Carbon Steel from 0 to Z ( Industrial Chemistry ) Part 1

CARBON STEELS
Industrial Chemistry| Part 1
BY : Mahmoud Galal Zidan

MAIN DEFINATIONS
• is an alloy of iron and carbon , in which the carbon content is within the range of 0.05% -1.7% .
Steel
• Iron is a chemical element with symbol Fe and atomic number 26 , it’s a metal that belongs to the first transition series and group 8 of
the periodic table .
• Iron is too weak and too soft for most engineering and structural applications.
Iron
• Carbon is a chemical element with symbol C and atomic number 6 , it’s a non-metal that belongs to P-block series and group 14 (
carbon group ) .
Carbon
by: Mahmoud Galal Zidan
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CONTENT
Alloy ………………………………………………………..……. 3
Iron ……………………………………………………………………. 11
Carbon ……………………………………………….………… 21
Steel ………………………………………….………………… 29
Heat treatment …………………………………….…………. 43
Cold & Hot Forming ………………………………………….. 51
Rolling Processes …………………………………………...… 56
Hot & cold Rolling…………………………………………….. 60
Next Part …………………………………………………………66
About us ………………………………………………………… 67

ALLOY
An alloy is an admixture of metals, or a metal combined with one or more other elements. For example,
combining the metallic elements gold and copper produces red gold, gold and silver becomes white gold,
and silver combined with copper produces sterling silver. Combining iron with non-
metallic carbon or silicon produces alloys called steel or silicon steel.
The resulting mixture forms a substance with properties that often differ from those of the pure metals,
such as increased strength or hardness. Unlike other substances that may contain metallic bases but do not
behave as metals, such as aluminium oxide (sapphire), beryllium aluminium silicate (emerald) or sodium
chloride (salt), an alloy will retain all the properties of a metal in the resulting material, such as electrical
conductivity, ductility, opacity, and luster.
Alloys are used in a wide variety of applications, from the steel alloys, used in everything from buildings to
automobiles to surgical tools, to exotic titanium alloys used in the aerospace industry, to beryllium-copper
alloys for non-sparking tools. In some cases, a combination of metals may reduce the overall cost of the
material while preserving important properties. In other cases, the combination of metals imparts synergistic
properties to the constituent metal elements such as corrosion resistance or mechanical strength.
Examples of alloys are steel, solder, brass, pewter, duralumin, bronze, and amalgams.
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An alloy may be a solid solution of metal elements (a single
phase, where all metallic grains (crystals) are of the same
composition) or a mixture of metallic phases (two or more
solutions, forming a microstructure of different crystals within
the metal). Intermetallic compounds are alloys with a
defined stoichiometry and crystal structure. Zintl phases are
also sometimes considered alloys depending on bond types
(see Van Arkel–Ketelaar triangle for information on
classifying bonding in binary compounds).
Alloys are defined by a metallic bonding character. The alloy
constituents are usually measured by mass percentage for
practical applications, and in atomic fraction for basic science
studies. Alloys are usually classified as substitutional
or interstitial alloys, depending on the atomic arrangement
that forms the alloy. They can be further classified as
homogeneous (consisting of a single phase), or
heterogeneous (consisting of two or more phases)
or intermetallic.
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ALLOY THEORY
Alloying a metal is done by combining it with one or more other elements. The most common
and oldest alloying process is performed by heating the base metal beyond its melting point
and then dissolving the solutes into the molten liquid, which may be possible even if the
melting point of the solute is far greater than that of the base. For example, in its liquid
state, titanium is a very strong solvent capable of dissolving most metals and elements. In
addition, it readily absorbs gases like oxygen and burns in the presence of nitrogen. This
increases the chance of contamination from any contacting surface, and so must be melted in
vacuum induction-heating and special, water-cooled, copper crucibles. However, some metals
and solutes, such as iron and carbon, have very high melting-points and were impossible for
ancient people to melt.
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alloying (in particular, interstitial alloying) may also be performed with one or
more constituents in a gaseous state, such as found in a blast furnace to
make pig iron (liquid-gas) , nitriding , carbonitriding or other forms of case
hardening (solid-gas), or the cementation process used to make blister
steel (solid-gas). It may also be done with one, more, or all of the
constituents in the solid state, such as found in ancient methods of pattern
welding (solid-solid), shear steel(solid-solid), or crucible steel production
(solid-liquid), mixing the elements via solid-state diffusion.
By adding another element to a metal, differences in the size of the atoms
create internal stresses in the lattice of the metallic crystals; stresses that
often enhance its properties.
For example, the combination of carbon with iron produces steel, which is
stronger than iron, its primary element.
The electrical and thermal conductivity of alloys is usually lower than that of
the pure metals. The physical properties, such as density, reactivity, Young's
modulus of an alloy may not differ greatly from those of its base element, but
engineering properties such as tensile strength, ductility, and shear
strength may be substantially different from those of the constituent
materials.
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This is sometimes a result of the sizes of the atoms in the alloy, because
larger atoms exert a compressive force on neighbouring atoms, and smaller
atoms exert a tensile force on their neighbours, helping the alloy resist
deformation. Sometimes alloys may exhibit marked differences in behaviour
even when small amounts of one element are present. For example,
impurities in semiconducting ferromagnetic alloys lead to different properties,
as first predicted by White, Hogan, Suhl, Tian Abrie and Nakamura . Some
alloys are made by melting and mixing two or more metals. Bronze, an alloy
of copper and tin, was the first alloy discovered, during the prehistoric period
now known as the Bronze Age. It was harder than pure copper and originally
used to make tools and weapons, but was later superseded by metals and
alloys with better properties. In later times bronze has been used
for ornaments, bells, statues, and bearings. Brass is an alloy made
from copper and zinc.
Unlike pure metals, most alloys do not have a single melting point, but a
melting range during which the material is a mixture of solid and liquid phases
(a slush). The temperature at which melting begins is called the solidus, and
the temperature when melting is just complete is called the liquidus. For many
alloys there is a particular alloy proportion (in some cases more than one),
called either a eutectic mixture or a peritectic composition, which gives the
alloy a unique and low melting point, and no liquid/solid slush transition.
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Heat-treatable alloys
Alloying elements are added to a base metal, to
induce hardness, toughness, ductility, or other desired properties. Most
metals and alloys can be work hardened by creating defects in their
crystal structure. These defects are created during plastic
deformation by hammering, bending, extruding, et cetera, and are
permanent unless the metal is recrystallized.
Otherwise, some alloys can also have their properties altered by heat
treatment. Nearly all metals can be softened by annealing, which
recrystallizes the alloy and repairs the defects, but not as many can be
hardened by controlled heating and cooling. Many alloys of aluminum ,
copper ,magnesium ,titanium, and nickel can be strengthened to some
degree by some method of heat treatment, but few respond to this to
the same degree as does steel.
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The base metal iron of the iron-carbon alloy known as steel, undergoes a change in the
arrangement (allotropy) of the atoms of its crystal matrix at a certain temperature (usually
between 1,500 °F (820 °C) and 1,600 °F (870 °C), depending on carbon content). This allows
the smaller carbon atoms to enter the interstices of the iron crystal. When
this diffusion happens, the carbon atoms are said to be in solution in the iron, forming a
particular single, homogeneous, crystalline phase called austenite. If the steel is cooled slowly,
the carbon can diffuse out of the iron and it will gradually revert to its low temperature allotrope.
During slow cooling, the carbon atoms will no longer be as soluble with the iron, and will be
forced to precipitate out of solution, nucleating into a more concentrated form of iron carbide
(Fe3C) in the spaces between the pure iron crystals. The steel then becomes heterogeneous,
as it is formed of two phases, the iron-carbon phase called cementite (or carbide), and pure
iron ferrite. Such a heat treatment produces a steel that is rather soft. If the steel is cooled
quickly, however, the carbon atoms will not have time to diffuse and precipitate out as carbide,
but will be trapped within the iron crystals. When rapidly cooled, a diffusionless (martensite)
transformation occurs, in which the carbon atoms become trapped in solution. This causes the
iron crystals to deform as the crystal structure tries to change to its low temperature state,
leaving those crystals very hard but much less ductile (more brittle).
While the high strength of steel results when diffusion and precipitation is prevented (forming
martensite), most heat-treatable alloys are precipitation hardening alloys, that depend on the
diffusion of alloying elements to achieve their strength. When heated to form a solution and
then cooled quickly, these alloys become much softer than normal, during the diffusionless
transformation, but then harden as they age. The solutes in these alloys will precipitate over
time, forming intermetallic phases, which are difficult to discern from the base metal. Unlike
steel, in which the solid solution separates into different crystal phases (carbide and ferrite),
precipitation hardening alloys form different phases within the same crystal. These intermetallic
alloys appear homogeneous in crystal structure, but tend to behave heterogeneously, becoming
hard and somewhat brittle.
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SUBSTITUTIONAL AND INTERSTITIAL ALLOYS
When a molten metal is mixed with another substance, there are two mechanisms that can cause
an alloy to form, called atom exchange and the interstitial mechanism. The relative size of each
element in the mix plays a primary role in determining which mechanism will occur. When the
atoms are relatively similar in size, the atom exchange method usually happens, where some of
the atoms composing the metallic crystals are substituted with atoms of the other constituent.
This is called a substitutional alloy. Examples of substitutional alloys include bronze and brass, in
which some of the copper atoms are substituted with either tin or zinc atoms respectively.
In the case of the interstitial mechanism, one atom is usually much smaller than the other and
can not successfully substitute for the other type of atom in the crystals of the base metal.
Instead, the smaller atoms become trapped in the spaces between the atoms of the crystal
matrix, called the interstices. This is referred to as an interstitial alloy. Steel is an example of an
interstitial alloy, because the very small carbon atoms fit into interstices of the iron matrix.
Stainless steel is an example of a combination of interstitial and substitutional alloys, because the
carbon atoms fit into the interstices, but some of the iron atoms are substituted by nickel and
chromium atoms.
by: Mahmoud Galal Zidan 10

