Published on 27-May-2021

Cast Iron and Its Types

Cast Iron and Its Types

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.

cast iron

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.

Grey cast 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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