Cast Iron | Types, Advantages, Disadvantages, Uses, Properties

Cast iron is a ferrous alloy which has more than 2% carbon in it. Though it can have any percentage of carbon between 2% to 6.67%, but practically it is in between 2% to 4% only.

It has got its name due to its excellent casting qualities. It is hard and brittle.

There is a basic difference between cast iron and steel. Steel contains less than 1% carbon and cast iron contains more than 2% carbon.

Other alloying elements which are generally used in it are

• Manganese: Increases resistance to wear and abrasions
• Chromium: Increases hardenability, wear resistance, corrosion and oxidation resistance
• Nickle: Increases tensile strength
• Tungsten: It increases hot hardness and hot strength
• Molybdenum: Increases hardenability
• Vanadium: Increases hardenability and hot hardness
• Silicon: Increases hardenability and electrical resistivity
• Aluminum: Works as deoxidizer in steel
• Titanium: Works as deoxidizer in steel
• Niobium: It reduces hardenability and increases ductility, which results in increased impact strength
• Cobalt: It reduces hardenability and resists softening at elevated temperatures

Types of cast iron

In the above table you can find the composition of different types of cast irons

Following are some important types of it

• Grey
• Ductile
• Compacted graphite
• White
• Malleable
• Abrasion resistant
• Nodular or spheroidal
• Austenitic

Now we will discuss properties of each of them briefly.

1. White cast iron

Carbon is present here in the form of Iron carbide (Fe₃C).

Its properties are

• It has High compressive strength
• It is difficult to machine
• It has Good hardness
• It has Resistance to wear

2. Gray cast iron

Carbon here is mainly in the form of graphite. It is inexpensive.

Its properties are

• It has Good machinability
• It has Good resistance to galling and wear
• It has high compressive strength
• It is brittle

3. Ductile cast iron

Its properties are

• It has High ductility
• It has High strength

4. Malleable cast iron

They are made malleable with the help of annealing. They are used to make parts where forging is expensive like, brake supports, hubs of wagon wheels etc. They are in expensive.

Its properties are

• They have High ductility
• They are tougher than gray cast iron
• They can be twisted or bent without fracture
• They have excellent machining capabilities

5. Nodular or spheroidal cast iron

Here graphite is present in the form of spheres or nodules.

Its properties are

• They have high tensile strength
• They have good elongation properties

Advantages of cast iron

• It has Good casting properties
• It is available in large quantities, hence produced in mass scale. Tools required for casting process are relatively cheap and inexpensive. This results into low cost of its products.
• It can be given any complex shape and size without using costly machining operations
• It has three to five times more compression strength compared to steel
• It has Good machinability (gray cast iron)
• It has excellent anti-vibration (or damping) properties hence it is used to make machine frames
• It has good Sensibility
• It has excellent resistance to wear
• It has constant Mechanical properties between 20 to 350 degree Celsius
• It has very low notch sensitivity
• It has Low stress concentration
• It bears Low cost
• It has Durability
• It has Resistance to deformation

Disadvantages of cast iron

• It is Prone to rusting
• It has poor tensile strength
• Its parts are section sensitive, this is due to slow cooling of thick sections.
• failure of Its parts is sudden and total, it does not exhibit yield point.
• It has poor impact resistance
• Compared to steel it has poor machinability
• It has High weight to strength ratio
• It has High brittleness
• It is Non machinable (white cast iron)

Applications of cast iron

It is used in making following things

• It is used in making pipes, to carry suitable fluids
• It is used in making different machines
• It is used in making automotive parts
• It is used in making pots pans and utensils
• It is used in making anchor for ships.

Image source

Table of composition