Heat Treatment of Metals

Heat treatment for recycled material of DD494 alloy turbine blade

Yang Shanjie, Hao Zhibo, Yuan Xiaofei

2024, 49(6): 1-7. doi:10.13251/j.issn.0254-6051.2024.06.001

Abstract ( 77 )

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Effect of three types heat treatment processes on the microstructure, creep rupture properties and fracture mechanism of recycled material of the DD494 alloy turbine blade was studied. The initial melting temperature of the alloy was determined by metallographic observation. The effect of solution treatment temperature on the dissolution of γ/γ′ eutectic and γ′ phase morphology, and the effect of first aging heat treatment temperature on the size, quantity and distribution of γ′ phase were analyzed by using scanning electron microscope (SEM). The results show that the initial melting temperature of the alloy is between 1310 ℃ and 1315 ℃. After heat treatment at 1300 ℃ for 4 h followed by air cooling, the number of γ/γ′ eutectic and the size of γ′ phase are decreased compared to that of 1290 ℃ for 4 h followed by air cooling. Compared to single step solution, segmented solution treatment can reduce the eutectic content in the alloy. It is found that the higher first aging heat treatment temperature (1140 ℃ compared with 1080 ℃) causes the growth of primary γ′ phase and a large amount of fine secondary particles γ′ precipitated in the γ matrix. The optimal heat treatment process for the alloy is segmented solution treatment+high temperature first aging+secondary aging, i.e. 1280 ℃×1 h+1290 ℃×2 h+1300 ℃×6 h, AC+1140 ℃×3 h, AC+870 ℃×20 h, AC. The average creep rupture life of the alloy treated with the optimal process is 175.05 h, which is more than twice that of the specimen treated with “single step solution+low temperature first aging+secondary aging”.

Effect of annealing temperature on microstructure and mechanical properties of low-density steel for bogie frame

Wu Si, Li Feifan, Wang Xuemin, Shang Xueliang, Xu Xiangyu

2024, 49(6): 8-16. doi:10.13251/j.issn.0254-6051.2024.06.002

Abstract ( 59 )

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Effect of annealing temperature on the microstructure and mechanical properties of a medium-Mn low density medium thick plate for bogie was designed and investigated by means of Thermo-Calc calculations, scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), tensile tests and machine learning from the perspectives of phase transformation, densities of geometrically necessary dislocations, grain boundary types and grain boundary density. The results show that the hot-rolled microstructure of the low-density steel at room temperature consists of δ-ferrite, austenite, and martensite. The matrix undergoes reverse transformation and the growth of prior austenite during annealing treatment, and the stability of austenite decreases with the increase of annealing temperature. The densities of geometrically necessary dislocations of the tested steel decrease with the increase of annealing temperature. The growth of the grains and the merging of martensite laths during annealing lead to a decrease in the density of prior austenite grain boundaries and martensite lath boundaries. The annealed tested steel shows significantly higher elongation than that of the hot-rolled state, with yield strength decreasing as the annealing temperature increasing. The tested steel under both hot-rolled and annealed states shows uniform deformation and cleavage fracture during tensile test. After annealing at 820 and 880 ℃, the yield strength of the tested steel reaches 491 and 413 MPa, respectively.

Effect of decarburizing annealing process on texture and magnetic properties of thin-gauge oriented silicon steel

Wang Yitong, Liu Xuming, Guo Han, Geng Zhiyu, Xue Feng

2024, 49(6): 17-22. doi:10.13251/j.issn.0254-6051.2024.06.003

Abstract ( 68 )

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Microstructure,texture and magnetic properties of thin-gauge oriented silicon steel after annealing at different temperatures (820, 840, 860 ℃) and time (120, 150 s) were compared by means of EBSD and XRD. The results show that increasing the decarburization annealing temperature and decreasing the decarburization annealing time can reduce the grain size, increase the proportion of favorable texture and recrystallization ratio of the oriented steel, which provide the basis for the abnormal growth of Goss grains in the process of secondary recrystallization, so as to improve the magnetic properties of the oriented silicon steel. When the decarburization annealing temperature is 860 ℃ and the annealing time is 120 s, the oriented silicon steel specimen obtains the best magnetic properties, with the magnetic induction intensity J₈₀₀ of 1.807 T and the core loss P_1.7 of 1.07 W·kg^-1.

Effect of annealing process on tensile deformation behavior of the SLM AlSi10Mg alloy

Liu Yiran, Li Lei

2024, 49(6): 23-28. doi:10.13251/j.issn.0254-6051.2024.06.004

Abstract ( 39 )

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With the aid of scanning electron microscope, optical microscope, tensile testing machine, effects of annealing temperature and annealing time on selective laser melted (SLM) AlSi10Mg alloy tensile deformation behavior were studied, and the regional strain under different annealing were analyzed. The results show that with the increase of annealing temperature and annealing time, the phase size of eutectic Si in the SLM AlSi10Mg alloy increases, the lap grain of the specimen gradually disappears, and the eutectic structure gradually becomes uniform and spheroidized. The plastic deformation of the alloy specimen is obvious, the large deformation area is enlarged, and the local large deformation area is necked. The tensile strength of the alloy decreases, the elongation increases and the microhardness decreases. After annealing at 500 ℃ for 1 h, the elongation of the alloy increases from 6.7% to 15.1%, and the tensile strength decreases from 252 MPa to 150 MPa. The alloy has good strength and plasticity.

Effect of annealing temperature on microstructure and mechanical properties of Al-3.5Mg alloy sheet for deep drawing

Wu Zhenyu, Qin Yiming, Li Yongdi, Zhou Peilin, Zhou Jiaju, Li Qu

2024, 49(6): 29-35. doi:10.13251/j.issn.0254-6051.2024.06.005

Abstract ( 36 )

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Effect of annealing temperature on the microstructure, conventional tensile properties and formability of Al-3.5Mg alloy sheet for deep drawing was studied by means of optical microscope, scanning electron microscope (SEM) and tensile test. The results show that with the increase of annealing temperature, the strength and yield ratio of the Al-3.5Mg alloy decreases in a ladder-shape, while the elongation gradually increases. The n, r- value and LDR value significantly increases, and the anisotropy increases first and than decreases. When the annealing temperature is raised from 340 ℃ to 360 ℃, the microstructure undergoes complete recrystallization evolution. An Hall-Petch empirical formula is established between yield strength and grain size. Engineering practice confirms that industrial production annealed at 360 ℃for 8 h can ensure the quality of deep drawing forming.

Effect of reverse phase transformation annealing on microstructure evolution and mechanical properties of medium manganese steel

An Qingsheng, Wan Decheng, Ma Shaokang, Li Jie, Zhang Qianxi

2024, 49(6): 36-42. doi:10.13251/j.issn.0254-6051.2024.06.006

Abstract ( 34 )

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The initial structure of lath martensite of 0.22C-3.97Mn-1.57Si-0.1Al-0.043Nb medium manganese steel was obtained by pre-quenching, and then reverse phase transformation annealing was performed at different temperatures. The microstructure evolution and mechanical properties of the steel were studied by means of scanning electron microscopy (SEM), X-ray diffractometer (XRD) and tensile test machine. The results show that the microstructure of the experimental steel after reverse phase transformation annealing is ferrite, lath martensite and retained austenite. With the increase of annealing temperature, the tensile strength of the experimental steel gradually increases, the yield strength gradually decreases, the elongation and product of strength and elongation first increases and then decreases. When annealed at 670-690 ℃, the coordinated deformation of the multi-phase structure and the TRIP effect of retained austenite are obvious, and the experimental steel shows excellent mechanical properties. When annealed at 690 ℃, the best mechanical properties can be obtained with the tensile strength of 1062 MPa, the elongation after fracture of 27.0%, and the product of strength and elongation of 28.7 GPa·%. When the annealing temperature is higher than 690 ℃, the hard phase martensite content increases, the mechanical stability of retained austenite is poor, and the tensile strength of the experimental steel increases but the plasticity decreases. The work hardening ability of ferrite increases and the mechanical stability of retained austenite decreases, which inbibite the occurrence of Lüders and sawtooth rheology.

