- Email: [email protected]
Recrystallization of nickel-270
Metallography
239
Recrystallization J. T. HOUSTON Metals
and Ceramics
Division,
of NickeL270a
AND
K. FARRELL
Oak Ridge National
Laboratory,
Oak Ridge,
Tennessee
Nickel-270, a commercially pure nickel, when cold-worked through reductions in area of 10 to 94 %, displays slight recovery hardening after annealing in the temperature range 200” to 300 “C. The 30-minute recrystallization temperatures are in the range 290 to 400 “C and are inversely proportional to the degree of prior cold work. The time dependence of recrystallization in specimens deformed 94 y0 yields an apparent activation energy of about 40 kcal/mole, which is in better agreement with that for zone-refined nickel than with that for substantially less pure nickel.
Introduction In 1937, Fe& reviewed recovery and recrystallization data on cold-worked nickel. He pointed out that some of the major factors influencing these phenomena were the amount,
method,
temperature,
annealing time, and, more important, recrystallization
temperatures
and speed of cold working, the
the purity of the nickel. At that time,
for most grades of nickel that had been cold-
worked more than 50% usually exceeded 600°C. Fetz discussed the effects of various impurities and alloying elements and then demonstrated that electrolytic nickel of 99.866 y. purity, cold-rolled 82 %, would recrystallize at approximately 450°C
during a 30-minute
anneal; lesser deformations
shifted recrystallization
to higher temperatures. Earlier, Ransley and Smithells had shown that refined and subsequently melted electrolytic nickel of only 99.62% purity, cold-drawn through a 70%
reduction in area, would recrystallize at 480°C in an unspecified
time. Since then, zone refining has brought about progressive reductions in recrystallization temperature. 3 The lowest value attained seems to be 235°C for zone-refined
nickel cold-rolled 80%
and annealed for 30 minutes.4 The purpose
of this paper is to report a low recrystallization temperature for commercially pure nickel and to show the effects of annealing time and degree of prestrain. 8.Research sponsored by the U. S. Atomic Energy Commission under contract with the Union Carbide Corporation. Metallography, Copyright
0
1969 by American
2 (1969)
239-246
Elsevier Publishing Company,
Inc.
240
J. T. Houston and K. Farrell
Experimental Nickel-270
Procedure is prepared
from carbonyl
Nickel Company (INCO).
nickel powder by the International
Its nominal nickel content is 99.98%,
with specified
maxima of 200 wt ppm carbon, 50 iron, and 10 each of other impurities.5 Our material was purchased in the form of hot-rolled, 0.50-inch-diameter rod. Chemical analyses for interstitial impurities gave 20 wt ppm carbon, 6 hydrogen, 2 nitrogen, and 74 oxygen. A semiquantitative
spectrographic
analysis indicated
that most other impurities were each less than 10 wt ppm, with the exceptions of 15 wt ppm iron, t30 tungsten, <30 zirconium, and <200 zinc; these latter figures are the limits of measurement-the actual analyses may be considerably less. The
as-received
rod was cold-swaged
through
88 %, 75 %, and 34 y. ; we also cold-stretched
reductions
in area of 94’$$,
one piece of rod in tension through
a 10% reduction in area. Disks cut from the wrought rods were annealed in air for 30 minutes. This included a heatup period of approximately 4 minutes. The annealed specimens were mounted and polished for metallography measurements.
Diamond
pyramid hardness
impressions,
and hardness
using a 500-g
load,
were made randomly on the polished and etched cross sections of the rods, the average of at least three impressions being used for the hardness value. The. temperature”recrystallization temperature was read as the “half-hardness that is, that annealing temperature
that caused the room-temperature
hardness
of the specimen to fall to a value midway between that for the as-worked material and that for the fully annealed condition. This sort of indirect measurement
has
been commonly used on nickel in the past, and Bollmans has demonstrated its acceptability by using transmission electron microscopy to show that changes in the
room-temperature
recrystallization
hardness
transformation
of wrought
correspond
nickel
annealed
through
to the stages of recovery,
the
primary
recrystallization, and secondary recrystallization or grain growth. The sharpest change in hardness is associated with primary recrystallization, the hardness remaining
practically
unchanged
during secondary
recrystallization.
