EFFECTS OF MO AND AL ADDITIONS ON THE SULFIDATION BEHAVIOR OF 310-STAINLESS-STEEL

The high-temperature sulfidation behavior of 310 stainless steel (310S S) with Mo and Al additions (up to 10 at.%) was studied over the tempe rature range 700-900 degrees C in pure-sulfur vapor over the range of 10(-3) to 10(-1) atm. The corrosion kinetics followed the parabolic ra te law in all cases and the sulfidation rates increased with increasin g temperature and sulfur pressure. The sulfidation rates decreased wit h increasing Mo and Al contents and it was found that the addition of 10 at.% Mo resulted in the most pronounced reduction among the alloys studied. The scales formed on 310SS with Mo additions were complex, co nsisting of an outer layer of iron sulfide (with dissolved Cr), (Fe, N i)(9)S-8, and Cr2S3/Cr3S4 (with dissolved Fe), and an inner heterophas ic layer of Fe1-xS, Cr2S3/Cr3S4, NiCr2S4, Fe1.25Mo6S7.7, FeMo2S4, and MoS2. The scales formed on 310SS with Mo and Al additions had a simila r mixture as above, except that Al0.55Mo2S4 was also observed in the i nner layer. The formation of MoS2 and Al0.55Mo2S4 partly blocked the t ransport of cations through the inner scale, resulting in the reductio n of the sulfidation rates compared to 310SS.