Heat Treatment of Metals

Effect of post-rolling cooling and heat treatment processes on microstructure and mechanical properties of Nb-microalloyed V140 steel for OCTG

Fan Zhongtao, Gao Xiuhua, Yuan Guo, Kang Jian

2020, 45(12): 1-6. doi:10.13251/j.issn.0254-6051.2020.12.001

Abstract ( 122 )

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Effects of different processes and the function of Nb on the mechanical properties and microstructure of V140 steel for OCTG (oil country tubular goods) were studied through hot rolling and post-rolling heat treatment experiments. The results show that Nb(C, N) precipitated at high temperature can inhibit the recrystallization of austenite, make the finishing rolling process possible in the non-recrystallization zone and refine grains, thus improving the strength and toughness of the steel. Under three kinds of processes including post-rolling air cooling+offline quenching and tempering, post-rolling fast cooling+tempering, and post-rolling fast cooling+offline quenching and tempering, the microstructures of the steel are all uniform ones of tempered sorbite with excellent mechanical properties. Moreover, the post-rolling fast cooling+tempering process can meet the requirements of mechanical properties, shorten the production process and save cost, with the best tempering temperature and time being 660 ℃ and 30 min, respectively.

Effect of annealing temperature on microstructure and mechanical properties of FeMoCrVTiSi_x high entropy alloy

Xue Yanjun, Yu Wenchao, Wang Maoqiu, Shi Jie

2020, 45(12): 7-12. doi:10.13251/j.issn.0254-6051.2020.12.002

Abstract ( 88 )

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Effect of different annealing temperatures (400, 600, 800, 1100 ℃) on the microstructure and mechanical properties of FeMoCrVTiSi_x(x=0, 0.3) alloy was studied by using X-ray diffractometer(XRD), scanning electron microscope(SEM), differential thermal scanning analyzer(DSC), microhardness tester and universal material testing machine. The results show that the addition of Si improves the thermal stability of the FeMoCrVTi high entropy alloy. After annealing treatment, the microstructure of FeMoCrVTiSi_x high entropy alloy is still mainly composed of BCC solid solution phase, but a black fine Ti-rich phase appears at the edge of the dendrite, and its content increases with the increase of annealing temperature until it re-dissolves at 1100 ℃. The precipitation of Ti-rich phase is conducive to the improvement of the hardness. The hardness of the specimen reaches the maximum value annealed at 800 ℃, with that of the FeMoCrVTi and FeMoCrVTiSi_0.3 alloys reaching 932 HV0.2 and 998 HV0.2, respectively.

Continuous cooling transformation of non-quenched and tempered 45MnSiVSQ steel under different deformation conditions

Wang Yunlong, Chen Yinli, Yu Wei

2020, 45(12): 13-18. doi:10.13251/j.issn.0254-6051.2020.12.003

Abstract ( 81 )

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Dynamic and static dilatometric curves of non-quenched and tempered steel 45MnSiVSQ were measured on Gleeble-3500 thermal simulator and thermal dilatometer. The dynamic and static continuous cooling transformation (CCT) curves of the 45MnSiVSQ steel were measured by the tangent method combining with microstructure and hardness analysis, and the effects of deformation temperature and cooling rate on the phase transformation and the interlamellar spacing of the 45MnSiVSQ steel were investigated. The results show that as the cooling rate increases, the pearlite interlamellar spacing gradually decreases when the cooling rate is in the range of 0.1-3 ℃/s. Compared with the static and dynamic CCT curves of the 45 MnSiVSQ steel at 950 ℃, it can be seen that the deformation shortens the phase transformation incubation period especially in the ferrite and pearlite phase transformation range, but it has little effect on the incubation period in the bainite and martensite phase transformation zone, so that the dynamic CCT curves move to the upper left compared to the static CCT curves. By comparing the CCT curves at different deformation temperatures, it is found that bainite phase transformation occurs at 0.5-20 ℃/s when deformed at 950 ℃, while at 0.8-10 ℃/s when deformed at 850 ℃. Low temperature deformation is more conducive to the occurrence of ferrite and pearlite phase transformation, and reduces the probability of occurrence of non-ideal structures such as bainite and martensite.

Effect of heat treatment process on microstructure and mechanical properties of a hypereutectoid steel for rail

Cui Jianwei, Chen Lin, Zhao Leicheng, Zou Yun

2020, 45(12): 19-23. doi:10.13251/j.issn.0254-6051.2020.12.004

Abstract ( 77 )

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Changing laws of microstructure and properties of a hypereutectoid steel for rail under different heat treatment processes were studied by means of microhardness tester, impact testing machine, universal testing machine and scanning electron microscope. The results shows that, compared with that of the states as rolled and as factory heat treated, the microstructure and mechanical properties of the tested steel are improved by heat treatment, and the main influencing factors are cooling rate and the decrease of isothermal time. With the increase of cooling rate and the decrease of isothermal time, the precipitation of cementite in the matrix increases, the size of pearlite decreases, and the large lamellar pearlite disappears gradually. In addition, the hardness, impact absorbed energy and tensile strength increase first and then decrease with the increase of cooling rate, showing a polyline trend, the roughness of tensile fracture increases, and the fracture mode changes from cleavage to quasi cleavage, while the impact absorbed energy increases with the increase of isothermal time. Finally, the optimum heat treatment process is the isothermal temperature of 630 ℃, isothermal time of 30 s, and cooling rate of 8 ℃/s. The corresponding mechanical properties are the best, with the hardness, the impact absorbed energy, the tensile strength, the elongation and the percentage reduction of area being 402 HBW, 2.9 J, 1312 MPa, 12.24% and 23.96%, respectively.

Effect of solution and aging treatment on microstructure and tensile properties of Ti-5322 alloy

Wang Andong, Zhang Luxiang, Chen Caifeng, Mao Yongquan, Ni Lei

2020, 45(12): 24-28. doi:10.13251/j.issn.0254-6051.2020.12.005

Abstract ( 83 )

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Through solution and aging treatment, the microstructure and tensile properties of Ti-5322 alloy were studied. The results show that when the solution treatment temperature is below the transformation point, the primary α phase decreases with the increase of solution treatment temperature, and the volume fraction of the β phase increases. When the solution treatment temperature is above the transformation point, the primary α phase is completely dissolved into the β phase, and the higher the temperature, the coarser the grains. During the aging at 510-590 ℃, the secondary α phase plates precipitate in the β matrix, which plays a precipitation strengthening role. As the aging temperature increases, the secondary α phase grows up and its volume fraction is reduced, leading to a decrease in the strength and an increase in the plasticity of the alloy. The room temperature tensile test shows that compared with the solution treatment in β single-phase region then aging, the strength and plasticity of the alloy are more excellent after solution treatment in the α+β two-phase region and aging, so it is most suitable to select the solution treatment in the two-phase region, and the optimum process is solution at 870 ℃ for 1 h and aging at 550 ℃ for 6 h.

