What is molybdenum today?

　　Molybdenum is a very important alloying element in high-performance nickel based alloys. Nickel based alloys are divided into two basic types:

　　Corrosion resistant alloys and high-temperature alloys

　　High temperature alloys can be further divided into two categories:

　　Solid solution strengthening type

　　Age hardening type

　　Tables 1 and 2 provide the nominal chemical composition (weight%) of some important alloy grades in each type of alloy.

　　Table 1: The nominal chemical composition of certain corrosion-resistant nickel based alloys:



　　Table 2: The nominal chemical composition of certain high-temperature alloys:



　　In corrosion-resistant nickel based alloys, an important role of molybdenum is to endow the alloy with the ability to withstand non oxidizing media such as hydrogen halide acids (HCl, HBr, and HF) and sulfuric acid. Therefore, the alloy with the strongest corrosion resistance to this type of environment is B3 alloy with a molybdenum content of 28.5%. At the same time, molybdenum, together with chromium, provides the alloy with corrosion resistance to localized corrosion such as pitting and crevice corrosion. Alloys such as C22 and C2000 have excellent corrosion resistance to this type of corrosion.

　　Corrosion resistant nickel based alloys are widely used in industries such as chemical, oil and gas, petrochemicals, pharmaceuticals, and pollution control, where highly corrosive environments are common.

　　In high-temperature alloys, molybdenum is often added to resist high-temperature creep damage. For solid solution strengthening alloys, the characteristic of slow diffusion of molybdenum in nickel is utilized. Due to the fact that high-temperature creep is usually diffusion controlled, adding molybdenum is very effective in reducing creep rate. For utilization γ'、 Ni 3 (Al, TI) precipitated age hardening alloy, adding molybdenum can strengthen the matrix and reduce the interaction between the matrix and γ' The lattice mismatch between phases improves the stability of the precipitates. The role of molybdenum in alloy 242 is very unique. The specific combination of molybdenum and chromium promotes the formation of long-range ordered Ni2 (Mo, Cr) phase particles, resulting in the alloy having high strength without a significant decrease in ductility. In addition, the addition of molybdenum is also very effective for reducing the coefficient of thermal expansion.

　　In order to fully utilize this effect, the gas turbine sealing ring is made of alloy 242 with high molybdenum content. Superalloys are widely used in gas turbine components such as turbine disks, combustion chambers, transition pipes, turbine casings, seal rings, afterburner components and thrust reversers. They are also used for industrial heating devices, heat treatment, heat exchangers, mineral processing, and garbage incineration.

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