Heat Treatment of Metals

Effect of heat treatment on microstructure homogeneity and tensile properties of hybrid fabricated AerMet100 ultra-high strength steel

Wang Yudai, Liu Yang, Zhu Yanyan, Tian Xiangjun, Cheng Xu, Ran Xianzhe, Qian Tingting

2022, 47(4): 1-9. doi:10.13251/j.issn.0254-6051.2022.04.001

Abstract ( 145 )

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Microstructure homogeneity of the hybrid fabricated AerMet100 steel under different heat treatment processes was studied, room temperature tensile properties of the specimens were tested, and the fracture mechanism was analyzed. The results show that microstructure of the as-deposited hybrid fabricated AerMet100 steel is very inhomogeneous, and the specimen contains laser deposited zone, forged zone, heat affected zone of the forged plate. After standard heat treatment commonly used for forged part, columnar grains transform to equiaxed grains for the laser deposited zone, and microstructure of all the three zones as mentioned above is the similar tempered martensite. However, the element segregation in the laser deposited zone is still observed. After homogeneity heat treatment at 1200 ℃ before heat treatment, microstructure of the hybrid fabricated AerMet100 steel becomes very homogeneous, the element segregation in the laser deposited zone is basically eliminated. the room temperature tensile properties are the best which are comparable with the forged zone, and the corresponding tensile specimen indicates ductile fracture mechanism, of which fracture occurs in the laser deposited zone.

Effect of solution and aging treatment on microstructure and corrosion resistance of Mg-4Sm-3Gd-0.5Zr alloy

Zhang Ziyan, Chen Jun, Chen Xiaoya, Li Quan'an, Liu Jianxin

2022, 47(4): 10-16. doi:10.13251/j.issn.0254-6051.2022.04.002

Abstract ( 92 )

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Microstructure, phase composition and corrosion morphology of Mg-4Sm-3Gd-0.5Zr (mass fraction, %) alloy before and after solution and aging treatment were studied by means of optical microscope, X-ray diffractometer and scanning electron microscope, and the static weight loss experiment and electrochemical test were carried out in NaCl solution with mass fraction of 3.5%. The results show that the as-cast Mg-4Sm-3Gd-0.5Zr alloy is composed of α-Mg matrix and coarse network eutectic phases Mg₄₁Sm₅ and Mg₅Gd distributed along grain boundaries. After solution and aging treatment, the type of eutectic phases is not changed, but the network eutectic microstructure disappears, a large number of fine and dispersed second phases are precipitated in the grain and the grain boundaries are clearer. After solution treated at 525 ℃ for 8 h and aged at 225 ℃ for 8 h, the corrosion rate of the alloy decreases from 0.185 mg·cm^-2·h^-1 to 0.116 mg·cm^-2·h^-1, and the corrosion current density decreases from 1.599×10^-4 A·cm^-2 to 0.924×10^-4 A·cm^-2, at which the corrosion resistance is significantly improved.

Effects of Al and Cu additions on microstructure and mechanical properties of 40CrNi3MoV steel

Liang Enpu, Xu Le, Yang Yong, Wang Maoqiu

2022, 47(4): 17-23. doi:10.13251/j.issn.0254-6051.2022.04.003

Abstract ( 86 )

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Change of microstructure and mechanical properties of 40CrNi3MoV steel with Al and Cu additions after oil quenched at 900 ℃ and then tempering at 450-650 ℃ was studied by OM, SEM, TEM and mechanical properties test. The results show that the microstructure of the tested steel after quenching and tempering is mainly tempered sorbite with nano-scale NiAl-Cu precipitates and the range of optimal tempering temperature is 500-550 ℃. The precipitation of NiAl precipitates with nano-scale B2 structure in the matrix has a strong hindering effect on the propagation of micro-cracks in the tested steel with Al addition, and the resulted maximum increase of tensile strength of the steel is 200 MPa. While after further addition of Cu, the yield strength increment of the tested steel is 150 MPa due to the interaction of the Cu-rich phase and dislocations. In such state, the tested steel owns tensile strength and yield strength of 1706 MPa and 1505 MPa respectively, and its tensile and impact fractures show typical cleavage fracture characteristics with obvious tearing edges.

Effect of original microstructure of medium manganese TRIP steel containing Al on microstructure and mechanical properties after intercritical annealing

Qi Xiaoliang, Li Yan, Ding Wei, Zhao Zengwu

2022, 47(4): 24-29. doi:10.13251/j.issn.0254-6051.2022.04.004

Abstract ( 87 )

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Microstructure and mechanical properties of 0.2C-5.0Mn-0.5Si-1.0Al TRIP steel with different original microstructure after intercritical annealing were studied by Factsage software, SEM, XRD, etc. The results show that the microstructure of the steel treated by different pretreatment processes are as follows: ferrite+blocky type retained austenite (pretreatment at 700 ℃ for 10 min), ferrite+martensite+small amount of retained austenite (pretreatment at 800 ℃ for 5 min), and martensite+small amount of carbides (pretreatment at 900 ℃ for 5 min). The residual austenite with different morphologies can be obtained by different pretreatment processes. By pretreatment at 700 ℃ and intercritical annealing, blocky-type retained austenite is obtained, and the film-type one can be obtained by the other processes. The specimen pretreated at 800 ℃+intercritical annealing has the best mechanical properties with the yield strength of 840 MPa, the tensile strength of 1121.5 MPa, the elongation of 33.25 %, and the product of strength and plasticity of 37.29 GPa·%. The morphology of retained austenite has a significant impact on the work hardening performance. The blocky-type retained austenite pretreated at 700 ℃ and intercritical annealing has poor stability, showing high work hardening rate, but the continuous interval is short. However, the stability of film retained austenite pretreated at 800 ℃ and intercritical annealing is better, showing higher work hardening rate and longer duration.

Effect of chemical composition on microstructure and properties of high strength Al-Mg-Si alloy

Chen Baoan, Zhang Jingyuan, Zhu Zhixiang, Han Yu, Pan Xuedong, Zhang Lei, Chen Suhong

2022, 47(4): 30-38. doi:10.13251/j.issn.0254-6051.2022.04.005

Abstract ( 74 )

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Effect of alloy composition on microstructure and properties of five kinds of Al-Mg-Si alloys was investigated by using universal tensile testing machine, SEM, TEM, etc. The results show that the microstructure, mechanical properties and conductivity of the five alloys are strongly depended on the Mg and Si contents. With increase of Mg and Si contents, the tensile strength of the alloy increases, whereas the conductivity tends to decrease. Although the total atoms of Mg and Si are equal for the Al-0.7Mg-0.5Si and Al-0.6Mg-0.6Si alloys, the different ratios of Mg to Si between the two alloys lead to distinct microstructure, so causing obvious difference in their performance. The Ce-microalloyed Al-0.7Mg-0.6Si-0.2Ce alloy aged at 175 ℃ for 4 h exhibits a good combination between mechanical properties and electrical properties, the tensile strength is up to 325 MPa, and the electrical conductivity is 56.2%IACS.

