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Kinetics of chromium carbide precipitated in austenitic matrix of Fe-15Mn-4.5Si-10Cr-5Ni shape memory alloys

Li Jiarui, Yang Zhongmin, Zhao Kai, Chen Ying, Cao Yanguang, Li Zhaodong

Heat Treatment of Metals 2022, 47 (1): 7-12. doi:10.13251/j.issn.0254-6051.2022.01.002

Abstract （98）

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As the main strengthening phase of austenite in Fe-15Mn-4.5Si-10Cr-5Ni shape memory alloy, the second phase particle Cr₂₃C₆ plays an important role in the shape memory properties. According to the classical grain boundary nucleation kinetics theory, the theoretical calculation of a series of related parameters including phase transition chemical free energy and interface energy of Cr₂₃C₆ and the selection principle of key parameters are analyzed and solved. This study proposes a relative quantitative theoretical method for calculating the precipitation of Cr₂₃C₆ in the austenitic matrix of Fe-15Mn-4.5Si-10Cr-5Ni shape memory alloys, that produces results consistent with experimental results. The calculated PTT curve (precipitation-temperature-time curve) can be used as a theoretical basis for the selection of aging treatment parameters of Fe-15Mn-4.5Si-10Cr-5Ni shape memory alloys.

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Continuous cooling transformation of austenite in Nb-V microalloyed high-grade pipeline steel

Ma Qilin, Liu Gang, Zheng Jian, Yin Shubiao, Li Ba, Liu Qingyou

Heat Treatment of Metals 2022, 47 (1): 13-18. doi:10.13251/j.issn.0254-6051.2022.01.003

Abstract （104）

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Continuous cooling transformation behavior of subcooled austenite of three different Nb, V microalloyed high-grade pipeline steels with different composition was studied by using thermal simulation test machine, dynamic CCT curve was drawn, and three tested steels were analyzed and compared. The microstructure, microhardness value and dynamic CCT curve. The results show that the ratio of 0.05Nb-0.03V can increase the starting transformation temperature of polygonal ferrite, from 650-700 ℃ for Nb steel to 700-800 ℃, narrowing the temperature transition range of polygonal ferrite, and expanding bainite temperature transformation range of Nb steel is 400-650 ℃, and it is expanded to 350-680 ℃. At the same time, the polygonal ferrite phase transformation is suppressed, so that the pipeline steel can easily obtain the required bainite acicular ferrite structure.

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In-situ observation of austenite continuous cooling transformation characteristics of Cu-bearing steel

Lü Jinyi, Zhang Yiwei, Luo Xiaobing, Yuan Xiaomin

Heat Treatment of Metals 2022, 47 (1): 19-24. doi:10.13251/j.issn.0254-6051.2022.01.004

Abstract （85）

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By using in-situ dynamic microstructure observation with high temperature confocal laser scanning microscope (HT-CLSM), and through identification of martensite relief and bainite relief under the dynamic view field, the microstructure transformation law and phase transformation point determination method of Cu-bearing steel austenite during continuous cooling were studied. The results show that as the cooling rate increases from 5 ℃/s to 20 ℃/s, the microstructure of the specimen gradually changes from bainite to lath martensite. During the dynamic observation process of HT-CLSM, the bainite formation rate is slow, and the growth process is accompanied by the “interlocking” phenomenon, resulting in shallow relief. As the cooling rate increases, the martensite relief produced has an explosive and staged trend, mostly in bundles and parallel distribution, and the martensite relief is deeper. When the cooling rate reaches to 20 ℃/s, by using the formation of bundled martensite under dynamic observation as the criterion, the Ms point is measured as 447.6 ℃. The microstructure is lath martensite at room temperature, meanwhile the microhardness is as high as 301 HV10, which is similar to the measurement result of other methods.

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Thermodynamic calculation of retained austenite content in Q&P steel

Hou Yaqing, Zhang Yu, Yu Mingguang, Wang Jingjing, Yang Li, Su Hang

Heat Treatment of Metals 2022, 47 (1): 25-31. doi:10.13251/j.issn.0254-6051.2022.01.005

