High temperature sulfidation-oxidation of stainless steels

The alloys 153MA, 253MA and 353MA, Type 310S stainless steel, Type 309S stainless steel and IN601 were all exposed at 900 °C to a complex gas mixture of CO/CO2/SO2/N2, corresponding to a sulfur partial pressure of 1.3 x 10-3 atm and oxygen partial pressure of 3.2 x 10-l4 atm. The corrosion kinetics were parabolic in all cases. The rate for IN601 was unacceptably high due to extensive liquid sulfide formation. The other materials all formed solid external scales as well as undergoing some interna1 corrosion. The rates for all three MA alloys were less than those of the two conventional stainless steels. The corrosion behaviour of all the materials was dominated by sulfide formation as only relatively small amounts of oxides were formed. The same materials were exposed at 800 °C to a gas mixture corresponding to a sulfur partial pressure of 1.7 x 10-3 atm and an oxygen partial pressure of 4.9 x 10-l6 atm. No liquids were formed, and the corrosion products consisted of an outer scale layer of (Fe, Ni)l-xS, and an inner layer containing mixtures of sulfides and oxides. Reaction kinetics were again parabolic. The rates were rather similar, with IN601 reacting fastest, and 353MA slowest.