Technical Field
[0001] The present invention relates to an iron-based powder mixture including iron-based
power mixed with a lubricant, and alloying powder as needed. The iron-based powder
mixture of the invention is suitable for powder metallurgy, and particularly suitable
for compaction in a temperature range from normal temperature to less than 100°C.
[0002] The invention further relates to a powder mixture for powder metallurgy, which is
preferable for manufacturing of high-strength sintered parts for automobiles.
[0003] Moreover, the invention relates to a method of manufacturing an iron-based compacted
body using the iron-based powder mixture as a material, and a method of manufacturing
an iron-based power sintered-body using the iron-based compacted body as a material.
Background Art
[0004] The iron-based powder mixture for powder metallurgy is typically manufactured in
a way that iron-based powder is added with a lubricant and alloying powder and mixed,
and furthermore added with powder of free machining additives and mixed as needed.
[0005] Here, the iron-based powder is a main component of the powder mixture, and iron powder
(including pure iron powder), or alloyed steel powder is mainly used as the iron-based
powder. The alloyed steel powder contains an alloyed element. While steel powder containing
no C may be used as the alloyed steel powder, steel powder containing C and iron powder
containing no C are generally called alloyed steel powder herein. In addition to the
above, partly diffused alloyed steel powder may be used, in which an alloy element
is bonded to pure iron powder or the like by partial diffusion. In the application,
the partly diffused alloyed steel powder is assumed to be a type of the alloyed iron
powder.
[0006] The lubricant is an additive that is added particularly for facilitating compaction
or ejection of a compacted body from a die after compaction. While various substances
can be used for the lubricant, the lubricant is selected in consideration of a mixing
property with iron-based powder or a decomposition property during sintering. As an
example of the lubricant, zinc stearate, aluminum stearate, lead stearate and the
like are listed. Various lubricants are exemplified in
US Patent No.5,256,185 and the like.
[0007] The alloying powder is added mainly for adjusting a composition and/or a structure
of an iron-based compacted body or an iron-based sintered body, and includes graphite
powder, copper powder, iron phosphide powder, molybdenum powder, and nickel powder.
[0008] The powder of free machining additives (or free machining elements), such as S or
MnS, is added particularly for improving machining performance of the sintered body.
[0009] Recently, with increase in demand for increasing strength of sintered parts, as disclosed
in Japanese Unexamined Patent Application Publication
JP-A-2-156002 (1990), Japanese Examined Patent Application Publication
JP-B-7-103404 (1995), and
US Patent No.5,368,630, a warm compaction technique has been developed, in which an iron-based powder mixture
is compacted while being heated, thereby increase in density and increase in strength
of a compacted body can be achieved. According to the technique, density of a compacted
body can be increased at a relatively low load by using a phenomenon that iron-based
powder is gradually reduced in resistance to plastic deformation as the powder is
heated.
[0010] However, such an iron-based powder mixture has the following problems. That is, the
warm compaction is a technique that a die and powder are heated to high temperature
beforehand, then the iron-based powder mixture is compacted. As the heating temperature,
while a range of 70 to 120°C is described in
JP-A-2-156002, heating is substantially preferably performed at 100°C or more as described in
JP-B-7-103404 and
USP 5,368,630. However, since it is very difficult that the iron-based powder mixture having low
heat conductivity is uniformly heated to 100°C or more, and kept at the temperature,
productivity of sintered parts have been likely reduced. Moreover, the iron-based
powder mixture is heated for a long time, resulting in a problem that the iron-based
powder mixture is oxidized.
[0011] JP-A-9-104901 (1997) or
JP-A-10-317001 (1998) discloses a technique that an inorganic compound having a layered crystal such as
MoS
2, carbon fluoride, and graphite is used as the lubricant. However, when MoS
2 is used, the MoS
2 may be decomposed during sintering, causing generation of harmful sulfur gas that
possibly contaminates a furnace. When carbon fluoride is used so that the iron-based
powder mixture is sintered in a hydrogen atmosphere, there is fear that corrosive
hydrogen fluoride may be generated.
[0012] Therefore, it is desired to develop an iron-based powder mixture having high compressibility
similar to that of a warm-rolled, iron-based powder mixture, even if it is not subjected
to warm rolling.
[0013] On the other hand, for the iron-based powder mixture, the problem of machining performance
is also desired to be solved.
[0014] When parts of various machines such as automobiles are manufactured by a powder metallurgy
technique, a powder mixture for powder metallurgy is filled in a die and compacted,
and furthermore sintered. Parts of various machines obtained in this way (hereinafter,
called sintered parts) typically have a density of 5.0 to 7.2 g/cm
3 respectively. Moreover, since each of the sintered parts is good in dimension accuracy,
a part having a complicated shape can be produced.
[0015] The sintered parts are used for parts of various machines. In particular, parts for
automobiles (for example, gears) are required to have high strength and high fatigue
characteristics. Thus, a technique of using a powder mixture for powder metallurgy,
which is added with an alloyed element, is variously investigated in order to manufacture
a sintered part having high strength and high fatigue characteristics. For example,
JP-B-45-9649 (1970) discloses a powder mixture for powder metallurgy, which includes pure Fe powder
diffusion-bonded with powder of Ni, Cu, Mo or the like, and is preferable for manufacturing
a sintered part having high strength and high fatigue characteristics, and is excellent
in compressibility. Moreover, as a powder mixture for powder metallurgy preferable
for manufacturing a sintered part having high strength,
JP-A-61-163239 (1986) discloses a powder mixture for powder metallurgy, which includes low alloyed-steel
powder, in which C and Mo are contained, and Mn and Cr are substantially not contained,
the steel powder being added with Cu powder and/or Ni powder, and furthermore, added
with graphite powder. Moreover,
JP-A-63-114903 (1988) discloses a powder mixture for powder metallurgy, in which Cu powder is diffusion-bonded
to alloyed steel powder containing Mo, Mn and C.
[0016] However, even if powder metallurgy techniques are used, when a sintered part, which
is required to have extremely strict dimension accuracy, is manufactured, the sintered
part needs to be subjected to machining (such as cutting or drilling) after sintering.
However, since a sintered part is bad in machining performance, a cutting tool used
in the machining is significantly worn. As a result, machining cost is increased,
leading to increase in manufacturing cost of a sintered part. Such degradation in
machining performance of a sintered part is caused by a phenomenon that a solid surface
intermittently appears in the inside of a work material due to pores within the sintered
part, which intermittently give a shock to a tool during cutting, in addition, heat
conductivity of the sintered part is thus decreased, and consequently temperature
of the sintered part is increased during cutting. The machining performance is significantly
degraded as strength of a sintered part is increased.
[0017] As described before, it is previously known that the powder mixture for powder metallurgy
is added with free machining additives, thereby machining performance of a sintered
part is improved. The free machining additives have an effect of easily breaking chips,
or an effect of forming a thin built-up edge on a surface of a cutting tool to improve
lubricity of the cutting tool (particularly, on a rake face).
[0018] However, free machining additives containing S as a main component, like MoS
2 described above, contaminate a furnace. Moreover, in the techniques disclosed in
JP-B-45-9649,
JP-A-61-163239, and
JP-A-63-114903, since hardness of the obtained sintered part is particularly high, even if the free
machining additives are added to the powder mixture for powder metallurgy, significant
improvement of machining performance cannot be expected.
[0019] As a technique of eliminating a bad effect on the furnace to improve machining performance
of a sintered part, a technique of using an MgO-SiO
2 composite oxide is proposed. For example,
JP-A-1-255604 (1989) discloses a technique that an MgO-SiO
2 composite oxide (for example, anhydrous talc), in which MgO/SiO
2 is 0.5 or more and less than 1.0 in mol ratio, and crystallization water is not contained,
is blended to iron-based powder as means of improving machining performance without
reducing mechanical properties (for example, strength) of a sintered body. Moreover,
JP-A-64-79302 (1989) discloses a technique that free machining additives including a MgO-SiO
2 composite oxide and/or glass powder are contained in reduced iron powder in a configuration
that the additives stay inside of each iron powder particle (that is, the additives
are added to iron powder raw material before reduction).
