On

Under the guidance of:

Mr. Souvik Banerjee (Manager, LD#1-Operations)

Submitted by:

RISHAV GHOSH

Department of Metallurgical & Material Engineering

STUDY OF CARBON

VARIATION IN WR3 GRADE

Jadavpur University, Kolkata

A

Technical Report

Technical Report

1

Certificate

This is to certify that the work hereby presented by Rishav Ghosh in the project, titled “Study of

Carbon Variation in WR3 grade” for the one-month training program at Tata Steel Ltd.,

Jamshedpur, is a genuine account of work carried out during the period from 26th May, 2015 to

22nd June, 2015 under the guidance of Mr Souvik Banerjee, Manager LD#1 - Operations, Tata

Steel Ltd. Jamshedpur.

The matter embodied in the project report to the best of my knowledge is a complete bonafide

piece of work.

RISHAV GHOSH

Department of Metallurgical & Material Engineering

Jadavpur University, Kolkata

Date: 22nd June, 2015

This is to certify that the above declaration is true to the best of my knowledge.

Souvik Banerjee

Manager

LD#1- Operations

Tata Steel Ltd. Jamshedpur

2

Acknowledgment

This two months project at SMLP, LD#1 has been a steep learning curve for me. Working on this

project not only helped me to understand the entire Secondary Steel-making Process, but also

appreciate its importance and gain practical knowledge in this field. Being a novice in the area the

project could not have been successful without the encouragement and backing provided to me by

various people at different stages of the project.

I am extremely grateful to Mr Souvik Banerjee, Manager, LD#1 – Operations for providing me

with this opportunity. I would also like to thank my guides at LD#1 - Mr Ram Bachchan Kumar

(Senior Manager, LD#1 Technical Services) and Ms. Khushboo Sinha(Manager, LD#1 Technical

Services) for their infallible support and constant encouragement throughout.

I am highly grateful to SNTI for providing me the opportunity to work on the given problem.

Lectures and discussion organized by SNTI were very useful in enhancing my knowledge about

the manufacturing industry. These lectures will definitely help me to become a better professional

in future.

Finally, I would like to thank all the staff of SMLP, LD#1 for their constant support, time &

valuable advice from their experience throughout my project.

Rishav Ghosh

Department of Metallurgical & Material Engineering

Jadavpur University, Kolkata

3

Table of Content

1. Company Profile 4

2. Major Units of Steelmaking Shop 6

2.1 Hot Metal Receiving and Handling (Torpedo Control) 6

2.2 Scrap Handling 6

2.3 Hot Metal Desulphurisation (HMDS) 7

2.4 Basic Oxygen Steelmaking (PSM) 8

2.5 Secondary Metallurgy Ladle Practice (SMLP) 9

2.6 Continuous Caster 10

3. Secondary Metallurgy

3.1 Why Secondary Metallurgy ? 11

3.2 Secondary Metallurgical Processes 11

4. Ladle Furnace 12

4.1 What Is A Ladle Furnace 12

4.2 Functions Of A Ladle Furnace 13

4.3 Ladle Refractory 13

5. Introduction

5.1 What is WR3 grade ? 14

5.2 Diversion of WR3 Heat 14

5.3 Diversion due to carbon variation 15

5.3.1. On-Line Purging Carbon 15

5.3.2. Treatment Time 17

5.3.3. Arcing Duration 18

5.3.4. Bypass Purging 19

5.3.5. Top lancing 20

6. Recommendations 21

4

1 . Company Profile

Tata Steel Limited (formerly Tata Iron and Steel Company Limited (TISCO)) is an Indian

multinational steelmaking company headquartered in Mumbai, Maharashtra, India, and a

subsidiary of the Tata Group. It is the 6th largest steel producing company in the world, with an

annual crude steel capacity of 23.8 million tonnes, and the largest private-sector steel company in

India measured by domestic production.

