Effects of room-temperature deformation and three-stage heat treatment on microstructural characteristics and precipitation-strengthening mechanisms in Fe–Cr–Ni–Al stainless steel

A semi-austenitic precipitation-hardenable Fe-Cr-Ni-Al stainless steel is a promising candidate for fatigue-resistant parts in surgical instruments and high-performance automotive components; however, its practical use is limited by softening during solution treatment and an insufficient martensite volume fraction. To overcome these constraints, a novel three-stage heat treatment without annealing was designed, comprising pre-deformation, intermediate-temperature homogenization, aging, and a shallow cryogenic treatment, combined with a 0°C quench that provides a higher driving force for transformation than conventional quenching, to achieve a strength of 1200 MPa/EL: 20% standard. Pre-deformation introduces stored energy that facilitates grain refinement during homogenization, while subsequent uniform aging precipitations provide strengthening and assistance for phase transformation. A subsequent shallow cryogenic treatment (−12°C) further enhances phase stability. The strengthening is primarily attributed to a high density of martensitic grain boundaries formed by second-phase-assisted heterogeneous nucleation, together with hard Ni 3 Al precipitation. These synergistic effects underscore the potential of Fe-Cr-Ni-Al stainless steel for high-strength, heat-resistant applications and provide useful guidance for the development of optimized heat treatments for precision stainless-steel components.