U.S. patent application number 17/001351 was filed with the patent office on 2021-07-29 for method of strengthening binder metal phase of sintered body.
The applicant listed for this patent is FUJI KIHAN CO., LTD.. Invention is credited to Yoshio MIYASAKA.
Application Number | 20210230729 17/001351 |
Document ID | / |
Family ID | 1000005048508 |
Filed Date | 2021-07-29 |
United States Patent
Application |
20210230729 |
Kind Code |
A1 |
MIYASAKA; Yoshio |
July 29, 2021 |
METHOD OF STRENGTHENING BINDER METAL PHASE OF SINTERED BODY
Abstract
Spherical shaped ejection particles are ejected against a
surface of a sintered body including hard particles and a binder
metal phase bonding the hard particles together, with a compressed
gas at an ejection pressure of from 0.2 MPa to 0.6 MPa or at an
ejection velocity of from 80 m/s to 200 m/s and the spherical
ejection particles having a hardness not less than the hardness of
the binder metal phase and that is a hardness of 1000 HV or less
and being particles having an average particle diameter from 20
.mu.m to 149 .mu.m. Thus, plastic deformation resulting from such
impact and the instantaneous temperature rise and cooling occurring
at the impact sites micronizes the structure of the binder metal
phase, causes a change to a dense structure, and imparts
compressive residual stress thereto. This results in strengthening,
and enables prevention of brittle fracture in the sintered
body.
Inventors: |
MIYASAKA; Yoshio; (Aichi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJI KIHAN CO., LTD. |
Aichi |
|
JP |
|
|
Family ID: |
1000005048508 |
Appl. No.: |
17/001351 |
Filed: |
August 24, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22F 1/16 20130101; C21D
7/06 20130101; B24C 1/10 20130101 |
International
Class: |
C22F 1/16 20060101
C22F001/16; C21D 7/06 20060101 C21D007/06; B24C 1/10 20060101
B24C001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 27, 2020 |
JP |
2020-011102 |
Claims
1. A method of strengthening a binder metal phase of a sintered
body, the binder metal phase strengthening method comprising:
ejecting spherical shaped ejection particles against a surface of a
sintered body that includes hard particles and a binder metal phase
bonding the hard particles together, by ejecting the spherical
shaped ejection particles together with a compressed gas at an
ejection pressure of from 0.2 MPa to 0.6 MPa or at an ejection
velocity of from 80 m/s to 200 m/s and the spherical ejection
particles having a hardness that is not less than the hardness of
the binder metal phase and that is a hardness of not more than 1000
HV and being particles of from 100 grit to 800 grit, having an
average particle diameter of from 20 .mu.m to 149 .mu.m.
2. The sintered body binder metal phase strengthening method of
claim 1, wherein a sintered body employed as a treatment subject is
a sintered body having a hard coating film coated on at least a
portion of surface at a thickness of not more than 5 .mu.m, and the
ejection particles are ejected against the sintered body at the
portion of the surface coated with the hard coating film.
3. The sintered body binder metal phase strengthening method of
claim 1, wherein the ejection particles are metal particles,
ceramic particles, or a mixture of metal particles and ceramic
particles.
4. The sintered body binder metal phase strengthening method of
claim 1, wherein a hardness of the ceramic particles employed is
not more than 800 HV.
5. The sintered body binder metal phase strengthening method of
claim 2, wherein the ejection particles are metal particles,
ceramic particles, or a mixture of metal particles and ceramic
particles.
6. The sintered body binder metal phase strengthening method of
claim 2, wherein a hardness of the ceramic particles employed is
not more than 800 HV.
7. The sintered body binder metal phase strengthening method of
claim 3, wherein a hardness of the ceramic particles employed is
not more than 800 HV.
8. The sintered body binder metal phase strengthening method of
claim 5, wherein a hardness of the ceramic particles employed is
not more than 800 HV.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a method for strengthening
a phase of a binder metal (referred to as a "binder metal phase" in
the present invention) in a sintered body in which hard particles
of a carbide, oxide, nitride, boride, silicide, or the like are
sintered together with a binder metal such as Fe, Ni, or Co, such
as in a cemented carbide, a cermet, or cBN.
2. Description of the Related Art
[0002] Taking an example of a cemented carbide as an example of
such a sintered body, the cemented carbide is configured by fine
particles (normal particles of cemented carbide have a particle
diameter of a few .mu.m, and ultrafine particles of cemented
carbide have a particle diameter of from about 0.5 .mu.m to about
0.8 .mu.m) of a carbide (WC, TiC, TaC) of a metal such as tungsten
(W), titanium (Ti), Tantalum (Ta) sintered together using as a
binder a metal such as iron (Fe), nickel (Ni), or cobalt (Co). As
narrowly defined, cemented carbide sometimes refers to only WC--Co
based alloys configured from particles of tungsten carbide (WC)
sintered together using a cobalt (Co) binder.
[0003] Such cemented carbides are materials have remarkable
hardness, in a hardness range of from 1000 HV to 1800 HV, and
excellent wear resistance, and are accordingly employed as the
material for tools, machine components, and the like where wear
resistance is demanded, such as cutting tools.
[0004] However, although cemented carbides have high hardness, they
have the disadvantage of being brittle, and brittle fracture is
liable to occur. This means that, for example, cracks, nicks, and
the like are liable to occur at the cutting-edge of cutting tools
made from cemented carbide. This reduces productivity due to the
need to either replace cutting tools partway through a job when
such cracks or nicks have occurred, or to perform a regrinding
operation or the like to regenerate the cutting tools
cutting-edge.
[0005] There is accordingly a desire for the provision of a
cemented carbide that, while having high hardness, also has
excellent toughness and is not susceptible to brittle fracture such
as cracks or nicks.
[0006] The mechanical characteristics, such as hardness and
toughness, of cemented carbides are known to vary according to the
particle diameter of the hard particles and the addition amount of
the binder metal.
[0007] Accordingly, it might be supposed that the particle diameter
of the hard particles and the addition amount of the binder metal
should be changed to obtain a cemented carbide having the targeted
hardness and toughness.
[0008] However, as illustrated in FIG. 1, the relationships of
hardness and toughness against the particle diameter of the hard
particles are relationships in which the hardness of the cemented
carbide increases but the toughness decreases as the average
particle diameter of the hard particles decreases, and conversely
the fracture toughness increases but the hardness decreases as the
average particle diameter of the hard particles increases.
[0009] Moreover, as illustrated in FIG. 2, the relationships of
hardness and toughness against the addition amount of binder metal
are relationships in which the hardness of the cemented carbide
increases but the toughness decreases as the addition amount of the
binder metal is decreased, and the toughness of the cemented
carbide increases but the hardness decreases as the addition amount
of the binder metal is increased.
