U.S. patent application number 16/309694 was filed with the patent office on 2019-05-16 for method for manufacturing fine free carbon dispersion type cemented carbide, cutting tip with exchangeable cutting edge, machined.
The applicant listed for this patent is UGEL CORPORATION. Invention is credited to Yoshihiko DOI.
Application Number | 20190144973 16/309694 |
Document ID | / |
Family ID | 62491900 |
Filed Date | 2019-05-16 |
![](/patent/app/20190144973/US20190144973A1-20190516-D00001.png)
United States Patent
Application |
20190144973 |
Kind Code |
A1 |
DOI; Yoshihiko |
May 16, 2019 |
METHOD FOR MANUFACTURING FINE FREE CARBON DISPERSION TYPE CEMENTED
CARBIDE, CUTTING TIP WITH EXCHANGEABLE CUTTING EDGE, MACHINED
PRODUCT FORMED FROM ALLOY, AND METHOD FOR MANUFACTURING SAME
Abstract
The present invention relates to a cemented carbide and coated
cemented carbide which contain free carbons, and provides a
cemented carbide which enables to remove or reduce the
disadvantages of the free carbons even if the cemented carbide
contains the free carbons, specifically to decrease in the strength
is reduced by finely dispersing the free carbons even if the
cemented carbide contains the free carbons and to obtain a
beautiful mirror surface on a mirror-finished surface by finely
dispersing free carbons in the cemented carbide. The present
invention is a cemented carbide composed of tungsten carbide (WC)
and cobalt (Co), which contains carbon in such an amount range that
no solid carbon is contained in a liquid phase while the liquid
phase is present at a high temperature, characterized in that the
maximum diameter of the pores resulting from the free carbons is 20
.mu.m or smaller.
Inventors: |
DOI; Yoshihiko; (Osaka-shi,
Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UGEL CORPORATION |
Osaka-shi, Osaka |
|
JP |
|
|
Family ID: |
62491900 |
Appl. No.: |
16/309694 |
Filed: |
December 7, 2017 |
PCT Filed: |
December 7, 2017 |
PCT NO: |
PCT/JP2017/044080 |
371 Date: |
December 13, 2018 |
Current U.S.
Class: |
428/546 |
Current CPC
Class: |
B22F 1/0007 20130101;
C22C 1/051 20130101; C22C 1/05 20130101; B22F 3/1035 20130101; B22F
2998/10 20130101; C22C 29/04 20130101; C22C 29/08 20130101; B22F
2998/10 20130101; C22C 29/08 20130101; B22F 1/007 20130101; B22F
3/02 20130101; B22F 3/1035 20130101 |
International
Class: |
C22C 1/05 20060101
C22C001/05; C22C 29/08 20060101 C22C029/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 9, 2016 |
JP |
2016-239026 |
Aug 9, 2017 |
JP |
2017-153862 |
Claims
1-7. (canceled)
8. A method for manufacturing a cemented carbide composed of
tungsten carbide (WC) and cobalt (Co), wherein: the cemented
carbide contains 0.02 mass % or more to 0.15 mass % or less of free
carbons; free carbons are finely dispersed in the cemented carbide;
shrinkage during sintering occurs evenly; the cemented carbide in
which a maximum diameter of pores resulting from the free carbons
is 20 .mu.m or smaller is defined as Cemented carbide A; the
cemented carbide in which a maximum diameter of pores resulting
from the free carbons is 15 .mu.m or smaller is defined as Cemented
carbide B; the cemented carbide in which a maximum diameter of
pores resulting from the free carbons is 10 .mu.m or smaller is
defined as Cemented carbide C; the Cemented carbide A, B or C to
which chromium carbide or chromium nitride is added in an amount of
2 to 18 mass % based on cobalt (Co) content is defined as Cemented
carbide D; the Cemented carbide A, B, C or D in which a part of
tungsten carbide (WC) is replaced by any one or combinations of: a
carbide, a nitride or a carbonitride of transition metal of groups
4 and 5 in the periodic table; and a double carbide or a double
carbonitride of tungsten (W) with the carbide, the nitride or the
carbonitride of the transition metal is defined as Cemented carbide
E; and the Cemented carbide E in which a .beta.-free layer is
formed on a surface of the cemented carbide and the .beta.-free
layer has a thickness of 1 to 30 .mu.m is defined as Cemented
carbide F, the Cemented carbide A, B, C, D, E or F in which a
lattice constant of an fcc in a binder phase (Co phase) of the
cemented carbide is 3.560 .ANG. or higher is defined as Cemented
carbide G, the method is characterized in that, when manufacturing
any of the Cemented carbides A, B, C, D, E, F and G, after
sintering a mixed powder for producing the cemented carbide at a
sintering temperature not lower than a liquid-phase appearance
temperature, the method comprises: a step of rapidly cooling from
the temperature not lower than the liquid-phase appearance
temperature; or a step of reheating to the temperature not lower
than the liquid-phase appearance temperature and then rapidly
cooling.
9. The method for manufacturing the cemented carbide according to
claim 8, wherein, in the step of rapidly cooling and the step of
reheating and rapidly cooling, a cooling rate from the temperature
not lower than the liquid-phase appearance temperature to
800.degree. C. is set to 30.degree. C./min or higher.
10. A method for manufacturing a coated cemented carbide, wherein
the cemented carbide manufactured by the method for manufacturing
the cemented carbide according to claim 8 is used as a base
material when manufacturing the coated cemented carbide.
11. An edge replacement-type cutting tip formed of a cemented
carbide composed of tungsten carbide (WC) and cobalt (Co), wherein:
the cemented carbide contains 0.02 mass % or more to 0.15 mass % or
less of free carbons; free carbons are finely dispersed in the
cemented carbide; shrinkage during sintering occurs evenly;
dimensional accuracy is improved; the cemented carbide in which a
maximum diameter of pores resulting from the free carbons is 20
.mu.m or smaller is defined as Cemented carbide A; the cemented
carbide in which a maximum diameter of pores resulting from the
free carbons is 15 .mu.m or smaller is defined as Cemented carbide
B; the cemented carbide in which a maximum diameter of pores
resulting from the free carbons is 10 .mu.m or smaller is defined
as Cemented carbide C; the Cemented carbide A, B or C to which
chromium carbide or chromium nitride is added in an amount of 2 to
18 mass % based on cobalt (Co) content is defined as Cemented
carbide D; the Cemented carbide A, B, C or D in which a part of
tungsten carbide (WC) is replaced by any one or combinations of: a
carbide, a nitride or a carbonitride of transition metal of groups
4 and 5 in the periodic table; and a double carbide or a double
carbonitride of tungsten (W) with the carbide, the nitride or the
carbonitride of the transition metal is defined as Cemented carbide
E; the Cemented carbide E in which a .beta.-free layer is formed on
a surface of the cemented carbide, and the .beta.-free layer has a
thickness of 1 to 30 .mu.m is defined as Cemented carbide F; and
the Cemented carbide A, B, C, D, E or F in which a lattice constant
of an fcc in a binder phase (Co phase) of the cemented carbide is
3.560 .ANG. or higher is defined as Cemented carbide G, the edge
replacement-type cutting tip is characterized in that the edge
replacement-type cutting tip is formed of any of the Cemented
carbides A, B, C, D, E, F and G, or any of coated cemented carbides
using the Cemented carbide A, B, C, D, E, F or G as a base
material.
12. A cemented carbide machined product such as tools, molds and
parts formed of a cemented carbide composed of tungsten carbide
(WC) and cobalt (Co), wherein: the cemented carbide contains 0.02
mass % or more to 0.15 mass % or less of free carbons; free carbons
are finely dispersed in the cemented carbide; shrinkage during
sintering occurs evenly; dimensional accuracy and/or machinability
is improved; the cemented carbide in which a maximum diameter of
pores resulting from the free carbons is 20 .mu.m or smaller is
defined as Cemented carbide A; the cemented carbide in which a
maximum diameter of pores resulting from the free carbons is 15
.mu.m or smaller is defined as Cemented carbide B; the cemented
carbide in which a maximum diameter of pores resulting from the
free carbons is 10 .mu.m or smaller is defined as Cemented carbide
C; the Cemented carbide A, B or C to which chromium carbide or
chromium nitride is added in an amount of 2 to 18 mass % based on
cobalt (Co) content is defined as Cemented carbide D; the Cemented
carbide A, B, C or D in which a part of tungsten carbide (WC) is
replaced by any one or combinations of: a carbide, a nitride or a
carbonitride of transition metal of groups 4 and 5 in the periodic
table; and a double carbide or a double carbonitride of tungsten
(W) with the carbide, the nitride or the carbonitride of the
transition metal is defined as Cemented carbide E; the Cemented
carbide E in which a .beta.-free layer is formed on a surface of
the cemented carbide, and the .beta.-free layer has a thickness of
1 to 30 .mu.m is defined as Cemented carbide F; and the Cemented
carbide A, B, C, D, E or F in which a lattice constant of an fcc in
a binder phase (Co phase) of the cemented carbide is 3.560 .ANG. or
higher is defined as Cemented carbide G, the cemented carbide
machined product is characterized in that any of the Cemented
carbides A, B, C, D, E, F and G is machined by one or combinations
of following machining methods: an electric discharging,
grinding/polishing or cutting.
Description
TECHNICAL FIELD
[0001] The present invention relates to a fine free carbon
dispersion-type cemented carbide, a coated cemented carbide,
machined products made thereof, and a manufacturing method
thereof.
