a e exp essed in mm.
.............................................................................................................................................. 59
Figu e 28. Samples cu o XRD measu emen s om ensile specimens a e he applica ion
o di e en s ains. ................................................................................................................ 60
Figu e 29. Vicke s ha dness es p inciple. .......................................................................... 61
Figu e 30. Pin-on-disk sys em. ............................................................................................. 61
Figu e 31. C oss-sec ional a eas o he wea ack employed o he measu emen o wea
a e. ....................................................................................................................................... 62
Figu e 32. S anda d subsize specimen dimensions (ASTM A370). .................................... 63
Figu e 33. Dila ome y cu es o he applied Q&P cycles: 2Mn s eel (a), 4Mn s eel (b), 6Mn
s eel (c), and 6Mn2Ni s eel (d). ............................................................................................ 68
Figu e 34. Rela i e change in leng h measu ed du ing he pa i ioning s age o he e cycle.
.............................................................................................................................................. 69
Figu e 35. Rela i e change in leng h measu ed du ing he pa i ioning s age o he QT10-
P 1000 and he QT25-P 1000 cycles: 6Mn (a) and 6Mn2Ni (b) s eels. E olu ion o he
aus eni e o med du ing he pa i ioning ( e e ed γ) in he QT10-P 1000 and he QT25-
P 1000 cycles in he 6Mn (c) and 6Mn2Ni (d) s eels. .......................................................... 69
Figu e 36. Re ained aus eni e con en s as a unc ion o pa i ioning ime measu ed a e he
applica ion o all Q&P cycles. ............................................................................................... 71
Figu e 37. FE-SEM mic og aphs co esponding o he QT25-P 1000 cycle o he 6Mn (a),
and 6Mn2Ni (b) s eels; he QT10-P 1000 cycle o he 6Mn (c), and 6Mn2Ni (d) s eels; and
he QT10-P 3600 cycle o he 6Mn2Ni s eel (e). ................................................................. 73
Figu e 38. EBSD scans co esponding o he QT25-P 1000 cycle o he 6Mn (a), and 6Mn2Ni
(b) s eels; and he QT10-P 1000 cycle o he 6Mn (c), and 6Mn2Ni (d) s eels. ................. 74
Figu e 39. TEM analysis o 6Mn2Ni s eel: Mic og aphs and SAD pa e ns o he QT25 (a)
and he QT10 (b) condi ions; EDS analysis ep esen ing he dis ibu ion o Mn concen a ion
o he QT25 (c) and QT10 (d) condi ions, and Ni concen a ion o he QT25 (e) and QT10
( ) condi ions; concen a ion p o iles o Mn and Ni line scans pe o med wi hin he a eas
ma ked in (a) and (b) o he QT10 (g) and QT25 (h) condi ions. ........................................ 76

Figu e 40. TEM mic og aphs o he 6Mn s eel (a) and he 6Mn2Ni s eel (c) a e QT10-P 1000
cycle, TEM-EDS spec um o a globula ca bide ma ked in (a) (b), and composi ional
mapping o he (c) mic og aph (d). In he mic og aph (c), acicula and globula ca bides a e
isible; in he composi ional map (d) a highe concen a ion o Mn is isible in he globula
and acicula ca bides............................................................................................................ 77
Figu e 41. Enginee ing s ess-s ain cu es ob ained a e Q&P ea men s o he 2Mn s eel.
.............................................................................................................................................. 78
Figu e 42. Enginee ing s ess-s ain cu es ob ained a e Q&P ea men s o he 4Mn s eel.
.............................................................................................................................................. 78
Figu e 43. Enginee ing s ess-s ain cu es ob ained a e Q&P ea men s o he 6Mn s eel.
.............................................................................................................................................. 78
Figu e 44. Enginee ing s ess-s ain cu es ob ained a e Q&P ea men s o he 6Mn2Ni
s eel. ..................................................................................................................................... 79
Figu e 45. Rela ionship be ween o al elonga ion (%) and ensile s eng h (MPa) ob ained
a e Q&P cycles in 2Mn, 4Mn, 6Mn and 6Mn2Ni s eels. .................................................... 81
Figu e 46. Enginee ing s ess-s ain cu es ob ained o he QT10-P 1000 condi ion and RA
measu ed a di e en s ains o he 6Mn (a) and 6Mn2Ni (b) s eels. ................................. 82
Figu e 47. TEM mic og aph o he 6Mn2Ni s eel a e he QT10-P 1000 condi ion (a); and line
scans o Mn and Ni weigh concen a ion (b), co esponding o he line shown in (a). ....... 87
Figu e 48. DICTRA simula ions o 6Mn2Ni s eel a 640 ºC: schema ic o he ini ial condi ions
o he simula ions o se up (1) (a); esul s o se up (1), showing a compa ison be ween he
g ow h o aus eni e in QT10 and QT25 wi h P 1000 and di usion o Mn (b) and Ni (d) ( he
ini ial in e ace was se in he same posi ion o QT10 and QT25), and showing he
compa ison be ween he g ow h o aus eni e wi h P 300, P 1000, and P 3600 in QT10 and
di usion o Mn (c) and Ni (e). ............................................................................................... 89
Figu e 49. DICTRA simula ions o 6Mn2Ni s eel a 640 ºC: schema ic o he ini ial condi ions
o he simula ions o se up (2) (a), and esul s o se up (2) con igu a ion, whe e aus eni e
nuclea ed a θ/α in e ace (b). .............................................................................................. 91
Figu e 50. Tensile p ope ies o he Q&P ea ed samples: yield s eng h (a); ensile s eng h
(b); o al elonga ion (c); and TEL x TS p oduc (d). .............................................................. 93
Figu e 51. G aphical ep esen a ion o he ela ionship be ween he p oduc o ensile
s eng h and o al elonga ion and RA o each Q&P cycle o he 6Mn and 6Mn2Ni s eels. 93
Figu e 52. Volume pe cen o each phase in he 6Mn and 6Mn2Ni s eels a e he applica ion
o Q&P cycles calcula ed based on dila ome y cu es and RA measu ed by XRD. .......... 94
Figu e 53. E olu ion o no malized RA du ing ensile es s s opped a di e en s ains o 6Mn
and 6Mn2Ni s eels a e QT10-P 1000 cycle. ...................................................................... 95
Figu e 54. Dila ome y cu es, ha dness and RA con en o he 1.2990 s eel a e he PT300
(a) PT400 (b) cycles; o he 1.2344 s eel a e he PT300 (c) and PT400 (d) cycles; and o
he 300M s eel a e he PT300 (e) and PT400 ( ) cycles. ................................................... 97
Figu e 55. Dila ome y cu es o he he mal Q&P cycle applied in he u naces and sal ba hs
o he 1.2990 and 300M s eels. ........................................................................................... 98
Figu e 56. Rela i e change in leng h measu ed du ing he pa i ioning s age o he Q&P
cycle applied o he 1.2990 and 300M s eels. ...................................................................... 99
Figu e 57. SEM mic og aph o he 300M s eel a e he Q&P ea men . ............................ 99
Figu e 58. SEM mic og aphs (a) and (b), and EDS analysis o he ma ix (c), globula ca bide
(d), and coa se ca bides (e) and ( ) o he 1.2990 s eel a e he Q&P ea men . ............ 100
Figu e 59. Phase ac ion as a unc ion o empe a u e o (a) 1.2990 and (b) 300M s eels,
and composi ion o 1.2990 s eel (c) M7C3 and (d) M23C6 phases ob ained by The mo-Calc
calcula ions. ........................................................................................................................ 101
Figu e 60. Ha dness alues measu ed in he 1.2990 and 300M s eels a e he applica ion o
Q&T o Q&P hea ea men s. ............................................................................................ 103
Figu e 61. Wea a e (mm3/N.m) calcula ed om he PoD es s. Compa ison be ween Q&P
and Q&T ea ed 1.2990 (a) and 300M (b) s eels; and compa ison be ween Q&P ea ed
1.2990 and 300M s eels es ed wi h he same linea eloci y (c). ..................................... 104
Figu e 62. RA measu ed in he su ace and wea acks o med du ing PoD cha ac e iza ion
o he 1.2990 and 300M s eels. .......................................................................................... 105
Lis o Tables
Table 1. Sho e iew o ypical s eels wi h Fe-C-Mn-Si/Al composi ions employed in Q&P
p ocess. .................................................................................................................................. 9
Table 2. Sho e iew o s eels wi h Fe-C-Mn-Si composi ions and Ni and/o C addi ions
employed in Q&P p ocess. ................................................................................................... 10
Table 3. Sho e iew o composi ions employed in Q&P s eels wi h Mo and/o V addi ions.
.............................................................................................................................................. 10
Table 4. Tensile p ope ies and olume % o e ained aus eni e ob ained by Q&P. ........... 24
Table 5. Typical mechanical p ope y anges o indus ially p oduced QP980 and QP1180.
Adap ed om [151]. .............................................................................................................. 27
Table 6. Replacing DP590 wi h QP980 allows o downgauging. Adap ed om [157]. ...... 27
Table 7. Composi ion (w .%) o he medium Mn s eels employed in his wo k. .................. 40
Table 8. Composi ion (w .%) o he medium and high C s eels employed in his wo k. ...... 43
Table 9. Phase ans o ma ion empe a u es (Ac1, Ac3, Ms and M ), c i ical cooling a es (CCR)
and he aus eni e measu ed in he quenching s a e o all he s eels employed in his wo k.
.............................................................................................................................................. 45
Table 10. QT25, QT10 and TART alues employed in he Q&P cycles co esponding o each
s eel. ..................................................................................................................................... 48
Table 11. Selec ion o he QT, PT and P pa ame e s employed in each Q&P cycle. ........ 49
Table 12. Summa y o condi ions ca ied ou in each s eel. ................................................ 49
Table 13. Q&P cycle pa ame e s (QT, PT and P ) employed in each condi ion and s eel.. 51
Table 14. Pa ame e s used o he pin-on-disk es s. .......................................................... 62
Table 15. Compa ison be ween e ained aus eni e con en (RA %) measu ed by XRD and
EBSD. A e age aus eni e g ain size (RA nm) measu ed by EBSD. ................................... 74
Table 16. Summa y o ensile p ope ies o he 2Mn, 4Mn, 6Mn and 6Mn2Ni s eels a e
each Q&P ea men . ............................................................................................................ 79
Table 17. Summa y o he aus eni e and seconda y ma ensi e alues es ima ed and
measu ed a he end o he pa i ioning and in he inal mic os uc u e. .............................. 84
6
Figu e 2. Schema ic o a ypical Q&P cycle ep esen ing he di e en mic os uc u es and C
con en o each phase wi hin he cycle, whe e α’ is ma ensi e, α’sec is seconda y ma ensi e and γ
is aus eni e.
De elopmen o Q&P ea men has so a been ocused o shee p ocessing di ec ed o
au omo i e indus y. Howe e , de elopmen o Q&P ype mic os uc u es in hicke sec ions
is o in e es o hea y indus y, including mining and mine al p ocessing. Fo such
applica ions, he hicknesses o he s eel shee s a e oo low and he e o e s eel pla es a e
equi ed. In ha aspec , only a ew s udies conside ed he possibili y o applying Q&P in s eel
pla es [9–11].
1.2.2 Ca bon pa i ioning
Ca bon supe sa u a ion in ma ensi e is o dina ily elimina ed by mechanisms like ca bide
p ecipi a ion du ing empe ing [12,13]. In addi ion, he empe a u e which is used no mally in
s eel ea men p ocesses is oo low o subs an ial amoun s o ca bon di usion o occu [12].
Consequen ly, al hough ca bon-en iched e ained aus eni e in ma ensi ic s eels was no
unknown [14], he he modynamics o ca bon pa i ioning be ween ma ensi e and e ained
aus eni e has been sca cely conside ed.
Recen ly, a model has been de eloped in o de o add ess ca bon pa i ioning om
as-quenched ma ensi e in o aus eni e. This model p edic s he endpoin o pa i ioning when
ma ensi e is in me as able equilib ium wi h aus eni e. I assumes ha he di usion o
α’sec
Tempe a u e (ºC)
Time (s)
γ
γ
γ
γ
Cγ= Ci/ Cα’ = Ci
Cγ= Ci
Cγ> Ci/ Cα’ < Ci
α'
γ
γ
γ
γ
γ
γ
γ
γ
γ
γ
γγ
Ac1
Ac3
Ms
QT
PT

7
subs i u ional a oms is es ic ed, he ma ensi e/aus eni e in e ace is immobile, and ca bide
o ma ion and ca bon seg ega ion o disloca ions in ma ensi e a e assumed o be
supp essed [6]. In pa icula , i has been ecen ly sugges ed ha he ca bon pa i ioning om
ma ensi e in o aus eni e is con olled by he cons ained ca bon equilib ium (CCE) c i e ion
[12,13,15]. Acco ding o his, o each he me as able ma ensi e/aus eni e equilib ium by he
comple ion o ca bon pa i ioning, bo h equal chemical po en ial o ca bon in ma ensi e and
aus eni e and conse a ion o all subs i u ional a oms in each phase a e equi ed.
The esul s o he CCE model se ed o success ully p opose he no el Q&P p ocess.
Howe e , he g ain size o he aus eni e and i s mechanical s abili y due o he appea ance
o disloca ions du ing cooling can a ec bo h he Ms empe a u e [16] and he p edic ions o
he phase ac ions [17]. The mo phology o he aus eni e and he cha ac e is ics o he
ma ensi e, such as ca bon supe sa u a ion and disloca ion densi y [18,19], can also
in luence ca bon di usion, along wi h he coupling o aus eni e wi h neighbo ing phases.
A la e analysis [20] abou he cha ac e o he in e ace in he pa i ioning s age included he
possibili y o a mobile in e ace based on expe imen al e idence o in e ace mig a ion. In
ecen s udies [21,22], i was ound ou ha he in e ace mig a es du ing he pa i ioning s ep.
This mig a ion was e iden since hey measu ed a signi ican inc ease in aus eni e ac ion
a e pa i ioning as compa ed o he as-quenched condi ion. Zhong e al. [23] ound ha in
Q&P s eels wi h high amoun o C he in e ace p obably mig a es o inc ease he aus eni e
ac ion, whe eas in low C Q&P s eels i p obably mig a es o educe i .
1.2.3 Compe ing eac ions du ing Q&P hea ea men
In addi ion o ca bon pa i ioning in o aus eni e, o he p ocesses could occu du ing he
pa i ioning s ep. Including decomposi ion o aus eni e o o he phases, such as baini e,
o ma ion o cemen i e and/o ansi ional ca bides, and ca bon apping in ma ensi e
in e aces and disloca ions.
1.2.3.1 Ca bides p ecipi a ion
Con olling he p ecipi a ion o ca bides is o i al impo ance o ob ain he desi ed
mic os uc u es in a Q&P p ocess [12]. Since he s abiliza ion o he aus eni e is based on i s
ca bon-en ichmen , i is c ucial ha ca bon is no los in compe i i e eac ions. Thus, i is
necessa y o unde s and and con ol any ca bide p ecipi a ion ha migh occu du ing he
Q&P cycle. The un ans o med aus eni ic egion du ing he i s quench can a y depending
on i s mo phology, which can be in e la h-lamella o blocky, o he composi ion o he s eel
8
[13]. Fu he mo e, he exac dis ibu ion o he aus eni ic egions a quenching empe a u e
is no known. The e o e, i can be concluded ha he ca bon escape ou e may a y o each
case.
In he ma ensi e, ine ansi ion ca bides gene ally a e no conside ed de imen al, whe eas
cemen i e can be mo e conce ning. The e o e, he g ea es e o has been made o
unde s and when ansi ion ca bides a e eplaced by cemen i e [24,25], a he han he
ini ia ion o ansi ion ca bides p ecipi a ion i sel . Howe e , any ansi ion ca bide
p ecipi a ion dec eases aus eni e ca bon-en ichmen po en ial in Q&P p ocessing and,
hence, i is necessa y o de elop a be e unde s anding o he ini ia ion o ansi ion ca bide
o ma ion, including composi ion and p ocessing e ec s [26,27].
Ca bon chemical po en ial is qui e highe in as-quenched ma ensi e han in e ained
aus eni e, so he ca bide nuclea ion is mo e likely o occu in BCC e i e han in aus eni e
[27,28]. The α/γ in e ace is also a p opi ious si e o ca bide o ma ion [28]. Ca bon apping
a c ys allog aphic de ec s, and aus eni e decomposi ion o e i e and cemen i e as a esul
o ma ensi e empe ing du ing Q&P is consis en wi h he lowe expe imen al aus eni e
ac ions o en achie ed compa ed wi h p edic ions [18,19,29–31].
1.2.3.2 O he phase ans o ma ions
Apa om ca bide p ecipi a ion, aus eni e decomposi ion can also ake place du ing he
pa i ioning. The no mally employed ange o pa i ioning empe a u es (350 ºC – 450 ºC)
enables he baini e- e i e o ma ion om aus eni e [32]. Some au ho s demons a ed ha
baini ic ans o ma ion in aus eni e–ma ensi e mix u e is as e han ha s a ing om single-
phase aus eni e [33,34]. The au ho s sugges ed ha he bounda y be ween ma ensi e and
aus eni e se es as a nuclea ion si e o baini ic e i e. Baini e o ma ion dec eases he
amoun o aus eni e a ailable o ca bon en ichmen and he e o e is o en undesi able [35].
Some esea che s assume ha small amoun s o baini e a e o med mos ly in he beginning
o pa i ioning [36]. Fu he en ichmen o emaining aus eni e wi h ca bon lowe s he Bs
empe a u e which should signi ican ly supp ess he baini ic eac ion so ha e en ually Bs
can d op below he pa i ioning empe a u e and baini ic eac ion can s op comple ely.
In some ecen s udies [37–39], in which he employed pa i ioning empe a u e was highe
han usual, decomposi ion o un ans o med aus eni e in o pe li e was obse ed. The apid
ca bon en ichmen o aus eni e and he highe pa i ioning empe a u e p omo e pea li e
o ma ion a p io aus eni e g ain bounda ies and cemen i e p ecipi a ion wi hin aus eni e
9
ilms [38]. This ans o ma ion is ob iously undesi ed, as consumes ca bon o aus eni e
en ichmen and dec eases he e ained aus eni e con en .
The las compe ing eac ion is he o ma ion o seconda y ma ensi e du ing he inal cooling.
I compe i i e eac ions occu ed du ing he pa i ioning s age, pa o he aus eni e migh no
be su icien ly ca bon-en iched o be s able a oom empe a u e and, consequen ly, i migh
ans o m in o seconda y ma ensi e a he las cooling [13,38,40,41], which was conside ed
as de imen al o duc ili y [40,42].
1.2.4 Alloying elemen s employed in Q&P s eels
In his sec ion he in luence o di e en alloying elemen s on Q&P p ocess and esul an
p ope ies is analyzed. The ole o alloying elemen s in Q&P s eels could be desc ibed in his
way:
• P e en any compe ing eac ion such as ca bide p ecipi a ion o decomposi ion o
aus eni e in o e i e, baini e o pea li e du ing pa i ioning [6,13,43]; he addi ion o
silicon as alloying elemen is he key o ob ain he desi ed esul s.
• Imp o e he ha denabili y and inal mechanical p ope ies o he s eel [43,44]; he
addi ion o manganese is he simples key in his ques ion, exis ing o he possibili ies.
Alloying elemen s also in luence on phase ans o ma ion empe a u es (Ac1, Ac3, Ms, and
M ), which a e impo an o design Q&P cycles. F om he indus ial poin o iew, he lowe
hese empe a u es, he mo e educ ion in he ene gy consump ion and cos s. In Table 1,
Table 2 and Table 3 a sho e iew o ypical composi ions con aining he elemen s discussed
in he nex sec ions is shown. The ypical Q&P s eels con ain Fe, C, Mn and Si, while o he
elemen s could be also added depending on he pu pose.
Table 1. Sho e iew o ypical s eels wi h Fe-C-Mn-Si/Al composi ions employed in Q&P p ocess.
S udies wi h Fe-C-Mn-Si/Al composi ions
Re .
C
Mn
Si
Al
[45]
0.25
3.00
1.50
-
[46]
0.29
3.00
1.40
-
[47]
0.25
3.00
1.50
0.02
[48]
0.20
3.50
1.54
-
0.20
3.50
0.45
0.22
[49]
0.2
3.00
1.60
0.06
0.29
2.95
1.59
0.06
0.28
4.95
1.64
0.06
[50]
0.29
1.49
1.47
0.26
[51]
0.19
1.61
0.35
1.10
10
Table 2. Sho e iew o s eels wi h Fe-C-Mn-Si composi ions and Ni and/o C addi ions employed
in Q&P p ocess.
S udies wi h Fe-C-Mn-Si composi ions and Ni and/o C addi ions
Re .
C
Mn
Si
Ni
C
[52]
0.19
6.00
-
-
-
0.19
5.80
1.40
-
-
0.19
6.00
-
2.10
-
0.19
5.70
1.40
1.60
-
[53]
0.24
1.38
1.39
0.03
-
0.21
1.44
1.44
1.01
-
0.28
1.41
1.46
1.99
-
[54]
0.2
1.54
1.30
0.07
1.48
0.19
1.52
1.32
1.53
0.01
[55]
0.21
4.00
1.60
-
1.00
[56]
0.22
1.30
0.25
-
0.20
0.27
1.50
1.61
-
-
0.28
1.46
1.58
-
0.97
[57]
0.12
0.87
0.26
-
12.00
Table 3. Sho e iew o composi ions employed in Q&P s eels wi h Mo and/o V addi ions.
S udies wi h Mo and/o V addi ions
Re .
C
Mn
Si
Ni
C
Mo
V
[58]
0.43
0.59
2.03
0.07
1.33
0.03
-
0.43
0.59
2.03
0.07
0.03
-
[59]
0.37
2.27
2.45
1.47
0.80
0.58
-
0.22
2.42
2.49
1.39
0.72
0.49
-
0.39
2.39
2.64
4.83
0.78
0.50
-
0.28
2.37
3.00
5.30
0.71
0.60
-
[60]
0.20
1.50
1.50
-
-
0.13
-
[61]
0.21
1.65
1.67
-
0.03
-
0.20
0.22
1.89
0.52
-
0.03
-
-
[62]
0.24
1.90
1.50
-
-
-
-
0.24
1.88
1.47
-
-
-
0.03
0.24
1.83
1.52
-
-
-
0.16
[9]
0.10
1.51
1.48
-
-
0.30
0.04
1.2.4.1 Ca bon
C is impo an in Q&P s eels because i helps e aining aus eni e and signi ican ly inc eases
he s eng h o he ma ensi e [63]. C also dec eases Ms empe a u e and he e o e, i
su icien aus eni e ca bon-en ichmen occu s, aus eni e e en ion a oom empe a u e is
enhanced. Mo i o e al. [64] epo ed ha , inc easing C con en up o 0.6 w .%, also inc eased
disloca ion densi ies o as-quenched ma ensi ic mic os uc u es. These esul s sugges ha
he s eng hening om inc easing C con en may be s ongly co ela ed wi h he esul ing
11
disloca ion densi y. Howe e , he C con en is gene ally kep a le els in which he ca bon
equi alen emains in he ange o weldable s eels.
The e ec o inc easing C con en om 0.2 w .% o 0.3 w .% on ensile p ope ies o Q&P
s eels has been s udied in [49] o a s eel con aining 3 w .% Mn and 1.6 w .% Si. In he ully
aus eni ized condi ion, he 0.2 w .% C s eel exhibi ed ul ima e s eng h le els o
1200-1450 MPa and o al elonga ions o 9–15% and inc easing i o 0.3 w .% inc eased he
ul ima e ensile s eng h le els in o a ange o 1400–1700 MPa and also o al elonga ion
le els o 11–17%. The esul s ob ained in he s udy a e ep esen ed in Figu e 3.
Figu e 3. To al elonga ion e sus ensile s eng h diag ams a e he applica ion o Q&P hea
ea men s showing he e ec o C and Mn addi ions [49].
1.2.4.2 Silicon and Aluminum
I is known ha he o ma ion o undesi able cemen i e can be inhibi ed by adding Si, Al, o
hei combina ion. Mos o he Q&P s udies employ Si-bea ing g ades wi h 1–2.5 w .% Si
( ypically a ound 1.5 w .% Si is added) [56,65]. Si plays an impo an ole in ca bon
p ecipi a ion supp ession du ing Q&P p ocess [62,66]. Since he solubili y o Si in cemen i e
is negligible, o cemen i e p ecipi a ion o occu du ing empe ing, Si mus di use in o he
ma ix om he ca bide-ma ix in e ace. Simul aneously, ca bon needs o di use in he
opposi e di ec ion. A low Si le els, his p ocess is con olled by ca bon di usion, while a
highe Si le els, Si di usion begins o con ol cemen i e p ecipi a ion.
Fu he mo e, Owen [67] epo ed ha highe empe ing empe a u es a e equi ed o he
decomposi ion o aus eni e wi h highe Si con en s. Ea lie esea che s showed ha Si
e a ds o e en elimina es baini e o ma ion in he pa i ioning s ep due o he nea - o-ze o

