Heat Treatment of Metals

Effect of aging process on σ phase precipitation of 2205 duplex stainless steel

Gao Xiaodan, Ren Xueping, Li Jingkun, Yan Qiang, Yuan Aoming

2020, 45(10): 1-5. doi:10.13251/j.issn.0254-6051.2020.10.001

Abstract ( 103 )

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2205 duplex stainless steel was solid-solution treated at 1050 ℃ and 1350 ℃ for 30 min, and then aged at 650-1000 ℃ for 0.5-1440 min. The microstructure and σ phase were characterized by optical microscope (OM) and scanning electron microscope (SEM). The results show that the precipitation of σ phase in the 2205 duplex stainless steel after solid solution treatment at 1050 ℃ occurs during aging treatment at 650-850 ℃. At 850 ℃, the precipitation of σ phase is the fastest, and the precipitation rate decreases when the aging temperature deviates from 850 ℃. After solid solution treatment at 1350 ℃, the precipitation temperature of σ phase rises in overall, and its range is wider. The σ phase coarsens quickly after precipitation and the volume fraction reaches 0.25%-0.75% within 3 h, then the growth rate of σ phase decreases with the increase of aging time. The σ phase precipitates at the phase boundary between ferrite and austenite with the morphology of quasi-spherical particles less than 1 μm, then it grows in the narrow region of several microns along the width of ferrite phase. The aging temperature affects the precipitation behavior of 2205 duplex stainless steel, and the aging temperature should be away from 850 ℃ to avoid the precipitation and growth of σ phase.

Effect of quenching water temperature on mechanical properties and corrosion resistance of Al-Mg-Si series alloy

Wei Manxiang, He Lizi

2020, 45(10): 6-10. doi:10.13251/j.issn.0254-6051.2020.10.002

Abstract ( 70 )

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Effect of water temperature on properties of Al-Mg-Si series alloy during solution treatment was studied by means of tensile properties test, optical microscope, scanning electron microscopy, and electrochemical performance test. The results show that with the increase of quenching water temperature during solution treatment, the tensile strength and yield strength of the alloy are not changed significantly, and the elongation and hardness of the alloy are decreased, that is, the alloy has good comprehensive mechanical properties when quenched at 20 ℃, the microhardness, the tensile strength and the yield strength are 129.4 HV0.3, 352.2 MPa, 300.9 MPa, respectively.Meanwhile, the resistance to intergranular corrosion of the alloy is gradually decreased, but the resistance to spalling corrosion is changed a little, which are both PC grades. Therefore, the alloy has the best resistance to intergranular corrosion when quenched in water at 20 ℃, and the maximum corrosion depth is 231.4 μm, which is in accord with the results of electrochemical performance test, the maximum corrosion potential is -0.834 V.

Effect of quenching-partitioning process on decomposition of retained austenite in steel during secondary quenching

Li Changyun, Zhang Shanshan, Kang Renmu, Xu Lei, Mi Guofa

2020, 45(10): 11-16. doi:10.13251/j.issn.0254-6051.2020.10.003

Abstract ( 71 )

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0.26C-1.72Si-1.56Mn steel was treated by quenching-partitioning (Q-P) with different carbon partitioning time, and the Q-P microstructure, especially the decomposition of austenite during the secondary quenching stage of the Q-P process, was investigated. The results show that the mix microstructure of lath martensite and secondary quenching microstructure is formed after Q-P treatment, with existence of twin martensite in the secondary quenching microstructure. After Q-P treatment, the C content in retained austenite is higher than 1.0 wt% and the content of retained austenite is not less than 11%(volume fraction) with the partitioning time in the range of 10-300 s, which is beneficial to the improvement of toughness. The morphologies and size of the untransformed austenite after primary quenching are the key factors affecting its stability. The film austenite between primary martensite laths is easy to become retained austenite. Compared with the block untransformed austenite, the strip-shaped untransformed austenite is easy to form secondary quenching martensite and lamellar retained austenite.

Research progress in preparation and heat treatment of high entropy alloy

Jia Zhixuan, Chu Yanpeng, Feng Yunli, Li Jie

2020, 45(10): 17-23. doi:10.13251/j.issn.0254-6051.2020.10.004

Abstract ( 86 )

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Compared with traditional alloys, high-entropy alloys(HEAs) have outstanding characteristics such as high strength and toughness, good soft magnetic properties, high temperature stability, and corrosion resistance. The application potential is huge in many fields. The research progress, advantages and disadvantages of preparing HEAs by means of vacuum melting, powder metallurgy, laser cladding and magnetron sputtering were mainly introduced. The influence of different heat treatment processes on the microstructure and properties was analyzed. And the prospects of high-entropy alloy preparation and simulation calculation were put forward.

Hot deformation behavior and hot processing map of 30CrNi3MoV steel

Chu Tao, Shen Hui, Si Tingzhi

2020, 45(10): 24-30. doi:10.13251/j.issn.0254-6051.2020.10.005

Abstract ( 62 )

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Unidirectional thermal compression tests on 30CrNi3MoV steel were carried out by using Gleeble-3500 thermal-mechanical simulator, the hot deformation behaviors at deformation temperatures of 950-1150 ℃ and strain rates of 0.01-10 s^-1 were studied, the strain-compensated flow stress constitutive equation and the processing map were established for the 30CrNi3MoV steel. The results show that the true stress-strain curves of the 30CrNi3MoV steel have three characteristics:(i)under conditions of high temperature and small strain rate, being typical dynamic recrystallization process; (ii) under conditions of low temperature and small strain rate,characterized as dynamic recovery; and (iii) when the strain rate is large, the stress increases with the increase of strain, and there is no obvious peak stress. The modified strain coupled flow stress constitutive equation displays highest accuracy when constructed by using the 5-degree polynomial fitting, by which the obtained mean relative error between the predicted and the experimental values is 3.2%, and the correlation coefficient R is 0.993.The hot processing map shows that the optimum deformation temperature and strain rate ranges for the 30CrNi3MoV steel are 1020-1150 ℃ and 0.03-0.35 s^-1, respectively.

Hot deformation behavior and high temperature plastic constitutive equation of LZ50 steel for axle

Zheng Xiaohua, Bai Yongqing, Jia Xiaobin

2020, 45(10): 31-34. doi:10.13251/j.issn.0254-6051.2020.10.006

Abstract ( 58 )

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Taking LZ50 steel for high-speed railway axle as the research object, Gleeble-1500D thermal simulation machine was used to conduct the hot deformation compression experiment at the temperature of 1050-1200 ℃, with the strain rate of 0.01-1 s^-1, and 50% deformation.The true stress-strain curves of LZ50 steel under different process parameters were obtained by experiments.And the plastic constitutive equation of LZ50 steel at high temperature was deduced by Arrhenius hyperbolic sine function.The dynamic recrystallization behavior of LZ50 steel under different thermal deformation conditions was analyzed.The results show that LZ50 steel is sensitive to the changes of temperature and strain rate. With the increase of temperature and the decrease of strain rate, the flow stress decreases.The deformation activation energy of LZ50 steel is 217 920.626 J/mol.The higher the deformation temperature, the lower the strain rate is, and the dynamic recrystallization is more likely to occur.

