Numerische Simulation des Presshärtprozesses unter Berücksichtigung der Gefügeumwandlung

Numerical simulation by means of Finite-Element-Method has become an indispensable tool for process design of metal-forming processes. But new steels and new processes, e. g. hot stamping, require advanced material models for valid simulation. For a more realistic prediction of the final properties of components made by hot stamping it is essential to consider the complex effects of phase transformation in the simulation. These effects mainly have a wide influence on residual stresses and distortion. A thermal-mechanical sequential coupled simulation including phase transformation of a model process is presented in this paper. A material model was implemented in the commercial FE-Code LS-Dyna. The diffusion-controlled phase transformation is basically modelled with the JOHNSON-MEHL-AVRAMI equation. Moreover, the formation of martensite is modelled by the KOISTINEN-MARBURGER equation for diffusionless transformation. The transport form furnace to the press and closing of the tools is also simulated in order to get a realistic temperature distribution in the sheet at the beginning of the forming process.