Ferrosilicon Alloy

  • FS Metal
  • Jan 10, 2023
  • Blog

Ferrosilicon alloy is an iron alloy product characterized by the presence of abundant Si, and trace elements such as Fe, Mn, Al, C, P, and S. The raw materials for ferrosilicon alloys mainly include quartz stone, charcoal, steel shavings, pig iron, etc. The raw materials are heated in an electric furnace to melt them, and carbon-reducing agents such as charcoal are used to reduce the SiO₂ in the quartz stone and precipitate out the Si, thus producing a chemical reaction with the elements in other raw materials, after cooling, ferrosilicon alloys of different contents are produced.

What Is Ferrosilicon Alloy?

Ferrosilicon alloy is not naturally occurring but is a multifaceted alloy produced by electric furnace smelting, which effectively enhances the overall level of steel-making and casting processes. Currently, the widely used grades of ferrosilicon alloys are mainly 75#, 72#, 65#, 45#, etc., and the particle size is generally in the range of 0mm~10mm, 10mm~50mm, and 50mm~100mm. Usually, the manufacturers will process the produced ferrosilicon alloy into different sizes for the convenience of users according to their requirements.

Ferrosilicon alloys contain a large amount of elemental silicon, which is of high purity and can be used in industries that depend on it for their use. China has become the world's largest producer of ferrosilicon alloys due to its better raw material resources. 74% of the ferrosilicon alloys consumed worldwide are statistically from China, and most of their ferrosilicon alloys are used in steel-making and casting processes.

Ferrosilicon Chemical And Physical Properties

The melting point of ferrosilicon 75 is 1300 to 1330°C and that of ferrosilicon 45 is 1250 to 1360°C. Since the alloy has no melting point, the temperature range that makes ferrosilicon melt is 1250°C to 1360°C. In the process of melting and casting ferrosilicon, as the liquid ferrosilicon cools, the less dense silicon will float up while the denser ferrosilicon will sink, causing the composition of ferrosilicon to deviate, which results in the density of ferrosilicon decreasing as the silicon increases. In order to reduce the deviations of ferrosilicon, it is necessary to reduce the temperature of ferrosilicon during casting and control the thickness of ferrosilicon by casting in layers, thus accelerating the cooling rate of ferrosilicon liquid.

Ferrosilicon Chemical And Physical Properties

According to the experiment, when the silicon content in ferrosilicon is 53.5%~56.5%, there will be ζ phase in ferrosilicon, and it will be transformed from ζ phase to FeSi2 during the process of cooling, and the cooled ferrosilicon will undergo obvious volume change, which will cause cracks inside and cause ferrosilicon pulverization, and affect the quality of ferrosilicon. Impurities in ferrosilicon are dominated by phosphide and arsenide, which gather between the grains. When the moisture in the air penetrates into the cracks within the ferrosilicon and then reacts chemically with the phosphide and arsenide gathered between the grains, toxic PH3 and AsH3 gases are generated, which is the main cause of ferrosilicon pulverization.

What Are The Products Of Ferrosilicon Alloys?

According to different raw materials and production processes, the elemental silicon in ferrosilicon alloys is not the same. To facilitate the differentiation of ferrosilicon alloys with different silicon content, the staff will classify ferrosilicon alloys into grades based on the amount of silicon content. The common ones are ferrosilicon 75, ferrosilicon 72, ferrosilicon 65, ferrosilicon 45 and so on. In order to facilitate the distinction, we provide the following table to facilitate the user distinguish different ferrosilicon alloys products.

Model Chemical Composition (%)
Si Mn Al C P S
FeSi75A 75.0-80.0 ≤0.4 ≤2.0 ≤0.2 ≤0.035 ≤0.02
FeSi75B 73.0-80.0 ≤0.4 ≤2.0 ≤0.2 ≤0.04 ≤0.02
FeSi75C 72.0-75.0 ≤0.5 ≤2.0 ≤0.1 ≤0.04 ≤0.02
FeSi70 72.0   ≤2.0 ≤0.2 ≤0.04 ≤0.02
FeSi65 65.0-72.0 ≤0.6 ≤2.5 —— ≤0.04 ≤0.02

Ferrosilicon Alloys Production Process

The main raw materials for the production of ferrosilicon alloy are quartz stone, carbon, steel scrap, and pig iron. After the qualified quartz stone, carbon-reducing agent, and steel scrap are proportionally dosed by an electronic scale, the weighed furnace charge is poured into the hopper and sent to the furnace roof bin by belt or inclined bridge feeder. Depending on the demand for the furnace charge, the furnace charge can be added directly to the furnace from the material pipe under the bunker or added to the furnace with the charging machine. The material surface of the furnace mouth should keep a certain shape, the electrodes should be surrounded by a wide and flat cone shape, and the height of the cone is 200~300mm. The material surface of the furnace mouth area between three electrodes should be controlled higher, and it is better to be bun-shaped, in order to adapt to the characteristics of concentrated heat and fast materialization in this area.

