Ferroalloys are alloys of iron with metals such as silicon, manganese, chromium, molybdenum, etc., which are raw materials used in metallurgy industries, especially in iron and steel production. Among ferroalloys, ferrosilicon has the highest consumption in the industry. Depending on the type of application, ferrosilicon is produced in various compositions, but generally its composition ratio includes 10–90% silicon and the remainder iron. At the same time, impurity elements such as aluminum, calcium, manganese, etc., are also present.
Industrial Applications of Ferrosilicon
Silicon has a higher oxidation tendency compared to many main metals in metallurgy industries (such as iron, copper, nickel, etc.) and thus is used as a deoxidizer for many industrial alloys. This element is notably applied in steelmaking and steel casting industries.
Ferrosilicon used for deoxidation is applied alone or mixed with other deoxidizing materials. The amount of silicon consumed per ton of steel varies in different factories and ranges between 0.3% - 0.5%. Considering the use of 75% ferrosilicon for deoxidation, the consumption amount per ton of steel is between 4 - 6 kilograms.
More than ninety percent of the produced ferrosilicon is consumed in steel deoxidation. Therefore, the demand for this product is proportional to the global steel production rate.
Silicon is one of the alloying elements in the family of ferrous alloys. The most important industrial alloys containing silicon are:
- Cast irons
Silicon is one of the main elements and in fact the second alloying element in all common cast irons. The silicon content in these cast irons is usually 1 to 2.7 percent. Raw cast iron contains necessary amounts of silicon due to reduction reactions by carbon, but oxidation of silicon during the melting process of these ingots requires increasing silicon content to 1 to 1.5 percent in the form of ferrosilicon alloys. On the other hand, due to the production of cast iron by scrap iron in induction furnaces or using a percentage of scrap in other methods, the silicon deficiency is usually compensated by 2.5 to 3.5 percent. This increase in silicon is usually done using ferrosilicon alloys with different composition ratios. Grey cast irons, containing more than 10 up to about 22 percent silicon and generally acid-resistant, are produced by melting in blast furnaces or electric furnaces with the addition of silicon metal.
- Steels
They usually contain less than 0.3 percent silicon, which is obtained from the residue of the deoxidation process, but silicon steels containing 3 to 5 percent silicon also exist and are generally used as transformer steels. The increase of silicon in these steels is also done by inoculating ferrosilicon alloys.
In the primary classification of cast irons, there are two completely distinct groups: white cast irons and grey cast irons. The difference between these two types lies in the microscopic structure of carbon presence. In white cast irons, carbon mainly appears combined with iron (hematite), whereas in grey cast irons, carbon content mainly appears as graphite grains. The formation of carbon structure in cast irons depends on various factors, but one reliable method to produce grey cast irons is the use of inoculants.
Production of some ferroalloys is done by the silicothermic method. In these processes, silicon acts as a reducing agent and ferrosilicon is added to the charge mix. Some processes that use ferrosilicon as a reducing agent are as follows:
- Production of magnesium by the Pidgeon process
- Production of ferromolybdenum
- Production of ferrovanadium
- Also, in some processes such as magnesium ferrosilicon production, ferrosilicon is used as a raw material.
Physical Properties
Melting point: 1240 to 1350 °C
Bulk density: 1.6
Specific gravity: 3.2
Grain Size (mm):
Ferrosilicon 0-3
Ferrosilicon 3-10
Ferrosilicon 10-60
The following table shows the chemical composition of 75% ferrosilicon based on the Iranian Standard No. 5825 from the Institute of Standards and Industrial Research of Iran:
| Chemical Analysis and Percentage | Material | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Ti
Max |
Cr
max |
Mn
max |
C
max |
S
max |
P
max |
Al | SI | |||
| Up to | More than | Up to | More than | |||||||
| 0/2 | 0/3 | 0/5 | 0/15 | 0/04 | 0/05 | 1/0 | - | 80/0 | 72/0 | FeSi75Al1 |
| 0/2 | 0/3 | 0/5 | 0/15 | 0/04 | 0/05 | 1/5 | 1/0 | 80/0 | 72/0 | FeSi75Al1.5 |
| 0/3 | 0/5 | 0/5 | 0/20 | 0/04 | 0/05 | 2/0 | 1/5 | 80/0 | 72/0 | FeSi75Al2 |
| 0/3 | 0/5 | 0/5 | 0/20 | 0/04 | 0/05 | 3/0 | 2/0 | 80/0 | 72/0 | FeSi75Al3 |