[0020] Any of the publications describes that the composite oxide is preferably added in
a range of 0.1 to 1.5 wt%. However, according to a result of investigation on iron-based
powder containing a lubricant (zinc stearate of 1 wt%) or the like, as an added amount
of the composite oxide is increased, an effect of improving machining performance
is increased, and particularly large effect is obtained in a range of 0.5 to 1.0 wt%,
but on the other hand, mechanical properties are reduced (Table 3 in
JP-A-1-255604, and Figs 6 and 8 in
JP-A-64-79302). That is, the techniques are not necessarily advantageous in a point of quality
of a sintered body.
Disclosure of the Invention
Problems that the Invention is to Solve
[0021] The invention advantageously solves the problems, and an object of the invention
is to propose an iron-based powder mixture for powder metallurgy, which has no adverse
effect on furnace environment during sintering a compact, and provides excellent compaction
performance that the powder mixture can be compacted at high density even in a low
temperature region of less than 100°C.
[0022] Moreover, in consideration of increase in demand for improving machining performance
of a sintered part to reduce machining cost, another object of the invention is to
provide an iron-based powder mixture for powder metallurgy preferable for machining
a sintered part having excellent machining performance, and particularly preferable
for machining a high-strength sintered part.
[0023] Still another object of the invention is to propose a method of manufacturing an
iron-based compacted body using the iron-based powder mixture as a material, and furthermore,
a method of manufacturing an iron-based sintered body using the iron-based compacted
body as a material.
Means for Solving the Problems
[0024] As a measure for solving the problems, the inventors made earnest investigations
on a particular lubricant, by which when an iron-based powder mixture is compacted,
furnace environment is not adversely affected, and even if the iron-based powder mixture
is compacted at a relatively low heating temperature of the iron-based powder mixture,
and preferably even if it is compacted without being heated, a high-density compacted
body can be manufactured.
[0025] As a result, they had a finding that when talc or steatite was used as a lubricant,
and furthermore, fatty acid amide was used, rearrangement of iron-based powder particles
was accelerated during compaction, consequently even if compaction temperature was
low, that is, about room temperature, an iron-based compacted body having high compaction
density was obtained.
[0026] Moreover, it was found that when metallic soap was added, an extremely high effect
of improving machining performance was obtained by talc or steatite in a low added
amount compared with a previously known amount, which had no adverse influence on
mechanical properties.
[0027] The invention is designed based on the above findings.
[0028] That is, summary and a configuration of the invention are as follows.
- (1) An iron-based powder mixture, characterized by containing iron-based powder, and
containing as additives;
■ at least one selected from talc and steatite, and
■ fatty acid amide.
- (2) The iron-based powder mixture according to the above (1), characterized in that
the additives further contain metallic soap.
- (3) The iron-based powder mixture according to the above (1) or (2), characterized
in that the iron-based powder mixture is further blended with alloying powder.
- (4) The iron-based powder mixture according to the above (3), characterized in that
the iron-based powder is water-atomized alloyed steel powder containing Mo of 0.3
to 0.5 mass%, Mn of 0.1 to 0.25 mass%, and the remainder being Fe and inevitable impurities,
and the alloying powder is Cu powder of 1 to 3 mass% and graphite powder of 0.5 to
1.0 mass%.
- (5) An iron-based powder mixture, characterized in that the iron-based powder mixture
is formed by mixing water-atomized alloyed steel powder containing Mo of 0.3 to 0.5
mass%, Mn of 0.1 to 0.25 mass%, and the remainder being Fe and inevitable impurities,
Cu powder of 1 to 3 mass%, graphite powder of 0. 5 to 1.0 mass%, at least one selected
from talc and steatite in a range of 0.05 to 0.5 mass% in total, and fatty acid amide.
- (6) The iron-based powder mixture according to the above (5), wherein the iron-based
powder mixture further contains metallic soap.
- (7) A method of manufacturing an iron-based compacted body, characterized in that
the iron-based powder mixture according to any one of the above (1) to (6) is filled
in a die, and then compacted at a temperature of less than 100°C.
- (8) A method of manufacturing an iron-based sintered body, characterized in that the
iron-based powder mixture according to any one of the above (1) to (6) is filled in
a die, then compacted at a temperature of less than 100°C, and then an obtained iron-based
compacted body is sintered.
[0029] Each of the content of an alloyed element (including Mo or Mn) in the iron-based
powder, the amount of alloying powder (including Cu powder and graphite powder) to
be added, and the added amount of talc or steatite refers to percentage of mass of
the iron-based powder mixture.
Best mode for Carrying Out the Invention
[0030] Hereinafter, the invention is specifically described.
[0031] First, materials of the iron-based powder mixture of the invention are described.
The content of each of alloyed elements in the iron-based powder, and the blending
amount of each of the materials (alloying powder, lubricant and the like) are expressed
in a weight percent of mass (100 mass%) of an iron-based powder mixture obtained by
mixing those, that is, the weight percent is expressed using a numerical value included
in a numerical value of the mass of the powder mixture. However, such a weight percent
is not significantly different in numerical value from that in the case that the alloy
content (including the amount of partly diffused alloy) and the like in the iron-based
powder is expressed in a weight percent of mass of the iron-based powder.
<Iron-based powder>
[0032] In the invention, as the iron-based powder, pure iron powder such as atomized iron
powder or reduced iron powder, or alloyed steel powder is exemplified. As the alloyed
steel powder, partly-diffused alloyed steel powder and prealloyed steel powder (in
which alloyed elements are already contained when melted) are exemplified, and furthermore,
hybrid steel powder is exemplified, in which alloyed elements are partly diffused
in the prealloyed steel powder.
[0033] The content of impurities in the iron-based powder may be about 3 mass% or less in
total. The content of each of typical impurities is as follows: C is 0.05 mass% or
less, Si is 0.10 mass% or less, Mn (in the case that Mn is not added as an alloy element)
is 0.50 mass% or less, P is 0.03 mass% or less, S is 0.03 mass% or less, O is 0.30
mass% or less, and N is 0.1 mass% or less.
[0034] For the alloyed steel powder, Cr, Mn, Ni, Mo, V, Ti, Cu, Nb and the like can be alloyed.
In particular, Ti, Ni, Mo, Cu and the like can be added even by diffusion bonding.
If the precondition as the iron-based powder (Fe content is 50 mass% or more) is satisfied,
other alloy elements are not particularly limited in content.
[0035] Average particle diameter of the iron-based powder is preferably adjusted to be in
a typically used range for powder metallurgy, that is, in a range of about 70 to 100
µm. The particle diameter of the powder is shown as a measurement value by a sieving
method according to JIS Z 2510, unless otherwise specified.
[0036] Hereinafter, a specific composition of alloyed steel powder particularly preferable
for a material of a high-strength sintered body is exemplified.
(Iron-based powder example 1)
[0037] As a first example, prealloyed steel powder is preferably shown, which contains Mo
of 0.3 to 0.5 mass%, Mn of 0.1 to 0.25 mass%, and the remainder being Fe and inevitable
impurities. In the light of productivity, the steel powder is preferably water-atomized
alloyed steel powder, which is manufactured by water-atomizing the steel having the
above composition.
[0038] The reason for a preferable range of each component is as follows.
• Mo: 0.3 to 0.5 mass%
[0039] Mo is an element that increases strength of a sintered part by solution hardening
or improvement in hardenability (quench hardenability) of alloyed steel powder. When
Mo content is less than 0.3 mass%, an effect of increasing strength of the sintered
part by Mo is not obtained. On the other hand, when the content is more than 0.5 mass%,
since the effect of increasing strength of the sintered part is saturated, machining
performance is unnecessarily reduced. Therefore, Mo content is preferably adjusted
to be in a range of 0.3 to 0.5 mass%.
• Mn: 0.1 to 0.25 mass%
[0040] Mn is an element that increases strength of a sintered part by solution hardening
or improvement in hardenability of water-atomized alloyed steel powder. When Mn content
is less than 0.1 mass%, an effect of increasing strength of the sintered part by Mn
is not obtained. On the other hand, when the content is more than 0.25 mass%, oxidation
of Mn easily proceeds, leading to reduction in strength and compressibility of alloyed
steel powder. Therefore, Mn content is preferably adjusted to be in a range of 0.1
to 0.25 mass%.
