Sulfidation properties of Fe-Cr alloys at 1073 K in H2S-H2 atmospheres of sulfur pressures 10−2 and 10−5 Pa

An investigation is reported on the sulfidation properties of Fe-Cr alloys over their complete compositional range in H₂S -H₂atmospheres at 1073 K. Sulfidation of alloys containing less than 60 at. % Cr obeyed parabolic kinetics and alloys of larger chromium content and chromium followed linear kinetics. Scales were composed of two distinct layers: an outer columnar grained sulfide and an inner equiaxed grained sulfide layer of increased relative thickness and porosity at larger alloy chromium contents. The scales on quenched specimens were composed of either (CrFe)₅S₆or (FeCr)S plus small amounts of (FeCr)₃S₄at =10^–2Pa and of (CrFe)₅S₆at =10^–5Pa. Internal sulfidation was most pronounced in the high chromium content alloys and at the low sulfur pressure. The parabolic sulfidation rate at =10^–2Pa was large and of practically constant value irrespective of alloy composition. These kinetics at =10^–5Pa, however, increased from a very low value by three orders of magnitude as the alloy chromium content was increased from 5–60 at.%.