Prevention of porosity in deep partial penetration laser and hybrid welding with minimum solute oxygen in the weld metal Available to Purchase

Prevention of porosity is essential in laser welding of heavy section plate members. In the previous paper, the authors demonstrated that a small amount of oxygen addition in the shielding gas was effective in preventing the porosity. However, solute oxygen in the weld metal reduces the weld metal toughness. In the present study, prevention of the porosity has been attempted with minimum dissolved 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 oxygen could be reduced in the weld metal 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.