Heat Treatment of Metals

Stress corrosion behavior of TP347H stainless steel and BT700-l alloy

Li Dongsheng, Liu Rencai, Tu Yuhang, Lan Keyu

2024, 49(8): 1-8. doi:10.13251/j.issn.0254-6051.2024.08.001

Abstract ( 54 )

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Stress corrosion cracking (SCC) behavior of TP347H stainless steel and BT700-l alloy in high concentration salt corrosion environment was studied by using slow strain rate tensile (SSRT) stress corrosion test. The results show that there is no SCC behavior between the TP347H stainless steel and BT700-l alloy in high concentration salt solution with different pH values. The TP347H stainless steel and BT700-l alloy show a certain SCC tendency under the condition of Cl^- sensitization and H⁺ catalysis in acidic corrosion environment, and the fractures are tough-brittle mixed cracking. The stress corrosion resistance of the BT700-l alloy in acid corrosion environment is significantly higher than that of the TP347H stainless steel.

Effects of carbon content and heat treatment on microstructure and mechanical properties of TiAl alloys with high Nb

Gao Yukui, Fang Wenyi

2024, 49(8): 9-14. doi:10.13251/j.issn.0254-6051.2024.08.002

Abstract ( 60 )

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Taking Ti-44Al-8Nb-xC(x=0, 0.3, 0.6) alloys as the research object, the effects of three different carbon contents and two aging temperatures on the microstructure, microhardness and high-temperature tensile properties were studied. The results show that when the carbon content increases to 0.6%, Ti₂AlC precipitates in the alloy. When the aging temperature increases from 800 ℃ to 900 ℃, Ti₃AlC precipitates in the alloy containing carbon. The increase in carbon content and aging temperature are all beneficial to improving the microhardness and tensile strength at 850 ℃ of the alloy, where the highest microhardness is (477.6±9.1) HV0.3, and the highest tensile strength at 850 ℃ is (605.07±5.01) MPa, which increases by 32.7% compored to the lowest tensile strength. The elongation is related to the number and size of carbides, and all the tensile fractures show brittle fracture. The alloy with 0.3% carbon has the best plasticity when aged at 900 ℃, the highest elongation is 5.41%±0.42%, which increases by 67.5% compared to the lowest elongation.

Austenite grain growth of HRB400E steel during isothermal treatment and effect of vanadium precipitates

Chen Shi, Wang Jiahan, Zhang Yunxiang, Luo Yanping, Sun Zhaoyang, Ye Chuanlong

2024, 49(8): 15-21. doi:10.13251/j.issn.0254-6051.2024.08.003

Abstract ( 45 )

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Austenite grain growth behavior during the isothermal heating processes at different heating temperatures(950-1200 ℃) holding for 30 min of vanadium containing steel HRB400E and the effect of vanadium precipitates on the austenite grain growth was studied by using high-temperature laser scanning confocal microscope and transmission electron microscope(TEM). The results show that the effect of heating temperature on the austenite grain growth in the tested steel is significantly greater than that of the holding time, and the isothermal growth rate of austenite grains increases significantly when the heating temperature exceeds 1100 ℃. The TEM observation shows that the growth behavior of austenite grains in the steel is influenced by V(C, N) particles in the matrix. When the heating temperature is 950 ℃, there is a large amount of undissolved V(C, N) particles in the steel, which can effectively pin the austenite grain boundaries and slow the grain growth. When the heating temperature rises to 1100 ℃, the fine V(C, N) particles dissolve and coarsen with the prolongation of the holding time, the pinning effect decreases, at this time the austenite grains grow rapidly. A kinetic model for the isothermal growth of austenite grains in the tested steel is established based on the measured austenite grain size and combined with the Sellers model and Anelli model, and it is found that the calculated values of the model are in good agreement with the measured values.

Research progress on C-Si-Mn partitioned steel

Zhang Hongliang, Zhou Chunbo, Hou Yan, Jiang Zhiqiang

2024, 49(8): 22-30. doi:10.13251/j.issn.0254-6051.2024.08.004

Abstract ( 35 )

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Quenched and partitioned(Q&P) steel has the characteristics of low cost, good properties, and relatively simple process, and becomes a key research object of the third generation of advanced high strength steel(AHSS). C, Si and Mn elements are the basic alloying elements of the Q&P steel, which have a significant impact on the microstructure and properties of the Q&P steel. Nowadays, most of the research is based on C-Si-Mn system partitioned steel. The production process of the Q&P steel is introduced, the effect of alloy elements on the microstructure and properties of the Q&P steel is clarified, as well as the relationship between the microstructure and mechanical properties of the Q&P steel. The focus is on the influence of process parameters on microstructure and properties of the Q&P steel, and prospects for the development of the Q&P steel are made.

Effects of cooling rate and Nb microalloying on microstructure and hardness of 25MnV non-quenched and tempered steel

Liu Yunna, Sun Lican, Dai Guanwen, Liu Xianda, Song Renbo, Zhang Chaolei

2024, 49(8): 31-35. doi:10.13251/j.issn.0254-6051.2024.08.005

Abstract ( 50 )

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Effect of cooling rate on microstructure and hardness of two non-quenched and tempered forged steels microalloyed with V and V-Nb was studied by single compression test carried out on a Gleeble-3800 thermal simulator. The results show that the cooling rate has a significant effect on the microstructure and hardness of the tested steels. Under the condition of continuous cooling, with the increase of cooling rate in the range of 0.1-0.5 ℃/s, the ferrite content decreases, the pearlite content increases, and the microstructure is refined. With the increase of cooling rate in the range of 1-3 ℃/s, the microstructure is further refined, and bainite transformation begins to occur, which promotes the increase of hardness. The addition of Nb element generates large-size (V, Nb)(C, N) precipitated particles, which further refines the grains by pinning the grain boundary and inducing the formation of intragranular ferrite. At the same time, the solute drag effect of Nb atom on C atom reduces the content of pearlite in the V-Nb steel. The higher hardness(218-242 HV) of the V steel in the cooling rate range of 0.1-0.5 ℃/s is due to its higher content of pearlite, and the higher hardness(256-291 HV) of the V-Nb steel within the cooling rate range of 1-3 ℃/s is due to the refinement of the microstructure and higher bainite content.

Effect of mixed addition of light and heavy rare earth elements on microstructure and mechanical properties of Al-Si-Mg alloy

Zeng Xiangjun, Shi Zhiming, Zhao Ge, Lian Hao, Liu Jiacheng

2024, 49(8): 36-41. doi:10.13251/j.issn.0254-6051.2024.08.006

Abstract ( 26 )

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Effect of mixed addition of light and heavy rare earth elements (La, Ce, Gd, Ho, Er) on the microstructure and mechanical properties of Al-6.9Si-0.36Mg alloy was studied by using optical microscope, scanning electron microscope/energy dispersive spectroscopy, and mechanical property testers. The results show that the refinement effect of α-Al grains in the as-cast alloy is significant with total rare earth addition of 0.1%. As total amount of rare earth added is 0.4%, the improvement effect on the eutectic Si phase is significant, and the eutectic Si phase changes from coarse needle-shaped to granular. After T6 heat treatment, the eutectic Si phase further transforms into small particles and uniformly distribute in the matrix, reducing the cutting effect on the matrix. When the total amount of rare earth elements added is 0.4%, the mechanical properties of the T6 heat treated alloy are the best with tensile strength of 285.4 MPa, elongation after fracture of 7.0%, and hardness of 89.2 HBW.

