Heat Treatment of Metals

Effect of notch type on impact properties of Cr5-series hot work die steels

Wei Xiaojie, Zuo Pengpeng, Wu Xiaochun

2024, 49(1): 1-8. doi:10.13251/j.issn.0254-6051.2024.01.001

Abstract ( 129 )

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The changing mechanism of impact properties of three Cr5 steels (H13, H11 and DVA) with unnotched, U-notched and V-notched at different tempering temperatures was studied. The fracture morphologies and microstructure were observed by using body microscopy and scanning electron microscope(SEM) and the difference of notch type in characterizing toughness was discussed. The results show that the V(U)-notched impact energy acts more on the crack extension, reflecting the ability of the material to resist crack propagation, which can be used to measure the crack sensitivity of the material, and the V-notch is more suitable for characterizing the crack sensitivity of the material due to the smaller radius of curvature on the notch tip. The unnotched impact energy acts on crack initiation and propagation, which can reflect comprehensive toughness and metallurgical defects due to the cracks are easily formed at crystal defect. Through comparison, it's that in the common tempering temperature range, 600 ℃ V-notch impact absorbed energy reaches its maximum value, indicating that the heat treatment state of the material resistance to crack expansion ability of the best; notchless impact absorbed energy of the H13, DVA, H11 steel at 560, 580, 560 ℃ is higher, and the hardness decreased less, respectively, 53.1, 50.6, 52.2 HRC, the comprehensive strength and toughness of the best.

Effect of long-term aging on microstructure and properties of nickel-based superalloy

Cai Chenyang, Cao Tieshan, Wang Wei, Chi Qingxin, Cheng Congqian, Zhao Jie

2024, 49(1): 9-15. doi:10.13251/j.issn.0254-6051.2024.01.002

Abstract ( 92 )

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Microstructure of nickel-based superalloy with different aging time was observed to explore the evolution law of microstructure and properties in the process of high temperature aging. By using OM and SEM to observe and analyze the microstructure of the alloy before and after aging, a method for quantitative analysis of microstructure evolution was proposed, and the hardness of the alloy before and after aging was tested and analyzed. The results show that after aging at 900 ℃ for 20 h without loading, the γ′ phase is cuboidal and the size does not change obviously. When aging for 100 h, the γ′ phase changes from cube to circle. After aging for 500 h, the shape of γ′ phase becomes more irregular. Some γ′ phases are connected with neighboring γ′, showing a long strip shape, but some of them remain cubic shape. When aging for 2000 h, γ′ phase is coarsened obviously and cubed degree is decreased obviously. With the aging time, the size of γ′ phase grows gradually, and the hardness of the alloy shows a decreasing trend.

Effect of thermal exposure on microstructure and mechanical properties of Ti55 alloy

Song Tijie, Wang Changyu, Wang Jue, Yu Yanyan, Lu Zengwei, Jin Dongyan

2024, 49(1): 15-21. doi:10.13251/j.issn.0254-6051.2024.01.003

Abstract ( 105 )

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Effect of thermal exposure at 400-800 ℃ on the microstructure and mechanical properties of forged Ti55 alloy was studied. Meanwhile, the fatigue fracture micro morphology characteristics at elevated temperature were analyzed. The results show that the yield strength and tensile strength are basically stable under long-term thermal exposure below 550 ℃, while the elongation decreases with the increase of exposure temperature. Thermal exposure below 800 ℃ does not change the microstructure type of the Ti55 alloy, but with the increase of thermal exposure temperature, the β phase coarsens locally at the α intersection of phase bundles. When exposed above 550 ℃, Si is obviously concentrated in the grain boundary region, and the maximum concentration is up to 1%. With the increase of thermal exposure temperature, the characteristics of high-temperature fatigue fracture of the Ti55 alloy change from transgranular toughness to intergranular brittleness.

Effect of annealing on microstructure, mechanical properties and magnetic properties of FeCoNi_2-xMnGa_x high-entropy alloys

Zhu Jiawu, Ouyang Sheng

2024, 49(1): 22-31. doi:10.13251/j.issn.0254-6051.2024.01.004

Abstract ( 64 )

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FeCoNi_2-xMnGa_x(x=0, 0.5, 0.75, 1.0, 1.25) high-entropy alloy ingots were prepared by non-consumable vacuum arc melting furnace, and then annealed at 800 ℃ and 1000 ℃ for 8 h. The effects of annealing on microstructure, mechanical properties and magnetic properties of the alloys were studied. The results show that with the increase of Ga content, the microstructure of the as-cast alloy changes from single FCC phase without Ga (x=0) to FCC+BCC dual phase, then to single BCC phase with 25at%Ga (x=1.25). After annealing at 800 ℃ and 1000 ℃, rod-like precipitates form inside the FCC phase. The compressive properties and magnetic properties of the FeCoNi_2-xMnGa_x alloy with dual phase are good, and improved after annealing. The FeCoNi_1.25MnGa_0.75 alloy annealed at 1000 ℃ possesses the best compressive performance, its compressive stress are 1852.5 MPa when the deformation amount is 20%. The FeCoNi_1.0MnGa_1.0 alloy annealed at 1000 ℃ possesses the highest saturation magnetization of 121.8 emu/g.

Differences in hardness and microstructure of ultra-thick die steel 3Cr2Mo at different cooling rates

Li Zhongbo, Yuan Qing, Xu Shaopu, Zhang Tao, Chen Xi, Mo Jiaxuan, Ren Jie

2024, 49(1): 31-38. doi:10.13251/j.issn.0254-6051.2024.01.005

Abstract ( 55 )

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Microstructure and hardness tests of an ultra-thick specification 3Cr2Mo die steel were carried out along the thickness direction. The hardness distribution and phase transformation along the thickness direction with different cooling rates were investigated. The results show that the main reason for the hardness difference along the thickness direction is the difference of the tempered sorbite lamellar spacing, which is smaller in the edge specimens and slightly larger in the heart specimens. When the cooling rate is less than or equal to 0.3 ℃/s, the high-temperature pearlite transformation and medium-low temperature bainite/martensite transformation are observed. When the cooling rate is greater than or equal to 0.5 ℃/s, only martensitic transformation occurs. The cooling rate of 0.5 ℃/s is the critical cooling rate for the martensite transformation. From this, it is inferred that the cooling rate in the thickness direction of the thick plate floats at 0.05 ℃/s, and the cooling rate of the surface does not exceed 0.1 ℃/s under which the pearlite microstructure is obtained.

Comparison on microstructure and properties of 6016 aluminum alloy sheet with different coils number of furnace charging

Sun Ning, Xu Zhiyuan, Yang Limin, Li Xinghui, Zhang Hao, Li Yancheng, Li Tao

2024, 49(1): 39-47. doi:10.13251/j.issn.0254-6051.2024.01.006

Abstract ( 34 )

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Microstructure and properties of 6016 aluminum alloy sheet with different coils number of furnace charging were systematically studied by means of OM, SEM, EBSD, TEM, XRD and tensile tests. The results show that the tensile strength and yield strength of the 6016 aluminum alloy sheet with two coils of furnace charging are relatively low, and the uniform elongation is higher, and the effect of roping line on the surface of the sheet is good. The size of the dispersed phase in the 6016 aluminum alloy sheet is different. The precipitated Mg₂Si phase at the grain boundary is mainly distributed in strips and blocks, but the size of the precipitated phase in the sheet with three coils of furnace charging is relatively larger. This is because the longer heating and cooling time during the intermediate annealing process causes the precipitated phase to grow and coarsen to a certain extent. In addition, the 6016 sheet with three coils of furnace charging exits aggregated Goss texture and Cube texture, which can easily cause roping lines on the surface of the sheet and be harmful to the surface quality of the sheet.

