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December 201234

Indian Galvanised Steel Industry :An Overview

teel is a versatile product. The unique position of steel among the family of various products

remains unchallenged even today. Indeed, life Swithout iron and steel remains unimaginable. Steel

touches every aspect of our daily life. During the last three decades, the world has witnessed

many innovations in the process of steelmaking and various up-gradation in technology for making steel

competitive. Steel producers all over the world are giving major thrust on value addition and for producing superior

quality of products in a cost-effective and eco-friendly manner.

Steel has a wide range of applications in the automobile sector, railway system, ship building, aircrafts,

oil exploration, nuclear power stations, space satellites, generation, transmission and distribution of power, big engineering and construction projects, housing and all

infrastructural projects.However, perhaps the only demerit of steel is its natural tendency to corrode. Corrosion eats away steel, causing

significant loss to the economy of a country and sometimes leads to accidents. It has been estimated by

experts that corrosion costs about 4 percent of the G.D.P. of an industrialized country.

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December 201236

Coil CoatingCoil coating, the continuous

coating of steel coils, is a step in the manufacture of industrial products for use in automobiles, construction projects, building facades and all types of white goods.

Coils provide corrosion resistance, colour and texture of the steel surface. Once the metal strip has been coated, the panels are cut, shaped and fitted, which often involves high complex processing stages such as deep drawing and roll forming. The coating surface should be able to withstand mechanical damage, heat, chemicals and moisture. For example, a building has to withstand wind, rain and sun attack. In the white goods sector, surfaces are often exposed to various uses during use.

Besides the above, there is a multiplicity of application for coil – coated materials. For each material used and each step in various production stages, there is an acknowledged state-of-the-art process which represents current knowledge about the material and its processing.

New Process in Coil CoatingIn the thermal drying process, the

metal strip is heated to a temperature of about 2400C for 20 to 30 seconds in 40-50 mm long continuous curing ovens so that the solvents evaporate and the print film crosslinks. The strip is then coated down to room temperature. The process is expensive and environmentally unfriendly.

U-V Curable PrimersO n e a p p r o a c h t o

simplifying the drying process is to initiate cross linking using Ultra – Violet (UV) radiation rather than by thermal m e a n s . T h i s represents a complete departure from the traditional methods as t h e p r i m e r s a r e required to have a new

formulation with different raw materials, based on a

completely new type of binders and crosslinkings

agents. They have to be sensitive to UV light and within

seconds. Solvents are no longer necessary for such primer formulation and viscosity is adjusted by using water. This reduces the dwell time in the oven of 25 seconds in a traditional process, which is now reduced to 5/6 seconds.

Since no solvents are involved in this process, the thermal oxidation of oven exhausted gases, which is necessary in case of solvent – based technology is no longer required. The advantages of this UV curable system are noted below :

l Low energy consumption

l Reduced environmental pollution

l Smaller plant foot print

l Paint quality is as good as the solvent – based system.

Compared with conventional coil coatings, which involves degrassing the metal strip, pre-treatment, post-treatment, drying the surface and finally applying and curing the primer the use of UV – curable – pre-treatment primer enables a great deal of complexity to be removed. The process is shorter and lower temperatures are used. It is also possible to build a coating unit of this type downstream of a galvanizing line so that the primer can be applied at an early stage and pre-primed steel sheet can be produced without a separate coil coating line.

C h r o m a t e C o a t i n g a n d Chromate Free Coil Coating

The vast majority of traditional coil coating primers contain chromium

compounds such as strontium and zinc chromate to achieve the necessary corrosion resistance of the final product. Hexavalent Chromium Compounds (Chromium VI) serves an electro-chemical coupler that can inhibit corrosive reactions on metal surfaces. However, hexavalent chromium compounds, are classified as CARCINOGENS (Category 1 and 2), as well as being toxic and dangerous to environment.

Development of Chromate Free Primers

BASF Coatings started to explore various options for replacing toxic chromate pigment in early 1980s. It was clear that an alternative to chromate – containing primers should not only be chromate free but have to match or surplus the performance of its chromate containing rivals.