[0041] The rest of the powder other than the above components preferably is Fe and inevitable
impurities. The inevitable impurities inevitably gets into the steel in a stage that
an ingot being a material of the water-atomized alloyed steel powder is produced,
or in a stage that water-atomized alloyed steel powder is manufactured from the ingot.
[0042] A preferable method of manufacturing the water-atomized alloyed steel powder is described,
the method being preferably used in the invention. An ingot containing a predetermined
composition (that is, the above composition) is produced, and then the ingot is formed
into powder by a water atomizing method. Furthermore, the obtained powder is subjected
to finish reduction and crushing (or pulverizing) thereby obtaining water-atomized
alloyed steel powder. An apparatus for obtaining powder from an ingot by the water
atomizing method is not limited to a particular type, and any previously known apparatus
may be used as the apparatus.
<Alloying powder>
[0043] As the alloying powder, graphite powder, metal powder of such as Cu, Mo and Ni, boron
powder, cuprous oxide powder and the like are exemplified. Such alloying powder is
mixed to the iron-based powder, so that strength of a sintered body can be increased.
[0044] The blending amount of the alloying powder is preferably adjusted to be about 0.1
to 10 mass% in the iron-based powder mixture. The reason for this is that the alloying
powder is blended by 0.1 mass% or more, so that strength of an obtained sintered body
is advantageously improved, on the other hand, when it is blended by more than 10
mass%, dimension accuracy of the sintered body is reduced.
[0045] In the case of the iron-based powder example 1, particularly Cu powder of 1 to 3
mass% and graphite powder of 0.5 to 1.0 mass% are preferably added.
[0046] C being a main component of graphite powder is an element that increases strength
of a sintered part by solution hardening or improvement in hardenability of water-atomized
alloyed steel powder. When the added amount of graphite powder is less than 0.5 mass%,
a desired effect is not sufficiently obtained in the iron-based powder example 1.
On the other hand, when the content is more than 1.0 mass%, strength of the sintered
part is increased beyond necessity, and consequently machining performance is unnecessarily
reduced. Therefore, the content of graphite powder is adjusted to be in a range of
0.5 to 1.0 mass%.
[0047] Cu is an element that increases strength of a sintered part by solution hardening
or improvement in hardenability of alloyed steel powder. Moreover, Cu powder is melted
during sintering and thus changed into a liquid phase, causing adhesion of particles
of the alloyed steel powder to one another. When the added amount of Cu powder is
less than 1 mass%, a desired effect is not sufficiently obtained in the iron-based
powder example 1. On the other hand, when the amount is more than 3 mass%, since the
effect of increasing strength of the sintered part is saturated, machining performance
is unnecessarily reduced. Therefore, the content of Cu powder is adjusted to be in
a range of 1 to 3 mass%.
[0048] When Cu powder is added, if the added amount is within the above range, an adding
method may be a method where alloyed steel powder is added with Cu powder and then
simply mixed, or a method of adhering Cu powder on a surface of water-atomized alloyed
steel powder via a binder. Moreover, it is acceptable that the alloyed steel powder
and the Cu powder are mixed and subjected to heat treatment, so that the Cu powder
is diffusion-bonded on a surface of the alloyed steel powder so as to be formed into
partly-diffused alloyed steel powder (or hybrid alloyed steel powder).
<Talc/steatite>
[0049] In the invention, it is important that at least one selected from talc (3MgO-4SiO
2) and steatite is blended. Steatite is sometimes called fired talc, and contains enstatite
(MgO-SiO
2) as a main component.
[0050] When talc or steatite is added together with fatty acid amide, it exhibits a particularly
large effect as a lubricant. Moreover, while talc or steatite is one of MgO-SiO
2 composite oxides known as free machining additives, if talc or steatite is further
added together with metallic soap, it exhibits a particularly large effect even as
a free machining additive.
[0051] The talc or steatite is blended as the lubricant, thereby compressibility of a compacted
body is improved, in addition, ejection force in compaction process is reduced, so
that compaction performance is remarkably improved. The reason for this is considered
as follows.
[0052] That is, it is considered that when talc, steatite, and boron nitride are subjected
to shear stress between iron-based powder particles during compaction, each of the
substances tends to be cleaved along a crystal face, therefore frictional resistance
between particles within a compacted body is reduced, and thus the particles easily
move with respect to each other, as a result, density of the compacted body is improved.
Such an effect is effective in a region of a relatively low compressive stress. On
the other hand, in a high pressure region, fatty acid amide exhibits an effect that
it thinly enters into a space between the particles so as to reduce frictional resistance.
It is considered that since the frictional resistance is reduced over all the compressive
regions in this way, a synergetic effect is exhibited for increasing density of the
compacted body.
[0053] Moreover, it is considered that when talc or steatite exists between a compacted
body and a die, since the talc or steatite is cleaved due to shear stress applied
from a die surface during ejecting the compacted body, slidability of the compacted
body on the die surface is improved, leading to reduction in ejection force.
[0054] Since the effects are exhibited regardless of temperature of an iron-based powder
mixture, the iron-based powder mixture is not necessarily heated, and the effects
effectively contribute to increasing density of an iron-based compacted body in compaction
even at normal temperature. Moreover, when the iron-based powder is heated, since
plastic deformation resistance of the iron-based powder is decreased during compaction,
higher density of a compacted body can be obtained. Therefore, while heating temperature
of the iron-based powder can be appropriately set depending on a required density
of a compacted body, sufficient heating temperature is less than 100°C. More preferably,
the heating temperature is 80°C or less.
[0055] While the reason why machining performance is remarkably improved is not elucidated,
it is possibly considered that a metal component in metallic soap reacts with talc/steatite
during sintering, so that the metal component acts as an auxiliary free machining
additive. A sintered part manufactured by using the powder mixture for powder metallurgy
of the invention may have high strength similar to that of a usual high-strength sintered
part, and in addition, may have extremely excellent machining performance.
[0056] The blending amount of the talc or steatite is preferably adjusted to be about 0.01
to 0.5 mass% in total in the iron-based powder mixture. The reason for this is that
such a lubricant blended by 0.01 mass% or more, thereby density of a compacted body
can be adequately increased during compaction, and ejection force can be adequately
decreased during ejecting the compacted body. Moreover, when an effect of improving
machining performance is intended to be obtained, the lubricant is preferably added
by 0.01 mass% or more, too. When alloyed steel powder for a high-strength sintered
body (for example, the iron-based powder example 1) is used, to secure a stronger
effect of improving machining performance, the added amount of talc and/or steatite
is preferably adjusted to be 0.05 mass% or more in total.
[0057] On the other hand, when the blending amount is more than 0.5 mass% or more, compressibility
of the powder mixture is reduced, which may reduce mechanical strength and the like
of a sintered body obtained by sintering the compacted body. More preferably, an upper
limit of the blending amount is 0.3 mass%, and the upper limit is preferably adjusted
to be 0.2 mass% or less to substantially eliminate influence on mechanical properties
of the sintered body.
[0058] Preferably, talc has a monoclinic or triclinic crystal structure, steatite has a
monoclinic crystal structure, and boron nitride has a hexagonal crystal structure.
[0059] Size of talc or steatite is preferably about 1 to 10 µm in particle diameter.
<Fatty acid amide>
[0060] In the invention, at least one of fatty acid amides is blended as a lubricant. Here,
as the fatty acid amide, at least one selected from fatty acid monoamide (such as
stearic acid monoamide), and fatty acid bisamide (such as ethylene-bis-stearoamide
and methylene-bis-stearoamide) is preferably used.
[0061] Each of them acts as not only a lubricant, but also a binder. Therefore, by using
each of them, segregation or dusting of the relevant iron-based powder mixture is
effectively prevented, and flowability and compaction performance can be further improved.
While a fatty acid is sometimes mixed in fatty acid amide, this is not particularly
prohibited.
[0062] The blending amount of the fatty acid amide is preferably adjusted to be about 0.01
to 0.5 mass% in the iron-based powder mixture. The reason for this is that when the
blending amount is less than 0.01 mass%, the adding effect is poor, and on the other
hand, when the blending amount is more than 0.5 mass%, strength of a compacted body
(or green compact) is decreased. A lower limit of the blending amount is more preferably
0.03 mass% in the case that the iron-based powder is pure iron powder, and 0.05 mass%
in the case that it is alloyed steel powder. An upper limit of the blending amount
is more preferably 0.4 mass%, and in the case that the iron-based powder is pure iron
powder, 0.3 mass% is further more preferable as the upper limit.
