Ferrosilicon

Alloy of silicon and iron

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Ferrosilicon is an alloy composed of iron and silicon, typically containing silicon in the range of 15–90% by weight and a significant proportion of iron silicides.

Production and Reactions of Ferrosilicon

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The production of ferrosilicon involves the reduction of silica or sand with coke in the presence of iron, often sourced from scrap iron or millscale. For ferrosilicons with up to 15% silicon, blast furnaces lined with acid fire bricks are utilized.

Higher silicon content ferrosilicons are manufactured in electric arc furnaces. Common market formulations include ferrosilicons with 15%, 45%, 75%, and 90% silicon, with the remaining composition mostly iron and about 2% comprising other elements like aluminium and calcium. Excess silica usage helps in preventing the formation of silicon carbide, and microsilica is a beneficial byproduct.

The mineral perryite, with a composition similar to ferrosilicon (Fe5Si2), slowly produces hydrogen upon contact with water. This hydrogen production is accelerated in the presence of a base. The melting point and density of ferrosilicon vary according to its silicon content, presenting two nearly-eutectic points near the Fe2Si and FeSi2-FeSi3 composition ranges.

Physical properties of ferrosilicon[3][4] Si mass fraction (%) 0 20 35 50 60 80 100 Solidus point (°C) 1538 1200 1203 1212 1207 1207 1414 Liquidus point (°C) 1538 1212 1410 1220 1230 1360 1414 Density (g/cm3) 7.87 6.76 5.65 5.1 4.27 3.44 2.33

Applications of Ferrosilicon

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Ferrosilicon serves as a silicon source to reduce metals from their oxides and deoxidize steel and other ferrous alloys, thus preventing carbon loss from the molten steel (referred to as blocking the heat). Similar materials like ferromanganese, spiegeleisen, and calcium silicides are also used for this purpose. It contributes to the production of other ferroalloys and is utilized in manufacturing silicon, corrosion-resistant and high-temperature-resistant ferrous silicon alloys, and silicon steel for electromotors and transformer cores. In cast iron production, ferrosilicon facilitates graphitization by inoculating the iron. It is also present in some arc welding electrode coatings.

Ferrosilicon forms the basis for prealloys like magnesium ferrosilicon (MgFeSi), used in producing ductile iron. MgFeSi contains 3–42% magnesium with trace amounts of rare-earth metals. Additionally, ferrosilicon is critical in casting irons to regulate the initial silicon content.

Magnesium ferrosilicon helps form nodules in ductile iron, providing flexibility by creating graphite nodules instead of flakes, making it resistant to cracking.

It is also a key component in the Pidgeon process for magnesium production from dolomite.

Ferrosilicon and Silanes Synthesis

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A high-silicon ferrosilicon treated with hydrogen chloride forms the industrial basis for synthesizing trichlorosilane.

In manufacturing transformer sheets, ferrosilicon is used in a 3–3.5% ratio for magnetic circuit production.

Hydrogen Production with Ferrosilicon

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Hydrogen production via ferrosilicon has been a technique since World War I, offering more controlled hydrogen generation compared to steam over hot iron methods. Sodium hydroxide (NaOH), ferrosilicon, and water (H2O) are used in this process. The "silicol" process involves a steel pressure vessel filled with sodium hydroxide and ferrosilicon; upon closing, controlled water addition heats the mixture to around 93 °C, initiating the reaction and producing sodium silicate, hydrogen, and steam.

2NaOH + Si + H2O → Na2SiO3 + 2H2

The military utilizes ferrosilicon for rapid hydrogen production for balloons due to the small generator size and stable, non-combustible nature of the materials, requiring minimal electric power and generating hydrogen only when mixed.

The US military reported this method in the early 20th century, but it wasn't thoroughly explored for about a century.

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   The iron is intentionally omitted

References

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Further Reading

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Ferrosilicon (FeSi) is an iron-silicon alloy mainly used in steelmaking for deoxidation and as an alloying agent. Elkem, one of the top suppliers of high-grade ferrosilicon ferroalloys globally, can help you find the optimal product for your application.

