Current Issue

• MATERIALS RESEARCH

  Effect of alloying of nickel and iron and aging time on phase transformation behaviour of MnCu based damping alloy

  Niu Hongkang, Wang Diwei, Tian Qingchao

  2022, 47(5):  1-6.  doi:10.13251/j.issn.0254-6051.2022.05.001

  Abstract ( 99 )   PDF (640KB) ( 74 )  

  Three alloys with different composition gradients of Mn-20Cu, Mn-20Cu-5Ni and Mn-20Cu-5Ni-2Fe were prepared, the relationships between elastic modulus and internal friction versus temperature were measured by using a dynamic mechanical analyzer to investigate the effects of chemical composition and aging time on antiferromagnetic transformation and martensitic transformation of the alloys. The results show that the characteristic phase transformation temperature of the three alloys is positively correlated with the square root of the aging time, the alloying elements act on the characteristic temperature by influencing the diffusion of solute atoms during spinodal decomposition and that the l-value describing the coupling strength between applied oscillating stress and phase interface is one of the key factors reflecting the damping alloy material.

  Influence of heat treatment on microstructure and mechanical properties of W-core SiC filaments

  Liu Shuai, Luo Xian, Huang Bin, Yang Yanqing

  2022, 47(5):  7-13.  doi:10.13251/j.issn.0254-6051.2022.05.002

  Abstract ( 83 )   PDF (561KB) ( 40 )  

  Scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Raman spectrometer analysis and tensile test were employed to study the microstructure of the components in W-core SiC filaments and its mechanical properties after different heat treatments in a low vacuum environment. The results show that the tensile strength of the W-core is much higher than that of the W-core SiC filaments after experiencing the same heat treatment. The structural stability of the W/SiC interfacial reaction layer and the SiC deposit can be well retained after heating at 800 ℃ for 50 h, which enables the tensile strength of the W-core SiC filaments to reach 3.10 GPa. Further increasing the temperature during the heat treatment not only promotes the growth of the W/SiC interfacial reaction layer as well as the interfacial voids, but also severely damages structural stability of the SiC deposit through the coarsening of the interior columnar grains and the formation of grooves on the surface, which leads to the Weibull modulus of W-core SiC filaments after heating at 900 ℃ for 50 h and the tensile strength after heating at 1000 ℃ for 50 h decrease to 9.7 and 1.12 GPa, respectively.

  Research status of high-temperature creep properties of novel alumina-forming austenitic heat-resistant steel

  Yuan Zhi, Zhang Hailian, Zhang Huijie, Ma Qingshuang, He Xiang, Bi Changbo, Li Huijun, Gao Qiuzhi

  2022, 47(5):  14-24.  doi:10.13251/j.issn.0254-6051.2022.05.003

  Abstract ( 86 )   PDF (555KB) ( 52 )  

  Novel alumina-forming austenitic steel (AFA steel) is a new type of heat-resistant steel developed in recent years. It has better high-temperature oxidation resistance and creep properties than traditional heat-resistant steel, and is expected to be used in key components of ultra-supercritical units. Starting from the regulation of alloying elements of different AFA steels, the design principles of AFA steel was expounded, the influence of alloying element difference on precipitated phase was analyzed, in order to reveal the precipitation and coarsening kinetics and the relationship between creep properties and coarsening kinetics of precipitated phase, and the creep fracture mechanism at elevated temperature was summarized and the potential factors that affected the creep properties were discussed. The strengthening idea and future application of AFA steel were also prospected.

  Constitutive model and hot processing map of Ti80 titanium alloy during high temperature deformation in two-phase region

  Zhou Xiaofeng, Fu Wen, Li Chengning, Cheng Fangjie

  2022, 47(5):  25-30.  doi:10.13251/j.issn.0254-6051.2022.05.004

  Abstract ( 64 )   PDF (559KB) ( 31 )  

  In order to determine the best process window for hot deformation of Ti80 titanium alloy, high temperature compression test of Ti80 titanium alloy was carried out by Gleeble3500 thermal simulation test machine with deformation temperature between 850-1050 ℃, and the strain rate between 0.05-1 s^-1. The results show that Ti80 titanium alloy is very sensitive to deformation temperature and strain rate, and the flow stress increases significantly with the increase of strain rate and the decrease of deformation temperature. In the near β region, the distribution of flow stress will change suddenly. The high temperature constitutive equation of the Ti80 titanium alloy is established by using the linear regression method. The deformation activation energy of the Ti80 titanium alloy in the two-phase region is calculated to be 308 kJ/mol. Based on the Prasad instability criterion, the hot processing map of the Ti80 titanium alloy is established. Finally, it is determined that the Ti80 titanium alloy can fully recrystallize at high strain rate when the deformation temperature is between 880-930 ℃, and then ideal microstructure and properties can be obtained.

  Hot deformation behavior and processing maps of X12CrMoWVNbN steel

  Li Rongbin, Li Bo, Zhang Zhixi, Peng Wangjun, Guo Yanbing

  2022, 47(5):  31-39.  doi:10.13251/j.issn.0254-6051.2022.05.005

  Abstract ( 63 )   PDF (559KB) ( 36 )  

  Using Gleeble3180 thermal simulation testing machine, under the conditions of temperature between 950-1100 ℃, strain rate between 0.001-1 s^-1, and true strain 0.7, high temperature unidirectional thermal compression experiments were carried out on X12CrMoWVNbN steel. The effects of temperature and strain rate on mechanical behavior of the tested steel during hot deformation were analyzed by high temperature flow curves under different conditions. Based on the Arrhenius equation as the constitutive model, a constitutive equation that can predict the flow stress of the steel was established. Based on the dynamic material model, experimental parameters and results, the processing maps of the steel under different strains were drawn, and the microstructure analysis was carried out combined with the maps. The results show that the flow peak stress and steady state stress increase with the decrease of temperature and increase of strain rate, the power dissipation coefficient increases with the decrease of strain rate and the increase of deformation temperature, the values of the power dissipation coefficient η in the optimal hot working areas are all above 0.4, and the deformed microstructure in these areas is uniform and fine. The optimal hot working regions at strain of 0.3, 0.4, 0.5 and 0.6 are all in the range of deformation temperature of 1050-1100 ℃ and strain rate of 0.001-0.003 s^-1.

  Corrosion resistance of (FeCoNiCr)_100-xMn_x high entropy alloys in NaCl and NaOH solutions

  Zhao Kun, Jiang Peng, Wang Huhu, Wang Bo, Wang Peijin, Yang Xingzhong

  2022, 47(5):  40-46.  doi:10.13251/j.issn.0254-6051.2022.05.006

  Abstract ( 71 )   PDF (567KB) ( 24 )  

  Microstructure and corrosion resistance in NaCl and NaOH solutions of the (FeCoNiCr)_100-xMn_x(x=4,8,12,20) high entropy alloys prepared by spark plasma sintering were studied. The results show that (FeCoNiCr)_100-xMn_x alloys are mainly composed of FCC single phase structure and a small amount of BCC phase. (FeCoNiCr)₈₈Mn₁₂ alloy has the best corrosion resistance in 3.5wt%NaCl solution. The addition of Mn enhances the corrosion resistance of the alloy in 1 mol NaOH solution. Annealing has little effect on corrosion resistance of the alloy in 1 mol NaOH solution. The corrosion resistance of the (FeCoNiCr)_100-xMn_x alloys in 3.5wt%NaCl solution and 1 mol NaOH solution is better than that of the 304S stainless steel.

