Heat Treatment of Metals

Effect of Zn/Mg ratio on microstructure, mechanical properties and corrosion resistance of 7075 aluminum alloy

He Zongzheng, Wu Mingdong, Yuan Shuo, Yao Shuwei, Xiao Daihong, Huang Lanping, Liu Wensheng

2024, 49(5): 1-9. doi:10.13251/j.issn.0254-6051.2024.05.001

Abstract ( 144 )

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Effect of Zn/Mg ratio (mass fraction) on microstructure, mechanical properties, and corrosion resistance of 7075 aluminum alloys was investigated by means of optical microscope, scanning electron microscope, transmission electron microscope, tensile test, microhardness test and corrosion test. The results show that with the increase of Zn/Mg ratio from 1.76 to 2.90, the grain size of the as-cast alloy increases, the T6 age-hardening rate of the alloy is accelerated, and the time to reach peak hardness is shortened. The increase in Zn/Mg ratio results in a decrease in the recrystallization rate of the T6 peak-aged alloy and an increase in the percentage of the low-angle grain boundaries. The tensile strength of the alloy under the T6 peak-aging treatment with the Zn/Mg ratio of 2.10 is 634 MPa, the yield strength of the alloy is 588 MPa, and elongation is 8.4%. The tensile strength of the T74 aged alloy is 613 MPa, yield strength is 542 MPa, and elongation is 8.9%, and alloys with Zn/Mg ratio of 2.10 in both aging states exhibit good strength while maintaining high elongation. The corrosion resistance of the aged alloy decreases as the Zn/Mg ratio increases from 1.76 to 2.90. The corrosion resistance of the alloy after T74 aging treatment is better than that of the alloy under the T6 peak-aging state.

Comparison on microstructure and mechanical properties of TP347HFG steel tubes served for different terms

Bao Zheng, Cheng Xiang, Wang Ruomin, Miao Chunhui, Chen Guohong, Tang Wenming

2024, 49(5): 10-16. doi:10.13251/j.issn.0254-6051.2024.05.002

Abstract ( 42 )

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Microstructure and mechanical properties of the TP347HFG high-temperature reheater steel tubes were studied comparatively in supplied state and that serviced for about 50 000 h and 110 000 h at 600 ℃, respectively. The results show that for the TP347HFG steel tube serviced for 50 000 h, normal austenite grain growth takes place, and the accompanying precipitation of the tiny M₂₃C₆ particles leads to the increase of dispersion strengthening effect, resulting in the yield strength higher than that of the steel tube in supplied state. However, the microstructure of the TP347HFG steel tube serviced for 110 000 h is severely degenerated with some abnormally growing austenite grains. Moreover, the coarse M₂₃C₆ particles have an increased separation effect on grain boundaries, resulting in a significant decrease of mechanical properties at room temperature and high temperature. Moreover, with the service time increasing, the impact properties and plastic deformation characteristics at fracture of the TP347HFG steel tube are continuously degraded, and the effect of microstructure aging on mechanical properties of the TP347HFG steel tubes in service for different terms turns to be more pronounced.

Microstructure and properties of S30432 steel tube after long-term service at high temperature

Yang Xirui, Jiang Baoshi, Hu Fengtao, Li Yanjun, Sheng Chaojie, Wang Chen

2024, 49(5): 17-21. doi:10.13251/j.issn.0254-6051.2024.05.003

Abstract ( 50 )

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Microstructure and mechanical properties of the S30432 steel tube after high temperature service for 79 000 h in ultra supercritical units were studied by means of room temperature tensile and impact test, hardness test, high temperature tensile test, metallographic microscope, scanning electron microscope and energy dispersive spectrometer. The results show that the room temperature hardness and tensile strength of the 79 000 h long-term serviced S30432 steel tube increase, while the plasticity and toughness significantly decrease, the elongation is lower than the standard requirement. The tensile strength and plasticity at high temperature significantly decrease, and the tensile strength at 670 ℃ is lower than the standard extrapolation value. The microstructure of the tube material is seriously aged, and the twins disappear. Except for carbides such as NbC and M₂₃C₆, σ phases precipitate to varying degrees in the grain or at the grain boundary, which is the main reason for the significant decrease in plasticity, toughness and high temperature tensile strength.

Effect of V on microstructure and properties of Fe-rich non-equiatomic FeCrCoNi high-entropy alloy

Wang Shuliang, Mao Yidian, Li Qilin, Zhou Lujiang, Xi Yuchen, Zhang Huali

2024, 49(5): 22-28. doi:10.13251/j.issn.0254-6051.2024.05.004

Abstract ( 31 )

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FeCrCoNi high-entropy alloys were prepared using mechanical ball milling and discharge plasma sintering, the V element was introduced by decreasing the content of Co and Ni elements, and the effect of V on microstructure and mechanical properties of the Fe₄₅Cr₁₅Co₁₀Ni₃₀ alloy was investigated. The results show that the V-containing high-entropy alloys form V-rich BCC phases compared with the Fe₄₅Cr₁₅Co₁₀Ni₃₀ alloy, the morphology and distribution of the BCC phases change with the increase of V content. The yield strength and compressive strength of the Fe₄₅Cr₁₅Co_2.5Ni_22.5V₁₅ alloy reach the highest of 869 ± 8 MPa and 1675 ±5 MPa, respectively, and the strain rate of 46.1%±1.7%, also maintains a high level. The introduction of V effectively improves the hardness and compressive properties of the Fe₄₅Cr₁₅Co₁₀Ni₃₀ alloy, and the alloy with good strength and plasticity matching can be obtained.

Effect of copper content on morphology of sulfides and mechanical properties of 303 free-cutting steel

Wang Yinghu, Wang Enuo, Cai Xiaowen

2024, 49(5): 29-35. doi:10.13251/j.issn.0254-6051.2024.05.005

Abstract ( 34 )

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Influence of copper content on sulfide morphology and mechanical properties of 303 and 303Cu austenitic free-cutting steels was investigated by means of Thermal-Calc thermodynamic calculation software, scanning electron microscope(SEM), Phenom Particle X scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS). The results show that the proportion of sulfides with a length-width ratio ≤ 3 in the as-cast 303 steel is 94.75%, while in the as-cast 303Cu steel is 88.37%. Sulfides are predominantly spherical, ellipsoidal, spindle-shaped, or short rod-shaped and distributed along grain boundaries in clusters, characteristic of a type II sulfides. In the forged steels, sulfides are elongated along the forging deformation direction, with increased length-width ratio, dimensions, and decreased quantity per unit area. Thermal-Calc software calculations indicate that with copper content increasing, the precipitation temperature and content of sulfides increase. Additionally, the addition of copper leads to the precipitation of CuS, which reduces the mechanical properties of the material. The as-forged 303Cu steel exhibits a tensile strength of 582.5 MPa, yield strength of 363.7 MPa, and impact absorbed energy of 62.1 J, while the as-forged 303 steel shows superior comprehensive mechanical properties with a tensile strength of 821.9 MPa, yield strength of 410.4 MPa, and impact absorbed energy of 147.5 J. The tensile properties and impact absorbed energy of the as-forged steels are significantly improved compared to that of the as-cast steets, it indicates that forging deformation contributes to enhancing the mechanical properties of the 303 and 303Cu austenitic free-cutting steels.

