Knowledge

There are four basic types of cast iron:

• Gray cast iron.
• Ductile cast iron.
• Malleable cast iron.
• White cast iron.
• Alloy cast Iron

#1. Gray Cast Iron.

Grey Cast iron refers to a type of cast iron that has been processed to produce free graphite (carbon) molecules in the metal. 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 fractures 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 an 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 the excellent damping capacity of Grey Cast Iron makes it ideal for engine blocks, flywheels, manifolds, and cookware.

Composition:

• Carbon – 2.5 to 4%
• Manganese – 0.4 to 1%
• Sulphur – 0.02 to 0.15%
• Silicon – 1 to 3%
• Phosphorous – 0.15 to 1%
• Remaining is iron

Characteristics:

• Good compressive strength
• Good torsional & shear strengths
• Good corrosion resistance
• Good Wear resistance
• Excellent machinability

#2. 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.

White Cast Iron is used primarily for its wear resistant properties in pump housings, mill linings and rods, crushers, and brake shoes.

Composition:

• Carbon – 1.8 to 3%
• Manganese – 0.25 to 0.8%
• Sulfur – 0.10 to 0.30%
• Silicon – 0.5 to 1.9%
• Phosphorous – 0.05 to 0.2%
• The remaining is iron

Characteristics:

• Hard & Brittle
• High abrasion resistance
• High tensile strength & low compressive strength

#3. 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. It can also withstand thermal cycling better than other cast iron products.

Ductile Cast Iron is predominantly used for its relative ductility and can be found extensively in water and sewerage infrastructure. The thermal cycling resistance also makes it a popular choice for crankshafts, gears, heavy-duty suspensions, and brakes.

Composition:

• Carbon – 3.2 to 4%
• Manganese – 0.2 to 0.5%
• Sulphur – 1.8 to 3%
• Silicon – 1.8 to 3%
• Phosphorous – 0.08% max
• Remaining is iron

Characteristics:

• Good fatigue strength
• Good impact strength
• Hardness & high modulus of elasticity
• Corrosion resistance similar to that of grey iron
• Excellent castability & wear resistance
• Good machinability
• Ability to resist oxidation at high temperatures

 

#4. Malleable Cast Iron.

Malleable Cast Iron is a type of cast iron that is manufactured by heat treating White Cast Iron to break down the iron carbide back into free graphite. This produces a malleable and ductile product that has good fracture toughness at low temperatures.

Malleable Cast Iron is used for electrical fittings, mining equipment and machine parts.

Composition:

• Carbon – 2.0 to 3.0%
• Manganese – 0.2 to 0.6%
• Sulphur – 0.10%
• Silicon – 0.6 to 1.3%
• Phosphorous – 0.15 %
• The remaining is iron.

Characteristics:

• Good ductility & machinability
• High yield strength & tensile strength
• Excellent impact strength
• Not as brittle as grey cast iron
• High Young’s modulus & low coefficient of thermal expansion.
• Good wear resistance & vibration damping capacity
• Excellent machinability

#5. Alloy Cast Iron.

Alloy cast iron is produced by adding some alloying elements in cast iron like nickel, chromium, copper, etc. It has increased properties according to the alloying element. This cast iron is produced to get the desired properties of cast iron.