Types Of Cast Iron

Cast irons are popularly classified based on three factors: their carbon and silicon content, alloying with other elements, and melting, casting, and heat treatment processes used to make them.

Let’s explore the Different Types Of Cast Iron in this article.

In the past, cast iron was initially categorized into two types based on its fracture: white cast iron and grey cast iron.

However, as knowledge about cast iron grew and metallurgy advanced, other classifications based on microstructural features emerged. Later, alloy content-based further classification was added. 

Based on the above factors, cast irons are popularly classified as Gray Cast Iron, White Cast Iron, Ductile Cast Iron, Malleable Cast Iron, and Compacted graphite iron.

This article will discuss the metallurgical classification of cast iron types and evaluate them to find the best one! 

Types of Cast Iron

The types of cast iron depend primarily on carbon content and silicon. For instance, increasing the carbon content makes cast iron harder and more brittle, while lower carbon levels result in greater ductility.

Varying carbon content can influence the iron’s hardness and wear resistance. Silicon promotes graphite formation, which enhances cast iron’s ability to dampen vibrations and reduce shrinkage during cooling. 

To modify its properties, cast iron can be modified by adding alloying elements like nickel, chromium, molybdenum, and copper.

For instance, nickel and chromium enhance corrosion resistance and high-temperature strength, while molybdenum improves wear resistance. Copper is added for improved machinability.

How iron is melted, and cast affects its microstructure and mechanical properties. Heat treatment processes, such as annealing, quenching, and tempering, can further change the cast iron’s hardness, strength, and toughness. 

Overall, there are 5 major types of cast iron categories 

Grey Cast Iron

Grey cast iron is known for its dark grey fracture colour due to its unique graphitic microstructure.

This iron contains graphite flakes because of silicon, which helps stabilize carbon in the form of graphite rather than iron carbide.

Grey cast iron is commonly used in various applications where its properties like stiffness, machinability, vibration dampening, heat capacity, and thermal conductivity are advantageous.

Key Features of Gray Cast Iron

• Grey cast iron typically contains 2.5% to 4.0% carbon and 1.0% to 3.0% silicon.
• It has a grey fracture surface with ferrite and dispersed graphite flakes.
• Known for high compressive strength, fatigue resistance, wear resistance, and good machinability.
• It is commonly classified according to its tensile strength. 

Major Applications of Gray Cast Iron

• Internal combustion engine cylinder blocks
• Flywheels
• Gearbox cases
• Manifolds
• Disk brake rotors
• Cookware
• It is also used in vibration damping and moderate thermal shock applications.

White Cast Iron

White cast iron is another type with a white fracture colour, primarily due to iron carbide or cementite (Fe3C).

This differs from grey cast iron due to its lower silicon content, which prevents the formation of graphite during solidification, resulting in massive carbides.

White cast iron is known for its extreme hardness but is also brittle.

Key Features of White Cast Iron

• White cast iron typically contains 1.8% to 3.6% carbon, 0.5% to 1.9% silicon, and 1.0% to 2.0% manganese.
• It has a white, crystalline fracture surface with iron carbide plates.
• High compressive strength and excellent resistance to wear and abrasion.

Major Applications of White Cast Iron

White cast iron is used in parts that require extreme wear resistance, such as shell liners, slurry pumps, ball mills, and abrasion-resistant components like crushers and pump impellers.

Ductile Cast Iron or Nodular Iron

Ductile cast iron, also known as nodular cast iron or spheroidal graphite cast iron, is characterized by spherical nodules of graphite.

Unlike white cast iron, ductile cast iron is not formed through heat treatment but has a specific chemical composition that encourages the formation of spherical graphite inclusions. 

Key Features of Ductile Cast Iron or Nodular Iron

• Ductile cast iron typically contains 3.2% to 3.6% carbon, 2.2% to 2.8% silicon, and 0.1% to 0.2% manganese.
• Contains spheroid nodular graphite particles in a ferrite or pearlite matrix.
• Combines high strength with ductility, good load strength, wear resistance, shock resistance, and a high modulus of elasticity.

Major Applications of Ductile Cast Iron or Nodular Iron

Ductile cast iron is used in various applications, from automotive parts to infrastructure components, due to its unique combination of strength and ductility.

Malleable Cast Iron

Malleable cast iron is formed through a slow annealing heat treatment of white cast iron. This process converts the iron carbide (Fe3C) in white iron to graphite, producing a ferrite or pearlite matrix with spherical or nodular graphite shapes.

Malleable cast iron offers good malleability and ductility and has lower silicon content than other cast irons.

Key Features of Malleable Cast Iron

• Malleable cast iron is similar to white cast iron but with graphite in spherical or nodular shapes.
• It offers good malleability, ductility, and fracture toughness, especially at low temperatures.
• Microstructure consists of ferrite and free graphite particles.

Major Applications Malleable Cast Iron

Malleable cast iron is used in applications such as

• Electrical fittings
• Hand tools
• Pipe fittings
• Brackets
• Farm equipment
• Mining hardware.

Compacted Graphite Iron

Compacted graphite cast iron, also known as vermicular iron, has a unique graphite structure with interconnected eutectic cells.

The graphite in this iron is coarser and more rounded than grey cast iron, and its microstructure is intermediate between grey cast iron and ductile cast iron.

Key Features of Compacted Graphite Iron

• Graphite in compacted graphite cast iron is coarser and more rounded, forming interconnected eutectic cells.
• It offers a unique combination of properties superior to grey and ductile cast irons.
• Produced by controlling the amount of magnesium added during casting.
• Properties include high strength, ductility, wear resistance, shock resistance, and good tensile strength.

Major Applications of Compacted Graphite Iron

Compacted graphite cast iron is commonly used in critical components like disc brake rotors and diesel engine heads, where its unique properties are highly advantageous.

Conclusion: Cast Iron Type

Cast iron is a group of iron-carbon alloys with various types, each with distinct characteristics and uses.

The best type of cast iron will depend upon the application and the desired properties. Factors such as tensile strength, hardness, ductility, and resistance to wear and heat must be considered. 

For instance, while grey cast iron would suit applications requiring high damping capacity, ductile or nodular cast iron would be preferred for parts that must endure heavy loads.

Thus, understanding the specific requirements and desired properties is crucial in making the right choice.

As innovators in the iron casting field, with production capacity for casting up to 3 tones,  Mahadev Precision Cast can be your dependable ally for iron casting requirements.

They serve various sectors, including Machine Tool Casting, Defense, Power Generation, Heavy Engineering, Earth Moving Equipment, and many more.

Their diverse product line includes housing castings, off-highway components, and machine tool castings. 

FAQ | Different Types Of Cast Iron