On the application of the additivity rule in pearlitic transformation in low alloy steels

It is considered that the transformed fraction of pearlite from the decomposition of austenite contains contributions from both nucleation and growth transformed fraction and that they can be calculated using classic nucleation theory and the diffusional growth equation. The present study demonstrated that for the pearlite transformation in low alloy steels, the fraction of pearlite formed from nucleation is additive and that from growth is not. This suggests that additivity from isothermal data is not always valid in continuous cooling transformation. Only in special cases, i.e., when the ratio of rate of nucleation and rate of growth remains constant, does the pearlite transformation obey the additivity rule.