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  • MATERIALS RESEARCH
    Austenite grain distribution law in 34CrNi3MoV steel
    Zheng Bing, Xu Dong, Wang Yiqun, Wang Xuexi, Zhao Hongyang, Ju Dongying
    2023, 48(7):  1-7.  doi:10.13251/j.issn.0254-6051.2023.07.001
    Abstract ( 102 )   PDF (2733KB) ( 118 )  
    Effects of different holding temperature and holding time on austenite grain growth of 34CrNi3MoV steel were studied. The effects of holding temperature and holding time on average grain size, major axis and minor axis were analyzed by means of metallography. The results show that in the Gaussian distribution equation, the standard deviation and expectation increase with the increase of holding temperature and holding time. The size of the major axis and minor axis of grains is closely related to the average size, and the ratio has a simple linear relationship. During the grain growth, the ratio of the major axis to the minor axis basically remains unchanged. The distribution probability expressions of average grain size, major axis size and minor axis size are obtained by regression. At the same time,a new way of thinking and possible explanation for the heredity in materials science in terms of mathematical laws is provided.
    Effect of primary recrystallization annealing temperature on microstructure and texture of low temperature Hi-B steel
    Liu Lei, Guo Feihu, Shi Pengzhao, Qiao Jialong, Qiu Shengtao
    2023, 48(7):  8-14.  doi:10.13251/j.issn.0254-6051.2023.07.002
    Abstract ( 59 )   PDF (6017KB) ( 51 )  
    Effect of annealing temperature of primary recrystallization on the microstructure, texture and grain boundary characteristics of low-temperature Hi-B steel was studied by means of metallographic microscope, X-ray diffractometer and EBSD. The results show that the annealing temperature of the primary recrystallization directly affects the microstructure uniformity and the average grain size of the low-temperature Hi-B steel. With the increase of annealing temperature, the average grain size of the primary recrystallization structure increases from 15.2 μm to 26.7 μm, the primary recrystallization microstructure has the best uniformity after annealing at 820 ℃. The main texture types of primary recrystallization are: γ texture, α texture, {001}<120> texture and {114}<481> texture. When the annealing temperature rises to 880 ℃, the texture strength of {001}<120> increases obviously. With the increase of annealing temperature, the number of Goss grains decreases, area fraction of {114}<481> first decreases and then increases, while area fraction of {111}<112> begins to decrease after the annealing temperature rises to 840 ℃. When the annealing temperature is 800 ℃, the proportion of misorientation 20°-45° angle between {110}<001> grains and adjacent grains is the highest, which is 89.2%. The distribution of CSL grain boundaries around {110}<001> grains varies at different annealing temperatures.
    Isothermal microstructure and strength and toughness of 20Si2Mn2CrNi steel below Ms
    Wu Zhongchao, Zhou Yongjun, Duan Baoyu, Hou Yuan, Hu Yunfei, Gao Zhanyong
    2023, 48(7):  15-21.  doi:10.13251/j.issn.0254-6051.2023.07.003
    Abstract ( 44 )   PDF (6483KB) ( 28 )  
    Phase transformation kinetics of a low carbon low alloy B/M dual-phase high-strength 20Si2Mn2CrNi steel during isothermal quenching around 386 ℃ was studied using thermal expansion method. The volume fraction of martensite below the Ms point during isothermal quenching was qualitatively calculated using the K-M model, and the influence of microstructural transformation under different isothermal quenching processes on the mechanical properties was investigated. The results show that the experiment steel transforms to upper bainite when it is isothermally quenched above 386 ℃, while forming not only martensite but also low-temperature bainite with the same kinematics as bainite transformation from austenite above 386 ℃ when it is isothermally quenched below 386 ℃. When the experimental steel is isothermally quenched at 300 ℃, the volume fraction of martensite is 91.74%, the hardness is 41.7 HRC, and the impact absorbed energy is 91.7 J, showing good comprehensive mechanical properties of strength and plasticity due to the well-coordinated deformation between bainite and martensite microstructure.
    Analysis of continuous cooling transformation products of WB36CN1 steel
    Zhao Qian, Qiao Zhixia, Dong Ji, Zhang Yaran, He Biao, Qian Kuo
    2023, 48(7):  22-25.  doi:10.13251/j.issn.0254-6051.2023.07.004
    Abstract ( 36 )   PDF (2369KB) ( 26 )  
    Continuous cooling transformation products of WB36CN1 steel at the cooling rate of 50 ℃/s were investigated by using Gleeble thermal simulation testing machine. The results show that after continuous cooling from 900 ℃ to room temerature, the matrix of WB36CN1 steel includes a small amount of acicular ferrite, bainite ferrite, martensite, massive ferrite and membranous retained austenite distributed at the martensite lath boundary, and the precipitates include rod-like cementite (θ-carbide) and spherical NbC particles which are completely coherent with the matrix.
    Effect of elevated-temperature aging on creep-fatigue crack growth behavior of G115 steel
    Zhao Xin, Chen Zhengzong, Tang Zhengxin
    2023, 48(7):  26-31.  doi:10.13251/j.issn.0254-6051.2023.07.005
    Abstract ( 34 )   PDF (4201KB) ( 49 )  
    Creep-fatigue crack growth behavior of G115 steel aged at 650 ℃ for 1000, 2000 and 3000 h was investigated under the condition of holding time 600 s and initial stress intensity factor 23 MPa·m0.5. The results reveal that the creep-fatigue crack growth rate da/dN increases with the aging time, causing the decrease of the crack propagation life. However, the change of aging time has no significant effect on crack propagation mechanism, which is a transgranular dominant mixed fracture mode with a large number of creep damage. The rapid nucleation and growth of Laves phase along the boundaries and the reduction of solid solution effect are the main reasons for the reduction of creep-fatigue crack growth life of G115 steel after aging.
    Microstructure and mechanical properties of heterostructured medium carbon dual-phase steel wire
    Liu Yilin, Chen Rugan, Jia Yuxin, Li Yusheng, Fan Wen, Zheng Xiaoteng
    2023, 48(7):  32-37.  doi:10.13251/j.issn.0254-6051.2023.07.006
    Abstract ( 30 )   PDF (3015KB) ( 42 )  
    Heterogeneous medium carbon duplex steel wire was prepared by cold drawing and subsequent annealing process based on the emerging heterogeneous materials concept. The microstructure and mechanical properties were studied by means of optical microscope, scanning electron microscope, hardness and tensile tests, and the relationship between microstructure and mechanical properties was investigated. The results show that cold drawing with large deformation combined with short-time intercritical annealing can effectively control the microstructure, which can promote martensite transformation and reduce ferrite recrystallization, and an ideal heterogeneous duplex structure of fine ferrite surrounded by a large amount of martensite was introduced. With the increase of cold drawing strain and annealing temperature, the volume fraction of martensite increases, the grain size of ferrite decreases, and the strength and hardness of the steel wire are significantly improved, which is equivalent to that of high carbon steel wire. The superior properties of the heterogeneous medium carbon duplex steel wire is come from ferrite grain refinement, a large number of dislocations generated in ferrite during martensitic transformation, and non-uniform deformation caused by mechanical incompatibility of heterostructure structures of martensite/ferrite.
