U.S. patent application number 17/017824 was filed with the patent office on 2021-03-11 for precipitation hardening stainless steel powder, compound, granulated powder, precipitation hardening stainless steel sintered body, and method for producing precipitation hardening stainless steel sintered body.
The applicant listed for this patent is SEIKO EPSON CORPORATION. Invention is credited to Junichi KUDO, Hidefumi NAKAMURA.
Application Number | 20210069780 17/017824 |
Document ID | / |
Family ID | 1000005108058 |
Filed Date | 2021-03-11 |
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United States Patent
Application |
20210069780 |
Kind Code |
A1 |
NAKAMURA; Hidefumi ; et
al. |
March 11, 2021 |
PRECIPITATION HARDENING STAINLESS STEEL POWDER, COMPOUND,
GRANULATED POWDER, PRECIPITATION HARDENING STAINLESS STEEL SINTERED
BODY, AND METHOD FOR PRODUCING PRECIPITATION HARDENING STAINLESS
STEEL SINTERED BODY
Abstract
A precipitation hardening stainless steel powder, containing Cr
at a concentration A within a range of 15.00 mass % or more and
17.50 mass % or less, Si at a concentration B within a range of
0.30 mass % or more and 1.00 mass % or less, Nb at a concentration
C within a range of 0.15 mass % or more and 0.45 mass % or less, Ni
at a concentration D within a range of 3.00 mass % or more and 5.00
mass % or less, Mn at a concentration E within a range of 0.05 mass
% or more and 1.00 mass % or less, and Cu at a concentration F
within a range of 3.00 mass % or more and 5.00 mass % or less,
wherein a value of .delta. defined by the following formula (1) is
10.0 mass % or more and 14.0 mass % or less.
.delta.=3(A+1.5B+0.5C)-2.8(D+0.5E+0.5F)-19.8 (1)
Inventors: |
NAKAMURA; Hidefumi; (Aomori,
JP) ; KUDO; Junichi; (Aomori, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEIKO EPSON CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
1000005108058 |
Appl. No.: |
17/017824 |
Filed: |
September 11, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 38/02 20130101;
C22C 38/42 20130101; B22F 1/0011 20130101; C22C 38/48 20130101;
B22F 1/0059 20130101; B22F 2304/10 20130101; B22F 3/10 20130101;
C22C 38/04 20130101; B22F 2301/35 20130101 |
International
Class: |
B22F 1/00 20060101
B22F001/00; B22F 3/10 20060101 B22F003/10; C22C 38/42 20060101
C22C038/42; C22C 38/02 20060101 C22C038/02; C22C 38/04 20060101
C22C038/04; C22C 38/48 20060101 C22C038/48 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 2019 |
JP |
2019-165252 |
Jun 10, 2020 |
JP |
2020-100714 |
Claims
1. A precipitation hardening stainless steel powder, comprising: Cr
at a concentration A within a range of 15.00 mass % or more and
17.50 mass % or less; Si at a concentration B within a range of
0.30 mass % or more and 1.00 mass % or less; Nb at a concentration
C within a range of 0.15 mass % or more and 0.45 mass % or less; Ni
at a concentration D within a range of 3.00 mass % or more and 5.00
mass % or less; Mn at a concentration E within a range of 0.05 mass
% or more and 1.00 mass % or less; and Cu at a concentration F
within a range of 3.00 mass % or more and 5.00 mass % or less,
wherein a value of .delta. defined by the following formula (1) is
10.0 mass % or more and 14.0 mass % or less:
.delta.=3(A+1.5B+0.5C)-2.8(D+0.5E+0.5F)-19.8 (1)
2. The precipitation hardening stainless steel powder according to
claim 1, wherein O is contained at a concentration within a range
of 0.01 mass % or more and 0.70 mass % or less.
3. The precipitation hardening stainless steel powder according to
claim 2, wherein O is contained at a concentration within a range
of 0.33 mass % or more and 0.53 mass % or less.
4. The precipitation hardening stainless steel powder according to
claim 1, wherein an average particle diameter is 0.50 .mu.m or more
and 50.00 .mu.m or less.
5. A compound, comprising the precipitation hardening stainless
steel powder according to claim 1 and an organic binder.
6. A granulated powder, comprising the precipitation hardening
stainless steel powder according to claim 1 and an organic
binder.
7. A precipitation hardening stainless steel sintered body,
comprising: Cr at a concentration A within a range of 15.00 mass %
or more and 17.50 mass % or less; Si at a concentration B within a
range of 0.30 mass % or more and 1.00 mass % or less; Nb at a
concentration C within a range of 0.15 mass % or more and 0.45 mass
% or less; Ni at a concentration D within a range of 3.00 mass % or
more and 5.00 mass % or less; Mn at a concentration E within a
range of 0.05 mass % or more and 1.00 mass % or less; and Cu at a
concentration F within a range of 3.00 mass % or more and 5.00 mass
% or less, wherein a value of .delta. defined by the following
formula (1) is 10.0 mass % or more and 14.0 mass % or less:
.delta.=3(A+1.5B+0.5C)-2.8(D+0.5E+0.5F)-19.8 (1).
8. A method for producing a precipitation hardening stainless steel
sintered body, comprising: molding the compound according to claim
5 or the granulated powder according to claim 6, thereby obtaining
a molded body; and firing the molded body, thereby obtaining a
sintered body, wherein a carbon atom concentration in the sintered
body is less than a carbon atom concentration in the precipitation
hardening stainless steel powder.
Description
[0001] The present application is based on, and claims priority
from JP Application Serial Number 2019-165252, filed on Sep. 11,
2019, and 2020-100714, filed on Jun. 10, 2020, the disclosure of
which is hereby incorporated by reference herein in its
entirety.
BACKGROUND
1. Technical Field
[0002] The present disclosure relates to a precipitation hardening
stainless steel powder, a compound, a granulated powder, a
precipitation hardening stainless steel sintered body, and a method
for producing a precipitation hardening stainless steel sintered
body.
2. Related Art
[0003] In a powder metallurgy method, a composition containing a
metal powder and an organic binder is molded into a desired shape,
and thereafter, the obtained molded body is degreased to obtain a
degreased body, and further, the degreased body is fired, whereby a
sintered body is produced. In such a process for producing a
sintered body, a phenomenon of atomic diffusion occurs among
particles of the metal powder, whereby the molded body is gradually
densified, resulting in sintering.
[0004] In such a powder metallurgy method, when the molded body is
degreased, the organic binder is thermally decomposed and removed
by heating the molded body. When the organic binder remains in the
molded body, the properties of the sintered body are deteriorated,
and therefore, various studies on the method for removing the
organic binder have been conducted.
[0005] For example, JP-A-4-247802 (Patent Document 1) discloses
that a degreasing treatment is performed by heating a molded body
including a metal material powder and a binder containing a
polyoxymethylene resin in an acid-containing atmosphere. By
performing the degreasing treatment in an acid-containing
atmosphere in this manner, the acid decomposes the binder, and
therefore, the binder can be efficiently removed. Therefore, the
above-mentioned problem can be reduced.
[0006] In the method described in Patent Document 1, it is
considered that most of the organic binder is removed in the
degreasing treatment. However, apart of the organic binder remains
in the molded body, and is removed concurrently with the progress
of sintering of the metal material powder in the subsequent firing
treatment. At that time, for example, when the particle diameter of
the metal material powder to be used is small or the like, the
progress of sintering tends to accelerate. That is, sintering
starts at a lower temperature stage in some cases. In such a case,
the organic binder may be confined in the molded body during the
firing treatment. As a result, there is a concern that an increase
in the carbon atom concentration in the sintered body is caused,
and the mechanical properties of the sintered body are
deteriorated.
SUMMARY
[0007] A precipitation hardening stainless steel powder according
to an application example of the present disclosure contains:
[0008] Cr at a concentration A within a range of 15.00 mass % or
more and 17.50 mass % or less;
[0009] Si at a concentration B within a range of 0.30 mass % or
more and 1.00 mass % or less;
[0010] Nb at a concentration C within a range of 0.15 mass % or
more and 0.45 mass % or less;
[0011] Ni at a concentration D within a range of 3.00 mass % or
more and 5.00 mass % or less;
[0012] Mn at a concentration E within a range of 0.05 mass % or
more and 1.00 mass % or less; and
[0013] Cu at a concentration F within a range of 3.00 mass % or
more and 5.00 mass % or less, wherein
[0014] a value of .delta. defined by the following formula (1) is
10.0 mass % or more and 14.0 mass % or less.
