U.S. patent application number 15/389271 was filed with the patent office on 2017-06-29 for method of manufacturing heat-resistant component using metal granules.
This patent application is currently assigned to Pim Korea Co., Ltd.. The applicant listed for this patent is Pim Korea Co., Ltd.. Invention is credited to Kyoung Hwa Eum, Jae Ok Jung, Min Chul Kim, Sang Koo Kwon, Ho Jin Lee, Young Min Leem, Sang Min Park.
Application Number | 20170182559 15/389271 |
Document ID | / |
Family ID | 56875152 |
Filed Date | 2017-06-29 |
United States Patent
Application |
20170182559 |
Kind Code |
A1 |
Jung; Jae Ok ; et
al. |
June 29, 2017 |
METHOD OF MANUFACTURING HEAT-RESISTANT COMPONENT USING METAL
GRANULES
Abstract
Disclosed is a method of manufacturing a heat-resistant
component using granules. More particularly, the method of
manufacturing a heat-resistant component includes a step of
preparing granules by spraying a mixture including a metal powder
and a slurry material into a housing equipped with a disc and
rotating the disc; a step of preparing a molded object by
compression-molding the granules; a step of preparing a sintered
object by sintering the molded object at about 1,000.degree. C. to
about 1,600.degree. C.; and a step of adjusting dimensions by
cutting the sintered object, wherein the housing is sealed and hot
air at about 70.degree. C. to about 200.degree. C. is supplied into
the housing.
Inventors: |
Jung; Jae Ok; (Daegu,
KR) ; Kwon; Sang Koo; (Gyeonggi-do, KR) ;
Leem; Young Min; (Jeollabuk-do, KR) ; Eum; Kyoung
Hwa; (Gyeongsangbuk-do, KR) ; Kim; Min Chul;
(Gyeongsangbuk-do, KR) ; Park; Sang Min;
(Gyeongsangbuk-do, KR) ; Lee; Ho Jin; (Daegu,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pim Korea Co., Ltd. |
Dalseong-gun |
|
KR |
|
|
Assignee: |
Pim Korea Co., Ltd.
Dalseong-gun
KR
|
Family ID: |
56875152 |
Appl. No.: |
15/389271 |
Filed: |
December 22, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 30/00 20130101;
B22F 2301/15 20130101; B22F 2301/35 20130101; B22F 3/24 20130101;
C22C 38/04 20130101; B22F 2998/10 20130101; B22F 2003/247 20130101;
B22F 9/10 20130101; C22C 38/002 20130101; B22F 2302/45 20130101;
B22F 1/0062 20130101; B22F 5/106 20130101; C22C 38/58 20130101;
C22C 27/06 20130101; B22F 2003/247 20130101; B22F 9/10 20130101;
B22F 1/0074 20130101; C22C 38/40 20130101; C22C 38/38 20130101;
B22F 2998/10 20130101; B22F 3/1021 20130101; C22C 19/058 20130101;
B22F 3/225 20130101; B22F 3/02 20130101; B22F 3/1021 20130101; C22C
38/02 20130101; C22C 38/08 20130101; B22F 2301/20 20130101; B22F
1/0074 20130101; B22F 3/16 20130101 |
International
Class: |
B22F 3/16 20060101
B22F003/16; B22F 1/00 20060101 B22F001/00; B22F 3/10 20060101
B22F003/10; B22F 3/24 20060101 B22F003/24; B22F 5/10 20060101
B22F005/10; C22C 30/00 20060101 C22C030/00; C22C 19/05 20060101
C22C019/05; C22C 27/06 20060101 C22C027/06; C22C 38/58 20060101
C22C038/58; C22C 38/40 20060101 C22C038/40; C22C 38/38 20060101
C22C038/38; C22C 38/08 20060101 C22C038/08; C22C 38/04 20060101
C22C038/04; C22C 38/02 20060101 C22C038/02; C22C 38/00 20060101
C22C038/00; B22F 9/10 20060101 B22F009/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2015 |
KR |
10-2015-0187154 |
Claims
1. A method of manufacturing a heat-resistant component, the method
comprising: preparing granules by spraying a mixture comprising a
metal powder and a slurry material into a housing equipped with a
disc and rotating the disc; preparing a molded object by
compression-molding the granules; preparing a sintered object by
sintering the molded object at about 1,000.degree. C. to about
1,600.degree. C.; and adjusting dimensions by cutting the sintered
object, wherein the housing is sealed and hot air at about
70.degree. C. to about 200.degree. C. is supplied into the
housing.
2. The method according to claim 1, wherein the metal powder
comprises about 0.1 to 3% by weight of carbon, greater than 0 and
less than or equal to about 5% by weight of silicon, greater than 0
and less than or equal to about 15% by weight of manganese, greater
than 0 and less than or equal to about 1% by weight of phosphorus,
greater than 0 and less than or equal to about 1% by weight of
sulfur, greater than 0 and less than or equal to about 90% by
weight of nickel, greater than 0 and less than or equal to about
50% by weight of iron, and greater than 0 and less than or equal to
about 50% by weight of chromium.
3. The method according to claim 1, wherein an average size of the
granules is about 20 .mu.m to about 200 .mu.m.
4. The method according to claim 1, wherein an average particle
size of the metal powder is about 0.01 .mu.m to about 50 .mu.m, and
a particle size distribution of the metal powder is about 0.001
.mu.m to about 100 .mu.m.
5. The method according to claim 1, wherein solid loading (S/L) of
the mixture is about 10% by volume to about 45% by volume.
6. The method according to claim 1, wherein a rotational speed of
the disc is about 4,000 rpm to about 20,000 rpm.
7. The method according to claim 1, wherein the slurry material
comprises a solvent and a binder.
