U.S. patent application number 17/611192 was filed with the patent office on 2022-09-01 for free-cutting copper alloy casting, and method for producing free-cutting copper alloy casting.
This patent application is currently assigned to MITSUBISHI MATERIALS CORPORATION. The applicant listed for this patent is MITSUBISHI MATERIALS CORPORATION. Invention is credited to Hiroki Goto, Keiichiro Oishi, Kouichi Suzaki.
Application Number | 20220275479 17/611192 |
Document ID | / |
Family ID | 1000006373691 |
Filed Date | 2022-09-01 |
United States Patent
Application |
20220275479 |
Kind Code |
A1 |
Oishi; Keiichiro ; et
al. |
September 1, 2022 |
FREE-CUTTING COPPER ALLOY CASTING, AND METHOD FOR PRODUCING
FREE-CUTTING COPPER ALLOY CASTING
Abstract
This copper alloy casting includes, in terms of mass %: Cu:
higher than 58.5% and lower than 65.0%; Si: higher than 0.40% and
lower than 1.40%; Pb: higher than 0.002% and lower than 0.25%; P:
higher than 0.003% and lower than 0.19%; and Bi: 0.001% to 0.100%
as an optional element, with the balance being Zn and inevitable
impurities, the total content of Fe, Mn, Co, and Cr is lower than
0.45% and the total content of Sn and Al is lower than 0.45%, a
relationship of
56.0.ltoreq.f1=[Cu]-5.times.[Si]+0.5.times.[Pb]+0.5.times.[Bi]-0.5.times.-
[P].ltoreq.59.5 is satisfied, when Bi is included, a relationship
of 0.003<f0=[Pb]+[Bi]<0.25 is further satisfied.
Inventors: |
Oishi; Keiichiro;
(Sakai-shi, JP) ; Suzaki; Kouichi; (Sakai-shi,
JP) ; Goto; Hiroki; (Sakai-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI MATERIALS CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
MITSUBISHI MATERIALS
CORPORATION
Tokyo
JP
|
Family ID: |
1000006373691 |
Appl. No.: |
17/611192 |
Filed: |
February 17, 2020 |
PCT Filed: |
February 17, 2020 |
PCT NO: |
PCT/JP2020/006037 |
371 Date: |
November 15, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22F 1/08 20130101; B22D
21/00 20130101; C22C 9/10 20130101 |
International
Class: |
C22C 9/10 20060101
C22C009/10; B22D 21/00 20060101 B22D021/00; C22F 1/08 20060101
C22F001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2019 |
JP |
2019-116914 |
Jul 12, 2019 |
JP |
2019-130143 |
Jul 31, 2019 |
JP |
2019-141096 |
Sep 9, 2019 |
JP |
2019-163773 |
Dec 11, 2019 |
JP |
PCT/JP2019/048438 |
Dec 11, 2019 |
JP |
PCT/JP2019/048455 |
Dec 23, 2019 |
JP |
PCT/JP2019/050255 |
Claims
1. A free-cutting copper alloy casting comprising: higher than 58.5
mass % and lower than 65.0 mass % of Cu; higher than 0.40 mass %
and lower than 1.40 mass % of Si; higher than 0.002 mass % and
lower than 0.25 mass % of Pb; higher than 0.003 mass % and lower
than 0.19 mass % of P; and higher than or equal to 0.001 mass % and
lower than or equal to 0.100 mass % of Bi as an optional element,
with the balance being Zn and inevitable impurities, wherein among
the inevitable impurities, the total content of Fe, Mn, Co, and Cr
is lower than 0.45 mass % and the total content of Sn and Al is
lower than 0.45 mass %, when a Cu content is represented by [Cu]
mass %, a Si content is represented by [Si] mass %, a Pb content is
represented by [Pb] mass %, a Bi content is represented by [Bi]
mass %, and a P content is represented by [P] mass %, a
relationship of
56.0.ltoreq.f1=[Cu]-5.times.[Si]+0.5.times.[Pb]+0.5.times.[Bi]-0.5.ti-
mes.[P].ltoreq.59.5 is satisfied, when Bi is not included, [Bi] in
f1 is 0, when Bi is included, a relationship of
0.003<f0=[Pb]+[Bi]<0.25 is further satisfied, in constituent
phases of a metallographic structure excluding non-metallic
inclusions, when an area ratio of .alpha. phase is represented by
(.alpha.)%, an area ratio of .gamma. phase is represented by
(.gamma.)%, and an area ratio of .beta. phase is represented by
(.beta.)%, relationships of 20.ltoreq.(.alpha.).ltoreq.80,
18.ltoreq.(.beta.).ltoreq.80, 0.ltoreq.(.gamma.)<5,
20.times.(.gamma.)/(.beta.)<4,
18.ltoreq.(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.[Si].sup.2-
+1.5.times.[Si]).ltoreq.82, and
33.ltoreq.(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.[Si].sup.2-
+1.5.times.[Si])+([Pb]+[Bi]).sup.1/2.times.38+([P]).sup.1/2.times.15
are satisfied, when Bi is not included, [Bi] in the expression is
0, and a compound including P is present in .beta. phase.
2. A free-cutting copper alloy casting comprising: higher than 59.0
mass % and lower than 65.0 mass % of Cu; higher than 0.50 mass %
and lower than 1.35 mass % of Si; higher than 0.010 mass % and
lower than 0.20 mass % of Pb; higher than 0.010 mass % and lower
than 0.15 mass % of P; and higher than or equal to 0.001 mass % and
lower than or equal to 0.100 mass % of Bi as an optional element,
with the balance being Zn and inevitable impurities, wherein among
the inevitable impurities, the total content of Fe, Mn, Co, and Cr
is lower than 0.40 mass % and the total content of Sn and Al is
lower than 0.40 mass %, when a Cu content is represented by [Cu]
mass %, a Si content is represented by [Si] mass %, a Pb content is
represented by [Pb] mass %, a Bi content is represented by [Bi]
mass %, and a P content is represented by [P] mass %, a
relationship of
56.0.ltoreq.f1=[Cu]-5.times.[Si]+0.5.times.[Pb]+0.5.times.[Bi]-0.5.ti-
mes.[P].ltoreq.59.5 is satisfied, when Bi is not included, [Bi] in
f1 is 0, when Bi is included, a relationship of
0.020.ltoreq.f0=[Pb]+[Bi]<0.20 is further satisfied, in
constituent phases of a metallographic structure excluding
non-metallic inclusions, when an area ratio of .alpha. phase is
represented by (.alpha.)%, an area ratio of .gamma. phase is
represented by (.gamma.)%, and an area ratio of .beta. phase is
represented by (.beta.) %, relationships of
25.ltoreq.(.alpha.).ltoreq.75, 25.ltoreq.(.beta.).ltoreq.75,
0.ltoreq.(.gamma.)<3, 20.times.(.gamma.)/(.beta.)<2,
25.ltoreq.(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.[Si].sup.2-
+1.5.times.[Si]).ltoreq.76, and
40.ltoreq.(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.[Si].sup.2-
+1.5.times.[Si])+([Pb]+[Bi]).sup.1/2.times.38+([P]).sup.1/2.times.15
are satisfied, when Bi is not included, [Bi] in the expression is
0, and a compound including P is present in .beta. phase.
3. A free-cutting copper alloy casting comprising: higher than 59.5
mass % and lower than 64.5 mass % of Cu; higher than 0.60 mass %
and lower than 1.30 mass % of Si; higher than 0.010 mass % and
lower than 0.15 mass % of Pb; higher than 0.020 mass % and lower
than 0.14 mass % of P; and higher than 0.020 mass % and lower than
or equal to 0.100 mass % of Bi, with the balance being Zn and
inevitable impurities, wherein among the inevitable impurities, the
total content of Fe, Mn, Co, and Cr is lower than 0.35 mass % and
the total content of Sn and Al is lower than 0.35 mass %, when a Cu
content is represented by [Cu] mass %, a Si content is represented
by [Si] mass %, a Pb content is represented by [Pb] mass %, a Bi
content is represented by [Bi] mass %, and a P content is
represented by [P] mass %, relationships of
0.040<f0=[Pb]+[Bi]<0.18 and
56.5<f1=[Cu]-5.times.[Si]+0.5.times.[Pb]+0.5.times.[Bi]-0.5.times.[P].-
ltoreq.59.0 are satisfied, in constituent phases of a
metallographic structure excluding non-metallic inclusions, when an
area ratio of .alpha. phase is represented by (.alpha.)%, an area
ratio of .gamma. phase is represented by (.gamma.)%, and an area
ratio of .beta. phase is represented by (.beta.)%, relationships of
30.ltoreq.(.alpha.).ltoreq.70, 30.ltoreq.(.beta.).ltoreq.70,
0.ltoreq.(.gamma.)<2, 20.times.(.gamma.)/(.beta.)<1,
30.ltoreq.(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.[Si].sup.2-
+1.5.times.[Si]).ltoreq.70, and
45.ltoreq.(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.[Si].sup.2-
+1.5.times.[Si])+([Pb]+[Bi]).sup.1/2.times.38+([P]).sup.1/2.times.15
are satisfied, a compound including P is present in .beta. phase,
and a particle including Bi is present in .alpha. phase.
4. The free-cutting copper alloy casting according to claim 1,
wherein a solidification temperature range is 25.degree. C. or
lower.
5. The free-cutting copper alloy casting according to claim 1,
wherein a Vickers hardness is 105 Hv or higher, and an impact value
obtained when a U-notch impact test is performed is 25 J/cm.sup.2
or higher.
6. The free-cutting copper alloy casting according to claim 1,
which is used for a mechanical component, an automobile component,
an electrical or electronic apparatus component, a toy, a sliding
component, a pressure vessel, a measuring instrument component, a
precision mechanical component, a medical component, a fitting for
construction, a faucet fitting, a drink-related device or
component, a device or component for water drainage, or an
industrial plumbing component.
7. A method for producing the free-cutting copper alloy casting
according to claim 1, the method comprising: a melting and casting
step, wherein in the melting and casting step, an average cooling
rate in a temperature range from 530.degree. C. to 450.degree. C.
in a process of cooling after casting is in a range of 0.1.degree.
C./min or higher and 55.degree. C./min or lower.
8. The free-cutting copper alloy casting according to claim 2,
wherein a solidification temperature range is 25.degree. C. or
lower.
9. The free-cutting copper alloy casting according to claim 3,
wherein a solidification temperature range is 25.degree. C. or
lower.
10. The free-cutting copper alloy casting according to claim 2,
wherein a Vickers hardness is 105 Hv or higher, and an impact value
obtained when a U-notch impact test is performed is 25 J/cm.sup.2
or higher.
11. The free-cutting copper alloy casting according to claim 3,
wherein a Vickers hardness is 105 Hv or higher, and an impact value
obtained when a U-notch impact test is performed is 25 J/cm.sup.2
or higher.
12. The free-cutting copper alloy casting according to claim 4,
wherein a Vickers hardness is 105 Hv or higher, and an impact value
obtained when a U-notch impact test is performed is 25 J/cm.sup.2
or higher.
13. The free-cutting copper alloy casting according to claim 2,
which is used for a mechanical component, an automobile component,
an electrical or electronic apparatus component, a toy, a sliding
component, a pressure vessel, a measuring instrument component, a
precision mechanical component, a medical component, a fitting for
construction, a faucet fitting, a drink-related device or
component, a device or component for water drainage, or an
industrial plumbing component.
14. The free-cutting copper alloy casting according to claim 3,
which is used for a mechanical component, an automobile component,
an electrical or electronic apparatus component, a toy, a sliding
component, a pressure vessel, a measuring instrument component, a
precision mechanical component, a medical component, a fitting for
construction, a faucet fitting, a drink-related device or
component, a device or component for water drainage, or an
industrial plumbing component.
15. The free-cutting copper alloy casting according to claim 4,
which is used for a mechanical component, an automobile component,
an electrical or electronic apparatus component, a toy, a sliding
component, a pressure vessel, a measuring instrument component, a
precision mechanical component, a medical component, a fitting for
construction, a faucet fitting, a drink-related device or
component, a device or component for water drainage, or an
industrial plumbing component.
16. The free-cutting copper alloy casting according to claim 5,
which is used for a mechanical component, an automobile component,
an electrical or electronic apparatus component, a toy, a sliding
component, a pressure vessel, a measuring instrument component, a
precision mechanical component, a medical component, a fitting for
construction, a faucet fitting, a drink-related device or
component, a device or component for water drainage, or an
industrial plumbing component.
17. A method for producing the free-cutting copper alloy casting
according to claim 2, the method comprising: a melting and casting
step, wherein in the melting and casting step, an average cooling
rate in a temperature range from 530.degree. C. to 450.degree. C.
in a process of cooling after casting is in a range of 0.1.degree.
C./min or higher and 55.degree. C./min or lower.
18. A method for producing the free-cutting copper alloy casting
according to claim 3, the method comprising: a melting and casting
step, wherein in the melting and casting step, an average cooling
rate in a temperature range from 530.degree. C. to 450.degree. C.
in a process of cooling after casting is in a range of 0.1.degree.
C./min or higher and 55.degree. C./min or lower.
19. A method for producing the free-cutting copper alloy casting
according to claim 4, the method comprising: a melting and casting
step, wherein in the melting and casting step, an average cooling
rate in a temperature range from 530.degree. C. to 450.degree. C.
in a process of cooling after casting is in a range of 0.1.degree.
C./min or higher and 55.degree. C./min or lower.
20. A method for producing the free-cutting copper alloy casting
according to claim 5, the method comprising: a melting and casting
step, wherein in the melting and casting step, an average cooling
rate in a temperature range from 530.degree. C. to 450.degree. C.
in a process of cooling after casting is in a range of 0.1.degree.
C./min or higher and 55.degree. C./min or lower.
Description
TECHNICAL FIELD
[0001] The present invention relates to free-cutting copper alloy
castings having excellent machinability and castability, a high
strength, and a significantly reduced lead content and a method for
producing the free-cutting copper alloy castings. The present
invention relates to free-cutting copper alloy castings that are
used for mechanical components, sliding components, measuring
instrument components, precision mechanical components, medical
components, automobile components, electrical and electronic
apparatus components, pressure vessels, fittings for construction,
daily necessaries, toys, drink-related devices and components,
devices and components for water drainage, industrial plumbing
components, and components relating to liquid or gas such as
drinking water, industrial water, drainage water, or hydrogen, and
a method for producing the free-cutting copper alloy castings.
Examples of specific component names include valves, joints, stems,
faucet fittings, faucets, waste plugs, gears, flanges, bearings,
sleeves, and sensors. The present invention relates to these
free-cutting copper alloy castings used for the components that are
made by machining, and a method for producing the free-cutting
copper alloy castings.
[0002] The present application claims priority on Japanese Patent
Application No. 2019-116914 filed on Jun. 25, 2019, Japanese Patent
Application No. 2019-130143 filed on Jul. 12, 2019, Japanese Patent
Application No. 2019-141096 filed on Jul. 31, 2019, Japanese Patent
Application No. 2019-163773 filed on Sep. 9, 2019, International
Patent Application No. PCT/JP2019/048438 filed on Dec. 11, 2019,
International Patent Application No. PCT/JP2019/048455 filed on
Dec. 11, 2019, and International Patent Application No.
PCT/JP2019/050255 filed on Dec. 23, 2019, the contents of which are
incorporated herein by reference.
BACKGROUND ART
[0003] Conventionally, a Cu--Zn--Pb alloy (so-called a free-cutting
brass bar, brass for forging, or brass for casting) or a
Cu--Sn--Zn--Pb alloy (so-called bronze casting: gunmetal) having
excellent machinability was generally used for automobile
components, electrical, home appliance, and electronic apparatus
components, mechanical components, stationaries, precision
mechanical components, medical components, and devices and
components relating to liquid or gas such as drinking water,
industrial water, drainage water, or hydrogen, specific component
names of which include valve, joint, faucet fitting, sensor, nut,
and screw.
[0004] A Cu--Zn--Pb alloy includes 56% to 65 mass % Cu, 1 to 4 mass
% Pb, and the balance is Zn. A Cu--Sn--Zn--Pb alloy includes 80% to
88 mass % Cu, 2 to 8 mass % Sn, 1 to 8 mass % Pb, and the balance
is Zn.
[0005] However, recently, Pb's influence on human body and the
environment is becoming a concern, and momentum to regulate Pb is
increasing in various countries. For example, a regulation for
reducing the Pb content in drinking water supply devices to 0.25
mass % or lower came into force in January 2010 in California, the
United States. In countries other than the United States also, such
regulation is rapidly being established, and development of a
copper alloy material that meets the requirements of the regulation
on Pb content is in demand.
[0006] In addition, in other industrial fields such as those of
automobiles, electrical and electronic apparatuses, and machines,
strengthening of regulations on Pb content including elimination of
exemptions has been actively discussed like in the field of
drinking water although in European regulations of ELV and RoHS,
free-cutting copper alloys are exceptionally allowed to include up
to 4 mass % Pb.
[0007] While there is a trend to strengthen Pb regulations for
free-cutting copper alloys, alloys like (1) Cu--Zn--Bi alloy or
Cu--Zn--Bi--Se alloy including Bi having machinability (machining
performance, machinability-improvement function) or, in some cases,
including not only Bi but also Se instead of Pb, (2) Cu--Zn alloy
including a high concentration of Zn in which the amount of .beta.
phase is increased to improve machinability, (3) Cu--Zn--Si alloy
or Cu--Zn--Sn alloy including large amounts of .gamma. phase and
.kappa. phase having machinability instead of Pb, (4)
Cu--Zn--Sn--Bi alloy including a large amount of .gamma. phase and
Bi are proposed.
[0008] For example, Patent Documents 1 and 15 disclose a method of
improving corrosion resistance and machinability by adding about
1.0 to 2.5 mass % Sn and about 1.5 to 2.0 mass % Bi to a Cu--Zn
alloy such that .gamma. phase precipitates.
[0009] However, alloys including Bi instead of Pb have many
problems. For example, Bi has lower machinability than Pb. Bi may
be harmful to human body like Pb. Bi has a resourcing problem
because it is a rare metal. And, Bi embrittles a copper alloy
material.
[0010] In addition, as disclosed in Patent Document 1, even if
.gamma. phase is precipitated in a Cu--Zn--Sn alloy, .gamma. phase
including Sn has poor machinability as demonstrated by the fact
that it requires co-addition of Bi having machinability.
[0011] Further, it is absolutely impossible to replace a
free-cutting copper alloy containing lead with a Cu--Zn binary
alloy including a large amount of .beta. phase since even though
.beta. phase contributes to improvement of machinability, it has
lower machinability than Pb.
[0012] For this reason, Cu--Zn--Si alloys including Si instead of
Pb are proposed as free-cutting copper alloys in, for example,
Patent Documents 2 to 10.
[0013] Patent Documents 2 and 3 mainly disclose alloys containing
69 to 79 mass % Cu and 2 to 4 mass % Si, in which excellent
machinability is realized without including Pb or with a small
amount of Pb by the excellent machinability of .gamma. phase, or,
in some cases, .kappa. phase formed in an alloy comprising high
concentration of Cu and Si. By including higher than or equal to
0.3 mass % Sn and higher than or equal to 0.1 mass % Al, formation
of .gamma. phase having machinability is further increased and
accelerated such that the alloys' machinability can be improved.
Further, improvement of corrosion resistance is devised by
formation of a large amount of .gamma. phase.
[0014] Also, In Patent Document 4, excellent machinability is
obtained by adding an extremely small amount (0.02 mass % or less)
of Pb and simply defining the total area of the .gamma. phase and
the .kappa. phase contained mainly in consideration of the Pb
content.
[0015] Further, Patent Documents 5 and 6 propose casting products
made of Cu--Zn--Si alloy in which extremely small amounts of P and
Zr are included in order to reduce the size of crystal grains of
the casting, and recite that the P/Zr ratio and the like are
important.
[0016] Patent Document 7 proposes a copper alloy in which Fe is
included in a Cu--Zn--Si alloy.
[0017] Patent Document 8 proposes a copper alloy in which Sn, Fe,
Co, Ni, and Mn are included in a Cu--Zn--Si alloy.
[0018] Patent Document 9 proposes a Cu--Zn--Si alloy having an
.alpha. phase matrix including .kappa. phase in which area ratios
of .beta. phase, .gamma. phase, and .beta. phase are limited.
[0019] Patent Document 10 proposes a Cu--Zn--Si alloy in which the
length of the longer sides of .gamma. phase and the length of the
longer sides of .mu. phase are defined.
[0020] Patent Document 11 proposes a Cu--Zn--Si alloy to which Sn
and Al are added.
[0021] Patent Document 12 proposes a Cu--Zn--Si alloy in which
.gamma. phase is distributed in the form of particles at a phase
boundary between .alpha. phase and .beta. phase to improve
machinability.
[0022] Patent Document 13 proposes improvement of cold workability
by having a Cu--Zn alloy contain Si such that .beta. phase is
dispersed.
[0023] Patent Document 14 proposes a Cu--Zn alloy to which Sn, Pb,
and Si are added.
[0024] Patent Document 15 proposes a Cu--Zn alloy whose corrosion
resistance is improved by including Sn.
[0025] Now, as described in Patent Document 13 and Non-Patent
Document 1, in Cu--Zn--Si alloys, it is known that, even when
looking at only those containing Cu at a concentration of 60 mass %
or higher, Zn at a concentration of 40 mass % or lower, and Si at a
concentration of 10 mass % or lower, 10 kinds of metallic phases
--.beta. phase, .gamma. phase, .delta. phase, .epsilon. phase,
.zeta. phase, .eta. phase, .kappa. phase, .beta. phase, and .chi.
phase, in some cases, 13 kinds of metallic phases including
additional phases of .alpha.', .beta.', and .gamma.' are present
aside from the matrix of .alpha. phase. Further, it is empirically
known that, as the number of additive elements increases, the
metallographic structure becomes complicated, and a new phase or
intermetallic compound may appear. In addition, it is also
empirically well known that there is a large difference in the
constitution of metallic phases between what an equilibrium phase
diagram shows and that of an actually produced alloy. Further, it
is well known that the compositions of these phases change
depending on the concentrations of Cu, Zn, Si, and the like in a
copper alloy and processing heat history.
[0026] Incidentally, in Cu--Zn--Pb alloys including Pb, the Cu
concentration is about 60 mass % whereas in all the Cu--Zn--Si
alloys described in Patent Documents 2 to 10, the Cu concentration
is 69 mass % or higher, and a reduction in the concentration of
expensive Cu is desired from a viewpoint of economic efficiency and
the like.
[0027] In Patent Document 11, Sn and Al are contained in a
Cu--Zn--Si alloy as indispensable elements in order to obtain
excellent corrosion resistance. The alloy also requires a large
amount Pb, or Bi in order to realize excellent machinability.
[0028] Patent Document 12 discloses copper alloy castings free of
Pb containing Cu at a concentration of about 65 mass % or higher
and having good castability and mechanical strength. It also
discloses that machinability is improved by .gamma. phase, and some
examples containing large amounts of Sn, Mn, Ni Sb, and B are
described in the document.
[0029] In addition, for conventional leaded free-cutting copper
alloys, it is expected that machining such as turning or drilling
can be performed without troubles for at least 24 hours and without
replacement of cutting tool or adjustment such as polishing of
cutting edge for 24 hours. Although depending on the degree of
difficulty of machining, the same level of machinability is
expected for alloys containing a significantly reduced amount of
Pb.
