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Effect of nickel on thermal fatigue properties of novel hot working die steel

Cheng Xi, Gu Pengcheng, Zeng Yan, Wu Xiaochun

Heat Treatment of Metals 2023, 48 (11): 55-61. doi:10.13251/j.issn.0254-6051.2023.11.009

Abstract （232）

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Thermal fatigue test of SDDVA steel and a novel hot work die steel SDYZ1 was carried out by Uddeholm self-constrained thermal fatigue test method. The surface morphology, cross-section crack, microstructure and hardness of the materials after thermal fatigue were compared and analyzed. The effect of nickel element on the cold and thermal fatigue properties of the material was discussed. The results show that compared with the SDDVA steel, the number of cracks in the SDYZ1 steel is obviously less, the depth is shallower, and the degree of high temperature surface softening is smaller. This is mainly due to the fact that Ni element accumulates near grain boundaries and carbides, which has a pinning effect on carbide growth, and the SDYZ1 steel has higher high temperature strength, which can resist crack propagation. The SDYZ1 steel precipitates carbides with smaller size during thermal fatigue, and the accumulation of carbides at grain boundaries can effectively hinder grain growth, thereby improving the fatigue resistance of the material. Through transmission observation and analysis, the main forms of coarse carbide particles after thermal fatigue of the SDYZ1 steel are irregular spherical and slender rods, and the main types are M₂₃C₆ and M₆C, and the size of carbides in the SDYZ1 steel is smaller than that in the SDDVA steel.

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Measurement of CCT curves and carbide intergranular precipitation temperature of 4Cr5Mo2V hot-working die steel

Gao Xingcheng, Wu Boya, Wu Xiaochun

Heat Treatment of Metals 2024, 49 (9): 72-79. doi:10.13251/j.issn.0254-6051.2024.09.012

Abstract （221）

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Microstructure and hardness of 4Cr5Mo2V steel at different cooling rates were observed and measured by using thermal expansion meter, resistance meter and hardness tester, combined with scanning electron microscope and energy dispersive spectroscopy. CCT curves of the tested steel were plotted, and the temperature of carbide intergranular precipitation in the steel was determined. The results show that as the cooling rate decreases, the hardness decreases and the microstructure transforms into martensite, bainite and pearlite in sequence. The critical cooling rates for pearlite and bainite transformation are 0.015 ℃/s and 0.25 ℃/s, respectively. When the cooling rate is not greater than 0.25 ℃/s, carbides precipitate along the grain in the steel, and as the cooling rate decreases, the temperature of carbide precipitation along the grain increases. At a cooling rate of 0.01 ℃/s, the highest precipitation temperature is 1022 ℃.

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Element segregation and homogenization heat treatment of DIEVAR hot working die steel

Du Simin, Cheng Wenxiong, Hu Fengrong, Ren Jinqiao, Cui Xiaokang, Zhou Zhiming

Heat Treatment of Metals 2024, 49 (7): 139-145. doi:10.13251/j.issn.0254-6051.2024.07.021

Abstract （198）

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As-cast microstructure, precipitated phases and element segregation characteristics of DIEVAR hot working die steel electroslag ingot were analyzed by the means of optical microscope (OM), scanning electron microscope (SEM/EDS), electron probe (EPMA), Thermo-Calc thermodynamic calculation. Then the effect of homogenization heat treatment on the microstructure and carbide and element distribution was studied. The results show that the as-cast dendrite structure of the tested steel is well developed, and the secondary dendrites are obvious. The Cr and Mo and V elements are inter-dendritically enriched, and the segregation order is Mo>V>Cr. The interdendritic precipitated phases are M₂₃C₆, M₆C and MC carbides. With the increase of homogenization temperature and the extension of holding time, the dendrite microstructure gradually becomes fuzzy and even disappears, and the carbide redissolution forms a certain element diffusion zone and gradually diffuses until it is fully redissolved into the matrix, the element diffusion rate is Cr>Mo>V during the homogenization heat treatment. According to dendrite morphology, carbide redissolution, element diffusion and residual segregation index of Mo element after homogenization heat treatment, and considering the actual industrial production cost, the optimal homogenization heat treatment process of the DIEVAR steel is 1280 ℃×8 h.