Analysis on friction and wear properties of materials for circular gear of harmonicgear reducers

Shao Zhuhao, Yang Dawei, Wu Yongjin, Liu Zhao, Zhao Liang

2024, 49(1): 47-52. doi:10.13251/j.issn.0254-6051.2024.01.007

Abstract ( 40 )

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Friction behaviors of two nodular cast irons (QT1 and QT2) and 40Cr steel used for domestic circular gear were studied by quantitative analysis of alloy composition, microstructure and wear resistance. The results show that for the QT1 and QT2 cast irons, the matrix is composed of pearlite, retained austenite and acicular ferrite, while the spheroidal graphite has very high nodularity and fine size. The worn positions of the QT1 and QT2 cast irons are concentrated with small fluctuations, and the maximum worn surface depths are 3.7 μm and 2.6 μm respectively. The wear morphologies of the 40Cr steel are furrows with varying depths and large fluctuations, and the maximum depth is 7.6 μm. Compared to the 40Cr steel, the QT1 and QT2 cast irons have excellent wear performance and lower friction coefficient. Domestic harmonic reducer enterprises can use nodular cast iron as circular gear material instead of the 40Cr steel.

Isothermal transition characteristics of bainitic spring steels with segregation

Yu Jinrui, Wu Kangjun, Yu Xinhong, Feng Yisheng, Zhao Ertuan

2024, 49(1): 53-60. doi:10.13251/j.issn.0254-6051.2024.01.008

Abstract ( 38 )

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Microstructure evolution of bainitic steels with segregation during isothermal process was studied by means of ultra high temperature laser confocal microscope, OM, SEM and XRD. The results show that the segregation results in mixed crystals, and the grain size gradually decreases from the diluted zone to the enriched region of alloying elements. The higher the alloying element content, the longer the incubation period of bainite and the slower the transformation rate is. Therefore, the bainite structure nucleates and grows rapidly in the alloying element diluted zone, and expands to the untransformed zone layer by layer with the extension of isothermal time. During the isothermal process, the content of retained austenite increases first and then decreases under the control of bainite transformation rate and carbide precipitation rate. At different stages of bainite transformation, the effects of segregation are different. When bainite transformation is not completed, the hardness difference between bainite and martensite microstructure is large and the banded structures are formed. When the bainite transformation is completed, the banded structures are eliminated, and the segregation results in differences in alloying elements, grain size and bainite morphology at different segregation sites.

Comparison of simulated seawater slurry erosion and wear behavior of low alloy steel with different microsturcture

Ren Wubin, Ma Heng, Cui Shaohua, Wang Menghu, Liang Xiaokai, Sun Xinjun

2024, 49(1): 61-68. doi:10.13251/j.issn.0254-6051.2024.01.009

Abstract ( 42 )

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Microstructure of the dual-phase steel and fully martensitic steel was characterized by using optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The corrosion resistance of this two steels was studied by means of potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The erosion corrosion behavior of the steels in simulated seawater mortar environment was analyzed by means of MSH erosion corrosion testing machine, and the surface morphology was characterized by using white light interferometer. The results show that the microstructure of the dual-phase steel is martensite matrix with ferrite volume fraction of 9.8%±0.6%.The microstructure of the fully martensitic steel is single lath martensite. Compared with fully martensitic steel, dual-phase steel has lower yield strength, tensile strength, hardness and corrosion resistance, but shows higher erosion-corrosion resistance. The reason is that the microhardness of martensitic phase in dual-phase steel is significantly higher than that of fully martensitic steel, and the coordination of soft and hard phases makes it difficult for microcracks to propagate in dual-phase steel, thus reducing the erosion-corrosion mass loss.

Particle size distribution of γ′ phase precipitate in Inconel X-750 alloy

Luo Lei, Wang Limin

2024, 49(1): 69-75. doi:10.13251/j.issn.0254-6051.2024.01.010

Abstract ( 27 )

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Particle size distribution of γ′ phase precipitate in Inconel X-750 alloy after solution treatment with different cooling rates and aging at different temperatures was investigated by means of scanning electron microscope, X-ray small angle scattering particle size analyzer combined with quantitative analysis of precipitates. The results show when the Inconel X-750 alloy is solution treated at 1060 ℃ for 1 h with water cooling, oil cooling, air cooling and furnace cooling, respectively, due to the fast cooling rate of water cooling and oil cooling, the precipitation of γ′ phase in the alloy is inhibited, and the size of γ′ phase particles is mostly concentrated in the range of 5-18 nm after subsequent aging at 670 ℃ for 15 h. While the secondary γ′ phase precipitated in the alloy after solution treatment with furnace cooling is hardly grows after aging, the newly precipitated tertiary γ′ phase particle size is in the range of 1-5 nm, and the precipitated γ′ phases in the alloy transform from spherical to cubic. With the increase of aging temperature, the size of the γ′ phase particles gradually increases, as its average diameter grows from 11.5 nm aged at 690 ℃ to 34.4 nm aged at 810 ℃, and the growth of the γ′ phase particles is consistent with Ostwald ripening mechanism. With the decrease of cooling rate, the mass fraction of γ′ phase particles with the size of 1-60 nm gradually increases, which is the main reason for the strength increase of alloy. However, with the decrease of cooling rate, M₂₃C₆ phase gradually grows and coarsens at the grain boundary and connects into strips, resulting in a decrease in the impact property of the alloy.

Rheological behavior and microstructure evolution of SCM435 steel under thermal compression

Du Zhongze, Qi Zejiang, Dang Xue, Yang Tongyao

2024, 49(1): 76-83. doi:10.13251/j.issn.0254-6051.2024.01.011

Abstract ( 39 )

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Thermal simulation compression test of SCM435 steel was carried out under the deformation temperature of 750-1100 ℃ and the strain rate of 0.1-20 s^-1 by Gleeble-3500 thermal simulation testing machine. Based on the stress-strain curves of the steel, the influence of deformation temperature and deformation rate on the flow stress was analyzed. The constitutive equation of SCM435 steel with strain of 0.6 was established, and the microstructure evolution and deformation mechanism were discussed. The results show that the flow stress decreases with the increase of deformation temperature and increases with the increase of strain rate. By constructing the strain-compensated Arrhenius constitutive model, the hot deformation activation energy (Q) of the SCM435 steel is about 344.564 kJ/mol, the linear correlation coefficient (R) and the average relative error (AARE) of the established constitutive model are about 0.9921 and 4.39%, respectively. With the increase of deformation temperature, the deformation mechanism of the SCM435 steel changes from dynamic recovery (DRV) to dynamic recrystallization (DRX), and with the increase of strain rate, DRX grains gradually refine, indicating that increasing deformation temperature and increasing strain rate can promote the occurrence of DRX behavior and inhibit grain growth. The average misorientation angle of the SCM435 steel under high temperature and low strain rate (1100 ℃, 0.1 s^-1) is the smallest, which is 1.27°, indicating that the dislocation density is the lowest.

