U.S. patent application number 10/907155 was filed with the patent office on 2005-12-15 for method for making sintered body with metal powder and sintered body prepared therefrom.
Invention is credited to Hwang, Kuen-Shyang, Lu, Yung-Chung.
Application Number | 20050274222 10/907155 |
Document ID | / |
Family ID | 35459133 |
Filed Date | 2005-12-15 |
United States Patent
Application |
20050274222 |
Kind Code |
A1 |
Hwang, Kuen-Shyang ; et
al. |
December 15, 2005 |
METHOD FOR MAKING SINTERED BODY WITH METAL POWDER AND SINTERED BODY
PREPARED THEREFROM
Abstract
The present invention relates to a metal powder sintered body by
using fine powders as the raw material and the fabrication method
thereof. The sintered body has a characteristic composition
including iron (Fe), carbon (C), nickel (Ni) and at least one
strengthening element, in the ratios as follows: Ni: 3.0-12.0%,
carbon: 0.1-0.8%, the strengthening element: 0.5-7.0%, and the
remaining portion being Fe. The sintered body has high tensile
strength, high hardness, and good ductility, without treatment with
the quenching process.
Inventors: |
Hwang, Kuen-Shyang; (Taipei,
TW) ; Lu, Yung-Chung; (Taipei, TW) |
Correspondence
Address: |
JIANQ CHYUN INTELLECTUAL PROPERTY OFFICE
7 FLOOR-1, NO. 100
ROOSEVELT ROAD, SECTION 2
TAIPEI
100
TW
|
Family ID: |
35459133 |
Appl. No.: |
10/907155 |
Filed: |
March 23, 2005 |
Current U.S.
Class: |
75/246 ;
419/29 |
Current CPC
Class: |
B22F 3/225 20130101;
B22F 2998/00 20130101; B22F 2998/10 20130101; B22F 3/1028 20130101;
B22F 1/0096 20130101; B22F 3/225 20130101; B22F 3/1021 20130101;
B22F 3/24 20130101; B22F 3/02 20130101; B22F 2003/248 20130101;
B22F 2998/10 20130101; B22F 2998/00 20130101; C22C 33/0257
20130101; B22F 3/1028 20130101; B22F 2998/10 20130101; C22C 33/02
20130101 |
Class at
Publication: |
075/246 ;
419/029 |
International
Class: |
B22F 003/24 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 1, 2004 |
TW |
93126297 |
Jun 10, 2004 |
TW |
93116634 |
Claims
What is claimed is:
1. A metal powder sintered body by using fine powders as a raw
material, and an alloy of the sintered body comprising: Iron (Fe),
Carbon (C), Nickel (Ni) and at least one strengthening element,
wherein the alloy includes 3.0-12.0% nickel, 0.1-0.8% carbon, and
0.5-7% the strengthening element, while a remaining portion of the
alloy is iron, and diameters of the fine powders range from 0.1-30
.mu.m.
2. The sintered body as recited in claim 1, the strengthening
element is selected from the group consisting of Molybdenum (Mo),
Chromium (Cr), Copper (Cu), Titanium (Ti), Aluminum (Al), Manganese
(Mn), Silicon (Si), and Phosphorous (P).
3. The sintered body as recited in claim 1, wherein a source of
carbon is from graphite.
4. The sintered body as recited in claim 1, wherein a source of
carbon is from carbonyl iron powder.
5. The sintered body as recited in claim 1, wherein the sintered
body has a tensile strength over 1400 MPa, a hardness over HRC35,
and a ductility over 1%.
6. A method for fabricating the sintered body as recited in claim
1, comprising: providing powders and binders; kneading the powders
and the binders, so that the powders and the binders mix into a
homogenous feedstock; performing an injection molding process so as
to discharge the feedstock to obtain a green compact; debinding the
green compact to remove the binders in order to form a body;
sintering and cooling the body in a sintering furnace; and
performing a post-sintering thermal process.
7. The method as recited in claim 6, wherein the powders are
elemental powders or prealloyed powders with diameters ranging from
0.1.about.30 .mu.m.
8. The method as recited in claim 6, wherein the sintering furnace
is a vacuum furnace or a continuous furnace.
9. The method as recited in claim 6, wherein sintering conditions
for the sintered body include a sintering temperature of
1100-1350.degree. C. for 0.5-5 hours, and a cooling rate of
3-30.degree. C./minute.
