Chapter 1: Introduction

1.1 Steel –

Steel has had a major influence on our lives, the cars we drive, the buildings we work in, the homes

in which we live and countless other facets in between. Steel is used in our electricity-power-line

towers, natural-gas pipelines, machine tools, military weapons-the list is endless. Steel has also

earned a place in our homes in protecting our families, making our lives convenient, its benefits are

undoubtedly clear.

Steel is by far the most important, multi-functional and most adaptable of materials. The

development of mankind would have been impossible but for steel. The backbone of developed

economies was laid on the strength and inherent uses of steel.

The various uses of steel which in turn is a measure of adaptability of steel can be judged from the

following characteristics of steel :

- Hot and cold formable

- Weldable

- Suitable machinability

- Hard, tough and wear resistant

- Corrosion resistant

- Heat resistant and resistance to deformation at high temperatures.

Steel compared to other materials of its type has low production costs. The energy required for

extracting iron from ore is about 25 % of what is needed for extracting aluminum. Steel is

environment friendly as it can be recycled. 5.6 % of element iron is present in earth's crust,

representing a secure raw material base . Steel production is 20 times higher as compared to

production of all non-ferrous metals put together.

The steel industry has developed new technologies and has strived hard to make the world's strongest

and most versatile material even better. There are altogether about 2000 grades of steel developed of

which 1500 grades are high grade steels. There is still immense potential for developing new grades

of steel with varying properties .The large number of grades gives steel the characteristic of a basic

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production material Steel has enjoyed an important position in our lives and will continue to do so in

the years to come. However, the degree to which it maintains its dominant position will depend on if

steel can exploit its potential by developing new higher grades and adaptable grades . This can be

achieved by refining the structure and applying alloying techniques and thus furthering its utility

value. We will have to find out ways to use steel and be ready to face a stiff competition from

Aluminium in the future.

1.1.1 Advantages and Disadvantages of Steel:

1.1.1.a Advantages:

1. Greater hardenability

2. Less distortion and cracking

3. Greater ductility at high strength

4. Greater high temperature strength

5. Greater stress relief at given hardness

6. Better machine ability at high hardness

7. High elastic ratio and endurance strength.

1.1.1.b Disadvantages:

1. Tendency toward austenite retention

2. Cost

3. Special handling

4. Temper brittleness in certain grades.

1.1.2 Purpose of alloying:-

1. Strengthening of the ferrite 7. Improved toughness

2. Improved corrosion resistance 8. Better wear resistance

3. Better hardenability 9. Improved cutting ability

4. Grain size control 10. Improved case hardening properties etc.

5. Greater strength 11. Improved high or low temperature stability.

6. Improved machinability 12. Improved ductility

3

1.1.3 Classification of the steels according to purpose –

ELEMENT = % = NAME = CHARACTERISTICS = USES

-Mn= 12-15 = magnetic steel = very hard & corrosions free = railway track road roller

-Cromium= 11.5 = stainless steel = hard & rust free = valve, ball bearing, blade utensils

-cromium+vanadium= 1+0.15 =crom vanadium steel = high weighing capacity &

unbreakable = ball bearings gear bon chessis of motors

-tungsten= 10-20 = tungsten steel = very hard & strong = high speed machines instruments

blade spring magnets

-nickel= 3.5 = nickel steel = hard electric low probability of rusting = aeroplane, motor

electric wire clock

1.1.4 Raw materials & Fluxes :-

1. Hot metal – Chemical composition : 4.3% C, 0.7% Si, <0.3% Mn, 0.2% P, 0.05 – 0.07% S.

2. Scrap –Chemical composition : 0.2% C, 0.2% Si, 0.5% Mn, 0.5% P, 0.025% S, 99.0% Fe t ,

0.45% FeO.

3. IronOre –Chemical composition : 0.08% P, 0.02% S, 94.8% Fe2O3, 1.3% SiO2,1.6% Al2O3,

2% LOI (max.), 0.2% Others. Grain size 10 – 50.

4. DRI – (Direct Reduced Iron) Chemical composition : 0.2% C, 0.6% P, 0.02% S, 90.1% Fe t

or 81.1% Fe net + 11.6% FeO.

5. Calcined lime – Chemical composition : 87.0% CaO, 3.3% MgO, 3 – 5% SiO2, <1.5%

Al2O3, 2.5 – 5% LOI, 1.95% Others. Grain size 10 – 50.

6. Calcined dolomite – Chemical composition : 53% CaO, 35% MgO, 3.5% SiO2, 1.1% Al2O3,

4% LOI, 4.9% Others. Grain size 10 – 50.

4

1.1.5 The grades of steel produced by primary steel making can be given as:

1. Drawing Quality (D.Q.):-This type of steel contains 0.08% of carbon, 0.03% of silicon, 0.017%

of sulphur and the alloying elements less than 0.13%.

2. Commercial Quality (C.Q.):-The percentage of carbon, silicon &sulphur present in commercial

steel is same as in ―Drawing Steel‖ but the alloying element can be present up to 0.21%.

3. Alloy Steel:-The carbon and sulphur percentage is same as above but the silicon is increased to

0.13% and the alloying elements increased to 1.75%.

