ENMAT101A Engineering Materials and Processes
Associate Degree of Applied Engineering
(Renewable Energy Technologies)
Lecture 15 – Cast Iron
http://www.sicoconrod.net
www.highered.tafensw.edu.au
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Cast Iron
Reference Text
Section
Higgins RA & Bolton, 2010. Materials for Engineers and Technicians,
5th ed, Butterworth Heinemann
Ch 15
Additional Readings
Section
EMMAT101A Engineering Materials and Processes
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Cast Iron
Note: This lecture closely follows text (Higgins Ch15)
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Cast Iron
(Higgins 15.1)
READ HIGGINS 15.1
Ordinary cast iron is similar in composition to the crude pig iron
produced by the blast-furnace.
Cast Iron is still important today;
• It is cheap because it is close to the composition of ordinary pig iron.
• Mechanical rigidity and strength under compression are good.
• It machines with ease when a suitable composition is selected.
• Easy to cast because very fluid
• High-duty cast irons: e.g. spheroidal-graphite irons are strong,
whilst malleable irons are tough.
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Cast Iron
(Higgins 15.1)
Cast Iron in the
Iron-Carbon
equilibrium
diagram.
http://www.msm.cam.ac.uk/pha
se-trans/2001/adi/cast.iron.html
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Composition of cast irons (Higgins 15.2)
Ordinary cast irons contain the following elements,
Carbon 3.0-4.0%, (as graphite: grey CI, or iron carbide: white CI)
Silicon 1.0-3.0%, (breaks down Fe3C, prefers grey CI)
Sulphur up to 0.1%, (encourages Fe3C, but embrittlement)
Manganese 0.5-1.0%, (toughens by reversing Sulphur, modify ferrite)
Phosphorus up to 1.0%, (Brittle: keep to minimum, raise fluidity)
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Composition of cast irons (Higgins 15.2)
White cast iron
Higgins
Figure 15.2
The effects of
silicon content
on the structure
of cast iron.
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Composition of cast irons (Higgins 15.2)
White cast iron
University of
Cambridge
http://www.doitpo
ms.ac.uk/miclib/m
icrograph_record.
php?id=797
Source:
http://www.msm.c
am.ac.uk/phasetrans/2001/adi/ca
st.iron.html.
EMMAT101A Engineering Materials and Processes
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Composition of cast irons (Higgins 15.2)
Fine grey iron
Higgins
Figure 15.2
The effects of
silicon content
on the structure
of cast iron.
EMMAT101A Engineering Materials and Processes
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Composition of cast irons (Higgins 15.2)
Coarse grey iron
Higgins
Figure 15.2
The effects of
silicon content
on the structure
of cast iron.
EMMAT101A Engineering Materials and Processes
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Composition of cast irons (Higgins 15.2)
Coarse grey iron
COARSE GREY IRON
The aggregate of graphite
flakes in gray cast iron,
deeply etched, SEM.
Mag. bar is 30 μm
http://www.sciencedirect.com/scien
ce/article/pii/S1044580305000021
EMMAT101A Engineering Materials and Processes
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Composition of cast irons (Higgins 15.2)
Coarse grey iron
COARSE GREY IRON
Flake graphite close to the
edge of mounted round
specimen, OPTICAL.
Mag. bar is 50 μm
http://www.sciencedirect.com/scien
ce/article/pii/S1044580305000021
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The influence of cooling rate on the properties
of a cast iron
(Higgins 15.3)
Adding silicon makes cementite
unstable, decomposing slowly.
If cooled rapidly cementite is
trapped and forms white iron.
If cooled slowly the cementite
can decompose into graphite,
forming grey iron.
More slowly > coarser gray iron.
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The influence of cooling rate on the properties
of a cast iron
(Higgins 15.3)
Deliberate “chilling” of a
portion of the casting to
produce a hard-wearing
surface of white iron. The
rest of the casting cools
more slowly forming the
tougher but softer grey
iron structure.
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'Growth' in cast irons
(Higgins 15.4)
When cast iron is used
above 700°C, cementite
decomposes into graphite
and iron. This swells the
iron, causing warping and
cracks.
To prevent this 'growth' in
cast iron, cementite must
be eliminated by using a
high silicon content, like
5%. (Cementite
decomposes during
solidification)
http://www.cgprimorje.com
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Ordinary cast irons
(Higgins 15.5)
Ordinary cast irons fall into two main groups:
engineering irons and fluid irons.
READ HIGGINS
15.5.1 Engineering irons
Higgins
made-in-china.com
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Iron
Bridge
1779
http://common
s.wikimedia.or
g/wiki/File:Iro
nbridge_6.jpg
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Ordinary cast irons
(Higgins 15.5)
15.5.2 Fluid irons
Fluid irons are for decorative castings with
intricate detail.
