INTRODUCTIONAluminium and its alloys are well known for their light

weight, high strength to weight ratio, excellent corrosion resistance, high electrical conductivity, increased thermal conductivity, non-toxicity, good reflectivity, attractive appearance, non-magnetic nature and so on, making it a versatile one for suitable for varied applications. It has been a long cherished desire for Steel to enter into the areas dominated by aluminium which led to the evolution of Special Steels covering alloy/stainless Steels & Steels with restricted alloy content. Today, a mammoth of special Steels are produced in the world conferring properties like high strength to weight ratio, aesthetic appeal, high corrosion resistance, non-magnetic nature, high temperature resistance, increased stiffness, non-toxicity, improved strength, low temperature toughness etc. paving way towards a plethora of applications.

However, there still remain many areas where aluminium continues to be the Numero Uno. It is not surprising to say that aluminium played a pivotal role in development of many special Steels. The concept of killed Steels for production of low oxygen content for increased fatigue resistance, low

B. V. R. RAJA,Senior Manager - Q AAlloy Steels Plant, SAIL

SWOT ANALYSIS OF

ALUMINIUM &

SPECIAL STEEL

FOR VARIOUS

APPLICATIONS

sulphur for improved toughness, corrosion resistance & bendability, strain aging resistance, finer grain size and increased toughness in Steels are attributed to Aluminium addition in Steels. Also, high aluminium in Steels help to form effective nitride case through nitriding treatment for improved wear resistance and for use as heating elements. Along with the above, increased corrosion and weather resistance in cold rolled Steel sheets are achieved through application of zincalume and galvalume methods where in aluminium is used as one of the important metals for coating.

As a matter of fact, cost plays an important role in selection of the material. Here, special Steels have an edge over aluminium alloys. However, other parameters like durability, safety, atmosphere friendliness etc. along with the properties the materials play a pivotal role in material selection.

There is a need to understand the properties conferred

by aluminium alloys and special Steels for selection to suit the applications. This provides a bird's eye view on their strengths and weaknesses.

BASIC COMPARISON OF PROPERTIES

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PROPERTIES SPECIAL Steel ALUMINIUM ALLOYS

WEIGHT & DENSITY Heavier in weight with density of 7.85 gm/cu.cm. Lighter in weight with density approx. rd 1/3 of that of Steel. The density is about

2.72 gm/cu.cm.

ELASTIC MODULUS & Elastic modulus of 210 Gpa [longitudinal i.e. Elastic modulus of 70 Gpa. It has shock BENDING SPECIFIC Youngs modulus] which is 3 times more absorption tendency finding use in STIFFNESS than that of aluminium. Austenitic Stainless automobile bumpers. Bending specific

Steels possess elastic modulus of about 193Gpa. stiffness value for hollow sections is 25.64. Bending specific stiffness value of 26.75 which It possesses advantage for use as outer skinis more than aluminium providing the Steel the surface in automobile because of the goodadvantage for use in structures like front crash specific bending stiffness for flat productsrails, b-pillars etc. or any other hollow sections if only elastic materials are considered. in automobiles. Possess lower spring back than aluminium.

THERMAL Less thermal conductive than aluminium 3 times more thermal conductive than SteelCONDUCTIVITY making it a choice in heat exchange

applications.

FATIGUE Fatigue performance of Steel is more than twice Structural aluminium grade of 5XXXthat of aluminium. Steels such as DUAL series doesnot reach an endurance limitPHASE 600 and TRIP 600 have endurance and continue degrading at higher cycles.limits of 307 Mpa & 336 Mpa respectively. Aluminium grade 5052-0 reach 124 Mpa

at 500 million cycles.rdFORMABILITY High formable range than aluminium making it Formability is approximately 2/3 of

suitable for vehicle styling and overall that of Steelmanufacturing robustness.

ELECTRICAL No where near aluminium High electrical conductivity for use as CONDUCTIVITY electrical conductor in power transmission lines, transformers, bus bars etc.

REFLECTIVITY Lesser reflective than aluminium. Buffed Excellent reflector of radiant energy austentic stainless Steels [ AISI 304, 316] through entire range of wave lengths. possess some reflectivity. Light reflecting capacity of over 80%

making it suitable for lighting fixtures. Inroofing, it reflects high amount of sun heatpromoting cool interior atmosphere insummer, yet insulating against heat loss inwinter.