    Carbide evolution and its effect on corrosion resistance of martensitic stainless steel during tempering
    Chen Jun, Zhang Qinyi, Deng Jinqiang, Yuan Shengfu, Zhou Hongfeng, Wu Dong
    2023, 48(7):  38-43.  doi:10.13251/j.issn.0254-6051.2023.07.007
    Abstract ( 43 )   PDF (2981KB) ( 36 )  
    Carbide evolution of 1.4116 martensitic stainless steel during tempering was studied by means of microstructure observation, energy spectrum analysis and hardness test, and the corrosion resistance after tempering at different temperatures was studied through salt spray corrosion test and electrochemical test. The results show that when the tempering temperature exceeds 500 ℃, a large number of Cr-rich carbides are precipitated, which is the main reason for the decrease of corrosion resistance. When tempering at 580 ℃, the self-corrosion potential is the lowest and the corrosion resistance is the worst, however, when the tempering temperature exceeds 600 ℃, the self-corrosion potential increases and the corrosion resistance is significantly improved. In actual production, the 1.4116 martensitic stainless steel should not be tempered at 500-600 ℃.
    Segregation behavior and homogenization treatment of Ni-Cr-Al based alloy ESR-CDS ingots
    Zhang Yawei, Liu Yuwei, Liang Yingkai, Zhang Ji
    2023, 48(7):  44-48.  doi:10.13251/j.issn.0254-6051.2023.07.008
    Abstract ( 33 )   PDF (4334KB) ( 39 )  
    Ni-Cr-Al based superalloy ingots were prepared by electroslag remelting (ESR) and directional solidification (CDS), and the elemental segregation behaviors of the alloy was observed and analyzed, and the homogenization treatment was studied accordingly. The results show that the microstructure of the Ni-Cr-Al based alloy ingots is uniform, with little difference in primary and secondary dendrite arm spacing. The average secondary dendrite spacing and the segregation coefficients of the main alloy elements Al, Cr, and Fe are smaller than those of traditional ESR ingots. The optimal homogenization treatment of the alloy is 1150 ℃×15 h, that makes the segregation coefficient of Al, Cr, Fe to 1.0 effectively, and the microstructure shows no dendrite morphology. The γ′ phase is smaller and well distributed, and especially the carbides on grain boundaries are dispersed in granular shape that are beneficial to the hot work plasticity during the following fogging process.
    Effect of trace Ni element addition on precipitation behavior and properties of Cu-Cr alloy
    Wu Fan, Gong Qinghua, Xie Weibin, Wu Yu, Chen Huiming, Wang Hang
    2023, 48(7):  49-53.  doi:10.13251/j.issn.0254-6051.2023.07.009
    Abstract ( 34 )   PDF (3199KB) ( 55 )  
    Cu-Cr and Cu-Cr-Ni alloys were prepared by vacuum melting in argon atmosphere, followed by solid solution at 950 ℃ for 1 h and aging at 450 ℃. The properties and microstructure of the two alloys were analyzed and characterized by means of Vickers hardness tester, DC digital resistance tester, metallographic microscope and transmission electron microscope (TEM). The results show that the hardness of the Cu-Cr-Ni alloy reaches the peak value of 124.6 HV0.5 after aging at 450 ℃ for 8 h, and the conductivity is 83.2%IACS, while the hardness of the Cu-Cr alloy reaches the peak value of 116.7 HV0.5 after aging at 450 ℃ for 1 h, which indicates that the addition of Ni increases the hardness of the Cu-Cr alloy and maintains a high conductivity. At the beginning of aging (1 h), bcc-Cr phase is observed in the Cu-Cr-Ni alloy, which indicates that the addition of Ni accelerates the precipitation rate of precipitates, and promotes the transformation of precipitates from fcc-Cr structure to bcc-Cr structure. In addition, the Cr precipitates of the Cu-Cr-Ni alloy still maintain a semi-coherent relationship with the matrix after aging for 12 h.
    Effect of aging treatment on phase transformation thermal stability of Ni-Ti-Hf-Nb high temperature shape memory alloy
    Zhao Guojian, Li Haoyuan, Yang Jie, Xu Ruiyao, Huang Xingmin, Jin Mingjiang
    2023, 48(7):  54-60.  doi:10.13251/j.issn.0254-6051.2023.07.010
    Abstract ( 24 )   PDF (3250KB) ( 53 )  
    Effect of aging treatment on martensitic phase transformation behavior and thermal cycling stability of (Ni50Ti35Hf15)90Nb10 high temperature shape memory alloy were investigated by combining differential scanning calorimetry, microhardness, and energy spectrum analysis. The results show that during aging treatment at 450 ℃, both the austenite phase transformation peak temperature (Ap) and martensite phase transformation peak temperature (Mp) of the experimental alloy increase first and then decrease with the extension of aging time. During aging treatment at 550 ℃ and 650 ℃, as the aging time increases, both the Ap and Mp gradually decrease. The phase transformation temperatures decrease more significantly during aging at 650 ℃ compared to aging at 550 ℃. The specimen aged at 550 ℃ for 1 h exhibits the best thermal cycling stability, with ΔAp and ΔMp of 1.5 ℃ and 5.8 ℃, respectively, after 10 thermal cycles.
    Transformation law of super-cooled austenite and phase transformation model of X80 pipeline steel
    Tan Huijie, Bao Xiaoguang, Wu Zhongwang, Wang Haiyan
    2023, 48(7):  61-65.  doi:10.13251/j.issn.0254-6051.2023.07.011
    Abstract ( 32 )   PDF (2762KB) ( 47 )  
    Phase transformation law of super-cooled austenite in X80 pipeline steel was studied by means of L78RITA dilatometer, and continuous cooling transformation curves of the tested steel were plotted combining with metallographic hardness method. The results show that with the increase of cooling rate, ferrite transformation, bainite transformation and martensite transformation occur in the super-cooled austenite of the X80 pipeline steel, respectively. When the cooling rate is less than 3 ℃/s, the microstructure is ferrite and bainite. When the cooling rate is 3-20 ℃/s, only bainite is found in the microstructure. When the cooling rate is higher than 40 ℃/s, martensite begins to appear, and with the further increase of the cooling rate, the content of martensite gradually increases, while the bainite gradually decreases and disappears. The hardness of the tested steel increases gradually with the increase of the cooling rate. Based on the CCT curves, the relationship model of phase transformation temperature-cooling rate is established, phase transformation model with high fit degree is gained by regression calculation, and the calculated value and test value are nearly similar that proves the feasibility of the phase transition model.
    Thermal conductivity and tempering stability of a novel Cr-Mo-V hot stamping die steel
    Li Shuang, Wang Zhen, Fu Junwei, Xia Mingmei, Hua Yingli, Zhang Zheng
    2023, 48(7):  66-72.  doi:10.13251/j.issn.0254-6051.2023.07.012
    Abstract ( 26 )   PDF (2557KB) ( 22 )  
    Thermal conductivity and tempering stability of a new Cr-Mo-V alloyed hot stamping die steel (GYCM) were studied and compared with H13 steel by means of laser thermal conductivity instrument, scanning electron microscope and transmission electron microscope. The results show that after austenitizing at 1030 ℃ for 30 min and oil quenching, the hardness of both the GYCM steel double tempered at 600 ℃ for 2 h and the H13 steel double tempered at 580 ℃ for 2 h are about 50 HRC. Under the same test conditions and with the same hardness, the thermal conductivity of GYCM steel and the H13 steel varies with temperature in different trends. With increase of temperature, the thermal conductivity of GYCM steel decreases, while that of the H13 steel increases. The thermal conductivity of GYCM steel is 20.42%-36.63% higher than that of the H13 steel in the temperature range of 100-500 ℃. When tempered at 600 ℃ and 650 ℃, a large number of size-stable nanoscale Mo and V carbides are precipitated from the GYCM steel,the coarsening degree is lower at higher temperature and for longer time, which effectively reduces the softening degree of tempered martensite. Therefore, the GYCM steel has higher tempering stability than the H13 steel.