Microstructure and properties of Fe-0.13C-2.0Mn-0.6Al multiphase steels annealed at different temperatures

Zhang Miao, Wan Decheng, Zhang Bo, Feng Yunli

2024, 49(6): 43-48. doi:10.13251/j.issn.0254-6051.2024.06.007

Abstract ( 34 )

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Effect of annealing temperature on the microstructure and mechanical properties of cold-rolled Fe-0.13C-2.0Mn-0.6Al high strength multiphase steel were studied by means of scanning electron microscope, electron backscattering diffraction and tensile testing machine. The results show that the microstructure of the cold-rolled sheet of the multiphase steel is composed of ferrite, martensite, bainite and some carbides. The microstructure of the annealed sheet at room temperature is mainly equiaxed ferrite, granular bainite and block martensite. With the increase of annealing temperature, the content of martensite and bainite in the microstructure increases first and then decreases, the proportion of large angle grain boundary increases gradually, and the degree of recrystallization of ferrite grains increases. At the same time, the average grain size of the annealed sheet increases first, then decreases and then increases, the yield strength increases first and then decreases, and the tensile strength decreases gradually. When the annealing temperature is 750 ℃, the average grain size of the annealed sheet is 2.11 μm, the proportion of martensite and bainite is 40.4%, the product of strength and plasticity reaches 19.80 GPa·%, and the comprehensive mechanical properties are the best.

Effect of oxidation process on oxidation resistance of GH2132 alloy

Xu Chaofan, Chen Jiajun, Wang Shouqian, Zhao Shouzhong, Shen Jiabao, Min Liang

2024, 49(6): 49-54. doi:10.13251/j.issn.0254-6051.2024.06.008

Abstract ( 36 )

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Oxidation test of GH2132 alloy was carried out at 900 ℃ and 650 ℃, the main products of the oxide film were analysed by XRD, the surface and cross-section morphologies of the oxide film were observed by scanning electron microscope, and the oxidation mechanism of the GH2132 alloy was investigated combining with the data of EDS energy spectra. The results show that at 900 ℃, the oxide film of the GH2132 alloy is mainly composed of Cr₂O₃+Fe₂O₃, and the antioxidant property changes from antioxidant properties to complete antioxidant properties in 100-200 h. With the extension of the oxidation holding time, internal oxidation phenomenon occurs and the generated oxide film flakes off, and the depth of internal oxidation reaches 110.34 μm by 500 h. At 650 ℃, the GH2132 alloy surface oxide film mainly consists of Fe₂O₃ and small amounts of Fe+2Cr₂O₄ and Fe_0.64Ni_0.36, which is always completely antioxidant properties with compact oxide film, and there is no internal oxidation phenomenon. When up to 1600 h, the thickness of the oxide film is 15.17 μm, indicating that the alloy can be used for a long time at 650 ℃.

Effects of austempering and tempering process on microstructure and mechanical properties of Cr-Ni-Mo-V alloy steel

Yu Guining, Tian Ze, Wang Xuanru, Yan Sujia, Zhou Cong, Cao Tieshan, Qi Lin

2024, 49(6): 55-61. doi:10.13251/j.issn.0254-6051.2024.06.009

Abstract ( 50 )

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Microstructure and mechanical properties of Cr-Ni-Mo-V alloy steel with bainite/martensite duplex structure formed by austempering during tempering were investigated. The orthogonal experiment scheme was designed with austempering temperature, austempering time and tempering temperature as factors. The effects of austempering and tempering process on the mechanical properties of the Cr-Ni-Mo-V ultra-high strength and toughness steel were explored by means of the impact testing machine combined with Vickers hardness tester, and the microstructure changes of the material were analyzed by scanning electron microscope and metallographic microscope. The results indicate that both the austempering temperature and tempering time have a significant effect on the microstructure and mechanical properties of the material, with the tempering time having a greater impact. During the tempering process, bainite transforms to tempered troostite and M/A islands gradually decompose. After austempering at 280 ℃ for 12 h and tempering at 560 ℃, the specimen shows the best impact property. After austempering at 280 ℃ for 50 min and non-tempering, the specimen shows the highest hardness, and the best heat treatment parameters are obtained after austempering at 280 ℃ for 12 h and tempering at 560 ℃, with impact absorbed energy of 60.0 J and the hardness of 518.7 HV2.

Effect of single-stage solution temperature on microstructure evolution of spray deposited 2195 Al-Li alloy

Sun Shuli, Hou Xiaohu, Guo Wenxia, Zhang Jing, Wang Chao, Zhao Xueping, Cao Yu

2024, 49(6): 62-68. doi:10.13251/j.issn.0254-6051.2024.06.010

Abstract ( 71 )

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Effect of single-stage solution temperature on the second-phase particles, grain size, low-angle grain boundaries, recrystallization fraction and residual stress of spray-deposited 2195 aluminum-lithium alloy was quantitatively analyzed by means of scanning electron microscopy (SEM) and the accompanying electron backscatter diffraction (EBSD) analyzer. The mechanical properties of the alloy were tested using an electronic universal testing machine. The results show that after solution treatment at 510 ℃ for 40 min, the average grain size is increased from 4.57 μm in as-extruded to 13.96 μm, the proportion of low-angle grain boundaries is decreased from 73.1% (as-extruded) to 52.1%, the proportion of second-phase particles is decreased from 9.4% (as-extruded) to 0.73%, and the residual stress is decreased significantly. Meanwhile the recrystallization and subgrain fractions are increased from 31.4% and 22.2% to 41.8% and 53.6% respectively, the proportion of deformed grains is decreased from 46.4% to 4.6%, the hardness reaches 101.5 HV, and the tensile strength reaches 441.6 MPa. With the increase of solution treatment temperature, the microstructure of the alloy changes significantly, and the mechanical properties show a trend of first increasing and then decreasing.

Effects of shot peen strengthening and solution strengthening combined treatment on corrosion resistance of 2024 aluminum alloy

Qiao Jingzhen, Zhang Xiaowen, Zhang Huanyue, Fu Xuesong, Zhou Wenlong, Chen Guoqing

2024, 49(6): 69-76. doi:10.13251/j.issn.0254-6051.2024.06.011

Abstract ( 76 )

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Effects of shot peening strengthening, solution strengthening and shot peening strengthening+solution strengthening on the salt spray corrosion resistance of as-aged 2024 aluminum alloy were studied. The results show that there are numerous secondary phase particles in the primitive specimen microstructure, with the longest particle size of about 83 μm. After solution treatment, some of the secondary phase particles dissolve in the matrix, and the remained particle size is reduced to 17 μm. After the combined treatment of shot peening and solution treatment strengthening, almost all of the secondary phase particles near the surface are dissolved. When the salt spray corrosion test time is 3 h, the diameter of the corrosion pit of the primitive specimen is approximately ø90 μm, the corrosion pit diameter of the shot peening and solution strengthened specimen is about ø50 μm, the corrosion depth of the shot peening specimen is about 38.75 μm, while the corrosion depth of the shot peening and solution strengthened specimen decreases to 12.5 μm. This indicates that the combined treatment of shot peening and solution treatment strengthening contributes to dissolve the second phase particles, improves the uniformity of material structure and composition, and thereby enhances the corrosion resistance of aluminum alloys.