.delta.=3(A+1.5B+0.5C)-2.8(D+0.5E+0.5F)-19.8 (1)
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The FIGURE illustrates a process chart showing a method for
producing a precipitation hardening stainless steel sintered body
according to an embodiment.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0016] Hereinafter, embodiments of a precipitation hardening
stainless steel powder, a compound, a granulated powder, a
precipitation hardening stainless steel sintered body, and a method
for producing a precipitation hardening stainless steel sintered
body according to the present disclosure will be described in
detail.
1. Precipitation Hardening Stainless Steel Powder
[0017] First, a precipitation hardening stainless steel powder
according to an embodiment will be described.
[0018] In a powder metallurgy technique, a sintered body having a
desired shape can be obtained by molding a composition containing a
metal powder and a binder into a desired shape, followed by a
degreasing treatment and a firing treatment. According to such a
powder metallurgy technique, a sintered body with a complicated and
fine shape can be produced in a near-net shape, that is, a shape
close to a final shape as compared with the other techniques.
[0019] The precipitation hardening stainless steel powder according
to an embodiment is a powder constituted by a precipitation
hardening stainless steel containing Cr, Si, Nb, Ni, Mn, and Cu. In
such a powder, Cr is contained at a concentration A within a range
of 15.00 mass % or more and 17.50 mass % or less, Si is contained
at a concentration B within a range of 0.30 mass % or more and 1.00
mass % or less, Nb is contained at a concentration C within a range
of 0.15 mass % or more and 0.45 mass % or less, Ni is contained at
a concentration D within a range of 3.00 mass % or more and 5.00
mass % or less, Mn is contained at a concentration E within a range
of 0.05 mass % or more and 1.00 mass % or less, and Cu is contained
at a concentration F within a range of 3.00 mass % or more and 5.00
mass % or less. Further, in such a powder, a value of .delta.
defined by the following formula (1) is 10.0 mass % or more and
14.0 mass % or less.
.delta.=3(A+1.5B+0.5C)-2.8(D+0.5E+0.5F)-19.8 (1)
[0020] According to such a precipitation hardening stainless steel
powder, sinterability can be suppressed while maintaining excellent
mechanical strength derived from the precipitation hardening
stainless steel. Due to this, in the firing treatment, the
temperature at which sintering starts can be increased. As a
result, an organic binder remaining in a molded body can be more
reliably removed, and an increase in the carbon atom concentration
in a sintered body can be suppressed. Therefore, the precipitation
hardening stainless steel powder according to the embodiment
enables production of a sintered body having high mechanical
strength.
[0021] Hereinafter, the alloy composition of the precipitation
hardening stainless steel powder according to the embodiment will
be described in further detail. In the following description, the
precipitation hardening stainless steel powder is sometimes simply
referred to as "metal powder".
1.1 Cr
[0022] Cr (chromium) is an element which mainly imparts corrosion
resistance to a sintered body to be produced. By using the metal
powder containing Cr, the corrosion resistance is enhanced, so that
a sintered body having good corrosion resistance is obtained.
[0023] The concentration A of Cr in the metal powder is set to
15.00 mass % or more and 17.50 mass % or less, but is set to
preferably 15.20 mass % or more and 16.90 mass % or less, more
preferably 15.50 mass % or more and 16.70 mass % or less. When the
concentration A of Cr is less than the above lower limit, the
corrosion resistance of the sintered body to be produced may be
insufficient depending on the overall composition. On the other
hand, when the concentration A of Cr exceeds the above upper limit,
the sinterability is deteriorated depending on the overall
composition, and therefore, it becomes difficult to increase the
density of the sintered body, so that the corrosion resistance or
the mechanical properties of the sintered body may be
deteriorated.
[0024] Note that the mechanical properties of the sintered body
refer to, for example, properties such as mechanical strength and
hardness.
1.2 Si
[0025] Si (silicon) is an element which mainly imparts corrosion
resistance and high mechanical properties to a sintered body to be
produced. By using the metal powder containing Si, the corrosion
resistance and the mechanical properties are enhanced, so that a
sintered body having good corrosion resistance is obtained.
[0026] The concentration B of Si in the metal powder is set to 0.30
mass % or more and 1.00 mass % or less, but is set to preferably
0.35 mass % or more and 0.95 mass % or less, more preferably 0.40
mass % or more and 0.90 mass % or less. When the concentration B of
Si is less than the above lower limit, the corrosion resistance,
the surface properties, or the mechanical properties of the
sintered body to be produced may be deteriorated depending on the
overall composition. On the other hand, when the concentration B of
Si exceeds the above upper limit, the balance of the composition is
likely to be lost depending on the overall composition, and
therefore, the corrosion resistance, the surface properties, or the
mechanical properties of the sintered body to be produced may be
deteriorated.
[0027] Note that the surface properties of the sintered body refer
to, for example, properties such as specularity and smoothness.
1.3 Nb
[0028] Nb (niobium) is an element which enhances the mechanical
properties of a sintered body to be produced by precipitating a
precipitate in the sintered body.
[0029] The concentration C of Nb in the metal powder is set to 0.15
mass % or more and 0.45 mass % or less, but is set to preferably
0.20 mass % or more and 0.40 mass % or less, more preferably 0.25
mass % or more and 0.35 mass % or less. When the concentration C of
Nb is less than the above lower limit, precipitation of a
precipitate is restricted in the sintered body, and therefore, the
mechanical properties of the sintered body may not be able to be
sufficiently enhanced. On the other hand, when the concentration C
of Nb exceeds the above upper limit, a precipitate is excessively
precipitated, and the density of the sintered body is decreased,
and also the mechanical properties of the sintered body are
deteriorated instead.
1.4 Ni
[0030] Ni (nickel) is an element which mainly imparts corrosion
resistance and heat resistance to a sintered body to be produced.
By using the metal powder containing Ni, the corrosion resistance
and the heat resistance are enhanced, so that a sintered body
having good corrosion resistance and surface properties is
obtained.
[0031] The concentration D of Ni in the metal powder is set to 3.00
mass % or more and 5.00 mass % or less, but is set to preferably
3.50 mass % or more and 4.70 mass % or less, more preferably 3.80
mass % or more and 4.50 mass % or less. When the concentration D of
Ni is less than the above lower limit, the corrosion resistance or
the surface properties of the sintered body to be produced may not
be sufficiently enhanced depending on the overall composition. On
the other hand, when the concentration D of Ni exceeds the above
upper limit, the balance of the composition is likely to be lost
depending on the overall composition, and therefore, the corrosion
resistance or the surface properties of the sintered body to be
produced may be deteriorated.
1.5 Mn
[0032] Mn (manganese) is an element which imparts corrosion
resistance and high mechanical properties to a sintered body to be
produced in the same manner as Si. By using the metal powder
containing Mn, the corrosion resistance and the mechanical
properties are enhanced, so that a sintered body having good
corrosion resistance and mechanical properties is obtained.
[0033] The concentration E of Mn in the metal powder is not
particularly limited, but is preferably 0.05 mass % or more and
1.00 mass % or less, more preferably 0.07 mass % or more and 0.50
mass % or less, further more preferably 0.10 mass % or more and
0.40 mass % or less. When the concentration E of Mn is less than
the above lower limit, the corrosion resistance, the surface
properties, or the mechanical properties of the sintered body to be
produced may not be sufficiently enhanced depending on the overall
composition. On the other hand, when the concentration E of Mn
exceeds the above upper limit, the corrosion resistance, the
surface properties, or the mechanical properties may be
deteriorated instead.
1.6 Cu
[0034] Cu (copper) is an element which enhances the mechanical
properties of a sintered body to be produced by precipitating an
intermetallic compound in the sintered body.
[0035] The concentration F of Cu in the metal powder is set to 3.00
mass % or more and 5.00 mass % or less, but is set to preferably
3.10 mass % or more and 4.50 mass % or less, more preferably 3.20
mass % or more and 4.20 mass % or less. When the concentration F of
Cu is less than the above lower limit, precipitation of an
intermetallic compound is restricted in the sintered body, and
therefore, the mechanical properties of the sintered body may not
be able to be sufficiently enhanced. On the other hand, when the
concentration F of Cu exceeds the above upper limit, an
intermetallic compound is excessively precipitated, and the density
of the sintered body is decreased, and also the mechanical
properties of the sintered body are deteriorated instead.
1.7 Value of .delta.
[0036] In the precipitation hardening stainless steel powder
according to this embodiment, the value of 0.3 defined by the
following formula (1) is 10.0 mass % or more and 14.0 mass % or
less.