    Effect of MnS inclusion morphology on elongation of Ti-microalloyed steel after cold rolling and continuous annealing processing
    Huang Weili, Li Hongbin, Wang Xingjuan, Chen Liansheng, Tian Yaqiang, Niu Yuewei, Chen Siping
    2023, 48(7):  73-78.  doi:10.13251/j.issn.0254-6051.2023.07.013
    Abstract ( 24 )   PDF (3237KB) ( 33 )  
    Taking Ti-microalloyed steel as the research object, the evolution behavior of MnS inclusions during the cold rolling process was analyzed by using OM, SEM, etc. Subsequently, the specimens with different deformation amounts were annealed, and their tensile properties and hardness were tested to analyze the influence of MnS inclusion morphology on fracture behavior. The results show that with the increase of cold rolling deformation, the maximum length of MnS inclusions increases, and at the same time, the morphology of MnS inclusions changes from banded to intermittent short linear or granular. With the increase of cold rolling reduction, the elongation of the specimen gradually deteriorates, mainly due to the increase in the interface area of the loading direction caused by granular MnS inclusions, which promotes the initiation of interface cracks.
    PROCESS RESEARCH
    Effect of tempering temperature on microstructure and mechanical properties of N63 steel
    Han Shun, Li Gang, Yang Hao, Li Xinyang, Li Yong, Wang Chunxu
    2023, 48(7):  79-83.  doi:10.13251/j.issn.0254-6051.2023.07.014
    Abstract ( 36 )   PDF (3084KB) ( 44 )  
    Effect of tempering temperature on mechanical properties and microstructure of the N63 steel was studied by means of scanning electron microscopy, transmission electron microscopy and so on. The results show that the N63 steel hardly generates reverse austenite after tempering, and has good tempering resistance. The main precipitated phase of the N63 steel after low tempering at 260-600 ℃ is ε-carbide. When the tempering temperature rises to around 480 ℃, M2C carbide is precipitated from the matrix, and the tensile strength and yield strength reach the peak value of 1483 MPa and 1138 MPa, respectively. Then, the strength decreases rapidly with the increase of tempering temperature. The precipitated phase consists of cementite and M23C6 at 600 ℃, and the decomposition of martensitic matrix laths of N63 steel is serious whose tensile strength drop to only 1009 MPa. The impact absorbed energy decreases first, then increases and then decreases with the tempering temperature, which reaches the lowest value of 79 J when tempering at 420 ℃. Based on the microstructure and mechanical properties at different tempering temperature, N63 steel has excellent matching of strength and toughness when tempered at 480 ℃.
    Heat treatment of high performance rolled steel balls for large ball mills
    Zhang Laichao, Jin Yunxue, Zhu Xuwei, Wang Bingsheng, Jia Boshan
    2023, 48(7):  84-90.  doi:10.13251/j.issn.0254-6051.2023.07.015
    Abstract ( 26 )   PDF (5197KB) ( 51 )  
    The influence of heating temperature, quenching temperature and tempering process on the microstructure and properties of B3 steel balls during the production process were studied, and the impact resistance test was carried out on the trial steel balls. The results show that at 980-1080 ℃ heating temperature, the quenched structure of the B3 steel is martensite+retained austenite, and when the heating temperature reaches 1080 ℃, the martensite structure size exceeds 20 μm, and the hardness and impact properties of the steel balls are reduced. Under the same heating conditions, as the quenching temperature increases, the content of retained austenite in the steel ball decreases, and the internal lamellar martensite of the steel ball gradually increases. For quenching temperature of 750-780 ℃, lamellar martensite + lath martensite mixture appears in the steel ball, and both the hardness and the impact properties are the best. After cooling and low-temperature tempering treatment, the microstructure of the steel ball is tempered martensite, with almost no hardness difference from the surface to the core, while the impact properties are substantially improved compared to that of the untempered. The most suitable heat treatment process for large diameter ?125 mm rolled steel balls is: heating temperature of 980-1030 ℃, quenching temperature of 750-780 ℃, after the surface of the steel ball cooled to 50 ℃ then low temperature tempering treatment. The surface of the steel ball is still in good condition after a 9 m high, 29 000 times ball drop test, which meets the requirements of large ball mills.
    Effect of deformation heat treatment on microstructure and properties of Cu-6Ni-3Ti alloy
    Jing Qingxiu, Wei Dandan, Wei Miao, Yang Xueqing, Xiao Xiangpeng, Hang Xiaodong
    2023, 48(7):  91-96.  doi:10.13251/j.issn.0254-6051.2023.07.016
    Abstract ( 20 )   PDF (2941KB) ( 66 )  
    Morphology and composition of Cu-6Ni-3Ti alloy were characterized by means of X-ray diffractometer(XRD), scanning electron microscope(SEM) and transmission electron microscope(TEM). The effect of deformation heat treatment on microstructure and properties of the alloy was studied. The results show that microstructure of the as-cast alloy is dendritic and mainly composes of α-Cu and CuNiTi phases. The hardness of the alloy decreases significantly after heat treatment. With the increase of cold deformation, the conductivity of the alloy increases significantly after aging, but the hardness of the alloy decreases greatly after peak hardness. After aging at 450 ℃ for 2 h with 90% deformation, the hardness and conductivity of the alloy are 203 HV0.5 and 52%IACS, respectively.
    Effect of solution-aging treatment on microstructure and damping properties of Mg-4Zn-0.3Zr alloy
    Zhu Jiaxin, Sun Youping, Xie Shangheng, Fang Dejun, Zhou Yong
    2023, 48(7):  97-102.  doi:10.13251/j.issn.0254-6051.2023.07.017
    Abstract ( 19 )   PDF (3274KB) ( 33 )  
    Effect of solution and aging treatment on microstructure and damping properties of Mg-4Zn-0.3Zr magnesium alloy was studied by means of optical microscope, scanning electron microscope, dynamic mechanical thermal analyzer and X-ray diffractor. The results show that grain size of the as-cast alloy is about 121 μm, the grain boundary is thick and distributed with MgZn, MgZn2 and Mg7Zn3 phases. After solution treatment, MgZn, MgZn2 and Mg7Zn3 phases on grain boundaries are basically dissolved into the matrix. After aging, a small amount of granular MgZn and MgZn2 phases are precipitated on grain boundaries. In the low strain amplitude region, the damping properties of the as-cast alloy is the best, however, in the high strain amplitude region, the damping properties of solution treated alloy is the best, moreover, the slope of the damping curves of the solution treated + aged alloy is the largest. The damping peaks of the alloys with three states in the low temperature region are the superposition of grain boundary damping peaks and dislocation damping peaks. The damping peaks in the high temperature region of the solution treated and solution treated + aged alloy are relaxation damping peaks.
    Effect of tempering parameters on microstructure and mechanical properties of G95Cr18 martensitic stainless steel
    Liu Yongbao, Zhou Lina, Liu Ming, Gao Xiang, Shi Dongdan
    2023, 48(7):  103-110.  doi:10.13251/j.issn.0254-6051.2023.07.018
    Abstract ( 20 )   PDF (5056KB) ( 31 )  
    Effect of tempering parameters on microstructure of the G95Cr18 steel was investigated by means of OM, SEM and XRD. In addition, the effects of different tempering temperatures and times on hardness, tensile properties and impact property were studied by using Vickers hardness tester, electronic universal testing machine and drop hammer impact testing machine. The results show that the retained austenite content of the G95Cr18 steel decreases gradually with the increase of tempering temperature. When the tempering temperature is 200 ℃, the decomposition amount of retained austenite is less than 3.6%, which is caused by the increase of thermal stability due to the carbon partitioning effect. When the tempering temperature is higher than 400 ℃, the retained austenite content can meet the requirement of<6%.The hardness of the G95Cr18 steel first decreases and then increases with the increase of tempering temperature, and the secondary hardening temperature is 400 ℃. With the tempering temperature increasing, the impact absorbed energy of the G95Cr18 steel increases first and then decreases. When the tempering temperature is 300 ℃, the impact absorbed energy reaches the maximum, which is 7.1 J. When the tempering temperature is lower than 300 ℃, increasing tempering times has little effect on the microstructure and strength and toughness of the G95Cr18 steel. When the tempering temperature reaches 500 ℃, the comprehensive properties of the G95Cr18 steel decreases with tempering times increasing.
