U.S. patent application number 16/271620 was filed with the patent office on 2019-08-22 for hard particle powder for sintered body.
The applicant listed for this patent is DAIDO STEEL CO., LTD.. Invention is credited to Takahisa ENDO, Hiroki HATTORI, Syunsuke KONO, Iwane NAGASE, Tomomi YAMAMOTO.
Application Number | 20190256955 16/271620 |
Document ID | / |
Family ID | 67616707 |
Filed Date | 2019-08-22 |
United States Patent
Application |
20190256955 |
Kind Code |
A1 |
NAGASE; Iwane ; et
al. |
August 22, 2019 |
HARD PARTICLE POWDER FOR SINTERED BODY
Abstract
Provided is a hard particle powder for a sintered body,
consisting of: 0.01.ltoreq.C.ltoreq.3.5 mass %,
0.5.ltoreq.Si.ltoreq.4.0 mass %, 0.1.ltoreq.Mn.ltoreq.10.0 mass %,
0.1.ltoreq.Ni.ltoreq.35.0 mass %, 0.1.ltoreq.Cr.ltoreq.40.0 mass %,
5.0.ltoreq.Mo.ltoreq.50.0 mass %, 0.1.ltoreq.Fe.ltoreq.30.0 mass %,
and 0.01.ltoreq.REM.ltoreq.0.5 mass %, with a balance being Co and
inevitable impurities.
Inventors: |
NAGASE; Iwane; (Nagoya-shi,
JP) ; YAMAMOTO; Tomomi; (Tokyo, JP) ; ENDO;
Takahisa; (Nagoya-shi, JP) ; KONO; Syunsuke;
(Tokyo, JP) ; HATTORI; Hiroki; (Nagoya-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DAIDO STEEL CO., LTD. |
Nagoya-shi |
|
JP |
|
|
Family ID: |
67616707 |
Appl. No.: |
16/271620 |
Filed: |
February 8, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F01L 2800/18 20130101;
C22C 1/0433 20130101; F01L 2303/00 20200501; B22F 2999/00 20130101;
B22F 2301/35 20130101; C22C 33/0278 20130101; C22C 33/0207
20130101; B22F 1/0003 20130101; B22F 2998/10 20130101; C22C 1/045
20130101; C22C 33/0285 20130101; F01L 3/02 20130101; B22F 2302/40
20130101; F01L 2810/02 20130101; B22F 3/16 20130101; C22C 30/00
20130101; B22F 2998/10 20130101; B22F 1/0059 20130101; B22F 3/02
20130101; B22F 3/10 20130101; B22F 2999/00 20130101; B22F 2201/013
20130101; B22F 2201/02 20130101 |
International
Class: |
C22C 30/00 20060101
C22C030/00; B22F 1/00 20060101 B22F001/00; B22F 3/16 20060101
B22F003/16 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2018 |
JP |
2018-026177 |
Claims
1. A hard particle powder for a sintered body, consisting of:
0.01.ltoreq.C.ltoreq.3.5 mass %, 0.5.ltoreq.Si.ltoreq.4.0 mass %,
0.1.ltoreq.Mn.ltoreq.10.0 mass %, 0.1.ltoreq.Ni.ltoreq.50.0 mass %,
0.1.ltoreq.Cr.ltoreq.40.0 mass %, 5.0.ltoreq.Mo.ltoreq.50.0 mass %,
0.1.ltoreq.Fe.ltoreq.30.0 mass %, and 0.01.ltoreq.REM.ltoreq.0.5
mass %, with a balance being Co and inevitable impurities.
2. The hard particle powder for a sintered body, according to claim
1, wherein the content of Mn is: 4.0.ltoreq.Mn.ltoreq.7.0 mass
%.
3. The hard particle powder for a sintered body, according to claim
1, wherein the content of Ni is: 0.2.ltoreq.Ni.ltoreq.30 mass
%.
4. The hard particle powder for a sintered body, according to claim
1, wherein the content of Fe is: 2.0.ltoreq.Fe.ltoreq.20 mass
%.
5. A sintered body comprising: a hard particle powder, a pure iron
powder, and a graphite powder, wherein the hard particle powder
consists of: 0.01.ltoreq.C.ltoreq.3.5 mass %,
0.5.ltoreq.Si.ltoreq.4.0 mass %, 0.1.ltoreq.Mn.ltoreq.10.0 mass %,
0.1.ltoreq.Ni.ltoreq.35.0 mass %, 0.1.ltoreq.Cr.ltoreq.40.0 mass %,
5.0.ltoreq.Mo.ltoreq.50.0 mass %, 0.1.ltoreq.Fe.ltoreq.30.0 mass %,
and 0.01.ltoreq.REM.ltoreq.0.5 mass %, with a balance being Co and
inevitable impurities.
6. The sintered body according to claim 5, wherein the content of
Mn is: 4.0.ltoreq.Mn.ltoreq.7.0 mass %.
7. The sintered body according to claim 5, wherein the content of
Ni is: 0.2.ltoreq.Ni.ltoreq.30 mass %.
8. The sintered body according to claim 5, wherein the content of
Fe is: 2.0.ltoreq.Fe.ltoreq.20 mass %.
