Unit 3- topic- Engineering

materials( EME)

Engineering Materials: Types and applications of Ferrous &Nonferrous metals

Ferrous metals- cast iron and carbon steels Non ferrous metals- copper, aluminium,

lead, tin, etc. Timber- soft wood and hard wood,

seasoning of wood Abrasive material, silica, ceramics, glass,

graphite, diamond, Plastic and polymer 

Part A -Engineering Materials

For improving the quality of life human beings are always in search of better and newer materials. Either materials are used as they occur naturally or different materials are produced using natural materials.

They use these Materials for making houses, clothing, tools, weapons, utensils, musical instruments, printing etc. Use of various materials is learnt by mankind in different ages.

In the beginning of human life on Earth there was Stone Age, people used only natural materials, like stone, clay, skins, and wood. Later when people found copper and learned how to make it harder by alloying, the Bronze Age started around 3000 BC.

1.1 Material and civilization

The use of iron and steel started around 1200 BC. Use of Iron and steel was advantageous in wars. The next big discovery was the development of a commercial cheap process for making steel around 1850 AD. This enabled development of railroads, high rise buildings and modern infrastructure of the industrial world. The success of a particular civilization was dependent on the best material known to that civilization.

TITANIC – A WONDER OF ENGINEERING

Failure of titanic on hitting the iceberg

The great Columbia shuttle of NASA

Pictures were taken by of the Columbia explosion from an Israeli satellite in space.

Failure of Columbia shuttle of NASA

For Overall development of society we have to realize the importance of engineering materials, so we discussed some points here –

Extraction and processing of raw material develops: Efficient, cleaner and systematic methods of raw-material extraction are developed.

Industrial growth takes place: New industries for manufacturing new products are created.

Infrastructure Improves: Power, transport and communication improves.

IMPORTANCE OF ENGINEERING MATERIALS

Technical education improves: To work in industry skilled man power is required. Technical education improves.

Gross National Product of the country improves: Improvement in material production leads to increase in GNP.

Standard of living of people improves: Salaries and wages of trained personnel improves which leads improvement in overall living standard of people.

Technological and economic development takes place.

Metal and their alloyNon- Metals and Composite materials

Classification of Materials

1.0 Ferrous metals: In Ferrous metals Iron (Fe) is the major constituent. Examples: Cast Irons and Steels. They are strongest material available. They are used for making bridges, railway lines, railway engines, railway wagons, strong parts of automobiles, steel wires, rods, plates etc.

2.0 Non-Ferrous metals are those metals in which major constituent is other than Iron (Example: Gold, Silver, Copper, Zinc, Brass, Tin, Bronze, and Lead etc.). Their mechanical strength is less.

Metals classification

Synthetic Non-Metals such as plastics and adhesives do not exist in nature, they are manufactured from natural substances such as oil, coal and clay. They have good mechanical strength and can be easily manufactured. Plastics are extensively used from utensils to structural members. Synthetic adhesives are used for joining.

Natural Non-Metals: Some non-metals such as wood, rubber, glass, emery, ceramic, diamonds, oils and silicon are naturally occurring. They are obtained from nature and given desired shape for use

Non metals classification

Composite materials are combination of two or more materials. They exhibit different properties then those materials of which they are made of. Some example composite material are fiber glass, Clad metals, Cemented Carbides, Reinforced plastics etc.

Composite materials

Ferrous materials are those materials in which chief constituent is Iron. In these materials Iron is mixed with Carbon, Silicon, Chromium, Nickel, Manganese etc. to form alloys such as Steels and Cast Irons.

Ferrous materials are classified into two categories namely Steels and Cast Irons based on Carbon content in them

Ferrous materials:

Steels: Steels are those alloys of Iron and Carbon in which carbon content is less than 2%. Depending upon % of other alloying elements, Steels are further named as Carbon Steels, Stainless Steels or Tool steels.

Cast Iron: Cast Irons are those alloys of Iron and Carbon in which Carbon content is 2% to 6.67%. Cast Irons are normally produced from cupola furnace. Depending upon % of Carbon and other alloying elements various Cast Irons are produced. 

