Haseeb Ullah Khan Jatoi
Department of Chemical Engineering
UET Lahore
 An alloy is a mixture or metallic solid solution composed of
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two or more elements.
An alloy will contain one or more of the three: a solid
solution of the elements (a single phase); a mixture of
metallic phases (two or more solutions); an inter-metallic
compound with no distinct boundary between the phases.
May or may not be homogenous depending upon thermal
history of the material
May be substitution alloy, or interstitial alloy
Brass (Copper + Zinc)
Pewter (Tin 85-99% + Copper + Antimony + Bismuth)
Phosphor Bronze (Copper + Tin + Phosphorus)
Amalgam ( Mercury + Metal)
 To understand design and control of heat treating
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procedures
To understand properties and microstructure of alloys
Components (Pure constituents)
System (E.g. Iron-Carbon System)
Solubility Limit (May be temp dependent or
composition etc.)
Phase (homogenous portion of system having uniform
physical and chemical properties)
Homogenous and heterogeneous
Most metallic alloys are heterogeneous
 Microstructure is subject to direct microscopic
observation, using optical or electron microscopes
 Depends on:
 Alloying elements present
 Their concentration
 Heat treatment of alloy (Temperature, heating time,
cooling rate)
 Temperature , Pressure, and Composition are three
parameters that are played
 One component diagram (Unary)
 Two component diagram (Binary)
 Multi-component diagram
 L = homogeneous liquid solution composed of both
copper and nickel
 α= substitution solid solution consisting of both
copper and nickel
 Liquidus and solidus
 Two extremities represent melting temperatures of
two components
 Phases present
 Phase composition (Tie Line)
 Phase amounts (Lever Rule)
 α= solid solution rich in copper or pure copper
 β = solid solution rich in silver or pure silver
 Eutectic (easily melted) point and eutectic reaction
 Solvus, solidus, liquidus, invariant point
 Iron is the prime constituent
 Produced largely and abundantly used as engineering
construction materials
 ‘All-purpose alloys’, but one big disadvantage i.e. Corrosion.
 Why prefer ferrous alloys?
 Iron-containing compounds exist in abundant quantities
within the earth’s crust ( ores are cheaper)
 Metallic iron and steel alloys may be produced using relatively
economical extraction, refining, alloying, and fabrication
techniques
 They are extremely versatile (can be fashioned to have
versatile desired properties)
 Iron making – Iron is reduced from its ores
 Steel making – Iron is then refined to obtain desired
purity and composition (Alloying)
 The principal ore used in the production of iron and
steel is hematite (Fe2O3)
 Other iron ores include magnetite (Fe3O4), siderite
(FeCO3), and limonite (Fe2O3-xH2O, where x is
typically around 1.5)
 Iron ores contain from 50% to around 70% iron,
depending on grade (hematite is almost 70% iron)
 Scrap iron and steel are also widely used today as raw
materials in iron and steel making
 Coke
 Supplies heat for chemical reactions and produces
carbon monoxide (CO) to reduce iron ore
 Limestone (CaCO3)
 Used as a flux to react with and remove impurities in
molten iron as slag
 Hot gases (CO, H2, CO2, H2O, N2, O2, and fuels)
 Used to burn coke
 Blast furnace - a refractory-lined chamber with a
diameter of about 9 to 11 m (30 to 35 ft) at its widest
and a height of 40 m (125 ft)
 To produce iron, a charge of ore, coke, and limestone
are dropped into the top of a blast furnace
 Hot gases are forced into the lower part of the chamber
at high rates to accomplish combustion and reduction
of the iron
 Using heated air (O2) with coke:
2C + O2
heat + 2CO
 Using hematite as the starting ore:
Fe2O3 + CO
2FeO + CO2
 CO2 reacts with coke to form more CO:
CO2 + C (coke)
2CO
 This accomplishes final reduction of FeO to iron:
FeO + CO
Fe + CO2
 Iron tapped from the blast furnace (called pig iron)
contains over 4% C, plus other impurities: 0.3-1.3% Si,
0.5-2.0% Mn, 0.1-1.0% P, and 0.02-0.08% S
 Further refinement is required for cast iron and steel
 A furnace called a cupola is commonly used for
converting pig iron into gray cast iron
 For steel, compositions must be more closely
controlled and impurities brought to much lower
levels
 Since the mid-1800s, a number of processes have been
developed for refining pig iron into steel
 Today, the two most important processes are
– Basic oxygen furnace (BOF)
– Electric furnace
 Both are used to produce carbon and alloy steels
 Accounts for almost 70% of steel production in U.S
 Adaptation of the Bessemer converter
 Bessemer process used air blown up through the
molten pig iron to burn off impurities
 BOF uses pure oxygen
 Typical BOF vessel is typically 5 m (16 ft) inside
diameter and can process 150 to 200 tons per heat
 Cycle time (tap-to-tap time) takes almost 45 min
 Accounts for 30% of steel production in U.S.
 Scrap iron and scrap steel are primary raw materials
 Capacities commonly range between 25 and 100 tons
per heat
 Complete melting requires about 2 hr; tap-to-tap time
is 4 hr
 Usually associated with production of alloy steels, tool
steels, and stainless steels
 Noted for better quality steel but higher cost per ton,
compared to BOF
 Steels produced by BOF or electric furnace are
solidified for subsequent processing either as cast
ingots or by continuous casting
 – Casting of ingots – a discrete production process
 – Continuous casting – a semi-continuous process
 Steel ingots = discrete castings weighing from less
than one ton up to 300 tons (entire heat)
 Molds made of high carbon iron, tapered at top or
bottom for removal of solid casting
 The mold is placed on a platform called a stool
 After solidification the mold is lifted, leaving the
casting on the stool
 Continuous casting is widely applied in aluminum and
copper production, but its most noteworthy
application is steel-making
 Dramatic productivity increases over ingot casting,
which is a discrete process
 For ingot casting, 10-12 hr may be required for casting
to solidify
 Continuous casting reduces solidification time by an
order of magnitude
 An alloy of iron containing from 0.02% and 2.11%
carbon by weight
 Often includes other alloying elements: nickel,
manganese, chromium, and molybdenum
 Steel alloys can be grouped into four categories:
1. Plain carbon steels
2. Low alloy steels
3. Stainless steels
4. Tool steels
 Steel and its application in chemical engineering