Heat Treatment of Metals

Heat treatment for toughening technology of cold working die steel SKD11

Yuan Zhizhong, Wang Mengfei, Zhang Bocheng, Duan Xubin, Li Biaomin, Yang Haifeng, Luo Rui, Cheng Xiaonong

2023, 48(9): 1-7. doi:10.13251/j.issn.0254-6051.2023.09.001

Abstract ( 142 )

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SKD11 steel plate after hot rolling and spheroidizing annealing was used. Two kinds of complex phase heat treatment processes, A-Q-A (Austempering-Quenching-Austempering) and Q-T-A (Quenching-Tempering-Austempering), as well asconventional Q-T(Quenching-Tempering) heat treatment process were carried out.The effect of heat treatment process on the microstructure, hardness and impact absorbed energy was studied. The results show that the microstructure of the specimens after A-Q-A and Q-T-A is the combination of lower bainite (LB) and martensite (M). The content of retained austenite is 13.2% and 18.6% for A-Q-A and Q-T-A, respectively. After A-Q-A, Q-T-A and conventional heat treatment Q-T, the hardness of the specimens is 58.5, 58.6 and 60.5 HRC and the impact absorbed energy is 31.3, 27.6 and 15 J, respectively. The excellent combination of strength and toughness of the SKD11 steel plate is realized by the duplex-phase heat treatments, which does a beneficial exploration in improving the toughness of the cold working die steel.

Effects of forced cooling and low temperature aging on microstructure and mechanical properties of FSW joint of 2198-T3/7A04-T6 dissimilar aluminum alloy

Sun Bo, Nie Jiamin, Li Xiaodan, He Changshu

2023, 48(9): 8-13. doi:10.13251/j.issn.0254-6051.2023.09.002

Abstract ( 62 )

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2198-T3/7A04-T6 dissimilar aluminum alloy was friction stir welded under air cooling and forced cooling respectively, and the joint was aged at low temperature after welding. The effects of forced cooling and low temperature aging on the microstructure characteristics and mechanical properties of the welded joint were studied. It's found that a low hardness zone appears in the heat affected zone of the 2198-T3 aluminum alloy side under both conditions, but the hardness value of the low hardness zone of the joint under forced cooling+low temperature aging conditions is significantly higher, reaching 94.5 HV0.1. The average yield strength, tensile strength and elongation of the joint are 312 MPa, 443 MPa, and 8.9%, respectively. The yield strength and tensile strength reach 97.5% and 96.9% of the base material strength, respectively. However, under air cooling and low temperature aging conditions, they are only 89.0% and 91.6% of the base material strength. The main reason for the better mechanical properties of joint under forced cooling and low-temperature aging conditions is that applying forced cooling during the welding can effectively suppress the dissolution and coarsening of θ′ and T1 phases in the low hardness zone of the joint, enabling it to achieve better aging strengthening effect in the subsequent low-temperature aging treatment.

Effect of final rolling temperature on phase transformation behavior and residual stress of NM400 steel

Chen Hao, Ding Wenhong, Fang Yu, Lu Xiaoxuan, Zhou Yingtao, Chen Hao

2023, 48(9): 14-22. doi:10.13251/j.issn.0254-6051.2023.09.003

Abstract ( 69 )

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In order to study the difference of shape defects of NM400 steel at different finishing rolling temperatures, the expansion test under compressive stress load was carried out by means of Gleeble-3500 thermal simulation testing machine. The effect of finishing rolling temperature on the phase transformation kinetics and phase transformation plasticity of the NM400 steel was studied, and the ABAQUS finite element model was established by using the modified phase transformation kinetics and phase transformation plasticity parameters. The residual stress of the NM400 steel was tested by crack flexibility method, and the accuracy of the finite element model was verified by comparing the measured and simulated results. At the same time, EBSD was used to characterize and analyze the microstructure of specimens with different finishing rolling temperatures. The results show that the formation of residual stress in the continuous cooling process is divided into three stages, including the dominant stage of temperature stress, the dominant stage of surface phase transformation and the dominant stage of core phase transformation. When the final rolling temperature is 860 ℃, the phase transformation rate is the largest, resulting in the surface phase transformation volume is 17 % larger than that at 820 ℃, so that the tensile stress level at the beginning of phase transformation becomes larger, and the residual stress after rolling is also the largest, resulting in plate shape problems during production and processing. The finishing rolling temperature has little effect on the microstructure and transformation plasticity parameter K after rolling, which is not the decisive factor causing the difference of residual stress after rolling.

Influence of quenching process on microstructure and wear resistance of GCr4Mo4V steel

Cui Yi, Cui Jihong, Wang Yan, Zhang Yunfei, Yu Feng, Zhao Yingli, Cao Wenquan

2023, 48(9): 23-29. doi:10.13251/j.issn.0254-6051.2023.09.004

Abstract ( 89 )

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Annealed GCr4Mo4V steel prepared by the process of “VIM+ESR” was oil quenched at 1090, 1120 and 1150 ℃ for 30, 60 and 120 min respectively, and then tempered three times continuously. The dry wear test was carried out on UMT TriboLab wear tester, and the evolution of its microstructure, surface hardness, wear scratch morphology and wear rate were analyzed, and the influence of quenching process on the microstructure and dry wear characteristics of the GCr4Mo4V steel were investigated. The results show that the quenching temperature of 1150 ℃ is the critical temperature for the rapid growth of grains. The increase of quenching temperature promotes the dissolution of large particle carbides. The prolongation of holding time is more conducive to the dispersion distribution of carbides after tempering. The quenching temperature has a greater effect on the refinement of large particle carbides than the holding time. The refinement and dispersion of grain structure and carbides have a positive effect on the improvement of wear resistance of the GCr4Mo4V steel.

Influence of DQ-T process on microstructure and properties of 1000 MPa high strength steel

Wang Yi, Han Jie, Liu Chao, Deng Lingrui, Li Hui, Xu Rongchang

2023, 48(9): 30-34. doi:10.13251/j.issn.0254-6051.2023.09.005

Abstract ( 63 )

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Effect of direct quenching+tempering process on the microstructure and mechanical properties of 1000 MPa grade high strength steel was studied. The microstructure was characterized by means of metallographic microscope and transmission electron microscope, and the Vickers hardness and tensile properties were tested. The results show that as the tempering temperature increases, the decreasing trend of microhardness and tensile strength is divided into three stages: slowly descending Ⅰ_σ stage (room temperature to 350 ℃), rapidly decreasing Ⅱ_σ stage (350-500 ℃) and basically stable Ⅲ_σ stage (above 500 ℃). There is a peak in yield strength after tempering at 250-400 ℃, and the yield strength ratio increases significantly. When the tempering temperature reaches above 500 ℃, the elongation can reach over 15%. After finishing rolling at 850 ℃ and tempering at 350-450 ℃ for 30-60 min, a good combination of strength and toughness can be obtained, which meets the performance indicators of the 1000 MPa grade high-strength steel. There are a lot of dislocation substructures in the martensite structure, in which the movable dislocation can alleviate the local stress concentration, reduce the possibility of microcrack formation, so that the material can obtain large uniform plastic deformation.

Effect of sintering temperature on microstructure and magnetic properties of 2∶17H type high-performance SmCo alloy

Chen Yanrui, Lü Ke, Li Yan, Ren Shaoqing, Zhao Mingjing, Dong Rui, Ding Wei

2023, 48(9): 35-41. doi:10.13251/j.issn.0254-6051.2023.09.006

Abstract ( 49 )

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A 2∶17H type high-performance SmCo alloy was smelted in vacuum melting furnace. The effect of sintering temperatures of 1195, 1200, 1205, and 1210 ℃ on the magnetic properties and microstructure of the alloy magnets was studied. Then, the density and magnetic properties of the magnets with four sintering temperatures were tested, and the microstructure was characterized. The results show that the magnetic properties of the sintered magnets increase with the increasing sintering temperature appropriately, but greatly reduced due to excessively high sintering temperature. When the sintering temperature is 1205 ℃, the sintered magnet has the best comprehensive magnetic properties, with B_r of 11.41 kGs, H_cj of 1.05 kOe, (BH)_max of 7.365 MGOe. The magnetic properties of sintered magnets are affected by the element distribution, grain uniformity and size, magnet density, Sm₂O₃phase, and Zr-rich phase, respectively.

