Current Issue

• MICROSTRUCTURE AND PROPERTIES

  Recrystallization behavior and texture evolution of cold rolled TA5 titanium alloy during annealing

  Zhang Shijin, Li Kai, Yi Danqing, Liu Huiqun

  2022, 47(2):  1-8.  doi:10.13251/j.issn.0254-6051.2022.02.001

  Abstract ( 131 )   PDF (645KB) ( 78 )  

  Electron backscatter diffraction (EBSD) was used to characterize the grain size, recrystallization and texture of cold-rolled and annealed TA5 titanium alloy plates, the effects of deformation non-uniformity on recrystallization behavior and texture evolution were discussed. The results show that <0002>//TD-oriented grains are more prone to deforming than <0002>//ND-oriented grains, combined with the limited-slip system of hcp structure, which jointly determine the non-uniformity of cold-rolled deformation of TA5 alloy plates. In the early stage of annealing, the recrystallization rapidly nucleates in the high-stored-energy regions, and the greater the deformation, the more nucleation number, and the smaller the grain size of the sample after recrystallization. The recrystallized grains rapidly complete nucleation through the "oriented nucleation" mechanism in high-stored-energy regions during the early stage of annealing and then grow, including a small amount of residual severely deformed <0002>//TD-oriented grains. At the same time, the recrystallized grains nucleate slowly through the "strain-induced boundary migration" mechanism in the regions with low-stored-energy during the entire recrystallization process. These two mechanisms work together to weaken the texture of the annealed plate, but the cold-rolled state basal texture is still dominated. The hardness curve can well reflect the degree of recrystallization, however, the hardness values of different test surfaces affected by the texture are significantly different. The larger the angle between the loading axis and the crystal c axis, the smaller the hardness value.

  Effect of Ti microalloying on microstructure and properties of fire-resistant construction steel

  Zhang Pengcheng, Wu Huibin

  2022, 47(2):  9-13.  doi:10.13251/j.issn.0254-6051.2022.02.002

  Abstract ( 87 )   PDF (556KB) ( 47 )  

  Three kinds of tested steels were designed with low Mo and Ti multi-microalloying, and reasonable thermo-mechanical control process(TMCP) was explored. The low cost 460 MPa grade fire-resistant steel was successfully developed. Through the test of mechanical properties and microstructure analysis, the results show that the ideal microstructure of fire-resistant steel is obtained, which is granular bainite and M/A island. With the increase of Ti content, the average grain size of the tested steel decreases. The room temperature yield strength of the three tested steels are all higher than 460 MPa, and the yield strength at high temperature of 600 ℃ for 3 h is higher than 307 MPa, which indicates that the three tested steels all have excellent mechanical properties at high temperature. Under the combined action of phase transformation strengthening, precipitation strengthening, fine grain strengthening and dislocation strengthening, the tested steels with different Ti contents obtain good high temperature mechanical properties. Among them, the YS value (600 ℃ yield strength/room temperature yield strength) of the tested steel with 0.07% Ti is 0.68, which fully meets the using standard of fire-resistant steel.

  Effect of B-Ce composite microalloying on microstructure and mechanical properties of S31254 super austenitic stainless steel

  Wang Shujing, Wang Tonghao, Wang Jian, Li Yuping, Han Peide

  2022, 47(2):  14-19.  doi:10.13251/j.issn.0254-6051.2022.02.003

  Abstract ( 173 )   PDF (559KB) ( 26 )  

  Microstructure and mechanical properties of the S31254 super austenitic stainless steel after B-Ce composite microalloying was investigated by means of SEM and tensile tests. The results show that the B and B-Ce composite microalloying can inhibit the precipitation of σ phase and improve the precipitation morphology of σ phase. Under the same solution treatment conditions, the B-Ce composite microalloyed specimens are more conducive to the complete redissolution of σ phase. Under the same aging conditions, the B-Ce composite microalloying has a more obvious effect on inhibiting σ phase precipitation. The dimples at tensile fracture of the B and B-Ce composite microalloyed specimens are larger and deeper, and the elongation of the materials is also significantly increased, indicating that microalloying is beneficial to further improve the toughness of the S31254 steel.

  Microstructure and properties of Al₂₅Nb₂₀Ti₃₀Zr₂₅ low density high entropy alloy

  Liu Hongwu, Li Zhiang, Gao Fan, Li Zhenxi, Wang Qingfeng

  2022, 47(2):  20-25.  doi:10.13251/j.issn.0254-6051.2022.02.004

  Abstract ( 58 )   PDF (566KB) ( 26 )  

  Microstructure, high temperature structure stability and hot workability of the Al₂₅Nb₂₀Ti₃₀Zr₂₅ alloy were studied by means of Thermo-Calc software calculation, microstructure multi-scale characterization and thermal simulation test. The results show that the ingot microstructure of Al₂₅Nb₂₀Ti₃₀Zr₂₅ alloy is mainly composed of BCC matrix and Zr₅Al₃ precipitates. The Zr₅Al₃ phase is continuously precipitated at the BCC grain boundary. The Zr₅Al₃ phase inside the grains is distributed in a block shape with an average size of about 750 nm. After holding at 750-1000 ℃ for 24 h, the grain size of matrix does not change significantly, with the increase of temperature, the content of Zr₅Al₃ phase is decreased slightly, and the high temperature structure stability of alloy is better. The constitutive equation of the alloy is established, $\dot{ε}$=4.5×10¹⁴[sinh(0.0063σ_p)]^2.8exp(-419/RT), and the energy dissipation coefficient map of the alloy is drawn. Under the deformation condition of 1050 ℃/1 s^-1, the energy dissipation coefficient reaches the peak value of 0.69, and under this deformation condition, a complete forging disc without crack is isothermally forged with a size of $\phi$180 mm×20 mm. The original continuous Zr₅Al₃ phases at grain boundary are decomposed into short rods by forging, which are evenly distributed in the BCC matrix, and the BCC matrix undergoes dynamic recovery and partial recrystallization.

  Hot compression behavior and microstructure analysis of as-rolled 6082-T6 aluminum alloy

  Ye Tuo, He Yubing, He Wenpeng, Liu Wei, Yuan Haodeng, Wu Yuanzhi, Liu Wei, Liu Jizhao

  2022, 47(2):  26-30.  doi:10.13251/j.issn.0254-6051.2022.02.005

  Abstract ( 70 )   PDF (556KB) ( 25 )  

  Hot compression test of the as-rolled 6082-T6 aluminum alloy was carried out by using a thermal simulator. The flow stress of the alloy was analyzed under the condition of deformation temperature of 100-400 ℃ and strain rate of 0.01 s^-1, and the microstructure at different hot deformation temperatures was characterized. The results show that the mechanical properties of the as-rolled 6082 aluminum alloy are affected by deformation temperature and rolling direction. The stress of the alloy shows negative temperature sensitivity during deformation, that is, the higher the deformation temperature, the lower the stress. The alloy shows obvious anisotropy of mechanical properties. The compressive strength is higher at 0° and 90° to the rolling direction and lower at 45°. After hot compression deformation, the grain structure of the as-rolled 6082-T6 aluminum alloy in three directions is distorted along the direction of shear force, and the effect of deformation temperature on grain structure is slight. With the increase of deformation temperature, the dislocation density in the alloy matrix decreases obviously, and coarsening of the precipitates is observed.

