Hot working involves plastically deforming metals above their recrystallization temperature but below melting point. This allows new crystals to form through recrystallization, improving properties like toughness. Cold working deforms metals below the recrystallization temperature through strain hardening, increasing properties like strength but decreasing ductility. The main differences are that hot working eliminates hardening, improves uniformity, and does not produce internal stresses, while cold working increases strength and hardness at the cost of ductility and produces internal stresses.

1. HOT AND COLD WORKING PROCESS IN METAL
FORMING
AND
THEIR EFFECT ON MECHANICAL PROPERTIES
Prepared by,
Hiren vaghani

2. PRESENTATION CONTAIN
 Introduction
 Hot working process
 Cold working process
 Difference between hot and cold working
process

3. INTRODUCTION
 Metal forming, is the metal working process of
fashioning metal parts and objects through mechanical
deformation; the work piece is reshaped without adding
or removing material, and its mass remains unchanged.
 Forming operates on the materials science principle
of plastic deformation, where the physical shape of a
material is permanently deformed.
 Metal forming process is classified into two category,
1) Hot working process
2) Cold working process

4. HOT WORKING PROCESS
 Hot working refers to processes where metals are
plastically deformed above their recrystallization
temperature but below the melting point.
 when the workpiece is hot worked, the atom of
workpiece reach a certain higher energy level
developed due to heat and force.As a result new
crystals start forming, is called recrystallization.
 Generally recrystallization temp. is 30% to 40% of
melting temp. and hot working temp. is 70% to 90% of
melting temp.

5. EFFECTS OF HOT WORKING PROCESS ON MECHANICAL
PROPERTIES OF METAL METAL
 If properly carried out, no change in hardness and
ductility due to continuous recrystallization.
 Improved toughness
 does not affect tensile strength & corrosion
resistance.
 Promotes uniformity of material by breaks up hard
impurities, e.g.Cementite in steel
 Oxide forms rapidly on metal surface.
 Hot working refines grains structure.

6. COLD WORKING PROCESS
 Cold working is the plastic deformation of
metals below the recrystallization temperature.
 In most cases, such cold forming is done at
room temperature.
 The major cold-working operations can be
classified basically as squeezing, bending,
shearing and drawing.

7. EFFECTS OF COLD WORKING PROCESS ON MECHANICAL
PROPERTIES OF METAL
 Increase
 UTS,
 yield strenth,
 Hardness
 Fatigue strenth
 residual stresses
 Decreases
 Impact strenth
 Ductility

8. DIFFERENCE BETWEEN HOT AND COLD WORKING PROCESS
Cold working Hot working
1.It is done at a temperature below the
recrystallization temperature.
Hot working is done at a temperature
above recrystallization temperature.
2.It is done below recrystallization
temperature so it is accomplished by
strain hardening.
Hardening due to plastic deformation is
completely eliminated.
Cold working decreases mechanical
properties of metal like elongation,
reduction of area and impact values.
It increases mechanical properties.
Crystallization does not take place. Crystallization takes place.
Material is not uniform after this
working.
Material is uniform thought.

9. Cold working Hot working
Cold working increases ultimate tensile
strength, yield point hardness and fatigue
strength but decreases resistance to
corrosion.
In hot working, ultimate tensile strength, yield
point, corrosion resistance are unaffected.
Internal and residual stresses are produced. Internal and residual stresses are not
produced.
There is more risk of cracks. There is less risk of cracks.
Cold working required more energy for plastic
deformation.
It requires less energy for plastic deformation
because at higher temperature metal
become more ductile and soft
It does not require pickling because no
oxidation of metal takes place.
Heavy oxidation occurs during hot working so
pickling is required to remove oxide
Embrittlement does not occur in cold working
due to no reaction with oxygen at lower
temperature.
There is chance of embrittlement by oxygen
in hot working hence metal working is done
at inert atmosphere for reactive metals
DIFFERENCE BETWEEN HOT AND COLD WORKING PROCESS