U.S. patent application number 09/891650 was filed with the patent office on 2002-02-07 for copper-base alloys having resistance to dezincification.
This patent application is currently assigned to DOWA MINING CO., LTD.. Invention is credited to Dong, Shu-xin.
Application Number | 20020015657 09/891650 |
Document ID | / |
Family ID | 18696927 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020015657 |
Kind Code |
A1 |
Dong, Shu-xin |
February 7, 2002 |
Copper-base alloys having resistance to dezincification
Abstract
Copper-base alloys are provided that maintain high hot
forgeability and cuttability and low-cost feature and which still
are improved in resistance to dezincification. The alloys comprise
57-69% of Cu, 0.3-3% of Sn and 0.02-1.5% of Si, all percentages
based on weight, with a Si/Sn value in the range of 0.05-1, and the
balance being Zn and incidental impurities.
Inventors: |
Dong, Shu-xin; (Iwata-gun,
JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN, LANGER & CHICK, P.C.
25th Floor
767 Third Avenue
New York
NY
10017
US
|
Assignee: |
DOWA MINING CO., LTD.
Tokyo
JP
|
Family ID: |
18696927 |
Appl. No.: |
09/891650 |
Filed: |
June 26, 2001 |
Current U.S.
Class: |
420/470 ;
420/469 |
Current CPC
Class: |
C22C 9/04 20130101 |
Class at
Publication: |
420/470 ;
420/469 |
International
Class: |
C22C 009/00; C22C
009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2000 |
JP |
2000-198825 |
Claims
What is claimed is:
1. A dezincification resistant copper-base alloy comprising 57-69%
of Cu, 0.3-3% of Sn and 0.02-1.5% of Si, all percentages based on
weight, with a Si/Sn value in the range of 0.05-1, and the balance
being Zn and incidental impurities.
2. A dezincification resistant copper-base alloy comprising 57-69%
of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, all
percentages based on weight, with a Si/Sn value in the range of
0.05-1, and the balance being Zn and incidental impurities.
3. A dezincification resistant copper-base alloy comprising 57-69%
of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with a Si/Sn
value in the range of 0.05-1, further containing in a total amount
of 0.02-0.2% at least one element selected from the group
consisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As,
all percentages based on weight, and the balance being Zn and
incidental impurities.
4. A dezincification resistant copper-base alloy comprising 57-69%
of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with a Si/Sn
value in the range of 0.05-1, further containing in a total amount
of 0.01-3% of at least one element selected from the group
consisting of 0.01-2% of Fe, 0.01-2% of Ni, 0.01-2% of Mn, 0.01-2%
of Al, 0.01-2% of Cr, 0.01-3% of Bi, 0.01-2% of Be, 0.01-2% of Zr,
0.01-3% of Ce, 0.01-2% of Ag, 0.01-2% of Ti, 0.01-2% of Mg, 0.01-2%
of Co, 0.01-1% of Te, 0.01-2% of Au, 0.01-2% of Y, 0.01-2% of La,
0.01-2% of Cd and 0.01-1% of Ca, all percentages based on weight,
and the balance being Zn and incidental impurities.
5. A dezincification resistant copper-base alloy comprising 57-69%
of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with a Si/Sn
value in the range of 0.05-1, further containing in a total amount
of 0.02-0.2% at least one element selected from the group
consisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As,
still further containing in a total amount of 0.01-3% of at least
one element selected from the group consisting of 0.01-2% of Fe,
0.01-2% of Ni, 0.01-2% of Mn, 0.01-2% of Al, 0.01-2% of Cr, 0.01-3%
of Bi, 0.01-2% of Be, 0.01-2% of Zr, 0.01-3% of Ce, 0.01-2% of Ag,
0.01-2% of Ti, 0.01-2% of Mg, 0.01-2% of Co, 0.01-1% of Te, 0.01-2%
of Au, 0.01-2% of Y, 0.01-2% of La, 0.01-2% of Cd and 0.01-1% of
Ca, all percentages based on weight, and the balance being Zn and
incidental impurities.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to copper-base alloys having high
resistance to dezincification corrosion which would otherwise occur
during use in corrosive aqueous solutions. The alloys also have
good hot working and cutting properties.
