The investigation of mechanical and microstructure relation between laser welded different types high and ultra high strength steels

In recent years, in the automotive industry R&D activities are generally focused on vehicle weight reduction. For this reason, the automotive sector has begun to use ultrahigh strength steel sheets in automotive structural components, side impact beams and bumpers that will allow for lighter designs. The use of these steels in the automotive industry is increasing day by day. And, its important research topic to joining these steels with high quality. The importance of laser welding in industrial manufacturing has been increasing, as its provides a precise and high quality joint. Compared to conventional welding methods, the superiority of the laser welding is based on the principle of high energy density and low beam focusing diameter. This means a narrower area affected by welding heat. In this sense, low heat input, lower residual stresses and distortions, high welding speed, deep penetration, perfect welding profile, high structural strength, aesthetically pleasing appearance, no grinding requirement, narrow weld seam with high depth / width ratio and suitability for automation are among the primary advantages that the laser welding provides. In all current welding methods, undesirable strength decreases occur in the weld zone and its around due to the applied welding methods. The welding quality can only be achieved at the desired level by selecting appropriate welding parameters. In the thesis, the relationship between microstructure, mechanical and fracture properties of selected ultrahigh strength steel sheets (DP800, DP1000, DP1200 and Usibor 1500 steels) according to their welding parameters will be determined and the laser welding parameter range (or parameters) that can be used in the automotive sector will be determined.