U.S. patent application number 10/266316 was filed with the patent office on 2003-06-05 for metallurgical powder compositions and methods of making and using the same.
Invention is credited to Baran, Michael C., Narasimhan, K.S.V.L..
Application Number | 20030103858 10/266316 |
Document ID | / |
Family ID | 23722409 |
Filed Date | 2003-06-05 |
United States Patent
Application |
20030103858 |
Kind Code |
A1 |
Baran, Michael C. ; et
al. |
June 5, 2003 |
Metallurgical powder compositions and methods of making and using
the same
Abstract
The present invention provides iron-based metallurgical powder
compositions and a method of making and using the same. The
metallurgical powder compositions of the present invention contain
certain amounts of an iron-alloy powder having iron and at least
one alloying additive; substantially pure iron powder; and a carbon
powder, such as graphite. The metallurgical powder compositions are
prepared by admixing the iron-alloy powder with the iron powder and
carbon powder. The metallurgical powder compositions thus produce
and when formed into metal parts have, for example, improved
machinability properties.
Inventors: |
Baran, Michael C.; (Croydon,
PA) ; Narasimhan, K.S.V.L.; (Moorestown, NJ) |
Correspondence
Address: |
WOODCOCK WASHBURN LLP
ONE LIBERTY PLACE, 46TH FLOOR
1650 MARKET STREET
PHILADELPHIA
PA
19103
US
|
Family ID: |
23722409 |
Appl. No.: |
10/266316 |
Filed: |
October 8, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10266316 |
Oct 8, 2002 |
|
|
|
09434000 |
Nov 4, 1999 |
|
|
|
Current U.S.
Class: |
419/30 ; 75/255;
75/343 |
Current CPC
Class: |
C22C 33/0207
20130101 |
Class at
Publication: |
419/30 ; 75/255;
75/343 |
International
Class: |
C22C 032/00; B22F
009/00 |
Claims
What is claimed is:
1. A method of making a metallurgical powder composition comprising
the steps of: (a) providing an iron-alloy powder comprising iron
and at least one alloying additive, wherein the alloying additive
is present in an amount of from about 0.01 weight percent to about
7 weight percent and the iron is present in an amount of at least
85 weight percent based on the total weight of the iron-alloy
powder; and (b) admixing with the iron-alloy powder a substantially
pure iron powder and carbon to form a metallurgical powder
composition, wherein the metallurgical powder composition comprises
from about 5 weight percent to about 40 weight percent of the
iron-alloy powder, at least 55 percent by weight of the
substantially pure iron powder, and at least 0.1 weight percent of
the carbon based on the total weight of the metallurgical powder
composition.
2. The method of claim 1 wherein the alloying additive in the
iron-alloy powder is selected from the group consisting of
molybdenum, chromium, vanadium, tungsten, and combinations
thereof.
3. The method of claim 2 wherein the alloying additive is
molybdenum.
4. The method of claim 3 wherein the molybdenum is present in the
iron-alloy powder in an amount of from about 0.1 to about 2.0
weight percent, based on the total weight of the iron-alloy
powder.
5. The method of claim 1 wherein the metallurgical powder
composition further comprises at least one alloying powder.
6. The method of claim 5 wherein the alloying powder comprises
copper, nickel, or combinations thereof.
7. The method of claim 1 wherein the metallurgical powder
composition further comprises copper, nickel, graphite, manganese
sulfide, or combinations thereof.
8. The method of claim 1 wherein the metallurgical powder
composition comprises from about 10 weight percent to about 30
weight percent of the iron-alloy powder based on the total weight
of the metallurgical powder composition and wherein the iron-alloy
powder comprises from about 0.1 weight percent to about 2 weight
percent molybdenum based on the total weight of the iron-alloy
powder.
9. The method of claim 8 wherein the metallurgical powder
composition comprises from about 70 weight percent to about 95
weight percent of the substantially pure iron powder, from about
0.1 weight percent to about 3 weight percent carbon, and from about
0.10 to about 3.0 weight percent copper, based on the total weight
of the metallurgical powder composition.
10. An improved metallurgical powder composition comprising: (a)
from about 5 weight percent to about 40 weight percent of an
iron-molybdenum alloy powder comprising iron and molybdenum,
wherein the amount of molybdenum is from about 0.10 weight percent
to about 7.0 weight percent and the amount of iron is at least 85
weight percent based on the weight of the iron-molybdenum alloy
powder; (b) at least 55 weight percent of a substantially pure iron
powder; and (c) from about 0.1 weight percent to about 3 weight
percent of carbon.
11. The metallurgical powder composition of claim 10 wherein the
metallurgical composition further comprises at least one alloying
powder.
12. The metallurgical powder composition of claim 10 wherein the
metallurgical composition further comprises nickel, copper,
graphite, manganese sulfide, or combinations thereof.
13. The metallurgical powder composition of claim 10 wherein the
metallurgical powder composition comprises from about 10 weight
percent to about 30 weight percent of the iron-molybdenum alloy
powder, from about 70 weight percent to about 95 weight percent of
the substantially pure iron, from about 0.1 weight percent to about
2 weight percent of the carbon, and from about 0.10 to about 3.0
weight percent copper, based on the total weight of the
metallurgical powder composition.
