use of ferro silicon in steel industry

The mainstream grades of ferrosilicon are FeSi75 (Si 72%-80%, Fe 20%-28%) and FeSi70 (Si 68%-75%, Fe 25%-32%), with impurities of Al≤1.5%, S≤0.05%, and P≤0.04%.

Physical properties: Melting point 1250-1350℃, density 6.9-7.1 g/cm³, appearing as silvery-gray lumps (10-50mm) or granules (1-10mm), exhibiting strong reducing properties at high temperatures.

Core advantages: High deoxidation efficiency, low alloying cost, strong process adaptability, and a ferrosilicon consumption of approximately 3-8 kg per ton of steel, making it the most cost-effective composite functional material in the steelmaking industry.

(1) Core Function 1: High-Efficiency Deoxidation

Ferrosilicon is the preferred deoxidizer in steelmaking. It removes harmful impurities through the reaction of silicon with oxygen in molten steel, ensuring the purity of the steel:

Reaction Mechanism:

Si + 2FeO → SiO₂ + 2Fe (spontaneous reaction in molten steel at 1500-1600℃), the density of the generated SiO₂ is 2.65g/cm³, much lower than that of molten steel (7.8g/cm³), and it easily floats and is removed with the slag;

Quantitative Effect:

Adding 0.3%-0.8% FeSi75 can reduce the oxygen content of molten steel from 80-100ppm to 35-55ppm, with a deoxidation efficiency of 45%-65%;

Comparative Advantages:

Compared with pure silicon, ferrosilicon deoxidation is gentler, avoiding violent boiling of molten steel; when used in conjunction with aluminum deoxidation, it can generate low-melting-point... Al₂O₃・SiO₂ composite inclusions further enhance the deoxidation effect, reducing the total amount of oxide inclusions by 60%-70%;

(2) Core Function Two: Alloying Strengthening

Silicon-iron steel comprehensively improves the mechanical properties of steel through the solid solution strengthening effect of silicon, adapting to the needs of steel of different strength grades:
Strengthening Mechanism: Silicon atoms are incorporated into the ferrite and pearlite lattice, causing lattice distortion, hindering dislocation movement, and refining the grains, thereby improving the strength, hardness and wear resistance of the steel;

 Quantitative Performance Improvement:

Low alloy structural steel (Q355): Adding 0.2%-0.5% FeSi75, controlling the silicon content in the steel to 0.3%-0.6%, the tensile strength increases from 345MPa to 380-400MPa, and the yield strength increases by 10%-15%;
Electrical silicon steel (50W470): Adding 1.0%-1.5% FeSi75%, the silicon content reaches... 3.0%-4.5%, increasing magnetic permeability by 20%-30%, reducing iron loss by 15%-25%, suitable for transformer and motor core manufacturing;

Wear-resistant steel (NM450): Adding 1.5%-2.0% FerroSilicon 75, forming a Fe₃C-SiC composite hard phase with carbon, increasing the steel hardness (HRC) from 25 to 45-50, and improving wear resistance by 40%-60%.

(3) Core Function Three: Process Optimization

Ferrosilicon can improve the fluidity of molten steel, regulate temperature, and refine grain size, ensuring the stability of steelmaking and casting processes:

 Improving the fluidity of molten steel:

Mechanism of action: Silicon reduces the viscosity and surface tension of molten steel, improving filling capacity;

Quantitative effect: Adding 0.3%-0.5% FeSi75 increases the fluidity of molten steel by 15%-20%, and reduces the defect rate of "incomplete filling" and "cold shut" in complex structure castings from 1.2% to 0.3%;

Regulating the temperature of molten steel: The reaction between silicon and oxygen is exothermic. Adding 0.5% FeSi75 can increase the temperature of molten steel by 30-50℃, avoiding solidification defects caused by low temperature;

 Refining grain size:

Mechanism of action: Silicon inhibits austenite grain growth and promotes the formation of fine grain structure;

Quantitative effect: Adding 0.4% FerroSilicon 75% to low alloy steel refines the grain size from 80μm to 40-50μm, and improves impact toughness (-20℃). 20%-30%.

Performance Priority: For high-end steels (electrical silicon steel, wear-resistant steel), select FeSi75 to ensure deoxidation efficiency and alloying effect;
Cost Balance: For ordinary steels and recycled steels, select low-to-medium grades (FeSi70/FeSi65) to control raw material costs;