A Coupled Thermomechanical Approach for Hot Rolling by a 3D Finite Element Method

A finite element model of hot rolling is described. It is based upon the flow formulation, with a Norton-Hoff purely viscoplastic behavior. We use a steady state approach with free surface updating by minimizing the material flux through the surface. To compute stresses, smoothed derivatives of the velocity are obtained and the strain rate tensor and stress deviator computed from them. Then the pressure field is calculated by a least squares method on the residual of equilibrium equations. A simplified thermal transfer equation is obtained by neglecting internal conduction. Boundary conditions include a contact temperature accounting for a thermal contact resistance and heat generated by friction. Thermomechanical coupling is performed. It is applied to simulation of a multipass blooming sequence in order to evaluate metallurgical evolution of the product. The interest of stresses computation is demonstrated for predicting surface crack opening and closing in shape rolling, with comparison to experimental trends.