The kinetics of the austenite-ferrite phase transformation of Fe-Mn: differential thermal analysis during cooling

Differential thermal analysis (DTA) has been employed to study the austenite-ferrite phase transformation of Fe-1.89at% Mn upon cooling. The transformation has been shown to occur in two stages. The first stage is not thermally activated; the second stage is thermally activated. A phase transformation model, incorporating a new impingement correction, has been used for the extraction, from the DTA experiments, of data for the velocity of the austenite-ferrite interface. It follows that the interface velocity does not only depend on temperature, but also on transformed fraction. This has been interpreted as the consequence of the (non-neglectable) dissipation of energy by the volume misfit of the austenite and ferrite phases during the transformation. This misfit accommodation Gibbs energy has been assessed quantitatively; it has been shown to be of the same order of magnitude as the chemical Gibbs energy. (C) 2002 Acta. Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.