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  • OVERVIEW
    Research progress on precipitation strengthening of FCC structure high-entropy alloys
    Lu Wenjie, Luo Xian, Huang Bing, Li Pengtao, Yang Yanqing
    2020, 45(9):  1-9.  doi:10.13251/j.issn.0254-6051.2020.09.001
    Abstract ( 83 )   PDF (697KB) ( 173 )  
    High entropy alloys (HEAs) are a new kind of alloys,which break through the traditional alloy design with one or two elements as principal constituent and a few elements as auxiliary constituent.As an important branch of high entropy alloy system,FCC structure HEAs show excellent properties,such as high damage tolerance,good irradiation resistance,high wear resistance and corrosion resistance.However,the strength-ductility tradeoff dilemma of FCC structure HEAs severely limits their engineering applications.Previous researches indicate that precipitation strengthening can effectively improve the strength of FCC structure HEAs and produce excellent strength-ductility synergy properties.The research progress on precipitation strengthening of FCC structure HEAs was mainly introduced,including incoherent and coherent precipitates.The current research status and underlying influence mechanisms of precipitation-strengthening were briefly reviewed.The future prospective of precipitation-strengthening in FCC structure HEAs was also discussed.
    Research status of thermal fatigue mechanisms and performance improvement of hot work die steel
    Zhang Xu, He Wenchao, Li Donghui, Xiao Maoguo, Li Shaohong
    2020, 45(9):  10-20.  doi:10.13251/j.issn.0254-6051.2020.09.002
    Abstract ( 72 )   PDF (614KB) ( 24 )  
    Thermal fatigue performance of hot work die steel is the main factor that affects the service life of dies.The research status and evaluation methods of thermal fatigue performance of hot work die steel were overviewed,the effects of structural evolution,crack initiation and propagation on thermal fatigue performance were analyzed.At the same time,the factors influencing the thermal fatigue performance and the methods to improve the thermal fatigue performance were discussed and summarized,and the trend of the thermal fatigue research of hot work die steel was prospected.
    Research progress of stress corrosion cracking (SCC) of Al-Zn-Mg alloy
    Liu Jingfu, Zhou Xiangchun, Qu Yingdong
    2020, 45(9):  21-28.  doi:10.13251/j.issn.0254-6051.2020.09.003
    Abstract ( 64 )   PDF (618KB) ( 22 )  
    In view of the fact that stress corrosion cracking has become a bottleneck problem for further application of Al-Zn-Mg alloys,the research progress in recent years is summarized in this paper for the stress corrosion cracking of Al-Zn-Mg alloys at home and abroad.The effects of main alloying elements and trace elements on the stress corrosion cracking (SCC) of the alloy are described,and the function rule of heat treatments (including high temperature pre-precipitation,single-stage aging,two-stage aging,three-stage aging and so on) on both the precipitated phase and the stress corrosion sensitivity are also analyzed.In view of the existing research problems on the stress corrosion cracking of Al-Zn-Mg alloy,the future research directions are put forward.
    PROCESS RESEARCH
    Effect of solid solution temperature on aging precipitation behavior and properties of Ti-1300 alloy
    An Yi, Kou Wenjuan, Gao Ting, Sun Qiaoyan
    2020, 45(9):  29-36.  doi:10.13251/j.issn.0254-6051.2020.09.004
    Abstract ( 61 )   PDF (622KB) ( 169 )  
    Precipitation behavior of α phase and mechanical properties of Ti-1300 alloy after solution treatment followed by aging with low heating rate were investigated.The microstructure and mechanical properties of the Ti-1300 alloy with different solution treatment temperatures were observed and tested by means of SEM,TEM and tensile testing.The results show that when the solid solution treatment temperature is decreased from 820 ℃ to 790 ℃,the size of αp (primary α phase) changes a little,while the area fraction of αp increases from 0.8% to 6.7%.Subsequently,aging at 500 ℃ for 4 h with the heating rate of 4 ℃/min results in that the length of αs (secondary α phase) increases from 0.098 μm to 0.440 μm.In addition,the decrease of solution treatment temperature increases the strengh and platisity of the alloy,and resulting in that the tensile fracture changes from intergranular brittle fracture to dimple-type ductile fracture.The tensile strength of the specimen solution-treated at 820 ℃ is 1358 MPa with platisity below 2%.While solution treated at 790 ℃,an excellent combination of strenth (1548 MPa) with platisity (10.2%) is obtained,the main reason of which is the high content of primary α phase in micrometer scale,and the lamella-shaped αs precipitated in the matrix has significant strengthening effect.
    Effect of intercritical rolling on microstructure and mechanical properties of ferrite/martensite dual-phase steel
    Pang Zhuorui, Fu Liming, Suo Zhongyuan, Shan Aidang
    2020, 45(9):  37-40.  doi:10.13251/j.issn.0254-6051.2020.09.005
    Abstract ( 55 )   PDF (618KB) ( 24 )  
    By combination of rolling in (α+γ) dual-phase region and short-time heat preservation treatment in the dual-phase region,a high-strength high-toughness low-carbon low-alloy ferrite/martensite dual phase steel was prepared.The effect of different rolling processes on the microstructure and mechanical properties of the ferrite/martensite dual-phase steel were investigated by scanning electron microscopy (SEM),tensile test at room temperature and Vickers hardness test.The results show that,compared with the common continuous rolling process,the combination of the isothermal rolling with the short-time heat preservation treatment between passes has an important influence on the phase ratio,morphology and size of the ferrite/martensite dual phase steel.The microstructure of the dual-phase steel after isothermal rolling and short-time heat preservation treatment is obviously refined.The martensite phase ratio is increased,and the structure uniformity is significantly improved.The yield strength is increased by 34% to 1229 MPa,and the yield ratio is as high as 0.78.The fracture surface is ductile fracture type characterized by small dimples and showing good comprehensive mechanical properties.
    High temperature deformation behavior and processing map of Incoloy901 alloy
    Chen Peng, Guo Chuangli, Gao Yuan, Xi Shengqi, Wang W enbin
    2020, 45(9):  41-45.  doi:10.13251/j.issn.0254-6051.2020.09.006
    Abstract ( 62 )   PDF (629KB) ( 25 )  
    Hot deformation behavior of Incoloy901 alloy at deformation temperature between 950-1150 C,strain rate between 0.005-1 s and true strain of 0.6 was studied with Gleeble-3800 thermal simulator machine.The results show that the true stress-strain curve of Incoloy901 alloy presents dynamic recrystallization characteristics when the deformation temperature is higher than 1000 C and the strain rate is greater than0.01 s.According to the stress-strain curve,the constitutive equation and hot working diagram of Incoloy901 alloy are constructed,and the deformation activation energy Q=439.401 kJ/mol is obtained.The optimal hot work ing process consists of deformation at temperature of 1050-1 150 C with strain rate between 0.005-0.1 s-1.Within this process range,the high temperature deformation power dissipation cofficient (η) of the alloy is higher,up to 37%,and better dynamic recrystallization structure can be obtained.
