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Effect of shielding conditions in welding and of surface preparation quality on corrosion resistance of welded joints in zirconium

The main problem in fusion welding structures of zirconium and its alloys is caused by the high susceptibility to absorption of gases in heating to temperatures above 300°C. Nitrogen content higher than 0.003%, oxygen content higher than 0.1% and hydrogen content higher than 0.005% result in a large decrease of corrosion resistance and ductility.' At present, zirconium alloys are welded by vacuum electron beam welding (EBW) and argon-shielded welding in a chamber with a controlled atmosphere (AAW-C). Gas saturation of the surface layer of metal welded joints and the HAZ results in a decrease in the corrosion resistance of the surface of the zones and the mechanical properties of welded joints, in particular ductility. It is well-known that the degree of saturation of a metal surface with gases depends on conditions of shielding the welding areas. However, there is insufficient data for preparation of technically justified requirements on the conditions of shielding the metal in fusion welding, especially in AAW. The aim of this work was to determine the optimum , conditions of shielding the metal in EBW and AAW and surface treatment of the welded joints prior to corrosion tests. The material for the investigations was non-alloyed zirconium produced by the iodide method in order to prevent alloying elements affecting corrosion resistance of welded joints. The experiments are carried out on specimens produced from 1.5 mm sheets prepared by cold rolling and subjected to vacuum annealing and pickling. Investigations were conducted on the following welding methods, differing in conditions of shielding the welded joints: