Current Issue

• MATERIALS RESEARCH

  High-temperature elastic-plastic characteristics and constitutive model of aging strengthened high-nickel alloy Inconel-718

  Qu Huapeng, Wang Liubing, Wang Donghui, Wu Bingjie, Feng Hanqiu, Xu Bin, Song Danrong, Lang Yuping

  2021, 46(8):  1-7.  doi:10.13251/j.issn.0254-6051.2021.08.001

  Abstract ( 55 )   PDF (708KB) ( 29 )  

  High-temperature elastic-plastic characteristics from 150 ℃ to 650 ℃ of aging strengthened 0Cr20Ni55Mo3Nb5Ti (Inconel-718) nickel-based alloy used for nuclear reactor spring were researched, and various functional models were used to fitting calculation and comparison of the constitutive relations based on the measured stress-strain data at high temperature. The results show that higher R_p0.01 value and room temperature elongation of the Inconel-718 alloy are obtained after 3-steps heat treatment of 970 ℃×1 h, air cooling+720 ℃×8 h, furnace cooling+620 ℃×8 h, air cooling. It is found that Boltzmann model has good fitting effect and prediction calculation precision for high-temperature σ-ε constitutive relations of the aging strengthened Inconel-718 alloy, so that it is also appropriate for the structure design and material selection for nuclear reactors.

  High temperature constitutive model and dynamic recrystallization model of IN690 alloy

  Li Dongsheng, Zhao Enxu, Wang Wei, Tan Li, Zhang Junpeng, Tian Zhenyu

  2021, 46(8):  8-14.  doi:10.13251/j.issn.0254-6051.2021.08.002

  Abstract ( 54 )   PDF (629KB) ( 27 )  

  During hot working process of the IN690 alloy, some complex metallurgical phenomena (including: work hardening (WH), dynamic recovery (DRV) and dynamic recrystallization (DRX), etc.) are emerged. In order to study these phenomena, the high temperature constitutive equation and DRX mode of the IN690 alloy through hot compression test were created, and the DRX mechanism of the alloy was discussed. In addition, the DRX process of the alloy was simulated by using finite element software (Deform-3D). The experimental results show that the dynamic recrystallization volume fraction (X_DRX) of the IN690 alloy increases with the increase of deformation temperature or the decrease of strain rate for a given strain.

  Precipitation behavior in V-N microalloyed CrSiMn low alloy cast steel

  Wang Xiaodong, Chen Yunbo, Zuo Lingli, You Long, Chen Chong, Mao Feng, Zhang Junjia

  2021, 46(8):  15-19.  doi:10.13251/j.issn.0254-6051.2021.08.003

  Abstract ( 52 )   PDF (620KB) ( 22 )  

  V-N microalloyed CrSiMn low alloy cast steel was calculated by means of JMatPro software, the equilibrium phase composition of the cast steel with different V contents was obtained. The precipitation behavior of each precipitated phases in the microalloyed steel at equilibrium state was emphatically studied. The results show that during the heating process, the increase of V content promotes the phase transformation resistance of ferritic to austenite. The V content has little influence on precipitation behavior of cementite and M₇C₃. The content of V has a great influence on precipitation of nitrides and carbonides. When V content increases from 0 to 0.18% (mass fraction), the initial precipitation temperature of nitrides and carbonides increases from 734.2 ℃ to 1133.93 ℃, and the mass fraction of the maximum precipitation amount increases from 0.07% to 0.24%.

  Analysis of transient creep behavior of P91 steel

  Wang Ni, Liu Xinbao, Zhu Lin, Li Bo, Quan Chen

  2021, 46(8):  20-25.  doi:10.13251/j.issn.0254-6051.2021.08.004

  Abstract ( 44 )   PDF (681KB) ( 20 )  

  Transient creep deformation behavior of the P91 steel under different stress levels at 600 ℃ and 620 ℃ respectively was systematically studied. By coupling the interaction between internal dislocations and precipitated phases in the material during creep process to the internal stress, combined with Orowan equation, the transient creep model parameters were determined by the nonlinear fitting method, and the deformation curve of the P91 steel in the transient creep stage was numerically simulated. The results show that the numerical simulation results are in good agreement with the experimental data, indicating that it is feasible to apply the model to study the transient creep behavior of the P91 steel. At the same time, combined with the fact that the transient creep time and normalized transient strain depend on the temperature and the stress, it is further confirmed that the transient creep of the P91 steel at 600 ℃ and 620 ℃ respectively and in the stress range of 135-175 MPa is mainly controlled by the dislocation climbing process.

  Effect of microalloying element niobium on dynamic recrystallization behavior of high carbon alloy steel

  Ji Guang, Gao Xiuhua, Long Jinhua

  2021, 46(8):  26-29.  doi:10.13251/j.issn.0254-6051.2021.08.005

  Abstract ( 50 )   PDF (619KB) ( 22 )  

  In order to study the effect of microalloying element Nb on dynamic recrystallization behavior of the high carbon alloy steel, a single pass compression test was carried out by using Gleeble-3500 thermal simulation tester, and the flow stress curve of the high carbon alloy steel at the deformation temperature of 950-1150 ℃ and the strain rate of 0.01-5 s^-1 was measured. The dynamic recrystallization grain morphology of austenite was observed by means of Zeiss optical microscope, the corresponding activation energy of recrystallization was obtained through regression calculation, and the thermal deformation equation was established. The results show that the dynamic recrystallization is easier to occur at higher deformation temperature and lower strain rate. The grain size of dynamic recrystallization of the high carbon alloy steel containing Nb increases with the increase of deformation temperature. When the deformation temperature is 1050 ℃, a large number of dynamic recrystallization grains in the high carbon alloy steel containing Nb can be obtained. The addition of 0.040% niobium to the high carbon alloy steel delays the onset of dynamic recrystallization of the steel by about 2.23 s when the strain rate is 0.1 s^-1 and the deformation temperature is 1150 ℃, and increases the activation energy of dynamic recrystallization deformation by 52.26 kJ/mol.

  Microstructure transformation and metallographic analysis of Ni-based wrought superalloy during heat treatment

  Tian Wei, Chang Song, Zhou Changshen, Zhang Wendi, Feng Zhihao, Sun Xinyang, Su Ru

  2021, 46(8):  30-35.  doi:10.13251/j.issn.0254-6051.2021.08.006

  Abstract ( 60 )   PDF (624KB) ( 28 )  

  Strengthening method of the nickel-based wrought superalloy and microstructure transformation under different heat treatment processes were summarized. Grain size, inclusion, transformation mechanism of precipitated phase and metallographic evaluation method were concluded. It is expected to provide a reference for optimization of the microstructure and performance and inspection of the nickel-based wrought superalloy.

  Effect of Cu addition on microstructure and properties of SiC_p/Al-Si composites

  Ren Junpeng, Wang Yu, Dong Cuige, Zhao Jun

  2021, 46(8):  36-41.  doi:10.13251/j.issn.0254-6051.2021.08.007

  Abstract ( 48 )   PDF (623KB) ( 35 )  

  Influence of different content of Cu addition on microstructure and properties of the SiC_p/Al-Si composites prepared by powder metallurgy was studied by means of X-ray diffraction, scanning electron microscopy, precision electronic balance and universal testing machine. The results show that the addition of Cu element leads that the density, hardness, tensile strength, friction and wear resistance of the material are improved greatly, and the strength reaches the maximum when the Cu content is 4% (mass fraction). Since the Cu element is added in the form of copper powder in the matrix, a liquid phase can be formed through mutual diffusion at the Al-Cu boundary even at a lower temperature, thereby filling the gaps, holes and other defects in the matrix and at the interface. During rapid cooling of the green compact to room temperature, α-Al and Al₂Cu phases are produced and both have strengthening effect on material, which improves the comprehensive mechanical properties of the SiC_p/Al-Si composites.