.delta.=3(A+1.5B+0.5C)-2.8(D+0.5E+0.5F)-19.8 (1)
[0037] The value of .delta. defined by such a formula (1) enables
suppression of the sinterability of the precipitation hardening
stainless steel powder without impairing the mechanical properties
of a sintered body to be produced using the precipitation hardening
stainless steel powder. Specifically, the first term of the right
side of the formula (1) is a term related to elements for mainly
producing a ferrite, and the second term is a term related to
elements for mainly producing an austenite. In the ferrite, the
diffusion rate during sintering is higher than that in the
austenite, and therefore, the ferrite contributes to the
enhancement of the sinterability of the precipitation hardening
stainless steel powder.
[0038] In view of this, in this embodiment, by optimizing the
ratios of the concentrations of the elements for producing the
ferrite to the concentrations of the elements for producing the
austenite based on the formula (1), the sinterability is suppressed
while maintaining excellent mechanical strength derived from the
precipitation hardening stainless steel in the sintered body to be
obtained. More specifically, by setting the value of .delta.
defined by the formula (1) within the above range, the
sinterability of the precipitation hardening stainless steel powder
is suppressed while maintaining the mechanical strength of the
sintered body, and the diffusion rate can be decreased as compared
with the related art. According to this, when the molded body is
subjected to a firing treatment, the temperature at which sintering
of the metal powder starts can be further increased. As a result,
the organic binder remaining in the molded body can be more
reliably removed at a stage before the metal powder starts to
sinter.
[0039] The removal of the organic binder refers to volatilization
of the organic binder or a decomposition product thereof,
volatilization of a reaction product resulting from a reaction of a
carbon atom contained in the organic binder with an oxygen atom
contained in the metal powder or an oxygen atom adsorbed to the
metal powder, or the like.
[0040] Here, the organic binder contains an organic compound as a
main material, and therefore contains a carbon atom. When the
organic binder in the molded body cannot be sufficiently removed,
there is a concern that carbon atoms remain in the sintered body
more than in the related art to decrease the mechanical strength of
the sintered body. On the other hand, in this embodiment, by
suppressing the sinterability of the precipitation hardening
stainless steel powder, the removal efficiency of the organic
binder in the sintering treatment can be increased. According to
this, the carbon atom concentration in the sintered body can be
suppressed, and a sintered body having high mechanical strength can
be produced.
[0041] The value of .delta. is set to 10.0 mass % or more and 14.0
mass % or less, but is set to preferably 10.5 mass % or more and
13.5 mass % or less, more preferably 11.0 mass % or more and 13.0
mass % or less. When the value of .delta. is less than the above
lower limit, the concentrations of the elements for producing the
austenite become high. In that case, although the sinterability of
the precipitation hardening stainless steel powder is lowered, the
sinterability tends to become too low, and the density of the
sintered body is hardly increased. As a result, a decrease in the
mechanical strength of the sintered body to be obtained is caused.
On the other hand, when the value of .delta. exceeds the above
upper limit, the concentrations of the elements for producing the
ferrite become high. In that case, the sinterability of the
precipitation hardening stainless steel powder becomes too high,
and the carbon atom concentration in the sintered body to be
obtained becomes high. As a result, a decrease in the mechanical
strength of the sintered body is caused.
1.8 Fe
[0042] Fe (iron) is an element whose content ratio is the highest
among the elements contained in the precipitation hardening
stainless steel powder according to the embodiment, that is, a
principal component and has a great influence on the properties of
the sintered body to be produced. The content ratio of Fe is not
particularly limited, but is preferably 50 mass % or more, more
preferably 60 mass % or more.
1.9 Other Elements
[0043] The precipitation hardening stainless steel powder according
to the embodiment may contain, other than the above-mentioned
elements, at least one element of C, Mo, W, N, S, and P as
needed.
[0044] C (carbon) is an element which causes solid solution
hardening as an interstitial element or causes precipitation
hardening by a precipitate containing C or another element in a
sintered body to be produced. By using the metal powder containing
C, a sintered body having high mechanical properties is obtained.
On the other hand, when the concentration of C, that is, the carbon
atom concentration is too high, the mechanical properties, for
example, the hardness of the sintered body is lowered.
[0045] The concentration of C in the metal powder is set to 0.07
mass % or less, but is preferably set to 0.01 mass % or more and
0.05 mass % or less. When the concentration of C exceeds the above
upper limit, the balance of the composition is likely to be lost
depending on the overall composition, and therefore, the mechanical
properties of the sintered body to be produced may be
deteriorated.
[0046] Mo (molybdenum) is an element which strengthens the
corrosion resistance of a sintered body to be produced.
[0047] The concentration of Mo in the metal powder is not
particularly limited, but is preferably 1.00 mass % or less, more
preferably 0.01 mass % or more and 0.50 mass % or less. By setting
the concentration of Mo within the above range, the corrosion
resistance of the sintered body to be produced can be further
strengthened without causing a significant decrease in the density
of the sintered body.
[0048] W (tungsten) is an element which strengthens the heat
resistance of a sintered body to be produced.
[0049] The concentration of W in the metal powder is not
particularly limited, but is preferably 1.00 mass % or less, more
preferably 0.01 mass % or more and 0.50 mass % or less. By setting
the concentration of W within the above range, the heat resistance
of the sintered body to be produced can be further strengthened
without causing a significant decrease in the density of the
sintered body.
[0050] N (nitrogen) is an element which enhances the mechanical
properties such as proof stress of a sintered body to be
produced.
[0051] The concentration of N in the metal powder is not
particularly limited, but is preferably 1.00 mass % or less, more
preferably 0.001 mass % or more and 0.50 mass % or less, further
more preferably 0.05 mass % or more and 0.30 mass % or less. By
setting the concentration of N within the above range, the
mechanical properties such as proof stress of the sintered body to
be produced can be further strengthened without causing a
significant decrease in the density of the sintered body.
[0052] When the metal powder to which N is added is produced, for
example, a method in which a nitrided raw material is used, a
method in which nitrogen gas is introduced into a molten metal, a
method in which the produced metal powder is subjected to a
nitriding treatment, or the like is used.
[0053] S (sulfur) is an element which enhances the machinability of
a sintered body to be produced.
[0054] The concentration of S in the metal powder is not
particularly limited, but is preferably 0.50 mass % or less, more
preferably 0.001 mass % or more and 0.30 mass % or less. By setting
the concentration of S within the above range, the machinability of
the sintered body to be produced can be further strengthened
without causing a significant decrease in the density of the
sintered body.
[0055] P (phosphorus) is an element which causes solid solution
hardening as an interstitial element or causes precipitation
hardening by a precipitate obtained by combination with another
element in a sintered body to be produced. By using the metal
powder containing P, a sintered body having high mechanical
properties is obtained.
[0056] The concentration of P in the metal powder is set to 0.50
mass % or less, but is set to preferably 0.001 mass % or more and
0.35 mass % or less, more preferably 0.005 mass % or more and 0.30
mass % or less. When the concentration of P is less than the above
lower limit, the mechanical properties of the sintered body may not
be able to be sufficiently enhanced depending on the overall
composition even if P is added. On the other hand, when the
concentration of P exceeds the above upper limit, the balance of
the composition is likely to be lost depending on the overall
composition, and therefore, the mechanical properties of the
sintered body to be produced may be deteriorated.
[0057] O (oxygen) may also be intentionally added or inevitably
contained, however, the concentration thereof is preferably 0.01
mass % or more and 0.70 mass % or less, more preferably 0.15 mass %
or more and 0.60 mass % or less. By making the concentration of 0
in the metal powder fall within the above range, silicon oxide is
precipitated on the surface of the particle of the metal powder,
and therefore, oxidation of an element such as Mn or Cr can be
suppressed. As a result, the corrosion resistance and the surface
properties of the sintered body to be finally produced can be
enhanced.
[0058] When the content ratio of 0 is less than the above lower
limit, the precipitation amount of silicon oxide is decreased, and
therefore, oxidation of an element such as Mn or Cr may proceed. In
that case, the corrosion resistance, the surface properties, and
the mechanical properties of the sintered body to be produced may
be deteriorated. On the other hand, when the content ratio of 0
exceeds the above upper limit, not only silicon oxide, but also an
oxide of Mn or Cr is produced at the time of producing the metal
powder. Due to this, it becomes difficult to increase the density
of the sintered body to be produced, and further, along with this,
the corrosion resistance, the surface properties, and the
mechanical properties may be deteriorated.
