Ferrosilicon (FeSi) plays an important role in modern steelmaking processes due to its dual functionality, a deoxidizer and an alloying agent. The following are the details of its applications:
1. Deoxidation
Purpose: Removal of dissolved oxygen (O₂) from molten steel to prevent defects such as porosity and inclusions.
Mechanism: Silicon reacts with oxygen to form silica (SiO₂), which floats into the slag:
Si+O2→SiO2 (exothermic reaction).
Advantages over aluminum:
It forms liquid slag, improving the purity of steel.
There is less chance of nozzle clogging during continuous pouring.
Typical dosage: 3-5 kg FeSi per ton of steel (adjustable according to the steel grade).
2. Alloying
Silicon as an alloying element:
Improved properties:
Strength and hardness: Silicon increases tensile strength (e.g., structural steels).
Magnetic permeability: Critical for electrical steels (3-5% Si) used in transformers and motors.
Corrosion resistance: Stainless steels benefit from silicon's oxidation resistance.
Common steel grades:
Silicon steel (e.g. M15): Contains 2.5-4.5% Si for electromagnetic applications.
Spring steel (e.g. 55Si7): 1.5-2.5% Si increases elasticity and fatigue strength.
3. Slag modification
Slag Liquid:
SiO₂ from ferrosilicon reacts with the main components of the slag (e.g., CaO) to form calcium silicates (CaSiO₃), reducing the viscosity of the slag.
Advantage: Efficient removal of impurities (S, P) and non-metallic inclusions.
4. Cost-effective silicon additive
Advantage over pure silicon:
A lower melting point (1200-1400°C versus 1414°C for pure Si) allows for faster dissolution in molten steel.
The iron content acts as a carrier, reducing energy consumption.
5. Grades of ferrosilicon used in steelmaking
Si content Main applications
FeSi75 72-80% High purity deoxidation, alloy steels
FeSi65 65-72% General purpose deoxidation, low-cost FeSi45 steels
40-47% Foundry, basic carbon steels
6. Process integration
Oxygen Furnace (BOF):
It is added during loading to deoxidize and regulate the silicon content.
Electric Arc Furnace (EAF):
It is used in the alloying stages for precise control of the composition.
Ladle metallurgy:
Fine-tuning the silicon level by injecting FeSi powder.
7. Economic and environmental impact
Cost savings:
Reduced reliance on expensive aluminum-based deoxidizers.
Environmental friendliness:
Lower carbon footprint compared to aluminium (FeSi production emits ~8-10 tCO₂/t compared to ~15 tCO₂/t for aluminium).
Summary of key benefits
Function Advantage
Deoxidation Cleaner steel, fewer defects
Alloying Improved mechanical and electromagnetic properties
Slag control Efficient impurity
removal Cost-effective Reduced energy and material costs compared to alternatives
