lECTURE 1.ppt

Lecture 1:I,
STEEL & STEELMAKING

A brief introduction :
The association of mankind with iron and steel is
thousand of years old.
Extremely large volume of steel is daily consumed for
building roads, bridges, skyscrapers, automobiles and so
on.
A modern day life without steel is certainly beyond
imagination.
Steelmaking, Refractories and Plant Practices, IIT, Kanpur
What is steel?
Chemically, steel is an alloy of iron and other elements (such
as C, Si, Mn, Cr, Ni etc.). From an engineer’s perspective,
steel a material with a range of mechanical properties that is
second to none. Versatile mechanical properties coupled with
immense recycling potential helped steel consolidate its
position as a primary engineering material in the society.

Steel is manufactured from either molten iron (produced from
iron ore in an iron blast furnace) or direct reduced iron (briefly
DRI; produced via a variety of solid state iron production
techniques).
It is also produced by recycling steel scraps, mixing the same
with some DRI, melting and refining the later in electrical
steelmaking furnaces such as an arc or an induction furnace.
How is steel made?
Steelmaking essentially involves refining of molten iron at elevated
temperature (1873 K or so) in refractory lined vessels. Chemical
and thermal interactions among various phases and constituents
result in the production of molten steel which is finally converted
into solid form through casting processes.
Distinguishing feature of steelmaking

In steelmaking, primarily changes in chemistry and form
are involved. These changes facilitate transformation of
liquid steel in to useful solid products ( e.g., sheets, coils
,bars……)

How are these changes brought about?
Through interactions among various phases (Gas ,solid
and liquid) at high temperature
Thermodynamics determines the feasibility of
such changes
while
chemical kinetics and/or transport phenomena
determines the rate at which the changes occur.
Issues like production of clean steel, refining rates and
hence productivity are dictated at a fundamental level
by metallurgical thermodynamics and kinetics.

Contribution of Sir Henry Bessemer
First attempt to refine hot metal with air
Henry Bessemer melted pig iron in an externally heated fire
clay crucible, deeply submerged a fire clay blow pipe from above
and blew air into the metal bath.
Invention followed by commercialization ( of Bessemer
steelmaking process) and journey began more than 150 years ago
Since the days of Bessemer, during the past 150 years or so,
phenomenal changes have taken place in practically all realms
of steelmaking. These includes energy efficient giant blast
furnaces, enormous turnover rates of oxygen steelmaking
furnaces, continuous and near net shaped casting etc.
What follows in the presentation is an over view of the
modern steelmaking technology.

Before the era of oxygen steelmaking, Hearth and Bessemer
steelmaking were popular. Today more than 95% of world
steel is produced through BOS ( Basic oxygen steelmaking)
and EAF( Electric arc furnace steelmaking) combined.
Growth and decay of some steelmaking
processes over the last seven decays
Recent trend in global steel
production
0
200
400
600
800
1000
1200
1400
E
U
N
A
F
T
A
J
a
p
a
n
C
h
i
n
a
A
s
i
a
,
T
o
t
W
o
r
l
d
Nation/Group of nations
Steel
production,
Million
Metric
Tons
2005
2006
2007

Present day steelmaking process route involves two dominating technologies
namely, oxygen steelmaking (basic oxygen steelmaking or briefly BOS) and
electric steelmaking (electric arc furnace steelmaking or briefly EAF) respectively.
Primary steelmaking
Secondary steelmaking
Continuous casting
Final finishing operations

Primary steelmaking is concerned with the production of crude steel
which is subsequently refined both in terms of its composition and
cleanliness through a host of secondary steelmaking processes. The
initial, intermediate and final steel compositions are shown below to
illustrate the extent of refining during the first two stages of
steelmaking. Molten steel with desired composition, cleanliness and
temperature is finally transformed into solid products through
continuous casting.
Product Process route Typical composition Temp.,K
Hot metal Blast furnace [%C]= 4.5 [%S]=0.05 [%P]=0.15 [%Si]= 1.5
[%Mn]=1.0 [O]< 1 ppm
1573-1673
Crude
steel
BOS [%C]=0.05 [%S]=0.02 [%P]=0.008 [%Si]=0.1
[%Mn]=0.2, [O]~400 ppm and [N]~40ppm
1823-1923
Finished
steel
Secondary
steelmaking
[%C]=0.05 [%S]=0.008 [%P]=0.008 [%Si]=0.1
[%Mn]=0.2[O]~15 ppm , [N]~10ppm &
[H]~1ppm
1823-1853
Steelmaking, Refractories and Plant Practices,
IIT, Kanpur

