Heat Treatment of Metals

Microstructure evolution and mechanical properties of DD6 single crystal superalloy during heat treatment process

Yang Yuxuan, Wang Ye, Liu Guohuai, Wang Zhaodong

2022, 47(11): 1-11. doi:10.13251/j.issn.0254-6051.2022.11.001

Abstract ( 83 )

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Evolution of microstructure during heat treatment and the formation mechanism of incipient melting microstructure of DD6 single crystal superalloy were studied. The effects of different solution and aging treatments on morphology, size distribution and volume fraction of γ′ phase were studied. The microhardness and tensile properties of the alloy after complete heat treatment were analyzed to determine the optimum heat treatment process. The results show that the incipient melting temperature of the alloy determined by differential scanning calorimetry(DSC) and the metallographic observation method is 1300-1310 ℃. The sizes of dendritic core and inter dendritic of γ′ phase are equivalent after solution treatment at 1315 ℃ for 4 h, and γ′ phase is uniformly arranged in cubic form. The melting γ/γ′ eutectic produces irregular incipient melting microstructure during the solution treatment. Under different primary aging processes, γ′ phase has better cubic degree and more uniform size distribution after aging at 1120 ℃ for 4 h and air cooling (AC). The optimum heat treatment of the alloy is 1290 ℃×1 h+1300 ℃×2 h+1315 ℃×4 h, AC+1120 ℃×4 h, AC+870 ℃×32 h, AC. After complete heat treatment, the strength of the alloy reaches the peak as the tensile temperature increases from the room temperature to 850 ℃. As the tensile temperature further increases, the strength decreases. The plasticity is the worst at 760 ℃, and as the tensile temperature raises from 760 ℃ to 950 ℃, the plasticity improves.

Microstructure and recrystallization annealing of Cr20Ni80 alloy pipe used for sputtering target

Duan Xubin, Wu Yuning, Yuan Zhizhong, Wang Mengfei, Qin Haibiao, Zhong Chengming, Luo Rui, Cheng Xiaonong

2022, 47(11): 12-19. doi:10.13251/j.issn.0254-6051.2022.11.002

Abstract ( 68 )

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Microstructure and recrystallization annealing process of cold-rolled Cr20Ni80 alloy pipe used for sputtering target were studied. Firstly, the microstructure variation along the axial and radial directions of the cold-rolled pipe was observed. Secondly, the phase diagram of the Cr20Ni80 alloy was calculated by JMatPro and the recrystallization annealing process was designed. Finally, the recrystallization annealing processes were carried out and the microstructure, grain size and hardness were characterized. The results show that the microstructure of the cold-rolled pipe along the axial direction is all elongated crystals, and there are a lot of twins. The grain size of the pipe along the radial direction decreases due to the increase of deformation. The cold-rolled pipe begins to recrystallize when the recrystallization annealing temperature is 690 ℃. The deformed grains have been completely recrystallized at 790 ℃ for 30 min, and the average grain size is 24.1 μm, which is the optimal recrystallization annealing process. The recrystallized grains of the specimen gradually grow as the temperature is further increased and the holding time is prolonged. Moreover, the hardness decreases with the increase of annealing temperature.

Effect of cooling method of intercritical annealing process on austenite stability and mechanical properties of Nb-containing medium Mn steel

Zhao Shuai, Song Renbo, Zhang Yu, Huo Weifeng, Wang Yongjin, Wang Xinwei, Chen Xinghan

2022, 47(11): 20-24. doi:10.13251/j.issn.0254-6051.2022.11.003

Abstract ( 48 )

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Experiments of intercritical annealing at different temperatures (700 ℃, 750 ℃ and 800 ℃) and cooling methods (air cooling and water quenching) were carried out for a Nb-containing medium Mn steel. The results show that the product of strength and elongation and the content of retained austenite increase first and then decrease with the increase of intercritical annealing temperature. When intercritical annealed at 750 ℃, the mechanical properties of the tested steel are the best, with the yield strength of 750 MPa, the tensile strength of 1820 MPa, and the elongation after fracture of 13.9%. As the intercritical annealing temperature increases, the dissolution of cementite promotes the increase of C and Mn contents in the matrix, and the content of C and Mn partitioning into austenite increases during heat preservation process, making the austenite more stable and the retained austenite content increasing. When the intercritical annealing temperature continues to increase, the increase of austenite content during heat preservation leads to the decrease of C and Mn partitioning into austenite, which leads to the decrease of austenite stability and the formation of a large amount of martensite during cooling. The increase of martensite content and the precipitation of large-sized clusters of (Nb, Mo)C lead to high strength and low ductility of the tested steel annealed at 800 ℃. At the same intercritical annealing temperature, the phase composition of the water cooled and air cooled tested steels is the same. At the intercritical annealing temperature of 800 ℃, the differences of the two cooling methods on the retained austenite content and mechanical properties are the most obvious, which is related to the more sufficient partitioning of C and Mn into austenite during air cooling.

Effect of annealing temperature on microstructure and properties of cold rolled 8Mn steel after low temperature hot stamping

Zhang Boming, Xu Dechao, Teng Huaxiang, Zhao Haifeng, Han Yun

2022, 47(11): 25-31. doi:10.13251/j.issn.0254-6051.2022.11.004

Abstract ( 58 )

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Effect of annealing temperature on microstructure and properties of cold rolled 8Mn steel before and after low temperature hot stamping was studied by means of optical microscope, SEM, electronic tensile testing machine, EBSD and XRD analysis techniques. The results show that the austenite content decreases with the increase of annealing temperature before hot stamping. The microstructure of the annealed tested steel after stamping consists of martensite, ferrite and retained austenite. After hot stamping, the tensile strength of the tested steel annealed at different temperatures is about 1400 MPa, the yield strength is about 900 MPa, and the elongation is about 10%. It is concluded that the annealing temperature has little effect on mechanical properties of the 8Mn steel after low temperature hot stamping.

Microstructure and hot deformation behavior of Al-Mg-Mn alloy after homogenization

Ma Baoxia, Qiao Yang, Mao Mingxuan, Sun Jianghui, Wu Changtong, Liu Zeyu

2022, 47(11): 32-38. doi:10.13251/j.issn.0254-6051.2022.11.005

Abstract ( 70 )

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Microstructure evolution of Al-Mg-Mn alloy prepared by the direct chill casting was studied during the homogenization process. The plastic deformation behavior of the alloy at high temperature was investigated by using Gleeble-1500 thermal simulation testing machine. The relationship between flow stress and deformation temperature, deformation amount of the alloy was analyzed, and the microstructure change of the alloy during deformation was also discussed. The results show that after homogenization, coarse non-equilibrium precipitates of the as-cast alloy gradually dissolve and decrease in the amount, and become fine, break, tend to spheroidize, appear as bead chains. During the thermal simulating deformation process, the flow stress of the alloy homogenization annealed at 475 ℃ for 15 h decreases with the increase of deformation temperature, and the peak value of the flow stress increases with the increase of deformation amount. As the deformation temperature rises, the hot deformed microstructure firstly recovers slowly, the dislocation density decreases, then forms sub-grains and microstructure with recrystallized grain characteristics.