[0002] Specifically, the present invention relates to: (1) a method
for manufacturing a cemented carbide containing free carbons in
which the free carbons are finely dispersed to minimize decrease in
the strength and on which mirror finish can be made; (2) an aspect
that an .eta. phase caused at a boundary between a coat and a base
material can be reduced in a CVD-coated cemented carbide, (3) an
aspect that a high-accuracy cemented carbide sintered compact can
be prepared by dispersing fine free carbons, and a high-accuracy
edge replacement-type cutting tip using the cemented carbide or the
coated cemented carbide can be prepared by using this technology,
(4) an aspect that a machined product of the cemented carbide is
machined after sintering by one or combinations of following
machining methods: an electric discharging, grinding/polishing or
cutting, and a machined product of the cemented carbide can be
prepared at low machining cost by using this cemented carbide, and
the like.
[0003] It should be noted that "free carbon" may be referred to as
"free graphites" or "uncombined carbons."
BACKGROUND ART
[0004] Conventionally, cemented carbides obtained by mixing a
tungsten carbide (WC) particle and cobalt (Co) as a binder metal at
an appropriate ratio and sintering them have been known. Depending
on the application, there have been many cemented carbides in which
a part of WC is replaced by a carbide such as TiC and TaC, a
nitride, a carbide or carbonitride composite thereof. Since the
cemented carbide has a high hardness, a high strength and the like,
it is used as a cutting tool, a mold and the like in many
fields.
[0005] The cemented carbide is manufactured by a powder metallurgy
method using a powder as a raw material. Thus, there is a risk that
pores remain in the cemented carbide after sintering, and it is
always required to decrease sizes and numbers of the pores. This is
because the pore decreases the strength, the hardness and the like,
and the performance as the cemented carbide is deteriorated.
[0006] The pore refers to a fine hole or void appearing inside the
cemented carbide structure, which is one of material defects also
called "pore". The state of the pore is defined as "porosity" in
the Standard CIS006C-2007 "Classification Standard for Porosity of
Cemented Carbide" of Japan Cemented Carbide Tool Manufacturer's
Association (this standard conforms to the international standard
ISO 4505-1978 (Hardmetals-Metallographic determination of porosity
and uncombined carbon)). In this standard, the types of pores are
classified into three types, type A, type B and type C, and divided
into 4 levels (grade) depending on the size and the number of the
pore, and the reference degrees of the pores are shown in 100 to
200-power photomicrographs.
[0007] According to CIS006C, the size of the A-type pore is defined
to be 10 .mu.m or smaller. The A-type pore is considered to result
from trace amounts of gas and impurity (Non-Patent Document 4, p.
176).
[0008] The size of the B-type pore is defined to be 10 to 25 .mu.m.
The B-type pore is considered to result from impurities somewhat
larger than the A-type pore, such as a Co powder and an
unpulverized lubricant (Non-Patent Document 4, p. 176).
[0009] The C-type pore is considered to result from free carbons,
and its size is normally defined to be 25 .mu.m or larger
(Non-Patent Document 4, p. 176). The C-type pore is not a pore in
actual fact and contains free carbons therein. However, it is
classified as a kind of pores due to its appearance like a
pore.
[0010] One of the most important matters for quality control of the
cemented carbide is proper control/management of the carbon content
in the alloy. If the carbon content is large, free carbons remain
in the alloy, pores are generated, resulting in decreased
strength.
[0011] When the pore of the free carbon is observed with a
100-power microscope, punctiform small pores aggregate in a
dendritic shape to form one pore. FIG. 1. 71 on p. 66 in Non-Patent
Document 1 shows a photograph of a pore observed at magnification
as high as 500, and its dendritic shape can be better
understood.
[0012] The pore resulting from the free carbon is specified to be
type C in Appendix 4 of the CIS standard 006C. Also in C-type 002
to be applied to the pore which is the smallest in the four stages,
the size of the pore is at most about 70 .mu.m. Such a large pore
causes not only a decreased strength but also a defected mirror
surface for the application of using a mirror surface. For this
reason, disposal losses and reconditioning charges of defective
products are caused, or a delivery date is delayed.
[0013] Even if pores of the free carbons are generated, the
strength and hardness are not decreased as long as the sizes can be
decreased, and the quality of the mirror surface is also improved,
and thus such losses can be avoided.
[0014] The inventor of the present application has extensively
studied a cemented carbide in which a maximum diameter of free
carbon pores is 20 .mu.m or smaller, which has not been achieved so
far, and a method for manufacturing the cemented carbide, and this
study has achieved the present invention.
[0015] Additionally, in the cemented carbide coated by a CVD
method, an abnormal phase called an .eta. phase (decarburized
phase) is generated at the boundary between the coat and the
cemented carbide, which causes decrease in the strength of the
coated cemented carbide (Non-Patent Document 3). The problem of the
.eta. phase at the boundary between the coat and the base material
has been reduced due to the progressively improved technology in
recent years, but basically the cemented carbide is produced
constantly in a state including the risk of generating the .eta.
phase to a greater or lesser extent.
[0016] Thus, there is always a potential demand to suppress the
generation of the phase. Although the cemented carbide has been
processed into tools and parts for many applications such as
cutting and wear resistance, the cemented carbide is difficult to
process due to high hardness, and electric discharging methods and
grinding/polishing methods using diamond grindstones are mainly
utilized. However, all methods are high-cost machining methods and
have a great problem of reduction in machining cost. For this
purpose, it is important to reduce stock allowances by improving
the dimensional accuracy of the cemented carbide sintered
compact.
[0017] Recently, cutting of the cemented carbide has become
possible with advance of diamond tools and diamond-coated tools in
the field of cutting tools. With regard to wear-resistant tools
such as a mold, technologies for streamlining the machining by
cutting the cemented carbide have been actively developed for the
purpose of reducing the machining cost and shortening the delivery
time. Consequently, a cemented carbide with good cutting
machinability has been increasingly required.
[0018] In addition, the edge replacement-type cutting tip which is
the main application of the cemented carbide has good cutting
performance, and simultaneously a tip which can be used while
maintaining the sintered skin with a high dimensional accuracy has
been required. Since the dimensional accuracy of the edge
replacement-type cutting tip directly affects a dimensional
accuracy of a product machined by the cutting tip, the grades of
the edge replacement-type tips are defined in JIS and ISO, so that
a user can easily select a tip. Naturally, the higher the
dimensional accuracy is, the more expensive the tip is. A
high-accuracy edge replacement-type tip is made by high-accuracy
grinding. On the other hand, a non-ground (inexpensive type not
ground or partially ground) edge replacement-type tip is also
strongly required, and has also been increasingly used, resulting
in development race for improving the dimensional accuracy of the
non ground edge replacement-type tip. The present invention meets
these demands.
[0019] Cemented carbides containing free carbons can be exemplified
by Patent Documents 4, 5, 6, and 7.
[0020] Patent Document 4 relates to a cemented carbide containing a
large amount of carbon and having solid carbons in a liquid phase
state, and the solid carbon content corresponds to a range of 0.15
to 0.17% or more in terms of free carbons. On the other hand, the
present invention relates to a cemented carbide having no solid
carbon in a liquid phase state, i.e. having a lesser amount of free
carbons (see FIG. 1).
[0021] In addition, claim 1 in Patent Document 4 describes that the
free carbon content is 1.1 to 8% per a cross-sectional area. On the
other hand, in the present invention, the free carbon content is
0.15% or less by weight. Since the free carbon has a specific
gravity lower than that of the cemented carbide mainly comprising
WC/Co, the free carbon content is about 0.6% by volume, and the
present invention relates to a range out of the range in Patent
Document 4.
[0022] Patent Document 5 is characterized in that the cemented
carbide has a double structure and there is difference in the free
carbon content between the inside and the outer periphery, but is
not intended to decrease the size of the free carbon.
[0023] Patent Document 6 relates to a special cemented carbide
regarding a discharge electrode with a minute diameter for which
the application is limited. Both the material evaluation method and
the performance evaluation method for the cemented carbide are
limited methods unique to this application.
[0024] In Patent Document 7, a cemented carbide has a double
structure to form a layer containing free carbons on the outside in
order to improve the quality of the CVD-coated cemented carbide,
but the size of the free carbon is not controlled.
PRIOR ART DOCUMENTS
Patent Documents
[0025] Patent Document 1: Japanese Patent No. 5826138 [0026] Patent
Document 2: Japanese Patent No. 4673189 [0027] Patent Document 3:
Japanese Patent Application Laid-Open No. 2009-035802 [0028] Patent
Document 4: Japanese Patent Application Laid-Open No. 2005-271093
[0029] Patent Document 5: Japanese Patent No. 5978671 [0030] Patent
Document 6: Japanese Patent No. 4535493 [0031] Patent Document 7:
Japanese Patent Publication No. 62-023041
Non-Patent Documents
[0031] [0032] Non-Patent Document 1: Hisashi Suzuki, "Cemented
Carbide and Sintered Hard Material" (1986), Maruzen Publishing Co.,
Ltd. [0033] Non-Patent Document 2: Standard of Japan Cemented
Carbide Association "Porosity Classification Standard for Cemented
Carbide CIS060C-2007" (2007), Japan Cemented Carbide Association
[0034] Non-Patent Document 3: Hayashi, Suzuki and Doi, "Influence
of Carbon Content in Base Material on Transverse Rupture Strength
of WC-Co Carbide Coated with Titanium Carbide by CVD Method" in
"Powder and Powder Metallurgy", 31 (1984) 136 [0035] Non-Patent
Document 4: Gopal S. Upadhyaya, "Cemented Tungsten carbides"
(1998), Royes Publications. [0036] Non-Patent Document 5: Suzuki
and Hayashi, "Decrease in Strength of Coated WC-Co Cemented Carbide
by Chemical Vapor Deposition" in "Powder and Powder Metallurgy", 28
(1981) 257
SUMMARY OF INVENTION
Problem to be Solved
[0037] The problems to be solved by the present invention can be
roughly classified into two categories. One problem is to improve a
yield. That is, the problem is to prepare a cemented carbide in
which the strength is not decreased even when it contains
finely-dispersed free carbons.