Effect of Sc on growth behavior of interface compounds of Al/Fe layered composites

Wang Zhen, Gao Kunyuan, Zhang Xiaojun, Nie Zuoren, Huang Hui, Wu Xiaolan

2024, 49(1): 84-90. doi:10.13251/j.issn.0254-6051.2024.01.012

Abstract ( 27 )

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Effect of Sc element on the growth, type and micromorphology of intermetallic compounds at the Al/Fe composite interface was studied by means of SEM, EDS and other methods. The results show that the cold-rolled composite Al/Fe composite plates produce continuous interfacial compounds after annealing at 475-640 ℃ for 1 h, and the change trend of intermetallic compound thickness at 560 ℃and below is basically the same, but above 560 ℃, the growth trend of intermetallic compounds at the interface of Sc-containing composite plates slows down significantly, and the thickness is greatly reduced. This indicates that the addition of Sc elements on the Al side does not completely inhibit the production of intermetallic compounds at the interface. At the same time, the addition of Sc elements does not change the type and distribution of interface compounds, which are FeAl₃, Fe₂Al₅ and FeAl from Al side to Fe side. The Fe₂Al₅ phase at Fe side is finely jagged when annealed at 475 ℃, but the whole morphology is very flat, however, it becomes coarse finger-like morphology and uneven when annealed at 580 ℃.

40Cr/Q345B bimetallic composite behavior and interfacial microstructure evolution

Yuan Hairui, Chen Yubo, Wang Peijie, Li Zhenjiang

2024, 49(1): 90-95. doi:10.13251/j.issn.0254-6051.2024.01.013

Abstract ( 33 )

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Vacuum diffusion bonding test of 40Cr/Q345B bimetallic material was carried out under the hot compression temperature of 1000-1200 ℃, strain rate of 0.01 s^-1 and reduction of 10%-50%. The effects of hot compression temperature and reduction on the stress-strain curve and bonding interface of the bimetallic material were analyzed. The results show that the peak stress of the stress-strain curve decreases with the increase of hot compression temperature, but is not sensitive to the change of the reduction. There is an unbound zone at the interface under the condition of low temperature and low reduction. With the increase of hot compression temperature and reduction, the unbound zone at the interface disappears, the martensite gradually passes through the interface, and the grains at the interface change from straight grain boundary to curved grain boundary until the interface disappears, and the metallurgical bonding forms.

Effect of Fe content on microstructure and properties of Cu-Ti-Ni-xFe alloys

Jing Qingxiu, Peng Yong, Xiao Xiangpeng, Wei Dandan, Yang Xueqing, Hang Xiaodong

2024, 49(1): 96-102. doi:10.13251/j.issn.0254-6051.2024.01.014

Abstract ( 39 )

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Phase diagram of Cu-2.5Ti-2Ni-xFe quaternary alloy was drawn by Pandat software, and the existing form of Fe in the alloy was predicted. Subsequently, four Cu-2.5Ti-2Ni-xFe(x=0, 0.4, 0.8, 1.5) alloys with different Fe contents were prepared by vacuum melting, annealing, hot rolling, solid solution treatment, cold rolling and aging to investigate the effects of Fe content on the microstructure and properties of the as-cast and aged Cu-Ti-Ni-xFe alloys. The results show that Fe exists in the form of FeTi phase and Fe₂Ti phase in the Cu-2.5Ti-2Ni-xFe alloys, and the addition of Fe leads to the formation of coarse second phase in the as-cast microstructure, which reduces the hardness of the alloy. However, after aging, the hardness and electrical conductivity of the alloys with Fe addition are obviously improved, and the high temperature softening resistance is also better. Among the alloys, the Cu-2.5Ti-2Ni-0.8Fe alloy has the best properties, its hardness and electrical conductivity are 274.26 HV and 17.6%IACS, respectively, and its softening temperature reaches 526 ℃.

Hot ductility of Inconel 617 alloy for A-USC turbine rotor application

Li Hongmei, Bai Yaguan,Guo Wei, Nie Yihong

2024, 49(1): 103-107. doi:10.13251/j.issn.0254-6051.2024.01.015

Abstract ( 39 )

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Effect of different temperatures on high temperature tensile thermoplasticity of Inconel 617 alloy ingot was investigated. The results show that the Inconel 617 alloy has good thermoplasticity above 900 ℃, in which conditions the tensile fracture has obvious necking and the percentage reduction of area is more than 90%. With the increase of tensile temperature, the necking becomes more obvious, the dimples become more deeper, and the plasticity becomes more better. Dynamic recrystallization occurs locally during the tensile process. The higher the temperature, the more complete the recrystallization. The grains grow rapidly above 1200 ℃, and melting occurs at the fracture.

Grain growth behavior of X19CrMoVNbN11-1 blade steel

Song Mingqiang, Wang He, Song Jingjing, Liu Songfeng

2024, 49(1): 108-112. doi:10.13251/j.issn.0254-6051.2024.01.016

Abstract ( 33 )

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Effects of heating temperature, holding time, heating rate and original state on austenite grain growth of X19CrMoVNbN11-1 blade steels were studied by 3 groups different heat treatment. The results show that the growth low of austenitic grain of the X19CrMoVNbN11-1 steel is significantly different, which is mainly affected by the original microstructure. The order of effects of various heat treatment parameters on grain growth is, heating temperature, heating rate, heating time. The grain size grade and uniformity of the X19CrMoVNbN11-1 steel after subsequent quenching and tempering can be effectively improved after heating at 500 ℃/h to 1050 ℃ for 3 h, and the grain size can be controlled at the level of 5-6 grade after heating at 1100 ℃ for 3 h. Under the test conditions, when the steel is heating at 1100 ℃, the appropriate heating rate (500 ℃/h) and holding time (3 h) can achieve better grain refinement effect.

Effect of Nb element on grain coarsening of automobile carburized gear steel 20CrMnTi during heat treatment

Zheng Daoyou, Zhang Rui, Tang En

2024, 49(1): 113-118. doi:10.13251/j.issn.0254-6051.2024.01.017

Abstract ( 46 )

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Grain growth and precipitation particle distribution of two kinds of industrial carburized gear steels under the same pseudo-carburizing process were analyzed. Besides, the role of Nb element in automobile gear carburized steel was clarified. The results show that the addition of 0.02%wt Nb reduces the addition of 0.02%wt Mo and 0.02%wt Ti, and the austenite grain size of the Nb-Ti-Mo steel is slightly smaller than that of the Ti-Mo steel after carburizing at 960 ℃ for 4 h. Furthermore, the degree of mixed crystal is reduced in the Nb-Ti-Mo steel. In addition, with the addition of the Nb, the volume fraction of precipitated particles in Nb-Ti-Mo steel after carburizing at 960 ℃ for 4 h is slightly less than that of the Ti-Mo steel, but the average size of precipitated particles is smaller than that of the Ti-Mo steel, providing better pinning effect and grain refinement. The addition of the mass fraction of 0.02wt%Nb improves the thermal stability of precipitated particles and provides better precipitation strengthening effect, and the contribution of precipitation strengthening is 87.54 MPa.

Effect of solution temperature on microstructure and tensile properties of DD416 nickel-based single crystal superalloy

Chen Bowen, Zeng Qiang, Li Gang, Peng Wenya, Liu Guohuai

2024, 49(1): 119-126. doi:10.13251/j.issn.0254-6051.2024.01.018

Abstract ( 76 )

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Effect of solution treatment temperature on microstructure and tensile properties of the first generations nickel-based single crystal superalloy DD416 with high strength and low density was studied. The results show that there are obvious component segregation and element segregation in the as-cast specimens. After solution treatment, the component segregation and element segregation in the alloy are obviously improved. With the increase of solution temperature, the content of eutectic structure in the alloy decreases gradually. The pores in the as-cast alloy are cast porosity. After solution treatment, a small number of solution pores appear due to the different diffusion rates of elements, and many hollow pores in the alloy also affect the properties of the alloy. According to the 760 ℃ high temperature tensile data, the tensile properties of the alloy are significantly improved after complete heat treatment. With the increase of solution temperature, the tensile strength and yield strength of the alloy increase, and the elongation after fracture and the percontage reduction of area significantly increase. As a result, after solution treatment+aging, with the increase of solution temperature, the strength and plasticity of the alloy are improved.