Effect of controlled forging and cooling process on mechanical properties of GCr15 bearing steel

Guo Hao, Hu Linzhuang, Lei Jianzhong, Liu Yang, Du Sanming, Zhang Yongzhen

2020, 45(10): 35-39. doi:10.13251/j.issn.0254-6051.2020.10.007

Abstract ( 71 )

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Effect of different controlled forging and cooling processes on mechanical properties of GCr15 steel was investigated by means of testing the tempering stability, impact property and rolling contact fatigue life. The results show that the tempering stability of the specimens can be improved by using controlled forging and controlled cooling technology, the impact property can be increased by more than 50%, and the contact fatigue life can be increased by more than 40%.

Effect of cold rolling deformation on microstructure and properties of 7A75 aluminum alloy

Zhu Pengcheng, Liu Wenwen, Zhang Yanzhi, Jiang Yalin, Jiang Lijun

2020, 45(10): 40-43. doi:10.13251/j.issn.0254-6051.2020.10.008

Abstract ( 50 )

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Effect of cold rolling deformation on microstructure and mechanical properties was investigated, the mechanism of second phase particles simulated nucleation was discussed. The microstructure was characterized by using OM and TEM. The mechanical properties were tested by using tension tester machine. The IE value was tested by using sheet forming test machine. The results indicate that the strength and elongation increases with the increase of deformation, and the increase rate of yield strength is higher than tensile strength. When the deformation is 50%, the yield strength and tension strength reach 435 MPa and 460 MPa respectively, which have an increase of 190 MPa and 110 MPa respectively compared to those without deformation. Meanwhile, the elongation increases to 14%, and the IE value also increases with the increase of deformation. When the deformation is 30%, 50% and 70%, the average grain size is about 31.5, 13.5 and 13.0 μm respectively, which shows that the greater the deformation, the smaller and more uniform the matrix grain size. The precipitation phase MgZn₂ lager than 0.5 μm simulates the nucleation of recrystallization grain after cold rolling process during the solution treatment, while the ones which has the size of 50-100 nm pins the grain boundaries and inhibits the growth of recrystallization grains.

Effect of pre-strain and aging treatment on residual stress, microstructure and properties of 7A55 aluminum alloy

Wang Shuhui, Yang Chunmiao, Song Wei, Sheng Guangying

2020, 45(10): 44-47. doi:10.13251/j.issn.0254-6051.2020.10.009

Abstract ( 71 )

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Effect of pre-strain and aging treatment on the residual stress, microstructure evolution and mechanical properties of 7A55 aluminum alloy were investigated by using TEM, EBSD, XRD and micro-hardness tester. The results indicate that the surface stress of the solution treated specimens is compressive, being -75 MPa and -115 MPa along rolling and transversal directions respectively. The residual stress decreases with the increase of pre-strain and almost being eliminated after 2% pre-strain. The subduction rate of residual stress for aging at 180 ℃ is obviously quicker than that at 100 ℃ and 140 ℃. The hardness increases with the increase of pre-strain, and after 3% pre-strain it increases to 92 HV0.5, i.e. by 27.8%. The hardness increases first and then decreases with the increases of aging time, and reaches 135, 143 and 162 HV0.5 respectively when aging at 100, 140 and 180 ℃ for 15 h. When aging at 100 ℃ for 15 h where the peak hardness is obtained, the metastable η′ phase is mainly precipitated inside grains and has a coherent relation with the matrix. When aging at 140 ℃, the size of the intragranular precipitated phase increases, and semi-coherent disk-like η′ phase appears. While aging at 180 ℃, short rod-like η′ phase with a size of 5-20 nm appears, and the grain boundary with small angles (<10°) accounts for more than 80%.

High-temperature diffusion annealing process of GH4738 alloy

Su Xing, Shi Songyi, Lü Xudong

2020, 45(10): 48-53. doi:10.13251/j.issn.0254-6051.2020.10.010

Abstract ( 65 )

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Equilibrium solidification phase diagram of GH 4738 superalloy was calculated by using Thermal-calc software, based on which experimental parameters of homogenization treatment was established.The segregation of as-cast GH4738 superalloy was observed by using OM and SEM ,the laws of element segregation in the as-cast alloy with as-cast and different diffused annealing state at different temperatures were studied by using EPMA technique.The results show that Ti element segregation is the most serious in the as-cast alloy, the segregation of Ti element is significantly improved after the alloy treated by high-temperature diffusion annealing process, and the effect is the most significant after annealing at 1200 ℃ for 50 h. Meanwhile, the change curves of the residual segregation index versus temperature is calculated, and the calculated results are basically in accord with the experimental results.

Effect of tempering temperature on microstructure and properties of 0.6C super bainitic steel quenched by different methods

Sun Lin , Hong Zhenjun, Hu Kun, Su Zhen, Xu Xinle, Jin Yang, Dong Dashan

2020, 45(10): 54-59. doi:10.13251/j.issn.0254-6051.2020.10.011

Abstract ( 77 )

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Microstructure and mechanical properties of the 0.6C super bainitic steel were analyzed after isothermal salt bath quenching and quenching-partitioning-tempering (Q-P-T) respectively and then tempering at different temperatures. The results indicate that the reversible temper brittleness appears in the temperature range of 360-500 ℃ after treated by two-step austempering at 230 ℃×10 h and 320 ℃×7 h, while the tempering brittleness temperature range of Q-P-T specimen is 450-470 ℃. Respectively, after Q-P-T process, the tempering brittleness temperature range is obviously narrowed and the mechanical properties of the specimen are improved. The microstructural characterization by SEM, TEM and XRD reveals two main factors resulting in the mechanical properties of the Q-P-T specimen superior to those of the isothermal treatments: after the Q-P-T treatment, the microstructure is more refined, and with the increase of subgrain boundaries, the stability of the microstructure is further enhanced, and the carbide segregation to the grain boundaries is hindered, so it is difficult to connect into a network. Therefore, after the Q-P-T treatment, the reversible temper brittleness temperature range is greatly reduced; after the Q-P-T treatment, the film-like retained austenite increases in the content and is more stable, which is beneficial to weaken the influence of reversible temper brittleness.

Effect of natural aging effect and pre-aging treatment on microstructure and properties of 7A20 aluminum alloy

Jiang Shaojing, Wang Zuping

2020, 45(10): 60-63. doi:10.13251/j.issn.0254-6051.2020.10.012

Abstract ( 47 )

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Natural aging effect and effect of pre-aging treatment on the microstructure and mechanical properties of 7A20 aluminum alloy were investigated by means of OM, TEM, Vickers hardness tester and multifunctional tensile testing machine. The results indicate that the solution treated 7A20 aluminum alloy has obvious natural aging hardening effect, and the microhardness increases by 117.86% after natural aging for 12 days, from 56 HV0.5 to 122 HV0.5. After the pre-aging treatment at 120 ℃×10 min, the natural aging hardening increment is the lowest, reduced by 16 HV0.5 compared to the solution treated alloy. Simultaneously, this pre-aging treatment improves the baking hardening effect, the yield strength and tensile strength increase by 166 MPa and 51 MPa respectively, while the elongation decreases by 7%. Before the bake hardening process, the strengthening effect in the grains comes mainly from GP zones coherent with the matrix; and after the baking treatment, it comes from dispersed strengthening phase η′ with a size of less than 5 nm.

