2. INTRODUCTION
o Steel forms an intermediate stage between cast- iron and wrought-iron.
o Cast- Iron contains 2-4% of carbon.
o Wrought- Iron contains max. .15% of carbon.
o In steel carbon content varies from 0.25% to 1.50%.
o The carbon content in excess does not combine with iron and remain as free
graphite. If there is no free graphite than it is steel. Presence of free graphite
indicates cast-iron.
o With the increase in carbon content steel becomes harder and tougher.
o The cast iron can take up only compressive stresses, while wrought – iron is of
fibrous nature and is suitable to resist tensile stresses.
o On the other hand, steel is equally strong in compression as well as tension.
o There are two main categories of steel:
Mild Steel
Hard steel
3. PROPERTIES OF STEEL
Properties of Mild Steel
o Readily forged and welded.
o Magnetised permanently
o Cant be easily hardened and
tempered
o Fibrous Structure
o Malleable and Ductile
o Not easily attacked by salt water.
o Tougher and elastic
o Rust easily
Properties of Hard Steel
o Granular structure
o Tougher and elastic than mild steel
4. MANUFACTURING OF STEEL
Two major steel producing industries in
India :
1.)SAIL-(Steel Authority Of India
Limited)
2.) TATA Steel
Manufacture
Some of the technological options of
converting iron ore into steel products is
schematically shown in the next slide.
Hot metal and crude still process are also
interlinked among themselves and
represented by arrows.
5. THE ELECTRIC ARC FURNACE
o The electric arc furnace as the name suggests is a furnace
in which heat is generated with the aid of electric arc
produced by graphite electrodes.
o The main components of the electric arc furnace are :
a) Furnace shell with tapping device and work opening
b) Removable roof with the electrodes
c) Tilting device
o Normally, the furnace is charged with its roof removed.
When scrap is added, a charging bucket travels over the
furnace, the bottom opens and the scrap is charged into
the furnace within a few minutes.
o During the process, a control system advances the slow
burning electrodes. High voltage is transformed into low
voltage and high amperage. The most important
parameter for the efficiency of an electric arc furnace is
the "specific apparent power of the transformer" - Values
range from 300 to 750 kVA/t (kilo-volt-ampere per
tonne). In some cases, as much as 1,000 kVA/t has been
installed.
7. The electric arc furnace process generally follows the
following pattern:
o ChargingMeltingOxidisingDeoxidising or refining-
Besides scrap or sponge iron, the charge also includes the
ores, fluxes (lime, flourspar), reducing agents (carbon)
and alloying elements in the form of ferroalloys. These
can be added through the work opening before or during
oxidizing.
o Process begins with the ignition of the electric arc. After
melting, further scrap can be added. An additional
injection of oxygen or some other fuel-gas mixture can
accelerate the melting phase.
o The maximum transferable electric power and the heat
stability of the refractory lining determine the time needed
for melting. The most up-to-date furnaces with a hi
specific apparent power (UHP furnaces) achieve melting
periods of about 40 to 60 minutes and tap-to-tap times of
about 1.5 hours.
o During the refining stage, iron oxides included in the slag
react with the carbon of the bath. This gives rise to the
gaseous carbon monoxide, which causes the heat to boil,
and rinses impurities such as phosphorus, hydrogen,
nitrogen and non-metallic compounds from the heat.
These impurities escape as gases or are included in the
slag. Sulphur cannot be completely eliminated.
THE MELTING
PROCESS
8. MARKET FORMS OF STEEL
o ANGLE SECTIONS:
• It could be of EQUAL or UNEQUAL LEGS.
EQUAL ANGLE SECTIONS are
available variable sizes :
20mm x 20mm x 3mm - 200mm x
200mm x 25mm.
UNEQUAL ANGLE SECTIONS are
available in variable sizes :
30mm x 20mm x 3mm – 200mm x 150mm x
18mm.
• These are used in structural steel work, in
construction of steel roof trusses, and filler
joists floor .
9. MARKET FORMS OF STEEL
o CHANNEL SECTIONS:
• These consist of a web with two equal
flanges .
• These are available in sizes varying from
100mm x 45mm - 400mm x 100mm.
• These are widely used as structural members
of steel framed structures.
o CORRUGATED SHEETS:
• Formed by passing steel sheets through
grooves , that bend and press steel sheets
forming corrugations on the sheets .
• These are galvanized and referred as G.I.
sheets.
• Used for roof coverings.
10. MARKET FORMS OF STEEL
o EXPANDED METAL:
• Available in variable shapes and sizes, and
is prepared from sheets of mild steel.
• Diamond mesh appearance through out the
area of the sheet.
• Widely used for reinforcing concrete in
foundations, roads, floors etc and as lathing
material and for partitions.
o FLAT BARS:
• Available in suitable widths varying from
10mm – 400mm with thickness varying
from 3mm – 40mm.
• Used in steel grill work for windows and
gates.
11. MARKET FORMS OF STEEL
o I – SECTIONS:
• Also called rolled steel joists or beams.
• Available in various sizes varying from
75mm x 50mm – 600mm x 210mm.
• R.S. joists are economical in material and
suitable for floor beams, lintels, columns,
etc.
o PLATES:
• Available in thickness varying from 5mm x
50mm .
• Used to connect steel beams for extension of
length, to serve as tensional members of steel
roof truss and to form built up sections of a
steel.
12. MARKET FORMS OF STEEL
o RIBBED TOR STEEL BARS:
• They are produced by controlled cold twisting
of hot rolled bars.
• Used for major types of reinforces concrete
structures.
• Available in sizes varying from 6mm – 50mm
dia.
o ROUND BARS:
• Available in circular cross section with dia.
Varying from 5mm – 250mm.
• Used as reinforcement in concrete structures,
construction of steel grill work, etc.
13. MARKET FORMS OF STEEL
o SQUARE BARS:
• Available in square cross section, with sides
varying from 5mm – 250mm.
• Used in construction of steel grill work, for
windows and gates.
o T – SECTION:
• Available in sizes varying from 20mm x
20mm x 3m – 150mm x 150mm x 10mm.
• Use as members of steel roof trusses and to
form built-up sections.
14. MECHANICAL TREATMENT OF STEEL
o The purpose of giving mechanical treatment to the steel is to give desired shape to
the ingots, so as to make steel available in market forms.
o Following are the operations involved in the treatment process:
DRAWING:
• It is carried out to reduce the cross section and increase the length
proportionately.
• In this operation metal is drawn through especially shaped tool.
• Drawing is continued till wire of required dia. Or cross section is obtained.
• This process is used to prepare wires and rods.
FORGING:
• This is carried out by repeated blows under a power hammer.
• The metal is heated above the critical temperature range, is then placed on
anvil & is subjected to blows of hammer.
• It increases the density and improves grain size of metal.
15. MECHANICAL TREATMENT OF STEEL
PRESSING:
• A slow process and carried out in an equipment known as press.
• Advantage: It does not involve any shock.
• Press consist of a die and a punch, are suitably shaped to get article of desired
shape.
• The metal is pressed between a die and a punch, under a heavy pressure to obtain
the article of desired shape.
• Economical when produced in bulk.
ROLLING:
• Carried out in rolling mills.
• The ingots, while still red got, are passed in succession through different rollers
until desired shape is achieved.
• The various forms are obtained by the process of rolling.
• It is also possible to prepare joint less pipe.
