Heat Treatment of Metals

Microstructure and texture evolution of differential speed rolled Mg-3Zn-2(Ce/La)-1Mn alloy

Song Xudong, Yuan Gecheng, Li Xiaohui, Feng Longbiao

2020, 45(2): 1-6. doi:10.13251/j.issn.0254-6051.2020.02.001

Abstract ( 49 )

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In order to investigate the microstructure and texture evolution of magnesium alloy subjected to differential speed rolling (DSR) with different speed ratios, four different speed ratios were carried out on extruded Mg-3Zn-2(Ce/La)-1Mn alloys. The results indicate that the more uniform and finer microstructure is obtained after DSR compared to the initial extruded specimen. With the increment of SR, the amount of recrystallized grains increases, the size of grains and secondary phase particles are reduced, then the extent of homogenization of microstructure is improved. There are mainly two kinds of second phases in the sample, namely α-Mn phase and Mg_xZn_y-Mn-(Ce/La) phase. The <c+a> pyramidal slip and the basal <a> slip both play a major role during DSR. The basal plane orientation is inclined by 30°-45° from the RD toward the TD, and the texture gradually trends to be randomized. The introduction of intensive shear strain, trigger of the <c+a> pyramidal slip and tilting of basal poles have a significant effect on the randomization of the texture.

Effect of heat treatment on grain growth behavior of C-276 alloy seamless tube

Lu Yan, Gao Pei

2020, 45(2): 7-10. doi:10.13251/j.issn.0254-6051.2020.02.002

Abstract ( 57 )

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Effect of different heat treatment processes on the grain growth behavior of cold rolled C-276 alloy seamless tubes was studied. The results show that the grain size of the alloy increases gradually with the increase of heat treatment temperatures at the same holding time, and the trend of grain growth is the same at different holding time. The grain growth is relatively rapid when the heat treatment temperature is 1040-1080 ℃, then slows down when the temperature is 1080-1160 ℃, and accelerates again in the range of 1160-1200 ℃. The apparent activation energy of the grain boundary migration of the C-276 alloy is 313.77 kJ/mol after holding at 1040-1200 ℃ for 10 min. When the heat treatment temperature is 1040 to 1080 ℃, the grain grows slowly with the increase of holding time. When the temperature is 1120 to 1160 ℃, the grain grows faster within 10 min, and slows down when more than 10 min. When the temperature rises to 1200 ℃, the grain growth trend is more gradual with the increase of holding time. The grain growth kinetics time index η of the C-276 alloy increases first and then decreases with the increase of temperatures in the range of 1040-1200 ℃.

Effect of microstructure on long-term aging stability of 2.25Cr-1Mo steel

Han Shaoqiang, Zhao Jiqing, Wan Rundong, Yang Gang

2020, 45(2): 11-18. doi:10.13251/j.issn.0254-6051.2020.02.003

Abstract ( 72 )

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The stability of microstructure and mechanical properties of 2.25Cr-1Mo steel with different morphology during long-term aging at 530 ℃ for 2000 h were studied by means of mechanical properties test, microstructure analysis and phase analysis. The results show that as the normalizing cooling rate decreases, the content of large-sized equiaxed ferrite increases and the bainite content decreases. When the content of bainite in the microstructure is high, the strength and toughness of the steel are well matched, and the coarsening of secondary phase carbide is not obvious in the aging process, the microstructure stability is higher. The strength of large-sized equiaxed ferrite matrix is low, and in the aging process the interface carbide has a fast coarsening and aggregation rate and distributes along grain boundary, the microstructure stability is poor. The ferrite content is >40%, and the aging embrittlement phenomenon is remarkable.

Effect of room temperature and liquid nitrogen temperature control on mechanical properties and texture of rolled Al-Sc alloy

Luo Zhiyong, Li Heng, Wang Zhen, Li Ming

2020, 45(2): 19-22. doi:10.13251/j.issn.0254-6051.2020.02.004

Abstract ( 59 )

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Effects of 80% rolling deformation at room temperature and liquid nitrogen temperature controlled on microstructure and properties of Al-Sc alloy were investigated by means of microhardness, tensile test, metallographic structure, scanning electron microscopy(SEM) and backscattered electron diffraction analysis(EBSD), respectively. The results show that the hardness of the alloy after room temperature rolling and liquid nitrogen temperature controlled rolling is 105 HV0.3 and 162 HV0.3 respectively, and the tensile strength, yield strength and elongation are 335 MPa, 296 MPa, 5.5% and 443 MPa, 415 MPa and 6.7%, respectively. After rolling, the grain boundary of the alloy is mainly comprised of small-angle grain boundaries and the average grain sizes after room temperature rolling and liquid nitrogen temperature controlled rolling are approximately 40 μm and 1 μm, respectively. Due to the influence of stacking fault energy, the main texture types of the Al-Sc alloy after liquid nitrogen temperature controlled rolling are Brass texture {110}<112> and S texture {123}<634>, as well as the Copper texture {112}<111>.

Cold deformation behavior of GH4169 alloy

Wen Bo, Lü Xudong, Du Jinhui

2020, 45(2): 23-28. doi:10.13251/j.issn.0254-6051.2020.02.005

Abstract ( 51 )

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The constitutive equation of GH4169 alloy during cold deformation was established by means of room temperature compression test, mathematical model fitting, optical microscope (OM), electron backscatter diffraction (EBSD) and microhardness test. The effect of cold deformation rate and deformation amount on the microstructure and properties of GH4169 alloy were studied. The results show that the work hardening law of GH4169 alloy basically conforms to Hollomon equation during cold deformation, in which the deformation rate has little effect on work hardening, and the deformation amount is the main factor affecting work hardening; with the increase of deformation, the deformation degree of grain increases; the low-angle grain boundary within grain increases with the deformation amount, and some low-angle boundaries change to high-angle ones. The microhardness of the alloy increases with the increase of deformation.

Effect of cold drawing deformation on microstructure and properties of Cu-Al₂O₃ dispersion strengthened copper alloy wire

Peng Dongdong, Lu Shiqiang, Gan Chunlei, Wang Shuncheng, Zhang Dongping

2020, 45(2): 29-35. doi:10.13251/j.issn.0254-6051.2020.02.006

Abstract ( 77 )

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The annealed Cu-0.2%Al₂O₃ dispersion strengthened copper alloy was cold-drawn with the maximum deformation amount of 99%. The effect of cold drawing deformation on the microstructure, texture, electrical conductivity and mechanical properties of the alloy was studied by means of optical microscope, scanning electron microscopy, X-ray diffraction and mechanics tester. The results show that with the increase of cold drawing deformation amount the microstructure of the alloy changes from coarser elongated structure to fibrous one. When the deformation amount is 0%, the textures of Cu-0.2%Al₂O₃ alloy are composed by brass {011}<211> and cube {001}<100> textures. After 60% cold deformation amount some cube and brass textures are gradually transformed into goss {011}<100> and copper {112}<111> texture. And the cold drawing deformation amount has almost no effect on the conductivity. The microhardness of the alloy increases from 141 HV0.3 to 161 HV0.3. While the tensile strength increases from 492 MPa to 637 MPa, yield strength increases from 452 MPa to 605 MPa, and the elongation decreases from 14.0% to 1.0%, respectively. It is found that the tensile fracture of the alloy is ductile. Therefore, it can be concluded that the Cu-0.2%Al₂O₃ dispersion strengthened copper alloy has excellent plastic workability.

