Microstructural changes during deformation of AISI 300 grade austenitic stainless steels: Impact of chemical heterogeneity

ScienceDi ec A ailable online a www.sciencedi ec .com A ailable online a www.sciencedi ec .com ScienceDi ec S uc u al In eg i y P ocedia 00 (2016) 000–000 www.else ie .com/loca e/p ocedia 2452-3216 © 2016 The Au ho s. Published by Else ie B.V. Pee - e iew unde esponsibili y o he Scien i ic Commi ee o PCF 2016. XV Po uguese Con e ence on F ac u e, PCF 2016, 10-12 Feb ua y 2016, Paço de A cos, Po ugal The mo-mechanical modeling o a high p essu e u bine blade o an ai plane gas u bine engine P. B andãoa, V. In an eb, A.M. Deusc* aDepa men o Mechanical Enginee ing, Ins i u o Supe io Técnico, Uni e sidade de Lisboa, A . Ro isco Pais, 1, 1049-001 Lisboa, Po ugal bIDMEC, Depa men o Mechanical Enginee ing, Ins i u o Supe io Técnico, Uni e sidade de Lisboa, A . Ro isco Pais, 1, 1049-001 Lisboa, Po ugal cCeFEMA, Depa men o Mechanical Enginee ing, Ins i u o Supe io Técnico, Uni e sidade de Lisboa, A . Ro isco Pais, 1, 1049-001 Lisboa, Po ugal Abs ac Du ing hei ope a ion, mode n ai c a engine componen s a e subjec ed o inc easingly demanding ope a ing condi ions, especially he high p essu e u bine (HPT) blades. Such condi ions cause hese pa s o unde go di e en ypes o ime-dependen deg ada ion, one o which is c eep. A model using he ini e elemen me hod (FEM) was de eloped, in o de o be able o p edic he c eep beha iou o HPT blades. Fligh da a eco ds (FDR) o a speci ic ai c a , p o ided by a comme cial a ia ion company, we e used o ob ain he mal and mechanical da a o h ee di e en ligh cycles. In o de o c ea e he 3D model needed o he FEM analysis, a HPT blade sc ap was scanned, and i s chemical composi ion and ma e ial p ope ies we e ob ained. The da a ha was ga he ed was ed in o he FEM model and di e en simula ions we e un, i s wi h a simpli ied 3D ec angula block shape, in o de o be e es ablish he model, and hen wi h he eal 3D mesh ob ained om he blade sc ap. The o e all expec ed beha iou in e ms o displacemen was obse ed, in pa icula a he ailing edge o he blade. The e o e such a model can be use ul in he goal o p edic ing u bine blade li e, gi en a se o FDR da a. © 2016 The Au ho s. Published by Else ie B.V. Pee - e iew unde esponsibili y o he Scien i ic Commi ee o PCF 2016. Keywo ds: High P essu e Tu bine Blade; C eep; Fini e Elemen Me hod; 3D Model; Simula ion. * Co esponding au ho . Tel.: +351 218419991. E-mail add ess: amd@ ecnico.ulisboa.p P ocedia S uc u al In eg i y 2 (2016) 2299–2306 Copy igh © 2016 The Au ho s. Published by Else ie B.V. This is an open access a icle unde he CC BY-NC-ND license ( h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/ ). Pee e iew unde esponsibili y o he Scien i ic Commi ee o ECF21. 10.1016/j.p os .2016.06.288 10.1016/j.p os .2016.06.288 A ailable online a www.sciencedi ec .com ScienceDi ec S uc u al In eg i y P ocedia 00 (2016) 000–000 www.else ie .com/loca e/p ocedia 2452-3216 © 2016 The Au ho s. Published by Else ie B.V. Pee - e iew unde esponsibili y o he Scien i ic Commi ee o ECF21. 