What are Ferroalloys? Definition and Types
Ferroalloy refers generally to alloys of iron which contain a high proportion of one or more other elements than carbon. These include elements such as chromium, manganese or aluminum. The steel industry is the largest consumer of ferroalloys, as they impart various properties to steel alloys and stainless steel. In addition, ferroalloys play an important role in the production of the metal. For example, ferroalloys prevent the negative effects of sulfur in the production and improve the corrosion resistance in steels.
In general, ferroalloys are produced in a blast furnace or an electric arc furnace, whereby the importance of the latter method declined steadily in the 20th century.
Other possibilities for the production of ferroalloys are by carbothermic reactions, the addition of elements into molten iron and by direct reduction.
Different types of ferroalloys
Since each ferroalloy serves a different purpose, many types exist. These are the most common.
Ferrochrome, also known as ferrochromium, typically consists of 50 to 70 % of chromium by weight. Basically, it is an alloy of chromium and iron. Ferrochrome is mainly used in the production of steel, which makes up for about 80 % of the world’s consumption.
In general, ferrochrome is produced in an electric arc furnace. The production process is essentially a carbothermic reaction which is carried out at extreme temperatures near 2800 °C. A large amount of electricity is needed to reach these high temperatures. As a result, production in countries with high electricity costs is very expensive. The leading producer of ferrochrome is China, South Africa and Kazakhstan.
Ferromanganese is characterized by a very high content of the element manganese. It can be produced in a blast furnace. However, more common is the production in a submerged arc furnace, which is a type of electric arc furnace. This is achieved through carbothermic reduction. For this process, a mixture of manganese oxide, iron oxide and carbon is heated.
High-carbon ferromanganese is the most consumed ferroalloy worldwide in terms of quantity and is widely used in steelmaking. China is the main manufacturer of this ferroalloy.
Ferromolybdenum combines molybdenum and iron. This ferroalloy has a molybdenum content of 60 – 75 %. In the production process, molybdenum oxide is mixed with iron oxide and aluminium. An aluminothermy reaction follows. To purify the end product, an electro-beam melting is applied. The addition of ferromolybdenum leads to an improved corrosion and wear resistance and weldability.
Ferromolybdenum is mainly used in the production of ferrous alloys. Further applications are machine tools and equipment, military hardware, cars, trucks and ships. Moreover, it can also be applied in high speed tools steels and superalloy applications. The leading producers of ferromolybdenum are China, Chile and the US.
Ferronickel is characterized by a nickel content of 35 %. The ferroalloy is obtained by a carbothermic reaction and is often applied in the production of austenitic stainless steels and nickel alloy steels. In 2008, the steel making industry made up to 98 % of the ferronickel consumption in the US. Further applications are electronics and the manufacture of batteries. The main ferronickel producers are Japan, New Caledonia and Colombia.
Ferrosilicon is a ferroalloy which contains about 15 – 90 % of silicon by weight. Particularly high is the proportion of iron silicides. The manufacturing of the ferroalloy is carried out by reduction. In the process, silica, sand with coke or iron are used.
The main applications of ferrosilicon are in steel production. The ferroalloy helps to deoxidize steel and ferrous metals. Further, it improves hardness, strength and corrosion resistance. China is the main producer of ferrosilicon.
Ferrotitanium is a ferroalloy which consists of 45 – 75 % of titanium. Further, iron and sometimes small amounts of carbon is added. For production, an induction furnace is used. In this, titanium, steel and iron are melted. Ferrotitanium is characterized by superior corrosion resistance, high strength and low density.
Mostly, ferrotitanium is applied in steel production. Further, the ferroalloy is used for deoxidizing and desulphurization. Main producers of ferrotitanium are Brazil, China and India.
Ferrotungsten is a ferroalloy which is a combination of iron and tungsten. It is categorized into grade A (75 – 82 % W) and B (70 – 75 % W). In the production process, tungsten is converted into tungsten oxide. In the next step, it is heated with hydrogen or carbon. The resulting powder is mixed with iron. The raw material required is found in wolframite, scheelite and ferberite. The use of ferrotungsten increases the melting point of an alloy. As a result, the material is often used when the workpiece has to withstand high temperatures, for example in the aerospace industry.
The main manufacturers of ferrotungsten are China, Bolivia and Russia.
Ferrovanadium is an alloy which consists of 35 – 85 % of vanadium. Vanadium has the property of deoxidizing steel. Further, it has a beneficial effect on the hardness and toughness of steel. It also improves the resistance to impact and the corrosion resistance of metals. The alloy can be produced in two ways, namely by silicon reduction and aluminium reduction.
The main producers of ferrovanadium are China, Russia and South Africa.
OTHER WAYS TO CHANGE THE PROPERTIES OF STEEL
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