10. The method as recited in claim 6, wherein the post-sintering
thermal process is a low temperature tempering process, with a
tempering temperature ranging from 150-400.degree. C. for 0.5-5
hours.
11. The method as recited in claim 6, wherein the sintered body has
a tensile strength over 1400 MPa, a hardness over HRC35, and a
ductility over 1%.
12. A method for fabricating the sintered body as recited in claim
1, comprising: providing powders and binders; performing a powder
granulation process so that the powders and the binders are joined
into round granules; sieving the round granules to select granules
with a predetermined flowability for a compacting machine;
performing a compacting process by filling the granules in a die
cavity and pressing them out, so as to generate a green compact;
debinding the green compact to remove the binders to form a body;
sintering and cooling the body inside a sintering furnace; and
performing a post-sintering thermal procedure.
13. The method as recited in claim 12, wherein the powders are
elemental powders or prealloyed powders with diameters ranging from
0.1.about.30 .mu.m.
14. The method as recited in claim 12, wherein the sintering
furnace is a vacuum or a continuous furnace.
15. The method as recited in claim 12, wherein sintering conditions
for the sintered body include a sintering temperature of
1100-1350.degree. C. for 0.5-5 hours, and a cooling rate of
3-30.degree. C./minute.
16. The method as recited in claim 12, wherein the post-sintering
thermal process is a low temperature tempering process, with a
tempering temperature ranging from 150-400.degree. C. for 0.5-5
hours.
17. The method as recited in claim 12, wherein the sintered body
has a tensile strength over 1400 MPa, a hardness over HRC35, and a
ductility over 1%.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority benefits of Taiwan
application serial no. 93116634, filed Jun. 10, 2004, and no.
93126297, filed Sep. 1, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to a sintered body
and fabrication method thereof. More particularly, the present
invention relates to compositions of sinter-hardening powders, the
sintered body by using fine powders as raw materials, and the
fabrication method thereof.
[0004] 2. Description of Related Art
[0005] As is well known in the art, the design of the alloy of
powder metallurgy is always the critical starting point for the
development of powder metallurgy. By combining different alloying
elements and different amounts of additives, various alloy steels
can be developed and applicable to diversified circumstances. In
general, powder metallurgy components are required to possess
mechanical properties suitable for their application fields. Thus,
hardening thermal processes like quenching followed by tempering
are normally applied to the sintered components in order to obtain
the desirable mechanical properties.
[0006] However, while the quenching is performed, several problems
like deformation, size inconsistency, or cracking after quenching
may be caused by the fast cooling procedure. In addition, the
thermal processes performed on the components will cause additional
costs. Therefore, sinter-hardening powders have been developed, by
adding high hardenability alloying elements such as molybdenum
(Mo), nickel (Ni), manganese (Mn) or chromium (Cr) to iron powders,
then pressing out the green compact through the conventional
compacting process and then sintering the green compact, with the
hardness above HRC30. Examples of alloys produced by this method
are Ancorsteel 737SH (Fe-0.42MN-1.40Ni-1.25Mo--C) from Hoegananes
Corp. and ATOMET 4701 (Fe-0.45Mn-0.90Ni-1.00Mo-0.45Cr--C) from
Quebec Metal Powders Limited. The components made from these
powders are cooled at rates of a minimum of 30.degree. C. per
minute in the sintering furnace to generate martensite and
bainite.
[0007] Although the alloying elements in these sinter-hardening
components are still not homogenized completely using the regular
sintering conditions of 1120.degree. C. and 30-40 minutes, these
sinter-hardening powders provide better mechanical properties than
those possible using non sinter-hardening powders. Although
sinter-hardening powders can reduce costs due to the elimination of
the quenching process, a high cooling rate system has to be
installed in the sintering furnace. Furthermore, the aforementioned
cooling rates, while slower than quenching, are still fast enough
to cause problems such as deformation, inconsistency of the
dimensions, and even cracking. According to U.S. Pat. No.
5,682,588, the claimed powders are compacted by the conventional
pressing process, sintered between 1130-1230.degree. C., and then
cooled at rates of 5-20.degree. C./minute in order to reach the
desired sinter-hardening effects. This has improved the process by
lowering the minimum cooling rate of 30.degree. C./min, as
described in the previously mentioned processes. However, the
mechanical properties, in particular, the ductility, are still
unsatisfactory.