  Effect of pulsed magnetic field heat treatment on microstructure and texture of CGO oriented silicon steel during decarburization annealing

  Dong Lili, Ma Yonglin, Su Pengji, Yang Xuefeng

  2022, 47(2):  31-34.  doi:10.13251/j.issn.0254-6051.2022.02.006

  Abstract ( 54 )   PDF (558KB) ( 22 )  

  Self-developed pulsed magnetic field annealing device was used to apply magnetic field of different intensities during decarburization annealing of an oriented silicon steel, and microstructure and macro-texture of the specimens after decarburization annealing in a pulsed magnetic field were studied by using optical microscope and X-ray diffractometer. The results show that the average grain size of the oriented silicon steel increases with the application of pulsed magnetic field during decarburization annealing. The maximum average grain size is 13.06 μm when the magnetic field intensity is 40 mT. In addition, the strength of cube texture {001}<100> of the oriented silicon steel specimen is weakened, while the Goss texture {110}<001> and {111}<112> are strengthened, which is conducive to obtain better texture and magnetic properties of the finished product.

  MATERIALS RESEARCH

  Effect of C content on microstructure and mechanical properties of cold-rolled Fe-6Mn-1Al medium manganese steel

  Zhao Yanle, Zou Yuming, Ding Hua

  2022, 47(2):  35-40.  doi:10.13251/j.issn.0254-6051.2022.02.007

  Abstract ( 79 )   PDF (557KB) ( 28 )  

  Annealed microstructure of cold-rolled medium manganese Fe-6Mn-1Al steel with C content of 0.06%, 0.15% and 0.30%(mass fraction), and the mechanical properties after tensile testing at room temperature were studied. The results show that the microstructure of annealed tested steel with different C contents is composed of ferrite+austenite after annealing at 660 ℃. With the increase of C content, the volume fraction of austenite in the tested steel increases from 19.34% to 38.70%, and the increase of C content leads to the increase of partitioning of C and Mn to austenite, which improves the stability of austenite. The TRIP effect in the deformation process of the tested steel with higher C content is more significant, which improves the work hardening ability of the tested steel and obtains better comprehensive mechanical properties. The product of strength and elongation of the tested steel raises from 28.0 GPa·% to 51.4 GPa·% as the C content increases from 0.06% to 0.30%.

  Effect of Zr on static recrystallization kinetics of deformed austenite and precipitates in Ti-Mo composite microalloyed steel

  Hao Tianci, Wu Yonghao, Yin Shubiao, Cao Jianchun, Luo Hanyu

  2022, 47(2):  41-47.  doi:10.13251/j.issn.0254-6051.2022.02.008

  Abstract ( 63 )   PDF (555KB) ( 19 )  

  Through two-pass compression simulation experiment on the Gleeble-3500 thermal simulation test machine, the static recrystallization process of deformed austenite of Ti-Mo microalloyed steel and Ti-Zr-Mo microalloyed steel at four deformation temperatures of 875, 925, 975 and 1025 ℃ was studied. The true stress-true strain curves of the two kinds of tested steels during two-pass compression simulation were analyzed. The static recrystallization kinetic models of the tested steels were established. The austenite static recrystallization activation energy of the tested steels was calculated. After two-pass compression at different temperatures, the morphologies and types of the deformation-induced precipitated phase and the large-particle undissolved phase in the tested steels were observed by a high-resolution transmission electron microscope. And the deformation energy storage density in the tested steels was simply compared. The results show that the addition of Zr can increase the deformation resistance of Ti-Mo microalloyed steel during deformation, increase the accumulated deformation storage energy during the hot deformation, reduce the static recrystallization activation energy of deformed austenite, and make the recrystallization of austenite easier to occur. Zr can replace Ti to form the undissolved phase with O, S and other elements, so that finer and more dispersed deformation-induced precipitates in the tested steel are precipitated during static recrystallization, and the static recrystallization process of deformed austenite of the tested steel is delayed.

  Effect of stress on recrystallization of single crystal superalloy

  Li Yongshun, Xuan Weidong, Duan Fangmiao, Zhao Yujuan, Li Junjie, Wang Baojun, Ren Xingfu, Ren Zhongming

  2022, 47(2):  48-52.  doi:10.13251/j.issn.0254-6051.2022.02.009

  Abstract ( 60 )   PDF (558KB) ( 23 )  

  Effect of stress on recrystallization formation law of single crystal superalloy was studied through a combination of experiment and theoretical calculation. The results show that the formation of recrystallization is closely related to stress. Recrystallization only occurs when the applied stress is higher than the critical stress, but not occur when the applied stress is lower than the critical stress, meanwhile the critical stress of recrystallization decreases with the increase of temperature. At the same temperature, the thickness of recrystallization layer of the tested alloy increases linearly with the increase of stress. Under the same stress, the thickness of recrystallization layer increases exponentially with the increase of temperature. In addition, with the increase of temperature, the increasing rate of recrystallization layer thickness accelerates due to the increase of stress.

  Kinetics of austenite grain growth of 15Cr12CuSiMoMn steel

  Yang Jie, Ren Huiping, Liu Zongchang

  2022, 47(2):  53-58.  doi:10.13251/j.issn.0254-6051.2022.02.010

  Abstract ( 66 )   PDF (626KB) ( 20 )  

  15Cr12CuSiMoMn steel was heated to the austenitizing temperature range between 900-1100 ℃ in a box-typed furnace for 15-120 min respectively. The growth behavior of prior austenite grains under different austenitizing temperatures and soaking time was studied. The experimental results show that with the increase of austenitizing temperature, the grain size increases continuously, and the growth behavior shows a law of power function. Heated above 1000 ℃, grain coarsens obviously. With the prolongation of time, the grain growth behavior is similar to the parabolic uniform deceleration law. When the soaking time is less than 60 min, the grain growth rate is faster, and tends to be stable when the soaking time is more than 60 min. Based on Arrhenius formula, a dynamic model of grain growth is established through the linear regression analysis of experimental data. The error(2%＜ΔXi＜5%) between model calculation and actual measured data is compared and the accuracy and reliability of the model are verified.

  Effect of hot deformation on recrystallization behavior of niobium-bearing austenitic stainless steel 07Cr18Ni11Nb

  Shu Wei, Song Liqiang, Zhang Wei

  2022, 47(2):  59-64.  doi:10.13251/j.issn.0254-6051.2022.02.011

  Abstract ( 67 )   PDF (555KB) ( 24 )  

  Effect of hot deformation on recrystallization behavior of niobium-bearing austenitic stainless steel 07Cr18Ni11Nb was investigated by thermal simulated compression test and pilot hot rolling test. The results show that the recrystallization degree of the steel increases with the increase of deformation temperature, deformation amount and holding time. When the deformation temperature and deformation amount are higher, the holding time required for recrystallization is shorter. The longer the holding time, the more obvious the growth of recrystallized grains. During rolling deformation, recrystallization is easier to occur at the quarter thickness of hot-rolled plate. With the increase of rolling temperature and deformation amount, fully recrystallized grains can be obtained at 1050 ℃ with rolling deformation of 25%.