[0010] The hardness and toughness of the cemented carbide
accordingly have conflicting relationships in that increasing one
causes a decrease in the other. This means that a cemented carbide
possessing the two conflicting properties of having excellent
toughness while also having high hardness and is accordingly
difficult to obtain by adjusting the particle diameter of the hard
particles and adjusting the addition amount of the binder
metal.
[0011] Proposed methods to improve toughness without reducing the
hardness of cemented carbides accordingly include, for example: a
method of coating a surface of a base body made from a cemented
carbide with a hard coating layer including a toughened zone of
excellent toughness (see abstract of Japanese Patent KOKAI (LOPI)
No. 2000-246509 (JP2000-246509A); and a method to raise the
fracture toughness of only a surface portion while maintaining the
overall hardness of a cemented carbide, which is achieved by
providing a surface layer of a toughness that has been raised by
increasing the WC particle diameter and/or increasing the Co
concentration at the surface of a cemented carbide (see abstract of
Japanese Patent KOHYO (LOPI) No. 2004-514790 (JP2004-514790A)).
[0012] Note that although not directed toward raising the toughness
of a sintered body such as a cemented carbide, the inventors of the
present invention have proposed an instantaneous heat treatment
method for a metal article directed toward forming
micro-structures, dimples, and the like on a surface by shot
peening. In this instantaneous heat treatment method, substantially
spherical shaped shot, having a higher hardness than the base
material hardness of a workpiece and including three or more
different approximate ranges of grain size lying in a range of from
100 grit to 800 grit (average particle diameter: 20 .mu.m to 149
.mu.m), are mixed together and a mixed fluid of the shot combined
with compressed air is ejected intermittently, at from 0.1 seconds
to 1 second and intervals of from 0.5 seconds to 5 seconds, onto
the workpiece. This ejection is performed at an ejection pressure
of from 0.3 MPa to 0.6 MPa, at an ejection velocity of from 100 m/s
to 200 m/s, and with an ejection distance of 100 mm to 250 mm, so
as to form numerous random fine indentations having substantially
circular bottom faces and a diameter of from 0.1 .mu.m to 5 .mu.m
on the surface of the workpiece (claim 1 of Japanese Patent KOKAI
(LOPI) No. 2012-135864 (JP2012-135864A)). Note that an example is
described in Japanese Patent KOKAI (LOPI) No. 2012-135864
(JP2012-135864A) in which a "carbide" is employed as the workpiece
(see Table 11-1 in Japanese Patent KOKAI (LOPI) No. 2012-135864
(JP2012-135864A)).
[0013] In the related art described above, in a configuration in
which a hard coating layer including a toughened zone is provided
on the surface of a cemented carbide, as in the configuration
described in Japanese Patent KOKAI (LOPI) No. 2000-246509
(JP2000-246509A), forming the hard coating layer provided with the
toughened zone of high toughness on the surface while maintaining
the hardness of the cemented carbide unaffected, enables toughness
to be imparted while maintaining the characteristics of a cemented
carbide i.e. high hardness.
[0014] However, this method requires an operation to form the hard
coating layer provided with the toughened zone on the surface of
the cemented carbide using a method such as physical vapor
deposition (PVD), chemical vapor deposition (CVD), or the like.
Forming the hard coating film in this manner requires extensive
investment in equipment etc., such as the need for a costly vacuum
deposition system.
[0015] Moreover, the reason high toughness is achieved in this
method is that a hard coating film is formed on the surface, and
not because the toughness is increased of the cemented carbide
itself, which means that the toughness is lost if the hard coating
film detaches.
[0016] However, a configuration such as that described in Japanese
Patent KOHYO (LOPI) No. 2004-514790 (JP2004-514790A), in which a
surface layer of high toughness is provided on a cemented carbide
by increasing the WC particle diameter and/or increasing the Co
concentration, enables the toughness to be raised locally for only
a surface layer portion without lowering the hardness within the
cemented carbide.
[0017] However, a surface layer having increased WC particle
diameter and/or increased Co concentration in this manner has a
hardness that is decreased as a result of increasing the toughness.
The wear resistance thereof is accordingly decreased (see FIG. 1
and FIG. 2), and wear readily occurs when employed in an
application in which direct contact or sliding occurs against other
members.
[0018] Thus in the treatment described in Japanese Patent KOHYO
(LOPI) No. 2004-514790 (JP2004-514790A), in cases in which there is
a further wear resistant coating film formed on the surface layer
described above, preparatory treatment is performed to prevent
detachment of the wear resistant coating film (Japanese Patent
KOHYO (LOPI) No. 2004-514790 (JP2004-514790A), [0001]). However,
forming the surface layer in this manner does not enable both
toughness and hardness to be obtained in the cemented carbide
itself.
[0019] Thus, even though there is a strong desire to impart a
cemented carbide with both hardness and toughness, none of the
related art listed above is able to provide a solution to such a
desire.
[0020] Thus the inventors of the present invention have performed
diligent investigations into what is required to enable the
toughness of a cemented carbide itself to be raised without forming
a hard coating film or the like as described above.
[0021] As a result, the inventors have considered whether the
occurrence of brittle fracture such as cracks or nicks can be
suppressed if the binder metal phase can be strengthened at least
in the vicinity of the surface of a cemented carbide 1.
[0022] Namely, as illustrated in FIG. 3, the cemented carbide 1 has
a structure in which hard particles 10, such as WC, are bonded
together by a binder metal phase 20, such as Co, having a higher
ductility than that of the hard particles 10.
[0023] The hard particles 10 therein have extremely high hardness,
for example 1780 HV for WC, 3200 HV for TiC, and 1800 HV for TaC,
and hardly deform. Any plastic deformation occurring when an
external force is imparted to the cemented carbide 1 can
accordingly be logically inferred to have occurred mainly in the
portion where the binder metal phase 20, such as the Co, is
present. This provides support as to why the overall toughness
(deformability) of the cemented carbide 1 is raised by increasing
the addition amount of the binder metal (see FIG. 2).
[0024] In this manner, the deformation of the cemented carbide 1 is
thought to mainly occur in the binder metal phase 20 portion, and
brittle fracture, such as cracks or nicks occurring in the cemented
carbide 1, is thought to be generated by cracking of the binder
metal phase 20 due to strain accompanying deformation, which grows
as more strain is imparted, and which eventually leads to
fracturing occurring.
[0025] Following on from the above prediction, if the binder metal
phase 20 portion of the cemented carbide 1 could be strengthened,
and in particular the binder metal phase 20 in the vicinity of the
surface of the workpiece where fractures tend to originate could be
strengthened, then this should enable the ability to withstand
brittle fracture such as cracks or nicks, namely the fracture
toughness, to be raised.
[0026] Moreover, strengthening the binder metal phase 20 is thought
to contribute to making brittle fracture less liable to occur and
to raising the toughness of a sintered body, not only for the
cemented carbide 1, but also for sintered bodies in general having
a similar structure of the hard particles 10 bonded together with
the binder metal phase 20, such as a cermet, cBN, or the like.
