Note: Descriptions are shown in the official language in which they were submitted.
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TITL~ QF THE INVENTION
Alloy steel powders for injection molding use, their compounds
and a method for making sintered parts from the same.
BACKGROUND OF THE INVENTTION
The present invention relates to metal powders for
injection molding use, their compounds and the method for
producing sintered parts from the same.
(l) Sintered steel, which is a kind of sintered metal bodies,
is partially replacing ingot stainless steel, since the former
offers advantages over the latter with respect to improvement
of the yield and reduction of machining cost.
With regard to the molding method for the sintered steel,
great hopes are entertained of such injection molding methods
that will readily enable molding of parts having complex
three-dimensional configurations in place of the compression
molding whose limitation is that the produclble parts are
limited to those of two-dimensional designs.
However, since the manufacture of sintered steel bodies
by injection molding started only recently, there are
still variety of technical problems which remain unresolved,
and, in particular, there is room for major improvement in the
raw material powder.
Generally, it isessen~lal for the raw material powder
for injection molding of a 20 microns or less average particle
diameter that it is in the spherical shape and in the form of
ine particles. An advantage of the spherical powder is that
it imparts good slip among the particles, that is to say, it
has excellent injection moldability. For instance, by
comparison of a spherical powder with an irregular shape
powder, both of which have been added with an organic binder
of an identical kind and in an identical quantity, it is found
that the former offers a lower viscosity and demonstrates
better injection moldabili~y. Furthermore, an equivalent
level of injection moldability can be achieved with a less
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quantity of the binder. For the said reasons, it becomes
possible to shorten the debinding cycle, and also to achieve a
high density by dint of a finer particle si~e of the powder.
For the purpose of achieving such properties required of
the raw material powder, modification of operational
parameters for the atomizing apparatus, e.g. the pressure and
flow rate of the atomizing medium and adjustment of the
diameter of the metallic melt injection nozzle, has been the
conventionally adopted means. However, no other means for the
intended improvement has been adopted through the route of
altering the chemical composition of the raw material powder,
but such chemical composition that is similar to that adopted
for the raw material powder intended for compression molding,
whose average particle diameter is about 80 microns, that is
to say, the chemical composition form which such impurities as
may interfere with the compressiblity in the case of
compression molding have been removed to the bare m; n;ml~m, has
been conventionally adopted.
Nonetheless, problems have been experienc~ in that
satisfactory injection moldability cannot be achieved with
fines for injection molding of the conventional chemical
composition (Ref.: The "Tokushu-ko (Special Steel)", Vol.36,
No.6, page 52, Table 1, June 1, 1987), since spherical
particle formation does not take place to a sufficient extent
in that powder.
(2) The present circumstance is that being in current use as a
raw material powder for the injection molding use are those
powders which are essentially sintering fine powders for the
compression molding use as described in the Japanese Patent
Publication No. 1761/84, the ~Funtai Oyobi Funmatsu Yakin
(Powders and Powder Metallurgy)", Vol. 12, No. 1 (February,
1965), page 25 to page 32, by Tamura et al. and the "Funtai
Oyobi Funmatsu Yakin", Vol. 22, No. 1 (March, 1975), page 1 to
page 11, by Kato et al., but have chemical compositions not at
all different from those of the powders intended for powder
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metallurgy, namely, comprising 1.5% or less by weight of
silicon, 0.4% or less by weight of manganese, and less than 1
Manganese/Silicon ratio(ordinarily, the Manganese/Silicon
ratio is less than 0.3).
What has remained problematic is that the said powders
are not necessarily satisfactory with respect to the injection
moldability and the sintering characteristics, since the
traditional technological philosophy centering on prevention
of oxidation in the atomizing step by keeping the
Manganese/Silicon ratio at less than 0.3 has been followed
strictly so that chemical compositions having extremely
reduced contents of carbon and manganese, which deteriorate
the compressibility and moldability in the compression molding
oparation, have been conventionally used, while such practice
resulted in insufficient development of such expertise for
producing spherical powder and handling oxides on the surface,
which is required of stainless steel powder (the average
particle diameter: 20 microns or less).
(3) Iron-Cobalt-type alloy is known as a soft magnetic
material having the highest saturated magnetic flux density
among all magnetic materials. In other words, Iron-Cobalt-
type alloy can be said to exhibit a higher magnetic energy
with a given volume among all magnetic materials. Great hopes
are entertained of this material, by virtue of its excellent
magnetic characteristics, for applications associated with
electric motors, magnetic yoke, and the like which require
high magnetic energy generated from small-size parts.
On the other hand, ingot Iron-Cobalt-type alloy is in
such a dilemma that industrial production of small-size parts
is virtually impossible due to its poor cold workability.
Powder metal-urgy is considered to be a valid means by
which to overcome such inferior workability, and variety of
methods have been proposed. For instance, there are the
Japanese Patent Laid Open No. 291934/86, the Japanese Patent
Laid Open No. 54041/87, and the Japanese Patent Laid Open No.
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142750/87 concerning Iron-Cobalt-type sintered materials, and
the Japanese Patent Publication No. 38663/82 (The Japanese
Patent Laid Open No. 85649/80) concerning Iron-Cobalt-type
sintered materials containing phosphorus and the Japanese
Patent Laid Open No. 85650/80 concerning Iron-Cobalt-type
sintered materials containing boron. Furthermore, there is
the Japanese Patent Laid Open No. 75410/79 concerning Iron-
Cobalt-Vanadium-type sintered materials.
However, all of the hitherto proposed methods, which
depend on the principle of compression molding, are
accompanied by such limitation that so-called mixed powder,
namely, a powder prepared by a~m;xing iron-cobalt alloy
powder, cobalt-vanadium alloy powder, iron-phosphorus alloy
powder, and/or iron-boron alloy powder with iron powder and
cobalt powder, so that the raw material powder will enable
molding in a mold for the compression molding press, while the
a~m;x;ng or blending ratio had to be limited to an extent that
does not deteriorate the compressibility.-
For the said reason, it has been the object of theconventional technique to overcome low sintered density and
low magnetic characteristics attributable to the said
limitations. The method proposed in the Japanese Patent Laid
Open No. 291g34/86 is intended for improvement in the
compressibility by utilizing rapidly quenched iron-cobalt
alloy, in which no regular lattice structure is formed, as
well sinterability by dint of the blend of such rapidly
quenched iron-cobalt alloy powder with cobalt powder, the
method proposed by the Japanese Patent Laid Open No. 54041/87
is for improvement in the sintered density by HIP (hot
isostatic press) Method, and the method proposed by the
Japanese Patent Laid Open No. 142750/87 aims at improvement in
the magnetic characteristics by means of improved green
density (compressed powder density) and sintered density by
com~bination of coarse Iron-Cobalt-type alloy powder with
cobalt fines.
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There are methods proposed in the Japanese Patent
Publication No. 38663/82 (The Japanese Patent Laid Open No.
85649/80) and the Japanese patent Laid Open No. 856S0/80, both
of which are intended for improving magnetic characteristics
by means of achieving high sintered density that unblended
powders. The former method comprises sintering a pulverized
iron-phosphorus alloy (26.5% by weight of P) so that the
phosphorus content will be 0.05 to 0.7%. The latter method
comprises sintering of pulverized iron-boron alloy (19.9% by
weight of B) so that the boron content will be 0.1 to 0.4%.
Furthermore, the sintered material disclosed in the
Japanese Patent Laid Open No. 75410/79 is intended to improve
magnetic characteristics by increasing the sintered density of
Iron-Cobalt-Vanadium-type alloy as sintering material through
liquid phase sintering of a composition prepared by blending
pulverized vanadium-cobalt alloy ground powder consisting of
35 to 45% by weight of vanadium, comprising 38% vanadium
eutectic composition, with iron powder and cobalt powder.
The conventional methods as proposed hereinabove are, however,
intended for compression molding using a mold, and are not
applicable to injection molding, since the raw material powder
is essentially a mixture of various single-element metal
coarse powders having inferior sintering characteristics and
two-element alloy powders, and said powders differ from one
another in the particle size and the particle shape due to
difference in the manufacturing methods employed.
In the present days, Iron-Cobalt-type sintered material
is replacing a part of the ingot iron-cobalt alloy material on
account of the former's advantage with respect to the yield
and the mach; n; ng cost. In particular, with regard to the
molding process, expectation is entertained of future
development of the injection molding method which is capable
of readily giving three ~;mensional profile parts,
substituting the compression molding method which is merely
capable of producing two ~;mensional parts.
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Nevertheless, since it is only recent that the
manufacture of Iron-Cobalt-type sintered material, depending
on the injection molding technique, was started, there still
remain various technical problems which are yet to be
resolved. In particular, with regard to raw material powder,
there is much to be improved.
Generally, the raw material powder intended for injection
molding are required to be fines in the spherical particle
shape, and has oxides on the surface of the particle which can
be reduced, in the case of Iron-Cobalt-type sintered material
as was described in relation to the Stainless Steel-type
sintered material.
However, even in the case of Iron-Cobalt-type sintered
material, alteration of the chemical composition of the raw
material powder has not been adopted as a means for realizing
improvement, as was the case with Stainless Steel-type
sintered material, but a same composition as the raw material
powder (having an average particle diameter of about 80
microns) predicated on an assumption that it be used for the
compression molding only has been adopted.
Namely, chemical compositions in which such impurities as
will deteriorate the compressibility and the proces-sability in
the compression molding step have been conventionally used.
However, there existed problems in that said chemical
compositions are not necessarily satisfactory with respect to
the injection moldability and sintering characteristics, since
there are not available sufficient knowledge and experiences
regarding the method by which to obtain the spherical particle
shape and oxides on the surface for the fine powder for the
injection molding use having the conventional composition (the
average particle diameter is 20 microns or less).
RRIFF DESCRIPTION OF TH~ DRAWINGS
Fig. 1 (a) is a graph which shows a relationship between
the carbon content and the apparent density.
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Fig. 1 (b) is a graph which shows a relationship between
the carbon content and the tap density.
Fig. 1 (c) is a graph which shows a relationship between
the carbon content and the specific surface area.
Fig. 1 (d) is a graph which shows a relationship between
the carbon content and the viscosity temperature.
Fig. 2 is a graph which shows the carbon content after
sintering.
Fig. 3 is a graph which shows a relationship between the
relative density ratio of sintered material and the relative
density ratio after HIP (hot isostatic press) treatment.
