Development of Tubing Technique for High-Purity Low Activation Vanadium Alloys

Abstract

The tubing processes for high-purity low-activation V-4Cr-4Ti alloys were developed. From examination on the fabrication process parameters, suitable annealing condition prior to the 3-directional rolling, intermediate annealing condition, and limit for reduction of area for 1 pass at the rolling, were obtained. From microstructural observations, cracks induced during the 3-directional rolling can be attributed to the banding structure of Ti precipitates. Resulting tubes were evaluated by impurity tracing, ultrasonic inspection, eddy current testing, measurements on grain size after recrystallization and tensile tests. Grain size of the tubes after recrystallization was larger than that of the plate with the same thickness at an annealing temperature of 1273 K. At lower annealing temperature, the difference was small, however. Carbon and oxygen contaminations of about 60 and 200 wppm at the maximum, repectively, and defects on the tube wall surface were detected. They can be improved by minor change in the current process. The contamination increased tensile strength, whereas the surface defects smaller than 20 μm did not induce significant degradation of tensile properties. The examination of fabrication process parameters and evaluation of the resulting tubes successfully demonstrated the feasibility of vanadium alloys for component materials for fusion reactors.