Steel making and alloy of steel

 Ans:Steel may be classified into various
ways.They are given below:
 A.Depending on the amount of carbon present in it:
a)High carbon steel (.8-1.5% C)
b)Medium carbon steel (.30-.80% C)
c)Mild steel (.15-.30% C)
B.Depending upon manufacturing process:
a)Steel manufactured by cementation process
b) Steel manufactured by crucible process
c) Steel manufactured by bessemer process
d) Steel manufactured by open hearth process
e) Steel manufactured by electric furnace process
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 f)Steel manufactured by duplex process
 C.Depending on alloying metal
 a)Manganese steel
 b)Nickel Steel
 c)Chromium steel
 d) Tungsten steel
 e)Molybdenum steel
 f)Vanadium steel
 D.Depending on type of stainless steel
 a)Austenitic stainless steel
 b)Ferritic stainless steel
 c)Martensitic stainless steel
 E.Depending on the engineering property of steel
 a)Boiler clung-fire steel
 b)Care hardening steel
 c)Corrosion and heat resistant steel
 d)Electric steel
 f)Structural steel
 g)Tool steel
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The uses of steel are given below:
i.Nickel steel (2.5 – 5.0% Ni):It is used in manufacturing cable,motor
car and airplane parts,tank,propeller handle etc
ii.Chromium steel (1.5- 2.0% Cr):ammunition of tank,pressing
arrangement,knife,scissors,etc are produced from these steel.
iii.Chrome vanadium steel (.15% V,1%Cr):it is used in manufacturing
of spring,axels and handles of machine,frame of vehicles etc
iv.Manganese steel (12-15% Mn):ore grinder,iron safe,rail line etc are
made from this steel
v.Tungsten steel(14-20 % W):it is used for making high velocity tools.
vi.Rustless steel(18% Cr,8% Ni):Used for making cutting tools such as
knife,scissors,blades etc
vii. Inver (36% Ni):oscillator and scale are made from this.

Ans:Nowadays most of the high quality steel is made in open hearth
process.open hearth process is of two types:
a)Basic open hearth process
b)Acidic open hearth process
The principle and even designs of furnace are the same in two
process.Only the difference in the inner layer of one is basic type
and another is acidic type.The basic open hearth process is
excessively used and it is described in below:
The structure of the furnace:The furnace proper is a rectangular brick
structure ,supported on the sides and ends by steel buckstays
which are bound together at their tops by rods and stays.Furnace
have been built with hearth capacitiesranging all the way from 15-
300 tons,with 100 tons are the most common size.The overall
outside dimensions of the 100 tons furnace will be about 80 ft in
length and 20-22 ft in width,with a hearth depth of 24-30 in.Most
modern furnace have insolution on the roof,side walls, and
checkers to conserve heat and to permit better control over
consumption and furnace atmosphere.
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Fuel cost account for about 4%of the total cost of steel making
in open hearth process.In addition to the actual cost per BTU
,other factors must be considered in the selection of the fuel
for open hearth process.
i. The temperature attainable with the fuel.
ii. The case with which proper direction may be given to the
flame.
iii. The sulfure content of the fuel
iv. The luminosity of the flame produced by the fuel
v. The cleanness of the fuel.
vi. The design of the furnace.
The fuel used up in open hearth furnace is natural gas,coke
oven gas, producer gas,pulverized coal,fuel oil,tar an blast
furnace gas.
2/17/2018 27

The open hearth raw materials are given below:
i.Solid or molten pig iron.
ii.Steel scrap.
iii.Iron ore or mill scale
iv.Limestone
Minor raw material:
i.Burnt llime
ii.Fluorspar and dolomite as slag addition
iii.Anthracite coal,coke or wash metal for recarburizing
iv.Ferroalloys for deoxidation and meeting specification on
alloyinbg constituents
v.A considerable variety for the maintainance and repair of
ladles and furnace .
2/17/2018 28

