Types of cast iron: Grey cast, ductile cast, malleable cast and more

Cast iron is made from molten pig iron or re-melting pig iron with limestone and carbon. It is typically used to make cookware, machine tool bodies, pipe fittings, etc. It is a cheap metal available in the market and as the name mentions showcases good casting characteristics. It is a versatile metal with a wide range of commercial applications. The applications depend on the types of cast iron being used.

What is cast iron?

Cast iron meaning: Cast iron is an iron alloy containing more than 2% of carbon. The carbon content varies from 1.7% to 2.5%.  It showcases excellent tensile and compressive strength. However, cast iron is brittle and therefore is not used in machinery subject to shock.

Also read: Difference between cast iron and iron

Types of cast iron

There are primarily 4 different types of cast iron based on the different processing techniques used to produce the desired type of casting:

Grey cast iron

This is an ordinary type of commercial cast iron recommended for machine parts. It is identified by its grey color and small fractures on the surface. This is the most common type of cast iron and contains carbon in the form of graphite molecules.

Grey cast iron is made by adding free graphite (carbon) molecules in the metal during the processing phase. The size and structure of the graphite molecules being added is controlled by adjusting the cooling rate of the iron and by adding silicon to stabilise the graphite. When grey cast iron fractures, it fractures along the graphite flakes and has a grey appearance at the fracture site.

Also read: Cast iron vs steel: Properties, weight, price

White cast iron

White cast iron is as common as gray cast iron. It gets its name from the appearance of white fractures on the surface. It is one of the hardest cast iron types and requires cutting tools to shape the metal.

The production process of white cast iron involves controlling the carbon content, restricting the silicon content and controlling the cooling rate of iron. This process ensures that there are no graphite molecules in the iron which makes the iron hard, brittle, extremely wear resistant and gives it high compressive strength.

Ductile cast iron

Ductile cast iron is made by adding small amounts of nodulising elements to the pig iron. Nodulising means forming round shapes by exposing the iron ore to gyratory, rotary, or oscillatory motion without exposing it to pressure.

Usually, magnesium is the nodulising element added to make ductile cast iron. While the pig iron goes through nodulising, the graphite in the iron form nodules or spheres instead of angular flakes. The formation of spherical inclusions eliminates fractures on the surface of the cast iron.

Also read: Iron vs steel: Differences and which is better?

Malleable cast iron

Malleable cast iron is a type of cast iron that is manufactured by exposing white cast iron to annealing heat treatment. This breaks down the iron carbide in the iron back into free graphite leading to malleability of the cast iron. The annealing process allows the carbon in the iron to form spherical particles. Therefore, malleable cat iron can be bent without fractures.

Uses and applications

Cast iron cookware and utensils are the most common use of the alloy. However, depending on the properties of the cast iron, each type of cast iron has specific applications it can perform. Let us have a look at applications of each type of cast iron:

White cast iron uses

• Rollers for crushing grains
• Jaw crusher plates
• Car wheels

Grey cast iron uses

• Pipe and pipe fittings
• Automotive cylinder blocks and heads
• Flywheel

Ductile cast iron uses

• Rolls for rolling mills
• Pipes for water supply and drainage systems
• Hydraulic cylinders

Malleable cast iron uses

• Automotive crankshafts
• Wagon wheels
• Electrical pipes
• Hand tools

Cast iron types have multiple applications across industries. Being a cheap and commercialised metal many manufacturers depend on cast iron for their production requirements.

If you are looking to procure iron and steel products, visit Tata nexarc, a one stop shop for all your steel requirements. We have tie-ups with numerous steel suppliers and manufacturers who can match your steel requirements at affordable prices.

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