KR20150111476A - Sintered body of cemented carbide for cutting tools - Google Patents

Abstract

The present invention relates to a hard-metal sintered body for a cutting tool capable of cutting objects using a sharp knife tip by controlling fine particles of a hard-metal sintered body, obtaining excellent toughness and preventing the separation of carbides particles, and minimizing a decrease in damage resistance while improving chipping resistance and durability and, more specifically, to a hard-metal sintered body for a cutting tool suitable for the cutting tool. The hard-metal sintered body for the cutting tool according to the present invention comprises 75-90 wt% of WC, 8-13 wt% of Co, 1-12 wt% of carbides of 4a and 5a group elements or 6a group elements, and at least one kind of additives selected from nitrides and carbonitrides. The present invention is characterized by a fact that the fine particles of the sintered body include 70% or higher of the particles with a size of 3μm or less with respect to the total area of the WC particles, and the particles of which 90% or higher of an interface is in contact with the WC particles while being in no contact with the Co is 70% or higher with respect to the total area of the particles of the additives.

Description

Technical Field [0001] The present invention relates to a sintered body for a cutting tool,

The present invention relates to a cemented carbide sintered body for a cutting tool, and more particularly, to a cemented carbide sintered body for a cutting tool, which can control the microstructure of a cemented carbide body, To a cemented carbide sintered body which is particularly suitable for cutting tools by minimizing deterioration of breakage resistance.

The cemented carbide for cutting tool is a typical dispersion type alloy of WC hard phase and Co bonded metal phase and its mechanical properties basically depend on the grain size of WC hard phase and the amount of Co bonded metal phase and hardness and toughness are inversely proportional to each other There is a relationship.

In addition, at the time of cutting, a high temperature environment is formed by a large amount of heat due to the friction between the cutting tool and the workpiece. In order to increase the high temperature hardness and prevent the plastic deformation in response to such high temperature environment, Carbides made of other metals Contain a certain amount of so-called tartanite.

Generally, at the time of processing stainless steel or other hard materials, the lifetime of the cutting tool is terminated due to the build-up edge due to uneven chip discharge and thin film damage and particle drop due to repetition of fine welding and detachment.

Accordingly, there is a demand for a sintered body for cemented carbide that has a fine WC grain structure to such an extent that a sharp edge shape can be formed, and at the same time, has high toughness and high heat resistance, in order to improve the service life of a cutting tool during processing of a hard material such as stainless steel .

However, when the WC particles are made finer, it is advantageous to form a sharp edge, and hardness can be obtained by improving the hardness due to grain refinement. However, since the specific surface area is increased and weakened by plastic deformation due to slip, There is a problem that the fracture property is deteriorated.

In addition, while tartanization enhances high temperature properties and enhances heat resistance during cutting, the low thermal conductivity of tartaric material and the low wettability of WC and Co induce local high temperature to induce particle dropout and form on the surface of cemented carbide There is a problem that the adhesion to the functional thin film is also lowered.

For this reason, there is a demand for development of a cemented carbide sintered body for a cutting tool capable of sharp edge sharpening, good toughness and preventing dropout of tartan powder, thereby minimizing the deterioration of breakage resistance while improving chipping and abrasion resistance , So far, the development of a hardened carbide sintered body corresponding thereto has been limited.

The following patent documents disclose methods for controlling the WC particle size, the size of the titanate particles, the size of the Co bond phase, the composition of the sintered body, and the like in order to achieve the properties of chipping resistance, high heat resistance and high toughness. However, There is a limitation in that it is possible to perform sharp edge processing and to prevent breakage resistance and dropout of tartan powder.

Korean Patent Registration No. 10-0645409 Korean Patent Publication No. 10-0584702

The present invention relates to a method of controlling the microstructure of a cemented carbide by controlling the microstructure of a cemented carbide while suppressing grain boundary slip and using the fine grain WC to improve breakage resistance and reduce the addition amount of the titanate, Which is capable of suppressing a decrease in the degree of adhesion of a thin film formed on the cemented carbide sintered body, thereby improving the service life of the cutting tool.

As a means for solving the above problems, the present invention provides a method for producing a carbide, a nitride, a nitride and a nitride of WC, 75 to 90% of WC, 8 to 13% of Co, and 1 to 12% of 4a, 5a or 6a group elements, And at least one additive selected from the group consisting of carbon nanotubes, carbonitride, and carbonitride, wherein in the microstructure of the sintered body, particles having a size of 3 m or less in the particles of the WC are 70% , 90% or more of the interface is not in contact with Co, and particles contacting with WC are 70% or more of the total additive particle area.