Effect of heat treatment process on manganese sulfide inclusions in resulfurized free-cutting stainless steel

Wang Yinghu

2020, 45(10): 64-69. doi:10.13251/j.issn.0254-6051.2020.10.013

Abstract ( 60 )

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Effect of heat treatment process on the morphology, length-width ratio, size and number of manganese sulfide in resulfurized free-cutting stainless steel was studied by means of OM and SEM-EDS. The results demonstrate that the manganese sulfide in the tested steel is mainly distributed in chain or network along the grain boundary. At the temperatures ranging from 900 ℃ to 1100 ℃, with the increase of temperature, the manganese sulfide is fused and broken. After 1200 ℃ heat treatment, the manganese sulfide matures and grows up, the globular and spindle-shaped manganese sulfide increases and the distribution changes from aggregation to dispersion. During the heat treatment at 1100 ℃ for 1-3 h, with the increase of time, the manganese sulfide is fused and breaks. After heat treatment for 4 h, the manganese sulfide matures and grows up and the globular and spindle-shaped manganese sulfide increases. The manganese sulfide gradually changs from aggregation to dispersion and the distribution tends to be uniform. The appropriate heat treatment process can improve the morphology, length-width ratio, size and number of manganese sulfide in resulfurized free-cutting stainless steel.

Effect of heating temperature on microstructure and hardness of 19CrNi5 steel

Zhang Boying, Tan Biao, Zhao Haidong, Wu Yongxiao, Yin Liangqiu

2020, 45(10): 70-72. doi:10.13251/j.issn.0254-6051.2020.10.014

Abstract ( 64 )

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The 19CrNi5 steel with hardness higher than 200 HRB after rolling was selected as the research object, the steel specimens were heated to 800, 850, 900, 950, 980, 1050 and 1100 ℃ in the same carbon-silicon rod box-type high temperature furnace. The specimens were hold at the selected temperature for 40 min, then air cooled at 15 ℃,the cooling rate of the steel was measured by infrared thermometer, the hardness was tested by hardness testing device, and the metallographic microstructure of the steel was tested by means of scanning electron microscope(SEM). According to the research results, the main reason is the high proportion of bainite structure that affects the hardness of the steel. When the heating temperature ≥1000 ℃, and the cooling rate ≥2.5 ℃/s, the higher the heating temperature is, the quicker the cooling rate is, the larger the proportion of bainite in the steel is,the higher the hardness of the steel is. When the heating temperature <1000 ℃, cooling rate <1.0 ℃/s, the austenite is completely transformed into pearlite, and finally pearlite and ferrite structure are formed during the cooling process with low hardness of the steel. In actual production, the final rolling temperature is controlled below 1000 ℃, and the cooling rate <1.0 ℃/s, which can slow down or eliminate the formation of bainite structure in the steel.

Effect of annealing temperature on microstructure and properties of EB melted low cost TC4 titanium alloy wide and thick plate

Zhang Qiang, Li Bobo, Pei Teng, Hao Xiaobo, Liu Yinqi

2020, 45(10): 73-78. doi:10.13251/j.issn.0254-6051.2020.10.015

Abstract ( 48 )

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TC4 alloy slab ingot was used as a direct-rolled billet in the EB furnace at one time. A low cost TC4 alloy wide plate with a size of 46 mm×2650 mm×8700 mm was successfully prepared on a 4200 mm wide and thick plate mill, the effect of annealing temperature on the microstructure and mechanical properties of the low cost TC4 alloy plate was studied. The results show that the EB smelted TC4 alloy slab is subjected to dual reversing rolling, and the coarse as-cast microstructure is broken. The microstructure of the hot-rolled TC4 alloy plate has a high content of equiaxed α-phase or strip α-phase, small transverse and longitudinal room temperature tensile properties differences, and the transverse room temperature impact absorbed energy is less than the longitudinal direction, and the strength of the core part is higher than the surface layer. When annealed at 750-900 ℃, the transverse and longitudinal section of the TC4 alloy sheet are equiaxed structure, when annealed at 950 ℃, the transverse and longitudinal section are dual-state structure, when over 980 ℃, the cross-section is dual-state structure, and the longitudinal section is widmanstatten structure. As the annealing temperature increases, the tensile strength and the proof strength plastic extension of TC4 alloy sheet show a downward trend, and the elongation is basically unchanged. The impact absorbed energy at room temperature first increases and then decreases. After annealing at 900 ℃, the strength, elongation and impact absorbed energy achieve the best match.

Effect of heat treatment on microstructure and properties of welded joints of X80 steel used for bent pipe under extremely cold service conditions

Bi Zongyue, Wei Feng, Zhang Wanpeng, Li Jie, Zhang Min

2020, 45(10): 79-84. doi:10.13251/j.issn.0254-6051.2020.10.016

Abstract ( 72 )

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Effects of different heat treatment processes on the microstructure and low-temperature impact property of the welded joints of X80 steel used for bent pipe were studied by means of microstructure analysis, low-temperature impact test, and fracture analysis. The results show that, when normalized in the range of 890-980 ℃, the microstructure of welded joints gradually coarsens with the increase of normalizing temperature, and the number of M-A components and carbides rises, the aggregation extent increases gradually, and the low-temperature impact property decreases. When tempered in the range of 620-680 ℃, with the increase of tempering temperature, the mixed microstructure of bainite and acicular ferrite in the welded joints undergoes recovery and recrystallization, the content of carbide precipitates and proeutectoid ferrite increases, and the hard and brittle M-A components decompose gradually, the impact absorbed energy at low temperature increases first and then decreases, and the microhardness decreases gradually. The microstructure of the welded joints after heat treatment is mainly composed of acicular ferrite (AF) and granular bainite (GB), while a small amount of proeutectoid ferrite (PF) and dispersed M-A components are present. When normalized at 920 ℃ and then tempered at 660 ℃, the impact absorbed energy at low temperature of the welded joints is the best (148 J), while the microhardness is fluctuated slightly, and the radiation zone of the impact fracture is quasi-cleavage fracture, without large-scale cracks and with partial dimples, showing that the bent pipe treated by this heat treatment process can meet the service requirements under the extreme cold condition of -45 ℃.

Development of heat treatment process of camshaft for a type of intelligent diesel engine

Yang Jing, Wang Yongkun, Liu Gaosong, Ran Qiyan, Yang Huan, Shang Rongkai

2020, 45(10): 85-89. doi:10.13251/j.issn.0254-6051.2020.10.017

Abstract ( 54 )

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Heat treatment of a camshaft with a large ratio of length and diameter for a type of intelligent diesel engine is difficult to produce, and need special technology to deal with. In order to find a solution for this, a series of equipment including multi-purpose furnace, vacuum tempering furnace, pit type carburizing furnace, cryogenic box, pit type furnace, straightening machines and other equipment was used on the base of key technics analysis. The production practice indicates that the camshaft with a high hardness, good microstructure and high mechanical properties, and less distortion can be produced by the processes of cleaning, stop-off coating and drying, preheating, carburizing and high temperature tempering and alignment, stress relieving in vacuum, machining, hardening, cryogenic treatment, and tempering. It is pointed out that multiple cycle carburizing with high and low carbon potential in turn in multi-purpose furnace has more obvious advantages than the traditional two stages carburizing, such as higher carburizing speed, better carbide morphology, higher hardness, flatter hardness gradient, shorter carburizing time, and higher production efficiency. The heat treatment process scheme of this part is adopted, and the final processed specimens fully meet the requirements of users.

