U.S. patent application number 15/097354 was filed with the patent office on 2016-10-20 for zirconium alloy having excellent corrosion resistance and creep resistance and method of manufacturing the same.
This patent application is currently assigned to KEPCO NUCLEAR FUEL CO., LTD.. The applicant listed for this patent is KEPCO NUCLEAR FUEL CO., LTD.. Invention is credited to Min Young CHOI, Dae Gyun GO, Tae Sik JUNG, Jae Ik KIM, Yoon Ho KIM, Chung Yong LEE, Seung Jae LEE, Yong Kyoon MOK, Yeon Soo NA.
Application Number | 20160304991 15/097354 |
Document ID | / |
Family ID | 55649936 |
Filed Date | 2016-10-20 |
United States Patent
Application |
20160304991 |
Kind Code |
A1 |
CHOI; Min Young ; et
al. |
October 20, 2016 |
ZIRCONIUM ALLOY HAVING EXCELLENT CORROSION RESISTANCE AND CREEP
RESISTANCE AND METHOD OF MANUFACTURING THE SAME
Abstract
A zirconium alloy is manufactured through melting; solution heat
treatment at 1,000 to 1,050.degree. C. for 30 to 40 min and
.beta.-quenching using water; preheating at 630 to 650.degree. C.
for 20 to 30 min and hot rolling at a reduction ratio of 60 to 65%;
primary intermediate vacuum annealing at 570 to 590.degree. C. for
3 to 4 hr and primarily cold-rolled at a reduction ratio of 30 to
40%; secondary intermediate vacuum annealing at 560 to 580.degree.
C. for 2 to 3 hr and secondarily cold-rolled at a reduction ratio
of 50 to 60%; tertiary intermediate vacuum annealing at 560 to
580.degree. C. for 2 to 3 hr and tertiarily cold-rolled at a
reduction ratio of 30 to 40%; and final vacuum annealing at 440 to
650.degree. C. for 7 to 9 hr.
Inventors: |
CHOI; Min Young; (Daejeon,
KR) ; MOK; Yong Kyoon; (Daejeon, KR) ; KIM;
Yoon Ho; (Daejeon, KR) ; NA; Yeon Soo;
(Daejeon, KR) ; LEE; Chung Yong; (Daejeon, KR)
; JUNG; Tae Sik; (Daejeon, KR) ; GO; Dae Gyun;
(Daejeon, KR) ; LEE; Seung Jae; (Daejeon, KR)
; KIM; Jae Ik; (Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KEPCO NUCLEAR FUEL CO., LTD. |
Daejeon |
|
KR |
|
|
Assignee: |
KEPCO NUCLEAR FUEL CO.,
LTD.
Daejeon
KR
|
Family ID: |
55649936 |
Appl. No.: |
15/097354 |
Filed: |
April 13, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 16/00 20130101;
B22D 7/005 20130101; C22C 1/02 20130101; C22F 1/186 20130101; B22F
1/00 20130101 |
International
Class: |
C22C 16/00 20060101
C22C016/00; C22F 1/18 20060101 C22F001/18; B22D 7/00 20060101
B22D007/00; C22C 1/02 20060101 C22C001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 14, 2015 |
KR |
10-2015-0052711 |
Claims
1. A zirconium alloy, comprising: 1.1 to 1.2 wt % of Nb, 0.01 to
0.2 wt % of P, 0.2 to 0.3 wt % of Fe, and a balance of Zr.
2. The zirconium alloy of claim 1, wherein P is added in an amount
of 0.02 to 0.07 wt %.
3. The zirconium alloy of claim 1, further comprising 0.01 to 0.15
wt % of Ta.
4. The zirconium alloy of claim 3, wherein Ta is added in an amount
of 0.03 to 0.1 wt %.
5. A method of manufacturing a zirconium alloy, comprising steps
of: (1) melting a mixture comprising 1.1 to 1.2 wt % of Nb, 0.01 to
0.2 wt % of P, 0.2 to 0.3 wt % of Fe, and a balance of Zr, thus
preparing an ingot; (2) subjecting the ingot prepared in step (1)
to solution heat treatment at 1,000 to 1,050.degree. C.