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Chapter 2: Observation Work

Fig. 1 – Overview of steel making processes

6

BOKARO STEEL PLANT MAJOR DEPARTMENTS

Fig: 2 Bokaro steel plant major departments

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2.1 Sintering Plant:

Fig 3 – Sintering Plant

• Agglomerated mass of iron ore, flux

• Increases efficiency, reducibility,

• reduces coke rate

• Fed into sinter furnace on moving pallets

• Crushed cooled

• +5mm crushed sinter sent to BF & rest reused

• It is the function of the sintering plant to process fine grain raw material into coarse grained

iron ore sinter for charging the blast furnace.

• To begin with, meticulously prepared mixtures are created consisting of fine ore,

concentrates, extras and undersizes arising from screening lumpy burden components at the

blast furnace. Ferriferous fine grain discharges from the production chain of the entire steel

works are also put into the mixtures. By igniting suitable fuel, iron ore sinter is produced by

down draft process. Normally, coke breeze from screening lump coke at the blast furnace is

used as fuel.

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2.2 Coke ovens and Bi Product Plant:

a) Coke: It is a hard porous substance that is principally pure carbon. Coke is a processed

form of coal, made in oven by driving off volatile elements. In blast furnaces, coke helps generate the

3000o F temperatures and reducing gases needs to smelt iron ore. About 1,000 pounds of coke are

needed to process a ton of pig iron, an amount which represents more than 50% of an integrated steel

mill's total energy use.

Processed coke, however, burns steadily inside and out, and is not crushed by the weight of the iron

ore in the blast furnace. Coal is heated without oxygen for 18 hours to drive off gases and impurities.

b) Types: There are three principal kinds of coke, classified according to the methods by

which they are manufactured :Low, medium and high-temperature coke, Coke used for metallurgical

purposes must be carbonized in the higher ranges of temperature (between 900o and 1095o) if the

product is to have satisfactory physical properties. Even with good coking coal, the product obtained

by low-temperature carbonization between 450o and 760o is unacceptable for good blast furnace

operation.

c) Coke Making - Coal Carbonisation: Coking coals are the coals which when heated in the

absence of air, first melt, go in the plastic state, swell and resolidify to produce a solid coherent mass

called coke. When coking coal is heated in absence of air, a series of physical and chemical changes

take place with the evolution of gases and vapours, and the solid residue left behind is called coke.

Conventional cokemaking is done in a coke oven battery of ovens sandwiched between heating walls.

They are carbonised at a temperature around 1000o-1100o C upto a certain degree of devolatization

to produce metallurgical coke of desired mechanical and thermo-chemical properties.

Coke Oven is mainly consist of 4 sections

1. Coal Handling Plant(CHP)- In this section coal from different sources

(India- prime coking coal from Jharia, Dugda and Moonidih and medium

coking coal form Kargali, Kathara and Mahuda & Imported coal from

Australia, Newzealand,China,Russia.) are stored. There are 81 coal storage

chambers where coal is stored and then from here coal is send to the Hammer

crusher (9 in number and have capacity to crush 350 tonne/hour). Here coal is

crushed for better burning. After crushing they are forwarded to ovens.

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2. Batteries: A set of ovens that process coal into coke. Coke ovens are

constructed in batteries of 69 ovens(20-22 tonne capacity each) that are 5

meter tall, 15 meter long, and less than two feet wide. Coke batteries, because

of the exhaust fumes emitted when coke is pushed from the ovens, often are

the dirtiest area of a steel mill complex. Oven is heatedwith the mixture of CO

gas and BF gas(9:1 ratio).During carbonization, coking coals undergo

transformation into plastic state at around 350o-400o C swell and then

resolidify at around 500o-550o C to give semi-coke and then coke. In coke

ovens, after coal is charged inside the oven, plastic layers are formed adjacent

to the heating walls, and with the progress of time, the plastic layers move

towards the centre of oven from either side and ultimately meet each other at

the centre. During coke making, two opposite reactions take place, viz.

condensation and pyrolysis. The quality and quantity of plastic layer is of

extreme importance and it determines the inherent strength of coke matrix.

3. Coke sorting plant(CSP):

4. Bi Product Plant(BPP): With addition to steel, SAIL makes the turn over of

14-15 crore per month with its bi products only which is produced my exhaust

gases of coke ovens. Main bi products which they make are tar(Napthene),

fertilizers(ammonium sulphate) and Benzene.

MATERIAL BALANCE FOR 1 T OF IRON

Table 1: Material balance for 1 T of iron

BLAST

FURNACE

AIR 2.42 T

SINTER 1.25 T

+ ORE 0.45 T LDS/LS 0.005 T

COKE 0.600 T

GAS 3.615 T

DUST 0.045 T

PIG IRON 1.0 T

SLAG 0.400 T

INPUT OUTPUT

QTZ. 0.001 T

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2.2.1 Description of the Charge Materials:

i. Iron bearing materials :

Major iron bearing materials used in Blast furnaces are Iron Ore Lump and sinter. The

detailed specification of raw Materials is given in Page no …… At present the burden is

composed of 30 % Iron Ore Lump and 70 % Sinter. Percentage of Sinter can be raised to 80

% cost effectively subject to its availability. Sinter is a porous lump containing reduced iron,

lime as formed slag & FeO upto 10 %. Sinter used reduced heat & reducing gas requirement

thereby decreases coke rate and improves productivity.

ii. Fluxes :

The major function of the fluxes, limestone and/or LD Slag is to combine with the ash in the

coke and the gangue in the ores to make a fluid slag that can be drained readily from the

furnace hearth.