Abstract （84）

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Based on CALPHAD method, the diffusion model of Q&P steel during partitioning process was established, and a set of task flow for calculating the microstructure transformation of specific components under specific Q&P process was established. By calculating the martensite/retained austenite content in the primary quenching process of Q&P steel and the carbon enrichment of retained austenite in the partitioning process, combined with the built-in constitutive model of martensite transformation based on Gibbs free energy in Thermo-Calc software, the retained austenite content at room temperature was predicted. The model was used to calculate the retained austenite content at room temperature of steel grades (Fe-0.2C-1.28Mn-0.37Si-0.0018B, wt%) in the literature. The results show that the calculated martensite transformation temperature is 60 ℃ higher than the experimental data, and the calculated retained austenite content at room temperature is 4.41%, which is basically consistent with the experimental data, thus verifying the semi-quantitative nature of the calculation model. This model is used to further calculate and analyze the influence of carbon and manganese content and heat treatment system on the primary retained austenite content of AQT980 and AQT1180 steels. The calculation results show that the increase of carbon and manganese content can reduce the temperature of phase transformation points (A₃, Ms, Mf) in steel. At a fixed quenching temperature, the increase of carbon content and manganese content in the steel can significantly increase the primary retained austenite content. When the contents of carbon and manganese are constant, the increase of primary quenching temperature will significantly increase the primary residual content.

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Effect of heat treatment process on microstructure and abrasive wear properties of dredging engineering ship steel

Gao Yaping, Shi Zhongran, Jia Juan, Luo Xiaobing, Song Xinli

Heat Treatment of Metals 2022, 47 (1): 32-37. doi:10.13251/j.issn.0254-6051.2022.01.006

Abstract （78）

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In order to improve the wear resistance of low-carbon low-alloy wear-resistant steel for dredging engineering ships, three kinds of heat treatment processes of quenching-tempering at 200 ℃ (Q-T), quenching-partitioning at 250 ℃ (Q-P), and cyclic heat treatment (CR) were carried out respectively on the tested steel. The microstructure and precipitated phase were analyzed by scanning electron microscope (SEM) and transmission electron microscopy (TEM), the wear mass loss and the hardness were tested respectively by abrasive wear tester and hardness tester. The results show that after the quenching-tempering treatment, tempered martensite still with lath substructure and a small amount of carbides are obtained. Martensite and more retained austenite are obtained in the tested steel after quenching-partitioning. After cyclic heat treatment, the martensite laths in the tested steel disappear, and there are granular (Nb,Ti)C precipitates in the matrix. The hardness of the tested steel after quenching-tempering, quenching-partitioning and cyclic heat treatment is 39.5, 40.5, and 30.8 HRC, respectively, and the wear resistance of the tested steel is proportional to the hardness. The tested steel has the largest amount of wear mass loss and the worst wear resistance after cyclic heat treatment, while the tested steel has the second best wear resistance after quenched-tempering, and the tested steel has the best wear resistance after quenching-partitioning. For all the 3 groups of tested steel specimens, a large number of furrows appear on the surface of the specimens after abrasive wear, and the wear mechanism is mainly plastic deformation.

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Corrosive wear resistance of low alloy martensitic steel containing antimony

Wang Xin, Liang Xiaokai, Sun Xinjun

Heat Treatment of Metals 2022, 47 (1): 38-43. doi:10.13251/j.issn.0254-6051.2022.01.007

Abstract （73）

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Two martensitic steels containing 0％Sb and 0.2% Sb were analyzed to research the influence of the addition of Sb on the wear resistance under corrosive environment. The microstructure and corrosion products were characterized by OM and SEM. Then the hardness, mechanical properties and corrosive wear properties were tested. The results show that the tested steels have high tensile strength, high hardness and good impact performance at low temperature (-20 ℃), which can be over 1400 MPa, 40 HRC and 45 J respectively, while the steel containing 0.2%Sb has better corrosive wear resistance. The Sb addition improves the corrosion resistance of the steel in acidic high chloride ion and high sulfate ion environment, improving abrasion resistance as mechanical properties and hardness ensured.

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Solid solution treatment for improving cryogenic temperature toughness of Cr-Ni-Mo-Ti maraging stainless steel

Qiu Xuyangfan, Yang Zhuoyue, Ding Yali

Heat Treatment of Metals 2022, 47 (1): 44-48. doi:10.13251/j.issn.0254-6051.2022.01.008