[0030] Now, in Patent Document 7, the Cu--Zn--Si alloy includes Fe,
and Fe and Si form an intermetallic compound of Fe--Si which is
harder and more brittle than .gamma. phase. This intermetallic
compound has problems like reducing tool life of a cutting tool
during machining and generation of hard spots during polishing,
which impairs the external appearance. In addition, since Si, an
additive element, is consumed as an intermetallic compound as it
combines with Fe, the performance of the alloy deteriorates.
[0031] In addition, in Patent Document 8, Sn, Fe, and Mn are added
to a Cu--Zn--Si alloy. However, Fe and Mn both combine with Si to
form hard and brittle intermetallic compounds. Therefore, such
addition causes problems during machining or polishing as disclosed
by Patent Document 7.
PRIOR ART DOCUMENTS
Patent Document
[0032] Patent Document 1: PCT International Publication No.
WO2008/081947 [0033] Patent Document 2: Japanese Unexamined Patent
Application, First Publication No. 2000-119775 [0034] Patent
Document 3: Japanese Unexamined Patent Application, First
Publication No. 2000-119774 [0035] Patent Document 4: PCT
International Publication No. WO2007/034571 [0036] Patent Document
5: PCT International Publication No. WO2006/016442 [0037] Patent
Document 6: PCT International Publication No. WO2006/016624 [0038]
Patent Document 7: Published Japanese Translation No. 2016-511792
of the PCT International Publication [0039] Patent Document 8:
Japanese Unexamined Patent Application, First Publication No.
2004-263301 [0040] Patent Document 9: Japanese Unexamined Patent
Application, First Publication No. 2013-104071 [0041] Patent
Document 10: PCT International Publication No. WO2019/035225 [0042]
Patent Document 11: Japanese Unexamined Patent Application, First
Publication No. 2018-048397 [0043] Patent Document 12: Published
Japanese Translation No. 2019-508584 of the PCT International
Publication [0044] Patent Document 13: U.S. Pat. No. 4,055,445
[0045] Patent Document 14: Japanese Unexamined Patent Application,
First Publication No. 2016-194123 [0046] Patent Document 15: PCT
International Publication No. WO2005/093108
Non-Patent Document
[0046] [0047] Non-Patent Document 1: Genjiro MIMA, Masaharu
HASEGAWA, Journal of the Japan Copper and Brass Research
Association, 2 (1963), p. 62 to 77
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
[0048] The present invention has been made in order to solve the
above-described problems in the conventional art, and its object is
to provide free-cutting copper alloy castings having excellent
machinability and castability, a high strength, excellent
toughness, and a significantly reduced lead content, and a method
for producing the free-cutting copper alloy castings.
[0049] In this specification, drilling refers to making holes with
a drill. Unless specified otherwise, excellent machinability refers
to low cutting resistance and good or excellent chip breakability
during turning with a lathe or drilling. Cooling rate refers to the
average cooling rate in a given temperature range. Conductivity
refers to electrical conductivity and thermal conductivity. In
addition, .beta. phase includes .beta.' phase, .gamma. phase
includes .gamma.' phase, and .alpha. phase includes .alpha.' phase.
Particles containing Bi refer to particles that contain both Bi and
Pb (particles of an alloy comprising Bi and Pb) and is sometimes
simply denominated as Bi particles. Copper alloy casting is
sometimes simply denominated as alloy. 24 hours refer to one day.
P-containing compound is a compound including P and at least either
Si or Zn or both Si and Zn, in some cases, further including Cu
and/or inevitable impurities such as Fe, Mn, Cr, or Co. A
P-containing compound is a compound such as P--Si, P--Si--Zn,
P--Zn, or P--Zn--Cu. P-containing compound is also denominated as a
compound including P, Si, and Zn.
Solutions for Solving the Problems
[0050] In order to solve the above-described problems and to
achieve the above-described object, the present inventors conducted
a thorough investigation and obtained the following findings.
[0051] Patent Documents 4 and 6 disclose that in Cu--Zn--Si alloys,
.beta. phase does not substantially contribute to but rather
inhibits machinability. Patent Documents 2 and 3 recite that when
.beta. phase is present, .beta. phase is changed into .gamma. phase
by heat treatment. In Patent Documents 9 and 10, also, the amount
of .beta. phase is significantly limited.
[0052] First, the present inventors diligently studied .beta. phase
that had been known to have no effect on machinability of a
Cu--Zn--Si alloy in the conventional art, and discovered a
composition of .beta. phase that has a large effect on
machinability.
[0053] However, there still was a significant difference in
machinability in terms of chip breakability and cutting resistance
compared with a free-cutting brass including 3 mass % Pb even if
.beta. phase containing Si, an element that has a significant
effect on machinability, was present.
[0054] Then we learned that there was a way to make a further
improvement in the metallographic structure for the solution of the
problem. First, in order to improve the machinability (machining
performance, machinability-improvement function) of .beta. phase
itself, P was added to a Cu--Zn--Si alloy casting so that it was
solid solubilized in .beta. phase and P-containing compounds (for
example, P--Si, P--Zn, P--Si--Zn, or P--Zn--Cu, etc.) having a
dimension of about 0.3 to 3 .mu.m were precipitated in .beta.
phase. As a result, the machinability of .beta. phase improved
more.
[0055] However, .beta. phase with improved machinability has poor
ductility and toughness. In order to improve ductility of .beta.
phase without impairing its machinability, the amounts of .beta.
phase and .alpha. phase were controlled to appropriate levels. On
the other hand, .alpha. phase has poor machinability. In order to
complement the weakness of .alpha. phase and obtain excellent
machinability, a very small amount Pb was added to the casting
where an appropriate amount of .beta. phase having further improved
machinability was present. As a result, improvement of chip
breakability and reduction of cutting resistance were realized. A
copper alloy casting according to the present invention having
machinability comparable to that of a copper alloy casting to which
a large amount of Pb is added was thus invented by selectively and
skillfully combining the following two improvement means.
[0056] (1) Enhance the machinability of .alpha. phase itself by
including a very small amount of Bi that is known to have a
slightly less machinability improvement effect than Pb instead of
Pb.
[0057] (2) Improve the machinability by including a small amount of
.gamma. phase.
[0058] A free-cutting copper alloy casting according to the first
aspect of the present invention includes: higher than 58.5 mass %
and lower than 65.0 mass % of Cu; higher than 0.40 mass % and lower
than 1.40 mass % of Si; higher than 0.002 mass % and lower than
0.25 mass % of Pb; and higher than 0.003 mass % and lower than 0.19
mass % of P, and higher than or equal to 0.001 mass % and lower
than or equal to 0.100 mass % of Bi as an optional element, with
the balance being Zn and inevitable impurities, wherein among the
inevitable impurities, the total content of Fe, Mn, Co, and Cr is
lower than 0.45 mass % and the total content of Sn and Al is lower
than 0.45 mass %, when a Cu content is represented by [Cu] mass %,
a Si content is represented by [Si] mass %, a Pb content is
represented by [Pb] mass %, a Bi content is represented by [Bi]
mass %, and a P content is represented by [P] mass %, a
relationship of
56.5.ltoreq.f1=[Cu]-5.times.[Si]+0.5.times.[Pb]+0.5.times.[Bi]-
0.5.times.[P].ltoreq.59.0 is satisfied,
[0059] when Bi is not included, [Bi] in f1 is 0,
[0060] when Bi is included, a relationship of
0.003<f0=[Pb]+[Bi]<0.25 is further satisfied,
[0061] in constituent phases of a metallographic structure
excluding non-metallic inclusions, when an area ratio of .alpha.
phase is represented by (.alpha.)%, an area ratio of .gamma. phase
is represented by (.gamma.)%, and an area ratio of .beta. phase is
represented by (.beta.)%, relationships of
20.ltoreq.(.alpha.).ltoreq.80,
18.ltoreq.(.beta.).ltoreq.80,
0.ltoreq.(.gamma.)<5,
20.times.(.gamma.)/(.beta.)<4,
18.ltoreq.(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.[Si].sup.-
2+1.5.times.[Si]).ltoreq.82, and
33.ltoreq.(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.[Si].sup.-
2+1.5.times.[Si])+
([Pb]+[Bi]).sup.1/2.times.38+([P]).sup.1/2.times.15
are satisfied, when Bi is not included, [Bi] in the expression is
0, and
[0062] a compound including P is present in .beta. phase.
[0063] A free-cutting copper alloy casting according to the second
aspect of the present invention includes: higher than 59.0 mass %
and lower than 65.0 mass % of Cu; higher than 0.50 mass % and lower
than 1.35 mass % of Si; higher than 0.010 mass % and lower than
0.20 mass % of Pb; higher than 0.010 mass % and lower than 0.15
mass % of P; and higher than or equal to 0.001 mass % and lower
than or equal to 0.100 mass % of Bi as an optional element, with
the balance being Zn and inevitable impurities,
[0064] wherein among the inevitable impurities, the total content
of Fe, Mn, Co, and Cr is lower than 0.40 mass % and the total
content of Sn and Al is lower than 0.40 mass %,
[0065] when a Cu content is represented by [Cu] mass %, a Si
content is represented by [Si] mass %, a Pb content is represented
by [Pb] mass %, a Bi content is represented by [Bi] mass %, and a P
content is represented by [P] mass %,
[0066] a relationship of
56.0.ltoreq.f1=[Cu]-5.times.[Si]+0.5.times.[Pb]+0.5.times.[Bi]-
0.5.times.[P].ltoreq.59.5 is satisfied,
[0067] when Bi is not included, [Bi] in f1 is 0,
[0068] when Bi is included, a relationship of
0.020.ltoreq.f0=[Pb]+[Bi]<0.20
[0069] is further satisfied,
[0070] in constituent phases of a metallographic structure
excluding non-metallic inclusions, when an area ratio of .alpha.
phase is represented by (.alpha.)%, an area ratio of .gamma. phase
is represented by (.gamma.)%, and an area ratio of .beta. phase is
represented by (.beta.)%, relationships of
25.ltoreq.(.alpha.).ltoreq.75,
25.ltoreq.(.beta.).ltoreq.75,
0.ltoreq.(.gamma.)<3,
20.times.(.gamma.)/(.beta.)<2,
25.ltoreq.(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.[Si].sup.-
2+1.5.times.[Si]).ltoreq.76,
and
40.ltoreq.(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.[Si].sup.-
2+1.5.times.[Si])+
([Pb]+[Bi]).sup.1/2.times.38+([P]).sup.1/2.times.15
are satisfied,
[0071] when Bi is not included, [Bi] in the expression is 0,
and
[0072] a compound including P is present in .beta. phase.
[0073] A free-cutting copper alloy casting according to the third
aspect of the present invention includes: higher than 59.5 mass %
and lower than 64.5 mass % of Cu; higher than 0.60 mass % and lower
than 1.30 mass % of Si; higher than 0.010 mass % and lower than
0.15 mass % of Pb; higher than 0.020 mass % and lower than 0.14
mass % of P; and higher than 0.020 mass % and lower than or equal
to 0.100 mass % of Bi,
[0074] with the balance being Zn and inevitable impurities,
[0075] wherein among the inevitable impurities, the total content
of Fe, Mn, Co, and Cr is lower than 0.35 mass % and the total
content of Sn and Al is lower than 0.35 mass %,
[0076] when a Cu content is represented by [Cu] mass %, a Si
content is represented by [Si] mass %, a Pb content is represented
by [Pb] mass %, a Bi content is represented by [Bi] mass %, and a P
content is represented by [P] mass %, relationships of
0.040.ltoreq.f0=[Pb]+[Bi]<0.18 and
56.5.ltoreq.f1=[Cu]-5.times.[Si]+0.5.times.[Pb]+0.5.times.[Bi]-
0.5.times.[P].ltoreq.59.0
are satisfied,
[0077] in constituent phases of a metallographic structure
excluding non-metallic inclusions, when an area ratio of .alpha.
phase is represented by (.alpha.)%, an area ratio of .gamma. phase
is represented by (.gamma.)%, and an area ratio of .beta. phase is
represented by (.beta.)%, relationships of
30.ltoreq.(.alpha.).ltoreq.70,
30.ltoreq.(.beta.).ltoreq.70,
0.ltoreq.(.gamma.)<2,
20.times.(.gamma.)/(.beta.)<1,
30.ltoreq.(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.[Si].sup.-
2+1.5.times.[Si]).ltoreq.70,
45.ltoreq.(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.[Si].sup.-
2+1.5.times.[Si])+
([Pb]+[Bi]).sup.1/2.times.38+([P]).sup.1/2.times.15
are satisfied,
[0078] a compound including P is present in .beta. phase, and a
particle including Bi is present in .alpha. phase.
[0079] A free-cutting copper alloy casting according to the fourth
aspect of the present invention is the copper alloy casting
according to any one of the first to third aspects of the present
invention in which a solidification temperature range is 25.degree.
C. or lower.
[0080] A free-cutting copper alloy casting according to the fifth
aspect of the present invention is the copper alloy casting
according to any one of the first to fourth aspects of the present
invention in which a Vickers hardness is 105 Hv or higher, and an
impact value obtained when a U-notch impact test is performed is 25
J/cm.sup.2 or higher.
[0081] A free-cutting copper alloy casting according to the sixth
aspect of the present invention is the free-cutting copper alloy
casting according to any one of the first to fifth aspects of the
present invention, which is used for a mechanical component, an
automobile component, an electrical or electronic apparatus
component, a toy, a sliding component, a pressure vessel, a
measuring instrument component, a precision mechanical component, a
medical component, a fitting for building construction, a faucet
fitting, a drink-related device or component, a device or component
for water drainage, or an industrial plumbing component.
[0082] A method for producing a free-cutting copper alloy casting
according to the seventh aspect of the present invention is a
method for producing the free-cutting copper alloy casting
according to any one of the first to sixth aspects of the present
invention which includes a melting and casting step, wherein in the
melting and casting step, an average cooling rate in a temperature
range from 530.degree. C. to 450.degree. C. in a process of cooling
after casting is in a range of 0.1.degree. C./min or higher and
55.degree. C./min or lower.
Effects of Invention
[0083] According to one aspect of the present invention, a
free-cutting copper alloy casting having excellent machinability
and castability, a high strength, excellent toughness, and a
significantly reduced amount of lead content, and a method for
producing the free-cutting copper alloy casting can be
provided.
BRIEF DESCRIPTION OF DRAWINGS
[0084] FIG. 1 is a picture showing a metallographic structure of a
copper alloy of Test No. T07.
[0085] FIG. 2 is a picture showing a metallographic structure of
the copper alloy of Test No. T35.
[0086] FIG. 3 is a picture showing a metallographic structure of
the copper alloy of Test No. T106.
[0087] FIG. 4 is a diagram showing a cross-section of a casting
obtained by casting in a Tatur mold in a Tatur Shrinkage Test.
[0088] FIG. 5 shows a macrostructure of a cross-section of a
casting made of Alloy No. S01 obtained by performing a Tatur
Shrinkage Test.
[0089] FIG. 6 is a picture of chips generated in the machining test
of Test No. T07.
[0090] FIG. 7 is a picture of chips generated in the machining test
of Test No. T35.
[0091] FIG. 8 is a picture of chips generated in the machining test
of Test No. T106.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
[0092] Below is a description of free-cutting copper alloy castings
according to an embodiment of the present invention and a method
for producing the free-cutting copper alloy castings.
[0093] The free-cutting copper alloy castings according to the
embodiment are used for mechanical components such as valves,
joints, parts and components for water supply and drainage, or
pressure vessels, automobile components, electrical components,
home appliance components, and electronic components, and devices
and components which come in contact with liquid or gas such as
drinking water, industrial water, or hydrogen.
[0094] Here, in this specification, an element symbol in
parentheses such as [Zn] represents the content (mass %) of the
element.
[0095] In embodiments of the present invention, using this content
expressing method, composition relational expressions f0 and f1 are
defined as follows.
[0096] When Bi is included, the expressions are defined as
follows.
f0=[Pb]+[Bi] Composition Relational Expression
f1=[Cu]-5.times.[Si]+
0.5.times.[Pb]+0.5.times.[Bi]-0.5.times.[P] Composition Relational
Expression
[0097] When Bi is not included, [Bi] in f1 is 0. Therefore, in that
case, f1=[Cu]-5.times.[Si]+0.5.times.[Pb]-0.5.times.[P].
[0098] Further, in the embodiments, in constituent phases of the
metallographic structure excluding non-metallic inclusions, area
ratio of .alpha. phase is represented by (.alpha.)%, area ratio of
.beta. phase is represented by (.beta.)%, and area ratio of .gamma.
phase is represented by (.gamma.)%. Area ratio of each of the
phases will also be referred to as "amount of each of the phases",
"proportion of each of the phases", or "proportion that each of the
phases occupies". In the embodiments, plural metallographic
structure relational expressions and metallographic structure and
composition relational expressions are defined as follows.
f2=(.alpha.) Metallographic Structure Relational Expression
f3=(.beta.) Metallographic Structure Relational Expression
f4=(.gamma.) Metallographic Structure Relational Expression
f5=20.times.
(.gamma.)/(.beta.) Metallographic Structure Relational
Expression
f6=
(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.+1.5.times.[Si])
Metallographic Structure Relational Expression
f6A=(.gamma.).sup.1/2.times.3(.beta.).times.(-0.5.times.[Si].sup.2+1.5.t-
imes.
[Si])+([Pb]+[Bi]).sup.1/2.times.38+([P]).sup.1/2.times.15
Metallographic Structure and Composition Relational Expression
[0099] When Bi is not included, [Bi] in f6A is 0. Therefore, in
that case,
f6A=(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.[Si].sup.2+1.5.t-
imes.[Si])+([Pb]).sup.1/2.times.38+([P]).sup.1/2.times.15.
[0100] A free-cutting copper alloy casting according to the first
embodiment of the present invention includes: higher than 58.5 mass
% and lower than 65.0 mass % Cu; higher than 0.40 mass % and lower
than 1.40 mass % Si; higher than 0.002 mass % and lower than 0.25
mass % Pb; and higher than 0.003 mass % and lower than 0.19 mass %
P; and higher than or equal to 0.001 mass % and lower than or equal
to 0.100 mass % Bi as an optional element, with the balance being
Zn and inevitable impurities, in which, among the inevitable
impurities, the total content of Fe, Mn, Co, and Cr is lower than
0.45 mass % and the total content of Sn and Al is lower than 0.45
mass %, when Bi is included, the composition relational expression
f0 is in a range of 0.003<f0<0.25, the composition relational
expression f1 is in a range of 56.0.ltoreq.f1.ltoreq.59.5, the
metallographic structure relational expression f2 is in a range of
20.ltoreq.f2.ltoreq.80, the metallographic structure relational
expression f3 is in a range of 18.ltoreq.f3.ltoreq.80, the
metallographic structure relational expression f4 is in a range of
0.ltoreq.f4.ltoreq.5, the metallographic structure relational
expression f5 is in a range of f5<4, the metallographic
structure relational expression f6 is in a range of
18.ltoreq.f6.ltoreq.82, the metallographic structure and
composition relational expression f6A is in a range of
33.ltoreq.f6A, and a compound including P is present in .beta.
phase.
[0101] A free-cutting copper alloy casting according to the second
embodiment of the present invention includes: higher than 59.0 mass
% and lower than 65.0 mass % Cu; higher than 0.50 mass % and lower
than 1.35 mass % Si; higher than 0.010 mass % and lower than 0.20
mass % Pb; higher than 0.010 mass % and lower than 0.15 mass % P;
and higher than or equal to 0.001 mass % and lower than or equal to
0.100 mass % Bi as an optional element, with the balance being Zn
and inevitable impurities, in which, among the inevitable
impurities, the total content of Fe, Mn, Co, and Cr is lower than
0.40 mass % and the total content of Sn and Al is lower than 0.40
mass %, when Bi is included, the composition relational expression
f0 is in a range of 0.020.ltoreq.f0<0.20, the composition
relational expression f1 is in a range of
56.3.ltoreq.f1.ltoreq.59.2, the metallographic structure relational
expression f2 is in a range of 25.ltoreq.f2.ltoreq.75, the
metallographic structure relational expression f3 is in a range of
25.ltoreq.f3.ltoreq.75, the metallographic structure relational
expression f4 is in a range of 0.ltoreq.f4<3, the metallographic
structure relational expression f5 is in a range of f5<2, the
metallographic structure relational expression f6 is in a range of
25.ltoreq.f6.ltoreq.76, the metallographic structure and
composition relational expression f6A is in a range of
40.ltoreq.f6A, and a compound including P is present in .beta.
phase.
[0102] A free-cutting copper alloy casting according to the third
embodiment of the present invention includes: higher than 59.5 mass
% and lower than 64.5 mass % Cu; higher than 0.60 mass % and lower
than 1.30 mass % Si; higher than 0.010 mass % and lower than 0.15
mass % Pb; higher than 0.020 mass % and lower than 0.14 mass % P;
and higher than 0.020 mass % and lower than or equal to 0.100 mass
% Bi, with the balance being Zn and inevitable impurities, in
which, among the inevitable impurities, the total content of Fe,
Mn, Co, and Cr is lower than 0.35 mass % and the total content of
Sn and Al is lower than 0.35 mass %, the aforementioned composition
relational expression f0 is in a range of 0.040.ltoreq.f0<0.18,
the composition relational expression f1 is in a range of
56.5.ltoreq.f1.ltoreq.59.0, the metallographic structure relational
expression f2 is in a range of 30.ltoreq.f2.ltoreq.70, the
metallographic structure relational expression f3 is in a range of
30.ltoreq.f3.ltoreq.70, the metallographic structure relational
expression f4 is in a range of 0.ltoreq.f4<2, the metallographic
structure relational expression f5 is in a range of f5<1, the
metallographic structure relational expression f6 is in a range of
30.ltoreq.f6.ltoreq.70, the metallographic structure and
composition relational expression f6A is in a range of
45.ltoreq.f6A, a compound including P is present in .beta. phase,
and a particle including Bi is present in .alpha. phase.
[0103] It should be noted here that, in a free-cutting copper alloy
casting according to any one of the first to third embodiments of
the present invention, it is preferable that a solidification
temperature range is 25.degree. C. or lower.
[0104] In addition, it is preferable that a free-cutting copper
alloy casting according to any one of the first to third
embodiments of the present invention has a Vickers hardness of 105
Hv or higher and an impact value obtained by a U-notch impact test
(an impact value measured by a U-notch impact test) is 25
J/cm.sup.2 or higher.
[0105] The reasons why the component composition, the composition
relational expressions f0 and f1, the metallographic structure
relational expressions f2, f3, f4, f5, and f6, the metallographic
structure and composition relational expression f6A, and the
metallographic structure are defined as described above are
explained below.
[0106] <Component Composition>
[0107] (Cu)
[0108] Cu is a main element of copper alloy castings according to
an embodiment of the present invention. In order to achieve the
object of the present invention, it is necessary to contain Cu in
an amount exceeding 58.5 mass % at least. When the Cu content is
58.5 mass % or lower, the proportion of .beta. phase exceeds 80%
although depending on the contents of Si, Zn, P, and Pb and the
production process, and as a result, a material made of such an
alloy has poor ductility and toughness. Accordingly, the lower
limit of the Cu content is higher than 58.5 mass %, preferably
higher than 59.0 mass %, more preferably higher than 59.5 mass %,
and still more preferably higher than 60.5 mass %.
