U.S. patent application number 16/615093 was filed with the patent office on 2021-06-03 for method for manufacturing sintered member.
The applicant listed for this patent is SUMITOMO ELECTRIC INDUSTRIES, LTD., SUMITOMO ELECTRIC SINTERED ALLOY, LTD.. Invention is credited to Shigeki EGASHIRA, Tomoyuki ISHIMINE, Munehiro NODA.
Application Number | 20210162499 16/615093 |
Document ID | / |
Family ID | 1000005402716 |
Filed Date | 2021-06-03 |
United States Patent
Application |
20210162499 |
Kind Code |
A1 |
ISHIMINE; Tomoyuki ; et
al. |
June 3, 2021 |
METHOD FOR MANUFACTURING SINTERED MEMBER
Abstract
A method for manufacturing a sintered member includes a step of
preparing a raw material powder containing an iron-based powder; a
step of forming a green compact having a relative density of 97% or
more and having a solid cylindrical shape or hollow cylindrical
shape by compacting the raw material powder; and a step of
sintering the green compact. The raw material powder contains at
least one of a mixed powder containing pure iron powder and Ni
powder and an iron alloy powder containing Ni as an additive
element. The total amount of the Ni powder and Ni serving as the
additive element in the raw material powder is 1 mass % or
more.
Inventors: |
ISHIMINE; Tomoyuki; (Osaka,
JP) ; EGASHIRA; Shigeki; (Osaka, JP) ; NODA;
Munehiro; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO ELECTRIC INDUSTRIES, LTD.
SUMITOMO ELECTRIC SINTERED ALLOY, LTD. |
Osaka
Okayama |
|
JP
JP |
|
|
Family ID: |
1000005402716 |
Appl. No.: |
16/615093 |
Filed: |
May 8, 2018 |
PCT Filed: |
May 8, 2018 |
PCT NO: |
PCT/JP2018/017803 |
371 Date: |
November 19, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 2301/35 20130101;
B22F 2301/10 20130101; B22F 5/106 20130101; B22F 2301/15 20130101;
B22F 3/162 20130101; B22F 2301/30 20130101 |
International
Class: |
B22F 3/16 20060101
B22F003/16; B22F 5/10 20060101 B22F005/10 |
Foreign Application Data
Date |
Code |
Application Number |
May 26, 2017 |
JP |
2017-105088 |
Claims
1. A method for manufacturing a sintered member, the method
comprising: a step of preparing a raw material powder containing an
iron-based powder; a step of forming a green compact having a
relative density of 97% or more and having a solid cylindrical
shape or hollow cylindrical shape by compacting the raw material
powder; and a step of sintering the green compact, wherein the raw
material powder contains at least one of a mixed powder containing
pure iron powder and Ni powder and an iron alloy powder containing
Ni as an additive element, and a total amount of the Ni powder and
Ni serving as the additive element in the raw material powder is 1
mass % or more.
2. The method for manufacturing a sintered member according to
claim 1, further comprising a step of cutting the green compact
between the forming step and the sintering step.
3. A method for manufacturing a sintered member, the method
comprising: a step of preparing a raw material powder containing an
iron-based powder; a step of forming a green compact having a
relative density of 97% or more and having a solid cylindrical
shape or hollow cylindrical shape by compacting the raw material
powder; and a step of sintering the green compact, wherein the raw
material powder contains at least one of a mixed powder containing
pure iron powder and Ni powder and an iron alloy powder containing
Ni as an additive element, a total amount of the Ni powder and Ni
serving as the additive element in the raw material powder is 1
mass % or more, the iron alloy powder containing at least one
selected from Cu, Sn, Cr, Mo, Mn, and C, and a total amount of
powders of Cu, Sn, Cr, Mn, and Mo selected from the above alloying
elements is 0.1 mass % or more and 2.0 mass % or less relative to
100 mass % of the raw material powder.
4. The method for manufacturing a sintered member according to
claim 3, further comprising a step of cutting the green compact
between the forming step and the sintering step.
