Kinetics of Graphitization of Cementite

Dilatometric measurements were carried out during the first-stage graphitization of white cast irons. It has turned out that the data can not be analyzed consistently by the rate equations proposed by Johnson-Mehl or Austin-Ricketts. A new type of rate equation, y=1−exp{−(t⁄τ1)n1[1−e−(t⁄τ2)n2][1−e−(t⁄τ3)n3]−1} has been derived and proposed to interprete the data in terms of the following model: The rate of graphitization is controlled by the rate of interfacial reaction by which cementite dissolves in the austenite, and the number of dissolving cementite particles increases with the increase of volume of voids in which graphite nodules are formed.