U.S. patent application number 11/418211 was filed with the patent office on 2006-09-07 for co-based water-atomised powder composition for die compaction.
This patent application is currently assigned to HOGANAS AB. Invention is credited to Owe Mars, Christophe Szabo.
Application Number | 20060198751 11/418211 |
Document ID | / |
Family ID | 36944287 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060198751 |
Kind Code |
A1 |
Szabo; Christophe ; et
al. |
September 7, 2006 |
Co-based water-atomised powder composition for die compaction
Abstract
The present invention concerns a powder metal composition for
producing powder metal components comprising a Co-based pre-alloyed
powder, with irregularly shaped particles comprising at least 15%
by weight Cr and less than 0.3% by weight C, admixed with graphite.
The invention also concerns a method for producing PM components by
pressing of articles to shape from the powder metal composition
according to the invention and sintering them.
Inventors: |
Szabo; Christophe;
(Ratingen, DE) ; Mars; Owe; (Hoganas, SE) |
Correspondence
Address: |
BUCHANAN INGERSOLL PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
HOGANAS AB,
Hoganas
SE
|
Family ID: |
36944287 |
Appl. No.: |
11/418211 |
Filed: |
May 5, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10801647 |
Mar 17, 2004 |
|
|
|
11418211 |
May 5, 2006 |
|
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Current U.S.
Class: |
419/11 ;
75/252 |
Current CPC
Class: |
B22F 2998/10 20130101;
B22F 2999/00 20130101; B22F 2201/02 20130101; B22F 1/0059 20130101;
B22F 2009/0828 20130101; B22F 2201/013 20130101; B22F 3/10
20130101; B22F 3/10 20130101; B22F 9/082 20130101; B22F 3/02
20130101; B22F 2999/00 20130101; B22F 2998/10 20130101; C22C 1/0433
20130101 |
Class at
Publication: |
419/011 ;
075/252 |
International
Class: |
C22C 19/07 20060101
C22C019/07; C22C 1/05 20060101 C22C001/05 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 2003 |
SE |
0300881-0 |
Claims
1-13. (canceled)
14. A Co-based water-atomised prealloyed powder for die compaction,
said powder having irregularly shaped particles and comprising at
least 15% by weight Cr and less than 0.1% by weight C.
15. A Co-based water-atomised pre-alloyed powder for die
compaction, said powder having irregularly shaped particles and
consisting of: 15-35% by weight Cr, 0-20% by weight W, 0-25% by
weight Ni, 0-5% by weight Si, 0-5% by weight Fe, 0-10% by weight
Mo, less than 0.1% C and the balance being Co.
16. A Co-based water-atomised pre-alloyed powder for die
compaction, said powder having irregularly shaped particles and
consisting of: 15-35% by weight Cr, 0-20% by weight W, 0-25% by
weight Ni, 0-5% by weight Si, 0-5% by weight Fe, 0-10% by weight
Mo, less than 0.05% C and the balance being Co.
Description
[0001] This is a Continuation of U.S. patent application Ser. No.
10/801,647, filed Mar. 17, 2004, and claims the benefit under 35
U.S.C. .sctn.119(a)-(d) of Swedish Patent Application No.
0300881-0, filed Mar. 27, 2003, and under 35 U.S.C. .sctn.119(e) of
U.S. Provisional Patent Application No. 60/482,866, filed Jun. 27,
2003.
FIELD OF THE INVENTION
[0002] The present invention concerns powder metallurgy. More
specifically the present invention concerns a cobalt-based powder
metal composition and a method for producing components thereof,
especially for heavy duty applications.
BACKGROUND OF THE INVENTION
[0003] Cobalt-based alloys, such as Stellite.RTM. (Trade Mark for
Co--Cr--W alloys) are hard alloys that are extremely resistant to
many forms of wear. Products of these alloys show high hardness
over a wide temperature range and are resistant towards corrosion.
These products are used for inter alia casting of various kinds of
components such as machine parts (bearing shells, valve seat
inserts etc) or other components where high density, high strength
and wear resistance are required.
[0004] Cast material often suffers from micro structural defects
and carbide segregation. Carbide segregation leads to
inhomogenously distributed hard phases. Disadvantages with such
materials are lack of fracture toughness and poor
machinability.