    Influence of stress relieving annealing on surface residual stress,microstructure and properties of B10 colomony equal diameter tee
    Wang Junliang, Zhou Tiezhu, Fu Liguo, Yu Yan, Li Chunhui
    2023, 48(7):  111-116.  doi:10.13251/j.issn.0254-6051.2023.07.019
    Abstract ( 19 )   PDF (1897KB) ( 22 )  
    Vacuum stress relieving annealing of the B10 colomony equal diameter tee formed by internal high pressure was implemented at different temperatures and holding time. The evolution of mechanical properties and residual stress of the B10 colomony equal diameter tee during stress removal annealing was researched. The results show that the surface residual stress of the main pipe and branch pipe of equal diameter tee is compressive stress, and the surface residual stress of the transition position between the main pipe and branch pipe of equal diameter tee is tensile stress. On the premise of not damaging mechanical properties, stress removal annealing can obviously eliminate the surface residual stress of the B10 colomony equal diameter tee. In the range of orthogonal, axial and shear residual stresses of pipe fitting are basically eliminated after annealing at 300 ℃ for 1 h and cooling with the furnace.
    Effect of tempering temperature on microstructure and properties of 20Cr1Mo1VTiB bolt steel
    Gong Xueting, Zhao Jiqing, Yang Gang, Yang Bin
    2023, 48(7):  117-123.  doi:10.13251/j.issn.0254-6051.2023.07.020
    Abstract ( 27 )   PDF (5168KB) ( 33 )  
    Microstructure and mechanical properties of 20Cr1Mo1VTiB bolt steel at different tempering temperatures were studied by means of SEM, EBSD, TEM, tensile tester, impact tester and hardness tester. The results show that the width of lath bainite in the steel increases and the bainite transforms into polygonal ferrite gradually with the increase of tempering temperature. Meanwhile, the increasing tempering temperature also promotes the coarsening and morphology transformation of carbides precipitation. The VC on grain boundary grows, the acicular M3C grows into short rod-like and the tetragonal TiC grows and transforms into spherical. By testing the mechanical properties, it is recommended that the bolts should be tempered at 690 ℃×4 h and the nuts should be tempered at 720 ℃×4 h to obtain an ideal hardness matching.
    Manufacturing technology of cutter ring with gradient properties based on induction tempering
    Zhao Heming
    2023, 48(7):  124-130.  doi:10.13251/j.issn.0254-6051.2023.07.021
    Abstract ( 30 )   PDF (4273KB) ( 45 )  
    Induction heating method of local high temperature tempering was applied to cutter ring of H13E steel, and the influences of tempering temperature and induction tempering time on microstructure, hardness, impact absorbed energy and tensile strength were studied. The results show that the microstructure is tempered sorbite when tempered in the range of 580-680 ℃, and with increase of the tempering temperature, the amount of precipitated granular carbide increases, the hardness of cutter ring decreases gradually, while the impact absorbed energy increases gradually. With the increase of induction tempering time, the microstructure, hardness and impact absorbed energy of cutter ring change significantly at the beginning, and the properties tend to be stable when the tempering time is longer than 30 min. After induction tempering at 640 ℃ for 30 min, and then testing the hardness distribution of cutter ring section and microstructure at different positions, the feasibility of the method and process of cutter ring with gradient properties by induction tempering is proved.
    Effect of aging time on microstructure and properties of 7075-T6 aluminum alloy
    Tang Peng, Huang Jialiang, Liu Qiannan, Deng Songyun
    2023, 48(7):  131-137.  doi:10.13251/j.issn.0254-6051.2023.07.022
    Abstract ( 36 )   PDF (3419KB) ( 38 )  
    Effect of aging time on microstructure and properties of 7075-T6 aluminum alloy were systematically studied by means of hardness test, tensile test, conductivity test, metallography microscope, X-ray diffractometer and scanning electron microscope. The results show that the microstructure of the 7075-T6 aluminum alloy changes significantly with the extension of aging time. The grain size is refined from 88.76 μm of the original state(0 h) to 35.78 μm after aging for 18 h, and then coarsened to 67.88 μm after aging for 24 h. The hardness and conductivity of the 7075-T6 aluminum alloy increase with the extension of aging time, and the maximum values appear when aging for 4 h and 24 h, respectively. It can be seen from the microstructure evolution that the increase of aging time will reduce the G.P. zone and increase the η′(MgZn2) phase, while both the η′phase and the G.P. zone can inhibit the dislocation movement, and improve the strength and conductivity of the alloy. When the aging time is too long, the overaging occurs, the grains coarsen again, and the mechanical properties of the alloy are reduced.
    Effect of tempering process on microstructure and properties of Q125 high strength oil well pipe steel
    Xiong Xuegang, Chen Shu, Chen Shu, Lü Bing, Zhang Kaihua, Zhou Leilei, Zhou Wei
    2023, 48(7):  138-142.  doi:10.13251/j.issn.0254-6051.2023.07.023
    Abstract ( 26 )   PDF (2652KB) ( 31 )  
    Heat treatment test of Cr-Mo-V-microalloyed Q125 steel was carried out to study the effect of tempering temperature on its microstructure and properties. The results show that the Q125 steel exhibits good mechanical properties and low temperature impact properties after quenching at 920 ℃ and tempering at 600-615 ℃, which can meet the requirements of API 5CT standard. As the tempering temperature increases from 580 ℃ to 630 ℃, the yield strength and tensile strength decrease, the low-temperature impact absorbed energy increases. At the same time, the diffusion of carbon promoting by temperature increasing, results in that the phase boundary of tempered martensite shift outward gradually, and the lath martensite coarsens from 0.5 μm to 0.7 μm, the small island martensite gradually fuses into the lath martensite, the lath martensite boundary changes from zigzag to flat, the precipitates at the martensitic lath boundary gradually coarsen from 100 nm to 300 nm with the morphologies change from spherical to short rod, and the proportion of fine precipitates in the martensitic lath gradually decreases.
    Effect of pre-treatment on properties of 6082 aluminium alloy profiles
    Hu Wu, Wu Yanmei, Huang Xianzan, Huang Yanyi, Liao Bin
    2023, 48(7):  143-147.  doi:10.13251/j.issn.0254-6051.2023.07.024
    Abstract ( 33 )   PDF (2325KB) ( 61 )  
    Effect of pre-treatment, including pre-aging and pre-tensile deformation, on mechanical properties and conductivity of 6082 aluminium alloy after aging was investigated through analysis and comparison, and the effect mechanism of pre-treatment on conductivity and mechanical properties of the tested alloy after aging was elucidated. The results show that the recrystallization and grain growth are easy to be induced in the surface layers of profiles by the off-line solution treatment, and then when the solution treated specimens are stretched, the PLC(Portevin-Le Chatelier) phenomenon is observed in the stress-strain curve. The conductivity of the profiles decreases after pre-treatment(pre-deformation and pre-aging), increases before aging(placed for 6 h after pre-treatment), and then significantly increases after aging.
