A detailed description of the BASIC STEELMAKING PROCESS (BOS) which is, nowadays, the most common way to produce steel.

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BASIC OXYGEN
STEELMAKING
The Processing Route
BEGINNER LEVEL
Author: Eng. Matteo Sporchia
Copyright – P4S – PRODUCTS 4 STEELMAKING
All Rights Reserved

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SUMMARY
INTRODUCTION …………………………………………………………………………………. PAG. 3
BLAST FURNACE …………………………………………………………………………………. PAG. 4
BASIC OXYGEN FURNACE ………………………………………………………………….. PAG. 10
SECONDARY METALLURGY ……………………………………………………………….. PAG. 13
CONTINUOUS CASTING …………………………………………………………………….. PAG. 15

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INTRODUCTION
Nowadays, about 67% of the total worldwide crude steel production is made by a
Basic Oxygen Steelmaking processing route, which involves the following stages:
Ø BLAST FURNACE (BF)
Ø BASIC OXYGEN FURNACE (BOF)
Ø SECONDARY METALLURGY
Ø CONTINUOUS CASTING (CC)

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BLAST FURNACE (BF)
A typical blast furnace consists of a cylindrical steel shell lined with a refractory.
The shell is tapered at the top and at the bottom. The lower portion of the
furnace, called the bosh, is equipped with several tubular openings
or tuyeres through which the air blast is forced. Near the bottom of the bosh
there is a hole through which the molten pig iron flows when the furnace is
tapped, and above this hole, but below the tuyeres, there is another hole
for draining the slag. The top of the furnace, which is about 25-30 m in height,
contains vents for the escaping gases, and a pair of round hoppers closed with
bell-shaped valves through which the charge is introduced into the furnace. The
materials are brought up to the hoppers in small dump cars or skips that are
hauled up an inclined external skip hoist.
BLASTFURNACE-LAYOUT

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IRON ORE COKE
LIME
STONE
The basic materials used for the manufacture of pig iron (also
called hot metal) are iron ore, coke, and limestone. The coke
is burned as a fuel to heat the furnace; as it burns, the coke
gives off carbon monoxide, which combines with the iron
oxides in the ore, reducing them to metallic iron.
BLASTFURNACE–RAWMATERIALS

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The limestone in the furnace charge is used as an additional
source of carbon monoxide and as a “flux” to combine with
the infusible silica present in the ore to form fusible calcium
silicate. Calcium silicate plus other impurities form a slag
that floats on top of the molten metal at the bottom of the
furnace. Ordinary pig iron as produced by blast furnaces
contains about 92 % iron, 3 to 4 % carbon, 0.2 to 0.8 %
silicon, 0.25 to 2.5 % manganese, 0.08 to 0.18 %
phosphorous and a trace of sulfur.
BLASTFURNACE–SLAGFORMATION

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BASIC OXYGEN FURNACE (BOF)
From the blast furnace, molten pig iron (hot metal) is poured into a
torpedo car and subsequently into a ladle. The metal in the ladle is sent
directly to the basic oxygen furnace (BOF) or to a pretreatment stage. A
water cooled lance is lowered down into it. This lance blows 99% pure
oxygen into the converter, igniting the carbon dissolved in the steel and
burning it to form a carbon monoxide and carbon dioxide, causing the
temperature to rise about 1700 °C. This melts the scrap, lower the carbon
content of the molten iron and helps remove unwanted chemical
elements. Moreover, fluxes (like burnt lime) are fed into the vessel to form
slag, which absorbs impurities of the steelmaking process.
BOF-PROCESS

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Typical BOF has a vertical vessel
lined with refractory bricks.
Only 8-12 % of the volume is
filled with the treated molten
steel. The converter is capable
to rotate about its horizontal
axis. This rotation is necessary
for charging raw materials,
sampling the melt and pouring
the steel out of the converter.
At the end of the entire process
the BOF is tilted again and steel
is poured into a giant ladle.

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SECONDARY METALLURGY
The ladle is transferred to a device called Ladle Furnace (LF), where it's places under
a cover equipped with three graphite electrodes columns which are connected to
an AC transformer.
The primary functions of the LF is the reheating of liquid steel through electric
power conducted by the graphite electrodes and homogenization of steel
temperature and chemistry through inert gas stirring. In fact the ladle bottom has a
porous plug which allows the gas inert argon supply.
Moreover the LF stand is also equipped with an addition hopper mounted on the
cover (ferroalloys addition) and a lance for injection of desulfurizing agent.
During the treatment, molten steel is covered by a layer of slag. The fumes formed
during the operation are extracted through a suction system installed at the cover.
LADLEFURNACE-PROCESS

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Additional devices, such as
RH degasser, VD (vacuum
degasser) could be adopted
in the secondary metallurgy
in order to produce special
kind of steel.

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CONTINUOUS CASTING
The molten metal is now cast
through a mold, the casting
takes the two dimensional
profile of the mold but its
length is indeterminate. The
casting will keep traveling
downward and its length
increases with time. New
molten steel is constantly
supplied to the mold with a
specific rate to keep up with
the solidifying casting.

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Molten metal, from the ladle, is poured into a tundish, which is a container that is
located above the mold, it holds the liquid metal for the casting. This particular casting
operation uses the force of gravity to fill the mold and to help move along the
continuous metal casting. The tundish is constantly supplied with molten steel to keep
the process going. The whole process is controlled to ensure there is smooth flow of
molten steel through tundish.
Further, the impurities and slag are filtered in tundish before they move into the
mold. The entrance of the mold is filled with inert gases to prevent reaction of molten
steel with the gases in the environment like oxygen. The molten metal moves swiftly
through the mold and it does not completely solidify in it. The entire mold is cooled
with water that flows along the outer surface.
The metal casting moves outside the mold with the help of different sets of rollers.
While one set of rollers bend the metal cast, another set will straighten it. This helps
to change the direction of flow of the steel slab from vertical to horizontal.
CONTINUOUSCASTING-PROCESS