Effect of multi-cycle closed die compression on microstructure and wear resistance of AZ31 alloy with different Si contents

Guo Wei, Guan Bo, Chen Wei, Wu Dan

2024, 49(5): 36-39. doi:10.13251/j.issn.0254-6051.2024.05.006

Abstract ( 33 )

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AZ31-2%Si alloy was prepared by adding Si to the AZ31 melt. AZ31 and AZ31-2%Si alloy were processed by multi-cycle closed die compression at high temperature, and the microstructure and wear resistance were studied. The results show that the as-cast AZ31 alloy is composed of Mg and Mg₁₇Al₁₂, while the as-cast AZ31-2%Si alloy is composed of Mg, Mg₁₇Al₁₂ and Mg₂Si. After five cycles compression at 400 ℃, grain of the AZ31 alloy is transformed from coarse equiaxed grain to fine recrystallized grain and Mg₁₇Al₁₂ phase is dissolved, and the vast majority of Mg₁₇Al₁₂ phase in the AZ31-2%Si alloy is dissolved into the matrix, the coarse Mg₂Si phase is broken into fine particles and dispersed around grain boundaries. After sliding friction for 2500 m, the wear loss of the as-cast and five cycles compressed AZ31 alloy is 26.4 mg and 22.1 mg, respectively. The wear loss of the as-cast and five cycles compressed AZ31-2%Si alloy is 22.7 mg and 21.0 mg, respectively. The main factor for improving of wear resistance of the AZ31 alloy after compression is grain refinement. The main factors for improving of wear resistance of the AZ31-2%Si alloy after compression are grain refinement, Mg₂Si phase refinement and its dispersive distribution.

Dissolution and precipitation law of carbides in 3Cr17NiMo corrosion-resistant plastic mold steel

Xia Yunfeng, Zhou Zhongcheng, Lei Xiaojuan, Yu Shenjun

2024, 49(5): 40-46. doi:10.13251/j.issn.0254-6051.2024.05.007

Abstract ( 33 )

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Dissolution and precipitation of carbides in 3Cr17NiMo corrosion-resistant plastic mold steel were studied by means of JMatPro simulation calculation software and experimental research. The experimental results show that when austenitized at 1140 ℃, the 3Cr17NiMo steel undergoes isothermal annealing within the range of 740-1040 ℃, the carbides first precipitate at austenite grain boundaries in the form of fine rods or needles, and gradually grow into obvious network structure as the temperature decreases, without any phenomenon of spheroidization precipitation. Once network carbides are formed in the steel, they are extremely difficult to dissolve and eliminate. When the solution temperature is 1100 ℃, the carbides distributed in needle or rod shape are significantly reduced. With the extension of solution time, the austenite grain gradually tends to be equiaxed grain distribution, and the grain begins to coarsen. When the solution time is more than 10 h, due to the phenomenon of recrystallization, the grains are refined instead. After double solution treatment at 1100 ℃ for 20-30 h and 1060 ℃ for 3 h, the morphology of network carbides in the 3Cr17NiMo steel can be effectively improved, and good microstructure with a uniform structure and refined grains is obtained.

Numerical simulation of laser hardening of 40Cr steel hob textured surface

Zhang Shuaikun, Zhang Chaoyong, Wu Jianzhao, Tang Limei

2024, 49(5): 47-54. doi:10.13251/j.issn.0254-6051.2024.05.008

Abstract ( 42 )

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Numerical simulation was conducted on the textured surface of 40Cr steel shield tunneling cutter after laser hardening. By simulating the temperature changes during laser hardening, the phase transformation caused by temperature changes during laser hardening was analyzed, as well as the formation mechanism of the laser hardened layer. The morphology of the hardened layer on the 40Cr steel shield tunneling cutter after laser hardening was observed. Friction and wear tests were projected on 40Cr steel, 40Cr steel shield tunneling cutter textured surface, and laser hardened 40Cr steel shield tunneling cutter textured surface to study their friction and wear properties. The results show that there is a parallel groove like texture on the surface of the 40Cr steel shield tunneling cutter. This texture and laser hardening can effectively improve the wear resistance of the cutter. After laser hardening, the textured surface of the shield tunneling cutter has the highest wear resistance, with a cross-sectional worn area of 47.3% of the textured surface of the shield tunneling cutter and 37.3% of the non textured surface of the 40Cr steel. The finite element numerical simulation is reliable and laser hardening can effectively improve the wear resistance of the shield tunneling cutter.

Numerical simulation and experimental verification of heat treatment after forging of SA508-3 steel for steam generator

Feng Xingwang, Zhang Ke, Liu Jiujiang, Shi Ruxing, Su Wenbo, Liu Shuai, Li Zhipeng, Yang Bin

2024, 49(5): 55-61. doi:10.13251/j.issn.0254-6051.2024.05.009

Abstract ( 32 )

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Taking SA508-3 steel forging for steam generator as research object, the thermophysical parameters for the steel were calculated by JMatpro software. After heat treatment, the microstructure and hardness of the forging were simulated by Deform-3D software. And the experimental verification was carried out by small specimen physical simulation method. The results show that the microstructure and hardness of both the experimental test and numerical simulation are in good agreement. It can be seen that numerical simulation technology is an effective tool to determine the rationality of heat treatment process for large forgings, which has significant value in shortening production cycle and reducing cost.

Numerical simulation on influence of post-weld heat treatment on residual stress in 150 mm thick vessel steel plate

Shi Hongchang, Huang Anming, Liu Xing, Qiang Bin

2024, 49(5): 62-67. doi:10.13251/j.issn.0254-6051.2024.05.010

Abstract ( 29 )

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Post-weld heat treatment (PWHT) can effectively reduce residual stress in welded joint. The residual stress field before and after PWHT for 150 mm thick vessel steel butt-welded joint was simulated by using finite element analysis. The evolution of residual stress during PWHT was systematically analyzed, and a comparative analysis was conducted on the residual stress relief effect of relevant PWHT process parameters. The results indicate that the PWHT significantly reduces the peak values of longitudinal and transverse residual stresses, but the impact on the distribution pattern of residual stress is relatively small. Stress relief primarily occurs during the heating stage of the treatment, with minimal relief or even rebound during the soaking and cooling stages. The analysis of process parameters reveals a nonlinear evolution of stress relief with changes in soaking time and heating temperature. Therefore, practical PWHT should consider the combined effects of influencing factors to optimize stress relief effectiveness and cost.

Numerical simulation of microstructure and distortion evolution behavior of C-type specimens during carburizing and quenching

Xu Yong, Liu Ke, Deng Yaoyao, Yang Bing, Lu Hailong, Luo Yi

2024, 49(5): 68-73. doi:10.13251/j.issn.0254-6051.2024.05.011

Abstract ( 32 )

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Taking C-type specimen of 18Cr2Ni2MoNbA steel as the study object, the microstructure and distortion evolution behavior of the C-type specimens under suspension during carburizing and quenching were studied by using finite element method to establish a multi-field coupling model of temperature field, structure field and strain field. The results show that the calculated distortion results are in good agreement with the actual measurements. The maximum distortion is at the notch position of the C-type specimen. The maximum temperature difference between the center position of the maximum width and the surface position of the notch during cooling process appears at 2.78 s and reaches 383.437 ℃. The martensitic transformation first starts from the core of the notch position, and the content of martensite in the core of C-type specimen can generally reach over 94%. During quenching, the surface martensite transformation of the C-type specimen lags behind the core, the surface martensitic transformation content is significantly lower than that of the core under the influence of retained austenite, and the final transformation content is about 83%.