(.beta.-phase range) for 30 to 40 min and then to .beta.-quenching
using water; (3) preheating the ingot treated in step (2) at 630 to
650.degree. C. for 20 to 30 min and subjecting the ingot to hot
rolling at a reduction ratio of 60 to 65%; (4) subjecting the
material hot-rolled in step (3), to primary intermediate vacuum
annealing at 570 to 590.degree. C. for 3 to 4 hr and then to
primarily cold-rolled at a reduction ratio of 30 to 40%; (5)
subjecting the material primarily cold-rolled in step (4), to
secondary intermediate vacuum annealing at 560 to 580.degree. C.
for 2 to 3 hr and then to secondarily cold-rolled at a reduction
ratio of 50 to 60%; (6) subjecting the material secondarily
cold-rolled in step (5), to tertiary intermediate vacuum annealing
at 560 to 580.degree. C. for 2 to 3 hr and then to tertiarily
cold-rolled at a reduction ratio of 30 to 40%; and (7) subjecting
the material tertiarily cold-rolled in step (6), to final vacuum
annealing at 440 to 650.degree. C. for 7 to 9 hr.
6. The method of claim 5, wherein in step (1), P is added in an
amount of 0.02 to 0.07 wt %, and in step (7), the final vacuum
annealing temperature is 460 to 600.degree. C.
7. The method of claim 5, wherein in step (1), the mixture further
comprises 0.01 to 0.15 wt % of Ta.
8. The method of claim 7, wherein Ta is added in an amount of 0.03
to 0.1 wt %, and in step (7), the final vacuum annealing
temperature is 460 to 530.degree. C.
9. The method of claim 5, wherein P is compacted before melting the
mixture in step (1).
10. The method of claim 6, wherein P is compacted before melting
the mixture in step (1).
11. The method of claim 8, wherein P is compacted before melting
the mixture in step (1).
12. The method of claim 8, wherein P is compacted before melting
the mixture in step (1).
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a zirconium alloy having
excellent corrosion resistance and creep resistance and a method of
manufacturing the same and, more particularly, to a zirconium alloy
composition and annealing conditions, suitable for use in nuclear
fuel cladding tubes and spacer grids for light and heavy water
reactor nuclear power plants.
[0003] 2. Description of the Related Art
[0004] Zirconium alloys, having a low neutron absorption
cross-section, superior corrosion resistance and mechanical
properties, have been widely used for decades as materials for
nuclear fuel cladding tubes, nuclear fuel assembly spaer grids, and
internal structures in nuclear reactors.
[0005] Among the alloys, Zircaloy-2 (Sn: 1.20 to 1.70 wt %, Fe:
0.07 to 0.20 wt %, Cr: 0.05 to 1.15 wt %, Ni: 0.03 to 0.08 wt %, O:
900 to 1500 ppm, Zr: balance) and Zircaloy-4 (Sn: 1.20 to 1.70 wt
%, Fe: 0.18 to 0.24 wt %, Cr: 0.07 to 1.13 wt %, O: 900 to 1500
ppm, Ni: <0.007 wt %, Zr: balance) are widely used in nuclear
industry.
[0006] With the goal of reducing nuclear fuel cycle cost in order
to improve the economic efficiency of reactors, high-burnup nuclear
fuel is receiving increased consideration these days. Mechanical
properties of conventional zircaloy, such as corrosion and creep
properties in severe operating conditions may deteriorate.
[0007] Accordingly, the need for a material having high corrosion
resistance and creep resistance, which are difficult to ensure
under conditions of high burn-up and extended fuel cycles, has come
to the fore, and thus research into appropriate zirconium alloys,
such as Zr--Nb alloys, etc., is ongoing.
[0008] With regard to conventional techniques, U.S. Pat. No.