Effect of rare earth La on microstructure and mechanical properties of Cu-bearing martensitic stainless steel

Cao Yue, Gao Xueyun, Wang Haiyan, Xing Lei, Lin Hongliang

2024, 49(8): 42-47. doi:10.13251/j.issn.0254-6051.2024.08.007

Abstract ( 33 )

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Cu-bearing Cr13 martensitic stainless steels without La and with 0.012% La were taken as the test materials, which were subjected to solution treatment at 980 ℃, following by oil cooling, and aging at 500 ℃ for different time. Effect of rare earth addition on microstructure and mechanical properties of the steel was studied by means of optical microscope, scanning electron microscope, EBSD, combined with mechanical property tests. The results show that rare earth La significantly reduces the δ ferrite volume fraction in the steel, leading to an increase of martensite after quenching, which in turn leads to the increase of dislocations in the matrix, and thus improves the hardness and strength of the tested steel. During the aging process, by the continuous precipitation of Cu-rich particles, about 200 MPa can be contributed to the yield strength of the tested steels at the peak stage of aging strengthening, but the rare earth La has no significant effect on the precipitation kinetics of Cu-rich phases. At the same time, the plasticity of the tested steels is significantly improved due to the continuous reduction of low-angle grain boundaries and the increase of high-angle grain boundaries during the aging process.

Effect of aluminum content on microstructure and mechanical properties of high manganese high aluminum lightweight steels

Bai Rui, Du Yunfei, He Xiuli, Liang Hongyu

2024, 49(8): 48-52. doi:10.13251/j.issn.0254-6051.2024.08.008

Abstract ( 35 )

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Mechanical properties and the precipitation evolution of second phase of high manganese high aluminum lightweight steels as-cast and solution treated with different aluminum contents (10%, 12%, 14%, mass fraction) were investigated by using methods such as phase analysis, microstructural characterization and room temperature tensile and hardness tests. The results show that under as-cast state, with the increase of Al content, the content of ferrite in the tested steels increases and precipitating discontinuously between austenite grains, the size of κ-carbides continuously increases and mainly precipitating within austenite grains. After solution treatment at 1100 ℃, the tested steels exhibit improved strength and plasticity. The tested steel with 12% aluminum obtains excellent comprehensive properties, of which the density is 6.41 g·cm^-3, the specific strength is 157 MPa·cm³·g^-1, the elongation after fracture is 26.2%.

Influence of heat treatment process on mechanical properties and service performance of 51CrV4 steel journal box spring for high-speed trains

Xu Chao, Cao Xinwang, Wang Chenyang, Wang Yuting, Zhang Qian, Yang Qiquan, Hu Jie

2024, 49(8): 53-59. doi:10.13251/j.issn.0254-6051.2024.08.009

Abstract ( 38 )

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Influence of heat treatment process on the service performance of 51CrV4 steel journal box spring for high-speed trains was investigated, the optimal heat treatment process was determined, and the tensile properties, impact properties and fatigue strength evolution of the 51CrV4 spring after quenching at 840-900 ℃ and tempering at 380-520 ℃ were analyzed. The service performance evaluation method for the 51CrV4 steel journal box spring based on material fatigue limit was established, and the influence of heat treatment process on the critical service load of springs was studied. The results show that with the increase of quenching temperature, the tensile strength and fatigue strength of the 51CrV4 spring steel increase. With the increase of tempering temperature, the tensile strength decreases, but the toughness increases. The tensile strength subjected to lower quenching temperature and higher tempering temperature is lower than that of the standard TB/T 2211—2018, and the impact absorbed energy at lower tempering temperature is close to the lower limit of the standard. Considering the mechanical and service properties of the 51CrV4 steel spring, the optimum heat treatment processes of 900 ℃ quenching + 460-480 ℃ tempering and 880 ℃ quenching + 460 ℃ tempering are recommended.

Effect of aging treatment on properties and fracture behavior of 2319 aluminum alloy fabricated by wire arc additive manufacturing

Hua Wenjuan, Zhang Jianxun

2024, 49(8): 60-66. doi:10.13251/j.issn.0254-6051.2024.08.010

Abstract ( 27 )

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Effect of aging time on microstructure and mechanical properties of 2319 aluminum alloy fabricated by wire arc additive manufacturing was studied, and the fracture mechanism of tensile specimens was analyzed. The results indicate that with the prolongation of aging time, the number and size of precipitated phases in the alloy gradually increase. The precipitates are mainly Al₂Cu phase, as well as Fe- and Mn-rich impurity phases. After aging, the tensile strength in horizontal direction of the alloy increases to 450 MPa, and the tensile strength in vertical direction reaches 350 MPa, but the elongation decreases. The aggregation of small pores, as well as the segregation of θ(Al₂Cu) phase and Fe- and Mn-rich impurity phases along grain boundaries, result in the anisotropy of the alloy in both horizontal and vertical directions. At the same time, a large number of micro pores are distributed along the interlayer, and they aggregate and grow together, forming cracks that lead to the fracture and failure of the specimen.

Effect of Q&P process on microstructure and properties of 1000 MPa grade high strength steel

Guo Chengyu, Zhang Zhe, Zhang Chi, Dai Chunduo, Hou Huaxing, Li Jiangwen

2024, 49(8): 67-73. doi:10.13251/j.issn.0254-6051.2024.08.011

Abstract ( 26 )

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Microstructure transformation of two 1000 MPa grade high strength steels with different chemical compositions during salt bath Q&P treatment was analyzed through microstructure observation by scanning electron microscope and Gleeble thermal simulation test. The effect of microstructure transformation on mechanical properties was further analyzed by combining mechanical properties and XRD dislocation density calculation. The results show that two-stage phase transformation occurs during the salt bath Q&P treatment, where the salt-bath partitioning process has a tempering effect on the lath martensite formed in the first phase transformation stage to form a multi-phase tempered lath martensite with different strengths, making the yield ratio of both the tested steels not higher than 0.87. As the salt bath quenching temperature increases, the yield strength and yield ratio decrease, while as the partitioning temperature increases, the strength and yield ratio do not change much. When salt bath partitioned at 450 ℃, the lath martensite structure is partially decomposed and the dislocation density decreases, leading to a significant reduction in the strength.

Microstructure and properties of high strength steel treated by IQ&P process and low temperature C-partition

Wang Dihe, Pang Qihang, Zhao Xingyu, Li Weijuan, Zhao Lidong, Shi Jinming

2024, 49(8): 74-81. doi:10.13251/j.issn.0254-6051.2024.08.012

Abstract ( 25 )

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During intercritical quenching and partitioning (IQ&P) treatment of high strength steel, element C tends to segregate towards retained austenite at low temperature partitioning stage, which can stabilize the retained austenite and improve its strength and plasticity. The ferrite+pearlite (F+P) high strength steel was subjected to IQ&P treatment. The microstructure, properties and C element partition of the high strength steel at low temperature were studied by means of scanning electron microscope, tensile testing machine and multi-function internal friction instrument. The results show that in the high temperature partitioning stage (two-phase intercritical quenching at 820 ℃ for 240 s), the microstructure is austenitized gradually, and then the martensite, M/A and carbide are formed during the quenching process. The product of strength and elongation and volume fraction of retained austenite are 14.4 GPa·% and 5.65%, respectively. During low temperature partitioning stage (at 350 ℃ for 300 s), tempered martensite is formed, M/A structure, retained austenite and cementite are retained. The product of strength and elongation and volume fraction of retained austenite are 18.6 GPa·% and 9.26%, respectively. C atoms interact with defect-type and movable edge dislocations at low temperature partitioning stage, forming Snoke peak and SKK peak, which increase the volume fraction of retained austenite and are the main reason for the improvement of the product of strength and elongation of the high strength steel.

