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  • MICROSTRUCTURE AND PROPERTIES
    Effect of homogenization treatment on microstructure of Mg-9.8Gd-3.5Y-2Zn-0.5Zr alloy
    Huang Yuanchun, Wang Zhou, Ma Shangkun
    2022, 47(10):  1-9.  doi:10.13251/j.issn.0254-6051.2022.10.001
    Abstract ( 71 )   PDF (658KB) ( 56 )  
    Microstructure evolution of Mg-9.8Gd-3.5Y-2Zn-0.5Zr alloy ingot after homogenization treatment at 505-535 ℃ for 0-84 h was studied by means of DSC, SEM, EDS and OM. The results show that the as-cast microstructure is dendrite, and the content of the second phase is 19.86%. The intergranular second phase mainly consists of white spot-like eutectic phase and massive LPSO phase, and the intragranular second phase consists of a small amount of needle-like LPSO phase, petal-like Zr cluster phase and square rare-earth rich phase. The morphology of LPSO phase after homogenization treatment is intergranular block and intragranular lamellar. The content of intragranular lamellar LPSO phase is affected by homogenization temperature and time. At 505-525 ℃, the growth rate of intragranular lamellar LPSO phase increases with the increase of homogenization temperature. The intragranular lamellar LPSO phase precipitates along the grain boundary into the matrix with the extension of holding time at the same temperature and begins to coarse after penetrating the grain. At 535 ℃, the intergranular massive LPSO phase transforms into W phase, and the intragranular lamellar LPSO phase dissolves into matrix. The intergranular LPSO phase plays a role of pinning relative to grain boundary migration. Homogenized at 505-525 ℃, with the extension of holding time, grain growth is not obvious. Homogenized at 535 ℃, the intergranular LPSO phase dissolved in large quantities and the grains begin to grow rapidly.
    Effect of heat treatment on microstructure and mechanical properties of GH4169 alloy prepared by 3D printing
    Sun Bingbing, Jiang Tao, Lei Yang, Chen Bingqing, Zeng Tianyi, Wang Wei
    2022, 47(10):  10-14.  doi:10.13251/j.issn.0254-6051.2022.10.002
    Abstract ( 72 )   PDF (582KB) ( 39 )  
    The plate-like GH4169 alloy was prepared by 3D printing using selective laser melting (SLM), and was heat treated. The microstructure and mechanical properties of the alloy before and after heat treatment were studied by three-dimensional atom probe (3DAP) and scanning electron microscopy (SEM) with in-situ tensile techniques. The results show that both the molten pool and the grain inside of the as-printed GH4169 alloy are solidification dendrites, with a homogeneous distribution of alloying elements.After heat treatment,there are a large number of fine γ″ and γ′ precipitates formed in the matrix. The tensile test results show that after heat treatment, the 3D printed GH4169 alloy has better mechanical properties, which is attributed to the disappearance of dendrite structure and harmful δ phase reduction and a large number of nanosized γ″ and γ′ precipitates in matrix.
    Isothermal aging precipitation behavior of maraging steel
    Fang Huiliang, Hu Zhiyu, Lü Meng, Wu Jian, Zhai Tingting, Xue Chunjiang, Wang Haiyan
    2022, 47(10):  15-18.  doi:10.13251/j.issn.0254-6051.2022.10.003
    Abstract ( 63 )   PDF (579KB) ( 26 )  
    A maraging steel was solution treated at 900 ℃ and then isothermal aged at 500 ℃. The change of microstructure, precipitates and hardness of the tested steel during aging was characterized by means of optical microscope, scanning electron microscope and Vickers hardness tester. On this basis, the effect of aging process on hardening behavior of the tested steel was analyzed. The results show that the hardness of the tested steel increases obviously in the early stage of aging, and reaches the peak value of 585 HV30 when aging for 12 h. With the aging time further extended, the tested steel enters the over-aging state, and the hardness begins to decline slowly. The tested steel matrix is composed of lath martensite and retuined austenite, and the second phase particles are distributed in the matrix. When aging for 0.5 h, the precipitate size is about 5-10 nm; and when aging for 12 h, the precipitate grows slowly to 20-25 nm.
    Effect of tempering temperature on microstructure and properties of V-N microalloyed cast steel
    Wang Xiaodong, Chen Yunbo, Zuo Lingli, Mao Feng, Zhang Cheng, Chen Chong, Wang Shu, Cui Hailin
    2022, 47(10):  19-23.  doi:10.13251/j.issn.0254-6051.2022.10.004
    Abstract ( 66 )   PDF (579KB) ( 33 )  
    Two microalloyed cast steels with different V contents were prepared in a vacuum melting furnace and heat treated by normalizing, quenching and tempering at different temperatures. Effect of tempering temperature on microstructure and properties of the two tested steels with different V contents was studied. The results show that the effect of V content promotes the carbonitride precipitates and reduces the solid solubility of C and N elements in the martensite, resulting in the improvement of impact absorbed energy. When tempering temperature is below 400 ℃, the dominant strengthening mechanism is solution strengthening. When tempering temperature is above 400 ℃, the dominant strengthening mechanism is precipitation hardening. The increase of V content also promotes the carbonitride precipitates shape translating from short rod to granular, and the brittleness of high temperature tempering is improved.
    Effect of thermo-mechanical heat treatment on microstructure and properties of Cu-Ti-Fe-Sn alloy
    Jing Qingxiu, Sun Yuqing, Xiao Xiangpeng, Wei Miao, Peng Yong, Huang Xiaodong
    2022, 47(10):  24-30.  doi:10.13251/j.issn.0254-6051.2022.10.005
    Abstract ( 52 )   PDF (583KB) ( 31 )  
    Cu-3Ti-0.2Fe-1Sn alloy was prepared by the vacuum melting method. The alloy was treated by homogenization annealing, solution treatment, cold rolling(deformation of 40%, 60% and 80%, respectively) and aging at 450 ℃. The effect of thermo-mechanical on microstructure, conductivity and hardness of the alloy were investigated. The results show that microstructure of the as-cast Cu-3Ti-0.2Fe-1Sn alloy prepared by vacuum melting contains a large amount of dendritic microstructure, and grain growth occurs in the microstructure after solution treatment. The hardness and conductivity of the as-cast alloy are 178.1 HV and 10.85%IACS, respectively. After solution treatment, the hardness and conductivity of the alloy are reduced to 102.7 HV and 4.58%IACS, respectively. After cold deformation and aging treatment, the hardness is obviously improved. When the deformation is 60%, the hardness aging for 480 min reaches the peak value, the hardness and conductivity of the Cu-3Ti-0.2Fe-1Sn alloy are 310.2 HV and 18.59%IACS, respectively.
    Effect of annealing time on microstructure of cold rolled medium carbon Cr-Mo steel
    Lin Ran, Yang Lina, Feng Yunli, Li Jie
    2022, 47(10):  31-35.  doi:10.13251/j.issn.0254-6051.2022.10.006
    Abstract ( 61 )   PDF (582KB) ( 26 )  
    Microstructure evolution of a cold-rolled medium-carbon Cr-Mo steel annealed at 600 ℃ for different time was investigated by means of SEM and EBSD. The results show that the distribution of cementite particles becomes more dispersive and the spheroidization becomes more and more obvious as the annealing time increases, and the deformed ferrite strips are transformed into equiaxed ferrite grains. The cementite particles inside the grains are relatively fine, while those at the grain boundaries are large and partially distributed continuously. The grain size increases continuously, but the grain growth is not obvious when the annealing time is less than 240 min, and the grain size growth becomes faster when the holding time is further extended. The average ferrite grain size increases from 0.670 μm to 0.732 μm and then 2.000 μm when the holding time is extended from 15 min to 120 min and then 480 min. The grain growth rates are 55.7%, 9.7%, 74.3%, and 42.9% respectively for the annealing periods of 0-120, 120-240, 240-360, and 360-480 min. Among them, the percentage of grain size growth from 0 to 15 min is as high as 42.6%. Considering that the grain growth rate is relatively larger in the annealing period of 0-120 min, and the annealing time can be set at 120 min from the viewpoint of energy saving.
