Intercritical rolling induced ultrafine microstructure and excellent mechanical properties of the medium-Mn steel

The medium manganese steel (0.2C5Mn) was first intercritically annealed and then intercritically rolled up to thickness reduction of 77.5%. It was found that intercritical rolling resulted in a microduplex microstructure with ferrite and austenite lath thickness continuously thinned and gradually rotated to be parallel to the rolling plane with increasing rolling strain, and during which the austenite was most retained after intercritical rolling. Mechanical properties examination indicated that the yield stress increased from 492 MPa to 980 MPa, and the tensile strength increased from 1030 MPa to 1296 MPa, but the failure elongation (31.7%) was almost the same with increasing rolling strain. Based on the experimental results, it was proposed that the microstructural refinement of the 0.2C5Mn steel was carried by the geometric thinning of laths and the suppression of recrystallization of ferrite phase and austenite phase. The significantly enhanced mechanical properties by intercritical rolling were attributed to the refined microstructure and the TRIP effects of the large fractioned austenite phase.