Dual role of dislocations in enhancing strength-ductility synergy in a TRIP-assisted steel

Dislocations can act as barrier to the glissile martensite/austenite interface, resulting in mechanical stabilization of austenite. In contrast, dislocations can also assist martensitic transformation by providing mechanical interaction energy via elevated flow stress. The present work harnesses the competing role of dislocations in affecting the mechanical stability of austenite through one-step warm rolling process. The warm rolling process results in elevated dislocation density and brings triple benefits: (i) enhancing flow stress, (ii) preserving high initial austenite volume fraction, and (iii) improving martensitic transformation rate. The triple benefits, coordinated by the high dislocation density in affecting austenite stability, renders a medium Mn steel achieving sustained high strain hardening rate at high flow stress level across large strain regime, substantially enhancing the yield strength and ultimate tensile strength with no ductility loss. The present strategy can be applied to other metastable metals, such as high entropy alloys and titanium alloys.