    Effect of cold extrusion on corrosion resistance of high alloyed 7000 series aluminum alloy
    Wei Hongbo, Xu Xiaojing, Zhu Liangliang, Wang Yang, Wu Huafeng, Zhu Jingsong
    2020, 45(9):  46-49.  doi:10.13251/j.issn.0254-6051.2020.09.007
    Abstract ( 52 )   PDF (614KB) ( 29 )  
    Microstructure and corrosion resistance of high alloyed Al-12.3Zn-3Mg-2.5Cu-0.18Zr-0.07Sr aluminum alloy treated by solution-aging and solution-cold extrusion-aging were studied.The results show that the grains of the high alloyed aluminum alloy treated by solution-aging and solution-cold extrusion-aging show obvious zonal distribution,but the proportion of sub-grains in the solution-cold extrusion-aging treated alloy increases obviously.Compared with the solution-aging treatment,the solution-cold extrusion-aging treatment can obviously improve the corrosion resistance (exfoliation corrosion and intergranular corrosion) of the alloy,which means that cold extrusion can effectively improve the corrosion resistance of 7000 series aluminum alloy.
    Pilot-scale study of water-air alternative timed quenching technology for U20Mn steel rail
    Zuo Xunwei, Zhang Miansheng, Chen Nailu, Chen Liangqi, Rong Yonghua, Cai Jianxu
    2020, 45(9):  50-56.  doi:10.13251/j.issn.0254-6051.2020.09.008
    Abstract ( 60 )   PDF (618KB) ( 21 )  
    In order to improve the mechanical properties of heavy-load rail,this study attempts to replace the traditional air-cooling or fogcooling processes with water-air alternating controlled quenching (ATQ),and carries out a pilot-scale study of the ATQ technology (process+equipment) for U20Mn steel rail with water spray quenching.Firstly,the problem of rail operation obstruction caused by distortion is solved through the improvement of equipment and technology and finite element simulation of the distortion,then two ATQ processes were studied in laboratory to obtain different relative quantities of martensite and bainite respectively.Finally,the bainite-dominated ATQ process was selected to carry out the pilot-scale production for 7 m long steel rail,and the results show that the mechanical properties of all the steel rails treated by this ATQ process with 260 C tempering for 16 h or 30 h exceed the technical requirements.
    Effect of heat treatment on microstructure and grain size of imported P92 steel
    Zhao Yongtao, Jiang Yajun, Lu Haitao, Tian Zhihua
    2020, 45(9):  57-61.  doi:10.13251/j.issn.0254-6051.2020.09.009
    Abstract ( 82 )   PDF (614KB) ( 30 )  
    Imported P92 steel was treated by quenching at different temperatures (1040,1060,1080 ℃) and quenching at 1060 ℃ plus tempering at different temperatures (740,760,780 ℃) for different time(1,3,5,7 h).Effect of heat treatment on microstructure,grain size and hardness of the steel was studied.The results show that after quenching,the microstructure of the steel consists of lath martensite and retained austenite.With the increase of quenching temperature,the martensite lath gradually becomes coarser and the average grain size increases from grade 9 to 7.After quenching at 1060 ℃,the hardness of P92 steel gradually decreases with the increase of tempering temperature and the tempering time.The tempered martensite lath gradually merges and transfers to tempered sorbite.During the tempering process,carbides precipitate and grow up at the grain boundaries and inside of the grains.
    Effect of partitioning time on microstructure and properties of Q&P steel
    Chen Mengyuan, liu Zhuo, Wu Run, Wu Teng
    2020, 45(9):  62-65.  doi:10.13251/j.issn.0254-6051.2020.09.010
    Abstract ( 71 )   PDF (618KB) ( 20 )  
    On the basis of the traditional C-Mn-Si steel,the microstructure and mechanical properties of the experimental Q&P steel after on-line one-step quenching and partitioning treatment were studied by metallographic microscope,scanning electron microscope and tensile test.The effect of partitioning time on the microstructure and properties of the steel was also discussed.The results show that the experimental steel structure consists of lath martensite and retained austenite.With the increase of partitioning time,a small amount of bainite is formed,and the retained austenite content first rises and then falls,and the lath structure of martensite is gradually blurred and softened;the tensile strength and yield strength are gradually reduced,and the elongation first increases and then decreases.The best comprehensive performance is achieved under the partitioning time of 30 s,the tensile strength is 989 MPa,the elongation is 23.5%,and the product of strength and elongation is 23.24 GPa·%.
    Effect of rolling parameters on microstructure and mechanical properties of 460 MPa grade low yield ratio fire-resistant weathering steel
    Ma Longteng, Wang Yanfeng, Yang Yongda, Han Chengliang, Ma Changwen, Tian Zhihong
    2020, 45(9):  66-70.  doi:10.13251/j.issn.0254-6051.2020.09.011
    Abstract ( 55 )   PDF (614KB) ( 21 )  
    Microstructure of low yield ratio fire-resistant weathering steel after cooling at different rates was determined by thermal simulation method.By comparing the effects of post-rolling relaxing process or not and final cooling temperature after hot rolling on mechanical properties of the steel,the effect of different processes on microstructure was investigated by using OM,SEM and TEM.The results show that with cooling rate increasing,the microstructure of the steel plates changes from polygonal ferrite to (acicular ferrite+granular bainite) duplex microstructure.Due to the transformation of undercooled austenite into polygonal ferrite during relaxation treatment,the yield strength and yield ratio of the steel plates decrease.With the decrease of final cooling temperature,the yield strength and yield ratio of the steel plates increase,which is due to the refinement of acicular ferrite and the dispersion strengthening of M/A constituent.Good match of high strength and low yield ratio of the steel plates are successfully achieved by the combination of direct water-cooling after hot rolling and controlled final cooling temperature between 500 ℃ to 560 ℃.
    Effect of strain rate on microstructure and properties ofhigh strength steel for automobile
    Hou Yudong, Jing Cainian, Ding Xiaoyun, Wu Cong
    2020, 45(9):  71-76.  doi:10.13251/j.issn.0254-6051.2020.09.012
    Abstract ( 73 )   PDF (614KB) ( 20 )  
    High speed impact compression tests of QP980 and TRIP590 steel were carried out under different strain rates by means of split Hopkinson pressure bar testing machine and scanning electron microscope.The microstructure and properties of the two kinds of high strength steel for automobile under different strain rates were analyzed.The results show that the relative error between the calculated stress and the measured stress of the steels is 1.2%-3.3%,which is small and stable,so the experimental data are basically consistent with the two wave formula.The engineering stress of the two kinds of high strength steel for automobile increases with the increase of strain rate,but the maximum engineering stress of QP980 steel plate is larger than that of TRIP590 steel plate.After impact test,the microstructure of QP980 steel plate becomes more lath and fine,and the microstructure is uniform ferrite and martensite.While the microstructure of TRIP590 steel plate after impact becomes coarse and uneven,and with the increase of strain rate,the ferrite in the original structure gradually expands to the surroundings during the extrusion process,the bainite is covered by the larger ferrite structure,and the martensite content increases.
