Effects of Mo and Al additions on the sulfidation behavior of 310 stainless steel

Abstract

The high-temperature sulfidation behavior of 310stainless steel (310SS) with Mo and Al additions (up to10 at.%) was studied over the temperature range700-900°C in pure-sulfur vapor over the range of 10-3 to 10-1 atm. Thecorrosion kinetics followed the parabolic rate law inall cases and the sulfidation rates increased withincreasing temperature and sulfur pressure. Thesulfidation rates decreased with increasing Mo and Al contents and it wasfound that the addition of 10 at.% Mo resulted in themost pronounced reduction among the alloys studied. Thescales formed on 310SS with Mo additions were complex, consisting of an outer layer of ironsulfide (with dissolved Cr), (Fe,Ni)9S8, andCr2S3/Cr3S4(with dissolved Fe), and an inner heterophasic layer ofFe1-xS,Cr2S3/Cr3S4,NiCr2S4,Fe1.25Mo6S7.7, FeMo2S4, andMoS2. The scales formed on 310SS with Mo andAl additions had a similar mixture as above, except thatAl0.55Mo2S4 was alsoobserved in the inner layer. The formation ofMoS2 andAl0.55Mo2S4 partly blocked the transport of cations throughthe inner scale, resulting in the reduction of thesulfidation rates compared to 310SS.