  Grain growth behavior of Ti-22Al-27Nb alloy

  Qin Chun, Li Ning, Dong Fuyuan, Li Yongquan

  2021, 46(8):  42-45.  doi:10.13251/j.issn.0254-6051.2021.08.008

  Abstract ( 48 )   PDF (626KB) ( 22 )  

  Grain growth behavior of the Ti-22Al-27Nb alloy under different isothermal annealing temperatures and time was studied through measuring and calculating the grain size of the alloy. The results show that the grain size of the alloy increases with the increase of isothermal annealing temperature and time, while the grain growth rate decreases with the increase of isothermal annealing time. The grain growth index is 0.38 and 0.44 when the isothermal annealing temperature is 1070 ℃ and 1090 ℃ respectively. The grain growth activation energy of the Ti-22Al-27Nb alloy increases with the increase of isothermal annealing time, in the range of 132.8-267.2 kJ·mol^-1.

  Effect of Si on microstructure and high temperature oxidation resistance of high-entropy alloy coatings

  Ma Zhizhen, Zhu Jiahao, Zhang Hui

  2021, 46(8):  46-50.  doi:10.13251/j.issn.0254-6051.2021.08.009

  Abstract ( 54 )   PDF (630KB) ( 22 )  

  Effect of Si content on microstructure, phase structure and high temperature oxidation resistance of the narrowband/broadband laser clad NiCoFeCrSi_xAlCuTiMoB_0.4 (x=1.0, 0.5) high-entropy alloy coatings was studied. The results show that the narrowband clad coating is mainly composed of simple BCC solid solution with dendritic microstructure. In the broadband coating, the phases transform to BCC solid solution with a small amount of B(Fe,Si)₃ and Cr₂B precipitates which are between dendrites, and the content of B(Fe,Si)₃ reduces with the decrease of Si content. After oxidizing at 800 ℃ for 50 h, the oxidation scale of the broadband clad coating is mainly composed of Cr-rich outer oxide layer and Al-rich inner oxide layer, and the increase of Si content improves the high temperature oxidation resistance of the coating, especially significantly reduces the thickness of internal oxide layer.

  MICROSTRUCTURE AND PROPERTIES

  Hydrogen embrittlement susceptibility of a hot-rolled ultra-high strength complex phase steel

  Wang Haibo, Xu Zhenlin, Hu Xuewen, Peng Huan

  2021, 46(8):  51-55.  doi:10.13251/j.issn.0254-6051.2021.08.010

  Abstract ( 53 )   PDF (621KB) ( 31 )  

  Hydrogen escape behaviour and hydrogen trap of the hot-rolled ultra-high strength complex phase steel M950 were studied by means of electrochemical hydrogen charging experiment and thermal desorption spectroscopy (TDS). The hydrogen embrittlement susceptibility of the tested steel was analysed by means of slow strain rate tensile (SSRT) test. And the fracture morphology was observed using field emission scanning electron microscope (FESEM). The results show that hydrogen trap activation energy of the tested steel is 15.0 kJ/mol. The main hydrogen trap of the steel is grain boundary. With the prolongation of electrochemical hydrogenation time, the hydrogen content of the tested steel increases gradually, and the plasticity decreases significantly, but the decline of tensile strength is not obvious. The tensile fracture morphology changes from pore-concentrating ductile fracture to quasi-cleavage and intergranular brittle fracture.

  Microstructure and properties of a hypoeutectic high-Cr cast iron under different heat treatment conditions

  Yu Hongjun, Song Chuansongxin, Cheng Fuchao, Gao Zhizhe, Chen Xiaoyan, Wang Yongjin, Zhang Yingchao

  2021, 46(8):  56-60.  doi:10.13251/j.issn.0254-6051.2021.08.011

  Abstract ( 62 )   PDF (625KB) ( 26 )  

  Effects of different heat treatment condition on microstructure and properties of a hypoeutectic high chromium cast iron were studied by means of optical microscope, scanning electron microscope, X-ray energy dispersive spectrometer and mechanical properties test. The results show that the hardness and impact absorbed energy of the tested cast iron firstly increases and then decreases with the increase of quenching temperature and time. The maximum hardness and impact absorbed energy of the tested cast iron can reach 58 HRC and 15 J after quenching plus tempering, respectively.

  Oxidation analysis on surface of Ni-based Ni-Co-W-Ta-Al-Cr-Mo-Re-Nb-Hf single crystal superalloy after vacuum heat treatment

  Kong Lingli, He Ruijun, Liu Hang, Cheng Yifei

  2021, 46(8):  61-64.  doi:10.13251/j.issn.0254-6051.2021.08.012

  Abstract ( 180 )   PDF (621KB) ( 29 )  

  Ni-based Ni-Co-W-Ta-Al-Cr-Mo-Re-Nb-Hf single crystal superalloy specimens were solution treated and aged in a vacuum furnace, and the surface of the specimens showed different oxidation colors due to equipment status or other reasons. The oxidation microstructure and oxide composition on the surface of the single crystal superalloy specimens with different oxidation colors were observed and tested by means of OM, SEM and EDS. The results show that the microstructure status and composition of surface oxides change with the deepening of oxidation degree in different degrees. The oxidation phenomenon showing different oxidation colors should be analyzed for the reasons in detail and treated symptomatically, so the single crystal superalloy with a surface quality that meets the technical requirements can be obtained.

  Microstructure and properties of bainitic non-quenched and tempered steel with different section size

  Li Mengge, Cheng Juqiang, Yin Sibo

  2021, 46(8):  65-69.  doi:10.13251/j.issn.0254-6051.2021.08.013

  Abstract ( 51 )   PDF (631KB) ( 22 )  

  Microstructure and mechanical properties of the bainitic non-quenched and tempered steel bar with different diameters air-cooled at 920 ℃ and tempered at 300 ℃ were studied. The results show that the microstructure of the bainitic steel bar with different diameters after air cooling and tempering is the bainite ferrite and retained austenite, which belongs to non-carbide bainitic structure. The microstructure of the bars with diameter smaller than ϕ30 mm changes a little after heat treatment, but the core microstructure of the bars with diameter larger than ϕ50 mm becomes coarser and the amount of granular bainite increases. After heat treatment, with the increase of diameter, the strength and hardness of the bars tend to decrease. The impact absorbed energy of the bars with diameter larger than ϕ50 mm decreases with the increase of diameter. The tensile strength of the ϕ70 mm bar at R/2 is 1226 MPa, and the core impact absorbed energy is 61.3 J. Bainitic non-quenched and tempered steel with larger diameter has good combination of strength and toughness.

