Chloridation-oxidation of nine commercial high-temperature alloys at 800°C

Abstract

Chloridation-oxidation studies of nine commercial high-temperature alloys were carried out at 800°C in three different H₂-HCl-H₂O(ν) environments: (A) both low HCl and H₂O(ν) partial pressures, where either Cr₂O₃ or FeCr₂O₄ is stable, (B) both high HCl and H₂O(ν) partial pressures, where FeCrO₄ is stable and CrCl₂ is metastable, and (C) high HCl partial pressure in the absence of H₂O(ν), where either CrCl₂ or Cr₂O₃ is stable. Although alloy 600 has the lowest Cr content of these nine alloys, it showed excellent corrosion resistance in all three environments because of its high Ni content. Alloy 304, with the lowest Ni content of the nine alloys, exhibited poor corrosion resistance in the environment C, fair resistance in the environment B and good resistance in the environment A. Alloy 800 showed very good resistance in Environment A, and fair corrosion resistance in Environment B; however, it suffered linear weight-loss kinetics when exposed to Environment C The alloys 617, 214, HR-160, X, 230 and 86 have good corrosion resistance in Environments A and B because of their relatively high contents of oxide-scale-forming elements Cr and/or Al. In Environment C, chlorine dramatically decreased the adhesion of the scale on the surface, and aluminum in alloys 617 and 214 hardly showed its usual beneficial effect in combating corrosion, nor does silicon in alloy HR-160. Different corrosion mechanisms are proposed for the alloys in the different environments.