[0027] Note that Japanese Patent KOKAI (LOPI) No. 2012-135864
(JP2012-135864A) discloses an instantaneous heat treatment method
performed by ejecting beads made from high-speed steel (HSS) onto a
treatment subject for an Example of a draw punch made from cemented
carbide (Table 11-1 of Japanese Patent KOKAI (LOPI) No. 2012-135864
(JP2012-135864A)).
[0028] However, Japanese Patent KOKAI (LOPI) No. 2012-135864
(JP2012-135864A) is significantly different from the present
invention in that an essential element is that such treatment
should be performed with ejection particles harder than the
treatment subject (claim 1 of Japanese Patent KOKAI (LOPI) No.
2012-135864 (JP2012-135864A)).
[0029] Moreover, Japanese Patent KOKAI (LOPI) No. 2012-135864
(JP2012-135864A) includes the advantageous effects of increasing
hardness by micronization of the surface structure using the
instantaneous heat treatment method, and preventing seizing and the
like by dimples formed thereby functioning as oil reservoirs. There
is also a reference to "wear resistance" being increased, however
there is no reference whatsoever to raising the ability to
withstand nicking and cracking such as chipping, called "brittle
fracture", namely no reference whatsoever to increasing
toughness.
[0030] Following on from the prediction by the inventors, the
present invention is directed towards solving the disadvantages in
a sintered body such as a cemented carbide mentioned above of low
fracture toughness, and proposes a method to strengthen the binder
metal phase 20 in the vicinity of the surface of the sintered body
1 using a comparatively simple method. An object of the present
invention is to make brittle fracture less liable to occur (to
impart toughness) while maintaining the characteristic high
hardness of sintered bodies, such as cemented carbides, cermets,
and cBN.
SUMMARY OF THE INVENTION
[0031] The following description of means for solving the problem
is appended with reference signs employed in embodiments for
implementing the invention. These reference signs are employed to
clarify correspondence between the recitation of the scope of
patent claims and the description of embodiments for implementing
the invention, and obviously do not limit the interpretation of the
technological scope of the present invention.
[0032] In order to achieve the object of the present invention, in
a method of strengthening a binder metal phase of a sintered body,
the method of strengthening a binder metal phase 20 of a sintered
body 1 comprises:
[0033] ejecting spherical shaped ejection particles 30 against a
surface of a sintered body 1 such as cemented carbide that includes
hard particles 10 such as tungsten carbide (WC) and a binder metal
phase 20 such as cobalt (Co) bonding the hard particles 10
together, by ejecting the spherical shaped ejection particles 30
together with a compressed gas at an ejection pressure of from 0.2
MPa to 0.6 MPa or at an ejection velocity of from 80 m/s to 200 m/s
and the spherical ejection particles 30 having a hardness that is
not less than the hardness of the binder metal phase 20 and that is
a hardness of not more than 1000 HV and being particles of from 100
grit to 800 grit (having an average particle diameter of from 20
.mu.m to 149 .mu.m).
[0034] In the strengthening method, a sintered body 1 employed as a
treatment subject is a sintered body 1 having a hard coating film
(not illustrated in the drawings) coated on at least a portion of
surface at a thickness of not more than 5 .mu.m, and the ejection
particles 30 may be ejected against the sintered body 1 at the
portion of the surface coated with the hard coating film.
[0035] Moreover, the ejection particles 30 may be any of metal
particles, ceramic particles, or a mixture of metal particles and
ceramic particles, and a hardness of the ceramic particles employed
is preferably not more than 800 HV.
EFFECT OF THE INVENTION
[0036] The following significant advantageous effects can be
obtained by strengthening the binder metal phase 20 of the sintered
body 1 using the configuration of the present invention and the
method of the present invention as described above.
[0037] Ejection particles 30 ejected against the surface of the
sintered body 1 impact the surface of the sintered body 1. The
sintered body 1 is configured by the hard particles 10 made from
WC, TiC, or TaC, and by the binder metal phase 20 such as a Co
phase bonding between the hard particles 10 (see FIG. 3).
[0038] The hard particles 10, such as WC (1780 HV), TiC (3200 HV),
or TaC (1800 HV), have higher hardness than the ejection particles
30, which have a hardness of not more than 1000 HV. When the
ejection particles 30 having a hardness not less than the hardness
of the binder metal phase 20 impact the surface of the sintered
body 1 serving as the workpiece, as illustrated in FIG. 4B,
although there is no deformation of the hard particles 10 in the
sintered body 1, the binder metal phase 20 present between the hard
particles 10 undergoes plastic deformation and moves the hard
particles 10, causing the surface of the sintered body 1 to
deform.
[0039] Plastic deformation resulting from such impact and the
instantaneous temperature rise and cooling (instantaneous heat
treatment) occurring at the impact sites micronizes the structure
of the binder metal phase 20 in the vicinity of the surface of the
sintered body 1, causes a change to a dense structure, and also
imparts compressive residual stress thereto. This results in
strengthening.
[0040] In this manner, the method of the present invention enables
the binder metal phase 20 in the vicinity of the surface of the
sintered body 1 to be strengthened, and enables good prevention of
the occurrence of brittle fracture such as cracks or nicks in the
sintered body 1, which arise from cracking and breaking occurring
at the grain boundaries of the hard particles 10.
[0041] Strengthening the binder metal phase 20 in this manner may
be similarly performed in cases in which a hard coating film (not
illustrated in the drawings) of 5 .mu.m or less is formed on the
surface of the sintered body 1, enabling the binder metal phase 20
of the sintered body below the hard coating film to be strengthened
even after the hard coating film has been formed on the surface of
the sintered body 1.
[0042] Moreover, the cohesion strength of the hard coating film can
be increased and detachment made less liable to occur by
strengthening the binder metal phase 20 in this manner.
[0043] Moreover, the micronization and densification occurring in
the structure of the binder metal phase 20, and the compressive
residual stress that has been imparted thereto by the ejection of
the ejection particles 30 might be lost by heating the sintered
body 1. Thus film forming of the hard coating film by a method
involving heating the sintered body 1 is not able to be performed
after the binder metal phase 20 has been strengthened by ejecting
the ejection particles 30. However, the sintered body 1 after film
forming a hard coating film in this manner can be employed as the
treatment subject, and so this does not provide a limitation to the
method of forming the hard coating film.
