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

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 M23C6 nucleated at the interface between matrix and the Z-phase precipitates after exposing to high temperature showed semicoherency between M23C6 and the matrix and no coherency with the Z-phase. Plates developed on the oxide scale surface consist of Cr2O3 crystals separated by amorphous SiO2.