Nickel Tube is a rare metal material, which has good weldability, but during the welding process, the contamination of gas pollutants can easily cause embrittlement of welded joints of nickel tube materials. Under normal temperature conditions, nickel is relatively stable. As the temperature gradually increases, its properties will change, and its ability to absorb nitrogen, hydrogen and oxygen will increase significantly. Experiments have shown that nickel is slightly oxidized in high temperature air at 500 °C, and violently oxidized when the temperature reaches 750 °C.
As the oxygen content of the weld in the nickel tube increases, the tensile strength and hardness of the weld of the nickel tube material increase significantly, while the plasticity of the weld decreases significantly, and the weld becomes brittle due to oxygen pollution. The solubility of nitrogen in high temperature liquid metal increases with the increase of the partial pressure of oxygen. The effect of nitrogen on the strength, hardness and plasticity of the weld is more significant than that of oxygen. That is to say, the contamination and embrittlement effect of nitrogen is stronger than that of oxygen. The influence of the nickel tube weld is mainly on the impact toughness. The increase of nitrogen content makes the impact toughness of the weld of the nickel tube material decrease significantly.
Manufacturers often want to prevent the embrittlement of nickel tube welded joints from gas impurity pollutants. When industrial pure nickel welding is carried out, special requirements are put forward for its welding process, because ordinary gas welding and manual arc welding cannot meet the requirements. welding quality.
TIG welding is a reasonable method for welding nickel tube materials. It is worth noting that the usual welding torch structure and process are not enough to ensure the quality of welded joints. Because the gas protective layer formed by this welding torch structure can only protect the welding pool of nickel-containing materials from air pollution, it has no protective effect on the solidified and high-temperature nickel tube weld and its heat-affected zone.
Nickel also has a strong ability to absorb nitrogen and oxygen in the air, which will inevitably cause the weld of the nickel tube material to become brittle, and the plasticity will be seriously reduced. If the backside of the weld of nickel tube material is not effectively protected, similar results will be produced. The molten pool and droplet metal melted at high temperature are more likely to be contaminated by gas impurities. Therefore, a series of protective measures must be taken to improve the welding quality of nickel tubes.
