Achieving High Strength and Low Yield Ratio via Direct Quenching and Aging in Cu-Precipitation-Strengthened Steel

The high yield ratio remains a critical challenge restricting the widespread application of ultra-high-strength steels. This study investigates a direct quenching and aging (DQA) route without solution treatment in a Cu-precipitation-strengthened steel, aiming to achieve high strength combined with a low yield ratio, and compares it with the conventional solution treatment plus aging (SQA) process. The DQA sample exhibits an excellent yield strength of 1205 MPa, a low yield ratio of 0.93, and an impact energy of 105 J at -20 °C. Microstructural analysis reveals that the high dislocation density and refined grain structure generated during rolling provided numerous nucleation sites for fine, dense Cu precipitates during DQA treatment, thereby enhancing precipitation strengthening. The reduced yield ratio is primarily attributed to the high initial dislocation density and deformation substructure, which enhance work-hardening capacity and consequently lower the yield ratio. The toughness mechanisms of both processes are also discussed in detail. These findings offer valuable insights into optimizing the strength-toughness balance of ultra-high-strength steels.