Influence of Thermomechanical Processing on the Austenite-Pearlite Transformation in High Carbon Vanadium Microalloyed Steels

Multipass torsion tests were carried on with several V-microalloyed high carbon steels, using different deformation sequences in order to modify the austenite state prior to transformation. Both recrystallized and deformed austenite microstructures were studied. After deformation, different cooling rates were applied. The results show that accumulating strain in the austenite before transformation seems to slightly increase the interlamellar spacing for a given cooling rate, this increase being related to the pearlite transformation taking place at higher temperatures because of the increase in the austenite grain boundary area per unit volume (SV). On the other hand, the retained strain significantly contributes to a refinement of the “ferrite units”, this effect being more significant as vanadium and nitrogen contents rise. A relationship between the mean “ferrite unit” size with SV and cooling rate was determined. Similarly, empirical expressions to predict strength as a function of vanadium microalloying addition, SV and cooling rate were derived.