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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）

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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.

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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）

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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.

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Effect of heat treatment process and copper content on texture of high-silicon non-oriented silicon steel

Xue Rundong, Fang Xizhen

Heat Treatment of Metals 2024, 49 (4): 78-82. doi:10.13251/j.issn.0254-6051.2024.04.013

Abstract （139）

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Effect of copper content on the texture of two high-silicon non-oriented silicon steels without Cu and with trace Cu was analyzed by EBSD technology, and the microscopic mechanism was also investigated. The results indicate that after high temperature annealing at 1000 ℃, the addition of trace Cu element has an obvious harmful effect on the texture of finished silicon steel product. The high temperature annealing process plays a more full role in optimizing the texture by the shear bands, while such optimizing effect is inhibited obviously by adding of trace Cu to the non-oriented silicon steel, which is attributed to the dispersive distribution of the copper precipitates in the steel matrix.

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Microstructure and mechanical properties of ultrafine grained heterostructured dual-phase steel prepared by warm rolling and intercritical annealing

Yan Wenchao, Gao Bo, Xiao Lirong, Zhou Hao

Heat Treatment of Metals 2024, 49 (7): 54-62. doi:10.13251/j.issn.0254-6051.2024.07.009

Abstract （136）

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Comprehensive mechanical properties of the low-carbon steel were greatly improved by producing the ultra-fine grained heterostructured dual-phase (UFG-HSDP) structure. First, the initial structure of the low carbon dual-phase structure is refined by warm rolling at 300 ℃, and then the ultra-fine grained heterostructured dual-phase steel with high martensite content (volume fraction of77%) is obtained by intercritical annealing at 740 ℃. The average grain size of ferrite and martensite is 0.78 and 0.39 μm, respectively. The UFG-HSDP steel shows excellent comprehensive mechanical properties, with yield and tensile strengths of 1.26 and 1.75 GPa, respectively, while maintaining a uniform elongation of 6.2%. The mechanical incompatibility between ferrite and martensite in the UFG-HSDP steel during tensile deformation results in significant hetero-deformation induced hardening, which enhances the total strain hardening rate and thus improves the strength-ductility match of low-carbon steel.

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Variant selection of α phase in β-type Ti-15Mo alloy

Ren Cheng, Min Xiaohua, Fei Qi

Heat Treatment of Metals 2024, 49 (9): 1-10. doi:10.13251/j.issn.0254-6051.2024.09.001

Abstract （128）

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SEM and EBSD were used to investigate the variant selection behaviour of the α phase in the β matrix and at the β grain boundaries in the Ti-15Mo alloy after solution treatment and aging. The results show that the solution treated specimen consists of single β grains without any preferred orientation. In the solution treated and aged specimen, the intragranular α phase does not undergo variant selection, instead, self-accommodation occurs among α variants, leading to a cross distribution of α phase variants at 60°. The variant selection of the film-like grain boundary α phase is influenced by the misorientation of adjacent β grains. A minor misorientation causes α phase to retain a Burgers orientation relationship with β grains on either side, whereas a major misorientation affects the precipitation of the α phase due to the interface orientation. The variant selection of the grain boundary Widmanstätten microstructure relies on the nucleation site. When the nucleation takes place at the film-like grain boundary α phase, it selects the same variants as the film-like grain boundary α phase. Nonetheless, when the nucleation occurs at the interface between the film-like grain boundary α phase and the β matrix, it is influenced by both.

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Microstructure and texture evolution of cold-rolled deformed Fe-1.5%Si non-oriented silicon steel

Yang Jie, Hou Diwen, Wang Jiale, Fang Feng, Zhang Yuanxiang, Wang Yang, Zhang Xiaoming

Heat Treatment of Metals 2023, 48 (12): 166-174. doi:10.13251/j.issn.0254-6051.2023.12.028

Abstract （127）

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The influence of cold rolling reduction rate on microstructure and texture of Fe-1.5%Si non-oriented silicon steel at each process stage was analyzed. The results show that the initial structure of the hot-rolled plate is fine equiaxed crystal. The average grain size is 18 μm in the surface layer and 36 μm in the middle layer. After cold rolling at reduction rates of 25%-64%, the plate forms strong α and λ texture and weak α^* texture. After cold rolling at reduction rates of 64%-73%, the plate forms strong γ and sub-strong α texture. The cold-rolled Cube texture mainly rotates along four paths: ① rotating along the λ texture to {100}<021> and then along the α^* texture line; ② rotating along the λ texture to {100}<011> then along the α texture line; ③ rotating along {013}<031>, {110}<110> and nearby orientations; ④ rotating along the η texture line. In the early stage of annealing, Cube and Goss-oriented grains are preferentially nucleated, but with the extension of annealing time, their proportions are always small, the Cube recrystallization ratio is 0.55%-1.94%, and the Goss recrystallization ratio is 0.54%-2.85%, and the proportion of γ-oriented grains increases rapidly. After annealing, complete recrystallization occurs, and the recrystallization texture is mainly composed of strong γ texture, α texture and weak η texture. Unfavorable textures account for the main component.

