Heat Treatment of Metals

Numerical simulation of vacuum isothermal quenching process of H11 steel large module for die-casting dies

Tu Yujie, Li Bingchen, Chen Hao, Wu Xiaochun

2024, 49(7): 1-8. doi:10.13251/j.issn.0254-6051.2024.07.001

Abstract ( 87 )

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Based on the metal-thermo-mechanical coupled theory, multi-field coupled numerical models of the H11 steel large module (500 mm×500 mm×500 mm) during vacuum isothermal quenching was established, and the numerical simulation of different vacuum isothermal quenching processes was carried out to study the evolution of the temperature field, structure field and stress field. The results show that compared with direct quenching, isothermal quenching can effectively reduce the temperature difference and the stress between the core and surface during the cooling process of the module to avoid the risk of distortion and cracking. Vacuum isothermal quenching can increase the volume fraction of bainite in the core of the module while avoiding pearlite formation and carbides precipitating along the grain boundary, and with the increase of the isothermal time, the more core bainite will be generated. The experimental verification of vacuum isothermal quenching at 500 ℃ for 1 h carried out by using industrial equipment indicates that the temperature curves at different positions of the module are in good agreement with the simulation results, and the type of bainite formed in the core of the module after vacuum isothermal quenching is lower bainite with good toughness.

Numerical simulation of temperature uniformity of large thin-walled shell parts during high pressure gas quenching

Wang Jing, Zhang Xiaojuan, Tong Daming, Gu Jianfeng, Zhou Zhongping, Bai Lu, Zhu Lijian

2024, 49(7): 9-15. doi:10.13251/j.issn.0254-6051.2024.07.002

Abstract ( 52 )

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Fluid-solid coupling simulations were carried out for the large thin-walled shells during high pressure gas quenching. The numerical model was included the vacuum high-pressure gas quenching furnace and the large thin-walled shells which were aerospace components. The temperature uniformity of the shell during high pressure gas quenching in the vacuum furnace was evaluated, and the shell temperature distribution was simulated corresponding to the different gas outlet positions, different furnace charging and flow diversion conditions. The results show that compared with the original model, the quenching methods of one-outlet scheme, one-shell charging in the center of furnace and adding baffles can improve the temperature uniformity of the shell by 8%, 30% and 12.5% respectively, and the results provide an optimized quenching scheme for controlling the deformation of the shell.

Numerical simulation of spiral bevel gear quenching based on thermo-fluid-solid coupling model

Liu Ganhua, Deng Shiyi, Huo Xiaodong

2024, 49(7): 16-21. doi:10.13251/j.issn.0254-6051.2024.07.003

Abstract ( 40 )

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Based on thermo-fluid-solid coupling simulation, quenching and cooling process of 45 steel spiral bevel gears was numerical simulated, and the influence of quenching medium flow rate on quenching results was studied. It is found that the maximum relative errors between the cooling curves of thermo-fluid-solid coupling simulation and traditional simulation and experimental measurement are 9.2% and 7.4%, respectively. Moreover, more accurate prediction of temperature distribution under quenching medium flow conditions is achieved, verifying the accuracy and convenience of this method. When the inlet flow rate is 2 m/s, the maximum hardness value is 52.0 HRC, and the residual stress is mainly favorable compressive stress.

Analysis and distortion control optimization of carburization and quenching for spacecraft gears

Yang Kai, Wang Pengpo, Zhang Yumei, Zeng Hong, Zhang Bin, Wang Tianming, Ma Yuliang, Wang Yanzhong

2024, 49(7): 22-28. doi:10.13251/j.issn.0254-6051.2024.07.004

Abstract ( 44 )

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According to the chemical composition of the steel for a spacecraft power gear, the thermal-physical property parameters of the material were calculated by means of JMatPro simulation software. Based on the gear model and heat treatment process parameters, carburizing and quenching simulation analysis was carried out in Deform finite element software to determine the change of carbon content on the tooth surface during carburizing process, and the change of microstructure of the gear teeth during quenching process. Finally, according to the characteristics of herringbone gears and the precision control requirements of spacecraft gears, the distortion of the gear teeth after quenching is optimized by changing the quenching process parameters. The results show that when the quenching process is pre-cooling in air for 30 s, quenching in hot oil at 80 ℃ for 1200 s and then deep cooling at -100 ℃ for 7200 s, the amount of distortion is controlled better and meets the product requirements.

Simulation of thermal compression and texture evolution of TB6 titanium alloy

Mo Hongsheng, Cui Xia, Zhu Enrui, Ouyang Delai, Yang Chao

2024, 49(7): 29-37. doi:10.13251/j.issn.0254-6051.2024.07.005

Abstract ( 46 )

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Thermal deformation behavior of TB6 titanium alloy under different deformation conditions (deformation temperature of 1173-1323 K, strain rate of 0.001-1 s^-1) was studied by means of Thermecmaster-Z thermal simulator. Hot compression process was stimulated by finite element simulation software, and stress and strain distribution under different deformation conditions was analyzed. The results show that stress-strain curves obtained by numerical simulation is consistent with the experimental values. Finite element software is conducted secondary development and the ODF diagram of the compressed alloy is simulated, which has a high degree of agreement with the measured ODF diagram. The distribution of equivalent stress and equivalent strain is uneven, and the maximum stress and maximum strain occur at the center of the specimen. The stress and strain increase with the decrease of deformation temperature or the increase of strain rate. After hot compression, the main texture of the alloy is R-Cube_ND {001}<110>texture and Cube {001}<100>texture, and it has a certain degree of heritability. Increasing the deformation temperature or strain rate can strengthen the main texture.

Optimization of heat treatment process of bainitic rails based on simulation software

Chen Yanzi, Liu Xinyu, Su Hang, Xie Benchang, Cen Yaodong, Chen Lin

2024, 49(7): 38-41. doi:10.13251/j.issn.0254-6051.2024.07.006

Abstract ( 39 )

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DEFORM finite element software was used to simulate the quenching process of bainitic rails, and the microstructure and hardness of the rails were compared with that of the actual quenched rails to study the accuracy of the finite element simulation. The test results show that after simulated quenching, the hardened layer thickness at the rail head is 12 mm, and the hardness is 40.42-42.23 HRC, which are similar to the actual measured hardened layer thickness of 11 mm, and the hardness of 40.20-43.40 HRC, respectively. Using the color metallographic method and Image-Pro software, the bainite content at the rail head is about 63.80%, and the martensite+retained austenite content is about 36.20%. Compared with the simulation results (bainite content of 57.7%, martensite+retained austenite content of 42.3%), the errors are all around 6%. The accuracy of finite element simulation results is confirmed, which can be used to guide the actual production.

Simulation and calculation of heat treatment parameters and thermophysical properties of 16CrSiNi steel using JMatPro software

Ma Luyi, Du Qingyin, Li Shijian, Yang Lixin, Liu Gang, Wang Xinyu

2024, 49(7): 42-46. doi:10.13251/j.issn.0254-6051.2024.07.007

Abstract ( 47 )

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Thermodynamic equilibrium phase composition, Jominy hardenability, phase transition, thermophysical properties and mechanical properties after quenching and tempering of the 16CrSiNi steel were simulated by using JMatPro software, and the thermodynamic equilibrium phase compositions, hardenability curves, TTA curves, TTT curves, CCT curves, quenching microstructure, mechanical properties after quenching and tempering, thermophysical properties under different temperatures as density, thermal conductivity, Young's modules, specific heat, Poisson's ratio and enthalpy were obtained.