[0109] On the other hand, when the Cu content is 65.0 mass % or
higher, the proportion of .beta. phase decreases and the proportion
of .gamma. phase increases although depending on the contents of
Si, Zn, P, and Pb and the production process. In some cases, .beta.
phase and/or other phases appear. As a result, excellent
machinability cannot be obtained. Also, the alloy's ductility and
toughness are poor. In addition, the solidification temperature
range having a close relationship with castability widens.
Accordingly, the Cu content is lower than 65.0 mass %, preferably
lower than 64.5 mass %, more preferably lower than 64.2 mass %, and
still more preferably lower than 64.0 mass %.
[0110] (Si)
[0111] Si is a main element of free-cutting copper alloy castings
according to an embodiment of the present invention and contributes
to formation of metallic phases such as K phase, .gamma. phase,
.beta. phase, .beta. phase, and phase. Si improves the
machinability, strength, wear resistance, and stress corrosion
cracking resistance, reduces the viscosity of the melt, improves
the fluidity of the melt, and improves the castability of the
free-cutting copper alloy castings. Regarding machinability, the
present inventors found out that .beta. phase formed by including
Cu, Zn, and Si in the above-described content ranges has excellent
machinability. Examples of representative .beta. phase having
excellent machinability include .beta. phase containing about 60
mass % Cu, about 1.3 mass % Si, and about 38.5 mass % Zn. In
addition, the present inventors also found out that .gamma. phase
formed by including Cu, Zn, and Si in the above-described content
ranges has excellent machinability if .beta. phase is present.
[0112] Examples of representative composition of .alpha. phase
include about 67 mass % Cu, about 0.8 mass % Si, and about 32 mass
% Zn. Although machinability of .alpha. phase contained in an alloy
having a composition within the range of an embodiment of the
present invention is also improved by including Si, the degree of
improvement brought by Si to .alpha. phase is far less than that
brought to .beta. phase.
[0113] In addition, due to inclusion of Si, .alpha. phase and
.beta. phase are strengthened by solid-solubilization, which in
turn strengthens the alloy and also affects its ductility and
toughness. When Si is included, the electrical conductivity of
alloy decreases, but the electrical conductivity is improved by
formation of .beta. phase.
[0114] In order for a copper alloy casting to obtain excellent
machinability and high strength, and improve fluidity of the melt
and castability, it is necessary to include Si in an amount
exceeding 0.40 mass %. The Si content is preferably higher than
0.50 mass %, more preferably higher than 0.60 mass %, and still
more preferably higher than 1.00 mass %.
[0115] When the Si content is higher than 0.40 mass %, preferably
higher than 0.50 mass %, and more preferably higher than 0.60 mass
%, even if the amount of Bi is small, Bi particles come to be
present in .alpha. phase. Further, when a large amount of Si is
included, the number of Bi particles present in .alpha. phase
increases. As a result, Bi that is said to have a lower effect on
machinability than Pb can be utilized more effectively.
[0116] On the other hand, when the Si content is excessive, the
amount .gamma. phase increases excessively. In some cases, .mu.
phase precipitates. .gamma. phase has lower ductility and toughness
than .beta. phase and deteriorates the ductility of copper alloy
castings. In particular, when the amount of .gamma. phase is
excessive, the thrust value in drilling increases. If the Si
content is increased, the electrical conductivity of alloy
deteriorates. In addition, although depending on the proportions of
Cu and Zn contained, when the Si content is excessively high, the
solidification temperature range is widened, and the castability is
deteriorated. In the embodiments, obtaining good strength,
toughness, and conductivity in addition to excellent castability is
also aimed at. Therefore, the upper limit of the Si content is
lower than 1.40 mass %, preferably lower than 1.35 mass %, more
preferably lower than 1.30 mass %, and still more preferably lower
than 1.25 mass %. Although depending on the production process and
the Cu concentration, when the Si content is lower than about 1.3
mass %, the amount of .gamma. phase is lower than about 2%.
However, by appropriately increasing the proportion of .beta.
phase, excellent machinability can be maintained, and high strength
and excellent toughness can be obtained.
[0117] When a Cu--Zn binary alloy as a base alloy includes third
and fourth elements and the contents of the third and fourth
elements increase or decrease, the properties and characteristics
of .beta. phase change. As described in Patent Documents 2 to 6,
.beta. phase present in an alloy including higher than or equal to
about 69 mass % Cu, higher than or equal to about 2% Si, and Zn as
the balance does not have the same properties or characteristics as
.beta. phase formed in an alloy of an embodiment of the present
invention, for example, an alloy including about 63 mass % Cu,
about 1.2 mass % Si, and Zn as the balance. Further, when a large
amount of inevitable impurities are included, the characteristics
of .beta. phase also change. In some cases, properties including
machinability change for the worse. In the case of .gamma. phase
also, the characteristics of .gamma. phase to be formed change when
the amounts of main elements or the blending ratio between them are
changed. Also, when a large amount of inevitable impurities are
included, the characteristics of .gamma. phase change. Further,
even when the composition is the same, the kinds of phases that are
present, their amounts, the distribution of each element in each
phase change depending on the production conditions such as cooling
rate.
[0118] (Zn)
[0119] Like Cu and Si, Zn is a main element of free-cutting copper
alloy castings according to an embodiment of the present invention,
and is an element necessary to enhance machinability, strength,
high temperature properties, and castability. Zn is described as
the balance in the composition, but to be specific, its content is
lower than about 41 mass % and preferably lower than about 40 mass
% and higher than about 33 mass %, preferably higher than 34 mass
%.
[0120] (P)
[0121] In a Cu--Zn--Si alloy comprising .alpha. phase and .beta.
phase, P is preferentially distributed in .beta. phase. First of
all, P can improve the machinability of .beta. phase including Si
by solid solubilizing in .beta. phase. Further, by containing P and
adjusting the production process, P-containing compounds having an
average diameter of 0.3 to 3 .mu.m are formed within .beta. phase.
Due to the compounds, in the case of turning, the three force
components--principal cutting force, feed force, and thrust force
decrease. In the case of drilling, the torque decreases among
others. The three force components during turning, the torque
during drilling, and the chip shape correlate to each other. The
smaller the three force components and the torque, the more broken
the chips get.
[0122] In addition, P has an action of reducing the size of crystal
grains of .alpha. phase, and the machinability of copper alloy
casting is improved by the action.
[0123] Basically, P-containing compounds are not formed at a
temperature higher than 530.degree. C. in the process of
solidification and cooling after casting. P is solid-solubilized
mainly in .beta. phase during cooling, and P-containing compounds
precipitate mainly in .beta. phase or at .alpha. phase boundary
between .beta. phase and .alpha. phase when cooled at a certain
critical cooling rate or one lower than that. P-containing
compounds rarely precipitate in .alpha. phase. When observed with a
metallographic microscope, precipitates including P appear to have
a small granular shape with an average particle size of about 0.5
to 3 .mu.m. .beta. phase including such precipitates can obtain
even more excellent machinability. P-containing compound hardly
affects the life of a cutting tool and does not substantially
impair the ductility or toughness of copper alloy casting. Compound
composed of Fe, Mn, Cr or Co and Si or P contributes to improvement
of strength and wear resistance of copper alloy casting, but
consumes Si and P in the alloy, causes the cutting resistance of
the alloy to increase, deteriorates chip breakability, shortens the
tool life, and impairs ductility of the alloy.
[0124] In addition, when P is added together with Si, P also
exhibits an effect of facilitating the presence of Bi-containing
particles in .alpha. phase, contributing to the improvement of
.alpha. phase's machinability.
[0125] In order to exhibit the above-described effects, the lower
limit of the P content is higher than 0.003 mass %, preferably
higher than 0.010 mass %, more preferably higher than 0.020 mass %,
and still more preferably higher than 0.030 mass %. If P is
contained in an amount exceeding 0.010 mass %, P-containing
compounds become visible with a 500.times. metallographic
microscope. When the P content is higher than 0.020 mass %,
P-containing compounds can be more clearly observed.
[0126] On the other hand, when P is contained in an amount of 0.19
mass % or more, precipitates are enlarged and the machinability
improving effect of P is saturated. In addition, Si concentration
in .beta. phase is decreased causing machinability to deteriorate
rather than improve, and ductility and toughness are also
decreased. In addition, the solidification temperature range is
widened, and the castability is poor. Therefore, the P content is
lower than 0.19 mass %, preferably lower than 0.15 mass %, more
preferably lower than 0.14 mass %, and still more preferably lower
than 0.10 mass %. Even when the P content is lower than 0.05 mass
%, a sufficient amount of P-containing compounds are formed.
[0127] Incidentally, the component ratio in the composition of a
compound including, for instance, P or Si, gradually changes if the
amount of an element that easily combines with Si or P such as Mn,
Fe, Cr, or Co is increased. That is, P-containing compound having a
significant effect of improving the machinability of .beta. phase
gradually changes into a compound having a less effect on
machinability. Accordingly, at least the total content of Mn, Fe,
Cr, and Co needs to be limited to less than 0.45 mass %, preferably
less than 0.40 mass %, and more preferably less than 0.35 mass
%.
[0128] (Pb)
[0129] In embodiments of the present invention, machinability is
improved by .beta. phase including Si, P, and in which P-containing
compounds are present. Further, by including a small amount of Pb,
excellent machinability as a copper alloy casting can be achieved.
By causing Pb to be present in the form of fine Pb particle in the
metallographic structure where .beta. phase having excellent
machinability is present, Pb exhibits its effects of improving chip
breakability and reducing cutting resistance. In an alloy
composition according to an embodiment of the present invention,
about 0.001 mass % Pb is solid-solubilized in the matrix, and the
amount of Pb in excess of about 0.001 mass % is present in the form
of Pb particles having a diameter of about 0.1 to about 3 .mu.m.
When the Pb content is higher than 0.002 mass %, the effects are
exhibited. The Pb content is higher than 0.002 mass %, preferably
higher than 0.010 mass %, and more preferably higher than 0.020
mass %.
[0130] On the other hand, Pb is significantly effective as a means
for improving the machinability of copper alloy castings but is
harmful to human body and the environment. Therefore, the Pb
content is required to be lower than 0.25 mass %, preferably lower
than 0.20 mass %, more preferably lower than 0.15 mass %, and still
more preferably 0.10 mass % or lower.
[0131] (Bi)
[0132] About 0.001 mass % Bi is solid-solubilized in the matrix,
and the amount of Bi that exceeds about 0.001 mass % is present in
the form of particles having a diameter of about 0.1 to about 3
.mu.m. In embodiments of the present invention, the objective is to
obtain excellent machinability with the content of Pb, a substance
that is harmful to human body, limited to lower than 0.25 mass %,
preferably lower than 0.20 mass %, more preferably lower than 0.15
mass %, and still more preferably 0.10 mass % or lower. It is known
that Bi has a lower effect on machinability than Pb. However, it
was found that, by adding Bi together with Pb, Bi exhibits
substantially the same effect as Pb or, in some cases, higher
effect than Pb on machinability. When Bi is contained in the
presence of Pb, Pb and Bi are present together in most part, and
the effect of particles in which Pb and Bi are present together on
machinability is less impaired than that of Bi particles or Pb
particles. The influence of Bi on the environment and human body is
yet to be known at present but is presumed to be less than Pb.
Therefore, by reducing the Pb content by including Bi, the
influence on the environment and human body will be reduced. In
addition, in the embodiments, due to the action of Si, it is
possible to make particles containing Bi preferentially present in
.alpha. phase, and in turn, the machinability of .alpha. phase is
improved. This means the machinability of copper alloy casting can
be improved by a different means.
[0133] That is, if the number of particles including Bi that are
present in .alpha. phase increases, the machinability of .alpha.
phase is improved, and eventually, the effect of improving the
machinability by the particles including Bi comes to exceed the
machinability improvement effect of Pb particles. In a copper alloy
casting according to an embodiment of the present invention,
immediately after solidification, .alpha. phase is not present, and
the proportion of .beta. phase is 100%. As the temperature
decreases, specifically, in the process of cooling from about
850.degree. C. to about 600.degree. C., .alpha. phase precipitates
from .beta. phase. At this time, particles including Bi is a melt
(liquid). In the case of a Cu--Zn alloy not including Si, when
.alpha. phase precipitates, Bi particles are present either in
.beta. phase or at a boundary between .alpha. phase that has
precipitated and .beta. phase, and scarcely present in .alpha.
phase. On the other hand, as described above, when the Cu--Zn alloy
includes Si, particles including Bi are likely to be present in
.alpha. phase due to the action of Si.
[0134] Bi is included as an optional element and is not required to
be included. When Bi is included and its content is 0.001 mass % or
higher, the effect is exhibited due to the presence of Pb. Bi's
position is mainly a replacement for Pb. On the other hand, when
the Bi content exceeds 0.020 mass %, particles including Bi start
to be present in .alpha. phase, causing the machinability of
.alpha. phase to be improved, which further improves the
machinability of the alloy. In addition, the Bi content is
preferably 0.030 mass % or higher under harsh cutting conditions
such as (1) the cutting speed is high; (2) the feed rate is high;
(3) the cutting depth when turning is deep; and (4) the diameter of
a hole to drill is large. On the other hand, Bi has a
characteristic of embrittling copper alloy castings. The upper
limit of Bi is 0.100 mass % or lower and preferably 0.080 mass % or
lower in consideration of its influence on the environment and
human body and likely problems of deterioration in the ductility
and the toughness of copper alloy casting, and cracking that may
occur during production of the casting.
[0135] (Inevitable Impurities, in particular, Fe, Mn, Co, and Cr;
Sn and Al)
[0136] Examples of the inevitable impurities in an embodiment of
the present invention include Mn, Fe, Al, Ni, Mg, Se, Te, Sn, Co,
Ca, Zr, Cr, Ti, In, W, Mo, B, Ag, and rare earth elements.
[0137] Conventionally, a free-cutting copper alloy, in particular,
free-cutting brass including higher than or equal to about 30 mass
% Zn is not mainly formed of quality raw material such as
electrolytic copper or electrolytic zinc but is mainly formed of
recycled copper alloy. In preliminary steps (downstream step,
working step) in this field of art, machining is performed on
almost all the parts and components, during which a large amount of
copper alloy accounting for 40 to 80% of the material is disposed
of. Examples of such disposed copper alloy include chips, mill
ends, burrs, runners, and products having production defects. These
disposed copper alloys are the main raw material. If cutting chips,
mill ends, and the like are not properly separated, Pb, Fe, Mn, Si,
Se, Te, Sn, P, Sb, As, Bi, Ca, Al, Zr, Ni, and/or rare earth
elements mix in as part of a raw material from a leaded
free-cutting brass, a free-cutting copper alloy not containing Pb
but containing Bi or the like, a special brass alloy including Si,
Mn, Fe, and Al, or other copper alloys. In addition, cutting chips
include Fe, W, Co, Mo, and the like which originate from tools.
Wasted materials include plated products, and thus Ni, Cr, and Sn
mix in.
[0138] In addition, Mg, Sn, Fe, Cr, Ti, Co, In, Ni, Se, and Te are
mixed into pure copper-based scrap that is used instead of
electrolytic copper. Brass-based scraps that are used instead of
electrolytic copper or electrolytic zinc are often plated with Sn,
resulting in contamination by a high concentration of Sn.
[0139] From a viewpoint of reuse of resources and costs, scraps
including these elements are used as a raw material to the extent
that there is no bad influence on the properties at least. In a
leaded JIS free-cutting brass bar, C3604 (JIS H 3250), including
about 3 mass % Pb as an essential element, Fe may be contained up
to 0.5 mass % and Fe+Sn (the total content of Fe and Sn) may be
contained up to 1.0 mass % as impurities.
[0140] In a leaded JIS standard brass casting (JIS H 5120), about 2
mass % Pb is contained as an indispensable element, the upper
limits of the remaining components are 0.8 mass % for Fe, 1.0 mass
% or less for Sn, 0.5 mass % for Al, and 1.0 mass % or less for Ni.
Actually, some free-cutting brass bar and brass casting contain Fe,
Sn, Al, or Ni at a high concentration that is close to the upper
limit defined by JIS standards.
[0141] Fe, Mn, Co, and Cr are solid-solubilized in .alpha. phase,
.beta. phase, and .gamma. phase of a Cu--Zn alloy to a certain
concentration. However, if Si is present then, Fe, Mn, Co, and Cr
are likely to compound with Si. Fe, Mn, Co, and Cr may combine with
Si potentially resulting in consumption of Si, an element that is
effective for machinability. Fe, Mn, Co, or Cr that is compounded
with Si forms a Fe--Si compound, an Mn--Si compound, a Co--Si
compound, or a Cr--Si compound in the metallographic structure.
Since these intermetallic compounds are extremely hard, cutting
resistance increases, and the tool life decreases. In addition,
when the content of Fe, Mn, Co, or Cr is high, these elements can
be combined with P-containing compound, which may cause the
composition of the P-containing compound to change, and the
original function of P-containing compound may be impaired.
Therefore, the content of each of Fe, Mn, Co, and Cr is required to
be limited to preferably lower than 0.30 mass %, more preferably
lower than 0.20 mass %, and still more preferably 0.15 mass % or
lower. In particular, the total content of Fe, Mn, Co, and Cr is
required to be limited to lower than 0.45 mass %, preferably lower
than 0.40 mass %, more preferably lower than 0.35 mass %, and still
more preferably 0.25 mass % or lower.
[0142] On the other hand, Sn and Al mixed in from free-cutting
brass, plated waste products, or the like promote formation of
.gamma. phase in an alloy according to an embodiment of the present
invention, which is seemingly effective for machinability. However,
as the contents of Sn and Al increase, the inherent characteristics
of .gamma. phase comprising Cu, Zn, and Si gradually change. In
addition, larger amounts of Sn and Al are distributed in .beta.
phase than in .alpha. phase and gradually change characteristics of
.beta. phase. As a result, the alloy's ductility, toughness, or
machinability may deteriorate. Therefore, it is necessary to limit
the contents of Sn and Al, too. The Sn content is preferably lower
than 0.40 mass %, more preferably lower than 0.30 mass %, and still
more preferably 0.25 mass % or lower. The Al content is preferably
lower than 0.20 mass %, more preferably 0.15 mass % or lower, and
still more preferably 0.10 mass % or lower. In particular, from a
viewpoint of influence on machinability, ductility, and human body,
the total content of Sn and Al is required to be limited to lower
than 0.45 mass %, preferably to lower than 0.40 mass %, more
preferably to lower than 0.35 mass %, and still more preferably to
0.25 mass % or lower.
[0143] As other main inevitable impurity elements, empirically
speaking, in many cases, Ni often mixes in from scraps and the
like, but the influence on properties is less than that of Fe, Mn,
Sn and the like. The Ni content is preferably lower than 0.3 mass %
and more preferably lower than 0.2 mass %. It is not necessary to
particularly limit the content of Ag because Ag is commonly
considered as Cu and does not substantially affect various
properties of an alloy. Nevertheless, the Ag content is preferably
lower than 0.1 mass %. Te and Se themselves have free-cutting
characteristics, and contamination by a large amount of Te or Se
may occur although it is rare. In consideration of influence on
ductility or impact resistance, each content of Te and Se is
preferably lower than 0.2 mass %, more preferably 0.05 mass % or
lower, and still more preferably 0.02 mass % or lower. In addition,
corrosion-resistant brass includes As and/or Sb in order to improve
its corrosion resistance. In consideration of influence on
ductility and impact resistance, each content of As and Sb is
preferably lower than 0.05 mass % and 0.02 mass % or lower
respectively.
[0144] The content of each of Mg, Ca, Zr, Ti, In, W, Mo, B, and
rare earth elements as other elements is preferably lower than 0.05
mass %, more preferably lower than 0.03 mass %, and still more
preferably lower than 0.02.
[0145] Incidentally, the content of the rare earth elements refers
to the total content of one or more of the following elements: Sc,
Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, and
Lu.
[0146] Accordingly, the total content of the inevitable impurities
is preferably lower than 1.0 mass %, more preferably lower than 0.8
mass %, and still more preferably lower than 0.7 mass %.
[0147] (Composition Relational Expression f1)
f1=[Cu]-5.times.[Si]+
0.5.times.[Pb]+0.5.times.[Bi]-0.5.times.[P] Composition Relational
Expression
[0148] When Bi is not included, [Bi] in f1 is 0. Therefore, the
expression reads as follows:
f1=[Cu]-5.times.[Si]+0.5.times.[Pb]-0.5.times.[P].
[0149] The composition relational expression f1 is an expression
indicating a relationship between the composition and the
metallographic structure. Even when the amount of each of the
elements is in the above-described defined range, unless this
composition relational expression f1 is not satisfied, the
properties targeted in embodiments of the present invention cannot
be obtained. When f1 is lower than 56.0, the proportion of .beta.
phase increases, and the ductility and the toughness decline even
if the production process is modified. Accordingly, the lower limit
of f1 is 56.0 or higher, preferably 56.3 or higher, and more
preferably 56.5 or higher. As the composition becomes more
preferable within the defined range of f1, the proportion of
.alpha. phase increases, excellent machinability can be maintained,
and good impact resistance can be obtained.
[0150] On the other hand, the upper limit of the composition
relational expression f1 affects the proportion of .beta. phase or
the proportion of .gamma. phase. When the composition relational
expression f1 is higher than 59.5, the proportion of .beta. phase
decreases, and excellent machinability cannot be obtained. At the
same time, the proportion of .gamma. phase increases, the toughness
and the ductility decrease, and the strength also decreases. In
some cases, .beta. phase also appears. In addition, the upper limit
of f1 relates to castability, and when f1 exceeds the upper limit,
the number of defects present in the finally solidified portion
increases. Further, castability and the solidification temperature
range are closely related, and when the solidification temperature
range is wide, the castability deteriorates. When f1 exceeds the
upper limit, the solidification temperature range exceeds
25.degree. C., and the number of defects present in the finally
solidified portion increases. Accordingly, the upper limit of f1 is
59.5 or lower, preferably 59.2 or lower, more preferably 59.0 or
lower, and still more preferably 58.5 or lower. Although depending
on the composition or the process, as the value of f1 decreases,
the amount of .beta. phase increases, the machinability improves,
the strength increases, the solidification temperature range
narrows, and the castability improves.
[0151] Free-cutting copper alloy castings according to an
embodiment of the present invention have machinability, a property
that requires a kind of brittleness obtained by decreasing cutting
resistance so that finely broken chips are generated. The castings
also have toughness and ductility, properties that are completely
opposite to machinability. By discussing not only the composition
but also the composition relational expression f1, the
metallographic structure relational expressions f2 to f6 and the
metallographic structure and composition relational expression f6A,
which will be described later, in detail, an alloy more suitable
for intended purpose and use can be provided. Incidentally, Sn, Al,
Cr, Co, Fe, Mn, and inevitable impurities, that are separately
defined, are not defined by the composition relational expression
f1 because their influence on the composition relational expression
f1 is small if the content is within the range that can be treated
as inevitable impurities.
