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  Effect of subcritical heat treatment on microstructure and properties of high chromium cast irons Yuan Zhizhong, Liu Haiming, Ju Yulin, Chen Lu, Niu Zongran, Wang Zhiyuan, Cao Fuyang, Cheng Xiaonong Heat Treatment of Metals    2024, 49 (10): 1-7.   doi:10.13251/j.issn.0254-6051.2024.10.001 Abstract （244）      PDF （4765KB）（173）       Knowledge map    Aiming at the problem of high energy consumption in conventional quenching and tempering process of high chromium cast irons, the subcritical heat treatment tests of three kinds of high chromium cast irons were carried out. Moreover, the effect of the process on the microstructure, hardness and surface wear resistance was studied. The results show that the microstructure of high chromium cast irons is primarily composed of retained austenite, M7C3 carbide, (Fe, Cr)23C6 carbide, Mo2C carbide and pearlite when subjected to holding temperatures ranging from 500 ℃ to 650 ℃ for 1 h to 14 h. A peak value in hardness is observed for the three high chromium cast irons when holding at 550 ℃ to 600 ℃ for 6 h to 12 h, with the highest peak hardness being 57.4 HRC. The hardness is most significantly influenced by the Mo element. During the insulation process, the pearlite phase transformation of austenite is promoted by the precipitation of secondary carbides in high chromium cast irons. The effects of pearlite transformation strengthening and precipitation strengthening of secondary carbides gradually decrease with prolonged holding time. The eutectic high chromium cast iron with the highest carbon content exhibits the best wear resistance when holding at 600 ℃ for 8 h. It can be seen that the first step to improve the wear resistance of high chromium cast irons is to increase the amount of eutectic carbides, and then to add elements such as Mo to enhance the precipitation strengthening effect. Reference | Related Articles | Metrics

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  Effect of cryogenic treatment on microstructure and mechanical properties of H13 steel Di Yingnan, Ma Dangshen, Zhou Jian, Chi Hongxiao, Gu Jinbo Heat Treatment of Metals    2024, 49 (10): 38-42.   doi:10.13251/j.issn.0254-6051.2024.10.006 Abstract （240）      PDF （3226KB）（67）       Knowledge map    Microstructure evolution and mechanical properties of the H13 steel during cryogenic treatment for different time (0-4 h) were studied. The phases and microstructure were analyzed by XRD and SEM, and the mechanical properties were characterized by hardness, impact and tensile tests. The experimental results show that the cryogenic treatment can refine martensite laths, promote the transformation of retained austenite to martensite and the precipitation of banded carbide. The increase of C content in martensite results in increasing in lattice constant and in lattice distortion effect, and a shift to the left in the XRD diffraction peak. With the prolongation of cryogenic treatment time, the strength and hardness of the steel show an upward trend, while the toughness and plasticity gradually decrease. Under the condition of maintaining the same hardness, the plasticity of the H13 steel after cryogenic treatment is comparable to that of the normal heat treatment, and its strength and toughness are improved. Reference | Related Articles | Metrics

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  Heat treatment for toughening technology of cold working die steel SKD11 Yuan Zhizhong, Wang Mengfei, Zhang Bocheng, Duan Xubin, Li Biaomin, Yang Haifeng, Luo Rui, Cheng Xiaonong Heat Treatment of Metals    2023, 48 (9): 1-7.   doi:10.13251/j.issn.0254-6051.2023.09.001 Abstract （235）      PDF （5140KB）（289）       Knowledge map    SKD11 steel plate after hot rolling and spheroidizing annealing was used. Two kinds of complex phase heat treatment processes, A-Q-A (Austempering-Quenching-Austempering) and Q-T-A (Quenching-Tempering-Austempering), as well asconventional Q-T(Quenching-Tempering) heat treatment process were carried out.The effect of heat treatment process on the microstructure, hardness and impact absorbed energy was studied. The results show that the microstructure of the specimens after A-Q-A and Q-T-A is the combination of lower bainite (LB) and martensite (M). The content of retained austenite is 13.2% and 18.6% for A-Q-A and Q-T-A, respectively. After A-Q-A, Q-T-A and conventional heat treatment Q-T, the hardness of the specimens is 58.5, 58.6 and 60.5 HRC and the impact absorbed energy is 31.3, 27.6 and 15 J, respectively. The excellent combination of strength and toughness of the SKD11 steel plate is realized by the duplex-phase heat treatments, which does a beneficial exploration in improving the toughness of the cold working die steel. Reference | Related Articles | Metrics

