Ultra High Strength FeMn TWIP Steels for Automotive Safety Parts

Energy savings are among the most important goals of steel users. But generally, the increase of Tensile Strength for a given metallurgy is obtained to the detriment of ductility. ARCELOR develops new ultra high strength steel with TWinning Induced Plasticity (TWIP) effect for weight reduction and impact resistance. This product based on a manganese (Mn) alloying metallurgy has a tensile stress higher than 1000 MPa for a total elongation superior to 50%. This text deals with mechanical testing, welding and different design solutions which could be associated with this new steel grade in comparison with conventional UHS steel (HSLA, DP, TRIP, etc.). Tensile and formability properties are presented first by means of basic tests (stretching, bending, etc.) in order to classify the different steels. Then welding parameters and mechanical behavior of spot weld are presented.

In addition to this, the crash resistance is investigated by using a dynamic axial compression test and a dynamic three point bending test on structural components with closed and open cross sections. For each steel grade, the estimated weight saving potential is compared with respect to parts manufactured in high drawing ability steel. Fatigue resistance is also investigated on this material and on welding assembly by using cyclic test. The exceptional mechanical characteristics of this product permit to propose innovative steel design solutions for automotive safety component.