Heat Treatment of Metals

Hot deformation behavior and microstructure evolution of a novel Co-Ni-based superalloy

Fu Zhiqiang, He Guoai, Wu Yunjie, He Cunxiao

2024, 49(2): 1-7. doi:10.13251/j.issn.0254-6051.2024.02.001

Abstract ( 128 )

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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.

Evolution of copper-rich phases and antibacterial properties of 304Cu and 430Cu antimicrobial stainless steels

Mo Jinqiang, Feng Guanghong, Xu Mei, Zhang Wei, Deng Shuaishuai

2024, 49(2): 8-15. doi:10.13251/j.issn.0254-6051.2024.02.002

Abstract ( 46 )

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304Cu and 430Cu antibacterial stainless steels were prepared by adding appropriate amount of Cu. By means of XRD, OM and TEM, the effect of different annealing temperatures on microstructure and antibacterial properties of the two steels was investigated, and the evolution of Cu-rich phases was analyzed. The results show that the microstructure of the 430Cu stainless steel is mostly composed of polygonal ferrite, with a small amount abnormally grown grains distributed locally, while the microstructure of the 304Cu stainless steel is composed of irregular austenite. The copper-rich phases in the 304Cu antibacterial stainless steel is round in shape, the number of which increases and the size grows with the increase of annealing temperature, though the growth rate becomes slower when the annealing temperature exceeds 850 ℃. While in the 430Cu antibacterial stainless steel, the size of copper-rich phases grows with the annealing temperature rising, and the shape of copper-rich phase changes from spherical or ellipsoid to rod when the annealing temperature reaches 900 ℃. After annealing at 850 ℃, both the 304Cu and 430Cu stainless steels exhibit excellent antibacterial properties, which can delay the spoilage process of soybean products and rice in contact with it, and it can also form a bacteriostatic environment around itself.

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

Du Zhaoyang, Zhao Jie, Chen Xiangang, Cao Tieshan

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

Abstract ( 58 )

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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.

Uniaxial tensile and low cycle fatigue properties of high strength and toughness bridge steel Q690q

Peng Ningqi, Zhou Wenhao, Jin Donghao, Wu Huibin

2024, 49(2): 25-31. doi:10.13251/j.issn.0254-6051.2024.02.004

Abstract ( 34 )

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For the Q690q bridge steel plates produced by two processes of thermo-mechanical control process+tempering (TMCP+T) and quenching and tempering (QT), the uniaxial tensile and low cycle fatigue (LCF) tests were conducted on the surface and core of the plates. The microstructure and the prior austenite grain sizes (PAGS) of the surface and core were observed and measured by means of optical microscope (OM) and scanning electron microscope (SEM), and their influences on the tensile properties and LCF properties were analyzed. The results show that the microstructure of the TMCP+T-processed steel mainly consists of lath bainite (LB), granular bainite (GB), and a small amount of martensite-austenite islands (M/A). The LB is the majority on the surface and is finer than that of the core, and the surface PAGS is also more uniform. Compared with that of the core, the yield strength, tensile strength, yield ratio, and elongation of the surface are all increased, and the LCF life is significantly improved. The microstructure of the QT-processed steel is mainly tempered sorbite (TS) and GB. The proportion of GB in the core is increased, but it is finer than that of the surface, and the PAGS is also finer and more uniform. Compared with that of the surface, the yield strength, tensile strength, elongation, and yield ratio of the core are all decreased, but the LCF life is increased. Comparison between the two processes, whether being the surface or the core, the TMCP+T-processed steel has lower yield strength, higher tensile strength, lower yield ratio, and lower elongation. However, the LCF life change ranges of the tested steel obtained by the two processes are very similar, implying that on which the process difference has a little effect. In addition, the correlation between the tensile properties and the LCF test data shows that the fatigue strength coefficient is linearly correlated to the tensile strength, and the fatigue ductility coefficient is linearly correlated to the elongation.

Microstructure and properties of ultra-high strength martensitic steel prepared by ultra-fast cooling process

Liu Ziquan, Li Kejian, Zhang Longzhu, Li Shouhua, Feng Yi, Cao Pengjun

2024, 49(2): 32-39. doi:10.13251/j.issn.0254-6051.2024.02.005

Abstract ( 30 )

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Ultra-high strength martensitic steel with different Mn additions (1.01%, 1.41% and 1.74%, mass fraction) was prepared by ultra-fast cooling process, and the differences of microstructure, such as the prior austenite grain size, high-angle grain boundary ratio, thickness of martensite lath and nanoprecipitates were compared by XRD, SEM, EBSD and TEM. The hydrogen embrittlement property of the steel was analysed by TDA. The first-principles were used to study the hydrogen trap at the interface of the Cu precipitates and steel matrix. The results show that with the increase of Mn addition, the prior austenitic grain size of 1500 MPa grade martensitic steel is about 7 μm, but the martensitic lath in higher Mn specimen is thinner and denser. First-principles calculations show that harmless hydrogen traps can be formed at the interface between Cu and martensitic steel matrix, and a large number of various interfaces in the martensitic structure help to form more dispersed hydrogen traps in the steel, so that hydrogen is not easy to accumulate locally in the material, thereby reducing the risk of hydrogen embrittlement of the material. Based on the ultra-fast cooling process, the increase of Mn addition can achieve finer microstructure of 1500 MPa grade martensitic steel, and the Cu precipitation can also improve the hydrogen embrittlement resistance of the steel.

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

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

Abstract ( 67 )

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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.

Effect of Si addition on microstructure and properties of as-cast CoCrFeMnNi high entropy alloy

Li Rongbin, Zong Zaikang, Zhang Zhixi, Zhang Rulin

2024, 49(2): 45-52. doi:10.13251/j.issn.0254-6051.2024.02.007

Abstract ( 41 )

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CoCrFeMnNiSi_x(x=0,0.3, 0.6, 0.9) high entropy alloys were fabricated by cold crucible levitation melting. The changes of the microstructure of the alloy after the addition of silicon were analyzed by means of X-ray diffraction, scanning electron microscope and the attached energy spectrometer. A series of tests on the hardness, room temperature friction and wear and room temperature compression properties of CoCrFeMnNiSi_x alloy were carried out. The results show that CoCrFeMnNi alloy is a single-phase FCC structure. With the increase of silicon content, Mn, Ni and Si elements are enriched at the grain boundary of the FCC base phase, and silicide are gradually precipitated, finally resulting in fine grain strengthening and dispersion strengthening, which improves the hardness, wear resistance, compressive strength and yield strength of the alloy. Among them, CoCrFeMnNiSi_0.9 has the best comprehensive performance.

