Molybdenum resources
Storage molybdenum never appears as a natural element, but is always combined with other elements. Although many molybdenum minerals have been discovered, molybdenite (MoS2), a natural sulfide of molybdenum, is the only one with industrial mining value. Molybdenite has a general grade of 0.01% ～ 0.50% and is often combined with sulfides of other metals (especially copper). Molybdenum resources in the world are mainly distributed in the United States and the western mountainous areas of South America. The United States is the largest molybdenum producing country in the world, and also the largest molybdenum reserves in the world, with 5.4 million tons, accounting for almost half of the total molybdenum reserves in the world. 2. Ore deposit molybdenum deposit can be divided into the following three types: primary molybdenum ore, mainly extracting molybdenite concentrate; secondary molybdenum ore, separating molybdenum from the main product copper; symbiotic molybdenum ore, in which molybdenum and copper have equal industrial mining value.
As a result, the main application of molybdenum alloy in the production of steel and steel is as follows ● reduce temper brittleness; ● resist hydrogen embrittlement; ● resist stress cracking caused by sulfide; ● improve high strength; ● improve corrosion resistance of stainless steel, especially chloride pitting corrosion; ● improve welding performance of high strength low alloy steel. Molybdenum is an important additive element in most superalloys and many Ni based and Ti based alloys. At high temperature, molybdenum can effectively accelerate solid strengthening, prevent chloride pitting corrosion and improve corrosion resistance in reducing solution. Molybdenum based alloy molybdenum and molybdenum alloy are widely used because of its many characteristics, such as high strength (2000 ℃), low coefficient of thermal expansion, excellent thermal conductivity and conductivity, high corrosion resistance to molten glass, molten salt and molten metal, and improvement of wear resistance of thin coatings. Molybdenum steel molybdenum is a special steel alloy element. Molybdenum not only brings many excellent properties into steel, but also easily adds to molten metal. Adding molybdenum oxide, ferromolybdenum or molybdenum containing scrap to steel can greatly reduce smelting loss.
Toughness of molybdenum. It is especially effective for parts with large cross-section, such as gears. As an effective hardener, molybdenum will not lead to surface cracks and spalling. Compared with other alloy elements, the molybdenum atom of valve high steel with high corrosion resistance and 20% molybdenum content cast by Hastelloy cw6m is very large. Therefore, it is a very effective strengthening agent, which can improve the creep strength of steel to the extent that it can be used at about 600 ℃. Its size effectively prevents arsenic atoms from migrating to the grain boundary, thus preventing temper embrittlement. Hydrogen diffusion is also prevented and the degree of hydrogen induced cracking is minimized. The first high steel to which these properties of molybdenum were applied was 0.50% c-mo steel. It has been replaced by Cr Mo series steels containing 0.50% ～ 2.0% mo. 2.25cr-1.0% Mo steel is a kind of main alloy steel, which is widely used in petroleum refining plants, power plants and petrochemical plants. High strength low alloy (HSLA) steel molybdenum plays an important role in the development of low carbon microalloyed HSLA steel. The addition of 0.1% ～ 0.3% Mo can refine the acicular ferrite grain structure and enhance the precipitation hardening effect obtained from other alloy elements. High yield strength of 450-600 MPa (65-85 Ksi) can be obtained without strengthening heat treatment. As the ductile brittle transition is as low as - 60 ℃, these materials are widely used in the construction of pipelines leading to remote oil and gas fields. The thin size molybdenum containing HSLA steel has good formability, and its high strength / weight ratio makes it an ideal material for automobile components. The continuous exploration of new sources of oil by petroleum industry pipes has made it necessary to develop and develop deep oil layers, which are often polluted by corrosive hydrogen sulfide, carbon dioxide and high chloride brine. Therefore, AISI 4100 series Cr Mo steel containing 0.15% - 0.25% Mo is widely used. The modified 4140 series with Mo content of 0.4% ～ 0.6% is the most resistant low alloy steel to sulfide stress corrosion cracking (SCC) and can be used in sour wells. With the deepening of drilling depth and the deterioration of service conditions, the application of stainless steel and nickel based alloys