The ratio of basic oxides to acid oxides must be controlled carefully to preserve the sulfur-

holding power of the slag, as well as its fluidity and melting point. In instances where the

acids in the coke ash and ore gangue are not sufficient to make enough slag volume to provide

control of the process, silica gravel or quartzite may be added with the charge.

iii. Coke :

The main functions of coke are :

To produce the heat required for smelting

To supply the chemical reagents—carbon and carbon monoxide (generated at the tuyeres) for

reducing the iron ore.

To support the burden (with adequate permeability)

In addition, it supplies the carbon that dissolves in the hot metal, Because carbon sublimes

rather than melts, the coke retains its strength at temperatures above the melting temperature of pig

iron and slag and provides the structural support that keeps the un-melted burden materials

from falling into the hearth and provides a lattice through which the reducing gasses generated at the

tuyeres can pass. Size of coke charged in Blast Furnace is +25 to –80mm.

As a result of chemical equilibrium limitations, all of the carbon monoxide produced in the

blast furnace cannot be consumed in the reduction of the burden. Consequently, the gas issuing from

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the top of the furnace contains sufficient carbon monoxide to have a calorific value of 800 – 900 Kcal

/ Nm3 of gas.

This gas is typically used to preheat the blast air and to generate power for running the turbo-

blowers; thus, much of the energy is returned to the blast furnace operation. The excess gas is often

used in other portions of the plant. As a consequence of economic and technical supremacy the blast

furnace process continues to become more and more efficient.

2.2.2 Quality of Charge Materials

The important parameters are :-

i. Particle size and size consist

Resistance to flow increases with reduction in particle diameter

Heat & mass transfer increases with reduction in particle diameter

For optimizing above parameters it has been found that spheres ranging from 3/8‖

to 2‖ dia are suitable.

The void fraction of a mixture of particles is less than that of either size.

The void fraction decreases only slightly for a ratio of 0.5.

So upper size limit should be about 2 times the lower one.

Physical strength

Maximum breakdown i.e. disintegration of iron ore occurs between 400 – 6000 C. So a

high driving rate decreases this phenomenon.

Presence of alkali causes faster degradation.

Softening due to temp is detrimental to indirect reduction due to closure of pores which is

aggravated by mechanical load. So, the Cohesive range should be small.

ii. Chemical considerations:– chemistry, reducibility, reactivity, mineralogy.

iii. Uniformity of chemical composition:- It can be achieved by blending.

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2.3 BLAST FURNACE:

Fig. 4 Blast Furnace

2.3.1 Raw Material Sources for Blast Furnace

1. Iron Ore

2. Sinter

3.Mn Ore

4. LD Slag

5. Coke

6. Pig Iron Chips

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2.3.2 Progressive steps by which the two-bell top permits charging of materials

a) Bell type with movable throat armour (MTA)

The trajectory of falling material can be varied by varying the throat dia by means of a set of

variable armoured plates (Called MTA) so that desired burden distribution is achieved.

Adjustments are totally circumferential, but there is a limit to how much adjustment can be

attained.The two-bell system requires less height than other systems and it is a comparatively

simple device. The MTA is hydraulically operated & controlled through PLC. The system is

depicted in the figures below.

Fig. 5: Bell type furnace with MTA

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b) Bell-Less Top

In case of BLT, there are no bells, as the nomenclature states. This top charging unit was

developed to solve the problem of gas sealing under a high-pressure operation, to provide flexibility

for the most advantageous distribution of burden, and to reduce maintenance time and frequency for

the equipment. When the furnace stockline has descended to the desired level, the lower seal valve

opens and allows the charge to flow onto the distribution chute. The distribution chute rotates around

the vertical axis of the furnace and changes to predetermined angles with respect to the horizontal

plane.

The skips dump the materials to a receiving hopper which is separated from the BLT by upper

material gate and upper gas seal valve. After opening of upper material gate & upper seal valve,

material is discharged into BLT material bin placed over lower material gate & lower gas seal valve.

Then the UMG & USV closed to seal the furnace from the atmosphere & receiving hopper is ready to

receive material from the skips.To dump the material into the furnace, lower seal valve opens and

then lower material gate opened. The material is dumped through a rotating chute which can dump

material at any position of the furnace and can complete the dumping in variable number of rotation

so that desired burden distribution is achieved. This system has the flexibility of charging the

materials in distinctive rings, in spiraling rings of smaller diameter, or of point/spot area filling. The

whole BLT system is hydraulically operated & PLC controlled. Besides achieving perfect burden

distribution, BLT ensures very good gas sealing at the furnace top so that furnace can be operated at

high top pressure.

Fig 6: Bell Less Top furnace

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Fig. 7: CHEMISTRY OF THE BLAST FURNACE PROCESS

CROWN

RING CONE

THROA

T

STACK OR SHAFT

BELLY

HOT METAL, 13200

C

SLAG, 14200 C

TUYERE ZONE,

16000 C

FUSION ZONE

1200 – 16000 C

LOWER REDUCTION

ZONE

900 – 12000 C

UPPER REDUCTION

ZONE

300 – 9000 C

PRE-HEATING ZONE

150 – 3000 C

TUYER

E

BOS

H

TAP

HOLE

SLAG

BIGINS TO

FORM

PIG IRON

BIGINS

MELTING COKE

BURNS

SLAG

FORMATION

ENDS

MOISTUR

E

REMOVA

L REDUCTIO

N OF IRON

BREAK UP

OF CaCO3

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2.3.3 Production of Heat and Reduction of Iron

When the burden materials and coke that are charged into the top of the

blast furnace descend through the stack, they are preheated by the hot gases ascending from the

tuyeres. As a result of this preheat, the coke burns with great intensity when it reaches the lower

portion of the furnace adjacent to the tuyeres and comes in contact with the hot-blast air.

