Recrystallization of Cold-Worked Steel Wire

Santa Rosa Junior College
Fall 2011
December 14, 2011
Cold Working
Grain Growth
To document the
recrystallization, and
grain growth phases
of cold-worked carbon
 Increasing strength through
plastic deformation and
increasing dislocations
 “Cold working” because
deformation temperature
drastically less than melting
 Higher dislocation density,
more hindered dislocation
movement, increase hardness
 Elongates grains
% =
 Applied heat increases
dislocation motion
 Metal decreases in hardness as
dislocations leave faster
 Additionally, original electrical
and physical properties are
 Continuation of recovery
 Continued decreasing
dislocation density
 New grains form between
larger grains
 Start small, eventually
engulf parent grain
 Recrystallization
temperature for carbon
steel is about 1000˚F
 Possible to increase rate
of recrystallization by
increasing %CW
 Recrystallization
completes, continued
applied heat
 Grain growth due to
migration of grain
boundaries outward
 Large range of grain sizes
 Cold work a 40 cm long carbon steel
wire to approximately 55% CW
 Cut wire into 12 equally sized pieces
and assort into two groups of 6
 Heat one group at 500˚F and the
other at 800˚F
 Take one metal out of each after 1, 5,
10, 30, 60 minutes, and 24 hours
 Make two molds of each group taking
note of how to distinguish between
the samples
 Sand, polish and etch the samples
 Use the microscope to photograph
each sample
Annealing Temperature: 500˚F
Time: 1 minute
Magnification: 300x
Description: Recovery and minor
recrystallization. Visible grain
Annealing Temperature: 500˚F
Time: 5 minutes
Magnification: 300x
Description: Stretching not visible.
New grains forming.
 Annealing Temperature: 500˚F
 Time: 10 minutes
 Magnification: 300x
 Description: New grains continuing to
form. Increasing grain boundaries.
Dislocation density begins to decrease
due to the increased motion of the
 Annealing Temperature: 500˚F
 Time: 30 minutes
 Magnification: 300x
 Description: Grain size of larger grains
increasing. Smaller grain boundaries are
forced smaller. Dislocation density
continues to decrease.
Annealing Temperature: 500˚F
Time: 60 minutes
Magnification: 300x
Description: Large grain boundaries
continuing to increase, forcing other
grains smaller.
 Annealing Temperature: 500˚F
 Time: 24 hours
 Magnification: 300x
 Description: Very large and very small
grain sizes visible. Grain growth is
apparent. Number of dislocations is
much less than at the beginning of
Annealing Temperature: 800˚F
Time: 1 minute
Magnification: 300x
Description: More visible grain
stretching than in 500 F. Recovery
Annealing Temperature: 800˚F
Time: 5 minutes
Magnification: 300x
Description: New grains forming,
much larger than those formed in
500 F at same annealing time.
Annealing Temperature: 800˚F
Time: 10 minutes
Magnification: 300x
Description: Large grains
increasing size, pushing adjacent
grains smaller.
Annealing Temperature: 800˚F
Time: 30 minutes
Magnification: 300x
Description: Large grains continue
to grow, forcing others smaller.
Dislocation density is decreasing.
Annealing Temperature: 800˚F
Time: 60 minutes
Magnification: 300x
Description: Large grains are very
apparent. Notice the wide variety of
grain sizes.
 Annealing Temperature: 800˚F
 Time: 24 hours
 Magnification: 300x
 Description: Grain growth is very
apparent in larger grains. Smaller grains
are much smaller than in previous
slides. Dislocation density is at its
Although some of the pictures of the recrystallization of
carbon steel did not match perfectly with the theoretical
outcomes we expected, we think that our experiment
was still successful because the overall stages still
followed the recrystallization model very closely.
 Lack of a control sample makes it difficult to
compare the other metals without a base
frame of reference. Although the first metal
was only heated for 1 minute, the fact that the
steel was so thin may have caused drastic
changes in the grain patterns.
 Pictures did not come
out as clearly as we had
liked; over-etching and
excessive scratching
made the patterns in the
grains less noticeable or
difficult to see.
 The extreme thinness of the carbon steel may
have caused the recrystallization process to
end much faster, resulting in the grain growth
phase occurring much sooner.
 The relatively small surface area of each metal
may have caused the patterns in the grains to
be distorted. Near the edges of each metal
there was stretching of grains and other
deformations. The inside of the metal were so
close to the edges of the metal that the
deformations may have extended to some of
the grains in the middle.
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