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  • MICROSTRUCTURE AND PROPERTIES
    Microstructure and wear resistance of AlCoCrFeMnZr near-eutectic high-entropy alloy
    Wang Zhixin, Yang Cheng, Ma Mingxing, Wang Bozhen, Dong Chen, Li Shangzhi, Hou Runsen
    2023, 48(1):  1-5.  doi:10.13251/j.issn.0254-6051.2023.01.001
    Abstract ( 177 )   PDF (695KB) ( 154 )  
    AlCoCrFeMnZr near-eutectic high-entropy alloy was prepared by vacuum melting, then its crystal structure, morphology, hardness and wear resistance were tested by means of XRD, SEM, microhardness tester and friction and wear testing machine. The results show that the phase structure of the AlCoCrFeMnZr alloy is BCC+HCP dual-phase structure, composing of primary phase and fine lamellar eutectic. The primary phase consists of the HCP phase enriched in Cr, Fe, and Zr, which grows in a dendritic manner. The main elements in the dendrite region (α phase) of the lamellar eutectic structure are Co, Cr and Fe, and the main elements in the intergranular (β phase) are Al and Zr, which conforms to the structure and element distribution of high-entropy alloys. The wear model changes from adhesive wear and abrasive wear to oxidative wear, and the friction factor shows a trend of increasing first and then decreasing, and the average friction factor is 0.5432, the microhardness is 768.8 HV0.5, that means the alloy has excellent hardness and wear resistance.
    Effect of Er on microstructure and wear properties of Al-Zn-Mg alloy
    Ding Xuxu, Wu Xiaolan, Wang Wei, Rao Mao, Mao Xuejing, Gao Kunyuan, Wei Wu, Huang Hui
    2023, 48(1):  6-11.  doi:10.13251/j.issn.0254-6051.2023.01.002
    Abstract ( 95 )   PDF (609KB) ( 89 )  
    Effect of Er on microstructure and mechanical properties of Al-Zn-Mg alloy as well as the wear behavior of the alloy under different loads were studied by means of scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), transmission electron microscopy (TEM) and material surface comprehensive tester. The results show that with the addition of Er, the elongation of the alloy is increased by about 30% and the grain size is significantly refined as the average grain size reduces by about 68%. The alloy experiences two stages of running-in and stable wear during wear process, and the wear factor curves fluctuate with the increasing of load. The enrichment of O element in the tribolayer indicates the oxidation wear mechanism. Under the load of 30 N, the wear mechanism is mixed up by the abrasive wear, fatigue wear and adhesive wear. Under the load of 70 N, the wear mechanism was mainly the abrasive wear with fatigue wear, and the wear loss is reduced due to the decrease of surface delamination of the alloy with the addition of Er.
    Effect of grain size on fretting wear behavior of Inconel 690 alloy
    Li Xiao, Xin Long
    2023, 48(1):  12-17.  doi:10.13251/j.issn.0254-6051.2023.01.003
    Abstract ( 87 )   PDF (611KB) ( 70 )  
    In order to prevent and mitigate the harm of fretting damage to nuclear reactor steam generator tube, the effect of grain size on fretting wear behavior of Inconel 690 alloy was investigated systemically. Fretting wear test was conducted to study fretting wear characteristics of the Inconel 690 alloy, and microstructure, hardness and worn scars characterization of the alloy at different solution temperature were observed by means of OM, Vickers hardness tester, SEM, EDS and LSCM. The results indicate that the grain size increases with the increase of solution temperature, whereas the hardness decreases. In the gross slip regime, the friction factor hardly changes with the variation of grain size and hardness, which is 0.48. The grain size of the Inconel 690 alloy with the value of 112 μm, while the ratio of hardness of SS304 alloy to the Inconel 690 alloy with the value of 260∶176.4 are proved to favor for the alloy to acquire the lowest level of wear volume. With different grain size and hardness, the main mechanism of fretting wear for the Inconel 690 alloy are delamination wear, abrasive wear and adhesive wear.
    Effect of Cr content on microstructure and properties of CrxMoNbTiZr high-entropy alloys
    Guo Jingping, Xiao Yifeng, Wu Liang, Zhang Qiankun, Liu Ziyi, He Pengcong
    2023, 48(1):  18-22.  doi:10.13251/j.issn.0254-6051.2023.01.004
    Abstract ( 70 )   PDF (615KB) ( 56 )  
    CrxMoNbTiZr high-entropy alloys (x=0, 0.5, 1, 1.5) were prepared by vacuum arc melting. X-ray diffractometer (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), microhardness tester and electrochemical workstation were used to study the effect of Cr content on the crystallographic structure, microstructure, hardness and corrosion resistance of the high-entropy alloy. The results show that the addition of Cr makes the alloy change from a single-phase BCC structure to a dual-phase BCC structure of Zr-rich phase and Mo-Nb-rich phase. With the increase of Cr content, there is also a Cr-rich Laves phase precipitate in the Zr-rich phase. The Cr1.5MoNbTiZr alloy has the highest hardness of 765.53 HV, which is due to the combined effect of the second phase precipitation strengthening, solution strengthening and high-entropy alloy lattice distortion. The addition of Cr increases the corrosion tendency of the CrxMoNbTiZr high entropy alloy in 3.5%NaCl solution (mass fraction), but reduces the corrosion rate of this high entropy alloy. Meanwhile, it is found that the addition of Cr has a critical value to ensure the pitting resistance of the alloy, beyond which the alloy is more prone to pitting.
    Effect of heat treatment on microstructure and properties of selective laser melting Co-Cr Alloy
    Deng Yuhua, Li Zhenhua, Yao Bibo, Teng Baoren, Li hao
    2023, 48(1):  23-28.  doi:10.13251/j.issn.0254-6051.2023.01.005
    Abstract ( 66 )   PDF (613KB) ( 59 )  
    In order to clarify the effect of heat treatment on microstructure and properties of selective laser melting (SLM) cobalt-chromium alloy, the changes of microstructure and properties of the cobalt-chromium alloy SLMed under laser power of 290 W and scanning speed of 950 mm/s before and after heat treatment of heating at 1150 ℃ for 6 h were investigated by means of OM, SEM, XRD, EBSD, EPMA, mechanical properties and electrochemical corrosion test. The results show that after heat treatment, the typical molten pool morphology disappears, and obvious carbide precipitates can be observed in the grain boundaries and intergrains, meanwhile, the grains change from coarse columnar to fine equiaxed grains, the corrosion resistance decreases, the hardness changes little, the elongation increases by about 30%. Finally, through heat treatment, uniform microstructure can be obtained, the volume fraction of γ phase can be increased, and the plasticity can be improved, but the electrochemical corrosion performance is reduced.
    Effect of Nb microalloying on microstructure and mechanical properties of Cr-Ni-Mo-V high-strength steels
    Zhang Weifeng, He Xiaofei, Yu Wenchao, Li Li, Wang Maoqiu
    2023, 48(1):  29-34.  doi:10.13251/j.issn.0254-6051.2023.01.006
    Abstract ( 96 )   PDF (617KB) ( 51 )  
    After quenching at 880 ℃ for 1 h and tempering at 300 ℃ for 3 h, the microstructure and precipitated phases of the tested Cr-Ni-Mo-V high-strength steels with and without Nb were observed and analyzed by means of SEM, EBSD, TEM and physicochemical phase analysis. The results show that with the addition of 0.035%Nb, the microstructure of the tested steel is refined, the martensite lath block size decreases from 3.1 μm to 2.9 μm, and the content of MC-type precipitated phase increases, the size distribution of the precipitated phases is optimized, and the content of the precipitated phases with the size ranging from 18 to 200 nm is significantly increased. Due to the increase in precipitated phase content, the decrease of C content in solid solution, and the slightly lower total C content in the Nb-containing steel, so that the strength of the steel decreases slightly, but still reaching the level of 2000 MPa. The toughness of the Nb-containing tested steels is improved by the refinement of the martensite microstructure and the optimization of the size distribution of the precipitated phases, the room temperature and -40 ℃ low temperature impact absorbed energy (KU2) are both increased to 44 J.