Effect of deformation heat treatment on microstructure and properties of Ti₄₅Zr₂₀Nb₁₅V_(10-x)Al₁₀Mo_x refractory high entropy alloy

Li Zhenglong, Pang Jingyu, Tang Guangquan, Cheng Lufan, Zhang Caiwei, Hou Xingyu, Li Wen, Zhang Haifeng

2024, 49(7): 47-53. doi:10.13251/j.issn.0254-6051.2024.07.008

Abstract ( 33 )

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Ti₄₅Zr₂₀Nb₁₅V_(10-x)Al₁₀Mo_x (x=0, 0.5, 1.0) refractory high entropy alloy was prepared by adding trace amounts of Mo element to the Ti₄₅Zr₂₀Nb₁₅V₁₀Al₁₀ refractory high entropy alloy matrix, which strain hardening ability and plasticity were improved by deformation heat treatment. Microstructure and mechanical properties of the as-cast specimen and cold-rolled (deformation of 80%) and annealed (600 ℃×5 h and 800 ℃ for 1 h) specimen were investigated using X-ray diffractometer, field emission scanning electron microscope, and universal mechanical testing machine. The test results show that the as-cast alloy has a single-phase BCC structure, and the addition of Mo element increases the yield strength and maintains a fracture elongation of about 10%. After cold rolling and annealing, the microstructure of the alloy becomes BCC+Al₃Zr₄ dual phase with a large amount of approximately spherical nanoscale Al₃Zr₄ particles precipitated at and near grain boundaries, causing the alloy to transition from strain softening to strain hardening, and the yield strength of the alloy is maintained at 1100 MPa, while the fracture elongation is significantly improved. When the Mo content is 0.5%, the fracture elongation of the alloy after cold rolling annealing increases from 9.9% in as-cast state to 16.9%, exhibiting excellent strength plasticity matching and a density of only 5.638 g/cm³.

Microstructure and mechanical properties of ultrafine grained heterostructured dual-phase steel prepared by warm rolling and intercritical annealing

Yan Wenchao, Gao Bo, Xiao Lirong, Zhou Hao

2024, 49(7): 54-62. doi:10.13251/j.issn.0254-6051.2024.07.009

Abstract ( 29 )

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Comprehensive mechanical properties of the low-carbon steel were greatly improved by producing the ultra-fine grained heterostructured dual-phase (UFG-HSDP) structure. First, the initial structure of the low carbon dual-phase structure is refined by warm rolling at 300 ℃, and then the ultra-fine grained heterostructured dual-phase steel with high martensite content (volume fraction of77%) is obtained by intercritical annealing at 740 ℃. The average grain size of ferrite and martensite is 0.78 and 0.39 μm, respectively. The UFG-HSDP steel shows excellent comprehensive mechanical properties, with yield and tensile strengths of 1.26 and 1.75 GPa, respectively, while maintaining a uniform elongation of 6.2%. The mechanical incompatibility between ferrite and martensite in the UFG-HSDP steel during tensile deformation results in significant hetero-deformation induced hardening, which enhances the total strain hardening rate and thus improves the strength-ductility match of low-carbon steel.

Recrystallized grain growth behavior and its effect on aging behavior of cold-rolled Ti-3.5Al-5Mo-4V alloy sheet

Ji Xuanming

2024, 49(7): 63-69. doi:10.13251/j.issn.0254-6051.2024.07.010

Abstract ( 23 )

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Recrystallized grain growth behavior of the cold-rolled Ti-3.5Al-5Mo-4V alloy after annealing at 800-1020 ℃ for 15 min was studied by means of X-ray diffractometer, optical microscope and scanning electron microscope. The effects of grain size on mechanical properties and aging precipitation were also investigated. The results show that with the increase of annealing temperature, the grains grow rapidly, and the tensile strength and elongation of the alloy at room temperature decrease. The activation energy of grain growth is 84.949 kJ/mol, and the relationship between grain size and temperature is D=400 312exp(-84 949/RT). After annealing at 800 ℃ and aging at 500 ℃ for 8 h, the microstructure of the cold-rolled sheet is fine equiaxed β grains uniformly distributed with needle-like secondary α phase. The tensile strength of the alloy reaches 1530.0 MPa, while the elongation remains 5.5%.

Effect of Al content and homogenization on microstructure and damping properties of Mg-Al binary alloys

Liu Huashen, Sun Youping, He Jiangmei, Luo Guojian, Pei Mengyu

2024, 49(7): 70-77. doi:10.13251/j.issn.0254-6051.2024.07.011

Abstract ( 26 )

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Effects of Al content (0.25%, 0.5% and 1.0%, mass fraction) and homogenization (420 ℃ for 24 h) on microstructure, mechanical properties and damping properties of as-cast Mg-Al alloys were investigated by using optical microscope, X-ray diffractometer, scanning electron microscope and tensile testing machine. The results show that the addition of Al element reduces the average grain size of the alloy, and the more the addition, the smaller the average grain size, while the average grain size significantly increases after homogenization. The mechanical properties of as-cast Mg-Al alloy gradually increase with the increase of Al content, and the tensile strength, yield strength and elongation of the Mg-1.0%Al alloy are 148.320 MPa, 135.862 MPa, and 8.467%, respectively. After the homogenization, the mechanical properties of Mg-Al alloy decrease due to the increase of average grain size, while the elongation of Mg-0.5%Al and Mg-1.0%Al alloys is increased compared to the as-cast state. The damping properties of the Mg-Al alloys decrease with the increase of Al content, and the critical strain amplitude gradually increases, the damping value Q^-1 for the as-cast Mg-1.0%Al alloy at ε_0.1 is 0.1160, which belongs to the category of highly damped magnesium alloys (Q^-1≥0.01), meanwhile, the damping values of the Mg-Al alloys after homogenization is all higher than that of as-cast state. The damping properties decreases with the increase of Al content for a specific frequency, and decreases with the increase of frequency when the Al content is constant, and the effect of homogenization on the damping properties at high temperatures is not apparent.

Effect of long-term aging on microstructure and properties of 21-4NWNb steel

Zhao Shouzhong, Wang Shouqian, Zhu Zhiyuan, Min Liang, Xu Chaofan, Shen Jiabao

2024, 49(7): 78-83. doi:10.13251/j.issn.0254-6051.2024.07.012

Abstract ( 30 )

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Microstructure evolution and mechanical properties change of the 21-4NWNb steel after standard heat treatment (1050 ℃×30 min+750 ℃×4 h) during long-term aging at 750 ℃ were studied. The results show that the grain size of 21-4NWNb steel does not change obvious during long-term aging. When aged for 200 h, a small amount of regular block M₂₃C₆ carbides are distributed in the steel. When the aging time extends to 500 h, σ phase (AB) gradually appears in the grain. The hardness of the 21-4NWNb steel reaches the highest value of 324 HV when aged for 200 h with a maximum tensile strength of 971 MPa and a elongation of 22.2%. With the prolong of aging time from 200 h, the hardness and tensile strength show a gradual decline, and the elongation of the steel drops below 15% after aging for 2000 h.

Effect of hot-dip galvanizing on mechanical properties of Nb-Ti microalloyed S550GD+Z steel

Liu Anqi, Qi Haiquan, Guo Chuncheng, Wang Weimin, Xue Qihe, Li Wentong, Wan Yu, Da Zhongzhong

2024, 49(7): 84-90. doi:10.13251/j.issn.0254-6051.2024.07.013

Abstract ( 19 )

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Microstructure, precipitated phase and reinforcement mechanism of the Nb-Ti microalloyed S550GD+Z hot-rolled steel plate and hot-dip galvanized plate were analyzed by using TEM, EBSD, physical and micro-chemical phase analysis, and the mechanism of strength improvement of the plate by galvanizing was studied. The tensile test results show that the yield strength of the galvanized plate is increased by about 34.6 MPa compared with the hot rolled plate, of which the strength increment of the zinc layer contributes about 15 MPa, while the calculation shows that the comprehensive increment of strength caused by solution treatment strengthening, grain refinement strengthening, dislocation strengthening and the zinc layer strength increment is increased by about 47.8 MPa. Thus, the strength increment of zinc layer is the main reason for the strength improvement of the Nb-Ti microalloyed S550GD+Z steel plate after galvanizing.

