Heat Treatment of Metals

Effect of mechanical alloying time on microstructure and corrosion resistance of laser clad coating of Ni₆Cr₄W_1.5Fe₉Ti high-entropy alloy

Sun Defu, Sun Zhicheng, Gu Zhen, Xi Shengqi, Sun Chongfeng, Li Shiliang, Su Chengming, Wang Chunchang

2023, 48(3): 1-7. doi:10.13251/j.issn.0254-6051.2023.03.001

Abstract ( 126 )

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Clad coating of mechanical alloyed Ni₆Cr₄W_1.5Fe₉Ti high-entropy alloy powder was prepared by laser melting deposition. The effect of mechanical alloying time on microstructure and corrosion resistance of the coating was studied. The results show that the increase of mechanical alloying time can promote the homogenization of alloy powder composition, the densification of coating and the grain refinement of microstructure. After mechanical alloying rod grinding for 4 h, the components of high-entropy alloy powder are evenly distributed, and the FCC+BCC two-phase solid solution structure is formed. After laser melting deposition, the structure of two-phase solid solution is transformed into FCC single-phase solid solution, which is mainly composed of 4-6 μm equiaxed crystals and a small amount of cellular crystals. Among them, the coating prepared by powder mechanical alloying rod grinding for 4 h has the highest density, hardness and the best corrosion resistance, and its corrosion resistance is nearly two orders of magnitude higher than that of the coating prepared by powder mechanical alloying rod grinding for 0 h.

Effect of low heating rate aging treatment on properties of Al-Zn-Mg-Er-Zr alloy

Qiu Chen, Rong Li, Wei Wu, Wang Wei, Wen Shengping, Huang Hui, Dong Yang, Wang Yugang

2023, 48(3): 8-11. doi:10.13251/j.issn.0254-6051.2023.03.002

Abstract ( 70 )

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Effect of two different aging processes at 120 ℃ on mechanical properties and electrical conductivity of Al-5Zn-3Mg-0.1Er-0.1Zr alloy was studied by scanning electron microscope (SEM), microhardness tester and conductometer. The results show that compared with the aging process by directly putting specimens at 120 ℃, the conductivity of the tested alloy after 5 h slow heating to 120 ℃ aging process is increased to 30.77%IACS, and the hardness, tensile strength, yield strength and elongation are increased to 186.6 HV0.2, 538 MPa, 454 MPa and 17.5%, respectively. Both the fracture modes are ductile-brittle mixed fracture for the alloy treated by the two different aging processes, but for the alloy treated by 5 h slow heating to 120 ℃ aging, the dimple density is higher, and the shear plane characteristic is reduced.

Effect of tempering temperature on hydrogen embrittlement sensitivity of a high strength low alloy steel containing V and Nb

Wang Zhaofeng, Cheng Xiaoying, Li Xiaoliang, Peng Hao, Cai Zhenxiang

2023, 48(3): 12-18. doi:10.13251/j.issn.0254-6051.2023.03.003

Abstract ( 70 )

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Effect of tempering temperature (560, 600 and 640 ℃) after 920 ℃ ice-water quenching on hydrogen diffusion and hydrogen embrittlement sensitivity of a high strength low alloy steel with 0.15%V and 0.05%Nb (mass fraction) was investigated by hydrogen penetration and dynamic hydrogen charging tensile test, and the microstructure of the tempered specimens was observed and analyzed by metallographic microscope, X-ray diffractometer and transmission electron microscope. The results show that with the increase of tempering temperature, the hydrogen diffusion coefficient increases, the hydrogen diffusion activation energy and hydrogen embrittlement sensibility decrease, which is because that with the increase of tempering temperature, the decrease of dislocation density reduces the density of hydrogen traps, and the diffusible hydrogen content decreases under the same hydrogen charging condition.

Effect of post rolling heat treatment on phase transformation microstructure and hardness of pearlitic steel rail

Jiang Hongli, Wang Dongmei, Wang Yeshuang, Zhang Heng, Chen Lin

2023, 48(3): 19-24. doi:10.13251/j.issn.0254-6051.2023.03.004

Abstract ( 60 )

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Microstructure and hardness of the tested steel under different heat treatment processes after rolling were studied by means of double-pass hot compression test on Gleeble-3500 thermal simulation tester. The effects of isothermal time, different cooling rates and isothermal temperatures after hot deformation on pearlite lamella and hardness and their mechanisms were analyzed. The results show that the pearlite + a small amount of ferrite are all obtained after 1 ℃/s continuous cooling, rapid cooling after quenching isothermal transformation at 1 ℃/s (1 ℃/s-580 ℃-30 s), rapid cooling after quenching isothermal transformation for 60 s at 3 ℃/s (3 ℃/s-580 ℃-60 s) and rapid cooling after quenching isothermal transformation at 620 ℃ at 5 ℃/s (5 ℃/ s-620 ℃-60 s), respectively. However, martensite or bainite structure appears after 3 ℃/s continuous cooling and rapid cooling after quenching isothermal transformation for 60 s at 3 ℃/s (3 ℃/s-580 ℃-60 s) due to insufficient isothermal time. Compared with continuous cooling at 1 ℃/s, rapid cooling after quenching isothermal transformation at 1 ℃/s plays a positive role in reducing the lamellar spacing of pearlite and increasing the hardness. The lamellar spacing of the tested steel obtained after rapid cooling after quenching isothermal transformation for 60 s at 3 ℃/s (3 ℃/s-580 ℃-60 s) is the smallest, reaching 73.19 nm. The lamellar orientation is diverse, and some cementite flakes are broken. The small increase of hardness is related to the increase of pearlitic structure content. The pearlite lamellae of the tested steel after 1 ℃/s continuous cooling is the coarsest, and the hardness is the lowest due to the excessive growth of precipitated phase NbC and the spheroidization of fractured cementite. The relatively complete and fine pearlitic lamellae and the existence of residual dislocation make the higher hardness of the tested steel when rapid cooled after quenching isothermal transformation at 620 ℃ at 5 ℃/s (5 ℃/s-620 ℃-60 s), reaching 42.0 HRC.

Effect of annealing process path on microstructure and properties of 980 MPa grade high-strength steel

Qiu Musheng, Han Yun, Teng Huaxiang, Bai Zhenhua

2023, 48(3): 25-31. doi:10.13251/j.issn.0254-6051.2023.03.005

Abstract ( 53 )

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In order to improve the local formability of 980 MPa high-strength steel, the microstructure and mechanical properties of 980 MPa high-strength steel with different annealing process paths were studied by means of universal testing machine, field emission scanning electron microscope(SEM), electron backscattering diffraction(EBSD) and comprehensive forming testing machine. Moreover, its effect on hole expansion ratio and local formability were evaluated. The results show that in addition to the two phases of ferrite and martensite, the microstructure of the new quenching & tempering(Q&T) process also contains tempered martensite, the average grain size of ferrite and martensitic is 3.14 μm and 2.62 μm, respectively, and the martensite area fraction is 61.0%, while the typical ferrite and martensitic dual phases are obtained under the traditional process, the average grain size of ferrite and martensite is 4.77 μm and 2.77 μm, respectively, and the martensite area fraction is 35.8%. The elongation of the two processes is comparable, but the yield strength and hole expansion ratio are significantly different, and the higher yield ratio and hole expansion ratio are achieved under the new Q&T process, which is attributed to its smaller ferrite grain size and the difference in ferrite and martensite hardness. The ratio of true fracture strain(TFS) to true uniform strain(ε_u) of the traditional process is 7.0, while the new Q&T process is 15.2, therefore the new Q&T process has excellent characteristics in local formability.

