Types of Cast Iron Part-1
Types of Cast Iron:
Following are the common types of Cast Iron used in
engineering materials.
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.
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 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.
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