  Microstructure and properties of bainitic steel for frog used in intercity and high-speed railway track

  Li Yuan, Luan Daocheng, Hu Zhihua, Deng Tianxin, Ren Yang, Zuo Chengming, Wang Zhengyun

  2021, 46(8):  70-72.  doi:10.13251/j.issn.0254-6051.2021.08.014

  Abstract ( 50 )   PDF (619KB) ( 20 )  

  Microstructure and mechanical properties of bainitic steel for intercity and high-speed railway frog were studied by means of optical microscope, scanning electron microscope, XRD, impact tester and universal tester. The results show that the bainite structure of the tested steel can be obtained under air cooling condition, and the structure is carbide free bainite determined by XRD analysis. The tensile strength of the tested steel is 1410 MPa, and the impact absorbed energy at room temperature is up to 89 J. The steel has a higher hardness, and good match of strength and toughness. The low-temperature impact test results show that the tested steel can meet the application requirements of the frog for intercity and high-speed railway track under low-temperature environment.

  Microstructure and properties of a low-cost 800 MPa galvanized ultra-high strength dual-phase steel

  Liu Jingbao, Tian Xiugang, Zhang Jie, Wei Huanjun, Yang Lina, Wang Zhao, Li Mengxing

  2021, 46(8):  73-76.  doi:10.13251/j.issn.0254-6051.2021.08.015

  Abstract ( 54 )   PDF (623KB) ( 18 )  

  Microstructure of hot-rolled, cold-rolled and hot-dip galvanized 800 MPa grade dual-phase steel was observed by means of optical microscope and transmission electron microscope (TEM). The mechanical properties at different positions of the whole rolled plate after hot-dip galvanizing were analyzed and compared. The results show that when the tested steel is annealed at 795 ℃ for 150 s and hot-dip galvanized, the microstructure is mainly composed of ferrite and martensite, the grain size of ferrite is between 2.3-6.0 μm, and the volume fraction of martensite is about 21%. After galvanizing, the tensile strength and yield strength are 825 MPa and 505 MPa respectively, the elongation after fracture is 19%, and along the width of the plate, the fluctuation of tensile strength is within 20 MPa, that of the yield strength is within 4 MPa, and that of the elongation is within 1%. When the transverse 180° bending test with bending diameter of 3 times of the plate thickness was conducted, the results show that no cracking happens from the head to the tail of the hot-dip galvanized whole coil steel, indicating that the requirements of user for high bending performance are met.

  NUMERICAL SIMULATION

  Development of a dedicated finite element solver for heat treatment

  Chen Zhenhao, Xu Jun, Wang Jing, Gu Jianfeng

  2021, 46(8):  77-84.  doi:10.13251/j.issn.0254-6051.2021.08.016

  Abstract ( 43 )   PDF (622KB) ( 23 )  

  A dedicated finite element solver is the core technology for realizing simulation and computation for heat treatment process. Though foreign commercial software companies have been taking the lead in this area for a long time, a dedicated finite element solver MetalX for heat treatment is independently developed. After introducing its fundamental mathematical models for physical fields, features and calculation process, the MetalX solver was applied to simulate the carburization process of 18CrNiMo7-6 steel and its result was compared with the result of a mainstream commercial finite element software MSC.Marc. The results indicate that the MetalX solver can realize four-field coupled non-linear analysis of thermo-phase transformation-diffusion-structure, and is used to predict temperature, microstructure, carbon concentration, deformation and residual stress of the component during the whole process of heating, carburization and quenching, with similar calculation accuracy of the mainstream commercial finite element software.

  PROCESS RESEARCH

  Effect of extrusion on microstructure, mechanical properties and corrosion behavior of Mg-5Li-5Al-0.6Y alloy

  Ye Jiayu, Feng Yan, He Yuqing, Yang Liuzhong

  2021, 46(8):  85-91.  doi:10.13251/j.issn.0254-6051.2021.08.017

  Abstract ( 43 )   PDF (632KB) ( 38 )  

  Mg-5Li-5Al-0.6Y alloy was prepared by casting and hot extrusion. Effect of extrusion on phase and microstructure of the as-cast alloy was studied by means of optical microscopy, scanning electron microscopy and X-ray diffractometer. Effect of extrusion on mechanical properties of the alloy was studied via tensile testing at room temperature and fracture morphology analysis before and after extrusoin. Effect of extrusion on corrosion behavior of the alloy was analyzed by means of hydrogen evolution, mass loss, potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS). The results indicate that extrusion refines the grain of the Mg-5Li-5Al-0.6Y alloy and the second phases are broken into finer and dispersed particles along the extrusion direction in the α-Mg matrix. Extrusion improves the ultimate tensile strength and elongation of the Mg-5Li-5Al-0.6Y alloy to 243.33 MPa and 7.31%, respectively. Extrusion declines the corrosion rate (calculated from mass loss) of the Mg-5Li-5Al-0.6Y alloy from 17.60 mm·y^-1 to 8.41 mm·y^-1, improving the corrosion resistance of the alloy.

  Effect of FW&TMCP treatment on wear resistance of as-cast high manganese steel frog

  Lin Zhiqing, Zhang Fucheng, Ma Hua, Wang Lin, Chen Chen, Xu Ming

  2021, 46(8):  92-98.  doi:10.13251/j.issn.0254-6051.2021.08.018

  Abstract ( 51 )   PDF (620KB) ( 21 )  

  Casting high manganese steel is one of the widely used wear-resistant materials. However, due to casting defects such as shrinkage porosity, porosity, and coarse grains in cast high manganese steel, it has problems such as reduced mechanical properties and poor service stability. In order to reduce the defects of cast high manganese steel frog holes and refine the austenite grains, the effect of forge welding and thermomechanical heat treatment (FW&TMCP) on wear resistance of the cast high manganese steel frogs was studied. First, the conventional tensile properties of the cast high manganese steel and FW&TMCP high manganese steel were tested and then friction and wear test of the cast high manganese steel and FW&TMCP high manganese steel were carried out under different loads. The results show that the strength and plasticity of the FW&TMCP high manganese steel are much higher than that of the cast high manganese steel, and the strain hardening rate is also higher than that of the cast high manganese steel. The microstructure results show that the porosity of the FW&TMCP high manganese steel is reduced by 82%, and the density is increased greatly. The friction coefficient of the two high manganese steel decreases gradually with the increase of wear load. Under the same wear load, the friction coefficient of the cast high manganese steel is less than that of the FW&TMCP high manganese steel, and the FW&TMCP high manganese steel has less plastic deformation and higher wear resistance. The wear mechanism of the two high manganese steel changes from adhesive wear to abrasive wear with the increase of wear load.

  Effect of tempering temperature on microstructure and mechanical properties of 40CrNiMo steel for flexible gear

  Liu Xiaoxiao, Zhang Zheng, Zhang Jie, Yang Ran, Yu Chengshuang, Han Lina, Qiao Junwei

  2021, 46(8):  99-104.  doi:10.13251/j.issn.0254-6051.2021.08.019

  Abstract ( 57 )   PDF (678KB) ( 25 )  

  Through pre-treatment (solid solution), austenitizing and tempering at different temperatures, effect of austenitizing temperature on growth rate of austenitic grain and the hardness of the 40CrNiMo steel was studied by means of optical microscope, scanning electron microscope, Rockwell hardness tester, tensile testing machine and impact testing machine, and the effect of tempering temperature on microstructure and mechanical properties of bainite/martensite multiphase steel was explored. The results show that the austenitic grains grow slowly first and then rapidly with the increase of austenitizing temperature during the pre-treatment, but the hardness value of the steel remains about 56 HRC. A large number of fine carbides precipitate and microstructure remains the original plate strip shape at the temperature range from 250 ℃ to 500 ℃, and the strength and hardness of the tested steel decrease, while the plasticity and toughness decrease first and then increase with the increase of tempering temperature. When tempered at 400 ℃, the lowest elongation and the lowest impact absorbed energy are obtained, which indicates that tempering brittleness occurs when tempered at 400 ℃. When the tempering temperature rises to 600 ℃, the matrix structure transforms into tempering sorbite, and the strength and hardness of the tested steel are the lowest but the impact absorbed energy is up to 147 J.

