• Most widely used structural metals due to their wide
range of mechanical, physical and chemical properties.
• Contains iron as their base metal.
• Ferrous alloys are produced as
o Sheet steels for automobiles and containers
o Plates for boilers, ships and bridges
o Structural members – I-beam, bar products, crankshafts, railroad rails.
o Gears, tools, dies and molds
o Fasteners – bolts, rivets and nuts
Iron-carbon alloy consist 0.005% C called pure iron.
Characteristics : soft, ductile, low strength
Used in : magnetic device and enameling steels.
Invention of blast furnace made production of iron in large quantities.
3 basic materials used in iron production :
◦ Iron ore
Is one of the most abundant element in world, making up about
5% of the earth’s crust ( in the form of various ores)
4 compositions of iron ores :
Hematite ( an iron-oxide mineral)
Limonite (an iron-oxide containing water)
Siderite (Carbonate iron)
Category : Oxide mineral
Colour : black, gray with brownish tint in reflected sun
Hardness : 5 – 6
Category : oxide mineral
Colour : metallic gray, dull to bright red
Hardness : 5.5 – 6.5
Category : amorphous, mineraloid
Colour : varoius shades of brown and yellow
Hardness : 4 – 5.5
Siderite ( carbonate iron)
Category : carbonte mineral
Colour : yellow, gray, brown, black and sometimes
Hardness : 3.75 – 4.25
Iron ore processing
◦ Crushing into fine particles
◦ Removal of impurities by various means ( such as magnetic
◦ Pellets, balls or briquettes formation by using water and
binders. ( some iron-rich ores used directly without pelletizing)
Obtained from a soft coal rich in volatile hydrocarbons and tarry
matter that are heated in vertical oven and then cooled with water
Functions of coke :
◦ Generating the high level of heat required for the chemical
reactions in iron making to take place.
◦ Producing carbon monoxide ( a reducing gas to removes
oxygen) which is used to reduce iron oxide to iron.
Function of limestone:
◦ Remove impurities from the molten iron
◦ Reacts chemically with impurities, acting as flux (flow as
fluid) that causes the impurities to melt at a low
◦ Combine with impurities to form slag, which is light, floats
over the molten metal and is removed
Iron ore, limestone and coke added into the blast furnace. (charging
The charge mixture is melted in a reaction at 1650˚C, with the air preheated
(to produce sufficient high temperature) to about 1100 ˚C and blasted into
furnace through nozzles (tuyeres)
Oxygen reacts with carbon to produce carbon monoxide.
Produced carbon monoxide reacts with iron oxide and reduces it to iron.
The molten metal accumulates at the bottom of the blast furnace, while the
impurities floats to the top of the metal.
The molten metal in tapped into ladle cars.
The molten metal at this stage is called pig iron or hot metal.
Composition of pig iron : 4%C, 1.5%Si, 1%Mn, 0.04%S, 0.4%P and the rest
is pure iron.
an alloy of iron
Carbon content between 0.002% and 2.1% by
Used in : buildings, infrastructure, tools, ships,
automobiles, machines and weapons
Steel can be produced by
Basic Oxygen Furnace
Electric Arc Furnace
Is the fastest steel making process
Processes in BOF :
a) Molten pig iron and scrap charged into vessel
b) Pure oxygen in blown into furnace through lance(long tube)
c) Fluxing agents (lime) are added through a chute
d) Oxygen refines the molten metal by an oxidation process in which iron oxide is
e) The oxide reacts with the carbon in the molten metal, producing carbon
monoxide and carbon dioxide.
f) The furnace is tapped by tilting
g) The slag is removed by tilting the furnace in opposite direction
Source of heat : continuous electric arc formed between the
electrodes and the charged metal. (temperature generated :
Steel scrap, a small amount of carbon and limestone dropped
into the electric furnace through the open roof
Roof closed and electrodes are lowered
Metal melts after around 2 hours the power has been turned on
Current turned off, and the electrodes raised.
