Manufacturing of Steel

Process involved in manufacturing

• Carbonization of COKE

• Blast furnace

• Basic Oxygen Steel making [BOS]

• Electric arc method

Carbonization of COKE

• Well graded coal is selected

• Heated or carbonized to COKE

• Heated coal is cooled

• And Proper COKE are fed into the Blast furnace for the farther process.

What is a Blast Furnace?

•The purpose of a blast furnace is to reduce and convert iron oxides into liquid iron called "hot metal".

•The blast furnace is a huge, steel stack lined with refractory brick.

•Iron ore, coke and limestone are put into the top, and preheated air is blown into the bottom.

Why does Iron have to be extracted in a Blast Furnace???

•Iron can be extracted by the blast furnace because it can be displaced by carbon.

•This is more efficient method than electrolysis because it is more cost effective

•Here the continues process can be achieved, i.e. Till the detoriation of refractory bricks occurs (nearly about 10 years)

Three substances are needed to enable to extraction of iron from its ore. The combined mixture is called the charge:

Iron ore, haematite - often contains sand with iron oxide, Fe2O3.

Limestone (calcium carbonate).

Coke - mainly carbon

The charge is placed a giant chimney called a Blast furnace. The blast furnace is around 30 metres high and lined with fireproof bricks. Hot air is blasted through the bottom.

The Method

•Oxygen in the air reacts with coke to give carbon dioxide:

C(s) + O 2(g) CO2(g)

•The limestone breaks down to form carbon dioxide:

CaCO3(s) CO2 (g) + CaO(s)

•Carbon dioxide produced in 1 + 2 react with more coke to produce carbon monoxide:

CO2(g) + C(s) 2CO(g)

Several reactions take place before the iron is finally produced...

• The carbon monoxide reduces the iron in the ore to give molten iron:

3CO(g) + Fe2O3(s) 2Fe(l) + 3CO2(g)

• The limestone from 2, reacts with the sand to form slag (calcium silicate):

CaO(s) + SiO(s) CaSiO3(l)

•Both the slag and iron are drained from the bottom of the furnace.

•The slag is mainly used to build roads.

•The iron whilst molten is poured into moulds and left to solidify - this is called cast iron and is used to make railings and storage tanks.

•The rest of the iron is used to make steel.

• Hot metal from the blast furnace and steel scrap are the principal materials used in Basic Oxygen Steel making (BOS)

• Modern furnaces, or ‘converters’ will take a charge of up to 350 tonnesand convert it into steel in around 15 minutes.

• A water-cooled oxygen lance is lowered into the converter and high-purity oxygen is blown on to the metal at very high pressure.

• The oxygen combines with carbon and other unwanted elements, eliminating them from the molten charge.

• These oxidation reactions produce heat, and the temperature of the metal is controlled by the quantity of added scrap.

• The carbon leaves the converter as a gas, carbon monoxide, which can, after cleaning, be collected for re-use as a fuel.

• lime is added as a flux to help carry off the other oxidized impurities as a floating layer of slag .

• the converter is tilted and the steel is tapped into a ladle. Typically, the carbon content of the steel at the end of refining is about 0.04%.

• uses only cold scrap metal.

• employed in making more widely used steels, including alloy and stainless grades as well as some special carbon and low-alloy steels.

• Modern electric arc furnaces can make up to 150 tonnes of steel in a single melt.

• The electric arc furnace consists of a circular bath with a movable roof, through which three graphite electrodes can be raised or lowered.

• At the start of the process, the electrodes are withdrawn and the roof swung clear. The steel scrap is then charged into the furnace from a large steel basket lowered from an overhead travelling crane.

• When charging is complete, the roof is swung back into position and the electrodes lowered into the furnace.

• A powerful electric current is passed through the charge, an arc is created, and the heat generated melts the scrap.

• Lime and fluorspar are added as fluxes and oxygen is blown into the melt. As a result, impurities in the metal combine to form a liquid slag.