8. The method according to claim 7, wherein the solvent comprises
one or more of water, hexane, acetone, and alcohol having a carbon
number of 1 to 10.
9. The method according to claim 7, wherein the binder comprises
one or more of polyvinyl butyral, polyvinyl alcohol, wax, and
polyethylene glycol.
10. The method according to claim 1, wherein the compression
molding is performed under a pressure of about 0.1 ton/cm.sup.2 to
about 10 ton/cm.sup.2.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to Korean Patent
Application No. 10-2015-0187154, filed on Dec. 28, 2015 in the
Korean Intellectual Property Office, the entire disclosures of
which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of manufacturing a
heat-resistant component using granules.
DISCUSSION OF THE RELATED ART
[0003] Recently, the demand for industrial parts with superior
dimensional accuracy and mechanical properties has been
increasing.
[0004] Such industrial parts can be manufactured using powder
metallurgy technology, metal powder injection molding technology,
etc. Powder metallurgy is a technology for manufacturing a molded
metal object having a predetermined shape by compression molding a
metal powder and then sintering the same.
[0005] FIG. 1 illustrates a powder metallurgy method. Referring to
FIG. 1, the powder metallurgy method may include molding, sintering
and cutting steps.
[0006] For example, the powder metallurgy method may include a
molding step S1 in which a metal powder is mixed with a binder, as
a bonding agent, and then a resultant mixture is subjected to
compression to make an ingot, followed by manufacturing a product
into a designed shape by a cutting or pressing process; a sintering
step S2 in which the product, which has undergone the molding step
S1, is heated in a sintering furnace; and a cutting step S3 in
which the product, which has undergone the sintering step S2, is
ground or cut to designed dimensions.
[0007] Since a coarse powder with a particle size of about 50 to
200 .mu.m is used in the powder metallurgy method, it is difficult
to secure mechanical properties, i.e., density, strength, hardness,
etc., and thus, a produced product cannot be applied to a car
turbocharger, etc.
[0008] In the molding step, mechanical properties may be improved
by increasing compressive strength when the metal powder is fed
into a mold and compressed. However, in this case, there is a
limitation in increasing compressive strength because a mold can be
damaged thereby. Accordingly, there is a disadvantage in that a
subsequent process, such as forging or heat treatment, is
required.
[0009] In addition, in the powder metallurgy method, a coarse
powder with a particle size of 50 .mu.m to 200 .mu.m should be used
to secure moldability and produce a uniform product. However, a
powder with this size forms large pores in a molded object during a
molding process. Such large pores may reduce the density of a
molded object.
[0010] Meanwhile, metal powder injection molding technology uses
micro metal particles with a size of nothing more than about 5
.mu.m to about 10 .mu.m. When performing a powder metallurgy
method, application of micro metal particles, which are used in
metal powder injection molding, has been attempted. However, when
micro metal particles with this size are applied, the particles are
not closely packed in a mold due to cohesive force between the
particles, and thus a problem of non-uniform density occurs in a
molding process. In addition, the uniformity of a product is
deteriorated due to a non-uniform filling amount.
[0011] Moreover, since powder fineness is proportional to
difficulty in plastic deformation, the fine powder is under a lot
of stress, which is a factor that can cause cracks during heat
treatment. Furthermore, a fine powder which has a size smaller than
a tolerance between molds causes damage to the molds, and thus the
fine powder has a lot of problems in application to powder
metallurgy.
[0012] FIG. 2 illustrates a metal powder injection molding method.
Referring to FIG. 2, the metal powder injection molding method may
include a kneading step S100, an injection molding step S200, a
degreasing step S300, a sintering step S400, and a cutting S500
step.
[0013] More particularly, the metal powder injection molding method
may include a mixing step in which a metal powder and a binder, as
a bonding agent, are mixed in a mixer; an injection molding step in
which a resultant mixture, which has undergone the mixing step is
injected, into an injection molding machine and then subjected to
compression molding to make a product with a designed shape; a
degreasing step in which the product, which has undergone the
injection molding step, is heated in a degreasing furnace to remove
the binder; a sintering step in which the product, which has
undergone the degreasing step, is heated in a sintering furnace;
and a cutting step in which the product, which has undergone the
sintering step, is ground or cut to a designed size.
[0014] The degreasing step is provided to secure the fluidity of
the metal powder within the injection molding machine. In addition,
since the binder, e.g., wax, a polymer, or the like, may remain as
carbon upon heat treatment under an inert atmosphere, the binder
should be removed by the degreasing step.
[0015] In addition, when performing the metal powder injection
molding method, a cumbersome procedure of heating from room
temperature to 1,000.degree. C. for about 12 hours to about 60
hours exists in the degreasing step. This causes a decrease in
productivity and an increase in fuel costs, and, accordingly,
production costs increase. Such a method for manufacturing a
heat-resistant component that includes the degreasing step has been
disclosed in Korean Patent No. 1202462.
[0016] In addition, while a linear shrinkage in the powder
metallurgy method is about 1% to about 5%, a linear shrinkage in
the metal powder injection molding method is about 12% to about
22%. Thus, the metal powder injection molding method exhibits a
considerably large linear shrinkage and has a problem that it is
difficult to three-dimensionally control linear shrinkage.
SUMMARY OF THE INVENTION
[0017] In accordance with an aspect of the present invention, there
is provided a method of manufacturing a heat-resistant component
using granules.
[0018] In an embodiment of the present invention, the method of
manufacturing a heat-resistant component includes a step of
preparing granules by spraying a mixture including a metal powder
and a slurry material into a housing equipped with a disc and
rotating the disc; a step of preparing a molded object by
compression-molding the granules; a step of preparing a sintered
object by sintering the molded object at about 1,000.degree. C. to
about 1,600.degree. C.; and a step of adjusting dimensions by
cutting the sintered object, wherein the housing is sealed and hot
air at about 70.degree. C. to about 200.degree. C. is supplied into
the housing.