Fig. 4 is a graph which shows a relationship between the
chromium (as alloy) content of Ferrite-type stainless steel
sintered material and the corrosion velocity in a boiling 60%
nitric acid solution.
Fig. 5 is a graph which shows a relationship between the
relative sintered density ratio of Ferrite-type stainless
steel sintered material with which nickel, molybdenum and
copper are alloyed and the corrosion velocity in a boiling 1%
sulfuric acid solution maintained at 25C.
Fig. 6 is a graph which shows a relationship between the
relative sintered density ratio of Austenite-type stainless
steel sintered material and the corrosion velocity in a
boiling 60% nitric acid solution.
Fig. 7 is a graph which shows a relationship between each
of the nickel, molybdenum, copper, and C (as alloy) contents
of Austenite-type stainless steel sintered material and the
corrosion velocity in a boiling mixture of 40% acetic acid and
1% formic acid solutions.
Fig. 8 is a graph which shows a relationship between each
of the tin, sulfur, selenium, and tellurium (as alloy) content
of each of Ferrite-type stainless steel sintered material and
Austenite-type stainless steel sintered material and the
drilling torque.
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Figure 9 is a graph which shows a relationship between
the relative density ratio of sintered material and the relative
density ratio after HIP (hot isostatic press) treatment.
SUMMARY OF THE INVENTION
The present inventors r by way of carrying out elaborate
experiments relating to the manufacture of stainless steel powder
as a raw material for sintered steel and the manufacture of
sintered steel by injection molding, have engaged in search for
such chemical compositions that will not at all impair the
corrosion resistance of the sintered body and also will give the
spherical particle shape as powder which is suitable for injection
molding. The present inventors thereby have completed the present
invention.
A first aspect of the present invention provides a steel
powder of a spherical particle shape having excellent injection
moldability in the manufacture of sintered steel parts which
depend on injection molding.
A first major embodiment of this aspect provides
stainless steel powder for use in the injection moldingr
consisting essentially of spherically-shapedr water jet atomized
silicon-containing stainless steel alloy particles having an
average particle diameter of 20 ~m or less r
wherein the silicon-containing stainless steel alloy
contains:
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0.20 to 1.00% by weight of silicon;
manganese in an amount satisfying that a
manganese/silicon weight ratio is at least 1.00;
substantially 0 to 1.20% by weight of carbon;
8.0 to 30.0% by weight of chromium;
(i) substantially 0, (ii~ 1.0 to 4.0% by weight or (iii)
8.0 to 22.0% by weight of nickel;
the stainless steel may contain one or more elements
selected from the group consisting of (iv) 0.05 to 2.00% by weight
of tin,(v) 0.02 to 0.50% by weight of sulfur, (vi) 0.05 to 0.20%
by weight of selenium, (vii) 0.05 to 0.20% by weight of tellurium,
(viii) 0.3 to 4.0% by weight of molybdenum and (ix) 0.5 to 5.0% by
weight of copper; and
the balance of the stainless steel alloy is
substantially iron and inevitable impurities.
A second major embodiment of this aspect provides iron-
cobalt-type alloy steel powder for use in the injection molding,
consisting essentially of spherically-shaped, water jet atomized
alloy steel particles having an average particle diameter of 20 ~m
or less,
wherein the alloy steel contains:
substantially 0 to 1.00% by weight of silicon;
substantially 0 to 1.00% by weight of carbon;
substantially 0 to 2.00% by weight of manganese,
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provided that a manganese/silicon weight ratio is at least 1.00:
15 to 60% by weight of cobalt;
the alloy steel may contain at least one element
selected from the group consisting of (i) 0.02 to 1.00% by weight
of boron, ~ii) 0.05 to 1.00% by weight of phosphorus; (iii) up to
1.0% by weight of carbon, (iv) up to 1.0% by weight of silicon and
(v) 1.0 to 4.0% by weight of vanadium; and
the balance of the alloy steel is substantially
iron and inevitable impurities.
A second aspect of the present invention provides a
compound for use in the preparation of a sintered alloy steel body
by injection molding, which compound comprises the steel powder
mentioned above and an organic binder in an amount sufficient to
bind the powder.
A third aspect of the present invention provides a
method for manufacturing the above-mentioned steel powder by
atomizing a melt of the steel with highly pressurized water.
A fourth aspect of the present invention provides a
process for manufacturing a sintered alloy steel body, which
comprises injection molding a compound comprising the steel powder
and an organic binder into a desired shape of the body, debinding
the molded body, and sintering the debound body.
A fifth aspect of the present invention, provides a
sintered alloy body manufactured by the process mentioned above.
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The present inventors have acquired the following
knowledge after having carried out elaborate experiments aimed at
accomplishing the above-mentioned objects, and have come upon the
present invention.
Stainless steel powders having an average particle
diameter of 20 microns or less (as herein used, the "average
particle diameter" means a particle diameter of the particle size
group (powder fraction) with whose addition the cumulative volume
measured from the finer particle group reaches the 50% level of
the total volume) which have particle shapes suitable for
injection molding and such surface construction (the surface
comprising a certain oxide composition) as gives excellent
sintering characteristics can be produced by atomizing a melt of a
chromium-containing stainless steel having the composition of
0.20% or more by weight of silicon and a manganese/silicon ratio
of 1.00 or higher, and a Chromium-type stainless steel having the
composition
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of 1.20% or less by weight of carbon, 0.20% or more by weight of
silicon, a manganese/silicon ratio of 1.00 or higher, and 8.0 to
30.0% by weight of chromium, or Chromium-Nickel-type stainless
steel
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having the composition of 8.0 to 30.0% by weight of chromium
and 8.0 to 22.0% by weight of nickel.
As shown in detail by Examples of the present invention,
it is possible to obtain by sintering stainless steel powder
having the above-mentioned compositions sintered stainless
steel materials constructed with closed pores which have a
relative density ratio ~the ratio to true density) of 92% or
higher and excellent corrosion resistance with their 0.05% or
less by weight carbon contents.
Also, an improvement is achieved in the corrosion
resistance of the sintered stainless steel material at carbon
content levels of 0.05% or lower by weight by means of
alloying with Chromium-type stainless steel or Chromium-
Nickel-type stainless steel one or more of 1.0 to ~.0% by
weight of nickel, 0.3 to 4.0% by weight of molybdenum, and 0.5
to 5.0% by weight of copper.
~ Moreover, an improvement is achieved in the cutting
efficiency of the sintered stainless steel at carbon content
levels of 0.05% or lower by weight by means of alloying wlth
Chromium-type stainless steel or Chromium-Nickel-type
stainless steel with one or more of 0.05 to 2.00% by weight of
tin, 0.02 to 0.05% by weight of sulfur, 0.05 to 0.20% by
weight of selenium, and 0.05 to 0.20% by weight of tellurium.
(2) It is possible to manufacture iron-cobalt fine powder of
an average particle diameter of 20 microns or less having a
particle shape suitable for injection molding and comprising
the surface (the surface containing a certain oxide
composition) which imparts excellent sintering characteristics
by means of producing metal fines by the atomizing method from
an iron-cobalt melt, the composition of which being 2.00% or
less by weight of manganese, and 15 to 60% by weight of
cobalt, the balance being substantially iron except
impurities. Accordingly, it is possible to obtain by
sintering the above-mentioned alloy fine powder sintered
material containing closed pores and superior in magnetic
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characteristics which has a relative density ratio (the ratio
to true density) of 92% or higher and has a carbon content of
0.02% or less by weight.
Also, it is possible to manufacture Iron-Cobalt-type or
Iron-Cobalt-Vanadium-type powder of an average particle
diameter of 20 microns or less having a particle shape
suita~le for injection molding and comprising the surface of
the particle (the surface containing a certain oxide
composition) which imparts excellent sintering characteristics
by means of producing metal fines by the atomizing method from
Iron-Cobalt-type or Iron-Cobalt-Vanadium-type melt, the
composition of which being 1.00% or less by weight of carbon,
1.00% or less by weight of silicon, 2.00% or less by weight of
manganese, and 1.00 or higher Manganese/Silicon ratio.
Accordingly, it is possible to obtain by sintering the above-
mentioned alloy powder sintered material having closed pores
and superior in magnetic characteristics ~hich has a relative
density ratio (the ratio to true density~ of 92% or higher and
has a carbon content of 0.02% or less by weight.
Moreover, an improvement can be achieved in the apparent
density and the tap density of the alloy powder of an average
particle diameter of 20 microns or less and in magnetic
characteristics at carbon content levels of 0.02% or lower by
weight in accordance with increase in the sintered density by
means of alloying with the above-mentioned melt one or both of
0.02 to 1.00% by weight of boron, 0.05 to 1.00% by weight of
phosphorus and atomizing the alloy into fine powder.
DF.TAILED DESCRIPTION OF T~F INVENTION
(A) Metal fine powder for the injection molding use
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(1) Silicon-containing alloyl powder
The composition of silicon-containing alloy powder
offered to uses in the manufacture of sintered silicon-
containing allow material by injection molding is
based on l.20% or less by weight of carbon, 0.20% or more by
weight of silicon, l.00 or higher Manganese/Silicon ratio, and
20 microns or le~s average particle diameter.
Mor~ specifically, it is 1.2~ or less by weight of carbon,
0.20% or more by weight of silicon, l.00 or hiyher
Manganese/Silicon ratio, and 8.0 to 30.0% by weight of
chromium, the balance being substantially iron except
impurities, with an average particle diameter of 20 microns or
less.
(a) Moreover, the above-mentioned composition may contain l.0
to 4.0% by weight of nickel or 8.0 to 22.0% by weight of
nickel.
(b) Or, the above-mentioned composition may contain 0.3 to
4.0% by weight of manganese, without containing nickel. It
may contain 0.3 to 4.0% by weight of molybdenum in addition to
the nickel therein contained.
(c) Or, the above-mentioned composition may contain 0.5 to
5.0% by weight of copper, without containing nickel. It may
contain 0.5 to 5.0% by weight of copper in addition to the
nickel therein contained.
(d) Or, the above-mentioned composition may contain 0.3 to
4 0% by weight of molybdenum and 0.5 to 5.0% by weight of
copper in addition to l.0 to 4.0% by w~ight of nickel or 8.0
to 22.0% by weight of nickel therein contained.
(e) Moreover, the composition as set forth in (a) through (d)
above may contain one or more of 0.05 to 2.00% by weight of
tin, 0.02 to 0.50% by weight of sulfur, 0.05 to 0.20% by
weight of selenium and 0.05 to 0.20% by weight of tellurium.