In the sintered body according to the present invention, 70% or more of the additive particles existing within a depth of 5 占 퐉 from the surface portion of the sintered body may have a size of 2 占 퐉 or less.

In the sintered body according to the present invention, when the additive particles existing within a depth of 5 占 퐉 from the surface portion of the sintered body were observed with a scanning microscope, when a thin film was formed on the surface portion in an area of 30 占 퐉 25 占 퐉 The number of additive particles in contact with the thin film may be 3 or less.

Since the present invention is made of fine WC particles through the control of the microstructure as described above, sharp edge processing is possible and high hardness can be obtained.

Also, the sintered body according to the present invention suppresses particle dropout of tartanide by controlling the microstructure of the tartanate, specifically, by making the material contacted with the tartanite to have a greater WC than Co and minimizing the amount of the tannate bound to the surface. And the adhesion of the thin film can be increased.

1A shows a microstructure of a cemented carbide sintered body according to an embodiment of the present invention.
Fig. 1B shows the microstructure of the cemented carbide sintered body according to the comparative example.
2A shows a microstructure of a surface portion of a sintered body of a cemented carbide sintered body according to an embodiment of the present invention.
2B shows the microstructure of the surface portion of the sintered body of the cemented carbide body according to the comparative example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

In the present invention, 'particle size of WC' and 'particle size of additive' are the diameters of the maximum inscribed circle inside the particle shape, and the particle size is determined by scanning electron microscopy (SEM) And a size within an area (30 占 25 占 퐉) observed at 3000 magnification.

The 'area fraction' is based on an area of a microstructure of 30 μm × 25 μm observed by a scanning electron microscope.

In addition, among the additive particles, "at least 90% of the interface of the interface with the WC without contact with Co" refers to a particle in contact with the WC in the microstructure observed by a scanning electron microscope Refers to particles having a length in which at least 90% of the total length of the interface is in contact with WC, and less than 10% is a length in contact with Co.

The inventors of the present invention have studied about a method capable of suppressing the dropout of tartanide and preventing the peeling of the thin film formed on the surface of the cemented carbide sintered body without reducing the content of the tantalum particles contained in the sintered body of the cemented carbide, , When tartanized particles are brought into contact with mainly WC and the size of the talcum particles is controlled to a predetermined size or less from the surface of the sintered body to a predetermined depth and the tantalum particles contacting the surface of the sintered body are minimized, And the peeling of the thin film can be minimized, and the life of the cutting tool can be considerably improved, leading to the present invention.

The cemented carbide sintered body according to the present invention is a carbide, nitride and carbonitride of WC of 75 to 90%, Co of 8 to 13%, and a group 4a, 5a or 6a group of 1 to 12% by weight, Wherein at least 90% of the boundaries of the WC particles have a particle size of not more than 3 mu m and not more than 70% of the total WC particle size, The particles contacted with the WC without contact are 70% or more of the total additive particle area.

First, the reason for limiting the composition of the hard metal alloy sintered body will be described.

When the content of WC is less than 75% by weight, hardness, which is an advantage of cemented carbide, is significantly lowered. When the content of WC is more than 90% by weight, intrinsic toughness and heat resistance of the sintered body are very poor and it is difficult to simultaneously improve cutting toughness and wear resistance By weight and 75 to 90% by weight, respectively.

When the content of Co is less than 8% by weight, it is difficult to obtain a dense sintered body due to the lack of the liquid phase volume ratio in the liquid phase sintering (in particular, the more the WC-bonded phase particles are fine), and when it exceeds 13% by weight, , It is preferably in the range of 8 to 13% by weight.

If the content of the additive is less than 1% by weight, it is difficult to improve the heat resistance and the abrasion resistance. If the additive content exceeds 12% by weight, the physical properties of the entire sintered body are deteriorated due to the poor self-characteristics (wettability with the binding phase, etc.) This is not a problem when processing a general steel, but problems such as chipping and breakage frequently occur when a hard material such as stainless steel is machined.