    Effect of heating parameters on grain growth behavior of 12%Cr steel
    Zhang Xuezhong, Liu Jiansheng, He Wenwu, Yan Xiaoxia, Yang Chunpeng
    2020, 45(9):  77-80.  doi:10.13251/j.issn.0254-6051.2020.09.013
    Abstract ( 59 )   PDF (614KB) ( 24 )  
    Austenite grain growth behavior of 12%Cr ultra-supercritical rotor steel with different heating process parameters (heating temperature 1050-1300 ℃,holding time 0.25-24 h) was studied.The change rule of grain size was observed by optical microscope (OM),and the mathematical model of grain growth was established.The results show that with the increase of heating temperature,the grain size increases gradually.When the heating temperature is lower than 1150 ℃,the grain size increases obviously.When the temperature is higher than 1150 ℃,the grain size tends to be stable.With the increase of holding time,the grain size increases gradually,and when the holding time increases to 3 h,the increasing trend of grain size slows down.The mathematical model of grain growth under different heating process parameters is established by using nonlinear regression method and Arrhenius grain growth model.
    Effect of laser shocking parameters on residual stress field of 7050 aluminium alloy
    Ge Liangchen, Hua Guoran, Cao Yupeng, Yang Cong, Wang Shuai, Zhang Yue, Cao Chen
    2020, 45(9):  81-85.  doi:10.13251/j.issn.0254-6051.2020.09.014
    Abstract ( 50 )   PDF (617KB) ( 22 )  
    Effect of laser shocking parameters (spot diameter,laser characteristics and peak pressure) on the formation mechanism of residual stress field of 7050 alloy were studied by means of simulation and experiment.The results show that the optimum peak pressure is 1500 MPa when the flat-topped laser is loaded with facula diameter of 2 mm,3 mm and 4 mm.When the Gauss laser is loaded,the optimum peak pressure is 1500 MPa,2000 MPa and 3000 MPa with facula diameter of 2 mm,3 mm and 4 mm,respectively.And the maximum residual stress after the flat-topped laser shock is increased by about 10% than Gauss laser when the peak pressure is 1500 MPa.When the peak pressure is greater than 2000 MPa,affected by surface convergence wave,the maximum residual compressive stress after shocking by flat-topped laser is less than that of Gauss laser.When shocked by the flat-topped laser,the actual optimal solution of peak pressure is consistent with the theoretical optimal solution,which is 1500 MPa.In the case of Gauss laser shocking,the actual optimal solution of peak pressure increases gradually with the increase of the spot diameter.When the peak pressure exceeds 2000 MPa,the residual compressive stress no longer increases significantly,and stress defects such as residual stress holes are more likely to occur.
    Influence of post-weld annealing process on fatigue life of cross joint
    Li Jitao, Zhao Wenzhong, Tian Changliang
    2020, 45(9):  86-90.  doi:10.13251/j.issn.0254-6051.2020.09.015
    Abstract ( 60 )   PDF (618KB) ( 19 )  
    Consideration of welding residual stress in fatigue assessment criteria was summarized based on the analysis of fatigue assessment standards for welding structure,then it was clarified from the perspective of fatigue life calculation that the influence of residual stress requires no additional consideration.A batch of cross joint specimens were designed and anufactured,on which the fatigue test was carried out,and the fatigue test data were analyzed according to BS 7608:2014+Al:2015 standard.The result shows that there is no significant difference in fatigue life of as-welded cross joint specimens and that after different post-weld annealing process.
    Influence of quenching transfer time on microstructure and mechanical properties of Ti-1023 alloy
    Tong Jianbo, Huang Lijun, Zhang Wenqiang, Yan Mengqi, Li Xuefei
    2020, 45(9):  91-95.  doi:10.13251/j.issn.0254-6051.2020.09.016
    Abstract ( 55 )   PDF (617KB) ( 23 )  
    Influence of transferring time for quenching on the microstructure evolution and mechanical properties of Ti-1023 alloy was investigated by means of tensile test,fracture analysis and microstructure characterization.The results indicate that with the increase of transfer time for quenching,α phase precipitated from supersaturated β phase is observed,leading to the volume fraction of equiaxed α phase and supersaturated β matrix increase and decrease,respectively,and the content and dispersion of secondary αs phase precipitated after aging decrease,which result in the strength reduction and the ductility improvement of Ti-1023 alloy.For Ti-1023 alloy bars or forgings with thickness of 80 mm,the microstructure and properties of the alloy will not be significantly affected with transferring time for quenching controlled in 120 s.
    Effect of cryogenic treatment on hardness and wear resistance of 42CrMo steel
    Zhang Haidong, Yan Xianguo, Chen Zhi, Zhao Minna, Gao Yuan, Li Junji, Li Jinfeng, Gao Limei
    2020, 45(9):  96-98.  doi:10.13251/j.issn.0254-6051.2020.09.017
    Abstract ( 80 )   PDF (696KB) ( 31 )  
    Based on the conventional treatment of 42CrMo steel,cryogenic treatment was added.Effects of shallow cryogenic treatment and deep cryogenic treatment on hardness and wear resistance of 42CrMo steel were studied.The results show that after shallow cryogenic treatment and deep cryogenic treatment,the retained austenite in 42CrMo steel transforms to martensite,and the precipitation of carbides increases,which leads to the improvement of hardness and wear resistance of the steel,and the improvement extent of hardness and wear resistance after deep cryogenic treatment is higher than that of shallow cryogenic treatment.
    Effect of intermediate adjustment treatment on microstructure and properties of 17-4PH stainless steel
    Liu Kaixuan, Xue Song, Wang Peng, Gao Zhigang, Zhao Xiuming, He Xiancong
    2020, 45(9):  99-104.  doi:10.13251/j.issn.0254-6051.2020.09.018
    Abstract ( 63 )   PDF (616KB) ( 24 )  
    Based on the traditional solid solution treatment+aging process,the 17-4PH stainless steel used for oil valve block was treated by solid solution treatment+intermediate adjustment+aging process.The microstructure and mechanical properties of the specimens were analyzed by using optical microscope,scanning electron microscope,XRD and mechanical property test,and the effect of intermediate treatment on the microstructure and mechanical properties was studied.The results show that with the increase of solid solution treatment temperature,the carbon and alloy elements dissolved in the matrix increase,the microstructure composition is more uniform,and the hardness of the material is higher under the same aging conditions.After adding the intermediate adjustment treatment and then aging,the content of reverse transformed austenite is significantly increased,and the plasticity and impact properties of the material are significantly increased,but the strength is reduced.