12
solubili y o Si in he cemen i e phase [68]. These s udies sugges ha be ween 1.25 and
2 w .% Si is equi ed o supp ess baini e o ma ion du ing ehea ing [69–72].
Si con en may a ec he inal mechanical p ope ies. Howe e , inc easing he Si amoun o
1.5–2 w .% does no seem o conside ably a ec ha dness alues. By con as , o he
in es iga ions epo ed a sligh enhancemen o ha dness [69,73].
The p oblem associa ed wi h high Si con en s is he o ma ion o Si supe icial oxide, oge he
wi h he i on oxide, du ing he ho olling. These oxides a e di icul o emo e by pickling and
cause su ace inish p oblems by educing ho dip gal anizabili y [74,75]. A possible
al e na i e is he use o Al which, like Si, is no soluble in cemen i e and hence p e en s
ca bide o ma ion wi hou de e io a ion o gal anizabili y [35]. Aluminum alloying has been
shown o esul in signi ican e ained aus eni e ac ions, and o inc ease aus eni e ca bon
con en in TRIP s eels [35,76,77]. Howe e , u iliza ion o aluminum in s eels o Q&P
p ocessing is limi ed because i has such a s ong e ec on he Ac3 empe a u e ha only he
in e c i ical ini ial hea ing is possible.
The esponse o bo h Si and Al in Q&P s eels has been in es iga ed in mul iple s udies
[48,50,51,78–80], as displayed in Table 1. In [80] he esul s show ha inc easing Al con en s
leads o a dec ease in e ained aus eni e ac ion, s eng h and elonga ion le els, compa ing
wi h Si alloyed s eel. San o imia e al. [48] s udied wo Q&P s eels wi h di e en Si and Al
con en s and hey ound ha he pa ial subs i u ion o Si by Al lead o lowe e ained aus eni e
and highe cemen i e ac ions. Fu he mo e, hey epo ed a dec ease in he s eng h le els.
Ande and Slui e [81] conduc ed a densi y unc ional heo y (DFT) calcula ion and hey
showed ha Si is almos wice mo e e ec i e han Al supp essing ca bides. Al has also been
epo ed o delay s ain-induced ma ensi e ans o ma ion, enhancing TRIP e ec
[76,82,83].
1.2.4.3 Manganese
Aus eni e s abiliza ion is mainly con olled by C en ichmen al hough o he aus eni e
s abilizing elemen s, such as Mn, can be e ec i e as well [66]. Mn is a common alloying
elemen in his ype o Q&P s eels since i has e ec i e aus eni e s abiliza ion capaci y, i
inc eases ha denabili y by e a ding aus eni e o e i e, pe li e o baini e ans o ma ion
du ing ini ial as cooling, i helps lowe ing phase ans o ma ion empe a u es (s ongly
dec eases he Ms empe a u e), and con ibu e o he o e all s eng h o he s eel by solid
solu ion s eng hening [84]. Mn con en s added o Q&P s eels a e ypically in he o de o
1.5 w .%, wi h he aim o a oiding di usional ans o ma ions du ing he quenching s ep.
13
Fu he mo e, since Mn e a ds baini ic eac ion can be in en ionally added o a oid compe ing
eac ions also in he pa i ioning. Highe con en s o Mn a e conside ed o enhance aus eni e
e en ion, employing he aus eni e s abilizing e ec s o Mn o adjus he ela i e amoun s o
ma ensi e and aus eni e [85].
In ecen Q&P s udies [37,45–49,55], in e es ing ensile p ope ies we e ob ained wi h s eels
con aining inc eased Mn con en s. Fo example, he use o Mn addi ions o 3 w .% and 5
w .% in Q&P s eels has been success ul in de eloping e y high s eng h cold- o mable shee
s eels wi h ensile s eng hs exceeding 1500 MPa, in combina ion wi h o al elonga ions
abo e 20% (Figu e 4) [86]. Howe e , an ea lie s udy o he same au ho s showed ha , a e
a pa i ioning s age a 400 ºC, he 5 w .% Mn con aining s eel showed a mic os uc u e wi h
un empe ed ma ensi e, leading o e y low duc ili y wi h mos samples ailing a s ains lowe
han 2% [85].
Figu e 4. To al elonga ion e sus ul ima e ensile s eng h o Q&P ea ed 0.3C-Mn-1.6Si s eels
con aining a ious le els o manganese [86].
High Mn con en s lead o he de elopmen o s ong band s uc u e, which migh educe TRIP
e ec and, consequen ly, he duc ili y o he s eel [84]. As a medium ca bide- o ming elemen ,
Mn will dec ease he di usi i y o C in aus eni e and hus, slow down he g ow h kine ics o
baini ic e i e [87].
1.2.4.4 Ch omium and Nickel
Addi ions o Ni and C ha e bo h been epo ed o inc ease e ained aus eni e amoun s a e
Q&P [56,58]. Pie ce e al. [54] also obse ed ha a compa able ac ion o aus eni e was
s abilized in he alloy wi h C wi h espec o he alloy wi h Ni, being C a he cheape .
C addi ions up o ~7 w .% a e epo ed o be aus eni e s abilize s in Fe-C bina y s eels,
while highe amoun s s a s o s abilize e i e a he han aus eni e [90]. The easons why C
14
is a good aus eni e s abilize is because i lowe s Ms empe a u e and conside ably educes
he C di usi i y in aus eni e, inc easing he esis ance o ma ensi e o empe ing [88],
slowing aus eni e decomposi ion kine ics [89] and, consequen ly, delaying baini e
ans o ma ion [56]. E. J. Seo e al. [56] analyzed he ole o Q&P ea men on a Si (1.6 w .%)
and C (1 w .%) added medium Mn s eel. They obse ed ha he addi ion o C esul ed in
an inc ease in he e ained aus eni e amoun and, consequen ly, signi ican ly imp o ed
plas ici y wi hou dec easing o he s eng h.
On he o he hand, Ni also educes he Ms empe a u e bu is a signi ican ly s onge aus eni e
s abilize han C and enhances he kine ics o C di usion in aus eni e [88]. Addi ionally, i
can assis in con olling majo compe ing eac ions, such as p ecipi a ion o ca bides inside
aus eni e and pea li e o ma ion, and in inc easing he mal s abili y o aus eni e [52].
Inc easing w .% Ni also lead o g ain e inemen and inc eases he e ained aus eni e ac ion
in olume. Howe e , due o he highe cos , Ni con en should be kep o a minimum [91].
Rizzo e al. [59] obse ed ha a high Ni con en s eel, appa en ly ha ing la ge amoun s o
e ained aus eni e ela i e o he o he expe imen al alloys, had less desi able
s eng h/duc ili y combina ions. On he con a y, o he esea che s epo ed ha lowe
addi ions o e be e mechanical p ope ies because o a la ge ac ion o e ained aus eni e
in olume [56,92,93]. Finally, Kibum e al. [53] obse ed ha inc easing Ni con en he
amoun and s abili y o e ained aus eni e inc eased. The Ni addi ion also led o g ain
e inemen . The s ain-induced ans o ma ion kine ics we e e a ded and hey also epo ed
solid-solu ion s eng hening e ec . Consequen ly, an imp o emen in ensile s eng h and
elonga ion, and ha dness was achie ed.
1.2.4.5 Molybdenum and Vanadium
No mally, he composi ion o he Q&P s eel does no con ain any ca bide o ming elemen s,
such as Nb, V, Ti, Mo, e c. This means ha he Q&P s eel excludes he ad an age o
p ecipi a ion s eng hening o ca bides and ine-g ain s eng hening [94]. Howe e , he e a e
se e al s udies which in es iga e he in luence o hese elemen s in Q&P p ocess [65,86–
95].
The addi ion o Mo and/o V o he composi ions o Q&P s eels pu sues he s eng hening
p oduced by ca bide p ecipi a ion. Some s udies ca ied ou an addi ional empe ing a e he
quenching and pa i ioning p ocess o u he p omo e his [10,98,99]. Mo is also epo ed o
imp o e he ha denabili y o he s eel [9]. Ano he p ope y o bo h Mo and V is ha hey ac
as aus eni e g ain e inemen [9,60,97,98]. Rega ding mechanical p ope ies V addi ion
15
imp o es s eng h and wo k ha dening [60] and also wea esis ance [95] o he Q&P ea ed
s eels. Zhang e al. [60] also epo ed ha V addi ion imp o ed he duc ili y by e ining he
g ain size and enhancing he aus eni e s abili y.
1.2.5 Q&P cycle pa ame e s
The o iginal Q&P p ocess (Figu e 2) can be summa ized in ou main s eps:
• Aus eniza ion: In his s ep he s eel is ully aus eni ized (o , some imes, pa ially, in
o de o in oduce e i e in o he mic os uc u e wi h he aim o dec easing yield
s eng h and aising elonga ion [100]). The ini ial mic os uc u e [101,102], soaking
empe a u e (ST) [103,104] and soaking ime (S ) [103] in luence on he
cha ac e is ics o he aus eni e o med in his s ep.
• Quenching: The s eel is quenched om he ST o a empe a u e be ween Ms and M ,
called quenching empe a u e (QT), wi h he aim o ob aining a pa ially ma ensi ic
and pa ially aus eni ic mic os uc u e (and pa ially e i ic in he case o he pa ially
aus eni ized s eels). The a e o cooling du ing quenching is impo an because i is
necessa y o p e en he o ma ion o lowe baini e in case o cooling a e ull
aus eniza ion.
• Pa i ioning: Du ing his s ep he ca bon mig a es om ma ensi e in o aus eni e. In
one-s ep Q&P cycles he pa i ioning empe a u e (PT) is he same han QT, whe eas
in wo-s ep Q&P cycles i is highe , and usually abo e Ms. In he ime ha s eel
emains in PT, called pa i ioning ime (P ), compe i i e eac ion such as ca bide
p ecipi a ion o aus eni e decomposi ion migh occu .
• Final cooling: The s eel is cooled o oom empe a u e. I aus eni e is su icien ly
ca bon-en iched, seconda y ma ensi e o ma ion is supposed o be a oided.
The con ol o p ocessing pa ame e s such as quenching empe a u e, pa i ioning
empe a u e and pa i ioning ime is c ucial o ob ain he desi ed mic os uc u es, and
he e o e mechanical p ope ies. Hence, nume ous s udies ha e been ca ied ou o
in es iga e he in luence o hese pa ame e s.
1.2.5.1 Quenching empe a u e (QT)
Quenching empe a u e de e mines he aus eni e and ma ensi e ac ions o he ollowing
pa i ioning s ep. I QT is oo low, nea o M , a small amoun o aus eni e will be a ailable o
ca bon-en ichmen and inal e en ion. On he con a y, a high QT, sligh ly below Ms, le li le
ma ensi e o p o ide ca bon o he aus eni e and, consequen ly, aus eni e is unlikely o be
22
is s able. On he o he hand, Si helps o s abilize aus eni e by supp essing cemen i e
p ecipi a ion, hus lea ing mo e C a ailable o en ich he aus eni e [122]. The e o e,
inc easing he addi ion o aus eni e s abilize elemen s can lead o a highe e ained aus eni e
amoun .
Ca bon con en in aus eni e depends on pa i ioning pa ame e s and, ypically, was ound o
each ~1 w .%. Howe e , as men ioned abo e, C g adien s may appea wi hin ei he bulk o
s eel o ac oss a single aus eni e g ain and consequen ly he less ca bon-en iched a eas
may ans o m in o seconda y ma ensi e du ing inal cooling.
S abiliza ion o aus eni e du ing pa i ioning s ep comp omised wo impo an s ages: ca bon
di usion om ma ensi e in o aus eni e, which in gene al is a quick s age (i can ake place
in less han 1 s), and homogeniza ion o ca bon wi hin he aus eni e, which was ound o
need much longe ime [123]. DICTRA simula ion can be o g ea help when s udying hese
wo s ages [38,124]. Hidalgo e al. [38] simula ed ca bon pa i ioning a he pa i ioning s age
in a 0.3C-4.5Mn-1.5Si s eel and hey ound ha , a 400 ºC, less han 1 s was needed o
ca bon pa i ioning o occu . Howe e , 50 s we e necessa y o i s dis ibu ion o become
homogenized in a 100 nm hickness aus eni e la h.
In addi ion, some ecen s udies epo ed ha he s abili y o e ained aus eni e also depends
on i s mo phology and he e o e on he loca ions whe e i was o med du ing mic os uc u e
e olu ion. Nume ous s udies p o ed he coexis ence o blocky and ilm-like e ained aus eni e
mo phologies, being epo ed he ilm-like aus eni e as he mos s able. Sun e al. ound h ee
ypes o e ained aus eni e in 0.2C–1.5Si–1.9Mn s eel, including aus eni e ilms loca ed
be ween he ma ensi e la hs wi h a wid h o abou 100 nm, blocky aus eni e inco po a ed
in o e i ic ma ix, and ul a ine aus eni e ilms, o abou 20–30 nm hick, be ween he pla es
o e i ic baini e [106]. On he o he hand, A laza o e al. [125] in es iga ed he ole he g ain
size plays in he mal s abili y o aus eni e in a Medium-Mn s eel and hey ound ha a g ain
size smalle han 0.5 μm clea ly lowe ed he Ms, inc easing aus eni e s abili y.
1.3.2 Mechanical s abili y o he aus eni e
The mechanical s abili y o e ained aus eni e is he s abili y agains he o ma ion o
ma ensi e unde he in luence o de o ma ion o ans o ma ion-induced plas ici y (TRIP)
e ec . The TRIP e ec inc eases he wo k ha dening a e and delays necking, he eby
imp o ing uni o m elonga ion (UE). The s udies pe o med wi h Q&P s eels o en indica e no
di ec co ela ion be ween olume ac ion o e ained aus eni e and duc ili y o s eel, which

