Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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COMPOSITIONS AND METHODS FOR SINTERING POWDERED
METAL COMPACTS USING LITTLE OR NO HYDROGEN
CROSS-REFERENCE TO RELATED APPLICATIONS
[OM] The present application claims benefit from U.S. Provisional Patent
Application
Ser. No. 62/431,970 filed December 9, 2016, which is incorporated herein by
reference.
BACKGROUND OF INVENTION
[0002] Field of Invention
[0003] The present invention relates to compositions and methods for
sintering
powdered metal compacts using little or no hydrogen gas in pressed powder
metallurgy
processes.
[0004] Brief Description of Related Art
[0005] In pressed powder metallurgy, a substantially dry metal powder
composition is
charged into a die cavity of a die press and compressed to form a green
compact.
Pressing causes the metal powder particles in the metal powder composition to
mechanically interlock and form cold-weld bonds that are strong enough to
allow the
green compact to be handled and further processed. After pressing, the green
compact
is removed from the die cavity and sintered at a temperature that is below the
melting
point of the major metallic constituent of the metal powder composition, but
sufficiently
high enough to strengthen the bond between the metal powder particles,
principally
through solid-state diffusion.
[0006] In pressed powder metallurgy applications, a lubricant may be added
to the dry
metal powder composition before it is pressed to form the green compact.
Lubricant helps
the metal powder particles to move into all portions of the die cavity, allows
for some
particle-to-particle realignment during pressing, and serves as a release
agent that
facilitates removal of the green compact from the die cavity after pressing.
The least
amount of lubricant necessary to obtain good flow and release is usually used.
This is
because lubricants can also detrimentally impact green density and result in
the evolution
of undesirable effluents during delubing and the sintering operations.
Lubricants can also
contribute to low final density in metal parts, protracted furnace time
necessary for
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removing the lubricants in a "delubing" operation, and the formation of cracks
and blisters
during sintering.
[0007] Conventionally, after pressing the lubricant is removed from the
green compact
in a delubing operation, which can involve gradually heating the green compact
at a
relatively low heating rate (e.g., about 15 F/min) until the lubricant melts,
boils, and/or
thermally decomposes (e.g. burns off) so that it is completely removed from
the green
compact. Delubing is typically accomplished during a preheating stage before
sintering,
or during an initial heating stage at the beginning of the sintering process.
The lubricant
is completely removed from the green compact at a temperature that is lower
than the
sintering temperature.
[0008] It is a common practice in the powdered metal processing of iron
based
powdered metal parts to sinter in a reducing atmosphere such as disassociated
ammonia,
endo gas, or a hydrogen/nitrogen mixture. This atmosphere helps to remove
metal oxides
from the surface of metal powder. Removal of the metal oxides from the
surfaces of the
metal powder allows the metal powder to more fully sinter to form a metal part
having
higher densities and/or better properties with density similar to the green
density of the
metal powder compact. However, all of these conventional systems have some
safety,
operational, and cost concerns. In recent years a hydrogen/nitrogen mixture
has been
mostly adopted due to convenience and in-plant part-to-part reproducibility.
Hydrogen is
generally believed to be necessary for effective sintering due to its ability
to act as a
reducing agent for the metal oxides that are commonly on the surfaces of metal
powder.
Iron powder for example typically contains 1,000 to 1,500 ppm or higher of
oxides on the
metal particle surface prior to sintering. Such oxides are believed to inhibit
sintering
together of the metal powder particles, and thus present a barrier to
achieving an
acceptable sintered density and acceptable resulting properties for the metal
part.
[0009] Ideally, the sintered density of a final part would be 100% of the
theoretical
density of the metallic constituents of the metal powder composition used to
form the part.
However, the sintered density of parts formed from most conventional metal
powder
compositions does not approach 100% of theoretical density. Using conventional
high
carbon or low alloy steel metal powder compositions and pressed powder
metallurgy
methods, only a sintered density of about 93% to 94% of theoretical density
can be
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achieved in one pressing and sintering. For stainless steels, sintered
densities are
typically less than 90% of theoretical density for conventional powder
metallurgy
compositions. Additional processing steps, such as forging and repressing are
required
to increase the density of the sintered metal part.
