Mechanics Of Metal Forming The phenomenon where ductile metals becomes stronger and harder when they are deformed plasticity is called work hardening

1. Work Hardening
Prepared By : Patel Shreyash K.
Branch : M.E. (Production)
Pen No. : 170490728016
Subject : Mechanics of Metal Forming
Guided By : Dr. Shakil Kagzi
SHRI SITARAMBHAI NARANJIBHAI PATEL INSTITUTE
OF TECHNOLOGY AND RESEARCH CENTRE
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2. CONTENTS
 INTRODUCTION
 PRINCIPAL
 STAGES OF WORK HARDENING
 FACTORS OF WORK HARDENING
 ADVANTAGES
 DISADVANTAGES
 INDUSTRIALAPPLICATION
 LITERATURE REVIEW
 CONCLUSIONS
 REFERENCES
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3. Introduction
What is Work Hardening?
The phenomenon where ductile metals
becomes stronger and harder when they are
deformed plasticity is called work
hardening.
Work hardening is also known as strain
hardening or cold working.
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4. Work hardening, is the strengthening of a
metal by plastic deformation. In the
plastic region, the true stress increases
continuously, meaning that when a metal
is strained beyond the yield point, more
and more stress is required to produce
additional plastic deformation and the
metal seems to have become stronger and
more difficult to deform.
This implies that the metal is becoming
stronger as the strain (work) increases.
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5. This strengthening occurs because of
dislocation movements and dislocation
generation within the crystal structure of
the material.
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6. PRINCIPAL
The ability of metal to plastically deform
depends on the ability of dislocation to
move.
When loaded, the strain increase with
stress and the curve reaches the point A in
the plastic range.
If at this stage , the specimen is unloaded ,
the strain does not recover along the
original path AO , but moves along AB .
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7. 7

8. If the specimen is reloaded immediately ,
the curve again rises from B to A ,but via
another path , and reaches the point C ,
after which it will follow the curvature , if
loading is continued .
If the specimen would not have been
unloaded , after point A , the stress–strain
curve would have followed the dotted
path AD’ .
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9. A comparison of paths ACD and AD’
shows that the cold working (plastic
deformation) has increased the yield
strength and ultimate strength of the
metal.
Increasing temp. lowers the rate of strain
hardening and thus the treatment is given
the usually at temp. well below the
melting point of the material. This
treatment is known as cold working.
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10. The consequence of strain hardening a
material is improved strength and
hardness but material ductility be reduced.
After performing this process to the
material their dislocation of atoms become
more difficult which make the material
stronger.
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11. Stages of work hardening
A typical shear stress – shear strain curve
for a single crystal shows three stages of
work hardening .
STAGE 1 – Easy Glide Region
STAGE 2 – Linear Hardening Region
STAGE 3 – Parabolic Hardening Region
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12. Graphical Represtation of Stages
of Work Hardening
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13. Easy Glide Region
 Shear stress is almost constant .
 Very low work hardening rate .
 BCC system do not exhibit an easy glide.
Linear Hardening Region
 Hardening rate is high as well as constant.
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14. Parabolic Hardening Region
 Low hardening rate
 Shape is parabolic
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15. Factors of Work Hardening
During plastic deformation most of the
metals and alloys become stronger due to
work hardening and develop directional
properties.
The work hardening effect may be taken
as consisting of following two factors.
1) Isotropic work hardening
2) Kinematic work hardening
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16. Isotropic work hardening
In this case the yield strength increases
equally in all direction.
The magnitude of work hardening is
generally related to plastic work done or the
total strain suffered by the material.
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17. Kinematic work hardening
In this case the yield strength may not
increase in magnitude but the whole of the
yield diagram shifts in the direction of
strain vector.
The magnitude of shift may be related to
the magnitude of strain suffered.
Very few attempts have been made to
determine this relationship.
The data on the relationship of shift of
yield diagram with the strain suffered by
the material is still very scanty.
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18. 18
Graphical representation of kinematic work
hardening

19. Advantages
No heating required
Better surface finish
Superior dimensional control
Better reproducibility and
interchangeability
Directional properties can be imparted
into the metal
Contamination problems are minimized
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20. Disadvantages
Greater forces are required
Heavier and more powerful equipment
and stronger tooling are required
Metal is less ductile
Metal surfaces must be clean and scale-
free
Intermediate anneals may be required to
compensate for loss of ductility that
accompanies strain hardening
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21. The imparted directional properties may
be detrimental
Undesirable residual stress may be
produced
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22. INDUSTRIAL APPLICATION
Construction materials – High strength
reduces the need for material thickness
which generally saves weight and cost.
Machine cutting tools need be much
harder than the material they are operating
on in order to be effective.
Knife blades – a high hardness blade
keeps a sharp edge.
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23. Anti-fatigue – Hardening can drastically
improve the service life of mechanical
components with repeated
loading/unloading, such as axles.
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24. Literature Review
Sr No. Title Name of
Publicati
on
Author Objective Conclusion
1 Excellen
t ductility
and
strong
work
hardenin
g effect
of as-
cast Mg-
Zn-
Zr-Yb
alloy at
room
tempera
ture
Elsevier Dongdong
Zhang a, b,
Deping
Zhang a, *,
Fanqiang
Bu a, Xinlin
Li b,
Baishun Li
a,
Tingliang
Yan b, c,
Kai Guan
a, Qiang
Yang a,
Xiaojuan
Liu a, Jian
Meng a, **
In this paper,
we report a
new single
phase solid
solution as-
cast Mg-1Zn-
0.4Zr-0.2Yb
alloy that
possesses
excellent
ductility (df ¼
38.5%) and
strong work
hardening
effect (n ¼
0.38) at room
temperature.
Introduction of
trace Yb in ZK10
alloy affects its
ductility and
work hardening
effect. As
compared with
ZK10 alloy,
ZK10Yb alloy
exhibits higher
ductility (df ¼
38.5%) and
stronger work
hardening
effect (n ¼ 0.38)
at room
temperature.
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25. CONCLUSIONS
 The low stacking fault energy (SFE) in Mg-1Zn-
0.4Zr-0.2Yb alloy could be attributed to the minor
Yb addition. The low SFE is conducive to
promoting the activity of basal dislocation slip,
activations of non-basal dislocation slips and the
formation of deformation twins during tensile
deformation, and these can ultimately lead to the
development of the ductility in ZK10Yb alloy.
The strong work hardening effect of ZK10Yb
alloy is due to the formation of SFs and
deformation twins induced by low SFE, which
can remarkably store dislocations, restrict
dislocation motions and result in multiplication
and storage of dislocations at twin boundaries.
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26. REFERENCES
1. A textbook Of Material Science And
Metallurgy – O.P. Khanna
2. http://www.elsevier.com/locate/jalcom
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27. Thank you
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