    Effect of solution treatment on microstructure and properties of cold rolling7B04 aluminum alloy sheet
    Li Min, Li Yun, Xu Yuguo, Wang Diangang
    2020, 45(9):  105-110.  doi:10.13251/j.issn.0254-6051.2020.09.019
    Abstract ( 63 )   PDF (577KB) ( 19 )  
    7B04 aluminum alloy were prepared in the laboratory,which was further prepared into 7B04 aluminum alloy sheets by casting+homogenization annealing+hot rolling+intermediate annealing+cold rolling process,then the effect of solid solution treatment on the microstructure and properties of the alloy sheet was studied.The results show that the recrystallization of cold rolling aluminum alloy sheet treated by solution treatment at 470 ℃ for 1 h and aged at 120 ℃ for 21 h is obvious,though a small amount of grains are in elongated state,and except for the coarse secondary phase particles,no small secondary phase particles are found.The comprehensive mechanical properties are good,the tensile strength is 596 MPa,the yield strength is 537 MPa,and the elongation is 14.88%.When the solution treatment temperature reaches 480 ℃,the alloy recrystallizes obviously,but the holding time should not exceed 0.5 h,otherwise the strength and plasticity of the cold rolling alloy sheet will be decreased.
    Effect of aging on microstructure and properties of laser remelted layer of Fe-based alloy
    Du Xiaojie, Hong Yongchang, Shan Junzhan
    2020, 45(9):  111-115.  doi:10.13251/j.issn.0254-6051.2020.09.020
    Abstract ( 49 )   PDF (574KB) ( 16 )  
    Microstructure and properties of thermal spraying welded layer and laser remelted layer with different aging treatment at 500 ℃ of an Fe-based alloy were compared and analyzed by using field emission scanning electron microscope(FE-SEM),transmission electron microscope(TEM),X-ray diffractometer(XRD) and electrochemical workstation.The results show that the microstructure of the thermal spraying welded layer after flame spraying is relatively coarse,which is markedly refined as composed of fine dendrites with lamellar eutectic evenly distributed in between after laser remelting.With the increase of aging time,columnar crystals closer to the eutectic structure in the remelting layer start to spheroidize,Cr7C3 and Cr23C6 carbides are further precipitated in the matrix and distribute in the lamellar eutectic structure between the dendrites.The hardness of the laser remelting layer aged for 6 h is the highest,as up to 507 HV0.5.With the aging time continues to increase,the hardness decreases,but it is still higher than that of the laser remelted layer without aging.After laser remelting,the corrosion resistance of the thermal spraying welded layer is significantly improved to the maximum,and that aged for 6 h is not significantly reduced,while that aged for 48 h is significantly reduced.
    Effect of tempering temperature on microstructure and mechanical properties of Nb microalloyed NM500 steel
    Xu Hui, Li Tiansheng
    2020, 45(9):  116-120.  doi:10.13251/j.issn.0254-6051.2020.09.021
    Abstract ( 55 )   PDF (577KB) ( 20 )  
    Nb microalloyed NM500 steel was quenched at 930 9C and tempered at 210,240,270 and 300 C,respectively.Effects of tempering temperature on microstructure and mechanical properties of tested steel were analyzed.The microstructure,impact fracture morphology and strengthening mechanism of the tested steel tempered at different temperatures were studied by SEM and TEM.The results show that the tested steel has the best comprehensive mechanical properties when quenched at 930 C and tempered at 240 C,and the corresponding strengthening mechanism is a combination of solution strengthening,phase transformation strengthening,precipitation strengthening and fine grain strengthening.
    Effect of annealing temperature on microstructure and properties of hot rolled 0Cr25Al5 wire steel
    Yan Shicai, Li Ying
    2020, 45(9):  121-124.  doi:10.13251/j.issn.0254-6051.2020.09.022
    Abstract ( 51 )   PDF (575KB) ( 18 )  
    Effect of annealing temperature on microstructure and properties of hot rolled 0Cr25Al5 wire steel was studied by means of microstructure analysis and molecular dynamics simulation.The results show that with the increase of temperature,the grain size is increased gradually and tends to be stable,but the percentage elongation and percentage reduction of area after fracture is decreased sharply at 950 ℃.The OM and SEM microstructure of the specimens annealed at 800 ℃ or 950 ℃ have no obvious difference.And the free energy of 0Cr25Al5 steel ternary system is calculated by molecular dynamics simulation.With the increase of ordered phase size of FeAl with B2 structure or Fe3Al with DO3 structure,the free energy of the system is first decreased and then increased,and with the increase of annealing temperature,its minimum value is moved to the direction of the decreasing size of ordered phase particles.At the high temperature of 1273 K,the size of ordered phase particles is still remained about 60 nm.Therefore,it is speculated that the decrease toughness of 0Cr25Al5 steel in the temperature range above 950 ℃ is due to the ordered phase of FeAl with B2 structure or Fe3Al with DO3 structure at about 60 nm,which is independent of grain size.Therefore,for the kinds of steels,to eliminate defects,a low temperature annealing shall be adopted to make the recovery of the matrix,which can inhibit from the diffusion of matrix atoms.
    Effect of annealing temperature on microstructure and properties of ferrite/martensite dual-phase steel
    Suo Zhongyuan, Du Yang, Fu Liming, Shan Aidang
    2020, 45(9):  125-128.  doi:10.13251/j.issn.0254-6051.2020.09.023
    Abstract ( 82 )   PDF (577KB) ( 19 )  
    Effect of intercritical annealing temperature on the microstructure and mechanical properties of a ferrite/martensite dual-phase steel was investigated by means of scanning electron microscopy (SEM),room-temperature tensile and impact tests.The results show that the microstructure of the hot rolled dual-phase steel is composed of ferrite+martensite,and the content of ferrite is 32.8%.With the annealing temperature increasing from 720 C to 830 9C,the ferrite content decreases from 45.7% to 23.6%,and the martensite content increases gradually.The yield ratio of the tested steel is increased from 50% of that hot rolled to 60% of that annealed at 830 C,and the relationship between the impact absorbed energy and the ferrite content is linear.
    Effect of water jet peening on microstructure and crack propagation of carburized steel
    Fan Lei, Zhang Renqi, Li Bo, Wang Lingxu, He Jinhang, Zou Changfei, Liang Yu
    2020, 45(9):  129-133.  doi:10.13251/j.issn.0254-6051.2020.09.024
    Abstract ( 44 )   PDF (581KB) ( 19 )  
    Effect of water jet peening on microstructure and fatigue crack growth rate of carburized layer was studied by water jet peening on the surface of carburized and quenched low carbon steel.The results show that water jet peening with fine glass beads can significantly refine the surface substructure and increase the density of small angle grain boundaries,and also brings effective residual compressive stress to the carburized layer.Under the condition of 300 MPa water pressure and 600 mm/min scanning rate,the residual compressive stress with a depth of about 100 μm and a maximum of 1244 MPa can be achieved and the corresponding surface roughness Ra is 0.195 μm.The results of fatigue crack rate test show that the crack growth rate da/dN has an increasing trend after water jet peening,which is mainly due to the formation of surface compressive stress and the increase of the tensile stress in the center,and the deformation strengthening of the surface layer reduces the plastic zone at the crack tip.