Effect of cryogenic treatment on microstructure characteristics and tensile properties of laminated punctured C_f/Al composites

Liang Xiang, Gao Xiang, Li Yunlong, Xu Zhifeng, Zhang Zheng, Yan Liqing, Yu Huan

2024, 49(5): 74-80. doi:10.13251/j.issn.0254-6051.2024.05.012

Abstract ( 23 )

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Using M40J-6K laminated punctured structure carbon fiber as reinforcement and ZL301 alloy as matrix, a laminated punctured C_f/Al composite was prepared by vacuum pressure infiltration method. The effects of single cryogenic treatment time (6, 12, 48 h) and cryogenic treatment cycles (1, 3, 9) on microstructure and tensile properties of the composites were studied, and the reasons for the improvement of tensile properties were analyzed. The results indicate that cryogenic treatment can improve the tensile properties and microstructure of the laminated punctured C_f/Al composites. Cryogenic treatment for 1 cycle can improve the tensile strength of the composites, while the impact on tensile modulus is relatively small. The maximum increase in tensile strength is achieved when the cryogenic time is 6 h, which increases from 559 MPa(without cryogenic treatment) to 664 MPa, by an increase of 18.8%. When the treatment time is further extended to 12 and 48 h, the effect is not significant. Compared with 1 cycle cryogenic treatment, cyclic cryogenic treatment can further improve the tensile strength and modulus of the laminated punctured C_f/Al composites. After 3 cycles of cryogenic treatment, the tensile strength and elastic modulus increase to 706 MPa and 138 GPa, respectively, compared to 676 MPa and 125 GPa under cryogenic treatment for 1 cycle, by an increase of 4.4% and 10.4%, respectively. When cryogenic treatment further increases to 9 cycles, the tensile strength and modulus are stabilized. The stress release and state change, increased density, preferred grain orientation, and increased matrix dislocation density after cryogenic treatment are the reasons that affect the improvement of macroscopic tensile properties of the laminated punctured C_f/Al composites.

Effect of natural aging on Portevin-Le Chatelier effect of TiB₂/7050 aluminum matrix composites

Shang Hongshuai, Han Wenfeng, Jie Zhaocai, Yuan Binxian

2024, 49(5): 81-87. doi:10.13251/j.issn.0254-6051.2024.05.013

Abstract ( 25 )

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Effect of natural aging time on Portevin-Le Chatelier effect (PLC effect) of TiB₂/7050 aluminum matrix composites was investigated. Firstly, room temperature constant strain rate tensile tests were carried out on the TiB₂/7050 aluminum matrix composites, which was solution treated and water cooled, and then naturally aged for different time. Then the average serration amplitude, fall time, recovery time and critical strain were analyzed to study the influence of natural aging time on PLC effect. Finally, the morphology of the tensile fracture was observed by means of scanning electron microscope. The results show that the natural aging time within 1 h has a little effect on strength of the TiB₂/7050 aluminum matrix composites, but the yield and tensile strengths increase significantly when the natural aging time is more than 1 h. The type of PLC bands evolves with the prolongation of natural aging time from the class B (0-1 h) with jumping nature to the class A (1.5 h) with continuous propagation, and then to the class D (2-4 h) with step propagation characteristics. When the natural aging time exceeds 1 h, the tensile fracture dimples of the TiB₂/7050 aluminum matrix composites become significantly shallower and the size becomes smaller, indicating that the plasticity of the composite decreases with the extension of natural aging time. Therefore, the interval between solution treatment and artificial aging of the TiB₂/7050 aluminum matrix composite should not beyond 1 h.

Effect of solution treatment and aging on microstructure and properties of 21-4NWNb alloy

Zang Kai, Wang Shouqian, Zhu Zhiyuan

2024, 49(5): 88-93. doi:10.13251/j.issn.0254-6051.2024.05.014

Abstract ( 30 )

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Effects of solution treatment and aging on microstructure and properties of 21-4NWNb alloy were investigated by means of XSL-4-12 box resistance furnace, ZEISS metallographic microscope, ZEISS Merlin Compact field emission scanning electron microscope, KB 30S automatic hardness test system, CMT5305 electronic universal testing machine, and JEM-2100F field emission transmission electron microscope. The results show that solution treatment can effectively improve the grain structure of the alloys. When the solution treatment temperature is in the range of 1150-1200 ℃, a large amount of carbides in the alloy almost completely dissolve into the austenite matrix, and the Nb(C, N) phases cannot completely dissolve even at the solution treatment temperature of 1200 ℃. The hardness of the alloy decreases with the increase of solution treatment temperature. The grain size of the alloy remains basically unchanged after different aging treatments. At higher aging temperatures (650-800 ℃), hardness of the alloy shows a trend of first increasing and then decreasing with the increase of aging temperature. After solution treatment at 1150 ℃ for 0.5 h and then aging at 750 ℃ for 4 h, the tensile strength of the 21-4NWNb alloy reaches 1042 MPa, and there is a (110)_WN//(220)_γ relationship between the WN precipitate phases in the alloy and the Fe matrix.

Effect of heat treatment on microstructure of Mg-Gd-Y-Zr alloy

Wang Haoyu, Li Hairan, Gao Yonghao

2024, 49(5): 94-99. doi:10.13251/j.issn.0254-6051.2024.05.015

Abstract ( 33 )

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Mg-Gd-Y-Zr alloy was annealed at 350 ℃, and the surface oxidation behavior during the annealing process was systematically characterized using optical microscope, scanning electron microscope, and X-ray diffraction. The results show that significant changes occur in the alloy during the annealing process, with Gd and Y elements aggregating along the initial grain boundaries and alloy surface. The specimen undergoes uneven oxidation, where the oxidation rate at the initial grain boundary is higher than that inside the grain. The main component of the oxide film is (Gd_x,Y_2-x)O₃.

Effect of solution treatment and aging on microstructure and properties of Ti-5Al-3.5Fe-7Mo-4Cr alloy

Zhao Qian, Dong Fuyu, Wu Fuchuan, Zhang Yue, Xu Xin

2024, 49(5): 100-105. doi:10.13251/j.issn.0254-6051.2024.05.016

Abstract ( 26 )

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A novel low-cost high-strength β titanium alloy Ti-5Al-3.5Fe-7Mo-4Cr was self-designed, and the effect of solution treatment and aging on its microstructure and tensile properties was investigated by means of room temperature tensile testing, EBSD, SEM, TEM and EDS analysis. The results show that compared with that solution treat in single-phase region and aging, the properties of the alloy solution treated in α+β two phase region and aged are better. Under these two different solution treatment systems, as the aging temperature increases, the precipitation amount of secondary α phase and strength of the alloy both increase first and then decrease, while the elongation shows an increasing trend. When the aging temperature is higher, the needle-like secondary α phase grows and its interspacing increases. After solution treatment at 820 ℃ for 0.5 h and aging at 440 ℃ for 8 h, the tested titanium alloy achieves good strength-plasticity match, with the tensile strength of 1257 MPa, yield strength of 1135 MPa, and elongation of 4%, meeting the strength requirements of high-strength titanium alloys. The high strength of the tested β titanium alloy is mainly due to the second phase strengthening, smaller secondary α phase interspacing, the increase in volume fraction of α phase and hierarchical size structure having a significant strengthening effect on the alloy.

Effect of pre-aging treatment on microstructure and mechanical properties of metastable β titanium alloy TB18

Li Bo, Xiang Wei, Zhang Feng, Qin Fengying, Yuan Wuhua

2024, 49(5): 106-111. doi:10.13251/j.issn.0254-6051.2024.05.017

Abstract ( 32 )

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Relationships of microstructure and mechanical properties of high-strength metastable β titanium alloy TB18 after different heat treatments were investigated. The results show that many precipitation-free zones (PFZs) still retains in the β matrix of the TB18 alloy after solution treatment and aging at 525 ℃ for 4 h, where the alloy has an ultimate tensile strength of 1309 MPa, a yield strength of 1227 MPa, and an elongation of 6.6%. When the TB18 alloy is pre-aged at 300 ℃ for 2 h and aged, the microstructure and mechanical properties are not changed significantly. While the pre-aging temperature is increased to 400 ℃, there are no longer significant PFZs distributed in the microstructure after aging, and the strength and plasticity of the alloy are significantly increased, where the tensile strength, yield strength, and elongation are 1355 MPa, 1278 MPa, and 7.0% respectively, showing a better strength-plasticity matching. In addition, all the tensile specimens are fractured in a mixed mode, but the specimens after solution, pre-aging at 400 ℃ and aging have fewer deconstructive features on the section and a greater proportion of ductile fracture.

