Tailored Blanks of High Strength Steels — Comparison of Welding Processes

Abstract

The purposes of this work are: 1) To determine optimum welding parameters for high strength steels, and to define an upper steel strength limit that can be welded. 2) To obtain fundamental data on the formability and the fatigue properties of high strength steels. 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 methods to high strength steels, formability and fatigue performance were investigated. Laser, mash seam and plasma welding were employed to 590 MPa and 780 MPa high strength steels. The results suggested that laser welding was the best welding process for both formability and fatigue performance. The mash seam and plasma welding thermal cycles deteriorate the mechanical properties of the weld metal and HAZ. As a result, the mash seam and arc welded 780 MPa steel sheet broke at the weld or in the HAZ during forming. Laser and arc welded high strength steel sheets exhibited a high fatigue strength. However, the fatigue strength of the mash seam welds was low due to stress concentration.