NON-MAGNETISM Steels in general are magnetic. Austenitic It is highly nonmagnetic and hence findsstainless Steels are non-magnetic with AISI extensive use for electrical shielding such304LN, 316LN Steel grades possessing very as bus bar, magnetic compass housings,low magnetic permeability for use in structures computer disk manufacturing, parabolicclose to sensitive electronic devices or magnetic antennas etc.resonance medical equipment.

HIGH TEMPERATU-RE Steels like T-11, T-22, Martensitic stainless and Poor high temperature resistance.RESISTANCE austenitic stainless Steel like AISI 310 are highly

creep resistant with ability to resist deformationat high temperatures. Steels containing 8% aluminium [Kanthal] are used as heating elements.

LOW TEMPERATU-RE Steels in general possess poor low temperature Shows excellent toughness at low TOUGHNESS toughness. Austenitic Stainless Steels show temperatures finding use in refrigeration.

excellent toughness at low temperatures making them very good choice low temperatures.

PHYSICAL PROPERTIES – I

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PROPERTIES SPECIAL Steel ALUMINIUM ALLOYS

TENSILE STRENGTH Much higher than aluminium and its alloys. Tensile strength of pure aluminium is verymuch lower but, the mechanical properties are improved by additions of Mn, Si, Cu &Mg and through tempering, Aluminiumalloy 6114-T4 has tensile strength of 295 Mpa similar to that of mild Steels.

YIELD STRENGTH Very much higher than aluminium and its alloys. The mechanical properties are improved byadditions of Mn, Si, Cu & Mg and throughtempering, Aluminium alloy 6114-T4 hasyield strength of 165 Mpa similar to that ofmild Steels.

MACHINABILITY Shows good machinability in high sulphur Shows excellent machinability\ Steels [free cutting variety] and lead bearing Steels.

HARDNESS Harder than aluminium. Lower hardness than Steel. Fall of stone Denting tendency less than aluminium. chips affects the surface quality of

aluminium body.

DAMPING Ability to attenuate air borne noise due to its huge Inability to attenuate air borne noiseCHARACTERITICS mass over aluminium. compared to Steel.

STRAIN RATE Highly strain rate sensitive displaying positive Not strain rate sensitive and has poor crashSENSITIVITY strain rate performance. At higher strain rates worthiness.

typically associated with crash events, Steel possess higher strength and consequently higher energy absorption for a given part weight.

PHYSICAL PROPERTIES – II

PROPERTIES SPECIAL STEEL ALUMINIUM ALLOYS

CORROSION & Austenitic stainless Steels like AISI 304 & 316 Good corrosion resistance and the rate ofthWEATHER show excellent corrosion resistance. Shows corrosion is 1/25 of high resistance Steels.

RESISTANCE good galvanic, pit and inter-granular Earlier, coal carrying cars used to be made ofcorrosion resistance. Finds use in structurals in aluminium for its corrosion resistance.marine/industrial atmospheres and chemical Excellent weather resistant. Corrosionindustries. For coal cars, stainless Steel AISI behaviour poor when in contact with409M is increasingly being applied globally. dissimilar metals, presence of crevices, with For weather resistance, CORTEN type concrete. Aluminium surfaces in direct special Steels are used. contact with concrete are to be coated with

bituminous paints. It finds good use in food processing industry.

NON-TOXICITY Austenitic stainless Steels [300 series] are known Highly non-toxic. Aluminium foil wrappingfor their non-toxic nature and finds use in dairy and [a foil of 0.007 mm thickness is completely food processing industry. These Steels provide impermeable and let neither aroma nor taste hygienic environment and used in hospitals also. out] and containers are common in food Tin plate Steels are used for preserving food, edible industry promoting hygienic environment oils, as beer cans etc. for food processing.

AESTHETIC APPEAL Excellent for austenitic stainless Steels with Attractive appearance with low maintenancelow maintenance costs. Used in cladding and costs. Finds use in cladding , hardware etc.hardware.

