Abstract
Sulfidation behavior of Fe-26at%Cr, -36at%Cr, and -12at%Mn alloys at temperatures of 1073 and 1173K was investigated at a sulfur pressure lower than the dissociation pressure of ferrous sulfide at each temperature. External sulfide scales of (Cr, Fe)3 S4 or (Mn, Fe) S were formed with or without formation of an internal sulfide. The general internal sulfidation appeared for the Fe-Mn alloy at both temperatures and for an Fe-26Cr alloy at 1173K. The former was due to the smaller diffusivity in the alloy and the latter was due to an α to γ phase change. The sulfidation of an Fe-26 at%Cr alloy at 1073 K was confined within grain-boundaries. This was caused by a high sulfur solubility there. A mixture of general and grain-boundary sulfidation appeared when the Fe-36 at%Cr alloy was sulfidized at 1173K. The internal sulfidations of general, grain-boundary and their mixtures were explained by applying the criterion for external or internal oxidation proposed by Wagner.