[0019] In an embodiment of the present invention, the metal powder
may include about 0.1% to 3% by weight of carbon (C), greater than
0 and less than or equal to about 5% by weight of silicon (Si),
greater than 0 and less than or equal to about 15% by weight of
manganese (Mn), greater than 0 and less than or equal to about 1%
by weight of phosphorus (P), greater than 0 and less than or equal
to about 1% by weight of sulfur (S), greater than 0 and less than
or equal to about 90% by weight of nickel (Ni), greater than 0 and
less than or equal to about 50% by weight of iron (Fe), and greater
than 0 and less than or equal to about 50% by weight of chromium
(Cr).
[0020] In an embodiment of the present invention, an average size
of the granules may be about 20 .mu.m to about 200 .mu.m.
[0021] In an embodiment of the present invention, an average
particle size of the metal powder may be about 0.01 .mu.m to about
50 .mu.m, and a particle size distribution of the metal powder is
about 0.001 .mu.m to about 100 .mu.m.
[0022] In an embodiment of the present invention, solid loading
(S/L) of the mixture may be about 10% by volume to about 45% by
volume.
[0023] In an embodiment of the present invention, a rotational
speed of the disc may be about 4,000 rpm to about 20,000 rpm.
[0024] In an embodiment of the present invention, the slurry
material may include a solvent and a binder.
[0025] In an embodiment of the present invention, the solvent may
include one or more of water, hexane, acetone, and alcohol having a
carbon number of 1 to 10.
[0026] In an embodiment of the present invention, the binder may
include one or more of polyvinyl butyral (PVB), polyvinyl alcohol
(PVA), wax, and polyethylene glycol (PEG).
[0027] In an embodiment of the present invention, the compression
molding may be performed under a pressure of about 0.1 ton/cm.sup.2
to about 10 ton/cm.sup.2.
[0028] Therefore, it is an objective of the present invention to
provide a method of manufacturing a heat-resistant component for
preparing spherical granules, and to uniformly fill the interior of
a mold with the granules.
[0029] It is another objective of the present invention to provide
a method of manufacturing a heat-resistant component, the method
providing superior press moldability and a sintered object with
superior mechanical strength.
[0030] It is a still objective of the present invention to provide
a method of manufacturing a heat-resistant component, the method
minimizing linear shrinkage of a product while providing a product
with superior surface and internal quality and superior molding
density.
[0031] It is yet another objective of the present invention to
provide a method of manufacturing a heat-resistant component, the
method providing superior productivity and having advantages in
terms of processing time and energy consumption.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The above and other objectives, features and advantages of
the present invention will become more apparent to those of
ordinary skill in the art by describing exemplary embodiments
thereof in detail with reference to the accompanying drawings, in
which
[0033] FIG. 1 illustrates a powder metallurgy method;
[0034] FIG. 2 illustrates a metal powder injection molding
method;
[0035] FIG. 3 illustrates a method of manufacturing a
heat-resistant component according to an embodiment of the present
invention;
[0036] FIG. 4 illustrates a method of preparing granules according
to an embodiment of the present invention;
[0037] FIG. 5 illustrates a method of preparing granules according
to an embodiment of the present invention;
[0038] FIG. 6 illustrates a molding machine for preparing granules
according to an embodiment of the present invention;
[0039] FIG. 7(a) is an optical microscope image of a metal powder
used in an example of the present invention, and FIG. 7(b) is an
optical microscope image of granules prepared according to an
example of the present invention;
[0040] FIG. 8(a) is an optical microscope image of granules
according to an Example for the present invention, FIG. 8(b) is an
optical microscope image of granules according to a comparative
example for the present invention, and FIG. 8(c) is an optical
microscope image of granules according to a comparative example for
the present invention;
[0041] FIG. 9(a) is an optical microscope image of granules
according to an example of the present invention, FIG. 9(b) is an
optical microscope image of granules according to a comparative
example for the present invention;
[0042] FIG. 10(a) is an image of a heat-resistant component
according to an example of the present invention, and FIG. 10(b) is
an X-ray image of the heat-resistant component;
[0043] FIG. 11(a) is an image of a heat-resistant component
according to an example of the present invention, and FIG. 11(b) is
an image of a heat-resistant component according to a comparative
example for the present invention;
[0044] FIG. 12(a) is an image of a heat-resistant component
according to a comparative example for the present invention, FIG.
12(b) is an image of a heat-resistant component according to an
example of the present invention, FIG. 12(c) illustrates a heat
treatment result of the heat-resistant component of the comparative
example, and FIG. 12(d) illustrates a heat treatment result of the
heat-resistant component of the example;
[0045] FIG. 13(a) is an electron microscope image illustrating a
microstructure of a heat-resistant component according to a
comparative example for the present invention, FIG. 13(b) is an
electron microscope image illustrating a microstructure of a
heat-resistant component according to an example of the present
invention, FIG. 13(c) is an electron microscope image illustrating
a microstructure of the heat-resistant component of the comparative
example which has been subjected to heat treatment, and FIG. 13(d)
is an electron microscope image illustrating a microstructure of
the heat-resistant component of the example which has been
subjected to heat treatment; and
[0046] FIG. 14(a) is an electron microscope image illustrating a
surface oxidation layer formed on a heat-resistant component
according to an example of the present invention which has been
subjected to heat treatment in ambient conditions, and FIG. 14(b)
is an electron microscope image showing a surface oxidation layer
formed on the heat-resistant component according to the example
which has been subjected to heat treatment in a continuous
annealing furnace.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0047] Exemplary embodiments of the present invention are described
in detail so that those of ordinary skill in the art can easily
carry out the present invention with reference to the accompanying
drawings. The present invention may be implemented in various
different forms and is not limited to these embodiments. To clearly
describe the present invention, a part not related to the
description is omitted in the drawings, and the same or similar
elements are designated with the same reference numbers in the
entire specification.