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Effect of long-term aging on microstructure and properties of GH4169 alloy

Tao Tiancheng, Zang Kai, Zhu Zhiyuan

Heat Treatment of Metals 2024, 49 (4): 83-88. doi:10.13251/j.issn.0254-6051.2024.04.014

Abstract （120）

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After standard heat treatment of 960 ℃×1 h+720 ℃×8 h+620 ℃×8 h, GH4169 alloy was subjected to long-term aging at 650 ℃ for 100-4000 h. The microstructure evolution law mechanical properties and their relationship of the alloy during long-term aging was explored. The results show that after aging at 650 ℃ for 100-800 h, a large number of γ″ and γ′ phases precipitate in the grain, δ phase precipitates at the grain boundary, and the hardness of the alloy increases. After aging for 1600-2400 h, γ″ and γ′ phases grow up gradually, δ phase coarsens gradually and γ″ poor zone appears around the δ phase, and the alloy hardness increases slowly. After aging for 3200-4000 h, γ″ and γ′ phases coarsen obviously and a large number of γ″ phases change into δ phase, and the hardness of the alloy decreases. Meanwhile, the tensile strength and yield strength of the alloy after long-term aging are consistent with the change of hardness, and the plasticity shows a decreasing trend.

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Comparative study of high temperature chloride corrosion resistance and mechanism of Inconel625 and Inconel601 alloys

Wu Yong, Meng Shixu, Sun Qingyun, Chen Hui, Xia Siyao, Yang Fu, Xia Chunhuai, Yang Hanzhe

Heat Treatment of Metals 2023, 48 (9): 208-213. doi:10.13251/j.issn.0254-6051.2023.09.035

Abstract （113）

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High temperature chloride ion corrosion resistance and corrosion mechanism of Inconel625 and Inconel601 alloys were studied by means of SEM, EDS and XRD. The corrosion kinetics curves, corrosion products and surface and cross section morphology of the corrosion layer of the two alloys were compared and analyzed under the condition of chloride ion corrosion at 1100 ℃. The results show that both Inconel625 and Inconel601 alloys exhibit rapid corrosion in the early stage and gentle corrosion in the later stage. The high temperature chloride corrosion resistance of the Inconel625 alloy is better than that of the Inconel601 alloy. In the corrosion process of the Inconel625 alloy, an oxide film containing complex oxides is formed. The main corrosion products of the Inconel601 alloy are Cr₂O₃, AlFeO₃ and Al₁₈Cr₅ phases, while the main corrosion products of the Inconel625 alloy are Al₂O₃, Fe₂O₃, Cr₅O₁₂ and NiCrO₄ phases. The Inconel625 alloy has better corrosion resistance than the Inconel601 due to the pinning effect of Nb element and the formation of NiCrO₄ with spinel structure, which increases the adhesion of oxide film.

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Texture evolution in subsequent process flow of low-temperature and high magnetic induction oriented silicon steel slab

Sun Wenke, Wu Zhongwang, Ren Huiping, Zhang Huimin, Guo Huan, Zhao Xiaolong, Luo Xiaoyang, Di Yanjun

Heat Treatment of Metals 2024, 49 (2): 40-44. doi:10.13251/j.issn.0254-6051.2024.02.006

Abstract （111）

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Taking a high magnetic oriented silicon steel slab prepared under low temperature heating process as starting material, the main composition of texture and the Goss texture distribution in hot-rolling, normalizing, cold rolling and primary recrystallization stages were analyzed by using EBSD technology. The results show that the surface layer of hot-rolled sheet is the origin of Goss texture, and in the transition zone, the {100}, {110} and {111} plane textures have a certain proportion, and the {100}<110> cubic texture accounts for the largest proportion of central deformation zone. There are more{110}<112> brass texture and{110}<001> Goss texture on the surface of the normalized sheet, and there are more {114}＜418> oriented textures in the transition zone and the central deformation zone, and {112}<110> α linear texture accounts for the largest proportion in the central deformation zone. The cold rolled texture is dominant by {112}<110> α texture, though there are many {100}<110> textures. After decarburization annealing and nitriding, the primary recrystallization texture is dominant by both of the{114}<418> oriented texture and {111}<112> γ linear texture.