Microstructure, properties and dynamic recrystallization behavior of 20Mn23AlV non-magnetic structural steel hot rolled plate

Luo Xiaoyang, Cheng Ganghu, Jin Ke, Zhou Weilian, Hou Yuanyuan, Tang Xingchang

2024, 49(7): 91-99. doi:10.13251/j.issn.0254-6051.2024.07.014

Abstract ( 21 )

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Experimental study on the density, microstructure, and mechanical properties of 20Mn23AlV non-magnetic structural steel hot-rolled plate was conducted. Additionally, multi-pass thermal simulation tests were performed to investigate the changes in microstructure and magnetic properties before and after the tests. The results show that, due to the addition of the Al element, the density of the tested steel is reduced by approximately 0.192 g/cm³ compared to that of common steels. The average tensile strength of the hot-rolled plate of non-magnetic steel is 721 MPa, the yield strength is 371 MPa, and the elongation after fracture is 69.5%, indicating good strength-ductility matching. It is found that through multi-pass thermal simulation experiments with 60% hot compression deformation, the tested steel undergoes dynamic recrystallization behavior at 950 ℃, with the average austenite grain size decreasing from 10.24 μm to 6.08 μm. There is no phase transformation before and after the multi-pass thermal simulation tests, and the relative permeability measured is 1.001 and 1.002, respectively, which meets the requirements for the magnetic properties of non-magnetic steel.

Effect of rare earth addition on microstructure and properties of Al-Mg-Si alloy

Chen Baoan, Li Menglin, Chen Rui, Duo Junlong, Han Yu, Zhu Zhixiang, Yang Changlong, Miao Yaojun

2024, 49(7): 100-105. doi:10.13251/j.issn.0254-6051.2024.07.015

Abstract ( 29 )

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Single wires of Al-Mg-Si alloys with rare earth addition (Ce or Sc) and without rare earth(RE) addition were prepared by hot rolling and cold drawing, and aged at 175 ℃ for different time. Microstructure of the alloy wires was observed by SEM and TEM, while the tensile strength and elongation were obtained by tensile test with electrical universal testing machine, and the resistance was also tested on digital micro-ohmmeter. The results show that the morphologies and size characteristics of micro-scale AlFeSi particles are improved owing to the RE addition. During the aging process, Ce has no obvious effect on the characteristics of nanoscale precipitates, while Sc can inhibit the precipitation and growth process of nanoscale precipitates. Therefore, the β″ phase in Sc-containing alloys possesses minimum size and well-dispersed distribution. After aging at 175 ℃ for 4 h, considerably well-performed comprehensive properties are obtained for all the 3 alloys, among which the Ce-added alloy has the highest electric conductivity (about 56.2%IACS), while the Sc-added alloy exhibits the highest tensile strength (about 350 MPa).

Hydrogen embrittlement of V+Ti microalloyed Mn-Cr bainitic forging steel

Zhou Lei, Wang Ying, Zhang Yongjian, Zhao Xiaoli, Hui Weijun

2024, 49(7): 106-112. doi:10.13251/j.issn.0254-6051.2024.07.016

Abstract ( 25 )

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Hydrogen desorption and hydrogen embrittlement (HE) behavior of a V+Ti microalloyed Mn-Cr bainitic forging steel in the as-forged and 500 ℃ tempered conditions were studied by using electrochemical pre-hydrogen-charging, hydrogen thermal analysis (TDA) and slow strain rate tensile (SSRT) testing combined with SEM, TEM and EBSD microstructural analyses. The results show that the blocky martensite/austenite (M/A) constituents decompose with the precipitation of nano-sized (V,Ti)(C,N) and cementite particles, which causes a decrease of tensile strength while a significant increase of yield strength. The result of TDA reveals that most of absorbed hydrogen is diffusible hydrogen and the hydrogen content in the tempered specimen is slightly lower than that of the as-forged specimen. The HEI expressed by the relative loss of notch tensile strength before and after hydrogen-charging significantly decreases from 31.8% for the as-forged specimen to 12.8% for the tempered specimen, which is mainly due to the microstructural changes caused by the tempering treatment.

Effect of Al and N contents on austenite grain size of gear steel

Guo Tao, Sui Yue, He Xiaofei, Xue Yanjun, Huang Feng

2024, 49(7): 113-120. doi:10.13251/j.issn.0254-6051.2024.07.017

Abstract ( 42 )

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Austenite grain growth behavior of two gear steels with different contents of Al and N austenitized at 980, 1050 and 1100 ℃ was experimentally studied. Equilibrium dissolution of AlN precipitates and its effect on austenite grain size were studied by means of optical microscope(OM), scanning electron microscope(SEM), transmission electron microscope(TEM) and carbon film replicas. The results show that with the increase of Al and N content, the critical temperature for abnormal growth of austenite grains in the gear steel also increases. When Al content is 0.038% and N content is 0.019%, the austenitizing temperature of the tested steel can be increased to 1050 ℃, at which after holding for 6 h, the austenite grains are still small and uniform, with grain size levels ranging from 7.5 to 8. Through the analysis of AlN precipitates, it is found that with the increase of austenitizing temperature, the AlN precipitates transforms from polygonal and nearly spherical to elongated rod-shaped, and its size continuously increases. When its equivalent radius is greater than 30 nm, the AlN precipitates cannot pin the austenite grain boundaries, resulting in mixed grains. Due to the coarsening and dissolution of the AlN precipitates, the growth rate of the ultimate grain size of austenite becomes faster and faster, and the ultimate pinning force for abnormal growth of austenite grains is between 0.045 and 0.095 J/cm³.

Continuous cooling transformation law of V-Nb microalloyed Q420B large size angle steel

Huang Jiantao, Zhang Minghe, Feng Yunli, Yin Shaojiang, Chen Chunsheng, Wang Houxin

2024, 49(7): 121-127. doi:10.13251/j.issn.0254-6051.2024.07.018

Abstract ( 20 )

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Continuous cooling transformation behavior of V-Nb microalloyed Q420B large angle steel was tested under undeformed (static) and deformed (dynamic) conditions by using thermal dilatometer and Gleeble-3500 thermal simulation machine. Microstructure of the tested steel after continuous cooling was observed by using optical microscope, and the static and dynamic CCT curves of the tested steel were plotted. The results show that the dynamic CCT curve of the tested steel moves to the upper left compared to the static CCT curve, indicating that the deformation accelerates the phase transformation of the tested steel and increases the starting and ending temperatures of the phase transformation. In addition, the deformation expands the pearlite transformation zone of the tested steel and reduces the bainite transformation zone. During the process of static and dynamic continuous cooling transformation, as the cooling rate increases, the microstructure of the tested steel gradually transforms from ferrite and pearlite to bainite and martensite formed under faster cooling rate conditions, and the hardness value of the tested steel gradually increases. Microstructure obtained after deformation of the tested steel in the austenitic unrecrystallized zone is uniformly finer than that obtained without deformation. An increase in the cooling rate results in a lower phase transformation temperature Ar₃ and finer ferrite grains, while at the same time the bainite microstructure is finer.

High temperature-steam oxidation behavior of Zr-Sn-Nb alloy

Chen Yao, Yu Hongxing, Yang Zhongbo, Zhang Lin, Zhang Kun, Yue Huifang, Wu Zhouzhi

2024, 49(7): 128-131. doi:10.13251/j.issn.0254-6051.2024.07.019

Abstract ( 26 )

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High temperature steam oxidation tests between 600-1200 ℃ for Zr-Sn-Nb and Zr-4 alloy cladding tubes were conducted to study the effect of oxidation temperature and time on the oxidation kinetics, microstructure and oxidized film thickness. The results show that the oxidation laws of the Zr-Sn-Nb and Zr-4 alloy in high temperature steam are the same, and the oxidation rate is mainly related to temperature. The oxidation mass gain of the Zr-4 alloy is obviously higher than that of the Zr-Sn-Nb alloy after oxidation between 950-1200 ℃ for 5000 s. When the oxidation temperature is low, the matrix of the alloys is single α phase. With the increase of oxidation temperature, brittle α-Zr(O) phase is formed in the matrix. When steam oxidation at 1050 ℃ for 2500 s, the brittle α-Zr(O) phase formed in the Zr-Sn-Nb alloy is significantly less than that in the Zr-4 alloy. When the oxidation temperature is high, the oxide film of the Zr-Sn-Nb alloy is still compact and intact, while the oxide film of the Zr-4 alloy begins to appear loose and porous. At 950-1200 ℃, Zr-Sn-Nb alloy shows better high temperature oxidation resistance.