    Effect of Ti content on microstructure and properties of martensitic wear resistant steel with high Ti
    Liu Haisheng, Zhang Xiaojuan, Yuan Shaoqiang, Li Leilei, Wu Huibin, Yang Yuehui
    2023, 48(1):  35-39.  doi:10.13251/j.issn.0254-6051.2023.01.007
    Abstract ( 81 )   PDF (608KB) ( 54 )  
    Mechanical properties and wear resistance of low alloy martensitic wear resistant steels with 0.31%Ti and 0.55%Ti were measured, and the corresponding microstructure was analyzed by SEM and inclusion automatic scanning system, then the effect of Ti content in the steel on microstructure and properties was discussed. The results show that compared with the steel containing 0.31%Ti, the steel containing 0.55%Ti has more precipitation of TiC particles, which reduces the C equivalent of the matrix, resulting in a significantly lower tensile strength of the quenched steel, but more TiC precipitation also produces stronger precipitation strengthening, which makes the yield strength and hardness of the two steels close to each other. On the other hand, when the Ti content is higher, the micron-sized TiC particles in the steel increase correspondingly, which significantly improves the wear resistance of the tested steel.
    Effect of alloying element content on microstructure and mechanical properties of 610L steel for automobile beam
    Yang Wenqing, Shi Kexin, Dong Junhai, Sun Shenghui, Cai Minghui, Zhang Xiaoming, Ding Hua
    2023, 48(1):  40-45.  doi:10.13251/j.issn.0254-6051.2023.01.008
    Abstract ( 71 )   PDF (609KB) ( 58 )  
    A new type of 610 MPa grade Ti-Nb-Si microalloyed low carbon steel for automotive beam was designed based on the alloy design concept of increasing Si slightly, reducing Nb and raising Ti, combining with optimizing the thermo-mechanical control process (TMCP) parameters. The results show that the microstructure of the steel with 0.04%Si, 0.03%Nb and 0.06%Ti water cooled (15-20 ℃/s) to the coiling temperature after hot rolling is ferrite + pearlite, with high density nano-precipitates distributing in the ferrite matrix, exhibiting a good comprehensive properties with the yield strength of 539 MPa,the tensile strength of 633 MPa, the elongation of 20.5% and the hole expansion ratio of 66.4%, all meeting the requirements of both the mechanical properties and the hole expansion formability of 610L steel.
    Microstructure and properties of bainitic alloy steels with different carbon contents after austempering
    Hao Xiaoge, Zhao Leijie, Wang Yanhui, Ma Penghui, Zhang Zi, Yue Yun, Xiong Peng
    2023, 48(1):  46-51.  doi:10.13251/j.issn.0254-6051.2023.01.009
    Abstract ( 72 )   PDF (612KB) ( 51 )  
    Effect of carbon content on microstructure transformation and mechanical properties of bainitic steels with different carbon contents (0.22C, 0.34C and 0.45C) was studied after austenitizing at 960 ℃ and then austempering at above Ms point 10-50 ℃. The results show that the carbide-free bainite microstructure composing of bainite ferrite and retained austenite is obtained after austempering. With the decrease of carbon content, the bainite transformation time is significantly shortened, the bainitic ferrite laths become thicker, and the hardness and tensile strength show a downward trend, while the impact property is obviously improved, which is mainly related to the higher bainite transformation temperture of the low carbon steel, the thick bainitic ferrite laths and the decrease of high carbon blocky retained austenite.
    Microstructure evolution and mechanical properties of laser melting deposited 2195 aluminum-lithium alloy
    Gu Hai, Zhang Jie, Sun Jianhua, Wu Guoqing, Sun Zhonggang
    2023, 48(1):  52-59.  doi:10.13251/j.issn.0254-6051.2023.01.010
    Abstract ( 52 )   PDF (609KB) ( 49 )  
    2195 aluminum-lithium alloy was prepared by laser melting deposition (LMD) technology. The optimal process parameters of laser melting deposited 2195 Al-Li alloy were analyzed by single-channel and overlap-track experiments, and the microstructure of the alloy was systematically studied by optical microscope (OM) and other characterization methods. The results show that the optimum deposition process parameters are scanning power of 1400 W, scanning rate of 480 mm/min and scanning spacing of 1.6 mm, and precipitated Al7Cu4Li (TB) phase is found to distribute along grain boundary in the alloy 5-layer stacked blocks printed by the optimal process parameters, and then the precipitated phase gradually dissolves into the matrix after solution treatment at 450 ℃ for 2 h. After aging at 155 ℃ for 32 h and water cooling, stable second phase precipitates from unstable supraturated solid solution Al7Cu4Li and forming stable aging structure, so that the hardness of the aged specimen is significantly higher than that of the specimen solution treated.
    Fatigue properties and influencing factors of carburized gear steel 18CrNiMo7-6
    Zhang Xiaolu, Hai Xianü, Gui Weimin, Yu Wenchao, Shi Jie, Wang Maoqiu
    2023, 48(1):  60-67.  doi:10.13251/j.issn.0254-6051.2023.01.011
    Abstract ( 69 )   PDF (608KB) ( 72 )  
    Taking 18CrNiMo7-6 gear steel as base steel, a tested 18CrNiMo7-6 gear steel was prepared by traditional vacuum degassing smelting + Nb microalloying + electroslag remelting smelting, then the fatigue properties and influencing factors of both steels were comparatively studied by rotary bending fatigue test combined with analyses and characterization of microstructure, hardness distribution, inclusions and fatigue fracture. The results show that the fatigue limit of the tested steel smelted by electroslag remelting and Nb microalloyed is 90 MPa higher than that of the base steel, the service life under the same load is significantly increased, the grain size of the carburized layer of the tested steel is refined from grade 7.5 of the base steel to grade 9, but the surface hardness is decreased due to the increase of retained austenite content. The Aspex inclusion characterization shows that the number of inclusions in the tested steel is significantly lower than that in the base steel, and there are fewer hard oxide inclusions, which is consistent with the fracture characterization results. The comprehensive analysis shows that the grain refinement and decrease of non-metallic inclusion level are the main influencing factors to improve the fatigue properties of the tested steel.
    MATERIALS RESEARCH
    Aging precipitation behavior of super austenitic stainless steel 654SMO at 900 ℃
    Zhao Zhengxiang, Li Jingyuan, Liao Luhai, Xu Fanghong, Zhang Wei
    2023, 48(1):  68-74.  doi:10.13251/j.issn.0254-6051.2023.01.012
    Abstract ( 64 )   PDF (618KB) ( 42 )  
    Super austenitic stainless steel 654SMO was aged at 900 ℃ for different time. The microstructure of the precipitated phase was observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The composition and structure of the precipitated phase were analyzed by energy spectrum analysis and selected area electron diffraction. The precipitation kinetics was studied by JMA equation. The results show that the precipitated phases in the super austenitic stainless steel 654SMO are mainly σ phase and Cr2N phase.During the aging process from 10 min to 1 h,the precipitated phases in the steel is mainly σ phase. The precipitation position of σ phase is grain boundary, non-coherent twin boundary, coherent twin boundary, and finally within grains in the sequence. During the aging process from 2 h to 12 h, the σ phase begin to form needle-like phase in the grain.With the prolongation of aging time, the amount of precipitated phases become more and more.In addition, they interlace with each other and form a network in the grain.After aging for 24 h and 48 h, because σ phase is rich in Cr element and the grain boundary structure is very different between σ phase and austenite phase,Cr2N phases nucleate on the σ phases in strips or irregular chunks.The precipitation kinetics equation of precipitated phase in the steel 654SMO is X=1-exp(-0.0487t0.729).