[0044] Furthermore, metal particles, ceramic particles, and a
mixture of both metal particles and ceramic particles may all be
employed as the ejection particles 30. In cases in which ceramic
particles are employed, making the hardness of such ceramic
particles not more than 800 HV enables the toughness to be
increased more certainly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] The objects and advantages of the invention will become
understood from the following detailed description of preferred
embodiments thereof in connection with the accompanying drawings in
which like numerals designate like elements, and in which:
[0046] FIG. 1 is a graph to explain relationships of hardness and
toughness of a cemented carbide against particle diameter of hard
particles therein;
[0047] FIG. 2 is a graph to explain relationships of hardness and
toughness of a cemented carbide against addition amount of binder
metal therein;
[0048] FIG. 3 is a schematic diagram to explain a structure of a
sintered body (a WC--Co based cemented carbide); and
[0049] FIG. 4 is an explanatory diagram of states of deformation
arising when ejection particles have impacted a workpiece of higher
hardness than the ejection particles, FIG. 4A is for a general
workpiece other than a sintered body, and FIG. 4B is for a sintered
body workpiece including a binder metal phase having a hardness not
more than the hardness of the ejection particles.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] Explanation follows regarding a method of the present
invention to strengthen a binder metal phase 20 of a sintered body
1.
[0051] Treatment Subject
[0052] In the present invention, a sintered body configured by the
hard particles 10 sintered together with a binder metal is employed
as a treatment subject. The hard particles 10 are not limited to
being a single type of hard particle, and plural types of hard
particle may be mixed together and employed therefor. Similarly,
the binder metal is also not limited to being a single type of
metal, and an alloy may be employed therefor.
[0053] Examples of such a sintered body 1 include a cemented
carbide, a cermet, and cBN. All of these have a structure such as
that schematically illustrated in FIG. 3 in which the hard
particles 10 are bonded together by the binder metal phase 20.
[0054] The "cemented carbide" of the sintered body 1 is configured
by the hard particles 10 made from a carbide (WC, TiC, TaC) of a
metal such as tungsten (W), titanium (Ti), Tantalum (Ta) sintered
together with a binder of a metal such as iron (Fe), nickel (Ni),
or cobalt (Co). As narrowly defined, cemented carbide sometimes
refers to only a WC--Co based alloy of particles of tungsten
carbide (WC) sintered together using a binder of cobalt (Co). The
present invention is not limited to a WC--Co based alloy, and a
cemented carbide containing any of the above carbide particles may
be employed as the treatment subject.
[0055] Moreover, such WC--Co based alloys encompass, in addition to
a WC--Co alloy, alloys containing carbide particles other than WC,
such as a WC--TiC--Co alloy, a WC--TiC--TaC(NbC)--Co alloy, or a
WC--TaC(NbC)--Co alloy. Moreover, the binder metal is not limited
to being a single metal such as Fe, Ni, or Co, and another metal
such as an alloy of these metals may also be employed.
[0056] The "cermet" of the sintered body 1 is a sintered body
configured by the hard particles 10 of a ceramic such as a carbide,
oxide, nitride, boride, or silicide, bonded together with a binder
metal, and within a wide definition may include the cemented
carbides listed above.
[0057] Examples of such cermets include a TiC--Mo--Ni cermet, and
also a TiC based cermet with the addition of TiN, TaN thereto, an
A1.sub.2O.sub.3--Cr cermet, and the like. Any of these may be
employed as the treatment subject of the present invention.
[0058] Furthermore, the "cBN" of the sintered body is a sintered
body of hard (fine) particles 10 of cubic boron nitride of which
hexagonal boron nitride is modified by ultrahigh pressure and high
temperature, that is sintered using a binder metal such as Co.
[0059] The sintered body 1 may be employed in various forms and
applications, such as in cutting tools such as a milling cutter or
drill, shaping tools such as a wire drawing die or a centering
tool, wear resistant components such as a roller, gage or dot pin
of a printer, a corrosion-resistant tool in a mining application
such as a rock cutter or coal cutter, as well as a mold or the
like. These may variously be employed as the treatment subject,
irrespective of form and application thereof.
[0060] Moreover, the above tools and components do not need to be
formed entirely of a sintered body, and, for example, a sintered
body may be attached to a portion of the tool or component, such as
in a cutting tool or the like in which, for example, a sintered
body is attached as the cutting-edge portion alone by brazing.
[0061] Moreover, the treatment subject may be a sintered body in
which the surface of the sintered body serving as the treatment
subject has a hard coating film (ceramic coating film) of, for
example, TiN, TiCN, TiAlN, DLC, TiCrN, CrN, or the like formed
thereon at a film thickness of not more than 5 .mu.m by physical
vapor deposition (PVD) or chemical vapor deposition (CVD).
[0062] Note that for cases in which attachment by brazing or hard
coating film forming accompanied by heating is performed, then such
treatment is preferably completed on the sintered body 1 prior to
performing the strengthening method of the present invention, since
the advantageous effects of strengthening by the micronization and
densification of structure, imparting of compressive residual
stress to the binder metal phase 20, and the like, are sometimes
lost if heat is applied after the treatment by the method of the
present invention.
[0063] Treatment Content
[0064] Dry ejection of the ejection particles 30 together with
compressed gas is performed on the surface of the sintered body 1
serving as the above treatment subject.
[0065] There is no particular limitation to the material employed
for the ejection particles 30 as long as the material lies within
the hardness range described below. As well as the ejection
particles 30 being made from a metal, those made from a ceramic
(including glass) may also be employed. Moreover, not only ejection
particles 30 made from a single type of material, but also ejection
particles 30 made from a mixture of plural materials may also be
employed.
[0066] The objective of ejecting the ejection particles 30 is to
perform micronization and densification of the structure by
plastically deforming the binder metal phase 20, and to impart
compressive residual stress and the like thereto, i.e. the
objective thereof is to obtain the advantageous effects of what is
referred to as "shot peening", and so spherical shaped (spherical
shaped particles) are employed therefor.
[0067] Note that reference to "spherical shaped" in the present
invention need not refer strictly to a "sphere", and includes a
wide range of non-angular rounded shapes, such as spheroid shapes
or barrel shapes.
[0068] Such spherical shaped ejection particles 30 may be obtained
by an atomizing method for metal based materials, and may be
obtained by crushing and then melting for ceramic based
materials.
[0069] The hardness of the ejection particles 30 employed is a
hardness not less than the hardness of the binder metal phase 20
and ejection particles of not more than 1000 HV are employed.
Moreover, when the ejection particles 30 are ceramic particles,
then preferably those of not more than 800 HV are employed
therefor.
[0070] For example, the respective melting points for Co, Mo, Ni
that may be employed as the binder metal are 1495.degree. C.,
2625.degree. C., 1455.degree. C. Sintering is performed at a high
temperature in the vicinity of the melting point of the binder
metal, and a hardness of the binder metal phase 20 after sintering
is from 500 HV to 800 HV (for example, about 500 HV for Ni, and
about from 700 HV to 800 HV for Co).
[0071] Thus for the sintered body 1 having a Co phase as the binder
metal phase 20, alumina-silica beads (792 HV), HSS beads (1000 HV),
or the like are for example suitably employed as the ejection
particles 30. However, for the sintered body 1 having a Ni phase as
the binder metal phase 20, preferably glass beads (565 HV) are
employed as the ejection particles 30.
