Cast iron is a group of iron-carbon alloys with a carbon content greater than 2%. Cast iron is known for its excellent castability, good machinability, and wear resistance. Cast iron is also less brittle and more ductile than cast steel. There are several types of cast iron, each with a unique composition and properties that make them suitable for different types of cast iron.

  1. Grey Cast Iron Grey cast iron is the most common type of cast iron. It is named after the grey color it exhibits when fractured. Grey cast iron contains 2.5% to 4.0% carbon, 1% to 3% silicon, and small amounts of sulfur, manganese, and phosphorus. The carbon in grey cast iron exists in the form of graphite flakes, which gives the material its characteristic grey color. The presence of graphite flakes also makes grey cast iron brittle but provides excellent wear resistance and good machinability. Grey cast iron is commonly used for engine blocks, pipes, and machinery parts.

  2. Ductile Cast Iron Ductile cast iron, also known as nodular cast iron, is a type of cast iron that contains nodules of graphite in its matrix. The graphite nodules provide ductile cast iron with improved strength, toughness, and ductility over grey cast iron. Ductile cast iron contains 3.0% to 4.0% carbon, 1.8% to 2.8% silicon, and small amounts of sulfur, manganese, and phosphorus. The nodules of graphite in ductile cast iron are formed by the addition of magnesium to the molten iron before casting. Ductile cast iron is commonly used for gears, crankshafts, and suspension components.

  3. White Cast Iron White cast iron is a type of cast iron that contains cementite (iron carbide) in its matrix. White cast iron is hard and brittle and exhibits a white color when fractured. White cast iron contains 2.5% to 4.0% carbon, 0.5% to 1.9% silicon, and small amounts of sulfur, manganese, and phosphorus. White cast iron is used in applications where hardness and wear resistance are essential, such as in the production of grinding balls and liners for mills and crushers.

  4. Malleable Cast Iron Malleable cast iron is a type of cast iron that has been annealed or heat-treated to make it more ductile and malleable. Malleable cast iron contains 2.0% to 2.5% carbon, 1.2% to 1.8% silicon, and small amounts of sulfur, manganese, and phosphorus. Malleable cast iron is produced by first casting the material as white cast iron and then annealing it in a furnace at temperatures between 800°C and 900°C for several days. The annealing process transforms the cementite in the white cast iron into graphite, which makes the material more ductile and malleable. Malleable cast iron is commonly used for pipe fittings, agricultural machinery, and construction equipment.

  5. Compacted Graphite Iron Compacted graphite iron is a type of cast iron that has a graphite structure that is intermediate between grey cast iron and ductile cast iron. Compacted graphite iron contains 2.5% to 4.0% carbon, 1.8% to 2.8% silicon, and small amounts of sulfur, manganese, and phosphorus. The graphite in compacted graphite iron is shorter and thicker than the graphite in grey cast iron but less spherical than the graphite in ductile cast iron. This unique graphite structure gives compacted graphite iron improved strength, toughness, and fatigue resistance over grey cast iron.