Description
TECHNICAL FIELD
[0001] The present invention relates to a hard particle powder for
a sintered body. More specifically, the present invention relates
to a hard particle powder to which rare earth metal (REM) is added,
which is excellent in terms of powder characteristics or sintering
characteristics and which can give a high wear resistance when a
sintered body (e.g., a valve seat for car engine) is produced by
using the same.
BACKGROUND ART
[0002] TRIBALOY (registered trademark) T-400 is well known as a
Co-based hard particles that have a high wear-resistance and form a
hard phase mainly containing a Mo silicide. A
Co-2.5Si-28Mo-8.5Cr-based alloy powder which is an equivalent
material of TRIBALOY (registered trademark) T-400 has been
frequently used as hard particles that significantly contribute to
an improvement of the wear resistance of a valve seat for car
engine (hereinafter, simply referred to as "valve seat") in a car
engine to which a high load is applied. Therefore, a number of
prior arts have been proposed.
[0003] For example, Patent Document 1 discloses a method for
manufacturing a wear-resistant sintered member, aiming to disperse
a larger amount of a hard layer in a base without impairing wear
resistance, strength, or the like. The method includes
compression-molding a raw material powder containing a base-forming
powder (iron, SUS316, SUS304, SUS310, or SUS430) and a hard
layer-forming powder (Co-28Mo-2.5Si-8Cr), and performing sintering.
The method is characterized in that 90 mass % or more of the
base-forming powder is a fine powder having a maximum particle
diameter of 46 .mu.m, and a proportion of the hard layer-forming
powder in the raw material powder is from 40 mass % to 70 mass
%.
[0004] In addition, Patent Document 2 discloses a method for
manufacturing a wear-resistant iron-based alloy material for a
valve seat, aiming to obtain an iron-based sintered alloy material
having excellent wear resistance. The method includes (a)
compression-molding an iron-based alloy powder obtained by adding
from 0.2 to 3.0 parts by weight of a solid lubricating material
powder (sulfide or fluoride) and/or from 0.2 to 5.0 parts by weight
of an oxide-stabilizing powder (Y.sub.2O.sub.3, CeO.sub.2, or
CaTiO.sub.3, which is an oxide of a rare earth element) to 100
parts by weight of an iron-based alloy powder containing a pure
iron powder, an alloy iron powder, a carbon powder, a fine
carbide-precipitated steel powder, and a hard particle powder
(Cr--Mo--Co-based powder, Ni--Cr--Mo--Co-based powder, etc.); and
then (b) performing sintering, thereby obtaining a sintered
body.
[0005] However, in response to an increase in a load on
engine-demanded characteristics, there has been a demand for higher
wear resistance for valve seat materials. Therefore, there has been
a problem in that the hard particles disclosed in Patent Documents
1, 2, and the like cannot sufficiently satisfy the wear resistance
that is demanded for valve seat materials. Furthermore, it is
necessary to consider that an attempt to improve the wear
resistance that is demanded for valve seat materials is likely to
impair powder characteristics (moldability) or sintering
characteristics. Therefore, there is a demand for a technique for
improving the wear resistance that is demanded for valve seat
materials without impairing powder characteristics and sintering
characteristics.
[0006] Furthermore, in recent years, in order to cope with
global-scale social issues such as CO.sub.2 reduction and depletion
of petroleum resources, fuel-saving lean-burn combustion techniques
such as a direct-injection engine and a homogeneous-charge
compression ignition (HCCI) engine, and bioethanol fuel engines
using a plant raw material in which no fossil fuel is used are
promoted.
[0007] A lean-burn combustion engine or an alcohol fuel engine
generates a small amount of soot during combustion as compared with
a conventional engine. Therefore, there is a concern that, in a
low-temperature state after engine ignition, the valve seat is not
protected by soot and may be easily worn.
[0008] Patent Document 1: JP-A 2007-107034
[0009] Patent Document 2: JP-A 2003-193173
SUMMARY
[0010] An object that the present invention attempts to achieve is
to provide a hard particle powder for a sintered body which is hard
particles that are added to a raw material powder of a sintered
body and is capable of improving the wear resistance of the
sintered body without impairing powder characteristics and
sintering characteristics.
[0011] In order to achieve the above-described object, a hard
particle powder for a sintered body according to the present
invention includes:
[0012] 0.01.ltoreq.C.ltoreq.3.5 mass %,
[0013] 0.5.ltoreq.Si.ltoreq.4.0 mass %,
[0014] 0.1.ltoreq.Mn.ltoreq.10.0 mass %,
[0015] 0.1.ltoreq.Ni.ltoreq.50.0 mass %,
[0016] 0.1.ltoreq.Cr.ltoreq.40.0 mass %,
[0017] 5.0.ltoreq.Mo.ltoreq.50.0 mass %,
[0018] 0.1.ltoreq.Fe.ltoreq.30.0 mass %, and
[0019] 0.01.ltoreq.REM.ltoreq.0.5 mass %,
[0020] with a balance being Co and inevitable impurities.
[0021] The present inventors found that, when a component is
optimized in Co-based hard particles including REM, the wear
resistance of a sintered body including the hard particles can be
improved without impairing powder characteristics and sintering
characteristics. This is considered to be because, when an
appropriate amount of REM is added to the hard particles, an oxide
coating is generated on a surface of the sintered body in a low
temperature range of approximately 600.degree. C. and this oxide
coating exhibits a lubrication action.
