U.S. patent application number 12/880429 was filed with the patent office on 2010-12-30 for forged beryllium-copper bulk material.
This patent application is currently assigned to NGK Insulators, Ltd.. Invention is credited to Naokuni MURAMATSU.
Application Number | 20100329923 12/880429 |
Document ID | / |
Family ID | 41113443 |
Filed Date | 2010-12-30 |
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United States Patent
Application |
20100329923 |
Kind Code |
A1 |
MURAMATSU; Naokuni |
December 30, 2010 |
FORGED BERYLLIUM-COPPER BULK MATERIAL
Abstract
The present invention provides a forged beryllium-copper bulk
material, wherein the hardness of the central portion is 0 to 10%
higher than that of the front surface, the Vickers hardness of the
central portion is 240 or more, the tensile strength is 800
N/mm.sup.2 or more, and the bulk material having uniformity to such
an extent that variation in measured values of the tensile strength
in arbitrary directions is within 5%.
Inventors: |
MURAMATSU; Naokuni;
(Nagaoya-City, JP) |
Correspondence
Address: |
BURR & BROWN
PO BOX 7068
SYRACUSE
NY
13261-7068
US
|
Assignee: |
NGK Insulators, Ltd.
Nagaoya-City
JP
|
Family ID: |
41113443 |
Appl. No.: |
12/880429 |
Filed: |
September 13, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/JP2009/053449 |
Feb 25, 2009 |
|
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|
12880429 |
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Current U.S.
Class: |
420/485 ;
420/494 |
Current CPC
Class: |
C22C 9/00 20130101; C22F
1/08 20130101; C22C 9/06 20130101 |
Class at
Publication: |
420/485 ;
420/494 |
International
Class: |
C22C 9/06 20060101
C22C009/06; C22C 9/00 20060101 C22C009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2008 |
JP |
2008-087628 |
Claims
1. A forged beryllium-copper bulk material, at least comprising Be
and Cu, the hardness of the central portion being 0 to 10% higher
than that of the front surface, the Vickers hardness of the central
portion being 240 or more, the tensile strength being 800
N/mm.sup.2 or more, and the bulk material having uniformity to such
an extent that variation in measured values of the tensile strength
in arbitrary directions being within 5%.
2. The forged beryllium-copper bulk material according to claim 1,
wherein the tensile strength in three forging directions that are
orthogonal to each other and the tensile strength measured, on a
plane including two forging directions that are orthogonal to each
other, in a direction making an angle of 45.degree. with the two
forging directions are 1100 N/mm.sup.2 or more.
3. The forged beryllium-copper bulk material according to claim 1,
comprising a weight ratio of Cu.sub.100-(a+b)Be.sub.aCo.sub.b
(0.4%.ltoreq.a.ltoreq.2.0%, 0.15%.ltoreq.b.ltoreq.2.8%,
a+b.ltoreq.3.5%) or a weight ratio of
Cu.sub.100-(c+d)Be.sub.cNi.sub.d (0.05%.ltoreq.c.ltoreq.0.6%,
1.0%.ltoreq.d.ltoreq.2.4%, c+d.ltoreq.3.0%), wherein, Fe, S and P
as impurities are limited to be lower than 0.01% in terms of the
weight ratio.
4. The forged beryllium-copper bulk material according to claim 1,
wherein the Vickers hardness of the central portion is 240 to 450
and the tensile strength is 1100 to 1500 N/mm.sup.2.
5. The forged beryllium-copper bulk material according to claim 1,
comprising grains having an average grain size of 2 .mu.m or lower,
wherein the grains do not contain a shear band structure crossing a
plurality of grains and are stable in the shape, and have a
precipitated phase including the Be precipitated from the Cu.
6. The forged beryllium-copper bulk material according to claim 2,
comprising a weight ratio of Cu.sub.100-(a+b)Be.sub.aCo.sub.b
(0.4%.ltoreq.a.ltoreq.2.0%, 0.15%.ltoreq.b.ltoreq.2.8%,
a+b.ltoreq.3.5%) or a weight ratio of
Cu.sub.100-(c+d)Be.sub.cNi.sub.d (0.05%.ltoreq.c.ltoreq.0.6%,
1.0%.ltoreq.d.ltoreq.2.4%, c+d.ltoreq.3.0%), wherein Fe, S and P as
impurities are limited to be lower than 0.01% in terms of the
weight ratio.
7. The forged beryllium-copper bulk material according to claim 2,
wherein the Vickers hardness of the central portion is 240 to 450
and the tensile strength is 1100 to 1500 N/mm.sup.2.
8. The forged beryllium-copper bulk material according to claim 2,
comprising grains having an average grain size of 2 .mu.m or lower,
wherein the grains do not contain a shear band structure crossing a
plurality of grains and are stable in the shape, and have a
precipitated phase including the Be precipitated from the Cu.
Description
TECHNICAL FIELD
[0001] The present invention relates to forged beryllium bulk
material.
BACKGROUND ART
[0002] Beryllium copper bulk materials are used for machine
structural components in which durability and reliability are
demanded, such as bearings for airplanes, casings for under sea
cable repeaters, rotor shafts for ships, collars of oil field
drilling drills, injection molding dies, or welding electrode
holders. In general, the applications require machinability and
high hardness or strength of bulk materials.
[0003] Beryllium copper is a precipitation-hardening copper alloy
similarly as many high strength copper alloys, and bulk materials
thereof are manufactured through forging-homogenization
annealing-hot working-solution annealing (solid solution
treatment)-water quenching-age hardening, which is well-known to
persons skilled in the art. For example, Patent Document 1
discloses that grains are fined to a certain degree by carefully
selecting conditions of each treatment, and an increase in strength
and an improvement of a fatigue life, which are important for the
machine structural components, are achieved. Patent Document 2
discloses that grains can be fined to a degree that has not been
found in former cases by extensively examining a forging method and
treatment conditions during forging.
[0004] However, in the methods described in Patent Documents 1 and
2, differences in the temperatures between the near-surface
portions and the center core portion during water quenching cannot
be disregarded, and thus the strength (hardness) of the center core
portion which is hard to be cooled decreases compared with the
near-surface portions. Thus, when processing various components by
cutting from the obtained member, the residual stress due to
unbalanced strength remaining in which the strength varies
depending on portions of the member is released, and thus the
component has been distorted during cutting in some cases.