    Recrystallization and inhibitor precipitation behavior in high temperature ferrite zone of oriented silicon steel containing rare earth
    Hu Shuai, Jin Zili, Wu Zhongwang, Li Tao, Li Wei, Hu Yuqing, Bai Jin
    2023, 48(1):  75-79.  doi:10.13251/j.issn.0254-6051.2023.01.013
    Abstract ( 49 )   PDF (608KB) ( 36 )  
    Recrystallization and inhibitor precipitation behaviors of oriented silicon steel containg are earth hot rolled at 1200 ℃ in the ferrite zone with 30% deformation, held for different time and then cooled in water were analyzed by using Gleeble 1500D, SEM, TEM, ICP. The results show that after hot rolling at high temperature in the ferrite zone, only dynamic recovery occurs, no dynamic recrystallization occurs, and the amount of precipitated phase in the steel does not increase significantly. After hot rolling and holding for about 20 s, static recrystallization occurs, and the inhibitor precipitated phase starts to precipitate and grows. The higher the recrystallization rate, the faster the volume fraction increasing of precipitated phase. After deformation, the amount of Cu2S and MnS in the precipitated phase is similar. When the recrystallization rate is 64%, MnS increases by about 7.4% and Cu2S increases by about 19.34%. At the same time, most of the precipitated phases are precipitated in the grains, and with the prolongation of holding time, the precipitated phase nucleates and grows up gradually on the grain boundaries.
    High temperature oxidation resistance of Super304H austenitic stainless steel
    Li Lingxiao, Zhao Yanjun, Zhang Jingrui, Li Pingzhen, Feng Wei, Ye Boxi
    2023, 48(1):  80-86.  doi:10.13251/j.issn.0254-6051.2023.01.014
    Abstract ( 78 )   PDF (617KB) ( 40 )  
    Oxidation mechanism of Super304H austenitic stainless steel was studied by high temperature oxidation test at 550-800 ℃ and combining with the law of oxidation kinetics. The results show that the oxidation mass gain curve of the Super304H austenitic stainless steel follows the parabola law at 550-800 ℃, the trend of mass gain is the most obvious within 60 h at 750-800 ℃, and the mass gain is up to 0.005 mg·mm-2 after 100 h. A dense oxide film is gadually formed at 550-750 ℃, which is mainly composed of Cr2O3 and Fe3-xCrxNiO4 mixed oxides and a small amount of CuCrMnO4. Increasing temperature makes the Super304H austenitic stainless steel promote the selective oxidation of Cr, and make the Cr2O3 protective film crack. At 800 ℃, the exposed Fe matrix reacts with oxygen atoms to form tumor Fe3O4, and the oxide film is thick and peels off. when strain rate is 3.2×10-4 s-1, the tensile strength of the stainless steel decreases with the increase of oxidation temperature, and reaches 350 MPa as the maximum at 600 ℃. The elongation is the best at 700-750 ℃, which is 28%.
    Dynamic mechanical behavior and constitutive model of HST2425 titanium alloy
    Guo Fengting, Cong Liangchao, Guo Xinhu, Du Feifei, Sun Xudong
    2023, 48(1):  87-94.  doi:10.13251/j.issn.0254-6051.2023.01.015
    Abstract ( 49 )   PDF (611KB) ( 31 )  
    Quasi-static and dynamic mechanical properties of HST2425 titanium alloy at temperatures ranging from 293 K to 673 K and strain rates ranging from 0.0001 s-1 to 6500 s-1 were investigated by using an electronic universal testing machine and Split Hopkinson bar (SHPB) device. The results show that with the increase of strain rate, both the maximum stress and maximum strain of the HST2425 titanium alloy increase, but the increase rate of maximum stress decreases when the strain rate exceeds 3500 s-1, but the increase rate of maximum stress decreases when the strain rate exceeds 3500 s-1, and the increase rate of maximum strain decreases when the strain rate exceeds 5500 s-1. As the deformation temperature increases, the flow stress decreases significantly, and the temperature and strain rate have an interaction in the dynamic compression process. The original Johnson-Cook (J-C) model and its modified model of the HST2425 titanium alloy are established based on the experimental results, and the correlation between the modified model and the experimental values is better than the original model, indicating that the modified model has higher accuracy and applicability in predicting the dynamic impact deformation behavior of the HST2425 titanium alloy.
    Formation of reversed austenite and its effect on properties of Cr13Ni4Mo steel
    Zhao Shuai, Li Qingchun, An Haoying, Chen Shuying, Chang Guowei
    2023, 48(1):  95-99.  doi:10.13251/j.issn.0254-6051.2023.01.016
    Abstract ( 35 )   PDF (608KB) ( 29 )  
    Formation law, mechanism of reversed austenite and mechanical properties of Cr13Ni4Mo steel were studied by means of XRD, SEM, EBSD and tensile test. The results show that no reversed austeniteis formed in the Cr13Ni4Mo steel after first tempering at 550-730 ℃. When first tempering at 630 ℃ and second tempering at 530-630 ℃, the content of reversed austenite in the steel increases firstly and then decreases with the increase of the second tempering temperature, and the tensile strength, elongation and product of strength and elongation also increase first and then decrease correspondingly. When the second tempering temperature approaches 590 ℃, the content of reversed austenite reaches the peak and the comprehensive mechanical properties are the best. The reversed austenite is mainly formed in the martensite lath with shear mechanism when the second tempering temperature is 550 ℃, and with the increase of second tempering temperature, the formation of reversed austenite is gradually dominated by diffusion mechanism.
    Microstructure and typical properties of cast Ni-based superalloy K439B
    Chen Jingyang, Ren Xiaodong, Zhang Mingjun, Zhang Lihui, Tang Xin, Xiao Chengbo
    2023, 48(1):  100-104.  doi:10.13251/j.issn.0254-6051.2023.01.017
    Abstract ( 86 )   PDF (611KB) ( 47 )  
    Typical microstructure, long-term aging microstructural stability at 800 ℃ and main properties of cast Ni-based superalloy K439B were introduced and compared with that of K4169 and CM939 alloys. The results show that the K439B alloy has good comprehensive properties, and its tensile properties and temperature capability are equivalent to that of the CM939 alloy. The oxidation resistance and salt-coated hot-corrosion properties of the K439B alloy are better than that of the K4169 alloy at 800 ℃, and its gas hot-corrosion property is similar to that of the K4169 alloy at 800 ℃. Meanwhile, the K439B alloy is unsusceptible to the welding hot cracking. It has been applied in the casting of hot-section components for advanced aero engines and gas turbines such as combustor case, preswirl nozzle and nozzle ring, etc.
    Austenite grain growth and mechanical properties of Super304H heat-resistant steel during aging process
    Wu Yue
    2023, 48(1):  105-111.  doi:10.13251/j.issn.0254-6051.2023.01.018
    Abstract ( 49 )   PDF (563KB) ( 35 )  
    Super304H heat-resistant steel tube with different grain sizes obtained by pre-deformation and short-time solution treatment was aged at 750 ℃ for 129 h to simulate austenite grain growth of the Super304H steel tube during long-term service. The characteristics of austenite grain were characterized by means of OM, EBSD and TEM, and the mechanism of austenite grain growth during aging was revealed. The effect of different austenite grain sizes on room-temperature and high-temperature mechanical properties of the specimens was investigated. The results show that main texture of the Super304H steel tube after pre-deformation and short-time solution is <111>//RD (Rolling direction), and the oriented austenite grains furtherly grow at the cost of swallowing other highly distorted grains during aging. After high temperature aging, the tensile properties at room temperature and high temperature of the Super304H heat-resistant steel tube decrease monotonically with the increase of grain size, and the elongation decreases significantly with the increase of grain size. The elongation can be used as the key index of metal supervision of the Super304H heat-resistant steel tube in service.
