1998 Volume 84 Issue 9 Pages 650-657
A mathematical model for predicting precipitation kinetics of Nb(C, N) in austenite has been developed on the basis of the classical nucleation theory and the diffusion controlled growth theory. The local equilibrium condition is assumed to maintain at the interface in which the contribution of the interfacial energy due to the curvature of precipitates is taken into account. With this modification, the changes in diameter and its distribution of precipitates can be evaluated as well as the fraction precipitated in the overall reaction including the Ostwald ripening. Calculated diameters and fractions of Nb(C, N) in both extra low carbon and HSLA steels are in good agreement with those observed. The present model predicts the existence of stasis in the change in average diameter of precipitates prior to the Ostwald ripening. This stasis can be understood as a result of the change in the diameter distribution of precipitates due to the change of the principal driving force for the movement of the interfaces.