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Research status of high-temperature mechanical properties and deformation mechanism of FeMnCoCrNi high-entropy alloy

Sheng Jian, Li Dazhao, Yan Zhijie, Bai Shaobin, Chen Yongan, Xie Ruofei

Heat Treatment of Metals 2024, 49 (10): 211-219. doi:10.13251/j.issn.0254-6051.2024.10.035

Abstract （187）

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As a class of emerging advanced metal materials in recent years and based on the unique multi-principal element alloy design concept, high-entropy alloys (HEAs) are expected to break through the performance limit of traditional single-principal element alloys. Among them, FeMnCoCrNi HEA is one of the most widely studied systems with excellent mechanical properties and broad application prospects. The unique “four core effects” of HEAs were firstly introduced, including high entropy effect, lattice distortion effect, hysteresis diffusion effect and cocktail effect. Secondly, the research status of FeMnCoCrNi high entropy alloy in high temperature tensile properties, high temperature creep properties and corresponding deformation mechanisms was reviewed.

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Effect of Zn/Mg ratio on microstructure, mechanical properties and corrosion resistance of 7075 aluminum alloy

He Zongzheng, Wu Mingdong, Yuan Shuo, Yao Shuwei, Xiao Daihong, Huang Lanping, Liu Wensheng

Heat Treatment of Metals 2024, 49 (5): 1-9. doi:10.13251/j.issn.0254-6051.2024.05.001

Abstract （185）

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Effect of Zn/Mg ratio (mass fraction) on microstructure, mechanical properties, and corrosion resistance of 7075 aluminum alloys was investigated by means of optical microscope, scanning electron microscope, transmission electron microscope, tensile test, microhardness test and corrosion test. The results show that with the increase of Zn/Mg ratio from 1.76 to 2.90, the grain size of the as-cast alloy increases, the T6 age-hardening rate of the alloy is accelerated, and the time to reach peak hardness is shortened. The increase in Zn/Mg ratio results in a decrease in the recrystallization rate of the T6 peak-aged alloy and an increase in the percentage of the low-angle grain boundaries. The tensile strength of the alloy under the T6 peak-aging treatment with the Zn/Mg ratio of 2.10 is 634 MPa, the yield strength of the alloy is 588 MPa, and elongation is 8.4%. The tensile strength of the T74 aged alloy is 613 MPa, yield strength is 542 MPa, and elongation is 8.9%, and alloys with Zn/Mg ratio of 2.10 in both aging states exhibit good strength while maintaining high elongation. The corrosion resistance of the aged alloy decreases as the Zn/Mg ratio increases from 1.76 to 2.90. The corrosion resistance of the alloy after T74 aging treatment is better than that of the alloy under the T6 peak-aging state.

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Phase transformation behavior during continuous cooling of Cr8 back-up roll steel

Guo Yafei, Li Zhilong, Zhang Bo, Li Jie, Pang Qinghai

Heat Treatment of Metals 2023, 48 (8): 47-51. doi:10.13251/j.issn.0254-6051.2023.08.008

Abstract （158）

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In order to investigate the phase transformation behavior of Cr8 back-up roll steel during the continuous cooling process, the phase transformation parameters of the Cr8 back-up roll steel at different cooling rates were measured by Formastor-FⅡ automatic phase transformation analyzer. The CCT curves was established by thermal expansion method and metallographic method, and the influence of different cooling rates on microstructure and hardness of the Cr8 back-up roll steel was analyzed. The results show that the microhardness of Cr8 back-up roll steel increases gradually with the increase of cooling rate in the range of 2-60 ℃/min, and the hardness value increases from 238 HV2 to 570 HV2. The supercooled austenite transforms into a mixed structure containing pearlite when the cooling rate is less than 8 ℃/min. The pearlite transformation disappears and the supercooled austenite transforms into bainite+martensite or single martensite with higher hardness when the cooling rate is between 8 ℃/min and 60 ℃/min. Compared with Cr5 steel, the supercooled austenite of the Cr8 back-up roll steel has better stability, the steel has lower critical cooling rate and good mechanical properties, and is an ideal material for manufacturing large backup roll forgings.

