WO2021193159A1

WO2021193159A1 - Cutting tool made of wc-based cemented carbide

Info

Publication number: WO2021193159A1
Application number: PCT/JP2021/010161
Authority: WO
Inventors: 佳祐河原; 龍市川; 五十嵐　誠; 岡田　一樹
Original assignee: 三菱マテリアル株式会社
Priority date: 2020-03-26
Filing date: 2021-03-12
Publication date: 2021-09-30
Also published as: EP4129540A4; JPWO2021193159A1; EP4129540A1

Abstract

This cutting tool made of WC-based cemented carbide is characterized in that: 1) said cutting tool contains 8.0-14.0 mass% of Co, 0.1-1.4 mass% of Cr3C2, and 0.6-4.0 mass% of one or more selected from among TaC, NbC, TiC, and ZrC, with the remainder consisting of WC and inevitable impurities; and 2) when the boundary length between WC grains is denoted by L1, the boundary length between a WC grain and a bonded phase or γ phase is denoted by L2, the area ratio of the bonded phase is denoted by V(%), the average grain diameter of WC grains is denoted by D (μm), the theoretical volume fraction of the γ phase is denoted by Vγ, and a WC-WC boundary length ratio is denoted by R, R=(L1)/((L1)+(L2)), R≥(0.76-0.059×D)×(10/V)-Vγ×0.06, and 1.0≤D≤4.0 are satisfied.

Description

WC-based cemented carbide cutting tool

The present invention relates to a WC-based cemented carbide cutting tool (hereinafter, may be referred to as a WC-based cemented carbide tool). This application claims priority under 2020-56624, a Japanese application filed on March 26, 2020. All the contents of the application in Japan are incorporated herein by reference.

Since the WC-based cemented carbide has high hardness and toughness, the WC-based cemented carbide tool using this as a tool base exhibits excellent wear resistance and has a long life over a long period of use. It is used as a cutting tool to have.
On the other hand, in recent years, various proposals have been made to further improve the cutting performance and tool life of WC-based cemented carbide tools according to the type of work material, cutting conditions, and the like.

For example, in Patent Document 1, when the number of WC particles is A and the number of WC particles having one or less contact points with other WC particles is B, B / A ≤ 0.05 is satisfied. A WC-based cemented carbide cutting tool has been proposed, which is said to have improved plastic deformation resistance and a long life in wet continuous cutting of carbon steel and stainless steel.

Further, for example, in Patent Document 2, the amount of Co is 10 to 13% by mass, the ratio of the amount of Cr to the amount of Co is 2 to 8%, at least one of TaC and NbC is 0.2 to 0.5% by mass, and the balance. Is composed of WC and has a hardness of 88.6 to 89.5 HRA, and the ratio D80 / D20 of the WC integrated particle size 80% diameter (D80) and the integrated particle size 20% diameter (D20) in the area ratio on the polished surface is calculated. A WC-based cemented carbide cutting tool having a D80 of 2.0 to 4.0, a D80 of 4.0 to 7.0 μm, and a WC adhesion of 0.36 to 0.43 has been proposed. Is said to prevent adhesion of the work material and improve fracture resistance in cutting difficult-to-cut materials such as stainless steel.

Further, for example, in Patent Document 3, when the WC-WC bonding interface length is L1 and the WC-Co bonding interface length is L2,
R> (0.82-0.086 x D) x (10 / V)
R = (L1) / ((L1) + (L2))
D: The particle size (μm) of WC when the area ratio of WC is 50%, 0.6 ≦ D ≦ 1.5
V: Bonded phase volume (volume%), 9 ≦ V ≦ 14
A WC-based cemented carbide cutting tool that satisfies the above requirements has been proposed, and the tool is said to have improved heat-resistant plastic deformability and toughness in cutting Ni-based heat-resistant alloys.

Japanese Patent No. 6256415 Japanese Unexamined Patent Publication No. 2017-88999 JP-A-2017-179433

The present invention has been made in view of the above circumstances and the above proposals, and in particular, a WC-based cemented carbide cutting tool that exhibits excellent cutting performance over a long period of time even in cutting of stainless steel and the like. The purpose is to provide.

