Heat Treatment of Metals

Research progress of high strength and toughness eutectic high entropy alloys

Yang Tian, Xu Junfeng, Li Zhuo

2021, 46(2): 1-7. doi:10.13251/j.issn.0254-6051.2021.02.001

Abstract ( 86 )

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Eutectic high entropy alloys possess many excellent characteristics that traditional alloys cannot compare, such as high hardness, high corrosion resistance, high wear resistance, excellent casting property, excellent oxidation resistance and magnetic properties, so it is a breakthrough of alloy design in the field of traditional physical metallurgy, and it opens up a new platform for the exploration of new materials and new properties. Currently, many eutectic high entropy alloys with unique properties have been designed, however, the properties and design ideas of eutectic high entropy alloys are still lacking in macroscopic understanding. In this review article, the design methods of eutectic high entropy alloys (including the experimental method, the substitution method, the pseudo-binary method, and the CALPHAD method) were reviewed, the advantages and weaknesses of each method were further compared and analyzed. Subsequently, comprehensive effects of structural characteristics and thermo-mechanical processing on microstructure and mechanical properties of the eutectic high entropy alloys were analyzed. The possible problems in the design process of eutectic high entropy alloys were summarized and the future research direction was prospected.

Effect of nitrogen content on phase transformation of nickel-free austenitic stainless steel containing Mo

Weng Jianyin, Peng Wei, Ning Xiaozhi, Liu Tengshi, Bao Xianyong, Li Bei, Dong Han

2021, 46(2): 8-13. doi:10.13251/j.issn.0254-6051.2021.02.002

Abstract ( 64 )

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Based on Cr₁₈Mn₁₄Mo₃ steel, four high-nitrogen austenitic stainless steels with 0.004%-0.850% N were designed, and smelted into electroslag remelting ingots with measured nitrogen content of 0.008%-0.770% N. The thermodynamic calculation of equilibrium phase transformations of the steels was carried out, and the microstructure morphologies were observed. The results show that for 0.40%-0.85%N steels, there is a wide single-phase austenite region in 900-1200 ℃. The four calculated equilibrium phase transformation diagrams for the tested steels show that, the maximum precipitation amount of δ-ferrite is decreased with the increase of nitrogen content. When the nitrogen content is 0.77%, the maximum precipitation amount of δ-ferrite is about 30%, the relationship between the precipitation temperature T_δ of δ-ferrite and the nitrogen content (N) during the heating process is obtained as T_δ=876+433w(N). With the increase of nitrogen content, the precipitation temperature of Cr₂N increases gradually in cooling of the tested steels, and its quantitative relationship is obtained as T_Cr₂N=711+350w(N).

Effect of rare earth lanthanum on fatigue property of 300M steel

Liu Yue, Han Shun, Li Yong, Wang Chunxu, Gao Yuanhang, Wang Rui, Li Jianxin

2021, 46(2): 14-19. doi:10.13251/j.issn.0254-6051.2021.02.003

Abstract ( 64 )

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Effects of rare earth element La on the conventional mechanical properties and high cycle fatigue property of 300M steel and its modification effect on the morphology and size of nonmetallic inclusions in the steel were studied by mechanical property test, SEM analysis of fatigue fracture morphology and non-metallic inclusions at crack sources. The results show that, 0.006wt% lanthanum has little effect on the conventional mechanical properties, but significantly improves the high cycle fatigue property of the 300M steel, leading to that the high cycle fatigue limit σ_-1 of the 300M steel increases from 867 MPa to 940 MPa. The inclusions in the La-modified steel become larger in size, and change to rare earth inclusions containing S and O. The hardness, elastic modulus and expansion coefficient of the inclusions are closer to that of the steel matrix, which can effectively reduce the stress concentration around the inclusions and improve the high cycle fatigue properties of the steel.

Development and application of high strength circular chain 23MnNiMoCr54 steel for mining

Guo Xiaoxia, Wen Hui, Li Zhihao

2021, 46(2): 20-24. doi:10.13251/j.issn.0254-6051.2021.02.004

Abstract ( 67 )

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Base data of the 23MnNiMoCr54 steel were analyzed by means of Gleeble3500 thermal simulator, TEM and SEM, and then the composition design was optimized. Through formulating reasonable smelting, rolling and annealing process, high-strength ring chain steel for mining was successfully developed. The trial finished steel products was provided to the user, and through testing, all indicators reached the requirements of the C-class circular chain specified in GB/T 10560—2017.

Effect of Nb on CCT curves of Q345 low-Mo fire-resistant steel

Wan Rongchun, Sun Feng, Fu Liming, Shan Aidang

2021, 46(2): 25-29. doi:10.13251/j.issn.0254-6051.2021.02.005

Abstract ( 66 )

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Effect of Nb on continuous cooling transformation (CCT) curves of Q345 low-Mo (about 0.25wt%) fire-resistant steel was studied by measuring CCT curves of two Q345 steels with different Nb content. The results show that the CCT curve of Q345 low-Mo fire-resistant steel moves to the right and the critical cooling rate of bainite transformation decreases with Nb addition. At the same time, Nb addition can reduce the critical transformation temperature of austenite and inhibit the transformation from austenite to pearlite, which is beneficial to bainite transformation. In addition, in order to obtain the ideal microstructure (F+B+P) of the Q345 low-Mo fire-resistant steel, the optimal cooling rate of tested steel without addition of Nb should be about 0.28 ℃/s, and that of tested steel with addition of Nb should be about 0.14 ℃/s.

Research progress on microstructure of selective laser melted TC4 titanium alloy

Sun Jingli, Ke Linda, Xiao Meili, Du Lei, Chen Ge, Diao Wei, Nie Jingjing

2021, 46(2): 30-36. doi:10.13251/j.issn.0254-6051.2021.02.006

Abstract ( 81 )

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Selective laser melting forming technology is a promising method for manufacturing hard-to-machine metals such as TC4 alloy. The difficulty of the microstructure control is its bottleneck restricting in large-scale application. Research progresses on the effects of selective laser melting process parameters are summarized on the microstructure, residual stress distribution and microstructure change of TC4 alloy after heat treatment, and the microstructure-related future research directions are prospected.

