Numerical simulation of phase transformation during the hot stamping process

Product development is an important element of industrial competitiveness which has to face today's challenges such as globalization, outsourcing and time-to-market. In the major industrialized EU countries, product development is made even more difficult by state regulations and high labor costs. To meet these additional requirements, the potential of high strength steel grades can be used to produce car components with reduced sheet metal thickness and weight, which have the same or better performance compared to conventionally manufactured parts. A technology to manufacture highest-strength automotive components is hot stamping. This process combines forming and heat treatment of sheet metal material. During and after the hot stamping process, phase transformations from austenite to other phases occur. For a realistic prediction of the resulting component properties by means of numerical simulation, it is essential to consider the complex effects of phase transformation and their respective characteristics, such as flow properties. In respect of the numerical investigations, several aspects of a developed material model are presented that consider inter alia the transformation-induced stresses. The methods to determine the necessary material parameters with the help of a quench and deformation dilatometer are also presented. The model is tested by comparison of experimental and numerical results with respect to phase fractions, geometrical distortions and sheet thickness distribution.