Effect of hot working process on microstructure and properties of Nb₃₇Ti₂₀Al₁₅Zr₁₅Hf₅Ta₅Mo₂W₁ refractory high-entropy alloy

Shao Xu, Pang Jingyu, Ji Yu, Tang Guangquan, Liu Wenqiang, Cheng Lufan, Li Wen

2023, 48(9): 42-47. doi:10.13251/j.issn.0254-6051.2023.09.007

Abstract ( 42 )

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Nb₃₇Ti₂₀Al₁₅Zr₁₅Hf₅Ta₅Mo₂W₁(at%) refractory high-entropy alloy was produced by vacuum arc melting. Then the alloy was hot deformed+homogenized, and aged at 750 ℃ for 30-120 h. The as-cast structure, precipitation behavior and mechanical properties of the refractory high-entropy alloy after aging were studied by means of X-ray diffraction, scanning electron microscope, transmission electron microscope and universal mechanical testing machine. The results show that the structure of the as-cast alloy is composed of B2 matrix and antiphase boundaries. After aging, a large amount of vermicular Zr₅Al₃ phase are precipitated within the grain, and rod-shaped Zr₅Al₃ phase are precipitated at the grain boundaries, inducing intergranular fracture. After aging for 30 h, the compressive yield strength of the alloy is 1093.8±7.5 MPa. Due to the interaction between intergranular cracking and Zr₅Al₃ phase after aging, the compressive plasticity is anomaly only 5.8%. After aging for 60, 90, and 120 h, the compressive yield strength of the alloy is about 1300 MPa, and the plasticity is about 15%. It has excellent stability and the fracture is mainly intergranular fracture.

Effect of solution treatment on microstructure and corrosion resistance of Mg-1Zn-1Ca alloy

Wang Jian, Song Lei, Wang Yizhuo, Zhang Quanfu, Ren Naidong, Wu Weikang, Wang Hongxia, Luo Xiaoping

2023, 48(9): 48-53. doi:10.13251/j.issn.0254-6051.2023.09.008

Abstract ( 42 )

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Microstructure evolution of as-cast Mg-1Zn-1Ca alloy after solution treatment was studied by means of OM, SEM, EDS and XRD, and the effect of solution treatment on the corrosion resistance of the alloy was explored by electrochemical experiments and immersion experiments. The results show that the as-cast Mg-1Zn-1Ca alloy is composed of Mg matrix, Ca₂Mg₆Zn₃ phase and Mg₂Ca phase, while after solution treatment, the matrix grains gradually grow with the increase of solution temperature (400, 420, 440 ℃), the Ca₂Mg₆Zn₃ phase redissolves, the amount of second phases gradually decreases, the corrosion rate of the alloy first decreases and then increases. The alloy has the best corrosion resistance after solution treatment at 420 ℃ for 8 h, with the lowest average corrosion rate of 0.7725±0.016 mm/y. The improvement of corrosion resistance is attributed to the second phase redissolution, and the galvanic corrosion effect is weakened. While for the alloy after solution treatment at 440 ℃ for 8 h, the corrosion resistance deteriorates because the grain coarsening intensifies the local corrosion.

Hot deformation behavior and processing maps of a new type low-carbon high-alloy bearing steel

Wu Xueting, Wu Zhiwei, Zhang Jun

2023, 48(9): 54-59. doi:10.13251/j.issn.0254-6051.2023.09.009

Abstract ( 40 )

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High temperature unidirectional hot compression test of a new type low carbon and high alloy bearing steel was carried out by means of Gleeble-3500 thermal simulation machine under the conditions of deformation temperature of 900-1200 ℃, strain rate of 0.01-1 s^-1 and total deformation of 50%. The effect of the deformation temperature and strain rate on the mechanical behavior of the tested steel during hot deformation was analyzed through flow stress curves at high temperatures under different conditions. The Arrhenius equation was used as a constitutive model to develop the high-temperature constitutive equations for the tested steel, and the hot processing maps for the 50% deformation were drawn based on the Mutry instability criterion. The results show that the dynamic recovery characteristics of flow stress curves are obtained at low temperatures and small strain rates (900-1000 ℃, 0.01-0.05 s^-1), and dynamic recrystallization occurs at high temperatures and low strain rates (1050-1200 ℃, 0.01-0.1 s^-1) during deformation. At higher strain rate (1 s^-1), the flow stress increases with increasing strain, and the curves show no significant peak stress. At medium and high temperatures and low strain rates (1050-1200 ℃, 0.01-0.1 s^-1), the uniform fully dynamic recrystallized structure can be obtained, and the hot working performance of the material is the best.

Constitutive behavior of G13Cr4Mo4Ni4V bearing steel based on strain compensation

Jiang Xiaojuan, Hu Mengjun, Sun Tao, Xiao Xinrui, Dong Mengyao, Zhang Haicheng

2023, 48(9): 60-69. doi:10.13251/j.issn.0254-6051.2023.09.010

Abstract ( 32 )

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To study the flow stress behavior of G13Cr4Mo4Ni4V bearing steel at high temperature and acquire reasonable hot processing parameters, isothermal compression tests were carried out at deformation temperatures between 1223-1423 K and strain rates between 0.001-1 s^-1by Gleelle-3800. The relationship between flow stress and deformation temperature, deformation rate, strain and other factors was studied. In view of the influence of strain on material parameters, an Arrhenius constitutive model based on strain compensation was established within the high-temperature deformation temperature range. In addition, according to the power dissipation coefficient in the metal plastic deformation process and the instability criterion, the hot processing map of the bearing steel was jointly determined. The results show that the flow stress is negatively correlated with deformation temperature and positively correlated with strain rate. An Arrhenius constitutive model considering strain compensation is constructed, and the correlation coefficient R between the predicted flow stress and experimental data, as well as the absolute average relative error AARE, are 0.991 and 5.786%, respectively. The model has high prediction accuracy. Combined with power dissipation coefficient and instability criteria, the hot processing map of this alloy is calculated, which shows that the bearing steel has better hot processing property when the temperature is 1320-1400 K and the strain rate is 0.1-1 s^-1.

Effect of annealing temperature and cold deformation on microstructure and properties of 3003 aluminum alloy plate for power battery shell

Zeng Yongmou, Liu Ying, Liu Ziyuan, Hu Menghan, Cao Yu

2023, 48(9): 70-74. doi:10.13251/j.issn.0254-6051.2023.09.011

Abstract ( 53 )

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Effects of intermediate annealing temperature and cold deformation on the microstructure and properties of 3003 aluminum alloy plate for power battery shell were studied by means of muffle furnace, Brinell hardness tester, optical microscope and universal testing machine. The results show that with the increase of intermediate annealing temperature, the hardness, tensile strength and yield strength of the 3003 aluminum alloy plate with different cold deformation amounts decrease first, and then become stable at 380 ℃ and over, while the elongation is on the contrary. When the annealing temperature is at 200 ℃ and lower, both the strength of the alloy plate increases with the increase of cold deformation. With the increase of annealing temperature, the conductivity of the 3003 aluminum alloy plate increases slowly firstly, then stabilizes, and finally decreases rapidly. When the cold deformation amount is 85%, the conductivity of the alloy is the highest, while it decreases significantly when the cold deformation amount is 95%. The microstructure of the alloy plate changes from slender fiber to fine equiaxed recrystallized grains with the increase of annealing temperature. The greater the cold deformation, the lower the temperature at which the material begins to recrystallize and the finer the recrystallized grains, and the recrystallization is completed at 380 ℃. Overall, the optimal intermediate annealing temperature of the 3003 aluminum alloy plate for power battery shells is 380 ℃, and the optimal cold deformation is 85%.