  Effect of tempering temperature on microstructure and mechanical properties of a high performance fire-resistant steel

  Zhang Kaiguang, Tong Mingwei, Yi Xun

  2021, 46(8):  105-108.  doi:10.13251/j.issn.0254-6051.2021.08.020

  Abstract ( 62 )   PDF (595KB) ( 21 )  

  Effect of tempering temperature on microstructure and mechanical properties of a high performance fire-resistant steel was studied by means of optical microscope, transmission electron microscope and mechanical property test. The results show that the tested steel shows good high temperature performance and good match of strength and toughness after tempering, and the fire-resistance and low temperature impact property reach to the optimum when tempered at 650 ℃. Before and after tempering, the microstructure of the tested steel is mainly polygonal F+lath/granular B, and with a small amount of M/A islands, as well as many approximately spherical or elliptical carbides or complex carbonitride. With the increase of tempering temperature, the microstructure slightly coarsens, and some lath B merges into cellular structure. The M/A islands change little in number and morphology, though their effective size slightly decreases. After tempering at 600 ℃, the quantity of precipitated phases increases, and a large number of second phase particles with size below 50 nm precipitate when tempered at 650 ℃ and 680 ℃, which further ensures fire-resistance and low temperature impact property of the tested steel.

  Effect of solution treatment temperature on microstructure and properties of modified In617 alloy

  Li Qi, Chen Zhengzong, Jiang Xinliang, Liu Zhengdong, Zuo Liang

  2021, 46(8):  109-114.  doi:10.13251/j.issn.0254-6051.2021.08.021

  Abstract ( 53 )   PDF (597KB) ( 22 )  

  Effects of solution treatment temperature on microstructure and properties of modified In617 alloy were studied by means of OM and SEM characterization, EDS analysis and mechanical properties test. The results show that the average grain size of the alloy increases from 18 μm to 183 μm after solution treatment at 950-1200 ℃ for 2.5 h. The kinetic model of grain growth of the alloy during solution treatment at 950-1200 ℃ is established. When the solution treatment temperature is 1000 ℃, the M₂₃C₆ carbide at grain boundary is re-dissolved. When the solution treatment temperature exceeds 1100 ℃, the dissolution of M₆C carbides is basically completed, and only large-size MC carbides exist in the alloy. When the solid solution treatment temperature rises, the mixed grain phenomenon occurs, and the high temperature strength of the alloy gradually decreases, which is mainly due to the gradual redissolution of the carbides. When the solid solution treatment temperature is 1050 ℃, the strength of the alloy decreases a little due to insufficient dissolution of the carbides at grain boundary. When the solution treatment temperature increases to 1200 ℃, the strength of the alloy is greatly reduced due to that the carbides at grain boundary disappear and the grain growth.

  Effect of aging time on microstructure and properties of a low density ultra-high manganese cast steel

  Gao Zhizhe, Cheng Fuchao, Feng Yifan, Sun Jian, Wang Yongjin

  2021, 46(8):  115-120.  doi:10.13251/j.issn.0254-6051.2021.08.022

  Abstract ( 63 )   PDF (657KB) ( 24 )  

  To improve the initial hardness and strength, an low density ultra-high manganese cast steel was designed. After water toughening, the tested steel was carried out aging treatment at 550 ℃ for 1-4 h and the effect of aging time on microstructure and properties was investigated. The experimental results show that the tested steel can obtained optimum mechanical properties after aging for 2 h. Its tensile strength is 1041.7 MPa, yield strength is 1002.7 MPa, elongation is 17.6%, impact absorbed energy (V-notch) is 62.0 J, and hardness is 268.5 HBS. Compared with the as-water toughened, the yield strength and the hardness of the steel are increased by 107.3% and 28.8% respectively, which can be attributed to the precipitation-hardened effect originating from the precipitation of nano-sized κ-carbides.

  Effect of solution treatment temperature on mechanical and welding properties of GH4169 alloy forging

  Jian Xiaojun, Cui Baowei, Huang Yanjun, Kang Taotao, Wang Ping, Song Yue, Li Weiqiang

  2021, 46(8):  121-124.  doi:10.13251/j.issn.0254-6051.2021.08.023

  Abstract ( 67 )   PDF (597KB) ( 35 )  

  In order to satisfy simultaneously the mechanical and welding properties of the aerospace-used forged GH4169 alloy parts in solution treated state, the effect of solution treatment temperature on hardness and tensile properties of the alloy forging was studied, and the qualities of homogeneous welding and dissimilar metal welding for solution treated GH4169 alloy and 0Cr18Ni9 stainless steel were characterized at corresponding solution treatment temperatures. The results show that the solution treatment temperature has significant impact on microstructure and mechanical properties of the GH4169 alloy, the dissolved degree of coarse second phases (δ phase mainly) increases and both the hardness and the tensile strength reduce significantly with the increase of solution treatment temperature, while the elongation increases significantly. The experiment results of both the homogeneous welding between GH4169 alloy solution treated at different temperatures and the dissimilar metal welding with the stainless steel 0Cr18Ni9 indicate that their macrostructure, microstructure and X-ray test results all satisfy the requirement for using. Considering both the mechanical properties and welding properties, the optimal range of solution treatment temperature of the GH4169 alloy forging used in solution treated state is 900-940 ℃.

  Effect of solution treatment and aging on microstructure and properties of 8030 aluminum alloy conducting wire

  Han Xi, Li Maoyang, Qin Guofei, Li Xudong, Dong Chao, Zhang Meili, Dai Weili

  2021, 46(8):  125-132.  doi:10.13251/j.issn.0254-6051.2021.08.024

  Abstract ( 42 )   PDF (603KB) ( 22 )  

  Effect of solution and aging treatments on microstructure and properties of the 8030 aluminum alloy wire was studied. The results show that the untreated alloy wire consists of α-Al, Al₆Fe, Al₁₃Cu₄Fe₃ and AlMg₂Zn phases. After solution treatment at 480 ℃ for 6 h, the AlMg₂Zn phase is completely dissolved into the matrix, while the Al₁₃Cu₄Fe₃ phase and Al₆Fe phase are partially dissolved. After aging treatment at 240 ℃ for 6 h, the second phases are precipitated again. After solution and aging treatments, the conductivity of the 8030 aluminum alloy wire is improved. After solution treated at 480 ℃ for 6 h and then aged at 240 ℃ for 6 h, the conductivity reaches up to 56.67%IACS, which is 3.41% higher than that of the alloy without heat treatment. After solution and aging treatments, the elongation of the alloy wire is significantly increased. When solution treated at 480 ℃ for 6 h and then aged at 200 ℃ for 4 h, the elongation is increased from 3.75% (untreated alloy) to 31.25%.

