The 4 Types of Cast Iron

Cast iron has been a fundamental material in engineering and construction for centuries due to its versatility, cost-effectiveness, and ease of production. There are primarily four different types of cast iron. Each type of cast iron has unique properties that make it suitable for specific applications, ranging from heavy machinery to intricate architectural details.

Different processing techniques can be used to produce the desired type, which include:

• Grey Cast Iron
• White Cast Iron
• Ductile Cast Iron
• Malleable Cast Iron

Cast Iron is an iron-carbon alloy that typically contains greater than 2% carbon. It also includes small amounts of silicon, sulphur, manganese, and phosphorus, which can influence its characteristics and performance. The iron and carbon are mixed in the desired quantities and smelted together before being cast into a mould.

Grey Cast Iron

Grey Cast iron is a type of cast iron that has been processed to produce free graphite (carbon) molecules in the metal. Its microstructure, characterized by the graphite flakes, is responsible for many of its distinctive physical and mechanical attributes.

The size and structure of the graphite can be controlled by moderating the cooling rate of the iron and by adding silicon to stabilize the graphite. When Grey Cast Iron fractures, it occurs along the graphite flakes and has a grey appearance at the fracture site.

Grey Cast Iron is not as ductile as other cast irons; however, it has excellent thermal conductivity and the best damping capacity of all cast irons. It is also hard-wearing, making it a popular material to work with.

The high wear resistance, high thermal conductivity, and excellent damping capacity of Grey Cast Iron make it ideal for industrial and household settings. Common Grey Cast Iron examples include engine blocks, flywheels, manifolds, and cookware.

White Cast Iron

White Cast Iron is named based on the appearance of fractures. By tightly controlling the carbon content, reducing the silicon content, and controlling the cooling rate of iron, it is possible to consume all carbon in the iron in the generation of iron carbide. This ensures there are no free graphite molecules and creates an iron that is hard, brittle, extremely wear-resistant and has a high compressive strength. As there are no free graphite molecules, any fracture site appears white, giving White Cast Iron its name.

Due to its superior wear-resistant properties, White Cast Iron is highly valued in industrial applications that demand durability under abrasive conditions. White Cast Iron examples include pump housings, mill linings and rods, crushers and brake shoes.

Ductile Cast Iron

Ductile Cast Iron is produced by adding a small amount of magnesium, approximately 0.2%, which makes the graphite form spherical inclusions that give a more ductile cast iron. This modification in the microstructure significantly enhances the mechanical properties of the material. Unlike the graphite flakes found in grey cast iron, the spherical graphite inclusions in ductile cast iron prevent stress concentration points, allowing the material to bend or deform under tensile stress rather than fracture. This makes ductile cast iron stronger and more flexible than other types of cast iron.

Ductile cast iron can withstand thermal cycling better than other types of cast iron. This property ensures that ductile cast iron remains stable under fluctuating temperature conditions, making it well-suited for applications requiring long-term performance under thermal stress.

Ductile Cast Iron is predominantly used for its relative ductility and can be found extensively in water and sewerage infrastructure. Its ability to resist deformation under load makes it an ideal material for pipes and fittings in water distribution and waste management systems. The thermal cycling resistance also makes it a popular choice for crankshafts, gears, heavy-duty suspensions and brakes.

Malleable Cast Iron

Malleable Cast Iron is manufactured by heat treating White Cast Iron to break down the iron carbide back into free graphite. This process, known as annealing, involves heating the cast iron to approximately 920°C and then cooling it very slowly. The controlled breakdown of iron carbide into clusters of free graphite, often referred to as temper carbon, transforms the brittle White Cast Iron into a malleable, ductile product with good fracture toughness at low temperatures.

Malleable Cast Iron examples include electrical fittings, mining equipment and machine parts. These components benefit from Malleable Cast Iron’s ability to endure mechanical stress while maintaining shape and functionality.

If you’re looking for high-quality cast iron materials for your project, Metal Supermarkets has you covered. With a wide variety of metals, expert advice, and quick service, we are your one-stop shop for all things metal. Visit your nearest Metal Supermarkets location or shop online to find the perfect solution for your metal needs!