Effect of rolling route on microstructure and properties of ZK60 magnesium alloy sheets

Li Luobin, Jiang Peng, Ren Guangmeng, Zhang Ke, Wang Hao, Ran Ruiying, Zhang Yi

2020, 45(2): 36-41. doi:10.13251/j.issn.0254-6051.2020.02.007

Abstract ( 56 )

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Rolled and heat treated ZK60 magnesium alloy sheets were re-rolled for nine passes at 250 ℃ by different routes. Microstructure, room temperature tensile properties, fracture morphology and grains preferred orientation of ZK60 magnesium alloys after re-rolling were researched by means of optical microscopy, electronic universal testing machine, SEM and XRD. The results indicate that the rolling route has no obvious effect on the grain size of ZK60 magnesium alloy sheets, but the reduction has a great influence on the twin forming in the structure of magnesium alloy. The change of rolling route has greater effect on anisotropy and mechanical properties of ZK60 magnesium alloy sheet. The ZK60 magnesium alloy sheet rolled under the route of cross+45° has weak anisotropy and good comprehensive mechanical properties, its yield strength, tensile strength and elongation reach 244.31 MPa, 371.14 MPa and 25.46% respectively. The cross+45° rolling has a significant effect on the grains preferred orientation of ZK60 magnesium alloy sheets, which can improve the preferred grain orientation and anisotropy and the plastic deformation properties of ZK60 magnesium alloy.

Microstructure and properties of continuous annealed DP980 high strength steel

Liu Jingbao, Zhang Hongbo, Geng Zhiyu, Wei Huanjun

2020, 45(2): 42-45. doi:10.13251/j.issn.0254-6051.2020.02.008

Abstract ( 65 )

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Effect of different technological parameters on the microstructure and mechanical properties of continuous annealed DP980 steel (a 980 MPa grade dual-phase steel) were investigated, with the microstructure and mechanical properties being tested and analyzed by means of optical microscopy, TEM and tensile test. The results show that the microstructure of the annealed DP980 steel is mainly composed of ferrite, martensitic islands and a small amount of bainite, and the dislocation density near the martensite island is higher. With the increase of the over aging temperatures, the tensile strength and yield strength of the DP980 steel first decrease and then increase, and the elongation first increases and then decreases. With the increase of the tempering temperature, the tensile strength and yield strength of the DP980 steel decrease within a small range, while the elongation increases but not obvious, which indicates that adjusting the over aging temperature to regulate the mechanical properties is less effective.

Microstructure and properties of 7075 aluminum alloy hot compress bonding joint

Jiang Haiyang, Sun Mingyue, Wu Mingfang, Qiao Yanxin

2020, 45(2): 46-50. doi:10.13251/j.issn.0254-6051.2020.02.009

Abstract ( 53 )

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Hot compress bonding test of the 7075 aluminum alloy was carried out by a Gleeble-3500 thermal simulator. The joint interface microstructure under different temperatures and holding time was observed and analyzed by means of metallographic microscope and scanning electron microscope, and the tensile properties of the joint were tested. The results show that when the bonding temperature is 460 ℃ and the holding time is 24 h, no segregation of oxide at the interface is found by EDS analysis, and the mechanical properties are the best, the tensile strength reaches 444 MPa and the yield strength is 265 MPa.

Microstructure and properties of Al-Mg-Si aluminum alloy with different treatments

Zhang Guizhao, Jiang Feng, Zhou Wei, Wang Congkai, Ye Pengcheng

2020, 45(2): 51-55. doi:10.13251/j.issn.0254-6051.2020.02.010

Abstract ( 51 )

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Effect of heat treatment on the microstructure and mechanical properties of Al-Mg-Si aluminum alloy microalloying with Y and Zr was investigated by means of scanning electron microscopy, transmission electron microscopy, energy spectrum analysis and tensile test. The results show that the addition of Y and Zr can help to refine the grains of as-cast the alloy. The microstructure of the as-cast alloy has obvious segregation at the grain boundary. The segregation is improved after homogenization treatment at 535 ℃ for 14 h. There exist lots of second phases along the extrusion direction after hot extrusion. Increasing solution temperature, the second phases are dissolved into the aluminum matrix gradually. After aging treatment, a multitude of β″ phases and other fine precipitates are dispersed in the alloy and have a precipitation strengthening effect. The alloy has the best mechanical properties after solution treatment at 530 ℃ for 2 h and aging treatment at 180 ℃ for 8 h, by which the tensile strength is 408 MPa and the elongation is 14.8%.

Wear resistance of TiC particle reinforced low alloy ferritic wear-resistant steel

Liu Luojin, Sun Xinjun, Liang Xiaokai, Ye Xiaoyu

2020, 45(2): 56-60. doi:10.13251/j.issn.0254-6051.2020.02.011

Abstract ( 54 )

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Compared with the traditional low alloy ferritic steel, the abrasive wear resistance of 1.0vol% TiC particle-reinforced ferritic wear resistant steel prepared by in situ synthesis technique was studied. OM, SEM and EDS were used to analyze the microstructure morphology and distribution of precipitated particles in the tested steel, and the mechanical properties and wear resistance of the tested steel were analyzed and tested. The results show that the rolled TiC particles are evenly distributed in the tested steel. Nano-TiC particles have obvious precipitation strengthening effect, which improves the strength and hardness of the matrix and ensures good bending properties. TiC particles with size of 1-5 μm effectively hinder the plough-grinding effect of abrasive particles and improve the abrasive wear resistance. The wear weight loss of TiC-reinforced ferritic tested steel is only 60% of that of non-reinforced ferritic steel, which is equivalent with the wear resistance of unreinforced ferritic steel after quenching and tempering. The abrasive wear mechanism of TiC-reinforced ferritic tested steel includes both plow type abrasive wear and micro-cutting mechanism, which means that the improvement of wear resistance of the steel can be attributed to the combined action of nano-TiC and micro-TiC particles.

Formation mechanism of W(Al₈Cu₄Sc) phase in Al-Cu-Li-Sc alloy with high Cu content

Kong Debin, Li Caiqiong

2020, 45(2): 61-65. doi:10.13251/j.issn.0254-6051.2020.02.012

Abstract ( 49 )

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The microstructural evolution of an Al-2.35Cu-4.6Li-0.12Sc(at%) alloy with high Cu content and the formation mechanism of W(Al₈Cu₄Sc) phase during homogenization were studied by means of OM、SEM、EPMA、XRD and STEM. The results show that the main solidification phase is T_B (Al₇Cu₄Li) phase in as-cast, and Sc mainly exists in the form of supersaturated solid solution. After homogenization, the T_B phase dissolves completely, the content of Cu in the matrix increases and that of Sc decreases, the stable W phase forms at the same time. The analysis shows that the interface of T_B phase and Al matrix must be a preferred nucleation site for the W phase because of the incoherent interface of T_B phase and Al matrix. So the W phase nucleates preferentially here, and then transforms into the stable phases with a size of 1 μm by consuming the Sc atoms fixed in the supersaturate solid solution and Cu atoms in T_B phase.

