Factors that affect the mechanical properties of materials include grain size, heat treatment, temperature, and atmospheric exposure. Heat treatment operations like hardening, annealing, and tempering can increase properties like tensile strength, hardness, and wear resistance. These properties are also influenced by factors like grain size, recovery, recrystallization, work hardening, phase transformations, and residual stresses induced during forming processes like hot working and cold working. Hot working allows deformation with reduced energy at high temperatures and improves properties like ductility and impact strength, while cold working enhances properties like hardness and strength but reduces ductility.

1. Factors affecting mechanical properties
of a material
BY
Dr. K. SENTHILARASAN
ASSISTANT PROFESSOR
DEPARTMENT OF PHYSICS
E.G.S.PILLAY ARTS & SCIENCE COLLEGE
NAGAPATTINAM-611002

2. Factors affecting mechanical properties of a material
1. Grain size
2. Heat treatment
3. Temperature
4. Atmospheric exposure

3. Heat treatment
• An operation or combination of operations
involving heating and cooling under the controlled
conditions of a material in solid state, for the purpose of
obtaining certain desirable conditions or properties is
known as heat treatment.
• It has been observed that the heat treatment of a
metal increases its tensile strength, hardness, ductility,
shock resistance and machinability.
• Further grain refinement, softening, improvement
in cutting properties and increase in wear resistance can
be obtained from heat treatment. Further magnetization
and conductivity are also improved.

4. • Hardening
• Annealing
• Normalizing
• spheroidizing
• tempering
• carburising
• nitriding
• cyaniding

5. Hardening
• The heat treatment operation which improves the hardness of
steel is called hardening. Hardness improves the cutting ability of
tool steels, increases the wear resistance of steel articles, increases
the yield strength of steel machine parts followed by subsequent
tempering and improves the magnetization property of steels to
produce permanent magnets. The hardening process involves four
steps.
• Preparation of the specimen without any dust or oil on its surface.
• Raising the temperature of the specimen above its critical
temperature.
• Soaking the specimen by maintain it at that temperature for a
considerable time, depending upon its thickness. Thicker specimen
requires large soaking time.
• The soaked specimen is then quencined in a cooling medium like
water, oil, air, air stream, etc.,

6. Different types of hardening processes:
• Age hardening.
• Air hardening.
• Work hardening
• Induction hardening.
• Flame hardening.
• Hardening by heating and quenching.

7. Annealing process
It is the heat treatment process which mainly
improves softness and ductility in steels and other
already worked metals. Further it is also used to
refine the grain size, to relieve internal stresses, to
remove trapped gases and to alter electrical and
magnetic properties.
Different type of annealing process
• Full annealing
• Process annealing
• Patenting
• Stress- relief annealing
• Double annealing

8. Annealing of cold worked metal
The process of bringing a cold worked
metal piece to a strain free condition by raising
its temperature below its melting point and then
by slowly cooling it’s called annealing of cold
worked metal.
– Recovery
– Recrystallization
– Grain growth

10. Recovery:
The process of restoration to a strain Free State of a
cold worked metal by heating without any noticeable
change in micro-structure is called recovery. It is a low
temperature process. It is also called stress relieving
treatment. During recovery the tensile strength and
hardness are not greatly affected.
Recrystallization
It is the process by which distorted grains of cold
worked metal are replaced by new, strain free grains
during heating above a specific minimum temperature
called recrystallization temperature.
Grain growth:
It is the process by which the material is held for
linger times at a temperature above its recrystallization
temperature which results an increase in grain size.

11. s.no point Hot working Cold working
1 Definition Plastic deformation of metals
at a temperature slightly above
its recrystallisation
temperature.
Plastic deformation of metals
at a temperature below the
recrystallisation temperature.
2 Production
operation
Rolling, forging, pipe
welding, cupping, hot
spinning and hot extruding.
Drawing, squeezing, bending,
cold extruding, shearing, shot
peening and hobbling.
3 Recovery The deformation and recovery
take place simultaneously.
There is no recovery during
deformation.
4 Internal and
residual
stresses
These are not Produce in the
hot worked metal.
These are produced in the cold
worked metal.
5 Crystal
structure
Crystals are refined and there
is no elongation of grains.
Crystals are not refined and
grains are elongated.

12. 6 Mechanical
properties
a. Hardness
Since recovery and
deformation are
simultaneously taking
place, there is no change in
hardness.
Hardness increase due to
strain hardening.
b. Yield
point,
Tensile
strength and
Fatigue
strength.
No change.
All of these are increases in
cold worked metal.
c. Impact
strength and
ductility
These are increased in their
values.
These are decreased in their
values.
d.
Flowability
Higher Lesser
7 Resistance to
Corrosion
No change Decreases.

13. 8 Directional
properties
The greatest strength
of the hot rolled metal
exists in the direction
of flow.
No directional
properties are
produced by cold
working.
9 Energy for
deformation
Mechanical energy for
deformation is lesser
due to high working
temperature.
Mechanical energy for
deformation is more.
10 Porosity and
Blow holes
Generally, these are
eliminated.
These are continued.

14. 11 Advantage
s
1. Improvement in
toughness, impact
strength and ductility.
Improvement in tensile
and fatigue strengths.
1. Lesser energy for large
deformation without
fracture and elimination
of blow holes and
pores.
Better surface finish,
reduction loss of metal by
oxidation and better
dimensional tolerance
maintenance.
1. It is a rapid and
economical metal
forming process.
It produces better reactive
metals.
12 Disadvanta
ges
1. Loss of metal by
oxidation at high
temperatures.
More energy is required for
deformation.
1. Poor surface finish by
rapid oxidation.
Ductility is reduced.
1. The properties of metal
are not uniform over the
whole cross section.
There is an increase in
residual stress and
distortion of grain structure.