Calcium Silicon Alloy Lumps

Silicon calcium alloy lumps is an alloy product obtained by smelting silica, lime and coke in a strong reducing atmosphere at 1500-1800 degrees. It is composed of silicon and calcium, with silicon content usually between 40% and 65% and calcium content between 15% and 30%. Impurities may contain different amounts of impurities such as iron, aluminum, carbon, sulfur and phosphorus.

It is relatively stable at high temperatures. During the process of steel smelting, it can react chemically with oxygen and sulfur in molten steel to play a role in deoxidation and desulfurization. Silicon and calcium in the alloy have a strong affinity with oxygen and can generate stable oxides, thereby reducing the oxygen content in molten steel; calcium can also react with sulfur to generate sulfides such as calcium sulfide.

Steel industry

As a calcium additive, deoxidizer, desulfurizer and denaturant of non-metallic inclusions, it can reduce the oxygen and sulfur content in steel, change the shape and properties of inclusions, and improve the purity, strength, toughness, corrosion resistance and other properties of steel. It is used to produce clean steel, high-quality steel and special performance steel.

Cast iron industry

Used as an inoculant and modifier, it helps to form fine or spherical graphite, make the graphite in gray cast iron evenly distributed, reduce the tendency of white cast iron, increase silicon, desulfurize, and improve the quality of cast iron.

Other fields

In the power industry, it can be used to manufacture power equipment such as high-temperature cables, power station transmission lines and transformer cores; it can also be used to improve the heat resistance, wear resistance and oxidation resistance of refractory materials, and to produce ultra-pure silicon wafers.

Strong deoxidation ability:

Calcium and silicon in CaSi alloy have a strong affinity with oxygen in molten steel, and the deoxidation effect is thorough, which can deeply deoxidize molten steel.

Improve the morphology of inclusions:

It can change the shape and properties of non-metallic inclusions, make their particles larger and easier to float, which is conducive to quickly purifying molten steel and improving the quality of steel.

Improve the performance of steel:

It can improve the crystallization system of steel, reduce the size deviation of steel, improve the stability of steel, and improve the corrosion resistance of steel and extend the service life of steel.

Background
A mid-sized specialty steel plant in South Korea, producing high-grade bearing and spring steels, faced persistent challenges with non-metallic inclusions and inconsistent mechanical properties. The plant utilized conventional ferroalloys for deoxidation and inclusion modification, but final product rejection rates remained near 4.5%, primarily due to alumina-based inclusions and poor castability.

Objective
The plant sought to reduce inclusion-related defects, improve steel cleanliness, and achieve better control over inclusion morphology. After reviewing metallurgical options, the quality control team decided to trial Calcium Silicon Alloy Lumps (CaSi) as a combined deoxidizer and inclusion modifier.

Material Specifications
The selected CaSi alloy lumps (30–50 mm size) contained 31% calcium, 60% silicon, and less than 1.5% aluminum. The lump form minimized dust losses and provided a controlled, slow dissolution rate in the liquid steel bath.

Methodology
Over a four-week trial, CaSi alloy lumps were added during the ladle metallurgy stage (LF) after initial aluminum deoxidation. The addition rate was 0.8 kg per ton of liquid steel. Unlike previous practice using separate calcium wire and ferrosilicon, the single CaSi addition simplified handling and reduced oxygen pickup.

Results

Inclusion Modification – Scanning electron microscopy (SEM) analysis showed that solid, angular Al₂O₃ inclusions were effectively transformed into liquid or partially liquid calcium aluminates (e.g., 12CaO·7Al₂O₃). These globular inclusions were less harmful and more easily removed during argon stirring.

Cleanliness Improvement – Total oxygen content dropped from an average of 22 ppm to 11 ppm. The inclusion population density decreased by over 60%.

Castability – Clogging of submerged entry nozzles (SEN) was virtually eliminated. Nozzle life increased from three heats to over eight heats.

Yield & Quality – Final product rejection rate due to inclusion defects fell from 4.5% to 1.2%. Mechanical property consistency, especially fatigue life, improved significantly.

Economic Impact
Although the CaSi alloy lumps had a higher upfront cost than previous additions, the net steelmaking cost per ton decreased by approximately 8% due to:

Reduced nozzle replacements (saving downtime and refractory costs).

Lower rejection and rework rates.

Elimination of separate calcium wire treatment.

Conclusion
The case study confirms that using Calcium Silicon Alloy Lumps as a ladle metallurgy addition provides an effective, cost-efficient solution for inclusion control in high-quality steel grades. The lumps offer stable calcium recovery, operational simplicity, and significant improvements in both steel cleanliness and castability. The plant has since adopted CaSi alloy lumps as a standard practice across its specialty steel production lines.

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