Kinetics of the peritectic reaction in an Fe–C alloy

It is generally accepted that the peritectic reaction is controlled by diffusion of solute in the liquid phase, although experimental assessment of the kinetics of the peritectic reaction has been stymied by the difficulty of conducting in situ observations at the elevated temperatures at which this phase transition occurs. In the present study, high-temperature laser-scanning confocal microscopy (HTLSCM) was utilized to experimentally measure in situ, the kinetics of the peritectic reaction in an Fe–C alloy. The growth rate of the precipitating austenite phase, at a cooling rate of 20 K/min, was found to vary between 0.4 × 103 and 12.5 × 103 μm/s. These experimental observations are not consistent with solute diffusion control being the rate-controlling step of the peritectic reaction. Our observations and analysis provide evidence that the peritectic reaction is controlled by the rate of dissipation of heat of transformation, and a model is proposed that quantifies these new insights.