U.S. patent application number 10/946119 was filed with the patent office on 2005-05-05 for production method for sintered component made of stainless steel with high corrosion resistance.
This patent application is currently assigned to HITACHI POWDERED METALS CO., LTD.. Invention is credited to Chikahata, Katsunao, Yoshihiro, Tatsuaki.
Application Number | 20050095163 10/946119 |
Document ID | / |
Family ID | 34309069 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050095163 |
Kind Code |
A1 |
Yoshihiro, Tatsuaki ; et
al. |
May 5, 2005 |
Production method for sintered component made of stainless steel
with high corrosion resistance
Abstract
A production method for a sintered component made of stainless
steel with high corrosion resistance has steps of preparing a
perovskite composite oxide powder made of rare earth element,
transition metal element and oxygen, and a stainless steel powder
or a mixed powder having a stainless steel composition, mixing the
perovskite composite oxide powder and the stainless steel powder or
the mixed powder, whereby a raw powder in which the rare earth
element is 0.1 to 12 mass % is prepared, compacting the raw powder
in a predetermined shape, whereby a green compact is obtained, and
sintering the green compact. The sintered component obtained by the
production method is a component in which corrosion resistance can
be increased without parts of decreasing Cr concentration and
precise production processes and process control are not
necessary.
Inventors: |
Yoshihiro, Tatsuaki;
(Matsudo-shi, JP) ; Chikahata, Katsunao;
(Matsudo-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
HITACHI POWDERED METALS CO.,
LTD.
Matsudo-shi
JP
|
Family ID: |
34309069 |
Appl. No.: |
10/946119 |
Filed: |
September 22, 2004 |
Current U.S.
Class: |
419/20 |
Current CPC
Class: |
C22C 33/0228 20130101;
C22C 38/18 20130101; C22C 32/0089 20130101 |
Class at
Publication: |
419/020 |
International
Class: |
B22F 003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2003 |
JP |
2003-341527 |
Claims
What is claimed is:
1. A production method for a sintered component made of a stainless
steel with high corrosion resistance, comprising the following
steps of preparing a perovskite composite oxide powder made of rare
earth element, transition metal element and oxygen, and a stainless
steel powder or a mixed powder having a stainless steel
composition, mixing the perovskite composite oxide powder and the
stainless steel powder or the powder having a stainless steel
composition, thereby preparing a raw powder in which the rare earth
element is 0.1 to 12 mass %, compacting the raw powder in a
predetermined shape, thereby obtaining a green compact, and
sintering the green compact.
2. The production method for a sintered component made of a
stainless steel with high corrosion resistance according to claim
1, wherein the stainless steel powder or the mixed powder having a
stainless steel composition contains 11 to 32 mass % of Cr.
3. The production method for a sintered component made of a
stainless steel with high corrosion resistance according to claim
1, wherein the stainless steel powder or the mixed powder having a
stainless steel composition contains 11 to 32 mass % of Cr and 3.5
to 22 mass % of Ni.
4. The production method for a sintered component made of a
stainless steel with high corrosion resistance according to claim
1, wherein the stainless steel powder or the mixed powder having a
stainless steel composition contains 11.5 to 18 mass % of Cr and
0.15 to 1.2 mass % of C.
5. The production method for a sintered component made of a
stainless steel with high corrosion resistance according to claim
2, wherein the stainless steel powder or the mixed powder having a
stainless steel composition contains at least one of 0.3 to 7 mass
% of Mo, 1 to 4 mass % of Cu, 0.1 to 5 mass % of Al, 0.3 mass % or
less of N, 5.5 to 10 mass % of Mn, 0.15 to 5 mass % of Si, 0.45
mass % or less of Nb, 0.2 mass % or less of P, 0.15 mass % or less
of S, and 0.15 mass % or less of Se.
6. The production method for a sintered component made of a
stainless steel with high corrosion resistance according to claim
3, wherein the stainless steel powder or the mixed powder having a
stainless steel composition contains at least one of 0.3 to 7 mass
% of Mo, 1 to 4 mass % of Cu, 0.1 to 5 mass % of Al, 0.3 mass % or
less of N, 5.5 to 10 mass % of Mn, 0.15 to 5 mass % of Si, 0.45
mass % or less of Nb, 0.2 mass % or less of P, 0.15 mass % or less
of S, and 0.15 mass % or less of Se.
