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Mosten Alloy Co., Ltd.

Weldability of tungsten

  • Mosten
  • 10 Jun

Tungsten is a kind of silver white precious metal, high melting point is difficult to melt, the linear expansion coefficient of tungsten is very small, the elastic modulus and strength are very high, the deformation of thermal expansion and cold contraction is very small. Tungsten has good electrical and thermal conductivity, low vapor pressure and strong corrosion resistance. Pure tungsten is not only used as additive in iron and steel and non-ferrous metal metallurgy industries, but also plays an important role in many industries. For example, the manufacturing of electric contacts and high-temperature resistant components (rocket engine nozzles, high-temperature furnace heaters and reflective screens, etc.), the manufacturing of nuclear industry envelopment materials and high-temperature resistant components of reactors, etc. The welding characteristics of tungsten and its alloys mainly include the following points.

(1)Weld metal is easy to produce pores. Tungsten and its alloy are easy to absorb oxygen, nitrogen and other gases in the welding process. Oxidation will occur at about 300°C. After the metallurgical reaction of the arc, the oxides and nitride formed will generate carbon monoxide and water. If they cannot be precipitated in time, pores will be generated. Tungsten and hydrogen do not produce stable hydrides and do not produce hydrogen embrittlement, but when hydrogen is saturated, pores will form. The above is from the air gas pollution, therefore, in the tungsten welding to use inert gas protection to prevent the formation of pores.

(2) Welding crack tendency is large when welding tungsten and its alloy, welding crack will be generated, the main reasons for the crack are: A, tungsten and its alloy.

The brittleness of the alloy is large and the crack resistance is poor. B. When the content of oxygen and nitrogen in the weld is very high, nitrogen compounds and oxides will be generated and distributed at the grain boundary, which enhances the brittleness and increases the crack tendency at the same time. C, tungsten and its alloys have very low plasticity and high strength, so welding stress is easily generated during welding, which increases the crack tendency.

The commonly used welding methods of tungsten and its alloys are as follows:

(1) Fusion argon arc tungsten welding and gas fusion welding are two important welding methods of tungsten and its alloys, welding in a confined space, and the use of inert gas protection. In order to obtain good welding quality, do not fix the weldment in the welding process, which can effectively reduce the stress. At the end of the welding, it is better to use the lead plate. This prevents crater cracks at the end of the weld.

In air, tungsten and its alloys can also be welded with TIG to meet the joint performance requirements. But the quality of the joint is not very stable, direct current welding method should be adopted. After welding, stress relief treatment shall be carried out below the base metal recrystallization temperature.

(2) Electron beam welding of tungsten and its alloys Electron beam welding is the most ideal welding method for tungsten and its alloys. The vacuum is 1.33×10-4Pa before welding. Compared with argon arc welding, electron beam welding can get a joint with a greater depth of penetration and a narrower heat-affected zone.

(3) resistance welding of tungsten and its alloys in the industrial production of tungsten and its alloy sheet resistance welding application is more, with resistance butt welding or flash butt welding on the compact solid section welding parts. Spot - welded joints of thin plates are widely used in the manufacture of micro - structure electronic devices. Under high temperature, the tungsten has high hardness, strength, good electrical conductivity, using spot welding, the norms of generally weak, due to the heating time is long, under the influence of electrode pressure, end ministries occur deformation and wear of the electrode and bonding on the surface of the solder joint, this has influence on the stability of the spot welding and the quality of solder joint, the tungsten sheet in the main problems existing in the process of spot welding.

(4) Friction welding of tungsten and its alloys can get good welded joints by friction welding of tungsten and its alloys in a vacuum chamber. Compared with the friction welding of other metals, the friction welding of tungsten and its alloys requires high rotation speed and high forging force.

(5) Brazing of tungsten and its alloys

Due to tungsten's high hardness, high melting point and high brittleness at room temperature, brazing should be used in order to obtain good welded joints. The commonly used brazing methods of tungsten and its alloys are oxygen-acetylene flame brazing, in addition, brazing in controlled atmosphere furnace, brazing in vacuum furnace, brazing in induction furnace and brazing in resistance heating.