4,649,023 discloses a zirconium alloy composed essentially of 0.5
to 2.0 wt % of Nb and 0.9 to 1.5 wt % of Sn, and including 0.09 to
0.11 wt % of any one selected from among Fe, Cr, Mo, V, Cu, Ni and
W, and 0.1 to 0.16 wt % of O, and the balance of Zr. Also, there is
disclosed a method of manufacturing a product in which precipitates
having a small size of 80 nm or less are uniformly distributed in a
matrix using the above alloy.
[0009] U.S. Pat. No. 5,648,995 discloses a cladding tube using a
zirconium alloy comprising 0.8 to 1.3 wt % of Nb, 50 to 250 ppm of
Fe, 1600 ppm or less of 0, and 120 ppm or less of Si.
[0010] This alloy is annealed at 600 to 800.degree. C., extruded,
and subjected to cold rolling four to five times. As such,
intermediate annealing between the cold rolling processes is
performed in the temperature range of 565 to 605.degree. C. for 2
to 4 hr, and final annealing is performed at 580.degree. C.,
thereby manufacturing a nuclear fuel cladding tube.
[0011] As such, in order to increase creep resistance, the alloy
composition is configured such that the amounts of Fe and O are
limited to 250 ppm or less and 1000 to 1600 ppm, respectively.
[0012] U.S. Pat. No. 6,325,966 discloses an alloy having superior
corrosion resistance and mechanical properties, composed
essentially of 0.15 to 0.25 wt % of Nb, 1.10 to 1.40 wt % of Sn,
0.35 to 0.45 wt % of Fe, and 0.15 to 0.25 wt % of Cr, and including
0.08 to 0.12 wt % of any one selected from among Mo, Cu, and Mn,
1000 to 1400 ppm of O, and the balance of Zr.
[0013] As is apparent from the above conventional techniques,
research into high-burnup zirconium alloy compositions having
improved corrosion resistance and mechanical properties is carried
out by changing the kinds and amounts of added elements or changing
the annealing conditions in conventional zirconium alloys in which
Nb is added with Sn.
[0014] In this case, optimal conditions for ensuring superior
corrosion resistance and mechanical properties of zirconium alloys
are affected by the kinds and amounts of added elements, processing
conditions, and annealing conditions, and thus the establishment of
a suitable alloy design and annealing conditions is required above
all.
[0015] Therefore, the present inventors have ascertained that an
Zr--Nb alloy, from which Sn is removed and to which P, Ta and the
like are added, and which is controlled in terms of composition and
annealing temperatures, may improve creep resistance while
significantly increasing corrosion resistance, thus culminating in
the present invention.
CITATION LIST
Patent Literature
[0016] U.S. Pat. No. 4,649,023 (Registration Date: Mar. 10,
1987)
[0017] U.S. Pat. No. 5,648,995 (Registration Date: Jul. 15,
1997)
[0018] U.S. Pat. No. 6,325,966 (Registration Date: Dec. 4,
2001)
SUMMARY OF THE INVENTION
[0019] Accordingly, the present invention has been made keeping in
mind the problems encountered in the related art, and an object of
the present invention is to provide a zirconium alloy composition
and final annealing conditions, in which Sn, which negatively
affects corrosion resistance, is removed and Nb, P, Ta and the like
are added to maintain creep resistance, thus ensuring optimal
annealing conditions while improving corrosion resistance and creep
resistance.
[0020] In order to accomplish the above object, the present
invention provides a zirconium alloy, comprising: 1.1 to 1.2 wt %
of Nb, 0.01 to 0.2 wt % of P, 0.2 to 0.3 wt % of Fe, and the
balance of Zr.
[0021] Preferably, P is added in an amount of 0.02 to 0.07 wt
%.
[0022] Preferably, the zirconium alloy further comprises 0.01 to
0.15 wt % of Ta in order to improve corrosion resistance and creep
resistance.
[0023] More preferably, Ta is added in an amount of 0.03 to 0.1 wt
%.
