Corrosion behaviour of nanocrystalline 304 stainless steel prepared by equal channel angular pressing

► We use ECAP to synthesise nanocrystalline 304 SS (80–120 nm). ► We prove that nanocrystallisation of SS increases its corrosion resistance. ► Thickness and composition of passive film on nanocrystalline SS show no difference from as-received one. ► The improved corrosion resistance of ECAPed SS was caused by compactness and stability improvement of the passive film. Effect of microstructure change on the corrosion behaviour of equal channel angular pressed (ECAPed) 304 stainless steel (SS) was investigated. Nanostructure (80–120 nm) was obtained after 4 and 8 passes ECAP and exhibited a higher corrosion resistance than as-received SS. However, thickness and composition of the passive film formed in air at room temperature on both as-received and 8-pass samples show little difference, indicating that Cr diffusion is not enhanced by the formation of nanostructure. The improved corrosion resistance of ECAPed SS is not caused by thickness or composition change, but by compactness and stability improving of the passive film.