The classification of calcium silicon alloys is based on the calcium (Ca) and silicon (Si) content as core indicators. Common industrial grades and their composition ranges are as follows (compliant with GB/T 4701-2021 "Silicon Calcium Alloys" standard):
| Common Grades | Calcium (Ca) Content Range | Silicon (Si) Content Range | Maximum Impurity (Al+Fe) Content | Main Application Areas |
|---|---|---|---|---|
| Ca31Si55 | 30%-35% | 50%-58% | ≤8% | Steelmaking deoxidation and desulfurization |
| Ca28Si60 | 25%-30% | 58%-65% | ≤7% | Cast iron inoculation, steelmaking silicon supplementation |
| Ca20Si65 | 18%-22% | 63%-68% | ≤6% | Aluminum alloy casting, ordinary steel deoxidation |
| Electronic grade CaSi | ≥30%(Ca) | ≥60%(Si) | Total impurities≤0.1% | Semiconductor materials, electronic components |
Note: Some special grades may have their impurity content adjusted according to user requirements (e.g., low-aluminum Ca31Si55, Al≤1%).
Differences in the Application of Different Grades of Calcium Silicon Alloys in Steelmaking
CaSi alloys mainly perform deoxidation, desulfurization, and grain refinement functions in steelmaking. Different grades show significant differences in their suitable applications and effects:
Deoxidation Effect: High-calcium grades are superior.
High-calcium grades (e.g., Ca31Si55): Ca has a strong affinity for O. Adding 0.3%-0.5% (by mass of molten steel) can reduce the oxygen content of molten steel from 80-100ppm to 30-40ppm. The deoxidation efficiency is 40%-50% higher than that of ordinary ferrosilicon. It is suitable for high-quality steels (e.g., bearing steel, spring steel), and can reduce oxide inclusions (e.g., Al₂O₃), improving the fatigue life of steel.
Medium-calcium grades (e.g., Ca28Si60): The deoxidation efficiency is slightly lower than Ca31Si55, but silicon can be added simultaneously (increasing the Si content of molten steel).Calcium content: 0.1%-0.2%, suitable for steels requiring silicon content adjustment (such as low-alloy high-strength steel), balancing deoxidation and composition adjustment.
Desulfurization effect: Calcium content determines desulfurization capacity.
Ca31Si55 desulfurization rate can reach 60%-70% (reducing the sulfur content of molten steel from 0.03% to 0.009%-0.012%). The generated CaS inclusions have a high melting point (2450℃) and low density (2.58g/cm³), making them easy to float and remove. It is suitable for steels with strict sulfur content requirements (such as nuclear power steel and low-temperature container steel).
Ca20Si65 desulfurization rate is only 40%-50%, suitable only for ordinary carbon steel (sulfur content allowed ≤0.05%).
Grain Refinement: High-calcium grades improve the mechanical properties of steel.
The Ca in Ca31Si55 promotes the formation of carbonitrides (such as Nb(C,N)) from elements like Nb and Ti in the steel, acting as a grain refinement nucleus. This refines the grain size from 50μm to 20-30μm, increasing tensile strength by 15%-20% and impact toughness by 25%-30%, making it suitable for high-toughness steels (such as wear-resistant steel for engineering machinery).
Differences in the Application of Different Grades of SiCa Alloys in the Casting Field
In the casting field, silicon-calcium alloys are mainly used as inoculants and composition regulators. The selection of grades needs to match the type of casting and performance requirements:
Cast Iron Inoculation: High-Silicon Grades Adapt to Toughness Requirements
High-Silicon Grades (such as Ca28Si60, Ca20Si65): Si is the core element for graphitization of cast iron. Adding 0.2%-0.4% (by mass of molten iron) can increase the graphite spheroidization rate of gray cast iron from 70% to over 90%, and increase the impact toughness from 12J/cm² to 18-22J/cm². It is suitable for cast iron parts requiring high toughness (such as machine tool beds, automobile brake discs);
High-Calcium Grades (such as Ca31Si55): The inoculation effect is weaker, but it can improve the fluidity of molten iron (viscosity reduced by 15%-20%), reducing "incomplete pouring" of thin-walled cast iron parts (wall thickness 3-5mm). Defects, suitable for complex structural castings (such as precision valves).
Non-ferrous alloy casting: Matching composition requirements as needed
Aluminum alloy casting: Ca20Si65 can supplement Si into aluminum alloys (increasing alloy strength), while Ca can neutralize harmful elements such as Na and Li in aluminum alloys (generating CaNa₂ and CaLi₂), improving the "hot cracking tendency", suitable for the production of automotive aluminum alloy wheels;
Magnesium alloy casting: Ca in Ca31Si55 can refine magnesium alloy grains (from 100μm to 40-50μm), improving high-temperature strength (tensile strength at 200℃ increases by 30%), suitable for aerospace magnesium alloy components.
Differences in the Application of Different Grades of SiliconCalcium Alloys in Special Fields
Electronic Materials Field: High Purity Grades are Key
Electronic-grade silicon-calcium alloys (such as Ca30Si60, with a total impurity content ≤0.1%) require strict control of B and P content (≤0.0001%) to avoid affecting the electrical properties of semiconductor silicon wafers. They can be used to prepare polycrystalline silicon (through the reduction of SiO₂ by silicon-calcium), making them suitable for chip manufacturing. Ordinary industrial grades (such as Ca31Si55) cannot meet the requirements of the electronics industry due to excessively high impurity levels.
Special Alloys: Precise Composition Design
Stainless Steel Production: Adding Ca28Si60 improves the corrosion resistance of stainless steel (more uniform Cr content, avoiding Cr-deficient areas), extending the salt spray corrosion resistance time of stainless steel from 200h to over 350h;
Heat-Resistant Alloy Production: Ca in Ca31Si55 enhances the high-temperature oxidation resistance of the alloy (generating a dense CaO-Al₂O₃ protective film), reducing the oxidation rate of the heat-resistant alloy at 1000℃ by 50%, making it suitable for gas turbine blade manufacturing.
Core Principles for Selecting CalciumSilicon Alloy Grades
Prioritize "Core Functions":
Choose high-calcium grades (Ca31Si55) for applications requiring strong deoxidation/desulfurization, and high-silicon grades (Ca28Si60, Ca20Si65) for applications requiring inoculation/silicon supplementation;
Match according to "Material Purity Requirements":
Select high-purity grades for electronics and nuclear power applications, and conventional grades for general industrial applications;
Balance according to "Process Costs":
High-calcium grades are 20%-30% more expensive than high-silicon grades. For non-critical applications, medium-calcium grades (such as Ca28Si60) can be used to reduce costs.