[0002] Cu--Zn alloys, commonly called brasses, have good working
properties, both cold and hot, so they have found extensive use
from old times. Among the best known are forging brass bars (JIS C
3771), free-cutting brass bars (JIS C 3604) and high-strength brass
bars (JIS C 6782). These copper-base alloys share the common
feature of including a continuous .beta. phase for better
workability.
[0003] Zinc in the .beta. phase has high ionization tendency, so in
natural environment, particularly in the presence of a corrosive
aqueous solution, it is selectively leached from the
above-mentioned alloys. This is why those alloys are very poor in
resistance to dezincification.
[0004] Various proposals have recently been made with a view to
improving the resistance to dezincification of brasses that are
typically used in parts that are brought into contact with water.
According to Unexamined Japanese Patent Application (JPA) No.
183275/1998, Sn is added to Cu--Zn alloys and, after hot extruding,
various heat treatments are performed to control the proportion of
the .gamma. phase and the Sn level in the .gamma. phase, thereby
improving resistance to dezincification.
[0005] According to Unexamined Published Japanese Patent
Application (JPA) No. 108184/1994, Sn is added to Cu--Zn alloys
and, after hot extruding, the alloys are subjected to a heat
treatment so that they are solely composed of the .alpha. phase,
thereby enhancing their resistance to dezincification.
[0006] The new alloys described above are characterized by having
Sn added in larger amounts than the conventional brasses. However,
the high inclusion of Sn in brasses has its own problems.
[0007] First, with the increase in the Sn level, the local
solidification time of brasses increases and there occurs inverse
segregation of Sn during casting, producing ingots with surface
defects. At the same time, the adaptability to extrusion and other
hot working processes is impaired, causing a significant drop in
the yield of shaped products.
[0008] Secondly, in order to elicit the ability of Sn to improve
resistance to dezincification, hot extruding must be followed by a
heat treatment for generating a certain area of .gamma. phase at
grain boundaries of the .alpha. phase and causing Sn to diffuse
uniformly in the .gamma. phase. However, this adds to the overall
production cost.
[0009] What is specifically taught in JPA No. 183275/1998 is as
follows: a heat treatment is applied at between 500.degree. C.
(inclusive) and 550.degree. C. (inclusive) for at least 30 seconds,
then cooling to 350.degree. C. is done at a rate no faster than
0.4.degree. C./sec; alternatively, a heat treatment is applied at
between 400.degree. C. (inclusive) and 500.degree. C. (inclusive)
for at least 30 seconds, then cooling is done; or a heat treatment
is applied at between 500.degree. C. (inclusive) and 550.degree. C.
(inclusive) for at least 30 seconds, then cooling to 350.degree. C.
is done at a rate between 0.4.degree. C./sec (inclusive) and
4.degree. C./sec (inclusive). The teaching of JPA No. 108184/1994
comprises hot extruding or drawing the alloy, followed by a heat
treatment at 500-600.degree. C. for a period of 30 minutes to 3
hours.
[0010] These heat treatments involve various problems. For one
thing, in order to ensure the appropriate conditions, costly
equipment must be used. Secondly, depending on product size, the
difference in heat pattern between the interior and exterior of the
product can cause variations in microstructure, which makes the
process less cost-effective due to lower yield. Thirdly, products
of complex shape occasionally suffer from the problems of
dimensional changes, residual stress and so forth.
[0011] A recent proposal worth particular mention is free-cutting
copper alloys having Si added to Cu--Zn alloys (JPA Nos.
119774/2000 and 119775/2000). These alloys contain at least 1.8 wt
% of Si with a large portion of Cu/Si .gamma. phase at grain
boundaries of the .alpha. phase. Under environment of actual use,
the Cu/Si .gamma. phase has better resistance to dezincification
than the .beta. phase but is not as resistant as a Cu/Sn .gamma.
phase. If the Si content is 1.8% or more, the thermal conductivity
of the material drops considerably and the blade of a cutting tool
becomes unduly hot during cutting to cause many problems such as a
shorter life of the cutting tool, lower precision in cutting and
limit on the cutting speed.
SUMMARY OF THE INVENTION
[0012] The present invention has been accomplished under these
circumstances and has as an object providing copper-base alloys
that have outstanding resistance to dezincification, hot
forgeability and cuttability and which still can be fabricated at
reasonably low cost.