When the particles having a size of 3 탆 or less of the WC particles are less than 70% of the total WC particle area, the true toughness is relatively good, but the wear resistance is lowered and the chipping phenomenon caused by welding during the processing of hard materials such as stainless steel It frequently decreases the processing stability, and therefore, it is preferably 70% or more.

In addition, among the above additive particles, if particles 90% or more of the interface are not in contact with Co and contacted with WC is less than 70% of the total additive particle area, dropouts of the additive particles can easily occur and cracks can easily spread So that the intrinsic toughness may be deteriorated. Moreover, since the intergranular slip easily occurs and plastic deformation may easily occur, it is preferable that the tensile strength is 70% or more.

In addition, when the size of the additive particles existing within a depth of 5 占 퐉 from the surface portion of the sintered body is large, the particles may easily fall off or the thin film formed on the surface of the sintered body may easily peel off. Therefore, at least 70% .

Further, when additive particles existing within a depth of 5 占 퐉 from the surface portion of the sintered body were observed with a scanning microscope, when the number of additive particles in contact with the surface portion in an area of 30 占 퐉 25 占 퐉 was large, The peeling of the thin film formed on the substrate can be easily caused.

[Example]

A WC raw material powder having a particle size of about 0.5 to 1.5 탆 or a WC raw material powder having a particle size of about 0.5 to 1.5 탆 is mixed with a WC raw material powder having a particle size of 1.5 to 4.5 탆 at a ratio of 50 wt% WC powder was prepared so as to have a weight ratio of 70 to 92% by weight.

Further, a TaNbC raw material powder having a particle size of about 0.5 to 1.5 占 퐉 or a TaNbC raw material powder having a particle size of about 0.5 to 1.5 占 퐉 is mixed with a TaNbC raw material powder having a particle size of about 1.5 to 3.0 占 퐉 at a ratio of 50% , TaNbC powder was prepared so as to be 2 to 15% by weight based on the total weight of the sintered body.

Also, Co powders were prepared so that Co powder as a binder phase powder having a particle size of about 1.2 to 1.6 탆 was in a range of 5 to 15 wt% based on the total weight of the sintered body.

The mixed powders were prepared by spray drying for 10 to 15 hours and 5 to 8 hours at this time. The mixed powders were prepared by using three types of CNMG120408-VM, CNMG120408-HS and APMT160408-MM. A total of 20 sintered bodies having different compositions and microstructural characteristics were manufactured by sintering at 1380 캜 at different sintering methods by vacuum sintering or HIP sintering (isotropic sintering) 1.

division Furtherance
(weight%) Starting particle size (탆) Full
Mixing time
(hrs) Sintering
Temperature
(° C) Sintering
system Remarks WC Co TaNbC Furtherance
type WC
Departure particle size TaNbC
Departure particle size One 70 15 15 A 0.5 to 1.5 0.5 to 1.5 10 to 15 1380 HIP Comparative Example 2 75 13 12 B 0.5 to 4.5 0.5 to 1.5 10 to 15 1380 HIP Comparative Example 3 75 13 12 B 0.5 to 1.5 0.5 to 1.5 5 ~ 8 1380 HIP Comparative Example 4 75 13 12 B 0.5 to 1.5 0.5 to 3.0 10 to 15 1380 HIP Comparative Example 5 75 13 12 B 0.5 to 1.5 0.5 to 1.5 10 to 15 1380 vacuum Comparative Example 6 85 10 5 C 0.5 to 4.5 0.5 to 1.5 10 to 15 1380 HIP Comparative Example 7 85 10 5 C 0.5 to 1.5 0.5 to 1.5 5 ~ 8 1380 HIP Comparative Example 8 85 10 5 C 0.5 to 1.5 0.5 to 3.0 10 to 15 1380 HIP Comparative Example 9 85 10 5 C 0.5 to 1.5 0.5 to 1.5 10 to 15 1380 vacuum Comparative Example 10 90 8 2 D 0.5 to 4.5 0.5 to 1.5 10 to 15 1380 HIP Comparative Example 11 90 8 2 D 0.5 to 1.5 0.5 to 1.5 5 ~ 8 1380 HIP Comparative Example 12 90 8 2 D 0.5 to 1.5 0.5 to 3.0 10 to 15 1380 HIP Comparative Example 13 90 8 2 D 0.5 to 1.5 0.5 to 1.5 10 to 15 1380 vacuum Comparative Example 14 92 5 3 E 0.5 to 1.5 0.5 to 1.5 10 to 15 1380 HIP Comparative Example 15 75 13 12 B 0.5 to 1.5 0.5 to 1.5 10 to 15 1380 HIP Example 16 75 13 12 B 0.5 to 1.5 0.5 to 1.5 10 to 15 1380 HIP Example 17 85 10 5 C 0.5 to 1.5 0.5 to 1.5 10 to 15 1380 HIP Example 18 85 10 5 C 0.5 to 1.5 0.5 to 1.5 10 to 15 1380 HIP Example 19 90 8 2 D 0.5 to 1.5 0.5 to 1.5 10 to 15 1380 HIP Example 20 90 8 2 D 0.5 to 1.5 0.5 to 1.5 10 to 15 1380 HIP Example