21s Eu opean Con e ence on F ac u e, ECF21, 20-24 June 2016, Ca ania, I aly Mic os uc u al changes du ing de o ma ion o AISI 300 g ade aus eni ic s ainless s eels: Impac o chemical he e ogenei y Jiří Mana*, I o Kuběnaa, Ma ek Smagab, Ondřej Manc, An i Jä enpääd, Anja Weidne e, Zdeněk Chlupa, Ja osla Poláka aIns i u e o Physics o Ma e ials ASCR, Žižko a 22, 616 62 B no, Czech Republic bIns i u e o Ma e ials Science and Enginee ing, Uni e si y o Kaise slau e n, P.O. Box 3049, 67653 Kaise slau e n, Ge many cCEITEC, B no Uni e si y o Technology, Podnika elská 6, 616 69 B no, Czech Republic dCen e o Ad anced S eel Resea ch, Uni e si y o Oulu, 90014 Oulu, Finland eIns i u e o Ma e ials Enginee ing, TU Be gakademie F eibe g, Gus a -Zeune -S . 5, 09596 F eibe g, Ge many Abs ac The p esen wo k poin s ou he impo ance o chemical he e ogenei y on he des abiliza ion o aus eni ic s uc u e and he o ma ion o de o ma ion induced ma ensi e (DIM) in AISI 300 g ade aus eni ic s ainless s eels (ASSs) o di e en le el o aus eni e s abili y (316L, 304, 301LN). Colo e ching e eals ha he s uc u e o w ough C –Ni ype s eels is ne e ully chemically homogeneous. Con on a ion o dis ibu ion and mo phology o DIM o med in he olume o ma e ial a e s a ic and cyclic s aining unde well con olled di e en condi ions wi h he cha ac e is ic local a ia ions in chemical composi ion o di e se w ough semi-p oduc o ms (pla es, shee s, ba s) p o ed p ominen and e y impo an ole o chemical banding in he des abiliza ion o o iginally ully aus eni ic s uc u e. This ac should be conside ed especially when in e p e ing he esul s o hyd ogen emb i lemen ensile es ing o C –Ni ASSs wi h lowe ed Ni con en . An impac o chemical he e ogenei y on mic os uc u al changes du ing p oduc ion o UFG s uc u e o 301LN and i s cyclic s aining is highligh ed. © 2016 The Au ho s. Published by Else ie B.V. Pee - e iew unde esponsibili y o he Scien i ic Commi ee o ECF21. Keywo ds: w ough C –Ni aus eni ic s ainless s eels; de o ma ion induced ma ensi e; chemical banding; UFG s uc u e; colo me allog aphy * Co esponding au ho . Tel.: +420 532 290 383; ax: +420 541 218 657. E-mail add ess: [email p o ec ed] A ailable online a www.sciencedi ec .com ScienceDi ec S uc u al In eg i y P ocedia 00 (2016) 000–000 www.else ie .com/loca e/p ocedia 2452-3216 © 2016 The Au ho s. Published by Else ie B.V. Pee - e iew unde esponsibili y o he Scien i ic Commi ee o ECF21. 21s Eu opean Con e ence on F ac u e, ECF21, 20-24 June 2016, Ca ania, I aly Mic os uc u al changes du ing de o ma ion o AISI 300 g ade aus eni ic s ainless s eels: Impac o chemical he e ogenei y Jiří Mana*, I o Kuběnaa, Ma ek Smagab, Ondřej Manc, An i Jä enpääd, Anja Weidne e, Zdeněk Chlupa, Ja osla Poláka aIns i u e o Physics o Ma e ials ASCR, Žižko a 22, 616 62 B no, Czech Republic bIns i u e o Ma e ials Science and Enginee ing, Uni e si y o Kaise slau e n, P.O. Box 3049, 67653 Kaise slau e n, Ge many cCEITEC, B no Uni e si y o Technology, Podnika elská 6, 616 69 B no, Czech Republic dCen e o Ad anced S eel Resea ch, Uni e si y o Oulu, 90014 Oulu, Finland eIns i u e o Ma e ials Enginee ing, TU Be gakademie F eibe g, Gus a -Zeune -S . 