[0048] Method of Manufacturing Heat-Resistant Component Using
Granules
[0049] The present invention relates to a method of manufacturing a
heat-resistant component using granules. FIG. 3 illustrates a
method of manufacturing a heat-resistant component according to an
embodiment of the present invention. Referring to FIG. 3, the
method of manufacturing a heat-resistant component includes a step
of preparing granules (S10); a step of preparing a molded object
(S20); a step of preparing a sintered object (S30); and a cutting
step (S40).
[0050] More specifically, the method of manufacturing a
heat-resistant component includes a step of preparing granules by
spraying a mixture including a metal powder and a slurry material
into a housing equipped with a disc and rotating the disc (S10); a
step of preparing a molded object by filling a mold with the
granules and then compression-molding the granules (S20); a step of
preparing a sintered object by sintering the molded object at about
1,000.degree. C. to about 1,600.degree. C. in a sintering furnace
and then cooling the same (S30); and a step of adjusting dimensions
by cutting the sintered object (S40).
[0051] Hereafter, a detailed description of each step of the method
of manufacturing a heat-resistant component will be provided
below.
[0052] Step of Preparing Granules (S10)
[0053] This step relates to preparation of granules by spraying a
mixture including a metal powder and a slurry material into a
housing equipped with a disc and rotating the disc.
[0054] FIG. 4 illustrates a method of preparing granules according
to an embodiment of the present invention. Referring to FIG. 4, the
method of preparing granules may include a step of preparing a
mixture (S11), and a drying step (S12).
[0055] Step of Preparing Mixture (S11)
[0056] This step relates to preparation of a mixture including a
metal powder and a slurry material.
[0057] Metal Powder
[0058] In an embodiment of the present invention, the average
particle size of the metal powder may be about 0.01 .mu.m to about
50 .mu.m. In the present invention, the term "size" is defined as a
maximum length of a metal powder particle. When metal powder
particles with the above average size are applied, spherical
granules may be easily prepared, a mold may be uniformly filled
with the granules, and a heat-resistant product with superior
mechanical properties may be manufactured.
[0059] A size distribution of the metal powder may be about 0.001
.mu.m to about 100 .mu.m (90% or more of the powder). A metal
powder with this size distribution may be easily prepared into
granules.
[0060] In an embodiment of the present invention, the metal powder
may be a metal powder for a heat-resistant component which is
applied to turbocharged diesel and gasoline engines, etc. The metal
powder for a heat-resistant component may include about 18% or more
of chromium.
[0061] In an embodiment of the present invention, the metal powder
may include about 0.1 to 3% by weight of carbon (C), greater than 0
and less than or equal to about 5% by weight of silicon (Si),
greater than 0 and less than or equal to about 15% by weight of
manganese (Mn), greater than 0 and less than or equal to about 1%
by weight of phosphorus (P), greater than 0 and less than or equal
to about 1% by weight of sulfur (S), greater than 0 and less than
or equal to about 90% by weight of nickel (Ni), greater than 0 and
less than or equal to about 50% by weight of iron (Fe), and greater
than 0 and less than or equal to about 50% by weight of chromium
(Cr). When a metal powder within these ranges is used, the
heat-resistant component of the present invention may have superior
mechanical strength.
[0062] For example, the metal powder may include about 0.2 to 0.5%
by weight of carbon (C), about 0.75 to 1.3% by weight of silicon
(Si), greater than 0 and less than or equal to about 1.5% by weight
of manganese (Mn), about 0.2 to 0.3% by weight of molybdenum (Mo),
about 24 to 27% by weight of chromium (Cr), about 19 to 22% by
weight of nickel (Ni), about 1 to 1.75% by weight of niobium (Nb),
and residual iron (Fe) and inevitable impurities. When a metal
powder within these ranges is used, the heat-resistant component of
the present invention may be superior in mechanical strength.
[0063] In an embodiment of the present invention, HK-30 (ASTM
standard) may be used as the metal powder. In particular, HK-30 may
be used in a high temperature chemical instrument or a port for
heat treatment due to superior heat resistance thereof.
[0064] In an embodiment of the present invention, solid loading
(S/L) of the metal powder may be about 10% by volume to about 45%
by volume. Here, S/L is represented as a ratio of a volume of the
metal powder to a total volume of the mixture. The metal powder
within this range of S/L has superior compatibility and
moldability, and thus the metal powder may be easily prepared into
the granules. For example, S/L of the metal powder may be about 13%
by volume to about 40% by volume.
[0065] Slurry Material
[0066] The slurry material secures fluidity of the mixture, so that
the metal powder may be sprayed into the housing.
[0067] In an embodiment of the present invention, the slurry
material may include a solvent and a binder.
[0068] Solvent
[0069] The solvent may be included in the slurry material to secure
fluidity and compatibility of the mixture. In an embodiment of the
present invention, the solvent may be volatile. In the
specification of the present invention, the term "volatile" means
that, by drying with hot air which will be described below, a
solvent is vaporized at a temperature range of about 70.degree. C.
to about 200.degree. C.
[0070] In an embodiment of the present invention, the solvent may
include one or more of water, hexane, acetone, and alcohol having a
carbon number of 1 to 10. When the solvent is used, superior
fluidity and compatibility are exhibited and granules may be easily
prepared.
