High-Temperature Corrosion of Iron–Chromium Alloys in Oxidizing–Chloridizing Conditions

Abstract

An investigation has been carried out into the effects of 0.1 to 1.0% HCl onthe oxidation of Fe–28%Cr and Fe–28%Cr–1%Y inargon–20%O₂ at 600 and 700°C. At the higher temperature,the additions of HCl to the gas caused considerable increases in corrosionof the binary alloy, with the rates of metal loss actually being greaterthan those of iron in the 0.5 and 1% HCl-containing environments. Thick andmultilayered scales were observed; these were oxides, particularlyFeCr₂O₄ and Fe₂O₃, that developedfollowing formation and vapor phase transport of chlorine-containing speciesfrom the metal surface. The main metal-loss processes were evaporation ofFeCl₂, CrCl₂, and CrO₂Cl₂, withthe first two of these reacting with oxygen to form solid oxides in thescale, while the third was lost mainly to the environment. The addition of1% Y to the alloy resulted in a marked improvement in corrosion resistanceat 700°C, because of the reactive element facilitating rapidestablishment of a protective Cr₂O₃-rich layer andpromoting the formation of condensed chlorides rather than the more volatileCrO₂Cl₂ phase. At 600°C, additions of HCl toargon–20%O₂ caused formation of some localized condensedchlorides on both alloys, but the corrosion rates were relatively low,because of protection by a Cr₂O₃-rich oxide scale.