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Heat treatment process and mechanical properties of low alloy wear-resistant steel

Zhang Zhichun, Wen Jia, Chen Guorui, Wu Guanghui, Weng Zeju, Gu Kaixuan

Heat Treatment of Metals 2023, 48 (9): 220-224. doi:10.13251/j.issn.0254-6051.2023.09.037

Abstract （99）

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CCT curves of a low alloy wear-resistant steel were measured by using a DIL805 quenching dilatometer to study its phase transformation law during continuous cooling. The microstructure of the specimens at different cooling rates was observed by using OM. In addition, the low alloy wear-resistant steel was heat treated by using quenching+tempering process, quenching+cryogenic treatment+tempering process, and the specimens were analyzed by using SEM characterization, tensile and impact tests to study the effect of cryogenic treatment on the microstructure and properties of the tested steel. The results show that the critical cooling rate of martensite transformation of the tested steel is 5 ℃/s. The tensile strength and yield strength of the low alloy wear-resistant steel are increased by 136.5 MPa and 141.5 MPa, respectively, with the addition of cryogenic treatment. The impact property is decreased slightly while the plasticity remains unchanged after cryogenic treatment. The main mechanism of improvement of the strength and plasticity of low alloy wear-resistant steel caused by cryogenic treatment is to promote the refinement of martensitic lath.

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Isothermal phase transformation behavior and cooperative regulation of microstructure and properties and flat coil of hot rolling 65Mn steel strip

Tian Yaqiang, Yao Zhiqiang, Nian Baoguo, Zhang Junfen, Zhang Xiaolei, Song Jinying, Zhang Mingshan, Chen Liansheng

Heat Treatment of Metals 2024, 49 (9): 24-30. doi:10.13251/j.issn.0254-6051.2024.09.004

Abstract （94）

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Isothermal transformation curve (TTT curve) of 65Mn steel was obtained by quenching phase change machine. Based on this curve, the evolution of microstructure and mechanical properties at different coiling temperatures was studied, and the possible causes and control methods of flat coil were discussed. The results show that the typical microstructure of the 65Mn steel, namely proeutectoid ferrite and pearlite, is obtained between 600-750 ℃. The TTT curve presents a typical "C" shape, with a "nose tip" temperature of 550 ℃. The incubation period is relatively short at this temperature, only 0.25 s. Within the typical microstructure formation temperature range of the 65Mn steel, the incubation period gradually increases with the increase of temperature, and the content of proeutectoid proeutectoid ferrite increases, while the content of pearlite decreases. According to the actual production, the selected coiling temperature of the 65Mn steel is between 650-750 ℃, and the microstructure is proeutectoid ferrite and pearlite. With the coiling temperature decreases from 750 ℃ to 650 ℃, the proeutectoid ferrite content decreases from 19.4% to 4.1%, and the distribution gradually transitions from block distribution to network distribution. The pearlite lamellar spacing decreases from 277.0 nm to 178.0 nm, resulting in an increase in the yield strength of the 65Mn steel from 534 MPa to 637 MPa, an increase in ultimate tensile strength from 776 MPa to 899 MPa, an increase in hardness from 18.8 HRC to 24.3 HRC, and a decrease in percentage total extension at fracture from 28.9% to 19.4%. In actual production, the coiling temperature and the holding time before coil discharging are adjusted based on TTT curve and the evolution of microstructure and mechanical properties under different coiling temperatures can achieve synergistic regulation of microstructure, mechanical properties and flat coil defects.