Research progress of low alloy martensitic wear-resistant steel

Li Zhongbo, Wu Zhifang, Wu Run

2024, 49(7): 132-138. doi:10.13251/j.issn.0254-6051.2024.07.020

Abstract ( 28 )

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Research progress of low alloy martensitic wear-resistant steel was reviewed, mainly involving composition design, heat treatment process and its on microstructure and mechanical properties, and wear resistance. Composition design mainly adopts a small number of multi-component system, heat treatment processes include reheat quenching-tempering treatment, direct quenching-tempering treatment, subtemperature quenching-tempering treatment, quenching-partitioning treatment and quenching-partitioning-tempering treatment. By controlling the structure shape and distribution, the hardness and toughness can be matched reasonably. The wear resistance is improved by adjusting chemical composition, refining grain, optimizing rolling cooling process and proper tempering.

Element segregation and homogenization heat treatment of DIEVAR hot working die steel

Du Simin, Cheng Wenxiong, Hu Fengrong, Ren Jinqiao, Cui Xiaokang, Zhou Zhiming

2024, 49(7): 139-145. doi:10.13251/j.issn.0254-6051.2024.07.021

Abstract ( 25 )

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As-cast microstructure, precipitated phases and element segregation characteristics of DIEVAR hot working die steel electroslag ingot were analyzed by the means of optical microscope (OM), scanning electron microscope (SEM/EDS), electron probe (EPMA), Thermo-Calc thermodynamic calculation. Then the effect of homogenization heat treatment on the microstructure and carbide and element distribution was studied. The results show that the as-cast dendrite structure of the tested steel is well developed, and the secondary dendrites are obvious. The Cr and Mo and V elements are inter-dendritically enriched, and the segregation order is Mo>V>Cr. The interdendritic precipitated phases are M₂₃C₆, M₆C and MC carbides. With the increase of homogenization temperature and the extension of holding time, the dendrite microstructure gradually becomes fuzzy and even disappears, and the carbide redissolution forms a certain element diffusion zone and gradually diffuses until it is fully redissolved into the matrix, the element diffusion rate is Cr>Mo>V during the homogenization heat treatment. According to dendrite morphology, carbide redissolution, element diffusion and residual segregation index of Mo element after homogenization heat treatment, and considering the actual industrial production cost, the optimal homogenization heat treatment process of the DIEVAR steel is 1280 ℃×8 h.

Continuous cooling transformation of austenite in 390 MPa grade anti-collision hull steel

Chen Zuoning, Shi Zhongran, Hu Qian, Zhan Zhide, Luo Xiaobing

2024, 49(7): 146-151. doi:10.13251/j.issn.0254-6051.2024.07.022

Abstract ( 22 )

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Continuous cooling transformation behavior of 390 MPa grade anti-collision hull steel under dynamic and static conditions was studied by using Gleeble-3800 thermal simulation testing machine. The dynamic and static CCT curves of the tested steel were drawn by measuring the expansion curves of continuous cooling process at different cooling rates and combining with metallographic-hardness method. The results show that compared with the static condition, the cooling rate range of ferrite and pearlite transformation of the tested steel under dynamic condition is reduced from 0.1-20 ℃/s to 0.1-10 ℃/s, the cooling rate range of bainite transformation is expanded from 0.5-40 ℃/s to 0.1-40 ℃/s, and the cooling rate range of martensite transformation is expanded from 40 ℃/s to 10-40 ℃/s. The dynamic CCT curves moves to the upper left compared with the static CCT curves, indicating that the ferrite and pearlite phase transformation region enlarged and the bainite and martensite phase transformation region reduced.

Strip segregation in PH13-8Mo stainless steel and its evolution during heat treatment

Chen Suming, Yue Shan, Hu Shengshuang, Zhao Hu, Li Yi, Wu Haifeng, Ouyang Delai

2024, 49(7): 152-156. doi:10.13251/j.issn.0254-6051.2024.07.023

Abstract ( 23 )

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Taking a PH13-8Mo stainless steel shaft part as the research object, the microstructure characteristics of strip segregation in the PH13-8Mo stainless steel and its evolution during solution treatment and aging were studied. The results show that there exist two types of strip segregation in the microstructure of the steel, namely component segregation strip and δ-ferrite segregation strip. The component segregation strip distributes in a straight and continuous pattern, but the δ-ferrite segregation strip distributes in a straight and discontinuous pattern. In the component segregation strip with positive segregation of Ni and negative segregation of Fe, the content of Ni and Fe is 11% and 72%, respectively, lower and higher than the content of Ni and Fe elements in the steel. In the δ-ferrite segregation strip, the content of Ni and Fe is 4% and 71%, respectively, which are lower than the average content of Ni and Fe in the steel, the content of Cr, Mo and Al is 17%, 4.5% and 1.84%, respectively, which are higher than the average content of Cr, Mo and Al in the steel. The component segregation strip in the PH13-8Mo stainless steel can be effectively eliminated by solution treatment at 1100 ℃ for 2 h and then aging at 540 ℃ for 4 h, but the δ-ferrite segregation strip can not be effectively eliminated.

Continuous cooling transformation behavior of undercooled austenite in BTP500 steel plate

Dong Lili, Cui Chengbo, Yuan Xiaoming, Liu Zetian

2024, 49(7): 157-160. doi:10.13251/j.issn.0254-6051.2024.07.024

Abstract ( 17 )

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Continuous cooling transformation behavior of austenite of high properties rare-earth-microalloyed BTP500 steel plate was studied to clarify the phase types obtained under different cooling rates and the specific conditions for obtaining martensite of the designed BTP500 steel plate, and then to carry out small scale industrial trial production. The results show that the transformations of ferrite+pearlite (A→F+P), bainite (A→B) and martensite (A→M) occurr respectively during the continuous cooling process of the RE microalloyed BTP500 steel plate under different cooling rates. The critical cooling rate of BTP500 steel plate to obtain complete martensite is determined as 7 ℃/s by the CCT curve. Microstructure of industrial trial produced BTP500 steel plate by quenching at 780 ℃ and tempering at 210 ℃ is martensite, the mechanical properties meet the technical requirements and the comprehensive performance is excellent.

Grain size grading method based on improved UNet network and optimized algorithm of grain boundary

Qi Xueqian, Huang Xiaohong, Song Yue, Liu Yanping, Zhang Luyue, Zhang Qingjun

2024, 49(7): 161-167. doi:10.13251/j.issn.0254-6051.2024.07.025

Abstract ( 19 )

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Grain size has an undeniable impact on the properties of metal materials, and the manual grading methods of grain size is difficult to meet the current detection needs of metal materials. Therefore, for austenite microstructure, a grain size automatic grading method based on improved UNet network and grain boundary optimized algorithm was proposed, and the accuracy of the austenite grading results calculated by the method was analyzed by comparing with the manual grading results. The results show that when the improved UNet network is used to segment austenite grain boundaries, and then the Hough transform based grain boundary optimization algorithm is used to detect and remove twin grain boundaries and branch burr, the grain boundary extraction effect can be effectively optimized, and the accuracy of subsequent grain size calculation can be improved. The absolute error between the austenite grading results obtained by the proposed algorithm and that by the manual method is within 0.25, indicating that the algorithm can efficiently, conveniently and accurately complete the grading of austenite grain size.

Characteristics of alternating current field enhanced pack boriding for S32750 duplex stainless steel at medium temperature

Wu Xianlong, Xie Fei

2024, 49(7): 168-172. doi:10.13251/j.issn.0254-6051.2024.07.026

Abstract ( 17 )

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Conventional pack boriding (CPB) and alternating current field enhanced pack boriding (ACFPB) were performed at 800 ℃ on S32750 duplex stainless steel, and an ACFPB treated specimen was later subjected to solution treatment. The microstructure, thickness, hardness and phase structure of the borided layer were investigated by optical microscope, X-ray diffraction and microhardness testing, respectively. The results show that the morphology of the ACFPB layer is similar to that of the CPB layer, with a flat front and good bonding with the substrate, and the surface layer is composed of mainly FeB. Applying alternating current field (ACF) during boriding can effectively promote the diffusion of boron and increase the hardness of the borided layer. However, when the current increases to 6 A, more micropores appear in the borided layer. The solution treatment for the 5 A ACFPB treated S32750 steel results in a slight increase in the thickness of the borided layer, a significant decrease in the amount of FeB phase, an increase in the amount of Fe₂B, and the precipitated phase σ formed during boriding is dissolved into the matrix, which helps to improve the toughness of the duplex stainless steel.

