3. INTRODUCTION
Metals and their alloys are widely used in
industry
The steel is an alloy of iron and carbon
(c=2% max)
It is the most imp. Engineering metal and its
properties can be improved by heat treatment
The part of iron-corbon diagram described
represents the portion between pure iron and
iron-carbide 6.67% of corbon by weight.
7. S.NO. PHASE CRYSTAL
STRUCTURE
Relative
Hardness
1 Ferrite- Solid solution of
Corbon in α-iron
BCC Very soft
2 Austenite-solid solution of
Corbon in γ-iron
FCC Soft
3 Cementite- compound of
iron and corbon
Orthoerhombic Very hard
4 Pearlite- layers of ferrite
and cementite
---------- Medium hard
5 Ledubrite- mixture of
austenite and cementite
----------- Hard
8. Critical tempratures
The temperatures at which the phase
change occur during Heating and Cooling
are called Critical temperatures
TEMP. PHASE CHANGE
A0
(210 c)
Cementite changes from ferromagnetic to
paramagnetic
A1
(727 c)
Pearlite transforms to austenite
10. Invarient Reactions
. Invariant reaction is one at which the
degree of freedom is zero (F=0)
Point on which three phases are in
equilibrium is called invariant point.
In “FE-C” phase diagram 3 invariant
reactions takes place
1.Peritectic reaction.
2.Eutectic reaction
3.Eutectoid reaction