Numerical Simulation of Diffusion of Multiple Metal Vapours in a TIG Arc Plasma for Welding of Stainless Steel

Abstract

In the present paper, a TIG arc in helium or argon is modelled, taking into account the contamination of the plasma by the metal vapour from a stainless steel weld pool. Iron, chromium and manganese are considered the metal vapour species in this model. A viscosity approximation is used to express the diffusion coefficient in terms of the viscosities of the shielding gas and the metal vapour. The time-dependent, two-dimensional distributions of temperature, velocity and metal vapour concentrations of iron, chromium and manganese are predicted, together with the weld penetration, as a function of time for a 150 A arc at atmospheric pressure, for both helium and argon welding gases. The distribution of the metal vapours depends on the diffusion term and the convection term. Due to the cathode jet, the convection term has a strong effect. Consequently, it is found that the metal vapours expand in the radial direction and are concentrated around the weld pool surface. The concentration of manganese vapour is larger than those of iron and chromium vapours, despite the fact that the proportion of manganese in stainless steel is significantly smaller.