14. A method of forming a metal part comprising the steps of: (a)
providing a metallurgical powder composition comprising a mixture
of: (i) from about 5 weight percent to about 40 weight percent,
based on the weight of the metallurgical powder composition, of a
iron-alloy powder comprising iron and at least one alloying
additive, wherein the alloying additive is present in an amount of
from about 0.01 weight percent to about 7 weight percent and the
iron is present in an amount of at least 85 weight percent, based
on the total weight of the iron-alloy powder; (ii) at least 55
weight percent of substantially pure iron powder; and (iii) at
least about 0.1 weight percent of carbon; and (b) compacting the
metallurgical powder composition at a pressure of at least about 5
tsi to form a metal part.
15. The method of claim 14 wherein the alloying additive is
molybdenum and is present in the iron-alloy powder in an amount of
from about 0.1 to about 3.0 weight percent, based on the total
weight of the iron-alloy powder.
16. The method of claim 15 further comprising the step of sintering
the compacted metal part at a temperature of at least 1900.degree.
F. to form a machinable metal sintered part.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to improved iron-based
metallurgical powder compositions and methods of making and using
the same. The iron-based powder compositions contain a mixture of
substantially pure iron powder and an iron-alloy powder that
preferably contains molybdenum as an alloying additive. The
iron-based powder compositions thus produced have improved
machinability when formed into metal parts.
BACKGROUND OF THE INVENTION
[0002] Industrial usage of metal parts manufactured by the
compaction and sintering of metal powder compositions is expanding
rapidly into a multitude of areas. In the manufacture of such
parts, metal powder compositions are typically formed from
metal-based powders and other additives such as lubricants, and
binders. The metal-based powders are typically iron powders that
optionally may be alloyed with one or more alloying components.
[0003] A common technique for preparing an iron-alloy powder is to
form a homogeneous molten metal composition containing iron and one
or more desired alloying components, and water atomizing the molten
metal composition to form a homogeneous powder composition.
[0004] The metal-based powder, after any optional alloying, is
often mixed with other additives to improve the properties of the
final part. For example, the metal-based powder is often admixed
with at least one other alloying additive that is in powder form
("alloying powder"). The alloying powder permits, for example, the
attainment of higher strength and other mechanical properties in
the final sintered part.
[0005] The mixture of metal-based powder and optional alloying
powders are often also mixed with other additives such as
lubricants and binding agents to form the final metal powder
composition. This metal powder composition is typically poured into
a compaction die and compacted under pressure (e.g., 5 to 70 tons
per square inch (tsi)), and in some circumstances at elevated
temperatures, to form the compacted, or "green" part. The green
part is then usually sintered to form a cohesive metallic part and
optionally finished. Examples of types of finishing steps include
machining the metal part (e.g., cutting, shaving, drilling,
turning, milling, etc.) to the desired specifications.
[0006] One problem that occurs in the finishing of metal parts is
that the metal parts are often difficult to machine. For example, a
metal part may be difficult to drill, leading to longer machining
time, decrease in the life of the machine tool, and increased
energy usage to operate the machining equipment.
[0007] One solution to increasing the machinability of iron-based
metal parts is disclosed in U.S. Pat. No. 4,018,632 to
Schmidt(hereinafter "Schmidt"). Schmidt discloses that the
machinability of an iron-based metal part can be improved through
the use of a steel powder mixture of graphite and an
iron-molybdenum-manganese alloy. The steel powder after compaction
and sintering is heated and cooled according to certain temperature
profiles to improve the machinability of the metal part.
[0008] Another solution for increasing the machinability of
iron-based metal parts is disclosed in U.S. Pat. No. 5,599,377 to
Uenosono et al. (hereinafter "Uenosono"). Uenosono discloses a
metal powder containing a mixture of iron powder having less than
0.1 weight percent manganese and from about 0.08 weight percent to
about 0.15 weight percent sulfur; graphite; and from about 0.05 to
about 0.70 weight percent of at least one compound selected from
MoO.sub.3 or WO.sub.3. The iron powder is disclosed to have
excellent machinability and high strength due to the dissolution of
molybdenum or tungsten compounds in the ferrite particles upon
sintering of the compacted metal part in a hydrogen-containing
atmosphere.
[0009] Another solution proposed for improving the machinability of
metal parts is disclosed in U.S. Pat. No. 5,679,909 to Kaneko et
al. (hereinafter "Kaneko"). Kaneko discloses a sintered material
having good machinability, where the sintered material is prepared
by compacting and sintering a powder containing a mixture of
composite oxide of CaO--MgO--SiO.sub.2 and an iron dominant metal
matrix. The iron dominant metal matrix may be prepared from a
mixture of pure iron and "hard" particles of FeMo, FeCr, FeW, or
Tribaloy (containing Co--Ho--Cr and/or Co--Ho--Si). These hard
particles are believed to contain at least 50 weight percent of the
non-iron elements to provide the desired hardness.
[0010] Although the above compositions and/or methods provide ways
of improving the machinability of a metal part, it would be
desirable to develop alternate compositions and methods. Preferably
such alternate compositions and methods would result in metal parts
having comparable or improved machinability.
SUMMARY OF THE INVENTION
[0011] The present invention provides metallurgical powder
compositions and methods of making and using the same. The
metallurgical powder compositions, when formed into metal parts,
exhibit improved machinability. This improved machinability is at
least in part due to the presence of certain amounts of at least
one iron-alloy powder in the metallurgical powder compositions.
[0012] In one embodiment of the present invention, a method is
provided that includes providing an iron-alloy powder containing
iron and at least one alloying additive, where the alloying
additive is present in an amount of from about 0.01 weight percent
to about 7.0 weight percent and the iron is present in an amount of
at least 85 weight percent based on the total weight of the
iron-alloy powder. Admixed with the iron-alloy powder is a
substantially pure iron powder and carbon, typically a carbon
powder, to form the metallurgical powder composition. The
metallurgical powder composition preferably contains from about 5
weight percent to about 40 weight percent of the iron-alloy powder,
at least 55 percent by weight of the iron powder, and at least 0.1
weight percent carbon based on the total weight of the
metallurgical powder composition.