  Development of 800 MPa grade hot-rolled galvanized complex phase steel

  Zou Ying, Liu Huasai, Han Yun, Wang Chaobin, Wang Haiquan

  2022, 47(2):  65-69.  doi:10.13251/j.issn.0254-6051.2022.02.012

  Abstract ( 75 )   PDF (558KB) ( 16 )  

  A Nb and Ti microalloyed low-carbon complex phase steel was designed, and the evolution of microstructure, precipitates and mechanical properties of the hot-rolled complex phase steel during annealing and galvanizing was studied by means of SEM, TEM, mechanical properties test. Moreover, the industrial trial production of 800 MPa hot-rolled galvanized complex phase steel was carried out. The results show that, the microstructure of the hot-rolled complex phase steel is mainly composed of ferrite, martensite and M/A island. During annealing and galvanizing, the martensite and M/A island are decomposed to form high-temperature tempered martensite, and the density of glissile dislocation in ferrite is decreased, and the nano-scale composite carbides of Nb, Ti and Mo are precipitated at the same time, resulting in a decrease of tensile strength, a significant increase of yield strength and hole expansion ratio. The microstructure of the hot-rolled galvanized complex phase steel is mainly composed of ferrite and high-temperature tempered martensite. The yield strength, tensile strength, elongation after fracture and bake hardening value are 769 MPa, 852 MPa, 14.5% and 43 MPa, respectively, and the hole expansion ratio reaches 53%, indicating excellent mechanical properties and local formability.

  Effect of Ti content on recrystallization temperature and mechanical properties of IF steel

  Feng Yundong, Zou Yuming, Ding Hua

  2022, 47(2):  70-73.  doi:10.13251/j.issn.0254-6051.2022.02.013

  Abstract ( 55 )   PDF (563KB) ( 21 )  

  Effect of Ti content on recrystallization temperature and mechanical property change of the cold-rolled IF steel annealed at different temperatures was studied by means of hardness test, tensile test, field emission scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the size, distribution and volume fraction of nano-precipitates in the IF steel decrease with the decrease of Ti content, and the pinning effect and recrystallization temperature decrease. After annealing at 630 ℃ for 10 h, the yield strength, tensile strength, elongation, strain hardening exponent (n value) and plastic strain ratio (r value) of the IF steel with lower Ti content are 198 MPa, 312 MPa, 36.78%, 0.25 and 2.42, respectively, which meet the performance requirements of ultra-deep drawing steels.

  Oxidation behavior of Fe-40%Ni alloy at high temperature

  Li Jing, Yang Yuehui, Yuan Shaoqiang, Zhang Xiaojuan

  2022, 47(2):  74-77.  doi:10.13251/j.issn.0254-6051.2022.02.014

  Abstract ( 48 )   PDF (568KB) ( 25 )  

  Oxidation behavior of Fe-40%Ni alloy was studied by measuring the thickness of oxide layer generated at high temperature for different time, and the mathematical model for predicting the thickness of oxide layer was obtained by regression analysis. The results show that the thickness of oxide layer increases slowly when the temperature is lower than 1000 ℃, and increases significantly when the temperature is above 1000 ℃. With the extension of holding time, the thickness of oxide layer increases at a certain rate and has an approximate linear relationship with the holding time. At higher temperature, the relationship changes to parabolic type gradually. The result of regression analysis indicates that the oxide layer thickness(μm)can be calculated by the formula h=6700×t^0.44×e^-6870/T.

  PROCESS RESEARCH

  Effect of pre-treatment on microstructure and intergranular corrosion behavior of Al-Mg-Si alloy for automobile

  Min Xudong, Huang Yuanchun, Xiao Zhengbing, Liu Yu, Ren Xianwei, Zou Ti

  2022, 47(2):  78-85.  doi:10.13251/j.issn.0254-6051.2022.02.015

  Abstract ( 63 )   PDF (560KB) ( 33 )  

  Evolution laws of microstructure and intergranular corrosion behavior of the Al-Mg-Si alloy after bake hardening under different pre-treatment conditions were studied by tensile test, intergranular corrosion test, electrochemical test, metallographic microscope and transmission electron microscope. The results show that with the increase of pre-straining amount, the quantity density and size of grain boundary precipitates of the tested alloy decrease correspondingly, while the intragranular precipitates (β″ phase) increase in precipitation quantity and decrease in size, so that the tested alloy pre-treated differently has different comprehensive properties. The pre-treatment process composed of pre-straining and pre-aging is very beneficial to improve the comprehensive properties of Al-Mg-Si alloy, the intergranular corrosion resistance and bake hardening property are significantly improved, which is mainly attributed to the fact that the tested alloy do not form precipitation-free zone during bake hardening process, the grain boundary precipitates are less and discontinuous, and the matrix strengthening phase (β″ phase) is fully precipitated by consuming a large number of solute atoms.

  Preparation and mechanical properties of 304 stainless steel with heterogeneous lamella structure

  Yu Chonghao, Liu Jia, Deng Xiangtao, Wang Zhaodong

  2022, 47(2):  86-90.  doi:10.13251/j.issn.0254-6051.2022.02.016

  Abstract ( 48 )   PDF (556KB) ( 18 )  

  304 austenitic stainless steel with heterogeneous lamella structure (HLS) was fabricated by deformation induced martensite annealing reversion process. Microstructure was characterized by scanning electron microscope (SEM) and phase composition was analyzed by means of X-ray diffractometer (XRD). The mechanical properties of the 304 stainless steel with different grain sizes were studied systematically by means of quasi-static uniaxial tensile test at room temperature. The results show that after hot rolling with deformation of 34%, cold rolling with deformation of 75% and annealing at 700 ℃ for 12 min, the martensite in the tested steel reversely transforms to austenite, and part of the retained austenite is recrystallized. The original coarse grain structure is morphed into heterogeneous lamella structure, which is composed of nano/ultrafine grains, a proper amount of recrystallized grain clusters and retained austenite grains. Recrystallized grain clusters and retained austenite grains are sandwiched by nano/ultrafine grains. It is especially noted that a high yield strength of 940.1 MPa and a good percentage total extension at fracture of 43.1% can be simultaneously obtained for the HLS specimen with superior strength-ductility synergy.

  Effect of intercritical tempering temperature on microstructure and mechanical properties of Fe-4Mn-1.2Cr-0.3Cu-0.6Ni medium manganese steel

  Liu Tao, Wu Hongyan, Gao Xiuhua, Qin Dongyang, Du Linxiu

  2022, 47(2):  91-98.  doi:10.13251/j.issn.0254-6051.2022.02.017

  Abstract ( 50 )   PDF (556KB) ( 20 )  

  Effect of intercritical tempering temperature on microstructure and mechanical properties of Fe-4Mn-1.2Cr-0.3Cu-0.6Ni medium manganese steel was studied. The tested steel was prepared by direct quenching after hot rolling and intercritical tempering. The microstructure and mechanical properties of the quenched after rolling and tempered tested steels were characterized by means of optical microscope (OM), scanning function of electron probe microanalyzer (EPMA), transmission electron microscope (TEM), tensile test and impact test. The results show that the lath martensite with higher dislocation density can be obtained in the tested steel quenched after hot rolling, and the composite structure of retained austenite distributed on the tempered martensite matrix can be formed after intercritical tempering. With the increase of intercritical tempering temperature, the tensile strength of the tested steel increases, while the yield strength first decreases and then increases. The change trend of elongation is related to the content of retained austenite in the tested steel. The impact property first increases and then decreases with the increase of intercritical tempering temperature. The tensile properties of the tested steel tempered at 630 ℃ is the best, but the impact property of the tested steel tempered at 650 ℃ is the best, so that the optimum intercritical tempering temperature range is determined to be 630-650 ℃.

