U.S. patent application number 10/644217 was filed with the patent office on 2005-02-24 for copper alloy having excellent corrosion cracking resistance and dezincing resistance, and method for producing same.
Invention is credited to Dong, Shu-Xin, Yamagishi, Yoshinori.
Application Number | 20050039827 10/644217 |
Document ID | / |
Family ID | 34194034 |
Filed Date | 2005-02-24 |
United States Patent
Application |
20050039827 |
Kind Code |
A1 |
Yamagishi, Yoshinori ; et
al. |
February 24, 2005 |
Copper alloy having excellent corrosion cracking resistance and
dezincing resistance, and method for producing same
Abstract
A copper alloy having an excellent corrosion cracking resistance
and an excellent dezincing resistance consists of: 58 to 66 wt % of
copper (Cu); 0.1 to 0.8 wt % of Sn; 0.01 to 0.5 wt % of Si; at
least one of 0.3 to 3.5 wt % of lead (Pb), 0.3 to 3.0 wt % of
bismuth (Bi), 0.02 to 0.15 wt % of phosphorus (P), 0.02 to 3.0 wt %
of nickel (Ni) and 0.02 to 0.6 wt % of iron (Fe) if necessary; and
the balance being zinc (Zn) and unavoidable impurities, wherein the
proportion of an alpha phase is 80 vol % or more. The apparent
content of zinc (Zn) in the copper alloy is in the range of from 34
to 39 wt %.
Inventors: |
Yamagishi, Yoshinori;
(Chiba, JP) ; Dong, Shu-Xin; (Aichi, JP) |
Correspondence
Address: |
BACHMAN & LAPOINTE, P.C.
900 CHAPEL STREET
SUITE 1201
NEW HAVEN
CT
06510
US
|
Family ID: |
34194034 |
Appl. No.: |
10/644217 |
Filed: |
August 20, 2003 |
Current U.S.
Class: |
148/554 ;
420/473; 420/476 |
Current CPC
Class: |
C22F 1/08 20130101; C22C
9/04 20130101 |
Class at
Publication: |
148/554 ;
420/473; 420/476 |
International
Class: |
C22C 009/04 |
Claims
What is claimed is:
1. A copper alloy comprising 58 to 66 wt % of copper, 0.1 to 0.8 wt
% of tin, 0.01 to 0.5 wt % of silicon, and the balance being zinc
and unavoidable impurities, wherein a proportion of an alpha phase
is 80 vol % or more.
2. A copper alloy as set forth in claim 1, wherein an apparent
content B' of zinc in said copper alloy is in the range of from 34
to 39 wt %, said apparent content B' of zinc being expressed by the
following
expression:B'=[(B+t.sub.1q.sub.1+t.sub.2q.sub.2)/(A+B+t.sub.1q.sub.1+t.su-
b.2q.sub.2)].times.100wherein A denotes the content (wt %) of
copper and B denotes the content (wt %) of zinc, t.sub.1 and
t.sub.2 denoting zinc equivalents of tin and silicon, respectively
(t.sub.1=2.0, t.sub.2=10.0), and q.sub.1 and q.sub.2 denoting the
contents (wt %) of tin and silicon, respectively.
3. A copper alloy as set forth in claim 1, which further contains
at least one of 0.3 to 3.5 wt % of lead and 0.3 to 3.0 wt % of
bismuth.
4. A copper alloy as set forth in claim 1 or 3, which further
contains at least one of 0.02 to 0.15 wt % of phosphorus, 0.02 to
3.0 wt % of nickel, and 0.02 to 0.6 wt % of iron, the total amount
thereof being in the range of from 0.02 to 3.0 wt %.
5. A copper alloy as set forth in claim 4, wherein an apparent
content B' of zinc in said copper alloy is in the range of from 34
to 39 wt %, said apparent content B' of zinc being expressed by the
following
expression:B'=[(B+t.sub.1q.sub.1+t.sub.2q.sub.2+t.sub.3q.sub.3+t.sub.4q.s-
ub.4)/(A+B+t.sub.1q.sub.1+t.sub.2q.sub.2+t.sub.3q.sub.3+t.sub.4q.sub.4)].t-
imes.100wherein A denotes the content (wt %) of copper and B
denotes the content (wt %) of zinc, t.sub.1, t.sub.2, t.sub.3 and
t.sub.4 denoting zinc equivalents of tin, silicon, nickel and iron,
respectively (t.sub.1=2.0, t.sub.2=10.0, t.sub.3=-1.3,
t.sub.4=0.9), and q.sub.1, q.sub.2, q.sub.3 and q.sub.4 denoting
the contents (wt %) of tin, silicon, nickel and iron,
respectively.
