Kinetics of γ → α phase transformation in Fe-Mn alloys containing low manganese

Abstract

The kinetics of the γ → α phase transformation in Fe-Mn alloys with low Mn contents was studied using differential scanning calorimetry. Analysis of the measured heat capacity yielded both the austenite fractions as a function of temperature as well as the enthalpy difference between ferrite and austenite which decreases with increases in both the temperature and the Mn concentration. The transformation was modelled using an interface controlled growth model. It was assumed that the interface velocity is proportional to the chemical potential difference of the Fe lattice. The interface mobility has a simple exponential temperature dependence. Taking into account the austenite grain size distribution, the activation energy and the pre-exponential factor for the interface mobility were estimated from the heat effects at 140 kJ mol⁻¹ and 58 mm mol J⁻¹ S⁻¹ respectively.