[0008] Concerning the press-and-sinter process, there are standards
(the Year 2003 version) for sinter-hardening alloys set forth by
the Metal Powder Industries Federation (MPIF). FLNC-4408 (1.0-3.0%
Ni, 0.65-0.95% Mo, 1.0-3.0% Cu, 0.6-0.9% C, and the remaining
portion is Fe) is the example with the best mechanical properties.
After sinter-hardening and tempering, the above-mentioned alloy can
reach a tensile strength of 970 MPa under the density of 7.2
g/cm.sup.3, and the hardness can reach HRC30, while the ductility
is only 1.0%. Although this press-and-sintered alloy belongs to one
of the sinter-hardening type alloys, its mechanical properties are
still not satisfactory.
[0009] In the field of powder metallurgy, fine powders are commonly
used in the metal injection molding process. In contrast, the
powders used in the traditional powder metallurgy process (e.g.
press-and-sinter process) are much coarser. The particle size of
the powders used in metal injection molding is usually less than 30
.mu.m, while the particles used in the press-and-sinter process are
under 150 .mu.m in size. Since the diffusion distances in fine
powers are shorter, the added alloying elements can be homogenized
more easily in the matrix materials. Therefore, components sintered
from the fine powders possess mechanical properties better than
those of the traditional press-and-sintered components.
[0010] At present, the alloys commonly used for metal powder
injection molding are the Fe--Ni--Mo--C alloy series, exemplified
by MIM-4605 (1.5-2.5Ni, 0.2-0.5% Mo, 0.4-0.6% C, <1.0% Si, the
remaining portion is Fe), which has the best mechanical properties
according to the MPIF standards. This alloy, after sintering,
reaches a tensile strength of 415 MPa, a hardness of HRB62, and a
ductility of 15%. In order to attain the best mechanical
properties, the sintered product has to be heat-treated (quenched
and tempered). It then reaches a tensile strength of 1655 MPa, a
hardness of HRC48, and a ductility of 2.0%.
[0011] Although excellent mechanical properties of the metal
injection molded products can be obtained by heat treatment after
sintering, the costs of the heat treatment accounts for a large
part of the whole production cost. Hence, it is critical to lower
the costs of the heat treatment, for example, by using
sinter-hardening materials. However, according to the Metal Powder
Industries Federation Standards, no sinter-hardening alloys are
listed for the metal injection molding process.
[0012] As mentioned above, application of fine powders improves
homogenization of the alloying elements and mechanical properties
of the products. However, application of fine powders in the
traditional press-and-sinter process is difficult because of the
poor flowability of the powder, which in turn makes it difficult to
fill the powders into the die cavity, and thus automated pressing
can not be used. However, this problem can be overcome by
granulating the fine powders into large spherical particles, and
the granulated powders can then be applied in the press-and-sinter
process.
REFERENCE PAPERS
[0013] U. Engstrom, J. McLelland, and B. Maroli, "Effect of
Sinter-Hardening on the Properties of High Temperature Sintered PM
Steels", Advances in Powder Metallurgy & Particulate
materials-2002, Compiled by V. Arnhold, C-L Chu, W. F. Jandeska,
Jr., and H. I. Sanderow, MPIF, Princeton N.J., 2002, part 13, page
1-13.
[0014] K. Kanno, Y. Takeda, B. Lindqvist, S. Takahashi, and K. K.
Kanto, "Sintering of Prealloy 3Cr-0.5Mo Steel Powder in a
carbon/carbon Composite Mesh Belt Furnace", Advances in Powder
Metallurgy & Particulate materials-2002, Compiled by V.
Arnhold, C-L Chu, W. F. Jandeska, Jr., and H. I. Sanderow, MPIF,
Princeton N.J., 2002, part 13, page 14-22.
[0015] H. Suzuki, M. Sato, and Y. Seki, "Sinter Hardening
Characteristics of Ni--Mo--Mn--Cr Pre-Alloyed Steel Powder",
Advances in Powder Metallurgy & Particulate materials-2002,
Compiled by V. Arnhold, C-L Chu, W. F. Jandeska, Jr., and H. I.
Sanderow, MPIF, Princeton N.J., 2002, part 13, page 83-95.