  Effect of Al content on microstructure and properties of hot rolled FeMnCoCr high entropy alloy

  Zhao Sijie, Li Hang, Niu Lichong, Li Jie, Feng Yunli

  2022, 47(5):  47-52.  doi:10.13251/j.issn.0254-6051.2022.05.007

  Abstract ( 74 )   PDF (563KB) ( 42 )  

  Effect of Al content on microstructure, deformation mechanism and tensile properties of the (Fe₅₀Mn₃₀Co₁₀Cr₁₀)_100-xAl_x high entropy alloys was studied. The (Fe₅₀Mn₃₀Co₁₀Cr₁₀)_100-xAl_x cast alloys were melted by a vacuum electric arc furnace, and then hot rolled and water quenched with a reduction rate of 80%. The microstructure of the alloy was analyzed by using SEM and EBSD. The results show that with the increase of Al content (atom fraction, the same below) from 0% to 6%, the microstructure of the hot rolled and quenched alloy changes from FCC+HCP dual phase to FCC single phase, and BCC phase occurs when Al content is 8%. With the increase of Al content from 0% to 6%, the TRIP effect is inhibited, but the TWIP effect enhances obviously, the yield strength of the alloy changes a little, the tensile strength decreases slightly, while the elongation after fracture increases significantly. When the Al content is 6%, the elongation of the high entropy alloy reaches the highest, which is 79%.

  Influence of Cu content on microstructure and mechanical properties of Al-Cu-Mg-Sc alloy fabricated by gravity die casting

  Zheng Yuankai, Li Longfei, Jin Kang, Li Chunming, Zhang Wenliang, Liang Junning

  2022, 47(5):  53-58.  doi:10.13251/j.issn.0254-6051.2022.05.008

  Abstract ( 54 )   PDF (557KB) ( 41 )  

  Al-Cu-Mg-Sc alloy with different Cu contents (4%-6%, mass fraction, similarly hereinafter) was prepared by gravity die casting process, and a two-stage solution treatment(500 ℃×4 h＋520 ℃×6 h) with water cooling was carried out, subsequently aged at 175 ℃ for 5 h.Effect of Cu content on microstructure and mechanical properties of the tested alloy was investigated by means of Vickers hardness test, room temperature tensile test, scan electron microscope observation. Then, the optimized composition of Al-Cu-Mg-Sc alloy was obtained. The results show that when the Cu content increases from 4.26% to 5.58%, the precipitation content of Al₂Cu phase increases continuously after heat treatment, and the yield strength and tensile strength of the alloy increase from 191 MPa and 323 MPa to 216 MPa and 355 MPa, respectively, and the elongation is maintained around 13%. While the Cu content is higher (6.13%), the volume fraction of Al₂Cu phase in the microstructure is relatively high, and the amount of Al₂Cu phases dissolved into the matrix after solution treatment is limited, and a large amount of residual Al₂Cu phases remain at the grain boundary. After aging, the strengthening effect of the high-Cu alloy cannot continue to increase as the Cu content increases. Therefore, on the whole, with the increase of Cu content, the hardness and tensile strength of the alloys with high Cu content increase firstly and then stabilize, the elongation of the alloys first increases and then decreases. The cast Al-Cu-Mg-Sc alloy with Cu content of 5.58% after aging can achieve the best overall properties, of which the hardness is 117 HV, tensile strength and yield strength are 355 MPa and 216 MPa, respectively, and the elongation is maintained in 13.5%.

  Effect mechanism of rare earth Y on mechanical properties of TWIP steel

  Liu Peng, Yang Jichun, Liu Xiangjun, Sun Mengxiang, Yang Changqiao

  2022, 47(5):  59-64.  doi:10.13251/j.issn.0254-6051.2022.05.009

  Abstract ( 74 )   PDF (556KB) ( 24 )  

  Effect of rare earth Y on mechanical properties and inclusions of a TWIP steel (22Mn-1.5Al-0.6C) was investigated by means of GNT universal testing machine and Sigma 300 field emission scanning electron microscope. The results show that after adding rare earth Y, the tensile strength of the tested steel increases from 725 MPa to 752 MPa, the yield strength increases from 290 MPa to 312 MPa, and the impact absorbed energy increases from 178.9 J to 207.7 J, while the hardness and elongation after fracture decrease slightly. The rare earth Y refines the TWIP steel grain, and the MnS, Al₂O₃ and MnS+AlN inclusions in the steel are modified into Y₂S₃, Y₂S₃+Y₂O₃, AlN+Y₂S₃. The inclusion analysis results show that the quantity and size of most inclusions decrease significantly, which is beneficial to the improvement of comprehensive mechanical properties of the tested steel.

  Evolution of mechanical properties and its mechanisms of pre-twinned pure magnesium and AZ80 magnesium alloy during annealing

  He Jiejun, Wu Lushu

  2022, 47(5):  65-70.  doi:10.13251/j.issn.0254-6051.2022.05.010

  Abstract ( 64 )   PDF (555KB) ( 26 )  

  Extruded pure magnesium and AZ80 magnesium alloy prepared by the same process were pre-compressed by 6% respectively, then the specimens with and without pre-compressing were annealed at 180 ℃ for 20 h. The microstructure and mechanical properties were characterized by using optical microscope, scanning electron microscope, transmission electron microscope and compressive test machin, by which the evolution of mechanical properties during annealing and its mechanisms were investigated for the pre-twinned pure magnesium and AZ80 alloy. The results show that the yield strength of the 6% pre-compressed pure magnesium annealed at 180 ℃ for 20 h is lower than that of the unannealed, which indicates that no annealing hardening occurs in the pure magnesium. The yield strength of the AZ80 alloy without pre-compressing annealed at 180 ℃ for 20 h is nearly equal to that of the AZ80 alloy before annealing. However, the yield strength of the 6% pre-compressed AZ80 alloy annealed at 180 ℃ for 20 h is 20 MPa higher than that before annealing, which is resulted from a great deal of white second-phase particles precipitated in the twins and at the twin boundary that prevent dislocation gliding and twin expanding. Thus, the 6% pre-compressed AZ80 alloy has obvious annealing strengthening effect.

  Phase transformation law of H13 steel and numerical simulation of vacuum heat treatment for dies

  Guo Shuo, Fan Zhenyu, Wang Huizhen, Zhou Leyu, Zhai Yuewen

  2022, 47(5):  71-75.  doi:10.13251/j.issn.0254-6051.2022.05.011

  Abstract ( 77 )   PDF (555KB) ( 35 )  

  Aiming at numerical simulation for microstructure evolution predicting of H13 hot work steel dies in vacuum quenching heat treatment, continuous cooling phase transformation tests were performed on the H13 steel by using DIL805L thermal dilatometer, and the continuous cooling transformation curve (CCT curve) of the H13 steel was plotted by combining microstructure and hardness results. The effect of different cooling rate on microstructure and hardness of the specimens was studied, and the phase transformation factors in the Koistinen-Marburger equation were fitted to investigate the phase transformation law of the H13 steel. The results show that the critical cooling rate of martensite transformation is 1 ℃/s, the Ms point is 335 ℃, and with the increase of cooling rate, the hardness of the specimen increases to 660 HV. By importing the fitted martensitic phase transformation equation into finite element software by secondary development means to carry out numerical simulation calculation, the results show that the volume fraction of martensite at different sampling points of H13 steel die is 90%. It can be considered that the microstructure of H13 steel die after vacuum gas quenching is martensite and retained austenite.

