Calcium silicon alloy (Ca-Si) is a composite iron alloy primarily composed of calcium, silicon, and small amounts of iron. It serves as an efficient deoxidizer, desulfurizer, and inclusion modifier in metallurgy.
It is widely used in the production of:
- High-quality steel
- Low-carbon steel
- Stainless steel
- Special alloys
- Cast iron inoculants
- Ductile iron additives
- Converter steelmaking warming agent
Compared to traditional deoxidizers like aluminum, Ca-Si offers better performance in removing oxygen and sulfur, improving steel cleanliness and mechanical properties such as plasticity, toughness, and fluidity.
1. Historical Development
- First produced in France (around 1907) using the electric silicon thermal method.
- Later adopted the electric carbothermal method in electric furnaces.
- China began producing Ca-Si in Taiyuan (1950s).
2. Physical and Chemical Properties
- Calcium: Atomic weight 40.08, density 1.55 g/cm3, melting point ~839°C, highly reactive.
- Silicon-calcium compounds: CaSi, Ca?Si, and CaSi?, with CaSi? being most stable industrially.
- Industrial Ca-Si typically contains:
- ~77% CaSi?
- 5–15% CaSi
- <20% free Si
- <8% SiC
- Density: ~2.2 g/cm3
- Melting range: 980–1200°C
3. Key Applications
In Steelmaking:
- Deoxidation & Desulfurization: Removes O, S, N, H from molten steel.
- Inclusion Modification: Changes non-metallic inclusion shape and improves floatability.
- Degassing: Helps remove gases during refining.
- Nozzle Protection: Prevents clogging in continuous casting when replacing aluminum.
- Clean Steel Production: Enables ultra-low sulfur and oxygen steels.
In Casting:
- Acts as an inoculant in cast iron, promoting fine or spherical graphite formation.
- Reduces white iron tendency in gray cast iron.
- Enhances cast iron quality through desulfurization and silicon addition.
Other Uses:
- Warming Agent in converter steelmaking.
- Powder or Core Wire Injection in ladle metallurgy for precise control.
Summary
Calcium silicon alloy plays a crucial role in modern metallurgy, especially in producing clean, high-performance steels and cast irons. Its multifunctional use as a deoxidizer, desulfurizer, and inclusion modifier makes it indispensable in advanced steelmaking and foundry industries.