[0005] Powder metallurgy (PM) products generally possess a more
homogenous microstructure than cast products. Further advantages
with the PM production method are that costly machining into final
shape may be excluded or minimized in comparison with traditional
casting methods and that the method is more suitable for producing
large quantities of small articles.
[0006] Attempts have been made over the years to produce
cobalt-based products using the PM technology. Thus U.S. Pat. No.
4,129,444 discloses a process wherein atomised Co-based alloy
powders are coated with a binder and then consolidated to produce
discrete bodies that are dried, crushed and screened to obtain
agglomerates. The agglomerates are pressed into green compacts
which are sintered at high temperature. Furthermore U.S. Pat. No.
5,462,575 discloses a powder metallurgy component prepared of a gas
atomised Co--Cr--Mo alloy powder. The alloy powder is filled in a
canister and baked in vacuum to degas the powder and the powder
filled canister is thereafter consolidated, preferably by hot
isostatic pressing (HIP).
OBJECTS OF THE INVENTION
[0007] An object of the invention is to provide a new Co-based
powder metal composition which can be used in conventional PM
processes.
[0008] Another object is to provide a Co-based powder metal
composition with high compactibility which can be compacted to high
green density and high green strength.
[0009] Still another object is to provide a green body of a cobalt
based alloy which can be machined before sintering.
[0010] A further object is to provide a powder metal composition
which can be compacted and sintered to high density without high
sintering temperatures.
SUMMARY OF THE INVENTION
[0011] These objects as well as other objects that will be apparent
from the description below, have now been obtained according to the
present invention by providing a new Co-based powder metal
composition. Critical features of this composition are that the
composition comprises a Co-based pre-alloyed powder with
irregularly shaped particles admixed with graphite. Furthermore the
Co-based pre-alloyed powder should include less than 0.3% by weight
of carbon and at least 15% by weight Cr. The Co-based pre-alloyed
powder preferably comprises at least 30% by weight and preferably
less than 80% by weight Co.
[0012] The invention also concerns a method comprising the steps of
providing a powder metal composition according to the invention and
compacting the composition in a die at a pressure of at least 400
MPa to a component of desired shape.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The Co-based pre-alloyed powder in the composition according
to the invention may be produced by subjecting a melt having the
desired composition to atomising by water.
[0014] The Co-based pre-alloyed powder according to the invention
comprises less than 0.3% by weight carbon. The carbon content of
the powder is however preferably less than 0.1% by weight, and most
preferably less than 0.05% by weight (i.e. essentially free from C
except for inevitable impurities).
[0015] The Co-based pre-alloyed powder comprises at least 15% by
weight and preferably less than 35% by weight Cr.
[0016] The addition of Cr improves the strength of the Cobalt
matrix by solution hardening and/or carbide formation. These
effects are further improved by the addition of W and/or Mo.
[0017] Other elements which may be included in the Co-based
pre-alloyed powder may be chosen from Ni, Fe, Si, Mn, V and B.
[0018] A preferred pre-alloyed powder according to the invention
comprises 15-35% by weight Cr, 0-20% by weight W, 0-25% by weight
Ni, 0-5% by weight Si, 0-5% by weight Fe, 0-10% by weight Mo,
balance Co and less than 0.3% by weight C.
[0019] Another preferred powder according to the invention further
comprise 0-3% by weight Mn, 0-4% by weight V and 0-4% by weight
B.
[0020] A powder metal composition according to the invention
comprises a pre-alloyed powder according to the invention admixed
with graphite. The amount of graphite addition depends on the
desired content of carbides and on the content of carbide forming
elements. The graphite content is preferably at least 0.5% by
weight, more preferably at least 0.7% by weight and preferably less
than 3% by weight.
[0021] The powder metal composition may further comprise one or
more additives selected from the group consisting of alloying
elements, lubricants, processing aids and binders.
[0022] Other elements may be added for improving properties or
reducing costs.
[0023] The used lubricant plays an important role for the achieved
green properties. Good results have been achieved with Kenolube.TM.
(available from Hoganats AB, Sweden), amide wax, metal stearates
and other commonly used lubricants.
[0024] The processing aids used in the powder metal composition
according to the invention may consist of talc, forsterite,
manganese sulphide, sulphur, molybdenum disulphide, boron nitride,
tellurium, selenium, barium difluoride and calcium difluoride,
which are used either separately or in combination.