Moreover, there has been a problem in that the fatigue life is
likely to become short.
[0005] As described in JIS G4052 (Structural steels with specified
hardenability), the cause of such a phenomenon is presumed also
from the fact that values indicating the hardness notably decrease
with an increase in the dimension distance of bulk materials from
the surface portions to the inside. The phenomenon such that the
hardness values become lower from the front surface toward the
inside is a problem common to bulk materials of copper alloy
prepared through water quenching after heat treatment without being
limited to steel materials, and has notably appeared with an
increase in the size of bulk materials.
[0006] [Patent Document 1] Japanese Patent No. 2827102
[0007] [Patent Document 2] Japanese Unexamined Patent Application
Publication No. 2005-096442
DISCLOSURE OF INVENTION
[0008] In view of the above-described problem, it is an object of
the present invention to provide a forged beryllium-copper bulk
material that maintains uniform hardness from the front surface to
the inside, has high reliability, is excellent in a fatigue life,
and is hard to cause distortion during processing.
[0009] The present invention provides a forged beryllium-copper
bulk material, at least including Be and Cu,
[0010] the hardness of the central portion being 0 to 10% higher
than that of the front surface,
[0011] the Vickers hardness of the central portion being 240 or
more,
[0012] the tensile strength being 800 N/mm.sup.2 or more, and
[0013] the bulk material having uniformity to such an extent that
variation in measured values of the tensile strength in arbitrary
directions being within 5%.
[0014] The invention provides a forged beryllium-copper bulk
material that maintains uniform hardness from the front surface to
the inside, has high reliability, is excellent in a fatigue life,
and is hard to cause distortion during processing.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1 is a perspective view showing a forged
beryllium-copper bulk material according to one embodiment of the
invention.
[0016] FIG. 2 is a flow chart showing a method for manufacturing a
forged beryllium-copper bulk material according to one embodiment
of the invention.
[0017] FIG. 3(a) is a graph showing the relationship between the
treatment time and the temperature when the solid solution
treatment and the over-aging treatment of FIG. 2 are
discontinuously carried out and FIG. 3(b) is a graph showing the
relationship between the treatment time and the temperature when
the solid solution treatment and the over-aging treatment are
continuously carried out.
[0018] FIG. 4 is a table showing the relationship between the size
reduction rate and the strain according to one embodiment of the
invention.
[0019] FIG. 5(a) is a view showing the appearance of a forged
beryllium-copper bulk material according to one embodiment of the
invention, FIG. 5(b) is a graph showing the relationship between a
pressure and a cumulative strain during repeated pressurization at
a size reduction rate of 18%, and FIG. 5(c) is a table showing
changes in the surface temperature immediately after the repeated
pressurization.
[0020] FIG. 6(a) is a view showing the appearance of a former
forged beryllium-copper bulk material, FIG. 6(b) is a graph showing
the relationship between a pressure and a cumulative strain during
repeated pressurization at a size reduction rate of 33%, and FIG.
6(c) is a table showing changes in the surface temperature
immediately after the repeated pressurization.
[0021] FIG. 7(a) is a perspective view showing a test piece when
measuring the hardness of a forged beryllium-copper bulk material,
FIG. 7(b) is a graph showing the relationship between the distance
from a surface plane to the center plane and the Vickers hardness
of a beryllium bulk material according to one embodiment of the
invention immediately after cold forging treatment, and FIG. 7(c)
is a graph showing the relationship between the distance from a
surface plane to the center plane and the Vickers hardness of a
beryllium bulk material according to one embodiment of the
invention after age hardening treatment.
[0022] FIG. 8 is a graph showing the relationship between the
distance from a surface plane to the center plane and the Vickers
hardness of a former beryllium bulk material.
[0023] FIG. 9 is a schematic view showing distortion after
processing measurement results of a forged beryllium-copper bulk
material according to one embodiment of the invention and a former
forged beryllium-copper bulk material.
[0024] FIG. 10 is a graph showing a fatigue life curve of a forged
beryllium-copper bulk material according to one embodiment of the
invention.
[0025] FIG. 11 is a graph showing an example of ultrasonic
inspection test results of a forged beryllium-copper bulk material
according to one embodiment of the invention and a former
beryllium-copper bulk material.
[0026] FIG. 12 is a view showing observation results of a shear
band structure crossing a plurality of grains in a beryllium-copper
bulk material in a comparative example.
BEST MODES FOR CARRYING OUT THE INVENTION
[0027] Next, embodiments of the present invention will be described
with reference to the drawings. In the following description of the
drawings, the same or similar parts are designated by the same or
similar reference numerals. The following embodiments describe
examples of devices and methods for putting the technical idea of
this invention into effect, and, according to the technical idea of
this invention, the structure, arrangement, and the like of
constitutional components are not limited to the following
ones.
[0028] (Forged Beryllium-Copper Bulk Material)
[0029] As shown in FIG. 1, a forged beryllium-copper bulk material
1 according to the embodiment of the invention is an alloy
containing beryllium (Be) and copper (Cu) and is a rectangular
parallelepiped shaped alloy having the sides of a, b, and L
extending along the directions of the three axes (Z axis, X-axis,
and Y-axis of FIG. 1) that are orthogonal to each other.
[0030] The ratio of the length of the sides a, b, and L of the
forged beryllium-copper bulk material 1 is not particularly
limited. For example, a cubic shape of a:b:L=1:1:1 is acceptable.
The size of the forged beryllium-copper bulk material 1 is not
particularly limited. However, when the dimension of the sides a,
b, and L becomes excessively large, it becomes difficult to control
the manufacturing conditions described later due to influences of
process heat generation from the forged beryllium-copper bulk
material 1 during forging. Thus, with respect to the dimension of
the forged beryllium-copper bulk material 1, the a, b, and L can be
adjusted in the range of about 50 to 500 mm and preferably 80 to
400 mm, for example.