[0013] In another embodiment of the present invention, a
metallurgical powder composition is provided that contains from
about 5 weight percent to about 40 weight percent of an
iron-molybdenum alloy powder containing iron and molybdenum, where
the amount of molybdenum is from about 0.10 weight percent to about
7.0 weight percent and the amount of iron is at least 85 weight
percent based on the weight of the iron-molybdenum alloy powder.
The metallurgical powder composition also contains at least 55
weight percent of substantially pure iron powder, and from about
0.1 weight percent to about 3.0 weight percent carbon.
[0014] The present invention also provides a method of forming a
metal part that includes providing a metallurgical powder
composition of the present invention and compacting the
metallurgical powder composition at a pressure of at least about 5
tsi to form a metal part.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a graph showing the mean thrust (in pounds)
produced in drilling a metal part formed from an metallurgical
powder composition of the present invention (Example 5) in
comparison to metal parts made from metallurgical powder
compositions containing no iron-alloy powder (Comparative Examples
1 and 2).
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present invention provides improved metallurgical powder
compositions that when formed into metal parts have improved
machinability. By "machinability" it is meant the ability of a
metal part to be finished in some manner by machine operated tools.
For example, metal parts produced in accordance with the methods of
the present invention are preferably capable of being shaped,
shaved, drilled, cut, turned, milled, or any combination
thereof.
[0017] The metallurgical powder compositions of the present
invention are iron- based powder compositions containing
substantially pure iron powder, an iron-alloy powder, and carbon.
These metallurgical powder compositions may also optionally contain
alloying powders, one or more lubricants, one or more binders, any
other conventional powder metallurgy additive, or any combination
thereof.
[0018] It has been unexpectedly found that the machinability of
iron-based metal parts can be significantly improved through the
addition of certain amounts of iron-alloy powder in the
metallurgical powder composition used to form the metal part. The
iron-alloy powder useful in the present invention is preferably
made by partially or completely alloying iron with at least one
alloying additive (for example, molybdenum containing compounds)
that can provide a hard phase for improving machinability.
[0019] By "alloying" it is meant that the alloying additives and
iron are admixed in a manner to permit melting, diffusion bonding
or chemical bonding of the iron and alloying additive. Suitable
processes for alloying include for example "prealloying" and
"diffusion bonding."
[0020] Prealloyed and diffusion bonded iron-alloy powder may be
made according to any technique known to those skilled in the art.
For example, prealloyed iron-alloy powder can be prepared from a
melt of iron and one or more desired alloying additives.
Preferably, the melt is then atomized so that the atomized droplets
form a powder upon solidification. Diffusion bonded iron-alloy
powder can be prepared for example by blending iron powder with one
or more alloying additives, preferably in oxide form, and annealing
the resulting mixture at high temperatures (e.g., about 800
.degree. C. or greater). During annealing, the alloying compounds
diffuse and partially alloy into the outer surfaces of the iron
particles. A preferred diffusion bonding process is disclosed in GB
1,162,702, which is hereby incorporated by reference in its
entirety.
[0021] In a preferred embodiment of the present invention the
iron-alloy powder is formed by a prealloying process. Prealloying
has the advantage of facilitating complete alloying of the iron and
alloying additives.
[0022] Preferably, the iron-alloy powder is present in the
metallurgical powder composition at a concentration that is
effective in improving the machinability of the metal part in
comparison to a composition containing no iron-alloy powder.
Preferably, the amount of iron-alloy powder is from about 5 weight
percent to about 40 weight percent, more preferably from about 10
weight percent to about 30 weight percent, and most preferably from
about 12 weight percent to about 20 weight percent, based on the
total weight of the metallurgical powder composition.
[0023] Iron that can be used to form the iron-alloy powder is
preferably substantially pure iron containing not more than about
1.0% by weight, preferably no more than about 0.5% by weight, of
normal impurities. The iron may be in any physical form prior to
prealloying. For example, the iron may be in powder form or in the
form of scrap metal. For diffusion bonding, the iron is preferably
in powder form.
[0024] Examples of suitable alloying additives for forming the
iron-alloy powder include, but are not limited to elements,
compounds, or alloys of molybdenum, manganese, magnesium, tungsten,
chromium, silicon, copper, nickel, gold, vanadium, columbium
(niobium), or aluminum, or oxides thereof; binary alloys of copper
and tin or phosphorus; carbides of tungsten or silicon; silicon
nitride; sulfides of manganese or molybdenum, or combinations
thereof. Preferably, the iron-alloy powder contains at least one
alloying additive containing molybdenum, manganese, magnesium,
tungsten, chromium, silicon, copper, nickel, vanadium, oxides
thereof, or any combination thereof, and more preferably
molybdenum, chromium, vanadium, tungsten, or combinations
thereof.
[0025] The total amount of alloying additive in the iron-alloy
powder will depend upon the alloying additive(s) chosen. Typically,
the alloying additives are present in the iron-alloy powder in an
amount of from about 0.01 weight percent to about 7.0 weight
percent, preferably from about 0.10 weight percent to about 3.0
weight percent, and most preferably from about 0.10 weight percent
to about 2.0 weight percent, based on the total weight of the
iron-alloy powder.
