Note: Descriptions are shown in the official language in which they were submitted.
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MIXED POWDER FOR POWDER METALLURGY, METHOD OF
MANUFACTURING SAME, AND METHOD OF MANUFACTURING
IRON-BASED POWDER SINTERED BODY
TECHNICAL FIELD
[0001] The disclosure relates to a mixed powder for powder metallurgy
obtained by mixing an iron-based powder, an alloying powder, a machinability
improvement powder, and a lubricant and suitable for sintered parts of
vehicles and the like and a method of manufacturing the same, and a method
of manufacturing an iron-based powder-made sintered body by forming and
sintering the mixed powder. The disclosure is particularly intended to
improve the machinability of an iron-based powder-made sintered body.
BACKGROUND
[0002] The development of powder metallurgy technology has enabled parts
with high dimensional accuracy and complex shape to be manufactured in near
net shape. Products made using powder metallurgy technology are thus
utilized in various fields. Powder metallurgy technology has a feature of
high shape flexibility, as a die of the desired shape is filled with a powder
which is then formed and sintered. Hence, powder metallurgy technology is
often used for machine parts having complex shape such as gears.
[0003] In the field of iron-based powder metallurgy, a die of a predetermined
shape is filled with an iron-based mixed powder obtained by mixing an
iron-based powder (metal powder) with an alloying powder such as a copper
powder or a graphite powder and a lubricant such as zinc stearate or lithium
stearate, which is then press-formed into a compact and subjected to a
sintering process to obtain a sintered part. The sintered part obtained in
this
way typically has high dimensional accuracy. In the case of manufacturing a
sintered part for which extremely strict dimensional accuracy is required,
cutting work needs to be performed after sintering. The cutting work
includes processes such as lathe turning and drill boring at various cutting
speeds.
[0004] The sintered part has high porosity, and so has a high cutting
resistance as compared with a metal material processed by melting.
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Accordingly, to improve the machinability of the sintered body. Pb, Se, Te, or
the like has been conventionally added to the iron-based mixed powder in
powder form or in the form of being alloyed with the iron powder or
iron-based powder.
However, the use of Pb has a problem in that, since Pb has a low
melting point of 330 C, Pb melts in the sintering process but does not
dissolve in iron, and so it is difficult to uniformly disperse Pb in the
matrix.
The use of Se or Te has a problem in that the sintered body is embrittled and
as a result the mechanical property of the sintered body degrades
significantly.
[0005] Besides, due to poor thermal conductivity of the aforementioned pores,
when the sintered body is cutting, frictional heat during the cutting
accumulates and as a result the surface temperature of the tool tends to
increase. The cutting tool thus wears easily and has a shorter life. This
leads to the problem of an increase in cutting work cost and an increase in
manufacturing cost of sintered parts.
[0006] In view of these problems, for example, Patent Literature (PTL) 1
describes an iron powder mixture for sintered body production obtained by
mixing an iron powder with 0.05% to 5% by weight a fine manganese sulfide
powder of 10 um or less.
The technique described in PTL 1 is supposed to improve the
machinability of the sintered material without significant dimensional changes
and strength deterioration.
[0007] PTL 2 describes an iron-based sintered body manufacturing method of
adding alkaline silicate to an iron-based powder.
The technique described in PTL 2 is supposed to improve free
machinability without significant dimensional changes and strength
deterioration, by adding 0.1% to 1.0% by weight alkaline silicate.
[0008] PTL 3 describes an iron-based mixed powder for powder metallurgy
that is mainly composed of an iron powder and contains 0.02% to 0.3% by
weight a CaO-A1203-Si02 complex oxide powder (ceramic powder) of 50 um
or less in average particle size having an anorthite phase and/or a gehlenite
phase.
The technique described in PTL 3 is supposed to prevent tool material
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degradation and improve machinability, as the ceramic powder exposed on the
worked surface adheres to the tool surface and forms a tool protective film
(belag layer) during cutting.
[0009] PTL 4 describes an iron-based mixed powder obtained by mixing an
iron-based powder, an alloying powder, a machinability improvement powder
including a manganese sulfide powder and at least one of a calcium phosphate
powder and a hydroxyapatite powder, and a lubricant. According to PTL 4,
the manganese sulfide is effective in refinement of chips, whereas the calcium
phosphate powder and the hydroxyapatite powder have an effect of preventing
or suppressing tool surface alteration by adhering to the tool surface and
forming a belag layer during cutting.
The technique described in PTL 4 is thus supposed to improve
machinability without degradation of the mechanical property of the sintered
body.
[0010] PTL 5 describes an improvement in mechanical workability such as
machinability by adding, to iron or an iron-based alloy, 0.3% to 3.0% by
weight barium sulfate, barium sulfide, or both.
CITATION LIST
Patent Literature
[0011] PTL 1: JP S61-147801 A
PTL 2: JP S60-145353 A
PTL 3: JP H9-279204 A
PTL 4: JP 2006-89829 A
PTL 5: JP S46-39564 B
PTL 6: JP H04-157138 A
PTL 7: JP 2012-144801 A
PTL 8: JP 2001-114509 A
SUMMARY
(Technical Problem)
[0012] However, the techniques described in PTL 1 and PTL 4 have a problem
in that, since a manganese sulfide (MnS) powder is contained, the appearance
of the sintered body deteriorates, and also S or MnS remaining in the sintered
body promotes rusting of the sintered part and lowers its anti-corrosion
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,
property.
These techniques also have a problem in that, though MnS is excellent
in improving machinability in a low speed range where the cutting speed is
100 m/min or less, the machinability improvement effect of MnS is small in
high speed cutting of about 200 m/min.
[0013] The technique described in PTL 2 has a problem in that, since alkaline
silicate is hygroscopic, fixation occurs in the mixed powder and causes a
forming failure.
[0014] The technique described in PTL 3 has a problem in that impurities in
the ceramic powder need to be reduced and also the particle size needs to be
adjusted in order to prevent decreases in powder property and sintered body
property, which incurs a rising material cost. The technique described in
PTL 3 also has a problem in that, though excellent in improving machinability
at high speed, the machinability improvement effect is small in low speed
cutting.