Response of microstructure and mechanical behavior of metastable ARB-Cu to annealing process

Li Xiaohong, Jiang Qingwei, Li Min, Yang Peng

2021, 46(2): 37-44. doi:10.13251/j.issn.0254-6051.2021.02.007

Abstract ( 58 )

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Metastable ultrafine grained pure Cu was prepared by accumulative rolling bonding (ARB) and annealed at 100-250 ℃ for 10, 30 and 60 min respectively in order to study the effect of annealing heat treatment on its microstructure and mechanical properties. The microstructure, mechanical properties and fracture morphologies were analyzed by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), Vickers hardness tester and universal mechanical testing machine. The results show that, as the annealing temperature increases, the ARB-Cu grain size increases slightly, the sub-grains are dispersively distributed, the dislocation density decreases gradually, and the grain shape changes from irregular to equiaxed. After annealing at 100-250 ℃ for 10 min and 30 min, the yield strength and tensile strength of the ARB-Cu increase first and then decrease with the increase of annealing temperature. The microhardness gradually decreases with the increase of annealing temperature and annealing time. Annealing at 150 ℃ for 30 min, the strength and plasticity of the annealed ARB-Cu reach the best match. The fracture mechanism of the ARB-Cu changes from cleavage fracture in preparation state to ductile fracture in annealed state gradually, and the plastic deformation ability is improved.

Continuous cooling transformation behavior of hypereutectoid rail steel

Wang Dongmei, Zhao Leicheng, Chen Lin, Dong Rui

2021, 46(2): 45-49. doi:10.13251/j.issn.0254-6051.2021.02.008

Abstract ( 62 )

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Microstructure evolution and mechanical properties of the hypereutectoid rail steel with carbon content(mass fraction) above 0.9% were investigated by means of L78 quenching dilatometer during the continuous cooling process. The continuous cooling transformation curves were determined to providing a theoretical basis for the proper post-rolling controlled cooling process. The results show that at the cooling rate from 5 ℃/s to 10 ℃/s, the cementite precipitation and martensite formation are effectively prohibited, the interlamellar spacing of pearlite is refined, and the mechanical properties of the hypereutectoid rail steel are improved.

Precipitation behavior of M₂₃C₆ type carbides in GH3230 alloy

Du Xinglin, Ju Quan, Ma Huiping, Du Jinhui

2021, 46(2): 50-54. doi:10.13251/j.issn.0254-6051.2021.02.009

Abstract ( 66 )

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Precipitation behavior of M₂₃C₆ type carbides in solution-treated GH3230 alloy when aged at the range of 800-1100 ℃ were studied. The results show that, the solution-treatment microstructure of the GH3230 alloy consists of γ phase, primary granular carbides of M₆C, and granular carbides of M₂₃C₆ at the grain boundary. After short time aging treatment at the range of 800-1100 ℃, the M₂₃C₆ type carbides are precipitated at the grain boundary and in the grain. The granular carbides of M₂₃C₆ at the grain boundary are prone to grow along the grain, and gradually become cellular carbides. At the same aging temperature, the amount of carbides in the grain increases with the increase of aging time, and then gradually redissolves, the beginning of which can gradually advance with the increase of aging temperature.

Effect of heat treatment process on microstructure and properties of 5Cr5Mo2V steel

Yin Junwei, Zhou Jian, Jiang Yehua, Chi Hongxiao, Lin Peng

2021, 46(2): 55-60. doi:10.13251/j.issn.0254-6051.2021.02.010

Abstract ( 84 )

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Effects of austenitizing temperature and tempering temperature on microstructure and properties of the 5Cr5Mo2V steel for hot forging die were studied by Rockwell hardness tester and field emission scanning electron microscopy. The results show that after different quenching and tempering treatments, the microstructure of all the tested steel specimens is composed of tempered martensite, retained austenite and carbides. When quenched at 920-1030 ℃, the hardness of the 5Cr5Mo2V steel increases with the increase of quenching temperature and reaches the maximum value of 62.53 HRC at 1030 ℃, and then the hardness tends to be stabilized when quenched above 1030 ℃. The grains are finer when quenched at 1030 ℃, but the grains start to coarsen when the quenching temperature exceeds 1030 ℃. As tempered at 480-550 ℃, the hardness gradually increases with the increase of tempering temperature and a secondary hardening peak appears at 550 ℃. The impact absorbed energy of the tested steel is the lowest at 550 ℃, but when the tempering temperature is higher than 550 ℃, the impact properties of the tested steel gradually increase. When the tempering temperature is 600 ℃, the steel maintains a relatively high hardness (49 HRC) and the impact absorbed energy can reach 21 J. It is concluded that the optimum heat treatment process for the 5Cr5Mo2V steel is quenching at 1030 ℃ for 30 min with oil cooling and then tempering twice at 600 ℃ for 2 h with air cooling.

Annealing and dipping paint curing process of high saturation magnetic induction Fe₈₂Si_3.8B_13.9C_0.3 amorphous core

Song Su, Chen Wenzhi, Zhang Guangqiang, Liu Yang, Zheng Wei, Zhang Qian, Zhou Shaoxiong

2021, 46(2): 61-65. doi:10.13251/j.issn.0254-6051.2021.02.011

Abstract ( 65 )

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Effects of different annealing and dipping paint curing processes on the loss and magnetic properties of the Fe₈₂Si_3.8B_13.9C_0.3 amorphous alloy toroidal core were studied and compared with 1K101 alloy core. The results indicate that the optimum annealing temperature of the Fe₈₂Si_3.8B_13.9C_0.3 alloy core is lower than that of 1K101 alloy, and the lowest temperature is 330 ℃ in longitudinal magnetic annealing. Longitudinal annealed Fe₈₂Si_3.8B_13.9C_0.3 alloy core has higher saturation magnetic induction, B_{3500 A/m}=1.611 T. After annealing at 350 ℃ without magnetic field, the loss of the longitudinal annealed Fe₈₂Si_3.8B_13.9C_0.3 alloy is slightly higher than that of 1K101 alloy, P_{50 Hz, 1.4 T}=0.360 W/kg. After longitudinal magnetic annealing at 330 ℃, the loss is also higher than that of the 1K101 alloy, P_{50 Hz, 1.4 T}=0.257 W/kg. After transverse magnetic annealing at 350 ℃, the loss is lower than 1K101 alloy, P_{50 Hz, 1.4 T}=0.163 W/kg. After cured by dipping, the magnetic flux density of the Fe₈₂Si_3.8B_13.9C_0.3 alloy core is 15% higher than that of the 1K101 alloy and B_{800 A/m}=1.341 T. The core loss of the Fe₈₂Si_3.8B_13.9C_0.3 alloy is lower than that of the 1K101 alloy after longitudinal magnetic annealing and dipping paint curing, and the advantage is more obvious with the increase of frequency. When the frequency is higher than 1000 Hz, the loss value of longitudinal magnetic annealed and cured Fe₈₂Si_3.8B_13.9C_0.3 alloy core is lower than that of the uncured core.