Effect of rapid tempering on microstructure and properties of 690 MPa grade steel plate for construction machinery

Li Deming, Lei Ningning, Zhang Jingang, Gong Tao, Zhou Guanghao

2023, 48(9): 75-80. doi:10.13251/j.issn.0254-6051.2023.09.012

Abstract ( 36 )

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Effects of three different tempering heating rates of 20, 30 and 40 ℃/s and tempering time after offline quenching on microstructure and mechanical properties of a 690 MPa grade steel plate for construction machinery were studied by using OM, TEM and mechanical properties tests. The results show that the tempering heating rate has little influence on the tensile strength of the steel plate, while the yield strength changes significantly with the increase of tempering holding time. The microstructure of the steel plate is bainite+ferrite mostly after tempering, with the prolonging of tempering holding time, and the amount of ferrite increases, especially, the specimen with 15 min of holding time shows stable properties. Through analysis of the precipitates inside the specimen with 15 min of holding time, it is found that with the increase of tempering heating rate, the carbide aggregation phenomenon inside the steel plate first decreases and then increases, and the comprehensive mechanical properties of the specimen at 30 ℃/s is the best.

Application prospect of ultra high strength and toughness steel prepared by intensive quenching process

Ming Zhangsheng, Zhao Jie, Li Kejian, Cao Pengjun, Zhu Bin, Feng Yi

2023, 48(9): 81-87. doi:10.13251/j.issn.0254-6051.2023.09.013

Abstract ( 42 )

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Intensive quenching process has attracted extensive attention from foreign scholars in recent years due to its characteristics of low energy consumption, no pollution and “super strengthening” effect on materials. The development status of intensive quenching process at home and abroad was introduced and a database of intensive quenching process parameters urgent to establish. Because the microstructure and properties of the ultra high strength and toughness steel treated by the intensive quenching process fit well with the performance requirements of the ultra high strength and toughness steel used in special equipment, the prospect of applying the intensive quenching process to the development of ultra high strength and toughness steel is put forward.

Effect of quenching process on hardened depth and mechanical properties of 42CrMo steel cutter hub

Jiang Ying, Du Shuiming, Huang Qiaomei, Shen Zida, You Fei

2023, 48(9): 88-91. doi:10.13251/j.issn.0254-6051.2023.09.014

Abstract ( 88 )

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42CrMo steel cutter cub was quenched by using a multi-purpose furnace at different quenching temperatures, different quenching media and carbon potentials. The influence of various factors on mechanical properties and depth of hardened layer of the cutter cub was studied through the inspection of mechanical properties, microstructure and hardness. The results show that with the increase of quenching medium cooling rate, the tensile strength of the cutter cub quenched at 850-890 ℃ shows a trend of overall increase. When the quenching temperature is 850 ℃, the tensile properties of the cutter cub is the best when the quenching medium D is used, and the depth of quenched layer reaches 6.0 mm. When the quenching temperature is 870 ℃, after using C medium, the depth of quenched layer meets the customer's requirements. When the carbon potential is 0.6%, with the increase of quenching temperature, the depth of the quenched layer first increases and then decreases, the tensile strength decreases, and the yield strength and elongation increase.

Effect of heat treatment process on microstructure and properties of valve alloy NCF3015

Mao Fuxiang, Jiang Shaolong, Liu Wei, Shu Wenwu, Wang Lintao

2023, 48(9): 92-94. doi:10.13251/j.issn.0254-6051.2023.09.015

Abstract ( 33 )

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Microstructure changes of NCF3015 valve alloy at different solution temperatures were analyzed by means of metallographic microscope and scanning electron microscope, and the mechanical properties of the NCF3015 alloy at different solution and aging temperatures were studied by means of universal tensile testing machine. The results show that the grain size grows rapidly when the solution temperature exceeds 1010 ℃. The solution treated alloy matrix is mainly composed of austenite with equiaxed crystal structure, and a small amount of carbon nitride precipitates on the matrix. After aging, diffusively distributed spherical γ′ strengthened phase is precipitated from the alloy matrix. The size of strengthened phase is smaller with the increase of solution temperature. The high temperature tensile properties of the alloy show that the alloy has relatively good mechanical properties when used below 750 ℃.

Effect of deformation on mechanical properties of Ti80G alloy

Han Weisong, Du Feng, Li Jianfeng, Zhu Baohui, Shen Lihua, Liu Yi, Wang Peng

2023, 48(9): 95-98. doi:10.13251/j.issn.0254-6051.2023.09.016

Abstract ( 31 )

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φ93 mm Ti80G titanium alloy bar was forged with a deformation between 10%-40%, and the forged rod was annealed at 900 ℃ to study the effect of forging deformation on the mechanical properties of the annealed titanium alloy. The results show that with the increase of forging deformation, primary α phase volume fraction reduces and precipitation α volume fraction increases, the strength at room temperature and high temperature increases, the ductility first increases and then decreases, and the impact property increases. At 30% deformation, the Ti80G alloy achieves the best mechanical properties match, with room temperature/high temperature tensile strength of 901.0 and 565.0 MPa, room temperature/high temperature yield strength of 792.5 and 482.0 MPa, room temperature/high temperature elongation after fracture of 17.25% and 22.00%, and room temperature/high temperature percentage reduction of area of 45.0% and 69.0%, respectively. And impact absorbed energy reaches 100.60 J.

Effect of liquid phase plasma carbonitriding time on microstructure and properties of infiltration layer of H13 hot work die steel

Fan Xingping, Fan Wei, Xie Wen

2023, 48(9): 99-105. doi:10.13251/j.issn.0254-6051.2023.09.017

Abstract ( 32 )

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In order to improve high temperature oxidation resistance and hardness of H13 hot work die steel, the liquid phase plasma electrolytic carbonitriding technology was used to treat the H13 hot work die steel. The microstructure, composition, hardness and high temperature oxidation resistance of infiltration layer of the hot work die steel were tested by means of XRD, SEM and Vickers hardness tester, and the effect of carbonitriding time on microstructrue and properties of the infiltration layer was investigated. The results show that iron carbides and nitrides are formed on surface of the H13 hot work die steel after liquid phase plasma carbonitriding for 3, 5 and 7 min respectively at 200 V voltage. The phase composition of the infiltration layer includes Fe, Fe₁₉Mn, CrFe₄, Fe₃C and Fe_2-3N. With the extension of carbonitriding time, the molten particles gather more and more, which produces a “hillside” shape, making its surface more rough, and the thickness of the infiltration layer also increases. When the carbonitriding time is 7 min, the thickness of the infiltration layer is the largest, about 5.9 μm. The microhardness increases with the increase of carbonitriding time. The microhardness of the infiltrated layer after carbonitriding for 7 min is the highest, reaching 403.13 HV0.2. The high temperature oxidation resistance of the H13 hot work die steel is significantly improved after liquid phase plasma electrolytic carbonitriding.

Effect of tempering process under 1 T magnetic field on corrosion resistance of 25CrMo48V steel

Yang Saixuan, Yang Xiaobin, Lu Panpan, Zhao Qian, Dong Zhizhong, Dong Ji

2023, 48(9): 106-109. doi:10.13251/j.issn.0254-6051.2023.09.018

Abstract ( 34 )

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25CrMo48V ultra-high strength steel was quenched at 1000 ℃ for 30 min, then placed in a high temperature box furnace under 1 T magnetic field to carry out tempering at 600 ℃ for 0, 10, 30, 180, and 240 min, and tempering at 200, 300, 400, 500, and 600 ℃ for 60 min, respectively. The effect of tempering parameters under the same magnetic field on the corrosion resistance of the steel in 3.5%NaCl solution was studied. The effect of tempering parameter on the corrosion properties of the samples in 3.5%NaCl solution under the same magnetic field was observed and analyzed by optical microscopy, electrochemical impedance spectroscopy and potentiodynamic polarization curve. The results show that the electrochemical impedance spectroscopy plots of all the specimens are similar in shape, indicating that the electrochemical mechanism of the specimens is not changed after tempering, and the capacitive reactance capacitive reactance arc radius is large, the best corrosion resistance is obtained. The self-corrosion current density of the sample tempered at 400 ℃ for 60 min is the lowest.

