The document discusses the iron-carbon equilibrium diagram, focusing on the phases of steel and cast iron up to 6.67% carbon, including key structures such as ferrite, austenite, and cementite. It details the properties of iron and its allotropy, as well as the significance of temperature in phase changes and solubility limits of carbon in various iron forms. Furthermore, it outlines important reactions within the diagram and applications for tailoring steel properties and structural comparisons in metallurgy.

1. IRON-CARBON EQUILIBRIUM
DIAGRAM
PRESENTED BY:
ADITI RANA
A2305316090
B.Tech(IT-2X)

3. In their simplest form, steels are alloys of Iron (Fe) and
Carbon (C). The Fe-C phase diagram is a fairly complex one,
but we will only consider the steel and cast iron part of the
diagram, up to 6.67% Carbon.

4. COOLING CURVE FOR PURE IRON

5. IRON ALLOTROPY
 Iron is relatively soft and ductile metal.
 Iron is allotropic metal which means that it exist in more than
one type of lattice structure(BCC/FCC) depending upon
temperature.
 In normal room temperature state iron is BCC in lattice
arrangement where as at 908 deg.C
 it changes to FCC and then 1403 deg.C back to BCC again and
vice versa.
 About 770 deg.C the room temperature magnetic properties of
iron disappear and it becomes non magnetic called curie point..

6. Unit Cells of Various Metals
The unit cell for:-
(a) Austenite
(b) Ferrite
(c) Martensite

7. Various phases that appear on the Iron- Carbon
equilibrium phase diagram are as under:
•Ferrite
•Austenite
•Cementite
DIFFERENT STRUCTURES

8. FERRITE
 Ferrite is known as α solid solution.
 It is an interstitial solid solution of a small amount of carbon
dissolved in α (BCC) iron.
 Stable form of iron below 912 deg.C
 The maximum solubility is 0.025 % C at 723°C and it
dissolves only 0.008 % C at room temperature.
 It is the softest structure that appears on the diagram.

9.  Austenite is an solid solution of Carbon dissolved in
γ (F.C.C.) iron.
 Maximum solubility is 2.0 % C at 1130°C.
 High formability, most of heat treatments begin
with this single phase.
AUSTENITE

10. CEMENTITE
 Cementite or iron carbide, is very hard, brittle
intermetallic compound of iron & carbon, as
Fe3C, contains 6.67 % C.
 It is the hardest structure that appears on the
diagram, exact melting point unknown.

11. THE IRON CARBON DIAGRAM
A map of the temperature at which different phase changes
occur on very slow heating and cooling in relation to Carbon,
is called Iron- Carbon Diagram.
Iron- Carbon diagram shows:-
A. The type of alloys formed under very slow cooling.
B. Proper heat-treatment temperature and
C. How the properties of steels and cast irons can be radically
changed by heat-treatment.

12. It is the graphical representation of the effect of
temperature and composition upon the phase present
in alloy.
An equilibrium diagram is constructed by plotting temp.
along Y axis and % of C along X axis.
This diagram shows range of temp & composition
within which the various phases change are stable and
also the boundaries at which the phase change occurs.

15. Reactions:
• Peritectic L + δ = γ
• Eutectic L = γ + Fe3C
• Eutectoid γ = α + Fe3C
Various Features OF Fe-C Diagram
PHASES PRESENT
IMPORTANT:
Max. solubility of C in ferrite=0.022%
Max. solubility of C in austenite=2.11%

16. THREE PHASE REACTIONS
Peritectic, at 1490 deg.C, with low 0.16 wt% C alloys (almost no
engineering importance).
Eutectic, at 1130 deg.C, with 4.3wt% C, alloys called cast irons.
Eutectoid, at 723 deg.C with eutectoid composition of 0.8wt% C,
two-phase mixture (ferrite & cementite). They are steels.

18. The diagram shows three horizontal lines which indicate
isothermal reactions (on cooling / heating):
 First horizontal line is at 1490°C, and with low 0.16 %C where
PERITECTIC reaction takes place:
Liquid + δ iron <-> austenite
 Second horizontal line is at 1130°C, and with 4.3wt% C where
EUTECTIC reaction takes place:
Liquid <-> austenite + cementite
 Third horizontal line is at 723°C, and 0.8% C where EUTECTOID
reaction takes place:
Austenite <-> ferrite + cementite

19. The Austenite to ferrite / cementite transformation in
relation to Fe-C diagram:
Hypo-eutectoid steels: Steels having less than 0.8% carbon are called hypo-
eutectoid steels (hypo means "less than").
Consider the cooling of a typical hypo-eutectoid alloy along line y-y‘.
At high temperatures the material is entirely austenite.
Upon cooling it enters a region where the stable phases are ferrite and austenite.

20. Cont…
 The low-carbon ferrite nucleates and grows, leaving the remaining
austenite richer in carbon.
Hypo-eutectoid steels- At 723°C, the remaining austenite will
have assumed the eutectoid composition (0.8% carbon), and further
cooling transforms it to pearlite.
 The resulting structure, is a mixture of primary or pro- eutectoid
ferrite (ferrite that forms before the eutectoid reaction) and regions
of pearlite.

21. CAST IRON
Iron-Carbon alloys of 2.11%C or more are cast irons.
Typical composition: 2.0- 4.0%C,0.5-3.0% Si, less than
1.0% Mn and less than 0.2% S.
Si-substitutes partially for C and promotes formation
of graphite as the carbon rich component instead
Fe3C.

22. APPLICATIONS
It is used tailor properties of steel and to heat
treat them.
It is also used for comparison of crystal
structures for metallurgists in case of rupture or
fatigue.

23. THANK YOU