  Strengthening mechanism of Nb(C, N) precipitation and controlled cooling process optimization of Nb-containing steel bars under direct rolling condition

  Zhang Hongliang, Feng Guanghong, Wang Baoshan

  2021, 46(8):  133-138.  doi:10.13251/j.issn.0254-6051.2021.08.025

  Abstract ( 47 )   PDF (593KB) ( 25 )  

  In order to improve the problem of insignificant strengthening effect of Nb-containing steel bars when produced by billet direct rolling process, the kinetic behavior of Nb(C, N) precipitation in austenite was calculated through classical nucleation theory, then verified through field controlled cooling process experiments. The results show that the main precipitation modes of Nb (C, N) in austenite are grain boundary nucleation for rolling by using heating furnace and dislocation nucleation for billet direct rolling, and for the composition of tested Nb-containing steel bars, the corresponding nose tip temperature of PTT curves for grain boundary nucleation and dislocation nucleation is about 1000 ℃ and 900 ℃, respectively. The optimum strengthening effect of Nb(C, N) precipitation in direct rolling process can be obtained by setting multi-stage pre-penetrating water between finishing stands to ensure low-enough final rolling temperature.

  Production process of high strength and toughness weather-resistant bridge steel Q500qENH

  Peng Ningqi, He Hang, Luo Deng, Fan Ming, Li Zhongping

  2021, 46(8):  139-143.  doi:10.13251/j.issn.0254-6051.2021.08.026

  Abstract ( 51 )   PDF (593KB) ( 25 )  

  Thermal simulation test and heat treatment test were respectively performed on MMS-200 thermo simulator and laboratory electric heat treatment furnace, then the cooling process and heat treatment process of the high strength and toughness Q500qENH weathering steel for bridge were studied by means of hardness test, tensile and impact properties testing and metallurgical structure observation. The results show that the production process for high strength and toughness Q500qENH weathering steel for bridge includes thermomechanical control process(TMCP) plus tempering. When the cooling rate is 10-20 ℃/s, the re-reddening temperature is 500-550 ℃ and the tempering temperature is 450-500 ℃, the tested steel has better match of high strength-toughness and low yield-strength ratio. The microstructure by TMCP is mainly lath bainite, and after tempering, the microstructure gradually changes from bath to granular and the original austenite grain boundary becomes clearer. Tensile curve of the tested steel changes from vault type to Ludes type with the increase of tempering temperature.

  Hot deformation behavior of 2195 aluminum-lithium alloy

  Bao Zhangfei, Tang Lina, Wu Xingping, Luan Baifeng

  2021, 46(8):  144-149.  doi:10.13251/j.issn.0254-6051.2021.08.027

  Abstract ( 63 )   PDF (596KB) ( 29 )  

  Hot deformation behavior of the 2195 aluminum-lithium alloy at temperature range of 360-500 ℃ and strain rate of 0.1-10 s^-1 was studied by means of isothermal compression test on the Gleeble-1500 thermal mechanical simulator. The microstructure evolution of specimens upon hot deformation was characterized by using the optical microscopy (OM) and electron backscattered diffraction (EBSD). Processing map and constitutive equation of the 2195 alloy at strain of 50% were developed based on dynamic material model (DMM) theory and Zener-Holloman parameter. The results show that the flow stress increases with the decrease of deformation temperature or the increase of strain rate. The high temperature softening mechanism includes dynamic recovery and dynamic recrystallization. The best process parameters of hot deformation within the range of test parameters are 480 ℃/10 s^-1 by processing map and microstructure analysis; the deformed structure and recrystallized structure are alternately distributed in layers in the instability zone, and as the temperature decreases, the thickness of the deformed structure layers increases; the microstructure of the stable zone has obvious characteristic of dynamic recrystallization, and the deformed structure practically disappears.

  Effect of rolling process on microstructure and properties of V-Nb micro-alloyed HRB600E steel rebar

  Yang Xiaowei, Chen Huande, Zhou Yun, Zhang Yu

  2021, 46(8):  150-155.  doi:10.13251/j.issn.0254-6051.2021.08.028

  Abstract ( 50 )   PDF (600KB) ( 21 )  

  Effect of rolling process on microstructure, mechanical properties and precipitation of V-Nb micro-alloyed HRB600E steel rebar was researched by means of confocal laser scanning high-temperature microscope, HR-TEM and OM systematically. The results show that with the increase of heating temperature and holding time, austenite grain size of the tested steel rebar increases. When the rolling temperature increases 60 ℃, the proportion and size of pearlite colony in the tested steel rebar increase 10.9% and 5.1 μm respectively, and the tensile strength increases 30-40 MPa, while the elongation decreases 3%-5%. Meanwhile, the precipitation amount of V(C, N) decreases while the amount of VNb(C, N) increases, the precipitation amount of the whole precipitated particles decreases but their equivalent circular diameter increases. The precipitation strengthening effect of various rolling processes has little difference, the strengthening effect of phase transition in the tested steel rebar is superior to the precipitation in the whole.

  Heat treatment process and microstructure of a new SIMR tool steel

  Duan Wenfeng, Shi Quanqiang, Li Jihui, He Ling, Fan Yihao, Shao Pin, Yan Wei

  2021, 46(8):  156-163.  doi:10.13251/j.issn.0254-6051.2021.08.029

  Abstract ( 59 )   PDF (593KB) ( 24 )  

  The heat treatment process and microstructure of the SIMR, a high carbon and high chromium martensitic tool steel, were systematically studied by different quenching and tempering processes. Microstructure, morphologies and distribution of carbides and micro-hardness of the SIMR tool steel were researched by means of XRD, SEM, and TEM characterization methods, and the optimum heat treatment of the SIMR tool steel was obtained. The tested results show that the grain size of the SIMR tool steel gradually grows with the increase of quenching temperature, and the chromium-rich M₇C₃ type primary carbide which forms during the smelting solidification process, gradually re-dissolves with the increase of quenching temperature, and the micro-hardness increases first and then decreases. When the tempering temperature is between 150 ℃ and 300 ℃, the optimum heat treatment process for the SIMR tool steel is quenching at 1050 ℃ for 20 min, and then oil quenching, finally tempering at 150 ℃ for 90 min and then air cooling.

  Effect of sensitization on hydrogen embrittlement sensitivity of 304 austenitic stainless steel in different states

  Zhang Huiyun, Meng Xianming, Zheng Liuwei, Liang Wei

  2021, 46(8):  164-169.  doi:10.13251/j.issn.0254-6051.2021.08.030

  Abstract ( 54 )   PDF (595KB) ( 31 )  

  Hydrogen embrittlement sensitivity of the solid solution treated and cold rolled 304 austenitic stainless steels after sensitization treating at 650 ℃ for 2 h and 24 h respectively was studied. The results show that compared with that of the solid solution treated state, the hydrogen embrittlement sensitivity of the steel in cold-rolled state increases due to strain-induced martensite. Sensitization treatment increases the hydrogen embrittlement sensitivity of the solid solution treated steel. The longer the sensitization time is, the higher the hydrogen embrittlement sensitivity is. On the contrary, in the steel in cold-rolled state, the martensite is partially transformed into austenite during high temperature sensitization, which reduces the hydrogen embrittlement sensitivity of the tested steel to a certain extent. The longer the sensitization time is, the lower the hydrogen embrittlement sensitivity is.

