Quantitative analysis of the dilatation during an isothermal decomposition of austenites

The dilatation of hypoeutectoid steels during an isothermal transformation has been analysed. A model accounting for the effect of carbon redistribution has been developed which can be applied not only to the calculation of the dilatation during an isothermal transformation but also to the extraction of the phase change kinetics from a dilatation curve which may correspond to a multistep phase transformation. The model is validated by comparing it with the experimental results for an interstitial free steel. The dilatation of Fe–C steels during an isothermal transformation has been calculated and discussed. It is indicated that the isothermal formation of ferrite causes a different linear dependence of the relative length change on the volume fraction of the transformed austenite compared with the pearlite type decomposition. Isothermal transformation experiments have been carried out with an experimental bainitic grade steel. The model was successfully applied to extract the phase transformation kinetics from the dilatation curves of this steel.