[0071] In an embodiment of the present invention, as the alcohol
having a carbon number of 1 to 10, monohydric alcohols, including
methanol, ethanol, butanol, pentanol, hexanol, etc., dihydric
alcohols, including 1,2-pentandiol, 1,5-pentandiol, hexanediol,
heptanediol, octanediol, decanediol, etc., and trihydric alcohols,
including propylene glycol, 1,3-butylene glycol, glycerin, etc.,
may be used. These alcohols may be used alone or a mixture of two
or more thereof.
[0072] In another embodiment, the solvent may be included in an
amount of about 50 to about 90 parts by volume based on 100 parts
by volume of the mixed slurry material. For example, the solvent
may be included in an amount of about 60 parts by volume to about
70 parts by volume. For example, the solvent may be included in an
amount of about 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62,
63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
80, 81, 82, 83, 84, 85, 86, 87, 88, 89 or 90 parts by volume.
[0073] Binders
[0074] The binder may be included to form the granules by
agglomerating the metal powder. In an embodiment of the present
invention, the binder may include one or more of polyvinyl butyral
(PVB), polyvinyl alcohol (PVA), wax, and polyethylene glycol (PEG).
When the binder is included, the granules may be effectively
formed.
[0075] In an embodiment of the present invention, the binder may be
included in an amount of about 0.01 part by weight to about 5 parts
by weight based on 100 parts by weight of the metal powder. When
the binder is included within this weight range, the spherical
granules may be easily prepared. For example, the binder may be
included in an amount of about 0.05 parts by weight to about 5
parts by weight. For example, the binder may be included in an
amount of about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08,
0.09, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 4 or 5 parts by weight.
[0076] In an embodiment of the present invention, the solvent may
include ethanol. In an embodiment of the present invention, the
binder may include polyvinyl butyral (PVB). When the slurry
material including the solvent and the binder is applied, oxidation
of the metal powder may be effectively prevented.
[0077] In another embodiment of the present invention, the metal
powder and the binder may be included in a weight ratio of about
100:0.01 to about 100:6. When the metal powder and the binder are
included in this weight ratio, superior compatibility, workability,
and moldability are provided and the granules may be easily
prepared. For example, the metal powder and the binder may be
included in a weight ratio of about 100:0.05 to about 100:2.
[0078] FIG. 5 illustrates a method of preparing granules according
to an embodiment of the present invention. Referring to FIG. 5, in
an embodiment, the mixture may be prepared by injecting a metal
powder 10 into a solvent 20, dispersing the same, and injecting a
binder 12 there into.
[0079] In another embodiment, a slurry to be mixed with the metal
powder 10 may be prepared by injecting the solvent 20 into a
container and then dissolving the binder 12 in the solvent 20.
Alternatively, the mixture may be prepared by introducing the
solvent, the binder, and the metal powder into a ball mill
accommodated with balls and mixing the same. In addition, the
slurry may be prepared using a general mixer other than the ball
mill. In an embodiment of the present invention, the mixture may be
prepared by mixing the solvent, the binder, and the metal powder in
the mixer for 1 to 2 hours.
[0080] Drying Step (S12)
[0081] The drying step is a step in which granules are prepared by
spraying the mixture into a housing equipped with a disc, and
drying the solvent while rotating the disc.
[0082] FIG. 6 illustrates a molding machine for preparing granules
according to an embodiment of the present invention. Referring to
FIG. 6, the molding machine 1000 may include a housing 200 equipped
with a rotatable disc 300.
[0083] For example, the granules may be prepared by spraying the
mixture into the housing 200 equipped with the disc 300, and by
drying a solvent included in the mixture while rotating the disc
300. In an embodiment of the present invention, the housing 200 is
sealed, and hot air may be supplied to the interior of the housing
200 and may be discharged from the housing 200.
[0084] Referring to FIGS. 5(d) and (e), the sprayed mixture is
formed into agglomerated spherical particles by surface tension
during rotation of the disc 300 and the solvent therein is dried.
As a result, the granules 100 are formed.
[0085] In an embodiment of the present invention, hot air at about
70.degree. C. to about 200.degree. C. is supplied into the housing
200. When the disc is being rotated while supplying hot air with
the above condition, a formation rate and a formation ratio of the
granules may be superior without decomposition of the binder. When
hot air at less than about 70.degree. C. is supplied into the
housing, the mixture is not properly dried and thus shapes of the
granules are defective, whereby mechanical properties and an
appearance of a heat-resistant component may be deteriorated. On
the other hand, when hot air at greater than 200.degree. C. is
supplied into the housing, the binder in the mixture is decomposed
and thus shapes of the granules are defective, whereby mechanical
properties and an appearance of a heat-resistant component may be
deteriorated.
[0086] For example, hot air at about 80.degree. C. to about
150.degree. C. may be supplied. For example, hot air at about 70,
75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140,
145, 150, 160, 170, 180, 190 or 200.degree. C. may be supplied.
[0087] In an embodiment of the present invention, a rotational
speed of the disc may be about 4,000 rpm to about 20,000 rpm. At
this rotational speed, drying is effectively performed, and thus a
formation ratio of spherical granules may be superior. For example,
the rotational speed of the disc may be about 4000, 4500, 5000,
5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000, 9500, 10000, 11000,
12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000 or 20000
rpm.
[0088] In an embodiment of the present invention, the average size
of the granules may be about 20 .mu.m to about 200 .mu.m. When the
granules are formed in this size range, mold filling ability, and
mechanical properties of a heat-resistant component may be
superior. For example, the average size of the granules may be
about 30 .mu.m to about 150 .mu.m. In another example, the average
size of the granules may be about 30 .mu.m to about 90 .mu.m. For
example, the average size of the granules may be about 20, 25, 30,
35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110,
115, 120, 125, 130, 135, 140, 145, 150, 160, 170, 180, 190 or 200
.mu.m.
