In-Situ observation of the carburization of solid iron by graphite

The carburization of solid iron by graphite was investigated by using confocal laser scanning microscopy to understand the initial carburization reaction mechanism of solid iron by solid carbon at high temperatures. As the carburization was initiated, a liquid layer was formed at the interface and grew parallel to the interface after an incubating period for the liquid phase formation. This required incubation time decreased with an increasing temperature due to the decrease in the solubility limit of carbon in γ-Fe. A moving interface model was used to interpret the carburization and melting behavior of solid iron by solid carbon with consideration for the diffusion of carbon in both solid and liquid phases. Using the moving interface model, the diffusion coefficient of carbon in the liquid Fe-C alloys was obtained. $$D_L (m^2 /s) = 5.1 \times 10^{ - 7} \exp \left( { - \frac{{53.9 \times 10^3 }} {{RT}}} \right)\{ 1458 - 1623K\} $$ The rate of carburization in the solid and liquid phases was evaluated. As the liquid phase was formed, the contribution of solid phase in the carburization decreased from 9.5% at 1.3 s to 5.4% by 20 s.