Metals are the backbone of all
engineering projects and products.
Various metals are used in one form or
the other. Metals are found as
oxides, sulphates, carbonates, phosphat
es etc. in nature.
These compounds are known as ores.
Ores are treated to remove the
impurities and get the metal .
•Metals are… Solid at room temperature,
except mercury, which is liquid
•Metals have… very high melting point.
•Metals are… shiny when they cut.
•Metals are… good conductors of heat and
•Metals are… usually strong & malleable so
they can be hammered into
Ferrous Non-Ferrous Alloys
Containing iron & Do not contain iron. A mixture of
almost all are e.g. aluminium, metals, or a
magnetic. copper, silver, gold, metal & small
e.g. mild-steel, lid, tin etc. amount of
cast-iron, tool- other substance
Ferrous Alloys Non-Ferrous Alloys
e.g. e.g. brass (copper + zinc)
stainless steel bronze (copper + tin )
steel + chromium
OCCURRENCE OF IRON
Iron is never available pure in nature. It has
to be extracted in the form of pig iron from
the various iron ores.
Pig iron is the crudest and wrought iron is
the purest form of iron.
The ores from which iron is extracted are:
i. Magnite : it contains 70 to 75% iron.
ii. Haematite : It has about 70% iron.
iii. Iron Pyrites: It has about 47% iron.
iv. Siderite: It contains 40% iron
To remove impurities from the iron ore carbon
and flux are added while melting it.
The refined product so obtained is the crudest
form of iron and is called pig iron. It is cast into
rough bars called pigs.
It is hard and brittle as such it is neither ductile
It is difficult to bend.
It melts easily. The fusion temperature is 1200 o
It can be hardened but not tempered.
It can be magnetized.
It has very high compressive strength but
very weak in tension.
It does not rust.
It cannot be welded.
USES: cast iron, wrought iron and mild steel
are obtained by refining the pig iron.
Because of its high compressive strength it
is used in columns, base plates, door
brackets , wheel and pipe work.
Pig iron is remelted with limestone and
coke and poured into moulds of desired
shapes and sizes to get purer product
known as cast iron.
Moulding remelted pig iron removes
impurity and gives a more uniform
Carbon contents in cast iron vary from 2
Its structure is coarse crystalline and fibrous.
Freshly fractured surface has grayish white
It is brittle.
It cannot withstand shocks and impacts.
It cannot be welded.
It cannot be magnetized.
It does not rust.
It is fairly hard and cannot be worked with a
It is used for casting, rain water
pipes, gratings, railings, balustrades(
staircase side railing).
Because of high compressive strength it
is used in making columns, supports for
heavy machinery, carriage wheels etc.
It is the basic material for the
manufacturing of Wrought iron and
If all the carbon and other elements in pig
iron are oxidized and may be left with 0.25
percent of carbon then we obtain wrought
It is by far the purest form of iron in which
the total impurities do not exceed 0.5%.
Its structure is fibrous and has silky luster.
It is ductile and malleable.
It is tough and can withstand shocks and
impact better than cast iron.
It can be forged and welded.
It rusts easily
It is unaffected by saline water.
It cannot be permanently magnetized.
It is used in making roofing
sheets, corrugated sheets, rods, gas and
water pipes, boiler tubes and ornamental
iron works such as grills gates and railing
and window guards.
The essential difference between cast iron and
steel is the amount of their carbon contents.
Steel goes on becoming harder and tougher
with the increase in its carbon contents.
Up to a content of 1.5% all the carbon gets
into chemical combination with iron and none
of its exist in free state.
If carbon contents increase beyond 1.5% then
it does not combine with iron and is present as
free graphite. At this stage metals falls in a
category of cast iron.
For a material to be classified as steel
there should be no free graphite in its
If there is any free graphite in it then it
falls in the category of cast iron.
Depending upon carbon content steel is
classified into following categories.
1. Dead steel < 0.15%
2. Mild steel 0.15 to
3. Medium carbon steel 0.3 to 0.8%
4. High carbon steel 0.8 to 1.5%
High carbon steel with carbon percentage over
1% is also known as cast steel or carbon tool
Steel where carbon content is 0.15 to
0.3% is called mild steel, low carbon
steel or soft steel.
It is ductile and malleable.
