Note: Descriptions are shown in the official language in which they were submitted.
81801497
-1-
A METAL POWDER COMPOSITION
Field of the Invention
The present invention relates to a new metal powder composition
for the powder metallurgical industry. Particularly the invention
relates to a sponge-iron-based powder composition which includes a
lubricant for improving powder properties, compaction and
processing.
Background of the Invention
In industry, the use of metal products manufactured by compacting
and sintering iron-based powder compositions is becoming
increasingly widespread. The quality requirements of these metal
products are continuously raised and, as a consequence, new powder
compositions having improved properties need to be developed.
There is, thus, a need to improve powder properties, the
compaction process and also the sinter process. Parameters that
may be improved are e.g. characteristics of the metal powder
itself, or the type of, or characteristics, of various additives.
Additives may include alloying elements, flow agents, lubricants,
machinability enhancing agents, or hard phase materials. As
lubricants for low density PM applications, zinc stearate or amide
wax are commonly used due to their overall good performance.
As regards characteristics of the metal powder itself, interest
has focussed on the use of atomised metal powder, and in
particular on the use thereof together
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with certain types of lubricant. Atomized metal powder
may be prepared by disintegration of a thin stream of
molten metal through the impingement of high energy jets
of a fluid (e.g. water). Atomized metal powder may be
advantageous if high green density is sought in powder
metallurgy structural parts.
A first example of the use of atomized metal powder
together with particular lubricants is in US 2012/0187611
which reports the use of atomized metal powder together
with a lubricating combination of three components, named
substances A, B and C. Polyethylene wax is favoured for
substance A. Options for substance B include fatty acid
amides, fatty acid bisamides, saturated fatty alcohols
and saturated fatty acid glycerols. Substance C is an
amide oligomer which may have a molecular weight of
between 500 and 30,000. Substance C is generally used as
the main component of the lubricant. Substance A is
reported to have a negative effect on ejection behaviour.
Substance B is used in an amount which is at least half
as much as the amount of substance A, in order to
compensate for this negative effect seen in the
exemplified metal powder compositions, which are all
based on atomised metal powders.
A second example is in US 2001/0027170 which reports the
use of atomized metal powder together with a lubricant
combination of aggregate particles having a core of a
first lubricant (ethylene bis-stearamide (EBS) is
preferred), the surface of the core being coated with
particles of a second lubricant (preferably zinc
stearate). The Examples report that this particular
arrangement (i.e. having particles of the second
lubricant located on the surface of core particles of the
first lubricant) enables improved flow for resulting
compositions based on atomised metal powder, as compared
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to other ways of combining the first and second
lubricants.
A third example is in US 7,993,429 which reports the use
of atomized metal powder together with composite
lubricant particles having a core comprising a solid
organic lubricant, with fine carbon particles adhered to
the surface. Preferred solid organic lubricants for the
core include fatty acids, fatty acid monoamides and fatty
acid bisamides. The Examples report that having the
carbon particles adhered to the surface of the solid
organic cores helps avoid agglomeration and improve flow
for resulting compositions based on atomised metal
powder.
Another type of metal powder is the so-called sponge iron
powder. Components which are made by compacting sponge
iron powder, have a green strength which is quite high
compared to the green strength obtained when compacting
e.g. atomized powder. In order to improve performance
during compaction and ejection of compacted components
from the tools, a lubricant is normally added to the
powder mixture. This has the drawback of e.g. reducing
the flow rate of the powder which may cause longer
filling time.
In particular, the sponge powders exhibit a lower flow
rate compared to that of atomized powder. This further
complicates the use of lubricants in sponge iron based
powder compositions.
Adding commonly used lubricants, such as metal stearate,
to metal powder may result in residual lubricant deposits
in the furnaces used for sintering, and also results in
surface defects in the final product, leading to higher
scrap rates and costly maintenance.