7. The production method for a sintered component made of a
stainless steel with high corrosion resistance according to claim
4, wherein the stainless steel powder or the mixed powder having a
stainless steel composition contains at least one of 0.3 to 7 mass
% of Mo, 1 to 4 mass % of Cu, 0.1 to 5 mass % of Al, 0.3 mass % or
less of N, 5.5 to 10 mass % of Mn, 0.15 to 5 mass % of Si, 0.45
mass % or less of Nb, 0.2 mass % or less of P, 0.15 mass % or less
of S, and 0.15 mass % or less of Se.
8. The production method for a sintered component made of a
stainless steel with high corrosion resistance according to claim
1, wherein the rare earth element is selected from at least one of
Sc, Y, La, Ce and Gd.
9. The production method for a sintered component made of a
stainless steel with high corrosion resistance according to claim
1, wherein the transition metal element is selected from at least
one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo and W.
10. The production method for a sintered component made of a
stainless steel with high corrosion resistance according to claim
1, wherein an average grain diameter of the perovskite composite
oxide powder is 30 .mu.m or less.
11. The production method for a sintered component made of a
stainless steel with high corrosion resistance according to claim
1, wherein the sintering is performed at a sintering at
1000.degree. C. or more.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to an improvement in a sintered
component made of stainless steel with high corrosion resistance,
and specifically relates to a production method for a sintered
component made of stainless steel with high corrosion resistance
having the following property; oxidation and corrosion do not
easily occur even when the sintered component is exposed to
corrosive atmospheres in a high temperature.
[0003] 2. Related Art
[0004] As a sintered component made of stainless steel with high
corrosion resistance mentioned above, for example, a sintered
component disclosed in Patent Document No. 1 (Japanese Published
Unexamined Application No. 10-183315: sections [0014] and [0015])
is known. In the Patent Document No. 1, a Fe--Cr based sintered
alloy, in which Cr is 14 to 35 mass %, compound of at least La and
Y including O is a predetermined mass % of multiplying the Cr mass
% by a coefficient "a" (range of the "a" is 0.11 to 0.16.), and the
balance is Fe and inevitable impurities, and the sintered alloy has
a structure in which particles of compound of at least La and Y
including O are dispersed in a matrix, is disclosed.
[0005] In the above-mentioned sintered component made of stainless
steel with high corrosion resistance, chrome oxide
(Cr.sub.2O.sub.3) in the alloy surface and at least lanthanum oxide
and yttrium oxide added thereto are reacted in an oxidizing
atmosphere according to the reaction formula mentioned below,
whereby a stable perovskite composite oxide is formed. The
perovskite composite oxide acts as a protective coating, thereby
suppressing the advancing of the oxidation.
Cr.sub.2O.sub.3+La.sub.2O.sub.3=2LaCrO.sub.3
[0006] According to research by the present inventors, it is
apparent that although LaCrO.sub.3 is evidently formed in the
above-mentioned reaction described in the Patent Document No. 1, a
certain portion of the Cr used in the above-mentioned reaction is
supplied from the Cr solved in a matrix. Therefore, the Cr
concentration is decreased in the vicinity of an area where the
LaCrO.sub.3 is formed, whereby corrosion resistance in the vicinity
is decreased.
[0007] Moreover, it is apparent that although lanthanum oxide
powder is added in the case of producing the sintered component
made of stainless steel with high corrosion resistance, this
production method has a problem mentioned below. The lanthanum
oxide powder is easily agglomerated, whereby uniform mixing is
difficult. Therefore, in order to uniformly disperse the lanthanum
oxide powder, cumbersome treatments, in which stainless steel
powder is immersed in alcohol etc. dissolved lanthanum oxide, and
is dried, whereby lanthanum oxide coating is coated stainless steel
powder, are necessary. When a green compact is formed by raw
powder, lanthanum oxide inside of the green compact is hydrated
with moisture in the air. Then the hydroxide is formed to generate
expansion, and cracks are formed in the green compact. In order to
prevent the phenomenon, it is necessary to perform sintering
immediately after the forming, and to carefully control the
processes.
