Uses Of Various Steel In Civil EngineeringBY:- Engr. Ahmad Sameer Nawab

Kardan University Kabul, Afghanistan

METALS Metals are the backbone of all engineering projects and products.

Various metals are used in one form or the other. Metals are found as compounds like oxides, sulphates, carbonates, phosphates 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 andelectricity.

•Metals are… usually strong & malleable so they can be hammered into

shape.

METALS CHARACTERISTICS

METALS

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

Steel etc.

Ferrous Alloys Non-Ferrous Alloyse.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

PIG 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.

Properties:

It is hard and brittle as such it is neither ductile nor malleable.

It is difficult to bend.

It melts easily. The fusion temperature is 1200 o C.

PIG IRON

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.

CAST IRON

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 product,

Carbon contents in cast iron vary from 2 to 4.5%.

CAST IRON

PROPERTIES:

Its structure is coarse crystalline and fibrous.

Freshly fractured surface has grayish white appearance.

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 hand file.

CAST IRON

USES:

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 steel.

WROUGHT IRON

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 iron.

It is by far the purest form of iron in which the total impurities do not exceed 0.5%.

PROPERTIES:

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.

WROUGHT IRON

It can be forged and welded.

It rusts easily

It is unaffected by saline water.

It cannot be permanently magnetized.

USES :

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.

Gates

Windows

Railings and fence

STEEL

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.

STEEL

For a material to be classified as steel there should be no free graphite in its composition.

If there is any free graphite in it then it falls in the category of cast iron.

CLASSIFICATION OF STEEL

Depending upon carbon content steel is classified into following categories.

Steel Carbon content

1. Dead steel < 0.15%

2. Mild steel 0.15 to 0.3%

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

MILD STEEL

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 easily.

It is equally strong in tension and compression.

MILD STEEL(USES)

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 concrete.

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.

T-section

I-section

Angle iron

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 tougher.

It is more tough and elastic then mild steel.

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 carbon steel.

3. It is used to manufacture those parts of machinery that need a hard, tough, durable material capable of withstanding shocks and vibration

Drills

Files

Chisels

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 lighter.

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.

REINFORCING STEEL

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 purpose