[0059] In addition, the concentration of 0 is further more
preferably 0.20 mass % or more and 0.55 mass % or less, and
particularly preferably 0.33 mass % or more and 0.53 mass % or
less. By making the concentration of 0 in the metal powder fall
within the above range, in addition to the above-mentioned effect,
an oxygen atom in the metal powder can be reacted with a carbon
atom derived from the organic binder. For example, when an oxygen
atom in the metal powder is present as silicon oxide, by a reaction
represented by the following formula (2), the oxygen atom and the
carbon atom can be removed from the sintered body.
SiO.sub.2+2C.fwdarw.Si+2CO.uparw. (2)
[0060] By such a reaction, a carbon atom derived from the organic
binder is consumed using an oxygen atom, and therefore can be
removed. Accordingly, by incorporating a predetermined amount of
oxygen atoms, a carbon atom concentration derived from the organic
binder remaining in the sintered body can be suppressed.
[0061] When the concentration of O is less than the above lower
limit, the carbon atom may not be able to be sufficiently consumed
in the sintered body. On the other hand, when the concentration of
O exceeds the above upper limit, the balance of the composition is
likely to be lost, and therefore, the mechanical strength or the
corrosion resistance of the sintered body to be produced may be
deteriorated.
[0062] To the precipitation hardening stainless steel powder, other
than the above-mentioned elements, H, Be, B, Al, Co, As, Sn, Se,
Zr, Y, Ti, Hf, Ta, Te, Pb, or the like may be added in order to
enhance the properties of the sintered body. In that case, the
concentration of such an element is not particularly limited, but
is set to such a concentration that the above-mentioned properties
of the sintered body are not inhibited, and the concentration of
each element is preferably less than 0.1 mass %, and even the sum
of the concentrations is preferably less than 0.2 mass %. These
elements are sometimes inevitably incorporated.
[0063] The precipitation hardening stainless steel powder may
contain inevitable impurities. Examples of the impurities include
all elements other than the above-mentioned elements. The
concentration of each of these impurities may be any value as long
as it is less than the concentration of each of Fe, Cr, Si, Nb, Ni,
Mn, and Cu. Further, in particular, the concentration of each of
these impurities is preferably less than 0.03 mass %, and the sum
of the concentrations of these impurities is preferably less than
0.30 mass %. These impurities do not inhibit the effect as
described above as long as the concentrations thereof are within
the above range, and therefore may be intentionally added to the
powder.
[0064] The tap density of the precipitation hardening stainless
steel powder is preferably 3.5 g/cm.sup.3 or more and 5.5
g/cm.sup.3 or less, more preferably 4.0 g/cm.sup.3 or more and 5.0
g/cm.sup.3 or less. According to such a precipitation hardening
stainless steel powder, the interparticle filling property becomes
particularly high when obtaining a molded body. Therefore, a
particularly dense sintered body can be finally obtained.
[0065] The specific surface area of the precipitation hardening
stainless steel powder is preferably 0.10 m.sup.2/g or more and
0.70 m.sup.2/g or less, more preferably 0.15 m.sup.2/g or more and
0.50 m.sup.2/g or less. According to such a precipitation hardening
stainless steel powder, a surface activity (surface energy) is
optimized so that moderate sinterability is obtained. Due to this,
a sufficient sintering rate can be obtained while preventing the
organic binder or a decomposition product thereof, a reaction
product of a carbon atom, or the like from remaining in the
sintered body. As a result, a dense sintered body can be obtained
while reducing the carbon atom concentration.
1.10 Analysis Method
[0066] The compositional ratio of the precipitation hardening
stainless steel powder according to the embodiment can be
determined by, for example, Iron and steel--Atomic absorption
spectrometric method specified in JIS G 1257:2000, Iron and
steel--ICP atomic emission spectrometric method specified in JIS G
1258:2007, Iron and steel--Method for spark discharge atomic
emission spectrometric analysis specified in JIS G 1253:2002, Iron
and steel--Method for X-ray fluorescence spectrometric analysis
specified in JIS G 1256:1997, gravimetric, titrimetric, and
absorption spectrometric methods specified in JIS G 1211 to G 1237,
or the like. Specifically, for example, an optical emission
spectrometer for solids, model: SPECTROLAB, type: LAVMB08A
manufactured by SPECTRO Analytical Instruments GmbH, which is a
spark optical emission spectrometer, or an ICP device, model:
CIROS-120 manufactured by Rigaku Corporation is exemplified.
[0067] Note that JIS G 1211 to G 1237 are as follows.
[0068] JIS G 1211:2011: Iron and steel--Methods for determination
of carbon content
[0069] JIS G 1212:1997: Iron and steel--Methods for determination
of silicon content
[0070] JIS G 1213:2001: Iron and steel--Methods for determination
of manganese content
[0071] JIS G 1214:1998: Iron and steel--Methods for determination
of phosphorus content
[0072] JIS G 1215:2010: Iron and steel--Methods for determination
of sulfur content
[0073] JIS G 1216:1997: Iron and steel--Methods for determination
of nickel content
[0074] JIS G 1217:2005: Iron and steel--Methods for determination
of chromium content
[0075] JIS G 1218:1999: Iron and steel--Methods for determination
of molybdenum content
[0076] JIS G 1219:1997: Iron and steel--Methods for determination
of copper content
[0077] JIS G 1220:1994: Iron and steel--Methods for determination
of tungsten content
[0078] JIS G 1221:1998: Iron and steel--Methods for determination
of vanadium content
[0079] JIS G 1222:1999: Iron and steel--Methods for determination
of cobalt content
[0080] JIS G 1223:1997: Iron and steel--Methods for determination
of titanium content
[0081] JIS G 1224:2001: Iron and steel--Methods for determination
of aluminum content
[0082] JIS G 1225:2006: Iron and steel--Methods for determination
of arsenic content
[0083] JIS G 1226:1994: Iron and steel--Methods for determination
of tin content
[0084] JIS G 1227:1999: Iron and steel--Methods for determination
of boron content
[0085] JIS G 1228:2006: Iron and steel--Methods for determination
of nitrogen content
[0086] JIS G 1229:1994: Steel--Methods for determination of lead
content
[0087] JIS G 1232:1980: Methods for determination of zirconium in
steel
[0088] JIS G 1233:1994: Steel--Method for determination of selenium
content
[0089] JIS G 1234:1981: Methods for determination of tellurium in
steel
[0090] JIS G 1235:1981: Methods for determination of antimony in
iron and steel
[0091] JIS G 1236:1992: Method for determination of tantalum in
steel
[0092] JIS G 1237:1997: Iron and steel--Methods for determination
of niobium content
[0093] Further, when C (carbon) and S (sulfur) are determined,
particularly, an infrared absorption method after combustion in a
current of oxygen or after combustion in a high-frequency induction
heating furnace specified in JIS G 1211 (2011) is also used. As a
specific analyzer, a carbon-sulfur analyzer, CS-200 manufactured by
LECO Corporation is exemplified.
[0094] Further, when N (nitrogen) and O (oxygen) are determined,
particularly, a method for determination of nitrogen content in
iron and steel specified in JIS G 1228:2006 and a method for
determination of oxygen content in metallic materials specified in
JIS Z 2613:2006 are also used. As a specific analyzer, an
oxygen-nitrogen analyzer, TC-300/EF-300 manufactured by LECO
Corporation is exemplified.
[0095] In addition, in the sintered body produced using the
precipitation hardening stainless steel powder according to the
embodiment, a martensite crystal structure can be precipitated by
performing any of various heating treatments. The martensite
crystal structure imparts high hardness to the sintered body. It
can be determined whether or not the sintered body has a martensite
crystal structure by, for example, X-ray diffractometry.
[0096] The average particle diameter of the precipitation hardening
stainless steel powder is preferably 0.50 .mu.m or more and 50.0
.mu.m or less, more preferably 1.00 .mu.m or more and 30.00 .mu.m
or less, further more preferably 2.00 .mu.m or more and 10.00 .mu.m
or less. By using the precipitation hardening stainless steel
powder having such a particle diameter, pores remaining in the
sintered body are extremely reduced, and therefore, a sintered body
having a high density and excellent mechanical properties can be
produced.
[0097] When the average particle diameter of the precipitation
hardening stainless steel powder is less than the above lower
limit, the moldability is deteriorated when molding the shape which
is difficult to mold, and therefore, the sintered density may be
decreased. On the other hand, when the average particle diameter of
the precipitation hardening stainless steel powder exceeds the
above upper limit, a gap between particles become larger during
molding, and therefore, the sintered density may be decreased.