[0038] The other one is to provide a high-performance product in
applications taking advantages of the free carbon-containing
carbide. That is, as described below, the problem is to provide a
high-accuracy and high-performance edge replacement-type tip by
preparing a cemented carbide sintered compact with high dimensional
accuracy, and to provide a machined product of the cemented carbide
which can be efficiently machined with a low machining cost.
[0039] Specific examples will be explained below in accordance with
the objects and problems of the present invention.
[0040] The first object of the present invention is to reduce the
free carbon pore. This can improve the decreased yield and delivery
delay.
[0041] In the production process of the cemented carbide, there are
problems, e.g. when the cemented carbide contains free carbons
after sintering due to inappropriate adjustment of carbon, the
strength decreases (Non-Patent Document 1, p. 95, FIG. 1. 115), and
pores resulting from free carbons are observed on the
mirror-finished surface, and thus a beautiful mirror surface cannot
be obtained.
[0042] The degree of generation of the free carbons in the cemented
carbide is graded in accordance with reference photographs of
Appendix 4 in the Standard CIS006C-2007 "Classification Standard
for Porosity of Cemented Carbide" of Japan Cemented Carbide Tool
Manufacturer's Association (Non-Patent Document 2), including
grades C02 to C08 depending on the degree. When free carbons are
generated in a generally produced cemented carbide, the state is as
shown in Appendix 4, and the grade ranges from C02 that the free
carbons (pores) are smallest in number and size to C08 that the
free carbons (pores) are largest in number and size. Judging from
the sizes of the free carbons from the photographs in Appendix 4,
the maximum diameter of the pores resulting from the free carbons
of C02 is about 70 .mu.m. In C06, the maximum diameter is 100 .mu.m
or larger. As shown in the photograph of the free carbons in
Appendix 4, the free carbon pore is shaped in such a manner that
several small dots aggregate in a dendritic form to form one pore.
The size of this aggregate was measured as the size of the
pore.
[0043] Such free carbons serve as starting points of destruction
and decrease the strength. Also, when the surface is
mirror-finished, free carbons are observed as a kind of pore, which
inhibit the beautiful mirror surface. From the above reasons, a
cemented carbide containing free carbons is generally regarded as a
product failing the test from the viewpoint of quality problems,
and requires restoration and re-fabrication, resulting in decreased
yield and delivery delay.
[0044] Thus, in the present invention, by finely dispersing the
free carbons in the cemented carbide, the maximum diameter of the
pores in the cemented carbide is 20 .mu.m or smaller, preferably 15
.mu.m or smaller, more preferably 10 .mu.m or smaller to suppress
the decrease in strength, and a cemented carbide and a
manufacturing method thereof capable of obtaining a beautiful
mirror surface also on a mirror-finished surface are provided, and
thereby the decreased yield and the delivery delay can be
improved.
[0045] The second object of the present invention is to provide a
base material for a more stable CVD-coated cemented carbide.
[0046] Although coated cemented carbides prepared by the CVD method
are widely used today, TiC, TiCN and TiN are generally used for the
coat to be brought into contact with the cemented carbide. These Ti
compounds tend to absorb carbons in the cemented carbide and
produce an .eta. phase as a decarburized phase at the boundary
between the coat and the cemented carbide. The .eta. phase reduces
the strength of the coated cemented carbide (Non-Patent Document 5
and Patent Document 7). However, it is known that the free
carbon-containing cemented carbide has excess carbons, and thus
generation of the .eta. phase can be suppressed (Non-Patent
Document 3).
[0047] Consequently, in the present invention, the cemented carbide
in which free carbons are contained and furthermore the strength is
not decreased is provided as a base material for a CVD-coated
cemented carbide, so that a coated cemented carbide with reduced
.eta. phase generation can be provided.
[0048] The third object of the present invention is to provide a
free carbon fine dispersion-type cemented carbide and coated
cemented carbide with further improved performance in practical
use.
[0049] In the presence of free carbons, a lattice constant of the
fcc in the binder phase (Co phase) is constantly about 3.550 .ANG.
(Non-patent Document 1, p. 99 and FIG. 1.115 on the same page). It
is expected that the heat resistance is improved and thus the
cutting performance is improved by increasing an amount of tungsten
(W) in a solid solution state contained in Co to increase the
lattice constant. However, there has been no report that the
lattice constant can be increased in the presence of free
carbons.
[0050] In the present invention, a cemented carbide having a
lattice constant of 3.560 .ANG. or higher could be prepared by
rapidly cooling the cemented carbide in a liquid phase state to
800.degree. C. The cutting performance was equal to or superior to
that of the cemented carbide without free carbons. The cutting
performance was improved also in the coated cemented carbide using
this cemented carbide as a base material.
[0051] A cemented carbide having dispersed free carbons described
below can also improve the dimensional accuracy. The present
invention can also provide an edge replacement-type cutting tip
with good cutting performance and high dimensional accuracy.
[0052] The fourth object of the present invention is to provide an
edge replacement-type cutting tip with high dimensional
accuracy.
[0053] The cemented carbide is prepared by pressing a mixed powder
and sintering the pressed body, but when it changes from the
pressed body to a sintered compact, it shrinks by about 50% in
volume (about 20% in size). A pressed body is prepared with
estimating a shrinkage ratio to produce a sintered compact having a
desired size. When a plurality of pressed bodies have the same
weight and volume, the volumes of individual sintered compacts can
be the same, but their sizes vary. This is because, even if the
volumes of the sintered compacts are the same, they do not shrink
in similar shape, and the shrunk bodies have distortion and
dimensional unevenness. In addition, even if a plurality of the
same sintered compacts are prepared, there are differences among
the individuals.
[0054] One of the major reasons of distortion is a slight
unevenness of the carbon content in the sintered compact. This
unevenness of the carbon content is caused due to various factors
e.g. absorption of moisture from the surface of the pressed body,
influence of the atmosphere in the sintering furnace, or the like.
The melting point on the low carbon content side is 1357.degree.
C., and the melting point on the high carbon content side (side
having free carbons) is 1298.degree. C., and when increasing the
temperature for sintering, the high carbon content side with the
low melting point starts to shrink earlier, and the low carbon
content side with the high melting point shrinks later. In such a
way, distortion is generated in the sintered compact. Even if the
carbon content in the pressed body partially fluctuates, the
melting point does not change as long as free carbons are present,
and thus shrinkage is equally caused.
[0055] That is, when the cemented carbides change from the pressed
body to the sintered compact, the cemented carbides shrink by about
50% in volume, but the conventional cemented carbides without
dispersed free carbons do not shrink in similar shapes and cause
distortion, but the cemented carbides having dispersed free carbons
shrink in similar shapes and cause no distortion. Hence, the
cemented carbide in which free carbons are finely dispersed becomes
a sintered compact with a high dimensional accuracy.
[0056] In many cases, the edge replacement-type cutting tip is
prepared so as to have a complex shape on the upper face of the tip
by means of a mold, but it is industrially difficult to grind the
tip after sintering. In addition, the dimensional unevenness of the
edge of the tip determines the dimensional accuracy of the product
processed by the tip, and thus small dimensional unevenness among
the tips is always needed. Also, a high-accuracy tip is prepared by
grinding the side face of the tip, but this process involves high
machining cost, there is recently a tendency to use the whole or a
part of the side face while maintaining the sintered skin without
grinding (the surface as sintered), and it is needed to improve the
dimensional accuracy of the sintered compact.
[0057] The present invention provides such an edge replacement-type
cutting tip with a high dimensional accuracy. Furthermore, for a
rotary-cutting tool used in such a manner that a plurality of tips
is attached together to a rotator, unevenness in the dimensional
accuracy of the tip is more crucial. That is, in a milling tool
which is one of typical examples of the rotary-cutting tool, a
plurality of tips are incorporated, which are integrally used, and
if the dimensional unevenness is large, unevenness of attrition
among the tips is large, and thus the life of the milling tool is
shortened. For this rotary-cutting application, PVD-coated edge
replacement-type cutting tips are frequently used. Even if the tip
is coated by PVD, the accuracy is maintained at a high level and
does not change. For a lathe-cutting application, CVD-coated edge
replacement-type cutting tips are frequently used, and even the tip
is coated by CVD, the dimensional accuracy is maintained at a high
level.
[0058] The fifth object of the present invention is to provide a
cemented carbide machined product with low process cost.
[0059] Cemented carbides are widely used for cutting tools, various
molds, wear-resistant tools such as dies, civil/mining tools and
the like, and improvement of performances corresponding to various
purposes is promoted day and night.
[0060] On the other hand, cemented carbides are known as
difficult-to-cut materials which are very hard and difficult to
machine, and they are machined mainly using electric discharging
and grinding/polishing with a diamond grindstone. Both the
machining methods involve high cost. Recently, cutting tools have
also been advanced, a tool using sintered diamond and a
diamond-coated tool have been advanced so that some cemented
carbides can be processed by cutting, and improvement of machining
efficiency for the cemented carbides is expected. Cutting is an
inexpensive and efficient machining method compared to electric
discharging and grinding. However, in cutting of difficult-to-cut
materials like the cemented carbides, the tool life is short and
the machining time is long.
