Welcome to MSE 4101
1
Lecture 01
Introduction
Topics to discuss today ….
➢ Steels and their classifications
➢ Routes of steelmaking
➢ Principles of steelmaking
➢ Classification of steelmaking processes
➢ Steelmaking processes
Steels and their classifications
➢Steel is essentially a malleable alloy of iron and one
or more of other elements like C, Cr, Ni, Si, V, W or
almost any active elements (other than gas).
➢Chemical composition of steels divide them into
two major groups,
i) Plain carbon steels(PCS): alloys of Fe & C only
ii) Alloy steels: one or more elements other than C
are added to ensure better mechanical strength,
ductility, electrical & magnetic properties, corrosion
resistance & so on, is known as alloy steel.
➢ Steels may contain many other elements such as Al, Si, Mn,
S, P, O etc. which are not added specifically but are
inevitably present because of their association in the
process.
➢ These are known as impurities but have ‘safe limits’ &
should maintain below the limits.
Based on C contents PCS are broadly sub-divided into 4 major
types-
I. Soft or low C steels upto 0.15%C
II. Mild steel in the range of 0.15-0.35%C
III. Medium C steel in the range of 0.35-0.65%C
IV. High C steel in the range of 0.65-1.75%C
Based on total alloying elements present, alloy steels are sub-
divided into 3 groups-
I. Low alloy steels upto 5% total alloy contents
II. Medium alloy steels in range of 5-10% total alloying
III. High alloy steels above 10% total alloying
➢Once upon a time steels were classified based on their
process of manufacture; e.g. Bessemer, acid open hearth,
basic open hearth, electric & so on.
However, it has become totally irrelevant because steelmaking
processes are versatile
➢In terms of uses, steels are often classified as structural, deep-
drawing, rail, forging, flats & the like
Routes of Steelmaking
➢Steel cannot be produced directly from an iron bearing mineral
that occurs in nature on a commercial level.
➢Steel is produced from iron ores in minimum 2 stages,
production of iron by reduction smelting at first and its
subsequent refining in second stage.
➢Product obtained by reduction smelting of iron ore is called
‘pig iron’ if molten & ‘sponge iron’ if solid.
➢In liquid state pig iron may contain impurities like C, Si, Mn, S, P,
etc. which may add together upto 8wt% of iron.
➢In solid state the sponge iron may contain gangue of oxides of
iron ore like Al2O3, SiO2, CaO, MgO, etc
a
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Principles of Steelmaking
➢ Steelmaking is a process of selective oxidation of
impurities i.e. reverse of ironmaking
➢ The overall process includes charge preparation,
melting, refining, tapping, deoxidation, recarburisation,
alloying, teeming, stripping, etc.
➢ During steelmaking the impurities are oxidized to their
respective oxides (except S)
➢ The oxides are eliminated either as gas (C) or liquid
oxide product known as slag.
➢ In order to produce steel of right quality means right
chemical composition, slag of right chemical character
is aimed at
➢ It is assessed in terms of oxidizing power and basicity of
the slag
➢Basicity is the ratio of basic to acid oxides in the slag
➢Steel can be produced efficiently only if refining is
adequate means right quality slag is made and clean
slag and metal separation is brought about
➢Modern steelmaking in the early years used iron oxides
in the form of iron ore and millscale or air as the
oxidizing agents for refining
➢These are now almost completely replaced by oxygen
gas, nearly pure in form
➢Modern steelmaking is therefore often referred to as
‘oxygen steelmaking’.
Classification of steelmaking processes
➢Modern steelmaking is supposed to have been begun
with the advent of Bessemer process of steelmaking in
eighteen sixties in U.K.
➢Depending upon the impurities to be eliminated the
slag nature has to be adjusted even with external
additions
➢When only Si, Mn and C are to be removed as
impurities from iron, the slag produced is
predominantly acidic(silica saturated) and the furnace
lining has to be acidic, of silica, to contain the slag.
➢Such a process came to be known as ‘acid process’ of
steelmaking.
➢Whereas when P and perhaps S, alongwith Si, Mn, C
has to be removed the slag has to be adjusted by
external addition of flux like limestone.
➢The slag is basic in nature and basic lining becomes
necessary
➢Such a process came to known as ‘basic process’ of
steelmaking.
➢Acid steelmaking is exceptional, occasionally only used,
may be in foundries.
➢Modern steelmaking is carried out in basic slag, using
oxygen as refining media.
➢This is often called ‘basic oxygen furnace’ steelmaking
or BOF
➢The Bessemer, open hearth and the electric furnace
processes using iron oxide and air for refining and
because of their advent some hundred & fifty years ago
these are called ‘conventional processes’ of
steelmaking.
