Water Vapor Effects on Corrosion of Fe–Cr and Fe–Cr–Ni Alloys Containing Silicon in CO2 Gas at 818 °C

Model alloys Fe–20Cr and Fe–20Cr–20Ni, with and without Si additions (0.1, 0.2 and 0.5 wt%), were exposed to Ar–20CO2–20H2O gas at 818 °C. All undoped alloys underwent breakaway corrosion, resulting in iron-rich oxide scales and internal carbide precipitates. Silicon addition significantly improved both oxidation and carburization resistance in wet CO2, by forming a layer of silica beneath the chromia scale. Silicon-bearing austenitic alloys underwent scale spallation on cooling from reaction. The contributions of thermal and growth stresses to spallation, and of growth stresses to the onset of breakaway are discussed