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  • PROCESS RESEARCH
    Effect of aging on microstructure and properties of new Al-Zn-Mg-Cu alloy
    Xue Kemin, Li Yunhui, Xu Bing, Yan Siliang, Li Ping
    2021, 46(3):  1-6.  doi:10.13251/j.issn.0254-6051.2021.03.001
    Abstract ( 66 )   PDF (651KB) ( 39 )  
    Influences of one-stage and two-stage aging on the microstructure and comprehensive properties of a new Al-Zn-Mg-Cu alloy were studied by means of X-ray diffraction, optical metallography and scanning electron microscopy in combination with mechanical properties measurement and electrical conductivity measurement. The results show that with the increases of aging temperature and aging time, grain size increases slowly and the conductivity increases gradually. The optimal one-stage aging process of the as-cast new Al-Zn-Mg-Cu alloy is 135 ℃×12 h, the hardness of the alloy is 231.8 HV0.2, the tensile strength is 568 MPa, the elongation is 2.8%, the conductivity is 33.7%IACS. The optimal two-stage aging process is 155 ℃×4 h, the hardness of the alloy is 216.9 HV0.2, the tensile strength is 558.7 MPa, the elongation is 4.1%, and the conductivity is 35.2%IACS.
    Effect of heat treatment on corrosion resistance of 1Cr18Ni9Ti and 2Cr13 steel plate welded joint
    Wang Yufeng, Zhao Yongtao, Ma Honghao, Ren Huiping
    2021, 46(3):  7-11.  doi:10.13251/j.issn.0254-6051.2021.03.002
    Abstract ( 79 )   PDF (575KB) ( 24 )  
    1Cr18Ni9Ti and 2Cr13 steel plates were welded by TIG welding with adding welding materials, and post-weld heat treatment was carried out. The welded joint microstructure before and after heat treatment was observed and analyzed by means of SEM. The AC impedance and polarization curves of the welded joint were measured by simulated immersion test. The results show that the welded joint of 1Cr18Ni9Ti and 2Cr13 steel plate before heat treatment is a typical columnar crystal, and the structure is composed of lath martensite+ austenite+ second phase. The microstructure of welded joints after heat treatment is composed of tempered sorbite+ austenite+ second phase. Both the corrosion resistance order of welded joints before or after heat treatment from strong to weak is as follows: austenite base material>heat affected zone near austenite side>welded joint zone>heat affected zone near martensite side>martensite base material. In contrast, the corrosion resistance of martensite base material in the welded joint after heat treatment increases slightly, while the other areas decreases.
    Effect of quenching cooling rate on pearlite microstructure ofhypereutectoid rail steel
    Wang Dongmei, Zhao Leicheng, Chen Lin, Bao Xirong, Guo Ruihua
    2021, 46(3):  12-16.  doi:10.13251/j.issn.0254-6051.2021.03.003
    Abstract ( 68 )   PDF (572KB) ( 33 )  
    Effect of cooling rates on pearlite microstructure characteristics of the hypereutectoid rail steel in the quenching process was investigated by means of OM, SEM and hardness testes. The results show that with the increase of cooling rates, the pearlite interlamellar spacing and cementite thickness decrease from 302 nm and 43.6 nm to 205 nm and 29.2 nm, respectively. Moreover, the refined pearlite interlamellar spacing acts on the enhancement of hardness from 286 HV to 348 HV.
    Effect of relative extrusion ratio on microstructure and properties of different parts in Al-Zn-Mg alloy component
    Huang Yuanchun, Zhang Qiang, Nie Changchang, Tan Weiyang
    2021, 46(3):  17-23.  doi:10.13251/j.issn.0254-6051.2021.03.004
    Abstract ( 69 )   PDF (575KB) ( 20 )  
    Effect of relative extrusion ratio on the microstructure and properties of different positions in Al-Zn-Mg alloy component before and after heat treatment was investigated by using inductive coupled plasma (ICP), X-ray diffractometry (XRD), tensile tests and microstructure observation by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy disperse spectroscopy (EDS). The results show that Al3(Zr,Ti) particles exist in both the as-extruded and aged microstructure. The larger the relative extrusion ratio and the higher the content of Al3(Zr,Ti) particle is, the stronger the degree of recrystallization inhibition during heat treatment is, and large amount of fibrous tissue microstructure remains in the structure after heat treatment as well as the MgZn2 phase precipitates and aggregates at the grain boundaries. The larger the relative extrusion ratio is, the smaller the average grain size increment after heat treatment is, and the larger the increments of yield strength, tensile strength and elongation are.
    Rapid spheroidizing annealing process of 60Si2Mn cold drawn pearlite steel wire
    Yang Chen, Liu Yongning, Sun Junjie, Wang Hao, Zhao Ruishu
    2021, 46(3):  24-27.  doi:10.13251/j.issn.0254-6051.2021.03.005
    Abstract ( 66 )   PDF (573KB) ( 28 )  
    By austenitizing at 810 ℃ for 1.5 min, furnace cooling to 500 ℃ and then air cooling, a rapid spheroidizing annealing process was carried out for 60Si2Mn cold drawn pearlite steel wire, then the mechanical properties, spheroidizing effect, spheroidizing time and rapid spheroidizing mechanism were studied and compared with that of normal spheroidizing annealing and isothermal spheroidizing annealing processes. The results show that compared with the two common spheroidizing annealing process, the rapid spheroidizing annealing process can significantly shorten the spheroidizing time, and with better spheroidizing effect. The yield strength, tensile strength, elongation and reduction of area of the rapid spheroidizing annealed steel are 620 MPa, 745 MPa, 21% and 66.7%, respectively. The shortening of spheroidizing time is mainly due to the increase of dislocation density and distortion energy in the steel caused by cold drawing deformation, which enables the lamellar pearlite to change rapidly into disconnected parts by dissolving in the heating process, and promotes the spheroidization of cementite.
    Effect of ceramic anodizing pretreatment on micro-arc oxidation film of 6061 aluminum alloy in weak-acid electrolyte
    Wu Yuhao, Wei Xiaowei, Xie Xiaowei
    2021, 46(3):  28-32.  doi:10.13251/j.issn.0254-6051.2021.03.006
    Abstract ( 63 )   PDF (574KB) ( 19 )  
    Taking 6061 aluminum alloy as the research object, the composition and performance of its micro-arc oxidation (MAO) film in weak-acid electrolyte were analyzed, and the influence of ceramic anodizing pretreatment on the MAO film was discussed. The results show that in weak-acid electrolyte, the 6061 aluminum alloy MAO film with ceramic anodizing pretreatment is mainly composed of γ-Al2O3 and α-Al2O3, while amorphous Al2O3 also exists due to the residual ceramic anodizing film. Compared with the non-pretreated MAO film, the ceramic anodizing pretreatment can significantly increase the thickness, hardness and corrosion resistance of the oxidation film, of which the thickness and hardness after the pretreatment are 25.3 μm and 1690 HV0.1, respectively.
