Effect of aluminium addition on the oxidation and carburization behaviour of austenitic stainless in high-temperature SCO2 environments

The AFA stainless steels with 2.5 and 5 wt% Al were developed, and Al addition had a great influence on intermetallic compounds in AFA alloys, especially resulting in increasing of B2-NiAl phase. After 3000 h exposure in SCO2, the thickness of oxide scales for two AFA alloys was 5-7 times thinner than that of ASS without Al, and the structure of formed oxide scale significant changed, i.e., from single Cr2O3 to double-layer with Fe/Cr oxide and Al oxide. As for AFA-2.5%, the formed Al-riched oxide inner layer was amorphous and unstable, resulting in the severe internal oxidation and carburization occurrence.