We con-
firmed these observations qualitatively by transmission electron microscopy of our annealed 94% deformed material. Our optical metallography, made at the same time as the hardness measurements, Hardness-annealing
temperature
also agreed with the hardness changes.
curves for the cold-worked
Nickel-270
are
shown in Figs. 1 and 3b. Noteworthy features of the curves are that the hardness transitions occur at low temperature and are very sharp, and that prior to recrystallization
slight hardening takes place at temperatures
at which recovery
processes are expected to be active. The fractional hardness increase, relative to the asdeformed hardness, is very much bigger for the 34 y. deformed mater ial than for greater or lesser degrees of deformation. hardening
during recovery
in nickel.
Bridges
Others1 have found slight
and Ball’ state that Stage IV
Recrystallization recovery,
of Nickel-270
centered
241
at 26O”C, is detectable
in material
50 wt ppm carbon. They postulate that precipitation might lead to an increase in hardness.
containing of carbon
less than or carbides
In Fig. 2 the half-hardness recrystallization temperatures are plotted against the degree of prior cold deformation. In agreement with the data of Fe& for 200
i50
200
0
ANNEALING FIG. 1.
Hardness-annealing
on the curves
denote
prestrain
temperature in terms
400 TEMPERATURE curves
of reduction
for cold-worked in area.
600 (“C) Nickel-270.
Figures
242
J. T. Houston and K. Farrell
cold-rolled
electrolytic
nickel,
curves are widely displaced the relative contributions differences
the relationship
is inversely
linear,
but the two
on the temperature scale and are of different slope; of purity and deformation procedure to these
are unknown.
The International Nickel Company has published some earlier measurements of the recrystallization temperature of Nickel-270.5 These were also determined from
hardness
changes
Fig. 2, where
during
30-minute
anneals.
The
it can be seen that they are significantly
700
600
-l
NICKEL
A
INCO
0
PRESENT
in
the present
ELEC TRO-
FETZ’COLD-ROLLED LYTIC
/
are included than
I
I
•I
data
higher
DATA
NICKE :L 270
WOR
500
400
I ---_I_-
300
-L
200 0
25
75
50
DEFORMATION
400
(%I
FIG. 2. Variation of half-hardness recrystallization temperature with work. The deformation procedure for the INCO specimens is not known.
prior
cold
Recrystallization of Nickel-270 values. The discrepancies
243
here may be due in part to differences in deformation
procedures and perhaps to improvements in quality control. We have seen that the amount and type of impurity strongly influence the recrystallization temperature of nicke1.l This is probably because of their effects on grain boundary migration rates, since such migration is likely to be the process controlling
recrystallization.
aluminum
containing
A good example of this retarding effect is shown in
small amounts
of dissolved
copper.8 In recent
years,
however, it has become evident that the form and disposition of the impurities must also be considered. Work on aluminum containing a small amount of gold impurity9 has shown that if the gold is present as easily visible precipitates the material recrystallizes
as though it were zone-refined
gold is present in some submicroscopic
aluminum;
form grain boundary
but when the migration
rates
can be reduced by a factor of 10,000. Since the nature and distribution of impurities are functions of thermomechanical history, it is obvious that their effects in a commercial material may be quite complex. The time dependence
of recrystallization
given in Fig. 3. Experiments
in the 94%
with a thermocouple
prestrained
spot-welded
material is
to a specimen
established that it took an average time of 4 minutes to reach the furnace temperature. Nominal annealing times of 6 minutes, 30 minutes, 1 hour, and 24 hours were used to show that the recrystallization
temperature was markedly
decreased with increasing time. There might be a suggestion, too, that recovery hardening
was pushed to lower temperatures
for annealing times of 1 hours or
more. From Fig. 3 we can determine an activation energy for recrystallization. The general equation relating recrystallization time and temperature in terms of a single activation energy, QT , is 1
t,== where
t, is the time
required
to achieve X
fraction
of recrystallization
at
temperature T; C and R are constants. Since changes in hardness appear to be an acceptable measure of the progress of recrystallization in nickel, we can replace t, with the time to reach a given hardness.
