Evaluation of the occurrence of mechanical constriction of the Arc in A-TIG welding of austenitic stainless steels

Abstract

This paper evaluates indications of arc constriction by the thermal and electrical insulation caused by oxides of a single component in A-TIG welding of austenitic stainless steels. Changes in arc dimensions, in its electric voltage and in weld bead morphology caused by three oxide fluxes (SiO₂, Cr₂O₃ e Al₂O₃) applied with two surface densities (30 e 60 g/m2), and with and without a flux-free central strip (of 1, 2 and 4 mm) were studied. Results showed no significant change in the width of the electric arc for the experimental conditions used, therefore not supporting a possible mechanical constriction in the electric arc by oxide electrical and thermal insulation. Lateral filming indicated that the arc is delayed by the fluxes with silica causing the strongest effect. The presence of a clean central strip in the flux layer decreased weld penetration and weld bead cross section, besides the reduction of the width of the bead. Therefore, the results of the present work seem to support Marangoni convection as the main mechanism responsible for increasing penetration in A-TIG welding of stainless austenitic steels.

Keywords:

• GTAW
• A-TIG
• FB-TIG
• weld bead shape
• electric arc

Acknowledgments

The authors thank the National Board for Scientific and Technological Development (CNPq) and CAPES-PROEX for financial support for carrying out this work and for grants awarded to some of the authors.

Notes

Selected from Soldagem & Inspeção. 2016 21(4) 428–443.