First the raw materials are taken into the furnace step by step
.Fuel and air are introduced through one side of the
furnace.Fuel is ignited with air contact insiude the furnace
and at the time of releasing some of the gas,and brick wall
of the inlet temperature.When air and fuel are introduced in
the furnace they rtake the temperature and burn very
intensely in the furnace.Therefore the required temperature
is produced in the furnace.
The process of steel manufacturing is divided into following
tupes:
a)The harging and melting period
b)Period of the lime bouil
c)The refining period
d)The finishing period
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The pig iron and scrap are taken into the furnace.During the
period between the charging of the scarp and hot metal
afddition ,the scrap is subjected to considerable oxidation
by the raectkion with oxygen,water vapor and carbon
dioxide in the furnace gases.Iron also oxidised by Fe2O3.
2Fe+O2 = 2FeO
Fe + H2O = FeO + H2
Fe + CO2 = FeO +CO
Fe + Fe2O3 = 3FeO
As a consequence, when the hot metal is added there is
rather violent reaction between the Si, Mn ,P and some of
the carbon in the hot metal and the iron oxide on the
oxidised scrap leading rto the production to the slag.It is
high in SiO2,MnO and FeO and contains roughly half of
the phosphorous that was present in the charge.
2/17/2018 30

This slag is viscous.It is called renoff slag,the time during
which it is formed is often called the renoff period.
5FeO + 2P = P2O5 +5Fe
2FeO + Si = 2Fe + SiO2
FeO + Mn = Fe + MnO
FeO + C = Fe + CO
3Mn + P2O5 = Mn3(PO4)2
MnO + SiO2 = MnSiO3
Period of lime boil:temperature of the bottom of the hearth
reaches that required for the rapid calcinations of the
limestone and for completing the melting ofv the scrap and
CO2 is produced.This CO2 react with C or the bath and
produces CO.CaCO3 dissociates to CaO which react with
SiO2 and P2O5 to produce slag. This slag float on the bath .
2/17/2018 31

CaCO3 = CaO + CO2
CO2 + C = 2CO
CaO + SiO2 = CaSiO3
3CaO + P2O5 = Ca3(PO4)2
The refining period:The period during which ore and
stone addition is made is often called refining
period.Si was eliminated early in the heat,some
residual P,Mn and S still are present,but the
principle reaction during the refining period is the
oxidation of carbon.
In the refining reaction FeO and Fe2O3 are
transferred to the metal-slag interface by diffusion
and convection processes that are the more rapid
and lower the slag viscosity.2/17/2018 32

At the slag metal interface
FeO (slag) ↔FeO (in liq Fe)
Fe2O3 (slag) + Fe (liq) ↔ 3FeO (in liq Fe)
FeO in the metal bath then react with C,P and Mn as indicated
by the following reaction:
FeO (in liq Fe)+ C (in liq Fe)↔ Fe (l) + CO (g)
5FeO (in liq Fe) + 2P (in liq Fe)↔P2O5 (slag) + 5Fe (l)
P2O5 (slag) + 3CaO (slag)↔(CaO)3P2O5 (slag)
FeO (in liq Fe)+ Mn (in liq Fe)↔Fe (l)+MnO(slag)
FeS (in liq Fe)+Mn (in liq Fe)↔MnS (slag) +Fe (l)
MnS (slag)+CaO(slag)↔MnO(slag)+CaS (slag)
2/17/2018 33

After eliminating the slag,required amount of spiegel is added
well and the mixture is heated more times. Then the melted
steel is subjected to various shapes by pouring them into
moulds.
Done by Abdul Monnaf Mohon
ACCE-13055016
2/17/2018 34

Advantages:
i.Controlling of direction of incidence of flame or both of them
can be possible by controlled flow of oxygen.
ii.The great advantages of oxygen is elimination of carbon
becomes easy in the purification stage.The carbon
elimination rate increases three times than the normal
process.Therefore the purification time decrerases and the
fuel expanse decreases remarkably.Oxygen is passed after
almost completion of boiling.This process become
economical when there is 0.1% C.
iii.The elimination of S and P also increases partially with
carbon.
iv.Gaseous bubbles are produced if oxygen is introduced in
melted metal also.Carbon is deffused in the bubbles and the
CO gas is emitted with ease.
2/17/2018 35

i. A large amount of smoke is produced if oxygen is used.So
treatment of emitted gas is needed.
ii. The expanse increases comperatively.
iii. The longevity decreases due to corrosion of the lower portion.
Question:Describe how steel is manufactured by
converter process.Give the associated chemical
reaction.
Ans: The bessemer convertor process was invented by Henry
Bessemer,who received on english patel in 1856.
Construction of this converter:The Bessemer converter is pear
shaped steel vessels lined with refractory material and they
ordinarily hold 10 to 25 tons of molten metal.The bessemer
converter has an open mouth at the top and tuyeres for
introducing an air blast at the bottom.
2/17/2018 36