High silicon content Si 2.5 to 3.5%
High phosphorus content Pup to 1.5%
Very brittle
Cast Iron Decorative Panel
gumtree.com.au
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Videos:
Ordinary Cast Irons
Cast Iron Revival Keeps US Foundry Cooking (3:46 min)
http://www.youtube.com/watch?v=A5c1-xEFayM
EMMAT101A Engineering Materials and Processes
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High-duty cast irons
(Higgins 15.6)
Graphite flakes in grey cast are sharp, and
so act like fractures (stress raisers).
Strength and the toughness can be
improved by turning the flakes into balls
(spheroidal).
READ HIGGINS
15.6.1 Spheroidal-graphite (SG) cast iron
Also 'nodular iron', or 'ductile iron‘ (USA).
Graphite flakes converted to rounded
globules by adding magnesium Mg (0.1%).
Tensile strength up to 775 MPa.
Ductile Iron
http://www.ipsbelgium.com
Ductile iron is useful in
applications where strength
needs between aluminium
and steel.
EMMAT101A Engineering Materials and Processes
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Images:
15.6.1 Spheroidal-graphite (SG) cast iron
http://pwatlas.mt.umist.ac.uk
Pearlitic
matrix
Graphite
nodules
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High-duty cast irons
(Higgins 15.6)
READ HIGGINS
15.6.2 Compacted-graphite (CG) cast iron
Between ordinary grey iron (flakes) and SG irons.
CG Iron
CGI Engine Block
http://www.precisionenginetech.com
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Malleable cast irons
(Higgins 15.7)
These are irons would ordinarily cast into a white iron (cementite
structure).
But with heat-treatment cementite converted into;
Small spherical particles of carbon (the 'black-heart' process)
Or
Remove the carbon completely from the structure (the 'white-heart'
process)
READ HIGGINS 15.7
15.7.1 Blackheart malleable iron
15.7.2 Whiteheart malleable iron
15.7.3 Pearlitic malleable iron
Cast Iron Brake Disc
ehow.com
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Alloy cast irons
(Higgins 15.8)
Alloying elements improve the mechanical
properties of an iron, by:
• Refining the grain size.
• Stabilising hard carbides.
• Producing cast irons with a martensitic or austenitic structure.
1 Nickel: Graphitising effect on cementite (tends to grey iron). Refines
grains for heavy sections – improving toughness.
2 Chromium: Forms chromium carbide (harder than cementite). Wear
resistance. Less susceptible to cementite 'growth‘.
3 Molybdenum: Increases hardness and toughness of thick sections.
4 Vanadium: Increases strength and hardness. Better heat-resistance by
stabilising carbides so that they do not decompose on heating.
5 Copper: Not much solubility but resists rusting.
EMMAT101A Engineering Materials and Processes
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(Higgins)
EMMAT101A Engineering Materials and Processes
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A note about Meehanite.
Meehanite is a trademark for an engineering process to make many types of
cast iron. When a foundry advertises that it produces "Meehanite Iron" this
means the foundry is licensed by Meehanite Metal Corporation.
The Meehanite is a series of specific processing steps, which, when followed, will
produce, according to Meehanite, cast iron with uniform soundness, consistent
physical properties and dependable performance in service.
It covers most types of cast irons, and is not a specific alloy or material.
Meehanite it really a type of quality accreditation with a name that sounds like a
metallic grain.
http://en.wikipedia.org/wiki/Meehanite
EMMAT101A Engineering Materials and Processes
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Online Resources.
Cast Iron
http://www.msm.cam.ac.uk/phase-trans/2001/adi/cast.iron.html
Cast Iron Revival Keeps US Foundry Cooking (3:46 min)
http://www.youtube.com/watch?v=A5c1-xEFayM
Wikipedia: Cast Iron
EMMAT101A Engineering Materials and Processes
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GLOSSARY
Cast iron
Grey iron
Fine grey iron
White iron
Chills
Growth of CI
Fluid irons
SG iron
CG iron
Malleable CI
Blackheart malleable iron
Whiteheart malleable iron
Pearlitic malleable iron
Alloy cast irons
Carbide stabilizers
Grain refiners
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QUESTIONS
Moodle XML: Some questions in 10105 Steel
1. Define all the glossary terms.
2. Grey vs white cast Irons: Compare strengths and weaknesses of grey and white
cast irons. What is the main factor that determines whether white or grey iron is
formed? What constituents can be added to help ensure (a) white or (b) grey iron
is formed?
3. Describe SG iron with the aid of a sketch and explain why it helps, and how it is
generated. Compare it with grey iron.
4. Explain the difference between coarse and fine grey iron in terms of both the
casting process and the material properties.
5. A large lathe bed needs to be tough and crack resistant but with a hard wear
resistant sliding surface (ways). Investigate casting processes and select a
suitable method. Determine an appropriate cast iron type and describe some
methods of ensuring a hard metal surface along the ways. Explain why cast iron is
still used for machine bases and frames even though this has been the standard
method for more than a century.
6. Identify suitable cast iron for: Large water pipes, firebox grating for wood burning
fire, suspension arm of a truck, diesel engine block, cam shaft, cooking pot.
EMMAT101A Engineering Materials and Processes
TAFE NSW -Technical and Further Education Commission