Heat Treatment of Metals

Xu Yueming, Li Qiao, Luo Xinmin, Cong Peiwu

2020, 45(4): 1-4. doi:10.13251/j.issn.0254-6051.2020.04.001

Abstract ( 242 )

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The main characteristics and developing direction of high-end oriented heat treatment were analyzed in view of the process of realizing the high-quality development of heat treatment industry and industrial upgrading in China. Aiming at the developing requirements of materials heat treatment processes and heat treatment quality improvement under the background of intelligent manufacturing, the key technology roadmap for realizing high-end oriented heat treatment and the relative cutting-edge technologies were pointed out.

Study and consideration on pollution coefficient of metal heat treatment process

Wang Weilin, Tong Xiaohui, Wu Jinjun, Chen Xiaohui, Zhao Qiang, Liu Yun, Jiao Ju

2020, 45(4): 5-9. doi:10.13251/j.issn.0254-6051.2020.04.002

Abstract ( 133 )

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Energy conservation and environmental protection is the prerequisite for the transformation and upgrading of China's manufacturing industry. The green production and energy conservation of manufacturing industry is an important symbol of the development of manufacturing industry. Heat treatment is one of the main basic manufacturing technologies, its green and energy-saving level reflects the overall development of the manufacturing industry. It is of positive significance to study the wastes characteristics of heat treatment process itself. Based on the work results of the project “the second national census of industrial pollution sources and the production and emission accounting of industrial pollution sources”, and in view of metal heat treatment process and procedures, a profound study of its pollution generating characteristics and pollution coefficient,was carried out, in order to actively provide a inspection basis for the second national census of industrial pollution sources total pollution production accounting.

Continuous cooling transformation behavior of austenite in 0.6Ni alloyed medium carbon steel

Jiang Bo, Hu Xuewen, Zhou Leyu, Wang Zhilin, Zhao Haidong, Liu Yazheng

2020, 45(4): 10-15. doi:10.13251/j.issn.0254-6051.2020.04.003

Abstract ( 149 )

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The dynamic and static continuous cooling transformation and effects of deformation and nickel in 0.6Ni medium carbon steel were carefully investigated by means of hot simulation tests, optical microscope and SEM observations and Vickers hardness test. Experimental results show that the ferrite and pearlite transformations are effectively suppressed while the bainite and martensite transformations are greatly promoted by the deformation in austenite region of the tested steel. Then, the critical cooling rate of full martensite is also lowered from 5 ℃/s to 3 ℃/s. The hardness of full martensite is 810 HV0.1 at the cooling rate of 3 ℃/s under the dynamic continuous cooling condition. However, the hardness of full martensite is 689 HV0.1 at the cooling rate of 5 ℃/s under the static continuous cooling condition. The improvement of martensite hardness can be attributed to the refinement of martensite due to the deformation recrystallization of austenite. The ferrite and pearlite transformations are suppressed and the bainite and martensite transformations are promoted by the addition of 0.6Ni because of the improvement of austenite stability. Then, the Ms temperature is lowered from 329 ℃ to 304 ℃ and also the critical cooling rate of martensite transformation is reduced from 0.5 ℃/s to 0.3 ℃/s. Compared with that of the addition of 0.4Mn, the ferrite and pearlite transformation is largely hindered and the Ms temperature is lowered from 320 ℃ to 304 ℃ by the addition of 0.6Ni. At the same time, the microstructure after cooling is also effectively refined.

Effect of 0.2%Sn addition on microstructure and mechanical properties of Al-Si-Mg alloy

Yin Xin, Yin Dengfeng, Wang Kaixian, Li Jilin, Chi Guoming, Cao Hanquan

2020, 45(4): 16-21. doi:10.13251/j.issn.0254-6051.2020.04.004

Abstract ( 114 )

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Effect of 0.2%Sn addition on the microstructures and mechanical properties of Al-Si-Mg alloy with as-cast and T6 heat treated state was studied by optical microscopy (OM), scanning electron microscopy (SEM), energy spectrum analysis (EDS) and tensile testing. The results show that the addition of 0.2%Sn refines the morphology of the eutectic silicon phase and makes the primary α-aluminum grains more uniform, which reduces and improves the morphology and distribution of harmful impurities. At T6 state (solution treatment at 535 ℃ for 6 h+aging at 160 ℃ for 5 h), the proof strength, plastic extension and tensile strength of the alloy reach 262.3 MPa and 305.1 MPa respectively, is increased by 9.8% and 12.4% higher than that of the base alloy without Sn addition, and the elongation is 4.32%, which is increased by 22.6%.

Microstructure and properties of Mo_f/TiAl composites prepared by foil-fiber-foil method

Tao Guidong, Li Hengkui, Xu Zhongxuan, Chen Zhiyuan, Sun Hongliang

2020, 45(4): 22-28. doi:10.13251/j.issn.0254-6051.2020.04.005

Abstract ( 84 )

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Mo_f/Ti48Al composite was successfully prepared by foil-fiber-foil method and hot pressing sintering, and the effects of Mo fiber on the microstructure and mechanical properties of the TiAl alloy were analyzed. The results show that through the two-step low temperature hot pressing of 635 ℃, 3 MPa for 10 h+680 ℃, 3 MPa for 4 h, the Al has fully reacted and the TiAl foil laminated material forms a dense Ti/TiAl₃ plate nearly void-free. Then in the high temperature reaction annealing at 1200 ℃ for 36 h, Ti and TiAl₃ continue to react to form γ-TiAl and α-Ti₃Al phases. The diffusion reaction of Mo fiber with matrix alloy after high temperature annealing forms a diffusion region, in which the main phases are TiMo and AlMo₃. The Mo fiber and matrix alloy are closely combined through diffusion, and there are no voids or cracks formed in the interface. Compared with the alloy without adding Mo fiber, the flexural properties of the composite with 10vol% Mo fiber are obviously improved, and the Mo fiber plays a toughening role in the alloy.

Effects of Zr, Mn and Cr addition on microstructure and properties of Al-Zn-Mg alloy

Deng Ke, Sun Daxiang, Tang Weixue, Wan Li, Cai Zhizhi, Zhou Sigen

2020, 45(4): 29-33. doi:10.13251/j.issn.0254-6051.2020.04.006

Abstract ( 90 )

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Effects of Zr, Mn and Cr additions on microstructure and properties of Al-Zn-Mg alloy were investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy and tensile test. The results show that the combined addition of Zr, Mn and Cr in the Al-Zn-Mg alloys leads to precipitates of a large number of (Al,Cr)₃Zr particles with 10-20 nm size, which coherent with the matrix. These irregularity dispersoids can strongly pin the dislocation, and hinder the dislocation movement and subgrain boundary migration and significantly inhibit grain recrystallization and growth of subgrain. The tensile strength and yield strength of Al-Zn-Mg alloy added with Zr, Mn and Cr are increased by 34 MPa and 19 MPa, respectively, which has better processability and mechanical properties.