Effect of electropulse shocking treatment on microstructure and properties of TC11 titanium alloy

Wang Zhongqi, Song Yanli, Hua Lin, Yu Yongqing

2020, 45(12): 29-35. doi:10.13251/j.issn.0254-6051.2020.12.006

Abstract ( 70 )

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Effect of electropulse shocking treatment(EST) on microstructure and mechanical properties of TC11 titanium alloy was studied by means of metallographic microscope, scanning electron microscope, X-ray diffractometer, universal material testing machine and microhardness tester. The results show that the ratio of α phase in the microstructure of TC11 titanium alloy, the lath size of β transformation structure and residual compressive stress are significantly affected by different pulse numbers. With the increase of EST pulse number, the content of α phase and the content of secondary α phase in lath like β transformation structure increase firstly and then decrease. After treated by the ETC with the best process parameters (900 A, 50 Hz, 25 pulses), the α phase in the TC11 titanium alloy is fine and uniform, and the length, thickness and spacing of β transformation lath are reduced by 51.9%, 58.0% and 36.8%, respectively, compared with those before treatment. At this time, the mechanical properties of TC11 titanium alloy are improved most obviously: elongation increased by 12.7%, microhardness increased by 4.7%, and residual compressive stress increased by 48.4%.

Effect of annealing process on microstructure uniformity of cold-rolled low-carbon steel plate for hot dip galvanizing

Xu Xiaohan, Song Yifeng, Liu Zhiqiao, Yue Chongxiang

2020, 45(12): 35-40. doi:10.13251/j.issn.0254-6051.2020.12.007

Abstract ( 70 )

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Effect of annealing process on the microstructure uniformity of cold-rolled low-carbon steel plate for hot dip galvanizing was studied by simulated annealing experiment and industrial trial production. The causes of mixed grain microstructure in the steel were analyzed and the solution was developed. The results show that lower heating rate is the main reason for the mixed grain microstructure. With the increase of heating rate, the microstructure becomes finer and more uniform. At lower heating rate, both extending the soaking time and raise the annealing temperature aggravate the inhomogeneity of microstructure. Aiming at the problem of the mixed grain resulted from the rate decline during the galvanizing unit production and combined with the simulated annealing test results, it is found that lowering the annealing temperature can improve such mixed grain problem, and based on which the annealing process for the rate reducing production is formulated and applied to the actual production.

Effect of spheroidizing annealing on microstructure and mechanical properties of high-carbon martensitic stainless steel 8Cr13MoV

Yu Wentao, Li Jing, Xu Meng, Shi Chengbin

2020, 45(12): 41-47. doi:10.13251/j.issn.0254-6051.2020.12.008

Abstract ( 146 )

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In order to optimize the spheroidizing heat treatment process of high carbon martensitic stainless steel 8Cr13MoV and improve its cold working properties after annealing, the effects of austenitizing time and cooling rate on the spheroidization effect of 8Cr13MoV steel during the spheroidizing annealing process were investigated by microstructure analysis and tensile mechanical test. The obtained results indicate that with the increase of austenite holding time, the number of fine carbides decreases, while the number of sorbite increases. The hardness of the steel decreases first and then increases, and the elongation increases. The number of fine carbides and sorbite, the hardness and strength of the steel increase with the cooling rate increasing, while the elongation decreases. Comprehensive comparison shows that the comprehensive mechanical properties of the 8Cr13MoV steel are preferable when the austenitic holding time is 90 min, and the cooling rate should be controlled within 25 ℃·h^-1. Compared with holding time, the influence of cooling rate on the mechanical properties is more remarkable.

Effect of vacuum heat treatment on thermal cycling life of APS-NiCoCrAlY+APS-YSZ thermal barrier coating

Xue Wenli, Lu Tao, Huang Jiahua, Guo Deliang

2020, 45(12): 47-52. doi:10.13251/j.issn.0254-6051.2020.12.009

Abstract ( 73 )

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NiCoCrAlY+YSZ Coatings were deposited on HA188 alloy by using air plasma spray technique, some of which were subsequently heat treated at 1080 ℃ under low and high vacuum respectively. The 1100 ℃ thermal cycling tests were carried out on as-sprayed and heat-treated specimens, the microstructure and composition of specimens were studied before and after thermal cycling test by using SEM with EDS. The results show that after the vacuum heat treatment, the thermal cycling life is significantly improved, which thanks to continuous TGO layer growth between APS-NiCoCrAlY/APS-YSZ interface inhibited during thermal cycling, therefore, the cracking tensile stress induced by TGO is reduced. In addition, more oxides are found in vacuum heat treated APS-NiCoCrAlY after thermal cycling test, to some extent, which reduces the thermal expansion coefficient of APS-NiCoCrAlY, leading to reduction of cracking strain originated from thermal expansion mismatch. The failure cracks in low vacuum heat treated specimens don't continuously propagate as that in high vacuum heat treatment.

Effect of cold rolling on microstructure evolution and wear resistance of G20CrNi2MoA carburized bearing steel

Zeng Songwen, Liu Lu, Liu Yujian, Qian Dongsheng, Wang Feng

2020, 45(12): 53-59. doi:10.13251/j.issn.0254-6051.2020.12.010

Abstract ( 67 )

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Effect of cold rolling on the microstructure evolution and wear resistance of G20CrNi2MoA carburized bearing steel was studied by means of electron backscattered diffraction (EBSD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The results show that the cold rolling can refine the grain size of the raw materials. When the cold rolling reduction increases from 0% to 30%, the area fraction of carbides increases from 4.38% to 5.99% and the average diameter decreases from 0.15 μm to 0.13 μm after the secondary quenching. After the secondary low-temperature tempering, the gradients of both the carbon content and the microhardness are increased within about 0.9 mm depth of the surface carburized layer, the average friction coefficient decreases from 0.489 to 0.346 when the cold rolling reduction increases from 0% to 30%, and the wear rate also decreases from 27.2×10^-6 mm³·N^-1·m^-1 to 9.1×10^-6mm³·N^-1·m^-1. It indicates that the abrasive wear and fatigue are decreased gradually due to the increasing of area fraction of carbides and microhardness of the top surface after 30% cold rolling reduction, thus the wear resistance of the materials increases.

Effect of quenching process on microstructure and mechanical properties of U75V heavy rail steel

Ma Xiao, Cen Yaodong, Chen Lin, Wu Maowen

2020, 45(12): 59-62. doi:10.13251/j.issn.0254-6051.2020.12.011

Abstract ( 83 )

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Microstructure, mechanical properties and fracture morphology of U75V heavy rail steel as rolled and as quenched at 3 ℃/s and 5 ℃/s were studied by optical microscope, scanning electron microscope, hardness tester, impact testing machine and universal tensile testing machine. The results show that with the increase of quenching rate, the grain size of the steel is refined gradually, and the pearlite lamellar spacing decreases. Among them, the grain size and lamellar spacing of the steel as rolled are the largest, and that as quenched at 5 ℃/s are the smallest. Meanwhile, the comprehensive mechanical properties such as impact absorbed energy and hardness of the U75V steel are increased. Among them, the impact absorbed energy, hardness and tensile strength of the steel as rolled are the lowest, and that as quenched at 5 ℃/s are the best.

