The Effect of Ambient Pressure on the Nitrogen Content of Mild Steel Welds

To know the effect of ambient pressure on the nitrogen content of weld metal, mild steel specimens were welded using an iron electrode wire in air, N2, Ar-N2, and N2-O2 atmospheres at pressures between 1 atm and 9 atm.The changes in the shape of penetration and the arc phenomena due to the ambient pressure were also investigated.The main results obtained by this study are summarized as follows;1) In nitrogen welding atmosphere, the nitrogen content of weld metal increased gradually with the increase of the ambient pressure. The absorption of nitrogen does not obey the Sieverts' law.2) In air welding atmopshere, the nitrogen content of weld metal does not increase continuously with the ambient pressure, but it drops rather at pressures between 4 and 6 atm.3) In Ar-N2 welding atmosphere, the nitrogen content of weld metal increased with the partial pressure of nitrogen in the atmosphere of 1 to 6 atm pressure. The nitrogen content of weld metal made in the atmosphere of higher pressure is lower as compared with the one in the atmosphere of lower pressure at same partial pressure of nitrogen.4) In N2-O2 welding atmosphere, the enhancement of nitrogen absorption by steel welds due to the coexistence of oxygen is observed at higher pressures of welding atmosphere too. The oxygen precent of N2-O2 atmospheres, in which the maximum nitrogen content is to be expected, is lower at higher pressures of welding atmosphere.