[0031] The forged beryllium copper bulk material 1 has (1) a weight
ratio of Cu.sub.100-(a+b)Be.sub.aCo.sub.b
(0.4%.ltoreq.a.ltoreq.2.0%, 0.15%.ltoreq.b.ltoreq.2.8%,
a+b.ltoreq.3.5%) or (2) a weight ratio of
Cu.sub.100-(a+b)Be.sub.aCo.sub.b (0.4%.ltoreq.a.ltoreq.2.0%,
0.15%.ltoreq.b.ltoreq.2.8%, a+b.ltoreq.3.5%) and the content of Fe,
S, and P as impurities is preferably limited to lower than 0.01% in
terms of the weight ratio.
[0032] In (1) above, the weight ratio of Be is adjusted to 0.4% or
more for increasing the strength by a precipitated phase
constituted by Be and Cu and/or Be and Co. The weight ratio of Be
is adjusted to 2.0% or lower for increasing the strength by
suppressing coarsening of a precipitated phase constituted by Be
and Co. The weight ratio of Co is adjusted to 0.15% or more for
increasing the strength by adding Co. The weight ratio of Co is
adjusted to 2.8% or lower for suppressing coarsening of a
precipitated phase constituted by Be and Co.
[0033] In contrast, the combination of (2) is used for the weight
ratio of the forged beryllium-copper bulk material 1 to reduce the
ratio of Be for reducing the material cost by adding Ni, which is
less expensive than Be. Specifically, the weight ratio of Be is
adjusted to 0.05% or more for increasing the strength by a
precipitated phase constituted by Be and Ni. The weight ratio of Be
is adjusted to 0.6% or lower for sufficiently obtaining the effect
of reducing the cost by reducing the weight ratio of Be. The weight
ratio of Ni is adjusted to 1.0% or more for increasing the strength
by adding Ni. The weight ratio of Ni is adjusted to 2.4% or lower
for suppressing a reduction in electrical conductivity or an
increase in the melting point due to Ni contained in a matrix of
Cu.
[0034] The content of Fe, S, and P as impurities is limited to be
lower than 0.01% in terms of weight ratio because, the elements are
likely to be segregated in the grain boundary when these elements
are contained in a proportion of 0.01% or more, and thus a product
is likely to break during forging treatment.
[0035] The forged beryllium-copper bulk material 1 of FIG. 1 has a
fine grain structure (average grain size.ltoreq.2 .mu.m) and has a
precipitated phase at least containing Be which is precipitated
from Cu. Here, the "average grain size" refers to an average grain
size measured by the following measurement method.
[0036] (A) Conduct crystal orientation analysis using an SEM/EBSP
(Scanning Electron Microscope/Electron Back Scatter Diffraction
Pattern) method, and count boundaries with an misorientation angle
.theta. of 2.degree. or larger as grain boundaries to obtain a
distribution of grain sizes.
[0037] (B) Confirm that the average misorientation angle .theta. is
15.degree. or larger in the total count.
[0038] (C) Calculate an average grain size from the distribution of
grain sizes.
[0039] In general, structures constituted only by sub-grains having
an misorientation angle .theta. of
0.degree..ltoreq..theta.<4.degree. are not counted as crystal
grains. However, in this embodiment, since an observation result is
a capture of an arbitrary moment of a process of ultra-fining,
structures constituted only by sub-grains having an misorientation
angle .theta. of 0.degree..ltoreq..theta.<4.degree. are also
considered to form a part of the entire structure at that moment.
Therefore, structures having an misorientation angle of 15.degree.
or larger are counted as grains.
[0040] The forged beryllium-copper bulk material 1 is an alloy in
which the hardness is uniform (or becomes gradually harder) from
the near-surface portions to the center core portion, the hardness
of the central portion is 0 to 10% higher than that of the front
surface, the Vickers hardness (HV) of the front surface (end
portion) is 218 to 450 and more preferably 273 to 450, and the
Vickers hardness of the internal center is 240 to 450 and more
preferably 300 to 450. The "Vickers hardness" in this embodiment
refers to a measurement result obtained as follows. For example, a
plate 2 that is cut in parallel to the direction of the X-Z plane
in such a manner as to include the center of the forged
beryllium-copper bulk material 1 in the form of a rectangular
parallelepiped (cube) shown in FIG. 7(a) is used as a test piece,
and then an arbitrary point on the test piece is measured according
to JISZ2244 (Vickers hardness test method-Test method
(Corresponding international standard; ISO/6507-1; 1995 Metallic
materials-Vickers hardness test-Part 1; Test Method).
[0041] The forged beryllium-copper bulk material 1 is a polycrystal
having no anisotropy in the orientation (random orientation) from
the hardness, structure, ultrasonic inspection test, observation
results of the grains by the EBSP method described later, and the
tensile strength is 800 N/mm.sup.2 or more, preferably 800 to 1500
N/mm.sup.2, more preferably 1100 to 1500 N/mm.sup.2, and still more
preferably 1100 to 1300 N/mm.sup.2. When the tensile strength is
made smaller than 800 N/mm.sup.2, the mechanical strength or the
fatigue life decreases, and thus the forged beryllium-copper bulk
material 1 is not accepted in the market of machine structural
components in some cases.
[0042] The tensile strength values of the beryllium forge bulk
material 1 are isotropic (uniform) in an arbitrary forging
direction or in a direction making an angle of 45.degree. within
the plane including the arbitrary forging direction and the
variation in the measured tensile strength values (measurement
average value) was within 5%.
[0043] The measurement method of the tensile strength is as
follows. First, plates containing the X-Y plane, the Y-Z plane, and
the X-Z plane were cut out from the center of the beryllium forge
bulk material 1, and then tensile test pieces were machined so that
six directions (i.e., X, Y, Z, X-Y with an angle of 45.degree., Y-Z
with an angle of 45.degree., and X-Z with an angle of)45.degree.
which represent arbitrary directions correspond with the tensile
axis from each plate. The test pieces were produced according to
JISSZ2201, but the test pieces in which the dimension was reduced
to 1/2 due to the restriction of the size of raw materials were
used. The produced test pieces were measured according to JISZ2241
(Method of tensile test for metallic materials).
[0044] The reason for selecting the six directions as the arbitrary
directions resides in the fact that, when machine structural
articles are produced from the forged beryllium-copper bulk
material 1, the articles are usually produced based on the plane in
which the forging direction is the normal line and the tensile
stress mechanically applied in the X, Y, and Z directions are
important for products.
