This document discusses the iron-carbon phase diagram. It begins by outlining the intended learning outcomes, which are to revise phase diagrams, understand the iron-carbon phase diagram, and understand the effect of adding carbon to iron. It then provides background on the different forms of iron (α, γ, δ) and how they change with temperature. The main section describes the iron-carbon phase diagram, noting that steels contain less than 2.06% carbon while cast irons contain between 2.06-6.67% carbon. It shows the different phases on the diagram, including ferrite, austenite, cementite, and liquid.

1. MEC121
Manufacturing
Technology
Iron-Carbon Diagram
Dr. Dalia Nabil

2. 2
Intended Learning Outcomes
• Revise phase diagrams
• Understand the Iron-Carbon phase diagram
• Understand the effect of adding or increasing carbon % to Iron.
2

3. 3
Contents
• Introduction
• Phase Diagram Revision
•Solubility limits
•Binary systems
•Binary Eutectic systems
• Iron-Carbon Phase Diagram

4. 4
Steel making

5. 5
Iron-Carbon Phase Diagram
• Phase diagrams are graphical
representations of the phases present
in an alloy at different conditions of
temperature, pressure, or chemical
composition.
• Development and production of new alloys
based on application requirements.
• Development and control of appropriate
heat treatment

6. 6
Contents
• Introduction
• Phase Diagram Revision
•Solubility limits
•Binary systems
•Binary Eutectic systems
• Iron-Carbon Phase Diagram

7. 7
Solubility Limit
Solutions: solid solutions, single phase
Mixtures: more than one phase
Solubility Limit:
Max concentration for which only a single-phase solution
occurs.
Question: What is the solubility limit at 20°C?
Answer: 65 wt% sugar.
If Co < 65 wt% sugar: syrup
If Co > 65 wt% sugar: syrup + sugar.
65
Sucrose/Water Phase Diagram
Pure
Sugar
Temperature
(°C)
0 20 40 60 80 100
Co =Composition (wt% sugar)
L
(liquid solution
i.e., syrup)
Solubility
Limit L
(liquid)
+
S
(solid
sugar)
20
40
60
80
100
Pure
Water
Adapted from Fig. 9.1,
Callister 7e.

8. 8
Effect of T & Composition (Co)
• Changing T can change # of phases:
Adapted from
Fig. 9.1,
Callister 7e.
D (100°C,90)
2 phases
B (100°C,70)
1 phase
path A to B.
• Changing Co can change # of phases: path B to D.
A (20°C,70)
2 phases
70 80 100
60
40
20
0
Temperature
(°C)
Co =Composition (wt% sugar)
L
(liquid solution
i.e., syrup)
20
100
40
60
80
0
L
(liquid)
+
S
(solid
sugar)
water-
sugar
system

9. 9
Contents
• Introduction
• Phase Diagram Revision
•Solubility limits
•Binary systems
•Binary Eutectic systems
• Iron-Carbon Phase Diagram

10. 10
Phase Diagrams: Binary Systems
• Indicate phases as function of T, Co, and P.
-binary systems: just 2 components.
-independent variables: T and Co (P = 1 atm is almost always used).
• Phase Diagram for Cu-Ni system
Adapted from Fig. 9.3(a), Callister 7e.
(Fig. 9.3(a) is adapted from Phase
Diagrams of Binary Nickel Alloys, P. Nash
(Ed.), ASM International, Materials Park,
OH (1991).
• 2 phases:
L (liquid)
a (FCC solid solution)
• 3 phase fields:
L
L + a
a
wt% Ni
20 40 60 80 100
0
1000
1100
1200
1300
1400
1500
1600
T(°C)
L (liquid)
a
(FCC solid
solution)