Effect of Si on microstructure and properties of Al-1.5Cu-0.7Mg alloy

Tan Xinyu, Liu Jingjing, Liu Dongyu

2024, 49(2): 53-59. doi:10.13251/j.issn.0254-6051.2024.02.008

Abstract ( 33 )

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Effect of 0.3wt%Si addition on the microstructure and mechanical properties of Al-1.5Cu-0.7Mg alloy was studied by means of mechanical test, resistivity test at 20 ℃ and microstructure observation. The results show that with the 0.3wt%Si addition, the as-aged strength of the tested alloy is obviously increased. After peak aging at 473-493 K, its 20 ℃ resistivity is 3.638-3.667 μΩ·cm, and its tensile strength is 370-380 MPa, and then the relationship between the 20 ℃ resistivity and the relative volume fraction of the second phase precipitated during aging is established according to Matthiessen rule. The second phase precipitation activation energies in aging of the Al-1.5Cu-0.7Mg and Al-1.5Cu-0.7Mg-0.3Si alloys obtained by using JMA (Johnson-Mehl-Avrami) equation are 135 kJ/mol and 204 kJ/mol respectively, according to which to know that the S″ phase is dominant in the Al-1.5Cu-0.7Mg alloy and the S phase is dominant in the Al-1.5Cu-0.7Mg-0.3Si alloy. The resistivity under other aging parameters is also predicted by JMA equation, and the accuracy of the prediction model is all over 99%.

Measurement and analysis of SH-CCT curves of Q690CFD HSLA hydropower steel

Cao Jiali, Jin Hongze, Li Kangli, Xu Yapeng, Zhao Qiang, Wang Cuiping, Li Mengnan

2024, 49(2): 60-65. doi:10.13251/j.issn.0254-6051.2024.02.009

Abstract ( 22 )

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SH-CCT curves of Q690CFD high strength steel for hydropower were established by using Gleeble-3800 thermal simulation test machine, and the effect of cooling rate on the microstructure and hardness of the coarse grain heat affected zone of the tested steel was studied. The results show that three transformation forms as martensite, martensite and bainite and bainite occur in the heat affected zone (HAZ) of the tested steel at the measured cooling rate. When the cooling rate is 40 ℃/s, the hardness of the HAZ reaches the maximum of 344 HV10, and the microstructure is composed of lath martensite and bainite ferrite. With the decrease of cooling rate, granular bainite begins to appear, and the hardness of the matrix decreases gradually. At the same time, the shape of M-A component in bainite changes from granular and short rod to lamella. When the cooling rate is lower than 5 ℃/s, the microstructure of the HAZ is all granular bainite, and the hardness of the matrix is lower than that of the base metal.

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

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

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

Abstract ( 51 )

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

Effect of La content on solidification process and as-cast microstructure of GH5188 alloy

Jiang Shichuan, Wang Xiaochuan, Tang Pingmei, Li Jing, Zhou Yang

2024, 49(2): 71-76. doi:10.13251/j.issn.0254-6051.2024.02.011

Abstract ( 30 )

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The solidification process of GH5188 alloy with different La contents (0.03%, 0.07%, 0.10% and 0.40%) at the cooling rate of 10 ℃/min was dynamic in-situ observed by using confocal laser scanning microscope (CLSM), and the effects of La content on the solidification process, as-cast microstructure and precipitated phases of the GH5188 alloy were studied. The results show that with the increase of La content, the initial solidification temperature and the solid-liquid two-phase region of the GH5188 alloy become higher and larger. The solidification process is slow-rapid-slow solidification, and the higher the La content, the smaller the peak solidification rate. With the increase of La content, the as-cast microstructure of the alloy changes from dendrite to equiaxed crystal, and the size of the precipitated phases increases. When the La content reaches 0.40%, the precipitated phases change from M₆C+M₂₃C₆ to (Ni,Co)_xLa+M₂₃C₆, and the formed La-containing intermetallic compound is easy to crack during solidification.

Influence of Q&P process on mechanical properties and microstructure of 38MnB5Nb ultra high strength steel

Yang Jie, Wang Decheng, Li Xianjun, Wu Xiaolin, Hou Junqing, Yang Tao, Zhang Sai

2024, 49(2): 77-83. doi:10.13251/j.issn.0254-6051.2024.02.012

Abstract ( 28 )

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In order to improve the product of strength and elongation of advanced high-strength steel and meet the requirements of automotive lightweight development, advanced high-strength 38MnB5Nb steel was taken as the research object, the changes in mechanical properties and microstructure under Q&P processes with different partitioning temperatures and partitioning time were discussed, and the optimal Q&P process parameter window for this steel grade was determined. The results show that between Ms and Mf, using both low-temperature long-term partitioning and high-temperature short-term partitioning processes, the 38MnB5Nb steel can achieve good strength and plasticity matching. Among them, under the conditions of 90 s at 220 ℃ and 60 s at 280 ℃, the product of strength and elongation of the specimens exceeds 30 GPa·%, which are 35.09 GPa·% and 33.23 GPa·%, respectively. In terms of microstructure, the lath martensite coarsens gradually with the increase of partitioning temperature at the same partitioning time, and the tempering phenomenon of martensite becomes more obvious with the increase of partitioning time at the same partitioning temperature, accompanied by carbide precipitation.

Grain coarsening behavior during pseudo carburizing process of low-carbon gear steel 20CrMnTi for automobile

Wu Wei, Yuan Qing, Mo Jiaxuan, Ren Jie, Zhang Zhicheng, Xu Guang

2024, 49(2): 84-90. doi:10.13251/j.issn.0254-6051.2024.02.013

Abstract ( 38 )

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A 20CrMnTi gear steel without Nb addition was designed, and the influence and mechanism of pseudo-carburizing temperature on its prior austenite grain size were studied through grain size measurement and precipitate distribution analysis. The results show that the maximum pseudo-carburizing temperature of the designed steel is 970 ℃. The C content in (Ti, Mo)(C, N) particles is reduced, while the N content is opposite after pseudo-carburizing treatment compared with the hot-rolled steel, which confirms the redissolution and ripening of the second phase (Ti, Mo)(C, N) particles, and being more obvious when the pseudo-carburizing temperature is higher (980 ℃). Moreover, the volume fraction of the fine dispersed second phase (Ti, Mo)(C, N) particles decreases sharply when the pseudo-carburizing temperature is 980 ℃, at which the large size second phase (Ti, Mo)(C, N) particles increases, thus weakening the pinning effect on prior austenite grains and resulting in the abnormal grain growth.

Effect of annealing process on microstructure and properties of Fe-30Mn-10Al-1C low density steel

Hu Qiwen, Li Tianyi, Geng Xiaoxiao, Cheng Zhuo, Liu Wenyue, Wu Guilin

2024, 49(2): 91-97. doi:10.13251/j.issn.0254-6051.2024.02.014

Abstract ( 35 )

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Effect of different annealing processes on microstructure and mechanical properties of the Fe-30Mn-10Al-1C low density steel was systematically studied, and the ductile-to-brittle transition mechanism of the material was analyzed. The results show that κ carbides and ferrite are precipitated in the tested steel annealed at 800 ℃, of which the tensile strength is higher than 1100 MPa, while the impact property at -40 ℃ is poor. κ carbides disappear after annealing at 850 ℃, the product of strength and elongation of the tested steel are increased, and the toughness is improved. Austenitic single-phase structure is obtained after annealing at 900 ℃, obtaining a good match of strength-plasticity and strength-toughness. The toughness of the Fe-30Mn-10Al-1C steel is related to the formation of κ carbide and ferrite in the austenite matrix as well as the grain size of austenite, and there is an inverse size relationship between the toughness and the grain size of austenite.