    Effect of annealing temperature on recrystallization behaviors of cold-rolled high-purity CVD tungsten
    Tan Xiao, Hao Yupeng, Yu Xiaodong, Wang Yutian, Tan Chengwen, Hu Jin
    2021, 46(3):  33-38.  doi:10.13251/j.issn.0254-6051.2021.03.007
    Abstract ( 70 )   PDF (573KB) ( 27 )  
    Recrystallization behavior of chemical vapor deposited high purity tungsten after cold-rolling was studied by using annealing experiments at different temperatures. The results show that layered heterostructure is formed in the cold-rolled tungsten, which improves the strain hardening rate of the material, thereby improving the plasticity. After cold rolling, the ductile-brittle transition temperature is reduced to below 200 ℃, and the hardness is increased from 402 HV0.2 in deposited state to 547 HV0.2. After high temperature annealing, the cold-rolled tungsten recrystallizes at 1100 ℃, and the recrystallization temperature is reduced by 880 ℃ compared with the deposited tungsten. This is because the storage energy of the material is increased due to low-temperature plastic deformation, and the recrystallization driving force is increased, so the recrystallization temperature decreases. As the annealing temperature increases, the layered heterostructure gradually disappears due to the increase of grain size, the hardness rapidly decreases to 370 HV0.2 in the fully recrystallized state, and the yield strength gradually decreases from 1224 MPa in the cold-rolled state to 558 MPa after annealing at 1800 ℃, but the ductile-brittle transition temperature remains below 200 ℃.
    Study on boundary of efficient quenching and tempering process of 26CrMoVNbRE steel
    Shi Xiaoxia, Ren Huiping, Li Xiao, Wang Chao, Gong Xin
    2021, 46(3):  39-45.  doi:10.13251/j.issn.0254-6051.2021.03.008
    Abstract ( 73 )   PDF (575KB) ( 24 )  
    Effect of different quenching temperature, and holding time, tempering temperature and tempering time on the microstructure of 26CrMoVNbRE steel was studied. The results show that the microstructure is mainly composed of tempered sorbite after quenched at 870-900 ℃ and tempered at high temperatures, and the primary austenite grains are fine and uniform. The yield strength of the specimens quenched at 870 ℃ for 40 min is similar to that of quenched at 900 ℃ for 30 min. The former has good comprehensive mechanical properties, and the latter is more favorable to field high efficiency heat treatment. Mechanical properties of the BT110TS oil casing tubes made of the steel can meet technical requirements when quenched at 900 ℃ for 30 min and tempered at 720 ℃ for 60 min. The precipitates were observed by means of SEM and EDAS under different tempering temperatures. The results show that the second phase precipitates in the experimental steel are composite phases formed by M2C type molybdenum carbide and M3C type chromium carbide. With the decrease of tempering temperature, the precipitates distributed on the grain boundary increase, which is not conducive to low temperature impact properties and stress corrosion resistance.
    Effect of spheroidizing temperature on microstructure and properties of4Cr5Mo2V hot work die steel
    Chang Yong, Li Li, Wu Shaojun, Zuo Pengpeng, Wu Xiaochun
    2021, 46(3):  46-50.  doi:10.13251/j.issn.0254-6051.2021.03.009
    Abstract ( 67 )   PDF (575KB) ( 34 )  
    Metallographic microscope and scanning electron microscope were used to observe the microstructure change of 4Cr5Mo2V steel at different spheroidizing temperatures. The image processing software Image Pro Plus was used to quantitatively analyze the number, average particle size and volume fraction of carbides. Then the influence of annealing spheroidizing on the mechanical properties of the quenched and tempered 4Cr5Mo2V steel was studied. The results show that when the spheroidizing temperature is 820-900 ℃, the number of carbides per unit area, volume fraction and average particle size are between (10.0-14.0)×108 cm-2, 8.0%-10.0% and 0.30-0.43 μm, respectively. When the spheroidizing temperature is 840 ℃, the inhomogeneous annealing structure can be effectively eliminated, the average particle size of the carbide is 0.31 μm, and the impact absorbed energy at room temperature is 392 J, with good mechanical properties.
    Effect of heat treatment process on mechanical properties of ER7 wheel steel
    Huo Xiongbo, Dang Shu'e, Zhao Jiaxing, Zhang Xiaofeng, Chen Ying, Zhu Xuetong
    2021, 46(3):  51-55.  doi:10.13251/j.issn.0254-6051.2021.03.010
    Abstract ( 80 )   PDF (575KB) ( 26 )  
    Microstructure of ER7 wheel steel with different pearlite lamellar spacing and ferrite content was obtained by different heat treatment processes. The tensile properties and -20 ℃ impact properties were tested. The results show that as the cooling rate increases, the percentage of ferrite increases, and the pearlite lamellar spacing and pearlite pellet size decrease. Increasing the cooling rate will increase the yield strength, tensile strength, elongation and reduction of area of the wheel steel. As the pearlite lamellar spacing and grain size decrease, the fracture toughness of the wheel steel also increases accordingly. Wheel steel specimens heated at 850 ℃ and cooled by water mist have the best combination of strength and toughness and the best comprehensive mechanical properties.
    Heat treatment of selective laser melting GH3536 alloy
    Hu Yuheng, Peng Weikang, Run Changsheng, Dai Yanfeng
    2021, 46(3):  56-60.  doi:10.13251/j.issn.0254-6051.2021.03.011
    Abstract ( 74 )   PDF (573KB) ( 25 )  
    Effect of different heat treatment processes on the microstructure and mechanical properties of selected lasive melting GH3536 alloy was studied by means of OM, SEM, and mechanical properties tests. The results show that, with the solution treatment temperature increasing, the grain size increases, the tensile strength increases gradually at high temperature and decreases at room temperature. When the solution temperature reaches 1120 ℃, the tensile strengths of transverse and longitudinal specimens at room temperature can reach 816 and 731 MPa, respectively. While that of transverse and longitudinal test bars reach 189 and 204 MPa at 900 ℃, respectively. After aging at 800 ℃, the alloy matrix can precipitate fine carbides, which has an effect on second phase strengthening, and so that the strength can increase. With the increase of aging time, the carbides become denser, but the grain size changes a little, which leads to the increase of both tensile strength and percentage elongation after fracture at room temperature. When the aging time reaches 20 h, tensile strengths of the transversal and longitudinal test bars at room temperature reach 832 and 747 MPa, respectively. The percentage elongations after fracture of transversal and longitudinal test bars at 900 ℃ reaches 8.5% and 21.5%, respectively. Finally, the optimal heat treatment process for the selective laser melting GH3536 alloy is solution treated at 1120 ℃ for 1 h, and then aged at 800 ℃ for 20 h.