Steels and Cast iron

Carbon Steels and their classification based on % of Carbon: Higher percentage of carbon in steel makes it harder and tougher.

Carbon Steels are classified into following four categories:a) Low carbon steel , C %- 0.05-0.15b) Mild steel,C %- 0.16-0.29c) Medium carbon steel ,C %- 0.3-0.59d) High carbon steel C %- 0.60-1.7

Carbon Steels and their classification

s. no

Type of carbon steel

% of carbon

properties applications

1 Low carbon steel 0.05-0.15 soft, ductile , very little hardenability, good corrosion resistance.,good weld ability.

Welded or Seamless tubes, Thin sheets, Wire rods, Nails, Rivets, ,Stampings etc.

2 Mild carbon steel 0.16-0.29 Soft, ductile, Little hardenability,good weladbility

Forgings, Stampings, Structural sections (i.e. Angles, Channels, Beams, wire Rods, Ribbed bars etc.), Plates, Steel Castings

Types of carbon steel

s. no Type of carbon steel

% of carbon

properties applications

3 Medium carbon steel

0.30-0.59 Good strength and ductility. good hardenability and weldability. They can be hot or cold worked.

Drop forgings, Plates for boiler drums, Marine Shafts and axles, High tensile wires and tubes, Locomotive wheels, Wire ropes, hammers etc.

4 High carbon steel

0.60- 1.7 good hardenability, ductility and weldability are low.

for making Cutting Tools, Punches & Dies and high strength Rails.

Types of carbon steel

a) Low Carbon Steel or Dead mild steel: They have carbon content in the range of 0.05 – 0.15%. These steels are very soft, ductile and have very little hardenability. They have good corrosion resistance. They have good weld ability. They can be easily cold worked and they acquire hardness through cold working. They are used for making Welded or Seamless tubes, Thin sheets, Wire rods, Nails, Rivets, and Stampings etc.

  b) Mild Steel: They have Carbon Content from 0.16% - 0.29%. These

steels are soft, ductile and have very little hardenability. They acquire hardness through cold working. They have good weldability. They are used for making Forgings, Stampings, Structural sections (i.e. Angles, Channels, Beams, wire Rods, Ribbed bars etc.), Plates, Steel Castings etc.

 

c) Medium Carbon Steel: They have Carbon Content from 0.3%-0.59%. These steels have good strength and ductility. They have good hardenability and weldability. They can be hot or cold worked. They get hardened quickly while cold working, due to this they require frequent annealing while cold working. They are suitable for making Drop forgings, Plates for boiler drums, Marine Shafts and axles, High tensile wires and tubes, Locomotive wheels, Wire ropes, hammers etc.

  d) High Carbon Steel: They have Carbon Content from 0.6% to 1.7%.

These steels have very good hardenability. There ductility and weldability are low. They become so hard after quenching that tempering is normally required to reduce their brittleness and make them tougher. They are mostly used for making Cutting Tools, Punches & Dies and high strength Rails.

It is purest form of iron which contains 99.8 % of iron and produced by melting pig iron in puddling furnace.

Wrought Iron:

Cast Iron: Cast Iron is produced by melting Pig Iron* in Cupola furnaces or some other furnace (i.e. Induction furnace etc.). The chemistry of Pig Iron is suitably modified in cupola furnace to produce different grades of Cast Iron.

CAST IRON

Cast Iron has low tensile strength, but good compressive strength and good corrosion resistance. Cast Irons are very brittle and have no plasticity as a result they can not be forged.

It has self lubricating properties due to presence of free carbon and is therefore used for making surfaces over which sliding takes place (such as lathe bed etc.)

CAST IRON

a) Gray Cast Iron : In this Cast Iron most of the carbon is present in the form of free graphite. Under microscope this carbon is visible as flakes.

If a piece of this material is broken its fractured section shows the grayish color and that is why it is known as Gray Cast Iron. The gray color is due to presence of free carbon in the form of graphite flakes. In Gray Cast Irons the Carbon content in combined form (i.e. in the form of Fe3C) may vary from 0.3% to 0.9%.

