Factors affecting the welding performance of titanium plates

Titanium in the air melting welding is the biggest problem is the oxidation and the various pollution caused by the compounds and intermetallic compounds. The so-called pollutants refer to oxygen, nitrogen and other various oils, dust, etc., which will reduce the quality of titanium welding. Pollutants include not only oxygen, nitrogen, but also organic matter, inorganic and metal other than titanium. Such as mechanical processing of oil, lubricants and nearby workshop iron powder, paint powder, the surrounding water, moisture, sand, dust and so on. There is also tungsten mixed with the electrode. Pollutants in the air of oxygen, nitrogen, moisture is the greatest harm. Therefore, the welding should be protected by an inert gas. Usually titanium surface 40um thick oxide film, but after a few seconds to restore 80% of the thickness, after a few minutes can be restored to the original thickness. It is precisely because of this layer of oxide film. Titanium material has such a good corrosion resistance. The oxygen content in this range does not constitute a contaminant. However, titanium in the atmosphere encountered high temperature, it will respond with a lot of oxygen and nitrogen. This will produce contaminants. Atmospheric temperature of 427, the titanium oxide film thickness is 2 to 3 times the normal temperature. 650 above, the oxide film will increase. In the molten state, oxygen, nitrogen, etc. will enter the welding pool, and then spread from the welding metal to the base material. In order to prevent the air in the oxygen, nitrogen and other debris mixed into the welding process is compulsory through the inert gas protection welding surface and the inside. TIG welding of other metals generally do not require gas protection, the inside also mostly without gas protection. In addition, in order to prevent the production of grease-like debris, titanium and the operation table cannot be wiped with oil. Titanium melting welding, most of the technical problems are the way to avoid the occurrence of these pollutants. Measures to fight against pollutants are cumbersome and costly. However, the success of titanium welding is the prevention of pollutants. Intercity Titanium&Nickel 

Titanium and titanium alloy welding on the welding protection requirements are very strict, when the weld carbon content of 0.55%, the weld plastic almost completely disappears and becomes very brittle materials, heat treatment after welding cannot eliminate such brittle. GB technical conditions, titanium alloy base carbon content of not more than 0.1% of the carbon content of the weld is not greater than the carbon content of the base metal. There are many elements in the titanium alloy, which have an impact on the physical properties of titanium, in which carbon is titanium and titanium alloy common impurities, when the carbon content of 0.13% or less, the carbon due to deep in the α titanium, the weld strength limit Some increase, some plastic decline, but not the role of strong oxygen and nitrogen. However, when the carbon content of the weld is further increased, the number of reticulated TiC increases with the increase of the carbon content, so that the plasticity of the world decreases sharply, and the crack is prone to cracking under the welding stress.

1. The impact of carbon. Titanium and titanium alloy in the welding process, at room temperature, liquid droplets and molten pool metal has a strong absorption of hydrogen, oxygen, nitrogen role, and the solid state, these gases have been with its role. With the increase of temperature, titanium and titanium alloy to absorb hydrogen, oxygen, nitrogen capacity also increased significantly, about 250 ℃ or so titanium began to absorb hydrogen, from 400 ℃ began to absorb oxygen, from 600 ℃ began to absorb nitrogen, these Gas is absorbed, it will directly lead to embrittlement of welded joints, welding quality is an extremely important factor.

2. The effect of hydrogen. Hydrogen is the most serious factor influencing the mechanical properties of titanium in gas impurities. The influence of the change of hydrogen content on world impact is most significant. The amount of flaky or needle-like TiH2 precipitated in the weld. TiH2 strength is very low, so the sheet or needle-like HiH2 role in the case of a notch, impact resistance significantly reduced; weld hydrogen content changes on the strength and plasticity of the role of the reduction are not very obvious.

3. The effect of oxygen. The hardness and tensile strength of the weld is obviously increased, and the oxygen content of the weld is basically increased with the oxygen content of the argon. While the plasticity is significantly reduced. In order, to ensure the performance of welded joints, welding process should be to prevent the weld and welding heat affected zone oxidation.

4. The effect of nitrogen. Nitrogen and titanium plate will be a serious reaction, at 700 ℃ above the high temperature, the formation of brittle titanium nitride (TiN and nitrogen and titanium formation gap solid solution caused by lattice distortion degree, than the same amount of oxygen caused The effect is more serious, so the nitrogen to improve the industrial pure titanium weld tensile strength, hardness, reduce the plasticity of the weld than oxygen is more significant.When weld nitrogen content of 0.13% or more when the weld due to brittle and cracked.

Titanium plate weld defect is due to the titanium plate welding, due to argon arc welding gun formed by the argon gas maintenance layer can only maintain the welding pool from the harmful effects of the air, and has been solidified in the vicinity of the high temperature and the weld There is no protective effect in the vicinity of the area, and in this state of the titanium plate weld and its vicinity of the area is still very strong absorption of nitrogen and oxygen in the air capacity. Oxygen was absorbed from 400 C. Nitrogen was absorbed from 600 C, and rare species contained large amounts of nitrogen and oxygen. With the gradual increase in oxidation level, titanium plate weld color changes and weld plasticity of the law. Silver (no oxidation) Yellow (TiO, about 250 C or so titanium begins to absorb hydrogen. Slightly oxidized) blue (slightly oxidized by Ti2O3) Gray (TiO2 oxidizes heavily).