Effect of normalizing temperature on microstructure and mechanical properties of cryogenic pressure vessel steel plate

Xie Zhanglong, Chen Jiahui, Zhang Bingjun, Chen Feng

2023, 48(9): 110-115. doi:10.13251/j.issn.0254-6051.2023.09.019

Abstract ( 36 )

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Effect of normalizing temperature on microstructure and mechanical properties of a cryogenic pressure vessel P355NL2 steel plate with the thickness of 10 mm was studied. The results show that compared with that of hot-rolled, after normalizing, the ferrite grain is refined, the banded structure is improved, the bainite structure in the core has no obvious change, the strength reduces, the elongation increases, and the impact property at -60 ℃ greatly improves. With the normalizing temperature increases, the ferrite grains become coarsened and equiaxed gradually, and the volume fraction of ferrite decreases, while there is no significant change in strength and elongation, though the low-temperature impact property first increases and then decreases. Taking into account the influence of normalizing temperature on the microstructure and properties, the P355NL2 steel plate can achieve excellent comprehensive mechanical properties by selecting a normalizing temperature of 880-910 ℃.

Nitrogen titanium ion co-infiltration process for austenitic stainless steel

Wei Yongmei, Li Shuangxi, Wang Meitao, Zhao Yuxia, Gao Jie, Chen Lin

2023, 48(9): 116-121. doi:10.13251/j.issn.0254-6051.2023.09.020

Abstract ( 41 )

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In order to investigate the effect of Ti ions on the ion nitriding of austenitic stainless steel, a comparative experiment was conducted on the ion nitriding results of the austenitic stainless steel with or without sponge titanium under the same nitriding conditions. The infiltration depth, surface hardness, microstructure, and distribution of main alloying elements in the infiltration layer of the 022Cr17Ni12Mo2 stainless steel specimens under two experimental conditions were studied by means of microhardness testers, optical microscopes (OM), scanning electron microscope (SEM) and energy dispersive spectroscope (EDS). The infiltration effect of titanium on the 022Cr17Ni12Mo2 stainless steel and the infiltration mechanism of titanium were investigated. The results show that the 022Cr17Ni12Mo2 stainless steel achieves 220-240 μm infiltration layer and 1087-1122 HV0.3 surface hardness after ion nitriding at 560 ℃ for 9 h with sponge titanium added. The infiltration layer increases by about 78% compared to that of the specimen of the same ion nitriding process without titanium, while the surface hardness has no obvious change, which greatly reduces the hardness gradient of the infiltration layer. It is concluded that the energizing mechanism of the 022Cr17Ni12Mo2 stainless steel specimen with titanium is as follows: Sponge titanium provides the super strong nitride forming element Ti ion in the furnace, which strengthens the deposition in the formation process of nitride, thus effectively improves the nitriding efficiency.

Induction quenching process and distortion control of abnormity section at end of guide frame of rolling mill

Wang Jingwei, Fan Meixiang, Lin Yichou, Shi Ruxing, Xi Zhiyong, Liu Zhigang

2023, 48(9): 122-125. doi:10.13251/j.issn.0254-6051.2023.09.021

Abstract ( 80 )

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Heat treatment process and distortion control of induction quenching at the end of the rolling mill guide frame were studied, for which the corresponding end forgings were specially made and the inductor heating and cooling tests were carried out. At the same time, the relevant process tests were carried out. The hardness, distortion, cracking and other risks of the special-shaped section of the end of the guide frame were comprehensively evaluated. Based on the process test results of the end, an induction quenching process for the end of the guide frame was developed with the heating frequency of 1.7-4 kHz, the walking speed of 150 mm/min, and the power of 90×(14%-24%) kW. The magnetic displacement was designed for the inductor, and the continuous heating and continuous cooling induction quenching was adopted. The results show that based on end profiled structure designed by copying inductors by the process test, 40° guide end profiled induction quenching heat treatment can be realized. By setting the magnetic displacement area reasonably on the inductor, the sharp angle effect at the end of the noncircular section is effectively avoided, and is conducive to the uniformity of induction heating temperature. The C35E steel end after induction quenching hardness can reach 55-60 HRC. Through reverse distortion operation, the bending distortion of the end of the guide frame with a total length of 2120 mm can be controlled within 1 mm.

Effect of solution and aging treatment on impact property of 2A14 aluminum alloy

Tan Guoyin

2023, 48(9): 126-128. doi:10.13251/j.issn.0254-6051.2023.09.022

Abstract ( 38 )

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Impact property of 2A14 aluminum alloy after solution and aging treatment was studied by means of SEM and impact testing machine. The results show that the second phase existing in the as-casted specimen is mainly composed of AlCuMgSi phase particles with thin strip morphology. There is also a small amount of circular Al₂Cu phase in the grain. The strip-shaped AlCuMgSi phase particles have a high aspect ratio, which is brittle and easy to break from the middle of the particles when plastic deformation occurs, which cannot effectively improve the material impact property. The core of the short rod-like AlCuMgSi phase after solution and aging treatment contains more Fe and Cu with higher melting temperature, which improves the thermal stability of the second phase particles. With the process of aging, the second phase particles grow up with heat-resistant phase as its core, and evolve into short rod-like finally. After solution and aging treatment, the original reticulated second phase remelts into the matrix and transforms into a more stable short rod-like precipitate, which can absorb more impact loads. At the same time, the fine Al₂Cu phase in the grain also grows significantly. The dispersed precipitated phase particles can better coordinate the plastic deformation and further improve the impact property.

Effect of Gd content on microstructure and conductivity of 3003 aluminum alloy

Huang Yuanchun, Ma Shangkun, Liu Yu, Yan Jijun, Wu Zhenli

2023, 48(9): 129-135. doi:10.13251/j.issn.0254-6051.2023.09.023

Abstract ( 36 )

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Effect of Gd content on microstructure of as-cast and homogenized 3003 aluminum alloy was studied by means of phase diagram software (Pandat), optical microscope (OM), scanning electron microscope (SEM) and conductivity measurement. The results show that with the increase of Gd content from 0 to 0.3wt%, the average grain size in the homogenized structure decreases from 407.88 μm to 201.06 μm. The second phase of the as-cast 3003 aluminum alloy after adding Gd element is Al₆FeMn in long strip shape and Al₃Gd in bright white granular shape. After homogenization at 560 ℃ for 24 h, the second phase is mainly granular and acicular Al₆Mn and short rod GdMn₂Al₁₀. When the Gd content is 0.2wt%, fine grains and a uniformly distributed second phase can be obtained in the alloy, with the highest conductivity of 29.97%IACS.

Effect of V content on austenite grain growth of Cr-Mo-V steel for brake disc of 350 km/h high speed railway

Wu Dongsheng, Deng Wei, Wen Hui, Yu Liangji, Li Kaixin, Wang Fuming

2023, 48(9): 136-142. doi:10.13251/j.issn.0254-6051.2023.09.024

Abstract ( 34 )

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Based on Thermo-Calc thermodynamic calculations, optical microscopy, transmission electron microscopy, and austenite grain growth model calculations, the effects of different V contents (0.13%, 0.23% and 0.34%), austenitizing temperature and time on austenite grain growth in Cr-Mo-V high speed railway brake disc test steel were studied. The deviation between the Beck model of grain growth and actual grain growth was analyzed under different V contents. The results show that when the austenitizing time is 1 h and the austenitizing temperature is 950 ℃, the V content has no obvious effect on the austenite grain growth. Nevertheless, above 950 ℃, the austenite grain size decreases with the increase of V content. The austenite grain sizes of the tested steel grow gradually with the increase of austenitizing temperature. When the austenitizing temperature is below 1000 ℃, the grain size increases slowly with the austenitizing temperature increasing, while when the austenitizing temperature is above 1000 ℃, the austenite grains grows rapidly. At the same austenitizing temperature, the austenite grains grow slowly with the increase of austenitizing time. Based on combination of the measured austenite grain size data and the theory of austenite growth kinetics, the kinetic model of grain growth of 0.34%V steel is calculated to be D=111 974.$1 t^{0.095} \exp \left(-\frac{96319.4}{R T}\right)$. The predicted data of the model has a small deviation from the experimental data, and a good model fitting.