with higher molybdenum content, such as alloy C-22 (13% Mo) and alloy C-276 (16% Mo), will continue to increase. Stainless steel has corrosion resistance because chromium can naturally form a thin passivation film on the surface of steel. Molybdenum can strengthen the passivation film and regenerate it rapidly when it is destroyed by chloride. The increase of molybdenum content can improve the corrosion resistance of pitting and cracking on stainless steel. Type 316 (2% - 3% Mo) is the most widely used molybdenum containing stainless steel. It is designated as a material for cans, pipes and heat exchangers used in food processing and processing and pharmaceutical production. Increasing molybdenum content can enhance the resistance to chloride in the air, so Type 316 can be used as a choice material for offshore and coastal buildings. Type 316 is used to cover the exterior of the Canary Wharf building in London and the world's tallest building, Petronas tower in Kuala Lumpur, Malaysia. Duplex stainless steel (3% ～ 4% Mo) has high strength and excellent resistance to chloride stress corrosion cracking. Multi purpose stainless steel, which was originally used as a delivery pipe in the oil and gas industry, is now more widely used in the chemical processing and petrochemical industry, and as a digester in the pulp and paper industry. The most corrosion resistant stainless steel contains 6% - 7.3% mo. This kind of alloy steel is used as condenser of power plant, submarine pipeline and key components of nuclear power plant, such as industrial water pipeline. In 1996, stainless steel containing 6% Mo was used in an absorption tower equipped with more than 20 FGD scrubbers in a thermal power plant in South Korea. Pitting / intergranular corrosion passive chromium oxide layer is very sensitive near the grain boundary and non-metallic inclusions, which can form micro cell and produce pitting rapidly. Anoxic areas, such as under gaskets or laps, are sensitive to similar corrosion, which is often referred to as interstitial corrosion. Molybdenum is the most effective and cheap alloy element to prevent pitting corrosion and intergranular corrosion. Stress corrosion cracking (SCC) of stainless steel exposed to high and low corrosive media, especially chloride and sulfide containing corrosion media, will occur if there is additional or residual tensile stress. Increasing molybdenum content is one of the most effective methods to improve the stress corrosion cracking resistance of steel. The scrubber, pulp and paper making and chemical processing equipment of power plant working in extremely harsh operating environment need to use alloy with very high molybdenum content. Alloys with very high Mo content include typical alloys containing 6% - 8% Mo and nickel based alloys containing 10% - 16% mo. One of the earliest applications of molybdenum in tool steel and high speed steel is to replace tungsten in tool steel and high speed steel. The atomic weight of molybdenum is about half that of tungsten, so 1% molybdenum is roughly equivalent to 2% tungsten. Because these high alloy steels are used in machining, cutting and forming of metal parts, they must have high hardness, high strength and high toughness in a large range of degrees. Mo can improve the hardness and wear resistance of tool steel. By reducing the critical cooling rate, molybdenum can promote the formation of the best martensitic matrix, and can even be used in large complex castings which cannot be cooled rapidly without twisting or cracking. Molybdenum can be combined with elements such as chromium to form special hard wear-resistant carbides. As the performance requirements of tool steel are constantly improved, so its molybdenum content is also increasing. Mo% plastic casting steel 0.5 (maximum) cold deformed steel 0.5-1.0 hot deformed steel 3.0 (maximum) high speed steel when the total content of molybdenum, tungsten and vanadium in tool steel is more than 7% and the carbon content is more than 0.6%, it is called high speed steel. The term is a description of its ability to "high speed" metal cutting. Up to the 1950s, T-1 with 18% w was still the first choice for cutting steel. However, the appearance of controllable atmosphere heat treatment furnace made it possible for Mo to completely or partially replace W, which was very economical and effective. The typical composition (%) grade of selected high speed steel is C Cr Mo w V T-1 0.75 - - 18.0 1.1 m-2 0.95 4.2 5.0 6.0 2.0 M-7 1.00 3.8 8 8.7 1.6 2.0 m-42 1.10 3.8 9.5 1.5 1.2 The addition of 5% - 10% Mo can effectively make the hardness and toughness of high speed steel reach the best, and maintain these characteristics at the height produced during