Forging of tungsten, molybdenum and their alloys

• Mosten
• 3 July

1. Forging characteristics of tungsten, molybdenum and their alloys
The melting point of tungsten, molybdenum and their alloys is much higher than that of titanium, and the required forging temperature is very high, all above 1300 ℃. Even at such a high temperature, the deformation resistance is still very high. Therefore, the forging equipment is required to have large capacity and high strength, and the working temperature of the heating equipment is required to be high.

The casting state of tungsten, molybdenum and their alloys has coarse columnar crystal, and harmful impurities gather in the grain boundary, which weakens the intergranular strength and is easy to forge. Therefore, at present, the ingot is generally extruded to break the casting structure under three-dimensional force, improve the plasticity of the alloy, and then carry out free forging. The tungsten and molybdenum billets sintered by powder can be forged directly, but they need to be hammered quickly. When the ingot is deformed to a certain extent, the hammering can be increased.

Tungsten, molybdenum and their alloys are easily oxidized at high temperature, so heating should be carried out in a protective atmosphere, usually under the protection of hydrogen. If it is heated in an oil or gas stove, it must be controlled as a reducing atmosphere to avoid excessive oxidation. Tungsten and molybdenum alloys have good thermal conductivity and small expansion coefficient, so forging heating can be directly put into the furnace at high temperature, and its heating time is shorter than that of titanium alloy. In forging, because of the fast heat dissipation, it is required to operate quickly and reduce the temperature drop as much as possible.

2．Inlaying technology of tungsten, molybdenum and their alloys
Before forging, each ingot must be marked with alloy brand, batch number and ingot number, and its chemical composition and ingot specification shall meet the requirements; the ingot shall be peeled to remove oxide skin, subcutaneous pores and other defects, the surface finish shall not be less than ▽ 4, and there shall be no sharp transition of diameter, if any, it shall be polished with grinding wheel; the ingot shall also be subject to NDT, and there shall be no pores and cracks inside Defects such as shrinkage cavity, cold shut off, etc.; after the ingot is extruded and opened, it can be used as forging blank only after the shrinkage, fold, crack and other defects are removed through cutting head and tail, alkali washing, grinding or sandblasting and other processes. The density of pure molybdenum sintered billet is not less than 9.5g/cm3, and the Vickers hardness is not less than 140kg / mm² Tungsten, molybdenum and their alloys are heated by hydrogen molybdenum wire heating furnace or oil furnace and gas furnace with reducing atmosphere. Stress relief annealing should be carried out for the tungsten and molybdenum bars after extrusion. The temperature of stress relief annealing is close to that of forging heating. For simplicity, annealing and forging heating are generally combined.