  Influence of Cu-rich precipitates on recrystallization behavior of Fe-3%Si-Cu alloy

  Zhang Huimin, Zhang Chengyuan, Wu Zhongwang, Jin Zili, Ren Huiping, Wang Chaoyi

  2022, 47(5):  76-80.  doi:10.13251/j.issn.0254-6051.2022.05.012

  Abstract ( 54 )   PDF (561KB) ( 23 )  

  Taking 2 pieces of hot rolled Fe-3%Si-Cu alloy plates as the research object, over-aged and solution-treated respectively and multi-pass cold rolled, and then recrystallization annealed at 500-800 ℃, the recrystallization behaviors of the cold rolled Fe-3%Si-Cu alloy plates were researched by studying the microstructure after annealing and the hardness change with different annealing processes. The results show that when the hot-rolled specimens are over-aged at 650 ℃, the fcc ε-Cu phase is precipitated with the morphology of ellipsoidal or rod-shaped, and the size of the rod-shaped copper-rich phase is large, with its long axis being greater than or equal to 100 nm. Both the specimens treated by different heat treatments before cold rolling show that the complete recrystallization time is shortened with the increase of annealing temperature, while due to the precipitation of copper-rich phase, the fully recrystallization time of the specimen solution-treated is significantly shorter than that of the over-aged. When the annealing temperature is 500 ℃, because the softening caused by the recovery is not enough to offset the hardening caused by precipitation, the hardness curve of the solution-treated specimen shows an obvious aging hardening peak when the annealing time is 10⁴ s. When the annealing temperature is above 600 ℃, the solution-treated specimen shows the recrystallization dominated annealing characteristics, and without aging hardening peak on the hardness curve.

  Effect of chemical composition on microstructure and deformation behavior of 316L austenitic stainless steel

  Mo Jinqiang, Feng Guanghong, Xu Mei, Zhang Wei, Li Yang

  2022, 47(5):  81-86.  doi:10.13251/j.issn.0254-6051.2022.05.013

  Abstract ( 97 )   PDF (562KB) ( 33 )  

  Room temperature uniaxial tensile test was carried out by universal testing machine for hot-rolled 316L stainless steel plate with different nickel equivalents, then microstructure of the steel before and after the tensile deformation was observed by scanning electron microscope (SEM) and transmission electron microscope(TEM), and the effect of nickel equivalent(Nieq) on microstructure and properties of 316L stainless steel was explored. The results show that the microstructure at solid solution state is austenite and a small amocmt of high temperature δ phase, the strength decreases with the increase of Nieq, and the plasticity and toughness increase with the increase of Nieq. The tensile fracture is characterized by ductile fracture, and with the increase of Nieq, the number of dimples decreases while the size of dimples increases. The TEM observation shows that no martensitic transformation occurs in the deformed tested steel, when the Nieq is low, the dislocation density in the place with large deformation is high, dislocation interaction occurs, and deformation twins are formed locally. With the increase of Nieq, the density of deformation twin increases, and resulting in crossing and hysteresis.

  Microstructure and properties of new-type Cr8 cold working die steel used in passenger cars after vacuum gas quenching

  Yuan Sha, Zhou Leyu, Jiang Peng, Zhang Jianbo, Chen Hao

  2022, 47(5):  87-91.  doi:10.13251/j.issn.0254-6051.2022.05.014

  Abstract ( 39 )   PDF (555KB) ( 23 )  

  Comparative analysis was carried out on microstructure and mechanical properties of the two kind of Cr8 cold working die steel of domestic HNC53 and Japanese KD11max by means of hardness tester, metallographic microscope and SEM. The influence of carbide evolution on mechanical properties of the tested steels before and after heat treatment was analyzed. The results show that the content of P and S in HNC53 steel is within standard range. Compared with the KD11max steel, the massive eutectic carbide particles in the original microstructure of the HNC53 steel become smaller and more evenly distributed in the matrix. When vacuum gas quenched at 1030 ℃ and tempered at 520 ℃, the microstructure of the two steels is composed of martensite, large eutectic carbides and fine secondary precipitated carbides, compared with before heat treatment, the size and quantity of massive eutectic carbides are smaller and fewer. After tempering at 520 ℃, there are more precipitated secondary carbide particles in the HNC53 steel evenly distributed on the martensite matrix. Compared with KD11max steel, HNC53 steel has little difference in hardness and toughness.

  PROCESS RESEARCH

  Precipitation behavior of second phase in super duplex stainless steel 2507

  Gu Guochao, Li Ruifen, Xin Zhenmin, Yuan Zhaofu, Cui Shugang, Xu Wenhua, Lü Yupeng

  2022, 47(5):  92-97.  doi:10.13251/j.issn.0254-6051.2022.05.015

  Abstract ( 58 )   PDF (562KB) ( 23 )  

  Second phase precipitation behavior of solid solution treated (1100 ℃×30 min) super duplex stainless steel 2507 hot raled plate after aging at different temperatures (750-1000 ℃) and time (1-240 min) was investigated by using OM, SEM and EBSD. The results show that the microstructure of the tested steel is composed of austenite and ferrite after solution treatment, while after aging at 750-1000 ℃, σ phase and χ phase are detected and identified. When the aging temperature is lower, χ phase precipitates from ferrite phase and exists stably. With aging temperature increasing, the σ phase is formed mainly by the reaction α→σ+γ₂. In addition, with the longer holding time, the metastable χ phase dissolves and promotes σ phase precipitation. Additionally, the aging temperature influences the morphology of the precipitates. At higher aging temperatures (＞950 ℃), the morphology of precipitated phase is mainly sheet σ and γ₂, while at lower aging temperatures, the granular σ phase and χ phase are mainly observed. According to the precipitation behavior and the calculation of TTT diagram of the precipitates, it can be seen that hot rolling deformation shortens the nucleation incubation period of the second phases in the SDSS 2507, increases the precipitation rate, and the precipitation sensitive temperature is about 950 ℃.

  Effect of solution treatment on microstructure transformation and element diffusion of Fe-Cr-Ni-Al alloy

  Zhou Qiyun, Shi Zengmin, Xie Hao, Dai Lei

  2022, 47(5):  98-104.  doi:10.13251/j.issn.0254-6051.2022.05.016

  Abstract ( 138 )   PDF (561KB) ( 25 )  

  Diffusion of elements and phase transformation of the Fe-Cr-Ni-Al alloy during solution treatment process were studied by means of OM, SEM and other methods, and a JMAK model of γ phase transformation was established by DSC data at different cooling rates. The results show that the matrix phase at room temperature of the as-cast Fe-Cr-Ni-Al alloy is γ phase and δ phase. After solution treatment at 1150 ℃, the content of the γ phase in the alloy increases, and the content of the δ phase decreases. The phase change of δ→γ occurs in the heating stage, and the phase change of γ→δ occurs in the isothermal soaking stage. Through the solution treatment, δ phase and γ phase evolve into a more obvious Cr-rich phase and Ni-rich phase, the difference of Cr and Ni elements between σ phases which located in different positions increases, and the component segregation between σ phases and their matrix decreases gradually. It can be proved by the JMAK model of austenite phase transition that the greater the cooling rate, the lower the starting temperature of the γ phase transition, and the larger the temperature interval of the transition, the greater the energy change caused by the reaction.

  Effect of solution treatment on microstructure and mechanical properties of Ni48Cr21Cu2Mo alloy

  Liu Xuan, Huang Guoping, Liu Haiding, He Qubo, Zhang Nan

  2022, 47(5):  105-110.  doi:10.13251/j.issn.0254-6051.2022.05.017

  Abstract ( 64 )   PDF (601KB) ( 23 )  

  Evolution of microstructure and mechanical properties of the Ni48Cr21Cu2Mo alloy varied with solution treatment temperature were investigated by means of the material analysis simulation software (JMatPro), X-ray diffractometer (XRD) and scanning electron microscope (SEM). The calculated equilibrium phase results show that the matrix is almost γ phase when the temperature is above 990 ℃, and the Laves phase appears in the temperature range from 870 ℃ to 1008 ℃. The δ, γ′ and σ phases are precipitated when temperature below 870 ℃. The experimental results of microstructure indicate that the grain size increases and the granular phases are redissolved gradually with the increase of solution temperature. When solution treated at 1010 ℃, the microstructure is the most homogeneous and the particle phases are basically redissolved. The γ′ and γ″ phases and the granular δ and σ composite phases precipitated at grain boundaries occur after aging. The Ni48Cr21Cu2Mo alloy has excellent comprehensive mechanical properties under 1010 ℃×1 h solution treatment and 718 ℃×8 h+622 ℃×8 h aging.