6. A method for producing a copper alloy, said method comprising
the steps of: preparing raw materials of a copper alloy comprising
58 to 66 wt % of copper, 0.1 to 0.8 wt % of tin, 0.01 to 0.5 wt %
of silicon, and the balance being zinc and unavoidable impurities;
casting the raw materials to form an ingot; hot working said ingot;
cold or hot working the hot worked ingot; annealing the cold or hot
worked ingot at a temperature of 300 to 600.degree. C. for two
minutes to five hours; and cooling the annealed ingot at a cooling
rate of 0.2 to 10.degree. C./sec.
7. A method for producing a copper alloy as set forth in claim 6,
wherein an apparent content B' of zinc in said copper alloy is in
the range of from 34 to 39 wt %, said apparent content B' of zinc
being expressed by the following
expression:B'=[(B+t.sub.1q.sub.1+t.sub.2q.sub.2)/(A+B+t.sub-
.1q.sub.1+t.sub.2q.sub.2)].times.100wherein A denotes the content
(wt %) of copper and B denotes the content (wt %) of zinc, t.sub.1
and t.sub.2 denoting zinc equivalents of tin and silicon,
respectively (t.sub.1=2.0, t.sub.2=10.0), and q.sub.1 and q.sub.2
denoting the contents (wt %) of tin and silicon, respectively.
8. A method for producing a copper alloy as set forth in claim 6,
wherein said raw materials further contain at least one of 0.3 to
3.5 wt % of lead and 0.3 to 3.0 wt % of bismuth.
9. A method for producing a copper alloy as set forth in claim 6 or
8, wherein said raw materials further contain at least one of 0.02
to 0.15 wt % of phosphorus, 0.02 to 3.0 wt % of nickel, and 0.02 to
0.6 wt % of iron, the total amount thereof being in the range of
from 0.02 to 3.0 wt %.
10. A method for producing a copper alloy as set forth in claim 9,
wherein an apparent content B' of zinc in said copper alloy is in
the range of from 34 to 39 wt %, said apparent content B' of zinc
being expressed by the following
expression:B'=[(B+t.sub.1q.sub.1+t.sub.2q.sub.2+t.sub.3q.su-
b.3+t.sub.4q.sub.4)/(A+B+t.sub.1q.sub.1+t.sub.2q.sub.2+t.sub.3q.sub.3+t.su-
b.4q.sub.4)].times.100wherein A denotes the content (wt %) of
copper and B denotes the content (wt %) of zinc, t.sub.1, t.sub.2,
t.sub.3 and t.sub.4 denoting zinc equivalents of tin, silicon,
nickel and iron, respectively (t.sub.1=2.0, t.sub.2=10.0,
t.sub.3=-1.3, t.sub.4=0.9), and q.sub.1, q.sub.2, q.sub.3 and
q.sub.4 denoting the contents (wt %) of tin, silicon, nickel and
iron, respectively.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to a copper alloy
and a method for producing the same. More specifically, the
invention relates to a copper alloy having an excellent corrosion
cracking resistance and an excellent dezincing resistance, in
addition to characteristics of conventional brasses having an
excellent machinability or cutting workability and an excellent
recyclability, and a method for producing the same.
[0003] 2. Description of the Prior Art
[0004] Conventional brasses, such as free-cutting brass rods/bars
(JIS C3604) and forging brass rods/bars (JISC3771), which are
copper-zinc alloys containing lead (Pb), are widely used for metal
parts for water lines and valve parts due to their excellent
malleability, hot workability and cutting workability. In addition,
the scraps of brasses can be easily provided due to the large
amount of distribution, so that brasses have an excellent
recyclability and are low in costs.
[0005] In recent years, in order to improve the dezincing corrosion
resistance of brass materials for use in water contact parts and so
forth, various proposals have been made. For example, Japanese
Patent Laid-Open No. 10-183275 discloses that tin (Sn) is added to
a copper-zinc alloy to be extruded to control the concentration of
Sn in a gamma phase through various heat treatments to improve the
dezincing resistance of the alloy. In addition, Japanese Patent
Laid-Open No. 6-108184 proposes that Sn is added to a copper-zinc
alloy to be extruded to form a single alpha phase to enhance the
dezincing corrosion resistance of the alloy. That is, the above
described alloys are characterized in that a larger amount of Sn
than that in conventional brasses is added.
[0006] Moreover, Japanese Patent Laid-Open No. 2001-294956 proposes
that very small amounts of phosphorus (P) and tin (Sn) are added to
a copper-zinc alloy to be extruded and reduced to be heat-treated
to form a structure wherein a beta phase is separated by an alpha
phase, to improve the dezincing resistance of the alloy.