INTRODUCTION TO IRON
Iron is a chemical element with symbol Fe and atomic number 26. It is a metal that belongs to the first transition
series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in front
of oxygen (32.1% and 30.1%, respectively), forming much of Earth's outer and inner core. It is the fourth most
common element in the Earth's crust.
In its metallic state, iron is rare in the Earth's crust, limited mainly to deposition by meteorites. Iron ores, by
contrast, are among the most abundant in the Earth's crust, although extracting usable metal from them
requires kilnsor furnaces capable of reaching 1,500 °C (2,730 °F) or higher, about 500 °C (900 °F) higher than
that required to smelt copper. Humans started to master that process in Eurasia during the 2nd millennium
BCE and the use of iron tools and weapons began to displace copper alloys, in some regions, only around
1200 BCE. That event is considered the transition from the Bronze Age to the Iron Age. In the modern world,
iron alloys, such as steel, stainless steel, cast iron and special steels are by far the most common industrial
metals, because of their mechanical properties and low cost.
Pristine and smooth pure iron surfaces are mirror-like silvery- gray. However, iron reacts readily with oxygen
and water to give brown to black hydrated iron oxides, commonly known as rust. Unlike the oxides of some
other metals, that form passivating layers, rust occupies more volume than the metal and thus flakes off,
exposing fresh surfaces for corrosion. Although iron readily reacts, high purity iron, called electrolytic iron, has
better corrosion resistance.
The body of an adult human contains about 4 grams (0.005% body weight) of iron, mostly
in hemoglobin and myoglobin. These two proteins play essential roles in vertebrate metabolism,
respectively oxygen transport by blood and oxygen storage in muscles. To maintain the necessary
levels, human iron metabolism requires a minimum of iron in the diet. Iron is also the metal at the active site of
many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants and
animals.
Chemically, the most common oxidation states of iron are iron(II)and iron(III). Iron shares many properties of
other transition metals, including the other group 8 elements, ruthenium and osmium. Iron forms compounds in
a wide range of oxidation states, −2 to +7. Iron also forms many coordination compounds; some of them, such
as ferrocene, ferrioxalate, and Prussian blue, have substantial industrial, medical, or research applications.
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CHARACTARASICS
Allotropes
At least four allotropes of iron (differing atom arrangements in the solid) are known, conventionally
denoted α, γ, δ, and ε.
The first three forms are observed at ordinary pressures. As molten iron cools past its freezing
point of 1538 °C, it crystallizes into its δ allotrope, which has a body-centered cubic (bcc) crystal
structure. As it cools further to 1394 °C, it changes to its γ-iron allotrope, a face-centered
cubic (fcc) crystal structure, or austenite. At 912 °C and below, the crystal structure again becomes
the bcc α-iron allotrope.
The physical properties of iron at very high pressures and temperatures have also been studied
extensively, because of their relevance to theories about the cores of the Earth and other planets.
Above approximately 10 GPa and temperatures of a few hundred kelvin or less, α-iron changes
into another hexagonal close-packed (hcp) structure, which is also known as ε-iron. The higher-
temperature γ-phase also changes into ε-iron, but does so at higher pressure.
Some controversial experimental evidence exists for a stable β phase at pressures above 50 GPa
and temperatures of at least 1500 K. It is supposed to have an orthorhombic or a double hcp
structure. (Confusingly, the term "β-iron" is sometimes also used to refer to α-iron above its Curie
point, when it changes from being ferromagnetic to paramagnetic, even though its crystal structure
has not changed).
The inner core of the Earth is generally presumed to consist of an iron-nickel alloy with ε (or β)
structure.
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MELTING AND BOILING POINTS
The melting and boiling points of iron, along with its enthalpy of
atomization, are lower than those of the earlier 3d elements
from scandium to chromium, showing the lessened contribution of the 3d
electrons to metallic bonding as they are attracted more and more into
the inert core by the nucleus;[11] however, they are higher than the values
for the previous element manganese because that element has a half-
filled 3d sub-shell and consequently its d-electrons are not easily
delocalized. This same trend appears for ruthenium but not osmium.
The melting point of iron is experimentally well defined for pressures less
than 50 GPa. For greater pressures, published data (as of 2007) still
varies by tens of gigapascals and over a thousand kelvin.
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Below its Curie point of 770 °C, α-iron changes from paramagnetic to ferromagnetic:
the spins of the two unpaired electrons in each atom generally align with the spins of its
neighbors, creating an overall magnetic field. This happens because the orbitals of those two
electrons (dz2 and dx2 − y2) do not point toward neighboring atoms in the lattice, and
therefore are not involved in metallic bonding.
In the absence of an external source of magnetic field, the atoms get spontaneously
partitioned into magnetic domains, about 10 micrometers across, such that the atoms in each
domain have parallel spins, but some domains have other orientations.
Thus, a macroscopic piece of iron will have a nearly zero overall magnetic field.
Application of an external magnetic field causes the domains that are magnetized in the same
general direction to grow at the expense of adjacent ones that point in other directions,
reinforcing the external field. This effect is exploited in devices that needs to channel
magnetic fields, such as electrical transformers, magnetic recording heads, and electric
motors. Impurities, lattice defects, or grain and particle boundaries can "pin" the domains in
the new positions, so that the effect persists even after the external field is removed — thus
turning the iron object into a (permanent) magnet.
Similar behavior is exhibited by some iron compounds, such as the ferrites including the
mineral magnetite, a crystalline form of the mixed iron(II,III) oxide Fe3O4 (although the
atomic-scale mechanism, ferrimagnetism, is somewhat different). Pieces of magnetite with
natural permanent magnetization (lodestones) provided the earliest compasses for
navigation. Particles of magnetite were extensively used in magnetic recording media such
as core memories, magnetic tapes, floppies, and disks, until they were replaced by cobalt-
based materials.
MAGNETIC PROPERTIES
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ISOTOPES
Iron has four stable isotopes: 54Fe (5.845% of natural iron), 56Fe(91.754%), 57Fe (2.119%) and 58Fe (0.282%). 20-
30 artificial isotopes have also been created. Of these stable isotopes, only 57Fe has a nuclear spin (−1⁄2).
The nuclide 54Fe theoretically can undergo double electron capture to 54Cr, but the process has never been observed
and only a lower limit on the half-life of 3.1×1022years has been established.
60Fe is an extinct radionuclide of long half-life (2.6 million years).It is not found on Earth, but its ultimate decay product
is its granddaughter, the stable nuclide 60Ni.[17] Much of the past work on isotopic composition of iron has focused on
the nucleosynthesis of 60Fe through studies of meteorites and ore formation. In the last decade, advances in mass
spectrometry have allowed the detection and quantification of minute, naturally occurring variations in the ratios of
the stable isotopes of iron. Much of this work is driven by the Earth and planetary science communities, although
applications to biological and industrial systems are emerging.
In phases of the meteorites Semarkona and Chervony Kut, a correlation between the concentration of 60Ni,
the granddaughter of 60Fe, and the abundance of the stable iron isotopes provided evidence for the existence of 60Fe
at the time of formation of the Solar System. Possibly the energy released by the decay of 60Fe, along with that
released by 26Al, contributed to the remelting and differentiation of asteroids after their formation 4.6 billion years ago.
The abundance of 60Ni present in extraterrestrial material may bring further insight into the origin and early history of
the Solar System.
The most abundant iron isotope 56Fe is of particular interest to nuclear scientists because it represents the most
common endpoint of nucleosynthesis. Since 56Ni (14 alpha particles) is easily produced from lighter nuclei in the alpha
process in nuclear reactions in supernovae (see silicon burning process), it is the endpoint of fusion chains
inside extremely massive stars, since addition of another alpha particle, resulting in 60Zn, requires a great deal more
energy. This 56Ni, which has a half-life of about 6 days, is created in quantity in these stars, but soon decays by two
successive positron emissions within supernova decay products in the supernova remnant gas cloud, first to
radioactive 56Co, and then to stable 56Fe. As such, iron is the most abundant element in the core of red giants, and is
the most abundant metal in iron meteoritesand in the dense metal cores of planets such as Earth. It is also very
common in the universe, relative to other stable metals of approximately the same atomic weight. Iron is the sixth
most abundant element in the universe, and the most common refractory element.
Although a further tiny energy gain could be extracted by synthesizing 62Ni, which has a marginally higher binding
energy than 56Fe, conditions in stars are unsuitable for this process. Element production in supernovas and
distribution on Earth greatly favour iron over nickel, and in any case, 56Fe still has a lower mass per nucleon than 62Ni
due to its higher fraction of lighter protons. Hence, elements heavier than iron require a supernova for their formation,
involving rapid neutron capture by starting 56Fe nuclei.
In the far future of the universe, assuming that proton decay does not occur, cold fusion occurring via quantum
tunnelling would cause the light nuclei in ordinary matter to fuse into 56Fe nuclei. Fission and alpha-particle
emission would then make heavy nuclei decay into iron, converting all stellar-mass objects to cold spheres of pure
iron.
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CAST IRON
Cast iron was first produced in China during 5th century BC but was hardly in Europe until the medieval period. The earliest cast
iron artifacts were discovered by archaeologists in what is now modern Luhe County, Jiangsu in China. Cast iron was used
in ancient China for warfare, agriculture, and architecture. During the medieval period, means were found in Europe of
producing wrought iron from cast iron (in this context known as pig iron) using finery forges. For all these
processes, charcoal was required as fuel.
Medieval blast furnaceswere about 10 feet (3.0 m) tall and made of fireproof brick; forced air was usually provided by hand-
operated bellows.[107] Modern blast furnaces have grown much bigger, with hearths fourteen meters in diameter that allow them
to produce thousands of tons of iron each day, but essentially operate in much the same way as they did during medieval times.
In 1709, Abraham Darby I established a coke-fired blast furnace to produce cast iron, replacing charcoal, although continuing to
use blast furnaces. The ensuing availability of inexpensive iron was one of the factors leading to the Industrial Revolution.
Toward the end of the 18th century, cast iron began to replace wrought iron for certain purposes, because it was cheaper.
Carbon content in iron was not implicated as the reason for the differences in properties of wrought iron, cast iron, and steel
until the 18th century.
Since iron was becoming cheaper and more plentiful, it also became a major structural material following the building of the
innovative first iron bridge in 1778. This bridge still stands today as a monument to the role iron played in the Industrial
Revolution. Following this, iron was used in rails, boats, ships, aqueducts, and buildings, as well as in iron cylinders in steam
engines.[109] Railways have been central to the formation of modernity and ideas of progress and various languages (e.g. French,
Spanish, Italian and German) refer to railways as iron road.
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STEEL
Steel (with smaller carbon content than pig iron but more than wrought
iron) was first produced in antiquity by using a bloomery. Blacksmiths
in Luristan in western Persia were making good steel by
1000 BC. Then improved versions, Wootz steel by India
and Damascus steel were developed around 300 BC and AD 500
respectively. These methods were specialized, and so steel did not
become a major commodity until the 1850s.
New methods of producing it by carburizing bars of iron in
the cementation process were devised in the 17th century. In
the Industrial Revolution, new methods of producing bar iron without
charcoal were devised and these were later applied to produce steel. In
the late 1850s, Henry Bessemer invented a new steelmaking process,
involving blowing air through molten pig iron, to produce mild steel.
This made steel much more economical, thereby leading to wrought
iron no longer being produced in large quantities.
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Production of metallic iron
1. Laboratory routes
For a few limited purposes when it is needed, pure iron is
produced in the laboratory in small quantities by reducing the
pure oxide or hydroxide with hydrogen, or forming iron
pentacarbonyl and heating it to 250 °C so that it decomposes
to form pure iron powder. Another method is electrolysis of
ferrous chloride onto an iron cathode.
2. Main industrial route
production of iron or steel consists of two main stages. In the
first stage, iron ore is reduced with coke in a blast furnace, and
the molten metal is separated from gross impurities such
as silicate minerals. This stage yields an alloy—pig iron—that
contains relatively large amounts of carbon. In the second
stage, the amount of carbon in the pig iron is lowered by
oxidation to yield wrought iron, steel, or cast iron. Other metals
can be added at this stage to form alloy steels.
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3. Blast furnace processing
The blast furnace is loaded with iron ores, usually hematite Fe2O3 or magnetite Fe3O4, together with coke (coal that
has been separately baked to remove volatile components). Air pre-heated to 900 °C is blown through the
sufficient amount to turn the carbon into carbon monoxide:
2 C + O2 → 2 CO
This reaction raises the temperature to about 2000 °C. The carbon monoxide reduces the iron ore to metallic iron
Fe2O3 + 3 CO → 2 Fe + 3 CO2
Some iron in the high-temperature lower region of the furnace reacts directly with the coke:
2 Fe2O3 + 3 C → 4 Fe + 3 CO2
A flux such as limestone (calcium carbonate) or dolomite (calcium-magnesium carbonate) is also added to the
furnace's load. Its purpose is to remove salicaceous minerals in the ore, which would otherwise clog the furnace.
heat of the furnace decomposes the carbonates to calcium oxide, which reacts with any excess silica to form
a slag composed of calcium silicate CaSiO3 or other products. At the furnace's temperature, the metal and the slag
both molten. They collect at the bottom as two immiscible liquid layers (with the slag on top), that are then easily
separated.[118] The slag can be used as a material in road construction or to improve mineral-poor soils
4. Steelmaking
In general, the pig iron produced by the blast furnace process contains up to 4–5% carbon, with small amounts of
other impurities like sulfur, magnesium, phosphorus, and manganese. The high level of carbon makes it relatively
weak and brittle. Reducing the amount of carbon to 0.002–2.1% by mass produces steel, which may be up to 1000
times harder than pure iron. A great variety of steel articles can then be made by cold working, hot
rolling, forging, machining, etc. Removing the other impurities, instead, results in cast iron, which is used to cast
articles in foundries;
for example: stoves, pipes, radiators, lamp-posts, and rails.
Steel products often undergo various heat treatments after they are forged to shape. Annealing consists of heating
them to 700–800 °C for several hours and then gradual cooling.
It makes the steel softer and more workable.
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5. Direct iron reduction
Owing to environmental concerns, alternative methods of processing iron have been
developed. "Direct iron reduction" reduces iron ore to a ferrous lump called "sponge"
iron or "direct" iron that is suitable for steelmaking. Two main reactions comprise the
direct reduction process:
Natural gas is partially oxidized (with heat and a catalyst):
2 CH4 + O2 → 2 CO + 4 H2Iron ore is then treated with these gases in a furnace,
producing solid sponge iron:
Fe2O3 + CO + 2 H2 → 2 Fe + CO2 + 2 H2OSilica is removed by adding a limestone flux
as described above.
6. Thermite process
Ignition of a mixture of aluminium powder and iron oxide yields metallic iron via
the thermite reaction:
Fe2O3 + 2 Al → 2 Fe + Al2O3Alternatively pig iron may be made into steel (with up to
about 2% carbon) or wrought iron (commercially pure iron). Various processes have
been used for this, including finery forges, puddling furnaces, Bessemer
converters, open hearth furnaces, basic oxygen furnaces, and electric arc furnaces. In
all cases, the objective is to oxidize some or all of the carbon, together with other
impurities. On the other hand, other metals may be added to make alloy steels.
20