Abstract （70）

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Microstructure, room temperature strength and cryogenic temperature toughness of 12Cr-10Ni-Mo-Ti maraging stainless steel after solution treatment at 1000 ℃, repeated low temperature solution treatment at 750 ℃ and aging at different temperature were investigated. The amount of retained austenite/reverse transformation austenite under different solution and aging treatment conditions were analyzed by using XRD. The precipitation and aging strengthening rules of reverse transformation austenite in different solution treatment processes were compared and analyzed. The results show that the Cr-Ni-Mo-Ti maraging stainless steel after solution treatment at 1000 ℃ and followed low temperature solution treatment at 750 ℃ forms austenite by α′→γ shear reverse transformation, which not only inherits the grain morphology and size of austenite, but also increases the martensitic transformation resistance and significantly reduces the formation temperature of reverse transformation austenite due to the high density of defects in austenite, resulting in 16.4% retained austenite after double solid solution treatment at 750 ℃, more than 30% retained austenite/reverse transformation austenite is formed after peak value aging at 460 ℃, and the impact absorbed energy at cryogenic temperature is extremely high, reaching above 80 J. Moreover, the high density of defect in austenite is inherited into the martensite, which enhances the aging strengthening effect. Therefore, the low temperature impact property is significantly improved without significantly reducing the tensile strength and yield strength.

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Effect of tempering temperature on microstructure and properties of a new generation transmission gear steel C61

Dai Yanzhang, Han Shun, Li Yong, Zhou Min, Wang Chunxu

Heat Treatment of Metals 2022, 47 (1): 49-55. doi:10.13251/j.issn.0254-6051.2022.01.009

Abstract （108）

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Microstructure, carbide precipitation behavior and mechanical properties of C61 gear steel specimens after quenching at 1000 ℃ and tempering were studied by using SEM, TEM, XRD, microhardness tester, tensile testing machine and impact testing machine, etc. The results show that under the quenched and cryogenic conditions, the primary carbides in the tested steel are basically dissolved and the matrix is lath martensite. In this condition, the solid solution strengthening can provide a better basis for strengthening and toughening. When the tempering temperature is 420 ℃, the precipitated M₃C cementite provides higher strength, but the presence of which has greater damage to the impact property. The M₃C cementite will dissolve when tempered at 482 ℃, and the rod-shaped M₂C carbides with a size of 10-20 nm are dispersed and precipitated in the lath martensite, which not only provides higher strength but also improves the impact property. With the increase of tempering temperature, a large amount of reverse-transformed austenite is formed which not only effectively improves the impact property but also makes the strength decrease more obviously, meanuhile, the M₂C carbides become coarser and the strengthening effect of the second phase decreases. It can be concluded that the tested steel can achieve better matching of strength and toughness under the tempering condition of 482 ℃, at which the tensile strength is 1781 MPa, yield strength is 1546 MPa, impact absorbed energy is 97 J, and peak value hardness is 52 HRC.

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Effect of annealing after cold drawing on mechanical properties and recrystallization process of Monel 400 alloy wire

Zhang Tao, Zheng Wenjie, Li Caiju

Heat Treatment of Metals 2022, 47 (1): 56-62. doi:10.13251/j.issn.0254-6051.2022.01.010

Abstract （65）

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Tensile test of annealed Monel 400 alloy wire was carried out by using ETM105D electronic tensile testing machine, and the microstructure evolution, mechanical properties and their relationship of the cold drawn Monel 400 alloy wire after different annealing treatments were studied by using Matlab-MTEX software to calculate recrystallization volume fraction. The results show that the image obtained by processing EBSD data with Matlab-METX software can intuitively present the evolution of grain in the specimen after annealing treatment, and more accurate statistics of the volume fraction of recrystallization. Good plasticity and sufficient strength can be obtained by annealing at 825 ℃ for 20 min.

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Effect of heating temperature on oxide scale of 10CrNiCuSi steel

Zhao Lei, Li Jianming, Mu Xiaobiao, Chai Xiyang, Chai Feng, Pan Tao

Heat Treatment of Metals 2022, 47 (1): 63-68. doi:10.13251/j.issn.0254-6051.2022.01.011

Abstract （74）

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In order to improve the surface roughness of 10CrNiCuSi shipbuilding steel, the oxidation experiment at 1100-1300 ℃ under air condition was carried out in a resistance furnace. The exfoliation of the oxide scales was evaluated by bend tests. And the evolution of oxide scales at different temperature was studied. The results show that the oxidation rate and thickness of oxide layer increase with the increase of heating temperature. The scale of the tested steel is mainly composed of Fe₂O₃, Fe₃O₄, FeO and internal oxide layer, and the internal oxide layer consists of FeNiCu, Fe₂SiO₄ and FeO phases. The liquid eutectic Fe₂SiO₄/FeO products have a significant influence on the exfoliation of the oxide scales. At the conditions of 1100 ℃ and 1150 ℃, the Fe₂SiO₄ phases presented with granular or massive shape are dispersed in the internal FeO phases. The interface between the scale and the matrix is relatively straight and the scale is easily exfoliated. At the conditions of 1200, 1250 and 1300 ℃, the eutectic product of Fe₂SiO₄-FeO presents an anchor-like morphology, which is pinned to the interface of oxide scale and substrate resulting in rough bonding interface, and the anchor-like FeNiCu phases have a good bonding properties with substrate and the scale. The synergistic effects cause the oxide scale hard to exfoliate. Therefore, it is more appropriate to remove the oxide scales at 1100-1150 ℃.