[0152] (Composition Relational Expression f0)
[0153] When Bi is included, expressions are defined as follows.
f0=[Pb]+[Bi] Composition Relational Expression
[0154] In terms of machinability improvement of a copper alloy
casting, Bi can be evaluated to have an effect equivalent to that
of Pb, and may be optionally included as a replacement for Pb. To
that end, f0 that is the sum of [Pb] and [Bi] is required to exceed
0.003. f0 is preferably 0.010 or higher, more preferably 0.020 or
higher, and still more preferably 0.040 or higher. In particular,
f0 is preferably 0.040 or higher and more preferably 0.050 or
higher under harsh cutting conditions such as (1) the cutting speed
is high; (2) the feed rate is high; (3) the cutting depth when
turning is deep; (4) the diameter of a hole to drill is large; and
(5) the drill depth is deep. At the same time, it is preferable
that the Bi content exceeds 0.020 mass % and particles including Bi
are present in .alpha. phase.
[0155] On the other hand, the influence of Bi on the environment or
human body is unclear at present. Even if a part of Pb is replaced
with Bi, f0 still needs to be lower than 0.25. f0 is preferably
lower than 0.20 and more preferably lower than 0.18. Even when the
total content of Pb and Bi is lower than 0.18 mass %, by satisfying
f1 and relational expressions f2 to f6 and f6A described below, a
copper alloy casting having excellent machinability can be
obtained.
[0156] (Comparison with Patent Documents)
[0157] Here, the results of comparison between the compositions of
the Cu--Zn--Si alloys described in Patent Documents 2 to 15 and the
compositions of copper alloy castings according to embodiments of
the present invention are shown in Tables 1 and 2.
[0158] The embodiments and the alloys disclosed by Patent Documents
2 to 10 are different from each other in the contents of Cu and Si,
the main elements of the alloys. In Patent Documents 2 to 10, a
large amount of Cu is required.
[0159] In Patent Documents 2 to 4, 6, 9, and 10, .beta. phase is
depicted as a metallic phase that is not preferable to be present
in a metallographic structure because it impairs machinability. In
the machinability relational expressions, .beta. phase is expressed
as a negative phase (.alpha. phase to which a negative coefficient
is allocated). It is also disclosed that when .beta. phase is
present, it is preferable that .beta. phase changes into .gamma.
phase having excellent machinability through heat treatment.
[0160] Patent Documents 4, 9, and 10, in which an allowable amount
of .beta. phase is described, disclose that the amount of .beta.
phase is 5% or less at the maximum.
[0161] In Patent Document 11, the content of each of Sn and Al is
at least 0.1 mass % or higher in order to improve dezincification
corrosion resistance, and large amounts of Pb and Bi are required
to be included in order to obtain excellent machinability.
[0162] Patent Document 12 discloses a copper alloy casting having
corrosion-resistance which requires higher than or equal to 65 mass
% Cu and has excellent mechanical characteristics and castability
achieved by including Si and a small amount of Al, Sb, Sn, Mn, Ni,
B, or the like.
[0163] Patent Document 13 discloses that P is not included.
[0164] Patent Document 14 discloses that Bi is not included, higher
than or equal to 0.20 mass % Sn is contained, the material is held
at a high temperature of 700.degree. C. to 850.degree. C., and
subsequently hot extrusion is performed.
[0165] In Patent Document 15, in order to improve dezincification
corrosion resistance, higher than or equal to 1.5 mass % Sn is
contained. In addition, in order to obtain machinability, a large
amount Bi is required.
[0166] Further, none of these Patent Documents disclose or imply
any of the essential requirements of the embodiments that are
.beta. phase including Si has excellent machinability, .beta. phase
is required in an amount at least 18% or higher, fine P-containing
compounds are present in .beta. phase, and particles containing Bi
are present in .alpha. phase which is the third embodiment of the
present invention.
TABLE-US-00001 TABLE 1 Cu Si P Pb Bi Sn Al Others First Embodiment
58.5-65.0 0.40-1.40 0.003-0.19 0.002-0.25 0.001-0.100 Sn + Al <
0.45, Fe + Mn + Cr + Co < 0.45 Optional Second Embodiment
59.0-65.0 0.50-1.35 0.010-0.15 0.010-0.20 0.001-0.100 Sn + Al <
0.40, Fe + Mn + Cr + Co < 0.40 Optional Third Embodiment
59.5-64.5 0.60-1.30 0.020-0.14 0.010-0.15 0.020-0.100 Sn + Al <
0.35, Fe + Mn + Cr + Co < 0.35 Patent Document 1 59.5-66.0 -- --
-- 0.5-2.0 0.7-2.5 -- -- Patent Document 2 69-79 2.0-4.0 0.02-0.25
-- 0.02-0.4 0.3-3.5 1.0-1.5 -- Patent Document 3 69-79 2.0-4.0
0.02-0.25 0.02-0.4 0.02-0.4 0.3-3.5 0.1-1.5 -- Patent Document 4
71.5-78.5 2.0-4.5 0.01-0.2 0.005-0.02 0.01-0.2 0.1-1.2 0.1-2.0 --
Patent Document 5 69-88 2-5 0.01-0.25 0.004-0.45 0.004-0.45 0.1-2.5
0.02-1.5 Zr: 0.0005-0.04 Patent Document 6 69-88 2-5 0.01-0.25
0.005-0.45 0.005-0.45 0.05-1.5 0.02-1.5 Zr: 0.0005-0.04 Patent
Document 7 74.5-76.5 3.0-3.5 0.04-0.10 0.01-0.25 0.01-0.4 0.05-0.2
0.05-0.2 Fe: 0.11-0.2 Patent Document 8 70-83 1-5 0.1 or less -- --
0.01-2 -- Fe, Co: 0.01-0.3 Ni: 0.01-0.3 Mn: 0.01-0.3 Patent
Document 9 73.5-79.5 2.5-3.7 0.015-0.2 0.003-0.25 0.003-0.30
0.03-1.0 0.03-1.5 -- Patent Document 10 75.4-78.0 3.05-3.55
0.05-0.13 0.005-0.070 0.005-0.10 0.05 or less 0.05 or less --
Patent Document 11 55-75 0.01-1.5 less than 0.15 0.01-4.0 0.01-4.0
0.1 or more 0.1 or more -- Patent Document 12 65-75 0.5-2.0 -- --
-- 0.01-0.55 0.1-1.0 -- Patent Document 13 -- 0.25-3.0 -- -- -- --
-- -- Patent Document 14 60.0-66.0 0.01-0.50 0.15 or less 0.05-0.50
-- 0.20-0.90 -- Fe: 0.60 or less Patent Document 15 61.0-63.0
0.05-0.30 0.04-0.15 0.01 or less 0.5-2.5 1.5-3.0 -- Sb:
0.02-0.10
TABLE-US-00002 TABLE 2 Metallographic Structure First 20 .ltoreq.
.alpha. .ltoreq. 80, 18 .ltoreq. .beta. .ltoreq. 80, 0 .ltoreq.
.gamma. < 5 Embodiment Second 25 .ltoreq. .alpha. .ltoreq. 75,
25 .ltoreq. .beta. .ltoreq. 75, 0 .ltoreq. .gamma. < 3
Embodiment Third 30 .ltoreq. .alpha. .ltoreq. 70, 30 .ltoreq.
.beta. .ltoreq. 70, 0 .ltoreq. .gamma. < 2 Embodiment Patent
.alpha. + .gamma. structure or .alpha. + .beta. + .gamma. structure
Document 1 Patent .gamma. phase, in some cases, .kappa. phase is
present. .beta. Document 2 phase is turned into .gamma. phase by
heat treatment. Patent .gamma. phase, in some cases, .kappa. phase
is present. .beta. Document 3 phase is turned into .gamma. phase by
heat treatment. Patent 18 - 500Pb .ltoreq. .kappa. + .gamma. +
0.3.mu. - .beta. .ltoreq. 56 + 500Pb, Document 4 0 .ltoreq. .beta.
.ltoreq. 5 Patent .alpha. + .kappa. + .gamma. .gtoreq. 80 Document
5 Patent .alpha. + .gamma. + .kappa. .gtoreq. 85, 5 .ltoreq.
.gamma. + .kappa. + 0.3.mu. - .beta. .ltoreq. 95 Document 6 Patent
-- Document 7 Patent -- Document 8 Patent 60 .ltoreq. .alpha.
.ltoreq. 84, 15 .ltoreq. .kappa. .ltoreq. 40, .beta. .ltoreq. 2,
etc. Document 9 Patent 29 .ltoreq. .kappa. .ltoreq. 60, .beta. = 0,
etc. .kappa. phase is present in .alpha. Document 10 phase. Patent
-- Document 11 Patent -- Document 12 Patent -- Document 13 Patent
-- Document 14 Patent -- Document 15
[0167] <Metallographic Structure>
[0168] In a Cu--Zn--Si alloy, 10 or more kinds of phases are
present, a complicated phase change occurs, and desired properties
cannot be necessarily obtained simply by satisfying the composition
ranges and the relational expressions of the elements. It was
empirically known that the metallographic structure of a Cu--Zn--Si
alloy casting is more deviated from an equilibrium state regarding
constitution of the phases that appear and the proportions of the
phases than that of a copper alloy subjected to hot working such as
hot extrusion. In addition, even if two castings are made of an
alloy having the same composition, the amounts of .beta. and
.gamma. phases significantly vary between them depending on the
cooling rate in the production process of castings. By specifying
and determining the kinds of metallic phases present in the
metallographic structure and their area ratio ranges, desired
properties can be obtained in the end. Accordingly, the following
metallographic structure relational expressions are defined.
20.ltoreq.(.alpha.).ltoreq.80,
18.ltoreq.(.beta.).ltoreq.80,
0.ltoreq.(.gamma.)<5,
f5=20.times.(.gamma.)/(.beta.)<4,
18.ltoreq.f6=(.gamma.).sup.1/2.times.3+(.beta.).times.(-0.5.times.[Si].s-
up.2+1.5.times.[Si]).ltoreq.82, and
[0169] (.gamma. Phase, Metallographic Structure Relational
Expression f4)
[0170] As described in Patent Documents 2 to 6, 9, and 10, .gamma.
phase is a phase that contributes most to machinability in a
Cu--Zn--Si alloy in which the Cu concentration is about 69 mass %
to about 80 mass % and the Si concentration is about 2 to 4 mass %.
In embodiments of the present invention also, .gamma. phase was
confirmed to be contributing to machinability. However, it is
necessary to reduce .gamma. phase in order to obtain a good balance
between ductility and strength. Specifically, when the proportion
of .gamma. phase is 5% or higher, excellent ductility or toughness
cannot be obtained. Even when the amount of .gamma. phase is small,
.gamma. phase exhibits an effect of improving chip breakability in
drilling. However, when a large amount of .gamma. phase is present,
thrust resistance value in drilling increases since .gamma. phase
is hard. Providing that .beta. phase is present at a proportion of
18% or higher (in terms of area ratio; hereinafter, the unit for
the amount of phase shall be area ratio), the effect of .gamma.
phase on machinability corresponds to the value obtained by raising
the amount of .gamma. phase to the power of 1/2. When a small
amount of .gamma. phase is included, .gamma. phase has a large
effect on improving machinability. However, when the amount of
.gamma. phase is increased, the effect of improving machinability
decreases. In consideration of ductility and cutting resistance in
drilling and turning, the amount of .gamma. phase needs to be lower
than 5%. The amount of .gamma. phase is preferably lower than 3%
and more preferably lower than 2%. When the amount of .gamma. phase
is lower than 2%, the influence on toughness is reduced. Even when
.gamma. phase is not present, that is, (.gamma.)=0, excellent
machinability can be obtained by causing .beta. phase including Si
to be present at a proportion described below and also causing the
alloy to contain Pb, and Bi as an optional element.
[0171] (.beta. phase, Metallographic Structure Relational
Expressions f3 and f5)
[0172] In order to obtain excellent machinability with an amount of
.gamma. phase less than those disclosed by the Patent Documents and
without .kappa. phase or .beta. phase, it is important to optimize
the Si content, the blending ratio between Cu and Zn, the amount of
.beta. phase, and the amount of Si solid-solubilized in .beta.
phase. Incidentally, it should be noted that .beta. phase includes
.beta.' phase.
[0173] .beta. phase of an alloy whose composition falls within a
composition range according to an embodiment of the present
invention has lower ductility than .alpha. phase, but has much
higher toughness and ductility than .gamma. phase, a phase whose
ductility and toughness are poor. Compared with .kappa. phase or
.mu. phase, it also has higher toughness and ductility.
Accordingly, from a viewpoint of toughness and ductility, a
relatively large amount of .beta. phase can be included. In
addition, .beta. phase can obtain excellent conductivity although
it includes high concentrations of Zn and Si. The amounts of .beta.
phase and .gamma. phase are significantly affected not only by the
composition but also by the process though.
[0174] In a Cu--Zn--Si--P--Pb alloy or a Cu--Zn--Si--P--Pb--Bi
alloy casting according to an embodiment of the present invention,
in order to obtain excellent machinability while minimizing the
content of Pb, .beta. phase is required in an amount of 18% or
higher at least, and also, the amount of .beta. phase needs to be
more than five times the amount of .gamma. phase in order to obtain
good ductility and high strength. That is, it is necessary to
satisfy f5=20.times.(.gamma.)/(.beta.)<4 (a converted form of
f5: 5.times.(.gamma.)<(.beta.)). The area ratio of .beta. phase
is preferably 25% or higher, more preferably 30% or higher. Even
when the amount of .gamma. phase is less than 3%, or further, less
than 2%, excellent machinability can be obtained. When the amount
of .gamma. phase is less than 3%, or further, less than 2% and the
amount of .beta. phase is more than 10 times, or further, 20 times
the amount of .gamma. phase, better ductility and toughness as well
as high strength can be obtained. That is, it is necessary to
satisfy f5=20.times.(.gamma.)/(.beta.)<2 (when f5 is converted,
10.times.(.gamma.)<(.beta.) or
f5=20.times.(.gamma.)/(.beta.)<1. When the amount of .gamma.
phase is 0%, the amount of .beta. phase is preferably 25% or
higher, more preferably 30% or higher, and still more preferably
40% or higher. Even when the proportion of .beta. phase is about
50% and the proportion of .alpha. phase, which is a phase having
low machinability, is about 50%, the machinability of the alloy is
maintained at a high level. In free-cutting copper alloy castings
according to an embodiment of the present invention, obtaining
excellent corrosion resistance or dezincification corrosion
resistance is not aimed at. It is true that the corrosion
resistance of .alpha. phase and .beta. phase is improved by solid
solubilization of Si in .alpha. phase and .beta. phase, and the
alloy castings exhibit better corrosion resistance than a
free-cutting brass C3604 or a brass for forging C3771 not including
Si and including .beta. phase. However, their corrosion resistance
level is not as high as that disclosed by the above-mentioned
Patent Documents.
[0175] When an alloy contains P, and the proportion of .gamma.
phase in the alloy is 0% or lower than 2%, and the amount of .beta.
phase is about 40% or higher, the alloy has the machinability of a
.beta. single-phase alloy in which P-containing compounds are
present. It is presumed that soft .alpha. phase functions as a
cushioning material around .beta. phase, or a phase boundary
between soft .alpha. phase and hard .beta. phase functions as an
origin of chip breakage. Even when the amount of .beta. phase is
about 40% to about 50%, excellent machinability, that is, low
cutting resistance is maintained, and chip breakability is improved
in some cases. However, when the amount of .beta. phase is reduced
to about 18% to about 30%, the characteristics of .alpha. phase
become predominant, and when the amount of .beta. phase is reduced
to about 25%, machinability starts to deteriorate.
[0176] On the other hand, .beta. phase has poorer ductility and
toughness than .alpha. phase. As the proportion of .beta. phase
decreases, ductility improves. In order to obtain excellent
ductility and improve the balance between strength, ductility, and
toughness, the proportion of .beta. phase is required to be 80% or
lower, preferably 75% or lower, and more preferably 70% or lower.
When toughness and ductility are important, the proportion of
.beta. phase is preferably 60% or lower. The appropriate proportion
of .beta. phase slightly varies depending on the intended purpose
of use and application.
[0177] .beta. phase has a characteristic in which ductility is
excellent at a high temperature. When a copper alloy casting
including Pb or Bi is cooled to a room temperature after
solidification, Pb or Bi is present in a molten state until the
casting's temperature reaches about 300.degree. C. Therefore,
cracking is likely to occur due to thermal strain or the like. In
particular, Bi has a significant influence. In that case, if soft
.beta. phase having excellent ductility at a high temperature is
present at a proportion of at least 18% or higher, preferably 25%
or higher, cracking sensitivity caused by Pb or Bi, a metal having
low melting point, can be reduced. Basically, the amount of .beta.
phase present is larger at a high temperature than at a normal
temperature. Therefore, the larger the amount of .beta. phase at a
normal temperature, the lower the cracking sensitivity during
casting.
[0178] (Si Concentration and Machinability of .beta. Phase)
[0179] In a composition range of an embodiment of the present
invention, the higher the Si content solid-solubilized in .beta.
phase, the better the machinability. As a result of diligent study
on the relationship between the Si concentration in the alloy, the
amount of .beta. phase, and the machinability of the alloy, it was
revealed that, when Si concentration (mass %) is represented by
[Si] for facility and convenience, the machinability of the alloy
is well expressed by multiplying the amount of .beta. phase by
(-0.5.times.[Si].sup.2+1.5.times.[Si]). That is, when two 13 phases
are compared, one containing Si at a higher concentration has
higher machinability. This means that, for example, an alloy whose
Si concentration is 1.0 mass % requires 1.08 times the amount of
.beta. phase contained in an alloy whose Si concentration is 1.2
mass %. It should be noted, however, that the machinability
improvement effect of .beta. phase is saturated when the Si
concentration in the alloy is between about 1.3 mass % and about
1.5 mass %. Once the Si concentration exceeds about 1.5 mass %, the
machinability of .beta. phase deteriorates rather than improves,
and the higher the Si concentration, the lower the machinability of
.beta. phase.
[0180] On the other hand, the Si concentration in .beta. phase
needs to exceed at least 0.5 mass % to exhibit an effect on
machinability. The Si concentration in .beta. phase is preferably
higher than 0.7 mass % and more preferably 1.0 mass % or higher.
When the Si concentration in .beta. phase is about 1.6 mass %, the
effect on machinability starts to be saturated. When the Si
concentration in .beta. phase exceeds about 1.8 mass %, .beta.
phase becomes harder and embrittled, and the machinability
improvement effect starts to disappear. Accordingly, the upper
limit of the Si concentration in 13 phase is 1.8 mass %.
[0181] (.beta. Phase, Metallographic Structure Relational
Expression f6)
[0182] In addition to the metallographic structure relational
expressions f3 to f5, in order to obtain comprehensively excellent
machinability, ductility, and strength, the metallographic
structure relational expression f6 is expressed by assigning
coefficients to the proportions of .gamma. phase and .beta. phase,
respectively. As described above, .gamma. phase has an excellent
effect on chip breakability in drilling even if its content is
small. Therefore, a coefficient of 3 is multiplied by the amount of
.gamma. phase raised to the power of 1/2. Regarding .beta. phase,
importance is placed on the Si concentration of the alloy.
Therefore, the amount of .beta. phase is multiplied by
(-0.5.times.[Si].sup.2+1.5.times.[Si]), then the value obtained by
multiplying a coefficient of 3 by the amount of .gamma. phase
raised to the power of 1/2 is added, which is expressed as the
metallographic structure relational expression f6 for obtaining
machinability. The metallographic structure relational expression
f6 is important, but does not come into effect unless the
afore-mentioned composition relational expressions f0 and f1 and
the metallographic structure relational expression f2 to f5 are
satisfied. The lower limit value of the metallographic structure
relational expression f6 for obtaining excellent machinability is
18 or higher, preferably 25 or higher, and more preferably 30 or
higher. When machinability is important, the lower limit value of
the metallographic structure relational expression f6 is preferably
40 or higher. On the other hand, in consideration of properties
such as toughness, ductility, or strength, the upper limit value of
the metallographic structure relational expression f6 is 82 or
lower, preferably 76 or lower, and more preferably 70 or lower.
[0183] Incidentally, in the expressions f0 to f6, .alpha. phase,
.beta. phase, .gamma. phase, .delta. phase, .epsilon. phase, .zeta.
phase, .eta. phase, .kappa. phase, .mu. phase, and .chi. phase are
the subject metallic phases, and intermetallic compounds excluding
P-containing compounds, Pb particles, oxides, non-metallic
inclusions, non-melted materials, and the like are not their
subjects. P-containing compounds are mostly present in .beta. phase
or at a boundary between .alpha. phase and .beta. phase. Therefore,
it is assumed that .beta. phase includes the P-containing compounds
present in .beta. phase or at a boundary between .alpha. phase and
.beta. phase. Should any P-containing compounds be present in
.alpha. phase although it is rare, it is assumed that such
compounds are included in .alpha. phase. On the other hand,
Intermetallic compounds that are formed by Si, P, and/or inevitably
mixed-in elements (for example, Fe, Mn, Co, and Cr) are outside the
scope of the calculation of the area ratios of metallic phases. In
embodiments of the present invention, precipitates and metallic
phases having a size that can be observed with a metallographic
microscope having a magnification power of 500.times. or
distinguished and recognized with a metallographic microscope
having a magnification power of about 1000.times. are the subjects
of the area ratio calculation. Accordingly, the minimum size of a
precipitate or metallic phase that can be observed is about 0.5
.mu.m. For example, .gamma. phase having a size of 0.1 to 0.4 .mu.m
that is less than about 0.5 .mu.m can be present in .beta. phase.
However, since such .gamma. phase cannot be recognized with a
metallographic microscope, it is regarded as .beta. phase.
[0184] (Metallographic Structure and Composition Relational
Expression f6A)
[0185] As a conditional expression for having an alloy obtain good
machinability, it is necessary to add the effects of Pb, Bi, and P
for improving machinability through their respective actions to the
metallographic structure relational expression f6. Under a
condition where P-containing compounds are present in .beta. phase
including Si, as the amount of P solid-solubilized in .beta. phase
increases, or as the amount of P-containing compounds increases,
the machinability improves, and when P-containing compounds begin
to be observed with a metallographic microscope, machinability
further improves. If Pb is contained, even if the content is very
small amount, machinability improves. Bi has substantially the same
effect as Pb, and when particles including Bi are present in
.alpha. phase, machinability further improves. As a result of
diligent study, it was found that the degree of machinability
improvement brought by Pb, Bi, and P has a deep relationship with
the value obtained by raising the Pb content, the total content of
Pb and Bi, or the P content to the power of 1/2. It is presumed
that, as described above, Bi has the same effect as Pb in a simple
term and can be represented by Pb+Bi. That is, Pb, Pb+Bi, or P
exhibits a significant effect even if the amount contained is very
small, and as the content increases, the effect of improving
machinability increases. However, the degree of the improvement
gradually becomes mild.
[0186] In summary, the Si concentration in .beta. phase, the amount
of .beta. phase, the amount of P solid-solubilized in .beta. phase,
the amount of P-containing compounds present in .beta. phase, the
content of Pb present as fine particles, and the content of Pb+Bi
effect improvement of the machinability of the alloy through their
respective actions. When all the requirements are satisfied, a
large effect of improving machinability is exhibited due to a
synergistic action, and the machinability of the copper alloy
casting is significantly improved by including Pb, Pb+Bi, or P even
if the amount contained is very small.
