Surface tension of molten SUS304 and SUS316 stainless steels was measured by an oscillating droplet method using electromagnetic levitation furnace to investigate the influence of oxygen partial pressure, PO2, of atmosphere on surface tension and its temperature coefficient. We successfully measured the surface tension of molten stainless steels over a wide temperature range including an undercooling condition under Ar-He-5 vol.%H2 and Ar–He mixed gases. Although the surface tension of molten SUS304 stainless steel decreased with increasing temperature under the Ar-He-5 vol.%H2 mixed gas, the surface tension showed a boomerang temperature dependence when PO2 was fixed at 10–2 Pa under the Ar–He mixed gas; and surface tension increased and then decreased with increasing temperature. When the surface tension of molten SUS316 stainless steel was measured under the Ar-He-5 vol.%H2 and Ar–He mixed gases, the surface tension increased with increasing temperature regardless of the atmospheric gas due to the large sulfur content. The uncertainty of the measurement was evaluated as less than 5% in this study.