  Effect of tempering temperature on microstructure and properties of Q1100 ultra-high strength steel

  Liu Dan, Chen Jie, Liu Wenjian, Zhou Wenhao, Luo Deng, Zhang Qingxue

  2022, 47(5):  111-117.  doi:10.13251/j.issn.0254-6051.2022.05.018

  Abstract ( 90 )   PDF (601KB) ( 23 )  

  Effect of tempering temperature on microstructure and properties of Q1100 ultra-high strength steel was studied by mechanical properties test, metallographic observation and SEM observation. The results show that the tested steel is composed of tempered lath martensite when water quenched from 900 ℃ and then tempered at 200-300 ℃. After tempering at 400 ℃ and 500 ℃, the microstructure is tempered troostite. After tempering at 600 ℃, the microstructure is tempered sorbite. The tested steel has high tempering stability, the α ferrite still maintains the shape and orientation of lath martensite when tempered at 400-600 ℃. After tempering at 200 ℃, the content of low angle grain boundary is high, which hinders the propagation of microcracks and the steel has good toughness. With the increase of tempering temperature, the proportion of low angle grain boundary decreases gradually. After tempering at 400 ℃, the proportion of low angle grain boundary is relatively small, the precipitation of carbides deteriorates the toughness of the tested steel, the tempering brittleness occurs and results in the worst toughness. After tempering at 500 ℃ and 600 ℃, the proportion of low angle grain boundary is not significantly different from that at 400 ℃, but the recovery degree of the microstructure is large and partial recrystallization occurs after tempering at 600 ℃. The tempering softening effect is large and the toughness is high. When the tempering temperature is 200 ℃, the tested steel has the best comprehensive properties, of which the yield strength is 1164.38 MPa, the tensile strength is 1429.70 MPa, the elongation after fracture is 14.66%, the hardness is 430.27 HV3, and the impact absorbed energy of the standard specimen at -40 ℃ is 92.30 J.

  Effect of annealing on bonding interface microstructure and properties of TA1/5052 explosive welded composite plates

  Zhang Zhen, Ding Xu, Wang Xiaomiao, Zou Jie, Tian Xiaodong, Luo Hailong

  2022, 47(5):  118-125.  doi:10.13251/j.issn.0254-6051.2022.05.019

  Abstract ( 67 )   PDF (602KB) ( 21 )  

  TA1/5052 explosive welded composite plates were annealed at 350, 400 and 450 ℃ for 1, 3, 6 and 9 h, respectively. The microstructure and properties of the composite plates before and after annealing were studied. The results show that with the increase of annealing temperature, atomic diffusion intensifies and the diffusion layer formed at the interface becomes thicker. During annealing process, aluminum diffuses easily to the titanium side, while the bright white band and Kirkendall hole are mainly located in the side of 5052 aluminum alloy near the interface. The phase composition at the interface before annealing is α-Ti, α-Al and TiAl₃. After annealing at 350, 400 ℃ for 3 h and at 450 ℃ for 1, 3, 6, and 9 h, the phase composition is unchanged. After annealing at different temperatures, the tensile strength of the interface of the composite plates is lower than that before annealing, while the area shrinkage and elongation are significantly higher than that before annealing. The analysis of tensile fracture shows that the TAl side is ductile brittle mixed fracture with brittle fracture as the main and ductile fracture as the auxiliary, and the 5052 side is ductile fracture. When annealed at 350 ℃, the interfacial shear strength and peel strength of the composite plates are the highest, which is increased by 8.24% and 45.68%, respectively, compared with the explosion state. With the increase of annealing temperature, the interfacial shear strength and peel strength decreases. The hardness of the interface bonding zone before and after annealing is higher than that of both sides of the base plate, and with the increase of the distance from the interface, the hardness gradually decreases to the hardness of the base metal on both sides of Ti/Al. The hardness of the interface bonding zone after annealing is significantly lower than that of the explosion state.

  Effect of annealing temperature on microstructure and mechanical properties of cold-rolled Fe-0.4C-10Mn-6Al high strength steel

  Su Hongdong, Fan Wei, Feng Yunli

  2022, 47(5):  126-130.  doi:10.13251/j.issn.0254-6051.2022.05.020

  Abstract ( 49 )   PDF (600KB) ( 23 )  

  Effect of annealing temperature on microstructure and mechanical properties of the cold-rolled Fe-0.4C-10Mn-6Al high strength steel was studied by means of optical microscope, scanning electron microscope, electronic universal tensile test machine, X-ray diffraction and backscattered electron diffraction. The results show that microstructure of the tested steel after cold rolling consists of δ-ferrite, α-ferrite, austenite, martensite and carbide. The annealed microstructure is mainly composed of δ-ferrite, α-ferrite, austenite and carbide, and the austenite content increases with the increase of annealing temperature due to reversed transformation of martensite. With the increase of annealing temperature, the yield strength and tensile strength decrease gradually, while the elongation increases gradually. When the annealing temperature reaches 800 ℃, the product of strength and elongation of the tested steel reaches 27.84 GPa·%, and has good comprehensive mechanical properties.

  Effect of magnetic field pre-annealing on secondary recrystallization structure and texture of oriented silicon steel

  Su Pengji, Ma Yonglin, Dong Lili, Wen Kai, Luo Jiahao, Liu Baozhi

  2022, 47(5):  131-135.  doi:10.13251/j.issn.0254-6051.2022.05.021

  Abstract ( 65 )   PDF (604KB) ( 20 )  

  The 3.2%Si oriented silicon steel after secondary cold rolling but before high-temperature annealing was pre-annealed at different temperatures in a pulsed magnetic field pre-annealing tubular furnace independently designed and developed by the laboratory. The microstructure and texture were analyzed by optical microscope and XRD, and the magnetic properties of the specimen annealed at high temperature were analyzed by using the magnetic property test system for silicon steel sheet. The results show that on the whole, the average grain size of the oriented silicon steel decreases slightly with the increase of pre-annealing temperature, and the grain size is mainly in the range of 10-25 μm. According to the analysis of ODF diagram and {200} pole figure, after pulsed magnetic field pre-annealing, the strongest texture changes from {112}<110> texture to {223}<110> texture and {111}<110> texture with the increase of pre-annealing temperature, while the magnetic properties of the high temperature annealed specimen decrease.

  Microstructure and properties of 1.5Al medium-manganese steel after short time intercritical annealing

  Feng Jike, Ding Wei, Li Yan, Zhang Guangyin, Zhang Nan

  2022, 47(5):  136-140.  doi:10.13251/j.issn.0254-6051.2022.05.022

  Abstract ( 63 )   PDF (598KB) ( 20 )  

  Thermodynamic process window, microstructure and mechanical properties of 0.2C-5Mn-0.5Si-1.5Al medium manganese TRIP steel were studied by means of thermodynamic software, scanning electron microscopy (SEM), X-ray diffractometer (XRD) and tensile test, based on which, the effect of short time intercritical annealing temperature on microstructure evolution and mechanical properties of the tested steel was analyzed. The thermodynamic calculation results show that the optimal intercritical annealing temperature range is 640-670 ℃, and the actual optimal annealing temperature shifts to the right about 70 ℃. At the low temperature stage (700 ℃), the carbides are not completely dissolved, while at the high temperature stage (760-820 ℃), the stability of austenite decreases and martensite appears in the microstructure, which corresponding to both sides of the optimal process window respectively. After intercritical annealed at 730 ℃, the carbides are completely dissolved and the austenite is stable enough, the microstructure is composed of ferrite and austenite, and the optimal mechanical properties can be obtained, with the tensile strength of 1041 MPa, the yield strength of 921 MPa, the elongation of 42%, and the strength-elongation product being close to 43 GPa·%.

