Application of the maximum driving force concept for solid-state partitioning phase transformations in multi-component systems

A mixed-mode model is defined for solid-state phase transformation in multi-component systems. In contrast to diffusion-controlled phase transformation models, the mixed-mode nature of the presented transformation model takes the effect of a finite interface mobility into account over the entire temperature range of the transformation. In the model the maximum driving force concept is applied to determine the composition at the interface of the newly formed phase. This phase forms with the composition that gives the largest gain in free energy, i.e., the largest driving force. The model makes no a priori assumptions about the partitioning behaviour of any of the alloy components. As shown by example calculations on the austenite to ferrite transformation in an Fe–C–Mn steel, the model predicts a transition from partitioning to negligible partitioning of the substitutionally dissolved alloying elements during cooling.