Effects of carrier gas flow and overlap rate on morphology and stress field of laser clad coatings

Wang Jiasheng, Li Yunfeng, Shi Yan, Tang Shufeng, Jiang Guangjun, Wu Jianxin

2024, 49(6): 77-84. doi:10.13251/j.issn.0254-6051.2024.06.012

Abstract ( 25 )

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5 kW CO₂ laser was used to prepare Ni45 coating on the surface of 42CrMoA steel. The effects of carrier gas flow and overlap rate on the quality of the Ni45 clad coating were studied. Finite element method was used to study the effect of overlap rate on the temperature and stress fields of the molten coating. The gas-solid two-phase flow theory and FLUNT software were used to analyze the powder flow pattern in the powder feeding process, and study the influence of carrier gas flow on the coating morphology. The results show that the stress and cracks gradually increase with the increase of the overlap rate in the clad layer, while the coating cracks can be eliminated through a 300 ℃ isothermal annealing treatment. When the overlap rate is < 40%, the flatness of the coating is poor, but when the overlap ratio is ≥ 40%, the coating flatness is good and shows no much different. When the carrier gas flow ≤ 450 L/h, the coating surface is flat, but when the carrier gas flow > 450 L/h, the flatness of the coating begins to decrease. By studying the effects of the overlap rate and carrier gas flow, the optimal cladding process parameters are obtained:the carrier gas flow is 450 L/h, and the overlap rate is 40%.

Effect of vacuum annealing on residual stress,microstructure and properties of cold-drawn 34CrMo4 steel thin-walled pipe

Hou Ping, Wang Jingcheng, Wang Ze, Qian Jinjing

2024, 49(6): 85-90. doi:10.13251/j.issn.0254-6051.2024.06.013

Abstract ( 29 )

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34CrMo4 seamless steel pipe with wall thickness of 0.9 mm was prepared by cold drawing process, and the changes of residual stress, microstructure and properties of the cold-drawn pipe during vacuum annealing were studied by X-ray stress tester, scanning electron microscope (SEM), electron backscatter diffraction (EBSD) technology and universal tensile testing machine. The results show that the vacuum annealing can effectively reduce the residual stress of the tested steel after cold drawing, where the strength decreases, the plasticity increases, and the structure of the cold drawing zone recovers, but the streamline microstructure of the cold drawing deformation is still maintained. The cold drawing leads to increase in the density of small angle grain boundaries, while after vacuum annealing, small angle grain boundaries are gradually replaced by large angle grain boundaries. When vacuum annealed at 650 ℃, the effective ferrite grain size of the tested steel is 3.62 μm, the residual stress is -13.1 MPa, the tensile strength is 693 MPa, the elongation is 26.1%, which reduces the residual stress while obtains a good strength plasticity matching.

Heat treatment of type II clip for rail fastening system based on water-soluble quenching liquid

Yu Haoyong, Lü Mingkui, Fan Yanli, Liu Ruide

2024, 49(6): 91-95. doi:10.13251/j.issn.0254-6051.2024.06.014

Abstract ( 29 )

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Usage characteristics of a water-soluble inorganic quenching liquid (quenchant) were introduced, and the type II clips made of 60Si2Cr spring steel were quenched by using of quenching liquid with a concentration of 11% at different temperatures and then tempered. The hardness and microstructure of the quenched clips, and the residual deformation, buckle pressure, hardness and fatigue property of the tempered clips were tested and analyzed in accordance with the requirements of the relevant standards. The results show that when the water-soluble inorganic quenching liquid is used as quenching medium, all the properties of the clips after heat treatment can meet the technical requirements, thus the quenching liquid can replace the traditional quenching oil as the quenching medium of the clips. The suitable heat treatment process for the clips is austenitized at 860 ℃ for 30 min, quenched in the water-soluble inorganic quenching liquid, and then tempered at 530 ℃ for 100 min with water cooling.

Effect of stress relieving process on properties of 6063 aluminum alloy brazed parts

Zhou Yiwei, Guo Wenrui, Zheng Jianfeng

2024, 49(6): 96-99. doi:10.13251/j.issn.0254-6051.2024.06.015

Abstract ( 31 )

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Aiming at the distoration of 6063 aluminum alloy brazed parts during cutting process, the mechanism of residual stress generation in brazed parts of the 6063 aluminum alloy was analyzed, and the hardness and other properties were tested after stress relieving at different temperatures. The blind-hole method was firstly selected to test the brazed residual stress of the 6063 aluminum alloy, then under the premise of keeping the material state T6 of the brazed parts unchanged, the stress relief process parameters were verified, finally the optimal stress relief process parameters of the 6063 aluminum alloy are determined as temperature of 230 ℃ and holding time of 2 h. Under such a process, the alloy hardness is 69.8 HR15T, the residual stress relief rate of the 6063 aluminum alloy brazed parts is 48.7%, and the distoration of the 6063 aluminum alloy brazed parts during cutting process is effectively solved.

Homogenization process of high magnesium Al-Mg series aluminum alloy

Ma Liang, Sun Ning, Ma Junxing, Chen Tongshuai, Guo Fengjia, Wang Jingtao

2024, 49(6): 100-105. doi:10.13251/j.issn.0254-6051.2024.06.016

Abstract ( 33 )

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Homogenization process of self-melted high magnesium Al-6.5Mg-0.9Zn alloy was studied using techniques such as DSC, SEM and OM. The over heat temperature of the alloy, grain morphology and second phase composition were characterized and analyzed. The results indicate that the structure of the as-cast Al-6.5Mg-0.9Zn alloy is a quasi equiaxed crystal structure, but there is severe segregation of grain boundary elements and small areas of porosity defects. After homogenization treatment at 435, 442, 449 and 456 ℃ for 8 h, respectively, the dendrite arm spacing increases and the grain size increases from 137.31 μm to 173.83 μm. The retained phase changes from continuous distribution to discontinuous distribution, and the content of the second phase decreases from 0.561% to 0.138%. After homogenization treatment at 449 ℃ for 8 h, no low melting point non-equilibrium eutectic phase dissolution peak is found in the microstructure of the ingot, indicating that for the tested alloy, the optimal homogenization process is heating to 449 ℃ at 30 ℃/h and holding for 8 h.

Effect of annealing temperature on microstructure and properties of TZM superalloy

Zhang Huixia, Wei Kai, Zhao Wanfang

2024, 49(6): 106-109. doi:10.13251/j.issn.0254-6051.2024.06.017

Abstract ( 33 )

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Microstructure, hardness, mechanical properties and tensile fracture morphology of as-forged TZM superalloy annealed at different temperatures were investigated, and the reasons for the generation of different fracture morphologies were analyzed. The results show that the microstructure, mechanical properties and fracture morphologies of the TZM alloy with a deformation of 82% change significantly when annealed at different temperatures. With the increase of annealing temperature, the microstructure of the TZM alloy changes from as-forged to as-recrystallized and gradually coarsenes, where the strength and hardness also decrease, and the fracture morphology varies with the annealing temperature. When the annealing temperature is lower, the fracture morphology is of cleavage river pattern. While when the annealing temperature is higher, the morphology is of cleavage river pattern accompanied by partial intergranular fracture. When the TZM alloy is annealed at 1300 ℃ for 90 min, the microstructure and mechanical properties are preferable, and the fracture mode is ductile.

Effect of MA banded microstructure under different heat treatment states on HIC resistance of pipeline steel

Qu Zhiguo, Zhang Youjian, Wang Shiming, Yu Hao, Wang Dongming

2024, 49(6): 110-114. doi:10.13251/j.issn.0254-6051.2024.06.018

Abstract ( 28 )

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Formation and elimination of MA microstructure in pipeline steel with 0.13%C under different rolling and heat treatment processes were studied, and the effect of MA banded microstructure on the hydrogen induced cracking (HIC) resistance of the steel was analyzed. The results show that the MA banded microstructure has a significant HIC resistance of the tested steel plate. By high-temperature tempering, the MA banded microstructure can be largely decomposed, and the HIC resistance is improved, especially with a significant reduction in crack thickness rate. After normalizing and fully austenitizing, the uneven distributed solute elements in the steel diffuse evenly, and the microstructure transforms into fine ferrite+pearlite structure after phase transformation. Although there is still fine pearlite bands, good HIC resistance can still be obtained. By normalizing and tempering treatment, MA bands caused by insufficient normalizing and austenitizing can be eliminated, and the fine pearlite bands exhibit intermittent distribution characteristic, thus the uniformity of the microstructure and HIC resistance can be further improved.