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Application of Nb-V microalloyed high carbon steel in steel wire for flexible flat-top card clothing

Zhuo Chengzhi, Gao Li, Gu Weihua, Yong Qilong, Lu Zhong

Heat Treatment of Metals 2022, 47 (1): 69-72. doi:10.13251/j.issn.0254-6051.2022.01.012

Abstract （63）

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Changes of basic properties of the 72B steel wires before and after the addition of niobium were analyzed by comparing the microstructure, tensile curves, and number of bends before fracture of the steel wires. The results show that comparing with 72B steel wire, the grain size grade of the steel wire product with Nb addition increases from 12.5-13 to 14-14.5. At the same time, the yield strength increases by 20.7% from 1745.8 MPa to 2108 MPa, and the tensile strength increases by 14.4% from 1930.7 MPa to 2209.5 MPa. The bending test shows an increasement of 28.2% from 1041 to 1335 before the fracture. These improvements imply the possibility to have higher wear resistance and significant improvement in the life span of the flat top card clothing when the steel wire is applied in the operating environment. Such improvement has been verified by the field experiments, i.e., the life span of the flat top card clothing made of the new niobium microalloyed steel wire is improved by 30%.

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Effect of Co microalloying on microstructure and properties of M2 high speed steel

Li Liangjun, Zhang Jiamin, Chi Hongxiao, Zhou Jian

Heat Treatment of Metals 2022, 47 (1): 73-78. doi:10.13251/j.issn.0254-6051.2022.01.013

Abstract （53）

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Effect of Co microalloying on its tempered microstructure and properties of the M2 high speed steel was studied by means of Rockwell hardness tester, scanning electron microscope and transmission electron microscope. The results show that the microstructure of the two tested steels after tempering is tempered martensite+a small amount of retained austenite+carbides. The addition of 0.82% (mass fraction, the same below) Co makes the peak hardness of M2 high-speed steel increasing by about 0.3 HRC and the hot hardness of M2 high-speed steel after holding at 600 ℃ for 48 h increasing by about 0.8 HRC. It can be seen that Co microalloying has little effect on the improvement of hardness and hot hardness of M2 high-speed steel, but makes the bonding strength increasing by about 950 MPa, while slightly decrease of the toughness of M2 high-speed steel, which is a brittle fracture mode. Through the observation of carbides in the tested steel, it is found that the primary carbides precipitated in the two tested steels are mainly large particle MC and M₆C carbides. After TEM analysis, it is found that the addition of 0.82%Co increases the number of long needle-like M₂C secondary carbides precipitated in martensitic lath of the tested steel.

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Formation mechanism of κ-carbide in FeMnAlC low density steel

Cao Chenxing, Wang Cunyu, Cao Wenquan

Heat Treatment of Metals 2021, 46 (12): 1-6. doi:10.13251/j.issn.0254-6051.2021.12.001

Abstract （65）

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FeMnAlC steel is a new type of high strength and low density steel. The high content of alloying elements makes the microstructure and properties of the FeMnAlC steel have a large regulatory space. κ-carbide is a unique precipitated phase in the steel, and its precipitation position and size have a great influence on the properties of the FeMnAlC steel. Reasonable regulation of κ-carbide precipitation can effectively improve the strength of the steel, and with high plasticity and toughness. The formation mechanism of κ-carbide in the FeMnAlC steel was summarized, and the morphology characteristics and control methods of κ-carbide were explored by combining different cooling rates and short-term aging tests.The results show that the κ-carbide is generated by spinodal decomposition, and the structure is coherent with the matrix, which will coarsen with the extension of aging time and the increase of temperature. Si and Ni elements will promote the precipitation of κ-carbide, and Mo, Cr and other elements will inhibit the precipitation of κ-carbide.