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Research progress of low alloy martensitic wear-resistant steel

Li Zhongbo, Wu Zhifang, Wu Run

Heat Treatment of Metals 2024, 49 (7): 132-138. doi:10.13251/j.issn.0254-6051.2024.07.020

Abstract （138）

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Research progress of low alloy martensitic wear-resistant steel was reviewed, mainly involving composition design, heat treatment process and its on microstructure and mechanical properties, and wear resistance. Composition design mainly adopts a small number of multi-component system, heat treatment processes include reheat quenching-tempering treatment, direct quenching-tempering treatment, subtemperature quenching-tempering treatment, quenching-partitioning treatment and quenching-partitioning-tempering treatment. By controlling the structure shape and distribution, the hardness and toughness can be matched reasonably. The wear resistance is improved by adjusting chemical composition, refining grain, optimizing rolling cooling process and proper tempering.

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Effect of composite addition of trace amounts of Mn, Zn and Ti on microstructure and mechanical properties of Al-Cu-Li-Mg-Ag-Zr alloy

Xu Qing, Yin Dengfeng, Wang Hua, Xie Kaiwen, Song Zhuanzhuan

Heat Treatment of Metals 2024, 49 (11): 1-9. doi:10.13251/j.issn.0254-6051.2024.11.001

Abstract （134）

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Effect of composite addition of trace amounts of Mn, Zn and Ti on the microstructure and mechanical properties of Al-Cu-Li-Mg-Ag-Zr alloy was studied by using tensile testing machine, metallographic microscope, scanning electron microscope and transmission electron microscope. The results show that the composite addition of trace amounts of Mn, Zn and Ti elements can significantly refine the grain structure of the as-cast alloy, and at the same time, the insoluble second phase Al(CuMnFe) in the solution treated alloy is also refined. The composite addition of trace amounts of Mn, Zn and Ti elements can effectively promote the precipitation of the main strengthening phase T₁ in the T6 and T8 peak aged Al-Cu-Li-Mg-Ag-Zr alloy, improving the mechanical properties of the alloy. Compared with the T6 peak aged, the amount of T₁ phase precipitated in the T8 peak aged Al-Cu-Li-Mg-Ag-Zr alloy significantly increases, the size significantly decreases, the distribution is more uniform and dispersed, and the strength and plasticity are significantly improved.

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Austenite grain distribution law in 34CrNi3MoV steel

Zheng Bing, Xu Dong, Wang Yiqun, Wang Xuexi, Zhao Hongyang, Ju Dongying

Heat Treatment of Metals 2023, 48 (7): 1-7. doi:10.13251/j.issn.0254-6051.2023.07.001

Abstract （122）

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Effects of different holding temperature and holding time on austenite grain growth of 34CrNi3MoV steel were studied. The effects of holding temperature and holding time on average grain size, major axis and minor axis were analyzed by means of metallography. The results show that in the Gaussian distribution equation, the standard deviation and expectation increase with the increase of holding temperature and holding time. The size of the major axis and minor axis of grains is closely related to the average size, and the ratio has a simple linear relationship. During the grain growth, the ratio of the major axis to the minor axis basically remains unchanged. The distribution probability expressions of average grain size, major axis size and minor axis size are obtained by regression. At the same time,a new way of thinking and possible explanation for the heredity in materials science in terms of mathematical laws is provided.