SUMMARY OF THE INVENTION
[0008] The invention aims to provide a production method for a
sintered component made of stainless steel with high corrosion
resistance in which corrosion resistance is increased without parts
of decreasing Cr concentration and precise production processes and
process control are not necessary.
[0009] A production method of a sintered component made of
stainless steel with high corrosion resistance of the present
invention is characterized in that a powder of perovskite composite
oxide containing a rare earth element, transition metal element and
oxygen is prepared, a stainless steel powder or a mixed powder
having a stainless steel composition is prepared, and these powders
are mixed, whereby a raw powder in which the rare earth element is
0.1 to 12 mass % is prepared, the raw powder is compacted in a
predetermined shape, and is sintered.
[0010] In the production method of a sintered component made of
stainless steel with high corrosion resistance of the present
invention, the perovskite composite oxide containing a rare earth
element, transition metal element and oxygen is added as a powder.
Therefore, the reaction formula is not generated. Accordingly, the
transition metal element, for example Cr, is not absorbed from the
matrix to the oxide coating, whereby the concentration of the
transition metal element in every part of the matrix is uniform,
resulting in increasing the corrosion resistance. Moreover, the
powder of the perovskite composite oxide is not easily
agglomerated, and the powder is stable, whereby the above-mentioned
hydration reaction is not generated.
[0011] A sintered component made of stainless steel with high
corrosion resistance obtained by the above-mentioned method is
characterized in that a rare earth element is contained at 0.1 to
12 mass %, and the rare earth element is dispersed with a
transition metal element and oxygen as a perovskite composite oxide
in a matrix of the stainless steel.
[0012] In the sintered component made of stainless steel with high
corrosion resistance mentioned above, the rare earth element is
dispersed with a transition metal element and oxygen as a
perovskite composite oxide in a matrix of the stainless steel.
Therefore, corrosion resistance is increased without parts of
decreasing Cr concentration. That is, the Cr amount in the matrix
of the sintered stainless steel with high corrosion resistance
obtained by using the production method of the present invention is
substantially uniform.
[0013] When a content of the rare earth element in the overall
composition is less than 0.1 mass %, oxide coating in the matrix is
not effectively strengthened. On the other hand, when the content
is more than 12 mass %, perovskite composite oxide in the matrix is
excessive, whereby the amount of the matrix is low, resulting in
decreasing strength and wear resistance of the component.
[0014] According to the present invention, corrosion resistance can
be increased by no part of decreasing the concentration of the
transition metal element in the matrix. Moreover, in the present
invention, cumbersome processes to uniformly disperse the rare
earth element are not necessary, and the problem in which cracks
are formed in the green compact does not occur even in the case of
having a pause between compacting and sintering.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a graph showing a relationship between increase in
weight by oxidation and La content in the overall composition in
the Practical Example 1 of the present invention.
[0016] FIG. 2 is a graph showing a relationship between tensile
strength and La content in the overall composition in the Practical
Example 1 of the present invention.
[0017] FIG. 3 is a graph showing increase in weight by oxidation in
the case of using various powders in the Practical Example 2 of the
present invention.
[0018] FIG. 4 is a graph showing increase in weight by oxidation in
the case of using various powders in the Practical Example 3 of the
present invention.
[0019] FIG. 5 is a graph showing a relationship between increase in
weight by oxidation and grain diameter of the LaCrO.sub.3 powder in
the Practical Example 4 of the present invention.
EMBODIMENTS OF THE INVENTION
[0020] Hereinafter, the preferable embodiments of the present
invention will be described.
[0021] Any stainless steel can be used to form the matrix. For
example, ferritic stainless steel in which 11 to 32 mass % of Cr is
contained and corrosion resistance to oxidizing acid is high can be
used. Moreover, martensitic stainless steel in which 0.15 to 1.2
mass % of C is additionally contained in the ferritic stainless
steel and strength and wear resistance are comparatively increased
is obtained, and this stainless steel can be used. Furthermore, an
austenitic stainless steel, in which 11 to 32 mass % of Cr and 3.5
to 22 mass % of Ni is contained and corrosion resistance to
nonoxidizing acid is increased, can be used.