[0089] Referring to FIG. 6, the mixture may be dispersed in a shape
of water droplets from an upper part of the housing 200 to a lower
part of the housing 200 (or a lower part of the housing 200 to an
upper part of the housing 200) due to centrifugal force generated
by rotation of the disc 300. Here, the solvent in the mixture
formed in a spherical shape is dried and spherical granules may be
formed. In an embodiment of the present invention, a plurality of
the metal powder particles are combined by binding force of the
binder and cohesive force (van der Waals force) of the metal
powder, and thus the granules may be formed in a spherical
shape.
[0090] Step of Preparing Molded Object (S20)
[0091] This step relates to preparation of a molded object by
filling a mold with the granules and by compression-molding the
granules. In an embodiment of the present invention, a press mold
may be filled with the granules to prepare an ingot of a
predetermined shape, which is then subjected to compression
molding.
[0092] In an embodiment of the present invention, the compression
molding may be performed under a pressure of about 0.1 ton/cm.sup.2
to about 10 ton/cm.sup.2. The size of the granules may be about ten
or more times a size of the metal powder. In addition, since the
granules have a spherical shape, fluidity, which is affected by
gravity, may be superior. Accordingly, the interior of a mold may
be uniformly filled with the granules. That is, the comparison of
the granules vs. the metal powder may be explained by a case that a
mold is more uniformly filled with rice grains than flour.
[0093] In an embodiment of the present invention, the molded object
may be prepared to conform to the shape of a heat-resistant
component by press-molding the granule-filled mold. For example, a
mold may be filled with the granules to prepare an ingot with a
shape of a block or a circular plate.
[0094] In an embodiment, when a mold of a press machine is filled
with the granules to prepare an ingot with a predetermined shape,
followed by compression molding, a granular shape of the granules
is broken and the granules are split into a fine metal powder,
whereby the interior of the mold may be uniformly filled with the
fine metal powder.
[0095] Step of Preparing Sintered Object (S30)
[0096] This step relates to preparation of a sintered object by
sintering the molded object in a sintering furnace and then cooling
the same.
[0097] In an embodiment of the present invention, the sintering may
be performed at about 1,000.degree. C. to about 1,600.degree. C. In
this temperature range, the binder contained in the mixture is
easily removed, and thus the sintered object may exhibit superior
mechanical strength and surface properties. When the sintering is
performed at less than about 1000.degree. C., a reduction in
density, and a reduction in surface and mechanical properties of
the sintered object may occur due to incomplete sintering. On the
other hand, when the sintering is performed at greater than about
1600.degree. C., shape defects occur due to melting and mechanical
properties of the sintered object may be deteriorated. For example,
the sintering may be performed at about 1000, 1050, 1100, 1150,
1200, 1250, 1300, 1350, 1400, 1450, 1500, 1550 or 1600.degree.
C.
[0098] In an embodiment of the present invention, the sintered
object may be prepared by heating the molded object at the
temperature described above in a sintering furnace and subsequently
cooling the same to room temperature.
[0099] The binder may be decomposed and removed during the
sintering. In an embodiment of the present invention, when
polyvinyl butyral is used as the binder, polyvinyl butyral is
easily removed from a sintering furnace, whereby efficiency of the
sintering process is superior and mechanical strength and surface
properties of the sintered object are superior.
[0100] In an embodiment of the present invention, the sintering may
be performed in a gas atmosphere including one or more of hydrogen,
nitrogen, and argon. When the sintering is performed in the gas
atmosphere, an oxidation phenomenon, which is caused by inflow of
oxygen, may be prevented. In an embodiment of the present
invention, the sintering may be performed in a gas atmosphere of
Ar--N.sub.2 or N.sub.2--H.sub.2.
[0101] Cutting Step (S40)
[0102] The cutting step relates to adjustment of dimensions by
cutting the sintered object. In an embodiment of the present
invention, the dimensions of the sintered object may be adjusted by
cutting the sintered object prepared in the step of preparing a
sintered object to a desired size.
[0103] Heat-Resistant Component Manufactured by Method of
Manufacturing Heat-Resistant Component
[0104] According to another aspect of the present invention, a
heat-resistant component is manufactured by the method of
manufacturing a heat-resistant component using granules.
[0105] When the powder metallurgy method of using the granules
according to the present invention is applied, the shape of the
prepared granules is close to a spherical shape, and the grain size
of the granules is about 20 .mu.m to about 200 .mu.m, and the
fluidity of the granules is less than about 40 sec/50 g.
Accordingly, the granules have properties similar to a powder for
powder metallurgy. Therefore, an interior of a mold may be easily
filled with the granules.
[0106] In addition, when the granulated powder is subjected to
press molding, the granulated powder is broken into a fine powder
and thus may uniformly fill the interior of the mold. In addition,
a relative density may be increased up to about 99% or more after
sintering and a heat-resistant component with superior mechanical
properties may be manufactured.
[0107] In addition, since fine metal powder particles are
granulated and agglomerated, followed by being compressed in a
molding step, interior uniformity may be increased compared to a
case of compressing a metal powder. In addition, due to a
relatively large driving force for sintering, a high density may be
obtained after sintering. Thus, even though the powder metallurgy
method is used, a product having superior mechanical properties
compared to a product manufactured by a metal powder injection
molding or casting method may be obtained.
[0108] In addition, since, as in the metal powder injection molding
method, a degreasing process is not necessary, a manufacturing
process is simple. Moreover, since heating is not required for
degreasing, energy consumption and processing time are reduced.
Therefore, productivity may be improved, and production costs may
be reduced.
[0109] Further, it may be confirmed that a higher molding density
results in a low linear shrinkage after sintering. According to the
present invention, since a fine metal powder is used and molding is
performed by compressing granules, a molding density may be
increased compared to an existing powder metallurgy method. In
addition, the control of linear shrinkage is easy compared to a
metal powder injection molding method, and thus, after molding, a
molded object may be sintered to have dimensions close to
predetermined dimensions. Therefore, since work is completed by
only the cutting process, an effect of reducing processing and
production costs is excellent.
