Effect of Direct Quenching+Tempering and Cr Content on Cu Precipitation-strengthened Steel

The influence of direct quenching+tempering（DQ&T） and conventional solution treatment+tempering（ST&T）processes on the mechanical properties and microstructure of Cu precipitation-strengthened ultra-high-strength steel was systematically investigated. And the influence mechanism of Cr content（0.6 wt% and 1.6 wt%） on the strength and toughness of the Cu precipitation-strengthened steel was revealed. The results show that the DQ&T process significantly enhances strength and work-hardening capacity without compromising toughness, which is primarily attributed to the preservation of high-density dislocations from hot rolling+quenching, which improves tensile strength, while simultaneously promotes finely dispersed Cu precipitate formation. Under the identical DQ&T conditions, the high-Cr steel（1.6 wt% Cr） exhibits 50-70 MPa higher yield strength and impact toughness at-20 ℃ significantly improves compared to low-Cr steel（0.6 wt% Cr）. This is mainly due to the fact that the Cr element improves the hardenability, resulting in more lath martensite structure, and the precipitation of Cr/Mo enriched M₂C carbides is promoted, which enhances the secondary hardening ability and improves the toughness.