Using torsional tests in the austenite phase, the dynamic recrystallization of a selection of low alloy and microalloyed steels was studied and Avrami's equation was modelled. The model is based on the experimental determination of flow curves and their subsequent modelling, making it possible to calculate the recrystallized fraction (Xd) as a function of all the variables which intervene in hot deformation: temperature, 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 expressed as a function of the content of each alloy. The start of dynamic recrystallization was determined by regression, finding a value of 0.95ϵp. In testing conditions all the elements were found in solution in the austenite, except Ti which was found partially precipitated. The results of these tests indicate that C, Si (low content), Mn and V have hardly any influence on the start of recrystallization while Mo, Ti and especially Nb delay it. Finally, the dynamic recrystallization kinetics are illustrated through the study of the microstructure during deformation.

This work has been undertaken in CENIM (Madrid) and the authors are grateful for the financial support of the DGICYT of Spain (Project PB89- 0022). Hernandez’s studies are sponsored by the UNAM (México)

Peer reviewed