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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）      PDF （4151KB）（46）       Knowledge map    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. Reference | Related Articles | Metrics

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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）      PDF （5564KB）（36）       Knowledge map    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 ℃. Reference | Related Articles | Metrics

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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）      PDF （6795KB）（29）       Knowledge map    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. Reference | Related Articles | Metrics

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  Effect of long-term aging on microstructure and properties of nickel-based superalloy Cai Chenyang, Cao Tieshan, Wang Wei, Chi Qingxin, Cheng Congqian, Zhao Jie Heat Treatment of Metals    2024, 49 (1): 9-15.   doi:10.13251/j.issn.0254-6051.2024.01.002 Abstract （198）      PDF （3643KB）（86）       Knowledge map    Microstructure of nickel-based superalloy with different aging time was observed to explore the evolution law of microstructure and properties in the process of high temperature aging. By using OM and SEM to observe and analyze the microstructure of the alloy before and after aging, a method for quantitative analysis of microstructure evolution was proposed, and the hardness of the alloy before and after aging was tested and analyzed. The results show that after aging at 900 ℃ for 20 h without loading, the γ′ phase is cuboidal and the size does not change obviously. When aging for 100 h, the γ′ phase changes from cube to circle. After aging for 500 h, the shape of γ′ phase becomes more irregular. Some γ′ phases are connected with neighboring γ′, showing a long strip shape, but some of them remain cubic shape. When aging for 2000 h, γ′ phase is coarsened obviously and cubed degree is decreased obviously. With the aging time, the size of γ′ phase grows gradually, and the hardness of the alloy shows a decreasing trend. Reference | Related Articles | Metrics

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  Effect of secondary forging deformation on microstructure and impact properties of Cr-Mo-V die steel after spheroidal annealing Xia Yunfeng, Ma Danning, Yang Qiang, Zhou Zhongcheng, Wang Jiaoqi Heat Treatment of Metals    2024, 49 (10): 99-104.   doi:10.13251/j.issn.0254-6051.2024.10.016 Abstract （192）      PDF （3596KB）（37）       Knowledge map    Effect of secondary forging deformation on microstructure, precipitation and impact properties of Cr-Mo-V die steel was studied by means of metallographic microscope, scanning electron microscope, high resolution transmission electron microscope and impact testing machine. The results show that compared with conventional upsetting and drawing deformation, the microstructure and network carbides of the die steel after spheroidizing annealing under secondary radial forging and secondary upsetting and drawing deformation processes are significantly optimized, the impact absorbed energy are improved by 12% and 58%, respectively, and the precipitated carbides increases in quantity and is dispersed. Reference | Related Articles | Metrics

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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）      PDF （4238KB）（80）       Knowledge map    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. Reference | Related Articles | Metrics

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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）      PDF （9223KB）（127）       Knowledge map    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. Reference | Related Articles | Metrics

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  Effect of stacking fault energy on deformation mechanism in face centered cubic high-entropy alloy Zhang Bo, Li Jie, Wu Kaidi, Niu Lichong, Wan Decheng, Feng Yunli Heat Treatment of Metals    2023, 48 (8): 225-234.   doi:10.13251/j.issn.0254-6051.2023.08.037 Abstract （180）      PDF （4336KB）（150）       Knowledge map    Properties of high-entropy alloys can be tuned by changing the types and ratios of alloying elements, which affect the stacking fault energy and phase stability of the alloy system, then the plastic deformation mechanism of the alloy can be changed, thus the optimal comprehensive mechanical properties can be obtained. The factors that affect the stacking fault energy of face centered cubic high-entropy alloys, and the influence of stacking fault energy on deformation mechanism, are reviewed. And the methods that can affect the mechanical properties by changing the activation order of deformation mechanisms by adjusting the stacking fault energy are prospected. Reference | Related Articles | Metrics