Effect of nitrogen content on microstructure and properties of 25Mn2CrVS bainite type non-quenched and tempered steel

Cai Mengru, Duan Meiqi, Hong Zhiwei, He Yizhu, Wang Ruizhen

2020, 45(4): 34-39. doi:10.13251/j.issn.0254-6051.2020.04.007

Abstract ( 77 )

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Effect of nitrogen content (mass fraction of 0.016%, 0.029% and 0.049% respectively) on the microstructure and mechanical properties of 25Mn2CrVS bainite type non-quenched and tempered steel was studied. The results show that the microstructure of all the tested steels consists of lath bainite, granular bainite and ferrite. When the nitrogen content increases from 0.016% to 0.029%, the strength and toughness of the tested steel increase, and the microstructure is refined. When the nitrogen content increases to 0.049%, the strength of the steel is basically unchanged, but the toughness drops sharply, the microstructure is obviously coarsened, and the grain boundary ferrite is formed. Vanadium in solid solution can promote the formation of lath bainite at grain boundary, and VN particles precipitated from austenite can promote the formation of acicular ferrite.

Effect of Mg₂Si phase on microstructure and mechanical properties of as-extruded AZ31 magnesium alloy

Zheng Liuwei, Liang Wei, Zhang Huiyun, Nie Huihui, Hao Xinwei

2020, 45(4): 40-44. doi:10.13251/j.issn.0254-6051.2020.04.008

Abstract ( 75 )

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Mg₂Si phase was introduced into AZ31 magnesium alloy by replacing Al with Al-Si master alloy combined with hot extrusion. Effect of Mg₂Si phase on the microstructure and mechanical properties of AZ31 magnesium alloy was studied by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD) and electronic universal testing machine.The results show that the Mg-3(Al-Si)-Zn extrusion microstructure presents obvious bimodal distribution, and the Mg₂Si particle phase can promote dynamic recrystallization by particle stimulated nucleation (PSN), and the microstructure is refined dramatically around Mg₂Si particles. The yield and tensile strength of Mg-3(Al-Si)-Zn alloy are improved to 175 MPa and 269 MPa, respectively, while the elongation decreases slightly after the introduction of Mg₂Si strengthening phase.

Recrystallization law of micro-carbon low alloy deep drawing dual phase steel

Zhou Liutao, Pan Hongbo, Pan Shuo, Wu Jiewen

2020, 45(4): 45-50. doi:10.13251/j.issn.0254-6051.2020.04.009

Abstract ( 74 )

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Recrystallization microstructure evolution and recrystallization kinetics of a micro-carbon low alloy steel during batch annealing were studied. According to the calculation of the Johnson-Mell theory and the Arrhenius recrystallization activation energy, the thermodynamic model of the relationship between recrystallization volume fraction and annealing temperature and isothermal time was established, and so was the dynamic model of the relationship between the annealing temperature and the time required for complete recrystallization. The results show that the two models verify each other and the recrystallization incubation period and completion time are shortened with the increase of annealing temperature. At the same temperature, the volume fraction of recrystallization increases until complete recrystallization with the increase of holding time. In addition, it is found that there is a competition phenomenon between recrystallization and phase transformation when annealing temperature is near Ac₁. The recrystallization process is the main phenomenon as the holding time is short while phase transformation process has a perfectly advantage as the holding time is long.

Comparison and analysis of cooling transformation for 2.25Cr-1Mo and 2.25Cr-1Mo-0.25V steels

Hou Jingchao, Li Jie, Wu Yanyang, Yuan Jincheng, Yin Weijiang, Niu Hongxing

2020, 45(4): 51-54. doi:10.13251/j.issn.0254-6051.2020.04.010

Abstract ( 86 )

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Cooling transformations of 2.25Cr-1Mo and 2.25Cr-1Mo-0.25V steels were researched by phase change instrument, OM and SEM, and the effect of V on the cooling transformation was analyzed. The results show that compared with the CCT curves of 2.25Cr-1Mo steel, both the ferrite and the bainite transformation zones of the CCT curves for 2.25Cr-1Mo-0.25V steel shift right. Pearlite transformation zone is unable to be observed under existing test conditions. Adding V into 2.25Cr-1Mo steel improves the hardenability. 2.25Cr-1Mo-0.25V steel can transform into martensite partially under 48 000 ℃/h cooling rate. V can refine microstructure of the steel, the microstructure of 2.25Cr-1Mo-0.25V steel is finer than that of 2.25Cr-1Mo steel under 800 ℃/h cooling rate.

Microstructural evolution of Al-Cu-Mg-Mn-Sc-Zr alloy during homogenization

Liao Simin, Su Yuchang, Hai Fenglong

2020, 45(4): 55-59. doi:10.13251/j.issn.0254-6051.2020.04.011

Abstract ( 73 )

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The microstructure evolution of Al-Cu-Mg-Mn-Sc-Zr alloy was investigated by electron probe microanalysis (EPMA). The results show that there are a large number of the eutectic network-like Al₂Cu phase and Al₆(Mn,Cu) phase in the grain boundary, and there is less formation of the primary Al₃(Sc,Zr) and Al₂CuMg phases. The W (AlCuSc) phase in the alloy can not be detected. Al₂Cu almost all dissolves into the Al matrix after homogenizing at 520 ℃ for 12 h and dissolves completely after 16 h, which is basically consistent with the kinetics analysis result of the homogenization process for 14.1 h. However, the Al₆(Mn,Cu) phase can not dissolve. Furthermore, some coarse and discontinuous arranged W phase particles can form during the homogenization process. So the microstructural evolution during the homogenization is affected by the Sc addition.

Microstructure and properties of TP347HFG steel after high temperature service

Song Tao, Wang Zhiwu

2020, 45(4): 60-62. doi:10.13251/j.issn.0254-6051.2020.04.012

Abstract ( 66 )

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The microstructure and properties of superheater tube made of TP347HFG steel after running for 1.2×10⁴ h and 7.5×10⁴ h at high temperature was analyzed by means of metallographic microscope, SEM, EDS and universal testing machine. The results show that the TP347HFG steel after service for 1.2×10⁴ h and 7.5×10⁴ h at high temperature can still maintain obvious twin characteristics, the NbC precipitated is conducive to maintaining the structural stability of the material. The mechanical properties of the material can remain stable after service at high temperature, the strength increased with the serviced time extend while the plasticity changed little.

