T.M.C.P. (Thermo Mechanical Control Process) has been widely used in the steel industry. We have produced fine grain hot strips and hot plates through high reduction and low temperature rolling. However austenite structure before ferrite transformation has not been clarified, since it is impossible to freeze the austenite structure in carbon steels. The fine ferrite grains are generally inherited from parent austenite grains through phase transformation at high temperature.
Electron backscattering diffraction with field-emission scanning electron microscopy (EBSD) was recently used to analyze the martensite structure with Kurdjumov-Sachs orientation relationship by the use of the pole figures. In this work, the computational variant analysis method using the rotational matrix of Euler angle data measured by EBSD was applied to determine the prior austenite grain boundaries. The prior austenite structures were constructed from the ferrite/pearlite structures of the multiple hot-compression test samples and of the hot strips at the actual tandem hot strip mill. The accuracy of the prior austenite grain size obtained by the present method is coincided well with the results from corresponding compression experiments. By employing the numerical method as an effective tool, a comprehensive investigation into the fine grain ferrite structure would be very useful.
