Abstract

In this study the microstructure and mechanical properties of laser welded complex phase steel lap joints were evaluated. Three different welding parameters were used in the experiments. The weld geometry and microstructure of the weld were studied. The joints were evaluated by hardness measurements, shear strength and fatigue strength tests. The geometry of the lap joints was affected by the welding parameters, and the width of the joint increased the lower the welding speed was. The weld metal (WM) microstructure with highest welding speed exhibits a fine columnar grain structure. As welding speed increased, the dendritic grain structure was coarser. With lowest welding speed, the microstructure changed to an equiaxed grain structure due to slower cooling. The WM with highest welding speed had the highest hardness with an average value 413 HV. The shear strengths of the joints were markedly influenced by the welding speed. With the lowest welding speed, the shear strength of the single weld was 222% higher than that of the highest welding speed. A joint with multiple welds achieved shear strength corresponding to the strength of the base material (1000 MPa). Fatigue limit of the lap joint with lowest welding speed was low < 20 MPa.