U.S. patent application number 11/182638 was filed with the patent office on 2006-02-16 for sintered valve guide and manufacturing method thereof.
Invention is credited to Katsunao Chikahata, Hiroki Fujitsuka, Koichiro Hayashi, Toru Tsuboi.
Application Number | 20060032328 11/182638 |
Document ID | / |
Family ID | 35276214 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060032328 |
Kind Code |
A1 |
Chikahata; Katsunao ; et
al. |
February 16, 2006 |
Sintered valve guide and manufacturing method thereof
Abstract
Disclosed is a sintered valve guide guide formed of a sintered
alloy consisting essentially of 3.5 to 5% copper, 0.3 to 0.6% tin,
0.04 to 0.15% phosphorus, 1.5 to 2.5% carbon and the balance iron,
by mass, and as occasion needs, further containing 0.46 to 1.41%
metal oxide, and MnS and/or magnesium silicate. The metallographic
structure has: a matrix containing a pearlite phase, a Fe--P--C
compound phase and a Cu--Sn alloy phase; pores; and a graphite of
1.2 to 1.7% by mass of the sintered alloy. In the cross section,
the ratio of the pearlite phase to the matrix is 90 area % or more,
the ratio of the Fe--P--C compound phase is 0.1 to 3 area % of the
cross section, the ratio of the Cu--Sn alloy phase to the cross
section is 1 to 3% by area, and the ratio of a portion of the
Fe--P--C compound phase having a thickness of 15 microns or more is
10 area % or less of the whole Fe--P--C compound phase.
Inventors: |
Chikahata; Katsunao; (Chiba,
JP) ; Hayashi; Koichiro; (Chiba, JP) ;
Fujitsuka; Hiroki; (Chiba, JP) ; Tsuboi; Toru;
(Chiba, JP) |
Correspondence
Address: |
JOHN S. PRATT, ESQ;KILPATRICK STOCKTON, LLP
1100 PEACHTREE STREET
ATLANTA
GA
30309
US
|
Family ID: |
35276214 |
Appl. No.: |
11/182638 |
Filed: |
July 14, 2005 |
Current U.S.
Class: |
75/243 ;
419/11 |
Current CPC
Class: |
B22F 2998/00 20130101;
C22C 9/02 20130101; C22C 33/0228 20130101; C22C 38/002 20130101;
C22C 38/008 20130101; C22C 33/0214 20130101; F01L 3/02 20130101;
C22C 38/16 20130101; F01L 3/08 20130101; B22F 2999/00 20130101;
F01L 2301/00 20200501; B22F 2998/00 20130101; C22C 33/0221
20130101; B22F 3/1028 20130101; B22F 2999/00 20130101; C22C 33/0207
20130101; B22F 9/082 20130101; B22F 9/22 20130101 |
Class at
Publication: |
075/243 ;
419/011 |
International
Class: |
C22C 33/02 20060101
C22C033/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 15, 2004 |
JP |
P2004-209064 |
Claims
1. A sintered valve guide formed of a sintered alloy consisting
essentially of 3.5 to 5% copper, 0.3 to 0.6% tin, 0.04 to 0.15%
phosphorus, 1.5 to 2.5% carbon and the balance iron, by mass,
wherein the sintered alloy has a metallographic structure
comprising: a matrix having a pearlite phase, a Fe--P--C compound
phase and a Cu--Sn alloy phase; pores; and a graphite phase being
dispersed at a ratio of 1.2 to 1.7% by mass of the sintered alloy,
and wherein, in a cross section of the metallographic structure of
the sintered alloy, the ratio of the pearlite phase to the matrix
is 90% by area or more, the ratio of the Fe--P--C compound phase to
the cross section of the metallographic structure is 0.1 to 3% by
area, the ratio of the Cu--Sn alloy phase to the cross section of
the metallographic structure is 1 to 3% by area, and the ratio of a
portion of the Fe--P--C compound phase having a thickness of 15
microns or more to whole of the Fe--P--C compound phase is 10% by
area or less.
2. A sintered valve guide formed of a sintered alloy consisting
essentially of 3.5 to 5% copper, 0.3 to 0.6% tin, 0.04 to 0.15%
phosphorus, 1.5 to 2.5% carbon, 0.46 to 1.41% metal oxide and the
balance iron, by mass, wherein the sintered alloy has a
metallographic structure comprising: a matrix having a pearlite
phase, a Fe--P--C compound phase, a Cu--Sn alloy phase and a metal
oxide phase; pores; and a graphite phase being dispersed at a ratio
of 1.2 to 1.7% by mass of the sintered alloy, and wherein, in a
cross section of the metallographic structure of the sintered
alloy, the ratio of the pearlite phase to the matrix is 90% by area
or more, the ratio of the Fe--P--C compound phase to the cross
section of the metallographic structure is 0.1 to 3% by area, the
ratio of the Cu--Sn alloy phase to the cross section of the
metallographic structure is 1 to 3% by area, and a portion of the
Fe--P--C compound phase having a thickness of 15 microns or more to
whole of the Fe--P--C compound phase is 10% by area or less.
3. A sintered valve guide formed of a sintered alloy consisting
essentially of 3.5 to 5% copper, 0.3 to 0.6% tin, 0.04 to 0.15%
phosphorus, 1.5 to 2.5% carbon, 1% or less of at least one solid
lubricant selected from the group consisting of manganese sulfide
and magnesium silicate minerals, and the balance iron, by mass,
wherein the sintered alloy has a metallographic structure
comprising: a matrix having a pearlite phase, a Fe--P--C compound
phase and a Cu--Sn alloy phase; pores; a graphite phase; and said
at least one solid lubricant being dispersed in the pores or
intergranularly dispersed in the metallographic structure, and
wherein, in a cross section of the metallographic structure of the
sintered alloy, the ratio of the pearlite phase to the cross
sectioin of the metallographic structure is 80% by area or more,
the ratio of the Fe--P--C compound phase to cross section of the
metallographic structure is 0.1 to 3% by area, the ratio of the
Cu--Sn alloy phase to the cross section of the metallographic
structure is 1 to 3% by area, the graphite phase is dispersed in
the pores at a ratio of 0.8 to 3.2% by area of the cross section of
the metallographic structure, and the ratio of a portion of the
Fe--P--C compound phase having a thickness of 15 microns or more to
whole of the Fe--P--C compound phase is 10% by area or less.
4. A sintered valve guide formed of a sintered alloy consisting
essentially of 3.5 to 5% copper, 0.3 to 0.6% tin, 0.04 to 0.15%
phosphorus, 1.5 to 2.5% carbon, 0.46 to 1.41% metal oxide, 1.6% or
less of at least one solid lubricant selected from the group
consisting of manganese sulfide and magnesium silicate minerals,
and the balance iron, by mass, wherein the sintered alloy has a
metallographic structure comprising: a matrix having a pearlite
phase, a Fe--P--C compound phase, a Cu--Sn alloy phase and a metal
oxide phase; pores; a graphite phase; and said at least one solid
lubricant being dispersed in the pores or intergranularly dispersed
in the metallographic structure, and wherein, in a cross section of
the metallographic structure of the sintered alloy, the ratio of
the pearlite phase to the cross sectioin of the metallographic
structure is 90% by area or more, the ratio of the Fe--P--C
compound phase to cross section of the metallographic structure is
0.1 to 3% by area, the ratio of the Cu--Sn alloy phase to the cross
section of the metallographic structure is 1 to 3% by area, the
graphite phase is dispersed in the pores at a ratio of 0.8 to 3.2%
by area of the cross section of the metallographic structure, and
the ratio of a portion of the Fe--P--C compound phase having a
thickness of 15 microns or more to whole of the Fe--P--C compound
phase is 10% by area or less.
5. The sintered valve guide as set forth in claim 2, wherein the
metal oxide includes at least one oxide of a metal selected from
the group consisting of aluminum, silicon, magnesium, iron, calcium
and tin.
6. The sintered valve guide as set forth in claim 1, wherein, in
the cross section of the metallographic structure, the ratio of
another portion of the Fe--P--C compound phase having a thickness
of 5 microns or more and less than 15 microns to whole of the
Fe--P--C compound phase is 10 to 40% by area, and the balance
Fe--P--C compound phase has a thickness of less than 5 microns.
7. A method of manufacturing a sintered valve guide, comprising:
preparing a powder mixture comprising, by mass: 0.27 to 0.7% of a
Fe--P alloy powder; 3.93 to 5.44% of a Cu--Sn alloy powder; 1.7 to
2.7% of a graphite powder and the balance iron powder, wherein the
Fe--P alloy powder consists essentially of 15 to 21% phosphorus, an
inevitable amount of impurities and the balance iron, the Cu--Sn
alloy powder consists essentially of 8 to 11% tin, an inevitable
amount of impurities and the balance copper; forming the powder
mixture into a tubular compact by pressing the powder mixture in a
tubular cavity; and sintering the tubular compact in a
non-oxidizing atmosphere at a sintering temperature of 950 to 1,050
degrees C.
8. The manufacturing method as set forth in claim 7, wherein the
iron powder includes an ore reduced iron powder containing 0.5 to
1.5% by mass of metal oxide.
9. The manufacturing method as set forth in claim 7, wherein the
iron powder is a mixture of an ore reduced iron powder and an
atomized iron powder, wherein the content of the atomized iron
powder in the mixture is 10 to 30% by mass.
10. The manufacturing method as set forth in claim 7, wherein the
iron powder has a maximum particle size of 104 to 200 microns.
11. The manufacturing method as set forth in claim 7, wherein the
Fe--P alloy powder has a maximum particle size of 61 to 104
microns, and the Cu--Sn alloy powder has a maximum particle size of
35 to 61 microns.
12. The manufacturing method as set forth in claim 7, wherein the
sintering time is 15 to 90 minutes.
13. The manufacturing method as set forth in claim 7, wherein the
preparing of the powder mixture further comprises: mixing at least
one powder of a manganese sulfide and magnesium silicate minerals
into the powder mixture to adjust the ratio of said at least one
powder in the powder mixture to 1.6% by mass or less.
14. The manufacturing method as set forth in claim 7, wherein the
tubular cavity is tapered at a ratio of 1/5000 to 1/1000 by
inclining at least one of an inner bore surface of a die and a
circumferential surface of a punch which define the tubular
cavity.
15. The manufacturing method as set forth in claim 7, further
comprising: dipping in an oil the sintered compact obtained by the
sintering.
16. The manufacturing method as set forth in claim 7, further
comprising: cooling the sintered compact obtained by the sintering
at a cooling rate of 8 degrees C./min.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a valve guide for use in
internal-combustion engines, and in particular, a sintered valve
guide made of a sintered alloy superior in wear resistance and
machinability, and a method of manufacturing the same.
[0003] 2. Related Art
[0004] Valve guides made of cast iron have been conventionally used
in internal-combustion engines, and sintered alloy valve guides are
also used recently, from the viewpoints of wear resistance and mass
production. The applicant of the present application has proposed
valve guide materials superior in wear resistance, for example, in
the patent applications (Japanese Patent Application Publication
(JP-B) No. 55-34858 and Japanese Patent 2680927).
[0005] The valve guide material disclosed in the document of JP-B
No. 55-34858 has a composition consisting of C: 1.5 to 4%, Cu: 1 to
5%, Sn: 0.1 to 2%, P: 0.1 to 0.3%, and Fe: the balance, by weight
ratio, and has a structure that iron-phosphorus-carbon compound
phase made of an eutectic Fe--P--C compound, Cu--Sn phase and free
graphite are dispersed in the matrix which is mixture of pearite
and ferrite. It has wear resistance better than that of
conventional cast iron valve guides and a machinability better that
that of the conventional iron-based sintered alloys, and thus has
been used in many car manufacturers although it's processing is
relatively difficult in comparison with the cast iron products.
[0006] On the other hand, the valve guide material disclosed in the
document of Japanese Patent 2680927, which is a valve guide
material improved from that disclosed in JP-B No. 55-34858, has
machinability improved by dispersing a magnesium silicate mineral
into the area of grain boundary in the metallographic structure of
JP-B No. 55-34858, without impairing the wear resistance.
[0007] The valve guide material disclosed in Japanese Patent
2680927 exhibits an excellent wear resistance which is equivalent
to that of the valve guide material disclosed in JP-B No. 55-34858,
but its machinability is lower than that of cast iron products
although improved to some extent. Therefore, further improvement in
the machinability is desirable. The applicant of the present
application have conducted studies aimed at improving the
machinability even at sacrifice of wear resistance to some extent,
and the valve guide material disclosed in Japanese Patent
Application Laid-Open (JP-A) No. 2002-69597 has been developed.
[0008] The valve guide material disclosed in JP-A No. 2002-69597
has a composition consisting of C: 1.5 to 4%, Cu: 1 to 5%, Sn: 0.1
to 2%, P: 0.01 to 0.1%, and Fe: the balance, by weight ratio, and
has a structure containing free graphite dispersed in the matrix
whose main body is pearlite.