Solution hardening behavior of oxygen atom in oxygen-rich layer of hot rolled TC4 titanium alloy plate

Cui Yan, Chen Yudong, Dong Changqing, Sun Xinjun

2020, 45(10): 90-93. doi:10.13251/j.issn.0254-6051.2020.10.018

Abstract ( 56 )

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Distribution law of oxygen concentration in the oxygen-rich layer of hot rolled TC4 titanium alloy plate was studied by spectrum analysis of the oxygen concentration at different depth from the surface. The effect of the oxygen concentration on the hardness of oxygen-rich layer was also studied.The results show that the thickness of oxygen-rich layer is about 60 μm; with the increase of distance from the surface, the oxygen concentration in the oxygen-rich layer decreases gradually; the thickness of the hardened layer is equal to that of the oxygen-rich layer, and the hardness decreases with the increase of distance from the surface. The interstitial solution hardening effect of oxygen atoms in the oxygen-rich layer leads to the formation of hardened layer in the alloy. The relationship between oxygen concentration, depth from surface and microhardness is established.

Effect of annealing temperature on microstructure and properties of HA/Ti-24Nb-4Zr composites

Lei Yutao, Zhu Bin, Zhang Yuqin, Jiang Yehua

2020, 45(10): 94-98. doi:10.13251/j.issn.0254-6051.2020.10.019

Abstract ( 55 )

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HA/Ti-24Nb-4Zr biocomposites were prepared by spark plasma sintering (SPS) technology, and the effects of different annealing temperatures on the microstructure and mechanical properties (compressive strength, yield strength, yield ratio, compressive elastic modulus) of the composites were investigated. The results show that the as-sintered composites consist of matrix of β-Ti phase, residual of primary α-Ti phase and HA(hydroxyapatite) phase. With the increase of annealing temperature, the content and grain size of the β-Ti phase in the composite matrix are increased gradually, while the needle-like secondary α-Ti phases are precipitated continuously within the grain boundary and inside the grain. Meanwhile, the microstructure and content of HA phase have little change. Compared with that of the as-sintered, the strength and elastic modulus of the composites annealed at different temperatures are increased slightly at first and then decreased, while the ductility tends to be improved continuously after annealing. After annealing at 850 ℃, the compressive strength, yield strength, yield ratio and elastic modulus of the composites are 1507 MPa, 1270 MPa, 0.84 and 42 GPa respectively, that is, the ductility of the composites is improved obviously. This suggests that the HA/Ti-24Nb-4Zr biocomposite is a potential biomaterial for orthopedic replacement or implants.

Microstructure and texture evolution of rare-earth non-oriented silicon steel for new energy vehicles during production

Zhang Jingyuan, Ren Huiping, Jin Zili, Wu Zhongwang, Zhang Jishun

2020, 45(10): 99-103. doi:10.13251/j.issn.0254-6051.2020.10.020

Abstract ( 52 )

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Microstructure and texture evolution in the whole production process of non-oriented silicon steel containing rare earth were studied by means of optical microscope, X-ray diffractometer and scanning electron microscope. The results show that the hot-rolled sheet has significant delamination in the thickness direction, that is, the recrystallized layer of the surface layer, the transition layer, and the deformed structure layer of the intermediate layer, and the texture mainly includes copper-type and brass-type texture. After normalizing, the grains are completely recrystallized, and the texture type is basically unchanged from that of hot rolling, but the strength is weakened; the texture after two cold rolling is all fibrous, forming a texture type dominated by α and γ linear textures. There are also high-strength anti-Gaussian textures such as {001}<110>, {112}<110>, {111}<110>; partial recrystallization occurs after decarburization annealing, and the α and γ linear texture strength is reduced comparing to that after cold rolling; during the high temperature annealing stage, the crystal grains recrystallize, there are {111}<112>, {111}<110> mainly γ texture, and {100}<001> texture.

Microstructure and texture of typical Fe-Cr-Al and Ni-Cr-(Fe) electrothermal alloy wires

Zhang Qiang, Zhu Zhixiang, Chen Baoan, Ding Yi, Chen Xin, Zhang Ning, Meng Li

2020, 45(10): 104-107. doi:10.13251/j.issn.0254-6051.2020.10.021

Abstract ( 51 )

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Two kinds of typical electrothermal Fe-Cr-Al alloy wires including domestic 0Cr25Al5 alloy wire and imported 0Cr22Al5 alloy wire and Ni-Cr-(Fe) alloy wires including domestic Cr20Ni80 and Cr20Ni30 alloy wires were investigated, and the microstructure as well as texture of different samples were compared and analyzed. The results show that more uniform microstructure is observed in imported Fe-Cr-Al alloy wire, in which larger average grain size and weak texture are shown. For the domestic 0Cr25Al5 alloy wires, rather heterogeneous microstructure is displayed, and the weaker texture and higher average grain size in coarser wires are attributed to lower deformation strain during preparation process. Regarding the Ni-Cr-(Fe) alloy wires, heterogeneous microstructures are obtained in both Cr20Ni80 and Cr20Ni30 alloys, but the higher fraction of large grains are shown in Cr20Ni30 alloy wires. The lower wire diameter leads to finer microstructure, as well as strengthening <111> texture which exists in both kinds of Ni-Cr-(Fe) alloy wires.

Effect of solid solution temperature on carbide evolution and mechanical properties of Cr-Co-Mo martensitic steel

Yuan Xiaohong, Yang Maosheng, Gan Jianzhuang

2020, 45(10): 108-113. doi:10.13251/j.issn.0254-6051.2020.10.022

Abstract ( 57 )

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Effect of solution treatment temperature on the carbide evolution behavior and mechanical properties of a Cr-Co-Mo martensitic steel were investigated by SEM and TEM methods. The results show that as the solution treatment temperature increases, the M₆C carbides re-dissolve into the matrix, the yield strength decreases, while the impact absorbed energy at room temperature increases; concurrently, the prior austenite grains grow rapidly due to the lack of pinning by spherical M₆C carbides on the grain boundaries, which weakens the grain refinement strengthening effect, but improves the toughness by reducing the crack origins at the grain boundaries. When solution treated at 1120 ℃, the grain size is the largest, but the yield strength does not decrease significantly after grain growth, and the toughness is not reduced. The reasons for this is that the average particle size and the area fraction of nanoscale M₂C carbide are the smallest and the highest respectively, and the particle spacing is the shortest, so that the precipitation strengthening effect effectively makes up for the loss of the grain refinement strengthening effect; and simultaneously, the coherent precipitation of nano scale rod-like M₂C carbide with the matrix results in that both the deformation compatibility of the matrix and the toughness are improved.

Effect of heat treatment on microstructure and properties of Fe-Cr-Ni low carbon martensitic stainless steel

Xu Rongjun, Tian Weiguang, Xu Jialin, Lu Haifei, Yin Yanxiong

2020, 45(10): 114-118. doi:10.13251/j.issn.0254-6051.2020.10.023

Abstract ( 48 )

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Fe-13Cr-3.5Ni stainless steel was prepared by vacuum arc melting method, and the effects of different heat treatment processes on its microstructure and hardness were systematically studied. The results show that the Fe-13Cr-3.5Ni stainless steel in smelting-casting state is of typical lath martensite structure. After solid solution treatment at different temperatures and tempered at 600 ℃, the steel consists of lath martensite and a small amount of retained austenite. The content of retained austenite increases firstly and then decreases with the increase of solution treatment temperature, but the hardness firstly decreases and then increases, with the minimum hardness being 101.5 HRB. After quenched at 1000 ℃ and tempered at different temperatures, the steel microstructure is composed of tempered lath martensite and retained austenite. When tempered below 650 ℃, the austenite content gradually increases with the increase of tempering temperature. When the tempering temperature reaches 700 ℃, the retained austenite content decreases, and the Rockwell hardness decreases first and then increases with the increase of tempering temperature, and is in the range of 99-107 HRB.