[0015] The machinability improvement by belag layer formation described in
PTL 3 and PTL 4 is effective in reducing cutting power in lathe turning, but
has poor chip removability in drilling as chips are not refined. Thus, there
is
still a problem with drill machinability.
[0016] The technique described in PTL 5 has a problem in that the
machinability improvement effect is small in high speed cutting of about 200
m/min, as in the case of using MnS.
[0017] It could therefore be helpful to provide a mixed powder for powder
metallurgy that enables obtainment of a sintered body having excellent
machinability and particularly excellent lathe machinability (hereafter also
referred to as lathe turnability) and excellent drill machinability, and a
method
of manufacturing the same. It could also be helpful to provide a method of
manufacturing an iron-based powder-made sintered body having excellent
machinability including both excellent lathe turnability and excellent drill
workability.
(Solution to Problem)
[0018] We made intensive research on various factors, especially alkaline
silicate, affecting the machinability of the sintered body. As a result of
conducting a test of high-temperature heat treatment to reduce the
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,
hygroscopicity of alkaline silicate, we discovered that alkaline silicate
crystallized in layers by the heat treatment significantly improves the
machinability of the sintered body.
[0019] The mechanism of this improvement is still unclear. However, PTL 6,
for example, describes that a magnesium metasilicate-based mineral or a
magnesium orthosilicate-based mineral is cleavable and so functions as a solid
lubricant, and as a result improves the free machinability, slidability,
conformability, and wear resistance of the alloy. We assume that crystalline
layered alkaline silicate has the same mechanism.
[0020] We also discovered that crystalline layered alkaline silicate has a
greater machinability improvement effect than a magnesium
metasilicate-based mineral or magnesium orthosilicate, and is effective in
machinability improvement even at relatively low speed, that is, effective in
machinability improvement in a wide range from low speed to high speed.
The mechanism of this improvement is still unclear. However, given
that MnS and the like have been reported to have an action of fostering a
ductile fracture of a shear zone under low strain shear rate deformation, the
same mechanism is estimated to function more advantageously.
[0021] Based on the aforementioned discoveries, we determined that
crystalline layered alkaline silicate can simultaneously improve machinability
of different requirements, namely, machinability by a lathe (lathe
turnability)
and machinability by a drill (drill machinability).
[0022] We also discovered that lathe turnability at low speed can be further
improved by adding, as a machinability improvement powder (additive), not
only crystalline layered alkaline silicate but also a powder including at
least
one selected from a group consisting of Si02 and MgO.
[0023] The mechanism of the synergistic machinability improvement of the
sintered body is still unclear, but we assume the following.
According to the description of PTL 7, the addition of a powder
including one selected from a group consisting of Si02 and MgO allows a soft
phase and a hard phase to be simultaneously dispersed in the matrix phase of
the sintered body during the sintering process. Therefore, when a powder
including one selected from a group consisting of Si02 and MgO is added to
crystalline layered alkaline silicate, the function of the crystalline layered
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alkaline silicate as a solid lubricant becomes more apparent, and decreases
the
drag of the soft metal compound phase exerted on the tool. This facilitates
the function of suppressing wear, deformation, or cracking of the tool, and
facilitates cracking in chips by the hard metal compound phase, contributing
to enhanced removability of chips during drill boring.
We thus discovered that adding crystalline layered alkaline silicate to
the additive described in PTL 7 produces the synergistic effect of
machinability improvement in drilling.
[0024] We further discovered that lathe turnability at low speed can be
further
improved by adding, as a machinability improvement powder (additive), not
only crystalline layered alkaline silicate but also a powder including at
least
one selected from a group consisting of alkali metal sulfates and alkaline
earth
metal sulfates.
The mechanism of the synergistic machinability improvement of the
sintered body is still unclear, but we assume the following.
According to the description of PTL 5, BaSO4 does not melt or
dissolve in any metal and is soft, and such BaSO4 scatters in crystal grain
boundaries and grains and develops a notch effect during cutting, thus
lowering the cutting resistance and improving the machinability by cutting.
[0025] Therefore, when a powder including at least one selected from a group
consisting of alkali metal sulfates and alkaline earth metal sulfates is added
to
crystalline layered alkaline silicate, the function of the crystalline layered
alkaline silicate as a solid lubricant becomes more apparent, and decreases
the
drag of the soft compound phase exerted on the tool. This further enhances
the function of suppressing wear, deformation, or cracking of the tool.
We thus newly discovered that adding crystalline layered alkaline
silicate to the additive described in PTL 5 produces the synergistic effect of
machinability improvement in drilling and the like at low speed.
[0026] The disclosure is based on the aforementioned discoveries and further
studies. We thus provide the following.
1. A mixed powder for powder metallurgy obtained by mixing an
iron-based powder, an alloying powder, a machinability improvement powder,
and a lubricant, wherein the machinability improvement powder comprises
crystalline layered alkaline silicate heat-treated in a range from 400 C to
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1100 C, and a mix proportion of the machinability improvement powder is in
a range from 0.01% to 1.0% by mass in terms of total content of the
iron-based powder, the alloying powder, and the machinability improvement
powder.
[0027] 2. The mixed powder for powder metallurgy according to the
foregoing I, wherein the machinability improvement powder further
comprises at least one selected from a group consisting of an enstatite
powder,
a talc powder, a kaolin powder, a mica powder, a granulated slag powder, a
levigated clay powder, a magnesium oxide (MgO) powder, and a powder
mixture of silica (Si02) and magnesium oxide (MgO), in a range from 10% to
80% by mass in terms of total content of the machinability improvement
powder.
[0028] 3. The mixed powder for powder metallurgy according to the
foregoing 2, wherein the machinability improvement powder further
comprises an alkali metal salt powder in a range from 10% to 80% by mass in
terms of total content of the machinability improvement powder.
[0029] 4. The mixed powder for powder metallurgy according to the
foregoing 3, wherein the alkali metal salt powder is one or two selected from
a
group consisting of an alkali carbonate powder and an alkali metal soap.
[0030] 5. The mixed powder for powder metallurgy according to any one of
the foregoing 1 to 4, wherein the machinability improvement powder further
comprises a calcium fluoride powder.
