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• PROCESS RESEARCH

  Effect of tempering temperature on microstructure and properties of particle reinforced low-alloyed wear resistant steel

  Huang Long, Deng Xiangtao, Wang Zhaodong

  2022, 47(3):  1-6.  doi:10.13251/j.issn.0254-6051.2022.03.001

  Abstract ( 176 )   PDF (670KB) ( 105 )  

  Microstructure, mechanical properties and wear resistance of particle reinforced low-alloyed wear resistant steel tempered at different temperatures were studied. The results show that a large number of micron-scale and nanoscale TiC particles are uniformly dispersed in the rolled particle reinforced low-alloyed wear resistant steel. With the tempering temperature increasing, more ε-carbides are precipitated in the matrix, the yield strength of the tested steel overall increases first and then decreases, the tensile strength, hardness and impact absorbed energy gradually decrease, while the elongation gradually increases. The tested steel shows the best comprehensive mechanical properties and three-body abrasive wear properties when tempered at 200 ℃.

  Application of low temperature nitriding process with double power supplies on 316 stainless steel

  Luo Jiandong, Hu Yanhong, Lin Yuzhou

  2022, 47(3):  7-13.  doi:10.13251/j.issn.0254-6051.2022.03.002

  Abstract ( 89 )   PDF (593KB) ( 33 )  

  Effects of AC pulse voltage, DC pulse bias voltage and temperature on surface hardness and nitrided layer thickness of 316 stainless steel were studied by orthogonal test, and the optimal process parameters of double power supplies for low temperature nitriding were obtained. The properties of the nitrided specimens treated by optimal process were evaluated by means of optical microscope (OM), X-ray diffraction (XRD), microhardness tester, electrochemical workstation and friction and wear tester. The results show that the order of factors affecting properties of the nitrided specimens is: AC pulse voltage＞temperature＞DC pulse bias voltage. The optimum process parameters are AC pulse voltage of 360 V, DC pulse bias voltage of 270 V, and temperature of 380 ℃. Compared with single power supply, the thickness of nitrided layer treated by double power supplies is 43.4 μm, which is 8.5 times of single power supply; the surface hardness is 1350 HV0.025, which is 3.1 times of single power supply; the self-corrosion potential increases from -256 mV(vs SCE) to -180 mV(vs SCE), and the self-corrosion current density decreases from 13.90 μA/cm² to 0.45 μA/cm²; the friction coefficient is reduced from 0.55 to 0.42. The increase of nitriding rate of double power supplies is due to the surface structure defects caused by high energy ion bombardment and the high dissociation of nitriding gas.

  Effects of solution treatment and aging on microstructure and hardness of BT25y titanium alloy

  Wang Jingyuan, Wu Songquan, Zhang Bohua, Xin Shewei, Yang Yi, Wang Hao, Huang Aijun

  2022, 47(3):  14-19.  doi:10.13251/j.issn.0254-6051.2022.03.003

  Abstract ( 107 )   PDF (600KB) ( 43 )  

  Effects of solution and aging treatments on microstructure, phase composition and microhardness of BT25y titanium alloy were investigated. The results show that the structure of the forged specimen presents a typical duplex microstructure. Below the β transformation temperature(T_β), with the increase of solution treatment temperature, the content of primary α phase gradually decreases while that of the β transformed structure gradually increases, the thickness of the lamellar secondary α phase and the content of β phase gradually increase. After solution treatment above T_β, the primary α phase disappears completely, and the duplex microstructure completely transforms into the fully lamellar structure. After aging treatment, the shape and size of the primary α phase are not significantly changed, but the β transformed structure is obviously decomposed, and the content of β phase slightly decreases in the solution treated specimens below T_β but increases in the solution treated specimens above T_β. As known, both the increasing content of lamellar β transformed structure and the refinement of microstructure can significantly strengthen the two-phase titanium alloys, but the increase of content of the β phase softens the two-phase titanium alloys. Compared to the solution treated specimen, the microhardness of the aged specimen significantly increases when solution treated below T_β, which is attributed to both the reduction of β phase content and the refinement of microstructure, while the microhardness of the aged specimen slightly increases when solution treated above T_β, which is attributed to both the increase of β phase content and the refinement of microstructure.

  Analysis of EDM process parameters on imprint mould surface texture

  Liang Huainan, Liu Zhiqi, Chen Dongliang, Song Jianli, Lin Naiming

  2022, 47(3):  20-27.  doi:10.13251/j.issn.0254-6051.2022.03.004

  Abstract ( 152 )   PDF (594KB) ( 35 )  

  Circular micropit arrays with diameters of ø100, ø200 and ø300 μm and regular morphologies were prepared on the surface of graphite electrodes, the electrode was used to fabricate a micro bulge array imprint mold on the surface of 45 steel by electrical discharge machining (EDM). Effect of processing current on its surface properties was investigated. The surface morphologies of graphite electrodes and the 45 steel specimens treated by EDM were analyzed by means of ultra-depth of field microscope and scanning electron microscope. At the same time, Rockwell hardness tester, roughness tester and electronic balance scale with an accuracy of 0.01 mg were used to detect the micro bulge array on the surface of the 45 steel. Effect of processing current on material removal rate (MRR) of the 45 steel and the electrode wear rate (EWR) of graphite electrode was discussed. The results show that, the micro bulge array with corresponding size is successfully formed on the surface of the 45 steel by the principle of EDM reverse etching, and the higher surface microhardness and surface roughness values are obtained, which increase with the increase of EDM current, among them, the specimen with ø200 μm micro-bulge obtains a maximum microhardness of 34 HRC, and the specimen with ø300 μm micro-bulge obtains a maximum surface roughness of 12.56 μm. In addition, when the diameter of the micro-pits or micro-bulges on the specimens is constant, the MRR and EWR values also increase with the increase of processing current.

  Effect of intercritical warm-rolling reduction ratio on microstructure and properties of medium manganese steel treated by quenching and partitioning

  Chen Liansheng, Fang Ning, Cao Zhongqian, Yang Zixuan, Li Hongbin, Pan Hongbo, Tian Yaqiang

  2022, 47(3):  28-33.  doi:10.13251/j.issn.0254-6051.2022.03.005

  Abstract ( 79 )   PDF (589KB) ( 26 )  

  Microstructure, carbide precipitation, volume fraction of retained austenite and C content, and mechanical properties of 0.1C-7.2Mn steel with intercritical warm-rolling quenching and partitioning treatment were studied by means of SEM, TEM, XRD and room temperature tensile test. The results show that the martensite lath of specimen after quenching and partitioning by intercritical warm-rolling is refined and parallel to the rolling direction gradually with the increase of warm-rolling reduction ratio. The microstructure of the specimen is composed of martensite and retained austenite, and carbides are precipitated after intercritical warm-rolling quenching and partitioning treatment.With the increase of warm-rolling reduction ratio, the average size of carbide coarsens, the volume fraction of retained austenite gradually increases, and the C content in retained austenite, the yield strength and tensile strength first increase and then decrease, but the elongation decreases first and then increases. When the reduction ratio of warm-rolling is 80%, the product of strength and elongation reaches the maximum of 31.50 GPa·%.