23
means ha he ole o s abili y o he aus eni e looks mo e impo an han ha o i s olume
ac ion. I he aus eni e in o ma ensi e phase ans o ma ion occu s a small s ains i is
unable o e a d he necking o he ma e ial. On he con a y, i i is o s able (i.e., no phase
ans o ma ions a la ge s ains) hen i will no con ibu e o he TRIP-e ec [126,127].
The s abili y o RA in s eels ha exhibi he TRIP e ec is a ec ed by chemical composi ion
[126] (mainly C con en ), g ain size [128], mo phology [129], and su ounding mic os uc u e
[130]. The e o e, a be e unde s anding o RA s abili y can aid in designing a mic os uc u e
ha will p o ide he desi ed combina ion o s eng h and o mabili y.
Jacques e al. [126] pe o med expe imen s on s eels wi h low and high silicon con en s and
simila amoun s o RA. The di e ence be ween he RA in he wo s eels consis ed in he C
con en and he amoun o he su ounding phases, being he g ain sizes simila in bo h
s eels. The high silicon s eel’s aus eni e had he highe C con en , due o he ca bide
p ecipi a ion occu ed in he low Si s eel, and he s udies demons a ed ha highe C con en
dec eased he aus eni e ans o ma ion a e du ing s aining. The e o e, hey concluded ha
he high silicon s eels had a slowe RA ans o ma ion a e du ing s aining due o he mo e
ca bon-en iched RA equi ed a highe amoun o s ain o ans o m in o ma ensi e.
Xiong’s e al. [129] esea ches e ealed ha al hough blocky aus eni e had highe ca bon
con en (1.14 w .%) compa ed o ha in ilm-like aus eni e (0.64 w .%) loca ed be ween
ma ensi e la hs, “high C” blocky RA appea ed o be less esis an o ma ensi e
ans o ma ion. The blocky aus eni e began o ans o m in o ma ensi e a ensile s ain o
2% and by 12% s ain all blocky aus eni e had ans o med. Ne e heless, nume ous ilm-like
aus eni e g ains we e s ill p esen a ha s ain, indica ing ha ca bon con en is no always
a domina ing ac o . This could be explained by de di e ences in yield s eng h o he
su ounding phases. In he wo k [129] he Q&P cycle was s a ed wi h a pa ial aus eniza ion
in he in e c i ical ange, and blocky aus eni e was su ounded by e i e, while ilm-like
aus eni e was su ounded by highe yield s eng h ma ensi e la hs and he ma ensi e
ans o ma ion equi ing olume expansion could be supp essed.
The o he ac o is g ain size e ec . Gene ally, i was epo ed ha coa se aus eni e g ains
a e less s able han he ine ones. In [83] i was s udied he in luence o g ain size on
aus eni e s abili y o Q&P s eels and hey concluded ha he op imal aus eni e g ain size was
be ween 0.01 and 1 μm. RA g ain sizes abo e 1 μm ans o med in o aus eni e a qui e low
s ains, whe eas a size below 0.01 μm led o a oo s able aus eni e ha did no ans o m
e en a high s ain le els.
24
Finally, De Knij e al. [131] epo ed ha aus eni e s abili y was nega i ely a ec ed by he
appea ance o seconda y ma ensi e. As seconda y ma ensi e is o med, he dis ibu ion o
s ains in he mic os uc u e can be signi ican ly a ec ed, since he amoun o s ain ha can
be accommoda ed in empe ed ma ensi e is d as ically educed. Consequen ly, he
ans o ma ion s abili y o aus eni e dec eases.
1.4 Rela ionship be ween mic os uc u e and
mechanical p ope ies
Q&P s eels a e o signi ican in e es o gene a e desi able combina ions o s eng h and
o mabili y. The key o hese p ope ies is he mic os uc u e combining a ma ensi ic ma ix
wi h signi ican ac ions o ca bon-en iched e ained aus eni e [17]. Howe e , he co ela ion
be ween mechanical p ope ies wi h he pa ame e s o mic os uc u e and i s cons i uen s is
s ill a subjec o s udy. Table 4 shows some examples o he ensile p ope ies ob ained in
Q&P ea ed s eels and he e ained aus eni e measu ed a e he ea men .
Table 4. Tensile p ope ies and olume % o e ained aus eni e ob ained by Q&P.
S eel
UTS (MPa)
TEL (%)
RA (%)
Re .
0.2C1.96Mn1.49Si0.25Mo
1280-1510
4-15
11-16
[80]
0.3C3Mn1.6Si
1500
17
1-15
[49]
0.2C3.5Mn1.5Si
1415-1630
15-23
8-19
[48]
0.2C1.57Mn1.55Si
1220-1340
12-16
6-14
[132]
0.5C2.01Mn1.03Si1.58C 0.34Mo0.11Ti
1741-1931
2-12
12-28
[133]
0.28C4.08Mn1.42Si
1399-1548
13-16
12-19
[134]
Se e al s udies on Q&P s eels epo ed he end ha he inc ease in RA is accompanied by
inc easing o al elonga ion (TEL) bu no so much by uni o m elonga ion (UE), which e lec s
he con ibu ion o TRIP e ec . As men ioned in he p e ious sec ion, i is he s abili y o he
e ained aus eni e, a he han i s amoun , which de e mines he inal mechanical p ope ies.
Seo e al. [135] concluded ha , in Q&P p ocessed medium Mn s eels, he key ac o s
de e mining he mechanical p ope ies we e he kine ics o he mechanically-induced
aus eni e o ma ensi e ans o ma ion and he amoun o seconda y ma ensi e. One
cha ac e is ic o Q&P s eels is he ele a ed YS/TS a io due o a conside able amoun o
empe ed ma ensi e and, he e o e, he s ain ha dening a e o hese s eels is ela i ely low.
This esul s a o able o hole expansion, bu he p esence o seconda y ma ensi e
signi ican ly educe YS and, consequen ly, he YS/TS a io [8].
25
1.5 Medium Mn s eels (MMnS)
Medium manganese s eels (MMnS), wi h Mn con en s be ween 4 w .% and 10 w .% [52], a e
conside ed ano he p omising hi d gene a ion AHSS due o hei combina ions o p ope ies.
These s eels a e based on a concep p oposed by Mille [136] in 1972. In his case, cold
olled ma ensi ic mic os uc u es a e in e c i ically annealed o ming aus eni e by he
so-called Aus eni e Re e se T ans o ma ion (ART) phenomenon [137]. Aus eni e
s abiliza ion can be achie ed h ough di usion o subs i u ional elemen s, such as Mn, (and
also C) in o aus eni e du ing high empe a u e p ocessing [138,139], esul ing in a he high
con en s o e ained aus eni e (20–40%) [140–142]. A schema ic o his p ocess is shown in
Figu e 9. The s abili y o e ained aus eni e and ul a- ine mic os uc u e in MMnS, seem o
play a key ole in he imp essi e s eng h/duc ili y balance o hese s eels [143–145].
Figu e 9. Schema ic o he ypical p ocessing ou e o medium-Mn s eels, whe e α’ is ma ensi e, α
is e i e and γ is aus eni e.
In e c i ical annealing s age ca ied ou in MMnS implies much longe imes ( ypically hou s)
han he pa i ioning s age in Q&P p ocess ( ypically anging om a ew seconds o ew
minu es). On he o he hand, ha ing bo h a empe ed ma ensi e ma ix, he ul a ine-g ained
e i e in medium Mn s eels is so e . The e o e, he s eng h o Q&P s eels is gene ally highe
han ha o medium Mn s eels, bu Q&P s eels ha e a much lowe elonga ion due o a lowe
RA ac ion [146].
Al hough las yea s ad anced, he unde s anding o medium manganese s eels is s ill unde
de elopmen . The mic os uc u e e olu ion, mic os uc u e-p ope ies ela ionship, he e ec
o alloying elemen s and con en s, e ec s o p ocessing and pos -manu ac u ing, e c. a e
Ac3
RT
Tempe a u e (ºC)
Time (s)
α'
Ho olling
Ac1
Ms
Cold olling
α'
α'
α'
γ
γ
γγ
ART annealing
γ
γ
γγ
α
α
26
some o he aspec s which need o be app oached. Mo eo e , al hough i is easie han o
second-gene a ion ad anced high s eng h s eels, such as TWIP s eels, p ocessing o MMnS
in indus ial en i onmen s is s ill challenging due o hei ela i ely high alloy con en s [147].
E en hough he phase ans o ma ion beha io gi en in medium Mn s eels du ing i s
p ocessing is ela i ely unde s ood, he p ecipi a ion and dissolu ion o he ca bides and how
does i a ec aus eni e e e sion equi ed u he s udy. Speci ically, he unde s anding o
how he hea ing a e and aus eni e e e sion empe a u e a ec s he e olu ion o ca bides
would o e new awa eness o he no el mic os uc u e designs in MMnS [146].
1.6 Q&P ea men o au omo i e indus y
The equi emen s o he au omo i e indus y o weigh educ ion, imp o ed uel e iciency,
and CO2 mi iga ion along wi h c ash sa e y s anda ds imposed by go e nmen s make he
de elopmen o hi d gene a ion AHSS a p io i y o he s eel indus y, as hey p o ide an
oppo uni y o he de elopmen o cos -e ec i e and ligh -weigh pa s wi h imp o ed sa e y
and op imized en i onmen al pe o mance [148–150].
The ul a-high s eng h and excellen duc ili y, o o mabili y, o Q&P s eels make hem well
sui ed o weigh educ ion in ca bodies, while inc easing occupan sa e y. Q&P s eels ha e
a highe s e ch- o ming capabili y han con en ional high s eng h s eels (HHS) due o he
signi ican ly highe a e o wo k ha dening. Fu he mo e, compa ed o mos HSS wi h he
simila ensile s eng h, Q&P s eels ha e subs an ially highe o mabili y; he e o e, hey a e
especially sui able o s uc u al and sa e y pa s o au omobiles, such as c oss membe s,
longi udinal beams, B-pilla ein o cemen s, sills, and bumpe ein o cemen s, which a e
di icul o cold o m wi h con en ional HSS wi h he same s eng h [151]. Q&P s eels a e s ill
a an ea ly s age o indus ial implemen a ion and migh be de eloped o bo h high-s eng h
componen s in au omo i e and o he applica ions.
1.6.1 Comme cialized Q&P s eels
To da e, wo le els o Q&P s eels a e in global p oduc ion, wi h 980 MPa and 1180 MPa in
ensile s eng h. The enhanced p ope ies o Q&P s eels o e bene i s o e simila s eng h
s eels o o he mic os uc u es. Fo example, compa ed agains Dual Phase s eel wi h simila
yield and ensile s eng h, Baos eel p oduce a Q&P s eel which shows highe uni o m
elonga ion, o al elonga ion, wo k ha dening index, and highe lowes poin on he o ming
27
limi cu e (FLC0) [152]. A celo Mi al epo s simila s eng h and elonga ion p ope ies o
he QP980 s eel, wi h a a ge ed 23% hole expansion a io [153].
QP980 is unde going inc easing use in au omo i e p oduc ion. In 2016 Gene al Mo o s
p esen ed he i s applica ion in he Che ole Sail om SAIC-GM [154]. La e , he 2021 Fo d
B onco used ho dip gal anized QP980 in i e componen s o he on and ea loo
assemblies [155]. 60% o he body s uc u e o he 2021 Jeep G and Che okee L is made
om AHSS, wi h some pa s s amped om 3 d gene a ion AHSS [156]. Table 5 con ains
ypical mechanical p ope y anges o indus ially p oduced QP980 and QP1180 [151].
Table 5. Typical mechanical p ope y anges o indus ially p oduced QP980 and QP1180. Adap ed
om [151].
Ma e ial
Yield s eng h (MPa)
Tensile s eng h (MPa)
To al elonga ion (%)
QP980
650-800
980-1050
17-22
QP1180
950-1150
1180-1300
8-14
A ecen con e ence highligh ed se e al applica ions (Table 6) whe e hinne gauge QP980
eplaced DP590 in Gene al Mo o s ehicles [157]. The same p esen a ion showed he
example o QP980 eplacing p ess ha dening s eels in B-pilla ein o cemen s and doo
an i-in usion beams in a Fi s Au o Wo ks ehicle.
Table 6. Replacing DP590 wi h QP980 allows o downgauging. Adap ed om [157].
Pa
Ma e ial
Pa model
Pa p o o ype
Kick Down
Lowe
DP590 1.8 → QP980 1.6
Weigh sa ing: 0.38 kg
A Pilla Inne
Lowe
DP590 1.2 → QP980 1.0
Weigh sa ing: 0.20 kg
Hinge Pilla
Inne
DP590 1.2 → QP980 1.0
Weigh sa ing: 0.58 kg
A Pilla Inne
uppe
DP590 1.2 → QP980 1.0
Weigh sa ing: 0.30 kg
1.6.2 Weldabili y o Q&P s eels
In addi ion o low weigh and good mechanical beha io , high le els o weldabili y a e
impo an o ha e a compe i i e ma e ial o he au omo i e indus y since high-quali y welded
join s a e equi ed o ensu e he ehicle body's sa e y [158,159]. Howe e , nume ous s udies

28
demons a ed ha , due o he he mal e ec o welding, appa en ma e ial so ening can
occu du ing di e en ypes o welding me hods, such as lase welding (LW) [160–162],
esis ance spo welding (RSW) [163–165], gas me al a c welding (GMAW) [160,166] o
ic ion s i welding (FSW) [167–170], in AHSSs like DP s eel [160,165–168], TRIP s eel
[161,169,171], and ma ensi ic s eel [162,166,171]. Usually, p ope y losses a e ela ed wi h
he empe ing o he ma e ial, which p oduces he e ogenei ies in he mic os uc u e o he
hea -a ec ed zone whe e local s ess o s ain concen a ion is p e e en ially de eloped
du ing de o ma ion.
In Q&P s eels he ma ensi e is empe ed du ing pa i ioning, while he aus eni e is s abilized.
The e o e, he in e nal s uc u es o Q&P s eels a e mo e s able. Recen s udies e i ied he
ex ao dina y welding pe o mance o QP980 s eel du ing LW [172–174] and FSW [175,176],
and equal s eng h join s o he s eel we e success ully ab ica ed wi h negligible
hea -a ec ed zone so ening. Wang e al. [177] demons a ed he iabili y o achie ing high
s eng h join s in he QP1180 s eel, while in TRIP [169] and DP [170] s eels wi h simila
s eng h le els a e di icul o achie e such join s eng h le els.
The pe o mance o he join is de e mined by he welding me hod since, unde a ious hea
sou ce ene gies, welding speeds, and cooling a es, he dimension and deg ee o so ening
o he hea -a ec ed zone can a y conside ably [160,178,179]. Al hough se e al wo ks
showed ha Q&P s eels ha e high welding pe o mance [172,173,175,177,180], u he
esea ch is equi ed o de e mine he in luence on he mic os uc u e and mechanical
p ope ies, especially in ul ahigh s eng h s eels (>1 GPa).
1.7 Q&P ea men o applica ions equi ing wea
esis ance
I is complex o es ima e he wea esis ance o a ma e ial, as i is de ined by he conjunc ion
o many p ope ies o he ma e ial and a ies wi h he wea condi ion, en i onmen , and
mechanism. Typically, wea esis ance is di ec ly ela ed wi h ha dness, al hough many o he
ac o s mus be conside ed. Inc eased ha dness is gene ally ob ained by inc easing he
ca bon con en o he s eel. Howe e , he highe ca bon con en ypically leads o a dec ease
in o he p ope ies o in e es , such as oughness, bendabili y, and weldabili y [181].
The e o e, o he me hods a e being in es iga ed o inc ease he wea esis ance o s eel
wi hou d as ic loss o o he impo an p ope ies.
29
Al hough quenched and empe ed (Q&T) s eels show good ab asi e wea pe o mance,
some s udies demons a ed ha mic os uc u es con aining RA, despi e ha ing lowe
ha dness, p esen ed be e wea esis ance. The bene i s o RA we e obse ed in block on
ing es ing o aus empe ed duc ile i on [182], pin on-disk es ing o bo h mo led cas i on
[183] and a D-2 ool s eel [184] and a non-s anda d impac -ab asion es o a 13.8 w .% C ,
2.7 w .% Mn con aining s eel [185].
Mo e ecen ly, Q&P s eels ha e been s udied in a wea con ex and ha e shown o be o
in e es o wea applica ions. All he Q&P s udies ela ed o wea a e e y ecen and mos
o hem co espond o he mining indus y. In gene al, i is concluded ha he e ained
aus eni e is e y bene icial o he ibological beha io (wea and ic ion). Unde mechanical
loading, a highe amoun o e ained aus eni e helps o ob ain a hicke ha dened laye due
o ans o ma ion in o ma ensi e. In Q&P s eels, apa om he di ec ela ionship be ween
ha dness and wea esis ance, he la e also depends on he mic os uc u e and, he e o e,
on he Q&P p ocess condi ions (QT, PT, P ) [186]. Gene ally, highe aus eni e con en
ansla es in o be e ab asi e wea pe o mance. A clea example o his phenomenon is
shown in he wo k o Wasiak e al. [187], who obse ed ha wea is educed by p ac ically
50% in he case o Q&P compa ed o Q&T in a 35C SiMn5-5-4 s eel, so ha he imp o emen
ob ained is subs an ial. The employed Q&P cycle consis ed o a ull aus eniza ion ollowed
by an oil quenching o 235 ºC and a pa i ioning a 260 ºC, ob aining 20% o RA.
P. Wol am e al. [188] calcula ed he olume loss o Q&P ea ed 9260 s eel wi h no malized
samples wi h espec o he pe o mance o AR400F samples du ing d y sand and ubbe
wheel (DSRW) wea es s, and he e also a bene icial e ec o aus eni e was con i med. In a
subsequen s udy, he ma e ial was examined in a simula ed wea ack a e con olled
sc a ch es s o di e en mic os uc u al condi ions: a e as quenching and a e quenching
and empe ing (Q&T) and quenching and pa i ioning (Q&P). The apidly cooled ma e ial
ac u ed ou o he wea ack in esponse o he inden a ion o ce. In Q&T, he wea ack
edges showed a chipping mechanism, while much less agmen a ion was obse ed wi h he
aus eni e-con aining Q&P condi ion, which helps explaining he imp o ed wea esis ance o
he Q&P mic os uc u es. The same eam also con i med ha he high Si Q&P p ocessed
s eel exhibi ed a be e combina ion o ha dness and wea esis ance han he same Q&T
p ocessed s eel.
Ano he ecen s udy [189] s udied he wea esis ance o di ec quenched and pa i ioned
(DQ&P) s eels subjec ed o impelle - umble impac -ab asi e wea es ing [189]. This s udy
30
ound ha wea pe o mance depended solely on ha dness, ega dless o mic os uc u e,
and did no see imp o emen s wi h inc easing RA. Howe e , i mus be conside ed ha he
wea esis ance measu ed a labo a o y le el depends on he es s ca ied ou , and hese
a e e y sensi i e o he es pa ame e s.
Gene ally, wea applica ions equi e hicke ma e ials han hose used in he au omo i e
indus y. The e o e, he e is a need o unde s and he he mal g adien s ha can a ise when
applying Q&P o hicke samples. S ewa e al. [190] ca ied ou some simula ions o
ep oduce he he mal his o y ha would occu in a 300M pla e s eel o 18 mm hick a
di e en hicknesses, obse ing di e en quenching empe a u es and non-iso he mal
pa i ioning depending on he hickness. Then, hey e alua ed he mic os uc u es a ising
om each he mal cycle, disco e ing ha he e ained aus eni e a ied be ween 5% and 27%
be ween he su ace and he cen e o he sample. As app eciable amoun s o aus eni e we e
e ained h ough he simula ed pla e hickness ega dless o ini ial quench, hey concluded
ha he insensi i i y o quenching condi ions migh sugges beha io ha would be
conside ed bene icial in he amewo k o obus indus ial implemen a ion.
1.7.1 Toughness in Q&P s eels o wea applica ions
In Q&P s eels o wea applica ions, oughness is usually a desi ed p ope y. Repo ed
li e a u e show ha gene ally his pa ame e is imp o ed in Q&P s eels wi h espec o hose
ea ed by a con en ional Q&T ea men [191–193]. This imp o emen is likely due o he
lowe ha dness alues measu ed in Q&P s eels. Figu e 10 shows a compa ison be ween he
Cha py impac ene gies ob ained o a Fe-0.19C-1.5Si-1.46Mn s eel ea ed by wo di e en
Q&P and Q&T cycles [194]. As i can be seen, he imp o emen achie ed by he Q&P
ea men is subs an ial, specially a high empe a u es.
Figu e 10. Compa ison o Cha py impac ene gies a di e en empe a u es o Q&T and Q&P
ea ed specimens [194].
31
Chap e 2
Mo i a ion and objec i es
38