[0013] The present inventors conducted intensive studies in order
to ensure that the addition of Sn would prove effective in
preventing dezincification of copper-base alloys to the fullest
extent and found the following: when Si as well as Sn were added
and the ratio of Si to Sn was adjusted to lie in an appropriate
range, secondary dendrite arms grew sufficiently thinner and longer
during solidification to suppress segregation of Sn; upon hot
working, the .gamma. phase was dispersed uniformly between regions
of .alpha. phase. This phenomenon made a great contribution to
improvements in resistance to dezincification and hot working
properties.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The stated object can be attained by any one of the
following copper-base alloys having improved resistance to
dezincification.
[0015] (1) A dezincification resistant copper-base alloy comprising
57-69% of Cu, 0.3-3% of Sn and 0.02-1.5% of Si, all percentages
based on weight, with a Si/Sn value in the range of 0.05-1, and the
balance being Zn and incidental impurities.
[0016] (2) A dezincification resistant copper-base alloy comprising
57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, all
percentages based on weight, with a Si/Sn value in the range of
0.05-1, and the balance being Zn and incidental impurities.
[0017] (3) A dezincification resistant copper-base alloy comprising
57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with
a Si/Sn value in the range of 0.05-1, further containing in a total
amount of 0.02-0.2% at least one element selected from the group
consisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As,
all percentages based on weight, and the balance being Zn and
incidental impurities.
[0018] (4) A dezincification resistant copper-base alloy comprising
57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with
a Si/Sn value in the range of 0.05-1, further containing in a total
amount of 0.01-3% of at least one element selected from the group
consisting of 0.01-2% of Fe, 0.01-2% of Ni, 0.01-2% of Mn, 0.01-2%
of Al, 0.01-2% of Cr, 0.01-3% of Bi, 0.01-2% of Be, 0.01-2% of Zr,
0.01-3% of Ce, 0.01-2% of Ag, 0.01-2% of Ti, 0.01-2% of Mg, 0.01-2%
of Co, 0.01-1% of Te, 0.01-2% of Au, 0.01-2% of Y, 0.01-2% of La,
0.01-2% of Cd and 0.01-1% of Ca, all percentages based on weight,
and the balance being Zn and incidental impurities.
[0019] (5) A dezincification resistant copper-base alloy comprising
57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of Pb, with
a Si/Sn value in the range of 0.05-1, further containing in a total
amount of 0.02-0.2% at least one element selected from the group
consisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As,
still further containing in a total amount of 0.01-3% of at least
one element selected from the group consisting of 0.01-2% of Fe,
0.01-2% of Ni, 0.01-2% of Mn, 0.01-2% of Al, 0.01-2% of Cr, 0.01-3%
of Bi, 0.01-2% of Be, 0.01-2% of Zr, 0.01-3% of Ce, 0.01-2% of Ag,
0.01-2% of Ti, 0.01-2% of Mg, 0.01-2% of Co, 0.01-1% of Te, 0.01-2%
of Au, 0.01-2% of Y, 0.01-2% of La, 0.01-2% of Cd and 0.01-1% of
Ca, all percentages based on weight, and the balance being Zn and
incidental impurities.
[0020] On the following pages, the criticality of the compositional
ranges for the ingredients in the copper-base alloy of the
invention is described in detail.
[0021] Cu:
[0022] An increase in the Cu content adds to the .alpha. phase and
improves corrosion resistance but if its content exceeds 69%, there
occurs a marked drop in hot forgeability. Since Cu is more
expensive than Zn, the Cu content is desirably minimized from an
economical viewpoint. If the Cu content is smaller than 57%, the
proportion of the .beta. phase increases to improve forgeability at
elevated temperature; on the other hand, resistance to
dezincification decreases and so do the strength and elongation of
the material. Considering these merits and demerits, the
compositional range of Cu is specified to lie between 57 and 69%,
preferably between 59 and 63%, on a weight basis.
[0023] Sn:
[0024] Adding at least 0.3% of Sn is effective in improving
resistance to dezincification. What is more, the improvement in
resistance to dezincification is marked if the addition of Sn is
increased. However, adding Sn in excess of 3% not only induces deep
defects in the surface of ingots being cast but also fails to bring
out a corresponding improvement in the resistance to
dezincification. In addition, Sn is more expensive than Zn and Cu,
so it is a factor in increasing the production cost. For these
reasons, the content of Sn in the copper-base alloy of the
invention is specified to lie between 0.3 and 3%, preferably
between 0.5 and 2%.