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As regards examples of uses of lubricants with sponge
metal powders, reference may be made to e.g. GB 391,155
wherein a fatty acid such as stearic acid, palmitic acid
or oleic acid may be used to lubricant sponge iron. A
more recent example is US2010/0116240, where a synthetic
wax such as ethylene bis-stearamide wax is described for
use with sponge iron powder.
Summary of the Invention
The present invention is based, inter alia, on the
surprising finding that for sponge iron particles (or
sponge iron-based particles), the use of a combination of
two or more different fatty acid amides helps address the
flowability issue noted above. In particular, the use of
such combinations enables the provision of metal powder
compositions having excellent flowability, whilst also
providing a suitable apparent density. The use of such
combinations also provides further advantages which will
become apparent from the description of the invention as
set out below.
Thus, the present invention relates to a metal powder
composition comprising sponge iron particles (or sponge
iron-based particles) and a lubricant. In particular,
the present invention relates to a new powder composition
comprising (i) a sponge iron powder or a sponge iron-
based powder, and (ii) a specific lubricant. Thus,
optionally the sponge iron powder may include at least
one alloying agent, in which case it is referred to
herein as sponge iron-based powder (or particles). The
lubricant imparts lower ejection force in the process of
manufacturing compacted components, with a minimal
negative influence on the flow rate.
81801497
-4a-
In one aspect, the present invention provides metal powder
composition comprising (i) sponge iron particles or sponge iron-
based particles, and (ii) a lubricant comprising a mixture of
behenamide, stearamide and palmitamide, wherein the amount of
lubricant is between 0.2wt% and 1.4wt%.
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The invention also relates to a component made by the
powder composition.
Detailed Description of the Invention
5
Sponge iron is produced from direct reduction of iron ore
(in the form of lumps, pellets or fines) by a reducing
gas which may be produced from natural gas or coal. Such
iron can be milled or crushed to produce particles. These
particles typically have an irregular shape, high surface
area, and internal porosity. A plurality of such
particles forms a powder. The metal powder may be
annealed after milling or crushing.
The present invention provides a metal powder composition
comprising (i) sponge iron particles or sponge iron-based
particles, and (ii) a lubricant comprising at least two
different fatty acid amides.
The sponge iron powder particles may consist essentially
of iron or may be so-called iron-based and include other
alloying elements, such as C, Cu, Ni, or Mo (preferably
Cu, Ni, or Mo; alternatively, in one particular preferred
embodiment, both C and Cu are used). When C is used as
an alloying element, it is preferably used in the form of
graphite.
Thus, in one preferred aspect of the invention component
(i) of the metal powder composition is sponge iron-based
particles which comprise sponge iron particles together
with one or more of C, Cu, Ni and Mo (as alloying
elements). In particular, the sponge iron-based
particles preferably comprise sponge iron particles
together with particles of one or more of C, Cu, Ni and
Mo. In both of these aspects it is preferred for both C
and Cu to be used.
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Preferably in this regard the sponge iron-based particles
comprise at least 80% by weight, more preferably at least
90% by weight, and more preferably still at least 95% by
weight of sponge iron particles. Thus, the sponge iron-
based particles preferably comprise 20% by weight or
less, more preferably 10% by weight or less, and more
preferably still 5% by weight or less of the alloying
element(s) (which, as noted above, are preferably one or
more of C, Cu, Ni and Mo, typically in particulate form).
The metal powder compositions according to the invention
contain sponge iron- or sponge iron-based powders, such
as MH80.23, NC100.24 and SC100.26 (available from Hoganas
AS, Sweden), optionally at least one alloying element,
and at least one lubricant.
Alloying elements which can be added in powder form to
the iron powder may include graphite, or metal powders
other than iron (such as Cu, Ni, or Mo).
The lubricant for use in the present invention comprises
at least two different fatty acid amides. The lubricant
may comprise two, three, four, five or more different
fatty acid amides. Preferably, though, it comprises at
least three different fatty acid amides, such as three or
four fatty acid amides.