5. The method for manufacturing a sintered member according to
claim 3, wherein the iron alloy powder containing C powder, and a
total amount of powders of C powder is 0.1 mass % or more and 2.0
mass % or less relative to 100 mass % of the raw material powder.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a method for manufacturing
a sintered member. This application claims priority to Japanese
Patent Application No. 2017-105088 filed May 26, 2017, which is
incorporated herein by reference in its entirety.
BACKGROUND ART
[0002] The method for manufacturing a sintered body in PTL 1 is
known as a method for manufacturing a sintered member used for, for
example, automobile components and general machinery components.
This method for manufacturing a sintered body includes a step of
producing a compact by compacting metal powder, a step of
calcinating the compact, a step of machining the calcined body, and
a step of firing the machined calcined body after the machining
step. In the step of producing a compact, the pressure during
compaction is 100 MPa to 1500 MPa.
CITATION LIST
Patent Literature
[0003] PTL 1: Japanese Patent Application Laid-Open No.
2007-77468
SUMMARY OF INVENTION
[0004] A method for manufacturing a sintered member according to
the present disclosure includes:
[0005] a step of preparing a raw material powder containing an
iron-based powder;
[0006] a step of forming a green compact having a relative density
of 97% or more and having a solid cylindrical shape or hollow
cylindrical shape by compacting the raw material powder; and
[0007] a step of sintering the green compact.
[0008] The raw material powder contains at least one of a mixed
powder containing pure iron powder and Ni powder and an iron alloy
powder containing Ni as an additive element.
[0009] The total amount of the Ni powder and Ni serving as the
additive element in the raw material powder is 1 mass % or
more.
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIG. 1 is a graph showing the relationship between
compacting pressure and green density in Test Example 1.
[0011] FIG. 2 is a graph showing the relationship between green
density and tensile strength in Test Example 1.
DESCRIPTION OF EMBODIMENT OF PRESENT DISCLOSURE
[0012] First, features of an embodiment of the present disclosure
will be listed and described.
[0013] (1) A method for manufacturing a sintered member according
to an aspect of the present disclosure includes: [0014] a step of
preparing a raw material powder containing an iron-based
powder;
[0015] a step of forming a green compact having a relative density
of 97% or more and having a solid cylindrical shape or hollow
cylindrical shape by compacting the raw material powder; and
[0016] a step of sintering the green compact,
[0017] wherein the raw material powder contains at least one of a
mixed powder containing pure iron powder and Ni powder and an iron
alloy powder containing Ni as an additive element, and
[0018] a total amount of the Ni powder and Ni serving as the
additive element in the raw material powder is 1 mass % or
more.
[0019] According to the above features, a sintered member having
high density and high strength can be manufactured. Since the green
compact has a relative density of 97% or more and shrinks during
sintering, the relative density of the sintered member is larger
than the relative density of the green compact. The sintered member
has high relative density and thus has high strength.
[0020] (2) The method for manufacturing a sintered member according
to one aspect further includes a step of cutting the green compact
between the forming step and the sintering step.
[0021] According to the above features, a sintered member having
high density and complicated shape can be manufactured easily. Even
when the green compact contains 1 mass % of Ni, which degrades
cutting workability, in the form of powder or contains 1 mass % or
more of Ni in the form of alloy additive element, the green compact
is softer and less viscous than a sintered member or wrought
material having the same composition. It is thus easy to cut the
green compact. In addition, the green compact has very high
relative density and relatively high strength although it is softer
than a sintered member or wrought material. The green compact is
thus unlikely to undergo chipping or cracking during cutting.
<<Details of Embodiment of Present Disclosure>>
[0022] The details of the embodiment of the present disclosure will
be described below.