    Influence of controlled forging and cooling process on microstructure evolution of GCr15 bearing steel
    Hu Linzhuang, Guo Hao, Lei Jianzhong, Liu Yang, Du Sanming, Zhang Yongzhen
    2020, 45(9):  134-138.  doi:10.13251/j.issn.0254-6051.2020.09.025
    Abstract ( 55 )   PDF (575KB) ( 27 )  
    Microstructure evolution and network carbide distribution of GCr15 bearing steel treated by traditional process and controlled forging and cooling process were comparatively studied by using the way of microstructure characterization.And the statistics and analysis about change rules of grain size and retained austenite content under different processes were made.The results show that after treating by controlled forging and cooling process,the microstructure of granular pearlite in GCr15 bearing steel is relatively smaller,the distribution of C element in the matrix after quenching and rolling is more uniform,and the Rockwell hardness is increased by 0.7 HRC.In addition,the retained austenite content of GCr15 bearing steel is decreased,accompanied with the refinement of carbide particle,and the average particle size is decreased by more than 40%,meanwhile,the formation of coarse carbide network is inhibited.In addition,the austenite grain size can be refined to more than 2 grades.
    Heat treatment process for small ring forgings of 30CrNiMo8 steel
    Jia Tuosheng, Wen Qi, Zhang Xiaofeng, Wei Huacheng, Zhang Lei, Li Qiulan
    2020, 45(9):  139-141.  doi:10.13251/j.issn.0254-6051.2020.09.026
    Abstract ( 70 )   PDF (578KB) ( 22 )  
    30CrNiMo8 steel small ring forgings used in rail vehicles were produced by the conventional processes including ash-cooling or pit-cooling after forging,then quenching and tempering.The corresponding mechanical properties are excellent,but it is found according to the metallographic examination that the grain size is coarse,even is grade 0 for individual batches,which cannot be eliminated even adding a normalizing pretreatment before quenching and tempering.The research results show that 30CrNiMo8 steel has strong microstructure heredity,so the coarse grains are inherited to the subsequent process after forging and cannot be easily refined by the subsequent heat treatment processes.So in the conventional process flow an isothermal annealing process is added before quenching and tempering,which eliminates the coarse grains after forging,and effectively solves the problem of coarse grains in the small ring forgings of 30CrNiMo8 steel.
    MICROSTRUCTURE AND PROPERTIES
    Microstructure and mechanical properties of laser 3D printedAlSi10Mg aluminum alloy lattice materials
    Liu Peiling, Chen Kangmin, Zhao Zhenhua
    2020, 45(9):  142-148.  doi:10.13251/j.issn.0254-6051.2020.09.027
    Abstract ( 60 )   PDF (581KB) ( 26 )  
    AlSi10Mg aluminum alloy lattice materials were prepared by selecting different laser 3D printing parameters,and the optimized printing parameters were explored.The microstructure and properties of aluminum alloy lattice materials and the influence of subsequent heat treatment on it were studied.The results show that the optimal printing parameters include printing temperature (80 ℃),microns powder layer thickness (30 μm),lasing beam diameter (80 μm),laser energy(370 W),and laser scanning speed (1300 mm/s).The prepared aluminum alloy lattice material has few cavity defects,high compactness,and the microstructure is a layer upon layer crisscrossing laser molten pool,which is composed of small α-Al equiaxial cellular crystal and spherical Si particle phase,and has good performance.After heat treatment,the features of the original laser molten pool defects and equiaxial cellular crystals disappear,the Si particle phase continuously precipitates and grows up,meantime,the hardness and platform stress decrease under the compression performance,so does the static compression properties.
    Microstructure and properties of laser alloyed Mo1 B,Cr,coating on 45 steel
    Liu Dexin, Zhang Hongxing, Zhang Leitao, Zhang Weiqiang, Wang Xuesong, Dai Jiaoyan, Xu Jinfu
    2020, 45(9):  149-154.  doi:10.13251/j.issn.0254-6051.2020.09.028
    Abstract ( 56 )   PDF (584KB) ( 23 )  
    Mo B,Cr,alloyed coating was prepared on the 45 steel substrate by laser alloying technology.The effect of Cr content on the microstructure and properties of the coating was studied.The results show that the best laser alloying process parameters for Mo,B.Cr.coating are laser power of 3.3 kW,scanning speed of 900 mm/min,overlap rate of 30%.By adopting this process,the coating shows a good metallurgical bonding with the substrate without voids and cracks,the alloying zone is composed of Fe-Mo,Fe2B,Fe-Cr,Cr,B,Cr,Fe,solid solutions and compounds,and the coating hardness,friction coefficient,and wear rate gradually decrease when the Cr content increases from1.1% to 23.3%.When the Cr content is 1.1%,the maximum coating hardness is 1005 HV0.1.When the Cr content is 23.3%,the wear resistance is the best,the friction cofficient is 0.475,the wear rate is0.574 x10 *m2/(N·m),and the form of coating wear is mainly a combination of abrasive wear and adhesive wear.
    Dynamic mechanical properties of high carbon silicon manganese steel
    Yuan Wufeng, Wu Run, Yu Wenchao, Xuan Yang, Yan Yongming
    2020, 45(9):  155-160.  doi:10.13251/j.issn.0254-6051.2020.09.029
    Abstract ( 55 )   PDF (575KB) ( 15 )  
    Microstructure,deformation degree and dynamic mechanical properties of high carbon steel quenched at different temperatures were studied by means of scanning electron microscopy,Hopkinson pressure bar and tensile testing machine.The results show that as the quenching temperature increases,the amount of residual carbides in the experimental steel decreases.At 880 ℃,the residual carbides in the experimental steel are all dissolved.After the dynamic mechanical test,due to the dissolution of the residual carbide,the increase in dynamic strength of the specimen quenched at 880 ℃ is small.And because it is insensitive to the strain rate,the uniform deformation becomes broken.There are holes in the area of the adiabatic shear band and away from the adiabatic shear band.Far from the area of the shear band,the holes are disorderly distributed and accompanied by carbides.The carbides near the adiabatic shear zone are unevenly distributed.And the holes inside the adiabatic shear bands expand along the heat propagation direction,forming cracks distributed along the shear band.
    Microstructure and properties of selective laser melted 316Lstainless steel in different directions
    Zhang Renqi, Fan Lei, Zhou Baogang, Liang Yu
    2020, 45(9):  161-166.  doi:10.13251/j.issn.0254-6051.2020.09.030
    Abstract ( 73 )   PDF (578KB) ( 40 )  
    Microstructure and properties in transversal and longitudinal directions of 316L stainless steel additive manufacturing specimens produced by selective laser melting(SLM) were analyzed.The results show that the substructure of the SLM additive manufacturing specimens is composed of cellular microstructure with the size of 0.4 μm,and with no obvious composition segregation.Their transversal and longitudinal tensile strengths are 808 MPa and 713 MPa,respectively.After heat treatment at 1050 ℃,some of the cellular microstructures disappear,and the transversal and longitudinal strengths are reduced to 673 MPa and 579 MPa,respectively,which still have obvious strength advantages compared with the conventional hot rolled 316L steel(550 MPa).There are unfused defects in the SLM specimens,and the directivity and geometry of the defects have significant effect on the ability of the defects joining into a crack under the action of tensile stress.The elongation of the longitudinal specimen with defect length direction parallel to the tensile direction is 47.5%,and that of the transversal specimen is 20% after heat treatment.The elongation of the SLM specimen is significantly lower than that of the hot rolled 316L steel specimen.The unfused defect is one of the main factors leading to the decrease of plastic properties of the 316L stainless steel specimens processed by SLM.