Improving impact property of 52CrMoV4 spring flat steel by high temperature diffusion

Min Yongan, Shao Jiajun, Zhang Wentao, Liu Chao, Han Xiaoli

2024, 49(1): 126-130. doi:10.13251/j.issn.0254-6051.2024.01.019

Abstract ( 26 )

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In order to improve the plasticity and toughness of 52CrMoV4 spring flat steel with large section, the hot rolled 52CrMoV4 flat steel was hot forged and high temperature diffused. The impact property of the hot-rolled, forged and high temperature diffused flat steel after quenching and tempering was measured, as well as the impact fracture morphology, microstructure and hardness were investigated. The results show that compared with the hot-rolled flat steel, the effect of hot forging on improving the microstructure and properties of the flat steel is limited. High temperature diffusion at 1220 ℃ can homogenize the composition and microstructure of the flat steel, the transverse impact absorbed energy at core of the flat steel is increased by about 45%.

Effect of aging on mechanical properties of medium and high volume fraction SiC_p/2024Al composites

Cui Yan, Liang Jiarui, Cao Leigang, Yang Yue, Liu Yuan

2024, 49(1): 131-136. doi:10.13251/j.issn.0254-6051.2024.01.020

Abstract ( 38 )

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SiC_p/2024Al composites with SiC_p volume fractions of 35%, 45% and 55% were prepared by hot isostatic pressing(HIP). The effects of solution and aging treatment on the hardness, bending strength and impact property of the composites were studied. The results show that the composites with different SiC_p volume fractions are all composed of Al, SiC and Al₂Cu phases and have high density, indicating the good bonding between SiC_p reinforcement and matrix alloy. The hardness of the composites can be significantly enhanced by solution and aging treatment (T6). The aging-hardness curves of the SiC_p/Al composites with SiC_p volume fractions of 35%, 45%, 55% are basically the same, with the peak-aging time being 2 h, and the hardness increment of which are 51.56%,41.51% and 18.78%, respectively. The SiC_p/2024Al composite with SiC_p volume fractions of 35% presents the most significant increase in bending strength, being from 622.48 MPa to 838.11 MPa. As the SiC_p volume fraction increases, the impact absorbed energy of the HIP state composite decreases gradually from 3.43 J to 1.00 J, which can be further reduced after T6 treatment.

Effect of normalizing temperature on microstructure and mechanical properties of G18CrMo2-6 cast steel

Chen Yubo, Wang Peijie, Yuan Hairui, Li Zhenjiang

2024, 49(1): 137-141. doi:10.13251/j.issn.0254-6051.2024.01.021

Abstract ( 35 )

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Effect of normalizing temperature (850-1000 ℃) on microstructure and mechanical properties of G18CrMo2-6 steel was studied. The results show that the microstructure is granular bainite composed of bainite ferrite (BF) and M-A island after normalizing at different temperatures. With the increase of normalizing temperature, the quantity and size of M-A islands decreases first and then increases, so that impact absorbed energy of the steel increases first and then decreases. When the normalizing temperature below 940 ℃, with the increase of normalizing temperature, the quantity of M-A islands decreases, C, Cr and other elements spread into BF, leading to increase yield strength. When the normalizing temperature is 940 ℃, the tensile strength and impact absorbed energy of the steel are the highest, which are 942 MPa and 28 J, respectively. When the normalizing temperature is further increased, the dislocations in BF are reduced and the grains are coarsened, resulting in a decrease in yield strength.

Effect of annealing temperature on microstructure and properties of Al-Ti toughened CrCoNi medium-entropy alloy

Xu Shuanghui, He Guoai

2024, 49(1): 142-147. doi:10.13251/j.issn.0254-6051.2024.01.022

Abstract ( 26 )

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By electron backscattering diffraction (EBSD) and Vickers hardness test, the microstructure evolution low and hardness change of Al-Ti toughened medium-entropy alloy annealed at different temperatures were studied. The results show that when the annealing temperature is higher (1100 ℃), the density of annealed twins is higher, the twin morphology is more straight and regular. The relationship of recrystallization and grain growth and annealing temperature is not simple linear. When the annealing temperature exceeds the critical temperature, the processes of recrystallization and grain growth are accelerated obviously. When annealed at 1100 ℃ for 1 h, the equiaxial grains with average size of 20.89 μm are obtained, and the hardness of the alloy decreases to 302.9 HV0.2 due to the stress release.

Effect of solution and aging treatment on microstructure and properties of AlMg5Si2Mn aluminum alloy

Di Yifei, Li Jia, Li Yong, Zhao Rongda, Xiang Jun, Wu Fufa

2024, 49(1): 148-153. doi:10.13251/j.issn.0254-6051.2024.01.023

Abstract ( 29 )

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Effects of solution and aging treatment on microstructure and properties of the AlMg5Si2Mn aluminum alloy were studied by means of hardness testing, microstructure observation, XRD, tensile testing and cross-section fracture observation. The results show that after solution and aging treatment, the morphology of Mg₂Si in the alloy changes from labyrinth and rod to fine spherical shape and distributes more uniform, and thardness of the alloy is significantly improved, which increases first and then decreases as the solution treatment temperature increases, meanwhile, the tensile properties are also significantly improved. After solution treatment at 530 ℃ for 30 min and aging at 190 ℃ for 6 h, the hardness of the AlMg5Si2Mn aluminum alloy is high and up to 49.5 HRB, the tensile strength, yield strength and elongation after fracture is 260 MPa, 173 MPa, 17%, respectively.

Effect of laser power on microstructure and properties of SLM additive manufactured 316 stainless steel

Song Tao, Li Ziyao, Peng Yafang, Wang Zhiwu

2024, 49(1): 154-159. doi:10.13251/j.issn.0254-6051.2024.01.024

Abstract ( 32 )

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Specimens of 316 stainless steel were prepared by selective laser melting additive manufacturing technology under different laser powers. The crystallographic characteristics and hardness of the steel specimens were analyzed by means of OM, EBSD and Vickers hardness tester. The results show that with the decrease of laser power, the amount of precipitated phase decreases, but the input energy during manufacturing is low, the cooling rate of molten pool is high, the critical nucleation radius of dendrite is small, the nucleation rate and the number of nucleation are high during solidification, which is conducive to the grain refinement and the formation of equiaxial crystal, showing a high hardness value. The steel shows fiber texture with high degree of orientation under high laser power, while cube texture with low degree of orientation under low laser power. The main texture of the steel under laser power of 320 W is {110}<110> and {112}<111>, that under laser power of 290 W is {112}<110> and {112}<111>, and that under laser power of 260 W is {001}<110>.