[0026] The iron-alloy powder may also contain residual impurities,
such as from the iron used to form the iron-alloy powder.
Generally, the iron-alloy powder contains minimum residual
impurities of at least about 0.15 weight percent and more
preferably of at least about 0.25 weight percent, and preferably
contains maximum residual impurities of up to about 1.0 weight
percent, and more preferably up to about 0.9 weight percent, based
on the total weight of the iron-alloy powder.
[0027] The balance of the iron-alloy powder is preferably iron.
Iron is preferably present in the iron-alloy powder in an amount of
at least 85.0 weight percent, more preferably at least about 90.0
weight percent, and most preferably from about 94.0 weight percent
to about 99.8 weight percent.
[0028] In a preferred embodiment of the present invention, the iron
is prealloyed with at least one alloying additive that contains
molybdenum to form an iron-molybdenum prealloy powder. Molybdenum
additive useful in forming an iron-molybdenum prealloy powder is
any element, compound, or alloy that contains molybdenum and is
capable of alloying with iron in the prealloying process. The
molybdenum additive may be, for example, an oxide of molybdenum
such as molybdenum trioxide or a ferromolybdenum alloy. The
molybdenum additive may also be substantially pure elemental
molybdenum (preferably having a purity of greater than about 90 wt
%). Preferably, the molybdenum additive is an oxide of molybdenum
such as molybdenum trioxide.
[0029] In a most preferred embodiment of the present invention, the
iron-molybdenum prealloy powder preferably contains from about 0.40
weight percent to about 1.6 weight percent molybdenum, based on the
total weight of the iron-molybdenum prealloy powder, and from about
97.4 weight percent to about 99.50 weight percent iron. The
iron-molybdenum prealloy powder preferably contains maximum
residual impurities of about 0.03 weight percent sulfur, about 0.02
weight percent silicon, and about 0.01 weight percent nitrogen
based on the total weight of the prealloy powder.
[0030] Examples of suitable iron-molybdenum prealloy powders
commercially available include Hoeganaes' ANCORSTEEL 150HP steel
powder, 85 HP steel powder, 50HP steel powder, or combinations
thereof. The amounts of molybdenum in the 150 HP, 85HP, and 50 HP
steel powders are respectively about 1.5 weight percent, 0.85
weight percent, and 0.55 weight percent based on the total weight
of the prealloy. These iron-molybdenum prealloy powders contain
less than about 0.75 weight percent of materials such as manganese,
chromium, silicon, copper, nickel, or aluminum, and less than about
0.02 weight percent carbon, with the balance being substantially
iron. Another example of a commercially available iron-molybdenum
prealloy powder is Hoeganaes' ANCORSTEEL 4600V steel powder, which
contains about 0.5-0.6 weight percent molybdenum, about 1.5-2.0
weight percent nickel, about 0.1-0.25 weight percent manganese,
less than about 0.02 weight percent carbon, and the balance
preferably being substantially iron. Other ANCORSTEEL
iron-molybdenum prealloy powders that are useful in the present
invention include for example ANCORSTEEL 2000 and 737 steel
powders. The 150HP, 85HP, or 50HP steel powders are preferred for
use as the prealloy powder in the present invention.
[0031] The metallurgical powder compositions of the present
invention also contain substantially pure iron powder. Preferably,
the substantially pure iron powder is present in the metallurgical
powder composition in an amount of at least about 55 weight
percent, more preferably from about 60 weight percent to about 95
weight percent, and most preferably from about 70 weight percent to
about 90 weight percent, based on the total weight of the
metallurgical powder composition.
[0032] Substantially pure iron powder that can be used in the
invention are powders of iron preferably containing not more than
about 1.0% by weight, more preferably no more than about 0.5% by
weight, of normal impurities. Examples of such highly compressible,
metallurgical-grade iron powders are the ANCORSTEEL 1000 series of
pure iron powders, e.g. 1000, 1000B, and 1000C, available from
Hoeganaes Corporation, Riverton, N.J. For example, ANCORSTEEL 1000
iron powder, has a typical screen profile of about 22% by weight of
the particles below a No. 325 sieve (U.S. series) and about 10% by
weight of the particles larger than a No. 100 sieve with the
remainder between these two sizes (trace amounts larger than No. 60
sieve). The ANCORSTEEL 1000 powder has an apparent density of from
about 2.85-3.00 g/cm.sup.3, typically 2.94 g/cm.sup.3.
[0033] The particles of iron-alloy powder and substantially pure
iron powder have a distribution of particle sizes. Typically, these
powders are such that at least about 90% by weight of the powder
sample can pass through a No. 45 sieve (U.S. series), and more
preferably at least about 90% by weight of the powder sample can
pass through a No. 60 sieve. These powders typically have at least
about 50% by weight of the powder passing through a No. 70 sieve
and retained above or larger than a No. 400 sieve, more preferably
at least about 50% by weight of the powder passing through a No. 70
sieve and retained above or larger than a No. 325 sieve. Also,
these powders typically have at least about 5 weight percent, more
commonly at least about 10 weight percent, and generally at least
about 15 weight percent of the particles passing through a No. 325
sieve. As such, these powders can have a weight average particle
size as small as one micron or below, or up to about 850-1,000
microns, but generally the particles will have a weight average
particle size in the range of about 10-500 microns. Preferred are
iron-alloy particles or substantially pure iron particles having a
maximum weight average particle size up to about 350 microns; more
preferably the particles will have a weight average particle size
in the range of about 25-150 microns, and most preferably 80-150
microns. Reference is made to MPIF Standard 05 for sieve
analysis.