➢The ones using only oxygen for refining and beginning
of recent origin are called as ‘modern processes’ of
steelmaking.
➢Conventional processes had to be modernized using
oxygen to stand competition, came to be known as
‘modified processes’ of steelmaking and became
popular after 2nd world war.
➢Now only oxygen steelmaking is universally adopted for
steel production.
Steelmaking Processes
Cementation process:
➢The earliest process of steelmaking consisted of heating wrought
iron with a carbonaceous material in a covered furnace.
➢This was known as the cementation process.
Crucible process:
➢Following sufficient recarburisation, the melting point of steel
decreased to such an extent that it could be easily melted using
the earlier furnaces.
➢This is known as the crucible process, pioneered by Huntsman in
the UK in 1740.
Bessemer Process:
➢Steelmaking went through a paradigm shift when Henry
Bessemer patented his process in 1856 by blowing cold air
through molten iron and producing molten steel
➢Bulk steel production using the Bessemer process started soon
thereafter, first in the UK and later in America
➢Thus, the introduction of the Bessemer process is looked upon
as a second industrial revolution.
➢A major limitation of the process, it could not remove sulphur
and phosphorus present in hot metal and high level oxygen
➢In 1864, Mushet found that deoxidation of liquid steel using
ferromanganese lowered the oxygen level. This also increased
the Mn content of steel, which preventing hot shortness arising
from high levels of sulphur.
➢The phosphorus issue was tackled following the invention of the
Thomas process by Sidney G. Thomas in England in 1879.
Open Hearth Process:
➢The Bessemer process was incapable of producing low nitrogen
steel, and precise control of the final composition and
temperature were also difficult.
➢These problems were resolved with the advent of the open
hearth process.
➢Open hearth steelmaking was introduced in 1868, and
dominated the world steel production thereafter for almost a
century.
➢However, the process was slow and required external heat input,
as a result of which it had to give way to oxygen steelmaking,
beginning in the late 1950s.
Electric Furnace Steelmaking:
➢The first successful commercial application of electric
furnace steelmaking was carried out by Heroult in 1899 by
melting steel scrap using electric arc
➢Electric arc furnaces are capable of making even better
quality of steel than that made by open hearth furnaces
➢Another type of electric melting furnace is the coreless
induction furnace, which was first patented by Ferranti in
Italy in 1877. The process is capable of making high-quality
special and alloy steels.
Basic Oxygen Steelmaking:
➢Around the year 1950, the Linde-Frankle process devised a
more efficient air separation process, which made bulk oxygen
available at affordable price
➢These led to the development of LD, Kaldo and the Rotor
processes of steelmaking using pure oxygen as refining agent.
➢This is the beginning of modern oxygen steelmaking or more
popularly as basic oxygen furnace process of steelmaking.
Secondary Steelmaking:
➢Earlier, the only operations carried out in the ladle were
deoxidation by ferromanganese, ferrosilicon, etc. followed by
minor alloying additions
➢At present, the ladle is used as a reactor where a variety of
secondary processing of liquid steel is carried out. This
includes: degassing, desulphurisation, reheating, etc. as well as
deoxidation.
➢All these unit processes can be grouped into the broad
category of secondary steelmaking.
Continuous Casting of Steel:
➢For more than 150 years till the 1960s, liquid steel was batch
cast into ingots of various sizes/weights for further shaping by
rolling/forging, after reheating the solidified ingots.
➢In the 1960s, continuous casting in which liquid steel is directly
cast into slabs/blooms/billets of appreciable lengths, appeared
on the scene.
Another major development that has occurred over the last 40
years or so is what is known as hot metal pre-treatment.
Liquid metal tapped from blast furnaces is treated with different
reagents in a ladle for lowering the sulphur, silicon, and
sometimes even the phosphorus contents, before it is charged
into the steelmaking furnace.
This helps in the production of purer steel at the primary
steelmaking stage itself.
Introduction to the Course MSE 4101
Steel Making:
Primary Steel Making: History of Steel Making; Principles of Steel Making;
Raw Materials and Various Steelmaking Process: Open Hearth Furnace, Basic
Oxygen Steelmaking; Induction Furnace Steelmaking, Electric Arc Furnace
Steelmaking; Stainless Steel Making; Sources of Slag and Role of Slag.
Secondary Steelmaking and Casting: Ladle Refining Furnace, De-oxidation
(or "killing"), Vacuum degassing, Alloy addition, Inclusion removal, Ingot
casting and Continuous Casting; Casting Defects.
Reference Books
1. An Introduction to Modern Steel Making by Dr. R.H. Tupkary and V.R.
Tupkary
2. IRONMAKING AND STEELMAKING: Theory and Practice by Ahindra Ghosh
and Amit Chatterjee