Tata Steel has manufacturing operations in 26 countries, including Australia, China, India, the

Netherlands, Singapore, Thailand and the United Kingdom, and employs around 81,600 people.

Its largest plant is located in Jamshedpur, Jharkhand. In 2007 Tata Steel acquired the UK-based

steel maker Corus in what was the largest international acquisition by an Indian company to date.

Tata Steel is listed on the Bombay Stock Exchange, where it is a constituent of the BSE SENSEX

index, and the National Stock Exchange of India. It is ranked 401st in the 2012 Fortune Global 500

ranking of the world's biggest corporations. It is the eighth most-valuable Indian brand according

to an annual survey conducted by Brand Finance and The Economic Times in 2010.

Tata Steel is headquartered in Mumbai, Maharashtra, India and has its marketing headquarters at

the Tata Centre in Kolkata, West Bengal. It has a presence in around 50 countries with

manufacturing operations in 26 countries including: India, Malaysia, Vietnam, Thailand, Dubai,

Daggaron, Ivory Coast, Mozambique, South Africa, Australia, United Kingdom, The Netherlands,

France and Canada.

Tata Steel primarily serves customers in the automotive, construction, consumer goods,

engineering, packaging, lifting and excavating, energy and power, aerospace, shipbuilding, rail

and defence and security sectors.

Tata Steel has set a target of achieving an annual production capacity of 100 million tons by 2015;

it is planning for capacity expansion to be balanced roughly 50:50 between Greenfield

developments and acquisitions. Overseas acquisitions have already added an additional 21.4

million tonnes of capacity, including Corus (18.2 million tonnes), NatSteel (2 million tonnes) and

Millennium Steel (1.2 million tonnes). Tata plans to add another 29 million tonnes of capacity

through acquisitions.

5

Major Greenfield & Brownfield steel plant expansion projects planned by Tata Steel include:

• A 6 million tonne per annum capacity plant in Kalinganagar, Odisha, India.

• an expansion of the capacity of its plant in Jharkhand, India from 6.8 to 10 million tonnes per

annum;

• A 5 million tonne per annum capacity plant in Chhattisgarh, India

• A 3 million tonne per annum capacity plant in Iran;

• A 2.4 million tonne per annum capacity plant in Bangladesh; A 10.5 million tonne per

annum capacity plant in Vietnam

• A 6 million tonne per annum capacity plant in Haveri, Karnataka.

6

2. Major Units of Steelmaking Shop

2.1 Hot Metal Receiving and Handling (TORPEDO CONTROL)

The hot metal, or liquid pig iron, is the primary source of iron units and energy in the oxygen

steelmaking process. Hot metal is usually produced in blast furnaces, where it is cast into

submarine shaped torpedo cars and transported either to a desulfurization station or directly to the

steelmaking shop.

The chemical composition of hot metal can vary substantially, but typically it contains about

%C %Mn %Si %S %P TEMP.(oC)

HOT METAL 4.3 0.2-0.3 0.2 – 1.5 0.05 0.17-0.2 1330-1400

STEEL 0.03 0.1 0 0.005-0.015 0.01 1620-1720

The composition of the hot metal depends on the practice and charge in the blast furnace.

Generally, there is a decrease in the silicon content and an increase in the sulphur of the hot metal

with colder blast furnace practices. The phosphorus contents of the hot metal increases if the BOF

slag is recycled at the sinter plant.

Carbon and silicon are the chief contributors of energy. The hot metal silicon affects the amount

of scrap charged in the heat. If the hot metal silicon is high, there will be greater

Amount of heat generated due to its oxidation, hence more scrap can be charged in the heat. Hot

metal silicon also affects the slag volume, and therefore the lime consumption and resultant iron

yield.

In LD#1, hot metal is poured into transfer ladles kept in torpedo pit which is then carried by torpedo

cranes to the desulphurisation station. The weighing of the hot metal is done on a scale while it is

being poured into the transfer ladle. It is very important that the weight of the hot metal is

accurately known, as any error can cause problems in turndown chemistry, temperature and heat

size in the BOF. This weight is an important input to the static charge model.

