Cast iron is an iron-carbon alloy with a carbon content greater than 2.11% (generally 2.5 to 4%). It is a multi-element alloy with iron, carbon and silicon as the main constituent elements and contains more impurities such as manganese, sulfur and phosphorus than carbon steel. Sometimes in order to improve the mechanical properties or physical and chemical properties of cast iron, a certain amount of alloying elements can also be added to obtain alloyed cast iron. What are the classifications of cast iron?

According to the different forms of carbon in cast iron, cast iron can be divided into：

✔️white cast iron

Except for a small amount of carbon that dissolves in ferrite, the rest of the carbon exists in the cast iron in the form of cementite, and its fracture is silvery white, so it is called white cast iron. At present, white cast iron is mainly used as raw material for steelmaking and blank for the production of malleable cast iron. 

✔️grey cast iron

All or most of the carbon exists in the cast iron as flake graphite, and its fracture is dark gray, so it is called gray cast iron. 

✔️hemp cast iron

Part of the carbon exists in the form of graphite, similar to gray cast iron; the other part exists in the form of free cementite, similar to white cast iron. There are black and white pockmarks in the fracture, so it is called pockmarked cast iron. This type of cast iron also has greater hardness and brittleness, so it is rarely used in industry. 

According to the different forms of graphite in cast iron, cast iron can be divided into：

✔️grey cast iron

Graphite in cast iron exists in flake form. 

✔️malleable cast iron

Graphite in cast iron exists in flocculent form. It is obtained by annealing white cast iron with a certain composition at high temperature for a long time. Its mechanical properties (especially toughness and plasticity) are higher than that of gray cast iron, so it is customarily called malleable cast iron. 

✔️ductile iron

Graphite in cast iron exists in spherical form. It is obtained after being spheroidized before molten iron casting. This type of cast iron not only has higher mechanical properties than gray cast iron and malleable cast iron, and the production process is simpler than malleable cast iron, but also can further improve its mechanical properties through heat treatment, so it is widely used in production.

What are the characteristics of cast iron?

The tensile strength, ductility and toughness of cast iron are lower than those of carbon steel. Although the mechanical properties of cast iron are not as good as that of steel, due to the existence of graphite, it gives cast iron many properties that steel cannot match. Such as good wear resistance, high vibration damping, low notch sensitivity and excellent machinability. In addition, the carbon content of cast iron is high, and its composition is close to the eutectic composition, so the melting point of cast iron is low, about 1200 ° C, and the fluidity of molten iron is good. Due to the volume expansion of graphite during crystallization, the transmission shrinkage rate is small, and its casting performance is excellent. For steel, it is usually used to make castings by casting method, so it is called cast iron.

Conclusion

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