The WC-based cemented carbide cutting tool according to the embodiment of the present invention
1) Co: 8.0 to 14.0% by mass,
Cr ₃ C ₂ : 0.1 to 1.4% by mass,
One or more selected from TaC, NbC, TiC and ZrC: 0.6 to 4.0% by mass
Including
The rest are WC and unavoidable impurities,
2) The interface length between WC particles is L1,
The interface length between the WC particles and the bound phase or γ phase is L2,
The area ratio of the bonded phase is V (%),
The average particle size of WC particles is D (μm),
The theoretical volume fraction of the γ phase is Vγ,
When the WC-WC interface length ratio is R, respectively,
R = (L1) / ((L1) + (L2)),
R ≧ (0.76-0.059 × D) × (10 / V) -Vγ × 0.06,
1.0 ≤ D ≤ 4.0
To be satisfied.

Further, the WC-based cemented carbide cutting tool according to the embodiment may satisfy either or both of the following (1) and (2).

(1) The average particle size of the γ phase is 0.2 to 4.0 μm.
(2) A coating layer is formed on the cutting edge.

According to the above, it is possible to obtain a WC-based cemented carbide cutting tool having excellent high-temperature hardness, plastic deformation resistance, and chipping resistance even in the processing of stainless steel and the like.

It is a schematic diagram which shows an example of the structure of the WC-based cemented carbide cutting tool which concerns on this embodiment. It is a schematic diagram which shows the side surface of the flank surface which shows an example of the measurement of the flank plastic deformation amount of a cutting edge.

The present inventor has recognized the following matters as a result of diligent studies on the WC-based cemented carbide cutting tools described in Patent Documents 1 to 3.

(1) In the WC-based cemented carbide cutting tool proposed in Patent Document 1, the plastic deformation resistance of the WC-based cemented carbide cutting tool is improved by controlling the number of contact points between WC-WC particles. However, the plastic deformation resistance is insufficient.

(2) In the WC-based cemented carbide cutting tool proposed in Patent Document 2, the fracture resistance and adhesion resistance of the WC-based cemented carbide cutting tool are improved by controlling the WC particle size distribution and the like. However, since TaC and NbC are contained only in the range where they are solid-dissolved in the bonding phase, the γ phase formed by them adheres between the WC-WC particles to cause WC-WC interfacial slip. It works to suppress, the high temperature hardness is insufficient, and the tool life is short in turning cutting of stainless steel etc.

(3) According to the WC-based cemented carbide cutting tool proposed in Patent Document 3, although the adhesive interface ratio between WC-WC particles is controlled to improve the plastic deformation resistance. It does not contain the γ phase component, the high temperature hardness is insufficient, and the focus is only on increasing the interface length ratio between the WC-WC particles, and the γ phase adheres between the WC-WC particles. Since the effect of suppressing the grain boundary slip of the WC-WC particles may not be sufficiently obtained, the plastic deformation resistance may be insufficient in the cutting process of stainless steel or the like.

Therefore, the present inventors have conducted diligent studies based on these recognitions. As a result, the following findings (1) to (4) were obtained in the WC-based cemented carbide cutting tool.

(1) After securing a predetermined amount of the bound phase without reducing the Co content forming the bound phase,
Increasing the ratio of the contact length (hereinafter referred to as "WC-WC interface length") at the interface where WC particles having a high Young's modulus contact each other (hereinafter referred to as "WC-WC interface") causes the WC particles to undergo plastic deformation. Acts as a skeleton that interferes with
Furthermore, by including an appropriate amount and an appropriate particle size of γ phase in the WC-based cemented carbide cutting tool, the grain boundary slip at the WC-WC interface is reduced.
Improve the plastic deformation resistance of WC-based cemented carbide cutting tools.

(2) When the average particle size of the WC particles is coarser than a predetermined value, the ascending motion of the blade-shaped dislocations in the bonded phase is suppressed, and in addition, Cr ₃ C ₂ is contained in the bonded phase. Since the bonded phase is solid-solved and strengthened by being contained, the plastic deformation resistance of the WC-based cemented carbide cutting tool is further improved.

