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Ferro niobium is an iron alloy whose main component is niobium and iron. It also contains impurities such as aluminum, silicon, carbon, sulfur, and phosphorus. According to the amount of niobium in the alloy, it is divided into FeNb50, FeNb60, and FeNb70. Iron alloys produced with niobium-tantalum ore containing tantalum are called niobium-tantalum iron. Ferro niobium and niobium-nickel alloys are used as niobium additives in vacuum-melted iron-based alloys and nickel-based alloys. Low gas content and low harmful impurities such as Pb, Sb, Bi, Sn, and As are required, and the limit is less than 2×10, hence the name "VQ" (vacuum quality), such as VQFeNb, VQNiNb, etc. Niobium manganese iron alloy (Nb10%～15%) is used as an alloying agent for low-alloy steel and as a niobium processing agent for carbon steel.
Niobium is a high melting point metal, gray steel color, atomic weight is 92.9064, outer electron structure is 4d5s, melting point is 2467℃, boiling point is 4740℃, and the density (20℃) is 8.6g/cm3. There are two eutectic points and a MgZn2-type Laves phase ε-NbFe2. The two eutectic points are located at Nb11.6%, 1360℃ and Nb about 55%, 1560℃, respectively. The melting temperature range of industrial production of ferro niobium (FeNb60) is 1520~1600℃, with a density of about 8.0g/cm3.
Ferro niobium is mainly used for refining high-temperature (heat-resistant) alloys, stainless steel, and high-strength low-alloy steel.In stainless steel and heat-resistant steel, niobium forms stable niobium carbide with carbon in the steel. It is uniformly distributed at the grain boundaries of the steel, preventing the growth of grains at high temperatures and refining the structure of the steel, which can improve the strength, toughness, and creep properties of the steel.
The chemical affinity between niobium and carbon is much greater than that between chromium and carbon, therefore, when niobium is present in stainless steel, it prevents the precipitation of chromium carbide at the grain boundaries of the steel, thus improving the corrosion resistance of the steel. Niobium and nitrogen in steel generate stable niobium nitride, which improves the corrosion resistance of the steel surface layer. Niobium in steel and oxygen to generate stable niobium oxide, so that the surface of the steel to form a niobium oxide film, can prevent the diffusion of oxygen to the internal role of antioxidant.
Carbon steel added Nb0.015% to 0.05%, can play a role in refining the organization, so that the steel has good formability and welding properties. Niobium has a strong blocking effect on the austenite recrystallization of steel, making the steel at higher temperatures, effective control of rolling, and control of rolling toughness effect is very significant. So niobium as a micro-alloy element in the amount of carbon steel has increased significantly. The amount of niobium used in microalloys in the United States, in 1959 only 1.9% of the total consumption of niobium, while in 1988 rose to 68%.
Niobium plays a solid solution strengthening and carbide precipitation strengthening role in high temperature alloys, increasing the yield strength and surface stability of high temperature alloys. The weight of niobium is one of the lighter of the refractory metals and is one of the factors behind the large use of high-temperature alloys. Niobium-nickel alloys are used as additives to nickel-based high-temperature alloys, mainly for the production of 718 alloys. Niobium is added to permanent magnet alloys to improve the coercivity properties of the alloy.
The addition of niobium to cast iron contributes to the formation of spheroidization and pearlite organization. It acts as a breeder and refinement of the casting organization. Niobium improves the strength, toughness, hardness and service life of castings at high temperatures. Electric welding electrodes use ferro-niobium as a solder component to improve the quality of the weld.