[0187] In the metallographic structure and composition relational
expression f6A, the value obtained by multiplying a coefficient of
38 by the Pb content or the content of Pb+Bi ([Pb] or [Pb]+[Bi])
raised to the power of 1/2 and the value obtained by multiplying a
coefficient of 15 by the P content (mass %, [P]) raised to the
power of 1/2 are added to f6, the effect representing the
machinability of .beta. phase. In order to obtain good
machinability, f6A is at least 33 or higher, preferably 40 or
higher, more preferably 45 or higher, and still more preferably 50
or higher. Even when the metallographic structure relational
expression f6 is satisfied, unless f6A in which the effects of Pb
or Pb+Bi and P are added is satisfied, good machinability cannot be
obtained. Incidentally, as long as the contents of Pb or Pb+Bi and
P are within the ranges defined by an embodiment of the present
invention, the influence on ductility or the like is not required
to be defined by f6A since it is defined by the upper limit of the
relational expression f6. Besides, even when the value of f6 is
relatively low, the machinability improves if the contents of Pb,
Pb+Bi, and/or P are increased. Further, under harsh cutting
conditions such as (1) the cutting speed is high, (2) the feed rate
is high, (3) the cutting depth when turning is deep, (4) the
diameter of a hole to drill is large, or (5) the drill depth is
deep, it is effective to increase the value of f6A. In particular,
it is preferable to increase the term Pb or Pb+Bi in f6A.
[0188] Incidentally, f6 and f6A are only applicable when each
element is within the concentration range defined by an embodiment
of the present invention and f0 to f5 are also satisfied.
[0189] (.alpha. phase, Metallographic Structure Relational
Expression f2)
[0190] .alpha. phase is a main phase forming the matrix together
with .beta. phase or .gamma. phase. .alpha. phase including Si
indicates higher machinability index than .alpha. phase without Si
but only by 3 to 10 percentage points. However, as the Si content
increases, machinability improves. When .beta. phase accounts for
100%, there is a problem in the ductility and the toughness of the
alloy. Therefore, an appropriate amount of .alpha. phase is
required. Even if a .beta. single-phase alloy comes to include a
relatively large amount of .alpha. phase, the machinability of the
.beta. single-phase alloy is maintained under appropriate
conditions. For example, even when .alpha. phase is contained at
about 50% in terms of area ratio, it is considered that .alpha.
phase itself functions as a cushioning material such that
boundaries between .alpha. phase and hard p phase become stress
concentration source during machining. As a result, chips are
broken, excellent machinability that a .beta. single-phase alloy
has is maintained, and machinability is improved in some cases.
[0191] As a result of a series of diligent study, it was found that
the amount of .alpha. phase is required to be 20% or higher,
preferably 25% or higher, more preferably 30% or higher, and still
more preferably 35% or higher considering the ductility, the
toughness, and the balance between ductility and strength of the
alloy. When toughness is important, it is preferable that .alpha.
phase is 40% or higher. On the other hand, in order to obtain good
machinability, the upper limit of the amount of .alpha. phase is
80% or lower, preferably 75% or lower, and more preferably 70% or
lower. When machinability is important, the amount of .alpha. phase
is preferably 60% or lower.
[0192] (.mu. Phase, .kappa. Phase, and Other Phases)
[0193] In order to obtain high ductility, toughness, and strength
together with excellent machinability, presence of phases other
than .alpha., .beta., and .gamma. phases is also important. In
embodiments of the present invention, considering the properties of
the alloy, .kappa. phase, .mu. phase, .delta. phase, .epsilon.
phase, .zeta. phase, or .eta. phase is not particularly required.
When the sum of the constituent phases (.alpha.), (.beta.),
(.gamma.), (.mu.), (.kappa.), (.delta.), (.epsilon.), (.zeta.), and
(.eta.) that form the metallographic structure is represented by
100, it is preferable that (.alpha.)+(.beta.)+(.gamma.)>99, and
it is most preferable that (.alpha.)+(.beta.)+(.gamma.)=100
providing that measurement error and number rounding (rounding off)
are disregarded.
[0194] (Presence of P-Containing Compound)
[0195] By including Si, the machinability of .beta. phase is
significantly improved, and the machinability is further improved
by including P and solid-solubilization of P in .beta. phase.
Further, by causing a compound formed with P having a particle size
of about 0.3 to about 3 .mu.m and Si and/or Zn to be present in
.beta. phase, the machinability of .beta. phase can be further
improved. Machinability of a .beta. single-phase alloy including
0.01 mass % Pb, 0.05 mass % P, and about 1 mass % Si is improved by
about 10% points if described simply in terms of machinability
index as compared to a .beta. single-phase alloy to which P is not
added by the presence of a sufficient amount of P-containing
compounds.
[0196] The machinability is also affected by the P content and the
amount and size of the P-containing compounds to be formed.
P-containing compound is a compound including P and at least either
or both of Si and Zn. In some cases, it can further includes Cu
and/or inevitable impurities such as Fe, Mn, Cr, or Co.
P-containing compounds are affected by inevitable impurities such
as Fe, Mn, Cr, or Co, too. When the concentration of the inevitable
impurities exceeds the afore-mentioned defined amount, the
composition of P-containing compound changes such that P-containing
compound may no longer contribute to improvement of
machinability.
[0197] Incidentally, P-containing compounds are not present in a
temperature range of about 550.degree. C. or higher in the process
of cooling after casting. They are formed at a temperature of lower
than 550.degree. C. during cooling at a critical cooling rate.
However, that is not necessarily the case when a large amount of
inevitable impurities are included because the configuration
(composition) of P-containing compound may change as described
above. As a result of diligent study, it was found that cooling is
preferably performed at a cooling rate of 55.degree. C./min or
lower in a temperature range from 530.degree. C. to 450.degree. C.
in the process of cooling after casting. The cooling rate in a
temperature range from 530.degree. C. to 450.degree. C. is more
preferably 50.degree. C./min or lower and still more preferably
45.degree. C./min or lower. On the other hand, when the cooling
rate is excessively low, P-containing compounds are likely to grow
bigger, which causes their effect on machinability to decrease. The
lower limit of the cooling rate in a temperature range from
530.degree. C. to 450.degree. C. is preferably 0.1.degree. C./min
or higher and more preferably 0.3.degree. C./min or higher. The
upper limit value of the cooling rate, 55.degree. C./min, varies to
some extent depending on the P content, and when the P content is
large, P-containing compounds are formed at a higher cooling
rate.
[0198] (Bi Particles (Particles including Bi) present in a
Phase)
[0199] The machinability of a .beta. single-phase alloy including
Si, and also, that of a .beta. single-phase alloy including P in
which P-containing compounds are present are similar to the level
of machinability of a free-cutting brass including 3 mass % Pb. In
embodiments of the present invention, .alpha. phase is included and
functions as a cushioning material between .beta. phases and as an
origin of chip breakage, and contributes to better chip
breakability. As a result, a copper alloy casting having excellent
machinability can be obtained even though the amount of Pb
contained is very small. Here, contribution of Bi included as an
optional element to machinability is slightly less than that of Pb.
Yet, when Bi particles are present in .alpha. phase, the
machinability is improved by a different action. That is, the
machinability of .alpha. phase is slightly improved by including
Si, but such an effect of Si is limited. By the presence of Bi
particles in .alpha. phase, the machinability of .alpha. phase
itself is improved. The more the number of Bi particles present in
.alpha. phase, the better the machinability of .alpha. phase, and
in turn the machinability of the alloy is improved.
[0200] Bi hardly solid-solubilizes in copper alloy and is present
as circular particles having a dimension of 0.3 .mu.m to 3 .mu.m
when observed with a metallographic microscope. Bi has a lower
melting point, a larger atomic number, and a larger atomic size
than those of Cu or brass, an alloy comprising Cu and Zn.
Therefore, in the case of a brass casting that does not include Si
but contain .beta. phase in an amount exceeding about 20%, Bi
particles are scarcely present in .alpha. phase. They are mainly
present at a phase boundary between .alpha. phase and .beta. phase,
and as the amount of .beta. phase increases, the amount of Bi
particles present in .beta. phase increases. In an embodiment of
the present invention, it was found that the number of Bi particles
present in .alpha. phase increases due to the action of Si on the
Cu--Zn alloy. The action becomes clear as the Si content increases
to higher than 0.40 mass %, higher than 0.50 mass %, and 0.70 mass
% or higher. Further, the number of Bi particles that are present
in .alpha. phase is increased by inclusion of P as well. It is
known that Bi has lower machinability than Pb. However, in
embodiments of the present invention, by causing Bi particles to be
present in .alpha. phase, the same level of effect on machinability
as Pb, or, in some cases, even a better effect than Pb can be
eventually obtained. When Bi and Pb are added together, Bi and Pb
coexist in many of the particles, but they exhibit substantially
the same effect on machinability as when Bi is included alone.
Incidentally, in order to increase the machinability of .alpha.
phase by increasing the number of Bi particles present in .alpha.
phase, it is preferable that Bi is included in an amount exceeding
0.020 mass %.
[0201] Here, FIGS. 1 to 3 show pictures of metallographic structure
of various alloys.
[0202] FIG. 1 is a picture showing a metallographic structure of
the alloy of Test No. T07. It is an alloy including 62.5 mass % Cu,
1.00 mass % Si, 0.063 mass % P, 0.016 mass % Pb, and Zn as the
balance (Alloy No. S02), and was produced under the conditions
where the cooling rate in a temperature range from 650.degree. C.
to 550.degree. C. after casting was 40.degree. C./min, the cooling
rate in a temperature range from 530.degree. C. to 450.degree. C.
was 30.degree. C./min, and the cooling rate in a temperature range
from 430.degree. C. to 350.degree. C. was 25.degree. C./min (Step
No. 1).
[0203] FIG. 2 is a picture showing a metallographic structure of
the alloy of Test No. T35 which contains 62.2 mass % Cu, 1.02 mass
% Si, 0.067 mass % P, 0.073 mass % Pb, 0.042 mass % Bi, and Zn as
the balance (Alloy No. S20). The casting of Test No. T35 was
produced under the conditions where the cooling rate in a
temperature range from 650.degree. C. to 550.degree. C. after
casting was 40.degree. C./min, the cooling rate in a temperature
range from 530.degree. C. to 450.degree. C. after casting was
30.degree. C./min, and the cooling rate in a temperature range from
430.degree. C. to 350.degree. C. after casting was 25.degree.
C./min (Step No. 1).
[0204] FIG. 3 is a picture showing a metallographic structure of
the alloy of Test No. T106 which contains 63.1 mass % Cu, 1.08 mass
% Si, 0.001 mass % P, 0.025 mass % Pb, and Zn as the balance (Alloy
No. S53). The casting of Test No. T106 was produced under the
conditions where the cooling rate in a temperature range from
650.degree. C. to 550.degree. C. after casting was 40.degree.
C./min, the cooling rate in a temperature range from 530.degree. C.
to 450.degree. C. was 30.degree. C./min, and the cooling rate in a
temperature range from 430.degree. C. to 350.degree. C. was
25.degree. C./min (Step No. 1).
[0205] The granular black precipitates having a size of about 0.5
to 3 .mu.m in FIG. 1 are P-containing compounds. From this figure,
it can be seen that a large amount of P-containing compounds are
present in .beta. phase. In FIG. 2, particles including Bi having a
dimension of about 1 .mu.m are observed in .alpha. phase, and
P-containing compounds are observed in .beta. phase.
[0206] On the other hand, FIG. 3 shows that P-containing compounds
are not observed with a metallographic microscope because the P
content is 0.001 mass %. In addition, since the P content is 0.001
mass %, .alpha. phase crystal grains are large.
[0207] (Content of Si Solid-Solubilized in .beta. Phase and
Machinability)
[0208] The contents of Cu, Zn, and Si in .alpha. phase, .beta.
phase, and .gamma. phase formed in an alloy having a composition
that falls within a composition range according to an embodiment of
the present invention roughly have the following relationships.
The Cu concentration: .alpha.>.beta..gtoreq..gamma..
The Zn concentration: .beta.>.gamma.>.alpha..
The Si concentration: .gamma.>.beta.>.alpha..
[0209] Regarding test samples "a" to "d" described below, the
concentrations of Cu, Zn, and Si in .alpha., .beta., and .gamma.
phases were quantitatively analyzed with an X-ray microanalyzer
using secondary electron images and compositional images of the
samples taken at a magnification of 2000.times.. The measurement
was performed using "JXA-8230" (manufactured by JEOL Ltd.) under
the conditions of acceleration voltage: 20 kV and current value:
3.0.times.10.sup.-8 A. The results are shown in Tables 3 to 6.
[0210] Test sample "a": an alloy including 63.1 mass % Cu, 1.18
mass % Si, 0.048 mass % P, and Zn as the balance, which is produced
under the conditions where the cooling rate in a temperature range
from 650.degree. C. to 550.degree. C. after casting was 40.degree.
C./min, the cooling rate in a temperature range from 530.degree. C.
to 450.degree. C. was 30.degree. C./min, and the cooling rate in a
temperature range from 430.degree. C. to 350.degree. C. was
25.degree. C./min (Step No. 1)
[0211] Test sample "b": an alloy including 63.1 mass % Cu, 1.18
mass % Si, 0.048 mass % P, and Zn as the balance, which is produced
under the conditions where the cooling rate in a temperature range
from 650.degree. C. to 550.degree. C. after casting was 40.degree.
C./min, the cooling rate in a temperature range from 530.degree. C.
to 450.degree. C. was 30.degree. C./min, the cooling rate in a
temperature range from 430.degree. C. to 350.degree. C. was
25.degree. C./min. After being cooled to a room temperature, the
test sample was subjected to low-temperature annealing in which the
alloy was held at 350.degree. C. for 20 minutes (Step No. 8)
[0212] Test sample "c": an alloy including 61.4 mass % Cu, 0.81
mass % Si, 0.044 mass % P, and Zn as the balance, which is produced
under the conditions where the cooling rate in a temperature range
from 650.degree. C. to 550.degree. C. after casting was 40.degree.
C./min, the cooling rate in a temperature range from 530.degree. C.
to 450.degree. C. was 30.degree. C./min, and the cooling rate in a
temperature range from 430.degree. C. to 350.degree. C. was
25.degree. C./min (Step No. 1)
[0213] Test sample "d": an alloy including 62.8 mass % Cu, 0.98
mass % Si, 0.053 mass % P, and Zn as the balance, which is produced
under the conditions where the cooling rate in a temperature range
from 650.degree. C. to 550.degree. C. after casting was 40.degree.
C./min, the cooling rate in a temperature range from 530.degree. C.
to 450.degree. C. was 30.degree. C./min, and the cooling rate in a
temperature range from 430.degree. C. to 350.degree. C. was
25.degree. C./min (Step No. 1)
[0214] The concentration of the Si solid-solubilized in .beta.
phase is about 1.5 times that in .alpha. phase. That is, 1.5 times
the amount of Si in .alpha. phase is distributed in .beta. phase.
For example, when the Si concentration in the alloy is 1.15 mass %,
about 0.9 mass % Si is solid-solubilized in .alpha. phase, and
about 1.4 mass % Siis solid-solubilized in .beta. phase.
[0215] Incidentally, an alloy having a representative composition
of Patent Document 2, that is, 76 mass % Cu, 3.1 mass % Si, and Zn
as the balance, was prepared and analyzed with an X-ray
microanalyzer (EPMA). The result was that the composition of
.gamma. phase was 73 mass % Cu, 6 mass % Si, and 20.5 mass % Zn.
This composition of .gamma. phase is significantly different from
the composition of 60 mass % Cu, 3.5 mass % Si, and 36 mass % Zn,
which is the composition of .gamma. phase in an embodiment of the
present invention. Therefore, it is expected that characteristics
of the .gamma. phases of the alloys are also different.
TABLE-US-00003 TABLE 3 Test sample a: Alloy of Zn-63.1 mass %
Cu-1.18 mass % Si-0.048 mass % P (Step No. 1) Cu Zn Si .alpha.
phase 66.0 33.0 0.9 .beta. phase 60.0 38.5 1.5
TABLE-US-00004 TABLE 4 Test sample b: Alloy of Zn-63.1 mass %
Cu-1.18 mass % Si-0.048 mass % P (Step No. 8) Cu Zn Si .alpha.
phase 65.5 33.0 0.9 .beta. phase 60.0 38.5 1.4 .gamma. phase 60.0
36.0 3.5
TABLE-US-00005 TABLE 5 Test sample c: Alloy of Zn-61.4 mass %
Cu-0.81 mass % Si-0.044 mass % P (Step No. 1) Cu Zn Si .alpha.
phase 64.0 35.0 0.6 .beta. phase 58.5 40.0 1.0
TABLE-US-00006 TABLE 6 Test sample d: Alloy of Zn-62.8 mass %
Cu-0.98 mass % Si-0.053 mass % P (Step No. 1) Cu Zn Si .alpha.
phase 65.0 34.0 0.8 .beta. phase 60.0 38.5 1.3
[0216] (Machinability Index)
[0217] In general, machinability of various copper alloys is
expressed by numerical value (%) by comparison with a free-cutting
brass including 3 mass % Pb which is used as a standard, i.e., 100%
refers to the machinability of the standard alloy. Machinability of
copper alloys is described, for example, in "Basic and Industrial
Technique of Copper and Copper Alloy (Revised Edition)" (1994,
Japan Copper and Brass Association), p. 533, Table 1, and "Metals
Handbook TENTH EDITION Volume 2 Properties and Selection:
Nonferrous Alloys and Special-Purpose Materials" (1990, ASM
International), p. 217 to 228.
[0218] Alloys A to F in Tables 7 and 8 are alloys including 0.01
mass % Pb prepared in a laboratory by melting with an electric
furnace in the laboratory, pouring the melt into a casting mold
having an inner diameter of 100 mm and a depth of 200 mm, then
hot-extruding to .phi.22 mm using an extrusion test machine in the
laboratory. Alloys G to I are alloy castings including 0.01 mass %
Pb that were produced in a laboratory. In the case of Cu--Zn binary
alloys, containing a small amount of Pb hardly affects the
machinability of the alloy. Therefore, 0.01 mass % Pb, which falls
within a component range according to an embodiment of the present
invention, was added to each of the alloys. The hot extrusion
temperature of Alloys A and D was 750.degree. C., and the hot
extrusion temperature of the other alloys, Alloys B, C, E, and F,
was 635.degree. C. After the extrusion, a heat treatment was
performed at 500.degree. C. for 2 hours to adjust the
metallographic structure. Alloys G and H are alloys including 0.01
mass % Pb and were obtained by casting the melt at 1000.degree. C.
into a metal mold having an inner diameter of 35 mm and a depth of
200 mm after melting. The castings of these alloys were prepared by
taking out the alloys from the mold in the course of cooling when
the alloys were at about 700.degree. C., cooling to 350.degree. C.
under the conditions where the average cooling rate in a
temperature range from 650.degree. C. to 550.degree. C. was
40.degree. C./min, the average cooling rate in a temperature range
from 530.degree. C. to 450.degree. C. was 30.degree. C./min, and
the average cooling rate in a temperature range from 430.degree. C.
to 350.degree. C. was 25.degree. C./min, and subsequently,
air-cooling at an average cooling rate of 20.degree. C./min. The
turning and drilling tests described below were performed to find
out the machinability of the castings. A commercially available
free-cutting brass, C3604 (comprising 59 mass % Cu, 3 mass % Pb,
0.2 mass % Fe, 0.3 mass % Sn, and Zn as the balance) was used as
the standard free-cutting brass material.
TABLE-US-00007 TABLE 7 Metallo- Component Composition graphic (mass
%) Structure (%) Material Cu Zn Si Pb P .alpha. .beta. Alloy A
.alpha. brass 65.0 35.0 0.0 0.01 0 100 0 Alloy B 50% .beta. brass
58.1 41.9 0.0 0.01 0 52 48 Alloy C .beta. brass 54.0 46.0 0.0 0.01
0 0 100 Alloy D .alpha. brass with 69.1 30.0 0.88 0.01 0 100 0 0.9
Si Alloy E .beta. brass with 59.8 38.8 1.3 0.01 0 0 100 1.3 Si
Alloy F .beta. brass with 59.6 39.0 1.3 0.01 0.05 0 100 P + 1.3 Si
Alloy G .beta. brass 59.9 38.7 1.3 0.01 0 0 100 casting with 1.3 Si
Alloy H .beta. brass 59.8 38.8 1.3 0.01 0.05 0 100 casting with P +
1.3 Si Alloy I .beta. brass 58.6 40.3 1.0 0.01 0.05 0 100 casting
with P + 1.0 Si
TABLE-US-00008 TABLE 8 Machin- Turning Hole Drilling ability
Cutting Cutting Resistance Overall Resistance Overall Torque Thrust
(%) (%) Chips (%) (%) (%) Chips Alloy A 31 33 x 28 26 30 x Alloy B
44 39 x 49 46 52 x Alloy C 51 41 x 61 53 68 x Alloy D 38 39 x 36 33
39 x Alloy E 75 79 .DELTA. 71 65 76 .DELTA. Alloy F 85 93 76 74 77
Alloy G 75 78 .DELTA. 71 64 77 .DELTA. Alloy H 84 92 76 73 78 Alloy
I 81 88 74 72 76
[0219] The above-mentioned Patent Documents describe that the
machinability index of an .alpha. single-phase brass comprising 70%
Cu and 30% Zn is 30%. In an embodiment of the present invention, as
shown in Tables 7 and 8, the machinability of an alloy comprising
65% Cu and 35% Zn, which is also an .alpha. single-phase brass
(Alloy A), was 31%. In an .alpha. single-phase brass in which the
contents of Cu and Zn were adjusted and the Si content was about
0.9 mass %, that is, an .alpha. single-phase brass in which 0.9
mass % Si was solid-solubilized in .alpha. phase (Alloy D), the
machinability index was about 7% points higher compared with an
.alpha. brass not including Si. Chips of Alloys A and D generated
in the turning and drilling tests were both continuous.
[0220] In turning, the force applied to the blade (bite) can be
decomposed into a principal cutting force, a feed force, and a
thrust force, and their combined force (three force components) was
regarded as cutting resistance. In the case of drilling, the force
applied to the drill was decomposed into torque and thrust, and
their average values are shown in the "Overall" column in the "Hole
Drilling" section. Further, cutting resistance during turning and
that during drilling were averaged and the resultant values are
shown in the "Overall" column in the "Machinability" section as
overall machinability index (evaluation).
[0221] The "Cutting Resistance" in the "Turning" section in Table 8
corresponds to the combined force (machinability index) in the
description of Examples. The "Torque", the "Thrust", and the
"Overall" in the "Drilling" section in Table 8 correspond to the
torque index, the thrust index, and the drill index that appear in
the description of Examples, respectively. The evaluation criteria
applied to the evaluation of chips are the same as those applied to
the Examples.
[0222] In a .beta. single-phase brass in which the contents of Cu
and Zn were adjusted and Si was not included (Alloy C comprising
54% Cu and 46% Zn), the "overall" machinability index improved
about 20% points compared with .alpha. phase not including Si
(Alloy A). Yet, there was little improvement in chip shape, and the
chip evaluation remained the same. In a .beta.-phase alloy
including 1.3 mass % Si (Alloy E), the "overall" machinability
index was improved by about 24% points as compared to a .beta.
single-phase brass not including Si (Alloy C). Chips generated
during turning and drilling were slightly improved and were broken,
but the difference from those of a free-cutting brass including 3
mass % Pb was large.
