Interface mobility in case of the austenite-to-ferrite phase transformation

The kinetics of the austenite(γ)-to-ferrite(α) phase transformation in steel grades with a sufficiently small amount of substitutional and interstitial components (e.g., ultra low carbon and interstitial free steels) is assumed to be controlled by the interface reaction only. Long-range diffusion of the components does not influence the kinetics. Experimental data (e.g., from dilatometer tests) provide the time dependence of a quantity related to the volume fraction of ferrite. For the steel grade considered in this work simple, however, realistic geometrical assumptions (e.g., planar growth, spherical growth) are made with respect to the shape of the ferrite phase. The numerical results imply planar growth for the initial transformation stages. Based on this analysis the effective mobility of the α–γ interface is determined. Furthermore, reasonable values for the intrinsic, thermally activated mobility are found by considering solute drag.