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Effect of Cu on mechanical properties of 390 MPa grade CrNiMo series low-alloy ship steel plates

Li Weixian, Peng Wei, Hu Jie, Liu Tengshi, Zhou Luhai, Dong Han

Heat Treatment of Metals 2024, 49 (4): 1-7. doi:10.13251/j.issn.0254-6051.2024.04.001

Abstract （117）

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CrNiMo low-alloy marine steels without Cu(961-Base) and with 1wt% Cu(961-Cu) quenched twice and then tempered at high temperature were prepared, and then the effect of Cu on microstructure, mechanical properties, precipitated phase and texture characteristics of the steel was investigated by thermal dilatometer, optical microscope(OM), scanning electron microscope(SEM), electron backscatter diffractometer(EBSD) and transmission electron microscope(TEM). The results show that the Ac₁ and Ac₃ temperatures of the 961-Base steel are 767 ℃ and 905 ℃, and that of 961-Cu steel are 762 ℃ and 895 ℃, respectively. The ferrite/bainite transformation temperatures of the 961-Cu steel are lower than that of the 961-Base steel. The microstructure of the tested steels after heat treatment is dominated by lath bainite(LB) and a small amount of quasi-polygonal ferrite(QPF). The lath of the 961-Cu steel is more refined, which increases the proportion of large-angle grain boundaries by 6.8% and is more beneficial to hinder crack propagation. Compared with that of the 961-Base steel, the yield strength and tensile strength of the 961-Cu steel are increased by 84 MPa and 68 MPa, respectively, and the low-temperature impact absorbed energy are increased from 220 J to 267 J. The impact fracture of the tested steels is dominated by the shear lip and fiber zone, with the 961-Cu steel having a greater shear section ratio. The Cu-rich phase (fcc structure) is non-uniformly precipitated in the matrix and on dislocation line in the form of globular or rods, producing a precipitation strengthening effect. Both the tested steels are characterized by α and γ textures, with the 961-Cu steel containing a higher proportion of γ textures that is conducive to deformation.

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Carbide evolution law of high chromium and high vanadium powder metallurgy tool steel M390 during austenitizing

Deng Jinqiang, Zhang Qinyi, Chen Jun, Wu Dong, Liu Wei, Zhou Hongfeng

Heat Treatment of Metals 2023, 48 (11): 1-7. doi:10.13251/j.issn.0254-6051.2023.11.001

Abstract （115）

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Evolution of carbides in the M390 steel during different austenitizing processes was studied using analysis methods such as SEM-EDS, TEM, and Image-Pro Plus. The results show that under the austenitizing conditions of heating at 1075-1150 ℃ and holding for 15-120 min, the volume fraction and average size of carbides in the M390 steel show a decreasing trend as the quenching temperature increases. At the same quenching temperature, with the prolongation of holding time, the amount of carbides decreases as a whole, the average size of carbides decreases first and then increases, while the amount of small carbides and hardness increase first and then decrease. The types of undissolved carbides in high temperature oil quenched steel are mainly M₇C₃ and M₈C₇. During austenitizing, the change of carbides in the M390 steel is mainly the dissolution, growth and dissolution of M₇C₃.

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Microstructure of 11%Cr ferritic/martensitic steel in normally heat-treated state before and after irradiation

Wo Jianxing, Shen Yinzhong

Heat Treatment of Metals 2025, 50 (1): 6-11. doi:10.13251/j.issn.0254-6051.2025.01.001