[Method for Manufacturing Sintered Member]
[0023] A method for manufacturing a sintered member according to an
embodiment includes a step (raw material preparation step) of
preparing a raw material powder, a step (forming step) of forming a
green compact by compacting the raw material powder, and a step
(sintering step) of sintering the green compact. One of
characteristics of the method for manufacturing a sintered member
is that a particular raw material powder is prepared in the raw
material preparation step and a green compact satisfying a
particular relative density is produced in the forming step. Each
step will be described below in detail.
[Raw Material Preparation Step]
[0024] The raw material preparation step involves preparing a raw
material powder containing an iron-based powder having iron-based
particles. The term iron-based refers to pure iron or an iron alloy
containing iron as a main component. The raw material powder has
any one of a mixed powder containing Ni in the form of powder, an
iron alloy powder containing Ni as an additive element, and a
composite powder containing both the mixed powder and the iron
alloy powder.
(Mixed Powder)
[0025] The mixed powder contains pure iron powder and Ni powder.
The amount of the pure iron powder is, for example, 90 mass % or
more, or 95 mass % or more relative to 100 mass % of the raw
material powder. The amount of the Ni powder is, for example, 1
mass % or more relative to 100 mass % of the raw material powder.
When the amount of the Ni powder is 1 mass % or more, the
hardenability is improved so that the sintered member has improved
mechanical characteristics. The amount of the Ni powder may be, for
example, 2 mass % or more and 10 mass % or less. The mixed powder
is sintered in the later sintering step to form an iron-based
alloy.
[0026] The mixed powder may further contain alloying element powder
that forms an iron-based alloy during sintering in the later
sintering step. The alloying element is, for example, at least one
selected from Cu, Sn, Cr, Mo, Mn, and C. The alloying element
improves the mechanical characteristics of the sintered member. The
total amount of powders of Cu, Sn, Cr, Mn, and Mo selected from the
above alloying elements is, for example, more than 0 mass % and 5.0
mass % or less, or 0.1 mass % or more and 2.0 mass % or less
relative to 100 mass % of the raw material powder. The amount of C
powder is, for example, more than 0 mass % and 2.0 mass % or less,
or 0.1 mass % or more and 1.0 mass % or less relative to 100 mass %
of the raw material powder.
(Iron Alloy Powder)
[0027] The iron alloy powder contains iron as a main component and
has iron alloy particles containing Ni as an alloying element.
[0028] The amount of iron is, for example, 90 mass % or more, or 95
mass % or less relative 100 mass % of the iron alloy. The amount of
Ni is, for example, 1 mass % or more, or 2 mass % or more and 10
mass % or less relative to 100 mass % of the iron alloy.
[0029] The iron alloy may further contain at least one additive
element selected from Cu, Sn, Cr, Mo, Mn, and C. The iron alloy may
contain inevitable impurities. Specific examples of the iron alloy
include Fe--Ni--Mo alloy, Fe--Ni--Mo--C alloy, Fe--Ni--C alloy,
Fe--Ni--Mo--Cr alloy, Fe--Ni--Mo--Mn alloy, Fe--Ni--Cr alloy,
Fe--Ni--Cu alloy, Fe--Cu--Ni--Mo alloy, and Fe--Ni--Mo--Cu--C
alloy. The total amount of Cu, Sn, Cr, Mn, and Mo in the iron alloy
is, for example, more than 0 mass % and 5.0 mass % or less, or 0.1
mass % or more and 2.0 mass % or less. The amount of C in the iron
alloy is, for example, more than 0 mass % and 2.0 mass % or less,
or 0.1 mass % or more and 1.0 mass % or less. Carbon C may be
contained in the form of powder in the raw material powder instead
of being contained as an alloying element in the iron alloy. In
other words, the raw material powder may contain C powder in
addition to the iron alloy powder.
(Composite Powder)
[0030] The composite powder contains both the mixed powder and the
iron alloy powder. Specifically, the composite powder contains pure
iron powder, Ni powder, and iron alloy powder having iron alloy
particles containing iron as a main component and Ni as an alloying
element. The total amount of the pure iron powder and iron
contained in the iron alloy in the raw material powder is, for
example, 90 mass % or more, or 95 mass % or more relative to 100
mass % of the entire raw material powder. The total amount of the
Ni powder and Ni contained as an alloying element in the raw
material powder is, for example, 1 mass % or more, or 2 mass % or
more and 10 mass % or less relative to 100 mass % of the entire raw
material powder.