However, because of the very high temperature (approx. 1650°C) and the large quantity of carbon

(C) present as coke, the carbon dioxide (CO2 ) formed is not stable and immediately reacts with

additional carbon to form carbon monoxide (CO). Consequently, the combustion of carbon (coke) in

the blast furnace can be expressed by the chemical equation :

C + O2 = CO ; ΔH = +110,458 kJ/kmol

This reaction is the main source of heat for the smelting operation and also produces a

reducing gas (CO) that ascends into the furnace stack where it preheats and reduces most of the iron

oxide in the burden as it descends to the hearth.

Any moisture (H2O) in the blast air also reacts with some of the carbon in the coke in the

combustion zone. This reaction does not produce heat as combustion does but, rather, consumes heat.

However, for every unit of carbon, this reaction produces more reducing gas than that is produced

when carbon is burned in air . (When carbon burns in air, it produces only one unit of CO, but when

it reacts with H2O, it produces one unit of CO and one unit of H2 .)

Consequently, in certain instances, where the inherent reduction rate of the burden materials

is lower than normal and where a relatively high hot-blast temperature is available—between 1000°C

and 1100°C — it has been thought to be advantageous to keep the moisture content of the blast at a

uniformly high level by moisture (steam) additions to increase the reducing power of the blast

furnace gas. Natural gas injection provides a similar benefit.

The chemical reaction is expressed by the following equation :

C + H2O = CO + H2 ; ΔH = +131,378 kJ/kmol

An additional benefit is derived from the introduction (or increase) of hydrogen in the furnace

reducing gases, as the percentage of hydrogen decreases the density of the gas. This results in an

equivalent volume of reducing gas providing less resistance to burden decent. The ascending gases

start to reduce the iron oxide of the burden in the upper portion of the blast furnace where the

temperature is below 925°C. At this temperature, chemical equilibrium prevents all of the CO and H2

from being used for reduction.

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2.3.4 Various reduction reactions taking place inside BF is given below:

1/2 Fe2O3 + 3/2 CO = Fe + 3/2 CO2 ; ΔH = +12,866 kJ/kmol

1/3 Fe3O4 + 4/3 CO = Fe + 4/3 CO2 ; ΔH = +3940 kJ/kmol

FeO + CO = Fe + CO2 ; ΔH = –16,108 kJ/kmol

1/2 Fe2O3 + 3/2 H2 = Fe + 3/2 H2O ; ΔH = +48,953 kJ/kmol

1/3 Fe3O4 + 4/3 H2 = Fe + 4/3 H2O ; ΔH = +51,0421 kJ/kmol

FeO + H2 = Fe + H2O ; ΔH = +25,104 kJ/kmol

FeO + CO = Fe + CO2 ; ΔH = –16,108 kJ/kmol

CO2 + C = 2CO ; ΔH = +172,590 kJ/kmol

FeO + C = Fe + CO ; ΔH = +156,482 kJ/kmol

FeO + H2 = Fe + H2O ; ΔH = +25,104 kJ/kmol

H2O + C = CO + H2 ; ΔH = +131,378 kJ/kmol

FeO + C = Fe + CO ; ΔH = +156,482 kJ/kmol

FeO + H2 = Fe + H2O ; ΔH = +25,104 kJ/kmol

H2O + C = CO + H2 ; ΔH = +131,378 kJ/kmol

FeO + C = Fe + CO ; ΔH = +156,482 kJ/kmol

2.3.4.1 Reduction of Manganese, Phosphorus and Silicon:

MnO2 + CO = MnO + CO2 ; ΔH = +147,904 kJ/kmol

Mn3O4 + CO = 3MnO + CO2 ; ΔH = –51,254 kJ/kmol

MnO + C = Mn + CO ; ΔH = +274,470 kJ/kmol

This reaction (the last one) takes place only at temperatures above 1500°C and absorbs large

quantities of heat. The manganese that is reduced dissolves in the hot metal while the unreduced

portion remains as part of the slag.

There are two different reactions governing silicon transfer to the hot metal. Silicon monoxide

gas is formed when coke burns in front of the tuyeres because the silica in the ash is reduced and

volatized. The silicon monoxide reacts with molten iron and the silicon content of the iron increases.

SiO(g) + Fe = Si + FeO ; ΔH = –218,954 kJ/kmol

SiO2 + 2C = Si + 2CO ; ΔH = +658,562 kJ/kmol

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For any particular burden and slag composition the silicon content of the hot metal is proportional to

the hot metal temperature. The percentage of silicon in the hot metal can be increased by increasing

the silicon content of the charge and the coke rate.

The reduction of phosphorus is expressed by the reaction :

P2O5 + 5C = 2P + 5CO ; ΔH = +995,792 kJ/kmol

The final reduction of phosphorus also takes place only at very high temperatures; however, unlike

manganese and silicon the phosphorus is essentially completely reduced. For this reason, virtually all

of the phosphorus in the charge will dissolve in the hot metal. The only means of controlling the

phosphorus content of the hot metal is by limiting the amount charged to the furnace.