5, 09596 F eibe g, Ge many Abs ac The p esen wo k poin s ou he impo ance o chemical he e ogenei y on he des abiliza ion o aus eni ic s uc u e and he o ma ion o de o ma ion induced ma ensi e (DIM) in AISI 300 g ade aus eni ic s ainless s eels (ASSs) o di e en le el o aus eni e s abili y (316L, 304, 301LN). Colo e ching e eals ha he s uc u e o w ough C –Ni ype s eels is ne e ully chemically homogeneous. Con on a ion o dis ibu ion and mo phology o DIM o med in he olume o ma e ial a e s a ic and cyclic s aining unde well con olled di e en condi ions wi h he cha ac e is ic local a ia ions in chemical composi ion o di e se w ough semi-p oduc o ms (pla es, shee s, ba s) p o ed p ominen and e y impo an ole o chemical banding in he des abiliza ion o o iginally ully aus eni ic s uc u e. This ac should be conside ed especially when in e p e ing he esul s o hyd ogen emb i lemen ensile es ing o C –Ni ASSs wi h lowe ed Ni con en . An impac o chemical he e ogenei y on mic os uc u al changes du ing p oduc ion o UFG s uc u e o 301LN and i s cyclic s aining is highligh ed. © 2016 The Au ho s. Published by Else ie B.V. Pee - e iew unde esponsibili y o he Scien i ic Commi ee o ECF21. Keywo ds: w ough C –Ni aus eni ic s ainless s eels; de o ma ion induced ma ensi e; chemical banding; UFG s uc u e; colo me allog aphy * Co esponding au ho . Tel.: +420 532 290 383; ax: +420 541 218 657. E-mail add ess: [email protected] Copy igh © 2016 The Au ho s. Published by Else ie B.V. This is an open access a icle unde he CC BY-NC-ND license ( h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/ ). Pee - e iew unde esponsibili y o he Scien i ic Commi ee o ECF21. 2300 Jiří Man e al. / P ocedia S uc u al In eg i y 2 (2016) 2299–2306 2 Au ho name / S uc u al In eg i y P ocedia 00 (2016) 000–000 1. In oduc ion The AISI ype 300 (C –Ni) aus eni ic s ainless s eels (ASSs) cons i u e an impo an class o ma e ials widely used in enginee ing p ac ice a oom, ele a ed and c yogenic empe a u es (Lacombe e al. (1993), Lo e al. (2009)). The aus eni ic s uc u e o hese alloys is me as able, i.e. ma ensi ic ans o ma ion γ→α’ can occu du ing cooling and/o de o ma ion (Lec oisey and Pineau (1972), Olson and Cohen (1972),Tamu a (1982)); o a ecen e iew see e.g. Lo e al. (2009) and Heds öm and Odq is (2015). Des abiliza ion o aus eni e and o ma ion o de o ma ion induced ma ensi e (DIM) s ill ep esen an impo an opic o hese s eels and is pu sued a p esen om a ious s andpoin s: (i) pe spec i e ool o he con olled s eng hening (Spence e al. (2004), Mülle -Bollenhagen e al. (2010)), (ii) possible use o NDT moni o ing o a igue damage and/o assessmen o esidual a igue li e (Lebe e al. (2007), Smaga e al. (2008)), (iii) magne ic s abili y (supe conduc ing magne s) (Toble e al. (1997)), (i ) he ole o DIM in hyd ogen en i onmen emb i lemen (HEE) (Michle e al. (2008, 2009), Webe e al. (2011), San Ma chi (2012)) and ( ) g ain e inemen ia so called ma ensi e- o-aus eni e e e sion a e p e ious cold de o ma ion (see e.g. Poulon-Quin in e al. (2009), Sun e al. (2015), Mis a e al. (2015), Behja i e al. (2016)). The s abili y o ASSs depends p ima ily on he chemical composi ion and empe a u e – see wo cha ac e is ic h eshold empe a u es calcula ed using empi ically de i ed equa ions and designa ed as Ms and Md30 (Picke ing (1978), Smaga e al. (2006) and Lo e al. (2009)). Al hough se e al e y a e wo ks indica ed a p ominen ole o local chemis y on DIM o ma ion in w ough AISI 300-g ade s eels de o med unde a ious condi ions (Lich en eld e al. (2006), Michle e al. (2008, 2009), Mülle -Bollenhagen e al. (2010), Webe e al. (2011), Ma échal (2011)), in majo i y o p esen abundan s udies his ac is ei he simply o e looked o no de ec ed due o he incomple e s uc u e cha ac e iza ion. Thus only he nominal chemical