BRIEF DESCRIPTION OF DRAWINGS
[0022] FIG. 1 is a cross-sectional view illustrating an outline of
a wear tester for a single valve seat.
[0023] FIG. 2 is a view for describing a measurement place of a
wear amount of a wear test specimen.
[0024] FIG. 3 is a view showing the relationships between
temperature and weight increase in hard particle powders obtained
in Example 2 and Comparative Example 13.
EMBODIMENTS
[0025] Hereinafter, an embodiment of the present invention will be
described in detail.
1. Hard Particle Powder for Sintered Body
[0026] A hard particle powder for a sintered body according to the
present invention includes elements as described below, and the
balance is Co and inevitable impurities. The kinds of component
elements, content ranges thereof, and limitation reasons thereof
are as described below.
[0027] (1) 0.01.ltoreq.C.ltoreq.3.5 Mass %:
[0028] In the case where the content of C is excessive, toughness
degrades due to the generation of a carbide. Therefore, the content
of C needs to be 3.5 mass % or less in the hard particle powder for
a sintered body. The content of C is preferably 2.0 mass % or
less.
[0029] On the other hand, a decrease in the content of C larger
than necessary does not make any difference in the effect and does
not produce any practical benefit. Therefore, the content of C
needs to be 0.01 mass % or more in the hard particle powder for a
sintered body. The content of C is preferably 0.5 mass % or
more.
[0030] (2) 0.5.ltoreq.Si.ltoreq.4.0 Mass %:
[0031] Si is a component element added aiming to improve hardness
due to the generation of a silicide. In the case where the content
of Si is too small, the hardness becomes too poor, and the hard
particle powder does not function as hard particles. Therefore, the
content of Si needs to be 0.5 mass % or more in the hard particle
powder for a sintered body. The content of Si is preferably 0.8
mass % or more.
[0032] On the other hand, in the case where the content of Si is
excessive, the hardness becomes too high. As a result, hard
particles crack and drop from a sintered body including the hard
particles, and, conversely, the wear amount of the sintered body
becomes large. Therefore, the content of Si needs to be 4.0 mass %
or less in the hard particle powder for a sintered body. The
content of Si is preferably 3.0 mass % or less.
[0033] (3) 0.1.ltoreq.Mn.ltoreq.10.0 Mass %:
[0034] In the case where the content of Mn is too small, the oxide
coating is not easily generated on a surface of the powder, leading
to a decrease in lubrication property. As a result, wear resistance
deteriorates. Therefore, the content of Mn needs to be 0.1 mass %
or more in the hard particle powder for a sintered body. The
content of Mn is preferably 0.2 mass % or more and more preferably
4.0 mass % or more.
[0035] On the other hand, in the case where the content of Mn is
excessive, sintering characteristics deteriorate due to an increase
in a powder oxidation amount. The content of Mn needs to be 10.0
mass % or less in the hard particle powder for a sintered body. The
content of Mn is preferably 7.0 mass % or less.
[0036] (4) 0.1.ltoreq.Ni.ltoreq.35.0 Mass %:
[0037] In the case where the content of Ni is too small, the wear
resistance deteriorates due to the degradation of heat resistance.
Therefore, the content of Ni needs to be 0.1 mass % or more in the
hard particle powder for a sintered body. The content of Ni is
preferably 0.3 mass % or more and more preferably 9.0 mass % or
more.
[0038] On the other hand, in the case where the content of Ni is
excessive, the wear resistance deteriorates due to the degradation
of the heat resistance. Therefore, the content of Ni needs to be
35.0 mass % or less in the hard particle powder for a sintered
body. The content of Ni is preferably 30.0 mass % or less.
[0039] (5) 0.1.ltoreq.Cr.ltoreq.40.0 Mass %:
[0040] Cr is an element added aiming to impart oxidation
resistance. In the case where the content of Cr is too small, the
wear resistance deteriorates due to the degradation of the
oxidation resistance. Therefore, the content of Cr needs to be 0.1
mass % or more in the hard particle powder for a sintered body. The
content of Cr is preferably 3.0 mass % or more.
[0041] On the other hand, in the case where the content of Cr is
excessive, the wear resistance deteriorates due to the degradation
of the heat resistance. Therefore, the content of Cr needs to be
40.0 mass % or less in the hard particle powder for a sintered
body. The content of Cr is preferably 30.0 mass % or less.
[0042] (6) 5.0.ltoreq.Mo.ltoreq.50.0 Mass %:
[0043] Mo is a component element added aiming to maintain the
hardness of powder particles. In the case where the content of Mo
is too small, the wear resistance of the sintered body including
the hard particle powder becomes insufficient. Therefore, the
content of Mo needs to be 5.0 mass % or more in the hard particle
powder for a sintered body. The content of Mo is preferably 14.0
mass % or more.
[0044] On the other hand, in the case where the content of Mo is
excessive, the hardness becomes too high. As a result, the hard
particles crack and drop from the sintered body including the hard
particle powder, and, conversely, the wear amount of the sintered
body becomes large. Therefore, the content of Mo needs to be 50.0
mass % or less in the hard particle powder for a sintered body. The
content of Mo is preferably 40.0 mass % or less.
