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Material Science

Metals

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Metallic Materials

Metallic materials have a wide range of properties, pure metallic materials have quite limited commercial use

Metal alloys, which are combinations of at least two elements, are far more versatile and for this reason are the form in which more metals are produced and used by industry

In general, they are classified into two broad families – ferrous and non-ferrous

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The type of steel depends on two factors: The carbon content The alloy element

Ferrous Materials

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Classification of Ferrous Materials

High Speed Steel

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Plain Carbon Steel

Divided into 3 categories:

Low Carbon Steel : up to 0.3% carbon Medium Carbon Steel : 0.3 – 0.6% carbon High Carbon Steel : 0.6 – 1.4% carbon

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Low Carbon Steel Plain Carbon Steel The hardness of a steel is increased by

the addition of the carbon Since the proportion of carbon is low the

hardness figure is low These materials normally have good

ductility and are easily worked Steel with carbon content between 0.15

and 0.3% are called mild steel This is a very common steel extensively

used throughout industrial

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Low Carbon Steel Plain Carbon Steel

Application: Rivet, wire, nail, chain, seam-welded

pipes, I-beam, U-channel, angle iron, sheet and plate, Levers, shafts

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Medium Carbon Steel Plain Carbon Steel

Since the carbon content is increased, the hardness of the steel also increases

This increase means that the material loses some of its ductility

It is offset by an increase in strength The hardness can be increased by ‘Heat

treatment’ It is also called ‘Yellow label steel’

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Medium Carbon Steel Plain Carbon Steel Application:

Shafts, connecting rods, crane hooks Gears, crankshaft Rails, wire rope, leaf spring

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High Carbon Steel Plain Carbon Steel

Since the carbon content is very the steel is much harder

Further degree of hardness can be achieved by heat treatment

Used extensively in the manufacture of hand and machine cutting tools

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High Carbon Steel Plain Carbon Steel

Application:

Dies, saw blades, anvil faces Chisels, punches, shear blades Drills, lathe tools, taps, reamers

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Stainless Steel Alloy Steel

Stainless Steels contain a minimum of about 12% Chromium, which permits a thin, protective surface layer of chromium oxide to form when steel is exposed to oxygen.

The addition of chromium and sometimes nickel to the steel greatly improves the resistance to corrosion.

The ’18-8’ stainless steel often refers to a steel having about 18% chromium and 8% nickel

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Stainless Steel Alloy Steel

Application:

Wire, tubing, sheets Surgical and dental instrument Poppet valves for internal-combustion

engines, turbine blades, pump shafts Chemical, dairy, laundry, and oil

equipment

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High Speed Steel Alloy Steel High Speed Steel (HSS) designates a number of

steels that have several properties which enhance their value as cutting tool material

They can be hardened to a hardness ranging from 63 Rc to 70 Rc

The principal alloying elements of HSS are tungsten, molybdenum, chromium, vanadium and carbon

HSS can be used for cutting tools such as drills, reamers, taps, dies, milling and turning cutters

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Cast Irons

The carbon content of CI is between 2 – 4%

It is hard and brittle When molten it has good fluidity,

producing good component features

It is rigid and has very good compressive strength

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White Cast Irons Cast Iron

It is given the name because the appearance of a fracture surface is bright and silvery

It is very hard with good strength but there is a tendency to brittleness

Very difficult to machine Its most common applications are

grinding mill part, rolls for cement, ceramic and mining industrial and as a basis when producing malleable irons

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Grey Cast Irons Cast Iron It is given the name because the appearance

of a fracture surface is dull grey It is softer with a lower tensile strength Grey irons are very strong in compression and

also absorb vibration It has low point and with good fluidity giving

good casting properties Good machinability Typical applications are cylinder blocks for

cars, machine tool beds, wheel drum, industrial furnace parts, water pipes and pistons

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Copper Non-ferrous metal Copper is a material which has been used for

thousands of years It can be used as pure metal or in combination

with other elements as an alloy The pure metal possesses desirable properties:

High electrical conductivity High thermal conductivity High ductility Good malleability High corrosion resistance

Typical applications are conductors, electrical components, tubing, wire, sheet, electrodes

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Brass Non-ferrous metal Brass is an alloy of copper and zinc but also

contain small amounts of other alloying elements

70/30 brass, because of its ductility, can be used in pressing and drawing operations, and is used for condenser tubes

60/40 brass is used where the material is to be hot-worked. It is ideal for producing hot stampings and extruded bars, rods and sections

High tensile brass, is basically a 60/40 brass with additional alloying elements such as tin, iron and aluminium. This material can be cast, forged, and extruded. Uses include valves, pumps, propellers, screws

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Bronze Non-ferrous metal Bronze is essentially an alloy of copper and

tin, but also contain additional elements such as zinc and phosphorus

Bronze with 5% tin and 0.4% phosphorus, it has good elastic properties and is used for springs

Bronze with 10% tin and 0.5% phosphorus, it is used for bearing applications

Bronze with 10% tin and 2% zinc, is largely used for naval purposes – valves, pump bodies, and fittings of water and steam

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Aluminium and its alloys Non-ferrous metal

Light metal, having approximately 1/3 of the density of steel

The oxide film gives excellent corrosion resistance High thermal and electrical conductivity High malleability, possible to produce very thin

foil Major disadvantage: lack of strength To overcome the problem aluminium is therefore

alloyed with magnesium, manganese, copper, silicon and tin

Increase the strength and hardness and enables the material to be heat-treated to give additional properities

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Aluminium and its alloys Non-ferrous metal

Applications: Plate, tube, wire, bars, extruded sections Floor section, superstructure of hovercraft,

variety of components in aircraft Large and small cable, foil, strip winding for

coil and transformer Roofing and structural applications, door and

window frame, decorative items Watches, photographic equipment, component

for machine tools Pans, furniture, packaging uses for food and

drink

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Magnesium and its alloys Non-ferrous metal

Density is approximately 2/3 of aluminium Highly reactive when contact with oxygen Weak and unsuitable for general use, so alloys are

formed aluminium and zinc are commonly added After alloying, obtained a high strength-weight ratio Its most important applications are in the aircraft

industrial or other areas where weight is a limiting factor

Can be supplied in a number of forms: sand or die-cast, forged, extruded, rolled in sheet or plate

Typical applications: wheels for racing cars, crankcase and gearbox for aircraft and cars, airframe components, camera cases, business machines

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Lead Non-ferrous metal

Lead in its pure state is very soft and has low mechanical strength

High corrosion resistance, widely used in chemical industrial

Used for radiation shielding Two of its largest uses are as cable

sheaths for power cables and in the manufacture of connectors and grids in lead-acid batteries

Lead-tin alloys give a range of soft solders

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Zinc Non-ferrous metal

Its largest single use is as a zinc coating (galvanizing) on iron and steel.

Zinc alloy containing 4% aluminium is most widely used for die-casting alloys

The low cost and low melting point of zinc alloys make them especially suitable for die-cast parts

Their excellent castability allows production of smooth-surface

Machinability is good, but zinc alloys are difficult to weld and solder.

Uses include the mass production of car parts, camera parts, power tools, clock parts and domestic appliances

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Tin Non-ferrous metal

Tin is a white or silvery metal with a density close to that of steel.

Commercially pure tin is rarely used alone except as a coating material.

Tin with the addition of 0.4% copper is used as foil and for collapsible tubes.

The major use of tin and its alloys is in corrosion-resistant products. More than 40% of the world's tin is used as a coating for steels and copper.

Tinfoil is used for liners for bottle caps and electrical condensers. Heavy-walled tin pipe and tin-lined copper pipe is used in the food and beverage industries.

And, tin wire is used for electrical fuses and for packing glands in pumps of food machinery.

Alloys of tin and lead are used extensively as solders