[0010] In recent years, powdered metal process plants have reduced the
amount of
hydrogen in the sintering atmosphere for reasons such as cost and safety.
Typical
sintering is presently conducted using an atmosphere consisting of between 5-
25 volume
percent hydrogen for iron sintered parts, with the balance being nitrogen.
Some sintered
parts use higher percentages of hydrogen including up to 100% for some alloys
such as
stainless steel. If the amount of hydrogen in the sintering atmosphere could
be
substantially reduced or eliminated, there would be significant cost savings
(estimated to
be up to 6 cents per pound of the final sintered product) and reduced safety
hazards.
BRIEF SUMMARY OF THE INVENTION
[0011] In one aspect, a method a method of forming a metal part comprises
providing
a composition comprising metal powder and at least 0.5 wt% lubricant system.
The
lubricant system includes 10-30 wt% stearic acid, 0.1-5 wt% guanidine
material, 0.1-0.8
wt% antioxidant, 5-15 wt% microcrystalline wax, 10-30 wt%
polyethylene/polypropylene
copolymer wax, and 40-60 wt% ethylene bis(stearamide). Pressure is applied to
the
composition to thereby form a green compact, and the green compact is delubed
in a
delubing atmosphere that contains less than 5 volume % hydrogen gas, and more
preferably 0% hydrogen gas, to thereby form a metal part. The method can
further include
sintering the green compact in a sintering atmosphere that contains less than
5 volume
% hydrogen gas, and more preferably 0% hydrogen gas.
[0012] In another aspect, a lubricant system comprises 10-30 wt% stearic
acid, 0.1-5
wt% guanidine material, 0.1-0.8 wt% antioxidant, 5-15 wt% microcrystalline
wax, 10-30
wt% polyethylene/polypropylene copolymer wax, and 40-60 wt% ethylene
bis(stearamicle). When the lubricant system is combined in an amount of at
least 0.5 wt%
with metal powder and compressed into a green compact, and the green compact
is
delubed and sintered in an atmosphere that contains less than 5 volume %
hydrogen gas,
and more preferably 0% hydrogen gas, to thereby form a metal part.
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[0013] The foregoing and other features of the invention are hereinafter
more fully
described below, the following description setting forth in detail certain
illustrative
embodiments of the invention, these being indicative, however, of but a few of
the various
ways in which the principles of the present invention may be employed.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The present invention provides a solid lubricant system for use in
powder
metallurgy. The lubricant system is solid at ambient conditions, but upon
application of
press pressure (forming pressure and stress) it transforms to a liquid phase.
In addition
to the lubricant system, the present invention also provides a composition
further
including metal powder, and a method of using the lubricant system and metal
powder
composition to form a metal part. The lubricant system of the present
invention may also
be used in connection with the pressing of ceramic powders.
[0015] The lubricant system provides lubrication during powder metallurgy
processes,
and results in good flow of the metal powder composition, ease of removal of
the green
part from the mold cavity, the formation of minimal effluents during heating,
and can be
used at low loading levels. Because less lubricant system is utilized, green
density
increases due to less volume of lubricant system and due to particle-to-
particle
rearrangement caused by slippage at low pressure. As green density improves,
final part
properties also improve (e.g., sintered density, strength, hardness, greater
uniformity and
fewer defects). By use of the lubricant system of the present invention,
excellent green
densities are achieved without the use of special equipment such as added
heating
devices as used in conventional hot pressing or the use of die wall
lubricating systems.
[0016] Metal powder compositions according to the present invention
comprise metal
powder, e.g. one type or a blend/mixture of different types of metal
particles, and a
lubricant system, which can be include in an amount of at least 0.5 wt%, 0.5-3
wt%,
wt%, 0.5-0.6 wt%, or 0.5 wt% of the metal powder composition.