[0025] Si:
[0026] Silicon is added for the particular purpose of improving
castability and eliciting the ability of Sn to improve resistance
to dezincification. Adding a suitable amount of Si is effective in
improving the fluidity of a melt during casting and suppressing the
segregation of Sn. As a result, in the absence of any heat
treatment after hot extruding and forging, the ability of Sn to
improve resistance to dezincification is elicited to the fullest
extent, thereby providing consistent and outstanding
dezincification resistance and mechanical characteristics.
[0027] If the Si content exceeds 1.5%, an increased amount of Si/Cu
.gamma., .kappa. or .beta. phase appears at grain boundaries of the
.alpha. phase to deteriorate the resistance to dezincification. In
addition, the increased amount of Si oxide is detrimental to
castability and hot workability. If the Si content further
increases to 1.8% or more, the thermal conductivity of the material
drops considerably and the blade of a cutting tool becomes unduly
hot during cutting to cause many problems such as a shorter life of
the cutting tool, lower precision in cutting and limit on the
cutting speed.
[0028] If the Si content is less than 0.02%, there is obtained no
effect of improving castability or suppressing the segregation of
Sn. For these reasons, the compositional range of Si is specified
to lie between 0.02 and 1.5%, preferably between 0.06 and 0.6%.
[0029] Si/Sn:
[0030] The Si/Sn value is specified in the present invention since
in order to maximize the ability of Sn to improve resistance to
dezincification, Si must be added in an optimum amount that depends
on the amount of Sn addition. If the Si/Sn value is controlled at
an appropriate level, secondary dendrite arms grow in a
sufficiently finer and longer form during solidification to
suppress the segregation of Sn and, after hot working, the .gamma.
phase is dispersed uniformly between regions of .alpha. phase to
improve resistance to dezincification while assuring hot
deformability. If the Si/Sn value is greater than 1, the Si content
is excessive. Due to the high zinc equivalent of Si, there occurs
increased precipitation of the .beta. phase and the .beta. phase
surrounding the .alpha. phase cannot be fragmented by the .gamma.
phase, which results in impaired resistance to dezincification. If
the Si/Sn value is smaller than 0.05, the intended effect of
suppressing the segregation of Sn is not attained and in order to
elicit the effect of improving resistance to dezincification, a
heat treatment must be performed after hot working. Therefore, the
Si/Sn value is preferably in the range of 0.05-1, more preferably
in the range of 0.1-0.5.
[0031] P, Sb, As:
[0032] These elements are effective in suppressing dezincification
without impairing cuttability and forgeability. If their addition
is less than 0.02%, the intended effect of suppressing
dezincification is not obtained. If their addition exceeds 0.2%,
boundary segregation occurs to reduce ductility while increasing
stress corrosion cracking sensitivity. Hence, the contents of P, Sb
and As are each specified to lie between 0.02 and 0.2%.
[0033] Pb:
[0034] Lead is added to improve the cuttability of the material. If
its addition is less than 0.5%, the desired cuttability is not
attained. If the Pb addition exceeds 3%, hot working such as
extruding or forging is difficult to perform. If Pb is to be added,
its compositional range is between 0.5 and 3%, preferably between
1.5 and 2.3%.
[0035] If desired, the copper-base alloy of the invention may
further contain at least one element selected from the group
consisting of 0.01-2% of Fe, 0.01-2% of Ni, 0.01-2% of Mn, 0.01-2%
of Al, 0.01-2% of Cr, 0.01-3% of Bi, 0.01-2% of Be, 0.01-2% of Zr,
0.01-3% of Ce, 0.01-2% of Ag, 0.01-2% of Ti, 0.01-2% of Mg, 0.01-2%
of Co, 0.01-1% of Te, 0.01-2% of Au, 0.01-2% of Y, 0.01-2% of La,
0.01-2% of Cd and 0.01-1% of Ca; these elements may be contained in
a total amount of 0.01-3%. If added in amounts within the specified
ranges, these elements are effective in improving mechanical
characteristics and cuttability without damaging resistance to
dezincification and hot workability.
[0036] The copper-base alloy of the invention with its composition
adjusted to the ranges set forth above has outstanding resistance
to dezincification, hot forgeability and cuttability and still can
be fabricated at reasonably low cost.
[0037] The mode for carrying out the present invention is described
below with reference to examples.