39
Chap e 3
Ma e ials and expe imen al
p ocedu es
In his chap e he ma e ials and echniques employed in his wo k a e desc ibed. The
easons o selec ing he chemical composi ions, as well as he p ocedu es employed o ca y
ou he Q&P cycles a e p esen ed. Finally, he me hods and expe imen al echniques
employed o pe o m bo h mic os uc u al and mechanical cha ac e iza ion a e also
desc ibed.
3.1 Ma e ials and p ocessing
3.1.1 Ma e ials
The ma e ials employed in his wo k we e di ided in wo g oups:
• Low C medium Mn s eels wi h di e en Mn and Ni addi ions o be ea ed by high
pa i ioning empe a u e Q&P ea men s and s udy o hei mic os uc u e and
s eng h-duc ili y beha io . These ma e ials we e p oduced in he labo a o y in he
o m o cold olled shee s and we e s udied as po en ial candida es o he au omo i e
sec o .
• Medium and high C s eels employed o in es iga e he bene i s o Q&P hea
ea men in ela ion wi h wea applica ions. Se e al comme cial g ades we e Q&P
ea ed and cha ac e ized in e ms o mic os uc u e and ha dness, wea esis ance
and oughness p ope ies. In his case, classical Q&P cycles we e applied, and he
applica ion o high pa i ioning empe a u es was planned as pa o a u u e wo k.
3.1.1.1 Medium Mn s eels
Fou s eels, e e ed o as 2Mn, 4Mn, 6Mn and 6Mn2Ni, and which composi ion is shown in
Table 7, we e s udied. The 2Mn s eel, which has a ypical composi ion o a Q&P s eel, was
es ablished as he e e ence s eel. The o he s eels we e medium Mn s eels and 6Mn2Ni
40
s eel also con ained Ni. Alloying elemen s and hei amoun s we e selec ed in o de o s udy
he in luence o Mn addi ions ( he 4Mn and 6Mn s eels wi h espec o he 2Mn s eel), and Ni
addi ions ( he 6Mn2Ni s eel wi h espec o he 6Mn s eel). The addi ion o bo h Mn and Ni
was made o p omo e he pa i ioning o hese elemen s in o de o inc ease he s abili y o
he aus eni e. The addi ion o Ni was also mo i a ed by i s lowe seg ega ion in compa ison
wi h Mn. Silicon was added o sup ess ca bides o ma ion.
Table 7. Composi ion (w .%) o he medium Mn s eels employed in his wo k.
S eel e .
C
Mn
Ni
Si
P
S
N
2Mn
0.2
2.0
-
1.5
0.013
0.0015
0.0031
4Mn
0.19
3.8
-
1.4
0.012
0.0017
0.0035
6Mn
0.19
5.8
-
1.4
0.011
0.0013
0.003
6Mn2Ni
0.19
5.7
1.6
1.4
0.014
0.0019
0.0041
Ingo s o ou s eel g ades we e p oduced in he labo a o y (A celo Mi al, F ance, in he
ame o he HIGHQP p ojec , g an No 709855) using a acuum induc ion mel ing u nace.
The ingo s we e ehea ed o ~1250 ºC and a oughing s age was pe o med o dec ease he
hickness om 60 mm o 30 mm. The ob ained slabs we e hen cu in o i e small ingo s
which we e ho olled a e being ehea ed o ~1250 ºC. The ho olling consis ed o i e ho
olling passes (Tend o olling app oxima ely abo e 900 ºC) and coiling a 500 ºC. The ho
olled shee s o abou 4 mm hickness we e g ound on bo h su aces o dec ease he
hickness o 2.8 mm. A so ening anneal was applied be o e cold olling which consis ed o
holding a 600 °C o 1 h ollowed by wa e quench. Then, he shee s we e cold olled wi h
app oxima ely 50% educ ion o ob ain a inal hickness o 1.5 mm.
Ho olled ma e ials we e cha ac e ized be o e and a e so ening annealing by
mic os uc u e obse a ion wi h a ligh op ical mic oscope (LOM) a e polishing down o 1 μm
and e ching wi h sodium me abisul i e (A celo Mi al, F ance, in he ame o he HIGHQP
p ojec , g an No 709855). Vicke s mic oha dness es s wi h 9.8 N load we e also pe o med
wi h he ho olled samples. The esul s o he ha dness measu emen s o ho olled ma e ials
a di e en s eps, oge he wi h some examples o he obse ed mic os uc u es, a e
p esen ed in Figu e 11. The ha dness o he 2Mn s eel was 224 HV, which was accep able
o u he cold olling and he e o e was no hea ea ed. In con as , he ob ained ha dness
o o he s eels was qui e high (420 HV–490 HV). This means ha di ec cold olling o hese
ho olled shee s was di icul , and he e o e speci ic so ening ea men s we e applied as
explained in he p e ious pa ag aph. A e he so ening ea men s, he ob ained ha dness
was in ange o 280 HV–320 HV, which allows o labo a o y cold olling p ocedu es.
41
Figu e 11. Ligh op ical me allog aphy (LOM) images and ha dness o he ho olled
mic os uc u es. The 2Mn (a), 4Mn (b), 6Mn (c) and 6Mn2Ni (d) s eels a e ho olling, and he 4Mn
(e), 6Mn ( ) and 6Mn2Ni (g) s eels a e so annealing.
As can be seen in he mic og aphs o Figu e 11, he 2Mn s eel mainly p esen ed a
e i e-pea li e s uc u e wi h some mino ac ions o baini e and ma ensi e. The
mic os uc u e in he emaining s eels consis ed o a mix u e o baini e–ma ensi e. In he
case o he 4Mn s eel, he majo phase seemed o be baini e and in he 6Mn and 6Mn2Ni
s eels, i was ma ensi e. These mic os uc u e obse a ions we e in ag eemen wi h he
measu ed mic oha dness le els o he di e en ho olled shee s. The p esence o ha d
phases such as baini e and ma ensi e was a consequence o he highe Mn and Ni con en s
added o he s eels. So ening annealing pe o med on he 4Mn, 6Mn, and 6Mn2Ni s eels
esul ed in he eco e y o he s uc u e (dec ease o disloca ion densi y), which was help ul
in he educ ion o s eel ha dness and, in some cases, led o he p ecipi a ion o ca bides.
3.1.1.2 Medium and high C s eels
Fo his pa o he wo k, h ee comme cial medium and high C s eels we e selec ed (Table
8). The ca bon con en o he selec ed s eels was high enough o gua an ee a minimum
ha dness, allowing o achie e wea esis ance alues simila o hose cu en ly achie ed in
ields whe e wea esis ance is equi ed. In addi ion, i was ensu ed ha he s eels o be
s udied con ained a signi ican amoun o silicon in hei chemical composi ion in o de o
a oid he o ma ion o cemen i e in he pa i ioning s age o he Q&P ea men . On he o he
hand, i mus be conside ed ha Q&P ea men has been ypically s udied in low hickness
p oduc s (such as cold olled shee s). Howe e , he p oduc s employed in wea applica ions
may show highe hickness. As ha denabili y is a cons ain i Q&P is applied in high hickness
p oduc s, he s eels we e in ended o con ain a se ies o chemical elemen s ha ensu e
(a) 2Mn, 224 HV1 (b) 4Mn, 427 HV1 (c) 6Mn, 484 HV1 (d) 6Mn2Ni, 481 HV1
Ho Rolled
(e) 4Mn, 281 HV1 ( ) 6Mn, 310 HV1 (g) 6Mn2Ni, 315 HV1
So -Annealed
42
ha denabili y, as Mn, C , e c. A he same ime, hese elemen s we e in ended o e a d he
o ma ion o baini e in he pa i ioning s age and ha den he ma ensi ic ma ix.
The selec ion o he 3 comme cial s eel g ades was done suppo ed by JMa P o ( 10.2)
he modynamic so wa e. Using his so wa e c i ical cooling a es o a oid di usion-based
phase ans o ma ions (CCR) and ha dness in he as-quenched s a e we e calcula ed o
se e al comme cial s eel g ades. Based on hese esul s, 1.2990, 1.2344, and 300M s eels
we e selec ed (Table 8) wi h he c i e ia ha c i ical cooling a es we e minimized, and he
ha dness alues we e maximized, ensu ing a sui able con en o Si. The con inuous cooling
ans o ma ion (CCT) diag ams calcula ed by JMa P o employed o he p edic ions o CCR
and ha dness o he selec ed s eels a e shown in Figu e 12. The i s wo s eel (1.2990 and
1.2344) a e ool s eels which a e ypically hea ea ed by quenching and empe ing. These
s eels con ain high amoun s o ca bides o ming elemen s (C , Mo, V), which gi e ise o he
seconda y ha dening phenomenon in he empe ing. The main di e ence among bo h s eels
is he C con en . The hi d s eel, 300M, was selec ed mainly due o he high Si con en .
Figu e 12. Theo e ical CCT cu es o 1.2990 (a), 1.2344 (b), and 300M (c) s eels ob ained wi h
JMa P o.
(a) 1.2990 (b) 1.2344
(c) 300 M
43
Table 8. Composi ion (w .%) o he medium and high C s eels employed in his wo k.
S eel e .
C
Si
Mn
C
Mo
Ni
V
1.2990
0.92
0.96
0.36
7.9
1.0
-
1.5
1.2344
0.39
0.97
0.37
5.1
1.2
-
0.92
300M
0.41
1.6
0.83
0.78
0.38
1.8
0.06
3.1.2 Design o he Q&P cycles based on dila ome y
A LINSEIS L78 RITA dila ome e (Tecnalia, Spain) was used o ob ain he phase
ans o ma ion empe a u es, c i ical cooling a es , Q&P cycle pa ame e s, and hen
physically simula e he whole Q&P cycles o unde s and mic os uc u e e olu ion by he
analysis o he expansion/con ac ion beha io . A pic u e o L78 RITA dila ome e is
p esen ed in Figu e 13. The dila ome e ollows he leng h a ia ions o he sample occu ing
du ing he imposed hea ea men . The samples we e hea ed and main ained a empe a u e
by induc ion hea ing. Tempe a u e con ol was done by Type K he mocouples. The samples
we e main ained by e ical hollow qua z ods, being he uppe od mobile. Hence, when
leng h a ia ions occu ed, one od mo ed, and he linea displacemen was cap u ed by an
LVDT (Linea Va iable Di e en ial T ansduce ) senso .
Figu e 13. Global iew on L78 RITA dila ome e .
In he p esen wo k, cylind ical samples, o 3 mm diame e and 10 mm leng h, we e used.
A e machining, he samples we e cleaned by imme sion in e hanol wi hin an ul asound
ba h ( o emo e di and oils om machining) and jus be o e he es , hey we e cleaned
again wi h e hanol. Type K he mocouple was welded in he middle o he clean su ace o
he sample. To a oid oxida ion du ing ea men acuum was done in he expe imen al
chambe , hen, a small amoun o helium (He) was injec ed.

44
3.1.2.1 Ob en ion o phase ans o ma ion empe a u es and c i ical cooling a es
Fi s , Ac1 and Ac3 phase ans o ma ion empe a u es we e de e mined by dila ome y. Fo
ha , samples we e hea ed up o 1000 °C (in he case o Medium Mn s eels) and 1100 ºC (in
he case o medium and high C s eels) a 5 °C/s (medium Mn s eels) and 10 ºC/s (medium
and high C s eels) and hen, a e 120 s o main enance, cooled down o oom empe a u e.
Two es s we e ca ied ou o each medium Mn s eel, whe eas only one es was ca ied ou
o each medium and high C s eel. Once he dila ome y cu e was ob ained, Ac1 and Ac3
empe a u es we e de e mined by he applica ion o he angen me hod. As in medium Mn
s eels a de ia ion was obse ed jus be o e aus eni e ans o ma ion cu e, Ac1 was
conside ed he empe a u e wi h maximum ela i e change in leng h jus be o e
ans o ma ion s a ed. As e e ence o each Ac1 ob en ion me hods, in Figu e 14 he cu es
o he 2Mn and 1.2344 s eels showing Ac1 and Ac3 empe a u es a e p esen ed. The
dila ome y cu es o all s eels a e shown in Appendix A. The esul s o all s eels a e shown
in Table 9. I can be seen ha , in medium Mn s eels, Mn addi ions led o lowe aus eniza ion
empe a u es and Ni addi ion esul ed in a u he dec ease. Since he medium and high C
s eels ha e di e en amoun s o di e en alloying elemen s i is no possible o s ablish a
di ec co ela ion be ween he aus eniza ion empe a u es.
Figu e 14. Dila ome y cu es ep esen ing he de e mina ion o Ac1 and Ac3 empe a u es o he
2Mn (a) and 1.2344 (b) s eels. In (a) Ac1 was de e mined as he empe a u e wi h maximum change
in leng h jus be o e ans o ma ion s a ed and Ac3 was de e mined by he angen me hod; in (b)
bo h empe a u es we e ob ained by he angen me hod.
Once Ac3 empe a u es we e de e mined, c i ical cooling a es o a oid any undesi able
ans o ma ion du ing quenching we e expe imen ally de e mined by dila ome y. The
0.006
0.008
0.010
0.012
0.014
0.016
0.018
0.020
600 700 800 900 1000
Rela i e change in leng h (ΔL/L0)
Tempe a u e (ºC)
Ac1
Ac3
(a) 2Mn s eel
0.012
0.014
0.016
0.018
0.02
0.022
0.024
800 900 1000 1100
Rela i e change in leng h (ΔL/L0)
Tempe a u e (ºC)
Ac1 Ac3
(b) 1.2344 s eel
45
p ocedu e o ob ain hese alues was as ollows: i s , samples we e hea ed up o a soaking
empe a u e 50 ºC abo e Ac3 and a e a soaking ime o 120 s we e cooled down o oom
empe a u e employing di e en cooling a es. The i s cooling a e selec ed o each s eel
was based on heo e ical esul s ob ained by a he modynamic so wa e. I ha cooling a e
esul ed in any u he ans o ma ion apa om ma ensi ic a highe one was es ed. The
dila ome y cu es o all s eels a e shown in Appendix A and all CCR a e p esen ed in Table
9. I can be seen ha inc easing Mn in medium Mn s eels led o a conside able dec ease o
his pa ame e and he alloying con en s o he medium and high C s eels we e also su icien
o achie e low CCRs.
Table 9. Phase ans o ma ion empe a u es (Ac1, Ac3, Ms and M ), c i ical cooling a es (CCR) and
he aus eni e measu ed in he quenching s a e o all he s eels employed in his wo k.
S eel e .
Ac1
(ºC)
Ac3
(ºC)
Ms
(ºC)
M
(ºC)
CCR
(ºC/s)
As-quenched RA
(%)
Medium Mn s eels
2Mn
760
920
363
215
60
1
4Mn
730
873
313
101
0.5 – 2
3
6Mn
695
841
252
<RT
<0.1
7
6Mn2Ni
690
793
219
<RT
<0.1
7
Medium and high C s eels
1.2990
881
987
342
<RT
0.5 – 1
<5
1.2344
866
993
317
~RT
<1
-
300M
758
875
270
~RT
<2
-
3.1.2.2 Ob en ion o ma ensi ic ans o ma ion cu e
The e a e di e en ways o ob ain he ma ensi ic ans o ma ion cu e. The i s me hod,
pu ely heo e ical, consis s in calcula ing he Ms empe a u e by means o he And ews
equa ion (1) [195] and, hen, calcula e he aus eni e ac ion co esponding o each
empe a u e by means o he Kois inen-Ma bu ge equa ion (2) [196]:
𝑀𝑠=539 −423𝐶 − 30.4𝑀𝑛 −17.7𝑁𝑖 −11.0𝑆𝑖 −12.1𝐶𝑟 − 7.5𝑀𝑜
(1)
whe e he alloying elemen s a e exp essed in weigh pe cen .
𝑓
𝛾= exp(−𝛼𝑚×(𝑀𝑠− 𝑇))
(2)
whe e γ is aus eni e olume ac ion; T is cu en empe a u e, ºC; and αm is a cons an
coe icien wi h a alue equal o 0.011 K-1.
O he me hod, he one employed in his wo k, is o ob ain he ans o ma ion cu e
expe imen ally by dila ome y. Thus, he samples we e hea ed up o Ac3 + 50 ºC a 5 ºC/s
46
(medium Mn s eels) and 10 ºC/s (medium and high C s eels) and, a e 120 s, we e cooled
down o oom empe a u e. The applied cooling a e was 100 ºC/s in he 2Mn s eel, 20 ºC/s
in he medium Mn s eels, and 45 ºC/s in he medium and high C s eels. Then, he samples
we e ehea ed up o 500 ºC a 5 ºC/s. Applying he le e ule be ween he expansion o he
un ans o med aus eni e cu e and ha om he ehea ing, ma ensi e ans o ma ion cu es
we e calcula ed. The inal change in leng h was associa ed wi h he amoun o ma ensi e in
he as-quenched s a e, which was ob ained om he ollowing dila ome y: a sample was
quenched o oom empe a u e om Ac3 + 50 ºC a e aus eni izing i o 120 s, conside ing
he same cooling a e as be o e. Then, aus eni e con en o he sample was measu ed by
magne iza ion in medium Mn s eels (TU Del , he Ne he lands, in he ame o he HIGHQP
p ojec , g an No 709855), and X- ay di ac ion in medium and high C s eels (SGIke ,
UPV/EHU, Spain). The measu ed alues a e collec ed in he las column o Table 9. F om
he ma ensi ic ans o ma ion cu e, Ms and M empe a u es we e ob ained as he
empe a u es in which 5% and 95% o he ma ensi e ans o ma ion occu ed, espec i ely.
As an example, in Figu e 15a he dila ome y cu e o he 2Mn s eel is shown and he Ms and
M empe a u es o all he s eels a e p esen ed in Table 9. The dila ome y cu es o all
s eels used o ob ain he ma ensi ic cu e a e shown in Appendix A. The QTs selec ed o
each Q&P cycle we e ob ained om he co esponding ma ensi ic ans o ma ion cu e and
a e de ailed in he nex sec ion. In Figu e 15b he p ocedu e o ob ain a QT co esponding o
25% o un ans o med aus eni e (QT25) is ep esen ed by ed a ows.
Figu e 15. Dila ome y cu e o he 2Mn s eel o he de e mina ion o Ms, M and ma ensi e
ans o ma ion cu e (a) and he co esponding ma ensi ic ans o ma ion cu e showing he
de e mina ion o he empe a u e co esponding o a ans o ma ion o 75% ma ensi e (b).
0.000
0.005
0.010
0.015
0.020
0.025
0 100 200 300 400 500
Rela i e change in leng h (ΔL/L0)
Tempe a u e (ºC)
B
A
C
Le e ule:
α’ = AB/AC
(a)
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400 500
Ma ensi e ( ol.%)
Tempe a u e (ºC)
(b)
47
3.1.2.3 Design o he hea ea men s (QT, PT and P )
The selec ion o he he mal cycle pa ame e s ollowed a di e en s a egy depending on he
equi ed inal p ope ies. The e o e, a se ies o ea men s was designed o medium Mn
s eels and ano he o medium and high C s eels.
Design o cycle pa ame e s in medium Mn s eels:
In all cases, ull aus eniza ion was pe o med by hea ing a Ac3 + 50 ºC. Then, a e 120 s o
soaking, samples we e cooled down o he selec ed QTs a a cooling a e abo e CCR. A e
5 s a he QT, samples we e hea ed up o he es ablished PT. Finally, once he pa i ioning
ime was comple ed, samples we e cooled down o oom empe a u e.
In a i s s age, h ee Q&P cycles we e designed: A e e ence cycle wi h a ypical pa i ioning
empe a u e o 400 ºC and a quenching empe a u e co esponding o 25% o un ans o med
aus eni e (QT25), and wo high pa i ioning empe a u e cycles wi h di e en quenching
empe a u es, one o which coincided wi h ha used in he e e ence cycle and o he
co esponding o 10% o un ans o med aus eni e (QT10). In his way, bo h he in luence o
PT and QT on he mic os uc u e could be in es iga ed.
High pa i ioning empe a u e was selec ed as he empe a u e in which aus eni e e e se
ans o ma ion s a s (TART). The selec ion o TART as pa i ioning empe a u e was mo i a ed
om p e ious wo k, in which i was obse ed ha empe a u es beyond he in e c i ical ange
lead o undesi able decomposi ion o aus eni e in o pea li e [39]. Highe pa i ioning
empe a u es migh also lead o excessi e aus eni e which would be di icul o s abilize.
Ne e heless, he in es iga ion o he e ec o pa i ioning empe a u es a ound TART would
be in e es ing as pa o a u u e wo k.
The conside a ion o wo QT condi ions (QT10 and QT25) ollowed by a pa i ioning s age a
TART, aimed a in es iga ing he in luence o di e en con en s o p e-exis ing aus eni e on
he o ma ion o e e ed aus eni e. The p e-exis ing aus eni e con en s we e de ined based
on a p e ious wo k [112] whe e i was epo ed ha duc ili y s ongly dec eased when
p e-exis ing aus eni e was highe han 30% due o he p esence o seconda y ma ensi e.
The o ma ion o seconda y ma ensi e was epo ed o be he consequence o insu icien
aus eni e s abiliza ion du ing he pa i ioning s age. The e o e, in his hesis, p e-exis ing
aus eni e con en s we e kep below 30%.
The empe a u e o he s a o aus eni e e e se ans o ma ion (TART) upon hea ing om
he QT, was de e mined by dila ome y o each s eel. Fo his, samples we e hea ed o
54
B agg’s law ela es he angle θ, he wa eleng h o he beam (λ) and he spacing be ween he
planes o a oms in he ma e ial (d), and n is an in ege ep esen ing he o de o he di ac ion
peak:
𝑛𝜆 = 2𝑑 sin 𝜃
(3)
Addi ionally, he olume o ma e ial ha has planes wi h he same space and o ien a ion o
he di ac ion and he in ensi y o a di ac ed beam in a pa icula di ec ion a e p opo ional.
Thus, om he ela i e in ensi ies o he di ac ed beams, he ela i e olume o a
polyc ys alline ma e ial phases can be es ima ed [197].
The samples s udied in his wo k a e assumed o be consis ed o e i e (which ep esen
ma ensi e) and aus eni e. Acco ding o ASTM E975-13, he olume ac ion o aus eni e (Vγ)
can be calcula ed as ollows:
𝑉
𝛾=𝐼𝛾𝑅𝛾
⁄
𝐼𝛼𝑅𝛼
⁄+ 𝐼𝛾𝑅𝛾
⁄
(4)
whe e Iγ and Iα a e he measu ed in ensi ies o a pa icula (hkl) peak abo e he backg ound
o aus eni e and e i e, espec i ely; and Rγ and Rα a e he calcula ed in ensi ies o a
pa icula (hkl) aus eni e and e i e peak (s anda d alue), espec i ely. In his wo k, he
employed (hkl) peak o bo h aus eni e and e i e was (200), being he co esponding R
alues 34.78 and 20.73, espec i ely.
Thus, in his wo k, o he measu emen o RA in he Q&P samples, X- ay powde di ac ion
pa e ns we e collec ed by using a B uke D8 Disco e di ac ome e (SGIke , UPV/EHU,
Spain) equipped wi h a C Twis ube, V il e (λ = 2.291 Å), PolyCapTM (1μ single c ys al
cylinde s) sys em o pa allel been gene a ion (di e gence o 0.25°), and a 1-D LynxEye
de ec o (ac i e leng h in 2θ 2.7º). The samples we e moun ed on a Eule ian C adle wi h
au oma ic con olled X-Y-Z s age. Da a we e collec ed om 50 o 120° 2θ (s ep size = 0.04
and ime pe s ep = 1 s). Peak a ea in ensi y was e alua ed using he peak- i op ion o he
WinPLOTR so wa e.
3.2.2 Scanning Elec on Mic oscope (SEM and FE-SEM)
Scanning elec on mic oscopy (SEM) is a mic os uc u al cha ac e iza ion echnique in which
a high-ene gy elec on beam is ocused on o a ine p obe ha sca e s inelas ically when i
s ikes he su ace o a solid sample. The elec ons a e inelas ically sca e ed, hus
gene a ing a ious signals om he sample ha a e collec ed and ampli ied. Scanning he