Influence of Y₂O₃ addition on microstructure and wear resistance of ultra-high-speed laser-clad IN718 alloy coatings

Li Rui

2024, 49(7): 173-180. doi:10.13251/j.issn.0254-6051.2024.07.027

Abstract ( 22 )

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IN718 alloy composite coatings with Y₂O₃ addition were prepared by ultra-high-speed laser-cladding technology. The effect of Y₂O₃ addition on coating microstructure and morphology, phase composition, hardness and wear resistance was analyzed. The results show that the addition of Y₂O₃ reduces the pore defects in the coating and forms a dense and refined grain. The hardness of the coatings is the highest when Y₂O₃ content is 1.0% which average value is 380.2 HV0.1, meanwhile, it has superior wear resistance with the friction coefficient of 0.66 and the wear rate of 5.03×10^-4 mm³/(N·m), and the wear mechanism is combined of abrasive wear, adhesive wear and oxidative wear. The dispersed Y₂O₃ in the coatings forms nucleation point, resulting in the refinement of grains and improvement of hardness and wear resistance.

Effect of matrix type on wear resistance of plasma clad V-containing Fe-based coating

Li Baiqi, Li Ting, Tang Wenbo, Zhang Mengliang, Wang Xiaosheng, Li Wenqiang

2024, 49(7): 181-185. doi:10.13251/j.issn.0254-6051.2024.07.028

Abstract ( 17 )

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Two kinds of wear-resistant alloy coatings with the microstructure of "ferrite+VC particles" (VC_F) and "lath martensite+VC particles" (VC_M) were prepared on the base metal of Q235 steel plate by using powder plasma surfacing equipment, and the microstructure, hardness, wear resistance and wear morphology of VC_F and VC_M coatings were observed, respectively. The results show that the microstructure of the VC_F coating is a ferrite distributed with hard phase particles, and the microstructure of the VC_Mcoating is a lath martensite distributed with hard phase particles. The hardness and wear resistance of the VC_M coating are higher than that of the VC_F coating, indicating that the wear resistance of the coatings not only depends on the number of hard phases, but also has a significant relationship with the microstructure type of the coalings matrix.

Effect of medium-low temperature annealing on morphology, structure and electrical properties of MoS₂ nano films

Liu Chunquan, Xiong Fen, Ma Jiayi, Zhou Jintian, Liang Zexun, Huang Jianping

2024, 49(7): 186-194. doi:10.13251/j.issn.0254-6051.2024.07.029

Abstract ( 15 )

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MoS₂ nano films with different thicknesses were prepared by radio frequency (RF) magnetron sputtering via deposition at room temperature, and then annealed by different processes in 95%Ar+5%H₂ mixed atmosphere. The structure, surface morphology and electrical properties of the MoS₂ films were studied by means of atomic force microscope(AFM), Raman spectrum, four-probe and Hall tester. The results show that the MoS₂ films grown on the silicon substrate are uniform and continuous. The annealing process can effectively remove the impurity oxygen in MoS₂ films and improve its crystallinity, stability and structural integrity. The comprehensive properties of the MoS₂ films are better when the deposition time is 40 min (the thickness is about 300 nm), while the crystallinity and electrical properties of the films after annealing at 500 ℃ for 60 min are all better.

Preparation and high-temperature friction behavior of TiN coating on valve disc cone surface based on dual glow technology

Luo Changzeng, Zeng Xiaoxiao, Wei Dongbo, Li Xucong, Chen Yuechun, Lin Muyao, Zhang Pingze

2024, 49(7): 195-199. doi:10.13251/j.issn.0254-6051.2024.07.030

Abstract ( 15 )

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TiN coatings were prepared on NCF3015 valve alloy steel using double-layer glow plasma surface metallurgy technology. The microstructure, hardness and high-temperature wear resistance of the coatings were studied by SEM, EDS, XRD, microhardness tester and high-temperature friction and wear tester. The results show that the TiN coating grows uniformly in an island-like manner and has a dense surface structure. The average surface hardness of the coating can reach 1265.2 HV0.05. Under 5 N and 10 N loads, the specific wear rate of the coating is reduced by 79.3% and 79.7% compared to the valve substrate, respectively. It is an ideal material for valve surface protection under high temperature and harsh conditions, and can significantly improve the service life of valves in engines.

Effect of B₄C addition on morphology and properties of Stellite6+B₄C laser clad layers on 42CrMo steel surface

Zhang Zejiang, Li Xinmei, Zhu Chunjin, Li Hang, Yang Dingli

2024, 49(7): 200-207. doi:10.13251/j.issn.0254-6051.2024.07.031

Abstract ( 19 )

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In view of the surface modification of shearer picks, effect of B₄C addition (3%, 5% and 7%) on the cross-section morphology, microhardness, wear resistance and corrosion resistance of the Stellite6+B₄C laser clad layers on 42CrMo steel was studied by means of X-ray diffractometer, scanning electron microscope, Vickers microhardness tester, multifunctional friction and wear testing machine and electrochemical workstation. The results show that the cross-section morphology of the clad layer is good when the B₄C addition is 3% and 5%, however, when the B₄C addition is 7%, there are many defects on the surface of the clad layer. With the increase of B₄C addition, the microhardness of the clad layer increases from 781.04 HV to 1044.72 HV, the average friction coefficient decreases and the wear loss decreases first and then increases. When the B₄C addition is 7%, the average friction coefficient of the clad layer is 0.42, but due to the poor forming quality, the wear loss is the highest as 1.9 mg. When the B₄C addition is 5%, the wear loss is the least as 0.6 mg. The corrosion resistance of the clad layer first increases and then decreases with the increase of B₄C addition. When the B₄C addition is 5%, the self-corrosion potential of the clad layer is the highest, the self-corrosion current density is the smallest, and the charge transfer resistance R_ct is the largest, the best corrosion resistance of the clad layer is obtained.

Optimization of carburizing and quenching process for 20MnCr5 steel inner star wheel

Ding Zhong, Meng Xianggang, Li Xiaotian, Gu Jiacheng, Xu Jie

2024, 49(7): 208-211. doi:10.13251/j.issn.0254-6051.2024.07.032

Abstract ( 22 )

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In order to improve the surface hardness and wear resistance of inner star wheel and ensure the toughness of the core, the carburizing and quenching process of 20MnCr5 steel inner star wheel was optimized. The results show that the hardness and the depth of effective hardening layer of the 20MnCr5 steel inner star wheel meet the technical requirements after (935±10) ℃×295 min+830 ℃×30 min carburizing and quenching with diffusion carbon potential of 0.75%, quenching carbon potential of 0.65%, and the oil cooling stirring speed of 1100 r/min. After 400 cycles life test, wear and peeling appear on the surface of the inner star wheel treated by the original carburizing and quenching, while only slight scratches appear on the surface of the inner star wheel treated by optimized carburizing and quenching. The wear resistance is significantly improved compared to the original carburizing and quenching.

Deformation heat treatment technology of 30MnNbRE steel for oil well pipe based on TMCP

Tang Xuejiao, Bao Xirong, Wang Xiaodong, Song Cao

2024, 49(7): 212-219. doi:10.13251/j.issn.0254-6051.2024.07.033

Abstract ( 18 )

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Recrystallization behavior of 30MnNbRE steel for oil well pipe was studied through hot compression test on Gleeble-3500 thermal simulation machine. Based on the PQF process, the TMCP on-line deformation heat treatment process of 30MnNbRE steel was designed and simulated, and the microstructure and mechanical properties were compared with the traditional off-line heat treatment process. The results show that dynamic recrystallization controlled rolling, static recrystallization controlled rolling and non-recrystallization controlled rolling can be used for actual perforation process, continuous rolling process and diameter-fixing process, respectively. Compared with the traditional off-line heat treatment process, the martensitic lath of the 30MnNbRE steel produced by TMCP on-line deformation heat treatment can be refined to 0.536 μm, the NbC size is about 88.9 nm, the yield strength is increased to 1169 MPa, and the impact absorbed energy is increased to 98.7 J.

