Ferrosilicon is a binary alloy of iron and silicon, with silicon (Si) and iron (Fe) as its core components. It is produced through high-temperature smelting in a submerged arc furnace.
Raw materials: Quartz sand (SiO₂ ≥ 99%), coke (fixed carbon ≥ 85%), and scrap steel (Fe ≥ 98%). Coke acts as a reducing agent, reducing the silicon in the quartz sand at 1700-2000℃, which then fuses with the iron to form an alloy.
Core characteristics: Melting point 1200-1300℃, density 6.8-7.2 g/cm³. Higher silicon content results in greater hardness and brittleness, and stronger deoxidation and inoculation functions.
Industrial value: Possessing multiple functions including deoxidation, desulfurization, alloying, and inoculation, it is a core representative of "multi-functional, low-cost" raw materials in the metallurgical industry.
Ferrosilicon Grade System
FeSi grades are divided into "silicon content + impurity grade". The composition limits and applicable scenarios of the core grades are clearly defined, and there are a total of 21 grades. The key grades are as follows:
| Grade | Silicon (Si) Content Range | Maximum Content of Major Impurities (Al/Fe/C/S/P) | Core Characteristics | Typical Applications |
| FeSi90Al0.5 | 87.0%-95.0% | 0.5%/ margin / 0.2%/0.05%/0.04% | High purity, low impurities | Raw materials for high-end electronic alloys and semiconductor materials |
| FeSi90Al3.0 | 87.0%-95.0% | 3.0%/ margin / 0.2%/0.05%/0.04% | High silicon, medium impurities | Inoculants for special alloy smelting and precision casting |
| FeSi75Al0.5-A | 72.0%-80.0% | 0.5%/ margin / 0.15%/0.05%/0.04% | High cost-performance ratio, low aluminum | Deoxidizers for high-quality steel and spheroidizing agents for ductile iron |
| FeSi75Al1.0-B | 72.0%-80.0% | 1.0%/ margin / 0.15%/0.05%/0.04% | Versatile, moderate cost | Deoxidizers and alloying supplements for ordinary steel |
| FeSi65Al2.0 | 60.0%-67.0% | 2.0%/ margin / 0.2%/0.05%/0.04% | Medium silicon, suitable for casting | Inoculants for gray cast iron and low alloy steel production |
| FeSi45Al4.0 | 40.0%-47.0% | 4.0%/ margin / 0.3%/0.05%/0.04% | Low silicon, high toughness | Reducing agents for small cast iron parts and magnesium smelting |
Note: The unit of impurity content is mass fraction. C, S, and P are general limits. Some special grades can be customized for impurity requirements (such as low-sulfur FeSi75, S≤0.03%).
Core Application Scenarios and Technical Parameters of Ferrosilicon
(1) Steelmaking Industry: Deoxidation, Alloying and Auxiliary Functions
Ferrosilicon is the "core functional material" of steelmaking, and it is compatible with different smelting equipment such as converters and electric furnaces:
Deoxidation function:
Silicon has a low free energy for reaction with oxygen, and it preferentially combines with oxygen in molten steel to form SiO₂, which is removed with the slag. FeSi75 is a mainstream deoxidizer, added at 0.3%-0.8% of the molten steel mass. It can reduce the oxygen content of the molten steel from 80-100 ppm to 30-50 ppm, reducing porosity and inclusion defects.
Alloying function:
It supplements silicon to improve the strength and hardness of steel. For example, when producing Q355 low-alloy steel, adding 0.5% FeSi75 increases tensile strength by 10%-15%, making it suitable for steel used in construction and machinery.
Heating agent function:
Ferrosilicon powder (100-200 mesh) releases a large amount of heat when burned. Used as a heating agent for ingot caps, it can increase the ingot yield by 10%-15% and reduce shrinkage defects.
(2) Foundry Industry: Inoculants and Spheroidizing Agents
Ferrosilicon is a "performance regulator" in cast iron production, primarily suitable for gray cast iron and ductile iron:
Inoculants:
Ferro Silicon 75 and Ferro Silicon 65 are used as inoculants, added at 0.2%-0.5% of the molten iron mass, promoting graphitization precipitation, refining graphite grains, and increasing the impact toughness of gray cast iron by 20%-30%, suitable for engine blocks and machine tool beds;
Spheroidizing Agents:
High-silicon ferrosilicon (FeSi 75%) combined with magnesium alloys is used as a spheroidizing agent for ductile iron, promoting the spheroidization of graphite, achieving a spheroidization rate of over 90%, increasing the tensile strength of ductile iron from 300MPa to over 450MPa, suitable for automotive wheel hubs and engineering machinery parts.
(3) Alloy Production and Magnesium Smelting
Ferroalloy Reducing Agent:
High-silicon ferrosilicon (FeSi90), due to its low carbon content (≤0.2%), is used as a reducing agent for low-carbon ferrochrome and ferrosilicon-manganese alloys. Its reduction efficiency is 30%-40% higher than coke, avoiding carbon increase in the alloy.
Core Raw Material for Magnesium Smelting:
In the Pidgeon process for magnesium smelting, 75# FeSi is used as a reducing agent to reduce magnesium in CaO·MgO. 1.2-1.3 tons of Ferro Silicon 75% are consumed for every ton of metallic magnesium produced. The reduction temperature is controlled at 1100-1200℃, and the magnesium recovery rate can reach over 85%.
(4) Other Special Applications
Mineral Processing Industry:
FeSi powder (200-300 mesh) is used as a suspended phase in slurry to adjust slurry density (1.2-1.5 g/cm³), improving the separation efficiency of complex ores and increasing concentrate grade by 5%-8%;
Welding Materials:
FeSi65 is used as a coating material for welding electrodes, achieving deoxidation during welding, reducing weld porosity and slag inclusions, and improving weld tensile strength and corrosion resistance, suitable for structural steel and pipeline welding;
Chemical Industry:
High-silicon ferrosilicon (FeSi90) is used to produce organosilicon. Silicon reacts with chloromethane to produce methylchlorosilane, which is further synthesized into silicone rubber, sealants, and other products, suitable for the construction and electronic packaging fields.
Selection Logic and Considerations for Ferrosilicon Grades
(1) Core Selection Principles
Based on "Purity Requirements":
For high-end electronics and special alloys, choose the FeSi90 series (low aluminum, low impurities); for ordinary steelmaking and casting, choose the FeSi75 series (high cost-effectiveness); for small cast iron parts, choose the FeSi45 series (low silicon, high toughness);
Based on "Functional Requirements":
For deoxidation, prioritize Ferro Silicon alloy 75 (moderate silicon content, high reaction efficiency); for inoculation, choose FeSi65 (high impurity tolerance, low cost); for reducing agents, choose FeSi90 (low carbon, strong reducing ability).
(2) Precautions for use
Dosage control:
Excessive addition can easily lead to embrittlement of steel/cast iron (e.g., if the FeSi75 addition exceeds 1.0%, the impact toughness of the steel will decrease by more than 20%);
Storage conditions:
Store in a dry and ventilated environment, avoid moisture oxidation (after oxidation, a SiO₂ film will form on the surface, reducing the reactivity);
Standard compatibility:
Export products must conform to international standards (e.g., FeSi75 corresponds to ASTM A480 Grade 75, EN 15597-1 Type FeSi75).