55
p obe beam ac oss he sample su ace o ms a digi ized image displaying one o mo e o he
collec ed signals on a moni o ha has he same ime base as he p obe scan. Va ious signals
a e gene a ed as a esul o he impac o he inciden elec ons, being he seconda y
elec ons he mos commonly used, al hough cha ac e is ic X- ays, high ene gy
backsca e ed elec ons, isible ca hodoluminescence and he ne specimen cu en ha e all
been used o acqui e mic os uc u al in o ma ion om samples examined in he scanning
elec on mic oscope [198]. In his wo k a ield emission sou ce o he elec on beam was
used in some o he medium Mn s eel samples o imp o e he pe o mance o SEM
(FE-SEM).
Samples selec ed o FE-SEM (JEOL® JSM7000F) (Colo ado School o Mines, EEUU) we e
p epa ed by con en ional polishing o 1 µm, ollowed by a inal polishing wi h colloidal silica.
Then, he e we e e ched wi h 2% Ni al o 30 s. Cha ac e iza ion condi ions we e a beam
ol age o 15 KV, a medium p obe cu en , and a wo king dis ance o 10 mm.
SEM (QUANTA 200 FEI) (Tecnalia, Spain) cha ac e iza ion was pe o med o he Q&P
samples o he 1.2990 and 300M s eels. In his case, samples we e p epa ed by con en ional
polishing o 1 µm and e ched wi h 2% Ni al o 1 min. A beam ol age o 25 KV, and a wo king
dis ance o 10 mm we e employed. In addi ion, ene gy-dispe si e X- ay spec oscopy (EDS)
analysis was ca ied ou in o de o iden i y he composi ion o some o he phases p esen ed
in he 1.2990 s eel.
3.2.3 Elec on Backsca e Di ac ion (EBSD)
Elec on backsca e di ac ion (EBSD) is a scanning elec on mic oscope (SEM) based
echnique. I allows he measu emen o mic o ex u e ( ex u e on he scale o he
mic os uc u e) [199], mic os uc u e quan i ica ion [200], g ain and phase bounda y
cha ac e iza ion [201,202], phase iden i ica ion [203] and s ain de e mina ion [204] in
c ys alline mul iphase ma e ials o any c ys al s uc u e.
By ocusing an elec on beam on a c ys alline sample, di ac ed pa e ns a e ob ained, which
a e subsequen ly e alua ed and indexed. Gene ally, his is done au oma ically, and he da a
is ou pu g aphically and s a is ically. The mos e sa ile and illumina ing esul s a e he OIM
maps, which a e a quan i a i e ep esen a ion o an a ea o he analyzed mic os uc u e in
e ms o i s c ys allog aphic cons i uen s [205]. One such map is image quali y (IQ), which is
a me ic ha desc ibes he quali y o a di ac ed pa e n. An IQ map is cons uc ed by
mapping he measu ed IQ alue o each di ac ion pa e n ob ained du ing an OIM scan o
56
a g ay o colo scale. Bo h he "pe ec ion" o he c ys al la ice and he a oms p esen wi hin
he di ac ion olume a ec he IQ [206,207].
In his wo k, scans we e pe o med on a ield emission scanning elec on mic oscope
(FE-SEM, JEOL® JSM7000F) (Colo ado School o Mines, EEUU) wi h a beam ol age o
20 KV and a medium p obe cu en . The acquisi ion o EBSD scans was done using a s ep
size o 0.06 μm. Selec ed samples we e p epa ed by con en ional polishing o 1 µm, ollowed
by a inal polishing wi h colloidal silica. The ob ained esul s consis ed on IQ maps and
iden i ica ion o a e age g ain size o he e ained aus eni e.
3.2.4 T ansmission Elec on Mic oscopy (TEM)
The ansmission elec on mic oscope (TEM) can be comp ehended as a ool enginee ed
speci ically o he analysis and isualiza ion o samples a mic ome ic and nanome ic scale.
This kind o elec on mic oscope has capabili y o e eal highly complex le els o de ail which
a e inaccessible by a con en ional ligh mic oscope.
In he TEM high ene gy elec ons a e elas ically sca e ed as hey pene a e a hin specimen.
The ansmi ed elec ons a e hen ocused by elec omagne ic lenses o o m a well- esol ed
image ha can be iewed on a luo escen sc een o a cha ge-coupled de ice [208].
In his wo k mic os uc u e cha ac e iza ion o some o he Q&P ea ed medium Mn s eel
samples was done by means o a TEM (Talos F200i ield emission gun ins umen equipped
wi h a B üke X-Flash100 XEDS spec ome e ) (SGIke , UPV/EHU, Spain). Elemen al maps
we e ob ained by XEDS in he STEM mode unde a high annula da k ield (HAADF) de ec o
o Z con as imaging in STEM condi ions (came a leng h o 160 mm) using a pixel size o
2 nm, a dwell ime o 900 s and an image size o 512 x 512 pixels.
Thin- oil specimens we e p epa ed o he obse a ion in he ansmission elec on
mic oscope. A hin- oil is a 3 mm diame e disk wi h a cen al hole a ound which he TEM
obse a ion was pe o med. The hin- oil specimens mus be less han 100 nm in hickness
o minimize inelas ic sca e ing o he ansmi ed beam as i passes h ough he specimen.
Good specimen p epa a ion is c i ical. The p ocedu e employed in his wo k o he
p epa a ion o he oils was as ollow:
• Fi s , shee s o Q&P ea ed ma e ial we e cu in o pieces o abou 10 mm x 10 mm.
• Once he sample was cu , i was glued o a esin block o a me allic unnel (Figu e
23) wi h Loc i e. 250 μm hick coppe ape was glued o each side o he sample and
he sample was sanded down o ha hickness.
57
• Ha ing hinned he sample o 250 μm, being he las pass wi h 1200 g i sandpape ,
he sample was peel o and s ick i back o polish he o he side. This ime, 100 μm
apes we e placed and sample was hinned down o ha hickness, inishing he
polished wi h 1 μm clo h.
Figu e 23. Funnel whe e samples we e glued o be polished.
• In his way samples had app oxima ely 100 μm hickness, and 3 mm diame e disks
could be ob ained. This is done lowe ing he ed le e o he "hand d ill" shown in
Figu e 24. As many disks as possible we e ob ained om each sample.
Figu e 24. Hand d ill employed o ake ou 3 mm diame e discs om he samples hinned down o
100 μm.
• Nex , he side o he disk ha was polished only down o 1200 g i sandpape , was
inished by polishing down o 1 μm clo h.
58
• Thus, disks we e comple ely mi o polished on bo h sides. To make he cen al hole,
a ound which he TEM obse a ion was o be ca ied ou , an elec opolishing ba h
was used. The employed elec oly e was a mix u e o 5% pe chlo ic acid and 95%
e hanol (absolu e). The equipmen has a sample holde o place he discs (Figu e
25).
Figu e 25. Sample holde o he elec oly ic ba h and elec opolishing equipmen .
• Once he i s disc was placed, a scan was ca ied ou a di e en empe a u es o
ind he app op ia e ol age and empe a u e o make he hole by elec opolishing.
Th ough hese scans, he in ensi y- ol age cu e was ep esen ed a he empe a u e
o he ba h. The cu e mus consis o 3 pa s (Figu e 26), a i s ascending pa in
which he sample would be a acked, a second in which a pla eau is ound, whe e
he sample would be polished, and a hi d, also ascending, in which he sample would
be spoiled by chopping. Tes ing wi h empe a u es o -10 °C and -15 °C was
impossible o dis inguish he pla eau. A oom empe a u e i was clea ly seen ha
he pla eau was a 29 V.
Figu e 26. In ensi y-Vol age cu e.
mA
V
Sui able V
E ching a ea
Polishing a ea
Chopping a ea
59
• Once he ol age and empe a u e o be used we e es ablished, i was ad isable o
ca y ou he elec opolishing wi h a new disk, since when pe o ming he scanne in
a wide ol age ange, he sample likely was al eady e ched, polished and e en
chopped.
• The equipmen was he e o e p og ammed o ope a e a 29 V. A sensi i i y o 10%
was se ( his is measu ed by de ec ing he ligh ha passes h ough he sample so
ha he es ends as soon as he hole has been made, a ound o 1 minu e wi h hese
samples).
• Once elec opolished, he disk was quickly imme sed in e hanol o emo e any aces
o acid and was passed om one e hanol ba h o ano he by imme sing he sample
up o h ee di e en ba hs.
• Finally, he disk was le o d y, and i was obse ed i he holes we e pe o med by
an op ical mic oscope.
3.3 Mechanical beha io
3.3.1 Tensile es
Tensile Tes ing is a o m o ension es ing whe eby con olled ension is applied o a sample
un il i ully ails. This is one o he mos common mechanical es ing echniques. I is used o
ind ou how s ong a ma e ial is and how much i can be s ained be o e i b eaks. In his
wo k, his es me hod was used o de e mine yield s eng h, ensile s eng h, and duc ili y o
all he medium Mn s eels Q&P ea ed in he u naces and sal ba hs. Two es s we e
pe o med o each s eel/Q&P condi ion. Tensile specimens we e wa e cu om he ea ed
shee s. The dimensions o he specimens co esponded o a s anda d geome y o 50 mm
gauge leng h and a e speci ied in Figu e 27.
Figu e 27. Dimensions o he ensile specimens. All measu emen s a e exp essed in mm.

60
Tes s we e pe o med in a uni e sal INSTRON ensile es ing machine (Tecnalia, Spain),
wi h a s ain a e o 0.001 s-1 and a con ac ex ensome e ollowing he UNE-EN ISO
6892-1:2019.
3.3.2 In e up ed ensile es
In e up ed ensile es s we e pe o med o he selec ed s eels and Q&P condi ions in o de
o assess he e olu ion o he RA unde mechanical loading. Fo ha , once he o al
elonga ion was known o a gi en s eel/Q&P condi ion, di e en s ain le els we e selec ed
o s op he ensile es s. Then, he RA ac ion was measu ed by X- ay di ac ion in he way
a o emen ioned in he sec ion 3.2.1. In he ensile specimens wi h low s ains he cen e
sec ion o he specimen was selec ed o he measu emen o RA, whe eas in specimens
wi h highe s ains he hinne a ea o he ensile specimen was selec ed. RA was measu ed
in b oken specimens as well. In Figu e 28 he di e en sec ions employed o RA
measu emen s a e shown.
Figu e 28. Samples cu o XRD measu emen s om ensile specimens a e he applica ion o
di e en s ains.
3.3.3 Ha dness
Ma e ials wi h wea esis ance equi emen s mus ha e a ela i ely high ha dness. Thus, in
medium and high C s eels s udied in his wo k ha dness was an impo an pa ame e .
Ha dness measu emen s we e ca ied ou in a Vicke s Ha dness Tes e FV-700 model
(FUTURE-TECH) (Tecnalia, Spain) using a 10 kg load, applied o 10 s acco ding o he ISO
6507-1. To minimize e o s, 5 inden a ions pe sample we e pe o med.
The Vicke s es consis s o an inden e in he o m o a s aigh py amid wi h a squa e base
and wi h a speci ic angle be ween opposi e aces a he e ex (α), which is in oduced wi h
Low s ain
High s ain
F ac u ed specimen
61
a ce ain o ce (F) on he su ace o he specimen o he ma e ial o be es ed. Subsequen ly,
he diagonals o he imp in (d1 and d2) emaining on he su ace a e measu ed and, inally
ha dness alue is ob ained by means o (5), whe e “d” is he a e age alue be ween d1 and
d2. The Vicke s ha dness es p inciple is depic ed in Figu e 29.
𝐻𝑉 =0.189 × 𝐹
𝑑2
(5)
Figu e 29. Vicke s ha dness es p inciple.
3.3.4 T ibology: pin-on-disk (PoD)
To cha ac e ize he wea esis ance o medium and high C s eels, pin-on-disk (PoD) es s
we e ca ied ou in a MICROTEST ibome e (Tecnalia, Spain) o he Q&P and Q&T ea ed
samples o 1.2990 and 300M s eels. The PoD consis s in placing wo ma e ials in con ac ,
keeping one o hem in mo ion and bo h subjec ed o cons an p essu e o a de e mined ime
o dis ance. As shown in Figu e 30, his es ep oduces he unidi ec ional sliding p ocess
be ween wo di e en ma e ials unde ce ain condi ions.
Figu e 30. Pin-on-disk sys em.
In hese es s, he disks (ma e ials in es iga ed in his wo k) a e he ones in mo ion. The pin
can be a cylinde wi h a la su ace, sphe ical o a ball. In his case, he pin was a 6 mm
diame e ball. The dimension o he disk o he applica ion o PoD we e 4 mm hickness
F
α
d1
d2
62
disks, wi h a diame e o 100 mm and 35 mm in he 1.2990 and 300M s eels, espec i ely,
and an inne hole o 5.5 mm diame e . The es pa ame e s a e summa ized in Table 14. Two
es s we e pe o med o each s eel/Q&P condi ion.
Table 14. Pa ame e s used o he pin-on-disk es s.
S eel e .
1.2990
300M
Tes adius (mm)
15 and 45
15
Lineal eloci y (cm/s)
78.3 and 208.3
78.3
Load (N)
20
20
Tempe a u e (ºC)
RT
RT
Rela i e humidi y (%)
50
50
Pin ma e ial
Al2O3
Al2O3
Pin dimensions (mm)
Ø6
Ø6
Dis ance (m)
15000
5638
A e ca ying ou he es , he wo n olume was e alua ed on he disk, measu ing a se ies
o wea p o iles. The e alua ion consis s o making 4 p o iles on he ack le in he es , hus
ob aining 4 c oss-sec ional a eas (Figu e 31). This ope a ion was ca ied ou using a Dek ak
150 Con ac P o ilome e . Then, he wea olume was calcula ed by he ollowing geome ical
ela ion:
𝑉 = 2𝜋𝑟 ∙ 𝐴
(6)
whe e is he es adius in mm, and A is he a e age wea a ea ob ained by p o ilome e ,
exp essed in mm2.
Figu e 31. C oss-sec ional a eas o he wea ack employed o he measu emen o wea a e.
Finally, he speci ic wea a es (K) in mm3/N∙m o he in es iga ed ma e ials we e ob ained.
This a e is de ined as he olume wo n di ided by he no mal load and he es dis ance
using he ollowing equa ion:
K = 𝑉
𝐿 ∙ 𝑑
(7)
Being V he olume o wea (mm3), L he no mal load (N) and d he o al dis ance o he
es (m).
63
3.3.5 Toughness
Toughness is he abili y o a ma e ial o abso b ene gy and plas ically de o m wi hou
ac u ing. The oughness o a ma e ial can be measu ed using a small specimen o ha
ma e ial. A ypical es ing machine is a Cha py V-no ch impac es . This is a dynamic es in
which a no ched specimen is s uck and b oken by a single blow in a specially designed
es ing machine.
In his wo k, a p elimina y oughness s udy was ealized wi h he 1.2990 s eel o compa e
he ene gy abso p ion capaci y o Q&P and Q&T ea ed s eels. Due o ma e ial limi a ion,
s anda d subsize specimens we e used. Th ee es pe hea ea men we e pe o med.
Figu e 32 shows he dimensions o he s anda d subsize specimens acco ding o ASTM
A370.
Figu e 32. S anda d subsize specimen dimensions (ASTM A370).
The equipmen used o ca y ou he impac es s was an AMSLER RKP 300 model pendulum
om ROELL + KORTHAUS (Uni e si y o Can ab ia, Spain), wi h a capaci y o 300 J and a
hamme weigh o 20.4 kg (200 N), wi h a a el angle o up o 150 ° and maximum impac
speed o 5.42 m/s.
70
The dila ome y cu es du ing inal cooling o oom empe a u e we e analyzed o s udy he
possible o ma ion o seconda y ma ensi e (Figu e 33). The cu e was linea in all he QT10
condi ions excep o he 2Mn s eel, which showed a seconda y ma ensi e ans o ma ion
empe a u e (Ms2) o 167 ºC. This means ha he o ma ion o seconda y ma ensi e was no
signi ican in he s eels wi h a leas 4 w .% o Mn and, he e o e, mos o he aus eni e
a ailable a he end o pa i ioning was e ained in he inal mic os uc u e. In his sense, he
QT10 condi ion seemed o be bene icial o he s abiliza ion o aus eni e. In con as , o he
QT25 condi ion, he dila ion cu es de ia ed om linea con ac ion, which deno ed
seconda y ma ensi e ans o ma ion du ing inal cooling. The seconda y Ms2 we e
de e mined o be 157 ºC, 133 ºC, 103 ºC and 57 ºC in he 2Mn, 4Mn, 6Mn and 6Mn2Ni s eels,
espec i ely. The lowe Ms2 empe a u e obse ed wi h he inc ease o he alloying con en
in he s eels indica ed ha aus eni e s abiliza ion was enhanced, which was likely due o he
known s abiliza ion capaci y o Mn [66] and Ni [37,52,53,210].
4.1.2 Mic os uc u e a e he Q&P hea ea men s
The e ained aus eni e con en s we e measu ed by XRD o all Q&P condi ions and s eels.
Then, he mos in e es ing condi ions we e selec ed o being analysed by means o FE-SEM,
EBSD and TEM.
The e ained aus eni e con en s measu ed by XRD a e shown in Figu e 36 as a unc ion o
pa i ioning ime o all Q&P cycles and s eels. Rega ding e cycle, he alloying con en
g ea ly in luenced on he s abiliza ion o aus eni e. In he 2Mn s eel only 7% o he 25%
aus eni e a ailable a he QT was s abilized. As men ioned in he p e ious sec ion, g ea e
expansion was obse ed du ing pa i ioning in his s eel which was ela ed o baini e
o ma ion, hus, i is likely ha a conside able amoun o aus eni e ans o med in o baini e
du ing pa i ioning esul ing in a lowe con en o inal aus eni e. Wi h highe alloying con en s
he aus eni e was e ec i ely e ained a oom empe a u e, achie ing o s abilize all o i in
he 6Mn2Ni s eel.
A e he high pa i ioning empe a u e cycles wi h a pa i ioning ime o 1000 s, almos no
e ained aus eni e was de ec ed in he 2Mn s eel ega dless o he QT condi ion, showing
ha 2 w .% Mn was no enough o s abilize aus eni e. In he es o he s eels, all he cycles
esul ed in a inal e ained aus eni e con en g ea e han he aus eni e con en exis ing a he
QT wi h he excep ion o he QT25-P 1000 cycle in he 4Mn s eel, likely due o he seconda y
ma ensi e ans o ma ion obse ed in he dila ome y cu e (Figu e 33b). In he case o he