Effect of solution treatment on microstructure and properties of rare earth modified Al-Zn-Mg-Cu alloy

Deng Hongling, Zhang Siyu, Zhong Huilong, Li Shengci, Qi Liang, Chen Jiqiang

2023, 48(3): 32-38. doi:10.13251/j.issn.0254-6051.2023.03.006

Abstract ( 43 )

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Effects of solution treatment time at 475 ℃ on the microstructure and properties of Al-Zn-Mg-Cu alloys with different contents(7055, 7055-Pr, 7055-Er, 7055-Pr-Er alloys) were studied by OM, SEM, EDS and tensile test. The results show that the strengths of the four alloys all increase firstly and then decrease with the increase of solution treatment time. The addition of rare earth Pr and Er can reduce the residual phases in the matrix, refine the grains, thereby improving the elongation of the alloys. The rare earth Pr has a better effect on improving elongation of the tested alloy than the rare earth Er, while the Er has a greater effect on the strength improvement of the tested alloy. Appropriate solution treatment can optimize the number and size of residual phases and secondary phases in the matrix, thereby affecting the fracture morphologies and mechanical properties of the alloys. After solution treatment at 475 ℃ for 60 min, the tensile strength of the 7055-Er alloy reaches the maximum value of 665 MPa, while the elongation of the 7055-Pr alloy reaches the maximum value of 14.9%.

Effect of pulsed magnetic field on microstructure and properties of two-stage aged Al-6.15Zn-1.41Mg-1.45Cu alloy

Zhou Jinxin, Ma Yonglin, Liu Yongzhen, Chen Zhongyi, Gong Meina, Xing Shuqing

2023, 48(3): 39-44. doi:10.13251/j.issn.0254-6051.2023.03.007

Abstract ( 36 )

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After solution treatment at 477 ℃ for 1 h, the Al-6.15Zn-1.41Mg-1.45Cu alloy was treated by two-stage aging based on pulsed magnetic field. The effect of pulsed magnetic field on the precipitated phase and mechanical properties of the Al-6.15Zn-1.41Mg-1.45Cu alloy during aging was studied by changing the aging time and comparing with the conventional two-stage aging structure and properties. The diffusion mechanism of precipitated phase accelerated precipitation in the Al-6.15Zn-1.41Mg-1.45Cu alloy during two-stage aging in pulsed magnetic field was analyzed with kinetics. The precipitation phase and tensile fracture morphology of the Al-6.15Zn-1.41Mg-1.45Cu alloy were observed by SEM, and the mechanical properties were tested. The results show that the pulsed magnetic field increases the diffusion coefficient and nucleation rate of the precipitated phase during aging process of the Al-6.15Zn-1.41Mg-1.45Cu alloy, resulting in the appearance of diffusely fine precipitated phases in the matrix after aging. After two-stage aging pulsed magnetic field (121 ℃×90 min+177 ℃×60 min), the tensile strength is 495.43 MPa, and hardness is 156.3 HV5. Compared with the conventional two-stage aging treatment, the tensile strength increases by 20.83%, hardness increases by 17.89% and the aging holding time reduces by 87.5%.

Effect of I&Q&P process on microstructure and mechanical properties of C-Si-Mn-Nb dual-phase steel

Wu Qiuyun, Pan Hongbo, Liu Yonggang, Zhan Hua, Cui Lei

2023, 48(3): 45-50. doi:10.13251/j.issn.0254-6051.2023.03.008

Abstract ( 33 )

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I&Q&P annealing experiments were carried out on the traditional C-Si-Mn dual-phase steel adding 0.05%Nb by means of CCT-AY-II continuous annealing simulator. The effects of Nb element and I&Q&P process on microstructure evolution and mechanical properties of the tested steel were studied. The microstructure and mechanical properties of the tested steel at partitioning temperature of 350 ℃ and 450 ℃ for different partitioning times (300, 450 and 600 s) were investigated by means of metallographic microscope, scanning electron microscope and X-ray diffraction. The results show that the content of lath martensite decreases and the ferrite increases with the increase of partitioning temperature and partitioning time. The tensile strength of the tested steel shows a decreasing trend, while the elongation shows an increasing trend. The product of strength and plasticity of the steel is optimum when partitioning at 450 ℃ for 450 s, which is 20.48 GPa·%.

Homogenization heat treatment of 6070 aluminum alloy

Zhao Yu, Wei Wu, Huang Hui, Liu Zhenshan, Ren Simeng, Dong Yang, Wang Yugang, Shi Wei

2023, 48(3): 51-56. doi:10.13251/j.issn.0254-6051.2023.03.009

Abstract ( 47 )

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Homogenization heat treatment process and microstructure evolution of 6070 alloy were studied by means of OM, SEM, EDS, DSC and conductivity measurements. The results show that in the as-cast 6070 alloy, a large amount of Mg₂Si primary phases produced by non-equilibrium solidification are aggregated and distributed along the grain boundary, and disc-shaped Q phase is distributed in the grains. After 535 ℃×12 h homogenization heat treatment, the primary phase in the as-cast alloy is basically redissolved, and the homogenization effect is good. After homogenization, the alloying elements are mainly precipitated in the aluminum matrix in the form of fine dispersed phase, leading to the increase of conductivity. The overburning starting temperature of the alloy is 550 ℃, at which the overburned characteristics including nearly-triangular remelting phase and grain boundary widening by remelting begin to appear in the alloy. With the increase of homogenization temperature and extension of time, the overburning of the alloy increases and the conductivity decreases, the grain size and Mn containing dispersed phase size become larger, and the coarse overburned phase Q is formed concurrently.

Effect of heat treatment on microstructure and properties of ZG45Cr5Ni2Mo wear-resistant steel

Fan Shichong, Sun Jinzhao, Shen Zhihao, Lu Kefeng, Liu Yafan, Wang Hongqi, Yin Fengshi

2023, 48(3): 57-61. doi:10.13251/j.issn.0254-6051.2023.03.010

Abstract ( 67 )

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Based on the equilibrium phase composition and CCT curves calculated and analyzed by JMatpro 9.0 thermodynamic software, the ZG45Cr5Ni2Mo wear-resistant steel was oil quenched at 900 ℃, and tempered for 2 h at 180, 300, 400, 500 and 600 ℃, respectively, then air cooled. The microstructure and mechanical properties of the heat treated steel were studied by means of scanning electron microscope, Rockwell hardness tester and impact tester. The results show that with the increase of tempering temperature, the hardness decreases gradually, and the impact absorbed energy fluctuates greatly. The hardness of the tested steel tempered at 300 ℃ is 51.9 HRC, and the impact absorbed energy is 48 J, which has a combination of high hardness and good ductility.

Effect of rolling temperature and post-treatment on microstructure and mechanical properties of AZ31 magnesium alloy

Song Xianhe, Liu Xiaoye, Bi Rengui, Lu Liwei, Liu Yanfeng, Huan Xihong

2023, 48(3): 62-70. doi:10.13251/j.issn.0254-6051.2023.03.011

Abstract ( 56 )

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AZ31 magnesium alloy plates were rolled at different temperatures, and the rolled plates were immediately subjected to different post-treatments (water cooling, air cooling and annealing). The effects of rolling temperature and post-treatment on microstructure and mechanical properties of the tested magnesium alloy were investigated. The results show that when rolled at 250 ℃ and 300 ℃, there are a lot of twins in the plates after water cooling and air cooling. When rolled at 350 ℃, the number of twins is small due to the higher rolling temperature, the average grain size after water cooling is smaller than that after air cooling, and the number of twins after air cooling is slightly smaller than that after water cooling. After annealing following the 350 ℃ rolling, the grains tend to be equiaxed and finer with low lattice distortion. At the same rolling temperature, the yield strength, tensile strength and hardness of the rolled alloy plate after water cooling are higher than that of other treatments. After annealing, the elongation of the plates can be significantly increased, but the yield strength and tensile strength are slightly decreased. When the rolling temperature increases, the maximum difference of yield strength and tensile strength between the three post-treatment methods decreases.