Microstructure and mechanical properties of 0.2C-5Mn-1.5Al medium manganese TRIP steel

Wang Runxun, Wang Baofeng, Li Yan, Ding Wei, Pan Hongbo

2020, 45(4): 63-68. doi:10.13251/j.issn.0254-6051.2020.04.013

Abstract ( 71 )

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The equilibrium phase diagram, microstructure and mechanical properties of 0.2C-5Mn-1.5Al medium manganese TRIP steel under different annealing processes was studied by means of calculation of phase diagram (CALPHAD) method, scanning electron microscopy (SEM), X-ray diffractometry (XRD), and tensile test. The influence of Al on equilibrium phase diagram, intercritcal annealing process, and mechanical properties are also studied. The results show that Al addition expands the intercritical region and shift the region to higher temperatures. The intercritical annealing temperature is increased, the austenite reverse transformation process is accelerated, the annealing time is shortened, the aggregation of C and Mn elements is promoted. The retained austenite content is effectively improved, and the deformation process TRIP effect is enhanced. With the increase of annealing temperature, the austenite content and elongation of 0.2C-5Mn-1.5Al steel show a trend of increasing first and then decreasing, while the yield strength decrease slightly, tensile strength continue to increase. And annealing at 760 ℃ for 3 min, the best mechanical properties are obtained, the elongation is 32%, and the strong plastic product is 35 GPa·%, which show that the addition of Al element effectively increases the comprehensive mechanical properties of manganese TRIP in 0.2C-5Mn.

Microstructure and mechanical properties of low carbon medium manganese steel treated by Q&P process

Feng Shuming, Wan Decheng, Wang Yating, Li Jie, Cui Yan

2020, 45(4): 69-74. doi:10.13251/j.issn.0254-6051.2020.04.014

Abstract ( 88 )

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The multiphase microstructures comprising tempered matensite, fresh martensite and retained austenite with the low carbon medium manganese steel containing silicon was obtained by full austenitizing Q&P process. The microstructure and mechanical properties of the steel under different heat treatment processes were studied by means of SEM, TEM, XRD and tensile testing.The results show that with the increase of quenching temperature, the tensile strength decreases at first and then increases, the yield strength decreases,and the total elongation first increases and then decreases. When quenching temperature is 250 ℃, the tested steel gain excellent comprehensive mechanical properties with tensile strength of 1331 MPa, the total elongation of 17.3%, and the product of strength-plasticity up to 23 GPa·%. This is mainly due to the multiphase microstructures with a certain proportion of film-like retained austenite which give play to TRIP effect. The continuous work-hardening ability during the tensile deformation stagewhich is helpful for the improvement of strength and plasticity. Increasing the quenching temperature to 270 ℃, the stability of retained austenite decreases, a large number of fresh martensite exists, which both makes the plasticity decrease.

Microstructure and properties of 1060 Al-based multi-layered composite reinforced with Fe-based amorphous alloy

Wang Shaohua, Sun Yueying, Ye Xi, Xie Niansuo, Jing Ran

2020, 45(4): 75-78. doi:10.13251/j.issn.0254-6051.2020.04.015

Abstract ( 63 )

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1060 Al/Fe-based amorphous alloy multi-layered composites were prepared by means of accumulative roll bonding and intermediate annealing. The microstructure, fracture morphologies, phases and mechanical properties of the Al-based composites were analyzed by using optical microscope, scanning electronic microscope, X-ray diffraction and tensile test. The results show that the Fe-based amorphous alloy undergoes partial crystallization during the intermediate annealing process at 300 ℃, and breaks up during the cumulative deformation rolling process, and the degree of breaking up increases with increasing rolling deformation passes. The composite plates softens evidently in the first 6 passes of cumulative deformation rolling, the softening effect is more obvious with the increasing passes. With the increase of accumulated rolling deformation passes, the mechanical properties of Al-based composites have changed obviously. After the second rolling deformation, the yield strength and tensile strength of the composites reach the maximum values of 140 MPa and 156 MPa respectively, and the elongation is 5.53%, reaching the best comprehensive properties.

Microstructure and texture evolution of Cu-containing low temperature oriented silicon steel during rolling process

Zhang Jishun, Ren Huiping, Jin Zili, Wu Zhongwang, Ren Dong

2020, 45(4): 79-83. doi:10.13251/j.issn.0254-6051.2020.04.016

Abstract ( 52 )

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Microstructure and texture evolution of Cu-containing low temperature oriented silicon steel during hot rolling, first cold rolling, decarbonization annealing and second cold rolling were studied by Zeiss optical microscope and X-ray diffraction. The results show that the microstructure and texture of the hot rolled specimen show obvious inhomogeneity in thickness direction. The surface and transition layers of the specimens is recrystallized, the transition layer has strong Goss texture, and the central layer has strong α texture dominated by {001}<110>. After first cold rolling, the microstructure of the specimen is compressed into a fibrous structure distributed along the rolling direction, and the texture is mainly strong α texture and weak γ texture. The recrystallization occurs after decarbonization annealing, the average grain size is 15.69 μm, and the overall texture intensity decreases, but the Goss texture intensity increases. After second cold rolling, the microstructure changes from equiaxed grain to spindle structure, and the texture is mainly weak α and strong γ texture, of which {111}<112> has the highest intensity.

Microstructure and properties of Cu-Cr-Fe-Ni alloy during thermo-mechanical heat treatment processing

Jing Qingxiu, Zhang Zehui, Wang Hang, Yang Bin

2020, 45(4): 84-89. doi:10.13251/j.issn.0254-6051.2020.04.017

Abstract ( 58 )

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Cu-0.59 Cr-0.078 Fe-0.081 Ni alloy was prepared by non-vacuum melting+hot rolling+solid solution treatment+cold rolling+aging. The effects of heat treatments and deformation processes on the microstructure, electrical conductivity and hardness of the alloy were investigated. The results show that after atmospheric melting and casting, the Cu-Cr-Fe-Ni alloy shows obvious dendritic structure. After solid solution treatment, the alloy recrystallizes, and the hardness and conductivity of it decrease correspondingly, with values of 65.9 HV0.2 and 41.7%IACS, respectively. After cold rolling, the hardness of the alloy increases significantly. When the deformation amount reaches 90%, the hardness of the alloy is as high as 144.7 HV0.2. After the deformation, the alloy hardness first increases and then decreases during the aging process at 450 ℃. When the alloy deformation is 60%, the peak aging is reached at aging 30 min, leading the hardness and conductivity to 155.5 HV0.2 and 71.4%IACS, respectively.

Microstructure and properties of bainitic steel for new heavy-duty railway frog

Wang Nan, Hu Zhihua, Wang Zhengyun, Wang Simin, Chen Jie, Luan Daocheng

2020, 45(4): 90-93. doi:10.13251/j.issn.0254-6051.2020.04.018

Abstract ( 66 )

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Microstructure and properties of a new-developed bainitic steel for heavy-duty railway frog were analyzed by using optical microscope scanning electron microscope,X-ray diffraction analyzer,impact test machine and universal test machine.The results show that bainite structure can be obtained under normalizing,XRD patterns show that the microstructure is carbide-free bainite.After normalizing followed by tempering at 300 ℃,the tensile strength of the material is up to 1380 MPa, and the imact absorbed energy is up to 63.33 J. The steel has high hardness and good anti-tempering stability, low temperature impact test,which shows that the material meets the technical requirements in low temperature environment.

