Microstructure and fracture toughness of joint under different welding conditions

The combination of vibratory submerged-arc welding (V-SAW) process and normal submerged-arc welding (SAW) process is used in ball valve welding. Metallographs show that a refined joint is produced under vibratory welding. The fusion area and the overheated zone are narrowed. And the dimension of widmanstaten structure is reduced. The effect of mechanical vibration on the toughness of the welded joint is analyzed from the point of view of fracture mechanics. The results indicate that the fracture toughness of the weld is obviously higher than that of HAZ (heat-affected zone). And the crack tip opening displacement value of the weld and HAZ under V-SAW condition is greater than that under normal SAW condition. And the difference in different regions of the welded joint is evidently reduced by applying vibratory SAW. Thereby, the fracture toughness is uniform. From fractography, it can be seen that the dimple density of the weld under V-SAW condition is greater than that under normal SAW condition.