CHLORIDATION-OXIDATION OF 9 COMMERCIAL HIGH-TEMPERATURE ALLOYS AT 800-DEGREES-C

Chloridation-oxidation studies of nine commercial high-temperature all oys were carried out at 800 degrees C in three different H-2-HCl-H2O(v ) environments. (A) both low HCl and H2O(v) partial pressures, where e ither Cr2O3 or FeCr2O4 is stable, (B) both high HCl and H2O(v) partial pressures, where FeCrO4 is stable and CrCl2 is metastable, and (C) hi gh HCl partial pressure in the absence of H2O(v), where either CrCl2 o r Cr2O3 is stable. Although alloy 600 has the lowest Cr content of the se nine alloys, it showed excellent corrosion resistance in all three environments because of its high Ni content. Alloy 304, with the lowes t Ni content of the nine alloys, exhibited poor corrosion resistance i n the environment C, fair resistance in the environment B and good res istance in the environment A. Alloy 800 showed very good resistance in Environment A, and fair corrosion resistance in Environment B; howeve r, it suffered linear weight-loss kinetics when exposed to Environment C. The alloys 617, 214, HR-160, X, 230 and 86 have good corrosion res istance in Environments A and B because of their relatively high conte nts of oxide-scale-forming elements Cr and/or Al. In Environment C, ch lorine dramatically decreased the adhesion of the scale on the surface , and aluminum in alloys 617 and 214 hardly showed its usual beneficia l effect in combating corrosion, nor does silicon in alloy HR-160. Dif ferent corrosion mechanisms are proposed for the alloys in the differe nt environments.