Application of the cyclic phase transformation concept for investigating growth kinetics of solid-state partitioning phase transformations

A heat treatment involving cyclic partial phase transformations has been analyzed to determining growth kinetics of the austenite to ferrite phase transformation and vice versa more accurately. The mixed-mode model and the diffusion-controlled phase transformation model, including the soft impingement effects at the later stage of phase transformation, are reformulated for the cyclic austenite to ferrite and ferrite to austenite transformation. A new growth mode parameter H is defined for the mixed-mode model. It shows that not all partitioning phase transformations starts as pure interface-controlled growth but all of them shift gradually towards pure diffusion control when thermodynamic equilibrium is approached. The diffusion-controlled model predicts that the ferrite to austenite transformation should be faster than the austenite to ferrite, while the simulation of the mixed-mode model shows that the transformation rate ratio is a function of the ratio of interface mobility.