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  Effect of austenitization temperature on microstructure and mechanical properties of 40CrMnSi2Mo steel under air cooling Yu Linran, Liu Geng, Yang Zhuoyue, Su Jie, Ning Jing, Ding Yali Heat Treatment of Metals    2024, 49 (12): 1-8.   doi:10.13251/j.issn.0254-6051.2024.12.001 Abstract （179）      PDF （5846KB）（158）       Knowledge map    Effect of austenitization temperature (875-975 ℃) on the microstructure and mechanical properties of the novel Cr-Mn-Si series high strength medium carbon low alloy 40CrMnSi2Mo steel under air cooling condition was studied by means of optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and laser scanning confocal microscope (LSCM). The results show that when austenitized at 875 ℃ and 900 ℃, the microstructure is dominated by martensite with a small amount of the undissolved precipitates (NbC). The prior austenite grains are fine and stable. The tensile strength is 1997 MPa and 2003 MPa, the elongation is 11.0% and 12.0%, and the fracture toughness is 70.3 MPa·m1/2 and 73.6 MPa·m1/2, respectively. When austenitized at 975 ℃, the solubility of NbC increases and the pinning effect decreases. The growth of austenite grain size decreases the thermal stability so that the coarse bainite/martensite multiphase is obtained under air cooling. The tensile strength is 1980 MPa, the elongation is 10.5%, and the fracture toughness is only 77.6 MPa·m1/2. The effect of the austenite grain refinement on the strength and toughness of the 40CrMnSi2Mo steel is not obvious. The fine bainite/martensite multiphase can be obtained after austenitizing at 950 ℃. The mechanical properties achieve an excellent combination, with the tensile strength of 2040 MPa, the elongation of 12% and the fracture toughness of 86.6 MPa·m1/2. Reference | Related Articles | Metrics

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  Effect of spheroidization annealing process on austenite grain size of 16MnCr5 steel for carburizing Zheng Xiaowei, Lin Zaiyong, Zhang Jianfeng, Jin Tao Heat Treatment of Metals    2023, 48 (5): 283-286.   doi:10.13251/j.issn.0254-6051.2023.05.045 Abstract （167）      PDF （1777KB）（73）       Knowledge map    In order to study the effect of spheroidizing annealing on austenite grain size of 16MnCr5 steel hot rolled wire rods during the process of modification, hot-rolled wire rod specimen and specimens isothermally spheroidizing annealed at 700, 720, 740, 760 and 780 ℃, respectively, for 5 h were subjected to water quenching at 940 ± 5 ℃ for 1 h. The austenite grain size of the specimens was measured and compared. The results show that the “double high” processes (heating temperature of 1200-1250 ℃, finishing rolling temperature of 950-980 ℃) and rapid cooling between 800-600 ℃ (air cooling, cooling rate ≥ 10 ℃/s) are used in the rolling process to ensure that aluminum and nitrogen atoms are in a solid solution state. During the heat treatment process before austenite grain detection, AlN is uniformly and finely precipitated, resulting in fine and uniform austenite grains in the 16MnCr5 steel. When spheroidizing annealed at 700 and 720 ℃, AlN particles are uniformly and finely precipitated. Although Ostwald aging and growth occur, the AlN particles are still smaller than the critical radius, and the austenite grains are still fine and uniform. With the further increase of spheroidizing annealing temperature, the second phase particles undergo Ostwald aging and growth. The second phase particles in local areas exceed the critical radius, and local austenite grains grow abnormally, resulting in mixed grains. In practical production, in order to obtain uniform and fine austenite grains, as well as good spheroidized microstructure and mechanical properties, 16MnCr5 steel is spheroidizing annealed at 720 ℃. Through the above controlled rolling process and spheroidizing annealing process, the austenitic grain size of 16MnCr5 steel can reach 7.5 grade to 7 grade, meeting the requirements of austenitic grain size ≥ 5 grade and without mixed grains. Reference | Related Articles | Metrics