[0017] The metal powder and the lubricant system are mixed together to form a
metal
powder composition. The lubricant system is capable under pressure or heat, of
transforming from a solid to a viscous liquid, and includes one or more
organic
compounds that upon delubing, are capable of depositing a reactive carbon
residue on
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the metal powder. It is believed that the reactive carbon residue is
effectively spread onto
the surface of each iron particle since the lubricant transforms from a solid
into a viscous
liquid, thereby making a very efficient mechanism to coat the iron particles
with reactive
carbon residue.
[0018] Applicant theorizes that when the metal powder compositions
according to the
invention are delubed (which is also sometimes referred to in the art as
"debound") in
nitrogen, one or more organic compounds present in the lubricant system react
and/or
thermally decompose to form highly reactive carbon-containing species that are
deposited as a residue layer on the surface of the metal particles.
[0019] The carbon-containing species on the outer surface of the metal
powder are
thus available during subsequent sintering to react with the metal oxides on
the outer
surface of the metal particles to thereby form volatile compounds such as
carbon
monoxide and/or carbon dioxide. This mechanism removes metal oxides from the
outer
surface of the metal particles at temperatures well below where solid state
diffusion and
liquid phase formation occurs.
[0020] With the removal of metal oxides from the outer surface of the metal
powder,
the metal powder can therefore more fully sinter and achieve a metal part with
better
properties, and without the need for a hydrogen-containing sintering
atmosphere.
[0021] Applicant previously disclosed compositions and methods for pressed
powder
metallurgy in U.S. Pat. No. 8,062,582, which is hereby incorporated by
reference in its
entirety. The compositions and methods disclosed therein sought to remove
oxides from
the outer surface of metal particles in situ in order to achieve near full
density metal parts
when powdered metal compacts formed of such particles were sintered. To
achieve near
full density upon sintering, such compositions and methods utilized relatively
low loadings
(0.1% to about 4% by volume) of an organics package, which was intended to
leave only
a small amount of a carbon residue on the outer surface of the metal particles
subsequent
to a delubing heating cycle.
[0022] Applicant has surprisingly discovered that one can modify the
compositions and
methods previously disclosed in U.S. Pat. No. 8,062,582 to produce sintered
powdered
metal compacts in nitrogen only that have properties equivalent or better than
can be
achieved in conventional sintering processes where hydrogen is present.
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[0023] The metal powder included in the metal powder composition can comprise
one
or more populations of metal particles, including particles of a single
metallic element
(e.g., iron powder), pre-alloyed particles (e.g., low-alloy steel powders or
stainless steels
powders), agglomerations, blends, or mixtures of two or more populations of
particles that
are made from different metallic elements (e.g. a mixture of iron powder and
nickel
powder). Suitable metallic elements include, for example, iron, copper,
chromium,
aluminum, nickel, cobalt, manganese, niobium, titanium, molybdenum, tin and
tungsten.
It will be appreciated that metal powder compositions according to the
invention can
include other additive elements, such as bismuth, vanadium and manganese
(typically in
the form of manganese sulfide) for example, and other conventional additives.
[0024] The metal particles used in the metal powder compositions according
to the
invention tend to have outer surfaces that are oxidized, typically as a result
of contact with
oxygen in the atmosphere or with water vapor. Metal particles comprising iron,
which are
frequently used in pressed powder metallurgy to form steel parts, have
surfaces that are
oxidized in the form of iron oxide, which oxide is present typically at 1,000
to 1,500 ppm
of the metal powder. Applicant believes that metal oxides on the surface of
metal particles
may interfere with solid-state diffusion bonding between such particles during
sintering.
The metal oxides on the surface of the metal particles may also inhibit the
solid state
diffusion and formation of liquid phase alloys, which can be used to solder,
weld or
otherwise bind the individual metal particles together.
[0025] In several embodiments, the lubricant system includes or consists of
stearic
acid, guanidine material, antioxidant, microcrystalline wax,
polyethylene/polypropylene
copolymer wax ("PE/PP wax"), and ethylene bis(stearamide). In one embodiment,
the
lubricant system is free of lauric acid.
[0026] The stearic acid may be included at 5-35 wt%, 10-30 wt% or 15-25 wt% of
the
lubricant system. A suitable stearic acid may be Emersol 120, Emersol 132 F,
Emery
400, Emery 405, Emery 410, Emery 420, Emery 422, Edenor0 C1865 MY,
Edenor0 C1892 MY, and Emersol 153 NF available from Emery Oleochemicals,
Selangor, Malaysia. In one embodiment, a rubber grade stearic acid, such as
Emery
420 is used.
