What is ferrosilicon?

How is ferrosilicon made?

Ferrosilicon, commonly abbreviated FeSi, is an iron&#;silicon alloy that also contains smaller proportions of other elements. The most popular grade of ferrosilicon contains 75 wt% silicon (&#;FeSi75&#;), but the amount can range from 15&#;90 wt% depending on the application.

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The highest-quality ferrosilicon is made in an electric arc furnace by reducing silica with coke in the presence of iron (usually derived steel scrap or iron ore). The ferrosilicon usually takes the form of shiny, metallic-grey lumps, but is also available as pre-formed briquettes.

The role of ferrosilicon in steelmaking

In steelmaking, ferrosilicon is used for:

• Product performance &#; Ferrosilicon is a convenient way of adding silicon as an alloying element, to improve various properties of the final steel.
• Slag reduction &#; In the manufacture of stainless steels, the presence of silicon reduces chromium oxides in the melt, improving recovery of metallic chromium.
• Deoxidation &#; Ferrosilicon provides quick-acting removal of oxygen from the melt, so avoiding the presence of inclusion-forming oxides and avoiding loss of desirable elements.
• Fuel &#; Some steel mills add ferrosilicon to the melt so that it can be burnt off to get heat into the furnace, and so reduce energy costs.

What are the types of ferrosilicon?

Ferrosilicon is often categorized according to the levels of various minor components, depending on the application requirements. These categories include:

• Low-carbon ferrosilicon and ultra-low-carbon ferrosilicon &#; Used to avoid re-introducing carbon during the manufacture of stainless steel and electrical steel.
• Low-titanium (high-purity) ferrosilicon &#; Used to avoid TiN and TiC inclusions in electrical steel and some special steels.
• Low-aluminium ferrosilicon &#; Used to avoid the formation of hard Al2O3 and Al2O3&#;CaO inclusions in a range of steel types.
• Special ferrosilicon &#; A general term that covers a range of tailor-made products containing other alloying elements.

Ferrosilicon from Elkem

Ferrosilicon for all steel applications

As well as providing STD 75, STD 50 ferrosilicon and ferrosilicon briquettes, we offer a range of premium ferrosilicon compositions that provide optimum results for high-performance steel grades. We&#;d be delighted to talk about your requirements and find the best product for you.

• Electrical steel &#; Our ELEKSIL&#; ferrosilicon is available in a range of grades tailored to the needs of electrical steel manufacture, with inherently low levels of carbon and titanium, and precisely-defined proportions of minor elements.
• Stainless steel &#; Our STAINSIL&#; ferrosilicon portfolio include low-carbon and ultra-low-carbon grades.
• Special steel &#; Our PURISIL&#; ferrosilicon products provide reliably low levels of trace elements such as aluminium, making them perfect for manufacturing a range of special steels.

Clean, consistent ferrosilicon

Ferrosilicon from Elkem is among the cleanest available anywhere, helping you to meet the demands of exacting steel compositions while streamlining production and reducing energy costs.

Thanks to our strong quality management, our ferrosilicon is highly consistent in purity and size grading from batch to batch. This means that you can eliminate worries about shifting performance, unpredictable dissolution times, or variable downstream alloying requirements.

Unbeatable expert support

In contrast to other suppliers, we take care to ensure that the ferrosilicon we provide will give you the best possible results.

So whatever you want to ask us about &#; from the optimum way of introducing our ferrosilicon into the melt, to trialling a new grade in your steel mill &#; then we&#;re ready to listen to you.

Timely and reliable delivery

With a global presence and regional knowledge, we can supply ferrosilicon to all major steel-producing areas, as quickly as you need it. So whatever grade of ferrosilicon you need, if you need it delivered urgently, then we won&#;t let you down.

The Elkem advantage

Sustainability in mind

The production of silicon ferroalloys uses carbon to remove the oxygen from silica, releasing carbon dioxide in the process. The high temperatures needed in our furnaces also consume a lot of energy. But we&#;re committed to doing what we can to reduce this CO&#; footprint, by increasing the proportion of renewably-sourced carbon we use, moving to renewable power sources, or embarking on an ambitious project for carbon capture and storage. You can read more about our plans in our global climate roadmap.

