The document discusses iron-carbon systems and the iron-carbon phase diagram. It describes the different allotropic forms of iron (α, γ, δ) and how carbon influences the phase transformation temperatures. The cooling curve for pure iron is shown and the three key areas of the Fe-C phase diagram are outlined: (1) the delta region involving the peritectic reaction, (2) the eutectic region where austenite transforms to cementite and liquid, and (3) the eutectoid region where austenite transforms to ferrite and cementite. Common microstructures like pearlite and ledeburite are also defined.

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CHAPTER 04
IRON CARBON SYSTEMS
MATERIAL SCIENCE & METALLURGY

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Steels and cast irons are among the most extensively used range of
engineering materials in the world today.
IRON CARBON SYSTEMS

3. Allotropic forms of pure iron
• Iron is an allotropic metal i.e. it can exist in more
than one type of the lattice structure depending
upon temperature.
• A study of cooling curve of pure iron shows that it
can exist in more than one allotropic form.
• Example: allotropic forms of Fe are α, γ , δ.
• The temperature at which the allotropic changes
take place in iron is influenced by alloying
elements, the most important of which is carbon

4. Cooling curve for pure iron
1538
1340
910
768
Liquid
δ Fe (BCC)
γ Fe (FCC)
Non-Magnetic
α Fe (BCC)
Non-Magnetic
α Fe (BCC)
Magnetic
Time
Temperature,
o
C
Fig 5.1 Cooling curve for pure iron
Non-Magnetic

5. •All the allotropic changes give off heat
(exothermic) when iron is cooled and absorb heat
(endothermic) when iron is heated.

6. THE IRON–IRON CARBIDE (Fe–Fe3
C) PHASE DIAGRAM

7. Iron – Iron carbide phase diagram

8. Fe-C binary system

9. The first horizontal line MB at 1495o
C indicates the Peritectic reaction. This region is called as
the delta region because of the solid solution δ. The point P is known as the peritectic point at
1495o
C & 0.18%C.
The Delta Region

11. (b) The Eutectic Region
C
D
E
4.33C
2%C
L
L + γ
L + Fe3
C
γ +Fe3
C
γ 1148o
C

12. Fe-C binary
system:
Eutectic Zone

13. (c) The Eutectoid Reaction
912o
C
724o
C
γ
α
γ+α
γ+Fe3
C
α+Fe3
C
0.8% C
H
J
K
C
The Eutectoid Region

20. Fe-C binary system: Eutectoid Zone

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28. Definition of structures
Leduburite:-
❖ It is the eutectic mixture of austenite and
cementite.
❖ It contains 4.3 % C and formed at 11300
C
❖ It has got layered structure.
❖ It is brittle cannot be forged or rolled.
❖ It is found in cast iron region.
❖ It posses good lubricating property.

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30. Lever Rule

31. Lever Rule

32. Lever Rule
Pearlite

33. Different microstructures