White cast iron

All the carbon in white cast iron exists in the form of permeable carbon (Fe3C) because the fracture is bright white. Therefore, it is called white cast iron. Due to a large number of hard and brittle Fe3C, white cast iron has high hardness, and brittleness and is difficult to process. Therefore, it is rarely used directly in industrial applications and is only used for a few parts requiring wear resistance without impact, such as wire drawing die, ball mill iron ball, etc. Most of them are used as billets for steel making and malleable cast iron.

Grey cast iron

Most of all of the carbon in cast iron exist as free-state flake graphite. The fracture is gray. It has good casting performance, good machinability, good wear resistance, and wear resistance. In addition, it has simple melting ingredients and low cost. It is widely used to manufacture castings and wear-resistant parts with complex structures.

According to different matrix structures, grey cast iron can be divided into ferrite-based grey cast iron, pearlite ferrite-based grey cast iron, and pearlite-based grey cast iron.

Because of the existence of flake graphite in gray cast iron, graphite is a component with low density, low strength, low hardness, and zero plasticity and toughness. Its existence is like a large number of small notches on the steel matrix, which not only reduces the bearing area but also increases the crack source. Therefore, gray cast iron has low strength and poor toughness, and cannot be processed under pressure. To improve its performance, a few inoculants such as ferrosilicon and calcium silicon are added to the molten iron before pouring to refine the pearlite matrix.

Malleable iron

Malleable iron is a kind of white cast iron with graphitization treatment, which is made of iron-carbon alloy with low carbon and silicon content, and then decomposed into flocculent graphite after long-time high-temperature annealing treatment.

Malleable cast iron can be divided into two types according to the microstructure after heat treatment; One is black core malleable iron and pearlescent malleable iron. The structure of black core malleable cast iron is mainly ferrite (f) basic + flocculent graphite; The microstructure of pearlitic malleable cast iron is mainly pearlitic (P) matrix + flocculent graphite. The other is white core malleable cast iron. The structure of white core malleable cast iron depends on the section size. The small section takes ferrite as the matrix, the large section takes ferrite as the surface area, and pearlite and annealed carbon as the core.

Graphite becomes fine and evenly distributed. Cast iron after this inoculation treatment. It is called inoculated cast iron.

Ductile iron

A certain amount of modularizing agent (commonly used silicon iron, magnesium, etc.) is added before the pouring of molten iron (nodular pig iron) to modularize the graphite in cast iron. The tensile strength, yield strength, plasticity, and impact toughness of nodular cast iron are greatly improved because carbon (graphite) exists in the matrix of cast iron as a sphere to improve its splitting effect on the matrix. With the advantages of wear resistance, shock absorption, good process performance, and low cost, it has widely replaced malleable cast iron and some cast steel and forged steel parts, such as crankshaft, connecting rod, roll, automobile rear axle, etc.

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