Effect of welding rate and heat treatment conditions on the structure and properties of niobium welded joints

Welded joints of niobium under the effect of static and alternating loadings are destructed over HAZ at the distances 1...2 mm from fusion zone. It is established that destruction of niobium welded joints takes place over the grain boundaries. It is related to mutual displacement of the grains and their turn. It is shown that with an increase in niobium welding rate from 2.8 to 16.6 mm/s the grain size in HAZ sections adjoining the fusion zone decreases by a factor of 2, which results in metal strengthening of the sections. Niobium welding at increased rates and subsequent heat treatment of the joints permit to reduce to the minimum their chemical heterogeneity and to increase mechanical properties