Product Code: ICA10_1803

Prevention of Porosity in Deep Partial Penetration Laser and Hybrid Welding with Minimum Solute Oxygen in the Weld Metal
Authors:
Susumu Tsukamoto, National Institute for Materials Science; Tsukuba, Ibaraki Japan
Lin Zhao, National Institute for Materials Science; Tsukuba, Ibaraki Japan
Goro Arakane, National Institute for Materials Science; Tsukuba, Ibaraki Japan
Tomohiro Sugino, IHI Corp.; Yokohama Japan
Koichi Yasuda, Jfe Steel Corp.; Chiba Japan
Presented at ICALEO 2010

Formation of some weld defects is one of the serious problems in laser and laser/arc hybrid welding of heavy section steel plates. Especially in the partial penetration welding, the porosity is easily formed due to the closure of unstable keyhole. In the previous paper, the authors indicated that a small amount of oxygen addition in the shielding gas was effective in preventing the porosity. However, the solute oxygen in the weld metal reduces the toughness of the welded joint. In the present study, prevention of the porosity has been attempted with minimum solute oxygen in the weld metal. From some experimental results, it was clarified that the porosity suppression by oxygen was attributed to formation of CO in the keyhole. CO formed by the reaction between solute carbon and oxygen in the molten pool stabilises the keyhole due to increase in the static vapour pressure in the keyhole. The porosity prevention was also achieved, but the solute oxygen could be reduced by CO2 addition in the shielding gas, because CO is directly formed through decomposition of CO2 in the keyhole. Dissolution of oxygen in the molten pool is not always necessary in CO2 addition.