  Aging and annealing process of X80 pipeline steel after uniform plastic deformation

  Xu Yan, Liu Yinglai, Li Liang, Nie Xianghui, Feng Zhenjun, Guo Lei, Liu Zhipeng

  2021, 46(8):  170-173.  doi:10.13251/j.issn.0254-6051.2021.08.031

  Abstract ( 46 )   PDF (593KB) ( 22 )  

  Uniform plastic deformation before necking of the X80 pipe steel was simulated by setting different extent of pre-strains, and the effect of different heat treatment method (strain aging and annealing) on properties of the pipeline steel with such uniform plastic pre-deformation was studied. The results show that tensile curves of the X80 pipeline steel without heat treatment have the feature of continuous yield without obvious yield platform. After pre-tension in the stage of uniform plastic deformation, the pipe has obvious work hardening, and the maximum increment of yield strength reaches 148 MPa. The elongation and strain hardening index of the pipe reduce with the increase of pre-strain. After aging at 260 ℃, the tensile curves of the pre-strain pipe show a yield platform, the yield strength continues to rise, but the elongation continues to decrease, and the strain hardening performance has no obvious change. After annealing at 660 ℃, the tensile curves of the pre-strain pipe show an obvious yield platform, the yield strength is lower than that of the original pipe, and the performance parameters, such as yield ratio, elongation and strain hardening index, are significantly improved.

  Effect of intermediate annealing on microstructure and properties of 6016 aluminum alloy

  Ding Xuan, Gan Yurong, Zhang Chunju, Wang Liqiang, Yang Mingqiu, Li Hui

  2021, 46(8):  174-179.  doi:10.13251/j.issn.0254-6051.2021.08.032

  Abstract ( 64 )   PDF (598KB) ( 23 )  

  Microstructure evolution in production process and effect of intermediate annealing on comprehensive performance of the 6016 aluminum alloy for automobile body sheet were studied by using scanning electron microscope and transmission electron microscope. The results show that continuous annealing has stronger grain refinement effect than furnace annealing. The reduction amount of cold rolling before intermediate annealing has a remarkable effect on fragmentization of the crystalline phases, decreasing the size from 4.38 μm to ~3.2 μm, i.e., reduced by ~27%, and the intermediate annealing treatment can weaken uneven yield elongation of the T4P automobile body sheet. Whereas the slow heating rate of furnace annealing and long holding time at medium temperature lead to grain boundary precipitation and coarsening of Mg₂Si.

  Change of microstructure and properties of 60Si2Mn spring steel during annealing

  Zhao Yanglei, Wang Lingshui, Qiu Shengwen, Dong Shengchao, Chen Liyang

  2021, 46(8):  180-183.  doi:10.13251/j.issn.0254-6051.2021.08.033

  Abstract ( 91 )   PDF (595KB) ( 31 )  

  Microstructure evolution and change of properties of the 60Si2Mn hot rolled spring steel annealed at the temperature slightly lower than the initial austenite transformation temperature Ac₁ were studied by means of metallographic, EDS analysis and mechanical property tests. The results show that the strength and hardness of the tested steel first decrease and then increase with the increase of annealing time. While the plasticity and toughness first increase and then decrease. The results of metallographic analysis show that during annealing, the cementite lamellae in the pearlite are firstly thickened and the spacing increases, and then the cementite lamellae are fractured and spheroidized, and the spheroidization rate increases with the increase of annealing time. When the annealing time exceeds 10 h, the “island structure” appears in the specimen, with its volume fraction increasing with the increase of annealing time, and reaching 20% when annealed for 30 h. Further analysis demonstrates that the “island structure” is the martensite, in which the Si content is significantly lower than that in the matrix, while the Mn content is significantly higher than that in the matrix.

  Effect of magnetic field cryogenic treatment on wear resistance of YG11C cemented carbide

  Lan Dongsheng, Yan Xianguo, Chen Zhi, Jiang Yijiang, Yuan Ruize, Yao Yongchao, Su Hang

  2021, 46(8):  184-188.  doi:10.13251/j.issn.0254-6051.2021.08.034

  Abstract ( 53 )   PDF (599KB) ( 25 )  

  Based on the temperature field provided by cryogenic treatment and the uniform magnetic field provided by permanent magnets, the magnetic field cryogenic treatment of YG11C cemented carbide was carried out, and compared with that of the conventional and cryogenic treatment processes. The results show that the wear resistance of the cryogenic treated YG11C cemented carbide is about 35% higher than that of conventional treatment, and that of the magnetic field cryogenic treated is about 21% lower. The main reason for the improvement of wear resistance is that the amount of η phase carbide in the alloy increases. After magnetic field cryogenic treatment, the transformation from α-Co to ε-Co increases, which results in that the bonding phases are more brittle and the plastic deformation capacity is reduced, so that the wear resistance is reduced.

  Vacuum heat treatment of 0Cr17Ni4Cu4Nb stainless steel base

  He Li

  2021, 46(8):  189-191.  doi:10.13251/j.issn.0254-6051.2021.08.035

  Abstract ( 50 )   PDF (600KB) ( 22 )  

  In order to meet the requirements of mechanical properties and control distortion during quenching, a vacuum solid solution and aging process of 0Cr17Ni4Cu4Nb stainless steel base was determined via a series of experiments. The results show that after solution treatment at 1060 ℃ for 1.5 h, oil cooling and aging at 460 ℃ for 4 h, and then air cooling, the tensile strength of the workpiece is ≥1420 MPa, hardness is ≥42.5 HRC, and flatness of mounting surface is ≤0.5 mm. In addition, the dimension control can be realized by adjusting the quenching oil temperature and prolonging the charging precooling time in the vacuum quenching furnace.

  Effect of annealing treatment on microstructure and properties of 3D printed CoCrFeMnNi high-entropy alloy

  Wu Ying, Zeng Qiang, Xiao Huijin, Zhu Shaowei

  2021, 46(8):  192-196.  doi:10.13251/j.issn.0254-6051.2021.08.036

  Abstract ( 53 )   PDF (596KB) ( 22 )  

  Equimolar CoCrFeMnNi high-entropy alloy (HEA) was prepared by using selective laser melting (SLM) process, and the tested alloy was annealed at 650 ℃ and 900 ℃ for 1 h, respectively. Combined with microstructure, tensile properties and fracture characteristics analysis, effect of annealing process on microstructure and mechanical properties of CoCrFeMnNi HEA prepared by SLM was studied. The results show that the yield strength, tensile strength and elongation of the as-printed specimen are 672 MPa, 751 MPa and 34.3%, respectively. After annealing at 650 ℃ for 1 h, the yield strength, tensile strength and elongation decrease slightly, which are 583 MPa, 718 MPa and 33.5%, respectively. After annealing at 900 ℃ for 1 h, the yield strength and tensile strength decrease to 494 MPa and 707 MPa, respectively, while the elongation increases to 46.6%.The fracture surface shows typical dimple characteristics, and the deformation mechanism is nano-twinning.

  Electrical conductivity of heat-resistant Al-Fe-Cu-0.25La-Zr alloy for electric wire and cable

  Hu Xiaomei, Liu Lining, Su Feng, Wang Jiaming, Chen Xiangguang, Xu Hao

  2021, 46(8):  197-200.  doi:10.13251/j.issn.0254-6051.2021.08.037

  Abstract ( 46 )   PDF (594KB) ( 20 )  

  In order to investigate the electrical conductivity and mechanical properties of the Al-Fe-Cu-0.25La-Zr alloy for electric wire and cable under different annealing processes, the microstructure and performance indexes such as electric conductivity, tensile strength and elongation were tested by means of conductivity tester, universal tensile testing machine and metallographic microscope, respectively. The results show that when annealed at 350 ℃ for 2 h, the peak value of electric conductivity of the alloy reaches 62.8%IACS, with the tensile strength of 101.5 MPa and the elongation of 32.4%. After annealing at 300 ℃ for 2 h, the electric conductivity of the alloy reaches 62.1%IACS, with the tensile strength of 125.0 MPa and the elongation of 13.4%. When annealed at 300 ℃ for 4-10 h, the electric conductivity of the alloy is relatively stable, and is higher than that when annealed at 350 ℃ for 4-10 h, indicating that the alloy has better thermal stability at 300 ℃. The optimal annealing process of the Al-Fe-Cu-0.25La-Zr alloy is 300 ℃×2 h, after treating by this process the alloy wire meets the requirements of electrical and mechanical properties of electric wire specified in the national standard and can reduce the production cost.