[0061] Since the cemented carbide according to the present
invention contains free carbons, it has a property of a low melting
point. It is known that inclusion of free carbons decreases the
melting point (Non-Patent Document 1, p. 96), and the melting point
of the free carbon-containing carbide is 1298.degree. C., and the
melting point on the low carbon content side is 1357.degree. C.
[0062] As described above, the cemented carbide according to the
present invention has a lower melting point compared to a cemented
carbide without free carbons, and thus a desirable cutting
machinability is expected. Actually, the desirable cutting
machinability could be demonstrated in Example 6. The cutting
machinability is largely governed by other properties of the
cemented carbide such as a grain size of WC and an amount of Co,
but with the same composition, the present invention can provide a
cemented carbide with good cutting machinability.
[0063] In addition, it is known that a free carbon-containing
cemented carbide has a low melting point and a low electric
resistance (Non-Patent Document 1, p. 63), and Non-Patent Document
1 describes that a specific resistance on a low carbon content side
in a cemented carbide containing 10% of Co is about 23 .mu..OMEGA.
cm, and a specific resistance of a free carbon-containing cemented
carbide is 17.8 .mu..OMEGA. cm. Consequently, improvement of the
electric discharge machinability can be expected.
[0064] The improved dimensional accuracy is required not only for
the edge replacement-type cutting tip described in the fourth
object. A cemented carbide machined product such as a mold is
machined from a sintered compact into a finished mold or the like
by electric discharging, cutting, grinding/polishing, but if the
dimensional accuracy is poor due to distortion or the like, the
stock allowance in machining is increased, the machining time is
long, attrition of tools such as a cutting tool and a grindstone is
also increased, resulting in high cost. If distortion is small, the
machining time is also short, wear of tools is also decreased, and
the machining cost can be saved.
[0065] The sixth object of the present invention is to utilize the
cemented carbide for other applications that are difficult to
practicalize due to defects and problems caused by free carbons
contained in the cemented carbide.
[0066] For example, the object is to provide a cemented carbide
with a low frictional coefficient. Currently the cemented carbide
with the low frictional coefficient is not practicalized because a
good mirror surface cannot be obtained by the presence of free
carbons in the cemented carbide. However, the mirror surface can be
obtained by finely dispersing free carbons in the cemented carbide,
thus a cemented carbide in which the lubricity is improved by
exploiting the lubricity of the free carbons can be provided. Other
applications are also expected to be developed in the future.
[0067] In view of such problems, the main object of the present
invention relates to (1) a free carbon-containing cemented carbide,
a coated cemented carbide, machined products thereof and a
manufacturing method thereof, and is to remove or reduce the
disadvantages of the free carbons even if the cemented carbide
contains free carbons, specifically to provide a cemented carbide
and a manufacturing method thereof in which even if the cemented
carbide contains free carbons, decrease in the strength is reduced
by finely dispersing the free carbons, and a beautiful mirror
surface can be obtained also in a mirror-finished face by finely
dispersing free carbons in the cemented carbide.
[0068] Furthermore, the object of the present invention is to
provide a high-performance cemented carbide which can exploit the
advantage of containing free carbons in the cemented carbide, and
object (2) is to provide a CVD-coated cemented carbide in which
generation of an .eta. phase is suppressed by providing a cemented
carbide containing finely-dispersed free carbons as a base material
for the CVD-coated cemented carbide. Object (3) is to prepare a
cemented carbide sintered compact with high dimensional accuracy
and to provide an edge replacement-type cutting tip having good
cutting performance and high dimensional accuracy. Object (4) is to
develop a cemented carbide with high dimensional accuracy and good
machinability and to provide a machined product of a cemented
carbide which can be machined at low machining cost in a shorter
time.
Solution to Problem
[0069] The present invention is a cemented carbide composed of
tungsten carbide (WC) and cobalt (Co), which contains carbon in
such an amount range that no solid carbon is contained in a liquid
phase while the liquid phase is present at a high temperature,
characterized in that the maximum diameter of the pores resulting
from the free carbons is 20 .mu.m or smaller.
[0070] The present invention relates to a cemented carbide composed
of tungsten carbide (WC) and cobalt (Co) containing
finely-dispersed free carbons, characterized in that the free
carbon content is 0.02% to 0.15%, and the maximum diameter of the
pores resulting from the free carbons is 20 .mu.m or smaller.
[0071] Still more preferably, the cemented carbide according to the
present invention is characterized in that the maximum diameter of
the pores resulting from the free carbons is 15 .mu.m or
smaller.
[0072] Even more preferably, the cemented carbide according to the
present invention is characterized in that the maximum diameter of
the pores resulting from the free carbons is 10 .mu.m or
smaller.
[0073] According to FIG. 1 (Non-Patent Document 1, p. 96, FIG. 1.
112 (b)), when the free carbon content is about 0.15% to 0.17%,
free carbons are present as solids even at the time that the liquid
phase appears (which is said to be about 1298.degree. C. or
higher), and furthermore the free carbons continue to exist even at
the time that the liquid phase is solidified by cooling. This
content range is not generally used for the cemented carbide
because the free carbons are excessive. At a content range of 0.01%
to 0.15%, all carbons are dissolved in the liquid at the time that
the liquid phase appears, and free carbons precipitates from the
liquid phase at the time of solidification. The present invention
is intended to fine the size of the free carbons. The details will
be described also in <Method for Fining Free Carbon>.
[0074] In addition, the reason why the free carbon content was set
to 0.02% or more rather than 0.01% or more is because the content
of 0.01% or less decreases both the number and the size of the
pores resulting from the free carbons and prevents defects
resulting from the free carbons from appearing in many cases.
[0075] The degree of generation of free carbons in the cemented
carbide is classified as C-type pore in the Standard CIS006C-2007
"Classification Standard for Porosity of Cemented Carbide" of Japan
Cemented Carbide Tool Manufacturer's Association, and the degree of
generation is judged in accordance with C02 to C08 in Appendix 4
(Non-Patent Document 2). When free carbons are generated in a
generally-produced cemented carbide, the cemented carbide is
classified as the C-type pore in Appendix 4. Depending on the size
and the number of free carbon pores, the grade ranges from C02 that
the porositiy is smallest to C08 that the porositiy is largest.
When judging the diameter of the free carbon from these photographs
in Appendix 4, even C02 with a small amount of pores includes mixed
pores of about 25 to 70 .mu.m.
[0076] Appendix 4 shows a photograph that the free carbon pore has
a shape that several small dots aggregate in a dendritic form to
form one pore. The size of this aggregate was measured as the size
of the pore. Such a pore (free carbons) serves as a starting point
of destruction and decreases the strength. (Non-Patent Document 1,
p. 99, FIG. 1.115). Also, when the surface is mirror-finished, free
carbons are observed as a kind of pore, and thus the beautiful
mirror surface is inhibited. When the free carbons are dispersed so
that the sizes (maximum diameters) of the pores are minified to 20
.mu.m or smaller, the pores become almost invisible with naked eye.
Consequently, defects of the mirror surface are improved or solved,
the strength is also improved, and the cemented carbide is close to
or almost equivalent to the cemented carbide without free
carbons.
[0077] The inventor of the present application has invented a
cemented carbide and a manufacturing method of the cemented
carbide, in which a mixed powder for producing a cemented carbide
is sintered and rapidly cooled from a liquid phase-including state
at a cooling rate of 30.degree. C./min, 50.degree. C./min and
70.degree. C./min, so that the maximum diameter of the free carbon
pores is 20 .mu.m or smaller, 15 .mu.m or smaller, 10 .mu.m or
smaller which have not been achieved so far.
[0078] According to the present invention, a cemented carbide in
which the strength (transverse rupture strength), the hardness and
the mirror surface quality are further improved compared to the
case of the pore maximum diameter of 20 .mu.m is provided by
further setting the size (maximum diameter) of the free carbon pore
to 15 .mu.m or smaller.
[0079] According to the present invention, a cemented carbide in
which the strength (transverse rupture strength), the hardness and
the mirror surface quality are further improved compared to the
case of the pore maximum diameter of 20 .mu.m is provided by
further setting the size (maximum diameter) of the pore to 10 .mu.m
or smaller.
[0080] The cemented carbide of the present invention is
characterized in that chromium carbide or chromium nitride in an
amount of 2 to 18% based on cobalt (Co) content is added.
[0081] According to the present invention, also a cemented carbide
with chromium carbide or chromium nitride added can have almost the
same strength and hardness as those of the cemented carbide without
free carbons by finely dispersing free carbons.
[0082] It is considered that chromium (Cr) in a solid solution
state improves the compressive strength, the heat resisting
strength and the fatigue strength of the cemented carbide (Patent
Document 1). However, when the chromium content is 2% or less based
on the cobalt (Co) content, no effect is shown, and when it is 18%
or more, a crystal of the chromium carbide precipitates, resulting
in a risk of decreasing the strength of the cemented carbide.
Hence, the proper range is designated to be 2 to 18%.
[0083] The cemented carbide according to the present invention is
characterized in that a part of the tungsten carbide (WC) is
replaced by any one or combination of: a carbide (but excluding W),
a nitride or a carbonitride of transition metal of groups 4, 5 and
6 in the periodic table; and a double carbide or a double
carbonitride of W with the carbide, the nitride or the carbonitride
of the transition metal.