    Microstructure evolution of 3003-H16 aluminum alloy coil in production process
    Luo Xudong, Zu Licheng, Wang Fei, Zhang Xinyu, Chen Jinsheng, Qin Junjie
    2022, 47(10):  36-45.  doi:10.13251/j.issn.0254-6051.2022.10.007
    Abstract ( 53 )   PDF (583KB) ( 21 )  
    Microstructure evolution of 3003-H16 aluminum alloy coil in production process was studied by means of thermal analyzer, optical microscope, SEM and EDS. The results show that the grain size, secondary dendrite spacing and the size of grain boundary compounds decrease gradually from center to surface of the ingot. When the homogenization temperature is 590 ℃, fine granular Al6Mn precipitates in α-Al crystal. With the increase of homogenization temperature, the granular precipitates dissolve continuously and promote the growth of needle-rod precipitates. When the homogenization temperature is 640 ℃, the rod-shaped precipitates begin to dissolve, and completely dissolve at 650 ℃.The intermetallic compounds Al6(Fe,Mn) and Al6Mn become smooth and spheroidized with the increase of homogenization temperature, and some Al6(Fe,Mn) transforms into Al(Fe,Mn)Si during homogenization. The grain structure of the the 3003 aluminum alloy hot rolled coil is non-uniform in thickness direction, which is improved after cold rolling and intermediate annealing. The compounds in the 3003 aluminum alloy coil are arranged in rows along the rolling direction, with obvious directionality. The proportion of large-sized compounds decreases with the increase of reduction ratio. Homogenization can improve the composition and microstructure uniformity of the 3003 aluminum alloy and improve the plasticity of the alloy. Deformation processing can improve the strength of the 3003 aluminum alloy and reduce the plasticity of the alloy. The fibrous deformed structure is transformed intorecrystallized structure during the intermediate annealing, which eliminates the hardening phenomenon and improves the plasticity of the alloy.
    MATERIALS RESEARCH
    Effect of rare earth La on isothermal precipitation behavior of NbC at 700 ℃
    Lei Zihua, Fang Qi, Jin Zili, Sun Wei, Xiong Dongdong
    2022, 47(10):  46-51.  doi:10.13251/j.issn.0254-6051.2022.10.008
    Abstract ( 61 )   PDF (581KB) ( 21 )  
    By solution treated at 1250 ℃ and salt bath isothermally treated at 700 ℃, the effect of rare earth on isothermal precipitation behavior of NbC in Nb-microalloyed steels with adding La of 0, 0.0006% and 0.0048%, respectively, in the ferrite region for different time was studied. The results show that the addition of rare earth La into the steel can promote the dissolving of niobium at 1250 ℃ and reduce the number of undissolved second phases. When isothermally treated at 700 ℃, the promotion effect of rare earth is relatively weak at the beginning of precipitation, and gradually becomes significant with the increase of isothermal time. Rare earth La makes the NbC precipitation kinetic curve shift to the left. The addition of 0.0048% rare earth reduces the precipitation start time from 199 s to 125 s, and the end time from 35 183 s to 29 128 s. When isothermally treated at 700 ℃ for 104.25 s, the size of the second phase NbC precipitated in the ferrite area of the steel containing rare earth is smaller compared with that in the steel without rare earth. The size of the precipitated NbC in the steel without La is mainly in the range of 10-20 nm, accounting for 42.8%, while the size of the precipitated NbC in the steel containing 0.0006%La and 0.0048%La is mainly in the range of 1-10 nm, accounting for 53.6% and 64.3%, respectively, which indicates that the addition of rare earth La can refine the size of NbC significantly.
    High temperature thermoplastic of medium manganese steel for shaft forgings
    Luan Yuqi, Wu Hongyan, Wang Wanqi, Gao Xiuhua, Du Linxiu
    2022, 47(10):  52-57.  doi:10.13251/j.issn.0254-6051.2022.10.009
    Abstract ( 48 )   PDF (581KB) ( 21 )  
    High temperature thermoplastic of medium manganese steel for shaft forgings was studied. High temperature tensile tests were carried out on the tested steel at different strain rates and different temperatures, and the thermoplastic curves of the tested steel under different conditions were drawn. The fracture mechanism of the tested steel was analyzed by studying the morphology and structure distribution of high temperature tensile fracture. The results show that the reduction of area of the tested steel is more than 60% in the range of 650-1200 ℃, and the steel has good thermoplasticity and no brittleness temperature zone. The microstructure near high temperature tensile fracture of the tested steel is martensitic and there is a small amount of proeutectoid ferrite in microstructure corresponding to the temperature point (750, 900 ℃) with poor thermoplasticity. The fracture mode of the tested steel is transgranular ductile fracture in the range of 650-1050 ℃, but intergranular fracture in the range of 1100-1200 ℃.
    Hot deformation behavior of martensite TiAl alloy
    Xing Chen, Cheng Liang, Zhu Bin, Chen Yi
    2022, 47(10):  58-64.  doi:10.13251/j.issn.0254-6051.2022.10.010
    Abstract ( 46 )   PDF (588KB) ( 27 )  
    In order to study the hot deformation behavior of martensite TiAl alloy, Ti-42.1Al-8.3V alloy was oil-quenched at 1320 ℃ to obtain martensite structure, and then hot deformed compressively at deformation temperature of 1000-1150 ℃ and strain rate of 0.001-1 s-1 by using Gleeble-1500D thermal-mechanical simulator. The effect of hot deformation parameters on microstructure of the Ti-42.1Al-8.3V alloy was studied by means of BSE and EBSD, and the constitutive equation was established according to the true stress-true strain curves of the tested alloy and the hyperbolic sine equation. The results show that the flow stress curves of the alloy conform to the dynamic recrystallization characteristics, and the peak stress increases with the decrease of deformation temperature and the increase of strain rate. The constitutive equation of the tested alloy with martensitic structure is established, in which the calculated n value is 2.175, and the deformation activation energy Q is 595.79 kJ/mol. After hot deformation, the martensite arranged in equilateral triangles transforms into α2/γ lamellar structure. With the increase of deformation temperature and the decrease of strain rate,the lamellar α2/γ is replaced by recrystallized grains gradually, and completely transforms into equiaxed grains at deformation temperature of 1100 ℃ and strain rate of 0.001 s-1. In addition, with the decrease of strain rate and the increase of deformation temperature, the grains grow fully and gradually coarsen.
    Effect of cooling rate on microstructure and properties of in-situ formed bulk metallic glass composites Ti40.9Zr30.4Nb4.2Cu7Ni1.7Be15.8
    Xia Shichao, Geng Tieqiang, Li Wen, Li Hong, Zhu Zhengwang
    2022, 47(10):  65-70.  doi:10.13251/j.issn.0254-6051.2022.10.011
    Abstract ( 42 )   PDF (579KB) ( 19 )  
    Effect of cooling rate on microstructure and mechanical properties of in-situ formed bulk metallic glass composites (BMGCs) Ti40.9Zr30.4Nb4.2Cu7Ni1.7Be15.8was studied. The BMGCs were prepared by a copper casting method, with the cooling rate of which being controlled by the sizes of BMGCs, the larger the BMGCs, the slower the cooling rate. The microstructure and the properties were characterized by XRD, SEM, DSC and universal mechanical testing machine, respectively. The results show that with the decrease of cooling rate, the dendrites are ripening and the size increases. Compression tests show that the cooling rate largely influences the compression properties of the BMGCs. The lower the cooling rate, the stronger the work hardening ability, the higher the compressive strength; and the maximum compressive strength reaches 1921 MPa, but the yield strength decreases slightly. Tensile tests show that the cooling rate does not have a significant effect on the tensile properties of the BMGCs, and the maximum tensile strength reaches 1469 MPa.