Effect of shot peening on high-temperature steam oxidation behavior of martensitic heat-resistant steel

Shen Kang, Cai Wenhe, Du Shuangming, Dong Shuqing, Gao Dawei, Bai Yin

2021, 46(2): 66-73. doi:10.13251/j.issn.0254-6051.2021.02.012

Abstract ( 62 )

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High temperature steam oxidation behavior of the P92 and G115 steel with and without shot peening was studied by using a high temperature steam oxidation test device. The results show that, the steam oxidation kinetic curves of the three specimens conform to the law of ΔW=ktⁿ at 650 ℃. The oxidation mass gain of the G115 steel is much smaller than that of the P92 steel under the same steam oxidation time, mainly because of the formation of rich Cr layer in the steel and the precipitation of rich Cu phase at the interface of the oxidized layer. G115 steel treated by shot peening has less oxidation mass gain than G115 steel without shot peening. The surface of G115 steel after shot peening produces a large amount of plastic deformation, which leads to the introduction of high-density dislocation and slip bands. Martensite lath of the inner wall breaks down, which leads to the increase of martensite lath boundary. The massive increase of slip bands, dislocations and martensite lath boundaries provides diffusion channels of Cr elements to the surface, which accelerates the diffusion rate of Cr elements in the matrix to the surface, and becomes the main reason for improvement of anti-vapor oxidation performance.

Effect of shot peening and hydrochloric acid pickling on oxide layer microstructure of 2205 duplex stainless steel hot-rolled sheet

Wang Jian, Meng Haojie, Li Peng, Li Guoping, Li Jun, Liu Jie, Han Peide

2021, 46(2): 74-80. doi:10.13251/j.issn.0254-6051.2021.02.013

Abstract ( 76 )

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Optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS) were used to study the oxide layer microstructure of the 2205 duplex stainless steel hot-rolled sheet after annealing and shot peening treatment, and to analyze the microstructure of the surface passive film after pickling with hydrochloric acid and mixed acid (HNO₃+HF). The corrosion resistance of the steel after pickling was analyzed by using electrochemical testing methods. Further, an evolution model of oxide layer removal during shot peening and pickling of the hot rolled 2205 duplex steel sheet after annealing was proposed. The results show that the shot peening treatment has significant effect on the removal of Fe-rich oxide in the 2205 duplex steel surface layer, but the dense Cr-rich oxide layer within the inner layer cannot be removed. Hydrochloric acid pre-pickling can further remove the dense oxide layer from outside to inside after shot peening, and the final pickling with nitric acid and hydrofluoric acid can remove the Cr-poor layer produced by annealing, so that a Cr₂O₃-rich passive film is formed on the steel surface. The 2205 duplex steel after mixed acid pickling shows higher self-corrosion potential and larger arc resistance radius than that of hydrochloric acid pre-acid pickling, indicating that mixed acid pickling is beneficial to improve the corrosion resistance of 2205 duplex stainless steel.

Shot peening process test for spur gear parts

Yang Yang, Che Yongping, Hai Xianü, Li Yang, Wang Ye

2021, 46(2): 81-86. doi:10.13251/j.issn.0254-6051.2021.02.014

Abstract ( 59 )

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Based on the development of peening process of a part of a company, the peening process test for spur gear parts was completed under the research and design of Almen test strip tooling simulating spur gear. It ensures the consistency of peening state and residual stress between tooth flank and tooth, which provides a new idea for subsequent shot peening process development.

Effect of tempering temperature on hydrogen diffusion and hydrogen embrittlement susceptibility of DP600 steel

Wang Zhen, Liu Jing, Huang Feng, Bi Yunjie, Ke Shuzhong

2021, 46(2): 87-94. doi:10.13251/j.issn.0254-6051.2021.02.015

Abstract ( 56 )

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Effect of tempering temperature on the hydrogen embrittlement susceptibility and hydrogen diffusion behavior of DP600 steel was explored by slow strain-rate tensile test and double cell hydrogen permeation test, and combined with SEM, TEM and EBSD techniques. The results show that the hydrogen embrittlement susceptibility and the effective hydrogen diffusion coefficient of the DP600 steel decrease with the increase of tempering temperature, which is mainly related to the decrease of concentrations of reversible hydrogen traps such as dislocation and small angle grain boundary, and the increase of concentrations of irreversible hydrogen traps such as carbide/matrix interface and large angle grain boundary. Among them, the dispersed carbides make the captured hydrogen atoms distribute evenly, which results in the decrease of hydrogen embrittlement susceptibility index from 44.6% (270 ℃) to 1.8% (350 ℃). Considering the influence of tempering temperature on the strength and hydrogen embrittlement susceptibility, the optimum tempering temperature of the DP600 steel is 330 ℃.

Multi-objective optimization model of deep cryogenic process for conical pick

Yan Xianguo, Li Fan, Chen Zhi, Yao Yongchao

2021, 46(2): 95-99. doi:10.13251/j.issn.0254-6051.2021.02.016

Abstract ( 48 )

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For optimization of the conical pick performance indexes including hardness, wear resistance and impact property, deep cryogenic treatment was carried out on the material of conical pick and achieved good results. In order to obtain the optimal conical pick cryogenic process, a multi-objective optimization model of conical pick cryogenic process was proposed based on QFD model from the perspective of multi-objective programming. Then the optimal cryogenic process parameter group is found and experimentally verified as follows: cryogenic temperature of 77 K, cryogenic time of 24 h and alternation number of 2, so that the effectiveness of the model is also verified.

Effects of different gas flow ratio on structure and tribological properties of Cu/a-C∶H films

Meng Jie, Tian Linhai, Liu Ying, Zhou Bing, Wu Yucheng, Yu Shengwang, Wu Yanxia

2021, 46(2): 100-104. doi:10.13251/j.issn.0254-6051.2021.02.017

Abstract ( 51 )

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Cu/a-C∶H thin films with different Cu contents were prepared by using magnetron sputtering technology combined with plasma vapor deposition technology with adjusting the gas flow ratio of CH₄ and Ar. The effects of gas flow ratio on the existence form of Cu and on the structure of the composite films were analyzed by XPS, Raman and other characterization methods. The hardness and elastic modulus of the composite films were measured by nano indentation. The tribological properties and related mechanisms of the composite films in air were analyzed by reciprocating friction and wear tester, white-light interferometry and FESEM. The results show that with the increase of CH₄ proportion in the mixed gas, the sp²C content in the composite films increases, the content and grain size of Cu decrease, and the hardness of the composite films increases gradually, while the toughness decreases. Additionally, when the CH₄ gas flow ratio is 60% and Cu content is 6.68at%, the composite films are of high hardness, good toughness, and the lowest friction coefficient (0.091) and wear rate (1.77×10^-6 mm³·N^-1·m^-1) in air, which are related to the content of sp²C and the size and content of Cu nanoparticles in the composite films.

