Micro-Structure Evolution in the Press Hardening Process with Respect to Tool and Contact Thermal Properties

With the press hardening technology, it is possible to produce automotive structural components with a tailor-made material property distribution. The properties can range from a soft ferrite dominated micro-structure to ultra-high strength martensitic structure. Tailor-made material property distribution is especially useful in components subjected to crash deformation. With this technique it is possible to account for structural integrity and in the same time maximize the energy absorption in the structure. The present work is based on a complete thermomechanical material model for simulation of press hardening and similar processes. The model accounts for and predicts time dependent and time-independent phase transformations, mechanical and thermal properties as well as transformation plasticity during the complete cooling and deformation process from 900 degrees C to room temperature. The model predicts the microstructure evolution during the complete process and the final fractions of martensite, bainite, perlite and ferrite. The thermal properties in the contact between the blank and the tools as well as the thermal properties in the tools are of significant importance during development of tooling and processes for tailor-made material properties. Variations of these properties as well as data from previous studies of the contact heat transfer are used in a parameter study to predict the tailor-made material properties due to the tool material and relevant process parameters.