[0031] 6. The mixed powder for powder metallurgy according to any one of
the foregoing 1 to 5, wherein the machinability improvement powder further
comprises one or two selected from a group consisting of a metal boride
powder and a metal nitride powder.
[0032] 7. The mixed powder for powder metallurgy according to the
foregoing 6, wherein the metal boride powder consists of at least one selected
from a group consisting of TiB2, ZrB2, and NbB2, and the metal nitride powder
consists of at least one selected from a group consisting of TiN, AIN, and
Si3N4.
[0033] 8. The mixed powder for powder metallurgy according to any one of
the foregoing 1 to 7, wherein the machinability improvement powder further
comprises at least one selected from a group consisting of an alkali metal
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sulfate and an alkaline earth metal sulfate, in a range from 10% to 80% by
mass in terms of total content of the machinability improvement powder.
[00341 9. A method of manufacturing a mixed powder for powder metallurgy,
the method comprising: mixing an
iron-based powder, an alloying powder, a machinability improvement powder,
and a lubricant to obtain a mixed powder, wherein the machinability
improvement powder comprises crystalline layered alkaline silicate
heat-treated at 400 C to 1100 C, and a mix proportion of the machinability
improvement powder is 0.01% to 1.0% by mass in terms of total content of the
iron-based powder, the alloying powder, and the machinability improvement
powder, and the mixing includes; primary mixing in which a part or whole of
the machinability improvement powder and a part of the lubricant are added,
as a primary mixture material, to the iron-based powder and the alloying
powder and heated to perform mixing while melting at least one type of the
lubricant, and a resulting mixture is cooled for solidification; and secondary
mixing in which a remaining powder of the machinability improvement
powder and the lubricant is added, as a secondary mixture material, to the
mixture to perform mixing.
[0035] 10. The method of manufacturing a mixed powder for powder
metallurgy according to the foregoing 9, wherein the machinability
improvement powder further comprises at least one selected from a group
consisting of an enstatite powder, a talc powder, a kaolin powder, a mica
powder, a granulated slag powder, a levigated clay powder, a magnesium
oxide (MgO) powder, and a powder mixture of silica (Si02) and magnesium
oxide (MgO), in a range from 10% to 80% by mass in terms of total content of
the machinability improvement powder.
[0036] 11. The method of manufacturing a mixed powder for powder
metallurgy according to the foregoing 10, wherein the machinability
improvement powder further comprises an alkali metal salt powder in a range
from 10% to 80% by mass in terms of total content of the machinability
improvement powder.
[0037] 12. The method of manufacturing a mixed powder for powder
metallurgy according to the foregoing 11, wherein the alkali metal salt powder
is one or two selected from a group consisting of an alkali carbonate powder
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and an alkali metal soap.
[0038] 13. The method of manufacturing a mixed powder for powder
metallurgy according to any one of the foregoing 9 to 12, wherein the
machinability improvement powder further comprises a calcium fluoride
powder.
[0039] 14. The method of manufacturing a mixed powder for powder
metallurgy according to any one of the foregoing 9 to 13, wherein the
machinability improvement powder further comprises one or two selected
from a group consisting of a metal boride powder and a metal nitride powder.
[0040] 15. The method of manufacturing a mixed powder for powder
metallurgy according to the foregoing 14, wherein the metal boride powder
consists of at least one selected from a group consisting of TiB2, ZrB2, and
NbB2, and the metal nitride powder consists of at least one selected from a
group consisting of TiN, AIN, and Si3N4.
[0041] 16. The method of manufacturing a mixed powder for powder
metallurgy according to any one of the foregoing 9 to 15, wherein the
machinability improvement powder further comprises at least one selected
from a group consisting of an alkali metal sulfate and an alkaline earth metal
sulfate, in a range from 10% to 80% by mass in terms of total content of the
machinability improvement powder.
[0042] 17. A method of manufacturing an iron-based powder sintered body,
by filling a die with a mixed powder for powder metallurgy manufactured by
the method according to any one of the foregoing 9 to 16,
compression-forming the mixed powder into a compact, and subjecting the
compact to a sintering process to obtain a sintered body.
(Advantageous Effect)
[0043] It is possible to manufacture a sintered body having excellent
machinability that includes both excellent lathe turnability and excellent
drill
machinability, at low cost. This remarkably reduces the manufacturing cost
of metal sintered parts, and so has an industrially significant advantageous
effect. Since cutting can be performed in a wide range of cutting conditions
from low speed to high speed, the advantageous effect is particularly
noticeable in works, such as drilling, where the cutting speed varies between
center and peripheral portions.
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=
Another advantageous effect is that a compact can be formed without a
decrease in green density and an increase in ejection force.
DETAILED DESCRIPTION
[0044] The disclosed components and methods are described in detail below.
The disclosed mixed powder for powder metallurgy is described first.
The disclosed mixed powder for powder metallurgy is a mixed powder
obtained by mixing an iron-based powder, an alloying powder, a machinability
improvement powder, and a lubricant.
[0045] The iron-based powder may be any of the iron-based powders
including: a pure iron powder such as an atomized iron powder or a reduced
iron powder; a pre-alloyed steel powder (completely alloyed steel powder)
obtained by pre-alloying an alloying element; a partial diffusion-alloyed
steel
powder obtained by partially diffusing and alloying an alloying element in an
iron powder; and a hybrid steel powder obtained by further partially diffusing
an alloying element in a pre-alloyed steel powder (completely alloyed steel
powder). As the iron-based powder, an iron-based powder mixture including
an alloying powder and a lubricant in addition to the aforementioned
iron-based powder may be used.
[0046] The alloying powder is, for example, a graphite powder, a non-ferrous
metal powder such as Cu (copper) powder, Mo powder, or Ni powder, a
cuprous oxide powder, or the like. The alloying powder is selected from
these powders and mixed depending on the desired sintered body property.
Mixing such an alloying powder with the iron-based powder increases the
strength of the sintered body, and ensures the desired sintered part strength.