[0031] The iron-based powder may be, for example, water atomized
powder, reduced powder, gas atomized powder, or carbonyl powder.
The iron-based powder has an average particle size of, for example,
20 .mu.m or more and 200 .mu.m or less. When the iron-based powder
has an average particle size in this range, it is easy to handle
and compact the iron-based powder. In particular, it is easy to
ensure the fluidity of the iron-based powder when the iron-based
powder has an average particle size of 20 .mu.m or more. It is easy
to form a sintered body having a dense structure when the
iron-based powder has an average particle size of 200 .mu.m or
less. The iron-based powder has an average particle size of, for
example, 50 .mu.m or more and 150 .mu.m or less. The average
particle size of the iron-based powder refers to a particle size
(D50) at 50% cumulative volume in the volume particle size
distribution determined with a laser diffractometry particle size
distribution measuring apparatus.
[0032] The raw material powder may contain at least one of a
lubricant and an organic binder. However, the amount of lubricant
and organic binder is preferably as small as possible. The total
amount of lubricant and organic binder is, for example, 0.1 mass %
or less. In the case where the raw material powder contains at
least one of a lubricant and an organic binder in this range, the
metal powder accounts for a large proportion of the compact, which
makes it easy to form a dense green compact. In the case where the
raw material powder is free of lubricant or organic binder, it is
not necessary to degrease the green compact in a later step.
[Forming Step]
[0033] The forming step involves compacting the raw material powder
into a green compact having a relative density of 97% or more. The
relative density is preferably 98% or more and more preferably 99%
or more. The shape of the green compact is, for example, a shape in
conformity with the final shape of the sintered member, a shape
suitable for cutting in a later step, specifically, a solid
cylindrical or hollow cylindrical shape. The green compact is
produced by using, for example, a suitable forming device (mold)
that allows the raw material powder to form into the
above-described shape. Specifically, a mold that enables uniaxial
pressing so as to perform press-forming in the axial direction of
the solid cylinder or the hollow cylinder is preferably used.
Uniaxial pressing may use a mold including a die having openings on
its top and bottom and a pair of punches to be fitted into the
openings on the top and bottom. The cavity in the die of the mold
is filled with the raw material powder, and the raw material powder
in the cavity is compressed with the upper and lower punches to
produce a green compact.
[0034] The compacting pressure (surface pressure) is, for example,
1560 MPa or more. At a high compacting pressure, a green compact
having high relative density can be produced. The compacting
pressure is preferably 1660 MPa or more or 1760 MPa or more, or
more preferably 1860 MPa or 1960 MPa or more. There is no upper
limit of the compacting pressure.
[0035] The forming step is preferably performed by a mold
(external) lubricating method in which a lubricant is applied to
the inner circumferential surfaces of the mold (the inner
circumferential surface of the die and the press surfaces of the
punches). It is thus easy to prevent galling of the raw material
powder on the mold. Examples of the lubricant include higher fatty
acids, metallic soaps, fatty acid amides, and higher fatty acid
amides. Examples of metallic soaps include zinc stearate and
lithium stearate. Examples of fatty acid amides include stearamide,
lauramide, and palmitamide. Examples of higher fatty acid amides
include ethylene bis stearamide.
[0036] The relative density of the green compact to be produced is
preferably 98% or more and more preferably 99% or more. The
relative density of the green compact is obtained from "{(green
density of green compact)/(true density of green
compact)}.times.100". The green density of the green compact is
obtained by immersing the green compact in an oil and calculating
the green density in accordance with "oil-impregnated
density.times.{(mass of green compact before oil
impregnation)/(mass of green compact after oil impregnation)}". The
oil-impregnated density is a value obtained by dividing the mass of
the green compact after oil impregnation by the volume of the green
compact after oil impregnation.