composi ion o s eels is ypically conside ed in hese s udies. The aim o he p esen wo k is o show how he ela i ely small bu speci ic a ia ions in chemis y o w ough aus eni ic s ainless s eels can ha e an impo an e ec on he mechanical des abiliza ion o hei s uc u e. This is demons a ed on se e al wo king examples wi h s eels o di e en aus eni e s abili y – 316L, 304 and 301LN de o med unde a ious condi ions. Fo his pu pose di e se mic oscopic echniques we e adop ed including colo e ching echnique o cha ac e ize dis ibu ion and mo phology o DIM. The o igin and ex en o he cha ac e is ic chemical he e ogenei y in he o m o chemical banding is discussed in he con ex o he solidi ica ion beha io and con empo a y s eel p oduc ion ou e. Dis inc i e ole o inhomogeneous dis ibu ion o DIM in a eas in which i should no be igno ed he ea e a e b ie ly poin ed ou . 2. Expe imen al Chemical composi ion and he o m o indus ially p oduced s eels oge he wi h wo cha ac e is ic h eshold empe a u es Ms and Md30 calcula ed using empi ical equa ions de i ed by Picke ing (1978) a e lis ed in Table 1. All s eels excep 301LN s eel (see below) we e es ed in he solu ion-annealed s a e; g ain size o ully aus eni ic s uc u e was ypically in he ange 30–40 µm. Fe i oscopic measu emen s p io mechanical s aining p o ed no de ec able p esence o - e i e in he s uc u e o ASS. 304 and 316L(N) s eels we e cyclically de o med unde plas ic s ain con ol wi h low cons an s ain a e a oom and dep essed empe a u es espec i ely ( o u he de ails see Smaga e al. (2006) and Man e al. (2011)). Smoo h cylind ical specimens wi h he dimensions 4 × 24 mm we e machined om cen al and ci cum e en ial pa o 316L s eel ba (see Table 1). Tensile es s we e pe o med a 223 K wi h s ain a e o 5×10–4 s–1. Table 1. Semi-p oduc o m, chemical composi ion (w . %) and cha ac e is ic h eshold empe a u es Ms and Md30 o aus eni ic s ainless s eels. Semi-p oduc o m C Si Mn C Ni Mo N Cu Ms Md30 AISI 316L(N) 25 mm hick pla e 0.018 0.42 1.68 17.6 13.8 2.6 0.071 … –367 °C –126 °C AISI 316L ba , dia. 22 mm 0.015 0.41 1.66 16.5 10.05 2.03 0.025 … –156 °C –3 °C AISI 304 ba , dia. 20 mm 0.030 0.58 1.75 18.42 9.05 0.37 0.05 0.03 –116 °C 0 °C AISI 301LN hin shee (see he ex ) 0.017 0.52 1.29 17.3 6.5 0.15 0.15 0.2 –133 °C 35 °C Jiří Man e al. / P ocedia S uc u al In eg i y 2 (2016) 2299–2306 2301 Au ho name / S uc u al In eg i y P ocedia 00 (2016) 000–000 3 c b a Fig. 1. Dis ibu ion o DIM in aus eni ic s ainless s eels a igued o he end o a igue li e (Be aha II, OM). (a) 304 s eel, ap = 6×10–3, 293 K; (b) 316L(N) s eel, ap = 2×10–3, 143 K; (c) 316L(N) s eel, ap = 2×10–3, 113 K. Axial sec ion o specimen, s ess axis is ho izon al. Fig. 2. De ail o mo phology o DIM in a igued (a) 304 and (b) 316L(N) s eel. ECCI, SEM–FEG. S ess axis is ho izon al. 301LN s eel in he o m o a hin shee wi h ul a ine g ain (UFG) size o 1.4 µm was p oduced by special he mo-mechanical ea men based on he ma ensi e- o-aus eni e e e sion annealing a e cold wo king. LCF es s we e pe o med a ambien empe a u e in ension-comp ession unde o al s ain con ol wi h cons an s ain a e o 2×10–3 s–1. Fu he de ails a e gi en elsewhe e (Chlupo á e al. (2014)). Tes ing specimens a e comple ion o di e en es s we e sec ioned by spa k e osion and ca e ully polished mechanically and elec oly ically. Two colo e ching echniques ha e