High-temperature sulfidation of Al- and Mo-modified 310 stainless steel

High-temperature sulfidation behavior of 310-stainless-steel-based alloys (containing various amounts of Al and Mo up to 10 at.%) was studied over the temperature range of 700-900°C in sulfur vapor under 0.01 and 0.1 atm. The corrosion kinetics followed the parabolic rate law and decreased with increasing Al and Mo contents. The scales formed on the alloys were complex and multilayered. The outer scale consisted of iron sulfide (with dissolved Cr), (Fe,Ni)₉S₈ and chromium sulfides (Cr₂S₃/Cr₃S₄ with dissolved Fe), while the inner layer was a heterophasic mixture of Cr₂S₃/Cr₃S₄ Fe_1.25Mo₆S_7.7, MoS₂, Al_0.55Mo₂S₄ and FeS. Platinum markers were found to be located at the interface between the inner and outer scales, suggesting that the outer scale grew by the outward transport of cations (Fe , Ni and Cr) and the inner scale grew by the inward transport of sulfur.