Influence of CO2 purity on the oxidation of a 12Cr ferritic – martensitic steel at 550°C and importance of the initial stage

Abstract It has been shown that ferritic – martensitic (F/M) steels with 12 wt% Cr can form a protective oxide layer depending on the CO2 purity from the first stages of oxidation. The impurities which could explain this difference could be O2. In the case where O2 concentration in the gas phase was significant (>ppm), a thick duplex oxide layer was observed, whereas, if the O2 concentration was low (<ppm), a Cr rich oxide layer about hundred times thinner was formed. These results strongly suggested that O2 reacted before CO2 on the steel surface and that the protective oxide layer was formed by reactions between chromium and O2.