Production of high strength hollow shafts using tool hardening and Q-P process
1 Research Centre of Forming Technology – FORTECH, University of West Bohemia, Pilsen, Czech Republic
2 Fraunhofer Institute for Machine Tools and Forming Technology IWU, Chemnitz, Germany
3 Faculty of Mechanical Engineering, University of Applied Sciences, Mittweida, Germany
Innovation opens new opportunities in the field of processing hollow semi-products, as it offers the potential for manufacturing complex-shaped structural parts with enhanced properties. This introduces a manufacturing route comprising the following steps: internal high pressure forming, hot stamping and thermomechanical Q&P processing. In this manufacturing route, the demonstration product, a tube–shaped stock, is first austenitized. It is then expanded in a closed die by internal pressure of nitrogen until the material touches the die wall. As a result, it cools down quickly and martensite begins to form. At a temperature above the Mf, the cooling is interrupted and the workpiece is transferred to a furnace and tempered. The furnace temperature is below the Ms temperature. Within several minutes, a mixed microstructure forms, consisting of martensite and stabilized retained austenite. Thanks to this microstructure, the material exhibits a favourable combination of high strength and adequate ductility. Martensite imparts sufficient strength to the material whereas the retained austenite provides ductility. At a carbon level of approximately 0.4 % and with a simple Si-Mn-Cr-based chemistry, strengths of 2000 MPa and A5 mm elongations of 15% can be achieved.
© Owned by the authors, published by EDP Sciences, 2015
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