HC Silicon 6515 (Si65C15) is a high-performance ferroalloy tailored for metallurgical applications, defined by its core composition of ~65% silicon (Si) and ~15% carbon (C). As a dual-functional additive, it serves as both an alloying agent and carburizer in steelmaking, while acting as a key raw material for inoculants and spheroidizers in casting. Its unique combination of high silicon and carbon content addresses critical needs like deoxidation, carbon adjustment, and graphite optimization-making it indispensable for high-carbon steel, tool steel, and ductile iron production.

High Carbon Silicon 6515 belongs to the high-carbon silicon alloy family, distinguished by strict control of silicon, carbon, and impurity contents. Unlike standard ferro silicon (low carbon ≤0.1%), its high carbon content enables dual functionality, eliminating the need for separate carburizers in steelmaking.

HC Silicon 6515

Core Chemical Composition

Below is the typical composition of High Carbon Silicon 6515 and related grades:

Grade	Silicon (Si) ≥	Carbon (C) ≤	Aluminum (Al) ≤	Sulfur (S) ≤	Phosphorus (P) ≤	Iron (Fe)	Key Application
Si65C15	65%	15%	3%	0.1%	0.05%	Balance	High-carbon steel, ductile iron casting
Si68C18	68%	18%	3%	0.1%	0.05%	Balance	Tool steel, heavy-duty castings
Si60C10	60%	10%	3%	0.1%	0.05%	Balance	Low-carbon alloy steel, gray iron
Customized	40–68%	12–20%	Negotiable	Negotiable	Negotiable	Balance	Special alloy production

Critical Notes:
Sulfur (S) and phosphorus (P) are strictly limited-S>0.1% causes hot brittleness, while P>0.05% induces cold brittleness in steel .
Aluminum (Al) ≤3% avoids excessive oxide inclusions, ensuring steel/cast iron purity.

Production Process

Raw Material Preparation:

Silicon source: High-purity silica sand (SiO₂ ≥99.5%, Fe₂O₃ ≤0.1%).

Carbon source: Low-ash petroleum coke (fixed carbon ≥85%, ash ≤5%).

Iron source: Scrap iron or iron ore (Fe ≥95%, S/P ≤0.05%).

Proportion: Silica:sand:coke:iron = 6:3:1 (adjusted for target Si/C content).

Electric Furnace Smelting:

Equipment: Submerged arc furnace (power 12.5–30 MVA).

Parameters: Furnace temperature 1800–2000°C, smelting time 8–12 hours, reducing atmosphere (CO-rich) to prevent oxidation.

Reaction: SiO₂ + 2C → Si + 2CO↑ (silicon reduction); carbon dissolves in molten iron-silicon alloy.

Casting & Crushing:

Molten alloy is cast into ingots, cooled, and crushed to specified sizes (0–3 mm to 10–100 mm).

HC Silicon 6515

Why High Carbon Silicon 6515 Outperforms Single-Function Additives

HC Silicon 6515's value lies in the synergy of silicon and carbon, addressing multiple metallurgical needs in one additive-unlike separate ferro silicon (alloying only) and carburizers (carbon adjustment only).

2.1 Deoxidation & Alloying (Steelmaking Core Function)

Silicon's Role:

Silicon reacts with dissolved oxygen in molten steel to form stable SiO₂ (2Si + O₂ → 2SiO₂). SiO₂ combines with CaO (from lime) to form low-melting-point CaSiO₃, which floats to the slag layer-reducing oxide inclusions by 35% .

Alloying Effect:

Silicon enhances steel's strength, hardness, and wear resistance by solid solution strengthening. For example, adding HC Silicon 6515 to Q355 low-alloy steel increases tensile strength by 10–15% .

2.2 Carburization: Precise Carbon Adjustment

Carbon's Role:

With ~15% carbon content, HC Silicon 6515 acts as an efficient carburizer. It dissolves in molten steel to release [C], adjusting carbon content to 0.6–1.2% for high-carbon steel (e.g., 45# carbon steel) or tool steel (e.g., T10 steel).

Advantage Over Traditional Carburizers:

Compared to coke or graphite, HC Silicon 6515's carbon is more evenly distributed, avoiding carbon segregation (a common defect in thick-walled steel components). A Chinese steel mill reported a 20% reduction in carbon segregation after switching to HC Silicon 6515.

2.3 Graphitization Promotion (Casting Application)

Mechanism:

In cast iron production, silicon promotes graphite precipitation and refines graphite morphology (from flake to spherical in ductile iron). Carbon supplements the carbon content required for graphitization, ensuring uniform nodule formation.