Effect of solid solution treatment on microstructure and carbides of 53Cr21Mn9Ni4N heat-resistant steel

Wang Yinghu, Zheng Huaibei, Liu Tingyao, Song Lingxi, Bai Qingqing

2022, 47(4): 39-45. doi:10.13251/j.issn.0254-6051.2022.04.006

Abstract ( 93 )

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Phase diagrams of 53Cr21Mn9Ni4N heat-resistant steel were calculated by using the FSstel database of FactSage software, the influence of nitrogen on phase transformation and precipitation during solidification and cooling was analyzed, and the equilibrium solidification and cooling phase transformation path diagram of the 53Cr21Mn9Ni4N heat-resistant steel was obtained. The microstructure and carbide evolution of the 53Cr21Mn9Ni4N heat-resistant steel were studied after solution treatment at 1200 ℃ respectively for 3 min, 10 min, 20 min, 40 min and 60 min by OM, SEM, XRD and EDS. The results indicate that the full-phase transformation path of 53Cr21Mn9Ni4N heat-resistant steel during the cooling process from 1600 ℃ to 300 ℃ is as follows: Liquid+Gas → Liquid → Liquid+δ-Ferrite → Liquid+δ-Ferrite+γ-Austenite → Liquid+γ-Austenite → γ-Austenite → γ-Austenite+M₂₃C₆→ γ-Austenite+M₂(C,N)+M₂₃C₆→ γ-Austenite+M₂(C,N)+M₂₃C₆+α-Ferrite → γ-Austenite+M₂(C,N)+M₂₃C₆+α-Ferrite+σ. The precipitation temperature of M₂₃C₆ decreases with the increase of nitrogen content, the precipitation temperature of M₂(C,N) increases with the increase of nitrogen content, and the precipitation of M₂₃C₆ is inhibited by the precipitation of M₂(C,N). The as-cast microstructure of the 53Cr21Mn9Ni4N heat-resistant steel is very uneven, the austenite grows in the form of dendrites and a large number of lamellar carbides precipitate between the dendrites. With the increase of solution treatment time, the lamellar carbides distributed between the dendrites gradually become massive and rod-shaped, the quantity of carbides gradually decreases, and the thick dendrites gradually become finer. The microstructure and carbides of the 53Cr21Mn9Ni4N heat-resistant steel after solution treatment at 1200 ℃ are all obviously improved.

Effect of solution treatment on microstructure of GH4080A superalloy

Lian Yibo, Yang Chunlei, Wang Guodong, Song Wei

2022, 47(4): 46-52. doi:10.13251/j.issn.0254-6051.2022.04.007

Abstract ( 87 )

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Effect of different solution treatment on microstructure of GH4080A superalloy was studied by using electron backscatter diffraction (EBSD) technology. The results show that the dynamic recrystallization during the rolling process of the initial hot-rolled bar is insufficient, and there are unrecrystallized grains as well as many inside-grain small-angle grain boundaries. When the solution treatment temperature is 1020 ℃, the recrystallization is mainly in the stage of nucleation. With the increase of solution treatment temperature, the recrystallization nucleation is completed basically and the grain growth stage begins. The recrystallization process is accompanied by the transformation from small-angle misorientation to large-angle misorientation, and lamellar {111} twin structure and a large number of Σ3 grain boundaries are found during the recrystallization process.

Effect of aging treatment on microstructure and mechanical properties of AlSi9Cu3 HPDC aluminum alloy

Chen Dongjun, Li Guangyang, Liu Gang

2022, 47(4): 53-56. doi:10.13251/j.issn.0254-6051.2022.04.008

Abstract ( 71 )

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Effect of aging treatment (T5 treatment, 160 ℃ for 6 h) on microstructure, mechanical properties and tensile fracture morphology of AlSi9Cu3 HPDC aluminum alloy was studied by means of tensile test, optical microscope (OM), scanning electric microscope (SEM) and energy disperse spectroscopy (EDS) analysis. The results indicate that microstructure of the aged AlSi9Cu3 HPDC alloy is composed of equiaxed primary α-Al, eutectic Si and precipitated phase of θ-Al₂Cu and α-Fe. The precipitated phase θ-Al₂Cu is observed on the grain boundary, which results in significant increase of tensile strength and hardness of the AlSi9Cu3 alloy. After aging, the tensile strength, yield strength, elongation and hardness of the AlSi9Cu3 alloy can reach 375 MPa, 258 MPa, 4.0% and 94 HBW, respectively. Meanwhile, the quasi cleavage fracture and a small amount of intergranular fracture are observed at tensile fracture of the AlSi9Cu3 alloy.

Segregation and influence of alloying elements at fcc-Fe/NbX (X=C, N) interface

Yang Jing, Dong Nan, Jiang Zhouhua, Han Peide

2022, 47(4): 57-62. doi:10.13251/j.issn.0254-6051.2022.04.009

Abstract ( 56 )

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Based on the first-principles method of density functional theory (DFT), the segregation behavior of Si, Ni, Mn, Cr, and Mo at the fcc-Fe/NbX (X=C, N) interface was studied, and the influence of alloying element segregation on interface system was analyzed. The results show that the bonding strength of the fcc-Fe/NbN interface is slightly improved compared to that of the fcc-Fe/NbC interface. Si exists stably in the Fe matrix, Ni and Mn have a slight tendency to segregate at the interface, and Cr and Mo segregate in the interface and NbX (X=C, N). Among them, Mo has a greater tendency to segregate toward the interface. The segregation of Cr and Mo at the fcc-Fe/NbC interface reduces the bonding ability of the interface to a certain extent, but the stability of the system is improved. The segregation of Cr and Mo at the fcc-Fe/NbN interface improves the bonding ability of the interface to a certain extent, but Mo reduces the stability of the system.

CCT curves and microstructure and properties of low-carbon high strength marine steel

Chen Liansheng, Zhang Luyou, Tian Yaqiang, Yang Zixuan, Li Hongbin, Pan Hongbo, Wei Yingli

2022, 47(4): 63-68. doi:10.13251/j.issn.0254-6051.2022.04.010

Abstract ( 91 )

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Continuous cooling transformation curve (CCT curve) and effect of final cooling temperature after hot rolling on microstructure and properties of low-carbon high strength marine steel were studied by Gleeble-3500 thermal simulation test machine, optical microscope and scanning electron microscope. The results show that only ferrite and bainite transformations take place during the continuous cooling transformation of the tested steel. In the process of air cooling immediately after hot rolling and rapid cooling to different final cooling temperature, the room temperature microstructure is bainitic and polygonal ferrite, and the content of bainitic increases with the decrease of final cooling temperature. Compared with direct air cooling to room temperature, with the increase of final cooling temperature, the strength of the tested steel decreases at first and then increases, However, when the final cooling temperature increases to 650 ℃, the strength of the tested steel decreases. When the final cooling temperature is 600 ℃, the yield strength and tensile strength is the highest, as 644.28 MPa and 679.71 MPa respectively, and the best impact absorbed energy is 112 J at -20 ℃.