Effect of silicon content and finish rolling temperature on magnetic properties of electromagnetic pure iron for shielding

Duan Meiqi, Cao Jianchun, Wang Ruizhen, Cai Mengru, Ge Xin

2020, 45(2): 66-71. doi:10.13251/j.issn.0254-6051.2020.02.013

Abstract ( 56 )

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Effects of Si content and finish rolling temperature (770-920 ℃) on the electromagnetic properties of electromagnetic pure iron for shielding were investigated in order to optimize such properties. The results show that as the Si content increases to 2.0%, the maximum magnetic conductivity increases first and then decreases, and the coercive force is the opposite, while the saturation magnetic induction intensity decreases gradually but the decrease is small. With the increasing final rolling temperature, the [111]component in the hard-to-magnetization direction of the grain first decreases sharply and then increases slowly. The favorable (110)[001]component slowly increases, and the deviation degree first decreases and then increases. The composition and process for the best magnetic properties of the experimental steels are final rolling of electromagnetic pure iron containing 1.4%Si at 840 ℃ and annealing at 1100 ℃, where the maximum magnetic conductivity is 37.84 mH/m, the coercive force is 16.85 A/m, the saturation magnetic induction is 1.80 T, and the shielding effectiveness is 13.92 dB in low-frequency DC magnetic field environment.

Effect of Nb addition on microstructure of Fe-Co-2V soft magnetic alloy

Wang Xuandong, Wang Dongling, Zhang Jinglin, Yu Yipeng, Wu Bin, Zhang Jianfu

2020, 45(2): 72-75. doi:10.13251/j.issn.0254-6051.2020.02.014

Abstract ( 50 )

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Fe-49Co-2V and Fe-49Co-2V-0.3Nb alloys were hot and cold rolled into sheets respectively, then annealed at 850 ℃ for 2 h. The microstructure of the alloys was investigated by means of transmission electron microscope(TEM) and selected area electron diffraction(SAED). The results show that the adding of Nb facilitates the formation of precipitates, which is small particles composed with Nb, Co and Fe, while V is not detected. The chemical formula of the precipitate is Co₃Nb, in which some Co atoms are partly substituted by Fe atoms. The precipitates in different shapes are also detected in as-cast specimens which might be the source of precipitates in the sheet specimens. In addition, lath-like twin structures are detected closing to the precipitates in the alloy containing Nb, which might be beneficial to the improvement of ductility and grain refinement.

Effect of continuous annealing on microstructure and properties of 440 MPa grade high strength IF steel containing lanthanum

Ren Zhiheng, Ren Huiping, Jin Zili, Li Wei

2020, 45(2): 76-80. doi:10.13251/j.issn.0254-6051.2020.02.015

Abstract ( 57 )

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Microstructure, precipitates and properties of 440 MPa grade high strength IF steel containing lanthanum under different continuous annealing conditions were studied by thermal simulation tester. The influence of continuous annealing process on the microstructure and properties of the tested steel was analyzed. The results show that, under the continuous annealing process of 800 ℃-120 m/min, complete recrystallization occurs, the grain size is refined effectively by increasing the running speed of the strip, the precipitation of FeTiP is reduced, and the texture is optimized, thereby improving the hardness and deep drawing properties of the sheet then obtaining qualified products.

Hot rolling process of 00Cr22Ni13Mn5Mo2N austenitic stainless steel

Li Bingbing, Chen Haitao, Lang Yuping, Chen Qingming

2020, 45(2): 81-86. doi:10.13251/j.issn.0254-6051.2020.02.016

Abstract ( 48 )

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Hot compression deformation behavior of 00Cr22Ni13Mn5Mo2N austenitic stainless steel was studied by using Gleeble-3800 thermal simulator at deformation temperature of 1000-1200 ℃, deformation of 50%, 60%, 70% and strain rate of 0.05 s^-1. The microstructure after deformation behavior and after solution heat treatment at 1080 ℃ was observed and analyzed. Observing the morphology of the structure before and after solution heat treatment obtains that performing thermal compression deformation at 1000-1150 ℃, the dynamic recrystallization is more complete as the deformation increasing, and after solution heat treatment, the static recrystallization is more complete. However, when the temperature is too high at 1200 ℃, the recrystallization has been completed and the grains grow. When the deformation is 50%, 60% and 70%, with the increase of the deformation temperatures, the recrystallization is more complete, and after solution heat treatment, the recrystallization becomes more complete. The optimum rolling temperature for hot rolling of 00Cr22Ni13Mn5Mo2N austenitic stainless steel is 1100 ℃ and the compression deformation is 70%.

Influence of quenching and partitioning treatment on microstructure and mechanical behaviors of forged Fe-0.2C-9Mn-3.5Al steel

Li Jinxin, Huang Xingmin, Zhang Lei, Lü Chao, Dai Guangze

2020, 45(2): 87-93. doi:10.13251/j.issn.0254-6051.2020.02.017

Abstract ( 48 )

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Influence of quenching and partitioning treatment on the microstructure and mechanical behaviors of forged Fe-0.2C-9Mn-3.5Al steel was analyzed. The results show that the multiphase microstructure of the heat-treated steel mainly consists of granular δ-ferrite, martensite and lath retained austenite. With the increase of isothermal quenching temperature, the volume fraction of retained austenite increases and reaches the maximum at 310 ℃. When partitioning at 400 ℃ for 3 min after quenching at 310 ℃, preferable comprehensive mechanical properties can be obtained. The tensile strength and elongation reach 1175 MPa and 21.50% respectively, and the product of strength and elongation reaches 25.26 GPa·%. In addition, there are obvious serration fluctuations in the corresponding engineering stress-strain curves, which may be related to the concentrated transformation of the metastable retained austenite to martensite.

Effect of heat treatment on mechanical properties of NiTi shape memory alloy

Zhang Hao, Li Yanjie, Han Guang, Yang Lingqiang, Gao Rui

2020, 45(2): 94-99. doi:10.13251/j.issn.0254-6051.2020.02.018

Abstract ( 51 )

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Effect of heat treatment on the mechanical properties of 50.8at% Ni-Ti shape memory alloy undergone solution treatment and aging at different temperatures was studied by conducting unidirectional tensile test to obtain the yield strength, tensile strength, elastic modulus and Poisson's ratio. The microstructures were observed before and after the heat treatments by metallographic microscope, the corresponding grain sizes were estimated, and the effect of grain size on the yield strength was analyzed based on Hall-Petch theory. The results show that after solution and aging treatments, significant improvement is found in the mechanical properties of the NiTi shape memory alloy. The conclusion provides the experimental foundation for the engineering applications of the NiTi shape memory alloy and is beneficial to enlarge its application range.

Effect of heat treatment process on microstructure and mechanical properties of 51CrV4 steel

Zhang Wei, Xu Zhou, Gao Donghong, Liu Chao

2020, 45(2): 100-104. doi:10.13251/j.issn.0254-6051.2020.02.019

Abstract ( 61 )

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The effects of quenching+tempering and isothermal quenching on the microstructure, mechanical properties and fatigue properties of 51CrV4 steel were studied. The results show that compared with the traditional quenching+tempering process, the microstructure of the 51CrV4 steel after isothermal quenching treatment is multiphase of lower bainite+martensite+residual austenite, the tensile strength, elongation after fracture, fracture toughness and fatigue limit is increased by 14%, 24%, 34% and 15%, respectively. The comprehensive mechanical properties of high strength, high plasticity, high toughness and excellent fatigue performance are obtained.