    Investigation on alloying to improve hardenability of medium carbon Cr-Mn-Si steel
    Zhang Xianwu, Ding Yali, Yang Zhuoyue, Gao Qi, Wang Shengmin
    2023, 48(1):  112-114.  doi:10.13251/j.issn.0254-6051.2023.01.019
    Abstract ( 38 )   PDF (571KB) ( 36 )  
    Effectiveness of adding Mo, Mo+B and Mo+Ni to improve the hardenability of a medium carbon Cr-Mn-Si steel was studied by means of traditional end quenching test method.The results show that the granular bainite phase transformation tendency of the medium carbon Cr-Mn-Si steels with adding Mo, Mo+B and Mo+Ni respectively is large, and the air-cooled end of Jominy end-quenching specimens forms granular bainite. Therefore, the quantitative hardenability information such as ideal critical diameter (DI) cannot be obtained from the end quenching curve in accordance with SAE J406 standard.However, the correspondence between the hardness of the end quenching curve and the microstructure proves that the addition of Mo, Mo+B and Mo+Ni in turn reduces the tendency of granular bainite transformation, increases martensite forming ability and improves hardenability.Although adding Mo+B can inhibit granular bainite transformation and improve hardenability effectively, it is susceptible to the influence of smelting residual Al and N in steel. While adding Mo+Ni has more advantages in improving hardenability, and it is not affected by smelting residual Al and N in steel. Therefore, adding Mo+Ni becomes the optimal alloying direction to improve the hardenability of medium carbon Cr-Mn-Si steel.
    Hot deformation behavior and processing map of Mg-6Gd-1.2Y-0.53Zr alloy
    Hu Jianling, Zhu Huaming, Yan Hongge, Chen Jihua, Xia Weijun, Zhang Meng
    2023, 48(1):  115-121.  doi:10.13251/j.issn.0254-6051.2023.01.020
    Abstract ( 38 )   PDF (567KB) ( 41 )  
    Influence of deformation temperature (340-500 ℃) and strain rate (0.01-25 s-1) on critical strain and volume fraction of dynamic recrystallization (DRX) of homogenized Mg-6Gd-1.2Y-0.53Zr alloy was studied by thermal simulation test. The range of hot processing parameters was optimized by constructing processing maps. The results show that the DRX critical strain increases with the increase of deformation temperature in the low strain-rate range of 0.01-1 s-1, while it decreases slightly with the increase of deformation temperature in the high strain-rate range of 10-25 s-1. The volume fraction of DRX increases with the increase of strain rate and deformation temperature. The dynamic recrystallization volume fraction is the highest and reaches 90.0% at 500 ℃, 25 s-1. According to the constructed processing map, when the deformation is 30%-80%, the better hot processing range is 400-500 ℃, 0.01-1 s-1 and 420-500 ℃, 10-25 s-1. At the strain rate of 10-25 s-1, when the deformation amount is 10%-80%, the most appropriate deformation temperature of the alloy is 460-500 ℃.
    Effect of NbC precipitates on grain growth of 17Cr2Ni2MoVNb gear steel
    Song Shaowei, Dong Mingzhen, Yu Wenchao, Yan Yongming, Wang Maoqiu, Zhou Yun
    2023, 48(1):  122-126.  doi:10.13251/j.issn.0254-6051.2023.01.021
    Abstract ( 60 )   PDF (569KB) ( 45 )  
    Pinning effect of NbC precipitates on grain size of the 17Cr2Ni2MoVNb steel at high temperature was analyzed by means of the coarsening model, the Zener grain growth model and experimental verification. The model and experimental results show that the pinning effect of NbC on grain growth is reduced due to its coarsening and re-solution. When the isothermal temperature is lower than 1000 ℃, NbC precipitate relative to the growth of austenite grains can play an effective inhibition, with the increase of isothermal temperature, the inhibition of NbC precipitation relative to the growth of austenite becomes weaker and weaker.
    CCT curves and impact property of Q355D hot rolled H-steel
    Wang Wenzheng, Ma Yongfu, Ma Jinhong, Zhang Guiying, Tian Yaqiang, Cheng Xinchao, Li Hongbin, Chen Liansheng
    2023, 48(1):  127-132.  doi:10.13251/j.issn.0254-6051.2023.01.022
    Abstract ( 132 )   PDF (574KB) ( 36 )  
    Continuous cooling transformation rule of Q355D hot-rolled H-steel was investigated on Glebble-3500 thermal simulation test machine by means of expansion method and metallography hardness method. In addition, static CCT curves were obtained. The results show that from the CCT curves, the microstructure of the steel is composed of ferrite and pearlite when the cooling rate is less than 1 ℃/s, ferrite, pearlite and bainite when the cooling rate is 1-10 ℃/s, and ferrite, bainite and martensite when the cooling rate is 20-50 ℃/s. With the increase of cooling rate, the hardness of the Q355D hot-rolled H-steel increases, and the hardness increases from 171 HV0.2 to 301 HV0.2. According to CCT curves, different rolling experiment schemes are worked out. When the total reduction is 75%, the strain rate is 0.3 s-1 and the deformation temperature is 1150 ℃, the ferrite grain size of the tested steel is 8.13 μm, and the impact absorbed energy at -20 ℃ is 146 J, with the best performance.
    PROCESS RESEARCH
    Effect of tempering temperature on microstructure and mechanical properties of 55NiCrMoV7 hot working die steel
    Yuan Yasha, Wang Yuchang, Wang Wenyan, Shi Ruxing, Yuan Sha, Zhang Yudong
    2023, 48(1):  133-138.  doi:10.13251/j.issn.0254-6051.2023.01.023
    Abstract ( 57 )   PDF (569KB) ( 44 )  
    The expansion curves of 55NiCrMoV7 steel during continuous coolingwith different speeds were measured by using Formastor-FII dilatometer, and the phase transformation temperature points were determined by expansion method and metallographic-hardness method, and then the CCT curves of the steel were drawn. Effect of tempering temperature on microstructure and mechanical properties of the 55NiCrMoV7 steel were studied by means of scanning electron microscope (SEM), optical microscope (OM), Rockwell hardness tester, tensile tester and impact tester. The results show that when the tempering temperature is in the range of 520-600 ℃, as tempering temperature increases, both the hardness and tensile strength of the 55NiCrMoV7 steel decrease, while the plasticity and toughness gradually increase. When the tempering temperature is 560-580 ℃, the hardening stress of the material is basically eliminated, martensite decomposing and retained austenite transformation is basically complete. The preferable mechanical properties of the 55NiCrMoV7 steel are obtained, with tensile strength, elongation and impact absorbed energy of 1300 MPa, 14.5% and more than 30 J, respectively.
    Effect of normalizing pretreatment on microstructure and mechanical properties of 28MnB5 steel for high-speed plough
    Huang Hao, Ni Haohao, Ju Yulin, Yuan Zhizhong, Guo Shun, Chang Ya'nan, Wang Dongfa
    2023, 48(1):  139-144.  doi:10.13251/j.issn.0254-6051.2023.01.024
    Abstract ( 42 )   PDF (567KB) ( 42 )  
    Aiming at solving the problem of insufficient strength and toughness of domestic soil-engaging components,the influence mechanism of normalizing-quenching-tempering (N-Q-T) process on microstructure and mechanical properties of 28MnB5 steel was studied, and compared with the high-speed ploughing parts produced by quenching-tempering (Q-T) process.The results indicate that the microstructure of N-Q-T and Q-T 28MnB5 steel is mainly comprised of lath martensite. However, the average width of lath martensite of N-Q-T 28MnB5 steel(0.9 μm) is significantly lower than that of Q-T 28MnB5 steel(1.5 μm), and the strength and toughness of N-Q-T 28MnB5 steel are significantly higher than that of Q-T 28MnB5 steel. A further analysis based on the Hall-Petch relationship reveals that the strength improvement of N-Q-T 28MnB5 steel is related to the refinement of lath martensite. At the same time, due to the refinement of lath martensite,the high angle grain boundaries ratio of N-Q-T 28MnB5 steel (34.9%) is higher than that of Q-T 28MnB5 steel (25.1%), which is beneficial for generating more retained austenite to inhibit the crack propagation and indirectly improve toughness.