Effect of Ce on microstructure and mechanical properties of 30MnNbRE steel after quenching and tempering

Song Cao, Wang Xiaodong, Bao Xirong, Chen Lin, Tang Xuejiao

2023, 48(9): 143-149. doi:10.13251/j.issn.0254-6051.2023.09.025

Abstract ( 30 )

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Effect of rare earth element Ce on microstructure and mechanical properties of 30MnNbRE steel after quenching and tempering were studied by means of scanning electron microscope, X-ray diffractometer, hardness test, tensile test and impact test. The results show that Ce promotes the solution of Nb in γ-Fe and increases the hardness after quenching, while Ce promotes the precipitation of nanoscale (FeMnNb)₃C with a size of about 40 nm during tempering, resulting in a significant precipitation strengthening effect. At the same time, the pinning effect of (FeMnNb)₃C precipitated between laths refines the thickness of the martensite laths, and finally obtain a uniform and refined nanoscale martensite lath structure. When the addition amount of Ce is 0.01%, the mechanical properties of the 30MnNbRE steel are the best. After tempering at 450 ℃, the hardness can reach 42.6 HRC, the tensile strength increases to 1135 MPa, the fine spherical inclusions with a size of about 1 μm are obtained, concurrently the elongation after fracture is the largest which reaches 13.8%, and the fracture shows ductile fracture characteristics.

Effect of Nb micro-alloying on granular bainite transformation and SH-CCT curves in simulated heat-affected zone of high strength low alloy steel

Yan Wenze, Yan Wenqing, Lin Xuanyi, Wang Honghong

2023, 48(9): 150-156. doi:10.13251/j.issn.0254-6051.2023.09.026

Abstract ( 25 )

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Four kinds of high strength low alloy steels with niobium content were designed, and the effect of niobium microalloying on the granular bainite transformation in the simulated weld heat affected zone was studied by using the Gleeble-3500 thermal simulator, which was characterized by SH-CCT (Simulated heat affected zone continuous cooling transformation). The result shows that the transformation temperature of continuous cooling transformation decreases with the addition of Nb. The continuous cooling phase transformation temperature is about 700 ℃ to 500 ℃ at the range of medium welding heat input, where the granular bainite transformation takes place. The t_8/5 range of the granular bainite transformation increases with the increase of Nb content. When the Nb content in the tested steel is increased to 0.180wt%, the range of cooling rate t_8/5 for transformation of granular bainite is around 3-150 s. The increase of Nb content promotes the continuous cooling granular bainite transformation and expands the t_8/5 range. The microhardness increases with the increase of Nb content. The higher the Nb content, the higher the microhardness at the same t_8/5condition. When the content of Nb is 0.085wt%, the change of microhardness value is the smallest in the large heat input range (t_8/5=15-80 s). The microhardness value varies from 183 HV to 192 HV. The SH-CCT curves provides a theoretical design of niobium microalloyed steel based on the weldability.

Effect of boron content on microstructure and properties of Ti-Zr-Nb-B alloys

Li Wengang, Chui Pengfei, Cheng Zunpeng, Li Chunmei, Jing Ran, Li Jianghua, Liao Zhongni

2023, 48(9): 157-164. doi:10.13251/j.issn.0254-6051.2023.09.027

Abstract ( 32 )

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Ti-Zr-Nb-B alloys with different boron contents were prepared by non-consumable vacuum arc furnace. The microstructure, mechanical properties and corrosion resistance of the alloys were studied by means of X-ray diffractometer (XRD), optical microscope (OM), universal testing machine and electrochemical workstation. The results show that the boron element causes the appearance of a small amount of acicular α phase in the alloy, the microstructure of the alloy changes from equiaxed to dendritic structure and the grain is obviously refined, and TiB and ZrB₂ compounds are precipitated at the dendrite arms, and the dendrite is coarsened when the atom fraction of boron is 2.0% and 4.0%. With the increase of boron content, the hardness of the alloy increases, the plasticity decreases, and the yield strength increases at first, then decreases, and then increases. When the atom fraction of boron is 4.0%, the yield strength and hardness of the alloy reach the maximum values of 843 MPa and 281 HV0.2. The corrosion test in 3.5%NaCl solution shows that the addition of boron reduces the corrosion resistance of the alloy, the (TiZr)₉₀Nb₁₀ alloy has the best corrosion resistance, and the (TiZr)_89.5Nb₁₀B_0.5 alloy has the worst corrosion resistance.

Effect of Si content on microstructure and properties of high carbon bainitic steel

Dai Zhao, Guo Zhi, Long Xiaoyan, Feng Xiaoyong, Liu Wei, Zhang Fucheng, Li Yanguo

2023, 48(9): 165-173. doi:10.13251/j.issn.0254-6051.2023.09.028

Abstract ( 34 )

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Four kinds of high carbon bainitic bearing steels with different Si contents were designed. Under the same heat treatment condition, the effect of Si content on phase transformation, microstructure characteristics and mechanical properties of the high carbon bainitic bearing steels was studied by means of thermal expansion phase change meter, X-ray diffractometer, scanning electron microscope, transmission electron microscope techniques. The results show that Si can prolong the bainite transformation incubation period, decreases the bainite transformation rate and increase the phase transformation points of Ac₁, Ac_cm of the high carbon bainitic bearing steels. With the increase of Si content in the high carbon bainitic bearing steels, the volume fraction of retained austenite of the high carbon bainitic bearing steels increases, but the size of bainitic ferrite lath decreases. When the Si content reaches 1.4%, the size of bainite ferrite lath reaches nanometer level and no carbides precipitates in it. The results of mechanical properties show that the hardness of the steels decreases with the increase of Si content, and the toughness increases with the increase of Si content. The steel with the Si content of 1.4% has the best comprehensive mechanical properties.

Effect of trace Zr on microstructure and mechanical properties of deep cryogenic rolled Al-Cu-Mg alloy

Xie Shangheng, Sun Youping, Zhu Jiaxin, Fang Dejun

2023, 48(9): 174-179. doi:10.13251/j.issn.0254-6051.2023.09.029

Abstract ( 37 )

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Effect of trace Zr addition on microstructure and mechanical properties of deep cryogenic rolled Al-Cu-Mg alloy sheet was studied by means of optical microscope (OM), electronic universal testing machine, X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that the trace Zr addition refines the Al-Cu-Mg alloy grains, and makes the size of second-phase particles reduce and more evenly distribute, mainly as the θ-Al₂Cu phase. The addition of Zr effectively improves mechanical properties of the Al-Cu-Mg alloy, the tensile strength, elongation and Brinell hardness of which are 610 MPa, 10.3% and 176 HBW, and increases by 67 MPa, 2.5% and 22 HBW relative to the Al-Cu-Mg alloy without Zr addition, respectively. The contribution of dislocation enhancement is significant to the strength enhancement of the Al-Cu-Mg-Zr alloy, reaching 325 MPa. In addition, the Zr addition enhances the texture pole density of the Al-Cu-Mg alloys in the (111), (200) and (220) crystal planes after deep cryogenic rolling, but the texture type is not changed.

Effect of rare earth microalloying on gas nitriding propertiesof 42CrMo steel

Chen Hai, Cui Ding

2023, 48(9): 180-182. doi:10.13251/j.issn.0254-6051.2023.09.030

Abstract ( 34 )

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Effects of rare earth elements on microstructure and hardness of 42CrMo steel under nitriding heat treatment were investigated. The results show that after nitriding treatment, the white layer of the 42CrMo steel added with rare earth elements, is obviously thickened, the surface hardness and effective hardening layer depth are significantly increased, and the pulse structure of the permeability layer is improved. It shows that the rare earth microalloying has an obvious effect on the nitriding process of the 42CrMo steel, it can accelerate the diffusion of nitrogen atoms, and increase nitriding speed.