  Microstructure, wear and corrosion resistant properties of TA2 titanium alloy after vacuum induction carbonitriding

  Xiang Qing, Jiang Xueting, Wu Liangyin, Ran Xiaoxiao, Liu Jing, Yang Feng

  2022, 47(2):  99-104.  doi:10.13251/j.issn.0254-6051.2022.02.018

  Abstract ( 74 )   PDF (556KB) ( 27 )  

  Pure titanium alloy (TA2) was modified by vacuum induction carbonitriding at 900 ℃, and the microstructure, wear and corrosion resistance properties of the surface strengthening layer of TA2 titanium alloy after carbonitriding were studied. The results show that a composite layer of C_0.3N_0.7Ti is formed on the surface of TA2 titanium alloy after carbonitriding at 900 ℃, the microhardness of the surface layer is as high as 2236 HV0.25, which is about 4.4 times higher than that of the specimen without carbonitriding. After carbonitriding, the specimen shows typical mild oxidation wear characteristics. In addition, in simulated body fluid (SBF) solution, corrosion potential of the TA2 titanium alloy after carbonitriding moves forward, the self-corrosion current density decreases obviously and the corrosion resistance improves.

  Effect of quenching temperature on microstructure evolution and mechanical properties of Nb microalloyed gear steel 18CrNiMo7-6

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

  2022, 47(2):  105-111.  doi:10.13251/j.issn.0254-6051.2022.02.019

  Abstract ( 77 )   PDF (637KB) ( 24 )  

  Effect of quenching temperature on microstructure and mechanical properties of the Nb microalloyed gear steel 18CrNiMo7-6 was studied by means of Thermo-calc thermodynamic calculation software, scanning electron microscope, optical microscope, impact test and tensile test. The results show that with the increase of quenching temperature, the average austenite grain size of the Nb microalloyed gear steel increases, but remains below 20 μm, and the grain boundary stability is high. According to Thermo-calc thermodynamic calculation results, the main precipitates are Cr₇C₃, Cr₂₃C₆, NbC and AlN, among which the solution temperatures of Cr₇C₃ and Cr₂₃C₆ are relatively low (730 ℃ and 749 ℃, respectively), while the solution temperatures of NbC and AlN are relatively high (1180 ℃ and 1070 ℃, respectively). NbC and AlN are the carbonitrides that mainly pin grain boundaries and refine grains. There is a small amount of N element in NbC precipitates, and NbC tends to change to Nb(C, N) at a certain temperature. The yield strength decreases with the increase of quenching temperature, the tensile strength plateaus at 860 ℃, and the impact absorbed energy increases first and then decreases. The Nb microalloyed gear steel 18CrNiMo7-6 has a wide process design window. The optimal heat treatment process is quenching at 860 ℃ and tempering at 180 ℃, after which the tensile strength is 1455 MPa, the yield strength is 1229 MPa, the impact absorbed energy is 100 J, and the hardness is about 44 HRC.

  Effect of forging heating temperature on austenite grain growth and mechanical properties of 20Cr2Ni4A steel

  Chen Jianwen, Yuan Wufeng, Jiang Yizhou, Zhang Chen, Yi Huaqing, Gao Yiqiang

  2022, 47(2):  112-118.  doi:10.13251/j.issn.0254-6051.2022.02.020

  Abstract ( 62 )   PDF (635KB) ( 22 )  

  Effects of forging heating temperature (1050-1200 ℃) and holding time (40-120 min) on grain growth behavior of austenite of the 20Cr2Ni4A steel with same forging deformation were studied, and the mechanical properties of the quenched 20Cr2Ni4A steel at different forging temperatures were tested. The results show that the austenite grain growth law of the 20Cr2Ni4A steel after forging still conforms to the Beck model when the forging temperature is lower than 1150 ℃, and the model calculated value is consistent with the actual measured value. As the forging heating temperature increases, the growth of austenite grains shows a law of increasing slowly and then rapidly. When the forging heating temperature exceeds 1150 ℃, a large number of second phase particles dissolve and the pinning effect on grain boundaries decreases sharply. Considering the austenite grain size uniformity after forging, mechanical properties test results after heat treatment and forgeability factors of the 20Cr2Ni4A steel, the optimal forging heating temperature is 1150 ℃.

  Effect of induction hardening on microstructure and properties of 42CrMo steel crankshaft connecting rod journal

  Wu Hui, Lin Shengyao, Li Xinkai, Gong Yuhui, Wei Deqiang

  2022, 47(2):  119-124.  doi:10.13251/j.issn.0254-6051.2022.02.021

  Abstract ( 77 )   PDF (694KB) ( 21 )  

  Effect of induction hardening treatment on sectional microstructure and residual stress of the 42CrMo steel crankshaft connecting rod journal was analyzed by means of OM, SEM, X-ray stress analysis and mechanical property test. The effect of quenching power on morphology, microstructure and mechanical properties of the hardened layer was discussed. The results show that the 42CrMo steel crankshaft connecting rod journal is composed of three parts: the hardened layer, the transition layer and the matrix. The microstructure of the hardened layer is uniform and fine martensite, the transition layer is a mixture of martensite and tempered sorbite, and the matrix is tempered sorbite. After induction hardening, the surface residual stress of the 42CrMo steel crankshaft connecting rod journal changes from tensile stress to compressive stress. With the increase of induction hardening power, the depth of hardened layer increases and the microstructure is refined continuously. When the quenching power is 2500 W, the microstructure is the most uniform and fine, the surface hardness reaches 751.3 HV0.1, and the wear resistance is greatly improved. However, too high induction hardening power will lead to microstructure coarsening. When the induction hardening power is 2600 W, the microstructure is coarsened and the hardness is reduced.

  Effect of quenching temperature on microstructure and mechanical properties of GE1014 ultra-high strength steel

  Liu Yue, Han Shun, Li Yong, Wang Chunxu, Yan Xiaohong, Li Jianxin

  2022, 47(2):  125-129.  doi:10.13251/j.issn.0254-6051.2022.02.022

  Abstract ( 51 )   PDF (636KB) ( 26 )  

  Effect of quenching temperature on mechanical properties and microstructure of the GE1014 ultra-high strength steel was studied by means of mechanical property test, transmission electron microscope (TEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and other analysis methods. The results show that with the increase of quenching temperature, the tensile strength of the tested steel increases first and then decreases and the peak value is 2112 MPa when quenched at 925 ℃, the proof strength, plastic extension decreases slightly with the increase of quenching temperature. The reduction of area and U-notched impact property of the tested steel increase slowly with the increase of quenching temperature, and decrease at near 950 ℃. Both the prior austenite grain size and martensite block size of the tested steel increase with the increase of quenching temperature. When the quenching temperature exceeds 925 ℃, the prior austenite grain coarsens rapidly, while the martensite block grows slowly throughout the whole process. In the range of 850-925 ℃, the volume fraction of retained austenite in the matrix decreases significantly with the increase of quenching temperature. When the quenching temperature is lower than 900 ℃, there are spherical Mo-rich M₆C carbides in the tested steel, while when higher than 900 ℃, no insoluble phase is observed.

