An integrated system for analysis of metal flow and microstructural evolution in hot rolling

The microstructure and properties of hot rolled steel products are strongly influenced by the processing conditions. Designing a rolling sequence is currently a trial and error process often requiring a large number of production trials to produce parts to the required specifications. Increased competitiveness among steel companies and demand for better quality has accentuated the need to produce rolled steel products with increased consistency, improved tolerances and shorter lead times. There is therefore a strong need for the development of an off-line analysis tool that would enable production of parts to the correct specifications in a short time and at the lowest cost.; The objective of this dissertation work is to develop a computer based integrated system for analyzing metal flow and microstructural evolution during shape rolling. Development of such a system is complicated by the fact that the mechanics of metal flow are strongly influenced by the evolving microstructure which changes continuously during the process. It therefore requires an integrated approach encompassing deformation mechanics and physical metallurgy. In recent years, the finite element method (FEM) based on rigid-plastic formulation has become a powerful tool for analyzing metal forming processes including hot rolling. However, experience shows that FEM based on phenomenological flow stress models, lacks the ability to model accurately the material flow and rolling loads. The focus of this study is on developing procedures to integrate the microstructural evolution models into FEM.; A three dimensional finite element model for analyzing deformation and heat transfer in rolling was developed and tested under industrial settings during the first phase of this research. Next, semi-empirical microstructural evolution models as well as microstructure dependent flow stress models were developed by conducting controlled laboratory experiments and integrated into the finite element program. One of the controversial topics in microstructural modeling is the application of constant strain rate and temperature models to changing strain rate and temperature conditions. In this dissertation these issues are addresses by means of systematic experiments and procedures to integrate these models into FEM are developed. This integrated approach towards modeling shape rolling has resulted in superior predictions of rolling loads and metal flow. Predictions of metal flow, rolling loads and microstructural evolution were validated by means of industrial hot rolling experiments under production settings.