With the global steel industry trending towards higher quality and higher performance, the stringent requirements for steel purity and inclusion control have made calcium silicon alloys an indispensable ladle refining material in modern steelmaking processes.

AON METALS' steelmaking-grade silicon calcium alloys are composite alloys produced via the electrosilicon thermal process. They feature precise content of the main elements calcium (Ca) and silicon (Si), with strict control over impurities such as carbon (C), sulfur (S), and phosphorus (P). Integrating strong deoxidation, deep desulfurization, and inclusion modification, it is the standard configuration for producing high-end steel grades such as pipeline steel, automotive steel, bearing steel, and spring steel.

Element	Content Range	Core Functions in Steelmaking
Ca	28%-35%	High-efficiency deoxidation and desulfurization: Strongly affinity for oxygen and sulfur, generating high-melting-point CaO and CaS; Inclusion modification: Transforms brittle Al₂O₃ into liquid calcium aluminate.
Si	55%-65%	Synergistic deoxidation: Forms composite deoxidation products with calcium, facilitating flotation; Alloying: Some silicon is absorbed by the molten steel, increasing strength.
Fe	≤5%	Acting as a carrier, ensuring stable and uniform melting of alloys in molten steel.
C	≤0.5%	Strictly controlled, suitable for low-carbon and ultra-low-carbon steel smelting.
S,P	≤0.03%,≤0.04%	Harmful elements: Strictly controlled to avoid adverse effects on steel.

Calcium silicon

The irreplaceable role of silicon calcium alloys in steelmaking

1. Synergistic and Efficient Deoxidation, Minimizing Oxygen Content

Mechanism: Calcium has an extremely low dissolved oxygen equilibrium concentration (<10ppm) in molten steel at 1600℃, making its deoxidizing capacity far superior to silicon and manganese. In SiCa alloys, calcium rapidly and deeply deoxidizes, generating CaO that combines with SiO₂ to form low-melting-point calcium silicate, which easily polymerizes and floats to the surface for removal.

Empirical Evidence: After final deoxidation and calcium treatment using CaSi alloys, the total oxygen content in molten steel can be stably controlled at ≤20ppm, and for some steel grades, it can reach ≤10ppm, a reduction of more than 40% compared to deoxidation using only aluminum or ferrosilicon.

2. Deep Desulfurization, Adapting to Stringent Standards

Mechanism: Calcium reacts with sulfur to form extremely stable CaS, which is insoluble in molten steel, making it crucial for achieving ultra-low sulfur steel ([S]≤0.001%) smelting.

Data: Feeding a casi wire into the late stage of LF refining can improve desulfurization efficiency by 25-30% compared to traditional lime powder injection, especially suitable for the production of pipeline steel resistant to hydrogen-induced cracking (HIC).

3. Inclusion Modification, Overcoming the "Sprue Clogging" Problem

Mechanism: High-melting-point, clustered Al₂O₃ inclusions (melting point 2050℃) generated by aluminum deoxidation are the root cause of continuous casting nozzle clogging and fatigue cracking in steel. Calcium in the siliconcalcium alloy can reduce Al₂O₃ to generate low-melting-point liquid calcium aluminate (such as 12CaO·7Al₂O₃, melting point ~1455℃).

Effects: The modified inclusions are spherical, small, and uniformly distributed, preventing nozzle clogging during casting and significantly increasing the number of consecutive casting heats. Simultaneously, the transverse impact toughness of the steel is increased by more than 20%, and fatigue life is extended, meeting the stringent requirements of the automotive and aerospace industries.

4. Precise control of the dosage for optimal performance

Insufficient dosage: Incomplete removal of oxygen and sulfur, incomplete Al₂O₃ modification, high risk of nozzle blockage, and increased brittle inclusions in the steel.

Suitable dosage: High purity of molten steel, inclusions are small, spherical, and uniformly distributed, achieving an optimal balance of strength, toughness, and plasticity in the steel.

Excessive dosage: May form excessive CaS or high-calcium aluminates, which can reduce steel performance or lead to excessive calcium content, affecting hot working properties.

calcium silicon Alloy

Impact on steel quality

Purity:

The appropriate amount of addition can effectively remove impurities such as oxygen and sulfur in the molten steel and improve the purity of the steel. Insufficient addition and insufficient removal of impurities will cause more oxides and sulfides to be included in the steel, reducing the quality of the steel. Excessive addition, although the impurities are removed more thoroughly, may introduce new impurities, such as excessive calcium, which may form some harmful calcifications in the steel, affecting the performance of the steel.

Mechanical properties:

An appropriate amount of SiCa alloy can improve the organizational structure of the steel, refine the grains, and improve the mechanical properties of the steel, such as strength, toughness and plasticity. Insufficient addition cannot fully play its role in improving the organizational structure of the steel, and the mechanical properties are not significantly improved. Excessive addition may cause changes in the organization of the steel, resulting in a decrease in the toughness of the steel and problems such as cold brittleness.

Inclusion morphology:

The appropriate amount of inclusions can make the inclusions small, dispersed and spherical, reducing the damage to the steel performance. If the amount of inclusions is not appropriate, the morphology and distribution of the inclusions may not be effectively improved, and the inclusions may even aggregate, reducing the fatigue performance and corrosion resistance of the steel.

Chemical composition:

When the amount of inclusions is appropriate, the silicon and calcium content in the steel can reach the expected range and meet the requirements of the steel grade. Too much or too little addition will cause the silicon and calcium content in the steel to deviate from the target value, affecting the performance of the steel.

Calcium silicon Alloy

FAQ

Q1: Why is aluminum content in silicon calcium alloys important to control?

A1: One of the main purposes of calcium treatment is to modify Al₂O₃ inclusions. If the aluminum content in the calcium silicon alloy itself is too high, it will introduce additional aluminum, increasing the total Al₂O₃ in the steel and burdening subsequent calcium treatment. Therefore, high-quality sica alloys (especially those used in pipeline steel and bearing steel) must have strictly controlled aluminum content (≤2.4%).

Q2: What are the advantages of CaSi alloys compared to ferrosilicon and metallic calcium?

A2:

vs Ferrosilicon: Silicon calcium alloys can modify inclusions and achieve deep desulfurization, which fesi alloy cannot achieve.

vs Calcium metal: Metallic calcium is very reactive, has a low density (easily floats), reacts violently when added to molten steel, has an extremely low yield, and produces a lot of fumes. Calcium in silicon-calcium alloys exists in alloy form, has a moderate density, reacts stably, has a high yield (5-10 times that of pure calcium), and is safe to handle.

Q3: How should silicon calcium alloys be stored? What is the shelf life?

A3: Calcium is a reactive element, therefore storage is crucial:

Sealed: Keep the original packaging (aluminum foil/vacuum bag) intact.

Dry: Store in an indoor warehouse with relative humidity <60%.

First-In, First-Out: It is recommended to use within 6 months.

If the product is found to be clumping, powdering, or heating up, it may have become damp and ineffective; discontinue use.

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