Types of Cast Iron

Properties : It is very brittle and posses no ductility or plasticity as a result it can

not be forged. High brittleness makes it unsuitable for making parts which are subjected to shock loading.

It has good machinability. It has good compression strength (1250 Kg/Sq.cm) and low tensile

strength 650 Kg/ Sq. cm). Due to good compressive strength it is most suitable for making Compressive load bearing members such legs and beds of heavy machinery.

It has good fusibility which makes it suitable for making castings. Due to presence of free graphite it has self lubricating property

and hence it is suitable for making sliding surfaces.

Properties of Gray cast iron

White Cast Iron : It is called white cast iron because its fractured section shows

whitish color. Most of the carbon present in this cast Iron is in the combined form (i.e. iron carbide which is called Cementite). Cementite is white in color and makes the structure white.

Cementite is very hard and brittle. Cenmentite is formed due to rapid cooling of iron after melting. It is due to this reason that all the chilled parts of castings are hard and brittle.

White cast iron is hard and brittle and highly wear resistant. Its fluidity is not good and is not suitable for general casting

purpose.

White cast iron

  c) Malleable cast Iron : It has fairly good amount of

malleability. It is produced in two steps. First cast iron castings are produced by melting white cast iron in cupola furnace. These castings are packed in Iron boxes containing material rich in O2. These boxes are kept for four days in annealing furnaces at a temperature of 815oC to 1010oC and then allowed to cool slowly along with the furnace. This allows Cementite to decompose into iron and carbon.

d)Nodular Cast Iron : This is also known as Spheroidal Graphite ( or simply SG) Cast Iron, Ductile Cast Iron or High Strength Cast Iron. For its production the shape of graphite present in cast iron is changed from flakes to spheroids or nodules.

This is achieved by adding magnesium metal to the molten cast iron just after tapping. This magnesium treated metal when cast into moulds gives SG cast iron. This changed shape of graphite prevents formation and propagation of cracks and enhances ductility of Cast Iron. It has chemistry similar to gray cast iron

Nodular cast iron

Alloy Steels : All steels in addition to Iron and Carbon contain

other elements like silicon, manganese, sulphur and phosphorous. In some steels special elements like Nickel, Chromium, Molybdenum, Vanadium and Tungsten etc. are added to enhance their mechanical properties. These steels are called alloy steels.

They have their properties as per the alloying elements in them. These steels are named normally on the basis of their principal alloying element.

ALLOY STEELS

These are various types-Stainless steelTool steelSpring steel

Alloy steel

Stainless steels : They are corrosion resistant steels. Their principal alloying element is chromium, while other elements like nickel, manganese can also be present in small amounts.

To impart high corrosion resistance to steels Chromium up to 12% is added.

The chromium present in steels reacts with O2 in air to form a strong layer of chromium oxide on the surface of the metal. This layer protects the metal from corrosion. Stainless steels carrying more than 12% chromium are known as true stainless steels. 

STAINLESS STEELS

These alloy steels have special application in manufacture of cutting tools for those applications where tools made of carbon steel will either fail to perform or will have a very short life. They are put into two categories namely :

TOOL STEEL

High Speed Steel : It is a high alloy tool steel used for making cutting tools suitable for high temperature applications.

Main Constituents in HSS are Carbon, tungsten, chromium, vanadium and molybdenum. High Speed Steel has high wear resistance, high abrasion resistance and high red hardness. They retain their hardness up to 620oC.

The most commonly used high speed steel is 18-4-1 which carries 18% Tungsten, 4% Chromium, 1% Vanadium, 0.7% Carbon and rest Iron.

It has good red hardness, wear resistance shock resistance and widely used for making cutting tools for lathe, shapers, slotters, milling machines, drill etc

HIGH SPEED STEEL( HSS)

Non ferrous Metals are those which do not contain Iron. Most commonly used nonferrous metals are Aluminium, Copper, Magnesium, Lead, Tin, Nickel, Zinc etc. Also they form useful alloys among themselves.

NON FERROUS METALS

Non ferrous metals have following advantages over ferrous metals

Very good electrical and thermal conductivity Good castabilty Good formability Good cold working property High corrosion resistance Attractive appearance Lower density and high strength to weight

ratio.

