What is cast iron?
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.
There is a basic difference between cast iron and steel. Steel contains less than 1% carbon and cast iron contains more than 2% carbon.
Cast iron has got its name due to its excellent casting qualities.
Other alloying elements which are generally used in cast iron 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
There are four basic types of cast iron (not taking Compacted Graphite, since its composition is almost same as Gray cast iron).
In the above table you can find the composition of different types of cast iron.
Now we will discuss properties of each of them briefly.
White cast iron
Properties of white cast iron are
- It has High compressive strength
- It has Good hardness
- It has Resistance to wear
Gray cast iron
Properties of gray cast iron
- It has Good machinability
- It has Good resistance to galling and wear
Ductile cast iron
Properties of ductile cast iron
- It has High ductility
- It has High strength
Malleable cast iron
Properties of malleable cast iron
- It has High ductility
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 is 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.