    Effect of aging time on microstructure and mechanical properties of T91 steel
    Zhang Renshan, Zhang Peng, Zong Xiaohui, Kang Xueqin
    2023, 48(1):  145-148.  doi:10.13251/j.issn.0254-6051.2023.01.025
    Abstract ( 50 )   PDF (564KB) ( 46 )  
    Microstructure and mechanical properties of T91 steel tube after aging at 680 ℃ for 240, 480, 720, 1200, 1680 and 2160 h were studied by means of optical microscopy, scanning electron microscopy, room temperature tensile testing and hardness testing. The results show that the microstructure of the T91 steel is tempered martensite before and after aging at 680 ℃ for different time, the grain boundaries of microstructure become more and more obvious with the increase of aging time, and the grains become coarser gradually. With the increase of aging time, the hardness of the T91 steel decreases slowly, the lower yield strength and tensile strength decrease first, then increase, then decrease and finally decrease slowly, and the elongation increases first, then decreases and finally decreases slowly. The tensile fracture of the T91 steel changes from microporous fracture to quasi cleavage fracture.
    Effect of over-aging temperature on microstructure and properties of DP1180 steel under continuous annealing process
    Zhang Jiahao, Chen Liansheng, Gao Tianyang, Xu Haiwei, Han Yun, Li Hongbin, Tian Yaqiang
    2023, 48(1):  149-154.  doi:10.13251/j.issn.0254-6051.2023.01.026
    Abstract ( 51 )   PDF (568KB) ( 35 )  
    Microstructure and mechanical properties of the DP1180 steel were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and room temperature tensile techniques. The results show that microstructure of cold-rolled annealed steel is mainly composed of ferrite (F), martensite (M) and a small amount of bainite. When over-aged at 230 ℃, the martensite is mainly lath-like, the ferrite is polygonal, and the content of granular bainite is less. With the increase of over-aging temperature, the content of lath-like martensite decreases, granular bainite increases and carbides increase obviously. With the increase of over-aging temperature, the tensile strength decreases and the elongation increases. When the over-aging temperature is 270 ℃, the tensile strength is 1255.0 MPa, the elongation is 11.39%, and the product of strength and elongation is 14.29 GPa·%, and the comprehensive mechanical properties are the best. The reasonable over-aging temperature range of the DP1180 steel should be 230-306.8 ℃.
    Effect of TMCP on microstructure and mechanical properties of Ti-Mo-Nb microalloyed low carbon steel
    Zhang Jincheng, Sun Shenghui, Cai Minghui, Zhao Wenzhu, Ding Hua
    2023, 48(1):  155-162.  doi:10.13251/j.issn.0254-6051.2023.01.027
    Abstract ( 46 )   PDF (566KB) ( 30 )  
    Effect of cooling rate of TMCP on microstructure and mechanical properties of Ti-Mo-Nb microalloyed steel was studied. The results show that as the cooling rate decreases, the ferrite grains become equiaxed and the volume fraction and grain size of the ferrite gradually increase. Reducing the cooling rate can significantly refine the size of the precipitates and increase its volume fraction, and the precipitation behavior changes from dispersive precipitation to interphase precipitation. The precipitation strengthening of ferrite improves the strength of the tested steel, as well as the formability. When the cooling rate is 28 ℃/s, an excellent combination of strength and ductility is obtained as the tensile strength of 853 MPa, the yield strength of 750 MPa, the elongation of 18.6%and the hole expansion rate of 68.5%. The grain refinement strengthening and precipitation strengthening are the main strengthening mechanisms of the tested steel, when the cooling rate is 28 ℃/s, the strength increments of grain refinement strengthening and precipitation strengthening are 206 MPa and 328 MPa, respectively.
    Effect of quenching temperature on microstructure and mechanical properties of new gear steel
    Dai Jianke, Han Shun, Li Yong, Liu Yu, Lei Simin, Wang Chunxu
    2023, 48(1):  163-168.  doi:10.13251/j.issn.0254-6051.2023.01.028
    Abstract ( 57 )   PDF (564KB) ( 43 )  
    Effect of quenching temperature on microstructure and mechanical properties of new gear steel were studied by means of scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) combined with tensile test, fracture toughness test and hardness test. The results show that after quenching at 850-1050 ℃, cryogenic treatment and tempering, the tensile strength, yield strength and hardness of the steel increase first and then decrease with the quenching temperature increasing, all reaching the maximum values at 900 ℃ and the tensile strength is 1483 MPa. Moreover, the fracture toughness reaches the maximum value 62.4 MPa·m1/2 when the quenching temperature is 1000 ℃.The spherical Mo-rich M6C carbides precipitate on grain boundary and martensite when the quenching temperature is below 1000 ℃. The M6C carbides dissolve gradually with the quenching temperature increasing, and dissolve completely into the substrate at 1000 ℃. The prior austenite grain size grows slowly with the increase of quenching temperature, when the quenching temperature is above 1000 ℃, the austenite grain coarsens rapidly, the fracture toughness and percentage reduction of area also substantially decrease.
    Optimization of annealing process of G50 ultra-high strength steel large forgings
    Gao Qi, Yang Zhuoyue, Ding Yali
    2023, 48(1):  169-174.  doi:10.13251/j.issn.0254-6051.2023.01.029
    Abstract ( 94 )   PDF (568KB) ( 36 )  
    Take 30CrMnSiA steel as comparison, phase transition process of the G50 ultra-high strength steel with typical chemical composition when heated and cooled near Ac1 was studied, meanwhile the relationship between annealing hardness and annealing specification was analyzed. The results show that the present G50 steel annealed at the temperature slightly below the Ac1 measured by means of the expansion method forms austenite and consequently cooling forms untempered martensite which leads to the hardness rise, and the original 680 ℃ annealing temperature is no longer applicable, resulting in the phenomenon of the longer the annealing time, the higher the hardness. Verification experiment of multiple batches shows that although some austenite is formed by annealing at 660 ℃ for 6 h, more softening degree of the original normalized martensite can effectively reduce the hardness of the G50 steel forgings, and it has universal applicability.
    Influence of normalizing treatment on lamellar tearing resistance of super thick H-section steel for building structure
    Zhao Peilin, Yang Dong, Wu Huiliang, Liu Chao, Li Chao, Li Chunchuan, Zheng Li
    2023, 48(1):  175-180.  doi:10.13251/j.issn.0254-6051.2023.01.030
    Abstract ( 43 )   PDF (571KB) ( 30 )  
    Ultra-thick hot-rolled H-section steel for building structure was normalized at 920 ℃, the microstructure of hot-rolled and normalized H-section steel was observed by using optical microscope and scanning electron microscope, and the difference of lamellar tearing resistance (Z-direction performance) and its relationship with microstructure were compared and analyzed.The results show that after normalizing,fine ferrite+ultrafine pearlite structure is obtained,the microstructure uniformity is significantly improved, and the grain refinement is obviously. Comparing with the hot-rolled steel, the tensile strength of the normalized steel increases by about 12 MPa, and the percentage reduction of area increases by about 13%. The refinement of matrix structure and spheroidization of inclusions after normalizing have a greater improvement on Z-direction mechanical property of the H-section steel.
