Comparison of impact property of Japanese and US reference heats of V-4Cr-4Ti after gas-tungsten-arc welding

Charpy impact tests of Japanese and US reference V-4Cr-4Ti alloys, NIFS-HEAT-1 (180 wppm oxygen) and US832665 (310 wppm Oxygen), were examined after gas-tungsten-are (GTA) welding in a purified argon atmosphere. To investigate the effects of further reduction of oxygen level in the fusion zone, filler wires made of HP thigh-purity V-4Cr-4Ti, 36 wppm oxygen) were used as well as those made of the reference alloys. Charpy impact property of NIFS-HEAT-1 in as-CTA-welded condition was superior to that of US832665. Use of the high-purity filler wires improved the impact property further. Good correlation was obtained between ductile-brittle-transition temperature (DBTT) and the oxygen level in the fusion zone. Since oxygen contamination from the atmosphere is avoidable by controlling its impurity level, oxygen reduction in weld materials, such as plate and wire, is crucial to obtain good weldability. Only contamination element detected in this study was hydrogen. Contamination occurred not only in fusion zone but also in base metal. Degassing of hydrogen after the welding may improve the impact property further.