[0022] Furthermore, 0.3 to 7 mass % of Mo can be contained in the
above-mentioned stainless steels in order to improve creep
resistance, acid resistance, corrosion resistance, pitting
corrosion resistance or machinability. Moreover, 1 to 4 mass % of
Cu can be contained in the above-mentioned stainless steels in
order to improve acid resistance, corrosion resistance or pitting
corrosion resistance, or to give precipitation hardening
performance. Furthermore, 0.1 to 5 mass % of Al can be contained in
the above-mentioned stainless steels in order to improve
weldability or heat resistance, or to give precipitation hardening
performance. Additionally, 0.3 mass % or less of N can be contained
in the above-mentioned stainless steels in order to arrange crystal
grains and to decrease Ni content, and 5.5 to 10 mass % of Mn can
be contained in the above-mentioned stainless steels in order to
decrease Ni content.
[0023] 0.15 to 5 mass % of Si can be contained in the
above-mentioned stainless steels in order to improve oxidation
resistance, heat resistance or sulfuric acid resistance, 0.45 mass
% or less of Nb can be contained in the above-mentioned stainless
steels in order to improve grain boundary corrosion resistance or
weldability, and 0.15 mass % or less of Se, 0.2 mass % or less of P
or 0.15 mass % or less of S can be contained in the above-mentioned
stainless steels in order to improve machinability.
[0024] The rare earth element can be selected from at least one of
Sc, Y, La, Ce and Gd, and representative elements mentioned above
are Y and La. The transition metal element can be selected from at
least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo and W. When
Cr is selected in the elements to form perovskite composite oxide,
stability of the oxide is specifically excellent, and handling
performance and corrosion resistance of the oxide are good.
Additionally, as the perovskite composite oxide, RMO.sub.3,
R.sub.2MO.sub.4, R.sub.3M.sub.2O.sub.7 and R.sub.4M.sub.3O.sub.10
(R: rare earth element, M: metal element) can be cited, at least
one of R and M are formed by multiple elements in some perovskite
composite oxides.
[0025] Average grain diameter in the perovskite composite oxide
powder is preferably 30 .mu.m or less, whereby dispersion
performance in mixing the powder and stainless steel powder can be
improved. That is, when the grain diameter is increased,
segregation in the matrix is increased, whereby some parts in which
corrosion resistance is improved and other parts in which corrosion
resistance is not improved are generated. Moreover, the sintering
after compacting the raw powder into predetermined shape is
preferably performed at a sintering at 1000.degree. C. or more.
[0026] Next, the overall composition of the sintered component made
of stainless steel with high corrosion resistance of the present
invention is, basically, Cr: 7.51 to 31.96 mass %, rare earth
element: 0.1 to 12 mass %, 0: 0.02 to 6.48 mass %, and balance: Fe
and inevitable impurities. This overall composition is changed by
selecting transition metal elements in perovskite composite oxide.
For example, when Cr is selected as a transition metal element, Cr
is 7.51 to 31.99 mass %. Moreover, when Ni is selected instead of
selecting Cr, a composition in which 0.04 to 7.82 mass % of Ni is
added to the above-mentioned composition is obtained. Similarly,
when Ti is selected, a composition in which 0.02 to 6.47 mass % of
Ti is added to the above-mentioned composition is obtained. When V
is selected, a composition in which 0.02 to 6.88 mass % of V is
added to the above-mentioned composition is obtained. When Mn is
selected, a composition in which 0.02 to 7.42 mass % of Mn is added
to the above-mentioned composition is obtained. When Co is
selected, a composition in which 0.02 to 7.95 mass % of Co is added
to the above-mentioned composition is obtained. When Zr is
selected, a composition in which 0.03 to 12.13 mass % of Zr is
added to the above-mentioned composition is obtained. When Nb is
selected, a composition in which 0.03 to 12.54 mass % of Nb is
added to the above-mentioned composition is obtained. When Mo is
selected, a composition in which 0.03 to 13.21 mass % of Mo is
added to the above-mentioned composition is obtained. In the ranges
of the respective transition metal elements, at least one of the
above-mentioned transition metal elements can be added, and the
overall composition becomes compositions in which at least one of
the transition metal elements is added to the above-mentioned
composition.