Effect of heat treatment on microstructure and properties of 7175 aluminum alloy prepared by SLM for sports equipment

Wang Lei, Jia Liangliang

2024, 49(6): 115-119. doi:10.13251/j.issn.0254-6051.2024.06.019

Abstract ( 26 )

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Microstructure, hardness and phase transformation of 7175 aluminum alloy prepared by selective laser melting(SLM) after solution treatment and two-stage aging were investigated by means of OM, scanning electron microscope (SEM), transmission electron microscope (TEM) and microhardness tester. The experimental results reveal that the microstructure of the SLMed 7175 alloy shows significant inter-channel heterogeneity. After solution and two-stage aging treatment, the alloy shows uniform and fine microstructure, and the channel structure disappears. The hardness of the alloy after heat treatment is higher than that of the SLMed alloy (83 HV0.3), reaching an average of about 162 HV0.3. The precipitation S phase (Al₂CuMg) and θ phase (Al₂Cu) at the grain boundaries are the strengthening phases of alloy hardness, which provides the effect of dispersion strengthening and precipitation strengthening.

Effect of stress-relief heat treatment on microstructure and residual stress of 06Cr13 martensitic stainless steel

Mi Dawei, Ji Cuicui

2024, 49(6): 120-122. doi:10.13251/j.issn.0254-6051.2024.06.020

Abstract ( 32 )

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For 06Cr13 martensitic stainless steel parts that have completed quenching and tempering treatment and rough machining, stress-relief treatment was carried out under different process conditions. Microstructure, Brinell hardness and residual stress of the specimens under different stress-relief heat treatment processes were analyzed by means of Zeiss microscope, microhardness tester and X-ray stress tester. The results show that the stress-relief heat treatment process below the tempering temperature has almost no effect on the microstructure and hardness of the 06Cr13 martensitic stainless steel. As the stress-relief heat treatment temperature increases, the residual stress gradually decreases, and under the stress-relief heat treatment at 560 ℃, there is basically no residual stress.

Effect of annealing temperature on microstructure and mechanical properties of rolled Mo-Re alloy tubes

Chen Cheng, Zhu Qi, Xi Sha, Zeng Xueliang, Zhang Xuesu

2024, 49(6): 123-128. doi:10.13251/j.issn.0254-6051.2024.06.021

Abstract ( 29 )

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In order to address the inherent severe anisotropy issue caused by large plastic deformation in the processing of thin-walled molybdenum-rhenium (Mo-Re) alloy tubes, different annealing temperatures(900, 1050, 1200 ℃) were investigated to control the microstructure and mechanical properties of the Mo-Re alloy thin-walled tubes. The results show that there is a significant <101>//TD texture in the Mo-Re alloy bars, indicating obvious anisotropy. The Mo-Re alloy billet, which is subjected to annealing at 1050 ℃ for 1 h after forging, effectively achieves simultaneous improvement in anisotropy and strength and toughness of the thin-walled molybdenum tube. The room temperature tensile strength reaches 838 MPa, the high-temperature tensile strength at 1300 ℃ reaches 198 MPa, and the average hardness is 230.5 HV0.3. The Mo-Re alloy prepared through annealing at 1050 ℃ for 1 h exhibits excellent strength and toughness, which is mainly attributed to the distribution of grain size after annealing treatment. The average grain size of the Mo-Re alloy bars annealed at 1050 ℃ was 23.1 μm, which is smaller than that of the Mo-Re alloy bars annealed at 1200 ℃, resulting in higher strength and plasticity. Additionally, the concentration of grain size is higher compared to the Mo-Re alloy bars annealed at 900 ℃, indicating better deformation coordination during plastic deformation.

Effect of furnace pressure on ion nitriding of gear

Li Shuangxi, Shen Yaqiu, Bai Xiaobo, Gao Jie, Chen Lin

2024, 49(6): 129-134. doi:10.13251/j.issn.0254-6051.2024.06.022

Abstract ( 25 )

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Inject ammonia and argon into the ion nitriding furnace, the ammonia flow rate of 0.5 L/min was maintained, and the furnace pressure was controlled by changing the argon flow rate (argon flow rates of 0, 0.45, 0.60 and 0.85 L/min, respectively) to study the effect of furnace pressure on the uniformity and microstructure of the nitrided layer of small modulus gears. The results show that as the argon gas flow rate increases, the uniformity of the ion nitrided layer also increases. Under an ion nitriding process at 540 ℃ for 8 h, when the furnace pressure is below 180 Pa, nitrogen cannot penetrate into the root area of gear teeth. When the furnace pressure is higher than 330 Pa, due to the thin glow thickness inside the furnace, the probability of arcing increases and the uniformity of furnace temperature deteriorates. With the increase of argon gas input, the thickness of the compound layer decreases and to some extent improves the nitriding rate, but has no significant effect on the looseness of the nitriding layer and the level of vein like nitrides.

Microstructure and mechanical properties of typical hot formed parts

Shi Baoliang, Jiang Fatong, Liu Xuliang, Song Wenbin, Jin Yuming, Qiao Meng, Guo Qiuyan

2024, 49(6): 135-141. doi:10.13251/j.issn.0254-6051.2024.06.023

Abstract ( 35 )

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Microstructure and mechanical properties of different hot formed parts based on a body-in-white were systematically studied. The results show that the microstructure of the typical hot formed parts is mainly lath martensite, and some parts have residual austenite structure in local areas. The microstructure of the soft zone in the mold is mainly composed of ferrite, martensite and a small amount of bainite, where the martensite has no obvious lath characteristics and relatively low proportion. The decarburization layer thickness of the left front/rear door collision beam is distributed between 38.55-45.57 μm. The average force value of the three-point bending of the left front door anti-collision beam is 6962 N, and the maximum force value is 9709 N; while the average force value of the left rear door anti-collision beam is 8740 N, and the maximum force value is 11 392 N. The surface of the parts is in good condition and there are no cracks generate after three-point bending. The performance of the anti-collision beams meets the requirements of vehicle safety collision testing. For the typical hot formed parts, the average hardness distribution is 456-507 HV10, the yield strength is greater than 1000 MPa, the tensile strength is greater than 1400 MPa, and the elongation is ≥5.5%. While in the soft zone, the hardness distribution is between 225-243 HV10, the yield strength is greater than 470 MPa, the tensile strength is greater than 650 MPa, and the elongation is ≥17%. The performance of the parts meets the standard requirements.

Microstructure and strengthening mechanism of 2100 MPa grade ultra-high strength spring steel

Lu Wei, Tu Tianquan, Deng Xiaoyun, Luo Suhui, Xing Xianqiang, Luo Zhichao

2024, 49(6): 142-149. doi:10.13251/j.issn.0254-6051.2024.06.024

Abstract ( 39 )

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Three ultra-high strength steels (1900, 2000 and 2100 MPa) were prepared by optimizing the alloy compositions and quenching and tempering processes. Their microstructure, mechanical properties and strengthening mechanisms were comparatively investigated. The results show that the prior austenite grain size decreases from 28.8 μm to 16.0 μm with the increase of C and V content in the steel. The tensile strength of 2100 MPa grade steel actually reaches 2130 MPa, and the percentage reduction of area is 42%. Further research shows that, the retained austenite in the 2100 MPa grade steel is up to 16.2% in volume fraction, and contributes a transformation-induced plasticity (TRIP) effect during tensile deformation, which significantly improves the work-hardening ability and uniform elongation of the steel. The strength of the 2100 MPa grade spring steel wire mainly comes from solution strengthening, dislocation strengthening and precipitation strengthening, and their contribution values are 391, 808 and 469 MPa, respectively. The fine prior austenite grain size and the TRIP effect from the retained austenite are the key to the excellent strength and ductility of the 2100 MPa grade ultra-high strength spring steel.