High temperature tensile deformation behavior and microstructure evolution law of 40CrNiMo steel

Jia Changyuan, Huo Yuanming, He Tao, Huo Cunlong, Liu Keran

2022, 47(4): 69-74. doi:10.13251/j.issn.0254-6051.2022.04.011

Abstract ( 82 )

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High temperature tensile tests of 40CrNiMo steel at different temperatures (950, 1050 and 1150 ℃) and different strain rates (0.5, 1.0 and 5.0 s^-1) were carried out by using smooth and notched tensile specimens. The mechanical properties, microstructure evolution and plastic damage formation mechanism of 40CrNiMo steel during high temperature tensile were investigated, and the influence of different stress triaxiality on high temperature plastic damage was analyzed. The results show that increasing deformation temperature or decreasing strain rate reduce peak stress. When the strain rate increases from 0.5 s^-1 to 5 s^-1, the unevenness of grain size increases, and the material is more prone to plastic damage. When the deformation temperature increases from 950 ℃ to 1150 ℃, the grain size increases by nearly three times. The damage undergoes three steps: nucleation, growth and formation of microcracks. The stress triaxiality is negatively correlated with the notch radius. The increase of the stress triaxiality aggravates the occurrence of ductile damage and reduces the fracture strain value of tensile specimens. In the actual rolling process of the axle, under the premise of ensuring a certain production efficiency, the forming angle of the cross wedge rolling die should be reduced as far as possible, and the widening angle should be appropriately increased to reduce the dynamic stress triaxiality value of the material during plastic deformation and reduce the probability of damage.

Two-pass hot compression deformation and softening behavior of commercially pure titanium TA1

Wang Qingjuan, Tian Yunfei, Gao Beite, Shi Jiamin, Wu Huan, Cai Jun

2022, 47(4): 75-79. doi:10.13251/j.issn.0254-6051.2022.04.012

Abstract ( 63 )

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Commercially pure titanium TA1 was subjected to one-pass and two-pass hot compression experiments on Gleeble-3500 thermal simulator with deformation temperature of 650-850 ℃, the pass interval time of 1-60 s, and the deformation rate of 10 s^-1. The static and dynamic softening behaviors of the commercially pure titanium TA1 during the one-pass and two-pass hot compression were studied. The microstructure evolution of the commercially pure titanium TA1 under different deformation conditions was studied by optical microscope. The results show that the hardening and softening behaviors of the commercially pure titanium TA1 is obvious during both the one-pass and the two-pass hot compression deformation. Before the peak stress, it is work hardening, and after the peak stress, it is work softening. Finally, the dynamic softening and work hardening reach the dynamic equilibrium. The static softening occurs in the interval time. The static softening rate increases with the increase of interval time as well as the temperature. The recrystallization between passes becomes more sufficient, and the grains grow up obviously after the second pass deformation with the increase of interval time and temperature. When complete recrystallization occurs, the softening rate reaches the maximum. During the hot compression deformation, dynamic softening occurs. Dynamic recrystallization is dominated at 650 ℃ and 750 ℃ and dynamic recovery at 850 ℃.

Effect of austenitizing temperature on isothermal transformation and mechanical properties of bainite steel

Wang Yunlong, Yu Wei, Zhang Yi, Shi Jiaxin, Li Minghui

2022, 47(4): 80-85. doi:10.13251/j.issn.0254-6051.2022.04.013

Abstract ( 79 )

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Effect of austenitizing temperature on isothermal phase transformation kinetics, microstructure and mechanical properties of a medium carbon bainitic steel was studied by isothermal transformation test at 300 ℃ after austenitizing at 880-1050 ℃ with thermal dilatometer and thermal simulation testing machine. The results show that the increase of austenitizing temperature leads to the increase of grain size, the decrease of Ms point and the prolonging of the incubation period of bainite isothermal phase transformation. Decreasing the austenitizing temperature can significantly shorten the time of peak bainite transformation rate, indicating that lower austenitizing temperature is conducive to accelerating the bainite transformation. In the temperature range of this experiment, the specimens treated by austenitizing at 880 ℃ have excellent comprehensive mechanical properties, with the tensile strength of 1671 MPa and elongation of 13.3%.

Effect of Mg content on microstructure and mechanical properties of 2A14 aluminum alloy

Chen Sijun , Chen Songyi, Chen Geng, Yuan Dingling, Chen Kanghua

2022, 47(4): 86-92. doi:10.13251/j.issn.0254-6051.2022.04.014

Abstract ( 73 )

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Effect of different Mg contents on microstructure and mechanical properties of 2A14 aluminum alloy were studied by means of optical microscope (OM), scanning electron microscopy (SEM), hardness tester, tensile tester and impact tester. The results show that with the increase of Mg content, the residual crystalline phase in the aged alloy increases obviously, the strength increases first and then decreases, and the impact property decreases slightly when the strength is the highest. The increase of Mg content promotes the formation of Cu-Mg clusters, which provides nucleation sites for subsequent θ′ and Q′ phases, so that the number of θ′ and Q′ increases significantly and the strength increases accordingly. However, excessive Mg content significantly increases the residual crystalline phases (Al₂Cu, AlCuMgSi, AlSiMnFe, etc), resulting in stress concentration, which reduces impact property and tensile properties.

Effect of Mn element on microstructure evolution of galvanized coating of hot stamping steel

Liu Liyan, Bi Wenzhen, Wei Xicheng

2022, 47(4): 93-99. doi:10.13251/j.issn.0254-6051.2022.04.015

Abstract ( 75 )

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Surface morphology and cross-sectional microstructure of the galvanized coating of hot stamping steel after holding at 800 ℃for different time were characterized by means of SEM and XRD, and the influence of Mn element on microstructure evolution of the coating during the interdiffusion of elements was analyzed by means of EPMA、WDX、EDS and GDOES. The results show that with the extension of holding time from 3 min to 7 min, the surface morphology of coating evolves from “hill” to “crater”, then gradually spheroidizes. The “crater” morphology on coating surface leads to uneven coating thickness and large fluctuation after holding for 5 min. The coating phase changes with the prolongation of holding time. The coating is mainly composed of Fe₄Zn₉ and δ phases after holding for 3 min. When prolonging the holding time to 5 min, the coating is mainly composed of Fe₄Zn₉ and α-Fe(Zn) phases, and Mn is enriched in the α-Fe(Zn) phase near the substrate to form a manganese-rich sublayer. After holding for 7 min, the area of Mn enrichment decreases and moves towards the coating surface due to the continuous diffusion of Mn element from the substrate to the surface of the coating.

Research progress of light-weight high-entropy alloys

Luo Zaibin, Fan Zize, Peng Zhen

2022, 47(4): 100-107. doi:10.13251/j.issn.0254-6051.2022.04.016

Abstract ( 79 )

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High-entropy alloys is a new emerging class of metallic alloys which are constituted by multiple elements with an equi-molar or near equi-molar mixing. But its larger density greatly limits its application. In order to reduce the density of high-entropy alloys, light-weight high-entropy alloys composed of light alloy elements such as Al, Li, Mg, Ti, etc. appeared. Because of its potential application prospects in transportation and aerospace fields, it has attracted widespread attention. The current research status of lightweight high-entropy alloys is described, and the component design methods, phase formation and preparation processes of lightweight high-entropy alloys are analyzed, and then the various properties of different types of lightweight high-entropy alloys are summarized, including high strength, high hardness, high temperature oxidation resistance, corrosion resistance, etc. Finally, some existing problems of light-weight high-entropy alloys are summarized and the future research directions of light-weight high-entropy alloys are prospected.