By 1992, the first generation universal chromate free primers for exterior applications were introduced. In 1995, there was a further decisive breakthrough, as BASF's chromate free universal primer or galvanized steel processing gave superior results over both chromate – free and chromate containing pre-treated coil. Thus, the first completely chromate – free coil coating system came into being. Continuous adaptation and optimization of coil coating technology during the subsequent years led to its further improvements.

The main resin system of chromate – free primers consists of a mixture of high molecular weight polyester and epoxy resins, cross-linked in a system based on amino res ins . The pigmentation too is, of course not only chromate – free, but also free of any other heavy metal or carcinogenic materials.

The coil coating technology, with its progressive development in the last decade or so, has created a significant market for it in the chemical and coated steel industry.

Zinc CoatingZinc-coated or galvanized steel

sheets offer a unique combination of high strength, formability, light weight, corrosion resistance aesthetic, recyclable and low cost material that is

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December 201238

unmatched by any other material. As a result, galvanized steel is an ideal material for multitude of applications like buildings, automobiles, household appliances including white goods, residential, commercial and industrial construction.

The function of the zinc layer on block steel is mainly three-fold :

l To retain the steel intact with its full initial strength.

l To provide the surface a more pleasing appearance.

l To increase the life of any suitable system applied over it.

Two Fold Advantage of Zinc Coating

(a) Zinc coating protects steel from corrosive attack in most atmosphere, acting as a continuous and lasting shield between the steel and atmosphere, as long as the zinc sheath remains unbroken.

(b) It acts as a galvanic protector, sacrificing itself slowly in presence of corrosive elements, by continuing to protect the steel even when moderate size areas of the bare metal have been exposed. This ability of zinc results from the fact that zinc is more electro-chemically active than steel of all industrial coating materials, zinc alone possesses this dual capability.

Due to the above qualities of zinc coating, the manufacturers and consumers of steel all over the world are now demanding a higher content of zinc in construction, automotive and white goods sectors. There are more than 800 galvanising line in operation throughout the world at present.

When steel is water-logged in molten zinc, the chemical reaction enduring bonds the zinc to the steel through the process of galvanizing. So, the zinc cannot be termed as a sealer like paint, as it does not coat the steel, it actually becomes at part of it. The zinc goes through a reaction with iron molecules within the steel itself to form galvanized steel.

Galvanising ProcessThere are two major processes

used in the manufacture of galvanized steel. These are :

l Hot – dipped Galvanising

l Electrolytic Galvanising

Hot – Dipped GalvanisingIt is one of the basic and efficient

corrosion resistant techniques for producing galvanized steel. During this process, steel coils are previously cleaned and pickled and then dipped in a bath of molten zinc to form a series of zinc / iron alloys integrated with the surface of steel. As steel is removed from the zinc bath, a layer of relatively pure zinc is deposited on the top of the alloy layer.

On solidification, the zinc assumes a crystalline metal structure, often called 'Spangling.' Spangles can be enhanced or reduced depending on the end-use.

In this process, the temperature of the molten zinc bath is kept at about 4600C. Exposed to atmosphere, zinc is converted to zinc oxide which again reacts with carbon dioxide to form zinc carbonate that helps further corrosion protection of the steel below.

Earlier, hot-dipped galvanized products effectively met the corrosion resistance but had a limited formability and lacked in surface quality. Hence, they were used in non-stringent areas like the construction sector but were uncapable to the automobile and white goods sector.

However, with the dramatic innovations during the last two decades, like use of radiant tube furnace, coating control and specially, after the development of galvanealing (GA) process, there has been a significant shift in the use from electro galvanizing to hot-dipped galvanized steel, particularly in the automobile sector.

Electro GalvanisingIn the electro-galvanising process,

zinc ions from the electrolyte is deposited on the strip surface (cathode) under the influence of electric current using either soluble or insoluble anodes. The electrolyte is usually zinc sulphate or zinc chloride or mixed. The electro-galvanised strips are past-treated with passivation solutions such as phosphate or chromate.

The plating process controls the coating thickness and help to achieve much thinner sheets as well as double side coating. These sheets have excellent surface finish and press formability for protection of auto body fuel tanks, exhaust pipes etc.

The investment cost of an Electro Galvanising Line (EGL) is almost the same as that of Continuous Hot-dipped Galvanizing Line (CGL) with GA facility. However, the EGLs do not have the annealing and temper cooling facilities in-built in the system.