Effect of cryogenic treatment and post-cryogenic tempering on wear resistance of cemented carbide head for pick

Dong Liang

2021, 46(2): 105-108. doi:10.13251/j.issn.0254-6051.2021.02.018

Abstract ( 64 )

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YG8 cemented carbide was selected as the material of cemented carbide head for pick of roadheader. The effects of cryogenic treatment and post-cryogenic tempering on the wear resistance and average friction coefficient of YG8 cemented carbide were studied. The changes of microstructure of each phase in YG8 cemented carbide caused by the two kinds of processes were investigated by means of SEM, EDS and XRD. The results show that post-cryogenic tempering treatment can obviously reduce the wear loss and average friction coefficient of YG8 cemented carbide. The content of η phase in YG8 cemented carbide is basically the same after cryogenic treatment and post-cryogenic tempering, but it is easier to promote the uniform distribution of η phase after post-cryogenic tempering.

As-cast microstructure characteristics and homogenization treatment of GH4169 alloy

Jiang Shichuan, Zhang Jian, Han Fu

2021, 46(2): 109-117. doi:10.13251/j.issn.0254-6051.2021.02.019

Abstract ( 84 )

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As-cast microstructure of the GH4169 alloy and effects of homogenization treatment on grain size, precipitated phases, oxidized layer thickness and solute element uniformity were studied by means of CLSM, OM and SEM. The results show that in the as-cast microstructure, the precipitated phases of Laves phase, δ, γ′ and MC type carbide exist between dendrites, and the segregation of main segregating element Nb is the most serious in central part of the ingot. The two-stage homogenization treatment of 1160 ℃×16 h and 1190 ℃×30 h can achieve the most suitable uniformity of solute elements in the alloy ingot, and after which, the residual segregation coefficient of Nb element is about 0.2, the average grain size is about 6117 μm and the oxidized layer thickness is about 41.6 μm.

Induction heating treatment of online heat treatment steel rail with forming heel-end for high-speed and heavy haul railway

Zhang Dawei

2021, 46(2): 118-124. doi:10.13251/j.issn.0254-6051.2021.02.020

Abstract ( 68 )

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In order to make the structure and properties of forming heel-end of the steel rail for high-speed and heavy haul railway to meet the new standard and railway application requirements after heat treatment, the heat treatment experiment was carried out on 60AT2-U71MnG and 60AT1-U75V steel rail forming heel-end for high-speed and heavy haul railway after online heat treatment by using self-developed automatic production line of full section induction heating and cooling. The microstructure of hardened layer was observed by means of optical microscopy. The chemical composition, depth of hardened layer, the hardness of cross-section and surface, the tensile strength and elongation and fatigue property were measured for the rail. The results show that the 60AT2-60 kg/m(U71MnG) and 60AT1-60 kg/m(U75V) steel rail forming heel-end after heat treatment, the depth of hardened layer in rail head tread of it is more than 30 mm, the microstructure is sorbite. The hardness of surface is more than 320 HBW, the tensile strength is more than 1200 MPa, and the elongation is more than 11%. The change range of surface hardness is less than 30 HBW. After heat treatment, heat affected soften zone is less than 40 mm. There is no fracture by bending fatigue test when cycled more than two million times. All data of the AT steel rails can meet the corresponding technical requirements, and the steel rail can meet the requirements for application.

Effects of quenching and tempering on microstructure and properties of 10Cr5MoVRE steel and second phase precipitation behavior

Shi Xiaoxia, Li Xiao, Ren Huiping, Jin Yan, Jia Pengxia

2021, 46(2): 125-129. doi:10.13251/j.issn.0254-6051.2021.02.021

Abstract ( 59 )

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Taking 10Cr5MoVRE steel as the research object, the microstructure and properties of as-rolled and quenched+tempered(QT) specimens were compared, and the precipitates of quenched+tempered specimens were observed and analyzed by means of TEM and energy spectrometer. The mechanical property test results show that the strength and toughness of the quenched+tempered specimens are matched, and the elongation is increased by 93.8% and the impact abserbed energy under the condition of 0 ℃ is increased by more than 6 times compared with that of the rolled one. With the help of the SEM observation, the low temperature impact fracture morphology of the rolled specimen is brittle cleavage fracture and the quenched+tempered specimen is ductile dimple fracture. By means of OM observation and analysis, the microstructure of the rolled specimen is granular bainite and the quenched+tempered specimen is tempered sorbite. The second phase precipitates of the quenched+tempered 10Cr5MoVRE steel specimen were observed and analyzed by means of TEM and energy spectrometer, the results show that the carbide precipitates are mainly compound phase composed of vanadium carbide, molybdenum carbide and chromium carbide, while the inclusions is composed of Al₂O₃, MnS, Ca₃(PO₄)₂ and rare earth compounds.

Effect of solution pretreatment after forging on annealed microstructure and impact property of H13 steel

Sun Liguo, Zhou Jian, Ma Dangshen, Chi Hongxiao

2021, 46(2): 130-135. doi:10.13251/j.issn.0254-6051.2021.02.022

Abstract ( 54 )

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Effects of different solution pretreatment and isothermal spheroidizing on the microstructure and impact property of H13 hot work die steel were studied by means of phase analysis, SEM, TEM, and equilibrium phase diagram of the H13 steel was calculated by Thermo-Calc software. The results show that after solution pretreatment at 1000 ℃, 1050 ℃ and 1100 ℃, the quantity of MC type undissolved carbides dominated by V gradually decreases with the increase of solution temperature. After solution pretreatment at 1100 ℃, undissolved carbides are basically dissolved and the grains are coarsened. After solution pretreatment and isothermal spheroidizing, the distribution uniformity and roundness of the carbides are improved, but the grain size is coarsened at 1100 ℃, and a coarse network is formed and nucleated along the coarse martensite interface during the annealing process, which reduces the structure uniformity. The impact property of the H13 steel is better when solution pretreated at 1000 ℃ and then isothermally spheroidized, and with the increase of solution pretreatment temperature, the impact property of the tested steel shows a significant downward trend.

Effect of tempering temperature on microstructure and properties ofCr5NiMoVNb steel for backup roll

Li Yanlong, Wu Qiong, Liu Changsheng

2021, 46(2): 136-139. doi:10.13251/j.issn.0254-6051.2021.02.023

Abstract ( 46 )

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Effect of tempering temperature on microstructure and mechanical properties of Cr5NiMoVNb steel for backup roll was studied by means of scanning electron microscope, X-ray diffractometer, Rockwell hardness tester, tensile tester and impact tester. The results show that tempered martensite-predominantly matrix is observed in Cr5NiMoVNbb steel with a small amount of residual austenite when temped at different temperatures. The precipitation of carbides and the phase transition of residual austenite occur during tempering process. The strength (tensile strength and yield strength) and the hardness of Cr5NiMoVNb steel gradually decrease with the increase of tempering temperature. The plasticity (reduction of area) and the toughness (impact absorbed energy) of the Cr5NiMoVNb steel gradually increase with the increase of tempering temperature. When tempering temperature is 520 ℃, the preferable mechanical properties of Cr5NiMoVNb steel are obtained, leading the hardness, tensile strength, reduction of area and impact absorbed energy to 53.5 HRC, 1735 MPa, 25.2% and 7.3 J, respectively.

Effect of tempering time on mechanical properties and microstructure of A-100 steel

Hu Shengshuang, Shi Lili, He Kun, Zhao Gang, Wang Qing, Wang Wenbo, Wang Yaxing

2021, 46(2): 140-143. doi:10.13251/j.issn.0254-6051.2021.02.024

Abstract ( 57 )

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Effect of tempering time on microstructure and mechanical properties of A-100 ultra-high strength steel after quenching+cryotreatment was studied by means of mechanical properties test, microstructure observation and fracture failure analysis. The results show that, when the A-100 steel tempered at 482 ℃, the reversed austenite is precipitated at the grain boundary of lath martensite, and M₂C-type carbide is precipitated around martensite. With the increase of tempering time, the amount of reversed austenite increases and disperses more uniformly, and the grain size of the martensite increases. With the increase of tempering time from 5 h to 8 h, the proof strength, plastic extension decreases from 1890 MPa to 1728 MPa; the tensile strength decreases from 2045 MPa to 1988 MPa, decreasing by about 8.57% and 2.78% respectively. However, the fracture toughness increases from 98.75 MPa·m^1/2 to 114.3 MPa·m^1/2, increasing by about 15.74%. When increasing tempering time, the dimple area of impact fracture decreases, and the average dimple area accounts for roughly is 86.2% of the total area after tempering for 5 h, while decreasing by about 70.1% when tempering for 8 h.

Effect of heat treatment temperature on microstructure and properties of environmentally friendly chromium layer of narrow and deep groove parts

Hong Zikang, Luo Yilan, Zhu Qiaolian, Zhu Shigen

2021, 46(2): 144-148. doi:10.13251/j.issn.0254-6051.2021.02.025

Abstract ( 57 )

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Chromium coating was prepared on narrow and deep groove parts by using environment-friendly trivalent chromium electroplating process, and then heat treated at different temperatures (0-400 ℃) to investigate the effect of heat treatment temperature on the microstructure and properties of the chromium coating. The micromorphologies, phase structure, microhardness, bonding force and wear resistance of the chromium coating before and after heat treatment were analyzed. The results show that there are micro-cracks on the surface of the as-electroplated coating, and the micro-crack gap expands after the heat treatment. As the heat treatment temperature increases, the structure of the coating gradually changes from amorphous to crystalline, and the microhardness, binding force and wear resistance can be improved. When heat treated at 400 ℃, the microhardness, bonding force and wear resistance are improved, reaching the best value of 781 HV0.1, over 40 N and the smallest wear volume 0.0136 mm³, respectively.

Effect of annealing temperature on microstructure and texture of Ce-bearing non-oriented electrical steel for new energy automobiles

Kong Xiangbing, Ren Huiping, Jin Zili, Li Tao, Wu Zhongwang

2021, 46(2): 149-152. doi:10.13251/j.issn.0254-6051.2021.02.026

Abstract ( 64 )

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Effect of annealing temperature on microstructure and textures of Ce-bearing non-oriented electrical steel for new energy automobiles was studied by means of SEM, EBSD and XRD. The results show that recrystallized and sub-crystalline microstructure can be observed in both edge and center after annealing at 800 ℃, the intensity of {112}<110> orientation in α texture is highest, but that of {111}<112> orientation in γ texture is weaken. In addition, a small amount of η texture exists in the annealing sheet. After annealing at the range of 830-920 ℃, the higher annealing temperature, the more sufficient recrystallization is, the intensity of α texture decreases while γ texture increases, but η texture totally disappears. The complete recrystallization of tested steel annealed at 950 ℃ has occurred, at which state the average grain size is 48.29 μm and the highest intensity of {111}<112> orientation in γ texture can reach 11.36.

Heat treatment process of large diameter forged wear-resistant steel ball

Gao Limei, Hou Jianmin, Liang Zhu, Sun Xiaolei

2021, 46(2): 153-156. doi:10.13251/j.issn.0254-6051.2021.02.027

Abstract ( 71 )

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Secondary heating quenching and low temperature tempering processes were used to improve the performance of ø120 mm forged wear-resistant steel balls, and the effects of heating rates and cooling time in secondary heating quenching process on the hardness distribution, impact property and microstructure of the steel balls were studied. The optimized heat treatment process of the steel ball is as follows: heating to 840 ℃ with the rate of 2.8 ℃/min and holding for 1 h, air cooling to 800 ℃, quenching into 35 ℃ water for 350-400 s, and then air cooling to below 80 ℃; tempering at 200 ℃ for 4 h, furnace cooling to below 80 ℃, and then air cooling. After treating by the optimized process, the hardness from surface to core of the wear-resistant steel ball is all in the range of 58-60 HRC, the impact absorbed energy at core of the ball at room temperature is ≥15 J, and the number of single falling test is more than 5000 times, which proves that this process can improve the quality and life of large-diameter forged wear-resistant steel balls.

Effect of heat treatment on microstructure and properties of dual FCC-phase CoCrFeNiCu high entropy alloy

Zhang Xiao, Liu Liang, Shang Jian, Zhao Zuofu, Zhang Yue, Qi Jingang, Wang Bing

2021, 46(2): 157-160. doi:10.13251/j.issn.0254-6051.2021.02.028

Abstract ( 67 )

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CoCrFeNiCu high entropy alloy was prepared by vacuum induction melting, and the effects of different annealing temperatures on microstructure and mechanical properties were studied. The results show that the as-cast CoCrFeNiCu alloy has a dual FCC-phase crystal structure, which are copper-rich phase and copper-dilute phase, respectively. The phase separation is gradually obvious as the heat treatment temperature increases. The microstructure of the as-cast alloy is a typical dendritic structure, and as the heat treatment temperature increases, the copper-rich phase increases, and the interdendritic region becomes wider, in which a large number of nanoparticles are precipitated. After heat treatment at 600 ℃, the yield and fracture strength of CoCrFeNiCu alloy are significantly improved, the yield strength reaches 233 MPa, and the fracture strength is close to 3 times of the as-cast alloy, however, the elongation of the alloy is basically unchanged.