Precipitation behavior of σ phase in 2507 super duplex stainless steel

Bai Qingqing, Zhang Zhihong, Zheng Huaibei, Wang Yinghu

2022, 47(4): 108-115. doi:10.13251/j.issn.0254-6051.2022.04.017

Abstract ( 75 )

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Precipitation of σ phase in 2507 (S32750) super duplex stainless steel aged at 700-1000 ℃ for different time and its influence to impact property and corrosion resistance were studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and electrochemical workstation. The results show that the precipitation rate of σ phase is very fast in 2507 super duplex stainless steel, and the precipitation amount increases first and then decreases gradually with the extension of aging time. Precipitation of σ phase is the fastest after aging at 850-900 ℃, which leads to the serious reduction of impact toughness and corrosion resistance of the steel. It is recommended that the aging temperature should not be lower than 950 ℃.

Influence of rolling heating temperature on microstructure and impact property of a high strength low alloy steel

Chen Gang, Luo Xiaobing, Chai Feng, Yang Caifu, Zhang Zhengyan, Yang Li

2022, 47(4): 116-121. doi:10.13251/j.issn.0254-6051.2022.04.018

Abstract ( 83 )

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Effect of rolling heating temperature on microstructuree and －40 ℃ impact property of high strength low alloy(HSLA) steel was investigated. The results show that the microstructure of HSLA steel is composed by granular bainite. The size of M/A island increases with the increase of rolling heating temperature. When the rolling heating temperature is 1000-1150 ℃, the impact property is good, the M/A islands in the microstructure are finely dispersed, and the large-angle grain boundary density is relatively large. The grain size of the prior austenite is obviously coarser above 1150 ℃, the M/A islands produced after the phase transformation are significantly coarser, and the large-angle grain boundary density is lower. With the increasing of the rolling heating temperature, the M/A islands coarsened and the density of the large-angle interface decreased result in a decrease in impact toughness.

Effect of quenching temperature on microstructure and mechanical properties of high Ti low alloy wear-resistant steel

Fu Xibin, Chen Zihao, Zhang Ke, Zhao Shiyu, Sun Xinjun, Zhu Zhenghai, Liang Xiaokai, Yong Qilong

2022, 47(4): 122-127. doi:10.13251/j.issn.0254-6051.2022.04.019

Abstract ( 76 )

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Effect of quenching temperature on microstructure, precipitated phase and hardness of a high Ti low alloy wear-resistant steel was investigated, and the reasons of the change of microstructure and mechanical properties were analyzed. The results show that the microstructure after quenching and tempering is lath martensite with high dislocation density; the size of precipitated phase is mainly divided into micron-, submicron-, and nano-scales, in which the micron-sized precipitates are rod-shaped, and the sub-micron and nano-sized precipitates are spherical; fine (Ti, Mo)C precipitates are distributed on the martensite laths. As the quenching temperature increases, the yield strength, tensile strength and hardness of the steel first increases and then decreases, and reaching the maximum values of 1248 MPa, 1535 MPa and 434 HV respectively when the quenching temperature is 920 ℃, meanwhile, the elongation reaches 10%. With the increase of the quenching temperature, the nano-scale precipitates gradually dissolves and decreases in content but the size gradually increases; and the sizes of the prior austenite grain and the martensitic lath are slightly increased by flattening along the rolling direction, while the width of martensite laths does not increase significantly. The dispersed (Ti, Mo)C precipitates of 5-10 nm in large quantity are the main factor for promoting the hardness increase of the wear-resistant steel. As the quenching temperature increases, the coarsening of both the fine (Ti, Mo)C phase and the prior austenite grain are not conducive to the improvement of the hardness of the wear-resistant steel.

Effect of magnetic field pre-annealing on microstructure and texture of CGO steel

Su Pengji, Ma Yonglin, Dong Lili, Yang Xuefeng

2022, 47(4): 128-132. doi:10.13251/j.issn.0254-6051.2022.04.020

Abstract ( 75 )

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CGO oriented silicon steel with 3.12%Si was pre-annealed in the different pulsed magnetic fields, and the microstructure and texture of the steel were analyzed by means of metalloscope and XRD. The results show that the average grain size of the oriented silicon steel is refined and the microstructure distribution is uniform after the pre-annealing treatment with pulse magnetic field. Based on the analysis of the ODF map and orientation line, it can be seen that the pulse magnetic field pre-annealing has a significant promoting effect on the favorable texture of {111}<112>, especially when the annealing temperature is 760-800 ℃ and the pulsed magnetic fieldintensity is 20 mT and the magnetic time is 1 min, the best effect can be obtained.

Heat treatment process optimization for 4Cr5Mo2VCo steel

Li Li, Zeng Yan, Wu Xiaochun

2022, 47(4): 133-140. doi:10.13251/j.issn.0254-6051.2022.04.021

Abstract ( 61 )

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Hardness and impact property of 4Cr5Mo2VCo steel treated by different processes were measured, and the microstructure and fracture morphology were analyzed by SEM. The results show that in the quenching temperature range of 1000-1100 ℃, the hardness of the 4Cr5Mo2VCo steel first increases and then decreases, up to 59.2 HRC. The number of undissolved carbides decreases with the increase of quenching temperature, and almost all of the carbides dissolve into the matrix at 1100 ℃. During tempering, the secondary hardening peak temperature of the 4Cr5Mo2VCo steel is 520 ℃, and the hardness decreases subsequently with the increase of tempering temperature. The impact absorbed energy of the specimens quenched at different temperatures increases firstly and then decreases gradually with the increase of tempering temperature. In the hardness ranger of 44-46 HRC, the optimum heat treatment process of the 4Cr5Mo2VCo steel is quenching at 1060 ℃ for 30 min and tempering twice at 600-610 ℃ for 2 h, under which, the average impact absorbed energy can reach 410 J.

Microstructure transformation and strengthening-plasticization mechanism of S32205 duplex stainless steel after cold rolling and annealing

Lü Jiesheng, Song Zhigang, He Jianguo, Feng Han, Zheng Wenjie, Zhu Yuliang

2022, 47(4): 141-145. doi:10.13251/j.issn.0254-6051.2022.04.022

Abstract ( 53 )

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A novel process of cold rolling and annealing was designed to improve mechanical properties of S32205 duplex stainless steel. Both the tensile strength and the elongation were enhanced by this process. The microstructure characteristics and the strengthening mechanism of the new-designed microstructure were investigated by means of room temperature tensile tests, optical microscope, electron back-scattered diffraction analysis and thermodynamic calculations, etc. The results show that the microstructure of the S32205 duplex stainless steel obtained by the process exhibits a bimodal grain size distribution with fine austenite precipitated in the ferrite phase. Under the combined effect of fine-grained strengthening and back stress strengthening caused by the incompatible deformation between the two phases, the strength and plasticity of the tested steel are both improved compared with the conventional solution heat treatment process.

Effect of tempering temperature on microstructure and properties of 1100 MPa grade high-strength steel

Wang Qi, Wu Guangliang

2022, 47(4): 146-150. doi:10.13251/j.issn.0254-6051.2022.04.023

Abstract ( 123 )

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Microstructure and mechanical properties of 1100 MPa grade high-strength steel after water quenching at 920 ℃ and tempering at different temperatures were studied. The results show that when the tempering temperature is 250 ℃, the tested steel obtains the optimum mechanical properties, the tensile strength, yield strength, hardness, elongation after fracture and impact absorbed energy are 1423 MPa, 1220 MPa, 446 HV5, 14.2% and 56 J, respectively. With the increase of tempering temperature, the tensile strength, yield strength and hardness show a downward trend as a whole, and the impact absorbed energy first decreases and then increases. When the tempering temperature is 150 ℃, the microstructure is composed of tempered martensite and slender rod-shape precipitated ε carbides. After the tempering temperature rises to 250 ℃, the martensite laths are slightly coarsened, and the ε carbides grow up. With further increase of tempering temperature, the lath martensite gradually transforms to equiaxed ferrite, the ε carbides also transform to cementite and gradually spheroidize and coarsen.

