CaSi Deoxidizer

 

CaSi Deoxidizer is a ferroalloy composed of calcium (Ca) and silicon (Si). It's widely used in the metallurgy industry for deoxidation, desulfurization, and inoculation during steelmaking and cast iron production.

 

Typical composition:

Calcium: 28%–35%

Silicon: 55%–65%

Minimal impurities (like aluminum, carbon, sulfur)

 

It's available in lumps, granules, or powder-each tailored to different furnace and ladle refining needs.

 

 

 

During steelmaking, oxygen reacts with molten metal, forming unwanted oxides that:

 

• Reduce steel quality 
• Cause inclusions and defects 
• Weaken mechanical properties 

 

Deoxidizers like CaSi neutralize these effects by bonding with oxygen to form stable oxides that float to the top of the melt and are removed as slag.

This results in:

 

• Cleaner steel
• Better toughness and ductility
• Improved surface finish and structural integrity

 

 

 

When added to molten steel, calcium and silicon each serve a unique role:

• Calcium reacts with oxygen and sulfur, forming CaO and CaS, which are easily separated from the melt.
• Silicon acts as a strong deoxidizer, forming SiO₂.

 

Together, they reduce harmful non-metallic inclusions and lower the sulfur and oxygen content, especially in high-strength low-alloy steels (HSLA), stainless steels, and rail steels. 

 

 

 

1. Steel Industry

Used in both BOF (Basic Oxygen Furnace) and EAF (Electric Arc Furnace)

Improves flowability and casting performance

Vital in producing clean, high-grade steel

 

2. Foundry and Cast Iron

Acts as an inoculant in gray and ductile iron

Enhances microstructure, reducing shrinkage defects

 

3. Ferroalloy Production

Used in compound alloy production as a raw material

 

4. Aerospace & Automotive

Helps achieve stringent metal purity requirements

Enhances strength-to-weight ratio and fatigue resistance 

 

 

 

Strong Deoxidizing Power

Compared to traditional agents like ferrosilicon or aluminum, CaSi has a more reactive profile, efficiently removing oxygen even at lower concentrations.

 

Effective Sulfur Removal

Calcium has a high affinity for sulfur, helping to desulfurize steel, which is crucial for applications where ductility and machinability are important.

 

Improved Inclusion Control

CaSi promotes the formation of soft, globular inclusions, which are easier to remove and far less harmful than angular oxides.

 

Energy Efficiency

Its high reactivity ensures quick reaction, reducing processing time and energy consumption 

 

Versatile Use

Suitable for alloy steels, stainless steels, tool steels, and more.

 

 

Background

A medium-sized special steel mill producing high-quality bearing steel and wire rod grades was facing persistent quality challenges. The plant operated a 120-ton Electric Arc Furnace (EAF) followed by a Ladle Furnace (LF) and a Ruhrstahl–Heraeus (RH) vacuum degasser. Despite a well-established deoxidation practice using aluminum and ferrosilicon, the final products showed occasional but unacceptable levels of non-metallic inclusions-particularly alumina clusters and elongated manganese sulfides. These defects led to customer complaints, increased reject rates, and reduced fatigue life in finished components. The mill sought a cost-effective solution to improve inclusion morphology control without major capital investment.

 

Challenge

The root cause analysis revealed that while aluminum was efficient in reducing bulk oxygen, the resulting Al₂O₃ inclusions were hard, angular, and prone to clustering during casting. These clusters frequently clogged submerged entry nozzles (SENs), disrupting continuous casting schedules and lowering yield. Furthermore, conventional calcium wire injection provided only temporary improvements, with inconsistent recovery rates due to deep lance positioning and variations in ladle slag basicity. The steelmaker needed a more stable, slag-friendly deoxidizing agent that could not only lower dissolved oxygen but also modify remaining oxides into low-melting-point calcium aluminates that would float out easily or remain harmlessly dispersed.

 

Solution: Adoption of CaSi Deoxidizer

After reviewing alternative deoxidants, the plant trialed a high-grade calcium silicon (CaSi) alloy with a nominal composition of 30% calcium and 60% silicon, balance iron and minor elements. The material was supplied in 0–10 mm granular form to ensure rapid dissolution and consistent feeding through the alloy addition system. The CaSi deoxidizer was introduced during the LF refining stage in two strategic steps: first, a bulk addition of 1.5 kg/t steel immediately after slag making, followed by a top-up of 0.8 kg/t steel 10 minutes before vacuum degassing. The existing aluminum practice was reduced by approximately 40%, making calcium silicon the primary deoxidizer while aluminum served as a secondary back-up.

 

Results and Observations

The transition yielded measurable improvements across multiple performance indicators:

Oxygen Control – Total oxygen (T.O.) in the tundish dropped from an average of 18 ppm to 12 ppm, with batch-to-batch variation narrowing significantly. This indicated more consistent deoxidation efficiency, attributed to the strong affinity of calcium for oxygen and the synergistic effect of silicon in stabilizing the reaction.

Inclusion Modification – Scanning electron microscopy (SEM) analysis of final rolled products showed a clear shift from sharp-edged Al₂O₃ to globular calcium aluminate inclusions (e.g., 12CaO·7Al₂O₃), which are fluid at steelmaking temperatures. The proportion of inclusions below 10 μm increased from 62% to 81%, enhancing fatigue performance.

Castability Improvement – SEN clogging incidents decreased by 70% over the three-month trial. The plant extended average sequence casting lengths from 6 heats to over 10 heats per submerged nozzle, reducing refractory consumption and improving overall productivity.

Desulfurization Synergy – The calcium released from the deoxidizer also contributed to desulfurization. Sulfur levels in the final steel decreased from 0.008% to 0.005%, and sulfide inclusions were largely spheroidized, eliminating the risk of anisotropic properties in subsequent forming operations.

Cost Efficiency – Although CaSi alloy is more expensive per ton than ferrosilicon, the reduced aluminum usage, lower reject rates, and fewer casting interruptions produced a net cost saving of approximately $3.50 per ton of liquid steel.

 

Conclusion

This case study demonstrates that carefully implemented CaSi deoxidizer can significantly enhance steel cleanliness, modify harmful inclusions, and improve continuous castability. For the mill, the switch not only solved immediate quality issues but also provided a robust platform for producing higher-value grades with tighter inclusion specifications. The success has prompted the plant to adopt CaSi as a standard part of its refining practice across all bearing and spring steel production lines, proving that targeted alloy selection often outperforms process tweaks in addressing metallurgical challenges.

 

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