Strengthening and toughening mechanisms of quenching–partitioning–tempering (Q–P–T) steels

► Performances of Q–P–T treated low cost steels show ultra-high strength associated with considerable toughness and ductility. ► Toughening and ductility mechanism in Q–P–T steel has been discussed. ► The considerable amount retained austenite and refining martensite give Q–P–T steel the excellent strength and ductility. Performances of quenching–partitioning–tempering (Q–P–T) treated low cost steels showing ultra-high strength associated with considerable toughness and ductility are summarized. Strengthening mechanisms, containing high density of dislocations in lath martensite, carbon pinning in dislocation, small block and packet as well as fine lath of martensite between flake-like retained austenite and large driving force for martensite transformation as well as fine carbides precipitation during tempering are discussed. Toughening and ductility mechanism in Q–P–T steel is mainly attributed to considerable amount retained austenite obtained by choice of a proper quenching temperature. The present author emphasizes that refining martensite lath size as to nanoscale and flake-like retained austenite with width of several tens nanometer should give Q–P–T steel with the excellent combination of strength and ductility. The realization and application of Q–P–T process in engineering will be briefly introduced.