[0007] However, if conventional copper-zinc alloys are used in warm
water in a corrosive water quality environment, the ionization
tendency of zinc in a beta phase is strong to give the elution of
zinc priority, so that they have a very low dezincing corrosion
resistance. In addition, the stress corrosion cracking sensing
resistance of copper-zinc alloys increases as the amount of zinc
increases. In particular, brasses of an alpha-plus-beta phase, such
as forging brass rods/bars (JIS C3771) and free-cutting brass
rods/bars (JIS C3604), have an inferior stress corrosion cracking
resistance.
[0008] In the method for adding the large amount of Sn to improve
the dezincing resistance, the local coagulation time of brass
increases with the increase of the amount of Sn, so that the
inverse segregation of Sn occurs during forging to cause surface
detects on an ingot and to damage hot workability in extrusion and
so forth. Therefore, there is a problem in that the yields of
products are remarkably deteriorated. In addition, Sn is more
expensive than copper-zinc scraps, so that there is a problem in
that the costs increase if the amount of Sn to be added is
large.
[0009] Moreover, the method for adding the very small amounts of Sn
and P to carry out heat treatments can be inexpensively carried out
to improve the dezincing resistance due to the small amount of
additives. However, there is a problem in that this method can not
improve the stress corrosion cracking resistance of the alloy.
SUMMARY OF THE INVENTION
[0010] It is therefore an object of the present invention to
eliminate the aforementioned problems and to provide a copper alloy
having an excellent corrosion cracking resistance and an excellent
dezincing resistance while maintaining excellent characteristics of
conventional brasses, and a method for producing the same.
[0011] In order to accomplish the aforementioned and other objects,
the inventors have diligently studied and found that it is possible
to provide a copper alloy having an excellent corrosion cracking
resistance and an excellent dezincing resistance while maintaining
excellent characteristics of conventional brasses, by adding
appropriate amounts of tin (Sn) and silicon (Si) (and at least one
of lead (Pb), bismuth (Bi), nickel (Ni), phosphorus (P) and iron
(Fe) if necessary) to a conventional brass material and by carrying
out a heat treatment on appropriate conditions to control the
structure of the alloy. Thus, the inventors have made the present
invention.
[0012] According to one aspect of the present invention, a copper
alloy comprises 58 to 66 wt % of copper, 0.1 to 0.8 wt % of tin,
0.01 to 0.5 wt % of silicon, and the balance being zinc and
unavoidable impurities, wherein a proportion of an alpha phase is
80 vol % or more.
[0013] In this copper alloy, an apparent content B' of zinc in the
copper alloy may be in the range of from 34 to 39 wt %, the
apparent content B' of zinc being expressed by the following
expression:
B'=[(B+t.sub.1q.sub.1+t.sub.2q.sub.2)/(A+B+t.sub.1q.sub.1+t.sub.2q.sub.2)-
].times.100, wherein A denotes the content (wt %) of copper and B
denotes the content (wt %) of zinc, t.sub.1 and t.sub.2 denoting
zinc equivalents of tin and silicon, respectively (t.sub.1=2.0,
t.sub.2=10.0), and q.sub.1 and q.sub.2 denoting the contents (wt %)
of tin and silicon, respectively.
[0014] The copper alloy may further contain at least one of 0.3 to
3.5 wt % of lead and 0.3 to 3.0 wt % of bismuth.
[0015] In addition, the copper alloy may further contain at least
one of 0.02 to 0.15 wt % of phosphorus, 0.02 to 3.0 wt % of nickel,
and 0.02 to 0.6 wt % of iron, the total amount thereof being in the
range of from 0.02 to 3.0 wt %.
[0016] In this case, an apparent content B' of zinc in the copper
alloy may be in the range of from 34 to 39 wt %, the apparent
content B' of zinc being expressed by the following expression:
B'=[(B+t.sub.1q.sub.1+t-
.sub.2q.sub.2+t.sub.3q.sub.3+t.sub.4q.sub.4)/(A+B+t.sub.1q.sub.1+t.sub.2q.-
sub.2+t.sub.3q.sub.3+t.sub.4q.sub.4)].times.100, wherein A denotes
the content (wt %) of copper and B denotes the content (wt %) of
zinc, t.sub.1, t.sub.2, t.sub.3 and t.sub.4 denoting zinc
equivalents of tin, silicon, nickel and iron, respectively
(t.sub.1=2.0, t.sub.2=10.0, t.sub.3=-1.3, t.sub.4=0.9), and
q.sub.1, q.sub.2, q.sub.3 and q.sub.4 denoting the contents (wt %)
of tin, silicon, nickel and iron, respectively.