<Metallic soap>
[0063] In the invention, metallic soap can be further blended. According to a previous common
idea, the metallic soap is also counted as a lubricant.
[0064] As the metallic soap, zinc stearate, lithium stearate, calcium stearate and the like
are listed. Among them, the zinc stearate and the lithium stearate are particularly
preferable.
[0065] The blending amount of the metallic soap is preferably adjusted to be about 0.01
to 0.5 mass% in the iron-based powder mixture. The reason for this is that when the
blending amount is less than 0.01 mass%, the adding effect is poor, and on the other
hand, when the blending amount is more than 0.5 mass%, strength of a compacted body
is decreased. A lower limit of the blending amount is more preferably 0.05 mass% or
more, and an upper limit thereof is more preferably 0.3 mass%.
[0066] The added amount of the fatty acid amide and the metallic soap in total is preferably
adjusted to be 0.1 mass% to 1.0 mass%. The lower limit is more preferably 0.2 mass%,
and the upper limit is more preferably 0.6 mass%.
[0067] Furthermore, the blending amount of the talc/steatite, the fatty acid amide, and
the metallic soap in total is preferably adjusted to be about 0.01 to 2.0 mass% in
the iron-based powder mixture. The lower limit is more preferably 0.15 mass%, and
the upper limit is more preferably 0.8 mass%.
<Other materials>
[0068] While other additives are not particularly needed for the iron-based powder mixture
of the invention, a known additive such as surface modification agent (including siloxanes)
may be further added by about 0.5 mass% or less.
<Method of manufacturing powder mixture>
[0069] Next, a method of manufacturing the iron-based powder mixture of the invention is
described.
(First method)
[0070] Iron-based powder is added with the respective materials (such as talc, steatite,
fatty acid amide, metallic soap, and alloying powder), and then subjected to primary
mixing. Then, a mixture after primary mixing is agitated while it is heated to a melting
point or higher of at least one of the fatty acid amide and metallic soap, and then
the mixture is gradually cooled while being mixed. As a result, the alloying powder
or other material powder is adhered on the iron-based powder by an effect of the melted
material.
[0071] That is, the material, which is melted and used for adhesion, acts even as a binder.
(Second method)
[0072] As a method similar to the first method, it is also possible that the iron-based
powder is added with only some of the materials, and subjected to primary mixing,
and then further added with the rest of the materials, and subjected to secondary
mixing. The material subjected to secondary mixing exists in the powder mixture in
a free state. As a particularly preferable example, a method is given, in which at
least part of the metallic soap is supplied for the secondary mixing, and the rest
of the materials is supplied for the primary mixing, and fatty acid amide, or a co-melt
of the fatty acid amide with the metallic soap is used for the binder. According to
the method, the added amount of each material to be blended to the iron-based powder
can be minimized.
[0073] Mixing means of the iron-based powder and each material is not particularly limited,
and any of previously known mixers can be used. In particular, a high-speed mixer,
counter current mixer, plough share mixer, and conical mixer, in each of which the
material powders being easily heated, are particularly advantageously suited.
<Method of manufacturing compacted body and sintered body>
[0074] Next, a method of manufacturing an iron-based compacted body using the iron-based
powder mixture of the invention, and a method of manufacturing an iron-based sintered
body (sintered part) are described.
[0075] The iron-based powder mixture of the invention can be made into a compacted body
by a typical compaction method. Specifically, the iron-based powder mixture is filled
into a die, and furthermore subjected to compaction. As a typically preferable condition
of compaction, pressing force is preferably adjusted to be 400 to 1000 MPa. Moreover,
the die may be heated to 50 to 70°C. Alternatively, the powder mixture for powder
metallurgy and the die may be heated to 80 to 130°C.
[0076] The iron-based powder mixture of the invention can be adequately compacted in high
density even at normal temperature, and preferably compacted at normal temperature
in the light of productivity. However, the iron-based powder mixture or the die may
be advantageously heated, and the die may be advantageously coated with a lubricant.
[0077] When the powder mixture is compacted in a heated surround, temperature of the iron-based
powder mixture or temperature of the die is preferably adjusted to be less than 100°C.
The reason for this is that since the iron-based powder mixture according to the invention
is high in compressibility, the powder mixture exhibits excellent compaction performance
even at a temperature of less than 100°C, and when the temperature is more than 100°C,
there is fear that the powder mixture may be degraded due to oxidation. More preferably,
the temperature is 80°C or less.
[0078] Next, the high density, iron-based compacted body obtained in the above way is ejected
from the die, then subjected to sintering so as to be formed into a high-density sintered
body. A sintering method is not particularly limited, and any of previously known
sintering methods can be preferably used. In the sintering, preferably, heating temperature
is 1100 to 1600°C, and heating time is 10 to 60 min.
[0079] Sintering is performed in this way, thereby a sintered part having excellent strength
and excellent machining performance (particularly, a high-strength sintered part in
the case of using alloyed steel powder) is obtained.
[0080] After sintering, a sintered part can be subjected to heat treatment such as carburizing
and quenching (gas carburizing heat treatment), bright hardening, induction hardening,
and carbonitriding heat treatment, so that strength of the (high strength) sintered
part can be further increased. Furthermore, tempering may be performed.
[Examples]
[0081] Hereinafter, the invention is specifically described according to examples.
[0082] Table 1 shows various types of iron powder for powder metallurgy (each having an
average particle diameter of about 80 µm) used as the iron-based powder in examples
1 to 4. Particularly, in the case of alloyed steel powder, whether the alloyed steel
powder is prealloyed steel powder, partly alloyed steel powder, or hybrid steel powder
in which the prealloyed steel powder is partly diffused with an alloyed element is
distinctively shown.
Table 1
Symbol |
Type of iron-based powder |
Category of alloyed steel powder |
A |
Atomized pure iron powder |
- |
B |
Reduced pure iron powder |
- |
C |
Fe-2%Cu |
Partly alloyed steel powder |
D |
Fe-4%Ni-1.5%Cu-0.5%Mo |
Partly alloyed steel powder |
E |
Fe-2%Ni-1%Mo |
Partly alloyed steel powder |
F |
Fe-0.5%Ni-0.5%Mo |
Prealloyed steel powder |
G |
Fe-0.6%Mo |
Prealloyed steel powder |
H |
(Fe-0.6%Mol-[0.2%Mo] |
Hybrid steel powder* |
I |
Fe-0.45%Mo |
Prealloyed steel powder |
J |
(Fe-0.45%Mo)-[0.15%Mo] |
Hybrid steel powder* |
K |
(Fe-1.5%Mo)-[2%Ni] |
Hybrid steel powder* |
* inside of parenthesis: composition of prealloyed steel powder
inside of bracket: composition being diffusion-bonded to the prealloyed steel powder |
(Example 1)
[0083] Various types of iron-based powder as shown in Table 2, and natural graphite powder
(average particle diameter of 5 µm) and/or copper powder (average particle diameter
of 25 µm) were added with various types of lubricant powder (primary additives), then
heated to 140°C while being mixed by a high-speed mixer, and then cooled to 60°C or
lower, and further added with various types of lubricant powder (secondary additives),
and agitated for 1 min at 500 rpm. Then, a powder mixture was discharged from the
mixer. A type and blending amount of each of the primary and secondary additives are
collectively shown in Table 2. The added amount (part by mass) of a lubricant is expressed
in percentage of total mass of 100% of the iron-base powder, natural graphite powder,
and copper powder. While the percentage is expressed using a numerical value being
not included in that of the total mass, the percentage is approximately the same as
in the case that it is expressed using a numerical value being included in that of
the total mass. Average particle diameter of the talc powder and average particle
diameter of the steatite powder were 6µm and 4µm respectively.
[0084] For comparison, powder mixtures were prepared (refer to Table 3) in a way that various
types of powder having the same components as the above, each including the iron-based
powder, and natural graphite powder and/or copper powder, were added with zinc stearate
of 0.8 mass%, then the powder was mixed by a V-container-turning mixer. Each of the
comparative materials has a composition typically used in normal compaction.