Effect of electric field tempering on microstructure and properties of T8A steel

Liu Fengfang, Gong Minglong, Bai Jing, Gao Qiuzhi, Zhao Xiang

2020, 45(4): 94-98. doi:10.13251/j.issn.0254-6051.2020.04.019

Abstract ( 66 )

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Microstructure and mechanical properties of as-quenched T8A steel treated at different tempering temperature (170 ℃ and 400 ℃) for 2 h were studied without and with a 4 kV/cm DC electric field were studied by SEM, TEM. The results show that the electric field has no obvious effect on SEM micrographs of the T8A steel. After the electric field tempering, the carbides of the T8A steel has obvious spheroidizing tendency, which indicates that the electric field accelerates the tempering process. The hardness of the tempered specimen with electric field is lower than that without electric field. The impact absorbed energy of the tempered specimen with electric field at 400 ℃ decreases about 27% than that without electric field,but which at 170 ℃ increases about 14%.

Effect of two-stage aging on microstructure and properties of deformed 2A12 aluminum alloy

Yan Fan, Xu Jian, Zhang Xing, Yan Lin

2020, 45(4): 99-104. doi:10.13251/j.issn.0254-6051.2020.04.020

Abstract ( 71 )

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Effect of two-stage aging on the microstructure and properties of deformed 2A12 aluminum alloy were studied by using tensile testing machine, scanning electron microscope, metallographic microscope and other instruments. The results show that the microstructure of the alloy tends to be uniform after homogenized and annealed at 495 ℃×12 h, and more dispersed T phases are precipitated. The two-stage aging has more significant effect on improving the tensile strength of upset deformed aluminum alloy than the single-stage aging, and the temperature and time of the two-stage aging are the main factors for improving the strength. The second-stage aging temperature can't exceed 200 ℃, and the time should not exceed 6.5 h, otherwise it will cause over-melted of the material and decrease the strength.Therefore, the best heat treatment process for 2A12 aluminum alloy is 495 ℃×1 h solid solution, 100 ℃×2 h+180 ℃×6.5 h aging. After this process, the grains are refined, the secondary phase strengthening is enhanced, and the comprehensive properties of the alloy are excellent.

Low cycle fatigue behavior of Cu-Cr-Zr alloy

Jie Xiao, Zhong Qiangqiang, Wang Junfeng, Chen Jinshui, Xiao Xiangpeng

2020, 45(4): 105-109. doi:10.13251/j.issn.0254-6051.2020.04.021

Abstract ( 62 )

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The low-cycle fatigue properties and cyclic deformation behavior of Cu-Cr-Zr alloys were studied by means of low cycle fatigue (LCF) tests at room temperature. The microstructure and fatigue fracture of the alloy were analyzed by electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), and scanning electron microscopy(SEM). The results show that the relationship between the elastic strain amplitude, the plastic strain amplitude and the number of cycles can be expressed by Basquin and Coffin-Manson formulas, respectively. The cyclic hardening occurs at the later stage of fatigue deformation with a high applied total strain amplitude (Δε_t/2=0.6%), the cyclic deformation microstructure is a mixed structure of dislocation walls, dislocation clusters, and cellular substructure, and the formation of twins is observed. In addition, the fatigue fracture characteristics of the selected material at an applied total strain amplitude of 0.4% exhibit multiple fatigue sources, a large number of tearing edges, dimples, and furrows are observed in the fatigue crack propagation area.

Solution and precipitating behaviors of TiC particles in high Ti low alloy steel

Liu Luojin, Liang Xiaokai, Sun Xinjun

2020, 45(4): 110-114. doi:10.13251/j.issn.0254-6051.2020.04.022

Abstract ( 63 )

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Evolution of TiC particles during heating and cooling of high Ti (0.6wt% Ti) low alloy steel was observed by means of high temperature laser scanning confocal microscopy (LSCM). The morphology and distribution of TiC particles in the steel were analyzed by means of OM, SEM, EDS, etc and combined with Thermo-Calc software calculation. The precipitating behaviors of TiC particles were studied. The test results show that the TiC particles formed in different temperature stages have different shapes, and gradually precipitate from the matrix according to the particle diameter order from large to small. The inhibition of precipitation of small-sized TiC particles by high temperature is more remarkable. At high temperature, a plurality of adjacent large-sized TiC particles aggregate on the surface to form a flocculent morphology. And TiC particles precipitated at high temperature solid phase change from a spherical unstable state to a cubic stable morphology, but the degree of coarsening is negligible.

Effect of rolling process on microstructure and properties of 14Cr1MoR steel plate

Liu Jianfeng, Dong Fujun, Ge Qilu, Qiu Shengtao

2020, 45(4): 115-119. doi:10.13251/j.issn.0254-6051.2020.04.023

Abstract ( 71 )

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Microstructure and properties of 14Cr1MoR hot rolled steel plate with 60 mm thickness after normalizing+tempering, and simulated post-weld heat treatment were studied by using optical microscope, scanning electron microscope, tensile and impact testing machine. The results show that compared the steel plate of one-stage controlled rolling with that of two-stage controlled rolling, when the final rolling temperature is high and the cooling rate after rolling is slow, the ferrite grain size is coarser and the pearlite content is higher; the steel plate has lower strength, higher elongation, and lower impact value. After simulated post-weld heat treatment at 655 ℃ for 3 h, the yield strength and tensile strength of the two-stage controlled rolling steel plate decrease by 44 MPa and 24 MPa, respectively, and the impact absorbed energy decreases. When the simulated holding time is extended to 12 h, the strength and impact properties do not change much. The two-stage controlled rolling 14CrMoR steel plate has good mechanical properties after normalizing+tempering+simulated post-weld heat treatment at 655 ℃.

Effect of aging temperature on microstructure and pseudoelasticity of Fe_42.5Ni₂₈Co₁₇Al_11.5Ta₁ shape memory alloy

Chen Zhaoxia, Peng Wenyi

2020, 45(4): 120-123. doi:10.13251/j.issn.0254-6051.2020.04.024

Abstract ( 60 )

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Fe_42.5Ni₂₈Co₁₇Al_11.5Ta₁ (at.%) alloy was aging treated at different temperatures. Microstructure observation and phase analysis of the aged alloy were carried out by scanning electron microscopy and X-ray diffractometer, and the lattice parameters were determined through Origin Peak Fit Module software. Meanwhile, the hardness and pseudoelasticity of the alloy aged at different temperatures were measured at room temperature. The results show that, the precipitates in the grain interior change from γ′ phase to γ′ and β phases when the aging temperature increases from 600 ℃ to 650 ℃ and 750 ℃ with 60 h aging time maintained. The precipitation of β phase is related to the increase of solid solubility of Ta element in the matrix at higher aging temperature. In the single-phase precipitation mode, the alloy exhibits pseudoelasticity at room temperature, with a recoverable strain of 10.01%. However, in the two-phase precipitation mode, the alloy exhibits superelasticity at room temperature, with a small stress hysteresis and a recoverable strain of 12.41%. After aging at 650 ℃, the alloy exhibits the best pseudoelasticity at room temperature.

