Vacuum metallurgy technology
Vacuum metallurgy refers to metallurgical operations at less than atmospheric pressure.
I. vacuum metallurgy characteristics
1.1. It has a beneficial effect on all compatibilization reactions.
(1) The boiling point of the material decreases in vacuum when the material is gasified from M condensate to M gaseous state and the metal is gasified and evaporated.
(2) Oxide MO is reduced by reductant R+MO condensate M condensate RO gaseous state and metal oxides are reduced to solid or liquid metals.
(3) R+MO condensed state, M gaseous +RO gaseous phase, metal oxide reduced to gaseous metal.
(4) the gas released from the metal G G is released from the gas, G metal to G.
(5) the compounds formed by metal and gas decompose MG, M+G, and thermal decomposition of metal compounds. Vacuum is beneficial to these processes, that is, to speed up the reaction or to lower the temperature of the reaction.
1.2. Very few gases participate in reaction vacuum. The gas is thin. Very few gases participate in the reaction. Metals do not dissolve gases when they melt in vacuum; metals rarely oxidize when they are heated to higher temperatures in vacuum, whether they are solid or liquid; gases follow the ideal gas equation.
1.3_The material flow vacuum system inside and outside the controllable system is a relatively closed system, which is basically separated from the atmosphere. The residual gas in the vacuum system is sent into the atmosphere only through pipes and pumps. The atmosphere can not be pumped into the vacuum system. The material flow inside and outside the system is completely controlled.
1.4 Non-polluting If the process requires a higher temperature (greater than the softening temperature of the vacuum chamber wall material), then the heating system should be heated by electricity in the furnace thus the vacuum system has no fuel combustion problems. Such as SO2, gas emission, dust collection, environmental pollution and so on.
1.5_Gas molecules are small or very dispersed when small metals or oxides form gases in a vacuum. In vacuum, polyatomic molecules tend to break down into molecules with fewer atoms, forming small gas molecules with a diameter of 10-10 M.
Two. vacuum metallurgy methods several main
2.1. Vacuum reduction of metal oxides or compounds in vacuum with carbon, aluminum, silicon and other reductants. Vacuum reduction can greatly reduce the reduction temperature and complete some operations which can not be completed under normal pressure. The reduction of five oxidized two niobium by carbon is taken as an example. At atmospheric pressure carbon can not completely reduce niobium, but to form a variety of niobium carbide, the highest reduction temperature reached 2834 calories, but when the vacuum reached 10-2 Pa, its initial reduction temperature dropped to 1956 calories, when 10-4 Pa to 164 calories. Other vanadium, tantalum, titanium, zirconium, tungsten and molybdenum are also similar. In vacuum, carbon and carbide can also be used to reduce alkali and alkaline earth metals.
Vacuum melting 2.2. vacuum smelting is to purify metal in high temperature smelting under vacuum. Commonly used vacuum melting methods are:
Vacuum induction smelting
(1) Vacuum induction smelting, that is, the use of high-frequency induction furnace or medium-frequency induction furnace in the vacuum chamber smelting metal. It is mainly used for smelting superalloy, high strength steel and ultra high strength steel.
(2) vacuum arc melting, that is, heating metal melts through low voltage and strong current in vacuum. The electrode can be self - consuming or non - loss. It is mainly used for smelting tungsten, molybdenum, tantalum, niobium and titanium.
(3) electroslag melting, that is, the method of remelting and casting special shaped castings for metal remelting.
(4) Electron beam smelting, also known as electron bombardment smelting, is a high-energy electron beam emitted by one or more cathode electron guns at a higher vacuum (1.33 *10-2-1.33 *10-6 Pa), bombarding the molten material (as a pole), converting the kinetic energy of electrons into thermal energy, melting the furnace charge and dropping it into water-cooled copper crystals and solidifying it into ingots. .
2.3. Vacuum distillation and refining vacuum distillation and refining is a method of purifying materials by removing impurities with vacuum evaporation technology. There are two main methods of work: one is vacuum distillation separation, that is, in vacuum by the different vapor pressure between different metals, through the evaporation and condensation process to purify or separate metals. Many industries are distilled in resistance furnace or induction furnace. The other is chemical migration reaction, which uses metal and gas to react to form compounds, migrate to other parts and then react inversely to form gas products and pure metals.
Vacuum sintering of 2.4.
Vacuum sintering furnace
Vacuum sintering refers to the sintering of metal, alloy or metal compound powders into metal products and metal billets at a temperature below the melting point in a vacuum (10_10-3 Pa). In vacuum sintering, there is no reaction between metal and gas, and there is no effect of adsorbing gas. It not only has good densification effect, but also can purify and reduce the sintering temperature. The sintering temperature and the sintering ratio at room temperature can be reduced by 100 ~150 C. It can save energy, improve the life of sintering furnace and obtain high quality products.
2.5. vacuum degassing
Vacuum degassing refers to the removal of harmful gases (oxygen, hydrogen, nitrogen, etc.) from liquid metals or alloys in a vacuum. After degassing, the structure of the metal will not be affected by the gas discharged during casting, and the strength and physical properties of the metal will be obviously improved by reducing the impurities at grain boundaries. Therefore, it is an important means to improve the quality of steel and improve the mechanical and physical properties of steel. It is the most widely used and the largest technology in vacuum metallurgy.
2.6. vacuum heat treatment
vacuum heat treatment
Vacuum heat treatment is to heat metals in vacuum (1_10-8_Pa) to change their structure and improve their physical and chemical properties. Vacuum heat treatment is mainly divided into three categories: vacuum quenching, vacuum annealing and vacuum chemical treatment. Vacuum quenching is heated in vacuum, and then in different cooling medium. Vacuum annealing is mainly used in high temperature alloys, refractory metals and alloys. Vacuum chemical heat treatment commonly used are vacuum carburizing, vacuum carbonitriding, vacuum ion carburizing, vacuum chromizing, plasma beryllium carburizing and so on.
Vacuum coating 2.7.
Vacuum coating is a metal vapor or sputtering process in which metal atoms or ions are condensed on other metals or materials to form the required metal film or coating. The metallurgical industry commonly has vacuum plating aluminum or tin, vacuum plating cadmium, nickel, zirconium or stainless steel.