In zirconium welding, the weld and heat affected zone are easy to be polluted by oxygen, hydrogen, nitrogen and other elements in the air, generating hard and brittle compounds, and producing brittle needle-like organization, so that the hardness and strength of the welded joint increase, plastic decline, corrosion resistance also decreased significantly. Therefore, during zirconium welding, the pool, weld and heat affected zone should be adequately protected to completely isolate air.
Zirconium alloy welding is usually performed by tungsten inert gas arc welding method, other welding methods include: electron beam welding, plasma arc welding and resistance welding, etc. Its welding performance is close to that of titanium. Due to the small thermal expansion coefficient and elastic modulus of zirconium, the welding deformation and weld residual stress are relatively small. It is recommended that the stress relief time of the weld at 1100°F (594 ° C) is 1 hour/inch thickness.
In the case of no contamination, the weld is not easy to appear crystal crack and cold crack.
Zirconium is generally easy to react with the atmosphere at high temperature. It begins to absorb oxygen at 200℃, hydrogen at 300℃ and nitrogen at 400℃. The higher the temperature, the more intense the reaction will be. Because zirconium is reactive to oxygen, nitrogen and hydrogen, welding must be done with a high purity inert gas or in a good vacuum chamber.
Another major problem with zirconium welding is that the weld tends to be too soft in the weld, which can cause the welds to mismove and the root pass to burn through. Therefore, when welding zirconium, the welds should be properly fixed and double-sided as far as possible. Zirconium cannot be welded directly with other metals except titanium, niobium, silver, and vanadium.
Therefore, in the process of zirconium alloy welding, choosing a clean operating environment and strengthening the isolation protection of the weld and heat affected zone are the key to ensure the welding quality.