Effect of aging temperature on microstructure and friction properties of Ti-29Nb-13Ta-4.6Zr alloy

Liu Ran, Wang Chuanting, Gao Yuan, Wei Zhenghang, Fu Chao

2020, 45(4): 124-127. doi:10.13251/j.issn.0254-6051.2020.04.025

Abstract ( 60 )

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Ti-29Nb-13Ta-4.6Zr alloy ingot was prepared by vacuum melting. After solid solution treatment at 800 ℃ for 2 h, isothermal aging was carried out at 300-500 ℃ to study the microstructures and wear resistance of the alloy via aging hardening. The results show that, the alloy has a metastable undercooling near-β single-phase microstructure after solid solution treatment. After low temperature aging, the dispersed α phase appears inside the grains, however, at the temperature above 450 ℃ the α phase is no longer dispersively distributed but enriched at the grain boundaries. With the increase of aging temperature, the hardness of the alloy increases gradually and reaches the maximum of 253 HV0.3 at 500 ℃, and then decreases rapidly, while the friction coefficient also increases first then decreases with the increase of aging temperature. The comprehensive properties of the samples aged at 450 ℃ is the best, which has smaller friction coefficient and exhibits adhesive wear characteristics.

Effect of service temperature on shear strength of TA2/Q235 explosive composite plate

Yang Hongbo, Wang Hao, Yao Peiwen, Liu Huan, Shao Mingzeng

2020, 45(4): 128-131. doi:10.13251/j.issn.0254-6051.2020.04.026

Abstract ( 62 )

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The service process of TA2/Q235 explosive composite plate was simulated by heat treatment, and the influence of service conditions on the microstructure and shear properties of composite plate was revealed, the mechanism of shear damage was discussed, and the service temperature range of TA2/Q235 is defined. The results show that the higher the service temperature (>200 ℃) or the longer the service time is, the lower the shear strength. The main reasons for the decrease of bonding strength of TA2/Q235 explosive welded composite plate during high temperature service are the secondary recrystallizing of the interface bonding zone, and the further growth of intermetallic compounds. The TA2/Q235 explosive welded composite plate is suitable for long service below 500 ℃, and the service duration can't exceed 7 days at 500-600 ℃. If the service temperature of this material is increased to more than 500 ℃, the formation of intermetallic compounds must be strictly restricted.

Effect of annealing time on microstructure and properties of warm rolled 45 steel with pseudoeutectoid type initial microstructure

Zhang Xinyue, Yang Mingwei, Feng Yunli, Cao Kuo, Li Jie

2020, 45(4): 132-136. doi:10.13251/j.issn.0254-6051.2020.04.027

Abstract ( 83 )

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Effect of annealing time on the microstructure evolution and mechanical properties of warm rolled 45 steel with pseudoeutectoid type initial microstructure was studied by means of scanning electron microscopy, electron backscatter diffraction and tensile test. The results show that the microstructure of the warm rolled steel is of multiphase and multiscale, and the cementite is fragmented. With the increase of annealing time, the cementite gradually spheroidizes, grows up and gradually distributes evenly, and the multiphase and multiscale structure is weakened. With the annealing time increases from 15 min to 120 min, the average ferrite grain size increases from 2.32 μm to 5.62 μm, the proof strength, plastic extension decreases from 1057 MPa to 662 MPa, and the uniform elongation reaches the maximum when annealed at 120 min. Overall, the comprehensive mechanical properties of the tested steel reaches the best when warm rolled at 500 ℃, then annealed at 600 ℃ for 15 min.

Low temperature QPQ accelerating nitriding for 40Cr steel by applying DC electric field

Du Hang, Luo Defu, Chen Shengyi, Luo Jun

2020, 45(4): 137-140. doi:10.13251/j.issn.0254-6051.2020.04.028

Abstract ( 67 )

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Using 40Cr as the matrix material, the low temperature QPQ nitriding process at 450 ℃ was accelerated by applying direct current (DC) electric field and the corresponding mechanism was studied. The microstructure, thickness, hardness and phases of the nitriding layer of the treated samples were analyzed. The results show that when the DC electric field is applied and holding for 2 h, the compound layer thickness of the sample can reach 18 μm, which is similar to that of nitriding for 17 h without DC electric field. It means that the DC electric field significantly increases the nitriding speed. The surface hardness of the steel reaches 813 HV0.1 after applying DC electric field, which is 1.3 times of that without DC electric field. The DC electric field can make more CNO^- ions to exist around the anode sample, providing extra energy for the decomposition of CNO^- ions and obtaining more active nitrogen atoms required for nitriding, so as to achieve the accelerating effect of infiltration.

Effect of quenching process on microstructure and hardness of Cr26 high chromium wear resistant cast iron

Liang Xiujuan, Ji Haixu

2020, 45(4): 141-143. doi:10.13251/j.issn.0254-6051.2020.04.029

Abstract ( 144 )

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Effects of different quenching processes on the microstructure and hardness of Cr26 high chromium wear resistant cast iron were studied by means of optical microscope and Rockwell hardness tester. The results show that the microstructure of as-cast Cr26 high chromium cast iron is mainly composed of primary austenite and carbide. After quenching and air-cooling at different temperatures from 980 ℃ to 1060 ℃, a large amount of secondary carbides are precipitated from the microstructure of high chromium cast iron. With the increase of quenching temperature, the secondary carbides precipitated in the microstructure first increase and then decrease, and the hardness of the specimen first increases and then decreases. The hardness of quenched specimens at 1020 ℃ reaches peak value, which is 65.7 HRC. When the high chromium cast iron quenched at 1020 ℃ in air, oil or water, carbide particles in the microstructure of high chromium cast iron, carbide proportion, and the hardness of the high chromium cast iron all increase gradually with the increase of cooling rate. The hardness of water quenched high chromium cast iron reaches the maximum value of 68.2 HRC.