2.2 Scrap Handling Scrap is the second largest source of iron units in the steelmaking operation after hot metal. Scrap

is basically recycled iron or steel, having Fe content of almost 92% that is either generated within

the mill (e.g. slab crops, pit scrap, cold iron or home scrap), or purchased from an outside source.

The scrap is weighed when loaded in the scrap box by using electromagnets and is mixed based

on requirements of the upcoming heat. Then the box is transported to the BOF. It is important that

the crane operator loads correct amounts and types of scrap (WRP, POOLED IRON, CLEAN)

Otherwise the turndown performance of the heat will be adversely affected.

7

Normally, the lighter scrap is loaded in the front, and the heavier scrap in the rear end of the box.

This causes the lighter scrap to land first in the furnace as the scrap box is tilted. It is preferable

that the lighter scrap fall on the refractory lining first, before the heavier scrap, to minimize

refractory damage. Also, since heavy scrap is more difficult to melt than light scrap, it is preferable

that it sits on top so that it is closest to the area of oxygen jet impingement and hence melts faster.

Unmelted scrap can cause significant problems in process control. It may result in high

temperatures or missed chemistries at turndown.

Most steelmaking shops typically use about 20 to 35% of their total metallic charge as scrap, with

the exact amount depending on the capacity of the steelmaking process. Scrap pieces that are too

large to be charged into the furnace are cut into smaller pieces by means of shears or flame cutting.

2.3 Hot Metal Desulphurization (HMDS)

Sulphur is an undesirable element in steel and is kept to the lowest level. Sulphur in steel mainly

comes from coal/coke charged in blast furnaces.

Hot metal is desulphurised in the transfer ladle by the injection of a mixture of calcium carbide

and magnesium, through a refractory coated immersed lance. There are two

-possible injection combinations of the desulphurization reagents including

calcium carbide on its own (monoinjection) and calcium carbide and

magnesium in combination (co-injection). Prior to treatment, the weighed

hot metal transfer ladle is placed on a ladle car with tilting frame by the

overhead ladle handling crane. The ladle car is driven inside refractory

faced enclosures, which are sealed when the ladle is inside the enclosure

by sliding doors. A sample taken from the transfer ladle prior to treatment

is analyzed, and the result is used to calculate the amount of calcium

carbide and magnesium required to achieve the necessary Fig 1: Desulphurization

amount of desulphurization. The injection lance, which is a thick walled steel tube inside a

refractory coating, is positioned above the ladle, and then lowered through a port in the enclosure

cover.

Before the tip of the lance enters the hot metal surface, the powder transport gas N2 is

switched on, and then the calcium carbide powder begins to flow though the lance. Once

powder flow is established, the lance is driven down into the hot metal to a predetermined

position above the refractory bottom of the ladle. After sometime, Magnesium is injected

and the calcium carbide injection rate is reduced.

8

When injection is complete, the carry-over slag plus the slag formed on top of the ladle during

injection is removed by a slag skimming machine (Raking). This is done by rotating the ladle in

its tilting frame on the transfer car. Slag is collected in slag pots placed on one end of the transfer

car. Once a slag pot is filled up the car will transfer the same through the unit and out into the slag

bay where the filled-up slag pot will be picked up by the overhead crane and replaced by a fresh

slag pot.

DS IN DS OUT

% Sulphur 0.06 0.005

2.4 Basic Oxygen Furnace (Primary Steel Making)

The purpose of the Basic Oxygen Steelmaking (BOS) process is to refine the hot metal produced

in the blast furnace into raw liquid steel. Steel is made in discrete batches called heats. The furnace

or converter is a barrel shaped, open topped, refractory lined vessel that can rotate on a horizontal

trunion axis.

