Material Technology

Steel Making process

Dr. Mahendra S. Gaikwad

Department Of Chemical Engineering
NIT Raipur

Steel making process

1. Bessemer process
2. Open hearth process
3. L-D process
4. Electric process
5. Crucible process
6. Cementation process

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Blast furnace

The Blast Furnace is a large steel structure about 30

metres high.
It is lined with refractory firebricks that can withstand
temperatures approaching 2000oC.
Pre-heated air at about 1000oC is blasted into the furnace
through nozzles near its base.
Modern blast furnaces range in hearth diameters of 6 to
14 m (20 to 45 feet),
Raw materials: ore, coke and flux called as charge.
Capacity: 1,000 to almost 10,000 tons of pig iron daily.

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Molten iron (pig iron) can be used in many ways:

Cast in pig bed

Cast in pig casting machine

Transferred in hot metal ladles direct to an adjacent steel

making process.

Bessemer process

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Bessemer process…
‘Sir Henry Bessemer’ invented
and patented the process in
1856.
Bessemer process is done in
‘Bessemer converter’.
It is a special type of furnace
with refractory linings.
Refractory linings: based on
acidic or basic process.

Bessemer process…
Construction…
◦ A special furnace named Bessemer converter is used
having shape like concrete mixer.
◦ It is wide at bottom and narrow at top.
◦ Mounted on two horizontal trunnions to tilt or rotate at
suitable angle.
◦ Tuyeres are provided at bottom to blow air from air
duct through pig iron.
◦ The converter is made of steel plates lined with
refractory material based on type of process.
Continue….

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 Bessemer process…
◦ In acid process, the lining material used is acidic in nature like
clay, quartz, silica brick etc.
◦ It is adopted when iron ore contain very small amount of
sulphur and phosporus.
◦ Acid process does not remove sulphur and phosporus.

◦ In basic process, the lining material used is basic in nature like

lime, magnesia and dolomite.
◦ It is adopted when iron ore contain any type of impurities.
◦ Basic process is able to remove phosphorus and Sulphur upto
some extent.

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 Bessemer process…
Working….
◦ Converter is tilted and charged with molten pig iron from cupola
or blast furnace.

◦ Converter is brought in upright position and a blast of hot air is

forced through tuyeres.

◦ Air passes through the molten pig iron and oxidizes the impurities
of pig iron and reddish yellow flame is seen at nose of converter.

◦ Impurities oxidizes are Si, C, Mn, P and S within 10 to 15 minutes

loud roaring sound of flame.
◦ When the intensity of the flame has reduced considerably, blast is
shut off and some amount of extraneous material is added to get
desired quality.

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Continue….

Bessemer process…
Working….
◦ Material added are deoxidizer and quality makers like
ferromanganese, ferrosilicon, aluminum etc.

◦ At last, converter is tilted in discharge position and

molten metal is carried into containers.

◦ Molten metal is then poured into large rectangular

mould to solidify.

◦ Solidified mass is known as “ingot” which are further

treated to form commercial pattern.

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 Open hearth process

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Open hearth process

Started in 1865 closed by the early 1990s

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Open hearth process (Fig. reference Encylopedia Britannica )

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The scrape iron, pig iron, steel and iron oxide, limestone is
melted into furnace.

The metal lies into shallow pool on the furnace bottom or

hearth.

The furnace is surrounded by a roof and walls of refractory

bricks.
The charge is added through charging door.
Heated to 1600 oC to 1650 oC by radiation heat.
Heat is generated by burning gaseous fuel.
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A mixture of preheated heat and gas is allowed to pass

over the hearth.

So mixture catches the fire and produce intense heat

and impurities of metal are oxidized.

As the impurities are brought down to the required

level, the metal is tapped off through tap hole.

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Addition of ferrous manganese and ferrous silicon is to
made steel of required quality.
and later aluminium is added to deoxidize the metal
further to make steel of required quality

Acid slag cannot remove the phosphorus.

Basic practice: a manganese lining is done and limestone is

added with the charge.

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Molten metal is poured into moulds for forming ingots.

Ingots are further treated to form commercial pattern.
Advantages:
1. Basic slag obtained from process contain phosphorus
so it is used as a good fertilizer in powder form.
2. Great economy can be achieved by providing
regenerative chambers on either side of the hearth.
3. The operation involved in process are simple.

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4. This process makes it possible to utilize a high
percentage of scrap which is converted to new useful
steel by this process.

5. Steel manufactured by this process is homogeneous

in nature.