71
QT25-P 1000 cycle applied o he 6Mn s eel, he inc ease in aus eni e con en was small, bu
in he 6Mn2Ni s eel was conside able. This is in good ag eemen wi h he Ms2 measu ed in
he dila ome y cu es (Figu e 33), whe e his empe a u e dec eased wi h he alloying
con en o he s eel. In all QT10 condi ions, a e y subs an ial inc ease was obse ed. The
maximum con en o RA was 47%, which was ob ained a e he applica ion o he
QT10-P 1000 cycle in he 6Mn2Ni s eel.
The Ni addi ion clea ly esul ed in a signi ican inc ease in RA con en , ega dless o he
he mal ea men condi ions. Fu he mo e, compa ing he QT25-P 1000 and he
QT10-P 1000 condi ions, i can be seen ha a lowe aus eni e con en a he QT clea ly
esul ed in an inc eased con en o aus eni e in he inal mic os uc u e o he 6Mn and
6Mn2Ni s eels.
As o he in luence o pa i ioning ime in he QT10 condi ion, inc easing pa i ioning ime om
300 o 1000 s also inc eased RA con en . Howe e , a u he inc ease o 3600 s esul ed in
a sligh dec ease in RA con en . The in luence o pa i ioning ime on RA con en was e y
simila o he 6Mn and 6Mn2Ni s eels.
Figu e 36. Re ained aus eni e con en s as a unc ion o pa i ioning ime measu ed a e he
applica ion o all Q&P cycles.
0
5
10
15
20
25
30
35
40
45
50
55
0 500 1000 1500 2000 2500 3000 3500 4000
RA (%)
Pa i ioning ime (s)
6Mn –QT10
γ = 25 %
γ = 10 %
6Mn2Ni –QT10
6Mn2Ni –QT25
6Mn –QT25
4Mn –QT25
4Mn –QT10
2Mn –QT25
2Mn –QT10
2Mn – e
4Mn – e
6Mn2Ni – e
6Mn – e
72
The 6Mn and 6Mn2Ni s eels a e QT10-P 1000 and QT25-P 1000 condi ions we e selec ed
o being obse ed in he FE-SEM due o he high e ained aus eni e con en s. Addi ionally,
he mic os uc u e a e QT10-P 3600 cycle was obse ed in he 6Mn2Ni s eel o analyse he
in luence o pa i ioning ime. The mic os uc u e expec ed in hese samples can be
desc ibed as ollows: A e hea ing o ob ain a ully aus eni ic mic os uc u e, he Q&P s eels
we e quenched o he p ede e mined QT in o de o o m a pa ially aus eni ic and pa ially
ma ensi ic mic os uc u e. Then, hea ing o a pa i ioning empe a u e, which co esponded
o he aus eni e e e sion ans o ma ion s a empe a u e, he p e-exis ing aus eni e was
expec ed o g ow and be en iched by Mn and C p o ided by he ma ensi e [13,49]. In he
6Mn2Ni s eel, Ni en ichmen could also occu [211]. Thus, a e inal quenching, he aus eni e
which con ained enough C and Mn would become s able and be e ained a oom
empe a u e [13,49], whe eas he less en iched aus eni e would ans o m in o seconda y
ma ensi e (α’sec). In his way, he expec ed inal mic os uc u e should consis o C and Mn
deple ed p ima y ma ensi e (M1), RA la hs and blocky RA, and ma ensi e/aus eni e (MA)
islands consis ing o seconda y ma ensi e wi h ine RA. Ca bide p ecipi a ion was also
expec ed as a esul o he empe ing o ma ensi e due o he high pa i ioning empe a u e
employed.
In he FE-SEM mic og aphs ob ained in he p esen wo k (Figu e 37), b igh hin ilms we e
obse ed in all mic og aphs, which we e likely e ained aus eni e. The da k phase was
in e p e ed o be p ima y ma ensi e (M1) con aining a conside able amoun o ca bides. The
ca bides exhibi ed bo h acicula /pla e and globula mo phologies. Mn e a ds cemen i e
dissolu ion, so obse ed ca bides could include some cemen i e ha did no dissol e in p io
s eps, along wi h cemen i e o med as a consequence o empe ing o he ma ensi e. The
egions wi h da k-g ey cen e and whi e edges a e gene ally ecognized as MA islands.
In he QT25-P 1000 mic og aphs la ge a eas o MA we e e iden . Howe e , as shown la e ,
he amoun o seconda y ma ensi e de e mined om he dila ome y cu es and XRD esul s
was no signi ican . The e o e, he in e p e a ion o hese a eas in he FE-SEM images was
no en i ely clea , bu was p esumably indica i e o ans o ma ion du ing cooling nea QT. In
bo h s eels, he mic os uc u e obse ed a e he QT25-P 1000 cycle p esen ed coa se and
blocky cons i uen s, whe eas a e he QT10-P 1000 cycles he mic os uc u e was hinne
and exhibi ed a la h- ype appea ance. The mic os uc u e ea u es in he 6Mn2Ni s eel a e
he QT10-P 3600 cycle (Figu e 37e) we e hinne han a e he QT25-P 1000 cycle, bu
coa se han a e he QT10-P 1000 cycle.
73
Figu e 37. FE-SEM mic og aphs co esponding o he QT25-P 1000 cycle o he 6Mn (a), and
6Mn2Ni (b) s eels; he QT10-P 1000 cycle o he 6Mn (c), and 6Mn2Ni (d) s eels; and he
QT10-P 3600 cycle o he 6Mn2Ni s eel (e).
EBSD phase maps we e ob ained o all he P 1000 condi ions o he 6Mn and 6Mn2Ni s eels.
EBSD phase maps a e shown in Figu e 38, whe e he ed phase was iden i ied as RA, g een
was ma ensi e, and black indica es uniden i ied egions. F om EBSD measu emen s,
e ained aus eni e con en and size we e ob ained. In Table 15 a compa ison be ween he
RA con en measu ed by XRD and EBSD is shown. The aus eni e con en measu ed by
EBSD was lowe han ha measu ed by XRD, which migh be due o h ee easons. Fi s ,
he da k egions in he EBSD maps can be MA islands con aining e ained aus eni e.
Howe e , hese egions a e mos ly ecognized as uniden i ied egions. Second, de ec ion o
Acicula ca bides
Globula ca bides
M1
MA
(a) 6Mn –QT25-P 1000 (b) 6Mn2Ni –QT25-P 1000
RA la hs
(c) 6Mn –QT10-P 1000 (d) 6Mn2Ni –QT10-P 1000
( ) 6Mn2Ni –QT10-P 3600
74
nanome e sized ilm like e ained aus eni e s abilized be ween he ma ensi ic la hs is di icul
o iden i y wi h EBSD due o low esolu ion. Thi d, he a ea and dep h o he measu emen s
we e di e en , playing an impo an ole he s ep used in EBSD cha ac e iza ion. Mos o he
da k zones in he QT25 cycles (Figu e 38a-b) likely co esponded o MA islands, whe eas
he hin da k zones be ween ma ensi e a eas in he QT10 condi ion (Figu e 38c-d) likely
included nanome e sized ilm-like e ained aus eni e. In Table 15, a e age RA sizes
es ima ed om EBSD measu emen s a e also shown. In he 6Mn s eel, he QT10-P 1000
condi ion esul ed in a coa se a e age aus eni e size in compa ison wi h he QT25-P 1000
condi ion. Howe e , in he QT10-P 1000 condi ion, he minimum aus eni e size was 110 nm
and ine scale ilm-like e ained aus eni e a eas we e mos ly no de ec ed in he
measu emen .
Figu e 38. EBSD scans co esponding o he QT25-P 1000 cycle o he 6Mn (a), and 6Mn2Ni (b)
s eels; and he QT10-P 1000 cycle o he 6Mn (c), and 6Mn2Ni (d) s eels.
Table 15. Compa ison be ween e ained aus eni e con en (RA %) measu ed by XRD and EBSD.
A e age aus eni e g ain size (RA nm) measu ed by EBSD.
Q&P cycle
6Mn
6Mn2Ni
XRD
(RA %)
EBSD
(RA %)
EBSD
(RA nm)
XRD
(RA %)
EBSD
(RA %)
EBSD
(RA nm)
QT25-P 1000
26
17.4
168
38
25.2
220
QT10-P 1000
43
20.4
237
48
17.6
161
(a) 6Mn –QT25-P 1000 (b) 6Mn2Ni –QT25-P 1000
(c) 6Mn –QT10-P 1000 (d) 6Mn2Ni –QT10-P 1000
75
In Figu e 39, TEM cha ac e iza ion esul s a e p esen ed o he 6Mn2Ni s eel. Figu e 39a
and Figu e 39b show TEM mic og aphs a e he applica ion o he QT25-P 1000 and
QT10-P 1000 cycles, espec i ely. In bo h cases, he mic os uc u e consis ed o la h- ype
cons i uen s which we e iden i ied as ma ensi e and aus eni e by means o Selec ed A ea
Di ac ion (SAD). Ca bides we e also obse ed, and hei cha ac e iza ion is desc ibed la e .
In gene al, he aus eni e and ma ensi e la hs appea ed hinne in he QT10-P 1000
condi ion. Mo eo e , a la ge numbe o la hs we e hinne han he de ec ion limi employed
in EBSD analysis (~100 nm). The la hs iden i ied as aus eni e in he QT25-P 1000 condi ion
had a wid h o 53 ± 5 nm, which would explain he lowe RA con en s measu ed by EBSD in
compa ison wi h XRD measu emen s.
Wi h he aim o unde s anding he pa i ioning beha iou o Mn and Ni, TEM – Ene gy
Dispe si e Spec oscopy (EDS) analysis was pe o med and he composi ional maps (Figu e
39c- ) and concen a ion p o iles (Figu e 39g-h) we e ob ained o Mn and Ni alloying
elemen s. The composi ional maps e ealed ha he Mn concen a ion was no
homogeneous, wi h aus eni e ilms en iched in his elemen . On he con a y, Ni
concen a ion was mo e homogeneous. The concen a ion p o iles ob ained o he
QT25-P 1000 condi ion (Figu e 39g), e ealed high Mn en ichmen in he egion iden i ied as
aus eni e by SAD, ob aining a maximum concen a ion o 15 w .%, and a lowe Mn
concen a ion in he la hs iden i ied as ma ensi e. In he la e , Mn con en was a ound he
nominal alue (g ey la hs) o abo e his alue (whi e la hs), and consequen ly, he la hs we e
deduced o be p ima y and seconda y ma ensi e, espec i ely. Likely, ini ial aus eni e la hs
exis ing a QT25 we e oo la ge o be comple ely en iched in Mn and, as a consequence, a
Mn g adien was obse ed om he bounda y o he cen e o he ini ial aus eni e la h, exis ing
a highe Mn concen a ion nea he bounda y. Hence, seconda y ma ensi e ans o med
om he in e io o he aus eni e la hs emaining om cooling o he QT, o igina ing MA
islands in he inal mic os uc u e [112,114].
On he con a y, in he QT10 condi ion (Figu e 39h) a highe pe cen age o he la h was
en iched in Mn and he concen a ion p o ile was mo e homogeneous. Fu he mo e, he Mn
concen a ion in he en iched la hs was signi ican ly highe han in he QT25 condi ion.
The e o e, i can be concluded ha in he high pa i ioning empe a u e Q&P cycles applied
in his wo k, Mn pa i ioning occu ed and he lowe QT condi ion was bene icial o he Mn
en ichmen o aus eni e la hs, which likely con ibu ed o aus eni e s abiliza ion. Ni
concen a ion p o iles did no show such clea concen a ion di e ences be ween la hs as

76
hose o Mn, al hough in he QT10-P 1000 cycle Ni concen a ion p o ile showed a end
simila o ha shown by Mn. The e ec o Ni is u he discussed in sec ion 4.1.6.
Figu e 39. TEM analysis o 6Mn2Ni s eel: Mic og aphs and SAD pa e ns o he QT25 (a) and he
QT10 (b) condi ions; EDS analysis ep esen ing he dis ibu ion o Mn concen a ion o he QT25
(c) and QT10 (d) condi ions, and Ni concen a ion o he QT25 (e) and QT10 ( ) condi ions;
concen a ion p o iles o Mn and Ni line scans pe o med wi hin he a eas ma ked in (a) and (b) o
he QT10 (g) and QT25 (h) condi ions.
6Mn2Ni –QT10-P 1000
6Mn2Ni –QT25-P 1000
0
5
10
15
20
0.0 0.2 0.4 0.6 0.8
w .%
Dis ance (μm)
0
5
10
15
20
0.0 0.2 0.4 0.6 0.8
w .%
Dis ance (μm)
α’
(h)
Ni
200 nm
Ni
200 nm
Mn
200 nm
Mn
200 nm
(c)
(g)
Mn
Ni
Mn
Ni
RA RA
α’sec
RA
RA
RA
RA
α’
α’
200 nm
(b)
200 nm
(a)
01-1
10-1
[111]
α’
[101]
-202
020
-202
020
[101]
020
200
[001] α’ γ
α’
(d)
(e) ( )
α’ α’
γα’
77
The mic os uc u e cha ac e iza ion was inished by pe o ming a TEM-EDS analysis o he
ca bides obse ed in he mic os uc u e. As p esen ed be o e, globula and acicula /pla e
ca bides we e p esen in he mic os uc u e. The TEM-EDS analysis o he ca bides e ealed
ha he ca bides con ained Mn. As an example, he EDS spec um o a globula ca bide
obse ed in he 6Mn s eel a e he QT10-P 1000 cycle is shown in Figu e 40b. Composi ional
mapping in an a ea examined in he 6Mn2Ni s eel a e he QT10-P 1000 cycle, which
con ained bo h globula and acicula ca bides, e ealed he en ichmen o bo h ypes o
ca bides wi h Mn (Figu e 40d). In he 6Mn2Ni s eel, he TEM-EDS analysis did no show he
p esence o Ni in he ca bides. The o ma ion o Mn en iched ca bides esul ed in less C and
Mn a ailable o aus eni e s abiliza ion.
Figu e 40. TEM mic og aphs o he 6Mn s eel (a) and he 6Mn2Ni s eel (c) a e QT10-P 1000 cycle,
TEM-EDS spec um o a globula ca bide ma ked in (a) (b), and composi ional mapping o he (c)
mic og aph (d). In he mic og aph (c), acicula and globula ca bides a e isible; in he
composi ional map (d) a highe concen a ion o Mn is isible in he globula and acicula ca bides.
4.1.3 Tensile p ope ies
Figu e 41, Figu e 42, Figu e 43 and Figu e 44 show he s ess-s ain cu es o all Q&P
cycles o he 2Mn, 4Mn, 6Mn and 6Mn2Ni s eels, espec i ely. All da a ob ained om he
ensile es s a e summa ized in Table 16: Yield s eng h (YS), ensile s eng h (TS), YS/TS
a ion, o al elonga ion (TEL), and TS x TEL p oduc . These da a co espond o he a e age
alues ob ained om wo es s. In Appendix C he pho og aphs o one ac u ed ensile
specimen pe s eel and condi ion is shown. Tensile p ope ies a e ela ed o he
mic os uc u e in sec ion 4.1.8.
200 nm
(a) 6Mn –QT10-P 1000
0
100
200
300
400
500
600
700
800
0 2 4 6 8
In ensi y (Coun s)
Ene gy (keV)
C
(b) EDS spec um
Mn-L
Fe-L
Si
Mn-Kα
Fe-Kα
Mn-Kβ
Fe-Kβ
200 nm 200 nm
Acicula ca bides
Globula ca bides
Acicula ca bides
Globula ca bides
(c) 6Mn2Ni –QT10-P 1000 (d) 6Mn2Ni –QT10-P 1000 Mn
78
Figu e 41. Enginee ing s ess-s ain cu es ob ained a e Q&P ea men s o he 2Mn s eel.
Figu e 42. Enginee ing s ess-s ain cu es ob ained a e Q&P ea men s o he 4Mn s eel.
Figu e 43. Enginee ing s ess-s ain cu es ob ained a e Q&P ea men s o he 6Mn s eel.
0
200
400
600
800
1000
1200
1400
0 5 10 15 20 25 30
Enginee ing S ess (MPa)
Enginee ing S ain (%)
QT10-P 1000
QT25-P 1000
e
2Mn
0
200
400
600
800
1000
1200
1400
0 5 10 15 20 25 30
Enginee ing S ess (MPa)
Enginee ing S ain (%)
QT10-P 1000
QT25-P 1000
e
4Mn
0
200
400
600
800
1000
1200
1400
0 5 10 15 20 25 30
Enginee ing S ess (MPa)
Enginee ing S ain (%)
QT10-P 300
QT10-P 1000
QT10-P 3600
QT25-P 1000
e
6Mn
79
Figu e 44. Enginee ing s ess-s ain cu es ob ained a e Q&P ea men s o he 6Mn2Ni s eel.
Table 16. Summa y o ensile p ope ies o he 2Mn, 4Mn, 6Mn and 6Mn2Ni s eels a e each Q&P
ea men .
S eel e .
Q&P cycle
YS (0.2% o se )
(MPa)
TS
(MPa)
YS/TS
a io
TEL
(%)
TS x TEL
(GPa%)
2Mn
e
974
1273
0.76
9.9
12.5
QT25-P 1000
512
767
0.67
18.3
14.0
QT10-P 1000
523
759
0.69
20.1
15.2
4Mn
e
833
1259
0.66
3.7
4.7
QT25-P 1000
581
1182
0.49
13.6
16.1
QT10-P 1000
524
1064
0.49
20.3
21.5
6Mn
e
735
993
0.74
0.6
0.5
QT25-P 1000
585
1251
0.47
6.9
8.6
QT10-P 300
644
1158
0.56
24.6
28.5
QT10-P 1000
651
1199
0.54
24.9
29.9
QT10-P 3600
584
1204
0.48
17.4
20.9
6Mn2Ni
e
896
1170
0.77
1.6
1.9
QT25-P 1000
580
1329
0.44
11.1
14.7
QT10-P 300
727
1182
0.61
23.7
28.0
QT10-P 1000
694
1207
0.57
28.1
33.8
QT10-P 3600
705
1222
0.58
28.8
35.2
I can be seen ha in he Q&P cycles wi h a pa i ioning empe a u e o 400 °C ( e cycle),
he inc ease in Mn esul ed in a no iceable dec ease in elonga ion, and, also, in ensile
s eng h. The u he addi ion o Ni in 6Mn2Ni did no esul in an imp o emen o ensile
p ope ies, ob aining, also in his case, a low elonga ion.
0
200
400
600
800
1000
1200
1400
0 5 10 15 20 25 30
Enginee ing S ess (MPa)
Enginee ing S ain (%)
QT10-P 300
QT10-P 3600
QT10-P 1000
QT25-P 1000
e
6Mn2Ni
86
aus eni e e e sion kine ics would be in he PLE-1 s age. Du ing his s age he aus eni e
ac ion was s ill g owing, bu he e e ed aus eni e amoun o med so a led o a ela i ely
high amoun o RA. By 1000 s o pa i ioning he g ow h o aus eni e was slowed and i is
likely ha he kine ics we e a he end o he PLE-1 s age o he beginning o he PLE-2 s age.
Re e ed aus eni e was no a om i s maximum and hus ou s anding alues o RA we e
ob ained in his condi ion. Finally, a 3600 s o pa i ioning, he con olling kine ics would
al eady be in he PLE-2 s age and no inc ease o aus eni e ac ion occu ed, leading o he
sligh dec ease o RA measu ed by XRD.
F om a chemical poin o iew, a la ge di e ence in aus eni e s abili y was no expec ed
be ween he 1000 s and 3600 s pa i ioning ime condi ions. Howe e , in FE-SEM
mic os uc u es (Figu e 37d and Figu e 37 ) a coa sening o aus eni e la hs was obse ed.
This beha io was hypo hesized o occu due o he coalescence o aus eni e g ains du ing
g ow h [218]. As men ioned abo e, g ain size migh in luence he he mal s abili y o aus eni e
[125], which can explain he sligh dec ease in RA measu ed a e 3600 s pa i ioning ime
cycles in compa ison wi h 1000 s cycles, whe e hinne aus eni e was obse ed.
4.1.6 Analysis o he in luence o Ni on mic os uc u e and aus eni e
s abiliza ion
The addi ion o Ni in he 6Mn2Ni s eel was bene icial o inc easing RA con en in he inal
mic os uc u e in all hea ea men condi ions. The Ni addi ion did no seem o a ec
signi ican ly he aus eni e o ma ion kine ics (as deno ed by he simila con ac ion obse ed
in he pa i ioning s age, Figu e 33 and Figu e 35). Howe e , Ni was e ec i e in s abilizing a
highe con en o aus eni e. The la e could be ela ed o an en ichmen o aus eni e no only
wi h Mn, bu also wi h Ni. The beha iou o Ni pa i ioning was analyzed based on
composi ional maps and concen a ion p o iles shown in Figu e 39. In he QT10 condi ion,
some edis ibu ion o Ni can be app ecia ed in he composi ional map (Figu e 39 ), al hough
i was no as dis inc i e as in he Mn map. Howe e , he concen a ion p o ile was e y simila
o ha shown by Mn (Figu e 39h), wi h a eas en iched in Ni (appa en ly aus eni e) and a eas
deple ed in Ni (iden i ied as ma ensi e), in he same posi ions as in he Mn p o ile. The eby,
he QT10 condi ion also seemed a ou able o Ni pa i ioning. In he case o he QT25
condi ion, he Ni pa i ioning beha iou was less clea and would equi e u he in es iga ion.
On he o he hand, as p esen ed in sec ion “4.1.2 Mic os uc u e cha ac e iza ion”, he
TEM-EDS analysis e ealed ha he ca bides con ained Mn. Besides, in he 6Mn2Ni s eel,
he analysis seemed o indica e ha Ni was no p esen in he ca bides. The composi ion o