Effect of aging rolling on microstructure, texture and magnetic properties of low-temperature oriented silicon steel

Liu Huidan, Yin Licheng, Zhu Jiqiao, Liu Jing, Cheng Zhaoyang, Dai Fangqin, Dai Huilei

2024, 49(8): 82-87. doi:10.13251/j.issn.0254-6051.2024.08.013

Abstract ( 45 )

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Effect of aging rolling on the microstructure, texture and magnetic properties of the low-temperature oriented silicon steel was studied by conducting aging rolling tests at 250 ℃ for different time using a single cold rolling method. The results indicate that the aging rolling has no significant effect on the cold rolling and primary recrystallization microstructure of low-temperature oriented silicon steel, but it can significantly improve the primary recrystallization texture. The contents of favorable Goss and {111}<112> textures in the primary recrystallization microstructure increase first and then decrease with the increase of aging rolling time, reaching the maximum value at 5 min. An increase in favorable texture content can improve the secondary recrystallization microstructure and enhance the magnetic properties of the final sheet. The magnetic induction intensity of the final sheet increases first and then decreases with the prolongation of aging rolling time, and the iron loss shows the opposite trend. When the aging rolling time is 3-7 min, the final sheet has excellent magnetic properties.

Effect of QLT heat treatment on microstructure and tensile properties of 5.5Ni steel

Zang Yan, Zhu Yingguang, Zhang Chi, An Tao, Liu Wenyue

2024, 49(8): 88-93. doi:10.13251/j.issn.0254-6051.2024.08.014

Abstract ( 32 )

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Microstructure, reversed austenite content and tensile properties of 5.5Ni steel after quenching + intercritical quenching + tempering (QLT) heat treatment were studied by means of scanning electron microscope (SEM), electron backscatter diffraction (EBSD), transmission electron microscope (TEM) and X-ray diffraction (XRD). The effect of quenching temperature in two-phase region on the microstructure and tensile properties of the 5.5Ni steel was analyzed. The results show that the microstructure of the tested steel after QLT heat treatment is tempered martensite + critical ferrite + reversed austenite. The quenching temperature in the two-phase region has great influence on the content of reversed austenite, yield strength and yield ratio, but the quenching and tempering temperature have a little influence. With the increase of quenching temperature in the two-phase region, the content of reversed austenite increases, the tensile strength is basically unchanged, and the yield strength and yield ratio decrease at the same time. The stress-induced transformation of bulk reversed austenite at the triple junction into martensite during the tensile process is the main reason for the difference in yield ratio of the 5.5Ni steel quenched in the two-phase region at different temperatures.

Effect of annealing on microstructure and hardness of Co_xFe₃₅Mn₂₅Cr₁₅Ni₁₀Ti₅ high entropy alloys

Liu Jing, Zhao Ke, Wang Lige

2024, 49(8): 94-101. doi:10.13251/j.issn.0254-6051.2024.08.015

Abstract ( 18 )

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Taking Co_xFe₃₅Mn₂₅Cr₁₅Ni₁₀Ti₅ (x=7,11,15) high entropy alloys as the research object(named as Co₇HEA, Co₁₁HEA and Co₁₅HEA, respectively), the effect of annealing process on the microstructure and hardness was studied by means of metallographic microscope, scanning electron microscope, X-ray diffractometer and Vickers hardness tester. The results show that with the increase of Co element, the compatibility between the black network phase and the gray phase in the alloys is improved, leading to precipitation strengthening and recrystallization during annealing. After annealing, the distribution of Cr, Fe, Ni and Ti elements in the alloys is more pronounced than that in the as-cast. The annealing temperatures corresponding to the highest hardness of the annealed alloys are concentrated at 800 ℃. After annealing at 800 ℃ for 12 h, the hardness of the Co₇HEA alloy and Co₁₁HEA alloy is 422.4 HV0.3 and 778.3 HV0.3, respectively, while the hardness of the Co₁₅HEA alloy is 325.8 HV0.3 after annealing at 800 ℃ for 8 h. When the annealing temperature reaches 1000 ℃, the Co_xFe₃₅Mn₂₅Cr₁₅Ni₁₀Ti₅ alloys undergo varying degrees of recrystallization.

Effect of annealing on microstructure and properties of CoCrFeNiMnhigh entropy alloy

Wang Chunxing, Li Ming

2024, 49(8): 102-107. doi:10.13251/j.issn.0254-6051.2024.08.016

Abstract ( 21 )

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Effect of annealing temperature on microstructure and properties of the as-cast CoCrFeNiMn high entropy alloy was studied by annealing at different temperatures (600, 850 and 1000 ℃). The results show that both the as-cast and annealed CoCrFeNiMn high entropy alloys have a single-phase FCC structure, the microstructure is a typical dendritic structure, and there are grain like particles precipitated between dendrites. Compared with the as-cast state, after annealing at 600 ℃, the precipitates in the alloy are discontinuous and redissolved, the tensile strength increases to 468.21 MPa, the elongation after fracture increases to 42.38%, and the hardness decreases to 143 HV0.2. After annealing at 850 ℃, the precipitates in the alloy increase and are uniformly dispersed, the tensile strength decreases to 446.61 MPa, the the elongation after fracture increases to 50.56%, and the hardness increases to 161 HV0.2. After annealing at 1000 ℃, the precipitates in the alloy dissolve again, the tensile strength decreases to 436.54 MPa, the elongation after fracture decreases to 44.54%, and the hardness decreases slightly. By comprehensive comparison, the comprehensive mechanical properties of the alloy annealed at 850 ℃ are the best.

Effect of T6 heat treatment on microstructure and properties of high pressure die cast ADC12 aluminum alloy

Ren Yunfei, Pan Xinyuan, Wan Tianjian, Li Jinghui, Zhang Mingya

2024, 49(8): 108-112. doi:10.13251/j.issn.0254-6051.2024.08.017

Abstract ( 19 )

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Effect of T6 heat treatment on microstructure and mechanical properties of high pressure die cast ADC12 aluminum alloy was studied. The results show that after solution treatment at 510 ℃ for 1 h and artificial aging at 200 ℃ for 6 h, the microstructure of the ADC12 aluminum alloy die casting is composed of fine eutectic structure and α solid solution, where the fine eutectic structure is formed during the high pressure die casting process. After heat treatment, eutectic Si phase and Al₂Cu phase in the aluminum alloy mainly exist as approximately spherical particles. After T6 heat treatment, the transition phase of the aluminum alloy die casting completely precipitates from the matrix phase, forming a stable θ phase and an α solid solution. After solution treatment at 510 ℃ for 1 h and artificial aging at 200 ℃ for 6 h, the hardness of the ADC12 aluminum alloy die casting reaches the maximum, being 128 HBW, this is caused by the precipitation strengthening phase Al₂Cu, which makes the supersaturated solid solution has a special crystal structure.

Effect of intermediate annealing temperature on microstructure and properties of 6016 aluminum alloy

Chi Rui, Xu Zhiyuan, Meng Shuang, Li Yancheng, Xu Yangfan, Li Tao

2024, 49(8): 113-118. doi:10.13251/j.issn.0254-6051.2024.08.018

Abstract ( 27 )

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Microstructure and properties evolution of 6016 aluminum alloy intermediate annealed at different temperatures were analyzed using metallographic microscopy, scanning electron microscopy, X-ray diffraction and mechanical performance testing machines. The results show that under different annealing temperatures, the mechanical properties of the 6016 aluminum alloy do not change much, but hemming factor f and Δr value change significantly. The values of f (0.60) and Δr(0.24) at the intermediate annealing temperature of 360 ℃ are lower than the values of f (0.75) and Δr(0.28) at the intermediate annealing temperature of 410 ℃, indicating that the hemming property at the intermediate annealing temperature of 360 ℃ is better than that at the intermediate annealing temperature of 410 ℃. As the annealing temperature increases, the surface grain size and grain boundary precipitate Mg₂Si phase size also increase, the maximum size of Mg₂Si phase increases from 1.41 μm to 2.09 μm, and the morphology of most Mg₂Si phase change from rounded to elongated. The proportion of Cube texture and R texture at the intermediate annealing temperature of 360 ℃ is 12.04% and 5.37%, respectively. The proportion of Cube texture and R texture at the intermediate annealing temperature of 410 ℃ is 14.25% and 3.43%, respectively. Among them, the proportion of R texture at the intermediate annealing temperature of 360 ℃ is higher, which reduces the Δr value and is conducive to improving the hemming property. The crack propagation of the 6016 aluminum alloy at the intermediate annealing temperature of 410 ℃ is faster than that at the intermediate annealing temperature of 360 ℃, which is related to the coarse Mg₂Si phase on the grain boundaries.