Effect of intermediate annealing on microstructure and properties of Al-Mg-Si series aluminum alloy automobile sheet

Liu Xiaoteng, Zhao Jialei, Sun Youzheng, Cheng Rence, Lü Zhengfeng, Zhao Guoqun

2020, 45(10): 119-123. doi:10.13251/j.issn.0254-6051.2020.10.024

Abstract ( 55 )

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Effect of different intermediate annealing (IA) treatment, i.e. without IA, IA at 300 ℃ for 2 h and at 420 ℃ for 2 h, on the Al-Mg-Si series alloy sheet was investigated by means of optical microscopy observation, XRD analysis, TEM analysis, Topology instrument inspection and tensile test. The results indicate that IA treatment has obvious effect on the microstructure, texture, roping line and mechanical properties of the T4P treated sheets. Increasing the IA temperature is beneficial for obtaining equiaxed grains, increasing strain hardening exponent (n value) and reducing anisotropy (Δr value). But the average Lankford coefficient (r value) decreases. Furthermore, the sheet which IA at 300 ℃ for 2 h has the best surface quality after 10% prestretching, but the sheet without IA or IA at 420 ℃ for 2 h have a horrible roping line after pre-stretching. These differences can be attributed to the microstructure and texture transformation during the IA treatment. It can be concluded that the IA treatment of 300 ℃×2 h is better for the comprehensive performance of the Al-Mg-Si series alloy sheet.

Effect of heat treatment process on banded structure and impact properties of 15CrMoR steel

Liu Dan, Chen Guangxing, Xu Chen, Xu Xiaochang

2020, 45(10): 124-128. doi:10.13251/j.issn.0254-6051.2020.10.025

Abstract ( 70 )

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Evolution of banded structure during heat treatment and its effect on impact properties of the 15CrMoR steel were analyzed by means of optical microscope, scanning electron microscope and impact testing machine. The results show that ferrite-pearlite banded structure appears when cooling slowly after austenitization, and can be inhibited by increasing cooling rate, but fast cooling may result in non-equilibrium structures such as granular bainite.During tempering, the martensite-austenite islands and bainitic ferrite in the granular bainite decompose gradually to form carbides in the segregation area of carbide-forming elements such as Cr and Mo, leading to the emergence of carbide-rich band and deteriorating the transverse impact properties of the 15CrMoR steel. Homogenized at 1100 ℃ for 7 h could eliminate the banded structure, and improve the transverse impact properties of the steel.

Effects of retrogression and re-aging treatment on microstructure and properties of extruded thick plate of spray formed 7055 aluminum alloy

Tang Zhihao, Ye Qingfeng, Zhou Jiandang, Fan Xi, Zhang Hao, Feng Di

2020, 45(10): 129-134. doi:10.13251/j.issn.0254-6051.2020.10.026

Abstract ( 75 )

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Effects of retrogression and re-aging(RRA) treatment on the microstructure and properties of extruded thick plate of spray formed 7055 aluminum alloy were studied by means of mechanical properties test, exfoliation corrosiontest and transmission electron microscopy (TEM) observation. The results show that although when adopting the retrogression temperature of thick plates as the plate loading temperature, the specimon heating process still needs to take a long time, and increasing the retrogression temperature is beneficial to shortening the staying time of specimens in the low temperature stage. After RRA treatment with pre-aging at 120 ℃ for 14 h, retrogression at 185 ℃ for 130 min and at 190 ℃ for 118 min, re-aging at 120 ℃ for 24 h, the longitudinal yield strengths of the specimens are 649.3 MPa and 652.6 MPa respectively, which are higher than 621.5 MPa of the T76 specimens, and the exfoliation corrosion resistance is close to that of the T76 specimen and reaches the EB level. After RRA treatment, the precipitated phase in the matrix is mainly η′ phase with a small amount of GP zone, the size of which is 3-10 nm, and the precipitates at grain boundary distribute intermittently. Increasing the heating rate of the thick plate specimen in the low temperature stage of retrogression process is beneficial to increasing the strength of the specimen after re-aging, and increasing the retrogression temperature seems to be beneficial to improving the exfoliation corrosion resistance of the RRA specimen.

Effect of rare earth Ce on as-cast precipitates of Cu-containing low-temperature grain-oriented silicon steel

Zhang Xin, Jin Zili, Ren Huiping, Wu Zhongwang

2020, 45(10): 135-139. doi:10.13251/j.issn.0254-6051.2020.10.027

Abstract ( 51 )

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Effect of rare earth element Ce on the as-cast microstructure and precipitates of Cu-containing grain-oriented silicon steel was investigated by means of laser scanning confocal microscope and transmission electron microscope. The results show that rare earth element Ce can refine grains in the as-cast microstructure of the Cu-containing grain-oriented silicon steel. In addition, there are coarse (Cu,Mn)S+AlN composite precipitates and a small amount of separate precipitates including MnS and Cu₂S in the ingot cast without Ce addition. By adding Ce, the types of the as-cast precipitates do not change, while their amounts decrease significantly and their sizes increase somewhat.

Properties of M2052 Mn-Cu alloy powder prepared by VIGA method and its SLM prints

Ma Conghui, Wang Changjun, Shen Tao, Hu Jiaqi, Liang Jianxiong

2020, 45(10): 140-147. doi:10.13251/j.issn.0254-6051.2020.10.028

Abstract ( 57 )

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The M2052 alloy powder was prepared by the vacuum induction melting gas atomization(VIGA) method, and its physical properties and microstructure were analyzed. Then the Mn-Cu specimens were prepared by selective laser melting (SLM) technology and the microstructure and mechanical properties of the SLM printed specimens were analyzed. The results show that, the VIGA method can effectively control the shape of metal powders, and the VIGA Mn-Cu powders with a particle size range of 15-53 μm have high yield, high bulk density, and good degree of sphericity, thus effectively meet the requirements for that of SLM. The microstructure of SLM printed Mn-Cu alloy is different in the horizontal and the vertical directions, and gradually changes into cellular crystals as the interior of the molten pool extends.Columnar crystals are formed along the welding interface, and the further away from the molten pool, the finer the columnar crystals. Compared with the as-cast, the SLM printed alloy has obvious difference in mechanical properties, with the tensile strength and the proof strength, plastic extension being 611 MPa and 504 MPa respectively, which are much higher than 454 MPa and 172 MPa of the as-cast master alloy. The reason is that the fine grain strengthening effect is obvious, but the existence of microcracks is not good for the plasticity.

Prediction and verification of CCT curves of A668 steel

Liu Xianqiang, Bu Hengyong, Li Qi, Li Mengnie

2020, 45(10): 148-153. doi:10.13251/j.issn.0254-6051.2020.10.029

Abstract ( 40 )

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In order to reduce the cost of drawing CCT curves and obtain more accurate calculation models of phase transformation to predict the properties and residual stress distribution of large components, the Li model was used to predict the CCT curves of A668 steel, and an enough and essential experimental group was developed based on the predicted results. After completing the phase transformation expansion experiment, the experimental results were used to correct the prediction model and the new model calculated the complete and accurate CCT curves. According to the expansion curves and metallographic results measured by DIL-805-ADT phase transformation dilatometer, the transformation type and transformation volume at different cooling rates were determined. The difference between the results which was calculated by original model and JMatPro software and the experimental results were compared. The process of modifying the prediction model and drawing the CCT curves was described. K-M equation for calculating martensite transformation was fitted. The relationship between different cooling rates and phase transformation was illustrated. A more accurate predictive model and complete CCT curves were obtained to guide actual production.