    Effect of Mg on inclusion and austenite grain size of X80 pipeline steel
    Tian Jun, Su Lijuan, Wu Jing, Huang Shenglong, Wang Deyong
    2022, 47(10):  71-77.  doi:10.13251/j.issn.0254-6051.2022.10.012
    Abstract ( 49 )   PDF (585KB) ( 19 )  
    Magnesium treatment and heat treatment were carried out on X80 steel in a laboratory, and the effect of Mg on inclusion and austenite grain size of the steel was analyzed. The results show that the content of calcium aluminate inclusion decreases and the content of MgO·Al2O3 inclusion increases in the steel after magnesium treatment. With the further increase of Mg content in the steel, MgO inclusions are formed, resulting in the decrease of MgO·Al2O3 content and Al2O3 content. Magnesium treatment has a little effect on the type and content of sulfide, carbide and nitrides in the steel. After magnesium treatment, the quantity percentage of small-sized inclusion is increased and the average size of inclusion is decreased in the steel. The main inclusion is MgO·Al2O3 with a size of less than 1 μm in the magnesium treated X80 steel after heat treatment, which has an effect of pinning grain boundaries, and significantly reduces the austenite grain size of the steel.
    Influence of alloying element change on properties of 20MnCr5 steel gear after carburizing and quenching
    Zhang Yuquan, Chen Yong, Zang Libin, Ju Dongying, Zhou Leyu, Wang Zaizhou, Jia Jipeng
    2022, 47(10):  78-87.  doi:10.13251/j.issn.0254-6051.2022.10.013
    Abstract ( 63 )   PDF (578KB) ( 22 )  
    In order to investigate the influence of alloying element change on properties of gears during carburizing and quenching, mild steel 20MnCr5 gears were used as the research object, and the performance parameters of two kinds of 20MnCr5 steel with different alloying elements were calculated by using JMatPro software. The carburizing and quenching processes of gears were simulated and analyzed based on the finite element method, and a mathematical model for the carburizing and quenching process was established according to the actual heat treatment process route. By using COSMAP software to numerical simulate the heat treatment process, and the effect of alloying element on temperature, microstructure, and hardness of the carburized 20MnCr5 steel gears was compared The results show that the simulated values are verified to be in good agreement with the experimental values. The temperature field and carburized layer have no obvious response to the change of material element content, while the microstructure distribution and hardness distribution after carburizing and quenching are more influenced by the change of alloying elements such as C, Mn, Cr and Al.
    Determination and analysis of SH-CCT curve of Q345FRE fire-resistant steel
    Liu Pan, Wang Honghong, Yan Wenze, Peng Siyuan
    2022, 47(10):  88-93.  doi:10.13251/j.issn.0254-6051.2022.10.014
    Abstract ( 34 )   PDF (584KB) ( 20 )  
    Welding thermal simulation of Q345FRE fire-resistant steel was carried out by using Gleeble-3500 testing machine. And the phase transition temperature of welding HAZ in the Q345FRE steel under different t8/5 conditions was measured by means of expansion method, lever method, metallographic analysis and hardness, then SH-CCT curve of the Q345FRE steel was drawn, and the microstructure change of welding HAZ in the Q345FRE steel under different t8/5conditions was studied. The results show that the microstructure of HAZ in the Q345FRE steel is bainite when t8/5 is in the range of 3-80 s; when t8/5 is in the range of 80-300 s, the microstructure is bainite, ferrite and pearlite; when t8/5 is in the range of 300-600 s, the microstructure is ferrite and pearlite. As t8/5 increases, the hardness of HAZ in the Q345FRE steel decreases. In order to maintain the microstructure stability, it is suggested that the proper welding line energy of the Q345FRE fire-resistant steel should be selected in the range of 15-150 kJ/cm.
    Effect of Co on microstructure and properties of Cu-Cr alloy
    Gong Qinghua, Liu Jian, Chen Huiming, Xie Weibin, Wang Hang, Yang Bin
    2022, 47(10):  94-98.  doi:10.13251/j.issn.0254-6051.2022.10.015
    Abstract ( 60 )   PDF (582KB) ( 28 )  
    Microstructure and properties of Cu-Cr-Co alloys after cold rolling with deformation of 80% and aging at 450 ℃ were studied and compared with Cr-Cr alloy. The results show that when aging at 450 ℃ for 4 h, the properties of Cu-0.66Cr-0.05Co and Cu-0.62Cr-0.22Co alloy reach the peak, and the tensile strength, hardness and conductivity are 376 MPa and 410 MPa, 143.7 HV0.5 and 138.4 HV0.5, 84.1%IACS and 66.2%IACS, respectively. The precipitates of the peak-aged Cu-Cr-Co alloy have a body centered cubic (bcc) structure with a Nishiyama-Wassermann orientation to the matrix, and the Co content has little effect on the grain morphology of Cu-Cr-Co alloy. Compared with Cu-Cr alloy, the addition of Co prolongs the aging time of the alloy, increases the hardness, improves the softening resistance, but decreases the tensile strength and conductivity. As Cu and Co have a certain degree of solution above 422 ℃, some of the Co gradually dissolves into the matrix during aging, forming solid solution, and is not distributed in the periphery of the precipitation phase as predicted, reducing the comprehensive properties of the alloy.
    Influence of thermal deformation process on morphology evolution of sulfide in cerium-sulfur containing free-cutting stainless steel
    Wang Yinghu, Zheng Huaibei, Song Lingxi, Liu Tingyao
    2022, 47(10):  99-106.  doi:10.13251/j.issn.0254-6051.2022.10.016
    Abstract ( 43 )   PDF (584KB) ( 22 )  
    Influence of thermal deformation process on morphology evolution of sulfide in cerium-sulfur containing free-cutting stainless steel was studied by means of Gleeble-3500, OM and Phenom Partical X SEM-EDS. The sulfides in cerium-sulfur containing free-cutting stainless steel casting billet are spherical, ellipsoidal, spindle shape or short-bar-like, and distributed in clusters along the grain boundary, belonging to a type II sulfide. At the temperature ranging from 800 ℃ to 1100 ℃, the distribution density of sulfide increases and the average area decreases with the increase of deformation. At the temperature ranging amount from 800 ℃ to 1000 ℃, the proportion of sulfide with length-width ratio≤3 gradually decreases with the increase of deformation amount from 10% to 70%. When the deformation temperature is 1100 ℃ and the deformation increases to 70%, the proportion of sulfide with length-width ratio≤3 increases slightly, and the sulfide melts or re-nucleates. When the deformation amount is in the range of 10%-70%, the relative plasticity of sulfide increases and then decreases gradually after reaching the peak value at 30% deformation. At the temperature ranging from 800 ℃ to 1100 ℃, the relative plasticity of sulfide decreases with the increase of deformation temperature when the deformation amount is constant.It is easier to obtain uniformly dispersed fine sulfide at high temperature and large deformation.
    PROCESS RESEARCH
    Microstructure and thermal processing map of Inconel 600 alloy
    Zhou Yusen, Cheng Xiaonong, Luo Rui, Gao Pei, Liu Yu, Yuan Zhizhong
    2022, 47(10):  107-112.  doi:10.13251/j.issn.0254-6051.2022.10.017
    Abstract ( 92 )   PDF (567KB) ( 26 )  
    Thermal processing map of Inconel 600 alloy was obtained through thermal compression experiment by using Gleeble-3500 testing machine, and the microstructure corresponding to different zones of the thermal processing map was studied. Finally, the actual hot extrusion production was carried out by using the thermal processing window given by the thermal processing map. The results show that when the strain is 0.6, the thermal processing window is generally stable in the low strain rate region of 0.01-0.1 s-1 and the high strain rate 10 s-1 at 1150-1200 ℃. The actually produced pipe has a good macro morphology, and the microstructure is basically equiaxed recrystallized grains with twins, which are refined comparing with that of as-annealed alloy.