  Solidification segregation characteristic and homogenization treatment of GH141 superalloy

  Xiao Dongping, Zhou Yang, Fu Jianhui, Yang Haodi

  2022, 47(5):  141-147.  doi:10.13251/j.issn.0254-6051.2022.05.023

  Abstract ( 60 )   PDF (600KB) ( 24 )  

  Segregation characteristics and microstructure of the as-cast GH141 superalloy ingot prepared by vacuum induction melting (VIM) and vacuum arc remelting (VAR) were investigated by means of optical microscope (OM), scanning electron microscope and energy dispersive spectroscopy (EDS). Meanwhile, the effect of homogenization temperature and time on evolution of microstructure, precipitates and segregation of the GH141 superalloy was also studied. The results show that the as-cast GH141 alloy exhibits dendritic segregation, in which Ti and Mo are segregated to the interdendritic regions, while Al, Co and Cr are segregated to the dendrites. The main precipitates are MC, M₆C and M₂₃C₆ carbides in interdendritic regions. With the increase of homogenizing temperature and holding time, dendrite structure is eliminated, carbides are redissolved and segregation elements are gradually distributed evenly by diffusion. It is found that the element segregation is basically eliminated and most of the carbides are redissolved in the GH141 alloy after homogenization at 1190 ℃ for 48 h.

  Influence of bulk energy density on corrosion resistance of 316L stainless steel formed by SLM

  Li Peng, Kong Linghua, Lian Guofu, Huang Xu, Li Zhu

  2022, 47(5):  148-154.  doi:10.13251/j.issn.0254-6051.2022.05.024

  Abstract ( 59 )   PDF (598KB) ( 19 )  

  In order to explore the effect of different bulk energy density on corrosion resistance of SLM formed 316L stainless steel, SLM 316L stainless steel formed parts were prepared under different laser power, scanning spacing and scanning speed by orthogonal test method. The microstructure and self-corrosion potential were observed and measured by means of scanning electron microscope and electrochemical test. The results show that if the bulk energy density is too large or very small, there are more defects such as pores and holes on the surface of the molded parts, the self-corrosion potential is decreased, and the corrosion resistance is deteriorated. When the bulk energy density is 44.64 J/mm^-3, the self-corrosion potential of SLM 316L stainless steel molded parts is the highest, the defects such as pores on the surface are relatively few, and the corrosion resistance is the best. The order of the factor of laser power, scanning distance and scanning speed on the corrosion resistance of SLM 316L stainless steel molded parts is: laser power > scanning distance and scanning speed. The best combination of process parameters is laser power of 250 W, scanning spacing of 0.14 mm and scanning speed of 800 mm/s.

  Effect of vacuum annealing on microstructure and mechanical properties of selective laser melted TA2 pure titanium

  Zhang Chunyu, Yan Yu, Chen Xianshuai, Du Ruxu

  2022, 47(5):  155-160.  doi:10.13251/j.issn.0254-6051.2022.05.025

  Abstract ( 65 )   PDF (604KB) ( 30 )  

  The medical TA2 pure titanium specimens were prepared by the selective laser melting process. Effect of vacuum annealing on microstructure and mechanical properties of the specimens was been compared and analyzed by means of optical microscope (OM), scanning electron microscope (SEM), universal material experiment machine and Vickers hardness tester. The change of oxygen content in the specimens were also studied by means of combined determination apparatus for oxygen, nitrogen and hydrogen. The results show that appropriate vacuum heat treatment process can obviously change the microstructure of specimens from martensite structure to near-equiaxial structure, and effectively change the mechanical properties of the specimens, reduce the tensile strength and yield strength, and increase the plasticity. In addition, vacuum heat treatment could reduce the oxygen content and hardness. When annealed in vacuum at 800 ℃ for 1 h, the microstructure of specimens is the near-equiaxial structure,and the mechanical properties are satisfied with the requirement of the GB/T 13810—2017 Wrought titanium and titanium alloy for surgical implants,and the R_m, R_p0.2, A and Z are 670.3 MPa, 609 MPa, 20% and 44.7%, respectively.

  Microstructure control and properties of U76CrRE steel rail during heat treatment

  Wang Huijun, Tao Ya, Chen Lin, Liang Zhengwei, Wang Yongming

  2022, 47(5):  161-165.  doi:10.13251/j.issn.0254-6051.2022.05.026

  Abstract ( 56 )   PDF (598KB) ( 23 )  

  Cooling process of the U76CrRE steel rail during heat treatment was optimized, and the abnormal upper bainite microstructure in the decarburization layer of the steel rail was therefore eliminated. The causes of abnormal microstructure were analyzed, and the best heat treatment process of U76CrRE steel rail was put forward. During the stage cooling process, the forced cooling intervention temperature of U76CrRE steel rail is 568 ℃. The temperature condition for the abnormal upper bainite microstructure is that the latent heat of phase transformation inside the rail and the extremely cold surface layer easily form an isothermal layer in the decarburization layer of the rail. Simultaneously, severe decarburization at the grain boundary near surface of the rail provides the condition of chemical composition for the formation of upper bainite structure. The optimum heat treatment process of the U76CrRE steel rail consists of quenching cooling starting temperature of 780 ℃, quenching time of 120 s (20 s+100 s), quenching final cooling temperature of 410 ℃ and back temperature of 540 ℃.

  Microstructure and properties of carburized layer of 20Cr2Ni4A steel and 17Cr2Ni2MoVNb steel

  Zhu Xu, Chen Jianwen, Jiang Yizhou, Liu Ke, Luo Zixiang, Gao Yiqiang, Xiang Zhendong

  2022, 47(5):  166-170.  doi:10.13251/j.issn.0254-6051.2022.05.027

  Abstract ( 49 )   PDF (598KB) ( 22 )  

  Microstructure and properties of the carburized layers of 20Cr2Ni4A steel and 17Cr2Ni2MoVNb steel under the same heat treatment process were investigated. The results show that the grains of 17Cr2Ni2MoVNb steel before and after heat treatment are finer than that of the 20Cr2Ni4A steel. After quenching and low temperature tempering, the core grain size grade of the 20Cr2Ni4A steel is grade 7, and that of the 17Cr2Ni2MoVNb steel is grade 8. The grain size of the carburized layer changes gradually, and that of the outermost layer in the carburized layer is the biggest but still is the same as the core grain size due to the pinning effect of the carbide formed by trace elements such as V and Nb on the grain boundary. At the same time, more content of the carbide particles make the microhardness of the 17Cr2Ni2MoVNb steel slightly higher than that of the 20Cr2Ni4A steel. The carburized layer of 17Cr2Ni2MoVNb steel has higher hardness and more carbides than that of 20Cr2Ni4A steel, so its wear resistance is better.

  Carbide precipitation law in vacuum carburized 18CrNiMo7-6 steel

  Zhang Minghao, Han Haoyuan, Xu Yueming, Li Qiao, Gao Zhi, Zhou Leyu

  2022, 47(5):  171-176.  doi:10.13251/j.issn.0254-6051.2022.05.028

  Abstract ( 64 )   PDF (600KB) ( 32 )  

  Using quenching dilatometer for simulation, carbide precipitation law during cooling of the vacuum carburized 18CrNiMo7-6 steel was studied by characterizing the microstructure and hardness distribution. The results show that after austenitizing at 980 ℃ for 30 min, the carbides are completely dissolved. After cooling quickly to 600 ℃ and holding for 20 min, the infiltration layer microstructure is fully transformed into fine lamellar microsturcture with pearlite morphology. Then after heating to 830 ℃ and holding for 20 min and cooling with protective atmosphere at 20 ℃/s to room temperature, carbides with different shapes appear, and the martensite is finer than that in the original microstructure before the heat treatment. Besides, the hardness is higher and the depth of hardened layer is deeper than those before the heat treatment.