Effects of cold deformation and annealing process on microstructure and properties of Ti45Nb alloy

Wang Zelong, Feng Zhaolong, Li Wei, Sun Sibo

2024, 49(5): 112-117. doi:10.13251/j.issn.0254-6051.2024.05.018

Abstract ( 31 )

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Cold deformation of Ti45Nb alloy wire was carried out using roller die drawing technology. The effects of cold plastic forming and annealing process on microstructure and mechanical properties of the Ti45Nb alloy wire were studied by means of OM, EBSD and tensile test. The results indicate that with the increase of cold deformation, the grain size of the Ti45Nb alloy wire gradually decreases, the orientation density index of the grains gradually increases, and the <110> silk texture dominates. At the same time, the tensile strength and yield strength of the Ti45Nb alloy wire gradually increase, but its shear strength does not change significantly. The use of water cooling can significantly improve the plasticity of the annealed Ti45Nb alloy wires and prevent cracking during compression deformation. The complete recrystallization temperature of the Ti45Nb wire is around 670 ℃. As the annealing temperature increases, the grain size significantly increases, and the tensile strength and yield strength show an upward trend.

Effect of cold rolling, annealing and aging on microstructure and properties of Fe₅₀Ni₂₅Cr₁₅Al₁₀ high entropy alloy

Xing Zhenqiang, Pang Jingyu, Zhang Hongwei, Ji Yu, Zhu Zhengwang, Zhang Long, Wang Aimin, Zhang Haifeng

2024, 49(5): 118-123. doi:10.13251/j.issn.0254-6051.2024.05.019

Abstract ( 25 )

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Effects of cold rolling, annealing and aging on the microstructure and mechanical properties of the Fe₅₀Ni₂₅Cr₁₅Al₁₀ high entropy alloy were investigated. The results show that the as-cast Fe₅₀Ni₂₅Cr₁₅Al₁₀ high entropy alloy has FCC+B2 bi-phase structure. After cold rolling, annealing and aging, the FCC phase is transformed from dendrite to equiaxial grains, the annealing twins accounting for 43.7% are produced, and the average grain size is refined from 228.84 μm to 4.51 μm. The B2 phase exhibits two precipitation modes, namely chain like large-sized intergranular precipitated phase and small-sized ellipsoidal phase dispersing inside the grains, and the proportion of B2 phase increases from 0.9% to 13.3%. The yield strength and tensile strength of the high entropy alloy are increased from 254 MPa and 528 MPa to 466 MPa and 760 MPa, respectively, and the percentage total extension at fracture is 31.5%, showing good strength-plasticity matching.

Effect of quenching temperature on microstructure and properties of 690 MPa grade steel for pressure vessels with low welding crack sensitivity

Liu Chenxi, Hu Xinming, Ouyang Xin, Xing Mengnan, Wang Chu

2024, 49(5): 124-129. doi:10.13251/j.issn.0254-6051.2024.05.020

Abstract ( 20 )

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Microstructure evolution and mechanical properties of a 690 MPa grade pressure vessel steel with low welding crack sensitivity at different quenching temperatures were studied by means of optical microscope, scanning electron microscope, high-temperature confocal microscope, electronic tensile testing machine and fully automatic impact testing machine. The results show that the microstructure of the designed tested steel is mainly composed of granular bainite, lath bainite and ferrite after rolling and quenching at 820-970 ℃. Under a high-temperature confocal microscope, it is observed that during the quenching process at 970 ℃, when the temperature drops to 520 ℃, some grains begin to undergo shear transformation and form lath bainite. After quenching and tempering, part of the quenched microstructure is retained due to the genetic effect of the microstructure. When the quenching temperature rises to above 950 ℃, the strength level of the quenched and tempered tested steel can reach 690 MPa grade.

Effect of annealing temperature on microstructure and mechanical properties of laser welded joint of Ti60 titanium alloy

Zhang Zengguang, Shi Jipeng, Wang Xinyu, Liu Yanmei, Yang Lixin, Kang Chong, Liu Gang

2024, 49(5): 130-134. doi:10.13251/j.issn.0254-6051.2024.05.021

Abstract ( 24 )

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Butt welding test for the high temperature titanium alloy Ti60 was carried out by laser welding. The surface forming state and macrostructure morphology of the welded joint were observed. And the laser welded joint was annealed at 600, 750 and 900 ℃, respectively, and the microstructure, hardness, residual stress and tensile properties at room temperature of the welded joint annealed were tested and analyzed by means of metallographic microscope, hardness tester, X-ray residual stress detector and tensile testing machine. The results show that with the increase of annealing temperature, the α′ needle-like structure content in the fusion zone of the laser welded joint of the high temperature titanium alloy Ti60 gradually decreases, while that in the heat affected zone gradually increases, and the α phase content in the base metal zone gradually increases. The residual stress of the welded joint gradually decreases. When the annealing temperature exceeds 750 ℃, the residual stress remains basically unchanged. The tensile properties of the welded joint are optimal after annealing at 750 ℃. As the annealing temperature increases, the hardness of the melted zone and heat affected zone of the welded joint gradually decreases, while the hardness of the base metal zone is higher after annealing at 900 ℃ than that after annealing at 600 ℃ and 750 ℃.

Effects of S content and aging on reliability of Cu/Sn-8Zn-3Bi-xS/Cu solder joints

Shuai Gewang, Huang Huizhen

2024, 49(5): 135-139. doi:10.13251/j.issn.0254-6051.2024.05.022

Abstract ( 19 )

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Effects of S addition and aging on the reliability of Cu/Sn-8Zn-3Bi-xS/Cu solder joints were investigated. The wettability of the solder was evaluated by spreading area on Cu substrate. The Cu/Sn-8Zn-3Bi-xS/Cu solder joints were prepared by lap welding and the mechanical properties of the solder joints aged at 90 ℃ for different time were measured. The morphology and constituents of the fracture surface of the solder joints were observed by scanning electron microscopy (SEM), and the intermetallic compounds formed at the interface of the solder joints were identified by X-ray diffractometer (XRD). The results show that the wettability of the Sn-8Zn-3Bi-xS solder enhances by the addition of S, and the optimal S content is 0.05wt%. When the aging time is the same, the shear strength of the solder joints increases first and then decreases with the increase of S content and reaches the maximum value when the S content is 0.05wt%. When the S content is the same, the shear strength of the solder joints increases first and then decreases with the increase of aging time. When aging time is 4 h, the shear strength is the maximum. Addition of S does not change the composition of intermetallic compounds at the solder joints interface.

