A Study on Practical Fabrication Method in Tee Type Full Penetrated Welded Joint under Long Distance Welding Fabricated by the Laser-Arc Hybrid Welding

Abstract

With the aim of introducing laser-arc hybrid welding (LAHW) into the field of large steel shipbuilding, a study was carried out to construct a T-shaped fully penetrating welded joint with a weld length of 3,000 mm in one pass. Tack welding for the installation of members, which is a preliminary step of LAHW, was carried out by CO2 gas shielded arc welding. Since the effect of the main welding by LAHW on the tack welding has not been sufficiently confirmed, preliminary investigations were also carried out. As a result of repeated preliminary experiments, a T-shaped fully penetrating welded joint with a weld length of 3,000 mm was completed by the arc welding before the laser irradiation, unlike previous studies. The performance of the joint was evaluated by Radiographic test and macroscopic observation of the weld line cross-section in accordance with the "Laser-Arc Hybrid Welding Guideline" published by the Nippon Kaiji Kyokai, (ClassNK) and it was confirmed that the T-shaped joint could be obtained within the acceptable range. Considering that fatigue is the main cause of damage in welded joints, the fatigue performance of the joints was also investigated. As a result, the fatigue strength of the T-joint by LAHW using flux-cored wire was superior to that of the joint by LAHW preceded by laser irradiation using solid wire. Furthermore, all the fatigue cracks, which were fluctuating in the previous study, were located at the weld toe on the back side of the flange in the method proposed in this study. This result is favorable or the maintenance of the joint because it reduces the number of monitoring positions for fatigue cracks. In addition, it was confirmed that the application of the Λ-shaped groove is promising as a method to increase the welding speed and to extend the range of possible thicknesses, which is a challenge for the LAHW method of welded joints in thick plates.