[0009] However, in a trend toward improving efficiency of the
manufacturing process, there exist an increasing demand for
improvement in the processability of valve guide materials and thus
an increasing need for a valve guide material more superior in
machinability.
BRIEF SUMMARY OF THE INVENTION
[0010] With the above problems in mind, it is therefore an object
of the present invention to provide a novel sintered valve guide
higher in durability which is manufactured efficiently with use of
a sintered alloy having well-balanced wear resistance and
machinability as a valve guide material, and a manufacturing method
thereof.
[0011] In order to achieve the above-mentioned object, a sintered
valve guide, according to one aspect of the present invention, is
formed of a sintered alloy consisting essentially of 3.5 to 5%
copper, 0.3 to 0.6% tin, 0.04 to 0.15% phosphorus, 1.5 to 2.5%
carbon and the balance iron, by mass, wherein the sintered alloy
has a metallographic structure comprising: a matrix having a
pearlite phase, a Fe--P--C compound phase and a Cu--Sn alloy phase;
pores; and a graphite phase being dispersed at a ratio of 1.2 to
1.7% by mass of the sintered alloy, and wherein, in a cross section
of the metallographic structure of the sintered alloy, the ratio of
the pearlite phase to the matrix is 90% by area or more, the ratio
of the Fe--P--C compound phase to the cross section of the
metallographic structure is 0.1 to 3% by area, the ratio of the
Cu--Sn alloy phase to the cross section of the metallographic
structure is 1 to 3% by area, and the ratio of a portion of the
Fe--P--C compound phase having a thickness of 15 microns or more to
whole of the Fe--P--C compound phase is 10% by area or less.
[0012] A sintered valve guide, according to another aspect, is
formed of a sintered alloy consisting essentially of 3.5 to 5%
copper, 0.3 to 0.6% tin, 0.04 to 0.15% phosphorus, 1.5 to 2.5%
carbon, 0.46 to 1.41% metal oxide and the balance iron, by mass,
wherein the sintered alloy has a metallographic structure
comprising: a matrix having a pearlite phase, a Fe--P--C compound
phase, a Cu--Sn alloy phase and a metal oxide phase; pores; and a
graphite phase being dispersed at a ratio of 1.2 to 1.7% by mass of
the sintered alloy, and wherein, in a cross section of the
metallographic structure of the sintered alloy, the ratio of the
pearlite phase to the matrix is 90% by area or more, the ratio of
the Fe--P--C compound phase to the cross section of the
metallographic structure is 0.1 to 3% by area, the ratio of the
Cu--Sn alloy phase to the cross section of the metallographic
structure is 1 to 3% by area, and a portion of the Fe--P--C
compound phase having a thickness of 15 microns or more to whole of
the Fe--P--C compound phase is 10% by area or less.
[0013] A sintered valve guide, according to another aspect, is
formed of a sintered alloy consisting essentially of 3.5 to 5%
copper, 0.3 to 0.6% tin, 0.04 to 0.15% phosphorus, 1.5 to 2.5%
carbon, 1.6% or less of at least one solid lubricant selected from
the group consisting of manganese sulfide and magnesium silicate
minerals, and the balance iron, by mass, wherein the sintered alloy
has a metallographic structure comprising: a matrix having a
pearlite phase, a Fe--P--C compound phase and a Cu--Sn alloy phase;
pores; a graphite phase; and said at least one solid lubricant
being dispersed in the pores or intergranularly dispersed in the
metallographic structure, and wherein, in a cross section of the
metallographic structure of the sintered alloy, the ratio of the
pearlite phase to the cross sectioin of the metallographic
structure is 90% by area or more, the ratio of the Fe--P--C
compound phase to cross section of the metallographic structure is
0.1 to 3% by area, the ratio of the Cu--Sn alloy phase to the cross
section of the metallographic structure is 1 to 3% by area, the
graphite phase is dispersed in the pores at a ratio of 0.8 to 3.2%
by area of the cross section of the metallographic structure, and
the ratio of a portion of the Fe--P--C compound phase having a
thickness of 15 microns or more to whole of the Fe--P--C compound
phase is 10% by area or less.
[0014] A sintered valve guide, according to another aspect, is
formed of a sintered alloy consisting essentially of 3.5 to 5%
copper, 0.3 to 0.6% tin, 0.04 to 0.15% phosphorus, 1.5 to 2.5%
carbon, 0.46 to 1.41% metal oxide, 1.6% or less of at least one
solid lubricant selected from the group consisting of manganese
sulfide and magnesium silicate minerals, and the balance iron, by
mass, wherein the sintered alloy has a metallographic structure
comprising: a matrix having a pearlite phase, a Fe--P--C compound
phase, a Cu--Sn alloy phase and a metal oxide phase; pores; a
graphite phase; and said at least one solid lubricant being
dispersed in the pores or intergranularly dispersed in the
metallographic structure, and wherein, in a cross section of the
metallographic structure of the sintered alloy, the ratio of the
pearlite phase to the cross sectioin of the metallographic
structure is 90% by area or more, the ratio of the Fe--P--C
compound phase to cross section of the metallographic structure is
0.1 to 3% by area, the ratio of the Cu--Sn alloy phase to the cross
section of the metallographic structure is 1 to 3% by area, the
graphite phase is dispersed in the pores at a ratio of 0.8 to 3.2%
by area of the cross section of the metallographic structure, and
the ratio of a portion of the Fe--P--C compound phase having a
thickness of 15 microns or more to whole of the Fe--P--C compound
phase is 10% by area or less.
[0015] A method of manufacturing a sintered valve guide, according
to one aspect of the invention, comprises: preparing a powder
mixture comprising, by mass: 0.27 to 0.7% of a Fe--P alloy powder;
3.93 to 5.44% of a Cu--Sn alloy powder; 1.7 to 2.7% of a graphite
powder and the balance iron powder, wherein the Fe--P alloy powder
consists essentially of 15 to 21% phosphorus, an inevitable amount
of impurities and the balance iron, the Cu--Sn alloy powder
consists essentially of 8 to 11% tin, an inevitable amount of
impurities and the balance copper; forming the powder mixture into
a tubular compact by pressing the powder mixture in a tubular
cavity; and sintering the tubular compact in a non-oxidizing
atmosphere at a sintering temperature of 950 to 1,050 degrees
C.
[0016] In accordance with the above construction, a sintered valve
guide that is higher in durability is efficiently manufactured with
use of a valve guide material having well-balanced abrasion
resistance and machinability.
BREIF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic view illustrating the cross section of
the metallographic structure of a sintered valve guide according to
the present invention.
[0018] FIG. 2 is a schematic view illustrating the cross section of
the metallographic structure of a sintered valve guide having a
higher ratio of iron-phosphorus-carbon compound phase.
[0019] FIGS. 3A-3D are graphs showing the relationships of the
phosphorus content in the whole composition with the ratio of
iron-phosphorus-carbon compound phase (FIG. 3A), the ratio of
copper-tin alloy phase (FIG. 3B), the amount of free graphite phase
(FIG. 3C), and the ratio of ferrite phase (FIG. 3D).
[0020] FIGS. 4A-4D are graphs showing the relationships of the
phosphorus content in the whole composition with the thickness of
the iron-phosphorus-carbon compound phase (FIG. 4A), wear amount
(FIG. 4B), machinability index (FIG. 4C), and radial crushing
strength constant (FIG. 4D).
[0021] FIGS. 5A-5D are graphs showing the relationships of the tin
content in the whole composition with the ratio of
iron-phosphorus-carbon compound phase (FIG. 5A), the ratio of
copper-tin alloy phase (FIG. 5B), the amount of free graphite phase
(FIG. 5C), and the ratio of ferrite phase (FIG. 5D).
[0022] FIGS. 6A-6D are graphs showing the relationships of the tin
content in the whole composition with the thickness of the
iron-phosphorus-carbon compound (FIG. 6A), wear amount (FIG. 6B),
machinability index (FIG. 6C), and radial crushing strength
constant (FIG. 6d).
[0023] FIGS. 7A-7D are graphs showing the relationships of the
copper content in the whole composition with the ratio of
iron-phosphorus-carbon compound phase (FIG. 7A), the ratio of
copper-tin alloy phase (FIG. 7B), the amount of free graphite (FIG.
7C), and the ratio of ferrite phase (FIG. 7D).
[0024] FIGS. 8A-8D are graphs showing the relationships of the
copper content in an entire composition with the thickness of the
iron-phosphorus-carbon compound phase (FIG. 8A), wear amount (FIG.
8B), machinability index (FIG. 8C), and radial crushing strength
constant (FIG. 8D).
[0025] FIGS. 9A-9D are graphs showing the relationships of the
carbon content in the whole composition with the ratio of
iron-phosphorus-carbon compound phase (FIG. 9A), the ratio of
copper-tin alloy phase (FIG. 9B), the amount of free graphite (FIG.
9C), and the ratio of ferrite phase (FIG. 9D).
[0026] FIGS. 10A-10D are graphs showing the relationships of the
carbon content in the whole composition with the thickness of the
iron-phosphorus-carbon compound phase (FIG. 10A), wear amount (FIG.
10B), machinability index (FIG. 10C), and radial crushing strength
constant (FIG. 10D)
[0027] FIGS. 11A-11D are graphs showing the relationships of the
sintering temperature with the ratio of iron-phosphorus-carbon
compound phase (FIG. 11A), the ratio of copper-tin alloy phase
(FIG. 11B), the amount of free graphite (FIG. 11C), and the ratio
of ferrite phase (FIG. 11D).
[0028] FIG. 12A-12D are graphs showing the relationships of the
sintering temperature with the thickness of the
iron-phosphorus-carbon compound phase (FIG. 12A), wear amount (FIG.
12B), machinability index (FIG. 12C), and radial crushing strength
constant (FIG. 12D).
[0029] FIGS. 13A-13D are graphs showing the relationships of the
sintering time with the ratio of iron-phosphorus-carbon compound
phase (FIG. 13A), the ratio of copper-tin alloy phase (FIG. 13B),
the amount of free graphite phase (FIG. 13C), and the ratio of
ferrite phase (FIG. 13D).
[0030] FIGS. 14A-14D are graphs showing the relationships of the
sintering time with the thickness of the iron-phosphorus-carbon
compound phase (FIG. 14A), wear amount (FIG. 14B), machinability
index (FIG. 14C), and radial crushing strength constant (FIG.
14D).
[0031] FIGS. 15A-15D are graphs showing the relationships of the
cooling rate with the ratio of iron-phosphorus-carbon compound
phase (FIG. 15A), the ratio of copper-tin alloy phase (FIG. 15B),
the amount of free graphite phase (FIG. 15C), and the ratio of
ferrite phase (FIG. 15D).
[0032] FIGS. 16A-16D are graphs showing the relationships of the
cooling rate with the thickness of iron-phosphorus-carbon compound
phase (FIG. 15A), wear amount (FIG. 15B), machinability index (FIG.
15C), and radial crushing strength constant (FIG. 15D).
[0033] FIGS. 17A-17D are graphs showing the relationships of the
oxide content in iron powder with the ratio of
iron-phosphorus-carbon compound phase (FIG. 17A), the ratio of
copper-tin alloy phase (FIG. 17B), the amount of free graphite
phase (FIG. 17C), and the ratio of ferrite phase (FIG. 17D).
[0034] FIGS. 18A-18D are graphs showing the relationships of the
oxide content in iron powder with the thickness of the
iron-phosphorus-carbon compound phase (FIG. 18A), wear amount (FIG.
18B), machinability index (FIG. 18C), and radial crushing strength
constant (FIG. 18D).
[0035] FIGS. 19A-19D are graphs showing the relationships of the
amount of atomized iron powder with the ratio of
iron-phosphorus-carbon compound phase (FIG. 19A), the ratio of
copper-tin alloy phase (FIG. 19B), the amount of free graphite
phase (FIG. 19C), and the ratio of ferrite phase (FIG. 19D).
[0036] FIGS. 20A-20D are graphs showing the relationships of the
amount of atomized iron powder with the thickness of the
iron-phosphorus-carbon compound phase (FIG. 20A), wear amount (FIG.
20B), machinability index (FIG. 20C), and radial crushing strength
constant (FIG. 20D).
[0037] FIGS. 21A-21D are graphs showing the relationships of the
amount of machinability-improving component powder with the ratio
of iron-phosphorus-carbon compound phase (FIG. 21A), the ratio of
copper-tin alloy phase (FIG. 21B), the amount of free graphite
phase (FIG. 21C), and the ratio of ferrite phase (FIG. 21D).
[0038] FIGS. 22A-22D are graphs showing the relationships of the
amount of machinability-improving powder with the thickness of the
iron-phosphorus-carbon compound phase (FIG. A), wear amount (FIG.
22B), machinability index (FIG. 22C), and radial crushing strength
constant (FIG. 22D).