Effect of sulfur content on sulfide morphologies and properties of Y12Cr18Ni9 free-cutting steel

Wang Yinghu

2023, 48(9): 183-190. doi:10.13251/j.issn.0254-6051.2023.09.031

Abstract ( 28 )

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Effect of sulfur content on sulfide morphology and properties of Y12Cr18Ni9 free-cutting steel was studied by means of SEM, SEM-EDS, EPMA and EBSD, etc. The phase diagram and equilibrium solidification transformation path of the Y12Cr18Ni9 free-cutting steel were calculated by TCFE10 database of Thermo-Clac software, and the effect of sulfur content change on sulfide precipitation was analyzed. The result show that the main equilibrium phases in the Y12Cr18Ni9 free-cutting steel are Liquid, MnS, δ, γ, M₂₃C₆, σ and α. The sulfides are spherical, ellipsoidal, spindle shape or short-bar-like, which are distributed in chains at grain boundaries or clustered at the trident junction, belonging to a type of II sulfide. With the increase of sulfur content, the amount of sulfide precipitation per unit area in the tested steel increases, and the average area of sulfide increases. The increase of sulfur content can promote the precipitation of sulfide in the Y12Cr18Ni9 free-cutting steel. With the increase of the number of cluster sulfides in the tested steel, the quasi-cleavage surface area of the tensile fracture increases, gradually transforms into brittle fracture, and the mechanical properties of the material decrease.

Continuous cooling transformation and microstructure control of a Mn-Cr-V-S bainitic non-quenched and tempered steel

Wang Zhilin, Gao Xing, Jiang Bo, Wang Leiying, Zhao Haidong, Wu Han

2023, 48(9): 191-196. doi:10.13251/j.issn.0254-6051.2023.09.032

Abstract ( 34 )

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Continuous cooling transformation behavior of a Mn-Cr-V-S bainitic non-quenched and tempered steel was studied by using Gleeble-3800 thermal simulation test machine. The effect of cooling rate on the continuous cooling transformation curves, microstructure and micro-hardness of the steel was analyzed. In addition, the step-cooling process was set up to control microstructure for the tested steel. The results show that ferrite+pearlite, ferrite+pearlite+bainite, ferrite+bainite, ferrite+bainite+martensite, and ferrite+martensite transformations occur successively in the Mn-Cr-V-S bainitic non-quenched and tempered steel with the increase of cooling rate. When the cooling rate is 1 ℃/s, the area fraction of bainite in the tested steel is the highest and reaches 68%, and the microstructure uniformity is preferable. When the cooling rate is higher than 1.5 ℃/s, the martensite begins to appear in the steel. In order to reduce the content of ferrite and increase the content of bainite, the step-cooling process is adopted. When the cooling process is final rolling cooled to 550 ℃ at 5 ℃/s, followed by 1 ℃/s to room temperature, the uniformity of microstructure of the tested steel is the best, and the content of bainite can reach 86.8%.

Microstructure evolution and mechanical properties of 20Cr1Mo1VTiB bolt steel after long-term aging at high temperature

Li Xin, Wu Zhiguang, Zhao Jiqing, Yang Gang

2023, 48(9): 197-202. doi:10.13251/j.issn.0254-6051.2023.09.033

Abstract ( 51 )

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Microstructure evolution and mechanical properties of 20Cr1Mo1VTiB bolt steel aged at 530 ℃ for 10 000 h at most were studied. The results show that during the aging process, the MC phases are mainly precipitated and distributed in the bainite laths and at the lath boundaries, and the precipitated amount of MC phases increases but the size does not show significant coarsening. With the increase of aging time, the bainite lath boundaries become blurred gradually and the lath width of bainite increases. After aging for up to 10 000 h at 530 ℃, the strength of the 20Cr1Mo1VTiB bolt steel has no significant change at room temperature and high temperature, the impact property at low temperature increases, and the microstructure recovery effect is obvious, indicating that the steel has good microstructure stability at 530 ℃.

Precipitates change and effect on hardness of HR3C steel after long-term service

Zhou Jiang, Xiang Guodong, Xu Chang, Zhang Xiancheng, Xia Xianxi, Zhu Baoyin, Zhao Yanfen, Jin Xiao

2023, 48(9): 203-207. doi:10.13251/j.issn.0254-6051.2023.09.034

Abstract ( 29 )

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Scanning electron microscope (SEM), transmission electron microscope (TEM) and electron backscattered diffraction(EBSD) techniques were used to examine the microstructure of the un-serviced HR3C steel specimens and these with service durations of 15 501 h, 35 564 h, and 67 705 h, respectively, and hardness of the HR3C steel was measured and analyzed under the corresponding conditions. The results show that the appearance of continuously distributed and similarly sized M₂₃C₆ phases on the grain boundaries of the HR3C steel developes into an inhomogeneous coarsening chain structure as service time increasing, whereas the appearance of nanoscale secondary NbCrN and M₂₃C₆ phases in the grain and their resulting precipitation strengthening effects are the main reasons for the significant increase in hardness values of the HR3C steel.

Comparative study of high temperature chloride corrosion resistance and mechanism of Inconel625 and Inconel601 alloys

Wu Yong, Meng Shixu, Sun Qingyun, Chen Hui, Xia Siyao, Yang Fu, Xia Chunhuai, Yang Hanzhe

2023, 48(9): 208-213. doi:10.13251/j.issn.0254-6051.2023.09.035

Abstract ( 33 )

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High temperature chloride ion corrosion resistance and corrosion mechanism of Inconel625 and Inconel601 alloys were studied by means of SEM, EDS and XRD. The corrosion kinetics curves, corrosion products and surface and cross section morphology of the corrosion layer of the two alloys were compared and analyzed under the condition of chloride ion corrosion at 1100 ℃. The results show that both Inconel625 and Inconel601 alloys exhibit rapid corrosion in the early stage and gentle corrosion in the later stage. The high temperature chloride corrosion resistance of the Inconel625 alloy is better than that of the Inconel601 alloy. In the corrosion process of the Inconel625 alloy, an oxide film containing complex oxides is formed. The main corrosion products of the Inconel601 alloy are Cr₂O₃, AlFeO₃ and Al₁₈Cr₅ phases, while the main corrosion products of the Inconel625 alloy are Al₂O₃, Fe₂O₃, Cr₅O₁₂ and NiCrO₄ phases. The Inconel625 alloy has better corrosion resistance than the Inconel601 due to the pinning effect of Nb element and the formation of NiCrO₄ with spinel structure, which increases the adhesion of oxide film.

Phase transformation behavior of high strength cord steel LX82ACr during dynamic continuous cooling

Li Zhanwei, Shen Kui, Ma Han, Zhang Yu

2023, 48(9): 214-219. doi:10.13251/j.issn.0254-6051.2023.09.036

Abstract ( 30 )

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Characteristics of LX82ACr cord steel during dynamic continuous cooling were studied by thermal simulation, and the microstructures at different cooling rates were analyzed by using optical microscope. The pearlite lamellar spacing and hardness were measured at different cooling rates, and the tensile strength was converted from the hardness. The variation characteristics of phase transformation temperature, undercooling degree, pearlite lamellar spacing, and tensile strength with cooling rate were studied, respectively. The results show that when the cooling rate is 3 ℃/s and below, the microstructure is pearlite and sorbite. When the cooling rate reaches 5 ℃/s, the martensite begins to appear and its quantity increases with the increase of cooling rate. When the cooling rate reaches 30 ℃/s and above, the microstructure is mainly martensite. The phase transformation temperature decreases and the undercooling degree increases with the increase of cooling rate, and the regression analyses show that the goodness of each fitting reaches above 0.97. The pearlite lamellar spacing decreases and the tensile strength increases with the increase of cooling rate, and the regression analyses show that the goodness of each fit is also above 0.97. When the cooling rate increases from 0.1 ℃/s to 9 ℃/s, the pearlite lamellar spacing decreases from 0.1929 μm to 0.0739 μm, and the tensile strength increases from 993.2 MPa to 1388.4 MPa.

