Tungsten has a high melting point, is hard and brittle, and is difficult to process. However, as long as there is a reasonable process, tungsten can be processed into materials through powder metallurgy, extrusion, forging, rolling, spinning, and drawing. With the improvement of the degree of plastic processing of tungsten, its microstructure, tensile strength, and plastic-brittle transition temperature have greatly improved

prepare

Qualified billets are one of the key factors in the production of tungsten materials, and the first step in preparing billets is to select qualified tungsten powder. The characteristics of powder (average particle size, particle size distribution, chemical composition), mixing, forming, and sintering processes have a direct impact on the composition, density, and microstructure of the billet, and strongly affect the processing and usage performance of the product. The silicon, aluminum, and potassium elements added to the non sagging tungsten wire are added in the form of oxides in tungsten trioxide or "blue tungsten" (a mixture of various low valent tungsten oxides). The mixture is commonly washed with a solution containing hydrofluoric acid to remove impurities in the powder. The billets for producing silk and small sheets are mostly formed on a press, and can also be formed by isostatic pressing. The size of the powder billet is generally 12 × twelve × 400mm, and larger round, square, or rectangular rods are also used. The powder is first pre fired in a hydrogen atmosphere at 1200 ℃ for 1 hour to obtain a certain strength and conductivity, and then subjected to self resistance sintering with electricity. Electric self resistance sintering, commonly known as "vertical melting", is a method developed in tungsten processing. The principle is to directly pass the current through the sintered billet, which generates Joule heat due to the resistance of the billet itself. This heat is used to sinter the billet, and the sintering current is usually 90% of the fusing current. The obtained billet is a self resistant sintered strip (also known as a vertical fused strip). The general standard for vertical melt strips that can be processed into wire is to control the number of grain grains per square millimeter to approximately 10000 to 20000, and the density to be 17.8 to 18.6 grams/cm3. For pipes, sheets, or other large-sized products, isostatic pressing (pressure above 2500 kgf/mm2) is often used for forming, and sintering is carried out under vacuum or hydrogen protection at a high temperature of 2300-2700 ℃.

Rotary forging

It is a commonly used plastic processing method for producing tungsten wire billets and fine rods. Bars of different sizes are heated to 1400~1600 ℃ in a hydrogen atmosphere and subjected to rotary forging on different models of rotary forging machines. The initial deformation amount should not be too large, and then the deformation amount can be appropriately increased. During the deformation process of rotary forging, graphite is used to lubricate the workpiece and mold. The density of the processed tungsten rod can reach 18.8-19.2 g/cm3. Due to the different deformations in various parts of the square billet forged into a round billet, resulting in uneven microstructure, recrystallization annealing should be carried out at this time. The final diameter of the rotary forged bar is about 3 millimeters. The wire drawing blank can be produced by rotary forging or rolling method; The billet produced by rolling method has a large amount of deformation in each pass and a relatively uniform structure, which is beneficial for future processing. Tungsten wire is drawn from tungsten wire billets using the "warm drawing" method. Firstly, pull to a diameter of 1.3 millimeters on a chain stretching machine, and then perform rough, medium, and fine pulling to achieve diameters of 0.2, 0.06, and less than 0.06 millimeters. As the diameter decreases, the heating temperature should decrease and the wire drawing speed should increase. The deformation amount of each pass is generally between 10-20%. The wire drawing is heated by a mixture of gas and air at a temperature of 900-400 ℃. The coarse wire is drawn using a hard alloy mold, while the fine wire is drawn using a diamond mold. The material of the mold, hole type, and grinding technology have a significant impact on the quality of the wire, and the quality, particle size, ratio, and coating method of graphite lubricant also affect the quality of the wire. The non-uniformity of wire diameter is one of the main reasons for wire breakage during use, and a deviation of 0.2-0.4 microns can greatly reduce the lifespan of tungsten wires in vacuum tubes. The diameter of the fine wire material can be measured using the gravimetric method or the vacuum standard current method. During the wire drawing process, as the diameter decreases, the deformation resistance increases (for example, the fracture strength of tungsten wire with a diameter of 0.1-0.3mm can reach up to 350 kgf/mm2), and its plasticity also decreases accordingly. In order to improve the reprocessing performance, stress relieving intermediate annealing is generally required. In addition, the wire can be processed into fine wires with a diameter less than 0.01 millimeters using electrolytic corrosion method.