Introduction
Ferroboron (Ferroboron) and ferrosilicon (Ferrosilicon) are two ferroalloys with complementary applications in steelmaking. Ferrosilicon is one of the most widely used ferroalloys in the world and is present in almost every steel heat. Ferroboron, by contrast, is used in very small quantities but has a significant effect—particularly in hardenable steels and rail steels.
Part One: Ferrosilicon (FeSi)
What Is Ferrosilicon?
Ferrosilicon is an alloy of iron and silicon. The most common grade in the global market is FeSi75, which contains approximately 72–80% silicon. It is produced by reducing quartz with coke in an electric arc furnace.
Common grades:
| Grade | Silicon | Main Application |
|---|---|---|
| FeSi75 | 72–80% | Steelmaking (deoxidation) |
| FeSi65 | 65–72% | Cast iron production |
| FeSi45 | 40–47% | Production of other ferroalloys |
| FeSi90 | 88–92% | Electrical steels |
Technical Specifications of FeSi75:
- Silicon: 72–80%
- Aluminum: below 1.5%
- Calcium: below 1%
- Carbon: below 0.1%
- Size: 10–50 mm or 0–10 mm
The Role of Silicon in Steelmaking
Deoxidation: Silicon reacts with dissolved oxygen in molten steel to form SiO₂. Silicon is a stronger deoxidizer than manganese but weaker than aluminum. In most steel heats, silicon and manganese are used together to create a more effective deoxidation system.
Strength Improvement: Every 0.1% silicon increases the tensile strength of steel by approximately 8–10 MPa. In spring steels, silicon levels of 1.5–2% are a major contributor to strength.
Improved Magnetic Properties: Silicon increases the electrical resistivity of steel and reduces magnetic losses. Silicon steels containing 1.5–4.5% silicon are used in transformer cores and electric motors.
Oxidation Resistance: Silicon contents above 2% improve the high-temperature oxidation resistance of steels.
Applications of Ferrosilicon
Steelmaking in EAFs and Converters: Used as a primary deoxidizer in molten steel.
Gray and Ductile Cast Iron: Silicon promotes graphitization and improves the microstructure of cast iron. In ductile iron, 2–3% silicon is essential for the formation of spheroidal graphite.
Electrical Steel: FeSi90 is used to achieve high silicon levels of 3.5% or more in transformer steels.
Spring Steel: Spring steels such as 60Si2Mn contain 1.5–2% silicon, providing high fatigue strength.
Silicomanganese (SiMn) Production: Ferrosilicon is a raw material used in the production of silicomanganese—an alloy that both deoxidizes steel and supplies manganese.
Magnesium Production (Pidgeon Process): Ferrosilicon is used in the production of metallic magnesium from dolomite.
Part Two: Ferroboron (FeB)
What Is Ferroboron?
Ferroboron is an alloy of iron and boron. The most common grades include:
FeB17–20:
- Boron: 17–20%
- Carbon: below 0.5%
- Silicon: below 2%
- Aluminum: below 1%
FeB10–15:
- Boron: 10–15%
- Used in higher addition rates for certain steels
Size: 10–50 mm
The Role of Boron in Steelmaking
Boron is one of the most powerful and economical elements for increasing steel hardenability. Just 0.001–0.003% boron—equivalent to 10–30 ppm—can increase steel hardenability to an extent comparable to 0.3% molybdenum or 0.5% chromium.
Mechanism: Boron segregates at austenite grain boundaries and suppresses the formation of proeutectoid ferrite. This allows martensitic transformation to occur deeper within the component, resulting in greater hardenability.
Important Note: Boron should be added in the presence of sufficient titanium or aluminum to stabilize free nitrogen. Free nitrogen reacts with boron to form BN, eliminating boron’s hardenability effect. For this reason, ferrotitanium is often added before or at the same time as ferroboron.
Applications of Ferroboron
Boron Steels: Grades such as 10B21, 15B25, 20MnB5, and similar steels. These steels are used in the automotive industry for bolts, nuts, and components that are hardened after forming. Their main advantage is achieving properties comparable to chromium- or molybdenum-alloyed steels at a lower cost.
Rail Steel: In high-speed rail steels, boron, together with ferrotitanium, improves rolling contact fatigue resistance. Repeated contact between train wheels and rails causes surface fatigue, and boron-containing steels help reduce this problem.
Cost-Effective Hardenable Steels: When a plain carbon steel requires greater hardenability but adding chromium, molybdenum, or nickel is too expensive, boron provides one of the most economical solutions.
Case-Hardening Steels: In steels whose surfaces are hardened through carburizing or nitriding, boron can improve core hardenability.
Comparison of Ferroboron and Ferrosilicon
| Feature | Ferrosilicon | Ferroboron |
|---|---|---|
| Addition Rate | 0.3–2% in steel | 0.001–0.003% in steel |
| Main Role | Deoxidation, strength improvement | Hardenability |
| Common Grade | FeSi75 | FeB17–20 |
| Global Consumption | Very high | Low (microalloying) |
| Relative Price | Moderate | High, but used in very small quantities |
Ferroboron and Ferrosilicon Prices
Ferrosilicon: Global ferrosilicon prices are tracked through Metal Bulletin indices. China is the world’s largest producer, and electricity prices in China are one of the most important factors affecting FeSi price fluctuations.
Ferroboron: Ferroboron prices are linked to the price of boron oxide (B₂O₃). Turkey is the world’s largest producer of boron.
For current ferroboron and ferrosilicon prices, contact the Nik Arad team.
Nik Arad — Ferroboron and Ferrosilicon Supplier
Nik Arad supplies both ferroalloys with guaranteed chemical analysis, Mill Certificates, and industrial-scale supply capabilities.
Conclusion
Ferrosilicon and ferroboron are two ferroalloys with different but complementary roles. Ferrosilicon is a fundamental deoxidizer in steelmaking and also plays an important structural role in cast iron and electrical steels. Ferroboron, even in extremely small quantities, economically increases steel hardenability—making it an ideal lower-cost alternative to chromium and molybdenum in hardenable steels.