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[0027] The guanidine material may be included at up to 5 wt%, 0.1-5 wt%, or
1-4 wt%
of the lubricant system. In one embodiment, the guanidine material is a
reaction product
of guanidine and an acid selected from a fatty acid, an organic acid, or a
stronger acid.
The guanidine material is a reaction product which may be an amide or a
hydrated salt.
For example, according to the CRC Handbook of Chemistry and Physics, 74th Ed.,
guanidine acetate has the formula (H21\)2,C=NH.CH3COOH, rather than an amide-
type
formula such as H2N¨C=NH(NH)COCH3, as would be expected for an amide. This is
due
to the fact that guanidine is a very strong base, and is much more likely to
simply extract
a proton from a relatively weak organic acid, rather than react with the
organic acid in a
"standard" amidization reaction forming an amide with concomitant loss of H20.
However,
in some cases, the reaction of guanidine and the acid may yield an amide in
the "standard"
manner. For this reason, the guanidine material of the present invention will
be referred
to herein as the reaction product of guanidine and an acid. The term "reaction
product of
guanidine and an acid" includes both of the above-described forms of the
product of a
reaction between or mixture of guanidine and an acid, and mixtures of these
forms or
other possible forms.
[0028] The particular acid used to make the reaction product of guanidine
and an acid
is selected based upon obtaining desired effects when mixed with other
compounds. In
one embodiment, the guanidine material is guanidine stearate. In one
embodiment, the
guanidine material includes guanidine ethyl hexanoate. In other embodiments,
the
guanidine material may be the reaction product of guanidine and other acids.
[0029] According to the present invention, the guanidine material may
include the
reaction product of guanidine and other organic acids in the C,to C.range.
Thus, for
example the reaction product of guanidine and oleic acid (C,H33CO2H) would be
suitable.
Other suitable acids include such saturated fatty acids as (common names in
parentheses) dodecanoic (lauric) acid, tridecanoic (tridecylic) acid,
tetradecanoic
(myristic) acid, pentadecanoic (pentadecylic) acid, hexadecanoic (palmitic)
acid,
heptadecanoic (margaric) acid, octadecanoic (stearic) acid, eicosanoic
(arachidic) acid,
3,7,11,15-tetramethylhexadecanoic (phytanic) acid, monounsaturated, di
unsaturated,
triunsaturated and tetraunsaturated analogs of the foregoing saturated fatty
acids.
Additional organic acids include acids such as ethylhexanoic acid (C7HõCO21-
1), hexanoic
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acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, and
dodecanoic acid.
Branched-chain carboxylic acids in the CA C2 range may also be used.
[0030] According to the present invention, the reaction product of
guanidine and
stronger acids such as sulfonates, phthalates, benzoates, phosphates and
phenols may
be used. For example, the reaction product of guanidine and an acid such as
benzenesulfonic acid may be used. As an alternative, intermediate acids may be
selected
for reaction with guanidine. Alternatively, the guanidine material used in the
lubricant
system may be the reaction product of guanidine and a weaker acid such as
benzoic acid.
[0031] In a one embodiment, the guanidine material comprises a mixture of
guanidine
stearate and guanidine ethyl hexanoate. A suitable guanidine material is APEX
Special
Purpose Additives - Surface Agent Mixture, available from Apex Advanced
Technologies
LLC, Cleveland, Ohio.
[0032] The antioxidant can be included at up to 1 wt%, 0A-0.8 wt%, 010.1-
0.5 wt% of
the of the lubricant system. Suitable antioxidants include, but are not
limited to, tris (2,4-
di-tert-butylphenyl) phosphite, bis (2,4-dicumylphenyl) pentaerythritol
diphosphite, bis
(2,4-dicumylphenyl) pentaerythritol diphosphate, bis (2,4-dicumylphenyl)
pentaerythritol
diphosphite, distearyl pentaerythritol diphosphite, and combinations thereof.
