Ferrous Alloys
Chapter 12 – 4th Edition
Chapter 13 – 5th Edition
Where Does Iron Come
From?

Naturally
occurring
iron exists
as ironoxide (rust)
Iron ore mine in
Labrador,
Canada
http://upload.wikimedia.org/wikipedia
/commons/f/f1/Iron_ore_mine01_(xndr).jpg
Iron is also recycled
The only naturally occurring metallic
iron on earth comes from meteorites
The largest meteorite discovered in
Antarctica is about 2 feet by 2 feet by
1.5 feet. Due to its size it was not
able to be thawed in the 100%
nitrogen atmosphere and therefore
the ice inside melted. The liquid water
dissolved minerals inside the
meteorite, and when it evaporated,
white salts were left on the surface of
the meteorite. NASA Lyndon B.
Johnson Space Center, Houston, TX.
http://www2.ifa.hawaii.edu/newsletters/images/23largeMete
orite.jpg
Iron oxide is converted to metallic
iron in a blast furnace

The main chemical reaction producing the
molten iron is:



Fe2O3 + 3CO → 2Fe + 3CO2[32]
Preheated blast air blown into the furnace
reacts with the carbon in the form of coke
to produce carbon monoxide and heat.
The carbon monoxide then reacts with
the iron oxide to produce molten iron and
carbon dioxide
Blast Furnace
http://en.wikipedia.org/wiki/File:VysokaPec.jpg
1. Hot blast from
Cowper stoves
2. Melting zone
3. Reduction zone
of ferrous oxide
4. Reduction zone
of ferric oxide
5. Pre-heating
zone
6. Feed of ore,
limestone and
coke
7. Exhaust gases
8. Column of ore,
coke and
limestone
9. Removal of slag
10. Tapping of
molten pig iron
11. Collection of
waste gases
Pig Iron
An intermediate product – the result
of smelting with iron ore and carbon
 Iron and typically about 4% carbon

Also includes sulphur phosphorus and
other impurities
 Brittle and not very useful

http://www.manufacturer.com/images/buyLeads/www.alibaba.com/1118/u/Pig_iron.jpg
Steel

It wasn’t possible to make
steel until about 1850



We don’t call it steel
unless it is less than 2%
carbon
An open hearth furnace
was used to burn off the
excess carbon up until the
1990’s
Carbon can also be burned
off with


Electric Furnace
Oxygen Furnace
Sheet and Tube Open Hearth Furnace – Youngstown Ohio
Steel is a major structural
component
Photo by Ian Britton
http://www.freefoto.com/preview/42-12-6?ffid=42-12-6

The Palmer is named
for a U.S. seal hunter
who sailed along the
west coast of
Antarctica in 1820
looking for seal
rookeries. Many
believe he was the
first to discover the
continent.
Photograph courtesy Woods Hole Oceanographic
Institution http://www.nationalgeographic.com/sealab/antarctica/ship.html
Carbon composition

Steel generally has less than about
0.7% C, but can have up to
2.11% C.

Look at the iron phase diagram to
remind yourself why
1600
C
d
L
1400
C
1200
C
g
1000
C
800
C
a
600 C
400 C
Fe
Steel
1% C
Cast
Iron
2% C
3% C
4% C
5% C
6% C
6.70% C
Steel and Iron
The phase diagram only strictly
applies to an iron – carbon
combination
 Steel and iron often have other
alloying elements in them, which
modify the phase diagram

Stainless Steel Phase
Diagram at 9000C
18-8 Stainless
steel is the most
common
composition –
The terminology
refers to 18%Cr
and 8% Ni –
with the balance
Fe (and other
trace elements)
http://www.sv.vt.edu/classes/MSE2094_NoteBook/96ClassProj/experimental/ternary2.html
Stainless Steel Solidus
Temperatures
http://www.sv.vt.edu/classes/MSE2094_NoteBook/96ClassProj/experimental/ternary2.html
Cast Iron



Has quite a bit more
cementite in it than
steel
That makes it hard
and brittle
But cementite is a
“metastable”
compound, that can
decompose into iron
and graphite with the
appropriate thermal
treatment
http://www.trademadesimple.co.uk/companies/
olymberyl-manufacturers/images/cast-ironstove-hf332-1.jpg
http://www.georgesbasement.com/Microstructures/CastIronsHighAlloy
SteelsSuperalloys/Lesson-1/Introduction.htm
George Langford, Sc.D., Massachusetts Institute of Technology,
Wrought Iron


This iron is ductile
and malleable and
can be “wrought”
into a final shape
Wrought iron was
the primary high
strength structural
material until steel
became available in
the 19th century
http://upload.wikimedia.org/wikipedi
a/commons/b/bd/Eiffel_tower_from_
below.jpg
The Eiffel Tower was
made from Puddle Iron
– a form of Wrought
Iron
Heat Treatments

Process Annealing
Heat the steel just below the eutectoid
 Removes the effect of cold work


Austenitizing

Heat into the a region to dissolve the
carbon
Microstructure


We’ve already discussed the formation of
the eutectoid microstructure
If you force the phase change to occur
just below the equilibrium transformation
temperature you get spheroidite




Large spheroidal particles
Steel is easily machined
Low strength and hardness
After machining it is heat treated again to
improve the properties
Alloying Elements May…
Modify the phase diagram
 Modify the TTT curve
 Strengthen the steel by precipitation
hardening
 Reduce Corrosion

Stainless Steel





>12% Chromium
May also contain large amounts of nickel
In some stainless steels the austenite
structure survives at room temperature
Makes the steel especially corrosion
resistant
Non Magnetic
Iron Nickel Phase Diagram
http://www.calphad.com/graphs/Fe-Ni%20Phase%20Diagram.gif
Alloy Steel
Alloying elements make it harder to
predict the effect of heat treatments
 The equilibrium structures are not
always known
 Even if they are – they aren’t always
achieved

Shopping?
Moderate chromium steels can form
Martensite, which is hard and
corrosion resistant
 Austenitic steel is more corrosion
resistant and more ductile (less
brittle)

Stainless steel has a broad
range of properties

You want



Martensite for your
knives and
Austenite for your
bowls
Remember –
Austenite is not
magnetic
Ian O'Leary (c) Dorling Kindersley
Surface Treatments

Coatings


Tin, Zinc (galvanized), Aluminum
Surface Hardening
Heating, followed by quenching
 Diffusion of carbon or nitrogen

Welding


Problems with welds
do not usually occur
in the weld itself
The area around the
weld is heated, and
changes the
microstructure


Excessive grain growth
Formation of Martinsite
(makes it brittle)
Titanic
A detailed analysis of small pieces of the steel plating
from the Titanic's wreck hull found that it was of a
metallurgy that loses its elasticity and becomes brittle
in cold or icy water, leaving it vulnerable to dentinduced ruptures. The pieces of steel were found to
have very high content of phosphorus and sulphur
(4x and 2x respectively, compared to modern steel),
with manganese-sulphur ratio of 6.8:1 (compare with
over 200:1 ratio for modern steels). High content of
phosphorus initiates fractures, sulphur forms grains
of iron sulphide that facilitate propagation of cracks,
and lack of manganese makes the steel less ductile.
The recovered samples were found to be undergoing
ductile-brittle transition in temperatures of 32 °C (for
longitudinal samples) and 56 °C (for transversal
samples—compare with transition temperature of -27
°C common for modern steels—modern steel would
became so brittle in between -60 and -70 °C).