The reasons for limiting the carbon content to l.20% or
less by weight are set forth below.
Generally, in the case of ingot stainless steel, it is
necessary to reduce the carbon content to the bear minimum
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from the view point of ensuring an acceptable corrosion
resistance. In particular, raw material powders which are
offered to the manufacture of sintered stainless steel by
compression molding are required to have its carbon content
reduced to an extent lower than that of ingot steel, from the
view point of ensuring corrosion resistance as well as
compressibility in the compression molding.
On the other hand, it was found that in the manufacture
of sintered stainless steel, use of low carbon raw material
does not lead to improved injection moldability and does not
offer any merit with respect to corrosion resistance due to
contamination with carbon which is produced from organic
binder at the debinding stage.
Moreover, it was found that the carbon resulting from raw
material powder as well as the carbon resulting from the
organic binder can be removed by performing sintering in
vacuum.
Thus, an attempt was made to improve properties of the
powder by increasing the carbon content of the powder, rather
than reducing the same. As a result, it was found through the
experiments that addition of the carbon content improves the
compactness of powder obtained by the atomizing method for
which high pressure medium is utilized (for formation of the
spherical particle shape).
It is inferred that the atomized particle is shaped into
the spherical shape by dint of the decline in the oxygen
content of the melt which is caused by the carbon's getting
alloyed with constituents of stainless steel in the melt form
and also the decline in the viscosity and melting point of the
melt. For example, it is learned that in stainless steel fine
powder obtained by atomizing the melt with circular water jet
injected at a 1,000 Kgf/cm2 water pressure having an average
particle diameter of 8.0 to 9.0 microns as shown in Table 1
through Table 3, its apparent density and tap density are
recognized to increase in accordance with the increase in the
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amount of carbon alloy, hence the spherical particle formation
is known to have taken place in the powder.
Furthermore, even in the case of compounds having
equivalent powder-to-binder ratio, it is recognized that the
viscosity temperature of the compound declines in consequence
of increases in the alloyed carbon content of the stainless
steel powder.
However, the viscosity temperature of the compound
increases remarkably, if the alloyed carbon content of the
stainless steel powder exceeds the level of 1.20% by weight,
since the limit of deoxidation owing to the carbon-wit-oxygen
reaction is lowered to below the limit of deoxidation
corresponding to amounts of silicon and manganese alloyed in
the melt in consequence of the decline in the melt temperature
at the time of introduction of the melt for the atomizing
stage, thus causing the apparent density and the tap density
to drop on the contrary due to production of bubble-like
particles in which carbon monoxide gas is encapsulated.
Moreover, the alloyed carbon content of the stainless
steel powder is limited to 1.20% or less by weight, since in
case the said compound undergoes vacuum sintering and maximum
sintering time which are ordinarily adopted industrially,
namely, at l,350C and for 4 hours, the carbon content of the
sintered material cannot be reduced to 0.05% or less by
weight, and, consequently, the corrosion resistance is
deteriorated.
The reasons for limiting the Manganese/Silicon ratio to
1.00 or higher for 0.20% or more by weight of silicon are set
forth below.
Although the melt alloyed with chromium causes clogging
of the tundish nozzle with chromium oxide (Cr2O3) which
precipitates on the tundish nozzle due to drop of the melt
temperature, with addition of C, Si and Mn to the melt, it is
possible to adjust the oxygen content of the melt to below the
Cr-O deoxidation limit, which reaches the equilibrium at the
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melt temperature when melt passes through the tundish nozzle,
and thus the nozzle clogging can be prevented.
For instance, in case manganese is not added to the
stainless steel melt of 0.01% by weight of carbon and 30.0% by
weight of chromium maintained at 1,500C, the oxygen contents
of Cr-O and Si-O in the melt reach approximity of the
equilibrium at 0.20% by weight of Si content and the melt
passes through the tundish nozzle without clogging it, thus
making atomization possible. Hence, the silicon content is
limitéd to 0.20% or more by weight.
Moreover, if manganese is added to the melt, a further
satisfactory condition can be achieved by virtue of a complex
deoxidation effect of Si-Mn in that the melt is made into one
having a low oxygen content compared with the limit of Cr-O
deoxidation, thus eliminating the possibility of clogging the
tundish nozzle due to dropped melt temperature.
For instance, the spherical particle formation is known
to have occurred at a Manganese/Silicon ratio of 1.00 or
higher in the case of the alloy powder obtained by atomizing
the melt with water jet as shown- in Table 1 through Table 3,
since both apparent and tap densities increase and the
viscosity temperature of the compound is lowered. Moreover,
it is also learned that the sintered density increases and the
surface has been made into a condition which imparts fair
sinterability when the Manganese/Silicon ratio is 1.00 or
higher.
It is inferred that if the manganese content of the melt
increases, MnO of a low melting point is produced on the
surface of the particle in the atomization step, and before
the MnO solidifies, lowering of the melting point of the
surface layer of the particle, increase in the surface
tension, and decline of the viscosity occur, and consequently
the atomized particle assumes the spherical shape.
Moreover, the MnO is considered to be reduced into carbon
monoxide by the carbon content of the compound or the alloyed
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carbon content of the melt, thus not obstructing sintering, so
long as the said compound undergoes vacuum sintering at about
1,350C, which is the sintering temperature generally adopted
industrially.
On the contrary, silicon produces viscous silicon dioxide
(SiO2) on the surface of the particle in the atomizing stage
to make the particle shape irregular, and the silicon dioxide
can hardly undergoes reduction into carbon monoxide with
carbon in vacuum at a temperature of about 1,400C, hence
sintering is obstructed. Therefore, the Manganese/Silicon
ratio of the melt is limited to 1.00 or higher for the purpose
of achieving spherical particle formation and a surface of the
particle which imparts a fair sinterability in the atomizing
stage~
The reasons for limiting the chromium content to 8.0 to
30.0% by weight are set forth below.
Chromium is a basic alloy element of stainless steel,
which forms the passive state film and imparts corrosion
resistance. The chromium content is limited to 8.0 to 30.0~
by weight, since addition of chromium in an amount exceeding
30% by weight does not bring about any improvement in the
corrosion resistance, while the corrosion velocity remarkably
decreases at the chromium content level of 8.0% or higher by
weight, in the case of sintering a material constructed with~
closed pores having a s~ecific density ratio of 95% which ~
obtained by injection molding Chr~mium-containing powder of an
average particle diameter of 8.0 ~ ~.0 microns (5.0 to 33.0%
by weight of chromium, 0.02% by weight of carbon, 0.70% by
weight of silicon, 1.00% by weight of manganese, 0.02% by
weight of phosphorus, and 0.01% by weight of sulfur, the
balance being substantially iron) and vacuum sintering the
said injection molded material in vacuum at 1,350C for 4
hours at 10-4 torr, according to the corrosion resistance test
carried out on samples immersed in a boiling nitric acid as
`~
1 ~35~5~
shown in Fig. 4, which represents results of elaborate studies
made by the present inventors.
The reason for limiting the nickel content of Ferrite-
type sintered steel to 1.0 to 4.0% by weight are set forth
below. The process of achieving the passive state in
Chromium-containing sintered ferrite steel is enhanced by
nickel, and the corrosion resistance is thereby improved.
The nickel content for improving corrosion resistance of
sintered Ferrite-type stainless steel of the present invention
is limited to 1.0 to 4.0% by weight, since addition of nickel
in an amount exceeding 4.0% by weight does not bring about any
improvement in the corrosion resistance, while the corrosion
veloci~y remarkably decreases at the nickel content level of
1.0% by weight or higher, in the case of sintering material
constructed with closed pores having the relative density
ratio of 95% which is obtained by injection molding stainless
steel fine-powder of an average particle diameter of 8.0 to
9.0 microns (whose composition being 18% by weight of
~chromium, 0.02% by weight of carbon, 0.70% by weight of
silicon, 1.00% by weight of manganese, 0.02% by weight of
phosphorus, and 0.01% by weight of sulfur, the balance being
substantially iron) and vacuum sintering the said injection
molded material in vacuum at l,350C for 4 hours at 10-4 torr,
according to the corrosion resistance test carried out on
samples immersed in a 1% sulfuric solution maintained at 25C
as shown in Fig. 5, which represents results of elaborate
studies made by the present inventors.
The reasons for limiting the nickel content of Austenite-
type stainless steel to 8.0 to 22.0% by weight are set forth
below. Nickel is a basic alloy element of Austenite-type
stainless steel, which expands the gamma-phase area, thus
stabilizing Austenite. Nickel is electrochemically noble,
compared with iron and chromium, imparts corrosion resistance
against chlorides or nonoxidative acids, and intensified the
tendency of the passive state of oxides of chromium.
21 1 33~7~9
The nickel content is limited to 8.0 to 22.0% by weight,
since the sintered steel containing 8.0% by weight of chromium
of the present invention is made into Austenite to have
sufficient corrosion resistance against chlorides or
nonoxidative acids with the nickel content of 8.0% by weight
and for a 30.0% by weight chromium-containing steel, the
required nickel content is 22.0% by weight and addition of
nickel in an amount exceeding 22.0% by weight does not bring
about any improvement in the corrosion resistance of
Austenite-type sintered stainless steel of the present
invention.
The reasons for limiting the molybdenum content and the
copper content to 0.3 to 4.0% by weight and 0.5 to 5.0% by
weight, respectively, are set forth below. Molybdenum and
copper stabilize the passive state of Ferrite-type sintered
stainless steel and Austenite-type sintered sta-7nless steel
and improve their corrosion resistance.
The molybdenum content and the copper content are limited
to 0.3 to 4.0% by weight and 0.5 to 5.0% by weight,
respectively, since addition of molybdenum in an amount
exceeding 4.0~ by weight or addition of copper in an amount
exceeding 5.0% by weight does not bring about any improvement
in the corrosion resistance, while the corrosion velocity
decreases at the molybdenum content of 0.3% or more by weight
or the copper content of 0.5% or more by weight either
singularly or in combination, in the case of sintering a
material constructed with close pores and having a relative
density ratio of 95% which is obtained by injection molding
Austenite-type stainless steel fine powder of an average
particle diameter of 8.0 to 9.0 microns (18% by weight of
chromium, 14% by weight of nickel, 2.5% by weight of
molybdenum, 0.70% by weight of silicon, 1.00% by weight of
manganese, 0.02% by weight of phosphorus, and 0.01% by weight
of sulfur, the balance being substantially iron~ and vacuum
sintering the said injection molded material in vacuum at
22 ~ 5 ~
1,350C for 4 hours at 10-4 torr, according to the corrosion
resistance test carried out on samples immersed in a boiling
mixture of 40% acetic acid and 1% formic acid solution as
shown in Fig. 5 and Fig. 7, which represents esults of
elaborate studies made by the present investors.