87
ca bides in Ni con aining s eels was s udied in ecen wo k. Pie ce e al. [54] obse ed
pla e-like and globula ca bides in TEM a e pa i ioning a 450 ºC o 300 s in a
0.2C-1.5Mn-1.3Si s eel con aining 1.5% Ni. A om p obe omog aphy (APT) e ealed Mn
en ichmen o he ca bides. They did no obse e signi ican pa i ioning o Ni be ween
ca bide and ma ix. Thus, bo h he mo phology and chemical composi ion o he ca bides
obse ed in he p esen wo k we e in ag eemen wi h ha obse ed by Pie ce e al. Simila ly,
Cla ke e al. [219] epo ed no subs an ial pa i ioning o Ni be ween he ma ix and he
ca bide in 4340 s eel du ing empe ing a 450 ºC o 2 h. Howe e , Cla ke e al. showed ia
APT ha signi ican ejec ion o Ni om ca bides occu ed du ing empe ing a 575 ºC o 2 h,
wi h Ni en ichmen pe sis ing nea he ca bide/ e i e in e ace. Wi h he aim o u he
in es iga ing he possible Ni en ichmen in he ca bides, a line scan was pe o med in TEM
ac oss wo globula ca bides in he QT10-P 1000 condi ion o 6Mn2Ni s eel (Figu e 47b).
Bo h ca bides con ained a high amoun o Mn, bu no Ni en ichmen was e iden in he
ca bides o nea he ca bide/ma ix in e aces.
Figu e 47. TEM mic og aph o he 6Mn2Ni s eel a e he QT10-P 1000 condi ion (a); and line scans
o Mn and Ni weigh concen a ion (b), co esponding o he line shown in (a).
4.1.7 Theo e ical analysis o aus eni e s abiliza ion using DICTRA
As shown ea lie , he ART occu ed in he high pa i ioning empe a u e s age and Mn
pa i ioning om ma ensi e in o aus eni e was obse ed in TEM-EDS scans. The Mn
concen a ion p o iles we e di e en depending on he QT condi ion. Fu he mo e, a
subs an ial ca bide ac ion was obse ed, which con ained a signi ican con en o Mn.
Acco ding o ecen s udies [220–223], aus eni e is likely o nuclea e a ca bide in e aces.
The e o e, aus eni e o ma ion could be he esul o he g ow h o p e-exis ing aus eni e
along wi h o ma ion o new aus eni e a ca bide in e aces. Wi h he aim o be e
0
5
10
15
20
25
30
0 0.05 0.1 0.15 0.2
w .%
Dis ance (μm)
200 nm
Mn
Ni
(a) 6Mn2Ni –QT10-P 1000 (b) 6Mn2Ni –QT10-P 1000
88
unde s anding hese possible phenomena, DICTRA simula ions we e pe o med o he
6Mn2Ni s eel conside ing he pa i ioning condi ions employed in he p esen wo k. In he
simula ions wo di e en se ups we e conside ed. In he i s one, he g ow h o p e-exis ing
aus eni e in he aus eni e/ma ensi e mic os uc u es was simula ed. In he second one,
aus eni e nuclea ion a ca bide in e aces was simula ed. In bo h se ups, a single cell plana
geome y was used [224]. Because o symme y, only he hal hickness was conside ed in
he DICTRA calcula ion domain. Fe i e was conside ed ins ead o ma ensi e, since
ma ensi e is no included in he he modynamic and kine ic da abase. The esul s o hese
simula ions we e he Mn concen a ion p o ile in he conside ed sys ems and he g ow h o
aus eni e o di e en pa i ioning imes. The g ow h o aus eni e can be obse ed by he
displacemen o he in e ace.
In se up (1), 10 and 25 olume pe cen o aus eni e (QT10 and QT25 condi ions,
espec i ely) we e conside ed in he ini ial aus eni e/ma ensi e mic os uc u e. The
dimension o he ma ensi e was se o 0.200 μm. I was based on he TEM obse a ions o
K auss and colleagues, indica ing ha mos ma ensi ic la h wid hs ange om app oxima ely
0.150 o 0.200 μm [226,227], which seems consis en wi h he TEM analysis p esen ed in
his wo k. Co esponding aus eni e dimensions we e ob ained using he “cons an e i e
wid h app oach” [225]; i.e., he wid h o he aus eni e la h co esponded o a pe cen age o
he o al wid h (ma ensi e + aus eni e) equal o he olume pe cen o aus eni e ixed in he
QT. Thus, aus eni e ini ial la h wid hs equal o 0.22 o 0.66 μm we e ixed. In he case o he
QT10 condi ion, di e en P -s we e conside ed. A schema ic illus a ion o hese ini ial
condi ions is shown in Figu e 48a, and he esul s o he simula ion compa ing di e en QT
and P condi ions a e shown in Figu e 48b and Figu e 48d, and Figu e 48c and Figu e 48e,
espec i ely.
In se up (2), he a e age ca bide size and Mn composi ion measu ed om TEM analysis
we e conside ed, 0.020 μm and 24.6 w .%, espec i ely. The pa i ioning dimension in
ma ensi e was se o 0.200 μm, as in se up (1). The ini ial composi ion o α phase was
conside ed om he equilib ium composi ion o he 6Mn2Ni s eel a 640 ºC ob ained by
The mo-Calc (i.e., 0.003 C w .% and 1.998 Mn w .%). In addi ion, in o de o simpli y he
simula ion, he nuclea ion p ocess was igno ed, adding a 0.001 μm leng h aus eni e phase,
wi h he same composi ion as he ma ensi e, be ween he cemen i e and ma ensi e phases.
The ini ial condi ions o his se up a e shown in Figu e 49a and he ob ained esul s a e
shown in Figu e 49b.
89
Figu e 48. DICTRA simula ions o 6Mn2Ni s eel a 640 ºC: schema ic o he ini ial condi ions o he
simula ions o se up (1) (a); esul s o se up (1), showing a compa ison be ween he g ow h o
aus eni e in QT10 and QT25 wi h P 1000 and di usion o Mn (b) and Ni (d) ( he ini ial in e ace was
se in he same posi ion o QT10 and QT25), and showing he compa ison be ween he g ow h o
aus eni e wi h P 300, P 1000, and P 3600 in QT10 and di usion o Mn (c) and Ni (e).
In se up (1), aus eni e g ew in o he ini ial ma ensi e la h and was en iched conside ably in
Mn, while he ma ensi e was conside ably deple ed, almos eaching he equilib ium alue
(Figu e 48b). Wi h ega d o Ni, i can be seen ha , e en he aus eni e was pa ially en iched,
and he ma ensi e was pa ially deple ed, a 1000 s pa i ioning was no enough ime o each
he equilib ium composi ion. Fu he mo e, he dis ibu ion o he Ni in he aus eni e la h was
0
1
2
3
4
5
6
7
8
9
10
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14
Mn w .%
Dis ance (μm)
QT10
QT25
Ini ial γ/αin e ace
(b) 6Mn2Ni, se up (1), P 1000 condi ions
Eq. Mn in FCC
Eq. Mn in BCC
γ
α
0
1
2
3
4
5
6
7
8
9
10
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14
Mn w .%
Dis ance (μm)
Ini ial γ/αin e ace
P 300
P 1000
P 3600
(c) 6Mn2Ni, se up (1), QT10 condi ions
Eq. Mn in FCC
Eq. Mn in BCC
γ
α
γα
0.033 μm 0.100 μm
γα
0.100 μm0.011 μm
se up o he QT25 condi ion se up o he QT10 condi ion
(a) Ini ial condi ions o se up (1)
0
1
2
3
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14
Ni w .%
Dis ance (μm)
QT10
QT25
Ini ial γ/αin e ace
Eq. Mn in FCC
Eq. Mn in BCC
γ
α
(d) 6Mn2Ni, se up (1), P 1000 condi ions
0
1
2
3
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14
Ni w .%
Dis ance (μm)
P 300
P 1000
P 3600
Ini ial γ/αin e ace
Eq. Mn in FCC
Eq. Mn in BCC
γ
α
(e) 6Mn2Ni, se up (1), QT10 condi ions
90
qui e he e ogeneous (Figu e 48d). Rega ding he in luence o QT, he DICTRA calcula ions
appea o be in good ag eemen wi h he dila ome y esul s, whe e i was seen ha he QT10
condi ion led o a g ea e amoun o aus eni e o ma ion (Figu e 35). Thus, acco ding o
Figu e 48b and Figu e 48d, a e 1000 s a he PT, he aus eni e la h size g ew mo e in he
QT10 condi ion, ob aining a inal leng h 7.5 imes he ini ial one, whe eas o he QT25
condi ion he size was only 3.0 imes he ini ial. Wi h ega ds o Mn and Ni di usion dis ance,
he en iched wid h was qui e simila o bo h QT condi ions. Howe e , he pe cen age o he
la h size en iched in Mn was g ea e o he QT10 han he QT25 condi ion, speci ically 78%
and 60% aus eni e was en iched in he QT10 and he QT25, espec i ely. These pe cen ages
a e somewha lowe ega ding Ni di usion dis ance, speci ically 61% and 50% in he QT10
and he QT25, espec i ely. These obse a ions we e consis en wi h TEM-EDS line scans
(Figu e 39g and Figu e 39h), and would imply ha he quan i y o seconda y ma ensi e
o med in he QT25 condi ion du ing inal cooling would be highe .
Calcula ions o di e en P -s, employing QT10, a e shown in Figu e 48c and Figu e 48e. As
expec ed, he g ow h o he aus eni e was g ea e wi h inc eased pa i ioning ime, as he
in e ace was mo ed o longe dis ances. The g ow h inc emen di e ence wi h inc easing
pa i ioning ime om 300 o 1000 s was subs an ially la ge han inc easing i om 1000 s o
3600 s, al hough in hese DICTRA simula ions he a o emen ioned coalescence
phenomenon was no conside ed. A P 300, he e was a clea dis inc ion be ween he la h
egion en iched in Mn and he non-en iched egion, which migh lead o some seconda y
ma ensi e o ma ion. In addi ion, he ma ensi e la h was no comple ely Mn deple ed. A
P 1000, Mn was mo e homogeneously dis ibu ed ac oss he la h, bu he e was s ill a small
no en iched leng h, while a P 3600 all he leng h was somewha en iched, al hough a
composi ional di e ence wi hin he la h was s ill isible and, he eby, he less en iched pa
o he la h would po en ially ans o m in o seconda y ma ensi e. Rega ding Ni di usion, he
aus eni e leng h wi hou en ichmen was he same o he h ee P condi ions. Howe e , he
Ni dis ibu ion wi hin he la h was di e en . A P 300, he Ni en ichmen /deple ion in he
aus eni e and ma ensi e, espec i ely, was poo and e y localized nea by he in e ace. A
P 1000, he Ni en ichmen in he aus eni e con inued being loca ed nea he in e ace, bu
he maximum peak was o e he equilib ium composi ion. The Ni deple ion in he ma ensi e
led o a homogeneous dis ibu ion, al hough he con en was s ill o e he equilib ium alue.
Finally, a P 3600, he beha io was like a P 1000, ob aining a sligh ly highe Ni en ichmen
in he aus eni e nea he in e ace.
91
Figu e 49. DICTRA simula ions o 6Mn2Ni s eel a 640 ºC: schema ic o he ini ial condi ions o he
simula ions o se up (2) (a), and esul s o se up (2) con igu a ion, whe e aus eni e nuclea ed a
θ/α in e ace (b).
In se up (2), di e en aus eni e sizes and Mn p o iles we e ob ained when compa ing wi h
se up (1). Fi s , he Mn con en ac oss he aus eni e la h was almos cons an and e y close
o he equilib ium con en (8.4 w .%). Second, he aus eni e la h size was signi ican ly smalle
han he size ob ained in se up (1), speci ically, he o al size o he la h a e 3600 s o
pa i ioning did no each 0.008 μm, wi h e en lowe alues a e 1000 and 300 s, 0.005 and
0.003 μm, espec i ely. In addi ion, acco ding o DICTRA calcula ions, he aus eni e g ew
in o he ma ensi e a he han dissol ing he cemen i e. Yan e al. [228] also obse ed ha
he la h size o aus eni e was much smalle when i nuclea ed a he in e ace be ween
cemen i e and ma ensi e han when i nuclea ed a he bounda y o he ma ensi e. Howe e ,
compa ing wi h he se up (1) on his wo k, hey did no ha e p e-exis ing aus eni e in hei
simula ions and, compa ing wi h he se up (2). hey ound ha ca bides we e o ally dissol ed
a e holding o 2000 s a he in e c i ical empe a u e. Addi ionally, Luo e al. [229]
sugges ed ha he dissolu ion o cemen i e was he main eason o he high en ichmen o
aus eni e wi h Mn, and he limi ed di usion dis ance o Mn esul ed in a e ined aus eni e.
In gene al, Mn con en s measu ed expe imen ally in aus eni e (Figu e 39g-h) we e
signi ican ly highe han hose ob ained by DICTRA. Fu he mo e, in DICTRA simula ions,
he aus eni e wid h en iched in Mn was less han obse ed by TEM-EDS scans. The egions
θ α
0.010 μm 0.100 μm
(a) Ini ial condi ions o se up (2)
0
5
10
15
20
25
0.008 0.01 0.012 0.014 0.016 0.018
Mn w .%
Dis ance (μm)
P 300
P 1000
P 3600
Ini ial θ/αin e ace
Eq. Mn in FCC
Eq. Mn in BCC
0
5
10
15
20
25
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Mn w .%
Dis ance (μm)
(b) 6Mn2Ni, se up (2), γnuclea ed a θ/αin e ace
Zoom
γ/α
θ/γ

92
no en iched in Mn (o less en iched) would lead o a qui e highe ex en o seconda y
ma ensi e ans o ma ion han ha obse ed by dila ome y. This means ha DICTRA
calcula ions could unde es ima e Mn di usion h ough he aus eni e. As said be o e, in he
simula ions e i e was conside ed ins ead o ma ensi e, since ma ensi e is no included in
he he modynamic and kine ic da abase. The he modynamic p ope ies o ma ensi e a e
e y much he same as hose o e i e, howe e , he kine ic pa ame e s may de ia e be ween
he wo phases due o la ge numbe s o la ice de ec s, pa icula ly disloca ions, in
ma ensi e. Thus, mobili ies o all alloying elemen s in ma ensi e a e inc eased compa ed o
e i e [124], which could explain he di e ences be ween he simula ions and expe imen al
da a.
4.1.8 Rela ionship be ween mic os uc u e and ensile p ope ies
As p esen ed in “4.1.3 Tensile p ope ies” sec ion, ensile p ope ies s ongly dec eased by
he addi ion o Mn in he e cycle. The addi ion o Ni did no esul in an imp o emen o hese
p ope ies. Al hough he e ained aus eni e con en measu ed by XRD inc eased by he
addi ion o Mn and Ni, in he p esen case, his inc ease did no esul in be e ensile
p ope ies. By ising he pa i ioning empe a u e o he s a o ART empe a u e, i was
shown ha ensile s eng h dec eased, and elonga ion inc eased in he 2Mn and 4Mn s eels,
which was mainly ela ed o he empe ing o he ma ensi e phase.
F om now on, he ela ionship be ween mic os uc u e and ensile p ope ies is analyzed o
he 6Mn and 6Mn2Ni s eels hea ea ed by high pa i ioning empe a u e cycles. Fi s , wi h
he aim o be e analyzing he e ec o he Q&P cycle condi ions and he addi ion o Ni on
he ensile p ope ies, he ensile esul s a e shown as a unc ion o pa i ioning ime in Figu e
50. In gene al, he be e ensile p ope ies we e ob ained wi h he 6Mn2Ni s eel in he QT10
condi ions, excep o TS, which was highe a e he applica ion o QT25-P 1000 cycle. Fo
he 6Mn2Ni s eel, he p ope ies did no de e io a e wi h he inc ease o he P , whe eas in
he 6Mn s eel YS and TEL dec eased o he P o 3600 s.
The p oduc o ensile s eng h and o al elonga ion is a pa ame e o en applied o e alua e
and compa e s eels o he au omo i e sec o . In Figu e 51, TS x TEL is ep esen ed as a
unc ion o RA. Excep o QT10-P 300 condi ion in he 6Mn s eel, i can be said ha he
p oduc TS x TEL inc eased wi h he aus eni e con en . Thus, he p esence o a highe
con en o RA in Ni con aining s eel and a e he QT10 condi ion, likely con ibu ed o he
ou s anding TS x TEL alues ob ained in his case. Mo eo e , he ine aus eni e la hs o he
93
QT10 condi ion likely played an impo an ole in imp o ing he TS x TEL p oduc [230,231].
On he con a y, he g ea e amoun o seconda y ma ensi e educed he duc ili y o he
QT25 condi ion.
Figu e 50. Tensile p ope ies o he Q&P ea ed samples: yield s eng h (a); ensile s eng h (b);
o al elonga ion (c); and TEL x TS p oduc (d).
Figu e 51. G aphical ep esen a ion o he ela ionship be ween he p oduc o ensile s eng h and
o al elonga ion and RA o each Q&P cycle o he 6Mn and 6Mn2Ni s eels.
500
550
600
650
700
750
800
0 1000 2000 3000 4000
Yield S eg h (Mpa)
Pa i ioning ime (s)
(a)
6Mn2Ni –QT10
6Mn2Ni –QT25
6Mn –QT25
6Mn –QT10
1100
1150
1200
1250
1300
1350
1400
0 1000 2000 3000 4000
Tensile S eg h (Mpa)
Pa i ioning ime (s)
(b)
6Mn2Ni –QT10
6Mn2Ni –QT25
6Mn –QT25
6Mn –QT10
0
5
10
15
20
25
30
35
0 1000 2000 3000 4000
To al Elonga ion (%)
Pa i ioning ime (s)
(c) 6Mn2Ni –QT10
6Mn –QT25
6Mn2Ni –QT25
6Mn –QT10
0
5
10
15
20
25
30
35
40
0 1000 2000 3000 4000
TEL x TS (GPa%)
Pa i ioning ime (s)
(d)
6Mn2Ni –QT10
6Mn –QT25
6Mn2Ni –QT25
6Mn –QT10
0
5
10
15
20
25
30
35
40
20 25 30 35 40 45 50
TS x TEL (GPa%)
Re ained Aus eni e (%)
6Mn 6Mn2Ni
QT25-P 1000
QT10-P 300
QT10-P 1000
QT10-P 3600
94
The p esence o seconda y ma ensi e can be conside ed u he , as i can be c i ical o he
de e io a ion o ensile p ope ies [112]. E en hough seconda y ma ensi e ans o ma ion
was di icul o de ec by dila ome y o some o he condi ions, a deepe analysis allows an
app oxima ion o he amoun o each cons i uen in he inal mic os uc u e. Thus, he olume
ac ion o he phases exis ing in he inal mic os uc u e a e hea ea men s was es ima ed
employing RA measu emen s (XRD) and dila ome y cu es (Figu e 52). Seconda y
ma ensi e was ob ained by compa ing he change in leng h a he inal cooling wi h he
change in leng h gi en by he ma ensi e ans o ma ion cu e on he di ec ly quenched
sample, and p ima y ma ensi e was calcula ed by balance [37]. F om he g aph, i can be
con i med ha he g ea es con en o seconda y ma ensi e was ob ained a e he
QT25-P 1000 cycle, pa icula ly in he 6Mn s eel. The p esence o a ha d and b i le
seconda y ma ensi e in his condi ion can explain he lowe o al elonga ion and highe
ensile s eng h ob ained a e he QT25-P 1000 cycle (Figu e 50).
Figu e 52. Volume pe cen o each phase in he 6Mn and 6Mn2Ni s eels a e he applica ion o Q&P
cycles calcula ed based on dila ome y cu es and RA measu ed by XRD.
On he o he hand, i is widely accep ed ha he ans o ma ion o aus eni e in o ma ensi e
induced by de o ma ion is also a c i ical ac o ha de e mines ensile p ope ies. F om he
esul s ob ained in he in e up ed ensile es s, he e olu ion o no malized RA wi h s ain in
QT10-P 1000 cycles o he 6Mn and 6Mn2Ni s eels was ep esen ed (Figu e 53). In bo h
s eels, li le aus eni e ans o ma ion occu ed up o 10% s ain, whe e only abou 15% o he
aus eni e had ans o med. A e wa ds, he beha io was a he di e en in each s eel. In he
6Mn s eel he aus eni e con en g adually dec eased wi h s ain, whe eas in he 6Mn2Ni s eel
56 55
70
59 52 50 56 52
31
38
25
37
43
48
39
44
13 7545254
0
20
40
60
80
100
Phase olume (%)
p ima y ma ensi e e ained aus eni e seconda y ma ensi e
6Mn 6Mn2Ni6Mn 6Mn2Ni6Mn 6Mn2Ni
6Mn 6Mn2Ni
QT25-P 1000 QT10-P 300 QT10-P 1000 QT10-P 3600
95
he en i e y o he emaining RA a 20% s ain (77% o he ini ial RA) ans o med close o
he uni o m s ain, likely esul ing in a high ac ion o e y ha d ma ensi e and hus p o oking
ea ly ac u e and he absence o pos -uni o m elonga ion. Al hough he 6Mn s eel showed a
mo e g adual dec ease in he aus eni e ac ion, i is likely ha he amoun o ma ensi e
ans o med a s ains close o he uni o m elonga ion was s ill high and also p o oked he
absence o pos -uni o m elonga ion.
F om he e olu ion o RA wi h s ain, i can be deduced ha adding Ni inc eased he
mechanical s abili y o e ained aus eni e and e a ded he kine ics o he s ain-induced
ma ensi e ans o ma ion. I can be explained by conside ing he e ec o Ni on he s eng h
o ma ensi e. Fi s , acco ding o Hidalgo e al. [92] he s eng h o ma ensi e can a ec he
mechanical s abili y o aus eni e. They concluded ha aus eni e su ounded by a s onge
ma ensi ic ma ix was mechanically mo e s able han ha su ounded by a weake
ma ensi e. Second, in he p esen wo k, Ni dec eased he Ms empe a u e, so he ma ensi e
o med du ing he i s cooling o QT should con ain mo e disloca ions and, hus, i was likely
ha de and con ibu ed o he highe mechanical s abili y o aus eni e in his s eel.
Figu e 53. E olu ion o no malized RA du ing ensile es s s opped a di e en s ains o 6Mn and
6Mn2Ni s eels a e QT10-P 1000 cycle.
S ess-s ain cu es in Figu e 43 and Figu e 44 indica ed discon inuous yielding in
QT10-P 1000 and P 3600 cycles, bu no so in he sho e - ime P 300 condi ion. Raabe e al.
[231] ecen ly e iewed di e en mechanisms con ibu ing o he occu ence o discon inuous
yielding. They obse ed ha ul a- e ining he g ain sizes, ma e ials which no mally exhibi
con inuous yielding, such as pu e Al, aus eni ic s eels and in e s i ial- ee (IF) s eels, yield
discon inuously. In he p esen wo k, a e y ine ma ensi e/aus eni e mic os uc u e was
obse ed by TEM cha ac e iza ion a e he QT10-P 1000 cycle in he 6Mn and 6Mn2Ni
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30
No malized RA (%)
Enginee ing s ain (%)
6Mn2Ni –QT10-PT1000
6Mn –QT10-P 1000
102
As i can be seen in Figu e 59a, he main p ecipi a ed phase in 300M s eel was cemen i e,
he e o e, he ca bides obse ed inside he empe ed ma ensi e in Figu e 57 we e likely his
phase. In he 1.2990 s eel up o a ound 10% o M7C3 and M23C6 phases can be expec ed
in he mic os uc u e (Figu e 59b) acco ding o The mo-Calc, being M = Fe, C , V o Mo. The
composi ion o each phase as a unc ion o empe a u e is shown in Figu e 59c-d. Bo h
phases con ain a high con en o C , bu only M7C3 phase con ain a ela i ely high V con en .
Besides, M23C6 phase shows a conside able Mo con en , which was ba ely de ec ed by
EDS analysis. The e o e, i can be said ha he phases analyzed in Figu e 58a-b (poin s x2,
x3 and x4) migh be M7C3, al hough a u he esea ch would be needed o be e de e mine
he ype o ca bide. Acco ding o The mo-Calc, he dissolu ion empe a u e o M7C3 phase
(~1220 ºC) is signi ican ly highe han he aus eniza ion empe a u e employed in he Q&P
ea men s (1037 ºC), which means ha likely hese ca bides we e eu ec ic ca bides p esen
in he ini ial mic os uc u e o p ecipi a ed du ing aus eniza ion and we e no signi ican ly
a ec ed by he hea ea men [234,235]. In cas i ons wi h ele a ed con en s o C , eu ec ic
M7C3 ca bides end o ans o m in o M23C6 ca bides. Howe e , when C con en was below
10-25 w .% M7C3 ca bides do no appea o unde go any s uc u al changes [235]. On he
o he hand, he aus eniza ion and subsequen quenching migh led o a o ma ion o
seconda y sphe oid M7C3 pa icles (poin x2 in Figu e 58a) wi hin he p ima y aus eni ic
phase [236].
4.2.4 Ha dness
Ha dness measu emen s we e pe o med in he Q&T and Q&P ea ed samples in bo h
s eels. The a e age alues ob ained a e i e inden a ions a e shown in Figu e 60 and he
alues ob ained a e each inden a ion a e shown in Appendix D. The Q&P ea men esul ed
in a conside ably lowe ha dness, especially in he 1.2990 s eel. The 1.2990 s eel con ains
ela i ely high con en s o ca bides o ming elemen s like C (7.9%), V (1.5 w .%) and Mo
(1 w .%). Thus, in he empe ing, apa om elimina ing he s esses gene a ed du ing he
ma ensi ic ans o ma ion and so en he s uc u e es o ing he oughness o he ma e ial,
seconda y p ecipi a ion ha dening can be achie ed [10,98,99]. As i was seen in Figu e 58,
C , Mo and V con aining ca bides we e isible in he mic os uc u e o he Q&P ea ed 1.2990
s eel. Howe e , he o al amoun o ca bides was likely lowe han in he Q&T s eel.
Fu he mo e, he Q&P s eel con ained ca bon-en iched e ained aus eni e which likely
lowe ed he o e all ha dness alue [237].