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  Hot deformation behavior and microstructure evolution of a novel Co-Ni-based superalloy Fu Zhiqiang, He Guoai, Wu Yunjie, He Cunxiao Heat Treatment of Metals    2024, 49 (2): 1-7.   doi:10.13251/j.issn.0254-6051.2024.02.001 Abstract （166）      PDF （7060KB）（134）       Knowledge map    Gleeble-3800 thermal simulation testing machine was used to perform hot compression tests on a novel Co-Ni-based superalloy to study its hot deformation behavior and microstructure evolution at deformation temperature of 950-1100 ℃, strain rate of 0.01-10 s-1 and true strain of 0.693. The results show that the flow stress of the alloy decreases with the increase of deformation temperature or the decrease of strain rate. The average grain size of the alloy increases with the increase of deformation temperature and the dynamic recrystallization grains can be refined by reducing the deformation temperature and increasing the strain rate. The EBSD and TEM analysis results indicate that the discontinuous dynamic recrystallization (DDRX) is the main dynamic recrystallization (DRX) mechanism and the twin nucleation is the auxiliary nucleation mechanism during the hot deformation of the alloy. Reference | Related Articles | Metrics

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  Effect of quenching process on hardened depth and mechanical properties of 42CrMo steel cutter hub Jiang Ying, Du Shuiming, Huang Qiaomei, Shen Zida, You Fei Heat Treatment of Metals    2023, 48 (9): 88-91.   doi:10.13251/j.issn.0254-6051.2023.09.014 Abstract （160）      PDF （1962KB）（62）       Knowledge map    42CrMo steel cutter cub was quenched by using a multi-purpose furnace at different quenching temperatures, different quenching media and carbon potentials. The influence of various factors on mechanical properties and depth of hardened layer of the cutter cub was studied through the inspection of mechanical properties, microstructure and hardness. The results show that with the increase of quenching medium cooling rate, the tensile strength of the cutter cub quenched at 850-890 ℃ shows a trend of overall increase. When the quenching temperature is 850 ℃, the tensile properties of the cutter cub is the best when the quenching medium D is used, and the depth of quenched layer reaches 6.0 mm. When the quenching temperature is 870 ℃, after using C medium, the depth of quenched layer meets the customer's requirements. When the carbon potential is 0.6%, with the increase of quenching temperature, the depth of the quenched layer first increases and then decreases, the tensile strength decreases, and the yield strength and elongation increase. Reference | Related Articles | Metrics

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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）      PDF （4443KB）（51）       Knowledge map    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. Reference | Related Articles | Metrics

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  Effect of solution treatment on microstructure and low temperature impact properties of 022Cr22Ni5Mo3N duplex stainless steel Cui Liyun, Liu Qingtao, Luo Rui, Qian Xigen, Ding Hengnan, Sun Xi, Zhao Xiaotao, Liu Heng, Cheng Xiaonong Heat Treatment of Metals    2024, 49 (10): 18-24.   doi:10.13251/j.issn.0254-6051.2024.10.003 Abstract （155）      PDF （5070KB）（95）       Knowledge map    Solution treatment for as-forged 022Cr22Ni5Mo3N duplex stainless steel was carried out, and the effects of solution temperature (1000-1100 ℃) and time (1 h and 2 h) on the microstructure and -46 ℃ low temperature impact properties were studied. The results show that with the increase of solution temperature, the austenite content of the 022Cr22Ni5Mo3N stainless steel decreases, the phase boundary of austenite tends to be smooth and the number of needle-type and island austenite in ferrite decreases gradually. The low temperature impact properties increase first and then decrease with the increase of solution temperature. When the solution temperature is 1050 ℃, the low temperature impact absorbed energy of the 022Cr22Ni5Mo3N stainless steel is higher, which is about 260 J. The solution treatment can change the austenite phase morphology and adjust the phase content. Serrated phase boundaries(below 1050 ℃) and lower austenite phase content(above 1050 ℃) promote the brittle fracture of dual-phase steels at low temperatures, which is the main reason for the reduction of low-temperature toughness. Reference | Related Articles | Metrics