[0037] The relative density of the green compact can be obtained on
the basis of image analysis on the cross section of the green
compact with commercially available image analysis software. First,
the images of the cross sections of the green compact are obtained
from 10 or more fields of view. The cross sections may be freely
defined, and 10 or more cross sections are taken from fields of
view (one field of view per cross section or two or more fields of
view per cross section). The size of each field of view is 500
.mu.m.times.600 .mu.m. The image in each field of view is binarized
to obtain the area ratio of metal in each field of view, and the
area ratio is taken as a relative density in each field of view.
The mean relative density of all fields of view is obtained and
taken as the relative density of the green compact.
[Sintering Step]
[0038] The sintering step involves sintering the green compact. The
sintering provides a sintered member in which metal powder
particles are in contact with and bonded to each other. The
sintered member has a relative density of more than 97%. Since the
green compact has a relative density of 97% or more and shrinks
during sintering, the relative density of the sintered member after
sintering is larger than the relative density of the green compact.
Although the amount of shrinkage of the green compact is very small
during sintering because of the green compact having very high
density, the relative density of the sintered member is larger than
relative density of the green compact although.
[0039] The sintering conditions can be appropriately selected
according to the composition of the raw material powder. The
sintering temperature is, for example, 1100.degree. C. or more and
1400.degree. C. or less, or 1200.degree. C. or more and
1300.degree. C. or less. The sintering time is, for example, 15
minutes or more and 150 minutes or less, or 20 minutes or more and
60 minutes or less. The sintering conditions can be known
conditions.
[Other Steps]
[0040] In addition to the raw material preparation step, the
forming step, and the sintering step, the method for manufacturing
a sintered member may include at least one of a step (compact
processing step) of cutting the compact, a step (heat treatment
step) of carburizing, quenching, and annealing the sintered member,
and a step (finishing step) of finishing the sintered member.
(Compact Processing Step)
[0041] The compact processing step involves cutting the green
compact between the forming step and the sintering step. In
cutting, the green compact is processed into a predetermined shape
by using a cutting tool. Since the green compact before sintering
is cut, it is easy to manufacture a sintered member having high
density and complicated shape. Even when the green compact contains
1 mass % or more of Ni, which degrades cutting workability, in the
form of powder or contains 1 mass % or more of Ni in the form of
alloy additive element, the green compact is softer and less
viscous than a sintered member or wrought material having the same
composition. It is thus easy to cut the green compact. Moreover,
the green compact is softer than a sintered member or wrought
material, but has very high relative density and relatively high
strength. The green compact is thus unlikely to undergo chipping or
cracking during cutting. The green compact is formed by simply
compressing the raw material powder, and the metal powder particles
in the green compact are mechanically attached to each other. The
sintered member is formed by diffusion-bonding metal powder
particles to each other through sintering, and the metal powder
particles are strongly bonded to each other. Assuming that the
wrought material has the same size as the green compact, the
wrought material is an integrally formed object much larger than
metal particles that constitute the green compact.
[0042] In particular, the processing speed for producing the green
compact by using the mixed powder can be higher than the processing
speed for producing the green compact by using the alloy powder.
For example, in dry-cutting a green compact formed of the alloy
powder and a green compact formed of the mixed powder by using a
hob made of powder high-speed steel, the maximum peripheral speed
(cutting speed) of the tool is 350 m/min for cutting the green
compact formed of the alloy powder and 450 m/min for cutting the
green compact formed of the mixed powder. The maximum peripheral
speed of the tool is 150 m/min for cutting the wrought material and
150 m/min for cutting the sintered member.
[0043] Examples of cutting include milling and turning. Milling
includes drilling. Examples of the cutting tool include drills and
reamers for drilling; milling cutters and end mills for milling;
and tool bits and edge replaceable cutting tips for turning. In
addition, for example, a hob, a broach, or a pinion cutter may be
used, or a machining center that can automatically perform various
types of processing may be used.