[0024] In addition, the present invention provides a method of
manufacturing a zirconium alloy, comprising the steps of: (1)
melting a mixture comprising 1.1 to 1.2 wt % of Nb, 0.01 to 0.2 wt
% of P, 0.2 to 0.3 wt % of Fe, and the balance of Zr, thus
preparing an ingot; (2) subjecting the ingot prepared in step (1)
to solution heat treatment at 1,000 to 1,050.degree. C.
(.beta.-phase range) for 30 to 40 min and then to .beta.-quenching
using water; (3) preheating the ingot treated in step (2) at 630 to
650.degree. C. for 20 to 30 min and subjecting the ingot to hot
rolling at a reduction ratio of 60 to 65%; (4) subjecting the
material hot-rolled in step (3), to primary intermediate vacuum
annealing at 570 to 590.degree. C. for 3 to 4 hr and then to
primarily cold-rolled at a reduction ratio of 30 to 40%; (5)
subjecting the material primarily cold-rolled in step (4), to
secondary intermediate vacuum annealing at 560 to 580.degree. C.
for 2 to 3 hr and then to secondarily cold-rolled at a reduction
ratio of 50 to 60%; (6) subjecting the material secondarily
cold-rolled in step (5), to tertiary intermediate vacuum annealing
at 560 to 580.degree. C. for 2 to 3 hr and then to tertiarily
cold-rolled at a reduction ratio of 30 to 40%; and (7) subjecting
the material tertiarily cold-rolled in step (6), to final vacuum
annealing at 440 to 650.degree. C. for 7 to 9 hr.
[0025] Preferably, in step (1), P is added in an amount of 0.02 to
0.07 wt %, and in step (7), the final vacuum annealing temperature
is 460 to 600.degree. C., thereby optimizing corrosion resistance
and creep resistance.
[0026] Preferably, in step (1), the mixture further comprises 0.01
to 0.15 wt % of Ta, thereby further increasing corrosion
resistance.
[0027] More preferably, Ta is added in an amount of 0.03 to 0.1 wt
%, and in step (7), the final vacuum annealing temperature is 460
to 530.degree. C., thereby maximizing corrosion resistance and
creep resistance.
[0028] Preferably, P is compacted in order to prevent precipitation
thereof before melting the mixture in step (1).
[0029] According to the present invention, the zirconium alloy is
configured such that Sn is completely removed and the kinds and
amounts of added elements, such as P, Ta and the like, and final
annealing conditions are controlled, thus exhibiting corrosion
resistance superior to that of Zircaloy-4 and high creep
resistance. Therefore, this zirconium alloy can be effectively
utilized in nuclear fuel cladding tubes and the like inside reactor
cores for light and heavy water reactor nuclear power plants.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The above and other objects, features and advantages of the
present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0031] FIG. 1 is a graph illustrating the weight gain over time in
corrosion testing of the zirconium alloy according to the present
invention; and
[0032] FIG. 2 is a graph illustrating the creep strain in creep
testing of the zirconium alloy according to the present
invention.
DESCRIPTION OF SPECIFIC EMBODIMENTS
[0033] As disclosed in embodiments of the present invention,
specific structures or functional explanations are merely set forth
to illustrate exemplary embodiments according to the concept of the
present invention. It will be understood that such exemplary
embodiments are able to be variously modified, are not construed as
limiting the present invention, and include all variations,
equivalents and substitutions incorporated in the spirit and the
scope of the present invention.
[0034] Hereinafter, a detailed description will be given of the
present invention.
[0035] The present invention addresses a zirconium alloy,
comprising: 1.1 to 1.2 wt % of Nb, 0.02 to 0.05 wt % of P, 0.2 to
0.3 wt % of Fe, and the balance of Zr.
[0036] Also, the present invention addresses a zirconium alloy,
comprising: 1.1 to 1.2 wt % of Nb, 0.02 wt % of P, 0.2 to 0.3 wt %
of Fe, and the balance of Zr.
[0037] Also, the present invention addresses a zirconium alloy,
comprising: 1.1 to 1.2 wt % of Nb, 0.05 wt % of P, 0.2 to 0.3 wt %
of Fe, and the balance of Zr.
