Titanium materials and titanium plates are constantly being used in the industry. As their importance increases, the factors affecting the welding performance of titanium plates and titanium materials are receiving more and more attention. So what are the factors that can generally affect the welding performance of titanium plate and titanium material?
Titanium in the air melting welding of the larger problem lies in the oxidation and by a variety of pollution brought about by compounds and intermetallic compounds, etc.. By contaminants we mean oxygen, nitrogen and various other oils, dust, etc., which can reduce the quality of titanium welding. Contaminants include not only oxygen and nitrogen, but also organic and inorganic substances and metals other than titanium. Such as machining oil, lubricating oil and nearby workshop iron powder, paint powder, moisture, moisture, sand, dust, etc. around. In addition, there is tungsten mixed in from the electrode. Pollutants in the air of oxygen, nitrogen, moisture is more harmful. Therefore, welding is protected by inert gas. Usually the surface of titanium has a 40um thick oxide film, which can be restored to 80% of its original thickness in a few seconds after cutting, and to its original thickness in a few minutes. It is due to this oxide film that titanium has such good corrosion resistance. Oxygen levels in this range are not considered a contaminant. However, when titanium is exposed to high temperatures in the atmosphere, it reacts with large amounts of oxygen, nitrogen, etc. This generates pollutants. This generates pollutants. At an atmospheric temperature of 427°C, the thickness of the oxide film on the surface of titanium is two to three times that at room temperature. the oxide film increases at 650°C and above. In the molten state, oxygen and nitrogen enter the weld pool and diffuse from the weld metal into the base material. In order to prevent airborne oxygen, nitrogen and other debris from mixing, it is necessary to protect the welding surface and the inside of the weld by inert gas during the welding process. TIG welding of other metals generally does not require gas protection, and most of the inner side does not require gas protection. In addition, in order to prevent the generation of greasy debris, the titanium material and the surface of the operating table should not be wiped with oil. Most of the technical problems in fusion welding of titanium lie in avoiding the generation of the above mentioned contaminants. Countermeasures to prevent contaminants are troublesome and costly. However, the success of titanium welding depends on the preventive measures against contaminants.
Titanium and titanium alloy welding protection requirements for welding is very strict, when the weld carbon content of 0.55%, the weld plasticity almost completely disappeared and become very brittle material, post-weld heat disposal can not eliminate such brittleness. National standard technical conditions, titanium alloy base material carbon content of not more than 0.1% weld carbon content does not exceed the base material carbon content. Titanium alloy has many elements, they have an impact on the physical properties of titanium, of which carbon is titanium and titanium alloys in the common impurities, when the carbon content of 0.13% or less, carbon due to the deep in the α-titanium, weld strength limit of some improvement, plasticity, some decline, but less than the role of oxygen and nitrogen is strong. But when further increase the carbon content of the weld, the weld but the appearance of mesh TiC and its number increases with the carbon content, so that the weld plasticity decreased dramatically, weld stress is prone to cracking.
1. The effect of carbon. Titanium and titanium alloy in the welding process, at room temperature, the liquid molten droplets and molten metal has a strong absorption of hydrogen, oxygen, nitrogen, and in the solid state, these gases have been interacting with it. With the rise in temperature, titanium and titanium alloy absorption of hydrogen, oxygen, nitrogen capacity also rose significantly, about 250 ℃ titanium began to absorb hydrogen, from 400 ℃ began to absorb oxygen, from 600 ℃ began to absorb nitrogen, these gases are absorbed, will be directly caused by the welded joints embrittlement, is extremely important factors affecting the quality of welding.
2. The effect of hydrogen. Hydrogen is a gas impurity in the mechanical properties of titanium more serious factors. Changes in the amount of hydrogen in the weld on the impact properties of the weld is more significant. The weld precipitated flakes or needles TiH2 increase. TiH2 strength is very low, so the flakes or needles WeiHiH2 role in the case of notch, combined with a significant reduction in impact properties; weld hydrogen content changes in the strength and plasticity of the role of the reduction is not very obvious.
3. The effect of oxygen. Weld hardness and tensile strength increased significantly, weld oxygen content is basically with the increase in argon oxygen content and linearly rising with the rise in weld oxygen content. And plasticity is significantly reduced. In order to ** the performance of welded joints, the welding process should be strictly prevented weld and welding heat-affected zone hair oxidation.
4. The effect of nitrogen. Nitrogen and titanium plate will occur drastically hair should, at a high temperature of 700 ℃ or more, the formation of brittle hard titanium nitride (TiN and nitrogen and titanium formed in interstitial solid solution caused by the degree of lattice crooked than the same amount of oxygen caused by the consequences of a more serious, therefore, nitrogen on the improvement of tensile strength of industrial pure titanium weld, hardness, reduce the weld's plasticity performance than the oxygen is more significant. When the nitrogen content of the weld is above 0.13% the weld cracks due to excessive brittleness.
Titanium plate weld defects are due to titanium plate welding, because the argon arc welding gun formed by the argon gas maintenance layer can only maintain a good weld pool from the harmful effects of the air, and has solidified and is in a high-temperature state near the weld and its surrounding area has no protective effect, and in this state of titanium plate weld and its nearby areas still have a very strong absorption of nitrogen in the air and the ability of oxygen. From 400 ℃ to absorb oxygen, from 600 ℃ to absorb nitrogen, while the air contains a large amount of nitrogen and oxygen. With the oxidation level gradually aggravated, titanium plate weld color changes and weld plasticity decline in the law. Silver white (no oxidation) golden yellow (TiO, about 250 ℃ titanium began to absorb hydrogen. Slightly oxidized) blue (Ti2O3 oxidation is slightly serious) gray (TiO2 oxidation is serious).