Bauschinger effect and recovery heat treatment of 10CrNi8MoV steel

Guo Haodong, Yang Chaofei, Sun Lei, Zhang Yuxiang, Huang Dong, Tong Zhiyuan

2024, 49(8): 119-123. doi:10.13251/j.issn.0254-6051.2024.08.019

Abstract ( 15 )

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Bauschinger effect of quenched-and-tempered 10CrNi8MoV steel was studied at unidirectional tensile deformation of 0.5%-5%. The results show that the yield strength of the tested steel decreases rapidly in reverse compression test when the deformation is less than 1%, and the rate of decrease becomes slower when the deformation is greater than 1%. The Bauschinger effect is mainly attributed to the back stress generated during tensile deformation, and the magnitude of the back stress is mainly related to the initial dislocation density and the ability of the material to accommodate new dislocations. When tempered at 400-600 ℃ for 1.5 h, the back stress is released, which significantly improves the Bauschinger effect of the tested steel.

Effect of solution treatment temperature on microstructure and properties of ultra-low carbon 15-5PH precipitation hardened stainless steel

Xu Feng, Sun Qiang, Meng Jiwei

2024, 49(8): 124-129. doi:10.13251/j.issn.0254-6051.2024.08.020

Abstract ( 28 )

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Effect of solution treatment temperature(975, 1000, 1025 and 1050 ℃) on the microstructure and mechanical properties of a 15-5PH precipitation hardened stainless steel with ultra-low carbon (w(C)≤0.01%) was investigated. The microstructure of the tested steel solution treated at different temperatures was observed by metallographic microscope, the room temperature tensile properties and impact absorbed energy of the tested steel solution treated at different temperatures were determined, and the fracture morphologies of the tensile specimens and impact specimens were observed by scanning electron microscope. The results show that when the solution treatment temperature is increased from 975 ℃ to 1050 ℃, the average grain size of the tested steel grows from 27 μm to 150 μm, the elongation decreases from 14.5% to 8.5%, the reduction of area decreases from 55% to 32%, and the impact absorbed energy decreases from 35.6 J to 6.6 J, however the change of its strength is not obvious.

Continuous annealing process of 430 stainless steel

Yang Yongchao, Li Yugui, Zhao Zijun

2024, 49(8): 130-135. doi:10.13251/j.issn.0254-6051.2024.08.021

Abstract ( 23 )

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Annealing of 430 stainless steel hot rolled plate is generally carried out in the bell-type furnace, which has a long production cycle and seriously restricts the improvement of production capacity. Experimental research was conducted on the continuous annealing process of the 430 stainless steel hot rolled plates through optimization of chemical composition and annealing process. The results show that under laboratory conditions, the optimal heat treatment process of the 430 stainless steel is annealing at 880 ℃ and holding for 240 s. Austenite transformation occurs when annealed at 910 ℃. Based on the actual production conditions, the heat treatment temperature range for the annealing and pickling production line can be set to (880 ± 5) ℃. The strip structure of the hot rolled 430 stainless steel cannot be completely eliminated after continuous annealing. After cold rolling, finishing annealing and pickling, the elongation of the tested steel reaches over 26%, which can meet the usage needs of the shallow stamping industry.

Effect of heat treatment on microstructure and mechanical properties of 09MnNiDR low temperature steel welded joint

Zhang Yong, Li Ruyang, Ma Qingshan, Hu Xiaodong

2024, 49(8): 136-142. doi:10.13251/j.issn.0254-6051.2024.08.022

Abstract ( 22 )

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Microstructure, tensile properties and low-temperature impact properties of a 12 mm thick 09MnNiDR steel submerged arc welding butt welded plate were analyzed by means of optical microscope, tensile testing machine, impact testing machine and micro Vickers hardness tester after annealing, normalizing and normalizing+tempering treatments. The results show that normalizing treatment can improve the strength of the 09MnNiDR steel welded joints, but compared with stress relief annealing, it reduces the toughness. After normalizing and tempering treatment, the welded joint has good plasticity and toughness, which is related to the decomposition of M/A components at the weld seam and the evolution of granular bainite in the heat affected zone. Under three heat treatment methods (annealing, normalizing, normalizing+tempering), the M/A components at the weld seam are decomposed to varying degrees, resulting in an increase of impact absorbed energy. The impact absorbed energy after normalizing and tempering is the highest, increasing by 84% compared to the welded. Compared with the welded joint, normalizing slightly increases the hardness of the weld zone and heat affected zone, while annealing and normalizing + tempering make the hardness reduce. The granular bainite in the heat affected zone after normalizing is beneficial for improving hardness, while the more uniform microstructure after tempering makes the welded joint obtain better toughness.

Effect of tempering time on microstructure and properties of low welding crack sensitivity pressure vessel steel

Liu Chenxi, Hu Xinming, Ouyang Xin, Xing Mengnan, Bai Yunfeng

2024, 49(8): 143-146. doi:10.13251/j.issn.0254-6051.2024.08.023

Abstract ( 21 )

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Effect of tempering time on the microstructure and properties of a low welding crack sensitivity pressure vessel steel with designed chemical composition was studied using metallographic microscope, scanning electron microscope, transmission electron microscope, tensile testing machine, impact testing machine and hardness tester, etc. The tested steel was quenched at 950 ℃ after rolling and tempered at 610 ℃ for 12, 23, 45 and 180 min, respectively. The results indicate that the microstructure after quenching and tempering is mainly composed of tempered sorbite. With the increase of tempering time, the intragranular dislocation density decreases, and lath grains with different orientations are generated, and carbides are precipitated along the grain boundary, which ensures that the steel plate has a good low welding crack sensitivity. As the tempering temperature increases, the strength decreases first and then increases due to the influence of intragranular dislocation density and carbides of Nb and V elements, while the impact property and hardness are basically decreasing due to the precipitation of carbides M₂₃C₆.

Effect of simulated post weld heat treatment on microstructure and properties of thick gauge 16MnDR steel plate

Qu Zhiguo, Zhang Wanxin, Bai Xuefei, Wang Dongming, Zhang Youjian

2024, 49(8): 147-151. doi:10.13251/j.issn.0254-6051.2024.08.024

Abstract ( 15 )

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Simulated post weld heat treatment (PWHT) at 590 ℃ for different holding time (135, 405 min) was conducted on a 55 mm thick 16MnDR steel plate as-normalized and the effect of simulated PWHT on the microstructure and mechanical properties of the plate was studied. The results show that as the holding time of simulated PWHT increases, the strength of the normalized steel plate increases first and then decreases, but the overall change amplitude does not exceed 10 MPa. The impact absorbed energy at 1/4 and 1/2 thickness of the steel plate shows different trends, which decreases monotonically at 1/4 thickness, while increases first and then decreases at 1/2 thickness. After the simulated PWHTs, there are no significant change in the microstructure of the steel plate compared to the normalized state, which remains ferrite+pearlite, but the lamellar cementite gradually transforms into spherical or punctate cementite. The number of precipitated carbides in the steel increases with the increase of holding time, but the growth trend is not obvious, and the precipitation of cementite along grain boundaries is the main reason for the reduction of impact absorbed energy.