[0025] The powder metal composition according to the invention is
filled in a die and compacted at a pressure of at least 400 MPa to
a component of desired shape. This compaction yields a component
with high green strength and green density and the component may
even be green machined at this stage. This is an advantage as the
material in the final sintered component are hard and difficult to
machine.
[0026] The component is sintered at a temperature of at least
1080.degree. C., preferably in protective atmosphere or vacuum.
[0027] The components produced of the powder according to the
invention and according to the method of the invention are
especially suited for heavy-duty applications, such as valve seat
inserts for engines where the valve seats need to last the life
time of the engine, without replacement or service.
[0028] The following example, which is not intended to be limiting,
presents certain embodiments of the present invention.
EXAMPLE
[0029] The test mixtures (mix 1-5) listed in Tables 2 and 3 were
prepared from the water atomised pre-alloyed powders in Table 1 (%
by weight). TABLE-US-00001 TABLE 1 Co Cr Ni W Si Fe C 285 36.4 25.8
23.0 12.5 1.12 1.19 0.01 286 34.5 26.1 23.0 12.5 1.16 1.16 1.60
[0030] The pre-alloyed powders were further admixed with
lubricants, alloying elements and processing aids according to
Tables 2 and 3. In test mix 1, 3 and 4, 1.7% by weight graphite was
further included. TRS-samples, according to ISO 3995, were moulded.
The compacting operation was performed with the three different
types of samples at 600 and 800 MPa respectively.
[0031] The resulting components were tested for green density (GD)
and green strength (GS). After sintering at 1120.degree. C. for 30
minutes in a 90% N.sub.2/10% H.sub.2 atmosphere the components were
tested for sintered density (SD) and hardness (Hv10). Tables 4 and
5 discloses the results of the tests. TABLE-US-00002 TABLE 2 Mix 1
(% by weight) 2 (% by weight) Powder Balance Balance Powder 285
Powder 286 Lubricant 40 PEO:60 ORG* 40 PEO:60 ORG* 0.8 0.8 Graphite
1.7 0 (KS 44) *40% Polyethyleneoxide:60% Orgasol
[0032] TABLE-US-00003 TABLE 3 Mix 3 4 5 (% by weight) (% by weight)
(% by weight) powder Balance Balance Balance Powder 285 Powder 285
Powder 286 Fe 10 10 10 (MH 80, 23) Cu 5 5 5 (325) MoS.sub.2 1 1 1
Lubricant 40 PEO:60 ORG* Kenolube .TM. 40 PEO:60 ORG* 0.8 0.8 0.8
Graphite 1.7 1.7 0 (KS 44) *40% Polyethyleneoxide:60% Orgasol
[0033] TABLE-US-00004 TABLE 4 Mix Compaction 1 2 Pressure (MPa) 600
800 600 800 GD (g/cm.sup.3) 6.70 7.00 5.73 BF* GS (MPa) 13.1 19.7
1.3 BF* *Bars Fractured on ejection
[0034] TABLE-US-00005 TABLE 5 Mix Compaction 3 4 5 Pressure (MPa)
600 800 600 800 600 800 GD (g/cm.sup.3) 6.76 7.04 6.88 7.13 6.07
6.39 GS (MPa) 15.57 21.09 10.2 13.5 2.64 4.39 SD (g/cm.sup.3) 6.62
6.91 nm nm 6.11 6.40 Hv10 137 175 nm nm 103 129 nm = not
measured
[0035] Compaction of mix 2 and to some extent mix 5 did not work,
the components exhibited bad surfaces and frequent edge cracks and
were too fragile to handle.
[0036] Compaction of mix 1, 3 and 4, without C in the pre-alloyed
powder, showed a great improvement of the compressibility, as can
be seen in Tables 4 and 5, and high green strengths and green
densities were achieved for the resulting components. Components
with thin walls normally require a green strength of at least 7 MPa
to enable handling. Green strengths above 20 MPa normally enable
green machining.
[0037] The sintered mix 3 components exhibit a higher density and
hardness (Hv10) than mix 5 components.
[0038] Metallographic studies of the sintered components showed
that components made from mix 3 and 5 have similar structures. It
is thus possible to create the desired carbide structures in mix 3
components during sintering.
[0039] A comparison between mix 3 and mix 4 in Table 5 demonstrates
the influence of lubricants on the green strength and green density
of the compacted components. Kenolube.TM. gives a higher density
than the mix of polyethyleneoxide and Orgasol which enables better
performance in the sintered state.
* * * * *