    Grain boundary characteristics of non-abnormal grown Goss grains of Hi-B steel during secondary recrystallization annealing
    Xu Shuai, Bao Siqian, Ke Shanshan, Lei Xiaoling, Lu Weina
    2020, 45(9):  167-171.  doi:10.13251/j.issn.0254-6051.2020.09.031
    Abstract ( 57 )   PDF (576KB) ( 22 )  
    Grain boundary characteristics of non-abnormal grown Goss grains of Hi-B steel during secondary recrystallization annealing was studied by using interruption method combined with EBSD technique.The results show that the grain size of non-abnormal grown Goss oriented grains is not significantly different from that of matrix grains and adjacent grains.At the same time,the proportion of HE and CSL grain boundaries around the non-abnormal grown Goss grains has no significant difference with those of abnormal grown Goss grains.During the secondary recrystallization annealing,the size superiority,HE and CSL grain boundary,and Goss orientation deviation can't guarantee the abnormal growth of Goss oriented grains.With annealing temperature increasing,the Goss oriented grains tend to be closer to the standard Goss grains.
    Mechanical properties and microstructure of extruded 6061 aluminum alloy
    Liu Wei, Wu Yuanzhi, Deng Bin, Liu Anmin, Liu Wei, Xu Ziyan, Ye Tuo
    2020, 45(9):  172-177.  doi:10.13251/j.issn.0254-6051.2020.09.032
    Abstract ( 71 )   PDF (579KB) ( 23 )  
    As-extruded 6061 aluminum alloy was subjected to solution treatment and aging treatment,respectively.The mechanical properties of the alloy were tested by universal testing machine,and the microstructure was characterized by means of SEM and TEM to investigate the microstructure evolution law of the alloy in different heat treatment states.The results show that the extruded 6061 aluminum alloy after solution treatment and aging treatment show obvious anisotropic mechanical properties,and aging treatment can effectively improve the strength of the alloy.At the same time,the extruded alloy after aging treatment shows strain rate sensitivity,however,the alloy after solution treatment has no obvious strain rate sensitivity.The extruded 6061 aluminum alloy after solution treatment and aging treatment are composed of equiaxed grains with two kinds of grain sizes,which the larger one being up to 200 μm and the smaller one being less than 10 μm.The types and strength of texture components of the extruded 6061 aluminum alloy solution-treated or as-aged are the same,both are composed of strong {001} <100>cubic texture and weak {011} <100>Goss texture.After tensile deformation,a large number of dislocations pile up,and the short rod like precipitates will be evenly distributed in the alloy after aging treatment,which can effectively block the movement of dislocations and improve the deformation resistance of materials.
    Microstructure and properties of new hot work die steel for hot stamping
    Li Shuang, Gao Yunfei, Wang Chen, Wang Zhen, Shi Yongliang, Wu Xiaochun
    2020, 45(9):  178-184.  doi:10.13251/j.issn.0254-6051.2020.09.033
    Abstract ( 51 )   PDF (575KB) ( 19 )  
    Microstructure,thermo stability,thermal physical property and high temperature wear resistance of a new die steel for hot stamping of high strength steel were investigated by means of scanning electron microscope (SEM),transmission electron microscope (TEM),LF457 type laser flash thermal analyzer,DSC404 type differential scanning calorimeter and UMT-3 high temperature wear test system.The results show that the new hot stamping die steel has excellent resistance to tempering,thermo stability,thermal conductivity and high temperature wear resistance and better adapt to the working condition of high strength steel hot stamping process.There are mainly Mo2C and VC type carbides in the steel,these carbides ensure the steel with high resistance to tempering and thermo stability.The steel has high thermal conductivity,which is 1.4 times of H13 steel at room temperature.The low Si,Mn,Cr and high Mo alloying can be the reason for the high thermal conductivity of the steel.The new die steel has better high temperature wear resistance than that of H13 steel,especially when temperature is above 600 ℃,which can decrease the repair frequency and improve service life of the hot stamping die.
    EBSD characterization of recrystallization behavior of IF steel during annealing
    Cui Guibin, Ju Xinhua, Wang Zeyang, Yin Lixin, Yan Chunlian
    2020, 45(9):  185-190.  doi:10.13251/j.issn.0254-6051.2020.09.034
    Abstract ( 53 )   PDF (581KB) ( 25 )  
    Orientation evolution of ferrite rerstallized grains in IF steel from cold rolling to annealing was studied by means of EBSD.The results show that from the cold rolling to the annealing process,the ferrite grain orientation evolves toward the[111] grain parallel to the normal direction,while the[100] grain parallel to the normal direction gradually disappears;the crystal orientation of ferrite grains determines the difficulty of slip deformation during the cold rolling deformation process.Compared with[100] grains,[111] grains are more prone to slip deformation and resulting to the accumulation of a large number of dislocations inside the grains and a large amount of stored strain energy.During the subsequent annealing process,the higher strain energy[111] grains preferentially nucleate and grow for preferential recrytallization,while the recrstallization of [ 100 ] grains with lower strain energy is hindered.As the annealing temperature increases,the γ texture ([111]//ND) is significantly enhanced,especially its texture component (111)[112].
    Microstructure evolution and mechanical properties at different thickness of 7A75 aluminum alloy plate
    Wang Shuhui, Wang Shan, Sui Xinju, Meng Cuiyu
    2020, 45(9):  191-194.  doi:10.13251/j.issn.0254-6051.2020.09.035
    Abstract ( 58 )   PDF (578KB) ( 22 )  
    Microstructure evolution and mechanical properties at different thickness of as-hot rolled 7A75 aluminum after solution treatment were investigated.The microstructure,crack propagation and fracture morphologies were characterized by using OM and SEM.The texture constitution and residual stress were analyzed by using XRD,and the mechanical properties were tested by using tensile tester.The results indicate that at different thickness of the 7A75 aluminum alloy,the yield strength at surface,1/4 thickness and center are 200,200 and 185 MPa,while tension strength is 345,335 and 325 MPa respectively,but the elongation is 20%,19.5% and 22% respectively,which show that the center layer has the lowest strength and the highest elongation.The average grain size at surface,1/4 thickness and center are about 24.5,24.8 and 25.5 μm respectively,which are all within the range of 24-26 μm and no obvious difference.There are obvious plane strain texture which distributing along β orientation line at surface,mainly Copper texture {112}<111>at 1/4 thickness and weakened β orientation line texture at center.The residual stress at surface,1/4 thickness and center are -18.5,-3.5 and 7.5 MPa respectively,which show a compressive stress at surface and 1/4 thickness and a tensile stress at center.