Improvement of carbonitriding process for bearing rings

Zhou Ruihu, Fan Qigang, Zeng Zhipeng

2024, 49(8): 152-155. doi:10.13251/j.issn.0254-6051.2024.08.025

Abstract ( 30 )

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To address the issues of coarse surface structure and high scrap rate of high carbon chromium bearings after conventional carbonitriding treatment, improvements were made to the existing process. On the basis of the original carbonitriding + quenching and tempering process, an air cooling process was added after carbonitriding. The results show that the improved process effectively resolves the contradiction between the depth of infiltration layer and the level of microstructure, and improves the level of the martensite. Compared with the conventional carbonitriding process, the improved process results in smaller size distortion of the bearing inner ring, satisfactory surface microstructure and hardness, and the fatigue life of 5.5L₁₀.

Fixture induction hardening of bearing ring

Zhao Xiuhua, Zhang Chunbao, Wang Peizhang, Shen Guoli, Liu Rongge

2024, 49(8): 156-159. doi:10.13251/j.issn.0254-6051.2024.08.026

Abstract ( 21 )

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Aiming at the current situation of large distortion, difficult control of ellipticity, and high scrap rate after conventional quenching of carburized bearing rings, especially the outer ring of tapered roller bearings, a fixture induction hardening process equipment was proposed. It can not only correct the severe out of round of bearing ring after carburization, but also perform mold pressing hardening at the same time. The mass production test of the tapered roller bearing ring with an outer diameter of 72.25 mm was carried out. The results show that the elliptical distortion is limited to 0.09 mm, and the end face warping is limited to 0.03 mm. The microstructure, hardness and hardened layer depth can all meet the relevant requirements of JB/T 8881—2020, which can bring significant economic benefits to users.

Effect of quenching process on microstructure and hardness of 28MnCrMoRE oil well pipe steel

Sun Zhaoqi, Li Tao, Han Qiang, Zhang Xinggang, Bai Yansong, Gao Zhimin

2024, 49(8): 160-164. doi:10.13251/j.issn.0254-6051.2024.08.027

Abstract ( 22 )

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Taking 28MnCrMoRE steel oil well pipe as the research object, the effect of quenching process on microstructure and hardness of deep well oil well pipe was explored. The prior austenite grains after quenching were observed by using metallographic microscope, and the prior austenite grain size was obtained by Image-ProPlus software. The microstructure after quenching was observed and analyzed by using SEM. The hardness was measured by using Rockwell hardness tester. The results show that the average size of prior austenite grains increases from 8.21 μm to 12.67 μm in the 28MnCrMoRE steel after holding at 870, 900 and 930 ℃, respectively, for 30 min then water quenching. When quenched at 900 ℃ for 90 min, there is a significant abnormal growth of the prior austenite grains, when held for 30 min, the prior austenite grains in the tested steel are relatively small and uniform, and the grain size conforms to a normal distribution. The quenched microstructure of the 28MnCrMoRE steel is martensite + bainite + retained austenite. With the increase of quenching temperature or the extension of holding time, the content of martensite gradually decreases, the microstructure has a certain degree of coarsening, and the hardness of the tested steel first increases and then decreases, with a maximum value being 53.02 HRC.

Microstructure and properties of low carbon corrosion-resistant die steel 0Cr13NiN

Chen Jianli, Chu Baoshuai, Zhao Zhigang

2024, 49(8): 165-169. doi:10.13251/j.issn.0254-6051.2024.08.028

Abstract ( 14 )

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Microstructure and properties of low carbon corrosion-resistant die steel 0Cr13NiN under different heat treatment states were studied, and the mechanical properties and pitting resistance were compared with pre-hardened corrosion-resistant die steel 4Cr13. The results show that the annealed microstructure of the 0Cr13NiN steel is mainly composed of ferrite and carbides. Compared to pre-hardened 4Cr13 steel, pre-hardened 0Cr13NiN steel has better pitting resistance and toughness. The recommended pre-hardening heat treatment process for the 0Cr13NiN steel is quenching temperature of 980-1030 ℃, tempering temperature of 520-540 ℃, and tempering twice. The quenched microstructure is martensite +undissolved carbonitride + a small amount of retained austenite, and the tempered microstructure is tempered martensite +primary carbonitride + carbonitride.

Effect of quenching temperature on microstructure and hardness of 4Cr4Mo3W2V1 die steel

Liu Zifeng, Zhao Xuliang, Luo Hao

2024, 49(8): 170-173. doi:10.13251/j.issn.0254-6051.2024.08.029

Abstract ( 19 )

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Effect of quenching temperature (990-1070 ℃) on microstructure and hardness of 4Cr4Mo3W2V1 die steel was studied by means of OM, SEM and Rockwell hardness tester. The results show that the microstructure of the quenched 4Cr4Mo3W2V1 steel is mainly martensite, bainite and undissolved carbide. With the increase of quenching temperature, the grain size of the steel increases continuously, the number of carbides in the microstructure decreases continuously, and the hardness increases first and then decreases. Quenched at 1050 ℃, the carbide in the microstructure is basically dissolved into the matrix, the volume fraction of carbide is 0.41%, the grain size does not grow significantly, and the hardness reaches the maximum of 61.4 HRC. 1050 ℃ is the ideal quenching temperature for the 4Cr4Mo3W2V1 steel.

Effect of annealing temperature on microstructure and mechanical properties of Fe-0.12C-4.85Mn-0.24Si steel for automobile back door panels

Liang Ke, Wu Meng, Zhang Xiye, Xing Zhigang

2024, 49(8): 174-177. doi:10.13251/j.issn.0254-6051.2024.08.030

Abstract ( 16 )

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Effect of different temperatures annealing in the two-phase region on the microstructure and mechanical properties of Fe-0.12C-4.85Mn-0.24Si steel was studied using scanning electron microscopy, universal testing machine, X-ray diffraction instrument. The results show that with the increase of annealing temperature, the grain size of the Fe-0.12C-4.85Mn-0.24Si steel gradually increases, carbides gradually dissolve, and the volume fraction of austenite in the microstructure first increases and then decreases. The Fe-0.12C-4.85Mn-0.24Si steel annealed at 640 ℃ has the highest austenite volume fraction of 22.1%. As the annealing temperature increases, the tensile strength of the Fe-0.12C-4.85Mn-0.24Si steel gradually increases, and the product of elongation and strength first increases and then decreases. The elongation and product of strength and elongation of the Fe-0.12C-4.85Mn-0.24Si steel annealed at 640 ℃ are the highest, which are 30.4% and 28.47 GPa ·%, respectively.

Second phase precipitation of high nitrogen austenitic stainless steel for retaining ring

Zhang Ronghua, Song Wenzhi, Zhao Fuqiang, Zhang Shizhe, Liu Qian

2024, 49(8): 178-182. doi:10.13251/j.issn.0254-6051.2024.08.031

Abstract ( 15 )

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Second phase precipitation process of high nitrogen austenitic stainless steel was studied by XRD, OM, SEM and TEM. The morphology and the type of precipitated phases were analyzed and determined. The experimental results show that the microstructure of the solution treated specimen is composed of single-phase austenite grains and partial twins. After aging at 800-1040 ℃ for 2 h, Cr₂N precipitates in the steel, and the number of Cr₂N increases first and then decreases, which reaches the peak at 860 ℃. The precipitated phases of the tested steel are mainly carbide, nitride and intermetallic compound σ phase. Aged at 800 ℃, the intermetallic compound σ phase is precipitated, and M₂₃C₆ carbide is precipitated at 860 ℃. Only Cr₂N is precipitated after aging at 920 ℃, and MX phase is precipitated at 1040 ℃.