In one
embodiment, the antioxidant is Doverphos S-480, which is tris (2,4-di-tert-
butylphenyl)
phosphite available from Dover Chemical Corporation, of Dover, Ohio.
[0033] The microcrystalline wax can be included at 1-20 wt%, 3-18 wt%, 01 5-
15 wt%
of the lubricant system. A suitable microcrystalline wax is a lamination grade
microcrystalline wax available from Sovereign Chemicals & Cosmetics, of
Maharashtra,
India, which has a drop melting point of 70-80 C, a needle penetration at 25 C
of 25-45,
an oil content of less than 2%, a viscosity at 98.9 C of 15-20 CST.
[0034] The polyethylene/polypropylene copolymer wax ("PE/PP wax") may be
included at 5-35 wt%, 10-30 wt%, or 15-25 wt% of the lubricant system. A
suitable PE/PP
wax includes but is not limited to PE 520 available from Clariant
International Ltd., of
Charlotte, North Carolina.
[0035] The ethylene bis(stearamide) can be included at 35-65 wt%, 40-60
wt%, or 45-
55 wt% of the lubricant system. A suitable ethylene bis(stearamide) is
Struktol TR EBS,
or Struktol TR EBS VG, available from Struktol Company of America, of Stow,
Ohio.
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[0036] The lubricant system thus preferably comprises 10-30 wt% stearic
acid, 0.1-5
wt% guanidine material, 0.1-0.8 wt% antioxidant, 5-15 wt% microcrystalline
wax, 10-30
wt% polyethylene/polypropylene copolymer wax, and 40-60 wt% ethylene
bis(stearamide). In addition, the lubricant system or metal powder composition
can
optionally include various additives including a binder, a plasticizer, a
degreasing
promoting agent, a surfactant, etc. as desired. In another embodiment, the
lubricant
system consists essentially of 10-30 wt% stearic acid, 0.1-5 wt% guanidine
material, 0.1-
0.8 wt% antioxidant, 5-15 wt% microcrystalline wax, 10-30 wt%
polyethylene/polypropylene copolymer wax, and 40-60 wt% ethylene
bis(stearamide).
[0037] In a method of forming a metal part by powder metallurgy, a metal
powder
composition as disclosed herein is provided. The composition can include metal
powder,
and a lubricant system including stearic acid, guanidine material,
antioxidant,
microcrystalline was, PE/PP wax, and ethylene bis(stearamide) in the amounts
as
discussed herein. The method includes one or more of arranging the composition
in a
die cavity, applying pressure to the composition to thereby form a green
compact,
removing the green compact from the die cavity, delubing the green compact,
and
sintering the green compact to thereby form a metal part.
[0038] In one embodiment, the metal powder composition is arranged in a die
cavity
and pressed to form a green powder metal compact. During pressing of the
composition
in the die cavity, the lubricant system transforms from a solid to a viscous
liquid and then
flows around each metal particle and deposits onto an outer surface of the
metal powder
particles, and also flows to the walls of the die cavity to aid in release of
the green
compact.
[0039] In an embodiment, the green compact is delubed in a substantially
non-
hydrogen-containing atmosphere such as nitrogen. The one or more organic
compounds
that are part of the lubricant system, are capable of being reduced during the
delubing
step to form reactive carbon-containing species on the surface of the metal
powder
particles. One or more of the organic compounds present in the lubricant
system
decompose by being "carburized" during delubing. The term "carburize" as used
in this
application means that one or more of the organic compounds present in the
lubricant
system react or otherwise thermally decompose to form reactive carbon-
containing
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species that are deposited as solids in the form of a layer or coating on the
outer surface
of the metal particles during delubing. In one embodiment, the
microcrystalline wax is the
component in the lubricant system that provides the most reactive carbon
residue on the
metal powder. This reactive carbon coating substantially reduces, if not
eliminates, the
need for using a hydrogen gas atmosphere during sintering. Optimally, the
layer of
reactive carbon-containing species is present in an amount sufficient to
reduce oxides on
the surface of the metal particles as the temperature during the sintering
process rises to
final sintering temperature, but without substantially imparting carbon into
the sintered
metal part. Ideally, the one or more organic compounds present in the
lubricant system
are selected such that the carbon in the carbon-containing species deposited
on the
surface of the particles is present at a molar weight ratio so as to be
capable of removing
oxides on the metal surface (e.g., the carbon to oxygen molar weight ratio is
2.66 to 1 for
carbon dioxide, and 1.33 to 1 for carbon monoxide) during sintering. The
reactive carbon-
containing species have the ability to react with metal oxides to form carbon
monoxide or
carbon dioxide, and without diffusing carbon into the metal part in
significant amounts.
