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HIGH STRENGTH AND ULTRA HIGH STRENGTH STEELS FOR WEIGHT REDUCTION IN STRUCTURAL AND SAFETY RELATED APPLICATIONS

Steel manufacturing of today with the use of continuous annealing makes it possible to produce high strength and ultra high strength steels with up to 1400 MPa tensile strength. These steel grades are suitable for cold forming of structural and safety-related automotive components. The high strength level gives potential for considerable weight reduction and a cost-effective way to produce energy efficient vehicles. Conventional forming and joining techniques without any extra heat treatment involved can be used. This paper describes briefly the static properties, forming and joining characteristics of these steel grades as well as the crash resistance and energy absorption. Some examples of applications in safety related applications are shown. Both laboratory tests and full scale tests show that high strength and ultra high strength steels can be pressformed in both stretch forming and drawing operations. Conventional welding methods can be used if the welding parameters are adjusted to the alloying content of each grade. Static load carrying capacity and energy absorption in both axial crash tests and threepoint bending tests increases with increasing strength level of the steel which results in a considerable potential for cost-effective design of future lightweight vehicles. INTRODUCTION The trends, especially in the transport industry, towards reduced weight, increased performance and safety as well as a more rational and cost effective manufacturing has broadened the interest in high strength steels of good formability and weldability. For automotive applications high strength cold-rolled, rephosphorized, microalloyed, and dualphase grades with tensile strength up to 1400 MPa have been introduced.