11. 11
Phase Diagrams: Binary Systems
11
wt% Ni
20 40 60 80 100
0
1000
1100
1200
1300
1400
1500
1600
T(°C)
L (liquid)
a
(FCC solid
solution)
Cu-Ni
phase
diagram
• Rule 1: If we know T and Co, then we know:
--the # and types of phases present.
• Examples:
A(1100°C, 60):
1 phase: a
B(1250°C, 35):
2 phases: L + a
Adapted from Fig. 9.3(a), Callister 7e.
(Fig. 9.3(a) is adapted from Phase
Diagrams of Binary Nickel Alloys, P. Nash
(Ed.), ASM International, Materials Park,
OH, 1991).
B
(1250°C,35)
A(1100°C,60)

12. 12
Phase Diagrams: Binary Phases
wt% Ni
20
1200
1300
T(°C)
L (liquid)
a
(solid)
30 40 50
Cu-Ni
system
• Rule 2: If we know T and Co, then we know:
--the composition of each phase.
• Examples:
TA
A
35
Co
32
CL
At TA = 1320°C:
Only Liquid (L)
CL = Co ( = 35 wt% Ni)
At TB = 1250°C:
Both a and L
CL = Cliquidus ( = 32 wt% Ni here)
Ca = Csolidus ( = 43 wt% Ni here)
At TD = 1190°C:
Only Solid ( a)
Ca = Co ( = 35 wt% Ni)
Co = 35 wt% Ni
Adapted from Fig. 9.3(b), Callister 7e.
(Fig. 9.3(b) is adapted from Phase Diagrams
of Binary Nickel Alloys, P. Nash (Ed.), ASM
International, Materials Park, OH, 1991.)
B
TB
D
TD
tie line
4
Ca
3

13. 13
Phase Diagrams: Binary Systems
• Rule 3: If we know T and Co, then we know:
--the amount of each phase (given in wt%).
• Examples:
At TA: Only Liquid (L)
WL = 100 wt%, Wa = 0
At TD: Only Solid ( a)
WL = 0, Wa = 100 wt%
Co = 35 wt% Ni
Adapted from Fig. 9.3(b), Callister 7e.
(Fig. 9.3(b) is adapted from Phase Diagrams of
Binary Nickel Alloys, P. Nash (Ed.), ASM
International, Materials Park, OH, 1991.)
wt% Ni
20
1200
1300
T(°C)
L (liquid)
a
(solid)
30 40 50
Cu-Ni
system
TA
A
35
Co
32
CL
B
TB
D
TD
tie line
4
Ca
3
R S
At TB: Both a and L
%
73
32
43
35
43
wt
=
−
−
=
= 27 wt%
WL
= S
R +S
Wa
= R
R +S

14. 14
Phase Diagrams: Binary Systems
wt% Ni
20
1200
1300
30 40 50
110 0
L (liquid)
a
(solid)
T(°C)
A
35
Co
L: 35wt%Ni
Cu-Ni
system
• Phase diagram:
Cu-Ni system.
• System is:
--binary
i.e., 2 components:
Cu and Ni.
--isomorphous
i.e., complete
solubility of one
component in
another; a phase
field extends from
0 to 100 wt% Ni.
Adapted from Fig. 9.4,
Callister 7e.
• Consider
Co = 35 wt%Ni.
46
35
43
32
a: 43 wt% Ni
L: 32 wt% Ni
L: 24 wt% Ni
a: 36 wt% Ni
B
a: 46 wt% Ni
L: 35 wt% Ni
C
D
E
24 36

15. 15
Mechanical Properties: Cu-Ni System
• Effect of solid solution strengthening on:
--Tensile strength (TS) --Ductility (%EL)
--Peak as a function of Co --Min. as a function of Co
Adapted from Fig. 9.6(a), Callister 7e. Adapted from Fig. 9.6(b), Callister 7e.
Tensile
Strength
(MPa)
Composition, wt% Ni
Cu Ni
0 20 40 60 80 100
200
300
400
TS for
pure Ni
TS for pure Cu
Elongation
(%EL)
Composition, wt% Ni
Cu Ni
0 20 40 60 80 100
20
30
40
50
60
%EL for
pure Ni
%EL for pure Cu

16. 16
Contents
• Introduction
• Phase Diagram Revision
•Solubility limits
•Binary systems
•Binary Eutectic systems
• Iron-Carbon Phase Diagram