[0085] Next, each of the obtained iron-based powder mixtures was filled in a superhard tablet-shaped
die having an inner diameter of 11 mm, and compacted at 490 MPa and 686 MPa. In such
compaction, when a compacted body was ejected from the die, ejection force was measured,
and green density of each of obtained compacted bodies was measured.
[0086] Separately from this, the obtained iron-based powder mixtures were subj ected to
compaction for preparing test pieces for a machining test (outer diameter of 60 mm,
inner diameter of 20 mm, and length of 30 mm). In the compaction, pressing force was
590 MPa. Sintering was performed in an RX gas atmosphere, wherein heating temperature
was 1130°C, and heating time was 20 min. In evaluation of machining performance, while
a cermet cutting tool was used, a machining test was performed with cutting speed
of 200 m/min, feed of 0.1 mm per unit, depth of cut of 0.3 mm, and a cutting distance
of 1000 m, and flank wear width of the cutting tool was measured. Smaller flank wear
width of the cutting tool shows more excellent machining performance of a sintered
body.
[0087] Obtained results are shown in Table 4.
Table 2
|
Iron-based powder |
Natural graphite powder (mass%) |
Copper powder |
Primary additive lubricant* |
Secondary additive lubricant* |
type |
Blending amount (mass%) |
type |
Blending amount (mass%) |
type |
Blending amount (mass%) |
type |
Blending amount (mass%) |
Inventive example 1 |
C |
99.4 |
0.6 |
- |
0 |
STAM |
0.1 |
Steatite |
0.1 |
EBS |
0.1 |
STZN |
0.02 |
- |
- |
EBS |
0.08 |
- |
- |
STLI |
0.1 |
Inventive example 2 |
A |
97.2 |
0.8 |
Electrolytic copper powder |
2.0 |
STAM |
0.1 |
STZN |
0.1 |
EBS |
0.1 |
EBS |
0.02 |
Steatite |
0.1 |
STLI |
0.08 |
Inventive example 3 |
A |
97.9 |
0.6 |
Atomized copper powder |
1.5 |
STAM |
0.1 |
STZN |
0.02 |
EBS |
0.1 |
EBS |
0.08 |
Steatite |
0.1 |
STLI |
0.1 |
Inventive example 4 |
B |
97.2 |
0.8 |
Electrolytic copper powder |
2.0 |
STAM |
0.1 |
Steatite |
0.1 |
EBS |
0.1 |
STZN |
0.02 |
- |
- |
EBS |
0.08 |
- |
- |
STLI |
0.1 |
Inventive example 5 |
D |
99.7 |
0.3 |
- |
0 |
STAM |
0.1 |
STZN |
0.02 |
EBS |
0.1 |
EBS |
0.08 |
Steatite |
0.1 |
STLI |
0.1 |
Inventive example 6 |
F |
99.5 |
0.5 |
- |
0 |
STAM |
0.1 |
Steatite |
0.1 |
EBS |
0.1 |
STZN |
0.02 |
- |
- |
EBS |
0.08 |
- |
- |
STLI |
0.1 |
Invective example 7 |
G |
97.5 |
0.5 |
Electrolytic copper powder |
2.0 |
STAM |
0.1 |
Talc |
0.1 |
EBS |
0.1 |
STZN |
0.02 |
- |
- |
EBS |
0.08 |
- |
- |
STLI |
0.1 |
Inventive example 8 |
H |
99.5 |
0.5 |
- |
0 |
STAM |
0.1 |
Talc |
0.1 |
EBS |
0.1 |
STZN |
0.02 |
- |
- |
EBS |
0.08 |
- |
- |
STLI |
0.1 |
Inventive example 9 |
I |
97.2 |
0.8 |
Atomized copper powder |
2.0 |
STAM |
0.1 |
Steatite |
0.1 |
EBS |
0.1 |
STAM |
0.04 |
- |
- |
EBS |
0.04 |
- |
- |
STZN |
0.02 |
- |
- |
STLI |
0.1 |
* EBS: ethylene-bis-stearoamide, STZN: zinc stearate, STAM: stearic acid monoamide,
STLI: lithium stearate |
Table 3
|
Iron-based powder |
Natural graphite powder (mass%) |
Copper powder |
Added lubricant* |
type |
Blending amount (mass%) |
type |
Blending amount (mass%) |
Comparative example 1 |
C |
99.4 |
0.6 |
- |
0 |
0.8 mass% STZN |
Comparative example 2 |
A |
97.2 |
0.8 |
Electrolytic copper powder |
2.0 |
0.8 mass% STZN |
Comparative example 3 |
A |
97.9 |
0.6 |
Atomized copper powder |
1.5 |
0.8 mass% STZN |
Comparative example 4 |
B |
97.2 |
0.8 |
Electrolytic copper powder |
2.0 |
0.8 mass% STZN |
Comparative example 5 |
D |
99.7 |
0.3 |
- |
0 |
0.8 mass% STZN |
Comparative example 6 |
F |
99.5 |
0.5 |
- |
0 |
0.8 mass% STZN |
Comparative example 7 |
G |
97.5 |
0.5 |
Electrolytic copper powder |
2.0 |
0.8 mass% STZN |
Comparative example 8 |
H |
99.5 |
0.5 |
- |
0 |
0.8 mass% STZN |
Comparative example 9 |
I |
97.2 |
0.8 |
Atomized copper powder |
2.0 |
0.8 mass% STZN |
Table 4
|
Iron-based powder |
Green density (Mg/m3) |
Ejection force (MPa) |
Cutting tool |
|
Type |
490 MPa compaction |
686 MPa compaction |
490 MPa compaction |
686 MPa compaction |
Flank wear width (mm) |
Inventive example 1 |
C |
6.99 |
7.25 |
13 |
18 |
0.15 |
Inventive example 2 |
A |
7.01 |
7.26 |
13 |
18 |
0.20 |
Inventive example 3 |
A |
7.00 |
7.26 |
13 |
17 |
0.18 |
Inventive example 4 |
B |
6.86 |
7.09 |
11 |
20 |
0.21 |
Inventive example 5 |
D |
7.00 |
7.25 |
13 |
17 |
0.48 |
Inventive example 6 |
F |
6.91 |
7.19 |
14 |
18 |
0.15 |
Inventive example 7 |
G |
6.96 |
7.21 |
12 |
18 |
0.05 |
Inventive example 8 |
H |
6.98 |
7.22 |
11 |
18 |
0.12 |
Inventive example 9 |
I |
6.98 |
7.22 |
12 |
20 |
0.03 |
Comparative example 1 |
C |
6.96 |
7.11 |
11 |
19 |
0.35 |
Comparative example 2 |
A |
6.97 |
7.12 |
12 |
18 |
0.55 |
Comparative example 3 |
A |
6.97 |
7.12 |
12 |
17 |
0.48 |
Comparative example 4 |
B |
6.81 |
6.99 |
10 |
18 |
0.58 |
Comparative example 5 |
D |
6.94 |
7.15 |
13 |
18 |
0.98 |
Comparative example 6 |
F |
6.84 |
7.09 |
14 |
19 |
0.43 |
Comparative example 7 |
G |
6.85 |
7.08 |
13 |
19 |
0.22 |
Comparative example 8 |
H |
6.85 |
7.09 |
12 |
19 |
0.31 |
Comparative example 9 |
I |
6.85 |
7.09 |
13 |
20 |
0.11 |
[0088] As clear from a comparison between the inventive examples 1 to 9 and the comparative
examples 1 to 9 as shown in Tables 2 to 4, the lubricants according to the invention
are used as lubricants, thereby a high-density compacted body can be obtained without
significantly increasing ejection force even in the case of normal temperature compaction,
and furthermore, machining performance is remarkably improved.
(Example 2)
[0089] Various types of iron-based powder as shown in Table 5, and natural graphite powder
and/or copper powder were added with various lubricants (primary additives), then
heated to 140°C while being mixed by a high-speed mixer, and then cooled to 60°C or
lower, and further added with various lubricants (secondary additives), and agitated
for 1 min at 500 rpm. Then, a powder mixture was discharged from the mixer. A type
and blending amount of each of the primary and secondary additives are collectively
shown in Table 5. Used materials are those described in Table 1 as in the example
1.