The converter is mounted on trunnions and can be rotated into
the horizontal or vertical position.
The bessemer process may be either acid or basic,depending
upon the chemical composition of the refractory lining.
 Acid converters are lined with 25 to 40 cm of sandstone or
mica schist cemented in place with a mixture of ganister and
fireclay.
 Basic converter are lined burned dolomite.Basic liming lasts
less and at same time costs more.
The charge:Molten pig iron from the blast furnace forms the
charge to the converter.
 Cold steel scarp may be added to control the temperature
 No flux is added.
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2/17/2018 39
Slag consist of oxides formed by the oxidation of the
mettaloids in the pig iron are also used as charged.
Operation of the converter: First of all converter is set
horizontally,a charge of molten pig iron is poured through the
mouth and the air blast is turned on the converter,then is
rotated into vertical position and in this state ,the molted pig
iron supported by the steam of air coming into from
below.After 15-20 min,the converter is returned to the
horizontal position,the air blast shut off and the steel is ready
to be poured into ingot moulds.
Principle of operation:Since all steel making processes
including the bessemer process rely on the oxidation of
impurities contained in the molten pig iron,nearly all the
silicon and manganese,most of the carbon,and some of the iron
are oxidised by O2 in the air that is blown through the molten
pig iron.The oxidation reaction furnishes the necessary hear for
the process and the oxidation of iron,Si and Mn form a slag.

2/17/2018 40
When the bulk of these elements have been converted to
slag,the carbon begins to oxidize and this stage of the process
is accompanied by a rumbling noise in the converter and the
lengthening of a yellow flame (being projected from the mouth
of the converter) to a height of about 9 meters.
Unfortunately this flame is more spectacular than useful,for the
carbon is burn only to CO within the pig iron bath.The final
combustion CO to CO2 takes place outside the converter and
thus only one third of the heart in the carbon is actually used in
the heating metal.
Chemistry of the process: During the first stage of the
operation Si and Mn are oxidized.
2Fe + O2 → 2FeO ;ΔH = -128,000 cal
2FeO + Si → 2Fe + SiO2 ;ΔH =-70,200 cal
FeO +Mn → 2Fe + MnO ; ΔH= - 26,800 cal

2/17/2018 41
These exothermic provide most of the heat for the operation
and raise the temperature of the bath considerably.
The some SiO2,MnO and some FeO combine to form the slag.
Slag formation:
FeO + SiO2 → FeO.SiO2
MnO + SiO2 → MnO.SiO2
After most of Si and Mn are gone ,the carbon begins to burn
FeO + C → Fe + CO
FeO + Fe3C → 4Fe + CO
2CO + O2 → 2CO2
Carbon becomes CO in the bath and the CO escaping from the
bath burns to CO2 at the mouth of bessemer converter thereby
giving raise to a long flame.When this flame drops ,the blow is
over.
Formerly this end point was judge by visual appearance of the
flame,but today the photocell electric eye is employed to give a
more precise determination of the end point.