Microstructure evolution and mechanical properties of Nb-alloyed high manganese steel under different water toughening processes

Yu Hongjun, Cheng Fuchao, Ma Zetian, Wang Yongjin, Chen Junhao, Chen Zhengjia, Song Chuansongxin

2022, 47(4): 151-154. doi:10.13251/j.issn.0254-6051.2022.04.024

Abstract ( 60 )

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A high manganese steel with high strength and impact absorbed energy was obtained by Nb-alloying, and its microstructure evolution and properties under different water toughening temperatures and time were studied to explore the best water toughening condition. The results show that with the increase of water toughening temperature or time, the carbides in the steel are dissolved in the austenite matrix constantly, while the grains are growing, and the strength and impact absorbed energy of the steel increase firstly and then decrease. When the water toughening temperature is 1100 ℃ and the time is 1.5 h, the strength and impact absorbed energy of the steel reaches the peak value, as the tensile strength, yield strength, elongation, impact absorbed energy and hardness are 957.7 MPa, 415.3 MPa, 57.2%, 298 J and 222 HBW, respectively, showing the optimum mechanical properties.

Effect of aging temperature on microstructure and hardness of laser selective melting TC21 titanium alloy

Sun Kai, Chen Yan, Yang Shaobin

2022, 47(4): 155-158. doi:10.13251/j.issn.0254-6051.2022.04.025

Abstract ( 71 )

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Effect of aging temperature on microstructure and properties of laser selective melting (SLM) formed TC21 titanium alloy was systematically investigated by means of microstructure observation and hardness test. The results show that when the aging temperature is lower, the secondary α phase precipitates in the form of dispersive needle with the increase of temperature, the dispersion degree increases with the increase of temperature, and the volume fraction of β precipitates increases with the increase of temperature. When the aging temperature is too high, the secondary α phase is coarsened to form a larger flake α phase, and the strengthening effect decreases. When the aging temperature is 450 ℃, the microstructure of the SLM formed TC21 titanium alloy is the most dispersive and uniform, and the hardness is up to 575 HV5, which is 43.3% higher than that of the SLM formed state. It is proposed that the aging temperature of the SLM formed TC21 titanium alloy is controlled at 450 ℃ as the optimum.

Effect of ultrasonic vibration on microstructure and properties of aluminum alloy produced by CMT wire arc additive manufacturing

Zhang Jijun, Xing Yanfeng, Cao Juyong

2022, 47(4): 159-164. doi:10.13251/j.issn.0254-6051.2022.04.026

Abstract ( 55 )

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In order to reduce the pores and coarse grains in the aluminum alloy produced by arc additive manufacturing, the method of ultrasonic vibration assisted CMT (cold metal transfer) arc additive manufacturing was used to accumulate the thin-walled parts of 4043 aluminum alloy, and the effect of ultrasonic amplitude on microstructure and mechanical properties of the deposited material was studied. The results show that the aid of ultrasonic vibration breaks dendrites and promotes the formation of more nuclei to refine the grains. The columnar grains are also transformed into fine equiaxed grains under the vibration and stirring of the molten pool. Compared with the specimens without ultrasonic vibration, the average grain size is reduced by 22.5%. At the same time, the cavitation and acoustic flow effects caused by ultrasonic vibration reduce the size and number of pores in the specimens. However, as the ultrasonic amplitude increases, the energy inside the molten pool gradually increases, and the increase in heat input also causes the grains to coarsen. At the same time, excessive ultrasonic energy also destroys the structural integrity of the weld, resulting in holes in the weld. The tensile strength of the specimen with ultrasonic vibration is increased by 8.2%-16.3% compared with that of the specimen without ultrasonic vibration, and the anisotropy of the tensile and elongation gradually decreases with the increases of amplitude.

Surface quality and corrosion resistance of MnSi₂-reinforced 316L stainless steel composites fabricated by selective laser melting

Li Meng, Wu Meiping, Lu Peipei , Zhao Zishuo, Miao Xiaojin

2022, 47(4): 165-170. doi:10.13251/j.issn.0254-6051.2022.04.027

Abstract ( 53 )

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In order to improve the corrosion resistance of 316L stainless steel in marine environment, MnSi₂-reinforced 316L stainless steel composites were prepared by selective laser melting(SLM). The effect of laser power on density and corrosion resistance of the 316L stainless steel metal matrix composites was investigated by using Image-Pro Plus software, metallographic microscope, scanning electron microscope(SEM) and electrochemical work station. The corrosion resistance was evaluated by Tafel polarization curve and impedance spectrum, and the corrosion mechanism was revealed by pitting topography. The results show that adding MnSi₂ is an effective way to improve the corrosion resistance of 316L stainless steel. When the laser power reaches 190 W, the density of 2%MnSi₂/316L stainless steel composites is 99.80% and the corrosion potential is －0.053 V (vs SCE). At the same time, the 2% MnSi₂ can significantly improve the forming quality and corrosion resistance of the 316L stainless steel. The corrosion form is the corrosive pitting of chloride induced by chloride ions, and the pitting corrosion is mainly concentrated at the pore boundary.

Effect of aging after mechanical polishing process on drawing performance of 0Cr25Al5 electrothermal alloy

Hu Jing, Tao Ke, Yang Qingsong, Li Gang, Zhang Dehan

2022, 47(4): 171-177. doi:10.13251/j.issn.0254-6051.2022.04.028

Abstract ( 59 )

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Mechanical properties, microstructure and precipitates of mechanically polished 0Cr25Al5 Fe-Cr-Al electrothermal alloy after aging at different temperatures (150, 250, 350 ℃) and different time (1, 2, 3 h) were studied, and compared with those before and after mechanically polishing. The results show that after mechanical polishing, Cr₃C₂ is precipitated and distributed at the grain boundary with mainly rod-like and needle-like shape, accompanied by a small amount of spherical precipitates. After mechanical polihsing and then aging at 250 ℃ for 1 h, the hardness decreases, the tensile strength slightly increases, the elongation slightly decreases and the residual stress significantly decreases, meanwhile, the grain size remains the same and the precipitates is basically spherical with small size and distribution concentrated on grain boundaries, which is the Cr₇C₃ re-formed by exostatic precipitation from the dissolved Cr₃C₂. In addition, the oxide film does not regenerate which meets the requirements of subsequent drawing process. During the subsequent cold drawing production, the die loss and wire breakage rate of the 0Cr25Al5 Fe-Cr-al alloy after aging at 250 ℃ for 1 h decrease significantly comparing with that without aging treatment, and the finished product rate increases.

