Carburization of austenitic and ferritic steels in carbon-saturated sodium: preliminary results on the diffusion coefficient of carbon at 873 K

Three commercial steels were exposed to carbon-saturated sodium at 873 K for durations up to 5000 h. Analyses by optical microscopy, infrared-inductive carbon combustion, electron probe microanalysis and glow discharge optical emission spectrometry revealed important carburization of the steels. The carbon concentration at the metal-sodium interface reached equilibrium, and the carbon uptake varied with the square root of time. The carburization kinetics was well described by assuming that diffusion of carbon was coupled with rapid carbide precipitation and equilibrium partitioning of carbon between the metal and precipitates phases. (authors)