    Microstructure and properties of TC4 alloy sheet by EB melting slab straight rolling
    Zhang Qiang, Hao Xiaobo, Li Bobo, Pei Teng, li Yang, Liu Yinqi
    2020, 45(9):  195-202.  doi:10.13251/j.issn.0254-6051.2020.09.036
    Abstract ( 44 )   PDF (581KB) ( 23 )  
    TC4 alloy slab prepared by one -time EB melting was directly rolled,and the microstructure and mechanical properties of the hot rolled and annealed alloy sheet with different rlling times were studied.The results show that after 1 -3 rounds of direct rlling,the coarse as-cast micorstructure of the alloy is broken continuously,the quantity and the size of equiaxed a phase is gradually increased and reduced,respectively,and the mechanical properties of each rlling round sheet meet the standard requirements.With the increase of annealing temperature,the tensile strength and yield strength of the finished products of each rolling round show a downward trend,and the elongation increases first and then decreases.After annealing at 850 C,the TC4 alloy sheet can obtain the best combination of strength and toughness.The anneal temperature in the industrial batch production of EB primary melting slab direct-rolling TC4 alloy sheet is recommended to use 700-850 C,and the microstructure and mechanical properties can reach the technical requirements of the sheet prepared by forging billet.
    MATERIALS RESEARCH
    Effect of Si on microstructure and mechanical properties of low temperature bainitic steel with medium carbon
    Zheng Hua, Hu Feng, Ke Rui, Wu Kaiming
    2020, 45(9):  203-209.  doi:10.13251/j.issn.0254-6051.2020.09.037
    Abstract ( 47 )   PDF (559KB) ( 22 )  
    In order to investigate the effect of Si on the microstructure and mechanical properties of bainitic steels,low temperature bainite treatment process was carried out for medium carbon steels with Si content of 0.3wt% and 1.5wt%,respectively.The results show that the microstructure of the steels with different contents of Si are significantly different,the microstructure of the specimen containing 0.3%Si is mainly composed of bainitic ferrite,M/A island and a large amount of cementite,and the microstructure of the specimen containing 1.5% Si is mainly composed of bainitic ferrite and M/A island.The hardness and impact properties of the specimen containing 1.5%Si are higher than that of the specimen containing 0.3%Si.The higher hardness is mainly due to the solid solution strengthening and fine grain strengthening.The main reason for the higher impact properties is that the addition of proper amount of Si can inhibit the precipitation of cementite,thus increasing the volume fraction of retained austenite and its carbon content,thus producing a relatively significant TRIP effect.
    Effect of nitrogen content on microstructure and mechanical properties of HPD-1 duplex stainless steel
    Ning Xin, Song Zhigang, Feng Han, Huang Bo, Yu Zhichuan, Zheng Wenjie, He Jianguo, Zhu Yuliang
    2020, 45(9):  210-214.  doi:10.13251/j.issn.0254-6051.2020.09.038
    Abstract ( 51 )   PDF (559KB) ( 20 )  
    Effect of nitrogen content on hardness,tensile properties,low temperature impact toughness and fatigue properties of HPD-1 duplex stainless steel in the range of 0.08wt%-0.22wt% were studied by means of microstructure observation and mechanical properties testing.The results show that the γ/α phase ratio of the tested steel is significantly affected by the nitrogen content,when the nitrogen content is increased from 0.08wt% to 0.22wt%,the content of γ phase is increased from 38.1% to 56.5%.The hardness of α phase is increased from 273 HV10 to 343 HV10,and that of γ phase is increased from 238 HV10 to 299 HV10,resulting in the strength of the tested steel being dramatically improved.The low temperature impact properties of the tested steel is increased at first and then decreased,which is caused by the combined influence of nitrogen on the two phase ratio.The fatigue crack initiation and propagation can be inhibited due to a higher nitrogen content,which plays an important role in the fatigue performance at room temperature of the HPD-1 duplex stainless steel,meanwhile the tearing edge is the main characteristic of fatigue fracture.
    Effect of composite rare earth oxides on microstructure and tribological properties of Ti-Al/WC coating
    Zhao Yuncai, Peng Tao
    2020, 45(9):  215-219.  doi:10.13251/j.issn.0254-6051.2020.09.039
    Abstract ( 62 )   PDF (558KB) ( 45 )  
    Ti-Al/WC coatings of rare earth oxide-free and containing different composite rare earth oxides were prepared by plasma spraying.The worn surface,cross section microstructure,residual stress and wear mass loss of the coatings were observed and detected by using scanning electron microscopy with energy spectrometer,X-ray powder diffractometer and electronic balance.The wear resistance of the coatings was compared and analyzed by using friction and wear tester.The results show that the internal grains of the Ti-Al/WC coating containing rare earth oxide are refined,particulates are greatly reduced,holes are smaller and the number and size of cracks are significantly reduced.Compared with the coating containing only a kind of rare earth oxide,the composite rare earth oxides are more effective in improving microstructure of the coating.When CeO2,Y2O3 and La2O3 are all added into the coatings,the defects in microstructure are the least,the components are most evenly distributed,and the cross section morphologies are the best.At the same time,the residual stress of the coating reaches a minimum of 275.7 MPa,the wear resistance is the strongest and the total wear mass loss is only 16.8 mg,compared with the coating of rare earth oxide-free,they are reduced by 30.3% and 69.8% respectively.
    Influence of rare-earth element Ce on microstructure and texture of hot rolled oriented silicon steel
    Dong Lili, Lu Xiaoyu, Ma Yonglin
    2020, 45(9):  220-222.  doi:10.13251/j.issn.0254-6051.2020.09.040
    Abstract ( 51 )   PDF (557KB) ( 21 )  
    Alloy system of hot rolled oriented silicon steel strip produced by 2250 mm hot rolling line was designed,and a reasonable preheating and hot rolling process were formulated.The oriented silicon steel billet and hot rolled strip with the addition of rare earth element Ce were analyzed,and the effect of Ce on microstructure,hot rolled texture and magnetic properties of finished products were investigated.The results show that the rare earth element Ce can refine the microstructure of the continuous casting billet and hot rolled strip,and improve magnetic properties of oriented silicon steel products.
    Effect of Nb addition on high temperature and aged properties of FeCo based alloy
    Wang Dongling, Wang Xuandong, Zhang Jinglin, Yu Yipeng, Zhang Jianfu
    2020, 45(9):  223-226.  doi:10.13251/j.issn.0254-6051.2020.09.041
    Abstract ( 56 )   PDF (568KB) ( 29 )  
    Magnetic properties and mechanical properties of Fe 49Co-2V and Fe 49Co-2 V_0.3Nb alloys were measured at room temperature and high tempernature,respectively.The results show that the saturation magnetization B。and coercivity H。of both alloys decrease compared with room tempera ture,and tensile strength at 500 C of two kinds of alys is improved comparing with room temperature.The strengthening effct of Nb addition on mechanical properties is obvious.It is found that Fe 49Co-2V 0.3Nb alloy still has good mechanical properties after ageing at 500 C for 168 h.The addition Nb is helpful for the stabilty of high tempenature aging.
