MODELING OF THE DYNAMIC RECRYSTALLIZATION OF AUSTENITE IN LOW-ALLOY AND MICROALLOYED STEELS

Using torsional tests in the austenite phase, the dynamic recrystalliz ation of a selection of low alloy and microalloyed steels was studied and Avrami's equation was modelled. The model is based on the experime ntal determination of flow curves and their subsequent modelling, maki ng it possible to calculate the recrystallized fraction (X(d)) as a fu nction of all the variables which intervene in hot deformation: temper ature, strain rate, austenite grain size and the chemical composition of the steel. The influence of the first three variables is quantified using the Zener-Hollomon parameter where the activation energy is exp ressed as a function of the content of each alloy. The start of dynami c recrystallization was determined by regression, finding a value of 0 .95 epsilon(p). In testing conditions all the elements were found in s olution in the austenite, except Ti which was found partially precipit ated. The results of these tests indicate that C, Si (low content), Mn and V have hardly any influence on the start of recrystallization whi le Mo, Ti and especially Nb delay it. Finally, the dynamic recrystalli zation kinetics are illustrated through the study of the microstructur e during deformation.