[0027] Moreover, when a stainless steel containing 3.5 to 22 mass %
of Ni is selected as a matrix of stainless steel and Ni is not
selected as a metal element in perovskite composite oxide, Ni
content in the overall composition becomes 2.39 to 21.97 mass %. On
the other hand, when a stainless steel containing 3.5 to 22 mass %
of Ni is selected as a matrix of stainless steel and Ni is selected
as a metal element in perovskite composite oxide, Ni content in the
overall composition becomes 3.59 to 30.34 mass %.
[0028] Furthermore, when the C content in the matrix of the
stainless steel is 0.15 to 1.2 mass %, C content in the overall
composition becomes 0.12 to 1.20 mass %. Additionally, when at
least one of Mo, Cu, Al, N, Mn, Si, Nb, P, S and Se are contained
in the matrix of the stainless steel, at least one of Mo: 0.21 to
18 mass %, Cu: 0.68 to 4 mass %, Al: 0.07 to 4.99 mass %, N: 0.3
mass % or less, Mn: 3.76 to 9.99 mass %, Si: 0.1 to 4.99 mass %,
Nb: 0.44 mass % or less, P: 0.2 mass % or less, S: 0.15 mass % or
less, and Se: 0.15 mass % or less are added to the overall
composition.
EXAMPLES
[0029] Hereinafter, the invention will be described in more detail
along with Examples.
(Practical Example 1)
[0030] SUS310 powder which was defined by the JIS (Japan Industrial
Standards) and was equal to 310 defined by the AISI (American Iron
and Steel Institute) was prepared as a stainless steel powder
forming a matrix, and LaCrO.sub.3 powder and La.sub.2O.sub.3 powder
which had average grain diameters of 5 .mu.m were prepared as a
rare earth-oxygen composite powder. These powders were dispensed at
a rate shown in Table 1, and were mixed, whereby a raw powder was
obtained. The raw powder was compacted into a cylindrical shape
(diameter: 10 mm, height: 10 mm) and to a square block having a
square cross-section (width: 60 mm, depth: 10 mm, height: 10 mm),
in order to set the green density to be 6.7 g/cm.sup.3, obtained
green compacts were sintered in a hydrogen atmosphere at a
sintering temperature of 1250.degree. C. for 1 hour, whereby
samples shown by sample Nos. 1 to 12 were produced.
[0031] In the samples having the cylindrical shape, each sample was
set in a crucible made of aluminum per test piece, all the
crucibles were set in a muffle furnace, whereby oxidation test was
performed by heating in an air atmosphere at 850.degree. C. for 50
hours. Estimation was performed by measuring the difference in
weight between before and after the test, by dividing the measured
value by surface area, and by defining the divided value as an
increase in weight by oxidation (g/m.sup.2). The results are also
shown in Table 1 and are shown in FIG. 1 as a graph.
[0032] In the samples having the square block shape, each sample
was machined into a tensile test piece shape in a manner conforming
to JIS Z 2241, whereby tensile strength was measured. The results
are also shown in Table 1 and are shown in FIG. 2 as a graph.
1 TABLE 1 rare earth composition rate (mass %) element increase
stainless steel content in in weight powder LaCrO.sub.3 powder the
overall by tensile sample steel addition addition composition
oxidation strength number type amount type amount (mass %)
(g/m.sup.2) (MPa) 01 SUS310 balance -- -- 0.00 360 412 02 SUS310
balance LaCrO.sub.3 0.17 0.10 322 410 03 SUS310 balance LaCrO.sub.3
1.72 1.00 252 411 04 SUS310 balance LaCrO.sub.3 3.44 2.00 188 401
05 SUS310 balance LaCrO.sub.3 6.88 4.00 154 389 06 SUS310 balance
LaCrO.sub.3 13.75 8.00 97 361 07 SUS310 balance LaCrO.sub.3 20.63
12.00 87 335 08 SUS310 balance LaCrO.sub.3 27.51 16.00 84 276 09
SUS310 balance La.sub.2O.sub.3 0.12 0.10 327 410 10 SUS310 balance
La.sub.2O.sub.3 1.17 1.00 289 395 11 SUS310 balance La.sub.2O.sub.3
2.35 2.00 254 377 12 SUS310 balance La.sub.2O.sub.3 4.69 4.00 205
355 13 SUS310 balance La.sub.2O.sub.3 9.38 8.00 240 317 14 SUS310
balance La.sub.2O.sub.3 14.07 12.00 480 263 15 SUS310 balance
La.sub.2O.sub.3 18.76 16.00 680 190
[0033] According to the Table 1 and FIG. 1, increases in weight by
oxidation of samples in which LaCrO.sub.3 powder was used as a rare
earth-oxygen composite powder were smaller than those of samples in
which La.sub.2O.sub.3 powder was used as a rare earth-oxygen
composite powder, whereby the samples obtained by using LaCrO.sub.3
powder were apparently improved in corrosion resistance. This
effect was seen in the samples having La content of 0.1 mass % or
more. Moreover, when more than 8 mass % of La.sub.2O.sub.3 powder
was used, the increase in weight by oxidation was adversely
increased. On the other hand, in the samples in which LaCrO.sub.3
powder was used, as the La content was increased, the increase in
weight by oxidation tended to be decreased. However, when the La
content was more than 8 mass %, the effect in which the increase in
weight by oxidation was decreased by adding La became small for the
addition.
