2. 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.
3. 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
Alloys
are produced by melting or sintering two or more metals or metals
and a non-metal together.
Faceted glass objects
are sometimes called
crystals!
4. Materials used in the design and manufacture of products
• Plastics
• Wood
• Composites
• Ceramics
• Metals
• Fabrics
Acrylic lens
Balsa wood model
Layers of polycarbonate,
aluminium & acrylic
Tungsten carbide tool bit
Steel, aluminium
Linen, cotton, nylon, Kevlar
8. .
– Low Carbon (<0.25 wt% C)
– Medium Carbon (0.25 to 0.60 wt% C)
– High Carbon (0.6 to 1.4 wt% C)
• Steels - alloys of iron-carbon.
- May contain other alloying elements.
• Low Alloy (< 10 wt%)
– Stainless Steel (>11 wt% Cr)
- Tool Steel
•High Alloy
9. 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.
10. 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.
11.
12.
13. 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
14. - 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
15. 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
16.
17. Cast Iron
alloy of 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
grey in color
It contains:
C = 2.5 to 3.8%.
Si = 1.1 to 2.8 %
Mn = 0.4 to 1.0%
P = less than 0.15%
S = less than 0.1%
Fe = Remaining
White cast iron
White in color
C = 3.2 to 3.6%
Si = 0.4 to 1.1 %
Mg = 0.1 to 0.4%
P = less than 0.3%
S = less than 0.2%
Fe = Remaining
Ductile cast iron
Carbon = 3.2 to 4.2%
Silicon = 1.0 to 4.0 %
Magnesium = 0.1 to 0.8%
Nickel = 0.0 to 3.5%
Manganese = 0.5 to 0.1%
Iron = Remaining
18. 18
Wide range of applications (including pipes, machine and car parts, such as
cylinder heads, blocks and gearbox cases) due to:
low melting point,
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.
Cast iron coated with durable
porcelain enamel distributes heat
slowly and evenly.
19. 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
20. (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.