[0045] (7) 0.1.ltoreq.Fe.ltoreq.30.0 Mass %:
[0046] Fe is an element that plays a role of improving the
diffusivity of the hard particle powder into an iron powder. In the
case where the content of Fe is too small, the hard particles crack
and drop from the sintered body including the hard particle powder
due to the degradation of the diffusivity into the iron powder. As
a result, the wear resistance deteriorates. Therefore, the content
of Fe needs to be 0.1 mass % or more in the hard particle powder
for a sintered body. The content of Fe is preferably 2.0 mass % or
more.
[0047] On the other hand, in the case where the content of Fe is
excessive, the content of Co decreases. Fe is poorer than Co in
terms of heat resistance and wear resistance, and thus, in the case
where the content of Fe is excessive, the heat resistance and the
wear resistance significantly degrade. Therefore, the content of Fe
needs to be 30.0 mass % or less in the hard particle powder for a
sintered body. The content of Fe is preferably 20.0 mass % or
less.
[0048] (8) 0.01.ltoreq.REM.ltoreq.0.5 Mass %:
[0049] "REM" is defined as a group of elements consisting of Sc, Y
and lanthanoid elements (i.e., La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb,
Dy, Ho, Er, Tm, Yb, and Lu). The hard particle powder of the
present invention contains at least one kind of the lanthanoid
elements, and a preferred REM is a mischmetal such as an alloy or
mixture of La, Ce, Nd, Pr, Sm, and Y, from a view point of
industrial inexpensiveness. REM is a component element added to
improve the wear resistance of the sintered body including the hard
particle powder, without impairing powder characteristics and the
sintering characteristics. In the case where the content of REM is
too small, REM seldom contributes to the improvement of the wear
resistance of the sintered body. Therefore, the content of REM
needs to be 0.01 mass % or more in the hard particle powder for a
sintered body. The content of REM is preferably 0.05 mass % or
more.
[0050] On the other hand, in the case where the content of REM is
excessive, the sintering characteristics deteriorate due to an
increase in the powder oxidation amount, and furthermore, the wear
resistance also degrades. Therefore, the content of REM needs to be
0.5 mass % or less in the hard particle powder for a sintered body.
The content of REM is preferably 0.3 mass % or less.
2. Method for Manufacturing Sintered Body
[0051] The sintered body including the hard particle powder for a
sintered body according to the present invention can be
manufactured by (a) mixing the hard particle powder for a sintered
body according to the present invention, a pure iron powder, and a
graphite powder, to obtain a mixed powder, (b) compacting and
molding the mixed powder so as to produce a compact body, and (c)
sintering the compact body.
2.1. Mixing Step
[0052] First, the hard particle powder for a sintered body
according to the present invention (hereinafter, also simply
referred to as "the hard particle powder"), a pure iron powder, and
a graphite powder are mixed together (mixing step). As the blending
amounts of the respective components, optimal blending amounts are
preferably selected depending on the purpose. In addition, in order
to improve moldability, a molding lubricant is preferably added to
the raw materials.
[0053] In the case where the blending amount of the hard particle
powder is too small, the wear resistance of the sintered body
degrades. Therefore, the blending amount of the hard particle
powder is preferably 5.0 mass % or more in the mixed powder. The
blending amount of the hard particle powder is preferably 10.0 mass
% or more.
[0054] On the other hand, in the case where the blending amount of
the hard particle powder is excessive, the sintering
characteristics degrade. Therefore, the blending amount of the hard
particle powder is preferably 50.0 mass % or less in the mixed
powder. The blending amount of the hard particle powder is
preferably 30.0 mass % or less.
[0055] In the case where the blending amount of the graphite powder
is too small, the wear resistance of the sintered body degrades.
Therefore, the blending amount of the graphite powder is preferably
0.5 mass % or more in the mixed powder. The blending amount of the
graphite powder is preferably 0.8 mass % or more.
[0056] On the other hand, in the case where the blending amount of
the graphite powder is excessive, the sintering characteristics
degrade. Therefore, the blending amount of the graphite powder is
preferably 2.0 mass % or less in the mixed powder. The blending
amount of the graphite powder is preferably 1.5 mass % or less.
2.2. Compacting and Molding Step
[0057] Next, the mixed powder is compacted and molded, thereby
obtaining a compact body. Compacting and molding conditions are not
particularly limited, and optimal conditions can be selected
depending on the purpose. Generally, as a molding pressure
increases, a compact density further improves. After the molding,
the compact body may be burned in the atmosphere for
degreasing.
2.3. Sintering Step
[0058] Next, the compact body is sintered (sintering step).
[0059] As sintering conditions, optimal conditions are preferably
selected depending on a composition of the compact body. Generally,
as a sintering temperature increases, a more dense sintered body
can be obtained with a heat treatment of a shorter time. On the
other hand, if the sintering temperature is too high, there is a
problem in that the hard particles excessively diffuse into an
iron-based matrix or melt. Although the optimal sintering
conditions vary depending on the composition of the compact body,
generally, the sintering is preferably performed at from
1,100.degree. C. to 1,300.degree. C. for from 0.5 hours to 3 hours.