How is Ferrosilicon Manufactured?

Ferrosilicon, often abbreviated as FeSi, is an iron-silicon alloy also containing smaller amounts of other elements. The most common grade holds 75% silicon by weight (FeSi75), but the silicon content can vary from 15–90% depending on the application.

The highest quality ferrosilicon is produced in electric arc furnaces by reducing silica with coke in the presence of iron, usually derived from steel scrap or iron ore. Ferrosilicon typically appears as shiny, metallic-grey lumps but can also be available as pre-formed briquettes.

The Role of Ferrosilicon in Steelmaking

In steelmaking, ferrosilicon is utilized for:

• Enhancing Product Performance – Ferrosilicon is a convenient silicon source in alloying, improving various properties of the final steel.
• Slag Reduction – In stainless steel production, silicon presence reduces chromium oxides in the melt, enhancing metallic chromium recovery.
• Deoxidation – Ferrosilicon efficiently removes oxygen from the melt, preventing inclusion-forming oxides and the loss of desirable elements.
• Energy Efficiency – Some steel mills add ferrosilicon to the melt to burn off for extra heat, lowering energy costs.

Varieties of Ferrosilicon

Ferrosilicon classifications are based on varying minor component levels, tailored to specific application requirements. Categories include:

• Low-carbon and Ultra-low-carbon Ferrosilicon – To minimize carbon re-introduction in stainless and electrical steel production.
• Low-titanium (High-purity) Ferrosilicon – To avoid TiN and TiC inclusions in electrical steel and special steels.
• Low-aluminium Ferrosilicon – To prevent hard Al2O3 and Al2O3–CaO inclusions in multiple steel types.
• Special Ferrosilicon – Custom products containing additional alloying elements.

Ferrosilicon from Elkem

Ferrosilicon for Diverse Steel Applications

Along with offering the standard STD 75 and STD 50 ferrosilicon, Elkem provides premium ferrosilicon formulations for high-performance steel grades. We're eager to discuss your needs and identify the best product for you.

• Electrical Steel – Our ELEKSIL^TM ferrosilicon range caters to electrical steel manufacturing needs, featuring low carbon and titanium levels with precisely defined minor element proportions.
• Stainless Steel – Our STAINSIL^TM ferrosilicon portfolio includes low-carbon and ultra-low-carbon grades.
• Special Steel – PURISIL^TM ferrosilicon products with reliably low trace elements, ideal for various special steels.

Clean, Consistent Ferrosilicon

Elkem's ferrosilicon is among the cleanest available, aiding you in meeting exacting steel composition demands while streamlining production and reducing energy costs.

Our stringent quality management ensures high consistency in purity and size grading from batch to batch, eliminating concerns about fluctuating performance, unpredictable dissolution times, or variable downstream alloying requirements.

Unmatched Expert Support

Elkem prioritizes delivering optimal results with our ferrosilicon products by offering expert guidance throughout the production process.

We’re here to support you with any inquiries, from the best methods of introducing ferrosilicon into the melt to trialing new grades in your steel mill.

Timely and Reliable Delivery

With a global presence and regional expertise, we supply ferrosilicon to all major steel-producing areas promptly. Rest assured, we will deliver the grade of ferrosilicon you need when you need it.

The Elkem Advantage

Commitment to Sustainability

The silicon ferroalloy production process involves the use of carbon, resulting in carbon dioxide emissions. The high temperatures required in the furnaces also demand substantial energy consumption. Elkem is committed to reducing its CO₂ footprint by increasing the use of renewable carbon sources, shifting to renewable power, and undertaking ambitious carbon capture and storage projects.

You can explore our global climate roadmap for more details on these initiatives.

Partnership and Collaboration

Elkem is more than just a manufacturer. By collaborating with us for your ferrosilicon needs, we ensure to cater to your product requirements precisely, provide tailored ferrosilicon specifications for maximum quality and cost-effectiveness, and guide you through every stage of the production process.

Interested in learning more about Ferro Silicon? Contact us today to secure an expert consultation!