The Arrhenius
plot for the half-
hardness time is shown in Fig. 4. The apparent activation energy is approximately 40 kcal/mole. It is not clear how meaningful this is, since Qr may be sensitive to impurity level8 and to the extent of prior deformation.lOJ1 However, it may be more than coincidence
that a QT of 40 kcal/mole is much closer to Qr values
obtained for zone-refined nickel than it is to those for substantially less pure nickel. Detert and Dressier,* using quantitative metallography to study recrystallization
in cold-rolled,
zone-refined
nickel,
found Qr to be about 47 and
40 kcal/mole for the start and finish of recrystallization material,
and about 29 and 38 kcal/mole, respectively,
in 60%
deformed
for the case of 80%
244
J. T. Houston and K. Farrell
deformation.
Wensch
and Walker,ll
using 99.3 o/0 commercial-purity
nickel
cold-rolled 20%, 400/(, and 60%, found Qr for the finish of recrystallization 75.8, 73.3, and 69.5 kcal/mole, respectively.
to be
I
94%
R IN A
2oo F150 :
26 min
2 min
100
I-----
“E < -9
50
I--
(0)
m
w” z
g I
200
150 56 min 100
50
(cl 0
200 ANNEALING
400 TEMPERATURE
FIG. 3. Effect of annealing time on recrystallization cold-swaged through 94 o/0 reduction in area.
(“C) behavior
of Nickel-270
rod
Remystallization
of Nickel-270
245 TEMPERATURE
(“C)
400
250
200
1000
94%
R IN
A
100
1
0.1 1.4
1.6
1.0 “‘O/T
FIG. 4. Arrhenius annealing temperature
2.0
2.2
(OK)
plot of reciprocal of half-hardness time versus for 94 o/O reduction-in-area material.
reciprocal
of
Summary
In summary, Nickel-270, a commercially pure nickel, when cold-worked through reductions in area of 10 to 94%, displays slight recovery hardening after annealing in the temperature range 200” to 300°C. The 30-minutes recrystalli-
J. T. Houston and K. Farrell
246 zation temperatures
are in the range 290” to 400°C and are inversely proportional
to the degree of prior cold work. The time dependence of recrystallization in specimens deformed 94% yields an apparent activation energy of about 40 kcal/mole, which is in better agreement with that for zone-refined with that for substantially
nickel than
less pure nickel.
References 1. E. Fetz, Trans. Am. Sec. Metals, 2.5 (1937) 1030. 2. C. E. Ransley and C. J. Smithells, I. Inst. Metals, 49 (1932) 287. 3. B. Dubois, A. M. Wacht, F. Dabosi, and J. Talbot, Mm. Sci. Rev. Met., 60 (1963) 851. 4. K. Detert and G. Dressler, Acta Met., 13 (1965) 845. 5. Huntington Nickel Alloys, published by International Nickel Company, Inc., Huntington, West Virginia. 6. W. Bollman, I. Inst. Metals, 87 (1958-59) 439. 7. P. J. Bridges and C. J. Ball, Phil. Mug., 15 (1967) 1107. 8. P. Gordon and R. A. Vandermeer, Trans. AIME, 224 (1962) 917. 9. R. A. Vandermeer, p. 6 in Oak Ridge National Laboratory Report ORNL-3970(1966). 10. J. E. Bailey and P. B. Hirsch, Proc. Roy. SW., A267 (1962) 11. 11. G. W. Wensch and H. L. Walker, Trans. Am. Sot. Metals, 44 (1952) 1186.