Effect of heat treatment on microstructure and mechanical properties of laser additive manufactured Ferrium M54 steel

Zhao Zhongchao, Ning Jing, Su Jie, Jiang Qingwei

2022, 47(11): 39-44. doi:10.13251/j.issn.0254-6051.2022.11.006

Abstract ( 65 )

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Ferrium M54 steel was prepared by laser additive manufacturing (LAM), and the effect of traditional heat treatment on its microstructure and mechanical properties was studied. The microstructure and mechanical properties of the tested steel deposited and heat treated were analyzed by means of optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD), tensile testing machine and Vickers hardness tester. The results show that the laser additive manufactured M54 secondary hardening steel is composed of columnar crystals growing along the deposition direction. The longitudinal tensile strength and yield strength of the deposited specimen are 1832 MPa and 997 MPa, respectively, and the elongation after fracture and the percentage reduction of area is 9.5% and 28%, respectively. After the traditional heat treatment, the cellular structure formed by directional solidification disappears and the martensite structure is obtained. After solution treatment at 1075 ℃+oil quenching at 1060 ℃+cryogenic treatment at -73 ℃+aging at 510 ℃, the LAM Ferrium M54 steel has the best properties, with tensile strength of 1863 MPa, yield strength of 1594 MPa, elongation after fracture of 15%, percentage reduction of area of 59% and hardness of 603 HV.

Quenching crack analysis and heat treatment process optimization of 2Cr13 steel special-shaped die forging parts

Wang Gaoyuan, Wang Kai, Zhang Zhimei

2022, 47(11): 45-53. doi:10.13251/j.issn.0254-6051.2022.11.007

Abstract ( 118 )

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In order to solve the batch surface cracking problem of a 2Cr13 steel special-shaped die forging part after quenching and tempering by analyzing the reasons of cracking from reviewing production process, simulating surface stress change during quenching process and observing the microstructure of the parts and the crack morphology. Meanwhile the influence of quenching method on surface structure and mechanical properties of workpiece was verified by heat treatment tests. The results show that the cracking of 2Cr13 steel special-shaped die forging parts after quenching is related to the shape of the forging part, quenching heating method and quenching temperature. The risk of quenching cracking can be reduced by increasing the excess allowance of forging parts, or applying hot charging and lower quenching heating temperature. Quenching at 1000 ℃ via hot charging is adopted as the optimized heat treatment method of products.

Effect of heat treatment on microstructure and mechanical properties of Mg-8Gd-3Y-1.5Zn-0.6Zr alloy

Tian Kaikai, Li Quanan, Chen Xiaoya, Mei Wanwan, Chen Peijun, Li Xiangyu, Tan Jinfeng

2022, 47(11): 54-58. doi:10.13251/j.issn.0254-6051.2022.11.008

Abstract ( 41 )

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Effect of solid solution and aging treatment on microstructure and mechanical properties of Mg-8Gd-3Y-1.5Zn-0.6Zr alloy was investigated by means of optical microscope (OM), scanning electron microscopy (SEM), X-ray diffractometer (XRD) and universal mechanics tester. The results show that the microstructure of as-cast, solid solution treated and aged Mg-8Gd-3Y-1.5Zn-0.6Zr alloy are composed of α-Mg matrix, Mg₅(Gd, Y, Zn) phase and LPSO structure. After solid solution and aging treatment, the ultimate tensile strength is increased from 187.96 MPa(as-cast) to 241.93 MPa, which is increased by 28.71%, and the elongation is increased from 8.48%(as-cast) to 13.91%, which is increased by 64.03%. The tensile fracture morphologies of the alloy under different heat treatment states are mainly brittle fracture.

Effect of solution treatment on microstructure and mechanical properties of as-cast Mg-4.8Al-2.7Ca-0.4Mn alloy

Wang Jinwei, Zhou Jixue, Tang Shouqiu, Wu Jianhua, Zhang Linlin, Zhuang Haihua, Ma Baichang

2022, 47(11): 59-63. doi:10.13251/j.issn.0254-6051.2022.11.009

Abstract ( 42 )

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Microstructure evolution and mechanical properties of as-cast and solution treated Mg-4.8Al-2.7Ca-0.4Mn alloy were investigated by means of optical microscope, scanning electron microscope, X-ray energy spectrometer, X-ray diffractometer, hardness test and tensile property test, respectively. The results show that the α-Mg phase in the microstructure of as-cast Mg-4.8Al-2.7Ca-0.4Mn alloy presents typical dendrite morphology, and a large amount of Al₂Ca phases formed during solidification are distributed among dendrites. The solution treatment has a significant influence on the morphology of second phases. With the increase of solution treatment time, the dendrite segregation is weakened, and the Al₂Ca phase changes from reticular distribution to polygonal or fine blocky. The alloy solution treated at 500 ℃ for 4 h exhibits good comprehensive tensile properties, with the tensile strength of 222.0 MPa, the yield strength of 182.5 MPa, and the elongation of 4.5%.

Optimization of heat treatment process and analysis of mechanical properties of U76CrRE heavy rail steel

Wang Yeshuang, Liu Xinyu, Su Hang, Duan Yanan, Cen Yaodong, Chen Lin

2022, 47(11): 64-69. doi:10.13251/j.issn.0254-6051.2022.11.010

Abstract ( 73 )

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Effect of isothermal treatment process on microstructure and mechanical properties of the U76CrRE heavy rail steel was studied by optimizing the process based on the on-line heat treatment with continuous cooling. The results show that the cooling rate before phase transformation, isothermal temperature and isothermal time jointly affect microstructure and mechanical properties of the U76CrRE heavy rail steel. At the optimum cooling rate of 8 ℃/s before phase transformation, the lower the isothermal temperature and the shorter the isothermal time, the finer the pearlite structure obtained. The tensile strength of the U76CrRE heavy rail steel increases with the decrease of isothermal temperature and isothermal time. Isothermal treatment at 560 ℃ for 30 s is the optimum heat treatment process for the U76CrRE heavy rail steel, under which the comprehensive mechanical properties are the best, the tensile strength is 1370 MPa, the hardness is 390 HBS, the elongation after fracture is 9.33%, the percentage reduction of area is 41.32%, and the impact absorbed energy is 4.4 J.

Effect of cold rolling and aging on microstructure and properties of novel β-titanium alloys

Li Jian, Zhuang Yusheng, Li Chunhui, Li Zhuang, Cai Wenhao, Lü Kunqi, Zhang Li

2022, 47(11): 70-75. doi:10.13251/j.issn.0254-6051.2022.11.011

Abstract ( 64 )

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Microstructure and properties of two new types β-titanium alloys after cold rolling with different deformation and aging at 650 ℃ for different time were studied. The experimental results show that a lot of dislocations, twins and stress-induced martensite transformation are produced and the hardness increases with the increase of reduction of cold rolling. When aged at 650 ℃ for 9 h, the hardness and strength of the β-titanium alloys cold rolled with reduction of 30% and 40% reach the maximum values, which result from a lot of finely dispersed secondary α phase providing effective precipitation strengthening. When aged at 650 ℃ for 6 h and 3 h, respectively, Ti-3573 and Ti-3873 alloys cold rolled with reduction of 50% have more crystal defects due to increased deformation, secondary α phases preferentially nucleate at defects, and the hardness and strength reach the peak values. The mechanical properties of Ti-3873 alloy which is enriched in β-stabilizing elements are better than those of the Ti-3573 alloy.

