PROMISING TECHNOLOGY FOR MANUFACTURING CAST PARTS WITH OPTIMAL CHEMICAL COMPOSITION AND IMPROVED MECHANICAL PROPERTIES

THE VI INTERNATIONAL SCIENTIFIC CONFERENCE “SCIENTIFIC FOUNDATIONS FOR THE USE OF INFORMATION TECHNOLOGIES OF A NEW LEVEL AND MODERN PROBLEMS OF AUTOMATION”, NOVEMBER 20, 2025 644 PROMISING TECHNOLOGY FOR MANUFACTURING CAST PARTS WITH OPTIMAL CHEMICAL COMPOSITION AND IMPROVED MECHANICAL PROPERTIES Tilabov B.Q. д.т.н., профессор заведующий кафедрой «Материаловедение и современные инновационные технологии» Совместного Белорусско-Узбекского государственного межотраслевого института прикладных технических квалификаций в городе Ташкенте https://doi.org/10.5281/zenodo.17814622 Annotation. The article presents the results of studies cast parts made of white high chrome cast iron. Studied the chemical composition, mechanical properties and parameters of macro - and microstructure of white iron, local and imported. Defined hardness and microhardness of the samples before and after heat treatment, as well as abrasion tested on a work surface. It is proved that the wear resistance of components after heat treatment in a double phase recrystallization is increased twice or three times. Key words: composition and properties of white high-chromium cast iron, hardness and microhardness of cast samples, heat treatment with a double phase recrystallization, macro - and micro-structure, performance and abrasive wear resistance of cast products. Introduction. Currently, the development of the chemical, metallurgical and mechanical engineering industries, as well as other related branches of technology, largely depends on various factors to increase the profitability of production [1,2]. One way to increase productivity is to use optimal chemical elements to produce high-quality cast parts from high-chromium white cast iron. In this work, two main objects were studied: 1-cast worn impellers from a centrifugal sand pump for the metallurgical industry (fig.1a); 2-cast worn cylpebs constantly rotating inside large cement production drums (fig.1b). At the same time, crack formations are visible in the macrostructure (fig.1c,d). Both parts are made from white high-chromium cast iron castings in the foundry of Almalyk Mining and Metallurgical Plant JSC and Dalvarzinsky Repair Plant LLC. Currently, the plant and the plant are using cast parts produced locally and imported by Warman. The performance and wear resistance of cast parts produced locally by JSC "AGMK" and LLC "DRZ" are several times lower than those of imported production and are limited by the resistance to abrasive wear of cast iron grade ICHKH28N2, from which cast parts that are subject to abrasive and impact-abrasive wear are made. Therefore, to clarify the reasons for such a large difference, special studies were carried out on materials produced by Warman and working parts of AGMK JSC and DRZ LLC. In addition, the chemical compositions of various cast iron melts of AGMK JSC and DRZ LLC during the period of execution of the economic contract were analyzed. The compositions of white cast iron from both productions vary within fairly wide limits, sometimes going beyond the brand composition [3-5]. A number of melts were selected for research, differing significantly in the content of basic chemical elements and sulfur. THE VI INTERNATIONAL SCIENTIFIC CONFERENCE “SCIENTIFIC FOUNDATIONS FOR THE USE OF INFORMATION TECHNOLOGIES OF A NEW LEVEL AND MODERN PROBLEMS OF AUTOMATION”, NOVEMBER 20, 2025 645 Fig.1. Cast wear parts and macrostructures cast from high-chromium white cast iron: a-pump impeller; b-cilpebs of drum mills; c,d-cracks of the samples. Special imported samples of white high-chromium cast iron, cut from a used impeller and cylpebs, were used as a kind of standard in terms of chemical composition, mechanical properties and structural parameters. The purpose of this work is to develop an innovative technology for the production of cast parts in an earthen mold from high-chromium white cast iron with optimal chemical composition, mechanical properties and the necessary structure parameters, as well as increasing the hardness and wear resistance of parts using optimal heat treatment conditions with double-phase recrystallization [6-9]. Research methodology. The