Calcium silicon (CaSi) alloy is the most widely used composite deoxidizer and inclusion modifier in secondary steel refining. Its core functions include deep deoxidation, desulfurization, inclusion spheroidization and molten steel composition adjustment. Unlike single ferroalloy additives, CaSi alloy balances silicon deoxidation performance and calcium modification ability, which directly determines the final cleanliness and mechanical properties of finished steel.
In actual steel plant production, many quality problems such as continuous casting nozzle clogging, steel plate surface scratches, poor toughness and unstable batch performance are not caused by smelting processes, but by mismatched CaSi alloy grades. Using a unified CaSi specification for all steel types will either fail to meet high-standard steel requirements or cause unnecessary raw material cost waste.
Core Selection Basis for CaSi Alloy in Steelmaking
Steel grade differentiation is the primary principle for CaSi selection. Different steel types have distinct limits on oxygen, sulfur, inclusions and trace impurities. Four key indicators must be confirmed before selecting CaSi alloy:
Ca/Si Ratio: Silicon mainly performs deoxidation; calcium dominates desulfurization and inclusion modification. Low-carbon clean steel requires higher calcium ratio, while ordinary carbon steel can adopt balanced conventional grades.
Trace Impurity Control: P, S, Al and other residual impurities in CaSi must be strictly controlled for high-end steel to avoid introducing harmful elements into molten steel.
Size & Dissolution Performance: Lump materials are suitable for ladle manual feeding, while powder and graded particles match cored wire injection and pneumatic powder feeding systems.
Addition Volume & Recovery Rate: High-alloy steel requires higher calcium recovery rate, so high-activity low-impurity CaSi grades are preferred to reduce alloy consumption.
Mainstream Commercial CaSi Alloy Grades & Basic Properties
Global steelmaking industries mainly apply three mature CaSi alloy grades. Each grade has fixed metallurgical characteristics and applicable steel grade positioning, which cannot be substituted arbitrarily in production.
|
CaSi Grade |
Si Content |
Ca Content |
Max Impurity (P/S) |
Core Metallurgical Features |
|---|---|---|---|---|
|
CaSi 28/60 |
≥60% |
≥28% |
≤0.04% |
Balanced deoxidation and modification, stable activity, cost-effective universal grade |
|
CaSi 30/60 |
≥60% |
≥30% |
≤0.03% |
High calcium activity, strong desulfurization and inclusion modification capacity |
|
High-Purity CaSi 32/62 |
≥62% |
≥32% |
≤0.02% |
Ultra-low impurities, high recovery rate, exclusive for high-end clean steel |
Targeted CaSi Alloy Selection for Different Steel Grades
Combined with on-site refining effects and quality feedback, this section matches the most suitable CaSi grade, size and addition scheme for mainstream steel types.
3.1 Ordinary Carbon Structural Steel (Q235, Q355)
Recommended Grade: CaSi 28/60 Conventional Grade
Ordinary carbon steel has loose requirements for residual inclusions and trace impurities. The main smelting goal is basic deoxidation and slight desulfurization to stabilize molten steel composition. CaSi 28/60 alloy with balanced silicon and calcium elements can fully meet production needs. It avoids excessive alloy residue and effectively controls raw material costs for mass production.
Applicable size: 10–50mm lumps for ladle feeding; 0–3mm powder for conventional auxiliary refining
Recommended dosage: 0.8–1.0kg per ton of steel
3.2 Low-Alloy High-Strength Steel (HSLA Steel)
Recommended Grade: CaSi 30/60 High-Calcium Grade
Low-alloy high-strength steel requires high internal compactness and stable mechanical properties. Hard alumina inclusions generated during smelting will reduce steel toughness and fatigue resistance. High-calcium CaSi 30/60 can fully modify sharp hard inclusions into spherical calcium aluminate, improve molten steel purity, and significantly reduce internal defects of steel coils and steel plates.
Applicable particle size: 0.5–3mm graded particles, suitable for automatic feeding and cored wire filling
Recommended dosage: 1.0–1.2kg per ton of steel
3.3 Pipeline Steel & Vessel Steel (Clean Steel Series)
Recommended Grade: High-Purity CaSi 32/62 Low-Impurity Grade
Pipeline steel and pressure vessel steel belong to high-cleanliness steel. They have extremely strict restrictions on sulfur content, oxygen content and residual inclusions, which directly affect steel welding performance and pressure resistance. High-purity CaSi 32/62 alloy with ultra-low P and S impurities realizes deep desulfurization and ultra-pure modification, effectively preventing inclusion aggregation and improving steel long-term service stability.