[0045] The stress in the X, Y and Z directions are known to
theoretically originate from the shearing strength in the direction
of 45.degree. to the X, Y and Z directions ("Zairyo Kogaku Nyumon"
jointly translated by Ryo Horiuchi, Junichi Kaneko, and Masahisa
Otsuka; Uchida-Rokakuho Publishing Co., 3rd edition, 1990, p
123-142 or Original: M. F. Ashby and D. R. H. Jones "Engineering
Materials" PERGAMON PRESS; 1980). In addition, when the tensile
strength applied in the direction of 45.degree. to the X, Y, and Z
directions is measured, the shearing strength in the direction of
further 45.degree. (in the X, Y, and Z directions) from the point
is measured.
[0046] When the forged beryllium-copper bulk material 1 is
anisotropic in the direction shifted from the X, Y, and Z
directions only by specific angles of .alpha., .beta., and .gamma.
(specific directions having a particularly low strength), abnormal
values should be observed in some of the six directions insofar as
the forged beryllium-copper bulk material 1 is a polycrystal.
However, the variation in the tensile strength value when measured
in the six directions is within 5% in this embodiment, and no
abnormal values were measured. Thus, it can be said that the forged
beryllium-copper bulk material 1 according to this embodiment has
isotropy (uniformity) in the tensile strength in any arbitrary
direction and that the values are almost the same.
[0047] (Method for Manufacturing Forged Beryllium-Copper Bulk
Material)
[0048] Next, a method for manufacturing a forged beryllium-copper
bulk material according to the embodiment of the invention will be
described with reference to the flow charts shown in FIGS. 2, 3(a),
and 3(b).
[0049] First, in homogenizing treatment of Step S10 of FIG. 2, a
solid solution of Be (or a Be compound) is formed in a matrix of Cu
to generate a copper alloy in which dislocation does not occur in
grains.
[0050] Specifically, a copper alloy constituted by the weight ratio
of Cu.sub.100-(a+b)Be.sub.aCo.sub.b (0.4%.ltoreq.a.ltoreq.2.0%,
0.15%.ltoreq.b.ltoreq.2.8%, a+b.ltoreq.3.5%) or a weight ratio of
Cu.sub.100-(c+d)Be.sub.cNi.sub.d (0.05%.ltoreq.c.ltoreq.0.6%,
1.0%.ltoreq.d.ltoreq.2.4%, c+d.ltoreq.3.0%) is melted in a high
frequency melting furnace to produce an ingot. In the above, it is
preferable that the content of Fe, S, and P as impurities can be
limited to be lower than 0.01% in terms of the weight ratio. By
holding the obtained ingot under heat over a given retention time
(1 hour to 24 hours) in a solid solution temperature range (in the
range of 700.degree. C. to 1000.degree. C.), non-uniform structures
that adversely affect post treatment, such as segregation
generating in a nonequilibrium manner during casting, are removed
for homogenizing.
[0051] In forging treatment of Step S11, the copper alloy obtained
in S10 is forged to be processed into a rectangular parallelepiped
shaped copper alloy of a desired size. An oxidation film formed on
the surface of a plate-like copper alloy is removed by cutting.
[0052] In solid solution treatment of Step S12, the copper alloy
obtained in Step S11 is held under heat for a given solid solution
time (1 hour to 24 hours) in a solid solution temperature range (in
the range of 700.degree. C. to 1000.degree. C.) to solve Be (or Be
compound) in a matrix of Cu.
[0053] In over-aging treatment of Step S13, the copper alloy
obtained in Step S12 is held for a given period of time (2 to 6
hours) in an over-aging temperature range (in the range of 550 to
650.degree. C.). Thus, although the mechanism in which the
precipitated particles bring about preferable effects is being
elucidated, the precipitated particles of the copper alloy can be
grown to such a size (e.g., average particle diameter of about 1
.mu.m) that each manufacturing process on and after Step S13 is not
adversely affected. As shown in FIG. 3(a), the solution treatment
of Step S12 and the overaging treatment of Step S13 may be
independently (discontinuously) carried out or, as shown in FIG.
3(b), the solution treatment of Step S12 and the over-aging
treatment of Step S13 may be continuously carried out.
[0054] In cooling treatment of Step S14, the copper alloy obtained
in Step S13 is cooled by water-cooling, air-cooling, or allowing to
cool so that the surface temperature of the copper alloy is
20.degree. C. or lower. The cooling rate varies depending on the
size of the bulk material and is preferably adjusted to
-100.degree. C.s.sup.-1 or higher (preferably -200.degree.
C.s.sup.-1 or higher).
[0055] In cold forging treatment of Step S15, the copper alloy
after cooling is forged while cooling to remove heat. The forging
treatment is performed from each of the X-axis direction, the
Y-axis direction, and the Z-axis direction, which are orthogonal to
each other, of the rectangular parallelepiped. With respect to the
forging order, a pressure is preferably applied in order from the
axis direction corresponding to the longest side among the sides of
the copper alloy.
[0056] Specifically, first in Step S151, a pressure is applied from
the Z-axis direction to the copper alloy after cooling with a
forging device or the like. The surface temperature of the copper
alloy during pressurization is preferably maintained at 120.degree.
C. or lower (more preferably in the range of 20 to 100.degree. C.).
When the surface temperature exceeds 120.degree. C., a shear band
structure crossing a plurality of grains is likely to generate.
Thus, it becomes impossible to maintain the shape before processing
due to cracks, fracture, or the like that occurred. The pressure is
preferably adjusted to 1200 MPa or lower. When the pressure exceeds
1200 MPa combined with the over-aging conditions or the like, a
shear band structure crossing a plurality of grains is likely to
generate in the copper alloy, and thus there is a possibility that
cracks, fracture, or the like occurs.
[0057] The size reduction rate of one treatment of Step S151
(reduction rate (%)) is in the range of 18 to 30% and the plastic
strain (strain; .epsilon.) to be applied to the copper alloy is
preferably in the range of 0.2 to 0.36. The "size reduction rate"
is a ratio (reduction rate) obtained by dividing the reduction by
processing by the original height and is indicated by Strain=1n
(1-reduction rate). FIG. 4 shows the relationship between the size
reduction rate and the strain.
