Chloridation-Oxidation of Fe-Cr and Ni-Cr Alloys at 800°C

Abstract

Abstract The chloridation-oxidation behavior of Fe-Cr (0-25wt%Cr) and Ni-Cr (0-20wt%Cr) alloys was studied at 800°C in three different H2-HCl-H2O(v) environments. In a low HCl and low H2O(v) environment, where Cr2O3 is thermodynamically stable, the corrosion resistance of the Fe-Cr alloys increased with increasing Cr content in the alloys. In a high HCl and high H2O(v) environment, where FeCr2O4 is stable and CrCl2 is metastable, the corrosion resistance of the Fe-Cr alloys depended similarly on the Cr content. Low-Cr Fe-Cr alloys exhibited large weight losses, while Fe-Cr alloys with higher than 19wt%Cr showed good corrosion resistance. In an environment of high HCl in the absence of H2O(v), the evaporative corrosion rate was fast and limited by gas phase diffusion, and independent of the Cr content in the Fe-Cr alloys. Ni and Ni-Cr alloys generally showed good corrosion resistance in the environments of high H2O(v) because of the low NiCl2 vapor pressure and formation of a protective Cr2O3 scale. However, in the environment of high HCl in the absence of H2O(v), selective evaporation of CrCl2 occurs, which results in Cr depletion and even networks of voids for a high-Cr Ni-Cr alloy.