    Effect of annealing temperature on interface phase evolution and properties of copper-aluminum clad plate
    Zheng Weibo, Luo Zongan, Wang Mingkun, Xie Guangming, Wang Yuhao, Suo Jinggang
    2022, 47(10):  113-118.  doi:10.13251/j.issn.0254-6051.2022.10.018
    Abstract ( 45 )   PDF (565KB) ( 27 )  
    Effect of annealing temperature on interface phase evolution and properties of copper-aluminum clad plate prepared by cold rolling method was investigated. The interface structure was observed by electron probe micro-analyzer (EPMA). The phase composition was analyzed by using energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD). The bonding properties of clad plate were characterized by using peel and tensile test. The results show that the diffusion layer at the bonding interface becomes thicker as the annealing temperature increases, which is composed of CuAl2, Cu9Al4 and CuAl phases. CuAl2 and CuAl phases destroy the interface bonding, which results in a significant drop in peel strength. When annealed at 300 ℃ or above, the clad plate recovers and recrystallizes, and its overall tensile properties are excellent. Considering the tensile properties and peel strength, the optimal annealing temperature of the copper-aluminum clad plate prepared by cold rolling method is 300 ℃.
    Heat treatment process of refining microstructure of carbide-free bainitic steel seamless pipe
    Cheng Juqiang
    2022, 47(10):  119-123.  doi:10.13251/j.issn.0254-6051.2022.10.019
    Abstract ( 47 )   PDF (568KB) ( 20 )  
    Microstructure and mechanical properties of carbide-free bainitic seamless steel tube under different heat treatment processes were studied. The results show that the as-hot rolled carbide-free bainitic steel seamless pipe has coarse structure, high strength and low toughness. After hot rolling and low temperature tempering, the toughness improves a little, which is still low. After hot rolling, normalizing and low temperature tempering, the toughness improves, but there is still some coarse microstructure. After hot rolling and high temperature tempering at 690 ℃ for 300 min, then normalizing and low temperature tempering, the microstructure refines and the inheritance eliminates, which greatly improve the toughness of the carbide-free bainitic steel seamless pipe and cause the impact fracture characteristics to change from brittle fracture to ductile fracture.
    Influence of heating rate of bell annealing process on texture and properties of non-oriented silicon steel
    Su Zhihe, Jin Zili, Wu Zhongwang, Cui Yuanlin, Ren Huiping, Zhao Xiaolong, Luo Xiaoyang, Di Yanjun
    2022, 47(10):  124-128.  doi:10.13251/j.issn.0254-6051.2022.10.020
    Abstract ( 43 )   PDF (572KB) ( 21 )  
    Effect of heating rate on microstructure, texture and magnetic properties of 0.8%Si non-oriented silicon steel during bell annealing process was studied. The results show that after annealing with different heating rates, the recrystallized texture of the non-oriented silicon steel is mainly {111} texture, accompanied by {110} and {100} texture. With the increase of heating rate, the grain size gradually increases, the {111} texture appears to be significantly weakened, the {110} texture appears to increase significantly, and the {100} texture does not change significantly, meanwhile, the iron loss P1.5/50 gradually decreases, and the magnetic induction intensity B5000 gradually increases. However, when the heating rate is increased from 80 ℃/h to 100 ℃/h, the {111} texture appears to be strengthened to a certain extent, the {110} texture appears to weaken, and the {100} texture does not change obviously, moreover, the iron loss P1.5/50 increases and the magnetic induction intensity B5000decreases. When the heating rate of bell annealing process is 80 ℃/h, the optimum magnetic properties can be obtained as P1.5/50=4.249 W/kg, B5000=1.715 T.
    Post-treatment process for improving hardness of carburized and quenched gears
    Zhao Shaofu, Xu Hongxiang, Wang Hongwei, Li Ziyan, Chen Yan, Li Jiqiang, Chen Shengchao, Rong Zeyu
    2022, 47(10):  129-134.  doi:10.13251/j.issn.0254-6051.2022.10.021
    Abstract ( 60 )   PDF (565KB) ( 21 )  
    Effect of post-subzero treatment and post-low temperature tempering on surface hardness, CHD and core hardness of 20Cr2Ni4A steel gear when the hardness was low after carburizing and quenching and low temperature tempering was studied. The results show that the stabilization of retained austenite in the 20Cr2Ni4A steel after carburizing, quenching and low temperature tempering is not obvious, thus subzero treatment can still improve the hardness of the workpiece. A secondary hardening phenomenon after low temperture tempering appears when the 20Cr2Ni4A steel contains more retained austenite, thus increasing the low temperature tempering temperature can also increase the surface hardness. Therefore, the post-subzero and post-low temperature tempering treatment process can be used to improve the hardness, instead of the conventional rework process of re-high temperature tempering, carburizing and quenching and low temperature tempering. The post-subzero treatment temperature shall be determined according to the Mf point. For the process of carburizing, high temperature tempering, re-heating and quenching and low temperature tempering, the Ms and Mf cannot be calculated according to the traditional method, however, it can be estimated by the retained austenite content.
    Heat treatment process of 1000 MPa hot-rolled dual phase steel with different relaxation time
    Wu Teng, Zhang Guilin, Yin Licheng, Ke Deqing, Li Sijie, Da Guoyu, Sun Zhaokang
    2022, 47(10):  135-138.  doi:10.13251/j.issn.0254-6051.2022.10.022
    Abstract ( 38 )   PDF (572KB) ( 20 )  
    Based on the principle of automobile lightweight, a 1000 MPa hot-rolled dual phase steel was prepared by hot rolling, ultra fast cooling and relaxation heat treatment, and effect of relaxation time on microstructure and mechanical properties of the tested steel was studied. The results show that with the increase of relaxation time, the banded distribution of ferrite and martensite of the tested steel is more obvious, the ferrite grain size and volume fraction increase, the yield strength decreases and the elongation increases. The tensile strength first increases and then decreases, which is the result of the combined action of martensite volume fraction and carbon content. The yield ratio decreases, and the n value increases. The relaxation time affects the volume fraction, grain size and internal substructure of dual phase. When the relaxation time is 10 s, tensile strength, elongation, yield ratio and n value of the tested steel are 1025 MPa, 17.5%, 0.48 and 0.13, respectively, under which shows the best comprehensive properties. Considering the mechanical properties and production efficiency, the appropriate relaxation time of the tested steel under the process conditions is 7-10 s.
    Effect of quenching temperature on microstructure and precipitation behavior of 40Si2Ni2CrMoV steel
    Zhang Weifeng, He Xiaofei, Yu Wenchao, Li Li, Wang Maoqiu
    2022, 47(10):  139-146.  doi:10.13251/j.issn.0254-6051.2022.10.023
    Abstract ( 39 )   PDF (569KB) ( 22 )  
    Microstructure and mechanical properties of 40Si2Ni2CrMoV steel quenched at different temperatures (840, 860, 880, 900 ℃) and tempered at 300 ℃were studied by means of OM, SEM and TEM, and the precipitates in the steel were qualitatively and quantitatively characterized by phase analysis method. The results show that when quenched at 800-900 ℃, the microstructure of the tested steel is lath martensite and shows a trend of first refining and then coarsening with the increase of quenching temperature. When the quenching temperature is 880 ℃, the steel has the finest and most uniform microstructure, and the precipitates are dispersed in the martensite matrix. As the quenching temperature increases, the precipitates gradually dissolve into the matrix. Combining with the mechanical properties, it is considered that 880 ℃ is a suitable quenching temperature for the tested steel.
    Influence of tempering temperature on corrosion resistance of EH890 marine engineering steel
    Che Majun, Zhou Shengxuan, Du Xiaojie, Zhao Jinbin, He Yizhu, Xu Zhenlin
    2022, 47(10):  147-153.  doi:10.13251/j.issn.0254-6051.2022.10.024
    Abstract ( 44 )   PDF (566KB) ( 22 )  
    In order to investigate the influence of different tempering temperatures on the corrosion resistance of the EH890 marine engineering steel, the phase and microstructure of the steel originally quenched and tempered at different temperatures were analyzed by X-ray diffrotometry and field emission scanning electron microscopy. The corrosion behavior under different heat treatment conditions was studied by electrochemical experiments. The influence of tempering temperature on corrosion was calculated and analyzed in combination with microhardness and dislocation density. The results show that the original quenched microstructure of the EH890 steel consists of lath bainite, and a small amount of granular bainite and quasi-polygon ferrite with thin film retained austenite. With the increase of tempering temperature, the bainite lath is coarsened continuously, and the ferrite and retained austenite are decomposed and transformed. When the tempering temperature reaches 350 ℃, the fine dispersed carbides and the second phase begin to precipitate at the boundary of bainite. With the increase of the tempering temperature, the corrosion resistance of the steel shows a trend of increasing first and then decreasing. On the one hand, tempering can eliminate the high dislocation density caused by quenching and reduce the corrosion tendency of the specimen. On the other hand, with the increase of the tempering temperature, the dispersed second phase continuously precipitates from the matrix and forms local galvanic interaction with the matrix, which destroys the integrity of passivation film and reduces its protective effect on the matrix. Under the combined action of the two factors, a more protective passivation film is formed on the surface of the specimen tempered at 350 ℃, which shows optimized pitting resistance.
