| In recent years,my country's economy has developed rapidly,and the production and sales of automobiles are also increasing year by year.The automobile industry is facing challenges in energy conservation,environmental protection,emission reduction,and safety.The requirements for advanced high-strength steels for automotive steels are also getting higher and higher.In this paper,7.4Mn-1.77Si(wt%)medium manganese steel was designed and prepared,and the effect of quenching-partitioning process on the microstructure evolution and mechanical properties of medium manganese steel was studied.The effect of melting temperature on the properties of medium manganese steel.The microstructure evolution of medium manganese steel and the diffusion behavior of carbon and manganese elements under different processes were analyzed.Using Room Temperature Tensile Test,OM,SEM,EBSD,TEM,XRD and 3DAP and other characterization techniques,the effect of element diffusion on the volume fraction,grain size,grain orientation,work hardening strain of retained austenite was further explored.and other factors.The following conclusions were reached:(1)The microstructure of the test steel after heat treatment by Q?P processes are composed of martensite,ferrite and austenite at room temperature.Among them,the ferrite is massive;the martensite has two forms of lath and short rod,among which the lath is primary martensite,and the short rod is secondary martensite.The EBSD characterization results show that the formation of small austenite grains is related to the existence of thin strip martensite,which usually transforms during the deformation stage.The TEM characterization results show that the diffusion of C and Mn into austenite mainly depends on the current collector mechanism and dislocation tube,which increases the content of C and Mn in austenite and improves the stability of austenite.(2)The effect of partitioning time.The tensile strength of the test steel decreases with the extension of the partitioning time,the elongation increases with the extension of the partitioning time,and the volume fraction of retained austenite first increases and then decreases.When the partitioning time is 90 s,the retained austenite content is 12.17%,the tensile strength is 1530 MPa,the elongation is 22.6%,and the strength-plastic product is 34.6GPa·%.The comprehensive properties of the test steel are the best.(3)The effect of partitioning temperature.With the increase of the partition temperature,the tensile strength of the test steel showed a gradually decreasing trend,and the elongation showed a gradually increasing trend.As the partitioning temperature increases,the C obtains a larger diffusion activation energy during the diffusion,which makes the element obtain a larger kinetic energy during the partitioning,which increases the diffusion rate and makes more C and Mn diffuse into the austenite.It increases the stability of austenite and improves the comprehensive properties of the test steel.(4)The effect of austenitizing temperature.With the increase of austenitizing temperature,the tensile strength has an obvious upward trend,the elongation shows a gradually decreasing trend,and the strong plastic product shows an increasing trend;the volume fraction of retained austenite shows a gradually increasing trend,When the austenitization temperature is 680?,the volume fraction of retained austenite reaches 18.9%,and the comprehensive performance reaches the best.(5)The distribution of C and Mn elements at room temperature effectively increases the volume fraction of retained austenite.C and Mn are enriched at the martensite/austenite interface and retained austenite.The maximum concentrations of C and Mn in austenite are 1.8% and22.5%,respectively.Medium manganese steel has super high tensile strength(1400 ? 1600Mpa),large total elongation(20 ? 25%)and strong plastic product(27.11 ? 34.48 GPa·%).The uniform microstructure ratio,grain refinement and dislocation density lead to higher work hardening behavior. |
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