Numerical modeling of enhanced nitrogen dissolution during gas tungsten arc welding

Weld-metal nitrogen concentrations far in excess of Sieverts-Iaw calculatio ns during gas tungsten are (GTA) welding of iron are investigated both expe rimentally and theoretically. A transient, three dimensional mathematical m odel has been developed to calculate the residual nitrogen concentrations d uring GTA welding. This mode, combines calculations for the plasma phase wi th those for nitrogen absorption and for the transport of nitrogen by conve ction and diffusion in the weld metal and diffusion throughout the weldment . In addition, the model takes into account the roles of turbulence and the nitrogen desorption reaction in affecting the residual nitrogen concentrat ion in the weldment. Autogeneous GTA welding experiments in pure iron have been performed and the resulting nitrogen concentrations compared with the modeling results. Both experimental and modeled nitrogen concentrations fal l in a range between 2.7 and 4.7 times higher than Sieverts-law calculation s at a temperature of 2000 K. Modeled nitrogen concentrations correlate wel l with the experimental results, both in magnitude and in the general trend s, with changes in the travel speed and nitrogen addition to the shielding gas.