NUMERICAL-SIMULATION OF THE MICROSTRUCTURE IN THE RING ROLLING OF HOT STEEL

In the present work, the evolution of the microstructure, which influences the mechanical properties of the final products in ring-rolling, is investigated by a computer-simulation method, in which the plastic flow of the ring material and the local values of strain, strain rate and temperature are calculated by means of a proposed model employing a coupled thermomechanical three-dimensional rigid-plastic finite-element method and in which the development of the microstructure is analyzed by mathematical models that describe microstructural phenomena such as dynamic/static recrystallization, recrystallized grain size and grain growth. The variation of roll force and torque, and the distributions of austenite grain size and retained strain over the ring cross-section are obtained. The results show that although the thickness reduction per pass in ring-rolling is very small, an original coarse grain size can still be recrystallized to a fine grain size through continuous multi-pass rolling and careful control of the rolling speed, the temperature and the cooling conditions. The proposed method may be used also in the analysis of other forming processes, providing a means of microstructural engineering.