Effect of heat treatment on microstructure and incrustation inhibition properties of copper-zinc alloys

Hou Yanyang, Wu Yuxuan, Cao Zhu, Li Jingyuan

2024, 49(1): 160-165. doi:10.13251/j.issn.0254-6051.2024.01.025

Abstract ( 31 )

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In order to solve the problem of incrustation damage to boilers, pipelines and other industrial equipment, a new type of incrustation inhibition alloy was designed and melted. The microstructure and surface properties of the copper-zinc alloy before and after heat treatment were characterized by means of scanning electron microscope, EDS energy spectrometer, X-ray diffractometer, electrochemical workstation and contact angle measuring instrument. The test was conducted on the independently built water circulation platform, and the residual Ca²⁺ concentration in the solution and the change of incrustation inhibition rate of the Cu-Zn alloy were determined after the water circulation experiment. The incrustation in the circulating water was collected and analyzed for micro-morphology and crystal structure changes. The results show that the copper-zinc alloy has the best corrosion resistance after heat treatment at 600 ℃, with a self-corrosion current density of 4.27 μA·cm^-2, and has the best incrustation inhibition properties, and the incrustation inhibition rate of the test solution can reach 90.27% when it is left to stand for 0.5 h after being treated with the alloy heat-treated at 600 ℃, which is an improvement of 11.06% in comparison with that of the as-cast alloy, the as-cast alloy has a incrustation inhibition rate of 79.21%.The copper-zinc incrustation inhibition alloy treatment solution has a certain timeliness, incrustation inhibition effect in 2 h is the best. The copper-zinc alloy after heat-treatment at 600 ℃ has a stronger ability to transform the block calcite into needle aragonite, the ratio of calcite to aragonite after the generation of incrustation by treating the solution with which is 1.38∶1.

Effect of solution temperature on microstructure and damping properties of Ti-Ta alloy

Zhang Wenyu, Liu Xianlan, Wu Jie, He Wenpeng, Tian Zihao, Quan Yang

2024, 49(1): 166-171. doi:10.13251/j.issn.0254-6051.2024.01.026

Abstract ( 33 )

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A Ti-32Ta alloy was prepared by vacuum melting and cold rolling. After solution treatment at 600, 700 and 800 ℃, respectively, the microstructure and damping properties of the tested alloy were characterized by means of OM, XRD, SEM, DSC thermal analyzer and DMA dynamic mechanics analyzer. The effect of solution treatment temperature on microstructure and damping properties of the Ti-32Ta alloy was studied. The results show that the recrystallization temperature of the tested alloy is between 700 ℃ and 800 ℃, and the microstructure of the specimen treated at 600 ℃ is non-recrystallized, while the specimens treated at 700 ℃ and 800 ℃ have recrystallized equiaxed grains which increased with the temperature increasing. The phase transition point of the tested alloy increases after solid solution treatment. Compared with the phase transition point of 440 K (167 ℃) for the untreated Ti-32Ta alloy, the phase transition point of specimens treated at 600 ℃ and 700 ℃ increases by 39 ℃, and that of specimens treated at 800 ℃ increases by 18 ℃. The damping properties of the Ti-32Ta alloy are not affected by the solution treatment temperature, but are greatly affected by the working temperature. When the working temperature rises above 150 ℃, the damping properties of the tested alloy increase rapidly with the increase of temperature.

Effect of post-weld heat treatment on corrosion resistance of S30408/Q345R stainless steel clad plate

Liu Wenming, Zhang Xinming, Cheng Xinlu, Ouyang Kai

2024, 49(1): 172-178. doi:10.13251/j.issn.0254-6051.2024.01.027

Abstract ( 36 )

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Effect of post-weld heat treatment (PWHT) on microstructure, intergranular corrosion resistance and stress corrosion resistance of the weld joint of S30408/Q345R stainless steel clad plates was studied. The results show that after the PWHT (580 ℃ for 2 h), the alloying element diffusion occurs near the fusion line between transition layer weld and base layer weld of the weld joint, and the range of decarburization layer decreases. After the PWHT, the intergranular corrosion resistance of the weld joint decreases, and the corrosion crack is located near the weld fusion line. The PWHT has little influence on the stress corrosion resistance of weld joints. No secondary fracture is found at the tensile fracture of the weld joint, and the stress-corrosion cracking sensitivity ratio of the S30408 stainless steel clad layer is low, showing the stress corrosion sensitivity is small.

Effect of aging treatment on mechanical properties and microstructure of low pressure cast ZL114A alloy

Tian Shaokun, Jin Yuanping, Wang Ping, Yang Kun, Liu Xiaofei, Guo Zhan, Yu Ruixing, Fan Qingli

2024, 49(1): 179-185. doi:10.13251/j.issn.0254-6051.2024.01.028

Abstract ( 30 )

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Taking low-pressure cast ZL114A alloy as the research object, the microstructure and mechanical properties of the solution and aging treated alloy specimens were observed and tested by means of optical microscope, Brinell hardness tester and universal testing machine. At the beginning of aging treatment, the strength of the alloy increases rapidly, and the growth trend slows down with the aging time extension. After aging at 155 ℃ for 12 h, the tensile strength and yield strength of the alloy increases from 266.7 MPa and 161.7 MPa in solid solution state to 333.3 MPa and 272.3 MPa, respectively. The elongation of the alloy decreases with aging time increasing, from 12.00% in solid solution state to 7.00% after aging at 155 ℃ for 12 h. The higher the aging temperature, the greater the atomic diffusion driving force, the faster the strength of the alloy increases, the shorter the time is required to reach the peak, and the faster the elongation decreases. The reason for the increase of strength and decrease of elongation of the alloy is the segregation of Mg and Si atoms and the formation of stable Mg₂Si phase. With the precipitation and transformation of the second phase, the degree of coherency between the second phase and the matrix gradually decreases, and the strength of the alloy reaches the maximum when the second phase maintains a semi-coherent relationship with the matrix.

Effect of annealing temperature on microstructure and properties of 8111 aluminum foil

Xiao Changle, Wu Hongyan, Chen Wei, Kang Jichang, Chen Yunan, Liu Pengju, Wang Yiren, Wang Xiubin

2024, 49(1): 186-192. doi:10.13251/j.issn.0254-6051.2024.01.029

Abstract ( 29 )

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Effect of heat treatment process on microstructure and properties of 8111 alloy produced by casting and rolling process was studied. The results show that after cold rolling and homogenization treatment, the microstructure uniformity of the cast-rolling sheet is improved, the chain like second phase disappears, and the grain morphology changes from fiber to fine equiaxed recrystallized grains. With the increase of annealing temperature, the microstructure of the aluminum foil undergoes a process of recovery, recrystallization and grain growth. The recrystallization is completed when annealed at 330 ℃ for 2 h, with an average grain size of about 42 μm. When the annealing temperature is at 360 ℃, the average grain size is the largest, about 45 μm. Within the studied annealing temperature range, there was no significant change in the morphology of the second phase compound in the aluminum foil matrix. With the annealing temperature increasing, the tensile strength of the aluminum foil shows a decreasing trend, reaching the minimum value of 87 MPa when the annealing temperature is 360 ℃, while the elongation shows a trend of first increasing and then decreasing, reaching the maximum value of 10.2% when the annealing temperature is 330 ℃, and the electrical conductivity shows a trend of first increasing and then decreasing, basically unchanged when the annealing temperature is 330-360 ℃.

