Study On Microstructure Control Of Medium Manganese Steel With High Strength And Ductility

High-strength and high-plasticity automotive steel not only improves the impact energy absorption of parts,but also improves the formability of high-strength steel.The mediummanganese third-generation automotive steel obtains a large amount of metastable austenite through austenite reverse transformation annealing and is enhanced by its TRIP effect to obtain excellent mechanical properties during the deformation process.This article discusses the influence of preliminary heat treatment and austenite reverse transformation annealing process on the microstructure and mechanical properties of medium manganese steel.The purpose is to obtain ultra-high strength and high plasticity mechanical properties during short-time austenite reverse transformation annealing.The microstructure was characterized by XRD,SEM,EBSD,TEM and other means,and the mechanical properties were characterized by a uniaxial tensile test at room temperature.It was studied how the pretreatment structure affects the microstructure and properties of 0.2C-7Mn steel by austenite reverse transformation annealing.The results show that the medium phase manganese steel prepared by heat treatment at two phases under austenite reverse transformation annealing at 650 ? for 3 min,which is easier to obtain the mechanical properties of high strength and high plasticity,compared with the case of quenching and tempering as preliminary heat treatment.Compared with quenching treatment,residual austenite is transformed into fine martensite after cryogenic treatment,which provides more nucleation sites for reverse transformation austenite in the subsequent austenite reverse transformation annealing process.In addition,after inheriting the high carbon and high manganese of austenite,martensite can also provide austenite nucleation driving force,which is beneficial to obtain more stable and fine austenite structure and produce higher toughness and plasticity.The effect of reverse phase transformation annealing process parameters on the microstructure and mechanical properties of cold-rolled 0.2C-9Mn steel was explored.It was found that the two-step austenite reverse transformation annealing can refine the austenite grains and increase the austenite volume fraction,thereby improving the strong plastic.When the austenite reverse transformation annealing temperature is too high,austenite is prone to martensite transformation during subsequent cooling process,leading to deterioration of mechanical properties;Through the use of pre-heat treatment + austenite reverse transformation annealing process,medium manganese steel respectively obtained tensile strength-total elongation after breaking are excellent mechanical properties of 1382 MPa-37.2% and 1502 MPa-20% respectively...