Prediction of Microstructure and Resulting Rolling Forces by Application of a Material Model in a Hot Ring Rolling Process

Ring rolling is a versatile incremental bulk forming process. Due to the incremental character of the process, it consists of a large number of deformation and dwell steps. Finite element (FE) simulations of bulk forming processes are capable of predicting loads, stresses and material flow. In recent years, the finite element analysis of ring rolling processes has become feasible both in terms of calculation time as well as regarding the closed loop control of the kinematic degrees of freedom [1]. Accordingly, the focus of interest now includes the prediction of the microstructure evolution. The accuracy of such numerical simulations strongly depends on the models characterizing the material behavior and boundary conditions. In this paper, a finite element based simulation study was conducted, in order to evaluate the impact of boundary conditions such as transfer time, radiation, heat transfer and friction on the target values of the ring rolling process. The results of the simulation study were compared to ring rolling experiments on an industrial size ring rolling device. A good accordance regarding the evolution of the outer diameter and radial force was observed. Strong contingencies of transfer time on the forces throughout the process were detected and considered in the simulation study. In a post processing step, the evolution of the microstructure considering the dynamic and static recrystallization as well as the grain growth was calculated using the FE results. The calculated grain sizes show good accordance with the experimentally observed microstructure of the ring before and after the rolling. Furthermore, the impact of process parameters on the evolution of the grain size was investigated.