Titanium and its alloys have strong chemical activity. When the temperature exceeds 400 °C, it starts to react with oxygen, nitrogen, hydrogen and carbon, and when the temperature is higher than 600 °C, the reaction is violent. The increase of oxygen, nitrogen, hydrogen and carbon content will lead to embrittlement of titanium and its alloy weld metal, so gas protection during welding of TA2 titanium pipe is a key issue, while controlling the weld and heat affected zone To avoid the generation of coarse grains and overheated structure due to overheating, the mechanical properties of the metal will be reduced. Welding defects that are prone to occur in welding::
1. Crack problem. When welding titanium-based materials, due to the low content of sulfur and phosphorus impurities in the material, hot cracks rarely occur; however, when welding titanium materials, cold cracks are likely to occur and have a delay phenomenon. Mainly due to the poor thermal conductivity of titanium, slow heat loss, and coarse grains in the weld; when the gas impurity content is high, the plasticity of the welded joint is reduced, especially when more hydrogen is dissolved in the weld. Hydrogen embrittlement.
2. Gas protection. When welding titanium materials, due to the high purity requirements of the gas, we use 99.999% high-purity argon gas; the range to be protected by argon gas is the molten pool, the heat-affected zone, and the base metal of each 10mm area outside the fusion line on both sides. A special gas protection device is required for this purpose; the inside of the pipeline is protected by an argon gas chamber device.
3. Stomatal problem. When welding titanium and its alloys, it is often found that agglomerated pores are generated near the fusion line after the weld RT. The pores are mainly hydrogen pores; since the solubility of hydrogen in titanium decreases with the increase of temperature, the temperature near the fusion line is high during welding, which will cause hydrogen to dissolve out. If the hydrogen partial pressure in the atmosphere around the welding zone is high, the hydrogen in the molten metal is not easy to be precipitated, so it aggregates to form hydrogen pores.
After the welding is completed, the quality of the weld is mainly judged by the appearance and surface color of the weld. The color of the weld surface is mainly related to the argon protection and the cleanliness of the break. If the titanium tube appears blue on the weld surface during the welding process If there is a dark gray color on the surface of the welding seam, stop welding immediately for repair, remove all the dark gray parts, and re-weld.