Effect of sintering pressure on microstructure and properties of hot pressed calcium-doped lanthanum chromate ceramic

Lai Xuping, Yan Weiwen, Wang Lianghui

2022, 47(11): 76-81. doi:10.13251/j.issn.0254-6051.2022.11.012

Abstract ( 38 )

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High density calcium-doped lanthanum chromate ceramic (La_0.8Ca_0.2Cr_0.98O₃) was prepared by hot pressing under different sintering pressures. The effect of sintering pressure on microstructure, mechanical properties and electrical conductivity of La_0.8Ca_0.2Cr_0.98O₃ ceramic was studied. The results show that when the sintering pressure is greater than 58 MPa, the second phase CaCr₂O₄ can be detected in the sintered ceramics. There are two completely different forms of CaCr₂O₄ in the sintered ceramics. The increase of sintering pressure can not only improve the density of lanthanum chromate ceramic, but also inhibit the grain growth significantly. With the increase of sintering pressure, the flexural strength and hardness increase gradually, but the fracture toughness and conductivity decrease.

Effect of annealing temperature on microstructure and properties of low cost TC4LCA titanium alloy plate

Wang Jian, Feng Qiuyuan, Lei Ting, Zhang Yongqiang, Wang Xiaoxiang

2022, 47(11): 82-86. doi:10.13251/j.issn.0254-6051.2022.11.013

Abstract ( 53 )

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In order to improve the strength and impact properties of the low cost TC4LCA titanium alloy plate, different annealing temperatures were selected for heat treatment of the plate with typical dimensions. After annealing, the change law of the microstructure and properties of the alloy was investigated, and the effect of microstructure on strength and impact properties was analyzed. The results show that the long strip primary α phase transforms to be equiaxed with the increase of annealing temperature, meanwhile, the acicular or flake secondary α phase is precipitated from the β transformation microstructure. With the increase of annealing temperature, the long strip primary α phase decreases in amount and tends to be equiaxed obviously until to its coarsening, and the acicular or flake secondary α phase grows up. When the annealing temperature increases, the strength of the alloy first increases and then decreases, the elongation after fracture decreases slightly, while the impact absorbed energy increases. For comprehensive consideration, the strengths, plasticity and toughness of the TC4LCA titanium alloy plates can get optimum match when the annealing temperature is in the range of 800-880 ℃.

Effects of solution and aging treatment on quasi-static and dynamic mechanical properties of Ti-6Al-4V ELI titanium alloy

Gao Xuemin, Wang Han, Wang Kedi, He Yupeng, Cheng Dongsong

2022, 47(11): 87-90. doi:10.13251/j.issn.0254-6051.2022.11.014

Abstract ( 44 )

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Effect of solution and aging treatment on quasi-static tensile properties and dynamic compressive properties of the Ti-6Al-4V ELI titanium alloy was studied by means of universal mechanical testing machine and Hopkinson pressure bar test. The results show that after solution and aging treatment (solution temperature of 941 ℃), the yield strength and tensile strength can reach more than 1097 MPa and 1167 MPa, respectively. Compared with Ti-6Al-4V ELI titanium alloy before heat treatment, the strength is significantly improved and the plasticity indexes are maintained at a higher level. Meanwhile, the dynamic compression properties of the Ti-6Al-4V ELI titanium alloy is significantly improved at different strain rates. The relationship between the dynamic compression strength and the lgε· is linear, and the dynamic compression strength increases with the increase of strain rate.

Effect of multiple repeated solution and aging treatment on microstructure and mechanical properties of TB15 titanium alloy

Zhao An'an, Hu Shengshuang, Chen Suming, Zhang Yingyun, Zhao Hu, Zhang Ying

2022, 47(11): 91-94. doi:10.13251/j.issn.0254-6051.2022.11.015

Abstract ( 43 )

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Effect of multiple repeated solution and aging treatment on microstructure and mechanical properties of TB15 titanium alloy was studied by means of optical microscope, tensile testing machine and scanning electron microscope. The results show that with the increase of the repeating time of solution and aging treatment, the microstructure of the TB15 titanium alloy changes obviously, the secondary α phase merges and grows, and the original β grain boundary thickens. The mechanical properties of the alloy after one time solution and aging treatment is the best, however, with the increase of repeating time, the strength and fracture toughness of the alloy decrease, the elongation and reduction of area also decrease sharply, and the tensile fracture changes from ductile fracture to brittle fracture. In conclusion, multiple repeated solution and aging treatment with the same process parameters cannot improve the room temperature ductility of the alloy without drastically reducing the strength and fracture toughness.

Effect of tempering temperature on microstructure and properties of 30Cr3Si2NiMoWNb steel

Ning Jing, Yang Peng, Gao Qi, Su Jie

2022, 47(11): 95-99. doi:10.13251/j.issn.0254-6051.2022.11.016

Abstract ( 58 )

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Effect of tempering temperature on microstructure and properties of 30Cr3Si2NiMoWNb ultra-high strength steel was studied by means of scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and mechanical test. The resules show that the tempering temperature can greatly affect and regulate the mechanical properties of the steel. When tempered at 200-350 ℃, the microstructure is composed of tempered martensite and fine dispersed ε-carbides. The fluctuation of strength and toughness is small, the tensile strength grade is 1700 MPa, the yield strength grade is 1300 MPa. Due to the inhomogeneous precipitation of cementite when tempered at 350-500 ℃, the strength and toughness decrease at the same time, and the brittleness is the most serious at about 500 ℃, with impact absorbed energy decreasing to the lowest point. When tempered at 500-700 ℃, stable spherical cementite is formed, and strength decreases and toughness increases greatly. The influence mechanism of tempering temperature on strength and toughness is the evolution process of precipitates such as ε-carbide and cementite. Certain amount of Si can raise the forming temperature of cementite and temper brittleness temperature of the steel.

Medium and high temperature mechanical properties of martensitic stainless steel

Chen Rui, Bao Cuimin, Yang Zhipeng, Chen Wei, Wang Shengchi, Lin Lin

2022, 47(11): 100-105. doi:10.13251/j.issn.0254-6051.2022.11.017

Abstract ( 65 )

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Tensile test, creep test and linear expansion coefficient test of martensitic stainless steel FV520B at medium and high temperature were carried out by means of electronic universal testing machine, thermal dilatometer and other testing and analysis methods, and the fracture of the specimen was observed by means of SEM. The results show that the tensile properties of FV520B steel at medium and high temperatures are lower than those at room temperature. When the test temperature rises from 300 ℃ to 500 ℃, the strength decreases as a whole, but the plasticity is basically stable. The FV520B steel aged at 480 ℃ has good creep resistance at test temperature of 300 ℃ and load of yield strength. In the range of 300-500 ℃, the linear expansion rate of the FV520B steel presents a gentle growth trend.

Effects of compression and aging on microstructure and properties of A286 superalloy

Zhang Xiaobin, Zhang Cuiyu, Wei Liangliang, Wang Lili, Yu Maosong, Ding Yanhong, Ma Xu

2022, 47(11): 106-110. doi:10.13251/j.issn.0254-6051.2022.11.018

Abstract ( 29 )

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A286 alloy after solution treatment at 980 ℃ for 2 h was subjected to compression and aging treatment, and the element composition of the phase was observed by means of X-ray diffraction (XRD). Microstructure was observed by means of metallographic microscope (OM) and scanning electron microscope (SEM). Vickers hardness was measured by hardness tester, and the properties were compared to verify the effect of precipitation on properties of A286 alloy after aging. The results show that under the same compression conditions, with the increase of aging time, the number of precipitates increases, and the precipitates are mainly γ′ phase, TiC and chromium carbide. Under the same aging conditions, with the increase of deformation, the number of precipitates also increases. When aged at 680 ℃, with the increase of aging time, the hardness of the alloy with same deformation shows an increasing trend, but the increasing rate gradually slows down. The hardness of the alloy with compression of 35% reaches the peak value when aged at 720 ℃ for 8 h.