The reasons for limiting the tin content, the sulfur
content, the selenium content and the tellurium content, 0.05
to 2.00% by weight, 0.02 to 0.50% by weight, 0.05 to 0.20% by
weight, and 0.05 to 0.20% by weight, respectively, are set
forth below.
Tin, sulfur, selenium, and tellurium improve the cutting
efficiency of Ferrite-type sintered steel or Austenite-type
sintered steel, when one or more of them are added to it.
The tin content, the sulfur content, the selenium content
and tellurium content are limited to 0.05 to 2.00% by weight,
0.02 to 0.50% by weight, 0.05 to 0.20% by weight, and ~.05 to
0.20% by weight, respectively, since addition of tin in an
amount exceeding 2.00% by weight, addition of sulfur in an
amount exceeding 0.50% by weight, addition of selenium in an
amount exceeding 0.20% by weight or addition of tellurium in
an amount exceeding 0.20% by weight does not bring about any
improvement in the cutting efficiency, while the cutting load
(torque) decreases at the tin content of 0.05% or more by
weight, the sulfur content of 0.02% or more by weight, the
selenium content of 0.05% or more by weight, or the tellurium
content of 0.05% or more by weight either singularly or in any
combination, in the case of sintering a material constructed
with closed pores having a relative density ratio of 95% which
is obtained by injection molding Ferrite-type stainless steel
powder (comprising 0.70% by weight of silicon, 1.00% by weight
of manganese, and 18% by weight of chromium) and Austenite-
type stainless steel powder (comprising 0.70% by weight of
silicon, 1.00% by weight of manganese, 18% by weight of
chromium, and 14% by weight of nickel), each of which having
an average particle diameter of 8.0 to 9.0 microns and vacuum
`~
23 l 335759
sintering the said injection molded material in vacuum at
1,350C for 1 hour at 10-4 torr, according to the cutting
efficiency test carried out as shown in Fig. 8, which
represents results of elaborate studies made by the present
inventors.
The reasons for limiting the average particle diameter to
20 microns or less are set forth below. As Table 6 indicates,
the density and the corrosion resistance of the final sintered
material produced from the said stainless steel fine powder
are strongly influenced by the average particle diameter of
the said stainless steel powders.
The average particle diameter is limited to 20 microns or
less, since if the average particle diameter exceeds 20
microns, it becomes impossible to manufacture the sintered
material constructed with closed pores which has a relative
sintered density ratio of 92% or higher as shown in Fig. 3 and
the relative sintered density ratio falls short of 92%, thus
causing remarkable deterioration of the corrosion resistance
as shown in Fig. 5 and Fig. 6.
(3) Iron-Cob~lt alloy pow~er
Iron-Cobalt alloy powder utilized in the manufacture of
sintered iron-cobalt alloy material by injection molding of
the present invention comprises 2.0% or less by weight of
manganese and 15 to 60% by weight of cobalt, the balance being
substantially iron except impurities and has an average
particle diameter of 20 microns or less.
Furthermore, the above-mentioned composition may include
either one of 0.02 to 1.00% by weight of boron and 0.05 to
1.00% by weight of phosphorus.
More preferably, the composition may be 1.0% or less by
weight of carbon, 1.0% or less by weight of silicon, 2.0% or
less by weight of manganese, 1.0 or higher Manganese/Silicon
ratio, and 15 to 60~ by weight of cobalt, the balance being
~ 1 335759
24
substantially iron except impurities, and has an average
particle diameter of 20 microns or less.
(a) Moreover, the above-mentioned composition may contain 1.0
tG 4.0% by weight of vanadium.
(b) Or, the above-mentioned composition may contain at least
either one of 0.02 to 1.00% by weight of boron and 0.05 to
1.00% by weight of phosphorus. It may contain 1.0 to 4.0% by
weight of vanadium additionally.
The reasons for limiting the manganese content to 2.00%
or less by weight are set forth below. The manganese content
is limited to 2.00~ or less by weight, since the saturated
magnetic flux density of the sintered material declines to a
level lower than that of Fe-single constituent sintered
material at a manganese content level higher than 2.00% by
weight, although Iron-Cobalt-type melt or Iron-Cobalt-
Vanadium-type melt with an increased manganese content
produces low melting point MnO-FeO on the surface of the
particle at the atomizing stage, which lowers the melting
point in the surface layer of the particle before it
solidifies and enhances the spherical particle formation of
the atomized particle as a result of increase in the surface
tension and drop in the viscosity.
The reasons for limiting the carbon content to 1.00% or
less by weight are set forth below. Generally, in the case of
Iron-Cobalt-type or Iron-Cobalt-Vanadium-type high saturation
magnetic flux density sintered material, it is necessary to
reduce the carbon content to the bear minimum from the view
point of ensuring an acceptable magnetic characteristics.
In particular, raw material powders which are offered to
the manufacture of Iron-Cobalt or Iron-Cobalt-Vanadium
sintered material by compression molding are required to have
its carbon content reduced to an extent lower than that of
ingot steel, from the view point of ensuring compressibility
in the compression molding as well as of magnetic
characteristics.
` -
`7
1 335759
On the other hand, it was found that in the manufacture
of Iron-Cobalt-type or Iron-Cobalt-Vanadium-type sintered
stainless steel, use of low carbon raw material does not lead
to improved injection moldability and does not offer any merit
with respect to corrosion resistance due to contamination with
carbon which is produced from organic binder at the debinding
stage. Moreover, it was found that the carbon resulting from
raw material powder as well as the carbon resulting from the
organic binder can be removed by performing sintering in
vacuum.
Thus, an attempt was made to improve powder properties of
the powder by increasing the carbon content of the powder,
rather than reducing the same. As a result, it was found
through the experiments that addition of the carbon content
improves the compactness of atomized powder for which high
pressure medium is utilized (for formation of the spherical
particle shape).
It is inferred that the atomized particle is shaped into
the spherical shape by dint of the decline in the oxygen
content of the melt which is caused by the carbon's getting
alloyed with constituents of stainless steel in the melt form
and also the-decline in the viscosity and melting point of the
melt. For example, it is learned that in stainless steel
powder obtained by atomizing the melt with circular water jet
injected at a 1,000 Kgf/cm2 water pressure having an average
particle diameter of 9.0 to 10.0 microns as shown in Table 8,
its apparent density and tap density are recognized to
increase in accordance with the increase in the alloyed carbon
content, hence the spherical particle formation has taken
place in the powder.
Furthermore, even in the case of compounds having
equivalent powder-to-binder ratio, it is recognized that the
viscosity temperature of the compound declines in consequence
of the increase in the alloyed carbon content of a 50% iron-
containing cobalt fine powder.
26 1 335759
However, the viscosity temperature of the compound
increases remarkably, if the alloyed carbon content of 50%
iron-containing cobalt powder exceeds the level of 1.00% by
weight, since the limit of deoxidation owing to the carbon-
with-oxygen reaction is lowered to below the limit of
deoxidation corresponding to amounts of silicon and manganese
alloyed in the melt whose amounts are limited in the melt,
thus causing the apparent density and tap density to drop on
the contrary, due to production of bubble-like particles in
which carbon monoxide gas is encapsulated.
Moreover, the alloyed carbon content of Iron-Cobalt-type
alloy powder or Iron-Cobalt-Vanadium-type alloy powder is
limited to 1.00% or less by weight, since in case the said
compound undergoes vacuum sintering and the maximum sintering
time which are ordinarily adopted industrially, namely, for 4
hours, the carbon content of the sintered material cannot be
reduced to 0.02% or less by weight, and, consequently, the
magnetic characteristics are deteriorated.
The reasons for limiting the silicon content, the
manganese content, the Manganese/Silicon ratio to 1.0% or less
by weight, 2.00% or less by weight, and 1.00 or higher,
respectively, are set forth below. The silicon content and
the manganese are limited to 1.00% or less by weight and 2.00%
or less by weight, respectively, which correspond to the
limits within which the saturated magnetic flux density of
Iron-Cobalt-type or Iron-Cobalt-Vanadium-type sintered
material is higher than that of sintered single constituent-
iron material.
For instance, it is learned that in the case of the said
alloy powder obtained by atomizing the melt with water jet as
shown in Table 8, its apparent density and tap density are
recognized to increase and the viscosity temperature to
decrease when the Manganese/Silicon ratio is 1.00 or higher,
hence the spherical particle formation is known to have taken
place in the powder.
27 l 3357~9
Furthermore, in cases where the Manganese/Silicon ratio
is 1.00 or higher, it is recognized that the singered density
has increased and the surface condition of the particle has
become fair. Therefore, the Manganese/Silicon ratio is
limited to 1.00 or higher.
It is inferred that if the manganese content of the melt
increases, MnO, which has a low melting point, is produced on
the surface of the particle in the atomizing stage, the
melting point of the particle's surface layer drops before the
particle solidifies, thus increasing the surface tension and
lowering the viscosity of the atomized particle, whereby
causing spherical particle formation.
The MnO is considered to be reduced into carbon monoxide
by the carbon content of the compound or the alloyed carbon
content of the melt, thus not obstructing sintering, so long
as the said compound undergoes vacuum sintering at about
1,400C.
On the contrary, silicon produces viscous silicon dioxide
(SiO2) on the surface of the particle in the atomizing stage
to make the particle shape irregular, and the silicon dioxide
can hardly undergoes reduction into carbon monoxide with
carbon in vacuum at a temperature of about l,400C, hence
sintering is obstructed. Therefore, the Manganese/Silicon
ratio is limited to 1.00 or higher for the purpose of
achieving spherical particle formation and a surface of the
particle which imparts a fair sinterability in the atomizing
stage.
The reasons for limiting the cobalt content to 15 to 60%
by weight are set forth below. As is the case with ingot
steel, cobalt imparts an effect of increasing the saturated
magnetic flux density (Bs) by means of replacing iron.
However, the cobalt content is limited to 15 to 60% by weight,
since the said effect is meager if the cobalt content is less
than 15% by weight or in excess of 60% by weight.
28
While the Iron-Cobalt-type alloy powder consists of the
above-mentioned specified composition, the effect can be
further enhanced by means of adding the following
constituents.
The reasons for limiting the vanadium content to 1.0 to
4.0~ by weight are set forth below.
