Residual stress on the run out table accounting for multiphase transitions and transformation induced plasticity

The development of harder and thinner new steel grades requires computationally efficient numerical simulations of forming processes in order to optimize industrial conditions through parametric studies. Within this general framework, the present contribution deals with one particular process, namely the run out table. Thus, this paper focuses on the evolution of residual stresses of thin strips during cooling on the run out table. Due to the fact that the complete problem is a nonlinear multiphysics process, it is known that simulating such processes with fully coupled numerical procedures leads to high computational costs. Therefore, a simplified numerical strategy has been developed. This procedure consists of three steps: (i) solving the thermal problem coupled with multiphase transitions; (ii) computing thermal expansion, metallurgical deformation and transformation induced plasticity and (iii) solving the associated mechanical problem. Residual stress profiles through the strip thickness are also computed in order to evaluate classic flatness defects such as crossbow and longbow. A post-processing is also included in order to quantify out of plane displacements that would take place if the strip was cut off the production line. The post-processing consists in computing at finite strain the relaxation of residual stresses when the tension applied by the coiler is released. The proposed numerical strategy has been tested on common industrial conditions.