Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE DISCLOSURE
I. Field of the Invention
This invention relates to a process for producing powder metal
parts from an Fe-Ni Mn-Mo powder composition which contains small
amounts of copper.
II. Description of the Prior Art
Many commercial powder metals are available for fabrication
of metal parts by compacting, sintering, and heat treating. One
of the more frequently used and readily available metal powders
is manufactured and marketed by Hoeganaes Corp. under the trade
~k~ Ancorsteel 4600V. Although this metal powder when used in
the fabrication of parts has shown good results, it has certain
shortcomings which would be advantageous to eliminateO The
specific composition of Ancorsteel 4600V is 1.8% Ni, 0.25~ Mn,
0.5% Mo and the balance being Fe. This composition with appro-
priate amounts of carbon and zinc stearate will hereina~ter be
referred to as the known composition. It has been found that
using this composition results in too much shrinkage during the
sintering stage and the parts are generally difficult to machine.
Obviously, it would be advantageous if these shortcomings could
be eliminated without sacrificing the generally high strength
and ductility possessed in parts made from such a metal powder
composition.
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SUMMARY OP THE INVENTION
It has been found unusually advantageous to add a small
quantity of copper to the Xnown composition when metal parts are
to be fabricated. Including the small quantity of copper to the
known composition and processing parts made from these composi-
tions in accordance with the process described hereinbelow has
not only resulted in better machinability and reduction of
shrinkage of the parts, but surprisingly has yielded parts with
higher tensile strengths and higher toughness. The known com-
position with a small amount of copper will hereinafter be
referred to as the disclosed composition. Furthermore, all per-
cent figures described herein are percent by weight unless ex-
pressed otherwise.
The basic objects of this invention are achieved by proc-
essing powder metal parts by compacting a powder metal composition q
comprising 1.0 - 2.5% Ni, 0.3 - 0.7% Mo, O.lS - 0.30% Mn, 0~5 -
1.5~ Cu, 0.3 - 0~7~ Cr 0.5 - 1.0% zinc stearate, the balance being
Fe; and sintering the compressed part at a temperature ranging
from about 2000F to 2150E~ for about 15 to 30 minutes in a fur~
nace having a dew point ranging from about 20F to 60F and under
an endothermic atmosphere~ It is preferred that the powder be
compacted under sufficient pressure to form a part having a density
-ranging from about 6~4 g/cc to about 7.1 gjcc. Furthermore~ a sin-
tering temperature of about 2050F with a dew point of about 3Q -
35F has been found to be ideally suited for this process. Although
many of the known endothermic type atmospheres can be used, I have
found that an atmosphere comprising nitrogen, hydrogen and carbon
monoxide is preferred.
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~ESCRIPTION OF PREFERRED EMBGDIMENTS
It has been found tha~ adding 0.5 - 1.5% copper to known mix-
tures of 1.0 - 2.5% Ni, 0.15 - 0.30% Mn, 0~3 - 0.7~ Mo~ 0.3 0.7~ C
and 0.5 - 1.0% zinc stearate, the balance being iron, has resulted
in a metal powder which, when compacted, sintered and heat treated,
results in a metal part having unusually good properties. This
is particularly true of the metal part that results from the sin-
tering stage. As is known, it is advantageous to have a sintered
piece with high strength as the same may be subjected to stresses
during the heat treat stageO
In adding the copper to the known composition and sintering in
accordance with the process described herein, it was found that the
tensile strength increased after heat treating, the fracture tough-
ness increased after heat treating and as to machineabllity it was
found that drill bits used to machine the heat treated products
made in a~cordance with this invention lasted from 50 - 100% longer.
EXAMPLE I
. .
A composition was prepared having the following ingredients:
Material Amount
Copper 0.82
150 RXM
Glidden Metals Corp.
Graphite 0-55%
Grade 1651
Southwestern Çraphite Co.
Zinc Stearate 0.75%
Zinc Stearate PM
Penick Corp.
Pre-Alloyed Powder Ni 1.8
Ancorsteel 4600V Mo 0.6
Hoeganaes Corp. Mn 0.25~
Fe Balance
A 1.25" X 0.5" x ~25" transverse rupture bar was compacted
at 50 tsi and sintered at 2050F for 15 - 30 minutes, with a dew
point of 35 - 55F and under endothermic atmosphere. There was
only 0.0006" shrinkage in length. After carbonitriding at 1550~
for 30 minutes, the base was oil quenched and tempered at 350F
for one hour. There was only 0.0008" expansion.
In addition to maintaining stable dimensions, high strength
and toughness was also achieved.
