Effect of Tempering Temperature on Precipitates, Microstructure, and Mechanical Properties of Quenched Cu-Cr-Ni Ultra-High Strength Weathering Steel

• • Tempering at 550°C yields an optimal strength-toughness balance: yield strength of 895 MPa, tensile strength of 921 MPa, total elongation of 4.3%, and impact energy of 271 J at -40°C, suitable for structural applications requiring high strength and low-temperature toughness. • • Increasing tempering temperature from 500°C to 600°C reduces yield strength from 935 MPa to 866 MPa and tensile strength from 958 MPa to 888 MPa, while improving total elongation from 3.5% to 5.0% and impact energy from 249 J to 280 J at -40°C, indicating a trade-off between strength and ductility/toughness. • • MC precipitates (M = Ti, Nb, V, Mo) refine from an average size of 12.2 nm at 500°C to 9.9 nm at 600°C, enhancing precipitation strengthening and contributing to toughness improvement by reducing stress concentration. • • The transformation of rod-like cementite to spheroidized cementite with increasing tempering temperature mitigates stress concentration, improving ductility and impact toughness, which is critical for preventing brittle fracture in high-strength steels.