The most important use of niobium is the manufacture of various niobium alloys and as an additive in steel. Among all kinds of microalloying elements in steel, niobium is the most effective microalloying element. It is enough to change the mechanical properties of steel when 0.001%-0.1% niobium is added into the steel. The addition of niobium as a microalloying element to steel does not change the structure of iron, but combines with carbon, nitrogen, sulfur and other elements in steel to change the microstructure of steel. By fine grain strengthening and dispersion strengthening, Nb energy and carbon and nitrogen in steel produce stable carbides and carbonitride. At the same time, the carbide can be dispersed to form a steel with fine crystallization. This can greatly enhance the strength of steel. For example, when 0.1% niobium is added, the yield strength of steel can be increased 118MPa, in fact, only 0.03%-0.05% Nb is added in steel, the yield strength of steel can be increased by more than 30%. Steel costs have risen by just $1 a tonne. The yield strength of ordinary medium carbon steel is generally 250MPa, and the addition of trace niobium can increase the strength to 350-800MPa.
In addition, niobium can induce precipitation and control cooling rate to realize the dispersion distribution of precipitates, so as to adjust the toughness level of steel in a wide range. Therefore, the addition of niobium can not only improve the strength of steel, but also improve the toughness, high temperature oxidation resistance and corrosion resistance of steel. In addition, niobium can also reduce the brittle transition temperature of steel and obtain good welding property and forming property.
Niobium has a very high melting point, and a large proportion of niobium in the world is used in the production of nickel, chromium and iron-based superalloys in the form of pure metal or high-purity iron and nickel niobium alloys. These alloys are used in jet engines, gas turbine engines, rocket assemblies, turbochargers and heat-resistant combustion equipment. Niobium forms γ phase in the grain structure of superalloy. Such alloys generally contain up to 6.5 percent niobium.
