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Diploma in Mechanical Engineering (Material)
JF 302 MATERIAL TECHNOLOGY 1
www.pis.edu.my
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Week 8
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CLO 2 : Synthesis course knowledge into an effective
course assignment and present technical findings
both orally and in writing.
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Understand cold work
Understand hot work
Describe the casting process
Describe the heat treatment of steels
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cold work hot work casting process Heat treatment of steels
HEAT
TREATMENT
Principle of Operation:
Heat treatment may be defined as an operation involving heating and cooling of metal/alloy in solid
state to obtain desirable conditions and properties.
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cold work hot work casting process Heat treatment of steels
HEAT
TREATMENT
Principle of Operation:
Heat treatment may be defined as an operation involving heating and cooling of metal/alloy in solid
state to obtain desirable conditions and properties.
Stress relieving Better machinability
Improve ductility
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cold work hot work casting process Heat treatment of steels
CLASSIFICATION
OF HEAT
TREATMENT
PROCESS Classification of heat treatment: Various heat treatment processes can be classified
as:
1. Annealing
2. Normalizing
3. Quenching
4. Tempering
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cold work hot work casting process Heat treatment of steels
PURPOSES
OF HEAT
TREATMENT Purposes of heat treatment: 1. Relief of internal stresses which is developed
during cold working, welding, casting or forging
2. Harden and strengthen metal/alloy
3. Improve machinability
4. Change of grain size
5. Soften metal/alloy for further mechanical working
6. Improve ductility and toughness
7. Increase heat/wear and corrosion resistance
8. Improve magnetic and electrical properties
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cold work hot work casting process Heat treatment of steels
STAGES OF
HEAT
TREATMENT Stages of heat treatment:
1 2 3
1. Heating
2. Holding (Soaking)
3. Cooling
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cold work hot work casting process Heat treatment of steels
Think critically 3.5
Briefly describe the three basic
stages of heat treatment process.
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cold work hot work casting process Heat treatment of steels
Think critically 3.5
Briefly describe the three basic
stages of heat treatment process.
1. Heating the steel to define temperature
2. Soaking at that temperature for sufficient period to allow
necessary changes to occur
3. Cooling at a rate to obtain desired properties associated with
changes in the form, size and distribution of micro-constituents
(such as ferrite, pearlite and martensite)
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cold work hot work casting process Heat treatment of steels
Fig 3.1 Temperature range for heat treatment of steel
A1 - Eutectoid line
727C or
Lower critical
tempt
A1
A3
Acm A3 Upper critical tempt
Acm austenite + cementite line
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cold work hot work casting process Heat treatment of steels
ANNEALING
Definition:
Annealing is the process of heating a steel to a
temperature about 727C, which will remove the
instability or distortion and then cooling at a slow
rate (furnace cooled).
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cold work hot work casting process Heat treatment of steels
ANNEALING
Purposes:
1. Induce a completely stable structure (full
annealing)
2. Refine the structure
3. Reduce hardness
4. Improve machinability
5. Remove residual stresses
6. Improve mechanical, physical, electrical and
magnetic properties
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cold work hot work casting process Heat treatment of steels
Think critically 3.6
Give the classes of annealing of
steels.
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cold work hot work casting process Heat treatment of steels
Think critically 3.6
Give the classes of annealing of
steels.
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cold work hot work casting process Heat treatment of steels
Think critically 3.7
Briefly explain the annealing
temperatures.
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cold work hot work casting process Heat treatment of steels
Think critically 3.7
Briefly explain the annealing
temperatures.
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cold work hot work casting process Heat treatment of steels
Think critically 3.8
Explain the annealing for
hypoeutectoid steels .
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cold work hot work casting process Heat treatment of steels
Think critically 3.8
Explain the annealing for
hypoeutectoid steels .
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cold work hot work casting process Heat treatment of steels
NORMALIZING
Definition:
Normalizing is the process of heating a steel to a
temperature about 40-50C above its upper critical
temperature, holding it at that temperature for a
short time and then cooling in air at room
temperature.
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cold work hot work casting process Heat treatment of steels
NORMALIZING
Purposes:
1. Refine the grain size of steel
2. Reduce internal stresses
3. Produce a harder and stronger steel than
annealing
4. Improve machinability, ductility and toughness
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cold work hot work casting process Heat treatment of steels
Think critically 3.9
Why normalizing produces harder
and stronger steel than annealing?
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cold work hot work casting process Heat treatment of steels
Think critically 3.9
Why normalizing produces harder
and stronger steel than annealing?
Normalizing produces harder and stronger steel than annealing due
to a faster cooling rate. Thus, normalizing is often used as a
final heat treatment.
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cold work hot work casting process Heat treatment of steels
QUENCHING
Definition:
Quenching is the process of heating a steel with
sufficient carbon (0.35-0.7%) to a temperature
about 30-50C above A3 line (Fig 3.1), holding it at
that temperature from 15 to 30 minutes and then
cooling rapidly or quenched in a suitable medium
(brine, water or oil).
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cold work hot work casting process Heat treatment of steels
QUENCHING
Purpose:
1. Improve hardness
2. Improve wear resistance
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cold work hot work casting process Heat treatment of steels
Think critically 3.10
How does the cooling rate affect the
formation of martensite?
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cold work hot work casting process Heat treatment of steels
Think critically 3.10
How does the cooling rate affect the
formation of martensite?
During fast cooling rate, austenite cannot transform into ferrite due
to insufficient time for carbon atoms to diffuse out of austenite.
Most of the carbon atoms remain trapped in austenite to distort
the structure and become elongated. The structure is called
martensite. It is hard and brittle.
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cold work hot work casting process Heat treatment of steels
TEMPERING
Definition:
Tempering is the process of heating hardened steel
below the lower critical temperature, holding it at
that temperature from 3 to 5 minutes and then
cooling rapidly or quenched in a suitable medium
(brine, water or oil).
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cold work hot work casting process Heat treatment of steels
TEMPERING
Purposes:
1. Relieve residual stresses
2. Improve ductility
3. Improve toughness
4. Reduce hardness
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cold work hot work casting process Heat treatment of steels
Think critically 3.11
What happens during tempering?
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cold work hot work casting process Heat treatment of steels
Think critically 3.11
What happens during tempering?
During tempering, the excess carbon atoms, trapped in martensite,
gradually come out as extremely fine cementite particles and
the metastable martensite transforms into stable ferrite. The
resulting microstructure is called tempered martensite or bainite.
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List FOUR (4) types of surface hardening
processes?
cold work hot work casting process Heat treatment of steels
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List FOUR (4) types of surface hardening
processes?
cold work hot work casting process Heat treatment of steels
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cold work hot work casting process Heat treatment of steels
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cold work hot work casting process Heat treatment of steels
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cold work hot work casting process Heat treatment of steels
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cold work hot work casting process Heat treatment of steels
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cold work hot work casting process Heat treatment of steels
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cold work hot work casting process Heat treatment of steels
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cold work hot work casting process Heat treatment of steels
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cold work hot work casting process Heat treatment of steels
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cold work hot work casting process Heat treatment of steels
24/7/2014
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cold work hot work casting process Heat treatment of steels
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cold work hot work casting process Heat treatment of steels
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cold work hot work casting process Heat treatment of steels
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cold work hot work casting process Heat treatment of steels