EFFECT OF SULFUR ON THE STABILITY OF CEMENTITE

Cementite Fe3C is an unstable carbide, which should decompose to iron and graphite, It was possible to grow cementite on iron samples in flo wing CO-H-2-H2O-H2S mixtures at temperatures between 400-700 degrees C , The cementite is stabilized by adsorbed sulfur, preventing graphite deposition, which would initiate metal dusting. Thus, this corrosion p henomenon, occurring in CO-H-2-H2O and other strongly carburizing atmo spheres can be suppressed by the presence of some H2S. The range of H2 S/H-2 ratios and temperatures in which iron is inert against metal dus ting, corresponds to the range where a monolayer of sulfur is adsorbed in iron. It may be supposed that the iron carbide process, i.e. the p roduction of Fe3C by reduction of ores in methane, is possible only by the presence of some sulfur.