Furnace is tilted and the molten metal is poured into a ladle
(used for transferring and pouring molten metal)
Carbon composition in iron, steel and cast iron :
Pure iron : up to 0.008% C
Steels : 0.008 - 2.14% C
Cast Iron : 2.14 - 6.67% C ( most cast iron contain less than 4.5% C)
Pure iron experiences 2 changes in crystal structure before it melts at a
temperature of 1537˚C.
At rt, the stable form called ferrite(α iron) has BCC crystal structure.
Ferrite undergoes polymorphic transformation to FCC austenite (γ iron)
at around 912 ˚C.
At 1394 ˚C, austenite reverts back to a BCC phase known as δ ferrite
which finally melts at 1537 ˚C
IRON-IRON CARBIDE PHASE DIAGRAM
Fe-C liquid solution
•C is an interstitial impurity in Fe.
•It forms a solid solution with α, γ, δ phases of iron
•Maximum solubility in BCC α-ferrite is limited
(max.0.022 wt% at 727 °C) - BCC has relatively
small interstitial positions
•Maximum solubility in FCC austenite is 2.14 wt% at
1147 °C - FCC has larger interstitial positions
γ-austenite - solid solution of C in FCC Fe
• The maximum solubility of C is 2.14 wt % at 1148 °C
• Transforms to BCC δ-ferrite at 1394 °C
• Is not stable below the eutectoid temperature (727° C)
unless cooled rapidly
α-ferrite - solid solution of C in BCC Fe
• Stable form of iron at room temperature.
• The maximum solubility of C is 0.022 wt% at 727˚C.
• Transforms to FCC γ-austenite at 912 °C
•Soft, magnetic at temp below 768 ˚C
δ-ferrite solid solution of C in BCC Fe
• The same structure as α-ferrite
• Stable only at high T, above 1394 °C
• Melts at 1538 °C
Fe3C (iron carbide or
• This intermetallic compound is
• it remains as a compound
indefinitely at room T, but
decomposes (very slowly, within
several years) into α-Fe and C
(graphite)if heated at 650-700°C
• hard, brittle
•When alloy of eutectoid composition
(0.76 wt % C) is
cooled slowly it forms perlite,
• a lamellar or layered
structure of two phases: α-ferrite and
•Prop intermediate between
soft,ductile ferrite and the hard, brittle
At about 875°C microstructure
consist entirely of grain of the γ
At about 775°C, small α particles
will form along the original γ grain
At this point, α particles grown
As temperature lowered below
eutectoid , point d, all γ phase
transform to pearlite, but there is
no change in α phase.
(pearlite is not a phase!!)
Types of carbon steels Carbon content (%) Application
Less than 0.30% Bolts , nuts, sheets, plate, tubes and for
machine components that do not require
Medium-carbon Steel 0.30 – 0.60% Machinery. Automotive, agricultural
equipment parts, railroad equipment and
parts for metalworking machinery.
High-carbon Steel More than 0.60% Cutting tools, cable, springs, cutlery
Remember : The higher the carbon content of the steel, the higher is its
hardness, strength and wear resistance
A small increase in carbon has significant impact on
properties of the steel. As Carbon increases the steel:
◦ becomes more expensive to produce and less ductile, more
◦ becomes harder and less machinable and harder to weld
◦ has higher tensile strength and a lower melting point
A ferrous alloy that contains alloying elements ( other than C and
residual amounts of Mn, Si, S and P).
These alloying elements are added to improve mechanical and
corrosion resistance properties in steel.
Characteristics : high strength, hardness, creep and fatigue
Alloy steels are widely used in
o Construction and transportation industry for their high strength.
Manganese (Mg) Form stable carbide and increasing hardenability.
Silicon (Si) Fluidity and heat resistant.
Copper (Cu) Reduce rusting
Aluminum (Al) Reducing grain size which adds toughness, increase machinability
Boron (B) Increasing hardenability
Chromium (Cr) Stabilize α, Corrosion resistant, heat resistant and increases hardenability
Cobalt (Co) Permanent magnet
Molybdenum (Mo) Increase strength and hardenability.