[0090] For comparison, powder mixtures were prepared in a way that various types of powder
having the same components as the above, each including the iron-based powder, and
natural graphite powder and/or copper powder, were added with ethylene-bis-stearoamide
of 0.6 mass%, then the powder was mixed by a V-container-turning mixer (comparative
materials).
[0091] Next, each of the obtained iron-based powder mixtures was filled in a superhard tablet-shaped
die having an inner diameter of 11 mm, which was heated beforehand such that temperature
of a cavity wall surface was increased to 80°C, and then the powder mixture was compacted
at 490 MPa and 686 MPa. In such compaction, when a compacted body was ejected from
the die, ejection force was measured, and green density of each of the obtained compacted
bodies was measured.
[0092] Moreover, each of the comparative materials was compacted at a typical compaction
condition of warm compaction, that is, the comparative material was heated to 120°C,
then filled into a superhard tablet-shaped die having an inner diameter of 11 mm and
which was heated to 130°C, and then compacted at 490 MPa and 686 MPa. In such compaction,
when a compacted body was ejected from the die, ejection force was measured, and green
density of each of the obtained compacted bodies was measured.
[0093] Moreover, test pieces for a machining test were prepared by compaction as in the
example 1, so that machining performance was examined.
[0094] Obtained results are shown in Table 6.
Table 5
|
Iron-based powder |
Natural graphite powder (mass%) |
Copper powder |
Primary additive lubricant* |
Secondary additive lubricant* |
type |
Blending amount (mass%) |
type |
Blending amount (mass%) |
type |
Blending amount (mass%) |
type |
Blending amount (mass%) |
Inventive example 10 |
A |
97.2 |
0.8 |
Electrolytic copper powder |
2.0 |
STAM |
0.1 |
Talc |
0.1 |
EBS |
0.1 |
STZN |
0.02 |
- |
- |
EBS |
0.08 |
- |
- |
STLI |
0.1 |
Inventive example 11 |
D |
99.7 |
0.3 |
- |
0 |
STAM |
0.1 |
STZN |
0.02 |
EBS |
0.1 |
EBS |
0.08 |
Steatite |
0.1 |
STLI |
0.1 |
Inventive example 12 |
H |
99.35 |
0.65 |
- |
0 |
STAM |
0.1 |
Talc |
0.1 |
EBS |
0.1 |
STZN |
0.02 |
- |
- |
EBS |
0.08 |
- |
- |
STLI |
0.1 |
Inventive example 13 |
E |
99.4 |
0.6 |
- |
0 |
STAM |
0.05 |
Steatite |
0.1 |
EBS |
0.05 |
STZN |
0.02 |
- |
- |
EBS |
0.08 |
- |
- |
STLI |
0.1 |
Inventive example 14 |
J |
99.35 |
0.65 |
- |
0 |
STAM |
0.1 |
Steatite |
0.1 |
EBS |
0.1 |
STAM |
0.04 |
- |
- |
EBS |
0.04 |
- |
- |
STZN |
0.02 |
- |
- |
STLI |
0.1 |
Inventive example 15 |
K |
99.7 |
0.3 |
- |
0 |
STAM |
0.05 |
Steatite |
0.1 |
EBS |
0.05 |
STAM |
0.04 |
- |
- |
EBS |
0.04 |
- |
- |
STZN |
0.02 |
- |
- |
STLI |
0.1 |
Comparative example 10 |
A |
97.2 |
0.8 |
Electrolytic copper powder |
2.0 |
0.6 mass% % EBS |
Comparative example 11 |
D |
99.7 |
0.3 |
- |
0 |
0.6 mass% % EBS |
Comparative example 12 |
H |
99.35 |
0.65 |
- |
0 |
0.6 mass% % EBS |
Comparative example 13 |
E |
99.4 |
0.6 |
- |
0 |
0.6 mass% % EBS |
Comparative example 14 |
J |
99.35 |
0.65 |
- |
0 |
0.6 mass% % EBS |
Comparative example 15 |
K |
99.7 |
0.3 |
- |
0 |
0.6 mass% % EBS |
* EBS: ethylene-bis-stearoamide, STZN: zinc stearate, STAM: stearic acid monoamide,
STLI: lithium stearate |
Table 6
|
Iron-based powder |
Green density (Mg/m3) |
Ejection force (MPa) |
|
Type |
490 MPa compaction |
686 MPa compaction |
490 MPa compaction |
686 MPa compaction |
Inventive example 10 |
A |
7.10 |
7.30 |
14 |
15 |
Inventive example 11 |
D |
7.05 |
7.30 |
16 |
17 |
Inventive example 12 |
H |
7.01 |
7.26 |
18 |
19 |
Inventive example 13 |
E |
7.04 |
7.29 |
15 |
18 |
Inventive example 14 |
J |
7.02 |
7.27 |
18 |
20 |
Inventive example 15 |
K |
6.99 |
7.24 |
18 |
21 |
Comparative example 10 |
A |
7.11 |
7.30 |
15 |
16 |
Comparative example 11 |
D |
7.11 |
7.32 |
16 |
18 |
Comparative example 12 |
H |
7.03 |
7.27 |
17 |
20 |
Comparative example 13 |
E |
7.09 |
7.30 |
15 |
19 |
Comparative example 14 |
J |
7.02 |
7.27 |
17 |
19 |
Comparative example 15 |
K |
6.98 |
7.23 |
19 |
22 |
[0095] As clear from a comparison between the inventive examples 10 to 15 and the comparative
examples 10 to 15 as shown in Tables 5 to 6, the primary and secondary additives of
the invention were added as lubricants, thereby the die was simply heated to a relatively
low temperature of less than 100°C, so that even if the powder mixture was not heated,
a compacted body having high density, which was similar to that of a typical warm
compacted body, was able to be obtained without causing increase in ejection force.
[0096] Flank wear width (mm) of each inventive example was reduced to about 20 to 40% of
that of a comparative example in the same grouping (number), showing remarkable improvement
even in machining performance.
(Example 3)
[0097] Various types of iron-based powder as shown in Table 7, and natural graphite powder
and/or copper powder were added with various lubricants (primary additives), then
heated to 140°C while being mixed by a high-speed mixer, and then cooled to 60°C or
lower, and further added with various lubricants (secondary additives), and agitated
for 1 min at 500 rpm. Then, a powder mixture was discharged from the mixer. A type
and blending amount of each of the primary and secondary additives are collectively
shown in Table 7. Used materials are the same as in the example 1.
[0098] For comparison, powder mixtures were prepared in a way that each of various types
of powder was added with ethylene-bis-stearoamide having a respective weight, then
mixed by a V-container-turning mixer.
[0099] Next, each of the obtained iron-based powder mixtures was heated to 60°C, then filled
in a superhard tablet-shaped die having an inner diameter of 11 mm, which was heated
beforehand such that temperature of a cavity wall surface was increased to 80°C, and
furthermore coated with lithium stearate powder on its wall surface, and then the
powder mixture was compacted at 490 MPa and 686 MPa. In such compaction, when a compacted
body was ejected from the die, ejection force was measured, and green density of each
of the obtained compacted bodies was measured.
[0100] Moreover, each of the comparative materials was compacted at a typical compaction
condition of warm compaction, that is, the comparative material was heated to 120°C,
then filled into a superhard tablet-shaped die having an inner diameter of 11 mm and
which was heated to 130°C, and then compacted at 490 MPa and 686 MPa. In such compaction,
when a compacted body was ejected from the die, ejection force was measured, and green
density of each of the obtained compacted bodies was measured.
[0101] Moreover, test pieces for a machining test were prepared by compaction as in the
example 1, so that machining performance was examined.
[0102] Obtained results are shown in Table 8.