2.3.4.2 Elimination of Sulphur

Sulphur enters the blast furnace mainly through the coke and is released into the blast furnace gas

stream as H2S or a gaseous compound of carbon monoxide and sulfur (COS) when the coke is

burned. As the gas ascends through the stack some of the sulfur combines with lime in the flux and

some combines with the iron.

FeO + COS = FeS + CO2 ; ΔH = –80,124 kJ/kmol

FeS + CaO + C = CaS + Fe + CO ; ΔH = +182,422 kJ/kmol

The amount of sulfur removed depends on the temperature in the hearth, the slag volume, and the

ratio of basic oxides lime (CaO) and magnesia (MgO) to acid oxides silica (SiO2 ) and alumina

(Al2O3 ) in the slag.

2.3.4.3 Output Composition:

Hot Metal : 94% Fe, 4.0% C, 1.0% Si, 0.5% Mn, 0.2% P,

0.05% S, 1430 oC Hot Metal Temperature at Cast House.

Liquid Slag : 32-34% SiO2, 20-22% Al2O3, 28-30% CaO,

10-11% MgO, 1% max FeO, 0.94 Basicity.

BF Gas : 22-24% CO, 16-18% CO2, 2% H, 56-58% N,

CV-850 kcal/Nm3, dust content < 10 Mg/m

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2.4 Cast House

The operation of a blast furnace is a continuous process, and the furnace continues to produce

liquid iron and slag as long as it is in operation. The iron and slag accumulate in the hearth, but

because there is a limit to the amount that can be tolerated before it interferes with the furnace

operation, the slag and iron must be removed from the furnace at regular intervals.

The Cast House is the most important section of Blast Furnace. The function of cast

house is to tap the liquid metal & slag from the hearth of furnace on schedule, separate the

metal & slag in troughs and flow them through runners to metal ladles and slag pots

respectively. Production of Blast Furnace is greatly influenced by effective tapings which

depend on a good cast house practice.

Hydro pneumatic drill machines are used to drill the tap holeupto 2m into the hearth to tap the

metal & slag. Oxygen lancing through mild steel pipes is resorted to if taping is not possible by

drilling alone. The troughs & runners are made with special grade refractory mass to handle upto

40,000 T metal before repair. Few iron runners are also made with low cement castables to handle

more then 1 lakh ton metal before repair. Hydraulic powered mud guns are used to close the tap hole

after casting is over with anhydrous tap hole mass which get quickly hardened inside the tap hole.

The main components of cast house is the tap hole, troughs, iron runners, slag runners, iron &

slag spouts, mud gun and drill machine. Each cast house is provided with a EOT crane (15 T cap for

BF – I, II & II and 30 T for BF – IV). BF 1, 2 & 3 have one tap hole where as BF – 4 has two tap

holes with separate trough & runners for Iron & slag. More over BF – 4 cast house has two mud guns

for 2 tap holesbut one common drill machine. BF # 4 Cast house is provided with rocking runner &

pusher car in iron side.

The iron notch, which is used for tapping the hot metal from the furnace, is located slightly

above the floor of the hearth. When the furnace is in operation, the iron notch is completely filled

with a refractory material called taphole clay. To cast the hot metal from the furnace, a taphole is

drilled through this material, and after the cast has been completed, the hole is plugged again with

fresh clay that is extruded into the hole from a mud gun. The mud gun consists of a hollow,

cylindrical barrel and a plunger that pushes the clay out through a nozzle into the taphole. The

plunger is operated either electrically or hydro-pneumatically.

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As the hot metal leaves the taphole it is discharged into the trough which is a long, narrow basin. At

the far end of the trough there is a dam to hold back the hot metal until the depth of metal in the

trough is sufficient to contact the bottom of a refractory skimmer block. The skimmer holds back the

slag and diverts it into the slag runners.

The hot metal flows over the dam and down the iron runner where, by a series of gates, it is directed

in sequence to the train of ladles positioned under stationary spouts along the runner. A tilting spout

is positioned between two hot metal tracks. The spout is first tilted to fill the ladle on one track and

then tilted to back to fill the ladle on the other track. While the second ladle is being filled, the first

one can be replaced with an empty so that the cast can be continued uninterrupted while several

ladles are filled.

Fig8: Typical tilting runner arrangement

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2.5 Steel melting shops (SMS)

2.5.1 SMS I

The SMS I complex of BSL has 5 LD converters, each of 100/130 T capacity. Sin these

converters, technically pure oxygen (99.5%) is blown from top through a water cooled

lance so as to remove the impurities of hot metal oxidation. As a result of this oxygen

blowing process, hot metal converts into steel..

The steel produced at BSL is meant for products like plates and sheets and therefore, of

low carbon type. All the 3 types of steel viz. Killed, Semi Killed and Rimming is

produced at SMS-I. The rated capacity of shop is 2.5 MT of ingot steel.

In converter, the hot metal received from Blast Furnace is converted to steel by

removing carbon and other element present.

The change of this metal to steel is brought by blowing 99.5% pure oxygen in converter

by supersonic speed. Before starting the oxygen blowing, the converter is properly

charged in a defined sequence. At first lime is charged in the bottom. Then scrap

addition is done with the help of a charging crane. The reaction in the converter is

highly exothermic. At that time, the scrap acts as a coolant. Finally, hot metal is charged

and oxygen blowing is done by lowering the lance and opening the oxygen shut-off

valve. The lime is added as a flux and to maintain the basicity of bath.