  Effect of homogenizing on microstructure and properties of Invar alloy ingot

  Wu Yingfei, Sun Zhonghua, Wang Yufei, Wang Chengming, Zhang Yunfei, Peng Huifen

  2022, 47(2):  130-136.  doi:10.13251/j.issn.0254-6051.2022.02.023

  Abstract ( 78 )   PDF (638KB) ( 20 )  

  Effect of heat treatment on microstructure, thermodynamic properties and impact property of Invar alloy ingot was investigated through homogenization annealing. The results show that after annealing treatment, the as-cast microstructure of the alloy is changed, the composition segregation is improved, the room temperature impact property is increased by about 7 times. Moreover, the high temperature deformation resistance is reduced, the high temperature thermoplasticity is improved, the high temperature brittleness range is reduced, and the thermal processing window becomes broader, all of which are beneficial to improve the efficiency and yield rate of hot working of the Invar alloy.

  Effect of continuous annealing process on microstructure and properties of 4.5%Cr cold-rolled weathering steel

  Yu Bo, Zhang Yi, Wang Zhanye, Chai Litao

  2022, 47(2):  137-140.  doi:10.13251/j.issn.0254-6051.2022.02.024

  Abstract ( 82 )   PDF (634KB) ( 19 )  

  Effect of annealing process on microstructure and properties of 4.5%Cr cold-rolled weathering steel was studied by simulating continuous annealing process with Multipas annealing machine. The results show that with the increase of annealing temperature, the strength of the tested steel first decreases and then increases. When the annealing temperature is 830 ℃, the strength is the highest, the average yield strength is 353 MPa, and the average tensile strength is about 621 MPa. The cooling rate of 50 ℃/s and 30 ℃/s has limited effect on strength of the tested steel. When the annealing temperature is lower than 800 ℃, only recovery and recrystallization in the tested steel occur, and the microstructure is composed of ferrite, pearlite and carbide. When the annealing temperature is higher than 800 ℃, the ferrite is austenitized and bainite is formed in the tested steel after cooling. When the mass fraction of Cr increases to 4.5%, the relative corrosion rate of the tested steel is 26%(relative to Q345B steel), and compared with ordinary weathering steel SPA-C, its weathering performance is doubled.

  Effect of annealing process on microstructure and properties of laser solid formed TC21 titanium alloy

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

  2022, 47(2):  141-145.  doi:10.13251/j.issn.0254-6051.2022.02.025

  Abstract ( 77 )   PDF (635KB) ( 17 )  

  TC21 titanium alloy block was prepared by the BLT-C1000 laser three-dimensional forming equipment, and the single-stage and two-stage annealing treatments were carried out, respectively. The influence of the single-stage and double-stage annealing processes on microstructure and mechanical properties of the alloy was studied. The results show that the deposited structure of TC21 titanium alloy by laser solid forming is mainly a basket-like microstructure. The single-stage annealing temperature affects the size of the primary α-phase slats. When annealed below 550 ℃, the length and width of the primary α-phase slabs change slightly. When annealed above 650 ℃, the length and width of the primary α-phase slabs increase significantly and the width will be slightly reduced. With the increase of heating temperature, the yield strength and tensile strength is decreased, while the elongation and reduction of area after fracture is increased. During double-stage annealing, with the increase of the first-stage annealing temperature, the amount of primary α phase is decreased, with the increase of the second-stage annealing temperature, the size of the secondary α phase is increased. Considering comprehensively, the first-stage annealing temperature of 870-900 ℃ and the second-stage annealing temperature of 560 ℃ are optimal for double-stage annealing.

  Effect of annealing temperature on microstructure and properties of Fe-24.38Mn-0.44C TWIP steel

  Dai Yongjuan, Wu Xiangxiang, Li Jiakun, Guo Dong, Wang Bo

  2022, 47(2):  146-152.  doi:10.13251/j.issn.0254-6051.2022.02.026

  Abstract ( 64 )   PDF (635KB) ( 37 )  

  Evolution of microstructure and mechanical properties of the cold-rolled Fe-24.38Mn-0.44C steel at different annealing temperatures (partial recrystallization annealing, recrystallization annealing and high temperature annealing) was studied by means of OM, TEM and tensile test at room temperature. The results show that with the decrease of annealing temperature, the microstructure of the tested steel changes from the coarse undistorted equiaxed recrystallized grains to the mixture structure of nano deformed twins and fine recrystallized grains. The strengthening mechanism gradually changes from twin slip to dislocation slip, supplemented by nano twin strengthening, which leads to a rapid increase of yield strength, an increase of yield ratio from 0.36 to 0.49 and a decrease of elongation.

  Microstructure and fatigue crack growth of a bainitic steel under different heat treatments

  Dong Rui, Chen Lin, Cen Yaodong, Bao Xirong

  2022, 47(2):  153-158.  doi:10.13251/j.issn.0254-6051.2022.02.027

  Abstract ( 66 )   PDF (633KB) ( 20 )  

  Microstructure and fatigue crack growth rate of a bainitic steel under four different heat treatment processes were studied. The results show that the microstructure of the hot rolled tested steel mainly consists of granular bainite with a small amount of lath bainite, martensite and coarse M/A islands. The volume fraction of retained austenite is 16.2%, but with poor stability. The crack can propagate continuously by directly through the coarse M/A islands, and the fatigue crack propagation rate is the fastest. After austenitizing at 900 ℃ and air cooling, the microstructure turns into lath bainite and martensite mainly, still with coarse massive M/A islands, the content of retained austenite is reduced to 12.3%, and the fatigue crack growth rate is slightly reduced. After austenitizing at 900 ℃ plus holding in salt bath at 380 ℃ for 30 min then air cooling, the microstructure is mainly composed of fine and ordered lath bainite, the retained austenite content reduces to 10.2%, which is associated between bainite laths in the form of thin film. Both such lath bainite and thin film retained austenite can lead to the passivation, bifurcation and deflection of the crack tip, and enhance the ability of hindering crack propagation. After tempering at 350 ℃ for 240 min, the main microstructure evolves into martensite and lath bainite, and the content of retained austenite is 14.9%, which is lower than that of hot rolled tested steel. While, after tempering at 450 ℃ for 240 min, the microstructure mainly consists of lath bainite with a small amount of martensite distributed on it, and the volume fraction of retained austenite reduces to 8.6%, which is also associated between bainite laths in thin film form, with a large number of carbides precipitated, and the crack growth rate is the slowest.

  Effect of quenching process on microstructure and mechanical properties of medium manganese steel bearing Ni

  Chen Linheng, Tang Qibo, Wu Huibin, Zhao Jinbin, Bo Feihu

  2022, 47(2):  159-163.  doi:10.13251/j.issn.0254-6051.2022.02.028

  Abstract ( 47 )   PDF (632KB) ( 24 )  

  Effect of quenching process on microstructure and mechanical properties of a medium manganese steel containing 1% (mass fraction) Ni was studied by means of SEM observation, tensile test and low temperature impact test. The results show that with the increase of quenching temperature, the yield strength, tensile strength and impact property of the tested steel first increase, then decrease, and then gradually increase. The optimal quenching and tempering process of the tested steel is quenching at 900 ℃ and tempering at 600 ℃, at which the yield strength, tensile strength and elongation can reach 560 MPa, 640 MPa and 21.8%, respectively, and the impact absorbed energy of the tested steel at -50 ℃ can reach 270 J, the good comprehensive mechanical properties can be obtained. The quenched and tempered tested steel obtains ferrite and tempered martensite under different quenching processes, the proportion of martensite increases and the grain size gradually decreases with the increase of quenching temperature.