[0072] Note that in cases in which the same metal is employed as
the binder, differences in the hardness of the binder metal phase
20 arise according to the sintering conditions (heating
temperature, pressure, etc.), and so the hardness of the ejection
particles 30 is selected based on the respective hardness of the
binder metal phase 20.
[0073] In cases in which the hardness of the binder metal phase 20
is not known, for example, trials are performed, in which plural
types of ejection particles 30 of different hardness of not more
than 1000 HV are actually ejected against the surface of the
sintered body 1. The ejection particles 30 capable of rendering a
matt (or satin) finish on the surface of the sintered body 1 in
such trials may then be employed as ejection particles 30 having a
hardness not less than that of the binder metal phase 20.
[0074] Note that even in cases in which ejection particles 30
having a hardness of not more than 1000 HV are employed, sometimes
considerable damage is inflicted on the surface of the sintered
body 1 and the toughness thereof is actually lowered when ceramic
based (including glass) ejection particles 30 with a hardness
exceeding 800 HV thus toughness are lowered. Thus ejection
particles 30 having a hardness of not more than 800 HV are
preferably employed for ceramic based ejection particles 30.
[0075] Furthermore, the ejection particles 30 employed have a
particle diameter in the range of from 100 grit to 800 grit for
grain size distributions as defined by JIS R 6001(1987) (an average
particle diameter of from 20 .mu.m to 149 .mu.m). As long as the
particle diameter falls within this grain size range, a mixture of
plural types of ejection particles 30 of different particle
diameter may be employed.
[0076] The method for ejecting such ejection particles 30 against
the sintered body 1 which is the workpiece may employ various known
dry type blasting treatment apparatuses capable of ejecting
particles, and an air blasting treatment apparatus is preferably
employed therefor because this enables comparatively easy
adjustment of ejection velocity and ejection pressure.
[0077] Various examples of such air blasting treatment apparatuses
include direct pressure type, gravity suction type, and other types
of blasting treatment apparatus. Any of these types of blasting
treatment apparatus may be employed, and the type thereof is not
particularly limited as long as the blasting treatment apparatus
has the performance capable of ejecting the ejection particles at
an ejection pressure of from 0.2 MPa to 0.6 MPa, or at an ejection
velocity of from 80 m/sec to 200 m/sec.
[0078] Advantageous Effects Etc.
[0079] In the above manner, ejecting the ejection particles 30 and
causing the ejection particles 30 to impact the surface of the
sintered body 1 enables the sintered body 1 to be improved by
making brittle fracture not liable to occur and by achieving
excellent toughness properties.
[0080] Although the mechanism by which such advantageous effects
are obtained is not entirely clear, it is thought that
strengthening the binder metal phase 20 in the following manner
enables the toughness to be raised without decreasing the hardness
of the sintered body 1.
[0081] Namely, in cases in which the ejection particles 30 of lower
hardness than the workpiece are ejected against the workpiece and
the workpiece is an ordinary workpiece rather than a sintered body,
then normally plastic deformation as illustrated in FIG. 4A occurs
when the ejection particles 30 impact, with the plastic deformation
mainly occurring on the side of the ejection particles 30 of lower
hardness.
[0082] As a result, when ejection particles 30 of lower hardness
than the workpiece are employed, the surface of the workpiece is
not able to be plastically deformed, and the advantageous effects
that accompany plastic deformation, of micronization and
densification of structure, imparting of compressive residual
stress, and the like, are not able to be imparted to the
workpiece.
[0083] However, in a sintered body 1 having a structure in which
the hard particles 10 are bonded together by the binder metal phase
20, for example a WC--Co cemented carbide, although the hardness of
the WC particles configuring the hard particles 10 is a high
hardness of 1780 HV, the hardness of the Co phase configuring the
binder metal phase 20 is about 700 HV, giving a combined overall
hardness of about 1450 HV.
[0084] Thus although the hardness of the ejection particles 30 of
not more than 1000 HV is a hardness lower than the overall hardness
of the sintered body 1 (hardness of the WC--Co based cemented
carbide: 1450 HV) and lower than the hardness of the hard particles
10 (hardness of the WC particles: 1780 HV), the hardness of the
ejection particles 30 is not less than the hardness of the binder
metal phase 20 (hardness of the Co phase: 700 HV).
[0085] Moreover, the average particle diameter of the hard
particles in the sintered body 1 is generally a few .mu.m or so,
and for fine hard particles is from about 0.5 .mu.m to about 0.8
.mu.m, and this is sufficiently smaller than the particle diameter
of the ejection particles 30 at from 100 grit to 800 grit (an
average particle diameter of from 20 .mu.m to 149 .mu.m).
[0086] As a result, when the ejection particles 30 are caused to
impact the surface of the sintered body 1, as illustrated in FIG.
4B, even though no deformation can be achieved of the hard
particles 10 having a higher hardness than the ejection particles
30, the hard particles can be moved by deforming the binder metal
phase 20, and this is thought to deform the surface of the sintered
body 1 so as to enable processing to a slight matt finish.
[0087] Moreover, at the sites impacted by the ejection particles
30, localized heating and cooling instantaneously occurs at the
impact sites due to the heat generated when impact occurs, and this
is thought to result in fine crystallization of the binder metal
phase 20 by the instantaneous heat treatment performed thereby.
[0088] As a result, work hardening by the fine crystallization and
densification is accordingly thought to be induced in the binder
metal phase 20, at least in the vicinity of the surface of the
sintered body 1, with the hardness thereof raised thereby.
Moreover, the binder metal phase 20 is thought to be strengthened
by being imparted with compressive residual stress that suppresses
the generation and growth of cracks.
[0089] Such strengthening of the binder metal phase 20 is not only
obtained in cases in which the ejection particles 30 are caused to
directly impact the surface of the sintered body 1, and is also
obtained in cases in which the ejection particles 30 are caused to
impact a sintered body 1 having a hard coating film (not
illustrated in the drawings) such as a ceramic coating film or the
like coated on a surface thereof, by impacting from above the hard
coating film. The cohesion strength of the hard coating film is
improved thereby, enabling detachment etc. thereof to be made less
liable to occur.
[0090] It is thought that as a result, by suppressing breaks
(breaks in the binder metal phase 20) at the grain boundaries of
the hard particles 10, brittle fracture is less liable to occur
even when external force and strain is imparted to the sintered
body 1, and the toughness of the sintered body 1 can accordingly be
increased.
EXAMPLES
[0091] Next explanation follows regarding results of durability
tests on sintered bodies subjected to strengthening of the binder
metal phase with the method of the present invention.
Test Example 1: Cold Forging Punch (Carbide)
(1) Test Method
[0092] Ejection particles were ejected under the conditions listed
in Table 1 below against a cold forging punch (diameter 20 mm,
length 150 mm) made from a WC--Co cemented carbide (1450 HV).
