3. Phase A physical homogeneous distinct of a material system is
called phase.
Equilibrium State The state at which any phase reaction
initiate and goes to complete.
Phase Diagram The graphical representation of temperature
and composition of an alloy system.
Liquids A liquids is a line above which the substance is stable
in a liquid state.
Introduction
5. The diagram represent three horizontal lines
Peritectic The horizontal line at 1479oC is called Peritectic
line.
Eutectic The horizontal line at 1140oC is called Eutectic.
Eutectoid The horizontal line at 723oC is called Eutectoid.
Horizontal Lines
6. Peritectic reaction is that reaction in which 1 liquid
and 1 solid convert into 1 new solid and make
austenite the maximum solubility of carbon in delta
iron is 0.10% and structure is B.C.C
Liquid + ↔ austenite
Peritectic Reaction
7. Eutectic reaction is that reaction in which 1 liquid
convert into two new solid and make austenite and
cementite This occurs at 1140oC for steel when 4.3%
carbon is contained in the alloy.
liquid ↔ austenite + cementite
Eutectic Reaction
8. Eutectoid reaction is that reaction in which 1 solid
convert into two new solids the temperature is 723oC
austenite ↔ pearlite (mixture of ferrite & cementite)
Eutectoid Reaction
9. Austenite- (γ) gamma-iron: interstitial solid solution of
carbon (up to 2 wt%) dissolved in iron with a (F.C.C)
structure. Stable up to 1394 °C.
Austenite
10. Ferrite - (α ) alpha -iron, which is an interstitial solid
solution of a small amount (up to 0.022wt%) of carbon
dissolved in iron with a B.C.C crystal structure.
It is the soft structure on the iron-iron carbide
diagram. Magnetic below 768
°C.
Ferrite
11. Cementite - iron carbide: chemical formula, Fe3C,
contains 6.67 % wt. C.
It is a typical hard and brittle interstitial compound of
low tensile but high compressive strength.
Its crystal structure is orthorhombic.
Metastable phase: at~700 °C slowly (several years)
decomposes to α-iron and carbon.
Cementite
12. Pearlite (α + Fe3C): eutectoid mixture containing 0.76
%wt. C and is formed at 727 °C under slow cooling.
It is very fine plate-like or lamellar mixture of ferrite
(0.022 wt. % C) and cementite (6.7 wt. % C).
The structure of pearlite includes a white matrix
(ferrite background) which includes thin plates of
cementite.
Pearlite
