Cast irons are alloys containing more than 2% carbon (C) in their structure.  As the name suggests, the most common production method is casting. They are hard and brittle due to their high carbon content.

Cast irons do not show ductile behavior. Compressive strength is high for the same reason. Its melting temperature is low and it is possible to obtain cast iron with different properties by supporting it with alloying elements. For this reason, it is divided into types according to the alloying elements in its structure and casting conditions. These are gray cast iron, white cast iron, malleable cast iron, spheroidal graphite cast iron and compact graphite cast iron.

Gray Cast Iron

Gray cast iron is one of the commonly used cast iron types.  They contain up to 4% carbon in their composition. This carbon content appears as graphite in flakes (layer by layer). They have a hard structure and are brittle. It is very resistant to abrasion due to its hard structure. It is suitable for machining methods for final shaping. Its tensile strength is low, but its compressive strength is high. Gray cast irons are very good vibration dampers. This feature can be up to 25 times higher than steels and other cast types. It has high thermal capacity and heat conduction. Gray cast iron takes its name from the gray color that appears in the graphite layers when broken.

White Cast Iron

White cast iron , unlike gray cast iron, is a type of cast iron that almost does not contain graphite. It has a very hard structure due to the hard iron carbon compounds in its structure. This structure is one of the most important features of white cast iron. Provides high wear resistance and hardness. That's why it has a brittle feature. It is not suitable for machining. This situation prevents the widespread use of white cast iron. It has high compressive strength like other cast irons. It takes its name from the white color that appears when broken, similar to gray cast iron. The reason for the white color is that it does not contain graphite structure.

Tempered Cast Iron

Tempered cast iron , as the name suggests, is a type of cast iron obtained by changing the internal structure of the material with a method similar to tempering. It is obtained by heat treating white cast iron. The iron carbide compounds found in white cast iron are transformed into non-circular star-like graphite structures by heat treatment. Thus, a more ductile material is obtained. Temperable cast iron, which has properties close to low carbon steels, has higher tensile strength and ductility than other cast irons. The disadvantage is the negative effect of heat treatment, which is an extra process, on the product cost.
 

Nodular Graphite Cast Iron

Nodular graphite cast iron contains spherical graphite structures similar to malleable cast iron. But differently, graphite structures are obtained not by heat treatment but by adding alloying element (Mg) during casting. The added magnesium interacts with oxygen and sulfur. It shows higher ductility and toughness compared to cast irons. Graphite structures, unlike malleable cast iron, have a more rounded and spherical structure. It is widely used in the production of automobiles and other machinery equipment. 

Compact Graphite Cast Iron

Compact graphite cast iron is a type of cast iron that combines gray cast iron containing graphite in a layered structure and spherical graphite cast iron. These structures, which exist together, cannot be considered separately. The tensile strength is not as high as spheroidal graphite cast iron. But its thermal conductivity is better. Due to its properties, it is used in different areas.

Source: https://www.makloji.com/2020/10/dokme-demir-cesitleri-nelerin.html