Table 7
|
Iron-based powder |
Natural graphite powder (mass%) |
Copper powder |
Primary additive lubricant* |
Secondary additive lubricant* |
type |
Blending amount (mass%) |
type |
Blending amount (mass%) |
type |
Blending amount (mass%) |
type |
Blending amount (mass%) |
Inventive example 16 |
A |
97.2 |
0.8 |
Electrolytic copper powder |
2.0 |
STAM |
0.2 |
Steatite |
0.2 |
EBS |
0.2 |
STZN |
0.04 |
- |
- |
EBS |
0.16 |
Inventive example 17 |
G |
99.35 |
0.65 |
- |
0 |
STAM |
0.1 |
Talc |
0.1 |
EBS |
0.1 |
STZN |
0.02 |
- |
- |
EBS |
0.08 |
- |
|
STLI |
0.1 |
Comparative example 16 |
A |
97.2 |
0.8 |
Electrolytic copper powder |
2.0 |
0.8 mass % EBS |
Comparative example 17 |
G |
99.35 |
0.65 |
- |
0 |
0.6 mass % EBS |
* EBS: ethylene-bis-stearoamide, STZN: zinc stearate, STAM: stearic acid monoamide,
STLI: lithium stearate |
Table 8
|
Iron-based powder |
Compaction temperature |
Green density (Mg/m3) |
Ejection force (MPa) |
Type |
Powder (°C) |
Die (°C) |
490 MPa compaction |
686 MPa compaction |
490 MPa compaction |
686 MPa compaction |
Inventive example 16 |
A |
60 |
80 |
6.90 |
7.19 |
8 |
11 |
Inventive example 17 |
G |
60 |
80 |
7.04 |
7.29 |
15 |
19 |
Comparative example 16 |
A |
120 |
130 |
6.94 |
7.2 |
9 |
12 |
Comparative example 17 |
G |
120 |
130 |
7.00 |
7.26 |
16 |
19 |
[0103] As clear from a comparison between the inventive example 16 and the comparative example
16, and a comparison between the inventive example 17 and the comparative example
17 as shown in Tables 7 to 8, the primary and secondary additives of the invention
were added as lubricants, thereby the die and the powder were simply heated to a relatively
low temperature of less than 100°C, so that a compacted body having high density,
which was similar to that of a typical warm compacted body, was able to be obtained
with an extremely low ejection force.
[0104] Flank wear width (mm) of each inventive example was reduced to about 25 to 35% of
that of a comparative example in the same grouping (number), showing remarkable improvement
even in machining performance.
(Example 4)
[0105] Various types of iron-based powder as shown in Table 9, and natural graphite powder
and/or copper powder were added with various lubricants (primary additives), then
heated to 140°C while being mixed by a high-speed mixer, and then cooled to 60°C or
lower, and further added with various lubricants (secondary additives), and agitated
for 1 min at 500 rpm. Then, a powder mixture was discharged from the mixer. A type
and blending amount of each of the primary and secondary additives are collectively
shown in Table 9. Used materials are the same as in the example 1. A comparative example
20 was subjected to processing where the relevant powder was added with steatite powder
in place of the primary and secondary additives, then mixed by the high-speed mixer
at the same condition as in the above.
[0106] Next, each of the obtained iron-based powder mixtures was filled in a superhard tablet-shaped
die having an inner diameter of 11 mm, and compacted at 490 MPa and 686 MPa. In such
compaction, when a compacted body was ejected from the die, ejection force was measured,
and green density of each of obtained compacted bodies was measured.
[0107] Separately from this, the obtained iron-based powder mixtures were subjected to compaction
for preparing tensile test pieces according to Japan Powder Metallurgy Association
JPMA M04-1992, and test pieces for a machining test (outer diameter of 60 mm, inner
diameter of 20 mm, and length of 30 mm). In the compaction, pressing force was 590
MPa. Sintering was performed in an RX gas atmosphere, wherein heating temperature
was 1130°C, and heating time was 20 min. An evaluation method of machining performance
was the same as in the example 1.
[0108] Obtained results are shown in Table 10.
Table 9
|
Iron-based powder graphite |
Natural graphite powder (mass%) |
Copper powder |
Prima additive lubricant* |
Secondary additive lubricant* |
type |
Blending amount (mass%) |
type |
Blending amount (mass%) |
type |
Blending amount (mass%) |
type |
Blending amount (mass%) |
Comparative example 18 |
D |
99.4 |
0.6 |
- |
0 |
STAM |
0.1 |
STLI |
0.1 |
EBS |
0.1 |
STZ |
0.02 |
- |
- |
EBS |
0.08 |
Inventive example 18 |
D |
99.4 |
0.6 |
- |
0 |
STAM |
0.1 |
Steatite |
0.05 |
EBS |
0.1 |
STLI |
0.1 |
- |
- |
STZN |
0.02 |
- |
- |
EBS |
0.08 |
Inventive example 19 |
D |
99.4 |
0.6 |
- |
0 |
STAM |
0.1 |
Steatite |
0.1 |
EBS |
0.1 |
STLI |
0.1 |
- |
- |
STZN |
0.02 |
- |
- |
EBS |
0.08 |
Inventive example 20 |
D |
99.4 |
0.6 |
- |
0 |
STAM |
0.1 |
Steatite |
0.2 |
EBS |
0.1 |
STLI |
0.1 |
- |
- |
STZN |
0.02 |
- |
- |
EBS |
0.08 |
Inventive example 21 |
D |
99.4 |
0.6 |
- |
0 |
STAM |
0.1 |
Steatite |
0.3 |
EBS |
0.1 |
STLI |
0.1 |
- |
- |
STZN |
0.02 |
- |
- |
EBS |
0.08 |
Comparative example 19 |
D |
99.4 |
0.6 |
- |
0 |
STAM |
0.1 |
Steatite |
0.6 |
EBS |
0.1 |
STLI |
0.1 |
- |
- |
STZN |
0.02 |
- |
- |
EBS |
0.08 |
Inventive example 22 |
I |
97.2 |
0.8 |
Electrolytic copper powder |
2.0 |
STAM |
0.1 |
Steatite |
0.1 |
EBS |
0.1 |
STLI |
0.1 |
STZN |
0.1 |
- |
- |
Comparative example 20 |
I |
97.2 |
0.8 |
Electrolytic copper powder |
2.0 |
Steatite |
0.1 |
- |
- |
Inventive example 23 |
I |
97.2 |
0.8 |
Electrolytic copper powder |
2.0 |
STAM |
0.2 |
Steatite |
0.1 |
EBS |
0.2 |
- |
- |
Comparative example 21 |
I |
97.2 |
0.8 |
Electrolytic copper powder |
2.0 |
STZN |
0.2 |
Steatite |
0.1 |
|
|
STLI |
0.2 |
* EBS: ethylene-bis-stearoamide, STZN: zinc stearate, STAM: stearic acid monoamide,
STLI: lithium stearate |
Table 10
|
Iron-based powder |
Green density (Mg/m3) |
Ejection force (MPa) |
Sintered body |
Cutting tool |
|
Type |
490 MPa compaction |
686 MPa compaction |
490 MPa compaction |
686 MPa compaction |
Tensile strength (MPa) |
Flank wear width (mm) |
Comparative example 18 |
D |
6.99 |
7.24 |
14 |
18 |
630 |
0.92 |
Inventive example 18 |
D |
6.99 |
7.25 |
13 |
17 |
625 |
0.65 |
Inventive example 19 |
D |
7.00 |
7.25 |
12 |
16 |
610 |
0.54 |
Inventive example 20 |
D |
6.97 |
7.23 |
13 |
17 |
590 |
0.51 |
Inventive example 21 |
D |
6.95 |
7.21 |
13 |
18 |
550 |
0.45 |
Comparative example 19 |
D |
6.94 |
7.20 |
15 |
19 |
490 |
0.43 |
Inventive example 22 |
I |
6.99 |
7.23 |
12 |
18 |
620 |
0.03 |
Comparative example 20 |
I |
Compaction is disabled due to galling. |
Inventive example 23 |
I |
6.98 |
7.22 |
13 |
19 |
630 |
0.05 |
Comparative example 21 |
I |
6.96 |
7.20 |
20 |
20 |
610 |
0.06 |
[0109] As clear from a comparison between the inventive examples 18 to 21 and the comparative
examples 18 and 19 as shown in Tables 9 to 10, in the iron-based powder mixture in
which steatite and the like are added within a range of the invention, a high-density
compacted body can be obtained without increasing ejection force. In the comparative
example 19 in which steatite and the like are added in a range of more than 0.5 mass%,
mechanical properties are significantly reduced. Furthermore, it is known from the
inventive examples 18 to 21 that the added amount of steatite and the like is more
preferably 0.2 mass% or less in the light of the mechanical properties.