[0093] The hardness of the Co phase that is the binder metal phase
is approximately 700 HV.
TABLE-US-00001 TABLE 1 Comparative Comparative Treatment Conditions
Example 1 Example 1 Example 2 Blasting Device Gravity Type Gravity
Type Gravity Type Ejection Material HSS (SKII) Glass FeCrB
particles Hardness Approximately 534 HV Approximately 1000 HV 1200
HV Average particle Approximately Approximately Approximately
diameter 40 .mu.m 40 .mu.m 40 .mu.m Shape Substantially
Substantially Substantially spherical shaped spherical shaped
spherical shaped Ejection Pressure 0.6 MPa 0.6 MPa 0.6 MPa
conditions Nozzle 9 mm diameter - 9 mm diameter - 9 mm diameter -
diameter long long long Ejection 100 mm to 100 mm to 100 mm to
distance 150 mm 150 mm 150 mm Ejection Approximately Approximately
Approximately duration 30 seconds 30 seconds 30 seconds
[0094] The state of the surface of cold forging punches was
observed with the naked eye after ejection of the ejection
particles and on an un-processed cold forging punch. Each of the
cold forging punches of Example 1 and Comparative Examples 1 and 2
was employed to perform repeated cold forging (punching 20 mm
diameter holes), and the number of cycles (shot number) at the time
when chipping (nicking) occurred in the respective cold forging
punch was employed to evaluate the lifespan of the cold forging
punch.
(2) Test Results
[0095] The test results of Test Example 1 are illustrated in Table
2 below.
TABLE-US-00002 TABLE 2 Comparative Comparative Example 1 Example 1
Example 2 Unprocessed (HSS) (Glass) (FeCrB) Surface Smooth Slight
matt Smooth Matt state finish (no change) finish No. of punches
30,000 90,000 30,000 20,000 (lifespan) (no change)
(3) Interpretation
[0096] The above results enabled confirmation that in Example 1,
employing ejection particles of 1000 HV which is a higher hardness
than the hardness of the Co phase (approximately 700 HV),
deformation was induced of the surface of the treatment subject to
give a slight matt finish, and a lifespan of three times the
untreated case was achieved.
[0097] However, in the Comparative Example 1 employing ejection
particles of 534 HV which is a lower hardness than the hardness of
the Co phase (approximately 700 HV), the surface state of the
treatment subject was not changed and remained smooth, and there
was also hardly any change in the lifespan compared to the
untreated case.
[0098] Furthermore, in the Comparative Example 2 employing ejection
particles of 1200 HV i.e. higher hardness than the hardness of the
Co phase (approximately 700 HV) and also a higher hardness than the
ejection particles of Example 1, although plastic deformation was
induced in the surface of the treatment subject and a matt finish
could be achieved, the lifespan actually reduced relative to the
untreated case.
[0099] The ejection particles made from HSS employed in Example 1
had a hardness of approximately 1000 HV and a lower hardness than
the hardness of the cemented carbide (1450 HV) of the material
configuring the cold forging punch serving as the treatment
subject. Thus for the case of an ordinary workpiece as the
treatment subject, deformation occurring at the time of impact of
the ejection particles would occur at the ejection particle side
having lower hardness, and as a result hardly any plastic
deformation would be induced on the treatment subject side (see
FIG. 4A). The advantageous effects of micronization and
densification of the surface structure of the workpiece, imparting
of compressive residual stress, and the like would accordingly not
be obtained.
[0100] However, the sintered body 1 serving as the treatment
subject in the present invention, as illustrated in FIG. 3, has a
structure in which the WC particles 10 of high hardness, i.e. 1780
HV, are bonded together with the Co phase 20 having a lower
hardness of approximately 700 HV. This means that even when
ejection particles having a lower hardness than the overall
hardness (1450 HV) of the sintered body (carbide tool) are employed
as the ejection particles 30, due to employing ejection particles
of the hardness of the Co phase 20 (approximately 700 HV) or
greater, as explained with reference to FIG. 4B, although the
impact of the ejection particles 30 is not able to deform the WC
particles 10, the Co phase 20 bonding the WC particles 10 together
is deformed, moving the WC particles 10. This enables the surface
of the sintered body 1 to be deformed, and the Co phase 20 to be
strengthened by forming fine crystals and imparting compressive
residual stress accompanying such deformation. This is thought to
be the reason improvements can be achieved in making brittle
fracture, such as chipping and the like, less liable to occur, and
in imparting excellent toughness characteristics.
[0101] However, in the Comparative Example 1 employing the ejection
particles 30 of lower hardness than the Co phase, plastic
deformation of the WC particles is obviously not achieved, and
plastic deformation of the Co phase is also not achievable. This is
thought to be why, as a result, no change was obtained in both
appearance and lifespan compared to the untreated case.
[0102] Furthermore, in Comparative Example 2 employing the ejection
particles having a hardness of 1200 HV i.e. a lower hardness than
the sintered body 1 but a higher hardness than the Co phase,
plastic deformation can be induced in the Co phase. This could be
confirmed in the test results illustrated in Table 2 by a change of
the surface of the sintered body to a matt finish.
[0103] However, in the sintered body 1 treated under the conditions
of Comparative Example 2, a reduction in the lifespan was confirmed
relative to the untreated case, and brittle fracture, such as
chipping, was confirmed to actually be more liable to occur.
[0104] This confirmed that ejection particles having a hardness of
not less than the hardness of the binder metal phase (Co phase)
need to be employed as the ejection particles in order to increase
the toughness of the sintered body (cemented carbide), and that
ejection particles having a lower hardness than 1200 HV, and more
specifically preferably employed ejection particles have a hardness
of not more than 1000 HV such as those confirmed to strengthen the
Co phase in Example 1.
Test Example 2: Header Processing Die (Carbide)
[0105] Ejection particles were ejected under the conditions listed
in Table 3 below against a header processing die (outer diameter 50
mm, inner diameter 15 mm, height 30 mm) made from a WC--Co cemented
carbide (1150 HV).
[0106] Note that the hardness of the Co phase that is the binder
metal phase is approximately 700 HV.
TABLE-US-00003 TABLE 3 Treatment Conditions Example 2 Blasting
Device Gravity Type Ejection Material HSS (SKII) particles Hardness
Approximately 1000 HV Average particle Approximately diameter 40
.mu.m Shape Substantially spherical shaped Ejection Pressure 0.5
MPa conditions Nozzle diameter 9 mm diameter - long Ejection
distance 100 mm to 150 mm Ejection duration Approximately 40
seconds
[0107] The state of the surface of the header processing die was
observed with the naked eye after ejection of the ejection
particles 30. An un-processed header processing die, and the header
processing die treated under the above conditions (Example 2), were
each employed to perform repeated header processing (cold heading)
of SCM435, and the number of cycles (shot number) at the time when
damage occurred on the inner peripheral face of the die was
employed to evaluate the lifespan of the respective header
processing die.