17. 17
Phase Diagrams: Binary-Eutectic Systems
: Min. melting TE
2 components
has a special composition
with a min. melting T.
Adapted from Fig. 9.7,
Callister 7e.
• Eutectic transition
L(CE) a(CaE) + (CE)
• 3 single phase regions
(L, a, )
• Limited solubility:
a: mostly Cu
: mostly Ag
• TE : No liquid below TE
• CE
composition
Ex.: Cu-Ag system
Cu-Ag
system
L (liquid)
a L + a
L+
a + 
Co , wt% Ag
20 40 60 80 100
0
200
1200
T(°C)
400
600
800
1000
CE
TE 8.0 71.9 91.2
779°C

18. 18
Phase Diagrams: Binary-Eutectic Systems
L+a
L+
a + 
200
T(°C)
18.3
C, wt% Sn
20 60 80 100
0
300
100
L (liquid)
a 183°C
61.9 97.8

• For a 40 wt% Sn-60 wt% Pb alloy at 150°C, find...
--the phases present:
Pb-Sn
system
a + 
--compositions of phases:
CO = 40 wt% Sn
--the relative amount
of each phase:
150
40
Co
11
Ca
99
C
S
R
Ca = 11 wt% Sn
C = 99 wt% Sn
Wa=
C - CO
C - Ca
=
99 - 40
99 - 11
=
59
88
= 67 wt%
S
R+S
=
W =
CO - Ca
C - Ca
=
R
R+S
=
29
88
= 33 wt%
=
40 - 11
99 - 11
Adapted from Fig. 9.8,
Callister 7e.
EX: Pb-Sn Eutectic System (1)

19. 19
EX: Pb-Sn Eutectic System (2)
L+
a + 
200
T(°C)
C, wt% Sn
20 60 80 100
0
300
100
L (liquid)
a 
L+a
183°C
• For a 40 wt% Sn-60 wt% Pb alloy at 200°C, find...
--the phases present: Pb-Sn
system
Adapted from Fig. 9.8,
Callister 7e.
a + L
--compositions of phases:
CO = 40 wt% Sn
--the relative amount
of each phase:
Wa =
CL - CO
CL - Ca
=
46 - 40
46 - 17
=
6
29
= 21 wt%
WL =
CO - Ca
CL - Ca
=
23
29
= 79 wt%
40
Co
46
CL
17
Ca
220
S
R
Ca = 17 wt% Sn
CL = 46 wt% Sn

20. 20
Microstructures in Eutectic Systems
• Co = CE
• Result: Eutectic microstructure (lamellar structure)
--alternating layers (lamellae) of a and  crystals.
Adapted from Fig. 9.13,
Callister 7e.
Adapted from Fig. 9.14, Callister 7e.
160m
Micrograph of Pb-Sn
eutectic
microstructure
Pb-Sn
system
L+
a + 
200
T(°C)
C, wt% Sn
20 60 80 100
0
300
100
L
a 
L+a
183°C
40
TE
18.3
a: 18.3 wt%Sn
97.8
: 97.8 wt% Sn
CE
61.9
L: Co wt% Sn
Microstructures in Eutectic Systems:

21. 21
Lamellar Eutectic Structure
Adapted from Figs. 9.14 & 9.15, Callister
7e.

22. 22
Hypoeutectic & Hypereutectic
L+a
L+
a + 
200
Co, wt% Sn
20 60 80 100
0
300
100
L
a 
TE
40
(Pb-Sn
System)
Adapted from Fig. 9.8,
Callister 7e. (Fig. 9.8
adapted from Binary Phase
Diagrams, 2nd ed., Vol. 3,
T.B. Massalski (Editor-in-
Chief), ASM International,
Materials Park, OH, 1990.)
160 m
eutectic micro-constituent
hypereutectic: (illustration only)






Adapted from Fig. 9.17,
Callister 7e. (Illustration
only)
(Figs. 9.14 and 9.17
from Metals
Handbook, 9th ed.,
Vol. 9,
Metallography and
Microstructures,
American Society for
Metals, Materials
Park, OH, 1985.)
175 m
a
a
a
a
a
a
hypoeutectic: Co = 50 wt% Sn
T(°C)
61.9
eutectic
eutectic: Co =61.9wt% Sn

