Investigation of FIB-thinned TEM cross-sections of oxide scales formed on type 310 steel at 600°C in water vapour-containing oxygen atmospheres

Abstract

AbstractThe effect of water vapour on the oxidation of the type 310 (25Cr19Ni) austenitic stainless steel was studied through the detailed microstructure characterisation of the oxide scales formed at 600°C in dry O2, O2 containing 40% H2O at 0.5 cm/s, and O2 containing 40% H2O at 5 cm/s. FIB equipment was utilised for imaging and for producing thin foils containing the cross-section of oxide features for detailed analysis using TEM/EDS. Thin protective Cr-rich (Cr,Fe)2O3 was maintained in dry O2 atmosphere. Cr-loss through CrO2(OH)2 evaporation in H2O-containing O2 atmosphere from the oxide scale could, at sufficiently high flow rate, trigger local breakaway oxidation after 168 hours of exposure. These breakaway sites featured large oxide nodules, each consisting of an outward growing oxide island and an inward growing oxide crater. The local post-breakaway oxidation behaviour was discussed based on the composition and distribution of the various phases in these oxide nodules.