Magnetic-thermal coupling to reduce residual stress and dislocation density of cold-rolled oriented silicon steel

Luo Jiahao, Chen Zhongyi, Su Pengji, Liu Baozhi, Ma Yonglin, Xing Shuqing

2022, 47(11): 111-116. doi:10.13251/j.issn.0254-6051.2022.11.019

Abstract ( 24 )

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In order to obtain an efficient process for reducing residual stress of cold-rolled oriented silicon steel, a short-time magnetic-thermal coupling treatment test scheme with low temperature and low intensity pulsed magnetic field was developed. The residual stress and dislocation density before and after the treatment were measured by X-ray residual stress meter and XRD, respectively. The results show that the short-time magnetic-thermal coupling process with low temperature and low intensity pulsed magnetic field can effectively reduce the residual stress and dislocation density of cold-rolled silicon steel. When the process is applied for 3 min at 400 ℃ and with the peak current of 180 A, the best treatment effect can be obtained, and the residual stress can be reduced by 55.5%, which is better than simply applying low temperature thermal field or low intensity pulsed magnetic field. The decrease of macro-residual stress is closely related to the dislocation density, and the change rule of the both is basically the same. The microscopic mechanism of residual stress reducing by short-time, low-temperature and low pulsed magnetic field intensity magnetic-thermal coupling treatment is that the dislocation movement in the material is further improved under the coupling action of pulsed magnetic field and temperature field, and the local recovery is realized, so as to achieve the purpose of reducing dislocation density and residual stress.

Effect of annealing process on magnetic properties of flattening rolled 50W800 non-oriented silicon steel

Qiao Degao, Zhao Xiaolong, Di Yanjun, Guo Yuanqiang, Lin Xiaoliang

2022, 47(11): 117-121. doi:10.13251/j.issn.0254-6051.2022.11.020

Abstract ( 37 )

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In order to improve the sheet shape of the 50W800 non-oriented silicon steel, the silicon steel after recrystallization annealing needs to be flattened, but the magnetic properties of the silicon steel sheet will decrease after flattening. The stress relief annealing test of the flattening rolled 50W800 non-oriented silicon steel was designed at 400-800 ℃, the iron loss and magnetic induction strength were measured by a single chip measuring method and the microstructure and texture were analyzed by EBSD technology. The results show that the small angle grain boundary of the 50W800 non-oriented silicon steel increases after flattening, but the nonuniformity of grain leads to the decrease of magnetic properties. It is found that after stress relief annealing at 700 ℃ for 2 min, the magnetic properties of 50W800 non-oriented silicon steel are improved. EBSD technology analysis shows that the stress relief annealing can consume a large amount of small angle grain boundary, reduce the grain boundary content, increase the grain uniformity, and reduce the strength of unfavorable deformation texture {111} <112>, which is the main reason for the improvement of magnetic properties of the 50W800 non-oriented silicon steel.

Effect of annealing process on microstructure and properties of 980 MPa hot dip galvanized dual-phase steel

Liu Pengfei, Yang Bo, Chen Yu, Liu Hongliang

2022, 47(11): 122-125. doi:10.13251/j.issn.0254-6051.2022.11.021

Abstract ( 33 )

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Continuous annealing galvanizing process of 980 MPa dual-phase steel was simulated by Voestal pine thermal simulator, and the effect of soaking temperature and rapid cooling outlet temperature of continuous hot dip galvanizing process on microstructure and mechanical properties of the dual-phase steel was studied by means of tensile testing machine and optical microscope and scanning electron microscope. The results show that the microstructure of 980 MPa dual-phase steel consists of ferrite and martensite after annealing galvanizing process, and Nb, Ti carbonitrides distribute in the structure. With the increase of soaking temperature, the volume fraction of martensite increases, the yield strength and yield ratio increase. With the rapid cooling outlet temperature increasing from 340 ℃ to 430 ℃, tempering decomposition of martensite appears, which reduces the yield strength of the tested steel, but improves the elongation. When the rapid cooling outlet temperature is 400 ℃, the maximum value of the product of strength and elongation is 13.9 GPa·%. When soaked at 840 ℃ and rapid cooled at 460-480 ℃, the hot dip galvanized dual-phase steel can be obtained with the tensile strength above 980 MPa.

Microstructure homogenization of 17CrNiMo6 gear steel

Wang Jie, Dang Shue, Fan Zijing, Guo Lun, Zhu Xuetong

2022, 47(11): 126-133. doi:10.13251/j.issn.0254-6051.2022.11.022

Abstract ( 28 )

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Taking 17CrNiMo6 gear steel as the research object, and the forged specimens were annealed at different temperatures for different time. The formation of the banded structure and its homogenization behavior were studied and quantitatively analyzed by means of optical microscope, scanning electron microscope, energy dispersive spectrometer and data processing software Origin. The results show that the enrichment of C, Cr, Ni, Mn and Mo in the pearlite+bainite region is the root cause of the band structure of the 17CrNiMo6 gear steel. When the heating temperature is 1100 ℃ with the holding time of 11 h, or the heating temperature is 1250 ℃ with the holding time being more than 2 h, the banded structure is eliminated, but the non-uniformity of alloy elements is still high. When the heating temperature is 1250 ℃ and the holding time is 4 h, the segregation coefficients K for C, Cr, Mn, Ni, P, S, Mo are 1.02, 0.98, 1.02, 1.02, 1.01, 0.98, and 0.98, respectively, and the element distribution is also uniform.

Carburizing and quenching process of 18CrNiMo7-6 steel heavy-duty internal gear

Liu Jinde, Mi Pei, Ma Chunliang

2022, 47(11): 134-137. doi:10.13251/j.issn.0254-6051.2022.11.023

Abstract ( 51 )

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The heavy-duty internal gear of a reducer required carburizing and quenching treatment. Because the internal gear structure was a large thin-wall part, the tooth distortion after conventional carburizing treatment was large, and the common normal size after gear grinding could not meet the technical requirements, resulting in scrapping of the workpiece. By adding stress-relief annealing process before carburizing, increasing preheating process during carburizing, reducing both the carburizing temperature and the cooling intensity, the problem of tooth distortion deviation after carburizing of heavy-duty internal gear is solved, providing a quality guarantee for carburizing and quenching of the thin-wall and heavy-duty internal gear.

Effect of diffusion time on vacuum carburizing of 20MnCrS5 gear steel

Han Haoyuan, Zhang Zibo, Yu Wanhua, Zhai Yuewen, Zhou Leyu, Zhang Minghao

2022, 47(11): 138-142. doi:10.13251/j.issn.0254-6051.2022.11.024

Abstract ( 22 )

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The gear steel 20MnCrS5 was subjected to vacuum low pressure carburizing high pressure gas quenching treatment, and the effects of diffusion time on hardness gradient, carburized layer depth, microstructure, and carbon distribution were analyzed, and the vacuum carburizing process was optimized. The results show that carbon atoms diffuse from the surface to substrate with the prolongation of diffusion time. When the diffusion time exceeds 100 min, the diffusion speed of carbon slows down. When the carbon content exceeds 1.0%, it is easy to form large-sized retained austenite after quenching. While with the decrease of carbon content, the microstructure changes from twin martensite to dislocation martensite, and the hardness decreases. Under the experimental conditions, the suitable vacuum carburizing process for the 20MnCrS5 steel is vacuum low pressure carburizing at 930 ℃ for 42 min, diffusing for 140 min, and high pressure gas quenching at 0.6 MPa, then tempering at 160 ℃ for 2 h. After carburizing by this process, the carbide in the microstructure is Grade 1, the retained austenite is Grade 2, and the martensite is Grade 3. There is no internal oxidation on the surface layer, and the thickness of the carburized layer is about 0.91 mm, which meet the technical requirements.

