Generalized Nb(C, N) Precipitation Model Applicable to Extra Low Carbon Steel

Abstract

The isothermal precipitation behavior of Nb(C,N) in austenite has been investigated using steels of different carbon contents, Theobserved progress of the precipitation in extra low carbon steel is muchfaster and size of the precipitates is apparently larger than those in steels with higher carbon content even though their supersaturations are the same. To explain this phenomenon,the local equilibrium at the austenite/ Nb(C.N) interface has been introduced into the classical nucleation theory and the sphericai growth theory, and a generalized precipitation modei has been proposed which can predict the precipitation behavior of extra iow carbon steels as well as that of HSLAsteels. As a conclusion, this study clearly shows that the kinetics of MC-typeprecipitation is influenced not only by the precipitate-forming atomic product. M x C, but also by its ratio, MIC. © 1992, The Iron and Steel Institute of Japan. All rights reserved.