[0034] The metallurgical powder composition also preferably
contains carbon. The carbon is preferably added as a substantially
pure carbon powder, such as graphite. Preferably, the carbon powder
has a purity of at least about 99.0 weight percent and more
preferably a purity of at least about 99.5 weight percent. The
carbon powder may be in crystalline and/or amorphous form. Carbon
is preferably present in the metallurgical powder composition in an
amount of from about 0.1 weight percent to about 3.0 weight
percent, more preferably from about 0.2 weight percent to about 2.0
weight percent, and most preferably from about 0.3 weight percent
to about 1.2 weight percent, based on the weight of the
metallurgical powder composition.
[0035] The metallurgical powder compositions of the present
invention may also optionally contain alloying powders in addition
to the carbon powder. The term "alloying powder" as used herein
refers to any particulate element, compound, or alloy powder
physically blended with the metallurgical powder composition,
whether or not that additive ultimately alloys or partially alloys
with the metallurgical powder composition.
[0036] Examples of optional alloying powders that may be present in
the metallurgical powder composition include elements, compounds,
or alloys containing molybdenum, manganese, copper, nickel,
chromium, silicon, gold, vanadium, columbium (niobium), phosphorus,
aluminum, boron, or oxides thereof; binary alloys of copper and
tin, copper and nickel, or copper and phosphorous; ferro-alloys of
manganese, chromium, boron, phosphorus, or silicon; low melting
ternary and quaternary eutectics of carbon in combination with
elements selected from iron, vanadium, manganese, chromium,
molybdenum or combinations thereof; carbides of tungsten or
silicon; silicon nitride; aluminum oxide; and sulfides of manganese
or molybdenum, and combinations thereof. Preferred alloying powders
include elements, compounds, or alloys containing molybdenum,
manganese, copper, nickel, chromium, vanadium, phosphorus, or
combinations thereof, and more preferably elements, compounds, or
alloys containing copper, nickel, or combinations thereof.
[0037] The alloying powders are preferably present in the
metallurgical powder composition in amounts of up to about 10
weight percent, and typically in the range of from about 0.25 to
about 10 weight percent, preferably from about 0.25 to about 7
weight percent, and more preferably from about 0.5 to about 5
weight percent. The alloying powders generally have a weight
average particle size below about 100 microns, preferably below
about 75 microns, more preferably below about 30 microns, and most
preferably in the range of about 5 microns to about 20 microns. The
particle size of the alloying powders is generally relatively small
and can be analyzed by laser light scattering technology as opposed
to screening techniques. Laser light scattering technology reports
the particle size distribution in d.sub.x values, where it is said
that "x" percent by volume of the powder has a diameter below the
reported value. The alloying particles generally have a particle
size distribution such that they have a d.sub.90 value of below
about 100 microns, preferably below about 75 microns, and more
preferably below about 50 microns; and a d.sub.50 value of below
about 75 microns, preferably below about 50 microns, and more
preferably below about 30 microns.
[0038] In a preferred embodiment of the present invention, the
metallurgical powder composition contains an alloying powder
containing copper. The copper provides hardenability properties to
metal parts formed from the metallurgical powder compositions. The
copper containing powder is preferably elemental copper having
relatively few impurities. Preferably the copper containing powder
contains at least 90 weight percent, more preferably at least 98
weight percent, and most preferably at least 99.5 weight percent
copper based on the total weight of the copper containing
powder.
[0039] Preferably, the amount of copper containing powder present
in the metallurgical powder composition of the present invention is
such that there is at least 0.2 weight percent, more preferably
from about from about 0.5 weight percent to about 4.0 weight
percent, and most preferably from about 1.0 to about 3.0 weight
percent elemental copper, based on the total weight of the
metallurgical powder composition.
[0040] The metallurgical powder compositions of the present
invention may also include any special-purpose additive commonly
used with metallurgical composition such as lubricants, machining
agents, and plasticizers.
[0041] In a preferred embodiment of the present invention the
metallurgical powder composition contains a lubricant to reduce the
ejection force required to remove a compacted part from the die
cavity. Examples of typical powder metallurgy lubricants include
the stearates, such as zinc stearate, lithium stearate, manganese
stearate, or calcium stearate; synthetic waxes, such as ethylene
bisstearamide or polyolefins; or combinations thereof. The
lubricant may also be a polyamide lubricant, such as PROMOLD-450,
disclosed in U.S. Pat. No. 5,368,630, particulate ethers disclosed
in U.S. Pat. No. 5,498,276, to Luk, or a metal salt of a fatty acid
disclosed in U.S. Pat. No. 5,330,792 to Johnson et al., the
disclosures of which are hereby incorporated by reference in their
entireties. The lubricant may also be a combination of any of the
aforementioned lubricants described above.
[0042] The lubricant is generally added in an amount of up to about
2.0 weight percent, preferably from about 0.1 to about 1.5 weight
percent, more preferably from about 0.1 to about 1.0 weight
percent, and most preferably from about 0.2 to about 0.75 weight
percent, of the metallurgical powder composition.
[0043] Preferred lubricants are ethylene bisstearamide, zinc
stearate, Kenolube.TM. (supplied by Hoganas Corporation, located in
Hoganas, Sweden), Ferrolube.TM. (supplied by Blanchford), and
polyethylene wax. Preferably, these lubricants are added in an
amount of from about 0.2 weight percent to about 1.5 weight percent
based on the total weight of the metallurgical powder composition
formed.
[0044] Other additives may also be present in the metallurgical
powder compositions, such as plasticizers and machining agents.