At least one of the fatty acid amides for use in the
present invention is preferably a monoamide, and more
preferably is a monoamide of the formula R-C(0)-NH2,
wherein R is a hydrocarbyl group. Preferably, at least
two of the fatty acid amides for use in the present
invention should be monoamides, and more preferably
monoamides of the formula R-C(0)-NH2, wherein R is a
hydrocarbyl group.
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As noted above, the lubricant preferably comprises at
least three different fatty acid amides. In this regard,
preferably said at least three different fatty acid
amides should be monoamides, more preferably monoamides
of the formula R-C(0)-NH2, wherein R is a hydrocarbyl
group.
The hydrocarbyl group (R) should of course be different
for each different monoamide of formula R-C(0)-NH2.
Generally, however, the hydrocarbyl group (R) may contain
3 to 27 carbon atoms, such that the fatty acid amide
itself contains 4 to 28 carbon atoms in total.
It is also generally preferred for R to contain at least
7, more preferably at least 9, yet more preferably at
least 11, yet more preferably at least 13, and yet more
preferably at least 15 carbon atoms.
It is also generally preferred for R to contain 25 carbon
atoms or less, more preferably 23 carbon atoms or less,
yet more preferably 21 carbon atoms or less.
The hydrocarbyl group (R) may be straight-chain or
branched, but preferably it is straight-chain.
The hydrocarbyl group (R) may be saturated or
unsaturated. When unsaturated, it preferably contains
five alkene groups or less, more preferably four or less,
more preferably still three or less, yet more preferably
two or less, and typically just one. Preferably the
hydrocarbyl group (R) is saturated.
Preferred options for the fatty acid amides for use in
the invention include the saturated fatty acid amides
caprylic acid amide, capric acid amide, lauric acid
amide, myristic acid amide, palmitic acid amide, stearic
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acid amide, arachidic acid amide, behenic acid amide,
lignoceric acid amide and cerotic acid amide; and the
unsaturated fatty acid amides myristoleic acid amide,
palmitoleic acid amide, sapienic acid amide, oleic acid
amide, elaidic acid amide, vaccenic acid amide, linoleic
acid amide, linoelaidic acid amide, a-linolenic acid
amide, arachidonic acid amide, eicosapentaenoic acid
amide, erucic acid amide and docosahexaenoic acid amide.
Particularly preferred are saturated and unbranched fatty
acid monoamides (i.e. compounds wherein the hydrocarbyl
group (R) is n-alkyl), especially those wherein the
hydrocarbyl group (R) contains 13 to 23 carbon atoms, and
more preferably 15 to 21 carbon atoms. Thus, palmitic
acid amide (CH3(CH2)14C(0)NH2), stearic acid amide (CH3-
(CH2)16C(0)Nli2), arachidic acid amide (CH3(0H2)18C(0)N1-12)
and behenic acid amide (CH3(CH2)20C(0)NH2) are preferred
options for the fatty acid amide. The lubricant
preferably comprises at least three of such particularly
preferred fatty acid amides.
Preferably, at least one of the fatty acid amides (i.e.
at least one of the said at least two different fatty
acid amides) has a hydrocarbyl group (R) with 15 carbon
atoms or less. More preferably, at least one of the
fatty acid amides has a hydrocarbyl group (R) with 15
carbon atoms or less but also at least 13 carbon atoms.
More preferably still, at least one of the fatty acid
amides is palmitic acid amide.
In a specific preferred aspect of the invention the
lubricant is a mixture of stearamide and palmitamide, and
may further include arachidamide and/or behenamide. More
preferably, the lubricant is a mixture of (i) stearic
acid amide, (ii) palmitic acid amide, and (iii) arachidic
acid amide and/or behenic acid amide.
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The lubricant for use in the present invention preferably
contains the said at least two different fatty acid
amides as the major component. In particular, said at
least two different fatty acid amides preferably account
for at least 50% by weight of the lubricant, more
preferably at least 80%, yet more preferably at least 90%
by weight. Typically, the lubricant consists essentially
of the said at least two different fatty acid amides.
