<p>This study investigates the influence of quenching (Q), relatively low-temperature quenching (L), and tempering (T) processes on the mechanical performance of high-nickel steel, with a focus on improving low-temperature toughness and strength for demanding engineering applications. Compared to conventional quenching and tempering (QT) process, the QLT process leads to notable microstructural refinement, including reduced grain size and a more uniform dispersion of precipitates. These structural evolutions contribute to a significant enhancement in both tensile strength and impact toughness, particularly under cryogenic conditions. Compared to conventional QT process, after QLT heat treatment, samples under QLT treatment exhibited a modest reduction in tensile strength (from 1014 to 980 MPa) but a significant improvement in impact toughness (from 70 to 100 J), demonstrating a better balance between strength and ductility. Detailed microstructural and fractographic analyses reveal that the superior toughness is primarily attributed to grain boundary strengthening, carbide dispersion, and the stabilization of retained austenite induced by the intercritical quenching stage. These findings underscore the effectiveness of the QLT process as a viable heat-treatment strategy for developing high-nickel steels with a balanced combination of strength and toughness, especially for use in low-temperature and high-reliability structural applications.</p>