IRON CARBON DIAGRAM
An iron carbon alloy in the molten state is considered as the solution of fe3c in iron . This solution is cooled and solidifies it depends upon the amount of carbon present in alloy will solidifies as solid solution or eutectic . If carbon does not exceed 2% then alloy is sloidifies as solid solution . The solid solution in y - iron known as astenite . and all the solution regardless the amount of carbon ,which may range from nil to saturation point 2% . The solid solution sometimes known as 2% of astenite .If alloy exceed 2% of carbon then is solidifies as eutectic . which freezes at 1143 c and contain 4.3 carbon . The limit of carbon is recognised as the division of cast and steel iron , an iron carbon alloy is less than that of amount is defined as steel and more being as cast iron . The word everything on the left side of AB diagram consists solid solution . and right side eutectic .
The theory of heat treatment is based on the change takes place in the internal structure of the steel at specific temperature . Steel in its formed is composed as pure iron as small percentage of carbon is added . At normal temperature the steel consists as pure iron called as ferite and combined with iron carbide known as Cementite .
The iron carbon diagram equilibrium symbolise that carbon content affect the structure of steel during heat treatment . This term used in diagram is understood , pure iron ferrite and iron carbide . The ferrite and cementite combined in layers and resultant structure is known as pearlite . If heat process is continues beyond critical temperature then pearlite become austenite . The alloys contain 0.83 carbon then true pearlite is dissolved
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