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Microstructure evolution and mechanical properties of laser additive manufactured 316L stainless steel after annealing process

Zheng Lei, Xu Da, Lu Yujie, Liao Wenchao, Yin Anmin, Chen Hou

Heat Treatment of Metals 2024, 49 (4): 66-77. doi:10.13251/j.issn.0254-6051.2024.04.012

Abstract （93）

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The microstructure evolution and mechanical properties of laser additive manufactured 316L stainless steel after annealing process were studied by means of scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and tensile testing machine. The results show that after annealing at 700 ℃, the morphology of the fish-scale molten pool begins to gradually transform into an irregular strip shape as the temperature increases. After annealing at 750 ℃, the cellular and long columnar substructures in the molten pool transform into spherical substructure and triangular point-like pit-shaped microstructure. As the annealing temperature increases, the grain size first decreases and then increases, the dislocation density is reordered, the cellular substructure is dissolved, and the evolution of the substructure and large and small angle grain boundaries reflects the decrease in dislocation density, leading to decrease in strength and enhancement in plasticity. When the annealing at 600 ℃ for 120 min, the yield strength is 484.2 MPa, the tensile strength is 665.6 MPa, and the elongation is 47.7%. When annealing at 850 ℃ for 120 min, the yield strength is 410.4 MPa, the tensile strength is 639.1 MPa, and the elongation is 59.7%. As the holding time increases, the deformation zone transforms into substructure; when the holding time is increased from 30 min to 120 min at temperature of 650 ℃, the substructure increases from 24.1% to 82.3%; when the holding time is increased from 30 min to 120 min at temperature of 850 ℃, the substructure is increased from 24.9% to 59.2%.

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Microstructure and fatigue properties of SCM435 steel for engines

Jiang Chang, Lu Hengchang, Wei Xicheng, Dong Han

Heat Treatment of Metals 2024, 49 (3): 159-163. doi:10.13251/j.issn.0254-6051.2024.03.027

Abstract （93）

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Microstructure and mechanical properties of SCM435 steel quenched at 870 ℃ and tempered at 350-650 ℃ were studied by means of SEM, TEM and tensile test. The results show that when tempering temperature is 350 ℃, the structure is martensite lath and a small amount of carbide. With the increase of tempering temperature, the lath morphology of martensite gradually disappears, and carbides precipitate and grow along the direction of lath. The microstructure tempered at 525 ℃ still has obvious martensite lath morphology and short rod cementite is dispersed. By controlling the mechanical properties of the SCM435 steel within the studied tempering temperature range, it can meet the mechanical performance requirements of 8.8-12.9 level fasteners. The fatigue properties of the steel quenched at 870 ℃ and tempered at 525 ℃ is experimentally verified, with a median fatigue limit of 425 MPa, indicating good fatigue properties.

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Creep property and microstructure evolution at 700 ℃ of a novel Fe-Ni based superalloy

Jiao Chunhui, Pan Yanjun, Li Shengzhi, Bai Du, Li Bei, Deng Ge, Jia Xiaoshuai

Heat Treatment of Metals 2025, 50 (2): 1-7. doi:10.13251/j.issn.0254-6051.2025.02.001

Abstract （91）

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A novel Fe-Ni-based superalloy, intended for ultra-supercritical thermal power generating units, was evaluated under constant load conditions at 700 ℃ with varying stress levels of 250 MPa and 200 MPa. The service limit and creep life of the alloy were predicted, and the microstructure evolution during creep was analyzed. The results indicate that the creep life of the alloy at 700 ℃/250 MPa and 700 ℃/200 MPa is 2378 h and 12 716 h, respectively. Based on the Larson-Miller equation, the alloy can withstand stresses of approximately 152 MPa after 100 000 h and 134 MPa after 260 000 h at 700 ℃, fully meeting the service requirements (stress of 35 MPa, creep life of 100 000 h). Microstructure analysis reveals that high-density dislocations are distributed in the 700 ℃/250 MPa specimen, whereas fewer dislocations are observed in the 700 ℃/200 MPa specimen. The MC carbides with larger size within the grains predominantly exhibit blocky or rod-like morphologies, with faster growth rates under higher stress conditions. The smaller M₂₃C₆ carbides at grain boundaries precipitate primarily in chain form, and their width increases with prolonged creep exposure. The γ′ phase within the grains remains spherical but undergoes coarsening during creep. Notably, some grain boundary γ′ phases exhibit abnormal growth, forming PFZs/DCZs, which adversely affect the alloy's high-temperature creep performance.

