Nitrogen desorption by high-nitrogen steel weld metal during CO ₂ laser welding

Nitrogen desorption by high-nitrogen steels (HNSs) containing 0.32 and 0. 53 pct nitrogen during CO₂ laser welding in an Ar-N₂ gas mixture was investigated and the obtained data were compared with those for arc welding and at the equilibrium state predicted by Sieverts' Law. Although the nitrogen content in the weld metal during CO₂ laser welding was lower than that in the as-received base material in all conditions, the nitrogen desorption was larger in the top part of the weld metal than in the keyhole region. The nitrogen desorption in the Ar atmosphere was less during CO₂ laser welding than during arc welding. With the increase in nitrogen partial pressure, the nitrogen content in the weld metal sharply increased during arc welding, but only slightly increased during CO₂ laser welding. The nitrogen absorption and desorption of the HNS weld metal were much smaller during CO₂ laser welding than during arc welding.