Experimental and theoretical study of the formation and growth of pearlite colonies in eutectoid steels

Optical and electron-microscopy observations of pearlite structures in eutectoid steels are described. These observations suggest that in such steels the processes of sidewise growth of pearlite colonies along grain boundaries may occur even though they were not observed in noneutectoid steels. A simple theoretical model is proposed to study the thermodynamics and kinetics of pearlite transformations. Simulations of the growth of pearlite colonies carried out on this model reveal that, for the usually assumed mechanism of volume diffusion of carbon, such growth is always unstable, and the steady-state growth can only be realized via interfacial carbon diffusion. A model is proposed for the formation of pearlite colonies near the grain boundaries of austenite. This model is based on the assumption that the diffusion of carbon is strongly enhanced near these boundaries, and it can be applied to plastically deformed steels. The results of simulations with this model qualitatively agree with some microstructural features of the formation of pearlite colonies observed in such steels.