THE EFFECTS OF MANGANESE ADDITIONS ON THE SULFIDATION BEHAVIOR OF AN FE-28MO ALLOY

Iron-based alloys containing ca 28 a/o (atom per cent) molybdenum and up to 32 a/o manganese were sulfidized in flowing H-2/H2S gases corres ponding to p(S2) = 4 Pa at temperatures of 700-1000-degrees-C. Parabol ic sulfidation kinetics were invariably observed. Two-layered scales-a n outer FeS layer and an inner molybdenum-containing layer - developed on binary Fe-27Mo. Manganese additions to Fe-28Mo resulted in the for mation of an additional intermediate Mn(Fe)S-containing layer. The ove rall sulfidation rate was decreased by manganese additions of 24-32 a/ o at all temperatures and by additions of 10-18 a/o at higher temperat ures, but was increased by manganese additions of 10-18 a/o at lower t emperatures. This behavior is due to the combination of the improved p rotection provided by the Mn(Fe)S-containing layer, and the increased metal flux through the FexMO6S8-z phase in the inner layer.