[0223] In a .beta. single-phase alloy including 0.05 mass % P and
about 1.3 mass % Si (Alloy F), the machinability "overall" index
was improved by about 10% points as compared to a .beta.
single-phase brass including about 1.3 mass % Si without including
P (Alloy E). Presence of P improved turning performance by about
14% points and the torque during drilling by about 9% points. The
improvement of cutting resistance in turning and that of torque in
drilling are related to chip shape, and by including 0.05 mass % P,
the evaluation results of the chip shape in both the turning test
and the drilling test were improved from "L\" to "0". The
difference in the resistance during turning became very small
compared with a free-cutting brass including 3 mass % Pb, and chips
produced during turning and drilling remarkably improved as well.
According to Tables 7 and 8, whether extruded or cast did not make
a significant difference in the machinability of .beta.
single-phase test samples (between Alloys E and G and between
Alloys F and H). Based on this result, it should be safe to
consider that extruded material and cast material have equivalent
machinability.
[0224] Incidentally, cutting resistance is affected by the alloy's
strength, and the higher the strength, the higher the cutting
resistance when compared between hot extruded materials. .beta.
single-phase brasses and alloys according to an embodiment of the
present invention have higher strength than a free-cutting brass
including 3 mass % Pb. If the difference in strength is taken into
consideration, it can be said that the machinability of a .beta.
single-phase alloy including 1.3 mass % Si and 0.05 mass % P is
largely equivalent to the machinability of a free-cutting brass
including about 3 mass % Pb.
[0225] Tables 3 to 8 show that Alloys H and F, both of which are
.beta. single-phase brass, correspond to .beta. phase of a
free-cutting copper alloy casting according to an embodiment of the
present invention, and Alloy D corresponds to its .alpha. phase. A
free-cutting copper alloy casting according to an embodiment of the
present invention is formed of .beta. phase having machinability
that is comparable to that of a free-cutting brass including 3 mass
% Pb (Alloys H and F) and .alpha. phase in which the machinability
is improved by including Si (Alloy D). In a representative copper
alloy casting according to an embodiment of the present invention,
the proportion of .beta. phase is about 50%, the machinability of
the .beta. single-phase alloys, Alloys H and F, can be
substantially maintained, and this machinability is comparable to
that of a leaded free-cutting brass.
[0226] Alloy I is a .beta. single-phase alloy casting including P,
0.01 mass % Pb, and 1.0 mass % Si. The large difference between
Alloy I and Alloy H is the Si content. Even though the Si content
is reduced from 1.3 mass % to 1.0 mass %, Alloy I maintains a high
machinability index, and good chip breakability is also
secured.
[0227] Regarding a hot extruded material, Alloy B is a brass
including 0.01 mass % Pb and not including Si or P, in which the
proportion of .beta. phase is 48%. Reading Alloy B as a casting
based on the previous description, Alloy B has improved cutting
resistance both in turning and drilling compared with an .alpha.
single-phase brass (Alloy A). However, the cutting resistance is
higher than that of a 3 single-phase brass (Alloy C), and the
"overall" machinability evaluation is 44%. This "overall"
machinability evaluation is approximately 35% points lower than the
"overall" machinability evaluation of a free-cutting copper alloy
casting according to an embodiment of the present invention having
the same proportion of .beta. phase, and the chip shape of Alloy B
is totally different from that of a free-cutting copper alloy
casting according to an embodiment of the present invention. The
brass including 48% .beta. phase without including Si or P can
never be a replacement for a free-cutting brass including 3 mass %
Pb considering its cutting resistance and the chip shape.
[0228] A copper alloy casting according to an embodiment of the
present invention includes P-containing compounds in .beta. phase,
and has excellent machinability which can be obtained by containing
0.5 to 1.7 mass % Si in its 13 phase as shown in Tables 3 to 8.
[0229] <Properties>
[0230] (Strength, Toughness, Ductility)
[0231] In general, component segregation is more likely to occur to
a casting than to a material subjected to hot working, for example,
a hot extruded bar. Casting has larger crystal grains and some
micro defects. Therefore, casting is said to be "brittle" or
"weak", and is desired to have a high impact value in the
evaluation of toughness and ductility. On the other hand, it is
said that some kind of brittleness is necessary for a material
having excellent chip breakability during cutting. Impact
resistance is a property contrary to machinability in some
aspect.
[0232] There is a strong demand for reduction in the thickness and
weight of parts and components that are the target applications of
embodiments of the present invention such as mechanical parts. Of
course, they need to have excellent toughness and ductility.
Strength of casting relates to the Si content solid-solubilized in
.beta. phase and .alpha. phase, and a high strength can be obtained
by containing Si in an amount of at least about 0.5 mass % or
higher in .beta. phase. In a casting, as described above, component
segregation or micro defects are likely to occur, and it is
difficult to appropriately evaluate the strength. In embodiments of
the present invention, as a method for evaluating the strength,
hardness (Vickers hardness) is adopted, and for the evaluation of
toughness and ductility, impact test value (U-notch) is
adopted.
[0233] Cold working is rarely performed on a casting except for a
continuously cast bar. In order for a copper alloy casting to be
regarded as having a high strength, it is preferable that it has a
Vickers hardness of at least 105 Hv or higher. The Vickers hardness
is more preferably 120 Hv or higher. Hardness and tensile strength
have a correlation with each other. In embodiments of the present
invention, a Vickers hardness of 105 Hv corresponds to a tensile
strength of about 420 N/mm.sup.2, and a Vickers hardness of 120 Hv
corresponds to a tensile strength of about 450 N/mm.sup.2.
[0234] When a casting is used as a material for various components,
for example, mechanical components, automobile components, drinking
water supply devices such as valves or joints, metal fittings of
faucet, or those of industrial plumbing, as described above, the
casting needs to be a material not only having a high strength but
also having toughness that can resist to impact. To that end, when
a Charpy impact test is performed using a U-notched specimen, the
casting preferably has a Charpy impact test value of 25 J/cm.sup.2
or higher, more preferably 30 J/cm.sup.2 or higher, and still more
preferably 35 J/cm.sup.2 or higher. On the other hand, when the
Charpy impact test value is higher than 90 J/cm.sup.2 or 80
J/cm.sup.2, for example, so-called viscosity of the material
increases, causing the cutting resistance to increase and resulting
in deterioration in machinability which is demonstrated by, for
example, generation of continuous chips.
[0235] (Electrical Conductivity)
[0236] Applications of embodiments of the present invention include
electrical or electronic apparatus components, components of
automobile, an increasing number of models of which are
electric-powered, and other parts and components requiring high
electrical conductivity. Currently, phosphor bronzes including 6
mass % or 8 mass % Sn (JIS Standard Nos., C5191, C5210) are widely
used for these applications, and their electrical conductivities
are about 14% IACS and 12% IACS, respectively. Accordingly, there
is no serious problem related to electric conductivity as long as
the electrical conductivity is 13% IACS or higher. The electrical
conductivity is preferably 14% IACS or higher. That copper alloys
according to an embodiment of the present invention exhibit
electrical conductivity of 13% IACS or higher despite inclusion of
over 1 mass % Si, an element that deteriorates electrical
conductivity, and higher than or equal to about 33 mass % Zn, is
influenced by the amount of .beta. phase in the alloy and Si
solid-solubilized in the .beta. phase.
[0237] From the above-stated results of studies, the following
findings were obtained.
[0238] First, in the conventional art, it was known that .mu. phase
formed in a Cu--Zn--Si alloy has no effect on the machinability of
an alloy or has a negative effect on the machinability. However, as
a result of diligent study, the present inventors have ascertained
that 13 phase comprising, for example, about 1.3 mass % Si, about
60 mass % Cu, and about 38.5 mass % Zn, has excellent
machinability.
[0239] Secondly, it was found that, in order to further improve the
machinability of .beta. phase of a Cu--Zn--Si alloy, if P is added
and have a P-containing compound having a particle size of about
0.3 to about 3 .mu.m, for example, P--Si, P--Si--Zn, P--Zn, or
P--Zn--Cu exist in 13 phase, the cutting resistance further
decreases to lower than that of an alloy in which no P-containing
compound is present, and at the same time, the chip breakability
significantly improves.
[0240] Thirdly, it was ascertained that .gamma. phase formed in a
copper alloy casting according to an embodiment of the present
invention has an effect on chip breakability. The free-cutting
copper alloys of the Patent Documents have compositions different
than that of a free-cutting copper alloy casting according to an
embodiment of the present invention. Even though the copper alloys
of the Patent Documents and free-cutting copper alloy castings
according to an embodiment of the present invention both have
.gamma. phase, if their compositions are different, a large
difference is exhibited in machinability similarly to .beta. phase
as described above. It was also found that .gamma. phase present in
an alloy having a composition of an embodiment of the present
invention has excellent machinability. It was revealed that
free-cutting copper alloy castings of an embodiment of the present
invention has excellent machinability, in particular, chip
breakability of .gamma. phase during drilling among others, even
though the contents of Cu and Si are low. However, since .gamma.
phase hinders ductility and toughness, it was necessary to limit
its amount. It was found that even if the amount of .gamma. phase
contained is small or .gamma. phase is not contained, excellent
machinability can be obtained by adjusting the proportions of
.alpha. phase and .beta. phase.
[0241] Fourthly, it was revealed that providing that Pb is not
solid-solubilized in .beta. phase in effect and is present in the
form of Pb particle even when its content is very small, Si is
contained in the above-described predetermined amount or more, and
.beta. phase including a compound of P is present, a significant
effect is exhibited on improvement of chip breakability and a
reduction in cutting resistance.
[0242] Fifthly, it was verified that Bi has a lower effect on
machinability than Pb but can be a replacement for Pb. When Si was
added in the predetermined amount or more, particles including Bi
started to be present in .alpha. phase, and as a result, the
machinability of .alpha. phase improved. It was found that the
effect of Bi in this case is equivalent to or higher than that of
Pb.
[0243] Sixthly, .beta. phase including Si has high strength but its
ductility and toughness are low. A material containing an excessive
amount of .beta. phase was not suitable as an industrial material.
In order to obtain a copper alloy having excellent toughness,
ductility and high strength while maintaining machinability such as
excellent chip breakability and low cutting resistance, the amounts
of .alpha. phase, .beta. phase, and .gamma. phase and the like have
been optimized. Further, in the case of casting, not only
machinability but also castability is important. Therefore, the
free-cutting copper alloy castings according to an embodiment of
the present invention was completed by verifying the relationship
between the contents of Cu and Si, solidification temperature
range, and castability and the relationship between solidification
temperature range and castability and optimizing the relationship
between the contents of Cu and Si and the metallographic structure
of the casting.
[0244] (Castability)
[0245] In the embodiments of the present invention, it is essential
to provide a sound casting. Therefore, they should not have any
cracks, and it is desired that the amount of micro defects is
small. Regarding cracking during casting, what primarily matters is
whether or not any metal whose melting point is low is present as a
melt after the alloy is solidified but its temperature is still
high, and when such a metal having a low melting point is present,
the amount of the metal and whether or not the matrix has ductility
under a high temperature are the factors that determine whether
cracking occurs. Cracking is less likely to occur during casting to
the embodiments of the present invention because the amount of low
melting point metal such as Pb or Bi present in the form of a melt
in the matrix is significantly limited in the processes of
solidification and cooling of the casting. Further, if the
composition and various relational expressions of the embodiments
are satisfied, the adverse effect of the low melting point metal
that is contained in a small amount can be covered since .beta.
phase having excellent ductility under a high temperature is
contained in a large amount. Therefore, there is no problem of
cracking during casting.
[0246] In the embodiments of the present invention, the challenge
as a casting is to minimize micro defects. Micro defects are likely
to occur in the portion that solidifies last. In most cases, the
finally solidified portion is contained in the portion composed of
additionally poured melt by a good casting plan. However, in some
cases, the finally solidified portion is partially present in the
main body of the casting, or, depending on the shape of the
casting, is present in the main body of the casting in its
entirety. Micro defect can be found through a Tatur Shrinkage Test
performed in a laboratory. It was found that, in the case of
castings according to an embodiment of the present invention, the
result of the Tatur Shrinkage Test, the contents of Cu and Si, the
composition relational expression f1, and the solidification
temperature range have a close relationship with each other.
[0247] It was found that, when the Cu content is 65.0 mass % or
higher or the Si content is 1.4 mass % or higher, micro defects in
the finally solidified portion increases and that, when the
composition relational expression f1 exceeds 59.5, the amount of
micro defects increases. When the solidification temperature range,
that is, (liquidus temperature-solidus temperature) exceeds
25.degree. C., shrinkage cavities and micro defects during casting
appear to a remarkable level, and a sound casting cannot be
obtained. The solidification temperature range is preferably
20.degree. C. or lower and more preferably 15.degree. C. or lower.
When the solidification temperature range is 15.degree. C. or
lower, sounder castings can be obtained. Solidification temperature
range cannot be read from a ternary phase diagram.
[0248] <Production Process>
[0249] Next, a method for producing free-cutting copper alloys
according to the first to third embodiments of the present
invention will be described.
[0250] The metallographic structure of a free-cutting copper alloy
according to an embodiment of the present invention varies not only
depending on the composition but also depending on the production
process. As a method for producing casting, there are various
casting methods such as die casting, metal mold casting, sand mold
casting (including a continuous casting), and lost-wax casting.
Depending on the thickness and shape of the casting and the
material, thickness and the like of the metal mold or the sand
mold, the cooling rate of a casting after it is solidified is
roughly determined. The cooling rate can be changed by modifying
the cooling method, heat retention, and the like. On the other
hand, in the process of cooling after solidification, various
changes occur in the metallographic structure, and the
metallographic structure significantly changes depending on the
cooling rate. A change in metallographic structure refers to a
significant change in the kinds and the amounts of the phases that
constitute the metallographic structure. As a result of diligent
study on the cooling process, it was found that the cooling rate in
a temperature range from 530.degree. C. to 450.degree. C. is most
important and significantly affects machinability among others.
[0251] (Melting)
[0252] Melting is performed at about 950.degree. C. to about
1200.degree. C., a temperature that is about 100.degree. C. to
about 300.degree. C. higher than the melting point (liquidus
temperature) of a free-cutting copper alloy casting according to an
embodiment of the present invention. The melt is then poured into a
predetermined casting mold when it is at about 900.degree. C. to
about 1100.degree. C., a temperature that is about 50.degree. C. to
about 200.degree. C. higher than the alloy's melting point. After
the alloy solidifies, constituent phases change in various
ways.
[0253] (Casting)
[0254] Using the above-mentioned production method, high-strength
free-cutting copper alloys according to the first and second
embodiments of the present invention are produced. The cooling rate
after casting and solidification varies depending on the weight and
the thickness of the cast copper alloy and the material of the sand
mold, the metal mold, or the like. For example, in general, when a
conventional copper alloy casting is produced by casting using a
metal mold made of a copper alloy or an iron alloy, the casting is
removed from the mold after casting when the temperature is at
about 700.degree. C. or lower and then is cooled by forced cooling,
air cooling, or slow cooling at an average cooling rate of about
5.degree. C./min to about 200.degree. C./min. On the other hand,
when a sand mold is used, although depending on the size of the
casting and the material and the size of the sand mold, the copper
alloy cast into the sand mold is cooled at an average cooling rate
of about 0.05.degree. C./min to about 30.degree. C./min.
[0255] In free-cutting copper alloy castings according to an
embodiment of the present invention, the metallographic structure
immediately after solidification after casting is composed solely
of .beta. phase when the casting is at a high temperature like
800.degree. C. During subsequent cooling, various phases such as
.alpha. phase, .gamma. phase, .kappa. phase, and .mu. phase are
produced and formed. For example, when the cooling rate in a
temperature range from 450.degree. C. to 800.degree. C. is high,
the amount of .beta. phase is large. When the cooling rate in a
temperature range below 450.degree. C. is low, .gamma. phase is
likely to be produced.
[0256] It is difficult to significantly change the cooling rate
because the casting plan, the shape of the casting, and the like
are fixed. Therefore, castings are cooled with the average cooling
rate in a temperature range from 530.degree. C. to 450.degree. C.
adjusted to 0.1.degree. C./min or higher and 55.degree. C./min or
lower. By doing so, P-containing compounds are formed and can be
observed with a metallographic microscope having a magnification
power of 500.times.. By the effect of these P-containing compounds,
the chip breakability is improved, and the cutting resistance is
significantly reduced.
[0257] If the copper alloy is cooled in a temperature range from
430.degree. C. to 350.degree. C. at an average cooling rate of
0.1.degree. C./min or higher and 10.degree. C./min or lower,
.gamma. phase can be produced, or the amount of .gamma. phase can
be increased. This is also relevant to the alloy's composition
though. As a result, the torque during drilling can be reduced, and
the chip breakability can be improved. However, attention must be
paid to the fact that when a large amount of .gamma. phase is
included, the cutting resistance increases rather than decreases
because .gamma. phase reduces the impact value.
[0258] (Heat Treatment)
[0259] In order to improve drilling workability by the presence of
a small amount of .gamma. phase and to remove the residual stress
of the casting, heat treatment is sometimes performed. To that end,
it is preferable that the heat treatment is performed at
250.degree. C. or higher and 430.degree. C. or lower for 5 to 200
minutes.
[0260] It is preferable that the annealing conditional expression
f7=(T-200).times.(t).sup.1/2 satisfies 300.ltoreq.f7.ltoreq.2000.
In f7, T represents the temperature (.degree. C.), and t represents
the heating time (min). When the annealing conditional expression
f7 is lower than 300, the removal of the residual stress may be
insufficient, or the production of .gamma. phase may be
insufficient. On the other hand, when the annealing conditional
expression f7 exceeds 2000, the machinability may decrease due to
an increase in the amount of .gamma. phase and a decrease in the
amount of .beta. phase.
[0261] Using the above-mentioned production method, free-cutting
copper alloy castings according to the first to third embodiments
of the present invention are produced.
[0262] In a free-cutting copper alloy casting according to any one
of the first to third embodiment of the present invention having
the above-described constitution, since the alloy's composition,
the composition relational expressions f0 and f1, the
metallographic structure, the metallographic structure relational
expressions f2 to f6, and the metallographic structure and
composition relational expression f6A are defined as described
above, even though the content of Pb is small, excellent
machinability can be obtained, and the casting is able to have
excellent castability, good strength, toughness, and ductility.
EXAMPLES
[0263] Hereinafter, the results of the experiments that were
performed to verify the effects of embodiments of the present
invention will be described. The following Examples are presented
for the purpose of explaining the effects of the embodiments. The
constituent requirements, the processes, and the conditions
contained in the description of the Examples do not limit technical
ranges of the embodiments.
[0264] In a laboratory, various components were mixed, then testing
was performed at varied cooling rates after casting. Tables 9 to 11
show the alloys' compositions. Table 12 shows production steps.
Regarding alloy composition, "MM" refers to mischmetal and
represents the total content of rare earth elements.
[0265] (Steps Nos. 1 to 7)
[0266] In a laboratory, raw materials mixed at a predetermined
component ratio were melted. In this melting step, inevitable
impurities such as Fe or Sn were intentionally added in
consideration of actual commercial production. In particular,
regarding Alloys Nos. S27 to S36, an increased amount of inevitable
impurities were added. The melt at about 1000.degree. C. was cast
into an iron mold having an inner diameter of 35 mm and a depth of
200 mm.
[0267] In consideration of actual casting, when the temperature of
the casting came down to about 700.degree. C., the test samples
were taken out of the mold and cooled to a room temperature by
natural cooling, thermal insulation, or forced cooling at seven
different average cooling rates in the temperature ranges from
650.degree. C. to 550.degree. C., from 530.degree. C. to
450.degree. C., and from 430.degree. C. to 350.degree. C. Table 12
shows a list of the cooling conditions. Regarding temperature
measurement, the temperature of the casting was taken using a
contact thermometer, and the average cooling rate in each of the
temperature ranges was adjusted to a predetermined value.
[0268] (Step No. 8)
[0269] Heat treatment was performed on the castings made of Alloys
Nos. S01, S20, and S21 under the conditions shown in Table 12.
[0270] The above-described test materials were evaluated for the
following items. The evaluation results are shown in Tables 13 to
20.
[0271] (Observation of Metallographic Structure)
[0272] The metallographic structure was observed using the
following method, then the area ratios (%) of the respective phases
such as .alpha. phase, .beta. phase, .gamma. phase, .kappa. phase,
and .mu. phase were measured by image analysis method. It was
assumed that .alpha.' phase, .beta.' phase, and .gamma.' phase were
included in .alpha. phase, .beta. phase, and .gamma. phase
respectively.
[0273] Each of the test piece of casting was cut parallel to its
long side. Next, the surface was polished (mirror-polished) and was
etched with a mixed solution of hydrogen peroxide and ammonia
water. For etching, an aqueous solution obtained by mixing 3 ml of
3 vol % hydrogen peroxide water and 22 ml of 14 vol % ammonia water
was used. At a room temperature of about 15.degree. C. to about
25.degree. C., the polished metal surface was dipped in the aqueous
solution for about 2 seconds to about 5 seconds.
[0274] The metallographic structure was observed with a
metallographic microscope at a magnification of 500.times. to
obtain the proportion of each of the phases and investigate whether
or not any P-containing compounds were present. Regarding test
samples containing Bi, locations of Bi particles were checked.
Depending on the state of the metallographic structure, metallic
phases, Bi particles, and P-containing compounds were observed at a
magnification of 1000.times.. In micrographs of five visual fields,
respective phases (.alpha. phase, .beta. phase, .gamma. phase,
.kappa. phase, and .mu. phase) were manually painted using image
processing software "Photoshop CC". Next, the micrographs were
binarized using image analysis software "WinROOF 2013" to obtain
area ratio of each of the phases. Specifically, proportion of each
of the phases was obtained by averaging area ratios of each phase
in the five visual fields. In this area ratio calculation, the
aggregate of the area ratio of each and every constituent phase
excluding oxides, sulfides, Bi particles, Pb particles,
precipitates (P-containing compounds are excluded), and
crystallized particles constitutes 100%.
[0275] Then P-containing compounds were observed. The minimum size
of a precipitated particle of a P-containing compound that can be
observed with a metallographic microscope at a magnification of
500.times. is about 0.5 .mu.m. Among precipitates which can be
observed with the metallographic microscope and distinguished and
recognized at a magnification of 1000.times., whether or not any
P-containing compounds were present was determined first in the
same manner as when the proportion of the phases were observed.
Although depending on the P content and the production conditions,
several to several hundreds of P-containing compounds were observed
in one visual field of the microscope. As most of the P-containing
compounds were present in .beta. phase or at aphase boundary
between .alpha. phase and .beta. phase, they were assumed to be
included in .beta. phase. Further, .gamma. phase having a size of
less than 0.5 .mu.m is sometimes present in .beta. phase. Phases
having a size of less than 0.5 .mu.m are unable to be identified
with a metallographic microscope having a magnification power of
500.times. or in some cases even with one having a magnification
power of 1000.times.. Therefore, in embodiments of the present
invention, ultrafine .gamma. phase was treated as .beta. phase.
