Process design for refinement and homogenization of austenite grain size in bar rolling using FE analysis

Abstract

As the need for social infrastructures with large dimension and environment friendly light automobile increases, the importance of manufacturing steel with high strength is ever increasing. Among the various thermomechanical treatments, grain refinement is the only way to increase both the strength and toughness. Thus, it is of great importance to develop a technique to obtain finer grains in industry. Many studies have been carried out in developing mathematical models describing the relationship between the process parameters and mechanical properties of the rolled products. These models have been applied to industrial strip rolling process and many successful applications have been reported so far. In bar rolling area, not much study has been conducted due to the difficulties in modeling the three-dimensional material flow. To overcome this problem, several researchers in industry have developed approximate deformation models and predicted the average grain size. This approach can predict the microstructural changes for the industrial rolling having more than 30 passes only in a few seconds. Despite its computational advantage, the approach can provide only the average grain size with no information on local microstructures. Thus, more advanced approach which can predict the local microstructure in detail is required. In this study, an integrated microstructure modeling system was developed for prediction of the local microstructural change during bar rolling by combining the finite element (FE) analysis with a microstructural model. The metallurgical model available in the literature was adopted and integrated with the three-dimensional finite element analysis based on the rigid-thermoviscoplastic formulation. The current study focused on the prediction of austenite grain size (AGS) before the transformation stage during cooling. While several groups conducted studies on the FE based microstructural modeling, rigorous verification through bar rolling experi...