Effect of annealing on phase composition and morphology of AlCoCrFeMnTi high entropy alloy

Wang Zhixin, Zhou Jiachen, Ma Mingxing, Lu Jinbin, Zhu Dachuan, Zhang Deliang

2020, 45(4): 144-148. doi:10.13251/j.issn.0254-6051.2020.04.030

Abstract ( 79 )

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Effect of annealing temperature on the phase constitution, microstructure and hardness of AlCoCrFeMnTi high entropy alloy were tested by means of XRD, OM, SEM and microhardness tester. The results show that the phase structure of as-cast AlCoCrFeMnTi high entropy alloy is composed of bcc main phase and fcc phase, and the diffraction peaks of each phase are generally wider, which is due to lattice distortion caused by large difference of alloy atomic radius and fast cooling rate. The microstructure of AlCoCrFeMnTi alloy is composed of dendrite and intergranular, and is the typical dendrite structure. A new hcp phase is formed in this alloy when annealed at 600 ℃. The peak shape of the diffraction peak does not change significantly when annealed at 800 ℃ and 1000 ℃. The microstructure of the as-cast AlCoCrFeMnTi alloy and the annealed alloy are all typical dendritic structure. Typical amplitude-modulated decomposition structure is revealed by scanning electron micrograph after annealing at 1000 ℃. The hardness of the as-cast alloy is the largest (750 HV0.5) and decreases gradually with the increase of annealing temperature. After annealing at 1000 ℃, the alloy is deformed due to the amplitude-decomposing structure in the alloy. Supersaturated atoms are shifted in a large amount, which reduces the degree of lattice distortion and leads to a decrease of hardness. On the other hand, due to the increase of the annealing temperature, the atomic diffusion capacity is accelerated and the internal stress of the alloy is lowered. At this time, the hardness of the alloy drops to 604.9 HV0.5.

Annealing process of 7075-O aluminum alloy sheet for stamping

Liu Suwei, Guo Yuhang

2020, 45(4): 149-151. doi:10.13251/j.issn.0254-6051.2020.04.031

Abstract ( 89 )

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Influence of Zn content, annealing temperature and cooling rate on mechanical properties and microstructure of 7075 aluminum sheet were studied by means of tensile test and microstructure observation. The results show that with the increase of annealing temperature, the strength of 7075-O aluminum alloy sheet decreases, and the elongation increases initially but then decreases. With the increase of Zn content and cooling rate, the strength of 7075-O aluminum alloy sheet increases gradually, and the elongation decreased. In conclusion, to meet the requirements of 7075-O aluminum alloy sheet for stamping, the comparatively ideal condition are w(Zn)≤5.6%, annealing at 410 ℃ for 3 h with furnace cooling to 100 ℃ and then air cooling.

Influence of aging processes on microstructure and properties of Al-Zn-Mg-Cu aluminium alloy

Xu Xuefang, Wang Chunhua

2020, 45(4): 152-155. doi:10.13251/j.issn.0254-6051.2020.04.032

Abstract ( 67 )

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The influence of aging processes (including one-step, two-step and three-step aging) on the microstructure and properties of Al-Zn-Mg-Cu aluminium alloy with Ti addition was studied by alloy preparation and heat treatments. The as-cast microstructure, distribution patterns of phase precipitation, mechanical properties after aging and fracture morphology of the alloy were studied by OM, SEM, microcomputer controlled universal testing machine and microhardness tester. The results show that adding Ti can refine the grain size, reduce the dendritic segregation and strengthen the alloy. The strength of the alloy reaches its maximum of 586 MPa in the one-step aging process. But in the three-step aging process, the alloy has the highest hardness (183.2 HV0.1) and the best elongation (8.8%) with the strength (579 MPa) equivalent to that in the one-step aging process. It is revealed that the three-step aging treatment can achieve the most significant improvement in the mechanical properties of the alloy.

Effect of vacuum gas quenching pressure on hardness of martensitic stainless steels

Ren Wei, Tang Lina, Lü Chaojun, Wang Jianbo, Wu Guohua, Zhang Tiande

2020, 45(4): 156-160. doi:10.13251/j.issn.0254-6051.2020.04.033

Abstract ( 79 )

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Effect of vacuum gas quenching pressure on hardness of four martensitic stainless steels (2Cr13,9Cr18,1Cr17Ni2 and 0Cr17Ni4Cu4Nb) was studied. The results show that the core hardness of the 2Cr13 steel bars with diameter of 30,50 and 80 mm under the gas quenching pressure of 1.5, 3 and 5 bar is greater than 45 HRC, respectively, and the surface hardness for the three steels is greater than 49.5 HRC. When gas quenching pressure is increased, the hardness of 2Cr13 steel increases. The core hardness of the 2Cr13 steel bars with diameter of 30 mm is the same as the surface hardness. The core hardness of the 2Cr13 steel bars with diameter of 50 and 80 mm is lower than the surface hardness. The steel bars of 9Cr18, 1Cr17Ni2, 0Cr17Ni4Cu4Nb with diameters of 30,50 and 80 mm are all hardened under the gas quenching pressure of 1.5, 3 and 5 bar, and the core hardness is the same as the surface hardness.

Spheroidizing annealing of 42CrMoVNb high strength bolt steel

Yang Zhou, Zhao Xiuming, Sun Jianyu, Liu Kaixuan, Feng Yuyang, Wang Yangxin, Wang Lei

2020, 45(4): 161-165. doi:10.13251/j.issn.0254-6051.2020.04.034

Abstract ( 71 )

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Based on Ac₁ and Ac₃, i.e. 773 ℃ and 811 ℃ respectively, evaluated by the thermal simulation experiment, the spheroidizing annealing treatment with different heating temperatures and holding time was carried out on 42CrMoVNb high strength bolt steel. The spheroidizing evolution and hardness of the steel were analyzed by means of optical microscope, scanning electron microscope, Vickers hardness and cold heading tests. The results show that after spheroidizing annealing at 780 ℃(above Ac₁) for 0.5 h followed by low cooling to 710 ℃ for 6 h or at 750 ℃ (below Ac₁) for 3 h followed by slow cooling to 710 ℃ for 6 h, the steel has good spheroidized structure with low hardness, meanwhile, the morphology of carbides tends to be spherical and uniformly distributed, and the steel has good plasticity and cold heading properties. When spheroidized annealing at 750 ℃, the longer the holding time, the more obvious of carbide spheroidization.

Effect of carburizing quenching and tempering process on microstructure and properties of G20CrNi2Mo steel

Fu Ming, Wang Zhiyong

2020, 45(4): 166-170. doi:10.13251/j.issn.0254-6051.2020.04.035

Abstract ( 69 )

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The variety of hardness and microstructure for G20CrNi2Mo steel after different heat treatment was analyzed by means of the optical microscopy (OM) and scanning electron microscope (SEM). And the wear resistance for the steel was studied by the friction abrasion testing machine. The results show that the hardness and wear resistance of G20CrNi2Mo steel are improved obviously after carburizing and quenching and tempering. The microstructure is fine martensite, grain carbide, and a small amount of residual austenite after double quenching. After the second quenching and tempering, the microstructure and properties of low temperature tempering at 200 ℃ are the best, and the microstructure is tempered martensite, with hardness value and wear loss of 62.3 HRC and 12.9 g, respectively.