During the smelting process, the raw material should be added in batches using the method of small amounts and many times, and the operation of pouring the furnace on the raw material, so as to ensure a good permeability in the furnace. When the raw material is melted in the furnace and accumulated to a certain capacity, it should be ready, before which the iron ladle should be checked. Discharge when the iron is discharged, the impurities at the outlet should be dealt with in time to prevent the outlet from being blocked, and at the same time, the flow rate and time of the iron should be controlled. Clean the water outlet in time after the iron is released and pour immediately to prevent cooling. Ferrosilicon condensation stage, silicon is first for crystallization, because of its small density floating, the density of ferrosilicon will sink, after solidification, the upper layer of ferrosilicon silicon content is higher, and the lower layer of silicon content is lower, thus causing partial dialysis. In order to solve the problem of segregation, the temperature of iron pouring can be lowered and the thickness of the ferrosilicon can be reduced to speed up the cooling speed of the ferrosilicon. Finally, when the ferrosilicon is cooled and formed, use a crane to lift it It is lifted out of the mold and processed into different sizes of lump, grain, or powder using crushing equipment and packed into storage.

Why Ferrosilicon Alloys Used?

Many industries prefer to use ferrosilicon alloys as furnace additives, why is that? According to statistics, the use of ferrosilicon alloys in steelmaking and casting accounts for 83% of the total use, which means that ferrosilicon alloys are widely used in steelmaking and casting. Since steelmaking requires a high-temperature environment. Therefore, the first stage will be filled with oxygen in the furnace, so as to effectively raise the furnace temperature, and too much oxygen in the later stages will cause a large number of oxides, these oxides will affect the quality of steel, in the later stages will use deoxidizer to deoxidize the operation of the molten steel, and the price of deoxidizer is more expensive, thus caused a significant increase in steel production costs. The emergence of ferrosilicon alloy has improved the cost of steelmaking, using its internal silicon element, can effectively reduce the oxygen content of the molten steel, which is mainly the use of silicon and oxygen to produce a chemical reaction that is easy to produce the characteristics of silicon dioxide. Moreover, ferrosilicon alloy also has the advantage of improving the form of inclusions in the molten steel, so that impurities float on the surface of the steel, easy to clean. Price, ferrosilicon alloy compared to the traditional deoxidizer price is relatively low, effectively reducing the production costs of steel mills, and deoxidation efficiency effectively improve, as silicon and oxygen The chemical reaction between silicon and oxygen is more stable, so it provides a guarantee for the safety of the operator.

In casting, ferrosilicon alloys are widely used in the production of gray cast iron and ductile iron because the silicon in ferrosilicon alloys can effectively promote the inoculation effect. In the production of ductile iron, it is necessary to use inoculants to increase the number of eutectic spheres, thus improving the mechanical properties and quality of cast iron. The use of ferrosilicon alloy can effectively promote the number of eutectic pellets, significantly reduce the amount of inoculant, and also improve the fluidity of the molten iron, significantly reducing the blockage of the water outlet. The use of ferrosilicon alloy in ductile iron can effectively improve the distribution pattern of graphite from A-B and improve. The cutting performance of the ductile subjects. In general, the ferrosilicon alloy used for casting has low sulfur and low nitrogen characteristics, which is different from the steel-making process, which can significantly reduce the honeycomb holes and white mouth tendency that occur in castings.

Ferrosilicon Alloys Advantages

  1. Improves steel fluids purity.

  2. Effectively reduces oxygen in the steel making.

  3. Reduces oxide generation.

  4. Improves steel fluids flow properties.

  5. Has a thermal insulation effect.

  6. Reduces impurities in the steel fluids.

  7. Improves the toughness and cutting properties of steel fluids.

Ferrosilicon Alloy Development Trend

With the continuous development of ferrosilicon alloy production and processing process, ferrosilicon alloy is widely used in all walks of life, in addition to steel making and casting and other metallurgical industries, ferrosilicon alloy is also widely used in semiconductor, mineral processing, welding electrodes, and other industries, in the mineral processing industry, ferrosilicon is ground into powder and In the mineral processing industry, ferrosilicon is ground into powder and made into ferrosilicon alloy powder containing magnetic properties through atomization and other processes, and flotation is used to effectively differentiate the minerals, which can effectively reduce the cost of mineral processing due to the recycling properties of ferrosilicon powder. Some ferrosilicon alloys are also used to produce welding rods, which can effectively promote the fusion of electric The fusion of welding joints enhances the process. In a comprehensive view, in the future, ferrosilicon alloy will also be developed in various industries and become a more promising ferroalloy product.