DETAILED DESCRIPTION OF THE INVENTION
[0039] Sintered alloys produced by powder metallurgy have
metallographic structures different from each other, according to
the composition and the particle diameters of the raw powders used
and the manufacturing conditions such as heating temperature, etc.,
even if the whole composition is the same; and the material
properties such as mechanical strength of the sintered alloys vary
significantly depending on the structure of the sintered alloys. In
the present invention, taking into consideration the influence on
the material properties of the various phases which are present in
the sintered alloy, the metallographic structure of the valve guide
material is designed to impart to the sintered alloy the material
properties required for the final valve guide material, and it is
made a base for determining the raw materials and the manufacturing
conditions.
[0040] Valve guides demands both high strength and high wear
resistance. Conventional alloys for valve guides satisfy these
requirements but are still insufficient in machinability, and thus
there exists a strong need from the users for improvement of the
nonconformity during processing. Accordingly, to meet the needs of
the users, the present invention is aimed at improving the
machinability of valve guides, on the basis of an alloy containing
a matrix containing iron as the main component, and, for improving
wear resistance, a copper-tin alloy phase, an
iron-phosphorus-carbon compound phase and a free graphite phase.
Hereinafter, the metallographic structure of the sintered alloy for
the sintered valve guide according to the present invention will be
described. Here, it is noted, the ratio of each phase in the cross
section of the metallographic structure in the following
description by area % is indicated as an average value.
[0041] For improvement of strength, the matrix of the sintered
alloy is constructed with a pearlite structure, which is produced
by diffusion of carbon into a raw iron powder at sintering of the
raw iron powder mixed with a graphite powder. Since metal powders
containing carbon as a solid solution are hard and less
compressible, an iron powder and a graphite powder are used as raw
materials. Lack in amount of the graphite powder leads to decrease
in the amount of the carbon that binds to the base metal, and
consequently to the decrease in the strength of the matrix due to a
large amount of the ferrite (a-iron) phase formed in the matrix. In
this connection, it is noted that, as will be described below,
formation of the iron-phosphorus-carbon compound phases is often
accompanied by a small amount of ferrite phases produced around the
steadite phase. However, if pearlite occupies 90% or more, by area
ratio, of the matrix, production of ferrite in the balance portion
is still in the allowable range, because the deterioration in the
strength of matrix is still small.
[0042] The iron-phosphorus-carbon compound phase is dispersed in
the pearlite matrix. By blending an iron-phosphorus alloy powder
into the raw iron powder with the graphite powder and sintering the
raw powder mixture, the iron-phosphorus-carbon compound
precipitates in the thin film form on the grain boundary of the
pearlite phases, forming hard iron-phosphorus-carbon compound phase
and thus raising the wear resistance of the sintered alloy. The
increase in wear resistance is more significant when the ratio of
the iron-phosphorus-carbon compound phases appeared in the cross
section of the metallographic structure is 0.1 area % or more. On
the other hand, increase in the amount of the
iron-phosphorus-carbon compound phases produced leads to increase
in the thickness of the film and growth into plate-shaped
iron-phosphorus-carbon compound phase, and consequently to drastic
deterioration in the machinability of sintered alloy. Thus, it is
important to reduce the amount of the iron-phosphorus-carbon
compound phases produced and disperse the iron-phosphorus-carbon
compound phases in a thin form for prevention of the decrease in
the machinability of sintered alloy. Specifically, in the cross
section of metallographic structure, the ratio of the
iron-phosphorus-carbon compound phase in the cross section of the
metallographic structure should be 3 area % or less, and the ratio
of the a portion of the iron-phosphorus-carbon compound phase
having a thickness of 15 microns or more should be 10 area % or
less in the whole iron-phosphorus carbon compound phase. More
specifically, the ratio of a portion of the iron-phosphorus-carbon
compound phase having a thickness of 15 microns or more is
preferably 0.1 area % or less in the entire iron-phosphorus-carbon
compound phase; the ratio of another portion having a thickness of
5 microns or more and less than 15 microns is preferably 10 to 40
area %; and the other portion of the iron-phosphorus-carbon
compound phase are less than 5 microns in thickness, and such a
structure is preferably formed. The iron-phosphorus-carbon compound
phase often deprives the pearlite matrix of carbon during
generation, causing production of some ferrite phase surrounding
the iron-phosphorus-carbon compound phase. The ferrite phase, which
is lower in strength, may be allowed to produce in an amount in the
range of 10 area % or less in the matrix of sintered alloy, but
presence thereof in a greater amount is undesirable. That is, an
excessively large phosphorus content of raw powder may lead to
production of thick iron-phosphorus-carbon compound phase and, at
the same time, by depriving the pearlite matrix of carbon, to
dispersion of the ferrite phases lower in strength into the matrix
in a greater amount. Thus, the amount of the iron-phosphorus-carbon
compound phase produced should be controlled carefully so as to
prevent the above problems, and specifically, the ratio of the
iron-phosphorus-carbon compound phase in the cross section of the
metallographic structure should be kept in the range of 0.1 to 3
area %. Accordingly, the amount of the iron-phosphorus alloy powder
to use should be adjusted so as to make the phosphorus content in
sintered alloy 0.04 to 0.15 mass %. If attaching importance to
strength or wear resistance, the amount of iron-phosphorus alloy
powder is 0.1 to 0.15 mass %, and, if machinability is more
important, 0.04 to 0.1 mass %.
[0043] Copper-tin alloy phase is dispersed in the sintered alloy
according to the invention. The copper-tin alloy phase is soft and
effective in raising the wear resistance of the sintered alloy by
improving the compatibility with valves or sliding counterparts.
The effects of the copper-tin phase are more significant when it is
dispersed in the matrix at a ratio of 1 area % or more of the cross
section area of the metallographic structure, but the dimensional
stability of the product at sintering is impaired by the expansion
of the copper during sintering when this phase is present at a
ratio of more than approximately 3 area %, and thus, the blending
ratio in the raw powder is preferably adjusted so that the ratio of
the copper-tin alloy phase in the cross section area is 1 to 3 area
%. The copper-tin alloy phase possibly produces by using a simple
copper powder and a simple tin powder as raw materials, but in that
case, the composition and the distribution of the alloy phase
produced from them in the sintered alloy fluctuate more widely,
deteriorating the dimensional stability and the wear resistance of
sintered alloy. Therefore, use of a copper-tin alloy powder is
desirable. When the copper-tin alloy phase is dispersed in the
pearlite matrix in a fine form such as has a maximum grain size of
20 microns or less and is present at a ratio of 80 area % or more
in the entire copper-tin alloy phase, uniformity in the dispersion
of copper-tin alloy phase becomes high and it is more effective
from the view point of compatibility. Depending on the bridging
state of the powder particles on the preparation of green compact,
the copper-tin alloy powder may remain undiffused and a copper-tin
alloy phase having a grain size of 150 microns or more may be
produced by the undiffused copper-tin alloy powder. However, if its
ratio is 5 area % or less with respect to the entire copper-tin
alloy phase in the cross section, such an amount of presence is
allowable. The copper-tin alloy powder produces a liquid phase
during sintering, which contributes to accelerate sintering, and
copper and tin respectively reinforce the matrix as they are
dissolved in the matrix as solid solution. However, an excessive
amount of copper contained as solid solution leads to the
significant deterioration in dimensional stability due to expansion
of copper and an excessive amount of tin to embrittlement of the
matrix. For prevention of the problems above and more favorable
dispersion of the copper-tin alloy phases, the tin content in the
copper-tin alloy powder used is preferably 8 to 11 mass %. As a
result, the composition of the copper-tin alloy phase in the
sintered alloy also becomes in the range similar to above.
Accordingly, the suitable contents of copper and tin in the whole
alloy composition are respectively 3.5 to 5.0 mass % and 0.3 to 0.6
mass %, as determined based on the composition of copper-tin alloy
powder and the area ratio of the copper-tin alloy phases in the
cross section.
[0044] It is preferable but not essential that a ttace amount of
metal oxide phase is dispersed additionally in the pearlite matrix.
This metal oxide phase is composed of oxide of at least one metal
selected from the group consisting of aluminum, silicon, magnesium,
iron, titanium and calcium, and the oxide works as an easy-cutting
component and improves machinability. However, an excessive content
of the metal oxide leads to embrittlement of the matrix, and the
metal oxide in an amount of 0.46 to 1.41 mass % in the whole
composition is preferably dispersed in the pearlite matrix. It is
important to disperse such metal oxide phase uniformly in the
matrix, and use of an iron powder containing the metal oxide(s) as
the raw powder is desirable. Iron powders containing the metal
oxide(s) at a total amount of 0.5 to 1.5 mass % are preferable, and
such iron powders include ore reduced iron powders. Atomized iron
powders and mill scale reduced iron powders commonly used have a
lower content of metal oxide.
[0045] In addition, the free graphite phase is dispersed in the
metallographic structure. This phase originates from the raw
graphite powder and works as a solid lubricant to contribute to
improvement of the machinability and the wear resistance of
sintered alloy. Although it is difficult to determine the ratio of
free graphite phase in sintered alloy accurately from the
microscopic photograph of alloy cross section because of the loss
during sample preparation, it is possible to determine the mass
ratio of free graphite according to the method of quantitatively
determining free carbon specified by JIS-G1211 "Method for
determination of carbon content", and, based on the graphite
content obtained above and the specific gravity of graphite, the
effect of the free graphite phase in relation to the ratio of free
graphite phase is obtainable. According to the above, the effect of
the free graphite phase is more significant when the ratio of free
graphite phase is approximately 0.8 area % or more, and production
of a sintered alloy containing the free graphite phase in an amount
of more than 3.2 area % leads to precipitation of hard cementite
(Fe.sub.3C) in the matrix and consequently to deterioration in
machinability. An excessive amount of graphite powder also impairs
the compressibility of powder and reduces the ratio of the matrix
in the sintered alloy, resulting in deterioration of the strength
of sintered alloy. Accordingly, the ratio of free graphite phase is
preferably approximately 0.8 area % or more and 3.2 area % or less
in the alloy cross section.
[0046] For further improvement of the machinability, at least one
of manganese sulfide (MnS) powder and magnesium silicate mineral
powder can be blended as a solid lubricant in a total amount of 1.6
mass % or less with respect to the raw powder, and it is dispersed
in the pores or at the powder grain boundary of the sintered alloy.
The MnS phase and the magnesium silicate phases improve wear
resistance and are particularly effective in improving
machinability. In addition, the MnS phase protects the blade of
cutting tool and extends the tool lifetime, while the magnesium
silicate minerals, which have a cleavage property that cleave
easily during cutting, are effective in reducing machining force.
Both components have a chip-breaking action and are effective in
preventing the blade of tool from being heated and elongating the
tool lifetime by breaking chips into smaller pieces.
[0047] The sintered alloy described above having free graphite
phase, iron-phosphorus-carbon compound phase, copper-tin alloy
phase, metal oxide phase and, as occasion requires, solid lubricant
phase in the metallographic structure can be produced by the method
of production described below, and sintered valve guides are
manufactured, by settling the compacting step in the production of
the sintered alloy so that the sintered alloy obtained has a shape
suitable as valve guides. As a result, the sintered alloy and the
sintered valve guide produced have the following composition of
copper: 3.5 to 5 mass %, tin: 0.3 to 0.6 mass %, phosphorus: 0.04
to 0.15 mass %, carbon: 1.5 to 2.5 mass %, the metal oxide: 0.46 to
1.41 mass %, and iron: the balance. The amount of the solid
lubricant, if used, is 1 mass % or less with respect to the whole
alloy composition.
[0048] Valve guides commonly used have a density of 6.3 to 6.9
g/cm.sup.3 and contain pores in an amount of approximately 4 to 15%
by density ratio. The sintered valve guide according to the present
invention described above is the same from this point.
[0049] In producing the sintered alloy and the sintered valve
guide, a powder mixture is prepared first. Raw materials including
a graphite powder, an iron-phosphorus alloy powder, a copper-tin
alloy powder, an iron powder, and, as occasion requires, a solid
lubricant powder are blended uniformly, to give a powder mixture.
The raw powders will be described respectively in detail below.