been adop ed o cha ac e iza ion o mic os uc u e o all aus eni ic s ainless s eels: Be aha II (BII) o de ec ion and cha ac e iza ion o DIM and Lich enegge and Bloech I (LBI) o isualiza ion o chemical he e ogenei y; o de ails see Weck and Leis ne (1983). Fo a mo e de ail s udy o mic os uc u al changes ECCI (elec on channeling con as imaging) and EBSD (elec on backsca e di ac ion) echniques in high- esolu ion SEM–FEG (LYRA 3 XMU o MIRA 3 XMU om Tescan and FEI Ve ios 460L) we e u ilized. Local chemical analyses we e pe o med in he line scan mode using EDS (ene gy dispe si e spec oscopy). 3. Resul s and discussion 3.1. Case 1: LCF s aining o 304 and 316L s eels The p e ious sys ema ic s udy by Smaga e al. (2006) showed ha cons an plas ic s ain ampli ude cyclic s aining o 304 s eel al eady a oom empe a u e esul s in des abiliza ion o o iginally ully aus eni ic s uc u e. Figu e 1a shows ha DIM (= da k a eas in Fig. 1) is no homogeneously dis ibu ed wi hin he whole olume o he gauge pa o he longi udinally sec ioned specimen bu ins ead bands o high and low DIM densi y unning pa allel o he olling di ec ion, i espec i e o indi idual g ain o ien a ions, a e clea ly appa en . The same is ue also o mo e s able 316L(N) s eel a igued howe e a dep essed empe a u es (c. . Figs. 1b and 1c). Di e ences in he mo phology o DIM de ec ed in bo h s eels unde di e en empe a u es a e appa en om Fig. 2. Whe eas on he longi udinal sec ions o a igued specimens he dis ibu ion o DIM always esembles band-like a angemen , comple ely di e en iew on he dis ibu ion yields c oss-sec ions pe pendicula o he specimen axis, see Fig. 3. Depending on he o m o semi-p oduc used o ab ica ion o es ing specimens wo cha ac e is ic a angemen s o DIM (= black ea u es in Fig. 3) can be clea ly ecognized: (i) amoeba-shape in he case o 2302 Jiří Man e al. / P ocedia S uc u al In eg i y 2 (2016) 2299–2306 4 Au ho name / S uc u al In eg i y P ocedia 00 (2016) 000–000 Fig. 3. Cha ac e is ic dis ibu ion o DIM on specimen c oss-sec ions pe pendicula o he s ess axis. (a) 304 s eel, ap = 6×10–3, 293 K; (b) 316L(N) s eel, ap = 2×10–3, 113 K. BII e ching, OM. cylind ical ba (Fig. 3a) o (ii) lamella shape in he case o hick pla e (Fig. 3b). Compa ing Figs. 1 and 3 he h ee- dimensional na u e o DIM dis ibu ion in he ma e ial is appa en o bo h semi-p oduc s in ag eemen wi h he esul s by Michle e al. (2009). 3.2. Case 2: Tensile beha io o 316L s eel a dep essed empe a u es: cen e s. pe iphe y o ba p oduc Hyd ogen emb i lemen (HE) o C –Ni ASSs has been ex ensi ely s udied o se e al decades (San Ma chi (2012)). Small s ain a e ensile (SSRT) es s using bo h in e nal and ex e nal hyd ogen epea edly con i med ha he deg ee o HE o hese s eels s ongly depends on he nickel con en . E ec o a ious me allu gical a iables on HE has been moni o ed sys ema ically, ne e heless he ole o DIM has no been ully cla i ied ye . Recen ly Michle e al. (2008, 2009) pe o med an ex ensi e compa a i e s udy on HE o ASSs using ypical SSRT es s and i was i s ly ecognized ha he e is a di e ence in cha ac e is ic inhomogeneous dis ibu ion o DIM be ween he specimens machined om ba s and pla es in simila ashion shown in Figs. 1 and 3. This was a ibu ed by he au ho s o mac o-seg ega ion o nickel. Michle e al. (2008, 2009) in hei s udies un o una ely did no include he dimensions o he s eel semi-p