The required quantities of hot metal, scrap, oxygen, and fluxes vary according to their chemical

compositions and temperatures, and to the desired chemistry and temperature of the steel to be

tapped. Fluxes are minerals added early in the oxygen blow, to control sulphur and phosphorous

and to control erosion of the furnace refractory lining. The exothermic oxidation reactions that

occur during BOS generate a lot of heat energy - more than is necessary to attain the target steel

temperature. This extra heat is used to melt scrap and/or iron ore additions.

The energy required to raise the fluxes, scrap and hot metal

to steelmaking temperatures is provided by oxidation of

various elements in the charge materials. The principal

elements are iron, silicon, carbon, manganese and

phosphorous. The liquid pig iron or hot metal provides

almost all of the silicon, carbon, manganese and

phosphorous, with lesser amounts coming from the scrap.

Both the high temperatures of the liquid pig iron and the

intense stirring provided when the oxygen jet is introduced,

contribute to the fast oxidation (burning or combustion) of

these elements and a resultant rapid, large energy release.

Silicon, Manganese, Iron and Phosphorous form oxides,

which, combine with the flux to form Slag. The vigorous

stirring fosters a speedy reaction and enables the transfer of

energy to the slag and steel bath. Carbon, when oxidized,

leaves the process in gaseous form, principally as carbon

monoxide. During the blow, the slag, reaction gases Fig. 2: Sectional View of Vessel contact

9

and steel (as tiny droplets) make up a foamy emulsion. The large surface area of the steel droplets,

in with the slag, at high temperatures and vigorous stirring, allow quick reactions and rapid mass

transfer of elements from metal and gas phases to the slag. When the blow is finished the slag

floats on top of the steel bath.

Overall process of primary steel making in LD Vessel can be shown by following figure:

Fig. 3: Schematic of operational steps in oxygen steelmaking process (BOF)

2.5 Secondary Metallurgy and Ladle Preparation (SMLP) The steel after refining in the BOF and OLP is further sent to three LF Stations where

• Minute additions of ferro-alloys and micro alloying takes place to fine tune the steel

compositions.

• The molten steel is heated by arcing with graphite electrodes with a cover placed over the

ladle.

• It has provision for bottom Argon gas purging for temperature and bath homogenisation

Synthetic slag is added in ladle to trigger the formation of slag in the bath.

• Further steps for effective de-oxidation, de-phosphorisation, desulphurisation are taken.

Thus, various grades of steel are obtained based on the requirements of the consumer.

10

2.6 Continuous Caster

The liquid steel ladles after secondary treatment are brought to the ladle preparation aisle, lifted

by the ladle cranes and placed on the charging arm of the ladle turret. The steel ladle is then brought

to the casting position by rotating the turret by 180º.

In the meantime refractory lined and preheated tundish, travelling on tundish car is brought to the

casting position over the mould just before placing the turret. Once the turret is positioned over

the tundish, the liquid steel is allowed to flow into the tundish from the ladle by opening the ladle

slide gate. After the desired level is reached in the tundish, the tundish nozzle is opened and the

molten metal starts pouring into the mould. When the level is reached in the mould, the dummy

bar/strand withdrawal starts. The mould and spray cooling and the mould oscillation also starts

along with the dummy bar/cast strand withdrawal. The dummy bar which makes a temporary

bottom inside the mould pulls the cast strand and gets disconnected once the cast strand reaches

the withdrawal and straightening unit. The cast strand after straightening is transported into the

soaking furnace via roller table. A pendulum shear cuts the thin slab into the desired length.

Fig.4: Continuous Casting

11

3. Secondary Metallurgy

3.1 Why Secondary Metallurgy

To meet the ever increasing “Quality” demands of the market place, which is becoming

globally competitive.

Difficult to carry out certain aspects of refining in an oxygen steel making furnace.