Heat treatment process and mechanical properties of low alloy wear-resistant steel

Zhang Zhichun, Wen Jia, Chen Guorui, Wu Guanghui, Weng Zeju, Gu Kaixuan

2023, 48(9): 220-224. doi:10.13251/j.issn.0254-6051.2023.09.037

Abstract ( 35 )

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CCT curves of a low alloy wear-resistant steel were measured by using a DIL805 quenching dilatometer to study its phase transformation law during continuous cooling. The microstructure of the specimens at different cooling rates was observed by using OM. In addition, the low alloy wear-resistant steel was heat treated by using quenching+tempering process, quenching+cryogenic treatment+tempering process, and the specimens were analyzed by using SEM characterization, tensile and impact tests to study the effect of cryogenic treatment on the microstructure and properties of the tested steel. The results show that the critical cooling rate of martensite transformation of the tested steel is 5 ℃/s. The tensile strength and yield strength of the low alloy wear-resistant steel are increased by 136.5 MPa and 141.5 MPa, respectively, with the addition of cryogenic treatment. The impact property is decreased slightly while the plasticity remains unchanged after cryogenic treatment. The main mechanism of improvement of the strength and plasticity of low alloy wear-resistant steel caused by cryogenic treatment is to promote the refinement of martensitic lath.

Mechanical-chemical complex enhancement and wear resistance of TC4 titanium alloy

Deng Minxian, Dai Yan, Liu Gang, Mu Hong, Chen Taoyun, Liu Jing

2023, 48(9): 225-232. doi:10.13251/j.issn.0254-6051.2023.09.038

Abstract ( 30 )

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In order to improve the hardness and wear resistance of TC4 titanium alloy, the TC4 titanium alloy was subjected to mechanical lappling and vacuum nitriding composite modification treatment by planetary ball milling device and vacuum induction nitriding device. A self-made wear testing machine was used to conduct wear tests under different loads. The results show that after complex enhancement treatment, the infiltrated layer of the TC4 titanium alloy mainly consists of TiN and Ti phases. With the increase of the nitriding temperature, the thickness of the nitrided layer gradually thickens, and the cross-sectional hardness also significantly improves. There is a significant difference in the microstructure of the nitrided layer between the specimen treated with direct nitriding and composite strengthening. The nitrided layer of the direct nitrided specimen is thin and dense, with a clear boundary with the matrix and a lack of transition. The nitride phase in the composite strengthening specimen is distributed in a block or island like manner in the surface layer, without a clear bright white layer. The hardness gradient of the cross-section after composite strengthening treatment is smoother than that after direct nitriding treatment and the nitrided layer has less brittleness and higher surface plasticity. The wear resistance of the specimen after composite strengthening treatment is significantly improved, but slightly lower than that of the direct nitrided specimen.

Microstructure and properties of a grade 10.9 bolt steel with wide tempering time window

Wang Jiaojiao, Liu Hongchun, Liu Yong, Chen Hongwei, Tian Zhiqiang, Zhang Hongqi

2023, 48(9): 233-237. doi:10.13251/j.issn.0254-6051.2023.09.039

Abstract ( 30 )

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Microstructure and mechanical properties of a vanadium microalloyed Si-Mn-Cr bolt steel after quenching at 870 ℃+tempering at 550 ℃ for different time were studied by means of optical microscope, scanning electron microscope, transmission electron microscope, and Rockwell hardness test. The results show that the microstructure of the tested steel after quenching at 870 ℃ is lath martensite, and the microstructure after tempering at 550 ℃ for 40, 60 and 80 min, respectively, is clear martensie with accompaning by fine dispersed carbide precipitates. When the tempering time is 40-80 min, the tensile strength of the tested steel is 1081-1120 MPa, the yield strength is 993-1013 MPa, and the percentage reduction of area is 56.0%-56.3%, all of which are relatively stable, and the tensile fracture of the tested steel has obvious neck contraction phenomenon. The fracture source areas are all ductile fractures with small dimples and tearing edges, and the comprehensive mechanical properties are good. Therefore, the tempering time window of the 10.9 grade bolt steel is broad, and the comprehensive mechanical properties are stable, which is conducive to expanding the range of use of bolt steel.

Evolution of microstructure and macrotexture of 3.1%Si oriented silicon steel

Liu Yongzhen, Dong Lili, Liu Baozhi, Zhang Hao, Ma Yonglin

2023, 48(9): 238-241. doi:10.13251/j.issn.0254-6051.2023.09.040

Abstract ( 35 )

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Microstructure and macroscopic textures of 3.1%Si oriented silicon steel during first cold rolling, decarburizing annealing, second cold rolling, high temperature annealing and tensile leveling annealing were analyzed by means of Zeiss microscope, X-ray diffractometer and other testing instruments. The results show that microstructure of the oriented silicon steel is ferrite. The average grain size is 10.23 μm after first recrystallization during decarburizing annealing, and reaches 2.0 cm after second recrystallization during high temperature annealing, and grows to 2.3 cm with increasing of uniformity after tensile leveling annealing. The main texture type of the oriented silicon steel after decarburization annealing is γ fiber texture, with a small amount of Goss texture {110}<001>. After high temperature annealing, the texture type is mainly Goss texture {110}<001>. After tensile leveling annealing, the Goss texture reaches the strongest and sharpest degree.

Texture evolution law of IF steel during cold rolling and annealing

Shen Wenzhu, Wang Pengfei, Hu Xiangping, Bao Feifei, Hou Xinxin, Cao Lisheng

2023, 48(9): 242-246. doi:10.13251/j.issn.0254-6051.2023.09.041

Abstract ( 30 )

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Evolution of the texture of IF steel plates with different cold rolling reduction, and different annealed after hot rolling high temperature coils with 80% cold rolling reduction was studied by using X-ray diffraction (XRD). The results show that with the increase of cold rolling reduction, the weak {110}<110>, {110}<001> and {112}<110> textures of hot rolled coiled IF steel specimen gradually change to {110}<011> and{100}<011> textures, also a weak {111} plane texture is formed. For cold rolled IF steel plate with cold rolling reduction of 80%, the annealing conditions that are beneficial to formation of the γ-fiber texture in turn are as follows: 790 ℃/60 min, 670 ℃/10 min and 790 ℃/10 min. When annealed at a higher temperature of 850 ℃, the texture such as {112}<110> is liable to form, which inhibits the formation of γ-fiber texture and is not conducive to the improvement of deep drawing performance.

Design and implementation of materials database for heat treatment process simulation

Zhang Lunfeng, Wang Zhihan, Zhao Junyu, An Kang, Xu Jun, Gu Jianfeng

2023, 48(9): 247-252. doi:10.13251/j.issn.0254-6051.2023.09.042

Abstract ( 41 )

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Material parameters are the crucial data support in heat treatment process simulation. However, at present, there is a lack of relevant material databases in China, and a few existing databases have problems such as low data accuracy, poor integrity, and inability to share data, they only distinguish materials based on chemical composition, which cannot meet the parameter requirements of heat treatment process simulation. Therefore, a data structure focusing on chemical composition and microstructure was designed, and an online special material database was also independently developed. The database optimizes the data storage structure according to the characteristics of material parameters required for heat treatment process simulation. Adopting B/S architecture design realizes data sharing and improves the convenience of data use. Furthermore, by using data mining technology, the database introduces four machine learning algorithms: multivariable linear regression, Bayesian linear regression, decision tree, and random forest, and establishes an innovative data extraction mechanism. The effective data extraction strategy can be determined through the application analysis of existing data, and then the actual data requires at present can be obtained, which preliminarily solves the problem of data missing currently, and strongly supports the development of heat treatment process simulation.

Technology knowledge base framework of aluminum alloy heat treatment integrated management and control based on multi-parameter variables

Liu Qi, Wan Rutao, Chong Yonggang, Li Mutian, Qu Ming

2023, 48(9): 253-257. doi:10.13251/j.issn.0254-6051.2023.09.043

Abstract ( 26 )

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In response to the process characteristics of multi-parameter variables in heat treatment, aviation aluminum alloy material type and heat treatment process type were selected as variables, and a multi condition judgment rule was adopted to construct an integrated management and control knowledge base for aluminum alloy heat treatment. The temperature rise, holding, cooling, and quenching parameters during the aluminum alloy heat treatment process were digitized, and the integration of heat treatment control process knowledge base in the heat treatment information control system and directly interfaces with other information systems such as MES in the workshop were achieved. It automatically retrieves data-driven process parameters and completes distribution, promoting the direct control of the heat treatment information control system over the process of heat treatment equipment. This has theoretical and practical significance for promoting the informatization, integration, quality monitoring, and process management of special heat treatment process production.

