Changes of passes in binary metal systems deduced from the dynamic theory of clusters. application to fe-c

Abstract

From Binder and Stauffer's (1976a) master equation and Luiggi and Betancourt's (1997,  1994) particular models it is obtained the system of differential equations that defines the dynamics of phase transformation for the following schemes: 1) The solid solution decomposes directly into a stable phase passing through a critical size p and 2) The solid solution decomposes through a stable target phase of critical size q and a stable phase of critical size p. These models were applied to the Fe-C binary system at very low carbon concentrations. Our results show for the first model a sigmoidal evolution of the transformed fraction of Fe-C carbides at temperatures below 130ºC and of cementite above 150ºC, while the second model reports the presence of both carbides at all temperatures. It is corroborated that at higher temperatures and lower critical sizes kinetics occurs faster, while the dimer effect is more important for critical sizes q¹ p.