Effect of intermediate tempering on microstructure and mechanical properties of heat affected zone of 15Cr1Mo1V steel after repair welding

Zhang Zhenghua, Li Xiao, Wang Yansong, Xiao Shijun

2024, 49(5): 140-145. doi:10.13251/j.issn.0254-6051.2024.05.023

Abstract ( 18 )

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Heat affected zone of 15Cr1Mo1V steel after repair welding and intermediate tempering was simulated by Gleeble-3500 thermal simulation testing machine. The effect of intermediate tempering on the microstructure and mechanical properties of the heat affected zone of the long-term serviced 15Cr1Mo1V steel after repair welding was studied by means of metallographic observation, scanning electron microscopy analysis, microhardness test and impact test. The results show that the microstructure of serviced state is composed of ferrite+ granular bainite+intragranular dispersed carbide+grain boundary chain carbide. After repair welding, the microstructure of tempering zone is basically the same as that of long-term serviced state. The microstructure of incomplete transformation zone and complete transformation zone is ferrite+granular bainite+pearlite+granular grain boundary carbide, but there is dispersed carbide in the crystal of incomplete transformation zone. The coarse grain zone is composed of flat noodles bainite+a small amount of granular bainite. After intermediate tempering, there is an increase in carbides at the grain boundaries of the tempering zone. The carbides precipitated in the incomplete and complete phase transformation zones continuously aggregate and grow at the grain boundaries, while a large number of chain like carbides appear at the grain boundaries of the coarse grain zone. After repair welding, except for the high hardness of the coarse grain zone, the hardness level of the other heat affected zones is not significantly different from the serviced state. After intermediate tempering, the hardness value of the coarse grain zone remains at the level after repair welding, and the hardness of the other heat affected zones has slightly increased. Due to the presence of pearlite structure in the incomplete and complete phase transformation zones, the impact property is lower, while the impact property of the tempered zone and coarse grain zone is better. After intermediate tempering, the impact property of the tempered zone and coarse grain zone decreases, while the impact property of other heat affected zones is improved.

Post weld heat treatment characteristics of S11306 stainless steel thick plate

Zhang Yong, Ma Qingshan, Li Ruyang, Hu Xiaodong

2024, 49(5): 146-152. doi:10.13251/j.issn.0254-6051.2024.05.024

Abstract ( 21 )

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Residual stress, microstructure and mechanical properties of S11306 ferritic stainless steel thick plates were examined after welding and two heat treatment processes. The welding residual stress was determined both before and after heat treatment by using the blind hole method. The sequential coupling method and double ellipsoidal heat source were utilized to characterize the temperature and stress fields during welding. The microstructure evolution both before and after heat treatment was studied by using optical microscope. The results show that the error of the welding temperature field simulated by the heat source can be controlled within 10%. The difference between the stress results obtained through sequential coupling and the experimental values shall not exceed 23%. The heat treatment process can significantly reduce the peak residual stress in the weld zone. Compared to 770 ℃, the heat treatment temperature of 820 ℃ provides a greater residual stress-relieving impact on the 100 mm area surrounding the weld zone. The higher heat treatment temperature not only reduces the martensite content of the base metal, but also promotes the grain growth of the heat affected zone, concurrently the content of lower bainite and martensite composite phase (LB/M) in the weld zone is increased to 47.6%. The hardness values of the base metal and heat affected zone show a decreasing trend after heat treatment, while the hardness value of weld zone is increased by 33 HV0.05.

Hot rolled and normalized microstructure and texture of high strength non-oriented electrical steel at different finish rolling temperatures

Qiao Pengfei, Wu Zhongwang, Zhang Huimin, Jin Zili, Ren Huiping, Guo Huan

2024, 49(5): 153-157. doi:10.13251/j.issn.0254-6051.2024.05.025

Abstract ( 106 )

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Microstructure and texture of the high strength non-oriented electrical steel hot rolled at different finish rolling temperatures and normalized were studied by means of optical microscope (OM) and electron backscattering diffraction analysis (EBSD). The results show that the higher the finish rolling temperature of the hot rolled plate, the stronger the tendency of grain aggregation and growth, the stronger the dynamic recrystallization ability, the coarser the grains. When the finish rolling temperature is low, the deformation stored energy generated during hot rolling process is released during normalization process, and the recrystallization ability is stronger. Along the thickness direction, the surface texture of the hot rolled plate is mainly Goss texture ({110}<001>), and the center layer is mainly rotating cubic texture ({001}<110>). The texture of the normalized plate corresponds to that of the hot rolled plate, and with the increase of finish rolling temperature, the proportion of favorable texture raises.

Effect of intercritical annealing on microstructure and properties of ferrite/bainite dual-phase steel

Shi Lei, Tian Pengyong, Shi Ying, Bai Xue, Yang Fang

2024, 49(5): 158-161. doi:10.13251/j.issn.0254-6051.2024.05.026

Abstract ( 25 )

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Effect of intercritical annealing process on microstructure and mechanical properties of ferrite/bainite dual-phase steel was studied by means of thermal simulation test machine, microhardness tester, electronic universal tensile testing machine, optical microscope and scanning electron microscope. The results show that under traditional intercritical annealing process, the microstructure is composed of ferrite, bainite and a small amount of martensite, and showing banded structures. The quenching+intercritical annealing process can refine the microstructure, obtain lath ferrite/bainite dual-phase structures, and inhibit the formation of martensite. Moreover, different processes obtain similar volume fractions of ferrite. Compared with the traditional intercritical annealing process, the quenching+intercritical annealing process can significantly reduce yield ratio and improve elongation of the tested steel.

Effect of cooling rate on phase transformation behavior of ultra-high strength X90M pipeline steel

Liu Gan, Kong Xianglei, Huang Minghao, Wang Yang, Zhang Yinghui

2024, 49(5): 162-167. doi:10.13251/j.issn.0254-6051.2024.05.027

Abstract ( 26 )

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Phase transformation behavior of X90M pipeline steel at different cooling rates was studied by Gleeble-3800 thermal simulation tester. The dynamic CCT curves were plotted based on the thermal expansion curve, Vickers hardness, and microstructure analysis results. The results show that with the increase of cooling rate, the microstructure of the X90M pipeline steel undergoes polygonal ferrite (PF)+bainite (B) → acicular ferrite (AF) → bainitic ferrite (BF) transformation in turn, and its microhardness also gradually increases, showing an overall upward trend. And with the increase of cooling rate, the ferrite is in blocky, acicular and flat morphology in order. Meanwhile, the number of martensite/austenite(M/A) islands increases, the size is refined and the distribution gradually disperses. Under laboratory conditions, adopting a cooling rate of about 30 ℃/s can enable the X90M pipeline steel to obtain a microstructure with high-density dislocations and dispersed small M/A islands.

Effect of cryogenic treatment on microstructure and mechanical properties of X70 pipeline steel

Zhu Yanqiang, Li Yonggang, He Qiong, Liu Zhebing

2024, 49(5): 168-172. doi:10.13251/j.issn.0254-6051.2024.05.028

Abstract ( 20 )

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Effects of cryogenic treatment, quenching and tempering, and quenching and tempering+cryogenic treatment on microstructure and mechanical properties of the X70 pipeline steel were studied by means of optical microscope, scanning electron microscope, microhardness tester, and universal electronic tensile test machine. The results show that the microstructure of the X70 pipeline steel without treatment is ferrite+pearlite. After cryogenic treatment only, the microstructure is finer and more uniform, the content of pearlite decreases, the microhardness and tensile strength of the X70 pipeline steel increase respectively by 2.73% and 9.58%, and the tensile fracture morphology is equiaxed dimples, showing a ductile fracture characteristic. After quenching and tempering, the microstructure of the X70 pipeline steel is ferrite+tempered sorbite+bainite, the hardness and tensile strength increase by 13.62% and 5.64%, respectively, compared to that of the untreated specimen, and the tensile fracture is distributed with dimples and a small amount of quasi cleavage morphologies, showing a decrease in toughness. After quenching and tempering+cryogenic treatment, the microstructure of the X70 pipeline steel is ferrite+tempered sorbite+bainite, the microstructure is finer and more uniform, the ferrite content increases, the hardness and tensile strength increase by 22.52% and 16.76%, respectively, compared to that of the untreated specimen, and the cryogenic treatment improves the plasticity of the quenched and tempered specimen, thus the tensile fracture exhibits ductile fracture characteristics.