  Effect of solution treatment and aging on microstructure and hardness of Fe-Mn-Al-C light weight steel

  Sun Jian, Huang Zhenyi, Li Jinghui, Wang Ping

  2022, 47(3):  34-38.  doi:10.13251/j.issn.0254-6051.2022.03.006

  Abstract ( 99 )   PDF (592KB) ( 25 )  

  Microstructure and hardness of the Fe-Mn-Al-C light weight steel after solution and aging treatment were characterized by XRD, OM, SEM and Brinell hardness tester. The results show that, with the increase of solution treatment temperature, the austenite grain size in the tested steel increases gradually, and the grain size is 50-200 μm at 1050 ℃. With the increase of aging temperature, the austenite grain growth is not obvious, and the second phases such as κ-carbide and VC appear in the austenite matrix. With the increase of aging temperature, the morphologies of the second phase in the tested steel gradually change from sporadic distribution to flake aggregation, and then to chain distribution in the austenite matrix. The hardness of the tested steel decreases and increases with the increase of solution treatment temperature and aging temperature, respectively.

  Effects of longitudinal magnetic annealing and tensile stress on magnetic characteristics and iron loss of 1K101 amorphous alloy ribbon

  Gao Jie, He Chengxu, Song Wenle, Yang Fuyao, Liu Yang

  2022, 47(3):  39-43.  doi:10.13251/j.issn.0254-6051.2022.03.007

  Abstract ( 86 )   PDF (590KB) ( 25 )  

  Effects of longitudinal magnetic annealing and tensile stress on magnetic characteristics and loss of 1K101 amorphous alloy ribbon were investigated. Meanwhile, the magnetic domain morphologies of the alloy were also observed by Kerr method. The results show that macroscopic uniaxial anisotropy can be induced in the quenched 1K101 alloy by tensile stress, which makes the ribbon tend to be more easily magnetized along the stress direction, and the iron loss be decreased. These results are remarkably similar to the ribbon magnetization characteristics after the longitudinal magnetic annealing heat treatment. The magnetic domain observation shows that the original maze domains of the quenched alloy transform into Z-shape arrangement along the stress direction, indicating that the magnetic field energy consumed during magnetization reduces, which plays a key role in soft magnetic performance optimization.

  Influence of pre-aging time on microstructure and properties of 7A85 aluminum alloy during RRA process

  Yang Chunmiao, Wang Shan, Wang Shuhui, Li Yanzhen, Liu Wenwen

  2022, 47(3):  44-47.  doi:10.13251/j.issn.0254-6051.2022.03.008

  Abstract ( 78 )   PDF (593KB) ( 40 )  

  Influence of pre-aging time on microstructure and properties of the 7A85 aluminum alloy during RRA process was investigated. The thermodynamic equilibrium phase transformation and TTT curves were calculated by Jmat-Pro. The hardness and tensile properties were tested and microstructure was characterized by means of TEM. The results indicate that MgZn₂ phase begins to precipitate at 410 ℃ under thermodynamic equilibrium, volume fraction of which reaches about 9.5%. The GP zone is precipitated first during the isothermal process in the temperature range of room temperature to 175 ℃, and the nose tip temperature is about 150 ℃. With the extension of pre-aging time, the hardness first increases and then decreases, and reaches a peak hardness of 192 HV after aging for 20 h. The yield strength and tensile strength reach the peak value of 625 MPa and 675 MPa, respectively, when the pre-aging time is 20 h during the RRA process. During the heat preservation process at 120 ℃, under the peak aging state of 20 h, the size of the η′-MgZn precipitated phase is 5-10 nm. When the pre-aging time is 12 h, the Al-Zn-Mg-Cu quaternary phase particles with the size of 50-125 nm at the grain boundaries are discontinuously distributed after RRA treatment.

  Effects of cold rolling deformation and recrystallization on microstructure and properties of TC4 alloy

  Wang Guodi, Jing Ran, Zhang Manxue, Feng Tian, Yu Guoqing, Xie Niansuo

  2022, 47(3):  48-52.  doi:10.13251/j.issn.0254-6051.2022.03.009

  Abstract ( 86 )   PDF (591KB) ( 44 )  

  Effect of different cold deformations on microstructure and mechanical properties of TC4 alloy and effect of the recrystallization treatment on the degree of recrystallization of the alloy with different cold deformations were investigated by means of XRD, OM, EDS, SEM and universal testing machine. The results show that cold rolling makes TC4 alloy work harden, and the tensile strength of the specimens with 35% and 48% cold deformation increases by 451 MPa and 228 MPa than the solution specimens, respectively. Under the conditions of the same recrystallization process, it is found that as the deformation increases, the tensile strength of the alloy gradually decreases.

  Effect of annealing process on microstructure and mechanical properties of low carbon bainitic steel

  Liu Zhiqiao, Feng Qingxiao, Li Hualong, Li Tengfei

  2022, 47(3):  53-56.  doi:10.13251/j.issn.0254-6051.2022.03.010

  Abstract ( 129 )   PDF (588KB) ( 44 )  

  Effect of annealing process on microstructure and mechanical properties of a low carbon bainitic steel produced by twin-roll casting and rolling process was studied. The results show that microstructure of the tested steel is granular bainite, which is gradually decomposed after annealing. As the increase of soaking time, the yield strength and tensile strength increase gradually when annealed at 500 ℃ for long time, and the elongation does not change much. After annealing, the increase of strength is caused by NbC precipitation strengthening. The yield strength and tensile strength of the steel reach the maximum when annealed at 650 ℃ for 3 min.

  Effect of PWHT on microstructure and mechanical properties of electron beam welded joints of 31CrMoV9 steel

  Fan Yang, Yang Minghua, Chen Kaimin, Sun Bingyan

  2022, 47(3):  57-60.  doi:10.13251/j.issn.0254-6051.2022.03.011

  Abstract ( 68 )   PDF (589KB) ( 27 )  

  The microstructures and mechanical properties of 31CrMoV9 steel electron beam welded joints with different post-weld heat treatment (PWHT), including stress relief annealing and quenching and tempering, were investigated and compared to the matrix with the same strength level. The results indicate that the microstructure of the electron beam welded joints is lath martensite and a small amount of retained austenite. After quenching and tempering treatment, the microstructure of the welded joint is relatively uniform tempered sorbite. And the mechanical properties of the joint are equivalent to that of the matrix. Compared with post-weld stress relief annealing treatment, the Charpy impact properties of the quenched and tempered welded joints are improved significantly. The two types of post-weld heat treatment cannot eliminate the solidification structure morphology such as columnar dendrites. The post-weld quenching and tempering process can reduce the segregation of the columnar dendrite structure of the weld and refine it, making the structure and hardness of the weld and the base metal are more uniform. No cracking is found in the electron beam welded joint, by several repeated quenching, which indicates that the post-weld quenching and tempering process is feasible. Therefore, PWHT provides a practical process route for improving the properties of the welded joint.

  Effect of alkali heat treatment on corrosion resistance of friction stir processed AZ31 magnesium alloy

  Chen Shanyong, Wang Kuaishe, Qiao Ke, Wang Wen

  2022, 47(3):  61-66.  doi:10.13251/j.issn.0254-6051.2022.03.012

  Abstract ( 84 )   PDF (595KB) ( 29 )  

  Friction stir processing (FSP) was performed on AZ31 magnesium alloy, and alkali heat treatment (AHT) was performed on the basal material (BM) and FSPed specimens. The effect of AHT on microstructure and corrosion resistance of the friction stir processed AZ31 magnesium alloy was studied. The results show that the FSP can significantly refine the grains, the average grain size is decreased from 12.8 μm of BM to 3.1 μm after FSP, the proportion of high angle grain boundaries decreased from 75.9% of BM to 45.3% after FSP, and the grain boundary substructure is increased. The AHT induces the material to form a dense MgO and Al₂O₃ mixed coating on the surface, which effectively improves the immersion corrosion resistance of the AZ31 magnesium alloy.

