Effects of Si and SO2 on Corrosion of Fe–20Cr and Fe–20Cr–20Ni Alloys in Reducing Waste Combustion Gases

Abstract

Model alloys, Fe–20Cr and Fe–20Cr–20Ni (wt%) with and without 1% Si, were exposed to four different gas mixtures Ar–10H2O, Ar–10H2O–0.1HCl, Ar–10H2O–0.1HCl–10CO2, Ar–10H2O–0.1HCl–10CO2–0.5SO2 (vol.%) at 650 °C. The Fe–20Cr and Fe–20Cr–20Ni alloys underwent breakaway corrosion in Ar–10H2O–(0.1HCl)–(10CO2), forming Cr2O3 and Fe-rich oxide nodules. Silicon addition markedly increased corrosion resistance for both alloys by forming an additional SiO2 layer beneath the Cr2O3 scale. Addition of SO2 to Ar–10H2O–0.1HCl–10CO2 significantly suppressed the formation of Fe-rich oxide nodules on Fe–20Cr. Corrosion in the SO2-bearing gas resulted in (Cr, Fe, S)-rich precipitates in all alloys. The effects of gas composition and Si alloying on corrosion of both alloys are discussed in terms of transport processes within the scales.