Numerical simulation of the influence of oxygen content on the weld pool depth during activated TIG welding

The required amount of surface-active element dissolved in the weld pool remarkably influences the depth of penetration during activated tungsten inert gas (A-TIG) welding process. This is mainly attributed to the changes in the surface tension coefficient sign by oxygen content, which in turn controls the reversal of fluid flow and the nature of heat transfer. It emphasizes that there is a strong correlation between the surface-active element oxygen content and the development of the weld pool. This research intends to find out the critical oxygen content required in the weld pool to cause complete reversal of Marangoni flow and its influence on the weld bead dimensions by numerical simulation during A-TIG welding. Three-dimensional evolution of thermal and velocity fields in the weld pool is simulated using ANSYS Fluent for 200 A and 300 A welding currents respectively by altering the dissolved oxygen levels in a 0.01 m thick 316 LN stainless steel (SS) plate. The simulated weld bead profile for varying dissolved oxygen levels is validated for 300 A current by carrying out A-TIG welding experiments in a 0.01-m-thick plate with different fluxes in order to achieve the diverse amounts of oxygen content in the weld pool. The simulated and experimentally obtained weld bead dimensions exhibited good agreement for various dissolved oxygen contents in the weld. The complete reversal of fluid flow has been found to occur in the weld pool when the dissolved oxygen in the weld pool is 335 ppm at 300 A and 200 ppm at 200 A current.