Effect of flux density and the presence of additives in ATIG welding of austenitic stainless steel

Abstract

Active flux TIG (ATIG) welding is a simple variant of the conventional TIG process that allows increased penetration of the weld and enables welding in one pass, with total penetration and without chamfer opening, for joints with thicknesses of 5 mm or more. Different mechanisms have been proposed to explain this effect, with emphasis on contraction of the arc due to the presence of negative ions and alteration in the movement of liquid metal in the weld pool, associated with variations of surface tension as a function of temperature. This study evaluates the effect of the amount of one flux of one component (Cr₂O₃) placed on the surface of the work piece, and the additions of KClO₄ and Al₂O₃, on the shape of the weld bead. Three sets of bead-on-plate weld tests were performed on 5-mm-thick ABNT 304 stainless steel plates. In the first set, the amount of flux used varied; in the second set, the effect of the additions of KClO₄ was studied; and in the third, Al₂O₃. Electric current and voltage were measured during the welding, and width, penetration and area were measured on cross sections of the weld bead. Results indicated a small variation in the welding voltage (increase less than 1 V) during the transition from TIG to ATIG welding. Surface flux concentration affected the weld penetration, with a rapid increase of penetration and weld bead area occurring, to concentrations between 7.5 and 15 g/m², followed by a milder variation for greater concentrations (up to 120 g/m²). On the other hand, whereas the addition of KCLO₄ clearly reduced the increase of penetration caused by the flux, the addition of Al₂O₃ had a less significant effect on the process.

Keywords::

• flux
• weld bead shape
• stainless steel
• GTA welding

Acknowledgements

The authors thank APERAM SOUTH AMERICA and ESAB Comércio e Indústria Ltda. for providing materials used in this study, and the National Council for Scientific and Technological Development (CNPq) for support for this project.

Notes

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