As is the case with ingot steel, vanadium imparts an
effect of increasing the specific resistance of the sintered
material. However, the vanadium content is limited to 1.0 to
4.0% by weight, since the said effect is small if the vanadium
content is less than 1.0% by weight and the coercive force
(Hc) sharply increases, deteriorating the soft magnetism of
the material if the vanadium content exceed 4.0% by weight.
Although the melt alloyed with vanadium causes clogging
of the tundish nozzle with vanadium oxide (V2O3) which
precipitates on the tundish nozzle due to drop of the melt
temperature, it is possible to adjust the oxygen content of
the melt to below the V-O deoxidation limit, which reaches the
equilibrium at the melt temperature when the melt passes
through the tundish nozzle, and thus the nozzle clogging can
be avoided.
In this sense, it is beneficial from the economical
standpoint for the manufacture of alloy powder by atomizing to
get carbon, silicon and manganese alloyed with the melt either
singularly or in any combination at the content levels of
1.00% or less by weight for carbon, 1.00% or less by weight
for silicon, and 2.00% or less by weight for manganese.
More excellent Iron-Cobalt-type alloy powder can be
obtained by adding the following constituents.
The reasons for limiting the boron content and the
phosphorus content to 0.02 to 1.00% by weight and 0.05 to
1.00% by weight, respectively, are set forth below.
Although boron and phosphorus impart an effect of
producing atomized particles having the spherical particle
shape when they are added to the melt to get alloyed with
` -
1 335759
constituents therein either singularly or in combination, the
said effect is small if the boron content is less than 0.02%
by weight and if the phosphorus content is less than 0.05% by
weight and magnetic characteristics, in particular, the
m~xi mllm magnetic permeability (~max) and the coercive force
(Hc) of the sintered material are deteriorated. Therefore,
the boron content and the phosphorus content are limited to
0.02 to 1.00% by weight and 0.05 to 1.00% by weight,
respectively.
It can be inferred that the spherical particle formation
effect which is imparted by the alloying of boron and
phosphorus with the melt at the atomizing stage is attributed,
as was the case with manganese, to the drop in the melting
point and the decrease in the surface viscosity caused by
boron oxide and phosphorus oxide produced in the surface of
the particle, the increase in the sintered density is
attributed to the diffusion promoting effect due to alloying
of boron and phosphorus with the melt, and the presence of
excessive amounts of boron oxide and phosphorus oxide on the
surface of the particle obstruct sintering.
The reason for limiting the average particle size to 20
microns or less are set forth below. As Table 8 indicates,
the density and the magnetic characteristics of the final
sintered material produced from the said alloy powders are
strongly influenced by the average particle diameter of the
said alloy powders.
The average particle diameter is limited to 20 microns or
less, since the sintered material constructed with closed
pores which has a relative sintered density ratio of 92% or
higher cannot be produced and remarkable deterioration in
magnetic characteristics (the maxim saturation magnetic flux
density, m~x;mllm magnetic permeability, and the coercive
force) result if the average particle diameter exceeds 20
microns.
1 335759
(B) Injection mol~;ng compounds
(1) Compoun~ prepare~ from st~nless steel powder
The compounds of the present invention comprises
stainless steel powders which have the carbon content of 0.1
to 1.0% by weight and an average particle diameter of 20
microns or less and binder, and have excellent injection
moldability.
For the binder as applied to uses in the present
invention, organic binders whose principal constituents are
thermoplastics, or waxes, or mixtures thereof, and may be
added with plasticizer, lubricant, debinding promoting agents,
and/or inorganic binders, as the case may require.
As the thermoplastics, one or more kinds may be chosen
from among acrylic, polyethylene, polypropylene, and
polystyrene.
As the waxes, one or more kinds may be chosen from among
natural waxes, which are typically beewax, Japan wax, and
montan wax, and synthetic waxes, which are typically low-
molecular weight polyethylene, microcrystalline wax, and
paraffin wax.
The plasticizer may be selected on the basis of
combination with such waxes or waxes which constitute the
substantial part, and di-2-ethylhexyl phthalate (DOP), diethyl
phthalate (DEP), di-n-butyl phthalate (DHP), and the like may
be used.
As the lubricants, higher fatty acids, fatty acid amide,
fatty acid esters, and the like may be used, and, depending on
the need, waxes may be used as substitute lubricants.
As the debinding promoting agents, subliming substances
such as camphor may be added.
Although there is settled no specific limit to the ratio
of stainless steel powder to a binder, the binder content of
40 to 50% by volume to the total volume of the compound is
preferable.
31 l 335759
A batch-type kneader or a continuous-type kneader may be
used to mix and knead the metallic powder and the binder. A
pressurized kneader, a Banbury mixer, and the like favorably
suit for the batch kneader. A twin-screw extruder, and the
like favorably suit for the continuous kneader.
The compound for injection molding of the present
invention is obtained by pelletizing the kneaded material by a
pelletizer or a crusher (grinder).
(2) Compounds ~repared from silicon-contain; ng alloy powder
The compounds of the present invention comprises alloy
steel powder and a binder which have been described
hereinabove in detail, and have excellent injection
moldability.
As for specifics of the kind of binder to be used, the
amount of the binder, and the method of injection molding,
those set forth in the preceding Item (1) apply to this Item
(2).
t3) Co~poun~ prep~re~ from Jron-CDh~1t ~lloy powder
The compounds of the present invention comprises iron-
cobalt alloy steel powder and a binder which have been
described hereinabove in detail, and have excellent injection
moldability.
As for specifics of the kind of binder to be used, the
amount of the binder, and the method of injection molding,
those set forth in the preceding Item (1) apply to this Item
(3).
tC) Sintered mater;als obt~ined by sintering metallic powder
of the present invention
The high-density sintered stainless steel of the present
invention obtained by sintering the stainless steel powder as
set forth in tA)-(l) and (A)-(2) hereinabove has the carbon
content of 0.05% or less by weight and the bulk density ratio
32 l 335759
to true density (the relative sintered density ratio) of 92%
or higher.
The reasons for limiting the carbon content of the
sintered material to 0.05% or less by weight are set forth
below.
Influences of trace carbon, which is impurity, upon the
corrosion resistance can be clarified by a corrosion test
using organic acids.
The corrosion velocity of the sample immersed in a
boiling mixture of 40% acetic acid and 1% formic acid
solutions as shown in Fig. 7 which represents results of
elaborate studies made by the present inventors remarkably
increases when the carbon content exceeds 0.05% by weight.
Therefore, the carbon content of the sintered stainless steel
of the present invention is limited to 0.05% by weight.
The reasons for limiting the relative sintered density
ratio to 92% or higher are set forth below.
The relative sintered density ratio is an important
property value which has an immense influence upon the
corrosion resistance of the sintered material.
As Figs. 5 and 6 show, the corrosion resistance increases
remarkably when the relative sintered density ratio is 92% or
higher even in the case of Ferrite-type and Austenite-type.
That is due to the construction of the particle with
closed pores, as can be learned from the increase in the HI~
(hot isostatic press) density which is caused when the
relative sintered density ratio is 92% or higher, as shown by
Fig. 3. Therefore, the relative sintered density ratio of the
sintered stainless steel of the present invention is limited
to 92% or higher.
The stainless steel material of the present invention can
be manufactured in the following manner.
The stainless steel powder of the present invention and
an adequate organic binder are kneaded by a pressurized
kneader or the like, and a compound is thus prepared, and such
~ 1 335759
33
compound is injection molded by an injection molding apparatus
so that the injection molded part of a desired configuration
may be obtained. The obtained injection molded part is
subjected to a debinding treatment at a temperature between
200C and 600~C to obtain a debound part.
While the debinding treatment may be carried out in any
atmospherej so long as the atmosphere does not alter the shape
of the injection molded part, or causes the shape of the
injection molded part uninformly, even if it is altered, it is
preferable that, for instance, the debinding treatment is
carried out in a nonoxidating atmosphere or a reduced pressure
atmosphere.
The sintered stainless steel material of the present
invention can be manufactured by means of sintering the above-
mentioned debound part.
The high magnetic flux density sintered Iron-Cobalt alloy
material of the present inventionJ which is obtained by
sintering the Iron-Cobalt alloy powder described in (A)-(~)
hereinabove, has the carbon content of 0.02% or less by weight
and the bulk density ratio to true density of 92% or higher.
The reasons for limiting the carbon content of the
sintered material to 0.02% or less by weight are set forth
below. The presence of carbon, which is an impurity, gives an
adverse effect on magnetic characteristics, in particular, the
maximum magnetic permeability and the coercive force. The
carbon content is limited to 0.02% or less by weight, since
the m~X; ml~m magnetic permeability and the coercive force are
remarkably deteriorated when the carbon content exceeds 0.02%
by weight.
The reasons for limiting the relative sintered density
ratio to 92% or higher are set forth below. The relative
sintered density ratio is an important property value which
influences the saturated magnetic flux density (Bs), the
m~x;ml~m magnetic permeability (~max)~ and the coercive force
(Hc) of the sintered material.
34
1 335759
The saturated magnetic flux density, the maximum magnetic
permeability and the coercive force altogether are remarkably
deteriorated when the relative sintered density ratio is less
than 92%.
Based on the finding that the density does not increase
with the relative sintered density ratio being less than 92%
according to experiments relating to increases in the density
by HIP as shown in Fig. 9, the above-mentioned tendency is
attributed to the construction of the particle with closed
pores in it. Therefore, the relative sintered density ratio
is limited to 92% or higher, since the sintered material is
constructed with closed pores.
(D) The method of manufacturing sintered material
The above-mentioned sintered material of the present
invention is obtained preferably by the method as set forth
below.
A compound is obtained by mixing alloy steel powder,
stainless steel powder, or Iron-Cobalt alloy steel powder with
a binder, the obtained compound is injection molded, and then
the obtained injection molded part is sintered after it is
dewaxed.
In the above-mentioned steps, at least the first-stage of
the sintering step, is carried out in a reduced pressure
atmosphere.
The injection molding is carried out ordinarily by an
injection molding apparatus designed to handle plastics.
However, provisions against contamination or for extension of
the machine life can be made, depending on the need, by
carrying out an anti-abrasion treatment of the internal
surface of the machine with which the raw material comes in
contact.
The obtained injection molded part is subjected to a
debinding treatment in open atmosphere or neutral or reducing
gas atmosphere.