Thus, to produce annealed electro – galvanized products, annealing and temper cooling have to be done prior to electro – galvanizing. This requires additional investment cost on capacity in annealing unit and skin pass mill, which makes the EGL process more expensive.

The cost of electricity in India is much higher than that of developed countries, which makes the operation cost of EGLs more expensive. Hence, under the Indian conditions, Continuous Galvanizing Lines (CGLs) are more attractive.

GALVANISING PROCESS

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Spangled ProductsSpangles are flowery patterns

observed on the surface of galvanized sheets, formed by the natural crystallization of zinc. Spangles are produced by adding small quantities of lead, tin or antimony into the molten bath of zinc. Spangles are desirable in applications like corrugated sheets used for roofing or in applications where parts are not exposed or do not r e qu i r e p a i n t i n g . Fo r o t h e r applications, the strip has to undergo a mini-spangle treatment so that spangle formation can be minimized.

Special Quality Galvanised ProductsGalvanised (GA) Products

The galvannealing process was developed to satisfy the stringent quality requirements of automotive industry for corrosion protection of the outer and inner panels of automobiles at optimum cost. In this process, an intermediate layer of iron and zinc is formed on the surface of the strip by diffusing iron (to the extent of 7~12 percent) in the coating from the substrate into the zinc coating. The substrate characteristics become more important in galvannealing than in ordinary galvanizing. Typical range of coating in GA product is 60-200 gm/m2 (both sides). These steels are used in the automotive industry because of its improved manufacturing performance in models that use lighter and stronger grades of steel.

Galvalume or ZincalumeGalvalume (a lso known as

Zincalume) consists of 55 percent aluminium, 43.5 percent zinc and 1.5 percent silicon by weight.

Galvalume provides a tough barrier between the atmospheric condition and the inner core of steel. Protection is offered by the corrosion resistance of coating itself. Galvalume also protects steel from corrosion at cut edges and scratches which is achieved through the sacrificial protection provided by the zinc in coating. Galvalume has a life equivalent to almost three times more that of ordinary galvanized steel.

Advantages of Using Galvalume as a Substrate are :

Corrosion ResistanceR e s i s t a n c e t o

atmospheric corrosion, cut e d g e a n d c r a c k protection.

Yield AdvantageAluminium makes up

55 percent of Galvalume b y w e i g h t b u t i t comprises 80 percent by volume. So, the coating weighs less, giving the end users more square feet per t o n n e t h a n o r d i n a r y galvanized steel.

FormabilityGalvalume is suitable for all

but severe forming operations. It can be easily bent, rolled formed and drawn without sacrificing coating adhesion.

High Temperature ResistantGalvalume can easily withstand

temperature up to 6000F without surface discolouration. Galvalume, is therefore, not only a superior material for roofing but also ideal for a range of other applications such as toasters, ovens and gas heaters.

Thermal ReflectivityDue to its good thermal reflectivity,

Galvalume steel roofs combined with insulation, make it a cost-effective roofing system.

Limitations of Using GalvalumeGalvalume coated steel cannot be used in frameworks in contact with wet concrete, products to be embedded in concrete, animal shelters where ammonia levels are constantly high, fertilizer storage sheds, culverts where the material is buried in the ground, water tanks and in high alkaline environment.

GalfanGalfan is 95 percent zinc and 5

percent aluminium. We used as a substrate instead of ordinary galvanized steel, the longevity of the products increases significantly. Galfan finds applications in marine wire ropes, small springs, pre-painted building panels as well as in appliances and automotive parts. Galfan coated steel is noted for its outstanding coating adhesion, making it an ideal material for

d e e p d r awn and

'zero thickness' bend applications. It is

about three times more corros ion resistant than the commercial quality galvanized steel.

Galbo SheetsGalbo sheets are special zinc-

coated products in which the base material is cold-rolled in Grade-D, is skin passed and stretch leveled with normal spangles. It is highly corrosion resistant with good formability, durability and paintability. Galbo sheets are used in white goods manufacturing and in the production of colour coated sheets.

Galvano SheetsThis galvanized plain sheets with

'zero spangles' has been developed by Tata Steel under the brand name 'Galvano'. The product is available in sheet and coil form and is being used successfully for general engineering applications.