[0017] According to another aspect of the present invention, there
is provided a method for producing a copper alloy, the method
comprising the steps of: preparing raw materials of a copper alloy
comprising 58 to 66 wt % of copper, 0.1 to 0.8 wt % of tin, 0.01 to
0.5 wt % of silicon, and the balance being zinc and unavoidable
impurities; casting the raw materials to form an ingot; hot working
the ingot; cold or hot working the hot worked ingot; annealing the
cold or hot worked ingot at a temperature of 300 to 600.degree. C.
for two minutes to five hours; and cooling the annealed ingot at a
cooling rate of 0.2 to 10.degree. C./sec.
[0018] In this method, an apparent content B' of zinc in the copper
alloy may be in the range of from 34 to 39 wt %, the apparent
content B' of zinc being expressed by the following expression:
B'=[(B+t.sub.1q.sub.1+t-
.sub.2q.sub.2)/(A+B+t.sub.1q.sub.1+t.sub.2q.sub.2)].times.100,
wherein A denotes the content (wt %) of copper and B denotes the
content (wt %) of zinc, t.sub.1 and t.sub.2 denoting zinc
equivalents of tin and silicon, respectively (t.sub.1=2.0,
t.sub.2=10.0), and q.sub.1, and q.sub.2 denoting the contents (wt
%) of tin and silicon, respectively.
[0019] The raw materials may further contain at least one of 0.3 to
3.5 wt % of lead and 0.3 to 3.0 wt % of bismuth.
[0020] In addition, the raw materials may further contain at least
one of 0.02 to 0.15 wt % of phosphorus, 0.02 to 3.0 wt % of nickel,
and 0.02 to 0.6 wt % of iron, the total amount thereof being in the
range of from 0.02 to 3.0 wt %.
[0021] In this case, an apparent content B' of zinc in the copper
alloy may be in the range of from 34 to 39 wt %, the apparent
content B' of zinc being expressed by the following expression:
B'=[(B+t.sub.1q.sub.1+t-
.sub.2q.sub.2+t.sub.3q.sub.3+t.sub.4q.sub.4)/(A+B+t.sub.1q.sub.1+t.sub.2q.-
sub.2+t.sub.3q.sub.3+t.sub.4q.sub.4)].times.100, wherein A denotes
the content (wt %) of copper and B denotes the content (wt %) of
zinc, t.sub.1, t.sub.2, t.sub.3and t.sub.4 denoting zinc
equivalents of tin, silicon, nickel and iron, respectively
(t.sub.1=2.0, t.sub.2=10.0, t.sub.3=-1.3, t.sub.4=0.9), and
q.sub.1, q.sub.2, q.sub.3 and q.sub.4 denoting the contents (wt %)
of tin, silicon, nickel and iron, respectively.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] The preferred embodiments of a copper alloy having an
excellent corrosion cracking resistance and an excellent dezincing
resistance according to the present invention will be described
below.
[0023] In a preferred embodiment of the present invention, a copper
alloy having an excellent corrosion cracking resistance and an
excellent dezincing resistance consists of 58 to 66 wt % of copper
(Cu), 0.1 to 0.8 wt % of Sn, 0.01 to 0.5 wt % of Si, an appropriate
amount of at least one of Pb, Bi, P, Ni and Fe if necessary, and
the balance being zinc (Zn) and unavoidable impurities, wherein the
proportion of an alpha phase is 80 vol % or more.
[0024] If the amount of Cu is less than 58 wt %, a beta phase
increases, so that it is not possible to improve the dezincing
resistance of the alloy even if a heat treatment is subsequently
carried out. On the other hand, if the amount of Cu exceeds 66 wt
%, a beta phase does not sufficiently deposit even in a high
temperature range, so that the hot workability of the alloy
deteriorates. Therefore, the amount of Cu is preferably in the
range of from 58 to 66 wt %, more preferably in the range of from
60 to 62 wt %.
[0025] Tin (Sn) has the function of improving the dezincing
resistance of an alpha phase and a beta phase. If the amount of Sn
is less than 0.1 wt %, it is not possible to obtain a satisfied
dezincing resistance. If the amount of Sn exceeds 0.8 wt %, a hard,
friable gamma phase is easy to deposit, so that the extension of
mechanical characteristics deteriorates. Therefore, the amount of
Sn is preferably in the range of from 0.1 to 0.8 wt %, more
preferably in the range of from 0.3 to 0.5 wt %.
[0026] Silicon (Si) remarkably has the functions of improving the
dezincing resistance of a beta phase and of improving the stress
corrosion cracking resistance of the whole alloy if a predetermined
proportion of Si is solid-dissolved in beta and alpha phases. If
the amount of Si is less than 0.01 wt %, these functions can not be
obtained. Since the zinc equivalent of Si is a high value of 10, if
the amount of Si to be added exceeds 0.5 wt %, the proportion of a
beta phase increases, and the extension of mechanical
characteristics deteriorates. Therefore, the amount of Si is
preferably in the range of 0.01 to 0.5 wt %, more preferably in the
range of 0.1 to 0.2 wt %.
