Strong and ductile medium-Mn steel achieved via controlled martensite tempering

The present work simplifies the previous room-temperature quenching and partitioning (RT Q&P) process down to a single furnace cooling process, delivering a medium Mn steel with an ultimate tensile strength (UTS) of 1.7 GPa and a uniform elongation of 9.5%. The martensite tempering during furnace cooling is featured with slightly reduced dislocation density and is free of cementite precipitation, which is beneficial for ultrahigh UTS. Although the carbon partitioning is limited, the banded large austenite grains have proper mechanical stability owing to pre-existing high carbon content and the strong martensite matrix, allowing the gradual transformation-induced plasticity (TRIP) effect to enhance the work hardening behaviour and thus the good uniform elongation.