[0098] The average particle diameter of the precipitation hardening
stainless steel powder can be determined as a particle diameter
when the cumulative amount from the small diameter side reaches 50%
in a cumulative particle size distribution on a mass basis obtained
by laser diffractometry.
[0099] The maximum particle diameter of the precipitation hardening
stainless steel powder is not particularly limited as long as the
average particle diameter is within the above range, but is
preferably 200 .mu.m or less, more preferably 150 .mu.m or less. By
making the maximum particle diameter of the precipitation hardening
stainless steel powder fall within the above range, the particle
size distribution of the precipitation hardening stainless steel
powder can be made narrower, so that the density of the sintered
body can be further increased.
[0100] The maximum particle diameter refers to a particle diameter
when the cumulative amount from the small diameter side reaches
99.9% in a cumulative particle size distribution on a mass basis
obtained by laser diffractometry.
[0101] When the minor axis of each particle of the precipitation
hardening stainless steel powder is represented by S [.mu.m] and
the major axis thereof is represented by L [.mu.m], the average of
the aspect ratio defined by S/L is preferably about 0.4 or more and
1 or less, more preferably about 0.7 or more and 1 or less. The
precipitation hardening stainless steel powder having such an
aspect ratio has a shape relatively close to a spherical shape, and
therefore, the filling factor when the powder is molded is
increased. As a result, the density of the sintered body can be
further increased.
[0102] The major axis is the maximum possible length of the
particle in a projected image, and the minor axis is the maximum
possible length thereof in the direction perpendicular to the major
axis. Further, the average of the aspect ratio is an average of the
aspect ratio measured for 100 or more particles.
2. Method for Producing Precipitation Hardening Stainless Steel
Sintered Body
[0103] Next, a method for producing a precipitation hardening
stainless steel sintered body according to an embodiment will be
described.
[0104] The FIGURE illustrates a process chart showing the method
for producing a precipitation hardening stainless steel sintered
body according to the embodiment.
[0105] The method for producing a precipitation hardening stainless
steel sintered body shown in the FIGURE includes a composition
preparation step S1 of preparing a composition for producing a
sintered body, a molding step S2 of molding the composition, a
degreasing step S3 of subjecting the molded body to a degreasing
treatment, and a firing step S4 of subjecting the degreased body to
a firing treatment. Hereinafter, the respective steps will be
sequentially described.
2.1 Composition Preparation Step S1
[0106] First, the precipitation hardening stainless steel powder
and an organic binder are kneaded using a kneader, whereby a
kneaded material, that is, a compound according to an embodiment is
obtained. The kneaded material is a composition containing the
precipitation hardening stainless steel powder described above and
the organic binder. By using such a kneaded material, although the
organic binder is used, a sintered body having high mechanical
strength can be produced.
[0107] The precipitation hardening stainless steel powder is
produced by, for example, any of a variety of powdering methods
such as an atomization method such as a water atomization method, a
gas atomization method, or a spinning water atomization method, a
reducing method, a carbonyl method, and a pulverization method.
[0108] Among these, the precipitation hardening stainless steel
powder is preferably a powder produced by an atomization method,
more preferably a powder produced by a water atomization method or
a spinning water atomization method. The atomization method is a
method in which a metal melt is caused to collide with a liquid or
a gas sprayed at a high speed to atomize the metal melt into a fine
powder and also to cool the fine powder, whereby a metal powder is
produced. By producing the precipitation hardening stainless steel
powder through such an atomization method, an extremely fine powder
can be efficiently produced. Further, the shape of the particle of
the obtained powder is closer to a spherical shape by the action of
surface tension. Due to this, a powder having a high filling factor
when it is molded is obtained. That is, a powder capable of
producing a sintered body having a high density can be
obtained.
[0109] When a water atomization method is used as the atomization
method, the pressure of water to be sprayed onto the metal melt is
not particularly limited, but is set to preferably about 75 MPa or
more and 120 MPa or less, more preferably about 90 MPa or more and
120 MPa or less.
[0110] The water temperature of the atomization water is also not
particularly limited, but is preferably set to about 1.degree. C.
or higher and 20.degree. C. or lower.
[0111] The atomization water is often sprayed in a cone shape such
that it has a vertex on the falling path of the metal melt and the
outer diameter gradually decreases downward. In that case, the
vertex angle .theta. of the cone formed by the atomization water is
preferably about 10.degree. or more and 40.degree. or less, more
preferably about 15.degree. or more and 35.degree. or less.
According to this, a precipitation hardening stainless steel powder
having a composition as described above can be reliably
produced.
[0112] Further, by using a water atomization method, particularly,
a spinning water atomization method, the metal melt can be
particularly quickly cooled. Due to this, a powder having high
quality can be obtained in a wide alloy composition.
[0113] Further, the cooling rate when cooling the metal melt in the
atomization method is preferably 1.times.10.sup.4.degree. C./s or
more, more preferably 1.times.10.sup.5.degree. C./s or more. By the
quick cooling in this manner, a homogeneous precipitation hardening
stainless steel powder is obtained. As a result, a sintered body
having high quality can be obtained.
[0114] The thus obtained precipitation hardening stainless steel
powder may be classified as needed. Examples of the classification
method include dry classification such as sieving classification,
inertial classification, and centrifugal classification, and wet
classification such as sedimentation classification.
[0115] As the organic binder, a resin that can be decomposed in a
short time in a degreasing treatment or a firing treatment is used.
Examples of such a resin include polyolefins such as polyethylene,
polypropylene, and ethylene-vinyl acetate copolymers, acrylic
resins such as polymethyl methacrylate and polybutyl methacrylate,
styrenic resins such as polystyrene, polyesters such as polyvinyl
chloride, polyvinylidene chloride, polyamide, polyethylene
terephthalate, and polybutylene terephthalate, polyether, polyvinyl
alcohol, polyvinylpyrrolidone, and copolymers thereof, and various
types of waxes, paraffins, higher fatty acids, higher alcohols,
higher fatty acid esters, and higher fatty acid amides. Among
these, one type can be used or two or more types can be used by
mixing.
[0116] The mixing ratio of the organic binder is preferably about 2
mass % or more and 20 mass % or less, more preferably about 5 mass
% or more and 15 mass % or less with respect to the total amount of
the kneaded material. By setting the mixing ratio of the organic
binder within the above range, a molded body can be formed with
good moldability, and also the density is increased, whereby the
stability of the shape of the molded body and the like can be
particularly enhanced. Further, according to this, a difference in
size between the molded body and the degreased body, that is, a
so-called shrinkage ratio is optimized, whereby a decrease in the
dimensional accuracy of the sintered body to be finally obtained
can be prevented. That is, a sintered body having a high density
and high dimensional accuracy can be obtained.
[0117] In the kneaded material, a plasticizer may be added as
needed. Examples of the plasticizer include phthalate esters,
adipate esters, trimellitate esters, and sebacate esters, and among
these, one type can be used or two or more types can be used by
mixing.
[0118] Further, in the kneaded material, other than the
precipitation hardening stainless steel powder, the organic binder,
and the plasticizer, for example, any of a variety of additives
such as a lubricant, an antioxidant, a degreasing accelerator, and
a surfactant, or another metal powder, a ceramic powder, or the
like can be added as needed.
[0119] The kneading conditions vary depending on the respective
conditions such as the alloy composition and the particle diameter
of the precipitation hardening stainless steel powder to be used,
the composition of the organic binder, and the blending amount
thereof. However, in one example, the kneading temperature can be
set to about 50.degree. C. or higher and 200.degree. C. or lower,
and the kneading time can be set to about 15 minutes or more and
210 minutes or less.
[0120] Further, the kneaded material is formed into a pellet as
needed. The particle diameter of the pellet is set to, for example,
about 1 mm or more and 15 mm or less.
[0121] Note that depending on a molding method described below, in
place of the kneaded material, a granulated powder according to an
embodiment may be used. The kneaded material, the granulated
powder, and the like are examples of the composition to be
subjected to a molding step described below.
[0122] Such a granulated powder is obtained by binding a plurality
of metal particles to one another with an organic binder by
subjecting the precipitation hardening stainless steel powder to a
granulation treatment. That is, the granulated powder is a
composition containing the precipitation hardening stainless steel
powder and the organic binder described above. By using such a
granulated powder, although the organic binder is used, a sintered
body having high mechanical strength can be produced.
[0123] Examples of the organic binder to be used for producing the
granulated powder include the above-mentioned organic binders.