Effect of expanding ratio on strain capacity of X70 grade high deformability pipeline steel pipe

Shi Xianbo, Yan Wei, Zhang Chuanguo, Ren Yi, Shan Yiyin

2023, 48(3): 71-76. doi:10.13251/j.issn.0254-6051.2023.03.012

Abstract ( 28 )

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Effect of expanding ratio on strain capacity of the trial X70 UOE pipeline steel pipe with polygonal ferrite and bainite (PF+B) was studied by optical microscope (OM), electron backscattered diffraction (EBSD), transmission electron microscope(TEM) and tensile test. The results show that when the expanding ratio varies in the range of 0.4%-1.2%, the grain orientation, effective grain size and proportion of high and low angle grain boundaries in the microstructure of pipe remain basically unchanged. With the increase of expanding ratio, the dislocation density in PF increases, resulting in a slight increase in yield strength and tensile strength. After UOE pipe made, the strain capacity index decreases from 2.00 of the original steel plate to 0.78, 0.61 and 0.56 of different expanding ratio, and the strain capacity decreases significantly. However, there is little effect on strain capacity of UOE pipe when the expanding ratio varies in the range of 0.4%-1.2%. The strain hardening rate first decreases and then increases before necking with the increase of expanding ratio, while the strain values corresponding to the necking points are 9.7%, 8.6% and 8.5% respectively. The strain hardening rate decreases rapidly when the expanding ratio reaches 1.2%.

Effect of homogenization treatment on hot deformation behavior and texture of extruded Mg-Al-Zn-0.1Y alloy

Li Lei, Wang Jun, Cao Zhaoxun, Han Jungang, Shao Zhiwen, Xu Yongdong

2023, 48(3): 77-83. doi:10.13251/j.issn.0254-6051.2023.03.013

Abstract ( 30 )

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Taking extruded and homogenized Mg-Al-Zn-0.1Y magnesium alloy as research object, hot deformation behaviors of the alloy under isothermal hot compression at 250-400 ℃ and 0.01-10 s^-1 were studied by using a Gleeble 3500 thermal simulator to establish Arrhenius constitutive equations and processing maps, and effect of homogenization heat treatment on its deformation texture was studied by electron backscattered diffraction (EBSD). Based on the established processing map at strain of 0.5 which represents the steady-state flow, the results show that the homogenization treatment broadens the low-temperature processable zones and improves the low temperature processability of the alloy, the suitable processing zones of the as-extruded alloy are (325-375 ℃, 0.01-0.1 s^-1) and (350-375 ℃, 1-10 s^-1), and the optimum processing zone of as-homogenized alloy is (275-325 ℃, 0.01-0.1 s^-1). The EBSD results show that the homogenization treatment improves the dynamic recrystallization ability of the alloy, weakens the texture strength of the base surface of the extruded alloy, increases the proportion of soft orientation, and improves the hot formability of the extruded magnesium alloy.

Effect of tempering temperature on microstructure and properties of bainitic wear-resistant steel

Wang Kaikai, Ma Longteng, Luo Ping, Liu Meiyan, Lu Shiping, Di Guobiao, Wang Yanfeng, Ma Changwen

2023, 48(3): 84-90. doi:10.13251/j.issn.0254-6051.2023.03.014

Abstract ( 43 )

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Microstructure evolution and properties of bainitic wear-resistant steel produced by thermo-mechanical control process (TMCP) + tempering at different temperatures were studied. The results show that after TMCP and tempering at 200 ℃, an ideal carbide-free bainite/martensite complex structure is obtained, which contains 8.7vol% retained austenite. The optimal combination of strength and toughness is obtained under this process. The yield strength and tensile strength reach 1172 MPa and 1613 MPa, the elongation after fracture reaches 19.4%, and the impact absorbed energy at -20 ℃ is 47 J, and the hardness can meet the performance requirements of NM500 level. After tempering at 520 ℃, a large number of coarse carbides precipitate, and retained austenite almost decomposes completely, resulting in the decrease of strength and toughness of the steel.

Application practice of medium frequency induction heat treatment for welded joint of thick-wall P92 steel pipe

Zhang Jie, Zhong Yuan, Wen Zuowei, Shi Weidong, Guo Tong, Zhang Xiaowen, Luo Liangfei

2023, 48(3): 91-95. doi:10.13251/j.issn.0254-6051.2023.03.015

Abstract ( 63 )

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In view of the high technical requirements of post-weld heat treatment for main steam thick-wall (especially for that with wall thickness greater than 100 mm) P92 steel pipe welded joint of 1000 MW unit in thermal power plant, post-weld heat treatment of the pipe specimen was carried out for the main steam P92 steel pipe welded joint with 118 mm wall thickness of a 1000 MW secondary reheat unit by medium frequency induction heating. The results show that after the post-weld heat treatment, the microstructures of the weld and the base material are normal, and the hardness of the weld meets the standard requirements, and after further optimization of the heat treatment by appropriately reducing the heating rate and constant temperature and increasing the width of heat preservation, 121 heat-treated welded joints of the same type are one-time all qualified in the pipeline construction process. The successful application of medium frequency induction heat treatment scheme for welded joints of thick-wall P92 steel pipe can provide reference for the subsequent post-weld heat treatment of the same type of parts.

Effect of solution temperature on cryogenic mechanical properties of A286 alloy

Dai Libin, Yang Zhangcheng, Deng Xiong, Qiu Shijia, Zheng Chaoqing

2023, 48(3): 96-99. doi:10.13251/j.issn.0254-6051.2023.03.016

Abstract ( 40 )

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Mechanical properties at low temperatures (-50, -196, -269 ℃) of the A286 alloy after solution treatment at 900, 950 and 1000 ℃ for 1 h, water cooling and aging at 720 ℃ for 16 h, air cooling were studied by means of electronic universal testing machine, metallographic microscope, impact testing machine and electron probe. The results show that at the same test temperature, with the increase of solution treatment temperature, the tensile strength and yield strength change a little, the elongation after fracture is 33%-42%, and the percentage reduction of area is 45%-52%. At the same solution treatment temperature, with the decrease of test temperature, both the tensile strength and the yield strength increase, and the impact absorbed energy decreases, the minimum impact absorbed energy is 45 J, but the good toughness is still maintained.

Effect of aging time on microstructure and mechanical properties of PH13-8Mo stainless steel

Yang Kai, Zhu Hongwei, Yu Limin, Yu Ruixing

2023, 48(3): 100-103. doi:10.13251/j.issn.0254-6051.2023.03.017

Abstract ( 33 )

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PH13-8Mo stainless steel was solution treated at 925 ℃ for 70 min, cold treated at -70 ℃ for 2 h, and then aged at 535 ℃ for 3, 4, 5 and 6 h, respectively. The effect of aging time on microstructure and mechanical properties of the tested steel were studied by means of optical microscope and mechanical property tester. The results show that intermetallic compounds precipitate after aging at 535 ℃, and gradually grow with the extension of aging time. The tested steel has the highest hardness and strength after aging for 4 h, and maintains sufficient impact absorbed energy and has good comprehensive mechanical properties. With the extension of aging time, the hardness and strength of the tested steel decrease and the impact absorbed energy increases.

Application and progress of nitriding treatment in heavy duty gears

Chen Zhi, Li Baokui, Lu Jinsheng, Xu Hongxiang, Zhang Heng

2023, 48(3): 104-111. doi:10.13251/j.issn.0254-6051.2023.03.018

Abstract ( 64 )

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Commonly used surface heat treatment processes of heavy-duty gears include carburizing and quenching, induction hardening and nitriding process. Nitriding process has great advantages and broad application prospects in industrial production because of its advantages of small distortion and simple process. By increasing the depth of the nitrided layer and the hardness of the matrix, the bearing capacity of nitrided gears can be effectively improved, so as to expand the application of nitriding treatment in heavy-duty gears. Influence of nitriding treatment on the contact fatigue strength and bending fatigue strength of gears was introduced, as well as the influence of matrix properties on nitriding process, the research progress of nitrided gears was reviewsed, such as deep controlled ion nitriding, rare earth accelerated nitriding, aging hardening nitriding steel. It was pointed out that the ways to improve the loading capacity of nitrided gears are as follows: to carry out more in-depth basic research on nitrided gear, to improve the control level of nitriding process and to develop the new technology more actively.