The mix proportion of the alloying powder is in a range from 0.1% to 10% by
mass in terms of total content of the metal powder, the alloying powder, and
the machinability improvement powder, depending on the desired sintered
body strength. When the mixed proportion of the alloying powder is less
than 0.1% by mass, the desired sintered body strength cannot be ensured.
When the mixed proportion of the alloying powder exceeds 10% by mass, the
dimensional accuracy of the sintered body decreases.
[0047] The machinability improvement powder is crystalline layered alkaline
silicate heat-treated at 400 C to 1100 C. Alkaline silicate used here may be
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sodium silicate, potassium silicate, lithium silicate, or the like. These
substances are water-soluble. Accordingly, when any of these substances is
directly added to the mixed powder, its moisture absorption causes fixation
between the powders in the mixed powder, as a result of which the fluidity of
the powder deteriorates and a forming failure occurs.
[0048] In view of this, the alkaline silicate is heat-treated to reduce
silanol
groups on the surface, thus lowering the connectivity with water. It is
important to set the heating temperature to 400 C to 1100 C. When the
heating temperature is less than 400 C, the hygroscopicity reduction effect
is
insufficient. When the heating temperature exceeds 1100 C, the cost of the
treatment is not reasonable.
In the heat treatment, the alkaline silicate crystallizes into a layered
structure. This structure can be observed by analysis means such as an X-ray
diffractometer. The crystalline layered alkaline silicate is one type of
crystalline alkali metal layered silicate. The crystalline alkali metal
layered
silicate is well known as a detergent builder which is a material that, when
mixed in a detergent, significantly enhances detergency. The crystalline
alkali metal layered silicate is described in detail in PTL 8.
[0049] When forming the mixed powder into the compact and sintering it, a
soft metal compound powder is preferably added, as a machinability
improvement powder used together with the crystalline layered alkaline
silicate. The soft metal compound powder forms, in the matrix phase of the
sintered body, soft particles (soft phase) with lower hardness than the
average
hardness of the matrix phase and can form an amorphous phase at a low
temperature because of the low melting point.
In detail, the soft metal compound powder is at least one type selected
from an enstatite powder, a talc powder, a kaolin powder, a mica powder, a
granulated slag powder, a levigated clay powder, a magnesium oxide (MgO)
powder, and a powder mixture of silica (Si02) and magnesium oxide (MgO).
[0050] Of these additives to the mixed powder as a machinability
improvement powder, soft minerals such as an enstatite powder, a talc powder,
a kaolin powder, and a mica powder are metal compounds containing at least
Si or Mg, and 0 (Si02 or MgO), and a granulated slag powder is a deoxidation
product represented by a chemical composition such as CaO-Si02-A1203 or
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MgO-A1203-Si02. These powders which are compounds containing Si, Mg,
and 0 can each form a low-melting amorphous phase and disperse in the
matrix phase of the sintered body as a soft metal compound phase, when
sintering the green compact formed from the mixed powder. The
low-melting amorphous phase formed during sintering is a Si02-MgO-based
amorphous phase.
[0051] At least one selected from a group consisting of a levigated clay
powder, a magnesium oxide (MgO) powder, and a powder mixture of silica
(Si02) and magnesium oxide (MgO) which contains Si, Mg, and 0 as with an
enstatite powder and the like may be used as a machinability improvement
powder. The powder mixture of silica (Si02) and magnesium oxide (MgO)
can equally form a low-melting amorphous phase (amorphous particles) when
sintering the green compact formed from the mixed powder. The mixing
ratio Si02:Mg0 is preferably in a range from 1:2 to 3:1 by mass.
[0052] Preferably, an alkali metal salt powder is further added as a
machinability improvement powder. Further adding an alkali metal salt
powder to a powder containing Si02 and/or MgO, such as an enstatite powder,
facilitates the formation of the low-melting amorphous phase when sintering
the green compact.
[0053] During sintering, not only the alkali metal salt forms low-melting flux
by itself or by reacting with iron oxide on the surface of the iron-based
powder, but also other oxides such as Si02 and MgO included in the mixed
powder melt in the flux to form a Si02-MgO-alkali metal oxide-based
amorphous phase, which disperses in the matrix phase of the sintered body as
a soft phase.
Examples of the alkali metal salt include alkali carbonate and alkali
metal soap. Any one or a composite of these powders may be included.
The use of alkali metal soap is advantageous in that the lubrication effect by
the metal soap improves the density of the green compact in powder forming.
[0054] The mix proportion of the powder containing Si02 and/or MgO or the
alkali metal salt powder is preferably in a range from 10% to 80% by mass in
terms of total content of the machinability improvement powder. When the
mix proportion is less than 10% by mass, the aforementioned synergetic effect
cannot be expected. When the mix proportion exceeds 80% by mass, the
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machinability improvement effect at low speed decreases.
[0055] A calcium fluoride powder may further be included. The mix
proportion of the calcium fluoride powder is preferably in a range from
20% to 80% by mass in terms of total content of the machinability
improvement powder. When the mix proportion is less than 20% by mass,
the desired machinability improvement effect cannot be expected. When the
mix proportion exceeds 80% by mass, the mechanical strength of the sintered
body decreases.
[0056] A powder serving as hard particles is, for example, a metal boride
powder and/or a metal nitride powder. Examples of the metal boride powder
include a TiB2 powder. a ZrB2 powder, and a NbB2 powder, and a NbB2
powder is particularly preferable. Examples of the metal nitride powder
include a TiN powder, a MN powder, and a Si3N4 powder, and a Si3N4 powder
is particularly preferable.
The mix proportion of the metal boride powder and/or metal nitride
powder is preferably in a range from 10% to 80% by mass in terms of total
content of the machinability improvement powder. When the mix proportion
is less than 10% by mass, the desired machinability improvement effect
cannot be expected. When the mix proportion exceeds 80% by mass, the
powder compressibility and the sintered body strength decrease.
[0057] Moreover, when forming the mixed powder into the compact and
sintering it, at least one selected from a group consisting of alkali metal
sulfates and alkaline earth metal sulfates may be added as a machinability
improvement powder used together with the crystalline layered alkaline
silicate.