Furthermore, the sintering is preferably performed in a reducing
atmosphere (e.g., in a resolved ammonia atmosphere).
3. Action
[0060] In the Co-based hard particles including REM, when the
components are optimized, the wear resistance of the sintered body
including the hard particles can be improved without impairing the
powder characteristics and the sintering characteristics. This is
considered to be because, when an appropriate amount of REM is
added to the hard particles, an oxide coating is generated on a
surface of the sintered body in a low temperature range of
approximately 600.degree. C. and this oxide coating exhibits a
lubrication action.
EXAMPLES
Examples 1 to 30 and Comparative Examples 1 to 44
1. Production of Specimens
1.1 Production of Hard Particle Powders
[0061] Raw materials were blended so as to obtain compositions
(unit: mass %) shown in Table 1 and Table 2. Raw material mixtures
were melted, and hard particle powders were obtained through an
atomization method. REM used in the production was a mischmetal
that is a mixture of La, Ce, Nd, Pr, Sm, and Y. Table 1 and Table 2
also show sintered densities of the sintered bodies including the
hard particle powders and wear amounts of the sintered bodies when
a wear resistance test described below was carried out.
TABLE-US-00001 TABLE 1 Wear amount Sintered density C Si Mn Ni Cr
Mo Co Fe REM (.mu.m) (g/cm.sup.3) Ex. 1 1.5 2.5 5 10 10 19 Bal. 15
0.01 17 7.18 Ex. 2 1.5 2.5 5 10 10 19 Bal. 15 0.25 15 7.20 Ex. 3
1.5 2.5 5 10 10 19 Bal. 15 0.50 16 7.21 Ex. 4 0.01 2.5 5 10 10 19
Bal. 15 0.25 18 7.20 Ex. 5 0.75 2.5 5 10 10 19 Bal. 15 0.25 16 7.21
Ex. 6 2.5 2.5 5 10 10 19 Bal. 15 0.25 16 7.18 Ex. 7 3.5 2.5 5 10 10
19 Bal. 15 0.25 19 7.16 Ex. 8 1.5 0.5 5 10 10 19 Bal. 15 0.25 18
7.22 Ex. 9 1.5 1.5 5 10 10 19 Bal. 15 0.25 16 7.21 Ex. 10 1.5 3.5 5
10 10 19 Bal. 15 0.25 16 7.17 Ex. 11 1.5 4.0 5 10 10 19 Bal. 15
0.25 18 7.15 Ex. 12 1.5 2.5 0.1 10 10 19 Bal. 15 0.25 19 7.21 Ex.
13 1.5 2.5 3 10 10 19 Bal. 15 0.25 14 7.19 Ex. 14 1.5 2.5 10 10 10
19 Bal. 15 0.25 18 7.16 Ex. 15 1.5 2.5 5 0.1 10 19 Bal. 15 0.25 12
7.16 Ex. 16 1.5 2.5 5 20 10 19 Bal. 15 0.25 16 7.17 Ex. 17 1.5 2.5
5 27 10 19 Bal. 15 0.25 18 7.19 Ex. 18 1.5 2.5 5 35 10 19 Bal. 15
0.25 19 7.19 Ex. 19 1.5 2.5 5 10 0.1 19 Bal. 15 0.25 14 7.22 Ex. 20
1.5 2.5 5 10 20 19 Bal. 15 0.25 16 7.20 Ex. 21 1.5 2.5 5 10 30 19
Bal. 15 0.25 18 7.17 Ex. 22 1.5 2.5 5 10 40 19 Bal. 15 0.25 19 7.16
Ex. 23 1.5 2.5 5 10 10 5 Bal. 15 0.25 12 7.15 Ex. 24 1.5 2.5 5 10
10 14 Bal. 15 0.25 14 7.17 Ex. 25 1.5 2.5 5 10 10 35 Bal. 15 0.25
18 7.20 Ex. 26 1.5 2.5 5 10 10 50 Bal. 15 0.25 19 7.25 Ex. 27 1.5
2.5 5 10 10 19 Bal. 0.1 0.25 13 7.22 Ex. 28 1.5 2.5 5 10 10 19 Bal.
7 0.25 14 7.19 Ex. 29 1.5 2.5 5 10 10 19 Bal. 23 0.25 18 7.16 Ex.