Reduce the burden of primary steel making

To increase the Productivity

3.2 Secondary Metallurgical Processes

OLP, ARS

Ladle Furnace

CAS-OB

VD, VAD, VADR, VOD , DH, RH, RH-OB, RH-MFB

Stream Degasser

12

4. Ladle Furnace

4.1 What Is A Ladle Furnace

Fig. 5: Ladle Furnace

13

4.2 Functions of a Ladle Furnace

• Homogenization of Steel with respect to Temperature and Composition.

• Improvement of alloy Yield and to control final composition of steel to a narrow range.

• Flotation and removal of inclusion by metal stirring and absorption into top slags.

• Desulphurisation.

• Inclusion modification by injection of suitable reactants.

• Dephosphorization by special slags.

• The holding of ladles for sequence casting.

4.3 Ladle Refractory

Fig.6: Ladle Refractory

14

5. WR3-Introduction

5.1 What is WR3 grade?

WR3 grade is a special grade steel prepared specifically in LF#2 of LD#1 shop. These steels are

cast and shaped in the form of wire rods used specifically for MIG welding purposes. Lincoln

grade WR3 wire rods(ER70S-6) finds extensive applications in CO2 gas welding electrodes owing

to its favourable mechanical properties. The following table indicates the specifications of WR3

grade steel.

Table 1: Chemical specification of WR3 grade

Component

C

Mn

Si

S

P

N2 (ppm)

Min 0.06 1.42 0.80

Max 0.08 1.50 0.90 0.015 0.018 50

5.2 Diversion of WR3 Heat

Stringent quality demands along with tighter specifications by the market has made ladle treatment

one of the prime as well as key refining operations in the entire steelmaking process chain. This is

because the final adjustments in the chemistry of the finished product can’t be done after the

molten steel is tapped from the ladle for casting. Thus ladle treatment is necessary for attainment

of near complete homogenization with respect to chemical composition and melt temperature prior

to casting. In addition, the ladle treatment also involves deoxidation, inclusion floatation,

desulphurization, degassing and other metallurgical phenomenon.

In the past financial year (Apr ’14- Mar’15), several cases of diversion from WR3 grades to TMT

grades and other grades have been reported. Deviation in carbon, manganese, suplhur, silicon,

phosphorous and nitrogen from the desired specifications due to improper additions , faulty

process design, unsteady casting and top lancing have been accounted for as the main reasons for

such diversion.

The main causes of diversion can be understood properly from the comparison chart shown below.

As observed from the plot, the primary causes for heat diversion in WR3 grades are faulty process

design, high carbon, phosphorous, silicon and manganese percentage in the final product.

15

5.3 Diversion due to carbon variation

Diversion in heat due to increase in carbon content of the heat can be attributed to the following

causes :-

5.3.1. OLP(On-line Purging) Carbon

In most of the steel plants all over the world, after completion of each heat in the LD converter,

the liquid steel is tapped in ladle along with the addition of deoxidizers and ferro-alloys during

vessel tapping into the ladle. In LD-1 at Tata Steel, Jamshedpur the ladle is then transferred to the

Online Purging / Rinsing Station(OLP) where purging of argon gas into liquid steel bath contained

in the ladle through top lance is carried out to generate enough bath turbulence to produce thermal

and chemical homogeneity in liquid steel before treating in the secondary refining units and

sending to the caster as per the caster requirements. Any improper mixing of the liquid steel bath

at OLP may lead to increase in chemistry of the same during ladle treatment which lead to

diversion/ downgrading of heats- as is the case in the grade under consideration. An undue increase

in carbon content of liquid steel higher than prescribed specification have been observed in spite

of similar addition and homogenization practices. The following box plot shows the range of OLP

carbon for which the heat is not likely to be diverted.

10.8

3.7

11.1

0.7

4.2

16.3

3.73

1.63

0.59

1.9

0

2

4

6

8

10

12

14

16

18

% D

iver

sio

n

Causes of Diversion

16

It can be observed that the OLP-carbon level varies over a large range in diverted WR3 grades

compared to the proper heats. Hence, to meet desired specifications of WR3 grade, OLP carbon

in the range of 0.041-0.05 would indicate the possibility of a proper heat. Any deviation from this

range would result in diversion.