Preferably, these other additives are present in the metallurgical
powder composition in an amount of from about 0.05 weight percent
to about 1.5 weight percent, and more preferably from about 0.1
weight percent to about 0.5 weight percent based on the total
weight of the metallurgical powder composition. Plasticizers, such
as polyethylene-polypropylene copolymer, are typically used in
connection with binders and/or lubricants. Machining agents, such
as molybdenum sulfides, iron sulfides, boron nitride, boric acid,
or combinations thereof are typically used to aid in final
machining operations. In a preferred embodiment, manganese sulfide
is present in the metallurgical powder composition in an amount of
from about 0.1 weight percent to about 0.75 weight percent based on
the weight of the metallurgical powder composition.
[0045] The metallurgical powder composition may also contain one or
more binding agents to bond the different components present in the
metallurgical powder compostion so as to inhibit segregation. By
"bond" as used herein, it is meant any physical or chemical method
that facilitates adhesion of the components of the metallurgical
powder composition.
[0046] In a preferred embodiment of the present invention, bonding
is carried out through the use of at least one binding agent.
Binding agents that can be used in the present invention are those
commonly employed in the powder metallurgical arts. Examples of
such binding agents are found in U.S. Pat. No. 4,834,800 to Semel,
U.S. Pat. No. 4,483,905 to Engstrom, U.S. Pat. No. 5,154,881 to
Rutz et al., and U.S. Pat. No. 5,298,055 to Semel et.al., the
disclosures of which are hereby incorporated by reference in their
entireties.
[0047] Such binding agents include, for example, polyglycols such
as polyethylene glycol or polypropylene glycol; glycerine;
polyvinyl alcohol; homopolymers or copolymers of vinyl acetate;
cellulosic ester or ether resins; methacrylate polymers or
copolymers; alkyd resins; polyurethane resins; polyester resins; or
combinations thereof. Other examples of binding agents that are
useful are the relatively high molecular weight polyalkylene
oxide-based compositions described in U.S. Pat. No. 5,298,055 to
Semel et al. Useful binding agents also include the dibasic organic
acid, such as azelaic acid, and one or more polar components such
as polyethers (liquid or solid) and acrylic resins as disclosed in
U.S. Pat. No. 5,290,336 to Luk, which is incorporated herein by
reference in its entirety. The binding agents in the '336 Patent to
Luk can also advantageously act as lubricants. Additional useful
binding agents include the cellulose ester resins, hydroxy
alkylcellulose resins, and thermoplastic phenolic resins described
in U.S. Pat. No. 5,368,630 to Luk, which is incorporated herein by
reference in its entirety.
[0048] The binding agent can further be the low melting, solid
polymers or waxes, e.g., a polymer or wax having a softening
temperature of below 200.degree. C. (390.degree. F.), such as
polyesters, polyethylenes, epoxies, urethanes, paraffins, ethylene
bisstearamides, and cotton seed waxes, and also polyolefins with
weight average molecular weights below 3,000, and hydrogenated
vegetable oils that are C.sub.14-24 alkyl moiety triglycerides and
derivatives thereof, including hydrogenated derivatives, e.g.
cottonseed oil, soybean oil, jojoba oil, and blends thereof, as
described in WO 99/20689, published Apr. 29, 1999, which is hereby
incorporated by reference in its entirety herein. These binding
agents can be applied by the dry bonding techniques discussed in
that application and in the general amounts set forth above for
binding agents. Further binding agents that can be used in the
present invention are polyvinyl pyrrolidone as disclosed in U.S.
Pat. No. 5,069,714, which is incorporated herein in its entirety by
reference, or tall oil esters. Preferred binding agents are
polyethylene oxide and polyvinylacetate, or combinations thereof,
which are binding agents disclosed in WO 99/20689,
[0049] The amount of binding agent present in the metallurgical
powder composition depends on such factors as the density, particle
size distribution and amounts of the iron-alloy powder, the iron
powder and optional alloying powder in the metallurgical powder
composition. Generally, the binding agent will be added in an
amount of at least about 0.005 weight percent, more preferably from
about 0.005 weight percent to about 2 weight percent, and most
preferably from about 0.05 weight percent to about 1 weight
percent, based on the total weight of the metallurgical powder
composition.
[0050] In a preferred embodiment of the present invention, the
metallurgical powder composition contains from about 10 weight
percent to about 20 weight percent of an iron-molybdenum prealloy
powder, from about 80 weight percent to about 90 weight percent
substantially pure iron powder, from about 0.1 weight percent to
about 1.2 weight percent carbon that is preferably graphite powder,
and from about 0.1 to about 3.0 weight percent of copper that is
preferably in the form of a copper containing powder. In this
embodiment, the iron-molybdenum prealloy powder preferably contains
from about 0.4 weight percent to about 2.0 weight percent
molybdenum and from about 98 weight percent to about 99.6 weight
percent iron. The percentages of iron, molybdenum, carbon and
copper in the metallurgical powder composition can be determined
for example by an elemental analysis.
[0051] The present invention also provides methods of preparing
metallurgical powder compositions. In the methods of the present
invention, an iron-alloy powder that has preferably been prepared
in accordance with the methods as previously described herein is
provided. The iron-alloy powder is admixed with substantially pure
iron powder and preferably carbon powder, in the amounts previously
described herein, to form the metallurgical powder compositions of
the present invention. Additionally other additives can be added to
the metallurgical powder composition in the amounts previously
described herein. For example, any combination of alloying powders,
lubricants, binding agents, machining agents, plasticizers, or any
other conventional metallurgical powder additive may be added.