EXAMPLES
[0038] Samples of the dezincification resistant copper-base alloy
of the invention were prepared as described below. Comparative
samples were also prepared. The chemical ingredients listed in
Table 1 were melted in an induction furnace and cast
semicontinuously into billets (80 mm.sup..phi.) at temperatures of
the liquidus plus about 100.degree. C. The castability of each
composition was evaluated by checking the depth of surface defects
such as inclusions in the cast billets. The results are shown in
Table 1 as evaluated by the following criteria: .circleincircle.
(depth of surface defect<1 mm); .smallcircle. (1-3 mm); .times.
(>3 mm).
1TABLE 1 Sample Chemical ingredients (wt %) No. Cu Zn Sn Si Si/Sn
Pb P Fe Ni Invention 1 61.3 bal. 1.50 0.71 0.473 1.7 -- -- -- 2
59.5 bal. 1.38 0.65 0.471 1.8 -- -- -- 3 60.2 bal. 1.40 0.63 0.450
1.9 0.07 -- -- 4 58.5 bal. 2.50 0.24 0.096 2.0 -- -- -- 5 60.7 bal.
1.08 0.20 0.185 2.0 0.04 0.11 -- 6 61.2 bal. 0.87 0.21 0.241 1.9
0.05 0.13 0.17 7 61.8 bal. 1.00 0.12 0.120 1.7 0.05 0.10 0.30 8
61.2 bal. 1.50 0.18 0.120 1.6 0.07 0.17 -- 9 59.0 bal. 1.50 0.36
0.240 1.4 0.08 0.23 0.60 10 62.2 bal. 1.24 0.70 0.565 1.8 0.06 0.12
0.06 11 62.0 bal. 1.24 0.60 0.484 0.8 -- -- -- 12 61.8 bal. 1.16
0.30 0.259 1.5 -- -- -- 13 60.8 bal. 0.80 0.20 0.250 1.8 0.05 0.10
0.06 14 63.0 bal. 1.80 0.80 0.444 1.5 0.05 -- -- Comparison 15 62.0
bal. 1.50 -- -- 1.9 -- -- -- 16 60.6 bal. 0.46 1.00 2.174 2.0 0.05
-- -- 17 59.0 bal. 0.20 0.01 0.050 -- 0.04 -- -- 18 58.0 bal. --
2.5 -- 1.9 -- -- -- 19 61.0 bal. -- 3 -- -- -- -- -- 20 59.0 bal.
1.5 1.9 1.267 -- -- -- --
[0039] The 80-mm.sup..phi. billets were held at 800.degree. C. for
30 minutes and later hot extruded into bars having a diameter of 30
mm.
[0040] The as-extruded bars were evaluated for resistance to
dezincification, resistance to hot deformation, hardness, tensile
strength and elongation. The dezincification test was conducted by
two methods under different conditions, one specified in JBMA
T303-1988 and the other in ISO 6509-1981. Test samples as cut from
the extruded bars were set so that the direction of corrosion
coincided with the extruding direction. In order to investigate the
extent of the change in resistance to dezincification that was
caused by heat treatment, evaluation was also made for the
resistance to dezincification of samples that were subjected to a
heat treatment at 400.degree. C. for 3 hours.
[0041] To measure the resistance to hot deformation, cylindrical
samples 15 mm in both diameter and height were cut on a lathe from
the extruded bars and subjected to a drop-hammer test. The test
temperature and the distortion rate were 750.degree. C. and 180
S.sup.-1, respectively.
[0042] The cutting test was performed by cutting on a lathe and
chip fragmentation was evaluated by the following criteria:
.smallcircle. (all chips were completely fragmented); .times.
(chips were not fragmented). For sticking property, 10 cutting
tests were conducted with a continuous feed of 100 mm and the
results were evaluated by the following criteria: .times. (copper
stuck to the tip of the blade); .smallcircle. (no copper stuck).
The cutting conditions were as follows: rotating speed, 950 rpm;
depth of cut, 0.5 mm; feed speed, 0.06 mm/rev.; feed, 100 mm;
cutting oil, none; cutting tool material, superhard steel. The
hardness of the copper-base alloy was Vickers hardness and measured
according to JIS Z 2244 under a testing force of 49 N on a section
perpendicular to the extruding direction. The tensile test was
conducted in accordance with JIS Z 2241 on No. 4 specimens which
were stretched in a direction parallel to the extruding direction.
The results of the tests are shown in Table 2.
