Abstract
Submerged arc welding is widely used for butt welding of thick plates in large steel structures because of its high deposition rate and high weld quality. With thickness of 150mm or more, multi-layer welding is required and it takes a lot of time to finish build-up. Narrow gap welding with 1 to 3 degrees of groove angle is effective process to reduce the welding time. Recently, ultra-narrow gap welding with approx. 0 degree 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, it was clarified the influence of distance L between welding torch and groove wall on the welding defect with ultra-narrow gap SAW. Undercut is caused by arc gouging effect and excessive melt of groove wall. And relationship between lack of fusion and weld shape was elucidated. It was established the model for judging lack of fusion defined by heat input to groove HG and distance squared between heat source and groove corner r2 which calculated by heat input Q, bead width WB and cross sectional area of deposited metal AR. And with the model, appropriate range of L for each welding condition was determined.