[0034] In these samples, distribution of Cr and La in a surface
layer of metal structure cross section was confirmed by an EPMA
(Electron Probe Micro Analyzer) after the oxidation test. In the
samples obtained by using LaCrO.sub.3 powder, uniform distribution
of Cr in the matrix was confirmed. On the other hand, in the
samples obtained by using La.sub.2O.sub.3 powder, La and Cr were
detected in the same area and a part decreasing Cr concentration
was confirmed around the area.
[0035] As mentioned above, it was found that when a rare earth
element was supplied as a rare earth oxide, the rare earth oxide
absorbed Cr in the matrix during the oxidation test. Then a part in
the matrix decreasing corrosion resistance was generated. On the
other hand, it was found that when a rare earth element was
supplied as a stable perovskite composite oxide, corrosion
resistance in the matrix was not decreased because Cr concentration
is uniform. Moreover, it was found that as the amount of
La.sub.2O.sub.3 added was increased, decrease of corrosion
resistance in the matrix was large.
[0036] As shown in the Table 1 and FIG. 2, as the added amount of
the rare earth-oxygen composite powder was increased, tensile
strength tended to be decreased. The tendency in the decrease of
the strength was dominant in the samples using La.sub.2O.sub.3
powder rather than those using LaCrO.sub.3 powder. This fact was
also caused by decrease of Cr content in the matrix. In the samples
using La.sub.2O.sub.3 powder, the strength of a part decreasing Cr
content in the matrix was decreased, and thus total strength was
decreased. Moreover, it is confirmed that when the La content is
more than 12 mass % in both samples using LaCrO.sub.3 powder and
La.sub.2O.sub.3 powder, the strength is greatly decreased.
[0037] As mentioned above, the effect of using the perovskite
composite oxide powder was confirmed. When the added amount of rare
earth element content in the perovskite composite oxide powder was
not less than 0.1 mass %, the effect of improving the corrosion
resistance was obtained. While the added amount of rare earth
element content in the perovskite composite oxide powder was more
than 12 mass %, strength was greatly decreased. Therefore, it was
confirmed that the rare earth element content should be 0.1 to 12
mass %.
(Practical Example 2)
[0038] LaCrO.sub.3 powder and La.sub.2O.sub.3 powder used in the
Practical Example 1 were added to the stainless steel powder shown
in the Table 2, in order to set the La content in the overall
composition to 2 mass %, whereby a mixed raw powder was obtained.
Test pieces were produced by using the raw powder in the same
process of Practical Example 1, and oxidation testing was
performed. The results are also shown in Table 2 and are shown in
FIG. 3 as a graph. Additionally, SUS304 (JIS) is a steel type equal
to 304 defined by the AISI, and SUS430 (JIS) is a steel type equal
to 430 defined by the AISI.