    Optimum heat treatment process of Cu-Ni-Sn alloy by orthogonal test
    Li Jian, Feng Zaixin, Zuo Sen, Yao Yukang, Guo Xiaosen
    2021, 46(3):  61-66.  doi:10.13251/j.issn.0254-6051.2021.03.012
    Abstract ( 74 )   PDF (575KB) ( 25 )  
    Effect of pre-deformation and aging processes on mechanical properties of a new Cu-Ni-Sn alloy (in solid solution state) were studied by using orthogonal test, and the optimum process parameters were obtained by orthogonal range analysis. The results show that the factors affecting the hardness of the Cu-Ni-Sn alloy are: aging temperature>pre-deformation amount>aging time, the factors affecting the tensile strength of the alloy are: pre-deformation amount>aging time>aging temperature, and the factors affecting the percentage elongation after fracture of the alloy are: aging temperature>pre-deformation amount>aging time. Therefore, the optimum process is determined as: aging temperature 360 ℃, aging time 5 h and pre-deformation amount 40%. In addition, with the increase of aging temperature and pre-deformation, the tensile fracture morphologies of the alloy changes from ductile fracture with a large number of dimples to quasi-cleavage fracture with river-like morphologies, and then to intergranular brittle fracture, indicating that the plasticity of the alloy gradually decreases.
    Effect of secondary annealing temperature on microstructure and magnetic properties of non-oriented silicon steel
    Lu Jiadong, Wu Shengjie, Yue Chongxiang, Li Hualong
    2021, 46(3):  67-70.  doi:10.13251/j.issn.0254-6051.2021.03.013
    Abstract ( 87 )   PDF (577KB) ( 31 )  
    Secondary annealing experiment of 1.2% Si non-oriented silicon steel at different temperatures were carried out, and the effect of secondary annealing temperature on the microstructure and magnetic properties of the steel was investigated. The results show that the grain size of ferrite is increased and the core loss is reduced after secondary annealing processes. The core loss of experimental steel is reduced significantly in the annealing temperature range of 780-820 ℃. In this temperature range, the magnetic properties of non-oriented silicon steel is the best, the core loss reduction is 1.0 W/kg, and the average grain size is 83-114 μm. Besides, the precipitates of the experimental steels were investigated by means of SEM. The results show that the main precipitate in the experimental steel is MnS-CuxS. The amount of fine MnS-CuxS precipitate with the size of 0.1-0.2 μm is the lowest in the annealing temperature range of 780-820 ℃.
    Heat treatment process characteristics of age-hardening 20Cr3MnMoVnitriding die steel
    Du Shufang
    2021, 46(3):  71-75.  doi:10.13251/j.issn.0254-6051.2021.03.014
    Abstract ( 74 )   PDF (575KB) ( 23 )  
    Effect of heat treatment process parameters on the mechanical properties and nitriding hardening properties of 20Cr3MnMoV steel was investigated. The results show that the heat treatment of the 20Cr3MnMoV steel is composed of solid solution treatment, aging, preaging and nitriding. Reasonable controlling the aging process is the main technological characteristics of the heat treatment of the 20Cr3MnMoV steel. By using respectively solid solution treatment+ full aging, nitriding without preaging, and preaging+ nitriding, it can be adapted for dies and components at different working conditions, so that it satisfies the different requirements of wear resistance and strength-ductility. Nitrocarburizing of 20Cr3MnMoV steel can be used to realize fast nitriding, deep layer nitriding-hardening, and matrix hardening, which has wide-spread prospects of application.
    Influence of pre-deformation on microstructure and mechanical properties of Al-Zn-Mg aluminum alloy
    Tian Jingcheng, Zhong Weifeng, Qiao Yuxin, Sun Yanbo
    2021, 46(3):  76-79.  doi:10.13251/j.issn.0254-6051.2021.03.015
    Abstract ( 52 )   PDF (573KB) ( 22 )  
    Influence of pre-deformation temperature on microstructure and mechanical properties of Al-Zn-Mg aluminum alloy was investigated. The microstructure was characterized by using OM and TEM. The fracture morphology was investigated by using SEM. The texture was tested by using XRD tester. The mechanical properties were tested by using tensile testing machine. The results indicate that the optimum mechanical properties are achieved after hot deformation under 400 ℃, the yield strength and tensile strength respectively reaches 325 MPa and 455 MPa, while the elongation after fracture reaches 14%. The fracture morphology shows ductile fracture characteristics, and there are dimples with different numbers and sizes at the fracture surface. The dislocation entanglement inside the grains disappears and the dislocation wall is formed after deformation under 400 ℃. The dislocations inside the grains disappear and the recrystallization grains are formed under 450 ℃. The texture is composed of shear texture under 350 ℃ and 400 ℃, including rotation cube texture{001}<110> and brass R texture{111}<112> and {111}<110>. Obvious recrystallization texture CubeND {001}<310> is appeared after deformation under 450 ℃.
    Effect of solution treatment process on microstructure and hardness of as-extruded Mg-9.2Gd-1.9Y-1.8Zn-0.5Zr alloy
    Wu Xiaobao, Zhang Xing, Zhang Jinlu
    2021, 46(3):  80-85.  doi:10.13251/j.issn.0254-6051.2021.03.016
    Abstract ( 68 )   PDF (576KB) ( 32 )  
    Effects of different solution treatment processes on microstructure and mechanical properties of as-extruded Mg-9.2Gd-1.9Y-1.8Zn-0.5Zr alloy were studied by means of DSC, OM, SEM, and TEM. The results show that, after solid solution treatment the microstructure of the alloy consists of α-Mg matrix, Mg12Zn(Gd,Y) phase and phases rich in rare earth. With the increase of holding time, the regular striated LPSO phase is precipitated in the matrix when the tested alloy solution treated at 490 ℃, which plays an important role in second phase strengthening and remarkably improves the microhardness of the tested material. The optimum solution treatment process of the alloy is 490 ℃×13 h, at which the highest average microhardness of the tested alloy can reach 77 HV0.2.
    Aging behavior of cold-rolled Cu-Cr-Zr-Co-Si alloy
    Shuai Gewang, Wang Zhi, Liu Jinhui, Zhou Qingquan
    2021, 46(3):  86-89.  doi:10.13251/j.issn.0254-6051.2021.03.017
    Abstract ( 59 )   PDF (572KB) ( 33 )  
    By measuring the dynamic changes of the electrical conductivity of cold-rolled Cu-Cr-Zr-Co-Si alloy during isothermal aging, based on the approximate linear correlation between the electrical conductivity of the precipitation-strengthened alloy and the transformation ratio of precipitation transformation, the Avrami kinetic equations and curves of the aging precipitation process of the alloy with different cold deformation were established, on which the interaction between recrystallization and aging precipitation was analyzed. The results show that the electrical conductivity and transformation ratio of precipitation transformation of the alloy increase with the increase of deformation and aging time, which is the result of interaction of recrystallization and aging precipitation during aging. With the increase of cold deformation, the precipitation of strengthening phase is obviously accelerated, but the aging precipitation does not significantly prevent or delay the recrystallization softening process. Therefore, heavy cold deformation and short-term aging can lead to higher hardness peaks, but the optimum conductivity can't be obtained at the same time. Only on the premise that the precipitation starts earlier than the recrystallization, and the precipitates can significantly prevent the recrystallization, the best effect can be achieved by using the combined deformation and aging.