INTRODUCTION TO CARBON
Carbon (from Latin: carbo "coal") is a chemical element with the symbol Cand atomic number6. It is non-metallic
and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic
table. Carbon makes up only about 0.025 percent of Earth's crust.[15]Three isotopes occur naturally, 12C and 13C being stable,
while 14C is a radionuclide, decaying with a half-life of about 5,730 years.
Carbon is one of the few elements known since antiquity.
Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by
mass after hydrogen, helium, and oxygen. Carbon's abundance, its unique diversity of organic compounds, and its unusual
ability to form polymers at the temperatures commonly encountered on Earth enables this element to serve as a common
element of all known life. It is the second most abundant element in the human body by mass (about 18.5%) after oxygen.
The atoms of carbon can bond together in diverse ways, resulting in various allotropes of carbon. Well-known allotropes
include graphite, diamond, amorphous carbon and fullerenes. The physical properties of carbon vary widely with the
allotropic form. For example, graphite is opaque and black while diamond is highly transparent. Graphite is soft enough to
form a streak on paper (hence its name, from the Greek verb "γράφειν" which means "to write"), while diamond is
the hardest naturally occurring material known. Graphite is a good electrical conductor while diamond has a low electrical
conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal
conductivities of all known materials. All carbon allotropes are solids under normal conditions, with graphite being the
most thermodynamically stable form at standard temperature and pressure. They are chemically resistant and require high
temperature to react even with oxygen.
The most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon
monoxide and transition metal carbonyl complexes. The largest sources of inorganic carbon
are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil,
and methane clathrates. Carbon forms a vast number of compounds, more than any other element, with almost ten million
compounds described to date, and yet that number is but a fraction of the number of theoretically possible compounds
under standard conditions. For this reason, carbon has often been referred to as the "king of the elements".
21

CHARACTARASICS
The allotropes of carbon include graphite, one of the softest known substances, and diamond, the hardest naturally occurring
substance. It bonds readily with other small atoms, including other carbon atoms, and is capable of forming multiple
stable covalent bonds with suitable multivalent atoms. Carbon is known to form almost ten million compounds, a large majority of
all chemical compounds.[19] Carbon also has the highest sublimationpoint of all elements. At atmospheric pressure it has no melting
point, as its triple point is at 10.8 ± 0.2 megapascals (106.6 ± 2.0 atm; 1,566 ± 29 psi) and 4,600 ± 300 K (4,330 ± 300 °C;
7,820 ± 540 °F), so it sublimes at about 3,900 K (3,630 °C; 6,560 °F). Graphite is much more reactive than diamond at standard
conditions, despite being more thermodynamically stable, as its delocalised pi system is much more vulnerable to attack. For
example, graphite can be oxidised by hot concentrated nitric acid at standard conditions to mellitic acid, C6(CO2H)6, which preserves
the hexagonal units of graphite while breaking up the larger structure.
Carbon sublimes in a carbon arc, which has a temperature of about 5800 K (5,530 °C or 9,980 °F). Thus, irrespective of its allotropic
form, carbon remains solid at higher temperatures than the highest-melting-point metals such as tungsten or rhenium. Although
thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper, which are
weaker reducing agents at room temperature.
Carbon is the sixth element, with a ground-state electron configuration of 1s22s22p2, of which the four outer electrons are valence
electrons. Its first four ionisation energies, 1086.5, 2352.6, 4620.5 and 6222.7 kJ/mol, are much higher than those of the heavier
group-14 elements. The electronegativity of carbon is 2.5, significantly higher than the heavier group-14 elements (1.8–1.9), but close
to most of the nearby nonmetals, as well as some of the second- and third-row transition metals. Carbon's covalent radii are normally
taken as 77.2 pm (C−C), 66.7 pm (C=C) and 60.3 pm (C≡C), although these may vary depending on coordination number and what
the carbon is bonded to. In general, covalent radius decreases with lower coordination number and higher bond order.
Carbon compounds form the basis of all known life on Earth, and the carbon–nitrogen cycle provides some of the energy produced
by the Sun and other stars. Although it forms an extraordinary variety of compounds, most forms of carbon are comparatively
unreactive under normal conditions. At standard temperature and pressure, it resists all but the strongest oxidizers. It does not react
with sulfuric acid, hydrochloric acid, chlorine or any alkalis. At elevated temperatures, carbon reacts with oxygen to form carbon
oxides and will rob oxygen from metal oxides to leave the elemental metal. This exothermic reaction is used in the iron and steel
industry to smeltiron and to control the carbon content of steel:
Fe3O4 + 4 C(s) + 2 O2 → 3 Fe(s) + 4 CO2(g).
Carbon reacts with sulfur to form carbon disulfide, and it reacts with steam in the coal-gas reaction used in coal gasification:
C(s) + H2O(g) → CO(g) + H2(g).
Carbon combines with some metals at high temperatures to form metallic carbides, such as the iron carbide cementite in steel
and tungsten carbide, widely used as an abrasive and for making hard tips for cutting tools.
The system of carbon allotropes spans a range of extremes:
Graphite is one of the softest
materials known.
Synthetic nanocrystalline
diamond is the hardest material
known.
Graphite is a very good lubricant,
displaying superlubricity.
Diamond is the
ultimate abrasive.
Graphite is a conductor of
electricity.
Diamond is an excellent
electrical insulator, and has the
highest breakdown electric field
of any known material.
Some forms of graphite are used
for thermal insulation (i.e. firebreaks
and heat shields), but some other
forms are good thermal conductors.
Diamond is the best known
naturally occurring thermal
conductor
Graphite is opaque. Diamond is highly transparent.
Graphite crystallizes in
the hexagonal system.
Diamond crystallizes in the cubic
system.
Amorphous carbon is
completely isotropic.
Carbon nanotubes are among
the most anisotropic materials
known.
22

