Classification of Cast Iron
Cast iron can be divided into several different ways:
According to the color of the fracture
1. Grey cast iron：High carbon contentment(2.7%~4.0%), the carbon is mainly exists in the form of flake graphite, and the fracture is gray, that's why it is called gray iron. Grey cast iron has low melting point (1145 ~ 1250 ° C), small shrinkage during solidification, compressive strength and hardness close to carbon steel, good shock absorption. It has certain mechanical properties and good cutting performance. It is widely used in industry to manufacture structural parts such as machine bed, cylinder and box.
2. White cast iron：Low Carbon and silicon contentment, carbon is mainly exists in the form of cementite, and the fracture is silvery white. it is easy to produce shrinkage cavities and cracks when the solidification shrinks.High hardness, brittleness, can not withstand impact loads.
It is frequently used as a blank for malleable cast iron and as a wear-resistant part.
3. Mottled cast iron: it is a kind of cast iron between white cast iron and grey cast iron, with grey and white fracture.
It is rarely used as for the poor performance.
According to chemical components
1. Cast iron also can be divided into grey cast iron, malleable cast iron, ductile cast iron according to chemical components without any alloying elements.
2. Alloy cast iron: It can be achieved by adding an appropriate amount of alloying elements (such as silicon, manganese, phosphorus, nickel, chromium, molybdenum, copper, aluminum, boron, vanadium, tin, etc.) to ordinary cast iron. The alloying elements change the matrix structure of the cast iron to have corresponding properties such as heat resistance, wear resistance, corrosion resistance, low temperature resistance or no magnetism. Usually used in the manufacturing mining parts, chemical machinery and instruments, meters, etc.
According to production methods and texture properties
1. Common grey cast iron. Most of the carbon in this cast iron exists in the form of flake graphite in a free state, and its fracture is dark grey, has certain mechanical properties and good cutting performance, and is generally used in industry.
2. Inoculated cast iron: It is based on grey cast iron and treated with “deterioration treatment”, also called metamorphic cast iron.
Its strength, ductility and toughness are much better than common gray cast iron, and its structure is relatively uniform, mainly used for manufacturing of large castings with high mechanical properties and large variations in section size.
3. Malleable cast iron: It can be obtained by annealing the white cast iron. The graphite is distributed in a flocculent shape, also can be called as tough iron. It has uniform texture, wear resistance and good plasticity and toughness. It is used to make parts that are complex in shape and can withstand strong dynamic loads.
4. Ductile iron: It can be obtained by spheroidizing treatment of molten iron of grey iron , and the precipitated graphite is spherical, so we call it ductile iron for briefly. It has higher strength, better toughness and plasticity than common grey cast iron, mainly used in the manufacturing of internal combustion engines, auto spare parts and agricultural machinery.
5. Special performance cast iron: This is a cast iron with certain characteristics, which can be divided into wear-resistant cast iron, heat-resistant cast iron, and corrosion-resistant cast iron depending on the application. Most of them belong to alloy cast iron and are widely used in machinery manufacturing.
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