With you at every step

We&#;re more than just a manufacturer &#; buying ferrosilicon from us is a collaboration. We&#;ll listen carefully to your product requirements, work out the ferrosilicon specification that will deliver maximum product quality and cost-effectiveness for you, and offer expert guidance and insight at every stage of the production process.

Alloy of silicon and iron

Ferrosilicon is an alloy of iron and silicon with a typical silicon content by weight of 15&#;90%. It contains a high proportion of iron silicides.[1]

Production and reactions

Ferrosilicon is produced by reduction of silica or sand with coke in the presence of iron. Typical sources of iron are scrap iron or millscale. Ferrosilicons with silicon content up to about 15% are made in blast furnaces lined with acid fire bricks.[2]

Ferrosilicons with higher silicon content are made in electric arc furnaces.[2] The usual formulations on the market are ferrosilicons with 15%, 45%, 75%, and 90% silicon. The remainder is iron, with about 2% consisting of other elements like aluminium and calcium. An overabundance of silica is used to prevent formation of silicon carbide. Microsilica is a useful byproduct.

A mineral perryite is similar to ferrosilicon, with its composition Fe5Si2. In contact with water, ferrosilicon may slowly produce hydrogen. The reaction, which is accelerated in the presence of base, is used for hydrogen production. The melting point and density of ferrosilicon depends on its silicon content, with two nearly-eutectic areas, one near Fe2Si and second spanning FeSi2-FeSi3 composition range.

Physical properties of ferrosilicon

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Si mass fraction (%) 0 20 35 50 60 80 100 Solidus point (°C) Liquidus point (°C) Density (g/cm3) 7.87 6.76 5.65 5.1 4.27 3.44 2.33

Uses

Ferrosilicon is used as a source of silicon to reduce metals from their oxides and to deoxidize steel and other ferrous alloys. This prevents the loss of carbon from the molten steel (so called blocking the heat); ferromanganese, spiegeleisen, calcium silicides, and many other materials are used for the same purpose.[5] It can be used to make other ferroalloys. Ferrosilicon is also used for manufacture of silicon, corrosion-resistant and high-temperature-resistant ferrous silicon alloys, and silicon steel for electromotors and transformer cores. In the manufacture of cast iron, ferrosilicon is used for inoculation of the iron to accelerate graphitization. In arc welding, ferrosilicon can be found in some electrode coatings.

Ferrosilicon is a basis for manufacture of prealloys like magnesium ferrosilicon (MgFeSi), used for production of ductile iron. MgFeSi contains 3&#;42% magnesium and small amounts of rare-earth metals. Ferrosilicon is also important as an additive to cast irons for controlling the initial content of silicon.

Magnesium ferrosilicon is instrumental in the formation of nodules, which give ductile iron its flexible property. Unlike gray cast iron, which forms graphite flakes, ductile iron contains graphite nodules, or pores, which make cracking more difficult.

Ferrosilicon is also used in the Pidgeon process to make magnesium from dolomite.

Silanes

Treatment of high-silicon ferrosilicon with hydrogen chloride is the basis of the industrial synthesis of trichlorosilane.

Ferrosilicon is also used in a ratio of 3&#;3.5% in the manufacture of sheets for the magnetic circuit of electrical transformers.

Hydrogen production

The method has been in use since World War I. Prior to this, the process and purity of hydrogen generation relying on steam passing over hot iron was difficult to control.[6] The chemical reaction uses sodium hydroxide (NaOH), ferrosilicon, and water (H2O). While in the "silicol" process, a heavy steel pressure vessel is filled with sodium hydroxide and ferrosilicon, and upon closing, a controlled amount of water is added; the dissolving of the hydroxide heats the mixture to about 200 °F (93 °C) and starts the reaction; sodium silicate, hydrogen and steam are produced.[7] The overall reaction of the process is believed to be:[2][note 1]

2NaOH + Si + H2O &#; Na2SiO3 + 2H2

Ferrosilicon is used by the military to quickly produce hydrogen for balloons by the ferrosilicon method. The generator may be small enough to fit in a truck and requires only a small amount of electric power, the materials are stable and not combustible, and they do not generate hydrogen until mixed.[8]

One report notes that this method of hydrogen production wasn't thoroughly investigated for about century despite being reported by the US military in the beginning of 20th century.[2]

1. ^

   The iron is intentionally omitted

References

Further reading

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