  Vacuum low pressure carburizing and high pressure gas quenching process of pinion shaft of precision reducer for industrial robot

  Yin Heping, Xu Yueming, Yin Minjie, Cong Peiwu

  2022, 47(5):  177-182.  doi:10.13251/j.issn.0254-6051.2022.05.029

  Abstract ( 75 )   PDF (598KB) ( 19 )  

  Aiming at the distortion problem of pinion shaft of industrial robot planetary reducers during high-temperature carburizing and quenching, the vacuum low pressure carburizing and high pressure gas quenching processes of the precision shaft were studied. The results show that in the heating-up stage, the multi-step heating up method is adopted, the boost stage is used to carry out strong carbon infiltration and diffusion with the alternately pulsed input of acetylene-nitrogen, and the quenching cooling stage with accurately controlled and stabilized the nitrogen pressure at 1.8 MPa (18 bar), the total distortion of the pinion shaft can be controlled within 0.005-0.015 mm. The actual production results show that, by using vacuum low pressure carburizing and high pressure gas quenching technology, the martensitic grade of the pinion shaft in the carburized layer is grade 1, and the retained austenite and carbide are grade 1 to 2, the core microstructure is 1 to 2 grades, and the average surface hardness, core hardness and effective hardened depth of the precision pinion shaft produced by the mass production are 59.7 HRC, 38.6 HRC and 0.681 mm, respectively, all of which meet the technical requirements.

  Effect of nitriding and diffusion time ratio on microstructure and properties of nitrided layer on AISI 316 stainless steel

  Shen Tong, Yang Li, Li Zhen, Feng Lingxiao

  2022, 47(5):  183-188.  doi:10.13251/j.issn.0254-6051.2022.05.030

  Abstract ( 93 )   PDF (602KB) ( 22 )  

  AISI 316 stainless steel was nitrided by two-stage vacuum nitriding process under different strong nitriding and diffusion time. The microstructure and properties of the nitrided layers were analyzed by means of X-ray diffraction (XRD), scanning electron microscope (SEM), optical microscope (OM), microhardness test and friction and wear test. The results show that after vacuum nitriding for 12 h, the nitrided layer consisting of γ′-Fe₄N, ε-Fe_2-3N and CrN phases is formed on the surface of AISI 316 stainless steel. The surface hardness and wear resistance of the nitrided AISI 316 stainless steel are significantly improved compared with those of substrate. Among them, when the nitriding and diffusion time ratio is 1∶1 (strong nitriding for 6 h and diffusion for 6 h), the thickness of the nitrided layer is about 96 μm, the surface hardness is about 1069 HV0.5, which is 4.5 times of the surface hardness of the substrate, and the wear loss under the load of 20 N is about 1/3 of that of the substrate. When the nitriding and diffusion time ratio is 1∶2 (strong nitriding for 4 h and diffusion for 8 h), the nitrided layer thickness is about 120 μm, the diffraction peak of ε-Fe_2-3N phase is enhanced, and the wear loss under the load of 20 N is about 1/30 of that of the substrate. The prolonging of diffusion time can increase the thickness of nitrided layer, improve the surface morphology, and further improve the wear resistance of the AISI 316 stainless steel.

  Simulation and optimization of low-pressure carburizing process for 20CrMoH steel

  Wang Shuobin, Cong Peiwu, Chen Xuyang, Fan Lei, Wang Tong

  2022, 47(5):  189-193.  doi:10.13251/j.issn.0254-6051.2022.05.031

  Abstract ( 70 )   PDF (597KB) ( 26 )  

  Carburizing process of 20CrMoH steel was simulated by low pressure carburizing software, and the test was carried out on WZSTQ vacuum carburizing furnace according to the simulated output. The temperature was kept at 960 ℃, and the pressure was maintained under the carburizing pressure of 800 Pa for 25 s. The process was optimized by comparing the depth of effective carburizing hardened layer. The results show that the optimum carburizing time is 120 min. After process optimization, the deviation between the depth of effective hardened layer measured by the test and predicted by the software is within +0.23 mm, which meets the design requirements. The effective hardened layer depth predicted by the software is closer to the measured depth of the gear product, with a minimum deviation of +0.10 mm. Through the carburizing test at 930 ℃ and comparing the surface carbon content, it is proved that when the surface carbon content is 0.75% predicted by the software, it is basically consistent with the actual measured value, and the maximum deviation is -0.02%.

  Effect of laser power on microstructure and properties of clad layer on 27SiMn steel

  Shi Shuting, Shu Linsen, He Yajuan, Wang Jiasheng

  2022, 47(5):  194-198.  doi:10.13251/j.issn.0254-6051.2022.05.032

  Abstract ( 56 )   PDF (598KB) ( 22 )  

  In order to explore the influence of laser power on microstructure and properties of the clad layer, four different laser powers were designed to perform Fe-Cr-Ni clad layer preparation on the surface of 27SiMn steel. The microstructure, hardness, wear loss, and friction coefficient of the clad layers were studied by means of super depth of field microscope, microhardness tester and friction and wear tester. The results show that the clad layer of the specimens under four different laser powers has no defect such as pore and crack, and the dendrite growth directions of the specimen prepared under the laser power of 1800 W are relatively consistent. The cellular crystal and the secondary dendrite in the middle part of the clad layer prepared under the laser power of 2400 W are smaller and denser. As the laser power increases, the melting width, melting depth and dilution rate of the clad layer gradually increase, while the melting height first increases and then decreases. The laser power has little effect on hardness of the clad layer, but the increase of laser power can raise the hardness of the heat affected zone. The specimen prepared under the laser power of 2400 W has the minimum average friction coefficient, the least wear loss, the minimum wear depth, and its wear resistance is excellent.

  Effect of heat treatment on microstructure and properties of Al_0.5CoCrFeNi high-entropy alloy brazed joints

  Qi Haowei, Liu Xuewen, Liu Le, Cao Zhiming, Jia Dehao, Zhang Qiang

  2022, 47(5):  199-203.  doi:10.13251/j.issn.0254-6051.2022.05.033

  Abstract ( 79 )   PDF (598KB) ( 40 )  

  Al_0.5CoCrFeNi high-entropy alloy was brazed and connected with TiZrCuNi solder and then annealed, the effect of annealing time at 800 ℃ on microstructure and mechanical properties of the Al_0.5CoCrFeNi high-entropy alloy brazed joint was studied. The microstructure and phase composition of the brazed joints were analyzed by means of scanning electron microscope (SEM) and energy dispersive spectroscope (EDS). The shear strength of the specimens before and after heat treatment was measured by universal testing machine. The results show that the typical microstructure of brazed joint can be divided into weld zone, fusion zone and heat affected zone. The microstructure of weld zone mainly consists of high-entropy alloy phases and FeCr based solid solution with BCC structure. With the increase of annealing time, fine black phase gradually precipitates from the gray phase in the brazing seam, which has a certain dispersion strengthening effect on the joint, and the microstructure is finer and uniform. The shear strength of brazed joint increases from 554.8 MPa before annealing to 581.1 MPa after annealing at 800 ℃ for 12 h.

  Effect of cold rolling deformation on microstructure and properties of CrCoNi alloy

  Chen Jinliang, Feng Zhongxue, Zhang Limin , Yi Jianhong

  2022, 47(5):  204-207.  doi:10.13251/j.issn.0254-6051.2022.05.034

  Abstract ( 63 )   PDF (591KB) ( 19 )  

  Phase composition, microstructure, mechanical properties and corrosion resistance of the as-cast and cold rolled CrCoNi alloys after magnetic suspension melting were studied at room temperature with deformation of 50%. The results show that, before and after cold rolling, there is no phase change of the as-cast CrCoNi alloy, still being the FCC single phase structure. The distribution of as-cast microstructure is uneven. After rolling deformation, the grains are broken and elongated. With the increase of deformation pass, the strength of the alloy increases, while the plastic decreases. Meanwhile compared with the as-cast alloy, after rolling, the corrosion resistance of the CrCoNi alloy is improved, and both are better than that of the 304 stainless steel.

