Plausible extension of Anand's model to metals exhibiting dynamic recrystallization and its experimental validation

Modeling and optimization of industrial hot-working operations by means of commercial finite element computer codes require robust constitutive descriptions, which could be easily implemented. Also, it is expected that such formulations are able to describe as accurate as possible the flow stress, work-hardening and work-softening rate of the material, as a function of microstructure and deformation conditions. The present communication describes the development of a novel constitutive description of metals which exhibit dynamic recrystallization during deformation under hot-working conditions. The formulation is founded on the extension of the model earlier developed by Anand and co-workers for the constitutive description of metals which exhibit dynamic recovery as the only dynamic restoration mechanism during hot deformation. The advanced constitutive formulation has been validated by conducting axisymmetric compression tests with samples of a R260 steel employed for the manufacture of rail tracks. The specimens were deformed in a wide range of temperatures and strain rates, both under constant and variable strain rate conditions. The latter involve either an increase or a decrease in the Zener-Hollomon parameter as plastic deformation is applied. The results obtained indicate that the proposed constitutive description is able to reproduce quite accurately the experimental flow stress data. It has also been shown that the correct computation of the recrystallization time and volume fraction recrystallized dynamically, by means of an appropriate differential or incremental formulation of the Avrami equation, constitutes an essential aspect of the model. Such an approach is particularly important for predicting correctly the changes in flow stress under variable strain rate conditions.