[0050] An Example of the raw iron powder for the pearlite matrix is
an atomized iron powder having a particle size approximately of
-150 to -65 meshes (minus sieve of screen of 65 to 150 meshes,
maximum particle size: 104 to 200 microns). Alternatively, an ore
reduced iron powder having a particle size of -150 to -65 meshes
that contains the metal oxide(s) described above at a total metal
oxide amount of 0.5 to 1.5 mass % is favorably used, because it
improves machinability. Ore reduced iron powders contain metal
oxides in a greater amount inherently because of the preparative
methods, and the metal oxides are effective in improving
machinability. A metal oxide content below the above range may lead
to decrease in the improvement of machinability. A metal oxide
content higher than the above range leads to hardening and
deterioration in compressibility of the powder and it is thus
undesirable. Ore reduced iron powders are porous and absorb the
copper-tin alloy liquid phase generated during sintering by
capillary action, and use of them makes the distribution of the
components in the sintered alloy more uniform. Ore reduced iron
powders having a larger particle size make it difficult to increase
the density of powder, while those having a smaller particle size
reduce the flowability of powder, and thus, powders having a size
approximately of -150 to -65 meshes are favorable. However, ore
reduced iron powders, which contain a greater amount of metal
oxides, are slightly harder and lower in compressibility than
atomized iron powders or the like, and thus, the strength of the
sintered valve guides obtained is slightly lower than that of the
atomized iron powders. Thus, the raw iron powder for sintered valve
guide is selected according to one of the requirements in
properties: strength or machinability. Alternatively, combined use
of a powder mixture consisting of an ore reduced iron powder and an
atomized iron powder, for example a mixture containing the atomized
iron powder at a ratio of 10 mass % or more, improves the
compressibility of the powder and the strength of the sintered
alloy obtained. In such a case, an atomized iron powder
substitution ratio of more than 30 mass % may result in irregular
distribution of metal oxides and prohibition of the improvement in
machinability. Therefore, the substitution ratio is preferably 10
to 30 mass % when an atomized and ore reduced iron powder are used
in combination. The particle size of the atomized iron powder is
settled to be the same as or less than that of the ore reduced iron
powder.
[0051] The iron-phosphorus alloy powder is a material for supplying
phosphorus, which is used in the form of alloy for safer-handling
because phosphorus is unstable and flammable. Phosphorus diffuses
into the iron base, raising the strength of the pearlite matrix
metal and the wear resistance thereof by producing the
iron-phosphorus-carbon compound phased. Iron-phosphorus alloys
having a phosphorus content of approximately 10 to 13 mass %
generate the liquid phase of the iron-phosphorus alloy in the
temperature range of 950 to 1,050.degree. C. A greater amount of
liquid phase is undesirable as it impairs the dimensional stability
during sintering, but a suitable amount of liquid phase promotes
growth of the necks and improves the strength of the sintered
alloy. Therefore, an iron-phosphorus alloy powder having a
phosphorus content of 15 mass % or more is favorably used for
proper control of generation of the liquid phase. Phosphorus in the
iron-phosphorus alloy powders having a phosphorus content of 15
mass % or more diffuses into the iron powders during sintering; and
when the phosphorus content reaches the range above in some areas,
the alloy powders generate liquid phases. The liquid phase wets the
surface of iron powder, phosphorus therein diffuses rapidly from
the liquid phase into the iron powder, decreasing the phosphorus
content in the liquid phase to less than the range described above
and making the liquid phase solidify. Accordingly, the
iron-phosphorus alloy improves the strength by facilitating the
growth of necks among iron particles and prevents extreme
deterioration in dimensional stability by restricting liquid phase
generation partially and making the liquid phase solidify in a
shorter period of time. When the phosphorus content of the
iron-phosphorus alloy powder used is less than 15 mass %, the
composition of the iron-phosphorus alloy reach the range above
generating liquid phase by diffusion of phosphorus during
sintering, and as a result, the liquid phase is formed more
rigorously, which leads to deterioration of dimensional stability
and reduction in the amount of the iron-phosphorus-carbon compound
phase generated due to the diffusion of phosphorus into the entire
matrix. On the other hand, when the phosphorus content of
iron-phosphorus alloy powder is more than 21 mass %, the
iron-phosphorus alloy powder becomes harder and the compressibility
of powder mixture is reduced so that the green compact and sintered
alloys become lower in density, resulting in lower strength of the
sintered valve guides obtained. In addition, the
iron-phosphorus-carbon compound phase generated becomes thicker,
reducing the machinability of the sintered alloy. Thus, use of an
iron-phosphorus alloy powder having a phosphorus content of 15 to
21 mass % is preferable, and the amount thereof used is preferably
approximately 0.27 to 0.7 mass % with respect to the total powder
mixture amount. Use of an iron-phosphorus alloy powder having a
particle size of approximately -250 to -150 meshes (maximum
particle size: 61 to 104 microns) is preferable from the point of
the compressibility of powder mixture. The iron-phosphorus alloy
powder used may contain inevitable amounts of impurities, for
example, carbon, silicon, manganese and others in a total amount in
the range of 1.5 mass % or less.
[0052] The copper-tin alloy powder, which is used for reduction in
size and increase in dispersion homogeneity of the copper-tin alloy
phase in sintered alloy, preferably has a particle size smaller
than that of the iron powder. For prevention of the deterioration
in dimensional stability by expansion of copper and the
embrittlement of matrix by excessive solid solution of tin, use of
a copper-tin alloy powder having a tin content of 8 to 11 mass % is
preferable, and the amount thereof used is preferably approximately
3.93 to 5.44 mass % with respect to the total powder mixture
amount. According to the above, the copper content and the tin
content in powder mixture become respectively, approximately 3.5 to
5.0 mass % and 0.3 to 0.6 mass %. A copper-tin alloy powder having
a particle size smaller than that of the iron powder is preferably
used for uniform dispersion of the copper-tin alloy powder in
powder mixture and generation of fine copper-tin alloy phase
uniformly dispersed in sintered alloy. Preferably, a copper-tin
alloy powder having a particle diameter of -250 to -400 meshes
(max. particle size: 35 to 61 microns) is used. The copper-tin
alloy powder may contain inevitable amounts of impurities.
[0053] The graphite powder forms a pearlite structure and generates
an iron-phosphorus-carbon compound by bonding to the iron powder
and the iron-phosphorus alloy powder during sintering, and the
residual graphite forms a free graphite phase. The suitable carbon
content in the sintered alloy is 1.5 to 2.5 mass %, but,
considering the consumption for reduction of the metal oxides
contained in iron powder and loss by reaction with water in
environmental air, the amount of the graphite powder is preferably,
approximately 1.7 to 2.7 mass % with respect to the total powder
mixture amount. However, an excessive amount of graphite causes
precipitation of cementite in the pearlite matrix and also reduces
the compressibility of powder mixture, resulting in decrease in the
density of green compact and sintered alloy and the strength of
valve guides. When the particle size of the graphite powder used is
extremely smaller, the free graphite phases remaining after
sintering becomes scarce, while the graphite powder having a
excessively larger particle size makes the compressibility of
powder mixture significantly smaller, the distribution of the
components in the sintered alloy drastically irregular, and ferrite
phase tends to generate surrounding the iron-phosphorus-carbon
compound phases.
[0054] As described above, the solid lubricants used are a MnS
powder and/or a magnesium silicate mineral powder, and examples of
the magnesium silicate minerals include magnesium metasilicate
mineral and magnesium orthosilicate mineral. Typical examples of
the magnesium metasilicate minerals include enstatite,
clinoenstatite, enstenite, hypersten and the like, and examples of
magnesium orthosilicate minerals include forstelite, chrysolite and
the like. When using the solid lubricant, the amount of it is
preferably 1 mass % or less with respect to the total powder
mixture, for prevention of deterioration of the strength of
sintered alloy.
[0055] The powder mixture obtained by uniformly mixing the raw
powders as described above is then compression molded into a green
compact, using a mold. A mold of a suitable shape for a desirable
product is used during the compacting, and for use in preparing
valve guides, it has a long round tubular cavity. Specifically, a
mold consisting of a die having a cylindrical hole, a cylindrical
core rod that forms a long tubular cavity with the die as it is
placed at the center of the die cavity, and upper and lower punches
having a ring-shaped cross section to be inserted into the cavity
is used. A green compact is prepared by placing the lower punch in
the cavity, filling the powder mixture in the cavity, placing the
upper punch over the powder mixture, and compressing the powder
mixture between the upper and lower punches in the axial direction.
At this time, the compression pressure is preferably adjusted so
that the resulting green compact has a green density approximately
of 6.5 to 7.1 g/cm.sup.3.
[0056] In connection with the compacting step described above,
since the shape of the compact is long in the axial direction, the
compression pressure may not reach the middle part of the compact
in the axial direction, giving a green compact having a compression
density smaller in the middle part in the axial direction than
those at the both ends. In such a case, the strength of the
sintered valve guide obtained becomes lower in the middle region in
the axial direction. For overcoming the problem, it is effective to
incline at least one of the cavity wall of die and the
circumferential surface of core rod so that the cavity becomes
tapered slightly with respect to the punch-moving direction. If the
taper angle is small, the effect on the green compact dimension can
be compensated by the spring-back effect of powder particles, and
thus it becomes possible to make uniform the compression density,
by making the compression pressure reach the middle part in the
axial direction without a substantially adverse influence on the
dimension of the product. The taper rate is preferably,
approximately 1/5,000 to 1/1,000, and a rate of less than 1/5,000
results in insufficient improvement in the compression density of
the middle part, while a ratio of more than 1/1,000 in apparent
variation in diameter between two ends of the green compact.
[0057] The molded green compact is sintered at 350 to 1,050.degree.
C. in a nonoxidative atmosphere and then cooled. When sintered at a
temperature in the range above, graphite reacts with the iron
powder, forming a pearlite structure. In addition, a part of the
iron-phosphorus alloy powder forms a liquid phase facilitating
formation of the sintering bonds by diffusion of the powders, while
phosphorus diffuses in the iron powder and reacts with graphite,
forming iron-phosphorus-carbon compound phase, and the
iron-phosphorus-carbon compound phase precipitate in the cooling
process after sintering. The copper-tin alloy powder forms a liquid
phase in the heating process during sintering, accelerating
sintering and diffusing copper and tin into the iron base. The
sintered alloy after sintering and cooling contains
iron-phosphorus-carbon compound phase dispersed and precipitated in
the thin film form and minute copper-tin alloy phase dispersed and
precipitated from the liquefied copper and tin, in the pearlite
structure. The metallographic structure is formed in a period of
approximately five minutes, but elongation of the sintering time
improves the strength of the sintered product by further growth of
the necks among iron powder particles, and thus the sintering time
is preferably 20 minutes or more, more preferably 45 minutes or
more, from the point of strength. However, sintering at a sintering
temperature of more than 1,050.degree. C. or for a sintering time
of more than 90 minutes advances the diffusion of graphite into.
the matrix further, reducing the residual free graphite amount,
increasing the amount of precipitated iron-phosphorus-carbon
compound, and increasing the thickness of the
iron-phosphorus-carbon compound phase. Consequently, it leads to
drastic deterioration in machinability. On the other hand, at a
sintering temperature of less than 950.degree. C., sintering does
not proceed sufficiently, giving an undesirable metallographic
structure and reducing the strength markedly. Since the speeds of
generation and diffusion of the liquid phase vary in accordance
with the heating temperature during sintering, the green compact is
preferably sintered at a higher temperature for a shorter sintering
period or at a lower temperature for a longer period, for obtaining
a favorable metallographic structure. Because slower cooling leads
to increase in the amount of the iron-phosphorus-carbon compound
phase and the ferrite phase precipitated and also in the thickness
thereof, the cooling rate is preferably approximately 8.degree.
C./min or more, and more preferably approximately 10.degree. C./min
or more.
[0058] A crude sintered valve guide is obtained by the sintering
above, and subsequent step for high-precision mechanical processing
of the internal face thereof with a reamer gives a finished
sintered valve guide. The present invention achieves improvement of
the machinability of the sintered alloy for sintered valve guide,
and thus shortens the period needed for mechanical processing with
a reamer and reduces processing defects.
[0059] Immersion of the crude sintered valve guide in oil, which
causes adsorption of the oil in the pores by capillary action, is
effective for raising the air tightness of the sintered valve
guide. The oil also functions as a lubricant oil during the
mechanical processing, improving the machinability. The oil may be
embedded into the pores of the crude sintered valve guide forcibly
by vacuum deaeration during immersion. In addition, dispersion of
molybdenum disulfide or the like in the oil is favorable for
improving machinability and wear resistance.
[0060] The cross section of the metallographic structure in the
sintered valve guide according to the present invention obtained as
described above is shown schematically in FIG. 1. The
metallogrpahic structure comprises a matrix, pores P and graphite
phase G dispersed in the pores P, and the matrix contains: pearlite
phase PE that may contain metal oxide phase MO; copper-tin alloy
phase CS; and an iron-phosphorus-carbon compound phase FPC. The
iron-phosphorus-carbon compound phase FPC are dispersed thinly,
surrounded by a very small amount of ferrite phase F.
[0061] FIG. 2 is a schematic view illustrating the cross section of
the metallographic structure of a conventional sintered alloy
described, for example, in the document of JP-B No. 55-34858 that
has a greater phosphorus content. In this case, the ratio of a
thick portion of the iron-phosphorus-carbon compound phases, having
a thickness of 15 microns or more, is high and a ferrite phase
which is formed by carbon deficiency is present in a greater
amount, surrounding the iron-phosphorus-carbon compound phase.
Sintered alloys having such a metallographic structure are poorer
in machinability and strength than those having the structure shown
in FIG. 1. Namely, the sintered alloy described in document of JP-B
No. 55-34858 above contains the thick iron-phosphorus-carbon
compound phase shown in FIG. 2.