ALLOTROPES
Atomic carbon is a very short-lived species and, therefore, carbon is stabilized in various multi-atomic structures with diverse molecular
configurations called allotropes. The three relatively well-known allotropes of carbon are amorphous carbon, graphite, and diamond. Once
considered exotic, fullerenes are nowadays commonly synthesized and used in research; they include buckyballs,[31][32]carbon
nanotubes, carbon nanobuds and nanofibers. Several other exotic allotropes have also been discovered, such as lonsdaleite, glassy
carbon,[38] carbon nanofoam and linear acetylenic carbon (carbyne).
Graphene is a two-dimensional sheet of carbon with the atoms arranged in a hexagonal lattice. As of 2009, graphene appears to be the
strongest material ever tested. The process of separating it from graphite will require some further technological development before it is
economical for industrial processes. If successful, graphene could be used in the construction of a space elevator. It could also be used to
safely store hydrogen for use in a hydrogen based engine in cars .
The amorphous form is an assortment of carbon atoms in a non-crystalline, irregular, glassy state, not held in a crystalline macrostructure.
It is present as a powder, and is the main constituent of substances such as charcoal, lampblack (soot) and activated carbon. At normal
pressures, carbon takes the form of graphite, in which each atom is bonded trigonally to three others in a plane composed of
fused hexagonal rings, just like those in aromatic hydrocarbons. The resulting network is 2-dimensional, and the resulting flat sheets are
stacked and loosely bonded through weak van der Waals forces. This gives graphite its softness and its cleaving properties (the sheets slip
easily past one another). Because of the delocalization of one of the outer electrons of each atom to form a π-cloud, graphite
conducts electricity, but only in the plane of each covalently bonded sheet. This results in a lower bulk electrical conductivity for carbon
than for most metals. The delocalization also accounts for the energetic stability of graphite over diamond at room temperature.
At very high pressures, carbon forms the more compact allotrope, diamond, having nearly twice the density of graphite. Here, each atom is
bonded tetrahedrally to four others, forming a 3-dimensional network of puckered six-membered rings of atoms. Diamond has the
same cubic structure as silicon and germanium, and because of the strength of the carbon-carbon bonds, it is the hardest naturally
occurring substance measured by resistance to scratching. Contrary to the popular belief that "diamonds are forever", they are
thermodynamically unstable (ΔfG°(diamond, 298 K) = 2.9 kJ/mol) under normal conditions (298 K, 105 Pa) and should theoretically
transform into graphite. But due to a high activation energy barrier, the transition into graphite is so slow at normal temperature that it is
unnoticeable. However, at very high temperatures diamond will turn into graphite, and diamonds can burn up in a house fire. The bottom
left corner of the phase diagram for carbon has not been scrutinized experimentally. Although a computational study employing density
functional theory methods reached the conclusion that as T → 0 K and p → 0 Pa, diamond becomes more stable than graphite by
approximately 1.1 kJ/mol, more recent and definitive experimental and computational studies show that graphite is more stable than
diamond for T < 400 K, without applied pressure, by 2.7 kJ/mol at T = 0 K and 3.2 kJ/mol at T = 298.15 K. Under some conditions, carbon
crystallizes as lonsdaleite, a hexagonal crystal lattice with all atoms covalently bonded and properties similar to those of diamond.
23

ALLOTROPES
Fullerenes are a synthetic crystalline formation with a graphite-like structure, but in place of
flat hexagonal cells only, some of the cells of which fullerenes are formed may be pentagons, nonplanar
hexagons, or even heptagons of carbon atoms. The sheets are thus warped into spheres, ellipses, or
cylinders. The properties of fullerenes (split into buckyballs, buckytubes, and nanobuds) have not yet
been fully analysed and represent an intense area of research in nanomaterials. The
names fullerene and buckyball are given after Richard Buckminster Fuller, populariser of geodesic domes,
which resemble the structure of fullerenes. The buckyballs are fairly large molecules formed completely
of carbon bonded trigonally, forming spheroids (the best-known and simplest is the soccer ball-shaped
C60 buckminsterfullerene). Carbon nanotubes (buckytubes) are structurally similar to buckyballs, except
that each atom is bonded trigonally in a curved sheet that forms a hollow cylinder. Nanobuds were first
reported in 2007 and are hybrid buckytube/buckyball materials (buckyballs are covalently bonded to the
outer wall of a nanotube) that combine the properties of both in a single structure.
Of the other discovered allotropes, carbon nanofoam is a ferromagnetic allotrope discovered in 1997. It
consists of a low-density cluster-assembly of carbon atoms strung together in a loose three-dimensional
web, in which the atoms are bonded trigonally in six- and seven-membered rings. It is among the lightest
known solids, with a density of about 2 kg/m3. Similarly, glassy carbon contains a high proportion of
closed porosity, but contrary to normal graphite, the graphitic layers are not stacked like pages in a book,
but have a more random arrangement. Linear acetylenic carbon has the chemical structure −(C:::C)n−.
Carbon in this modification is linear with sp orbital hybridization, and is a polymer with alternating single
and triple bonds. This carbyne is of considerable interest to nanotechnology as its Young's modulus is 40
times that of the hardest known material – diamond.
In 2015, a team at the North Carolina State University announced the development of another allotrope
they have dubbed Q-carbon, created by a high energy low duration laser pulse on amorphous carbon
dust. Q-carbon is reported to exhibit ferromagnetism, fluorescence, and a hardness superior to
diamonds.
In the vapor phase, some of the carbon is in the form of dicarbon (C) .
When excited, this gas glows green.
24

ISOTOPES
Isotopes of carbon are atomic nuclei that contain six protons plus a number of neutrons (varying
from 2 to 16). Carbon has two stable, naturally occurring isotopes. The isotope carbon-12 (12C) forms
98.93% of the carbon on Earth, while carbon-13 (13C) forms the remaining 1.07%. The concentration
of 12C is further increased in biological materials because biochemical reactions discriminate
against 13C. In 1961, the International Union of Pure and Applied Chemistry (IUPAC) adopted the
isotope carbon-12 as the basis for atomic weights.[70] Identification of carbon in nuclear magnetic
resonance (NMR) experiments is done with the isotope 13C.
Carbon-14 (14C) is a naturally occurring radioisotope, created in the upper
atmosphere (lower stratosphere and upper troposphere) by interaction of nitrogen with cosmic rays.
It is found in trace amounts on Earth of 1 part per trillion (0.0000000001%) or more, mostly confined
to the atmosphere and superficial deposits, particularly of peat and other organic materials.[72] This
isotope decays by 0.158 MeV β− emission. Because of its relatively short half-life of 5730 years, 14C is
virtually absent in ancient rocks. The amount of 14C in the atmosphere and in living organisms is
almost constant, but decreases predictably in their bodies after death. This principle is used
in radiocarbon dating, invented in 1949, which has been used extensively to determine the age of
carbonaceous materials with ages up to about 40,000 years.
There are 15 known isotopes of carbon and the shortest-lived of these is 8C which decays
through proton emission and alpha decay and has a half-life of 1.98739 × 10−21 s. The exotic 19C
exhibits a nuclear halo, which means its radius is appreciably larger than would be expected if
the nucleus were a sphere of constant density.
25

ORGANIC COMPOUNDS
Correlation between the carbon cycle and formation of organic compounds. In plants, carbon dioxide formed by carbon
fixation can join with water in photosynthesis(green) to form organic compounds, which can be used and further
converted by both plants and animals.
Carbon can form very long chains of interconnecting carbon–carbon bonds, a property that is called catenation. Carbon-
carbon bonds are strong and stable. Through catenation, carbon forms a countless number of compounds. A tally of
unique compounds shows that more contain carbon than do not. A similar claim can be made for hydrogen because
most organic compounds contain hydrogen chemically bonded to carbon or another common element like oxygen or
nitrogen.
The simplest form of an organic molecule is the hydrocarbon—a large family of organic molecules that are composed
of hydrogen atoms bonded to a chain of carbon atoms. A hydrocarbon backbone can be substituted by other atoms,
known as heteroatoms. Common heteroatoms that appear in organic compounds include oxygen, nitrogen, sulfur,
phosphorus, and the nonradioactive halogens, as well as the metals lithium and magnesium. Organic compounds
containing bonds to metal are known as organometallic compounds (see below). Certain groupings of atoms, often
including heteroatoms, recur in large numbers of organic compounds. These collections, known as functional groups,
confer common reactivity patterns and allow for the systematic study and categorization of organic compounds. Chain
length, shape and functional groups all affect the properties of organic molecules.
In most stable compounds of carbon (and nearly all stable organic compounds), carbon obeys the octet rule and
is tetravalent, meaning that a carbon atom forms a total of four covalent bonds (which may include double and triple
bonds). Exceptions include a small number of stabilized carbocations (three bonds, positive charge), radicals (three bonds,
neutral), carbanions (three bonds, negative charge) and carbenes (two bonds, neutral), although these species are much
more likely to be encountered as unstable, reactive intermediates.
Carbon occurs in all known organic life and is the basis of organic chemistry. When united with hydrogen, it forms various
hydrocarbons that are important to industry as refrigerants, lubricants, solvents, as chemical feedstock for the manufacture
of plastics and petrochemicals, and as fossil fuels.
When combined with oxygen and hydrogen, carbon can form many groups of important biological compounds
including sugars, lignans, chitins, alcohols, fats, and aromatic esters, carotenoids and terpenes. With nitrogen it
forms alkaloids, and with the addition of sulfur also it forms antibiotics, amino acids, and rubber products. With the
addition of phosphorus to these other elements, it forms DNA and RNA, the chemical-code carriers of life, and adenosine
triphosphate (ATP), the most important energy-transfer molecule in all living cells.
26