Effect of quenching and tempering process optimization on microstructure and low temperature impact propery of ZG34CrNiMo steel

Li Ziyan, Cui Yu, Xu Hongxiang, Wang Xinhua, Zhao Shaofu, Guo Jingqiang, Chen Shengchao

2024, 49(7): 220-224. doi:10.13251/j.issn.0254-6051.2024.07.034

Abstract ( 22 )

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Effect of quenching and tempering process on microstructure, mechanical properties and impact fracture morphology of the core zone in U-shaped test block of ZG34CrNiMo steel was studied by means of optical microscope, scanning electron microscope and mechanical property test. The results indicate that compared to conventional quenching and tempering processes, when the ZG34CrNiMo steel istreated by optimized quenching and tempering process (high-temperature normalizing, higher cooling rate of quenching liquid and high-temperature tempering with fast cooling), the martensitic transformation can be fully completed in the core of the U-shaped specimen during quenching, the grain size is refined from grade 7.6 to 8.3, a large number of elliptical dimples appear in the impact fracture, and the average low-temperature impact absorbed energy at -35 ℃ is increased from 7.23 J to 43.00 J. By using trace amounts of vanadium or rare earth elements to improve the composition of the steel, the comprehensive mechanical properties of the core zone specimen are further improved significantly, especially with average low-temperature impact absorbed energy of 77.00 J at -35 ℃.

Effect of current annealing on properties and plastic deformation of Fe₇₈Si₉B₁₃ alloy

Niu Xiaomiao, Jin Tao, Wang Ze, Wang Tao

2024, 49(7): 225-230. doi:10.13251/j.issn.0254-6051.2024.07.035

Abstract ( 21 )

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The plasticity of Fe₇₈Si₉B₁₃ amorphous alloy thin strip was modified by conventional annealing and current annealing. Nanoindentation tests and plastic forming tests were carried out to evaluate the properties and forming effect of Fe₇₈Si₉B₁₃ amorphous alloy thin strip under the two annealing processes. The results show that when the temperatures of the two annealing processes are the same, the hardness and elastic modulus of the Fe₇₈Si₉B₁₃ amorphous alloy thin strips after current annealing are lower, and the plastic forming effect is better, in which the nanoindentation displacement after current annealing at 300 ℃ for 20 min is the largest, and the improvement of the plastic deformation behavior is also the most obvious.

Effects of thermal processing and rapid solidification on the microstructural evolution in Ni-Co-Al ternary alloys

Li Bokui, Zhou Fei, Cui Yanna, Li Ming, Zhou Yang, Wang Jun

2024, 49(7): 231-240. doi:10.13251/j.issn.0254-6051.2024.07.036

Abstract ( 23 )

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Due to the typical phase transformation process and good thermal processing performance, Ni-Co-Al ternary alloy has become an important model alloy in the research of phase transformation, structure and function application of Ni-based alloy. Based on the requirements of controlling the size and orientation of microstructure units in the functional applications of Ni-based alloys, the effects of different alloy compositions, thermal processing and rapid solidification processes on the grain size, grain orientation and microhardness of the alloys were investigated. The results show that the grain size of the alloy ingot obtained by arc melting process can be obviously refined after cold rolling-annealing treatment, and the average size is about 30 μm, while the grain size of the alloy strips obtained by rapid solidification process (vacuum melt spinning) can be further reduced to about 10 μm. In addition, the rapid solidification process can significantly change the grain orientation of the alloy, from the {101} orientation in the traditional processing to the preferred {100} orientation, which is conducive to the optimal control of the micro-nano structural unit and effective specific surface area of Ni-based alloys, further improving the structure and functional application potentials of the Ni-based alloys.

Effect of annealing temperature on microstructure and mechanical properties of selective laser melted TA15 titanium alloy

Jiang Junjie, Wang Yongbiao, Xiao Zhiling, Fan Jianglei, Zhang Zhengwen

2024, 49(7): 241-248. doi:10.13251/j.issn.0254-6051.2024.07.037

Abstract ( 17 )

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Effect of annealing temperature (650-900 ℃) on the microstructure and mechanical properties of TA15 titanium alloy prepared by laser selective melting (SLM) was studied. The results show that with the increase of annealing temperature, the acicular α′ martensite in the SLMed TA15 titanium alloy gradually decomposes into α+β phases, the α phase gradually transforms from acicular to lamellar, and the β phase is mainly precipitated in the α′ martensite intergranular and where rich in intragranular lattice defects. The grain misorientation distribution of the TA15 specimen after annealing is very similar to that of the as-SLMed specimen, which has strong microstructural inheritance. With the increase of annealing temperature in the range of 650-800 ℃, the strength and hardness of the specimen decrease, while the elongation increases. When the annealing temperature is 900 ℃, the tensile strength and elongation of the specimen are 1117 MPa and 11.2%, respectively, showing the best comprehensive mechanical properties.

Effect of normalizing temperature on microstructure and mechanical properties of 36MnVS4 and 46MnVS5 steels for fracture splitting connecting rod

Lu Mingxia, Zhang Lei, Wang Xinshe

2024, 49(7): 249-253. doi:10.13251/j.issn.0254-6051.2024.07.038

Abstract ( 18 )

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Mechanical properties and microstructure evolution of two medium carbon non-quenched and tempered steels 36MnVS4 and 46MnVS5 widely used for automotive fracture splitting connecting rod at different normalizing temperatures were compared and studied, and the strengthening mechanism was analyzed. The results show that with the increase of normalizing temperature, the yield strength, tensile strength and hardness of both the 36MnVS4 and 46MnVS5 steels increase gradually, and the tensile strength and hardness of the 46MnVS5 steel are higher than those of the 36MnVS4 steel. When normalized below 990 ℃, the yield strength of the 46MnVS5 steel is higher than that of the 36MnVS4 steel, while normalized above 990 ℃, the yield strength of the 46MnVS5 steel is lower. When normalized above 1140 ℃, the elongation and percentage reduction of area of the 36MnVS4 steel are higher than that of the 46MnVS5 steel, and the toughness is better. The difference in mechanical properties between the two steels is mainly due to both the content of proeutectoid ferrite and the precipitated strengthening phase V(C, N) in proeutectoid ferrite after normalizing at 1200 ℃ of the 36MnVS4 steel are more than that in 46MnVS5 steel, so the plasticity of 36MnVS4 steel is better. However, considering the production process and properties requirements of the fracture splitting connecting rod, the improvement of toughness is unfavorable to the fracture splitting processing of the connecting rod, and the 46MnVS5 steel has good comprehensive mechanical properties and more cost advantages than the 36MnVS4 steel. Therefore, the 46MnVS5 steel is better to be selected for the fracture splitting connecting rod.

Effect of annealing temperature on microstructure and properties of ultra-high strength non-oriented silicon steel

Jiang Shiyong, Chen Xiang, Lin Yuan, Zhang Wenkang

2024, 49(7): 254-260. doi:10.13251/j.issn.0254-6051.2024.07.039

Abstract ( 85 )

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Effect of different annealing temperatures with holding time of 2 min on the recrystallization structure, texture, mechanical properties and magnetic properties of 3.52%Si-1.10%Al non-oriented silicon steel was studied. The results show that the initial recrystallization temperature of the experimental steel is about 630 ℃. When annealed below 630 ℃, the microstructure of the annealed sheet is very similar to that of the cold rolled sheet, without no significant difference. When annealed above 630 ℃, recrystallization begins to occur in the annealed sheet, and the recrystallization fraction increases significantly with the increase of annealing temperature. The size of recrystallized grains slowly increases with the increase of annealing temperature, but without significant growth within the entire experimental temperature range of 500-790 ℃, far from reaching the optimal grain size. The texture of cold rolled sheet is mainly composed of α-fibre texture and γ-fibre texture, while η deformation texture strength is weak. As the annealing temperature increases, the deformed α-fibre texture decreases significantly, and the {001}<110>and {112}<110>textures have completely disappeared at 790 ℃, while the γ-fibre texture {111}<110> decreases first and then increases with the increase of annealing temperature. The variation pattern of {111}<112> texture is generally the same as that of {111}<110> texture. The intensity of η texture {100}<001> and {110}<001> which are beneficial for magnetic properties increases significantly when annealed at temperature over 690 ℃. As the annealing temperature increases, the iron loss P_1.5/50 of the product shows a monotonic decreasing trend, while the magnetic polarization intensities J₅₀₀₀ and J₁₀₀₀₀ show a monotonic increasing trend. As the annealing temperature increases, the yield strength shows a decreasing trend, but the rate of decrease varies within different temperature ranges. In the two temperature ranges of 610-630 ℃ at the beginning of recrystallization and 670-690 ℃ where the recrystallization ratio rapidly increases, there are two peaks in the decrease rate, while the decrease rate in other temperature ranges becomes more moderate. Annealing in the range of 630-670 ℃ can produce ultra-high strength non-oriented silicon steel products with R_p0.2≥650 MPa and excellent magnetic properties.