Abstract （109）

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The microstructure of 11%Cr ferritic/martensitic steel in the normally heat-treated state before and after irradiation was experimentally studied by using transmission electron microscopy and energy dispersive spectroscopy. The results show that the primary microstructure of the 11%Cr ferritic/martensitic steel before and after irradiation consists of tempered martensitic along with a small amount of δ-ferrite. Before irradiation, a small amount of precipitates with a relatively small size are present at martensite boundaries and within martensite laths. Some irregular, blocky, large black particles are present at the interface of δ-ferrite and matrix. There are no precipitates within δ-ferrite grains. After irradiation, a large number of rod-like and blocky precipitates appear at the boundaries and interior of the martensitic lath, while the number and size of precipitates significantly increase compared to that before irradiation. The number of irregular blocky black particles at the interface of δ-ferrite and matrix increase compared to that before irradiation. Inside the δ-ferrite, a large number of blocky and needle-like precipitates are formed which may be Cr-rich nitrides, Cr-rich carbonitrides and Fe-W type precipitates. After irradiation, the precipitates inside the martensitic laths are Cr-rich M₂₃C₆ phase. Compared with the Cr-rich M₂₃C₆ phase before irradiation, the Cr and Ta contents in the M₂₃C₆ phase slightly decrease, while the Fe and Nd contents slightly increase after irradiation. However, overall, the changes in the average metal element composition of the Cr-rich M₂₃C₆ phase are relatively small.

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Regulating microstructure and mechanical properties of 7075 aluminum alloy via microalloying

Chen Zijian, Lin Yejia, Li Chuanqiang, Deng Renxuan, Dong Yong, Zhang Zhengrong

Heat Treatment of Metals 2024, 49 (9): 58-63. doi:10.13251/j.issn.0254-6051.2024.09.010

Abstract （103）

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Microstructure, phase composition, tensile properties and hardness of a series of modified 7075 aluminum alloys were comparatively studied by co-adding trace elements of Ni, RE (La and Ce) and Mg, so as to regulate the microstructure and mechanical properties of the 7075 aluminum alloy. The results show that after Ni-RE-Mg microalloying, the type of second phases in as-cast 7075 aluminum alloy does not change, but their content increases, and also the grain size is refined to some extent. In addition, the tensile property of as-cast 7075 alloy is improved via Ni-RE-Mg microalloying, and the maximum tensile strength of the as-cast alloy is 338 MPa when the mass fraction of Ni-RE-Mg is 0.2%. After solution treatment and aging, the precipitated phases in the alloy increase and the age-hardening phenomenon is more obvious with the increase of microalloying element content. When the Ni-RE-Mg mass fraction is 1.0%, the maximum hardness of the 7075 alloy after solution treatment and aging (6 h) reaches 155 HV0.5.

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Application and research progress of ultra-high strength steel in automotive lightweight

Tang Yuanshou, Si Yu, Xu Zhengmeng, Yu Shuoshuo, Cao Pengjun, Li Kejian, Feng Yi, Gao Xiang

Heat Treatment of Metals 2023, 48 (10): 247-254. doi:10.13251/j.issn.0254-6051.2023.10.038

Abstract （102）

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The new generation of automobiles puts forward higher requirements for the use of ultra-high strength steels, which need to have lightweight and better safety performance. The matching of strength and toughness of the ultra-high strength steels is an important way to achieve this goal. The higher the strength of steel, the more prone to brittle fracture. Through matching of the composition design optimization and reasonable heat treatment process, the strength and toughness of the ultra-high strength steel can be effectively improved and the occurrence of accidents can be reduced. Development of hot stamping steel, quenching & partitioning steel, and cold forming martensitic steel was reviewed,the research status of ultra high strength steels in recent years was summarized, reference for the research and development of advanced steels with high strength and high plasticity was provided, and the optimal control ideas for ultra high strength steels was introduced. Finally, the development trend of ultra-high strength steels is forecasted from the aspects of production application and development status of ultra-high strength steels.

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Effect of Ni content on microstructure and mechanical properties of 40CrNi3MoV steel strengthened by NiAl-Cu

Liang Enpu, Xu Le, Yang Yong, Wang Maoqiu

Heat Treatment of Metals 2023, 48 (8): 1-7. doi:10.13251/j.issn.0254-6051.2023.08.001

Abstract （98）

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For 40CrNi3MoV steel strengthened by NiAl-Cu precipitation, the effect of different Ni content on microstructure and mechanical properties of the tested steel tempered at 450-650 ℃ was studied. The microstructure of the tested steel was characterized by OM, the precipitates in the the tested steel were characterized by means of TEM and EDS, and the mechanical properties of the tested steel were measured by room temperature tensile and low temperature impact tests. The results show that the Ni content has no obvious effect on the microstructure of the tested steel. The increase of Ni content (3.0%-4.0%) promotes the precipitation of Cu-rich phase and NiAl phase in the tested steel, and increases the amount of nano particles. With the increase of Ni content, the tensile strength and yield strength of the tested steel tempered at 500 ℃ are increased by 200 MPa and 100 MPa, respectively.