[0084] According to the present invention, also in the cemented
carbide in which a part of the tungsten carbide (WC) is replaced by
any one or combination of: a carbide (but excluding W), a nitride
or a carbonitride of transition metal of groups 4, 5 and 6 in the
periodic table; and a double carbide or a double carbonitride of W
with the carbide, the nitride or the carbonitride of the transition
metal, the strength and the hardness can be made almost equivalent
to those of the cemented carbide without free carbon pores by
finely dispersing the free carbons.
[0085] The present invention is characterized in that a .beta.-free
layer is formed on the surface of the cemented carbide, and the
.beta.-free layer has a thickness of 1 to 30 .mu.m.
[0086] Herein, the .beta.-free layer refers to a layer having no
.beta. phase, which has a slightly higher Co content and a slightly
lower hardness but is excellent in strength and toughness.
[0087] The cemented carbide according to the present invention is
utilized as a base material for CVD coating, and according to the
present invention, the brittleness of the coating film can be
reinforced by adding a nitrogen compound such as TiN and TiCN to a
cemented carbide including the .beta. phase to form a .beta.-free
layer, and the cemented carbide can be suitably used as a base
material for CVD coating.
[0088] Since the .beta.-free layer is intended to cover the
brittleness of the coating film, a thickness of 1 .mu.m or less
generates an insufficient effect, and a thickness of 30 .mu.m or
more decreases a tool performance because a high-temperature
hardness on a tool edge is poor when using the cemented carbide
according to the present invention for the tool edge.
[0089] The present invention is characterized in that the lattice
constant of the fcc in the binder phase (Co phase) of the cemented
carbide is 3.560 .ANG. or higher.
[0090] According to the present invention, a cemented carbide and a
coated cemented carbide having an improved cutting performance can
be provided by setting the lattice constant of the fcc in the
binder phase (Co phase) to 3.560 .ANG. or higher.
[0091] It is supposed that a cemented carbide with a high lattice
constant has a high heat resistance, an improved fatigue strength
and an improved cutting performance. Also, it is supposed that the
cemented carbide has an improved performance in a wear-resistant
tool (Patent Document 1, Patent Document 2). The cemented carbide
containing free carbons has a minimum lattice constant, about 3.550
.ANG. (Non-Patent Document 1, P. 99, and FIG. 1.115 on the same
page).
[0092] In order to finely disperse the free carbons, the mixed
powder for producing the cemented carbide is rapidly cooled from a
liquid phase-including state after sintering in the manufacturing
step for manufacturing the cemented carbide, but even if the state
becomes a solid phase, the powder is continuously rapidly cooled to
800.degree. C. It was found that, even in a state having free
carbons, the tungsten (W) progressively became a solid solution
state in the Co phase by this rapid-cooling effect, and the lattice
constant was increased. Although there was no large difference in
transverse rupture strength and hardness, the performance was
improved in a cutting test. It is considered that there is a
difference in performance also in applications other than the
cutting application for wear resistance or the like.
[0093] The inventor of the patent application consequently invented
a cemented carbide containing free carbons, in which the lattice
constant is 3.560 .ANG. or higher which has not been achieved so
far by finely dispersing free carbons in the cemented carbide even
in a case of the free carbon-containing cemented carbide.
[0094] Also in the coated cemented carbide comprising this cemented
carbide as a base material, the effect of the lattice constant
continued, and the cutting performance was improved. As will be
described below, the free carbon dispersion-type cemented carbide
also has a high dimensional accuracy. The present invention
characterized in that it provides a cemented carbide or a coated
cemented carbide in which free carbons are finely dispersed, a
dimensional accuracy is high, and a lattice constant of fcc in a
binder phase (Co phase) is 3.560 .ANG. or higher, and an edge
replacement-type cutting tip made thereof.
[0095] The cemented carbide according to the present invention is
used as a base material for a coated cemented carbide.
[0096] Coated cemented carbides prepared by the CVD method are
prevalent, but TiC, TiCN and TiN are commonly used as the films to
be brought contact with the cemented carbide. These Ti compounds
tend to absorb carbon in the cemented carbide to generate an .eta.
phase as the decarburized layer at the boundary between the coat
and the cemented carbide. The .eta. phase reduces the strength of
the coated cemented carbide (Non-Patent Document 5, Patent Document
7). However, the free carbon-containing cemented carbide contains
excess carbon and can suppress generation of the .eta. phase
(Non-Patent Document 3, Patent Document 7).
[0097] It is characterized that a coated cemented carbide having
improved strength with a small amount of .eta. phase at the
boundary portion is provide by using the cemented carbide according
to the present invention as a base material for the coated cemented
carbide.
[0098] The cemented carbide or the coated cemented carbide
according to the present invention are used as an edge
replacement-type cutting tip.
[0099] In addition, the cemented carbide or the coated cemented
carbide according to the present invention are used and machined,
so that they can be used as machined products such as tools, molds
and parts.
[0100] According to the present invention, a cemented carbide and a
coated cemented carbide having improved dimensional accuracy can be
manufactured. The present invention is characterized in that an
edge replacement-type cutting tip for which grinding is omitted or
reduced can be provided by improving the dimensional accuracy.
[0101] Also, in the cemented carbide according to the present
invention, the stock allowance for machining is small due to the
high dimensional accuracy, the machinability is also excellent, and
thus the machining cost can be reduced. Thus, it is characterized
that a cemented carbide machined product and a coated cemented
carbide machined product such as tools, molds and parts are
provided at a lower machining cost by using the cemented carbide
according to the present invention.
[0102] The method for manufacturing the cemented carbide according
to the present invention is characterized in that, when
manufacturing a fine free carbon dispersion-type cemented carbide,
after sintering a mixed powder for producing the cemented carbide
at a sintering temperature not lower than a liquid-phase appearance
temperature, the method comprises a step of rapidly cooling from
the temperature not lower than the liquid-phase appearance
temperature, or a step of reheating to the temperature not lower
than the liquid-phase appearance temperature and then rapidly
cooling.
[0103] The method for manufacturing the cemented carbide according
to the present invention is characterized in that the cooling rate
in the step of rapidly cooling and the step of reheating and
rapidly cooling is set to 30.degree. C./min or higher.
[0104] Here, the "step of rapidly cooling from a temperature not
lower than a liquid-phase appearance temperature" refers to a step
of rapidly cooling the cemented carbide from the temperature not
lower than the liquid-phase appearance temperature, which also
includes the sintering conditions "rapid cooling", "strong rapid
cooling" and "very strong rapid cooling" in Examples.
[0105] In addition, the "step of reheating and rapidly cooling"
refers to a step of reheating the sintered cemented carbide to the
temperature not lower than the liquid-phase appearance temperature
and then rapidly cooling it, which also includes the sintering
conditions "reheating and rapid cooling" and "reheating and strong
rapid cooling" in Examples.
[0106] The mixed powder blended so as to contain free carbons was
pressed and sintered. At this time, the free carbons were rapidly
cooled from a liquid phase-including state to finely disperse the
free carbons. The cooling rate from the liquid phase-including
state to 800.degree. C. is normally about 10.degree. C./min, but in
this case, the cemented carbide had the C-type pore in the Standard
CIS006C-2007 "Classification Standard for Porosity of Cemented
Carbide" of Japan Cemented Carbide Tool Manufacturer's
Association.
[0107] The same mixed powder was sintered and cooled from the
liquid phase-including state at a cooling rate of 20.degree. C./min
and 30.degree. C./min, and as a result, the cemented carbide cooled
at 20.degree. C./min had less pores having diameters of 20 .mu.m or
larger compared to a cemented carbide cooled at 10.degree. C./min,
but the pore remained. When cooled at 30.degree. C./min, there was
no pore having diameters of 20 .mu.m or larger.
[0108] Consequently, the cooling rate was set to 30.degree. C./min
or higher. In addition, if the cooling rate is increased, the
diameter of the pore became smaller. In a trial experiment, when
the cooling rate was about 50.degree. C./min, there were no pores
having diameters of 15 .mu.m or larger, and when the cooling rate
was 70.degree. C./min or higher, there were no pores having
diameters of 10 .mu.m or larger.
[0109] According to the present invention, pores can be dispersed
in the cemented carbide, and the diameters of the pores can be
decreased by sintering the mixed powder for producing the cemented
carbide at a sintering temperature not lower than the liquid-phase
appearance temperature, and then rapidly cooling or
reheating/rapidly cooling it, and by increasing the cooling
rate.
[0110] The method for manufacturing the cemented carbide according
to the present invention is characterized in that the cemented
carbide produced by the above manufacturing method does not contain
1% or more of molybdenum (Mo).
[0111] In addition, the edge replacement-type cutting tip or the
cemented carbide machined product according to the present
invention is characterized in that the cemented carbide to be used
does not contain 1% or more of molybdenum (Mo).
[0112] When molybdenum (Mo) is contained, molybdenum carbide,
molybdenum/tungsten double carbide and free carbons precipitate
when manufacturing the cemented carbide. Furthermore, since the
liquid-phase appearance temperature also changes, the present
invention is limited to the WC-Co carbide type containing no
molybdenum (Mo). The reason why the molybdenum (Mo) content is set
to 1% or less is because there may be a small amount of molybdenum
(Mo) as an impurity, and a content of 1% or less, if any, does not
exert influence.
Effects of Invention
[0113] According to the present invention, decreased yield and
delivery delay can be improved by providing the cemented carbide
and the manufacturing method thereof, in which the free carbons are
finely dispersed in the cemented carbide so that the maximum
diameter of the pores in the cemented carbide is 20 .mu.m or
smaller, preferably 15 .mu.m or smaller, more preferably 10 .mu.m
or smaller to suppress the decrease in strength, and a beautiful
mirror surface can be obtained also on a mirror-finished
surface.