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  Effect of annealing process on grain size and texture intensity of non-oriented silicon steel Wang Haijun, Niu Yuhao, Qiao Jialong, Ling Haitao, Qiu Shengtao Heat Treatment of Metals    2023, 48 (12): 44-55.   doi:10.13251/j.issn.0254-6051.2023.12.007 Abstract （151）      PDF （3414KB）（48）       Knowledge map    Annealing processes of non-oriented silicon steel are described, and the researches on the effects of annealing temperature, annealing time, heating rate and annealing atmosphere on grain size and texture intensity of non-oriented silicon steel in recent twenty years are reviewed. In addition, the differences of microstructure and texture evolution of the cold-rolled sheet before and after annealing are compared and analyzed. Finally, the evolution characteristics of grains and textures during annealing of the non-oriented silicon steel are summarized. Reference | Related Articles | Metrics

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  Heat treatment technologies for toughening of cold working die steel DC53 Yuan Zhizhong, Chen Lu, Zhang Bocheng, Wang Mengfei, Liu Haiming, Niu Zongran, Wang Zhiyuan, Cheng Xiaonong Heat Treatment of Metals    2023, 48 (10): 15-22.   doi:10.13251/j.issn.0254-6051.2023.10.002 Abstract （148）      PDF （6461KB）（56）       Knowledge map    Duplex phase heat treatments of austempering-quenching-austempering (A-Q-A) and austempering-quenching-tempering (A-Q-T) were processed to improve the toughness of cold working die steel DC53. The influence of heat treatments on microstructure and mechanical properties of the DC53 steel was analyzed and compared with conventional heat treatment of quenching-high temperature tempering (Q-T). The results show that lower bainite/martensite (LB/M) multiphase structures with retained austenite (AR) content of 21.7% and 16.5% is resulted from the A-Q-A and the A-Q-T specimens,respectively. The hardness of the A-Q-A and the A-Q-T specimens is 59.6 HRC and 59.9 HRC, respectively, slightly lower than that of Q-T, i.e. 62.3 HRC. However, the impact absorbed energy of these two processes are 84.9 J and 87.3 J, respectively, much higher than that of Q-T, i.e. 35.6 J. It is due to the fine grain strengthening of the duplex phase microstructure,deformation strengthening and the content increase in AR. Therefore, excellent coordination of strength and toughness can be achieved by LB/M duplex phase heat treatment, which enable the DC53 steel to be used in service environments with impact. Reference | Related Articles | Metrics

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  Mechanism of α lamellae spheroidization and strengthening plasticization of TC21 titanium alloy after post forging heat treatment Tao Cheng, Cui Xia, Ouyang Delai, Lan Xixin, Wan Xingcai Heat Treatment of Metals    2023, 48 (8): 138-143.   doi:10.13251/j.issn.0254-6051.2023.08.022 Abstract （145）      PDF （4261KB）（34）       Knowledge map    TC21 titanium alloy was subjected to spheroidization heat treatment after multi-directional forging under optimal parameters(920 ℃-0.92 single pass true strain-3 cycles-water cooling), and the tensile properties of the specimens before and after forging and after spheroidization heat treatment were tested. The evolution law of α lamellae spheroidization (equiaxation) under different heat treatment parameters (temperature of 830-920 ℃, holding time of 1-4 h) of the alloy was studied and the strengthening plasticization mechanism of the alloy was revealed. The results show that after optimal multi-directional forging, the preferred subsequent spheroidizing heat treatment parameters for the TC21 titanium alloy are 890 ℃-2 h-air cooling, which can promote α lamellae spheroidization, and make that the yield strength and elongation of the TC21 titanium alloy are significantly improved, reaching 894.0 MPa and 13.2%, respectively. The strengthening plasticization mechanism of the TC21 titanium alloy after spheroidization heat treatment is mainly fine grain strengthening caused by α phase grain refinement and dislocation strengthening induced by needle-like secondary α phase in β phase. Reference | Related Articles | Metrics