New insight on early oxidation stages of austenitic stainless steel from in situ XPS analysis on single-crystalline Fe–18Cr–13Ni

In situ X-ray photoelectron spectroscopy real-time measurements and angular-dependent high resolution core level analysis were used for the first time to investigate the Cr enrichment and oxide growth mechanisms on a model 304 austenitic stainless steel surface in the very initial stages of oxidation leading to pre-passivation. The oxidation kinetics was followed for increasing oxygen exposure and temperature, revealing an early nucleation regime (for exposure <10 L) leading to the formation of a strongly Cr-enriched Cr⁠³⁺/Fe^⁠3+ mixed layer followed by an oxide growth regime where preferential iron oxidation takes over and mitigate the initial chromium enrichment.