  Effect of rolling deformation on microstructure and mechanical properties of high-entropy alloy

  Mei Jinna, Jiang Fengyang, Wei Na, Liu Langlang, Si Fang, Liu Songtao, Wang Junbo, Liu Jiangnan

  2022, 47(3):  67-71.  doi:10.13251/j.issn.0254-6051.2022.03.013

  Abstract ( 80 )   PDF (590KB) ( 31 )  

  Annealing, cold rolling and hot rolling+cold rolling were carried out on (FeNi)₆₇Cr₁₅Mn₁₀Al₅Ti₃ high-entropy alloy. The phase composition, morphology and mechanical of the alloy were analyzed by means of X-ray diffractometer, SEM and universal testing machine. The results show that the as-cast and annealed (FeNi)₆₇Cr₁₅Mn₁₀Al₅Ti₃ high-entropy alloy is easier to form single-phase solid solution. The two-phase solid solution alloy with FCC+BCC structure is formed under the hot rolling+cold rolling with medium deformation, and its yield strength can be increased to 460.0 MPa. The fine intermetallic compound is formed under cold rolling with medium deformation, resulting in fine intermetallic compound strengthening. The yield strength of the cold rolled alloy is significantly increased to 722.0 MPa with elongation of 25.7%, which is of the best comprehensive mechanical properties.

  Effect of high temperature thermomechanical treatment on microstructure and properties of 20CrMnTiH steel forgings

  Feng Rui, Li Lilian, Tie Jinfang, Hou Jiaqiang, Mi Yiyuan

  2022, 47(3):  72-76.  doi:10.13251/j.issn.0254-6051.2022.03.014

  Abstract ( 57 )   PDF (601KB) ( 29 )  

  To investigate the reasons for the low acceptance rate of forgings after air cooling+normalizing+quenching+tempering, the influence of high temperature thermomechanical treatment on the process improvement, the microstructure transformation characteristics and mechanical properties of 20CrMnTiH forgings under two different processes were studied by means of metallographic observation and mechanical properties test. The results show that the insufficient cooling speed of the original process leads to the appearance of granular bainite, the tempered fragments ferrite resulting in insufficient hardness and discrete distribution, and insufficient refinement of grains resulting in low impact property. The improved process ensures sufficient cooling rate and finally obtains a large number of tempered troostite and a small amount of bainite. While a large number of plastic deformation dislocations retained by forging-quenching form sub-crystals during tempering, which greatly refines the grains. In addition, a large number of dispersed θ-Fe₃C particles in α phase pin the dislocations during tensile deformation, properties of the forgings is improved significantly.

  Effect of isothermal annealing treatment on microstructure and properties of Inconel 625 alloy foil

  Wang Fangjun, Liu Yinglong, Shi Yao, Wan Hong, Liu Binbin

  2022, 47(3):  77-81.  doi:10.13251/j.issn.0254-6051.2022.03.015

  Abstract ( 80 )   PDF (593KB) ( 36 )  

  Effects of isothermal annealing treatment at different temperatures and time on microstructure and properties of 50 μm thick Inconel 625 alloy foils were studied by means of OM, SEM and mechanical properties test. The results show that during isothermal annealing at 650 ℃ and 700 ℃, the foils recrystallize, the grain size decreases significantly, and a large number of Ti- and Nb-rich carbides are precipitated at the grain boundaries. Due to the combined effect of recrystallization-induced fine-grain strengthening and carbide-induced precipitation strengthening, the strength and plasticity of the foils are significantly improved, especially after isothermal annealing at 650 ℃ for 48 h, the tensile strength reaches 1513 MPa, which is nearly 90% higher than that of the unannealed foils, and elongation also is increased by 105%. However, after isothermal annealing at 700 ℃ for 48 h, the recrystallized grains become coarser, resulting in a significant decrease in mechanical properties. The tensile elongation of the foils is closely related to the grain size.

  Effect of annealing process on mechanical anisotropy of cold rolled commercial pure titanium coil

  Yu Shilun, Zhang Xiaojun, Kong Bin, Liu Zhengqiao, Yu Wei, Jiang Mengling

  2022, 47(3):  82-87.  doi:10.13251/j.issn.0254-6051.2022.03.016

  Abstract ( 54 )   PDF (595KB) ( 33 )  

  Anisotropy of mechanical properties is one of the major factors affecting the formability of commercial pure titanium sheet and strip. In order to fabricate commercial pure titanium coil with low anisotropy, the mechanical properties, microstructure and texture of cold rolled commercial pure titanium after annealing with different parameters were characterized by using room temperature tensile tests and EBSD technique. And the influence of annealing process on anisotropy of mechanical properties of commercial pure titanium coil was analyzed. The results show that at fixed annealing temperature, with prolonging annealing time, the yield strength of TA1 strip in rolling direction (RD) descends more rapidly than that in transverse direction (TD), resulting in the increase of anisotropy of mechanical properties . When annealing arrived at a certain duration, the anisotropy of mechanical properties tends to be stable. The stable value of difference in yield strength between RD and TD is 82 MPa when annealed at 700 ℃, but it becomes 58 MPa at 610 ℃. For fixed annealing time, the higher the annealing temperature, the higher the anisotropy of mechanical properties, within the study temperature range. Texture analysis indicates that with prolonging annealing time or/and increasing annealing temperature, the intensity of pyramid texture increases, while that of the basal texture decreases, which leads to the increase of the difference in Schmid factor for {1010}<1120> prismatic slip between RD and TD when stretched at room temperature, therefore causes more obvious anisotropy of mechanical properties.

  Effect of dual liquid quenching on microstructure and hardness of 9Cr2Mo steel roller

  Sun Guojin, Gao Zhiwen, Cui Xiaoyan, Gao Kekun, Sun Li

  2022, 47(3):  88-91.  doi:10.13251/j.issn.0254-6051.2022.03.017

  Abstract ( 116 )   PDF (590KB) ( 25 )  

  Effect of water-oil dual liquid quenching process on microstructure and hardness of 9Cr2Mo roller were researched, and the optimum cooling process of dual liquid quenching was obtained. The results show that after single liquid quenching, the surface microstructure of the roller is coarse tempered martensite, while after water-oil dual liquid quenching, the tempered martensite is obviously refined, a small amount of bainite and retained austenite are formed, and the service life of the roller is significantly improved due to proper surface hardness distribution of the roller, which is high in the middle and low in the edge. The optimum cooling process of water-oil dual liquid quenching for 9Cr2Mo steel roller of ø750 mm is as follows: the precooling time outside the furnace before water cooling is 300 s, and the interval precooling time between water cooling and oil cooling in dual liquid quenching is controlled at 60-180 s.