CHEMICAL PROPERTIES

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CONSUMPTION PATTERN IN INDIA

ALUMINIUM

Steel

The per capita consumption of aluminium is 25-30 kg in U.S.A. & Europe, 15 kg in Japan, 100 kg in Taiwan and 3 kg in China. However, in India , the per capita consumption continues to remain abysmally low at about 0.8 kg. Globally, the key consuming areas are transportation, power/electrical appliances, packaging, construction, pharmaceutical industry and waste water treatment.

In India, power sector is the largest consumer compared to transportation in the world and sector wise consumption of aluminium is shown in Fig.1.

From the above, the other sectors which consume 27% of the aluminium include packaging, electrical appliances, cook ware, food processing industry, pharmaceutical industry etc. Demand for aluminium is expected to grow at 6% to 8% per annum in view of the low per capita consumption in the sub-continent.

The per capita consumption globally stands at around 140

kg and in developed economies range from 300 kg to 600 kg. The key consuming sectors include construction, automobile, consumer durables, capital goods, engineering industry, petrochemical etc. The per capita consumption of Steel in India is as low as 31 kg.

The major Steel consuming sector in India is construction followed by capital goods and automobile sector. Sector wise consumption of Steel in India is shown in Fig.2.

In case of stainless Steel, the per capita consumption is as low as 1.06 kg. End use analysis of stainless Steel reveal that the largest consuming sector is kitchen ware [75%] followed by process industry [10 %], construction & transportation contributing 2% each, engineering industry [5%] and others about 6%. Other special Steels are used mainly in automotive sector, petrochemicals, consumer durables, capital goods, ship building industry etc. The stainless Steel market is expected to grow at 11% per annum in the next coming decade.

Aluminium, due to its strength and lightness, encourages its use in earth quake prone areas. It finds use as doors, window screens, hardware including tower bolts/ hinges/screws, roofing material etc. Aluminium building products help houses cool in summer and warm in winter. Metallic aluminium in massive flow will not burn. Due to its low melting temperature, aluminium vent early during a severe fire releasing heat.

One cannot imagine construction activity with out Steel. Steel finds extensive use in reinforced concrete structures. The application of thermo mechanically treated bars with special properties like corrosion resistance and earth quake resistance started making a new beginning in the world of construction. Also, application of austenitic stainless Steels as structural products in marine and industrial areas to combat corrosion, column cladding material in building construction, exterior/interior panels, lintels, hardware like tower bolts/hinges/pipe fittings, elevators, staircases and roofing of stadiums/platforms have gained momentum. Use of stainless Steels and other fire resistant Steels lead to fire protection of the buildings.

AREAS OF APPLICATION

CONSTRUCTION

Fig. 1 - Sector Wise Aluminium Consumption In India

Others 27%Power44%

Transportation12%

Infrastructure 17%

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TRANSPORTATION The success of commercial aviation is due to aluminium.

Aluminium alloys are c a p a b l e o f t a k i n g extraordinary pressures and stresses in high altitude flying. There are about 5300 commercial passenger aircrafts flying in the world. A Boeing 747 jumbo contains 75000 kg of aluminium. The structure of space shutt le is 90% a l u m i n i u m . I n r o a d transport, it is used for rugged hummer vehicle and off road land rover. With its

capability to absorb kinetic energy, in a large aluminium vehicle crash, only a larger portion of the shock is absorbed by the structure. Also, aluminium does not rust. Along with saving in energy, every ton of aluminium that replaces heavier metal/alloys saves 20 tons of CO equivalents over life time of an automobile.

Globally, 90% of the trailer trucks and long distance buses have aluminium bodies. Aluminium is widely used for truck and automobile engine/cylinder blocks, transmission housings, engine parts, automobile wheels and wheels/bumper reinforcements. Also, aluminium vehicle body outlasts a Steel chassis and tractor weight by 3 to 4 times. Aluminium bodies weigh 45% less than Steel bodies. LRC trains in Canada, TGV trains in France and latest version of 700 series of Japanese bullet trains all possess passenger cars made of aluminium. Most modern sub-way cars and most rail freight cars are made of aluminium in the world. Due to its non-reactivity, aluminium can haul bulk cargoes carrying coal, chemicals etc. Luggage racks, pipe fittings for seats in buses are being used by aluminium. Aluminium is being considered as important material in construction of freezer trucks. There is an emerging trend of aluminium built fast ferries running at speeds of 35-50 knots over short sea routes.