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Effects of carbon content and heat treatment on microstructure and mechanical properties of TiAl alloys with high Nb

Gao Yukui, Fang Wenyi

Heat Treatment of Metals 2024, 49 (8): 9-14. doi:10.13251/j.issn.0254-6051.2024.08.002

Abstract （96）

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Taking Ti-44Al-8Nb-xC(x=0, 0.3, 0.6) alloys as the research object, the effects of three different carbon contents and two aging temperatures on the microstructure, microhardness and high-temperature tensile properties were studied. The results show that when the carbon content increases to 0.6%, Ti₂AlC precipitates in the alloy. When the aging temperature increases from 800 ℃ to 900 ℃, Ti₃AlC precipitates in the alloy containing carbon. The increase in carbon content and aging temperature are all beneficial to improving the microhardness and tensile strength at 850 ℃ of the alloy, where the highest microhardness is (477.6±9.1) HV0.3, and the highest tensile strength at 850 ℃ is (605.07±5.01) MPa, which increases by 32.7% compored to the lowest tensile strength. The elongation is related to the number and size of carbides, and all the tensile fractures show brittle fracture. The alloy with 0.3% carbon has the best plasticity when aged at 900 ℃, the highest elongation is 5.41%±0.42%, which increases by 67.5% compared to the lowest elongation.

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Dynamic continuous cooling transformation behavior and transformation kinetics of 40Cr10Si2Mo martensitic heat-resistant steel

Wang Qinren, Wang Qingjuan, Zhao Xiaofei, Han Shudong, Zhang Wei, Xu Rong, Hu Nan

Heat Treatment of Metals 2023, 48 (11): 16-21. doi:10.13251/j.issn.0254-6051.2023.11.003

Abstract （94）

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Phase transformation behavior of a 40Cr10Si2Mo steel during continuous cooling at different cooling rates was investigated by Gleeble-3500 thermal simulator. The dynamic continuous cooling transformation (CCT) curves and the phase transformation kinetics models of the steel were established. The effects of different cooling rates on phase transformation and alloying element precipitation were analyzed and discussed by characterizing the microstructure at different cooling rates. It is observed that the microstructure consists of ferrite and carbides at cooling rate of 0.1-0.3 ℃/s. Subsequently the precipitation of Cr and Mo in carbides decreases with the increase of cooling rate. The microstructure is ferrite and lamellar pearlite and a small amount of martensite and network carbides at cooling rate of 0.5-0.8 ℃/s. When the cooling rate is greater than 3 ℃/s, the resulted microstructure is full lath martensite. According to the established models of both the Johnson-Mehl-Avrami(JMA) diffusive type and the Koistinen-Marburger (K-M) non-diffusive type, the phase transformation kinetics curves fit well with the experimental data.

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Thermal deformation behavior and hot processing maps of 1900 MPa grade heat-resistant bearing steel

Guo Chuncheng, Qi Haiquan, Chi Hongxiao, Gu Jinbo, Liu Anqi, Wang Weimin

Heat Treatment of Metals 2024, 49 (4): 26-34. doi:10.13251/j.issn.0254-6051.2024.04.005

