The Differences between Gray Cast Iron, White Cast Iron, Mottled Cast Iron and Ductile Cast Iron

Classification of cast iron

According to the form of carbon, the cast iron covers three categories: gray cast iron, white cast iron and mottled cast iron.

• Gray Cast Iron

Most of the carbon in gray cast iron is in the form of graphite. It is called gray cast iron, because its fracture is gray. Gray cast iron is the most common type, and which features a graphite microstructure consisting of many small fractures.

•  White Cast Iron

While not as common as gray cast iron, white cast iron is another type worth mentioning. The carbon in white cast iron is completely in the form of cementite, and the fracture is bright white. White cast iron is difficult to machine so that it is mainly used as raw material for steelmaking. 

• Mottled Cast Iron

The carbon in mottled cast iron exists in the form of a mixture of graphite and cementite, and the fracture is grayish-white. This cast iron has greater brittleness, so it is rarely used in industry.

According to the graphite form of cast iron, gray cast iron includes ordinary gray cast iron, vermicular cast iron, malleable cast iron and ductile cast iron.

Properties of cast iron 

• Gray cast iron

The structure of gray cast iron is composed of graphite and matrix. In addition, the main factors affecting the structure and performance of gray cast iron are chemical composition and cooling rate.

• Ductile cast iron

In actual engineering, with good casting performance, high tensile strength and high fatigue strength, ductile cast iron can replace steel to manufacture some important parts, such as crankshafts, connecting rods and camshafts.

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