Dynamic CCT curves and microstructure evolution of EH460 ship plate steel

Ma Haoran, Liu Hongbo, Liu Chong, Li Jianxin, Tian Zhiqiang, Zhang Peng

2020, 45(10): 154-157. doi:10.13251/j.issn.0254-6051.2020.10.030

Abstract ( 53 )

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Gleeble 3800-thermal simulation test machine was used to conduct double-pass compression tests on EH460 plate steel under deformation of 30% at 1050 ℃ and 30% at 850 ℃.The expansion curve of steel during continuous cooling at different cooling rates was plotted and the microstructure of the specimens at room temperature under different cooling rates was observed under optical microscope. The dynamic CCT curve of ship plate steel was plotted by Origin 8.0 software combining expansion method and metallographic method. The results show that when the cooling rate was 0.1-3 ℃/s, the obtained microstructure at room temperature was mainly ferrite and pearlite. When the cooling rate is greater than 5 ℃/s, granular bainite ppears. With the increase of cooling rate, bainite gradually increases, while ferrite and pearlite gradually decrease. When the cooling rate is 0-15 ℃/s, pearlite disappears and the microstructure was ferrite and granular bainite. With the increase of the cooling rate to 20-50 ℃/s, the ferrite phase transition does not occur, and only granular bainite can be found.

Influence of vanadium precipitation on hot ductility and microstructure of medium-carbon manganese non-quenched and tempered steel

Fang Jian, Hu Zhangyong, Yuan Zexi

2020, 45(10): 158-163. doi:10.13251/j.issn.0254-6051.2020.10.031

Abstract ( 59 )

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High temperature mechanical properties and microstructure of two medium-carbon and manganese non-quenched and tempered steels without and with vanadium addition were comparatively analyzed by thermal simulation test, and then the influence of V precipitation on the hot ductility and microstructure was studied. The results show that high temperature deformation induced V(C, N) precipitates can inhibit the dynamic recrystallization behavior and increase deformation resistance, and promote intragranular ferrite transformation; and therefore causing that the hot ductility is decreased, the temperature range of high ductility is narrowed, and the temperature range of low ductility is widened. On the other hand, VC phase precipitates mainly along the γ/α interface during the transformation from austenite to ferrite, and is beneficial to the ferrite growing toward the austenite grain insides. After solution treating at 1280 ℃ and then deforming at temperature range of 900-1100 ℃and 1000-1130 ℃ respectively, both the tested steels without and with vanadium addition can obtain high hot ductility.

Effect of Al on hardenability of 42CrMo bolt steel

Lü Chaoran, Shi Chao, Jiang Weibin, Liu Jinde, Xu Le, Wang Maoqiu

2020, 45(10): 164-170. doi:10.13251/j.issn.0254-6051.2020.10.032

Abstract ( 50 )

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Al and Ti elements were added to re-alloy the 42CrMo steel with basic composition. The effect of Al on the hardenability of 42CrMo steel was analyzed by means of end quenching test and section hardness test. The mechanical properties of the new 42CrMo steel were compared by conventional mechanical properties. The results show that the addition of Al and Ti can further improve the hardenability, and the strength of the steel reaches 1200 MPa, and KV₂≥27 J at －40 ℃, which meets the technical requirements at low temperature environment for the wind turbine bolt steel. Through chemical phase analysis test and TTT curves measurement, it is shown that Ti added to steel exerts obvious nitrogen fixation effect. Al is mostly dissolved in steel, making C curves shift to the right, which lowers the critical transformation temperature of austenite and significantly improves the hardenability of steel.

Effect of RE element Y on microstructure and mechanical properties of as-cast magnesium alloy

Zhang Xudong, Suo Zhuanxia, Wei Boxin, Wang Xin, Cao Guojian

2020, 45(10): 171-174. doi:10.13251/j.issn.0254-6051.2020.10.033

Abstract ( 47 )

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Mg-2.0Zn-0.2Ca and Mg-2.0Zn-0.2Ca-2Y alloys were prepared by melting. The as-cast microstructure and mechanical properties of the two alloys were investigated. The results show that the as-cast microstructure of Mg-2.0Zn-0.2Ca can be refined by addition of Y element. Mg-2.0Zn-0.2Ca alloy is mainly composed of α-Mg and a small amount of Mg₇Zn₃. The solid solubility of Zn in Mg matrix decreases with the addition of 2wt% Y, which reduces the effect of solid solution strengthening. At the same time, I phase and W phase form in the alloy. With the addition of Y, the yield strength of the alloy increases from 41.0 MPa to 50.6 MPa and the elongation decreases from 12.6% to 4.0%.

Wear and thermal fatigue properties of Ni60A/Cr₃C₂ coating prepared by PTA welding on H13 steel

Liu Qingyang, Wang Huajun, Hong Feng, Zhu Chundong, Wang Zhehan

2020, 45(10): 175-179. doi:10.13251/j.issn.0254-6051.2020.10.034

Abstract ( 61 )

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Ni60A/Cr₃C₂ surfacing coating was prepared on the surface of H13 steel by plasma transferred arc welding (PTA) technology, and its wear behavior and thermal fatigue properties were investigated. The results of pin-on-disk wear tests at 600 ℃ show that the wear resistance of the Ni-based Cr₃C₂-reinforced coating, is 2.8 times of that non-reinforced, and 11.6 times of that of the H13 steel. The nickel-based coating can significantly reduce the friction coefficient of H13 steel, and the addition of Cr₃C₂ will weaken the friction performance of the coating. The main wear mechanism evolves from oxidative wear to abrasive wear and adhesive wear as the wear progresses. The results of thermal fatigue test at 800 ℃ to room temperature show that the fatigue crack reaches 200 μm after 48 thermal cycles for the Ni-based Cr₃C₂-reinforced coating, earlier than after 62 cycles for the non-reinforced Ni-based coating. High temperature oxidation promotes the initiation of thermal fatigue cracks. The Cr₃C₂ reinforcing phase is peeled off from the Ni-based substrate, resulting in a decrease in thermal fatigue properties.

Effect of La₂O₃ additive and salt bath temperature on oxygen-boronized microstructure and properties of TC4 titanium alloy

Liu Yangguang, Xu Xiaojing, Song Zhenhua, Wang Yang, Zhu Liangliang, Zhu Jinsong

2020, 45(10): 180-186. doi:10.13251/j.issn.0254-6051.2020.10.035

Abstract ( 53 )

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Effect of lanthanum oxide (La₂O₃) additive and salt bath temperature on microstructure and properties of oxygen-boronized specimens were studied by means of OM, SEM, XRD, EDS, Vickers hardness tester and friction tester. The results show that the thickness of the oxygen-boronized layer increases first and then decreases with the increase of the amount of La₂O₃. When the content of La₂O₃ is 3%, the thickness of the layer reaches the maximum value (32.74 μm). Compared with that obtained at the low temperature (950 ℃), at high temperature (1000 ℃) the layer has a better surface, with higher thickness (34.19 μm), higher surface hardness (1211 HV0.2), larger interfacial bonding force (87.36 N), and lower friction coefficient (0.28). By analyzing the influence of temperature on the process of boronizing and the test results, it is concluded that the salt bath boronizing test with lanthanum oxide additive at 1000 ℃ is more valuable.