    Heat treatment for G115 large diameter pipe fittings
    Cong Xiangzhou, Peng Xingna, Peng Xiankuan, Wang Tao, Chen Zhengzong, Jiang Haifeng, Li Chuanyong, Zhang Shuying
    2021, 46(3):  90-95.  doi:10.13251/j.issn.0254-6051.2021.03.018
    Abstract ( 71 )   PDF (573KB) ( 20 )  
    The orthogonal test method was used to analyze the effects of heat treatment parameters (normalizing temperature, normalizing time, tempering temperature, and tempering time) on the properties of G115 steel, and the heat treatment process of G115 steel large diameter pipe fittings was studied by thermal simulation of hot pressed tee. The results show that the tempering temperature has the greatest comprehensive influence on the tensile strength, hardness and impact performance of the G115 steel. When the tempering temperature is 780 ℃, the strength and hardness are maintained at a higher level, and the impact performance is better. The recommended heat treatment process parameters for G115 steel large diameter pipe fittings are: normalizing temperature 1070-1090 ℃, holding time 1-2 min/mm and not less than 1.5 h; tempering temperature 770-790 ℃, holding time 3.5-5 min/mm and not less than 4 h. After the recommended process treatment, the properties of G115 steel large diameter pipe fittings meet the requirements of T/CSTM 00017-2017 standard.
    Effects of solution treatment and aging temperature on microstructure andmechanical properties of IMI834 titanium alloy plate
    Wang Ruiqin, Ge Peng, Hou Peng, Liao Qiang, Liu Yu
    2021, 46(3):  96-99.  doi:10.13251/j.issn.0254-6051.2021.03.019
    Abstract ( 56 )   PDF (579KB) ( 22 )  
    Effects of different solution treatment and aging temperature on microstructure and mechanical properties of IMI834 alloy were studied. The results show that there is no significant difference between the microstructure of IMI834 alloy plate heat treated at low temperature and that of as-rolled, and the room temperature strength is also basically unchanged. The bimodal structure of the alloy is obtained after heat treatment in α+β two-phase region, and with the increase of solid solution treatment temperature, the content of primary α phase decreases, the room temperature strength increases slightly, and the change law of plasticity is opposite to that of the strength. The decrease of primary α phase content has no obvious effect on the room temperature strength of the alloy plate. With the increase of aging temperature, the strength of the alloy plate at room temperature decreases and the plasticity decreases to some extent. The high temperature mechanical properties of the plate at 600 ℃ are similar to those at room temperature, but the reduction of area is better than that at room temperature. The optimum heat treatment process obtained in this experiment is 1035 ℃×1 h (air cooling)+ (700-750) ℃×4 h (air cooling).
    Effect of annealing soften on microstructure and hardness of high strength steel 300M
    Wang Hongli, Wu Chengchuan, Du Simin, Li Yuan, Luo Xianghua, Ye Wenbing
    2021, 46(3):  100-103.  doi:10.13251/j.issn.0254-6051.2021.03.020
    Abstract ( 74 )   PDF (577KB) ( 22 )  
    In order to improve the subsequent machinability of 300M steel and widen the application field, the effect of annealing process on microstructure and hardness of 300M steel was studied. The results show that annealing at 730 ℃ below Ac1, the microstructure of 300M steel is transformed from martensite to tempered sorbite with spherical or granular carbides. The microstructure is consisting of ferrite, lamellar pearlite with partial spheroid carbides when annealing at 780 ℃ in intercritical phase region. Annealing at 860 ℃ above Ac3, The microstructure is ferrite and lamellar pearlite with long thin sheet carbide. The cooling rate has a significant effect on the hardness of 300M steel, the slow cooling rate results in the spheroidization of carbides and the decrease of hardness. The softening effect of 300M steel is more obvious annealing at intercritical phase region with low cooling rate, and the hardness can be less than 240 HBW.
    Optimization of heat treatment process of SCM420 steel planetary gear for industrial robot
    Yin Heping, Yin Minjie
    2021, 46(3):  104-108.  doi:10.13251/j.issn.0254-6051.2021.03.021
    Abstract ( 74 )   PDF (633KB) ( 24 )  
    Aiming at the heat treatment distortion problem of SCM420 steel planetary gears used in industrial robots, a modified normalizing process was used to adjust the preparatory microstructure before carburizing, and then the gear distortion during carburizing and quenching was effectively controlled by using various measures including reasonable loading scheme, cooling method, and stepped heating process during carburizing. The results show that after the modified normalizing process, a uniform ferrite+pearlite microstructure can be obtained with a hardness of 170 to 180 HBW. And after the carburizing quenching and tempering, the surface hardness, core hardness and effective case depth of the planetary gears with mass production are 59.74 HRC, 40.44 HRC and 0.530 mm, respectively. The grade of martensite of carburized layer is level 1, and that of the retained austenite and carbides are level 1-2, and that of the core microstructure is level 1-2. The gear precision, plane warping, tooth groove amplitude and toothed ribs all meet the technical requirements.
    Effect of tensile/compressive cold deformation on strengthening of2A14 aluminum alloy after aging
    Li Yaojun, Han Zhen, Lan Jian
    2021, 46(3):  109-112.  doi:10.13251/j.issn.0254-6051.2021.03.022
    Abstract ( 55 )   PDF (638KB) ( 28 )  
    Strength of solution treated 2A14 aluminum alloy during aging process under tensile or compressive cold deformation conditions was studied by using X-ray diffractometer and DSC differential scanning calorimetry with the help of precipitation phase strengthening and dislocation strengthening theoretical model of aluminum alloy. The results show that compared with compressive cold deformation, the dislocation density introduced by tensile cold deformation is greater, so the dislocation strengthening effect is stronger; In the under-aging stage (before θ phase precipitates) of tensile cold deformation, the precipitation of the strengthening phase θ′ phase in the alloy is promoted. In the over-aging stage (after θ phase precipitates), the precipitation of the θ phase is suppressed, and the precipitation strengthening effect of tensile cold deformation is better. The strengthening effect of the 2A14 aluminum alloy after tensile cold deformation is more significant.
    Effect of heat treatment on distortion of Cr-Mo steel tool
    Zheng Yefang, Jiang Ying, Xie Xiaojun, Xia Yuliang, Li Quan, You Fei
    2021, 46(3):  113-115.  doi:10.13251/j.issn.0254-6051.2021.03.023
    Abstract ( 58 )   PDF (633KB) ( 22 )  
    For 25CrMo, 30CrMo and 42CrMo steel tools, quenching process at 860 ℃ was carried out, and the 42CrMo steel tool was tested for 860, 850, 830 ℃ quenching and preheating+ 830 ℃ quenching, for comparing the distortion data of the tool groove. The results show that with carbon content increasing, the distortion of low- and medium-carbon chromium-chromium steel tool groove quenched at 860 ℃ increases, and the max distortion is fluctuated between -0.15 and +0.15 mm. With quenching temperature decreasing, the distortion of 42CrMo steel tool groove is drops to -0.10-+0.09 mm.