Galvano is environmentally and economically advantageous. It has superior surface finish and mechanical properties with capabilities to meet the stringent quality requirements of the customers. Higher chrome passivation ensures better White Rust resistance. Zero spangles coupled with skin passing and uniform zinc coating ensures highest corrosion resistance. It has superior formability, bendability, durability and high paint adhesion quality.

Life of Galvanised Steell The use of galvanized steel for

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automotive body panels allows the present day automakers to guarantee a corrosion free life of 12 years or more, adding only a fraction of the total cost of production.

l In the appliances manufacturing sector, galvanized steel sheets are used in white goods and other house hold products providing a corrosion free life of over 15 years.

l In the construction sector, zinc-coated products have a useful corrosion free life of over 40 years.

Recyc lab i l i ty o f Coated Products

All types of zinc-coated galvanized steel products are recyclable. The Electric Arc Furnace (EAF) is the principal recycling route for zinc-coated steel. About 80 percent of the zinc available for recycling in India is being recycled.

EnvironmentZinc is a natural element that is

essential to all forms of life, including humans, animal, plants and micro-organs. While small quantities of zinc washes off coatings exposed to outer environment, this has a very little or no impact on the surrounding eco-system whatsoever.

On a macro-scale, the excellent corrosion protection provided by zinc coatings contributes significantly to the durability and life expectancy of steel products which in turn helps to conserve valuable natural resources and reduce the cost of maintenance, repair and replacement for the industry.

Indian Galvanised Steel IndustryThe Indian Galvanised Steel

Industry has developed its production process and upgraded its technology remarkably and is now capable of producing world-class products conforming to stringent international specifications for high end applications. These products have been well accepted in the global market.

Structure of Indian Galvanising Industry

Presently, India has 20 galvanising working unit with a capacity of 6.5 Mt. SAIL's new 1.2 Mtpy capacity CRM complex is likely to be operational by

2012-13. It will have a capacity to produce 0.36 Mtpy of coated steels.

Broad Sectorwise Consumption of Coated Sheets in India

According to industry sources, the broad sectorwise consumption pattern of coated sheets in India are as follows :

Sector

Share in Total

Consumption (%)

Construction 50

Consumer Durables 10

Drums/Barrel/Containers 6

Railways/Power/Irrigation 6

CPWD/PWDs/Other Govt. 5

Tube Makers

Furniture Makers

Engg. Units

Colour Coated Units

Automobile

Others

TOTAL

4

4

4

4

5

2

100

N.B. The figures are indicative.

Production of Coated (GP/GC) Sheets in India

Production of Coated Sheets in India between 2003-04 and 2011-12 are shown in Table – 1

Table – 1 : Production of Coated (GP/GC) Sheets in India 2003-04 and 2011-12 ('000 tonnes)

Year

2003-04

2004-05

2005-06

2006-07

2007-08

2008-09

2009-10

2010-11

2011-12 (P)

Production

3130

3672

3782

4321

4381

4554

4470

5556

5897

Y-o-Y Growth (%)

==

17.32

3.00

14.25

1.39

3.95

(-) 1.84

24.30

6.14

Table – 1 : Production of Coated (GP/GC) Sheets In India 2003-04 & 2011-12

('000 Tonnes)

The negative growth in 2009-10 over the previous year was due to a drop of 19.7 percent in the output of 'Other Secondary Producers' (except the

secondary major viz Essar, Ispat and JSWSL) whose production came down to 2.15 Mt in 2009-10 from 2.66 Mt in 2008-09.

ImportsImports of coated sheets (GP/GC)

by India between 2003-04 and 2011-12 are shown in Table -2.

Year

2003-04

2004-05

2005-06

2006-07

2007-08

2008-09

2009-10

2010-11

2011-12 (P)

Production Y-o-Y Growth (%)

Table – 2 : Imports of Coated Sheets by India : 2003-04 & 2011-12 ('000 tonnes)

102

106

134

195

268

294

287

353

365

==

3.92

26.42

45.52

37.44

9.70

(-) 2.38

23.00

3.40

The imports of coated sheets grew substantially after 2006-07 due to the robust domestic demand.