Effect of shot blasting pretreatment on gas carburizing efficiency and layer properties of 45 steel

Cao Pei, Gu Xiaowen, Yan Shaoyun

2022, 47(11): 143-146. doi:10.13251/j.issn.0254-6051.2022.11.025

Abstract ( 39 )

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Effect of shot blasting pretreatment on gas carburizing efficiency and layer properties of 45 steel was studied by means of optical microscope and microhardness tester. The results show that under the same gas carburizing process, shot blasting pretreatment can obviously promote the gas carburizing of the 45 steel, the effective hardening layer of the pretreated carburized specimen increases from 0.994 mm to 1.486 mm, the carburizing efficiency increases by more than 39%, and the surface hardness increases by more than 10%. Compared with the non-shot blasting carburized specimen, shot blasting pretreatment makes the gradient hardness of carburized specimen section increase and decrease more gently from the outside to the inside, reducing the brittleness of carburized layer.

Effect of plasma nitriding temperature on microstructure and properties of nitrided layer on Fe-C-Cr-Ni-Mn-V precipitation-hardened austenitic stainless steel

Zhou Wu, Wang Min, Zhao Tongxin, Lu Jun, Yang Qi

2022, 47(11): 147-151. doi:10.13251/j.issn.0254-6051.2022.11.026

Abstract ( 28 )

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The surface of a Fe-C-Cr-Ni-Mn-V precipitation-hardened austenitic stainless steel was modified by plasma nitriding. Microstructure and properties of the nitrided layer at different nitriding temperatures were investigated by means of optical microscope (OM),X-ray diffraction (XRD), electron probe microanalysis (EPMA) and Vickers hardness tester. The results show that nitrided layer with uniform thickness on the specimen surface is formed by plasma nitriding at temperatures ranging from 430 ℃ to 520 ℃ for 10 h, and the surface hardness is significantly improved. The thickness of the nitrided layer increases with the increase of nitriding temperature and reaches 78 μm at 520 ℃. The infiltration layer is composed of γ_N, CrN and γ′-Fe₄N phases after nitriding at 430 ℃, and composed of γ′-Fe₄N, CrN and ε-Fe_2-3N phases when the nitriding temperature increases to 520 ℃. Precipitation of CrN is found in the infiltration layer at all the three nitriding temperatures, resulting in the poor corrosion resistance compared with that of the substrate.

Effect of carburizing process on hardened depth of blind hole of 20CrMo steel

Su Yang, Shi Yousen, Zhang Zhichong, Wang Qin, Wang Meiqian, Mao Jun

2022, 47(11): 152-155. doi:10.13251/j.issn.0254-6051.2022.11.027

Abstract ( 40 )

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To solve the problem of blind hole carbonization, the carburizing capacity of conventional gas carburizing and vacuum low-pressure carburizing to the blind holes of 20CrMo steel were analyzed and compared. The results show that the carburizing capacity of vacuum low-pressure carburizing to the blind hole is much higher than that of the conventional gas carburizing, and the smaller the size of the blind hole, the higher the vacuum, the better the carburizing capacity is. The different gas states of the conventional gas carburizing and vacuum low-pressure carburizing are the main reasons for the different carburizing capacity of the two processes for blind hole inner surface.

Effect of annealing process on microstructure and properties of Cu-2Ag-0.075Y alloy wire bar

Zeng Yanqi, Yu Huihui, Li Jie, Zou Jin, Jiang Jiang, Liu Qi, Hu Xiaona

2022, 47(11): 156-159. doi:10.13251/j.issn.0254-6051.2022.11.028

Abstract ( 23 )

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Cu-2Ag-0.075Y alloy wire bar was prepared by vacuum induction melting, hot forging and cold drawing, and then its microstructure and properties under different annealing processes were studied by means of tensile property test, conductivity test and microstructure observation. The results show that the tensile strength of the Cu-2Ag-0.075Y alloy wire bar first decreases significantly to 300-435 MPa with the extension of annealing time, then the decline rate slows down obviously, and finally tends to be stable. The higher the annealing temperature is, the lower the tensile strength is. The change law of elongation and conductivity is opposite to that of tensile strength. Firstly, they increase rapidly, then the increase rate slows down and finally tends to be stable. The specimens annealed at 550 ℃ can obtain higher elongation and conductivity. With the increase of annealing temperature and annealing holding time, the recrystallization degree of the Cu-2Ag-0.075Y alloy wire bar can be increased. Using 550 ℃×60 min annealing process, the Cu-2Ag-0.075Y alloy wire bar can obtain fine and uniform equiaxed grain microstructure, good matching of elongation and conductivity, which is conducive to the subsequent ultra-fine wire drawing process.

Effect of laser hardening on microstructure and hardness of CrMo cast iron surface

Zhang Yonghui, Zhang Shuangjie, Wang Wei, Ma Shibo, Yan Huajun

2022, 47(11): 160-164. doi:10.13251/j.issn.0254-6051.2022.11.029

Abstract ( 69 )

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TH-3DC3000 laser processing system was used to laser hardening treatment on CrMo cast iron. The effects of different laser power and scanning speed on microstructure, surface hardness and hardened layer depth of CrMo cast iron were studied. The results show that after laser hardening, the microstructure of CrMo cast iron consists of three regions, which are hardened zone, transition zone and matrix. The microstructure of hardened zone is cryptocrystalline martensite, retained austenite and spherical graphite. The microstructure of transition zone is cryptocrystalline martensite, pearlite and spherical graphite. The microstructure of matrix is ferrite, pearlite and spherical graphite. When laser surface hardening does not have overheating effect on the test piece, the increase of laser power and the decrease of scanning speed will improve the surface hardness and hardened layer depth of the CrMo cast iron. Under the rectangular laser spot of 5 mm×20 mm, the optimal parameter combination is determined as laser power of 2300 W and scanning speed of 0.003 m/s. When this parameter combination is used for laser hardening of the CrMo cast iron, the surface hardness is 760 HV0.3, the average hardness of the hardened layer is 724 HV0.3, and the depth of hardened layer is more than 1.4 mm.

Relationship between quenching diameter and microstructure of 35CrMnSi low alloy steel

Zhang Xianwu, Ding Yali, Yang Zhuoyue, Gao Qi, Wang Shengmin

2022, 47(11): 165-167. doi:10.13251/j.issn.0254-6051.2022.11.030

Abstract ( 39 )

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35CrMnSi low alloy steel bars with different diameters were quenched by oil cooling at 900 ℃ and tempered at 230 ℃. The quenching critical diameter of the 35CrMnSi low alloy steel was explored by analyzing the relationship between the diameter of the steel bar and the hardness of the cross section and the microstructure of the center of the cross section. The results show that the correlation between quenched martensite volume and hardness is no longer consistent with the corresponding relationship provided by SAE J406 standard due to the presence of bainite. The martensite content of Ø60 mm steel rod is only about 40%, but the hardness of the center of the axis is close to the hardness corresponding to 90% martensite according to SAE J406 standard. The strength and toughness of the center of the axis are proved to meet the requirements of the strength and toughness of ultra-high strength steel, it can be determined that the quenching critical diameter of the 35CrMnSi low alloy high-strength steel is not less than Ø60 mm. The microstructure at the center of the axis of the Ø90 mm steel bar is granular bainite and upper bainite, which have limited influence on the hardness, and the hardness of 450 HV10 (46 HRC) is much higher than that of 50% martensite of SAE J406 standard, which also proves that quenching critical diameter of the 35CrMnSi steel predicted by the quenched martensite content of SAE J406 standard is much lower than the actual value.