(3) By containing at least one of Ta, Nb, Ti, and Zr, which are γ phase forming elements, in the bonded phase, excellent oxidation resistance and high temperature hardness are exhibited.

(4) When a WC-based superhard alloy cutting tool satisfying the above (1) to (3) is used for cutting a difficult-to-cut material such as stainless steel, the cutting tool has plastic deformation resistance and high-temperature hardness. Is improved, so that the occurrence of abnormal damage such as chipping due to deformation of the cutting edge of the tool and plastic deformation is suppressed, and the presence of the γ phase improves oxidation resistance and high temperature hardness. The life of the cutting tool should be extended.

Based on these findings, "WC-WC interface length" and "WC- (bonded phase or γ phase: bonded phase + γ phase) interface length" in a WC-based superhard alloy cutting tool is "" When the ratio R (WC-WC interface length ratio) of "WC-WC interface length" has a specific relationship with the area ratio of the bonded phase, the average WC particle size, and the theoretical volume ratio of the γ phase, the above-mentioned problem is solved. He found that it could be solved.

Hereinafter, the WC-based cemented carbide cutting tool according to the embodiment of the present invention will be described in detail.
In addition, in the present specification and claims, when a numerical range is expressed by "LM" (both L and M are numerical values), the range includes an upper limit value (M) and a lower limit value (L). The unit of the upper limit value (M) and the lower limit value (L) is the same. In addition, the numerical values include tolerances.

1. 1. Component composition The component composition will be described.

(1) Co
Co is contained as a component of the main binding phase. If the Co content is less than 8.0% by mass, the WC-based cemented carbide cutting tool cannot have sufficient toughness, while if the Co content exceeds 14.0% by mass, it rapidly softens and cuts. The desired hardness required for a tool cannot be obtained, and deformation and wear progress become remarkable. Therefore, the Co content in the WC-based cemented carbide cutting tool is preferably 8.0 to 14.0% by mass. The Co content is more preferably 8.5 to 12.0% by mass.

The bonded phase may contain W, C, and other unavoidable impurities. Further, Cr and at least one of Ta, Nb, Ti, and Zr, which are elements of the metal component constituting the γ phase, may be contained. When these elements are present in Co, it is presumed that they are in a solid solution state in Co.

Co has two types of crystal structures, an fcc structure and an hcp structure, and contains at least one of Ta, Nb, Ti, and Zr, which are elements of metal components constituting W, C, Cr, and the γ phase. However, the bound phase also has an fcc structure and an hcp structure, similarly to Co, which is a forming component of the main bound phase. Therefore, the bonded phase regions having these two crystal structures in the WC-based cemented carbide cutting tool are referred to as a bonded phase (fcc) and a bonded phase (hcp), respectively.

(2) Cr ₃ C ₂
Cr ₃ C ₂ is preferably contained in an amount of 0.1 to 1.4% by mass. Cr ₃ C ₂ is solid-solved as Cr in Co that mainly forms a bonding phase, and Co is solid-solved and strengthened to increase the strength of the WC-based cemented carbide cutting tool. This action is _{insufficient when the Cr 3} C ₂ content is less than 0.1% by mass, while when the content exceeds 10% with respect to the Co content, Cr is precipitated as a composite carbide with W. However, since there is a risk of a decrease in toughness and a starting point for the occurrence of defects, the upper limit of Co content of 14.0% by mass is taken into consideration, and 1.4% by mass, which is 10% of the upper limit, is the content of _{Cr 3} C _2. The upper limit of.

(3) TaC, NbC, TiC, ZrC
It is preferable to contain at least one or two or more selected from TaC, NbC, TiC and ZrC in a total amount of 0.6 to 4.0% by mass. All of these components are also components constituting the γ phase.

Part of the metal elements of these components are dissolved in Co forming the main bonding phase, thereby improving the high temperature hardness of the bonding phase. On the other hand, the metal elements of these components do not dissolve in the bonded phase and are present as a γ phase (which may further contain W in addition to the metal elements of these components), which is a carbide phase, so that they are oxidation resistant. It has a function of enhancing properties and crater wear resistance, and adheres to the WC-WC interface to suppress grain boundary slip at the WC-WC interface.