Steel has very little role to play in aviation industry and limited to airport construction and modernisation. Steel is a preferred material in automobile due to its inherent properties that provide ideal conditions for optimum crashworthiness, superior formability. Also, Steel sheet provides 3 times cost

saving over use of aluminium sheet. Galvanized Steel sheets are used for in bus and truck bodies extensively. Special Steels find applications in connecting rods, fasteners, stub axles, crankshafts, pinions, worms, transmission components, suspension rods, leaf springs, valves, exhaust systems, wheel caps etc. in an automobile. There is an increasing trend of applying stainless Steel for bus bodies.

In railways, Steel is a common material for use in coaches/cargoes, axles, wheels, bearings, cam shafts etc. Stainless Steel slowly and steadily has taken over areas like oil level gauge, gasket, wiper, air bag filter, center pipe, seat belt retractor, antenna, studs, wheel cap, mud guards, and spokes with frame etc., which were dominated by aluminium. Corten Steel made rail wagons are being extensively used to combat corrosion while 'AISI 409M stainless Steel' for coal carrying wagons is a revolutionary, improving the life of the wagons. Austenitic stainless Steels like AISI 301, AISI 304 etc. are being used for trough floor, hand rails, luggage rack in coaches, sole bars, toilet pans, wash basins, paneling, pantry cars etc. All stainless Steel passenger coaches have made a big beginning. Special Steels find an important role in ship building industry and naval applications.

Aluminium possesses high electrical conductivity and finds use as electrical conductor. The conductivity of electrical conductor grade [alloy 1350] is 62% of International Annealed Copper Standard. The major uses include overhead lines, electrical energy distribution cum transmission lines, energy cables for industrial use, electric motors, appliances, power systems etc. Aluminium replaced copper in high voltage transmission lines after 1945 and today, it is considered as the most economic material for transmitting electric power. It weighs

rd1/3 of copper plus 1 kg of aluminium carries twice the electricity than a 1kg copper. Sub-stations use aluminium where electricity is stepped to lower voltages. Other uses include bases of electric bulbs, television antennae, satellite dishes etc.

In power sector, Steel is used as the structural material for towers/civil construction. It is basically the pillar for infrastructure in power sector. Special Steels finds use as super

POWER

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heater tubes, turbine blades, pipes, bolts etc. for resisting high temperature in boilers/power stations.

Aluminium is used for protection, storage and preparation of food and beverages. Rolled into thin foils, aluminium is lighter, strong and act as a barrier possessing insulation qualities to preserve food, cosmetics, pharmaceutical products and protect them form ultra violet light, odour and bacteria.. Aluminium is able to withstand both heat and cold. The packages made of aluminium are secure, tamper proof, hygienic, easy to operate and recyclable.

Prime quality cold reduced electrolytic tin plate Steel sheets are used for packaging of food items/edible oils, processed fruits and vegetable, dairy and infant food, coffee, closures for beverage cans etc. Non-Prime quality tin plate Steel sheets are used for packaging talcum powder, paints, varnishes, pesticides, boot polish, pesticides, toys etc.

PACKAGING

DOMESTIC APPLIANCESAluminium is used for cook ware, furniture etc. Around

half of the cook ware sold globally each year is made of aluminium. This is because aluminium loses only about 7% of heat it receives leaving 93% heat to cook. Slowly and steadily, stainless Steel has entered into the arena of catering equipment globally and this sector is the largest consuming segment of stainless Steel in India. Even in furniture, stainless has made an entry and becoming a threat to aluminium.

Aluminium alloys and special Steels are a threat to each other in many applications. In spite of this, the unique characteristics of both these alloys make their presence strong in the individual area of application. Special Steels can never forget the role played by aluminium in their evolution. Aluminium continues to be an integral part of special Steel industry yet competing with it.

mmm

SANKET PRAKASHAN (A Division of ‘Chandekar Business Media Pvt. Ltd.’)