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L-D Process

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L-D process…
L-D process is the latest development in steel making
processes (in the year 1949)
It is modification of Bessemer process.
It is named as Linz-Donawitz process as it was invented in
Austria and adopted in two towns – Linz and Donawitz.
In this process, pure oxygen (99.5%) is used instead of air.
Air contains O2 and N2, so steel obtained from Bessemer
process contains N2 which makes steels more brittle.

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L-D process…
L-D Converter is made from steel and the height of vessel is
ranged from 7-10 m.
In L-D converter, a jet of pure oxygen is blown at high
pressure and extraordinary speed (super sonic speed) on
molten metal.
A water cooled lance is used to blow O2.
The intense heat is produced (2500 to 3000oC) which burns
away the impurities of metal and produce highly low &
pure carbon steel.
The process is very economical in initial cost and
maintenance cost.

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L-D process…
The blowing time is also less in this process compare to
Bessemer (about 18 to 20 percent).
Capacity of L-D converter is to produce about 40 tonnes of
steel per 40 minutes or so.
Disadvantages
• An oxygen plant is required to prepare Oxygen
• Can not treat all types and grade of pig iron
• Not possible to control temperature precisely

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Steps of L-D Process:

1. Charging
Pig iron + Scrap iron (30 – 33 %)
Flux: limestone and dolomite
2. Blowing: Pure oxygen using 99.5 % pure oxygen.
After charging vessel is turned upright and lance
is lowered to blowing position (1200 mm above
the molten layer).
Pure oxygen is fed at 9-11 atm which raises the
temperature about 2500 C to 3000 C (this burns
off impurities).
This blast for 15 – 20 min.
Blowing time reduced by 18 % because of scrap iron)

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3. Sampling
Thermocouple is inserted by turning converter
horizontal to check temperature.
The sample is taken out same time and analysed.

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4. Tapping:
If analysis result is appreciable than iron is tapped off
into ladle.
Alloying materials are added into ladle.

Time is around 40 – 50 min.

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5. Slag off:
At last the slag is taken out from converter into slag pot.

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Electric process

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 Electric arc furnace
Electricity is solely used for heating the mixture, it do not alter the
properties of steel.
The first successful and operational furnace was invented by James
Burgess Readman in Edinburgh, Scotland in 1888 and patented in
1889. In the 19th century, a number of people had employed an
electric arc to melt iron.

Major advantages:
1. It generate extremely high temperature about 2000 oC
2. This facilitate the removal of impurities from the molten iron.
3. The temperature can be easily controlled and regulated.
4. It also permit the addition of variety of additives such as
chromium, nickel, tungsten, etc.
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High grade steel are made using electric furnaces only.

Both acidic and basic process are used based on lining of furnace.

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 • Consist of steel shell lined with refractory materials.

• It has removable roof through which carbon or graphite

electrode (2 m long) are inserted.

• Graphite rods are highly resistant to current and are very

durable at high temperature.

• However they are highly expensive than carbon electrodes.

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working
• The electrode are lowered into the furnace and current is switched
on.
• The heat is generated with the spark between electrodes and
metallic charge (electric arcs are formed between electrodes and
surface of metals.)
The electrodes are consumed during the operation and thereby become
shorter.
► The definite distance has to be maintained therefor control systems
are required
► Oxygen is blown into the scrap, which melt down the pig iron.
► Slag formation will take place which consists of metal oxides, acts as
a destination for oxidised impurities,

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► Once the fire stops, the steel is taken out from the converter
by turning it in horizontal position.

► Average 6 – 8 hours are required for one batch of steel.

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Crucible Process

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Crucible steel

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In Europe, crucible steel was developed by Benjamin Huntsman in

England in the 18th century.
Crucible steel is made by melting pig iron (cast iron), iron, and
sometimes steel, often along with sand, glass, ashes, and other
fluxes, in a crucible.
The steel was often much higher in carbon content and in quality
(lacking impurities) in comparison with other methods of steel
production of the time because of the use of fluxes.
The crucible process continued to be used for specialty steels, but
is today obsolete.
Now, Quality steels are made with an electric arc furnace.

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Cementation process

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 Cementation process
The cementation process is an obsolete technology for making steel by
carburization of iron.
It was apparently developed before the 17th century.
The process was patented in England by William Ellyot and Mathias Meysey
in 1614.
The process begins with wrought iron and charcoal.
It uses one or more long stone pots inside a furnace.
Typically, in Sheffield, each pot was 14 feet by 4 feet and 3.5 feet deep.
Iron bars and charcoal are packed in alternating layers, with a top layer of
charcoal and then refractory matter to make the pot or "coffin" airtight.
Some manufacturers used a mixture of powdered charcoal, soot and mineral
salts, called cement powder.
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