Novel ultrahigh-strength nanolath martensitic steel by quenching-partitioning-tempering process

A modified heat treatment process designated quenching-partitioning-tempering (Q-P-T) process is developed based on the quenching and partitioning process proposed by J.G. Speer et al. [Acta Mater. 51, 2611 (2003)] and D.K. Matlock et al. [Mater. Sci. Forum 426-432, 1089 (2003)]. A Fe-0.485C-1.195Mn-1.185Si-0.98Ni-0.21Nb steel after Q-P-T process satisfies the designed requirement of tensile strength over 2000 MPa,and elongation over 10%. The microstructure characterization indicates that this ultrahigh-strength steel consists of nanomicrostructures including lath martensite, filmlike retained austenite, and dispersive Nb-containing carbides. The effect of tempering time on the mechanical properties is analyzed based on microstructures.