EXAMPLES
[0062] Hereinafter, the present invention will be described in more
detail with reference to Examples.
Example 1
[0063] (Samples 1 to 27)
[0064] Using an ore-reduced iron powder (metal oxide content: 0.1
mass %) or an atomized iron powder (metal oxide content: 0.2 mass
%) as the iron powder, powder mixture samples 1 to 27 were
prepared, respectively, by blending the iron powder with an
iron-phosphorus alloy powder, a copper-tin alloy powder and a
graphite powder in the mixing ratios shown in Table 1. The
composition of each powder mixture sample is shown in Table 2. The
particle diameters of the powders used were respectively as
follows: ore-reduced iron powder (150 microns or more: 5%, 45 to
150 microns: 75%, and less than 45 microns: 20%), atomized iron
powder (150 microns or more: 17%, 45-150 microns: 58%, and less
than 45 microns: 25%), iron-phosphorus alloy powder (63 microns or
more: 3%, 45 to 63 microns: 10%, and less than 45 microns: 87%),
and copper-tin alloy powder (150 microns or more: 7%, 45-150
microns: 73%, and less than 45 microns: 20%) and graphite powder
(average particle diameter: 0.6 to 0.8 mm).
[0065] Each powder mixture sample was compressed at a pressure of
550 MPa into a round tubular green compact (for abrasion test and
machinability test) having an outer diameter of 11 mm, an inner
diameter of 6 mm and a length of 40 mm, and a ring-shaped green
compact (for radial crushing test) having an outer diameter of 18
mm, an inner diameter of 10 mm and a length of 10 mm, both of which
were sintered at a temperature of 1,000.degree. C. for 60 minutes
in a nonoxidative atmosphere, then cooled from 1,000 to 600.degree.
C. at a rate of 12.degree. C./min and allowed to cool to room
temperature, to obtain each of sintered compact samples 1 to
27.
[0066] The cross section of the metal structure in each of the
sintered compact samples 1 to 27 was observed under microscope
(.times.340), and the ratios of the iron-phosphorus-carbon compound
phase and the copper-tin alloy phase in the cross section of
metallographic structure (area %), the ratio of the ferrite phase
in the matrix (area %), the ratio of the free graphite (mass %),
and the ratios (area %) of the regions, respectively, having a
thickness of: less than 5 microns; 5 microns or more and less than
15 microns; and 15 microns or more, in the iron-phosphorus-carbon
compound phase were determined. Results are summarized in Table
3.
[0067] Separately, each of the sintered compact samples 1 to 27 was
subjected to the following abrasion, machinability and radial
crushing tests for determination of the wear amount, the
machinability index and the radial crushing strength constant of
the samples. Results are summarized in Table 3.
[0068] (Abrasion Test)
[0069] The abrasion test of each tubular sintered compact was
carried out in a vertical valve guide abrasion tester. In the
abrasion test, a valve stem was connected to the bottom end of a
piston having its shaft line in the vertical direction, and a valve
was inserted inside the sintered compact and moved back and forth
in an exhaust gas atmosphere at 500.degree. C. while applying a
lateral load of 3 MPa to the piston. The stroke speed was then
3,000 rpm and the stroke width was 8 mm. After reciprocating motion
for 30 hours, the wear amount (micron) of the inner bore face of
sintered compact was determined.
[0070] (Machinability Test)
[0071] The inner bore face of a tubular sintered compact was reamed
by using a reamer made of sintered hard alloy, and the period
necessary for machining the sintered compact to a depth of 10 mm in
the axial direction was measured. The necessary period of each
sample was converted to an index value with respect to 100 of the
necessary period of the sample 13 (having the alloy composition
equivalent to that described in JP-B No. 55-034858, hereinafter
referred to as conventional alloy). Here, a smaller index indicates
that the sintered compact is more easily machinable and has a
shorter processing time, i.e., that it is superior in
machinability.
[0072] (Radial Crushing Test)
[0073] A ring-shaped sintered compact was pressed in the
diametrical direction gradually with an increasing pressure load
until the sintered compact broke down according to the method
regulated by JIS Z2507 "Sintering bearing--Determination of radial
crushing strength". The radial crushing strength constant K
(N/mm.sup.2) was calculated from the maximum pressure load above in
accordance with the following formula (1) (wherein, F: maximum load
(N) when the compact broke down; L: length of ring-shaped compact
(mm); D: outer diameter of ring-shaped compact (mm); and e: wall
thickness of ring-shaped compact (mm)). K=F(D-e)/(L.times.e.sup.2)
(1)
[0074] TABLE-US-00001 TABLE 1 Mixing Ratio mass % Fe--P Alloy
Cu--Sn Alloy Powder Powder Comp. Comp. Sample Fe Powder mass % mass
% Graphite No Type Fe P Cu Sn Powder Comments 01 92.45 ore reduced
0.15 80.00 20.00 5.00 90.00 10.00 2.40 Fe--P add.: <min.; P
cont.: <min. 02 92.33 ore reduced 0.27 80.00 20.00 5.00 90.00
10.00 2.40 Fe--P add.: min. 03 92.25 ore reduced 0.35 80.00 20.00
5.00 90.00 10.00 2.40 04 92.20 ore reduced 0.40 80.00 20.00 5.00
90.00 10.00 2.40 05 92.10 ore reduced 0.50 80.00 20.00 5.00 90.00
10.00 2.40 Fe--P add.: max. 06 91.90 ore reduced 0.70 80.00 20.00
5.00 90.00 10.00 2.40 07 91.60 ore reduced 1.00 80.00 20.00 5.00
90.00 10.00 2.40 Fe--P add.: >max.; P cont.: >max. 08 92.33
ore reduced 0.27 85.00 15.00 5.00 90.00 10.00 2.40 Fe--P add.:
min.; P in Fe--P: min.; P cont.: min. 09 91.90 ore reduced 0.70
79.00 21.00 5.00 90.00 10.00 2.40 Fe--P add.: max.; P in Fe--P:
max.; P cont.: max. 10 91.20 atomized 1.40 80.00 20.00 5.00 90.00
10.00 2.40 corresp. to alloy in JPB55-34858 11 92.46 ore reduced
0.40 80.00 20.00 4.74 95.00 5.00 2.40 Sn in Cu--Sn: <min.; Sn
cont.: <min. 12 92.31 ore reduced 0.40 80.00 20.00 4.89 92.00
8.00 2.40 Sn in Cu--Sn: min. 13 92.14 ore reduced 0.40 80.00 20.00
5.06 89.00 11.00 2.40 Sn in Cu--Sn: max. 14 91.91 ore reduced 0.40
80.00 20.00 5.29 85.00 15.00 2.40 Sn in Cu--Sn: >max.; Sn cont.:
>max. 15 94.20 ore reduced 0.40 80.00 20.00 3.00 90.00 10.00
2.40 Cu--Sn add.: <min.; Cu in Cu--Sn: <min. 16 93.20 ore
reduced 0.40 80.00 20.00 4.00 90.00 10.00 2.40 Cu--Sn add.:
<min. 17 92.70 ore reduced 0.40 80.00 20.00 4.50 90.00 10.00
2.40 18 91.80 ore reduced 0.40 80.00 20.00 5.40 90.00 10.00 2.40
Cu--Sn add.: >max. 19 91.20 ore reduced 0.40 80.00 20.00 6.00
90.00 10.00 2.40 Cu--Sn add.: >max.; Cu in Cu--Sn: >max. 20
93.27 ore reduced 0.40 80.00 20.00 3.93 92.00 8.00 2.40 Cu--Sn
add.: min.; Sn in Cu--Sn: min.; Sn cont.: min. 21 91.76 ore reduced
0.40 80.00 20.00 5.44 89.00 11.00 2.40 Cu--Sn add.: max.; Sn in
Cu--Sn: max.; Sn cont.: max. 22 93.27 ore reduced 0.40 80.00 20.00
3.93 89.00 11.00 2.40 Cu--Sn add.: min.; Sn in Cu--Sn: max.; Cu
cont.: min. 23 91.76 ore reduced 0.40 80.00 20.00 5.44 92.00 8.00
2.40 Cu--Sn add.: max.; Sn in Cu--Sn: min.; Cu cont.: max. 24 93.40
ore reduced 0.40 80.00 20.00 5.00 90.00 10.00 1.20 graphite add.:
<min.; C cont.: <min. 25 92.90 ore reduced 0.40 80.00 20.00
5.00 90.00 10.00 1.70 graphite add.: min.; C cont.: min. 26 91.90
ore reduced 0.40 80.00 20.00 5.00 90.00 10.00 2.70 graphite add.:
max.; C cont.: max. 27 91.60 ore reduced 0.40 80.00 20.00 5.00
90.00 10.00 3.00 graphite add.: >max.; C cont.: >max.
[0075] TABLE-US-00002 TABLE 2 Composition mass % Sample Metal No Fe
P Cu Sn C Oxide Comments 01 91.65 0.03 4.50 0.50 2.20 0.92 Fe--P
add.: <min.; P cont.: <min. 02 91.62 0.05 4.50 0.50 2.20 0.92
Fe--P add.: min. 03 91.61 0.07 4.50 0.50 2.20 0.92 04 91.60 0.08
4.50 0.50 2.20 0.92 05 91.58 0.10 4.50 0.50 2.20 0.92 Fe--P add.:
max. 06 91.54 0.14 4.50 0.50 2.20 0.92 07 91.48 0.20 4.50 0.50 2.20
0.92 Fe--P add.: >max.; P cont.: >max. 08 91.64 0.04 4.50
0.50 2.20 0.92 Fe--P add.: min.; P in Fe--P: min.; P cont.: min. 09
91.53 0.15 4.50 0.50 2.20 0.92 Fe--P add.: max.; P in Fe--P: max.;
P cont.: max. 10 92.32 0.28 4.50 0.50 2.20 0.18 corresp. to alloy
of JPB-55-34858 11 91.86 0.08 4.50 0.24 2.20 0.92 Sn in Cu--Sn:
<min.; Sn cont.: <min. 12 91.71 0.08 4.50 0.39 2.20 0.92 Sn
in Cu--Sn: min. 13 91.54 0.08 4.50 0.56 2.20 0.92 Sn in Cu--Sn:
max. 14 91.31 0.08 4.50 0.79 2.20 0.92 Sn in Cu--Sn: >max.; Sn
cont: >max. 15 93.58 0.08 2.70 0.30 2.20 0.94 Cu--Sn add.:
<min.; Cu in Cu--Sn: <min. 16 92.59 0.08 3.60 0.40 2.20 0.93
Cu--Sn add.: <min. 17 92.09 0.08 4.05 0.45 2.20 0.93 18 91.20
0.08 4.86 0.54 2.20 0.92 Cu--Sn add.: >max. 19 90.61 0.08 5.40
0.60 2.20 0.91 Cu--Sn add.: >max.; Cu in Cu--Sn: >max. 20
92.66 0.08 3.62 0.31 2.20 0.93 Cu--Sn add.: min.; Sn in Cu--Sn:
min.; Sn cont.: min. 21 91.16 0.08 4.84 0.60 2.20 0.92 Cu--Sn add.:
max.; Sn in Cu--Sn: max.; Sn cont.: max. 22 92.66 0.08 3.50 0.43
2.20 0.93 Cu--Sn add.: min.; Sn in Cu--Sn: max.; Cu cont.: min. 23
91.16 0.08 5.00 0.44 2.20 0.92 Cu--Sn add.: max.; Sn in Cu--Sn:
min.; Cu cont.: max. 24 92.79 0.08 4.50 0.50 1.00 0.93 graphite
add.: <min.; C cont.: <min. 25 92.29 0.08 4.50 0.50 1.50 0.93
graphite add.: min.; C cont.: min. 26 91.30 0.08 4.50 0.50 2.50
0.92 graphite add.: max.; C cont.: max. 27 91.00 0.08 4.50 0.50
2.80 0.92 graphite add.: >max.; C cont.: >max.
[0076] TABLE-US-00003 TABLE 3 Ratio in Met. Section area % Fe--P--C
Estimation Items Compound Phase Ferrite Radial Thickness Cu--Sn
Free Phase in Wear Machin- Crushing Sample .mu.m Alloy Graphite
Matrix Amount ability Str. Con. No <5 5-15 .gtoreq.15 Phase mass
% area % .mu.m Index MPa Comments 01 0.10 91 9 0 2.2 1.88 0.0 81
16.3 486 Fe--P add.: <min.; P cont: <min. 02 1.00 88 11 1 2.2
1.66 0.0 54 22.5 536 Fe--P add.: min. 03 1.50 84 13 3 2.3 1.52 0.0
47 25.0 579 04 1.90 81 15 4 2.3 1.42 1.2 46 28.8 596 05 2.20 76 18
6 2.2 1.33 2.6 43 30.0 613 Fe--P add.: max. 06 2.90 68 24 8 2.2
1.22 5.7 40 33.8 638 07 5.90 45 35 20 2.4 1.02 19.1 34 91.3 637
Fe--P add.: >max.; P cont.: >max. 08 0.30 90 10 0 2.3 1.67
0.0 56 17.5 517 Fe--P add.: min.; P in Fa--P: min.; P cont.: min.