Applicable size: 0.2–1.5mm fine powder, matching powder injection refining process
Recommended dosage: 1.2–1.5kg per ton of steel
3.4 Stainless Steel (304, 316 Series)
Recommended Grade: CaSi 30/60 Low-Impurity Optimized Grade
Stainless steel refining is sensitive to silicon and calcium element fluctuations. Excessive impurity elements will cause stainless steel surface streaks and corrosion resistance attenuation. CaSi 30/60 grade with stable low impurities can complete precise deoxidation and inclusion control, avoid excessive silicon precipitation, and ensure uniform surface finish and stable chemical composition of finished stainless steel.
Recommended dosage: 1.1–1.3kg per ton of steel
3.5 Tool Steel & Bearing Steel
Recommended Grade: High-Purity CaSi 32/62 Ultra-Fine Grade
Tool steel and bearing steel require extremely high hardness uniformity and wear resistance. Tiny impurity inclusions will become fatigue crack sources and reduce service life. High-purity CaSi alloy achieves precise micro-modification, controls ultra-fine inclusions, and ensures high compactness and uniformity of steel matrix.
Steel Grade & CaSi Alloy Quick Matching Table
This table helps smelting engineers and purchasers quickly confirm specifications to reduce trial and error costs and stabilize continuous production quality.
|
Steel Grade Type |
Best CaSi Alloy Grade |
Optimal Particle Size |
Core Smelting Purpose |
|---|---|---|---|
|
Ordinary Carbon Steel |
CaSi 28/60 |
10–50mm / 0–3mm |
Basic deoxidation, cost control for mass production |
|
Low-Alloy High-Strength Steel |
CaSi 30/60 |
0.5–3mm graded |
Modify inclusions, improve steel toughness |
|
Pipeline & Vessel Clean Steel |
High-Purity CaSi 32/62 |
0.2–1.5mm fine powder |
Deep desulfurization, ultra-pure molten steel |
|
304/316 Stainless Steel |
CaSi 30/60 Low-Impurity |
0.5–2mm |
Stable composition, ensure surface quality |
|
Tool & Bearing Steel |
High-Purity CaSi 32/62 |
0.2–1mm ultra-fine |
Micro-inclusion control, improve fatigue resistance |
Common Production Defects Caused by Wrong CaSi Selection
Most batch quality fluctuations in steel plants are related to mismatched CaSi alloy specifications, summarized from long-term refining data:
Nozzle clogging in continuous casting: Using low-calcium CaSi 28/60 for clean steel cannot fully modify alumina inclusions, resulting in inclusion accumulation at the nozzle.
Unstable steel mechanical properties: High-impurity CaSi alloy introduces trace harmful elements, reducing steel toughness and welding performance.
High alloy consumption cost: Blindly using high-purity CaSi 32/62 for ordinary carbon steel causes serious cost waste.
Steel surface defects: Unreasonable particle size leads to incomplete melting or excessive oxidation, causing composition segregation and surface scratches.
Purchasing & On-Site Application Tips
Grade matching first: Prioritize steel grade standards rather than price. High-end steel must use low-impurity high-calcium CaSi to avoid quality risks.
Batch COA inspection: Check Ca, Si, P, S indicators and size distribution for each batch to ensure batch consistency.
Standardized feeding: Match size according to feeding equipment; lump for manual feeding, graded powder for wire feeding and powder injection.
Dry sealed storage: CaSi alloy is prone to moisture absorption and oxidation. Humid storage will reduce surface activity and lower refining efficiency.
Proportional dosage control: Excessive addition leads to element exceeding standard; insufficient addition causes poor deoxidation and modification effect.
CaSi alloy selection must be based on the actual steel grade smelting requirements rather than unified specification application. For ordinary carbon steel, CaSi 28/60 is the most cost-effective choice to meet basic refining needs. Low-alloy steel and stainless steel are suitable for high-activity CaSi 30/60 grade to optimize inclusion morphology and stabilize steel performance. High-end clean steel, pipeline steel and tool steel must adopt high-purity CaSi 32/62 low-impurity alloy to achieve deep molten steel purification.
Scientific matching of CaSi alloy grade, size and dosage can effectively reduce steel defects, improve element recovery rate, stabilize batch quality, and reduce comprehensive smelting costs for steel enterprises.