metal cutting. Molybdenum has another advantage: at high temperatures, if the primary carbides of iron and chromium grow rapidly in size, the steel becomes soft and brittle. Molybdenum, especially molybdenum combined with vanadium, can recombine carbides into tiny secondary carbides which are stable at high and low temperatures, thus minimizing the softening and embrittlement of steel. The biggest use of high speed steel is to manufacture various cutting tools: drill, milling cutter, gear cutter, saw blade, etc. The useful cutting characteristics of high speed steel will be further improved by coating the surface of high speed steel with thin but hard titanium carbide coating. The coating can reduce wear and improve wear resistance, thus increasing cutting speed and tool life. The high wear resistance of molybdenum bearing high speed steel makes it ideal for application in the new field of automotive valve inserts and cam rings. The strength and hardness of cast iron can be improved by reducing the pearlite transformation. It can also improve the strength and creep resistance at high level. The high chromium cast iron containing 2% - 3% molybdenum shows higher impact toughness than the high chromium cast iron without molybdenum, and it is ideal for application under severe abrasion conditions, such as in mining, milling, crushing and other processes. These cast irons have qualified properties, which eliminates the need for expensive heat treatment, making them an inexpensive alternative to other friction materials. Reducing the content of austenite forming elements such as nickel and manganese also minimizes the retention of low austenite, a potential cause of premature failure. The application of high Si Mo ductile iron with Si content of 4% and Mo content of 1% has attracted more and more attention. Their excellent strength at 600 ℃ makes them an effective and inexpensive alternative to iron and steel with high alloy content in high applications, such as turbocharger housing, engine exhaust manifold and heater components. The austenite quenched ductile iron has unique microstructure, its strength is more than 1000 MPa (145 Ksi), and has good impact toughness. Their special properties make them ideal for special applications, such as large gears and shafts for power generation, ship engines and large mining equipment. The main limitation of increasing alloy content in high alloy ingot materials such as high speed steel by powder metallurgy is the tendency of segregation during slow cooling. Powder metallurgy technology makes the liquid steel atomized into droplets, and the droplets are cooled very quickly to prevent the occurrence of internal segregation. The steel produced by the condensation of these particles has a fairly uniform microstructure, which has numerous advantages compared with the steel of the same traditional brand. Many powder metallurgy (PM) high speed steels, stainless steels and nickel based alloys have been put into the market in large quantities, and this technology indicates that a new generation of high alloy steels may be produced in the future. In the super heat resistant alloy industry, powder metallurgy (PM) technology can produce key parts with high alloy content, such as gas turbine parts. The Mo / Cu and W / Cu heat sinks used for heat treatment in microelectronic devices are usually produced by powder metallurgy technology. Molybdenum powder is pressed into green billets by hydrostatic pressure and sintered at about 2100 ℃. Hot working was carried out in the range of 870 ~ 1260 ℃. When molybdenum is heated in air above 600 ℃, it forms volatile oxides, so its high application is limited to no oxidation or vacuum environment. The right figure shows the steel blade of steam turbine shaft with high molybdenum content. The molybdenum alloy has good strength and mechanical stability at high temperature (up to 1900 ℃). Their high ductility and toughness make them more tolerant to defects and brittle fracture than ceramics. The unique properties of molybdenum alloy make it have a variety of uses: high heating element, radiation protection screen, extrusion die, forging die, etc.; rotary X-ray anode for clinical diagnosis; electrode and parts of glass melting furnace resistant to molten glass corrosion; and ·Heat sink used as shock pad of semiconductor chip, its thermal expansion coefficient matches with silicon; sputtering layer, only a few angstroms (10-7 mm) thick, is used as gate and interconnection of integrated circuit chip; spray coating is used for automobile piston ring and machine parts to reduce friction and improve wear. Molybdenum tungsten alloys are well known for their excellent corrosion resistance to molten zinc.