If the total content of these metal components in terms of carbide (carbide in which the metal component and carbon are bonded at a ratio of 1: 1) is less than 0.6% by mass, the above-mentioned function is insufficient, while 4.0 mass. If it exceeds%, aggregates are likely to be formed, which may be a starting point for the occurrence of defects. Therefore, the total content is preferably 0.6 to 4.0% by mass.

Further, the average particle size of the γ phase is more preferably 0.2 to 4.0 μm, which makes the contact frequency with the WC particles appropriate. The average particle size of the γ phase is at least 300 by mirror processing any surface or cross section of a WC-based cemented carbide cutting tool, observing the processed surface with a scanning electron microscope (SEM), and performing image analysis. The area of each γ phase is obtained, and the diameter of a circle equal to the area is calculated and averaged. For mirror surface processing, for example, a focused ion beam device (FIB device), a cross section polisher device (CP device), or the like is used.

_{The contents of Cr 3} C ₂ and TaC, NbC, TiC, and ZrC described above are the Cr amount, Ta amount, and Nb amount measured by an electron probe microanalyzer (EPMA) for a WC-based cemented carbide cutting tool. , Ti amount, and Zr amount are all numerical values converted as the carbides.

(4) WC
WC is a residual component and may contain unavoidable impurities that are unavoidably mixed in during the manufacturing process.
Further, the content ratio of WC is obtained by converting into carbides on the assumption that W and C are combined at a ratio of 1: 1.

(5) Inevitable Impurities As described above, the remaining components and the bonding phase may contain impurities that are inevitably mixed in during the manufacturing process, and the amount thereof is 100% by mass for the entire WC-based cemented carbide cutting tool. When this is done, the outer number is preferably 0.3% by mass or less.

2. Structure The sintered body structure of the WC-based cemented carbide cutting tool has a WC-WC interface length ratio (R value), a WC area average particle size (D) (μm), and a bonded phase area ratio (V), γ. It is defined by the phase theoretical volume ratio.

The details will be described below.

(1) WC-WC interface length ratio (R)
Since the WC-WC interface length ratio (R) is high, WC particles with a high Young's modulus act as a skeleton that hinders plastic deformation, so that a WC-based cemented carbide cutting tool with excellent plastic deformation resistance can be obtained. be able to.

The WC-WC interface length ratio (R) is R = (L1) / ((L1) + (L2)) when the WC-WC interface length is L1 and the WC- (bonded phase + γ phase) interface length is L2. Can be obtained by.
Here, the WC-WC interface length is the interface length between WC particles, and the WC- (bonding phase + γ phase) interface length is the interface length between the WC particles and the bonding phase and the WC particles and the γ phase. ..

As described above, the bonded phase contains Co as a main component and the metal elements (Ta, Nb, Ti, Zr) of the W, C, Cr, and γ phase components are solid-dissolved, and the γ phase is Ta, Nb, Ti. , Zr, one or more of the carbide phases formed mainly of the metal element of the γ phase component.

A method for measuring the WC-WC interface length L1 and the WC- (bonded phase + γ phase) interface length L2 will be described with reference to FIG.
That is, an arbitrary surface or cross section of a WC-based cemented carbide cutting tool is ion-milled, and the processed surface is observed with a scanning electron microscope (SEM) equipped with a backscattering electron diffractometer (EBSD). I do. The size of one observation field of view is 24 μm × 72 μm, and an electron beam is transmitted to measurement points (expressed as points, which are regular hexagonal regions) in the field of view at intervals of 0.1 μm in the two-dimensional direction. Irradiate. The number of visual fields is set to a plurality so that the number of WC particles (1) is 4000 or more. Then, the WC particles (1), the bound phase (hcp) (3), the bound phase (fcc) (4), and the γ phase (5) are identified based on the EBSD pattern obtained by irradiating the electron beam.

At this time, since the γ phase (5) has an fcc structure, it cannot be separated from the bound phase (fcc) (4), and is actually as the bound phase (fcc) (4) + γ phase (5). Be identified.