[0040] One or more of the other organic compounds present in the lubricant
system
may "vaporize" during delubing. The term "vaporize" as used in this
application means
that one or more of the other organic compounds present in the lubricant
system react or
otherwise thermally decompose to form volatile gases, which are removed from
the green
compact during delubing.
[0041] Delubing and sintering can be performed in an atmosphere that
contains less
than 5 volume % hydrogen gas. In one embodiment, the delubing and/or sintering
atmosphere contains no intentionally added hydrogen gas. In another
embodiment, the
delubing and/or sintering atmosphere is free of hydrogen gas. In one aspect,
the delubing
and/or sintering atmosphere include or consists of nitrogen gas. Other inert
gases can
be used, such as argon. During delubing in a nitrogen atmosphere, certain
organic
compounds included in the lubricant system react or otherwise thermally
decompose to
form a highly reactive carbon-containing species that are deposited as solid
residue in
the form of a layer or coating on the outer surface of the metal particles.
[0042] Sintering is preferably conducted in an inert atmosphere, such as
nitrogen,
because an inert atmosphere allows the reactive carbon residue and the metal
oxide on
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the surfaces of the metal particles to react with each other. A hydrogen
atmosphere could
cleave the organics and/or interfere with the oxygen-scavenging/carbon residue
producing reactions. Delubing and/or sintering in a vacuum would promote
vaporization
of the organics, which again would interfere with the desired reactions.
[0043] Another mechanism for removing the metal oxides may occur when the
lubricant system comprises an organic acid and/or an organic compound having
acid-
functional groups. The acid may be available to react with metal oxides on the
outer
surface of the metal particles to form a metal salt residue, which can be
reduced to
elemental metal during sintering.
[0044] Both mechanisms may remove metal oxides from the outer surface of
the metal
particles at temperatures well below where solid state diffusion and liquid
phase formation
occurs. This can result in a complete or partial removal of oxides and
significantly
"cleaner" outer surfaces of the metal powder (i.e. less oxides present) that
make the
powder more susceptible to solid state diffusion and liquid phase bonding
during sintering.
In other words, the absence of an oxide layer, which is stripped during the
delubing step,
yields metal particles having very "clean" (Le., oxide-free or having very low
amounts of
oxide residues) surfaces, which are capable of bonding and fusing together
without the
need for liquid phase forming materials or precursors thereof.
[0045] During a subsequent sintering step, the reactive carbon can react
with metal
oxides already present on outer surface of the metal particles to form carbon
dioxide
and/or carbon monoxide, which are removed as gases prior to solid state
diffusion and
liquid phase bonding.
[0046] The present subject matter metal powder compositions including the
instant
lubricant system provides benefits such as lower tons per square inch (TS!)
needed to
make a green compact, lower ejection force required to remove the green
compact from
a die cavity, reduced amount of lubricant system needed in the metal powder
composition, improved green strength of the green compact, lower dimensional
change
in the sintered metal part, and allows for sintering without hydrogen gas, or
at least allows
for significantly reduced levels of hydrogen gas in the sintering atmosphere.
[0047] Examples
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[0048] Several evaluations were conducted in order to access the benefits
of the
present subject matter as follows. Table 1 shows data for evaluations of
Inventive
Example 1 in relation to Comparative Examples 1 and 2.