[0110] Hereinafter, the constitution and functions of the present
invention are described in more detail with reference to examples
of the present invention. However, the following examples are
merely provided as preferred embodiments and, therefore, the
present invention is not limited to the examples.
Examples and Comparative Examples
Example 1
[0111] According to contents shown in Table 1 below, a mixture
including a metal powder, polyvinyl butyral and ethanol was
prepared. A container with a volume of 1000 ml and a ball mill were
used. A mixture was prepared by mixing the metal powder, the
polyvinyl butyral, and the ethanol at room temperature for 1 hour
according to conditions shown in Table 1 below.
[0112] As the metal powder, HK-30 with an average particle size of
5 to 9 .mu.m, manufactured by Parmaco (Fischingen, Switzerland),
was used. The HK-30 includes 0.20 to 0.50% by weight of carbon (C),
24 to 27% by weight of chromium (Cr), 19 to 22% by weight of nickel
(Ni), 0.75 to 1.30% by weight of silicon (Si), greater than 0 and
less than or equal to 1.5% by weight of manganese (Mn), 0.2 to 0.3%
by weight of molybdenum (Mo), 1 to 1.75% by weight of niobium (Nb)
and residual iron (Fe) and inevitable impurities.
TABLE-US-00001 TABLE 1 Mixture Weight (g) Volume (ml) Metal powder
(HK-30) 150 19 Polyvinyl butyral 1.5 1.5 Ethanol 80 103 Solid
loading (S/L) 15.7%
[0113] Granules were prepared by injecting the mixture into a
molding machine including a sealed housing that was equipped with a
rotatable disc therein as illustrated in FIG. 6, and then supplying
130.degree. C. hot air into the housing while rotating the disc at
a rotational speed of 6000 rpm.
[0114] A mold was filled with the granules and subjected to
compression molding under a pressure of 100 MPa, i.e., about 1.01
ton/cm.sup.2, thereby manufacturing a molded object with a form of
a vane ring used in a turbocharger.
[0115] The molded object was sintered at 1,240.degree. C., which is
a temperature lower than a temperature at which a liquid phase is
formed, for 2 to 3 hours in a high temperature vacuum batch
furnace. The sintering was performed under a vacuum atmosphere in
the batch furnace and under a hydrogen atmosphere in a continuous
furnace to prepare a sintered object. Subsequently, the dimensions
of the sintered object were adjusted by cutting, thereby
manufacturing a heat-resistant component.
Example 2
[0116] A heat-resistant component was manufactured by the same
method as in Example 1, except that a mixture was prepared using
components and contents summarized in Table 2 below.
TABLE-US-00002 TABLE 2 Mixture Weight (g) Volume (ml) Metal powder
(HK-30) 375 48 Polyvinyl butyral 5.6 5.6 Ethanol 100 128 Solid
loading (S/L) 27.2%
Example 3
[0117] A heat-resistant component was manufactured by the same
method as in Example 1, except that compression molding was
performed under a pressure of 600 MPa, i.e., about 6.12
ton/cm.sup.2.
Example 4
[0118] A heat-resistant component was manufactured by the same
method as in Example 2, except that compression molding was
performed under a pressure of 600 MPa, i.e., about 6.12
ton/cm.sup.2.
Comparative Example 1
[0119] A heat-resistant component was manufactured by the same
method as in Example 1, except that granules were prepared by
supplying 65.degree. C. hot air to the housing.
Comparative Example 2
[0120] A heat-resistant component was manufactured by the same
method as in Example 1, except that granules were prepared by
supplying 215.degree. C. hot air to the housing.
[0121] Evaluation of Properties of Heat-Resistant Components
[0122] (1) Measurement of relative density, linear shrinkage,
apparent density and granule recovery ratio: with regard to
Examples 1 to 4 and Comparative Examples 1 to 2, relative
densities, linear shrinkages, apparent densities (g/cc), and
granule recovery ratios (%) of the manufactured heat-resistant
components are shown in Table 3 below.
TABLE-US-00003 TABLE 3 Relative Linear Apparent Granule density
shrinkage density recovery Classification (%) (%) (g/cc) ratio (%)
Example 1 97.6 12.2 2.1 90 Example 2 98.1 12.2 2.3 85 Example 3 98
7.5 2.1 90 Example 4 98.2 7.5 2.3 85 Comparative -- -- Unmeasurable
0 Example 1 Comparative 95 12 1.9 35 Example 2
[0123] Referring to Table 3, since, in the cases of Examples 1 to
4, molding was performed after granules had been compressed, a
packing density was increased during mold filling, compared to an
existing fine powder. Moreover, since the control of linear
shrinkage is easy, after molding, a molded object may be sintered
to have dimensions close to predetermined dimensions. Therefore, a
heat-resistant component may be manufactured by minimally cutting a
sintered object.
[0124] On the other hand, in the case of Comparative Example 1, a
granulated powder was not formed due to the absence of drying, and,
in the case of Comparative Example 2, a granule recovery ratio was
significantly lowered compared to Examples 1 to 4.
[0125] As illustrated below, FIG. 7(a) is an optical microscope
image (magnification: 1000.times.) of the metal powder used in
Example 1, and FIG. 7(b) is an optical microscope image
(magnification: 1000.times.) of the granules prepared according to
Example 1 of the present invention. Referring to FIG. 7, it may be
confirmed that an average particle size of the metal powder is 5
.mu.m to 9 .mu.m, and the granules prepared according to Examples 1
to 3 are prepared as particles having an average size of 30 .mu.m
to 90 .mu.m.
