In this paper, the surface tension of molten pure iron and 304L stainless steel is measured under different gas mixtures (pure argon and Ar-2.5 %vol. H-2). Measurements are realized by aerodynamic levitation with an acoustic excitation. The surface tension is measured between 1756 K and 2227 K. The addition of H-2 in the surrounding gas is supposed to create a desorption of oxygen and modify surface tension. The effect of oxygen on surface tension is then analyzed. Measurements show a linear variation of surface tension with temperature for pure iron under Ar-2.5 % vol. H-2 and a nonlinear relationship for the 304L stainless steel even when an active gas is used. This phenomenon can be explained by the short time at high temperature which does not allow oxygen desorption. Increasing the time at high temperature may change the surface tension but at the risk of evaporation of some alloy elements. The intensification of the evaporation would also disturb the surface tension measurements. In this study, the time spent at the liquid state is equivalent to that of welding and additive manufacturing processes, allowing to determine the thermocapillary coefficient (Marangoni effect) for both metals considered in these conditions. The comparison between our measurements and different data are consistent.
