Investigation of the Evolution of the Oxide Scale Formed on 310 Stainless Steel Oxidized at 600 °C in Oxygen with 40% Water Vapour Using FIB and TEM

Detailed microstructure investigations were performed on oxide scales formed on 310 stainless steel exposed isothermally at 600 °C to O2 with 40% water vapour for 1–336 h. FIB microscopy was used to study the evolution of the surface morphology and to prepare cross-section TEM thin foils of the oxide scales. The foils were investigated by analytical transmission electron microscopy. The results showed that a thin protective base oxide scale had formed after 1 h. Due to Cr loss from the oxide scale through water vapour induced Cr evaporation, local breakaway oxidation occurs, resulting in the formation of oxide nodules. The development of these nodules depends on whether a new Cr-rich healing layer is formed or not. A model for the evolution of the oxide scale is proposed based on the results regarding the composition and distribution of various phases in the oxide scale and subjacent steel.