Effect of annealing on magnetic properties and core magneto-induced vibration of amorphous alloy

Shi Yongheng, Zhu Lihua, Han Tianheng, Li Weizheng

2020, 45(4): 171-175. doi:10.13251/j.issn.0254-6051.2020.04.036

Abstract ( 59 )

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In order to study the effect of annealing treatment on the magnetic properties and the vibration of amorphous core, the magnetization and magnetostriction properties of amorphous strip before annealing and amorphous core after annealing were measured by using the magnetic property measuring equipment. Based on the measured data, the magnetic mechanical multi physical field coupling model of amorphous roll core was established. The flux density distribution and vibration of the two kinds of iron core before and after annealing were calculated and compared with the vibration measured data of the prototype.The results show that annealing can increase the saturation magnetic induction strength of the amorphous alloy, improve the magnetic permeability, and reduce the magnetostrictive coefficient, thereby effectively suppressing the transformer core vibration.

Influence of post weld heat treatment on microstructure and properties of MIG welded joint of Al-Zn-Mg-Cu alloy

Zhang Xiang, Chen Bo, Xie Dejie

2020, 45(4): 176-179. doi:10.13251/j.issn.0254-6051.2020.04.037

Abstract ( 68 )

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Al-4.6Zn-1.5Mg-0.15Cu alloy plate was welded by using metal inert-gas welding (MIG) with ER5356 welding wire as filler metal. And different post weld heat treatments were carried out on the welded joints.The microstructure evolution of the welded joints after different post weld heat treatments was investigated using optical microscopy (OM) and scanning electron microscope (SEM). In addition, the microhardness measurements and tensile tests were conducted. The results show that after solution and aging treatments, the tensile strength and microhardness of the welded joints are significantly improved. The microhardness of the welded joint is increased from 66 HV before heat treatment to 85 HV after solution and aging treatments, increasing by 28.8%. The tensile strength is increased from 263 MPa before heat treatment to 304 MPa after solution and aging treatments, increasing by 15.6%.After aging treatment, the inhomogeneity of microstructure and the distribution of strengthening phase are improved.After solution treatment, the second phase of the welded joint can be re-dissolved, and then aging treatment makes some unstable supersaturated solid solution re-precipitated and diffusely drstributed.

Effect of annealing temperature on recrystallization behavior of cold rolled low carbon steel

Wu Hao, Chai Litao, Xu Liu

2020, 45(4): 180-182. doi:10.13251/j.issn.0254-6051.2020.04.038

Abstract ( 76 )

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Effect of annealing temperature on recrystallization behavior of cold rolled low carbon steel was investigated by carrying out annealing experiment in thermo-induction muffle. The results show that at 565 ℃, recovery is the main softening mechanism and the grains remain lengthened. The yield and tensile strength decrease obviously, the elongation increases clearly and vickers hardness reduces sharply until the temperature rises to 580 ℃, that means recrystallization occuer in this state. The metallographic phase is consists of plentiful lamellar cementite and rare ferrite. When the temperature rises above 580 ℃, properties change unapparently, including yield and tensile strength, elongation and hardness, meaning that complete recrystallization finishes at 580 ℃.

New supersonic arc spraying coating for boiler water wall protection

Meng Dianwu, Zhang Jiantang, Shen Nan, Hu Xuefei, Lu Yu, Du Xiaodong

2020, 45(4): 183-187. doi:10.13251/j.issn.0254-6051.2020.04.039

Abstract ( 76 )

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In order to obtain a water wall protective coating with high service life under the operating conditions of thermal power plant boilers, a new developed coating was designed and manufactured on the basis of referring to the composition of existing coating. The developed FeCrNiBSi coatings and FeCrNi coating were prepared on Q235 steel by supersonic arc spraying. The high temperature corrosion resistance test of the two coatings were carried out respectively. The surface morphology and corrosion mechanism of the coatings before and after corrosion in molten salt environment were studied by means of metallographic microscope, scanning electron microscope and X-ray diffraction. The results show that the developed FeCrNiBSi coatings have better high temperature corrosion resistance and higher surface hardness than the FeCrNi coatings, and are more suitable for the protection coatings of boiler water wall in thermal power plants.

Microstructure and properties of 304 stainless steel laser cladding on 27SiMn steel surface

Wang Xiancai, Zhang Yapu, Chai Rongxia

2020, 45(4): 188-193. doi:10.13251/j.issn.0254-6051.2020.04.040

Abstract ( 84 )

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After finding the best laser power for 304 stainless steel laser cladding on 27SiMn steel surface by single laser cladding experiments under different laser power, multilayer accumulative 304 stainless steel laser clad layer was prepared by using such a power, and its microstructure was analyzed. The tensile properties and fracture morphology of the 27SiMn steel and the 304 stainless steel clad layer were compared. The results show that a good metallurgical bond is achieved between the clad layer and the substrate, and columnar crystals with typical directional solidification characteristics are present in the clad layer. The tensile strength of the clad layer is equal to that of the substrate, while the elongation is obviously higher than that of the substrate. The dimples with typical plastic fracture characteristics appear at the tensile fracture of both the clad layer and the substrate material, and the size and depth of the dimples of the clad layer are obviously larger than that of the substrate.

High temperature friction properties of NiCoCrAlYTa-Al₂O₃ composite coating by atmospheric plasma spraying

Liu Haijun, Gao Weimin, Tao Chong

2020, 45(4): 194-198. doi:10.13251/j.issn.0254-6051.2020.04.041

Abstract ( 80 )

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NiCoCrAlYTa-Al₂O₃ composite coatings were prepared on 0Cr25Ni20 austenitic stainless steel by atmospheric plasma spraying (APS). The microstructure, phase composition, micro-hardness and high temperature(500 ℃) friction properties of the coatings were studied. The results show that the NiCoCrAlYTa-Al₂O₃ coating has typical layered microstructure and good bonding among layers. There are a large number of micropores in the coating, and the hard phase and the soft phase are dispersedly distributed, which effectively inhibits the generation and propagation of cracks during high temperature wear process. The wear resistance of the coating is significantly better than that of the austenitic stainless steel. During the high temperature wear process, oxidation products are formed on the coating surface, which actassolid lubrications. The wear failure modes of the NiCoCrAlYTa-Al₂O₃ coating are abrasive wear, fatigue wear and adhesion wear.

Effect of Ti on microstructure and properties of plasma sprayed Fe-Al₂O₃-FeAl₂O₄ composite coating

Song Jinsong, Jia Zhining, Zhang Tianxu, Xu Xiaodong, Xie Ying, Yan Dianran

2020, 45(4): 199-203. doi:10.13251/j.issn.0254-6051.2020.04.042

Abstract ( 74 )

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Metal-ceramic nanocomposite coatings with different Ti contents were prepared by reaction plasma spraying. The phase composition, structure and morphology of the coating were analyzed by XRD and SEM. The results show that FeAl₂O₄, Fe_xAl_y, TiO₂, Fe phase as well as iron-titanium spinel phase are formed in the coating. The study of its mechanical properties shows that with the increase of Ti content, the microhardness gradually decreases, and the wear performance gradually increases. When the Ti content is 10%, the comprehensive mechanical properties of the composite coating are optimal.