    Effect of quenching and tempering process on microstructure and austenite grain growth of 42CrMo steel
    Li Hongjuan, Xiang Chenggong, Wu Qiong, Wang Zhengcai
    2023, 48(1):  181-185.  doi:10.13251/j.issn.0254-6051.2023.01.031
    Abstract ( 81 )   PDF (563KB) ( 78 )  
    Effect of 860-940 ℃ quenching and 200-600 ℃ tempering processes on microstructure of 42CrMo steel was studied, the austenite grain size of the steel was measured by using metallographic linear intercept method, and the austenite grain growth kinetic equation of the steel was established. The results show that with the increase of quenching temperature and holding time, the number of residual carbides in the 42CrMo steel decreases obviously, and the carbides gradually change from flake to granular. With the increase of quenching temperature, the lath martensite becomes more and more uniform and fine.With the increase of tempering temperature, the microstructure of the steel changes to tempered troostite and tempered sorbite. When the tempering temperature is 600 ℃, the tempered sorbite is more uniform and dense. The fitting results of austenite grain growth of the 42CrMo steel based on Beck model shows that the activation energy of austenite grain growth is 2.62×103J·mol-1
    Normalizing annealing process of 27QG090 high magnetic induction oriented silicon steel
    Lu Xiaoyu, Dong Lei, Huang Li, Liu Baozhi
    2023, 48(1):  186-189.  doi:10.13251/j.issn.0254-6051.2023.01.032
    Abstract ( 42 )   PDF (567KB) ( 39 )  
    Normalizing annealing of 27QG090 high magnetic induction oriented silicon steel was completed in laboratory by using pilot-scale test platform, and the microstructure and macro texture were analyzed by means of optical microscope, X-ray diffractometer, TEM and EDS. The results show that the microstructure of the 27QG090 steel after normalizing annealing is ferrite, the macro texture is mainly α, α* and copper texture, and with weak Gauss texture. The precipitate after normalizing annealing is mainly AlN, whose average size is about 40 nm. Comprehensive analysis shows that the optimal normalizing annealing process is heating at 1120 ℃ for 3 min and at 920 ℃ for 3 min, then 100 ℃ water quenching.
    Effect of hot isostatic pressing on soft magnetic properties of Fe-based amorphous/nanocrystalline alloy
    Yang Yuanzheng, Shi Junlei, Xiao Guihua, Xu Jia, Chen Mo, Luo Ting
    2023, 48(1):  190-192.  doi:10.13251/j.issn.0254-6051.2023.01.033
    Abstract ( 34 )   PDF (572KB) ( 31 )  
    Effect of hot isostatic pressing (HIP) process on soft magnetic properties of Fe-based amorphous/nanocrystalline alloys was investigated by introducing HIP into the annealing process of amorphous strip cores on the basis of the optimum annealing temperature for heat treatment at high-purity nitrogen atmosphere. The crystal structure, core inductance L and magnetic loss Ps of Fe-based amorphous strip were measured by X-ray diffractometer, precision magnetic component tester and soft magnetic AC equipment. The results show that at a high frequency of 100 kHz and working magnetic flax density Bm=0.1 T, the coercivity and magnetic loss of the nitrogen-protected annealed specimens are 2.04 A/m and 10.10 W/kg, while the hot isostatic pressed specimen are 1.33 A/m and 6.58 W/kg, which reduced by 53.4% and 34.9%, respectively. The effective permeability and quality factor of the nitrogen-protected annealed specimen are 11 579 and 0.46, while the hot isostatic pressed specimen are 15 980 and 0.70, which increased by 38.0% and 52.2%, respectively.
    Effect of tempering temperature on microstructure and properties of 40CrMoVNbTi steel
    Sun Yongzhen, Cheng Juqiang, Zhao Xiaohan
    2023, 48(1):  193-197.  doi:10.13251/j.issn.0254-6051.2023.01.034
    Abstract ( 62 )   PDF (631KB) ( 36 )  
    Effect of tempering temperature on microstructure and mechanical properties of 40CrMoVNbTi steel was investigated by means of 780 ℃ subcritical quenching and tempering at different temperatures. The mechanical properties, microstructure and impact fracture of the 40CrMoVNbTi steel tempered at different temperatures were observed and analyzed. The test results show that the strength decreases and the plastic index increases with the increase of tempering temperature, and the impact absorbed energy value tempered at 300 ℃ is the lowest and the temper brittleness occurs. The tensile strength of the 40CrMoVNbTi steel tempered at 200 ℃ is 2150 MPa and KV2 is 23.8 J. When tempered at 550-600 ℃,the microstructure of the 40CrMoVNbTi steel is tempered sorbite, the tensile strength is 1190-1070 MPa and KV2 is 94-123 J, and the mechanical properties can meet the requirements of AISI 4140 steel and have a high impact property.
    Spheroidizing of modified 4Cr5Mo2MnV1Si die-casting module steel
    Tian Wei, Li Nan, Lin Shengxiu, Pan Weiwei, Zhong Qingyuan
    2023, 48(1):  198-201.  doi:10.13251/j.issn.0254-6051.2023.01.035
    Abstract ( 42 )   PDF (564KB) ( 34 )  
    Spheroidized microstructure of modified 4Cr5Mo2MnV1Si die-casting module steel didn't meet the technical requirements by the traditional spheroidizing treatment of “residual heat annealing+normalizing+isothermal spheroidizing annealing”, then the traditional spheroidizing process was improved, and the microstructure and hardness of the specimens treated by the improved process were tested. The results show that after residual heat annealing+normalizing+isothermal spheroidizing annealing, and then heated at 1010 ℃ for 0.5 h by furnace cooling to different temperatures (820, 790 and 760 ℃) held for 1 h by air cooling, the microstructure of the steel is lath martensite and carbide particles uniformly dispersed on the matrix, but the hardness is higher than 400 HBW, which can not meet the requirement of spheroidizing structure with hardness less than 240 HBW. However, when heated at 1010 ℃ for 0.5 h air-cooled to room temperature and then tempered at 820, 790 and 760 ℃ for 1 h, the microstructure is equiaxed ferrite with particle-like carbides uniformly distributed, the hardness is 321, 235 and 245 HBW respectively. And the tempering effect at 790 ℃ is the best, the spheroidization grade reaches GB3, the hardness is less than 240 HBW. In conclusion, the spheroidizing treatment after forging of the modified 4Cr5Mo2MnV1Si die-casting module can be realized by using residual heat annealing+normalizing+high temperature tempering (790 ℃) instead of residual heat annealing+normalizing+isothermal spheroidizing annealing.
    SURFACE ENGINEERING
    Preparation of self-passivation W-Cr-Y alloy layer and its oxidation resistance
    Wang Juzhuang, Wu Tao, Tian Linhai, Lin Naiming, Wang Zhenxia, Qin Lin, Wu Yucheng
    2023, 48(1):  202-206.  doi:10.13251/j.issn.0254-6051.2023.01.036
    Abstract ( 33 )   PDF (610KB) ( 44 )  
    In order to prevent or alleviate the oxidation of tungsten oxidation, a W-Cr-Y self-passivation alloy layer was prepared on the surface of pure tungsten by using double-glow plasma surface metallurgy technology. The microstructure and phase compositions of W-Cr-Y alloy layer were analyzed by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The oxidation resistance of the alloy layer was studied under a high temperature atmospheric condition which simulating the cooling failure accident of the nuclear fusion power station. The results show that when the preparation temperature is 800, 900,1000, 1100 ℃, respectively, the W-Cr-Y alloy layer with a thickness of more than 20 μm and composed of W(Cr, Y) solid solution is all successfully formed on the surface of pure tungsten. Moreover, the thickness of the alloy layer prepared at 1000 ℃reaches 35 μm, the surface is smooth and compact, and an excellent defect free metallurgical bonding is obtained between the alloy layer and the tungsten matrix. After oxidation at 1000 ℃ for 10 h, no continuous self-passivation alloy layer is formed on the surface of the W-Cr-Y alloy layer prepared at low temperatures (800 ℃ and 900 ℃), and the oxidation resistance is poor, however,a compact and flat oxide skin is formed on the surface of the alloy layer prepared at high temperatures (1000 ℃ and 1100 ℃). The W-Cr-Y alloy layer prepared at 1000 ℃ has the minimum oxidation mass gain and the optimal antioxidant effect.