09 3.00 65 25 10 2.3 1.24 6.0 40 33.8 635 Fe--P add.: max.; P in
Fe--P: max.; P cont.: max. 10 10.00 1 45 54 2.3 0.71 26.1 30 100.0
602 corresp. to alloy of JPB55-34858 11 2.10 76 17 7 2.1 1.42 1.2
61 13.8 472 Sn in Cu--Sn: <min.; Sn cont.: <min. 12 2.10 80
15 5 2.2 1.42 1.2 52 25.6 584 Sn in Cu--Sn: min. 13 2.00 84 14 2
2.3 1.42 1.2 46 30.6 600 Sn in Cu--Sn: max. 14 2.10 85 14 1 2.5
1.42 1.2 44 36.9 529 Sn in Cu--Sn: >max.; Sn cont.: >max. 15
2.50 74 18 8 0.6 1.42 1.6 72 40.0 411 Cu--Sn add.: <min.; Cu in
Cu--Sn: <min. 16 2.30 79 16 5 1.2 1.42 1.4 58 32.5 547 Cu--Sn
add.: <min. 17 2.10 80 16 4 1.7 1.42 1.3 51 30.0 581 18 1.80 83
15 2 2.8 1.42 0.0 44 25.0 601 Cu--Sn add.: >max. 19 1.60 85 14 1
4.1 1.42 0.0 40 21.3 587 Cu--Sn add.: >max.; Cu in Cu--Sn:
>max. 20 2.40 76 16 8 1.1 1.42 1.4 76 10.6 488 Cu--Sn add.:
min.; Sn in Cu--Sn: min.; Sn cont.: min. 21 1.50 85 14 1 2.8 1.42
0.0 42 32.5 608 Cu--Sn add.: max.; Sn in Cu--Sn: max.; Sn cont.:
max. 22 2.30 76 17 7 1.0 1.42 1.5 57 36.3 518 Cu--Sn add.: min.; Sn
in Cu--Sn: max.; Cu cont.: min. 23 1.90 84 15 1 3.0 1.42 0.0 45
20.6 609 Cu--Sn add.: max.; Sn in Cu--Sn: min.; Cu cont.: max. 24
1.30 90 9 1 2.2 0.71 0.6 82 46.3 621 graphite add.: <min.; C
cont: <min. 25 1.50 85 13 2 2.3 1.02 0.9 55 37.5 607 graphite
add.: min.; C cont: min. 26 2.70 72 21 7 2.3 1.70 3.6 40 23.8 527
graphite add: max.; C cont.: max. 27 3.90 52 32 16 2.2 2.03 6.0 37
21.9 394 graphite add.: >max.; C cont.: >max.
[0077] The content of phosphorus in the whole composition changes
among samples 1 to 9; the content of phosphorus in the
iron-phosphorus alloy powder is kept constant among samples 1 to 7;
and the contents of phosphorus both in the entire composition and
in the iron-phosphorus alloy powder change among samples 8 and 9.
The relationships among the phosphorus content in the whole
composition and the ratios of the respective phases in these
samples and sample 10 (the sintered alloy disclosed in JP-B No.
55-034853, referred to below as conventional alloy) are shown in
FIGS. 3A-3D, and the relationship of the phosphorus content with
the thickness of the iron-phosphorus-carbon compound phase and the
material properties (wear amount, machinability index and radial
crushing strength constant) are shown in FIGS. 4A-4D.
[0078] As apparent from FIGS. 3A, 3C and 3D and FIG. 4A, the ratio
of copper-tin alloy phase does not vary according to the increase
in the phosphorus content (FIG. 3B), but the ratio and thickness of
iron-phosphorus-carbon compound phase increase drastically
according to increase in the phosphorus content, and the amount of
free graphite phase decreases and that of ferrite phase increases
in the phosphorus content range of more than 0.15 mass %. The
results indicate that formation of iron-phosphorus-carbon compound
is accelerated by the increase in phosphorus content but formation
of the iron-phosphorus-carbon compound consumes free graphite and
the carbon dissolved in the matrix, consequently-increasing the
ratio of ferrite phase. In addition, as shown in FIGS. 4B, 4C and
4D, the sintered compacts having a phosphorus content of less than
0.04 mass % are superior in machinability, but have a greater wear
amount and a smaller radial crushing strength constant. When the
phosphorus content is 0.04 mass % or more, the radial crushing
strength increases and the wear amount decreases, but the
machinability index decline, according to increase in phosphorus
content. In particular when the phosphorus content is 0.15 mass %
or more, the machinability index increases significantly.
[0079] As shown in FIGS. 3D, 4A and 4C, fluctuation in
machinability index has significant correlations with the ratio of
the iron-phosphorus-carbon compound phase produced and the ratio of
its portion having a thickness of 15 microns or more. In the
phosphorus content range of 0.15 mass % or more, the ratio of the
iron-phosphorus-carbon compound phase having a thickness of 15
microns or more becomes 10 area % or less and the machinability
index becomes smaller at 35 or less. That is, fineness or reduction
in dimensions of the iron-phosphorus-carbon compound phase leads to
improvement in machinability.
[0080] On the other hand, fluctuation of the radial crushing
strength has a correlation with the ratio of iron-phosphorus-carbon
compound phase. The radial crushing strength constant increases
along with increase in the ratio of iron-phosphorus-carbon compound
phase, and the sintered compacts have a sufficiently high radial
crushing strength constant of approximately 500 MPa or more in the
phosphorus content range of 0.04 mass % or more, in which the ratio
of iron-phosphorus-carbon compound phase becomes 0.1 area % or
more, and a radial crushing strength higher than that of the
conventional alloy is exhibited at a phosphorus content of 0.1 mass
% or more. However, the ratio of ferrite phase, which is lower in
strength, increases along with the increase in phosphorus content,
and a phosphorus content of 0.2 mass % or more on the contrary
leads to deterioration in strength.
[0081] Fluctuation in wear amount has a correlation with the ratio
of the iron-phosphorus-carbon compound phase generated, the wear
amount of sintered compacts decreases drastically in the range
where the phosphorus content is 0.04 mass % or more and the ratio
of iron-phosphorus-carbon compound phase is 0.1 area. That is, the
wear amount decreases along with the increase in phosphorus content
and in the ratio of the iron-phosphorus-carbon compound phase
produced.
[0082] The results above indicate that valve guides favorable in
all of radial crushing strength, machinability and abrasion
resistance can be obtained, when the phosphorus content in the
whole composition is 0.04 to 0.15 mass %, the ratio of
iron-phosphorus-carbon compound phase is 0.1 to 3 area %, and the
ratio of a portion of the iron-phosphorus-carbon compound phase
having a thickness of 15 ,,m or more relative to the whole
iron-phosphorus-carbon compound phase is 10% or less as area
ratio.
[0083] In samples 4 and 11 to 23, the tin content and/or the copper
content in the whole composition change. More specifically, the
copper content is constant among samples 4 and 11 to 14, the
composition of the copper-tin alloy powder used is the same among
samples 4 and 15 to 19, and the tin and copper contents in the
whole composition and the composition of copper-tin alloy powder
change among samples 20 to 23. For these samples and sample 13, the
relationship of the tin content in the whole composition and the
ratios of respective phases is shown in FIGS. 5A-5D, and the
relationships of the tin content with the thickness of the
iron-phosphorus-carbon compound phase and material properties (wear
amount, machinability index and radial crushing strength constant)
are shown in FIGS. 6A-6D. In addition, the relationship between the
copper content in the whole composition and the ratios of
respective phases is shown in FIGS. 7A-7D, and the relationships of
the copper content with the thickness of the iron-phosphorus-carbon
compound phase and material properties (wear amount, machinability
index and radial crushing strength constant) in FIGS. 8A-8D.
[0084] The change in the ratio of copper-tin alloy phase shown in
FIG. 5B varies significantly according to the manner of adding tin,
and, considering these results and those in FIG. 7B, the ratio of
copper-tin alloy phase seems to be more dependent on copper content
rather than on tin content. In addition, FIGS. 5A, 5C, 5D and FIG.
6A also indicate the tin content exerts a smaller influence on the
configuration of the phases in metallographic structure.
[0085] In contrast, the wear resistance and the radial crushing
strength increase while the machinability decreases, along with
increase in tin content. It is because of increase in the amount of
the tin dissolved in the matrix. When the tin content is 0.3 mass %
or more in the whole composition, the sintered compacts have
favorable wear resistance and radial crushing strength, i.e., a
wear amount of 70 microns or less and a radial crushing strength
constant of 500 MPa or more. From the point of machinability, a tin
content of 0.6 mass % or less is preferable.
[0086] According to FIG. 7A and FIG. 8A, increase in copper content
leads to decrease in the ratio and the thickness of
iron-phosphorus-carbon compound phase, resulting in improvement in
the machinability as shown in FIG. 8C. It is because the copper
improves the hardenability of the matrix and makes fast the
apparent cooling speed (influence by cooling speed will be
described below in detail.). In addition, FIG. 7B indicates that
increase in copper content raises the ratio of copper-tin alloy
phase. The presence of a copper-tin alloy phase, which is soft and
superior in compatibility, improves the wear resistance and
facilitates processing, and the sintered compacts show a favorable
machinability index of 35 or more in the copper content range of
3.5 mass % or more (FIG. 8C). Here, it is noted that the copper-tin
alloy also improves the radial crushing strength (FIG. 8D), but
reduces the strength at a content of 5.0 mass % or more because of
the excessive softness of the copper-tin alloy phase. From these
results, the content of tin is favorably in the range of 0.3 to 0.6
mass %, and that of copper in the range of 3.5 to 5.0 mass %.
[0087] In samples 4 and 24 to 27, the carbon content in the whole
composition is altered. The relationships between the carbon
content in the whole composition and the ratios of respective
phases of these samples and sample 13 are shown in FIGS. 9A-9D, and
the relationships of the carbon content with the thickness of the
iron-phosphorus-carbon compound phase and the material properties
(wear amount, machinability index and radial crushing strength
constant) are shown in FIGS. 10A-10D.
[0088] It is understood from FIGS. 9A and 10A, the ratio of
iron-phosphorus-carbon compound phase and the thickness thereof
increase along with the increase in carbon content. The amount of
free graphite phase also increases (FIG. 9C). However, FIG. 9D
shows that the ratio of ferrite phase increases drastically at a
carbon content of more than 2.5 mass %, indicating that the
production of the iron-phosphorus-carbon compound phase is
accompanied with removal of carbon from the matrix.
[0089] The machinability index shown in FIG. 10C is influenced by
the thickness of the iron-phosphorus-carbon compound phase as well
as the ratio of free graphite phase. That is, the machinability
index becomes minimal in the carbon content range of 1.5 to 2.5
mass %, in combination of: the reduction in machinability index
(improvement in machinability) caused by the increase of the free
graphite phase; and the increase in machinability index
(deterioration in machinability) caused by the increase and growth
of the iron-phosphorus-carbon compound phase. As to the wear
amount, it is regarded to decline with increase in the ratio of
iron-phosphorus-carbon compound phase. However, the radial crushing
strength constant, which is expected to be improved along with the
increase in the ratio of iron-phosphorus-carbon compound phase,
decreases as shown in FIG. 10D, especially drastically at a carbon
content of over 2.5 mass %. It is because the increase in the
carbon powder content leads to deterioration of the compressibility
of powder mixture and consequently to deterioration in the strength
of both green and sintered compacts. From these results, the range
of the carbon content most preferable from the points of radial
crushing strength, machinability and wear resistance is 1.5 to 2.5
mass %.
Example 2
[0090] (Samples 28 to 38)
[0091] Sintered compact samples 28 to 31 were prepared by using a
powder mixture having the same composition as that for sample 4 of
Example 1 and by repeating the operations (preparation of powder
mixture, formation of green compact, sintering, and cooling)
similar to those for sample 4, except that the sintering
temperature was changed to 900.degree. C. (sample 28), 950.degree.
C. (sample 29), 1,050.degree. C. (sample 30), or 1,100.degree. C.
(sample 31) as shown in Table 4. The composition of the entire
powder mixture of each sample is shown in Table 5.
[0092] Separately, sintered compact samples 32 to 36 were prepared
by repeating the operations similar to those for sample 4
(preparation of powder mixture, formation of green compact,
sintering, and cooling), except that the sintering period was
changed to 10 minutes (sample 32), 20 minutes (sample 33), 45
minutes (sample 34), 90 minutes (sample 35), or 120 minutes (sample
36).
[0093] Yet separately, sintered compact samples 37 and 38 were
prepared by repeating the operations similar to those for sample 4
(preparation of powder mixture, formation of green compact,
sintering, and cooling), except that the cooling rate after
sintering was changed to 8.degree. C./min (sample 37) or 4.degree.
C./min (sample 33).