30 1.5 2.5 5 10 10 19 Bal. 30 0.25 19 7.15
TABLE-US-00002 TABLE 2 Wear Sintered amount density C Si Mn Ni Cr
Mo Co Fe REM (.mu.m) (g/cm.sup.3) Comp. Ex. 1 4.0 2.5 5 10 10 19
Bal. 15 0.25 30 6.97 Comp. Ex. 2 1.5 5 5 10 10 19 Bal. 15 0.25 33
6.92 Comp. Ex. 3 1.5 2.5 0 10 10 19 Bal. 15 0.50 24 7.21 Comp. Ex.
4 1.5 2.5 12 10 10 19 Bal. 15 0.25 36 7.03 Comp. Ex. 5 1.5 2.5 5 0
10 19 Bal. 15 0.25 22 7.16 Comp. Ex. 6 1.5 2.5 5 36 10 19 Bal. 15
0.25 37 7.19 Comp. Ex. 7 1.5 2.5 5 10 0 19 Bal. 15 0.25 23 7.22
Comp. Ex. 8 1.5 2.5 5 10 41 19 Bal. 15 0.25 35 7.14 Comp. Ex. 9 1.5
2.5 5 10 10 4 Bal. 15 0.25 31 7.13 Comp. Ex. 10 1.5 2.5 5 10 10 55
Bal. 15 0.25 39 7.26 Comp. Ex. 11 1.5 2.5 5 10 10 19 Bal. 0 0.25 24
7.22 Comp. Ex. 12 1.5 2.5 5 10 10 19 Bal. 31 0.25 62 7.14 Comp. Ex.
13 1.5 2.5 5 10 10 19 Bal. 15 0 37 7.18 Comp. Ex. 14 0.01 2.5 5 10
10 19 Bal. 15 0 36 7.20 Comp. Ex. 15 3.5 2.5 5 10 10 19 Bal. 15 0
38 7.16 Comp. Ex. 16 1.5 0.5 5 10 10 19 Bal. 15 0 39 7.22 Comp. Ex.
17 1.5 4.0 5 10 10 19 Bal. 15 0 36 7.15 Comp. Ex. 18 1.5 2.5 0.1 10
10 19 Bal. 15 0 38 7.21 Comp. Ex. 19 1.5 2.5 12 10 10 19 Bal. 15 0
36 7.16 Comp. Ex. 20 1.5 2.5 5 0.1 10 19 Bal. 15 0 37 7.16 Comp.
Ex. 21 1.5 2.5 5 35 10 19 Bal. 15 0 39 7.19 Comp. Ex. 22 1.5 2.5 5
10 0.1 19 Bal. 15 0 36 7.22 Comp. Ex. 23 1.5 2.5 5 10 40 19 Bal. 15
0 39 7.16 Comp. Ex. 24 1.5 2.5 5 10 10 5 Bal. 15 0 40 7.15 Comp.
Ex. 25 1.5 2.5 5 10 10 35 Bal. 15 0 38 7.20 Comp. Ex. 26 1.5 2.5 5
10 10 50 Bal. 15 0 42 7.25 Comp. Ex. 27 1.5 2.5 5 10 10 19 Bal. 0.1
0 33 7.22 Comp. Ex. 28 1.5 2.5 5 10 10 19 Bal. 30 0 40 7.15 Comp.
Ex. 29 1.5 2.5 5 10 10 19 Bal. 15 0.7 42 6.98 Comp. Ex. 30 0.01 2.5
5 10 10 19 Bal. 15 0.7 40 7.02 Comp. Ex. 31 3.5 2.5 5 10 10 19 Bal.
15 0.7 41 6.95 Comp. Ex. 32 1.5 0.5 5 10 10 19 Bal. 15 0.7 40 7.02
Comp. Ex. 33 1.5 4.0 5 10 10 19 Bal. 15 0.7 43 6.94 Comp. Ex. 34
1.5 2.5 0.1 10 10 19 Bal. 15 0.7 41 7.01 Comp. Ex. 35 1.5 2.5 12 10
10 19 Bal. 15 0.7 40 6.96 Comp. Ex. 36 1.5 2.5 5 0.1 10 19 Bal. 15
0.7 42 6.95 Comp. Ex. 37 1.5 2.5 5 35 10 19 Bal. 15 0.7 43 6.97
Comp. Ex. 38 1.5 2.5 5 10 0.1 19 Bal. 15 0.7 39 7.02 Comp. Ex. 39
1.5 2.5 5 10 40 19 Bal. 15 0.7 44 6.96 Comp. Ex. 40 1.5 2.5 5 10 10
5 Bal. 15 0.7 38 6.94 Comp. Ex. 41 1.5 2.5 5 10 10 35 Bal. 15 0.7
43 7.00 Comp. Ex. 42 1.5 2.5 5 10 10 50 Bal. 15 0.7 43 7.04 Comp.
Ex. 43 1.5 2.5 5 20 20 19 Bal. 0.1 0.7 37 7.02 Comp. Ex. 44 1.5 2.5
5 20 20 19 Bal. 30 0.7 46 6.96
1.2. Production of Sintered Bodies
[0062] A mixture consisting of 69.2 mass % of pure iron powder
(ASC100.29), 30 mass % of the hard particle powder and 0.8 mass %
of a graphite powder (CPB) was prepared. To 100 parts by weight of
the mixture was further added 0.5 parts by weight of Zn--St
(molding lubricant), followed by mixing.
[0063] Next, the raw materials were compression-molded at a molding
pressure of 8 t/cm.sup.2. The shape of the compact body obtained
was set to be (a) a disc shape having a diameter of 35 mm and a
thickness of 14 mm or (b) a ring shape having an outer diameter of
28 mm, an inner diameter of 20 mm and a thickness of 4 mm
[0064] Next, the compact body was degreased at 400.degree. C. for
one hour in the atmosphere. Furthermore, the degreased body was
sintered at 1,160.degree. C. for one hour in a resolved ammonia
atmosphere (N.sub.2+3H.sub.2), thereby obtaining a sintered
body.