Microstructure, properties and microalloyed phase precipitation behavior of high-conductivity high-strength steel

Tang Xingchang, Zhou Weilian, Qi Dayang, Jia Zhihui, Zhang Zhijian, Cheng Ganghu, Hou Yuanyuan

2024, 49(6): 150-158. doi:10.13251/j.issn.0254-6051.2024.06.025

Abstract ( 27 )

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In order to study the deformation-induced precipitation behavior and property changes of the second phase particles in high-conductivity high-strength steel, the stress relaxation experiment was carried out by using the Gleeble-3500 thermal simulation testing machine, and then the microstructure and properties of the tested steel were observed and analyzed by means of metallurgical microscope, inductively coupled plasma spectrometer (ICP), Vickers hardness tester, and four-probe resistivity meter. The test results show that the relaxation process can be divided into three stages according to the slope of the stress relaxation curve, the first stage is recrystallization, the second stage is deformation-induced precipitation, and the third stage is inhibited by recrystallization and precipitation grows. The PTT curve obtained from the stress relaxation curves is "S" type, and the nose tip temperature is 950 ℃. At higher deformation temperatures, the precipitated phase precipitates rapidly, and the dislocation is nailed, and the grain size decrease. The overall hardness of the tested steel is low and fluctuates greatly, and the overall change trend is irregular, and the hardness is the highest when deformed at 850 ℃. The resistivity decreases first and then increases with the increase of deformation temperature, and the resistivity is the lowest when deformed at 800 ℃.

Microstructure and properties of laser cladding iron-based and nickel-based alloys on surface of locking pin

Qiao Qingfeng, Yao Xiaochun, Zhang Zhijian, Wei Jiaqi

2024, 49(6): 159-163. doi:10.13251/j.issn.0254-6051.2024.06.026

Abstract ( 22 )

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In view of the problem that the side A of locking pin was easy to corrode and the side B was easy to wear in engineering applications, cladding layers of nickel-based alloy and iron-based alloy were prepared by laser cladding on side A and side B of the 35CrMo steel locking pin respectively, and the microstructure, microhardness, strength, corrosion resistance and wear resistance of the two cladding layers were studied. The results indicate that metallurgical bonding can be achieved between the cladding layers and steel substrate, and the shear strength of the iron-based cladding layer and the substrate can reach above 573 MPa. The microstructure of the two cladding layers is composed of dendrites, columnar and equiaxed grains. The microhardness of the iron-based cladding layer is about 480 HV0.5, and the microhardness of the substrate is 280 HV0.5, so the laser cladding of iron-based alloy significantly increases the hardness of the side B of the lock pin, and its wear resistance is significantly higher than that of the substrate, which can reduce the risk of scratching the rail with too high hardness. The microhardness of the nickel-based alloy cladding layer is similar to that of the substrate. Both the iron-based and nickel-based alloy cladding layers show no corrosion after 240 h neutral salt spray test.

Forming limit properties and microstructure analysis of high strength dual phase steel DP980

Xue Feng, Geng Zhiyu, Liu Xuming, Bi Lian, Zhou Tianpeng

2024, 49(6): 164-168. doi:10.13251/j.issn.0254-6051.2024.06.027

Abstract ( 33 )

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The forming limit of high strength dual phase steel DP980 specimens with 1.4 mm thichness and different widths was tested. The strain degree of forming limit fracture and necking were studied, and the effect factors of microstructure on necking and cracking were analyzed. The microstructure and properties of the steel were analyzed by means of scanning electron microscope, electron backscatter diffraction, transmission electron microscope and tensile machine. The results show that there are multiple stress limit points in the forming limit test of the steel, where the FLD₀ value at the necking location is 0.14, while that for the rupture forming limit is 0.20. The tensile fracture results show that the Nb and Ti precipitates existing in the high strength dual phase steel DP980 make the fracture characteristics after necking change from mixed fracture to ductile. The TEM results show that the lath martensite hinders the dislocation movement in the steel DP980, and greatly increases the strength of the steel. The KAM results show that the massive dislocations pile up in the ferrite grains after necking leads to the formation of dislocation walls, which makes the material produce stronger work hardening.

Effect of grain size on wear resistance of high nitrogen high manganese austenitic steel

Yang Yang, Chen Chen, Dong Xu, Liao Pujiu, Zhang Fucheng

2024, 49(6): 169-176. doi:10.13251/j.issn.0254-6051.2024.06.028

Abstract ( 26 )

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Dry sliding friction and wear test was carried out for high nitrogen high manganese austenitic steel 60Mn18Cr7N. The microstructure, wear resistance and wear mechanism of the tested steel with different grain sizes were comparatively studied by means of scanning electron microscope, transmission electron microscope and electron backscattered diffraction. The results show that with the decrease of grain size, the yield strength increases, the impact toughness decreases, but the wear resistance increases first and then decreases. For the specimen with grain size of about 98 μm, the yield strength and impact absorbed energy are respectively 486 MPa and 236 J, the mass loss is the lowest as about 43 mg under 1000 N wear load for 120 min, and the surface hardness is 693 HV0.2. In the grain size range of 68-400 μm, the fine grains are beneficial for improving the yield strength, work hardening and resistance to surface plastic cutting ability, while the coarse grains enhance toughness and help suppress the initiation and propagation of cracks in the wear process. The combined action of these two factors is the main reason for the optimum wear resistance of the specimen with grain size about 98 μm. In addition, the higher wear load also leads to a mixed wear mechanism of abrasive wear and adhesive wear.

Plasticity control of TC18 titanium alloys by electron beam rapid manufacturing

Huang Zhitao

2024, 49(6): 177-182. doi:10.13251/j.issn.0254-6051.2024.06.029

Abstract ( 23 )

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For TC18 titanium alloy formed by electron beam rapid manufacturing, the microstructure characteristics, fracture behavior and fracture causes of the TC18 titanium alloy were studied by means of optical microscope(OM), scanning electron microscope(SEM) and energy spectrum analysis(EDS). The results show that the tensile fracture mode of the TC18 titanium alloy is a mixture of both positive fracture and cut-off fracture. The fracture mechanism is intergranular ductile fracture and transgranular dimple-fracture, which originate from the grain boundaries. After hot isostatic pressing, a large amount of Widmannstatten structure is produced, which is one of the important factors leading to the decrease of the plasticity. The grain boundary structure can be improved by high temperature treatment and the tensile plasticity along forming direction can be increased to more than 7% under the condition of little change in strength. Because the grain of the TC18 titanium alloy formed by electron beam fuse is abnormally coarse and grain size is not uniform, the thin-wall structure performance is greatly affected by a single grain.

Effects of hot extrusion and heat treatment on microstructure characteristics of uranium-2.1%molybdenum alloy

Du Jijun, Guo Hong, Xu Yong, He Jinming, Li Bo, Yang Ruonan

2024, 49(6): 183-189. doi:10.13251/j.issn.0254-6051.2024.06.030

Abstract ( 27 )

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The phase structure, composition and microstructure characteristics of uranium-molybdenum alloy with 2.1%Mo under different processing conditions such as hot extrusion, diffusion annealing, quenching and tempering were studied by using microstructure analysis techniques. The results show that the microstructure of the alloy varies greatly under different hot working processes. The hot extrusion process has little effect on the alloy phase composition but leads to obvious changes on the phase structure and microstructure characteristics, resulting in increased hardness and strength of the alloy. The quenching process causes significant changes in the alloy phase composition, structure and microstructure, transforming it into an α′_b single-phase martensitic structure close to that of the α phase, which significantly increases the alloy hardness and strength but reduces its plasticity and toughness. The diffusion annealing and tempering processes eliminate the effects of stress and strain or rapid phase transformations on the phase structure, phase composition and microstructure characteristics, restoring the relevant microstructure characteristics to a state of uniform annealing, and improving the plasticity and toughness of the alloy.

