Breakdown of chromium oxide scales in sulfur-containing environments at elevated temperatures

Abstract

Structural Fe-Cr-Ni alloys may be rapidly degraded in oxygen-sulfur mixed-gas environments at elevated temperatures unless protective oxide scales can be formed and maintained. The breakaway corrosion process was examined in model alloys of Fe-25wt.% Cr-20wt.% Ni with and without Nb and Zr additions. Oxide scales were preformed in S-free environments and subsequently exposed to oxygen-sulfur mixed-gas atmospheres. Preformed scales were found to delay the onset of breakaway corrosion. The beneficial effects of refractory metal additions were achieved via formation of a barrier layer at the Cr2O3 alloy interface.