Induction hardening process of internal spline in tulip of constant speed drive shaft

Huo Jinyuan, Chen Guojun, Zheng Dexin

2022, 47(4): 178-181. doi:10.13251/j.issn.0254-6051.2022.04.029

Abstract ( 84 )

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Special positioning tooling and two kinds of U-shaped inductors A and B with Π-shaped silicon steel sheet were designed. The induction hardening test of internal spline in tulip was carried out by using inductor A and B under the condition of spray protection of outer surface on the fully automatic quenching machine with frequency of 8-20 kHz and maximum output power of 300 kW. The results show that by using the method of positioning only the inner hole and end surface, the induction hardening is carried out with the U shaped inductor with Π-shaped silicon steel sheet under the condition of protective spraying on outer surface, which can meet the quenching requirements of internal spline in tulip. Compared with A type inductor, the heating power coefficient of B type inductor is lower, the heating time is shorter, and the energy saving and production increasing effect is more remarkable, which shows that the reasonable inductor design for the induction hardening of internal spline in tulip is an effective way for energy saving and production increasing.

Spherical annealing process for improving magnetic properties of low-carbon steel

Zhang Jianjun, Zhuang Xiaowei, Tang Xiaofeng

2022, 47(4): 182-184. doi:10.13251/j.issn.0254-6051.2022.04.030

Abstract ( 48 )

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Different annealing processes for improving the magnetic of low carbon steel was carried out. The results show that when the conventional complete annealing at 920 ℃ is replaced by spheroidizing annealing at 700 ℃, the magnetic properties are the same as those of the conventional annealing process, but the process time is only half of that of the conventional annealing. It is found that the morphology of cementite has a great influence on the magnetic properties. The lamellar cementite are broken and spheroidized during the spheroidizing annealing, which reduces the blocking effect on the magnetic circuit and improves the magnetic properties of the low carbon steel. The influence of spheroidization of tertiary cementite may be greater than that of eutectoid cementite.

Spheroidizing annealing process of 16MnCrS5 steel for cold forging gear

Zhang Jun, Zhao Sixin

2022, 47(4): 185-188. doi:10.13251/j.issn.0254-6051.2022.04.031

Abstract ( 85 )

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Effects of different spheroidizing processes on mechanical properties of 16MnCrS5 steel for cold forging gear were studied, and the effects of four spheroidizing processes on hardness, strength and elongation of the 16MnCrS5 gear steel were analyzed. The experimental results show that holding at 760 ℃ for 4 h, cooling to 710 ℃ at a rate of 12 ℃/h and holding for 3 h, then cooling to 680 ℃ at a rate of 12 ℃/h and holding for 2 h, and furnace cooling to 500 ℃, with this process, the hardness of the material reaches the minimum 123 HBW, the elongation reaches 39%, and the reduction of area exceeds 70%, which can meet the high plasticity requirements of the cold forging materials, and can provide a process reference for the heat treatment of 16MnCrS5 steel for cold forging gear.

Effect of quenching temperature on microstructure and properties of M390 powder metallurgical stainless steel for chopping knives and scissors

Liu Wenbin, Qiao Longyang, Pan Xinyu, Cheng Ge, Li Aina, Pei Xinjun

2022, 47(4): 189-195. doi:10.13251/j.issn.0254-6051.2022.04.032

Abstract ( 302 )

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Through calculation of equilibrium phases at different temperatures and carrying out vacuum quenching+low temperature tempering for powder metallurgical stainless steel M390, the effect of quenching temperature on microstructure and mechanical properties of the steel was analyzed. The results show that with the increase of quenching temperature, the size of carbides in the tempered M390 steel increases, the number of carbide particles per unit area decreases but the area fraction increases, thus the distribution uniformity of carbide decreases. Meanwhile, the hardness increases first and then decreases slightly, reaching the maximum value of 60.2 HRC after quenching at 1130 ℃ and decreases to 58.5 HRC after tempering. However, the flexural strength is little affected by quenching temperature, which is at the level of 4000 MPa. In order to obtain good properties, the quenching temperature should be controlled below 1200 ℃. In conclusion, vacuum gas quenching at 1130-1180 ℃ and tempering at 200 ℃ is the optimum heat treatment process for the M390 steel used for chopping knives and scissors.

Effects of solution cooling method on microstructure and properties of short-term servicing high-temperature titanium alloy plate

Wang Ruiqin, Ge Peng, Liao Qiang, Hou Peng, Liu Yu

2022, 47(4): 196-198. doi:10.13251/j.issn.0254-6051.2022.04.033

Abstract ( 65 )

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Effect of cooling method in solution treatment on microstructure and mechanical properties of the hot-rolled plate of a new type of short-term servicing high-temperature titanium alloy was studied. The results show that the microstructure of the tested titanium alloy plate is all α+β phases after solution treatment and cooling in different ways. The size of secondary α phases under all the three cooling methods is small, but the number of secondary α phases under furnace cooling is less than that of the other two cooling methods. The size and quantity of the secondary α phases under air cooling and water cooling are similar. With the increase of cooling rate, the strength of the alloy at room temperature, 600 ℃ and 700 ℃ increases, while the plasticity decreases. The titanium alloy can obtain excellent comprehensive mechanical properties by air cooling in solution treatment.

Effects of heat treatment and cold deformation on linear expansion coefficient of constant expansion alloy 4J32C

Wang Fangjun, Wang Dongzhe, Wan Hong, Shi Yao, Shen Tao

2022, 47(4): 199-203. doi:10.13251/j.issn.0254-6051.2022.04.034

Abstract ( 54 )

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Effects of different heat treatment systems and cold deformation on linear expansion coefficient of the constant expansion alloy 4J32C were studied. The results show that the linear expansion coefficient of the alloy is not significantly changed by small amount of cold deformation. With the increase of solution treatment temperature, the linear expansion coefficient of the alloy decreases gradually, reaches the lowest value at 850 ℃, and then increases slightly with the increase of solution temperature. The linear expansion coefficient of the alloy can be appropriately increased by prolonging the stabilization treatment time or increasing the stabilization treatment temperature.

Heat treatment for improving mechanical properties of hypoxic TC4-LC and remelted TC4 alloys

Wang Shaozhuo, Meng Han, Wang Fen, Fan Haiwei, Li Yan, Tang Chao

2022, 47(4): 204-207. doi:10.13251/j.issn.0254-6051.2022.04.035

Abstract ( 71 )

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Effects of heat treatment process(annealing, solution treatment, solution and aging treatment and β heat treatment) on microstructure and mechanical properties of the self-produced hypoxic TC4-LC alloy and remelted TC4 alloy were studied by microstructure analysis and mechanical properties test. The results show that the oxygen content has a significant effect on mechanical properties of the alloy, and the mechanical properties depend on the microstructure under the same composition. The mechanical properties of the hypoxic TC4-LC alloy can be only improved to a certain extent by heat treatment processes, which can not meet the requirements of TC4 alloy. The strength of remelted TC4 alloy is greatly improved under different heat treatments, In addition to the annealing treatment, the plasticity is improved, for other heat treatments the plasticity is reduced to varying degrees and the mechanical properties of which after annealing treatment and solution and aging treatment can meet the requirements of TC4 titanium alloy.