Laser quenching temperature field and phase transformation hardened zone of 45 steel

Ma Zhenghe, Adayi Xieeryazidan, Liu Junjie, Guli Nigaer

2023, 48(9): 258-264. doi:10.13251/j.issn.0254-6051.2023.09.044

Abstract ( 29 )

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Transient law of temperature field and phase transformation hardening law of 45 steel during quenching process were obtained by numerical simulation, and the influence of single factor change on phase transformation hardened zone was analyzed. The thermal coupling model of laser quenching process of the 45 steel was established based on software Comsol Multiphysics, the whole of which is then modified by JMatpro calculated phase transformation curves and CCT curves, and the change curves of some thermal physical parameters of the material with temperature. The phase transformation hardened zone was defined based on the phase transformation curve and CCT curve. The results show that the hardened layer has a Gaussian distribution, and the laser quenching hardened layer is obviously different under different process parameters. Under the same other conditions, the depth and width of phase transformation hardened layer are positively correlated with laser power, and negatively correlated with scanning speed and spot diameter. It is concluded that, by combining JMatpro with Comsol Multiphysics, a thermodynamic coupling model of laser quenching considering the change of thermal physical parameters can be established and calculated, by which the prediction of laser quenching temperature field and phase transformation hardened zone can be realized.

Effect of aging temperature on Cu-rich precipitates in Fe-Cu-Mn-Ni alloy studied by phase-field method

Wang Kanghong, Xu Yangyang

2023, 48(9): 265-270. doi:10.13251/j.issn.0254-6051.2023.09.045

Abstract ( 30 )

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A phase-field model for simulating the microstructure evolution in the solid-state phase transformation of multi-component alloys was constructed by coupling the CALPHAD thermodynamic database. Taking Fe-Cu-Mn-Ni alloy as an example, the effect of aging temperature on the precipitation mechanism of Cu-rich precipitates was revealed from the kinetic point of view. The results show that the transformation of α to γ phase and the formation of B2 ring depend on the size of Cu-rich phase. In addition, the change of aging temperature results in the change of the morphology and precipitation mechanism of the Cu-rich phase. The higher the aging temperature, the shorter the precipitation time of the Cu-rich phase, the larger the volume fraction and radius of the Cu-rich phase, and the faster the reduction rate of the precipitated phase quantity.

Formation mechanism and elimination of black structure in 2.25Cr-1Mo-0.25V steel

Du Junyi, Zhu Yongyou, Jiang Zhonghua, Duan Hongling

2023, 48(9): 271-278. doi:10.13251/j.issn.0254-6051.2023.09.046

Abstract ( 25 )

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Through analyzing the micro-area chemical composition, optical and SEM microstructure, the “black structure” of large 2.25 Cr-1Mo-0.25V steel forgings was studied. The results show that it is “M₂₃C₆ carbide accumulation area”. By verifying its evolution law, it is found that the “black structure” is the root cause of relative low and scattered low temperature impact property of the forgings, and its formation mechanism is related to the formation of large block M-A islands at grain boundary during quenching and then decomposing and transforming into carbide accumulation during tempering at high temperature tempering, while the formation of large block M-A islands is caused by the accumulated M₂₃C₆ carbides existed in the as-forged steel. Through the process test and based on its formation mechanism, it is further found that the “black structure” can be eliminated by annealing pretreatment above 940 ℃, and the mechanical properties of the forgings after reheat treatment are significantly improved.

Formation cause and elimination process of radial stripes in эи866 alloy forgings

Yang Shulin, Zhao Jiqing, Yan Lei, Yang Gang

2023, 48(9): 279-282. doi:10.13251/j.issn.0254-6051.2023.09.047

Abstract ( 27 )

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Formation reason of radial stripes in эи866 alloy forgings were analyzed by microstructure observation, mechanical properties and hardness testing. The heat treatment process to eliminate the radial stripes was also studied. The results show that the radial stripes are caused by the banded structure. A large amount of retained austenite remains after quenching, and transforms to secondary martensite in the tempering cooling process. The secondary martensite distributes alternately with the tempered martensite to form the banded structure, which results in the hardness nonuniformity and appears stripes after machining. Adding a secondary tempering after the performance heat treatment can make the martensite to decompose and recover, and the banded structure can be improved, but it is difficult to be completely eliminated. Adding preheat treatment before the performance heat treatment can raise the Ms point, make the martensite transformation sufficiently, and reduce the amount of retained austenite greatly after quenching, then a single uniform tempered martensite is formed, and the banded structure is eliminated completely. Thus, it is suggested to couple the preheat treatment with the performance heat treatment to improve the uniformity of the structure in the эи866 alloy forgings.

Failure analysis on quenching and tempering cracking of 42CrMo steel low-speed shaft thrust ring

Li Ziyan, Xu Hongxiang, Chen Yesheng, Liu Zhiqiang, Guo Jingqiang, Chen Yan, Zhao Shaofu

2023, 48(9): 283-287. doi:10.13251/j.issn.0254-6051.2023.09.048

Abstract ( 39 )

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42CrMo steel low-speed shaft thrust ring failed due to end face cracks after quenching and tempering treatment. The chemical composition, hardness gradient and microstructure of the fracture position were observed and detected, and the inclusions in the fracture were observed and analyzed by means of SEM and EDS. The results show that the cracks are caused by many factors, such as the inclusion in raw materials, the existence of rough tool marks on the workpiece surface, and the unreasonable structural design of the low-speed shaft part. The risk of quenching cracking at the thrust ring can be reduced by optimizing the rough turning process of machining, quenching auxiliary tooling and controlling the microstructure of raw materials.

Causes and improvement methods of induction quenching cracks in wind power inner gear ring

Zhang Haiying, Wen Chao, Bai Ling, Cai Yixin

2023, 48(9): 288-292. doi:10.13251/j.issn.0254-6051.2023.09.049

Abstract ( 34 )

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Induction hardening cracking of the inner gear ring of wind power was analyzed from the aspects of macro morphology, microstructure, decarburization layer and segregation. The analysis results show that carbon segregation and decarburization of forgings are important reasons for induction hardening cracking of the inner gear ring. When the carbon segregation degree of inner gear ring reaches above 0.04%, the risk of induction hardening cracking increases, and decarburization of tooth tip intensifies the risk of induction hardening cracking. The actual process improvement shows that the carbon segregation difference of the inner gear ring can be reduced to 0.02% by obtaining the blank with forging ratio greater than 7 by three-way forging, which can effectively avoid the carbon segregation. In the design of punching process, the segregation in the center of continuous casting slab can be eliminated by controlling the punching quality. When the blanking coefficient is greater than 0.019, the generation of micro defects and quenching cracks in the teeth can be avoided.

Cause analysis of carburizing quenching cracks of sun gear

Zhang Lei, Mi Pei, Ma Chunliang, Sun Yongpeng

2023, 48(9): 293-296. doi:10.13251/j.issn.0254-6051.2023.09.050

Abstract ( 48 )

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After carburizing and quenching, tooth cracks occurred in the sun gears of mining reducer, causing the products to be scrapped due to the deep cracks. In order to analyze the failure cause of the sun gear, the raw materials, heat treatment process, microstructure, grain size, and macro and micro morphological characteristics of the cracks were analyzed and discussed. The results show that the chemical composition of the material used for the sun gear conforms to the standard of the 18CrNiMo7-6 steel, and the cracks in the sun gear are typical intergranular quenching ones, the main reason of which is related to the coarse grain size. The coarse grains are not caused by the existing late heat treatment, but are mainly related to the improper heating temperature or forging process in the early process stages.

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