Achieving strength-ductility synergy in nanotwinned steels prepared by cryogenic deformation

Nanotwins introduced by cryogenic pre-deformation at the optimum temperature can remarkably improve both strength and ductility. In the present study, the effects of temperature on the tensile properties, stacking faults and mechanical twinning of Fe-17Mn-1.0Si-1.1C steel were systematically investigated to introduce mechanical nanotwins. With decreasing temperature, more stacking faults and thinner mechanical twins are produced in the solution-treated steel; however, the product of strength and ductility of the solution-treated steel is firstly increased and then decreased, achieving the greatest (about 125 GPa ▪ %) at −40°C. For the nanotwinned steel prepared by cryogenic pre-deformation, there exists an optimum pre-deformation temperature for the greatest strength-ductility combination. After introducing mechanical nanotwins at −40°C, the nanotwinned steel obtains the greatest strength-ductility combination of yield strength (1215 MPa), ultimate tensile strength (1521 MPa) and ductility (45.2%).