Weld appearance of CO₂ laser-gas metal arc hybrid welding for ultra-low carbon bainitic steel

Ultra-low carbon bainitic (ULCB) steel plates with 12 mm thickness were welded by using CO₂ laser-gas metal arc (GMA) paraxial hybrid process and multipass technique. The experimental results indicated that the good weld can be obtained by controlling the change of heat input on each pass when adopting three passes welding. In hybrid welding process, the focal point position is very important for the first filling pass and should be in the scale of the rootface. For the other filling passes the focal point position could be changed in a large scale. At the same time, in order to increase the utilization of laser energy, the higher wire feeding rate was used. Furthermore, the mechanical property tests showed that the tensile strength of weld in laser-GMA hybrid welding was over 95% as much as that of the base metal, and even to exceed partially the tensile strength of base metal. The tensile strength of the joint is 829.5 MPa when the specimens were failed in base metal. When the specimens were failed in welds, the defects led the specimens to fracture mainly.