On the Porosity of Weld Metal by Gas-Shielded Metal-Arc Welding (Report 1)

Effect of Nitrogen

Abstract

The object of this research is to clarify a relation between porosity of weld and volume percentage of nitrogen in the mixed gas supplied for shielding of arc and its neighborhood. Three kinds of mixed gas ; C0₂-N₂, A-N₂ and 0₂-N₂, were supplied.
The results of experiments showed the following facts
1. In the case of CO₂-N₂ arc welding, the weld metal becomes very porous regardless of content of deoxidizers in the base metal, when the volume percentage of nitrogen in supplied gas is over the limit value, 4.5%.
2. Also in the case of A-N2 arc welding this limit value is nearly the same. But the weld metal by A-N₂ arc welding has generally higher content of total nitrogen, including nitride, than that by C0₂-N₂ arc welding with the same mixed percentage of nitrogen.
3. The true partial pressure of nitrogen in arc atmosphere is deduced to be over about 0.1 atm., when a weld metal becomes porous.
And the difference between the above "true" value, about 10%, and the "supplied" value, 4.5%, was discussed.