After the corrective measures are taken temperature and samples are taken and if

found all right the heat is tapped. During tapping of steel, required amount of

Deoxidisers ( FeMn, FeSi, Al etc) are added in the teeming ladle depending upon the

quality of steel ie. whether Rimming, Semi Killed or Killed is made after tapping, the

converter is tilted to the other side of the rimming portion of slag in the converter is

dumped in the slag pot. The slag is then transferred to the slag yard. The teeming ladle

on the other hand is transferred to the teeming bay and teeming is done.

• Steel melting- process of removal of impurities like carbon and silicon.

• Oxygen blowing process.

• It receives hot metals from blast furnace.

• Output of sms1 is in ingot form.

• Output of sms2 is in slab form.

• From sms2 it goes to continuous casting shop.

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2.5.2 STEEL MELTING SHOP II

There are two LD Converters in the Shop each of 300 hundred Ton Capacity. SMS –II

differs with SMS-I mainly because of blowing process and gas recovery system. Unlike

SMS-I, SMS-II have got ―suppressed combustion system‖, where atmospheric air is not

allowed to enter in the hood area and the combustion of converter gas is suppressed.

Capacity of SMS-II is 2.25 MT of liquid Steel. At present, mainly Killed & Semi Killed

steels are produced in the shop.

Gas Cleaning Plant widely known as GCP is meant for treating the cases generated

from the Converter. It consists of hood, skirt, stack and down take, all fabricated of steel

tubes. The gases are cooled & cleaned while they pass through this system. This gas is

used by reheating furnaces and Soaking Pits.

Fig.9: Steel Melting Shop

23

2.5.2.1 CONTINUOUS CASTING:-

The main function of Continuous Casting Shop is to produce steel slabs directly from the

molten steel coming from SMS-II and sending them to Hot Strip Mill (HSM) for hot rolling.

• SRU : refining, composition, temperature

• Argon purging

a) Background – Continuous Casting is the process whereby molten steel is solidified

into a "semi-finished" billet, bloom, or slab for subsequent rolling in the finishing

mills. Prior to the introduction of Continuous Casting in the 1950s, steel was poured

into stationary molds to form "ingots". Since then, "continuous casting" has evolved to

achieve improved yield, quality, productivity and cost efficiency.

Fig.10: Vertical Continuous Casting

Steel from the electric or basic oxygen furnace is tapped into a ladle and taken to the continuous

casting machine. The ladle is raised onto a turret that rotates the ladle into the casting position

above the tundish. Liquid steel flows out of the ladle into the tundish, and then into a water-

cooled copper mold. Solidification begins in the mold, and continues through the First Zone and

Strand Guide. In this configuration, the strand is straightened, torch-cut, then discharged for

intermediate storage or hot charged for finished rolling.

Depending on the product end-use, various shapes are cast. In recent years, the

melting/casting/rolling processes have been linked while casting a shape that substantially

conforms to the finished product. The Near-Net-Shape cast section has most commonly been

24

applied to Beams and Flat Rolled products, and results in a highly efficient operation. The

complete process chain from liquid metal to finished rolling can be achieved within two hours.

Fig. 11: Conventional and Medium thickness slabs

b) Casting Overview –The continuous casting of steel is primarily a heat extraction

process. The heat or enthalpies are era extracted by a combination of heat transfer

mechanism: convection in the liquid pool due to the input of the momentum from the

tundish stream as well as buoyancy driver flow, heat conduction decreases

temperature gradient in the solid cell from the hotsolidification heat transfer does not

begin suddenly at the meniscus in the mould nor is its important limited to the mould,

spray and radiation cooling zone.

The continuous casting has technical and economical advantage. It is also free from

soaking, breakdown & roughing and smaller size product can be achived.

Factor affecting the solidification process :

1. Incoming steel temperature

2. Steel chemistry

3. Product size

4. mold- cooling characteristics

5. secondary cooling characteristics – intensity &time of spray cooling,

. -- time of radiation cooling

25

Fig.12: Continuous Casting Process

c) Equipments used in continuous casting :

(a) Ladle Turret (load capacity 2 x 280 ton.) ( g) TundishPriheating Station

(b) Ladle Cover Manipulator ( h ) Submerged Entry Nozzle (SEN)

Priheating Device

(c) Tundish ( i ) Mold Operator Pendent

(d) Tundish Cover ( j ) Emergency Runner System

(e) Tundish Stopper Rod Equipment

(f) Emergency Cut-off Gate

d) The casting process is comprised of the following sections:

1) A tundish, located above the mold to feed liquid steel to the mold at a regulated rate

2) A primary cooling zone or water-cooled copper mold through which the steel is fed from the

tundish, to generate a solidified outer shell sufficiently strong enough to maintain the strand

shape as it passes into the secondary cooling zone

26

3) A secondary cooling zone in association with a containment section positioned below the

mold, through which the still mostly-liquid strand passes and is sprayed with water or water

and air to further solidify the strand

4) Except straight Vertical Casters, an Unbending & Straightening section

5) A severing unit (cutting torch or mechanical shears) to cut the solidified strand into pieces for

removal and further processing

6) To minimize cracking, the casting surface should be maintained in the austenitic range, or in

general above 16000F.

e) Liquid steel transfer–

There are two steps involved in transferring liquid steel from the ladle to the molds.

