Effect Of ART Annealing And Rolling Condition On The Microstructure And Mechanical Properties Of Medium-Mn Steel

In recent years, application of high strength and ultrahigh strength steels is greatlyincreased in the automobile industry. This situation has driven the research anddevelopment of steel with a good combination of strength and ductility worldwide. Theput forward of microstructure control theory (M3: Multiphase, Metastable and Multiscale)makes a worldwide research of Medium-Mn steels.In this study, a new type of Mn steels (0.1C5Mn) produced by continuous casting inthe steel industry were used as experimental materials, which were ART annealing andthen rolling in intercritical region and austenite region respectively. Scanning electronmicroscopy, electron back scattering diffraction and transmission electron microscope wasused to characterize microstructure evolution during annealing and rolling process. Theresidual austenite content in the continuous casting billet after being annealed and rolledwas measured by X-ray diffraction. Tensile test and impact test were used to characterizemechanical properties. It was found that the tensile strength was gradually increased firstlyand then decreased with the annealing temperature, and it get a maximum product ofstrength and ductility at625℃to650℃. Ultrafine ferrite and austenite were formedduring intercritical rolling. The thickness of the ferrite laths was only about0.15μm with arolling reduction of83.5%. The tensile strength was increased and the elongation wasdecreased by quenching after intercritical rolling. Both tensile strength and elongationwere increased after tempering. The tensile strength was increased with rolling reductionby austenite region rolling. It was found that intercritical annealing cloud greatly improvesthe ductility but the tensile strength and yield strength was decreased the same time.Based on the analysis above, it was found that austenite reserved transformationannealing could improve the microstructure and enhance the mechaniacal properties of themedium-Mn steel. It cloud refine the grain size obviously by intercritical rolling, and it’s apromising way to produce steel with excellent combination of strength and ductility. Also,it can improve the ductility of medium-Mn steel by intercritical annealing.