    Microstructure and properties of TC4 titanium alloy butt welding brazed joint with B-Ti57CuZrNi solder
    Wang Haojun, Hu Shengshuang, Xiao Jun, Zhang Ying, Zhang Yingyun, Gao Tingting, Ouyang Delai
    2023, 48(7):  148-151.  doi:10.13251/j.issn.0254-6051.2023.07.025
    Abstract ( 28 )   PDF (2215KB) ( 34 )  
    TC4 titanium alloy was brazed with B-Ti57CuZrNi solder. The wettability of B-Ti57CuZrNi solder on the surface of TC4 titanium alloy and the effect of brazing parameters on microstructure and mechanical properties of TC4 titanium alloy brazed joint were studied. The results show that the B-Ti57CuZrNi solder is well spread on surface of the TC4 titanium alloy, and effective metallurgical bonding is formed. With the increase of brazing temperature and holding time, the overall width of the brazing weld zone becomes wider, and the needle-like α phase transition growing to the center of the weld becomes more and longer. When the welding temperature is low and the holding time is short, there are large Cu-rich and Ni-rich white as-cast microstructure in the joint. When the brazing temperature is 930 ℃ and the holding time is 15 min, the tensile strength of the joint at room temperature is low, which easily occurs brittle fracture at the weld zone, while the elongation of the joint at room temperature is low when the holding time is lower than 30 min. High brazing temperature (>960 ℃) and long holding time (>45 min) are unfavorable to the tensile strength and elongation of the joint at 400 ℃. Considering the excellent tensile properties of brazed joints at room temperature and 400 ℃, the brazing temperature should be 950 ℃ and the holding time should be 30 min.
    Effect of solution time on microstructure and mechanical properties of 2219 aluminum alloy
    Wang Huimin, Li Yanguang, Wu Jingyi
    2023, 48(7):  152-156.  doi:10.13251/j.issn.0254-6051.2023.07.026
    Abstract ( 27 )   PDF (1711KB) ( 53 )  
    Effect of solution time on microstructure and mechanical properties of 2219 aluminum alloy was studied by means of mechanical properties testing, scanning electron microscope (SEM), differential scanning calorimetry (DSC) and XRD analysis. The results show that, when the solution time is less than 1.5 h at 535 ℃, the primary phases dissolve in matrix and improve the supersaturation of the matrix with the solution time increasing, which is conducive to the improvement of mechanical properties of the alloy. When the solution time exceeds 2 h, the Cu-rich phases undergo segregation and grow up, resulting in the decrease of mechanical properties, especially elongation of the alloy. Therefore, the suitable solution treatment time of the alloy is 1.5 h at 535 ℃. After peak aging at 175 ℃ for 18 h, the ultimate tensile strength, yield strength and elongation of the aluminum alloy are 393.5 MPa、305.9 MPa and 8.7%, respectively.
    Grain refinement and strength-toughness improvement process of 20Si2Mn2CrNi steel after forging
    Li Shiwen, Xiong Wei, Zhang Wenliang, Wang Chao, Gao Zhanyong
    2023, 48(7):  157-161.  doi:10.13251/j.issn.0254-6051.2023.07.027
    Abstract ( 32 )   PDF (3512KB) ( 30 )  
    Microstructure and mechanical properties of Si-Mn-Cr-Ni low alloy high strength steel under different heat treatment processes were studied. The results show that when normalized at 820 ℃, the microstructure of the tested steel is fine and evenly distributed, when followed by quenching at 920 ℃ and tempering at 280 ℃, the hardness of the steel is 43.9 HRC, the impact absorbed energy KV2 is 82.6 J, the tensile strength is 1513.35 MPa, the yield strength is 1221.92 MPa and the elongation is 14.65%. Moreover, the microstructure is tempered lath martensite with fine grain size of grade 8.3,which achieves the best strength-toughness matching and the best comprehensive mechanical properties.
    Practice and analysis of eliminating non-uniformity of cold rolled low carbon steel strip by U-shaped cooling process for hot rolling
    Meng Yuerui, Lu Maosen, Gao Jiang, Wu Peifeng, Zhou Bowen
    2023, 48(7):  162-165.  doi:10.13251/j.issn.0254-6051.2023.07.028
    Abstract ( 26 )   PDF (2008KB) ( 36 )  
    Through microstructure observation and mechanical properties test, the effect of U-shaped laminar cooling process on improve the uneven microstructure and properties of the head, tail and middle of the cold rolled SPCC steel strip produced by the conventional laminar cooling process was studied. The results show that when using the conventional laminar cooling process, the ferrite grain size and carbide morphology of the head, tail and middle of the hot rolled steel strip after coiling are different due to the difference of temperature drop rates, and then inherites to the microstructure after cold rolling and annealing, resulting in the uneven properties of the final product. When using the U-shaped laminar cooling method, the coiling temperature of the head and tail of the steel strip increases, which reduces the microstructure difference, and then the microstructure and properties uniformity of the head, tail and middle part of the steel strip after cold rolling and annealing are significantly improved.
    Hot stamping process and application performance of a 2 GPa hot forming steel with high toughness
    Chen Bo, Yin Shuchun, Liang Zhenwei, Liu Liping, Zhang Jiguo, Zhai Changyuan, Liu Tao
    2023, 48(7):  166-175.  doi:10.13251/j.issn.0254-6051.2023.07.029
    Abstract ( 30 )   PDF (3888KB) ( 37 )  
    Hot stamping process of a2 GPa hot forming steel with high toughness was studied, as well as its performances of spot welding, bending, tensile, anti-delayed fracture and coating anti-corrosion performance. The results show that the recommended process for the tested steel is heating at 910-930 ℃ for 240-300 s,with thepressure holding time of 7-15 s.Under this process,the tested steel has good application performances, as the spot welding, bending, tensile, anti-delayed fracture and coating anti-corrosion performances meet or exceed the requirements of relevant standards.
    Effect of cooling process after hot-rolling on microstructure and drawing property of wire rod for high strength welding wire
    Zhen Xianfeng, Li Yang, Wang Guangshun, Hou Jianwei, Zheng Tongliang
    2023, 48(7):  176-180.  doi:10.13251/j.issn.0254-6051.2023.07.030
    Abstract ( 20 )   PDF (3431KB) ( 51 )  
    Characteristics of continuous cooling and isothermal phase transformation of C-Si-Mn-Mo-Ti welding wire were studied by means of thermal dilatometer and salt bath furnace, respectively. The industrial trial production of wire rod was completed by using Stelmor delayed cooling process and on-line salt bath process on the wire rod production line of high speed rolling mill, and then the non-annealing drawing test was carried out. The results show that the formation of martensite and bainite cannot be avoided when the C-Si-Mn-Mo-Ti welding wire steel is continuously cooled in the rate range of 0.1-20 ℃/s, and the formed martensite and bainite are in block shape of the equivalent size to the ferrite grain. After salt bath treatment, the content of bainite and martensite increases, the bainite shows an incompletely grown granular morphology, the martensite size greatly reduces to only a few microns, and their distribution is uniform and dispersed. When the wire rods produced by Stelmor delayed cooling process, brittle fracture with cup-shaped fracture caused by a large number of massive martensite of block shape occurs frequently in the core of the wire rods during the non-annealing drawing test, while the wire rods produced by in-line salt bath process are not fractured during the non-annealing drawing test, which can be directly drawn to the finished wire without annealing.
    Heat treatment process of 15CrMoR steel for medium temperature pressure vessel
    Yang Xiong, Li Peng
    2023, 48(7):  181-186.  doi:10.13251/j.issn.0254-6051.2023.07.031
    Abstract ( 29 )   PDF (2957KB) ( 31 )  
    Mechanical properties, microstructure and fracture morphologies of 15CrMoR steel plate under different heat treatment processes were analyzed by means of optical microscope, scanning electron microscope, tensile tester and impact tester. The results show that the mechanical properties of the steel plate tempered at 680-700 ℃ are moderate and meet the requirements, and the microstructure is composed of ferrite+pearlite+small or very small amount of bainite. After simulated post-weld heat treatment process of holding at 680 ℃ for 3-9 h, the normal temperature and 300-450 ℃ high temperature mechanical properties of the 15CrMoR steel plate can meet the standards and user requirements.
