Synergistic Optimization of Strength and Toughness in a Low‐Carbon Cu‐Bearing Steel via Tempering Temperature: Role of Reversed Austenite

This study focused on the relationship between the microstructure and mechanical properties of a Cu‐bearing steel treated by quenching and tempering. The evolution of strengthening and toughening mechanisms at different tempering temperatures was discussed in detail. The influence of tempering temperature on the quantity, morphology, and thermal stability of reversed austenite (RA) was systematically explored, thus revealing its mechanism in enhancing the low‐temperature toughness. At a tempering temperature of 650 °C, an optimal microstructure was obtained, characterized by a high content (15.3%) of film‐like RA, along with the appropriately sized Cu‐rich precipitates (about 11 nm) and fine lath structures. The steel achieved a yield strength of 824 MPa, tensile strength of 894 MPa, elongation of 23.60%, and impact energy of 204 J at −80 °C, demonstrating a remarkable combination of mechanical properties. On the contrary, only a small amount of blocky RA was formed at 630 °C, while tempering at 680 °C caused the decomposition of RA, both of which led to a significant decrease in toughness. These results revealed that the mechanical properties were significantly improved through optimized composition design and process refinement, providing theoretical support and practical approaches for designing high‐performance low‐carbon Cu‐bearing steels.