Effect of quenching and tempering on microstructure and hardness of 34CrNiMo6 steel forged connecting rods

Pu Bowen, Liu Yuting, Wang Yanrong, Diao Zhanying, He Jingwei

2024, 49(5): 173-178. doi:10.13251/j.issn.0254-6051.2024.05.029

Abstract ( 20 )

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Effect of quenching and tempering on microstructure and microhardness of 34CrNiMo6 steel forged connecting rods was studied by means of microstructure characterization, microhardness testing and phase diagram calculation. Based on the evolution of microstructure, the change regulation of surface and internal microhardness before and after quenching and tempering of the forged connecting rods was revealed. The results show that the forged connecting rod is composed of pearlite and sorbite, with slight decarburization on the surface. After quenching and tempering, the grain size of the forged connecting rod decreases and its local strain uniformity gets well. There is a non-significant decarburization layer and dispersed carbide particles on the near surface, thus the hardness variation of the near surface is obvious. Although the average micro-hardness after heat treatment is lower than that before heat treatment, the internal microstructure is uniform tempered sorbite, which reduces the dispersion of hardness.

Aging process of high-strength Al-Mg-Si-(Ag/Cu) alloy for automobile body sheet

Wu Wei, Chen Jiaying, Guo Rui, Wang Ru, Yuan Youyou, Qiu Quanqiang, Cheng Xiangxiang, Ju Jia

2024, 49(5): 179-185. doi:10.13251/j.issn.0254-6051.2024.05.030

Abstract ( 19 )

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Aging strengthening characteristics and microstructure of Al-Mg-Si,Al-Mg-Si Ag,Al-Mg-Si-Cu alloys under different aging treatment conditions were investigated by hardness testing,tensile testing,microscopic inspection. The results show that the addition of Ag improves the hardness value of the alloy during peak aging with a peak hardness of 141.01 HV0.5,representing an increase of 9.35% and 1.53% compared to that of Al-Mg-Si and Al-Mg-Si-Cu alloys. The smaller average size and wider dispersion of the precipitation-strengthening phase β″ formed during the peak aging stage of the Al-Mg-Si-Ag alloy contribute to a reduction in length by 40.05% and 23.09% compared to that of the Al-Mg-Si and Al-Mg-Si-Cu alloys,and the spatial distribution is more dispersed. According to comparative tests,the Ag microalloying has a more significant precipitation strengthening effect on Al-Mg-Si alloy. Therefore,the Al-Mg-Si-Ag alloy has better comprehensive properties,demonstrating that this research may provide some theoretical support for the development of heat treatment processes for designing new types of automobile body sheet.

Effect of solution treatment on microstructure and mechanical properties of 7175 aluminum alloy

Zhao Zhongchao, Ji Qingtao, Cao Shanpeng, Tang Hezhuang, Li Binliang, Niu Boya, Sun Youzheng

2024, 49(5): 186-192. doi:10.13251/j.issn.0254-6051.2024.05.031

Abstract ( 28 )

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Effect of solution treatment process on microstructure and properties of 7175 aluminum alloy was investigated through tensile property testing,hardness testing,optical microscope(OM),scanning electron microscope(SEM) and transmission electron microscope (TEM). The results show that when the 7175 aluminum alloy is solution treated at 485 ℃ for 3.5 h,the second phase contont gradually decreases, and there is a tendency for grain coarsening. When the 7175 aluminum alloy is solution treated at 475 ℃ for 2.5 h,MgZn₂ phase will rely on the Cr containing phase to nucleate at the grain boundary, playing a role in pinning the grain boundary and inhibiting grain growth. At the same time, with the increase of solution temperature and time, the tensile strength and microhardness of the alloy after aging at 120 ℃ for 12 h and 165 ℃ for 5.5 h show a trend of first increasing and then decreasing. When the solution treatment process is 475 ℃×2.5 h,the tensile strength is 631.2 MPa, the yield strength is 555.7 MPa and the elongation is 12.5%, with the optimal comprehensive mechanical properties.

Influence of solution treatment and aging on mechanical properties and microstructure of rare earth aluminum alloy

Liu Zizhi, Sun Fuzhen, Li Xiaoxu, Li Huiyu, Zhang Quanda, Mu Xuesong, Zhao Yan

2024, 49(5): 193-198. doi:10.13251/j.issn.0254-6051.2024.05.032

Abstract ( 23 )

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Solution treatment and aging process (solution treating at 480 ℃ for different time, water cooling, and aging at 120 ℃ for 24 h) of four thicknesses of rare earth aluminum alloy plates were studied, room temperature tensile tests were conducted on the alloy before and after heat treatment. The microstructure was qualitatively and quantitatively studied through EBSD, and the tensile fracture morphology was observed and analyzed. The results show that the solution treatment and aging process has a significant effect on improving the strength of rare earth aluminum alloy, with the most significant strengthening effect on the plate with thickness of 3.0 mm, in addition, it has a certain improvement effect on the plasticity of the alloy. After solution treatment and aging, the alloy with a thickness of 3.0 mm has stronger anisotropy compared to the alloy with a thickness of 1.2 mm, with more high and low angle grain boundaries, increased total length of grain boundaries, and smaller average grain size. Solution treatment and aging has a good effect on fine grain strengthening and dislocation strengthening of the rare earth aluminum alloy. The fracture mode of the rare earth aluminum alloy before heat treatment is ductile fracture, and the alloy with a thickness of 3.0 mm shows better plasticity than the 1.2 mm thick alloy. After solution treatment and aging, the fracture morphology of the 1.2 mm thick alloy specimen changes, and the plasticity further improves, while the plasticity of the 3.0 mm thick alloy decreases compared to that before heat treatment.

Effect of heat treatment on microstructure and mechanical properties of low carbon high copper HSLA steel

Wang Lipeng, Ge Junchao, Dai Kunhong

2024, 49(5): 199-203. doi:10.13251/j.issn.0254-6051.2024.05.033

Abstract ( 21 )

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Low carbon high copper HSLA steel was solution treated and aged at different temperatures. The effect of aging temperature on the microstructure and mechanical properties of the low carbon high copper HSLA steel was studied by means of scanning electron microscopy, transmission electron microscopy, tensile test, hardness test and low temperature impact test. The results show that after solution treatment at 880 ℃ for 1 h, with the increase of aging temperature, the tensile strength and hardness of the HSLA steel increase first and then decrease, the elongation increases gradually, and the impact absorbed energy at low temperature decreases first and then increases. The tensile strength and hardness of the HSLA steel aged at 440 ℃ reach the peak value, and the impact absorbed energy at low temperature is the lowest. A large number of 5-10 nm Cu particles precipitate from the HSLA steel matrix when aged at 440 ℃, which has a good strengthening effect on the HSLA steel. When the aging temperature reaches 600 ℃, the size of precipitated Cu particles reaches 20-30 nm, and the coarsening effect is weakened. The mechanical properties of the HSLA steel aged at different temperatures are jointly affected by two factors which are Cu particle phase precipitation strengthening and matrix softening. When the aging temperature is below 440 ℃, the strengthening effect of Cu particle phase precipitation is dominant. When the aging temperature exceeds 440 ℃, matrix softening plays a dominant role.

Effect of heat treatment system on microstructure and hardness of GH4698 superalloy

Zhang Rui, Zhang Xiaochen, Zhang Zheng, Cui Wenming, Yang Jiadian, Liu Yanxu, Wang Jixing, Bai Jiayuan

2024, 49(5): 204-209. doi:10.13251/j.issn.0254-6051.2024.05.034

Abstract ( 27 )

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Change law of microstructure and hardness of GH4698 superalloy under different heat treatment systems was studied. The results show that for the GH4698 superalloy standard heat treatment system, the primary aging cooling rate has a little effect on the size, content, spacing of γ′ precipitated phase and hardness. In the primary aging stage, the larger the cooling rate, the smaller the γ′ phase size and the higher the hardness. When the primary aging temperature is near 1000 ℃, the γ′ phase with size of 80-260 nm can precipitate effectively, which is more conducive to the subsequent secondary aging. In the secondary aging stage and in the temperature range of 725-775 ℃, the γ′ phase finer than 80 nm can fully precipitate, but when the temperature is below 725 ℃ and above 775 ℃, the γ′ phase finer than 80 nm cannot precipitate effectively.