Effect of B on microstructure and hardness of FeCoCrNiSiB_x high entropy alloy laser clad coating

Zhao Longzhi, Yu Shihao, Zhao Mingjuan, Tang Yanchuan, Jiao Haitao, Li Jin, Song Lijun

2020, 45(10): 187-190. doi:10.13251/j.issn.0254-6051.2020.10.036

Abstract ( 53 )

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FeCoCrNiSiB_x high-entropy alloy coating was prepared by laser cladding. The influence of trace boron element (molar ratio x=0, 0.02, 0.04, 0.06, 0.08) on the structure and hardness of FeCoCrNiSiB_x high-entropy alloy coating was study by using optical microscope, scanning electron microscopy, X-ray diffractometer and microhardness tester. The results indicate that the microstructure of FeCoCrNiSi high-entropy alloy coating can be mainly characterized by cellular. The addition of B promoted the formation of dendrites, resulting in fish-bone dendrites. However, the excessive content of B destroies the integrity of dendrites, leading to worm-like dendrite. In addition, the microstructure of the coating is composed of FCC and BCC phases. The addition of B element promotes the precipitation of Cr₂B particles of size 0.1-2.6 μm, which contributes the improvement of hardness of the clad coating. When the molar ratio of B is 0.06, the value of microhardness of the clad coating is highest as about 537 HV0.2.

Effect of boronizing on aluminum corrosion resistance of chromium carbide coating on H13 steel

Li Keju, Wang Huajun, Gao Ye, Wang Xueyang, Zhao Xiaoyu

2020, 45(10): 191-193. doi:10.13251/j.issn.0254-6051.2020.10.037

Abstract ( 49 )

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Specimens of untreated H13 steel, thermo-reactive diffusion (TRD)chromizing only and TRD (chromizing+boronizing) treating were immersed in molten aluminum to carry out hot-dipping aluminizing test.The cross section of the aluminized specimens was observed by microscope and composition of the aluminized layer was analyzedat fixed points. The results show that under the same hot-dipping aluminizing conditions, the thickness of aluminized layer of the chromium carbide coating without boronizing is equivalent to that of untreated H13 steel, showing that chromizing alone cannot improve the corrosion resistance of H13 steel to liquid aluminum. While the thickness of aluminized layer of boron-chromium composite coating specimen is only 67% of that of the chromium carbide coating without boronizing, which depicts that the application of boronizing treatment can effectively improve the aluminum corrosion resistance of the TRD chromium carbide coating. After hot-dipping aluminizing, the composition of Fe-Al intermetallic compound is mainly Fe₂Al₅.

Effect of decarbonized layer on plasma nitriding of 38CrMoAl steel

Wang Yanfang, Yin Tingfeng, Li Shuangxi

2020, 45(10): 194-198. doi:10.13251/j.issn.0254-6051.2020.10.038

Abstract ( 66 )

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Tower-like specimen of 38CrMoAl steel with different thickness decarbonized layer was plasma nitrided. Infiltration rate, surface hardness and microstructure of the specimen before and after nitriding was studied by microhardness tester, OM and SEM. The results show that the widmannstatten structure is found in residual decarbonized layer and gradually increases with increase of the decarbonized layer. The speed of plasma nitriding increases first and then decreases with the increase of decarbonized layer thickness. The diffusion expressway of nitrogen-atoms and formation of nitride is provided by ferrite in widmannstatten structure. There are many fishbone, net and nervation nitrides on the surface of diffusion layer and it exhibits increase tendency with the increase of number and depth of decarbonized layer. Although the residual decarburized layer on the surface of the 38CrMoAl steel can accelerate the penetration rate, it will increase the bad structure of the carburized layer and increase the risk of exfoliation. Therefore, the machining allowance of the 38CrMoAl steel workpieces should be appropriately increased.

Microstructure and properties of Fe-WC laser clad layer on 42CrMo steel surface

Cui Lujun, Yu Jihua, Cao Yanlong, Zeng Wenhan, Guo Shirui, Li Xiaolei

2020, 45(10): 199-203. doi:10.13251/j.issn.0254-6051.2020.10.039

Abstract ( 64 )

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Fe-WC alloy powder was laser cladded on the surface of 42CrMo steel by coaxial powder feeding method. The microstructure characteristics of the clad layer, the influence of WC ceramic particles on the microstructure and properties of the clad layer, the distribution characteristics of WC particles and the composition of bulk eutectic around WC particles were observed and analyzed by scanning electron microscope, metallographic microscope and energy spectrometer. The performance and mass loss of the matrix and the clad layer were measured by microhardness tester, friction and wear tester, and high precision electronic balance, and the reasons causing the change of performance curves were analyzed. The results show that the microstructure changes from the bottom to the top of the clad layer are planar grains, cellular grains with obvious grain boundary, columnar dendrite with staggered growth, closely arranged cellular grains and columnar dendrite with uniform direction. The WC particles have the ability to refine dendrites, to block dendrite growth and to enhance the clad layer performance. The WC particles are aggregated and distributed in the clad layer to form a wider ceramic belt, and the massive eutectic around the WC particles is obtained by partial decomposition of WC, and the constituent elements of the eutectic include C, W, Fe, P and Cr. The average hardness of the clad layer reaches 850 HV0.3, which is 3.4 times of that of the matrix. The friction factor is about 0.275, which is 0.525 smaller than that of the matrix. The mass loss of the matrix is more than 11 times that of the clad layer. This shows that the Fe-WC alloy clad layer can effectively improve the hardness and wear resistance of the matrix material.

Phase-field simulation of dynamic recrystallization process for SA508-3 steel

Xu Ting, Li Meie, Wu Bingjie, Du Hua, Wang Xiaotong, Fang Liang

2020, 45(10): 204-211. doi:10.13251/j.issn.0254-6051.2020.10.040

Abstract ( 51 )

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A multi-phase-field(MPF) model was adopted to simulate the growth of dynamical recrystallization (DRX) grains and the Kocks-Mecking(KM) equation to model the mechanical behavior. Hot compression tests under various temperatures and strain rates were carried out by using a thermo-mechanical simulator to obtain the flow stress-strain curves, from which the MPF-DRX simulation model parameters for SA508-3 steel were extracted and calculated. The microstructure evolution and the flow stress-strain curves in hot plastic deformation process predicted by the MPF-DRX simulation agree well with the experimental results. Both the experimental and numerical simulation results indicate that the flow stress increases with the increase of strain rate as well as with the decrease of deformation temperature. The strategy of the present study can be used to study the DRX behavior of other materials and provide a guidance for optimizing hot forging processes.