[0038] Further, the present invention addresses a zirconium alloy,
comprising: 1.1 to 1.2 wt % of Nb, 0.05 wt % of P, 0.03 to 0.04 wt
% of Ta, 0.2 to 0.3 wt % of Fe, and the balance of Zr.
[0039] Further, the present invention addresses a zirconium alloy,
comprising: 1.1 to 1.2 wt % of Nb, 0.05 wt % of P, 0.09 to 0.1 wt %
of Ta, 0.2 to 0.3 wt % of Fe, and the balance of Zr.
[0040] The preparation of the zirconium alloy having the above
composition according to the present invention is described
below.
[0041] The present invention addresses a method of manufacturing
the zirconium alloy, comprising the steps of: (1) melting a mixture
of zirconium alloy elements, thus preparing an ingot; (2)
subjecting the ingot prepared in step (1) to solution heat
treatment at 1,000 to 1,050.degree. C. (.beta.-phase range) for 30
to 40 min and then to .beta.-quenching using water; (3) preheating
the ingot treated in step (2) at 630 to 650.degree. C. for 20 to 30
min and subjecting the ingot to hot rolling at a reduction ratio of
60 to 65%; (4) subjecting the material hot-rolled in step (3), to
primary intermediate vacuum annealing at 570 to 590.degree. C. for
3 to 4 hr and then to primarily cold-rolled at a reduction ratio of
30 to 40%; (5) subjecting the material primarily cold-rolled in
step (4), to secondary intermediate vacuum annealing at 560 to
580.degree. C. for 2 to 3 hr and then to secondarily cold-rolled at
a reduction ratio of 50 to 60%; (6) subjecting the material
secondarily cold-rolled in step (5), to tertiary intermediate
vacuum annealing at 560 to 580.degree. C. for 2 to 3 hr and then to
tertiarily cold-rolled at a reduction ratio of 30 to 40%; and (7)
subjecting the material tertiarily cold-rolled in step (6), to
final vacuum annealing.
[0042] A better understanding of the present invention may be
obtained through the following examples.
Examples 1 to 12
Preparation of Zirconium Alloys
[0043] (1) Formation of Ingot
[0044] In step (1), 1.2 wt % of Nb, 0.02 to 0.05 wt % of P, 0.03 to
0.1 wt % of Ta, 0.2 wt % of Fe, and the balance of Zr were
subjected to VAR (Vacuum Arc Remelting), thus forming an ingot.
[0045] The Zr that was used is zirconium sponge (Reactor Grade ASTM
B349), and the added elements, such as Nb, P, Ta, Fe and the like,
have a high purity of 99.99% or more.
[0046] In order to prevent the segregation of impurities and the
non-uniform distribution of the alloy composition, this process was
repeated about three times, and the alloy was melted under the
condition that the chamber for VAR was maintained at a vacuum level
of 10.sup.-5 torr or less, thus forming an ingot. Unlike the other
alloy elements, P was melted after being compacted, in order to
prevent precipitation and segregation.
[0047] To prevent the surface of the sample from being oxidized
during the cooling, cooling was carried out inert gas environment
such as argon.
[0048] (2) .beta.-Solution Heat Treatment and .beta.-Quenching
[0049] In step (2) for .beta.-solution heat treatment and
.beta.-quenching, solution heat treatment was performed for 30 min
at 1,000 to 1,050.degree. C., corresponding to the .beta.-phase
range, and then, water cooling at a rate of about 300.degree.
C./sec or more was performed. This process was performed to
homogenize the alloy composition in the formed ingot and to
uniformly distribute the size of SPP (Secondary Phase Particles) in
the matrix.
[0050] To prevent oxidation of the ingot, the ingot was clad with a
1 mm thick stainless steel plate and was then spot welded.
[0051] (3) Annealing and Hot Rolling
[0052] In step (3), the .beta.-quenched sample was subjected to hot
rolling.
