Iron layer formation during cementite decomposition in carburising atmospheres

Abstract In the following report cementite (Fe3C) formation and subsequent decomposition is investigated on pure iron samples at 700 °C in CO–H2–H2O gas mixtures. The carbon activities of the atmospheres are aC=15.9 and 20, values higher than the value of the equilibrium α-Fe+Fe3C. During the carburisation process cementite forms at the surface. Graphite deposition at the surface initiates cementite decomposition. An iron layer of 1–3 μm thickness forms between cementite and graphite as a result of cementite decomposition. In previous studies of metal dusting on iron it was found that at lower temperatures T⩽650 ° C the decomposition product iron is found in the coke as small particles.