Titanium has the characteristics of corrosion resistance, low thermal conductivity, and good heat resistance. It is a good choice for condenser tubes in power plants. At the same time, titanium has high chemical activity, which makes it suitable for welding seams and welding. The dirt on the surface of the material is very sensitive, and preparations must be made before welding, and strict purity inspection of the welding shielding gas must be carried out to minimize the moisture content in the shielding gas.
Good corrosion resistance
Titanium is a very active metal, its equilibrium potential is very low, and the thermodynamic corrosion tendency in the medium is high. But in fact, titanium is very stable in many media. For example, titanium is corrosion-resistant in oxidizing, neutral and weak reducing media. This is because titanium exhaust flange and oxygen have a great affinity. In the air or in an oxygen-containing medium, a dense, strong adhesion and an inert oxide film are formed on the surface of titanium, which protects the titanium matrix from corrosion. Even due to mechanical wear, it will quickly heal itself or regenerate.
This shows that titanium is a metal with a strong tendency to passivation. The medium temperature of titanium is below 315 ℃, and its oxide film always maintains this characteristic.
Low thermal conductivity
The thermal conductivity of titanium is small, 1/5 of low carbon steel and 1/25 of copper.
Good heat resistance
The new titanium alloy can be used for a long time at a temperature of 600°C or higher.
Welding characteristics of titanium
At room temperature, due to the extremely dense surface passivation layer, titanium is very stable. However, as the temperature rises, its absorption capacity for oxygen, hydrogen and nitrogen continues to increase. In the atmosphere, titanium starts to absorb hydrogen at 250 ℃, oxygen at 400 ℃, and nitrogen at 600 ℃. After these elements are absorbed by titanium, it will obviously increase the hardness of titanium and cause embrittlement, which will affect the performance of titanium metal. Therefore, in the welding process, effective protective measures must be taken to avoid air pollution and the effects of oxygen and nitrogen. Before welding, it must be ensured that there is no grease or other hydrocarbons on the surface of the welded metal.
In addition, iron has a great influence on Grade 5 Ti-6Al-4V Titanium Plate. Iron ions are easy to form titanium-iron compounds in titanium, form galvanic cells in the welding area, corrode the oxide film on the surface of titanium metal, and leave opportunities for hydrogen to enter and cause hydrogen embrittlement.
Due to the high melting point, large heat capacity, and poor thermal conductivity of titanium, the weld and heat-affected zone are easy to grow grains under the action of the welding thermal cycle, which reduces the plasticity and toughness of the welded joint. If larger process parameters are used, the crystal grains will be coarser, so low current process parameters should be used and the interlayer temperature should be controlled.
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