[0058] In Step S152, the copper alloy obtained in Step S151 is
cooled. The cooling method may be any method of air-cooling,
water-cooling, allowing to cool, and the like, and cooling by
water-cooling is preferable considering the performance and
efficiency of repeated operations. The cooling is preferably
carried out so that the surface temperature generated from the
copper alloy by pressurization is 20.degree. C. or lower.
[0059] In Step S153, a pressure is applied from the Y axis
direction to the copper alloy after cooling with a forging device
or the like. The surface temperature of the copper alloy during
pressurization is preferably maintained at 120.degree. C. or lower.
The size reduction rate of one treatment of Step S153 (reduction
rate (%)) is in the range of 18 to 30% and the plastic strain
(strain; .epsilon.) to be applied to the copper alloy is preferably
in the range of 0.2 to 0.36. Thereafter, in Step S154, the copper
alloy obtained in Step S153 is cooled. The cooling is preferably
carried out so that the surface temperature of the copper alloy is
20.degree. C. or lower.
[0060] In Step S155, a pressure is applied from the X axis
direction to the copper alloy after cooling with a forging device
or the like. The surface temperature of the copper alloy during
pressurization is preferably maintained at 120.degree. C. or lower.
The size reduction rate of one treatment of Step S155 (reduction
rate (%)) is in the range of 18 to 30% and the plastic strain
(strain; .epsilon.) to be applied to the copper alloy is preferably
in the range of 0.2 to 0.36. Thereafter, in Step S156, the copper
alloy obtained in Step S155 is cooled. The cooling is preferably
carried out so that the surface temperature of the copper alloy is
20.degree. C. or lower.
[0061] In Step S157, an operator judges whether or not the number
of times of pressurizing the copper alloy with a forging device has
reached a given number of times. Here, the "number of times of
pressurization" refers to the number of times that is counted up
while defining the case where a pressure is applied to a copper
alloy from any one of the axis (X-axis, Y-axis, and Z-axis)
directions as one time.
[0062] The "given number of times of pressurization" refers to the
number of times in which the cumulative value of the plastic strain
applied to the copper alloy (cumulative strain; .epsilon. total)
becomes 1.8 or more, for example. When the number of times of
pressurization has not reached the given number of times of
pressurization, the treatment of each of Steps 5151 to 5156 is
repeated. When the number of times of pressurization has reached
the given number of times of pressurization, the process progresses
to Step S16.
[0063] In Step S16 (age-hardening treatment), by holding the copper
alloy obtained in Step S15 over a given age-hardening time (1 hour
to 24 hours) in a precipitation temperature range (in the range of
200.degree. C. to 550.degree. C.), the Be (or Be compound)
contained in the copper alloy is precipitated and hardened. Thus,
the forged beryllium-copper bulk material shown in FIG. 1 can be
manufactured.
[0064] According to the method for manufacturing a forged
beryllium-copper bulk material according to the embodiment, the
copper alloy after cooling is forged in the cold forging process of
Step S15 while cooling to remove heat so that the surface
temperature of the copper alloy after cooling is maintained at
120.degree. C. or lower. Thus, the plastic strain to be applied to
the copper alloy can be increased while reducing the influences of
process heat generation of the copper alloy during forging.
Therefore, a forged beryllium-copper bulk material having uniform
and fine grains and maintaining uniform hardness from the front
surface to the inside can be manufactured.
[0065] Hitherto, depending on the dimension of the former forged
beryllium-copper bulk material 1, the copper alloy has not been
uniformly cooled at a sufficient rate from the near-surface
portions to the center core portion simply by performing the
cooling treatment of Step S14 after the solid solution process of
Step S12. In particular, as the size of the forged beryllium-copper
bulk material 1 has been attempted to increase, the copper alloy
has not been rapidly cooled to the internal center simply by
cooling the front surface by water cooling or the like. When the
cold forging treatment of Step S15 is performed in the state where
the copper alloy is not sufficiently cooled to the internal center,
the deformation of a product becomes non-uniform, and fracture,
cracks during processing, distortion, or the like has easily
occurred.
[0066] Then, in this embodiment, the treatment conditions are
controlled so that the copper alloy is not rapidly cooled, which
has been performed in the former technique, and the copper alloy
after the solid solution treatment is inefficiently and slowly
cooled in Step S13. More specifically, by treating the copper alloy
after the solid solution treatment at an over-aging temperature
(550 to 650.degree. C.) for a given period of time (over-aging
time: 2 to 6 hours) in Step S13, the effect is obtained that the
moderately precipitated particles preferably act, and the copper
alloy efficiently and uniformly deforms to the inside. It has been
found that, due to the effect, the generation of a shear band
structure crossing a plurality of grains is suppressed and cracks
or fracture do/does not occur, and thus, a copper beryllium bulk
material is obtained that maintains uniform hardness from the front
surface to the inside, is excellent in the fatigue life, and is
difficult to cause distortion during processing.
[0067] When the over-aging temperature in Step S13 is lower than
550.degree. C., it is difficult to grow the precipitated particles
and when the over-aging temperature is higher than 650.degree. C.,
a solid solution of Be is formed in Cu, and thus the temperature
range above is not preferable. When the over-aging time is lower
than 2 hours, the precipitated particles do not grow to a certain
size. In contrast, even when the over-aging time is longer than 6
hours, the growth of the precipitated particles is completed to
some extent, and thus it is not efficient. Thus, the over-aging
temperature is 550 to 650.degree. C. and more preferably 570 to
630.degree. C. The over-aging treatment time is 2 to 6 hours and
more preferably 3 to 5 hours.
[0068] The method for manufacturing the forged beryllium-copper
bulk material 1 shown in FIG. 2 includes applying a pressure to the
copper alloy from all the Z-axis, Y-axis, and X-axis directions,
and then judging whether or not the number of times of
pressurization has reached a given number of times of
pressurization in step S157. However, the invention is not limited
to the above, it may be judged whether or not the number of times
of pressurization has reached a given number of times of
pressurization whenever a pressure is applied to the copper
alloy.
[0069] According to the method for manufacturing the forged
beryllium-copper bulk material 1 shown in FIG. 2, the copper alloy
after forging is cooled whenever one forging treatment in each axis
direction (Steps S151, S153, and S155) is completed in the cooling
process shown in Steps S152, S154, and S156. However, the purpose
can be achieved when the copper alloy is forged while maintaining
the surface temperature of the copper alloy to be processed at
120.degree. C. or lower. Thus, each cooling process shown in each
of Steps S152, S154, and S156 may be omitted as required.
[0070] The method for maintaining the surface temperature of the
copper alloy at 120.degree. C. or lower in Step S15 is not limited
to the case where the surface temperature of the copper alloy is
sufficiently cooled to be 20.degree. C. or lower, and then the
copper alloy is forged using a usual forging device.
[0071] For example, a temperature measuring mechanism, such as a
thermocouple, is attached to the surface of the copper alloy under
forging to control the temperature of the copper surface so that
the temperature is not equal to or higher than 120.degree. C. while
always monitoring the measurement results of the temperature
measuring mechanism, and when the surface temperature of the copper
alloy exceeds 120.degree. C., the operation is interrupted or the
copper alloy may be water-cooled, air-cooled, allowed to cool, or
the like.
EXAMPLES
[0072] Hereinafter, the evaluation results of the forged
beryllium-copper bulk material 1 manufactured by the manufacturing
method described above will be described with reference to the
drawings.
[0073] FIG. 5(a) is a schematic view showing the appearance of the
forged beryllium-copper bulk material according to the embodiment,
FIG. 5(b) is a graph showing the relationship between the pressure
and the cumulative strain during repeated pressurization under a
fixed size reduction rate, and FIG. 5(c) is a table showing changes
in the surface temperature immediately after repeated
pressurization. The rolling reduction of one pressurization during
repeated pressurization was 18% and the pressure was controlled not
to exceed 1000 MPa (<1200 MPa). As a result, as shown in FIG.
5(a), cracks or non-uniform deformation was not observed in the
appearance of the obtained forged beryllium-copper bulk material
1.
[0074] FIGS. 6(a) to 6(c) show an example of the result obtained
when a forged beryllium-copper bulk material was manufactured
according to a former method, i.e., without subjecting the copper
alloy after passing through Step S12 to the over-aging treatment
(Step S13 of FIG. 2) and the cooling treatment (Steps S152, S154,
and S156). In the former method, the size reduction rate was
controlled to 33% (strain of 0.40) so that the cumulative strain
was in the range of 0.3 to 0.7. As shown in FIG. 6(b), the pressure
was about 1300 MPa (>1200 MPa) and, as shown in FIG. 6(c), the
surface temperature immediately after the repeated pressurization
reached about 130.degree. C. (>130.degree. C.). As a result, as
shown in the schematic view of FIG. 6(a), the obtained forged
beryllium-copper bulk material non-uniformly deformed in the
appearance and was broken. When the internal structure in this case
was observed, it was found that a shear band structure crossing a
plurality of grains as shown in FIG. 12 produced.
[0075] FIGS. 7(a) to 7(c) each are views showing a method for
measuring the hardness of the forged beryllium-copper bulk material
according to the embodiment. As shown in FIG. 7(a), in the
measurement, the forged beryllium-copper bulk material 1 having a
cubic shape with one side of 100 mm was prepared, and a plate 2 was
cut out in such a manner as to include the central portion and the
surface portion (side end surface) of the cube to be used as a test
piece. The measurement was performed using the test piece according
to JISZ2244 (Vickers hardness test method-Test method
(Corresponding international standard; ISO/6507-1; 1995 Metallic
materials-Vickers hardness test-Part 1; Test Method). FIG. 7(b) is
a graph showing the measurement results of the hardness of the
copper alloy immediately after the forging treatment of Step S15 of
FIG. 2. FIG. 7(c) is a graph showing the measurement results of the
hardness of the forged beryllium-copper bulk material as the final
shape immediately after the aging treatment of Step S16 of FIG.
2.
[0076] As shown in FIG. 7(b), it was found that even in the case of
the copper alloy immediately after the forging treatment, the
hardness increased from the side end surfaces toward the central
portion. As shown in FIG. 7(C), by performing the aging treatment
after the forging treatment, the hardness value became high
throughout the copper alloy and the difference in the hardness
between the center and the inside became within 10%.
[0077] FIG. 8 is a graph showing the measurement results of the
hardness of a former forged beryllium-copper bulk material obtained
without performing the treatment of each of Steps S13 and S15. As
shown in FIG. 8, the hardness value of the former forged
beryllium-copper bulk material sharply decreased from the side end
surfaces toward the central portion.
[0078] FIG. 9 shows an example of the distortion measurement result
of the forged beryllium-copper bulk material. FIG. 9 shows results
obtained by placing a plate 2a (left-side in FIG. 9) cut out from
the former rectangular parallelepiped-shaped forged
beryllium-copper bulk material and a plate 2b (right-side in FIG.
9) cut out from the rectangular parallelepiped-shaped forged
beryllium-copper bulk material 1 according to the embodiment on the
same plane, and comparing the height of the curvature of each
plate. In the former plate 2a, distortion of about 1 mm or more
occurred but, in the plate 2a according to the embodiment above,
distortion hardly occurred.
[0079] FIG. 10 is a graph showing an example of the fatigue life
measurement result of the forged beryllium-copper bulk material 1
according to the embodiment above and the former forged
beryllium-copper bulk material. The measurement was performed
according to the rotating bending fatigue test of JISZ2274 using
test samples No. 2 to 8 in a room temperature atmosphere. Each plot
represents the point in which fatigue fracture occurred. According
to the forged beryllium-copper bulk material according to the
embodiment above, it was found that the fatigue life also becomes
longer than that the former bulk material.
[0080] FIGS. 11(a) and 11(b) each show an example of the ultrasonic
inspection test result of the forged beryllium-copper bulk material
according to the embodiment above. In FIGS. 11(a) and 11(b), a
surface layer of a cube-shaped forged beryllium-copper bulk
material having one side of 100 mm was cut to be processed into a
cube having one side of 70 mm, and then ultrasonic waves were
transmitted to the processed forged beryllium-copper bulk
material.
