NUMERICAL-SIMULATION OF THE MICROSTRUCTURE IN THE RING ROLLING OF HOTSTEEL

In the present work, the evolution of the microstructure, which influe nces 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-elem ent method and in which the development of the microstructure is analy zed by mathematical models that describe microstructural phenomena suc h as dynamic/static recrystallization, recrystallized grain size and g rain growth. The variation of roll force and torque, and the distribut ions of austenite grain size and retained strain over the ring cross-s ection are obtained. The results show that although the thickness redu ction per pass in ring-rolling is very small, an original coarse grain size can still be recrystallized to a fine grain size through continu ous multi-pass rolling and careful control of the rolling speed, the t emperature and the cooling conditions. The proposed method may be used also in the analysis of other forming processes, providing a means of microstructural engineering.