Corrosion Behaviour of Fe–Cr–(Mn, Si) Ferritic Alloys in Wet and Dry CO2–SO2 Atmospheres at 650 °C

Abstract

Model alloys of Fe–9Cr, Fe–20Cr and their ternaries containing 2Mn or 0.5Si (wt%) were exposed to Ar–20%CO2 and Ar–20%CO2–0.5%SO2 at 650 °C, and the results were compared with those in wet CO2, with and without SO2. In S-free, dry CO2, all 9Cr alloys went into breakaway, and the 20Cr alloys formed regions of protective Cr2O3, but also fast-growing Fe-rich nodules. Addition of SO2 to dry CO2 led to little change for 9Cr alloys and less protective scaling of 20Cr alloys, but decreased the extent of internal carburisation. Addition of H2O to CO2 caused breakaway for all alloys. Simultaneous addition of both H2O and SO2 to CO2, however, achieved the best results: passivation of 20Cr alloys, and partial protection of 9Cr alloys. The detection by XPS of sulphide species within the chromia scale allows a discussion of competitive adsorption of S-, C- and H-bearing species on oxide grain boundaries.