2. Testing Method
2.1. Powder Characteristics
[0065] For the obtained hard particle powders, powder
characteristics (particle size distribution, apparent density, flow
rate, powder hardness, and oxidation onset temperature) were
investigated. Here, (a) the particle size distribution was measured
according to Japanese Industrial Standards JIS Z 2510-2004, (b) the
apparent density was measured according to Japanese Industrial
Standards JIS Z 2504-2012, (c) the flow rate was measured according
to Japanese Industrial Standards JIS Z 2502-2012, (d) the powder
hardness was measured by using a microhardness measurement
instrument, and (e) the oxidation onset temperature was measured by
using a thermobalance, respectively.
2.2. Molding Characteristics and Sintering Characteristics
[0066] For the produced compact bodies and sintered bodies, molding
characteristics and sintering characteristics (compact density,
sintered density, chemical components, sintered body hardness, and
radial crushing strength) were investigated.
[0067] Here, the compact density and the sintered density were
measured according to Japanese Industrial Standards JIS Z 2508 and
JIS Z2509-2004. The chemical components was obtained through an
infrared absorption method. The sintered body hardness (HRA) was
measured by using a Rockwell hardness tester. The radial crushing
strength was measured by using the ring-shaped sintered body and an
Amsler tester.
2.3. Wear Resistance Test of Sintered Body
[0068] A wear resistance test was carried out for the sintered body
by using a wear tester for a single valve seat, as illustrated in
FIG. 1 (hereinafter, also simply referred to as "the wear tester").
Each of the disc-shaped sintered bodies (having a diameter of 35 mm
and a thickness of 14 mm) was worked to a valve seat shape and used
as individual wear test specimen. In addition, the wear test
specimen was set in the wear tester by being pressed into a sheet
holder.
[0069] The wear tester was driven under testing conditions shown in
Table 3. The wear test specimen was worn by a tapping that was
input by crank driving while indirectly heating the wear test
specimen by heating valves with a gas flame.
TABLE-US-00003 TABLE 3 Testing time 10 hours Fuel LPG Contact rate
3,000 times per minute Wear test specimen temperature 300.degree.
C. Valve driving Crank shaft Valve rotation rate 10 times per
minute Valve face Fe--21Cr--9Mn--4Ni--Co alloy Welding
[0070] The shape of the wear test specimen was measured by using a
shape measurement instrument before and after the wear test. As
illustrated in FIG. 2 (an enlarged view of a portion indicated by
an arrow A in FIG. 1), a difference D in a direction perpendicular
to the surface of the wear test specimen was obtained and used as a
wear amount of the wear test specimen.
3. Results
3.1. Powder Characteristics
[0071] Table 4 shows the powder characteristics of the hard
particle powders obtained in Examples 1 to 3 and Comparative
Examples 9 and 10. FIG. 3 shows relationships between a temperature
and weight increase of the hard particle powders obtained in
Example 2 and Comparative Example 13. From Table 4 and FIG. 3, the
following facts are found. (1) The particle size distributions and
the powder characteristics in Examples 1 to 3 were almost the same
as those in Comparative Examples 9 and 10. (2) Regarding the
particle size distributions in Examples 1 to 3 and Comparative
Examples 9 and 10, there were small differences therebetween both
in particle size distribution in -100 to +145 mesh and in particle
size distribution in -145 to +200 mesh. Therefore, the particle
size distributions is considered to result from variation during
the manufacturing of the powders. (3) The hardness in Examples 1 to
3 was almost the same as that in Comparative Examples 9 and 10. (4)
The oxidation onset temperature was lower in Example 2 than in
Comparative Example 13. This is because it became easy for the hard
particle powder to oxidize due to the addition of REM.
TABLE-US-00004 TABLE 4 Powder characteristics Particle size
distribution (mesh, %) Apparent Powder -80/ -100/ -145/ -200/ -250/
density Flow rate hardness +80 +100 +145 +200 +250 +350 -350
(g/cm.sup.3) (s/50 g) Hmv Ex. 1 0.0 0.1 8.2 17.1 12.7 23.0 38.9
3.51 20.4 781 Ex. 2 0.0 0.1 8.1 18.0 13.1 21.7 39.0 3.54 20.2 764
Ex. 3 0.0 0.1 8.4 17.5 14.1 20.7 39.2 3.57 20.6 750 Comp. 0.0 0.1
8.2 17.4 13.6 21.2 39.5 3.58 20.8 794 Ex. 9 Comp. 0.0 0.1 8.4 17.3
14.1 21.3 38.8 3.52 20.1 732 Ex. 10
3.2. Molding Characteristics and Sintering Characteristics
[0072] Table 5 shows characteristics of the compact bodies and the
sintered bodies obtained in Examples 1 to 3 and Comparative
Examples 9 and 10. From Table 5, the following facts are found. (1)
In Examples 1 to 3 and Comparative Examples 9 and 10, the
compositions were different from one another, but almost the same
compact density, sintered density, and sintered body hardness were
obtained. (2) The radial crushing strength was higher in Examples 1
to 3 than in Comparative Examples 9 and 10. The radial crushing
strength is attributed to the sintered body hardness, and thus,
when the sintered body hardness is higher, the radial crushing
strength also tends to become high.