    Microstructure and wear performance of Ni-WB2 composite clad layer
    Liu Lingbo, Yang Guirong, Song Wenming, Li Yamin, Ma Ying
    2023, 48(1):  207-216.  doi:10.13251/j.issn.0254-6051.2023.01.037
    Abstract ( 34 )   PDF (616KB) ( 28 )  
    Ni-WB2 composite clad layer was prepared on the 45 steel substrate through vacuum cladding technology. The microstructure of the clad layer was characterized by means of SEM, EDS and XRD, and wear performance was studied by using pin-disc type wear apparatus. The results show that the Ni-WB2 composite clad layer is dense, and a strong metallurgical bond formed at the interface between the clad layer and the substrate. The clad layer can be subdivided into reticular zone, transition zone and diffusion zone based on its microstructure, and the reticular composite zone is divided into area Ⅰ and area Ⅱ. The diffusion zone is mainly composed of Fe-based solid solution and Ni-based solid solution. The main phases of the transition zone are γ-Ni and chromium carbide, and the main compositions of the reticular composite zone are Ni-based alloy, chromium carbide, WB2, nickel silicon eutectic and complex comppund formed owing to the chemical combination between the WB2 and elements of nickel-based alloy. When the WB2 content is lower than 20%, both the wear rate and friction factor of the Ni-WB2 composite clad layer decrease gradually with the increase of WB2 content. When the WB2 content is 15%, the wear rate and friction factor of Ni-WB2 composite clad layer decrease by 48.94% and 14.62% respectively compared with that of the 45 steel substrate. During the wear process, the load supporting effect of the hard phase with network distribution and the formation of WOx oxide are conducive to reduce the friction and wear of the Ni-WB2 composite clad layer.
    Microstructure and properties of high speed laser clad Al-Si coating on Mg-Gd-Y-Zr magnesium alloy
    Yang Jiaoxi, Huang Kai, Wu Feiyu, Sun Hongbo, Yang Daijun, Li Shuguang, Ge Xueyuan, Wang Miaohui
    2023, 48(1):  217-223.  doi:10.13251/j.issn.0254-6051.2023.01.038
    Abstract ( 42 )   PDF (608KB) ( 34 )  
    Microstructure and properties of Al-Si coating prepared on the surface of Mg-Gd-Y-Zr magnesium alloy by high-speed laser cladding process were characterized by means of optical microscope (OM), X-ray diffractometer (XRD), scanning electron microscope (SEM) and electrochemical test and wear test, and the metallurgical mechanism and wear and corrosion resistance of the substrate and Al-Si coating were analyzed. The results show than the microstructure of clad coating consists of dendritic α-Mg solid solution, irregular massive Mg2Si, α-Mg+Mg17Al12 eutectic and petal-like Mg2Al3. Due to grain refinement strengthening and secondary phase strengthening, the hardness of the Al-Si coating reaches 160 HV0.1. In addition, compared with the magnesium alloy substrate, the corrosion resistance of the Al-Si coating is significantly improved, the self-corrosion potential is increased by about 200 mV, the self-corrosion current density is reduced by 2 orders of magnitude, and the anti-wear effect is increased by 30.7%, which indicate that the Al-Si coating is expected to become a more promising wear and corrosion resistant protective coatings for rare earth magnesium alloys.
    Influence of plasma spray welding pool temperature on microstructure and properties of welding layer based on real-time measurement
    Wu Mian, Pan Lin, Li Yinhua, Yu Siliang
    2023, 48(1):  224-231.  doi:10.13251/j.issn.0254-6051.2023.01.039
    Abstract ( 41 )   PDF (605KB) ( 29 )  
    Mainly due to the problems of relying on manual intervention and low level of automation, the molten pool temperature varies dramatically during plasma spray welding, and the quality of spray welding layers is significantly affected. As a result, real-time control of the molten pool temperature in the spray welding process is an unavoidable choice for the advancement of plasma spray welding technology. In order to study the influence of the temperature change of the molten pool on the microstructure and properties of the spray welding layers and to lay the groundwork for developing the real-time monitoring technology, the on-line monitoring method was adopted to measure the temperature of the molten pool during the spray welding process in real time, and the influence of the temperature of the molten pool on the macromorphology, microstructure composition and microhardness of the spray welding layers was analyzed. The results reveal that when the molten pool temperature is maintained at around 1400 ℃ in the plasma spray welding process, the spray welding layers have good microstructure and characteristics. When the molten pool temperature is too low during the spray welding process, it is easy to cause the formation of oxide inclusions in the near fusion zone. When the molten pool temperature is too high during the spray welding process, the dilution rate of the spray welding layer is likely to increase. When the spray welding current is 110 A, the microhardness of the front sprayed layer is (670±26) HV0.1, which is significantly higher than that of the middle sprayed layer as (550±20) HV0.1; when the spraying current changes from 70 to 110 and to 150 A, the microhardness of the spray welding layers shows a trend from high to low.
    Numerical simulation and experiments of laser cladding of nickel-based alloy coating on stainless steel surface
    Wang Bingtao, Xiong Zonghui, Sun Yaoning
    2023, 48(1):  232-237.  doi:10.13251/j.issn.0254-6051.2023.01.040
    Abstract ( 53 )   PDF (604KB) ( 37 )  
    In order to improve the cladding quality of stainless steel surface and explore the influence of energy densities on the cladding quality of nickel-based alloy coating prepared by laser cladding on stainless steel surface, the numerical simulation of laser cladding of the Ni35 alloy coating on the 304 stainless steel was carried out by using Visual-Environment software and based on Gaussian body heat source model by varying the laser power to obtain different energy density inputs, and the laser power corresponding to the energy density was used for the experiment verification. The simulation results show that when the laser power is 900 W, the scanning speed is 6 mm/s and the laser spot radius is 1 mm, the laser energy density is 75 J/mm2, then the obtained peak temperature of the simulated temperature distribution cloud map is 2459.55 ℃, which is in the reasonable temperature range(2400-2600 ℃). Under these parameters, the experiment verification results show that the macromorphology of the coating is fine, the microstructure is compact, and a good metallurgical bonding is formed between the coating and the substrate.
    Properties of cold spray repaired coating on 2Cr13 steel extrusion mold for PVC plastic
    Feng Zhongda, Adayi Xieeryazidan
    2023, 48(1):  238-244.  doi:10.13251/j.issn.0254-6051.2023.01.041
    Abstract ( 41 )   PDF (606KB) ( 28 )  
    To repair a failed PVC plastic extruder mold, Cu-Al2O3 coating was prepared on the surface of the 2Cr13 steel by low-pressure cold spray technology. By simulating the forming process of coating particles, it is found that the higher the inner energy of the coating closer to the substrate, the better the binding effect. In order to ensure the wear and corrosion resistance of the repaired mold, the coating were ground and polished to different thickness, and then the propertieswere compared. Scanning electron microscopy was used to observe morphology of the coating, immersion mass loss method and salt spray corrosion test were used to analyze the corrosion resistance of coatings, static indentation method was used to test the hardness of the coating, friction and wear testing machine was used to test the wear resistance of the coatings. The results show that the coating has a uniform structure, the porosity of the coating increases with the increase of the distance from the jointing surface, the corrosion resistance of the coating in HCl is better than that of the substrate, however in the salt spray test, the coating is obviously corroded, and AlCl3 and CuO products are formed. The closer the coating position is to the joining surface, the higher the hardness of the coating, the more obvious the work hardening effect, the smaller the wear amount when rubbing with hard alloy, and the wear resistance is gradually improved. When the thickness of the polished coating is 1 mm, the wear resistance of the coating is the best, and the extruder mold can be effectively repaired.