T73 two-stage aging process of 7050 high-strength aluminum alloy rivet wire

Li Huiqu, Wang Liang, Zang Jinxin, Hao Min, Chen Junzhou

2023, 48(3): 112-117. doi:10.13251/j.issn.0254-6051.2023.03.019

Abstract ( 30 )

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Properties of the domestic 7050 high strength aluminum alloy wire secondary aged at 177-182 ℃ for different time were studied by room temperature tensile, room temperature shearing and upsetting tests. The fracture morphology was studied by means of scanning electron microscope (SEM) and the precipitation phase was studied by means of transmission electron microscope (TEM). The results show that the tensile strength and the shearing strength decrease gradually with the increase of secondary aging temperature and secondary aging time. The upsetting specimens do not crack when the shear strength is less than 330 MPa. The TEM microstructure show that the higher the aging temperature and the long the aging time, the larger the size and the inter-spacing of precipitated phase are, but morphology of precipitated phase changes little. The tensile fracture morphologies show that the fracture mode is a mixture of ductile fracture and intergranular fracture. The dimple number and size increase and the intergranular fracture decreases with the increase of secondary aging temperature and aging time.

Effect of normalizing temperature on precipitation behavior of second phase in 2.5%Si non-oriented silicon steel

Shi Lili, Jin Chuanwei, Wu Yuanyuan, Zhang Jiming

2023, 48(3): 118-123. doi:10.13251/j.issn.0254-6051.2023.03.020

Abstract ( 35 )

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Precipitation behavior and evolution law of second-phase precipitates in high-grade non-oriented silicon steel with content of 2.5% silicon normalized at different temperatures were investigated by means of scanning electron microscopy, transmission electron microscopy and focused ion beam scanning electron microscopy. The results show that as the normalizing temperature increases from 850 ℃ to 1100 ℃, the micron-scale second-phase particles show the order of primary growth-precipitation-secondary growth-dissolution; When the normalizing temperature is lower than 920 ℃, the composite growth of AlN+MnS is dominant; then the number of small-sized MnS, AlN and their composite precipitates increases rapidly, reaching a peak at 950 ℃; When the normalizing temperature is further increased, the number of second-phase particles decreases rapidly and then slowly increases to equilibrium, and the large-size precipitates appear to partially dissolve. The nano-scale precipitates are mainly Cu₂S and Cu₂S+MnS composite precipitation. And when normalized at 950 ℃, 2.5%Si non-oriented silicon steel has the lowest iron loss.

Decarburization annealing process of high magnetic induction oriented silicon steel

Dong Lili, Huang Lulu, Lu Xiaoyu, Huang Li, Liu Baozhi

2023, 48(3): 124-128. doi:10.13251/j.issn.0254-6051.2023.03.021

Abstract ( 46 )

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Decarburization annealing process test was carried out on high magnetic induction oriented silicon steel 27QG090 in the laboratory by means of independently developed heat treatment test device. The microstructure and macroscopic texture of the specimens after decarburization annealing were analyzed by means of Zeiss microscope and X-ray diffractometer. The results show that the microstructure of the 27QG090 high magnetic induction oriented silicon steel after decarburization annealing is ferrite and its average grain size is 30-40 μm. The main types of macroscopic textures are α texture and α^* texture ({114}〈481〉、{113}〈361〉), together with some weak Gaussian texture{110}〈001〉. The best process selected through laboratory research is decarburization annealing at 850 ℃ for 7 min. The macroscopic texture of the industrial production line after decarburization annealing is the same as that of the decarburization annealed one in laboratory. When the average grain size is about 30 μm after decarburization annealing, the lowest iron loss is 0.80 W/kg, and the magnetic induction intensity reach 1.93 T.

Effect of quenching temperature on microstructure and properties of air-cooled bainite-martensite multiphase wear-resistant steel

Yan Hongtao, Wang Yongjin, Qi Hailong, Huang Yan, Zhang Keming, Zhang Huandou, Mu Rong

2023, 48(3): 129-134. doi:10.13251/j.issn.0254-6051.2023.03.022

Abstract ( 30 )

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An air-cooling bainite-martensite multiphase wear-resistant cast steel was designed, smelted, poured and heat treated. The effect of quenching temperature on microstructure and properties were studied by means of mechanical properties test, microstructure and fracture morphology observation, and X-ray diffraction analysis. The results show that after quenching at 900 ℃ for 1 h, air-cooling to room temperature, and then tempering at 300 ℃ for 2 h, and air-cooling to room temperature, the bainite-martensite multiphase wear-resistant cast steel with the best comprehensive mechanical properties is obtained, of which the tensile strength is 1729 MPa, elongation after fracture is 4.3%, Brinell hardness is 454 HBW, and V-notch impact absorbed energy is 19.31 J. Its microstructure contains about 10% retained austenite, which can improve the strength and toughness of the matrix.

Effect of heating temperature on microstructure and properties of 34MnB5 hot forming steel

Tian Xiugang, Wang Zhao, Sun Xu, Zhang Jingyu, Lu Zhiqiang, Han Xue

2023, 48(3): 135-138. doi:10.13251/j.issn.0254-6051.2023.03.023

Abstract ( 42 )

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Gleeble3500 thermal simulation machine was used to simulate annealing of 34MnB5 steel after continuous acid rolling. The optimum annealing temperature was analyzed and the flat die quenching test of different hot stamping processes was carried out. The effect of annealing temperature and quenching temperature on microstructure and properties of the hot formed steel was studied. The results show that when the annealing temperature is 790 ℃, the banded structure is almost disappeared, the equiaxation degree of grains is higher, the mixed grain phenomenon is improved obviously, the bainite grain structure is refined, and the two phases of ferrite and bainite are evenly distributed in the matrix. When annealing temperature is 790 ℃, quenching temperature is 930 ℃ and holding time is 5 min, the microstructure is fine and uniform lath martensite, and the comprehensive mechanical properties are the best. Yield strength reaches 1353 MPa, tensile strength reaches 2018 MPa, elongation reaches 7.5%, and the transverse and longitudinal three-point bending angle reach more than 50°.

A heat treatment process for improving carbide morphology of wear resistant high manganese steel

Zhao Jinzhu, Xie Zhifeng, Wei Hong

2023, 48(3): 139-142. doi:10.13251/j.issn.0254-6051.2023.03.024

Abstract ( 34 )

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A heat treatment process for improving carbide morphology of wear resistant high manganese steel was discussed. The results show that the morphology and distribution of precipitated carbides in this wear-resistant high manganese steel can be effectively improved by water toughening treatment combined with high pressure heat treatment and atmospheric pressure heat treatment. After water toughening treatment, the wear-resistant high manganese steel can obtain dispersed granular and short strip carbides after 5 GPa, high pressure heat treatment at 650 ℃ for 30 min and heat treatment at 750-800 ℃ for 60 min.

Process optimization and microstructure of C250 maraging steel prepared by SLM process

Liu Zaixi, Lu Dehong, Wang Changjun, Liu Yu

2023, 48(3): 143-150. doi:10.13251/j.issn.0254-6051.2023.03.025

Abstract ( 57 )

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C250 maraging steel was prepared by SLM process. Effect of SLM process parameters on relative density and microstructure of the C250 maraging steel by means of metallographic microscopes (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM) and density measurement devices. Morphology and microstructure of the C250 maraging steel prepared by optimizing SLM process were analyzed. The results show that when the energy density is 85-120 J/mm³, relative density is higher than 99.5%, and the microstructure is dense without obvious defects. When the laser power is 270 W, the scanning rate is 700 mm/s, the scanning spacing is 0.11 mm, and the powder layer thickness is 0.03 mm, the density of the C250 maraging steel reaches 100%. Under the optimal SLM process, main phase composition of the C250 steel is martensite, which reaches 97.13%, and its internal grains are extremely fine, about 2.7 μm. In the martensite matrix there are also strengthening phases and dislocations to strengthen the C250 steel.