[0114] Furthermore, according to the present invention, a coated
cemented carbide in which generation of an .eta. phase is
suppressed and the strength is stable can be provided by providing
a cemented carbide containing free carbons as a base material for
the CVD-coated cemented carbide.
[0115] In addition, according to the present invention, an edge
replacement-type cutting tip with a high dimensional accuracy for
which grinding is omitted or reduced can be provided by finely
dispersing free carbons in the cemented carbide to solve the
disadvantages of the pores due to the free carbons. If the
dimensional accuracy of the cutting tip is improved, the
dimensional accuracy of the cut product is also improved. In a
rotary-cutting application to integrally use a plurality of tips,
bad dimensional unevenness causes the edge to protrude, the edge is
worn out quickly, and as a result, the life of the rotary-cutting
tool is shortened. That is, the edge replacement-type tip with
finely dispersed free carbons can be utilized as a cutting tool
which is inexpensive, has a high dimensional accuracy and has a
long life.
[0116] Furthermore, according to the present invention, a cemented
carbide with a high dimensional accuracy and small machining stock
allowance can be provided by finely dispersing free carbons in the
cemented carbide to remove the disadvantages of the pores due to
the free carbons. If the machining stock allowance is small, the
times for machining such as electric discharging,
grinding/polishing and cutting are shortened, wear of the machining
tool is also reduced, and the machining efficiency is greatly
improved.
[0117] Additionally, for machining of cemented carbides,
conventionally electric discharging and grinding have been mainly
used, but recently a cutting method allowing greatly efficient
machining has been developed and started to spread. The fine free
carbon dispersion-type cemented carbide is easier to cut compared
to the conventional cemented carbide. As described above, a
machined product of the cemented carbide with a low machining cost
can be provided because of not only low machining stock allowance
but also good cutting machinability and electric discharge
machinability.
BRIEF DESCRIPTION OF DRAWINGS
[0118] FIG. 1 illustrates a WC-Co pseudo-binary vertical sectional
view (reprinted from Hisashi Suzuki, "Cemented Carbide and Sintered
Hard Material" (1986), p. 96, FIG. 1.112 (b), Maruzen Publishing
Co., Ltd.).
DESCRIPTION OF EMBODIMENTS
[0119] <Definition of Size of Pore Resulting from Free Carbon,
and Measurement Method Thereof>
[0120] The degree of the free carbon generation in the cemented
carbide is judged in accordance with C02 to C08 in Appendix 4 of
the quality standard CIS006C of Japan Cemented Carbide Tool
Manufacturer's Association. When free carbons are generated in a
generally produced cemented carbide, the state is as shown in
Appendix 4. The grade ranges from C02 that the free carbons are
smallest in number and size to C08 that the free carbons are
largest in number and size, and even in C02 with the fewest free
carbons, the maximum diameter is about 70 .mu.m. As shown in the
photograph of the free carbons in Appendix 4, the pore of the free
carbon is shaped in such a manner that several small dots aggregate
in a dendritic form to form one pore, and the size of this
aggregate was measured as the size of the pore. The size of the
free carbon pore is generally supposed to be 25 .mu.m or larger
(Non-Patent Document 4, p. 283 to 284).
[0121] In the present invention, for measurement of the size of the
free carbon pore, a test sample was polished in accordance with the
method described in CIS006C, and similarly observed and measured
with a 100-power microscope in the same manner as in Appendix 4 of
CIS006. In addition, a case that nets resulting from free carbons
with a size of 20 .mu.m or larger could not be observed in a visual
field (about 0.07.times.0.1 mm) with the same size as in Appendix 4
successively in two visual fields, or a case that 10 visual fields
are randomly observed and pores resulting from free carbons with a
size of 20 .mu.m or larger could not be observed in 7 visual
fields, are defined as cemented carbides with free carbon pores
having a maximum diameter of 20 .mu.m or smaller. The cemented
carbides with free carbon pores having maximum diameters of 15
.mu.m or smaller and 10 .mu.m or smaller were also determined in
the same measurement method.
[0122] However, note that if a pore resulting from free carbons is
a small pore of 20 .mu.m or smaller, the pore may be difficult to
distinguish from the A-type pore. In order to ascertain whether the
pore results from free carbons, it is also necessary to
concurrently observe and confirm the pore at a high magnification
of several hundreds or higher, as also described in paragraph 0003.
In addition, as shown in Tables 2, 4, 6, 7, 8, 9 of Examples,
generally chemical analysis (free carbon %) is concurrently carried
out, and thus, if there are free carbons, it can be confirmed that
the pore results from free carbons.
<Method for Fining Free Carbon>
[0123] FIG. 1 shows a WC-Co pseudo-binary vertical sectional view
(reprinted from Hisashi Suzuki, "Cemented Carbide and Sintered Hard
Material" (1986), p. 96, FIG. 1.112 (b), Maruzen Publishing Co.,
Ltd.).
[0124] There are two types of precipitation of free carbons in the
cemented carbide. According to FIG. 1,
(1) when the carbon content in the cemented carbide is 6.3% or more
in terms of WC, the composition is WC+liquid (L)+carbon (C) at the
time of appearance of a liquid phase. When the cemented carbide is
cooled and solidified while kept in this composition, the
composition is WC+.gamma.+C. (2) when the carbon content is 6.13%
to 6.3% in terms of WC, the composition is WC+liquid (L) at the
time of appearance of a liquid phase, however when the cemented
carbide is cooled while kept in this composition, the composition
is WC+.gamma.+C. Since the theoretical carbon content of WC is
6.13%, the content in terms of free carbons is 0.01 to 0.17%.
[0125] Here, .gamma. represents the binder phase mainly composed of
Co in the crystal structure fcc (typically referred to as Co
phase). The present invention is applied to only in the case of
(2). In the case of (1), this range is not generally used for the
cemented carbide, because carbons in the liquid phase remain as
they are also at the time of appearance of the solid phase, and
excessive free carbons are present. However, Patent Document 4
relates to the range of (1), which has been developed for a special
application.
[0126] In the case of (2), when the cemented carbide is converted
from the liquid phase to the solid phase at a temperature of the
melting point or lower, free carbons (C-type pore) precipitate from
the liquid phase. The cemented carbide according to the present
invention can be realized by finely dispersing the sizes of the
precipitated free carbons. Specifically, the cemented carbide is
rapidly cooled from the liquid phase to finely disperse
precipitation of the free carbons.
[0127] Theoretically, the quicker the rapid cooling is, the finer
the free carbons are. However, if the cooling rate is too high, the
internal stress may remain and the furnace may deteriorate
depending on the product. Hence, there are limits according to the
actual circumstances.
[0128] Also, the size of the free carbon is affected not only by
the amount of free carbons in the cemented carbide but also by the
composition and the shape/size of the sintered compact, and the
like.
[0129] Thus, it is desirable to previously select the optimum
cooling rate in accordance with the actual circumstance. In terms
of facility, a rate of 100.degree. C./min can be sufficiently
achieved because of the advanced gas rapid-cooling technology, and
examples of 1000.degree. C./min and 10000.degree. C./min have been
also reported (Patent Documents 2 and 3). Normally, when the free
carbons are examined by a 100-power microscope on the basis of
CIS006C, the C-type pore is observed, but when the free carbons are
finely dispersed, the pore looks like the A type in some cases.
Thus, for ascertaining whether the pore results from free carbons,
a method in which the pore is concurrently observed and confirmed
at a high magnification of several hundreds or higher is also used,
as also described in paragraph 0003. Furthermore, the pore can be
confirmed by chemical analysis (free carbon %) as shown in Tables
2, 4, 6, 7, 8, and 9 of Examples.
<Cooling Method>
[0130] For sintering and reheating, vacuum furnaces are normally
used. Recently, there have been many vacuum furnaces equipped with
a device capable of performing forced cooling with inert gas. It is
convenient to use this kind of vacuum furnace for production. The
cooling rate can be increased by increasing the gas amount or
increasing the gas pressure, and the cooling rate can be controlled
depending on the actual circumstance. When a large amount of
cemented carbide (product) is charged in a large furnace, the gas
amount and the gas pressure should be increased, and when the
charged amount is small and the product shape is also small, the
gas amount and the gas pressure may be small. The inert gas may be
Ar or N.sub.2 gas. The cooling effect of N.sub.2 is slightly larger
than that of Ar, and also N.sub.2 is industrially advantageous in
respect of cost.
[0131] Hereinafter, the best embodiment for carrying out the
present invention will be explained on the basis of Examples. Note
that the present invention is not limited to the following
embodiments, and known changes can be added to the present
invention within a scope substantially equal to or equivalent to
the scope of the present invention.
Example 1
[0132] An example of the WC-Co-based material will be described
below.
[0133] Mixed powders before sintering were prepared by a process in
which commercially available raw materials were blended in the
composition of (Table 1), mixed in a wet ball mill in accordance
with a common method using alcohol, and dried. Samples with
Cr.sub.3C.sub.2 added were designated as A, and samples with no
addition were designated as B. In A2 and B2, the carbon contents
were larger than that in A1 and B1 by 0.14%, and in B4 and B5, the
carbon contents were larger than that in B1 by 0.10% and 0.18%
respectively.
