MODELING THE EFFECTS OF ALLOYING ELEMENTS ON THE FERRITE FORMATION KINETICS

摘要

The solute drag theory of Purdy and Brechet has been incorporated into a mixed-mode model to describe the overall austenite-to-ferrite transformation kinetics. This model permits to describe ferrite growth under the influence of substitutional alloying elements from a fundamental perspective. Interfacial parameters related to intrinsic mobility and solute drag has to be adjusted to match experimental growth kinetics. The number of fit parameters is similar to that of the frequently used but empirical JMAK model. A limitation of the present fundamental model is that the solute drag theory predicts a non-vanishing drag pressure for zero interface velocity. As a result, ferrite growth is predicted to cease before its completion. This severely limits the application of the model to the final transformation stages, particularly in the isothermal case; the effect is less pronounced for continuous cooling. Thus, the current model may be used as an effective tool to describe continuous cooling transformation. However, it is suggested to modify the Purdy-Brechet solute drag theory such that the predicted solute drag pressure vanishes as the interface velocity approaches zero.