When observed with a metallographic microscope, P-containing
compound appears blackish grey. Therefore, it is distinguishable
from a precipitate or a compound formed of Mn or Fe which has a
light blue color.
[0276] Incidentally, when a test sample containing P is etched with
an etching solution according to an embodiment of the present
invention, phase boundaries between .alpha. phase and .beta. phase
can be viewed clearly as shown in FIGS. 1 and 2. When the P content
is about 0.01 mass % or more, the boundaries can be observed more
clearly, indicating that inclusion of P causes metallographic
structure to change.
[0277] Bi particles were observed with a metallographic microscope
in the same manner as when P-containing compounds were observed. Bi
particles and P-containing compounds can be clearly distinguished
in the metallographic micrograph of FIG. 2. In particular,
P-containing compounds are scarcely present in .alpha. phase.
Therefore, the particles present in .alpha. phase are Bi particles.
When it was difficult to distinguish them from one another, an
electron microscope having an analytical function, for example,
EPMA was used for the determination. If Bi particles were found in
a .alpha. phase crystal grain in a micrograph, it was determined
that Bi particles were present in .alpha. phase, and the evaluation
was "O" (present). If Bi particles were present at a boundary
between .alpha. phase and .beta. phase, it was determined that Bi
particles were not present in .alpha. phase. If Bi particles were
not present in .alpha. phase, the evaluation was "X" (absent).
[0278] When it was difficult to identify phases, precipitates,
P-containing compounds, and Bi particles, they were identified by
an electron backscattering diffraction pattern (FE-SEM-EBSP) method
in which a field emission scanning electron microscope (FE-SEM)
(JSM-7000F, manufactured by JEOL Ltd.) equipped with its accessory
EDS was used, at a magnification of 500.times. or 2000.times. under
the conditions of an acceleration voltage of 15 kV and a current
value of 15 (set value). When no P-containing compound was observed
in a test sample containing P at the stage of observation using a
metallographic microscope, presence of P-containing compound was
checked at a magnification of 2000.times..
[0279] In addition, regarding some alloys, when the Si
concentration in .alpha. phase, .beta. phase, and .gamma. phase
(particularly the concentration in .beta. phase) was measured and
when it was difficult to determine the presence of P-containing
compound, or when Bi particles were small, quantitative analysis or
qualitative analysis was performed with an X-ray microanalyzer on a
secondary electron image and a compositional image taken at a
magnification of 2000.times.. The measurement was performed using
"JXA-8230" (manufactured by JEOL Ltd.) at an acceleration voltage
of 20 kV and a current value of 3.0.times.10.sup.-8 A.
[0280] If P-containing compounds were observed with a
metallographic microscope, the alloy was evaluated as "O" (good) in
terms of presence of P-containing compound. If no P-containing
compound was found unless observed at a magnification of
2000.times., the alloy was evaluated as ".DELTA." (fair) in terms
of presence of P-containing compound. If no P-containing compound
was found, the alloy was evaluated as "X" (poor) in terms of
presence of P-containing compound. Those evaluated as ".DELTA."
(fair) regarding presence of P-containing compound are also
acceptable in embodiments of the present invention. In the tables,
the evaluation results regarding presence of P-containing compounds
are shown in the "P Compound" row.
[0281] (Measurement of Melting Point and Castability Test)
[0282] The remainder of the melt used for the preparation of test
samples of casting was used. A thermocouple was put into the melt
to take liquidus temperature and solidus temperature, then the
solidification temperature range was obtained.
[0283] In addition, the melt at 1000.degree. C. was cast into an
iron Tatur mold, and whether or not any defects such as holes or
shrinkage cavities were present at the portion that solidified last
or in its vicinity was closely examined (Tatur Shrinkage Test).
[0284] Specifically, the casting was cut so that a vertical section
including the finally solidified portion as shown in the
illustration of a vertical section of FIG. 4 can be obtained. The
surface of the test sample was polished with Emery paper of up to
400 grit, then a macrostructure was exposed using nitric acid to
easily identify defective portions. Next, whether or not micro
defects were present was examined by a penetration test. FIG. 5
shows the macrostructure of the vertical section after a Tatur
Shrinkage Test was performed on Alloy No. 501.
[0285] Castability was evaluated as follows. When, in the vertical
section, a pattern indicating that the portion was defective
appeared in a location within 3 mm from the surface of the finally
solidified portion or its vicinity but no defect appeared anywhere
more than 3 mm away from the surface of the finally solidified
portion or its vicinity, castability was evaluated as "O" (good).
When a pattern indicating that the portion was defective appeared
in a location within 6 mm from the surface of the finally
solidified portion or its vicinity but no defect occurred anywhere
more than 6 mm away from the finally solidified portion or its
vicinity, castability was evaluated as ".DELTA." (acceptable or
fair). When any defect occurred in a location more than 6 mm away
from the surface of the finally solidified portion or its vicinity,
castability was evaluated as "X" (defective or poor).
[0286] The finally solidified portion is usually present in the
portion comprising additionally poured melt due to a good casting
plan, but sometimes it is partially present in the main body of the
casting. In the case of an alloy casting according to an embodiment
of the present invention, the result of the Tatur shrinkage test
and the solidification temperature range have a close relationship.
When the solidification temperature range was 15.degree. C. or
lower or 20.degree. C. or lower, castability was evaluated as "O"
in many cases. When the solidification temperature range exceeded
25.degree. C., castability was evaluated as "X" in many cases. When
the solidification temperature range was 25.degree. C. or lower,
castability was evaluated as either "O" or ".DELTA.". In addition,
when the content of inevitable impurities was large, the
solidification temperature range was wide, and the evaluation of
the castability was bad.
[0287] (Electrical Conductivity)
[0288] For the measurement of electrical conductivity, an
electrical conductivity measurement device (SIGMATEST D2.068,
manufactured by Foerster Japan Ltd.) was used. In this
specification, the terms "electric conductivity" and "electrical
conductivity" are meant to have the same meaning. In addition,
thermal conductivity and electrical conductivity are closely
corelated. Therefore, the higher the electrical conductivity, the
better the thermal conductivity.
[0289] (Mechanical Properties)
[0290] (Hardness)
[0291] The hardness of each of the test materials was measured
using a Vickers hardness tester with a load of 49 kN applied. To be
a casting having a high strength, its Vickers hardness is
preferably 105 Hv or higher and more preferably 120 Hv or higher.
It can be said that such a casting is regarded as having a very
high level of strength among free-cutting copper castings.
[0292] (Impact Resistance)
[0293] The impact test was performed using the following method. A
U-notched specimen (notch depth: 2 mm, notch bottom radius: 1 mm)
according to JIS Z 2242 was taken. Using an impact blade having a
radius of 2 mm, a Charpy impact test was performed to measure the
impact value.
[0294] <Machinability Test using Lathe>
[0295] Machinability was evaluated by the machining test using a
lathe as described below.
[0296] A casting was machined to prepare a test material having a
diameter of 14 mm. A carbide tool (chip) K10 not equipped with a
chip breaker was attached to a lathe. Using this lathe, the
circumference of the test material having a diameter of 14 mm was
machined on dry conditions with a rake angle of 0.degree., a nose
radius of 0.4 mm, a clearance angle of 6.degree., a cutting speed
of 40 m/min, a cutting depth of 1.0 mm, and a feed rate of 0.11
mm/rev.
[0297] Signals emitted from a dynamometer (AST tool dynamometer
AST-TL1003, manufactured by Mihodenki Co., Ltd.) composed of three
portions attached to the tool were converted into electrical
voltage signals and recorded on a recorder. Next, these signals
were converted into cutting resistance (principal cutting force,
feed force, thrust force, N). In the machining test, in order to
suppress influence from wear on the insert, each test sample was
measured four times by reciprocating A.fwdarw.B.fwdarw.C.fwdarw. .
. . C.fwdarw.B.fwdarw.A twice. The cutting resistance can be
obtained from the following expression.
Cutting Resistance (Combined Force comprising Principal
cutting force, Feed Force, and Thrust Force)=((Principal
Cutting Force).sup.2+(Feed Force).sup.2 (Thrust
Force).sup.2).sup.1/2
[0298] Incidentally, each sample was measured four times, and their
average value was adopted. Assuming that the cutting resistance of
a commercially available free-cutting brass bar, C3604, made of an
alloy including 59 mass % Cu, 3 mass % Pb, 0.2 mass % Fe, 0.3 mass
% Sn, and Zn as the balance was 100, the relative value of the
cutting resistance (machinability index) of each sample was
calculated for relative evaluation. The higher the machinability
index, the better the machinability. Incidentally, the "combined
force" indicated in the tables refers to the combined force
comprising a principal cutting force, a feed force, and a thrust
force, which represents the machinability index.
[0299] Further, machinability index was calculated as follows.
An index representing the results of the machining test
performed on a test sample (machinability index)=(cutting
resistance of C3604/cutting resistance of the test
sample).times.
100
[0300] Concurrently, chips were collected, and machinability was
evaluated based on the shape of the chips. Problems that occur in
actual machining are entanglement of chips around the tool and
bulking of chips. Therefore, regarding chip shape, if the average
length of the generated chips was less than 7 mm, it was evaluated
as "0" (good). If the average length of the generated chips was 7
mm or more and less than 20 mm, it was determined that machining
could be performed although there might be some practical problems
and evaluated as ".DELTA." (acceptable, fair). When the average
length of the generated chips was 20 mm or longer, it was evaluated
as "X" (poor). Chips generated at the beginning of machining were
excluded from the subject of the evaluation.
[0301] Cutting resistance of a material depends on the shear
strength and the tensile strength of the material, and there is a
tendency that the higher the strength of the material, the higher
the cutting resistance. In the case of a high strength material, if
the cutting resistance is approximately 40% points higher than that
of a free-cutting brass bar including 1 to 4 mass % Pb, the cutting
resistance is considered to be practically good. Therefore,
machinability of embodiments of the present invention was evaluated
providing that about 70 was the boundary machinability index
(boundary value). Specifically, when the machinability index was
higher than 70, the alloy was evaluated to have good machinability
(evaluation: "O"; good). When the machinability index was 65 or
higher and 70 or lower, the alloy was evaluated to have acceptable
machinability (evaluation: ".DELTA."; fair) and graded as a pass.
When the machinability index was lower than 65, the alloy was
evaluated to have unacceptable machinability (evaluation: "X";
poor) and graded as a fail.
[0302] When there is little difference in strength, there is a
correlation between chip shape and machinability index aside from
some exceptions. That is, if the machinability index of an alloy is
high, the alloy's chip breakability tends to be good, and this
correlation can be numerically expressed.
[0303] Incidentally, the machinability index of an alloy comprising
58.1 mass % Cu, 0.01 mass % Pb, and Zn as the balance, which
constitutes a free-cutting copper alloy bar having a high Zn
concentration and including 0.01 mass % Pb with the proportion of
.beta. phase being about 50%, was 39, and the alloy's chip length
was longer than 20 mm. Likewise, the machinability index of an
alloy comprising 55 mass % Cu, 0.01 mass % Pb, and Zn as the
balance, which is a .beta. single-phase copper alloy not including
Si and including 0.01 mass % Pb, was 41, and the alloy's chip
length was longer than 20 mm.
[0304] FIG. 6 shows the external appearance of the chips generated
in Test No. T07 including 0.063 mass % P and 0.016 mass % Pb in
which P-containing compounds were present (Alloy No. S02). FIG. 7
shows the external appearance of the chips generated in Test No.
T35 including 0.067 mass % P, 0.073 mass % Pb, and 0.042 mass % Bi
and in which P-containing compounds were present and particles
including Bi were present in .alpha. phase (Alloy No. S20). FIG. 8
shows the external appearance of the chips generated in Test No.
T106 including 0.001 mass % P and 0.025 mass % Pb (Alloy No.
S53).
[0305] The average lengths of the chips generated in Test No. T07
(Alloy No. S02) and Test No. T35 (Alloy No. S20) including P and in
which P-containing compounds were able to be observed were about 2
mm and about 0.7 mm, respectively, and the chips were finely
broken.
[0306] In contrast, in Test No. T106 (Alloy No. S53) in which the P
content was 0.003 mass % or lower and P-containing compounds were
not observed, the chip length was more than 20 mm, and chips were
continuous.
[0307] <Drilling Test>
[0308] By using a drilling machine with a JIS standard drill made
of high-speed steel having a diameter of 3.5 mm attached, 10
mm-deep holes were drilled on dry conditions at a rotation speed of
1250 rpm and a feed rate of 0.17 mm/rev. Voltage fluctuation in a
circumferential direction and an axial direction were measured
during drilling using an AST tool dynamometer, and torque and
thrust during drilling were calculated. Each test sample was
measured four times, and their average value was adopted. Assuming
that the torque and the thrust of C3604, a commercially available
free-cutting brass bar comprising 59 mass % Cu, 3 mass % Pb, 0.2
mass % Fe, 0.3 mass % Sn, and Zn as the balance, was 100, the
relative values (torque index, thrust index) of the torque and the
thrust of each test sample were calculated for relative evaluation.
The higher the machinability index (torque index, thrust index,
drill index), the better the machinability. In the drilling, in
order to suppress influence from wear on the drill, each test
sample was measured four times by reciprocating
A.fwdarw.B.fwdarw.C.fwdarw. . . . B.fwdarw.A twice.
[0309] That is, the machinability index was obtained as
follows.
Index representing the results of drilling test
performed on a test sample (drill index)=(torque index+
thrust index)/2
Torque index of a test sample=(torque of C3604/torque
of the test sample).times.100
Thrust index of a test sample=(thrust of C3604/thrust
of the test sample).times.100
[0310] During the third test, chips were collected. Machinability
was evaluated based on the chip shape. Problems that occur in
actual machining are entanglement of chips around the tool and
bulking of chips. Therefore, regarding chip shape, if the average
number of windings per chip was one or less, it was evaluated as
"O" (good). If the average number of windings per chip was more
than one and three or less, it was evaluated as ".DELTA." (fair)
determining that drilling could be performed although there might
be some practical problems. If the average number of windings per
chip was more than three, it was evaluated as "X" (poor). Chips
generated at the beginning of drilling were excluded from the
subject of the evaluation.
[0311] If the torque and the thrust of a high-strength material are
higher than the cutting resistance of a free-cutting brass bar
including 1 to 4 mass % Pb by about 30% points, the material is
considered to be practically good regarding torque and thrust. In
embodiments of the present invention, the machinability was
evaluated providing that approximately 70 was the boundary
machinability index (boundary value). Specifically, when the drill
index was 71 or higher, the machinability was evaluated as good
(evaluation: "O"; good). When the drill index was 65 or higher and
lower than 71, the machinability was evaluated as acceptable
(evaluation: ".DELTA."; fair) determining that drilling could be
performed although there might be some practical problems. When the
drill index was lower than 65, the machinability was evaluated as
unacceptable (evaluation: "X"; poor). It should be noted, however,
that both torque index and thrust index need to be 64 or
higher.
[0312] When there is no difference in strength, chip shape and
torque index have a strong relationship aside from some exceptions.
When torque index is high, chip breakability tends to be high.
Therefore, chip shape can be numerically compared by torque
index.
[0313] Incidentally, the drill index of an alloy comprising 58.1
mass % Cu, 0.01 mass % Pb, and Zn as the balance, which is a
free-cutting copper alloy having a high Zn concentration and
including 0.01 mass % Pb with the proportion of .beta. phase being
about 50%, was 49 (the torque index was 46, and the thrust index
was 52), and the number of windings per chip exceeded 3. Likewise,
the drill index of a .beta. single-phase copper alloy comprising 55
mass % Cu, 0.01 mass % Pb, and Zn as the balance, which is an alloy
not including Si and including 0.01 mass % Pb, was 61 (the torque
index was 53, and the thrust index was 68), and the number of
windings per chip exceeded 3.
TABLE-US-00009 TABLE 9 Composition Relational Alloy Component
Composition (mass %) Inevitable Impurities (mass %) Expression No.
Cu Si P Pb Bi Zn Fe Mn Co Cr Sn Al Ni Sb Ag B MM f0 f1 S01 63.1
1.18 0.048 0.097 0 Balance 0.01 0.00 0.00 0.00 0.01 0.00 0.00 0.00
0.00 0.000 0.00 0.097 57.2 S02 62.5 1.00 0.063 0.016 0 Balance 0.00
0.00 0.00 0.00 0.00 0.08 0.00 0.00 0.00 0.000 0.02 0.016 57.5 S03
62.4 1.09 0.065 0.180 0 Balance 0.01 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00 0.000 0.00 0.180 57.0 S04 61.4 0.81 0.044 0.023 0 Balance
0.09 0.00 0.03 0.00 0.09 0.04 0.00 0.00 0.00 0.000 0.00 0.023 57.3
S05 61.9 1.11 0.110 0.006 0 Balance 0.03 0.00 0.00 0.03 0.00 0.05
0.00 0.00 0.00 0.000 0.00 0.006 56.3 S06 64.8 1.33 0.052 0.019 0
Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000 0.00
0.019 58.1 S07 60.1 0.46 0.019 0.156 0 Balance 0.00 0.00 0.00 0.00
0.00 0.00 0.00 0.00 0.00 0.000 0.00 0.156 57.9 S08 61.9 1.04 0.150
0.085 0 Balance 0.01 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.000
0.00 0.085 56.7 S09 60.7 0.65 0.070 0.037 0 Balance 0.01 0.00 0.00
0.00 0.00 0.00 0.00 0.00 0.00 0.000 0.00 0.037 57.4 S10 63.6 0.94
0.078 0.112 0 Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0.000 0.00 0.112 58.9 S11 62.0 0.89 0.053 0.212 0 Balance 0.07 0.08
0.00 0.00 0.03 0.09 0.05 0.01 0.01 0.000 0.00 0.212 57.6 S12 62.0
0.78 0.082 0.007 0 Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.000 0.00 0.007 58.1 S13 64.3 1.02 0.077 0.088 0.008 Balance
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000 0.00 0.096 59.2
S14 61.5 0.84 0.066 0.044 0.018 Balance 0.01 0.00 0.00 0.00 0.01
0.00 0.00 0.00 0.00 0.010 0.00 0.062 57.3 S15 61.6 0.71 0.013 0.051
0.004 Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000
0.00 0.055 58.1 S16 62.7 0.98 0.006 0.031 0.003 Balance 0.00 0.00
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000 0.00 0.034 57.8 S17 58.9
0.44 0.040 0.085 0.015 Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00 0.000 0.00 0.100 56.7 S18 60.9 0.51 0.034 0.078 0.010
Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000 0.00
0.088 58.4 Note: "MM" refers to mischmetal.
TABLE-US-00010 TABLE 10 Composition Relational Alloy Component
Composition (mass %) Inevitable Impurities (mass %) Expression No.
Cu Si P Pb Bi Zn Fe Mn Co Cr Sn Al Ni Sb Ag B MM f0 f1 S19 63.4
0.95 0.105 0.118 0.028 Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00 0.000 0.00 0.146 58.7 S20 62.2 1.02 0.067 0.073 0.042
Balance 0.08 0.00 0.00 0.00 0.07 0.00 0.05 0.00 0.00 0.001 0.00
0.115 57.1 S21 62.8 0.98 0.053 0.091 0.084 Balance 0.00 0.09 0.00
0.00 0.00 0.03 0.00 0.02 0.01 0.000 0.00 0.175 58.0 S22 60.5 0.61
0.037 0.084 0.025 Balance 0.00 0.08 0.00 0.00 0.00 0.07 0.08 0.00
0.01 0.000 0.01 0.109 57.5 S23 63.5 1.21 0.048 0.087 0.057 Balance
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000 0.00 0.144 57.5
S24 62.4 0.92 0.046 0.022 0.028 Balance 0.00 0.00 0.00 0.00 0.00
0.00 0.00 0.00 0.00 0.000 0.00 0.050 57.8 S25 62.5 0.82 0.066 0.065
0.033 Balance 0.00 0.00 0.02 0.02 0.00 0.00 0.06 0.00 0.00 0.000
0.00 0.098 58.4 S26 61.9 0.88 0.085 0.175 0.063 Balance 0.15 0.00
0.00 0.00 0.13 0.08 0.05 0.01 0.02 0.000 0.00 0.238 57.6 S27 61.4
0.70 0.047 0.065 0 Balance 0.08 0.04 0.00 0.00 0.09 0.03 0.00 0.00
0.00 0.000 0.00 0.065 57.9 S28 61.4 0.70 0.045 0.064 0 Balance 0.18
0.09 0.00 0.03 0.09 0.03 0.00 0.00 0.00 0.000 0.00 0.064 57.9 S29
61.5 0.71 0.045 0.064 0 Balance 0.09 0.04 0.00 0.00 0.19 0.09 0.00
0.00 0.00 0.000 0.00 0.064 58.0 S30 61.3 0.69 0.046 0.066 0 Balance
0.30 0.18 0.00 0.03 0.09 0.03 0.00 0.00 0.00 0.000 0.00 0.066 57.9
S31 61.4 0.70 0.047 0.065 0 Balance 0.08 0.03 0.00 0.00 0.29 0.19
0.00 0.00 0.00 0.000 0.00 0.065 57.9 S32 63.2 1.02 0.041 0.026
0.034 Balance 0.07 0.04 0.00 0.00 0.08 0.03 0.00 0.00 0.00 0.000
0.00 0.060 58.1 S33 63.1 1.01 0.042 0.024 0.034 Balance 0.13 0.17
0.03 0.00 0.09 0.04 0.00 0.00 0.00 0.000 0.00 0.058 58.1 S34 63.2
1.00 0.039 0.030 0.033 Balance 0.06 0.05 0.00 0.00 0.13 0.19 0.00
0.00 0.00 0.000 0.00 0.063 58.2 S35 63.1 1.01 0.040 0.027 0.032
Balance 0.19 0.27 0.03 0.00 0.08 0.04 0.00 0.00 0.00 0.000 0.00
0.059 58.1 S36 63.3 1.03 0.063 0.025 0.035 Balance 0.07 0.04 0.00
0.00 0.31 0.17 0.00 0.00 0.00 0.000 0.00 0.060 58.1 Note: "MM"
refers to mischmetal.
TABLE-US-00011 TABLE 11 Composition Relational Alloy Component
Composition (mass %) Inevitable Impurities (mass %) Expression No.