Advantages of non ferrous metals

High cost, High shrinkage, Lower strength at elevated temperature

Disadvantages of non ferrous metals :

Properties and usage of copper : High electrical conductivity : Used for making

cables and contactors. High heat conductivity : Used in heat

exchangers, heating vessels and appliances. Good corrosion resistance : Used to provide

base coating on steel prior to nickel and chromium plating.

High ductility : Can be easily cold worked, rolled, drawn and spun. Looses ductility in cold working requires annealing between the process.

copper

Properties and usage of Zinc :

High corrosion resistance : It is widely used for providing protective coating on iron and steel. It may be coated either by dip galvanizing, Electroplating, Sheradising* or just by painting.

Low melting point and high fluidity: Makes it most suitable for pressure die casting.

ZINC

Properties and usage of Tin Good resistance to acid corrosion and

used as coating on steel container for food. It is soft, has good plasticity and can be

easily worked. It can be easily rolled into thin foils but

can not be drawn into wires due to low strength.

It is used as alloying element in soft solders, bronzes and bearing metals.

TIN

Properties and usage of magnesium:

It the lightest metal, weighing two third of aluminum.

It can be easily cast into fine shapes. Is has good ductility so it can be easily cold

worked. When in powder form, it is likely to catch fire,

requiring adequate fire protection measures for its storage.

MAGNESIUM

Properties and usage of lead : Good corrosion resistance : Used for water

pipes and roof protection. Good resistance to chemical action: Used for

acid baths and containers in chemical industry. Its soft heavy and malleable and can be

easily worked and shaped. Used as alloying element in making solders. It is alloyed with Brass and Steel to impart them

free cutting properties.

LEAD

Properties and usages of Aluminium: High Electrical conductivity: Used for heavy

conductors and bus bars. High heat conductivity: Used in domestic utensils

and other heat conducting appliances. Good resistance to corrosion: Used for

manufacture of containers for chemical industry and window frames etc. The corrosion resistance can be further enhanced by anodizing*. (*Process of increasing the thickness of natural oxide layer on the metal surface. It is done through electrolysis. Metal forms anode of electrical circuit)

ALUMINIUM

Properties and usage of Nickel Good resistance to both acid and alkali

corrosion. Widely used for food processing equipment.

Has high tensile strength and can be easily hot or cold worked.

It is plated on steel to provide corrosion resistance surface.

NICKEL

-Brass – These are the alloy of copper and zinc

-Bronze-They are alloys of copper and Tin.

Brass and Bronze

Composite materials are combinations of two or more materials which differ in chemical composition and physical properties and are insoluble in each other. They are manmade or naturally occurring. Examples: Natural Wood, Fiber glass used for making bath tubs etc., imitation granite, cultured marble, plywood etc. .

COMPOSITE MATERIALS

There are two major components of composite materials: a) Reinforcements i.e materials that provide

strength to the composite. b) Matrix i.e the material that holds the

reinforcement in place

Natural Composites such as wood , human body etc

Synthetic composite all man made composites such as fiber glass, clad metal, plywood, reinforced plastics et.

Classification of composite materials:

Low density, high strength, high hardness and stiffness.

Corrosion resistant, weather resistant and tailored surface finish

Low thermal conductivity, low coefficient of thermal expansion

High dielectric strength, nonmagnetic, Radar transparency

Can withstand high temperature in corrosive environment

Good formability, good durability and good damping properties

Properties and advantages of composites

High cost of raw material and manufacturing

Matrix is weak giving rise to low toughness Environmental degradation takes place in

matrix. Composites ingredient can not be reused. Joining is difficult Difficult to analyze

Disadvantages of composites

Used as a replacement material in various engineering applications such as cylinder block liners, vehicle drive shafts, automotive pistons, bicycle frames etc

Hockey sticks, vaulting poles, golf carts etc Fuel and chemical storage tanks Aerospace applications : helicopter blades, engine

couplings, ducts etc Marine : Boats , ships , hulls etc Electronic and recreational industries high voltage power transmission lines and heat sinks

for electronic components As bio compatible materials

Application of composites