INORGANIC COMPOUNDS
Commonly carbon-containing compounds which are associated with minerals or which do not contain bonds to
the other carbon atoms, halogens, or hydrogen, are treated separately from classical organic compounds; the
definition is not rigid, and the classification of some compounds can vary from author to author (see reference
articles above). Among these are the simple oxides of carbon. The most prominent oxide is carbon
dioxide (CO2). This was once the principal constituent of the paleoatmosphere, but is a minor component of
the Earth's atmosphere today.[84] Dissolved in water,
it forms carbonic acid (H2CO3)
, but as most compounds with multiple single-bonded oxygens on a single carbon it is unstable. Through this
intermediate, though, resonance-stabilized carbonate ions are produced. Some important minerals are
carbonates, notably calcite.
Carbon disulfide (CS2) is similar.
Nevertheless, due to its physical properties and its association with organic synthesis, carbon disulfide is
sometimes classified as an organic solvent.
The other common oxide is carbon monoxide (CO). It is formed by incomplete combustion, and is a colourless,
odourless gas. The molecules each contain a triple bond and are fairly polar, resulting in a tendency to bind
permanently to haemoglobin molecules, displacing oxygen, which has a lower binding affinity. Cyanide (CN−),
has a similar structure, but behaves much like a halide ion (pseudohalogen). For example, it can form the
nitride cyanogen molecule ((CN)2), similar to diatomic halides. Likewise, the heavier analog of
cyanide, cyaphide (CP−), is also considered inorganic, though most simple derivatives are highly unstable.
Other uncommon oxides are carbon suboxide (C3O2), the unstable dicarbon monoxide (C2O), carbon
trioxide (CO3), cyclopentanepentone (C5O5), cyclohexanehexone (C6O6), and mellitic anhydride (C12O9).
However, mellitic anhydride is the triple acyl anhydride of mellitic acid; moreover, it contains a benzene ring.
Thus, many chemists consider it to be organic.
With reactive metals, such as tungsten, carbon forms either carbides(C4−) or acetylides (C2−
2) to form alloys with
high melting points. These anions are also associated with methane and acetylene, both very weak acids. With
an electronegativity of 2.5, carbon prefers to form covalent bonds. A few carbides are covalent lattices,
like carborundum (SiC), which resembles diamond. Nevertheless, even the most polar and salt-like of carbides
are not completely ionic compounds
27

Organometallic compounds by definition contain at least one carbon-metal covalent bond. A wide range of such
compounds exist; major classes include simple alkyl-metal compounds (for example, tetraethyllead), η2-alkene
compounds ( for example, Zeise's salt ), and η3-allyl compounds (for example, allylpalladium chloride
dimer); metallocenes containing cyclopentadienyl ligands (for example, ferrocene); and transition metal carbene
complexes. Many metal carbonyls and metal cyanides exist (for example, tetracarbonylnickel and potassium
ferricyanide); some workers consider metal carbonyl and cyanide complexes without other carbon ligands to be
purely inorganic, and not organometallic. However, most organometallic chemists consider metal complexes
with any carbon ligand, even 'inorganic carbon' (e.g., carbonyls, cyanides, and certain types of carbides and
acetylides) to be organometallic in nature. Metal complexes containing organic ligands without a carbon-metal
covalent bond (e.g., metal carboxylates) are termed metalorganic compounds.
While carbon is understood to strongly prefer formation of four covalent bonds, other exotic bonding schemes
are also known. Carboranes are highly stable dodecahedral derivatives of the [B12H12]2- unit, with one BH
replaced with a CH+. Thus, the carbon is bonded to five boron atoms and one hydrogen atom. The cation
[(Ph3PAu)6C]2+ contains an octahedral carbon bound to six phosphine-gold fragments. This phenomenon has
been attributed to the aurophilicity of the gold ligands, which provide additional stabilization of an otherwise
labile species.[96] In nature, the iron-molybdenum cofactor (FeMoco) responsible for microbial nitrogen
fixation likewise has an octahedral carbon center (formally a carbide, C(-IV)) bonded to six iron atoms. In 2016,
it was confirmed that, in line with earlier theoretical predictions, the hexamethylbenzene dication contains a
carbon atom with six bonds. More specifically, the dication could be described structurally by the formulation
[MeC(η5-C5Me5)]2+, making it an "organic metallocene" in which a MeC3+ fragment is bonded to a η5-
C5Me5
− fragment through all five of the carbons of the ring.
This anthracene derivative contains a carbon atom with 5 formal electron pairs around it.
It is important to note that in the cases above, each of the bonds to carbon contain less than two formal electron
pairs. Thus, the formal electron count of these species does not exceed an octet. This makes them
hypercoordinate but not hypervalent. Even in cases of alleged 10-C-5 species (that is, a carbon with five ligands
and a formal electron count of ten), as reported by Akiba and co-workers , electronic structure calculations
conclude that the electron population around carbon is still less than eight, as is true for other compounds
featuring four-electron three-center bonding.
ORGANOMETALLIC
28

STEEL
• Steel is an alloy made up of iron with typically a few tenths of a percent of carbon to improve its strength and fracture
resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion-
and oxidation-resistant need typically an additional 11% chromium. Because of its high tensile strength and low cost, steel is
used in buildings, infrastructure, tools, ships, trains, cars, machines, electrical appliances, and weapons. Iron is the base metal of
steel. Depending on the temperature, it can take two crystalline forms (allotropic forms): body centred cubic and face centred
cubic. The interaction of the allotropes of iron with the alloying elements, primarily carbon, gives steel and cast iron their range of
unique properties.
• In pure iron, the crystal structure has relatively little resistance to the iron atoms slipping past one another, and so pure iron is
quite ductile, or soft and easily formed. In steel, small amounts of carbon, other elements, and inclusions within the iron act as
hardening agents that prevent the movement of dislocations.
• The carbon in typical steel alloys may contribute up to 2.14% of its weight. Varying the amount of carbon and many other
alloying elements, as well as controlling their chemical and physical makeup in the final steel (either as solute elements, or as
precipitated phases), slows the movement of those dislocations that make pure iron ductile, and thus controls and enhances its
qualities. These qualities include the hardness, quenching behaviour, need for annealing, tempering behaviour, yield strength,
and tensile strength of the resulting steel. The increase in steel's strength compared to pure iron is possible only by reducing
iron's ductility.
• Steel was produced in bloomery furnaces for thousands of years, but its large-scale, industrial use began only after more efficient
production methods were devised in the 17th century, with the introduction of the blast furnace and production of crucible steel.
This was followed by the open-hearth furnace and then the Bessemer process in England in the mid-19th century. With the
invention of the Bessemer process, a new era of mass-produced steel began. Mild steel replaced wrought iron. The German
states saw major steel prowess over Europe in the 19th century.
• Further refinements in the process, such as basic oxygen steelmaking (BOS), largely replaced earlier methods by further lowering
the cost of production and increasing the quality of the final product. Today, steel is one of the most common man made
materials in the world, with more than 1.6 billion tons produced annually. Modern steel is generally identified by various grades
defined by assorted standards organisations.
29

MATERIAL PROPERTIES
Iron is commonly found in the Earth's crust in the form of an ore, usually an iron oxide, such as magnetite or hematite. Iron is extracted from iron ore by removing the oxygen
through its combination with a preferred chemical partner such as carbon which is then lost to the atmosphere as carbon dioxide. This process, known as smelting, was first
applied to metals with lower melting points, such as tin, which melts at about 250 °C (482 °F), and copper, which melts at about 1,100 °C (2,010 °F), and the combination, bronze,
which has a melting point lower than 1,083 °C (1,981 °F). In comparison, cast iron melts at about 1,375 °C (2,507 °F). Small quantities of iron were smelted in ancient times, in the
solid-state, by heating the ore in a charcoal fire and then welding the clumps together with a hammer and in the process squeezing out the impurities. With care, the carbon
content could be controlled by moving it around in the fire. Unlike copper and tin, liquid or solid iron dissolves carbon quite readily.
All of these temperatures could be reached with ancient methods used since the Bronze Age. Since the oxidation rate of iron increases rapidly beyond 800 °C (1,470 °F), it is
important that smelting take place in a low-oxygen environment. Smelting, using carbon to reduce iron oxides, results in an alloy (pig iron) that retains too much carbon to be
called steel. The excess carbon and other impurities are removed in a subsequent step.
Other materials are often added to the iron/carbon mixture to produce steel with the desired
properties. Nickel and manganese in steel add to its tensile strength and make the austenite form of the iron-
carbon solution more stable, chromium increases hardness and melting temperature, and vanadium also increases
hardness while making it less prone to metal fatigue.
To inhibit corrosion, at least 11% chromium can be added to steel so that a hard oxide forms on the metal surface;
this is known as stainless steel. Tungsten slows the formation of cementite, keeping carbon in the iron matrix and
allowing martensite to preferentially form at slower quench rates, resulting in high-speed steel. The addition
of lead and sulfur decrease grain size, thereby making the steel easier to turn, but also more brittle and prone to
corrosion. Such alloys are nevertheless frequently used for components such as nuts, bolts, and washers in
applications where toughness and corrosion resistance are not paramount. For the most part, however, p-
block elements such as sulfur, nitrogen, phosphorus, and lead are considered contaminants that make steel more
brittle and are therefore removed from the steel melt during processing.
30