Strengthening and toughening heat treatment of 60Si2Mn steel chipping blades for wood-chip machine

Tang Lili, Chen Kangmin, Luo Xinmin

2024, 49(1): 192-197. doi:10.13251/j.issn.0254-6051.2024.01.030

Abstract ( 37 )

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In according with the service conditions of wood-chip cutting machine, the preparatory heat treatment and strengthening and toughening heat treatment processes were designed for the 60Si2Mn hot-rolled steel blades, and the metallographic structure, bending strength, impact property and wear resistance were tested, and the heat treatment process of the cutting machine blades made of 60Si2Mn hot-rolled steel was optimized. The results show that the 60Si2Mn hot-rolled steel blades can obtain good combination of strength and toughness after double-refinement spheroidizing annealing, and quenching at 900-930 ℃ and tempering at 300-310 ℃, which the martensitic grade is grade 1. When quenched at 900 ℃ and tempered at 310 ℃, the bending strength reaches 4350 MPa, the impact absorbed energy is 10.3 J, and the total wear mass loss under the load of 98 N for 4 h is 14 mg, which fully meets the technical requirements of the blades of the light duty wood-chip machine.

Effect of annealing process on microstructure and properties of T4003 high strength ferritic stainless steel

Li Zhiping, Wang Hongxia, Zhao Gang, Wang Junhai

2024, 49(1): 198-201. doi:10.13251/j.issn.0254-6051.2024.01.031

Abstract ( 35 )

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Microstructure and mechanical properties of the T4003 high strength ferritic stainless steel annealed at 640-850 ℃ by using a box furnace in laboratory were analyzed by means of optical microscope, scanning electron microscope and tensile test. The results show that after annealing, the matrix is mainly composed of ferrite and a few fine carbide particles. When the annealing temperature is 640 ℃, the uneven grain size is obvious. When annealed at 680-780 ℃, the grain size is still uneven, but the number of fine grains increases with the increase of annealing temperature. When the annealing temperature is 830 ℃ and 850 ℃, the austenite transformation occurs and fine recrystallized grains are obtained. The as-hot-rolled tested steel has high strength and low plasticity, while with the increase of annealing temperature, the strength shows a trend of first decreasing and then increasing, and the elongation after fracture shows a trend of first increasing and then decreasing. The yield strength of the tested steel annealed at 640 ℃ is slightly lower than the requirement of high strength stainless steel(R_p0.2≥350 MPa), but that at other annealing temperatures meets the requirement. The reasonable annealing temperature can be selected according to the requirements of the strength level.

Effect of tempering process on microstructure and mechanical properties of A3 axle steel for railway

Zhao Zhigang, Chen Jianli, Zhang Jinwen, Wang Songwei, Wang Yutian

2024, 49(1): 202-205. doi:10.13251/j.issn.0254-6051.2024.01.032

Abstract ( 38 )

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Effects of different tempering processes on microstructure and mechanical properties of A3 axle steel for railway vehicles were investigated through experiments. The results show that microstructure of the A3 axle steel is tempered sorbite when quenched at 860 ℃ and tempered at 640-740 ℃, and the room temperature tensile strength and yield strength show a decreasing trend with the gradual increase of the tempering temperature, while the impact absorbed energy, elongation and percentage reduction of area show an increasing trend. When the tempering temperature is gradually increased in the range of 640-680 ℃, there is a significant increase in the impact absorbed energy. However, when the tempering temperature is gradually increased in the range of 680-740 ℃, the impact absorbed energy gradually increases but the increase extent is small. Under the process condition of quenching at 860 ℃, in order to meet the various properties of the A3 axle steel, its tempering temperature should be controlled at 680-720 ℃.

Microstructure and magnetic properties evolution of NiPt5 alloy during heat treatment and rolling

Zhang Qiaoxia, Zhang Bohou, Xu Guojin, Hao Haiying, Luo Junfeng, He Jinjiang

2024, 49(1): 206-210. doi:10.13251/j.issn.0254-6051.2024.01.033

Abstract ( 28 )

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Microstructure evolution of NiPt5 alloy at different heat treatment temperatures, and the influence of heat treatment conditions and different deformation amounts on magnetic properties were studied by means of optical microscope, magnetic permeability testing and simulation calculations. The results show that the recrystallization of the NiPt5 alloy is not complete after forging and rolling and then heat treatment at 750 ℃ for 2 h. When the temperature reaches 900 ℃, the grain size is fine and evenly distributed. The magnetic permeability of the NiPt5 alloy decreases significantly compared with that of the rolled state during the recovery and recrystallization process, with little fluctuation in this stage. The magnetic permeability decreases further at the stage of complete recrystallization and grain growth. Combined with the stress change simulation during rolling deformation, it is found that with the increase of deformation amount, the internal stress, the dislocation density and the barrier of domain walls movements increase, and the magnetic permeability increases significantly. Then with the increase of deformation amount, the stress and dislocation density reach saturation, the magnetic permeability tends to be stable, and the magnetic permeability volatility increases with the increase of deformation amount, but the internal stress distribution is uneven, showing an increasing trend.

Effect of diffusion annealing on microstructure and component segregation of H13 steel

Fan Mingqiang, Zhao Yingli, Li Sufang, Liang Jia, Wang Chao, Xu Junjun, Wang Jianqiang, Zhao Zhengrong

2024, 49(1): 211-214. doi:10.13251/j.issn.0254-6051.2024.01.034

Abstract ( 29 )

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Microstructure of as-cast H13 steel and microstructure evolution and component segregation during diffusion annealing were studied by means of OM and SEM. The results show that the as-cast microstructure of the electroslag remelt H13 steel is thick martensite+bainite+liquid-dissected carbides. High melting point liquid-dissected carbides and large size secondary carbides are distributed between dendrites and grain boundaries, and there are serious dendritic segregation and component segregation. With the increase of diffusion annealing temperature, the carbide gradually dissolve into the matrix, and the dissolution rate of carbides and the diffusion rate of elements in the dendrites are obviously faster than those at the interdendritic region and grain boundaries, which will preferentially meet the requirements of composition uniformity. When the diffusion annealing is 1240 ℃, the large size secondary carbides between dendrites are almost all dissolved back into the matrix, and the amount of high melting point liquid-dissected carbides at the grain boundary is obviously reduced, and only a few small particles of liquid-dissected carbides are left. For considering the energy saving and the yield improving, it is suggested that diffusion annealing at 1240 ℃ for 10 h is better process for the H13 steel.

Effect of homogenization process on microstructure of 6014 aluminum alloy

Chi Rui, Li Yancheng, Meng Shuang, Xu Zhiyuan, Yu Junpeng, Zhang Dezhen, Guo Fengjia, Sun Ning

2024, 49(1): 215-222. doi:10.13251/j.issn.0254-6051.2024.01.035

Abstract ( 27 )

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Effect of homogenization process on microstructure, iron-rich phase transformation, element distribution and dispersion phase uniformity of 6014 aluminum alloy was studied by means of bright and dark field images of optical microscope, differential scanning calorimetry, scanning electron microscope, transmission electron microscope. The results show that the dendrite segregation and non-equilibrium eutectic structure are found in the 6014 aluminum alloy ingot, the element content fluctuates greatly, and the grain is equiaxed. The content of the second phase in the ingot is significantly higher than that after homogenization treatment. Due to the different morphology and distribution of the second phase, it can be divided into α-AlFeMnSi, β-AlFeSi, Mg₂Si and Q-AlCuMgSi phase, respectively. After two-stage homogenization at 560 ℃ for 4 h and 540 ℃ for 6 h, the reticular dendrites are not completely broken. When the holding time of first-stage homogenization at 560 ℃is extended to 12 h, more β-AlFeSi phase is transformed into α-AlFeMnSi phase. After single-stage homogenization at 560 ℃for 19 h, the dendrites are basically changed from reticular morphology to chain morphology. After two-stage homogenization at 580 ℃ for 4 h and 540 ℃ for 6 h, the dispersed α-AlFeMnSi phase is distributed more uniform. When the holding time of first-stage homogenization at 580 ℃ is extended to 12 h, overburing occurrs and the size of the dispersion phase increases which enriches around the grain boundary.

