Prepared by

Lim Hooi Peng

DJJ30113 Chapter
Materials Science and
Engineering 6
Apply the
fundamental of
material science to
identify the materials,
properties, behavior,
Fabrication
processes and
treatment.
of Metals
CLO 1 Performed
appropriate material
testing according

CLO 2 to the Standard

Operating
Procedures.

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 Content
1. Metals forming processes
2. Casting processes
3. Other methods in fabrication of metals
4. Heat treatment of steels

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Metals forming 1 2 3 4
1

• Mechanical working of a metal is

Metals simply plastic deformation performed
to change dimensions, properties and
forming surface condition.
processes • It works for three purposes:
1. To produce a particular shape.
2. To break down the cast structure
and improve the properties of the
metal.
3. To impart a desirable dimension
and surface finish.

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Metals forming 1 2 3 4
1

• Metals forming processes are

Metals classified into:
1. Cold working
forming 2. Hot working
processes 3. Forging
4. Rolling
5. Extrusion
6. Drawing

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Hot working 1 2 3 4
1

Hot working of a metal is

carried out above its re-
crystallization temperature
but below its melting point.

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Hot working 1 2 3 4
1

Plastic deformation of a
metal which results in strain
hardening. It usually
involves working at room
temperature.

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Hot working 1 2 3 4
1

W H A T
is re-crystallization
temperature?

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Hot working 1 2 3 4
1

W H A T
is re-crystallization
temperature?
The approximate
minimum temperature at
which complete re-
crystallization of a cold
worked metal occurs
within a specified time.

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Hot working 1 2 3 4
1

Hot working refines grain

structure of the metals. The
coarse columnar dendrites of
cast metal are refined to
smaller grains and improve
the mechanical properties of
the component.

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Hot working 1 2 3 4
1

Surface finish of hot worked

metal is not as good as with
cold working, because of
oxidation and scaling.

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Hot working 1 2 3 4
1

Defects in the metal, such as

holes, internal porosity,
cracks; when they get
welded up during hot
working.

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Hot working 1 2 3 4
1

During hot working, self

annealing occurs and re-
crystallization takes place
immediately following
plastic deformation. This
will cause to loss of ductility.

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Hot working 1 2 3 4
1

No strengthening occurs
during deformation by hot
working.

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Hot working 1 2 3 4
1

To improve To produce raw

properties of the material to be
metal, as used for
compared to subsequent cold
those in cast working
condition. operations.

Purposes

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Hot working 1 2 3 4
1

To improve To produce raw

properties of the material to be
metal, as used for
compared to subsequent cold
those in cast working
condition. operations.

Purposes

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 Hot working 1 2 3 4
1

Advantages It promotes uniformly of

It does not affect tensile work piece by facilitating
strength, hardness, corrosion diffusion of alloy
resistance for work piece. constituents and breaks up
the brittle films or
impurities in metals.

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Hot working 1 2 3 4
1

Limitations The volumetric expansion

Oxide forms rapidly on of the work piece during
metal surface. heating and its contraction
Surface scaling of the during cooling preclude
product. the accurate final
Surface decarburization. dimension.

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Cold working 1 2 3 4
1

Cold working of a metal is

carried out below its re-
crystallization temperature.

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Cold working 1 2 3 4
1

Metal working performs

above room temperature that
the metal does not work
harden.

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Cold working 1 2 3 4
1

Cold working distorts grain

structure of the metals.
Good surface finish is
obtained.

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Cold working 1 2 3 4
1

Excessive cold working

gives rise to the formation
and propagation of cracks in
the metal.

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Cold working 1 2 3 4
1

The loss of ductility during

cold working has a useful
side effect in machining.
With less ductility, the chips
break more readily and
facilitate the cutting
operation.

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Cold working 1 2 3 4
1

Cold working provides

excellent dimensional
tolerances and surface
finishes.

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Cold working 1 2 3 4
1

It is an inexpensive method
for producing large numbers
of small parts. However, for
large parts, the amount of
cold work is limited. If too
much deformation is
attempted, the metal may fail
during processing.

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Cold working 1 2 3 4
1

In addition, high forces,

requiring large and
expensive forming
equipment, must be applied
to exceed the yield strength
in large parts.

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Cold working 1 2 3 4
1

Ductility, electrical
conductivity and corrosion
resistance are impaired by
the cold working process.
Residual stresses are
introduced during cold
working.

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Cold working 1 2 3 4
1

To obtain thinner To obtain greater

work piece dimensional
To obtain good accuracy
surface finish. To improve
mechanical
properties.

Purposes

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Cold working 1 2 3 4
1

To obtain thinner To obtain greater

work piece dimensional
To obtain good accuracy
surface finish. To improve
mechanical
properties.

Purposes

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Cold working 1 2 3 4
1

Advantages
Increase: No heating is required.
1. Ultimate tensile strength It is more economical than
2. Yield strength hot working for certain
3. Hardness ductile metals.
4. Fatigue strength

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Cold working 1 2 3 4
1

Limitations Metal surface must be

Possess less ductility. clean and scale free before
Strain hardening occurs. cold working.
Higher forces are required
for deformation than hot
working.

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Cold working 1 2 3 4
1

W H A T
is the effect of cold
working on the
mechanical
properties of
copper?

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Cold working 1 2 3 4
1

W H A T
is the effect of cold
working on the
mechanical
properties of
copper?
As the percent cold work increases, both the yield
strength and the tensile strength increase. However, the
ductility decreases and approaches zero.
The metal will break if more cold work is attempted.
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