Ferrovanadium (FeV) is an alloy formed by combining iron and vanadium with a vanadium content range of 35–85%. The production of this alloy results in a grayish silver crystalline solid that can be crushed into a powder called "ferrovanadium dust". Ferrovanadium is a universal hardener, strengthener and anti-corrosive additive for steels like high-strength low-alloy steel, tool steels, as well as other ferrous-based products. It has significant advantages over both iron and vanadium individually. Ferrovanadium is used as an additive to improve the qualities of ferrous alloys. One such use is to improve corrosion resistance to alkaline reagents as well as sulfuric and hydrochloric acids. It is also used to improve the tensile strength to weight ratio of the material. One application of such steels is in the chemical processing industry for high pressure high throughput fluid handling systems dealing with industrial scale sulfuric acid production. It is also commonly used for hand tools e.g. spanners (wrenches), screwdrivers, ratchets, etc.
Composition
Vanadium content in ferrovanadium ranges from 35% to 85%. FeV80 (80% Vanadium) is the most common ferrovanadium composition. In addition to iron and vanadium, small amounts of silicon, aluminum, carbon, sulfur, phosphorus, arsenic, copper, and manganese are found in ferrovanadium. Impurities can make up to 11% by weight of the alloy. Concentrations of these impurities determine the grade of ferrovanadium.
Synthesis
Eighty-five percent of all vanadium extracted from the Earth is used to create alloys such as ferrovanadium. There are two common ways in which ferrovanadium is produced: silicon reduction and aluminum reduction.
Reduction by silicon
Vanadium pentoxide (V2O5), ferrosilicon (FeSi75), lime (CaO) and slag (recycled vanadium containing waste) and are combined in an electric arc furnace heated to 1850 °C. Silicon in the ferrosilicon reduces the vanadium in V2O5 to vanadium metal. The vanadium then interacts with the iron to form ferrovanadium. Excess lime and V2O5 are added to use up the silicon and refine the metal. This process produces vanadium concentrations between thirty-five and sixty percent.
2 V2O5 + 5 (Fey/5Si)alloy + 10 CaO → 4 (Fey/4V)alloy + 5 Ca2SiO4
Reduction by Aluminum
Iron, V2O5, aluminum, and lime are combined in an electric arc furnace. Like the silicon, aluminum reduces the vanadium in V2O5 to vanadium metal. The vanadium metal dissolves into the iron and forms the ferrovanadium alloy. The resulting ferrovanadium has a vanadium concentration between seventy and eighty-five percent.
3 V2O5 + 10 Al → 6 V + 5 Al2O3
Vx + Fe1−x → (Fe1−xVx)alloy
Toxicology
Ferrovanadium dust is a mild irritant that affects the eyes when touched by contaminated skin and the respiratory tract when inhaled. The dust caused chronic bronchitis and pneumonitis in animals exposed to high concentration (1000–2000 mg/m3) at intervals for two months. However, no such long-term effects have been observed in humans.
Occupational exposure
The American Conference of Governmental Industrial Hygienists (ACGIH) states that an employee who is working eight hours a day, five days a week, can be exposed to ferrovanadium dust in their place of work at concentrations of up to 1.0 mg/m3 without adverse effects. Short-term exposures should be kept below 3.0 mg/m3. It is suggested that those working with high concentrations of ferrovanadium dust wear a respirator to prevent inhalation and irritation of the respiratory tract.
Steel
The most common use of ferrovanadium is in the production of steel. In 2017, 94% of domestic consumption of vanadium was to produce iron and steel alloys. Ferrovanadium and other vanadium alloys are used in carbon steel, alloy steel high strength steel, and HSLA (High Strength Low Alloy) steel. These steels are then used to make automotive parts, pipes, tools, and more.
The addition of ferrovanadium toughens the steel making it more resistant to temperature and torsion. This increase in strength is a result of the formation of vanadium carbides which have a rigid crystal structure as well as a finer grain size which decreases the ductility of the steel. In addition to adding to the composition of the steel, ferrovanadium can also be used as a coating on the steel. When coated with nitrated ferrovanadium, the abrasion resistance of steel increases 30-50%.