Analysis on factors affecting decarburization of hot forming steel

Chen Bo, Wei Huanjun, Geng Zhiyu, Hua Yongxing, Zhang Jiguo, Xue Liqiang, Bi Yanlei

2021, 46(2): 161-167. doi:10.13251/j.issn.0254-6051.2021.02.029

Abstract ( 70 )

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Hot forming process of T1500HS and CR1300/2000HS steels was simulated by using Gleeble-3500 thermal testing machine, and the influence of different heating temperature(890-950 ℃), holding time (240-1000 s), chemical compositions, and surface condition (oiled or oil-free) on the decarburization of the cold-rolled hot forming steels was studied. The results show that under normal heating temperature (910-950 ℃), holding time (240-480 s) and with good protective atmosphere in the furnace, there is little decarburization after hot forming for the cold-rolled steel. With the increase of heating temperature, holding time, the C content and the surface oiling, the depth of the decarburized layer is increased after forming for the cold rolled hot forming steel. When the depth of the decarburized layer is not more than 20 μm, the decarburization layer has little effect on the tensile properties of tested steel after hot forming. While the decarburized layer has great impact on the hardness of the hot forming steel, as the depth of the decarburized layer increases, the hardness decreases.

Hot compression mechanical behavior and microstructure of Al-Mg-Si alloy with different heat treatment

Liu Wei, Liu Wei, Zou Wenjie, Wu Yuanzhi, Deng Bin, Liu Anmin, Ye Tuo

2021, 46(2): 168-172. doi:10.13251/j.issn.0254-6051.2021.02.030

Abstract ( 64 )

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High temperature compression test of the Al-Mg-Si alloy with different heat treatment state was carried out by Gleeble-3500 thermal simulation test machine. The hot deformation behavior of the solid solution treated and aged alloy was studied under the condition of deformation temperature of 100-400 ℃ with strain rate of 0.01 s^-1. The results show that the alloy mainly undergoes two stages of strain hardening stage and steady-state deformation stage. The flow stress decreases with the increase of compression temperature, and at the same deformation temperature, the flow stress of aged alloy is higher than that of solid solution treated alloy. With the increase of deformation temperature, the flow stress difference between the solid solution treated and aged alloy becomes smaller and smaller. During the process of deformation, a large number of dislocation structures are produced in the alloy. And because the dispersedly distributed precipitated phase pins dislocation, the dislocation distribution of the aged alloy is more uniform, and the deformation resistance is larger. With the increase of deformation temperature, the dislocation density decreases, and the main mechanism of softening is dynamic recovery.

Effect of powder morphology on mechanical properties of selective laser melting 316L stainless steel

Zhang Yamin, Wu Yaosha, Yang Junbao, Liu Xiaoqing

2021, 46(2): 173-177. doi:10.13251/j.issn.0254-6051.2021.02.031

Abstract ( 76 )

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316L stainless steel bulk was prepared with aerosolized powders by plasma spheroidization (PS) and selective laser melting (SLM) technologies. The microstructure and mechanical properties of the PS powder and the 316L stainless steel bulk were characterized by XRD, SEM, laser scattering, tap-density tester and universal mechanical testing machine. The results show that the PS powder has more spherical particles and less irregular flat ones than that of the aerosolized powder, and its HR value (the ratio of vibrational density to loose density) reduces from 1.28 to 1.08, which indicating that the fluidity has been improved significantly. The phase composition in the SLM bulk is the same as that of raw material powder, which are typical austenitic stainless steel structure(γ-Fe+α-Fe). Compared with that of the 316L stainless steel bulk prepared by aerosolized powder, the mechanical properties and compactness of the PS bulk have a certain degree of improvement, which mainly due to the higher density of the precursor powder prepared by PS and its increased sphericity and better fluidity.

Effect of cooling rate on undercooling austenite transformation of 700 MPa automotive beam steel

Zhao Nan, Xue Feng, Pan Jin, Guo Weichao, Li Jianchao

2021, 46(2): 178-181. doi:10.13251/j.issn.0254-6051.2021.02.032

Abstract ( 62 )

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The continuous cooling transformation (CCT) curves of 700 MPa automotive beam steel 700L were determined by using DIL805L quenching dilatometer. Combined with metallography-hardness method, the phase transformation rules and microstructure as well as the influence factors were analyzed. The results show that the critical point of 700L steel is Ac₃=898 ℃, Ac₁=772 ℃. The transformation product of undercooling austenite is ferrite, pearlite and bainite when the cooling rate is less than 0.5 ℃/s, then pearlite disappears when the cooling rate is more than 0.5 ℃/s, ferrite disappears and the transformation product is all bainite when the cooling rate is 5 ℃/s. A few martensite appears in the transformation products when the cooling rate is 10 ℃/s, and with the increase of cooling rate, martensite increases and bainite decreases gradually until totally disappears. The hardness of the steel gradually increases with the increase of cooling rate, and increases significantly at 10 ℃/s.

Effect of nitriding temperature on post-oxidating infiltrated layer of 42CrMo steel part surface

Meng Xuan, Yue Jiahong, Kong Lingfei, Yang Yang, Jia Peng

2021, 46(2): 182-184. doi:10.13251/j.issn.0254-6051.2021.02.033

Abstract ( 78 )

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Effect of nitriding temperature on properties of the infiltrated layer of 42CrMo steel parts treated by the process of nitriding with post-oxidating was studied by means of hardness test, microstructure observation, and evaluation of brittleness grade and porosity grade. The results show that the thickness and porosity grade of the infiltrated layer increase with the increase of nitriding temperature, but the brittleness grade changes little. The surface hardness of the infiltrated layer increases first and then decreases with the increase of nitriding temperature. When the nitriding temperature is 560 ℃, the 42CrMo steel parts can obtain infiltrated layer with excellent properties, of which the surface hardness and the thickness of infiltrated layer is ≥600 HV and ≥15 μm respectively, the brittleness and the porosity of infiltrated layer is grade 1 and grade 2, respectively.