(2) Test Results
[0108] The test results of Test Example 2 are illustrated in Table
4 below.
TABLE-US-00004 TABLE 4 Unprocessed Example 2 Surface state Smooth
Slight matt finish No. of cycles 300,000 900,000 (lifespan)
(3) Interpretation
[0109] The above results enabled confirmation that in Example 2
employing ejection particles having a hardness of 1000 HV, which is
a higher hardness than the hardness of the Co phase (approximately
700 HV), plastic deformation was induced of the surface of the
treatment subject to give a slight matt finish. The lifespan was
also able to be extended to three times that of the untreated case.
Employing the ejection particles within the hardness range
stipulated by the present invention was confirmed to be effective
in increasing the toughness of the sintered body.
Test Example 3: Drill (Carbide)
(1) Test Method
[0110] Ejection particles were ejected under the conditions listed
in Table 5 below against a drill (5 mm diameter) made from a
WC--TiC--TaC--Co cemented carbide (91.5HRA (1600 HV)).
[0111] Note that the hardness of the Co phase that is the binder
metal phase is approximately 700 HV.
TABLE-US-00005 TABLE 5 Comparative Treatment Conditions Example 3
Example 3 Blasting Device Fine powder Fine powder suction type
suction type Ejection particles Material Alumina-silica
Zirconia-Silica Hardness 792 HV Approximately (Approximately 1000
HV 800 HV) Average particle Approximately <50 .mu.m diameter 38
.mu.m Shape Substantially Substantially spherical shaped spherical
shaped Ejection Pressure 0.4 MPa 0.6 MPa conditions Nozzle 7 mm
diameter - 7 mm diameter - diameter long long Ejection 100 mm to
100 mm to distance 150 mm 150 mm Ejection Approximately
Approximately duration 20 seconds 20 seconds
[0112] Holes were bored in ductile cast iron (FCD400) using the
drills that had been subjected to ejection of the ejection
particles.
(2) Test Results
[0113] In an untreated drill, regrinding of the cutting-edges was
needed due to chipping when 500 holes had been bored, however the
drill treated according to the method of the present invention was
able to bore up to 1300 holes without performing regrinding,
enabling the lifespan of the drill to be greatly extended.
[0114] Moreover, holes formed using the drill of Example 3 were
confirmed to have improved smoothness of inner peripheral faces
compared to cases in which the untreated drill was employed.
[0115] Moreover, in the example in which ejection particles were
ejected under the processing conditions of Comparative Example 3,
the lifespan of the drill was shortened by the occurrence of
chipping compared to an untreated drill.
[0116] The above results are thought to arise because, in cases
employing ejection particles made from a ceramic of lower toughness
than ejection particles made of metal, considerable damage is
imparted to the surface of the treatment subject compared to cases
employing ejection particles made from metal.
[0117] These results are thought to show that even in cases
employing the same ejection particles of 1000 HV, different results
are obtained for the same treatment subject in cases (Examples 1,
2) employing ejection particles made from metal (high-speed steel),
to cases (Comparative Example 3) employing the ejection particles
are made from ceramic (zirconia-silica).
[0118] Thus in cases employing ejection particles made from a
ceramic, preferably employed ejection particles have a hardness of
not more than 792 HV (approximately 800 HV) such as those for which
the advantageous effect of strengthening the binder metal phase (Co
phase) is confirmed in the Example.
Test Example 4: Cylinder Inner Diameter Turning Insert (Cermet)
(1) Test Method
[0119] Ejection particles were ejected under the conditions listed
in Table 6 below against a diamond shaped insert made from a
TiCN--NbC--Ni cermet (93HRA (1900 HV)) for turning the inner
diameter of a cylinder made from SUS304.
[0120] Note that the hardness of the Ni phase that is the binder
metal phase is approximately 500 HV.
TABLE-US-00006 TABLE 6 Treatment Conditions Example 4 Blasting
Device Fine powder suction type Ejection Material Glass particles
Hardness 565 HV Average particle Approximately diameter 38 .mu.m
Shape Substantially spherical shaped Ejection Pressure 0.4 MPa
conditions Nozzle diameter 7 mm diameter - long Ejection distance
100 mm Ejection duration Approximately 1 second on each
cutting-edge (each corner of diamond shaped insert)
[0121] The state of the surface of the insert was observed with the
naked eye after ejection of the ejection particles under the
conditions of Example 4. An un-processed insert and the insert of
Example 4 were each employed to turn the inner diameter of
cylinders made from SUS304.
(2) Test Results
[0122] The surface of the cutting-edge portions of the untreated
insert was smooth, and the cutting-edges of the insert after
treatment under the treatment conditions of Example 4 was a slight
matt finish. This confirmed that ejection of the ejection particles
enables plastic deformation to be induced in the cutting-edge
surfaces of the insert.
[0123] Moreover, although a lifespan of 1000 cycles of cylinder
processing was achieved with the untreated insert, 3000 cylinders
could be processed with the insert whose Ni phase had been
strengthened by the treatment conditions of Example 4, greatly
increasing the lifespan by a multiple of three.
[0124] Moreover, the finish on the inner diameter finished surface
was better on cylinders machined using the insert of Example 4 than
on cylinders machined using the untreated insert.
[0125] For the WC--Co cemented carbide illustrated in Table 1, when
glass beads of 565 HV were employed as the ejection particles in
Comparative Example 1, the binder metal phase (Co phase) was not
able to be strengthened due to the hardness of the binder metal
phase (Co phase) being 700 HV. However, in the Example 4 in which
the treatment subject was the TiCN--NbC--Ni cermet having a binder
metal phase (Ni phase) of approximately 500 HV, a greatly increased
lifespan was obtained by employing such glass beads of 565 HV as
the ejection particles. The present test results have been able to
confirm that the lower limit to a hardness of the ejection
particles capable of strengthening the binder metal phase is
decided in relation to the hardness of the binder metal phase.
Test Example 5: TiC Coated Cutting Insert (Carbide)
(1) Test Method
[0126] Ejection particles were ejected under the conditions listed
in Table 7 below against a diamond shaped cutting insert made from
a WC--TiC--TaC--Co cemented carbide (91.5HRA (1600 HV)) that had
been coated with a TiC film at a film thickness of approximately 3
.mu.m using a CVD method.
[0127] Note that the hardness of the Co phase that is the binder
metal phase is approximately 700 HV.
TABLE-US-00007 TABLE 7 Treatment Conditions Example 5 Blasting
Device Fine powder suction type Ejection Material Alumina-silica
particles Hardness 792 HV (Approximately 800 HV) Average particle
Approximately diameter 38 .mu.m Shape Substantially spherical
shaped Ejection Pressure 0.4 MPa conditions Nozzle diameter 7 mm
diameter - long Ejection distance 100 mm Ejection duration
Approximately 1 second on each cutting-edge (each corner of diamond
shaped insert)
[0128] Compressive residual stress values were measured in the
vicinity of the surface of an untreated insert and an insert on to
which ejection particles had been ejected under the conditions of
Example 5. Each of the insert was also employed to machine a shaft
made from SCM440.
