2015 Volume 33 Issue 4 Pages 349-357
In the shipbuilding and bridge construction industries, shop primer paint is coated to the surface of steel plates in order to protect them from rusting during a long fabrication period. However, when arc welding is applied to the primer-coated plates, the arc heat make decompose and vaporize the coating. Then, the generating gas will be enclosed in the weld metal during the solidification process, causing the porosity defect like the blowholes and the pits. In this study, the effects of penetration depth and non-penetrated joint root length on the blowholes generation were clarified with varied welding parameter, and a new horizontal fillet welding process called "Hybrid tandem MAG(HTM)" was developed by reflecting this knowledge, which uses combination with a solid wire for the leading electrode and a flux-cored wire for the trailing electrode featured deep penetration and excellent porosity resistance.
In order to reduce porosity in the fillet welding of primer-coated steel plate, it was found that the following measures are effective: (a) increasing the penetration depth, (b) decreasing the non-penetrated joint root length. The reduction of porosity by increasing the penetration depth is achieved by the formation of consistent ejection passage for vaporized gas. Estimated phenomenon mentioned above was be verified by observing directly the interior of the weld pool by using an X-ray video camera. It is effective to reduce the leading electrode torch angle and to use combination with the high-current and low-voltage welding condition to create the buried arc to realize above measures. In regards to improvement of blowhole resistance, blowholes by HTM process are reduced to approx. 1/10 against the conventional process, even at high welding speed of 1600mm/min.