Thermal deformation behavior of novel Al-Mg-Si-RE alloys

Ren Yupeng, Liu Ping, Chen Xiaohong, Zhou Honglei, Liang Xiaofei

2022, 47(11): 168-177. doi:10.13251/j.issn.0254-6051.2022.11.031

Abstract ( 27 )

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Four novel Al-Mg-Si alloys with different Mg/Si ratios and additions of Zr and B, and rare earth elements (Ce and Er) were designed and prepared, and the microstructure, electrical conductivity and tensile strength were studied. Then taking the Al-Mg-Si-RE alloy with a optimum chemical composition as the research object, the thermal compression test was carried out by Gleeble-3500 thermal simulator, and the thermal deformation behavior of the alloy was studied with the deformation temperature of 300-450 ℃ and the strain rate of 0.001-1 s^-1. The constitutive equation and hot processing map of the alloy were constructed through experimental data, and the evolution of microstructure was studied by optical microscope. The results show that when the Mg/Si ratio is 1.4, the alloy has excellent properties. The flow stress of the alloy decreases with the increase of deformation temperature and the decrease of the strain rate. The thermal deformation activation energy of the alloy is calculated to be 176.188 kJ/mol, the constitutive equation obtained has a guiding effect on the flow behavior of the alloy. The hot processing map shows that the suitable processing regimes are deformation temperature of 300-320 ℃, strain rate of 0.001-0.015 s^-1, and deformation temperature of 430-450 ℃, strain rate near 0.001 s^-1or 1 s^-1.

Effect of Ni on microstructure and mechanical properties of 30CrMnSi2 steel

Ma Jinwei, An Shengli, Jia Li, Fu Xueyi, Xue Rui, Gao Zhanyong

2022, 47(11): 178-183. doi:10.13251/j.issn.0254-6051.2022.11.032

Abstract ( 26 )

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Microstructure and properties of 30CrMnSi2 steel with different Ni contents after tempering at low temperature were studied. The results show that the microstructure of the tested steel consists of tempered lath martensite and M/A islands. With the increase of Ni content, the M/A islands are significantly refined, and changing from islands to elongated strips. The impact fracture is ductile fracture, with the increase of Ni content, the ductile area of the fracture increases, the equiaxial dimple deepens, the number of dimples increases, and the impact absorbed energy increases. When the Ni content is greater than 1.0%, the increasing trend of impact absorbed energy decreases. The tested steel with 1.0%Ni has the highest strength, good toughness and plasticity, and the best comprehensive properties.

Static recrystallization behavior of 17CrNiMo6 steel

Duan Xingwang, Li Kai, Jiao Yongxing, Wang Min, He Linfeng

2022, 47(11): 184-191. doi:10.13251/j.issn.0254-6051.2022.11.033

Abstract ( 49 )

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Under the conditions of compression temperature of 950-1050 ℃(interval 50 ℃), prestrain of 0.1-0.2 s^-1(interval 0.05), strain rate of 0.01-1 s^-1, different prior grain sizes and different pass intervals, double-hit hot compression test of the 17CrNiMo6 steel was carried out on Gleeble-1500 thermo-mechanical simulator. The effects of pass interval, compression temperature, prestrain, strain rate and prior grain size on static recrystallization behavior of the 17CrNiMo6 steel were discussed. According to the microstructure of the specimens after compression and the flow stress curves of static recrystallization under different deformation conditions obtained by regression analysis, the static recrystallization kinetics model and grain size model of the 17CrNiMo6 steel were established. The results show that the volume fraction of static recrystallization increases with the increase of compression temperature, interval time, prestrain and strain rate. The grain size of static recrystallization increases with the increase of compression temperature and prior austenite grain size, while decreases with the increase of prestrain and strain rate. By comparing the predicted results by the models with the experimental values of thermal compression test, it is found that the two are in good agreement, which proves the accuracy of the models is high.

Thermodynamic calculation of precipitates in microalloyed 2000 MPa hot stamping steel and its strength and toughness

Geng Zhiyu, Zhang Yu, Xue Han, Xue Feng, Zhou Tianpeng

2022, 47(11): 192-198. doi:10.13251/j.issn.0254-6051.2022.11.034

Abstract ( 27 )

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Thermodynamic software Thermo-Calc was used to calculate the equilibrium phase diagram, precipitation temperature of each phase, element content in the phase, growth law of carbides at different temperatures and the influence of Nb and V content on precipitation temperature and amount of carbides in the microalloyed 2000 MPa hot stamping steel. A steel with selected composition was smelted by 50 kg vacuum furnace, and hot rolling and cold rolling were carried out. The hot forming process was simulated by plate die quenching, the mechanical properties and three-point bending properties were tested, and the field emission scanning electron microscope and EBSD were used to characterize the microstructure. The results show that the main carbides in Nb and V microalloyed 2000 MPa hot stamping steel are NbC and VC, and the precipitation temperatures are above 1150 ℃ and 880 ℃, respectively, and the precipitation temperatures increase with the increase of Nb and V content, respectively. The tensile strength and elongation of hot stamping steel plate after plate die quenching are more than 2000 MPa and 8%, respectively. The tensile fracture is ductile fracture and the three-point bending angle is more than 66°. The results of SEM and EBSD show that the martensite structure is composed of packet, block and lath. The prior austenite grain size is about 10 μm, and the size of martensite block is <5 μm. The martensite block is composed of martensite lath, and the small angle grain boundary between the martensite lath is discontinuous, and most of the grain boundary orientations are less than 5°. Fine prior austenite grain and martensite block structure are the main reasons for the high strength and high plasticity of microalloyed 2000 MPa hot stamping steel.

High temperature mechanical properties of near α, (α+β) and near β type titanium alloys

Li Mingbing, Wang Xinnan, Shang Guoqiang, Zhu Liwei, Li Xing, Zhu Zhishou

2022, 47(11): 199-204. doi:10.13251/j.issn.0254-6051.2022.11.035

Abstract ( 35 )

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High temperature mechanical properties of near α type TA15 and Ti60, near β type TB17, (α+β) type TC21 titanium alloys at 100, 400, 500, 600, 650 and 700 ℃ were investigated. The results show that when the temperature is in the range of 100-500 ℃, the high temperature strength of TB17 alloy is the highest, and that of the TA15 alloy is the lowest. The high temperature strength of the TC21 alloy is higher than that of the Ti60 alloy. When temperature exceeds 600 ℃, the high temperature properties of the TB17 alloy change significantly, and the high temperature strength is the lowest. While the Ti60 alloy changes the least, and the high temperature strength is the highest. The high temperature strength of the TC21 alloy is between that of the TA15 and Ti60 alloys, and gradually closes to that of TA15 alloy. When the temperature is 100 ℃, the engineering stress-strain curves of the four alloys are in a relatively balanced state because of comparable strain hardening and strain softening effects. When the temperature is 400 ℃, the deformation mechanism of the TB17 alloy is dominated by strain softening, and the stress decreases significantly with the increase of strain. When the temperature is 600 ℃, the deformation mechanism of the TC21 and TA15 alloys is also dominated by strain softening, while the stress drop of the TA15 alloy is lower than that of the TC21 alloy. Until the temperature is 650 ℃, the deformation mechanism of the Ti60 alloy is dominated by strain softening.