Effect of deformation microstructure on reheating austenite grain growth of high strength bainite steel for hydropower

Zou Yang, Gao Yuemin, Zhang Suyuan, Zhang Xuefeng, Zhang Yuefei, Wang Kun, Liu Guoquan

2023, 48(3): 151-158. doi:10.13251/j.issn.0254-6051.2023.03.026

Abstract ( 39 )

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Combined tests of hot deformation and heat treatment for austenite grain growth of a 800 MPa quenched and tempered bainite high strength steel for hydropower were carried out on Gleeble-3500. The steel specimens were deformed by various hot compression and cooled to ambient temperature, and then reheated at 900-1200 ℃ for different holding time to study the influence of the difference of hot deformation microstructure on the austenite grain growth behavior in reheating. The results show that under different strain rates (0.01-10 s^-1), deformation temperatures (900-1150 ℃) and 60% engineering strain, the hot deformed microstructure can be roughly divided into three types: the microstructure with obvious deformation characteristics, the fully recrystallized uniform fine microstructure, and the coarsened recrystallized microstructure. The grain growth trend of the three types of microstructure is basically the same during reheating. The larger the initial grain size, the larger the final austenite grain size is, and when reheated at 950 ℃, the austenite grains of deformed specimens with the first type of deformation microstructure grow slowly at first and then coarsen rapidly. After evaluation and verification, the Sellars model, Beck model andHillert model grain growth kinetics equation have a relatively satisfactory prediction effect on the austenite grain growth behavior of the test steel. The activation energy of austenite growth in Hillert model and Sellars model corresponding to the three types of deformed microstructure is basically the same, indicating that the difference of initial structure of the same composition steel does not have an essential influence on the grain growth mechanism.

Microstructure and properties of particles reinforced Co-based coating by laser cladding on 42CrMo steel

Li Erpan, Liang Guoxing, Liu Donggang, Lü Ming

2023, 48(3): 159-165. doi:10.13251/j.issn.0254-6051.2023.03.027

Abstract ( 32 )

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Co-based composite coating was prepared on surface of 42CrMo steel by laser technology to improve the wear resistance of mining pick, and the microstructure, hardness and wear resistance of the coating were analyzed. The results show that the clad layer has good morphology and metallurgical bonding with the substrate. Under the action of laser, WC particles dissolve and react with various elements. The clad layer is mainly composed of γ-(Co, Fe) and carbides. The microstructure of the clad layer is gradient, and the clad zone consists of equiaxed dendrites and carbide particles rich in W and Ti, while the transition zone consists of planar, dendritic and columnar grains. The average microhardness of the clad layer is 995 HV, which is much higher than that of the substrate (328 HV), and the hardness of the heat affected zone is also greatly increased. Under the same wear conditions, the friction coefficient of the clad layer is low, and the volume wear amount is only 13.5% of the substrate. In the process of friction, the dispersed fine carbide particles gradually protrude and play the role of bearing load and resisting wear, so that the clad layer has good wear resistance, and the wear mechanism is slight abrasive wear. The particle reinforced Co-based coating prepared by laser cladding technology has dense structure and excellent performance, which can significantly improve the surface hardness and wear resistance of the 42CrMo steel.

Hot deformation behavior and hot working diagram of alumina-forming austenitic (AFA) steel

Zhang Jingrui, Zhao Yanjun, Su Ke

2023, 48(3): 166-173. doi:10.13251/j.issn.0254-6051.2023.03.028

Abstract ( 32 )

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In order to predict the thermal deformation behaviour of AFA steel, high temperature hot compression experiments were carried out on the AFA steel at temperatures of 950-1150 ℃, strain rates of 0.01-10 s^-1 and true strains of 0.51-1.2 using a Gleeble-3500 thermal simulation tester to construct the instantonal equations and build up a thermal processing map. The results show that the rheological stress of the AFA steel gradually decreases with increasing deformation temperature at the same strain rate, and increases with increasing strain rate at the same deformation temperature. The linear correlation coefficient R² is 0.998 53 between predicted and actual stresses at a true strain of 0.69 (50% deformation). The thermal processing map shows that as the strain increases, the instability region of the AFA steel first decreases and then increases, concentrated in the low temperature region. The high-efficiency region becomes larger and the high efficiency region is concentrated at deformation temperatures between 1100 ℃ to 1150 ℃ with strain rates of 0.01 s^-1to 0.1 s^-1, indicating that the AFA steel is suitable for thermal processing at high temperatures and low strain rates.

Deformation behavior of Q&P steel with ultrafine-grained ferrite matrix under constant stress

Ma Wanwan, Tang Zhengyou, Cheng Chi, Zhao Li, Ding Hua

2023, 48(3): 174-178. doi:10.13251/j.issn.0254-6051.2023.03.029

Abstract ( 27 )

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Pre-quenching heat treatment process was adopted to obtain Q&P steel with ultrafine-grained ferrite. The microstructure evolution and deformation behavior of the tested steel under a constant stress were studied through a load-holding control experiment. The results show that the mount of strain increases gradually with the increasing of holding stress, and the strain increases slightly with the prolonging of the holding time. When loading stress is lower than the yield stress, the strain does not change with the prolonging of the load-holding time. When loading stress is higher than the yield stress, the amount of strain increases significantly and the strain-induced transformation from retained austenite to martensite occurs during the deformation process. In addition, the stability of retained austenite first decreases and then increases with the increase of strain.

High temperature rupture properties of A286 alloy

Deng Shanshan, Sun Yongqing, Jiang Yehua, Liu Zhenbao, Liang Jianxiong, Wang Changjun

2023, 48(3): 179-187. doi:10.13251/j.issn.0254-6051.2023.03.030

Abstract ( 33 )

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In order to investigate high temperature rupture properties of A286 alloy, the high temperature rupture tests of the A286 alloy prepared by electric arc furnace+ladle furnace+vacuum arc remelting (EAF+LF+VAR) smelting process at different temperatures and stresses were carried out, and the Larson-Miller parameter (LMP) was used to predict the rupture life of the A286 alloy, the microstructure evolution of fracture was analyzed. The results show that the relationship between stress and LMP is σ=-107.30×LMP+3011.02. The fracture mode of the A286 alloy changes from ductile fracture consisting of tough nests and holes to brittle fracture intergranular fracture as the testing temperature decreases. At high stress and low temperature, cracks are mainly generated at MC and M₂₃C₆, while at low stress and high temperature, cracks are mainly generated at lamellar η phase. The strengthening mechanism at testing temperature of 650 ℃ and stress of 450 MPa is mainly precipitation strengthening by dislocation cutting through the γ′ phase. The strengthening mechanism at testing temperature of 750 ℃ and stress of 150 MPa is precipitation strengthening by dislocation cutting through the γ′ phase and dispersion strengthening by dislocation passing the γ′ phase. The nanoparticles such as TiP₂, (Ti, Nb)C, TiC, and NbC precipitated in the grains are favorable to the high temperature rupture properties.

Preparation and oxidation resistance of Al-Si coating on GH738 alloy

Guo Mengxin, Ran Xuelin, Zhang Jin

2023, 48(3): 188-194. doi:10.13251/j.issn.0254-6051.2023.03.031

Abstract ( 44 )

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Al-Si coating was prepared on the surface of GH738 alloy by thermal diffusion method. The morphology, thickness, phase composition and element distribution of the Al-Si coating were studied by means of X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS); the hardness of the coating was determined by hardness tester; the static high temperature oxidation resistance test was carried out at 1200 ℃ for 100 h. The results show that the coating thickness reaches 120 μm, the coating is an obvious double-layer structure, the outer layer is Al-Si layer, and the inner layer is inter-diffusion layer; the phase composition of the coating is mainly NiAl and Ni₂Al₃ with a small amount of Cr₃Si; the hardness of the coating reaches about 900 HV0.1, which is about 3.5 times of the matrix; the oxidation kinetics curve of the coating meets the parabolic law, and the oxidation rate constant is 0.0987 mg²·cm^-4·h^-1. The high temperature oxidation resistance of the relatively dense Al₂O₃ protective film formed on the alloy surface is about 5 times higher than that of the matrix.