As regards the relative amounts of each of the said at
least two different fatty acid amides, the ratio of one
such fatty acid amide to another Is preferably from 1:1
to 1:4, more preferably from 1:1 to 1:3, more preferably
still from 1:1 to 1:2. This does not of course exclude
the possible presence of other fatty acid amides in minor
amounts.
When the lubricant comprises at least three different
fatty acid amides, it preferably comprises at least 25%
of one fatty acid amide and at least 10% of each of the
other two fatty acid amides. More preferably it
comprises at least 40% of one fatty acid amide and at
least 20% of each of the other two fatty acid amides
(e.g. in a particularly preferred embodiment it comprises
50% of one fatty acid amide, and 25% of each of the other
two fatty acid amides). In this regard, as generally
herein, references to % are intended to mean % by weight
unless indicated otherwise.
In a preferred embodiment, the lubricant for use in the
present invention (and preferably also the metal powder
composition of the present invention) is essentially free
of organic lubricants other than the fatty acid amides.
In particular, it is preferably essentially free of
organic lubricants other than the preferred fatty acid
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monoamides for use in the present invention as described
herein. Thus, it is preferably essentially free of fatty
acids, fatty acid bisamides, fatty acid alcohols, fatty
acid glycerols, and/or relatively heavy amides (e.g.
5 amide oligomers with a molecular weight of 500 g/mol or
more). It is also preferably essentially free of metal
soaps, such as zinc stearate. The avoidance of metal-
containing lubricants such as metal soaps is advantageous
because it reduces the amount of undesirable "ash"
10 residue after the lubricant has decomposed.
In a specific preferred aspect of the invention, the
lubricant is a mixture of behenamide, stearamide and
palmitamide. The amounts are preferably 20-50wt%
stearamide, 20-50wt% palmitamide, and may further include
arachidamide, the balance being behenamide.
More preferably, the amounts are 25wt% stearamide, 25wt%
palmitamide, and 50wt% behenamide.
The present disclosure relates to a metal powder
composition comprising sponge iron particles and a
lubricant. Preferably, the lubricant is a mixture of
behenamid, stearamide and palmitamide.
The lubricant is preferably in particulate form. In this
regard, the lubricant may comprise separate particles of
each of the said at least two different fatty acid
amides. Alternatively, the lubricant may be a mixture of
the different fatty acid amides in particulate form (i.e.
with each individual particle generally comprising a
mixture of the different fatty acid amides).
The lubricant amount is preferably between 0.2wt% and
1.4wt%, preferably between 0.4wt% and 1.0wt%, or more
preferably between 0.6wt% and 1.0wt%. Thus, the metal
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powder composition of the present invention preferably
comprises the lubricant in such amounts.
Working temperature of the lubricant range from RT (room
temperature) in the compaction tool and to standard
working temperatures in longer series in production, e.g.
-60 C and up to 80 C.
In the metal powder composition of the present invention,
the sponge iron particles preferably have an average
particle size of at least 5 pm, more preferably at least
10 pm, more preferably still at least 20 pm, and more
preferably still at least 50 pm. The sponge iron
particles preferably have an average particle size of 500
pm or less, more preferably 300 pm or less, more
preferably still 200 pm or less, and more preferably
still 150 pm or less.
Alloying elements, when used, are preferably used in
particulate form. In this regard the alloying element
particles preferably have an average particle size of at
least 5 pm, more preferably at least 10 pm, more
preferably still at least 20 pm, and more preferably
still at least 50 pm. The alloying element particles
preferably have an average particle size of 500 pm or
less, more preferably 300 pm or less, more preferably
still 200 pm or less, and more preferably still 150 pm or
less.
As noted above, the lubricant may preferably be used in
particulate form. In this regard the lubricant particles
preferably have an average particle size of at least 0.5
pm, more preferably at least 1 pm, more preferably still
at least 2 pm, and more preferably still at least 5 pm.