  Effect of aging process on microstructure and mechanical properties of WE43 magnesium alloy

  Chen Lichao, Wang Changxi, Su Zhicheng, Wang Yuyu, Ren Jingtao, Li Jing, Deng Ting, Zhao Liping

  2022, 47(5):  208-212.  doi:10.13251/j.issn.0254-6051.2022.05.035

  Abstract ( 70 )   PDF (594KB) ( 22 )  

  Evolution of microstructure and mechanical properties of WE43 rare earth magnesium alloy under different heat treatment processes was studied in order to optimize the heat treatment process. The results show that the as-cast microstructure of the WE43 rare earth magnesium alloy is relatively uniform, with equiaxed grains of average grain size of 40 μm. During the process of solidification, the divorced eutectic forms along the grain boundaries. After solution treatment at 520 ℃ for 8 h, for the structure of the divorced eutectic, the number and morphology change significantly, the dendrite segregation is basically eliminated, and there are still a small amount of undissolved second phases on the grain boundary. After aging at 230 ℃ for 8 h, the amount of rare earth second phase increases, and dot-like dispersed rare earth phases are precipitated inside the grains. After aging at 250 ℃ for 16 h, the hardness of the alloy reaches its peak, the hardness of the alloy then decreases gradually as the ageing time extending. After solution treatment, the tensile strength of the WE43 rare earth magnesium alloy is about 162.59 MPa, and the elongation after fracture is about 5.0%, while after aging at 250 ℃, its tensile strength is significantly increased, and the elongation after fracture is about 4%.

  Heat treatment distortion and control of 125MN stretching machine track

  Zhang Pei, Lin Yichou, Shi Ruxing, Xi Zhiyong, Nie Xinlin, Yuan Yasha

  2022, 47(5):  213-216.  doi:10.13251/j.issn.0254-6051.2022.05.036

  Abstract ( 61 )   PDF (590KB) ( 27 )  

  In order to improve the warping distortion of the 125 MN stretching machine track after heat treatment in a large aircraft project, the distortion results were detected, combined with the data, theoretical and numerical simulation analysis were carried out, and the influence law of internal stress on heat treatment distortion was studied. According to the analysis results, by changing the enter way of the track into the quenching oil, the distortion of the track can be effectively reduced, and good results have been achieved in practical application, effectively improving the heat treatment distortion of the 125 MN stretching machine track.

  Effect of Q&P process on microstructure and properties of 5CrMnNiMo ultra-high strength steel

  Suo Zhongyuan, Du Yang, Fu Liming, Shan Aidang

  2022, 47(5):  217-220.  doi:10.13251/j.issn.0254-6051.2022.05.037

  Abstract ( 55 )   PDF (650KB) ( 29 )  

  Quenching and partitioning (Q&P) process was performed for 5CrMnNiMo ultra-high strength steel. The changes of microstructure and mechanical properties of the tested steel with isothermal partitioning for 5 min, 24 h and non-isothermal partitioning for 6 h under Q&P process were investigated by means of SEM, electronic universal testing machine, X-ray diffraction and EBSD. The results show that during Q&P treatment, the microstructure is composed of martensite, retained austenite and a small amount of granular carbide. The retained austenite gradually transforms from flake to block with the prolongation of isothermal partitioning time. After isothermal partitioning for 5 min, the ultra-high tensile strength of 2230 MPa is obtained. The tensile strength is decreased to 1360 MPa after isothermal partitioning for 24 h and the plastic deformation is increased from 3.92% (isothermal partitioning time of 5 min) to 14.62% (non-isothermal partitioning time of 6 h). The TRIP effect is the main reason for the increase of plastic deformation.

  Effect of heat treatment on magnetic properties of 35CrMo steel

  Shen Zhengxiang, Wu Caibao, Li Jinglin, Zhai Binbin, Cai Penghui, Huang Huandong, Chen Hu, Tan Jidong

  2022, 47(5):  221-225.  doi:10.13251/j.issn.0254-6051.2022.05.038

  Abstract ( 101 )   PDF (591KB) ( 26 )  

  Based on magnetic coercive force and magnetic Barkhausen noise (MBN) nondestructive testing methods, the magnetic properties of 35CrMo steel under different heat treatment states were studied, and the surface hardness test was used as a comparative verification. The results show that compared with the original state, the grain of 35CrMo steel after quenching is refined, the coercive force increases from 10.42 A/cm to 19.85 A/cm with an increment about 90.40%, and the MBN-stress concentration is obvious. After tempering, the microstructure becomes uniform, the MBN-stress level is reduced as a whole, and the coercive force decreases to 12.50 A/cm, but the final increment is 19.96%, which is consistent with the surface hardness. The measurement of magnetic property can effectively characterize the microstructure and mechanical properties of the steel under different heat treatment conditions, and provide technical reference for online product quality test.

  Effect of quenching process on microstructure and properties of martensitic stainless steel 6Cr13

  Li Zhaoguo, Pan Jixiang, Ji Xianbin, Wei Haixia, Wang Ke

  2022, 47(5):  226-229.  doi:10.13251/j.issn.0254-6051.2022.05.039

  Abstract ( 162 )   PDF (590KB) ( 21 )  

  Effect of quenching at 950-1150 ℃ with different cooling methods on microstructure and mechanical properties of martensitic stainless steel 6Cr13 was studied. The results show that with the increase of quenching temperature, the content of residual carbides decreases gradually, then at above 1050 ℃, the carbide dissolution rate increases and the grains begin to grow rapidly, and the content of residual austenite increases gradually, by which the hardness reaches the maximum at 1050 ℃ and then begins to decrease, and such decrease becomes the most obvious at 1150 ℃. The water-cooled hardness of the steel is higher than that air cooled at 950 ℃, but when air-cooled at above 950 ℃, the hardness is higher than that of water-cooled. Air cooling at 1050 ℃ can obtain a higher quenching hardness, a lower retained austenite content, and a carbide content of 8%, with better wear resistance and higher sharpness.

  Effect of final cooling temperature on microstructure and properties of Q345R steel

  Zhang Deyong, Feng Yangfeng, Li Weijuan, Li Wei, Xu Jiyong, Qi Minxiang

  2022, 47(5):  230-233.  doi:10.13251/j.issn.0254-6051.2022.05.040

  Abstract ( 155 )   PDF (591KB) ( 29 )  

  Final cooling test was carried out on the pressure vessel steel Q345R, and the effect of final cooling temperature on mechanical properties and microstructure of the as-rolled and normalized steel plate was studied. The results show that the mechanical properties of the as-rolled and normalized Q345R steel at different final cooling temperatures meet the standard requirements, but when directy air cooled after rolling, the performance margin is small. When the final cooling temperature is 650 ℃, the mechanical properties are relatively better. With the increase of final cooling temperature, the yield strength, tensile strength, and impact property of the steel plate have a downward trend, and the microstructure gradually becomes coarser. The microstructure of the as-rolled and normalized specimens are all typical ferrite+pearlite, and after normalization of the steel plate, the yield strength and tensile strength are significantly lower than that of the hot-rolled steel plate, while the impact property is significantly improved, and the microstructure becomes finer.

  NUMERICAL SIMULATION

  Numerical simulation on die quenching process of 9310 steel spiral bevel gear

  Tang Menglan, Wu Yixuan, Tong Daming, Gu Jianfeng

  2022, 47(5):  234-240.  doi:10.13251/j.issn.0254-6051.2022.05.041

  Abstract ( 52 )   PDF (592KB) ( 34 )  

  Thermal-phase transformation-strain/stress multi-physical coupled model was established for die quenching process of 9310 steel spiral bevel gear by finite element software, and the numerical simulation of die quenching process was carried out. The results show that the design of mold has significant effect on die quenching distortion. The distortion of gear is obviously reduced by optimization of assembly dimensions and pressure angle of the mold. The eccentricity of upper and lower mold causes the distortion of gear, while it can be avoided by adjustment of core mold dimensions.

