Determination of forming limits of the martensitic chromium steels in hot forming processes

• Applicant: Professor Dr.-Ing. Bernd-Arno Behrens
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 385989694

The aim of the planned research project is numerical simulation of the hot forming of a martensitic chromium steel taking into account the forming limit at elevated temperatures, the resulting microstructure and their effects on the product properties. In the sheet metal forming, hot forming of martensitic chromium steels has various advantages over hot stamping of manganese-boron steels, such as a lower critical cooling rate, a higher elongation at break (fracture strain) along with higher strengths and a better corrosion resistance of the material. During the hot forming processes, complex interactions between the workpiece temperature, the tool temperature and the process time exist which significantly influence the microstructure, the final component properties and the residual stresses as well as the component distortion thus numerical modelling and prediction of the process limits is of particular importance for this process. In particular, the higher material costs of martensitic chromium steels compared to the manganese-boron steels make a simulative process design vital in order to save resources, tests and thus reduce the costs. The planned development of a material model for the numerical simulation of hot forming of martensitic chromium steels will be carried out based on a material model which was developed in the DFG funded preceding research projects for hot stamping of the manganese-boron steel (22MnB5). A comprehensive material characterization is required in order to adapt the material model to the martensitic chromium steels and their microstructural behavior.For the determination of the forming limits of sheet metals, the use of forming limit diagrams is state of the art. As the flow behavior and the deformability of a material are dependent on the temperature, conventional forming limit diagrams obtained at room temperature cannot be used for hot forming processes. In order to predict the deformability of martensitic chromium steels as well as the influence of the forming temperature on the deformability in the hot forming process, the further objective of this project lies in the determination of temperature-dependent forming limit diagrams and their implementation in the numerical simulation. This allows a realistic evaluation of the forming limit and the resulting component properties after cooling. The numerical model is validated with the help of hot formed demonstrator components.

• DFG Programme: Research Grants (Transfer Project)
• Application Partner: Outokumpu Nirosta GmbH