This diagram is key diagram to explain transformation in alloys from pure iron to iron carbide {cementite}. This diagram has been drawn up to 6.67% carbon concentration beyond who is diagram is of little commercial significance.
Few important points and lines of this diagram are as follows:
Point,. A-- 1539℃,(melting point (pure iron)
B--1493℃; 0.5%C
E--1493℃; 01%C
F--1493℃;0 16%C
G--1401℃
M--723℃ ;0.25%C
ABCD represent the liquidus line.
AEFHCJD represent the solidus line.
EFB represent periye tic reaction taking place at constant temperature 1493℃.
Steel contain (0-2)%carbon.
Cast iron content (2-6.67)% carbon.
Hypoeutectoid steel Steel contain (0-0.8)%C .
Hypereutectoid Steel content (0.82-2)% carbon .
Hypoeutectic cast iron contains (2.0-4.3)% carbon.
Eutectic cast iron content 4.3% carbon
Hypoeutectic cast iron contains (4.32 -6.67)% carbon.
Few critical temperature of this diagram
A0(210℃)---Above this temperature paramagnetic property change to feroimagnetic.
A1(723℃)---Eutectic temperature below which austenite is unstable and eutectic mixture of ferrite and cementite {called parlite} forms in case of 0.8% Carbon Steel.
A2(768℃)---Ferromagnetic Alpha iron changes to paramagnetic Alpha iron which exist upto 910℃.
A3(910℃)---From 910℃ to 1401℃ paramagnetic gama iron exists.
A4(1401℃)---At this temperature paramagnetic guma iron transform to Alpha iron which is also paramagnetic and having B.C.C structure.
There are three invariant point taking different reaction:
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