As shown in FIG. 1, when adjacent WC particles (1) have an orientation difference of 2 ° to 180 °, the length of the interface is defined as the WC-WC interface (2) length L1.
The length of the interface where the WC (1) grain and the bound phase (hcp) (3) are adjacent to each other is the length of the WC-bonded phase (hcp) interface (6) length L2-1.
The length of the interface where the WC (1) grain and (bonded phase (fcc) (4) + γ phase (5)) are adjacent to each other is defined as WC- (bonded phase (fcc) + γ phase) interface (7) length L2-2. do.
Further, L2, which is the WC- (bonded phase + γ phase) interface length, is the sum of L2-1 and L2-2.

(2) Average particle size of WC particles (D)
The average particle size D (μm) of the WC particles is preferably 1.0 μm to 4.0 μm. By setting the average particle size D of the WC particles in this range, it is possible to obtain a WC-based cemented carbide sintered body structure in which plastic deformation due to the ascending motion of blade-shaped dislocations at a high temperature is unlikely to occur. The average particle size D (μm) of the WC particles is more preferably in the range of 1.6 to 3.0 μm or less.

Here, the average particle size D (μm) of the WC particles is obtained by ion-milling an arbitrary surface or cross section of a WC-based cemented carbide cutting tool in the same manner as when deriving the average particle size of the γ phase. The machined surface is determined by measuring with an SEM equipped with EBSD. That is, the area of at least 4000 individual WC particles in the observation area is determined by setting measurement points at intervals of 0.1 μm in the two-dimensional direction in a field having a size of 1 field of 24 μm × 72 μm. The measurement is performed, the WC particles are approximated to a circle having the same area, the area ratio occupied by the WC particles having the diameter is calculated together with the diameter, and the sum of the values obtained by multiplying the diameter and the area ratio of each WC particle is obtained.

(3) Area ratio of bonded phase (V)
The area ratio of the bonded phase is obtained on the premise that the area ratio of the bonded phase on the two-dimensional plane is the same in the three-dimensional direction. Multiple (for example, 3 fields of view) fields of view are selected on any surface or cross section of a WC-based superhard alloy cutting tool that has been mirror-finished, and an electrolytic emission scanning electron microscope (FE-SEM) is used in each field of view. Using, observation is performed at 2000 to 3000 times, a reflected electron image is taken, the image is binarized by image processing, the WC particles and the γ phase and the bound phase are separated, and the area of the bound phase with respect to the entire field of view of photography. Find the rate.

(4) Theoretical volume fraction of γ phase (Vγ)
The theoretical volume ratio Vγ of the γ phase has TaC, NbC, TiC, and ZrC densities of 14.4, 7.82, 4.92, and 6.66, respectively (Ge We Samsonov (Author), Lee M. Vinicky (Author), Japan-Soviet Newsletter Translation Department (Translation) "Databook Refractory Compounds Handbook", Japan-Soviet Union, December 1977), TaC, NbC, TiC measured by EPMA, Each content (mass%) of ZrC is obtained as the sum of the numerical values divided by the respective densities.

(5) Relationship between WC-WC interface length ratio (R), bonded phase area ratio (V), WC area average particle size (D) and theoretical volume ratio (Vγ) of γ phase WC-WC interface length ratio (R) ) Is a relational expression defined by the area ratio (V) (%) of the bonded phase, the WC area average particle size (D) (μm), and the theoretical volume ratio (Vγ) of the γ phase, that is, R ≧ (0). It is preferable to satisfy .76-0.059 × D) × (10 / V) −Vγ × 0.06.
When this relationship is satisfied, it exhibits excellent plastic deformation resistance and chipping resistance.

The upper limit of R is not particularly limited, but is preferably 0.70, more preferably 0.60. When R is not more than this upper limit value, minute chipping of the cutting edge can be suppressed more reliably.

3. 3. Manufacturing Method The WC-based cemented carbide cutting tool according to the present embodiment can be manufactured, for example, through the following steps (1) to (3).

