What is a cast iron?

Cast iron are ferrous alloys with greater than 2% carbon.

They also contain small amounts of other materials such as silicon, sulphur, manganese, & phosphorous.

In general it consists alloys of carbon & iron.

They are the least expensive of all metals and is found plentiful resource than next to aluminium.

What makes cast iron an important material?

1. It is a cheap metallurgical substance.
2. Good mechanical rigidity and good strength under compression.
3. Easy castablility.
4. Good machinability can be achieved when a suitable composition is selected.

Composition :

• Carbon – 3.0 to 4.0%
• Silicon – 1.0 to 3.0%
• Manganese – 0.5 to 1.0%
• Sulphur – upto 0.1%
• Phosphorus – upto 1.0%

Influence of cooling rate on the properties :

Types :

1. Grey (General purpose)
2. White (Hard & Wear resistant)
3. Malleable (Heat treated for ductility)
4. Spheroidal Graphite (Some ductility)

1. Grey Cast Iron:

It is the least expensive & the most common type of cast iron.

It is an alloy of carbon & silicon with iron.

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 :

1. Good compressive strength
2. Good torsional & shear strengths
3. Good corrosion resistance
4. Good Wear resistance
5. Excellent machinability
6. Outstanding sound and vibration damping capacity.

Applications :

Typical applications include;

Machine tool bodies, engine blocks, engine cylinders, brake drums, cam shafts, pipe & pipe fittings, household & agricultural appliances, etc.

2. White Cast Iron

White Cast iron derives its name from the fact that its fracture surface has white or silvery appearance.

Composition:

• Carbon – 1.8 to 3%
• Manganese – 0.25 to 0.8%
• Sulphur – 0.10 to 0.30%
• Silicon – 0.5 to 1.9%
• Phosphorous – 0.05 to 0.2%
• Remaining is iron.

Characteristics:

1. Hard & Brittle
2. High abrasion resistance
3. High tensile strength & low compressive strength

Applications :

Typical applications include;

Production of malleable, rolls, wear plates, pump linings, balls;

Used for inferior casting & in places where hard coating is required as in outer surface of car wheels.

3. Malleable Cast Iron:

It is a cast iron that has been heat treated so that it has significant ductility & malleability.

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 %
• Remaining is iron.

Characteristics :

1. Good ductility & machinability
2. High yield strength & tensile strength
3. Excellent impact strength
4. Not as brittle as grey cast iron
5. High Young’s modulus & low coefficient of thermal expansion.
6. Good wear resistance & vibration damping capacity
7. Excellent machinability

Applications :

Widely used in automobile industries, typical components include brake-shoes, pedals, levers, wheel-hubs, axle-housings, connecting rods, transmission gears & door hinges.

4. Spheroidal Graphite or Nodular Cast iron

Spheroidal graphite (SG)  is also known as ‘Nodular iron’ or as ‘ductile iron’.

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:

1. Excellent ductility, tensile, & yield strengths than grey & malleable cast iron
2. Good fatigue strength
3. Good impact strength
4. Hardness & high modulus of elasticity
5. Corrosion resistance similar to that of grey iron
6. Excellent castability & wear resistance
7. Good machinability
8. Ability to resist oxidation at high temperatures.

Applications :

Typical applications include;

Valves, pump bodies, crank shafts, gears, pinion, rollers, rocker arms, flanges, pipe fittings, power transmission equipment, earth moving machinery, & other machine components.

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