Effects of cerium and manganese on corrosion of Fe–Cr and Fe–Cr–Ni alloys in Ar–20CO2 gas at 818 °C

• CO2 gas is more corrosive than dry air for Fe–Cr and Fe–Cr–Ni alloys at 818 °C.
• Chromia scale grows faster in CO2 than in air.
• Cerium has no significant effect on reducing oxidation rate of the alloys in CO2.
• Manganese significantly improves oxidation resistance of Fe–20Cr and Fe–20Cr–20Ni alloys in CO2.

Model alloys Fe–9Cr, Fe–20Cr and Fe–20Cr–20Ni (wt.%) with Ce (0.05%, 0.1%) or Mn (1%, 2%) were exposed to Ar–20CO2 gas at 818 °C. Scales on Fe–9Cr alloys consisted of FeO and FeCr2O4, Fe–20Cr–(Ce) alloys formed only Cr2O3, and Fe–20Cr–(Mn) alloys formed Cr2O3 and MnCr2O4. All Fe–20Cr–20Ni alloys formed Fe3O4, FeCr2O4 and FeNi3. Cerium additions had little effects, but additions of 2% Mn significantly improved oxidation resistance of Fe–20Cr and Fe–20Cr–20Ni alloys. Most alloys also carburized. All alloys developed protective chromium-rich oxide scales in air. Different behavior in the two gases is attributed to faster Cr2O3 scaling rates induced by CO2.