TAILORED BLANKS OF HIGH STRENGTH STEELS - COMPARISON OF WELDING PROCESSES -

The strength of steel sheets used in tailored blanks for automotive bodies has been rising. In order to obtain guidelines for the choice of appropriate welding processes and materials, the formability of welded steel sheets were investigated. The purposes of this work are 1) to determine an upper steel strength limit that can be welded and 2) to obtain the requirements of materials from a viewpoint of formability. Laser, mash seam, and plasma arc welding were employed up to 980MPa high strength steels. The results suggested that laser welding was the best welding process because of its small heat input. It could be applied to 980MPa steels. 590MPa was the maximum steel strength grade to which mash seam and plasma arc welding could be applied, because the mash seam and the plasma arc welding thermal cycles softened the HAZ of high strength steel. The requirement of materials for the formability of laser welded steels is high elongation of base metals. On the other hand, the requirement for the formability of plasma arc welded steels is low weld hardness caused by low carbon content.