SULFIDATION BEHAVIOR OF FE-27MN-(0-17.3)MO(A O) ALLOYS/

Iron-base alloys containing ca. 27 a/o (atomic percent) manganese and up to 17.3 a/o molybdenum were sulfidized in H-2/H2S gases of 4 Pa sul fur partial pressure at temperatures of 700-1000-degrees-C. Three-laye red scales developed on all the molybdenum-containing alloys, and an i nternal sulfidation zone was observed in most cases. The overall scali ng process and individual layer growth all followed parabolic kinetics . The outer and intermediate layers comprised Fe(Mn)S and Mn(Fe)S, res pectively. Sulfidation rates varied with the morphology and constituti on of the inner layer. The reaction product FexMo6S8-z, which was rest ricted to the inner layer, is permeable to sulfur, iron and manganese, but not molybdenum. For high-molybdenum levels, the overall scaling r ate decreased, as a result of the slow diffusion of iron in FexMo6S8-z . For low-molybdenum levels, this beneficial effect is small and outwe ighed by the formation of an inner two-phase layer.