Effect of SiC content on microstructure and mechanical properties of SiC_p/2009Al composites

Xiao Zhitong, Wang Fangming, Yan Zehua, Zhang Yong, Cao Zhen, Hu Huaigang, Li Jiongli, Wang Xudong

2024, 49(6): 190-197. doi:10.13251/j.issn.0254-6051.2024.06.031

Abstract ( 28 )

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SiC_p/2009Al composites were prepared by introducing SiC particles with different mass fractions (0, 1%, 3% and 5%) into 2009Al alloy by hot isostatic pressing process, followed by hot extrusion, solution and aging treatment, and the effects of the process on microstructure and properties of the composites were investigated. The results show that the composites with uniform grain and uniform dispersion of SiC can be prepared by the hot isostatic pressing process, and the SiC particles are well bonded with the interface of Al matrix. the microstructure of the composites is obviously changed by the extrusion process, the reinforcing SiC particles are broken and refined and homogeneously distributed along the extruded flow in the matrix when the content of SiC is lower (≤3%), while when the SiC content is higher (>3%), there is a slight agglomeration of SiC particles. After solution and aging treatment, the uniformity of matrix grain size is improved, and the precipitated second phase is fine and uniformly dispersed in the matrix. By hot extrusion, solution and aging treatment, the SiC_p/2009Al composites can obtain superior comprehensive mechanical properties. When 3% SiC is introduced, the preferable mechanical properties of the composites are obtained with tensile strength of 492.7 MPa, yield strength of 400.9 MPa, elongation after fracture of 12.7%, hardness of 131 HBW, and a good wear resistance at room temperature.

Effect of SiC addition on microstructure and properties of CoCrFeNi high entropy alloy coating

Jiang Tingpu, Sun Ronglu, Niu Wei, Yang Jiawei

2024, 49(6): 198-205. doi:10.13251/j.issn.0254-6051.2024.06.032

Abstract ( 29 )

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Coatings of CoCrFeNi high entropy alloy with different SiC additions (0%, 5%, 10% and 15% by mass) were prepared on the surface of 45 steel by using RFL-C1000 fiber laser. The macro morphology, microstructure and wear morphology were analyzed by means of OM,XRD,SEM and EDS, and the microhardness, friction and wear property of the coatings were determined by using microhardness tester and friction-wear tester. The results show that all the coatings with 0%, 5%, 10% and 15%SiC additions are slightly prominent in the first pass, while the thickness of which formed in subsequent passes is relatively flat. The phase structure of 0%SiC coating is single FCC phase, while the 5%SiC coating contains FCC dendrites with interdendritic regions rich in C and Cr. The 10%SiC coating contains FCC matrix and (Cr, Fe)₇C₃, while the 15%SiC coating contains BCC matrix and (Cr, Fe)₇C₃ in the shape of strip or granular. As the addition of SiC increases, the microhardness and friction and wear properties of the high entropy alloy coating gradually increase. When the addition of SiC is 15%, the property of the high entropy alloy coating is optimal, with an average microhardness of 1329.56 HV0.3 and a wear mass loss of only 0.8 mg.

Effect of C microalloying on microstructure and mechanical properties of Fe-Mn-Cr-Ni medium entropy alloy

Li Na, Sun Shugang, Yang Jianchun, Wang Qi

2024, 49(6): 206-210. doi:10.13251/j.issn.0254-6051.2024.06.033

Abstract ( 27 )

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Fe₅₀Mn₂₅Cr₁₅Ni₁₀ and (Fe₅₀Mn₂₅Cr₁₅Ni₁₀)₉₉C₁ medium-entropy alloys (MEAs) were prepared by vacuum arc melting and copper mold suction casting. Then the alloys were rolled by 80% at room temperature and annealed at 900 ℃, the effects of C microalloying on microstructure and mechanical properties of the MEAs were studied by means of XRD, SEM and EBSD. The results show that the microstructure of Fe₅₀Mn₂₅Cr₁₅Ni₁₀ and (Fe₅₀Mn₂₅Cr₁₅Ni₁₀)₉₉C₁MEAs is FCC single phase structure. With the addition of C element, the grains of the alloy are refined. The yield strength and tensile strength of the MEAs annealed at 900 ℃ for 10 min increase from 381 MPa and 586 MPa to 535 MPa and 756 MPa at room temperature (25 ℃), and from 687 MPa and 1114 MPa to 980 MPa and 1352 MPa at low temperature (-196 ℃). With the decrease of temperature from 25 ℃ to -196 ℃, the strength and ductility of (Fe₅₀Mn₂₅Cr₁₅Ni₁₀)₉₉C₁ alloy increase at the same time, resulting in better product of strength and elongation, which are mainly attributed to the appearance of fine grain strengthening, solid solution strengthening and dislocation multiplication caused by the addition of C element.

Solution behavior of Ta in smelted Fe-based alloy

Shi Xianbo, Shang Ningbo, Bai Xuefei, Lu Lun, Yan Wei, Shan Yiyin

2024, 49(6): 211-216. doi:10.13251/j.issn.0254-6051.2024.06.034

Abstract ( 22 )

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Solution behavior of tantalum (Ta) in the smelted Fe-based alloy was experimentally studied by means of vacuum induction melting as well as SEM and EPMA observations. The results show that Ta as an alloying element is dissolvable in the Fe-based alloy during melting process. An appropriate amount of Ta can be completely dissolved in Fe-based metals. When smelted Ta-containing Fe-based alloys by vacuum induction, reducing oxygen content and extension of refining time can reduce Ta oxidation damage and promote Ta dissolution in the smelted Fe-based alloy. It is analyzed that oxidation loss of Ta can be reduced by adding C and Cr. However, the solution of Ta cannot be improved when Cr is involved.

Static recrystallization behavior of boron-containing cold heading steel 10B21 during hot deformation

Xue Yunze, Xu Dong, Zheng Bing, Shi Husheng, Yang Fengguo, Zheng Lei

2024, 49(6): 217-223. doi:10.13251/j.issn.0254-6051.2024.06.035

Abstract ( 26 )

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A single pass compression test was carried out on 10B21 cold heading steel by using Gleeble-1500 thermal simulator. The effects of deformation temperature (950, 1000 ℃), deformation rate (0.1, 1, 10 s^-1), pre-strain (0.10, 0.15, 0.20), prior grain size and interval time on the static recrystallization behavior of the 10B21 cold heading steel were studied. The austenite grains under different deformation conditions were observed, and the kinetic model of static recrystallization and the grain size model of the 10B21 cold heading steel were established. The results show that the volume fraction of static recrystallization is positively correlated with the deformation temperature, deformation rate, pre-strain and interval time. The static recrystallization grain size is positively correlated with deformation temperature, prior grain size, and negatively correlated with deformation rate and pre-strain. The static recrystallization activation energy of the 10B21 cold heading steel is 221 036 J/mol. The correlation coefficient R²=0.99 between the experimental value and the calculated value of the grain size model indicates that the accuracy of the predicted value of the model is high.

Dynamic recrystallization behavior of 1Cr12Ni3MoVN heat-resistant steel for aviation

Bai Qingqing, Liu Tingyao, Jin Lei

2024, 49(6): 224-231. doi:10.13251/j.issn.0254-6051.2024.06.036

Abstract ( 25 )

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Dynamic recrystallization behavior of 1Cr12Ni3MoVN steel under deformation conditions of 800-1100 ℃ and 0.01-10 s^-1 was studied by using Gleeble-3500 thermal simulation testing machine. The results show that the dynamic recrystallization characteristics are exhibited in all flow stress curves under various deformation conditions. The dynamic recrystallization structure is significantly affected by deformation temperature. The recrystallization volume fraction and grain size are the smallest for the steel with the strain rate of 1 s^-1, moreover mixed crystal structures are prone to present in the steel at low strain rates. The apparent activation energy of thermal deformation is 468.224 kJ/mol obtained by thermodynamic analysis of recrystallization. The mathematical relationship between critical parameters is obtained through θ-σ curve, furthermore the relationship between critical parameters and the Z parameters is established, and the dynamic recrystallization volume fraction model is $X_{\mathrm{DRX}}=1-\exp \left[-0.12\left(\frac{\varepsilon-\varepsilon_{\mathrm{c}}}{\varepsilon_{0.5}}\right)^{3.87}\right]$.

