A strong and ductile medium Mn steel manufactured via ultrafast heating process

•Flash processing (FP) could remarkably strengthen the cold-rolled 7Mn steel without sacrificing ductility.•Strain-induced martensite plays a key role for the rapid reverse transformation during FP.•Bimodal size distribution of retained γ grains results from austenitization of both strain-induced and thermal martensite.•A bainite-like displacive austenitization mechanism during FP is proposed due to C partition and higher As than T0′.