In Table 1, A type and E type are deviated from the sintered body composition of the present invention, and all other types belong to the sintered body composition range of the present invention.

Microstructure

FIG. 1A shows a microstructure of a cemented carbide sintered body according to an embodiment of the present invention, and FIG. 1B shows a microstructure of a cemented carbide sintered body according to a comparative example.

In Figures 1a and 1b, the brightest tissue is WC, the light gray tissue is tartan, and the darkest black tissue is Co.

As shown in the dotted line in FIG. 1A, in the microstructure of the cemented carbide sintered body according to the embodiment of the present invention, it can be seen that the tartanite is aggregated and most of the interface is in contact with the WC. On the other hand, as shown in a dotted line in FIG. 1B, it is shown that in the microstructure of the cemented carbide superconductor according to the comparative example, the tartanite is also substantially in contact with Co.

FIG. 2A shows the microstructure of the surface portion of the sintered body of the cemented carbide sintered body according to the embodiment of the present invention, and FIG. 2B shows the microstructure of the surface portion of the sintered body of the cemented carbide sintered body according to the comparative example.

2A and 2B, a thin film having a thickness of about 2 mu m is formed on the upper surface of the sintered body. As shown in FIG. 2A, in the microstructure of the cemented carbide sintered body according to the embodiment of the present invention, very fine-sized tartanite (dotted line) is distributed at a depth of about 5 탆 from the surface of the sintered body, And there is hardly any contact between these talc and the thin film formed on the surface of the sintered body. On the other hand, in the microstructure of the cemented carbide sintered body according to the comparative example, a relatively large size of tall cargo is formed at a depth of about 5 탆 from the surface of the sintered body, and these tall cargoes are in contact with the thin film.

Table 2 shows the results of analysis of the microstructure of the cemented carbide sintered body according to the embodiment of the present invention and the cemented carbide sintered body manufactured as a comparative example thereof.

division Microstructure Remarks WC particle size * Tartan cargo ** Surface layer
Tartan cargo *** Tangential
Tartan cargo number **** One 75 70 90 2 Comparative Example 2 40 75 90 0 Comparative Example 3 75 40 85 0 Comparative Example 4 75 75 40 0 Comparative Example 5 70 90 70 7 Comparative Example 6 30 75 90 One Comparative Example 7 85 30 80 0 Comparative Example 8 75 75 35 0 Comparative Example 9 70 90 70 6 Comparative Example 10 40 75 90 0 Comparative Example 11 80 40 85 0 Comparative Example 12 75 80 45 One Comparative Example 13 70 90 70 8 Comparative Example 14 70 75 90 0 Comparative Example 15 70 75 80 One Example 16 90 70 70 3 Example 17 75 75 70 0 Example 18 70 70 95 2 Example 19 80 70 70 3 Example 20 70 90 70 0 Example

* Represents an area fraction (%) of WC particles having a size of 3 탆 or less in the whole WC particles.

** represents the area fraction (%) of particles in contact with the WC over 90% of the interface in the total additive particles

*** represents an area fraction (%) occupied by particles having a size of 2 탆 or less among the additive particles existing within a depth of 5 탆 from the surface portion of the sintered body.