Effect of tempering temperature on microstructure and properties of 7Ni steel

Liu Wenbin, Zhan Guofeng, Huang Feng

2020, 45(12): 63-68. doi:10.13251/j.issn.0254-6051.2020.12.012

Abstract ( 61 )

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Changes of microstructure and reverse austenite content of 7Ni steel at different tempering temperatures during quenching, lamellarizing and tempering (QLT) were analyzed by means of OM, SEM, TEM and XRD, and the influence of tempering temperature on cryogenic strength and toughness of 7Ni steel was studied. The results show that with the increase of tempering temperature, the tensile strength of 7Ni steel increases gradually, while the low temperature toughness increases first and then decreases. In the process of tempering temperature increasing from 560 ℃ to 620 ℃, the martensite of the 7Ni steel changes from thick to uniform dispersion and fine, and the tensile strength of the steel gradually increases. When the tempering temperature is low, the martensite recovery in the steel is insufficient, the reverse austenite content is less, and the low temperature toughness is low. With the tempering temperature increasing, the reverse austenite content of the 7Ni steel increases continuously, but the stability decreases. A large number of unstable reversed austenite transforms at low temperature, which is detrimental to the improvement of low temperature toughness. The low temperature toughness of the 7Ni steel increases first and then decreases as the tempering temperature increases, and the best low temperature toughness is obtained at 580 ℃.

Effect of high temperature homogenization on carbide morphology and mechanical properties of 1.3C-5Cr-0.7Mo-0.6V steel

Dong Ziyao, Wang Rui, Kang Yan, Li Dazhao, Yan Zhijie

2020, 45(12): 69-75. doi:10.13251/j.issn.0254-6051.2020.12.013

Abstract ( 53 )

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To improve the primary carbides of 1.3C-5Cr-0.7Mo-0.6V steel, high temperature homogenization (HTH) was carried out at 1170 ℃ for different time, followed by water quenching to room temperature. Subsequently, a conventional heat treatment process, annealing, quenching and tempering, was further employed to obtain the final microstructure of the steel. The microstructure and mechanical properties of the specimens were analyzed by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction and compression tests. The results indicate that the size and morphology of the primary carbide are considerably improved by HTH. The network carbides are refined into small and spheroidal ones that distribute homogenously on the matrix. An outstanding compression mechanical property, compression strength of 4703 MPa and engineering strain of 37.3%, is obtained for the specimen due to 3 h HTH treatment. Compared with the untreated steel, the compression strength is enhanced by 14.5%, accompanied by an increase of 30.8% of the compression strain.

Effect of pre-treatment on formability of asynchronous rolled 6016 Al alloy sheet

Long Zhiyong, Yuan Gecheng, Chen Cheng

2020, 45(12): 76-81. doi:10.13251/j.issn.0254-6051.2020.12.014

Abstract ( 58 )

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Effect of pre-treatment before asynchronous rolling on the texture and formability of 6016 aluminum alloy sheet was investigated by tensile test, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that pre-aging treatment before asynchronous rolling can increase the strength of the aluminum alloy sheet without significantly reducing its plasticity, and its plane anisotropy IPA value is significantly reduced; plastic strain ratio $\bar{r}$ value and cupping value I_E are improved and reach 0.89 and 8.27 respectively. The main reason for the better comprehensive performance of the aluminum alloy sheet is the increase in the strength of the shear texture E{111}<110> and F{111} <112> and the decrease in the grain size.

Effect of tempering temperature on microstructure and tempering embrittlement of ultra-high strength steel for construction machinery

Zheng Dongsheng, Liu Dan, Luo Deng, Li Huizhong, Zhang Qingxue, Peng Ningqi, Jian Haigen

2020, 45(12): 82-86. doi:10.13251/j.issn.0254-6051.2020.12.015

Abstract ( 71 )

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Effect of tempering temperature on microstructure and tempering embrittlement of ultra-high strength steel for construction machinery was investigated by means of SEM, TEM and Charpy V-notch impact test at -20 ℃. And based on fracture characterization and microstructure, the crack propagation path was analyzed. The results show that carbides formed after martensite decomposition are precipitated gradually from martensite lath to the boundaries of prior austenite grain and martensite lath, the shape of which is changed from needle-like to granular and tends to coarsen with the increase of tempering temperature in the range of 200-500 ℃. Both tempering temperatures of 200 ℃ and 500 ℃ result in the ductile fracture in the unstable fracture zone of impact specimens. When the tempering temperature is 300 ℃, the tempered embrittlement is occurred, the crack propagation path is relatively straight in the unstable fracture zone of impact specimens, which is in accord with quasi-cleavage fracture. By microstrucrure analysis, a large number of needle-like carbides are precipitated along the boundaries of prior austenite grain and martensite lath. These carbides provide crack nucleation sites and promote crack propagation, which can result in the occurrence of tempered embrittlement.

Optimization of homogenization process of ultra-high strength 7055 aluminum alloy ingots

Chao Daiyi, Zhang Qian, Sun Youzheng, Zhao Zhiguo, Li Hui, Lü Zhengfeng, Cheng Rence

2020, 45(12): 87-91. doi:10.13251/j.issn.0254-6051.2020.12.016

Abstract ( 68 )

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Homogenization process of a large size of ultra-high strength 7055 series aluminum alloy for aviation was analyzed and optimized by means of metallographic microscope, scanning electron microscope, differential scanning calorimeter and transmission electron microscope. The method of increasing the homogenization temperature in-step was proposed to improve the ingot quality to the max extent without over-burning. The results show that the recrystallization ratio of subsequent extrusion deformation will be greatly reduced by the precipitation of Al₃Zr phase during pre-homogenization at low temperature. The process of 400 ℃×4 h+465 ℃×16 h+474 ℃×8 h homogenization can significantly eliminate the content of low melting point eutectic phase in ingot and obtain a high quality ingot, meanwhile it can save process time by about 13 h compared with the original process. The new homogenization process not only improves the production efficiency, but also provides a better quality ingot for the subsequent process.

Isothermal normalizing of TL-4521 steel for gear by residual heat after forging

Wang Huizhen, Zhai Yuewen, Zhou Leyu

2020, 45(12): 92-96. doi:10.13251/j.issn.0254-6051.2020.12.017

Abstract ( 47 )

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Taken TL-4521 steel as the research object, the isothermal normalizing process utilizing residual heat after simulated forging was carried out on Gleeble-3800 thermal simulation testing machine, and the effects of cooling rate, isothermal holding time and deformation on microstructure and hardness were analyzed. The results show that with the increase of cooling rate after warm forging, the ferrite content decreases, the microstructure is refined significantly, and the hardness increases; the longer the holding time, the more sufficient pearlite is, and the microstructure tends to be homogenized, and the hardness decreases. The larger the warm forging deformation, the more deformation bands are formed in austenite. During the subsequent cooling, the number of ferrite nucleation increases, the grains are refined, the deformation strengthening is significant, and the hardness increases.