Effect of Ti-modified plasma nitriding on properties of precipitation-hardened steel

Li Feng

2024, 49(8): 183-188. doi:10.13251/j.issn.0254-6051.2024.08.032

Abstract ( 17 )

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Plasma nitriding treatment for precipitation-hardened steel 20CrNi3Mn2Al was carried out with or without Ti (nitriding at 540 ℃ for 48 h with the infiltration agent of thermal decomposition NH₃). Then the hardness, effective nitrided layer depth, friction and wear performance, and corrosion performance of the nitrided layer after plasma nitriding were compared and analyzed, and the effect of Ti-modified plasma nitriding on properties of precipitation-hardened steel was studied. The results show that compared with conventional ion nitriding, the effective nitrided layer depth of Ti-modified ion nitriding specimen is increased by about 15%, and the hardness gradient is smoother. The maximum depth of scratches after friction and wear is 8.894 μm, and the depth of pits after corrosion is about 9 μm, which is reduced by about 45% and 36% compared to conventional plasma nitriding specimen, respectively. The wear resistance and corrosion resistance are significantly improved.

Improvement of carburizing and quenching process for 20Cr2Ni4A steel steering gear

Zhao Hourui, Liu Ke, Fan Pengyu, Ouyang Xuemei, Yang Bing, Zhai Pengyuan

2024, 49(8): 189-194. doi:10.13251/j.issn.0254-6051.2024.08.033

Abstract ( 26 )

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Aiming at the problem of excessive plane warping of 20Cr2Ni4A steering gears after carburizing and quenching, the optimization of the pressure quenching process was guided by finite element simulation carburizing and quenching simulation, and experimental verification was carried out. The results show that the loading method, machining allowance, and quenching pressure have a significant impact on the stress and distortion fields during the carburization and quenching process of the steering gear. The distortion is smaller when using hanging loading than flat loading. Increasing the thickness of the web plate can reduce the distortion. When the web plate thickens to 18 mm, the ellipticity after carburization can be controlled to 0.19 mm. When the outer ring pressure of pressure quenching is 3 MPa, the ellipticity after quenching can be controlled to 0.16 mm.

Single-phase Fe₂B layer prepared by variable electric field assisted pack-boriding at low temperature

Ding Hongzhen, Li Hang, Qiu Wanqi

2024, 49(8): 195-199. doi:10.13251/j.issn.0254-6051.2024.08.034

Abstract ( 13 )

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Using α-Al₂O₃ powder as boriding filler and 2% activated carbon as additive, the variation of boriding current was investigated under a constant AC electric field assisted pack-boriding carried out on 40CrNiMo steel. By adjusting the AC electric field voltage to obtain stable low temperature boriding temperature, a borided layer was prepared on the surface of 40CrNiMo steel and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and microhardness tester. The results show that a stable conductor is created as a result of activated carbon adhering to the Al₂O₃ powder's surface, which stabilizes the boriding current at different stages of the electric field assisted pack-boriding, resulting in a relatively stable boriding temperature. A dense single-phase Fe₂B borided layer on the surface of 40CrNiMo steel can be prepared by adjusting the electric field voltage to control the actual boriding temperature at a lower temperature (650, 680, 700 ℃). The SEM observation shows that the thickness of the borided layer is ≥13 μm. The surface hardness of the borided layer is relatively high and can reach about 1200 HV0.05 even at 650 ℃.

Homogenization for 3105 aluminium alloy ingots

Wang Gang, Yang Shunming, Kuang Guanghui

2024, 49(8): 200-203. doi:10.13251/j.issn.0254-6051.2024.08.035

Abstract ( 19 )

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Different homogenization processes were applied to 3105 aluminum alloy ingots, and microstructure, conductivity and hardness were tested. The results show that the precipitation of solute atoms and the redissolution of compounds occur simultaneously in the 3105 aluminum alloy during the homogenization process. The optimum homogenization process is 630 ℃×9 h. Under this process, the alloy has the lowest conductivity (22 MS/m), as well as a relatively high solid solubility, which is conducive to the subsequent product performance enhancement. The hardness is also the lowest (36.94 HV5), which can better satisfy the demand of low deformation resistance for extrusion hot working.

Quenching uniformity control techniques of high-pressure gas quenching for multiple large thin-wall cylindrical parts

Li Chuang, Li Qiong, Zhan Yuheng, Cong Peiwu, Lu Wenlin, Yao Jiawei, Han Yongzhen

2024, 49(8): 204-210. doi:10.13251/j.issn.0254-6051.2024.08.036

Abstract ( 18 )

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High-pressure gas quenching process of large thin-wall cylindrical parts under multi-piece loading conditions was investigated by establishing a suitable three-dimensional physical model and control equations. According to the numerical simulation results of the flow field and temperature field in the furnace under different loading conditions, it is found that addition of suitable deflector plate can effectively improve the flow field in the furnace, and enhance the homogeneity of the temperature field of the workpieces in condition of meeting the quenching and cooling demand, during the process of gas quenching. The method can be used to solve the non-uniform cooling problem, which exists in the gas quenching of multiple pieces at the same time. Finally, the correctness of the simulation results is verified through experiments, which provides a feasible path for the optimization of the high-pressure gas cooling system, and also provides a theoretical basis for the future improvement of the gas quenching effect of large-scale vertical vacuum gas quenching equipment.

Numerical simulation and experimental verification on heat-flow coupling during laser cladding of 420 stainless steel

Du Maohua, Zhang Zhenxin, Bi Guijun, Cao Lichao

2024, 49(8): 211-219. doi:10.13251/j.issn.0254-6051.2024.08.037

Abstract ( 14 )

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Influence of the main process parameters (laser power, scanning speed, powder feeding rate) on the molten pool temperature and the geometry of single track clad layer during laser cladding on 420 stainless steel, as well as the variation of temperature, temperature gradient and flow rate at different positions of the clad layer were studied. A heat-flow coupled 3D transient numerical model for laser cladding of 420 stainless steel powder on Q235 carbon steel substrate was established to simulate the forming process of laser cladding. The buoyancy force, Darcy resistance and Marangoni effect driven by surface tension in the molten pool were considered. The apparent heat capacity method was used to consider the latent heat of the material phase transition. The arbitrary Lagrangian-Eulerian (ALE) method was used to trace the free surface of the molten pool and simulate the growth of the molten pool. The results show that the molten pool temperature increases with the increase of laser power and powder feeding rate, but decreases with the increase of scanning speed. The process parameter that has the greatest influence on the clad layer width is the laser power and when it increases from 800 W to 1000 W, the cladding width increases by 175.4051 μm. The powder feeding rate has the greatest influence on the height and depth of clad layer. The powder feeding rate increases from 1.49 g/min to 3.17 g/min, the clad layer height increases by 309.8188 μm, while the clad layer depth decreases by 152.0495 μm. Under different laser cladding process parameters, the hardness from the top to the bottom of the clad layer decreases continuously. The experimental results show that the model can accurately predict the laser cladding process with different process parameters.

Numerical simulation of low pressure carburizing process for 20CrMnTi steel

Deng Xiaohu, Song Wenjuan, Fan Yuanyuan, Guo Jingyu, Wang Huizhen, Zhou Leyu, Xu Yueming, Ju Dongying

2024, 49(8): 220-224. doi:10.13251/j.issn.0254-6051.2024.08.038

Abstract ( 22 )

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Based on the principle of multiple factors such as temperature, diffusion, phase transformation and stress, finite element simulation technology was used to simulate and analyze the carburizing process of 20CrMnTi steel under low pressure environment. The simulation process fully considered the boundary condition characteristics of the alternating strong infiltration and diffusion in the low pressure carburizing process, and the strong infiltration and strong infiltration+diffusion were simulated separately, the carbon concentration, martensite volume fraction and hardness distribution were obtained. The results indicate that as the diffusion time increases, the surface carbon concentration of the specimen decreases and the depth of the carburized layer increases. The simulation results of carbon concentration distribution after carburizing are in good agreement with the experimental results, indicating high simulation accuracy. The volume fraction of martensite and hardness of the carburized layer after low pressure carburizing under strong infiltration+diffusion process are simulated, and the distribution of the two is consistent. Comparing the simulation and experimental results of hardness of the specimen after low pressure carburizing under strong infiltration + diffusion process, the measured value is slightly higher than the simulated value, because the simulation result is the calculated average of a larger area.