Simulation of heating process for martensitic heat resistant steel G115 heavy pipe blanks

Zhao Xin, Chen Zhengzong, Zhao Haiping

2022, 47(4): 208-212. doi:10.13251/j.issn.0254-6051.2022.04.036

Abstract ( 90 )

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In order to optimize the heating process of martensitic heat resistant steel G115 heavy ingot before punching, the effect of heating process on temperature field of ingot was analyzed by finite element method. The results show that the temperature difference between the edge of the end section and 1/2 of the length of the ingot is larger, and the maximum temperature difference is 93 ℃. The higher the ingot heating temperature, the smaller the temperature difference. The edge of the end section has the highest temperature and the fastest heating rate, and the center of section of 1/2 longth of the ingot has the lowest temperature and the slowest heating rate. The research results can recommend the heating process of G115 steel heavy ingot before billet making, which is the furnace temperature increases from 300 ℃ to 500 ℃ held for 4 h, then to 850 ℃ held for 4 h, and rises to 1000 ℃ for 4 h then increases to 1230 ℃ for 20 h, it can provide a reference for the heating process of other processes.

Corrosion resistance of Mg-4.0Zn-2.0Sr-0.4Ca alloy composite coating

Chen Zhijie, Cui Tong

2022, 47(4): 213-218. doi:10.13251/j.issn.0254-6051.2022.04.037

Abstract ( 52 )

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Through environmentally friendly anodizing process and polymer deposition technology, a composite coating of anodic oxide film, SiO₂ sol-gel, polydopamine (PDA) and chitosan (CS) were prepared layer by layer on the surface of Mg-4.0Zn-2.0Sr-0.4Ca alloy. The morphology of the coating was observed by using scanning electron microscope (SEM), the phase composition was determined by using X-ray diffractometer (XRD), and the corrosion resistance was tested by means of electrochemical testing and in SBF immersion. The results show that the composite coating is compact and complete without any defects. In the SBF solution, the composite coating gradually cracks and breaks with the prolongation of corrosion time, resulting in smaller corrosion pits, which shows the corrosion is controlled on the surface at a certain degree. However, the corrosion of uncoated Mg-4.0Zn-2.0Sr-0.4Ca alloy is mainly corrosion pits and local corrosion, and the corrosion intensifies with the prolongation of corrosion time. In addition, the corrosion current density, corrosion potential and average corrosion rate of the composite coating in SBF solution are 5.7039 μA/cm², -1.4203 V(vs SCE) and 0.163 g/(m²·h), which is better than that of the uncoated Mg-4.0Zn-2.0Sr-0.4Ca alloy, especially the average corrosion rate drops by more than 50%, which indicates that the prepared composite coating can significantly improve the corrosion resistance of the Mg-4.0Zn-2.0Sr-0.4Ca alloy.

Microstructure and properties of C69 gear steel for aviation after high temperature carburizing

Dai Jianke, Han Shun, Li Yong, Liu Xianmin, Wang Chunxu, Pang Xuedong, Li Jianxin

2022, 47(4): 219-225. doi:10.13251/j.issn.0254-6051.2022.04.038

Abstract ( 62 )

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Effect of different carburizing processes at 1050 ℃ on microstructure and properties of gear steel C69 for aviation was studied by using OM, SEM, TEM and Vickers hardness tester. The results show that after carburizing, cryogenic and tempering, the surface hardness of the carburized layer can reach about 950 HV0.3, and the microstructure is acicular martensite where the M₃C and M₂C carbides precipitate, and the M₇C₃carbides precipitate at grain boundary. At the sub-layer of the carburized surface, microstructure is composed of acicular martensite and lath martensite. At the core, the microstructure is lath martensite and the hardness is about 630 HV0.3. The cyclic carburizing has higher carburizing efficiency. With the increase of carburizing cycle, the thickness of carburized layer and surface carbon concentration increase continuously, and the size and quantity of the M₇C₃ at the grain boundary also increase. After four cycles carburizing, the surface carbon concentration is 1.14%, and the thickness of carburized layer is about 3.0 mm.

Effect of compound chemical heat treatment on microstructure and hardness of G13Cr4Mo4Ni4V steel

Su Yong, Wang Shuai, Wang Jixing, Yu Xingfu, Liu Hongxiu, Liu Jinling

2022, 47(4): 226-230. doi:10.13251/j.issn.0254-6051.2022.04.039

Abstract ( 48 )

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Effect of 140 h nitriding on the microstructure and hardness of carburized+quenched+tempered G13Cr4Mo4Ni4V steel was studied by using SEM, Rockwell hardness tester and Vickers microhardness tester. The results show that the depth of the effective carburized layer of G13Cr4Mo4Ni4V steel after carburizing+quenching+tempering is 1.45 mm, the highest hardness of the carburized layer is 785 HV, and the hardness of the core is 420 HV. The depth of the effective carburized and nitrided layer after nitriding treatment is reduced to 1.34 mm, the depth of nitrided layer is 0.22 mm, the highest hardness of the nitrided and nitrided layer can reach 948 HV, and the hardness of the core is 451 HV. Nitriding does not significantly improve the hardness of the core of the specimen. The surface Rockwell hardness of the G13Cr4Mo4Ni4V steel after carburizing+quenching+tempering and after nitriding treatment is similar, which is between 62 and 65 HRC, but the hardness of the specimen after nitriding treatment fluctuates relatively larger. The 140 h nitriding of carburized+quenched+tempered G13Cr4Mo4Ni4V steel achieves the goal of “hard surface and tough core”. The depth of the nitrided layer meets the engineering needs, but the network-like carbonization appears in the carburized and nitrided layer of the steel after nitriding treatment, so in the nitriding process, it is necessary to comprehensively consider the depth and microstructure of the nitriding layer to obtain good comprehensive mechanical properties.

High temperature carburizing process of 18CrNiMo7-6 steel in controlled atmosphere

Chen Qiang, Chen Linfang, Yang Minghua

2022, 47(4): 231-239. doi:10.13251/j.issn.0254-6051.2022.04.040

Abstract ( 123 )

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Based on the heat treatment process requirements of heavy load gear for locomotive, pseudo-carburizing process was carried out on 18CrNiMo7-6 steel within temperature range of 920-1050 ℃. The microstructure and mechanical properties of the tested steel after conventional carburizing and high temperature carburizing at different temperatures were compared. Combined with the process simulation results of Aichelin computer aided simulation design software, high temperature carburizing process was developed, and the high temperature carburizing process of the 18CrNiMo7-6 steel gear was carried out, and the microstructure and properties of the gear were compared with those of the conventional carburizing gear. The results show that the comprehensive mechanical properties of the 18CrNiMo7-6 steel are decreased after pseudo-carburizing at different temperatures and time, compared with that before heat treatment, but the comprehensive mechanical properties of the 18CrNiMo7-6 steel can be significantly improved by controlling the cooling process after carburizing. Increasing carburizing temperature and carbon potential can greatly improve carburizing efficiency. The carburizing efficiency of the 18CrNiMo7-6 steel gear is increased by about 65% at the temperature of 1050 ℃. Compared with the conventional carburizing gear, the microstructure, comprehensive mechanical properties and single-tooth bending fatigue strength of the gear are not decreased after high temperature carburizing.