Effects of different heat treatment processes on microstructure and properties of 9Ni cryogenic vessel steel

Li Cheng, Peng Qichun, Tong Zhibo, Liang Liang, Qi Jianghua, Xiao Aida, Dong Changfu

2024, 49(2): 98-103. doi:10.13251/j.issn.0254-6051.2024.02.015

Abstract ( 64 )

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Effects of QT and QLT treatments on mechanical properties of the 9Ni steel were studied, and the toughening mechanism was discussed. The results show that QT and QLT treatments have a significant impact on the mechanical properties of 9Ni steel. Compared with QT treated specimen, the tensile strength and yield strength of the specimen treated by QLT are decreased, but the elongation is increased slightly, the low temperature impact property is increased significantly by nearly 40 J. QT treated specimen has typical ductile fracture characteristics. There is a coarse martensite structure near the impact fracture. The segregation zone is mainly lath martensite, and there is a trend of multilateralization between martensitic lath. There is a certain amount of bright areas in the structure, which are mainly reversed austenite formed during tempering, and can significantly improve the low temperature toughness of the 9Ni steel. However, the lath martensite of the QLT treated specimen is finer and more uniform, there are more bright areas between the martensitic lath, and the specimen after low-temperature impact test has more dimples with smaller size and uniform distribution. After low temperature impact test, the volume fraction of reversed austenite in QT and QLT treated specimens is 0.88% and 6.60%, respectively, therefore the low temperature toughness of the QLT treated specimen is better, while the reversed austenite absorbs the solid solution strengthening elements in the substrate, resulting in the reduction of yield strength.

Effect of plastic deformation on diffusion bonding of 2219 aluminum alloy

Chen Xi, Meng Linggang, Xu Dazhao, Zhou Bingwen, Ya Bin, Zhang Xingguo

2024, 49(2): 104-112. doi:10.13251/j.issn.0254-6051.2024.02.016

Abstract ( 74 )

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Effect mechanism of plastic deformation on interface bonding of 2219 aluminum alloy by applying plastic deformation during holding was studied by diffusion bonding method. The diffusion bonding test was carried out at the diffusion temperature of 545 ℃, the holding time of 4 h, the pressure of 10 MPa with the plastic deformation of 0%, 10%, 30% and 50%. The results show that with the increase of plastic deformation, the interface is in a high energy state. The Al₂Cu phase at the interface is precipitated by solute atom diffusion, which encapsulates the original interface oxide and undergoes metallurgical reaction with oxide during heat preservation and deformation. The oxide decomposes and diffuses to the matrix till it disappears, achieving interface healing. The bonding strength reaches up to 116 MPa with plastic deformation of 50%, which is 90.6% of the base material.

Effect of heat treatment on microstructure of hot-rolled 4343/3003/4343 aluminum composite plate

Zhang Wei, Chen Zijian, Lin Yongcheng

2024, 49(2): 113-119. doi:10.13251/j.issn.0254-6051.2024.02.017

Abstract ( 21 )

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4343/3003/4343 aluminum alloy composite plate is widely used in the heat transmission. It is commonly compounded by hot rolling, however, the microstructure uniformity of the alloy after hot rolling is disappointing, which is very unfavorable to the subsequent cold rolling. Therefore, it is necessary to establish a reasonable heat treatment process for the hot rolled composite plate. The effect of heat treatment process on the microstructure of the 4343/3003/4343 aluminum composite plates was studied by means of optical microscope and scanning electron microscope. The results show that the annealing temperature, annealing time, and cooling rate after hot rolling have significant effects on the microstructure of the composite plate. Increasing the annealing temperature, prolongating the annealing time, and slowing down the cooling rate after hot rolling are beneficial to the polymerization/coarsening of the precipitate in the composite plate, but longer annealing time will lead to the redissolution of precipitation, which is not conducive to subsequent cold rolling processing. According to the experiment and theoretical analysis, the optimal heat treatment process is obtained as follows: annealing at about 500 ℃ for about 4 h, and preferring water cooling after the hot rolling.

Effect of different cold rolling reduction on microstructure and properties of invar alloy

He Chengyu, Cai Chen, Gu Yu, Li Jingyuan

2024, 49(2): 120-127. doi:10.13251/j.issn.0254-6051.2024.02.018

Abstract ( 46 )

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Effect of different cold rolling reduction of 20% to 90% on the microstructure, mechanical properties, thermal expansion properties, saturation magnetization, and texture evolution of invar alloy were studied by means of backscattered electron diffraction (EBSD), XRD, tensile testing, hardness testing, thermal expansion testing, and magnetic property testing. The results show that as the cold rolling reduction increases, the equiaxed grains after solution treatment deform through dislocation sliding, and the alloy is gradually flattened and elongated to form a specific orientation, resulting in an increase in both the strength and hardness of the alloy, while the plasticity decreases rapidly. At 90% reduction, the tensile strength of the alloy is 777 MPa, while the elongation is only 5%. When the cold rolling reduction does not exceed 80%, the average linear expansion coefficient in the temperature range of 20 ℃ to 100 ℃ and saturation magnetization of the alloy show a trend of first decreasing and then increasing, and the alloy achieves a minimum value at 60% reduction. In the alloy, the strength of {110}<112>Brass texture, {112}<111}Copper texture, and {136}<634>S texture raises with the increasing of deformation degree. When the cold rolling reduction reaches 80%, strong textures are formed in the alloy.

Effect of deformation on microstructure and microhardness of EH47 crack arrest steel

Zhang Jiuxin, Ren Xiaojian, Jin Dongzheng, Tian Yong

2024, 49(2): 128-134. doi:10.13251/j.issn.0254-6051.2024.02.019

Abstract ( 26 )

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Effect of deformation in non-recrystallization region on microstructure evolution and microhardness of EH47 crack arrest steel was studied by single pass compression test using MMS-200 thermal simulator. The results show that when the deformation increases from 15% to 60%, the length-width ratio of the prior austenite grain increases from 1.2±1.4 to 2.7±2.3, the microstructure changes from coarsened bainite to refined ferrite and bainite, the proportion of high-angle grain boundaries(HAGB) increases from 34.6% to 61.7%, the effective grain size decreases from 4.5±5.9 μm to 3.4±4.2 μm, and the microhardness decreases from 230 HV50 to 211 HV50. The austenite grains of the specimen with 60% deformation have an effective interfacial area per unit volume of 106.7 mm^-1 before the phase transformation, which is the main reason for the refined and uniform microstructure. The ferrite grains nucleated, grown and then intercontacted at the prior austenite grain boundaries enhances the proportion (21.5%) of HAGB within the misorientation range of 20° to 47°, resulting in a crucial aspect for its possession of 61.7% HAGB. The main reasons for the decrease of microhardness are the high content of ferrite, the decrease of dislocation density and the increase of the proportion of recrystallized grains.