[0052] The method of combining the iron-alloy powder, the
substantially pure iron powder, the carbon powder, and other
desired additives may be performed according to any technique well
known to those skilled in the art. Preferably, the method used
results in a uniformly mixed metallurgical powder composition that
does not readily segregate. Moreover, the order of addition of the
iron-alloy powder, the substantially pure iron powder, the carbon
powder, and other desired additives is not critical. Preferably,
however the order of addition is in a manner to achieve a uniform
mixture of the metallurgical powder composition.
[0053] In a preferred embodiment, the methods of the present
invention include adding a binding agent to the metallurgical
powder composition to bond the iron-alloy powder, the substantially
pure iron powder and other additives to inhibit segregation. The
binding agent can be added to the powder mixture according to any
technique known to those skilled in the art. For example, the
procedures taught by U.S. Pat. Nos. 4,834,800 to Semel; 4,483,905
to Engstrom; 5,154,881 to Rutz et al.; and 5,298,055 to Semel et
al.; and WO 99/20689, published Apr. 29, 1999, can be used, the
disclosures of which are hereby incorporated by reference in their
entireties. Preferably, the binding agent is added in a liquid form
and mixed with the powders until good wetting of the powders is
attained. Those binding agents that are in liquid form at ambient
conditions can be added to the powder as such, but it is preferred
that the binding agent, whether liquid or solid, be dissolved or
dispersed in an organic solvent and added as a liquid solution,
thereby providing substantially homogeneous distribution of the
binding agent throughout the mixture. The wet powder is thereafter
processed using conventional techniques to remove the solvent.
Typically, if the mixes are small, generally 5 lbs. or less, the
wet powder is spread over a shallow tray and allowed to dry in air.
On the other hand, in the case of larger mixes, the drying step can
be accomplished in the mixing vessel by employing heat and
vacuum.
[0054] Also, the sequence of addition of the binding agent and a
lubricant, if desired, can be varied to alter the final
characteristics of the metallurgical powder composition. For
example, the procedures taught in U.S. Pat. No. 5,256,185 to Semel
et al., which is hereby incorporated by reference in its entirety,
can be used. Also for example, the lubricant can be blended with
the iron-alloy powder, the substantially pure iron powder, the
carbon powder, the alloying powders and other optional additives,
and then, subsequently, the binding agent is applied to that
composition. In another method, a portion of the lubricant,
preferably from about 50 to about 99 weight percent, more
preferably from about 75 to about 95 weight percent, is added to a
mixture of the iron-alloy powder, the substantially pure iron
powder, and other additives, then the binding agent is added,
followed by removal of the solvent, and subsequently the rest of
the lubricant is added to the metal powder composition. One further
method is to add the binding agent first to a mixture of the
iron-alloy powder and other additives, remove the solvent, and
subsequently add the entire amount of the lubricant.
[0055] The metallurgical powder compositions of the present
invention thus formed can be compacted in a die according to
standard metallurgical techniques to form metal parts. Typical
compaction pressures range between about 5 and 200 tons per square
inch (tsi) (69-2760 MPa), preferably from about 20-100 tsi
(276-1379 MPa), and more preferably from about 25-60 tsi (345-828
MPa).
[0056] Following compaction, the part can be sintered, according to
standard metallurgical techniques at temperatures, sintering times,
and other conditions appropriate to the metallurgical powder
composition. For example, in a preferred embodiment, sintering
temperatures range from about 1900.degree. F. to about 2400.degree.
F. and are conducted for a time sufficient to achieve metallurgical
bonding and alloying. The metallurgical powder composition may also
be double pressed and double sintered by techniques well known to
those skilled in the art.
[0057] Metal parts of various shapes and for various uses may be
formed from the metallurgical powder compositions of the present
invention. For example, the metal parts may be shaped for use in
the automotive, aerospace, or nuclear energy industries.
[0058] It has been found that the metallurgical powder compositions
made in accordance with the methods of the present invention have
unexpectedly superior machinability properties. These improvements
are especially observed when the metallurgical powder composition
contains from about 10 weight percent to about 30 weight percent of
an iron-molybdenum prealloy powder, from about 70 weight percent to
about 90 weight percent of a substantially pure iron powder, from
about 0.1 weight percent to about 3.0 weight percent of a carbon
powder, and from about 0.1 weight percent to about 3.0 weight
percent of a copper containing powder. Preferably, the iron
molybdenum prealloy contains from about 0.40 to about 2.0 weight
percent molybdenum and from about 98 weight percent to about 99.6
weight percent iron. The machinability can be further enhanced
through the presence of a machining agent such as manganese sulfide
in the metallurgical powder composition.
EXAMPLES
[0059] Some embodiments of the present invention will now be
described in detail in the following Examples. Iron-based
metallurgical powder compositions were prepared in accordance with
the methods of the present invention. Comparative metal powder
compositions were also prepared. The powder compositions prepared
were compacted and sintered to form metal parts and evaluated for
machinability.
Comparative Examples 1 to 2 and Examples 3 to 10
[0060] Metallurgical powder compositions having the compositions
shown in Table 1 were prepared.