    Effect of tempering temperature on microstructure and properties of NM500 wear-resistant steel
    Zhu Zhenyu, Wu Zhifang, Wu Run
    2022, 47(10):  154-159.  doi:10.13251/j.issn.0254-6051.2022.10.025
    Abstract ( 47 )   PDF (566KB) ( 25 )  
    Effect of tempering temperature on microstructure, mechanical properties and wear resistance of NM500 low alloy high strength wear-resistant steel was studied by means of optical microscope (OM), scanning electron microscope (SEM) and material surface comprehensive performance tester. The results show that the typical tempered martensite structure is obtained in the NM500 steel after quenching and tempering. With the increase of tempering temperature, supersaturated carbon atoms in martensite laths are gradually precipitated, the hardness and low temperature impact absorbed energy of the NM500 steel decrease obviously after the carbides grow up. The hardness and impact absorbed energy at -20 ℃ of the NM500 steel after tempering at 200 ℃ are 513 HBW and 44.40 J, respectively, and the wear resistance is the best. When tempering at low temperature(200 and 250 ℃), a small amount of fine dispersed supersaturated carbon atoms precipitate, which improves the wear resistance of the steel. When tempering at 300 ℃ and above, the aggregated coarsened short rod cementite will reduce the hardness of the matrix, resulting in a continuous decrease in the wear resistance of the steel. The wear mechanism changes from abrasive wear to adhesive wear.
    Effect of solution cooling method on microstructure and mechanical properties of TB15 titanium alloy
    Hu Shengshuang, Xiao Jun, Zhao Hu, Jiang Yi, Wu Haifeng, Zhang Bingxian, Yan Jiawei
    2022, 47(10):  160-163.  doi:10.13251/j.issn.0254-6051.2022.10.026
    Abstract ( 57 )   PDF (569KB) ( 24 )  
    Mechanical properties, fracture morphology and microstructure of TB15 titanium alloy after solution treatment at 900 ℃ for 2 h with different cooling methods and aging at 530 ℃ for 8 h were studied by means of scanning electron microscopy, tensile and fracture toughness tests. The results show that cooling method of solution treatment significantly affects the strength and ductility of TB15 titanium alloy, but the effect on fracture toughness is not obvious. When using 0.1 MPa argon vacuum quenching, the comprehensive mechanical properties of the TB15 titanium alloy after solution and aging is the best, as the tensile strength is 1391 MPa, the elongation is 7.0%, the percentage reduction of area is 13.6%, and the fracture toughness is 70.3 MPa·m1/2. With the increase of solution cooling rate, the fracture toughness of the TB15 titanium alloy gradually decreases, but its varied range is not large. Under different solution cooling methods, the number, thickness and lamellar spacing of secondary α phase in TB15 titanium alloy after solution and aging are different. Compared with air cooling, the number and thickness of the lamellar secondary α phase increase when using 0.1 MPa argon vacuum quenching.
    Effect of deep cryogenic treatment on wear resistance of 18Cr2Ni2MoNbA steel
    Luo Zixiang, Liu Ke, Yang Bing, Wu Huanfen, Zhang Ling, Liao Beilei
    2022, 47(10):  164-168.  doi:10.13251/j.issn.0254-6051.2022.10.027
    Abstract ( 34 )   PDF (566KB) ( 23 )  
    Deep cryogenic treatment process parameters of 18Cr2Ni2MoNbA carburized steel were selected and optimized by using orthogonal test. The effect of cryogenic time, low temperature tempering temperature and low temperature tempering time on the wear resistance of the steel was studied, and the wear scar morphology, microstructure, retained austenite and microhardness were analyzed. The results show that when cryogenic treated at -196 ℃ after carburizing and quenching, the influence of cryogenic parameters on the wear amount of the 18Cr2Ni2MoNbA steel is in the following order of significance as cryogenic time, low temperature tempering time and low temperature tempering temperature. The cryogenic treatment can effectively increase the wear resistance of the steel, and the wear amount of the steel under the cryogenic parameters as cryogenic time of 1 h, low temperature tempering temperature of 120 ℃ and low temperature tempering time of 2 h is the smallest, which is reduced by 46.67% compared with the steel without cryogenic treatment, and the wear mechanism changes to abrasive wear and oxidation wear. The carbides in the carburized layer precipitate along the grain boundaries after cryogenic treatment, while small particles of carbides are diffused on the matrix. The cryogenic treatment can reduce the retained austenite content of the steel and increase the martensite content, which increase the microhardness of the surface carburized layer, and improve the wear resistance of the 18Cr2Ni2MoNbA steel.
    Effect of finished product annealing process on microstructure and properties of Cu-20wt%Fe in-situ composite strip
    Zeng Yanqi, Yu Huihui, Lu Deping, Zhang Youliang, Hu Qiang, Guo Junli, Hu Feifei, Zou Jin
    2022, 47(10):  169-172.  doi:10.13251/j.issn.0254-6051.2022.10.028
    Abstract ( 46 )   PDF (565KB) ( 36 )  
    Varying rules of tensile strength, electrical conductivity and iron-rich phase evolution of Cu-20wt%Fe in-situ composite strips under different finished product annealing processes were studied by means of tensile test, electrical conductivity test, SEM microstructure observation and energy spectrum analysis. The results show that after annealing, some iron-rich phases with small thickness can be dissolved into copper matrix. With the increase of annealing temperature, the dissolution of iron-rich phase increases, and the residual flat and long iron-rich phases eventually distribute intermittently. With the extension of annealing time, the tensile strength of the strip first decreases significantly to 380-440 MPa, then the decline rate slows down significantly, even fluctuates up slightly, and finally tends to be stable, meanwhile, the tensile strength decreases with the increase of annealing temperature. The conductivity of the strip increases rapidly to 31%IACS-37%IACS with the extension of annealing time, then changes slowly, fluctuates slightly, and finally tends to be stable. The ideal finished product annealing process for Cu-20wt%Fe in-situ composite strip is at 450 ℃ for 60 min.
    Effect of heat treatment on microstructure and properties of welded joint of X70 steel used for bent pipe under extremely cold service condition
    Zhang Xiazhou, Chen Yanqing, Zhao Yingjian, Dong Xianchun
    2022, 47(10):  173-178.  doi:10.13251/j.issn.0254-6051.2022.10.029
    Abstract ( 54 )   PDF (565KB) ( 18 )  
    X70 pipeline steel was welded through SMAW and then by simulating the induction pipe bending process, the welded joint was quenched at 950 ℃ and tempered at 500, 550 and 600 ℃. Effect of different tempering temperatures on the microstructure and properties of the welded joints were studied. The results show that the microstructure of the weld and the heat affected zone are tempered sorbite, and the low temperature impact absorbed energy at -45 ℃ of the weld and the heat affected zone reduces significantly after quenching and tempering. With the increase of the tempering temperature, the low temperature impact absorbed energy increases gradually, which is attribute to the increase of the content of carbide precipitates and acicular ferrite(AF) in the weld structure, and the carbide distribution gradually becomes uniform. The heat affected zone has the highest impact absorbed energy when tempered at 550 ℃, but it decreases obviously when tempered at 600 ℃, which is attribute to the coarsening of both the microstructure and the carbide precipitates. After quenching and tempering, the hardness of the weld is the highest, and the pipe during tensile test fractures in the base metal, the strength of the welded joint meets the requirements. Thus, the optimal matching of the impact toughness and tensile properties of the welded joint can be obtained when tempered at 550 ℃.