Accepted
July 29, 1969
239
Recrystallization J. T. HOUSTON Metals
and Ceramics
Division,
of NickeL270a
AND
K. FARRELL
Oak Ridge National
Laboratory,
Oak Ridge,
Tennessee
Nickel-270, a commercially pure nickel, when cold-worked through reductions in area of 10 to 94 %, displays slight recovery hardening after annealing in the temperature range 200” to 300 “C. The 30-minute recrystallization temperatures are in the range 290 to 400 “C and are inversely proportional to the degree of prior cold work. The time dependence of recrystallization in specimens deformed 94 y0 yields an apparent activation energy of about 40 kcal/mole, which is in better agreement with that for zone-refined nickel than with that for substantially less pure nickel.
Introduction In 1937, Fe& reviewed recovery and recrystallization data on cold-worked nickel. He pointed out that some of the major factors influencing these phenomena were the amount,
method,
temperature,
annealing time, and, more important, recrystallization
temperatures
and speed of cold working, the
the purity of the nickel. At that time,
for most grades of nickel that had been cold-
worked more than 50% usually exceeded 600°C. Fetz discussed the effects of various impurities and alloying elements and then demonstrated that electrolytic nickel of 99.866 y. purity, cold-rolled 82 %, would recrystallize at approximately 450°C
during a 30-minute
anneal; lesser deformations
shifted recrystallization
to higher temperatures. Earlier, Ransley and Smithells had shown that refined and subsequently melted electrolytic nickel of only 99.62% purity, cold-drawn through a 70%
reduction in area, would recrystallize at 480°C in an unspecified
time. Since then, zone refining has brought about progressive reductions in recrystallization temperature. 3 The lowest value attained seems to be 235°C for zone-refined
nickel cold-rolled 80%
and annealed for 30 minutes.4 The purpose
of this paper is to report a low recrystallization temperature for commercially pure nickel and to show the effects of annealing time and degree of prestrain. 8.Research sponsored by the U. S. Atomic Energy Commission under contract with the Union Carbide Corporation. Metallography, Copyright
0
1969 by American
2 (1969)
239-246
Elsevier Publishing Company,
Inc.
240
J. T. Houston and K. Farrell
Experimental Nickel-270
Procedure is prepared
from carbonyl
Nickel Company (INCO).
nickel powder by the International
Its nominal nickel content is 99.98%,
with specified
maxima of 200 wt ppm carbon, 50 iron, and 10 each of other impurities.5 Our material was purchased in the form of hot-rolled, 0.50-inch-diameter rod. Chemical analyses for interstitial impurities gave 20 wt ppm carbon, 6 hydrogen, 2 nitrogen, and 74 oxygen. A semiquantitative
spectrographic
analysis indicated
that most other impurities were each less than 10 wt ppm, with the exceptions of 15 wt ppm iron, t30 tungsten, <30 zirconium, and <200 zinc; these latter figures are the limits of measurement-the actual analyses may be considerably less. The
as-received
rod was cold-swaged
through
88 %, 75 %, and 34 y. ; we also cold-stretched
reductions
in area of 94’$$,
one piece of rod in tension through
a 10% reduction in area. Disks cut from the wrought rods were annealed in air for 30 minutes. This included a heatup period of approximately 4 minutes. The annealed specimens were mounted and polished for metallography measurements.
Diamond
pyramid hardness
impressions,
and hardness
using a 500-g
load,
were made randomly on the polished and etched cross sections of the rods, the average of at least three impressions being used for the hardness value. The. temperature”recrystallization temperature was read as the “half-hardness that is, that annealing temperature
that caused the room-temperature
hardness
of the specimen to fall to a value midway between that for the as-worked material and that for the fully annealed condition. This sort of indirect measurement
has
been commonly used on nickel in the past, and Bollmans has demonstrated its acceptability by using transmission electron microscopy to show that changes in the
room-temperature
recrystallization
hardness
transformation
of wrought
correspond
nickel
annealed
through
to the stages of recovery,
the
primary
recrystallization, and secondary recrystallization or grain growth. The sharpest change in hardness is associated with primary recrystallization, the hardness remaining
practically
unchanged
during secondary
recrystallization.