    Effect of heat treatment process on microstructure and tensile properties of metastable β-type titanium alloy
    Yue Xu, Zhang Mingyu, Yang Jialuo, Tong Xiaole, Zhao Zibo, Qiao Enli, Zhang Qi, Ye Hongchuan
    2023, 48(7):  187-192.  doi:10.13251/j.issn.0254-6051.2023.07.032
    Abstract ( 27 )   PDF (2510KB) ( 26 )  
    A new type of Ti-Al-Mo-V-Cr-Fe metastable β-type titanium alloy was heat treated with different processes, and then the tensile properties at room temperature were tested. The microstructure and phase composition of the alloy under different heat treatment processes were analyzed by means of scanning electron microscopse (SEM) and X-ray diffractometer (XRD). The results show that when single annealing at 750 ℃ in the α + β two-phase temperature region, the alloy contains a large number of equiaxed α phases; when single annealing at 820 ℃ in the β single-phase temperature region, the microstructure is composed of coarse β grains. After single annealing, the alloy has low strength and high plasticity, and the quantity of dimples in the fracture morphologies is large. After double annealing at 750 ℃×1 h+540 ℃×8 h or 820 ℃×1 h+540 ℃×8 h, the secondary α phase is precipitated in a large number, the strength of the alloy increases significantly, but the plasticity is low, and obvious secondary cracks appear in the fracture morphologies.
    Effect of heat treatment on microstructure and hardness of GH4169 alloy
    Zan Bin, Wang Qi, Xu Ning, Wang Xu, Wu Dali
    2023, 48(7):  193-196.  doi:10.13251/j.issn.0254-6051.2023.07.033
    Abstract ( 38 )   PDF (4995KB) ( 39 )  
    Effects of different solid solution and aging processes on microstructure and hardness of GH169 alloy were studied. The results show that when the solution treatment temperature is in the range of 900-1000 ℃, the microstructure of the GH4169 alloy has no obvious change, and the hardness decreases slightly with the solution treatment temperature rising. When the solution temperature is above 1050 ℃, with the increase of solution temperature and time, the recrystallized grains grow rapidly and the hardness decreases significantly. After solution treated at 1100 ℃ for 45 min, the recrystallization is completed and the hardness is basically unchanged. The aging temperature and time have significant influence on the precipitation of strengthening phases in the GH4169 alloy, which is manifested as the significant difference in hardness. The hardness of the GH4169 alloy reaches the highest after aging at 720 ℃ for 16 h.
    Effects of cold rolling and annealing on microstructure and mechanical properties of pure nickel welded joints
    Zhao Hulin, Gou Zanghong
    2023, 48(7):  197-200.  doi:10.13251/j.issn.0254-6051.2023.07.034
    Abstract ( 27 )   PDF (1988KB) ( 14 )  
    Welded joints of pure nickel sheets were cold rolled and annealed between 800-1100 ℃. The effects of cold rolling and annealing processes on microstructure and mechanical properties of pure nickel sheets were studied. The results show that after cold rolling with 75% deformation, the grains of the welded joints are broken, and the microstructure is linear and fibrous along the rolling direction, the tensile strength is about 611 MPa and the elongation is about 5.6%. When annealed at 800 ℃, the microstructure is partially recrystallized, but there are still a large number of elongated linear fibers, the tensile strength is 387.9 MPa and the elongation is 20.4%. When annealed at 900 ℃ most of the linear fibers recrystallized, the tensile strength is 363.5 MPa and the elongation is 23.7%. When annealed at 1000 ℃, all the linear fibers disappeared, and the microstructure is completely recrystallized,the tensile strength is 357.5 MPa and the elongation is 32.3%. When annealed at 1100 ℃, the change of microstructure and mechanical properties are not obvious compared with annealed at 1000 ℃, the tensile strength is 355.3 MPa and the elongation is 30.9%. Compared with the mechanical properties and microstructure, 1000 ℃ is the best intermediate annealing temperature.
    Continuous cooling transformation and normalizing process of EH36-Z35 steel for offshore platform
    Xiao Hongliang, Zhang Huijie
    2023, 48(7):  201-204.  doi:10.13251/j.issn.0254-6051.2023.07.035
    Abstract ( 27 )   PDF (1851KB) ( 12 )  
    Continuous cooling transformation curves of EH36-Z35 steel for offshore platform were obtained by using thermal simulation testing machine, and the microstructure of the steel under different normalizing processes was studied by using optical microscope to find out the reason of normalizing underheated structure appeared in production and to optimize the normalizing process. The results show that the Ac3 of the EH36-Z35 steel is 859 ℃, and the high temperature transformation structure of ferrite+pearlite can be obtained under the cooling rate of <2 ℃/s. Under the same cooling process, underheated structure appears after normalizing at 820 ℃ and 850 ℃, while normal ferrite plus dispersed pearlite is obtained after normalizing at 890 ℃. Through changing the heating rate and cooling rate, the reasonable normalizing process of the EH36-Z35 steel is as taking 130 min to heat from room temperature to 890 ℃, holding for 10 min, cooling to 730 ℃ with a cooling rate of 5 ℃/s, then cooling to 650 ℃ with a cooling rate of 0.2 ℃/s, and then cooling to 400 ℃ with a cooling rate of 0.15 ℃/s, followed by air cooling.
    Effect of aging temperature on microstructure of AlSi7Mg alloy prepared by selective laser melting
    Liu Song
    2023, 48(7):  205-213.  doi:10.13251/j.issn.0254-6051.2023.07.036
    Abstract ( 28 )   PDF (8674KB) ( 23 )  
    Effect of aging temperature on microstructure of AlSi7Mg alloy formed by selective laser melting (SLM) was studied by means of scanning electron microscope (SEM), optical microscope (OM) and energy dispersive spectrometer (EDS). The results show that micro pinholes occure in the SLM formed AlSi7Mg alloy, as well as net-like microstructure in scanning direction and scale-like microstructure in building direction, meanwhile, punctiform and short rod-like eutectic Si is evenly distributed in Al matrix as particles. With the increase of aging temperature, the porosity increases, the net-like and scale-like microstructure gradually blur until disappeare, and even dendritic morphology appears, while the eutectic Si grows up, showing needle-like and bulk-like morphology. When the aging temperature is blow 300 ℃, the separated Si and Mg precipitate in the ultrafine-grained structure of the AlSi7Mg alloy, which form Mg2Si strengthening phase. When the aging temperature is higher than 300 ℃, the grain of the AlSi7Mg alloy refines, the reticular eutectic Si are destroyed and grouped and grown, which increases the cleavage effect on Al matrix.
    Effect of vacuum annealing on microstructure and properties of 1J50 soft magnetic alloy
    Cheng Huiming, Liu Yongmou, Ma Wanjun
    2023, 48(7):  214-216.  doi:10.13251/j.issn.0254-6051.2023.07.037
    Abstract ( 29 )   PDF (2066KB) ( 21 )  
    Effect of vacuum annealing process on microstructure and properties of the 1J50 soft magnetic alloy was studied. The results show that the magnetic properties of the 1J50 soft magnetic alloy can meet the technical requirements when the annealing temperature is 1120-1180 ℃, the holding time is 4-6 h and the rapid cooling temperature is 500-600 ℃. With the increase of annealing temperature, the permeability and saturation magnetic induction intensity of the alloy are relatively reduced. With the extension of annealing time, the permeability, maximum permeability and saturation magnetic induction intensity of the alloy are relatively increased, while the coercivity is relatively reduced, the grain size is gradually increased, and the static mechanical properties are basically unchanged. When the annealing temperature is 1160 ℃, holding for 6 h with the rapid cooling temperature at 550 ℃, the magnetic properties of the 1J50 soft magnetic alloy are good, the Hc of which is 4.81 A/m, Bs is 1.555 T, μ0.4 is 8.81 mH/m, and μm is 91.60 mH/m.