[0094] By using each of the sintered compact samples 28 to 38, the
ratios of respective phases in the cross section of the
metallographic structure of the sintered compact were determined by
cross sectional area observation, and the abrasion, machinability
and radial crushing tests thereof were performed in a similar
manner to samples 1 to 27. The results are summarized in Table 6.
TABLE-US-00004 TABLE 4 Mixing Ratio mass % Ore Fe--20P Cu--10Sn
Sint. Sint. Cooling Sample Reduced Alloy Alloy Graphite Temp. Time
Rate No Fe Pwd. Powder Powder Powder .degree. C. min. .degree.
C./min. Comments 04 92.20 0.40 5.00 2.40 1000 60 12 28 92.20 0.40
5.00 2.40 900 60 12 sint. temp.: <min. 29 92.20 0.40 5.00 2.40
950 60 12 sint. temp.: min. 30 92.20 0.40 5.00 2.40 1050 60 12
sint. temp.: max. 31 92.20 0.40 5.00 2.40 1100 60 12 sint. temp.:
>max. 32 92.20 0.40 5.00 2.40 1000 10 12 33 92.20 0.40 5.00 2.40
1000 20 12 34 92.20 0.40 5.00 2.40 1000 45 12 35 92.20 0.40 5.00
2.40 1000 90 12 36 92.20 0.40 5.00 2.40 1000 120 12 sint. time:
>max. 37 92.20 0.40 5.00 2.40 1000 60 8 cooling rate: min. 38
92.20 0.40 5.00 2.40 1000 60 4 cooling rate: <min.
[0095] TABLE-US-00005 TABLE 5 Composition mass % Sample Metal No Fe
P Cu Sn C Oxide Comments 04 91.60 0.08 4.50 0.50 2.20 0.92 28 91.60
0.08 4.50 0.50 2.20 0.92 sint. temp.: <min. 29 91.60 0.08 4.50
0.50 2.20 0.92 sint. temp.: min. 30 91.60 0.08 4.50 0.50 2.20 0.92
sint. temp.: max. 31 91.60 0.08 4.50 0.50 2.20 0.92 sint. temp.:
>max. 32 91.60 0.08 4.50 0.50 2.20 0.92 33 91.60 0.08 4.50 0.50
2.20 0.92 34 91.60 0.08 4.50 0.50 2.20 0.92 35 91.60 0.08 4.50 0.50
2.20 0.92 36 91.60 0.08 4.50 0.50 2.20 0.92 sint. time: >miax.
37 91.60 0.08 4.50 0.50 2.20 0.92 cooling rate: min. 38 91.60 0.08
4.50 0.50 2.20 0.92 cooling rate: <min.
[0096] TABLE-US-00006 TABLE 6 Ratio in Met. Section area % Fe--P--C
Estimation Items Compound Phase Ferrite Radial Thickness Cu--Sn
Free Phase in Wear Crushing Sample .mu.m Alloy Graphite Matrix
Amount Machinability Str. Con. No <5 5-15 .gtoreq.15 Phase mass
% mass % .mu.m Index MPa Comments 04 1.90 81 15 4 2.3 1.42 1.2 46
28.8 596 28 0.00 0 0 0 2.0 2.03 96.6 95 10.0 297 sint. temp.:
<min. 29 0.29 85 15 0 2.2 1.52 8.9 68 15.0 509 sint. temp.: min.
30 2.93 55 36 9 2.2 1.22 3.8 43 35.0 615 sint. temp.: max. 31 4.44
39 43 18 2.2 0.51 26.7 40 42.5 476 sint. temp.: >max. 32 1.81 82
18 0 2.1 1.92 9.4 66 11.9 387 33 1.93 73 26 1 2.2 1.72 4.6 58 18.8
542 34 2.11 70 29 1 2.3 1.52 1.5 50 25.6 588 35 2.86 57 38 5 2.4
1.22 6.2 42 34.4 584 36 3.87 38 45 17 2.5 0.61 19.4 38 41.9 567
sint. time: >max. 37 2.96 56 35 9 2.3 1.42 4.3 43 30.0 591
cooling rate: min. 38 5.33 38 42 20 2.3 1.42 18.6 38 50.6 582
cooling rate: <min.
[0097] The relationships between the sintering temperature and the
ratios of respective phases in the whole composition in samples 4
and 28 to 31 are shown in FIGS. 11A-11D, and the relationships of
the sintering temperature with the thickness of the
iron-phosphorus-carbon compound phase and the material properties
(wear amount, machinability index and radial crushing strength
constant) are shown in FIGS. 12A-12D.
[0098] According to FIG. 11B, the ratio of the copper-tin alloy
phase is independent of the sintering temperature. On the other
hand, the iron-phosphorus-carbon compound phase is formed when it
is higher than 900.degree. C., and the ratio and the thickness
thereof increase along with elevation in the sintering temperature
(FIGS. 11A and 12A), while the ratio of free graphite decreases on
the contrary (FIG. 11C). It is because solubilization and diffusion
of graphite progress more rapidly at higher sintering temperature,
and the high ratios of ferrite phase at lower sintering temperature
are due to difficulty in diffusion of the graphite grains. However,
the ratio of ferrite phase increases at a sintering temperature of
over 1100.degree. C. because of the deficiency of carbon caused by
excessive formation of the iron-phosphorus-carbon compound phase
(FIG. 11D).
[0099] Definite correlations of the thickness of the
iron-phosphorus-carbon compound phase and the ratio of free
graphite phase with the machinability index are possibly observed
also in FIGS. 11A-11D and 12A-12D. The sintering temperature
leading to a machinability index of 35 or less is in the range of
1,050.degree. C. or less, wherein the ratio of
iron-phosphorus-carbon compound phase becomes approximately 3 area
% or less and the ratio of the iron-phosphorus-carbon compound
phase having a thickness of 15 microns or more becomes 10% or
less.
[0100] For the radial crushing strength, it has a correlation with
the ratio of iron-phosphorus-carbon compound phase as well as with
the ratio of ferrite phase, and the radial crushing strength
decreases at a higher ratio of ferrite phase. The sintering
temperature leading to a radial crushing strength of 500 MPa or
more is in the range of 950 to 1,050.degree. C., wherein the ratio
of iron-phosphorus-carbon compound phase becomes approximately 0.2
to 3 area % and that of ferrite phase approximately 9 area % or
less.
[0101] As described above, even if the composition is the same, the
metallographic structure formed and the material properties thereof
differ significantly depending on the sintering temperature. The
sintered valve guides exhibiting favorable material properties,
which are produced at a practical sintering temperature of
950.degree. C. to 1,050.degree. C., have the iron-phosphorus-carbon
compound phase at a ratio of approximately 0.2 to 3 area %, the
iron-phosphorus-carbon compound phase having a thickness of 15
microns or more at a ratio of 10% or less of the whole
iron-phosphorus-carbon compound phase, and the ferrite phase at a
ratio of approximately 9 area % or less.
[0102] For samples 4 and 32 to 36, the relationships between the
sintering time and the ratios of respective phases in the whole
composition and 32 to 36 are shown in FIGS. 13A-13D, and the
relationships of the sintering time with the thickness of the
iron-phosphorus-carbon compound phase and the material properties
(wear amount, machinability index and radial crushing strength
constant) are shown in FIGS. 14A-14D.
[0103] As apparent from FIGS. 13A, 13C and 13D, solid solution and
diffusion of carbon and formation of the iron-phosphorus-carbon
compound phase progress according as the sintering time is made
long, and the ratio of the ferrite phase increases when the carbon
diffusion is insufficient or when the iron-phosphorus-carbon
compound phase is formed excessively. These results resemble the
influences by sintering temperature.
[0104] Thus, the correlations of the ratio of
iron-phosphorus-carbon compound phase and the thickness and the
ratio of free graphite phase with the machinability index are
possibly observed also in FIGS. 13A-13D and 14A-14D, and the
sintering time leading to a machinability index of 35 or less is in
the range of 90 minutes or less, wherein the ratio of
iron-phosphorus-carbon compound phase becomes approximately 3 area
% or less, the ratio of the iron-phosphorus-carbon compound phase
having a thickness of 15 microns or more becomes approximately 10%
or less of the whole iron-phosphorus-carbon compound phase, and the
ratio of free graphite phase becomes 1 area % or more.
[0105] In addition, the sintering time leading to a radial crushing
strength of 500 MPa or more is in the range of 20 min or more. Even
at a sintering time of 20 min or less, the iron-phosphorus-carbon
compound phase is formed in an amount sufficient for exhibiting a
particular strength, and thus the metallographic structure per se
is formed. The increase in the strength of sintered compacts caused
by elongation of sintering time is due to growth of the necks
between iron particles, and the sintering time should be decided
properly according to desirable radial crushing strength and wear
resistance.
[0106] For samples 4, 37, and 38, the relationships between the
cooling rate and the ratios of respective phases in the whole
composition are shown in FIGS. 15A-15D and the relationships of the
cooling rate with the thickness of the iron-phosphorus-carbon
compound phase and the material properties (wear amount,
machinability index and radial crushing strength constant) are
shown in FIGS. 16A-16D.
[0107] As apparent from FIGS. 15A-15D and 16A, the amounts of
copper-tin alloy phase and free graphite phase do not vary
according to the cooling rate, but the amounts of
iron-phosphorus-carbon compound phase and ferrite phase declines,
and thus the thickness of the iron-phosphorus-carbon compound phase
also decreases at larger cooling rate.
[0108] Among material properties, machinability is most affected by
the change of the cooling rate. In general, according as the
cooling rate increases, the precipitation produced at
solidification of a liquid matter become smaller in dimensions at a
higher cooling rate. The iron-phosphorus-carbon compound phase
precipitated in the sintered valve guide becomes thinner and the
amount thereof smaller, accompanied by decrease in the ratio of
ferrite phase. As a result, the machinability of the resulting
compacts is improved. The precipitation of copper-tin alloy phase
precipitated from liquid phase also become smaller. The cooling
rate leading to a machinability index of 35 or less is in the range
of 8.degree. C./min or more, wherein the ratio of
iron-phosphorus-carbon compound phase becomes 3 area % or less, the
ratio of the iron-phosphorus-carbon compound phase having a
thickness of 15 microns or more becomes 10% or less of the whole
iron-phosphorus-carbon phase, and the ratio of ferrite phase
becomes 5 area % or less.
Example 3
[0109] (Samples 39 to 49)
[0110] Sintered compact samples 39 and 42 were prepared in
accordance with the powder mixture composition for each sample
shown in Table 7, by repeating the operations similar to those for
sample 4 (preparation of powder mixture, formation of green
compact, sintering and cooling), except that the content of oxides
in the raw iron powder was changed to 0.2 mass % (mill scale
reduced iron powder, sample 39), 0.5 mass % (sample 40), 1.5 mass %
(sample 41), or 2.0 mass % (sample 42). The composition of the
entire powder mixture for each sample is shown in Table 8.
[0111] Separately, sintered compact samples 43 to 49 were prepared
by repeating the operations similar to those for sample 4
(preparation of powder mixture, formation of green compact,
sintering, and cooling), except that a part or all of the ore
reduced iron powder is replaced with an atomized iron powder (oxide
content: 0.2 mass %) and the ratio thereof in the composition of
the entire powder mixture was changed to 5 mass % (sample 43), 10
mass % (sample 44), 15 mass % (sample 45), 20 mass % (sample 46),
30 mass % (sample 47), 40 mass % (sample 48), or 92.2 wt % (sample
49).
[0112] By using each of the sintered compact samples 39 to 49, the
ratios of respective phases in the cross section of the
metallographic structure of the sintered compact were determined by
cross sectional area observation, and the abrasion, machinability
and radial crushing tests thereof were performed in a similar
manner to samples 1 to 27. The results are summarized in Table 9.
TABLE-US-00007 TABLE 7 Mixing Ratio mass % Ore Reduced Iron Powder
Atomized Millscale Fe--20P Cu--10Sn Sample Oxide Iron Reduced Alloy
Alloy Graphite No mass % Powder Iron Pwd. Powder Powder Powder
Comments 04 92.20 1.00 0.40 5.00 2.40 10 91.20 1.40 5.00 2.40
corresp. to alloy of JPB55-34858 39 0.20 92.20 0.40 5.00 2.40 oxide
in Fe pwd.: <min., using millscale reduced Fe 40 92.20 0.50 0.40
5.00 2.40 oxide in Fe pwd.: min. 41 92.20 1.50 0.40 5.00 2.40 oxide
in Fe pwd.: max. 42 92.20 2.00 0.40 5.00 2.40 oxide in Fe pwd.:
>max. 43 87.20 1.00 5.00 0.40 5.00 2.40 44 82.20 1.00 10.00 0.40
5.00 2.40 45 77.20 1.00 15.00 0.40 5.00 2.40 46 72.20 1.00 20.00
0.40 5.00 2.40 47 62.20 1.00 30.00 0.40 5.00 2.40 48 52.20 1.00
40.00 0.40 5.00 2.40 49 92.20 0.40 5.00 2.40 using atomized Fe
pwd.