Effects of solution treatment and aging temperature on hardness and microstructure of precipitation hardening die steel 10Cr3Mo3NiCuAl

Chu Baoshuai, Wu Xiaoyan, Wang Haijun, Zhang Jinwen, Chen Jianli

2020, 45(12): 97-101. doi:10.13251/j.issn.0254-6051.2020.12.018

Abstract ( 52 )

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Effects of solution treatment and aging temperature on the microstructure and hardness of 10Cr3Mo3NiCuAl steel were studied by thermodynamic calculation, hardness test, metallography and scanning electron microscopy observation. The results show that when solution treated at 950 ℃, the tested steel is of uniform and fine microstructure with relative high hardness, mainly consisting of lath martensite and a small amount of retained austenite, and the carbides are basically dissolved in the matrix. With the increase of solution treatment temperature, the martensite lath coarsens. During aging at 520-540 ℃, a large amount of intermetallic compound Ni₃Al is precipitated from the matrix acting for precipitation strengthening, and the hardness reaches a higher level. With the increase of aging temperature, tempered sorbite appears in the microstructure, resulting in a rapid decrease in hardness. It is recommended that the optimal solution treatment temperature is 950 ℃ and the optimal aging temperature range is 520-540 ℃.

Effect of annealing process on microstructure and mechanical properties of cold rolled TRIP980 steel plate

Wu Jing, Dong Xinxin, Liu Liping

2020, 45(12): 102-105. doi:10.13251/j.issn.0254-6051.2020.12.019

Abstract ( 54 )

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Effects of annealing temperature, over-aging temperature and over-aging time on the microstructure and mechanical properties of cold rolled TRIP980 steel plate were studied. It is found that when the annealing temperature decreases from 800 ℃ to 760 ℃, with the decrease of austenitizing degree and the enhancement of original austenite stability, the hard phase content becomes lower and the retained austenite content becomes higher, macroscopically showing that the tensile strength decreases and the elongation increases. When the over-aging temperature increases from 360 ℃ to 400 ℃, the strength increases with the increase of bainite volume fraction. When the over-aging time increases from 600 s to 1500 s, the hard phase bainite softens and the stability of retained austenite increases, which result in the tensile strength decrease and the elongation increase.

Effect of reprocessing on residual stress of N18 zirconium alloy plate

Yang Pan, Zhang Hongzhi, Zhang Yiyong, Qiang Rui, Jiang Qiang, Zhao Yong, Xiao Ya

2020, 45(12): 106-110. doi:10.13251/j.issn.0254-6051.2020.12.020

Abstract ( 59 )

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N18 zirconium alloy plates were reprocessed through “hot rolling+cold rolling+annealing”. The surface residual stress was acquired by X-ray diffraction method. The disorientation angle distribution and the grain boundaries were analysed by means of EBSD. The results show that after hot rolling, the distribution of surface residual stress on the N18 zirconium alloy plate is no rule. After cold rolling, the surface residual stress increases with rise of cold rolling deformation quantity and entirely presents compression stress. After annealing, the surface residual stress level is low and reaches the lowest when annealing at 500 ℃ for 2 h. After annealing, the microstructure mainly consists of low angle grain boundaries, and the density of which shifts from increasing to stabilization with rise of annealing temperature.

Controlled water quenching cooling process of alloy steel shaft end for forklift

Xiao Jieliang, Huang Cheng, Ma Xianyin

2020, 45(12): 110-113. doi:10.13251/j.issn.0254-6051.2020.12.021

Abstract ( 92 )

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Cooling characteristics of water and principle of controlled cooling of water quenching were analyzed. The shaft end of 35CrMo alloy steel forklift was quenched and tempered by means of controlled water quenching cooling and traditional water quenching, and the microstructure and microcracks of the quenched and tempered shaft end were tested. The results show that the quenched and tempered shaft end by controlled cooling has a fine and uniform tempered sorbite microstructure with moderate hardness and no microcracks, which meets the technical requirements. While 1/3 of the shaft ends quenched and tempered by traditional cooling has cracks. It can be seen that by controlling the initial temperature of water, the mass ratio of water to workpiece and cooling time, the alloy steel shaft end with complex shape can be cooled controllably, thus satisfactory quenching effect can be obtained and clean heat treatment can be realized.

Effect of solution treatment on properties of DSS2205 laser weld seam

Wang Weidong, Bi Zongyue, Xian Linyun, Wang Haitao, Li Xiaolong, Liu Yudong, Yu Chenyang, Xu Xueli

2020, 45(12): 114-119. doi:10.13251/j.issn.0254-6051.2020.12.022

Abstract ( 69 )

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Aiming at the problem of disproportionate of ferrite and austenite of duplex stainless steel weld seam after laser welding, the DSS2205 laser weld seam was solution treated at different temperatures and time through the Gleeble-1300 thermal simulation tester. The results show that under different solid solution conditions, the austenite morphology and the two phase ratios change greatly. With the increase of temperature and holding time, the alloying elements fully diffuse and migrate in the two phases, and the austenite grain gradually grows, the content first increases and then decreases. After solution treated at 1050 ℃ for 5 min, the microstructure of the specimen is uniform, the proper proportion of ferrite and austenite phase can be obtained, the hardness gradient of weld seam is uniform, and the impact property becomes the best.

Ion nitriding process of PH13-8Mo steel

Zhang Yi, Meng Xuan, Zhu Zhiqiang, Zhao Zhipeng, Tong Wei, Wu Ruigang, Wang Jin

2020, 45(12): 119-122. doi:10.13251/j.issn.0254-6051.2020.12.023

Abstract ( 77 )

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Plasma nitriding process parameters of PH13-8Mo steel were studied, including nitriding temperature, nitriding time and surface roughness of parts. The results show that with the increase of nitriding temperature, nitriding time and the decrease of surface roughness, the nitrided layer thickness of the PH13-8Mo steel increases. The surface roughness of parts has great influence on the brittleness grade of nitrided layer, when the surface roughness of parts is 6.3 μm, the brittleness grade reaches grade III. Nitriding time, nitriding temperature and surface roughness have little effect on the hardness of nitrided layer. When the nitriding temperature is 540 ℃, the nitriding time is 22 h, and the surface roughness of parts is 0.8 μm, the nitrided layer thickness can reach 197.5 μm, the nitrided layer hardness can reach 1083 HV0.2, and the brittleness grade is grade II.