1 335759
In the steps of injection molding the compound for the
injection molding use, debinding the injection molded part and
sintering the debound part, it is necessary that at least the
first-stage of the sintering step is carried out in a reduced
pressure atmosphere.
Here "the first-stage of the sintering step" means the
process prior to which the density ratio of the sintered
material reaches about 90%.
The reason for that is that when the density ratio of the
sintered material exceeds 90%, a great majority of pores in
the sintered material become closed pores and it becomes
difficult to remove from within the pores in the sintered
material the carbon monoxide gas generated by reduction and
decarbonizing reaction which occur in a reduced pressure
atmosphere mentioned later, and thus the said reaction is kept
from progressing efficiently.
As for the atmosphere in which the sintering is carried
out, the atmosphere is to be capable to enabling reduction of
oxides of chromium, etc., which obstruct diffusion of atoms
during the sintering step, and also capable of removing carbon
contained in a large quantity in the debound parts after the
debinding treatment.
Hydrogen and a reduced pressure atmosphere are cited as
those meeting the above-mentioned requisite conditions, as is
the case with the manufacture of the ordinary sintered
stainless steel material.
Nevertheless, since the reduction and decarbonization in
a hydrogen atmosphere progress according to the following
equations, respectively:
MO + H2---------~ M + H20 (M: Metal) ....... ....Reduction
C + H20 -----~ CO + H2 (C: Solid solution carbon)
....... Decarbonization
The lower is PH20/PH2, the faster progresses the
reaction.
-
1 335759
36
The higher is PH2O/PH2, the faster progresses the
decarbonization.
Therefore, it is difficult to cause both reactions
progress efficiently simultaneously. Particularly, in case of
stainless steel, for instance, which contains chromium oxides
which are hardly reducible and the debound material contains a
high carbon value, it is not beneficial to utilize hydrogen
atmosphere.
On the other hand, reduction and decarbonization in a
reduced pressure atmosphere progress simultaneously as shown
by the following equation, and by means of removing carbon
monoxide gas as an exhaust gas, the reaction can be caused to
progress efficiently.
MO + C ~ M + CO ............ Reduction and
decarbonization
Moreover, since the amounts of oxygen and carbon
contained in the final sintered material tend to be lower
under a reduced pressure, compared with a hydrogen atmosphere,
sintering is performed under reduced pressure for th
manufacturing method according to the present invention.
For the purpose of causing the reduction and
deoxidization to progress efficiently in chromium oxides, the
pressure of reduced pressure atmosphere is preferably 0.01
torr or lower, and the temperature range is preferably between
1,100C and 1,350C.
Since a reduced pressure atmosphere is needed only during
the stage in which reduction and decarbonization are in
progress, in the stages following completion of the said
reactions, it is preferable that the atmosphere under reduced
pressure be replaced by an nonoxidating atmosphere, such as
inert gas (e.g. nitrogen, argon) atmosphere and a low dew
point hydrogen atmosphere as a protective atmosphere.
As mentioned above, it is possible to manufacture low-
carbon and low-oxygen sintered stainless steel material having
-
37 1 335759
excellent corrosion resistance efficiently by means of
performing sintering under reduced pressure.
38 l 335759
FXAMPT FS
Examples of the present invention are given below by way
of illustration, and not by way of limitation.
Example 1 and Comparative F.xample 1
Stainless steel powders added with carbon and comprising
the composition as shown in Table 1 was prepared by an
atomizing method using water. Results of studies made on
powder characteristics of those steel powders are shown in
Table 2.
T~hle 1.
No.Chemical composition (%) Remarks
C Si Mn P S Ni Cr Mo
Example 1 10.11 0.89 0.18Ø02 0.01 14.1 17.8 2.5 Corres-
2 0.25 0.85 0.20 0.20Ø01 14.2 18.0 2.5 ponds to
3 0.50 0.84 0.19 0.02 0.01 14.1 17.8 2.4 SUS316,
4 0.93 0.89 0.16 0.02 0.01 13.9 17.9 2.4 JIS
Comparative 5 1.20 0.87 0.19 0.02 0.01 14.0 17.8 2.4
Example 1 6 0.02 0.86 0.18 0.02 0.01 14.1 17.9 2.5
It is obviously learned from Table 2 that the steel
powders No. 1 through No. 4 prepared according to the present
invention have their tap density and bulk density increased,
have their specific surface area decreased, and have their
particles shaped into the spherical form, despite that all of
the powders are generally mutually equivalent with respect to
the average particle diameter and the particle size
distribution.
While the above-mentioned powder characteristics
represent an indirect evaluation of the injection moldability,
results of direct evaluation of such compounds that were
actually obtained by kneading the steel powders with an
39 ~ 33~59
organic binder added by 46% by volume are set forth
additionally in Table 2.
The said evaluation shows a temperature levels at which a
certain prescribed viscosity is learned to have been reached
by measuring the viscosity of compounds prepared by adding to
each samples of steel powder an equal amount of wax-type
binder and kneading them together. The lower is the
temperature, the lower becomes the viscosity. Through the
above-mentioned evaluation of compounds, it was found that the
steel powder No. 1 through No. 4 which were prepared according
to the present invention exhibit effective declines in the
viscosity of the compound, alike the changes in the powder
characteristics, whereby it is verified that the stainless
steel powders of the present invention excel in the injection
moldability.
Furthermorer a smaller quantity of the organic binder
than that of the steel powder in Comparative Examples 5 and 6
was sufficient to obtain a compound having the equal viscosity
level as that in the same Comparative Examples.
The compound used as the sample for viscosity measurement
was injection molded into specimens of 40 mm width, 20 mm
length and 2 mm thickness at 145C injection noz~le
temperature and 30C mold temperature. The injection molded
part was subjected to a debinding treatment in which it was
left to stand for 1 hour after having been heated to 600C
from room temperature at a rate of 10C rise per hour.
The debound part was sintered at 1,300C for 4 hours
under 0.0001 torr reduced pressure.
The carbon content of the sintered part is additionally
shown in Table 2. In the case where the steel powder of the
present invention were used, the carbon content could be
reduced to its bare m; n; mllm . However, in the case where the
reference steel powder No. 5 containing 1.2% carbon could not
have its carbon content reduced sufficiently in its sintered
form.
1 335759
Fx~mple 2 and Comparative Ex~le 2
The stainless steel powders having the composition as
shown in Table 3 were prepared by the water atomizing method.
Results of studies on powder characteristics of those
steel powders are summed up in Table 4. Next, results of
studies on sintered parts which were prepared under the same
conditions, except for the sintering condition, in Example 1
are shown in Table 4. The sintering was performed in two
steps, firstly for 2 hours at 1,135C under reduced pressure
of 0.0001 torr, and secondly immediately following the first
step, for another 2 hours at 1,350C in argon gas atmosphere
maintained at 1.02 atm, with argon gas introduced into the
same space.
It is learned from Table 3 and Table 4 that the steel
powders of the present invention excel in th injection
moldability and give sintered parts whose characteristics are
comparable with the conventional products over an extensive
composition range of stainless steel.
According to the present invention, stainless steel
powders having the spherical particle shape which are suitable
for injection molding are provided, production of sintered
stainless steel parts of complex configurations are readily
realized, whereby the scope of application of sintered
stainless steel can be enlarged.
Fxample 3 and Compar~tive Example 3
Presented in Table 5 through Table 7 are examples of the
present invention, along with a Comparative Example, for the
sintered material prepared by sintering Ferrite-type stainless
steel powder, Austenite-type stainless steel powder, and the
stainless steel powder of the present invention for high-
density sintering use obtained by the water atomizing method.
Ferrite-type stainless steel alloy powder and Austenite-
type stainless steel powder having their respective chemical
41 l 335759
compositions were prepared by perpendicularly dripping through
an orifice nozzle constructed of a refractory material
provided on the bottom of a tundish the melt of ingot Ferrite-
type stainless steel alloy and Austenite-type stainless steel
alloy manufactured by a high frequency induction furnace, and
atomizing the dripped melt by applying a conical water jet of
1,000 Kgf/cm2 pressure encircling the axis of the drip and
narrowing in the downward direction.
The obtained stainless steel alloy powder was analyzed on
a Microtrack grading analyzer for the average particle
diameter (the particle diameter of the particle size group
with whose addition the cumulative volume measured from the
finer particle size group reaches the 50% level of the total
volume), the apparent density and the tap density.
Next, the viscosity temperature (the temperature at which
the viscosity reaches 100 poise) was measured by extruding
through a die of 1 mm dia~eter and 1 mm length under a 10 kg
load provided on a flow tester a compound prepared by kneading
by a pressurized kneader each one of those alloy powders with
wax-type organic binders, the blending ratio of the latter
being 46% by volume.
The same compound as used as the sample for viscosity
measurement was injection molded into specimens of 40 mm
width, 20 mm length and 2 mm thickness at 145C injection
nozzle temperature and 30C mold temperature. The injection
molded part was subjected to a dewaxing treatment in which it
was left to stand for 1 hour after having been heated to 600C
from room temperature at a rate of 10C rise per hour.
The dewaxed part was sintered at 1,300C for 4 hours
under 0.0001 torr pressure.
The obtained sintered part was measured for the specific
gravity by means of weighing samples submerged in water, and
the relative sintered density ratios were calculated.
Other sintered materials prepared under the same
conditions were analyzed for their carbon contents. Using
1 3357~9
42
other sintered materials as samples, experiments were carried
out to determine increases in the density by HIP treatment as
shown in Fig. 3, and corrosion tests as shown in Fig. 4
through Fig. 7 were carried out to determine the corrosion
resistance. Furthermore, cutting tests were carried out on
other sintered materials as shown in Fig. 8.
As are obvious from No. 1 through No. lg of Example 3 in
Table 5 and No.55 through No. 69 of Example 3 in Table 7,
according as the Manganese/Silicon ratio increased, the
apparent density and the tap density registered high values,
and the viscosity of the compound registered low values (the
lower is the temperature, the lower becomes the viscosity), in
the case of Ferrite-type stainless steel powder which has an
average particle diameter of 20 microns or less and a chromium
content of 8.0 to 30.0% by weight, provided that it either
does not contain a substantial amount of carbon (0.01 to 0.02%
by weight of carbon) or, in case it contains carbon, has a
composition of 1.20% by weight of carbon, 0.20% or more by
weight of silicon and 1.00 or higher Manganese/Silicon ratio,
and in the case of Austenite-type stainless steel powder which
has an average particle diameter of 20 microns or less and has
a composition of 8.0 to 30.0% by weight of chromium and 8.0 to
22.0% by weight of nickel. Thus, it is known that spherical
particle formation has occurred in the powder and it has
acquired excellent injection moldability. Sintered material
which has the carbon content of 0.05% or less by weight and a
relative sintered density ratio of 92% or more was obtained.