Temperature field simulation for solid solution treatment of 7075 aluminum alloy support swing arm forging for automobile

Yang Hongbin, Bu Hengyong, Li Mengnie

2020, 45(10): 212-217. doi:10.13251/j.issn.0254-6051.2020.10.041

Abstract ( 60 )

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Temperature field of 7075 aluminum alloy automobile support swing arm forging in solid solution treatment process was simulated by ABAQUS finite element software, and the temperature field distributions of the forging under different heating ways, transfer time and quenching water temperatures were obtained. The results show that when heating up along with the furnace, the time required for the forging to reach the preset temperature is 112.1 min and the maximum temperature difference is 4.8 ℃; when the forging is loaded after the furnace reaches the preset temperature, the required time and the maximum temperature difference are 71.2 min and 10.4 ℃, respectively. When the transfer time is 3, 3.5 and 4 min, the temperature of the fastest cooling part in the forging decreases to 384.0, 375.9 and 367.8 ℃ respectively, so the transfer time is finally selected as less than 3.5 min. When quenched in 25 ℃ water, the cooling time is 95 s, the average cooling rate of the fastest and the slowest parts of the forging passing through the quench temperature sensitive zone is 782.8 and 19.1 ℃/s respectively, and the maximum temperature difference is 237.6 ℃. When quenched in 80 ℃ water, the cooling time is 56 s, and the average cooling rate of the fastest and slowest parts of the forging passing through the quenching temperature sensitive zone is 587.4 and 16.8 ℃/s respectively, and the maximum temperature difference is 216.0 ℃.

Numerical simulation of quenching process of integral steel rolling wheel

Sun Xiaoming, Yan Yan, Du Xiaozhong, Wang Wenbo

2020, 45(10): 218-224. doi:10.13251/j.issn.0254-6051.2020.10.042

Abstract ( 62 )

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Temperature field, stress field and microstructure change of an 840D wheel under different quenching processes were studied by using the DEFORM-HT software numerical simulation calculation, combined with the continuous cooling transition curve (CCT curve) of CL60 steel. The results show that the tread water quenching process is the optimal quenching project. It is concluded that the maximum equivalent stress of the wheel(the equivalent stress after unloading is the residual stress) after water quenching is 245 MPa, which is better than other schemes. The martensite transformation of the wheel tread during the quenching process can increase the wear resistance of the wheel. The hardness of the wheel rim surface is 33 HRC,which can meet the requirements of 27-34 HRC. According to the actual working conditions combined with the CCT curve of CL60 steel, the experimental scheme of water jet quenching is established. The microstructure of the specimen is observed and compared with the simulation results, which prove that the simulation results are reliable.

Establishment of surface strain prediction model of E690 high strength steel by laser shock processing

Wang Shuai, Yang Yang, Hua Guoran, Cao Yupeng, Ge Liangchen, Qiu Ming

2020, 45(10): 225-230. doi:10.13251/j.issn.0254-6051.2020.10.043

Abstract ( 44 )

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The ABAQUS finite element software was used to simulate the transformation of the surface strain and stress of E690 high strength steel loaded by laser shock wave, and the relationship between the stress diagram and plastic deformation under different shock wave pressures was analyzed. The strain prediction model of the E690 high strength steel by laser shock processing was established, and the model to verify accuracy of the experiment was designed. The results show that, the dynamic response of the E690 high strength steel under laser shock processing follows the Hugoniot elastic limit formula. The plastic deformation caused by the laser shock processing on the surface of the E690 high strength steel has a positive correlation with the residual stress of the surface. The experimental results are in good agreement with the simulation results.

Effect of loading rate on fracture toughness of H-charged SA508-3 steel

Liu Jiahua, Wang Lei, Yang Yufang, Cui Junjun, Geng Haopeng

2020, 45(10): 231-235. doi:10.13251/j.issn.0254-6051.2020.10.044

Abstract ( 47 )

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Hydrogen (H) was charged into SA508-3 steel by high-pressure thermal charging method. The J-integral method was used to compare the fracture toughness of the H-charged and uncharged SA508-3 steels at different loading rates, and the effect of H on the fracture toughness of SA508-3 steel was investigated. The results indicate that at the same loading rate, the fracture toughness of the H-charged SA508-3 steel is obviously lower than that of the uncharged, and the fracture of the H-charged steel shows a mixing of ductile and brittle morphologies. With the decrease of loading rate, the loss of fracture toughness increases, the area of quasi-cleavage increases, and the brittleness increases. Under the action of three-direction stress, the interaction energy between H and hydrostatic stress is greater than that between H and mobile dislocation, and the hydrostatic stress is easier to capture H. In the process of fracture toughness test of SA508-3 steel, the three-direction stress can induce and promote H to enrich at the interface between the carbide and the matrix at the crack tip, thus reducing the bond strength between the carbide and the matrix and weakening the ability to hinder crack growth, so the fracture toughness of steel decreases after H charging. With the decrease of loading rate and the increase of the time of three-direction stress acting on the crack tip, the concentration of H at the carbide/matrix interface increases, the hydrogen pressure increases, so the crack growth is promoted and the brittleness of the steel increases, and the fracture toughness loss increases.

Aging behavior of 60Si2MnA spring steel shims for steam turbine in nuclear power plant

Jia Wenqing, Liu Siwei, Yuan Shuai, Xu Yingjun, Jia Kaili, Chen Mingya, Lai Yunting

2020, 45(10): 236-240. doi:10.13251/j.issn.0254-6051.2020.10.045

Abstract ( 54 )

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The 60Si2MnA spring shims locating at the bottom of the roots of steam turbine blades subject to various aging effects such as potential corrosion, fatigue, and stress relaxation during service.Thus the aging effects caused by corrosion, wear and fatigue during service were comprehensively analyzed for the spring shims at roots of the last blade and the secondary blade in the low-pressure rotors in a nuclear power plant, and the aging behavior and service life of the shims were studied.The results show that the surface of the spring shims after service for 10 years has wearing traces formed by fretting wear, however, no obvious corrosion products or morphology have been found,which implies that the corrosion effect has a limited impact on the service life of the spring shims in the course of long service. Besides,certain differences exist between the disassembled spring shim and the original state because the material shows obvious strengthening and hardening characteristics during the initial cycles.Therefore,it should be explicited by the power plant that the installation instructions for new shims are not applicable for the installed ones.Moreover, the used spring shim after service for 10 years is estimated conservatively to serve for at least another 5 years based on the practical operating state, in consequence, the existing maintenance and replacement cycle can be extended to save the overhaul period and economic cost.

Reason analysis of punctiform and linear defects on GCr15 bearing steel ring after heat treatment

Wang Deyong, Zhang Qun, Qi Rui

2020, 45(10): 241-245. doi:10.13251/j.issn.0254-6051.2020.10.046

Abstract ( 73 )

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Suspected crack punctiform and linear defects in the surface of the finished ring were found in the production of bearing steel inner ring, which was analyzed by using nondestructive detection, optical microscope, scanning electron microscopy, energy spectrum analysis. The results show that a few big size of aluminum oxide and silicate compound inclusions exist. By improving the purity of molten steel by adopting measures such as “high carbon pulling”, “white slag operation”, “soft blowing” and “protective casting”, the recurrence of punctiform and linear defects disappear.

Cracking cause analysis of Cr12MoV steel cutting tool

Wang Ning, Ding Beidou, Cui Meng , Feng Zhaoping

2020, 45(10): 246-248. doi:10.13251/j.issn.0254-6051.2020.10.047

Abstract ( 82 )

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Early cracking of a Cr12MoV steel cutting tool occurred during the period of service. The chemical composition, microstructure, hardness and fracture morphology of the Cr12MoV steel tool were investigated by means of direct reading spectrometer, metallographic microscope, Rockwell hardness tester, stereo microscope and scanning electron microscope (SEM). The results show that the main cause for the early cracking of the tool is the massive eutectic carbides with angled shape existed in the material, and another main cause is the unreasonable design of the screw hole concave platform which causes stress concentration.

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