Microstructural Characterisation of Austenitic Heat Resistant Sanicro 25 Steel after Steam Oxidation

Abstract

Microstructural and morphological observations of the surface scale on a high Cr and Ni austenitic heat resistant steel oxidised in water vapour at 700 °C are reported. Analysis of microstructure was carried out by analytical techniques of transmission- and scanning electron microscopy. Investigation of M ₂₃C ₆ nucleated at the interface between matrix and the Z-phase precipitates after exposing to high temperature showed semicoherency between M ₂₃C ₆ and the matrix and no coherency with the Z-phase. Plates developed on the oxide scale surface consist of Cr ₂O ₃ crystals separated by amorphous SiO ₂.