We con-
firmed these observations qualitatively by transmission electron microscopy of our annealed 94% deformed material. Our optical metallography, made at the same time as the hardness measurements, Hardness-annealing
temperature
also agreed with the hardness changes.
curves for the cold-worked
Nickel-270
are
shown in Figs. 1 and 3b. Noteworthy features of the curves are that the hardness transitions occur at low temperature and are very sharp, and that prior to recrystallization
slight hardening takes place at temperatures
at which recovery
processes are expected to be active. The fractional hardness increase, relative to the asdeformed hardness, is very much bigger for the 34 y. deformed mater ial than for greater or lesser degrees of deformation. hardening
during recovery
in nickel.
Bridges
Others1 have found slight
and Ball’ state that Stage IV
Recrystallization recovery,
of Nickel-270
centered
241
at 26O”C, is detectable
in material
50 wt ppm carbon. They postulate that precipitation might lead to an increase in hardness.
containing of carbon
less than or carbides
In Fig. 2 the half-hardness recrystallization temperatures are plotted against the degree of prior cold deformation. In agreement with the data of Fe& for 200
i50
200
0
ANNEALING FIG. 1.
Hardness-annealing
on the curves
denote
prestrain
temperature in terms
400 TEMPERATURE curves
of reduction
for cold-worked in area.
600 (“C) Nickel-270.
Figures
242
J. T. Houston and K. Farrell
cold-rolled
electrolytic
nickel,
curves are widely displaced the relative contributions differences
the relationship
is inversely
linear,
but the two
on the temperature scale and are of different slope; of purity and deformation procedure to these
are unknown.
The International Nickel Company has published some earlier measurements of the recrystallization temperature of Nickel-270.5 These were also determined from
hardness
changes
Fig. 2, where
during
30-minute
anneals.
The
it can be seen that they are significantly
700
600
-l
NICKEL
A
INCO
0
PRESENT
in
the present
ELEC TRO-
FETZ’COLD-ROLLED LYTIC
/
are included than
I
I
•I
data
higher
DATA
NICKE :L 270
WOR
500
400
I ---_I_-
300
-L
200 0
25
75
50
DEFORMATION
400
(%I
FIG. 2. Variation of half-hardness recrystallization temperature with work. The deformation procedure for the INCO specimens is not known.
prior
cold
Recrystallization of Nickel-270 values. The discrepancies
243
here may be due in part to differences in deformation
procedures and perhaps to improvements in quality control. We have seen that the amount and type of impurity strongly influence the recrystallization temperature of nicke1.l This is probably because of their effects on grain boundary migration rates, since such migration is likely to be the process controlling
recrystallization.
aluminum
containing
A good example of this retarding effect is shown in
small amounts
of dissolved
copper.8 In recent
years,
however, it has become evident that the form and disposition of the impurities must also be considered. Work on aluminum containing a small amount of gold impurity9 has shown that if the gold is present as easily visible precipitates the material recrystallizes
as though it were zone-refined
gold is present in some submicroscopic
aluminum;
form grain boundary
but when the migration
rates
can be reduced by a factor of 10,000. Since the nature and distribution of impurities are functions of thermomechanical history, it is obvious that their effects in a commercial material may be quite complex. The time dependence
of recrystallization
given in Fig. 3. Experiments
in the 94%
with a thermocouple
prestrained
spot-welded
material is
to a specimen
established that it took an average time of 4 minutes to reach the furnace temperature. Nominal annealing times of 6 minutes, 30 minutes, 1 hour, and 24 hours were used to show that the recrystallization
temperature was markedly
decreased with increasing time. There might be a suggestion, too, that recovery hardening
was pushed to lower temperatures
for annealing times of 1 hours or
more. From Fig. 3 we can determine an activation energy for recrystallization. The general equation relating recrystallization time and temperature in terms of a single activation energy, QT , is 1
t,== where
t, is the time
required
to achieve X
fraction
of recrystallization
at
temperature T; C and R are constants. Since changes in hardness appear to be an acceptable measure of the progress of recrystallization in nickel, we can replace t, with the time to reach a given hardness.
