The aim of this research is to study the effect of the welding conditions and of an activating flux on the microstructure of the melted material of autogeneous A-TIG welds, made on austenitic stainless steel AISI 304, The increase of heat-input coarsened the microstructure, changed its morphology and decreased the delta-ferrite content retained in the microstructure. The use of a TiO2 activating flux does not significantly affect the microstructures. A thin layer tends to form in the surface of the welds, which microstructure and ferrite content are different from those observed in its core.