2/17/2018 42
Recarburizing: Carbon in the form of coke or graphite may
be added to the blown metal to have adesired carbbon content
of the finished steel.
Deoxidizing: Ferromanganese (80%Mn and 20% Fe)is added
to the blown metal to remove the ressidual oxygen remaining
in the metal.Because Mn has a greater affinity for oxygen than
iron .
FeO + Mn →MnO (slag) + Fe
So important is the addition of Mn that the bessimer process is
absoluetly depend on it for the removal of iron oxide ,the
presence of which would (FeO) weaken the steel.
Besides being deoxidizing Mn is desulphurizer also.
Mn + FeS → MnS (slag) + Fe

Advantages:
i.No external fuel is needed
ii.Various grade of steel can be made controlling the amount of
carbon
iii.The overall process is very fast.So it is economical.
iv.The quality of steel is better.bessemer steels have better
machining qualities,welding qualities,higher tensile
strength,higher degree of work hardening as compared to
open hearth steel of the same carbon content.
Disadvantages:
i.Which countries have no blast furnace they can not produce
bessemer steel because the raw materials here is pig iron.
ii.This is a batch process.
2/17/2018 43

2/17/2018 44
iii.The temperature can not be controlled properly.
iv. The process is so fast that it can not be controlled
properly.
v.Scrap can not be used.
vi.Air is blown so nitrogen content is high in the steel.
vii.The bessemer process con not eliminate S and P. So S
and P free ores are used.Hence these ores are going to be
ended quickly.
Question:What are the advantages and disavantages of
using oxygen in bessemer converter process?
Advantages:
i.The efficiency of converter increases due to being
exothermic reaction.
ii.No change of introducing nitrogen.

2/17/2018 45
iii.The wastes are removed quickly
iv.Time requirment is short
v.The direction of flame can be controlled.
Disadvantages:
i.The expanse is increased if oxygen is used
ii.Exess heat is produced if oxygen is used.Hence the
lower portion of the furnace corrodes and the longevity of
furnace decreases.
Question:What are the influence of minor elements of
carbon steels?
Ans: Si, Mn,S and P are assumed as the minor elements
of steel.Nut they are necessary in appropriate ratio in
some special mechanical processes.Their effects are given
below-

2/17/2018 46
Si:
Silicon is widely used in medium and high carbon steel as
deoxidizer.The rest Si is dissolved in ferrite phase as FeSi
and it increases the tensile strength.The steel containing
more than 0.5% carbon are called alloy steel.
2FeO +Si = 2Fe +SiO2
Mn:
It is used to rescue from harmful effects of Sulfur which is
relized from the following reaction
FeS (liq -Fe)+ Mn (liq -Fe)→Fe+ MnS (slag)
MnS (slag) + CaO (slag) →MnO (slag)+ CaS (slag)
MnO (slag) + C →Mn (liq -Fe)+CO (g)
Besides it increases tensile strength . The steel used in
building rail line and bridge should contai 1.0%- 1.9% Mn.

2/17/2018 47
Sulfur:
Sulfur forms FeS with Fe,which is soluble in liquid Fe but
insoluble in solid Fe.hence Sulfur is precipitated at the time
of solidification of iron.It causes hot shortness in steel
becauses of its low melting point.Therefore the steel may
crack down under hard works.The only advantages of
sulfur is it increases machinability of steel.
Phosphorus:
It remains as Fe3P in iron.It makes iron brittle in low
temperature.Usually cold ahortness is noticed if the (C+P) is
higher than 0.3%for high carbon steel.
Question:Why is nitrogen undesirable in steel?How do you
lower the nitrogen content in bessemer steel?
Ans:Nitrogen is undesirable in steel because nitrogen reacts
with iron and forms iron nitrite(FeNO2).
.

2/17/2018 48
The age hardening of iron nitrite is less. Therefore ,the age
hardening of the steel is reduced and the produced steel
can be broken any time.So nitrogen is undesirable.
The nitrogen in bessemer steel can be reduced by the
following processes:
i. If the temperature is controlled i.e the temperature is
kept in miniimum stage then the amount of nitrogen will
be less in steel.It also helps to reduce P.
ii. The transfer time of gas over bath should be reduced i.e
the metal gas contact time should be reduced.
iii. The partial pressure of nitrogen inblowing air should
be less.
iv. The layer thickness of the converter should be less
(20-22”)
v. If oxygen or steam is used instead of air then the
amount of nitogen will be reduced.

2/17/2018 49
vi. Nitrogen can not be entered up to the presence of
carbon.The blow should be stopped at the time of ending
caarbon.
vii.If the solubility of nitrogen in iron reduced.
THE END
THANKS ALL
FOR PATIENT

Steel making and alloy of steel

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