Ferrosilicon is mainly composed of silicon (Si) and iron (Fe), and may also contain a small amount of aluminum (Al), calcium (Ca), manganese (Mn), carbon (C), phosphorus (P), sulfur (S) and other elements. Common ferrosilicon includes FeSi75 with a silicon content of 75% and FeSi45 with a silicon content of 45%. It has strong chemical stability, but chemical reactions may occur under specific conditions such as high temperature and humidity. The silicon element in ferrosilicon has strong reducing properties and can react with oxygen, etc.
The role of ferrosilicon in steelmaking
Removing oxygen from molten steel:
During the steelmaking process, oxygen reacts with iron and other elements, resulting in a large amount of oxygen in the molten steel. These oxygens will combine with other elements to form oxide inclusions, such as iron oxide, which seriously affects the quality of steel and reduces the strength, toughness, ductility and other properties of steel. The silicon in ferrosilicon is a strong deoxidizer that can react chemically with oxygen in molten steel to produce silicon dioxide (SiO₂). Since the density of silicon dioxide is smaller than that of molten steel, it will float to the surface of the molten steel and enter the slag, thereby achieving the purpose of removing oxygen from the molten steel and improving the purity of the steel.
Preventing pores and looseness:
If the oxygen in the molten steel is not removed in time, defects such as pores and looseness will form during the solidification process. The deoxidation effect of ferrosilicon can effectively reduce the occurrence of these defects, make the organizational structure of the steel more compact, and improve the quality and performance of the steel.
Improving strength and hardness:
Silicon can be dissolved into the iron lattice to produce a solid solution strengthening effect, thereby improving the strength and hardness of the steel. When producing high-strength alloy steel, by adding an appropriate amount of ferrosilicon, the strength of the steel can be significantly improved to meet the high strength requirements of materials in engineering structures, machinery manufacturing and other fields.
Enhance corrosion resistance and oxidation resistance:
Silicon can form a dense oxide film on the surface of steel, which can prevent external oxygen, water vapor, etc. from contacting the steel matrix, thereby improving the corrosion resistance and oxidation resistance of the steel. In the production of stainless steel and heat-resistant steel, ferrosilicon is one of the important alloy additives, which helps to improve the service life of steel in harsh environments.
Grain refinement:
In the production process of some steel grades, ferrosilicon can be used as an inoculant. It can provide a large number of cores for the nucleation of grains during the solidification of molten steel, so as to refine the grains. Refined grains can improve the toughness, plasticity and fatigue properties of steel, and improve the overall performance of steel.
Improve the organizational structure:
The inoculation effect of ferrosilicon can also make the organizational structure of steel more uniform, reduce organizational defects, and improve the quality stability of steel.
The amount of ferrosilicon used in steelmaking
The amount of ferrosilicon used in steelmaking depends on many factors, such as the type of steel, furnace type, smelting process and the initial composition of raw materials. Generally speaking:
Ordinary carbon steel:
For the production of ordinary carbon steel, the amount of ferrosilicon added is usually relatively low, generally around 0.1% - 0.3% (mass fraction). For example, when producing Q235 steel, the amount of ferrosilicon added may be between 0.15% and 0.25%, mainly for deoxidation and proper adjustment of silicon content to ensure the basic properties of the steel.
Low alloy steel:
In the production of low alloy steel, the amount of ferrosilicon will increase according to the specific alloy design requirements, generally around 0.3% - 0.8%. For example, when producing 16Mn steel, the amount of ferrosilicon added may be 0.4% - 0.6% to improve the strength and other properties of the steel.
High alloy steel:
For some high alloy steels, such as stainless steel, heat-resistant steel, etc., the amount of ferrosilicon may be higher, sometimes up to 1% - 3% or even higher. For example, when producing 316L stainless steel, in order to ensure the corrosion resistance and high temperature performance of the steel, the amount of ferrosilicon added may be between 1.5% and 2.5%.
Different furnace types and processes:
In converter steelmaking, the amount of ferrosilicon added is generally around 5-15 kg per ton of steel; in electric furnace steelmaking, due to the different smelting characteristics of the electric furnace and the different raw material conditions, the amount of ferrosilicon used may be around 8-20 kg per ton of steel.
