AF_FM01_ Fabricació Mecànica. Ferrous Materials.
Unit 1 Ferrous materials: Iron, Steel and Cast Iron.
Contents.
1.1 Definitions.
1.2 Allotropes of Iron.
1.3 Cast Irons.
1.4 Questions
1.1 Definitions.
First of all, it's important to take a look at the definitions of the next words: iron, alloy, ferrous
materials, steel, cast iron and allotropy.
IRON /ˈaɪ.ərn/: Iron is a chemical element with the symbol Fe (from Latin: ferrum) and atomic
number 26. It is a metal in the first transition series, its relative atomic mass is equal to 55.8 . It
is by mass the most common element on Earth, forming much of Earth's outer and inner core. It
is the fourth most common element in the Earth's crust. 1 (Oxygen, Silicon, Aluminium and Iron).
Due to its abundance and good mechanical properties it has been widely used for structural purposes.
ALLOY /ˈælɔɪ/; /əˈlɔɪ/:
An alloy is an homogeneus mixture of two or more chemical elements
where at least one of them is a metal.
FERROUS MATERIALS /ˈfɛrəs məˈtɪərɪəlz/: Ferrous materials are alloys composed of iron
as a main component. Steel and Cast iron are examples of ferrous materials.
STEEL /stiːl/:
Steel is an alloy made out of at least two components: iron and carbon, often it
contains also small quantities of other elements. An Iron-Carbon alloy is called steel if the
weight of carbon in the alloy is less than 2% (wt% < 2%C).
CAST IRON /ˈkɑːst ˈaɪ.ərn/: Cast iron is an alloy made out of at least two components: iron
and carbon, often it contains also small quantities of other elements. An Iron-Carbon alloy is
called cast iron if the weight of carbon in the alloy is more than 2% (wt% > 2%C).
Take a look at the presentation below. It's very interesting but specially the page 3 where you
will find a classification of Ferrous materials.
Presentation Ferrous metals
ALLOTROPY : Allotropy2 is the property of some chemical elements to exist in two or more
different forms, known as allotropes of these elements. Allotropes are different structural
modifications of an element; the atoms of the element are bonded together in a different
manner. For example, the allotropes of carbon include diamond (where the carbon atoms are
bonded together in a tetrahedral lattice arrangement), graphite (where the carbon atoms are
bonded together in sheets of a hexagonal lattice), graphene (single sheets of graphite), and
fullerenes (where the carbon atoms are bonded together in spherical, tubular, or ellipsoidal
formations). The term allotropy is used for elements only, not for compounds. Allotropy refers
only to different forms of an element within the same phase (i.e. Different solid, liquid or gas
forms); these different states are not, themselves, considered to be examples of allotropy.
1
2
http://en.wikipedia.org/wiki/Iron (2014-05-13)
http://en.wikipedia.org/wiki/Allotropy (2014-05-13)
AF_FM01- Fabricació Mecànica. Ferrous materials / AF
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1.2 Allotropes of Iron.
Pure iron has 3 allotropes at atmospheric pressure. These allotropes are:
Delta iron (d-iron): Delta iron is the stable state of pure
iron at temperatures between 1390ºC and its melting point
(1540ºC), its crystalline structure is body-centered cubic
(BCC). It is paramagnetic.
Gamma iron (g-iron): Gamma iron is the stable state of
pure iron at temperatures between 910ºC and 1390ºC, its
crystalline structure is face-centered cubic (FCC). It is
paramagnetic.
Alpha iron (a-iron): Alpha iron is the stable state of pure
iron at temperatures below 910ºC , its crystalline structure
is body-centered cubic (BCC). It is ferromagnetic at
temperatures below 770ºC (Curie point).
BCC and FCC are different arrangements of the Fe atoms in the crystal structure.
BCC
Body-Centered Cubic
FCC
Face-Centered Cubic
alpha iron (a-iron)
delta iron (d-iron)
gamma iron (g-iron)
Read this article from Wikipedia about allotropes of iron and try to learn more about them.
TO KNOW MORE
Improve your knowledge playing these games on Quizlet
Quizlet – IRON and STEEL (1) IRON and STEEL (2)
Quizlet – ALLOTROPES OF IRON
Quizlet – IRON-CARBON system
AF_FM01- Fabricació Mecànica. Ferrous materials / AF
IRON and STEEL (3)
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1.3 Cast Irons.
As we have seen, Cast Iron is a ferrous alloy where carbon content in weight is more than 2% .
Although it will be possible to make a Cast Iron in the range between 2% and 6.7% (wt%C),
commercial cast irons usually have a carbon content lower than the eutectic composition 4.3%C
There are different types of Cast Iron : White, Gray, Ductile and Malleable. Read this article
about the Types of Cast Irons in Wikipedia and try to complete the descriptions of Cast Irons
with the sentences you will find on next page:
WHITE /waɪt/ :
White cast iron ...