Steelmaking: The key refining reactions are:
   
O
O 2
2 
      heat
MnO
O
Mn 


        heat
PO
Ca
CaO
O
P 


 4
3 (
3
5
      heat
CaS
FeO
CaO
FeS 


 )
(
      heat
CO
O
C 


      heat
SiO
O
Si 

 2
2
The reactions are essentially heterogeneous and to demarcate
participating phases, ( ), [ ] and { }are conventionally used to
represent slag, metal and gaseous phases respectively. Reaction of
impurities with dissolved oxygen ( not with FeO) is typically
exothermic and makes steelmaking autogeneous.
The rate of the reactions ( hence rate of steelmaking are typically
mass transfer controlled and therefore the intensity of stirring in the
steemaking reactor plays crucial roles.

Basic Oxygen Furnace and Basic Oxygen Steelmaking
In basic oxygen steelmaking process, molten iron from blast furnace is refined
under oxidizing and basic environment. The former is ensured by blowing oxygen
through molten steel while the latter by maintaining a highly basic slag
( ). Refining is carried out in a pear shaped vessel called “converter” (or
BOF; basic oxygen furnace)
 
 
2
2

SiO
CaO
Ist commercial LD
converter in Austria

Sequence of operations in BOS
Pattern of oxidation of
dissolved impurities in BOS

Combination blowing steelmaking process
Introducing a small amount of Argon gas from bottom improves
process performance tremendously (yield, Iron oxide content of slag
etc.).
Multi-hole water cooled lance through
which oxygen is introduced at supersonic
speed
A sub-lance is used and is periodically
lowered into the converter to collect
sample and monitor the progress of
refining

EAF steelmaking
Electrodes
EBT
Ladle
•Arc furnace steelmaking gained
momentum after the WW-II.
•It is a solid charge based
process and uses scrap and DRI
as chief iron bearing material.
• The extent of refining required
in an EAF is generally less than
that in a BOF
• The impurities present in DRI
and other charge materials are
eliminated through oxidation
and fixing the impurity oxides
with suitable fluxing agent, such
as CaO. To facilitate these,
iron ore (as oxidizing agent)
and lime (as flux) are both
added to EAF charge material.
The reactions between dissolved impurities and iron ore, in contrast to those with
dissolved oxygen, do not produce enough heat to make EAF steelmaking
autogeneous. The total energy required to make one ton of liquid steel in EAF is
approximately 6.7 GJ (electrical energy, burners and chemical energy combined).

De-oxidation :
The solubility of oxygen in
liquid steel is appreciable and
in BOS> 0.1wt%.
Dissolved oxygen, if left as it
is, seriously impairs mechanical
properties of steel and must be
removed from the melt prior to
casting.
The economics of steelmaking
necessitates that removal of
oxygen as well as subsequent
adjustment of composition and
temperature are carried out in a
vessel beyond the primary
steelmaking furnace such that
the latter can be used solely for
the production of crude steel
maximizing productivity.

Generally concerned with one or more of the following:
Composition control:
These include alloying additions for adjustment of melt chemistry,
powder injection for desulphurization and vacuum treatment for
removal of dissolved gases and production of ultra low carbon steel.
Cleanliness control:
This is concerned with the production of clean steel and s involves
synthetic slag preparation for better inclusion absorption, creating
correct flows in tundish and molds to aid inclusion float out and
injection techniques to modify morphology and composition of oxide
and sulfide inclusions and
Temperature control:
Melt heating is done through electrical energy. An arc is produced
between graphite electrodes and this generates enough heat
increasing the temperature of the melt.
Not all secondary steelmaking operations could be
recommended for every grade of steel
Secondary steelmaking and ladle metallurgy

Ladle and Ladle Furnace (LF):
All ladle techniques employ inert gas
injection. Gas stirring facilitates mixing,
thermal and particulate homogenization
as well as inclusion floatation.
Depending on the ladle process ( Rinsing,
alloying and desulphurisation), a wide
variety of argon flow rates is used.
Gas is introduced through one or two
porous plugs located at the base of the
ladle.
Temperature drop in ladles during
holding is about 0.5 C /min. Heat
losses and additional thermal
requirements are compensated
through arc heating in a LF