103
In 300M s eel, Q&P ea men esul ed in lowe ha dness as well, al hough he dec ease was
less signi ican in compa ison wi h he 1.2990 s eel. Unlike in he 1.2990 s eel, p ecipi a ion
ha dening does no occu in his s eel, only li le cemen i e p ecipi a ion inside he empe ed
ma ensi e was obse ed (Figu e 57). Thus, empe ing ea men is only employed o
elimina e esidual s esses p oduced du ing he quenching and es o e he oughness
[8,238]. As in he 1.2990 s eel, he p esence o ca bon-en iched aus eni e le less ca bon
a ailable o he empe ed ma ensi e, hus dec easing he o e all ha dness o he Q&P s eel.
Figu e 60. Ha dness alues measu ed in he 1.2990 and 300M s eels a e he applica ion o Q&T o
Q&P hea ea men s.
4.2.5 Wea beha io
Wea a es we e calcula ed om he pin-on-disk es s o bo h s eels and bo h Q&P and Q&T
ea men s. Figu e 61 shows compa isons be ween he alues ob ained wi h each s eel and
hea ea men . When compa ing he in luence o he hea ea men (Figu e 61a-b), he
di e ence in he wea a e was insigni ican bo h in he 1.2990 and he 300M s eels. Howe e ,
i was shown be o e ha he di e ence in ha dness be ween he Q&P and Q&T ea ed s eels
was conside ably high, especially in he 1.2990 s eel. Thus, Q&P ea ed samples showed a
signi ican ly lowe ha dness bu he same wea esis ance han Q&T samples. This beha io
demons a es ha ha dness was no he only pa ame e a ec ing he wea esis ance and
ha he e ained aus eni e may play a key ole [186].
On he o he hand, when compa ing he Q&P ea ed s eels a he same linea eloci y
condi ions (Figu e 61c), as expec ed, he 1.2990 s eel clea ly showed a be e wea
esis ance. Bo h s eels had a simila RA con en , hence, in his case, he ha dness and he
62.7
56.5
54.5 51.2
0
10
20
30
40
50
60
70
1.2990 300M
Ha dness (HRC)
Q&T Q&P
104
composi ion o he s eel we e decisi e when de e mining he wea esponse o each s eel.
The 1.2990 s eel has a highe C con en and ha dness and addi ionally, i is e y likely ha
he ca bides obse ed in he mic os uc u e o his s eel we e M7C3 and M23C6, as p edic ed
by The mo-Calc Figu e 59a), which esul ed bene icial o wea esis ance [239].
Figu e 61. Wea a e (mm3/N.m) calcula ed om he PoD es s. Compa ison be ween Q&P and Q&T
ea ed 1.2990 (a) and 300M (b) s eels; and compa ison be ween Q&P ea ed 1.2990 and 300M
s eels es ed wi h he same linea eloci y (c).
I is di icul o compa e he esul s ob ained in his wo k wi h hose epo ed in he li e a u e.
On he one hand, he e is e y li le li e a u e s udying he wea esis ance applied o Q&P
s eels, and e en less s udying he wea beha io h ough unidi ec ional sliding es s. On he
o he hand, he esul s ob ained om PoD es s s ongly depend on he es ing condi ions,
he e o e, he ob ained wea a e esul s a e speci ic o he employed condi ions. Howe e ,
mos o he esul s epo ed in he li e a u e show an imp o emen in he wea esis ance by
he applica ion o Q&P hea ea men s. Wasiak e al. [187], o example, obse ed ha , a e
being Q&P ea ed, he 35C SiMn5-5-4 s eel exhibi ed wice be e wea esis ance unde he
d y sliding ic ion han a e being Q&T ea ed. Wang e al. [240] ound ha by applying a
Q&P ea men o a duc ile cas i on wea esis ance was imp o ed and ha he employed
pa i ioning ime a ec ed he ob ained wea a e, i s inc easing wi h he inc ease o he
pa i ioning ime and hen dec easing wi h a u he ime inc easing. In [192], he au ho s
concluded ha compa ed wi h Q&T ea men , wea esis ance o a high C s eel was
imp o ed by applying a se ies o Q&PT (quenching & pa i ioning- empe ing) ea men s,
which was associa ed wi h he o ma ion o ilm-like and blocky aus eni e du ing pa i ioning
s age, bu an inc ease in he pa i ioning empe a u e om 250 ºC o 400 ºC was ound o be
disad an ageous due o an inc ease in cemen i e ca bide p ecipi a ion.
8.55 8.59
0
2
4
6
8
10
12
14
Q&P Q&T
K (x10-6 mm3N-1 m-1)
11.00
10.60
Q&P Q&T
8.78
11.00
1.2990 300M
(a) 1.2990 (208.3 cm/s) (b) 300M (78.3 cm/s) (c) Q&P (78.3 cm/s)
105
In he p esen wo k, wea esis ance was no imp o ed by he subs i u ion o he Q&T by
Q&P ea men . Howe e , only one Q&P condi ion was s udied, and i is possible ha he
op imiza ion o he Q&P cycle pa ame e s could esul in an imp o emen . Ne e heless, he
esul s showed simila wea a es a e bo h ea men s wi h signi ican ly lowe ha dness a e
Q&P, which migh be ad an ageous o o he p ope ies ypically equi ed in his ype o
s eels, such as oughness.
4.2.6 Re ained aus eni e s abili y
The aus eni e ans o ma ion in o ma ensi e i is hough o be esponsible o enhancing he
wea beha io in Q&P s eels [186]. The e o e, aus eni e s abili y was s udied measu ing he
RA con en in he wea ack o he PoD es ed disk in o de o examina e he ans o ma ion
gi en du ing he es s. In Figu e 62, he RA con en s measu ed by XRD in he wea ack a e
shown o bo h s eels and di e en linea eloci y condi ions employed ( he la e only o
1.2990 s eel) and hese alues a e compa ed wi h RA con en s measu ed be o e in he
su ace o he disks.
Figu e 62. RA measu ed in he su ace and wea acks o med du ing PoD cha ac e iza ion o he
1.2990 and 300M s eels.
In he 1.2990 s eel and he lowe linea eloci y condi ion, aus eni e ans o ma ion was no
obse ed, he e o e, ma e ial did no bene i om ans o ma ion ha dening. The highe linea
eloci y condi ion esul ed in he ans o ma ion o less han 20% o he ini ial RA con en .
The e o e, i can be said ha he mechanical s abili y o aus eni e agains ans o ma ion in
his s eel, and, in he es condi ions employed in his wo k, was oo high. I is known ha he
C con en is he main ac o a ec ing RA s abili y [129,241,242]. In he 1.2990 s eel he C
22
20
23
12
18
0
4
8
12
16
20
24
28
1.2990 300M
RA (%)
Su ace Wea ack (78.3 cm/s) Wea ack (208.3 cm/s)
106
con en was high (0.92%), and i is likely ha , in spi e o he high ac ion o ca bides p esen
in he mic os uc u e, he C con en in he RA a e he Q&P ea men was oo high o allow
ma ensi e ans o ma ion. Possibly, wi h a highe load o linea eloci y he imp o emen
h ough he applica ion o Q&P wi h espec o Q&T would be clea e , al hough u he s udy
is equi ed.
In he 300M s eel, due o ma e ial limi a ions, only he es wi h lowe linea eloci y was
pe o med. In his case, a highe amoun o he aus eni e ans o med du ing he es s,
speci ically 40% o he ini ial RA. This s eel con ains a lowe C con en (0.41%), which migh
esul in a lowe C con en in RA a e Q&P ea men and consequen ly in a highe
ans o ma ion in o aus eni e. Howe e , his ans o ma ion seemed o be s ill low o be
bene icial o wea esis ance. Same as in he 1.2990 s eel, i is likely ha employing a highe
load o lineal eloci y condi ions he esul s would show a clea e imp o emen a e he
applica ion o he Q&P ea men .
Apa om he C con en , i is known ha o he ac o s can a ec he s abili y o aus eni e. I
has been epo ed ha ilm RA can be mechanically mo e s able in ma ensi ic
mic os uc u es han blocky RA, sugges ing ha his s abili y may be due o su ounding
ma ensi e la hs supp essing he ans o ma ion o ilm RA [129,243,244]. In he SEM image
o he 300M s eel (Figu e 57) some a eas wi h blocky aus eni e we e obse ed, whe eas in
he 1.2990 s eel (Figu e 58) aus eni e la hs p edomina ed. Fu he mo e, in he case o he
1.2990 s eel, a s onge ma ix could lead o an inc ease in he mechanical s abili y o RA
and some imes his makes he ans o ma ion o RA o ma ensi e no o occu e en unde
he ac ions o s ess o s ain [191]. In his wo k, only a p elimina y s udy o he wea beha io
o Q&P s eels was pe o med, and u u e es s and cha ac e iza ion would be needed o
be e elucida e he ac o s de e mining he s abili y o aus eni e in bo h s eels and he
in luence o he mic os uc u e in wea beha io .
4.2.7 Toughness
As desc ibed be o e, 1.2990 s eel showed impo an ha dness di e ences be ween he Q&P
and Q&T ea ed samples whe eas he wea a es we e simila . The lowe ha dness alues
measu ed in Q&P samples we e expec ed o esul in a be e oughness [191–193], which
would be a clea ad an age, as hose applica ions equi ing wea esis ance gene ally also
equi e oughness. Thus, Cha py V-no ch impac es we e pe o med in bo h he Q&P and
Q&T samples employing subsize s anda d specimens.
107
The oughness alues ob ained a e summa ized in Table 18 and he pho og aphs o each
specimen a e shown in Appendix E. As i can be seen, he ob ained alues we e oo low o
make an accu a e compa ison be ween he Q&P and Q&T ea ed s eels. Pa icula ly, he
oughness o he Q&P s eel was qui e lowe han expec ed based on li e a u e esul s. Lai e
al. [192,193] epo ed impac oughness alues in he ange o 17-22 J/cm2 o a s eel
con aining 1.2 w .% C and RA and ha dness alues simila o hose ob ained in his wo k,
18% RA and 600 HV (~54,5 HRC), espec i ely. In addi ion, Liu e al. [191] measu ed an
impac oughness o 19.4 J/cm2 in a 0.95 w .% C s eel wi h 20% o RA and an app oxima e
ha dness o 600 HV, al hough he s eel had a baini ic ma ix a he han ma ensi ic.
An explana ion o he low oughness can be ela ed wi h he machining ope a ion o he
Cha py specimens. Due o he complexi y o machining he dimensions o he V-no ch, i was
done by wi e cu ing. The e is no way o p o e ha h ough his cu ing ope a ion he aus eni e
a ound he no ch did no ans o m in o ma ensi e, which could be a possible eason o
ob aining such low alues in he impac es s, al hough u he in es iga ions would be
equi ed.
Table 18. Toughness alues (J/cm2) ob ained in Cha py V-no ch impac es o he Q&P and Q&T
ea ed 1.2990 s eel.
Toughness (J/cm2)
Tes 1
Tes 2
Tes 3
A e age
Q&T
5.7
4.9
3.8
4.8
Q&P
4.5
3.7
3.7
4.0

108
109
Chap e 5
Conclusions
110
111
Chap e 5
Conclusions
In his hesis ou medium Mn and Ni s eel, and h ee medium and high C s eels ea ed by
di e en Q&P ea men s we e in es iga ed. In his chap e he conclusions d awn om all
he ob ained esul s a e p esen ed.
5.1 Q&P applied o medium Mn and Ni s eels
Con en ional Q&P cycles and high pa i ioning empe a u e Q&P cycles in which he
aus eni e e e se ans o ma ion phenomenon occu ed, we e in es iga ed in ou medium
Mn s eel wi h di e en Mn and Ni amoun s. The ollowing conclusions we e d awn:
1. The addi ion o 2 w .% Mn was no su icien o s abilize high amoun s o aus eni e. In he
e cycle compe ing eac ions occu ed du ing pa i ioning, likely decomposi ion o
aus eni e in o baini e. In high pa i ioning empe a u e cycles seconda y ma ensi e
ans o ma ion occu ed du ing inal cooling, esul ing in a inal mic os uc u e wi h less
han 5 w .% o RA.
2. In he s eels wi h ou o mo e w .% o Mn, bo h aus eni e con en and ensile p ope ies
we e imp o ed wi h he applica ion o he high pa i ioning empe a u e cycles,
independen ly o he QT and P condi ions o he cycle.
3. In he 6Mn and 6Mn2Ni s eels, ea ed wi h high PT cycles, la ge amoun s o e ained
aus eni e we e ob ained in he inal mic os uc u e, which we e compa able o hose
ob ained a e in e c i ical annealing o medium Mn s eels. The addi ion o Ni u he
inc eased he con en o e ained aus eni e. The p esence o p e-exis ing aus eni e (due
o in e up ed quenching) be o e he pa i ioning s age conside ably educed he
pa i ioning ime needed o aus eni e s abiliza ion in compa ison wi h some con en ional
in e c i ical annealing hea ea men s o medium Mn s eel.
4. In he 6Mn and 6Mn2Ni s eels, a lowe quenching empe a u e esul ed in as e aus eni e
o ma ion kine ics in he high empe a u e pa i ioning s age, less o ma ion o seconda y
ma ensi e in he inal cooling, and a inal mic os uc u e wi h a highe con en o RA,
which showed a la h- ype mic os uc u e wi h ine cons i uen s.
118
6.2 Q&P applied o medium and high C s eels
In his hesis, only a p elimina y s udy o he bene i s o Q&P ea men o wea esis ance
equi ing applica ions was pe o med. The e is s ill a lo o backg ound wo k o be done in
he s udy o Q&P s eels in ela ion o wea applica ions and oughness.
• The in luence o di e en mic os uc u es on he wea pe o mance o he s eels
should be s udied. Pa icula ly, he e ec ha he amoun o each phase as e ained
aus eni e, seconda y ma ensi e o baini e has in wea esis ance should be es ed.
• Besides aus eni e amoun , how i s ca bon con en and mo phology in luence on i s
s abili y agains wea es s mus be s udy. Fo ha pu pose, mic os uc u es wi h
di e en RA con en s, ca bon in RA and mo phology should be c ea ed and s udied
h ough wea es s employing di e en condi ions.
• Once he e ec o he mic os uc u e is unde s ood, an op imiza ion o Q&P cycle
pa ame e s is necessa y o achie e he desi ed mic os uc u es.
• In his wo k only pin-on-disk es we e ca ied ou . The beha io o Q&P s eels in
o he ypes o wea es s, such as ab asi e es , could be s udied.
• Rega ding oughness, in his wo k an imp o emen a e he applica ion o he Q&P
ea men was no e i ied, despi e he lowe ha dness. The e is unce ain y as o
whe he he e ained aus eni e ans o med du ing no ch machining, he e o e
Cha py es s could be pe o med on unno ched specimens o check whe he an
imp o emen in oughness is indeed seen a e applica ion o he Q&P cycle.
• Since he mal g adien s be ween he su ace and he cen e o he disks we e no
obse ed du ing he hea ea men s, he easibili y o applying he hea ea men
in o hicke specimens wi hou ob aining he e ogenei ies in he mic os uc u e could
be s udied.
• A s udy abou ene ge ical and economic ad an ages o eplacing he con en ional
Q&T ea men by he Q&P ea men should be pe o med.
• In his pa o he wo k, high pa i ioning empe a u e Q&P cycles we e no applied,
as u he s udy is s ill equi ed o be e unde s and he in luence o low pa i ioning
empe a u e ea men s on wea and oughness beha io . The applica ion o high
pa i ioning empe a u es could also be in e es ing as pa o u u e wo k.

119
Chap e 7
Bibliog aphy
120
121
Chap e 7
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