  Effect of quenching temperature on microstructure and properties of a low cobalt secondary hardening steel

  Xiong Jinsheng, Ning Jing, Su Jie, Jiang Qingwei

  2022, 47(3):  92-96.  doi:10.13251/j.issn.0254-6051.2022.03.018

  Abstract ( 77 )   PDF (593KB) ( 23 )  

  Types and contents of precipitated phases in the high temperature range of a new low cobalt secondary hardening steel were calculated by Thermo-Calc thermodynamic software. Combined with the experimental methods of optical microscope (OM), scanning electron microscope (SEM) and mechanical testing, the effect of quenching temperature on the microstructure and properties of the tested steel was studied. The results show that there are a large number of spherical W/Mo-rich M₆C precipitates on the lath martensite matrix when quenching at lower temperature. With the increase of quenching temperature, M₆C precipitates dissolves rapidly and completely dissolves at 1060 ℃. The dissolution of M₆C precipitates enhances the secondary hardening effect and improves the impact properties. At the same time, it causes the prior austenite grains to be significantly coarsened, which has an adverse impact on the strength and toughness. Finally, the tested steel obtains the optimal match of comprehensive mechanical properties after quenching at 1060 ℃.

  Ion nitriding technology of inner gear ring of 6.5 MW nuclear power pump

  Lu Jinsheng, Zhang Heng, Xu Hongxiang, Guo Shirui

  2022, 47(3):  97-101.  doi:10.13251/j.issn.0254-6051.2022.03.019

  Abstract ( 63 )   PDF (593KB) ( 25 )  

  To meet high power, long service life, high reliability and high precision requirements of nuclear power pump gear box, the deep controlled ion nitriding process experiments were carried out on the 42CrMo steel matrix with medium hardness. The results show that when three-stage ion nitriding process with nitrogen hydrogen mixing atmosphere is adopted and using the optimized total process time of about 60 h, a nitrided layer can be obtained with 0.90 mm thickness and gradeⅠsurface brittleness, and γ′ single-phase, and the maximum residual compressive stress amplitude of the nitrided layer achieves 620 MPa. This process is applied to deep nitriding of the gear ring with modulus of 12 mm and diameter of ø1400 mm for the circulating water pump gearbox for nuclear power plants and successfully passes the bench test, and is serviced in China's nuclear power plants for many years replacing the imported one.

  Effect of two-step solution process on microstructure and mechanical properties of 7050 aluminum alloy

  Jiang Zhongtao, Wang Xin, Zhou Zhiming, Lin Haitao, Yang Xusheng, Dai Fangfang

  2022, 47(3):  102-106.  doi:10.13251/j.issn.0254-6051.2022.03.020

  Abstract ( 85 )   PDF (613KB) ( 37 )  

  Effect of two-step solution process on microstructure evolution of the 7050 aluminum alloy and precipitate characteristics and mechanical properties after two-step aging was tudied by means of SEM analysis, electrical conductivity testing and room temperature tensile performance testing. The results show that compared with the single stage solution, two-step solution can completely dissolve the insoluble Al₂CuMg phase, significantly increase the number of aging precipitates within grains, and the precipitates on the grain boundary are distributed intermittently. The two-step solution treatment significantly increases tensile strength and conductivity of the 7050 aluminum alloy while maintaining better elongation, with 611.9 MPa of the tensile strength, 587.5 MPa of the yield strength, 42.43%IACS of the electrical conductivity, and 13.5% of the elongation.

  Effect of solution treatment on structure and properties of a novel nickel-based superalloy

  Cheng Tijuan, Gan Bin, Yu Hongyao, Zhou Haijing, Guo Caiyu, Bi Zhongnan, Du Jinhui

  2022, 47(3):  107-112.  doi:10.13251/j.issn.0254-6051.2022.03.021

  Abstract ( 114 )   PDF (671KB) ( 33 )  

  Effects of different solution time and cooling methods on the γ′ phase and hardness in a novel nickel-based superalloy at 1080 ℃ were studied by means of OM, SEM, DSC and hardness tester. The results show that with the prolongation of the solution time, the size of γ′ phase in the tested alloy decreases under both air-cooling and water-cooling conditions; When the solution time is the same, the size of γ′ phase in the air-cooled specimen is larger than that of the water-cooled specimen, and the hardness value is also higher. This is because under the condition of water cooling, the cooling rate is higher and the degree of supercooling is larger, which reduces the diffusion rate of atoms in the matrix, slowes down the growth of the γ′ phase, and makes the final size smaller. Therefore, the solution time should be less than 16 h, and the cooling method should be air cooling, by which the γ′ phase in the alloy is uniformly distributed, the size is greater than 20 nm, and hardness value of the alloy is higher than 425 HV0.2.

  Effect of pre-heat treatment before carburizing on distortion of gear shaft made of 17CrNiMo6 steel

  Fang Xiurong, Liu Liu, Xu Huihui, Gao Yang

  2022, 47(3):  113-118.  doi:10.13251/j.issn.0254-6051.2022.03.022

  Abstract ( 78 )   PDF (610KB) ( 52 )  

  Taking 17CrNiMo6 steel gear shaft as the research object, carburizing with pre-heat and direct carburizing processes of the gear shaft were quantitatively analyzed by finite element software, and the main pre-heat process parameters affecting the heat treatment distortion of the gear shaft were determined. The temperature field and stress field in the two processes were compared and analyzed, and the effect of pre-heat treatment on the heat treatment distortion of gear shaft was studied. The results show that pre-heat treatment at 400 ℃ for 3 h before carburizing can effectively reduce the heat treatment distortion of the gear shaft.

  Effect of solution temperature on microstructure and mechanical properties of 7075 aluminum alloy sheet

  Ye Tuo, Tang Ming, Liu Jizhao, Liu Wei, Wu Yuanzhi, Liu Wei, Xu Wen

  2022, 47(3):  119-123.  doi:10.13251/j.issn.0254-6051.2022.03.023

  Abstract ( 99 )   PDF (613KB) ( 45 )  

  Hardness and compression tests of 7075 aluminum alloy sheet treated by solution treatment at different temperatures were carried out. Microstructure evolution of the rolled 7075 aluminum alloy plate was analyzed by means of optical microscopy (OM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that with the increase of solution temperature, the hardness and maximum compressive strength of the 7075 aluminum alloy first increase and then decrease, which reaches the peak at 520 ℃. This is because the increase of solution temperature is conducive to dissolution of the second phase into the matrix, at the same time, the dislocation density decreases and the grains grow. The anisotropy of mechanical properties of the sheet decreases with the increase of solution temperature. This is because with the increase of solution temperature, the original deformed fiber structure transforms to equiaxed grains, and the phenomenon of grain growth occurs, and the preferred orientation decreases.

  Effect of heat treatment on microstructure and mechanical properties of laser solid forming TB18 titanium alloy

  Zhang Ying, Wang Haojun, Chen Suming, Hu Guang, Ouyang Delai, Cui Xia, Hu Shengshuang

  2022, 47(3):  124-129.  doi:10.13251/j.issn.0254-6051.2022.03.024

  Abstract ( 73 )   PDF (614KB) ( 25 )  

  As-deposited TB18 titanium alloy was prepared by using BLT-C1000 laser solid forming equipment, and then the effects of different heat treatment processes on microstructure and mechanical properties of the TB18 titanium alloy were studied by means of OM, SEM and tensile testing machine. The results show that the macrostructure of the as-deposited tested alloy is dominated by elongated β grains, which are composed of metastable β phases and acicular secondary α phases, and there are deposited layer lines running through the β-grains. With the increase of direct aging temperature, the shape of the original β grains changes a little, the thickness of the internal secondary α phases increases, and the morphology of secondary α phases changes from needle-like to flake-like. When the direct aging temperature is higher than 550 ℃, the deposition layer line disappears, and the microstructure is composed of all β grains at the direct solution temperature higher than 830 ℃. After solution and aging treatments, the microstructure mainly consists of crisscross fine lamellar secondary α phase. With the increase of direct aging temperature, the tensile strength and yield strength decrease and the elongation increases. The secondary α phase is precipitated after solution and aging treatments, and the tensile strength and yield strength increase significantly, while the elongation decreases. By comprehensive consideration, the optimal heat treatment process of the as-deposited TB18 titanium alloy in actual production is direct aging at 500 ℃ for 4 h, at which the strength and elongation are higher than the index requirements.