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GRAY /ɡreɪ/ :
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Grey cast iron ...
MALLEABLE /ˈmælɪəbəl/ :
Malleable cast iron ...
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DUCTILE /ˈdʌktaɪl/ : Ductile cast iron ...
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TO KNOW MORE
If you want to know more about this topic, you could do these online activities.
Quizlet – CAST IRONS
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SENTENCES ABOUT CAST IRONS
Before writing them on the previous page, it could be useful to write a letter at the beginning of
each sentence: G for grey, W for white, D for ductile and M per malleable cast irons.
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Carbon is in form of cementite (Fe3C) due to a low Si content and a fast cooling.
Composition Fe > 90%, C = 1.8 – 3.6%, Si = 0.5 – 2% .
Composition Fe > 90%, C = 2 – 2.6%, Si = 1.1 – 1.6% .
Composition Fe > 90%, C = 2.5 – 4%, Si = 1 – 3% .
Composition Fe > 90%, C = 3 – 4%, Si = 1.8 – 2.8% , S < 0.03% , P < 0.1%.
During the heat treatment carbide particles develop towards a stable spherical form.
It has been replaced by ductile cast iron, because ductile is cheaper and better.
It is called also Nodular cast iron.
It is hard but brittle. It has good wear resistance.
It is possible to cast parts with large sections.
It starts as a white cast iron and then is heat treated (malleablizing).
It's the hardest. Its hardness is about 450 BHN (Brinell Hardness Number) .
It's the most widely used cast material in weight.
Its compressive strength is comparable to steels but has less shock resistance.
Its fracture has a grey appearance due to its graphite microstructure.
Its fracture has a white appearance due to cementite in its microstructure.
Its microstructure has Carbon in form of graphite flakes.
Its microstructure has Carbon in the form of spheroidal and isolated particles of graphite.
Its microstructure has Carbon in the form of spheroidal particles of graphite.
Tiny amounts of Mg or Ce slow down the growth of graphite precipitates.
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1.4 Questions
1. Which is the most common metal on Earth? (Take a look at IRON definition)
a) Aluminum
b) Iron
c) Oxygen
d) Silicon
2. An alloy is composed by 97% Fe and 3% C. This alloy is a …
a) Cast Iron
b) Iron
c) Steel
d) None of the above.
3. An alloy is composed by 99.0 kg Fe and 1.00 kg C. Which is the Carbon content in
weight percent (Carbon, wt%)?
a) 0.01%
b) 1.00%
c) 1.01%
d) 99%
4. Previous alloy is a …
a) Cast Iron
b) Iron
c) Steel
d) None of the above.
5. An alloy is composed by 50.0 kg Fe and 0.500 kg C. Which is the Carbon, wt%?
a) 0.01%
b) 0.99%
c) 1.00%
d) 50%
6. Previous alloy is a …
a) Cast Iron
b) Iron
c) Steel
d) None of the above.
7. With 30kg of pure Iron, what's the maximum amount of Carbon needed to form a steel?
a) 0.02 kg
b) 0.06 kg
c) 0.61 kg
d) 2.00 kg
8. Which is the main element to make a ferrous product?
a) Al
b) C
c) Cast Iron
d) Fe
e) Steel
9. Which are the two elements necessary to make a cast iron?
a) Carbon and Graphite
b) C + Fe
c) Fe + Iron
d) Iron and Steel
10. Which are the two elements necessary to make a steel?
a) Carbon and Graphite
b) C + Fe
c) Fe + Iron
d) Iron and Steel
11. Which sentence is correct?
a) Steel has less Carbon than Cast iron
b) Cast iron has less Carbon than Steel
12. Name the three different allotropes of pure iron at atmospheric pressure.
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13. Which allotrop is ferromagnetic?
a) Alpha Iron
b) Beta Iron
c) Gamma Iron
d) Delta Iron
14. What is the melting point of pure iron?. Express the result in ºC, ºF and K .
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15. What does the acronym BCC mean?.
a) Body-Carbon Centered
b) Body-Centered Carbon
c) Body-Centered Cubic
16. What does the acronym FCC mean?.
a) Face-Carbon Centered
b) Face-Centered Carbon
c) Face-Centered Cubic.
17. How many degrees does room temperature represent? Express the result in ºC, ºF & K
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18. Which crystal structure has pure iron at room temperature?
a) ABC
b) BCC
c) FCC
d) SC
19. Which crystal structure has gamma iron?
a) ABC
b) BCC
c) FCC
d) SC
20. Which crystal structure has pure iron at 1500ºC?
a) ABC
b) BCC
c) FCC
d)SC
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