Microstructure and properties of laser clad stainless steel layer on surface of low carbon steel

Wang Ge, Fu Yuzhu, Yao Quantong, Tong Weiping

2021, 46(2): 185-189. doi:10.13251/j.issn.0254-6051.2021.02.034

Abstract ( 72 )

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The 316L stainless steel powder was cladded on the surface of 0.20%C low carbon steel by JHM-1GY-400 pulse Nb∶YAG laser. The phase composition and microstructure of the 316L clad layer were analyzed by OM, XRD and SEM. The wear resistance and corrosion resistance of the 316L clad layer and the substrate (0.20%C low carbon steel) were studied by rotary friction tester and electrochemical workstation. The results show that the clad layer is about 50 μm thick and is composed of γ phase(austenite) and α phase(ferrite). The microstructure of the clad layer mainly includes fine dendrites, coarse cellular crystals and planar front. The surface hardness of the clad layer is about twice of that of the substrate, while the friction coefficient is 0.0418 lower than that of the substrate, and the wear loss is lower, indicating that the stainless steel clad layer has a higher wear resistance than that of the substrate. Compared with the substrate, the clad layer has lower self-corrosion current and higher self-corrosion potential, indicating that the corrosion resistance of the stainless steel clad layer is better.

Effect of laser shock processing on residual stress and mechanical properties of 7050-T7451 aluminium alloy

Han Peipei, Quan Chunyi, Jiao Qingyang, Lu Ying, Zhao Dong, Qiao Hongchao, Zhao Jibin

2021, 46(2): 190-195. doi:10.13251/j.issn.0254-6051.2021.02.035

Abstract ( 49 )

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Effect of different laser power density and shock times on residual stress and properties of the 7050-T7451 aluminium alloy, the specimens were treated by laser shock processing (LSP). The results show that, laser shock processing can increase the hardness of the specimen, and the hardness increases with the increase of shock times. The maximum surface micro-hardness can reach 172 HV0.05, which is increased by 17% compared with untreated specimen, and the depth of hardened influenced layer is 750 μm. When the laser power density is 7.28 GW/cm² and shocked for once, the surface roughness is 0.279 μm which is decreased by 22.5% compared with the original ground surface, and the roughness increases with the increase of shock times, but all are less than the original surface roughness. The laser shock processing can increase the residual stress of the specimen. When the laser power density is 7.28 GW/cm² and shock for three times, the maximum surface residual stress is －227.0 MPa. When the laser power density is 4.37 GW/cm² and shock for three times, the fatigue life of the specimen can up to 10⁶ cycles, which is increased by 2.3 times compared to that of the untreated specimen. The higher hardness and residual compressive stress by LSP can effectively prohibit cracking initiation and propagation and then enhance the fatigue property resistance of the 7050-T7451 aluminium alloy.

Microstructure and wear resistance of laser clad TiAlSi+xB₄C coatings on Ti-6Al-4V alloy

Gao Yuan, Liu Ran, Wu Tao, Ma Wen, Yun Mingxiang, Zhu Yuanzhi

2021, 46(2): 196-199. doi:10.13251/j.issn.0254-6051.2021.02.036

Abstract ( 65 )

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TiAlSi+xB₄C coatings were prepared on the surface of Ti-6Al-4V alloy by laser cladding, and the effects of different B₄C content on microstructure, microhardness and wear resistance of the coatings were analyzed. The results show that different content of B₄C makes little difference in the phase type of the coating. The micro morphology of the clad coating is composed of granular crystals, layered crystals, cell crystals and short rod crystals. The microhardness distribution of the coatings with different content of B₄C is about the same, but is obviously improved compared with the substrate. With the increase of B₄C content, the microhardness tends to increase on the whole, when the content of B₄C is 8%, the microhardness reaches the highest, that is 1216 HV0.1, about 4.2 times of the substrate. However, when the B₄C content is much higher, the hardness decreases and microcracks appear. Wear experiments show that the wear resistance of the coatings with different content of B₄C is significantly better than that of Ti-6Al-4V alloy substrate, and the coating with 8% B₄C has the minimum wear loss. The results show that the cladding of coating with different content of B₄C obviously improves the surface properties of the Ti-6Al-4V alloy substrate.

Laser cladding remanufacturing technology of 12CrNi3A steel camshaft

He Jianqun, Wu Chengwu, Wang Jingwen, Wang Wentao, Liu Zhiwei, Han Jingwei, Yin Ziqiang, Cheng Wei

2021, 46(2): 200-203. doi:10.13251/j.issn.0254-6051.2021.02.037

Abstract ( 69 )

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A high hardness laser clad layer was obtained on the worn surface of 12CrNi3A steel camshaft cam for fuel injection pump by using a 2 kW fiber laser. The surface integrality, hardness, microstructure and properties of the clad layer were characterized by PT flaw detection, Vickers hardness tester, metallographic microscope and friction wear tester. The results show that the clad layer has a thickness of about 1 mm and microhardness of about 650 HV, compact microstructure and fine grains, and metallurgical bonding with the 12CrNi3A steel. The wear resistance of the clad layer is better than that of the cam base material, and the repair quality of the camshaft is good to meet the use requirements. It is concluded that the laser cladding technology can be used to repair the severe damaged camshaft surface of the fuel injection pump, and to overcome the distortion problem of the whole axis easily caused by the conventional repair method.

Development and application of mesomechanical modeling and simulation software for polycrystalline materials

Xue Xuan, Shen Gang, Yang Xingyun, Gu Jianfeng, Wang Jing, Zhang Weimin

2021, 46(2): 204-208. doi:10.13251/j.issn.0254-6051.2021.02.038

Abstract ( 59 )

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Thermal Prophet-RVE (THP-RVE), a real microstructure-based mesomechanical modeling and simulation toolkit, was independently developed recently for particular application to property predictions for polycrystalline materials. In this paper, the basic framework, key features and the implementation technologies of THP-RVE were firstly introduced, then the deformation caused by martensite transformation in steel production and the mesomechanical behaviors under tensile loads of a ferrite/martensite dual-phase steel were simulated separately by using THP-RVE. The results show that the microstructural model constructed based on the actual material microstructure data can highly revivify the geometrical topological relationship among phase compositions and grains in the microstructure, and the mesomechanical model so established can be used to predict the deformation behavior and overall mechanical properties of polycrystalline materials under complex thermo-mechanical coupling.

Numerical simulation and analysis of vacuum heating temperature field of hydrogen treatment furnace

Wang Tong, Lu Wenlin, Li Qing, Du Chunhui, Chen Xuyang, Xue Danruo

2021, 46(2): 209-212. doi:10.13251/j.issn.0254-6051.2021.02.039

Abstract ( 70 )

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Technology of heat hydrogen treatment of titanium alloy is a new technology which can improve the microstructure and machinability of titanium alloy by using the reversible effect of hydrogen in titanium alloy, and the heat hydrogen treatment furnace is an important equipment for hydrogen permeation and dehydrogenation of titanium alloy. The heating uniformity and heating efficiency are important factors to be considered in the design of heating chamber, and also important indexes to measure the performance of heat hydrogen treatment furnace. The design of heating chamber directly affects the efficiency and quality of titanium alloy in the process of heat hydrogen treatment. The numerical simulation of the temperature field in the vacuum heating process of the hydrogen heat treatment furnace suitable for titanium alloy was carried out, and the mathematical model of vacuum heating was established. The comparison of numerical simulation and experiment under no-load condition showed that they were basically consistent. On this basis, the influence of the design parameters, such as the heating power and the heating bandwidth, was carefully studied from the heating efficiency and the heating uniformity under load. The results show that the heating efficiency and heating uniformity can be properly improved by choosing reasonable heating power and width of heating zone.