A number of samples having the above dimensions from both
the known and the disclosed compositions were made in processes
similar to that described above. In one series of tests the per-
centages of components as stated above were kept constant and the
amount of copper was varied from 0O77 to 1. 22% r In another
series of tests the percentages of components were kept constant
as stated above and the carbon content was varied from 0.35 to
0.55%. All such samples were found to give superior results.
The samples resulting from Example I were found to have a
transverse rupture strength of approximately 160,~00 psi after
sintering and a transverse rupture strength of approximately
200,000 psi after heat treating for the disclosed composition.
This compares with a transverse rupture strength of approxi~ately
1~1,000 psi for the known composition in the sintered condition
and approximately 196,000 psi in the heated treated condition~
Th~ disclosed composition was found to have a fractured toughness
as sintered o~ approximately 21~000 psi-inl/2 and 23,000 psi-inl/2
in the heat treated condition. This compares with the known com-
position having a sintered fractured toughness of approximately
21,000 psi-inl/2 both in the sintered and heat treated condition.
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With respect to machineability, a test was run wherein a drill
bit with a load of 24 lbs. was applied to the above samples and
rotated at a speed of ltO00 RPM. These loades were applied to
samples whicn had a thickness of approximately 1/4". For the dis-
closed composition it was found that approximately 11 seconds were
re~uired to drill through a sample and for the known composition
approximately 15 seconds were required. Even more significant
was that the drill bit showed considerably more wear after drilling
through the known composition than it did after drilling through
the disclosed composition.
The tensile strength of samples made from the disclosed com-
position was measured at 81,000 psi sintered and 125,000 psi heat
treated whereas samples made ~rom the known composition were found
to be 75,000 psi and 110,000 psi respectively.
EXAMPLE I I
A composition was prepared having the following ingredients:
Material Amount
Copper 1.0%
150 RXM
G~idden Metals Corp.
Graphite 0.45
Grade 1651
Southwestern Graphite Co.
Zinc Stearate 0~75
Zinc Stearate PM
Penick Corp~
Pre-Alloyed Powder Ni 1.8%
Ancorsteel 4600V Mo 0,5%
-~ ~oeganaes Corp. Mn 0.2%
Fe Balance
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The above composition was compacted as follows:
Density Pressure
,
6.72 g/cc 40 tsi
6.4 ~/cc 28 tsi
The composition was sintered in a moving belt sintering
furnace under the following conditions:
Endothermic Atmosphere 60~ ~by vol.) N
20% (by volO) H2
20~ tby vol.) CO
Dew Point 31F and 61F
. . . _ .
Temperature 2050F (~ 50F)
Time at Temperature 15 minutes
(Belt speed of approxi-
mately 2 ft.~min.)
Cooling Rate 1.5 to 2.5 F/sec.
The properties of the sintered composition were as follows:
Transverse Dimensional Bulk
Dens ~ ~uptu.re Strength Chan~e Hardness
6.72 124,000 psi 0.0004'l
(shrinkage) RB 65
6.48 9~,000 psi 0.0007"
(shrinkage) ~ 50
When parts formed of the Ancorsteel 4600V alloy with 0.45%
carbon ~known composition) was sintered by the process described
herein the following properties were observed.
Transverse Dimensional Bulk
Density Ru~ture Strength Change Hardness
. . . ~
6.76 110,000 psi 0.0025"
(shrinkage) ~ 60
-~ 6.5 92,000 psi 0.0028"
- (shrinkage) ~ 50
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Example III
A composition was prepared having the following ingredients:
Material Amount
.
Copper ~o75%
Alcan 8081
Graphite 0-53
Grade 1651-B
Southwestern Graphite Co.
zinc Stearate 0.76
Mallinckrodt
Flowmet 2
Pre-Alloyed Powder Ni 1.85
Ancorsteel 4600V Mo 0.52~
Hoeganaes Corp. Mn 0.1~%
Fe Balance
The above composition was compacted as follows:
Density Pressure
7.~3 g/cc 50 tsi
The composition was sintered in a moving belt sintering
furnace under the following conditions.
Endothermic Atmosphe_e 40% tby vol.) N2
40% (by vol.) H2
20% (by vol.) CO
Dew Point 35F
: Tem~erature 2050F (_ 20F)
Time at Temperature 27 minutes
Cooling Rate 10F/se~.
The properties of the sintered composition were as follows:
Transverse DimensionalBulk
- Densit~ Rupture Strength chan~e Hardness
. . _ ~ . . _ . ~
7.03 ~/cc 175,000 psi 0.~002"
(shrinkage)RC 27
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As a consequence, it has been found that substantially better
results are achieved by making parts using the known composition
when 0.5 - 1.5~ of copper is added thereto, and by employing the
sinterin~ process as disclosed. These findin~s have been unexpected
as one would not expect the increased physical properties that have
been discovered.