Effect of heat treatment process on microstructure and strength of 8 mm thick TC4 titanium alloy plate

Ding Yi, Li Aiguo, Li Xianjun, Bai Yuhong, Jiang Qiue, Peng Guanghua, Luo Ping, Hou Junqing

2024, 49(7): 261-266. doi:10.13251/j.issn.0254-6051.2024.07.040

Abstract ( 26 )

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Effects of different heating temperatures, cooling rates and holding time on microstructure and strengths of 8 mm thick TC4 titanium alloy plate were studied. The results show that the heating temperature significantly affects the microstructure and strength of the TC4 titanium alloy plate. The recrystallization occurs and the α phase tends to be equiaxed when the heating temperature increases from 800 ℃ to 850 ℃, resulting in the strength decreasing, the fraction of equiaxed α increases, the size and content of β phase increase where a small amount of α′ phase precipitated inside when the heating temperature reaches 900 ℃, resulting in the strength increasing. When the cooling rate is higher than 10 ℃/s, the martensitic transformation occurs, and the faster the cooling rate, the greater the trend of martensitic transformation and the higher the strengths. When the holding time increases from 180 s to 600 s, the yield strength and tensile strength increase by 6.1% and 7.9%, respectively, and when the holding time further increases to 900 s, the strength increment is small.

Effect of annealing treatment on microstructure and mechanical properties of pure copper

Meng Pinpin, Zhang Xiaobo

2024, 49(7): 267-273. doi:10.13251/j.issn.0254-6051.2024.07.041

Abstract ( 21 )

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Microstructure and mechanical properties of T2 pure copper annealed with different processes were studied by using OM, SEM and tensile tests. The results show that the increase of annealing temperature and the extension of annealing time lead to increase in the content of recrystallized structure and annealing twin in the microstructure of the pure copper, thereby enhancing the plasticity of annealed pure copper. After annealing at 150 ℃ for 60 min, the pure copper achieves room temperature tensile strength of 309.1 MPa and elongation after fracture of 16.7% under the multiple effects of grain boundary strengthening, dislocation strengthening and twinning. Compared with the original pure copper, the room temperature tensile strength increases by 11.6% and the elongation increases by 34.7%. According to the tensile test at high temperature, the pure copper exhibits excellent thermal stability after annealing at 100 ℃ for 30 min.

Effect of heat treatment process on microstructure and mechanical properties of Al-6.5Zn-2.3Mg-2.5Cu-0.1Zr-0.2Sc alloy

Xu Shuangqian, Dai Zhiyong, Wang Ziyu

2024, 49(7): 274-280. doi:10.13251/j.issn.0254-6051.2024.07.042

Abstract ( 18 )

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An Al-6.5Zn-2.3Mg-2.5Cu-0.1Zr-0.2Sc cast aluminum alloy for the lightweight requirements of key components for high-speed trains was developed. The Al-6.5Zn-2.3Mg-2.5Cu-0.1Zr-0.2Sc alloy was melted and cast, and homogenization treatment and solution and aging(T6) treatment was carried out. The tensile properties of the T6 state alloy were tested at room temperature and 200 ℃, respectively, and their microstructure characteristics were characterized by means of optical microscope, scanning electron microscope and transmission electron microscope. The results show that when aged at 120 ℃ for 10 h, the main precipitates within the grain are the GP region. As the aging time increases, GP regions transform into η′ phase, and the η′ phase can be clearly observed when aged for 22 h. As extending the aging time to 34 h, the η′ phase gradually grows and transforms into the coarse η phase. The results of tensile tests at 200 ℃ show that the tensile strengths of the alloy aged for 22 h and 34 h are 617.7 MPa and 575.9 MPa, respectively, and the yield strengths are 600.5 MPa and 560.7 MPa, respectively, and both the fracture mechanisms are ductile fracture.

Effect of anodizing process on properties of Al-Li alloy in acid salt spray environment

Yu Juan, Feng Zhaohui, Chen Gaohong, Wu Lei

2024, 49(7): 281-286. doi:10.13251/j.issn.0254-6051.2024.07.043

Abstract ( 20 )

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Effect of anodizing process on the corrosion behavior and tensile strength of Al-Li alloy which exposed to acid salt spray environment was studied by means of surface morphology observation, corrosion rate analysis and room temperature tensile test. The results show that in acid salt spray environment, the unanodized Al-Li alloy occurs significant corrosion after 24 h with a corrosion area of 58.417%. After 144 h, the corrosion morphology is more uniform with a corrosion area of 88.350%. The corrosion mass gain rate decreases significantly with the extension of salt spray corrosion time. The tensile strength of the unanodized Al-Li alloy under different corrosion time is about 400 MPa. The corrosion of the sulfuric acid anodized and boron sulfuric acid anodized Al-Li alloy needs more time and the corrosion rate is slower. In acid salt spray environment, no obvious corrosion is found after 240 h, and the corrosion area is only about 7% after 360 h. The tensile strength of the Al-Li alloy under different corrosion time is about 500 MPa. After anodizing, an oxide film forms on the surface of the Al-Li alloy, which blocks the etching of Cl^- in corrosion solution, and significantly improves the corrosion resistance and the tensile strength of the Al-Li alloy in the acid salt spray environment.

Control of grain boundary cementite of high carbon steel wire rods based on carbon segregation index

Guo Dayong, Gao Hang, Pan Yang, Gong Wenhe, Wang Bingxi, Yang Yingqiang

2024, 49(7): 287-293. doi:10.13251/j.issn.0254-6051.2024.07.044

Abstract ( 17 )

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Control technology of grain boundary cementite(GBC) precipitation based on carbon segregation index of high carbon steel wire rods was investigated. The results show that when the carbon segregation index of 0.82%C high carbon steel reach 1.23 and 1.37, cooling rate of 20 ℃/s is not fast enough to prevent GBC precipitation, and at this cooling rate, martensite, proeutectoid cementite and pearlite coexist in the microstructure of the high carbon steel at room temperature. The wire rods with this type of microstructure are not suitable for drawing. When the carbon segregation index of the high carbon steel reaches 1.17, the cooling rate of 10 ℃/s is fast enough to produce 0 level of GBC, 90% sorbite and no martensite, which is beneficial to the drawing of high carbon steel wire rods. GBC dose not appear in the 0.8%C wire rods with carbon segregation index of 1.00 under the cooling rates of 0.25-10 ℃/s. According to above results, the setup of GBC control technology based on the carbon center segregation index is necessary to meet requirement of high carbon steel wire rod drawing of customers.

Production process optimization for low cost vanadium-free hot rolled HRB400E steel bars

Liu Yang, Gao Ming, Ma Li, Hu Zhen, Sun Zhongmei, Zhang Shizhen

2024, 49(7): 294-300. doi:10.13251/j.issn.0254-6051.2024.07.045

Abstract ( 19 )

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Temperature range of non-recrystallization region and dynamic CCT curves of vanadium-free coil-free snail steel bars HRB400E were studied, and the industrial production process of the steel bars was optimized. The results show that when the strain rate is 0.2 s^-1, obvious recrystallization occurs in the HRB400E steel when rolling at 970 ℃, while partially recrystallization or non-recrystallization occur when the rolling temperature is reduced to 850 ℃ and below. The microstructure of the steel is ferrite and pearlite when the cooling rate is less than 3 ℃/s, ferrite+pearlite+bainite when the cooling rate is in the range of 5-15 ℃/s, and pearlite+bainite when the cooling rate is over 15 ℃/s. According to the experiment results, the rolling start temperature, finishing rolling temperature and wire spinning temperature is preset as (950±15) ℃, (870±10) ℃, and (870±10) ℃, respectively, and the opening degree of No.1 to No.4 fans is 90%, 90%, 70% and 70%, respectively. When this optimized process is used in trial production, the yield strength of the steel bar R_p0.2≥409.5 MPa, the difference in the same circle ≤32.6 MPa, the maximum total elongation A_gt≥10.26%, the microstructure is composed of ferrite and pearlite, and the tonnes steel cost in the whole process is reduced by about 16 Yuan.

