Why gray cast iron is widely used in foundry processes?

Cast iron is an iron alloy with a carbon content greater than 2%. Although cast iron can have a carbon content between 2 and 6.67, the practical limit is usually between 2 and 4%. These are important mainly because of their excellent casting quality. Gray cast iron and ductile iron (also called ductile iron or ductile iron).

When cast iron cools slowly, cementite breaks down into iron and carbon in the form of graphite, called graphitization. Cast iron in which most of the cementite is decomposed due to graphitization is called gray cast iron. Cast iron that has not undergone graphitization, ie. e. All carbon exists in combined form and is called white cast iron. The graphitization process takes time, so when liquid cast iron cools rapidly, white cast iron is produced. The properties of white cast iron are comparable to those of high carbon steel. However, it is very brittle and therefore is not used in structural components. It is useful for parts with abrasive wear. Tensile strength varies from 170 to 345 MPa, typically around 240 MPa. Hardness range is 350 to 500 BHN. Due to its high hardness and poor machinability, grinding is generally used for finishing.

Dissociated carbon is in the form of graphite, which is very soft and does not have any strength. Therefore, it reduces the hardness and improves the machinability of cast iron. The shape of the graphite in cast iron greatly affects its strength. When graphite is in flake form (as in gray cast iron), the graphite destroys the continuity of the iron and greatly weakens the iron. But it also helps absorb vibration energy, so gray cast iron is often used for machine tool beds. Gray cast iron is easy to work and is the cheapest form of cast iron. It is widely used in casting processes due to its low melting temperature, high fluidity and negligible cooling shrinkage.