Research on heat treatment standards and implementation methods of nuclear power control rod driving mechanism and reactor internal components

Mi Dawei, Ji Cuicui

2024, 49(5): 210-214. doi:10.13251/j.issn.0254-6051.2024.05.035

Abstract ( 23 )

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In terms of the heat treatment operating standards and heat treatment process for nuclear power control rod driving mechanism and reactor internal components, the analysis was conducted, in combination with heat treatment production experience. It is concluded that the types of heat treatment of control rod driving mechanism and reactor internal components are divided into stress relief heat treatment (i.e. “dimensional stabilizing heat treatment”), heat treatment for improving material properties, annealing (including bright annealing), aging, local heat treatment, achieving the operating standards and processes that guide heat treatment of nuclear power control rod driving mechanism and reactor internal parts (components).

Effect of heat treatment on microstructure and properties of 40Cr13VTi stainless steel

Liu Yu, Sun Yingjian, Zhang Tiebi, Xi Yanmei

2024, 49(5): 215-219. doi:10.13251/j.issn.0254-6051.2024.05.036

Abstract ( 19 )

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After 1030 ℃ oil quenching, the effect of tempering temperature on the microstructure, precipitates and mechanical properties of the 40Cr13VTi steel containing V and Ti was studied to optimize the tempering process. The microstructure of the steel was analyzed by using optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Tensile, impact and hardness tests were conducted on the tested steel. The results show that as the tempering temperature increases, the carbide precipitates gradually increase in number, and gradually change from particles to flakes in shape, which are consistent with the original martensite lath direction, and most of them are concentrated at the martensite boundary. When the tempering temperature is 350 ℃, the comprehensive mechanical properties of the 40Cr13VTi martensitic stainless steel are the best, with yield strength of 1360 MPa, tensile strength of 1717 MPa, impact absorbed energy of 6.8 J, and hardness of 43.1 HRC.

Austempering process of 68CrNiMo steel hacksaw chain cutters

Li Cunzhi, Dai Yujie

2024, 49(5): 220-225. doi:10.13251/j.issn.0254-6051.2024.05.037

Abstract ( 19 )

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Austempering process of the 68CrNiMo steel hacksaw chain cutters was studied by using metal material simulation software JmatPro. The phase transformation temperatures of the 68CrNiMo steel are obtained through JmatPro simulation, and the critical austenite transformation temperature Ac₁ and Ac₃ in equilibrium state are 726.5 ℃ and 746.9 ℃, respectively. The austempering process of 68CrNiMo steel is proposed as follows: heating at 840 ℃ for 40 min, then directly falling into the isothermal salt tank from the discharge port for isothermal treatment, holding at 285-300 ℃ for 35 min, air cooling followed by 180 ℃×60 min tempering. The results show that, after the proposed austempering+tempering, the microstructure of the 68CrNiMo steel is composed of lower bainite, tempered martensite and retained austenite, the hardness is in the range of 54-56 HRC and relatively uniform, and there is no fracture when the cutter is bended for 90°, where the microstructure and properties meet the requirements of hacksaw chain.

Heat treatment process optimization of 35CrMo steel high strength bolt

Lü Mingkui, Xia Tian, Zhang Baoyao, Yang Donghui, Chen Jing

2024, 49(5): 226-230. doi:10.13251/j.issn.0254-6051.2024.05.038

Abstract ( 31 )

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Orthogonal test method was used to optimize the heat treatment process for three kinds of specimens with diameters of φ30, φ32 and φ36 mm in order to determine the suitable heat treatment process parameters to meet the bolt strength grade 10.9, where the heat treatment process of 35CrMo steel was investigated by using single-factor method, and that the hardness of the core reaching half martensite hardness was used as the basis for quenching, that the 1/2 radius and core hardness were used as the evaluation indexes. The results show that the optimal heat treatment parameters are the quenching temperature of 860 ℃, the holding time of 50 min, and the water-soluble quenching liquid for quenching, the tempering temperature of 480 ℃, and the tempering time of 80 min. After heat treatment with the optimized process, the hardness, tensile strength, yield strength, elongation and percentage reduction of area of all the specimens with three different diameters can meet the mechanical property requirements of 10.9 grade high strength bolts.

Austempering of ML45CrMo steel for grade 16.8 bolt

Tang Jianliang, Jiang Yangying, Yan Hongjun

2024, 49(5): 231-233. doi:10.13251/j.issn.0254-6051.2024.05.039

Abstract ( 21 )

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Domestic ML45CrMo steel was conducted austempering treatment tests. The specimens were heated and held in a SY805-5 mesh belt furnace, and then placed in a nitrate salt bath for austempering. The mechanical properties and microstructure of the austempered specimens were tested and observed by means of Vickers hardness tester, universal testing machine and metallographic microscope. The results show that after bainitic austempering, i.e. quenching at 850 ℃ for 80 min, austempering in nitrate at temperature of (320±10) ℃, holding for 60 min in nitrate, the ML45CrMo steel meets the property requirements of grade 16.8 bolts.

Optimization of aging temperature of 15-5PH precipitation hardened stainless steel based on quality analysis fitting curves

Zhao Guangjin, Ren Weibin, Zhao Jinlong, Li Xinyun

2024, 49(5): 234-236. doi:10.13251/j.issn.0254-6051.2024.05.040

Abstract ( 19 )

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Using a commonly used quality analysis software, the hardness and tensile strength test data of 15-5PH precipitation hardened stainless steel aged at different temperatures were fitted and analyzed. An aging temperature is obtained to satisfy concurrently the requirements of hardness and tensile strength of the 15-5PH precipitation hardened stainless steel, the heat treatment system is determined, the process testing cycle is shortened and the machining requirements of parts are met.

Intelligent scheduling of heat treatment based on multi-system information interaction

Liu Qi, Wan Rutao, Zhu Hongbin, Chong Yonggang, Qu Ming, Duan Xuefeng

2024, 49(5): 237-242. doi:10.13251/j.issn.0254-6051.2024.05.041

Abstract ( 20 )

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Focused on the heat treatment centralized control system that could centrally control multiple heating equipment scattered in the workshop, and an interactive model of heat treatment production information was generated by constructing multiple systems such as process knowledge base, measurement management system, quality management system, production ERP system and personnel authority management. The digital control and quality monitoring of the whole process for production management, process parameters and equipment management of heat treatment products are realized, as well as intelligent production scheduling and pull visual scheduling are established. The network integration of information such as operator, machines, materials, methods as well as environment of product production is completed, and a solution is found to the key issues such as artificial control of process, the randomness of production scheduling, the paper-based transmission of process records and poor traceability of heat treatment process in the heat treatment production process, which provides a new scheme for improving the management level of heat treatment workshop.