    Effect of electromagnetic stirring on Sr modified aluminum matrix composites for sports equipment
    Ji Wangqin, Wang Xiaobing, Zhou Yakun, Zhao Yin
    2023, 48(7):  217-222.  doi:10.13251/j.issn.0254-6051.2023.07.038
    Abstract ( 17 )   PDF (3124KB) ( 23 )  
    Sr modified Al3Ti/ADC12 aluminum matrix composites were prepared by electromagnetic stirring with Al-K2TiF6 as reaction system and ADC12 aluminum alloy as matrix for sports equipment. The effects of preparation process and process parameters on microstructure and mechanical properties of aluminum matrix composites were studied. The results show that both electromagnetic stirring and Sr modification can refine the microstructure of the Al3Ti/ADC12 aluminum matrix composites. The α-Al phase is refined to globular crystal, and the size of Al3Ti is reduced to 10 μm, the agglomeration phenomenon of Al3Ti is improved. The fishbone-like AlFeMnSi phase disappears, and the eutectic Si is refined from long needle to short rod. As the stirring current increases, the size of α-Al phase is smaller, and the morphology is rounder. When the stirring current is 35 A, the size of α-Al phase is the smallest, the morphology is the roundest, the porosity is the smallest, and the tensile strength and elongation are the largest, which are increased by 24.1% and 22.1%, respectively, compared with ADC12 aluminum alloy matrix. Electromagnetic stirring and Sr modification play a role in dispersion strengthening and fine grain strengthening of aluminum matrix composites.
    OVERVIEW
    Research progress on preparation technology and coating of nano-powder by plasma spraying
    Chen Baisen, Meng Junsheng, Wang You, Shi Xiaoping
    2023, 48(7):  223-236.  doi:10.13251/j.issn.0254-6051.2023.07.039
    Abstract ( 28 )   PDF (3299KB) ( 138 )  
    In modern industry, plasma spraying technology has become an important method to improve the wear resistance and corrosion resistance of the surface of mechanical parts. As a spraying material, the nano-powder can effectively improve the wear resistance, corrosion resistance, oxidation resistance and other aspects of plasma spraying coating, which has research value in the application of surface protection of parts and components. It is of great significance for the energy conservation and environmental protection, and has become a research hot spot in the field of surface modification at home and abroad. Based on this, on the basis of a large number of literature, the preparation method of nano powder from three aspects as solid phase method, liquid phase method and gas phase method is introduced, research on the regranulation technology of nano-powder at home and abroad is summarized, the preparation methods of nano-powder feed, including spray drying, mechanical grinding and liquid phase precursor synthesis are described, and the preparation method of liquid phase precursor synthesis method is focused on. From the selection of nano-powder for plasma spraying to the preparation of coating, the application results of nano-coating in wear resistance, corrosion resistance, thermal barrier and self-lubrication are reviewed in detail, furthermore, the influence of plasma spraying parameters (spraying power, spraying distance, moving speed of spray gun, spraying gas parameters) on quality of the nano-coating is inductively analyzed. Finally, the problems and shortcomings in the preparation of plasma sprayed nano-powder feed are discussed, and the future research direction of plasma sprayed nano-coating is prospected.
    Research progress on laser surface melting treatment of magnesium alloys
    Zhang Xi, Wen Jinhao, Wu Bingbing, Xie Fang, Ma Xinbo, Kong Fanxiao
    2023, 48(7):  237-244.  doi:10.13251/j.issn.0254-6051.2023.07.040
    Abstract ( 24 )   PDF (3858KB) ( 58 )  
    Magnesium alloys are excellent lightweight material and potential implant material for human body. However, they are active and have poor corrosion resistance. The laser surface melting (LSM) technology can quickly form a melting layer with fine grains on the surface of magnesium alloy and change the surface microstructure and composition, and has an important influence on improving the corrosion resistance and biocompatibility. The recent studies on laser surface melting of the magnesium alloys are reviewed. The effect of laser surface melting on microstructure, composition, wettability, corrosion resistance and biocompatibility of the magnesium alloys is analyzed. The development directions of laser melting treatment on microstructure transformation, corrosion mechanism and mechanical behavior, degradation behavior and biocompatibility of the magnesium alloys are summarized and prospected.
    Research progress of Q&P steel for automobiles
    Gao Xueran, Chen Xiaohu, Yuan Siyu, Wang Xu
    2023, 48(7):  245-253.  doi:10.13251/j.issn.0254-6051.2023.07.041
    Abstract ( 31 )   PDF (3984KB) ( 24 )  
    Current research status of Q&P steel was introduced through four aspects: the production process of Q&P steel, the role of alloying elements, the thermodynamics and dynamics of C composition and the influence of process parameters, and the future research direction of Q&P steel was prospected. The microstructure of Q&P steel after quenching and partitioning process is martensite and retained austenite, the martensite provides high strength and the retained austenite produces a TRIP effect to enhance the plastic deformation ability with effect of stress and strain. The heart of the Q&P process is to get the maximum availability of stable retained austenite, which depends critically on the partitioning process of C, and the optimal quenching temperature can be predicted by thermodynamic theoretical model calculations. The addition of alloying elements can inhibit the precipitation of carbides, refine austenite grains and stabilize austenite. The process parameters have a great influence on the microstructure and mechanical properties of the Q&P steel, the quenching temperature determines the content of initial martensite and the subsequent partitioning process, and the partitioning temperature and partitioning time significantly affect the diffusion power of C atoms, so it is particularly important to select the appropriate process parameters.
    SURFACE ENGINEERING
    Effect of laser shock peening on microstructure and fatigue property of TA15 titanium alloy with double holes
    Han Peipei, Zang Xu, Dong Zhi, Li Shijian, Jiao Qingyang, Deng Xiguang
    2023, 48(7):  254-258.  doi:10.13251/j.issn.0254-6051.2023.07.042
    Abstract ( 22 )   PDF (2135KB) ( 16 )  
    TA15 titanium alloy were treated by laser shock peening (LSP) to study the effect of LSP on microstructure and fatigue property of the titanium alloy specimens with double holes. The results show that when the specimens are treated by LSP with laser energy of 25 J, circular spot diameter of ?4 mm and shock times of 2, a large number of high-density dislocations and dislocation walls are formed in the TA15 titanium alloy crystal, and introducing residual compressive stress of up to -500 MPa simultaneously on the material surface which can balance the tensile stress generated under fatigue load, effectively suppress fatigue crack initiation and slow down crack propagation rate. The LSP can obviously improve the fatigue life of the titanium alloy specimens with double holes, which is increased by 60%-89% compared to that of the untreated specimen. This is because the large residual compressive stress introduced by LSP greatly reduces the effective stress intensity factor at the crack tip. When the effective force intensity factor is less than the fracture toughness of the material, the fatigue crack growth will be suppressed or stopped, thus improving the fatigue life.
