A MODEL FOR RECOVERY AND RECRYSTALLIZATION OF HOT DEFORMED AUSTENITE CONSIDERING STRUCTURAL HETEROGENEITY

A mathematical model for the recovery and recrystallization of austenite during a multi-pass hot rolling was developed. Contrasting to the conventional model, in which the condition of austenite before each deformation is expressed only by the average grain structure with homogeneous dislocation density, in the present model, the austenite is expressed taking into account the microstructure heterogeneity. Thereby, the distribution of grain size and dislocation density can be predicted. In modelling the microstructural change in the multi-pass hot deformation process, austenite was divided into a large number of small elements having, in each, different grain sizes as well as different dislocation densities. The distribution of grain size and dislocation density can be expressed by summing up the conditions of all the elements. The optimum number of elements were determined to be 100 considering the accuracy of prediction and the calculation time. The comparison of recrystallized fraction between the present and conventional models indicated that the present model gave much-improved results, especially when partially recrystallized austenite was hot rolled as often experienced in the latter stage of hot strip mill rolling and in the entire process of plate mill rolling.