Nitrogen Absorption of Iron Weld Metal in Pressurized Welding Atmospheres

A purified iron was welded in pressurized N2 and Ns-Ar atmospheres of 0.1〜3 MPa. Effects of welding conditions and the nitrogen partial pressure on the nitrogen content of the iron weld metal were systematically studied. In N_2 welding atmosphere, the nitrogen content of the weld metal decreases with an increase in welding current, and with a decrease in arc voltage and travel speed. The nitrogen content of the weld metal increases with the nitrogen pressure, but the degree of the in-crease diminishes with an increase in the nitrogen pressure. The nitrogen absorption of weld metal does not obey Sieverts' law. In N_2-Ar welding atmosphere, when the nitrogen partial pressure is constant, the nitrogen content of weld metal in high pressure welding atmosphere is smaller than that in low pressure welding atmosphere. A discussion on the nitrogen absorption of weld metal with thermodynamic data suggests that the reaction time in welding process is too short for the nitrogen content of weld metal to reach the equilibrium value in high pressure atmosphere.