A carbide-free bainite/martensite/austenite triplex steel with enhanced mechanical properties treated by a novel quenching–partitioning–tempering process

A novel quenching–partitioning–tempering (Q–P–T) process was employed in a Mn–Si–Cr alloyed steel to obtain a triplex microstructure comprising carbide-free bainite, martensite and retained austenite. The carbide-free bainite formed during the quenching step (rather than partitioning step) of Q–P–T process can enhance the mechanical properties (e.g. the product of strength and elongation, ∼31.4 GPa%) by extending the partitioning time up to 30 min. A good combination of strength and elongation (Ultimate tensile strength: ∼1655 MPa; Elongation: ∼19%) has been realized for the Mn–Si–Cr alloyed high strength steel without expensive alloying, e.g. Ni, Mo, Nb in previous Q&P/Q–P–T processes. The enhanced mechanical properties could be attributed to the various types of retained austenite in the Q–P–T treated carbide-free bainite/martensite/austenite triplex microstructure.