    MATERIALS RESEARCH
    Effect of La addition on as-cast microstructure and hardness ofFeMnCrNiCo high entropy alloy
    Dong Fang, Mao Ning, Qu Wei
    2021, 46(3):  116-120.  doi:10.13251/j.issn.0254-6051.2021.03.024
    Abstract ( 53 )   PDF (643KB) ( 32 )  
    Effect of La addition on as-cast microstructure and hardness of FeMnCrNiCo high entropy alloys (HEAs) was investigated. The microstructure and hardness of the FeMnCrNiCo and FeMnCrNiCoLa0.2 HEAs were analyzed by means of XRD, OM, EDS and Vickers hardness tester. The results show that with the addition of La, the dendrite of the HEA is refined by 49.1%, and the phase structure changes from a single fcc solid solution to the composite structure containing fcc phase and LaNi phase, and the brittle LaNi phase distributes continuously in the interdendrite region. The brittle LaNi compound and grain refinement increase the hardness of the alloy by 37%.
    Continuous cooling transformation of undercooled austenite of steel for H-grade high-strength anti-corrosive sucker rod
    Sun Xiaoran, Zheng Wenyue, Sun Yan, Bai Lijuan, Ding Hui
    2021, 46(3):  121-124.  doi:10.13251/j.issn.0254-6051.2021.03.025
    Abstract ( 50 )   PDF (633KB) ( 20 )  
    Effect of cooling rate on microstructure and hardness of steel for H-grade high-strength anti-corrosiue sucker rod during undercooled austenite continuous cooling transformation was studied by means of a DIL805L quenching dilatometer. The results show that the CCT curves show an obvious overall rightward shift and with very little pearlite transformation, and the ferrite-pearlite transformation zone is completely separated from the bainite-martensite transformation zone during the continuous cooling process of the tested steel. The hardness change with the cooling rate is divided into two stages, including rapid increasing at low cooling rate and tending to be stable at high cooling rate, which is related to the changing trend of microstructure. Bainite starts to form when the cooling rate is less than 1.5 ℃/s. In order to obtain excellent bainite structure, the selectable cooling rate range is very small. The experimental research can provide effective technical support for the microstructure control and process formulation of sucker rod steel.
    Microstructure and corrosion properties of solution treated AZ91-xCu alloys
    Sang Heng, Jing Hemin, Song Guangsheng, Chen Zheng
    2021, 46(3):  125-129.  doi:10.13251/j.issn.0254-6051.2021.03.026
    Abstract ( 51 )   PDF (647KB) ( 33 )  
    AZ91-xCu (x=0, 0.5, 1, 2) alloy was prepared by vacuum melting method, and solid solution treated at 400 ℃ for 12 h. The phase, microstructure and corrosion properties of the alloy were studied by means of X-ray diffraction, scanning electron microscopy, immersion mass loss method and polarization curve test. The results show that the substrates of as-cast and solid solution treated AZ91-xCu alloys are mainly composed of α-Mg and β-Mg17Al12 phases, and the addition of Cu leads to Mg2Cu and Cu5Zn8 phases precipitation in the substrates, among which a new phase Al2Cu appears in the solid solution treated AZ91-2Cu alloy. During the solid solution treatment, the β-Mg17Al12 phase of the alloy is largely dissolved into the substrate and the grain boundary is obvious. The remaining second phase is mainly distributed at the grain boundary and a little disperses in the grain. The addition of Cu and the solution treatment both accelerate the corrosion rate of AZ91 alloy, among which the corrosion rate of the solution treated AZ91-2Cu alloy is the highest.
    Effects of quenching temperature and nitrogen content on microstructure and properties of martensitic stainless steel
    Ji Xianbin, Li Zhaoguo, Wei Haixia, Qian Zhangxin
    2021, 46(3):  130-134.  doi:10.13251/j.issn.0254-6051.2021.03.027
    Abstract ( 65 )   PDF (649KB) ( 24 )  
    Effects of quenching temperature and nitrogen content on microstructure, mechanical properties and corrosion resistance of 20Cr13,20Cr13N and 20Cr13HN steels were investigated. The results show that with the increase of nitrogen content, the nitrides pinning effect is enhanced, the microstructure is refined obviously, the yield strength, tensile strength and Vickers hardness increase, but the elongation decreases. At the same quenching temperature and cooling rate, the Vickers hardness increases under the action of solid solution, precipitation and phase transformation strengthening. With the increase of cooling rate, the driving force of phase transformation increases, the lath martensite gradually changes to fine cryptocrystalline martensite and the hardness increases. The corrosion property and pitting potential increase with the increase of nitrogen content.
    Effect of Al/Si ratio on microstructure and wear resistance of Ti-Al-Si coating onTC4 alloy by laser cladding
    Liu Ran, Gao Yuan, Wu Tao
    2021, 46(3):  135-139.  doi:10.13251/j.issn.0254-6051.2021.03.028
    Abstract ( 55 )   PDF (638KB) ( 20 )  
    Ti-Al-Si coating was prepared on the surface of TC4 alloy by laser cladding and using Ti-Al-Si composite powder with different Al/Si ratio as raw material. Effect of Al/Si ratio on phase composition, microstructure, microhardness and friction and wear properties of the coating was investigated. The results show that there is a good metallurgical bonding between the coating and the substrate, and no obvious cracks and pores are found in the single pass coating. The main structures of the coatings with different Al/Si ratio are mainly the dendrite, which has the main component of α-Ti, the reinforcing phase is lamellar Ti5Si3 and Ti7Al5Si12, and TiAl, Ti3Al and TiAl3 phases are distributed among the dendrite. The higher the content of Si element, the more the content of in-situ reinforcing phase is in the coating. The highest microhardness of the coating is 1194 HV0.1, which is about 4.1 times of that of the substrate. However, the brittleness of the coating increases and the wear resistance decreases with the increase of the content of Si element. It is also found that the effect of reinforcing phases on hardness and wear resistance is stronger than that of grain refinement when the coating has more Al element.
    Effect of V on microstructure and tensile properties of high carbon pearlite steel
    Wan Zhijian, Liu Xuehua, Zhao Hai, Jiang Bo, Zou Qiang
    2021, 46(3):  140-145.  doi:10.13251/j.issn.0254-6051.2021.03.029
    Abstract ( 59 )   PDF (634KB) ( 24 )  
    The high carbon steel with vanadium mass fraction of 0%-0.13% was designed and smelted. The effect of vanadium content on the structure and tensile properties of high carbon pearlite steel was studied by means of metallographic microscope, scanning electron microscope, electron backscattering and tensile test. The results show that vanadium can improve the structure uniformity and increase ferrite content, and reduce the grain size, but when the vanadium content exceeds 0.08%, the grain refinement effect is weakened. When the mass fraction of vanadium is 0%-0.13%, the relationship between the pearlite lamellar spacing and strength is close, and the corresponding relationship is obtained. The plasticity of the tested steel is not sensitive to the vanadium content. When the vanadium content does not exceed 0.08%, the plasticity is slightly increased, otherwise, the plasticity is reduced.
