From the global consumption structure, molybdenum can indeed be called an ally of iron. 80% of the demand for molybdenum in Western developed countries comes from steel. Stainless steel absorbs 30% of molybdenum, low alloy steel absorbs 30%, drilling bits and cutting tools account for 10%, and cast steel accounts for 10%. Another 20% of molybdenum is consumed in molybdenum chemicals, molybdenum-based lubricants and petroleum refining. Quite typical, the consumption ratio of molybdenum in steel production in the United States in 1998 was 75%.
Molybdenum-based alloys are also increasingly used in the electronics, metal processing and aerospace industries.
1. Molybdenum alloy
TZM alloy has excellent high strength and comprehensive properties and is the most widely used molybdenum alloy. The United States uses TZM alloy to make turbine discs for engines, and its molybdenum usage accounts for 15% of the total molybdenum usage. my country produces no fewer than 22 brands of molybdenum materials, including TZM molybdenum alloys. In the early 1990s, my country's output of molybdenum and molybdenum products reached nearly 200 tons.
TZM and TZC molybdenum alloys have better mechanical properties than pure molybdenum and are widely used in the manufacture of high-tech, molds and various structural parts. As early as the 20th century, our country had successfully made them into hot-pierced plugs for various seamless steel pipes. This kind of sintered molybdenum plug manufactured with powder smelting technology reduces raw material consumption (50% of that in the cast state) and increases the average service life by 1.5 to 2 times.
Seamless tubes made of molybdenum-rhenium alloy (including 50Re) have excellent performance and can be used at temperatures close to their melting points. They are used as brackets, rings and grids for thermocouple sleeves and electron tube cathodes. etc. parts.
In addition to high strength, good electrical conductivity, thermal conductivity and low thermal expansion coefficient (similar to glass for electronic tubes), molybdenum and molybdenum alloys also have the advantage of being easier to process than tungsten, so they are produced using conventional processing methods Plates, strips, foils, tubes, rods, wires and profiles are used in electronic tubes (grids and anodes), electro-light source (support material) parts, metal working tools (die-casting and extrusion dies, forging dies, perforated plugs, liquid metal Filters) and turbine discs are widely used.
2． Alloying elements of steel
As an ally of steel, molybdenum, together with nickel and chromium, can reduce the embrittlement that often occurs in alloy steel during heat treatment. The United States is leading the way in solving the shortage of tungsten resources by using molybdenum instead of tungsten in high-speed steel. It has been calculated that molybdenum has twice the "power" of tungsten. In this way, steel containing tungsten 18 can be replaced by steel containing molybdenum 9 (chromium and vanadium are added at the same time), which greatly reduces the production cost of steel. The role of molybdenum in stainless steel is to improve corrosion resistance, increase high strength and improve weldability. It can be seen that molybdenum plays an extraordinary role in the steel industry.
3． Other applications
Molybdenum has extremely low vapor pressure at the temperatures and pressures in which vacuum furnaces operate. Therefore, molybdenum parts have the least contamination of the workpiece or working substance in the furnace, and evaporation losses will certainly not limit the service life of molybdenum-rich parts such as heating elements and thermal insulation envelopes.
Molybdenum's high strength makes it an ideal electrode and handling and processing equipment during rapid heating periods in the manufacture of glass products. Molybdenum is chemically compatible with most glass components, and will not cause harmful color effects due to small amounts of molybdenum dissolving in the glass melting tank. As a heating electrode in a glass melting furnace, its lifespan can be as long as 3 to 5 years.
4. Emerging Applications
The main way to solve the problems of low ductility and high oxidation of molybdenum is to develop an advanced composite material based on molybdenum disilicide (MoSi2).
Mo02 formed by the contact between molybdenum and oxygen sublimates at 800°C and obtains a yellow-white nebula-like substance when condensed, which poses serious engineering challenges to the advantages of molybdenum in high strength and creep resistance. question. A silicon-rich coating with self-healing ability is used for this purpose. However, this coating has extremely poor resistance to the effects of thermal cycling. Mo-Si-B, a composite material based on molybdenum disilicide, has excellent high strength and excellent oxidation resistance, but has poor ductility and is limited to the production of small batches of commercial products. In order to solve the ductility problem, the composition range of this molybdenum-silicon-boron composite material was determined, so that in addition to excellent oxidation resistance, high mechanical properties are comparable to TZM alloy. The composite material uses Mo5SiB (T2) as the matrix phase and metallic molybdenum as the second phase.
The metallic phase improves the ductility of the composite material, and the matrix phase can form a self-healing oxide scale. The prepared Mo-6Ti-2.2Si-1.1B composite material with titanium added is almost invisible to the naked eye when exposed to air at 1370°C for 2 hours, which is even better than TZM. This is a remarkable achievement for molybdenum-based alloys.
The second new achievement of molybdenum is the lining of charge-filled warheads (called charge shields in military terms), which can penetrate and cut to great depths in military and industrial applications. In this type of device, the explosives surrounding the lining are detonated in a controlled manner, causing the lining to deform in a very peculiar way. The deformation causes the lining material to produce rod-shaped fragments (ejectors) with extremely high speed and great tension that can penetrate deeply into the target material or target.
The development of molybdenum-lined medical masks is a new research field. The traditional warhead lining material is copper, but the sound speed of molybdenum is 5.12 kilometers/second (copper is 3.94 kilometers/second), and the density is 10.2 g/cm3 (copper is 8.93 g/cm3). To obtain high-speed coherent jets, the tip must have a high speed of sound. The spray design using molybdenum can enable the speed of the jet tip to be greater than 12 kilometers/second, while the speed using copper is less than 10 kilometers/second. The speed difference between the two is 20 to 25. The reason is that high sound speed increases the energy of the tip, which leads to increased penetration. The latest medical-type masks are preferably tapered and trumpet-shaped. Replacing copper with molybdenum will be an important reform in ordnance.
Molybdenum’s third new achievement is the manufacture of flat-panel display devices. In the electronics industry, flat-panel display devices still use active matrix liquid crystal display (LCD) technology. However, LCD is in full development with field emission display (FED), electroluminescence display (EL), plasma display panel (PDP), cathode ray luminescence display (CRT) and vacuum fluorescent display (VFD) which are in different stages of development. Fierce competition for position. In this display process, the display is realized by two glass sheets separated by a vacuum. The glass on the back serves as the cathode. On this glass, more than 500 million emitter tips are distributed in the form of a field emitter array. The intervals between emitters are much smaller than the pixels on a TV screen. The emitter tips are made of molybdenum and can be controlled individually or in groups during the display. In view of their wide viewing angle, fast response time, wide dimensional range tolerance, and especially low power consumption, together with the trend of clear, bright, removable, and durable, they have become the main driving force for the development of panel display technology. The display market has a market size of more than 10 billion US dollars. The flat panel display process uses electron beam evaporation to deposit molybdenum on the tip of the emitter. Although the amount is small, it has unlimited future for the development of large-screen and high-definition televisions.