Table 1
Example Inventive Comparative Comparative
Example 'I Example '1 Example 2
Metal powder FC 0208 FC 0208 FC 0208
Lubricant 0.5 wt% inventive 0.75 wt% Acrawax 0.75 wt% Caplube L
System lubricant system
Required TSI 36 TSI 50TSI 45TSI
Green Density 7.02 7.02 7.01
Peak 2023 1898 1742
Slide 1483 1725 1300
G.S. 1758 PSI 1512 PSI 1599 PSI
Dimensional 0.21% 0.25% 0.26%
Change
[0049] As seen in Table 1, Inventive Example 1 included metal powder
FCO208, which
is a copper/iron metal powder, and an inventive lubricant system including 10-
30 wt%
stearic acid, 0.1-5 wt% guanidine material, 0.1-0.8 wt% antioxidant, 5-15 wt%
microcrystalline wax, 10-30 wt% polyethylene/polypropylene copolymer wax, and
40-60
wt% ethylene bis(stearamide). Comparative Examples 1 and 2 included the same
metal
powder as Inventive Example 1, but Comparative Example 1 included Acrawax C
as a
lubricant, which is an N,N' ethylene bis(stearamide), available from Lonza,
Basel,
Switzerland; and Comparative Example 2 included Caplube L as a lubricant,
which is
available from H.L. Blachford, Montreal Canada. All three examples were
similarly
pressed, delubed, and sintered to form metal parts. As can be seen, Inventive
Example
1 required less amount of a lubricant system, but produced a sintered metal
part that had
a comparable green density, increased peak value, comparable slide value,
increased
green strength value, and less dimensional change than Comparative Examples 1
and 2.
[0050] Table 2 shows data for evaluations of Inventive Examples 2-4
including
different metal powders, which were sintered in a nitrogen-only atmosphere
(indicated as
"N2"), and in an atmosphere including nitrogen and 10 volume % hydrogen
atmosphere
(indicated as "H2").
Table 2
12
CA 03046637 2019-06-07
WO 2018/106581 PCT/US2017/064466
Example Inventive Inventive Inventive Inventive Inventive Inventive
Example Example Example Example Example Example
2 ¨ H2 2 ¨ N2 3 ¨ H2 3 ¨ N2 4 ¨ H2 4 ¨ N2
Metal FCO208 FCO208 FY-4500 FY-4500 F-0008 F-0008
powder
Inventive 0.5 wt% 0.5 wt% 0.5 wt% 0.5 wt% 0.5 wt% 0.5 wt%
lubricant
system
Green 7.0 7.0 7.29 7.29 6.8 6.8
Density
Sintered 6.88 6.90 7.32 7.32 6.98 6.98
Density
Hardness 86 86 69 70 69 69
TRS 158,426 158,570 118,001 132,051 110,847 109,192
Surface Good Good Good Good Good Good
Appearance
[0051] Metal powder FY-4500 is an iron phosphorous steel with 0.45%
phosphorous
and the remainder iron. Metal powder F-0008 is an iron carbon steel with 0.6-
0.9%
carbon and the remainder iron.
[0052] Inventive Examples 2-4 were each sintered for 20 minutes at 2050 F
in a
commercial furnace that is used for routine production. Inventive Example 2
had a Hall
Flow 32.4 seconds, an apparent density of 2.98 g/cc, a carbon content of 0.84
before
sintering and 0.804 after sintering in nitrogen only. Inventive Example 3 had
a Hall Flow
of 29.8 sec, an apparent density of 2.98 g/cc, a carbon content of zero added
carbon
before sintering and 0.038 after sintering in nitrogen only. Inventive Example
4 had a Hall
Flow of 32.1 sec, an apparent density of 3.14 g/cc, a carbon content of 0.79
before
sintering and 0.753 after sintering in nitrogen only. As can be seen in Table
2, the
properties when sintering in a nitrogen-only atmosphere were comparable to
those when
sintering in an atmosphere including nitrogen gas and 10 volume `)/0 hydrogen
gas.
[0053] Additional advantages and modifications will readily occur to those
skilled in
the art. Therefore, the invention in its broader aspects is not limited to the
specific details
and illustrative examples shown and described herein. Accordingly, various
modifications
may be made without departing from the spirit or scope of the general
inventive concept
as defined by the appended claims and their equivalents.
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