optimal chemical elements we propose for these castings were analyzed in the central laboratory of the mechanical repair plant of AGMK JSC and DRZ LLC and used to produce both cast iron parts of grade X28N2. The chemical compositions of the studied white cast iron samples are given in tables 1 and 2. The results obtained show that all melts based on the main elements can be classified as known grades of cast iron [7], but the following differences are observed: - melts No 910, 926, 939 and 1, 2, 3 have a clearly overestimated carbon content for the IChKh28N2 grade; - the sulfur content in all melts of AGMK JSC and DRZ LLC is several times higher than in Warman cast iron; - the chromium content in almost all melts is less than in «Warman» cast iron. Table 1 Chemical composition of the studied samples of white cast iron TsRMZ JSC "AGMK" Product, fuse Element content, mass % С Si Mn P S Cr Ni Mo Cu Impeller (Warman) 2,87 0,317 1,38 0,031 0,012 28,31 0,53 0,049 0,025 Impeller «AGMK» JSC 2,45 0,59 0,65 0,089 0,071 22,87 1,26 - - Smelting No 910 of JSC «AGMK» 3,49 0,51 0,57 0,067 0,032 28,86 1,54 0,057 0,2 Smelting No 926 of JSC «AGMK» 2,99 0,87 0,62 0,064 0,034 26,54 0,99 0,059 0,26 THE VI INTERNATIONAL SCIENTIFIC CONFERENCE “SCIENTIFIC FOUNDATIONS FOR THE USE OF INFORMATION TECHNOLOGIES OF A NEW LEVEL AND MODERN PROBLEMS OF AUTOMATION”, NOVEMBER 20, 2025 646 Smelting No 939 of JSC «AGMK» 2,92 1,35 0,33 0,036 0,035 23,0 1,16 0,053 0,22 To relieve internal stresses, improve machinability and prepare the structure for strengthening heat treatment, cast cylinders made of white high-chromium cast iron are subjected to softening annealing at 700-7300C for several hours, followed by cooling with a furnace to hardness HRC = 39-46. Table 2 Chemical composition of the studied samples of white cast iron LLC «DRZ» Product, fuse Element content, mass % С Si Mn P S Cr Ni Mo Cu Working cylpe bs (Warman) 2,88 0,318 1,39 0,032 0,013 28,30 0,54 0,050 0,026 Working cylpebs of «DRZ» LLC 2,47 0,61 0,67 0,091 0,073 22,84 1,27 - - Melting No1 LLC «DRZ» 3,45 0,53 0,59 0,069 0,034 28,85 1,56 0,058 0,2 Melting No2 LLC «DRZ» 2,98 0,89 0,64 0,066 0,036 26,53 0,99 0,060 0,27 Melting No3 LLC «DRZ» 2,94 1,36 0,35 0,037 0,038 24,0 1,18 0,054 0,23 After clarifying the entire complex of chemical composition of the samples, studies were carried out. In our experiments, samples of white high-chromium cast iron were subjected to annealing at 7000C for 2 hours, followed by cooling along with the furnace. The results of these experiments are presented in tables 3 and 4. Table 3 Chemical elements and hardness of white cast iron samples from TsRMZ JSC «AGMK» Product, melting Essential elements, % ΣС, Ni, Si Hardness, HRC Difference in HRC C Cr Ni Mn Si Before annealing after annealing Impeller «Warman» 2,87 28,31 0,538 1,38 0,317 3,22 57 44 13 Impeller of JSC «AGMK» 2,45 22,87 1,26 0,65 0,59 4,3 50 43,5 6,5 THE VI INTERNATIONAL SCIENTIFIC CONFERENCE “SCIENTIFIC FOUNDATIONS FOR THE USE OF INFORMATION TECHNOLOGIES OF A NEW LEVEL AND MODERN PROBLEMS OF AUTOMATION”, NOVEMBER 20, 2025 647 Smelting No 910 of JSC «AGMK» 3,49 28,86 1,54 0,57 0,51 5,54 50 49,66 0,34 Smelting No 926 of JSC «AGMK» 2,89 26,54 0,99 0,62 0,78 4,76 53,5 42,7 10,8 Smelting No 939 of JSC «AGMK» 2,92 23,0 1,16 0,33 1,35 5,43 55 51 4 Table 4 Chemical elements and hardness of white cast iron samples LLC «DRZ» Product, melting Essential elements, % ΣС, Ni, Si Hardness, HRC Differenc e in HRC C Cr Ni Mn Si before annealing after annealing THE VI INTERNATIONAL SCIENTIFIC CONFERENCE “SCIENTIFIC FOUNDATIONS FOR THE USE OF INFORMATION TECHNOLOGIES OF A NEW LEVEL AND MODERN PROBLEMS OF AUTOMATION”, NOVEMBER 20, 2025 648 Working cylpebs (Warman) 2,86 28,30 0,53 6 1,39 0,31 6 3,21 56 45 11 Working Cylpebs LLC «DRZ» 2,47 22,84 1,27 0,67 0,61 4,4 49 43 6 Melting №1 LLC «DRZ» 3,45 28,85 1,56 0,59 0,53 5,55 49 48,65 0,35 Melting №2 LLC «DRZ» 2,98 26,53 0,99 0,64 0,79 4,77 54,5 43,6 10,9 Melting №3 LLC «DRZ» 2,92 23,0 1,16 0,33 1,35 5,43 55 49 6 The presented tables show that after annealing at 700°C, hardness within the range of HRC = 39-46 is not achieved in all melts. Experimental studies. As we know, in high-chromium cast iron containing about 30%Cr, as the carbon content increases, the γ-region expands and the