23. 23
Eutectoid & Peritectic
Adapted from
Fig. 9.21, Callister 7e.
Eutectoid transition   + 
Peritectic transition  + L 
• Eutectoid - solid phase in equation
with two solid phases
S2 S1+S3
• Peritectic - liquid + solid 1 → solid 2
S1 + L S2
• Eutectic - liquid in equilibrium with two solids
L a + 
cool
heat
Cu-Zn Phase diagram

24. 24
Contents
• Introduction
• Phase Diagram Revision
•Solubility limits
•Binary systems
•Binary Eutectic systems
• Iron-Carbon Phase Diagram

25. 25
Steel making
2

26. 26
Iron-Carbon Phase Diagram
• Phase diagrams are graphical
representations of the phases
present in an alloy at different
conditions of temperature,
pressure, or chemical
composition.
• Development of new alloys based
on application requirements.
• Production of these alloys.
• Development and control of
appropriate heat treatment

27. 27
Iron Form
• α-iron → BCC crystal
• exists at The iron at room temperature to 912 ˚C
• body center cubic structure ( BCC)
• ductile but not very strong
• γ-iron → FCC crystal
• exists at temperature range 910°C to 1394°C
• face center cubic structure (FCC)
• soft and ductile
• δ-iron → BCC crystal
• exists at temperature range 1395°C to 1539°C
• body center cubic structure ( BCC)
• magnetic
27

28. 28
Iron-Carbon Diagram
• According to the carbon
percentage iron carbon
alloys can be classified
into steels and cast iron.
• Steels are iron-iron carbide
alloys with carbon content lower
than 2.06%.
• Cast iron forms with higher
carbon content up to 6.67%
carbon.
Cast Iron
Steel

29. 29
Iron-Carbon (Fe-C) Phase Diagram: Phases
Adapted from Fig. 9.24,Callister 7e.
Fe
3
C
(cementite)
1600
1400
1200
1000
800
600
400
0 1 2 3 4 5 6 6.7
L

(austenite)
+L
+Fe3C
a+Fe3C
L+Fe3C

(Fe) Co, wt% C
1148°C
T(°C)
a 727°C = Teutectoid
α-ferrite
• Existing at low temperatures and low
carbon content, α-ferrite is a solid
solution of carbon in BCC Fe.
• This phase is stable at room temperature.
• This phase is magnetic below 768°C.
• It has a maximum carbon content of
0.022 % and it will transform to γ-
austenite at 912°C as shown in the graph.

30. 30
Iron-Carbon (Fe-C) Phase Diagram: Phases
Adapted from Fig. 9.24,Callister 7e.
Fe
3
C
(cementite)
1600
1400
1200
1000
800
600
400
0 1 2 3 4 5 6 6.7
L

(austenite)
+L
+Fe3C
a+Fe3C
L+Fe3C

(Fe) Co, wt% C
1148°C
T(°C)
a 727°C = Teutectoid
γ-austenite
• This phase is a solid solution of
carbon in FCC Fe with a maximum
solubility of 2.14% C.
• On further heating, it converts into
BCC δ-ferrite at 1395°C.
• γ-austenite is unstable at
temperatures below eutectic
temperature (727°C) unless cooled
rapidly.
• This phase is non-magnetic.

31. 31
Iron-Carbon (Fe-C) Phase Diagram: Phases
Adapted from Fig. 9.24,Callister 7e.
Fe
3
C
(cementite)
1600
1400
1200
1000
800
600
400
0 1 2 3 4 5 6 6.7
L

(austenite)
+L
+Fe3C
a+Fe3C
L+Fe3C

(Fe) Co, wt% C
1148°C
T(°C)
a 727°C = Teutectoid
δ-ferrite
• This phase has a similar structure as
that of α-ferrite but exists only at
high temperatures.
• The phase can be spotted at the top
left corner in the graph.
• It has a melting point of 1538°C.