[0081] As shown in FIG. 11(a), in the former beryllium-copper bulk
material manufactured by the former method, the echo peak of a 70
mm thickness from the bottom surface appeared. However, as shown in
the region surrounded by the dotted line, the echo peak due to
multiple reflection did not appear near the thickness of 140 mm
(peak disappearance). This represents that the internal structure
of the forged beryllium-copper bulk material according to the
former method is coarse and non-uniform. As shown in the region
surrounded by the solid line in FIG. 11(a), it is assumed, also
from the fact that there are many noises in the waveform, that the
internal structure of the bulk material is coarse and
non-uniform.
[0082] In contrast, as shown in FIG. 11(b), when the forged
beryllium-copper bulk material according to the embodiment above
was tested, it is found that the echo peak of a 70 mm thick bottom
surface appears and the echo peak due to double reflection appears
also near 140 mm. This represents that the ultrasonic waves are not
disturbed or attenuated due to the internal structure of the forged
beryllium-copper bulk material. Compared with the case shown in
FIG. 11(a), it is assumed, from the fact that no noises appear in
the entire waveform, that the internal structure becomes denser and
more uniform compared with that of the former forged
beryllium-copper bulk material.
[0083] Tables 1 and 2 show differences in the properties between
the forged beryllium-copper bulk material according to one
embodiment of the invention and the forged beryllium-copper bulk
material according to a comparative example (former example).
[0084] As materials in Table 1, copper alloys constituted by the
weight ratio of Cu.sub.100-(a+b)Be.sub.aCo.sub.b
(0.4%.ltoreq.a.ltoreq.2.0%, 0.15%.ltoreq.b.ltoreq.2.8%,
a+b.ltoreq.3.5%) were prepared. Each copper alloy was melted in a
high frequency melting furnace to manufacture an ingot, and then
the obtained ingot was homogenized. The obtained ingot was
processed by forging treatment, and the oxidation film formed on
the surface was removed by cutting to be formed into a cubic shape
having one side of 100 mm, thereby obtaining sample members A1 to
A7, B1 to B7, A101 to A105, B101 to B105, and C101 to C103.
[0085] The sample members A1 to A7, B1 to B7, A101 to A105, B101 to
B105, and C101 to C103 were subjected to the treatment (over-aging
treatment, cooling treatment, and cold forging treatment) shown in
each of Steps S12 to S15 of FIG. 2 under the conditions shown in
Table 1. The "discontinuous/continuous" of the column of the
"over-aging treatment" of Table 1 indicates that the solid solution
treatment of Step 12 and the over-aging treatment of Step S13 were
carried out independently and discontinuously or carried out
continuously as shown in FIGS. 3(a) and 3(b). The "highest
temperature before pressurization" of the column of the "over-aging
treatment" represents the maximum value of the surface temperature
of the copper alloy measured immediately before carrying out the
cold forging process of Step S15.
[0086] The "highest pressure" of the column of the "pressurization
treatment" of Table 1 represents the maximum value of the pressure
to be applied to the copper alloy by a forging device. The "highest
temperature after-pressurization" represents the maximum value of
the surface temperature of the copper alloy that gradually
increases with the repetition of pressurization.
[0087] In the column of "forging results" of Table 1, the case
where the bulk material after passing through the cold forging
treatment shown in Step S15 of FIG. 2 was placed on the flat
surface, and the bulk material stood straight by itself was judged
as o and the case where the bulk material did not stand straight
was judged as x. With respect to the "presence of cracks/fracture",
it was visually judged whether or not cracks or facture occurred.
With respect to the "hardness uniformity", the Vickers hardness was
determined at least arbitrary 25 points on the half of the surface
including the central portion of the bulk material according to the
measurement method according to JISZ2244, and the case where the
hardness value increases within 10% from the surface to the inside
was judged as o and the case other than the case above was judged
as x. When cracks and fracture occurred after processing, the
hardness measurement was not performed. Thus, such as case was
judged as "unmeasurable".
[0088] The "hardness after aging" represents an average value of
the results of measuring 25 points after performing 2 hour
age-hardening treatment at 315.degree. C., and then cooling the
temperature to room temperature.
[0089] The "tensile strength" of Table 2 represents the results of
performing a tensile test in the 6 directions according to JISZ2241
and examining whether or not the average value and the six
numerical values are within 5%. As test pieces used for the tensile
test, plates including the X-Y plane, the Y-Z plane, and the X-Z
plane were cut out from the center of the forged beryllium-copper
bulk material 1 of FIG. 1, and test pieces were machined from each
plate so that the six directions (i.e., X direction, Y direction, Z
direction, X-Y with an angle of 45.degree., Y-Z with an angle of
45.degree., and X-Z with an angle of)45.degree. correspond with the
tensile axis. Then, the measurement was performed according to
JISZ2241 (Method of Tensile Test for Metallic Materials).
[0090] The "presence of a shear band structure" of Table 2
represents the results of examining whether or not a shear band
structure similar to that of FIG. 12 were observed when some of the
plates cut as described above were observed under an optical
microscope of 500.times. magnification. Before observation,
corrosion by a suitable chemical etching is performed subsequent to
the machine polishing of the plate surface which is known to
persons skilled in the art. The "shear band structure" refers to a
shear structure in which the phase of the arrangement position of
atoms (grains) has shifted with a boundary along a certain surface,
and, in particular, refers to a structure in which the phase has
shifted in the form of a band in the direction in which the
deformation has been applied as described above.