Microstructure and mechanical properties of Super304H superheater steel tube in service

Wu Yue

2022, 47(11): 205-210. doi:10.13251/j.issn.0254-6051.2022.11.036

Abstract ( 31 )

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Microstructure and mechanical properties of different areas of the Super304H superheater steel tube of an ultra-supercritical unit after 40 000 h service were analyzed by means of optical microscope, scanning electron microscope and transmission electron microscope. The results show that the Super304H steel tube has abnormally grown austenite grains in the outer wall after 40 000 h service. TEM test shows that the coarsening of M₂₃C₆ particles in the outer wall is obvious, and continuous M₂₃C₆ particles precipitate on grain boundary, while the growth of MX phase and Cu rich phase is not obvious. The abnormally grown grains cause the room temperature tensile strength and impact property of coarse-grained zone of outer wall of the Super304H steel tube in service to decrease by 21.9% and 50%, respectively, compared with the supply state. The fracture characteristics of the impact specimen in the coarse-grained zone are obvious, and its brittleness is significantly increased, which poses a threat to the service safety of the Super304H steel tube. Supervision should be strengthened to eliminate the potential safety hazards such as tube explosion caused by the abnormal growth of austenite grains on the outer wall.

High temperature oxidation properties of GX40CrNiSi25-12 austenitic heat resistant cast steel

Li Jie, Hu Jianwen, Lu Zitong

2022, 47(11): 211-215. doi:10.13251/j.issn.0254-6051.2022.11.037

Abstract ( 30 )

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High temperature oxidation resistance of the GX40CrNiSi25-12 austenitic heat resistant cast steel at different oxidation temperatures and time was studied by means of constant temperature oxidation test. The oxidation kinetics, morphologies and composition of oxide films were analyzed by means of oxidation mass gain method, optical microscope, scanning electron microscope and energy dispersive spectrum analysis, respectively. The results show that the oxidation kinetics curves at temperatures of 850 ℃, 950 ℃ and 1050 ℃ all follow parabolic law, and the average oxidation rates oxidized for 100 h at different temperatures are in the range of Grade one standard representing complete anti-oxidation level according to GB/T 13303—1991. At 850 ℃ and 950 ℃, the oxide films are flat and dense, which are composed of small, uniform and densely arranged irregular polygonal oxides. Significant oxide grain size inhomogeneity appears in the oxide film at 1050 ℃. The good high temperature oxidation resistance of the GX40CrNiSi25-12 austenitic heat resistant cast steel is related to the high content of Cr in the oxide film.

Microstructure of high chromium cast iron/TiC-SiC composites fabricated by infiltration method

Zhu Junxuan, Yang Fan, Yin Mengtao, Liu Haiyun

2022, 47(11): 216-222. doi:10.13251/j.issn.0254-6051.2022.11.038

Abstract ( 25 )

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High chromium cast iron/TiC-SiC composites were fabricated by SiC ceramic particles coating with TiC particles of few microns and pressureless infiltration under the protection of inert gas. The infiltration situation, microstructure characteristics and composition distribution were observed and analyzed by means of SEM/EDX. Finally, combined with the microstructure characteristics and infiltration behavior of high-chromium cast iron/Ti-SiC composites, the effect of TiC powder on infiltration behavior and composite structure was analyzed. The observation results show that Fe/Cr alloy cannot wet the preform SiC particles when TiC addition ≤10%(mass fraction, as follow), while the wettability between Fe/Cr alloy and preform is improved when TiC addition ≥ 20%, increasing the TiC content is more conducive to Fe/Cr alloy infiltration. The large-sized SiC particles in the matrix disappear, and strip-shaped elemental carbon with a size close to millimeters appeares, which is quite different from the microstructure of high-chromium cast iron/Ti-SiC composites. Comparing the microstructure of the two composite materials, it is found that the added Ti powder can combine with C to form TiC in the molten metal, while the added TiC particles are cobblestone-like in the microstructure with rounded edges, mutual dissolution between molten metal and ceramic particles occurs. During the infiltration process, the added TiC and Ti react differently with the infiltrated metal, and the high mass fraction of TiC can significantly promote the molten metal infiltration process.

Modification effect of rare earth Ce content on inclusions in 4Cr5MoSiV1 steel

Shi Xuehong, Yang Lilin, Xia Ming, Xu Qihao, Zhao Liping

2022, 47(11): 223-229. doi:10.13251/j.issn.0254-6051.2022.11.039

Abstract ( 42 )

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In order to explore the effect of Ce content on inclusions in hot work die steel and its action mechanism, the types, morphology, quantity, size and distribution of inclusions in 4Cr5MoSiV1 steel with different Ce contents were observed and statistically analyzed by means of field emission scanning electron microscope (SEM/EDS) and the attached automatic inclusion analysis system. The results show that the inclusions in the Ce-free specimen are not only larger in number, larger in average size but also more irregular in shape, mainly composing of Mg-Al-O type, MnS and Mg-Al-O covered with MnS. With the increase of Ce content, the number and average size of inclusions in the specimen decrease and change into spherical rare earth sulfur oxides. When the content of Ce in the steel is 0.0070%, the number and average size of inclusions are the least. With the increase of rare earth Ce content to 0.0120%, more sulfur oxide inclusions are formed, and the number and average size of inclusions tend to increase. With the solidification process going on, Ce mainly exists in the tested steel in the form of rare earth sulfur oxides, and more than 60% of the inclusions will be pushed by the solidification front and finally stay near the grain boundary.

Research progress of annealed strip flatness optimization technology for cold-rolled ultra-high-strength steel

Zhang Liyang, Wan Zhaotang, Zhang Wenjun

2022, 47(11): 230-237. doi:10.13251/j.issn.0254-6051.2022.11.040

Abstract ( 38 )

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Equipment configuration and development of the continuous annealing line was briefly introduced, and the development direction for annealed strip flatness optimization technology of cold-rolled ultra-high-strength steel was analyzed. For the problem of strip flatness, based on the analysis of the evolution mechanism of flatness during annealing process, the flatness optimization technology from the aspects of heating zone flatness optimization, cooling zone flatness optimization, skin-pass zone flatness optimization, annealing tension system optimization and furnace roll profile optimization was summarized. The effect of incoming strip flatness, annealing tension, annealing process, rapid heating and cooling technology, temperature uniformity along the width of the strip, furnace roll profile and skin-pass process on strip flatness of continuous annealing line was pointed out, which played an important guiding role in mastering the key process technology of strip flatness control in the continuous annealing process of ultra-high-strength steel and improving the core competitiveness of enterprises. Finally, the development trend of continuous annealing technology was also prospected.

Microstructure and properties of electro-spark deposited Invar/amorphous composite coatings

He Yanling, Wang Yanfang, Si Jiajia, Shi Zhiqiang

2022, 47(11): 238-244. doi:10.13251/j.issn.0254-6051.2022.11.041

Abstract ( 54 )

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Invar, Invar/amorphous and Invar/amorphous/Invar coatings were deposited on the 45Mn2 steel surface by electro-spark deposition technique using invar alloy electrode and pre-put Fe-based amorphous powders. The phase composition, microstructure, tribology behavior and electrochemical corrosion behavior in 3.5%NaCl solution of the deposited coatings were analyzed. The results show that the prepared coatings are continuous and uniform with a metallurgical bonding to the substrate. A 60 μm crack-free Invar/amorphous/Invar coating is obtained by an Invar bond layer produced on the substrate firstly. The Invar deposited coating is mainly consisted of FCC Fe-Ni solid solution, the Invar/amorphous and Invar/amorphous/Invar coatings are amorphous/solid composite structure. The average microhardness and friction coefficient of the Invar, Invar/amorphous and Invar/amorphous/Invar coatings are 176.6, 757.7, 772.8 HV0.1 and 0.44, 0.21, 0.19, respectively. Increasing the amorphous content of the deposited coating can improve the hardness, reduce the friction coefficient and improve the wear resistance. No obvious passivation phenomenon of the deposition coatings in 3.5% NaCl solution can be observed. The self-corrosion potential, self-corrosion current density of the substrate, Invar, Invar/amorphous and Invar/amorphous/Invar coatings are -0.74, -0.54, -0.34, -0.31 V and 7.08, 5.15, 3.78, 3.11 μA·cm^-2, respectively. The Invar/amorphous/Invar coating prepared by electro-spark deposition technology can effectively improve the wear resistance and corrosion resistance of the 45Mn2 steel substrate.