17

5.3.2. Treatment Time

Ladle treatment time has a profound effect on the carbon content of the heat prior to ladle

treatment. High ladle treatment would mean higher purging and duration which results in higher

amount of carbon pick-up due to electrode wash because of vigorous bath condition.

From the box plot above, we can observe a narrow treatment time range for proper heats of WR3

compared to a high treatment time range in case of diverted heats.

For proper heats, ladle treatment time, specifically, between 59-77 minutes should be ensured.

Treatment time higher than 77 minutes would lead to diversion due to prolonged period of carbon

pick-up. Higher treatment time would mean higher residence time of the heat in the ladle requiring

higher arcing duration to maintain the requisite temperature for casting resulting in more electrode

wash and hence, higher carbon pick-up.

18

5.3.3. Arcing duration

Arcing in ladle furnace is necessary to increase the temperature of the bath for melting of ferro-

alloy additions and other additions. Arcing is indispensable to increase the temperature to the

optimum limit as well as provide the adequate superheat to compensate for any heat loss.

Practically a minute of arcing raises the temperature of the bath by 3oC. A temperature of 1600-

1620oC is generally maintained in the bath before emptying it into the tundish. Thus arcing

duration plays a vital role in the temperature of the bath as well as the bath chemistry.

The box plot above shows that the arcing duration for good heats is lesser than the arcing duration

for diverted/bad heats.

Total arcing duration of 30-38 minutes would ensure the heat meeting its desired specifications.

Arcing time greater than 38 minutes would lead to improper steel chemistry leading to diversion.

Higher arcing duration would mean bath will have higher carbon pick-up due to increased duration

of electrode wash.

19

5.3.4. Bypass purging

Bypass purging refers to a higher rate of purging of argon gas through the ladle porous plug.

Bypass purging serves to perform two distinctive functions viz. i) to ensure proper homogensation

and mixing upon ferro-alloy addition and ii) for opening of jammed porous plug

The box chart shows that higher values of bypass purging duration leads to improper heat

compared to lower bypass purging duration in proper heats. An optimum bypass purging duration

of 3-11 minutes is necessary to obtain the desired chemistry in the heat. However, bypass purging

for more than 11 minutes would lead to deviation in the chemistry-higher carbon level

consequently leading to diversion of the WR3 grades to TMT grade. Probable explanation of such

behavior might be higher levels of carbon pickup as a result of electrode wash due to vigorous

condition of the bath.

20

5.3.5. Top lancing

Top lancing is done when the ladle porous plug is blocked and bottom purging is not possible.

However, the gas flow rate in top lancing is uncontrollable and bath splashing and bath

inhomogeneity is rampant in such cases.

The box plot shows that heats treated without top lancing are proper compared to the heats purged

with top lance. The primary reason that can be attributed to this behavior is bath splashing leading

to electrode wash. Also, the vigorous reaction rate in the bath might lead to an unstable slag with

the tendency of impurity reversion into the steel from the slag.

Thus, for casting of proper WR3 grade, top lancing should be avoided. Top lancing for any time

duration would lead to improper chemistry resulting in a diverted grade.

21

6.Recommendations

Based on the analysis of WR3 heats in the past financial year, for lesser diversion to substandard

grades , the following recommendations are to be implemented :-

OLP treatment should be optimized to attain a carbon chemistry of 0.041-0.045 in the melt

before treatment at the ladle furnace.

Treatment time in the ladle furnace should not exceed more than 77 minutes neither should

the treatment time be inadequate i.e. less than 59 minutes.

The total time duration of arcing in the ladle furnace should be maintained between 30-38

minutes.

Porous plug jamming should be analyzed and resolved to avoid bypass purging and top

lancing.