  MATERIALS RESEARCH

  Effects of Si content and quenching temperature on microstructure and properties of Q&P steel

  Shi Na, Liu Weiming, Liu Yonggang, Zhan Hua, Cui Lei, Pan Hongbo

  2022, 47(3):  130-135.  doi:10.13251/j.issn.0254-6051.2022.03.025

  Abstract ( 68 )   PDF (612KB) ( 28 )  

  Two kinds of tested steels with different silicon contents were quenched and partitioned by using salt bath, and microstructure and properties of the tested steels quenched at different temperatures were investigated by means of metallographic microscope, scanning electron microscope and tensile testing machine. The results indicate that microstructure of the tested steels is composed of ferrite, martensite, retained austenite and bainite. With the increase of silicon content, the volume fraction of retained austenite increases marginally, the tensile strength and yield strength increase significantly, and the elongation decreases. In addition, the strength fluctuates slightly with quenching temperature. After quenching at 260 ℃ and partitioning at 360 ℃, the tested steel with 2.13%(mass fraction) Si obtains high strength and good elongation simultaneously, the tensile strength is 958.66 MPa, the yield strength is 458.99 MPa, the elongation and product of strength and elongation reach 15.35 % and 14.66 GPa·%, respectively, therefore, the comprehensive mechanical properties are optimum.

  Effect of carbon content on microstructure and properties of Al_0.5Co_0.5NiCrFe high-entropy alloy coating

  Shi Haifang, Li Qiang

  2022, 47(3):  136-141.  doi:10.13251/j.issn.0254-6051.2022.03.026

  Abstract ( 59 )   PDF (610KB) ( 27 )  

  Al_0.5Co_0.5NiCrFe high-entropy alloy coatings with different carbon contents were prepared by argon arc cladding, and effect of carbon content on the microstructure and properties of the Al_0.5Co_0.5NiCrFe high-entropy alloy coating was studied. The results show that after the addition of carbon, the high-entropy alloys are all composed of a single FCC structure, and no other structure are characterized. However, according to the microstructure and energy spectrum analysis of the high-entropy alloy, it can be found that there is carbon and chromium between the dendrites of the high-entropy alloy. The microstructure of the high-entropy alloy coating is a typical dendritic structure, and the microstructure is continuously refined with the increase of carbon content. With the increase of carbon content, the hardness of high-entropy alloy coating increases continuously. When the carbon content is 4%, the highest hardness is 383.2 HV0.5, and the wear resistance is also the best. With the continuous increase of carbon content, the corrosion resistance of high-entropy alloy first increases and then weakens, and when the carbon content is 2%, corrosion resistance is the best. According to the oxidation mass gain per unit area, the oxidation resistance of the high-entropy alloy first increases and then decreases. When the carbon content is 2%, the coating has the best oxidation resistance.

  Effect of yttrium-based rare earth on inclusions and cryogenic temperature impact property of high strength shipbuilding steel

  Luo Diqiang, Yu Yinhong, Zhang Zhenming, Feng Xiaoming, Liu Min, Lai Chaobin

  2022, 47(3):  142-146.  doi:10.13251/j.issn.0254-6051.2022.03.027

  Abstract ( 69 )   PDF (613KB) ( 39 )  

  Effect of yttrium-based rare earth content on inclusions and cryogenic temperature impact property of the EH36 high strength shipbuilding steel was studied by means of scanning electron microscope and energy dispersive spectroscopy. The results show that the addition of proper amount of rare earth can significantly improve the low temperature impact property of the EH36 steel. When the rare earth content in the steel is 0.018%(mass fraction), the transverse impact property at -40 ℃ and -60 ℃ are increased by 59.4% and 65.7%, respectively. After the rare earth is added, the low temperature impact fracture morphology changes from the cleavage type without rare earth to the dimple fracture, and the small spherical rare earth composite inclusions at the bottom of the dimple buffers and hinders the crack growth. Meanwhile, the rare earth can modify long strip-like Al₂O₃-CaO-MnS inclusions in the EH36 steel into fine spherical rare earth inclusions, and the particle size of inclusions is refined from about 5 μm to less than 3 μm.

  Microstructure and corrosion resistance of as-cast Ti-20Zr-10Nb-xMo alloys

  Zhang Manxue, Jing Ran, Zhang Xiong, Zhang Qing, Wu Qian, Liu Yirou

  2022, 47(3):  147-150.  doi:10.13251/j.issn.0254-6051.2022.03.028

  Abstract ( 65 )   PDF (622KB) ( 26 )  

  Effect of Mo content on microstructure, phase composition, mechanical properties and corrosion resistance of as-cast Ti-20Zr-10Nb-xMo alloys (x=0,3,6,9,wt%) was studied by means of X-ray diffraction, optical microscope, microhardness test, compressive test and electrochemical workstation. The results show that with the increase of Mo content, the phase structure of Ti-20Zr-10Nb-xMo alloys obviously changes from α′+β→α″+β→β, and the average grain size decreases gradually with the increase of Mo content. When the Mo content is 9%,the average grain size of the alloy is about 45 μm. With the addition of Mo, the compressive strength and yield strength of the alloy first decrease and then increase, while the microhardness increases first and then decreases. When the Mo content is 9%, the compressive strength and compressive strain are 1610 MPa and 50.9%, respectively. The self-corrosion current density and R_p value of the tested alloy without Mo addition are the minimum of 33.19 nA·cm^-2, the maximum of 1531.52 kΩ·cm², respectively, and the corrosion resistance is the best.

  Effects of composition and cooling rate on solidification structure of Al-xEr alloy

  Ning Jing, Gao Kunyuan, Li Haonan, Wen Shengping, Huang Hui, Wu Xiaolan, Wei Wu, Nie Zuoren

  2022, 47(3):  151-154.  doi:10.13251/j.issn.0254-6051.2022.03.029

  Abstract ( 58 )   PDF (623KB) ( 22 )  

  Microstructure and phase structure of solidified structure of the Al-xEr (x=10, 20, 30, mass fraction, %) alloy were analyzed by means of scanning electron microscope (SEM) and X-ray diffractometer (XRD), respectively. The results show that at cooling rate of 60 ℃/h, the structure of Al₃Er phase in the Al-10Er alloy is L1₂ with size of about 200 μm, which are connected in a fishbone shape. With the increase of Er content to 30%, the primary Al₃Er phase transforms into a block with size of about 1 mm. For the Al-30Er alloy, as the cooling rate decreases, the primary Al₃Er phase changes from a straight L1₂ structure to a wavy hR20 structure, and the eutectic structure changes from flocculent to striped.