**** indicates that when the additive particles existing within a depth of 5 占 퐉 from the surface portion of the sintered body were observed with a scanning microscope and the surface of the sintered body was in contact with the thin film Number of additive particles

As shown in Table 2, the specimens Nos. 1 and 14 are each implemented in the same manner as the embodiments of the present invention, but the composition is deviated from the embodiment of the present invention. Specimen No. 2 has a microstructure in which WC particles having a size of 3 μm or less occupy 40% of the area fraction (%) of the total WC particles. Specimen No. 3 has a microstructure in which 90% or more of the interface has a low percentage (40%) of the area fraction (%) of particles in contact with WC in the total additive particles. Sample No. 4 has a microstructure in which an area fraction (%) occupied by particles having a size of 2 탆 or less among the additive particles existing within a depth of 5 탆 from the surface portion of the sintered body is as low as 40%. Sample No. 5 was prepared by observing the additive particles existing within a depth of 5 占 퐉 from the surface portion of the sintered body by a scanning microscope and measuring the additive amount of the additive in contact with the thin film when the thin film was formed on the surface portion in an area of 30 占 퐉 25 占 퐉 The number of particles is as large as seven microstructures.

 The specimens Nos. 6 to 13 each have a microstructure different from that of the embodiment of the present invention, such as WC particle size, tartrate, surface layer carbide, or tartrate water contacted with the thin film, as in specimen Nos. 2 to 5.

On the other hand, specimen Nos. 15 to 20 have microstructures having a WC particle size, a tartrate, a surface layer carbide or a thin layer of tartrate in contact with the thin film, and the specimens Nos. 15 and 16, 17 and 18, 19 and 20 have different compositions.

Evaluation of cutting property

On the surface of each of the sintered bodies manufactured as described above, the same TiAlN thin film having a thickness of about 2 탆 was formed by a general PVD method, and the cutting properties of the cemented carbide body were evaluated. The properties of the plastic deformation resistance, the chipping resistance, the fracture resistance and the abrasion resistance were evaluated in the cutting property evaluation, and the concrete evaluation methods are as follows.

≪ Evaluation of plastic deformation resistance &

During machining of alloy steel, the machining speed is lowered and the feed is increased relatively to the continuous machining without the interruption of the large workpiece, and locally high temperature is generated in the cutting tip to check the degree of plastic deformation (R part deflection) before abrupt wear And the degree of plastic deformation was confirmed by processing for 30 seconds. At the end of machining, the degree of plastic deformation (deflection of part R) was set to 0.1 mm or more.

Workpiece: Alloy steel (SCM440, 300 pie cylindrical outer diameter turning machining)

Cutting speed: 150 m / min

Cutting feed: 0.5mm / rev

Cutting depth: 2.0 mm

Coolant: Dry

≪ Evaluation of chipping resistance &

Generally, the milling process of stainless steel takes a large processing load due to the high shear stress. Therefore, chipping of the insert boundary is the main cause of the end of life. Therefore, stainless steel was subjected to shoulder milling, and the machining was performed in units of 200 mm under the following conditions, and the degree of occurrence of chipping in the insert working area was confirmed. The end of machining was defined as the time when chipping occurred.

Workpiece: Stainless steel (STS304, 100X200X300 hexahedron shoulder milling)

Cutting speed: 150 m / min

Cutting feed: 0.2mm / tooth

Cutting depth: ap = 10.0 mm, ae = 5.0 mm

Coolant: Dry

≪ Evaluation of fracture resistance &

The impact resistance evaluation of turning was carried out and the fracture resistance of the insert was evaluated by cross section machining of hexagonal alloy steel. One square face was processed as a unit under the following conditions to proceed to the point at which the insert processing portion was broken.

Workpiece: Alloy steel (SCM440, 100X100X300 hexahedron turning surface of square section)

Cutting speed: 120 m / min

Cutting feed: 0.2mm / rev

Cutting depth: 1.5mm

Coolant: Dry

≪ Evaluation of abrasion resistance &

SKD11 (HRC 40) was selected from the metal molds with high hardness, and the shoulder ring was processed. Mainly mechanical friction wear is the biggest cause of end of life. And the degree of abrasion of the insert portion was checked by processing in the unit of 200 mm under the following conditions. The end of machining was defined as the time when the amount of wear of the insert machining area caused by friction with the workpiece was 0.3 mm or more.