[0053] The sample was preheated at 630 to 650.degree. C. for about
20 to 30 min, and was then rolled at a reduction rate of about 60
to 65%. If the processing temperature falls out of the above range,
it is difficult to obtain the rolled material suitable for use in
subsequent step (4). Also, if the reduction rate of hot rolling is
less than 60%, the texture of the zirconium material becomes
non-uniform, which lead to undesirably deterioration in hydrogen
embrittlement resistance. On the other hand, if the reduction rate
is higher than 80%, subsequent processability may become
problematic.
[0054] The material hot-rolled was treated as follows: the clad
stainless steel plate was removed, an oxide film and impurities
were removed using a pickling solution comprising water, nitric
acid and hydrofluoric acid at a volume ratio of 50:40:10, and the
remaining oxide film was completely removed using a wire brush in
order to facilitate subsequent processing.
[0055] (4) Primary Intermediate Annealing and Primary Cold
Rolling
[0056] In order to remove residual stress after hot rolling and
prevent damage to the sample upon primary cold processing, primary
vacuum annealing was performed under the condition that a vacuum
level was maintained at 10.sup.-5 torr or less at about 580 to
590.degree. C. for about 3 to 4 hr.
[0057] Preferably, the intermediate vacuum annealing is carried out
at a temperature elevated to a fully recrystallization annealing
temperature. If the temperature falls out of the above range,
corrosion resistance may deteriorate.
[0058] After completion of the primary intermediate vacuum
annealing, the rolled material was subjected to primary cold
rolling at a reduction ratio of about 40 to 50% at an interval of
about 0.3 mm for each pass.
[0059] (5) Secondary Intermediate Vacuum Annealing and Secondary
Cold Rolling
[0060] After completion of the primary cold rolling, the rolled
material was subjected to secondary intermediate vacuum annealing
at 570 to 580.degree. C. for about 2 to 3 hr.
[0061] If the intermediate annealing temperature falls out of the
above range, corrosion resistance may deteriorate.
[0062] After completion of the secondary intermediate vacuum
annealing, the rolled material was subjected to secondary cold
rolling at a reduction ratio of about 50 to 60% at an interval of
about 0.3 mm for each pass.
[0063] (6) Tertiary Intermediate Vacuum Annealing and Tertiary Cold
Rolling
[0064] After completion of the secondary cold rolling, the rolled
material was subjected to tertiary intermediate vacuum annealing at
570 to 580.degree. C. for 2 to 3 hr.
[0065] If the intermediate annealing temperature falls out of the
above range, corrosion resistance may deteriorate.
[0066] After completion of the tertiary intermediate vacuum
annealing, the rolled material was subjected to tertiary cold
rolling at a reduction ratio of about 30 to 40% at an interval of
about 0.3 mm for each pass.
[0067] (7) Final Vacuum Annealing
[0068] After completion of the tertiary cold rolling, the rolled
material was finally annealed in a high vacuum of 10.sup.-5 torr or
less.
[0069] Final annealing was performed at 460 to 580.degree. C. for 8
hr.
[0070] The specific alloy compositions of the zirconium alloys
according to the present invention and the final annealing
temperatures are summarized in Table 1 below.
TABLE-US-00001 TABLE 1 Final Annealing Chemical Composition (wt %)
Temp. Nb Sn P Fe Ta Cr Zr (.degree. C.) Ex. 1 1.2 -- 0.02 0.2 -- --
Balance 460 Ex. 2 1.2 -- 0.05 0.2 -- -- Balance 460 Ex. 3 1.2 --
0.05 0.2 0.03 -- Balance 460 Ex. 4 1.2 -- 0.05 0.2 0.1 -- Balance
460 Ex. 5 1.2 -- 0.02 0.2 -- -- Balance 520 Ex. 6 1.2 -- 0.05 0.2
-- -- Balance 520 Ex. 7 1.2 -- 0.05 0.2 0.03 -- Balance 520 Ex. 8
1.2 -- 0.05 0.2 0.1 -- Balance 520 Ex. 9 1.2 -- 0.02 0.2 -- --
Balance 580 Ex. 10 1.2 0.05 0.2 -- 580 Ex. 11 1.2 -- 0.05 0.2 0.03
-- Balance 580 Ex. 12 1.2 -- 0.05 0.2 0.1 -- Balance 580 C. Ex. 1
-- 1.5 -- 0.2 -- 0.1 Balance Commercially Zircaloy-4 available C.