  Heat treatment process of 42CrMo4 steel wind power main shaft

  Shi Keqing, Guo Fu, An Longsen, Chen Yun, Du Ziyang, Wu Meng, Xu Qinpei

  2021, 46(8):  201-204.  doi:10.13251/j.issn.0254-6051.2021.08.038

  Abstract ( 64 )   PDF (646KB) ( 28 )  

  A certain model of 42CrMo4 steel wind power hollow spindle products experienced high proportion of quenching cracking, and reached nearly 20% of rejection rate. So the heat treatment process for the products were optimized based on physical and chemical tests by using of ARL8860 direct reading spectrometer, MTS universal testing machine, SANS impact testing machine and Leica metallographic microscope, and combining with relevant theoretical basis. The experimental results show that the risk of product cracking can be greatly avoided by the optimized quenching process of heating at 860 ℃ and precooling to 820 ℃, then water cooling for 20 min which can solve the technique difficulty. The so-obtained multi-phase microstructure by quenching at 860 ℃, precooling to 820 ℃, then water cooling for 20 min and then tempering at 610 ℃ is composed of tempered sorbite+granular bainite+bainitic ferrite blocks, which can meet the performance requirements as R_m＞700 MPa, and KV₂(-30 ℃)＞40 J.

  Quenching and tempering and gas nitriding processes of 30CrMoV9 steel for hydraulic piston pump

  Wang Juan, Hu Ke, Zhong Xiangling, Jin Yongqian

  2021, 46(8):  205-208.  doi:10.13251/j.issn.0254-6051.2021.08.039

  Abstract ( 69 )   PDF (568KB) ( 27 )  

  In order to improve the comprehensive performance and surface wear resistance and fatigue resistance of the 30CrMoV9 steel for hydraulic piston pump, the quenching and tempering process and the gas nitriding process after rough machining of the 30CrMoV9 steel were studied, and the quenched and tempered hardness, nitrided layer depth, nitrided microstructure and nitrided layer hardness were tested. The results show that after quenching at 900 ℃ and tempering at 630-640 ℃, the tested steel can meet the requirement of hardness in the range of 28-35 HRC. After gas nitriding, the average surface hardness of the quenched and tempered 30CrMoV9 steel can reach more than 750 HV0.5, which can effectively improve the contact fatigue strength of parts.

  SURFACE ENGINEERING

  Microstructure, properties and process optimization of laser nitrogen alloyed coating on 45 steel

  Li Haitao, Fan Shuaiqi, Zhang Leitao, Dai Jiaoyan, Xu Jinfu

  2021, 46(8):  209-213.  doi:10.13251/j.issn.0254-6051.2021.08.040

  Abstract ( 48 )   PDF (571KB) ( 26 )  

  Nitrogen alloyed layer was prepared on the surface of 45 steel by using laser alloying technology, and the alloying process parameters were optimized by orthogonal test, then the microstructure and properties of the alloyed layer obtained by the optimized process treatment were studied by means of OM, XRD, microhardness tester and friction-abrasion testing machine. The results show that with the increase of laser power and scanning speed, the hardness of alloyed layer increases at first and then decreases, reaching the maximum values of 782 HV0.3 and 725 HV0.3 at 1.0 kW and 500 mm·min^-1, respectively. With the increase of overlap ratio, the hardness of alloyed layer decreases gradually, and the optimal process is as follows: laser power of 1.0 kW, scanning speed of 500 mm·min^-1 and overlap ratio of 30%. The microstructure of the alloyed zone after optimized process treatment is composed of solid solution phases and compounds such as γ-(Fe, N), γ-(Fe, C), acicular martensite, γ′(Fe₄N), ε(Fe₂N) and Fe₃C, mainly consisting of columnar and cellular crystals, with a thickness of about 120 μm and an average hardness of about 816 HV0.3. The microstructure of the heat affected zone is composed of a small amount of acicular martensite and retained austenite. The thickness is about 200 μm, and the hardness is graded from 768 HV0.3 to 242 HV0.3. The friction coefficient of the alloyed layer is about 0.4827, and the wear rate is 8.218×10^-15 m³·N^-1·m^-1.

  Characteristics of alternating current field enhanced aluminizing-based pack chrom-aluminizing on Q195 steel

  Chen Chao, Xie Fei, Pan Jianwei

  2021, 46(8):  214-218.  doi:10.13251/j.issn.0254-6051.2021.08.041

  Abstract ( 44 )   PDF (570KB) ( 22 )  

  Alternating current field enhanced pack chrom-aluminizing (ACFPCA) and the conventional pack chrom-aluminizing (CPCA) at 800 ℃ on the surface of the Q195 steel specimens were carried out, respectively, in which the inward diffusion of aluminium dominated, and then adding chromium powder to the aluminizing agent. The layer structure, phase, thickness and distribution of microhardness along the depth direction of the layer were studied by means of metallographic microscopic observation, X-ray diffraction analysis and micro-Vickers hardness test. The results show that compared with single aluminizing, adding a small amount of chromium powder has little effect on structure and thickness of the CPCA layer except increasing the hardness of the subsurface layer. Alternating current field (ACF) promotes both aluminizing and chrom-aluminizing. Compared with single ACF enhanced pack aluminizing (ACFPA), the inward diffusion of Al is further accelerated by adding a small amount of chromium powder to the aluminizing agent in ACFPCA. However, adding a small amount of chromium powder has little effect on increasing the hardness of the subsurface. With the increase of chromium powder in the pack agent, the ACFPCA layer's thickness increases first and then decreases. When 0.1% chromium powder is added, the promoting effect is the most significant and the obtained layer is about 123 μm thick, while the thickness of the ACFPA layer is about 50 μm and that of CPA layer is only about 18 μm.

  Structure and corrosion resistance of CrTiN coating deposited by arc ion plating

  Wang Qishai, Zhang Lin, Li Borong, Zhang Baorong, Zhao Zhiyong

  2021, 46(8):  219-224.  doi:10.13251/j.issn.0254-6051.2021.08.042

  Abstract ( 58 )   PDF (569KB) ( 21 )  

  Cr_xTi_1-xN coatings were deposited on H13 mould steel substrate by arc ion plating, and the influence of Cr/Ti atomic ratio on structure, mechanical properties and corrosion resistance of the as-deposited CrTiN coating was investigated. The results show that the CrTiN coating with different Cr/Ti atomic ratios is obtained by adjusting arc current. The CrTiN coating is composed of solid solution fcc-(Cr,Ti)N and CrN phases. With the increase of Cr/Ti atomic ratio from 1.1 to 1.8, the structure of the coating changes from a random orientation to (111) preferred growth. Microhardness of the CrTiN coating is improved as compared with CrN coating and has a maximum value with the change of lattice distortion caused by solid solution. According to electrochemical impedance spectroscopy and potentiometric polarization curve analysis, the dense Cr_0.59Ti_0.41N coating shows the best corrosion resistance when the Cr/Ti atomic ratio is 1.4.