2 TABLE 2 rare earth composition rate (mass %) element increase
stainless steel rare earth-oxygen content in in weight powder
composite powder the overall by sample steel addition addition
composition oxidation number type amount type amount (mass %)
(g/m.sup.2) 04 SUS310 balance LaCrO.sub.3 3.44 2.00 188 11 SUS310
balance La.sub.2O.sub.3 2.35 2.00 254 16 SUS304 balance LaCrO.sub.3
3.44 2.00 335 17 SUS304 balance La.sub.2O.sub.3 4.69 2.00 407 18
SUS430 balance LaCrO.sub.3 3.44 2.00 343 19 SUS430 balance
La.sub.2O.sub.3 9.38 2.00 417
[0039] As shown in the Table 2 and FIG. 3, even when the steel type
of the stainless steel powder was changed, increases in weight by
oxidation of samples in which LaCrO.sub.3 powder was used as a rare
earth-oxygen composite powder were smaller than those of samples in
which La.sub.2O.sub.3 powder was used as a rare earth-oxygen
composite powder, as in the Practical Example 1. Therefore, it was
confirmed that the effect of the perovskite composite oxide powder
was obtained for any steel type.
(Practical Example 3)
[0040] Perovskite composite oxide powder having an average grain
diameter of 5 .mu.m shown in Table 3 was added to the stainless
steel powder (SUS310 powder), in order to set rare earth metal
element content in the overall composition to 2 mass %, and these
powders were mixed, whereby a mixed raw powder was obtained. Test
pieces were produced by using the raw powder in the same process of
Practical Example 1, and oxidation testing was performed. The
results are also shown in Table 3 and are shown in FIG. 4 as a
graph.
3 TABLE 3 rare earth composition rate (mass %) element increase
stainless steel rare earth-oxygen content in in weight powder
composite powder the overall by sample steel addition addition
composition oxidation number type amount type amount (mass %)
(g/m.sup.2) 04 SUS310 balance LaCrO.sub.3 3.44 2.00 188 11 SUS310
balance YCrO.sub.3 4.25 2.00 195 16 SUS304 balance CeCrO.sub.3 3.43
2.00 196 17 SUS304 balance LaFeO.sub.3 3.50 2.00 210 18 SUS430
balance LaNiO.sub.3 3.53 2.00 199 19 SUS430 balance La.sub.2O.sub.3
2.35 2.00 254
[0041] As shown in the Table 3 and FIG. 4, even when the rare earth
element and the metal element in the perovskite composite oxide
were changed, increase in weight by oxidation was slightly
suppressed in comparison with the case of supplying the rare earth
element in the rare earth oxide. Moreover, it was confirmed that
stable corrosion resistance improvement was observed for any rare
earth oxide and any metal element.
(Practical Example 4)
[0042] LaCrO.sub.3 powders having various average grain diameters
shown in the Table 4 were prepared. These LaCrO.sub.3 powders were
added to stainless steel powder (SUS310 powder), in order to set
the rare earth element content in the overall composition to 2 mass
%, whereby a mixed raw powder was obtained. Test pieces were
produced by using the raw powder in the same process as in
Practical Example 1, and oxidation testing was performed. The
results are also shown in Table 4 and are shown in FIG. 5 as a
graph.
4 TABLE 4 rare earth composition rate (mass %) element increase
stainless steel LaCrO.sub.3 powder content in the in weight powder
grain overall by tensile sample steel addition diameter addition
composition oxidation strength number type amount (.mu.m) amount
(mass %) (g/m.sup.2) (MPa) 04 SUS310 balance 5 3.44 2.00 188 411 24
SUS310 balance 15 3.44 2.00 206 378 25 SUS310 balance 30 3.44 2.00
222 367 26 SUS310 balance 75 3.44 2.00 560 278
[0043] As shown in the Table 4 and FIG. 5, when the average grain
diameter of the LaCrO.sub.3 powder was increased, increase in
weight by oxidation tended to be slightly increased. However, when
the average grain diameter was more than 30 .mu.m, increase in
weight by oxidation was greatly increased. Therefore, it is
confirmed that perovskite composite oxide powder having an average
grain diameter of 30 .mu.m or less is preferably used. The reason
is that, in a condition of setting the added amount of LaCrO.sub.3
powder to be constant, as the average grain diameter is increased,
segregation in the matrix is increased, whereby some parts in which
corrosion resistance is improved and other parts in which corrosion
resistance is not improved are produced.
* * * * *