Oxidation of Metals, Vol. 36, Nos. 5/6, 1991 High-Temperature Sulfidation of Fe-Mn-Cr Alloys G. Southwell* and D. J. Youngt Received February6, 1991 Alloys of composition (in weight percent) Fe-lOMn-lOCr, Fe-lOMn-25Cr, and Fe-25Mn-lOCr were reacted at temperatures of 973 and 1073 K with flowing hydrogen-hydrogen sulfide mixtures corresponding to equilibrium sul- fur partial pressures of 10- 3 and 8 Pa. Sulfide-scale-growth kinetics and mor- phologies were compared with those found on pure iron and on the binary alloys Fe-25 Cr and Fe-25 Mn. All alloys reacted according to parabolic kinetics after an initial period of slow approach to this steady state. Of the materials exam- ined, the binary Fe-25Mn showed the slowest sulfidation rates, except at 973 K and a sulfur pressure of 8 Pa, where Fe-lOMn-25Cr had the best performance. Ternary alloys provided improved performance only when a scale layer of Cr3S4 was formed, an event dependent on temperature and sulfur activity. Multilayered scales were always formed on the ternary alloys, and the role of these layers in controlling sulfidation rates is discussed. KEY WORDS: Fe-Mn Cr alloys; sulfidation; Cr3S4; multilayered scales. 1. INTRODUCTION Because of their high-temperature strength, weldability, and relative econ- omy, austenitic stainless steels are preferred materials for use in the process industries. These steels rely for their protection on the formation of Cr203 or spinel scales. However, these oxides are not formed under sulfidizing conditions, and catastrophically rapid corrosion can result 1 from the forma- tion of low-melting eutectic mixtures of nickel + Ni3S2. A possible way of *Department of Industrial Chemistry, Universityof New South Wales, P.O. Box 1, Kensington NSW 2033, Australia. ~'School of Materials Science and Engineering, University of New South Wales, P.O. Box 1, Kensington NSW 2033, Australia. 409 0030-770X/91/1200-0409506.50/0 9 1991 Plenum Publishing Corporation