TABLE-US-00005 TABLE 5 Com- Chemical Sintered Radial pact Sintered
components body crushing density density (mass %) hardness strength
(g/cm.sup.3) (g/cm.sup.3) C O N (HRA) (MPa) Ex. 1 6.99 7.18 1.35
0.16 0.033 41.9 524 Ex. 2 7.00 7.20 1.33 0.15 0.037 40.8 519 Ex. 3
7.01 7.21 1.38 0.13 0.034 39.5 507 Comp. 6.96 7.18 1.32 0.21 0.035
40.0 498 Ex. 9 Comp. 6.99 7.20 0.83 0.20 0.038 35.4 475 Ex. 10
3.3. Wear Resistance Test
[0073] Table 1 and Table 2 show the compositions of the respective
hard particle powders, the sintered densities of the sintered
bodies for which the hard particle powders were used, and the wear
amounts of the sintered bodies in the wear resistance test. From
Table 1 and Table 2, the following facts are found. (1) In all of
Examples 1 to 30, the wear amounts were less than 20 .mu.m. On the
other hand, in all of Comparative Examples 1 to 44, the wear
amounts were 20 .mu.m or more. That is, the wear amount became
smaller in Examples 1 to 30 than in Comparative Examples 1 to
44.
[0074] (2) When Examples 1 to 30 and Comparative Examples 13 to 28
are compared with one another, all of these examples satisfied the
preferred component ranges of the present invention except for the
presence or absence of REM. Therefore, it was found that, in the
component compositions (except for REM) according to Examples 1 to
30, the addition of REM has an effect of improving the wear
resistance of the sintered bodies (valve seats). (3) As
demonstrated in Comparative Examples 29 to 44, it is found that,
when the content of REM is too large, the effect of improving the
wear resistance of the sintered body (valve seat) cannot be
obtained. From these facts, it is found that the content of REM
preferably does not exceed 0.6 mass %. In addition, it is found
that the content of REM is preferably 0.5 mass % or less and more
preferably 0.25 mass % or less.
[0075] (4) In Comparative Example 1, the wear amount was large.
This is considered to be because the amount of C was too large and
thus, the hardness became high and the hard particle powder was
pulverized. (5) In Comparative Example 2, the wear amount was
large. This is considered to be because the amount of Si was too
large and thus, the hardness became excessively high and the hard
particle powder dropped. (6) In Comparative Example 3, the wear
amount was large. This is considered to be because the sintered
body did not include Mn and thus, no powder oxide film was formed
and the lubrication property degraded. (7) In Comparative Example
4, the wear amount was large. This is considered to be because the
amount of Mn was large and thus, the powder oxidation amount
increased and the sintering characteristics deteriorated. (8) In
Comparative Example 5, the wear amount was large. This is
considered to be because the sintered body did not include Ni and
thus, the heat resistance degraded. (9) In Comparative Example 6,
the wear amount was large. This is considered to be because the
amount of Ni was too large and thus, conversely, the amount of Co
which was a balancing element decreased, and the heat resistance
and the wear resistance degraded.
[0076] (10) In Comparative Example 7, the wear amount was large.
This is considered to be because the sintered body did not include
Cr and thus, the heat resistance degraded. (11) In Comparative
Example 8, the wear amount was large. This is considered to be
because the amount of Cr was too large and thus, conversely, the
amount of Co which was a balancing element decreased, and the heat
resistance and the wear resistance degraded. (12) In Comparative
Example 9, the wear amount was large. This is considered to be
because the amount of Mo was too small and thus, the hardness
degraded and the wear resistance degraded. (13) In Comparative
Example 10, the wear amount was large. This is considered to be
because the amount of Mo was too large and thus, the hardness
became too high and the hard particle powder dropped. (14) In
Comparative Example 11, the wear amount was large. This is
considered to be because the sintered body did not include Fe and
thus, the diffusivity into the iron powder degraded and the hard
particle powder was likely to drop. (15) In Comparative Example 12,
the wear amount was large. This is considered to be because the
amount of Fe was too large and thus, the heat resistance
degraded.
[0077] (16) In Comparative Examples 13 to 28, the wear amounts were
large. This is considered to be because the sintered bodies did not
include REM and thus, oxidation did not occur at low temperatures
and the lubrication property on the valve surfaces degraded. (17)
In Comparative Examples 29 to 44, the wear amount was large. This
is considered to be because the amounts of REM were too large and
thus, the powder oxidation amounts increased and the sintering
characteristics degraded.
[0078] Based on what has been described above, it was found that,
in the case where REM is added to a hard particle powder made of a
predetermined component system, the wear resistance of a sintered
body (valve seat) can be improved while rarely impairing powder
characteristics and sintering characteristics, and a sintered body
having excellent wear resistance can be obtained.
[0079] Hitherto, the embodiment of the present invention has been
described in detail, but the present invention is not limited to
the above-described embodiment, and a variety of modifications or
changes are possible within the scope of the gist of the present
invention.
[0080] The present application is based on Japanese Patent
Application No. 2018-026177 filed on Feb. 16, 2018, the entire
content of which is incorporated herein by reference.
INDUSTRIAL APPLICABILITY
[0081] The hard particle powder for a sintered body according to
the present invention can be used as a hard particle powder being
included to a variety of sintered bodies that are used as a valve
seat, a valve guide, or other mechanical structural components, for
the purpose of improving wear resistance.
* * * * *