    Comparison of tribological performance between ion sulfurized layer and liquid sulfurized layer of W6Mo5Cr4V2 steel
    Zheng Zhaozhuo, Jin Hong, Wang Fan, Jiang Haoning, Ma Xiaofeng, Ma Ning
    2023, 48(1):  245-248.  doi:10.13251/j.issn.0254-6051.2023.01.042
    Abstract ( 52 )   PDF (666KB) ( 40 )  
    Tribological performance as wear properties, wear scar morphology, wear degree and S content change of sulfurized layer on the surface of the W6Mo5Cr4V2 steel prepared by ion sulfurization and liquid sulfurization were analyzed by means of friction and wear test, wear surface morphology measurement and EDS analysis, and the stability and reliability of ion sulfurized part and liquid sulfurized part were comprehensively compared by appearance, size detection and microscopic wear morphology through operation test. The results indicate the friction coefficient, service life, maximum depth and area of wear scar and sulfur content of ion sulfurized layer are all equal to or better than those of liquid sulfurized layer. The operation test results show that both ion sulfuration and liquid sulfuration can meet the performance needs of the products.
    FAILURE ANALYSIS
    Analysis and improvement of unqualified magnetic properties of vacuum annealed DT4E electromagnetic pure iron
    Xu Feng, Wu Xiaowei
    2023, 48(1):  249-252.  doi:10.13251/j.issn.0254-6051.2023.01.043
    Abstract ( 45 )   PDF (616KB) ( 37 )  
    Coercivity of a DT4E electromagnetic pure iron part after vacuum annealing exceeds the design requirements. In order to solve this problem, the DT4E electromagnetic pure iron was vacuum annealed at 860-1150 ℃ for 4 h to analyze the effects of annealing temperature, magnetic test ring size and impurity compositions in raw materials on the magnetic properties. The results show that with the increase of annealing temperature, the magnetic induction intensity B2500 changes as “M” type, the coercivity Hc changes as “V” type, and the change trend of maximum permeability μm is opposite to that of the coercivity. The optimum vacuum annealing temperature is 900 ℃,at which the magnetic induction intensity B2500 is 1.63 T, the coercivity Hc is 25.19 A/m, and the maximum permeability μm is 23.64 mH/m, all meeting the design requirements.Moreover, the size of the magnetic test ring has no significant effect on the measurement results of the magnetic properties of the DT4E electromagnetic pure iron. The content of impurity elements in raw materials has a great influence on magnetic properties. When the C content is higher, the permeability decreases and the coercivity increases, which easily leads to unqualified magnetic properties.
    Fracture analysis of automobile stabilizer bar
    Liu Huadong, Shao Baiming, Li Junwan
    2023, 48(1):  253-256.  doi:10.13251/j.issn.0254-6051.2023.01.044
    Abstract ( 80 )   PDF (608KB) ( 54 )  
    A stabilizer bar of automobile broke was failed in a short mileage during the durability test, then the fracture cause was analyzed by physical and chemical inspection, metallographic inspection and fracture analysis of the failed parts with direct reading spectrometer, hardness tester, metallographic microscope and scanning electron microscope, and in combination with the processing process of the stabilizer bar. The results show that the fracture morphology of the failed stabilizer bar is mainly intergranular, there are fatigue striations in the extended region, and the final fracture is dimpled. This is mainly due to the introduction of hydrogen through pickling treatment during the processing of the stabilizer bar, resulting in delayed cracking of the stabilizer bar first, and then fatigue and propagation in the durability test until the final fracture.
    Cracking analysis of 42CrMo steel hexagon head bolt by hot dip galvanizing
    Zhao Quanyu, Liang Jiajun, Chen Xupeng, Tong Bo, Xia Guohua, Yan Qin, Ding Zhimin
    2023, 48(1):  257-260.  doi:10.13251/j.issn.0254-6051.2023.01.045
    Abstract ( 58 )   PDF (610KB) ( 47 )  
    Cracks were found at the round corners of the 42CrMo steel hexagon head bolts after hot dip galvanizing through magnetic particle inspection. Fracture, microstructure and composition analysis of the cracked bolt were carried out by means of optical microscope, SEM and EDS. The results show that the fracture of the cracked bolts conforms to the characteristics of hydrogen embrittlement, and the mass fraction of hydrogen near the fracture is as high as 4×10-6.The crack characteristics are consistent with the hydrogen embrittlement crack characteristics. The microstructure on both sides of the crack is normal quenched and tempered structure and zinc residue is found in the crack, which can exclude that the crack is caused by abnormal tissue or quenching. Therefore, it can be reasonably inferred that the crack of 42CrMo steel hexagonal bolt is hydrogen-induced cracking, which occurs in the process of hot dip galvanizing.
    Cracking failure analysis of ultra-high strength martensite steel
    Sun Lu, Li Jianying, Wei Huanjun, Li Zheng, Li Tao, Cheng Xiaoying
    2023, 48(1):  261-265.  doi:10.13251/j.issn.0254-6051.2023.01.046
    Abstract ( 61 )   PDF (604KB) ( 45 )  
    Cracked and uncracked ultra-high strength martensitic steel parts and the corresponding raw materials steels were analyzed due to phenomenon of cracking of the parts in their safe service period. The U-shaped bending beam experiment results in constant strain test show that both the raw materials of cracked and uncracked parts have good resistance to delayed cracking caused by hydrogen. Due to the difference of the production processes, the microstructure of the raw materials is plate martensite for the cracked part and lath martensite for the uncracked part, respectively. When machining into the same kind of parts, due to the structural difference of the martensite, the internal collaborative deformation uniformity is different in machining and forming processes, thus the residual stress in the cracked parts is larger. In addition, the stress concentration is caused by the formation of a large number of dislocation pile-ups in the structure of cracked parts, the local stress reaches the limit first, resulting in cracking.
    Analysis and improvement on quenching stripe of thin gauge wear resistant steel
    Huang Peng, Zhen Fan, Du Ping, Qu Jinbo
    2023, 48(1):  266-269.  doi:10.13251/j.issn.0254-6051.2023.01.047
    Abstract ( 47 )   PDF (607KB) ( 40 )  
    Quenching stripe with hardness difference problem of thin gauge wear resistant steel plates was studied by means of microstructure and hardness examination combined with equipment and process analysis. The results show that the main reasons for the problem are the different water flows and cooling rates between the groove and collar regions of spiral rollers of the quenching machine. By optimization of the quenching temperature, water flow, roller speed and roll gap, the quenching stripe problem is solved and good plate flatness is obtained.
    STANDARDIZATION
    Simple discussion on standards about post-weld heat treatment of 347H pressure pipe for hydrogen production unit
    Zhang Yucheng, Jia Haomei
    2023, 48(1):  270-276.  doi:10.13251/j.issn.0254-6051.2023.01.048
    Abstract ( 60 )   PDF (607KB) ( 42 )  
    Classification of post-weld heat treatment of the 347H stainless steel was introduced, and the status quo of domestic and foreign standards of post-weld heat treatment for austenitic stainless steels was analyzed. At present, domestic and foreign standards have different provisions on the post-welding heat treatment of the 347H stainless steel pipes. The NB/T 10068—2018 standard proposes that the operating temperature and thickness range should be used as the implementation conditions of post-weld heat treatment of the 347H stainless steel, which provides guidance for the post-welding heat treatment of the 347H pressurized pipe used in hydrogen production plant and has certain reference significance. But some of the provisions of the standard are not perfect, including some problems in ferrite measurement sequence, ferrite content qualified value and ferrite measurement method. So it is suggested to adjust the measurement of ferritic content of weld to before post-weld heat treatment, remove the lower limit of ferrite number of 3 FN after solution and stabilization heat treatment, add the qualified value requirement of ferrite content of E(R)16.8.2 cladding metal, and define the detection method of ferrite content. At the same time, the NB/T 10068—2018 standard is not perfect on the implementation conditions of post-welding stabilization heat treatment, so it is suggested that the exemption conditions for post-welding heat treatment should be set in combination with engineering practice experience and foreign advanced standards. For thin-walled workpieces with operating temperature ≥500 ℃ and welded joints with small constraint degree, the post-welding heat treatment should be exempted, so as to maintain the scientific and advanced nature of the standard. The NB/T 10068—2018 standard does not fully disclose the related patent information, thus the patent information disclosure should be done well subsequently to prevent intellectual property hijacking of standards.