1. The analysis of welding；
The data of titanium plate manufacturers shows that titanium and its alloys have a strong chemical activity, when the temperature is more than 400 degrees, it begins to react with oxygen, nitrogen, hydrogen and carbon, when the temperature higher than 600 degrees, it will have a strong reaction. While the increase of oxygen, nitrogen, hydrogen and carbon content will lead to the embrittlement of titanium and titanium alloy welding, so the gas protection is the key problem when TA2 titanium tube is welding, as the same time, controlling the temperature of weld metal and heat affected zone to avoid coarse grain and overheated structure to result in the decrease of the mechanical properties of the metal.
2. Welding defects:
A: Stomatal problem: When the titanium and its alloy is welding, it is often found that the aggregate pores are formed near the fusion line after welding RT. The main pore is hydrogen porosity. Because the solubility of hydrogen in titanium decreases with the increase of temperature, the temperature near the fusion line is high, which will lead to the dissolution of hydrogen. If the hydrogen pressure is high in the atmosphere around the welding zone, the hydrogen in the molten metal is not easy to precipitate, and then the hydrogen pores are formed.
B: Crack problem: Because the content of sulfur and phosphorus impurities is small in the welding of titanium based materials, there will be few hot cracks. However, it is very likely that there will be a cold crack in the welding of titanium, which is mainly due to the poor thermal conductivity of titanium and the heat loss is slow to be prone to appear weld coarse grain. When the gas impurity content is high, the plasticity of welding joint reduced, especially when more hydrogen is dissolved in the weld bead, it will form the hydrogen embrittlement.
3. Gas protection:
Due to the purity of the gas is highly required in the welding of titanium, we choose 99.999% high purity argon. To this end, it need to develop special gas protection device. The inside of the pipeline is protected by argon chamber.