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Effect of heat treatment process on precipitates and shape memory properties of Fe-15Mn-4.5Si-10Cr-5Ni shape memory alloy

Zhao Kai, Yang Zhongmin, Li Jiarui, Chen Ying, Cao Yanguang, Li Zhaodong

Heat Treatment of Metals 2021, 46 (12): 7-12. doi:10.13251/j.issn.0254-6051.2021.12.002

Abstract （59）

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Effects of direct aging, solution and aging heat treatment on the microstructure, precipitation of the second phase and shape memory effect of the tested alloy were studied by means of OM,TEM and physicochemical phase analysis in order to further improve the shape memory effect of Fe-15Mn-4.5Si-10Cr-5Ni shape memory alloy. The results show that,the shape memory performance of the specimen decreases obviously because the second phase particles redissolve greatly after solution heat treatment; At the same time, the direct aging treatment significantly increases the amount of Cr carbide second phase precipitation in the specimen compared with the solution and aging treatment, which greatly improves the shape memory performance of the specimen. The best shape recovery ultimately can be obtained by direct aging at 800 ℃.

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Effect of aging treatment on microstructure and mechanical properties of high quality GH738 alloy

Wu Yubo, Yang Chengbin, Hou Weixue, Rong Yi, Li Chun, Lu Yunjie, Li Lingli

Heat Treatment of Metals 2021, 46 (12): 13-18. doi:10.13251/j.issn.0254-6051.2021.12.003

Abstract （66）

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Effect of aging temperature and time on microstructure and properties of high quality GH738 alloy was studied by means of mechanical testing and microstructure observation. The results show that the aging temperature and time both affect the fraction and size of γ′ phase. When the aging temperature is between 720 ℃ and 800 ℃, with the increase of aging temperature, the strength of the alloy decreases, the primary and secondary γ′ phases grow up by 30 nm and 8 nm, respectively. The volume fraction of the primary γ′ phase increases, and that of the secondary γ′ phase decreases. When the aging temperature is 800 ℃, the volume fraction of the primary γ′ phase reaches the peak value as about 8%. When the aging time is between 0 and 48 h, with the increase of aging time, the alloy strength first increases and then decreases. The two types of γ′ phase grow up by 20 nm and 6 nm, respectively. The volume fraction of the primary γ′ phase increases first and then decreases, and that of the secondary γ′ phase just changes as the opposite. When the aging time is 8 h, the volume fractions of two types of γ′ phase reach their peak/valley values respectively, as about 8% and 12%. The changes in the size and volume fraction of the γ′ phase, especially volume fraction, lead to different effects of two strengthening mechanisms of dislocations, resulting in change in strength.

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Effect of cold deformation on microstructure and mechanical properties of 028 alloy containing nitrogen

Gong Fangyuan, Feng Hanqiu, Lang Yuping, Chen Haitao, Wang Baoshun, Zhong Qiang, Leng Chongyan

Heat Treatment of Metals 2021, 46 (12): 19-23. doi:10.13251/j.issn.0254-6051.2021.12.004

Abstract （50）

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Effect of cold rolling deformation on microstructure and mechanical properties of 028 alloy containing nitrogen was studied by means of optical microscope (OM), transmission electron microscope (TEM) and tensile test. The results show that when the amount of cold deformation is the same, the yield strength increases obviously with the increase of nitrogen content. When the cold deformation is increased from 0% to 70%, the tensile strength of the 0.25%N tested alloy is increased from 764 MPa to 1405 MPa, and the yield strength is increased from 390 MP to 1249 MPa. At low deformation, there are a large number of dislocations and plane slip structures in the alloy. With the increase of cold deformation, the number of deformation twins in the alloy increases gradually, and the dislocations multiply continuously. When the cold deformation continues to increase, the deformation twins are split and broken.

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Effect of Nb on microstructure and impact properties of H13 steel

Ouyang Weihao, Zhou Jian, Gao Peng, Lin Peng, Chi Hongxiao, Wang Wenjun

Heat Treatment of Metals 2021, 46 (12): 24-30. doi:10.13251/j.issn.0254-6051.2021.12.005

Abstract （69）

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Microstructure and mechanical properties of the H13 tested steel with Nb content of 0, 0.067% and 0.270% (mass fraction) after quenching and tempering were comparatively studied by means of OM, SEM, EDS, phase analysis, hardness test and impact properties test. The results show that quenching hardness of the tested steel decreases after adding Nb. As the quenching temperature increases, the grain size of the Nb-containing tested steels is smaller than that of the 0Nb tested steel, but there are some undissolved carbides in the Nb-containing tested steels. The secondary hardening peak of the three tested steels after tempering all appear at 510 ℃. After quenching at 1050 ℃ and tempering at different temperatures, the impact absorbed energy of the 0.067Nb tested steel is higher than that of the 0Nb tested steel. Due to the influence of large-size carbides, when the quenching temperature is below 1080 ℃, the impact absorbed energy of the 0.27Nb tested steel is not as good as that of the other two tested steels.

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Microstructure and mechanical properties of low density austenitic matrix hot rolling steel with different Ni contents

Wang Fengquan, Sun Ting, Wang Maoqiu, Yu Wenchao, Zhou Xiaolong

Heat Treatment of Metals 2021, 46 (12): 31-39. doi:10.13251/j.issn.0254-6051.2021.12.006

Abstract （60）

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The microstructure and mechanical properties of three kinds of Fe-18Mn-10Al-1C-(0, 3, 5)Ni-0.08V-0.03Nb (wt%) austenitic matrix low density dual phase steels after hot rolling were studied. The results show that the microstructure of the steel after hot rolling is composed of elongated austenite, band B2 and massive B2 particles along the grain boundaries of recrystallized austenite grains. In addition, nano-sized κ-carbide and DO₃ phase are formed in austenite grains and B2 grains, respectively. The yield strength of the tested 5Ni steel reaches 1352 MPa, which is mainly due to the precipitation strengthening effect of a large number of nano-sized B2 particles and VC phase in the austenite grain boundary. With the increase of Ni content, the strength and hardness of the steel increase, and the yield strength of 5Ni steel is 116 MPa higher than that of 0Ni steel, which is attributed to more B2 phase content (16.9%) in the 5Ni steel. However, while the strength of the Ni-containing steel increases, the plasticity of the steel is greatly lost, resulting in a very low elongation. The reason is that the banded B2 phase is mainly distributed at the austenite grain boundary, and the crack is easier to break along the grain boundary in the process of deformation. In the meantime, delamination can be observed on the fracture surface.

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Effect of heat treatment on microstructure and properties of 30Cr16Mo1VN steel

Cao Xin, Li Quan, Yang Yinhui

Heat Treatment of Metals 2021, 46 (12): 40-45. doi:10.13251/j.issn.0254-6051.2021.12.007

Abstract （73）

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In order to explore optimum heat treatment process of 30Cr16Mo1VN steel, the effect of quenching and tempering temperatures on the microstructure and mechanical properties was studied by impact and tensile tests, Rockwell hardness test, OM, SEM, XRD and TEM. The results show that the optimum austenitizing temperature for quenching of the steel is 1050 ℃, at which there are a small amount of M₂₃C₆ carbide and M₂N nitride to hinder the grain boundary migration in quenching, and the average grain size of prior austenite is 14.1 μm. However, most of the carbide and nitride are dissolved into the matrix, resulting in lowering of the Ms point and increasing the content of retained austenite up to 59.2%. After cryogenic treatment at -73 ℃, a large amount of retained austenite is quenched into martensite, and the hardness of the steel is increased to 57 HRC. After tempering at 300 ℃, the steel has a good match of strength and toughness, with the tensile strength and the area reduction up to 2030 MPa and 10.0% respectively. The tempering leads the matrix to recover and the dislocation density to decrease, while as the tempering temperature rises, the dispersed fine spherical carbide precipitates in the matrix to hinder the movement of dislocations and produce secondary hardening, and the hardness peak appears when tempering at 450 ℃. When the tempering temperature is lower than 500 ℃, the hardness is always greater than 55 HRC, the steel has good tempering resistance.

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Thermal deformation behavior of as-cast and as-forged GH4738 alloy

Su Xing, Lü Xudong

Heat Treatment of Metals 2021, 46 (12): 46-52. doi:10.13251/j.issn.0254-6051.2021.12.008

Abstract （51）

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By using MTS thermal simulator, compression tests were carried out on the as-cast and as-forged GH4738 alloy under the conditions of deformation temperature of 1000-1150 ℃ and strain rate of 0.01-1 s^-1, in which the reduction is 10%, 30% and 50%, respectively. The results show that the stress-strain curves of the alloy in two states both have typical characteristics of dynamic recrystallization, and there are three stages: work hardening, flow softening and steady-state flow. According to the stress-strain curves, the thermal deformation activation energies of as-cast and as-forged GH4738 alloy are Q=575.89 kJ/mol and Q=588.04 kJ/mol, respectively. The EBSD analysis shows that the dynamic recrystallization of as-forged GH4738 alloy occurs earlier and more significantly than that of as-cast alloy under the same thermal deformation parameters.

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