[0016] D. Milligan, A. Marcotte, J. Lingenfelter, and B. Johansson,
"Material Properties of Heat Treated Double Pressed/Sintered P/M
Steels in Comparison to Warm Compacted/Sinter Hardened Materials",
Advances in Powder Metallurgy & Particulate materials-2002,
Compiled by V. Arnhold, C-L Chu, W. F. Jandeska, Jr., and H. I.
Sanderow, MPIF, Princeton N.J., 2002, part 4, page 130-136.
[0017] B. Lindsley, "Development of a High-Performance Nickel-Free
P/M Steel", K. Kanno, Y. Takeda, B. Lindqvist, S. Takahashi, and K.
K. Kanto, "Sintering of Prealloy 3Cr-0.5Mo Steel Powder in a
carbon/carbon Composite Mesh Belt Furnace", Advances in Powder
Metallurgy & Particulate materials-2004, Compiled by W. B.
James, and R. A. Chernenkoff, MPIF, Princeton N.J., 2004, part 7,
page 19-27.
[0018] B. Hu, A. Klekovkin, D. Milligan, U. Engstrom, S. Berg, and
B. Maroli, "Properties of High-Density Cr--Mo Pre-alloyed Materials
High-Temperature Sintered", Advances in Powder Metallurgy &
Particulate materials-2004, Compiled by W. B. James, and R. A.
Chernenkoff, MPIF, Princeton N.J., 2004, part 7, page 28-40.
[0019] P. King, B. Schave, and J. Sweet, "Chromium-containing
Materials for High-Performance Components", Advances in Powder
Metallurgy & Particulate materials-2004, Compiled by W. B.
James, and R. A. Chernenkoff, MPIF, Princeton N.J., 2004, part 7,
page 70-80.
[0020] M. Schmidt, P. Thorne, U. Engstrom, J. Gabler, T. J.
Jesberger, and S. Feldbauer, "Effect of Sintering Time and Cooling
Rate on Sinter Hardenable Materials", Advances in Powder Metallurgy
& Particulate materials-2004, Compiled by W. B. James, and R.
A. Chernenkoff, MPIF, Princeton N.J., 2004, part 10, page
160-171.
[0021] MPIF Standard 35, Materials standards for Metal Injection
Molded Parts, 2000 edition, MPIF, Princeton N.J., pp. 12-13.
[0022] MPIF Standard 35, Materials standards for P/M Structural
Parts, 2003 edition, MPIF, Princeton N.J., pp. 46-47.
[0023] K. S. Hwang, C. H. Hsieh, and G. J. Shu, "Comparison of the
Mechanical Properties of Fe-1.75Ni-0.5Mo-1.5Cu-0.4C Steels made
from the PIM and the Press-and-Sinter Processes", Powder
Metallurgy, 2002, Vol. 45, No. 2, pp. 160-166.
[0024] U.S. Pat. No. 5,876,481, 1999.
[0025] U.S. Pat. No. 5,834,640, 1998.
[0026] U.S. Pat. No. 5,682,588, 1997.
[0027] U.S. Pat. No. 5,476,632, 1995.
SUMMARY OF THE INVENTION
[0028] The present invention is directed to a metal powder sintered
body, by using a new composition and by using fine powers as the
raw material. The particle size of the powders is between
0.1.about.30 .mu.m. The sintered body fabricated has a high
hardenability and the sintered body can attain excellent mechanical
properties under the normal cooling rate (3-30.degree. C./minute)
inside the traditional sintering furnace.
[0029] In accordance with one aspect of the present invention, a
metal injection molding fabrication method is provided, by using
the new compositions of the sinter-hardening metal powders in the
conventional metal injection molding process. The sintered compact
can be treated with low temperature tempering, without quenching,
to obtain excellent mechanical properties.
[0030] In accordance with another aspect of the present invention,
a powder metallurgy fabrication method is provided by using the new
compositions of the sinter-hardening metal powders in conventional
powder metallurgy processes (press-and-sinter process). The
sintered compact can be treated with low temperature tempering,
without quenching, to obtain excellent mechanical properties.