  Heat treatment properties of 8620H steel with refined graded hardenability

  Hai Xianü, Yang Yang, Huang Taiwei, Fan Wangzhan, Gui Weimin, He Liangliang

  2022, 47(3):  155-158.  doi:10.13251/j.issn.0254-6051.2022.03.030

  Abstract ( 73 )   PDF (610KB) ( 28 )  

  8620H steels with low hardenability and high hardenability were prepared by modifying chemical composition, and application on the intermediate shaft of the auxiliary box was studied. The results show that under the same heat treatment process, the high hardenability 8620H2 steel has a deeper effective hardened layer depth and higher core hardness than that of the low hardenability 8620H steel auxiliary box intermediate shaft. In addition, the heat treatment work station take time of the low hardenability 8620H steel auxiliary box intermediate shaft is 25.5 min, while that of the high hardenability 8620H2 steel can be significantly decreased to 20.5 min. It should be noted that, when developing the heat treatment process for the part of the 8620H2 steel with high hardenability, the technical indexes of heat treatment and the accuracy of tooth after heat treatment should be comprehensively considered.

  MICROSTRUCTURE AND PROPERTIES

  Thermodynamics of C and Mn element partitioning during austenite reverted transformation in medium manganese steel

  Tian Yaqiang, Cai Zhixin, Xu Haiwei, Zhang Hongjun, Han Yun, Di Guobiao, Chen Liansheng

  2022, 47(3):  159-164.  doi:10.13251/j.issn.0254-6051.2022.03.031

  Abstract ( 64 )   PDF (614KB) ( 26 )  

  Thermodynamic process of C and Mn elements partitioning in austenite reverted transformation(ART) process of 0.1C-7.2Mn medium manganese steel was simulated by Thermo-Calc software, and the heat treatment experiment of ART process was carried out according to the results. Thermodynamic calculation and experimental results show that when the annealing temperature is 640 ℃, the content of C and Mn in austenite is higher than that at 680 ℃. In the initial stage of partitioning, the mass fraction of C in austenite quickly reaches the highest point of 0.87%. In the process of interface movement controlled by Mn element, the mass fraction of Mn in austenite is close to 10%. The average rate of interface movement controlled by C partitioning is 2.5×10^-4 m·s^-1, the interface migration controlled by it accounts for 46.9% of the total migration distance. The interface movement rate controlled by Mn partitioning is only 2.5×10^-12 m·s^-1, the migration distance accounts for 53.1% of the total migration distance. When the specimen is kept at 640 ℃ for 30 min, the volume fraction of retained austenite reaches 36.5%, the tensile strength is 1041 MPa, and the product of strength and elongation reaches 24.36 GPa·%.

  Thermal fatigue properties of H13 and Dievar steels for hot-work die

  Wu Fangjun, Deng Xiaoyun, Jie Xiaohua, Zheng Kaihong, Luo Zhichao

  2022, 47(3):  165-172.  doi:10.13251/j.issn.0254-6051.2022.03.032

  Abstract ( 189 )   PDF (617KB) ( 31 )  

  Effect of tempering temperature on thermal fatigue properties of the H13 and Dievar hot-work die steels was investigated. The Uddeholm self-constrained thermal fatigue test was conducted on the specimens tempered at 520, 580 and 640 ℃, and the thermal fatigue damage factors were obtained to quantify the fatigue damage of the steels. The results show that the Dievar steel has a lower hardness but higher impact property than that of the H13 steel tempered at the same temperature, and possesses better thermal fatigue resistance. Tempered at 580 ℃, the carbide sizes of the H13 steel and Dievar steel are about 10.1 μm and 6.3 μm, respectively. The high carbide content and large size of the H13 steel result in the decrease of toughness and thermal fatigue resistance.

  Phase transformation and precipitation behavior of Cr-Mn-Ni-N high nitrogen steel for non-magnetic drilling collar during equilibrium solidification

  Wang Yinghu, Zheng Huaibei, Bai Qingqing, Song Lingxi, Yao Bin, Wang Liwei

  2022, 47(3):  173-180.  doi:10.13251/j.issn.0254-6051.2022.03.033

  Abstract ( 52 )   PDF (611KB) ( 21 )  

  Phase transformation and precipitation behavior of Fe-(15-25)Cr-(15-25)Mn-(0-5)Ni-(0-1)Mo-(0-1)N-(0-0.8)C multicomponent high nitrogen steel for non-magnetic drilling collar during equilibrium solidification were investigated by using Thermo-Calc software. The vertical sections of the phase diagram for this steel were calculated by using the TCFE9 database. Effects of Cr, Mn, Ni, Mo, N and C on phase transformation of the steel during solidification and cooling were analyzed, and the equilibrium solidification phase transformation path diagram was obtained. The results show that increasing Cr and Mn contents can significantly improve the solubility of nitrogen, Mo can slightly improve it, while Ni and C can significantly reduce it. With the increase of Ni, C and N contents, the single-phase austenite phase zone can be enlarged and the austenite can be stabilized. With the increase of Cr, Mo and Mn contents, the single-phase austenite phase zone can be reduced and the ferrite can be stabilized. The nitrogen can promote the precipitation of M₂(C,N) phase and inhibit the precipitation of M₂₃C₆ phase. The Cr and Mn can promote the precipitation of sigma phase, while C and N can inhibit the precipitation of sigma phase. The precipitation of M₂₃C₆ phase is mainly affected by the content of C, and with the increase of C content, the precipitation temperature of M₂₃C₆ phase increases significantly.

  Analysis of influencing factors on transverse impact properties of rare earth H13 die steel

  Li Kuo, Sun Mingyue, Xu Bin, Li Dianzhong

  2022, 47(3):  181-185.  doi:10.13251/j.issn.0254-6051.2022.03.034

  Abstract ( 66 )   PDF (610KB) ( 26 )  

  In order to explore the influence factors on transverse impact properties of the rare earth H13 die steel forgings, macrostructure analysis, microstructure analysis, SEM and EDS analysis of fracture surface were carried out on the riser end specimens of steel forgings. The results show that the macrostructure and microstructure (including banded structure, non-metallic inclusion and network carbide) of the H13 die steel with rare earth addition can meet the qualification requirements of various industry standards, and the purity of the steel is relatively high. The chain-like or network carbides precipitate along the grain boundary of the main deformation direction after simplex stretching, the large-scale liquidus carbides between dendrites, and the unwrought dendrite structure in the matrix are the main factors that seriously affect the transverse impact properties of the rare earth H13 die steel.

  Phase transformation and mechanical properties of 5Cr2NiMoVSi die steel

  Pang Qinghai, Lang Qingbin, He Chunjing, Wang Jiuhua, Yuan Yasha

  2022, 47(3):  186-190.  doi:10.13251/j.issn.0254-6051.2022.03.035

  Abstract ( 95 )   PDF (613KB) ( 26 )  

  Thermal expansion curves of 5Cr2NiMoVSi die steel under different cooling conditions was measured by means of Formastor-FⅡ full automatic transformation measuring apparatus. Combining microstructure and hardness results, the phase transformation characteristics of the 5Cr2NiMoVSi die steel was analyzed and the continuous cooling transformation curves were gained. The effect of tempering parameter on mechanical properties of the steel was studied. The results show that the supercooled austenite of 5Cr2NiMoVSi steel has good stability, and the continuous cooling transformation curve shifts to the right greatly. The hardness of materials has a great correlation with the cooling rate, and the hardness increases rapidly with the increase of cooling rate. The critical cooling rate of the steel is 0.4 ℃/s,and the martensitic hardness is basically maintained above 640 HV. When tempered between 550 ℃ and 590 ℃, the tensile strength of the material is not less than 1628 MPa, indicating good tempering stability.