STEEL PROPERTIES
The density of steel varies based on the alloying constituents but usually ranges between 7,750 and 8,050 kg/m3 (484 and 503 lb/cu ft), or 7.75 and 8.05 g/cm3 (4.48 and 4.65 oz/cu in).
Even in a narrow range of concentrations of mixtures of carbon and iron that make steel, several different metallurgical structures, with very different properties can form. Understanding such properties is essential
to making quality steel. At room temperature, the most stable form of pure iron is the body- centered cubic (BCC) structure called alpha iron or α-iron. It is a fairly soft metal that can dissolve only a small
concentration of carbon, no more than 0.005% at 0 °C (32 °F) and 0.021 wt% at 723 °C (1,333 °F). The inclusion of carbon in alpha iron is called ferrite. At 910 °C, pure iron transforms into a face-centered cubic (FCC)
structure, called gamma iron or γ-iron. The inclusion of carbon in gamma iron is called austenite. The more open FCC structure of austenite can dissolve considerably more carbon, as much as 2.1% (38 times that of
ferrite) carbon at 1,148 °C (2,098 °F), which reflects the upper carbon content of steel, beyond which is cast iron. When carbon moves out of solution with iron, it forms a very hard, but brittle material called cementite
(Fe3C).
When steels with exactly 0.8% carbon (known as a eutectoid steel), are cooled, the austenitic phase (FCC) of the mixture attempts to revert to the ferrite phase (BCC). The carbon no longer fits within the FCC
austenite structure, resulting in an excess of carbon. One way for carbon to leave the austenite is for it to precipitate out of solution as cementite, leaving behind a surrounding phase of BCC iron called ferrite with a
small percentage of carbon in solution. The two, ferrite and cementite, precipitate simultaneously producing a layered structure called pearlite, named for its resemblance to mother of pearl. In a hypereutectoid
composition (greater than 0.8% carbon), the carbon will first precipitate out as large inclusions of cementite at the austenite grain boundaries until the percentage of carbon in the grains has decreased to the
eutectoid composition (0.8% carbon), at which point the pearlite structure forms. For steels that have less than 0.8% carbon (hypoeutectoid), ferrite will first form within the grains until the remaining composition
rises to 0.8% of carbon, at which point the pearlite structure will form. No large inclusions of cementite will form at the boundaries in hypoeuctoid steel. The above assumes that the cooling process is very slow,
allowing enough time for the carbon to migrate.
As the rate of cooling is increased the carbon will have less time to migrate to form carbide at the grain boundaries but will have increasingly large amounts of pearlite of a finer and finer structure within the grains;
hence the carbide is more widely dispersed and acts to prevent slip of defects within those grains, resulting in hardening of the steel. At the very high cooling rates produced by quenching, the carbon has no time to
migrate but is locked within the face-centered austenite and forms martensite. Martensite is a highly strained and stressed, supersaturated form of carbon and iron and is exceedingly hard but brittle. Depending on
the carbon content, the martensitic phase takes different forms. Below 0.2% carbon, it takes on a ferrite BCC crystal form, but at higher carbon content it takes a body-centered tetragonal(BCT) structure. There is no
thermal activation energy for the transformation from austenite to martensite.[clarification needed] Moreover, there is no compositional change so the atoms generally retain their same neighbours.
Martensite has a lower density (it expands during the cooling) than does austenite, so that the transformation between them results in a change of volume. In this case, expansion occurs. Internal stresses from this
expansion generally take the form of compression on the crystals of martensite and tension on the remaining ferrite, with a fair amount of shear on both constituents. If quenching is done improperly, the internal
stresses can cause a part to shatter as it cools. At the very least, they cause internal work hardening and other microscopic imperfections. It is common for quench cracks to form when steel is water quenched,
although they may not always be visible.
31

STEEL CLASSIFICATION
Upon Phases Upon Microstructures Upon classes Other iron-based
materials
32

PHASES
Ferrite Austenite
Cementite Graphite
Martensite
33

MICROSTRUCTURES
Spheroidite Pearlite Bainite
Ledeburite
Tempered
martensite
Widmanstätten
structures
34

CLASSES
Crucible steel Carbon steel Spring steel Alloy steel
Maraging
steel
Stainless steel
High-speed
steel
Weathering
steel
Tool steel
35

OTHER IRON-BASED
MATERIALS
Cast iron
Gray iron
White iron
Ductile iron
Malleable iron
Wrought iron
36

CARBON STEEL
Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by
weight. The definition of carbon steel from the American Iron and Steel
Institute (AISI) states:
• no minimum content is specified or required for chromium , cobalt , molybdenum
, nickel , niobium, titanium, tungsten, vanadium, zirconium, or any other element
to be added to obtain a desired alloying effect;
• the specified minimum for copper does not exceed 0.40 per cent;
• or the maximum content specified for any of the following elements does not
exceed the percentages noted: manganese1.65 per cent; silicon 0.60 per
cent; copper 0.60 per cent.
The term carbon steel may also be used in reference to steel which is not stainless
steel; in this use carbon steel may include alloy steels. High carbon steel has many
different uses such as milling machines, cutting tools (such as chisels) and high
strength wires. These applications require a much finer microstructure, which
improves the toughness.
As the carbon percentage content rises, steel has the ability to
become harder and stronger through heat treating; however, it becomes less ductile.
Regardless of the heat treatment, a higher carbon content reduces weldability. In
carbon steels, the higher carbon content lowers the melting point.
37

CARBON STEEL TYPES
MILD OR LOW-CARBON STEEL HIGH-TENSILE STEEL HIGHER-CARBON STEELS
38

MILD OR LOW-CARBON STEEL
• Mild steel (iron containing a small percentage of carbon, strong and tough but not readily tempered), also
known as plain-carbon steel and low-carbon steel, is now the most common form of steel because its price is
relatively low while it provides material properties that are acceptable for many applications. Mild steel contains
approximately 0.05–0.30% carbon making it malleable and ductile. Mild steel has a relatively low tensile strength,
but it is cheap and easy to form; surface hardness can be increased through carburizing.
• In applications where large cross-sections are used to minimize deflection, failure by yield is not a risk so low-
carbon steels are the best choice, for example as structural steel. The density of mild steel is approximately
7.85 g/cm3 (7850 kg/m3 or 0.284 lb/in3) and the Young's modulus is 200 GPa (29,000 ksi).
• Low-carbon steels display yield-point runout where the material has two yield points. The first yield point (or
upper yield point) is higher than the second and the yield drops dramatically after the upper yield point. If a low-
carbon steel is only stressed to some point between the upper and lower yield point then the surface
develops Lüder bands. Low-carbon steels contain less carbon than other steels and are easier to cold-form,
making them easier to handle. Typical applications of low carbon steel are car parts, pipes, construction, and
food cans.
39

HIGH-TENSIL STEEL
• High-tensile steels are low-carbon, or steels at the lower end of the medium-carbon range, which
have additional alloying ingredients in order to increase their strength, wear properties or
specifically tensile strength.
• These alloying ingredients include chromium, molybdenum, silicon, manganese, nickel,
and vanadium. Impurities such as phosphorus and sulfur have their maximum allowable content
restricted.
• 41xx steel
• 4140 steel
• 4145 steel
• 4340 steel
• 300M steel
• EN25 steel – 2.521% nickel-chromium-molybdenum steel
• EN26 steel
40

HIGHER-CARBON STEELS
Carbon steels which can successfully undergo heat-treatment have a carbon content in the
range of 0.30–1.70% by weight. Trace impurities of various other elements can have a
significant effect on the quality of the resulting steel. Trace amounts of sulfur in particular
make the steel red-short, that is, brittle and crumbly at working temperatures. Low-alloy
carbon steel, such as A36 grade, contains about 0.05% sulfur and melts around 1,426–
1,538 °C (2,599–2,800 °F). Manganese is often added to improve the hardenability of low-
carbon steels. These additions turn the material into a low-alloy steel by some definitions,
but AISI's definition of carbon steel allows up to 1.65% manganese by weight.
41

AISI CLASSIFICATION
Low-carbon steel
0.05 to 0.25% carbon (plain
carbon steel) content.
Medium-carbon steel
Approximately 0.3–0.5% carbon
content. Balances ductility and
strength and has good wear
resistance; used for large parts,
forging and automotive
components.
High carbon steel
Approximately 0.6 to 1.0%
carbon content. Very strong,
used for springs, edged tools,
and high-strength wires.
Ultra-high-carbon steel
Approximately 1.25–2.0%
carbon content. Steels that can
be tempered to great hardness.
Used for special purposes like
(non-industrial-purpose) knives,
axles, and punches. Most steels
with more than 2.5% carbon
content are made using powder
metallurgy.
42

HEAT TREATMENT
The purpose of heat treating carbon steel is to change the mechanical properties of steel, usually ductility, hardness, yield
strength, or impact resistance. Note that the electrical and thermal conductivity are only slightly altered. As with most
strengthening techniques for steel, Young's modulus (elasticity) is unaffected. All treatments of steel trade ductility for
increased strength and vice versa. Iron has a higher solubility for carbon in the austenite phase; therefore all heat
treatments, except spheroidizing and process annealing, start by heating the steel to a temperature at which the austenitic
phase can exist. The steel is then quenched (heat drawn out) at a moderate to low rate allowing carbon to diffuse out of
the austenite forming iron-carbide (cementite) and leaving ferrite, or at a high rate, trapping the carbon within the iron
thus forming martensite. The rate at which the steel is cooled through the eutectoid temperature (about 727 °C) affects
the rate at which carbon diffuses out of austenite and forms cementite. Generally speaking, cooling swiftly will leave iron
carbide finely dispersed and produce a fine grained pearlite and cooling slowly will give a coarser pearlite. Cooling a
hypoeutectoid steel (less than 0.77 wt% C) results in a lamellar-pearlitic structure of iron carbide layers with α-
ferrite (nearly pure iron) between. If it is hypereutectoid steel (more than 0.77 wt% C) then the structure is full pearlite with
small grains (larger than the pearlite lamella) of cementite formed on the grain boundaries. A eutectoid steel (0.77%
carbon) will have a pearlite structure throughout the grains with no cementite at the boundaries. The relative amounts of
constituents are found using the lever rule.
43

THE TYPES OF HEAT TREATMENTS POSSIBLE:
Spheroidizing
Full annealing
Process annealing
Isothermal annealing
Normalizing
Quenching
Martempering ( marquenching )
Tempering
Austempering
44

Spheroidizing
• Spheroidite forms when carbon steel is heated to
approximately 700 °C for over 30 hours. Spheroidite
can form at lower temperatures, but the time
needed drastically increases, as this is a diffusion-
controlled process. The result is a structure of rods
or spheres of cementite within primary structure
(ferrite or pearlite, depending on which side of the
eutectoid you are on). The purpose is to soften
higher carbon steels and allow more formability.
This is the softest and most ductile form of steel.
Full annealing
• Carbon steel is heated to approximately 40 °C above
Ac3 or Acm for 1 hour; this ensures all
the ferrite transforms
into austenite (although cementite might still exist if
the carbon content is greater than the eutectoid).
The steel must then be cooled slowly, in the realm
of 20 °C (36 °F) per hour. Usually it is just furnace
cooled, where the furnace is turned off with the
steel still inside. This results in a coarse pearlitic
structure, which means the "bands" of pearlite are
thick. Fully annealed steel is soft and ductile, with no
internal stresses, which is often necessary for cost-
effective forming. Only spheroidized steel is softer
and more ductile.
45