[0027] Furthermore, if a small amount of a third element, such as
Sn, Si or Ni, is added to a copper-zinc alloy, it is often
solid-dissolved in alpha and beta phases without forming a specific
phase. In that case, such a structure that the amount of Zn
increases or decreases is produced in the copper-zinc alloy, so
that the alloy has properties corresponding thereto. Guillet has
proposed a method for expressing this relationship by using the
zinc equivalent of an additional element. That is, the apparent
zinc content B' of the third element is expressed by
B'=[(B+tq)/(A+B+tq)].times.100, wherein A denotes the content of Cu
(wt %), and B denotes the content of Zn (wt %), t denoting the zinc
equivalent of an additional element, and q denoting the content of
the additional element (wt %) (see "Fundamentals and Technologies
of Copper and Copper Alloys (Revised Edition), pp225-226" (Japan
Wrought Copper Association)).
[0028] If the proportion of an alpha phase is 80 vol % or more,
advantageous effects will be described below. In brasses of an
alpha-plus-beta phase, the beta phase is inferior to the alpha
phase with respect to both of stress corrosion cracking resistance
and dezincing resistance. The zinc equivalents of Sn and Si are 2
and 10, respectively, and the solid solutions of Sn and Si are
preferentially formed in a beta phase. If the amount of these
elements to be added increases, the proportion of the beta phase
increases, and the hardness of the whole material increases to
decrease the elongation thereof. If the proportion of the alpha
phase is set to be 80 vol % or more, the residual beta phase can be
reinforced by adding a very small amount of elements without
damaging the elongation of the whole material, and the stress
corrosion cracking resistance of the alpha phase can be improved by
the solid solution of Si. Therefore, the proportion of the alpha
phase is preferably 80 vol % or more, and more preferably 90 vol %
or more.
[0029] In a preferred embodiment of the present invention, a copper
alloy having an excellent stress corrosion cracking resistance and
dezincing resistance preferably contains at least one of 0.3 to 3.5
wt % of Pb and 0.3 to 3.0 wt % of Bi.
[0030] Lead (Pb) and bismuth (Bi) serve to improve the machin
ability or cutting workability of brasses, respectively. If the
amount of Pb is 0.3 wt % or more, it is possible to obtain a good
free-cutting workability. However, if the amount of Pb exceeds 3.5
wt %, the mechanical properties of brasses deteriorate to tend to
cause embrittlement. Therefore, the amount of Pb is preferably in
the range of from 0.3 to 3.5 wt %. In addition, since the material
cost of Pb is low, the amount of Pb is more preferably in the range
of 2.5 to 3.5 wt %. For the same reasons, if the amount of Bi is in
the range of from 0.3 to 3.0 wt %, preferably in the range of from
1.4 to 2.5 wt %, it is possible to obtain a good free-cutting
workability. Since Pb is harmful to the human body although Bi is
more expensive than Pb, Bi can be substituted for Pb.
[0031] In a preferred embodiment of the present invention, a copper
alloy having an excellent stress corrosion cracking resistance and
dezincing resistance preferably contains at least one of 0.02 to
0.15 wt % of P, 0.02 to 3.0 wt % of Ni, and 0.02 to 0.6 wt % of Fe,
the total amount of these elements being in the range of from 0.02
to 3.0 wt %.
[0032] Nickel (Ni) has the function of decreasing the size of
crystal grains, and also has the function of increasing the
proportion of the alpha phase since the zinc equivalent of Ni is
negative. If the amount of Ni is less than 0.02 wt %, it is not
sufficiently obtain these functions. On the other hand, if the
amount of Ni exceeds 3.0 wt %, there are problems on mechanical
characteristics and adding costs. Therefore, the amount of Ni is
preferably in the range of 0.02 to 3.0 wt %, and more preferably in
the range of 0.1 to 0.4 wt %.
[0033] Phosphorus (P) has the function of improving the dezincing
resistance of the alpha phase without damaging mechanical
characteristics. However, if the amount of P is less than 0.02 wt
%, it is not possible to obtain such a function, and if the amount
of P exceeds 0.15 wt %, intergranular segregation is caused to
deteriorate the ductility and stress corrosion cracking resistance
of the alloy. Therefore, the amount of P to be added is preferably
in the range of from 0.02 to 0.15 wt %.
