Influence of weld puddle shapes and the primary structures on a bead solidification defect in high speed welding. - Solidification process of submerged arc weld metals (Report 4)

When high speed submerged arc welding (SAW), was carried out using highly basic fluxes to decrease the oxygen content of weld metal of large diameter linepipes, a continuous shrinkage cavity happend to be formed on the bead surface and obstructured high-speeding of SAW in the past.To raise the welding speed of SAW through the solidification process improvement, findings concerning the weld puddle shape and the liquid metal flow in the fundamental studies of Reports Nos. 1 and 3 have been effectively applied to the present investigation.The method of preventing the shrinkage cavity has been experimentally examined from the aspects of weld puddle shapes and solidification structures. And it was elucidated that the shrinkage cavity occurred when the healing action of the liquid at the rear part of tear-drop typed weld puddle was insufficient, and would be prevented by positively forming the equiaxed dendrites at the bead center which approximate the rear part shape of the weld puddle to an elliptical one.