New insights into the effects of surface nanocrystallization on the oxidation of 321 austenitic stainless steel in a humid oxygen environment at 1000 °C

Abstract Oxidation behaviour of surface nanocrystallized 321 austenitic stainless steel (SN–321ASS) and its conventional polycrystalline counterpart (CP–321ASS) in O 2 + 10% H 2 O at 1000 °C was comparatively investigated. Uniform dense distribution of high diffusivity paths on the SN-321ASS greatly enhances the Cr and Mn diffusion throughout the oxidation front. Consequently: (i) formation of a thicker Cr-rich inner oxide layer on the SN–321ASS leads to a superior oxidation resistance, (ii) formation of Mn-rich spinel oxide as a uniform intermediate layer interrupts the easy access of oxygen and/or water to the Cr-rich inner oxide layer, thereby reducing the Cr-vaporization.