Heat treatment process and microstructure and properties of Q345/40Cr bimetal ring

Chang Yaodong, Qi Huiping, Jia Yanlong, Li Yongtang, Wu Yonghong

2023, 48(3): 195-202. doi:10.13251/j.issn.0254-6051.2023.03.032

Abstract ( 34 )

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Rolled Q345/40Cr bimetal rings were quenched at 860-950 ℃ and tempered at 520-610 ℃, the microstructure and properties after heat treatment was observed, analyzed and tested. The results show that the grains are refined after quenching, and coarsened with the increase of quenching temperature. The hardness of the 40Cr steel and hardness of its adjacent bonding layer decreases first and then increases, while the hardness of the Q345 steel decreases slightly, and the hardness of its adjacent bonding layer decreases. The alloying elements in the 40Cr steel side dissolves incompletely when quenched at 860 ℃, and the optimal quenching temperature is 890 ℃. The results of mechanical properties tests show that after 890 ℃ quenching and with the increase of tempering temperature, the tensile strength and hardness of the bimetal ring decrease, the elongation of the Q345 steel and its adjacent bonding layer increases first and then decreases, and the impact property of the bimetal ring is improved. The fracture position of bonding layer is on the side of Q345 steel. The comprehensive performance of the bimetal ring is the best after quenching at 890 ℃ and tempering at 550 ℃, which meets the practical application requirements.

Friction and wear performance of U76CrRE heavy rail steel under different post-rolling cooling modes

Ji Chunjiao, Cen Yaodong, Zhang Liang, Chen Lin, Guo Yaohui

2023, 48(3): 203-208. doi:10.13251/j.issn.0254-6051.2023.03.033

Abstract ( 46 )

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Taking U76CrRE heavy rail steel under different post-rolling cooling modes as the research object, the friction factor, wear amount, microstructure and wear-surface alloy element composition of the rail under water friction, dry friction and sand friction were analyzed by means of friction and wear tester, SEM (scanning electron microscope), EDX (energy dispersive spectrometer) and CLSM (laser confocal microscope). The results show that under same wear time, the average friction coefficient of air-blast-cooled specimen is smaller than that of air-cooled specimen, and the wear amount of air-blast-cooled specimen is much less than that of air-cooled specimen under sand friction. For the air-blast-cooled specimen, a small amount of scratches and peeling are formed after water friction, which are delamination wear; there are plough marks under dry friction and transverse cracks on the plough ridge, which are oxidized wear; and under sand friction, a large amount of wear debris appears and the most serious wear is abrasive wear. And the surface of the air-cooled specimen is flat and the pear groove is more obvious. The deformation layers of the air-blast-cooled specimens are all smaller than that of the air-cooled specimen, and the sand friction deformation layer is the largest. The U76CrRE heavy rail steel under air-blast-cooling has better wear resistance than that under air cooling.

Microstructure and mechanical properties of Sn-modified Ti-Zr-Cu-Ni filler metals

Liu Quanming, Xiao Junfeng, Long Weimin, Fu Li, Yang Haiying, Gao Sifeng

2023, 48(3): 209-214. doi:10.13251/j.issn.0254-6051.2023.03.034

Abstract ( 29 )

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Using self-made Ti-Zr-Cu-Ni-Sn filler metal to braze TA2 titanium alloy, the melting characteristics, microstructure and phase, wetting and corrosion resistance, and tensile strength of joints of modified Ti-Zr-Cu-Ni filler metals with different contents of Sn were studied. The results show that with the increase of Sn content, the solid and liquidus temperature of Ti-Zr-Cu-Ni-Sn filler metals basically increase, but the temperature difference is basically narrowed, which better inhibits the formation of brittle compounds at the brazing interface. The microstructure of the Ti-Zr-Cu-Ni-5Sn filler metals is composed of Ti, Zr matrix and crystal phase. Sn is more inclined to combine with Ti and Zr to form low melting point eutectic phases such as Ti₂Sn₃, Ti₆Sn₅, Zr₅Sn₃, et al. When Sn≤1.5%, the wettability of this filler metal to the TA2 titanium alloy is gradually deteriorated. Continuing to increase the Sn, the wettability of the filler metal is improved, and the filler metal containing 5%Sn has the best wetting to the matrix. The erosion of TA2 titanium alloy is weakened by adding 5%Sn and reducing the total amount of Cu and Ni. Under the same brazing process, the strength and plasticity of the brazed joint with 5% Sn are improved. With the increase of the brazing temperature, the Ti-Zr-Cu-Ni filler metals produces more strengthening phases, which leads to a significant increase in the strength of brazed joint, however, the strengthening effect of Sn-containing phase produced by Ti-Zr-Cu-Ni-5Sn filler metal on strength of brazed joint is limited. In contrast, the brazing temperature has a greater impact on the strength of brazed joints.

Microstructure evolution of α′ and α″ phase and mechanical properties of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy

Yue Xu, Zhang Mingyu, Tong Xiaole, Qiao Enli, Zhang Qi, Yang Jialuo, Ye Hongchuan

2023, 48(3): 215-220. doi:10.13251/j.issn.0254-6051.2023.03.035

Abstract ( 35 )

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Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy was subjected to solution and aging treatment. Effects of solution and aging on microstructure evolution of α′ phase and α′′ phase and mechanical properties of the alloy were analyzed by means of optical microscope, scanning electron microscope, XRD diffractometer, tensile test and impact property test. The results show that the size of primary α phase becomes smaller and tends to be equiaxed in the microstructure after solution treatment, and the smaller primary α phase dissolves and disappears, and the β transformation microstructure becomes insignificant. A large number of α_s phases are precipitated in the microstructure after aging, and the β transformation microstructure is more obvious. After solution treatment, the microstructure consists of α+α′+α″ phase. After aging treatment, the microstructure consists of α phase and β phase. After solution treatment, the tensile strength of the alloy is 1336 MPa, the yield strength is 1070 MPa, the elongation is 6%, the section shrinkage is 22%, and the impact absorbed energy is 16 J. After aging treatment, the strength of the bar increases with the increase of aging temperature, and the plastic trend is opposite, the impact toughness is almost unchanged. The tensile and impact fracture morphologies of the alloy after solution treatment are composed of dimples, which is a typical ductile fracture. After aging treatment, the micromorphologies of the tensile and impact fracture have obvious ups and downs. With the increase of aging temperature, the size and number of dimples decrease, and tear edges and voids appear. The fracture type has a tendency to brittle fracture, but it is still dominated by ductile fracture.

Grain growth behavior of GH4141 superalloy during solution treatment process

Xiao Dongping, Wang Fu, Zhou Yang, Fu Jianhui

2023, 48(3): 221-225. doi:10.13251/j.issn.0254-6051.2023.03.036

Abstract ( 35 )

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Effects of solution temperature and holding time on grain growth behavior of GH4141 alloy were studied, and the grain growth model of the alloy was established. The results show that when the solution temperature is less than orequal to 1080 ℃, the grain growth of the alloy is not obvious; while the grain size grows significantly when the temperature is higher than orequal to 1100 ℃. At different solution temperatures, the grain size grows rapidly when the holding time is less than or equal to 60 min; and the grain growth trends is slow with the increasing of the holding time especially when the holding time is over 60 min. The established grain growth kinetic model of the GH4141 alloy can accurately predict the grain size evolution during solution treatment.

Development of 800 MPa grade microalloyed steel for high toughness longitudinal welded pipe

Xiong Weiliang, Yan Lixin, Liang Liang, Wu Teng, Wu Run, Su Changzhu

2023, 48(3): 226-229. doi:10.13251/j.issn.0254-6051.2023.03.037

Abstract ( 30 )

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800 MPa high-toughness microalloyed steel longitudinal welded pipe was produced by ultra-fast cooling after hot rolling. Microstructure and properties of different regions of the tested steel were studied by means of OM, SEM, TEM and tensile testing. The results show that the hot-rolled structure of the tested steel is mainly granular bainite+a small amount of lath bainite, the amount of granular bainite in the welding heat affected zone reduces to 32.7%, and the lath bainite increases to 30.5%, acicular ferrite and a small amount of martensite appear in the microstructure. The hot rolling zone of the tested steel is mainly composed of Ti for composite microalloying, and the comprehensive application of solution strengthening, fine grain strengthening, dislocation strengthening and precipitation strengthening, the yield strength, tensile strength, and elongation are 804 MPa, 852 MPa and 21.5%, and shows high strong toughness.

