Cast iron is a general term for an alloy of iron, carbon and silicon. In these alloys, the carbon content exceeds the amount retained in the austenite solid solution at the eutectic temperature.
Cast iron can be divided into:
1. Gray cast iron
The carbon content is relatively high (2.7% to 4.0%), the carbon is mainly in the form of flake graphite, and the fracture is gray, referred to as gray iron. Low melting point (1145 ~ 1250 ° C), small shrinkage during solidification, compressive strength and hardness close to carbon steel, good shock absorption. Since the flake graphite exists, the wear resistance is good. Casting performance and cutting processing are better. Its brand number is followed by two sets of numbers under "HT". For example: HT20-40 (the first number indicates the lowest tensile strength and the second number indicates the lowest bending strength). This type of material can be for any centrifugal pumps for water with no solid particles or corrosive liquid.
2. White cast iron
Carbon and silicon content are low, carbon is mainly in the form of cementite, and the fracture is silvery white. When the solidification shrinks, it is easy to produce shrinkage cavities and cracks. High hardness, brittleness, and can not withstand impact loads. Used as a blank for malleable cast iron and as a wear-resistant part.
3. Malleable cast iron
After being annealed from white cast iron, the graphite is distributed in a flocculent shape, referred to as tough iron. It has uniform texture, wear resistance and good plasticity and toughness. Used to make parts that are complex in shape and can withstand strong dynamic loads.
4. Ductile iron
The gray cast iron hot metal is obtained by spheroidizing treatment, and the precipitated graphite is spherical, which is referred to as ductile iron. All or most of the carbon is present in the free state of spheroidal graphite, and the fracture is silvery gray. It has higher strength, better toughness and plasticity than ordinary gray cast iron. Its grade is indicated by two sets of numbers after "QT", for example: QT45-5 (the first set of numbers indicates the lowest tensile strength and the second set of numbers indicates the lowest elongation). This kind of material usually used for mines as the mining pump.
5. Vermicular graphite cast iron
The gray cast iron hot water is obtained by the creeping treatment, and the precipitated graphite is in the form of a worm. The mechanical properties are similar to those of ductile iron, and the casting properties are between gray cast iron and nodular cast iron.
6. Alloy cast iron parts
Ordinary cast iron is obtained by adding an appropriate amount of alloying elements (such as silicon, manganese, phosphorus, nickel, chromium, molybdenum, copper, aluminum, boron, vanadium, tin, etc.). The alloying elements change the matrix structure of the cast iron, and thus have the corresponding properties of heat resistance, wear resistance, corrosion resistance, low temperature resistance or no magnetism.