amount of ferrite in the base structure decreases. However, the γ region expands nickel, and silicon impedes the diffusion of carbon and the decomposition of solid solutions. Therefore, it was found that the total content of elements should be about 4,5% (C, Ni, Si). In high-chromium white cast iron of the IChKh28N2 (X28N2) grade, it is generally not advisable to exceed the carbon content of more than 3%. The result is hypereutectic cast iron with large primary carbides. These large carbide crystals crack already during the manufacturing process of the section, crumble under the influence of stress, and contribute to the formation of macro - and microcracks (see fig.1c, d). Macrostructural analysis showed that the fracture had a clearly defined columnar character, when the cast iron crystals along the long primary axis are perpendicular to the wheel blade, i.e. Crystal growth during cast iron solidification proceeded predominantly in the direction of relatively rapid cooling. Therefore, for research, thin sections were prepared both across the long axis of the crystals and along them. Macrostructural analysis was studied using an MBS-9 metallographic microscope. Research results and discussion. The research results showed that the condition of the surfaces of imported cast iron samples on the rubbing surfaces had thin grooves under the influence of abrasive particles. Occasionally there were isolated deep scratches. On the friction surface of locally produced white cast iron samples there are a lot of deep scratches caused by abrasive particles. In addition, areas of brittle chipping in the form of pits are clearly visible; on the longitudinal section of the sample of JSC "AGMK" and LLC "DRZ" there are even more areas of brittle chipping. On the longitudinal sample, not only deep plowing grooves are observed on the friction surface, but also very strong chipping along the fiber of the long axis of the carbides. This is due to the presence of a large amount of sulfides in the white cast iron of AGMK JSC and DRZ LLC, which was proven by our experimental studies. This suggests that the chemical composition of white cast iron contains five times more sulfur than imported iron. THE VI INTERNATIONAL SCIENTIFIC CONFERENCE “SCIENTIFIC FOUNDATIONS FOR THE USE OF INFORMATION TECHNOLOGIES OF A NEW LEVEL AND MODERN PROBLEMS OF AUTOMATION”, NOVEMBER 20, 2025 649 Metallographic microstructural analysis was carried out using a German microscope Neofot-21 and a Russian MIM-8M. For etching of thin sections, a reagent of the following composition was used: 1. Ferric chloride - 1.25 g; 2. Picric acid - 2.5 g; 3. Hydrochloric acid - 1 ml; 4. Ethyl alcohol - 45 ml. Metallographic analysis determined the type of structure, size of carbide particles and structural components of white cast iron. Research has shown that the considered white high-chromium cast iron, locally produced by TsRMZ JSC "AGMK" and LLC "DRZ", has a composition close to eutectic, on a transverse section with small carbide particles, the sizes of which vary within the range of 8.6-51 μm. A tendency to brittle chipping was discovered during the preparation of microsections [7]. Heat treatment aims to change the structure and properties of white cast iron in the desired direction. Therefore, heat treatment should always provide the required structure and properties [9,10]. Fig.2 shows heat-treated finished impellers (fig.2a), balls and drum cylinders (fig.2b,c) and the microstructure of fine carbide (fig.2d), which increases the hardness and wear resistance of these parts. The hardness of hardened samples and parts made of high-chromium white cast iron is HRC58-63 [11,12], and the mileage and performance reaches 2000-2500 hours. Fig.2. Finished cast parts cast from high-chromium white cast iron: a-pump impeller drum; b-ball; c-cilpebs of the drum; d-microstructure of fine carbide of white cast iron. X500 Conclusions. In conclusion, it should be noted that all experimental samples and cast parts were subjected to optimal heat treatment conditions with double phase recrystallization 92511500C followed by tempering. Heat treatment was carried out to increase the hardness and wear resistance of cast parts by two or more times. 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