Effect of tempering temperature on microstructure and properties of Cr-Ni alloy structural steel

Yang Xi, Su Chunxia, Chen Benwen, Li Peixing, Gao Shan, Li Fukun

2020, 45(2): 105-107. doi:10.13251/j.issn.0254-6051.2020.02.020

Abstract ( 55 )

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Microstructures and mechanical properties of Cr-Ni alloy structural steel under different tempering temperatures were studied by means of tensile tester, impact tester, hardness tester, metallographic microscope, scanning electron microscope, transmission electron microscopy and other equipments. The results show that the hardness and strength of the tested steel decline, plasticity and toughness decrease at first, then show a curve platform rising slowly and increase linearly at last with the increase of tempering temperatures. Under lower temperature the shear lip is composed of dimples, some of them are big and shallow. The core parts are quasi-cleavage fracture. The quantity of dimples increases with the rising of tempering temperatures. After quenching and tempering at 200 ℃, the microstructure is tempered martensite with small amount of carbide and clear lath boundaries, when tempered at 400 ℃, the microstructure is tempered troostite with rod carbide and fuzzy boundaries, and when tempered at 600 ℃, the microstructure is tempered sorbite with globular carbide and no lath boundaries.

Effect of heat treatment process on microstructure and hardness of high chromium cast iron roller produced by centrifuge casting

Cao Yu, Song Xinli, Zhen Aiqin, Chen Rongdong, Jia Juan, Bi Yunjie

2020, 45(2): 108-113. doi:10.13251/j.issn.0254-6051.2020.02.021

Abstract ( 60 )

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Microstructure, carbides and hardness of high chromium cast iron roller as-cast by centrifuge casting and quenched and tempered were studied by optical microscope, scanning electron microscope, X-ray diffractometer and Rockwell hardness tester. The results show that the microstructure of the roller as cast is mainly composed of austenite and a few martensite and coarse plate or blocky (Cr, Fe)₇C₃ carbide. After heat treatment at different temperatures, tempered martensite and (Cr, Fe)₇C₃ and Cr₇C₃ carbides are obtained, and the plate-like carbides are replaced by fine block or elliptical ones. The hardness of the as-cast high chromium roller is 56.0 HRC, then increases to about 65.5 HRC after 950 ℃ quenching +400 ℃ tempering.

Heat treatment of tunnel boring machine cutter ring for hard rock

Wei Jiabo, Cheng Xiaonong, Zhang Bocheng, Zhang Jie, Li Yangcheng, Luo Rui, Yuan Zhizhong

2020, 45(2): 114-119. doi:10.13251/j.issn.0254-6051.2020.02.022

Abstract ( 195 )

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The microstructure of H13 steel for cutter ring of tunnel boring machine was optimized by electroslag remelting, multi-directional forging and ultra-refining treatment. The optimized H13 steel was first subjected to conventional heat treatment to analyze the relationship between the hardness and impact toughness of the steel. According to this, the H13 steel cutter ring was subjected to the elastic hardening heat treatment. The results show that after the elastic hardening heat treatment, the blade edge forms a tempered martensite microstructure and the hardness is increased to 59 HRC; but the blade seat forms a tempered martensite microstructure, the hardness is reduced to 44 HRC, and the impact absorbed energy is increased to 23.5 J, achieving the combination of the high-hardness blade and the high-elasticity tool holder, which makes the cutter ring have the elastic characteristics of contraction and rebound and significantly improve the service life and rock breaking efficiency of the cutter ring.

Effect of solution treatment and aging on microstructure of low-nickel high nitrogen austenitic stainless steel

Chang Jinbao, Zhao Yingli, Ji Shuang, Zhang Fuli, Yang Xianliang, Pei Jianming

2020, 45(2): 120-124. doi:10.13251/j.issn.0254-6051.2020.02.023

Abstract ( 61 )

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Solid solution treatment and aging of hot rolled low-nickel high nitrogen austenitic stainless steel were carried out. Metallographic microscope, electron backscatter diffraction and phase diagram were used to systematically analyze the microstructure changes of the steel after solid solution treatment and aging. The results show that after solid solution treatment at 1050 ℃, the steel matrix is austenite with nearly equiaxial grains containing a large number of twins, and with a small amount of ferrite. After aging, the precipitated phases are mainly Cr₂N, CrN, and Cr₂₃C₆. With the increase of aging temperature from 650 ℃ to 800 ℃ under the same aging time of 5 h, the amounts of carbides and nitrides increase first and then decrease, reaching to the maximum at 750 ℃. With the increase of aging time in the range of 5-10 h at 750 ℃, the amount of precipitates has little change. The precipitation process of the precipitated phases is as follows: Firstly, cellular precipitation occurs at the triple junctions of grain boundaries. With the extension of aging time, strip precipitates are gradually precipitated at the grain boundaries, and begin to appear and grow up inside the grains, finally form pearlite-like lamellar precipitates.

Effect of heat treatment process on yield ratio of 34CrMo4 steel for high pressure gas cylinders

Zhang Yuyuan, Yang Gang, Fan Junming, Fan Guojin

2020, 45(2): 125-128. doi:10.13251/j.issn.0254-6051.2020.02.024

Abstract ( 83 )

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In order to adress the higher yield ratio issue of 34CrMo4 steel for high pressure gas cylinders, effect of different heat treating processes including quenching and tempering (QT), quenching in 7.5% PAG aqueous quenchant and tempering (Q₁T), intercritical quenching and tempering (IT) and quenching plus intercritical quenching and tempering (QIT) on yield ratio of the 34CrMo4 steel were investigated, and the relationship between yield ratio and microstructure was also studied. The results show that after QT process, the microstructure of the tested steel consists of sorbite, and the yield ratio is highest. After Q₁T process, the microstructure of the tested steel consists of coarse sorbite, and the yield ratio is higher. After IT process, sorbite with polygonal and lath ferrite as second phase is obtained, and the yield ratio is lower. After QIT process, the microstructure consists of sorbite with even distributed lath ferrite as second phase, and the yield ratio is lowest. Based on the results, the specimen has lower yield ratio when there is a soft phase ferrite distributed on tempered sorbite.

Effect of continuous annealing slow cooling outlet temperature on yield strength of SPCC cold rolled sheet

Zhou Bowen, Jiang Cailing, Fan Lei, Zhou Hua, Gao Yuan, Li Yu'nan, Ye Jiang

2020, 45(2): 129-133. doi:10.13251/j.issn.0254-6051.2020.02.025

Abstract ( 54 )

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Effect of continuous annealing slow cooling outlet temprature on microstructures and yield strength of SPCC cold rolled sheet was studied. The results show that the microstructure of the continuous annealed SPCC cold rolled sheet mainly consists of equiaxed ferrite grains, massive cementites on grain boundaries and spheroidite cementites in grains. With the increase of slow cooling outlet temprature from 680 ℃ to 700 ℃, the average grain size increases from 10.1 μm to 12.5 μm. In addition, increasing the slow cooling outlet temprature can promote the precipitation of fine cementites in grains by inhibiting the formation of massive cementites on grain boundaries. When the slow cooling outlet temprature increases from 680 ℃ to 700 ℃, the yield strength of the continuous annealed SPCC cold rolled sheet decreases by about 28 MPa.

