how is steel made
how do we produce enough heat to melt it
how do we get molten steel into a form
that we can use
and what is the best way of doing this
in this module
we will try to answer these questions by
looking at iron ore
blast and electric arc furnaces steel
making
and casting we also reveal how many
eiffel towers we could make in an hour
from the world steel production
iron ore is common in the earth's crust
and contains iron
chemically bonded to oxygen it is mined
in areas such as the americas and
australia
the mining involves using explosives to
break up rock
this is then crushed and the iron ore
separated from non-metals
iron ores from different locations are
blended together
this is combined with coke and heated to
make an iron-rich feedstock for the
blast furnace
called sinter sinter is added to the
blast furnace along with coke and lime
and a continuous hot air blast is
injected through nozzles
called to yells in the base of the
furnace
this air blast from which the process
gets its name helps raise the
temperature of the furnace to 2200
degrees celsius
or 4000 degrees fahrenheit this is high
enough to cause the chemical reduction
of the iron oxide from the center
carbon added as coke and oxygen from the
hot air blast
into molten iron and carbon dioxide
the lime forms with the impurities to
form a liquid called
slag which floats on the iron the liquid
iron collects in the bottom of the blast
furnace where it is drawn off
and the slack is skimmed off and used in
other industries
like cement manufacture making iron in a
blast furnace
is a continuous process and they often
run for many years at a time
the metallic iron produced in a blast
furnace contains substantial amounts of
impurities
such as sulfur phosphorus and silicon
these impurities make the iron virtually
useless without further processing
basic oxygen steel making is the main
batch production process for refining
iron from the blast furnace into steel
and accounts for approximately 1 200
megatons per year
this is enough steel to make nearly 19
eiffel towers every hour
in the basic oxygen steel making process
300
to 350 tons of iron can be converted
into steel in approximately 30
minutes first scrap steel
is put into the vessel then the molten
iron is added
a lance blows high purity oxygen onto
the iron
at approximately twice the speed of
sound
this causes the rapid oxidation of
carbon manganese and silicon in the
charge
these reactions which give off heat help
to melt the scrap
and aid in the refining process
the impurities in the metal are removed
by oxidation
and interaction with the slag the steel
is then processed further
in secondary steel making before we look
at secondary steel making
another process for producing steel is
the electric arc furnace
[Music]
the electric arc furnace accounts for
the majority of the remaining steel
production
and produces around 400 megatons per
year worldwide
that's the equivalent of melting down
one titanic
every hour in comparison with basic
oxygen steel making
the electric arc furnace has the
advantage of being able to start with a
solid charge
as it does not use iron from the blast
furnace but uses cold steel
scrap making it one of the world's
largest recycling processes
the electric arc furnace makes a steel
batch up to
150 tons in under one hour
and the process permits extremely close
control over temperature
composition and refining conditions for
each heat
making it particularly useful for
specialty steels like
stainless steel the furnace is filled
with steel scrap
the furnace lid is swung into place and
three graphite electrodes are lowered
into the furnace
a powerful electric current is passed
through the electrodes creating an arc
the arc reaches temperatures of about 12
000 degrees celsius
or 21 500 degrees fahrenheit
this is twice the temperature of the
surface of the sun
and consequently the heat generated
melts the steel scrap
once the first load of scrap is melted a
further one or two loads of scrap are
added
lyman floor spa a type of flux are added
and oxygen is usually blown into the
melt
causing impurities in the metal to
combine and form a slag
the steel is monitored for composition
and temperature
and then the steel is drawn off into a
ladle and sent for secondary steel
making
after basic oxygen steel making or the
electric arc furnace
secondary steel making is used to
further refine the steel
in secondary steel making fine editions
of alloys
are made to meet the customer
specification
temperature is controlled and gases such
as oxygen
are removed through the addition of
aluminium and silicon
the process also reduces impurities such
as
sulfur and phosphorus through slags that
will be built up in the ladle
this slag also retains heat in the ladle
and isolates the molten metal from the
air
following steel making casting is
required to solidify the molten steel
ready for shaping or forming into a
suitable profile
the three main ways of doing this are
sand
casting continuous casting and ingot
casting
sand casting sand casting
is a process for making a part by
pouring molten metal into a mold
having a cavity of the desired shape and
then allowing it to solidify
in sand casting sand mixed with water
and suitable binders
is the molding material the molding
material
is packed around a pattern often made of
wood
this pattern is slightly larger than the
finished part
due to the contraction of the metal on
solidification and cooling
when the pattern is removed from the
molding material
a cavity having the same shape as the
pattern remains
the sand must be packed or rammed to the
correct degree
