Modeling of AGS and recrystallized fraction of microalloyed medium carbon steel during hot deformation

In this paper, we have developed the equations for predicting austenite grain size (AGS) of microalloyed medium carbon steel during hot rolling. Dynamic recrystallization, which plays a major role in reducing the flow stress and AGS, was described by modifying Avrami's equation. In addition, for better AGS prediction of material during rolling, the fraction of dynamic recrystallization was expressed as a function of strain together with the Zener-Hollomon parameter. Torsion tests were performed in the temperature range of 900-1100 degreesC and the strain rate range of 5.0 x 10(-2)-5.0 x 10(0) s(-1) to study the softening behavior. To examine the validity of the developed equation, we have then applied it to a four-pass continuous deformation process simulated by hot torsion test. For the exact prediction of microstructural evolution during hot torsion test, the change of temperature was calculated using finite difference method. It was found that the calculated grain size of the alloy is in good agreement with the observed grain size. It is expected that a fine grained steel showing high strength and high toughness can be obtained by controlling deformation conditions on the basis of the newly developed equation. (C) 2003 Published by Elsevier Science B.V.