SIMULATION OF MATERIAL FLOW AND MICROSTRUCTURAL EVOLUTION DURING THE HOT-ROLLING OF FLAT PRODUCTS

A simulation system is presented in which the FEM calculation of the material flow is coupled on-line with simulation of the microstructural changes that occur during the hot rolling of steel to produce flat products. The local forming parameters and temperatures of the material concerned are determined by FEM simulation for the individual forming passes and used as the basis for advance calculation of the local microstructural changes using the metallurgically-oriented model. The latter takes account of factors such as austenitic grain growth on heating, recrystallization processes in the austenite during hot forming and in the intervals between forming as well as the gamma/alpha transformation during cooling after hot forming. The suitability of the simulation system for use in solving operational problems is shown by discussing an example taken from the area of hot strip production. The authors investigate the reasons for the microstructural inhomogeneities observed over the thickness of the strip. In addition, a critical appraisal is made of the widespread practice of effecting microstructural simulations with global forming parameters derived from the change in the external dimensions of the rolled material, instead of using local values.