[0110] As clear from a comparison between the inventive examples 22 and 23 and the comparative
examples 20 and 21, fatty acid amide and the like need to be added with steatite and
the like to obtain a high-density compacted body without increasing ejection force.
Moreover, it is known that metallic soap is further added, thereby machining performance
of a sintered body can be remarkably improved.
(Example 5)
[0111] Water-atomized alloyed steel powder having a composition shown in Table 11 was manufactured
by a water-atomizing method. The rest of the powder other than Mn and Mo is Fe and
inevitable impurities. The water-atomized alloyed steel powder was added with Cu powder,
graphite powder, talc, and steatite in a ratio as shown in the Table 11. Each of Mo
content and Mn content (mass%) in the water-atomized steel powder, or each of the
added amount (mass%) of the Cu powder, graphite powder, talc, and steatite to be added
to the water-atomized steel powder is shown in percentage of mass of a powder mixture
for powder metallurgy, the percentage being expressed using a numerical value included
in a numerical value of mass of the powder mixture.
[0112] Furthermore, a lubricant was added in a ratio as shown in Table 11. The added amount
(part by mass) of the lubricant is shown in percentage of mass (100 part by mass)
of a powder mixture for powder metallurgy obtained by mixing the water-atomized alloyed
steel powder and additives, the percentage being expressed using a numerical value
being not included in a numerical value of moss of the powder mixture (but, the percentage
is approximately the same as in the case that it is expressed using a numerical value
included therein).
[0113] Next, the materials were mixed by a V blender, then an obtained powder mixture for
powder metallurgy was filled in a die so as to be subjected to compaction for preparing
tensile test pieces according to Japan Powder Metallurgy Association JPMA M04-1992,
and test pieces for a machining test (outer diameter of 60 mm, inner diameter of 20
mm, and length of 30 mm). In the compaction, pressing force was 590 MPa. Sintering
was performed in an RX gas atmosphere, wherein heating temperature was 1130°C, and
heating time was 20 min.
[0114] Tensile strength obtained by a tensile test was as shown in Table 11.
[0115] In evaluation of machining performance, while a cermet cutting tool was used, a machining
test was performed with cutting speed of 200 m/min, feed of 0.1 mm per unit, depth
of cut of 0.3 mm, and a cutting distance of 1000 m, and flank wear width of the cutting
tool was measured. Results of the measurement are as shown in Table 11. Smaller flank
wear width of the cutting tool shows more excellent machining performance of a sintered
body.
[0116] In Table 11, inventive examples use a powder mixture for powder metallurgy that satisfies
the scope of the invention, and comparative examples use a powder mixture for powder
metallurgy that departs from the scope of the invention. In a prior-art example of
No. 22, a powder mixture for powder metallurgy using Fe-4Ni-1.5Cu-0.5Mo water-atomized
alloyed steel powder, which is previously practically used, is blended with a conventional
lubricant. Numerical values added to respective alloy elements of No. 22 are expressed
in mass%.
Table 11
No |
Powder mixture for powder metallurgy (mass%)*1 |
Lubricant 1 |
Lubricant 2 |
Sintered Cutting body tool |
Remarks |
Water-atomized alloyed steel powder |
Cu powder |
Graphite powder |
Talc |
Steatite |
Type *2 |
Added amount (part by mass) *3 |
Type *2 |
Added amount (part by mass) *3 |
Tensile strength (MPa) |
Flank wear width (mm) |
Mo |
Mn |
1 |
0.45 |
0.21 |
0.0 |
0.8 |
0.1 |
- |
EBS |
0.4 |
- |
- |
380 |
0.04 |
Inventive example |
2 |
0.45 |
0.21 |
1.5 |
0.8 |
0.1 |
- |
EBS |
0.4 |
- |
- |
520 |
0.08 |
Inventive example |
3 |
0.45 |
0.21 |
2.0 |
0.8 |
0.1 |
- |
EBS |
0.4 |
- |
- |
630 |
0.08 |
Inventive example |
4 |
0.45 |
0.21 |
3.0 |
0.8 |
0.1 |
- |
EBS |
0.4 |
- |
- |
650 |
0.15 |
Inventive example |
6 |
0.45 |
0.05 |
2.0 |
0.8 |
- |
0.1 |
STAM |
0.2 |
STZN |
0.2 |
480 |
0.02 |
Comparative example |
7 |
0.45 |
0.12 |
2.0 |
0.8 |
- |
0.1 |
STAM |
0.2 |
STZN |
0.2 |
550 |
0.02 |
Inventive example |
8 |
0.45 |
0.19 |
2.0 |
0.8 |
- |
0.1 |
STAM |
0.2 |
STZN |
0.2 |
640 |
0.04 |
Inventive examplee |
10 |
0.2 |
0.20 |
2.0 |
0.8 |
0.1 |
0.1 |
STAM |
0.4 |
- |
- |
430 |
0.07 |
Inventive example |
11 |
0.3 |
0.20 |
2.0 |
0.8 |
0.1 |
0.1 |
STAM |
0.4 |
- |
- |
540 |
0.07 |
Inventive example |
12 |
0.5 |
0.20 |
2.0 |
0.8 |
0.1 |
0.1 |
STAM |
0.4 |
- |
- |
630 |
0.07 |
Inventive example |
14 |
0.45 |
0.21 |
2.0 |
0.4 |
0.1 |
- |
EBS |
0.5 |
- |
- |
410 |
0.05 |
Inventive example |
15 |
0.45 |
0.21 |
2.0 |
0.6 |
0.1 |
- |
EBS |
0.5 |
- |
- |
530 |
0.05 |
Inventive example |
16 |
0.45 |
0.21 |
2.0 |
0.9 |
0.1 |
- |
EBS |
0.5 |
- |
- |
620 |
0.10 |
Inventive example |
18 |
0.45 |
0.21 |
2.0 |
0.8 |
- |
- |
EBS |
0.3 |
STLI |
0.15 |
650 |
0.30 |
Comparative example |
19 |
0.45 |
0.21 |
2.0 |
0.8 |
- |
0.3 |
EBS |
0.3 |
STLI |
0.15 |
640 |
0.02 |
Inventive example |
20 |
0.45 |
0.21 |
2.0 |
0.8 |
- |
0.5 |
EBS |
0.3 |
STLI |
0.15 |
600 |
0.02 |
Inventive example |
21 |
0.45 |
0.21 |
2.0 |
0.8 |
- |
0.7 |
EBS |
0.3 |
STLI |
0.15 |
460 |
0.01 |
Comparative example |
22 |
Fe-4Ni-1.5Cu-05Mo |
0.6 |
- |
|
EBS |
0.5 |
EBS |
0.5 |
590 |
0.48 |
Prior-art example |
*1 percentage of mass of powder mixture for powder metallurgy (by a numerical value
included in a numerical value of the mass)
*2 EBS: ethylene-bis-stearoamide, STZN: zinc stearate, STAM: stearic acid monoamide,
STLI: lithium stearate
*3 percentage of mass of powder mixture for powder metallurgy (by a numerical value
not included in a numerical value of the mass) |
[0117] As obvious from Table 11, particularly, any of sintered bodies obtained from the
powder mixtures for powder metallurgy of the inventive examples are excellent in mechanical
properties and machining performance. The prior-art example is particularly significantly
bad in machining performance of a sintered body.
[0118] When the water-atomized alloyed steel powder contains Mo of 0.3 to 0.5 mass% and
Mn of 0.1 to 0.25 mass%, and the powder mixture contains Cu powder of 1 to 3 mass%
and graphite powder of 0.5 to 1.0 mass%, a sintered body can be obtained, which has
a tensile strength of 500 MPa or more, and is excellent in machining performance.
Industrial Applicability
[0119] According to the invention, an iron-based powder mixture can be obtained, which gives
high compaction density and small ejection force even if the powder mixture is compacted
at low temperature of about room temperature. Moreover, according to a preferred invention,
a powder mixture for powder metallurgy can be obtained, which is preferable for machining
a sintered part having excellent machining performance, particularly, preferable for
machining a high-strength sintered part.
[0120] Moreover, according to the invention, the iron-based powder mixture is used as a
material, thereby an iron-based compacted body having high compaction density can
be obtained, and furthermore, an iron-based sintered body can be obtained, which has
high sintering density, or has further excellent machining performance.