Process annealing
• A process used to relieve stress in a
cold-worked carbon steel with less
than 0.3% C. The steel is usually
heated to 550–650 °C for 1 hour,
but sometimes temperatures as
high as 700 °C. The image
rightward shows the area where
process annealing occurs.
Isothermal annealing
• It is a process in which
hypoeutectoid steel is heated
above the upper critical
temperature. This temperature is
maintained for a time and then
reduced to below the lower critical
temperature and is again
maintained. It is then cooled to
room temperature. This method
eliminates any temperature
gradient.
Normalizing
• Carbon steel is heated to
approximately 55 °C above Ac3 or
Acm for 1 hour; this ensures the
steel completely transforms to
austenite. The steel is then air-
cooled, which is a cooling rate of
approximately 38 °C (100 °F) per
minute. This results in a fine
pearlitic structure, and a more-
uniform structure. Normalized steel
has a higher strength than
annealed steel; it has a relatively
high strength and hardness.
46

Quenching
• Carbon steel with at least 0.4 wt% C is heated to normalizing
temperatures and then rapidly cooled (quenched) in water,
brine, or oil to the critical temperature. The critical
temperature is dependent on the carbon content, but as a
rule is lower as the carbon content increases. This results in a
martensitic structure; a form of steel that possesses a super-
saturated carbon content in a deformed body-centered
cubic (BCC) crystalline structure, properly termed body-
centered tetragonal (BCT), with much internal stress. Thus,
quenched steel is extremely hard but brittle, usually too
brittle for practical purposes. These internal stresses may
cause stress cracks on the surface. Quenched steel is
approximately three times harder (four with more carbon)
than normalized steel.
Martempering (marquenching)
• Martempering is not actually a tempering procedure, hence
the term marquenching. It is a form of isothermal heat
treatment applied after an initial quench, typically in a
molten salt bath, at a temperature just above the
"martensite start temperature". At this temperature, residual
stresses within the material are relieved and some bainite
may be formed from the retained austenite which did not
have time to transform into anything else. In industry, this is
a process used to control the ductility and hardness of a
material. With longer marquenching, the ductility increases
with a minimal loss in strength; the steel is held in this
solution until the inner and outer temperatures of the part
equalize. Then the steel is cooled at a moderate speed to
keep the temperature gradient minimal. Not only does this
process reduce internal stresses and stress cracks, but it also
increases the impact resistance.
47

Tempering
• This is the most common heat treatment
encountered, because the final properties can be
precisely determined by the temperature and
time of the tempering. Tempering involves
reheating quenched steel to a temperature
below the eutectoid temperature then cooling.
The elevated temperature allows very small
amounts of Spheroidite to form, which restores
ductility, but reduces hardness. Actual
temperatures and times are carefully chosen for
each composition.
Austempering
• The austempering process is the same as
martempering, except the quench is interrupted
and the steel is held in the molten salt bath at
temperatures between 205 °C and 540 °C, and
then cooled at a moderate rate. The resulting
steel, called bainite, produces an acicular
microstructure in the steel that has great
strength (but less than martensite), greater
ductility, higher impact resistance, and less
distortion than martensite steel. The
disadvantage of austempering is it can be used
only on a few steels, and it requires a special salt
bath.
48

CASE
HARDENING
Case hardening processes harden only the exterior
of the steel part, creating a hard, wear resistant skin
(the "case") but preserving a tough and ductile
interior. Carbon steels are not very hardenable
meaning they can not be hardened throughout
thick sections. Alloy steels have a better
hardenability, so they can be through-hardened
and do not require case hardening. This property of
carbon steel can be beneficial, because it gives the
surface good wear characteristics but leaves the
core flexible and shock-absorbing.
49

Forging temperature of steel
Steel type
Maximum forging temperature Burning temperature
(°F) (°C) (°F) (°C)
1.5% carbon 1920 1049 2080 1140
1.1% carbon 1980 1082 2140 1171
0.9% carbon 2050 1121 2230 1221
0.5% carbon 2280 1249 2460 1349
0.2% carbon 2410 1321 2680 1471
3.0% nickel steel 2280 1249 2500 1371
3.0% nickel–chromium steel 2280 1249 2500 1371
5.0% nickel (case-hardening) steel 2320 1271 2640 1449
Chromium-vanadium steel 2280 1249 2460 1349
High-speed steel 2370 1299 2520 1385
Stainless steel 2340 1282 2520 1385
Austenitic chromium–nickel steel 2370 1299 2590 1420
Silico-manganese spring steel 2280 1249 2460 1350
50

Cold forming or cold working is any metalworking process in which metal is shaped below its recrystallization
temperature, usually at the ambient temperature. Such processes are contrasted with hot working techniques
like hot rolling, forging, welding, etc.
Cold forming techniques are usually classified into four major groups: squeezing, bending, drawing, and
shearing. They generally have the advantage of being simpler to carry out than hot working techniques.
Unlike hot working, cold working causes the crystal grains and inclusions to distort following the flow of the
metal; which may cause work hardening and anisotropic material properties. Work hardening makes the
metal harder, stiffer, and stronger, but less plastic, and may cause cracks of the piece.
The possible uses of cold forming are extremely varied, including large flat sheets, complex folded shapes,
metal tubes, screw heads and threads, riveted joints, and much more.
COLD FORMING
Hot working refers to processes where metals are plastically deformed above
their recrystallization temperature. Being above the recrystallization temperature allows the
material to recrystallize during deformation. This is important because recrystallization keeps
the materials from strain hardening, which ultimately keeps the yield strength and hardness low
and ductility high. This contrasts with cold working.
Many kinds of working, including rolling, forging, extrusion, and drawing, can be done with hot
metal.
HOT FORMING
51

ADVANTAGES &
DISADVANTAGES OF
COLD WORKING
• No heating required
• Better surface finish
• Superior dimensional control
• Better reproducibility and interchangeability
• Directional properties can be imparted into the metal
• Contamination problems are minimized
Advantages of cold working over hot working include
• The metal is harder, calling for greater forces, harder tools and dies, and
heavier equipment
• The metal is less ductile and malleable, limiting the amount of
deformation that can be obtained
• Metal surfaces must be clean and scale-free
• May leave undesirable anisotropy in the final piece
• May leave undesirable residual stress in the final piece
• The need for heavier and equipment and harder tools may make cold
working suitable only for large volume manufacturing industry.
Some disadvantages and problems of cold working are:
52

ADVANTAGES &
DISADVANTAGES OF
HOT WORKING
• Decrease in yield strength, therefore it is easier to work and uses less
energy or force
• Increase in ductility
• Elevated temperatures increase diffusion which can remove or reduce
chemical inhomogeneities
• Pores may reduce in size or close completely during deformation
• In steel, the weak, ductile, face-centered-cubic austenite microstructure
is deformed instead of the strong body-centered-
cubic ferrite microstructure found at lower temperatures
Advantages of Hot working include
• Undesirable reactions between the metal and the surrounding
atmosphere (scaling or rapid oxidation of the workpiece)
• Less precise tolerances due to thermal contraction and warping from
uneven cooling
• Grain structure may vary throughout the metal for various reasons
• Requires a heating unit of some kind such as a gas or diesel furnace or
an induction heater, which can be very expensive
Disadvantages and problems of Hot working are:
53

COLD WORKING PROCESS
Squeezing:
• Rolling
• Swaging
• Extrusion
• Forging
• Sizing
• Riveting
• Staking
• Coining
• Peening
• Burnishing
• Heading
• Hubbing
• Thread rolling
Bending:
• Angle bending
• Roll bending
• Draw and compression
• Roll forming
• Seaming
• Flanging
• Straightening
Shearing
• Sheet metal shear-cutting
• Slitting
• Blanking
• Piercing
• Lancing
• Perforating
• Notching
• Nibbling
• Shaving
• Trimming
• Cutoff
• Dinking
Drawing
• Wire drawing
• Tube drawing
• Metal spinning
• Embossing
• Stretch forming
• Sheet metal drawing
• Ironing
• Superplastic forming
by: Mahmoud Galal Zidan 54

HOT
WORKING
PROCESSES
Rolling
• Hot rolling
Hot Spinning
Extrusion
Forging
Drawing
Rotary piercing
55

ROLLING PROCESSES
• Rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness,
to make the thickness uniform, and/or to impart a desired mechanical property. The concept is similar to the rolling of dough.
Rolling is classified according to the temperature of the metal rolled. If the temperature of the metal is above
its recrystallization temperature, then the process is known as hot rolling. If the temperature of the metal is below its
recrystallization temperature, the process is known as cold rolling. In terms of usage, hot rolling processes more tonnage
than any other manufacturing process, and cold rolling processes the most tonnage out of all cold working processes.
• Roll stands holding pairs of rolls are grouped together into rolling mills that can quickly process metal, typically steel, into
products such as structural steel (I-beams, angle stock, channel stock), bar stock, and rails. Most steel mills have rolling mill
divisions that convert the semi-finished casting products into finished products.
• There are many types of rolling processes:
1. Ring rolling.
2. Structure shape rolling
I. Forge rolling
II. Controlled rolling.
3. Roll bending.
4. Roll forming.
5. Flat rolling.
56

• Ring rolling is a specialized type of hot rolling that increases the
diameter of a ring. The starting material is a thick-walled ring. This
workpiece is placed between two rolls, an inner idler roll and
a driven roll, which presses the ring from the outside. As the rolling
occurs the wall thickness decreases as the diameter increases. The
rolls may be shaped to form various cross-sectional shapes. The
resulting grain structure is circumferential, which gives better
mechanical properties. Diameters can be as large as 8 m (26 ft) and
face heights as tall as 2 m (79 in). Common applications include
railway tyres , bearings , gears , rockets , turbines , airplanes , pipes,
and pressure vessels.
Ring Rolling
57