Effect of tempering process on microstructure and mechanical properties of ZG30Mn cast steel

Tang Cai, Chen Bo, Fan Huiji

2020, 45(2): 134-137. doi:10.13251/j.issn.0254-6051.2020.02.026

Abstract ( 64 )

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The microstructure of tempered ZG30Mn cast steel under different tempering parameters was observed and analyzed by optical microscopy (OM). The mechanical properties of the steel were also tested, including tensile properties, Brinell hardness and impact properties. The results show that the microstructure of the steel treated by different tempering processes is mainly composed of tempered sorbite. When the holding time is 90 min, with the increase of the tempering temperature (580, 600, 620, 640 ℃), the hardness and strength gradually decrease, and the elongation and impact absorbed energy gradually increase. When the tempering temperature is 620 ℃, with the increase of tempering time(30, 60, 90, 120 min), the hardness and strength of the steel gradually decrease, while the elongation and impact absorbed energy increase first and then decrease. Tempering temperature plays a key role in the transformation process from martensite to sorbite. The increase of tempering temperature will affect the efficiency of recovery and recrystallization of α-Fe phase. The dispersed fine cementite gradually grows up and spheroidizes, resulting in the decrease of hardness and strength, and the increase of elongation and impact absorbed energy. Tempering holding time will determine the growth of cementite. With the increase of tempering time, the aggregation and growth of cementite will lead to the decrease of elongation and impact absorbed energy.

Effect of partitioning process on microstructure and mechanical properties of 301 austenitic stainless steel

Li Yunong, Zou Dening, Zhou Yuqing, Pang Yang, Zhao Bifang

2020, 45(2): 138-142. doi:10.13251/j.issn.0254-6051.2020.02.027

Abstract ( 47 )

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A new heat treatment process of quenching and partitioning was proposed to replace the cold deformation hardening process, so as to improve the mechanical properties of metastable austenitic stainless steel. Taking 301 stainless steel as the research object, the effect of partitioning heat treatment processes on its microstructure and mechanical properties was studied by using the metallographic microscope, scanning electron microscope, X-ray diffractometer, ferrite measuring instrument, universal test machine and hardness tester. The results show that the microstructure of the 301 metastable austenitic stainless steel is mainly composed of martensite, austenite and trace carbide after different quenching-partitioning treatments; the mechanical properties are not sensitive enough to the partitioning temperature, but continue to be optimized with the extension of the partitioning time. After partitioning at 450 ℃ for 30 min, the comprehensive mechanical properties of the steel are optimal, and the yield strength, tensile strength, elongation and hardness are 432.37 MPa, 1212 MPa, 44.28% and 193.16 HV0.2, respectively.

Effect of non-isothermal aging on microstructure and properties of 7003 aluminum alloy

Yu Gang, Xiang Jianbo, Zhao Zhongxin, Luo Fenghua

2020, 45(2): 143-148. doi:10.13251/j.issn.0254-6051.2020.02.028

Abstract ( 46 )

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The precipitation and strengthening rules of 7003 aluminum alloy during non-isothermal aging (NIA) process were researched by combining TEM analysis and mechanical properties test. The corrosion resistance of the alloy was evaluated based on the test results of electrical conductivity, intergranular corrosion and electrochemical corrosion. The test results show that when heated to 180 ℃ at 20 ℃/h, the hardness and strength of the alloy reach their peak values of 113 HV0.5 and 367.8 MPa respectively, which is equivalent to the T6 standard. In the cooling stage in the temperature range of 180-160 ℃, the alloy can obtain higher strength and similar electrical conductivity comparing to the T74 condition. The corrosion resistance is continuously improved during the non-isothermal aging process. GP zones and η′ phases are the primary precipitates at the heating stage, while the GP zones gradually disappear and the η′ phase coarsens, and new fine precipitates are formed in the matrix grains. From the beginning of the heating to the end of the cooling, the number and size of the precipitated phases at the grain boundaries are getting larger and larger, and they are distributed intermittently along the grain boundaries. The width of precipitate free zones also increases steadily.

Finite element analysis of quenching process of 7075 aluminum alloy profiled plate

Ye Mao, Wang Dezhi, Liu Zhichuan, Li Cunliang, Liang Wei, Liu Jian

2020, 45(2): 149-153. doi:10.13251/j.issn.0254-6051.2020.02.029

Abstract ( 57 )

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ABAQUS software was used to 3D model and simulate the quenching process of 7075 aluminum alloy profiled plate. With the secondary development of the software, the influence of quenching medium, quenching direction and quenching speed on the residual stress and quenching distortion of the profiled plate were studied. The simulation results show that UCON quenching solution with 10% concentration can reduce residual stress by 50.1% compared with water quenching. The residual stress is the smallest when the quenching direction is perpendicular to the plane of the profiled plate, and the quenching distortion is related to the quenching direction. The data show that the faster the quenching speed in a certain range, the reduction of residual stress is more significant.

Effect of isothermal annealing on microstructure and properties of 8030 aluminum alloy wire

Han Xi, Li Ying, Pang Hua, Li Chun, Cui Le, Wang Jinli, Liu Yanfeng

2020, 45(2): 154-160. doi:10.13251/j.issn.0254-6051.2020.02.030

Abstract ( 52 )

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Effects of different isothermal annealing processes on the microstructure and properties of 8030 aluminum alloy wire were studied. The results show that the aluminum alloy wires are both composed of α-Al matrix and Al₆Fe phase before and after the isothermal annealing. After the isothermal annealing, at the same isothermal temperature, the microstructure gradually becomes uniform with the extension of the isothermal time. Under the same isothermal time, as the isothermal temperature increases, the isothermal time at which the structure tends to be uniform is shortened. After isothermal annealing, the electrical conductivity of aluminum alloy wires is improved. After uniform annealing at 470 ℃ for 24 h and then at 240 ℃ for 4 h, the electrical conductivity of the alloy reaches the highest value of 57.21%IACS, which is 2.4%IACS higher than that of the untreated samples. After the isothermal annealing, the hardness and tensile strength of the aluminum alloy wire are reduced, but the plasticity is greatly improved. After annealing at 470 ℃ for 24 h and then isothermal treated at 260 ℃ for 8 h, the elongation of the alloy is up to 23.64 %. Before and after heat treatment, the alloys before and after heat treatment are both plastic fracture.

Effect of second phase size distribution on needle porosity of AA8111 aluminum foil

Ma Lizhen, Lu Guangxi, Guan Shaokang, Zhu Shijie, Zhu Qing

2020, 45(2): 161-165. doi:10.13251/j.issn.0254-6051.2020.02.031

Abstract ( 49 )

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Size distributions of the secondary phase in different blanks of AA8111 aluminum alloy were studied by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Image J and Nano Measurer. The results show that during the 5 passes of cold-rolling from 7 mm cast-rolled sheet to the finished blanks of 0.24 mm, the secondary phase breaks obviously and the size becomes smaller in the early stage, while with the increase of deformation resistance, the effect of subsequent rolling on the size of the secondary phase is getting smaller and smaller. The rod-shaped and disc-shaped Si elementary phases precipitated out during the homogenization annealing, have a great influence on the secondary phase size distributions and are heritable. The proportion of the secondary phase of greater than 6 μm in the finished blank is 8.9%, and there are some larger secondary phases of about 10 μm. Compared with the finished blanks of AA1235 and AA8079 alloys, it is concluded that the high proportion of the secondary phase size distribution greater than 6 μm in the AA8111 finished blanks is the main reason for the high needle porosity of the finished aluminum foil.