The lubricant particles preferably have an average
particle size of 500 pm or less, more preferably 200 pm
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or less, more preferably still 100 pm or less, and more
preferably still 50 pm or less.
As used herein, average particle size preferably refers
to the average particle size as measured by a laser
diffraction scattering method.
The powder composition has better flow which increases
productivity and quality of the final component.
The powder system exhibits low friction during the
compaction operation and reduces the ejection forces and
ejection energies that occur during ejection of the
component from the compaction tool. A reduction of these
energies results in less tool wear and less surface
defects in the final product.
The green strength is also improved and this mitigates
the risk for green cracks and other "green" related
damages on components before the sintering operation.
Higher green strength improves production efficiency and
reduces scrap rates in production.
By using the new mixed powder system it is possible to
reduce or avoid surface defects that normally appear when
using conventional lubricants in metal powder mixes.
The present invention also provides a process comprising
(i) compacting a metal powder composition of the present
invention as defined above, and (ii) sintering the thus
obtained compacted metal powder composition to produce a
metal product. The present invention also provides a
metal product obtainable or obtained by such a process.
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Example 1
Different iron-based powder metallurgical mixtures,
according to Table 1, were prepared. As iron-based powder
the sponge iron powders MH80.23, NC100.24 and SC100.26
(available from Hogands AB, Sweden), were used. Also used
were ABC100.30 (atomized iron powder), 2%Cu-100mesh
(copper powder from Poemton, Italy), DACu (Distaloy ACu
available from Hoganas AB, Sweden) and 0,5%C-UF4
(graphite from Kropfm0h1 AG, Germany).
Mark Chemistry Supplier
50%Behenamide/25%stearamide/25%palmitamide Abril
industrial
waxes
Znst Zinc stearate Fad, UK
Amidewax Ethylene bisstearamide Fad, Italy
PM
PS 50%Palmite/50%Stearamide Croda, UK
17%Behenamide/46%arachidic
amide/37%stearamide _____________________
Table 1.
1(inv) NCx0.4 NC100.24+2%Cu-100+0.5%C-UF4+0,4%X
2(inv) NCx0.6 NC100.24+2%Cu-100+0.5%C-UF4+0,6%X
5(inv) NCx0.8 NC100.24+2%Cu-100+0.5%C-OF4+0,8%X
4(inv) NCx1.0 NC100.24+2%Cu-100+0.5%C-UF4+1,0%X
5(comp) NCZ0.8 NC100.24+2%Cu-100+0.5%C-UF4+0,8%ZnSt
6(comp) NCA0.8 NC100.24+2%Cu-100+0.5%C-0F4+0,8%AmideWax PM
MH80.23+2%Cu-100+0.5%C-UF4+0.8%X
7(inv) MI-[x0.8
MH80.23+2%Cu-100+0.5%C-UF4+0.8%ZnSt
8(comp) MHZ0.8
9(comp) MHA0.8 ME80.25+2%Cu-100+0.5%C-UF4+0.8%AmideWax PM
10(inv) NCB0.8 NC100.24+2%Cu-100+0.5%C-UF4+0,8%B
11(comp) ARCx0.8 ABC100.30+1,5%Cu (DACu)+0.5%C-UF4+0.8%X
12(comp) ABCA0.8 ABC100.30+1,5%Cu (DACu)+0.5%C-UF4+0.8% Amide Wax
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PM
13(comp) ABCPS0.8 ABC100.30+1,5%Cu (DACu)+0.5%C-UF4+0.8%PS
Table 2. Iron-based powder metallurgical mixtures
prepared
The Hall flow (FH) rate was measured according to
ISO 4490 Flow Gustaysson (FG) and according to
IS013517:2013) and the apparent density was measured
according to ISO 3923.