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Precipitation behavior and mechanical properties of Inconel 718 alloy prepared by selective laser melting

Wang Yingzhi, Zheng Liuwei, Yang Fei, Nie Yujin, Meng Lixin, Yin Lei, Liang Wei

Heat Treatment of Metals 2024, 49 (3): 141-146. doi:10.13251/j.issn.0254-6051.2024.03.024

Abstract （89）

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Inconel 718 alloy was prepared by selective laser melting (SLM), and the as-deposited alloy was double aged (DA) and solution+double aged (SA). The precipitation behavior and tensile properties of the alloy under different heat treatment states were studied by means of scanning electron microscope, electron backscattered diffraction, transmission electron microscopy, and universal testing machine. The results show that aging alone cannot eliminate the Laves phase. After direct aging, the Laves phase still exists in the alloy, but the content of γ' and γ″ strengthened phase is higher than that of the deposited state. The strength of the material significantly increases, and the plasticity significantly decreases. After high-temperature solid solution treatment at 1150 ℃ followed by double aging, the alloy is completely recrystallized, and the substructure disappears. The brittle Laves phase dissolves completely, and the content of the strengthened phases γ' and γ″ phases increases significantly. The strength increases and plasticity decreases compared to the as-deposited specimen. The tensile strength, yield strength and elongation of the alloy reaches 1330 MPa, 1110 MPa and 16.73%, respectively. The solution+double aging process, while enhancing the material's strength, ensures plasticity, which makes the Inconel 718 alloy to have excellent comprehensive mechanical properties.

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Hydrogen trap and hydrogen embrittlement sensitivity of EH36 steel

Chen Cui, Lin Wenyang, Li Weijuan, Zhang Dazheng, Li Zhennan

Heat Treatment of Metals 2024, 49 (3): 147-152. doi:10.13251/j.issn.0254-6051.2024.03.025

Abstract （89）

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Hydrogen traps, hydrogen diffusion coefficient and hydrogen embrittlement sensitivity at the surface, quarter and half thickness of EH36 steel were investigated by means of hydrogen penetration test and slow tensile test. The results show that the microstructure of the surface and the quarter thickness is mainly bainite, the microstructure of the surface is relatively fine, and the half thickness is mainly ferrite and pearlite. The density of reversible and irreversible hydrogen traps decreases sequentially from the surface to the half thickness, and the hydrogen diffusion coefficient increases accordingly. As the hydrogen charging current density or time increases, the yield strength, tensile strength, and elongation of tensile specimens at various thicknesses decrease to varying degrees, and the hydrogen embrittlement sensitivity increases accordingly. The tensile fracture morphology gradually transitions from ductile dimples with ductile fracture characteristics to river like patterns with brittle fracture characteristics. The hydrogen embrittlement sensitivity is the smallest at the surface, and the hydrogen embrittlement sensitivity is the highest at the half thickness. Some hydrogen induced cracks are observed on the tensile fracture surface at the half thickness.

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Effect of quenching process on microstructure and mechanical properties of DH350 die steel

Du Zhaoyang, Zhao Jie, Chen Xiangang, Cao Tieshan

Heat Treatment of Metals 2024, 49 (2): 16-24. doi:10.13251/j.issn.0254-6051.2024.02.003

Abstract （86）

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Effects of different heat treatment processes on the microstructure and mechanical properties of DH350 steel were studied by means of optical microscope, scanning electron microscope, impact testing machine and hardness tester. The heat treatment processes included: oil quenching at 1030 ℃+tempering at 590 ℃+tempering at 600 ℃ (process I), air quenching at 1030 ℃+tempering at 590 ℃+tempering at 600 ℃ (process II), and oil quenching at 1030 ℃+oil quenching at 980 ℃+tempering at 590 ℃+tempering at 600 ℃ (process III). The results show that the microstructure of the tested steel is mainly tempered martensite+tempered sorbite+carbide under three heat treatment processes. The difference lies in the pronounced lath structure of the microstructure under process I, with fine carbides dispersed throughout. At this time, the hardness and impact property are high, and the fluctuation of impact absorbed energy is small, and the comprehensive property is good. Under process II, there is a pronounced coarsening of the lath structure in the microstructure, and carbides gather along the grain boundaries, resulting in reduced hardness and deteriorated impact property. Under process III, there is a significant refinement of the grain in the microstructure. However, there is a higher amount of undissolved carbides present, and mixed crystal phenomena occur. As a result, the impact absorbed energy is relatively high but exhibits greater fluctuation. Additionally, there is a noticeable decrease in hardness. Therefore, the optimal heat treatment process for the DH350 die steel is oil quenching at 1030 ℃, followed by tempering at 590 ℃, and tempering at 600 ℃. Under these conditions, the hardness and impact absorbed energy are measured to be 45.1 HRC and 22.4 J, respectively.