[0124] The mixing ratio of the organic binder is preferably about
0.2 mass % or more and 10 mass % or less, more preferably about 0.3
mass % or more and 5.0 mass % or less with respect to the total
amount of the granulated powder. By setting the mixing ratio of the
organic binder within the above range, a granulated powder can be
efficiently formed while preventing significantly large particles
from being granulated or a large amount of metal particles which
are not granulated from remaining. Further, since the moldability
is improved, the stability of the shape of the molded body and the
like can be particularly enhanced. Further, by setting the mixing
ratio of the organic binder within the above range, a difference in
size between the molded body and the degreased body, that is, a
so-called shrinkage ratio is optimized, whereby a decrease in the
dimensional accuracy of the sintered body to be finally obtained
can be prevented.
[0125] Further, in the granulated powder, other than the
precipitation hardening stainless steel powder, the organic binder,
and the plasticizer, for example, any of a variety of additives
such as a lubricant, an antioxidant, a degreasing accelerator, and
a surfactant, or another metal powder, a ceramic powder, or the
like may be added as needed.
[0126] Examples of the granulation treatment include a spray dry
method, a tumbling granulation method, a fluidized bed granulation
method, and a tumbling fluidized bed granulation method.
[0127] In the granulation treatment, a solvent which dissolves the
binder is used as needed. Examples of the solvent include inorganic
solvents such as water and carbon tetrachloride, and organic
solvents such as ketone-based solvents, alcohol-based solvents,
ether-based solvents, cellosolve-based solvents, aliphatic
hydrocarbon-based solvents, aromatic hydrocarbon-based solvents,
aromatic heterocyclic compound-based solvents, amide-based
solvents, halogen compound-based solvents, ester-based solvents,
amine-based solvents, nitrile-based solvents, nitro-based solvents,
and aldehyde-based solvents, and one type or a mixture of two or
more types selected from these solvents is used.
[0128] The average particle diameter of the granulated powder is
not particularly limited, but is preferably about 10 .mu.m or more
and 200 .mu.m or less, more preferably about 20 .mu.m or more and
100 .mu.m or less, further more preferably about 25 .mu.m or more
and 60 .mu.m or less. The granulated powder having such a particle
diameter has favorable flowability, and can more faithfully reflect
the shape of a molding die.
[0129] The average particle diameter is determined as a particle
diameter when the cumulative amount from the small diameter side
reaches 50% in a cumulative particle size distribution on a mass
basis obtained by laser diffractometry.
2.2 Molding Step S2
[0130] Subsequently, the kneaded material or the granulated powder
is molded, whereby a molded body having the same shape as that of a
target sintered body is produced.
[0131] Examples of the molding method include a powder compaction
molding method, a metal powder injection molding method, and an
extrusion molding method.
[0132] The molding conditions in the case of a powder compaction
molding method among these methods are preferably such that the
molding pressure is about 200 MPa or more and 1000 MPa or less
although varying depending on the respective conditions such as the
composition and the particle diameter of the precipitation
hardening stainless steel powder to be used, the composition of the
organic binder, and the blending amount thereof.
[0133] Further, the molding conditions in the case of a metal
powder injection molding method are preferably such that the
material temperature is about 80.degree. C. or higher and
210.degree. C. or lower, and the injection pressure is about 50 MPa
or more and 500 MPa or less although varying depending on the
respective conditions.
[0134] Further, the molding conditions in the case of an extrusion
molding method are preferably such that the material temperature is
about 80.degree. C. or higher and 210.degree. C. or lower, and the
extrusion pressure is about 50 MPa or more and 500 MPa or less
although varying depending on the respective conditions.
[0135] The shape and size of the molded body to be produced are
determined in anticipation of the shrinkage of the molded body in a
degreasing step and a firing step described below.
2.3 Degreasing Step S3
[0136] Subsequently, the thus obtained molded body is subjected to
a degreasing treatment, whereby a degreased body is obtained.
Specifically, the degreasing treatment is carried out by
decomposing and removing the organic binder.
[0137] Examples of the degreasing treatment include a method of
heating the molded body and a method of exposing the molded body to
a gas capable of decomposing the organic binder.
[0138] When the method of heating the molded body is used, the
heating conditions for the molded body are preferably such that the
temperature is about 100.degree. C. or higher and 750.degree. C. or
lower and the time is about 0.1 hours or more and 20 hours or less,
and more preferably such that the temperature is about 150.degree.
C. or higher and 600.degree. C. or lower and the time is about 0.5
hours or more and 15 hours or less although slightly varying
depending on the composition or the blending amount of the organic
binder. According to this, the degreasing of the molded body can be
necessarily and sufficiently performed without sintering the molded
body. As a result, it is possible to prevent a large amount of the
organic binder component from remaining inside the degreased
body.
[0139] The atmosphere when the molded body is heated is not
particularly limited, and examples thereof include an atmosphere of
a reducing gas such as hydrogen, an atmosphere of an inert gas such
as nitrogen or argon, an atmosphere of an oxidizing gas such as
air, and a reduced pressure atmosphere obtained by reducing the
pressure of such an atmosphere.
[0140] On the other hand, as the method of exposing the molded body
to a gas capable of decomposing the organic binder, for example, an
acid degreasing method is used. The acid degreasing method is a
degreasing method utilizing the catalytic action of an acid by
heating the molded body in an acid-containing atmosphere. By using
the acid degreasing method, the organic binder can be decomposed in
a short time even at a low temperature, and therefore, even the
molded body having a large volume can be efficiently subjected to
the degreasing treatment.
[0141] The acid-containing atmosphere refers to an atmosphere
containing an acid capable of decomposing the organic binder. As
the acid, for example, nitric acid, oxalic acid, ozone, and the
like are exemplified, and among these, one type or two or more
types in combination can be used. Further, a mixed gas obtained by
mixing such an acid with another gas may be used. As an example of
the mixed gas, fuming nitric acid is exemplified. The ambient
pressure may be an atmospheric pressure, a reduced pressure, or an
increased pressure.
[0142] The heating conditions for the molded body are preferably
such that the temperature is about 100.degree. C. or higher and
750.degree. C. or lower and the time is about 0.1 hours or more and
20 hours or less, and more preferably such that the temperature is
about 150.degree. C. or higher and 600.degree. C. or lower and the
time is about 0.5 hours or more and 15 hours or less although
slightly varying depending on the composition or the blending
amount of the organic binder or the type of the acid-containing
atmosphere. According to this, the degreasing of the molded body
can be performed in a short time even at a relatively low
temperature. In addition, the molded body can be prevented from
being sintered or oxidized.
[0143] Note that by dividing such a degreasing step into a
plurality of steps in which the degreasing conditions are
different, and performing the plurality of steps, the binder in the
molded body can be more rapidly decomposed and removed so that the
binder does not remain in the molded body.
[0144] Further, according to need, the degreased body may be
subjected to machining such as grinding, polishing, or cutting. The
degreased body has relatively low hardness and relatively high
plasticity, and therefore, machining can be easily performed while
preventing the degreased body from losing its shape. According to
such machining, a sintered body having high dimensional accuracy
can be finally easily obtained.
2.4 Firing Step S4
[0145] Subsequently, the obtained degreased body is subjected to a
firing treatment. By the firing treatment, surface diffusion occurs
at the boundary surface between the particles of the precipitation
hardening stainless steel powder, resulting in sintering. As a
result, a sintered body is obtained.
[0146] The firing temperature varies depending on the composition,
the particle diameter, or the like of the precipitation hardening
stainless steel powder used in the production of the molded body
and the degreased body, but is set to, for example, about
980.degree. C. or higher and 1330.degree. C. or lower, and is
preferably set to about 1050.degree. C. or higher and 1260.degree.
C. or lower.
[0147] Further, the firing time is set to 0.2 hours or more and 7
hours or less, and is preferably set to about 1 hour or more and 6
hours or less.
[0148] In the firing step, the firing temperature or the
below-mentioned firing atmosphere may be changed in the middle of
the step.
[0149] By setting the firing conditions within such a range, it is
possible to sufficiently sinter the entire degreased body while
preventing the sintering from excessively proceeding to cause
oversintering and increase the size of the crystal structure. As a
result, a sintered body having a high density and particularly
excellent mechanical properties can be obtained.
[0150] Further, the thus produced sintered body may be subjected to
an additional treatment as needed. Examples of the additional
treatment include a solid solution treatment, an age hardening
treatment, a double aging treatment, a sub-zero treatment, a
tempering treatment, a hot working treatment, and a cold working
treatment, and among these, one treatment or two or more treatments
in combination are used.