2 Maximum depth of Maximum depth of Resistance Cuttability Tensile
dezincification by JBMA dezincification Sample to hot sticking to
Chip Hardness strength Elongation after heat by ISO (.mu.m) No.
Castability deformation the blade tip fragmentation Hv MPa %
as-extruded treatment as-extruded Invention 1 .circleincircle. 78
.smallcircle. .smallcircle. 130 451 27 59 59 115 2 .circleincircle.
67 .smallcircle. .smallcircle. 132 445 28 65 64 130 3
.circleincircle. 67 .smallcircle. .smallcircle. 129 433 34 60 60
125 4 .smallcircle. 72 .smallcircle. .smallcircle. 141 452 25 41 39
80 5 .circleincircle. 75 .smallcircle. .smallcircle. 107 407 45 57
55 115 6 .circleincircle. 76 .smallcircle. .smallcircle. 105 399 46
59 58 115 7 .circleincircle. 74 .smallcircle. .smallcircle. 110 445
45 57 56 110 8 .circleincircle. 73 .smallcircle. .smallcircle. 118
418 44 53 51 95 9 .circleincircle. 68 .smallcircle. .smallcircle.
133 467 44 52 52 95 10 .circleincircle. 68 .smallcircle.
.smallcircle. 137 475 25 45 42 75 11 .circleincircle. 69
.smallcircle. .smallcircle. 135 437 28 52 50 85 12 .circleincircle.
71 .smallcircle. .smallcircle. 124 415 33 55 53 95 13
.circleincircle. 77 .smallcircle. .smallcircle. 102 398 40 58 58
105 14 .circleincircle. 73 .smallcircle. .smallcircle. 121 416 32
21 19 65 Comparison 15 X 79 .smallcircle. .smallcircle. 119 412 36
92 71 135 16 .circleincircle. 67 .smallcircle. .smallcircle. 132
423 25 115 116 450 17 .circleincircle. 85 .smallcircle. X 98 387 48
173 167 835 18 X 75 X .smallcircle. 140 440 21 134 135 745 19 X 73
X X 146 453 19 165 171 585 20 X 65 X X 165 527 26 155 157 95
[0043] Sample Nos. 1-14 prepared in accordance with the alloy
composition of the invention showed outstanding castability,
mechanical characteristics and cuttability, as well as low
resistance to hot deformation comparable to that of hot forging
alloy C 3771 (deformation resistance, 70 MPa). They all had high
resistance to dezincification since the maximum depth of
dezincification was no more than 65 .mu.m in JBMA T303-1988 and no
more than 130 .mu.m in ISO 6509-1981.
[0044] What was particularly interesting about the samples of the
invention was that the maximum depth of dezincification as measured
by JBMA was little different between the as-extruded state and the
heat-treated state. It was therefore clear that by adding suitable
amounts of Si, the copper-base alloys were given consistent and
outstanding resistance to dezincification even when they were just
subjected to hot working without any subsequent special heat
treatments.
[0045] Sample Nos. 15-20 were comparisons and had various defects.
Sample No. 15 did not contain Si, so it was not only low in
castability and resistance to dezincification but also
characterized by considerable difference in the maximum depth of
dezincification between the as-extruded state and the heat-treated
state. Sample No. 16 had a Si/Sn value beyond the range specified
by the invention, so an excessive .beta. phase surrounded the
.alpha. phase, deteriorating the resistance to dezincification.
[0046] Sample No. 17 contained less Sn and Si than the lower limits
specified by the invention, so the proportions of the .gamma. and
.kappa. phases were insufficient to prevent marked drop in
resistance to dezincification; what is more, the resistance to hot
deformation was great and chips could not be fragmented. Sample
Nos. 18 and 19 did not contain Sn, so they were poor in resistance
to dezincification; in addition, they contained more Si than
specified by the invention, so copper stuck to the tip of the
cutting blade showing how poor the cuttability of the material
was.
[0047] Sample No. 20 contained both Sn and Si but the Si/Sn value
exceeded the range specified by the invention; what is more, the Si
content was greater than 1.8%. Hence, the sample was poor in
resistance to dezincification and castability and copper stuck to
the tip of the cutting blade.
[0048] As described above, the present invention offers copper-base
alloys that have outstanding resistance to dezincification, hot
forgeability and cuttability and which still can be fabricated at
reasonably low cost.
* * * * *