Cu Si P Pb Bi Zn Fe Mn Co Cr Sn Al Ni Sb Ag B MM f0 f1 S51 65.4
1.47 0.058 0.026 0 Balance 0.06 0.02 0.00 0.00 0.04 0.03 0.00 0.00
0.00 0.000 0.00 0.026 58.0 S52 59.0 0.29 0.083 0.141 0.012 Balance
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000 0.00 0.153 57.6
S53 63.1 1.08 0.001 0.025 0 Balance 0.02 0.00 0.00 0.00 0.05 0.00
0.00 0.00 0.00 0.000 0.00 0.025 57.7 S54 64.1 1.09 0.075 0.001 0
Balance 0.01 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.000 0.00
0.001 58.6 S55 64.8 0.98 0.085 0.101 0.028 Balance 0.01 0.00 0.00
0.00 0.00 0.00 0.00 0.00 0.00 0.000 0.00 0.129 59.9 S56 60.9 1.05
0.031 0.061 0 Balance 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00
0.000 0.00 0.061 55.7 S57 62.5 0.72 0.025 0.033 0.007 Balance 0.05
0.00 0.00 0.00 0.08 0.00 0.00 0.00 0.00 0.000 0.00 0.040 58.9 S58
62.2 0.48 0.085 0.056 0.022 Balance 0.00 0.00 0.00 0.00 0.04 0.00
0.00 0.00 0.00 0.000 0.00 0.078 59.8 S59 60.4 0.46 0.024 0.023
0.005 Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000
0.00 0.028 58.1 S60 58.4 0.09 0.011 0.178 0.058 Balance 0.00 0.00
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000 0.00 0.236 58.1 S61 61.0
0.52 0.033 0.034 0 Balance 0.05 0.00 0.00 0.00 0.08 0.00 0.00 0.00
0.00 0.000 0.00 0.034 58.4 S62 60.8 0.42 0.078 0.163 0 Balance 0.00
0.07 0.00 0.00 0.00 0.05 0.00 0.00 0.00 0.000 0.00 0.163 58.7 S63
58.1 0.07 0.012 0.245 0 Balance 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0.00 0.00 0.000 0.00 0.245 57.9 Note: "MM" refers to
mischmetal.
TABLE-US-00012 TABLE 12 Low-Temperature Average Cooling Rate
Annealing Step during Casting (.degree. C./min) Temperature Time
No. 650-550.degree. C. 530-450.degree. C. 430-350.degree. C.
(.degree. C.) (min) f7 1 40 30 25 -- -- -- 2 50 40 30 -- -- -- 3 8
5 2 -- -- -- 4 20 2 10 -- -- -- 5 75 60 50 -- -- -- 6 60 45 30 --
-- -- 7 80 65 50 -- -- -- 8 40 30 25 350 20 671
TABLE-US-00013 TABLE 13 Metallographic Structure Bi Particle
Concentration Solidification Test Alloy Step in of Si in .beta.
phase Temperature No. No. No. f2 f3 f4 f5 f6 f6A P Compound .alpha.
Phase (mass %) Range (.degree. C.) Castability T01 S01 1 47 53 0 0
57 72 -- 1.5 14 T02 2 41 59 0 0 63 78 -- 1.4 T03 3 55 43 1.9 0.9 50
65 -- 1.5 T04 4 51 49 0 0 53 68 -- 1.5 T05 5 29 71 0 0 76 91
.DELTA. -- 1.3 T06 8 53 44 2.5 1.1 52 67 -- 1.4 T07 S02 1 48 52 0 0
52 61 -- 1.3 14 T08 S03 1 43 57 0 0 59 79 -- 1.3 13 T09 S04 1 51 49
0 0 43 52 -- 1.0 13 T10 2 44 56 0 0 50 59 -- 1.0 T11 3 57 43 0 0 38
47 -- 1.0 T12 4 54 46 0 0 41 50 -- 1.1 T13 S05 1 29 71 0 0 74 82 --
1.2 10 T14 S06 1 64 35 0.9 0.5 42 50 -- 1.7 19 .DELTA. T15 2 57 43
0 0 48 56 -- 1.7 T16 3 78 16 5.7 7.1 25 34 -- 1.4 T17 4 74 22 3.8
3.5 30 39 -- 1.5 T18 S07 1 54 46 0 0 27 44 -- 0.6 13 T19 6 45 55 0
0 32 49 .DELTA. -- 0.6 T20 7 36 64 0 0 37 54 x -- 0.5
TABLE-US-00014 TABLE 14 Properties Electrical Vickers Impact Lathe
Drill Test Alloy Step Conductivity Hardness Value Combined Torque
Thrust Drill No. No. No. (% IACS) (Hv) (J/cm.sup.2) Chips Force
Chips Index Index Index T01 S01 1 15.4 130 46 85 74 76 75 T02 2
15.6 134 42 86 75 76 76 T03 3 15.2 136 35 82 76 71 74 T04 4 15.3
127 47 83 72 75 74 T05 5 15.8 143 32 79 70 74 72 T06 8 15.2 138 30
82 75 72 74 T07 S02 1 17.0 132 51 80 71 74 73 T08 S03 1 16.1 136 43
86 75 77 76 T09 S04 1 18.5 126 50 77 71 73 72 T10 2 18.8 131 45 79
70 75 73 T11 3 18.4 120 55 75 69 71 70 T12 4 18.4 124 51 76 68 72
70 T13 S05 1 16.8 142 31 83 73 75 74 T14 S06 1 14.5 129 46 79 74 70
72 T15 2 14.7 127 48 82 72 73 73 T16 3 14.4 151 21 x 66 .DELTA. 71
61 66 T17 4 14.5 138 27 .DELTA. 72 72 65 69 T18 S07 1 21.5 119 62
72 .DELTA. 70 70 70 T19 6 21.6 122 57 .DELTA. 70 .DELTA. 67 69 68
T20 7 21.8 130 48 x 65 x 62 65 64
TABLE-US-00015 TABLE 15 Metallographic Structure Bi Particle
Concentration Solidification Test Alloy Step in of Si in .beta.
phase Temperature No. No. No. f2 f3 f4 f5 f6 f6A P Compound .alpha.
Phase (mass %) Range (.degree. C.) Castability T21 S08 1 36 64 0 0
65 82 -- 1.2 10 T22 S09 1 49 51 0 0 39 50 -- 0.8 11 T23 S10 1 73 27
0 0 26 43 -- 1.4 20 T24 S11 2 51 49 0 0 46 67 -- 1.1 14 T25 S12 1
60 40 0 0 35 42 -- 1.0 15 T26 S13 2 77 23 0 0 23 39 x 1.4 23
.DELTA. T27 S14 1 49 51 0 0 46 60 1.1 13 T28 S15 1 59 41 0 0 33 44
x 0.9 14 T29 5 45 55 0 0 45 55 x x 0.8 T30 S16 1 56 44 0 0 44 52
.DELTA. x 1.2 14 T31 S17 1 37 63 0 0 35 50 x 0.5 9 T32 S18 1 65 35
0 0 22 36 x 0.6 14 T33 S19 1 69 31 0 0 30 50 1.3 18 T34 2 63 37 0 0
36 55 1.3 T35 S20 1 48 52 0 0 53 69 1.3 14 T36 2 43 57 0 0 58 74
1.2 T37 3 54 45 0.9 0.4 48 65 1.3 T38 6 39 61 0 0 62 78 1.3 T39 7
31 69 0 0 70 86 .DELTA. 1.1 T40 8 56 42 1.6 0.8 46 63 1.2
TABLE-US-00016 TABLE 16 Properties Electrical Vickers Impact Lathe
Drill Test Alloy Step Conductivity Hardness Value Combined Torque
Thrust Drill No. No. No. (% IACS) (Hv) (J/cm.sup.2) Chips Force
Chips Index Index Index T21 S08 1 17.3 139 28 85 74 75 75 T22 S09 1
20.2 125 50 .DELTA. 75 68 71 70 T23 S10 1 17.0 113 67 75 70 72 71
T24 S11 2 18.0 126 47 84 75 74 75 T25 S12 1 17.0 113 65 72 .DELTA.
68 71 70 T26 S13 2 18.5 110 84 .DELTA. 71 .DELTA. 67 71 69 T27 S14
1 18.2 131 55 82 73 72 73 T28 S15 1 19.6 118 63 73 69 71 70 T29 5
20.1 125 55 x 66 x 61 67 64 T30 S16 1 17.2 123 54 .DELTA. 72
.DELTA. 68 73 71 T31 S17 1 22.0 123 47 .DELTA. 74 70 71 71 T32 S18
1 21.3 110 74 71 .DELTA. 67 70 69 T33 S19 1 17.0 114 73 80 72 73 73
T34 2 17.3 115 67 81 73 73 73 T35 S20 1 16.7 131 50 85 74 76 75 T36
2 17.0 133 51 86 75 75 75 T37 3 16.8 132 45 85 76 71 74 T38 6 16.7
127 48 84 74 75 75 T39 7 17.3 139 38 81 71 72 72 T40 8 17.0 136 39
83 76 70 73
TABLE-US-00017 TABLE 17 Metallographic Structure Concentration
Solidification Test Alloy Step Bi Particle of Si in .beta. phase
Temperature No. No. No. f2 f3 f4 f5 f6 f6A P Compound in .alpha.
Phase (mass %) Range (.degree. C.) Castability T41 S21 1 61 39 0 0
39 58 1.3 16 T42 2 54 46 0 0 46 65 1.2 T43 3 66 34 0 0 34 53 1.3
144 6 51 49 0 0 49 68 1.3 145 7 40 60 0 0 59 79 .DELTA. 1.1 T46 8
64 35 0.9 0.5 37 57 1.3 T47 S22 1 50 50 0 0 36 52 0.7 12 T48 S23 1
49 51 0 0 55 73 1.5 15 T49 S24 1 58 42 0 0 40 52 -- 1.2 15 T50 S25
1 66 34 0 0 30 46 1.2 17 T51 S26 1 51 49 0 0 46 69 1.1 12 T52 S27 1
56 44 0 0 35 48 -- 0.9 14 T53 S28 1 58 42 0 0 34 47 -- 0.9 16 T54
S29 1 55 45 0 0 37 49 -- 0.9 17 155 S30 1 63 37 0 0 29 42 -- 0.7 20
.DELTA. 156 S31 1 58 40 1.6 0.8 36 49 -- 0.8 24 x T57 S32 1 60 40 0
0 40 53 1.3 16 T58 S33 1 61 39 0 0 39 51 1.2 18 T59 S34 1 61 38 0.6
0.3 40 53 1.3 19 T60 S35 1 67 33 0 0 33 45 1.1 22 .DELTA. T61 S36 1
65 32 2.9 1.8 38 51 1.2 26 x
TABLE-US-00018 TABLE 18 Properties Electrical Vickers Impact Lathe
Drill Test Alloy Step Conductivity Hardness Value Combined Torque
Thrust Drill No. No. No. (% IACS) (Hv) (J/cm.sup.2) Chips Force
Chips Index Index Index T41 S21 1 17.5 124 54 83 73 74 74 T42 2
17.8 127 50 84 74 74 74 T43 3 17.6 120 57 81 71 74 73 T44 6 17.8
125 52 82 72 74 73 T45 7 18.0 137 37 78 .DELTA. 69 72 71 T46 8 17.5
127 53 83 75 70 73 T47 S22 1 20.8 118 55 78 72 72 72 T48 S23 1 15.2
134 49 87 75 77 76 T49 S24 1 17.0 113 60 81 72 74 73 T50 525 1 18.1
115 68 79 70 72 71 T51 S26 1 17.9 126 52 87 76 76 76 T52 S27 1 19.7
122 56 78 71 72 72 T53 S28 1 19.5 127 57 76 70 71 71 T54 S29 1 19.6
124 50 78 72 68 70 T55 S30 1 19.2 126 51 .DELTA. 67 x 63 67 65 T56
S31 1 19.5 135 35 x 70 .DELTA. 69 62 66 T57 S32 1 16.9 121 52 79 71
72 72 T58 S33 1 16.6 123 54 77 69 70 70 T59 S34 1 16.7 125 44 78 71
68 70 T60 S35 1 16.6 128 47 .DELTA. 68 x 64 65 65 T61 S36 1 16.5
135 28 .DELTA. 70 .DELTA. 68 61 65
TABLE-US-00019 TABLE 19 Metallographic Structure Concentration
Solidification Test Alloy Step Bi Particle of Si in .beta. phase
Temperature No. No. No. f2 f3 f4 f5 f6 f6A P Compound in .alpha.
Phase (mass %) Range (.degree. C.) Castability T100 S51 1 68 28 3.7
2.6 37 47 -- -- 27 x T101 2 59 38 2.2 1.2 47 57 -- -- T102 3 78 14
7.4 10.6 24 34 -- -- T103 4 76 18 5.6 6.2 27 37 -- -- T104 S52 1 52
48 0 0 19 38 x 0.3 -- -- T105 2 46 54 0 0 21 40 -- -- T106 S53 1 54
46 0 0 48 54 x -- -- -- -- T107 3 61 37 1.3 0.7 42 48 x -- 1.3 T108
S54 1 69 31 0 0 32 38 -- -- -- -- T109 S55 1 85 15 0 0 15 33 1.4 31
x T110 S56 1 14 86 0 0 88 100 -- 1.1 9 -- T111 S57 1 74 26 0 0 21
31 0.9 18 T112 S58 1 84 16 0 0 10 25 x 0.7 23 .DELTA. T113 S59 1 61
39 0 0 23 31 -- 0.6 13 -- T114 S60 1 52 48 0 0 6 26 x -- -- -- T115
S61 1 68 32 0 0 21 30 -- 0.7 15 -- T116 S62 1 71 29 0 0 16 35 --
0.5 17 -- T117 S63 1 47 53 0 0 5 26 -- -- -- --
TABLE-US-00020 TABLE 20 Properties Electrical Vickers Impact Lathe
Drill Test Alloy Step Conductivity Hardness Value Combined Torque
Thrust Drill No. No. No. (% IACS) (Hv) (J/cm.sup.2) Chips Force
Chips Index Index Index T100 S51 1 13.5 146 27 77 71 66 69 T101 2
13.7 139 34 82 74 70 72 T102 3 13.4 154 20 x 64 .DELTA. 65 61 63
T103 4 13.7 152 23 .DELTA. 67 .DELTA. 68 63 66 T104 S52 1 23.5 99
71 x 60 x 59 64 62 T105 2 23.7 103 -- x 61 x 61 65 63 T106 S53 1
17.1 124 53 x 66 x 63 68 66 T107 3 17.2 123 44 x 65 x 67 61 64 T108
S54 1 16.1 112 69 x 65 x 64 69 67 T109 S55 1 16.5 98 92 x 58 x 60
66 63 T110 S56 1 17.7 164 22 88 73 76 75 T111 S57 1 19.3 115 74 x
67 .DELTA. 67 68 68 T112 S58 1 20.6 82 95 x 54 x 55 59 57 T113 S59
1 21.2 107 65 x 64 x 64 67 66 T114 S60 1 25.1 93 -- x 55 x 58 63 61
T115 S61 1 21.0 102 72 x 63 x 62 68 65 T116 S62 1 22.0 95 77 x 64 x
63 69 66 T117 S63 1 25.4 92 -- x 56 x 59 63 61
[0314] From the above-described measurement results, the following
findings were obtained.
[0315] 1) By satisfying a composition of an embodiment of the
present invention, the composition relational expressions f0 and
f1, the metallographic structure-related requirements, i.e., the
metallographic structure relational expressions f2 to f6, and the
metallographic structure and composition relational expression f6A,
even if the content of Pb was small, a copper alloy casting having
good machinability, a solidification temperature range of
25.degree. C. or lower, good castability, electrical conductivity
of 13% IACS or higher, high strength (Vickers hardness), and good
toughness (impact resistance) was obtained (e.g., Alloys Nos. S01
to S12).
[0316] 2) By the effects of P contained in an amount higher than
0.003 mass % and presence of P-containing compounds having a size
of 0.3 to 3.0 .mu.m, chip breakability was improved and cutting
resistance was reduced. Even when the amount of .gamma. phase was
0%, excellent machinability was able to be secured. When P was
contained in an amount exceeding 0.010 mass % and cooling was
performed at an appropriate cooling rate, P-containing compounds
were able to be observed with a metallographic microscope having a
magnification power of 500.times. (e.g., Alloys Nos. S01 to S26,
Step No. 1).
[0317] 3) When the Si content was low, the machinability was poor.
When the Si content was high, the amount of .gamma. phase was
large, the impact value was low, and the machinability was also
low. When the Si content was lower than 0.4 mass %, even if the Pb
content or the total content of Pb and Bi was about 0.24 mass %,
the machinability was poor. From this result, it is presumed that
the machinability of .beta. phase significantly changes depending
on whether the Si content is below or above about 0.3 mass %
(Alloys Nos. S52, S51, S60, and S63).
[0318] 4) When the Si content in .beta. phase was in a range of 0.5
mass % or higher and 1.7 mass % or lower, excellent machinability
was obtained (Alloys Nos. S01 to S36).
[0319] 5) When the P content was 0.003 mass % or lower, chip
breakability during turning and drilling were both poor, and
cutting resistance was high (Alloy No. S53).
[0320] 6) When the Pb content was 0.002 mass % or lower, the
machinability was poor (Alloy No. S54). When the Pb content was
higher than 0.002 mass %, the machinability was better, and as the
Pb content was increased, the machinability improved (Alloys Nos.
S5 and S12).
[0321] 7) It was verified that Bi performs in place of Pb for the
most part. When particles including Bi were present in .alpha.
phase, the machinability was better. The reason for this
machinability improvement is presumed to be brought by improved
machinability of .alpha. phase. When Bi was contained in an amount
close to 0.10 mass %, the impact value was slightly lower (Alloys
Nos. S13 to S26). When the Si content was 0.1 mass %, even if the
Bi content was higher than 0.02 mass %, particles including Bi were
not observed in .alpha. phase, and the machinability was poor
(Alloy No. S60).
[0322] 8) It was verified that, even if inevitable impurities (Fe,
Mn, Cr, Co, Sn, or Al) were included in an amount actually included
in a commercially manufactured alloy, there was no significant
influence on the properties (Alloys Nos. S27 to S36). When the
total content of Fe, Mn, Cr, and Co exceeded the preferable range
of inevitable impurities, the machinability deteriorated. The
reason for this deterioration is presumed to be caused by a
decrease in the concentration of Si which has a positive effect on
machinability due to formation of intermetallic compounds between
Fe, Mn, or the like and Si. Further, it is presumed that the
composition of P-containing compound may have changed. In addition,
the castability was also poor (Alloys Nos. S30 and S35). When the
total content of Sn and Al exceeded the preferable range of
inevitable impurities, the amount of .gamma. phase increased, the
impact value decreased, and also the machinability slightly
deteriorated. It is presumed that the characteristics of .gamma.
phase and .beta. phase were changed by the large amounts of Sn and
Al contained. In addition, due to the large amounts of Sn and Al,
the solidification temperature range slightly widened and the
castability deteriorated (Alloys Nos. S31 and S36).
[0323] 9) When the composition relational expression f1 was lower
than 56.0, the amount of .beta. phase was large, and the impact
value was low. When f1 was higher than 59.5, the solidification
temperature range was wide, the hardness was also low, and the
machinability and castability were poor (Alloys Nos. S55, S56, and
S58). When the value of f1 was 56.3 or higher, the impact value was
better. On the other hand, when the value of f1 was 59.2 or lower,
59.0 or lower, and further, 58.5 or lower, the machinability was
further improved. When f1 was 58.0 or lower, the impact value was
further improved. In addition, the solidification range was
narrowed, and the result of the Tatur test was improved (Alloys
Nos. S01 to S26).
[0324] 10) When f3 representing the amount of .beta. phase was 45
or higher, or 50 or higher, and the relational expression f6 was 50
or higher, the machinability of .beta. single-phase alloy, Alloy F,
was substantially maintained (for example, Alloys Nos. S01 and
S03).
[0325] 11) When the amount of .beta. phase was less than 18%,
excellent machinability was not obtained. When the amount of
(.beta. phase was higher than 80%, the impact value was low (Alloys
Nos. S55, S56, and S58).
[0326] 12) Even when the amount of .gamma. phase was 0%, if an
appropriate amount of .beta. phase was present, excellent
machinability and mechanical characteristics were obtained (for
example, Alloys Nos. S02 and S03). When the amount of .gamma. phase
was 2% or lower and 20.times.(.gamma.)/(.beta.)<1, the torque
index was high, and chips generated in drilling were finely broken
(for example, Alloy No. S21; Test No. T46).
[0327] 13) When the amount of .gamma. phase was 5% or higher or
20.times.(.gamma.)/(.beta.) was larger than 4, the impact value and
the machinability index were low (Alloys Nos. S51 and S06; Test No.
T16).
[0328] 14) When the metallographic structure relational expression
f6 was 18 or higher, the machinability improved. When f6 was 25 or
higher, the machinability further improved. When f6 was 30 or
higher, or 40 or higher, the machinability improved even further.
When f6 was 82 or lower, the impact value was improved (Alloys Nos.
S03, S07, S08, and S05).
[0329] 15) When the relational expression f6A was 33 or higher,
excellent machinability was obtained. As the relational expression
f6A increased to 40 or higher, then to 45 or higher, the
machinability further improved (Alloys Nos. S01 to S26). On the
other hand, even when the composition range and the relational
expressions f0 to f5 were satisfied, unless both f6 and f6A were
satisfied, the machinability was poor (Alloys Nos. S57, S59, and
S61). Even if f6 and f6A were satisfied, when the Si content was
small, the machinability was poor (Alloy No. S52).
[0330] 16) As the cooling rate in each of the temperature ranges
after casting changed, the proportion of .beta. phase changed, and
due to the change in the cooling rate, whether or not .gamma. phase
was present, the amount of .gamma. phase, and the like also
changed. Along with the change in the metallographic structure, the
properties also changed (Steps Nos. 1 to 8).
[0331] 17) Although depending on the P content, the average cooling
rate of about 55.degree. C./min in a range from 530.degree. C. to
450.degree. C. in the process of cooling after casting was roughly
the boundary value that determines whether or not P-containing
compounds that are visible with a metallographic microscope having
a magnification power of 500.times. or an electron microscope
having a magnification power of 2000.times. were present. When
P-containing compounds were able to be observed with a
metallographic microscope having a magnification power of
500.times., the machinability was good (evaluation: "0") (Alloys
Nos. S01 to S26). The test samples in which the presence of
P-containing compounds was able to be detected with an electron
microscope having a magnification power of 2000.times. exhibited
slightly poorer machinability than that of the test samples in
which the presence of P-containing compounds was able to be
detected with a metallographic microscope having a magnification
power of 500.times., but excellent machinability was secured (for
example, Alloy No. S01; Step No. 5, and Alloy No. S21; Step No. 7).
The test samples in which the presence of P-containing compounds
was not detected exhibited poor machinability (Alloy No. S07; Step
No. 7, and Alloy No. S15; Step No. 5).
[0332] 18) When the casting was annealed at a low temperature,
.gamma. phase newly precipitated. When the amount of .gamma. phase
was appropriate, the torque index was good (for example, Alloy No.
S21; Test No. T46).
[0333] As described above, free-cutting copper alloy castings
according to an embodiment of the present invention in which the
content of each of the elements added, the composition relational
expressions, and the respective metallographic structure relational
expressions are in appropriate ranges have excellent machinability
and castability, and their mechanical characteristics are also
good.
INDUSTRIAL APPLICABILITY
[0334] Free-cutting copper alloy castings according to an
embodiment of the present invention have excellent castability and
machinability, high strength, and good toughness although the
amount of Pb contained is small. Therefore, the free-cutting copper
alloy castings are suitable for mechanical components, automobile
components, electrical or electronic apparatus components, toys,
sliding components, measuring instrument components, precision
mechanical components, medical components, fittings for
construction, faucet fittings, drink-related devices and
components, devices and components for water drainage, industrial
plumbing components, pressure vessels, and components relating to
liquid or gas such as hydrogen.
[0335] Specifically, the free-cutting copper alloys can be suitably
applied as a material that constitutes the items used in the
above-mentioned fields which go by the names including valve,
joint, tap water faucet, waste water plug, faucet fitting, gear,
bearing, sleeve, flange, and sensor.
* * * * *