STRUCTURAL SHAPE ROLLING
•Controlled rolling is a type of thermomechanical processing which integrates controlled deformation and heat treating. The heat which brings the workpiece above the
recrystallization temperature is also used to perform the heat treatments so that any subsequent heat treating is unnecessary. Types of heat treatments include the production
of a fine grain structure; controlling the nature, size, and distribution of various transformation products (such as ferrite, austenite, pearlite, bainite, and martensite in steel);
inducing precipitation hardening; and, controlling the toughness. In order to achieve this the entire process must be closely monitored and controlled. Common variables in
controlled rolling include the starting material composition and structure, deformation levels, temperatures at various stages, and cool-down conditions. The benefits of
controlled rolling include better mechanical properties and energy savings.
Controlled rolling
•Forge rolling is a longitudinal rolling process to reduce the cross-sectional area of heated bars or billets by leading them between two contrary rotating roll segments. The
process is mainly used to provide optimized material distribution for subsequent die forging processes. Owing to this a better material utilization, lower process forces and
better surface quality of parts can be achieved in die forging processes.
•Basically, any forgeable metal can also be forge-rolled. Forge rolling is mainly used to preform long-scaled billets through targeted mass distribution for parts such as
crankshafts, connection rods, steering knuckles and vehicle axles. Narrowest manufacturing tolerances can only partially be achieved by forge rolling. This is the main reason
why forge rolling is rarely used for finishing, but mainly for preforming.
•Characteristics of forge rolling:
•high productivity and high material utilization
•good surface quality of forge-rolled workpieces
•extended tool life-time
•small tools and low tool costs
•improved mechanical properties due to optimized grain flow compared to exclusively die forged workpieces
Forge rolling
58

•Roll bending produces a cylindrical shaped product from plate or steel metals Roll forming, roll bending, or plate rolling is a continuous bending operation in
which a long strip of metal (typically coiled steel) is passed through consecutive sets of rolls, or stands, each performing only an incremental part of the bend,
until the desired cross-section profile is obtained.
Roll Bending
•Roll forming is ideal for producing parts with long lengths or in large quantities. There are 3 main processes: 4 rollers, 3 rollers and 2 rollers, each of which has
as different advantages according to the desired specifications of the output plate.
Roll Forming
•Flat rolling is the most basic form of rolling with the starting and ending material having a rectangular cross-section. The material is fed in between two rollers,
called working rolls, that rotate in opposite directions. The gap between the two rolls is less than the thickness of the starting material, which causes it
to deform. The decrease in material thickness causes the material to elongate. The friction at the interface between the material and the rolls causes the
material to be pushed through. The amount of deformation possible in a single pass is limited by the friction between the rolls; if the change in thickness is too
great the rolls just slip over the material and do not draw it in.
•The final product is either sheet or plate, with the former being less than 6 mm (0.24 in) thick and the latter greater than; however, heavy plates tend to be
formed using a press, which is termed forging, rather than rolling. Often the rolls are heated to assist in the workability of the metal. Lubrication is often used to
keep the workpiece from sticking to the rolls. To fine-tune the process, the speed of the rolls and the temperature of the rollers are adjusted.
•h is sheet metal with a thickness less than 200 μm (0.0079 in). The rolling is done in a cluster mill because the small thickness requires a small diameter rolls. To
reduce the need for small rolls pack rolling is used, which rolls multiple sheets together to increase the effective starting thickness. As the foil sheets come
through the rollers, they are trimmed and slitted with circular or razor-like knives. Trimming refers to the edges of the foil, while slitting involves cutting it into
several sheets. Aluminum foil is the most produced product via pack rolling. This is evident from the two different surface finishes; the shiny side is on the roll
side and the dull side is against the other sheet of foil.
Flat Rolling
59

HOT & COLD ROLLING
Hot rolling is a metalworking process that occurs above the recrystallization
temperature of the material. After the grains deform during processing, they
recrystallize, which maintains an equiaxed microstructure and prevents the metal
from work hardening. The starting material is usually large pieces of metal, like semi-
finished casting products, such as slabs, blooms, and billets. If these products came
from a continuous casting operation, the products are usually fed directly into the
rolling mills at the proper temperature. In smaller operations, the material starts at
room temperature and must be heated. This is done in a gas- or oil-fired soaking pit for
larger workpieces; for smaller workpieces, induction heating is used. As the material is
worked, the temperature must be monitored to make sure it remains above the
recrystallization temperature. To maintain a safety factor a finishing temperature is
defined above the recrystallization temperature; this is usually 50 to 100 °C (90 to
180 °F) above the recrystallization temperature. If the temperature does drop below this
temperature the material must be re-heated prior to additional hot rolling.
Hot-rolled metals generally have little directionality in their mechanical properties or
deformation-induced residual stresses. However, in certain instances non-metallic
inclusions will impart some directionality and workpieces less than 20 mm (0.79 in) thick
often have some directional properties. Non-uniform cooling will induce a lot of
residual stresses, which usually occurs in shapes that have a non-uniform cross-section,
such as I-beams. While the finished product is of good quality, the surface is covered
in mill scale, which is an oxide that forms at high temperatures. It is usually removed
via pickling or the smooth clean surface (SCS) process, which reveals a smooth surface.
Dimensional tolerances are usually 2 to 5% of the overall dimension.
Hot-rolled mild steel seems to have a wider tolerance for the level of included carbon
than does cold-rolled steel, and is, therefore, more difficult for a blacksmith to use. Also
for similar metals, hot-rolled products seem to be less costly than cold-rolled ones.
Hot rolling is used mainly to produce sheet metal or simple cross-sections, such as rail
tracks.
60

TYPICAL USES FOR HOT-ROLLED METAL
Truck frames
Automotive clutch
plates, wheels and
wheel rims
Pipes and tubes
Water heaters
Agricultural
equipment
Strappings
Stampings
61

SHAPE ROLLING DESIGN
• Rolling mills are often divided into roughing, intermediate and finishing rolling cages. During shape rolling, an initial billet
(round or square) with edge of diameter typically ranging between 100–140 mm is continuously deformed to produce a
certain finished product with smaller cross section dimension and geometry. Starting from a given billet, different
sequences can be adopted to produce a certain final product. However, since each rolling mill is significantly expensive (up
to 2 million euros), a typical requirement is to reduce the number of rolling passes. Different approaches have been
achieved, including empirical knowledge, employment of numerical models, and Artificial Intelligence techniques. Lambiase
et al. validated a finite element model (FE) for predicting the final shape of a rolled bar in round-flat pass. One of the major
concerns when designing rolling mills is to reduce the number of passes. A possible solution to such requirements is the slit
pass, also called split pass, which divides an incoming bar in two or more subparts, thus virtually increasing the cross
section reduction ratio per pass as reported by Lambiase. Another solution for reducing the number of passes in rolling
mills is the employment of automated systems for Roll Pass Design as that proposed by Lambiase and Langella.
subsequently, Lambiase further developed an Automated System based on Artificial Intelligence and particularly an
integrated system including an inferential engine based on Genetic Algorithms a knowledge database based on an Artificial
Neural Network trained by a parametric Finite element model and to optimize and automatically design rolling mills.
62

COLD ROLLING
Cold rolling occurs with the metal below its recrystallization temperature (usually at room temperature), which increases the strength via strain hardening up
to 20%. It also improves the surface finish and holds tighter tolerances. Commonly cold-rolled products include sheets, strips, bars, and rods; these products
are usually smaller than the same products that are hot rolled. Because of the smaller size of the workpieces and their greater strength, as compared to hot
rolled stock, four-high or cluster mills are used.[2] Cold rolling cannot reduce the thickness of a workpiece as much as hot rolling in a single pass.
Cold-rolled sheets and strips come in various conditions: full-hard, half-hard, quarter-hard, and skin-rolled. Full-hard rolling reduces the thickness by 50%,
while the others involve less of a reduction. Cold rolled steel is then annealed to induce ductility in the cold rolled steel which is simply known as a Cold
Rolled and Close Annealed. Skin-rolling, also known as a skin-pass, involves the least amount of reduction: 0.5–1%. It is used to produce a smooth surface, a
uniform thickness, and reduce the yield point phenomenon (by preventing Lüders bands from forming in later processing). It locks dislocations at the surface
and thereby reduces the possibility of formation of Lüders bands. To avoid the formation of Lüders bands it is necessary to create substantial density of
unpinned dislocations in ferrite matrix. It is also used to break up the spangles in galvanized steel. Skin-rolled stock is usually used in subsequent cold-
working processes where good ductility is required.
Other shapes can be cold-rolled if the cross-section is relatively uniform and the transverse dimension is relatively small. Cold rolling shapes requires a series
of shaping operations, usually along the lines of sizing, breakdown, roughing, semi-roughing, semi-finishing, and finishing.
If processed by a blacksmith, the smoother, more consistent, and lower levels of carbon encapsulated in the steel makes it easier to process, but at the cost
of being more expensive.
Typical uses for cold-rolled steel include metal furniture, desks, filing cabinets, tables, chairs, motorcycle exhaust pipes, computer cabinets and hardware,
home appliances and components, shelving, lighting fixtures, hinges, tubing, steel drums, lawn mowers, electronic cabinetry, water heaters, metal containers,
fan blades, frying pans, wall and ceiling mount kits, and a variety of construction-related products.
63

64
Annealing, also described in the earlier section, is part of the manufacturing process of cold-formed steel sheet. It is a heat treatment technique that alters the
microstructure of the cold-reducing steel to recover its ductility.
Hot rolled Cold rolled
Material
properties
Yielding strength
The material is not deformed; there is no initial strain in
the material, hence yielding starts at actual yield value as
the original material.
The yield value is increased by 15%–30% due to
prework (initial deformation).
Modulus of elasticity 29,000 ksi 29,500 ksi
Unit weight Unit weight is comparatively huge. It is much smaller.
Ductility More ductile in nature. Less ductile.
Design
Most of the time, we consider only the global buckling of
the member.
Local buckling, Distortional Buckling, Global Buckling
have to be considered.
Main uses
Load bearing structures, usually heavy load bearing
structures and where ductility is more important (
Example Seismic prone areas)
Application in many variety of loading cases. This
includes building frames, automobile, aircraft, home
appliances, etc. Use limited in cases where high ductility
requirements.
Flexibility of
shapes
Standard shapes are followed. High value of unit weight
limits the flexibility of manufacturing wide variety of
shapes.
Any desired shape can be molded out of the sheets.
The light weight enhances its variety of usage.
Economy
High Unit weight increases the overall cost – material,
lifting, transporting, etc. It is difficult to work with (e.g.
connection).
Low unit weight reduces the cost comparatively. Ease of
construction (e.g. connection).
Research
possibilities
In the advanced stages at present.
More possibilities as the concept is relatively new and
material finds wide variety of applications.
Hot-rolled versus cold-rolled steel and the influence of annealing

Carbon Steel from 0 to Z ( Industrial Chemistry ) Part 1

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