Improving the strength and ductility of medium Mn steel by depleting the stress-assisted martensite

The present work investigates the role of martensite induced by either stress or strain on the tensile properties of medium Mn steel treated by quenching and partitioning/tempering. Different from the strain-induced martensite with isolated fine martensite blocks, the stress-assisted martensite is featured with large and continuous martensite blocks, which facilitates the propagation of cracks and results in the premature fracture and thus limited tensile ductility (12.8%). A pre-deformation and tempering strategy is employed to deplete the stress -assisted martensite while promote the strain-induced martensite, turning an original soft and brittle medium Mn steel into a strong and ductile one, leading to an increment of ultimate tensile strength and total elongation of 533 MPa and 28.4%, respectively.