HIGH STRENGTH STEELS FOR AUTOMOTIVE SAFETY PARTS

Energy savings are among the most important goals of steel users. Usinor proposes a wide range of very high strength steels (HSLA, DP, TRIP, etc.) for weight reduction and impact resistance. This text deals with the mechanical testing and different design solutions associated with these steel grades. Tensile and formability properties are presented first by means of basic tests (drawing, stretching, bending, etc.) in order to classify the different steels. A specific part of the text deals with a ultra high tensile strength pre-coated boron steel for hot forming. 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 drawability steel. Finally, two different designs are presented with steel solutions for safety parts. The first one shows the advantage of the use of TRIP steel and a hydroforming technique for a crash box instead of using a conventional forming technique. The second one deals with the design of a cross frontal sill with a complex cross section, formed using a profile rolling technique.