A comparative study of methods used for the prediction of nonisothermal austenite decomposition

In this paper, different phenomenological procedures applied to the prediction of the progress of nonisothermal austenite transformation are analyzed and compared. It is shown, that by formal generalization of the isothermal Avrami kinetic function, various types of kinetic differential equations can be generated. These are suitable for the phenomenological description of nonisothermal, diffusion-controlled, transformation processes. First, fundamental features of generalized kinetic differential equations and the additivity rule are discussed. Next, practical applications for prediction purposes are tested on the basis of dilatometric experiments. When studying the austenite/pearlite transformation in a low alloy eutectoid steel, transformation kinetics were measured under isothermal and nonisothermal conditions. Dilatometric measurements verified that both the ''semiadditive'' kinetic differential equations and the additivity rule can be successfully applied to predict the progress of nonisothermal austenite/pearlite transformation. It was found that the selected Avrami type semiadditive differential equation and the application of the additivity rule furnish practically identical results. This is due to the fact that there is a close theoretical relationship between the kinetic differential equations of separable types and the additivity principle.