Classification of Engineering Materials: by - Gaurav Singh

MATERIAL SCIENCE AND
ENGINEERING
Classification
of
Engineering Materials
By - GAURAV SINGH
INTRODUCTION
 Materials are an important aspect of engineering design
and analysis.
 The importance of materials science and engineering

can be noted from the fact that historical ages have been
named after materials
 There is a wide variety of materials available which have
shown their potential in various engineering fields ranging
from aerospace to house hold applications.
 The materials are usually selected after considering their

characteristics, specific application areas, advantages and
limitations.
Classification of Engineering Materials
METALS & ALLOYS
Metals
polycrystalline consisting of a great number of fine crystals
Possess low strength
Do not have the required properties
Faceted glass
objects are
sometimes called
crystals!
Alloys
are produced by melting or sintering two or more metals or metals
and a non-metal together.
CLASSIFICATION OF MATERIALS
 Materials used in the design and manufacture of

products
• Plastics
• Wood
• Composites
• Ceramics
• Metals
Linen,
Layers cotton,
Tungsten
Steel,
of nylon,
aluminium toolKevlar
polycarbonate,
carbide bit
• Fabrics Balsa
Acrylic
wood lens
model
aluminium & acrylic
Classification of Engineering Materials –
Classification of Metallic Materials -
Classification of Steels
FERROUS MATERIAL - STEELS
• Steels - alloys of iron-carbon.
- May contain other alloying elements.
• Low. Alloy (< 10 wt%)

– Low Carbon (<0.25 wt% C)
– Medium Carbon (0.25 to 0.60 wt% C)
– High Carbon (0.6 to 1.4 wt% C)
•High Alloy
– Stainless Steel (>11 wt% Cr)
- Tool Steel
Low Carbon Steel
Plain carbon steels - very low content of alloying
elements and small amounts of Mn.
Most abundant grade of steel is low carbon steel –

greatest quantity produced; least expensive.
Not responsive to heat treatment; cold working

needed to improve the strength.
Good Weldability and machinability
High Strength, Low Alloy (HSLA) steels - alloying

elements (like Cu, V, Ni and Mo) up to 10 wt %; have
higher strengths and may be heat treated.
MEDIUM CARBON STEEL
Carbon content in the range of 0.3 – 0.6%.
Can be heat treated - austenitizing, quenching
and then tempering.
Most often used in tempered condition –
tempered martensite
Medium carbon steels have low hardenability
Addition of Cr, Ni, Mo improves the heat treating
capacity
Heat treated alloys are stronger but have lower
ductility
Typical applications – Railway wheels and tracks,
gears, crankshafts.
HIGH CARBON STEEL
STAINLESS STEELS
MAIN TYPES OF IRON
1. Pig iron
2. Cast iron
(A) White cast iron
(B) Gray cast iron
(C) Malleable cast iron
(D) Ductile cast iron
(E) Meehanite cast iron
(F) Alloy cast iron
3. Wrought iron
PIG IRON
- Pig iron acts as the raw material for production
of all kinds of cast iron and steel products.
- It is obtained by smelting (chemical reduction of
iron ore in the blast furnace.
- It is of great importance in the foundry and in steel
making processes.
- The charge in the blast furnace for manufacturing pig
iron is :-
(a) Ore - Consisting of iron oxide or carbonate
associated with earth impurities.
(b) Coke - A fuel
(c) Limestone - A flux
Approximate composition of PIG IRON
Carbon — 4 to 4.5%
Phosphorus — 0.1 to 2.0%
Silicon — 0.4 to 2.0%
Sulphur — 0.4 to 1.0%
Manganese — 0.2 to 1.5 %
Iron — Remainder
CLASSIFICATION OF CAST IRON -
Cast Iron
 alloyof iron and carbon
 obtained by re-melting pig iron with coke, limestone and steel
scrap in a furnace known as cupola.
 The carbon content in cast iron varies from 1.7% to 6.67%.
Grey cast iron
Ductile cast iron
grey in color
Carbon = 3.2 to 4.2%
It contains:
Silicon = 1.0 to 4.0 %
C = 2.5 to 3.8%.
Magnesium = 0.1 to 0.8%
Si = 1.1 to 2.8 %
Nickel = 0.0 to 3.5%
Mn = 0.4 to 1.0% White cast iron
Manganese = 0.5 to 0.1%
P = less than 0.15% White in color
Iron = Remaining
S = less than 0.1% C = 3.2 to 3.6%
Fe = Remaining Si = 0.4 to 1.1 %
Mg = 0.1 to 0.4%
P = less than 0.3%
S = less than 0.2%
Fe = Remaining
CAST IRON
 Wide range of applications (including pipes, machine and
car parts, such as cylinder heads, blocks and gearbox
cases) due to: Cast iron coated with durable
porcelain enamel distributes
 low melting point,
heat slowly and evenly.
 good fluidity,
 relatively easy to cast,
 excellent machinability,
 resistance to deformation
 wear resistance
 Cast iron tends to be brittle, except for malleable cast

irons, so shaping these by deformation is very difficult.
18
GREY CAST IRON
Grey cast iron is named after its grey fractured
surface that occurs when the graphitic flakes
deflect a passing crack and initiate many new
cracks as the material breaks.
graphite flakes surrounded by a-ferrite or pearlite
matrix
weak & brittle in tension (the graphite flake tips
are sharp; act as stress raisers)
stronger in compression
excellent vibrational dampening
wear resistant 19
APPLICATIONS OF GREY CAST IRON :-
(i) Machine tool structures such as bed, frames, column etc.
(ii) Household appliances etc.
(iii) Gas or water pipes for under ground purposes.
(iv) Rolling mill and general machinery parts.
(v) Cylinder blocks and heads for I.C. engines.
(vi) Frames of electric motor.
(x) General machinery parts.

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MATERIAL SCIENCE AND

 The importance of materials science and engineering

 The materials are usually selected after considering their

 Materials used in the design and manufacture of

• Low. Alloy (< 10 wt%)

Most abundant grade of steel is low carbon steel –

Not responsive to heat treatment; cold working

Good Weldability and machinability

High Strength, Low Alloy (HSLA) steels - alloying

 relatively easy to cast,

 Cast iron tends to be brittle, except for malleable cast

(ii) Household appliances etc.

(iii) Gas or water pipes for under ground purposes.

(iv) Rolling mill and general machinery parts.

(v) Cylinder blocks and heads for I.C. engines.

(vi) Frames of electric motor.

(x) General machinery parts.

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