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Microstructure and properties of high hardenability high-carbon chromium bearing steel

Wang Bingnan, Jia Yuxin, Wang Shanshan, Zhang Yahui

Heat Treatment of Metals 2024, 49 (9): 31-35. doi:10.13251/j.issn.0254-6051.2024.09.005

Abstract （86）

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Martempering and austempering treatments were conducted on three types of high-hardenability high-carbon chromium bearing steels, namely GCr18MnMo steel, GCr18MnMo1 steel and GCr19SiMnMo1 steel. The differences in their microstructure, maximum hardenability size, retained austenite and impact properties were compared. The results show that the hardenability is ranked from high to low as GCr19SiMnMo1 steel > GCr18MnMo1 steel > GCr18MnMo steel. If the hardenability standard is that the core hardness is greater than or equal to 55 HRC, the maximum hardenability size of GCr18MnMo steel is approximately 70 mm, the maximum hardenability size of GCr18MnMo1 steel is approximately 100 mm, and the maximum hardenability size of GCr19SiMnMo1 steel is approximately 130 mm. When these three tested steels undergo austempering, the retained austenite content can be guaranteed to be less than 1%. During martempering, the retained austenite content of GCr18MnMo and GCr18MnMo1 steels is less than 15%, and for GCr19SiMnMo1 steel, the retained austenite content can be reduced to less than 1% by additional tempering while ensuring high hardness. The impact properties of these three specimen steels are very close, and the impact property after austempering is approximately 70% higher than that after martempering. Only GCr19SiMnMo1 steel can be used for parts with wall thickness or diameter more than ϕ100 mm to ensure that the core troostite meets the requirements.

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Effect of banded structure on mechanical properties of cold-rolled dual phase steel DP780

Xue Renjie, Dong Yikang, Ma Ziyang, Cao Xiao'en, Li Zhi'ang

Heat Treatment of Metals 2024, 49 (12): 191-197. doi:10.13251/j.issn.0254-6051.2024.12.032

Abstract （81）

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In order to study the segregation behavior of elements in the banded structure of cold-rolled duplex steel DP780 and its effect on mechanical properties, OM, SEM, EMPA, EBSD and other methods were used to characterize and analyze the morphology and element distribution characteristics of the banded structure, tensile properties and microstructure change during the tensile process, fracture mechanism, and so on. The research results show that the macroscopic segregation formed by redistribution of C, Mn, Al and Si solute elements during the solidification process leads to the formation of banded structure, which is mostly distributed parallel to the rolling direction at 1/2 and 1/4 of the plate thickness, the grain size distribution is obviously nonuniform, and the small angle grain boundary density of the banded structure is significantly higher than that of the equiaxed structure. Meanwhile, the properties and microstructure change in tensile process indicate that after 10% tensile pre-deformation, the fibrosis is more obvious in the banded structure specimen, increasing the resistance of dislocation movement during the deformation process and improving the strength. The banded structure can also cause dislocation pile-up and lattice distortion, deteriorating the ability to deform. The banded structure reduces the coordinated deformation ability of the matrix structure, resulting in prominent anisotropy. Further, the observation of fracture morphology shows that the initial crack initiation occurs at the M/F phase interface, and a tear ridge is formed at the M/F interface during fracture, while the location and size of the tear ridge are consistent with that of the banded structure. There is a martensite band region with poor plastic deformation ability between the tear ridges, and the ferrite side of the M/F interface has significant plastic deformation; the specimen with equiaxed structure exhibits uniform axial deformation and better fracture plasticity.

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Evolution of microstructure and macrotexture of 3.1%Si oriented silicon steel

Liu Yongzhen, Dong Lili, Liu Baozhi, Zhang Hao, Ma Yonglin

Heat Treatment of Metals 2023, 48 (9): 238-241. doi:10.13251/j.issn.0254-6051.2023.09.040

Abstract （80）

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Microstructure and macroscopic textures of 3.1%Si oriented silicon steel during first cold rolling, decarburizing annealing, second cold rolling, high temperature annealing and tensile leveling annealing were analyzed by means of Zeiss microscope, X-ray diffractometer and other testing instruments. The results show that microstructure of the oriented silicon steel is ferrite. The average grain size is 10.23 μm after first recrystallization during decarburizing annealing, and reaches 2.0 cm after second recrystallization during high temperature annealing, and grows to 2.3 cm with increasing of uniformity after tensile leveling annealing. The main texture type of the oriented silicon steel after decarburization annealing is γ fiber texture, with a small amount of Goss texture {110}<001>. After high temperature annealing, the texture type is mainly Goss texture {110}<001>. After tensile leveling annealing, the Goss texture reaches the strongest and sharpest degree.

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