Dynamic recrystallization kinetic model of 60Si2Mn steel

Cao Chenglong, Chen Qing'an, Huang Suxia, Shen Wenfei, Li Hezong, Cao Jingjing, Li Zihao

2024, 49(6): 232-238. doi:10.13251/j.issn.0254-6051.2024.06.037

Abstract ( 27 )

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Dynamic recrystallization (DRX) behavior of 60Si2Mn spring steel at deformation temperature of 730-1000 ℃ and strain rate of 0.01-5 s^-1 was studied. The flow stress curves were obtained by processing the data of single-pass hot compression test of the tested steel. The dynamic recovery curves under different hot deformation conditions were fitted by the work hardening rate, and the dynamic recrystallization kinetic model was established. According to the model, the dynamic recrystallization volume fraction under different hot deformation parameters was predicted. The results show that the dynamic recrystallization behavior of the spring steel is sensitive to deformation temperature and strain rate. With the decrease of strain rate or the increase of deformation temperature, the critical strain of dynamic recrystallization softening decreases and the volume fraction of DRX increases. The predicted values are in good agreement with the experimental values, which verifies the applicability of the dynamic recrystallization kinetic model established for the spring steel.

Temperature field simulation of liquid nitrogen assisted laser cladding and analysis of friction and wear property of clad layer

Wang Kaiming, Jiang Fulin, Bu Shanfei, Wang Chao, Jiang Zhiyong, Liu Qingyu

2024, 49(6): 239-247. doi:10.13251/j.issn.0254-6051.2024.06.038

Abstract ( 23 )

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Aiming at the process of preparing high-entropy alloy coating by liquid nitrogen assisted laser cladding, the temperature gradient and cooling rate of the clad layer under different liquid nitrogen application modes were analyzed by means of finite element analysis and experimental verification, and the theoretical basis of the influence of liquid nitrogen on the temperature gradient and cooling rate of the clad layer was revealed. The finite element simulation results show that when the laser power is fixed, the addition of liquid nitrogen assisted technology accelerates the cooling rate of the clad layer, increases the temperature gradient and reduces the residual stress. The maximum cooling rate is 8900 ℃/s, which is 1.505 times than that of air cooling. When the applied liquid nitrogen is fixed, the increase of laser power increases the temperature gradient of the clad layer and accelerates the cooling rate. The experimental results show that the addition of liquid nitrogen in the process of liquid nitrogen assisted laser cladding increases the hardness of the clad layer. When the laser power is 1500 W, the hardness increase is the most obvious, which is 1.3 times than that of air cooling. The friction coefficient of the clad layer is reduced, the average friction coefficient of the clad layer is 0.146, 0.256, 0.375, 0.351 and 0.382 at laser power of 1100-1900 W, which is lower than the average friction coefficient under air cooling condition. The wear volume of the clad layer is reduced. At laser power of 1700 W, the wear volume reduction is the most compared with that under air cooling condition, up to 55.4%, which improves the friction and wear property of the clad layer.

Effect of nano-cracks on heat conduction and ion diffusion of 8YSZ thermal barrier coatings

Chen Yuhui, Sun Jiaxiang, Jiang Pengyang, Chai Zonghua, Zhang Baiqiang

2024, 49(6): 248-253. doi:10.13251/j.issn.0254-6051.2024.06.039

Abstract ( 20 )

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Effect of nano-cracks on thermal transport properties and ion diffusion of 8YSZ (8mol% Y₂O₃, stabilizing ZrO₂) thermal barrier coating at 1473 K was studied by means of non-equilibrium molecular dynamics method. The effects of crack location, crack length and crack number on thermal conductivity and ion diffusion of the 8YSZ thermal barrier coating were described. The results show that the thermal conductivity of the material with the nano-cracks cross wise arrange on both sides of the model is lower than that with the cracks evenly distribute along the heat flow direction on the same side of the model, but the crack location distribution has a little effect on the diffusion of O^2-. With the increase of crack length or number, the thermal conductivity decreases and the O^2- migration slows down. It is found that small cracks with a large number and uniform distribution have a stronger inhibition on the thermal transport of the 8YSZ thermal barrier coating than those with a small number and long length.

Numerical simulation of charging coefficient for heat treatment of stainless steel bars with different cross sections

Liu Gang, Ren Jinyi, Yang Lixin, Ma Luyi, Li Changsheng

2024, 49(6): 254-260. doi:10.13251/j.issn.0254-6051.2024.06.040

Abstract ( 28 )

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For three different cross sections of stainless steel bars(square, round and hexagonal) under vacuum furnace thermal radiation conditions, finite element simulation combined with heat transfer principles was used to construct a standard sample library by using the "equivalent circular bar diameter comparison method". A study was conducted on the determination method of charging coefficient, and mathematical models were established for the loading spacing and charging coefficient of heat treatment in different fields. The results show that as the loading distance increases, the adjacent diameters, conditional thicknesses and charging coefficients of the three different shapes of stainless steel bars gradually decrease. Comparing the charging coefficient, it can be found that the charging coefficients of tightly arranged round stainless steel bars and hexagonal stainless steel bars are significantly smaller than that of the square stainless steel bars. In the actual production of stainless steel bars, under the condition of strictly following the provisions of the charging coefficient and calculating the correct conditional thickness, the bars can be arranged tightly without leaving gaps during furnace charging.

Research progress on influence of electromagnetic field on microstructure and properties of aluminum alloys

Zhong Zhendong, Fan Jintao, Wang Fusheng, Chen Yajun

2024, 49(6): 261-269. doi:10.13251/j.issn.0254-6051.2024.06.041

Abstract ( 28 )

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Electromagnetic field treatment process of aluminum alloys was summarized, and the influence of electromagnetic field treatment process on microstructure and properties of aluminum alloys was analyzed from three levels: microstructure, macroscopic properties, and action mechanism. The factors influencing the selection of electromagnetic field treatment process parameters on aluminum alloys is summarized, and the mechanism of optimizing the microstructure and properties of aluminum alloys by electromagnetic field is revealed. Finally, the focus and direction of future research on electromagnetic field treatment process are discussed.

Research progress on on-line heat treatment technology for U75V steel rail with 100-meter length

Zhanghui Zeying, Gao Mingxin, Song Hua, Wang Yang, Yang Jian

2024, 49(6): 270-276. doi:10.13251/j.issn.0254-6051.2024.06.042

Abstract ( 28 )

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Methods, characteristics and research progress of on-line heat treatment process for U75V steel rail with 100-meter length were summarized. Effects of heat treatment cooling process parameters and spray cooling process parameters on the production efficiency, microstructure and mechanical properties of the heat treated U75V steel rail with 100-meter length were introduced. Suggestions for future research on the heat treatment process of pearlite rail with 100-meter length were proposed. It is meaningful to study the effect of cooling process parameters on the microstructure and mechanical properties of the steel rails, with the goal of shortening the required heat treatment cooling time, and optimize them. Reducing the allowable fluctuation range of alloy composition content is beneficial for improving the properties of the U75V steel rail in combination with the optimization of heat treatment process. A nozzle or air spraying process that combines heat transfer capability and uniformity is beneficial for optimizing the heat treatment process of the steel rails and improving their properties.