The Arrhenius
plot for the half-
hardness time is shown in Fig. 4. The apparent activation energy is approximately 40 kcal/mole. It is not clear how meaningful this is, since Qr may be sensitive to impurity level8 and to the extent of prior deformation.lOJ1 However, it may be more than coincidence
that a QT of 40 kcal/mole is much closer to Qr values
obtained for zone-refined nickel than it is to those for substantially less pure nickel. Detert and Dressier,* using quantitative metallography to study recrystallization
in cold-rolled,
zone-refined
nickel,
found Qr to be about 47 and
40 kcal/mole for the start and finish of recrystallization material,
and about 29 and 38 kcal/mole, respectively,
in 60%
deformed
for the case of 80%
244
J. T. Houston and K. Farrell
deformation.
Wensch
and Walker,ll
using 99.3 o/0 commercial-purity
nickel
cold-rolled 20%, 400/(, and 60%, found Qr for the finish of recrystallization 75.8, 73.3, and 69.5 kcal/mole, respectively.
to be
I
94%
R IN A
2oo F150 :
26 min
2 min
100
I-----
“E < -9
50
I--
(0)
m
w” z
g I
200
150 56 min 100
50
(cl 0
200 ANNEALING
400 TEMPERATURE
FIG. 3. Effect of annealing time on recrystallization cold-swaged through 94 o/0 reduction in area.
(“C) behavior
of Nickel-270
rod
Remystallization
of Nickel-270
245 TEMPERATURE
(“C)
400
250
200
1000
94%
R IN
A
100
1
0.1 1.4
1.6
1.0 “‘O/T
FIG. 4. Arrhenius annealing temperature
2.0
2.2
(OK)
plot of reciprocal of half-hardness time versus for 94 o/O reduction-in-area material.
reciprocal
of
Summary
In summary, Nickel-270, a commercially pure nickel, when cold-worked through reductions in area of 10 to 94%, displays slight recovery hardening after annealing in the temperature range 200” to 300°C. The 30-minutes recrystalli-
J. T. Houston and K. Farrell
246 zation temperatures
are in the range 290” to 400°C and are inversely proportional
to the degree of prior cold work. The time dependence of recrystallization in specimens deformed 94% yields an apparent activation energy of about 40 kcal/mole, which is in better agreement with that for zone-refined with that for substantially
nickel than
less pure nickel.
References 1. E. Fetz, Trans. Am. Sec. Metals, 2.5 (1937) 1030. 2. C. E. Ransley and C. J. Smithells, I. Inst. Metals, 49 (1932) 287. 3. B. Dubois, A. M. Wacht, F. Dabosi, and J. Talbot, Mm. Sci. Rev. Met., 60 (1963) 851. 4. K. Detert and G. Dressler, Acta Met., 13 (1965) 845. 5. Huntington Nickel Alloys, published by International Nickel Company, Inc., Huntington, West Virginia. 6. W. Bollman, I. Inst. Metals, 87 (1958-59) 439. 7. P. J. Bridges and C. J. Ball, Phil. Mug., 15 (1967) 1107. 8. P. Gordon and R. A. Vandermeer, Trans. AIME, 224 (1962) 917. 9. R. A. Vandermeer, p. 6 in Oak Ridge National Laboratory Report ORNL-3970(1966). 10. J. E. Bailey and P. B. Hirsch, Proc. Roy. SW., A267 (1962) 11. 11. G. W. Wensch and H. L. Walker, Trans. Am. Sot. Metals, 44 (1952) 1186.
Accepted
July 29, 1969