The diffusion coefficient of carbon in cementite, Fe 3C, at 450°C

Abstract

The rate of formation of Fe 3C on fine iron powders at various carbon activities set by flowing CH 4/H 2 gas mixtures was determined at 723 K utilizing an automatic recording semimicro balance. The rate of growth of the Fe 3C was primarily parabolic. From the kinetics of formation and taking some freedoms with the geometries involved estimates of the diffusion coefficient of carbon in Fe 3C were made and were found to be in the range of 10 −16 to 10 −15 cm 2s −1 Because the diffusion coefficient of carbon increased somewhat as the carbon activity increased it was tentatively assumed that the carbon moves via an interstitial or interstitialcy mechanism.