As are obvious from No. 20 through No. 38 of Example 3 in
Table 5, No. 50 through No. 54 of Example 3 in Table 6, and
No. 70 through No. 88 of Example 3 in Table 7, the stainless
steel powders of the present invention which contain nickel,
molybdenum, copper, tin, sulfur, selenium and tellurium
singularly or in any combination are atomized powders which
are in the spherical particle form and exhibit excellent
injection moldability and gave sintered material whose carbon
` -
43 ~ 335759
content as sintered is 0.01% by weight and relative sintered
density ratio of 92% or higher.
As are obvious from No. 50 through No. 54 of Example 3 in
Table 6, in the case of nickel-containing Ferrite-type
stainless steel powder of the present invention having an
average particle diameter of 20 micron or less, its apparent
density and tap density increase with increases in the average
particle diameter and the viscosity of the compound decreases,
although its relative sintered density ratio decreases. With
an average particle diameter less than 20 microns, sintered
material having a relative sintered density ratio of 92% or
higher and an excellent corrosion resistance is obtained. The
said relationship between the average particle diameter and
the relative sintered density ratio also applies to Austenite-
type stainless steel powder and sintered material obtained
therefrom.
Fig. 3 shows a relationship between the relative density
ratio of sintered material, which has undergone an HIP
treatment carried out at 1,350 C for 1 hour in argon
atmosphere maintained at 100 Kgf/cm2, and the relative density
ratio after the said HIP treatment, which was measured on
samples prepared by injection molding compound made from
Ferrite-type and Austenite-type stainless steel powders shown
in No. 8 through No. 61 of Example 3, which are examples of
the present invention, in Table 5 and Table 7, and then
sintering the injection molded part at a temperature between
1,250 and 1,350 C for 4 hours.
As is obviously learned from the Figure 3, at a relative
density ratio of 92% or higher, intercommunicating pores in
the sintered material become closed pores and the relative
density ratio after the HIP treatment is further improved.
Fig. 4 shows results of a corrosion resistance test
performed in a boiling 60% nitric acid solution on sintered
materials constructed with closed pores and having a relative
density ratio of 95%, which was obtained by injection molding
44
1 335759
compound prepared from Ferrite-type chromium-containing steel
powder which has an average particle diameter of 8.0 to 9.0
microns and has the composition of 5.0 to 33.0% by weight of
chromium, 0.02 to 0.70% by weight of silicon, 1.00% by weight
of manganese, and 0.01% by weight of sulfur, the balance being
substantially iron, and vacuum sintered at 10-4 torr at 1350C.
As is obvious from the Figure 4, the corrosion velocity
remarkably decreases at a chromium content level of 8.0% or
more, and there is provided no effect of improving the
corrosion resistance even if the chromium content exceeds
30.0% by weight.
Fig. 5 shows results of a corrosion resistance test
performed in a 1% sulfuric acid solution maintained at 25 C
on sintered material having a relative density ratio of 90% or
higher, which was obtained by injection molding compound
prepared from Ferrite-type stainless steel powder which has an
average particle diameter of 8.0 to 9.0 microns and has the
basic alloy composition of 18.23% by weight of chromium, 0.02%
by weight of carbon, 0.70% by weight of silicon, 1.00% by
weight of manganese, 0.02% by weigh of phosphorus, and 0.01%
by weight of sulfur, the balance being substantially iron,
added with 0.8 to 5.0% by weight of nickel, 0.2 to 5.0% by
weight of molybdenum, and 0.2 to 6.0% by weight of copper
either singularly or in any combination, and vacuum sintering
the injection molded part at a temperature between 1,250 C
and 1,350 C for 4 hours at 10-4 torr.
As is obvious from the Figure 5, the corrosion velocity
decreases remarkably at a relative density ratio of 92% or
higher due to the particle construction with closed pores
which occur at such levels.
With the relative density ratio being at 95% due to
closed pores, the corrosion velocity remarkable deceases at
the nickel content of 1.0% or more by weight, the molybdenum
content of 0.3% or more by weight, the copper content of 0.5%
or more by weight singularly or in any combination, although
=~ = ~
1 335759
there is provided no effect of improving the corrosion
resistance, even if the nickel content exceeds 4.0~ by weight,
the molybdenum content exceeds 4.0% by weight, or the copper
content exceeds 5.0% by weight.
Fig. 6 shows results of a corrosion resistance test
performed with a boiling 60% nitric acid solution on sintered
material having a relative density ratio of 90% or higher,
which was obtained by injection molding compound made from
Austenite-type stainless steel powder listed as No. 61 of
Example 3, which is an example of the present invention, in
Table 7, and vacuum sintering the injection molded part at a
temperature between 1,250 C and 1,350 C for 4 hours at 10-4
torr
As is obvious from the Figure 6 Austenite-type stainless
steel has its corrosion velocity remarkably decreased at a
relative density ratio of 92% or higher, and the material. is
constructed with closed pores.
Fig. 7 shows results of a corrosion resistance test
performed with a boiling mixture of 40% acetic acid and 1%
formic acid on sintered materials have a relative density
ratio of 95% which was obtained by injection molding compound
made from Austenite-type stainless steel powder which has an
average particle diameter of 8.0 to 9.0 microns and has the
basic alloy composition of 18% by weight of chromium, 14% by
weight of nickel, 2.5% by weight of molybdenum, 0.70% by
weight of silicon, 1.00% by weight of`manganese, 0.02% by
weight of phosphorus, and 0.01% by weight of sulfur, the
balance being substantially iron (the carbon content as
sintered being 0.03% by weight) added with 4.0 to 25.0% by
weight of nickel, 0.3 to 5.0% by weight of molybdenum, 0.4 to
6.0% by weight of copper, and 0.01 to 0.08% by weight of
carbon, either singularly or in any combination, and vacuum
sintering the injection molded part at 1,350 C for 4 hours at
10-4 torr.
-
46 l 335759
As is obvious from the Figure 7, the corrosion velocity
remarkably decreases at a nickel content level of 8.0~ or
more, the molybdenum content of 0.3% or more by weight, the
copper content of 0.5% or more by weight, the carbon content
of 0.05% or less by weight either singularly or in any
combination, and there is provided no effect of improving the
corrosion resistance even if the nickel content exceeds 22.0%
by weight, the molybdenum content exceeds 4.0% by weight and
the copper content exceeds 5.0% by weight.
Fig. 8 shows results of a dry drilling /cutting test
performed with a 1 mm diameter drill constructed of SKH-9
revolving at a revolving velocity of 410 m/s on sintered
material, which was obtained by injection molding compound
made from Ferrite-type stainless steel powder having an
average particle diameter of 8.0 to 9.0 microns and the
composition of 0.70% by weight of silicon, 1.00% by weight of
manganese, 18% by weight of chromium, and ~ustenite-type
stainless steel powder having an average particle diameter of
8.0 to 9.0 microns and the composition of 0.70% by weight of
silicon, 1.00% by weight of manganese, 18% by weight of
chromium, and 14% by weight of nickel, both of which
constitution the basic alloy composition, added with 0.03 to
2.5% by weight of tin, 0.01 to 0.60~ by weight of sulfur,
0.025 to 0.25% by weight selenium, and 0.025 to 0.25% by
weight of tellurium, either singularly or in any combination,
and vacuum sintering the obtained injection molded part at
1,350 C for 4 hours at 10-4 torr.
As is obvious from the Figure 8, the cutting torque
remarkably decreases at the tin content of 0.05% or more by
weight, the sulfur content of 0.02% or more by weight, the
selenium content of 0.05% or more by weight, the tellurium
content of 0.05% or more by weight, either singularly or in
any combination, although there is provided no effect of
improving the cutting torque even if the tin content exceeds
2.00% by weight, the sulfur content exceeds 0.50% by weight,
-
47 1 335759
the selenium content exceeds 0.20% by weight and the tellurium
content exceeds 0.20% by weight.
As been described in detail in the foregoing, according
to the present invention, there is provided stainless steel
powders whose injection moldability and sinterability are
improved by achieving spherical particle formation and
modifying surface conditions of the particle by means of
atomizing the melt whose composition is so adjusted that the
carbon content, the silicon content and the Manganese/Silicon
ratio will become 1.20% or less by weight, 0.20% or more by
weight, and 1.00 or higher, respectively, from its basic melt
composition of 8.0 to 30% by weight of chromium and 8.0 to
22.0% by weight of nickel, to obtain fine powder of an average
particle diameter of 20 microns or less. Furthermore, there
is provided through use of the said stainless steel powder a
high-density, high corrosion resistance sintered stainless
steel material having a relative density ratio of 92% or
higher and the carbon content of 0.05% or less by weight.
According to the present invention, there is provided a
stainless steel powder, from which a superior sintered
material with remarkable improved corrosion resistance which
has a relative density ratio of 92~ or higher and a carbon
content of 0.05% or less by weight is obtained, and also
stainless steel powders for obtaining the said sintered
material by atomizing into fine powder of an average particle
diameter of 20 microns or less the above-mentioned melt, with
which 1.0 to 4.0~ by weight of nickel is alloyed in the case
of Ferrite-type, and one or both of 0.3 to 4.0% by weight of
molybdenum and 0.5 to 5.0% by weight of copper in the case of
Ferrite-type or Austenite-type.
Furthermore, according to the present invention, there is
provided a stainless steel powder, from which a superior
sintered material with remarkable improved cutting
characteristics which has a relative density ratio of 92% or
higher and a carbon content of 0.05% or less by weight is
-
48 1 33~7~9
obtained, and also stainless steel powders for obtaining the
said sintered material by atomizing into fine powder of an
average particle diameter of 20 microns or less the above-
mentioned melt, with which one or more of 0.05 to 2.00% by
weight of sulfur, 0.05 to 0.20% by weight of selenium, 0.05 to
0.20% by weight of tellurium is or are alloyed with the said
melt in case of Ferrite-type or Austenite-type.
Fxample 4 and Comparative F~xample 4
Presented in Table 8 is an example of the present
invention, along with a Comparative Example, for high
saturation magnetic flux density sintered material prepared by
sintering Iron-Cobalt-type alloy powder and Iron-Cobalt-
Vanadium-type alloy powder, both of which are for high
saturation magnetic flux density sintering use, obtained by
the water atomizing method.