It is more tough and more elastic than
wrought iron and cast iron. It corrodes
It is equally strong in tension and
1. In construction work it is chiefly used as
rolled structural sections like I-section, T-
section, angle iron.
2. Mild steel round bars are extensively being
used as reinforcement in reinforced cement
3. Plain and corrugated sheets of mild steel are
used as roof covering.
4. It is also used in the manufacturing of
various tools and equipments, for rail track,
transmission towers and industrial building.
HIGH CARBON STEEL
In this steel the carbon contents is
between 0.55 to 1.5%. High percentage
of carbon in it renders it harder and
It is more tough and elastic then mild
Comparatively it is more stronger in
compression than in tension.
It withstand shocks and vibrations
HIGH CARBON STEEL
1. It is used in making tools such as
drills, files and chisels.
2. Fine quality of cutlery is made of high
3. It is used to manufacture those parts of
machinery that need a
hard, tough, durable material capable of
withstanding shocks and vibration
HIGH TENSION STEEL
It is essentially a low carbon steel and the
percentage of carbon is kept lesser than
0.15%. It is also termed as high tension steel.
Because of increase tensile strength, lesser
weight of it used, as compared to mild steel at
the same job. The structure thus becomes
It withstand atmospheric corrosion better. It is
tougher and more elastic. It is more brittle and
less ductile then mild steel.
High tension steel wires are extensively used
in reinforcing prestressed concrete structures.
Plain cement concrete being strong in
compression but weak in tension.
Mild steel or high tension steel is
embedded as reinforcement in the
concrete to make it stronger in tension.
Though flats and square bars can be
used as reinforcement yet the round
bars are extensively used for the
RUSTING & CORROSION
Rusting is just oxidation of iron at the
surface. This process is activated by the
presence of moisture and carbon
Atmospheric pollution also accelerates
Corrosion is slow but steady eating
away of metal and is a consequence of
Following method could gainfully be
adopted to minimize rusting and corrosion.
Iron is dipped in hot coal tar so that a film
of it sticks to the surface which protects the
surface from rusting and corrosion.
Pipes or ends of poles to be embedded in
earth are usually given this protective
Paints usually the lead paints are applied on
the surface to be protected.
Exposed metal surfaces as in case of roof
trusses and bridge structure are given this
treatment which have to be repeated after
regular interval of time.
Enamellings provides better and long life
protection as compared to painting. This
treatment is given only to smaller surface.
depositing a thin film of zinc on the
iron/steel surface is termed as galvanizing.
The surface to be galvanized is first
cleared from all foreign materials by giving
it an acid wash to be followed by wash of
The surface is then dried and dipped in molten zinc.
The fine film of zinc that gets deposited protects the
surface from contact with atmosphere and
Surface to be treated is cleaned of all foreign deposits
by acid wash and then with clean water. It is then
dried and covered with zinc dust and enclosed in
steel boxes to be heated in furnace under controlled
temperature. Molten zinc spreads over the whole
surface and on cooling forms a thin protective layer.
Sheradising gives better protection then galvanizing.
After cleaning the surface with acid wash followed
by clean water and drying in is dipped in a bath
of molten tin. A protective layer is left on the
By the process of electrolysis a thin film of
nickel, chromium, cadmium, copper, zinc is
deposited on the surface to be protected.
The surface to be protected is made the
cathode and the metal to be deposited is made
Metals are joined together by any one of the
It is the method of joining two metal surfaces
by means of low melting alloy of lead and tin
(usually mixed in the ratio of 1:2),
This alloy known as solder melts and adheres
to the surfaces to be joined. It only serves to
fill up the joint.
It is similar to the operation of soldering but
is done at much higher temperature ( from
650 to 1100 C).
It consist of mixture of 1 part of tin, 3 parts
of zinc and four parts of copper. The
brazing solder is applied to the joint in the
presence of borax.
It is used in joining together iron, copper,
brass and gun metal
Two methods of welding:
By Pressure Welding
It can be applied to mild steel and
wrought iron with low carbon and silicon
content may be used to join the metal. In
it the surfaces to be joined are heated to
such a temperature as to render them
plastic and then pressure is applied to
join the metals.
By Fusion Welding:
In this welding the surfaces to be weld are
brought near to each other and then
locally heated either by gas or by
electric spark until the surfaces are melt.