(2) Test Results
[0129] The results of the above tests are illustrated in Table
8.
TABLE-US-00008 TABLE 8 Example 5 Untreated Residual stress at 5
.mu.m from -1050 MPa +130 MPa base material surface Number of
shafts machined 120 shafts 60 shafts (lifespan)
(3) Interpretation
[0130] With the untreated insert, the TiC coating detached when 60
shafts had been machined, and a replacement was needed due to
chipping occurring in the base material made from cemented carbide.
However, with the insert treated as Example 5, detachment of the
TiC film was prevented, enabling 120 shafts to be machined and
greatly increasing the lifespan.
[0131] Such an increase in the cohesion strength of the TiC film is
thought to be obtained by the increased toughness of the cemented
carbide serving as the base material.
[0132] Moreover, in the results of measurements of compressive
residual stress values for the residual stress at a position 5
.mu.m from the base material surface, although a tensile stress
(+130 MPa) remained in the untreated case, which is thought to
arise from heating when forming the TiC film using CVD, this
changed to a compressive stress (-1050 MPa) when the treatment of
Example 5 had been performed thereon.
[0133] These results have confirmed that employing the method of
the present invention enables the mechanical characteristics of the
sintered body base material in a layer below the hard coating film
to be changed without causing the hard coating film etc. to detach,
even in cases in which a sintered body coated with a hard coating
film such as TiC is the treatment subject.
[0134] Note that in Example 5, even with the TiC coating film
formed to a film thickness of 3 .mu.m, compressive residual stress
was confirmed to be imparted to at least a depth of 5 .mu.m in the
base material below (a total depth of 8 .mu.m when the 3 .mu.m
thickness of the hard coating film is included).
[0135] Thus the logical inference therefrom is that if the hard
coating film formed on the surface had a film thickness of up to
about 5 .mu.m, then compressive residual stress can be imparted at
least to a depth of about 3 .mu.m from the base material surface (a
total depth of 8 .mu.m when the 5 .mu.m thickness of the hard
coating film is included), and the binder metal phase in the
vicinity of the surface of the sintered body can be
strengthened.
Test Example 6: Cutting Insert (cBN)
(1) Test Method
[0136] Ejection particles were ejected under the conditions listed
in Table 9 below against a diamond shaped cutting insert made from
cBN (4700 HV) configured from cubic crystals of boron nitride
sintered together with a Co binder.
[0137] Note that in the cBN that has been sintered under ultrahigh
pressure, the hardness of the Co phase binder is higher than in a
carbide tool, and the hardness of the Co phase in the cBN of the
present Test Example is approximately 800 HV.
TABLE-US-00009 TABLE 9 Treatment Conditions Example 6 Comparative
Example 6 Blasting Device Gravity type Gravity type Ejection
Material HSS(SKH) Alumina-silica particles Hardness Approximately
1000 HV 792 HV Average particle Approximately Approximately
diameter 40 .mu.m 38 .mu.m Shape Substantially Substantially
spherical shaped spherical shaped Ejection Pressure 0.4 MPa 0.4 MPa
conditions Nozzle 9 mm diameter - 9 mm diameter - diameter long
long Ejection 100 mm 100 mm distance Ejection Approximately 1
second Approximately 1 second duration from each of 4 directions
from each of 4 directions at each cutting-edge at each cutting-edge
(each acute angled (each acute angled corner of diamond corner of
diamond shaped insert) shaped insert)
[0138] An untreated insert, and the inserts treated under the
conditions of Example 6 and Comparative Example 6 were each
employed to machine shafts of carburized and quenched steel, and
the differences in lifespan therebetween confirmed.
(2) Test Results
[0139] The results of the above tests were then that whereas an
untreated insert has a lifespan of machining 200 carburized and
quenched shafts, the insert against which ejection particles had
been ejected under the conditions of Example 6 was able to machine
double that amount at 400 carburized and quenched shafts.
[0140] The above results have confirmed that strengthening of the
binder metal phase can be performed not only for a cemented carbide
and cermet, but also for cBN. A logical inference therefrom is that
the method of the present invention applicable to sintered bodies
in general that have a structure in which hard particles are bonded
together by a binder metal phase.
[0141] Note that although strengthening of the Co phase could be
performed by employing ejection particles that were alumina-silica
beads of 792 HV in Example 3, in which a drill made from a cemented
carbide is the treatment subject, an increased lifespan was not
achieved for a sintered body having the same Co binder metal as the
treatment subject in the Comparative Example 6, in which a sintered
body of cBN is the treatment subject, even when ejection particles
of alumina-silica beads at 792 HV were ejected thereon, and
strengthening of the Co phase could not be achieved.
[0142] Such a difference is thought to be due to the cBN being
sintered under ultrahigh pressure as described above, making the
hardness of the Co phase, at about 800 HV, about 100 HV higher than
in a cemented carbide such that sufficient plastic deformation
could not be imparted to the Co phase by alumina-silica beads of
792 HV. This is thought to result in not being able to achieve
strengthening through work hardening from micronization of the
crystal structure and imparting compressive residual stress.
[0143] The present tests have accordingly confirmed that even in
cases in which the metal employed as the material for the binder is
the same, if the hardness of the binder metal phase is different
due to differences in the sintering conditions or the like, then
there is a need to select ejection particles to match the relevant
hardness.
[0144] Thus, the broadest claims that follow are not directed to a
machine that is configured in a specific way. Instead, said
broadest claims are intended to protect the heart or essence of
this breakthrough invention. This invention is clearly new and
useful. Moreover, it was not obvious to those of ordinary skill in
the art at the time it was made, in view of the prior art when
considered as a whole.
[0145] Moreover, in view of the revolutionary nature of this
invention, it is clearly a pioneering invention. As such, the
claims that follow are entitled to very broad interpretation so as
to protect the heart of this invention, as a matter of law.
[0146] It will thus be seen that the objects set forth above, and
those made apparent from the foregoing description, are efficiently
attained and since certain changes may be made in the above
construction without departing from the scope of the invention, it
is intended that all matters contained in the foregoing description
or shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense.
[0147] It is also to be understood that the following claims are
intended to cover all of the generic and specific features of the
invention herein described, and all statements of the scope of the
invention which, as a matter of language, might be said to fall
therebetween.
[0148] Now that the invention has been described;
DESCRIPTION OF REFERENCE NUMERALS
[0149] 1 Sintered body (cemented carbide)
[0150] 10 Hard particles
[0151] 20 Binder metal phase
[0152] 30 Spherical shaped ejection particles
* * * * *