In this investigation the heat, fluid flow, and mass transfer for linear autogenous gas tungsten arc (GTA) welding of austenitic stainless steel to low carbon steel is presented. A numerical model was built in COMSOL Multiphysics which included the electromagnetic field, fluid flow, and heat and mass transfer. The results show that there is a toroidal fluid motion at the center of the weld pool, which circulates the molten base metals and completely mixes them with each other. The numerical predictions of the weld-pool shape and the concentrations of iron (Fe), chromium (Cr) and nickel (Ni) were compared to the experimental determinations of the weld-zone and the concentrations of Fe, Cr and Ni. Both numerical and experimental results show that the alloying elements are uniformly mixed throughout the weld zone. The numerical predictions are quantitatively in reasonable agreement with the experimentally determined results. (C) 2015 Elsevier Ltd. All rights reserved.