Study on High Speed Submerged Arc Welding (Repart 2)

Effect of Arc Heat Source Shape on the Occurrence of Undercutting

Abstract

Undercutting occurs when molten metal is displaced more than a solidification ponit along a toe of weld pool. Therefore, it seems likely that the occurrence of undercutting can be suppressed by means of delaying solidification of weld pool and preventing the displacement of molten metal. Based on these results obtained in report 1 of this study, this investigation aimed to develop a new submerged arc welding technic which allows higher welding speed without undercutting than that of the conventional submerged arc welding.
The results were as follows,
(1) Oblate ratio of arc heat source to the welding direction affects the solidification pattern greatly. The higher oblate ratio becomes, the more the solidification of weld pool is delayed.
(2) The effect of heat source shape (electrode shape) on the solidification pattern is observed in welds which are performed with strip electrodes. But the application of strip electrode for high speed welding is not suitable because of an instability of its arc.
(3) Deformed arc heat source with a group of fine electrodes lined up along the welding direction allows higher welding speed without undercutting than that of the conventional submerged arc welding, as a result of delay of solidification and smaller displacement of molten metal.