Effect of environmentally friendly quenching process on microstructure and properties for thick-wall L80-13Cr steel pipe

Wang Jinyong, Gao Jie, Cao Hongbo, Shao Haili, Qi Xilun

2020, 45(12): 123-127. doi:10.13251/j.issn.0254-6051.2020.12.024

Abstract ( 49 )

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A thick-wall L80-13Cr seamless steel pipe was austenitized at 1000 ℃ for 150 min, and then cooled by air, water immersion and water spray respectively, followed by tempering at 710 ℃ for 200 min. The effects of the quenching media on the microstructure and mechanical properties of the steel pipe were studied by means of microstructure observation and mechanical property testing. The results show that the cooling performance of the three quenching media from high to low are water immersion cooling process, water spray cooling process, and air cooling process; the strength and impact absorbed energy are increased with the acceleration of cooling rate. After quenching of the steel pipe, the average impact absorbed energy and the tensile strength under air cooling are 23.67 J and 764 MPa respectively, that under water spray cooling are 42.00 J and 787 MPa respectively, and that under water immersion cooling are 50.33 J and 800 MPa respectively. However, the process of water immersion cooling is prone to quenching cracking and resulting in the scrapping of the material. The water spray cooling produces fine and uniform microstructure and excellent performance, so it is the most suitable quenching cooling method.

Heat treatment process improvement of pneumatic clutch wheel hub

Sun Guojin, Hou Miaoyu, Gao Jiawu, Ren Tai'an, Gao Daoxu

2020, 45(12): 128-131. doi:10.13251/j.issn.0254-6051.2020.12.025

Abstract ( 63 )

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Taken GCr15SiMn steel pneumatic clutch wheel hub as a object, the original quenching and tempering process was optimized in order to reduce the heat treatment distortion. The results show that the distortion of the hub is significantly reduced by adding stress relief annealing and cryogenic treatment processes, which meets the technical requirements of dimension, and the surface hardness distribution of the hub is more uniform.

Effects of rolling and annealing on microstructure and properties of T9S titanium alloy sheet

Zhang Qiang, Li Yang, Hao Xiaobo, Li Bobo, Zhou Hua, Liu Yinqi

2020, 45(12): 132-135. doi:10.13251/j.issn.0254-6051.2020.12.026

Abstract ( 63 )

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Effects of rolling deformation and annealing temperature on microstructure and mechanical properties of T9S titanium alloy sheet were studied. The results show that with the increase of rolling deformation of finished products, the microstructure of the sheet is finer, and the equiaxed α phase, the elongated α phase and boundary β phase are formed after annealing, but the deformation flow line is obvious, meanwhile, the room temperature strength and hardness of the sheet increase, the elongation decreases, and the elastic modulus increases. With the increase of annealing temperature, the room temperature strength and hardness of the sheet gradually decrease, the elongation gradually increases, the transverse elastic modulus decreases, and the longitudinal elastic modulus first increases and then decreases. After annealing at 750-790 ℃ for 45 min with air cooling, the sheet can obtain a better match between strength and plasticity.

Effect of low temperature heat treatment after welding on microstructure and properties of martensitic stainless steel

Shi Shunwang, Liu Bo, Mu Lei, Jiang Hongwei, Ge Rongfan

2020, 45(12): 136-139. doi:10.13251/j.issn.0254-6051.2020.12.027

Abstract ( 86 )

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Low temperature heat treatment (240 and 300 ℃) of ZG06Cr13Ni4Mo martensitic stainless steel after welding was carried out. The microstructure, mechanical properties, hardness and residual stress of the joints after different low temperature heat treatments were studied by means of OM, tensile and bending test, hardness test and residual stress test. The results show that after low temperature heat treatment, the microstructure of the HAZ of the joints is tempered martensitic and carbide, and the microstructure of the welding zone is low carbon martensitic, block martensitic and carbide. Meanwhile, the tensile strength of the joints varies little, and the hardness decreases slightly. The residual stress at welding zone of the joint after 240 ℃ low temperature heat treatment is relieved by 69.1%.

Effects of aging and thread rolling process sequence on mechanical properties of GH738 alloy bolt

Pei Lieyong, Dai Aili, Fan Kailun, Wang Yunlan, Liu Yongde, Liu Wencheng

2020, 45(12): 140-141. doi:10.13251/j.issn.0254-6051.2020.12.028

Abstract ( 60 )

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Effects of aging and thread rolling process sequence on the mechanical properties of GH738 alloy bolt were studied. The results show that the hardness, tensile strengths at room temperature and at high temperature, stress endurance life and tensile fatigue life of the GH738 alloy bolts manufactured by aging after thread rolling are all higher than those by thread rolling after aging.

Microstructure and properties of TiB₂/Al-Si-Mg-Er composite

Yang Zi’an, Xiang Zhilei, Chen Ziyong, Ren Weimin, Ma Xiaozhao

2020, 45(12): 142-148. doi:10.13251/j.issn.0254-6051.2020.12.029

Abstract ( 54 )

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Al-7Si-0.5Mg-0.1Er and 0.5TiB₂/Al-7Si-0.5Mg-0.1Er alloys were prepared by remelting and dilution method, and the microstructure and properties of TiB₂ particle reinforced Al-Si-Mg-Er composites were studied. The results show that the as-cast microstructure of the composites is mainly composed of α-Al matrix, eutectic Si phase and TiB₂ particles. The addition of TiB₂ particles reduces the secondary dendrite spacing of the Al-7Si-0.5Mg-0.1Er alloy by 7.1 μm. The tensile strength reaches 217.53 MPa, which is 12.1% higher than that of the Al-7Si-0.5Mg-0.1Er alloy. The optimal T6 heat treatment process for the TiB₂/Al-Si-Mg-Er composite is 530 ℃×12 h solid solution +160 ℃×7 h aging. After this process, the tensile strength of the TiB₂ /Al-Si-Mg-Er composite reaches 319.49 MPa, which is 46.9% higher than that before heat treatment, and 5.9% higher than that of the Al-7Si-0.5Mg-0.1Er alloy. The yield strength reaches 266.75 MPa, which is increased by 106.4% compared with that before heat treatment and is 14.9% higher than that of the Al-7Si-0.5Mg-0.1Er alloy. The improvement of the tensile strength of the composite materials mainly comes from the grain refinement, modification and heat treatment strengthening of TiB₂ particles.

Continuous cooling transformation of super cooled austenite of a low-cost ultra-high-strength steel G31L

Yang Peng, Ning Jing, Su Jie, Jiang Qingwei

2020, 45(12): 149-154. doi:10.13251/j.issn.0254-6051.2020.12.030

Abstract ( 80 )

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Thermal dilatometric curves of G31L steel were measured by Formastor-FⅡdilatometer, and the microstructure evolution and hardness at different cooling rates were studied, the supercooled austenite continuous cooling transformation(CCT) curves of the G31L steel were drawn, and the reliability of post-forging heat treatment process of real large deep blind hole forging was analyzed. The results show that the critical temperatures of the G31L steel as follows:Ac₁=740 ℃, Ac₃=816 ℃, Ms=315 ℃, and Mf=138 ℃. When the cooling rate is less than or equal to 0.028 ℃/ s, pearlite+ferrite+bainite mixed structure is obtained; when the cooling rate is 0.028-0.84 ℃/s, pearlite and ferrite disappear with the increase of cooling rate, and bainite decreases in content gradually until full martensite is obtained; when the cooling rate is greater than 0.84 ℃/s, full martensite is obtained. The large deep blind hole forgings actually produced are heat treated at 915 ℃ for 6 h and then oil quenched to room temperature and tempered. The solid head core of the forgings has a mixed structure of martensite and a small amount of bainite, while the R/2 and edge of the head and tail are all martensite, and the strength and plasticity of the forgings meet the product quality requirements.

