Influence of Welding Parameters and Shielding Gas Composition on GTA Weld Shape

Abstract

The interaction between the variable welding parameters and shielding gas composition in determining the weld shape in Ar-CO₂ shielded gas tungsten arc (GTA) welding with SUS304 stainless steel is discussed. The GTA weld shape depends to a large extent on the pattern and strength of the Marangoni convection on the pool surface, which is controlled by the content of surface active element, oxygen, in the weld pool and the welding parameters. Results showed that oxygen absorption into the liquid pool during the welding process is sensitive to the CO₂ concentration in the shielding gas. An inward Marangoni convection occurs on the pool surface when the oxygen content is over 100 ppm in the welding pool under Ar-0.3%CO₂ shielding. A low oxygen content in weld pool changes the inward Marangoni convection to an outward direction under the Ar-0.1%CO₂ shielding. The strength of the Marangoni convection on the liquid pool is a product of the temperature coefficient of the surface tension (dσ/dT) and the temperature gradient (dT/dr) on the pool surface. Different welding parameters will change the temperature distribution and gradient on the pool surface, and therefore, affect the strength of Marangoni convection and the weld shape.