Types of Cast Iron Part-1

Types of Cast Iron:

Following are the common types of Cast Iron used in engineering materials.

1. Grey Cast Iron:

 Gray Cast Iron

Grey forged iron is produced by melting the foundry iron or grey iron within the cupola furnace. It shows grey color when fractured. The grey color is due to the presence of free graphite.

The composition of Grey Cast Iron is:

i.          Iron – 92 percent.

ii.         Carbon – 3 to 3.5 percent (as graphite).

iii.        Carbon – 0.5 percent (combined).

iv.        Silicon – 1 to 2.75 percent.

v.         Manganese – 1 percent.

vi.        Phosphorus – 0.5 to 1 percent.

vii.       Sulfur – 0.02 to 0.15 percent.

2. White Cast Iron:

 White Cast Iron

It is white in color as there's no free graphite. In white Cast Iron, the entire carbon is in combined state. i.e., in the form of cementite, also known as Iron carbide. White Cast Iron is produced by melting the low phosphorus Pig Iron along with the Steel scraps in a cupola furnace. The Cast Iron thus obtained is in a molten state, and it is chilled, i.e., it is cooled rapidly. Therefore, it is also known as chilled Cast Iron. Due to rapid cooling, its outer surface becomes harder while its interior remains softer.

It has a shiny white color and a bright metallic white luster. It is very strong, hard, and immune to Wear and Tear. And quite brittle as well.

Its composition is as follows:

i.          Iron – 94 percent.

ii.         Carbon – 1.75 to 2.3 percent.

iii.        Silicon – 0.85 to 1.2 percent.

iv.        Manganese – 0.1 to 0.4 percent.

v.         Phosphorous – 0.05 to 0.2 percent.

vi.        Sulfur – 0.12 to 0.35 percent.

3. Malleable Cast Iron:

 Malleable Cast Iron

Malleable Cast Iron is the annealed White Cast Iron, i.e., white Cast Iron is heated slowly up to 900 to 950°C temperature for several days and then cooled at a slower rate. The Iron obtained is malleable also as ductile. It possesses useful properties of both forged iron and mild Steels. The lastingness of malleable forged iron is above that of grey forged iron and has good machinability.

It is used for hubs of wagon wheels, railway rolling stock, brake supports, parts of agricultural machinery, pipe fittings, door hinges, locks, etc.