TABLE-US-00001 TABLE 1 Added amount Sam- WC(4 .mu.m) Co Cr2C3 of
carbon ple (%) (%) (%) (%) A1 84.5 15 0.5 0 A2 84.5 15 0.5 0.14 B1
85 15 0 0 B2 85 15 0 0.14 B4 85 15 0 0.1 B5 85 15 0 0.18
[0134] A lubricant for press was added to these mixed powders, and
all powders were pressed at 1 ton/cm.sup.2, and vacuum-sintered.
Although the used mixed powders were the same, names of the samples
were classified depending on the sintering conditions and heating
conditions. The sintering conditions and characteristic values of
the samples are shown in (Table 2).
[0135] Here, the "slow cooling" in the sintering conditions refers
to a step in which the sample is vacuum-sintered at 1380.degree.
C., held for 1 hour, then cooled, and cooled (slowly cooled) from
1350.degree. C. to 800.degree. C. at 10.degree. C./min.
[0136] In addition, the "rapid cooling" in the sintering conditions
refers to a step in which the sample is vacuum-sintered at
1380.degree. C., held for 1 hour, then cooled, and cooled (rapidly
cooled) from 1350.degree. C. to 800.degree. C. at 30.degree. C./min
by introducing an inert gas, and the "strong rapid cooling" refers
to a step in which the sample is cooled (strongly and rapidly
cooled) from 1350.degree. C. to 800.degree. C. at 50.degree. C./min
by introducing an inert gas.
[0137] The "reheating and rapid cooling" in the sintering
conditions refers to a step in which the sintered compact is
reheated in a vacuum furnace at 1340.degree. C. for 15 minutes, and
cooled (rapidly cooled) from 1340.degree. C. to 800.degree. C. at
30.degree. C./min by introducing an inert gas, and the "reheating
and strong rapid cooling" refers to a step in which the sintered
compact is reheated in a vacuum furnace at 1340.degree. C. for 15
minutes, and cooled (strongly and rapidly cooled) from 1340.degree.
C. to 800.degree. C. at 50.degree. C./min.
[0138] Herein, the method for measuring the maximum diameter
(.mu.m) of the pore in (Table 2) accords to the above-described
<Definition of Size of Pore Resulting from Free Carbon, and
Measurement Method Thereof>.
TABLE-US-00002 TABLE 2 Transverse Vickers Maximum Free rupture,
hard- diameter Sam- carbon strength ness of pore ple (%) (MPa) (Hv)
(.mu.m) Sintering conditions A11 0 3230 1130 10 Slow cooling of A1
A21 0.08 3050 1020 100 Slow cooling of A2 A22 0.05 3200 1110 15
Reheating and rapid cooling of A21 A23 0.06 3220 1110 15 Rapid
cooling of A2 B11 0 3200 1110 10 Slow cooling of B1 B21 0.08 3070
1000 100 Slow cooling of B2 B22 0.07 3170 1070 20 Reheating and
rapid cooling of B21 B23 0.06 3220 1100 10 Reheating and strong
rapid cooling of B21 B24 0.07 3185 1090 15 Rapid cooling of B2 B41
0.06 3090 1020 70 Slow cooling of B4 B42 0.04 3200 1100 10
Reheating and strong rapid cooling of B41 B51 0.12 3000 980 150
Slow cooling of B5 B52 0.1 3160 1070 20 Reheating and rapid cooling
of B51
[0139] A11, A21, B11, B21, B41 and B51 are under a sintering
condition of "slow cooling". The samples (A11, B11) whose added
amount of carbon is 0 in (Table 1) had no free carbon also after
sintering, and their pores were evaluated as type A in Appendix 1
of CIS006C, and classified as A02 or lower. The samples (A21, B21,
B41, B51) with carbon added had free carbons also after sintering,
and their pores were evaluated as type C in Appendix 4 of CIS006C,
and classified as C02 to C06.
[0140] In relation to A21 and B21, as described more specifically,
powders were sintered, then polished so as to have a mirror
surface, and microscopically observed at magnification of 100, and
as a result, both samples were evaluated as around C04 in
accordance with CIS006C. That is, large free carbon pores of 80 to
100 .mu.m and small free carbon pores of about 25 .mu.m were found
in a mixed state in A21 and B21.
[0141] Also, A22 and B22 were prepared by a process in which the
A21 and B21 (sintered compact) were reheated in the same vacuum
furnace, held at 1340.degree. C. for 15 minutes, cooled, and cooled
(rapidly cooled) from 1340.degree. C. to 800.degree. C. at a
cooling rate of 30.degree. C./min. The samples were polished by a
method according to CIS006C in the same manner as for other
samples, and the states of these cemented carbide pores were
microscopically observed at magnification of 100.
[0142] The maximum diameter of the pore of A22 was 15 .mu.m or
smaller, and the maximum diameter of the pore of B22 was 20 .mu.m
or smaller. The transverse rupture strength and the hardness were
also measured. A23 and B24 were prepared by a process in which a
mixed powder was vacuum-sintered under the same conditions as
described above and then cooled (rapidly cooled) at 30.degree.
C./min. Also, the mixed powders for B4 and B5 were similarly
vacuum-sintered and then cooled. The sintering conditions and the
results are shown in (Table 2).
[0143] When A11 and B11 with the sintering condition of "slow
cooling" and 0% carbon addition amount were compared with A21 and
B21 with the sintering condition of "slow cooling" and 0.14% carbon
addition amount, A21 and B21 had a decreased transverse rupture
strength and hardness because the free carbons precipitated.
However, even if free carbons appear similarly to A22, A23, B22 and
B24, the free carbons can be finely dispersed by changing the
sintering conditions to "rapid cooling" or "reheating and rapid
cooling", and when the pore becomes smaller, the transverse rupture
strength becomes equivalent to that of A11 and B11 without free
carbons. Also, hardness of A21 and B21 tends to be slightly lower
compared to that of A11 and B11 without free carbons, but there is
almost no difference.
[0144] B52 had a slightly large amount of pores, and one pore
having a maximum diameter of 20 to 25 .mu.m was observed in each of
two visual fields out of ten visual fields. B23 was prepared by a
process in which B21 is reheated to 1340.degree. C. and strongly
and rapidly cooled to 800.degree. C. at 50.degree. C./min, and B23
had pores improved compared to that in B22, the sizes of the pores
in B23 were small and all of them were 10 .mu.m or smaller. Also,
sizes of all pores in B42 were 10 .mu.m or smaller.
[0145] As described above, normally, when the cemented carbide
contains free carbons which cause pores, the produced cemented
carbide has low transverse rupture strength and hardness compared
to a cemented carbide without free carbons by cooling with a
general sintering conditions/cooling method (slow cooling).
However, even if the cemented carbide contains free carbons, the
free carbon pores in the cemented carbide are dispersed by rapid
cooling or strong rapid cooling after sintering, or by slow cooling
after sintering and then reheating and rapid cooling or reheating
and strong rapid cooling. As a result, a cemented carbide having a
transverse rupture strength and a hardness equivalent to those of
the cemented carbide without free carbons can be produced.
Example 2
[0146] An example of a material for cutting tools will be described
below.
[0147] Mixed powders before sintering were prepared by a process in
which commercial raw materials were blended in the composition of
(Table 3), subjected to a wet ball milling and dried in accordance
with a general method using alcohol. A lubricant for press was
added to all of these mixed powders, which were pressed at 1
ton/cm.sup.2. C11 and C21 were vacuum-sintered at 1400.degree. C.,
held for 1 hour, then cooled, and cooled (slowly cooled) from
1380.degree. C. to 800.degree. C. at 10.degree. C./min
(corresponding to "slow cooling" in the sintering conditions).
[0148] On the other hand, C23 was vacuum-sintered at 1400.degree.
C., held for 1 hour, then cooled, and cooled (strongly and rapidly
cooled) from 1380.degree. C. to 800.degree. C. at 50.degree. C./min
by introducing an inert gas (corresponding to "strong rapid
cooling" in the sintering conditions).
[0149] In addition, C22 is prepared by reheating and rapidly
cooling C21. The "reheating and rapid cooling" in the sintering
conditions refers to a step in which the sample is held in a vacuum
furnace at 1380.degree. C. for 30 minutes and cooled at 30.degree.
C./min. C22 did not have pores with sizes of 20 .mu.m or larger.
The sizes of the pores in C23 were 10 .mu.m or smaller. The results
are shown in Table 4.
TABLE-US-00003 TABLE 3 WC (2 .mu.m) Co TiC TaNbC Cr2C3 Added amount
Sample (%) (%) (%) (%) (%) of carbon (%) C1 73 10 8.5 8.5 0 0 C2 73
10 8.5 8.5 0 0.22
TABLE-US-00004 TABLE 4 Transverse Vickers Maximum Free rupture
hard- diameter Sam- carbon strength ness of pore ple (%) (MPa) (Hv)
(.mu.m) Sintering condition C11 0 2195 1470 10 Slow cooling of C1
C21 0.08 2040 1400 90 Slow cooling of C2 C22 0.1 2150 1430 20
Reheating and rapid cooling of C21 C23 0.06 2190 1460 10 Strong
rapid cooling of C2.
[0150] In addition, C11, C21, C22 and C23 as base materials were
CVD-coated with TiC with a thickness of 7 .mu.m. C11 had an .eta.
phase with a thickness of 1 to 3 .mu.m at the boundary between the
TiC coat and the base material, but C21 had no .eta. phase. Data
for verifying Non-Patent Document 3 was obtained. Also C22 and C23
had no .eta. phase at the boundary between the TiC coat and the
base material, and the same result as for C21 was obtained. That
is, even if free carbons are finely dispersed in the base material,
the effect for reducing the .eta. phase is same.
