Characterization of the suitability of high manganese steels for the production of small sheet metal parts by multi-stage deep drawing

• Applicant: Professor Dr.-Ing. Gerhard Hirt
• Subject Area: Metallurgical, Thermal and Thermomechanical Treatment of Materials ; Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: from 2019 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 423190740

In the automotive industry, relatively small, sometimes complicated and tube-shaped components with paramagnetic properties are required. They are used as components for valve drives or injection nozzles and are produced in multi-stage combined deep drawing and ironing drawing processes, e.g. by the Hubert Stüken GmbH. The currently used chromium-nickel steels show low strengths and a weak austenite stability. Hence, a replacement by austenitic high manganese steels (HMnS) is aimed. Preliminary tests of the application partner with a commercially available HMnS with a composition comparable to alloys investigated in the SFB 761 part project B2 have shown fundamental potential in terms of formability and increasing strength. Nevertheless, an unfavorable change of the microstructure during the multi-stage deep drawing process occurs due to twinning and martensite formation, which affects the mechanical and magnetic properties of the components. In the automotive industry, for example, common limit values of 2 - 5 A/cm must be kept for the magnetic properties. Already established methods for the design of deep-drawing processes cannot predict the change of the magnetic properties by martensitic transformation during multi-stage deep-drawing. The working hypothesis of this project is, that the formation of martensite is favored by very large deformations of φ>5 and/or multi-axial stress states occurring in the deep-drawing processes. The aim is therefore to systematically investigate the microstructure changes under these complex loads and to develop empirical models specifically in order to design process sequences targeting the final microstructure. For this, it is necessary to understand the underlying mechanisms under different multi-axial stresses and for different deformation states. Only the cooperation with the application partner enables an adequate definition of the requirements regarding the process-dependent material behavior and component properties. Based on this, a characterization method is to be developed which emulates the microstructure development occurring during multi-stage deep-drawing processes. On the basis of this basic experiment, an empirical model for the microstructure development in multi-stage deep drawing processes will be developed and validated. This model will then be used to design a suitable process sequence, e.g. for components without martensitic transformation, which will finally be produced experimentally at the industrial facilities of the application partner. The basic experiment developed in this project can help to validate material models for high strains with regard to future questions and thus contribute to the improvement of the simulative process design.

• DFG Programme: Research Grants (Transfer Project)
• Application Partner: Hubert Stüken GmbH & Co. KG