  Effect of isothermal temperature on semi-solid microstructure of 7075 aluminum alloy prepared by rolling SIMA method

  Yu Xinlei, Zheng Xiaoping, Cao Tong, Tian Yaqiang, Chen Liansheng

  2022, 47(2):  164-167.  doi:10.13251/j.issn.0254-6051.2022.02.029

  Abstract ( 46 )   PDF (633KB) ( 24 )  

  7075 aluminum alloy semi-solid billets were prepared by strain induced melting activation(SIMA) method with pre-deformation modes of synchronous rolling and asynchronous rolling respectively. The effects of roll diameter ratio and isothermal temperature on microstructure evolution of pre-deformed sheet during heat treatment were studied. The results show that with the increase of isothermal temperature,a large amount of liquid phase are formed in the primary solid phase, and a large number of eutectic phases appear after solid inter-granular cooling. Under the same heat treatment conditions, the pre-deformation process of asynchronous rolling can produce more liquid phase and the semi-solid process is faster than the pre-deformation process of synchronous rolling. The optimum process conditions for obtaining semi-solid billets are asynchronous rolling pre-deformation and isothermal temperature of 610 ℃.

  Heat treatment distortion control of aero-engine output shaft made of 16Ni3CrMoE steel

  Lu Rui, Ke Wenmin, Kuang Qiao, Rao Liangbin, Ding Qi, Lu Jinxiang

  2022, 47(2):  168-172.  doi:10.13251/j.issn.0254-6051.2022.02.030

  Abstract ( 46 )   PDF (632KB) ( 19 )  

  After carburizing and quenching, an aero-engine output shaft made of 16Ni3CrMoE steel was occurred axial length shortening and internal spline deformation, the reasons of which were analyzed. The results show that the main influencing factors of heat treatment deformation are the comprehensive effect of thermal stress and transformation stress generated in the process of carburizing and quenching of the parts. There are differences in the composition of the surface and the core of carburized parts, which makes the stress distribution in the process of heat treatment more uneven and complicated. The heat treatment distortion of the parts is controlled within the process requirements by means of changing the mode of carburizing furnace, reducing the carburizing cooling rate, static oil austempering, adding stabilization treatment before carburizing.

  Effect of heat treatment process on microstructure and properties of Inconel 617 alloy tube

  Liu Yujun, Cheng Xiaonong, Luo Rui, Gao Pei

  2022, 47(2):  173-177.  doi:10.13251/j.issn.0254-6051.2022.02.031

  Abstract ( 271 )   PDF (639KB) ( 30 )  

  In order to explore the heat treatment process of the alloy tube, the effects of different heat treatment parameters on microstructure and mechanical properties of Inconel 617 alloy tube were studied by means of optical microscope (OM), hardness and tensile test at room temperature, etc. The alloy was characterized by optical microscope, and the variation rule of the grain size of the alloy was analyzed when the temperature between 1120-1200 ℃ and the holding time was 10 and 30 min, respectively, and the dynamic model of grain size growth was established. The results show that the average grain size increases with the increase of temperature, and there are more twins in the grain. At the same time, with the continuous increase of heat treatment temperature, the change trend of hardness and tensile strength of the alloy is the same, both of them show a decreasing trend with the increase of temperature. The elongation of the alloy increases with the increase of temperature. The apparent activation energy of grain boundary migration of the Inconel 617 alloy is 651.82 kJ/mol.

  Effect of heat treatment process on microstructure and properties of Cr15Ni2MnMoCuNbRE cast steel

  Song Yanpei, Chen Danping, Zhou Han, Lin Xiaoli, Li Li

  2022, 47(2):  178-182.  doi:10.13251/j.issn.0254-6051.2022.02.032

  Abstract ( 60 )   PDF (633KB) ( 19 )  

  Microstructure, mechanical properties and corrosive wear resistance of the Cr15Ni2MnMoCuNbRE cast steel treated by different heat treatment processes were investigated by means of SEM, mechanical property testing machine and corrosion-wear tester. The results show that the microstructure of the tested steel treated at 860 ℃ consists of austenite and network carbide. With the increase of heat treatment temperature, the microstructure and properties of the tested steel are improved. When heating temperature increases from 860 ℃ to 1000 ℃, the intergranular carbide amount of the tested steel decreases, the carbide morphology changes from network into fine rod shape, and the mechanical properties and corrosive wear resistance of the tested steel are improved significantly. Compared with that heat treated at 860 ℃, the hardness and impact absorbed energy of the tested steel heat treated at 1000 ℃ are increased by 5.9% and 49.8%, respectively, which reach 57.5 HRC and 35.5 J, and the corrosive wear resistance is increased by 1.88 times.

  Effect of cryogenic treatment on surface properties of TC4 titanium alloy

  Shi Youjie, Li Yonggang, Li Wenhui, Wang Xingfu

  2022, 47(2):  183-187.  doi:10.13251/j.issn.0254-6051.2022.02.033

  Abstract ( 95 )   PDF (636KB) ( 29 )  

  Effect of cryogenic treatment on barrel polishing and finishing and surface properties of the TC4 titanium alloy was studied. The TC4 titanium alloy specimen was subjected to cryogenic treatment, and the specimens under different cryogenic time were barrel polished and finished. After determining the appropriate cryogenic time according to the surface roughness, the changes of microstructure, microhardness and residual stress of the alloy specimens before and after cryogenic treatment were compared and analyzed. The change of surface morphology of the alloy after cryogenic treatment and barrel polishing and finishing was investigated by means of scanning electron microscope. The results show that the surface roughness of the specimen is the smallest after cryogenic treatment for 12 h, and the structure is affected by the internal stress of cold shrinkage, so that the proportion of α phase rises from 56.45%(untreated) to 85.42%, and the structure becomes uniform and dense. The microhardness of the alloy is the highest when cryogenic treated for 12 h, which is increased by 3.47% compared with untreated specimen. The surface residual compressive stress of the specimen increases by 26.26% after cryogenic treatment for 12 h and barrel polishing and finishing, compared with untreated specimen. Roughness measurement and scanning electron microscope results show that cryogenic treatment enhances the machinability of the titanium alloy specimen. The surface roughness of the specimen cryogenic treated for 12 h can reduce from about 0.500 μm(untreated specimen) to about 0.250 μm after barrel polishing and finishing, and the surface quality is significantly improved.

  Solution treatment and aging processes for a nickel-saving superalloy for automobile engine valve

  Zeng Yu, Wu Wei, Mo Yan

  2022, 47(2):  188-192.  doi:10.13251/j.issn.0254-6051.2022.02.034

  Abstract ( 72 )   PDF (632KB) ( 19 )  

  Microstructure, hardness and mechanical properties of a nickel-saving superalloy for automobile engine valve treated by different heat treatments were studied. The results show that the grain size of the tested alloy increases and the hardness decreases with the increase of solution treatment temperature in the range of 900-1100 ℃. When the temperature exceeds 1050 ℃, the grains grow clearly and coarsen rapidly. The solution treatment temperature should be controlled in the range of 1000-1050 ℃ to ensure the necessary precipitation conditions of the main strengthening phase and to obtain appropriate grain size. In the range of 700-760 ℃, the strength of the tested alloy increases gradually with the increase of aging temperature, but the ductility decreases gradually. When the solution treatment and aging processes are 1020 ℃×30 min(solution treatment with water cooling)+720 ℃×4 h(aging with air cooling), the tested nickel-saving superalloy can obtain preferable combination of strength and toughness and can meet the technical requirements.