Effects of cold deformation and recrystallization heat treatment on hardness of high-manganese austenitic cryogenic steel

Zhang Fuwei, Zhu Hai, Li Xiaochen, Wang Yangwen, Gao Peihua, Wang Honghong

2024, 49(1): 223-227. doi:10.13251/j.issn.0254-6051.2024.01.036

Abstract ( 29 )

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Effects of cold deformation and recrystallization heat treatment on hardness of hot-rolled Fe-Mn-Cr-C series high manganese austenitic cryogenic steel with deformation of 0, 12.5% and 50% were studied by means of EBSD, XRD, tensile test and hardness test. The results show that microstructure of the steel is still single austenite and no new phase is observed after cold deformation. With the increase of cold deformation, the quantity of twins in the steel increases. When the deformation is 12.5%, the deformation twins are formed in a small number of grains. When the deformation is 50%, the deformation twins are dense and intersecting with each other. The hardness of the steel increases from 262 HV to 400 HV with the increase of deformation from 0 to 50%, and decreases to 179 HV and 166 HV respectively after recrystallization heat treatment.

Comparison of HiB and CGO orientation silicon steels and its normalizing annealing process

Yang Yuanyuan, Wang Dong, Huang Li, Liu Baozhi

2024, 49(1): 228-234. doi:10.13251/j.issn.0254-6051.2024.01.037

Abstract ( 37 )

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Main differences between common oriented silicon steel (CGO) and high magnetic induction oriented silicon steel (HiB) were analyzed in detail from the perspective of chemical composition system and production process, and the laboratory research of normalizing annealing process and industrial trial production of the HiB steel were carried out. The results show that the main difficulty in transforming the production of the CGO steel to the HiB steel is the formulation of normalizing annealing process. The optimal laboratory normalizing annealing process of the HiB steel is the annealing temperature of 1120 ℃, annealing time of 4 min, and air cooling temperature from 900 ℃. The microstructure of the HiB steel after hot rolling and normalizing annealing is ferrite, and the microstructure after normalized annealing is mainly recrystallized grains distributed along the rolling direction. The main texture types of the industrial trial-produced HiB steel after normalizing annealing are Goss texture {110}<001> and copper texture {112}<111>.

Mechanical properties and corrosion resistance of steam oxidized T-250 steel

Zhang Xiaojuan, Wang Junxi, Bai Lu, Zhou Zhongping, Ni Linyu, Zhao Yuwei, Min Yongan

2024, 49(1): 234-241. doi:10.13251/j.issn.0254-6051.2024.01.038

Abstract ( 30 )

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T-250 steel after steam oxidation treatment and air oxidation treatment was tested by tensile, electrochemical polarization curve, damp heat, salt spray and other tests to explore the effect of steam oxidation on mechanical properties, such as tensile strength and elongation of the T-250 steel and its corrosion resistance in different environments. The results show that the T-250 steel treated by steam oxidation has good mechanical properties and better corrosion isolation effect than that treated by air oxidation, without obvious hydrogen induced delayed fracture caused by steam.

Microscopic mechanism of induction hardening of 34CrNiMo6 steel crankshaft journal

Wang Yingzhi, Xie Bo, Ji Chao, Wang Hongxia, Zheng Liuwei, Liang Wei

2024, 49(1): 242-248. doi:10.13251/j.issn.0254-6051.2024.01.039

Abstract ( 92 )

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Hardness value of 34CrNiMo6 steel crankshaft journal after induction hardening with intermediate frequency and tempering at 300 ℃ was tested under quenching voltages of 460 V, 480 V and 500 V through microhardness tester. The microstructure evolution of the journal under different quenching voltages, and the influence mechanism of microstructure evolution on the surface hardness of the crankshaft steel was observed and studied by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EBSD) and X-ray diffraction analyzer (XRD). The results show that after induction hardening at 460 V, 480 V and 500 V, the surface hardness of each specimen is significantly improved, and the hardness of the subsurface layer reaches the maximum. This is mainly due to the different microstructure, phase contents and dislocation densities in different regions of each specimen after surface induction hardening at different voltages. According to the different structures and hardness distribution, the journal can be divided into hardened layer, transition layer and core from the surface to the inside. The depth and hardness of the hardened layer are positively correlated with the quenching voltage.

Microstructure distribution and peak temperature model of 65Mn steel during laser surface treatment

Guo Shuaihan, Li Zhenxing, Cen Yiming, Zhu Yanming, Chen Fengchen, Yang Mingtao, Kong Jia

2024, 49(1): 249-256. doi:10.13251/j.issn.0254-6051.2024.01.040

Abstract ( 28 )

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Laser surface treatment of 65 Mn steel for agricultural machinery was carried out by using high power semiconductor laser. The effects of laser power (1.5-2.5 kW) and scanning speed (20-40 mm/s) on the microstructure and hardness distributions were studied. The temperature distribution during laser surface treatment was simulated by using ABAQUS software, the variation law of temperature field was analyzed, and the mathematical model of peak temperature was established. The results show that after laser surface treatment, the hardened layer of the 65Mn steel is composed of martensite and retained austenite, and the content of retained austenite decreases with the increase of depth from the surface. The depth of the hardened layer is 80-680 μm, and the hardness is 800-970 HV0.5. In addition, the simulation results show that the peak temperature increases with the decrease of scanning speed and the increase of laser power, and decreases with the increase of depth from the surface. The established peak temperature model is in good agreement with the simulation results, and the culculation results of the hardened layer depth are in good agreement with the measured values.

Corrosion properties of micro-arc oxidation coating on AZ80 extruded magnesium alloy

Tang Jiaqi, Xue Yuna, Wang Cankun, Shen Yi, Liu Xiaolong, Ji Yunzhuo, Fang Ye, Wang Boyao

2024, 49(1): 256-261. doi:10.13251/j.issn.0254-6051.2024.01.041

Abstract ( 25 )

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Aiming at the service environment and surface protection characteristics of magnesium alloy exposed moving parts, micro-arc oxidation (MAO) coating was prepared on AZ80 extruded magnesium alloy. The static corrosion properties of the AZ80 alloy substrate and MAO coating were studied by continuous slat fog corrosion test. Moverover, pre-corrosion of the AZ80 alloy substrate and MAO coating was carried out, and the effect of MAO coating and pre-corrosion time on the corrosion behavior of the AZ80 alloy were analyzed through slow strain rate tensile test. The results show that the MAO coating has good static protection properties. While after salt fog corrosion for 6 days, the pitting corrosion occurs, and then after the coating is damaged the corrosion depends on the corrosion resistance of the AZ80 alloy substrate. Under the slow strain rate tensile condition, the stress corrosion sensitivity increases with the prolongation of the pre-corrosion time, while the stress corrosion sensitivity index of MAO coating is obviously smaller than that of the AZ80 substrate. The MAO coating has obvious protective effect for the AZ80 substrate, which can effectively improve the dynamic corrosion resistance of the magnesium alloy.