[0044] Before cutting, a volatile solution or plastic solution in
which an organic binder is dissolved may be applied to the surface
of the green compact by coating or immersion. In this case, it is
easy to suppress cracking or chipping in the surface layer of the
green compact during cutting. Examples of the organic binder
include polyethylene, polypropylene, polymethyl methacrylate,
polystyrene, polyvinyl chloride, polyvinylidene chloride,
polyamide, polyester, polyether, polyvinyl alcohol, vinyl acetate,
paraffin, and various waxes.
[0045] Cutting may be performed with the compression stress applied
to the green compact to offset the tensile stress acting on the
green compact. In this case, it is easy to suppress cracking or
chipping of the green compact. For example, in the case where a
processing hole is formed in the green compact by using a broach, a
high tensile stress acts near the exit of the processing hole when
the broach is inserted into the green compact. In this case, plural
green compacts may be stacked in a multilayer manner. For example,
a dummy green compact or plate may be placed under the lowest green
compact. In the plural green compacts stacked in a multilayer
manner, the lower surfaces of the upper green compacts are pressed
against the upper surfaces of the lower green compacts, and
compression stress acts on the lower surfaces. When the green
compacts stacked in a multilayer manner undergo broaching from
above, it is possible to effectively prevent cracking or chipping
near the exits of processing holes formed in the lower surfaces of
the green compacts. In the case where processing grooves are formed
in the green compacts by using a milling cutter, a high tensile
stress acts near the exits of the processing grooves. In this case,
for example, plural green compacts are arranged in the direction in
which the milling cutter moves, and compression stress is applied
to parts for forming the exits of the processing grooves.
(Heat Treatment Step)
[0046] The heat treatment step involves carburizing, quenching, and
annealing the sintered member. This step improves the mechanical
characteristics, particularly hardness and toughness, of the
sintered member.
(Finishing Step)
[0047] The finishing step involves reducing the surface roughness
of the sintered member and adjusting the dimensions of the sintered
member to designed dimensions. For example, the surface of the
sintered member is polished.
[Applications]
[0048] A sintered member having high density and high strength can
be manufactured in the method for manufacturing a sintered member
according to the embodiment. It is also easy to manufacture a
sintered member having high density and complicated shape in this
method. The method for manufacturing a sintered member according to
the embodiment can be preferably applied to the manufacture of
various ordinary structural components (sintered components, such
as mechanical components, including sprockets, rotors, gears,
rings, flanges, pulleys, and bearings).
[Sintered Member]
[0049] The sintered member contains metal particles bonded to each
other and has a relative density of more than 97%. This sintered
member can be manufactured by using the method for manufacturing a
sintered member (the raw material preparation step, the forming
step, and the sintering step). Since the compact has a relative
density of 97% or more, the sintered member obtained after the
subsequent sintering step also has a relative density of more than
97%. The method for measuring this relative density is the same as
the method for measuring the relative density of the green compact.
The density of this sintered member in the range of 1 mm from its
surface does not substantially change. In other words, the density
is substantially uniform. This is because the sintered member does
not undergo rolling. The metallographic structure of the sintered
member has no streamline pattern formed by stretching metal
particles. This is because the sintered member does not undergo
forging.
Test Example 1
[0050] The sintered member was produced, and the relative density
and strength of the sintered member were evaluated.
[Sample No. 1-1 to No. 1-3, and No. 1-101 to No. 1-103]
[0051] The sintered members of Sample No. 1-1 to No. 1-3 and No.
1-101 to No. 1-103 were produced through the raw material
preparation step, the forming step, and the sintering step as in
the method for manufacturing a sintered member.
[0052] [Raw Material Preparation Step]
[0053] Carbon powder and iron alloy powder produced by water
atomization were prepared for raw material powder. The iron alloy
powder has a composition of 2 mass % Ni-0.5 mass % Mo with the
balance being Fe and inevitable impurities and has an average
particle size (D50) of 70 .mu.m. The carbon powder has an average
particle size (D50) of 5 .mu.m. The amount of the carbon powder is
0.3 mass % relative to 100 mass % of the raw material powder, and
the balance is iron alloy powder. The raw material powder is free
of lubricant or organic binder.