Effect of heat treatment temperature on microstructure and mechanical properties of TC4ELI alloy

Mao Jianghong, Yang Xiaokang, Luo Binli, Wei Fenrong

2020, 45(2): 166-174. doi:10.13251/j.issn.0254-6051.2020.02.032

Abstract ( 55 )

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In order to reveal the microstructure evolution, mechanical properties and phase composition of TC4ELI alloy with different heat treatment temperatures, the microstructure of TC4ELI alloy heat treated at 700-1000 ℃ with air-cooling conditions was studied, and the room temperature mechanical properties and XRD of the samples were tested. The results show that the alloy achieves crystallization when heat treated at 800 ℃. The α phase is homogeneous and equiaxial, and its volume fraction reaches the maximum. There are all diffraction peaks of the α phase in the XRD pattern but for the β phase. In the range of 700-800 ℃, the alloy can obtain the good comprehensive performance, and meet the requirement of related standards. In the temperature range of 850-950 ℃, the TC4ELI alloy is the bimodal microstructure with the precipitation of the secondary needle-like α phase. As the temperature increases, the strength and elastic modulus decrease due to the increase of grain size and volume fraction of the β phase in the alloy. After heat treated at 1000 ℃, the cubic martensite phase has strong (002)_α' and (101)_α' diffraction peaks, and the diffraction peak energy of other lattice orientations is very weak, and the elastic modulus of the alloy reaches a maximum of 110 GPa. Through microstructure observation, the start temperature of α+β→β transformation is in the range of 850-870 ℃, and the finish temperature of that is in the range of 950-970 ℃.

Effect of isothermal heat treatment on semi-solid microstructure of Mg-Gd-Zn-Zr alloy

Yin Jian, Lu Chunhui, Xie Shikun, Yi Rongxi, Huang Wenxian

2020, 45(2): 175-180. doi:10.13251/j.issn.0254-6051.2020.02.033

Abstract ( 109 )

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Semi-solid spheroidized microstructure was obtained by isothermal treatment on as-cast Mg-15Gd-2Zn-0.6Zr alloy at the temperature slightly higher than eutectic temperature. The effects of isothermal heat treatment temperature and holding time on semi-solid microstructure were studied, and the mechanism of semi-solid microstructure evolution and the composition design of semi-solid Mg-Gd-Zn-Zr alloy were discussed. The results show that the volume fraction of liquid phase has a low sensitivity to temperature. The mechanism of the liquid phase evolution is α-Mg surface melting and α-Mg dynamic precipitation. And the spheroidization mechanism of solid phase particles is as follows: α-Mg dendritic→dendritic arm coarsening→dendritic arm merging and irregular polygonization→spheroidization.

Vacuum breakdown properties of CuCr contacts prepared by hot isostatic pressing

Guo Yangyang, Wang Fazhan, Wang Yongbin, Lü Qinliang

2020, 45(2): 181-185. doi:10.13251/j.issn.0254-6051.2020.02.034

Abstract ( 42 )

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CuCr alloy materials with a nearly full density and low-oxygen nitrogen content were prepared by hot isostatic pressing (HIP).The Cr phase granularity, break down field strength and break down area were systemically investigated for the CuCr alloys under different sintering temperatures. The relationship between the Cr phase particle radius and the breakdown field strength of CuCr alloy was explored. The results indicate that on a certain range as the HIP sintering temperature increases, the particle size of the CuCr alloy materials gradually increases. Then the larger the particle radius of CuCr alloy Cr phase, the smaller the vacuum electric breakdown field strength will be. Finally, when the particle radius of CuCr alloy Cr phase increases, the break down ablation area tends to expand, and the ablation pit also slightly deepens.

Effect of annealing time on microstructure and properties of BAg45CuZn brazing filler metal

Zhang Guanxing, Xue Hangyan, Sun Huawei, Huang Junlan, Dong Hongwei

2020, 45(2): 186-188. doi:10.13251/j.issn.0254-6051.2020.02.035

Abstract ( 42 )

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Influence of annealing time on the microstructure and properties of the brazing filler metal BAg45CuZn commonly used in refrigeration and tools industries was analyzed. The results show that the main phases of BAg45CuZn alloy are Cu solid solution, Ag solid solution, Ag-Zn and Cu-Zn compounds. Annealing at 580 ℃ for different time, the main phases of the BAg45CuZn alloy keep unchanged, while the proportion and morphology of each phase are changed, especially the eutectic structure which changes from fine to coarse with the prolongation of holding time. The hardness of Cu-Zn and Ag-Zn compounds in the eutectic structure is higher, which leads to the increase of microhardness and brittleness, as well as poorer processability of the whole matrix. The flowability and the tensile strength of the filler metal annealed at 580 ℃ for different annealing time have significant changes.

Hardenability of D406A steel after vacuum high-pressure gas quenching

Lü Chaojun, Tang Lina, Ren Wei, Wang Jianbo, Zhang Tiande

2020, 45(2): 189-192. doi:10.13251/j.issn.0254-6051.2020.02.036

Abstract ( 53 )

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Effects of different gas pressure on mechanical properties, hardenability and microstructure of D406A steel were studied. The results show that the hardened depth of D406A steel increases with the increase of gas quenching pressure, the ø20 mm round D406A steel can be hardened fully when gas quenched under 5 bar pressure, and the ø10 mm round D406A steel can be hardened fully when gas quenched under 1.5 bar pressure. Mechanical properties of specimens quenched by gas can meet the standard requirements, and the microstructure is composed of uniform lath martensite.

Effect of tempering temperature on impact property of 37CrMnMo steel

Dun Yapeng, Yang Wei, Liu Jianyong, Sheng Xiaofei, Yang Yanyan, Liu Yaodong

2020, 45(2): 193-196. doi:10.13251/j.issn.0254-6051.2020.02.037

Abstract ( 42 )

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Microstructure, strength and impact property of 37CrMnMo steel for oil pipe joint tempered at different temperatures were studied by means of impact and tensile tests and microstructure observation. The experimental results indicate that the microstructure of the quenched 37CrMnMo steel oil pipe joint tempered at 500-640 ℃ is composed of tempered sorbite. With the increase of tempering temperature, the tensile strength and yield strength decrease from gentle to steep. Tempered at 500 ℃, the flake carbides are distributed on the original martensite boundaries, and the Charpy absorbed energy is 30.94 J. When the tempering temperature is 600 ℃, the carbides are evenly distributed, and the Charpy absorbed energy reaches a maximum value of 117.49 J. When the tempering temperature is 640 ℃, the carbides coarsen obviously and the Charpy absorbed energy reduces notably. Therefore, the morphology of carbides plays a key role in the strength and toughness of 37CrMnMo steel when quenched at 870 ℃ and tempered at different temperatures.

Effect of aging process on tensile and high temperature compressive properties of 25Cr-20Ni-2.5Al high strength heat-resistant steel

Gao Shasha, Sun Yuzhu

2020, 45(2): 197-201. doi:10.13251/j.issn.0254-6051.2020.02.038

Abstract ( 39 )

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25Cr-20Ni-2.5Al heat resistant steel was prepared by adding 2.5% Al in 25Cr-20Ni heat-resistant steel and its mechanical properties were characterized and analyzed by means of tensile and high temperature compression experiments, respectively. The results show that the tensile strength of the sample after 36 h aging treatment is significantly improved, and the tensile strength and elongation are 803 MPa and 27.1%, respectively. After 36 h aging treatment, the toughness of the tensile fracture is reduced and the traces of partial brittle fracture are generated. With the aging temperature increasing, the tensile strength of the heat-resistant steel increases first and then decreases, while the elongation decreases first and then increases. The turning point occurs at the aging temperature of 650 ℃, when the tensile strength and elongation are 451 MPa and 10.26%, respectively. When the deformation degree increases, the grain reaches a larger deformation extent, while the grain size of the heat-resistant steel does not change obviously after thermal compression treatment. Precipitation phase also exists at the grain boundary, and the number of precipitation phase increases slightly when the deformation increases.