    MICROSTRUCTURE AND PROPERTIES
    Effect of soaking temperature on microstructure evolution and hardness ofTi-V complex microalloyed steel
    Ni Lingling, Fu Xibin, Zhang Ke, Zhao Shiyu, Ren Wubin, Li Zhaodong, Li Jinghui, Zhang Mingya
    2021, 46(3):  146-152.  doi:10.13251/j.issn.0254-6051.2021.03.030
    Abstract ( 59 )   PDF (641KB) ( 22 )  
    Effect of soaking temperature on microstructure transformation and hardness of Ti-V microalloyed steel was investigated by means of OM, SEM and Vickers hardness tester. The reasons for microstructure evolution and hardness change were also clarified. The results show that the microstructure of Ti-V steel with different soaking temperatures is all martensite. As the soaking temperature rises from 1000 ℃ to 1250 ℃, the quenchened hardness of Ti-V steel decreases from 333 HV to 212 HV, and the prior austenite grain size increases from 52 μm to 209 μm. Above the total solution temperature, a small amount of TiN particles still exist and gradually dissolve with increasing of temperature. The pinning effect of the TiN on the grain boundaries is the main factor preventing the growth of grains. The influence of prior austenite size on the hardness of Ti-V steel gradually decreases with the increase of its size. Therefore, the soaking temperature should be below 1220 ℃ to avoid coarse grains.
    Microstructure and properties of V-Ti-Ni alloy for hydrogen separation treated by electroplastic rolling
    Huang Huanchao, Liu Meijuan, Sun Ming, Jiang peng
    2021, 46(3):  153-158.  doi:10.13251/j.issn.0254-6051.2021.03.031
    Abstract ( 60 )   PDF (634KB) ( 32 )  
    Multi-phase V-Ti-Ni alloys containing V-rich phases and eutectic Ni-Ti compounds can achieve a good balance between hydrogen permeability and hydrogen embrittlement resistance, so that they have broad application prospects in the field of hydrogen separation membranes. However, such alloys have large resistance for deformation, easiness to oxidize, and difficulty for low temperature forming. In order to improve the formability and rolling efficiency, and to reduce the manufacturing cost of alloy membranes, heat treatment and electricplastic rolling were carried out for multiphase V60Ti20Ni20 alloy, and then the influence of pulse current density on the microstructure, rollability and microhardness of the alloy during rolling was studied by means of optical microscope, scanning electron microscope, energy spectrometer, X-ray diffractometer and Vickers microhardness tester. The results show that the electricplastic rolling can effectively improve the rollability of the alloy by increasing the single-pass rolling ultimate reduction to 13.3%, which is an increase of 155% compared with that of the cold rolling of heat-treated alloy. During the electroplastic rolling process, as the pulse current density increases, the microstructure of the alloy deforms more uniformly, the rheological direction of the microstructure is more consistent, and the microhardness of the alloy decreases, which is due to the electroplastic effect promotes dislocation movement during rolling process, resulting a reduction of the dislocation entanglement.
    Hot compression deformation behavior and microstructure evolution of 13Cr super martensitic stainless steel
    Ji Huiling, Lü Jinyi, Zhang Yiwei, Yang Lei, Yin Yuande
    2021, 46(3):  159-165.  doi:10.13251/j.issn.0254-6051.2021.03.032
    Abstract ( 74 )   PDF (634KB) ( 31 )  
    The hot deformation behavior of 13Cr super martensitic stainless steel was studied by means of Gleeble-3500 thermal simulation mechanical simulator. The single pass compression experiment was conducted with the temperature range of 950-1150 ℃ and the strain rate range of 0.001-10 s-1. The constitutive equation of flow stress is established based on hyperbolic sine model, and the hot deformation activation energy of the experimental steel is obtained as about 412 kJ/mol. Based on the dynamic material model (DMM) theory, the processing map of the steel is established, from which the optimal ranges of hot deformation temperature and strain rate are determined as 1032-1072 ℃ and 0.039-0.087 s-1, respectively. The results of microstructure evolution study show that the experimental steel is prone to produce the dynamic recrystallization under high deformation temperature and low strain rate. When the deformation temperature rises from 950 ℃ to 1050 ℃ under 0.01 s-1 strain rate, the volume of dynamic recrystallization increases from 18.7% to 60.1%, and the recrystallization grains are fine and uniform. When the deformation temperature is 1050 ℃, the dynamically recrystallized grains grow and coarsen with the decrease of strain rate.
    Continuous cooling transformation of 960 MPa grade high strength steel
    Sun Yan, Zhao Nan, Xue Feng, An Zhiguo, Guo Yintao
    2021, 46(3):  166-169.  doi:10.13251/j.issn.0254-6051.2021.03.033
    Abstract ( 65 )   PDF (639KB) ( 23 )  
    Continuous cooling transformation of 960 MPa grade high strength steel was analyzed by using DIL850L thermal dilatometer combined with metallographic and scanning electron microscopes. The results show that when the cooling rate is in the range of 0.1-2 ℃/s, the room temperature microstructure is of ferrite, pearlite and bainite; the ferrite and bainite are obtained in the range of 2-10 ℃/s; and the microstructure is all bainite in the range of 20-80 ℃/s. The high temperature transformation zone and the medium temperature transformation zone in the CCT curves are not separated, and the phase transformation temperature decreases with the increase of cooling rate.
    Continuous cooling transformation curves of a bainitic wear-resistant cast steel for mining machinery
    Luo Ping, Li Xianjun, Zhang Wenliang, Deng Kun, Sun Lizhuang, Liu Junjie, Hou Junqing
    2021, 46(3):  170-174.  doi:10.13251/j.issn.0254-6051.2021.03.034
    Abstract ( 50 )   PDF (634KB) ( 24 )  
    Continuous cooling transformation (CCT) curves of a bainitic wear-resistant cast steel used for mining machinery were determined based on the dilatometric measurement, optical microstructure examination as well as microhardness test. The results show that the phase transformation temperatures Ac1, Ac3, and Ms (martensite starting transformation temperature) are 790 ℃, 845 ℃, and 303 ℃, respectively. For the cooling rate below 0.05 ℃/s, ferrite and pearlite are obtained; for that between 0.05 ℃/s and 0.1 ℃/s, the transformation products are ferrite, pearlite and bainite. For that between 0.25 ℃/s and 15 ℃/s, a bainite/martensite multiphase microstructure is obtained. When the cooling rate is higher than 30 ℃/s, the undercooled austenite almost completely transforms into martensite. The critical cooling rate of martensite is between 15 ℃/s and 30 ℃/s. With the increase of cooling rate, the microhardness increases rapidly at first and then tends to be 585 HV0.01.