In detail, at least one selected from a group consisting of alkali metal
sulfates such as sodium sulfate and lithium sulfate and alkaline earth metal
sulfates such as calcium sulfate, magnesium sulfate, barium sulfate, and
strontium sulfate may be added.
[0058] These are all soft substances, and do not melt or dissolve in any
metal.
Such a substance scatters in crystal grain boundaries and grains, and develops
a notch effect during cutting, thus lowering the cutting resistance and
improving the machinability by cutting. As a result, the function of the
crystalline layered alkaline silicate as a solid lubricant becomes more
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apparent, and decreases the drag of the soft compound phase exerted on the
tool. This enhances the function of suppressing wear, deformation, or
cracking of the tool.
The mix proportion of the alkali metal sulfate or alkaline earth metal
sulfate is preferably in a range from 10% to 80% by mass in terms of total
content of the machinability improvement powder. When the mix proportion
is less than 10% by mass, the desired machinability improvement effect
cannot be expected. When the mix proportion exceeds 80% by mass, the
powder compressibility and the sintered body strength decrease.
[0059] The mix proportion of the machinability improvement powder in the
mixed powder needs to be in a range from 0.01% to 1.0% by mass in terms of
total content of the iron-based powder, the alloying powder, and the
machinability improvement powder. When the mix proportion is less than
0.01% by mass, the machinability improvement effect is insufficient. When
the mix proportion exceeds 1.0% by mass, the green density decreases and the
mechanical strength of the sintered body obtained by sintering the compact
decreases. The mix proportion of the machinability improvement powder in
the mixed powder is therefore limited to a range from 0.01% to 1.0% by mass
in terms of total content of the iron-based powder, the alloying powder, and
the machinability improvement powder.
[0060] The mixed powder includes an appropriate amount of lubricant, in
addition to the aforementioned iron-based powder, alloying powder, and
machinability improvement powder. The lubricant is preferably metal soap
such as zinc stearate or lithium stearate, carboxylic acid such as oleic acid,
or
amide wax such as stearic acid amide, stearic acid bisamide, or
ethylene-bis-stearamide. The mix
proportion of the lubricant is not
particularly limited. As the external additive amount, the mix proportion is
preferably in a range from 0.1% to 1.0% by mass in outer percentage in terms
of total content of 100% by mass the metal powder, the alloying powder, and
the machinability improvement powder. When the mix proportion of the
lubricant is less than 0.1% by mass in outer percentage, the friction with the
die increases and the ejection force increases, causing a shorter die life.
When the mix proportion of the lubricant is large exceeding 1.0% by mass in
outer percentage, the forming density decreases and the density of the
sintered
Ref. No. P0134275-PCT-ZZ (14/29)
CA 02916153 2015-12-18
- 15
body decreases.
[0061] A preferable method of manufacturing the mixed powder is described
below.
The alloying powder, the machinability improvement powder
including one or more powders of the aforementioned types and mix
proportions, and the lubricant are added to the iron-based powder by
respective predetermined amounts. Desirably, they are mixed at one time or
in two or more times typically using a well-known mixer, to obtain the mixed
powder (iron-based mixed powder). The machinability improvement powder
does not necessarily need to be mixed all at once. Only a part of the
machinability improvement powder may be added and mixed (primary mixing),
after which the remaining part (secondary mixture material) is added and
mixed (secondary mixing). The lubricant is preferably added in two times.
Here, the iron-based powder that has been subjected to segregation
prevention treatment of causing a part or whole of the alloying powder and/or
machinability improvement powder to adhere to the surface of a part or whole
of the iron-based powder by a bonding material may be used. The
segregation prevention treatment may be the segregation prevention treatment
described in JP 3004800 B.
[0062] By heating to not lower than the minimum temperature of the melting
point of any of various types of lubricant included in the mixed powder. at
least one type of lubricant out of these lubricants melts to initiate primary
mixing, and then the mixture is cooled for solidification. After this, the
secondary mixture material composed of the remaining powder of the
machinability improvement powder and lubricant is added to initiate
secondary mixing.
[0063] The mixing means is not particularly limited, and may be any of the
conventionally well-known mixers. Mixers that facilitate heating, such as a
high-speed bottom stirring mixer, an inclined rotating pan-type mixer, a
rotating hoe-type mixer, and a conical planetary screw-type mixer, are
especially advantageous.
[0064] A preferable method of manufacturing the sintered body using the
mixed powder for powder metallurgy obtained by the aforementioned
manufacturing method is described below.
Ref. No. P0134275-PCT-ZZ (15/29)
CA 02916153 2015-12-18
- 16 -
First, a die is filled with the mixed powder for powder metallurgy
manufactured by the aforementioned method, which is then
compression-formed into a compact. As the forming method, any of the
well-known forming methods such as press forming may be suitably used.
The use of the disclosed mixed powder for powder metallurgy realizes high
forming pressure of 294 MPa or more, and enables forming at normal
temperature. To ensure stable formability, it is preferable to heat the mixed
powder or the die to appropriate temperature, or apply a lubricant to the die.
[0065] In the case of performing compression forming in a heating
atmosphere, the temperature of the mixed powder or die is preferably less than
150 C. This is because the mixed powder for powder metallurgy has high
compressibility and so exhibits excellent formability even when the
temperature is less than 150 C, and also because degradation due to oxidation
may occur when the temperature is 150 C or more.
[0066] The compact obtained by the aforementioned forming process is then
subjected to the sintering process to form the sintered body. The temperature
of the sintering process is desirably about 70% of the melting point of the
metal powder.
In the case of the iron-based powder, the temperature of the sintering
process is 1000 C or more, and preferably 1300 C or less. When the
temperature of the sintering process is less than 1000 C, the desired density
of the sintered body is unlikely to be achieved. A high temperature of the
sintering process exceeding 1300 C is not preferable because abnormal grain
growth tends to occur during sintering and decrease the strength of the
sintered body.
[0067] The atmosphere of the sintering process is preferably an inert gas
atmosphere such as nitrogen or argon, an inert gas-hydrogen gas mixture
atmosphere where hydrogen is mixed with the inert gas atmosphere, or a
reduction atmosphere such as ammonia decomposition gas, RX gas, or natural
gas.