Mechanical properties of CrCN coatings at different deposition temperatures

Liu Naiyu, Cao Lei, Zheng Shaomei

2022, 47(4): 240-244. doi:10.13251/j.issn.0254-6051.2022.04.041

Abstract ( 53 )

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CrCN coatings were prepared on 304 stainless steel surface by magnetron sputtering technique, then the effect of deposition temperature on structure and mechanical properties of the CrCN coating was studied. The results show that the grain size and surface roughness are the largest for the coating obtained at 250 ℃. With further increase of the deposition temperature, the grain size is gradually refined, and the surface roughness is gradually decreased, but the hardness shows a trend of increasing and then decreasing. The coating obtained at the deposition temperature of 350 ℃ presents the highest hardness and the best resistance to elastic deformation and plastic deformation, showing the excellent mechanical properties of the coating.

Microstructure and properties of boronized layer on AISI 410 steel by paste boronizing

Shi Mingxiao, Wang Xiongdong, Li Jingyong, Yang Zhidong, Mao Weidong, Ni Huifeng

2022, 47(4): 245-250. doi:10.13251/j.issn.0254-6051.2022.04.042

Abstract ( 47 )

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Surface of AISI 410 steel was strengthened by the process of paste boronizing, and the microstructure of boronized layer was analyzed. The hardness, wear resistance and corrosion resistance of the AISI 410 steel were tested. The results show that the boronized layer is mainly composed of FeB and Fe₂B phases, and the bonding interface between the boronized layer and matrix is flat. The microhardness of the outer zone of the boronized layer is higher than 1400 HV0.5, and the hardness of the inner zone is higher than 1100 HV0.5. After boronizing, the surface friction coefficient and worn area of the specimens are significantly reduced, and the wear resistance is improved. In the electrochemical corrosion test, the self-corrosive potential of the boronized specimen is higher than that of the base metal, the self-corrosive current density is lower than that of the base metal,indicating that boronized specimens are more resistant to corrosion, and the surface corrosion resistance is improved.

Effect of laser power on microstructure and corrosion resistance of FeCoNiCrMo high-entropy alloy/graphene oxide composite coating

Zhao Zishuo, Wu Meiping, Miao Xiaojin, Cui Chen, Gong Yuling

2022, 47(4): 251-257. doi:10.13251/j.issn.0254-6051.2022.04.043

Abstract ( 56 )

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FeCoNiCrMo high-entropy alloy/graphene oxide composite coatings were prepared on 17-4PH stainless steel substrate by laser cladding process with laser power of 1600, 1800, 2000 and 2200 W, and the microstructure, Composition of phase, microhardness and corrosion resistance of the coatings were investigated. The results indicate that the phase composition include solid solution with BCC structure and intermetallic compounds such as M₂₃C₆, M₇C₃ and Co₂C. With the increase of laser power, the number of dendrites formed by intermetallic compounds increases, the microhardness of the coating increases, and the corrosion resistance first increases and then decreases. When the laser power reaches 2200 W, the coating obtains the highest microhardness and the optimum corrosion resistance, the corrosion potential is 0.631 V, which is about 2.66 times that of the substrate, and the corrosion current density is 0.319 μA/cm². So it is found that the laser power is a significant factor affecting the microstructure and corrosion resistance of FeCoNiCrMo high entropy alloy/GO composite coating, and the increase of laser power promotes the growth of carbide precipitates in the coating, which is conducive to improving the hardness and corrosion resistance of the coating. However, excessive intermetallic compounds generated under high laser power increase the crack sensitivity of the coating, resulting in obvious cracks in the coating, and reducing the corrosion resistance of the coating.

Failure analysis on spindle bearing of numerical control machine tool

Li Tianfu, Qu Shen, Dong Chen, Zhang Zhefeng

2022, 47(4): 258-262. doi:10.13251/j.issn.0254-6051.2022.04.044

Abstract ( 66 )

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A spindle bearing of a numerical control machine tool appeared abnormal vibration after running for 613 h, and obvious damage marks were found on the surface of some steel balls of the failure bearing. Those damage marks were studied by means of macro and micro observation, chemical composition analysis, energy spectrum analysis. The results show that metal foreign particles enter the bearing raceway, resulting in adhesive wear occur between foreign matters and steel balls and form a “white layer” on the surface of the steel ball. Along with the adhesive wear effect aggravates, contact fatigue cracks generate inside the “white layer”, and the fatigue cracks propagation causes spalling of the steel ball surface, forms a peeling pit, causing the bearing failure. The hardness difference of each part of the failure bearing exceeds the standard, which accelerates the failure of bearing. Therefore, it is suggested that a dust cover or sealing ring should be added to the bearing, the cleanliness of lubricating grease should be improved to avoid the failure caused by metal foreign particles entered the bearing and the quality control of bearing materials should be strengthened in actual production.

Formation mechanism of quenching cracks in branch-shaped structure of steering knuckle forgings

Yang Jie, Wang Xi, Zhou Jie, Wu Jianxiang, Qu Zhiyuan, Dai Heping, Peng Haijun

2022, 47(4): 263-267. doi:10.13251/j.issn.0254-6051.2022.04.045

Abstract ( 55 )

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Cause of quenching cracks of the 42CrMo steering knuckle forging was studied by analyzing microstructure of the the forging shape and crack area, and combined with the numerical simulation of the quenching and forging stages. The results show that the shape of the steering knuckle is complex, and the cross-section changes drastically, so it is easy to produce stress concentration during quenching at the connection between the fork and the flange during quenching, and the fillet size at this place is within the dangerous size range, resulting in easier to form transverse cracks. In addition, the direction of the metal streamline is parallel to the length direction of the single branch, and there are inclusions along the direction of the metal streamline, resulting in low longitudinal mechanical properties and prone to longitudinal cracks.

Analysis of abnormal microstructure and properties of 18CrNiMo7-6 steel gear

Zhang Ning, Gao Xing, Wang Zhilin, Jiang Bo, Liu Yazheng

2022, 47(4): 268-273. doi:10.13251/j.issn.0254-6051.2022.04.046

Abstract ( 78 )

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18CrNiMo7-6 steel gear was difficult to machine in the root of the gear during the milling process because of its abnormal microstructure and properties. The reasons for abnormal micro structure and properties of 18CrNiMo7-6 steel gear were analyzed by metallographic microscope (OM), field emission scanning electron microscope (FESEM) and EPMA electron probe. The results show that the difficult-machining of the gear can be attributed to the formation of bainite in the root of the gear that results in excessive hardness. The EPMA electron probe verify that the appearance of bainite at tooth root is related to chemical composition segregation. The JMatPro calculation results show that the increase of C and alloying elements expand the temperature range of bainite transformation and reduces the critical rate of that. The bainite structure is formed at a low cooling rate. The influence of Cr and Mn elements on bainite transformation is the most significant factor. When the content of C, Cr and Mn is increased by about 50%, the critical cooling rate of bainite transformation decrease from 0.1 ℃/s to 0.02 ℃/s, and the bainite transformation temperature range at 0.1 ℃/s is expanded to 49 ℃.

Quenching test of water-soluble quenchant KR9180 for spring rod

Liu Hui

2022, 47(4): 274-278. doi:10.13251/j.issn.0254-6051.2022.04.047

Abstract ( 51 )

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Characteristics of water-soluble PVP polymer quenchant KR9180 was introduced, and the quenching teston spring rod by using KR9180 with 15% concentration was conducted. The results show that the hardness, metallographic structure and fatigue properties of spring rod can meet the technical requirements if the oil quenching is replaced by 15% KR9180 water-soluble quenchant.

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