First, the steel must be transferred (or teemed) from the ladle to the tundish. Next, the

steel is transferred from the tundish to the molds. Tundish-to-mold steel flow

regulation occurs through orifice devices of various designs: slide gates, stopper rods,

or metering nozzles, the latter controlled by tundish steel level adjustment.

Fig.13: Liquid Steel Transfer

27

f) Tundish –

The shape of the tundish is typically rectangular, but delta and "T" shapes are also

common. Nozzles are located along its bottom to distribute liquid steel to the molds.

The tundish also serves several other key functions:

Enhances oxide inclusion separation

Provides a continuous flow of liquid steel to the mold during ladle exchanges

Maintains a steady metal height above the nozzles to the molds, thereby keeping steel flow

constant and hence casting speed constant as well (for an open-pouring metering system).

Provides more stable stream patterns to the mold(s)

No. of burners per station 5, Calorific value 2100 Kcal/m3

g) Mold –

The main function of the mold is to establish a solid shell sufficient in strength to

contain its liquid core upon entry into the secondary spray cooling zone. Key product

elements are shape, shell thickness, uniform shell temperature distribution, defect-free

internal and surface quality with minimal porosity, and few non-metallic inclusions.

The mold is basically an open-ended box structure, containing a water-cooled inner

lining fabricated from a high purity copper alloy. Mold water transfers heat from the

solidifying shell. The working surface of the copper face is often plated with

chromium or nickel to provide a harder working surface, and to avoid copper pickup

on the surface of the cast strand, which can facilitate surface cracks on the product.

Mold heat transfer is both critical and complex. Mathematical and computer modeling

are typically utilized in developing a greater understanding of mold thermal

conditions, and to aid in proper design and operating practices. Heat transfer is

generally considered as a series of thermal resistances as follows:

Heat transfer through the solidifying shell

Heat transfer from the steel shell surface to the copper mold outer surface

Heat transfer through the copper mold

Heat transfer from the copper mold inner surface to the mold cooling water

Length of mold 1000 m

28

The casting mold interface can be divided into 3 sections –

2. From the meniscus to the point where the shell begin to form, in this region liquid

metal is separated from the mold by a thin layer of lubricating oil

3. The ragion over which the shell has insufficient strength to pull away from the

mold, but due to the condition of the casting surface, intermittent contect exists

4. The zone over which a definite gas exists, reduced heat transfer takes place by

radition& conduction across the gas in the gap

h) Mold Oscillator –

Mold oscillation is necessary to minimize friction and sticking of the solidifying shell,

and avoid shell tearing, and liquid steel breakouts, which can wreak havoc on

equipment and machine downtime due to clean up and repairs. Friction between the

shell and mold is reduced through the use of mold lubricants such as oils or powdered

fluxes. Oscillation is achieved either hydraulically or via motor-driven cams or levers

which support and reciprocate (or oscillate) the mold.

Mold oscillating cycles vary in frequency, stroke and pattern. However, a common

approach is to employ what is called "negative strip", a stroke pattern in which the

downward stroke of the cycle enables the mold to move down faster than the section

withdrawal speed. This enables compressive stresses to develop in the shell that

increase its strength by sealing surface fissures and porosity.

Types of mold :-

2. The solid block mold

3. Plant mold

4. Tubular mold

29

i) Mold Powder:

Used for the lubrication in the mold

Composition of mold powder : Fly ash 40 – 50%, Glass 10 – 23%, Calcium Fluoride

12 – 17%, Sodium Borate 1 – 8%, Sodium Carbonate 5 – 6%, Lime 3 – 6%, Iron

Oxide 3 – 4%, Gyolite 0 –4%, Sodium Silicofloride 0 – 1%.

j) Secondary Cooling –

Typically, the secondary cooling system is comprised of a series of zones, each

responsibleresponsible for a segment of controlled cooling of the solidifying strand as

it progresses through the machine. The sprayed medium is either water or a

combination of air and water.

Uniform spray cooling

Constant surface temperature

Multibank spray cooling

Radiant cooling

k) Nozzles –

Most frequently spray nozzle used on billet casting machine gives a full cone pattern

(round/square) although just under the mold one or two nozzle producing a V-pattern

are after employed; the length of the spray chamber may vary from as little as 0.5 m to

4 m. The spray chamber in a slab caster typically has a length in excess of 10 m.

l) Strand Containment –

The containment region is an integral part of the secondary cooling area. A series of

retaining rolls contain the strand, extending across opposite strand faces. Edge roll

containment may also be required. The focus of this area is to provide strand guidance

and containment until the solidifying shell is self-supporting.

In order to avoid compromises in product quality, careful consideration must be made

to minimize stresses associated with the roller arrangement and strand unbending.

30

Thus, roll layout, including spacing and roll diameters are carefully selected to

minimize between-roll bulging and liquid/solid interface strains.

Strand support requires maintaining strand shape, as the strand itself is a solidifying

shell containing a liquid core, that possesses bulging ferrostatic forces from head

pressure related to machine height. The area of greatest concern is high up in the

machine. Here, the bulging force is relatively small, but the shell is thinner and at its

weakest. To compensate for this inherent weakness and avoid shell rupturing and

resulting liquid steel breakouts, the roll diameter is small with tight spacing. Just

below the mold all four faces are typically supported, with only the broad faces

supported at regions lower in the machine.

m) Bending & Straightening –

Equally important to strand containment and guidance from the vertical to horizontal

plane are the unbending and straightening forces. As unbending occurs, the solid shell

outer radius is under tension, while the inner radius is under compression. The

resulting strain is dictated by the arc radius along with the mechanical properties of

the cast steel grade. If the strain along the outer radius is excessive, cracks could

occur, seriously affecting the quality of the steel. These strains are typically

minimized by incorporating a multi-point unbending process, in which the radii

become progressively larger in order to gradually straighten the product into the

horizontal plane.