  SURFACE ENGINEERING

  Preparation and corrosion resistance of highly adhesive superhydrophobic surface

  Lin Hongchun, Ma Dandan, Yu Shengwang, Ma Yong, Zhou Bing, Gao Jie, Hei Hongjun, Xue Yanpeng

  2022, 47(2):  193-199.  doi:10.13251/j.issn.0254-6051.2022.02.035

  Abstract ( 44 )   PDF (635KB) ( 17 )  

  Co-Ni transition layer was prepared on carbon steel substrate using electrochemical deposition, then Cr coating was deposited on the Co-Ni transition layer by double glow plasma surface alloying technique (DGPSA). After modification by PFTEOS solution, a superhydrophobic coating with high adhesion was prepared. The morphology, phase composition, wetting performance, adhesion property and corrosion resistance of the coating were characterized by means of scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffractometer (XRD), X-ray photoelectron spectrometer (XPS), contact angle measuring instrument and electrochemical test, respectively. The influence of deposition time of DGPSA technique on surface morphology and wetting performance was explored. The results show that the superhydrophobic surface with a papillary structure and high adhesion is prepared under the deposition temperature of 750 ℃ for 30 min. The water contact angle reaches 159° and the water droplet don't roll off even if the specimen is tilted 180°. The electrochemical test results demonstrate that the as-prepared superhydrophobic surface exhibits excellent corrosion protection for carbon steel substrate.

  Microstructure and properties of additional and in situ synthesized WC particle reinforced iron-based coatings prepared by plasma cladding

  Zhang Mengliang, Tang Wenbo, Li Baiqi, Wang Xiaosheng, Li Wenqiang, Wang Tengfei

  2022, 47(2):  200-204.  doi:10.13251/j.issn.0254-6051.2022.02.036

  Abstract ( 73 )   PDF (633KB) ( 16 )  

  Additional and in situ synthesized WC particle reinforced iron-based composite coatings were fabricated on Q235 steel substrate by plasma cladding technique with raw material of iron based alloy powder, nickel-coated graphite, tungsten iron powder, and cast tungsten carbide. The microstructure, phase composition, hardness and wear resistance were examined by SEM, XRD, hardness test and abrasive wear test, respectively. The results show that the coating with good metallurgical bonding to substrate can be obtained under optimal process parameters. Except for added WC particles, the coating has hard phases such as WC, W₂C, W₃C, Fe₃W₃C and Fe₂W₂C, which are in situ synthesized. With the increase of W content in the mixed powder except for added WC particles, the density of the alloy liquid in the molten pool increases, which can reduce the sinking of the additional WC particles. When the content of W reaches 15%, the added WC particles are evenly distributed in the coating, and there is no agglomeration of WC particles in the coating. And there are fine in situ synthesized WC particles around the additional WC particles, and the microhardness and wear resistance of the coating are significantly improved. The average microhardness of the coating with W content of 15% is capable of reaching about 1300 HV0.2, the wear resistance is 10 times that of the Q235 steel matrix.

  Research status and prospect of laser cladding technology on stainless steel surface

  Ding Tao, Zhang Yunhua, Li Junjie, Liu Jin, Liu Yan

  2022, 47(2):  205-212.  doi:10.13251/j.issn.0254-6051.2022.02.037

  Abstract ( 63 )   PDF (565KB) ( 23 )  

  Research status of laser cladding technology on stainless steel surface was reviewed. The research progress of materials used for laser cladding on stainless steel surface and the factors affecting the quality of clad layer were introduced in detail. The development directions of laser cladding technology on stainless steel surface are prospected.

  Effect of plasma surface metallizing Nb on diffusion welding performance of γ-TiAl alloy

  Sun Dingbang, Wang Yongsheng, Gao Jie, He Zhiyong, Wu Yanxia, Zhou Bing, Ma Yong, Yu Shengwang

  2022, 47(2):  213-218.  doi:10.13251/j.issn.0254-6051.2022.02.038

  Abstract ( 60 )   PDF (567KB) ( 17 )  

  Double glow plasma metallizing technology was used to prepare Nb coating on the surface of γ-TiAl alloy with a nominal composition of Ti-45Al-8.5Nb (W, B, Y). Effect of Nb depositing temperature and welding temperature on microstructure and properties of the γ-TiAl alloy diffusion welded joints was studied by SEM, EDS, XRD, etc. The results show that dense Nb coating can be formed on the γ-TiAl alloy at the Nb depositing temperature range of 800-950 ℃. The grain size and roughness of the Nb coating increase continuously with the increase of Nb depositing temperature. The typical joint structure from the substrate to welded center can be divided into 4 layers: layer I (diffusion layer between substrate and Nb coating), layer II (Ti-Nb miscible layer containing small amount of AlNb₂), layer III (Ti-riched TiNi layer), layer IV (near equiatomic TiNi layer). The shear strength of the joint increases first and then decreases with the increase of Nb depositing temperature and welding temperature. The joint prepared at Nb depositing temperature of 850 ℃ and diffusion welding temperature of 900 ℃ achieves the highest shear strength, up to 82.0 MPa.

  Comparative analysis of corrosion resistance in molten aluminum of H13 steel with different surface treatments

  Wang Duo, Zhao Guohua, Yang Wenhao, Wang Yupeng, Wang Shuaikang, Bao Mingdong

  2022, 47(2):  219-223.  doi:10.13251/j.issn.0254-6051.2022.02.039

  Abstract ( 79 )   PDF (566KB) ( 35 )  

  H13 steel specimens were subjected to nitriding and sulphonitrocarburizing treatments after vacuum heat treatment, and then immersed in 700 ℃ high temperature molten aluminum for corrosion test. And the cross-section microstructure, mass loss and phase composition of the specimens before and after corrosion were analyzed in detail. The results show that the interface bonding mode of infiltration layer is similar for the nitrided specimen and the sulphonitrocarburizing specimen, which is smooth and dense, the boundary between layer and matrix is relatively flat. There are Fe₃N, Fe₂N, FeS, Fe₃C phases in the surface compound area of the sulphonitrocarburized specimen, with the FeS phase being a typical close-packed hexagonal crystal structure with higher hardness. There are Fe₃N and Fe₂N phases in the surface compound area of the nitrided specimen, and the surface hardness of which is higher than that of the sulphonitrocarburized specimen. Under the same corrosion conditions, the mass loss and mass loss rate of the vacuum heat treated specimen are 7.5 g and 21.1%, respectively, those of the nitrided specimen are 4.1 g and 11.2%, respectively, those of the sulphonitrocarburized specimen are 0.8 g and 2.2%, respectively. The iron-aluminum compound of the specimens is embedded in the steel matrix in a zigzag shape, and the thickness is 184.75, 88.56 and 35.88 μm, respectively. The main compound after corrosion by molten aluminum is Fe₂Al₅, and the sulphonitrocarburized specimen can form FeS and Fe₃C with the H13 steel matrix due to the addition of S and C, showing the best high temperature corrosion resistance in molten aluminum.