[0151] Specific examples of the additional treatment include a
treatment in which a solid solution treatment of cooling from a
temperature of 1000.degree. C. or higher and 1250.degree. C. or
lower over a time of 30 minutes or more and 120 minutes or less is
performed, and thereafter, an age hardening treatment of cooling
from a temperature of 600.degree. C. or higher and 800.degree. C.
or lower over a time of 6 hours or more and 48 hours or less is
performed.
3. Precipitation Hardening Stainless Steel Sintered Body
[0152] The precipitation hardening stainless steel sintered body
according to this embodiment is a sintered body constituted by a
precipitation hardening stainless steel containing Cr, Si, Nb, Ni,
Mn, and Cu as described above. In such a sintered body, Cr is
contained at a concentration A within a range of 15.00 mass % or
more and 17.50 mass % or less, Si is contained at a concentration B
within a range of 0.30 mass % or more and 1.00 mass % or less, Nb
is contained at a concentration C within a range of 0.15 mass % or
more and 0.45 mass % or less, Ni is contained at a concentration D
within a range of 3.00 mass % or more and 5.00 mass % or less, Mn
is contained at a concentration E within a range of 0.05 mass % or
more and 1.00 mass % or less, and Cu is contained at a
concentration F within a range of 3.00 mass % or more and 5.00 mass
% or less. Further, in such a sintered body, a value of .delta.
defined by the following formula (1) is 10.0 mass % or more and
14.0 mass % or less.
.delta.=3(A+1.5B+0.5C)-2.8(D+0.5E+0.5F)-19.8 (1)
[0153] According to such a precipitation hardening stainless steel
sintered body, an increase in the carbon atom concentration is
suppressed, and therefore, a sintered body having high mechanical
strength derived from the precipitation hardening stainless steel
is obtained. In particular, even when a sintered body is small or
has a complicated shape, or the like, a carbon atom derived from
the organic binder is prevented from remaining, so that a sintered
body having high quality is obtained.
[0154] The precipitation hardening stainless steel sintered body
can be used, for example, as a material constituting the whole or a
part of a component for transport devices such as a component for
automobiles, a component for bicycles, a component for railroad
cars, a component for ships, a component for airplanes, or a
component for space transport devices, a component for electronic
devices such as a component for personal computers, a component for
cellular phone terminals, a component for tablet terminals, or a
component for wearable terminals, a component for electrical
devices such as a refrigerator, a washing machine, and a cooling
and heating machine, a component for machines such as a machine
tool and a semiconductor production device, a component for plants
such as an atomic power plant, a thermal power plant, a
hydroelectric power plant, an oil refinery plant, and a chemical
complex, or an ornament such as a component for timepieces,
metallic tableware, jewels, and a frame for glasses.
[0155] As described above, the method for producing a precipitation
hardening stainless steel sintered body according to this
embodiment includes a molding step of molding the compound or the
granulated powder containing the precipitation hardening stainless
steel powder, thereby obtaining a molded body, and a firing step of
firing the molded body, thereby obtaining a sintered body. In such
a production method, the carbon atom concentration in the sintered
body is preferably smaller than the carbon atom concentration in
the precipitation hardening stainless steel powder. This is derived
from the fact that the carbon atom concentration in the sintered
body is decreased by the reaction of a carbon atom and an oxygen
atom described above. By decreasing the carbon atom concentration
in the sintered body in this manner, even when the precipitation
hardening stainless steel powder having a high carbon atom
concentration is used, the carbon atom concentration in the
sintered body can be made to fall within the above range. According
to this, a sintered body having high mechanical strength can be
efficiently produced.
[0156] When the carbon atom concentration in the precipitation
hardening stainless steel powder is represented by a first
concentration c1 and the carbon atom concentration in the sintered
body is represented by a second concentration c2, (c1-c2)/c1 is
preferably 70 mass % or less, more preferably 50 mass % or less.
According to this, the first concentration c1 can be reliably
decreased, and therefore, the probability that the second
concentration c2 falls within the above range becomes high. As a
result, a sintered body having high mechanical strength, hardness,
and corrosion resistance derived from the precipitation hardening
stainless steel can be more reliably produced.
[0157] Hereinabove, the precipitation hardening stainless steel
powder, the compound, the granulated powder, the precipitation
hardening stainless steel sintered body, and the method for
producing the same according to the present disclosure have been
described with reference to preferred embodiments, however, the
present disclosure is not limited thereto. For example, to the
compound and the granulated powder, an arbitrary additive may be
added.
[0158] The method for producing a precipitation hardening stainless
steel sintered body according to the present disclosure may be a
method to which a step for an arbitrary purpose is added to the
above embodiment.
EXAMPLES
[0159] Next, Examples of the present disclosure will be
described.
4. Production of Sintered Body
Sample No. 1
[0160] [1] First, a precipitation hardening stainless steel powder
having a composition shown in Table 1 produced by a water
atomization method was prepared.
[0161] In the identification and quantitative determination of the
composition of the metal powder shown in Table 1, inductively
coupled high-frequency plasma optical emission spectrometry and an
ICP device, model: CIROS-120 manufactured by Rigaku Corporation
were used. Further, in the identification and quantitative
determination of C, a carbon-sulfur analyzer CS-200 manufactured by
LECO Corporation was used. Further, in the identification and
quantitative determination of 0, an oxygen-nitrogen analyzer
TC-300/EF-300 manufactured by LECO Corporation was used.
[0162] [2] Subsequently, the metal powder and an organic binder
were weighed at a mass ratio of 89:11 and mixed with each other,
whereby a mixed raw material was obtained. As the organic binder, a
resin obtained by mixing a polyacetal resin containing butanediol
at 2.5 mass % with polyethylene at a mass ratio of 50:6 was
used.
[0163] [3] Subsequently, the mixed raw material was kneaded using a
kneader, whereby a compound was obtained.
[0164] [4] Subsequently, the compound was molded using an injection
molding machine under the following molding conditions, whereby a
molded body was produced.
[0165] Molding Conditions [0166] Material temperature: 180.degree.
C. [0167] Injection pressure: 11 MPa (110 kgf/cm.sup.2)
[0168] [5] Subsequently, the obtained molded body was subjected to
a degreasing treatment under the following degreasing conditions,
whereby a degreased body was obtained.
[0169] Degreasing Conditions [0170] Degreasing temperature:
400.degree. C. [0171] Degreasing time: 1 hour (retention time at
the degreasing temperature) [0172] Degreasing atmosphere: a mixed
gas atmosphere of nitrogen and nitric acid, in which the
concentration of nitric acid was 2 vol %
[0173] [6] Subsequently, the obtained degreased body was subjected
to a firing treatment under the following firing conditions,
whereby a sintered body was obtained. The shape of the sintered
body was determined to be a circular cylindrical shape with a
diameter of 10 mm and a thickness of 5 mm.
[0174] Firing Conditions [0175] Firing temperature: 1300.degree. C.
[0176] Firing time: 3 hours (retention time at the firing
temperature) [0177] Firing atmosphere: argon atmosphere
[0178] [7] Subsequently, the obtained sintered body was
sequentially subjected to a solid solution treatment and an age
hardening treatment under the following conditions.
[0179] Conditions for Solid Solution Treatment [0180] Heating
temperature: 1120.degree. C. [0181] Heating time: 30 minutes [0182]
Cooling method: water cooling
[0183] Conditions for Age Hardening Treatment [0184] Heating
temperature: 700.degree. C. [0185] Heating time: 24 hours [0186]
Cooling method: water cooling
Sample Nos. 2 to 13
[0187] Sintered bodies were obtained in the same manner as in the
case of Sample No. 1 except that the composition and the like of
the precipitation hardening stainless steel powder were changed as
shown in Table 1, respectively. Note that for the production of the
powder of Sample No. 5, a gas atomization method was used.
[0188] In Table 1, among the precipitation hardening stainless
steel powders and the sintered bodies of the respective Sample
Nos., those corresponding to the present disclosure are denoted by
"Ex." (Example), and those not corresponding to the present
disclosure are denoted by "Comp. Ex." (Comparative Example).
[0189] Note that each sintered body contained very small amounts of
impurities, but the description thereof in Table 1 is omitted.
5. Evaluation of Precipitation Hardening Stainless Steel Powder and
Precipitation Hardening Stainless Steel Sintered Body
5.1 Measurement of Average Particle Diameter of Powder
[0190] With respect to the powders of the respective Sample Nos.
shown in Table 1, the average particle diameter was measured. The
measurement results are shown in Table 1.