Microstructure and properties of Al_0.1CoCrFeNi high entropy alloy coating fabricated by laser cladding

Fan Jiacheng, Liu Ning, Zhou Huiling, Zhang Xinghua, Niu Muye, Chang Haobo, Geng Yifan

2020, 45(12): 155-159. doi:10.13251/j.issn.0254-6051.2020.12.031

Abstract ( 68 )

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Al_0.1CoCrFeNi high-entropy alloy coating on the surface of H13 steel was prepared by using laser cladding technology. The results show that the structure of Al_0.1CoCrFeNi high-entropy alloy coating is single phase FCC type, showing as columnar grains at the junction of coating and substrate steel, while as equiaxed grains in other regions; and the maximum microhardness on the coating section is up to 560.2 HV0.5, which is about 2.5 times of that of the substrate. The coating exhibits better thermal shock resistance than that of the substrate. No cracks are found in the coating after thermal shocking at 600 ℃ and 800 ℃ for 50 cycles, but when undergone 7 cycles at a high temperature of 1000 ℃, the steel substrate is broken while there is no obvious cracks in the coating and the junction zone of coating and substrate. Both the friction coefficient and wear rate of the coating are lower than that of the substrate, which indicates oxidation wear is the main wear mechanism for the coating, while the substrate steel shows mixed mechanisms of oxidation wear and fatigue wear.

Stress corrosion behavior of novel nano-reinforced M&A dual-phase steel

Fu Hang, Liang Xiaokai, Sun Xinjun, Huang Tao

2020, 45(12): 160-168. doi:10.13251/j.issn.0254-6051.2020.12.032

Abstract ( 57 )

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Stress corrosion behavior of a novel M&A dual-phase steel in 3.5%NaCl solution was studied by using slow strain rate tension and WOL specimen stress corrosion experiments. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and physicochemical phase analysis were used to observe the microstructure of the M&A dual-phase steel, and the anti-stress corrosion mechanism was explained. The results show that the M&A dual-phase steel has a low stress corrosion sensitivity, strong crack resistance and excellent stress corrosion resistance. In addition, Cl^- can promote stress corrosion behavior of M&A dual-phase steel, resulting in a certain loss of stress corrosion performance in 3.5%NaCl solution compared with tensile test results in air.The metastable reversed austenite makes M&A dual-phase steel have good ductility and toughness, which weakens stress concentration and hinders crack growth. The common plane of dislocation group is poor, and it is not easy to produce corrosion sensitive channel. The secondary phase of carbide and Cu nanometer is precipitated at 600 ℃ after tempering, which greatly improves the strength of materials and the stability of stress corrosion of steel.

Microstructure and properties of laser clad multi-layer Ni-based coating on Cr12MoV steel surface

Shen Dachen, Ye Hong, Wang Yanqing, Liu Yue, Li Li, Xiao Xinyu, She Hongyan

2020, 45(12): 169-174. doi:10.13251/j.issn.0254-6051.2020.12.033

Abstract ( 68 )

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Ni20Cr and Ni60A multi-layer Ni-based alloy wear resistant coating was prepared by laser cladding on the surface of Cr12MoV die steel by pulsed Nd:YAG laser, the phases and microstructure of the coatings were analyzed by using X-ray diffractometer, scanning electron microscope, and energy spectrometer, meanwhile the hardness and wear resistance of both the coating and the substrate were analyzed by using Vickers microhardness tester, high-speed reciprocating friction and wear tester. The results show that using the Ni20Cr as the underlying layer of the multi-layer alloy coating can effectively improve the metallurgical bond between the coating and the substrate, which can greatly reduce the defects such as cracks and pores in the coating. The main phases of the coating surface are g-(Fe, Ni), FeNi₃, BNi₃, Cr₃C₂ and Ni-Cr-Fe. The structure of the coating from bottom to surface in turn is cellular dendrites, columnar dendrites, preferentially growing dendrites and equiaxed dendrites. The Ni60A coating can greatly improve the surface microhardness of Cr12MoV die steel, and the microhardness of the coating surface can reach up to 1000 HV0.2, which is about 1.6 times of the substrate. The wear resistance of the Ni60A coating is obviously better than that of the substrate, which is about 2.0 to 3.3 times higher than that of the substrate. After laser cladding of the multi-layer Ni-based alloy coating on the Cr12MoV die steel surface, hard phases such as Cr₃C₂ and Ni-Cr-Fe can be formed and effectively improve the surface hardness and wear resistance. The probability of scrapping due to friction and wear can be significantly reduced, thereby further extending the service life of the mold.

Cold work hardening and heat treatment softening of multilayered Ni/Al composites

Cui Yan, Sun Xinjun, Peng Xiying, Wang Licheng

2020, 45(12): 175-179. doi:10.13251/j.issn.0254-6051.2020.12.034

Abstract ( 60 )

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Ni/Al composite was successfully prepared by ARB process in laboratory. Effects of accumulative rolling pass and heat treatment on the hardness of composite were studied. The results show that the hardness of Ni, Al component and composite increases with the increase of rolling passes. The deformation of Al is restrained by the integrity of the material due to the layered structure of Ni component when the rolling pass is less than 3, which leads to the abnormal increase of the overall hardness of the composite. When the rolling pass n>3, the inlay effect of Ni particles in the Al component weakens the inhibition of deformation of Al component, which slows down the increase of overall hardness of the composite. The relationship model of n with Ni, Al component and overall hardness of composite are established. After 250 ℃×50 min heat treatment, the recrystallization and decrease of additional stress result in the decrease of the hardness of Ni, Al and composite materials as a whole; the degree of recrystallization of Ni layer particles is uneven due to the uneven deformation, which makes the hardness of Ni component fluctuate greatly.

Properties of atmospheric plasma-sprayed NiCr/Cr₃C₂ composite coating

Cao Yuxia, Liu Jinqiang, Sun Jingwei, Wang Zhilin, Zhao Wenwu, Hao Bin

2020, 45(12): 179-183. doi:10.13251/j.issn.0254-6051.2020.12.035

Abstract ( 54 )

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NiCr/Cr₃C₂ composite powder was prepared by chemical and metallurgical coating, solid state alloying and spray granulation technology, and the NiCr/Cr₃C₂composite coating was prepared by atmospheric plasma spraying technology (APS). The microstructure of both the powder and the coating, as well as the microhardness, tensile strength and oxidation property of the coating were studied by using SEM, microhardness tester, universal mechanical tester and muffle furnace. The results show that the coating has a typical layered structure with excellent tensile strength (27.4±5) MPa. The microhardness of the coating is about 850 HV0.2, which is 2.7 times of that of bonding layer. The fracture of the coating is a typical brittle fracture, and occurs between the layers in the coating. The oxidation kinetics curve of the coating at 850 ℃ basically conforms to the parabola law, and the oxide film is produced on the surface of the coating, and will fall off during the oxidation process. At the same time, the segregation phenomenon appears in the coating, and the metal Cr is precipitated.