The negative growth of 2.38 percent in 2009-10 was due to a lower domestic demand as stocks of the producers increased from 127,000 tonnes as on April, 2009 to 239,000 tonnes as on March 31, 2009 – an increase of 112,000 tonnes. The global meltdown that started in October 2008 was also responsible for the decline.

ExportsExports of coated sheets (GP/GC)

by India between 2003-04 and 2011-12 are shown in Table -3.

Year

2003-04

2004-05

2005-06

2006-07

2007-08

2008-09

2009-10

2010-11

2011-12 (P)

Production Y-o-Y Growth (%)

Table – 3 : Exports of Coated Sheets by India : 2003-04 & 2011-12 ('000 tonnes)

1486

1843

1244

2173

2026

1849

1287

1312

1309

47.48

50.19

32.89

50.29

46.25

40.60

28.79

23.61

22.20

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India recorded its highest export of 2.17 Mt in 2006-07 followed by 2.03 Mt in 2007-08. This was due to the high quality of Indian coated sheets which was well-accepted in the global market. Exports declined from 2009-10 due to the global crisis stat started in October, 2008 and the current Eurozone financial crisis which resulted in the decline of global demand and low prices in the global market. Besides, there was an increased demand in the domestic market.

India was a net exporter of coated sheets between 2003-04 and 2011-12.

Apparent ConsumptionThe apparent consumption of

coated (GP/GC) sheets in India between 2003-04 and 2011-12 are shown in Table – 4.

YearApparent

Consumption Y-o-Y Growth (%)

Table – 4 : Apparent Consumption Coated (GP/GC) Sheets In India : 2003-04 to

2011-12 ('000 tonnes)

2003-04

2004-05

2005-06

2006-07

2007-08

2008-09

2009-10

2010-11

2011-12 (P)

1691

1926

2051

2400

2617

3018

3358

4658

4885

==

13.90

6.49

17.02

9.04

15.32

11.27

38.71

4.87

India's consumption of coated sheets during 2010-11 and 2011-12 increased in volume term due to higher offtakes by the automobile, white good and construction sectors.

Special Application of Coated ProductsAutomobile Industry

Coated (GP/GC) steel sheets are being extensively used in building bus and truck bodies. Galvansied (GA) steel is used in the outer body panels of car because of its improved performance in models which use highter and stronger grades of steel. Electro-galvansied steel sheets have an ultra smooth surface coating thickness which is desirable for autobody external panels. Galfan steel is used for severally

formed components for auto body exterior panels.

Corros ion Protect ion of Autobody Panels

In case of autobody panels, corrosion is usually classified as either of cosmetic type or perforation type.

Cosmetic CorrosionThis means degradation of visible

external components of vehicles such as door panels, engine hoods, boot-hood caused by corrosion. This type of corrosion occurs mainly due to gravel import, small bumps, scratch edges and other minor injury.

Perforation CorrosionThis type of corrosion from local

pitting initiated on the unprotected inside surface or corners of the autobody where moisture or corrosive slush can be trapped or in the relatively in accessible areas difficult to treat and point.

Galvanized Reinforcement BarsGalvanized coatings provide

important advantages for protection of re inforcement . The corrosion r e s i s t a n c e o f c o a t e d s t e e l reinforcement are superior to uncoated bars while the bond strengths of galvanized and black steel bars to concrete are not very different.

Protection we assures against corrosion in reinforcement bars embedded in concrete rely on minimizing or preventing the corrosive electro-chemical process. Two types of protective measurers are mentioned below :

l Preventing access of harmful materials like water, oxygen, salts, carbon dioxide etc. to the steel surface.

l Modifying the electro-chemical process through use of corrosion inhibitors or by cathodic protection.

Galvanized Rebars have been used in India in many places. Some of these are :

l Lotus Temple, Delhi

l Residential buildings in JNPT, Uran

l Residential buildings, Wadala

l Mahanagar Gas Ltd., Mumbai

l Guest House, Mangalore

l Central Railway, Wadi Bunder

l Bus Stands built in many cities.

Colour Coated SheetsColour coating usually refers to the

application of liquid paint coat over the substrate in an automatic continuous process after pre-treatment. The pre-painted colour coated steel is a very high value-added product that combines the best properties of the substrate and organic coating importing it an aesthetic finish, high degree of durability and high corrosion resistance capability.

