Development and application of oxide-based flux powder for tungsten inert gas welding of austenitic stainless steels

The experiments reported in this study involved using a new activated flux developed by the National Pingtung University of Science and Technology (NPUST) to systematically investigate the influence of oxide-based flux powder and carrier solvent composition on the surface appearance, geometric shape, angular distortion, and ferrite content of austenitic 316L stainless steel tungsten inert gas (TIG) welds. The flux powders comprising oxide, fluoride, and sulfide mixed with methanol or ethanol achieved good spreadability. For the investigated currents of 125 to 225 A, the maximum penetration of stainless steel activated TIG weld was obtained when the coating density was between 0.92 and 1.86 mg/cm2. The depth of finger-like profile in the conventional TIG weld increased in conjunction with the current because of the induced strong arc pressure. The arc pressure also raised the penetration capability of activated TIG welds at high currents. The results show that higher current levels have lower ferrite content of austenitic 316L stainless steel weld metal than lower current levels.

Activated TIG welding shows a constriction of the arc column compared with the more diffuse conventional TIG welding at identical current levels. In addition, the oxygen from the decomposition of the oxide-based flux powder in the molten pool induces the centripetal Marangoni convection by inverting the surface tension gradient of the molten pool.Figure optionsDownload as PowerPoint slideHighlights
► Oxide-based flux powder mixed with methanol or ethanol provides good spreadability.
► The optimal coating density of activated flux increases with the weld current.
► Penetration improvement at higher currents is critical for activated TIG welding.
► The finger-like profile of TIG weld is dominated by the arc pressure.