    Effect of cold deformation before aging on microstructure and mechanical properties of Al-15Zn-0.5Mg-0.5Sc alloy
    Xiao Jijin, Liu Chongyu, Shi Lei, Sun Haoming, Zhang Lei
    2022, 47(10):  179-184.  doi:10.13251/j.issn.0254-6051.2022.10.030
    Abstract ( 42 )   PDF (569KB) ( 20 )  
    Solution-aging and solution-cold rolling-aging treatment were carried out for the hot rolled Al-15Zn-0.5Mg-0.5Sc alloy, and microstructure and mechanical properties of the alloy were studied by optical microscope, scanning electron microscope, transmission electron microscope and universal mechanical testing machine. The results show that cold rolling can decompose the saturated Al-Zn solid solution and dynamically precipitate Zn phase. At the same time, cold rolling also promotes the grain refinement and dislocation multiplication of the alloy. Artificial aging can lead to precipitation of high density η′ phase in the alloy. The high-density dislocations caused by cold rolling promote the precipitation process and accelerate the η′ phase transformation to η phase. Cold rolling before aging can obviously optimize the mechanical properties of the Al-15Zn-0.5Mg-0.5Sc alloy. After solution-cold rolling-artificial aging at 70 ℃, the yield strength and ultimate tensile strength of the Al-15Zn-0.5Mg-0.5Sc alloy are 413 MPa and 462 MPa, respectively. The strengthening mechanisms include fine grain strengthening, dislocation strengthening and precipitation strengthening. However, aging at 120 ℃ will accelerate dislocation annihilation and weaken the dislocation strengthening effect of the alloy.
    Effect of heat treatment on microstructure and properties of Ti-38644 titanium alloy bar
    Han Weisong, Zhu Baohuisup>1,2, Li Jianfeng, Liu Yanchang, Li Yonglin, Shen Lihua, Hu Gequan, Liu Yi
    2022, 47(10):  185-190.  doi:10.13251/j.issn.0254-6051.2022.10.031
    Abstract ( 48 )   PDF (571KB) ( 34 )  
    Heat treatment experiments on the Ti-38644 titanium alloy with ϕ68 mm diameter bars were implemented at different temperatures, holding time and cooling methods. Effect of different heat treatment processes on the microstructure and mechanical properties of the alloy bars were studied. The results show that the content of the precipitated α phase increases with the solid solution temperature increase. With the increase of aging temperature, the precipitated α phase tends coarser, which result in the strength decrease, and the elongation increase. The strengthening effect is slackened. As the aging holding time extended, the precipitated α phase increase. The strength appeares a tendency to increase firstly and then decrease, and the plasticity changes in contrast. The effect of the solid solution cooling method on the alloy microstructure properties are notable. Due to the accelerates of the cooling rate, the β grains obtained is relatively small, and therefore, accounted for the strength raise up and the elongation decrease sharply. In conclusion, a better matching of strength and plasticity can be obtained in solution and aging heat treatment process (810 ℃×1 h, oil cooling+510 ℃×8 h, air cooling).
    I&Q&P process of Nb microalloyed cold-rolled DP780 steel with high product of strength and elongation
    Yang Kang, Shi Na, Ding Jing, Yu Liang, Fang Qiang
    2022, 47(10):  191-197.  doi:10.13251/j.issn.0254-6051.2022.10.032
    Abstract ( 43 )   PDF (568KB) ( 18 )  
    Based on the theory of metastable austenite deformation induced phase transformation, the I&Q&P (intercritical annealing and quenching and partitioning) process of 800 MPa grade cold-rolled DP780 steel was investigated by using salt bath furnace in the laboratory. The microstructure and mechanical properties of the tested steel under different processes were studied by means of metallographic microscope, scanning electron microscope, tensile testing machine and XRD. The results indicate that the microstructure of the tested steel is composed of ferrite, martensite and retained austenite under the I&Q&P process. The ferrite grain size is mainly larger than 5 μm at annealing temperature of 830 ℃, however, the ferrite grain size is mainly smaller than 5 μm at annealing temperature of 860 ℃. The mechanical properties of the tested steel annealed at 830 ℃ fluctuate greatly with the change of quenching temperature, conversely, the mechanical properties of the tested steel annealed at 860 ℃ vary slightly. At annealing temperature of 860 ℃ and quenching temperature of 260 ℃, the optimum comprehensive mechanical properties are obtained with tensile strength of 802 MPa, elongation of 26.8%, and product of strength and elongation of 21.5 GPa·%, and the content of retained austenite in the steel is as high as 13.89%.
    Effect of double aging treatment on microstructure and properties of β21S titanium alloy bar
    Wang Xingyun, Huang Wenbin, Qiao Enli, Lei Wenguang, Yue Xu
    2022, 47(10):  198-202.  doi:10.13251/j.issn.0254-6051.2022.10.033
    Abstract ( 39 )   PDF (571KB) ( 22 )  
    Microstructure and properties of the β21S titanium alloy bar after double aging treatment were studied. The results show that the α phase occurs in the grain after first aging, and the temperature and time of the first aging treatment have a great influence on precipitated phase. After the first aging at 540 ℃ for 20 min and 550 ℃ for 10 min, relatively uniform and comparable amounts of precipitates can be obtained. After first aging and then second conventional aging at 510 ℃, the tensile strength of the specimen does not decrease significantly, but the elongation of the specimen increases more than 2% compared with the single solution aging. Under the same double aging treatment, as the solution temperature increasess, the tensile strength increases, while the elongation decreases. Double aging treatment has little effect on shear properties.
    Effect of intermediate annealing temperature on microstructure and properties of 4004/3003/4004 aluminum alloy composite sheet for new energy vehicles
    Bin Yuejing, Liu Ying, Cao Yu, Zeng Yongmou, Hu Menghan, Mo Zhuoqiang, Wang Zheying
    2022, 47(10):  203-207.  doi:10.13251/j.issn.0254-6051.2022.10.034
    Abstract ( 29 )   PDF (656KB) ( 20 )  
    Effect of intermediate annealing temperature on microstructure and properties of 4004/3003/4004 three-layer aluminum alloy composite sheet for power batteries of new energy vehicles was studied by means of optical microscope, scanning electron microscope and universal tensile testing machine. The results show that with the increase of annealing temperature, the cladding rate does not change obviously and has small deviation, the composite interface of the composite sheet is clear and straight. The Si particles in the 4004 aluminum alloy layer are fine and dispersed, and the size is 2-4 μm. All the grains of the core material 3003 aluminum alloy layer are recrystallized when the intermediate annealing temperature is 370 ℃. The tensile strength and yield strength of the composite sheet decrease sharply at first and then tend to be stable with the increase of intermediate annealing temperature, but the elongation shows an opposite trend. When the intermediate annealing temperature is 370 ℃, the strength and elongation of the composite sheet begin to be stable, thus 370 ℃ is the optimal intermediate annealing temperature of the composite sheet, at which the tensile strength and yield strength are 137 MPa and 80 MPa respectively and the elongation is 31%.
    Effect of cold deformation on mechanical properties and earing rate of 5052 aluminum alloy sheet
    Zeng Zhaofen, Qi Wengang, Zhao Fuyou, Kang Yuemin, Wang Xueping, Zhang Yi
    2022, 47(10):  208-210.  doi:10.13251/j.issn.0254-6051.2022.10.035
    Abstract ( 37 )   PDF (659KB) ( 18 )  
    Effect of cold deformation on grain size, mechanical properties and earing rate of 5052 aluminum alloy sheet was studied by metallographic microscope, tensile testing machine and earing rate tester. The results show that the yield strength of the 5052 aluminum alloy cold-rolled sheet has a linear relationship with the cold deformation rate. The change of tensile strength and yield strength caused by 10% deformation is about 20 MPa and 15 MPa, respectively. After recrystallization annealing, the grain size of the annealed sheet has a linear relationship with the cold deformation rate and yield strength. When the cold deformation rate is 50%-60%, the earing rate and plane anisotropy index Δr of the annealed sheet is smaller.
