Open Access Conference Proceedings

Press hardening is a modern forming technology for the production of shaped sheet parts. Its use has been growing in recent years because of its high production accuracy, reduced spring back effect and lower forming forces. This technology is also suitable for high strength TRIP steels (transformation induced plasticity). However, with dies at room temperature, undesirably high cooling rates are obtained, leading to the formation of martensitic structures with a low ferrite content. These structures possess high strength but low ductility. It is therefore important to interrupt the press hardening operation at the right time or even carry out additional heat treatment in a furnace.Two low-alloy TRIP steels with a carbon content of 0.2% and different niobium levels were selected for this experiment. At the first stage, the sheets were press-hardened between dies of a hydraulic press. The holding time was varied from 0 to 10 s and the sheet temperature after removal from the dies was measured with a thermal imaging camera. At the second stage, press hardening in a flat press hardening tool was followed by isothermal holding in a furnace. Mixed structures of martensite, bainite, proeutectoid ferrite and retained austenite were obtained when parameters were chosen properly.

Keywords: TRIP steel, multiphase structure, press hardening

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