Nickel (Ni) Stabilize , Grain refiner, corrosion,heat resistant, increase toughness,
strength and impact resistance
Tungsten (W) Stabilize , form very hard carbide, increase toughness and strength and
Vanadium (V) Increase hardenability, increase toughness and strength and impact
Steel alloys Main class Contents (%) Applications
Structural steel Carbon and low
0.55C, 0.70Mn Gears, cylinders and machine-tool
parts requiring resistant to wear.
Stainless steel 0.04C, 0.45Mn,
Kitchen tools (forks and spoons)
Conveyers chair and skids, heat
treatment box, recuperator valve, and
other furnace part.
Tool and die
Alloy tool steel 0.35C, 1.00Si,
Extrusion die, mandrels and noses for
aluminum and copper alloy. Hot
forming, piercing, gripping and
Magnetic steel Hard magnetic
1.88Ni Electric motor
•Composed of iron, carbon (2.1% ~ 4.5%), and silicon (1% ~
3.5%) – ferrous alloy.
•Cast irons classification according to the solidification
morphology from the eutectic temperature are :
o Gray cast iron or gray iron
o White cast iron
o Black Malleable cast iron
o White Malleable cast iron
o Nodular Cast Iron ( Ductile Cast Iron)
Gray Cast Iron
•Composition of 2.5% to 4% carbon and 1% to 3%) silicon.
•Graphite exists largely in the form of flakes.
•Properties of gray iron :
o Low (negligible) ductility
o Weak in tension
o Strong in compression
o Good vibration damping
•Products from gray iron include automotive engine blocks and heads,
motor housings, and machine tool bases.
Nodular Cast Iron (Ductile Iron)
• This is an iron with the composition of gray iron in which the molten metal
is chemically( added with magnesium) treated before pouring to cause the
formation of graphite spheroids rather than flakes.
• shock resistant , stronger
and more ductile iron.
• Applications include machinery components requiring high strength and
good wear resistance.
White Cast Iron
•Due to large amounts of iron carbide presence, the structure of
white iron is very hard, wear resistance and brittle.
•It is obtained either by cooling gray iron rapidly or by adjusting the
composition by keeping the carbon and silicon content low.
•Products from white iron include railway brake shoes.
•Obtained by annealing white iron in an atmosphere of carbon monoxide and
carbon dioxide, between 800oC~900oC, for several hours.
•2 types of malleable iron :
•Pearlite malleable(white malleable) – upon fast cooling of white iron
•Ferrite malleable (black malleable) – upon slow cooling of white iron
•The structure has good ductility, strength and shock resistance.
•Typical products include pipe fittings and flanges, railroad equipment parts.
Cast Irons Structure Properties Application
Gray Cast Iron Ferrite and Pearlite
with free graphite
High strength and
Pipe, engine blocks,
White Cast Iron Pearlite and Cementite Low Machinability and
component such as
rolls for steel
Ferrite and fine Carbon
melting point and
Ferritic structure near
the surface and
Pearlitic structure near
melting point and
higher fluidity. (Higher
Ferrite and Pearlite
Higher strength, reduce
gears, rolls for
Process Variable Condition Influences
Slow Produced ferrite and large flakes of graphite together with fine flakes
of graphite formed by the decomposition of the cementite after
Moderate The structure will consist of flake graphite in a matrix which is
Fast (Chilling) The structure will consist of pearlite and cementite.
Low to high High quantity of graphite will be produced in cast iron by increasing
the carbon content.
Thin to thick Thin cross section will make the solidification rate faster then the
thicker one. Longer solidification time will cause the differences of
mechanical properties and shrinkage effect.
Silicon Affect the properties in the different of percent in content.
Ferritic gray cast iron: with 3% silicon
Ferritic/pearlitic cast iron: with 2% silicon
Pearlitic cast iron: with 1.5% silicon
Sulphur Stabilizing the cementite and preventing the formation of flakes
graphite. Thus, sulphur harden the cast iron.
Manganese Remove the sulphur. Thus, softens the cast iron.
Phosphorus High phosphorus content produced a great fluidity. Cause hardness