    SURFACE ENGINEERING
    Effect of pre-nitriding on corrosion resistance of 20CrMnTi steel vacuum carburized layer
    Li Zhuocheng, Tian Yong, Wang Bin, Wang Haojie
    2022, 47(10):  211-217.  doi:10.13251/j.issn.0254-6051.2022.10.036
    Abstract ( 32 )   PDF (236KB) ( 29 )  
    20CrMnTi steel was pre-nitrided before vacuum carburizing, and the effect of pre-nitriding treatment on microstructure of the carburized layer and the morphology of the corroded surface was investigated by means of OM, SEM and XRD, and the corrosion resistance was evaluated by electrochemical tests and corrosion rate calculated by mass loss. The results show that the martensite of the carburized layer of the pre-nitrided and carburized specimen is finer with a large amount of cementite precipitates, and the corrosion resistance is significantly improved. The corrosion rate and the tendency of corrosion to occur are greatly reduced, the self-corrosion current density is reduced from 1.3608×10-5 mA·cm-2 to 2.9817×10-6 mA·cm-2 and the self-corrosion potential is increased from -0.7741 V to -0.6672 V, the corrosion rate calculated by mass loss is only half of that of the carburized specimen. This is mainly due to the finer martensite and cementite of the pre-nitrided and carburized specimen hindering the expansion of pitting and thus reduce the corrosion rate, and the nitrogen atoms in carburized layer will react chemically with the solution to generate NH+4 and NO-2 or NO-3, which will reduce the corrosion effect of Cl-.
    Effect of surface quenching process on hardened layer of 42CrMo steel for large bearing ring
    Wei Shitong, Wu Changjiang, Zheng Leigang, Hu Xiaoqiang, Lu Shanping
    2022, 47(10):  218-223.  doi:10.13251/j.issn.0254-6051.2022.10.037
    Abstract ( 51 )   PDF (652KB) ( 27 )  
    42CrMo medium carbon bearing steel was surface quenched with different temperatures and quenching mediums. Then the microstructure and hardness of different regions of the quenched specimens were tested and analyzed by means of Rockwell hardness tester, metallographic microscope, scanning electron microscope and transmission electron microscope. The results show that after surface quenching treatment, according to the hardness from large to small, the specimen can be divided into three different regions: hardened zone, transition zone and base material. The depth of surface hardened layer increases with the increase of surface quenching heating temperature, and that of oil quenching is significantly reduced compared with that of water quenching. Microstructure analysis shows that the microstructure in the water quenching hardened zones are all martensite, while the oil quenching has a slow cooling rate, which causes that the hardened zone is martensitic+ferrite. The transition zones under different surface quenching conditions are all martensite+tempering sorbite. Furthermore, the base material is the tempered sorbite in the original quenched and tempered state. Differences in the microstructure of hardened zone, transition zone and base material leads to differences in hardness in different regions. In practical applications, appropriate heating temperature for water quenching should be selected according to the required depth of the hardened layer.
    Influence of quenching temperature on microstructure and hardness of Fe-Cr-B-C alloy coating
    Wu Xianji, Song Yuanyuan, Yang Zhirong, Yan Desheng, Jiang Haichang, Hu Xiaofeng
    2022, 47(10):  224-227.  doi:10.13251/j.issn.0254-6051.2022.10.038
    Abstract ( 31 )   PDF (652KB) ( 21 )  
    Effect of quenching temperature (850, 950 and 1050 ℃) on microstructure of Fe-Cr-B-C alloy coating prepared by plasma overlaying was studied by means of OM, SEM and XRD, and the hardness was tested by using microhardness tester. The results indicate that the as-plasma overlaid Fe-Cr-B-C alloy coating comprises dendritic matrix and interdendritic boron carbide distributed in the form of continuous network. After quenching at 1050 ℃, the boron carbide in the Fe-Cr-B-C alloy coating dissolves and spheroidizes, the hardness is up to 64.3 HRC, and the comprehensive properties is the best.
    Influence of heating temperature on microstructure and properties of hot stamped steel with Al-Si coating
    Chen Zhong
    2022, 47(10):  228-233.  doi:10.13251/j.issn.0254-6051.2022.10.039
    Abstract ( 42 )   PDF (660KB) ( 18 )  
    Influence of heating temperature during hot stamping process on microstructure and properties of 22MnB5 hot stamped steel with Al-Si coating was researched by means of roughness meter, scanning electron microscope, hardness tester and glow discharge atomic emission spectrometer, respectively. The results indicate that with the increase of heating temperature, the migration amount of Fe from hot stamped steel substrate to coating surface along the direction perpendicular to surface becomes larger gradually. Meanwhile, the migration amount of O from coating surface to hot stamped steel substrate along the direction perpendicular to surface becomes larger gradually, and the maximum migration depth is about 2.80 μm. The migration amount of Fe from hot stamped steel substrate to Al-Si coating surface along the direction perpendicular to surface directly determines the morphology, formation position of Fe-Al-Si phase and interface bonding layer thickness. As the heating temperature rises, the surface roughness Ra and peak count value Rpc of Al-Si coating increase at first, and then decrease; when the heating temperature is 930 ℃, the surface roughness Ra and peak count value Rpc reach maximum values of 1.89 μm and 218, respectively. With the increase of heating temperature, the total thickness of Al-Si coating increases from 27.78 μm to 40.46 μm, the thickness of interface bonding layer increases from 1.08 μm to 15.11 μm. When heating temperature is 930 ℃, the hardness of the hot stamped steel substrate reaches maximum value of 505 HV0.2.
    Surface stress distribution of tooth root of carburized and quenched 18CrNiMo7-6 steel gear with different shot peening treatments
    Chen Yongxiang, Li Yong, Zhang Jinmeng
    2022, 47(10):  234-237.  doi:10.13251/j.issn.0254-6051.2022.10.040
    Abstract ( 34 )   PDF (658KB) ( 21 )  
    Surface stress distribution of tooth root of the carburized and quenched 18CrNiMo7-6 steel gear with modulus of 20 mm after different shot peening treatment was tested and compared with the specimen without shot peening. The results show that the top layer of the tooth root of the carburized and quenched 18CrNiMo7-6 steel gear before and after shot peening is all in compressive stress state, which increases first and then decreases from surface to inside. The residual stress at top layer of the tooth root without shot peening is about -75 MPa, and the maximum residual stress is about -250 MPa at the subsurface of 110-120 μm. Shot peening treatment can increase the surface compressive stress of tooth root by 4-5 times, the residual stress at top layer is about -350 MPa, and the maximum residual stress of -900 to -1000 MPa is beneath the subsurface of 90 to 110 μm.
    Coating structure transformation law of Al-Si coating with different coating weight during heating
    Zhou Shilong, Ye Shengwei, Deng Lulu, Deng Zongji, Lu Qianqian, Zheng Xiaofang
    2022, 47(10):  238-245.  doi:10.13251/j.issn.0254-6051.2022.10.041
    Abstract ( 44 )   PDF (652KB) ( 35 )  
    Microstructure transformation low of Al-Si coating with different coating weight on hot forming steel after heating at different temperatures for different time was studied by means of SEM and energy spectrum analysis. The results show that the structure of the fully alloyed Al-Si coating with different weight is the same, which is composed of diffusion layer, Fe-Al layer, Fe-Al-Si layer and Fe-Al surface layer from substrate to surface. With the heating going on, the thickness of the Fe-Al-Si layer and the diffusion layer gradually increases, and the Si content in the Fe-Al-Si layer gradually decreases, meanwhile, the thick coating AS150 does not appear the reduction in the number of coating layers, while the thin coatings AS40 and AS80 appear the reduction in the number of coating layers. Considering the coating structure, properties change and the using requirements of Al-Si coating on hot-forming steel, when using 22MnB5 steel with thickness of 1.4 mm as the base material, the optimal heating process for the thin coating AS40 and AS80 is heating at 900-930 ℃ for 3-6 min, and for the thick coating AS150 is heating at 900-930 ℃ for 4-6 min.