    Preparation of Al coatings by electro-explosive spray deposition
    Zhou Yi, Zhu Liang, Duan Jingbang, Zhang Aihua, Zhou Hui, Yan Weiliang
    2023, 48(7):  259-265.  doi:10.13251/j.issn.0254-6051.2023.07.043
    Abstract ( 25 )   PDF (3899KB) ( 51 )  
    A method for preparing Al coating by tape-loaded wire-confined electric explosion method was proposed. Polyethylene tape as a carrier was used to load Al wire and to send it automatically and continuously into the explosion cavity to explode and prepare Al coating, and then the Al coatings under different process parameters were investigated. The results show that when the initial charging voltage of energy storage capacitor is 9.375 kV and the deposition distance is 26 mm, the surface of the coating is dense and uniform, and the deposition efficiency is relatively high (about 51%), the surface roughness Ra of the coating is reduced from 2.51 μm to 1.29 μm, the maximum hardness of the layer is 116.8 HV and the thickness is about 200 μm. The coating and the substrate are typical metallurgical bonding. By the bending test carries out according to the national standard GB/T 5270—2005 “Metallic coatings on metallic substrates—Electrodeposited and chemically deposited coatings-Review of methods available for testing adhesion”, the result shows that there is no tearing, peeling or debonding between the coating and the substrate, which indicates a good adhesion strength between the coating and the substrate. It is concluded that the preparation of Al coating can be successfully realized by the method of restrained electric explosion with carrier wire.
    Laser quenching process optimization and microstructure and properties of H13 steel
    Ma Xin, Shi Qiang, Chen Yanzhong, Li Qiang, Zhang Yueting, Zhao Long
    2023, 48(7):  266-270.  doi:10.13251/j.issn.0254-6051.2023.07.044
    Abstract ( 26 )   PDF (2574KB) ( 49 )  
    Surface of H13 steel was strengthened by laser quenching, and the quenching process was optimized by range analysis of orthogonal test. The microhardness and friction and wear properties of the specimen under the optimum process parameters were studied, and the phase composition and microstructure of the laser quenching surface were analyzed. The results show that the optimum laser quenching process parameters are laser power of 600 W, scanning speed of 6 mm/s and lapping rate of 20%. Under this optimum process, the average hardness of hardened layer of the H13 steel is 774 HV0.1, which is about 3 times than that of the matrix, the depth of the hardened layer is 0.87 mm, and the friction coefficient and wear amount are about 0.367 and 0.0015 g, which are 50% and 60.5% lower than those of the matrix, respectively. The hardened layer is mainly composed of lath and acicular mixed martensite, retained austenite and a small amount of cementite.
    Effect of heat treatment on hardness and wear resistance of laser clad Co-based alloy coating
    Yang Dongjie, Bai Qiaofeng, Ouyang Changyao, Wang Rui, Wei Runze
    2023, 48(7):  271-276.  doi:10.13251/j.issn.0254-6051.2023.07.045
    Abstract ( 22 )   PDF (3881KB) ( 77 )  
    Co-based alloy coating was prepared on the surface of ductile iron by laser cladding technology. Microstructure of the specimens under different heat treatment processes was analyzed and the effects of different processes on the hardness and wear resistance of the cobalt-based alloy coating were discussed. Compared with untreated specimens, the hardness of heat-treated specimens is improved. The hardness changes of the specimens treated at 950 ℃ for 1 h and 2 h, respectively, are similar, which are 51.35 HRC and 51.15 HRC, and that subsequent aged at 825 ℃ are 52.50 HRC and 52.08 HRC. The wear amount of the untreated specimen is the highest and the wear resistance is the worst. The wear loss of the specimen treated by 950 ℃×1 h + 825 ℃×24 h reduces by 5.3%, and that of the treated by 950 ℃×3 h+825 ℃×24 h reduces by 12.8%, which shows better wear resistance.
    TEST AND ANALYSIS
    Cause analysis and control of surface cracking of 37Mn5 steel thick-walled oil casing
    Ren Zhilan, Tang Minghua, Bi Hongxia, Wu Yuanzhi, Zhou Yong
    2023, 48(7):  277-282.  doi:10.13251/j.issn.0254-6051.2023.07.046
    Abstract ( 23 )   PDF (2080KB) ( 38 )  
    Surface cracks were found on 37Mn5 steel thick-walled oil casing after quenching and high-temperature treatment, the analysis of cracking causes and research of process improvement were carried out by means of SEM, EDS and TEM. The results show that the cracks on the surface of the 37Mn5 steel oil casing are because of multiple factors coupling such as non-metallic inclusions in the steel, quenching stress concentration and high-temperature tempering brittleness, inclusions induce micro-cracking during the rolling process, the micro-crack is further expansion and extension under the action of quenching internal stress, coupled with the high temperature tempering brittleness reduces the toughness of the material, eventually a certain depth of macro cracks are formed on the surface of the pipe. By using improved sub-temperature quenching process treatment, the impact toughness of the 37Mn5 steel oil casing is significantly improved and the resistance to fracture failure on the premise basically not reduce the strength of material, inhibits high-temperature temper brittleness, basically eliminating the surface cracking phenomenon, and achieving good production application results.
    Strengthening and toughening mechanism of railway locomotive wheel
    Jia Tuosheng, Liu Cuirong, Zhang Xiaofeng, Wei Huacheng, Zhang Lei, Gao Kang
    2023, 48(7):  283-286.  doi:10.13251/j.issn.0254-6051.2023.07.047
    Abstract ( 28 )   PDF (2427KB) ( 42 )  
    Effect of minor added alloying elements on improving the strength and hardness of railway wheel steel was studied by means of mechanical properties test and inclusions and microstructure analysis. The results show that the strength and hardness of the tested steel are high, but the impact property is poor, which cannot meet the standard requirements. The addition of alloying elements causes the formation of a large number of composite inclusions in the steel, which has an adverse effect on the toughness of the wheel. In addition, a small amount of abnormal microstructure in the wheel caused by the segregation of the microalloying elements may also have an adverse effect on the toughness of the wheel.
    Cracking failure analysis on high-speed intermediate shaft gear
    Chen Shengchao, Chen Yesheng, Rong Zeyu, Wang Hongwei, Xu Hongxiang, Zhao Shaofu, Guo Jingqiang
    2023, 48(7):  287-291.  doi:10.13251/j.issn.0254-6051.2023.07.048
    Abstract ( 38 )   PDF (3021KB) ( 62 )  
    A 18CrNiMo7-6 steel high speed intermediate shaft gear of gearbox had abnormal vibration sound during the dynamic balance test after carburizing and quenching. After disassembly, it was found that the intermediate shaft gear had obvious axial crack at the axial diameter. After macro observation and multiple cutting, it was found that the crack source was located at the axle center of the large gear. The crack location of the main shaft was studied by chemical composition analysis and microstructure analysis. The results show that due to the incomplete dehydrogenation treatment of the large billet forgings, the hydrogen atoms gather to form hydrogen molecules over time, which causes the stress concentration inside the workpiece, leading to the delayed hydrogen embrittlement cracking of the gear shaft after carburizing and quenching, and resulting in the failure of the shaft gear.
    EQUIPMENT
    Contact type customized strength selective cooling equipment for ultra-high strength steel
    Chen Jiaheng, Li Xianjun, Luo Ping
    2023, 48(7):  292-296.  doi:10.13251/j.issn.0254-6051.2023.07.049
    Abstract ( 20 )   PDF (1922KB) ( 61 )  
    In response to the problems of wide transition zone width and unclear cooling boundary in the workpiece treated by the existing jet type customized strength heat treatment selective cooling equipment, a contact type customized strength heat treatment selective cooling equipment has been developed through a series of experimental verification and structural optimization design. The results show that the equipment can significantly reduce the width of the transition zone (30 mm→10 mm) by conducting heat transfer through contact between the insert and the plate, with clear cooling boundaries, and can better meet the needs of special soft areas.