Calcium silicon alloy (CaSi) is a core multifunctional additive in cast iron production. Through four core functions-graphite modification, deoxidation and purification, grain refinement, and sulfur control-it comprehensively enhances the strength, toughness, machinability, and reliability of cast iron, making it suitable for high-end applications such as automotive parts and industrial machinery.
Physical properties: Melting point 1250-1350℃, density 2.5-2.8g/cm³, silver-gray block (5-30mm) or powder, calcium readily volatilizes at high temperatures, exhibits strong reactivity, and has good compatibility with molten iron;
Core advantages: Multifunctional integration (spheroidization + deoxidation + refining), adding 0.2%-0.5% per ton of cast iron can achieve multi-dimensional performance improvement, with significant cost-effectiveness;
Core mechanism of silicon calcium alloy improving cast iron performance
(1) Graphite modification: from "flake" to "spheroid", toughness doubles
Mechanism of action:
Silicon enhances the carbon activity in molten iron, promoting graphite nucleation; Calcium, as a spheroidizing agent, adsorbs on the surface of graphite nuclei, inhibiting flake growth and guiding the formation of spheroid/worm-like graphite;
Key reaction:
Calcium combines with sulfur and oxygen, eliminating their interference with graphite spheroidization, while the generated CaC₂ can serve as a graphite nucleation core.
(2) Deoxidation and Purification: Reducing inclusions and improving purity.
Mechanism of action:
Silicon reacts with oxygen: Si + 2FeO → SiO₂ + 2Fe. The density of the generated SiO₂ is 2.65 g/cm³, much lower than that of molten iron (7.1 g/cm³), making it easy to float and form slag.
Calcium-enhanced deoxidation:
2Ca + O₂ → 2CaO. Calcium has a stronger affinity for oxygen than silicon, which can remove trace amounts of residual oxygen in molten iron. Simultaneously, it reacts with Al₂O₃ to form low-melting-point composite inclusions (CaO・Al₂O₃), facilitating separation.
(3) Grain Refinement: Refines the microstructure, balancing strength and toughness.
Mechanism of Action:
Tiny particles (such as CaS, SiO₂) in silicon-calcium alloys act as heterogeneous nucleation sites, promoting the formation of numerous fine grains rather than a few coarse grains during cast iron solidification.
Grain Boundary Strengthening:
Refined grains increase the number of grain boundaries per unit volume, hindering dislocation movement and dispersing stress, thus improving the overall material performance.
(4) Sulfur Control: Eliminates Hot Brittleness and Improves Machining Performance
Mechanism of Action:
Calcium preferentially reacts with sulfur: Ca + FeS → CaS + Fe. CaS has a melting point of 2450℃, is insoluble in molten iron, precipitates as solid particles, and floats to the slag, completely eliminating the harmful effects of sulfur.
Key Value:
Prevents FeS (melting point 1190℃) from forming a continuous network at grain boundaries, eliminating the "hot brittleness" phenomenon.
Key Usage Control Points:
Timing of Addition: Add to ductile iron after spheroidizing treatment and before inoculation; add to gray cast iron 5-10 minutes before tapping to ensure sufficient reaction.
Addition Method: Add CaSi Lump products directly; add SiCa Powder products through an inoculator; add CaSi cored wire products using a wire feeder (speed 3-5 m/s) to avoid calcium volatilization loss.
Dosage Control: Excessive addition (>0.5%) will lead to excessively high cast iron hardness (HB>250), increasing processing difficulty. Precise control is required according to the type of cast iron.
