A study of the effect of the deformation parameters on recrystallization behavior in the rod rolling process

Rod rolling is a process in which the deformation of the workpiece between the work rolls is quite different from the rod drawing process, but the area strains (natural logarithm of area reduction ratio) multiplied by a constant have been used in the calculation of the pass-by-pass evolution of austenite grain size in rod (or bar) rolling without any verification. Considering that the deformation parameters (strain and strain rate) at a given pass play a crucial role in determining recrystallization behavior, the calculation method for the deformation parameters associated with rod rolling should be examined. In this study, a series of numerical simulations has been carried out using an area strain model [5] and an analytic model [6] which calculate the pass-by-pass strain in the rod rolling process, focusing on the effect of the calculation method for the pass-by-pass strain on the recrystallization behavior and evolution of AGS (austenite grain size) during a given pass. These have been investigated for a six-pass rolling sequence (oval-round or round-oval) designed for this study by incorporating the recrystallization and AGS evolution model being widely used in hot rolling. It was found that the recrystallization behavior and evolution of AGS during a given pass were significantly influenced by the calculation methods for deformation parameters. The area strain model lacks mathematical grounds to be used as input to the equations for recrystallization and AGS evolution.