Effect of heat treatment on microstructure and hardness of Al₂O_3f/Mg-6Al-0.5Nd-0.5Gd composites

Zhang Sha, Wang Wuxiao, Sheng Qing, Du Sheng

2020, 45(2): 202-206. doi:10.13251/j.issn.0254-6051.2020.02.039

Abstract ( 37 )

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Effects of heat treatment on the microstructure and hardness of Al₂O_3f/Mg-6Al-0.5Nd-0.5Gd composites were investigated by means of optical microscopy, scanning electron microscope and Vivtorinox hardness tester. The results show that after T4 solution treatment, β-Mg_l7A1₁₂ phase disappears completely and dissolve in the α-Mg matrix, while the phase of rare earth compounds Al₂Nd and Al₂Gd cannot be decomposed and dissolved because of their high melting point, Al₂O_3f fibers become fine and uniform, and Mg₂Si phase shows a certain tendency of decomposition and spheroidization. After aging treatment, β-Mg₁₇Al₁₂ phase precipitates again and distributes in lamellar or dispersed granular shape, which optimizes the coarse network structure in as-cast state. At this time, the hardness of the composite reaches the maximum value, which is 47.5% higher than that in as-cast state.

Application of cryogenic treatment technology in photoelectronic precision parts of aluminum alloy

Wang Sanmin, Zhang Tao, Lian Jixi, Liang Bin, Liu Hongwu

2020, 45(2): 207-209. doi:10.13251/j.issn.0254-6051.2020.02.040

Abstract ( 44 )

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Based on the analysis of distortion reason of aluminum alloy precision parts and the comparison of conventional methods of eliminating residual stress, one of the ideal methods to eliminate residual stress by cryogenic treatment was proposed. The effect of cryogenic treatment on residual stress and dimensional accuracy of blank ware investigated. The results show that cryogenic treatment can effectively eliminate residual stress and improve dimensional stability.

Origin of surface soot and its effect on quality of carburized and quenched steel workpieces

Sun Bingchao, Chen Liqi

2020, 45(2): 210-213. doi:10.13251/j.issn.0254-6051.2020.02.041

Abstract ( 43 )

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The generating reason of the surface soot was analyzed by comparison of carburized and quenched 20CrMnTiH steel workpiece surface states with and without soot. Surface hardness, hardened depth and microstructure of the workpieces with soot were measured. Compared to that without soot, the results show that the hardened depth of the workpiece with soot is a little deeper, the surface hardness is more or less the same, and there are many non-granular carbides near the sharp corner of the soot-containing workpiece surface, and their morphologies are very different, among them the longest rod-like carbide is up to 12 μm in length. The analysis shows that temperature arising and strong carburizing periods too much propane during are the reason of the soot formation.

Effect of tempering temperature on microstructure and properties of composite steel plate for saw blade

Yang Yuehui, Yuan Shaoqiang, Guo Jifu, Han Huijie, Zhang Yanlong

2020, 45(2): 214-217. doi:10.13251/j.issn.0254-6051.2020.02.042

Abstract ( 39 )

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The composite steel plate for saw blade rolled by 45Mn2V/Q345 steel was tempered. The strength and elongation of the specimens tempered at different temperatures were measured, and the microstructures were observed, then the effect of tempering temperature on the microstructure and tensile properties of tested steel was analyzed. The results show that acicular martensite is obtained after quenching for 45Mn2V steel acting as clad layer and lath martensite is formed on Q345 steel used as substrate. Tempered at a temperature below 400 ℃, the carbides precipitated in 45Mn2V are fine and uniform and coarsened obviously after tempering at a higher temperature, then large amount of coarsening carbides can be observed when tempered at 480 ℃, which results in the strength of tested steel decreasing with the increase of tempering temperature, but increasing obviously at 480 ℃. On the other hand, the coarsening of martensite lath occurs mainly in the substrate steel, and the equiaxed recrystallized grains appear after tempered at 480 ℃. However, the change can not improve the plasticity of clad steel plate.

Effect of laser power on mechanical properties of ultrasonic assisted laser clad Al₂O₃-ZrO₂ ceramic

Li Cheng, Wang Yuling, Jiang Fulin, Zhang Jie, An Xianglong

2020, 45(2): 218-224. doi:10.13251/j.issn.0254-6051.2020.02.043

Abstract ( 45 )

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Al₂O₃-ZrO₂ ceramic coating was prepared on the Ti-6Al-4V substrate by laser cladding process. The effect of different ultrasonic assisted cladding laser power on the morphology and properties was investigated. The macroscopic morphology, section morphology, phase composition, microstructure, micro-hardness and wear behavior of the laser clad Al₂O₃-ZrO₂ coating were investigated by means of metallographic microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and micro-hardness test, respectively. The results show that the dilution rates of the coatings increase first and then decrease with the increase of laser power. The dilution rates are 65.86%, 68.55%, 76.04%, 71.57% and 68.23% with the laser power increasing from 1100 W to 1500 W, respectively. The clad layer is mainly composed of TiAl, TiO and ZrO₂ and the average microhardness of the clad layers increases first and then decreases with the increase of laser power. The average friction coefficient of the clad layers with a laser power of 1200 W is comparatively lower, about 0.27, compared with three other clad layers with a laser power of 1300, 1400 and 1500 W, its wear mechanism is abrasive wear, and the wear mechanism of the other three clad layers is abrasive wear and adhesive wear.

Microstructure and wear resistance of laser alloying coating on TC4 titanium alloy surface

Yi Jia, Peng Rushu

2020, 45(2): 225-230. doi:10.13251/j.issn.0254-6051.2020.02.044

Abstract ( 64 )

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Mixed powder of WC(with 0.1wt%C), Ni and Si was used as raw material, and the coating was prepared in situ on the surface of TC4 titanium alloy by laser alloying technology. The microstructure and composition of the coating were analyzed by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and energy spectrum (EDS). The microhardness and friction and wear properties of the coatings were measured by HXD-1000 Vickers microhardness tester and MMW21 vertical universal friction and wear testing machine. The results show that the coating with higher WC content prepared by optimized laser alloying parameters is uniform and compact, no crack is observed, and is metallurgical bonding with the TC4 alloy substrate. The phase of the coating is mainly composed of α-Ti, Ti₅Si₃, WC and TiNi. The hardness of the coating is 950 HV0.2, the average friction coefficient is 0.2, the average wear loss is 0.308 mg, and the wear resistance is remarkably improved.

