Effects of Silicon and Water Vapour on Corrosion of Fe–20Cr and Fe–20Cr–20Ni Alloys in CO2 at 650 °C

Abstract

Model alloys, Fe–20Cr and Fe–20Cr–20Ni without and with Si (0.1, 0.2 and 0.5 wt%), were exposed to Ar–20CO2 and Ar–20CO2–20H2O gases at 650 °C. The undoped alloys underwent breakaway corrosion in both gases, forming iron-rich oxide scales and internal carbide precipitates. Silicon additions markedly improved oxidation and carburization resistance of alloys in both gases by forming a duplex scale of chromia and silica layers. Chromia scales formed in wet gas were extremely fine-grained, but grew slower in wet gas than in dry. Selective oxidation of chromium and silicon is discussed in terms of diffusion theory.