5.2 Measurement of Tap Density of Powder
[0191] With respect to the powders of the respective Sample Nos.
shown in Table 1, the tap density was measured. In the measurement
of the tap density, a powder property evaluation device, Powder
Tester (registered trademark) PT-X manufactured by Hosokawa Micron
Corporation was used. The number of times of tapping was set to
125. The measurement results are shown in Table 1. Further, the
powder of Sample No. 5 has a large particle diameter, and
therefore, the measurement of the tap density was omitted.
5.3 Measurement of Specific Surface Area of Powder
[0192] With respect to the powders of the respective Sample Nos.
shown in Table 1, the specific surface area was measured. In the
measurement of the specific surface area, the BET method was used,
and a BET specific surface area measuring device HM-1201-010
manufactured by Mountech Co., Ltd. was used. The amount of a sample
was set to 5 g. The measurement results are shown in Table 1.
Further, the powder of Sample No. 5 has a large particle diameter,
and therefore, the measurement of the specific surface area was
omitted.
5.4 Measurement of Carbon Atom Concentration in Sintered Body
[0193] With respect to the sintered bodies of the respective Sample
Nos. shown in Table 1, the carbon atom concentration was measured.
The measurement results are shown in Table 1.
5.5 Evaluation of Mechanical Strength of Sintered Body
[0194] A test piece specified in ISO 2740:2009 was cut out from
each of the sintered bodies of the respective Sample Nos. shown in
Table 1. Then, the tensile strength of the test piece was measured
by the test method specified in JIS Z 2241:2011.
[0195] Subsequently, the tensile strength measured for the sintered
body of Sample No. 10 was assumed to be 1, and the relative value
of the tensile strength measured for each of the sintered bodies of
the respective Examples and the respective Comparative Examples was
calculated.
[0196] Then, the calculated relative value was evaluated according
to the following evaluation criteria.
Evaluation Criteria for Tensile Strength
[0197] A: The tensile strength is very high (the relative value is
more than 1.1).
[0198] B: The tensile strength is high (the relative value is more
than 1 and 1.1 or less).
[0199] C: The tensile strength is low (the relative value is more
than 0.9 and 1 or less).
[0200] D: The tensile strength is very low (the relative value is
0.9 or less).
[0201] The evaluation results are shown in Table 1.
5.6 Evaluation of Hardness of Sintered Body
[0202] With respect to the sintered bodies of the respective Sample
Nos. shown in Table 1, the Vickers hardness was measured.
[0203] Subsequently, the Vickers hardness measured for the sintered
body of Sample No. 10 was assumed to be 1, and the relative value
of the Vickers hardness measured for each of the sintered bodies of
the respective Examples and the respective Comparative Examples was
calculated.
[0204] Then, the calculated relative value was evaluated according
to the following evaluation criteria.
Evaluation Criteria for Hardness
[0205] A: The hardness is very high (the relative value is more
than
[0206] B: The hardness is high (the relative value is more than 1
and 1.1 or less).
[0207] C: The hardness is low (the relative value is more than 0.9
and 1 or less).
[0208] D: The hardness is very low (the relative value is 0.9 or
less).
[0209] The evaluation results are shown in Table 1.
5.7 Evaluation of Relative Density of Sintered Body
[0210] With respect to the sintered bodies of the respective Sample
Nos. shown in Table 1, the density was measured by a method
according to the Archimedes method. Then, the relative density of
each sintered body was calculated based on the measured density and
the true density of the precipitation hardening stainless steel
powder.
[0211] Then, the calculated relative density was evaluated
according to the following evaluation criteria.
Evaluation Criteria for Relative Density
[0212] A: The relative density is 98.0% or more.
[0213] B: The relative density is less than 98.0%.
[0214] The evaluation results are shown in Table 1.
5.8 Evaluation of Corrosion Resistance of Sintered Body
[0215] With respect to the sintered bodies of the respective Sample
Nos. shown in Table 1, the corrosion rate was measured according to
the method of sulfuric acid corrosion test for stainless steels
specified in JIS G 0591:2012. As the sulfuric acid, boiled 5 mass %
sulfuric acid was used.
[0216] Then, with respect to the corrosion rate measured for each
of the sintered bodies of the respective Sample Nos., the relative
value was calculated when the corrosion rate (unit: g/m.sup.2/h)
measured for the sintered body of Sample No. 10 was assumed to be
1. Then, the calculated relative value was evaluated according to
the following evaluation criteria.
Evaluation Criteria for Corrosion Resistance
[0217] A: The relative value of the corrosion rate of the sintered
body is less than 0.75.
[0218] B: The relative value of the corrosion rate of the sintered
body is 0.75 or more and less than 1.00.
[0219] C: The relative value of the corrosion rate of the sintered
body is 1.00 or more and less than 1.25.
[0220] D: The relative value of the corrosion rate of the sintered
body is 1.25 or more.
[0221] The evaluation results are shown in Table 1.
TABLE-US-00001 TABLE 1 Evaluation results of powder Average Alloy
composition of precipitation hardening stainless steel powder
particle Cr Si Nb Ni Mn Cu C O Fe .delta. diameter No. 1 Ex. 16.20
0.40 0.27 4.62 0.10 4.01 0.05 0.29 balance 12.32 7.11 No. 2 Ex.
16.53 0.36 0.31 4.54 0.16 4.06 0.05 0.33 balance 13.26 7.15 No. 3
Ex. 15.58 0.38 0.34 4.45 0.09 3.95 0.05 0.32 balance 11.04 6.89 No.
4 Ex. 15.25 0.40 0.25 4.38 0.11 3.87 0.05 0.32 balance 10.29 6.55
No. 5 Ex. 15.71 0.72 0.31 4.29 0.28 3.34 0.05 0.08 balance 13.96
15.31 No. 6 Ex. 15.10 0.78 0.39 4.56 0.35 3.85 0.05 0.66 balance
10.95 4.73 No. 7 Ex. 15.26 0.77 0.31 4.50 0.28 3.43 0.03 0.55
balance 12.12 4.78 No. 8 Comp. Ex. 15.54 0.37 0.28 4.75 0.22 4.15
0.05 0.25 balance 9.49 6.54 No. 9 Comp. Ex. 15.75 0.40 0.33 4.91
0.19 4.25 0.05 0.26 balance 9.78 7.52 No. 10 Comp. Ex. 16.91 0.55
0.25 3.46 0.15 3.98 0.05 0.29 balance 18.31 7.85 No. 11 Comp. Ex.
16.95 0.85 0.21 3.33 0.13 4.11 0.05 0.25 balance 19.93 6.78 No. 12
Comp. Ex. 17.10 0.83 0.35 3.43 0.12 3.43 0.05 0.28 balance 21.19
8.43 No. 13 Comp. Ex. 17.03 0.78 0.41 3.28 0.07 3.35 0.05 0.27
balance 21.44 6.91 Evaluation results of powder Specific Evaluation
results of sintered body Tap surface Carbon atom Mechanical
Relative Corrosion density area concentration strength Hardness
density resistance No. 1 4.57 0.21 0.03 A A A A No. 2 4.38 0.19
0.04 A A A A No. 3 4.61 0.22 0.02 A A A A No. 4 4.73 0.24 0.05 B B
A B No. 5 -- -- 0.07 B B B B No. 6 4.85 0.27 0.04 B B A B No. 7
4.80 0.26 0.01 A A A A No. 8 4.72 0.24 0.07 C C A C No. 9 4.48 0.21
0.07 C B A C No. 10 4.35 0.18 0.08 C C A C No. 11 4.44 0.19 0.11 C
C A C No. 12 4.25 0.23 0.15 D D A D No. 13 4.59 0.18 0.17 D D A
D
[0222] As apparent from Table 1, the sintered bodies of Examples
had favorable mechanical strength, hardness, and corrosion
resistance.
[0223] In addition, in the respective Examples, the carbon atom
concentration in the sintered body was lowered as compared with the
carbon atom concentration in the powder. Based on this, it is
considered that in the respective Examples, the reaction product of
a carbon atom is efficiently removed during the sintering
treatment, and as a result, the mechanical properties and the
corrosion resistance are improved.
[0224] Note that in the above description, the sintered body is
obtained using a molded body produced by an injection molding
method using a compound containing a precipitation hardening
stainless steel powder. On the other hand, also with respect to a
sintered body using a molded body produced by a compression molding
method using a granulated powder containing a precipitation
hardening stainless steel powder, the same evaluation as described
above was performed. As a result, the same tendency as in the case
of using the compound was observed.
* * * * *