oduc o ms. As will be shown in de ail elsewhe e (Man e al. (2016)) any indus ially p oduced ASS semi-p oduc is, howe e , usually seg ega ed ema kably only in i s cen e – see Fig. 4 showing homogenei y h ough he whole c oss-sec ion o 316L cylind ical ba wi h ela i ely low nickel con en (see Table 1). To sepa a e he e ec o seg ega ion on ensile beha io o he s eel, ensile specimens we e machined om bo h he cen al seg ega ed a ea and as well as om he ci cum e en ial, mo e homogeneous pa o he ba (da a on local chemis y a e gi en in pa 3.4). The specimens we e ensile de o med unde simila pa ame e s used in HE s udies, i.e. a s ain a e o 5×10–4 s–1 and 223 K. Al hough he s ess-s ain esponses o bo h se s o specimens we e p ac ically cong uen and e i oscopic measu emen s showed iden ical con en o DIM (50 ol.%), clea di e ence was e ealed using colo e ching in he dis ibu ion o DIM a e 30% ensile de o ma ion – see da ke ea u es in Figu e 5. Whe eas he specimens aken om ci cum e en ial pa o he ba show mo e o less ela i ely homogeneous dis ibu ion o DIM, he specimens aken om he cen al a ea indica e s a ing o ma ion o p ominen banded s uc u e consis ing o bands o high DIM densi y sepa a ed by s ongly de o med aus eni e only wi h low densi y o DIM. Al hough we b a Fig. 5. Cha ac e is ic dis ibu ion o DIM in specimens aken om pe iphe al and cen al pa o 316L s eel ba a e 30% ensile de o ma ion a 223 K. (a) gene al o e iew o axially sec ioned specimens, (b) de ail o mic os uc u e (BII e ching, OM). Fig. 4. Chemical he e ogenei y inside 316L s eel ba as e ealed by LBI e ching. Jiří Man e al. / P ocedia S uc u al In eg i y 2 (2016) 2299–2306 2303 Au ho name / S uc u al In eg i y P ocedia 00 (2016) 000–000 5 Fig. 6. S uc u e o 301LN s eel a e 70% cold olling educ ion e ealed on (a) c oss-sec ion and (b) su ace o he shee using BII colo e ching (OM). RD = olling di ec ion. Fig. 7. 301LN s eel wi h UFG s uc u e cycled wi h a = 5×10–3 o he end o a igue li e. (a) O e iew o specimen c oss-sec ion (BII, OM), (b) in e se p ole igu e and (c) phase map ob ained by EBSD om cen al pa (a). had no possibili y o pe o m ensile es wi h hyd ogen, his esul indica es ha also dimensions o ASSs semi- p oduc s and hus ue ex en o seg ega ed a ea should be conside ed in HE s udies (especially unde ex e nal hyd ogen). 3.3. Case 3: P oduc ion and LCF beha io o UFG 301LN s ainless s eel The ma ensi e- o-aus eni e e e sion is known o be an e ec i e ool o he g ain e inemen o me as able aus eni ic s eels (see e.g. Poulon-Quin in e al. (2009), Sun e al. (2015), Mis a e al. (2015), Behja i e al. (2016)). Depending on he deg ee o cold olling (CR) and pa ame e s o subsequen e e sion annealing ( empe a u e and ime) a ious mic os uc u al s a es can be ob ained including so called UFG (ul a ine g ained) s uc u e. Aus eni ic s eels wi h ully UFG s uc u e ac oss he shee hickness is, howe e , gene ally achie able only o hea y CR educ ions o 80–90% which a e di icul o pe o m in indus ial scale ( o a ecen e iew on his opic see Behja i e al. (2016)). Lowe hickness educ ions ollowed by p ope e e sion annealing we e ound o esul in complex mic os uc u e whe e UFG g ains coexis wi h a eas o coa se g ains (i.e. bimodal s uc u e) and some imes wi h only pa ially ec ys allized aus eni e. The eason o his mic os uc u al he e ogenei y has been discussed ei he in e