[0113] TABLE-US-00008 TABLE 8 Composition mass % Sample Metal No Fe
P Cu Sn C Oxide Comments 04 91.60 0.08 4.50 0.50 2.20 0.92 10 92.32
0.28 4.50 0.50 2.20 0.18 corresp. to alloy of JPB55-34858 39 92.52
0.08 4.50 0.50 2.20 0.18 oxide in Fe pwd.: (min., using millscale
reduced Fe 40 92.06 0.08 4.50 0.50 2.20 0.46 oxide in Fe pwd.: min.
41 91.14 0.08 4.50 0.50 2.20 1.38 oxide in Fe pwd.: max. 42 90.68
0.08 4.50 0.50 2.20 1.84 oxide in Fe pwd.: >max. 43 91.65 0.08
4.50 0.50 2.20 0.88 44 91.70 0.08 4.50 0.50 2.20 0.84 45 91.75 0.08
4.50 0.50 2.20 0.80 46 91.80 0.08 4.50 0.50 2.20 0.76 47 91.90 0.08
4.50 0.50 2.20 0.68 48 92.00 0.08 4.50 0.50 2.20 0.60 49 92.52 0.08
4.50 0.50 2.20 0.18 using atomized Fe pwd.
[0114] TABLE-US-00009 TABLE 9 Ratio in Met. Section area % Fe--P--C
Estimation Items Compound Phase Radial Thickness Cu--Sn Free
Ferrite Wear Crushing Sample .mu.m Alloy Graphite Phase in Amount
Machinability Str.Con. No <5 5-15 .gtoreq.15 Phase mass % Matrix
.mu.m Index MPa Comments 04 1.90 81 15 4 2.3 1.42 1.2 46 28.8 596
10 10.00 1 45 54 2.3 0.71 26.1 30 100.0 602 corresp. to alloy of
JPB55-34858 39 2.26 68 29 3 2.2 1.42 1.2 41 41.3 627 oxide in Fe
pwd.: <min., using millscale Fe 40 2.26 67 30 3 2.2 1.42 1.2 44
35.0 611 oxide in Fe pwd.: min. 41 2.27 66 31 3 2.3 1.42 1.2 53
18.8 567 oxide in Fe pwd.: Max. 42 2.27 67 30 3 2.2 1.42 1.2 71
12.5 471 oxide in Fe pwd.: >max. 43 2.26 68 31 1 2.3 1.42 1.2 46
30.6 604 44 2.26 67 31 2 2.3 1.42 1.2 44 31.9 607 45 2.27 65 33 2
2.3 1.42 1.2 42 33.1 612 46 2.28 66 32 2 2.3 1.42 1.2 42 34.4 615
47 2.26 68 31 1 2.3 1.42 1.2 41 36.3 620 48 2.27 67 32 1 2.3 1.42
1.2 41 36.9 625 49 2.27 67 30 3 2.3 1.22 1.2 40 38.1 650 using
atomized Fe pwd.
[0115] The relationships between the oxide content in iron powder
and the ratios of respective phases in the whole composition of
samples 4, 10 and 39 to 42 are shown in FIGS. 17A-17D, and the
relationships of the oxide content in iron powder with the
thickness of the iron-phosphorus-carbon compound phase and the
material properties (wear amount, machinability index and radial
crushing strength constant) are shown in FIGS. 18A-18D.
[0116] As shown in FIGS. 17A-17D and 18A, the oxide content in iron
powder has almost no influence on formation of other phases such as
iron-phosphorus-carbon compound phase and copper-tin alloy phase,
and the oxides are present singly in the metallographic structure.
On the other hand, the machinability index decreases as the oxide
content increases (FIG. 18C). However, the radial crushing strength
constant decreases and the wear amount increases at the same time
(FIG. 13D). Thus, from FIGS. 18B-18D, the oxide content in iron
powder leading to a machinability index of 35 or less, a radial
crushing strength constant of 500 MPa or more and a wear amount of
360 microns or less is in the range of approximately 0.5 to 1.5
mass %.
[0117] The relationships between the blending ratio of atomized
iron powder and the ratios of respective phases in the whole
composition of samples 4, 10, and 43 to 49 are shown in FIGS.
19A-19D, and the relationships of the blending ratio of atomized
iron powder with the thickness of the iron-phosphorus-carbon
compound phase and the material properties (wear amount,
machinability index and radial crushing strength constant) are
shown in FIGS. 20A-20D.
[0118] There is no observable influence of the blending ratio of
atomized iron powder on formation of other phases, also in FIGS.
19A-19D and 20A. As apparent from FIGS. 20B-20D, it has a small
influence on material properties, and specifically, the radial
crushing strength constant increases as the amount of the atomized
iron powder blended increases, and the strength is highest when
only an atomized iron powder is used. In addition, the
machinability index decreases when the amount of the atomized iron
powder blended is reduced, and in particular, the improvement in
machinability is more effective when the amount of the atomized
iron powder added is 30 mass % or less. The machinability index
when a mill scale reduced iron powder is used is almost identical
with that when an atomized iron powder is used, but is better than
that when an ore reduced iron powder is used, while the radial
crushing strength constant is slightly lower,compared to that when
an atomized iron powder is used. Thus, if higher strength is more
desirable for the sintered valve guide, use of atomized iron powder
is recommended, and use of an ore-reduced iron powder is
recommended when better machinability is more desirable. If an ore
reduced iron powder and an atomized iron powder are used in
combination, the mixing ratio of the atomized iron powder is
preferably approximately 30 mass % or less, at which the
improvement in machinability is more significant.
Example 4
[0119] (Samples 50 to 66)
[0120] Sintered compact samples 50 and 66 were prepared in
accordance with the powder mixture composition for each sample
shown in Table 10, by repeating the operations similar to those for
sample 4 (preparation of powder mixture, formation of green
compact, sintering, and cooling), except that, as a
machinability-improving component, manganese sulfide powder was
used additionally in an amount of 0.2 to 2.0 mass % (samples 50 to
55 and 62 to 66) or magnesium silicate powder in an amount of 0.2
to 2.0 mass % (samples 56 to 61 and 62 to 66). The composition of
the entire powder mixture for each sample is shown in Table 11.
[0121] By using each of the sintered compact samples 50 to 66, the
ratios of respective phases in the cross section of the
metallographic structure of the sintered compact were determined by
cross sectional area observation, and the abrasion, machinability
and radial crushing tests thereof were performed in a similar
manner to samples 1 to 27. The results are summarized in Table 12.
TABLE-US-00010 TABLE 10 Mixing Ratio mass % Ore Fe--20P Cu--10Sn
Sample Reduced Alloy Alloy Graphite MnS MgSiO.sub.3 No Fe Pwd.
Powder Powder Powder Pwd. Powder Comments 04 92.20 0.40 5.00 2.40
50 92.00 0.40 5.00 2.40 0.20 51 91.70 0.40 5.00 2.40 0.50 52 91.40
0.40 5.00 2.40 0.80 53 91.00 0.40 5.00 2.40 1.20 54 90.60 0.40 5.00
2.40 1.60 55 90.20 0.40 5.00 2.40 2.00 MnS add.: >max. 56 92.00
0.40 5.00 2.40 0.20 57 91.70 0.40 5.00 2.40 0.50 58 91.40 0.40 5.00
2.40 0.80 59 91.00 0.40 5.00 2.40 1.20 60 90.60 0.40 5.00 2.40 1.60
61 90.20 0.40 5.00 2.40 2.00 MgSiO.sub.3 add.: >max. 62 92.00
0.40 5.00 2.40 0.10 0.10 63 91.60 0.40 5.00 2.40 0.30 0.30 64 91.00
0.40 5.00 2.40 0.60 0.60 65 90.60 0.40 5.00 2.40 0.80 0.80 66 90.20
0.40 5.00 2.40 1.00 1.00 MgS & MgSiO.sub.3 add.: >max.
[0122] TABLE-US-00011 TABLE 11 Composition mass % Sample Metal No
Fe P Cu Sn C Oxide MnS MgSiO.sub.3 Comments 04 91.60 0.08 4.50 0.50
2.20 0.92 50 91.40 0.08 4.50 0.50 2.20 0.92 0.20 51 91.10 0.08 4.50
0.50 2.20 0.92 0.50 52 90.81 0.08 4.50 0.50 2.20 0.91 0.80 53 90.41
0.08 4.50 0.50 2.20 0.91 1.20 54 90.01 0.08 4.50 0.50 2.20 0.91
1.60 55 89.62 0.08 4.50 0.50 2.20 0.90 2.00 MnS add.: >max. 56
91.40 0.08 4.50 0.50 2.20 0.92 0.20 57 91.10 0.08 4.50 0.50 2.20
0.92 0.50 58 90.81 0.08 4.50 0.50 2.20 0.91 0.80 59 90.41 0.08 4.50
0.50 2.20 0.91 1.20 60 90.01 0.08 4.50 0.50 2.20 0.91 1.60 61 89.62
0.08 4.50 0.50 2.20 0.90 2.00 MgSiO.sub.3 add.: >max. 62 91.40
0.08 4.50 0.50 2.20 0.92 0.10 0.10 63 91.00 0.08 4.50 0.50 2.20
0.92 0.30 0.30 64 90.41 0.08 4.50 0.50 2.20 0.91 0.60 0.60 65 90.01
0.08 4.50 0.50 2.20 0.91 0.80 0.80 66 89.62 0.08 4.50 0.50 2.20
0.90 1.00 1.00 MnS & MgSiO.sub.3 add.: >max.
[0123] TABLE-US-00012 TABLE 12 Ratio in Met. Section area %
Estimation Items Fe--P--C Radial Compound Phase Cu--Sn Free Ferrite
Wear Crushing Sample Thickness .mu.m Alloy Graphite Phase in amount
Machinability Str. Con. No <5 5-15 .gtoreq.15 Phase mass %
Matrix .mu.m Index MPa Comments 04 1.90 81 15 4 2.3 1.42 1.2 46
28.8 596 50 2.24 67 30 3 2.3 1.42 2.6 48 23.8 564 51 2.16 65 31 4
2.3 1.42 4.0 50 21.3 538 52 2.09 64 32 4 2.3 1.52 5.4 51 17.5 527
53 2.05 61 35 4 2.3 1.62 7.2 54 15.0 512 54 1.95 60 35 5 2.3 1.72
9.4 68 12.5 490 55 1.72 58 36 6 2.3 1.92 28.2 81 8.8 374 MnS add.:
>max. 56 2.26 65 32 3 2.3 1.42 2.3 51 22.5 587 57 2.20 64 33 3
2.3 1.42 3.7 53 20.6 561 58 2.10 63 34 3 2.3 1.52 4.7 58 16.9 552
59 2.01 61 35 4 2.3 1.62 6.0 63 13.8 537 60 1.97 61 35 4 2.3 1.72
7.3 65 12.5 509 61 1.70 57 38 5 2.3 1.92 27.1 81 8.8 397
MgSiO.sub.3 add.: >max. 62 2.26 65 33 2 2.3 1.42 2.4 46 24.4 593
63 2.26 64 34 2 2.3 1.42 4.4 52 21.9 574 64 2.26 63 34 3 2.3 1.42
7.1 63 14.4 510 65 2.25 62 35 3 2.3 1.42 8.8 67 12.5 473 66 2.25 58
37 5 2.3 1.42 47.4 78 11.3 394 MnS & MgSiO.sub.3 add.:
>max.
[0124] For samples 4, 10, 50 to 66, the relationships between
addition of machinability-improving component powder to the powder
mixture and the ratios of respective phases in the whole
composition are shown in FIGS. 21A-21D, and the relationships of
the amount of the machinability-improving component powder added to
the powder mixture with the thickness of the iron-phosphorus-carbon
compound phase and the material properties (wear amount,
machinability index and radial crushing strength constant) are
shown in FIGS. 22A-22D.
[0125] According to FIGS. 21C and 22C, the ratio of free graphite
phase gradually increases and the machinability index gradually
decreases, according as the amount of the machinability-improving
component powder in the powder mixture increases. However, the
effect of the machinability-improving powder is relatively mild,
and the radial crushing strength constant gradually declines on the
contrary as the addition amount increases, such that, at the
addition amount of exceeding 1.6 mass %, the wear amount increases
drastically due to brittleness of the matrix caused by sintering
inhibition (diffusion inhibition). Therefore, it is difficult to
improve the machinability dramatically only with the
machinability-improving component powder. Accordingly, it is
important to optimize the influence of the ratio and the thickness
of iron-phosphorus-carbon compound phase, the ratio of free
graphite phase and others on the machinability, and it is necessary
to determine the composition and the manufacturing condition by
considering the balance between radial crushing strength and
abrasion resistance at the same time.
[0126] It must be understood that the invention is in no way
limited to the above embodiments and that many changes may be
brought about therein without departing from the scope of the
invention as defined by the appended claims.
* * * * *