[0034] Iron (Fe) has the functions of inhibiting the size of the
alpha phase from being increased and of stabilizing mechanical
characteristics. Since most of scrap materials include Fe, costs
increase if the amount of Fe is less than 0.02 wt %, and the
elongation of the alloy deteriorates if the amount of Fe exceeds
0.6 wt %. Therefore, the amount of Fe to be added is preferably in
the range of from 0.02 to 0.6 wt %.
[0035] If the total amount of Ni, Fe and P is less than 0.02 wt %,
the use of scraps is restricted to increase costs. On the other
hand, if the total amount exceeds 3.0 wt %, intergranular
segregation is caused to deteriorate the ductility of the alloy.
Therefore, the total amount of Ni, Fe and P is preferably in the
range of from 0.02 to 3.0 wt %, and more preferably in the range of
from 0.05 to 0.5 wt %.
[0036] A preferred embodiment of a method for producing a copper
alloy having an excellent stress corrosion cracking resistance and
dezincing resistance according to the present invention will be
described below.
[0037] First, raw materials having the above described compositions
are mixed so that an apparent content B' of Zn is in the range of
from 34 to 39 wt %, the apparent content B' being equal to
[(B+t.sub.1q.sub.1+t.sub.-
2q.sub.2+t.sub.3q.sub.3+t.sub.4q.sub.4)/(A+B+t.sub.1q.sub.1+t.sub.2q.sub.2-
+t.sub.3q.sub.3+t.sub.4q.sub.4)].times.100, wherein A denotes the
content (wt %) of Cu and B denotes the content (wt %) of Zn,
t.sub.1, t.sub.2, t.sub.3 and t.sub.4 denoting zinc equivalents of
Sn, Si, Ni and Fe, respectively (t.sub.1=2.0, t.sub.2=10.0,
t.sub.3=-1.3, t.sub.4=0.9), and q.sub.1, q.sub.2, q.sub.3 and
q.sub.4 denoting the contents (wt %) of Sn, Si, Ni and Fe,
respectively.
[0038] Then, after the mixture is cast to form an ingot, it is
extruded in a temperature range of from 600 to 850.degree. C. By
the mixing, it is possible to obtain an alpha-plus-beta phase
structure having a good hot workability in a high temperature
region. After the hot forging or cold reduction of a bar thus
obtained is carried out, the bar is heat-treated at a temperature
of 300 to 600.degree. C. for two minutes to five hours, and then
cooled at a cooling rate of 0.2 to 10.degree. C./sec to control the
structure.
[0039] By carrying out the heat treatment, the beta phase portion
after extruding is changed to an alpha or gamma phase except for a
part of the beta phase portion. At this time, the concentration of
additives in the residual beta phase increases, and the solid
solution of Si is formed in the alpha phase, so that the stress
corrosion cracking resistance and dezincing resistance of the bar
are improved. If the heat treatment temperature is lower than
300.degree. C., phase transformation is not sufficiently carried
out. If the heat treatment temperature is higher than 600.degree.
C., the beta phase is stable, so that no alpha-plus-gamma phase is
deposited. Therefore, the heat treatment temperature is preferably
in the range of from 300 to 600.degree. C. If the cooling rate is
higher than 10.degree. C./sec, there is the possibility that
distortion may be caused by cooling. If the cooling rate is lower
than 0.2.degree. C./sec, there are some cases where the size of
crystal grains increases to have an influence on dezincing
resistance. Therefore, the cooling temperature is preferably in the
range of from 0.2 to 10.degree. C./sec.
[0040] Examples of copper alloys having an excellent stress
corrosion cracking resistance and dezincing resistance and methods
thereof according to the present invention will be described below
in detail.
EXAMPLES 1 THROUGH 20
[0041] Raw materials of components in each of Examples 1 through 20
shown in Table 1 were mixed to be melted in an induction furnace to
be semi-continuously cast to form a bar having a diameter of 80 mm.
Then, the bar was hot-extruded so as to have a diameter of 30 mm,
and cold-drawn so as to have a diameter of 29.5 mm. Thereafter, in
each example, the bar was heat-treated on heat treatment conditions
shown in Table 2, and the cooling rate was in the range of from 0.2
to 10.degree. C./sec.
[0042] Table 1 shows the compositions of samples thus obtained, and
the apparent content B' of Zn, which is equal to
[(B+t.sub.1q.sub.1+t.sub.2q.-
sub.2+t.sub.3q.sub.3+t.sub.4q.sub.4)/(A+B+t.sub.1q.sub.1+t.sub.2q.sub.2+t.-
sub.3q.sub.3+t.sub.4q.sub.4)].times.100, wherein A denotes the
content (wt %) of Cu and B denotes the content (wt %) of Zn,
t.sub.1, t.sub.2, t.sub.3 and t.sub.4 denoting zinc equivalents of
Sn, Si, Ni and Fe, respectively (t.sub.1=2.0, t.sub.2=10.0,
t.sub.3=-1.3, t.sub.4=0.9), and q.sub.1, q.sub.2, q.sub.3 and
q.sub.4 denoting the contents (wt %) of Sn, Si, Ni and Fe,
respectively.