to avoid air or water vapor being
trapped in the molten metal
causing unsoundness the cavity is
usually created
in two or more sections that are then
fitted together to create a mold
the mold will have one or multiple holes
in which to pour the molten metal
there will be channels to direct the
molten metal and there will also be a
reservoir next to the cavity
so that when the molten metal in the
cavity solidifies and consequently
shrinks
any voids will be immediately filled
with more molten metal from this
reservoir
metal of the desired composition is
heated well above its melting points
in order to ensure good fluidity
if this is not done the molten metal may
solidify in the mold
and consequently be unable to completely
fill up
many casting grades of steel have higher
levels of silicon
as this helps to increase the fluidity
of the molten metal
after the metal has solidified the
finished casting can be
shaken or knocked out of the mold which
can only be used once
the advantages of sand castings include
low cost high flexibility virtually any
size
casting can be produced and it is a
simple
expedient way to make a wide range of
products
continuous casting usually
continuous casting uses feedstock from
the basic oxygen steel process
a ladle of steel is teamed or poured
through a gas type refactory nozzle
into a ton dish with special wears and
dams to aid in the removal of impurities
this tundish is a reservoir and it feeds
the steel through further gas tight
nozzles
into a number of water called copper
molds
the cooling is controlled and only the
outer skin of the steel is solidified
the molds are oscillated to ensure that
the solidifying shell
does not stick and break flux is also
added to aid lubrication
the steel shell grows as it is drawn
down through a curved arrangement of
support
rolls and water sprays it then emerges
horizontally as solid steel strands
and is cut to length with automatic gas
burners
depending on the size these solid
strands are called
billets blooms or slabs
the billet blooms and slabs are normally
processed through a rolling mill
where the cast structure is refined
initial setup of a continuous caster is
expensive
but it is a very efficient process has
an excellent throughput
and has yield benefits over other types
of casting
ingot casting ingot casting
is primarily used with the electric arc
furnace
and as with continuous casting it is an
intermediate process to solidify steel
to enable further shaping primarily in a
forged or rolling mill
it is a process where molten steel is
poured into a cast iron ingot mold
often cylindrical in shape the finished
ingots
can weigh anything from a few kilos to
hundreds of tons
the main ways of casting these ingots
are either
uphill teaming or vacuum casting
ingots that are uphill teamed use a
ladle either directly
or in a teaming car that is positioned
over a feeder system
to enable the ingots to be filled from
the bottom of the mold
the ladle is positioned over a funnel
called a trumpet
it is opened and the metal stream
established
the pouring rate is controlled
throughout this teaming process
powders which have an exothermic
reaction are often added to the top of
the ingot following teaming
to generate heat to aid in the feeding
of the ingot
minimizing voids called pipe insulating
material
is also added to aid in this
for ingots that are vacuum cast the mold
is placed in a vacuum tank
and an intermediate ladle is positioned
on top
the ladle that is on the vacuum tank is
filled with molten metal
and the tank's pressure is pumped down
to create a vacuum
pouring of the ingot is started and the
intermediate ladle
is fed with additional molten metal if
required
the ingot is filled the pressure vented
and the same exothermic and insulating
powders
are added to reduce voids in the ingot
cooled pipe
although these powders are added some
porosity and vacancies
will form within the material due to
shrinkage and gases liberated from the
operation
a large feeding pipe defect is cut from
the ingot
but most porosity in the ingot is
acceptable
since it will disappear through further
processing in the rolling mills or forge
in both continuous and ingot casting the
metal solidifies from the outside
progressing towards the center and thus
the ingots grain structure
develops as columnar and points in the
direction of solidification
this grain structure development is
typical of cast materials
hot rolling or forging will break up the
car structure
and form a smaller more uniform wrought
grain structure
ingot casting is better suited to one
offs and small batches
it is also able to produce large ingots
easily
and is the least complicated of the
casting techniques
so in summary the majority of steel
is processed through the blast furnace
basic oxygen steel making
secondary steel making and continuous
cast process
the electric arc furnace is more
versatile for small batches
and is very well suited to speciality
steels like
stainless steels secondary steel making
refines the steel and controls
parameters to meet the customer
specification
the advantages of sand casting include
low cost
high flexibility virtually any size
casting can be produced
and it is a simple expedient way to make
a wide range of products
ingot casting is used primarily with the
electric arc furnace
and is best suited for one-offs and
small batches
it is also able to produce large ingots
easily
and is the least complicated of the
casting techniques
continuous cast and ingot cast materials
are further worked in a rolling mill or
forge to refine the structure
whereas sand castings are not
[Music]
you