Comparative analysis of domestic and foreign standards for metallographic examination of α+β titanium alloy for surgical implants

Li Fan, Gao Na, Zhang Luwen, Guo Linlin, Lou Gui, Zhang Bo

2024, 49(6): 277-281. doi:10.13251/j.issn.0254-6051.2024.06.043

Abstract ( 24 )

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Microstructure requirements of titanium alloy in surgical implant standards in domestic and foreign were compared and analyzed. The microstructure of plates in GB/T 13810-2017 requires that the original β grain should be fully broken, and continuous grain boundary α phase is not allowed, the microstructure of bars and wires should conform to figure A.1 (a-i) of the standard. The latest versions of ISO 5832-3, ASTM F136, and ASTM F1472 all specify that the microstructure shall be equiaxial and/or elongated primary α phase distributed on the transformed β matrix, with no continuous α network on the prior β grain boundaries. Among them, the transverse microstructure of the bars in ISO 5832-3 shall correspond to A1-A9 in ISO 20160. Combined with the thermal mechanical processing technology of titanium alloy, when the temperature of hot processing and recrystallization is lower than the β transition temperature, or slowly cooling, high volume fraction of primary α phase and intergranular β will be obtained, recrystallization treatment at close to the β transition temperature will obtain equiaxial primary α phase uniformly distributed on the β matrix, which is represented by A1-A9 in the standard spectrum. After recrystallization above the β phase transition temperature, continuous grain boundary α, network α and lamellar α phases are obtained between the coarse β grains, which are manifested as A10-A24 in the standard diagram.

Detection and identification of network carbide defects in steel based on improved CAM-YOLOx-DeepSORT algorithm

Huo Jinliang, Cai Ying, Tong Haisheng

2024, 49(6): 282-286. doi:10.13251/j.issn.0254-6051.2024.06.044

Abstract ( 24 )

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In the detection and identification of network carbides defects in mold steels, algorithms based on image processing and machine learning are commonly used, which can achieve automation to a certain extent, while the identification accuracy still has limitations in cases where the number of network carbides is large and the morphology is complex. To address the limitations of low recognition rate mentioned above, an improved CAM-YOLOx-DeepSORT algorithm is proposed, which utilizes the CAM attention mechanism and combines with the YOLOx object detection algorithm and DeepSORT object tracking algorithm to realize automatic detection and identification of the network carbides in mold steels. The results show that the algorithm can efficiently and accurately detect network carbides,the detection accuracy reaches 99.1%, thus providing guidance for quality control of mold steels.

Mechanism analysis of 65Mn steel strip breakage during cold rolling caused by inhomogeneity of microstructure and properties

Tian Yaqiang, Yao Zhiqiang, Nian Baoguo, Zhang Xiaolei, Song Jinying, Zhang Mingshan, Chen Liansheng

2024, 49(6): 287-294. doi:10.13251/j.issn.0254-6051.2024.06.045

Abstract ( 26 )

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Microstructure and mechanical properties of 65Mn steel hot-rolled plate with strip breakage during the first cold-rolling were analyzed by means of optical microscope (OM), scanning electron microscope (SEM), tensile and hardness tests. The results show that the grain of 65Mn steel strip breakage plate is coarse and unevenly distributed along the transverse direction. The grain size coarsens from grade 6.0 to 4.5 at the edge to 1/2 of the strip breakage plate, and the prior austenite grain size coarsens from grade 5.5 to 4.0. The lamellar spacing of pearlite increases from 759.0 nm to 1128.0 nm, and the pearlite colony size increases from 26.1 μm to 31.3 μm. The transverse distribution of mechanical properties is also uneven. From the edge to 1/2 of the cold-rolled plate, the yield strength decreases from 541 MPa to 529 MPa, and the tensile strength decreases from 669 MPa to 651 MPa. The elongation increases from 9.6% to 11.7%, and the hardness decreases from 65.0 HRB to 62.2 HRB. When subjected to external stress, the deformation of 65Mn steel strip breakage plate is not coordinated due to the uneven microstructure and grains, which eventually leads to the occurrence of strip breakage defect. The incidence of plastic and toughness defects such as cold rolling cracking and strip breakage of the 65Mn steel is reduced to less than 0.15% after optimizing the hot rolling process.

Fatigue fracture failure analysis and heat treatment process improvement of high carbon steel spring component

Wang Yameng, Xu Zhiwen, Gao Jinfeng, Xu Jinling

2024, 49(6): 295-300. doi:10.13251/j.issn.0254-6051.2024.06.046

Abstract ( 27 )

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High carbon steel spring component of wireless headphone charger cracked in the fatigue test, for which the fracture mode and cause were determined through observation of the fracture and microstructure, hardness test, and combining with the heat treatment process and fatigue test conditions. The results show that the fracture mode is low stress fatigue fracture, the cause of which is that a lot of undissolved carbides exist in the microstructure after austempering and tempering, leading to stress concentration in the circular arc transition zone of the elastic arm of the spring component in the durability test, then leading to crack initiation, propagation, and finally resulting in fracture. By improving heat treatment process according to the actual production conditions, the optimum heat treatment process is found as: quenching at 830 ℃ for 20 min with carbon potential 0.75%+salt bath austempering at 305 ℃ for 35 min+tempering at 305 ℃ for 90 min. After heat treatment with the improved process, the Vickers hardness of the high carbon steel spring component is 584 HV0.2, and the durability test life is over 90 000 times.

Fracture failure analysis of hydraulic equipment bolts

Song Quan, Cao Huihui, Zhang Tianqi, Dan Ting, Ma Fang, Zhang Ying

2024, 49(6): 301-304. doi:10.13251/j.issn.0254-6051.2024.06.047

Abstract ( 36 )

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Three hydraulic equipment bolts fractured during hydraulic tests. The fracture mode and causes of the bolts were analyzed by SEM fracture morphology observation, chemical composition detection, metallographic observation and hardness test. The results show that the bolts are made of different materials. The material of two of the bolts is 30CrMnSiNi2A steel, which do not meet the design material requirements and do not match with the heat treatment, thus the bolts exhibit tempering brittleness. The material of another bolt is 30CrMnSiA steel, the microhardness and microstructure are abnormal after heat treatment, so the bolt cannot withstand the assessment pressure and fractures during the hydraulic test process.

Cause analysis of steel foot cracks

Bi Lian, Liu Dongjie, Xue Feng

2024, 49(6): 305-307. doi:10.13251/j.issn.0254-6051.2024.06.048

Abstract ( 28 )

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Cracks of steel foot were analyzed by means of metallographic microscope, Brinell hardness tester and inductively coupled plasma emission spectrometer. The results show that the steel foot has fewer non-metallic inclusions, the metallographic structure is quenched and tempered sorbite, which is consistent with the heat treatment process, and the chemical composition meets the requirements of GB/T 3077—2015.The fracture morphology is fine porcelain like, without any fatigue cracking characteristics. No decarburization, oxidation or folding morphology is observed on both sides of the entire crack, indicating a typical quenching crack morphology. The reason for cracking is that the large and small workpieces are treated in the same furnace, causing the cooling rate of small workpieces to be too fast and the stress to be too high, leading to crack.

Design of special-shaped inductor during induction hardening process

Zhou Shengli, Shen Hui, Lei Delang

2024, 49(6): 308-313. doi:10.13251/j.issn.0254-6051.2024.06.049

Abstract ( 30 )

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In order to meet the heat treatment technical requirements of some parts with complex geometric shapes and high technical requirements, such as universal joint transmission shaft R, King Pin parts and transmission shaft (stub shaft) ears, etc, high-properties digital induction heating power supply and microcomputer programming automatic control medium frequency special-shaped inductor were used for induction hardening. For different parts, special-shaped inductor are different from circular inductor in terms of structural design, which is simple structure, and low production cost. The quenched parts can meet the technical requirements of the effective hardened layer depth, and also have a small range of deviations in microstructure and mechanical properties, stable quality. By using the special-shaped inductor during induction hardening, the problem of R hardened layer and coarse grain of thin-wall of the transmission shaft fork is solved, greatly improving the service life of the parts.

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