After the sintering process, heat treatment such as gas carburizing heat
treatment or carburizing nitriding treatment is further performed according to
need, to obtain the product (sintered part, etc.) having the desired
properties.
Cutting work and the like are conducted as necessary to form the product
Rcf. No. P0134275-PCT-ZZ (16/29)
CA 02916153 2015-12-18
- 17
having predetermined dimensions.
EXAMPLES
[0068] Non-limiting examples according to the disclosure are described
below.
As the iron-based powder, the iron-based powders (average particle
size: about 80 m in each case) shown in Table 1 were used. The average
particle size was determined using laser diffractometry.
As shown in Table 1, the iron-based powders used are: (A) an
atomized pure iron powder; (B) a reduced pure iron powder; (C) a partial
diffusion-alloyed steel powder obtained by partially diffusing and alloying Cu
as an alloying element on the surface of an iron powder; (D) a partial
diffusion-alloyed steel powder obtained by partially diffusing and alloying
Ni,
Cu, and Mo as an alloying element on the surface of an iron powder; (E) a
pre-alloyed steel powder (completely alloyed steel powder) obtained by
pre-alloying Ni and Mo as an alloying element; (F) a pre-alloyed steel powder
(completely alloyed steel powder) obtained by pre-alloying Mo as an alloying
element; (G) a pre-alloyed steel powder (completely alloyed steel powder)
obtained by pre-alloying Mo as an alloying element; and (H) a steel powder
(hybrid alloyed steel powder) obtained by further partially diffusing and
alloying Mo as an alloying element in a completely alloyed steel powder
obtained by pre-alloying Mo.
[0069] [Table 1]
Table 1
Iron-based powder T ype Composition
symbol (%: mass%)
A Atomized pure iron powder Fe
Reduced pure iron powder Fe
Partial diffusion-alloyed steel powder Fe-2.0%Cu
Partial diffusion-alloyed steel powder Fe-4.0%Ni-1.5%Cu-0.5%Mo
Completely alloyed steel powder Fe-0.5%Ni-0.5%Mo
Completely alloyed steel powder Fe-0.6%Mo
Completely alloyed steel powder Fe-0.45%Mo
Hybrid alloyed steel powder (Fe-0.45%Mo) -0.15%Mo*
*) Steel powder obtained by diffusing and alloying 0.15%Mo in Fe-0.45%Mo
completely alloyed steel powder
Ref. No. P0134275-PCT-ZZ (17/29)
CA 02916153 2015-12-18
- 18 -
[0070] The alloying powder of each of the types and mix proportions shown
in Table 2, the machinability improvement powder of each of the types and
mix proportions shown in Table 2, and the lubricant of each of the types and
mix proportions shown in Table 2 were added to the corresponding one of the
aforementioned iron-based powders, and primary mixing was performed using
a high-speed bottom stirring mixer. In the primary mixing, each sample was
heated to 140 C while being mixed, and then cooled to 60 C or less. A
natural graphite powder added as the alloying powder is a powder of 5 lam in
average particle size, and a copper powder added as the alloying powder is a
powder of 20 jtm in average particle size.
Ref. No. P0134275-PCT-ZZ (18/29)
i.
Table 2
CD
Iron-based4::::+
Alloying powder Machinability improvement powder
Lubricant ---11
powder
l=-=
i-i
Mixed Primary mixing
Graphite powder Copper powder Secondary mixing
Primary mixing Secondary mixing
powder Symbol: Additive group I
Additive group II Remarks
Powder
H
symbol mix Proportion of
Type..... Type...==== A:
Type: mix proportion.*** proportion
Type: Type: mix proportion additive group : mix proportion : mi
Type: mix Type* Type**
x proportion
(mass%) proportion
(mass%) : mix proportion : mix
proportion
jj*** proportion
(mass%)
(mass%-outer (mass./0-outer CD
(mass%) (mass%) (mass%) (mass%)
b.)
(mass%)
percentage) percentage) 1....-I
Natural graphite:
M 1 A. 99.3 - a: 0.1 0- 0.1
AO: 0.1, Zn: 0.3 Zn: 0.4 Example
0.6
Natural graphite:
M 2 A99.2 - b,0.1 f:0.1 50- 0.2
AO: 01, Zn: 0.3 Zn: 0.4 Example
0.6
Natural graphite:
M 3 A: 97.1 Atomized copper: 2.0 a: 0.1 o-
0.1 AO: 0.1, Zn: 0.3 Zn: 0.4 Example =
0.8
Natural graphite:R
M 4 A: 97.0 Atomized copper: 2.0 c: 0.1 I: 0.05, rn
0.05 20 - 0.2 AM: 0.2, BS: 0.2 Li 0.1,Zn0.1,BS0.3
Example
0.8
0
ND
Natural graphite:so
M 5 A: 97.05 Atomized copper: 2.0 a: 0.05 g:
0.05,h: 0.05 67 0.15 AM: 0.2, BS: 0.2 Li 0.1,Zna 1,BS0.3 Example
==
0.8
di
Natural graphite:
5
w
M 6 B:99.2 - bØ1 i: 0.05, j: 0.05 50
- 0.2 AO: 0.2, BS: 0.2 Zn: 0.4 Example
0.6
ss
Natural graphite:-
,--, iji
M 7 B:99.2 c: 0.1 k: 0.1 25
0.2 AO: 0.2, BS: 0.2 Zn: 0.4 Example
0.6
,..0 4,
Natural graphite:,
M 8 B: 96.9 Electrolyte copper:2.0 a: 0.1 j: 0.1 33
Si,N4: 0.1 0.3 AM: 0.1, BS: 0.1 Zn: 0.1,BS0.5 Example
0.8
a
Natural graphite:
M 9 C:98.9- a: 0.1 FOGS, or 0.05 25
Til32: 0.2 0.4 AO: 0.1, Zn: 0.3 Zn: 0.4 Example
0.7
Natural graphite:
M 10 D:99.2 b: 0.2 n: 0.1 33
0.3 AO: 0.1, Zn: 0.3 Zn: 0.4 Example
- -
0.5
P:1 Natural graphite:
(0 M 11 E:99.3 - c: 0.1 o: 0.1
50 0.2 AO: 0.2, BS: 0.2 Zn: 0.4 Example
t.6 0.5
Natural graphite:
xample
-
0.5
.0 Natural graphite:
o M 13 G: 96.8 Atomized copper: 2.0 b:0.2 k: 0.1
25 ZrE32: 0.1 0.4 AM: 0.1, BS: 0.1 Zn: 0.1,BS0.5 Example
0.8
t...i
4. Natural graphite:
f 0.25,o: 0.25 71 - 0.7 AO: 0.1, Zn: 0.3 Zn: 0.4
Example
-
--.1 0.8
Natural graphite:Comparative
40 M 15 A: 99.4 - 0 -
0 AO: 0.1, Zn: 0.3 Zn: 0.4
- -
n
0.6 Example
0-4
*) a: crystalline layered sodium silicate, b: crystalline layered potassium
silicate, c: crystalline layered lithium silicate, d. unheated sodium
silicate, e: 350 C heated sodium silicate
rn...1 **) f: enstatite, g: talc, h: kaolin, i: mica, j: granulated slag,
k: Irrigated clay, I: MgO, m: Si02, n: lithium carbonate (alkali metal oak),
o: lithium stearate (metal soap)
N p: sodium sulfate, ci: calcium sulfate, r: barium sulfate
,-` ***) proportion of additive pinup II in all cuttabdity improvement
powder
-R--3 ****) Proportion of all euttability improvement powder in total
content of iron-based powder, alloying powder, and cuttability improvement
powder
`C, *****) Zn: zinc stearate, Li: lithium stearate, BS: ethylene-bis-
stearamide, AM: stearic acid monoamide, AO: oleic acid
.,
Table 2 (cont'd)
Iron-based
Alloying powder Machinability improvement
powder Lubricant
powder
Mixed Primary mixing
Graphite powder Copper powder Secondary mixing
Primary mixing Secondary mixing
powder Symbol: Additive group I
Additive group II Remarks
Powder
_____________________________________________________________________________ -
________
symbol mix
Proportion ofType**
***
Type: mix Type* Type** Type: mix
proportion**** TYPe*****
proportion Type: mix proportionadditive group : mix
proportion : mix proportion
(mass%) proportion
(mass%) : mix proportion : mix proportion
II*** proportion
(mass%)
(mass%-outer
(mass%-outer
(mass%) (mass%) (mass%) (mass%)
_____________________________________________________ (mass%)
percentage) percentage)
Natural graphite:
Comparative
M 16 A: 99.3 - d - - : 0.1 0 0.1
AO: 0.1, Zn: 0.3 Zn: 0.4
0.6
Example
Natural graphite:
Comparative
M 17 A'971 Atomized copper: 2.0 d 0.1 - 0
0.1 AO: 0.1, Zn: 0.3 Zn: 0.4
0.8
Example
...
Natural graphite:
Comparative
M 18 A;97.1 Atomized copper: 2.0 e: 0 - 1 0
0.1 AO: 0.1, Zn: 0.3 Zn: 0.4
0.8
Example R
1
Natural graphite:
Comparative 1c
M 19 A;97.1 Atomized copper: 2.0 - f: 0.1 100 -
El AO: 0.1, Zn: 0.3 Zn: 0.4 ND
0.8
Example
1-,
0.,
Natural graphite:
Comparative i
M 20 A: 97.1 Atomized copper: 2.0 - 1: 0.05, m: 0.05
25 0.1 AM: 0.2, BS: 0.2 Li: 0.1,Zn0.1,BS0.3 in
-
0.8
Example w
. ,
Natural graphite:
Comparative Iv
M 21 B: 97.0 Electrolyte copper: 2.0 - j: 0.1 50
Si3194: 0.1 0.2 AM: 0.1, BS: 0.1 Zn: 0_ LBS0. I 5
.
0.8
Example '5
- __________________________________________
Natural graphite:
Comparative
M 22 C. 99.3 -
- - 0 0 AO: 0.1, Zn: 0.3
Zn: 0.4 C., Ni
-
0.7
Example i
1-,
Natural graphite:- Comparative 00
-
M 23 D: 99.5 - 0 0
AO: 0.1, Zn: 0.3 Z II: 0.4
0.5
Example
Natural graphite:- -
Comparative
-
M 24 E: 99.5 o o
AO: 0.1, Zn: 0.3 Zn, 0.4
-
0.5
Example
Natural graphite:
Comparative
M 25 F. 99.25- - 1:0.1, in: 0.05 60
Til3,. 0.1 0.25 AM: 0.2, BS: 02 Li: 0.1,Zn0.1,BS0.3
,
0.5Example
a Natural graphite:
Comparative
'.- - - s M 26 G: 97.2 Atomized copper: 2.0
- 0 0 AM: 0.1, BS: 0.1 Zn: 0.1,BS0.5
0.8
Example
_
7,
P i v r 27 A: 99.2 Natural graphite:
- a: 0.1 p: 0.1 50 0.2 AO: 0.1, Zn: 0.3 Zn: 0.4
Example
0.6
'V _
0 M 28 A: 97.0 Natural graphite.
Atomized copper: 2.0 a:0.1 q: 0.1 20- 0.2
AM: 0.2, BS: 0_2 Li: 0.1,Zn0.LBS0.3 Example
0.8
La
.g. Natural graphite:
F.) M 29 A: 97.0 Atomized copper: 2.0 a: 01 r: 0.1
20 - 0.2 AM: 0.2, BS: 0.2 Li: 0.1,Zn0.1,BS0.3
Example
-4 0.8
v. .