Analysis and forecast of fatigue crack propagation behavior in HAZ of X80 pipeline steel by welding thermal simulation

Xu Pengfei, Zhao Zuopeng, Cheng Hongxia, Xiao Furen

2020, 45(12): 184-188. doi:10.13251/j.issn.0254-6051.2020.12.036

Abstract ( 60 )

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Fatigue crack propagation behavior in each heat affected zone (HAZ) of X80 dual-phase pipeline steels was investigated by using welding thermal simulation. The differences of the fatigue cracks propagation behavior between real welded and welding thermal specimens were also analyzed. And the feasibility on the prediction of fatigue cracks propagation life for applying welding thermal simulation was discussed. The results show that there is an obvious contrast between the fatigue crack growth rate curves (da/dN-DK curves) of the real welded and welding thermal specimens when the cracks are propagated in the CGHAZ and ICHAZ, which are attributed to variations of the microstructure change, thus leading to the change of cracks propagation resistance. Therefore, it is recommended to predict the fatigue crack propagation life through the da/dN-DK curve of integrated HAZ in the real welded specimens.

Microstructure and mechanical properties of P91 steel steam pipe after long service

Qi Quanyou, Yang Xu

2020, 45(12): 189-193. doi:10.13251/j.issn.0254-6051.2020.12.037

Abstract ( 70 )

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Microstructure of both the straight and the elbow section of P91 steel steam pipe served for 38000 h was studied by means of optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM), and corresponding mechanical properties were tested. The results show that the existence of a large amount of ferrite in the elbow microstructure is the main reason for sharp drop of its strength and hardness. It is concluded that the ferrite in the elbow is formed by the recrystallization of martensite during tempering due to the increase of energy caused by secondary deformation during bending.

Mechanical properties of large thickness SA387Gr11CL2 steel plate under the condition of limit PWHT

Li Yangbing, Liu Fufang, Zhao Guochang, Long Jie, Yuan Jincheng, Wu Yanyang

2020, 45(12): 193-196. doi:10.13251/j.issn.0254-6051.2020.12.038

Abstract ( 54 )

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According to the more strict requirements of PWHT put forward by the design institute and the manufacturer, the influence of the limit PWHT condition on the mechanical properties was studied with 136 mm thickness SA387Gr11CL2 steel plate. The results show that the tensile properties of the steel with full thickness (1.6 mm under the surface, 1/4 of plate thickness and 1/2 of plate thickness) at room temperature are still acceptable. However, at 0 ℃ and below, the corresponding impact absorbed energy decreases gradually with the decrease of impact temperature. The -20 ℃ impact absorbed energy at 1/2 of the plate thickness has reached the lower limit of the standard requirements, and the surplus is not enough. The microstructure analysis combined with metallography and SEM shows that the carbide in the microstructure will segregate and grow along the grain boundary due to excessive rigor PWHT, resulting in obviously worse toughness of the steel plate.

Effect of chemical composition on microstructure and mechanical properties of GH4169 alloy

Ma Jun, Shen Jialin, Li Maoming, Liang Yu

2020, 45(12): 197-204. doi:10.13251/j.issn.0254-6051.2020.12.039

Abstract ( 67 )

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The microstructure and tensile properties of GH4169 alloy with different Nb, Al and Ti contents were studied after solution and aging treatment. The results show that under certain Al/Ti and (Al+Ti)/Nb ratios, the δ phase increases in amount with the increase of Nb content and has better high temperature stability; meanwhile, the high temperature solution treatment can effectively prevent grain growth and ensure the fine grain strengthening by the stable δ phase. When the Al/Ti and (Al+Ti)/Nb ratios are relatively low, the contents of γ″ and γ' phases decrease, and the morphology of γ″ changes from lip-shape to disc-shape or sesame-like shape, in this case the Nb element will mainly form δ phase. The results of mechanical properties show that when the Al/Ti and (Al+Ti)/Nb ratios are similar, the tensile strength is mainly affected by grain size, while the effect of δ phase content is less. However, when the Al/Ti and (Al+Ti)/Nb ratios are relatively low, due to the quantity and morphology changes of the strengthening phases γ″ and γ', the tensile properties are significantly poorer, and the microhardness also decreases along with the decrease of tensile strength.

Effect of Nb microalloying on microstructure and properties of quasi-bainitic wear-resistant cast steel

Zhang Fang, Li Junping, Peng Jun, Zheng Lili, An Shengli

2020, 45(12): 205-211. doi:10.13251/j.issn.0254-6051.2020.12.040

Abstract ( 54 )

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Effect of niobium (Nb) microalloying on the microstructure and properties of quasi-bainite wear-resistant cast steel with low carbon (about 0.26%) and different niobium content was analyzed by means of thermal expansion tester, scanning electron microscope, tensile and impact test and wear test. The results show that the addition of Nb promotes the growth of the quasi-bainite and the prior austenite grains decrease from 120.81 μm to 87.65 μm when Nb content increases from zero to 0.062%, and the average grain size is reduced by 27.4%. Meanwhile, the addition of Nb caused a decrease in wear rate of the steel, and the hardness is also decreased, but the impact absorbed energy, lateral expansion value, yield strength, tensile strength and reduction of area are all increased. When Nb content is 0.024%, the wear rate reaches the lowest value of 0.104%, and the wear resistance is the best, moreover, the comprehensive mechanical properties are also the best with hardness of 420.4 HV0.1, impact absorbed energy of 42.6 J, side expansion value of 67%, yield strength of 826 MPa, tensile strength of 1326 MPa and percentage reduction of area of 7.7%, while the content of retained austenite is relatively high at 8.4%.

Effect of Nb on microstructure of medium-manganese trip steel during critical annealing

Han Fuguang, Li Yan, Zhao Zengwu, Ding Wei

2020, 45(12): 212-217. doi:10.13251/j.issn.0254-6051.2020.12.041

Abstract ( 46 )

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Carbide evolution behavior and the effects of niobium on the microstructure, retained austenite volume fraction and stability of two hot-rolled medium-manganese TRIP steels with and without niobium addition and under different intercritical annealing processes were studied by means of field emission scanning electron microscopy (FE-SEM). The results show that after the intercritical annealing treatment, an (ultrafine grained ferrite+retained austenite) dual-phase structure is obtained. With the increase of annealing temperature, the volume fraction of retained austenite first increases and then decreases; as the annealing time increases, the carbides dissolve gradually, the volume fraction of retained austenite increases gradually until equilibrium then unchanged. The Nb addition can refine austenite grains, delay carbide dissolution, delay austenite transformation, increase film austenite amount, and improve austenite stability.

