Ultrahigh strength-ductility steel treated by a novel quenching-partitioning-tempering process

A novel quenching-partitioning-tempering (Q-P-T) process was employed in two kinds of Fe-Mn-Si-Nb alloyed steels with 0.2 wt% and 0.4 wt% carbon additions to obtain a triplex microstructure comprising martensite, retained austenite and fine carbides. The good combination of strength and elongation has been realized for Fe-Mn-Si-Nb alloyed Q-P-T steels. The product of strength and elongation is high up to 31.4 GPa% for Q-P-T steel with 0.4 wt% carbon (Ultimate tensile strength: ~1549 MPa; Elongation: ~20.3%), which meets the mechanical properties theoretically predicted of next generation advanced high strength steel. The strength and ductility both enhance with increase of carbon content in Q-P-T steels. Two possible mechanisms are employed to explain the reason of good mechanical properties.