[0031] According to the above-mentioned and the other purposes of
the present invention, a metal powder sintered body is provided, by
using fine powders as the raw material with the sintered body
containing the characteristic composition including iron (Fe),
carbon (C), nickel (Ni), and at least one other strengthening
element, in the ratios as follows: Ni: 3.0-12.0%, carbon: 0.1-0.8%,
the strengthening elements: 0.5-7.0%, and the remaining portion is
Fe. The above-mentioned strengthening elements can be selected from
the group consisting of Molybdenum (Mo), Chromium (Cr), Copper
(Cu), Titanium (Ti), Aluminum (Al), Manganese (Mn), Silicon (Si),
and Phosphorous (P). The element carbon mentioned above can be
provided by adding graphite or using carbon-containing carbonyl
iron powders. The sintered body of the above-mentioned powders has
a tensile strength of over 1450 MPa, a hardness of over HRC38, and
a ductility of over 1% without the use of any quenching
process.
[0032] According to the above-mentioned and the other purposes of
the present invention, a metal injection molding fabrication method
is provided. The above-mentioned compositions of the
sinter-hardening metal powders can be applied to metal injection
molding. The method comprises providing the powders and binders,
while the diameters of elemental or alloyed powders are
0.1.about.30 .mu.m. The above-mentioned powders and binders are
homogenously kneaded to form a feedstock. The green compacts are
then molded from the feedstock using the injection molding machine.
The binders in the above-mentioned green compacts are removed using
the well-known solvent or thermal debinding methods. The debound
body is sintered and cooled at a cooling rate of 3-30.degree.
C./minute in the sintering furnace, which can be a regular furnace,
such as a vacuum furnace or a continuous pusher furnace. The
process after sintering is the low temperature tempering process
with the tempering temperature ranging from 150-400.degree. C. and
the time ranging from 0.5-5 hours, to improve the mechanical
properties of the sintered body.
[0033] According to the above-mentioned and the other purposes of
the present invention, a powder metallurgy method using the
above-mentioned compositions of the sinter-hardening metal powders
into powder metallurgy processes (press-and-sinter process) is
provided. The method comprises providing the powders and binders,
whereas elemental powders or alloying powders have diameters
ranging from 0.1.about.30 .mu.m. Then the powder granulation
process is performed to allow the powders and binders to bind into
round granules. Thereafter, the above round granules are sieved in
order to select appropriate particles with good flowability for the
compacting machine. The green compact is obtained by filling the
particles into the die cavity, and this is followed by compacting
the particles under high pressures. The binder in the above
mentioned green compact is removed during the debinding process.
After the debinding process, the body is sintered in the sintering
furnace, which can be a common furnace, such as a vacuum furnace or
a continuous pusher furnace. The cooling rate can range from
3-30.degree. C./minute. The post-sintering process is the low
temperature tempering process with the temperature ranging from
150-400.degree. C. and the time ranging from 0.5-5 hours to improve
the mechanical properties of the sintered body. It is noted that
the granulated powders in combination with the sinter-hardening
alloy ingredients from the present invention and with the
press-and-sinter processes can obtain components with excellent
mechanical properties without the quenching process.
[0034] According to the above, the present invention provides a
formulation for the fine sinter-hardening type powders, applicable
to the metal injection molding process or traditional powder
metallurgy process (press-and-sinter process) so as to produce the
sintered body (work piece) of high strength, high density, high
hardness, and high ductility, with a lower production cost.
[0035] It is to be understood that the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not restrictive of the invention, as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] The accompanying drawings are included to provide a further
understanding of the invention, and they are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention.
[0037] FIG. 1 is a cross-sectional view of the sample in example 1,
observing the ductile microstructure with dimple type fractures by
the scanning electronic microscope.
DESCRIPTION OF THE EMBODIMENTS
[0038] The foregoing descriptions of specific embodiments of the
invention have been presented for purposes of illustration and
description. They are not intended to be exhaustive or to limit the
invention to the precise forms disclosed. Obviously, many
modifications and variations are possible in light of the above
teaching. The embodiments were chosen and described in order to
explain the principles and the application of the invention,
thereby enabling others skilled in the art to utilize the invention
in its various embodiments and modifications according to the
particular purpose intended. The scope of the invention is intended
to be defined by the claims appended hereto and their
equivalents.
[0039] The element ingredients and the mechanical properties of the
sintered body are listed in Table 1 and Table 2, whereas examples
1-4 in Table 2 are the sintered bodies made from the metal
injection molding process; examples 5-6 are the sintered body made
from the traditional powder metallurgy process. Table 1 and Table 2
are used to illustrate the sintered body elements and the
fabrication method for the present invention, while examples 1-6
represent the present invention and examples A-D are used as the
comparison group according to the available literatures.