Example 3
[0151] An example of a cemented carbide having a .beta.-free layer
on its surface, which is frequently used for a CVD base material
will be described below.
TABLE-US-00005 TABLE 5 WC Co TiC TaNbC TiN Added amount Sample (%)
(%) (%) (%) (%) of carbon (%) E 87.5 5 2 5 0.5 0 F 87.5 5 2 5 0.5
0.18
TABLE-US-00006 TABLE 6 Transverse Vickers Maximum Free rupture
hard- diameter Sam- carbon strength ness of pore ple (%) (MPa) (Hv)
(.mu.m) Sintering conditions E1 0 -- 1510 10 Slow cooling of E F1
0.1 -- 1440 90 Slow cooling of F F2 0.07 -- 1490 15 Rapid cooling
of F
[0152] Mixed powders before sintering were prepared by a process in
which commercial raw materials were blended in the composition of
(Table 5), mixed in a wet ball mill and dried in accordance with a
general method using alcohol. A lubricant for press was added to
these mixed powders, all of which were pressed at 1 ton/cm.sup.2.
E1 and F1 were vacuum-sintered at 1400.degree. C., held for 1 hour,
then cooled, and cooled (slowly cooled) from 1380.degree. C. to
800.degree. C. at 10.degree. C./min (corresponding to "slow
cooling" in the sintering conditions).
[0153] On the other hand, F2 was vacuum-sintered at 1400.degree.
C., held for 1 hour, then cooled, and cooled (rapidly cooled) from
1380.degree. C. to 800.degree. C. at 30.degree. C./min by
introducing an inert gas (corresponding to "rapid cooling" in the
sintering conditions). The results are shown in (Table 6). All of
the samples E1, F1 and F2 had the .beta.-free layer with a
thickness of 10 to 20 .mu.m on the surface. Even if the free
carbons are finely dispersed, the .beta.-free layer can be made.
These samples had .beta.-free layers on their sintered surface, and
the transverse rupture strength was not measured.
Example 4
[0154] Experiments on the dimensional accuracy of the edge
replacement-type cutting tip were carried out.
[0155] A lubricant for press was added to mixed powders of C1 and
C2 in (Table 3) in Example 2, which was pressed at 1 ton/cm.sup.2
into a plurality of edge replacement-type cutting tips model no.
SNMA432, sintered, and dimensional accuracy was measured. Results
in (Table 7) were obtained. The sintering conditions are the same
between G11 and C11, between G21 and C21, between G22 and C22,
between G23 and C23.
[0156] The "dimensional difference inside the tip" in (Table 7)
refers to a difference between the maximum value and the minimum
value when four sides of one SNMA432 (square) are measured with a
micrometer.
[0157] The "difference between maximum and minimum values in 10
samples" in (Table 7) refers to a value obtained by subtracting the
minimum value from the maximum value when four sides of ten
SNMA432s are measured.
TABLE-US-00007 TABLE 7 Difference between Maximum Dimensional
maximum and minimum Sample Free diameter difference dimensions in
(model no. carbon of pore inside the tip 10 samples SNMA432)
Sintering condition (%) (.mu.m) (mm) (mm) G11 Slow cooling of C1 0
10 0.07 0.12 G21 Slow cooling of C2 0.08 90 0.05 0.09 G22 Reheating
and rapid 0.1 20 0.05 0.09 coding of G21 G23 Strong rapid cooling
0.08 10 0.04 0.07 of C2
[0158] In G22 and G23 having finely dispersed free carbons,
dimensional unevenness is smaller than that in G11 without free
carbons.
[0159] G11, G22 and G23 were coated with 2 .mu.m TiC.sub.2+3 .mu.m
TiN by ion plating which is one type of PVD, and subjected to the
same measurement. Both the PVD-coated G22, G23 and the PVD-coated
G11 had the same dimensional difference inside the tip and
difference between maximum and minimum values in 10 samples as
those before the coating. The coated G22 and G23 had smaller
dimensional unevenness than that of the coated G11.
[0160] Furthermore, G11, G22, G23 were coated with TiC with a
thickness of 7 .mu.m by a CVD method, and subjected to the same
dimensional measurement for comparison. As expected, the
dimensional unevenness was almost the same as before coating, and
the coated G22 and G23 had smaller dimensional unevenness than that
of G11.
Example 5
[0161] Cylindrical cemented carbide sintered compacts were
prepared, and compared and investigated for the dimensional
accuracy.
[0162] A lubricant for press was added to mixed powders of B1, B2
and B4 in Example 1, and pressed at 1 ton/cm.sup.2 to prepare a
plurality of sintered compacts having an outer diameter of 50D, an
inner diameter of 20d and a height of 50 (unit: mm), and compared
for the dimensional accuracy. The results are shown in (Table
8).
TABLE-US-00008 TABLE 8 Dimensional Difference between Maximum
difference in maximumand minimum Sample Free diameter one sintered
outer diameters Cylindrical carbon of pore compact in 3 samples
product Sintering condition (%) (.mu.m) (mm) (mm) H11 Slow cooling
of B1 0 10 0.5 0.7 H21 Slow cooling of B2 0.08 100 0.3 0.4 H24
Rapid cooling of B2 0.07 15 0.2 0.3 H41 Slow cooling of B4 0.06 70
0.25 0.3 H42 Reheating and strong 0.06 10 0.2 0.25 rapid cooling of
H41
[0163] The sintering conditions took over those for the B1, B2 and
B4 powders. In the dimensional measurement, the outer diameter of
the sintered compact was measured, and the difference between the
maximum diameter and the minimum diameter was determined in order
to judge whether or not the dimensional accuracy was good. The
difference between the maximum and minimum outer diameters of one
sintered compact, and the difference between the maximum and
minimum diameters of three sintered compacts were indicated. It can
be seen that H24 and H42 having finely dispersed free carbons have
better dimensional accuracy than that of H11 without free
carbons.
Examples 6
[0164] The machining efficiencies in preparing cemented carbide
machined products were compared.
[0165] Circumferences of H11 and H24 in (Example 5) as work
materials were cut by a lathe. As a cutting tool, model no. TNGA432
of a polycrystalline diamond sintered compact was used. Cutting was
carried out under a condition of cutting velocity (v)=15 m/min,
feeding rate (f)=0.1 mm/rev and cutting depth (d)=0.1 mm.
[0166] In relation to the time to remove the sintered skin on the
circumference, naturally, H11 having many distortions and large
stock allowance required 1.5 times more time than H24 with less
distortion.
[0167] Furthermore, in order to compare the machinability between
H11 and H24, the sintered skin was removed, then the tool was
changed with a new tool, cutting was performed for 20 minutes under
the same condition, and progress states of wear were compared
between the both tools.
[0168] An amount of the tool wear (flank wear) due to cutting of
H11 was 0.11 mm, and in the case of H24, it was 0.08 mm. This
indicates that H24 has better machinability than that of H11. That
is, the cemented carbide according to the present invention has not
only a good dimensional accuracy for the sintered compact, but also
an excellent machinability. Consequently, it was confirmed that
cemented carbide machined products with low machining cost could be
provided.
Example 7
[0169] The relationship between the lattice constant of the fcc in
the binder phase (Co phase) and the cutting performance was
investigated.
[0170] The C1 powder in (Example 2) was pressed into the SNMA432 at
1 ton/cm.sup.2, vacuum-sintered at 1400.degree. C., held for 1
hour, and then rapidly cooled (very strongly and rapidly cooled) at
a cooling rate of 70.degree. C./min. The sample was numbered as
G24. Also in (Example 4), the mixed powder was the same as in
(Example 2), and as samples, G11, G21, G22 and G23 in (Example 4)
and the above G24 were used, and compared for the lattice constant
and the cutting performance. X-ray diffraction using Cu as the
target was used for measuring the lattice constant.
TABLE-US-00009 TABLE 9 Sample Maximum Lattice Flank Shear drop on
rake face (model no. Free carbon diameter of constant wear of
coated cemented SNMA432) Sintering condition (%) pore (.mu.m)
(.ANG.) (mm) carbide (mm) G11 Slow cooling of C1 0 10 3.555 0.4
0.025 G21 Slow cooling of C2 0.08 90 3.55 0.55 0.034 G22 Reheating
and 0.1 20 3.562 0.35 0.023 rapid cooling of C21 G23 Strong rapid
0.08 10 3.568 0.25 0.02 cooling of C2 G24 Very strong rapid 0.06 10
3.571 0.2 0.016 cooling of C2
[0171] The flank wear of the tip was measured under a cutting
(lathe cutting) condition of work material: SCM3, cutting velocity
v=120 m/min, feeding rate f=0.4 mm/rev, cutting depth d=2 mm, and
cutting time t=30 min.
[0172] Furthermore, G11, G21 to G24 were PVD-coated with 2 .mu.m
TiC+3 .mu.m TiN, and subjected to a cutting test. Under a cutting
(lathe cutting) condition of work material: SK5, v=100 m/min, f=0.5
mm/rev, d=2 mm, and t=30 min, the coated cemented carbides using
G11, G21 to G24 were compared for the level of plastic deformation
(shear drop on edge rake face) of the blade after test. The results
are shown in (Table 9).
[0173] The performance of G21 containing free carbons in the
conventional form was inferior to that of G11. However, it is found
that both the cemented carbide and coated cemented carbide having a
high lattice constant and finely dispersed free carbons are
naturally superior to G21, but they are superior to G11 without
free carbons.
* * * * *