Iron-Cobalt-type and Iron-Cobalt-Vanadium-type alloy
powder having their respective chemical compositions shown in
Table 8 were prepared by perpendicularly dripping through an
ori~ice nozzle constructed of a refractory material provided
on the bottom of a tundish the melt of ingot Iron-Cobalt-type
and Iron-Cobalt-Vanadium-type steel manufactured by a high
frequency induction furnace, and atomizing the dripped melt by
applying a conical water jet of 1,000 Kgf/cm2 pressure
encircling the axis of the drip and narrowing in the downward
direction.
The obtained alloy powder was analyzed on a Microtrack
grading analyzer for the average particle diameter (the
particle diameter of the particle size group with whose
addition the cumulative volume measured from the finer
particle size group reaches the 50% level of the total
volume), the apparent density and the tap density.
Next, the viscosity temperature (the temperature at which
the viscosity reaches 100 poise) was measured by extruding
through a die of 1 mm diameter and 1 mm length under a 10 kg
.
-
49 l 335759
load provided on a flow tester a compound prepared by kneading
by a pressurized kneader each one of those alloy powders with
wax-type organic binders, the blending ratio of the latter
being 46% by volume.
Then, the compound was injection molded into rings of 53
mm outer diameter, 41mm inner diameter, and 4.7 mm height by
an injection molding apparatus at an injection molding
temperature of 150 C. The injection molded part was
subjected to a dewaxing treatment in nitrogen atmosphere in
which it was heated up to 600 C at a rate of 7.5 C rise per
hour and left to stand for 30 minutes.
Following the said dewaxing step, the dewaxed material
was sintered in hydrogen atmosphere in which it was heated up
to 700 C at a rate of 5 C rise per minute and left to stand
for 1 hour at 700 C, for another hour at 950 C and the
following 2 hours at 1,350 C. Up to the end of the 950 C
stage, the dew point was controlled to +30 C, and beyond the
said end point, the dew point was controlled to -20C or
lower.
The obtained sintered material was measure for the
specific gravity by means of weighing samples submerged in
water, and the relative sintered density ratios were
calculated.
Moreover, samples prepared under the same conditions had
wires wound around them and were measured by a self-
registering magnetic flux recorder for magnetic
characteristics. Results of the said measurement are shown in
Table 8.
As are obvious from No. 1 through No. 18 of Example 4 in
Table 8, in the case of Iron-Cobalt-type alloy powder of the
present invention having an average particle diameter of 20
micron or less and the cobalt of 10 to 60% by weight whose
composition comprises 1.00% or less by weight of carbon, 1.00%
or less by weight of silicon, 2.00% or less by weight of
l 335759
manganese, 1.00 or higher Manganese/Silicon ratio, its
apparent density and tap density increase with increases in
the manganese content, and the Manganese/Silicon ratio and the
carbon content.
Moreover, the compound prepared from the above-mentioned
powders exhibit low viscosity values (the viscosity decreases
with temperature drops), whereby it is learned that spherical
particle formation has been achieved in the powders, hence
they have excellent injection moldability.
Sintered material which has the carbon content of 0.02%
or less by weight and the relative sintered density ratio of
95% was obtained. Hence, sintered material having excellent
magnetic characteristics (the saturation magnetic flux
density, the maximum magnetic permeability, and the coercive
force) can be prepared.
As are obvious from No. 19 through 23 of Example 4 in
Table 8, in the case of Iron-Cobalt-~anadium-type alloy powder
of the present invention having the vanadium content of 1.0 to
4.0% by weight, atomized powders which are in the spherical
particle form and exhibit excellent injection moldability
could be manufactured by increasing the silicon content and
the manganese content, and controlling the Manganese/Silicon
ratio to 1.00 or higher by way of alloying vanadium with the
melt with a view to preventing clogging of the nozzle with the
melt.
A sintered material having the carbon content of 0.01% by
weight and a relative sintered density ratio of 95% which
exhibits excellent magnetic characteristics (Bs, ~max, Hc) can
be obtained.
As is obvious from No. 24 through No. 33 of Example 4 in
Table 8, in the case of Iron-Cobalt-type and Iron-Cobalt-
Vanadium-type alloy powders of the present invention whose
composition is 0.02 to 1.0% by weight of boron and 0.05 to
1.00% by weight of phosphorus, the apparent density and the
tap density increase by dint of alloying of boron and
51 1 335759
phosphorus with the melt and the viscosity of the compound
prepared therefrom drops, and the spherical particle formation
and the injection moldability are further improved, compared
with the case in which boron and phosphorus are not added (No.
3 of Example 4). A sintered material which has the carbon
content as sintered of 0.01% by weight and has more excellent
magnetic characteristics (Bs, ~max, Hc) with a high
compactness, i.e., a relative sintered density ratio of 96%
can be obtained.
As is obvious from No. 34 through No. 43 of Example 4, in
Table 8, in the case of Iron-Cobalt-type alloy powder of the
present invention having the average particle diameter of 20
microns or less, the apparent density and tap density of the
said alloy powder increase with increases in the average
particle diameter, the viscosity of the compound made
therefrom.decrease with increases in the average particle
diameter, although the relative sintered density ratio and,
accordingly, magnetic characteristics (Bs, ~max, Hc) decrease
with increases in the average particle diameter.
The same tendency applied to Iron-Cobalt-Vanadium-type
alloy powder.
Sintered material having excellent magnetic
characteristics can be obtained at the average particle
diameter level of 20 microns or lower.
52 1 335759
Fig. 9 shows a relationship between the relative density
ratio of sintered material, which has undergone an HIP
treatment carried out at 1,350C for 1 hour in argon
atmosphere maintained at 100 kgf/cm2, and the relative density
ratio after the said HIP treatment, which was measured on
samples prepared by injection molding compound made from Iron-
Cobalt-type alloy powder shown in No. 3 of Example 4, which is
an example of the present invention, in Table 8. As is
obviously learned from the Figure 9, at a relative density
ratio of 92% or higher, pores in the sintered material become
closed pores and the relative density ratio after the HIP
treatment is further improved.
53
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Table 3
No. Che~ical Analysis (X) Re-arks
C Si Mn P S Ni Cr
Exauple 2 7 0.22 1.28 0.21 0.02 0.01 12.8 19.6 Corresponds to SUS 304, JIS
8 0.45 1.32 0.23 0.02 0.01 12.7 19.7 Corresponds to SUS 304, JIS
9 0.19 0.98 0.15 0.02 0.01 - 12.8 Corresponds to SUS 410, JIS
0.52 0.99 0.13 0.02 0.01 - 12.8 Corresponds to SUS 410, JIS
Co-parative11 1.20 1.25 0.21 0.02 0.01 14.0 19.8 Corresponds to SUS 304, JIS
Exa~ple 2 12 0.02 0.95 0.13 0.02 0.01 - 12.9 Corresponds to SUS 410, JIS
Teble 4
Particle Size Distribution Tap Apparent Specific Viscosity Carbon Content
Density Density Surface Temperature of Sintered
D+~ Dso D_ ~ MV (g/cc) (g/cc) Area (~) Body
No. (ym) (~m) (~m) D+~/D50 D50/ D ~ (~m) lOmin (m2/g) lOOP ( % )
7 19.0 10.6 5.4 1.79 1.96 12.6 3.30 1.93 0.492 147.3 0.02
8 18.9 10.4 5.2 1.82 2.00 12.4 3.42 2.36 0.457 134.2 0.03
Example 2
9 16.7 9.8 4.9 1.70 2.00 11.2 3.64 2.23 0.412 112.6 0.02
16.5 9.7 4.8 1.70 2.02 11.0 3.77 2.59 0.401 101.3 0.03
Comparative 11 19.2 10.5 5.3 1.83 1.98 12.5 3.12 1.79 0.501 160.1 0.02
Example 2
12 16.6 9.8 4.9 1.69 2.00 11.2 3.42 2.12 0.434 133.7 0.01
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No. Cheaical Co-position t~t X) ~pparent Tap Average Co~poundSintered Carbon Corrosion Reurks
'` ib Density Particle YiscosibDensity Content of Velositv of
Diuleter Te~perature Ratio Sintered Sintered
Nateri~ll Yaterial
O C Si Mn P S Cr Ni AQ N ~Si Wc-') Wce') (~a) (-C)lOOP (S) (~ W2~ain)
0.43 0.010 0.71 0.23 0.02 0.01 18.1 0.80 0.004 0.03g 0.3 2.14 3.40 8.5 125.0 91 0.010 35 C ~,Li.~, Exa~pie
51 0.30 0.010 0.70 1.00 0.02 0.01 18.0 1.00 0.004 0.057 1.4 2.34 3.66 ~.7 101.5 95 0.010 10
52 0.36 0.020 0.70 1.00 0.02 0.01 18.2 4.00 0.004 0.061 1.4 2.68 4.08 12.5 100.0 94 0.010 0.4
53 0.35 0.020 0.70 1.00 0.02 0.01 1~.0 1.00 0.004 0.044 1.4 2.75 4.10 19.5 g8.5 92 0.010 20
54 0.37 0.010 0.70 1.00 0.02 0.01 18.3 1.00 0.004 0.048 1.4 2.80 4.15 21.5 98.0 91 0.010 50 C . .dti;~, Exa~le
* Corroslon test condition; 25 C, lX H2So~ solution x 8hr
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63 1 3 3 5 7 5 9
As have been described in detail in the foregoing,
according to the present invention, there is provided a
sintered material having relative density ratio of ~2% or
higher whose injection moldability and sinterability are
improved by achieving spherical particle formation by means of
atomizing the melt whose composition is so adjusted that the
carbon content, the silicon content, the manganese content and
the Manganese/Silicon ratio will become 1.00% or less by
weight, 1.00% or less by weight, 2.00% or less by weight and
1.00 or higher, respectively from Iron-Cobalt-type and Iron-
Cobalt-Vanadium-type alloy melts, to obtain fine powder of an
average particle diameter of 20 microns or less.
According to the present invention, there are provided
Iron-Cobalt-type and Iron-Cobalt-Vanadium-type alloy powders
with remarkably improved injection moldability and
sinterability by dint of improved spherical particie formation
by atomizing into powders of the average particle diameter of
20 microns or less the melt with which one or both of 0.02 to
1.00% by weight of boron and 0.05 to 1.00% by weight of
phosphorus is or are alloyed.
Moreover, there is provided a sintered material which has
a relative density ratio of 92% or higher and excellent
magnetic characteristics by using the above-mentioned powders.
