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.