    Effect of zinc coating weight on its growth law
    Ma Shalong, Ding Wenhong, Fang Yu, Lu Xiaoxuan, Hu Ying
    2022, 47(10):  246-250.  doi:10.13251/j.issn.0254-6051.2022.10.042
    Abstract ( 76 )   PDF (656KB) ( 18 )  
    Microstructure and phase distribution of the galvanized layer under different zinc coating weight were analyzed by means of scanning electron microscopy (SEM) and energy spectrum analyzer (EDS). The results show that when the zinc coating weight is 80 and 120 g/m2, the δ phase is fence-like, and the ζ phase changes from loose to dense, when the zinc coating weight is 275 g/m2, the δ phase is dense and the ζ phase is loose. Among the three types of zinc coating weight, the thickness of the δ phase accounts for the least proportion of the total thickness, and the thickness of each phase is proportional to the zinc coating weight. When the zinc coating weight is less, the surface of galvanized layer is loose and porous, with grooves similar to grain boundaries. With the increase of the zinc coating weight, the surface of galvanized layer becomes dense and flat, and the depth of the grooves becomes significantly shallower and less. Therefore, the zinc coating weight affects its microstructure, which in turn affects the zinc-iron alloy phase structure.
    EQUIPMENT
    Automatic material equipment for heat treatment
    Zhang Zhipeng
    2022, 47(10):  251-257.  doi:10.13251/j.issn.0254-6051.2022.10.043
    Abstract ( 30 )   PDF (652KB) ( 33 )  
    Automatic material equipment plays an important role in preventing mixing, reducing labor intensity, ensuring the quality of heat treatment and improving the degree of heat treatment automation. The characteristics, application conditions and practical application effects of automatic material equipment such as material conveying equipment, material storage equipment and material layout and collection equipment are introduced. It can provide assistance to heat treatment employee in the planning of heat treatment plants.
    NUMERICAL SIMULATION
    Influence of water-entering mode on residual stress during quenching for U-section aluminum alloy forging based on DEFORM
    Long Shuai, Zhou Jie, Wu Daoxiang, Wang Shuyan
    2022, 47(10):  258-262.  doi:10.13251/j.issn.0254-6051.2022.10.044
    Abstract ( 32 )   PDF (652KB) ( 21 )  
    Water-entering modes during quenching for a U-shape sectioned aluminum alloy forging after solution treatment were simulated and analyzed based on DEFORM software. The influence of four different water-entering modes of the forging and water-entering speeds of free-falling, 5 m/s and 2 m/s on the temperature field and residual stress was studied. The results reveal that the water-entering mode and speed of the forging dramatically influence the residual stress. When the forging is rotated 90° in U-face and free falls into water, the residual stress is the smallest and most evenly distributed.
    Simulation on continuous quenching process of rod based on segmented thermal boundary
    He Haoping, Wang Fazhan, Jing Shuowen, Xu Zhenghao, Huang Kepeng
    2022, 47(10):  263-269.  doi:10.13251/j.issn.0254-6051.2022.10.045
    Abstract ( 26 )   PDF (652KB) ( 19 )  
    A segmented thermal boundary method for numerical simulation of continuous quenching process is proposed, and the model segmentation criterion is obtained. Taking 30CrNi3MoV steel porous rod as an example, the water quenching simulation was carried out by using MARC software, and the temperature field, stress field, microstructure distribution ratio and hardness field were obtained. The simulation results show that the segmented thermal boundary method is more in line with the actual working conditions than the overall thermal boundary quenching simulation, and the internal temperature of the workpiece decreases with the increase of the water depth, and the stress of the workpiece decreases from the front end to the back end of the workpiece. The surface hardness after quenching is 51.9-53.7 HRC and the core hardness is 36.8 HRC, which is not more than 10% different from the hardness of the workpiece after actual quenching. The distortion of the hole to the center is 0.18-0.20 mm, and the distortion of the workpiece length is 1.85 mm. which is within 5% difference from the distortion of the hole and the workpiece. All that verifies the accuracy of the segmented thermal boundary method.
    TEST AND ANALYSIS
    Failure analysis on fatigue fracture of large finishing mill back up roller
    Zhang Qiang, Chen Yongping, Bi Guoxi, Wang Hongpeng
    2022, 47(10):  270-274.  doi:10.13251/j.issn.0254-6051.2022.10.046
    Abstract ( 27 )   PDF (662KB) ( 33 )  
    Back-up roller of finish rolling in 1580 production line suddenly broke during the rolling process. In order to figure out the cause of failure, microstructure, mechanical properties, fracture morphology and location of crack initiation source of the roller material were comprehensively analyzed by means of optical microscope, tensile and impact testing machine and scanning electron microscopy. The results show that core material of finish rolling support roller is nodular cast iron, mainly compounded by pearlite, rod cementite, spherical graphite and bovine eye ferrite gathered around graphite. The cleanliness of the structure is unsatisfactory, the non-metallic inclusions have the size concentrating in 10-15 μm and mainly are spherical Al2O3-MgO-SiO2, Al2O3-MgO, Al2O3oxides. The fracture surface of the backup roller presents typical rolling bending fatigue fracture characteristics. The crack source area is located inside the roller and shows as multi-source cracking. The fracture surface presented typical “Fish-in-Eye” characteristics, the largest inclusion in the “Fish-in-Eye” area has a diameter of 3 mm and is spherical Al2O3-MgO-SiO2. The maximum tensile stress of the crack source is 30 MPa, which reaches the fatigue strength of the material. When the crack starts around the inclusion, the maximum stress intensity factor(ΔK) at crack tip is 1.385 MPa·m1/2, larger than the threshold value of internal crack initiation and propagation(ΔKinc-th). Thus it is inferred that the cracks nucleate at the interface between the inclusions and the matrix. When the crack extends beyond the “Fish-in-Eye” area, the crack expands rapidly under the action of stress and converges to form a long crack, which eventually leads to the instantaneous fracture of the roller.
    Formation causes of white bright layer on surface of vacuum oil quenched martensitic stainless steel
    Ding Yahong, Zhu Kai, He Jun, Zhu Ling, Wang Qiaoli, Li Jianfei
    2022, 47(10):  275-282.  doi:10.13251/j.issn.0254-6051.2022.10.047
    Abstract ( 109 )   PDF (652KB) ( 36 )  
    Surface of martensitic stainless steel nut was prone to brown yellow rust in the air environment. The surface rust of martensitic stainless steel was analyzed by means of optical microscope, scanning electron microscopy and chemical element detection. The results show that a uniform white bright layer structure is formed on surface of the martensitic stainless steel after vacuum quenched in oil. The corrosion resistance of the white bright layer is worse than that of normal martensite. The white bright layer is easy to rust in the air, and the rust does not penetrate the white bright layer. Through the measurement of carbon content and mechanism analysis, it is considered that the necessary conditions for the formation of white bright layer are vacuum heating and oil cooling. Vacuum heating causes the depletion of alloy element Cr on the surface of stainless steel, and carbon infiltration due to the oil decomposition leads to the carburization of the surface, which leads to no martensitic transformation on the surface of stainless steel during quenching, forming a white bright layer structure with poor corrosion resistance.
    Distortion control of pull rod of short-stress line rolling mill in ion nitriding
    Sun Huayu, Zhao Yuxia, Li Shuangxi
    2022, 47(10):  283-289.  doi:10.13251/j.issn.0254-6051.2022.10.048
    Abstract ( 26 )   PDF (752KB) ( 19 )  
    Influence of various factors including the processing residual stress of the short-stress line rolling mill, the method of mounting, multiple heating and cooling on the distortion of rod-shaped workpieces caused by ion nitriding was investigated. The results show that the most important factor affecting the nitriding distortion is the processing stress of the pull rod, so for long rod-shaped workpieces, a reasonable stress relief process before finishing and nitriding can effectively control the nitriding distortion. In addition, slower heating, cooling and vertical suspension clamping methods can also reduce nitriding distortion. For long rod-shaped workpieces which requires multiple nitriding to meet the technical requirements of the drawings, rotating the workpiece by 180° after each nitriding can effectively control the nitriding distortion.