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Introduction of the welding process

At normal temperature, titanium and titanium alloy is relatively stable, titanium and titanium alloy as structural material has many advantages, such as small proportion, tensile strength and yield strength high, in 300 to 500 DEG C still has enough high strength, has excellent corrosion resistance in seawater and most of the acid, alkali and salt medium, in aviation, chemical industry, the nuclear industry has gained a wide range of applications。 However, with the increase of temperature, the ability of titanium and its alloys to absorb hydrogen, oxygen and nitrogen increased gradually。 Titanium from 250 degrees to start hydrogen absorption, starting at 400 degrees C, starting from 600 C。 Due to the high affinity of titanium alloy with O2, N2 and H2, the joint will become brittle and the impact property, ductility and toughness of the welded joint of titanium alloy can be reduced。 A delayed crack occurs in the heat affected zone when hydrogen is contained in the titanium alloy。 When the content of oxygen and nitrogen in the weld is high, the weld or heat affected zone will be crack under the action of large welding stress。 So it is very necessary to protect the inert gas (or vacuum chamber)。 Due to the high cost of using the vacuum chamber, the general use of inert gas protection methods。 Protection gas helium and argon, due to argon helium prices higher than, generally speaking, not to the special requirements of the titanium alloy welding joint and heat affected zone, using high pure argon gas protection can prevent oxidation。

The porosity of titanium welded joints is mainly affected by the cleanliness of the welded joints and the preparation of the welded joints as well as the welding time. Although the hydrogen absorption is the main cause of the gas hole in the arc welding joint, other factors such as oxygen, nitrogen, carbon dioxide and the inert gas used for protection may result in the formation of pores. Like aluminum oxide, titanium oxide has a moisture absorption, it is easy to absorb moisture from the atmosphere of the atmosphere. When the titanium component is welded with the joint of the water containing (or water vapor), the gas is dissolved into the joint, and a small hole is formed at the time of solidification. The reduction of titanium in welded joints. Tanyue: to porosity (1) titanium components and solder to dry. (2) the prepared solder is recommended for use in 48h. (3) the parts of the titanium parts to be welded and the solder to grease and clean. (4) using high pure argon or helium for protection. The selection of welding consumables is generally required components of welding consumables and welded titanium matched, but in order to improve the properties of welding joint, sometimes also can be selection of yield strength is lower than the parent metal of welding materials. The composition and properties of industrial pure titanium welding wire are specified in A5.16 AWS. The composition and properties of welding wire specified in the national standard are consistent with AWS. To ensure strict clean to be good weld area and protective gas, using as shown in Table 3 specification for welding, welding material selection and base metal composition of TA2 (AWS ERTi-2) wire, interlayer temperature control is less than or equal to 100 DEG C, interlayer clean clean surface of the weld. Protective effect of welding seam: silver white for the protection of the best; pale yellow for slight oxidation; blue indicates serious oxidation; gray is poor, according to the unqualified treatment.

Titanium pipe weld defect is due to the titanium tube welding, argon gas formed by argon arc welding gun maintenance can only maintain good weld pool due to air the harmful effects, and to have solidified in high temperature near the weld area and nearby no protective effect, and in this state of titanium tube and near the weld area still have a strong ability to absorb nitrogen and oxygen in the air. The absorption of oxygen from 400 degrees C, starting at 600 C, and the air species contains a large amount of nitrogen and oxygen. With the gradual increase of the oxidation level, the change of the color of the titanium pipe weld and the law of the plastic drop of the weld. Silver white (no oxidation) gold (TiO, about 250 degrees in titanium began to absorb hydrogen. Mild oxidation (Ti2O3) blue oxide slightly serious) gray (TiO2) severe oxidation.

1 carbon impact. Titanium and titanium alloy are relatively stable, but in the welding process, under normal temperature. Liquid droplet and molten pool metal have a strong absorption of hydrogen, oxygen, nitrogen, and in the solid state, these gases have their role. With the increase of temperature, titanium and titanium alloy absorption ability of hydrogen, oxygen and nitrogen also increases significantly increased, in about 250 DEG of titanium began to absorb hydrogen, from 400 DEG C began to absorb oxygen, from 600 DEG C began to absorb nitrogen, these gases are absorbed, will directly lead welding joint embrittlement, influencing the welding quality is very important factor.

2 Effects of nitrogen. Nitrogen and titanium plate play a role, more than 700 degrees Celsius under the high temperature. Formation of solid solution of brittle hard titanium nitride (tin and titanium and nitrogen to form a gap caused by the lattice crooked degree of Thebes, than the same amount of oxygen caused more serious consequences. Therefore, nitrogen to improve the industrial pure titanium welding joint tensile strength, hardness, reducing the weld of plastic properties than that of oxygen is more significant. When the amount of nitrogen content in the weld is more than 0.13%, the weld seam is crack due to the cracking.

3 hydrogen is affected. The main reason is that with the increase of hydrogen containing hydrogen seam, factors affecting mechanical properties of gas impurities in titanium is the most serious. The influence of hydrogen content in the weld seam on the impact property of the weld is the most significant. The amount of flake or needle like TiH2 in the weld is increased. TiH2 intensity is very low, so the effect of sheet or needle shaped HiH2 is significantly decreased, and the effect of hydrogen content change on the strength of the weld is not very significant.

4 the effect of oxygen. The hardness and tensile strength of the weld increased obviously, and the oxygen content in the weld was basically increased with the increase of the oxygen content in argon. And the plastic is significantly reduced. In order to ensure the performance of welded joints, should prevent the weld heat affected zone and welding in the welding process of oxidation hair.

点击次数:  更新时间:2016-6-15 8:46:32  【打印此页】  【关闭