Ex. 2 -- 1.5 -- 0.2 -- 0.1 Balance 460 Zircaloy-4
Comparative Example 1
[0071] As a commercially available zirconium alloy for use in
nuclear power plants, Zircaloy-4 was used.
Test Example 1
Corrosion Resistance Testing
[0072] In order to evaluate the corrosion resistance of the
zirconium alloy composition according to the present invention,
corrosion testing was performed as follows.
[0073] Each of the zirconium alloys of Examples 1 to 12 was
manufactured into a sheets through the above manufacturing process,
which was then fabricated a corrosion test sample having a size of
20 mm.times.20 mm.times.1.0 mm, followed by stepwise mechanical
polishing using #400 to #1200 SiC abrasive paper.
[0074] After completion of the surface polishing, the sample was
pickled using a solution comprising water, nitric acid and
hydrofluoric acid at a volume ratio of 50:40:10, sonicated with
acetone, and then completely dried in an oven for 24 hr or
longer.
[0075] In order to determine the extent of corrosion of the alloy,
the surface area and the initial weight of the alloy were measured
before the alloy was loaded into an autoclave.
[0076] The loaded sample was subjected to corrosion testing for 260
days using a static autoclave at 360.degree. C. in an 18.6 MPa pure
water atmosphere.
[0077] In the corrosion testing, the samples of Examples 1 to 12
and the commercially available Zircaloy-4 of Comparative Example 1
were placed in the autoclave together.
[0078] The samples were taken out a total of eight times during the
260 days subsequent to the corrosion testing, and the weight gains
were measured, after which the weight gains were calculated in
order to quantitatively evaluate the extent of corrosion. The
results are shown in the following tables.
[0079] The corrosion testing results were evaluated depending on 1)
when P was added in amounts of 0.02 wt % and 0.05 wt % in the
absence of Ta, and 2) when Ta was added in amounts of 0.03 wt % and
0.1 wt % in the presence of 0.05 wt % of P. As such, both 1) and 2)
were tested at all of three final annealing temperatures of
460.degree. C., 520.degree. C. and 580.degree. C.
[0080] 1) Results of Addition of 0.02 wt % and 0.05 wt % of P in
the Absence of Ta
TABLE-US-00002 TABLE 2 Weight Gain (mg/dm.sup.2) per Unit Surface
Area 360.degree. C., 18.6 MPa, Pure Water 50 days 110 days 170 days
260 days Ex. 1 (P 0.02 wt %) 18.1 26.6 28.4 33.5 Ex. 2 (P 0.05 wt
%) 17.5 27.0 32.9 37.6 Ex. 5 (P 0.02 wt %) 19.3 26.0 28.1 33.2 Ex.
6 (P 0.05 wt %) 16.1 23.8 25.2 28.7 Ex. 9 (P 0.02 wt %) 19.5 27.7
30.4 34.6 Ex. 10 (P 0.05 wt %) 14.9 20.2 25.6 31.1 C. Ex. 1 26.3
46.1 58.2 84.1
[0081] As is apparent from Table 2, the difference in corrosion
resistance was notable between Comparative Example 1 without P and
Example 1 in which 0.02 wt % of P was added and the final annealing
temperature was 460.degree. C. In particular, corrosion resistance
was higher in Examples 2, 6 and 10 using 0.05 wt % of P than in
Examples 1, 5 and 9 using 0.02 wt % of P.
[0082] Thus, since there is a significant corrosion resistance
difference so long as P is added even in a small amount, corrosion
resistance is considered to be obviously increased even when the
lower limit of the amount of P is 0.01 wt %, judging from Example 1
using 0.02 wt % of P.
