Modelling of primary recrystallization in stainless steels

A mathematical model, able to describe the primary recrystallization of stainless steels has been developed. This model concerns the evolution of deformation cells (subgrains) into grains, by applying the concepts of the grain growth statistical model. It supposes that the recrystallization nuclei are present in the deformed matrix of the metal as areas relatively free from dislocations, and they are statistically represented by their size distribution. When a deformed material is subjected to heat treatment, the movement of subgrain boundaries is activated. Such boundaries delimit the areas free from dislocations (relatively low angle grain boundary), and the subgrain growth in the deformed matrix (driving force proportional to the dislocation density difference) occurs against the boundary energy generated by the crystals misorientation. The grains, at first assumed as all activated at the same time, freely grow in the deformed matrix until they get in contact to each other, by means of a continuous passage from the growth activated by deformation gradient to a proper grain growth process activated only by grain boundary energy. This model, in its simplified version, allows to reproduce the role of incubation phenomena and relates it to the type of the initial distribution. Moreover it describes the continuous change of kinetics, from Avrami to grain growth type. Moreover it is also possible to describe the effect on the recrystallization microstructure of the heating rate during annealing. Results from the model are here discussed in comparison with available experimental data on bcc-iron and measurements performed on stainless steels. By this model it is possible to analyze the role of recovery process on the kinetics and on the generated recrystallized microstructure. In this framework, finally, it is relatively easy to perform the extension of the model to include texture and drag effects.