Corrosion resistance of vanadium doping ion carburized layer of TA2 titanium plates

Sun Weiwei, La Lingmin, Zhang Jing, Liang Fengxiao, Qin Lin

2023, 48(3): 230-235. doi:10.13251/j.issn.0254-6051.2023.03.038

Abstract ( 25 )

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In order to improve corrosion resistance and electrical conductivity of titanium-based bipolar plate, the surface of TA2 pure titanium was treated by double glow ion carburizing, and vanadium was doped in the carburizing process to reduce the carburizing temperature. The structure, chemical composition and phase composition of the modified layer were characterized by scanning electron microscopy, energy dispersive analysis and X-ray diffraction. The interface contact resistance and corrosion resistance of the modified layer were measured. The results show that under the optimized preparation process parameters, dense TiC modified layer and vanadium-doped carburizing modified layer are formed on the surface of TA2. When the compaction force is 140 N/cm², the interface contact resistivities of the vanadium-doped carburizing modified layer prepared at 730 ℃, TiC modified layer prepared at 850 ℃ and TA2 matrix are 1.17, 3.66 and 14.71 mΩ/cm². The self corrosion current densities of the vanadium-doped carburizing modified layer prepared at 730 ℃ and TiC modified layer prepared at 850 ℃ under the simulated bipolar plate working environment are 5.238 and 7.563 μA/cm², respectively, which are 1 order of magnitude lower than that of TA2 substrate. Doping vanadium in the process of ion carburizing can effectively reduce the process temperature of carburizing and improve the conductivity and corrosion resistance of TA2 matrix.

Effect of vanadium on microstructure and mechanical properties of nitrogen-containing martensitic stainless steel

Cao Xin, Li Quan, Yang Yinhui

2023, 48(3): 236-241. doi:10.13251/j.issn.0254-6051.2023.03.039

Abstract ( 23 )

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In order to improve the service performance of nitrogen-containing martensitic stainless steel at high temperature, two tested steels (one with 0.12%V (mass fraction) and one without V) were designed. The effect of adding a trace amount of vanadium on microstructure and mechanical properties of the nitrogen-containing martensitic stainless steel was studied by impact tester, tensile tester, hardness tester, Thermo-Calc software, OM, SEM and TEM. The results show that the hardness of nitrogen bearing martensitic stainless steel with 0.12%V tempered at 450-550 ℃ is 0.6-1.9 HRC higher and the impact absorbed energy is 1.2-3.8 J higher than that without V. After quenching at 1050 ℃, cryogenic treatment at -73 ℃ and tempering at 530 ℃, the plasticity and toughness of the 0.12%V steel are greatly improved, the fracture mode changes to ductile-brittle mixed fracture, and the prior austenite grain size decreases from 16.48 μm to 11.12 μm, the types and distribution of the secondary phases change from the short rod-like coarse carbides distributed as broken chains along the prior austenite grain boundary into dispersively distributed spherical carbides and carbonitrides. Thus the strength and ductility of the nitrogen bearing martensitic stainless steel are all improved by refining grains and uniformly distributing spherical carbides and carbonitrides.

Effect of rare earth Ce on microstructure of 4Cr5MoSiV1 steel

Yang Lilin, Xu Qihao, Zhao Liping

2023, 48(3): 242-247. doi:10.13251/j.issn.0254-6051.2023.03.040

Abstract ( 35 )

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The microstructure of 4Cr5MoSiV1 tested steel with different Ce content after hot-working treatment was observed and analyzed, and the effect of Ce content on its microstructure was studied. The results show that the addition of rare earth Ce can improve the microstructure of the 4Cr5MoSiV1 steel as-cast, and after hot forging, normalizing and spheroidizing annealing, refine the grain, modify the inclusion, reduce the composition segregation and eliminate the undissolved carbide. However, when the content of rare earth Ce exceeds 0.026%, the above improvement effect will gradually weaken and even worsen.

Effect of residual element Sb on mechanical properties of X80 pipeline steel

Chen Zihong, Xue Zhengliang, Liu Mengke, Zhang Xiang, Zheng Dingli, Ma Guojun

2023, 48(3): 248-253. doi:10.13251/j.issn.0254-6051.2023.03.041

Abstract ( 20 )

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X80 pipeline steel with different Sb contents was smelted in vacuum induction furnace, the effect of Sb on microstructure of the X80 pipeline steel and its existing form in the steel were investigated. The effect of Sb content on mechanical properties of pipeline steel was also studied by means of Vickers hardness testing, room temperature tensile testing and Charpy impact testing at -20 ℃. The results show that the residual element Sb in pipeline steel is uniformly distributed in the steel matrix. With the increase of Sb content from 0.0006% to 0.0980% in pipeline steel, the average size of ferrite and pearlite first increases and then decreases, the Vickers hardness firstly increases and then tends to be constant. The impact absorbed energy gradually decreases, basically, while the tensile strength and yield strength firstly decrease and then increase, and then slightly decrease. The yield ratio decreases firstly and then increases, and the elongation slightly decreases. In order to ensure mechanical properties of the X80 pipeline steel, the content of residual element Sb in the steel should be reduced as far as possible.

Effect of Ti addition on microstructure and wear resistance of AlCuFeMnNi high entropy alloy

Ma Mingxing, Wang Bozhen, Wang Zhixin,Yang Cheng, Li Shangzhi, Dong Chen, Hou Runsen

2023, 48(3): 254-258. doi:10.13251/j.issn.0254-6051.2023.03.042

Abstract ( 25 )

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In order to study the effect of Ti addition on microstructure and wear resistance of AlCuFeMnNi high entropy alloy, AlCuFeMnNi and AlCuFeMnNiTi alloys with equal molar ratio were prepared by vacuum arc melting technique. The phase composition, microstructure, hardness and tribological properties of the two alloys were tested by X-ray diffractometer, metallographic microscope, scanning electron microscope, microhardness tester and friction and wear tester. The results show that with the Ti addition, the phases of the AlCuFeMnNiTi alloy changes from FCC and BCC1 two-phase structure to FCC, BCC1 and BCC2 three-phase structure, and the lattice constant and cell volume of AlCuFeMnNiTi alloy increase. The microstructure of the both alloys are typical dendritic grains. The addition of Ti gradually refines the grains of the alloy, increases the area of the dendrite region, decreases the area of the intergranular region, and makes a small amount of leading phase BCC2 distributed dispersively in the dendrite region. After the addition of Ti, the hardness of the alloy increases from 423.5 HV0.5 to 498.0 HV0.5, the mass loss rate and friction coefficient decreases from 0.43% and 0.59 to 0.39% and 0.46, respectively, and the friction coefficient increases first and then stabilizes. The increase of hardness and wear resistance of the AlCuFeMnNiTi alloy is mainly due to the combined effects of fine grain strengthening, solution strengthening and crystal structure transformation to high strength phase caused by the Ti addition.

Effect of decreasing carbon and increasing nitrogen on microstructure and properties of quenched martensitic stainless steel

Ji Xianbin, Li Zhaoguo, Wei Haixia, Qian Zhangxin

2023, 48(3): 259-262. doi:10.13251/j.issn.0254-6051.2023.03.043

Abstract ( 24 )

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First air quenching 30Cr13 and 30Cr14N steels respectively at different temperatures (950, 1000, 1050, 1100 ℃) in muffle furnace, then the effect of nitrogen content on microstructure, carbides, hardness and corrosion resistance of the 30Cr13 steel was investigated by using laser scanning confocal microscope, scanning electron microscope, hardness tester, X-ray diffractometer, and salt spray tester. The results show that when quenched at the same temperature, the 30Cr14N steel has higher hardness, less carbide and better corrosion resistance than that of the 30Cr13 steel. Nitrogen not only affects the microstructure and hardness of the tested steel, but also avoid the intergranular corrosion caused by excessive carbide precipitation through decreasing carbon and increasing nitrogen, because FeNiN precipitation does not cause significant intergranular corrosion as Cr₂₃C₆ precipitation. Therefore, decreasing carbon and increasing nitrogen is an effective way to improve the microstructure and properties of martensitic stainless steel.