    TEST AND ANALYSIS
    Prediction of austenitization kinetics of 5CrNiMoV steel
    Peng Xu, Bu Hengyong, Li Mengnie
    2020, 45(9):  227-232.  doi:10.13251/j.issn.0254-6051.2020.09.042
    Abstract ( 54 )   PDF (568KB) ( 18 )  
    Dilations of 5CrNiMoV steel at different heating rates were measured by utilizing DIL-805ADT dynamic dilatometer,and dilationcruve was analyzed.Kinetic parameters in the Johnson-Mehl-Avrami (J-M-A) model for non-isothermal diffusion phase transitions were fitted from the dilation data using the Kissinger method.Such kinetic parameter as the activation energy Q,exponent n and lnk0 are determined to establish kinetic model for austenization.Calculated amounts of transformed austenite are in good agreement with the experimentally observed.The model can be used to predict isothermal austenization and to design austenitization process of the 5CrNiMoV steel in engineering practice.
    Calculation and verification of vacuum low pressure carburizing process based on saturation adjustment method
    Chen Xuyang, Cong Peiwu, Fan Lei, Wang Tong
    2020, 45(9):  233-236.  doi:10.13251/j.issn.0254-6051.2020.09.043
    Abstract ( 55 )   PDF (558KB) ( 19 )  
    Based on Fick's second law and saturation adjustment method,combining with the control process of vacuum low pressure carburizing process,an algorithm flowchart was given out and a calculation program for vacuum low pressure carburizing process was compiled by using mathematical calculation software,then the program was verified with 20Cr steel as the test object.The results show that the total time of the carburizing process for 20Cr steel is about 240 s faster than that of the traditional way,and the carburizing time is saved more than 600 s by adopting the vacuum low pressure carburizing process based on the saturation adjustment method.The calculation program for carburizing process can accurately predict the depth of carburizing layer,and can meet the higher technical requirements of surface carbide grade on the product and microstructure.
    Measurement and analysis of continuous cooling transformation curves for 42CrMo steel
    Li Kai, Hu Jianwen, Shi Shaokun
    2020, 45(9):  237-239.  doi:10.13251/j.issn.0254-6051.2020.09.044
    Abstract ( 88 )   PDF (560KB) ( 27 )  
    Microstructure transformation and bainite content at different cooling rates were analyzed to obtain the CCT curves of 42CrMo steel by using JMat-Pro software to simulate the continuous cooling transformation curve and by using DIL805L thermal dilatometer to determine the phases transformation temperatures.The results show that Ac1 and Ac3 of the 42CrMo steel are 743 ℃ and 792 ℃,respectively.When the cooling rates are less than 0.5 ℃/s,the transformation products are proeutectoid ferrite and pearlite.In the cooling rate range of 0.5-10 ℃/s,a certain amount of bainite appears which increases first and then decreases with the cooling rate increasing,meanwhile the martensite content increases gradualy and resulting to a large increase of hardness.When the cooling rate is over 10 ℃/s,the resulted microstructure is the mixed collective composed of martensite matrix and a small amount of bainite.
    Cause analysis and improvement measures of 4140 steel curved shell
    Wang Jinyong, Qi Xilun, Cao Hongbo
    2020, 45(9):  240-243.  doi:10.13251/j.issn.0254-6051.2020.09.045
    Abstract ( 57 )   PDF (560KB) ( 22 )  
    More fractures happened in the 4140 steel curved shellproduced by a drlling tool factory.The reason for fracture of the failed curved shell was studied by analysis of chemical composition,mechanical properties and microstructure,and the heat treatment process was optimized accordingly.The results show that the fracture of the failed curved shell is caused mainly by incomplete quenching,which results into a large quantity of strip ferrite and block ferrite in the microstructure and poor strength,hardness and impact toughness of the material.By adopting the optimized quenching process,the material life reaches the normal level.
    Failure analysis and improvement measures of quenched and tempered crack on42CrMoA steel pin shaft
    Jiang Qingbin, Zhang Zuozhi, Zhu Zhengwei, Zhou Yunjie
    2020, 45(9):  244-247.  doi:10.13251/j.issn.0254-6051.2020.09.046
    Abstract ( 112 )   PDF (727KB) ( 41 )  
    Causes of cracking of 42CrMoA steel pin shaft after quenching and tempering were analyzed by means of macroscopic and microscopic observation,chemical composition analysis,hardness test and microstructure test.The results show that the crack at the end thread hole of the pin shaft is due to quenching,which is mainly caused by unqualified raw material structure,too fast cooling rate of quenching medium and unreasonable structure design of parts.By optimizing the material,quenching medium and product structure,the quenching cracking of the pin shaft is avoided.
    EQUIPMENT
    Numerical simulation of floating heat transfer process and structure optimization of air cushion furnace
    Zhang Jiayuan, Li Ping, Zeng Qi
    2020, 45(9):  248-256.  doi:10.13251/j.issn.0254-6051.2020.09.047
    Abstract ( 58 )   PDF (558KB) ( 23 )  
    Air cushion furnace is a kind of advanced equipment for heat treatment of thin aluminum alloy sheet.Based on the structure of air cushion furnace designed by an aluminum factory,a three-dimensional calculation model of the whole air cushion furnace was established.And floating heat transfer process of sheet in this furnace was simulated by means of fluid-solid coupling FSI analysis method.The results show that the heat transfer in the furnace is basically uniform,but the downward distortion of the sheet is too large to achieve normal floatation.In order to reduce the sheet distortion,orthogonal experiments were used to optimize the nozzle layout parameters of the air cushion furnace in the optimum space,and the structure parameters of the air cushion furnace diversion device were optimized based on response surface and genetic algorithm.The results show that the air flow and pressure distribution on the upper and lower surfaces of the plate are more reasonable after optimization.The distortion of the sheet in the furnace is reduced from 110.3 mm to 41.4 mm,and the floatation of the sheet is realized.
    Optimal design of quenching fixture for multi-arc head used in aerospace
    Lin Lei, He Feifei, Lin Gang, Chen Yong, Ran Haijun
    2020, 45(9):  257-261.  doi:10.13251/j.issn.0254-6051.2020.09.048
    Abstract ( 45 )   PDF (563KB) ( 23 )  
    Quenching treatment method for a multi-arc head parts used in aerospace products was developed.Through the finite element analysis,the thermal tend for the multi-arc head under the constraint of the bottom was studied.The 3D model of the multi-arc head quenching fixture was established,and the basic structure of the multi-arc head quenching fixture was introduced.The results of thermal distortion distribution for the multi-arc head under the constraint of quenching fixture are obtained by the finite element analysis(FEM).The FEM results show that the total distortion of multi-arc head is 16.0 mm,in Z direction is 15.0 mm,and in X direction is 8.5 mm.Through the analysis of the local thermal distortion of the multi-arc head quenching fixture,the optimal design scheme of the quenching fixture is proposed.The thermal distortion distribution of the multi-arc head is optimized.The total distortion is 7.0 mm,in Z direction is 10.0 mm,and in X direction is 3.0 mm.The problem for large distortion of the multi-arc head heat treatment is solved and verified by production.

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