Microstructure and mechanical property regulation of hot-rolled Al-contained medium-Mn steel by double intercritical annealing

Usually，the initial microstructure of hot-rolled and quenched medium-manganese experimental steel is composed of lath martensite matrix and a small amount of tiny granular austenite， also existing apparent Mn-segregation bands. Using double intercritical annealing （holding 60 min at 750 ℃ followed by 60 min at 700 ℃）， austenite reversion transformation in Mn-rich and Mn-lean regions are modulated by stages， which efficiently promoting the refinement of retained austenite grains and the optimization of mechanical stability distribution without apparent variation of volume fraction of retained austenite. The results show that adequate and sustained strain-induced martensite transformation is favored and boosted during uni-axial tensile deformation. Due to synergistic toughening of transformation and twinning induced plasticity effects， excellent combination of strength and ductility， such as the ultra-high total elongation of 85.3% and product of strength and plasticity （PSE） of 73.4 GPa∙% are obtained eventually.