1TABLE 1 Apparent Content Ex. Cu Zn Sn Si Pb Bi P Ni Fe of Zn 1
60.9 35.44 0.39 0.02 2.93 0.00 0.06 0.00 0.23 37.5 2 61.8 34.83
0.39 0.12 2.60 0.00 0.04 0.02 0.21 37.4 3 62.8 33.72 0.37 0.03 2.93
0.00 0.09 0.00 0.11 35.7 4 59.9 36.54 0.38 0.05 2.90 0.00 0.05 0.03
0.15 38.8 5 61.0 35.39 0.38 0.11 2.67 0.00 0.08 0.08 0.29 38.0 6
62.1 34.38 0.42 0.04 2.65 0.00 0.05 0.10 0.26 36.5 7 61.1 35.40
0.42 0.05 2.65 0.00 0.05 0.18 0.15 37.5 8 62.9 33.07 0.60 0.10 3.00
0.00 0.05 0.21 0.12 35.8 9 61.9 33.93 0.71 0.10 3.00 0.00 0.05 0.30
0.03 36.8 10 63.1 32.33 0.77 0.20 3.00 0.00 0.05 0.51 0.08 35.9 11
62.2 33.40 0.65 0.10 3.00 0.00 0.05 0.48 0.16 36.2 12 63.0 33.06
0.40 0.20 3.00 0.00 0.05 0.11 0.17 36.3 13 60.4 35.68 0.41 0.11
2.00 0.00 0.10 1.30 0.00 37.3 14 59.2 36.99 0.32 0.05 2.30 0.00
0.04 0.87 0.23 38.6 15 65.7 30.41 0.65 0.34 2.60 0.00 0.08 0.12
0.10 34.8 16 63.4 34.21 0.51 0.09 1.41 0.00 0.11 0.15 0.12 36.2 17
61.3 36.02 0.63 0.02 1.20 0.50 0.06 0.17 0.10 37.9 18 62.1 35.21
0.39 0.10 0.20 1.80 0.05 0.04 0.11 37.4 19 61.5 36.02 0.70 0.03
0.00 1.50 0.01 0.13 0.11 38.0 20 60.9 35.68 0.45 0.12 0.00 2.60
0.06 0.06 0.13 38.3 (wt %)
[0043] The proportion of the alpha phase, hardness, dezincing
resistance and stress corrosion cracking resistance of each of the
obtained samples were evaluated.
[0044] The proportion of the alpha phase was obtained by the point
calculating method on a microphotograph of a cross section (see
"Handbook of Metals" (edited by Japan Society for Metals, the
revised fifth edition, Maruzen), p 289). Furthermore, 23.times.30
points were measured at intervals of 10 .mu.m in a lattice.
[0045] The dezincing resistance was evaluated on the basis of ISO
6509 by observing the depth of dezincing resistance after the
sample was dipped in a solution containing 12.7 g/L of
CuCl.sub.2.multidot.2H.sub.2O at a temperature of 75.+-.3.degree.
C. for 24 hours. The sample was tested so that the direction of
extruding was coincident with the direction of dezincing corrosion.
After the region of 10 mm.times.10 mm was measured, the dezincing
resistance was evaluated as "good" when the maximum dezincing depth
was 100 .mu.m or less, and the dezincing resistance was evaluated
as "not bad" when the maximum dezincing depth exceeds 100
.mu.m.
[0046] In order to evaluate the stress corrosion cracking
resistance, each of the samples before cold drawing was cut into
pieces having a thickness of 1.5 mm to be hot-rolled so as to have
a thickness of about 0.5 mm, and the surface thereof was
cold-rolled by about 0.03 mm. Thereafter, a heat treatment was
carried out, so that a sample having a thickness of 0.5 mm, a width
of 10 mm and a length of 140 mm was prepared. Then, a stress being
50% of the proof stress was applied to each of the samples by the
two-point load method based on JIS H8711, and each of the samples
was held in a desiccator including 14% NH.sub.3. In this state, the
time required to cause corrosion cracking was measured. The stress
corrosion cracking resistance was evaluated by "bad" when cracks
were produced within 5 hours, "not bad" when cracks are produced in
5 to 15 hours, and "good" when no cracks are produced after 15
hours or more.
[0047] Table 2 shows the proportions of the alpha phase and the
results of dezincing tests and stress corrosion cracking tests in
Examples 1 through 20. As can be seen from this table, in all
examples, the proportions of the alpha phase were 80 vol % or more,
and the stress corrosion cracking resistance and dezincing
resistance were good.