  Microstructure and wear resistance of oxynitriding layer on piston rod surface of 42CrMo steel

  Wang Zili, Chen Rongfa, Zheng Zhiwei, He Yulong, Shi Minjie, Wang Kai, Zhou Xiaojin

  2021, 46(8):  225-229.  doi:10.13251/j.issn.0254-6051.2021.08.043

  Abstract ( 50 )   PDF (574KB) ( 25 )  

  Surface modification and wear resistance of 42CrMo steel piston rod were studied by using gas oxynitriding composite process. The specimens treated by different surface processes were characterized and analyzed by means of metallographic analysis, microhardness test and dry friction and wear test. The results show that after gas oxynitriding treatment of the quenched and tempered 42CrMo steel for 8 h, at which the surface composed of oxide layer of 1-2 μm with Fe₃O₄ and compound layer of 18 μm with ε-Fe_2-3N and γ′-Fe₄N can be obtained. The effective modified thickness is about 340 μm. Under the same dry friction conditions, the wear mechanism of the specimens without treatment and with chromium plating treatment is abrasive wear accompanied by slight adhesive wear. After gas oxynitriding composite process, the specimen has the lowest average friction coefficient and wear rate, and the wear mechanism is abrasive wear, which has the best wear resistance.

  Influence of surface roughness on surface morphology and sputtering performance of magnetron sputtering etched area of pure Cu target

  Yang Wenhao, Bao Mingdong, Tang Bin, Wang Yupeng, Zhao Guohua, Wang Shuaikang, Wang Duo

  2021, 46(8):  230-235.  doi:10.13251/j.issn.0254-6051.2021.08.044

  Abstract ( 54 )   PDF (564KB) ( 25 )  

  By installing the pure Cu specimens with different roughness in the combined target to ensure the same tested conditions, and the influence of surface roughness on the surface morphology of the magnetron sputtering etched area of the metal target and its sputtering performance were studied by means of white-light interferometer, ion-plating machine, electronic analytical balance and SEM. The results show that the specimens with different roughness can seriously affect the surface morphologies after sputtering. Pits and continuous distributed protrusions are appeared in the deepest etched area of the target, while “bright spots” formed by sputtering pits and incompletely etched grains are appeared in the shallower etched areas. The inside of grains with different orientations and grain boundaries are etched with step-like morphologies, but the height and width of the steps in the grains are much smaller than that at grain boundaries, that is why the etching rate of the grain boundaries is faster than that of the grain internal. After sputtering for 10 h, the larger surface roughness of the initial specimens, the larger surface roughness in the deepest etched area. In the first 10 h of the sputtering process of the specimens, the smallest the initial surface roughness, the largest sputtering yield. Therefore, the film deposition rate and the stability of the sputtering process can be increased by reducing the surface roughness of the target material.

  Effect of laser power on microstructure and corrosion resistance of Ni60A/CeO₂ clad layer on TC4 alloy

  Gong Yuling, Wu Meiping, Cui Chen, Li Yang

  2021, 46(8):  236-240.  doi:10.13251/j.issn.0254-6051.2021.08.045

  Abstract ( 48 )   PDF (570KB) ( 20 )  

  In order to improve the corrosion resistance of the TC4 alloy substrate surface, Ni60A/CeO₂ composite clad layers were prepared on TC4 alloy substrate surface by laser cladding coaxial powder feeding technology with different laser power of 1200, 1500, 1800, 2100 and 2400 W. The effect of laser power on the corrosion resistance of the clad layer was studied by microstructure examination, electrochemical detection and surface observation after electrochemical corrosion. The results show that with the increase of laser power, the microstructure of clad layer becomes uniform and fine, and the electrochemical characteristics show that the corrosion resistance first increases and then decreases. When the laser power is 2100 W, the maximum electrochemical impedance can reach 25.74 kΩ·cm², and there is no obvious corrosion tunnel on the surface of the clad layer, with most of the corrosion products covering the surface of Ni60A/CeO₂ clad layer, and the corrosion resistance is good.

  TEST AND ANALYSIS

  Effect of oxidation time on evaluation of austenite grain size of low alloy spring steel

  Chen Jiping, Zhang Le, Xing Xianqiang, Sun Guoqing, Qian Jianqing

  2021, 46(8):  241-245.  doi:10.13251/j.issn.0254-6051.2021.08.046

  Abstract ( 39 )   PDF (569KB) ( 20 )  

  Oxidation method can be used to determine the grain size of steel. The effect of oxidation time on the evaluation of the austenite grain size of spring steel 50CrV was studied. It was found that the oxidation process can be divided into three stages. In the first stage, the excess ferrite phase is continuously transformed into austenite. In the second stage, the diffusion of anions and cations between the substrate and the oxide film is accelerated again, and the underlying metal substrate continues to oxidize and decarburize, and part of the austenite grain boundary on the surface of specimen is replaced. In the third stage, the austenite grains in the first and second stages gradually grow, and the old and new oxide films are superimposed to grow, which are verified in 55SiCr, 60Si2Mn and 65Si2CrV steels. Without affecting the accuracy of the test results, the oxidation time can be shortened from the standard 60 min to about half, and then the grain size can be obtained by modification, which is close to 11.00 grade of direct corrosion method and 11.09 grade of hydrogen induced intergranular fracture.

  Fracture failure analysis of 60Si2Mn spring steel

  Nie Xiaolong, Gao Jiaqiang, Meng Kairen, Wang Junyi, Liu Xinkuan

  2021, 46(8):  246-249.  doi:10.13251/j.issn.0254-6051.2021.08.047

  Abstract ( 62 )   PDF (564KB) ( 34 )  

  60Si2Mn spring steel fractured during normal service, and part of the original workpiece was lost after the fracture, the fracture origin position was determined according to the mechanics of materials and combined with the characteristics of the fracture. Microstructure, macro and micro fracture morphology and chemical composition of the remained fractured parts were analyzed by means of optical microscope, scanning electron microscope, stereo microscope, direct reading spectrometer, etc. to determine the origin and characteristics of the fracture. The results show that due to improper operation of the production process, there are micro-cracks on the surface of the spring. At the same time, due to the improper shot peening process, a deep stress line is formed on the surface of the spring, and then develops into cracking and shedding along the stress line. These microcracks, cracks and shedding act as the source of fatigue fracture of the spring, and cause the spring to fracture.

  Crack analysis of case-hardened 20Cr2Ni4 steel gear after assembly

  Xu Hongxiang, Wang Hongwei, Zhang Heng, Wang Jun, Zhao Shaofu

  2021, 46(8):  250-253.  doi:10.13251/j.issn.0254-6051.2021.08.048

  Abstract ( 88 )   PDF (569KB) ( 27 )  

  Failure reason of the case-hardened 20Cr2Ni4 steel gear after assembly was analyzed by means of OM, micro-hardness tester and spectrometer. The results show that the tooth top hardness and hardened case depth of the carburized and hardened gear all meet the requirements and the microstructure is good. The cracks source is at the weight-reducing hole of spoke, and the rough tool marks obviously formed in the inner wall of weight-reducing hole can lead to the stress concentration, resulting in the cracks of gear and axle after assembly expanding to the inner hole of gear gradually. And then the fracture failure is occurred, finally some improvement measures are put forward.