    Evolution law and mechanisms of electrical conductivity of Al-Mg-Si alloy wire
    Chen Qingyin, Sheng Yehong, Li Rui, Hou Jiapeng, Wang Qiang, Zhang Zhefeng
    2021, 46(3):  175-179.  doi:10.13251/j.issn.0254-6051.2021.03.035
    Abstract ( 59 )   PDF (633KB) ( 25 )  
    Thermal service environment of Al-Mg-Si alloy wire used for overhead transmission lines was simulated by annealing at different temperatures, the evolution law and mechanisms of electrical conductivity of the Al-Mg-Si alloy wire annealed at different temperatures were investigated. The results show that the electrical conductivity increasing of the annealed Al-Mg-Si alloy wire could be divided into three stages with the increase of annealing temperature. In the first stage (temperature ranges from 90 ℃ to 150 ℃), the electrical conductivity increases slightly, which is caused by the defect recovery. In the second stage (temperature ranges from 150 ℃ to 200 ℃), the growth of precipitates and the precipitation of solid solution atoms lead to the rapid increase of the electrical conductivity. In the third stage (temperature ranges from 200 ℃ to 300 ℃), the grain growth is the main reason for the slow increase of the electrical conductivity.
    Analysis of influencing factors of σ phase precipitation in2205 duplex stainless steel
    Liu Yan, Gao Renqiang, Chen Xingrun, Qian Zhangxin
    2021, 46(3):  180-183.  doi:10.13251/j.issn.0254-6051.2021.03.036
    Abstract ( 80 )   PDF (641KB) ( 25 )  
    Effects of aging temperature, aging time, solution temperature, Mn and Mo content on the precipitation quantity of σ phase in 2205 duplex stainless steel were analyzed. The results show that with the aging time increasing, the precipitation amount of σ phase increases. At the same aging time, the content of σ phase increases with the increase of aging temperature. The precipitation quantity of σ phase is largest when aged at 850 ℃. When the temperature exceeds 850 ℃, the quantity of the σ phase decreases with temperature increasing. Increasing the solution temperature, Cr content and Mo content can make precipitation time shorten and the precipitation quantity increase at the same aging time.
    COMPUTER APPLICATION
    Numerical simulation of heat treatment for 3Cr2NiMo steel module bulk after forging
    Wang Linchun, Wu Yongqiang, Wang Kaikun, Li Heng
    2021, 46(3):  184-190.  doi:10.13251/j.issn.0254-6051.2021.03.037
    Abstract ( 66 )   PDF (636KB) ( 32 )  
    Taking the forging module of 3Cr2NiMo die steel as the research object, the thermal physical parameters of which were calculated by JMatPro software. And the heat treatment after forging was studied by means of numerical simulation using Deform-3D software, the test verification was made at last. The results show that, the cooling rate of the outer surface of the module is higher than that of the core during quenching. The martensite transformation from the core to the surface does not simultaneously occur and the microstructure distribution from the surface to the core after quenching is martensite, bainite and ferrite in turn. The equivalent stress distribution along thickness direction is more uniform, but there is stress concentration at the edge position. The distribution of hardness values is positively correlated with the martensite distribution, and the average hardness value of the surface is 34.86 HRC. Meanwhile, the average thickness of martensite layer is 45 mm and the average hardness of surface is 36.23 HRC by the test verification. The error results between simulation and test are less than 10%, which has good accuracy.
    Heating process analysis and system design of continuous annealing furnace for cold-rolled stainless steel
    Li Zhiming, Li Chunming, Qin Fenghua, Hu Yinping
    2021, 46(3):  191-195.  doi:10.13251/j.issn.0254-6051.2021.03.038
    Abstract ( 63 )   PDF (636KB) ( 23 )  
    Based on the continuous annealing process and system analyses for cold-rolled stainless steel, the heating system of continuous annealing furnace was designed, and the furnace length configuration and the combustion power configuration were respectively calculated by the surface energy balance equation and the energy conservation equation. By comparison and analysis of the actual calculation example and the actual operation, it verifies that the design method is effective and has the ability to complete the design process from the product outline and process analysis basis to the unit heating system integration, arrangement and overall arrangement of equipment. Thus, it provides a theoretical basis for the secondary model of the heating system of the cold-rolled stainless steel continuous annealing furnace.
    Inpainting of metallographic image based on improved PatchMatch algorithm
    Li Songtao, Li Weigang, Shi Jingrui, Gan Ping
    2021, 46(3):  196-205.  doi:10.13251/j.issn.0254-6051.2021.03.039
    Abstract ( 56 )   PDF (636KB) ( 27 )  
    Combining the DCT pyramid compression algorithm and the multi-patch optimal matching mechanism to improve the traditional PatchMatch image repair algorithm, using different algorithms to repair and compare the metallographic images with pollution characteristics. The results show that the improved PatchMatch algorithm greatly improves the repair speed and repair quality. The repaired images are more effective than other image repair algorithms, the internal texture details of the metallographic images are restored more accurately and delicately, and metallurgical images repair can solve the problems that conventional metallurgical image segmentation can not eliminate the big noise.
    TEST AND ANALYSIS
    Failure analysis and heat treatment process optimization of Cr12MoV steel blanking die
    Gao Zhiyu, He Wei, Jing Xiukun, Fan Xianjin, Wang Yingxin, Bai Jiang, Wang Daliang
    2021, 46(3):  206-212.  doi:10.13251/j.issn.0254-6051.2021.03.040
    Abstract ( 70 )   PDF (543KB) ( 32 )  
    Early failure of Cr12MoV steel blanking die was caused by excessive wear. The service environment, chemical composition, hardness and microstructure were analyzed, and the temperature distribution of the die in service was calculated by finite element simulation. The results show that the chemical composition of the blanking die meets the requirements of the standard, the hardness is slightly lower than the technical requirements, the heterogeneity of eutectic carbides in the microstructure and the size of bulk carbides exceed the standard specification, the field test and the simulation calculation show that the service temperature of the blanking die is higher (<500 ℃). It is found that the causes for the early wear failure of blanking die include improper heat treatment process of the blanking die, defects in microstructure, poor tempering stability and thermal fatigue, tempering softening occuring in the service process due to high temperature. It is suggested that the heat treatment process with the characteristics of high quenching temperature and high tempering temperature should be adopted, and the secondary hardening effect of Cr12MoV steel should be used to give the blanking die good tempering resistance stability. The service life of the blanking die produced by the optimized heat treatment process is 4.62 times of the original one.