ms o di e en na u e o DIM (la h- ype s. disloca ion-cell ype) (Mis a e al. (2010)) o ex u e de eloping du ing cold- olling p ocess (Poulon-Quin in (2009)). Bo h indings a e in p inciple ue; howe e , as will be indica ed bellow, hey a e only consequences o cold olling o no ully chemically homogeneous aus eni ic s eel shee . Figu e 6 shows s uc u e o 301LN s eel shee a e CR educ ion o 70%. As i is seen om his igu e he aus eni e did no comple ely ans o m o DIM (da ke a eas in Fig. 6), nei he on he shee su ace no in he bulk o he shee (c. . Figs. 6a and 6b). Band–like cha ac e o DIM sepa a ed by he laye s o hea ily de o med aus eni e a angemen is clea ly appa en in he cen al pa o he shee c oss-sec ion (Fig. 6a). Adop ed e e sion annealing 800 °C/1 s esul ed in conside able g ain e inemen , ne e heless he s uc u e bo h on he su ace as well as inside he shee showed some deg ee o g ain bimodali y and he p esence o only pa ially ans o med aus eni e (Chlupo á e al. (2013)). Bo h hese ea u es a e appa en om Fig. 7b which yields he iew o he s uc u e om he same pe spec i e shown in Fig. 6a. The 301LN s eel shee s wi h bimodal-UFG ully aus eni ic s uc u e and i s coa se coun e pa we e cyclically s ained a oom empe a u e unde low-cycle- a igue condi ions (Chlupo á e al. (2014)). Whe eas he coa se g ained 301LN s eel showed a e LCF es s conside ably inhomogeneous dis ibu ions o DIM h ough he whole specimen c oss-sec ion (no shown he e), cyclic s aining o he same s eel wi h he bimodal-UFG g ain s uc u e yielded subs an ially di e en pic u e – see Fig. 7a. As can be seen om his igu e he g ain e inemen esul ed in conside ably homogeneous dis ibu ion o DIM excep he cen al pa o he shee whe e he e ec o chemical banding inhe i ed om he cas ing p ocess (see below) pe sis ed i espec i e o ine g ain size and hus nea ly 2304 Jiří Man e al. / P ocedia S uc u al In eg i y 2 (2016) 2299–2306 6 Au ho name / S uc u al In eg i y P ocedia 00 (2016) 000–000 Fig. 8. Chemical banding in 316L ype aus eni ic s ainless s eel as e ealed by colo e ching (LBI) in cen al pa o la w ough p oduc s o di e en hickness: (a) 25 mm hick pla e, (b) 5 mm hick s ip, (c) 3 mm hick shee . Rolling di ec ion is ho izon al in all mic og aphs, OM. compac a eas o DIM unning pa allel o he shee su ace and olling di ec ion can be de ec ed in he s eel s uc u e (c. . Figs. 7a and 7c). 3.4. O igin o chemical banding in C –Ni ASSs and i s impac De ailed discussion on he o igin o dis inc i e inhomogeneous dis ibu ion o alloying elemen s aligned in ibe s o pla es pa allel o he di ec ion o wo king axis o long o la p oduc s (i.e. ba s o pla es) espec i ely is beyond he scope o he p esen pape and will be published elsewhe e (Man e al. (2016)). He e i can be b ie ly s a ed ha i s o igin is p incipally he same as in he well-known case – i.e. e i e/pea li e banding in hypoeu ec oid s eels, namely seg ega ion du ing solidi ica ion (see e.g. O e man e al. (2002), K auss (2003)). In he case o ASSs s udied in he p esen wo k he complex solidi ica ion sequence is ollowed by he so called solid-s a e ans o ma ion  → (Lacombe e al. (1993), Allan (1995)). Among o he impo an ac o s in luencing he in ensi y and ex en o seg ega ed a ea belong cooling a e, o e all alloying le el and he ype o cas ing (ingo s. con inuous cas ing, labo a o y-scale cas ing). Seg ega ions wi hin cas ed