SubstrateColour coating is done on various

substrates to produce most cost effective, quality assured products with top coat compatible with environment.

The substrates usually used are :

l Hot Dipped Galvanised Steel

l Electro – Galvanised Steel

l Galvalume

l Galbo Sheets

l Aluminium

l Pre-treatment

Pre-treatment of the substrate is a very important operation required to better adhesion, formability of pre-painted steel sheets.

Leading colour coated sheet producers in India have introduced NO-RINSE technology in place of phosphating (phosphate coating) over galvanized strip because of better bath maintenance, uniform crystal structure of coating as well as to meet the demand of end-users for more flexibility of colour coated steel.

No-Rinse coating pre-treatment is a very thin layer of chemical treatment that bonds the coating surface of steel to the subsequently applied paint to ensure excellent paint adhesion and corrosion resistance of the steel surface.

PrimerAfter pre-treatment, a primer of

uniform layer is applied on the pre-treated surface. The primer provides flexibility to the paint system and helps corrosion resistance since it contains corrosion inhibitors. The primer is cured in the oven with accurate temperature controls with great precision.

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Various types of primers are available based on different resins like epoxy, polyester, polyurethane and PVC. Epoxy primers are preferred for use in roofing as it has chromate p igment for better corrosion resistance. The established dangers in using certain chromium coatings and the present trend towards the use of chromate – free coatings has been discussed earlier.

Top CoatAfter pre-treatment, the primer

surface is coated at uniformly coated thickness and then cured in the oven. The top quote contains combination of coloured pigments and additives which provide the required color and other performance properties like ultra-violet resistance. The coated products is then rigorously tested before clearing for further applications. Most of the roofing and construction markets for colour coated sheets use top coats which are based on polyester, Fluorocarbon (PVDF), silicon modified polyester (SMP) and plastisal for cost-effectiveness and durability.

Role of PrimerThe success of entire colour

coating system depends on the primer the crucial first coating layer applied on the pre-treated metal sheets.

Producers of Colour Coated Sheets in India

Essar Steel is now the biggest producer of colour coated sheets in

India with a total capacity of 450,000 tpy after acquiring SPSL and steel corporation of Gujarat with a capacity of 50,000 tpy JSW Ispat whose original capacity was 50,000 tpy is installing two new colour coating lines at Kalmeshwar to take its capacity to 1 Mtpy. Bhushan Steel has installed a 120,000 tpy colour coating line at Khopoli in Maharashtra. Uttam Galva has set up a colour coating line of 80,000 tpy also at Khopoli.

Tata Blue Scope joint venture on 50:50 basis is operating a metallic and colour coating / painting facility at Bara near Jamshedpur which has a capacity of 150,000 tpy of pre-painted zinc and aluminium steel called COLOR BOND.

Estimated DemandThe estimated demand of colour coated sheets in India is shown below :

YearY-o-Y

Growth (%)Domestic Demand

('000 tonnes)

2005-06

2006-07

2007-08

2008-09

2009-10

2010-11

85

110

140

175

215

260

==

29.41

27.27

25.00

22.86

20.93

P e r f o r m a n c e o f I n d i a n Galvanised Steel Industry in H1 of FY'13

The performance of Indian galvanized steel industry during April – September, 2012 (H1 of FY'12) is

H1 of FY'13 (P) H1 of FY'12 % Change

3237 2933 10.36

Imports ('000 tonnes)

225 156 44.23

Exports ('000 tonnes)

789 601 31.28

Consumption ('000 tonnes)

2729 2489 9.64

Production for Sale ('000 tonnes)

presented below :

ConclusionThe Indian galvanized steel industry

has developed significantly in the last decade. The major producers are upgrading their production technology in a continuous manner to produce GP / GC Sheets in a cost-effective and eco-friendly manner.

Indian galvanized products have been well-accepted in the global market and exports of these products have been the highest in volume terms among the finished carbon steel products in recent years. With the thrust on increasing rural consumption of steel the use of galvanized steel will increase substantially in future years.

Acknowledgments1. Articles by Dr. Lothar Jondel of BASF and P. Heffer

at all published in Steel Times International – January, 2005

2. Various articles by Dr. Amit Chatterjee, Formerly

Advisor, Tata Steel and L. Pugazhenthy, E.D., ILZDA