Effect of laser clad Stellite6+WC composite coating on water erosion resistance of stainless steel blades

Deng Dewei, Wan Hongming, Wang Hongsuo, Chen Wenbo, Lian Shiwei

2024, 49(5): 243-251. doi:10.13251/j.issn.0254-6051.2024.05.042

Abstract ( 21 )

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Stellite6+WC composite coating was deposited on the surface of 17-4PH stainless steel by using laser cladding method. The optimal cladding parameters suitable for Stellite6 alloy were obtained through orthogonal experiments, and then different contents of WC powder were added to the coating under these cladding parameters. By using optical microscope, microhardness tester and salt spray corrosion test chamber, the effects of WC addition and laser quenching technology on the microstructure, Vickers hardness, and salt spray corrosion resistance of the clad coating were compared and studied. The results indicate that the optimal cladding parameters are laser power of 1500 W, laser scanning speed of 18 mm/s, and focal distance of 13 mm. When the mass fraction of WC is within 30%, the microhardness and salt spray corrosion resistance of the Stellite6+WC clad coating gradually increase with the increase of WC content. However, when the mass fraction of WC is higher than 30%, the microhardness and salt spray corrosion resistance of the clad coating are not significantly improved compared to that of the cladding with 30%WC. Although the laser quenching process improves the microhardness and salt spray corrosion resistance of the cladding to some extent, the salt spray corrosion resistance of the coating after laser quenching at 3000 W is not further improved compared to that after laser quenching at 1000 W.

Effect mechanism of preheating temperature on crack of laser clad nickel-based tungsten carbide coating

Li Zhanfeng, Zhang Shu'ai, Guan Xiqiao, Xing Qin, Zhang Fenglong

2024, 49(5): 252-259. doi:10.13251/j.issn.0254-6051.2024.05.043

Abstract ( 19 )

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In order to solve the problem that the nickel-based tungsten carbide metal composite ceramic coating with high tungsten carbide (WC) content prepared by laser cladding on the surface of nickel-based superalloy is easy to crack, the effects of different laser cladding scanning speeds (300, 500, 700 mm/min) and substrate preheating temperatures (ambient temperature, 300 ℃, 500 ℃) on the heating and cooling processes of the weld pool were investigated by using self-assembled weld pool temperature detection equipment, and the cracking mechanism of the coating was analyzed by observing the microstructure of the coating. The results show that the laser cladding parameters and coating materials will affect the cracking behavior of the coating. On the one hand, the heating and cooling rates in the molten pool during laser cladding are positively correlated with the scanning speed, but negatively correlated with the preheating temperature. Lower scanning speed and higher preheating temperature can obtain smaller temperature change rate, which is more conducive to inhibiting the overall cracking of the coating. On the other hand, because of the great difference in melting point and thermal expansion coefficient between WC and NiCrSiBC, when the cooling rate of molten pool is too high or too low, it is easy to cause WC to crack or dissociate. Therefore, it is necessary to optimize the cooling rate of the molten pool in order to effectively improve the overall forming quality of the coating.

C-N-O-S multi-element co-infiltration and evolution of microstructure and properties of Q235 steel for leveling gaskets of extra-large railway steel beam bridges

Zhang Minmin, Wang Diantang, Li Jiangtao, Wang Zhongjun, Zhang Jibing, Zhang Qiang,Wei Shengmin, Zhang Qi, Li Jianguo

2024, 49(5): 260-266. doi:10.13251/j.issn.0254-6051.2024.05.044

Abstract ( 16 )

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In order to effectively extend the service life of Q235 steel beam bridge leveling gaskets, the surface modification of C-N-O-S multi-element infiltration technology was carried out. The effect of different parameters coupling on the microstructure, hardness, wear resistance and weather resistance of the modified layer was studied. The results show that the multi-layer structure of the modified layer is related to co-infiltration temperature, and there is a critical value between 640 ℃ and 650 ℃, below the critical temperature, it is composed of the compound layer, diffusion layer and oxidation layer. When the critical temperature is exceeded, the modified layer comprises compound and oxidation layers. The thickness of the modified layer is affected by co-infiltration temperature, ammonia and infiltration promoting agent flow rates, and the temperature and ammonia flow rate affect the structure of each layer. The infiltration promoting agent flow rate has an obvious effect on the diffusion layer. The hardness of the modified layer is 2-3 times of that of the substrate, the hardness of the three-layer structural layer decreases continuously from the surface to substrate. The hardness of the two-layer structural compound layer is uniform, with sharp decrease in hardness in the interface area. The lowest friction coefficient of the modified layer is 0.2468, which is about 1/3 of the base material. The highest free-corrosion potential of the modified layer is -0.4845 V, and the lowest free corrosion current density is 1.187×10^-6 mA/cm², which is reduced by 2 orders of magnitude compared to the substrate.

High-temperature oxidation resistance of bi-electrodes micro-arc oxidation ceramic coating on tantalum

Cai Mingliang, Tian Xue, Chen Xinxin, Zhang Daiyue, Hao Guodong

2024, 49(5): 267-271. doi:10.13251/j.issn.0254-6051.2024.05.045

Abstract ( 16 )

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Under silicate system and dual pulse constant pressure mode, the bi-electrodes micro-arc oxidation and traditional micro-arc oxidation techniques were used to grow ceramic coating in situ on the surface of tantalum metal. The thickness of the coating was tested by using thickness gauge. The phase composition, surface morphology and element content of the coating were analyzed by using X-ray diffractometor, scanning electron microscope and energy dispersive spectrometer. The high-temperature oxidation resistance of the coating was studied by using high-temperature oxidation mass gain test. The results indicate that the phase composition of the coating formed by traditional micro-arc oxidation and bi-electrodes micro-arc oxidation reactions is Ta₂O₅ phase. The coating thickness generated under traditional micro-arc oxidation mode is greater than that under bi-electrodes micro-arc oxidation mode. After high-temperature oxidation, the surface of the coating is smoother compared to that before oxidation, indicating that the oxides melt and collapse after oxidation, and there are obvious sintering traces, with some remained volcanic crater-like small pores. High temperature oxidation causes the oxide to extrude and expand, resulting in microcracks. Compared with the matrix, the specimens subjected to micro-arc oxidation have better resistance to high-temperature oxidation. The ceramic coating generated in situ by bi-electrodes micro-arc oxidation technology has less high-temperature oxidation mass gain and better resistance to high-temperature oxidation compared to that of traditional micro-arc oxidation technology.

Failure behavior of a low carbon alloy carburized steel roller

Lü Ben, Wan Xunzhi, Liu Cheng

2024, 49(5): 272-277. doi:10.13251/j.issn.0254-6051.2024.05.046

Abstract ( 26 )

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Fracture surface observation, microstructure observation, hardness distribution test and the basic stress analysis of a low carbon alloy carburized steel roller failed in roll forming process for manufacturing automobile flywheel, were investigated by means of optical microscope, scanning electron microscope, microhardness tester and finite element analysis. The results show that the carburized layer of the failed roller is mainly composed of acicular tempered martensite, small carbides and a few retained austenite. The microhardness decreases from the roller notch surface to the core. The distribution of microhardness near the failed roll notch is not uniform, the case depth of carburizing layer is lower than the design specification and low hardness microzones are formed in the carburized layer. Microcracks initiate from the roller notch bottom, then joint into a main crack and propagate from the notch bottom surface to the inner. The propagation direction of the main crack basically agrees with the result of finite element analysis. Both the heat treatment process and the complex loads in the service environment are attributed to the early failure of the roller.

Failure analysis and improvement of hydrogen removal process for 17-4PH steel screw

Guo Junlei, Han Yunzhao, Han Wenkai, Li Guosheng

2024, 49(5): 278-281. doi:10.13251/j.issn.0254-6051.2024.05.047

Abstract ( 28 )

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In response to the fracture of 17-4PH stainless steel screws during using, macroscopic and microscopic microstructure observation, energy spectrum composition analysis and hydrogen content comparison analysis were conducted on the 17-4PH steel fractured screws. Based on the testing results of the fracture hardness, strength, microstructure and other aspects of the fractured screw, it is analyzed and determined that the main cause of screw failure is hydrogen induced fracture. The hydrogen removal process is optimized, and applied to production with which good results have been obtained.

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