Improving the tensile ductility of the high-strength nanotwinned high manganese steel by a strategy combining cold rolling and warm rolling

Abstract

While a high density of nano twins can effectively enhance alloys, it also leads to a significant reduction in ductility, similar to other nanostructures. In this work, a deformation strategy combining cold rolling and warm rolling has been employed on a nanotwinned Fe-25Mn-0.5C steel to improve ductility. A high density of nano twins was introduced in the coarse-grained matrix first by cold rolling for high strength. Subsequent warm rolling at 500 °C sheared the large nano twin bundles, resulting in a mixed microstructure consisting of nano twins and more randomly oriented refined grains. Planar slipping of dislocations, instead of twinning, dominates the tensile processes, which brings strong pile-up and continuous work-hardening. Compared with the cold-rolled counterpart with full nano twins, the one with a mixed microstructure exhibits three times higher tensile elongation (21.3 % vs. 5.6 %) while maintaining similar tensile strengths (about 1440 MPa). The evolution of microstructures and the underlying strengthening mechanisms of the mixed microstructure were extensively discussed. Additionally, a cold-rolled and statically annealed sample was also included for comparison.