Microstructure and mechanical properties of laser clad VC-Cr₇C₃ composite layers

Wang Haomin, Wang Guoqing, Xiong Yangkai, Jiang Hao, Zhao Yuantao, Fang Zhiqiang, Li Wenge

2022, 47(11): 245-252. doi:10.13251/j.issn.0254-6051.2022.11.042

Abstract ( 25 )

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Composite clad layer of VC-Cr₇C₃ was in situ synthesized on the surface of Q235 steel using laser cladding technology, and the effect of laser scanning speed on microstructure and mechanical properties of the clad layer was studied. The microstructure and properties of the clad layer were analyzed by means of scanning electron microscope, X-ray energy dispersive spectrometer and X-ray diffractometer. The results show that laser cladding technology can cause in-situ reactions between mixed particles of V, Cr and C to form a composite clad layer of VC-Cr₇C₃. It is mainly composed of black gray VC phase, gray Cr₇C₃ phase and {FeM} bonding phase, in which Fe and Cr can form Cr₇C₃ phase (M₇C₃). The laser cladding solidification shape control factor K and the distribution of C element result in a large amount of carbide equiaxed crystals at the top of the clad layer, with a reduced amount of carbide equiaxed crystals in the middle and less carbide at the bottom due to the low C content. The carbide shape is influenced by the laser scanning speed, with carbide dendrites appearing at 1 mm/s and carbide equiaxed crystals at 1.5 mm/s. At the same time, the grain size of the clad layer at 1.5 mm/s is significantly smaller than 1 mm/s. The above changes in the structure and composition of the clad layer cause its hardness to decrease as the layer depth increases. As the scanning speed increases, the hardness of the clad layer gradually increases, with the hardness of the clad layer being more than three times higher than that of the Q235 steel. The friction coefficient of the clad layer is 0.4 at 1.5 mm/s, which is lower than the 0.6 of the Q235 steel substrate. The significant lower wear loss of the clad layer compared to that of the Q235 steel substrate indicates that the composite clad layer of VC-Cr₇C₃ can be used to modify the surface of the carbon steel for high hardness and wear resistance.

Preparation and properties of superhydrophobic Co-MoS₂ composite coating

Liu Cansen, Zhen Haowen, Huang Qishan, Chen Wanlin, Jie Xiaohua

2022, 47(11): 253-260. doi:10.13251/j.issn.0254-6051.2022.11.043

Abstract ( 21 )

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A superhydrophobic Co-MoS₂ composite coating with excellent wear and corrosion resistance was prepared by one-step electrodeposition method. The influence law and mechanism of current density and electrodeposition time on microstructure, wettability, self-cleaning effect, wear and corrosion resistance of the composite coatings were systematically studied by means of scanning electron microscope, X-ray diffractometer, laser confocal microscope, contact angle tester and electrochemical workstation. The results show that the Co-MoS₂ composite coatings possess the superhydrophobic effect with the maximum contact angle value about 151.4°, good self-cleaning and anti-fouling performance under the current density of 20 A/dm² and electrodeposition time of 30 min. The coating surface still maintains good hydrophobicity with contact angle higher than 146° after the abrasion with 800 grit sandpaper for 1200 mm under pressure of 2.5 kPa, showing excellent wear resistance. Besides, the superhydrophobic composite coating also displays good corrosion resistance. The simple, cost-effective and environment friendly one-step electrodeposition method for fabrication superhydrophobic composite coating with high-performance is expected to realize the practical application of superhydrophobic materials.

Effect of grain size of magnetron sputtering copper target on sputtering performance and deposition performance

Wang Shuaikang, Tang Bin, Bao Mingdong, Zhan Shangsong, Wang Duo, Yi Chenxi

2022, 47(11): 261-265. doi:10.13251/j.issn.0254-6051.2022.11.044

Abstract ( 22 )

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Three 6N high-purity copper square targets with average grain sizes of 30 μm, 70 μm and 150 μm respectively were placed in the same sputtering system for sputtering. The I-V characteristic curve, mass loss, and surface morphology, thickness and X-ray diffraction pattern of the coated film were detected and observed after sputtering. The results show that the grain size, as an important parameter of the target, affects the surface morphology and I-V characteristic curve of the target after sputtering. When the deposited film is thicker, the target grain size doesn't have much influence on mass loss of the target and the film crystallization, but the film deposition rate appears to be quite different.

Analysis of fatigue failure of automobile hollow gear shaft in bench test

Jin Guozhong, Wang Kaizhong, Hu Fangzhong, Yang Shaopeng, Yang Zhiqiang, Chen Shijie

2022, 47(11): 266-270. doi:10.13251/j.issn.0254-6051.2022.11.045

Abstract ( 54 )

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The fatigue failure behavior of new type hollow gear shaft in bench test was analyzed by means of optical microscope, microhardness tester and scanning electron microscope. The results show that the transition arc position is the failure position of the hollow gear shaft. The chemical composition of part material, austenite grain size and non-metallic inclusions all meet the design requirements, while the effective carburized layer depth just approaches the lower limit of the design requirements. The calculation results show that the radius of the transition arc of the hollow gear shaft should be greater than 3.16 mm, and during the carburizing the smaller transition arc radius is prone to the "sharp angle effect", resulting in coarse carbides and stress concentration, which may be one of the reasons for the low fatigue life. The simulation results of CAE software show that there is obvious stress concentration at the transition arc, and the maximum stress on the surface exceeds allowable stress of the part, which may be another reason for failure of the hollow gear shaft. The maximum stress on surface of the part increases with the increase of hollow size. The maximum size of the hollow should be less than Ø17.1 mm.

Detection and analysis of grinding burns of 20Cr2Ni4 steel carburized and quenched spiral bevel gears

Xu Hongxiang, Wang Hongwei, Pu Jiangyong, Zhao Shaofu, Chen Shengchao, Rong Zeyu

2022, 47(11): 271-275. doi:10.13251/j.issn.0254-6051.2022.11.046

Abstract ( 52 )

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Aiming at the cracks on the tooth surface of 20Cr2Ni4 steel spiral bevel gear after carburizing, quenching and grinding,the uncracked tooth surface(concave) and cracked tooth surface(convex) of the cutting tooth block were measured by using optical microscope and microhardness tester. The results show that the effective hardened layer depth and microstructure at the pitch circle of the uncracked tooth surface and cracked tooth surface away from the crack of the tooth block are normal, and there is no grinding burn characteristics. There are different degrees of grinding burn characteristics at the tooth root, especially in the cracks of the cracked tooth surface, the crescent-shaped white and black grinding burn morphology, the deepest part of the burn is about 0.9 mm, and the improved grinding process parameters are put forward to avoid grinding burn.

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