Effect of silicon in cast iron

Silicon in cast iron is usually added through ferrosilicon alloy. Ferrosilicon alloy is an ferro alloy containing a certain proportion of silicon, usually composed of an alloy of iron and silicon, which can provide the required silicon element to improve the performance of cast iron.

Common ferro silicon alloys are as follows

Low silicon ferrosilicon

The silicon content is generally between 15%-30%, which is suitable for the production of some low silicon content cast iron.

Medium silicon ferrosilicon

The silicon content is about 30%-50%, which is often used in the production of gray cast iron.

High silicon ferrosilicon

The silicon content is usually between 50%-90%, which is mainly used to produce high silicon cast iron, especially high strength cast iron or heat resistant cast iron.

Silicon aluminum alloy (FeSiAl)

In some cases, especially when producing high temperature resistant cast iron or cast iron with special performance requirements, silicon aluminum alloy may also be used as an additive. Silicon aluminum alloy contains both aluminum and silicon elements. In addition to providing the role of silicon, it can also improve the oxidation resistance and corrosion resistance of cast iron.

Silicon is usually added to cast iron as an alloying element, and has the following main functions:

Improving fluidity:

Silicon can improve the fluidity of cast iron, making it easier to fill the mold during the casting process, reducing the pores and inclusions of the casting, and improving the surface quality of the casting.

Promoting graphitization:

Silicon is one of the most important graphitizing elements in cast iron. It can promote the precipitation of graphite in cast iron, especially in gray cast iron. Graphitization helps the processability and wear resistance of cast iron, and improves its impact resistance and toughness.

Improving the oxidation resistance of cast iron:

Silicon can significantly improve the oxidation resistance of cast iron, especially in high temperature environments, where silicon can form a stable oxide film to protect cast iron from further oxidation.

Affecting the hardness and strength of cast iron:

The silicon content in cast iron can affect its hardness and strength. A higher silicon content makes cast iron harder and more brittle, while an appropriate silicon content helps to enhance the strength and wear resistance of cast iron. For high-silicon cast iron (such as the cast iron matrix in cast aluminum alloys), it has higher heat resistance and wear resistance.

Improve corrosion resistance:

Silicon has a certain effect on the corrosion resistance of cast iron, especially for some special cast irons such as heat-resistant cast iron. The increase in silicon content can improve its resistance to high-temperature oxidation and chemical corrosion.

Influence on the organization and performance of cast iron:

Silicon has a great influence on the microstructure of cast iron. Cast irons with different silicon contents (such as gray cast iron, malleable cast iron, etc.) have significant differences in their organizational structure, which determines their final performance. For example, a higher silicon content often leads to changes in the morphology of graphite, affecting the mechanical properties of cast iron.