High temperature tensile properties and fracture mechanism of P110H steel

Zhao Lin, Yang Junhu, Wei Wenlan, Ma Hai, Xue Yang, Ma Lijuan

2020, 45(4): 204-208. doi:10.13251/j.issn.0254-6051.2020.04.043

Abstract ( 81 )

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Referring to the service temperature of thermal recovery wells, the tensile test of P110H thermal recovery casing steel at high temperature was carried out. Then the fracture morphology at different temperatures was observed, and the fracture mechanism changes caused by temperature were analyzed. The results show that the yield strength of P110H steel decreases significantly with temperature increasing, while the tensile strength decreases slightly, and the yield strength ratio decreases with temperature increasing. Under the influence of high temperature, the fracture process changes from the combined fracture process of shear extension fracture induced by microporous polymerization to the ductile fracture process dominated by microporous polymerization. The main reason is that the activation energy of materials increases the plastic deformation ability of materials due to high temperature.

Analysis and improvement of fish scale defect formation mechanism on continuous annealed plate surface

Liu Xiaofei, Liu Lixia, Gai Yanqing

2020, 45(4): 209-211. doi:10.13251/j.issn.0254-6051.2020.04.044

Abstract ( 59 )

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The morphology and microstructure of the fish scale defects on the surface of continuously annealed plates were analyzed by means of scanning electron microscopy and focused ion beam analysis. The results show that the essence of the scale defects is a kind of surface micro scratch. The formation mechanism of the defects can be attributed to the water leakage of the thermometer water jacket, which causes the local oxidation of the strip surface at high temperature. And then, the micro scratch formed when the oxidation part was pressed by the furnace roll and the strip tension. A large number of nanocrystalline structures were observed at the defect section cutting by focused ion beam technology, which confirmed that the surface of the strip was quenched and oxidized. The results of the microstructure analysis provide a theoretical basis for the investigation and solution of the scale defects.

Comparative analysis of standards for determining average grain size

Bi Geping, Chen Jinzhe, Tan Wenhua, Li Qiao

2020, 45(4): 212-220. doi:10.13251/j.issn.0254-6051.2020.04.045

Abstract ( 105 )

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Five aspects of 17 standards for determining average grain size of metallic materials were compared and analyzed, including the definitions of the grain size, the chart comparison procedure, the planimetric procedure, the intercept procedure, and the accuracy. The consistencies, differences and shortcomings among these standards were clarified through comparative analysis, and the results were conducive to the selecting and using of the standards by metallographers and the continual improvement of standardization work.

Crack analysis of bearing chock and prevention measures

Chen Kaimin, Wen Chao, Liang Huilei

2020, 45(4): 221-223. doi:10.13251/j.issn.0254-6051.2020.04.046

Abstract ( 120 )

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The radial cracks were found on the inner hole steps of the bearing block. The cracking reason of the bearing chock was confirmed by site investigation, metallographic examination, chemical composition analysis and macrography examination. The results show that the cracks of bearing chock is caused by quenching, which results from workpiece diameter falling into the critical size of quenching of the step, right angle transition and some chemical elements content close to the upper limit. The problem is solved by changing the right angle to round angle, and fine tuning the quenching temperature according to the chemical composition.

Cause analysis of magnetic particle indication on 42CrMo steel crankshaft neck

Huang Bin, Lin Shengyao, Mao Xiaofeng, Li Liangqun, Zheng Qifeng, Gu Jianfeng, Liu Qingdong

2020, 45(4): 224-228. doi:10.13251/j.issn.0254-6051.2020.04.047

Abstract ( 83 )

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The hair-line magnetic particle indication was detected by magnetic particle testing at the neck part of 42CrMo steel crankshaft. The microstructure just below the magnetic particle indication was studied by OM,SEM and EDS. The results show that the microstructure is considerably uneven,and significant segregation bands are found with a width of about 20-50 μm and enriched with the C, Mn, S, Al and Cr elements. In addition, individual MnS inclusion is also detected. The segregation bands paralleling with the axis of columnar 42CrMo steel are rotated during die forging process, especially at the neck part of 42CrMo steel crankshaft with severe plastic distortion.The macro-segregation is inherited to the final crankshaft product. The heterogeneous compositional distribution leads to the difference of magnetic permeability and thus the appearance of magnetic particle indication. The forging process and the following quenching-tempering as well as surface induction quenching treatment can mitigate to some extent but cannot totally eliminate the segregation.

Degradation and regeneration of quenched nitrate

Zhang Fuquan, Xiao Yunwei

2020, 45(4): 229-235. doi:10.13251/j.issn.0254-6051.2020.04.048

Abstract ( 58 )

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The deterioration products of nitrate bath used for step quenching or austempering were comprehensively analyzed by means of SEM, EDS and chemical analysis.The results show that nitrate degradation is mainly caused by the reaction products of nitrate (Na₂CO₃, NaOH), oxidation products (FeO·Fe₂O₃·Fe₃O₄) of equipment (mainly salt bath, salt pump, pipeline and roller),fixtures,pans and workpieces and foreign substances (dust, carbon black) during the use of nitrate. Accordingly, the counter-measures to prevent deterioration of quenched nitrate are put forward, including choosing base salt with good quality or mixed salt with high thermal stability, keeping the temperature of the quenching salt bath uniform, controlling the temperature rise before and after quenching, trying to avoid “instantaneous” overheating and foreign impurities, and doing daily maintenance well. And the method of regeneration of quenched nitrate is also briefly introduced.

Development of non-standard immersion quenching equipment for aluminum parts

Luo Ping, Shi Yiqing, Li Xianjun, Zhang Wenliang, Zhou Tong, Sun Meng

2020, 45(4): 236-241. doi:10.13251/j.issn.0254-6051.2020.04.049

Abstract ( 66 )

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The principles of quenching process of aluminum parts, potential problems of aluminum parts in the quenching process and the relationship between heat transfer coefficient and temperature as well as the cooling velocity of quenchant were introduced. And a scientific basis of immersion quenching equipment of aluminum parts for customization was provided. Finally, several typical engineering examples are analyzed based on some critical issues during the design and industrialization, which are selected from dozens of cases of immersion quenching equipment of aluminum parts. Therefore, the solutions to reduce distortion under the premise of ensuring the expected performance of aluminum parts during quenching are clarified.

An electric spark strengthening and repairing device for planar surface

Ge Zhihong, Deng Jing

2020, 45(4): 242-244. doi:10.13251/j.issn.0254-6051.2020.04.050

Abstract ( 63 )

PDF (1019KB) ( 34 )

An electric spark strengthening device for metal planar repairing was studied. Through SEM analysis, MM200 wear test and hardness gradient distribution analysis, the strengthened repairing layer obtained by the device is relatively complete and has a certain thickness, which greatly improves the hardness and wear resistance of the part surface.

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