Mix AD PH FG
(g/cm3) (s/50g) (s/50g)
1(inv) NCx0.4 2,49 32 36
2(inv) NCx0.6 2,49 33 36
3(inv) NCx0.8 2,5 33 37
___________ 4(inv) NCx1.0 2,5 34 38
5(comp) NCZ0.8 2,72 35 41
6(comp) NCA0.8 2,5 39 45
7(inv) MHx0.8 2,34 34 35
8(comp) MHZ0.8 2,45 35 37
9(comp) MHA0.8 2,32 40 ____ 41
10(inv) NCB0.8 2,47 37 42
11(comp) ABCx0.8 3,06 29
12(comp) ABCA0.8 3,04 30
13(comp) ABCPS0.8 3,07 29
Table 3. Flow rate (FH and FG) and Apparent density (AD)
of iron-based powder metallurgical mixtures
Table 3 shows that the new sponge iron powder mix shows
similar apparent density levels as for mixes with amide
wax and highest apparent density was obtained for mixes
with zinc stearate. All mixes with X show improved
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flowability according to the two different methods to
measure flow. Also, the mix with -B (Mix 10) improved
flowability as compared to the metal-free bisamide wax
(Mix 6).
5
Iron powder AD FH
(g/cm3) (Sec/50g)
_
NC100.24 2,43 32
SC100.26 2,65 30
MH80.23 2,30 34
ABC100.30 2,99 23
Table 4. Flow rate (FH) and apparent AD (AD) of the metal
powders, without lubricant.
10 For all mixes, the lubricating properties were measured,
by recording the total energy per enveloped area needed
in order to eject a compacted sample from the die as well
as the peak ejection force per enveloped area. The
components were cylindrical having a diameter of 25 mm,
15 and a height of 15 mm, and the compaction pressures
applied were 250, 400 and 550MPa.
Mix E250 EE400 EE550 EF250 EF400 EF550
(J/cm' Wm' (J/cm2 (N/mm2 (N/1tm2 (N/mm2
) ) ) ) ) )
1(inv) NCx0.4 18,7 31,6 43,4 23,3 25,9 34,3
2(inv) NCx0.6 19 30,2 40,8 19,5 22,7 32
3(inv) NCx0.8 18,7 29,6 37,7 18,6 24,3 32,3
4(inv) NCx1.0 19,9 28,5 36,5 20,8 23 29,2
5(comp) NCZ0.8 21,9 33,2 47 23,5 25,8 35,5
6(comp) NCA0.8 22 34 42,5 22,5 25,4 34,5
7(inv) MHx0.8 17,6 27,8 37,9 21,2 23,8 29,6
8(comp) MHZ0.8 20,6 32,2 45,7 22,3 26 32
9(comp) MHA0.8 20,9 31,4 42,5 23 24 31,9
10(inv) NCB0.8 21,1 33,0 42,6 18,3 22,5 29,4
11(comp) ABCx0.8 24,6 33,3 38,9 16,1 22,7 28,1
12(comp) ABCA0.8 25,7 33,3 38 17,2 23,8 27,2
13(comp) ABCPS0.8 26,6 34,6 39,9 17 22,8 27
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Table 5 Peak ejection force and ejection energy
Table 5 for mixes 1 to 6 shows that reduced amounts of X
with NC100.24 give similar properties as for zinc
stearate and amide wax mixes at 0,8% lubricant levels.
The use of B (in Mix 10) also gave similar results.
Overall, X scored better than the comparative examples
except for the static ejection forces at 550MPa with
SC100.26 as base powder.
Green strength at 6.45g/cm3 was measured on all prepared
mixes. The green strength was tested on a TRS test bar.
GS at
Mix 6.45g/cm2
(N/mm2)
1 NCx0.4 24
2 NCx0.6 24
3 NCx0.8 23
4 NCx1.0 23
5 NCZ0.8 12
6 NCA0.8 15
7 MHx0.8 31
8 MHZ0.8 21
9 MHA0.8 24
10 NCB0.8 19
Table 6. Green strength
Green strength comparison for NC100.24 mixes shows
improvements with 50 to 75% when using X and improvements
were also seen when using B. For mixes with MH80.23 the
green strength increase were 30 to 50% better with X.