[Forming Step]
[0054] The raw material powder was compacted into a green compact
having a solid cylindrical shape (outer diameter: 75 mm, height: 20
mm). A mold that enables uniaxial pressing was used for production
of the green compact. This mold includes a die and upper and lower
punches. The die has openings on its top and bottom and a circular
insertion hole for forming the outer circumferential surface of the
green compact having a solid cylindrical shape. The upper and lower
punches each have a circular press surface for forming the opposite
end surfaces of the green compact having a solid cylindrical shape.
The inner circumferential surface of the die was coated with a
solution of myristic acid in alcohol, which was a lubricant.
[0055] The compacting pressure is as shown in Table 1. The
compacting pressure in Table 1 is a value obtained by converting "8
ton/cm.sup.2 to 20 ton/cm.sup.2" into "MPa" and rounding off
decimals.
[0056] The relative density of the produced green compact was
measured. The relative density of the green compact was obtained
from "{(green density of green compact)/(true density of green
compact)}.times.100". The green density of the green compact was
obtained by immersing the green compact in an oil and calculating
the green density in accordance with "oil-impregnated
density.times.((mass of green compact before oil
impregnation)/(mass of green compact after oil impregnation))." The
oil-impregnated density is a value obtained by dividing the mass of
the green compact after oil impregnation by the volume of the green
compact after oil impregnation. The true density of the green
compact (raw material powder) is about 7.8 g/cm.sup.3. The green
density and relative density of the green compact of each sample
are shown in Table 1. The relationship between the compacting
pressure (MPa) and the green density (g/cm.sup.3) of the green
compact of each sample is shown in FIG. 1. The horizontal axis of
the graph shown in FIG. 1 represents compacting pressure (MPa), and
the vertical axis represents green density (g/cm.sup.3). In FIG. 1,
the results of Sample No. 1-1 to No. 1-3 are plotted with black
circles, and the results of Sample No. 1-101 to No. 1-103 are
plotted with black rhombuses.
[Sintering Step]
[0057] The green compact was sintered to produce the sintered
member. The sintering conditions were as follows: the sintering
temperature was 1150.degree. C.; the sintering time was 60 minutes;
and the sintering atmosphere was a nitrogen atmosphere.
[Sample No. 1-111 to No. 1-117]
[0058] The sintered members of Sample No. 1-111 to No. 1-117 were
produced in the same manner as for Sample No. 1-1 except that the
mold was not coated with a lubricant, and the raw material powder
further contained a lubricant. The lubricant was ethylene bis
stearamide, and the amount of the lubricant in the raw material
powder was 0.6 mass %. The relative density of the green compacts
of Sample No. 1-111 to No. 1-117 was measured in the same manner as
for Sample No. 1-1. The green density and relative density of the
green compact of each sample are shown in Table 1. The relationship
between the compacting pressure (MPa) and the green density
(g/cm.sup.3) of the green compact of each sample is shown in FIG.
1. The results of Sample No. 1-111 to No. 1-117 are plotted with
white squares.
TABLE-US-00001 TABLE 1 Forming Step Green Compact Compacting Green
Relative Sample Pressure Density Density No. (MPa) (g/cm.sup.3) (%)
1-1 1569 7.63 97.82 1-2 1765 7.68 98.46 1-3 1961 7.70 98.72 1-101
980 7.28 93.33 1-102 1176 7.46 95.64 1-103 1372 7.56 96.92 1-111
784 7.04 90.26 1-112 980 7.21 92.44 1-113 1176 7.29 93.46 1-114
1372 7.34 94.10 1-115 1569 7.35 94.23 1-116 1765 7.36 94.36 1-117
1961 7.36 94.36
[0059] Table 1 and FIG. 1 show that the green compacts of Sample
No. 1-1 to No. 1-3 each have a relative density of 97% (green
density.apprxeq.7.57 g/cm.sup.3) or more. This result suggests that
the sintered members of Sample No. 1-1 to No. 1-3 each have a
relative density of more than 97% (green density.apprxeq.7.57
g/cm.sup.3).