EXAMPLE A
[0040] According to the standards from the MPIF-35, the elements of
MIM-4605 used in injection molding are shown in Table 1, while the
mechanical properties of the sintered body produced by the elements
of MIM-4605 are shown in Table 2.
EXAMPLE B
[0041] Same composition as in example A. After the heat treatment,
products improve enormously in terms of mechanical properties, as
shown in Table 2.
EXAMPLE C
[0042] According to the MPIF-35 standards, the elements of MIM-2700
used in injection molding are shown in Table 1, while the
mechanical properties of the sintered body produced by the elements
of MIM-2700 are shown in Table 2.
EXAMPLE D
[0043] According to the MPIF-35 standards, the elements of
sinter-hardening alloy FLNC-4408 used in the traditional
press-and-sinter process are shown in Table 1, while the mechanical
properties of the sintered body produced by the elements of
FLNC-4408 are shown in Table 2.
EXAMPLE 1
[0044] Following Table 1, the required powders with particle sizes
ranging from 0.1.about.30 .mu.m are mixed together with 7 wt % of
the binder, mixed in the Z type high shear rate mixer at
150.degree. C. for 1 hour, then cooled to room temperature to
obtain the granulated feedstock. Thereafter, the previously
mentioned granulated feedstock is filled into the injection molding
machine to produce the tensile test bar (e.g. the standard tensile
bar from the MPIF-50 standard.). The tensile bar is de-bound under
the procedure applied from the known arts in the industry, for
example, debinding for five hours using heptane as the solvent at
50.degree. C., then heating the tensile bar in the vacuum furnace
from the room temperature up to 650.degree. C. at a rate of
5.degree. C./minute, raising the temperature to 1200.degree. C. at
a rate of 10.degree. C./minute, sintering at 1200.degree. C. for
two hours, and then cooling to room temperature, so as to reach a
hardness of HRC51 and a ductility of 1.0%. The tensile bar, after
being tempered at 180.degree. C. for two hours, reaches a tensile
strength of 1800 MPa, a hardness of HRC45, and a ductility of 3%,
as shown in Table 2. FIG. 1 is a fracture surface of the sample in
example 1. The ductile microstructure with dimple type fractures is
observed using a scanning electronic microscope. This indicates
that products of high hardness, high tensile strength, and high
ductility can be produced from these alloying elements. Take the
as-sintered MIM-4605 as an example, which is an injection molding
material with the best mechanical properties listed by the MPIF.
The properties are 415 MPa, HRB62, and 15% ductility, as shown in
example A in Table 2. After quenching and tempering, the improved
MIM-4605 will possess 1655 MPa, HRC48, and a ductility of 2%, as
shown in example B in Table 2. MIM-4605 needs to be quenched and
tempered to reach the mechanical properties similar to those made
by the present invention. However, the sintered body of the present
invention possesses good mechanical properties without the need for
quenching.
EXAMPLE 2
[0045] The same processes as in example 1 but with the compositions
listed in example 2 in Table 1. After tempering, the tensile bar
has a tensile strength of 1780 MPa, a hardness of HRC-45, and a
ductility of 4%.
EXAMPLE 3
[0046] The same processes as in example 1, but with the
compositions listed in example 3 in Table 1. After tempering, the
tensile bar has a tensile strength of 1720 MPa, a hardness of
HRC-46, and a ductility of 4%.
EXAMPLE 4
[0047] The same processes as in example 1, but with the
compositions listed in example 4 in Table 1. After tempering, the
tensile bar has a tensile strength of 1450 MPa, a hardness of
HRC-28, and a ductility of 4%.