Effect of quenching and tempering process on microstructure and mechanical properties of a Cr-Ni-Mo-V ultra-high strength and toughness steel

Zhou Cong, Chen Xiangang, Cao Tieshan, Zhao Jie

2024, 49(2): 135-141. doi:10.13251/j.issn.0254-6051.2024.02.020

Abstract ( 28 )

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Effects of quenching at 780, 830, and 880 ℃ and high-temperature tempering at 500-580 ℃ on the microstructure and mechanical properties of a Cr-Ni-Mo-V ultra-high strength and toughness steel were studied by means of scanning electron microscope, metallographic microscope, impact testing machine, and Vickers hardness tester. The results show that with the increase of tempering temperature, the carbides with larger size undergo dissolution transformation, while the alloy carbides continuously precipitate out dispersively from the the matrix. Both the hardness and impact properties show a trend of first increasing and then decreasing with the increase of tempering temperature, which are related to the dispersion morphologies of the precipitated carbides and the decomposition of retained austenite. The tested steels quenched at three different temperatures all show secondary hardening peaks when tempering at 540 ℃, with the highest hardness values being 488, 517, and 532 HV20, respectively. The maximum impact absorbed energy is obtained when tempering at 540-560 ℃, with values of 49.7, 58.5, and 51.0 J, respectively. In order to fully ensure the strength and toughness of the steel, the optimal heat treatment process is subcritical quenching at 830 ℃ and then tempering at 560 ℃.

Influence of solution temperature and cooling method on microstructure and properties of 00Cr40Ni55Al3Ti alloy

Cui Yi, Cao Wenquan, Wang Yan, Cui Jihong, Ma Chao, Tian Zhongjie, Zhang Yunfei

2024, 49(2): 142-148. doi:10.13251/j.issn.0254-6051.2024.02.021

Abstract ( 31 )

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Hot rolled 00Cr40Ni55Al3Ti alloy was studied and 1150-1250 ℃ solution treatment+air cooling/water quenching process was conducted on the tested alloy in order to find out the influence of solution temperature and cooling method on microstructure and mechanical properties of the 00Cr40Ni55Al3Ti alloy. The results show that the size of grain and α-Cr phase increases with the increase of solution temperature in the range of 1150-1250 ℃, and the grain size grows rapidly when the solution temperature is over 1150 ℃. When the alloy is solution treated over 1200 ℃ followed by air cooling, α-Cr phase precipitates in a layered pattern at the grain boundary. The microhardness of the alloy decreases with the solution temperature increasing, and the impact absorbed energy peaks at 1200 ℃. When the water cooling is conducted, there is an inhibition in the precipitation of α-Cr phase and nano-sized γ′ particles, consequently, the hardness and impact absorbed energy decreases and increases, respectively, compared with air cooling. Tensile properties are strongly influenced by the cooling method, the tensile strength is relatively higher under air cooling. And there is a 26.5% decrease in the elongation when solution treated at 1250 ℃ followed by air cooling, due to the mixed grain and coarse layered microstructure at grain boundary.

Effect of double aging on mechanical properties of ZL205A alloy

Yang Jingping, Zhou Wenfeng, Wen Fulin, Liu Jianhui

2024, 49(2): 149-152. doi:10.13251/j.issn.0254-6051.2024.02.022

Abstract ( 33 )

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Double aging treatment was carried out for ZL205A alloy test piece, and the influence of double aging on the microstructure and mechanical properties was explored. The results show that the double aging can improve the microstructure and the comprehensive mechanical properties of the test piece, especially the elongation. After multi-stage solution heat treatment of 500 ℃×30 min+535 ℃×60 min+540 ℃×720 min and aging of 150 ℃×540 min+210 ℃×300 min, the ZL205A alloy exhibits the highest tensile strength of 428.5 MPa, the highest hardness of 126 HBW, and the highest elongation of 9.3%. This heat treatment process can stabilize the microstructure of castings for different batches, obtain good comprehensive mechanical properties.

Effect of artificial aging on micro-corrosion behavior of 7075 aluminum alloy

Tang Huizhen, Wang Shuai, Yan Lijuan, Zhang Yongchao, Shen Jun, Ge Binghui

2024, 49(2): 153-158. doi:10.13251/j.issn.0254-6051.2024.02.023

Abstract ( 51 )

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Effect of aging time on corrosion behavior of the 7075 aluminum alloy was investigated by means of corrosion electrochemical measurements, scanning electron microscope, transmission electron microscope and EDS elemental analysis. The results show that the specimen aged for 6 h at 120 ℃ has a higher self-corrosion potential and a lower corrosion driving force than the specimens aged for 2, 12 and 24 h, and the alloy aged for 6 h is less prone to corrosion. As the aging time increases, the overall corrosion profile of the alloy changes from intergranular corrosion to pit corrosion. Through the early corrosion morphologies of the substrate observed by using transmission electron microscope, the alloy aged for 6 h shows uniformly distributed shallow corrosion hollows on the surface, while the alloy aged for 24 h shows deep corrosion pits. The uniform distribution extent of solute elements in the substrate has a significant impact on the pitting behavior of the alloy.

Effect of heat treatment on microstructure and intergranular corrosion resistance of 7075 aluminum alloy

Gao Xuepeng, Sun Youzheng, Cao Shanpeng, Niu Boya, Li Binliang, Wang Ping

2024, 49(2): 159-165. doi:10.13251/j.issn.0254-6051.2024.02.024

Abstract ( 60 )

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Microstructure changes of Al-Zn-Mg-Cu 7075 aluminum alloy after single solution treatment, twice solution treatment and peak aging were investigated by means of optical microscope, X-ray diffractometer, scanning electron microscope and transmission electron microscope, and the effect of microstructure difference on intergranular corrosion sensitivity was analyzed. The results show that the composition uniformity of 7075 aluminum alloy increases and the intergranular corrosion sensitivity decreases significantly after twice solution treatment at 474 ℃ compared with single solution treatment. After peak aging, the grain boundary precipitates are chain-like, and precipitation-free precipitates appear on both sides, which hinders the formation of continuous corrosion channels. Cu enriched Mg(Zn,Cu)₂precipitates are formed at the grain boundary, and the corrosion potential difference with aluminum matrix is reduced, which improves resistance to intergranular corrosion of the material. The degree of supersaturated solid solution is increased in the twice solution treatment, which promoted the aging precipitation behavior. After the peak aging, the size and quantity of precipitated phase increase, and the spacing of the second phase at the grain boundary increases. The alloy shows better resistance to intergranular corrosion.

Solution and aging behavior of Al-9.2Zn-2.4Mg-1.5Cu aluminum alloy extrusion sheet in hydrothermal environment

Liu Yang, Qi Haiquan, Qin Xiangzhi, Han Xiangnan, Li Tianran

2024, 49(2): 166-171. doi:10.13251/j.issn.0254-6051.2024.02.025

Abstract ( 23 )

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The Al-9.2Zn-2.4Mg-1.5Cu aluminum alloy after extrusion was solution treated and aged, where the aging was completed in hydrothermal environment. The microstructure and mechanical properties of the alloy were studied by optical microscope, scanning electron microscope, microhardness tester and universal material tester. The results show that there is no recrystallization in the Al-9.2Zn-2.4Mg-1.5Cu aluminum alloy extrusion sheet after solution treatment, and the grains are still fibrous, though in which there are a lot of subgrain structures and the number of subgrains increases with the increase of solution treatment temperature. Secondly, due to the high content of Zn in the alloy, there are still more low-melting point T phase remaining after homogenization. After extrusion, the low-melting point T phase is distributed in chains along the extrusion direction, and part of the low-melting point T phase redissolves after solution treatment. When the solution treatment temperature is 475 ℃, the tensile strength of the alloy increases first and then decreases with the increase of aging time in hydrothermal environment, the hydrothermal aging time for the peak of the alloy is 10 h, the tensile strength is 733.53 MPa, the yield strength is 694.83 MPa, and the elongation is 13.00%.

Mechanical properties of quenched low alloy medium-carbon steel

Jin Dongliang, Wang Gaofeng, Ma Xiqiang, Yu Weitao, Di Zhengxian, Wei Shizhong

2024, 49(2): 172-178. doi:10.13251/j.issn.0254-6051.2024.02.026

Abstract ( 33 )

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A low-cost low alloy medium-carbon steel was produced, and its mechanical properties were investigated. The low-cycle fatigue behavior of the tested steel was investigated by controlling the total strain amplitude. The results show that the tested steel salt bath quenched at 302 ℃ for 2 h has a relatively high tensile strength of 957 MPa. As the salt bath quenching temperature increases to 312 ℃, the tensile strength decreases, but the U-notched impact property increases, with the salt bath temperature further increasing, the impact property is reduced. The increase of salt bath holding time results in the decrease of hardness of the tested steel. Under high strain amplitude (0.80%), the initial hardening rate of the steel salt bath quenched at 312 ℃ is lower, while the tested steel with higher strength martensite salt bath quenched at 302 ℃ has higher low-cycle fatigue strength and fatigue life.

Effect of post weld heat treatment on bending property of welded joints of TA15 titanium alloy plate

Zhu He, Liu Yanmei, Zhao Dong, Yang Lixin, Lu Yingfeng, Zhao Hongbo

2024, 49(2): 179-182. doi:10.13251/j.issn.0254-6051.2024.02.027

Abstract ( 28 )

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Effect of different annealing processes on the bending property of the welded joint of TA15 titanium alloy plate was studied. Through microstructure analysis, the microstructure transformation process of the welded joint with the change of heating temperature and holding time was explored. The effect of microstructure change on the bending property of welded joints through ultimate bending tests was verified, and ultimately the optimal annealing process was determined. The results indicate that the welded joint of the TA15 titanium alloy plate exhibits a typical columnar grain structure with needle-like α phases are distributed in different directions, and the welded joint has poor plasticity and poor bending property. Using general post weld stabilization annealing treatment (750 ℃×90 min and 750 ℃×120 min) can alleviate the welding stress, but with no significant improvement in microstructure and properties of the welded joint, which fails to effectively enhance the bending property. After annealing at 850 ℃ for 120 min with furnace cooling, the microstructure of welded joint is significantly improved, and at the same time, the bending property is improved.

Effect of heat treatment on microstructure and mechanical properties of Ti-6Al-4V titanium alloy formed by laser powder bed fusion

Cai Xiaoye, Cheng Zonghui, Dong Dingping, Bai Bin, Xie Suijie

2024, 49(2): 183-189. doi:10.13251/j.issn.0254-6051.2024.02.028

Abstract ( 29 )

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Ti-6Al-4V titanium alloy specimens formed by L-PBF (laser powder bed fusion) were heat treated at different temperatures, the microstructure and mechanical properties of which were observed and tested by means of optical microscope, scanning electron microscope, tensile testing machine and impact testing machine. The results show that at 600-800 ℃, with the increase of temperature, the fine acicular α′ martensite is decomposed into α+β phase, and the microstructure shows a similar hierarchical structure to the sedimentary specimens, interleaving each other and showing more orientations. When heat treated at 800 ℃, the specimens obtain excellent comprehensive mechanical properties, with the tensile strength up to 1019 MPa, elongation of 14.5% and impact absorbed energy up to 49 J, which can be used as the conventional heat treatment process for the Ti-6Al-4V titanium alloys formed by L-PBF. After heat treatment at the temperature above 1000 ℃, the primary β columnar grains gradually disappear, and the equiaxed β grains appear, and the parallel flaky α particles in the β grains form parallel α clusters. The strength and plasticity of the specimens treated over 1000 ℃ are poor, which should be avoided.

Effect of aging temperature on microstructure and mechanical properties of TB18 titanium alloy

Hu Shengshuang, Chen Suming, Yan Jiawei, Yue Shan, Gao Xiaoying, Ouyang Delai

2024, 49(2): 190-194. doi:10.13251/j.issn.0254-6051.2024.02.029

Abstract ( 38 )

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Effect of aging temperature on microstructure and mechanical properties of the TB18 titanium alloy was investigated by means of tensile testing machine, optical microscope and scanning electron microscope. The results indicate that with the aging temperature increasing, the tensile strength and yield strength decrease, while the elongation and the percentage reduction of area increase. Considering both the strength and plasticity, the best comprehensive mechanical properties of the alloy are achieved when aged at 530 ℃, where the tensile strength is 1285.5 MPa, the yield strength is 1206 MPa, the elongation is 7.8%, and the percentage reduction of area is 16%. The microstructure of forged TB18 titanium alloy is a typical equiaxed structure. After solution treatment at 870 ℃ for 2 h and then air cooling, the microstructure is consist of β grains with the size of 200-250 μm. After aging at different temperatures, the micro morphologies of the secondary α phases are similar, all with layered characteristics. With the increase of aging temperature, the size of secondary α phase lamella in the alloy showing an increasing tendency.

Effect of heat treatment temperature on microstructure and properties of TA15 titanium alloy pipe

Zhang Zhi, Luo Dengchao, Li Xusheng, Li Qian, Liang Jiawei, Su Songlin, Ren Weining, Wang Sha

2024, 49(2): 195-198. doi:10.13251/j.issn.0254-6051.2024.02.030

Abstract ( 26 )

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TA15 titanium alloy pipe specimens were heat treated in the temperature range of 750-1050 ℃ for 1 h, and then air cooled. The effect of different heat treatment temperatures on microstructure and mechanical properties of TA15 titanium alloy pipe was studied by means of optical microscope, electronic universal testing machine, and pendulum impact testing machine. When the heat treatment temperature rises from 750 ℃ to 850 ℃, α_p has no significant change, while the secondary α phase lamellae are coarsened. As the heat treatment temperature further increases to 950 ℃, the number of α_p decreases, the equiaxed degree increases, and secondary α phases completely transform to high temperature β phase, during further cooling, the β transformation phases re-precipitate. When the heat treatment temperature is further increased above 1000 ℃, the microstructure transforms into a typical Widmanstätten structure. Heat treatment below the phase transition point (<1000 ℃) results in a good match between strength and plasticity. As the heat treatment temperature increases, strength decreases and plasticity increases. The optimal match between strength and plasticity is reached when heat treated at 850 ℃. With the increase of heat treatment temperature, the impact property shows a trend of first increasing and then decreasing, among which the impact property is the best after heat treatment at 900 ℃.

Homogenization annealing process of Al-Si-Mg-B-Sr alloy

Li Dongyang, Li Yanxia

2024, 49(2): 199-202. doi:10.13251/j.issn.0254-6051.2024.02.031

Abstract ( 31 )

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As-cast Al-Si-Mg-B-Sr alloy was homogenization annealed under different temperatures and holding time. The effects of different homogenization annealing processes on microstructure, hardness and conductivity of the Al-Si-Mg-B-Sr alloy were studied by means of microstructure observation, hardness test and conductivity test. The results show that the microstructure of as-cast alloy has certain segregation phenomenon. After homogenization annealing at 550 ℃ for 9 h, the microstructure of the alloy is uniform and the segregation is basically eliminated. With the extension of homogenization annealing time, the hardness of the alloy increases first and then decreases, and the conductivity gradually increases. The hardness of the Al-Si-Mg-B-Sr alloy homogenization annealed at 550 ℃ for 9 h is the highest, which is 74.5 HV0.5. The conductivity of the alloy homogenization annealed at 550 ℃ for 15 h is the maximum, reaching 55.9%IACS.

Effect of pulsed magnetic field on microstructure and properties of TC18 titanium alloy during aging

He Xiaoyong, Xing Shuqing, Lang Ruiqing, Liu Yongzhen, Chen Zhongyi, Ma Yonglin

2024, 49(2): 203-207. doi:10.13251/j.issn.0254-6051.2024.02.032

Abstract ( 40 )

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A pulsed magnetic field was applied to TC18 titanium alloy during aging, and the effect of pulsed magnetic field on the precipitation behavior of the TC18 titanium alloy was investigated by observing and analyzing the nucleation and growth processes. The effect of pulsed magnetic field on the microstructure, strength and plasticity of the TC18 titanium alloy during the aging process was investigated by means of scanning electron microscope and tensile testing machine. The results show that the application of pulsed magnetic field can significantly increase the precipitation rate of the TC18 titanium alloy and thus shorten the aging time and improve the mechanical properties. Compared to 4 h of aging without pulsed magnetic field, 1 h of aging with pulsed magnetic field can increase elongation of the TC18 titanium alloy by 15%, and the tensile strength is also improved. The aging process of the TC18 titanium alloy is accelerated by the action of pulsed magnetic field, so that it enters the over-aging stage 3 h earlier. During the aging process of the TC18 titanium alloy, the pulsed magnetic field promotes the precipitation and growth of the secondary phases by increasing the diffusion coefficient of the atoms.

Effect of tempering time on microstructure and mechanical properties of Cr-Ni-Cu high strength steel for ships

Dong Xinxin, Wu Jing, Li Menghuan, Tian Yaqiang, Tang Qin

2024, 49(2): 208-214. doi:10.13251/j.issn.0254-6051.2024.02.033

Abstract ( 32 )

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The microstructure evolution and mechanical properties of Cr-Ni-Cu high strength steel for ships after quenching and tempering were studied by means of SEM, EDS, mechanical test and low temperature impact test. The results show that after directly quenching and quenching at 900 ℃ for 30 min, both the microstructure is composed of lath martensite and retained austenite, but the low-temperature impact absorbed energy of the latter is higher than that of the former at -20 ℃ (56 J and 64 J, respectively), which is mainly attributed to the larger lath spacing of martensite. When tempered at 500 ℃ for 30, 60, 120, 240 and 480 min, the yield strength, tensile strength and low-temperature impact absorbed energy of the alloy steel show a trend of increasing first and then decreasing. The maximum tensile strength is 1021 MPa, the maximum yield strength is 998 MPa, and the maximum low-temperature impact absorbed energy at -20 ℃ is 86 J.

Influence of cooling method on microstructure and mechanical properties of 45CrNiMoVA high-strength steel

Li Jiahui, Wang Fuxue, Fang Xiaoying, Wang Hongtao

2024, 49(2): 215-219. doi:10.13251/j.issn.0254-6051.2024.02.034

Abstract ( 30 )

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Microstructure and mechanical properties of the 45CrNiMoVA high-strength steel were studied using five cooling methods (furnace cooling, air cooling, forced air cooling, fog cooling, and water cooling) after full austenitization, as well as tempering treatment. The microstructure of high-strength steel was observed using optical microscope, and the tensile properties were measured using the MTS E45.105 universal testing machine. At the same time, the Vickers hardness was measured using HXD-1000TM digital Vickers hardness tester. The results indicate that under furnace cooling condition, the microstructure of the specimen is composed of pearlite and equiaxed ferrite. Under air cooling condition, the cooling rate increases, the microstructure of the specimen transforms into a mixed structure consisting mainly of bainite and martensite. As the cooling rate further increases, the content of bainite in the microstructure of the specimen decreases, while the content of martensite increases under forced air cooling and fog cooling conditions. Under water cooling, the microstructure of the specimen is completely martensite. The hardness and tensile strength of the specimen furnace cooled are the lowest, being 446.88 HV0.1 and 1430 MPa, respectively, while the microhardness and tensile strength of the specimen water cooled are the highest, being 815.66 HV0.1 and 2430 MPa, respectively. After tempering, the microhardness and tensile strength of the specimen decrease, but the percentage total extension at fracture increases, demonstrating excellent comprehensive mechanical properties.

Effect of heat treatment on microstructure and mechanical properties of high-pressure gas cylinder head

Wei Wei, Luo Xiong, Fan Junming, Chen Liubin, Wu Mingxia

2024, 49(2): 220-223. doi:10.13251/j.issn.0254-6051.2024.02.035

Abstract ( 30 )

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High pressure gas cylinder made of 34CrMo4 seamless steel tube prepared by flip plate spinning forming was treated by quenching+subcritical quenching+tempering, and then microstructure and mechanical properties of the cylinder head before and after heat treatment were studied by metallographic observation and tensile test. The results show that the grain size of the material is obviously refined by the heat treatment, and the coarse ferrite+sorbite structure in the cylinder head is transformed into fine tempered sorbite structure. After heat treatment, the tensile strength and yield strength of the cylinder head are improved, the yield ratio is reduced, and the plasticity of the cylinder is improved. It is proved that the heat treatment process of quenching+subcritical quenching+tempering is beneficial to optimize the microstructure and improve the mechanical properties of high-pressure gas cylinder made of 34CrMo4 steel.

Effect of heat treatment on residual resistivity ratio of metallic materials

Lan Xianhui, Liu Wei, Li Chao, Zhou Tao, Ma Peng, Ge Zhengfu

2024, 49(2): 224-226. doi:10.13251/j.issn.0254-6051.2024.02.036

Abstract ( 48 )

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The definition of residual resistivity ratio(RRR) was introduced and the significance of RRR for application of low-temperature superconducting metallic materials was analyzed. A heat treatment program for pure copper and high-purity aluminum was developed, and the residual resistivity ratio of the pure copper and high-purity aluminum was measured before and after heat treatment referring to GB/T 25897—2020/IEC 61788-4:2020 Residual resistivity ratio measurement—Residual resistivity ratio of Nb-Ti and Nb₃Sn composite superconductors. The test results show that heat treatment can effectively improve the RRR of the pure copper and high-purity aluminum, and vacuum heat treatment is more effective than ordinary atmospheric heat treatment; the processing state before heat treatment and the material source are different, although the difference in the RRR before heat treatment is small, but there is often a large difference after heat treatment, and it is recommended that the RRR value after heat treatment must be referred to when selecting materials for the design of the low-temperature thermal conductivity(LTC).

Numerical simulation and experiment on vacuum gas quenching of H11 steel large die cast module

Chen Hao, Tu Yujie, Jiang Zhipeng, Wu Xiaochun

2024, 49(2): 227-235. doi:10.13251/j.issn.0254-6051.2024.02.037

Abstract ( 40 )

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Effect of quenching pressure on temperature field, microstructure field and stress field of the H11 steel module (500 mm×500 mm×500 mm) during air quenching were studied by combining numerical simulation with experiment. The results show that greater quenching pressure, better cooling effect, but at the same time, it also causes greater quenching stress which can increase the risk of cracking. The overall cooling rate of the module increases as the quenching pressure increases, in the high temperature transformation zone (600-800 ℃), the maximum cooling rate of the module core under quenching pressure of 8 bar is 0.20 ℃/s, which is 0.06 ℃/s higher than that of 4 bar. The maximum stress of the module under quenching pressure of 8 bar and 4 bar is 655 MPa and 437 MPa, respectively. Through experiment verification, the carbides precipitated along the grain boundary appear in the core of the module under quenching pressure of 4 bar, therefore during the gas quenching process of H11 steel large modules, the cooling rate at the core should be at least ≥ 0.16 ℃/s at 600-800 ℃.

Numerical simulation of thermodynamic field and strengthening effect of H13 steel wire arc additive manufacturing under different inter layer cooling time

Zhu Yu, Chen Jufang, Chen Meng'en, Li Xiaoping, Peng Tianhao

2024, 49(2): 236-243. doi:10.13251/j.issn.0254-6051.2024.02.038

Abstract ( 28 )

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A finite element model for the wire arc additive manufacturing of single pass multi-layer H13 steel was established by using SYSWELD software. The model was validated by experiments, and the temperature field, stress field and distortion during the single pass multi-layer forming process under different inter layer cooling time (60, 90, 150, 300 s) were simulated and analyzed. The results show that the thermal cycle curve and stress distribution curve obtained by simulation are consistent with the measured results, which verifies the reliability of the finite element model. With the extension of inter layer cooling time, the heat dissipation condition of the formed part becomes stronger, the heat accumulation in the clad layer decreases, the number of weld bead remelting decreases, the maximum equivalent stress decreases from 434 MPa to 403 MPa, and the distortion decreases from 4.69 mm to 3.15 mm. When the inter layer cooling time is 300 s, the average hardness of clad zone of the wire arc additive manufactured part is 512 HV0.2, which is 2.38 times the average hardness of the annealed substrate (215 HV0.2), and the wear resistance is nearly 6 times higher than that of the annealed substrate.

Research progress on change of microstructure of 7000 series aluminum alloy during solution treatment and aging

Qi Qingwen, Bu Hengyong, Li Qin

2024, 49(2): 244-251. doi:10.13251/j.issn.0254-6051.2024.02.039

Abstract ( 24 )

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7000 series aluminum alloys are widely used in industrial areas such as aerospace and transportation due to the low density, high strength and good processing performance. As a high-strength heat treatable aluminum alloy, solution treatment and aging are important steps in heat processing, the microstructural changes caused by heat treatment have a significant impact on the properties of alloys. The research status of change of microstructure of 7000 series aluminum alloy during solution treatment and aging in recent years was reviewed. The heat treatment purpose, the influencing factors of heat treatment and the microstructure evolution, as well as the influence of typical precipitation on properties of aluminum alloys were described. Finally, prospects were made for the research directions related to the microstructure of 7000 series aluminum alloys.

Research progress of effects of rare earth on microstructure and corrosion resistance of composite coatings

Xu Ke, Yang Guirong, Song Wenming, Ma Ying

2024, 49(2): 252-258. doi:10.13251/j.issn.0254-6051.2024.02.040

Abstract ( 24 )

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With the development of research about the surface phenomena such as adhesion and adsorption, the new kinds of composite coatings are developed rapidly and gradually replacing traditional materials. The aim of various surface engineering techniques is to manufacture composite coatings with excellent corrosion resistance, high wear resistance and high temperature resistance. At present, there are still defects such as high internal porosity, low bond strength and low fracture toughness for the composite coating fabricated through various surface preparation techniques. Numerous studies show that the rare earth elements and their oxides have an important effect on improving the structure and properties of coatings. The effects of rare earth or its oxide additives on coatings are discussed, and an overview of the effects on refinement of coating microstructure is focused on, as well as the improvement of corrosion properties, and the mechanism of rare earth effects are illustrated in detail. On this basis, the future research prospects of rare earth modified coatings are also discussed.

Advances on surface treatment process of tantalum

Wang Zhehao

2024, 49(2): 259-264. doi:10.13251/j.issn.0254-6051.2024.02.041

Abstract ( 25 )

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Research advances and application examples of surface treatment technologies such as infiltration layer, micro-arc oxidation, chemical vapor deposition, and thermal spraying to improve the comprehensive properties of tantalum metal, reduce the failure behavior of tantalum materials, and enhance the service life of tantalum equipment were summarized. Finally, the development direction of surface reinforcement treatment for tantalum materials was discussed.

Current status and prospect of induction cladding technology

Wang Hao, Xi Yanjun, Ma Mingxing, Guan Xiaoyan, Zhang Ruijie, Liu Ying

2024, 49(2): 265-273. doi:10.13251/j.issn.0254-6051.2024.02.042

Abstract ( 72 )

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With the rapid development of industrial production, the traditional surface modification technology can no longer meet the needs of the industry, and there are obvious shortcomings, so the coatings with excellent wear resistance, corrosion resistance and high temperature oxidation resistance become research hotspot. Modern cladding technology, with its characteristics of stability, high efficiency and easy automation, has made achievements in the field of surface modification technology and has been widely used in industry. The development history of induction cladding technology is primarily reviewed, the aspects such as process parameters, multi-heat source composite cladding technology, and auxiliary techniques are summarized. The research on the simulation of the energy field in induction cladding is introduced, the reasons for the formation of defects in induction cladding technology are systematically analyzed, and the problems existing in both the technical processes and simulation research of induction cladding are identified. Based on the principles of induction cladding, the auxiliary techniques are focused on, and the shortcomings and solutions of various research directions in current induction cladding technology are proposed. Finally, in view of the needs for high performance integrated coating materials in stable service under extreme environment, the development of coating technology represented by composite technology for induction cladding is prospected.

Effect of surface mechanical rolling treatment on microstructure and mechanical properties of annealed TWIP steel

Wang Fuxue, Li Jiahui, Wang Qiang, Wang Hongtao

2024, 49(2): 274-280. doi:10.13251/j.issn.0254-6051.2024.02.043

Abstract ( 18 )

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Twining-induced plastic deformation (TWIP) steel has low yield strength and high plasticity, which is not conducive to its popularization and application. In order to improve the comprehensive mechanical properties of the TWIP steel, the surface mechanical rolling treatment (SMRT) is used to introduce a strengthened layer with certain thickness on the surface of annealed low-stacking faults energy single-phase austenitic TWIP steel. The surface feature, microstructure and fracture morphologies were investigated by means of laser scanning confocal microscope, optical microscope and scanning electron microscope respectively, and the hardness gradient and tensile properties were evaluated by Vickers hardness tester and MTS universal testing system. The results show that after the SMRT, the TWIP steel surface forms a strengthened layer of about 1.4 mm in thickness, and with good surface integrity. The microstructure analysis shows that the surface grains are refined, and the dislocation density and deformation twin density are increased. The mechanical property test results show that the surface hardness of the TWIP steel after SMRT reaches 647.5 HV0.1, which is about 2 times higher than that of the as-annealed state, though it decreases gradually from the surface to the as-annealed hardness of 230 HV0.1. The yield strength, tensile strength, and percentage total extension at fracture of the as-annealed TWIP steel are about 270 MPa, 878 MPa, and 73%, respectively. After the SMRT, the yield strength of the TWIP steel is increased to 1008 MPa, which is increased to about 3.7 times that of the annealed; the tensile strength and percentage total extension at fracture are increased to 1142 MPa and to about 20.5%, respectively, showing excellent comprehensive mechanical properties.

Influence of carrier gas flow rate on microstructure and corrosion resistance of laser clad Ni-based coatings with Y₂O₃

Li Yunfeng, Wang Jiasheng, Shi Yan, Jiang Guangjun, Tang Shufeng, He Xiaodong

2024, 49(2): 281-290. doi:10.13251/j.issn.0254-6051.2024.02.044

Abstract ( 25 )

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A 5 kW CO₂ laser was used for the preparation of pure Ni45 alloy coating and Ni45+0.4wt%Y₂O₃ coating on 42CrMoA steel substrate. Numerical simulation of the carrier gas flow rate was conducted using FLUENT software. The macroscopic morphologies and microstructure of the two coatings with different carrier gas flow rates were characterized using optical microscopy, scanning electron microscopy and XRD tester. The results show that as the carrier gas flow rate is increased from 500 L/h to 700 L/h, the powder deposition efficiency initially increases and then decreases. The solidification types of the two coatings consist of planar grains, cellular grains, columnar dendritic grains, and equiaxed grains, and with γ-Ni, M₂₃C₆, and Ni₃B phases. The microstructure refinement is most prominent when using a carrier gas flow rate of 600 L/h. The corrosion resistance increases initially, then decreases with the increase of carrier gas flow rate, and the coating produced with 600 L/h carrier gas flow rate has the best corrosion resistance.

Reason analysis and solution of rolling cracking of super duplex stainless steel S32750

Wang Hairui, Wang Jinyong, Liu Fuqiang, Qi Xilun, Gao Zhenglei

2024, 49(2): 291-296. doi:10.13251/j.issn.0254-6051.2024.02.045

Abstract ( 29 )

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Serious cracking occurred in the rolling process of a batch of pipes made of S32750 super duplex stainless steel. The chemical composition, non-metallic inclusions, microstructure and mechanical properties of the pipe materials were analyzed by means of spectrograph, metallographic microscope, scanning electron microscope, tensile tester and impact tester, and combined with rolling process and hot extrusion process. The results show that there are a lot of σ-intermetallic phases with Fe-Cr-Mo segregation in the microstructure before rolling, which is brittle and leads to cracking of the rolled steel pipe. After solution treatment at 1100 ℃ for 60 min before rolling, the intermetallic phase σ is fully dissolved, the strength and hardness are reduced, while the plasticity and toughness are improved, which can solve the rolling cracking problem.

Cracking failure analysis of 18CrNiMo7-6 steel gear shaft

Zhang Bing, Mao Yimeng, Jiang Tao, Liu Xin

2024, 49(2): 297-300. doi:10.13251/j.issn.0254-6051.2024.02.046

Abstract ( 34 )

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A gear shaft cracked during static standing after carburizing, quenching and tempering. In order to find out the failure mechanism of the gear shaft, macro and micro morphologies were observed and local chemical composition of the fracture surface was analyzed. In addition, the microstructure of the shaft near the fracture was examined, and the hardness and hydrogen content were tested. The results show that the failure mode of the gear shaft is delayed brittle cracking induced by hydrogen embrittlement. The crack initiated from the inside of the shaft and there is a large-size nonmetallic inclusion at the source zone, leading to greater stress concentration, which is the main cause for the hydrogen embrittlement cracking. Therefore, the material quality of the gear shafts should be strictly controlled, and nondestructive detection should be carried out to detect the large-size nonmetallic inclusions in the gear shafts so to prevent such failure.

Failure analysis and heat treatment process improvement of 40CrNiMoA steel upper joint

Liu Jinghong, Liu Jian, Liu Shuheng, Yao Mingfeng, Chen Jie

2024, 49(2): 301-306. doi:10.13251/j.issn.0254-6051.2024.02.047

Abstract ( 34 )

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In order to solve the fracture problem of the 40CrNiMoA steel upper joint, the main reasons for the fracture are the stress concentration caused by the small radius of variable diameter R, the over high hardness and the insufficient elongation via chemical composition analysis, metallographic analysis and mechanical property test of the workpiece fracture. The risk of crack fracture in heat treatment and use of the product can be reduced by optimizing the structural design and heat treatment processes. The results show that the mechanical properties of the workpiece material can meet the requirements of both product design and use by increasing the diameter rounded corner to R20, adopting intermediate heat preservation, controlling the heating rate to the quenching temperature of 810 ℃, cooling in slow oil, and subsequently, controlling the heating rate to the tempering temperature of 570 ℃ plus cooling in slow oil to prevent tempering brittleness. After testing in actual working conditions, no fracture accident occurs in the product life cycle.

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