Effects of quenching process and Nb addition on prior austenite grain size of 30MnB5 steel

Yang Zhirong, Yan Desheng, Yang Huaijun

2020, 45(12): 218-221. doi:10.13251/j.issn.0254-6051.2020.12.042

Abstract ( 63 )

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Effects of quenching processes and Nb addition on prior austenite grain size of 30MnB5 steel were studied by means of optical microscope (OM). The results show that the prior austenite grain size of 30MnB5 steel containing Nb is stable when the quenching temperature is 860-920 ℃ and the holding time is less than 60 min. When the quenching temperature reaches 950 ℃ and the holding time exceeds 30 min, the grain size of the prior austenite gradually increases with the holding time increasing. Thus, when the quenching temperature is lower than 950 ℃, Nb has an inhibitory effect on the growth of the prior austenite grains in the heat treatment process of 30MnB5 steel. When the quenching temperature reaches 1000 ℃, Nb only has a slight inhibitory effect on the growth of the prior austenite grain within 30 min. When the quenching holding time exceeds 60 min, Nb completely loses its inhibitory effect on the growth of the original austenite grain.

Effect of rare earth element Er on microstructure and properties of Ti-6Al-4V-0.5Si alloy

Liu Chao, Liu Guowei, Guo Leiming, Yang Jigang, Liu Kedi, Wang Zhaozhao

2020, 45(12): 222-226. doi:10.13251/j.issn.0254-6051.2020.12.043

Abstract ( 50 )

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Ti-6Al-4V-0.5Si-xEr (wt%) alloy was prepared by powder metallurgy process, and the effect of Er content on the microstructure and properties of the alloys solution-treated+aged (950 ℃×30 min (WQ)+480 ℃×4 h (AQ)) was studied by means of OM, XRD, TEM and tensile testing machine. The results show that the tested alloys are all duplex microstructure with equiaxed and lamellar feature after solution and aging treatment. The Er₂O₃ particles produced in the sintering process can be used as nucleation core to promote the precipitation of α and β phases and play a role in grain refinement. With the increase of Er content, the grain size is refined from 10-20 μm to 5-10 μm. When the Er content is 1.2%, the tensile strength of the tested alloy reaches the peak of 930.5 MPa, and the corresponding elongation is 9.24%, which are 22.3% and 10.0% respectively higher than that of Ti-6Al-4V-0.5Si alloy with no Er addition. The tensile fracture morphologies of the tested alloy show dimples, with only a small amount of cleavage steps. The existence of dimples can disperse the stress generated during the fracture of the material and makes the material withstand greater deformation before fracture.

Microstructure and hardness of Mg-12Zn-xCa alloy after T6 treatment

Wang Bo

2020, 45(12): 227-230. doi:10.13251/j.issn.0254-6051.2020.12.044

Abstract ( 47 )

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Microstructure and hardness of the as-cast Mg-12Zn-xCa (x=0, 1, 2, 3) alloys after T6 treatment were studied. The results show that after T6 treatment, the α-Mg phase in the alloys changes from dendritic crystals to equiaxed grains and is refined, the hardness of the alloy is increased obviously. With the increase of Ca content, the microstructure of T6 treated Mg-12Zn-xCa alloys is refined and the hardness is increased, but when the content of Ca is more than 2%, dendritic crystals appear in the structure and the hardness decreases.

Numerical simulation and experimental verification of Jominy test for SA508-3 steel

Xu Dacheng, Bo Hengyong, Zheng Shanjü, Li Mengnie

2020, 45(12): 231-237. doi:10.13251/j.issn.0254-6051.2020.12.045

Abstract ( 62 )

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Influence of continuous cooling on microstructure evolution of SA508-3 steel was studied by numerical simulation and Jominy test. The models for predicting the temperature field and the microstructure field in the SA508-3 steel during the Jominy test were established by using the FLIM and UMATHT subroutine of finite element ABAQUS software, and used to simulate the end quenching process. And finally, the simulation was verified by microstructure observation at different positions on the basis of Jominy test. The results show that no pearlite is produced in the specimens after the end quenching test. With the increase of distance from the quenching end, the microstructure in the specimen changes from martensite (M) to bainite (B) and retained austenite, and the semi-martensitic region appears at 9 mm from the quenching end. The test results are in good agreement with the predicted results.

Self-adaptive temperature control of vacuum furnace based on single neuron PID

Fan Zhanwen, Shan Qiongfei, Yin Chengkun, Yang Guangwen, Wang He, Cong Peiwu

2020, 45(12): 237-241. doi:10.13251/j.issn.0254-6051.2020.12.046

Abstract ( 57 )

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According to the characteristics of vacuum heat treatment system, the single neuron PID control algorithm was applied to the temperature control of vacuum heat treatment system. Combined with the nonlinear approximation ability of neural network and the characteristics of self-learning and self-adaptive, the single neural network was combined with PID control to realize the control of vacuum furnace temperature, so as to improve the quality of vacuum furnace temperature control. The simulation results show that the single neuron network PID control system can self-tuning the control parameters, it is more robust to temperature control, has stronger anti-interference ability and robustness. After building the experimental platform of vacuum furnace temperature control system, it is found that the temperature rise process of vacuum furnace system with single neuron PID control shows good stability, but the response speed of temperature control and the accuracy of heat preservation slightly decrease. In order to further improve the quality of temperature control, the single neuron PID control method needs to be further improved in response speed and control accuracy.

Intelligent information production scheduling technology of heat treatment process

Zhou Yulong, Zhang Zhen, Zhou Yongsong, Chen Jie, Yin Heping, Li Jie, Zhang Jiulin, Lin Xin

2020, 45(12): 242-247. doi:10.13251/j.issn.0254-6051.2020.12.047

Abstract ( 59 )

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Heat treatment is an important part in the manufacturing industry. In view of the multi variety and variable batch production mode of heat treatment enterprises, it is an urgent problem for heat treatment enterprises to reasonably coordinate workshop production resources, ensure product quality, improve production efficiency, reduce production energy consumption, and improve enterprise intelligent management level. Based on the actual production process of heat treatment, a set of intelligent control system platform of heat treatment was constructed by using the technology of internet of things information collection, heterogeneous information data fusion, production process information management and control, combined with production scheduling genetic algorithm. Through the system platform, the real-time production scheduling of heat treatment process is realized, the production efficiency is improved, and the control ability of quality consistency of heat treatment products is improved.

Temperature measurement and control of large bottom discharge furnace for aluminum alloy heat treatment

Chen Bo, Xiong Zhili, Tang Haiyan

2020, 45(12): 248-251. doi:10.13251/j.issn.0254-6051.2020.12.048

Abstract ( 64 )

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Heat treatment of aluminum alloy has strict requirements for temperature tolerance and temperature synchronization, and the solution treatment process of clad aluminum alloy has special requirements for the recovery time. In order to find a solution to the problems of abnormal high and low points, temperature overshoot, poor recovery time and temperature synchronization existed in the 8 m long furnace for aluminum alloy heat treatment, the temperature measurement and control method of large bottom discharge furnace were investigated. The results show that the furnace can meet the strict temperature tolerance requirements and special recovery time requirements of aluminum alloy heat treatment only by feeding back the result of temperature uniformity survey to temperature control, choosing correct process sensor and locating it to right position, scientifically setting PID parameters and heating power.

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