Natural graphite:
M 30 A: 97.05 Atomized copper: 2.0 a:
0.05 f: 0.05, p: 0.05 67- 0.15 AM: 0.2, BS: 0.2 Li
0.1,Zn0.1,1350.3 Example
(-) 0.8
H., *) a: crystalline layered sodium silicate, b: crystalline layered
potassium silicate, c: crystalline layered lithium silicate, d: unheated
sodium silicate, e: 350 C heated sodium silicate
N **) f: enstatite, g: talc, h. kaolin, i mica, j: granulated slag. IL:
levigated clay, 1: MgO, m: Si02, n: lithium carbonate (alkali metal salt), o:
lithium stearate (metal soap)
N
p: sodium sulfate, 44: calcium sulfate, r: barium sulfate
173
c., *55) proportion of additive group II in all cuttability improvement
powder
b..) ** *) Proportion of all cuttability improvement powder in total
content of iron-based powder, alloying powder, and cuttability improvement
powder
...., *****) Zn: zinc stearate, Li: lithium stearate, BS: ethylene-bis-
stearamide, AM: stcaric acid monoamide, AO: oleic acid
CA 02916153 2015-12-18
=
-21
100721 After the primary mixing, the secondary mixture material composed of
the machinability improvement powder and lubricant of each of the types and
mix proportions shown in Table 2 was further added, and secondary mixing of
stirring each sample for 1 minute was performed with the rotational frequency
of the mixer being 1000 rpm. After the secondary mixing, the mixed powder
was taken out of the mixer. Here, the machinability improvement powder
was added in two times, i.e. upon the primary mixing and upon the secondary
mixing. The mix proportion of the machinability improvement powder is
expressed in % by mass in terms of total content of the iron-based powder, the
alloying powder, and the machinability improvement powder. The mix
proportion of the lubricant as external addition is expressed in % by mass in
outer percentage in terms of total content of 100% by mass the iron-based
powder, the alloying powder, and the machinability improvement powder.
As a result of the aforementioned steps, the mixed powder in which
the iron-based powder, the alloying powder, and the machinability
improvement powder were uniformly mixed without segregation was
obtained.
As comparative examples, the iron-based powder, the alloying powder,
and the lubricant of each of the types and mix proportions shown in Table 2
were added and mixed at normal temperature using a V-type container rotating
mixer, thus obtaining a mixed powder.
[0073] Following this, a die (two types for lathe turning test and drilling
test)
was filled with the obtained mixed powder, which was then
compression-formed with a pressing force of 590 MPa to obtain a compact.
The compact was subjected to a sintering process at 1130 C for 20 min in an
RX gas atmosphere to obtain a sintered body.
The obtained sintered body was subjected to the lathe turning test and
the drilling test. The test methods are as follows.
[0074] (1) Lathe turning test
Three sintered bodies (ring-shaped, 60 mm (outer diameter) x 20 mm
(inner diameter) x 20 mm (length)) were overlaid on each other, and their side
surfaces were turned using a lathe. The turning condition is as follows: the
use of a cermet-made lathe turning tool; the turning speed of 100 m/min and
200 m/min; the feed rate of 0.1 mm per cycle; the turning depth of 0.5 mm;
Ref. No. P0134275-PCT-ZZ (21(29)
CA 02916153 2015-12-18
- 22 -
and the turning distance of 1000 m. After the test, the flank wear width of
the turning tool was measured. Based on the assumption that the tool life
corresponds to approximately the wear of 0.25 mm, in the case where the tool
life was reached when the turning distance is less than 1000 m, the sample
was marked as "1000 m not reached". It is thus evaluated that the sintered
body has more excellent machinability when the flank wear width of the
cutting tool is smaller.
[0075] (2) Drilling test
A sintered body (disk-shaped, 60 mm (outer diameter) x 10 mm
(thickness)) was bored to form a through hole under the conditions of 5,000
rpm in rotational frequency and 750 mm/min in feed rate, using a high speed
steel-based drill (2.6 mm in diameter). During this, the thrust component as
the cutting resistance in drilling was measured using a tool dynamometer. It
is evaluated that the sintered body has more excellent machinability when the
thrust component is smaller.
Table 3 shows each of the obtained results.
Ref. No. P0134275-PCT-ZZ (22/29)
CA 02916153 2015-12-18
*.
- 23 -
,
,
[0076] [Table 31
Table 3
Lathe turning test result Drilling test result
Sintered Turning speed Turning speed
Mixed powder Cutting resistance
body 100m/min 200m/min Remarks
symbol
No. Flank wear Flank wear Thrust
component
(mm) (mm) (N)
1 , M 1 0.07 0.09 241 Example
2 M 2 0.06 0.06 230 Example
3 M 3 0.08 0.09 250 Example
4 M 4 0.07 0.05 234 Example
M 5 0.07 0.08 244 Example
6 M 6 0.08 0.07 255 Example
7 M 7 0.06 0.05 226 Example
8 M 8 0.09 0.08 253 Example
9 M 9 0.08 0.08 249 Example
M 10 0.11 0.10 261 Example
11 M 11 0.10 0.09 254 Example
12 M 12 0.09 0.07 250 Example
13 M 13 0.08 0.07 238 Example
14 M 14 0.09 0.08 255 Example
1000m not 1000m not Comparative
M 15 301
reached reached Example
1000m not 1000m not Comparative
16 M 16 297
reached reached Example
Comparative
17 M 17 0.21 0.23 290
Example
Comparative
18 M 18 0.18 0.19 289
Example
Comparative
19 M 19 0.17 0.10 275
Example
Comparative
M 20 0.18 0.09 286
Example
Comparative
21 M 21 0.20 0.12 281
Example
1000m not 1000m not Comparative
22 M 22 300
reached reached Example
1000m not 1000m not Comparative
23 M 23 322
reached reached Example
1000m not 1000m not Comparative
24 M 24 312
reached reached Example
Comparative
M 25 0.22 0.12 289
Example
1000m not 1000m not
Comparative
26 M 26 294
reached reached Example
27 M 27 0.06 0.08 224 Example
28 M 28 0.07 0.07 220 Example
29 M 29 0.07 0.06 223 Example
M 30 0.07 0.10 233 Example
Ref No. P0134275-PCT-ZZ (23/29)
CA 02916153 2015-12-18
- 24 -
=
[0077] As shown in Table 3, Examples according to the disclosure all had
small flank wear width of the cutting tool, which indicates excellent lathe
machinability. Moreover, Examples had low thrust component in drill boring,
and thus were sintered bodies having excellent drill machinability, too. On
the other hand, Comparative Examples outside the range of the disclosure
especially had poor drill machinability.
Ref. No. P0134275-PCT-ZZ (24/29)