  SURFACE ENGINEERING

  Effect of multi-pass electron beam scanning overlap rate on microstructure and properties of 40Cr steel

  Wang Rong, Gong Yuhui, Yin Xuejun, Wei Deqiang

  2022, 47(3):  191-197.  doi:10.13251/j.issn.0254-6051.2022.03.036

  Abstract ( 78 )   PDF (614KB) ( 21 )  

  Multi-pass electron beam scanning surface modification was carried out on 40Cr steel with different overlap rates, and microstructure and properties was studied. The results show that after multi-pass electron beam scanning surface modification, tempered martensite and tempered sorbite are formed in the overlapping area of 40Cr steel due to tempering, and the martensite structure in the remelted layer becomes coarsen with the increase of overlap rate. When the overlap rate is 0%, the average microhardness of the electron beam treatment area is 627.4 HV0.2, with the increase of overlap rate, the microhardness of overlap area decreases. When the overlap rate is 25%, the surface of the specimen is smooth and flat, and the roughness is 1.083 μm. The surface roughness first decreases and then increases with the increase of overlap rate. In addition, the wear resistance of the 40Cr steel is significantly improved compared with that before electron beam treatment. The wear resistance first increases and then decreases with the increase of overlap rate.

  Effect of grinding parameter on grinding-hardened case and its uniformity of nodular cast iron QT400

  Zhao Xiaofeng, Liu Judong, Huang Songwei

  2022, 47(3):  198-203.  doi:10.13251/j.issn.0254-6051.2022.03.037

  Abstract ( 86 )   PDF (618KB) ( 20 )  

  Grinding-hardening was done on nodular cast iron QT400 by using two-passes grinding up-grinding+down-grinding on a surface grinder. The influence of depth of cut a_p and table speed v_w on grinding-hardened case and its uniformity was studied.The results show that there are three case of the hardened surface of the specimen, which are melted layer, completely hardened case and incompletely hardened case. Among them, the structure of the melted layer is secondary cementte, retained austenite and carbides. The microstructure of the complete transformation hardened case is acicular martensite, retained austenite and spheroidal graphite, and the structure of the incompletely hardened case is acicular martensite, ferrite, retained austenite and spheroidal graphite.The average value of the high hardness region in the microhardness distribution curve is between 850-950 HV0.2. Compared with the matrix (190-230 HV0.2), the microhardness is increased by nearly 3 times. With the increase of grinding depth a_p or the decrease of feed speed v_w, the surface layer of the specimen shows the changing order of "completely unhardened→incompletely hardened→completely hardened→melted", the range of the high hardness region in the microhardness distribution curve also becomes wider, the depth of the grinding-hardened case is also increased and the uniformity is better.

  Effect of high frequency Nd∶YLF flat-top laser shock on surface stress and micro-deformation of TC6 titanium alloy

  Zhu Ran, Xie Dihui, Zhu Shuaiguang, Zhang Yongkang

  2022, 47(3):  204-209.  doi:10.13251/j.issn.0254-6051.2022.03.038

  Abstract ( 65 )   PDF (575KB) ( 20 )  

  To study the effect of laser shock peening on surface stress and deformation of the TC6 titanium alloy under the condition of high frequency, a Nd∶YLF flat-top laser was used to perform laser shock peening test on TC6 titanium alloy specimens at a repetition frequency of 10 Hz, and the influence of laser energy and impact times on surface residual stress and deformation of the specimen was analyzed. The residual stress on the surface of the TC6 titanium alloy specimen was measured by using XL-640 X-ray stress tester before and after impact, and the three-dimensional morphology and surface roughness of the specimen were measured by using Contour GT-X3 white light interferometer. The results show that, for Nd∶YLF flat-top laser shock peening, the spot overlapping rate of 30% is more appropriate choice than that of 50%, because the overlapping rate of 50% is liable to cause surface ablation of specimen. With the increase of laser energy and impact times, the residual stress, surface deformation and surface roughness of the specimen surface all increase. For the single spot non-overlap area, the variation gradient of specimen surface deformation is relatively gentle, while in the spot overlap area, the surface deformation of specimen approximately presents a “V”-shaped change.

  Microstructure and properties of T250 steel after plasma nitriding

  Zhou Zhongping, Zhang Xiaojuan, Bai Lu, Yu Fangyin, Min Yong'an

  2022, 47(3):  210-214.  doi:10.13251/j.issn.0254-6051.2022.03.039

  Abstract ( 74 )   PDF (578KB) ( 29 )  

  Plasma nitriding tests of different time and temperatures were carried out on the solid solution treated T250 steel. Microstructure, microhardness, phase and depth of the nitrided layer were measured by means of metallographic analysis, hardness test and XRD. The results show that after ion nitriding, the surface hardness is capable of reaching above 900 HV0.3, and the substrate hardness about 500 HV0.3. The boundary between the diffusion layer of the infiltration layer and the matrix is obvious. The nitriding temperature is similar to the aging temperature of the T250 steel, and the aging strengthening of the steel can be achieved during the nitriding process.

  Research progress of laser modification technology for titanium alloy surface

  Lin Jihui, Wen Yahui, Fan Wenbo, Zhang Teng, Liu Chenyu, Xue Yuanlin

  2022, 47(3):  215-221.  doi:10.13251/j.issn.0254-6051.2022.03.040

  Abstract ( 104 )   PDF (573KB) ( 27 )  

  With the continuous expansion of application scope of titanium alloy, there are higher requirements for the performance of titanium alloy, so the surface modification of titanium alloy has become an important research hotspot. The application of laser alloying technology and laser cladding technology in the surface modification of titanium alloy is summarized, and the existing problems and developing trend are analyzed and summarized.

  NUMERICAL SIMULATION

  Micro- and thermoelectric properties of iridium and iridium-rhodium alloys

  Chen Jing, Wang Gao, Liang Haijian, Li Zhiling, Liu Yi, Zhang Jiankang

  2022, 47(3):  222-226.  doi:10.13251/j.issn.0254-6051.2022.03.041

  Abstract ( 81 )   PDF (578KB) ( 22 )  

  Based on first-principles calculations, the band structure and density of states of the thermal electrode iridium and iridium-rhodium alloys were investigated. A model of iridium-rhodium alloy was established by virtual crystal approximation (VCA). The thermoelectric properties of IrRh10-Ir thermocouple and IrRh40-Ir thermocouple were tested by the test platform. The results show that the calculated lattice constants of pure metals iridium and rhodium are in good agreement with the test parameters, and the iridium-rhodium alloy has good conductor properties and structural stability. The IrRh10-Ir thermocouple and IrRh40-Ir thermocouple have good linearity characteristics, and the sensitivity is 2.7 μV/℃ and 5.6 μV/℃, respectively. It is expected that the firstprinciples calculation and analysis will be applied to the selection of the thermal electrode materials.

  Predicting model of gear steel hardenability based on extreme learning machine

  Zhao Yiqi, Nie Xiaolong, Zhao Sixin, Gao Jiaqiang, Liu Xinkuan

  2022, 47(3):  227-233.  doi:10.13251/j.issn.0254-6051.2022.03.042

  Abstract ( 65 )   PDF (581KB) ( 24 )  

  Prediction of end-quenching hardness curve and chemical composition of 20Cr gear steel was studied by using extreme learning machine(ELM), and the prediction results were compared with the traditional prediction models. The results show that the ELM not only can predict the hardenability of the gear steel according to the chemical composition with calculation accuracy significantly higher than that of the traditional linear fitting and neural network models,but also can be used to backward predict the chemical composition from the hardenability curve with the element content error within 5%.