Numerical simulation on induction hardening of Cr12MoV die steel based on electromagnetic thermal coupling

Liu Shouhe, Yi Jianye, Xie Hui

2024, 49(8): 225-231. doi:10.13251/j.issn.0254-6051.2024.08.039

Abstract ( 17 )

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Finite element numerical simulation method was adopted to study the effects of power frequency, current density and induction coil moving speed on surface temperature field of the workpiece during induction hardening for the Cr12MoV die steel. According to Maxwell's equations and non-stationary thermal conductivity differential equations, a moving dual-loop induction coil model coupled with electromagnetic field and temperature field was established, by which the temperature field on surface of the workpiece was calculated. And the simulation results were verified by induction hardening experiments. The results show that the temperature rising curve at the center of the workpiece surface is a bimodal curve. The rate and amplitude of temperature rising increase with the increase of power frequency and current density, while decrease with the increase of induction coil moving speed. Through the hardness analysis in the thickness direction of the workpiece after hardening, it is found that the depth of the high-temperature region obtained by simulation calculation is roughly consistent with the depth of the hardened layer. The temperature rising curve measured in experiments basically matches the numerical simulation results, with a maximum error of about 7%, which shows that the process parameters for practical application can be optimized by numerical simulation method, realizing the precise control of depth of hardened layer and hardness of the workpiece after hardening.

Computational method for unsteady heat transfer on surface of 45 steel during laser quenching

Zhang Wen, Guo Yutong, Zhang Lingcong, Shen Rui, Shi Hui, Bao Hanwei, Li Gangyan

2024, 49(8): 232-241. doi:10.13251/j.issn.0254-6051.2024.08.040

Abstract ( 16 )

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Temperature distribution of unsteady heat transfer during laser quenching of 45 steel was obtained by solving an explicit two-dimensional finite difference equation, and the effect of laser power on the surface temperature after single pass laser quenching was analyzed. Utilizing JMatPro, comprehensive phase transformation curves, as well as temperature-dependent thermophysical properties and phase transformation critical temperatures during heating and cooling processes of the material, were derived. Incorporating both the laser heat source and latent heat of phase transformation, a unsteady heat transfer model for the surface laser quenching of 45 steel was established. This model was then employed to conduct heat transfer analysis under both fixed and moving heat source conditions during laser quenching. The results show that the error of the maximum temperature calculation under fixed heat source condition is within 7%. When the laser irradiation time is 0.5 s and the power is between 1300 W and 2600 W, the surface temperature of the specimen can be effectively controlled between 720 ℃ and liquidus 1495 ℃, ensuring the occurrence of solid phase transformation during laser quenching process. The model is applied to single pass moving heat source laser quenching at high power, which can better reflect the actual temperature change trend.

Numerical simulation and microstructure analysis of post-weld heat treatment for TC4 titanium alloy

Xie Benchang, Liu Xinyu, Zhang Le, Chen Yanzi, Cen Yaodong, Chen Lin

2024, 49(8): 242-247. doi:10.13251/j.issn.0254-6051.2024.08.041

Abstract ( 21 )

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Ansys software was used to simulate the welding and post-weld heat treatment(PWHT) process of the TC4 titanium alloy, and the changes of microstructure and residual stress of the welded and heat treated alloy were analyzed. The results show that during the welding process, the temperature of each layer of the weld varies due to different heat inputs. The peak temperature of the first layer weld is the lowest (2183.6 ℃), and the fifth layer is the highest (2337.8 ℃). Due to the different characteristics of thermal cycles experienced by each layer, the size of martensite in each layer of the weld zone changes from 19.5 μm to 96.2 μm. The weld zone after welding is mainly composed of α_m phase, a small amount of β phase, some α_t phase and precipitated α_g phase. After the PWHT, the α_m phase in the joint transforms into a secondary (α+β) phase, and it is XRD observed that the (0002)_α diffraction peak undergoes peak splitting, a new peak (110)_β appears at 2θ=39.6°, the full width at half maximum decreases by 5.56%-43.75%, indicating that the crystallinity of TC4 titanium alloy is improved with the elimination of residual stress. The residual stress after welding is mainly concentrated near the weld seam, which is a fracture prone location. The residual stress along the direction perpendicular to welding is symmetrically distributed, which is basically the same as the distribution of temperature field. After the PWHT, all the residual stresses are reduced.

Three-dimensional reconstruction of grain structure of a 0.2%C unalloyed steel annealed at different temperatures

Li Zihao, Huang Suxia, Zhang Bohan, Li Hezong, Cao Chenglong, Zhao Jinsong

2024, 49(8): 248-253. doi:10.13251/j.issn.0254-6051.2024.08.042

Abstract ( 18 )

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In order to investigate the grain characteristics of an unalloyed steel with 0.2%C annealed at different temperatures, the grains were studied by three-dimension (3D) reconstruction and geometric characterization based on serial cross-sectioning (SCS) method. Based on 132 two-dimensional metallographic cross section images with a size of 880 μm×390 μm, 298 and 446 grains of the steel annealed at 1100 ℃ and 1000 ℃, respectively, were reconstructed. A detailed flow of image processing and 3D reconstruction was established, and a 3D visual grain model was constructed. The results show that the 3D model constructed can be viewed at any directions in the 3D space, and the volume and surface area of individual grains can be obtained. The grain size is calculated according to the equivalent sphere volume (ESV) method, and compared with the grain size measured by the intercept method, showing that the grain size measured by the intercept method is larger than that by the ESV method. The higher the annealing temperature, the larger the maximum and average grain sizes of the specimen under the same annealing time.

Development and application of intelligent manufacturing system forheat treatment workshop

Chu Xizheng, Deng Xiaohu, Guo Jiayi, Wang Xuerui, Xiao Feng, Xu Wangli

2024, 49(8): 254-260. doi:10.13251/j.issn.0254-6051.2024.08.043

Abstract ( 19 )

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In order to improve the intelligence level of the heat treatment workshop and address the issues of backward workshop management and "isolated data island", the intelligent manufacturing system for the heat treatment workshop was designed and developed by taking into account the discrete production characteristics of the workshop. The results show that, by adopting the information technology to manage the entire workshop production process, the intelligent manufacturing system realizes the functions such as sharing workshop production information, ensuring transparent and controllable execution processes, and enabling the traceability of production history. Secondly, the system achieves the goals of equipment management, safe production and abnormal warning for the workshop by establishing a digital model, binding and storing real-time data, and meanwhile introducing the concept of safety and environmental protection in the design. Finally, based on the comprehensive workshop data, the data analysis technology is used to automatically calculate and analyze the energy consumption costs and working efficiency of each piece of equipment in the workshop, enabling the refined management of each indicator in the workshop. After the successful implementation of this system in the workshop, it improves the management of workshop production and equipment, enhances the intelligent level of the workshop, and provides supports for green manufacturing, energy conservation and emission reduction in the heat treatment workshop.