32. 32
Iron-Carbon (Fe-C) Phase Diagram: Phases
Adapted from Fig. 9.24,Callister 7e.
Fe
3
C
(cementite)
1600
1400
1200
1000
800
600
400
0 1 2 3 4 5 6 6.7
L

(austenite)
+L
+Fe3C
a+Fe3C
L+Fe3C

(Fe) Co, wt% C
1148°C
T(°C)
a 727°C = Teutectoid
Fe3C or cementite
• Cementite is a metastable
phase of this alloy with a fixed
composition of Fe3C.
• It decomposes extremely
slowly at room temperature
into iron and carbon (graphite).
• Cementite is hard and brittle
which makes it suitable for
strengthening steels.

33. 33
Iron-Carbon (Fe-C) Phase Diagram: Phases
Adapted from Fig. 9.24,Callister 7e.
Fe
3
C
(cementite)
1600
1400
1200
1000
800
600
400
0 1 2 3 4 5 6 6.7
L

(austenite)
+L
+Fe3C
a+Fe3C
L+Fe3C

(Fe) Co, wt% C
1148°C
T(°C)
a 727°C = Teutectoid
Fe-C liquid solution
• Marked on the diagram as ‘L’,
it can be seen in the upper
region in the diagram.
• As the name suggests, it is a
liquid solution of carbon in
iron.
• As we know that δ-ferrite
melts at 1538°C, it is evident
that the melting temperature
of iron decreases with
increasing carbon content.

34. 34
Iron-Carbon (Fe-C) Phase Diagram: Eutectic and Eutectoid
• 2 important points
-Eutectoid (B):
  a +Fe3C
-Eutectic (A):
L   +Fe3C
Adapted from Fig. 9.24,Callister 7e.
Fe
3
C
(cementite)
1600
1400
1200
1000
800
600
400
0 1 2 3 4 5 6 6.7
L

(austenite)
+L
+Fe3C
a+Fe3C
L+Fe3C

(Fe) Co, wt% C
1148°C
T(°C)
a 727°C = Teutectoid
A
S
R
4.30
Result: Pearlite =
alternating layers of
a and Fe3C phases
120 m
(Adapted from Fig. 9.27, Callister 7e.)
 


R S
0.76
C
eutectoid
B
Fe3C (cementite-hard)
a (ferrite-soft)

35. 35
Iron-Carbon (Fe-C) Phase Diagram: Eutectic and Eutectoid
Adapted from Fig. 9.24,Callister 7e.
Fe
3
C
(cementite)
1600
1400
1200
1000
800
600
400
0 1 2 3 4 5 6 6.7
L

(austenite)
+L
+Fe3C
a+Fe3C
L+Fe3C

(Fe) Co, wt% C
1148°C
T(°C)
a 727°C = Teutectoid
 


R S
0.76
C
eutectoid
B
Fe3C (cementite-hard)
a (ferrite-soft)
Pearlite
•consists of alternate layers of
ferrite and cementite in the
proportion 87:13 by weight.
•Formed from austenite at
eutectoid temperature 727°C
upon slow cooling.
•Mechanically, pearlite has
properties intermediate to soft,
ductile ferrite and hard, brittle
cementite.

36. 36
Iron-Carbon (Fe-C) Phase Diagram: Hypoeutectoid Steel
Adapted from Figs. 9.24 and 9.29,Callister 7e. (Fig.
9.24 adapted from Binary Alloy Phase Diagrams, 2nd
ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM
International, Materials Park, OH, 1990.)
Fe
3
C
(cementite)
1600
1400
1200
1000
800
600
400
0 1 2 3 4 5 6 6.7
L

(austenite)
+L
 +Fe3C
a+Fe3C
L+Fe3C

(Fe) Co, wt% C
1148°C
T(°C)
a
727°C
(Fe-C
System)
C0
0.76
Adapted from Fig. 9.30,Callister 7e.
proeutectoid ferrite
pearlite
100 m
Hypoeutectoid
steel
R S
a
wa =S/(R+S)
wFe3
C
=(1-wa)
wpearlite = w
pearlite
r s
wa =s/(r+s)
w =(1- wa)