TABLE-US-00001 TABLE 1 Over-aging treatment Pressurization
treatment Highest temp- Highest temp- Discontinuous/ Temp- erature
before Highest erature after Reduction Continuous erature Time
pressurization pressure pressurization rate No. -- .degree. C. h
.degree. C. MPa .degree. C. % Present A1 Discontinuous 550 2 16
1080 112 18 invention A2 Discontinuous 600 2 18 1120 104 18 A3
Discontinuous 650 2 17 1070 93 18 A4 Discontinuous 600 4 14 1010 72
18 A5 Discontinuous 600 6 12 990 66 18 A6 Discontinuous 600 2 14
1150 116 25 A7 Discontinuous 600 2 17 1170 119 30 B1 Continuous 550
2 16 1150 108 18 B2 Continuous 600 2 18 1110 98 18 B3 Continuous
650 2 17 1080 88 18 B4 Continuous 600 4 19 1040 86 18 B5 Continuous
600 6 17 1050 88 18 B6 Continuous 600 2 17 1150 104 25 B7
Continuous 600 2 18 1180 116 30 Comparative A101 Discontinuous 540
4 20 1320 135 18 exmaple A102 Discontinuous 660 2 17 1290 133 18
A103 Discontinuous 560 1.75 15 1340 137 18 A104 Discontinuous 600 2
18 1150 114 17 A105 Discontinuous 600 2 19 1370 138 33 B101
Continuous 535 2 20 1340 135 18 B102 Continuous 660 4 17 1330 140
18 B103 Continuous 570 1.75 18 1300 128 18 B104 Continuous 600 2 17
1310 128 17 B105 Continuous 600 2 19 1290 126 33 C101 -- -- -- 17
1220 128 18 C102 -- -- -- 16 1290 122 25 C103 -- -- -- 19 1330 126
30 Forging result Hardness after Maintaining Presence aging
Over-aging shape of of cracks/ Hardness End treatment bulk fracture
uniformity portion Center No. -- -- (within 10%) (Hv) (Hv) Present
A1 .largecircle. No .largecircle. 398 406 invention A2
.largecircle. No .largecircle. 395 397 A3 .largecircle. No
.largecircle. 400 402 A4 .largecircle. No .largecircle. 399 411 A5
.largecircle. No .largecircle. 397 401 A6 .largecircle. No
.largecircle. 400 405 A7 .largecircle. No .largecircle. 399 399 B1
.largecircle. No .largecircle. 393 397 B2 .largecircle. No
.largecircle. 395 399 B3 .largecircle. No .largecircle. 400 402 B4
.largecircle. No .largecircle. 401 408 B5 .largecircle. No
.largecircle. 389 398 B6 .largecircle. No .largecircle. 402 410 B7
.largecircle. No .largecircle. 405 408 Comparative A101 X Occurred
unmeasureable -- -- exmaple A102 X Occurred unmeasureable -- --
A103 X Occurred unmeasureable -- -- A104 .largecircle. No X 377 354
A105 X Occurred unmeasureable -- -- B101 X Occurred unmeasureable
-- -- B102 X Occurred unmeasureable -- -- B103 X No X -- -- B104 X
No X -- -- B105 X Occurred unmeasureable -- -- C101 X No X -- --
C102 X No X -- -- C103 X Occurred unmeasureable -- --
TABLE-US-00002 TABLE 2 Tensile strength Judgement of whether or
Presence of X Y Z XY45 YZ45 XZ45 Average not value is shear band
No. (N/mm2) (N/mm2) (N/mm2) (N/mm2) (N/mm2) (N/mm2) (N/mm2) within
5% structure Present A1 1211 1215 1232 1195 1203 1220 1213 within
5% No invention A2 1203 1211 1221 1200 1198 1208 1207 within 5% No
A3 1250 1264 1249 1255 1246 1258 1254 within 5% No A4 1175 1183
1188 1167 1187 1173 1179 within 5% No A5 1213 1211 1208 1207 1198
1210 1208 within 5% No A6 1222 1219 1224 1220 1220 1226 1222 within
5% No A7 1247 1239 1251 1244 1238 1242 1244 within 5% No B1 1231
1244 1239 1228 1235 1237 1236 within 5% No B2 1217 1234 1221 1222
1214 1216 1221 within 5% No B3 1233 1224 1222 1219 1227 1225 1225
within 5% No B4 1251 1247 1254 1253 1243 1238 1248 within 5% No B5
1202 1211 1209 1214 1208 1223 1211 within 5% No B6 1243 1237 1234
1248 1235 1233 1238 within 5% No B7 1256 1244 1253 1242 1257 1247
1250 within 5% No Comparative A101 -- -- -- -- -- -- -- -- Observed
exmaple A102 -- -- -- -- -- -- -- -- Observed A103 -- -- -- -- --
-- -- -- Observed A104 1240 980 1106 955 904 1073 1043 5% or more
No A105 -- -- -- -- -- -- -- -- Observed B101 -- -- -- -- -- -- --
-- Observed B102 -- -- -- -- -- -- -- -- Observed B103 -- -- -- --
-- -- -- -- Observed B104 -- -- -- -- -- -- -- -- No B105 -- -- --
-- -- -- -- -- Observed C101 -- -- -- -- -- -- -- -- No C102 -- --
-- -- -- -- -- -- Observed C103 -- -- -- -- -- -- -- --
Observed
[0091] As shown in Table 1, it is found that, in the cold forging
treatment of Step S15, by controlling the surface temperature of
the copper alloy to be equal to or lower than 120.degree. C.,
controlling the pressure to be equal to or lower than 1200 MPa, and
controlling the size reduction rate in the range of 18 to 30%, a
beryllium bulk material capable of maintaining almost uniform
hardness from the front surface to the inside can be manufactured.
In the samples A1 to A7 and the samples B1 to B7, the hardness of
the end portions (forged beryllium-copper bulk material surface)
after aging is 393 to 405 and the hardness of the center is 397 to
411, which shows that, in the forged beryllium-copper bulk material
according to this embodiment, the hardness is almost the same from
the near-surface portions and the center core portion and the
hardness of the center and the hardness of the inside are different
within 10%. In these Examples, the tensile strength in each
direction was almost the same and was stable, and no shear band
structures were observed in any place. As shown in the samples A101
to 105, B101 to B105, and C101 to C103, it is found that, when the
over-aging treatment of Step S13 is performed outside the range of
this embodiment or not performed, a given shape cannot be
maintained and causes cracks and the hardness or tensile strength
is unbalanced. In all the Comparative Examples, the shear band
structure was observed.
[0092] The present application claims the benefit of the priority
from Japanese Patent Application No. 2008-087628 filed on Mar. 28,
2008, the entire contents of which are incorporated herein by
reference.
INDUSTRIAL APPLICABILITY
[0093] The present invention can be utilized for machine structural
components in which durability and reliability are demanded, such
as bearings for airplanes, casings for under sea cable repeaters,
rotor shafts for ships, collars of oil field drilling drills,
injection molding dies, or welding electrode holders.
* * * * *