[0083] As such, a drastic increase in corrosion resistance can be
seen to be dependent on the experimental values ranging from 0.02
wt % to 0.07 wt %. Although the amount of P is 0.05 wt % in
Examples 2, 6 and 10, corrosion resistance is observed to be
increased more in the presence of 0.05 wt % of P than in the
presence of 0.02 wt % of P. Hence, a notable increase in corrosion
resistance is deemed to be assured even when the amount of P is
0.07 wt %.
[0084] 2) Results of Addition of 0.03 wt % and 0.1 wt % of Ta in
the Presence of 0.05 wt % of P
TABLE-US-00003 TABLE 3 Weight Gain (mg/dm.sup.2) per Unit Surface
Area 360.degree. C., 18.6 MPa, Pure Water 50 days 110 days 170 days
260 days Ex. 2 17.5 27.0 32.9 37.6 Ex. 3(Ta 0.03 wt %) 17.1 26.7
29.0 32.5 Ex. 4(Ta 0.1 wt %) 14.8 23.7 26.9 32.3 Ex. 6 16.1 23.8
25.2 28.7 Ex. 7(Ta 0.03 wt %) 15.7 23.9 26.4 29.1 Ex. 8(Ta 0.1 wt
%) 12.2 20.4 22.7 28.9 Ex. 10 14.9 20.2 25.6 31.1 Ex. 11(Ta 0.03 wt
%) 18.2 27.2 27.3 30.8 Ex. 12(Ta 0.1 wt %) 15.5 25.6 27.4 33.2 C.
Ex. 1 26.3 46.1 58.2 84.1
[0085] As is apparent from Table 3, only P was added, without Ta,
in Examples 2, 6 and 10, 0.03 wt % of Ta was added in Examples 3, 7
and 11, and 0.1 wt % of Ta was added in Examples 4, 8 and 12.
[0086] When the amount of Ta was 0.1 wt %, corrosion resistance was
significantly increased in Example 4 at a final annealing
temperature of 460.degree. C. and Example 8 at a final annealing
temperature of 520.degree. C. When the amount of Ta was 0.03 wt %,
corrosion resistance was insignificantly increased.
[0087] Based on the test results, corrosion resistance was
increased when Ta was added in an amount of 0.01 wt % to 0.15 wt %,
and was remarkably increased when Ta was added in an amount of 0.03
wt % to 0.1 wt %.
Test Example 2
Creep Testing
[0088] In order to evaluate the creep resistance of the zirconium
alloy composition according to the present invention, creep testing
was performed as follows.
[0089] Each of the zirconium alloys of Examples 1 to 4 was
manufactured into a sheets through the above manufacturing process,
which was then formed into a creep test sample.
[0090] To compare creep properties, a Zircaloy-4 sheet sample of
Comparative Example 2 was manufactured through the same process by
simulating the commercially available cladding tube of Comparative
Example 1. The final annealing temperature of Comparative Example 2
was set to 460.degree. C., as in Examples 1 to 4 and Comparative
Example 1, and creep testing was carried out.
[0091] The creep testing was performed at 350.degree. C. under a
predetermined load of 120 MPa for 120 hr, and the results thereof
were compared with those of Comparative Example 2. The results are
shown in Table 4 below.
TABLE-US-00004 TABLE 4 Creep Strain (%) 350.degree. C., 120 MPa,
240 hr Ex. 1 0.30 Ex. 2 0.33 Ex. 3 0.34 Ex. 4 0.22 C. Ex. 2
0.46
[0092] As is apparent from Table 4, based on the results of creep
testing for 10 days at 350.degree. C. under stress of 120 MPa using
the zirconium alloy compositions in Examples 1 to 4 according to
the present invention, creep strain was measured to be 0.22 to
0.34. In particular, as the amount of Ta was increased, creep
strain was remarkably decreased. However, creep strain of
Comparative Example 2 was 0.46, which was evaluated to be much
higher than in Examples 1 to 4.
[0093] Therefore, it can be confirmed that the addition of P in
even a small amount is effective at exhibiting creep resistance and
also that creep resistance is considerably enhanced with an
increase in the amount of Ta.
[0094] Although the preferred embodiments of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
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