Study on Proper Welding Condition for Ultranarrow Gap Submerged Arc Welding

Submerged arc welding (SAW) is widely used for butt welding of thick plates in large steel structures because of its high deposition rate and high weld quality. With a thickness of 150 mm or more, multilayer welding is required, and it takes a lot of time to finish build-up. Narrow gap welding with 1° to 3° of groove angle is an effective process to reduce the welding time. Recently, ultra-narrow gap welding with approximately 0° of groove angle has been studied. However, ultra-narrow gap SAW is hardly applied because of its risk of welding defects such as lack of fusion and undercut. In this study, the influence of distance L between the welding torch and groove wall on the welding defect with ultra-narrow gap SAW was clarified. Undercut is caused by the arc gouging effect and excessive melt of the groove wall. The relationship between lack of fusion and the weld shape was elucidated. The model for judging the lack of fusion defined by the heat input to groove H _G and the distance squared between the heat source and the corner of the groove bottom r ² was established, which were calculated by the heat input Q, bead width W _B and cross sectional area of the deposited metal A _R. With the model, appropriate range of L for each welding condition was determined.