    Analysis and improvement of point defects on surface of hot dipaluminum-silicon plated steel sheet
    Li Chao, Wang Teng, Sun Rongqiang, Yang Ping, Zhang Baiyong
    2021, 46(3):  213-217.  doi:10.13251/j.issn.0254-6051.2021.03.041
    Abstract ( 70 )   PDF (540KB) ( 21 )  
    In order to improve the surface quality of aluminum-silicon plated steel sheet, the microscopic morphology and composition of the point-like defects appeared on the surface of aluminum-silicon plated steel sheet were analyzed by using optical microscope(OM), scanning electron microscope(SEM) and energy spectrum(EDS). The results show that the point defects generated on the surface of the aluminum-silicon plated steel sheet are mainly divided into four categories. The type I point defect components are mainly Al-Si oxide and zinc oxide, which are caused by the adhesion of aluminum dross and zinc dust on the coating surface. The cause of type II point defects is that aluminum slag or foreign matter is pressed into the surface of the coating. The type III point defects are composed of Al-Fe-Si oxides, Al-Si oxides and W-Co-C alloy compounds, which are caused by co-adhesion with the aluminum dross on the surface of the coating. The type IV point defects have the microscopic morphology of middle depression and edge slight bulge, which are caused with surface scratching by foreign objects. In view of the above causes of the defects, some measures are proposed, such as strict controlling of the temperature of the aluminum pot, increasing the frequency of slag fishing, and reducing the oxygen content in the furnace nose.
    Fracture failure analysis of stainless steel tie rod joint
    Li Jiahua, Li Ping, Sun Song, Xie Hui, Zeng Yin
    2021, 46(3):  218-222.  doi:10.13251/j.issn.0254-6051.2021.03.042
    Abstract ( 72 )   PDF (545KB) ( 28 )  
    The O-shaped hole of the stainless steel 05Cr17Ni4Cu4Nb tie rod OU type joint used in a bridge project was broken during service. In order to find out the cause of the failure, the chemical composition, macroscopic fracture, microstructure, and mechanical properties were tested and analyzed. The results show that the chemical composition of the joint is in accordance with the standard of 05Cr17Ni4Cu4Nb in GB/T 1220—2007, the specified non-proportional elongation strength and tensile strength reaches the technical requirement of the steel aged at 480 ℃. However, the elongation after break and percentage reduction of area are lower than the requirements, revealing that the material is with poor plasticity, which should be due to the precipitated δ ferrite resulted from a high solution treatment temperature. Therefore, the overload brittle fracture of the joint occurs which is caused by its high surface notch sensitivity.
    Failure analysis of 30CrMnSiA steel countersunk bolt
    Yu Haihua, Yan Haiyan, Zhang Jingtong, Wang Yukui, Huang Zhiyong, Wu Jianxin, Wei Zhenwei
    2021, 46(3):  223-228.  doi:10.13251/j.issn.0254-6051.2021.03.043
    Abstract ( 81 )   PDF (547KB) ( 42 )  
    A 30CrMnSiA steel countersunk bolt used in an aircraft breaks during disassembly, and cracks were also found in the same batch of unused bolts detected by magnetic powder. In order to find out the cause of failure analysis, the broken and cracked bolts were analyzed by means of appearance inspection, macro-microscopic analysis of fracture surface, energy spectrum analysis, hardness test and metallographic analysis. The results show that the fracture type of broken and cracked bolts is hydrogen embrittlement. The hydrogen embrittlement fracture of bolt is mainly related to tensile strength and heat treatment process. By improving the heat treatment process parameters, the strength of bolt is appropriately reduced and the hydrogen content is reduced by increasing the hydrogen removal time after pickling. Thus the possibility of hydrogen embrittlement is avoided.
    Interlaboratory comparison analysis of grain size determined results
    Bi Geping, Chen Jinzhe, Tan Wenhua, Gao Yuqing, Wang Meimei, Lu Hongtao
    2021, 46(3):  229-233.  doi:10.13251/j.issn.0254-6051.2021.03.044
    Abstract ( 60 )   PDF (547KB) ( 23 )  
    Three CNAS-accredited laboratories were invited to determine the grain size G by using the ASTM E112 standard for 14 identical grain size pictures that were taken on the same aluminum alloy (AlSi1) sample, and the results were quantitatively evaluated. The results from three laboratories show that the statistical counts of intersections or grains are the main parameters for determining G and it is the key point of quality control of the effectiveness of determining G. By using the Intercept Procedure, the range of the intersection counts is 3 to 11, the relative standard deviation is 2.5% to 10.1%, and the range of G is 0.09 to 0.53. While by the Planimetric Procedure, the range of grain counts is 4.0 to 16.5, the relative standard deviation is 2.9% to 15.7%, and the range of G is 0.06 to 0.36. The results also show that laboratory - to - laboratory comparison activities should not focus only on the final results, but also on the comprehensive evaluation of the original observation results, intermediate results, and final results, so as to obtain opportunities for improvement and control the testing risk.
    Performance analysis and test of D-P type and W type radiant tube system
    Cheng Qibo, Wang Hongyu, Feng Xiaohong
    2021, 46(3):  234-238.  doi:10.13251/j.issn.0254-6051.2021.03.045
    Abstract ( 63 )   PDF (548KB) ( 25 )  
    Burner structures and combustion modes of W-type radiant tube system and dual P-type radiant tube system were analyzed, and the key performance indicators of the two kinds of radiant tube heating systems were tested and compared, including flue gas circulation rate, temperature deviation, fuel efficiency and NOx. The results show that the dual P-type radiant tube combustion system has greater value of popularization and application, because it has better uniformity of tube wall temperature, remarkable energy saving effect, and the ability to use higher power burner to reduce the number of heating system and control module and to reduce the investment cost.
    STANDARDIZATION
    Reasonableness discussion on hardness upper limit of normalized and tempered T22 steel tubes specified in ASME SA-213M
    Lai Xianhong, Zeng Hui, Yang Huachun, Zhang Wei
    2021, 46(3):  239-242.  doi:10.13251/j.issn.0254-6051.2021.03.046
    Abstract ( 73 )   PDF (541KB) ( 20 )  
    Simulated normalized and tempered tests with different parameters for T22 steel tubes were performed. The results show that it is very easy for hardness of normalized and tempered T22 steel tubes to exceed the hardness upper limit (163 HBW/170 HV/85 HRB) specified in ASME SA-213M standard, and it is difficult to avoid the spheroidizing microstructure even if the hardness constrainedly reduced to below the hardness upper limit according to special heat treatment parameters, and it is believed that the raising of hardness upper limit for normalized and tempered T22 steel tubes shall be considered. Meanwhile, the suitable raising extent of hardness upper limit is discussed, and further suggestions are that the hardness upper limit for normalized and tempered T22 steel tube specified in SA-213M should be raised from 163 HBW/170 HV/85 HRB to 179 HBW/190 HV/89 HRB.
    Current status of heat treatment standards for titanium and titanium alloys
    Hu Zhijie, Feng Junning, Ma Zhongxian, Xie Chen
    2021, 46(3):  243-246.  doi:10.13251/j.issn.0254-6051.2021.03.047
    Abstract ( 81 )   PDF (546KB) ( 47 )  
    The classification of titanium and titanium alloy heat treatment was introduced, and the common standards for the heat treatment of titanium and titanium alloys at home and abroad were summarized. The problems existing in the understanding and application of heat treatment system in titanium and titanium alloy processing enterprises in China were analyzed, and the future development trend of titanium and titanium alloy heat treatment standards was prospected.