Abstract （93）

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Gleeble-3500 thermal simulation testing machine was used to conduct hot compression tests on a 1900 MPa heat-resistant bearing steel to study its hot deformation behavior and microstructure evolution at strain of 0.8 in the deformation temperature range of 900-1150 ℃ and strain rate range of 0.001-10 s^-1. The effect of deformation temperature and strain rate on the flow behavior of the tested steel was analyzed, the constitutive equations with strain ranges of 0.1-0.8 were constructed based on the Arrhenius model, and the hot processing maps with strain values of 0.2, 0.4, 0.6 and 0.8 were drawn based on the dynamic material model (DMM). The microstructure evolution of the tested steel was analyzed in different hot working zones to verify the optimal hot working zone obtained. The results show that under deformation conditions of 0.001-10 s^-1 and 1050-1150 ℃, the true stress-true strain curves exhibit a clear plateau after work hardening, which reflects the characteristics of dynamic recovery (DRV), while under deformation conditions of 0.001-10 s^-1 and 900-1100 ℃, the curves exhibit a clear peak, which reflects the characteristics of dynamic recrystallization (DRX). By establishing and verifying the constitutive equations, it is found that the correlation coefficient between the tested and calculated values of flow stress is R=0.973, which indicates that the established flow stress constitutive model can accurately predict the flow stress of the alloy. The hot processing maps show that the optimal process parameters within the test range are deformation temperature of 1070-1150 ℃, and strain rate of 0.01-0.1 s^-1.

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Determination of continuous cooling transition curves and microstructure analysis of pearlitic rail steel

Zhang Le, Jiang Hongli, Xie Benchang, Wang Dongmei, Cen Yaodong, Chen Lin

Heat Treatment of Metals 2024, 49 (2): 66-70. doi:10.13251/j.issn.0254-6051.2024.02.010

Abstract （88）

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Continuous cooling transition curves of the supercooled austenite of the pearlitic rail steel was plotted by using the L78 quenching dilatometer. Combined with the metallographic structure analysis and hardness test results, the microstructure and mechanical properties of the pearlitic rail steel during continuous cooling were studied. The results show that the critical phase transition temperature of the test steel is as follows: Ac₁=735.3 ℃,Ac_cm=812.2 ℃, Ar₁=697.9 ℃, Ar_cm=773.8 ℃. The tested steel was heated to 860 ℃ at 10 ℃/s for 10 min to complete austenitization and then cooled. When the cooling rate is 3 ℃/s or below, the microstructure is pearlite and local ferrite. When the cooling rate is 4-8 ℃/s, the microstructure is pearlite and a little martensite. When the cooling rate is above 11 ℃/s, the microstructure is martensite and retained austenite. There is no bainite transition. To comprehensively analyze the microstructure and hardness of the rail steel, in order to form the refined pearlite microstructure and a small amount of martensitic microstructure, the cooling rate between 4-8 ℃/s should be selected.

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Prediction and validation of microstructure and thermophysical properties of 20Mn23AlV non-magnetic steel

Tang Xingchang, Cheng Ganghu, Zhang Jiaqi, Zhang Zhijian, Zhou Weilian

Heat Treatment of Metals 2023, 48 (11): 8-15. doi:10.13251/j.issn.0254-6051.2023.11.002

Abstract （86）

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Equilibrium phase composition, precipitated phase element composition, effect of austenitizing element content on microstructure, hardenability, mechanical properties and thermophysical properties of the 20Mn23AlV non-magnetic steel were simulated and predicted using JMatPro7.0 software. The simulation parameters were compared and analyzed with the data obtained by some experiments. The calculation results show that the austenite content of the non-magnetic steel accounts for 99.89%, the rest is the dispersed phase with second phase strengthening effect, and the carbon nitride with the highest proportion in the dispersed phase is vanadium metal. The non-magnetic steel does not cause microstructure transformation at different cooling rates, and it is all austenite. The content of Mn and Al should be controlled within a certain range to maximize the proportion of austenite. There is a little difference between the predicted and the measured mechanical properties. With the decrease of temperature, the linear expansion coefficient, specific heat, Poisson's ratio and thermal conductivity decrease, while the density, shear modulus, conductivity and Young's modulus increase.

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