[0126] FIG. 8(a) is an optical microscope image of granules
according to an Example 1, FIG. 8(b) is an optical microscope image
of granules according to a Comparative Example 1, and FIG. 8(c) is
an optical microscope image of granules according to a Comparative
Example 2; In addition, FIG. 9(a) shows an optical microscope image
of the granules of Example 1, FIG. 9(b) shows an optical microscope
image of the granules of Comparative Example 1. Referring to FIGS.
8 and 9, in the case of Example 2, it may be confirmed that
granules are prepared as particles with an average size of 30 to 90
.mu.m, whereas, in the case of Comparative Example 1, shapes of
granules are defective due to incomplete drying of a mixture, and,
in the case of Comparative Example 2, shapes of granules are
defective due to decomposition of a binder.
[0127] FIG. 10(a) is an image of a heat-resistant component of
Example 1, and FIG. 10(b) is an X-ray image of the heat-resistant
component of Example 1. Referring to FIG. 10, it may be confirmed
that appearance of the heat-resistant component of Example 1 is
superior and an interior of the heat-resistant component has no
defect.
[0128] FIG. 11(a) is an image of the heat-resistant component of
Example 1, and FIG. 11(b) is an image of the heat-resistant
component of Comparative Example 1. Referring to FIG. 11, it may be
confirmed that the heat-resistant component manufactured according
to Example 1 of the present invention has a superior appearance,
whereas the heat-resistant component manufactured according to
Comparative Example 1 has a defective appearance due to the
occurrence of cracks.
[0129] (2) Evaluation of heat resistance: Heat resistance of the
heat resistant components manufactured according to the present
invention was evaluated as described below. In Comparative Example
3, a heat-resistant component was manufactured by casting using the
metal powder of Example 1. Then, heat-resisting properties of the
heat resistant components, which were manufactured according to
Example 1 and Comparative Example 3 respectively, were evaluated by
thermally treating at 820.degree. C. for 50 hours.
[0130] FIG. 12(a) is an image of the heat-resistant component of
Comparative Example 3, FIG. 12(b) is an image of the heat-resistant
component of Example 1, FIG. 12(c) illustrates a result of
thermally treating the heat-resistant component of Comparative
Example 3, and FIG. 12(d) illustrates a result of thermally
treating the heat-resistant component of Example 1.
[0131] FIG. 13(a) is an electron microscope image showing a
microstructure of the heat-resistant component of Comparative
Example 3, FIG. 13(b) is an electron microscope image showing a
microstructure of the heat-resistant component of Example 1, FIG.
13(c) is an electron microscope image illustrating a microstructure
of the heat-resistant component of Comparative Example 3 which has
been subjected to heat treatment, and FIG. 13(d) is an electron
microscope image illustrating a microstructure of the
heat-resistant component of Example 1 which has been subjected to
heat treatment.
[0132] Referring to FIGS. 12 and 13, it may be confirmed that, when
compared to a microstructure of the casted heat-resistant component
of Comparative Example 3 (see FIG. 13(a)), a microstructure of the
heat-resistant component of Example 1 (see FIG. 13(b)) exhibits a
fine structure and superior homogeneity, but does not exhibit a
sigma phase.
[0133] Meanwhile, the sigma phase causes reductions in heat
resistance and erosion resistance of a heat-resistant component.
When the sigma phase is formed in a heat-resistant component, the
heat-resistant component may be remarkably damaged under a strong
acidic atmosphere, such as a nitrogen atmosphere. Accordingly, in a
heat-resistant component for a turbocharger, an area ratio of a
sigma phase is limited to be less than 2%.
[0134] FIG. 14(a) is an electron microscope image illustrating a
surface oxidation layer formed on the heat-resistant component
according to Example 1 which has been subjected to heat treatment
at 900.degree. C. for 500 hours in ambient conditions, and FIG.
14(b) is an electron microscope image showing a surface oxidation
layer formed on the heat-resistant component of Example 1 which has
been subjected to heat treatment at 900.degree. C. for 500 hours in
a continuous annealing furnace.
[0135] Referring to FIGS. 14(a) and 14(b), in the case of Example
1, when heat treatment was performed under a vacuum condition, a
maximum thickness of a surface oxidation layer was 12.405 .mu.m,
and, when heat treatment was performed in a continuous annealing
furnace, a maximum thickness of a surface oxidation layer was
15.405 .mu.m. Accordingly, it may be confirmed that the
heat-resistant component for a turbocharger according to Example 1
satisfies a thickness limit value, i.e., less than 30 .mu.m, for a
surface oxidation layer.
[0136] When manufacturing a heat-resistant component according to
the present invention, since the size of granules is ten or more
times the size of a metal powder, the granules are uniformly packed
in a mold, and, after sintering, the density of the heat-resistant
component is uniformly formed.
[0137] In addition, according to an embodiment of the present
invention, since a metal powder is granulated and then is
compressed in a molding step, the granulated metal powder is
uniformly packed in a mold compared to the case of compressing a
metal powder in a powder metallurgy process. In addition, since
densification of a structure may be induced during sintering due to
use of a fine metal powder with a superior sintering driving force,
a relatively high density may be obtained compared to an existing
powder metallurgy process.
[0138] Accordingly, when manufacturing a heat-resistant component
according to the present invention, a heat-resistant component with
superior mechanical properties may be obtained as in the metal
powder injection molding method.
[0139] In addition, a degreasing process, which is required for the
metal powder injection molding method, is not required for the
present invention, and thus a manufacturing process according to
the present invention is simple. Moreover, since heating, which is
required for degreasing, is not necessary, productivity is superior
and there are advantages in terms of processing time and energy
consumption.
[0140] It should be understood by those skilled in the art that
various changes in form and details may be made herein without
departing from the spirit and scope of the invention as defined by
the appended claims.
* * * * *