Introduction
Ferroaluminum (FeAl) is one of the strongest and most effective ferroalloys used in steelmaking, yet it receives relatively little attention. Aluminum is the strongest deoxidizer used in steel—even stronger than silicon and manganese. This makes it an essential component in the production of drawn steels, stainless steels, and specialty steels.
Aluminum also helps keep austenite grains fine and can improve magnetic properties in certain grades. However, it must be used carefully, as excessive aluminum can cause problems such as the formation of alumina inclusions.
What Is Ferroaluminum?
Ferroaluminum is an alloy of iron and aluminum, commonly supplied in two main grades:
FeAl40 (40% Grade):
- Aluminum: 35–45%
- Iron: 55–65%
- Silicon: below 1%
- Carbon: below 0.5%
FeAl20 (20% Grade):
- Aluminum: 15–25%
- Iron: 75–85%
- More commonly used in foundry applications
Typical Size: 10–50 mm or 0–10 mm for induction furnaces
The Role of Aluminum in Steelmaking
Deoxidation — The Strongest Deoxidizer
Aluminum reacts with dissolved oxygen in molten steel and forms aluminum oxide (Al₂O₃), which is transferred to the slag. Aluminum has a much stronger affinity for oxygen than manganese and silicon, so even small additions can reduce the dissolved oxygen level in the melt to below 5 ppm.
Steel deoxidized with aluminum is called killed steel—steel that does not generate gas during solidification and therefore develops a more uniform structure.
Grain Refinement
Aluminum forms aluminum nitride (AlN), which prevents excessive austenite grain growth during heating. As a result, the steel develops a finer-grained structure and improved mechanical properties after heat treatment.
Strain Aging Control
Aluminum binds free nitrogen in steel in the form of AlN. Free nitrogen can cause strain aging, a phenomenon in which hardness increases over time while ductility decreases. The presence of aluminum helps prevent this problem.
Applications of Ferroaluminum
Cold-Drawn Steels
Fine bars, wires, and steel strips that undergo cold drawing require a uniform structure with minimal gas-related defects. Aluminum-killed steels help meet these requirements.
Air-Hardening Steels
Steels such as D2, H13, and A-series grades require aluminum for grain control during austenitizing. Aluminum helps prevent excessive grain growth at temperatures above 900°C.
Ferritic Stainless Steels
In some ferritic stainless steel grades, such as 405 and 409, aluminum is used as a stabilizer to help prevent the formation of austenite at high temperatures.
TRIP Steels — Transformation-Induced Plasticity
TRIP steels used in automotive structural components contain approximately 1–2% aluminum. In these steels, aluminum helps control the Ms temperature, or martensite start temperature, and contributes to the stability of retained austenite.
Heat-Resistant Steels
Aluminum forms a protective aluminum oxide (Al₂O₃) layer on the steel surface, providing oxidation resistance at very high temperatures, up to approximately 1200°C. FeCrAl steels are commonly used in heating elements and furnaces.
Heat-Resistant Cast Iron — Ni-Resist and Similar Grades
Aluminum is used in certain heat-resistant cast irons to improve oxidation resistance at elevated temperatures.
Important Considerations When Using Ferroaluminum
1. Control the addition rate precisely: Aluminum levels above 0.08% in steel can cause problems such as alumina inclusion clusters, which may clog casting nozzles. For deoxidation, a residual aluminum content of approximately 0.02–0.05% is generally sufficient.
2. Addition timing: Ferroaluminum is typically added toward the end of the deoxidation process—after silicon and manganese—to achieve maximum effectiveness.
3. Aluminum and calcium: In steels with strict inclusion-control requirements, calcium is added after aluminum to convert solid Al₂O₃ inclusions into liquid calcium aluminates, which are more easily removed into the slag.
4. Proper particle size: For small induction furnaces, finer sizes of 0–10 mm dissolve more quickly. For EAFs and converters, 10–50 mm is generally more suitable.
Ferroaluminum vs. Pure Aluminum
A common question is why ferroaluminum is used instead of pure aluminum in the form of ingots or wire.
Advantages of ferroaluminum compared with pure aluminum:
- Lower melting point → faster dissolution in molten steel
- Higher density → better immersion in the melt, while pure aluminum tends to float
- More accurate dosage control → defined chemical composition
However, aluminum wire is widely used in wire injection systems and is a major alternative to ferroaluminum in such applications.
Ferroaluminum Price
The price of ferroaluminum depends on several factors:
- Primary aluminum price on the LME
- Grade / aluminum content: FeAl40 is more expensive than FeAl20
- Particle size: finer sizes, such as powder or granules, are typically more expensive
- Purchase volume
- Exchange rate
For current ferroaluminum prices, contact the Nik Arad team.
Nik Arad Ferroaluminum
Nik Arad supplies ferroaluminum with guaranteed chemical analysis, Mill Certificates, and industrial-scale supply capabilities.
Conclusion
Ferroaluminum is a low-volume but high-impact ferroalloy. As the strongest deoxidizer, a grain-refining agent, and a tool for controlling strain aging, it plays an important role in a wide range of quality steels. The key to using it effectively is precise control of both the addition rate and the timing of its addition to the melt.