Cause analysis on quenching cracking of 40CrNiMo7 steel forged shaft

Zhang Jiawen, Fu Tianliang, Wu Hao, Wang Zhaodong

2021, 46(2): 213-217. doi:10.13251/j.issn.0254-6051.2021.02.040

Abstract ( 80 )

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Causes of 40CrNiMo7 steel forged shaft cracking were analyzed by means of macroscopic morphology observation, chemical composition analysis, hardness test, metallographic analysis, energy spectrum analysis and other methods. The results show that the crack of the forged shaft is a longitudinal quenching crack, due to that the Cr element in the steel exceeds the standard, and increases the cracking tendency. The specimen surface has more TiN inclusions and Al₂O₃, MnS etc., and a decarburized layer of about 0.6 mm, which promotes the formation of cracks. The generated structural stress during quenching causes the surface to exhibit a tensile stress state, and with the help of decarburized layer and non-metallic inclusions, the fracture strength of the material is exceeded and cracking occurs.

Failure analysis of driving bevel gear of heavy truck rear axle

Cheng Yuan, Hu Fangzhong, Hu Naiyue, Wang Kaizhong, Wang Lianglin, Jin Guozhong, Hao Zhenyu

2021, 46(2): 218-222. doi:10.13251/j.issn.0254-6051.2021.02.041

Abstract ( 73 )

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Failure reasons of a failed gear of heavy truck rear axle were analyzed by using scanning electron microscope, optical microscope, spark discharge atomic emission spectrometer, hydrogen determination instrument and Brinell hardness tester. The results show that all the performance indexes of the failure gear meet the requirements of the standard, and the hydrogen content is relatively low. The main reason for the failure is the delayed fracture failure caused by the stress concentration at the connection between the hollow groove of the screw thread and the spline at the end of the gear shaft.

Failure analysis of joint reducer for robot and improvement measures

Huang Bin, Chang Anquan, Pan Anxia, Wang Xiaoyu

2021, 46(2): 223-227. doi:10.13251/j.issn.0254-6051.2021.02.042

Abstract ( 60 )

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Causes of contact fatigue failure of the cycloidal and planetary gears in joint reducer for robot during the life test were studied by means of physical and chemical testing and finite element stress analysis. The results show that the failure mode of cycloidal gear surface is scuffing, and the failure mode of planetary gear surface is excessive wear. The design values of contact fatigue strength of cycloidal gear and planetary gear face meet the technical requirements, and the materials used meet the specification. According to the results of metallographic examination, the surface heat treatment performance of planetary gear does not meet the requirements, and the reduction in the hardness of gear surface and contact fatigue strength becomes the main reason for the failure of planetary gear. Based on the analysis results, the improvement measures for the subsequent manufacturing process of planetary gear are put forward.

Crack defect analysis of 40CrMnMo steel drill pipe material

Zhong Bin, Chen Yiqing, Meng Fanlei, Gao Peng, Ai Fangfang, Li Lin, San Hongyu

2021, 46(2): 228-231. doi:10.13251/j.issn.0254-6051.2021.02.043

Abstract ( 63 )

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Failure analysis of the 40CrMnMo drill pipe material with cracks was carried out by means of OM, SEM and EDS. The results show that the microstructure of the specimen is tempered sorbite with fine and uniform grain size, and the inclusion grade is D0.5, the structure is in normal state. Cracks form during the quenching process, and thermal stress and microstructure transformation stress result in quenching cracking of the 40CrMnMo drill pipe material. Obvious oxidation phenomenon can be seen at the cracking location, no decarburization is observed, and secondary cracks appear as the cracks expand. After high temperature tempering, cracks continue to expand, and the tip of cracks continues to be oxidized. Based on the failure analysis, the cracking can be avoided by reducing the quenching temperature appropriately and stabilizing the properties of quenching oil.

Effect of H₂ content in cooling stage on properties and surface quality of 800 MPa grade hot dip galvanized dual phase steel

Fu Yujing, Liu Hongliang, Fu Donghe, Chen Yu, Ma Feng

2021, 46(2): 232-236. doi:10.13251/j.issn.0254-6051.2021.02.044

Abstract ( 57 )

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Aim at surface quality problem arose in the production process of hot galvanized dual phase steel which caused by adding alloying elements, such as small black spots and piping defect, the microstructure of the 800 MPa grade hot galvanized dual phase steel was analyzed and the effect of H₂ content in hot dip galvanization cooling section on mechanical properties and surface quality was studied. The results show that with the increase of H₂ content in cooling section, the yield strength and tensile strength of the specimen increase significantly, mainly because the increasing of H₂ content increases martensitic transformation amount in the process of cooling, so that improves the comprehensive mechanical properties. At the same time, the quantity of surface textured defect and small black spots decreases significantly, the specimen gets reduction in the cooling process so that the surface Mn and Si oxides are decreased, which ensures the formation of dense inhibition layer. However, the influence on surface quality is small and the elongation decreases significantly when the H₂ content is more than 10%, so considering the energy consumption, the H₂ input of cooling section should be controlled at 10%.

Cause and countermeasure of coarse grain defect in batch annealed Ti-IF steel

Tian Fei, Wang Zirong, Li Zhaodong, Li Lei

2021, 46(2): 237-241. doi:10.13251/j.issn.0254-6051.2021.02.045

Abstract ( 72 )

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Based on the analysis of distribution of coarse grain defects, the precipitation of FeTiP in specimen with different degree of coarse grain defects, and the precipitate dissolution temperature of FeTiP in the Ti-IF steel and the grain growth behavior, the causes of coarse grain defects were analyzed, and the method to solve the coarse grain defects was suggested. The results show that annealing at 780 ℃ or slightly higher the temperature becomes the grain coarsening critical temperature, and the dissolution of FeTiP precipitate phase significantly change the distribution state of precipitate phase, which becomes the root cause of abnormal grain growth and coarse grain defects. The local overheating of the outer ring in the steel coil due to the annealing temperature exceeding 780 ℃ causes the abnormal growth of grains in the outer ring of the steel coil and leads to the occurrence of coarse grain defects. The problem of coarse grain defects can be effectively solved by adding a heat insulation platform at a certain temperature during the high temperature rising stage of the batch annealing process.

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