Prediction of Microstructure Distribution in the Through-thickness Direction during and after Hot Rolling in Carbon Steels.

The combination of a mathematical model for recrystallization of austenite and a computer simulation for strain and temperature analyses were performed in order to predict the austenite grain size distribution in the through-thickness direction. The experimental grain size distribution was measured using laboratory one-pass and two-pass rolling tests in low carbon steels.Mathematical models for the critical strain for dynamic recrystallization, the grain size of dynamic and static recrystallizations, the fraction of dynamic and static recrystallizations and the grain growth of dynamically- and statically-recrystallized austenites are made to predict the austenite structure, based on the results of compression tests using hot deformation simulators. The temperature calculated with the finite element method (FEM) and the finite difference method (FDM) corresponded well with the temperature measured at the center and the quarter point of thickness of plates. Grain size distribution in the through-thickness direction increased with coarsening the initial austenite grain size and at rolling reduction ranging from 20 to 40%. The calculated grain size distributions obtained by computer simulation corresponded well with the experimental ones obtained with rolling tests at rolling reductions of 30 and 40%. The calculated values were, however, smaller than the experimental ones at a large rolling reduction of more than 50%. Since the difference between both values increased with increasing fraction of dynamic recrystallization, it is necessary for the mathematical model for it to improve.