Effect of microalloying element Zr on microstructure and properties of 5083 aluminum alloy

Sun Hongmei, Liu Cuiling, Chen Jian, Fang Hongjie

2023, 48(3): 263-268. doi:10.13251/j.issn.0254-6051.2023.03.044

Abstract ( 20 )

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5083 and 5083+0.1Zr aluminum alloys were melted and cast in laboratory by well crucible furnace, then rolled and annealed in the range of 100-450 ℃. The as-cast microstructure, fibre morphology of the plate, mechanical properties, corrosion resistance and the second phase particle compositions of the alloys were analyzed by means of metallographic microscope, microhardness tester, electronic universal testing machine and scanning electron microscope, so the effect of trace Zr addition on microstructure and properties of the tested alloys was studied. The results show that the addition of trace element Zr can refine the microstructure. Compared with that without Zr, the as-cast grain size of the 5083 alloy with 0.1Zr decreases from 123 μm to 73 μm. The trace addition of Zr can also reduce the size of the second phase Al₆Mn(Fe) particles, reduce the size of intergranular corrosion pits and improve the corrosion resistance of the alloy. Further, the trace addition of Zr can inhibit the recrystallization of the alloy plate, and there is no obvious recrystallization phenomenon when annealed at 300 ℃ for 1 h; and especially, after annealing at 250 ℃ for 1 h, the tensile strength of the 5083+0.1Zr alloy is 389.50 MPa, the yield strength is 215.62 MPa and the elongation is 18.2%, which still fully meet the application requirements.

Effect of Ni on microstructure and properties of 75Cr1 high carbon tool steel

Zeng Bin, Wan Yang, Liang Liang, Li Zhaodong, Yong Qilong

2023, 48(3): 269-274. doi:10.13251/j.issn.0254-6051.2023.03.045

Abstract ( 25 )

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In order to develop woodworking circular saw blade, band saw, spring and other hardware tools with high properties and long life, the Ni element with mass fraction of 0.2% and 0.4% was added to the 75Cr1 steel, respectively. The effect of different Ni content on mechanical properties and microstructure of the 75Cr1 steel as hot rolled and heat treated was studied by mechanical property test, microstructure analysis and heat treatment test. The results show that within the range of 0%-0.4% Ni addition, the strength and hardness of the hot rolled 75Cr1 steel can be reduced, but the plasticity improved, the higher its content is, the more significant the effect is, however, the impact property is not obvious change. Ni content has little effect on quenching hardness, when it reaches 0.4%, the hardness of the steel shows a trend of decreasing, but the plasticity after tempering is obviously improved; after tempering, the strength and hardness of the steel are reduced, but the impact absorbed energy is improved. The higher the Ni content, the more obvious the improvement effect. On the aspect of microstructure, Ni can refine the size and lamellar spacing of the hot rolled 75Cr1 steel pearlite colonies, promote the spheroidization of lamellar pearlite, and refine the microstructure after quenching and tempering. Considering economy and mechanical properties, the optimal addition of Ni in the 75Cr1 steel is 0.2%.

Effect of nano-sized TiC on microstructure and propertits of Al-Cu alloy

Lu Yalin, Huang Yong, Wang Jian

2023, 48(3): 275-279. doi:10.13251/j.issn.0254-6051.2023.03.046

Abstract ( 23 )

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Effects of nano-sized TiC particles on the microstructure of the Al-Cu alloy at as-cast, as-rolled, and heat-treated states and on the mechanical properties after heat treatment were studied. The results show that the microstructure of the alloy can be effectively refined by adding appropriate nano-TiC particles. When the TiC content is small, with the increase of TiC content, the alloy undergoes dynamic recrystallization during rolling deformation, and the average grain size decreases. When the TiC content exceeds 0.5% (mass fraction), the recrystallized grains gradually grow and coarsen. When the content of nano-TiC is 0.5%, the comprehensive properties of the alloy are the best. Compared with the matrix, the tensile strength and elongation increase by 18.6% and 7% respectively. During heat treatment, precipitates and a large number of dislocations are produced in the TiC/Al-Cu alloy, which is helpful to improve the mechanical properties of the material.

Three-dimensional quantitative characterization of non-metallic inclusions in steels

Yan Chunlian, Qin Hancheng, Qi Qige, Dai Jin, Feng Chao, Meng Yang

2023, 48(3): 280-286. doi:10.13251/j.issn.0254-6051.2023.03.047

Abstract ( 28 )

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Three-dimensional morphological observation and statistical quantification of typical inclusions as large-size Al₂O₃, MnS and oxysulfides were conducted in the ultra-low carbon steel, the free cutting steel and the pipeline steel by using optimized electrolytic extraction and automated inclusion analysis technique. Some factors affecting the three-dimensional quantitative characterization of inclusions, such as the electrolytic interfering substance, the dispersion state of inclusions and the setting of SEM parameters were discussed about how to influence three-dimensional quantitative results. Combined with two-dimensional analysis, three-dimensional morphological observation and statistical quantification of the inclusions will provide more comprehensive, reliable and accurate information.

Process improvement of inner ring made of 20Cr2Ni4A steel

Liu Ke, Chen Jianwen, Zuo Jingwei, Deng Yaoyao, Zhu Xu, Zou Wei

2023, 48(3): 287-291. doi:10.13251/j.issn.0254-6051.2023.03.048

Abstract ( 23 )

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Aiming at the problem that the round cover plate made of 20Cr2Ni4A steel inner ring of hydraulic torque converter after carburizing and quenching was warped too much to meet the machining requirements, the finite element method was used to simulate the effect of furnace charging mode and adding machining allowance at the upper and lower ends of the round cover plate on stress field and deformation field during the carburizing and quenching process of the inner ring, and the experimental verification was carried out. The results show that the charging method and increasing the machining allowance have a great influence on the stress field and deformation field during the carburizing and quenching process of the inner ring. The maximum deformation amount in the order from large to small after quenching with 4 furnace charging methods is long axis vertical placement, short axis vertical placement, horizontal placement and hanging placement. Using the hanging placement can effectively reduce the warpage deformation of the plane at thin wall of 215 mm to 0.29 mm, and the warpage of the horizontal furnace can be controlled to 0.21 mm. When the machining allowance at the top of the round cover plate is increased to 11 mm, the warpage can be controlled to 0.19 mm. In terms of overall production efficiency and cost, it is advisable to use horizontal placement for production.

Fracture failure analysis of high-temperature fastening bolt for turbine control valve

Sun Yunfei, Shi Xianda, Zhang Zhihao, Chen Hao, Lü Lei, Yun feng

2023, 48(3): 292-295. doi:10.13251/j.issn.0254-6051.2023.03.049

Abstract ( 35 )

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High temperature fastening bolt of the steam turbine IP governing valve was broken and failed during the unit maintenance in A thermal power plant. In order to determine the cause of failure and avoid the recurrence of similar events, macro morphology, fracture micro morphology, chemical composition, microstructure and mechanical properties of the fractured bolt were tested and analyzed by direct reading spectrometer, optical microscope, scanning electron microscope and pendulum impact tester. The results show that the main reason for the fracture of high temperature fastening bolt made of 20Cr1Mo1VTiB steel is that the forging temperature of the bolt in the manufacturing stage is too high or the quenching temperature is too high, which results in the coarse grain structure and the impact property of the material is reduced. Under the impact load generated by the frequent action of the turbine control valve, the bolt cracks along the coarse grain region and extends in the form of brittle cleavage fracture until the bolt is completely broken.

Analysis on quenching cracking of a heavy forging of wind turbine system

Li Xinsheng, Liu Yongchao, Liu Long, Xu Jian, Bi Jinghua, Liu Guoqiang, Yan Huaiying, Ding Ning

2023, 48(3): 296-300. doi:10.13251/j.issn.0254-6051.2023.03.050

Abstract ( 43 )

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Cause of quenching cracks in a heavy forging of wind turbine system was analyzed by means of scanning electron microscope and energy dispersive X-ray spectrum. The results show that the initial position of the quenching crack is located at the protuberance position on inner wall of central hole of the heavy forging. The quenching crack is caused by the combined action of the additional stress at the protuberance on inner wall and the internal stress generated in the segregation region during heat treatment.

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