[0060] However, it is found that the green compacts of Sample No.
1-101 to No. 1-103 and No. 1-111 to No. 1-117 each have a relative
density of less than 97%. This result suggests that the sintered
members of Sample No. 1-101 to No. 1-103 and No. 1-111 to No. 1-117
each have a relative density of less than 97%.
[Evaluation of Strength]
[0061] The strength of the sintered members was evaluated by
measuring tensile strength in tension testing. The sintered members
of Sample Nos. 2-1, 2-2, and 2-101 to 2-103 having a solid
cylindrical shape were produced in the manner as for Sample No.
1-1. The compacting pressure was controlled such that the green
density (relative density) of each sample was a value shown in
Table 2. The sintered member having a solid cylindrical shape was
processed into a predetermined shape and subjected to carburizing
and quenching to produce a test piece for measurement of tensile
strength. The test piece has a plate shape including a narrow part
and wide parts formed at the opposite ends of the narrow part. The
test piece has a thickness of 4 mm and a length of 72 mm. The
narrow part includes a central portion and shoulder portions each
having arc-shaped side surfaces formed from the central portion to
the wide part. The central portion has a length of 32 mm, a width
of 5.7 mm at its center, and a width of 5.96 mm at its opposite
ends. The side surfaces of the shoulder portions have a radius R of
25 mm. The wide parts have a width of 8.7 mm.
[0062] This test piece was subjected to tensile testing by using a
general-purpose tensile testing machine.
[0063] The results of tensile strength (MPa) are shown in Table 2.
The tensile strength (MPa) shown in Table 2 is a mean tensile
strength taken from evaluation number n=5. The relationship between
green density (g/cm.sup.3) and tensile strength (MPa) is shown in
FIG. 2. The horizontal axis of the graph shown in FIG. 2 represents
green density, and the vertical axis represents tensile strength.
In FIG. 2, the mean tensile strength of each of Sample No. 2-1 and
No. 2-2 is plotted with black circles, the mean tensile strength of
each of Sample No. 2-101 to No. 2-103 is plotted with black
rhombuses, and the maximum tensile strength and the minimum tensile
strength of these samples are indicated by error bars.
TABLE-US-00002 TABLE 2 Test Piece Green Relative Tensile Sample
Density Density Strength No. (g/cm.sup.3) (%) (MPa) 2-1 7.6 97.44
1803.8 2-2 7.7 98.72 1813.6 2-101 7.1 91.03 1214.6 2-102 7.4 94.87
1500.4 2-103 7.5 96.15 1675.4
[0064] Table 2 and FIG. 2 show that the tensile strength of the
test pieces (sintered members) of Sample No. 2-1 and No. 2-2 is
1700 MPa or more, or 1750 MPa or more, or 1800 MPa or more.
However, it is found that the tensile strength of the test pieces
(sintered members) of Sample No. 2-101 to No. 2-103 is less than
1700 MPa. It is thus revealed that sintering a green compact having
a relative density of 97% or more produces a sintered member having
high density and high strength.
[0065] The tensile strength of a common chromium molybdenum steel
(SCM415), which is used for structural components that experience
very high load, such as transmission gears for automobiles, was
measured in the same manner as for Sample No. 1-1 and the like. The
tensile strength was 1372 MPa. In other words, it is found that the
tensile strength of the sintered members of Sample No. 2-1 and No.
2-2 was very high.
[0066] It should be understood that the embodiment disclosed herein
is illustrative in any respect and non-restrictive from any
viewpoint. The scope of the present invention is defined by the
claims, rather than the above description, and is intended to
include all modifications within the meaning and range of
equivalency of the claims.
* * * * *