2TABLE 2 Stress Heat Proportion Corrosion Treatment of .alpha.
Phase Hardness Dezincing Cracking Ex. Conditions (vol %) (Hv)
Resistance Resistance 1 400.degree. C. .times. 2 hr 83 89.2 good
good 2 550.degree. C. .times. 1 hr 89 84.1 good good 3 600.degree.
C. .times. 3 hr 90 80.2 good good 4 550.degree. C. .times. 2 hr 95
90.6 good good 5 600.degree. C. .times. 2 hr 92 91.2 good good 6
450.degree. C. .times. 2 hr 92 94.1 good good 7 600.degree. C.
.times. 1 hr 81 90.4 good good 8 550.degree. C. .times. 3 hr 97
101.3 good good 9 450.degree. C. .times. 2 hr 86 108.6 good good 10
500.degree. C. .times. 2 hr 98 116.7 good good 11 550.degree. C.
.times. 1 hr 95 106.8 good good 12 550.degree. C. .times. 2 hr 96
98.6 good good 13 500.degree. C. .times. 3 hr 95 92.6 good good 14
550.degree. C. .times. 2 hr 94 103.1 good good 15 550.degree. C.
.times. 1 hr 82 107.5 good good 16 450.degree. C. .times. 2 hr 93
93.7 good good 17 500.degree. C. .times. 2 hr 86 102.4 good good 18
450.degree. C. .times. 3 hr 87 88.7 good good 19 500.degree. C.
.times. 2 hr 86 106.8 good good 20 400.degree. C. .times. 3 hr 84
88.3 good good
COMPARATIVE EXAMPLES 1 THROUGH 5
[0048] Raw materials containing elements in each of Comparative
Examples 1 through 5 shown in Table 3 were mixed to prepare samples
by the same method as that in the above described Examples. By the
same method as that in the above described Examples, the
compositions of the respective samples thus obtained were analyzed,
and their apparent contents of Zn were calculated. Table 3 shows
the results of analysis and the apparent contents of Zn.
3TABLE 3 Apparent Content Comp. Cu Zn Sn Si Pb Bi P Ni Fe of Zn 1
58.3 38.16 0.28 0.00 2.08 0.00 0.01 0.11 0.18 39.9 2 60.7 35.98
0.35 0.00 2.55 0.00 0.03 0.20 0.19 37.6 3 59.8 37.44 0.26 0.00 0.00
2.30 0.00 0.11 0.09 38.8 4 60.9 35.44 0.39 0.02 2.93 0.00 0.06 0.00
0.23 37.5 5 62.1 34.38 0.42 0.04 2.65 0.00 0.05 0.10 0.26 36.5 (wt
%)
[0049] With respect to each of the samples obtained in Comparative
Examples 1 through 5, the proportion of the alpha phase, hardness,
dezincing resistance and stress corrosion cracking resistance were
evaluated. The results thereof are shown in Table 4. As can be seen
from this table, in the case of Comparative Example 1, the amount
of Si to be added was zero, and the zinc equivalent was greater
than 39, so that the proportion of the alpha phase was not
sufficient and the stress corrosion cracking resistance and
dezincing resistance were inferior. Also in Comparative Examples 2
and 3, the amount of Si to be added was zero, so that the stress
corrosion cracking resistance was inferior. In Comparative Examples
4 and 5, the heat treatment conditions are not appropriate, so that
the proportion of the alpha phase was not sufficient. Therefore,
both of the dezincing resistance and stress corrosion cracking
resistance were inferior.
4TABLE 4 Proportion Stress Heat of .alpha. Corrosion Treatment
Phase Hardness Dezincing Cracking Comp. Conditions (vol %) (Hv)
Resistance Resistance 1 400.degree. C. .times. 2 hr 71 93.3 not bad
bad 2 550.degree. C. .times. 2 hr 85 101.6 good bad 3 500.degree.
C. .times. 3 hr 74 87.6 not bad bad 4 none 78 90.3 not bad not bad
5 700.degree. C. .times. 2 hr 84 100.4 not bad not bad
[0050] As described above, according to the present invention, it
is possible to inexpensively provide a copper alloy which has an
excellent corrosion cracking resistance and an excellent dezincing
resistance while maintaining excellent characteristics of
conventional brasses and which can be easily hot-worked.
[0051] While the present invention has been disclosed in terms of
the preferred embodiment in order to facilitate better
understanding thereof, it should be appreciated that the invention
can be embodied in various ways without departing from the
principle of the invention. Therefore, the invention should be
understood to include all possible embodiments and modification to
the shown embodiments which can be embodied without departing from
the principle of the invention as set forth in the appended
claims.
* * * * *