The aim of this study was to investigate the influence of welding parameters such as arc current, welding speed and wire feeding speed on the grain refining in weld metal of type 310S austenitic stainless steel. Besides, the effect of the grain refinement on mechanical properties such as tensile strength, hardness and ultrasonic transmission was examined. Equiaxed grains of about 15 μm formed by hot-wire GTAW in weld metal and the fine grain formed over a wide range stably. When the wire current was low, the fine grains formed at the lower part of the weld metal. On the other hand, when the wire current was high, the grains formed at the upper part. The area ratio of fine grain in weld metal corresponding to the amount of fine grain in weld metal depended on the wire current. Besides, the ratio increased with decreasing in the arc current, increasing the welding speed and wire feeding speed. The maximum area ratio of fine grain in weld metal was about 50%.
The hardness of the weld bead including the fine grain was higher than that without the fine grains. Besides, the formation of the fine grain showed higher strength and elongation. Moreover, a transmissivity of ultrasonic wave was improved significantly by including the fine grains in multi-pass weldment.