Effect of annealing on porosity of Cr coating on zirconium alloy surface

Li Zhikang, Wang Quanwei, Shen Xiaofeng, Huang Jiao, Fan Lifeng, Ma Wen, Zhang Pengxing

2024, 49(1): 262-267. doi:10.13251/j.issn.0254-6051.2024.01.042

Abstract ( 28 )

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Cr coating was prepared on Zr-4 alloy by supersonic flame spraying (high velocity oxygen fuel, HVOF), annealed at 700 ℃ for 2 h, and oxidized at 1000 ℃ in water vapor environment, and the densities of the coating were measured by a Haus balance density measurement kit to investigate the effect of annealing on the porosity of Cr coatings. The results show that annealing can significantly improve the Cr coating density and compensate for the high porosity of the coating by HVOF with the experimental process parameters. There is no significant change in the interface between the coating and the substrate. The oxidation resistance of the annealed Cr coating is better than that of the unannealed specimen. It indicates that appropriate annealing after coating preparation can enhance the oxidation resistance at high temperature by increasing the coating densities and improving the coating microstructure.

Effect of boronizing process on properties of 12Cr2Ni3Mo5 steel for automobile engine bearing

Hu Ruihai, Feng Song, Zu Runqing, He Yi

2024, 49(1): 268-272. doi:10.13251/j.issn.0254-6051.2024.01.043

Abstract ( 45 )

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Taking 12Cr2Ni3Mo5 steel for automobile engine bearing as the tested material, the boronizing process and the properties of the steel were studied. The thickness, microhardness distribution, wear resistance and microstructure of the boronizing layer of the steel after boronizing at 850-1000 ℃ for 2-6 h were analyzed. The results show that the thickness of borided layer increases with the increase of boronizing temperature or boronizing time. When the boronizing time is 5 h, the hardness of the boronizing layer increases with the increase of boronizing temperature, which is much higher than the substrate hardness of 420 HV0.5. When the boronizing temperature is 1000 ℃, the hardness of the boronizing layer reaches a maximum of 1520 HV0.5. When the wear time is 60 min, the wear mass loss of the steel is 4.5, 3.2, 2.2 and 2.0 mg at boronizing temperature of 850, 900, 950 and 1000 ℃, respectively, which is significantly lower than that without boronizing (11 mg), indicating that the boronizing treatment can improve the hardness and wear resistance of the 12Cr2Ni3Mo5 steel. However, when the boronizing temperature exceeds 950 ℃ and the boronizing time exceeds 5 h, the improvement effect decreases significantly. Therefore, considering the property after boronizing and economic cost of boronizing process, the boronizing temperature of 950 ℃ and the holding time of 5 h is the best boronizing process for the 12Cr2Ni3Mo5 steel. Under this process, the thickness of the boronizing layer is 83 μm, the maximum hardness can reach 1432 HV0.5, and the microstructure of the boronizing layer is mainly Fe₂B phase.

Cause analysis and improvement of tensile strength fluctuation in the same circle of large size SWRS82B steel wire rod

Li Yueyun, Wang Lei, Li Jianhua, Zhang Yu

2024, 49(1): 273-278. doi:10.13251/j.issn.0254-6051.2024.01.044

Abstract ( 36 )

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Tensile strength, chemical composition and microstructure of SWRS82B steel wire rod in the same circle were analyzed, and the reason for the large fluctuation of stensile trength was found as the presence of abnormal microstructure at the lapping point. The reason for the formation of abnormal microstructure was identified by analyzing the continuous cooling process of the SWRS82B steel wire rod through thermal simulation experiments and detecting the cooling condition of Stelmor. The results show that the addition of V element in the composition causes the separation of pearlite and bainite transformation zones. When the cooling rate is over or equals to 3 ℃/s and the temperature is below 550 ℃, the bainite transformation occurs. Due to the unreasonable set of Jialing device (a device which is installed on the Stelmor, and is used to adjust the wind distribution between the lapping point and non-lapping point) and the higher wind speed at the lapping point, the supercooled austenite undergoes a partial low-temperature transformation, and the phase transformation products are pearlite and bainite, resulting in significant fluctuations of the tensile strength in the same circle. The Jialing device and fan air volume are adjusted to reduce the cooling speed of the lapping point, the tensile strength fluctuation in the same circle is reduced from 102 MPa to within 49 MPa, and the tensile strength qualification rate is increased from 88% to 100%.

Failure cause analysis of 40Cr bolt used in hanger of train brake lever

Liu Yanfeng, Liu Xiaomin, Wang Fayun, Zhao Yuqing, Li Xiaozeng, Pan Yonghong

2024, 49(1): 279-283. doi:10.13251/j.issn.0254-6051.2024.01.045

Abstract ( 33 )

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40Cr bolt used in hanger of train brake lever was broken after running about two years. The reasons for failure of the 40Cr bolt were analyzed through fracture analysis, chemical composition analysis, metallography detection, hardness test and impact test. The results show that the microstructure of the failed bolt is banded structure consisting of tempered sorbite, upper bainite, low bainite, retained austenite and non-metallic inclusion, while the hardness and impact property of the bolt do not meet the standard requirements. During the running of train, the fastening nut become loose, and the long-term vibration and impact make the root of the thread at junction with the screw crack first, which leads to the subsequent intergranular brittle fracture of the bolt.

Numerical simulation and experimental verification of influence of quenching media on residual stress of 7075 aluminum alloy

Tang Peng, Lu Shengcheng, Xiao Peixin, Li Jiadong, He Wanyao

2024, 49(1): 284-290. doi:10.13251/j.issn.0254-6051.2024.01.046

Abstract ( 50 )

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Experimental verification method and numerical simulation of ABAQUS in different medias were used to explore the mechanism of three quenching medias (water, 10%NaCl solution and engine oil) on the mechanical properties and residual stress of 7075 aluminum alloy. The numerical simulation results show that the residual stress after quenching in three medias shows the typical stress distribution characteristics of "internal tension and external compression". Moreover, the residual stress of the specimen after quenching with 10%NaCl solution is the highest, and that with engine oil is the lowest, which is related to the heat exchange state of the aluminum alloy surface in different medias. The tested results show that the salt crystals precipitated in the brine quenching process can make the vapor film on the surface of the specimen broken and have a better heat exchange rate, while layer of oil film formed in the engine oil quenching process reduces the heat exchange rate between the specimen and oil, leading to differences in mechanical properties of the alloys quenched in different medias. According to the hardness values of the quenched specimen from large to small, the three quenching medias are 10%NaCl solution, water and engine oil, which is consistent with the order of residual stress in the simulation results.

Effect of quenching medium on microstructure and properties of 7050 aluminum alloy hot forgings

Shi Peifei, Zhang Hui

2024, 49(1): 290-295. doi:10.13251/j.issn.0254-6051.2024.01.047

Abstract ( 28 )

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A 7050 aluminum alloy hot forging for automobile was selected, and the specimens were rapidly heated to 746 K with a rate of 20 K/min and held for 1 h. Then the specimens were rapidly transferred to the PAG polymer solution with concentrations of 0% (water), 5%, 10%, 20%, 30% and air to quench respectively, and finally the aging treatment was carried out using the T74 process (393 K for 6 h and 436 K for 12 h). The effects of different PAG quenchant concentrations on the residual stress, second-phase particles, tensile strength and yield strength of the 7050 aluminum alloy specimens were analyzed. The results show that with the increase of PAG quenchant concentration, the residual stress of the aluminum alloy specimens gradually weakens, the volume fraction of the second phase gradually increases, and the tensile strength and yield strength gradually decrease. Considering comprehensively, the PAG quenchant concentration of 10%-20% can meet the technical requirements, with which the quenched specimens of the 7050 aluminum alloy have relatively low residual stress, the tensile strength is 512-519 MPa and the yield strength is 472-478 MPa, and meeting the mechanical properties requirements of tensile strength greater than 510 MPa and yield strength greater than 455 MPa.

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