  Finite element simulation of heat treatment distortion of precision parts with internal thread

  Hu Wanting, Yu Limin, Zhu Hongwei, Gao Qi, Ye Mao

  2022, 47(5):  241-245.  doi:10.13251/j.issn.0254-6051.2022.05.042

  Abstract ( 48 )   PDF (591KB) ( 29 )  

  Even though precision parts with internal threads produce slight distortion after heat treatment of quenching and low temperature tempering, it is not accepted for precision engineering, such as rocket engines and so on. Due to that in the subsequent process, these slight distortion might lead to serious consequences of assembly failure. The finite element software and its subroutines were used to calculate the temperature field, stress-strain field, residual stress distribution and distortion of parts during heat treatment process, considering the effect of stress on phase transformation and phase transformation plasticity. The distortion is basically consistent with that shown by the assembly results in the manufacturing process. Aiming at the problem of assembly difficulty, some suggestions to improve production process and finally to control the distortion are proposed combining with the finite element simulation results.

  SURFACE ENGINEERING

  Effect of defocusing amount on microstructure and properties of MoS₂ modified Fe-Cr-Mo-Si alloy coating

  Dong Yue, Shu Linsen

  2022, 47(5):  246-251.  doi:10.13251/j.issn.0254-6051.2022.05.043

  Abstract ( 45 )   PDF (593KB) ( 22 )  

  MoS₂ modified Fe-Cr-Mo-Si alloy coating was prepared on 40Cr steel substrate by laser cladding technology. The effect of defocusing amount on macro morphology, microstructure, microhardness and friction and wear resistance of the composite coating was studied. The results show that with the increase of defocusing amount, the smoother the composite coating surface, the better metallurgical bonding between the composite coating and the substrate. The upper part of the composite coating is fine equiaxed crystal, the middle is dendrite, and the bottom is columnar and plane crystal grown perpendicular to the fusion line. The grain size of equiaxed crystal decreases with the increase of defocusing amount. With the increase of defocusing amount, the hardness value of composite coating increases accordingly, and the highest microhardness value appears in the upper part of the composite coating when the defocusing amount is 2 mm, up to 696.1 HV0.5, about 3 times of that of the substrate (230.6 HV0.5). Under the same wear condition, the average friction coefficient and wear loss of composite coating decrease with the increase of defocusing amount. When the defocusing amount is 2 mm, the minimum wear loss is 0.010 g, which is only 21.7% of that of the Fe based coating. The wear mechanism of composite coating is abrasive wear and adhesion wear. With the increase of defocusing amount, the smaller the wear degree of the composite coating surface, the better the wear resistance.

  Analysis of cracks in laser clad Fe-based amorphous alloy coating

  Ouyang Changyao, Bai Qiaofeng, Han Binhui, Yan Xianguo

  2022, 47(5):  252-256.  doi:10.13251/j.issn.0254-6051.2022.05.044

  Abstract ( 62 )   PDF (596KB) ( 22 )  

  Cracks occurred when Fe-based amorphous alloy coating was cladding on the surface of 304 stainless steel substrate by using laser cladding technology. The crack forming mechanism was studied by means of qualitative analysis of the elements, hardness and precipitates around the cracks. The results show that the coating mainly contains α-Fe, α-Cr, carbides (M₇C₃, M₅C₂), silicides (CrSi₂, FeSi) and other phases. The cracks are mainly caused by the large thermal stress in the heat-affected zone and the high melting point and high hardness carbon silicide formed by the segregation of C and Si elements. The structure near the crack zone is relatively loose and there are more gaps and pores. At the same time, the combination of the hard phase is not strong, so that the hardness near the crack zone is lower than that of other defect-free areas at the same level.

  TEST AND ANALYSIS

  Analysis of grinding cracks on 4Cr13 steel spindle sleeve for gyratory crusher after laser quenching

  Shi Ruxing, Lin Yichou, Zhang Pei, Qi Guosai, Yu Wenping, Su Wenbo

  2022, 47(5):  257-261.  doi:10.13251/j.issn.0254-6051.2022.05.045

  Abstract ( 81 )   PDF (591KB) ( 31 )  

  Several cracks were found in the grinding stage of the 4Cr13 steel spindle sleeve for gyratory crusher after laser quenching, and having angles about 15° with the outer circle axis. Through macroscopic analysis, chemical composition analysis, hardness, effective hardened layer depth detection and microstructure observation, it is confirmed that the cracks of the 4Cr13 steel spindle sleeve are grinding crack. The cracks are mainly caused by the movement of tangential and axial directions in the grinding process of the grinding wheel. The tangential rotation speed is far greater than the axial moving speed. The resultant force of grinding tensile stress in the two directions results in an angle of about 15° between the crack and the axial direction. At the same time, the radial columnar crystal produced by laser melting reduces the bonding force between crystals. In addition, the residual temperature self-tempering method after laser quenching makes the stress distribution of hardened layer more complex, which makes it easy to crack in the grinding process.

  Analysis of unqualified impact property of 30CrNiMo steel castings

  Yin Yahao, Guo Lei, Su Jianfeng, Yue Xiaocan

  2022, 47(5):  262-265.  doi:10.13251/j.issn.0254-6051.2022.05.046

  Abstract ( 122 )   PDF (593KB) ( 34 )  

  In view of the unacceptable impact absorbed energy of 30CrNiMo steel casting after quenching and tempering, the main influence factors of which were analyzed through fracture analysis, metallography, hardness testing and chemical composition analysis. The results show that there are intergranular fracture of impact specimen of the 30CrNiMo steel castings, and the quenched specimen appears mischcrystal structure. Furthermore, a large number of NbC phases segregate at the grain boundary, which impedes the movement of grain boundary effectively. At the same time, abundant NbC phases also consolidate the inheritance phenomenon of grain by the pinning effect, which enhances ductile-brittle transition temperature significantly after the austenite grain coarsening. Ultimately, brittle transgranular fracture and low impact property are obtained when the specimen is impacted at room temperature.

  Macro-segregation analysis and rescue measure of TC11 alloy large round precision forged bar

  Zhao Minquan, Wang Yuan, Dong Jian, Yu Zhongliang, Xie Li, Guan Yulong

  2022, 47(5):  266-269.  doi:10.13251/j.issn.0254-6051.2022.05.047

  Abstract ( 57 )   PDF (595KB) ( 21 )  

  Speckles in the TC11 alloy large round precision forged bar were analyzed and studied by means of optical microscope, scanning electron microscope and EDS analysis. It is determined that the formation of low magnification speckles is mainly caused by the unreasonable setting of precision forging process, which belongs to a forging defect. The defect can be eliminated by high temperature diffusion at β phase zone and rolling into small round bars at α+β phase zone, which will avoid scrapping the material with such a defect.

  Cause analysis of slag inclusion-like defects on stainless steel metallographic specimen

  Tian Wei, Chang Song, Sun Xinyang, Zhou Changshen

  2022, 47(5):  270-274.  doi:10.13251/j.issn.0254-6051.2022.05.048

  Abstract ( 77 )   PDF (590KB) ( 25 )  

  Many irregular slag inclusion-like defects were found on the inspection surface of different stainless steels after grinding, coarse grinding, fine grinding and fine polishing for rating of the non-metallic inclusions. The morphology of defects was observed by means of optical microscope and scanning electron microscope, and the chemical composition of the defects was analyzed qualitatively and quantitatively by means of energy dispersive spectrometer. Meanwhile, the six elements of on-site quality management, namely human, machine, material, environment, method and measurement were used to conduct comparison and examination one by one in the whole process from steelmaking to specimen preparation, and to conduct the sandpaper comparison test with different materials. The results show that the slag inclusion-like defects mainly contain oxygen, aluminum and zirconium, and are caused by using zircon corundum sandpaper during grinding.