Workpiece: Mold steel (SKD11, 100X200X300 hexahedron shoulder milling)

Cutting speed: 150 m / min

Cutting feed: 0.2mm / tooth

Cutting depth: ap = 10.0 mm, ae = 5.0 mm

Coolant: Dry

The results of the above evaluation are shown in Table 3 below.

division Furtherance
type Evaluation of cutting property Remarks Chipping resistance Breakage resistance Abrasion resistance Plastic deformation One A 2 12 2 2 minutes 00 seconds Comparative Example 2 B 10 11 25 3 minutes 30 seconds Comparative Example 3 B 12 8 27 1 minute 30 seconds Comparative Example 4 B 9 8 29 3 minutes 30 seconds Comparative Example 5 B 8 8 28 3 minutes 30 seconds Comparative Example 6 C 15 15 27 2 minutes 30 seconds Comparative Example 7 C 18 11 29 1 minute 00 seconds Comparative Example 8 C 15 12 30 3 minutes 00 seconds Comparative Example 9 C 10 10 30 2 minutes 30 seconds Comparative Example 10 D 19 13 26 2 minutes 00 seconds Comparative Example 11 D 20 8 31 1 minute 00 seconds Comparative Example 12 D 20 8 32 2 minutes 30 seconds Comparative Example 13 D 12 8 30 2 minutes 00 seconds Comparative Example 14 E 2 (breakage) One 3 (breakage) 2 minutes 30 seconds Comparative Example 15 B 17 10 28 2 minutes 30 seconds Example 16 B 17 10 28 3 minutes 30 seconds Example 17 C 21 13 30 2 minutes 30 seconds Example 18 C 21 13 30 2 minutes 30 seconds Example 19 D 25 10 32 2 minutes Example 20 D 25 10 32 2 minutes Example

As shown in Table 3, in the case of specimen Nos. 1 and 14, the chipping resistance and abrasion resistance were remarkably low because they did not have such a composition as to realize the anti-corrosion property and abrasion resistance required in the present invention.

Specimen Nos. 2 to 5 have the same composition as specimen Nos. 15 and 16, and there are differences in microstructure.

Specifically, specimen Nos. 2 to 5 have microstructures in which any one of the WC particle size, the titanate structure, the surface layer tartan material, and the tartan material layer contacted with the thin film is out of the range specified in the present invention. , There is a large difference in the chipping resistance, and some specimens exhibit significantly lower characteristics than the embodiments of the present invention in terms of breakage resistance and plastic deformation resistance.

Specimen Nos. 6 to 9 are the same in composition as Specimen Nos. 17 and 18, and have a difference in microstructure.

Concretely, Specimen Nos. 6 to 9 have microstructures in which any one of the WC particle size, the titanate structure, the surface layer tartan material, and the tartan cargo layer in contact with the thin film is out of the range specified in the present invention. It shows poor physical properties in comparison with Examples of the present invention in terms of chipping resistance similar to Specimen Nos. 2 to 5, and in the case of the breakage resistance and plastic deformation resistance, some specimens have poor properties .

Specimen Nos. 10 to 13 are the same in composition as Specimen Nos. 19 and 20, and have a difference in microstructure.

Specifically, specimens Nos. 10 to 13 have microstructures in which any one of the WC particle size, the titanate structure, the surface layer titanate, and the tannin coating layer in contact with the thin film is out of the range specified in the present invention. In comparison with the examples of the present invention, similar to the specimen Nos. 2 to 5, the specimens exhibited poor physical properties compared to the embodiments of the present invention, and in terms of fracture resistance, abrasion resistance and plastic deformation resistance, Exhibit poor properties.

That is, when the microstructure according to the embodiment of the present invention is used, the properties of plastic deformation resistance, chipping resistance, breakage resistance and abrasion resistance can be maintained evenly, and can be suitably used particularly for the processing of hard materials such as stainless steel.

Claims (3)

And at least one additive selected from carbides, nitrides and carbonitrides of 75 to 90% WC, 8 to 13% Co, and 1 to 12% of 4a, 5a or 6a elements in weight percent As the sintered body,
Among the microstructure of the sintered body,
Among the particles of the WC, particles having a size of 3 m or less are 70% or more of the total area of the WC particles,
Wherein 90% or more of the interface of the additive particles is not in contact with Co and the particles contacting the WC are 70% or more of the total additive particle area. The method according to claim 1,
Wherein 70% or more of the additive particles existing within a depth of 5 占 퐉 from the surface portion of the sintered body have a size of 2 占 퐉 or less. The method according to claim 1,
When the additive particles existing within a depth of 5 占 퐉 from the surface portion of the sintered body were observed with a scanning microscope, when the thin film was formed on the surface portion in an area of 30 占 25 占 퐉, the number of additive particles Hardened cemented carbide for cutting tools.

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