A novel surface grain boundary engineering approach to improving corrosion resistance of a high-N and Ni-free austenitic stainless steel.

Grain boundary engineering (GBE) can effectively improve the corrosion resistance of materials, but the traditional thermal-mechanical process still exhibits some limitations. In the present work, a novel surface spinning strengthening (3 S) technology followed by heat treatment was applied to modify the microstructure near the surface (∼ 400 μm) of a high-N Ni-free austenitic stainless steel. Under an optimal condition of annealing at 1323 K for 60 min after 3 S, the fraction of special boundaries mainly involving Σ3 boundaries in GBE layer was significantly improved from 48.3 % to 69.1 %, thus achieving excellent resistances to intergranular corrosion and stress corrosion cracking. • Surface spinning strengthening technology followed by heat treatment was proposed forward as an effective surface GBE process. • Surface GBE markedly improves corrosion resistance while remaining mechanical strength. • Surface GBE introduces a high fraction of Σ3n boundaries in surface layer and diminishes random high-angle GB connectivity. • Σ3 boundaries greatly hinder the propagation of corrosion cracks along GBs. [ABSTRACT FROM AUTHOR]