1TABLE 1 Composition of Metal Powders Tested Fe Fe-Alloy Carbon Cu
MnS Lubricant Examples Powder Powder, wt % wt % wt % wt % wt %
Control Balance 0.0 0.5 2.0 0.0 0.0 Comp. Ex. Balance 0.0 0.6 1.75
0.0 0.75 1 Comp. Ex. Balance 0.0 0.6 1.75 0.35 0.75 2 Example 3
Balance 10.0 0.6 2.0 0.35 0.75 Example 4 Balance 15.0 0.6 2.0 0.35
0.75 Example 5 Balance 20.0 0.6 1.75 0.35 0.75 Example 6 Balance
20.0 0.6 2.0 0.35 0.75 Example 7 Balance 25.0 0.6 2.0 0.35 0.75
Example 8 Balance 30.0 0.6 2.0 0.35 0.75 Example 9 Balance 35.0 0.6
2.0 0.35 0.75 Example Balance 40.0 0.6 2.0 0.35 0.75 10
[0061] The compositions were prepared by uniformly blending all the
ingredients in the amounts shown in Table 1. The iron powder used
in all examples was Ancorsteel 1000A available from Hoeganaes
Corporation, located in Cinnaminson, N.J. The iron-alloy powder
used in all examples was Ancorsteel.TM. 85HP steel powder also
available from Hoeganaes Corporation. Ancorsteel 85HP is an
iron-molybdenum prealloy powder containing about 0.85 weight
percent molybdenum. The graphite used in all examples (shown as
"Carbon" in Table 1) had a weight average particle size of about 6
to 8 microns and was obtained from Asbury Graphite Mills, Inc.,
located in Asbury, N.J. The copper powder (shown as "Cu" in Table
1) used in all examples was Accupowder from Accupowder Corporation.
The copper powder had a weight average particle size of from about
10 microns to about 14 microns and a purity of 99.5 weight percent.
The "MnS" shown in Table 1 is manganese sulfide, a machining agent.
The lubricant shown in Table 1 was Acrawax.TM. C lubricant. Acrawax
C is a synthetic wax and was obtained from Algroup Lonza located in
Fair Lawn, N.J.
Example 11
[0062] The metal powder compositions of Comparative Examples 1 to 2
and Examples 3 to 10 were evaluated for machinability.
[0063] To evaluate machinability, each of the metallurgical powder
compositions in Table 1 were compacted into 4 inch diameter by 1
inch thick discs having a density of 6.8 g/cm.sup.3. The discs were
sintered at 2050.degree. F. for 30 minutes in an atmosphere of 10%
hydrogen and 90% nitrogen and allowed to cool to ambient
temperature.
[0064] Prior to conducting the machinability tests, each drill bit
was calibrated in the following manner. Twenty drill bits of 0.25
inch diameter were used to drill 0.95 inch deep holes in discs
formed from the "Control" powder shown in Table 1. Each drill bit
was used to drill approximately 2 to 3 holes for a total of about
40 to about 60 holes. The holes were drilled at a feed rate of
0.005 inches per revolution and a cutting speed of 2220 rpm. During
drilling the drill torque and drill thrust were measured
automatically for each drill bit, and an average drill torque and
thrust were calculated from all measurements. Only drill bits
having a drill torque and thrust within .+-.5 percent of the
average were used in the machinability tests.
[0065] Using the same equipment used to calibrate the drill bits,
discs formed from each of the metallurgical powder compositions
shown in Table 1 were drilled with holes having a depth of 0.95
inches until the drill bit failed (e.g., wear exceeds a
predetermined level). For each hole drilled, a feed rate of 0.005
inches per revolution and a cutting speed of 2220 rpm was used. The
drill torque and drill thrust were measured throughout the test,
and wear measurements on the drill bit were taken every ten holes
drilled. The wear measurements were taken by a Microdynascope Model
5E Universal Inspection and Gauging System, supplied by Vision
Engineering, located in Surrey, England. Table 2 shows the results
of the machinability testing. The mean thrust was the mean value of
thrust for all holes drilled prior to failure of the drill bit.
Table 2 also shows the number of holes drilled to failure that was
used for calculating the mean thrust. The number of holes drilled
to failure depended in part on the strength of the material
(increasing the strength decreases the number of holes to
failure).
2TABLE 2 Machinability Results Composition Wt % of Number of Holes
Mean Thrust, of Disc Prelloy Powder Drilled to Failure (lbs) Comp.
Ex. 1 0.0 95 273.0 Comp. Ex. 2 0.0 775 210.6 Example 3 10.0 34
161.6 Example 4 15.0 622 166.0 Example 5 20.0 838 167.2 Example 6
20.0 398 195.5 Example 7 25.0 550 223.3 Example 8 30.0 383 140.7
Example 9 35.0 435 129.5 Example 10 40.0 476 131.0
[0066] The results in Table 2 show that the addition of the
iron-alloy powder in an metallurgical powder composition reduces
the mean thrust of a drill bit during the drilling of a disc. For
example, although the mean thrust can be reduced somewhat by the
addition of manganese sulfide to an iron based powder composition
(see comparative Example 1 in comparison to Comparative Example 2),
further improvement can be achieved by addition of a iron-alloy
powder. The results for mean thrust obtained for Comparative
Examples 1 to 2 and Example 5 are shown in FIG. 1. FIG. 1 is a bar
graph showing mean thrust for discs prepared from Comparative
Examples 1 to 2 and Example 5. By reducing the mean thrust, there
is less wear on the drill bit leading to such benefits as increased
lifetime of the drill bit.
[0067] There have thus been described certain preferred embodiments
of the improved metallurgical powder compositions of the present
invention, and methods of making and using the same. While
preferred embodiments have been disclosed and described, it will be
recognized by those with skill in the art that variations and
modifications are within the true spirit and scope of the
invention. The appended claims are intended to cover all such
variations and modifications.
* * * * *