1. Chapter 11 -
MME-292
Arman Hussain
Lecturer
DGCE, BUET
Metallic Materials Sessional
Lecture 05
Cast Iron
September 7, 2014

2. Chapter 11 - 2
Chapter 11: Applications and
Processing of Metal Alloys
ISSUES TO ADDRESS...
• How are Cast Iron classified and what are their
common applications?
• What are some of the common fabrication techniques
for metals?
• What heat treatment procedures are used to improve the
mechanical properties of Cast Irons?

3. Chapter 11 - 3
Adapted from Fig. 9.24, Callister &
Rethwisch 8e. (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.)
Adapted from Fig.
11.1, Callister &
Rethwisch 8e.
Classification of Metal Alloys
Metal Alloys
Steels
Ferrous Nonferrous
Cast Irons
<1.4wt%C 3-4.5wt%C
Steels
<1.4wt%C
Cast IronsCast Irons
3-4.5wt%C3-4.5wt%C
Fe3C
cementite
1600
1400
1200
1000
800
600
400
0 1 2 3 4 5 6 6.7
L
γ
austenite
γ+L
γ+Fe3C
α
ferrite
α+Fe3C
α+γ
L+Fe3C
δ
(Fe)
Co , wt% C
Eutectic:
Eutectoid:
0.76
4.30
727ºC
1148ºC
T(ºC) microstructure: ferrite/Pearlite
graphite/cementite

4. Chapter 11 - 4
Cast Irons
• Ferrous alloys with > 2.1 wt% C
– more commonly 3 - 4.5 wt% C
• Low melting – relatively easy to cast,
amenable to cast
• Generally brittle→ casting is the most
favorable process of fabrication
• Cementite decomposes to ferrite + graphite
Fe3C  3 Fe (α) + C (graphite)
– generally a slow process

5. Chapter 11 - 5
Fe-C True Equilibrium Diagram
Graphite formation
promoted by
• Si > 1 wt%
• slow cooling
Adapted from Fig. 11.2,
Callister & Rethwisch 8e.
[Fig. 11.2 adapted from
Binary Alloy Phase
Diagrams, 2nd ed.,
Vol. 1, T.B. Massalski (Ed.-
in-Chief), ASM International,
Materials Park, OH, 1990.]
1600
1400
1200
1000
800
600
400
0 1 2 3 4 90
L
γ +L
α + Graphite
Liquid +
Graphite
(Fe) C, wt% C
0.65
740ºC
T(ºC)
γ + Graphite
100
1153ºCγ
Austenite 4.2 wt% C
α + γ

6. Chapter 11 -
Types of Cast Iron
Gray iron
Ductile iron
White iron
Malleable iron (Heat treated white iron)
6

7. Chapter 11 - 7
Gray iron
• C content: 2.5-4.0%
• Si Content 1.0-3.0%
• graphite flakes
• Fracture surface is gray
• weak & brittle in tension
• stronger in compression
• excellent vibrational dampening
• wear resistant
• Least expensive
• Application:
– Base of structure of machines
and heavy equipments
Adapted from Fig.
11.3(a) & (b),
Callister &
Rethwisch 8e.

8. Chapter 11 -
Ductile iron
• Add Mg and/or Ce
• graphite as nodules not
flakes
• Greatly influence
mechanical properties
• Matrix: pearlite or ferrite
depending on heat
treatment
• As-cast piece is pearlite
• stronger but less ductile
8

9. Chapter 11 -
Contd.
• Heat treatment for several hours at about
7000
C will yield a ferrite matrix
• Stronger and much more ductile
• Applications: valves, pump bodies, crank-
shaft, gears etc.
9

10. Chapter 11 -10
White iron
• < 1 wt% Si (low Si)
• Rapid cooling rate
• C remains as cementite instead of
forming graphite
• Fracture surface has a white
apperance
• Only suface layer is chilled, graphite
flake is formed in the interior
• pearlite + cementite
• very hard and brittle thus
unmachinable
Application: hard and wear resisting
surface without much ductility
i.e. rollers in rolling machine, bearings
etc.
Adapted from Fig.
11.3(c) & (d),
Callister &
Rethwisch 8e.

11. Chapter 11 -11

12. Chapter 11 -
Malleable iron
12
• heat treat white iron at 800-900ºC
for prolonged time in neutral atm.
• Decomposition of cementite
• graphite in rosettes surrounded by
ferrite or pearlite matrix
• reasonably strong and ductile
Applications: Connecting rods, transmission
gears, and differential
cases for the automotive industry, and also
flanges, pipe fittings, and valve parts
for railroad, marine, and other heavy-duty
services.

13. Chapter 11 -13

14. Chapter 11 -
Effect of Si
14
•• Si is a graphitizer
• Favors solidification to the
stable iron-graphite system
• C is precipitated at the form of
flake
• Introducing Mg or Ce promote
spheroidal graphite precipitation
instead of flake

15. Chapter 11 -
Effect of S in cast iron
• Commercial gray irons contains: 0.06 to 0.12
% S
• Effect of Si and S on the form of C are
reversed
• S content ↑ → Cementite formation ↑ →
promote white iron formation
• S reacts with Fe and form FeS → low M.P.
compound → increase possibility of cracking
• S↓ es fluidity → increases blow holes
• Mn is used for desulphurization
• MnS emains as dispersed inclusions
15

16. Chapter 11 -
Next Class
Structure properties
relationship
16