Degassing
During refining as well as transfer operations, Hydrogen and
Nitrogen find their way into the melt. Their presence in the final
product seriously impairs the performance of steel. It is therefore
desirable to regulate such unwanted elements within their
acceptable limits. This is accomplished via vacuum processes
commonly termed as “degassing” operations.
)
g
(
N
]
N
[ 2
2
1

Smaller is the ambient
pressure, smaller shall be
the equilibrium Nitrogen
in steel

I. Primary
steelmaking
II. Secondary
steelmaking
III.Continuous
casting
Final
finishing
operations
The three stages of
steelmaking are linked
via transfer steps or
operations (BOF to
ladle (i.e. tapping),
ladle to tundish to
mold (i.e. teeming).
The quality of steel
achieved during one
stage can be completely
lost during a
subsequent transfer
operation, if the latter
is not regulated
properly. Transfer
operations are of
immense importance to
steelmakers and their
engineering is vital to
fully exploit the
benefits of primary and
secondary steelmaking

Continuous
casting
Switching over from ingot casting to continuous
casting is also advantageous due to:
•A large number of moulds and their
maintenance could be eliminated altogether
•No need for ingot stripping ( large cranes etc.)
•The extent of mechanical working was
substantially reduced due to casting of billets ,
slabs and blooms directly
•Indeed switching over from ingot to continuous
casting accounted for 500 MJ of energy saving
per tonne of steel.
The tundish serves as an
important linkage between ladle
and mold. It distributes molten
metal to one or more molds and
also serves as a reactor (refining
vessel) in terms of removal of
inclusion etc.

Mold powders and mold lubricators :
Functions of mold powder
Molds are invariably lubricated to assist stripping. Moisture rape
seed oil was used in the beginning due to its minimum smoke and
flame. It also leaves no hard residue on the surface of mold. Low
melting point oxides serving both as mold powder and lubricator
(containing CaF2 , oxides of potassium and , sodium , silica has been
developed through engineering.
I.Water cooled copper mold
II. Water sprays
III. Support rollers
IV. Bending rollers
V.Straightener and VI.Cutter

Continuous casting products:
Electromagnetic stirring
and electromagnetic
braking:
Electromagnetic stirring (EMS)
is applied to induce motion
within the solidifying pool of
molten metal while
electromagnetic braking (EMBr)
is applied to retard motion. In
billet/bloom casters EMS is
applied, while in slab and thin
slab casting, EMBr is applied.

Near Net Shaped casting
Conventional continuous casting produces slabs, billets
and blooms which are required to be further worked so as
to be put into use. Mechanical working is energy intensive
and every effort is made to minimize this. Consequently,
near net shaped casting processes have been developed
to produce material more closer to the final customer
required shape and size.
Thin slab casting
( slab thickness 50-60 mm) Strip casting
( thickness 2-5 mm)

Process control and automation in steelmaking
BOF steelmaking
EAF
steelmaking
A diverse range of
of-line and on-line
measurements are
routinely carried out
in the industry.
These are used to
monitor, automate
and control
steelmaking
processes. Thus,
pressure,
temperature,
composition, volume
flow, speed, Force,
Position, Shape, and
Thickness etc. are
routinely measured
in steel plants.

25
Steelmaking and Future
In a foreseeable future, EAF and BOS will continue to
dominate the steel making scenario. Increased productivity
through enhanced process performance, reduced yield
losses etc. although will continue to assume importance.
Increasing thrust on the following are expected due to
greater economic and environmental constraints i.e.
1. Consistent productivity and quality 2. Zero emission
3.100% recycling & 4. Reduced specific energy
consumption.
Successful new strategies are
expected to evolve from a
knowledge based foundation of
models, measurements and a
solid understanding of the
fundamental aspects of the
steelmaking practice.
Physical
modeling
Mathematical
modeling
Pilot scale
trials
Complete
process
knowledg
e

Structure & Properties of Steel
Pure iron exists in different forms and unit cells of BCC
and FCC irons shown in figure below
BCC ( α iron ) is the stable structure at room temperature
and FCC (γ iron ) is stable at elevated temperature. As
temperature of Fe is raised from room temperature and
reaches a threshold value α → γ reaction occurs. This is a
phase transformation reaction

Steels can be divided into two main groups; plain carbon steels
and alloy steels.
The latter can be subdivided into many groups according to
(i) chemistry (e.g. low alloy and low carbon steels),
(ii) applications (e.g. tool steels, bearing steels ) or
(iii) properties (e.g. stainless steels, free cutting steel ) etc.
Low carbon steel C, Mn
Bearing steel C, Vr,Mn
Free cutting steel S or Pb
Stainless steel Ni and Cr
Carbon or structural steels are produced in bulk and typically in
integrated mills ( BF→BOF→LRF→CC route). On the other hand,
alloy steels , where requirement is small is generally produced in
special or alloy steel plants (EAF→LRF→VD→CC route).

