Enhancing strength and ductility combination via tailoring the dislocation density in medium Mn steel

Abstract

A novel strengthening strategy including warm rolling and intercritical annealing was proposed to optimize the strength and ductility of a Fe–10.2 Mn–2.2Al–0.41C-0.6V (wt.%) steel. Numerous microbands and nano-size V-carbide (VC) particles were generated in the warm-rolled samples with high stacking fault energy (SFE) and reasonable dislocation density. During tensile deformation, the dislocation density actively influenced microband evolution, deformation twins, and martensitic transformation. The strong interactions between the microbands, as well as between the microbands and dislocations, activated the transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects. Finally, the VC precipitates, microbands, dislocations, and TRIP and TWIP effects synergistically enhanced the ductility, tensile strength, and work hardening. The best tensile properties exhibited a yield strength of 1286 MPa, tensile strength of 1569 MPa, and total elongation of 21%. Meanwhile, dislocation hardening played an essential role in yield strength according to the calculation of individual contributions of grain size, VC precipitates, and dislocations toward yield strength. This work provided valuable insight into enhancing the combination of strength and ductility in medium Mn steels.