Abstract
Thick-section steel has been widely used in many heavy industries. Traditionally, very thick steel plates could be welded by using submerged arc welding and other welding processes. However, there were more or less drawbacks in these welding methods. Laser welding, a high-energy density welding method, is being considered for such structures to improve the production efficiency and reduce the residual stresses of the joints. In this study, butt joints with narrow gap were welded using a high-power CO2 laser. The effect of welding parameters including the relative position between the laser beam and the filler wire, welding speed, and the distance from the intersection of the beam and wire to root of the groove on the weld bead geometry and welding defects was studied. Additionally, high-speed photography was introduced in the experiment as an efficient method to record the total process of welding, especially the transfer of molten drop. The study found that when the beam was focused on the center of the groove, the filler wire could be melted successfully even though it would tremble slightly during welding process. The optimized distance from the intersection of the beam and wire to groove root was 3 mm. Later, butt weld joints of 70-mm-thick steel plate without lack of fusion can be obtained under optimized welding parameters.