  Optimization design of anti-distortion tooling for local heat treatment of large welded vessels

  Long Liang, Hu Qixian, Luo Yun, Zheng Hongxiang, Wang Yujie

  2022, 47(3):  234-238.  doi:10.13251/j.issn.0254-6051.2022.03.043

  Abstract ( 57 )   PDF (575KB) ( 28 )  

  Local heat treatment distortion of large pressure vessel was simulated by finite element method. Based on the maximum distortion of heat treatment, the optimal size of anti-distortion tooling was preliminarily designed. The influence of different diameters and wall thicknesses on local heat treatment distortion of cylinder was analyzed, and the optimal number of anti-distortion tooling suitable for different cylinder sizes was obtained. The results show that 0.2 m of supporting platform width and ø4 cm of support column diameter are the best anti-distortion tooling dimensions. The larger cylinder diameter is, the larger heat treatment distortion is. The thicker cylinder wall is, the smaller heat treatment distortion is. The more the number of anti-distortion tooling, the smaller heat treatment distortion.

  JMatPro calculation and experimental study of microstructure transformation of B1800HS hot-formed steel

  Guo Yazhou, Song Ninghong, Ni Lei, Ling Hua, Bi Wenzhen, Wei Xicheng

  2022, 47(3):  239-244.  doi:10.13251/j.issn.0254-6051.2022.03.044

  Abstract ( 84 )   PDF (575KB) ( 31 )  

  Taking B1800HS series prototype hot-formed steel as an example, the reliability of thermodynamic data calculated by JMatPro software was investigated. The austenitizing temperature, minimum critical cooling rate and phase transformation temperature range were obtained from the calculated TTT curves of the steels, and compared with that of experimental CCT curves measured by thermal dilatometer. The effects of Mo and V on microstructure and properties of the steel were studied. The results show that the austenitizing temperature and critical cooling rate calculated by JMatPro software are in good agreement with the experimental results, and the predicted range of microstructure transformation temperature has a slight deviation, indicating that the JMatPro software can provide guidance for the formulation of heat treatment scheme of the B1800HS series hot-formed steels. In addition, through the performance test, it is confirmed that molybdenum vanadium multi-microalloying can make the tested steels have more excellent comprehensive service performance.

  TEST AND ANALYSIS

  Analysis of outer ring dimension and stress variation characteristics of 8Cr4Mo4V steel bearing based on working temperature

  Xia Yunzhi, Yan Jiasen, Yu Xingfu, Wei Yinghua, Yang Wenwu, Liu Yujian

  2022, 47(3):  245-251.  doi:10.13251/j.issn.0254-6051.2022.03.045

  Abstract ( 60 )   PDF (578KB) ( 39 )  

  Variation characteristics of inner and outer diameter and surface residual stress of straight wall cylindrical bearing outer ring made of 8Cr4Mo4V steel at different working temperatures were measured, the factors causing the dimension variation and surface residual stress variation of bearing outer ring were analyzed, and the microstructure of the bearing outer ring was observed. The results show that at different working temperatures, the outer diameter increment of bearing outer ring all reaches 1-2 μm after holding for 300 h, which is greater than that of inner diameter; And the retained austenite transforms into martensite at the working temperatures, and deep tempering of martensite leads the surface compressive residual stress value at inner diameter of bearing outer ring to increase. When the working temperature is 150 ℃, the surface compressive residual stress absolute value increment on both the inner and outer diameter reach the most, and with the increase of temperature, the increment in surface compressive residual stress absolute value decreases. The increase of the surface compressive residual stresses on the inner and outer diameters of bearing outer ring is caused by the transformation of retained austenite into martensite, that resulted volume expansion. Deep tempering of martensite leads to volume shrinkage, and different shrinkage of inner and outer diameter will lead to different changes of compressive residual stress value on inner and outer diameter surface. The size shrinkage will lead to the increase of compressive residual stress on inner diameter and decrease of that on outer diameter.

  Distortion control method of parts with internal spline

  Cui Ding, Che Yongping

  2022, 47(3):  252-256.  doi:10.13251/j.issn.0254-6051.2022.03.046

  Abstract ( 56 )   PDF (578KB) ( 25 )  

  Due to the heat treatment distortion, the parts with internal spline cannot pass the plug gauge check has been a common problem. In view of the many factors influencing the heat treatment distortion of parts with internal spline, with the help of the concept of “quenching distortion tolerance zone”, the part structure type, part size before heat treatment process, heat treatment process parameters(including austenitizing temperature, soaking time, furnace volume, cooling rate, loading method), material type and normalizing process after forging on the heat treatment distortion of the parts with internal spline were comprehensively analyzed, and a series of solutions to solve the problem of heat treatment distortion of the parts with internal spline were proposed by coupling all those various factors.

  Failure analysis of hydrogen induced delayed fracture of 50CrVA steel spring

  Li Mingxiang, Yang Ping, He Wei, Zhang Meng, Wang Wenbo

  2022, 47(3):  257-260.  doi:10.13251/j.issn.0254-6051.2022.03.047

  Abstract ( 87 )   PDF (634KB) ( 61 )  

  After a period of service, a 50CrVA steel spring of the aircraft hatch door broke at the thread. The fracture morphology, microstructure, hardness, hydrogen content and chemical composition of the fractured spring were tested and analyzed, respectively. The results show that the failure of the spring is hydrogen induced delayed fracture, the fracture source area is intergranular cracking, and the typical hydrogen embrittlement fracture morphology exists on the grain surface. The investigation on the manufacturing process shows that more hydrogen is introduced into the matrix of the steel spring and the thread bears the bias load, both the factors promotes the fracture of the spring during service. The former factor is caused by without dehydrogenation when the cadmium plating with defects formed in the first cadmium plating process is removed and then replated, while the latter happens when the spring is assembled. The failure mode of hydrogen-induced delayed fracture is validated in the corresponding process experiment for the 50CrVA steel spring.

  Analysis of fracture cause of 1Cr17Ni2 steel small shaft of control box

  Yang Yuchuan, Li Wei, Xiong Yong

  2022, 47(3):  261-265.  doi:10.13251/j.issn.0254-6051.2022.03.048

  Abstract ( 73 )   PDF (670KB) ( 30 )  

  A small shaft of the aircraft engine control box broke during installation. The fracture properties and causes of the small shaft of control box were determined by means of fracture morphology, microstructure, hardness and chemical composition, contrast test and simulation test. The results show that the intergranular brittle fracture occurs in the small shaft after tempering in the tempering brittle zone of 570 ℃, the reason of which is not only due to the reduction the impact performance of the small shaft caused by the tempering at the temperature in the brittleness zone, but mainly because there is no ferrite in the matrix. The loss of ferrite reduces the total area of grain plane and phase interface, resulting in more weakened particles generates at grain boundary during tempering brittle zone, which intensifies the high temperature tempering brittleness, and finally leads to intergranular brittle fracture of the small shaft. The absence of ferrite in the matrix is due to the high content of austenite forming elements(Ni) and low content of ferrite forming elements(Cr,Si) in the small shaft.