FEM simulation of dynamic recrystallization during asymmetric hot rolling of high-speed steel M2

Abstract

Abstract. Dynamic recrystallization of high-speed steel (HSS) M2 occurs through a discontinuous mechanism, involving nucleation and growth of strain-free grains. The initiation and completion of discontinuous dynamic recrystallization (dDRX) must be carried out in a single rolling pass. The time for 99% dDRX depends on the critical strain, strain rate and equivalent strain, that generated in the workpiece material in a single rolling pass. The level of equivalent strain plays a key role in terms of the possibility to complete dDRX. High equivalent strain in conventional hot rolling for a single pass is limited by too high rolling forces. High equivalent strain at low rolling forces can be achieved by asymmetric hot rolling. Asymmetric rolling is a process based on purposefully created differences in the circumferential speeds of the work rolls. For such a process, a degree of asymmetry is defined by a speed ratio of the work rolls. The speed ratio is one of the most important parameters of the process, affecting the level of equivalent strain and the rolling force. In this work the single-pass asymmetric hot rolling process of HSS M2 at different temperatures in the range 850-1150 °C was simulated by FEM and JMAK model. The effects of speed ratio and thickness reduction on equivalent strain and rolling force were investigated. The effects of equivalent strain, strain rate and temperature on the recrystallized volume fraction and the average size of a dynamically recrystallized grains of HSS M2 are presented. Symmetric and asymmetric hot rolling processes are compared.