Effect of graphene on friction properties of miro-arc oxidation films produced on ZL109 aluminum alloy piston

Hu Haifeng, Li Xiao, Wang Lianhai, Ma Qiang, Liu Xinjian

2020, 45(2): 231-234. doi:10.13251/j.issn.0254-6051.2020.02.045

Abstract ( 50 )

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Graphene composite ceramic film was prepared on the surface of ZL109 aluminum alloy by micro arc oxidation with different concentration of graphene additive in the electrolyte. The film was tested by thickness gauge and hardness tester. Then, the friction and wear tests were carried out on the optimized concentration treated samples, and the friction coefficient and surface morphology were analyzed to evaluate the friction performance of the composite ceramic film prepared by micro arc oxidation with graphene additive and its action mechanism. The results show that the graphene additive makes the micro-arc oxidation film layer have better surface properties, anti-wear and friction reducing properties. When the concentration is 6 g/L, the film thickness reaches 29.68 μm, the hardness reaches 990.12 HV0.3, and the friction coefficient is stable at 0.19. The friction coefficient is significantly lower than that of ordinary ceramic coatings, up to 34.48%. During the friction process, graphene fills the grooves and scratches on the surface of the friction pair, and the surface honing is finer. At the same time, the composite additive forms a carbon film during the friction process, which plays a self-repairing role.

Effect of chromium on microstructure and properties of alternating current field enhanced pack borided layer

Cheng Wei, Xie Fei

2020, 45(2): 235-238. doi:10.13251/j.issn.0254-6051.2020.02.046

Abstract ( 35 )

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Alternating current field enhanced pack boriding (ACFEPB) was carried out for 45 steel at 750 ℃ with low boron potential boriding powder added with an appropriate amount of Cr powder, and the effect of Cr on the ACFEPB was studied. The microstructure, thickness, phases and microhardness of the borided layer were examined and analyzed by optical microscope, X-ray diffractometer and microhardness tester. The experimental results show that the borided layer obtained with the boriding powder containing 3% ferroboron is mainly saw-teeth-like Fe₂B phase. When the boriding powder is added with a very small amount of Cr powder, the maximum hardness remains almost unchanged, while when adding 0.2% Cr powder, the layer thickness increases and reaches the maximum which is about 80% increase compared with that without Cr addition. Along with further increase of the amount of Cr powder, the layer thickness decreases, and the maximum hardness of the borided layer starts to decrease when the amount of Cr powder is more than 3%. When the addition is ≥5%, various Cr-containing phases are also detected in the surface layer of the treated layer.

Quantitative characterization of 3D topology and orientation features of exceptional big grains in annealed pure iron

Wang Hao, Xue Weihua, Zhang Yifan, Liu Guoquan

2020, 45(2): 239-241. doi:10.13251/j.issn.0254-6051.2020.02.047

Abstract ( 37 )

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Three-dimensional (3D) characterization of the microstructure containing exceptional big grains of industrial pure iron was carried out by means of serial sectioning, 3D reconstruction,and EBSD analysis. The differences between the exceptional big grains and the normal grains were analyzed in emphases. The dimensions of the 3D reconstructed pure iron sample are 1920 μm×1219 μm×720 μm, containing 12354 grains which includes5whole exceptional big ones. Different from previous reconstructed 3D grain microstructures without crystallographic orientation information,the present reconstructed 3Dgrains containsimultaneously both the geometric configuration information and the crystallographic orientation information of grains.The results show that the numbers of interfaces of the 5 exceptional big grains studied arein the range of 128-669 (i.e., the largest grain contacts simultaneously 669 neighboring grains). The average misorientation between the exceptional big grains and theirneighboring grains, and theirmisorientationwith their neighbors in the range of 40°-55°, are evidently higher than that between ordinary grains.

Precipitated phase change of HR3C steel during aging characterized by nonlinear ultrasonic technique

Fan Deliang, Wang Zhiwu, Yuan Tingbi

2020, 45(2): 242-249. doi:10.13251/j.issn.0254-6051.2020.02.048

Abstract ( 40 )

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Microstructure change of HR3C steel during long-term aging at 700 ℃ and 750 ℃ was studied and characterized by nonlinear ultrasonic technique. Test results show that the main precipitated phases are M₂₃C₆ and Z-phase during aging, and their total area fraction and average diameter increase with the increase of aging time and temperature. The aged specimens were measured by nonlinear ultrasonic technique. The results show that the nonlinear ultrasonic coefficient increases with the increase of aging time and temperature, and the rising trend is correlated with the total area fraction of the precipitated phases, which indicates that the nonlinear ultrasonic coefficient is sensitive to the change of precipitates and can be used to characterize the microstructure change of HR3C steel during aging.

Hardness and Young's modulus of Al₃Sc single crystal studied by nanoindentation

Li Haonan, Gao Kunyuan, Ding Yusheng, Wu Xiaolan, Huang Hui, Wen Shengping, Nie Zuoren

2020, 45(2): 250-252. doi:10.13251/j.issn.0254-6051.2020.02.049

Abstract ( 49 )

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Orientation, hardness and Young's modulus of Al₃Sc single crystal were analyzed by using the electron back scatter diffraction (EBSD) and nanoindentation techniques. The results show that the Al₃Sc single crystal of about 1 mm in scale can be obtained by cooling eutectic Al-Sc alloy at rate of 60 ℃/h after heating to liquid. The hardness of the Al₃Sc single crystals orientated in (567), (139), (124), (113) and (144) directions is found to be between 3.7 and 4.3 GPa, and the composite elastic response modulus is between 143.6 and 146.1 GPa. By comparing the experimental and theoretical values of Young's modulus in each orientation under different Poisson's ratio, it can be concluded that the difference is the smallest when the Poisson's ratio is 0.188. The experimental Young's modulus in different orientations is between 157.5 and 160.6 GPa.

Influence of shot peening on fatigue property of maraging ultra-high strength steel

Kang Xia, Yin Guangqiang, Zhao Guiping

2020, 45(2): 253-256. doi:10.13251/j.issn.0254-6051.2020.02.050

Abstract ( 50 )

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Fatigue property of a maraging ultra-high strength steel in solution treated and aged state was improved by shot peening. A rotating bending fatigue experiment of the specimens before and after shot peening was performed at stress ratio R=-1. Fatigue lives and fatigue limit at 1×10⁷ cycles were tested using the group method and staircase method, and the S-N curves were fitted with a double weighted least square method. Using X - ray diffraction to determine the residual stress of the shot peening samples, and combined with the results of finite element, the effect of residual stress on fatigue property of the ultra-high strength steel was studied. The results show that shot peening can significantly improve the fatigue life and fatigue limit of the ultra-high strength steel, and the fatigue limit after shot peening is 1.37 times higher than that of the unshot-peened specimens. The residual stress caused by shot peening makes the fatigue source far away from the surface, and the smaller the loading stress, the farther the distances of the fatigue source from the surface, and the effect of fatigue life improvement is more obvious.

Exemption criterion of post-weld heat treatment for offshore platform thick plate

Zhao Cuihua, Shu Xinxin, Yang Fan, Huang Jiangzhong, Li Lianbo, Liu Yanlei

2020, 45(2): 257-261. doi:10.13251/j.issn.0254-6051.2020.02.051

Abstract ( 42 )

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Several judgment methods of post-weld heat treatment exemption were introduced and compared, with emphasis on the engineering critical evaluation method and how to apply this method to the evaluation of the necessity of post-weld heat treatment. Finally, taking the post-weld heat treatment of offshore pile of an offshore platform as an example, the effects of allowable defect size, stress and fracture toughness on the safety of the structure are analyzed quantitatively, which provides a new basis for the exemption of post-weld heat treatment for offshore platform thick plate.

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