Electrochemical corrosion behavior of FeCoCrNiMoBSi high-entropy alloy coating prepared by laser cladding

Du Xinyu, Zhai Changsheng, Rong Haisong, Xie Fang, Zheng Hongxing, Zhang Xi, Zhang Xin, Liu Gang

2024, 49(8): 261-267. doi:10.13251/j.issn.0254-6051.2024.08.044

Abstract ( 21 )

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FeCoCrNiMoBSi high-entropy alloy (HEA) coating was fabricated on the 316L stainless steel substrate via laser cladding. The microstructure, electrochemical corrosion and immersion corrosion properties of the HEA coating in H₂SO₄ solution were investigated. The results show that the laser clad HEA coating exhibits a bilayer structure, consisting of a columnar crystal at the bottom and an equiaxed crystal at the top. In the 0.3 mol/L H₂SO₄ solution, the self-corrosion potential, self-corrosion current density and polarization resistance of the HEA coating are 0.091 V, 11.499 μA/cm² and 9839.90 Ω, which are 2.12 times, 6.17% and 12.2 times, respectively, of the 316L stainless steel substrate. The HEA coating exhibits larger capacitance arc radius and impedance modulus value. Additionally, in the 50% H₂SO₄ solution, the corrosion rate of the HEA coating is lower, approximately 0.098 mg/(dm²·d), 316L stainless steel substrate shows conspicuous heterogeneous corrosion, whereas the corrosion surface of the HEA coating remains uniformly flat, showing homogeneous corrosion rate. The comprehensive results show that the corrosion resistance of the FeCoCrNiMoBSi high-entropy alloy coating on the 316L stainless steel substrate is significantly better than that of the substrate itself.

Effect of substrate surface rust on hot-dip galvanized and galvannealed coatings

Li Shanshan, Jin Xinyan

2024, 49(8): 268-274. doi:10.13251/j.issn.0254-6051.2024.08.045

Abstract ( 17 )

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Annealing and hot-dip galvanizing simulations were conducted on the cold-rolled IF steel sheet with localized surfacerust by using IWATANI hot-dip galvanizing simulator. Effects of substrate surface rust on annealed, hot-dip galvanized (GI) and galvannealed (GA) coatings were studied. The results show that after continuous annealing in an atmosphere of N₂+5% H₂ at 800 ℃, the rust is reduced to reduced iron with small grains, loose structure and numerous micropores between each other. During hot-dip galvanizing, the reduced iron rapidly diffuses with the molten zinc, causing the appearance of a zinc iron alloy phase in the coating and reducing the fluidity of the molten zinc, which further affects the control of the coating thickness when the specimen passes through the air knife, resulting in localized thickening of the GI coating at the rust location. After coating alloying, the morphology of the GA coating at the rust position is completely different from that of the normal coating, that is, the coating is flat and thick, and ultimately shows as white spot defects on the surface of the GA coating.

Effect of heat treatment process on microstructure and surface oxides of zinc coating galvanized on 22MnB5 hot formed steel

Zhao Jingxuan, Liang Jian, Zhang Lingling, Fan Longlong, Xiong Ziliu, Shen Chunguang, Miao Bin, Zheng Shijian

2024, 49(8): 275-280. doi:10.13251/j.issn.0254-6051.2024.08.046

Abstract ( 12 )

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Microstructure and surface oxide distribution of the galvanized layer of 22MnB5 hot formed steel were systematically characterized by scanning electron microscope (SEM) and energy dispersive spectroscope (EDS) at different austenitizing temperatures and holding time. The results show that when the austenitization temperature exceeds 850 ℃, the thickness of the galvanized layer increases, and a microstructure transformation occurs from pure Zn phase to α-Fe(Zn), and the interface with the matrix is blurred. As the austenitizing temperature rises from 850 ℃ to 900 ℃, the thickness of the zinc layer grows with the increase of temperature, and the zinc oxide particles become denser, interconnecting and agglomerating. When the austenitization temperature exceeds 900 ℃, large-sized Mn-rich oxides begin to emerge within the galvanized layer. When the austenitization time extends from 4 min to 8 min (austenitization temperature of 920 ℃), the degree of surface oxidation increases, the oxides increase in size and connect to each other in layers, resulting the α-Fe(Zn) layer being exposed and reducing the protective effect on the zinc layer, causing oxygen atoms to diffuse into the interior of the zinc layer to form Mn-rich oxides.

Brittle fracture characteristics and fracture behavior of hot rolled 60Si2Mn strip steel

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

2024, 49(8): 281-288. doi:10.13251/j.issn.0254-6051.2024.08.047

Abstract ( 20 )

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Decarburization, inclusions, segregation and brittle fracture of hot rolled 60Si2Mn steel strip were analyzed by means of optical microscope, scanning electron microscope and electronic tensile testing machine. Microstructure and mechanical properties of the specimens near the brittle fracture and away from the fracture were characterized, and the brittle fracture characteristics and fracture behavior of hot rolled 60Si2Mn steel strip were investigated. The results show that there is no obvious decarburization, inclusion and segregation at the brittle fracture, and the fracture presents brittle fracture. The content of proeutectoid ferrite in the specimens near the brittle fracture and away from the fracture is 12.45% and 0.66%, respectively, and the pearlite lamellar spacing is 578 nm and 236 nm, respectively. The main cause of brittle fracture of hot rolled 60Si2Mn steel strip is that the content of proeutectoid ferrite in the brittle fracture is higher than that in the position away from the fracture, and the pearlite lamellar spacing is larger, which leads to poor resistance to deformation and is prone to uneven deformation during the rolling process. Additionally, the stress difference between the coarse ferrite and cementite layers can easily lead to brittle fracture, and the cracks propagate along the two-phase interface. However, the plastic deformation of fine pearlite is relatively uniform, and cracks propagate through the layers of pearlite.

Cause analysis and solution of crack of hydraulic support column cylinder

Cui Leilei, Ma Ke, Lan Zhiyu, Wang Piaoyang, Deng Xiangtao

2024, 49(8): 289-294. doi:10.13251/j.issn.0254-6051.2024.08.048

Abstract ( 19 )

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Cracks in cylinder of a large hydraulic support column during service were analyzed by means of mechanical property detection, microstructure analysis and crack morphology characterization. The results show that the cracking of the cylinder of hydraulic support column is not directly related to the microstructure and properties of the matrix material, but is caused by the cladding defects. The cracks occur at the interface of the stainless steel clad layer and the matrix, and then expand to the matrix side and the clad layer side under the action of long-term load, finally, resulting in cracking failure. By improving laser cladding parameters, laser cladding defects can be effectively avoided.

Cracking analysis of 34CrNi3MoV steel transmission spindle quenched and tempered

Li Ziyan, Xu Hongxiang, He Xiao, Liu Zhiqiang, Guo Jingqiang, Chen Shengchao, Lu Jinsheng

2024, 49(8): 295-300. doi:10.13251/j.issn.0254-6051.2024.08.049

Abstract ( 18 )

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After quenching and tempering, a longitudinal quenching crack was detected on the outer circular surface of the 34CrNi3MoV steel transmission spindle during the semi precision turning process. The chemical composition, hardness gradient, microstructure near the crack source and quenching medium were detected, and the macroscopic morphology characteristics of the crack surface were analyzed. Metallurgical microscope, SEM and EDS characterizations were conducted on the cross section of crack surface. The results show that the contents of carbon and nickel elements in the transmission spindle exceed the upper limit of the standard range, resulting in inappropriate quenching and tempering process parameters. However, the presence of microcracks before quenching and tempering in the transmission spindle is the main factor leading to cracking failure.

Failure analysis of 20CrMnTi steel rotary drilling rig square head

Zhang Junhua, Zhou Dapeng, Yu Yonghao, Kang Xueqin

2024, 49(8): 301-304. doi:10.13251/j.issn.0254-6051.2024.08.050

Abstract ( 25 )

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20CrMnTi steel rotary drilling rig square head was fractured after use for 30 days. Failure analysis was conducted through fracture morphology observation, chemical composition analysis, mechanical properties and microstructure analysis. The results show that both the design criterion and the heat treatment process are not so rational, which leads to decreased strength and hardness of the square head. Overload fracture is easy to occur at the stress concentration area of the square head under the action of torsional stress during the using. When the P element content exceeds the standard requirement, the material has a tendency towards cold brittleness, showing brittle fracture. The quality inspection of raw materials should be strengthened to meet the standard requirements. Quenching and low-temperature tempering should be adopted to ensure that the strength and hardness of the square head material meet the technical requirements.

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