Local heat treatment of ultra high-strength steel

The main topics in automobile design today are weight and safety. A possibility to reduce weight and increase safety is offered by ultra high-strength sheet steels, either cold or hot formed. There are, however, limitations in design possibilities due to the complicated manufacturing. Springback and formability can cause problems. The high strength can put a limit to the weight reduction due to the appearance of other collapse modes caused by the thinner gauge. One way around these problems can be to work with local heat treatment. The objective for cold forming is here to introduce softer, more formable regions in the blank allowing for higher deformation and control of the collapse mode. For hot forming the objective is to produce parts with varying strength within the same piece, through a varying heat treatment over the part. The pieces can be designed to be strong where needed and deformable where needed. Various suitable sheet materials have been selected and the change in properties with varying heat treatment studied. Laser, induction and salt bath were used as heating methods. Suitable parameters for those methods and the selected materials have been determined. Material properties after heating have been determined, including static and dynamic mechanical properties and formability measures. Several industrial applications have been manufactured, all of which had limitations when virgin material was used but which could be solved with local heat treatment. The components have been tested for performance. An economical and technical evaluation of the investigated cases is included