 

a
a
a


 
 



37. 37
Iron-Carbon (Fe-C) Phase Diagram: Hypereutectoid Steel
Fe
3
C
(cementite)
1600
1400
1200
1000
800
600
400
0 1 2 3 4 5 6 6.7
L

(austenite)
+L
 +Fe3C
a +Fe3C
L+Fe3C

(Fe) Co, wt%C
1148°C
T(°C)
a
Adapted from Figs. 9.24 and 9.32,Callister 7e. (Fig.
9.24 adapted from Binary Alloy Phase Diagrams, 2nd
ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM
International, Materials Park, OH, 1990.)
(Fe-C
System)
0.76
Co
Adapted from Fig. 9.33,Callister 7e.
proeutectoid Fe3C
60 mHypereutectoid
steel
pearlite
R S
wa =S/(R+S)
wFe3C =(1-wa)
wpearlite = w
pearlite
s
r
wFe3C =r/(r+s)
w =(1-wFe3C)
Fe3C


 


 


 

38. 38
Mechanical Behavior of Fe-C Alloys
• Cementite is harder
phase and more brittle
than ferrite .
• increasing cementite
fraction therefore
makes harder, less
ductile material

39. 39
Alloying Steel with More Elements
• Teutectoid changes: • Ceutectoid changes:
Adapted from Fig. 9.34,Callister 7e. (Fig. 9.34
from Edgar C. Bain, Functions of the Alloying
Elements in Steel, American Society for Metals,
1939, p. 127.)
Adapted from Fig. 9.35,Callister 7e. (Fig. 9.35
from Edgar C. Bain, Functions of the Alloying
Elements in Steel, American Society for Metals,
1939, p. 127.)
T
Eutectoid
(°C)
wt. % of alloying elements
Ti
Ni
Mo
Si
W
Cr
Mn
wt. % of alloying elements
C
eutectoid
(wt%C)
Ni
Ti
Cr
Si
Mn
W
Mo

40. Solved Example

41. 41
41
Solved Example
For a 99.6 wt% Fe-0.40 wt% C at a temperature just below the
eutectoid, determine the following
a) composition of Fe3C and ferrite (a)
b) the amount of carbide (cementite) in grams that forms per 100 g of
steel
c) the amount of pearlite and proeutectoid ferrite (a)

42. 42
Solved Example
Solution:
g
3
.
94
g
5.7
C
Fe
g
7
.
5
100
022
.
0
7
.
6
022
.
0
4
.
0
100
x
C
Fe
C
Fe
3
C
Fe
3
3
3
=
a
=
=
−
−
=
−
−
=
a
+ a
a
x
C
C
C
Co
b) the amount of carbide
(cementite) in grams that
forms per 100 g of steel
a) composition of Fe3C and ferrite (a)
CO = 0.40 wt% C
Ca = 0.022 wt% C
CFe C = 6.70 wt% C
3
Fe
3
C
(cementite)
1600
1400
1200
1000
800
600
400
0 1 2 3 4 5 6 6.7
L

(austenite)
+L
 + Fe3C
a+ Fe3C
L+Fe3C

Co, wt% C
1148°C
T(°C)
727°C
CO
R S
CFe C
3
Ca

43. 43
Solved Example
c. the amount of pearlite and proeutectoid ferrite (a)
note: amount of pearlite = amount of  just above TE
Co = 0.40 wt% C
Ca = 0.022 wt% C
Cpearlite = C = 0.76 wt% C

 + a
=
Co −Ca
C −Ca
x 100 = 51.2 g
pearlite = 51.2 g
proeutectoid a = 48.8 g
Fe
3
C
(cementite)
1600
1400
1200
1000
800
600
400
0 1 2 3 4 5 6 6.7
L

(austenite)
+L
 + Fe3C
a+ Fe3C
L+Fe3C

Co, wt% C
1148°C
T(°C)
727°C
CO
R S
C
Ca

44. Thank you