Tetrahedral and Octahedral sites/voids in BCC and FCC iron
Most of the smaller size elements like C, N etc. reside in the
octahedral voids. These strain the lattice as a result hardens the
parent metal

Iron –Carbon Phase Diagram
Note that as carbon concentration increases melting point
decrease . Carbon has more solubility in FCC iron
(Austenite) than in BCC iron ( Ferrite)

Phase Transformations in Plain
Carbon Steels.
1045 steel bar. Structure is
fine lamellar pearlite (dark)
and ferrite (light).
Austenitizing rate-temperature curves
for commercial plain carbon eutectoid
steel

Non equilibrium phases: Bainite and Martensite.

Finer the grain
higher is the yield strength

Iron and Steelmaking in India
Steel plays a vital role in the
development of any modern
economy. “Per capita
consumption of steel” is
generally accepted as a
yardstick of socio-economic
development and living
standards of people. As such,
no developing country can
afford to ignore steel .
Nearly 60% of steel produced in India is currently used in
construction and remaining as automotive material, capital goods,
consumer durables, packaging material and so on.

From a meager 2 MMT of crude steel produced in the
country during 1950-51, nearly 80 MMT of finished steel
was produced in 2011. This is expected to increase further,
reaching a figure of about 200 MMTPA by the year 2020.
India is currently the second largest steel producer in the
world with annual production surpassing that of Japan
(>100 MMT). Target is to produce 300 MTPA by 2030.

The share of steel production due
to the private and public sector is
nearly in proportion to 80:20
Three different process routes for steelmaking namely BOF, EAF
and EIF (Electric induction furnace) are being followed in the
country. These contribute over 98% of total steel production. The
contributions from of BOF, EAF and EIF towards domestic steel
production are approximately in the ratio of 45:23:32. While BOF
and EAF processes are well established for production of quality
steel, EIF units, on the other hand, are seriously handicapped,
since not much refining is possible in existing set ups.
As of 2012, there are 36 EAF units in the country having divergent
sizes which are operated with different technology. Steel giants like
Essar steel, JSPL and Bhusan steel have adopted large, world class
EAFs.

Coal based DRI process has established itself as a
viable and dominant technology in India in terms of
locational flexibility, productivity and kiln campaign
life. It is estimated there are about 350 units in India
of varying module sizes ranging from 50 to 500
tonnes/day. Currently, India is the world’s largest
producer of sponge iron as also of coal based DRI.

PROBLEMS FACING DOMESTIC IRON AND STEEL
INDUSTRIES
(i) Higher coke rate
(ii) Energy consumption (i.e., coke oven-BF-BOF-CC route) is
about 7-8 Gcal/tcs compared to 4-5 Gcal/tcs in advanced
countries,
(iii) Higher rate of slag generation
(iv) 30% of production cost is energy as opposed to 25% in the
advanced countries,
(v) Of the total amount of steel produced, only about 30% of
finished steel is routed through the “ LF-VD” route,
(vi) Share of continuous casting to steel produced is relatively
low (~ 70%)
(viii) Process control and automation in domestic steel plants is
in its infancy and far from being satisfactory and finally,
(ix) Poor plant discipline, too many heads per tonne of steel
produced make Indian steel plants less competitive.

Parameters Unit Indian iron
and steel
sector
Global bench
mark
BF
productivity
t/day/m3 1.5-2.5 2.5-3.5
Energy
consumption
Gcal/tcs 6-6.5 4.4-5.5
Coke rate kg/thm 500-600 350-400
PCI kg/thm 50-100 150-250
SMS slag rate kg/tcs 180-200 <100
CO2 emission t/tcs 2.8-3.0 1.7-1.9
Comparative data for the Indian iron and steel sector vis a
vis the global bench mark.

The evolution of steelmaking and
progress made since the days of Sir
Henry Bessemer are outlined and a
brief account of steelmaking
technology is presented . Brief account
of structure and properties of steel is
also presented . The section concluded
with a discussion on the status of iron
and steelmaking in India
Summary

lECTURE 1.ppt

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