Penetration shape in carbon steel welds produced by a stationary TIG arc

Abstract

Summary The main factors associated with streaming in the weldpool are the electromagnetic, buoyancy, surface tension, and aerodynamic drag forces. This paper describes numerical calculations of heat and mass transfer in a stationary TIG arc weldpool with regard for the above four forces. The results are compared with the actual penetration shapes of mild steel and steels containing surface activation elements spot‐welded by a stationary TIG arc. The calculations suggest that surface tension driven flow is the major determinant of the penetration shape in the short arc process. However, there is no experimental evidence that surface tension plays the dominant role in actual welding of various steels. The actual penetration shape is well matched to the calculated one without the surface tension term. It is thus concluded that the electromagnetic force is the major determinant of the penetration shape and that the aerodynamic drag force plays a secondary role in arc welding with a short arc. The results further suggest that the value of surface tension measured in a vacuum or inert atmosphere may not be the same as that of liquid exposed to plasma. During arc welding with a long arc, however, the aerodynamic drag force of the arc plasma is the predominant force leading to a shallow centre Oust under the heat source) and deep peripheral penetration.