EXAMPLE 5
[0048] Following the compositions listed in example 5 in Table 1,
the powders having particle sizes ranging from 0.1.about.30 .mu.m
and the required components are mixed together with 1.5 wt % of the
binders. The powders, water, and binders (e.g.: Polyvinyl alcohol)
are blended into a slurry. The slurry is then atomized from the
nozzle at high speed and dried by hot air or hot nitrogen to
evaporate the water within. The fine powders are thus bonded with
each other by the binder to form granulated powders with good
flowability. The particle size of the graduated powder is about 40
.mu.m. The previously mentioned granulated powders are filled into
the die cavity to produce the green tensile bar by the automatic
compacting machine. The tensile bar is de-bound under the procedure
applied from the known arts in the industry. For example, the
temperature will be raised at the rate of 5.degree. C./minute up to
400.degree. C., and then at the rate of 3.degree. C./minute up to
1100.degree. C., maintained for one hour, and then raised at the
rate of 10.degree. C./minute up to 1200.degree. C., and sintering
will continue at this temperature for one hour. Afterwards, the
tensile bar is cooled as the temperature of the furnace drops, and
the tensile bar is tempered for 2 hours at 180.degree. C. without
the use of the quenching process. As shown in the Table 2, the
tensile bar has a tensile strength of 1690 MPa, a hardness of
HRC47, and a ductility of 3%. Compared to FLNC-4408 (the best
sinter-hardened press-and-sinter work piece listed by the MPIF),
FLNC-4408 has 970 MPa, HRC30, and 1% ductility, as shown in example
D in Table 2.
EXAMPLE 6
[0049] The process is the same as in example 5, but with the
compositions as shown in example 6 in Table 1. After 2 hours of
tempering at 180.degree. C., the tensile bar possesses a tensile
strength of 1650 MPA, a hardness of HRC43, and a ductility of
4%.
1TABLE 1 Commonly used percentages and elements for the examples
1-6 in the present invention and for cases A-D from the industry
and based on the Metal Powder Industries Federation(MPIF)standards
(weight percentage, wt %) Element Ex: 1 Ex: 2 Ex: 3 Ex: 4 Ex: 5 Ex:
6 Ex: A& B Ex: C Ex: D C 0.36% 0.34% 0.4% 0.45% 0.5% 0.4%
0.4-0.6% <0.1% 0.6-0.9% Ni 8.0% 9.0% 8.0% 4.5% 8.0% 7.5%
1.5-2.5% .sup. 6.5-8.5% .sup. 1.0-3.0% Mo 0.8% 0.8% 1.0% 1.0% 0.8%
0.8% 0.2-0.5% <0.5% 0.65-0.95% Cr 0.8% 0.8% 0.8% 0.5% 0.8% 0.5%
-- -- -- Mn 0.6% -- -- -- -- -- -- -- -- Cu -- -- 1.5% -- 0.5% --.
-- -- 1.0-3.0% Si 0.3% 0.3% 0.3% 0.3% 0.3% 0.3% <1.0 <1.0 --
Fe the rest the rest the rest the rest the rest the rest the rest
the rest the rest
[0050]
2TABLE 2 Comparison of mechanical properties of the alloys among
examples 1-6 and examples A-D Tensile Density Quench-hardening
strength Ductility Ex: (g/cm3) process (MPa) Hardness (%) A 7.5
None 415 HRB62 15 B 7.5 Yes* 1655 HRC48 2 C 7.6 None 440 HRB69 26 D
7.2 None** 970 HRC30 1.0 1 7.6 None** 1800 HRC45 3 2 7.6. None**
1780 HRC45 4 3 7.6 None** 1720 HRC46 4 4 7.5 None** 1450 HRC38 5 5
7.5 None** 1690 HRC47 3 6 7.5 None** 1650 HRC43 4 *Austenizied at
860.degree. C. and then oil quenched, then tempered at 180.degree.
C. for 2 hours. **Sintered and then tempered at 180.degree. C. for
2 hours.
[0051] In conclusion of the above description, compared to the best
injection molding alloy, MIM-4605 (after quenching and tempering),
and the best sinter-hardening alloy, FLNC-4408, for the
press-and-sinter work piece, listed by the Metal Powder Industries
Federation (MPIF); the sinter-hardening alloy of the present
invention can attain similar or even better mechanical properties
without the quench-hardening process. Besides, the problems derived
from quench-hardening in the prior art, including deformation,
inconsistency of the dimensions, and cracking after quenching, etc,
can be avoided in the present invention, and the costs from the
quench-hardening process can be eliminated. Although
sinter-hardening alloys are available for the pressing process in
traditional powder metallurgy, the cooling rate required for the
sintered body is much higher than that required in this study. The
sintered body of the present invention provides excellent
mechanical properties, and it also provides advantages in the areas
of dimensional control and lower costs.
[0052] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *