Impurity effects on gas tungsten arc welds in V-Cr-Ti alloys

Plates 6.4 mm thick of V-Cr-Ti alloys, mostly V-4Cr-4Ti, were welded in a glove box argon atmosphere. A hot titanium getter led to excessive hydrogen concentrations. A cold zirconium-aluminum getter was used to reduce both oxygen and hydrogen. It was observed that a major source of hydrogen was dissociation of water vapor by the electric arc of the welding torch. Careful monitoring of atmospheric impurities and successive pumping and backfilling cycles permitted welds of higher quality than previously achieved. Welds were evaluated primarily by the Charpy impact test. A ductile-to-brittle transition temperature (DBTT) of -28°C was achieved in V-4Cr-4Ti. Previous GTA welds in the same material seldom had a DBTT below room temperature. Electron beam welding can achieve a DBTT of below -90°C in the V-4Cr-4Ti alloy, indicating a lower limit to the DBTT by impurity control.