  Microstructure and reflectivity of Cr/AlCr(Si)N coating for sensors

  Liu Liping

  2022, 47(2):  224-228.  doi:10.13251/j.issn.0254-6051.2022.02.040

  Abstract ( 50 )   PDF (563KB) ( 17 )  

  Cr/AlCrN and Cr/AlCrSiN coatings were prepared on the surface of Ni-11Cr alloy by multi-arc ion plating process. The coatings were treated at 700-900 ℃ by vacuum heat treatment. The effects of heat treatment temperature and Si element on microstructure and infrared reflectivity of the Cr/AlCr(Si)N coatings were investigated. The results show that the characteristic peaks of Cr₂O₃ and Al₂CrO₃ are formed in the two coatings after vacuum heat treatment, and the characteristic diffraction peaks of oxide crystal structure increases obviously after heat treatment at 900 ℃. The microstructure of the two coatings are columnar. There are many hcp-CrN nanocrystals in the Cr/AlCrN coating. The hcp-AlN nanocrystals with uniform particle size are formed in the Cr/AlCrSiN coating. The higher the heat treatment temperature is, the higher the infrared reflectivity of the two coatings will be, and the diffusion coefficient of Ni increases monotonically with the increase of heat treatment temperature. The Cr/AlCrN coating has excellent low infrared reflectivity, while the Cr/AlCrSiN coating has higher infrared reflectivity.

  NUMERICAL SIMULATION

  Finite element analysis of novel martensitic heat-resistant steel G115 heavy castings

  Zhao Xin, Chen Zhengzong, Zhao Haiping

  2022, 47(2):  229-235.  doi:10.13251/j.issn.0254-6051.2022.02.041

  Abstract ( 42 )   PDF (566KB) ( 23 )  

  In order to optimize the normalizing and tempering treatment processes of G115 steel thick wall hollow castings, the influence of normalizing and tempering heat treatment process on the temperature field distribution of the casting was analyzed by finite element method. The results show that in the normalizing process, the temperature at the lower edge of the castings is the highest and the heating rate is the fastest, and the inner surface temperature at about 1/4 of the upper end is the lowest and the heating rate is the slowest. In the tempering process, the temperature variation of the castings is similar to that of the normalizing process. The holding time of the lower edge of the castings at the target temperature is the longest, and the holding time at the center of about 1/4 section thickness at the upper end is the shortest. Combined with heating rate, temperature difference, heating efficiency and production cost, normalizing process ② and tempering process ③ are optimized. The microstruture and mechanical properties of the G115 steel casting after heat treating by optimal process are uniform and significantly higher than those of the CB2 steel.

  Post weld heat treatment process to eliminate welding distortion of large structural parts

  Zhang Jingang, Chao Lining, Wang Qiang, Yang Xiaolong, Zhou Xinyi, Tang Jiarui

  2022, 47(2):  236-242.  doi:10.13251/j.issn.0254-6051.2022.02.042

  Abstract ( 61 )   PDF (566KB) ( 26 )  

  Distortion distribution of large welded structural parts before and after post weld heat treatment was simulated by using finite element software. The results show that the maximum distortion of the welded structural parts is mainly concentrated at the middle parting flange. By simulating the overall distortion and the distortion distribution of the structural flange, the results show that after post weld heat treatment at 650 ℃ for 6 h, the overal distortion of the structural parts is small, and the distortion distribution of the structural flange shows a good mirror symmetry with that of the welded one, which effectively improves the post welding distortion and is beneficial to the size stability of the structural parts.

  Influence law and mechanism of medium flow density on heat exchange rate of jet quenching interface of aluminum alloy

  Xu Rong, Li Luoxing

  2022, 47(2):  243-249.  doi:10.13251/j.issn.0254-6051.2022.02.043

  Abstract ( 62 )   PDF (570KB) ( 19 )  

  The heat exchange processes of water jet quenching, spray quenching and high speed air quenching on high temperature aluminum alloy surface were studied by jet quenching test. The heat flux (q) and heat transfer coefficient (h) of the three kinds of on-line quenching interface were calculated by back analysis method, and the influence law and mechanism of the medium flux density (q_s) on the interface heat exchange rate were mainly investigated. The results show that with the increase of q_s, the heat exchange rate of quenching interface increases first and then decreases. There is a critical q_s, when the critical heat current density (q_c) reaches the maximum value. When q_s is less than its critical value, the interfacial heat exchange rate increases with the increase of q_s. When q_s is greater than the critical value, the interfacial heat exchange rate decreases with the increase of q_s.The maximum heat absorption (Q_max) of the unit volume cooling medium in spray quenching is the highest, and when the quenching medium is the same, the Q_max decreases with the increase of q_s. Increasing q_s has the best effect on improving the heat exchange rate of water jet quenching surface.

  Thermal fatigue failure behavior of die-casting insert

  Cai Xianjie, Wu Boya, Zuo Pengpeng, Li Junwan, Guo Wei

  2022, 47(2):  250-256.  doi:10.13251/j.issn.0254-6051.2022.02.044

  Abstract ( 59 )   PDF (563KB) ( 20 )  

  Failure mechanism of the thermal fatigue failed die-casting insert used for 1200 times was analyzed, and thermo-mechanical coupled numerical analysis model of die-casting process was established. The evolution of temperature and stress field of the die-casting insert during working was studied, and its service life was predicted. The results show that the failure of the insert is due to the thermal fatigue behavior caused by the erosion of high temperature molten aluminum liquid and the rapid cooling of the coolant during the die casting process. During the cyclic die-casting, the stress concentration occurs at the corner of the bulge of the insert, and the maximum equivalent stress is about 788 MPa, where the thermal fatigue crack initiates and propagates. The low cycle fatigue life prediction law is used to predict the thermal fatigue life of the insert, and the result is about 1651 times, which is in agreement with the actual life. The thermo-mechanical coupled numerical model in this paper can provide a reference for the reliability design of the die-casting insert.

  Simulation of end quenching process and prediction of hardenability of Cr-Ni-Mo gear steel

  Zang Yan, Wang Jianjun

  2022, 47(2):  257-261.  doi:10.13251/j.issn.0254-6051.2022.02.045

  Abstract ( 63 )   PDF (565KB) ( 19 )  

  Hardenability curves of 20Cr, 20CrMo and 20CrNiMo steels were measured by end quenching experiments, and the effect of alloying elements on the hardenability was analyzed. The hardenability curves of the three steels with different compositions were simulated and calculated by using Abaqus software and Maynier microstructure prediction model. The results show that the hardenability of the 20Cr, 20CrMo and 20CrNiMo gear steels decreases in turn, and the measured values are in good agreement with those calculated by simulation, which indicates that this method can be used to predict the hardenability curve of the gear steel.

  FAILURE ANALYSIS

  Failure analysis of 20 steel equal-diameter tee

  Li Dejun, Gao Hua, Kong Xianglu, Yang Xiaoping, Li Ta, Dong Zhaoyuan, Zhang Xiaojia

  2022, 47(2):  262-266.  doi:10.13251/j.issn.0254-6051.2022.02.046

  Abstract ( 87 )   PDF (564KB) ( 43 )  

  Failure causes of failed 20 steel equal-diameter tee used in a metering skid were investigated through the fracture analysis, chemical composition analysis, microstructure analysis, Brinell hardness and electrochemical corrosion test combining with the manufacture process of the tee. The results show that the tee made of 20 steel seamless pipe by hydraulic cold expansion forming process does not meet the standard requirements of normalizing or annealing treatment. The embrittlement caused by work hardening is not eliminated, which leads to the reduction of defect tolerance of the tee, and then the brittle fracture. Moreover, the electrochemical corrosion properties of the failed tee decline clearly due to the cold deformation, and the corrosion of inner wall of the tee is aggravated, and then the corrosion pit on inner wall of the tee becomes the crack source of brittle fracture. It is recommended to enhance the quality supervision and ex-factory inspection of the tee.