Effect of pre-deformation before austenization on microstructure and properties of low carbon microalloyed nano steel

Liu Hongliang, Tang En, Lin Peng , Zhang Rui, Yuan Qing

2024, 49(7): 301-306. doi:10.13251/j.issn.0254-6051.2024.07.046

Abstract ( 19 )

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Pre-deformation before austenitizing was added into the conventional cold-rolling and annealing process to prepare low carbon nano steel. The effect of pre-deformation on microstructure, precipitation and properties of the low carbon microalloyed nano steel was analyzed. The results show that based on the conventional process the tensile strength and elongation of the nano steel prepared through pre-deformation before austenizing is 1043.1 MPa and 6.1%, respectively. Compared with the original coarse-structured steel, the strength increases by 524.5 MPa and the elongation decreases sharply. By the process of pre-deformation before austenizing+cold-rolling+annealing nano-sized ferrite grains can be obtained without affecting the precipitation of NbC particles, so the strength of the nano steel is guaranteed. However, the main reason for the decrease of elongation is that the pre-deformation provides defect energy for cementite particles at grain boundaries, which promotes the coarsening of cementite and deteriorates the strength of grain boundaries. In addition, coarsened cementite at grain boundaries lack the ability to pin geometrically necessary dislocations.

Heat treatment process of 600 MPa hydroelectric steel based on orthogonal analysis method

Chen Jie, Gao Tianyu, Wang Shuang, Wang Yong, Wang Liangliang

2024, 49(7): 307-312. doi:10.13251/j.issn.0254-6051.2024.07.047

Abstract ( 16 )

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Based on the orthogonal test analysis method, the effects of quenching temperature, quenching time, tempering temperature and tempering time on tensile strength and low temperature impact property of a 600 MPa hydroelectric steel were analyzed. The mechanical properties and microstructure evolution of the experimental steel under different heat treatment processes were studied. The results show that the main order of the influence on tensile strength of the experimental steel is quenching time, tempering temperature, quenching temperature and tempering time, and the main order of the influence on low temperature impact property is quenching time, tempering temperature, tempering time and quenching temperature. Prolonging the quenching time and increasing the quenching temperature are conducive to the increase of bainite content in the microstructure, which leads to the in strength of the experimental steel increase. The impact property of the experimental steel is positively correlated with the ferrite content in the microstructure. Under the heat treatment process of quenching at 900 ℃, holding for 75 min and tempering at 570 ℃, holding for 150 min, the microstructure of the experimental steel is lath bainite, granular bainite and a small amount of polygonal ferrite, which can achieve the optimal matching of strength and impact property.

Effect of annealing process on microstructure and corrosion resistance of high-Mn TWIP steel

Ai Gengen, Jiang Fengyang, Si Fang, Liu Jiangnan, Wei Na, Wang Junbo

2024, 49(7): 313-321. doi:10.13251/j.issn.0254-6051.2024.07.048

Abstract ( 21 )

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Microstructure of 25.8Mn-3.95Cr-2.83Al-0.33C-0.015N high-manganese TWIP steel after annealing at different temperatures and time was observed and analyzed by means of optical microscope and scanning electron microscope equipped with electron backscattering diffraction system, and its corrosion resistance was detected by using electrochemical workstation of standard three-electrode system. The results show that after annealing at 600-1000 ℃ for 25 min, the grains of the tested steel become larger sequentially with the increase of annealing temperature, and the proportion of Σ3 and Σ9 grain boundaries first increases and then decreases, reaching a maximum at 800 ℃. The full-scale corrosion resistance of the tested steel increases with the increase of annealing temperature, reaching an optimum at 1000 ℃, while the strongest localized corrosion resistance is achieved when annealing at 700 ℃. After annealing at 1000 ℃ for 5-25 min, the grain size of the tested steel also gradually augments with the increase of annealing time, the proportion of low-Σ grain boundaries also firstly increases and then decreases, the proportion of Σ3 and Σ9 grain boundary is the largest after annealing for 5 min, and the corrosion resistance is the best after annealing for 25 min.

Effect of tempering on microstructure and properties of direct quenched A387Gr11CL2 steel plate

Zhao Xiqing, Wang Fujie, Zhang Bingjun

2024, 49(7): 322-325. doi:10.13251/j.issn.0254-6051.2024.07.049

Abstract ( 14 )

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Direct quenching process of A387Gr11CL2 steel plate was carried out on the heavy plate production line, followed by tempering experiment at different temperatures. The results show that the direct quenching+tempering process can obtain the steel plate whose properties meet the requirements of the ASTM A387/A387M-17 standard, and the best tempering process is tempering at 750-760 ℃ for 100 min. When tempered at 740-750 ℃, the boundaries of the lath in the microstructure are clear, and there are large number of small carbides on the interface of the lath. When tempered at 760 ℃, the boundaries of the lath gradually disappear, while the carbides still exist. When tempered at 780 ℃, the laths merge and widen, and the carbides completely disappear. After the simulated post welding heat treatment, the strength and hardness of the tested steel plate decrease slightly, but there is no significant change in the impact absorbed energy at -30 ℃.

Effect of welding process on compatibility of 1Cr16Ni4Mo2Cu2W1VN steel and Co6B alloy surfacing layer

Wu Weijian, Liu Chengmiao, Li Quan

2024, 49(7): 326-330. doi:10.13251/j.issn.0254-6051.2024.07.050

Abstract ( 18 )

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Microstructure and properties of Co6B surfacing layer on the surface of 1Cr16Ni4Mo2Cu2W1VN steel before and after heat treatment were compared and analyzed under the two welding methods of oxyacetylene welding and argon arc welding, and the effect of welding method on the compatibility of the 1Cr16Ni4Mo2Cu2W1VN steel and Co6B alloy was explored. The results show that the 1Cr16Ni4Mo2Cu2W1VN steel has good compatibility with the Co6B alloy. Compared with the argon arc weld surfacing layer, the fusion transition zone of the oxyacetylene weld surfacing layer is wider, and the hardness is 7.3 HRC higher than that of the argon arc weld surfacing layer. After solid solution+cryogenic treatment+tempering, the oxyacetylene weld surfacing layer is dense, with fine and uniform structure, hardness of 45.3 HRC, and impact absorbed energy of 84.7 J, exhibiting better comprehensive performance.

Heat treatment process of 6014 aluminum alloy cold rolled sheets for automobile

Zhang Xinyu, Sui Xin, Luo Xudong, Cheng Suling, Zhang Yi, Chen Jinsheng, Zhang Wei

2024, 49(7): 331-335. doi:10.13251/j.issn.0254-6051.2024.07.051

Abstract ( 28 )

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Effect of solution treatment time on mechanical properties, electrical conductivity and microstructure of 6014 aluminum alloy cold-rolled sheet after artificial aging at 170 ℃ for 12 h was studied using room temperature stretching, electrical conductivity measurement, metallographic microscopy (OM) and scanning electron microscopy (SEM). The results show that with the extension of solution treatment time, the black Mg₂Si phase gradually dissolves back, and the size of the rich iron phase gradually decreases. When the solution treatment time is 120 min, β-Al₅FeSi phase to α-AlFeSi phases transition process is basically completed. The trend of the tensile properties is first increasing, then remaining unchanged, and then decreasing. When the solution time is 10 min, the properties of the aged sheets is the best, with tensile strength of 321.33 MPa, yield strength of 300.26 MPa, elongation of 10.93%, and conductivity of 51.53%IACS.

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