p oduc s (ingo s, blooms o slabs) a e du ing subsequen ho and cold wo king p ocess aligned o he o m o chemical banding and inhe i ed o he inal w ough s uc u e – see Fig. 8. As i is clea om his igu e he seg ega ion bands o di e en hickness a e unning ac oss he ully aus eni ic s uc u e i espec i e o he o ien a ion o indi idual g ains. Al hough an in ensi e wo king usually leads o he conside able ‘homogeniza ion’ o inal w ough semi-p oduc s, he chemical banding in hei cen al pa s is, howe e , pe sis ing e en a e a e y high wo king educ ion le els, c. . Figs. 4 and 8. Inhomogeneous dis ibu ion o DIM well documen ed in he p esen pape o he C –Ni ype ASSs s eel in se e al wo king examples can be co ela ed wi h bo h he in ensi y and cha ac e o local a ia ions o chemical composi ion (Man e al. (2016)). An example p esen s Fig. 9 which shows local a ia ions in C and Ni de e mined by line scan EDS analysis in bo h pe iphe al and cen al a ea o longi udinally sec ioned ba o 316L s eel shown in Fig. 4. Resul s o he line analysis pe o med in bo h cases pe pendicula ly o he ba axis indica e clea di e ence 0100 200 300 400 500 16 18 [w %] [µm] C 0100 200 300 400 500 16 18 [w %] [µm] C 0100 200 300 400 500 Fig. 9. Seg ega ion p o iles o C and Ni as ob ained by EDS in (a) p e iphe y and (b) cen e o cylind ical 316L ba shown in Fig. 4. (c) Compa ison o a ia ions in Md30 calcula ed o bo h egions o 316L ba . 6 8 10 12 14 [w %] [µm] Ni a 0100 200 300 400 500 6 8 10 12 14 [w %] [µm] Ni b 0100 200 300 400 500 -80 0 80 [µm] pe iphe y cen e o 22 mm / M d30 –22 °C M d30 [°C] 316L ba a e age c –18 °C Jiří Man e al. / P ocedia S uc u al In eg i y 2 (2016) 2299–2306 2305 Au ho name / S uc u al In eg i y P ocedia 00 (2016) 000–000 7 be ween bo h pa s o he ba . The same analysis has been pe o med as well o o he alloying elemen s, un o una ely, wi h he excep ion o ca bon and ni ogen (Man e al. (2016)). Unde p emise ha dis ibu ion o C and N is homogeneous in he whole olume, he p o ile Md30 empe a u e was calcula ed using Picke ing’s equa ions o bo h pa s o he ba (Fig. 9c). Al hough he a e age empe a u es Md30 a e nea ly iden ical o bo h pa s, clea and no insigni ican luc ua ions a e de ec able in he cen al pa o he ba . Thei impac on he aus eni e des abiliza ion in 316L s eel ensile de o med a 223 K has been demons a ed in Fig. 5. 4. Conclusion The p esen wo k showed ha he w ough AISI 300-g ade C –Ni aus eni ic s ainless s eels a e ne e ully chemically homogeneous. Local chemical a ia ions in he o m o chemical banding aligned in ibe s o pla es unning ac oss he s uc u e pa allel o he di ec ion o wo king axis i espec i e o indi idual g ain o ien a ions a e p esen in indus ially p oduced long (ba s o wi es) o la (pla es, shee s and s ips) p oduc s espec i ely. Since he s abili y (as well as s acking aul ene gy (SFE)) o aus eni e depends p ima ily on chemical composi ion and empe a u e (Ms, Md30) hese local, e en e y small, cha ac e is ic a ia ions in s eel chemis y will ha e an impo an e ec on bo h dis ibu ion and mo phology o de o ma ion induced ma ensi e. Al hough his ac may be i ele an o he echnical p ac ice he e a e a leas wo a eas whe e i should no be o e looked: he hyd ogen emb i lemen o ASSs wi h lowe ed nickel con en and he p oduc ion o UFG s uc u e in me as able ASSs. 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