After straightening, the strand is transferred on roller tables to a cut off machine,

which cuts the product into ordered lengths. Sectioning can be achieved either via

torches or mechanical shears. Then, depending on the shape or grade, the cast section

will either be placed in intermediate storage, hot-charged for finished rolling or sold as

a semi-finished product. Prior to hot rolling, the product will enter a reheat furnace to

adjust its thermal conditions to achieve optimum metallurgical properties and

dimensional tolerances.

31

2.6 Slabbing Mill:

• SMS 1 – Ingot route

• Ingot rolling

• Same function as CCS

• Rolling

• Shearing

• Piling

2.7 Hot strips mill(HSM):-

HSM is the customer of SMSII and Slabbing mill. In the furnaces of the hot-rolling mill, the slabs

produced in the continuous casting line are heated to a temperature of approximately 1,250°C, before

being rolled into hot-rolled wide strip. The finished material leaves the train (see diagram) at a

maximum speed of 20 m/s.

Fig. 14: Hot Strip Mill

32

01.) Slab roller table

02.) Deburring device

03.) Reheating furnace No. 5, walking

beam furnace

04.) Reheating furnace No. 4, pusher-type

furnace

05.) Reheating furnace No. 3, pusher-type

furnace

06.) Waste gas heat recovery furnaces 3, 4,

5

07.) High-pressure water descaling

08.) Sizing press

09) Roughing train

10.) Crop shear

11.) High-pressure water

descaling

12.) Finishing train

13.) Runout table/strip

cooling

14.) Downcoilers

15.) Transverse transport of

coils

16.) Longitudinal transport

of coils

17.) Coil weighting machine

18.) Walking beam conveyer

19.) V-plate conveyer

20.) Shear for cropping and

sampling

21.) Outer coil binding

22.) Binding through the

coil eye

23.) Finished coil weighting

machine

2.9 Cold Rolling Mill

Table 2 Cold Rolling Mill Process

Annealing

•Grains elongated, permanent strain, hard & brittle

•Heated then soaked, makes it soft

Skin Pass Mill

•Unrolled

•Rolled

•Surface hardening

Finishing

•SHEARING

•SLITTING

Pickling Line

• H2SO4

• HCl

Tandem Mill

• 5 stands(0.15mm)

• Hydraulic automation gauge control

• Computerized mill control

Temp. Control

• Emulsion spray

33

Chapter 3: RESULTS AND DISCUSSION

1. It’s is an integrated plan and all systems are accumulated at one place.

2. It follows 5W (What, When, Where, Who, Why) for its overall working.

3. BSL makes short coils, plates etc as its products.

4. Products: HR COILS, CR COILS, HR SHEETS, CR SHEETS, GC SHEET.

5. It’s BF has five furnaces

6. Each of the 3 furnaces has 3 strokes.

7. Furnace No. 2 has a modernized technique of usage.

8. It has a capability of 4500 T per day with 28 tours.

9. It has 2 SMS shops

10. SMS 1 only makes ingots and delivers it to Slabbing mill as it’s raw material.

11. It makes semi killed steel, so it has low C %.

12. It has 5 convertors out of which 3 are working at this time.

13. SMS2: It uses modernized technique of CCP.

14. So it’s a single process to form slab rather than ingots.

15. The final product of slabbing mill and SMS2 are the raw material of HSM.

16. Slabbing mill has ingot as its raw material which comes from SMS1.

17. In HSM thickness of slab is reduced using five strand roller and its products are steel

plates and steel sheet.

18. Sheets coming from HSM is fed as raw material to CRM.

19. And CRM has skin pass mill which is used for surface smoothing.

20. Its also had 4 strand Tandom mill which reduces the thickness between 0.6mm to 0.2

mm.

21. If required hood annealing of sheets is done in which coil is heated and then annealed.

22. It has CCAL (continuous cleaning and annealing line) where both cleaning and annealing

is done simultaneously.

23. Annealing is done to increase its ductility and machinability.

24. It also makes Galvanized sheets which is galvanized at 400 to 450 degree C with the help

of Zn coating over it.

34

Chapter 4: CONCLUSION AND FUTURE SCOPE

1. Only BF 2 is modernized so to increase the rate of production at a higher pace all of

the blast furnaces should be modernized.

2. SMS1 makes ingot which is then processed in slabbing mill to make slabs using

multiple processes and multiple machinery.

3. If SMS1 is modernized using CCP it can create slabs using just one process and one

setup.

4. Thus saving time and expenditure, increasing the production rate, leading to turn over.

5. SMS2 should be further modernized along with CCP in such a way that HRM is

included in the process thus producing Sheets and plates as final product.

35

REFRENCES

1. William Callister (2003). MATERIAL SCIENCE AND METALLURY.

DELHI: WILEY.

2. WILLIAM CALLISTER. (2011). MATERIAL SCIENCE AND METALLURY.

Available: http://en.wikipedia.org/wiki/Electric_arc_furnace. Last

accessed 20TH JUL 2013.

3. INTERNAL DOCUMENTS PROVIDED BY THE COMPANY