(1) Mixing with raw material powder Two types of WC powder with different particle size distributions (WC powder with the mode of particle size distribution r1 (μm) and WC powder with the same particle size distribution r2 (μm), where r1> r2) is blended so as to have a predetermined blending ratio and a predetermined particle size ratio, _{a raw material powder composed of Co powder and Cr 3} C ₂ powder is blended, and further, TaC powder, NbC powder, TiC powder, ZrC powder. A raw material powder containing one or more of the powders is added.

Then, for example, a mixed powder is prepared by blending and mixing under conditions that do not apply a large crushing force by medialess mixing such as an attritor with a reduced amount of media, preferably an ultrasonic homogenizer, or a cyclone mixer.

It is preferable that the ratio of the most frequent values of the particle size distribution, that is, r2 / r1 satisfies 0.15 to 0.60 for the blending of the two types of WC powders.

(2) Preparation and Sintering of Molded Body The mixed powder is molded to prepare a powder compact, and the powder compact is heated in a vacuum atmosphere at a heating temperature of 1300 to 1450 ° C., more preferably 1300 to 1400. Sintering is performed under the conditions of ° C. and heating holding time: 15 to 90 minutes, more preferably 15 to 60 minutes. As a result, changes in the shape and particle size distribution of WC particles due to grain growth are suppressed. After sintering, a solid phase sintering step of heat treatment at 1100 to 1200 ° C. for 5 to 100 hours is performed to increase the degree of adhesion between WC particles by diffusion of grain boundaries. This solid phase sintering step may be continuously performed after sintering, or may be performed once cooling is completed. As the atmosphere, an inert gas, a reducing gas atmosphere, or the like can be used, but it is preferable to carry out the atmosphere under vacuum.

(3) Post-treatment The sintered body is machined and ground to produce a WC-based cemented carbide cutting tool having a desired size and shape.

(4) at least in the cutting edge portion of forming the WC-based cemented carbide cutting tools of the coating layer, Ti-Al-based, Al-Cr-based carbides, nitrides, carbonitrides or _Al 2 _{O 3,} or the like coating layer May be produced by forming a coating by a film forming method such as PVD or CVD to produce a cutting tool made of a surface-coated WC-based cemented carbide.
When manufacturing a cutting tool made of a surface-coated WC-based cemented carbide, the type of film and the film forming method may be those already well known to those skilled in the art.

Next, the present invention will be described with reference to examples, but the present invention is not limited to the examples.

An example was prepared by the following procedure.

(1) Mixing with raw material powder As raw material powder for sintering, two types of WC powder with different particle size distribution (coarse grain WC powder having the most frequent value of particle size distribution of r1 (μm) and the most of the particle size distribution Shikichi is an r2 fine WC powder is ([mu] m)), was prepared Co powder, _Cr 3 _{C 2} powder, TaC powder, NbC powder, a TiC powder and ZrC powder.

Table 1 shows the compounding composition (mass%) of various powders, and also shows the mode values and the ratios of the particle size distributions of the two types of WC powders. The average particle size (D50) of the Co powder, Cr ₃ C ₂ powder, TaC powder, NbC powder, TiC powder, and ZrC powder was all in the range of 1.0 to 3.0 μm. Further, the unavoidable impurities were 0.3% by mass or less as an outside number when the entire cutting tool made of WC-based cemented carbide was taken as 100% by mass.

(2) Preparation of molded product The sintering powder blended in the compounding composition shown in Table 1 is wet-mixed at a rotation speed of 50 rpm for 8 hours by medialess attritor mixing, dried, and then press-molded at a pressure of 100 MPa. A powder compact was produced.

(3) Sintering After sintering these powder compacts at a heating temperature of 1340 to 1440 ° C. shown in Table 3 and a heating holding time of 0.5 to 1.5 hours in a vacuum atmosphere. In order to increase the degree of adhesion between WC particles due to intergranular diffusion, solid-phase sintering was continuously carried out at 1100 to 1200 ° C. for 10 to 100 hours to prepare a sintered body.

(4) Post-treatment The sintered body is machined and ground, and the WC-based cemented carbide cutting tools 1 to 10 (hereinafter referred to as Examples 1 to 10) shown in Table 5 of the insert shape of CNMG120408-GM are used. Made.

For comparison, WC-based cemented carbide cutting tools 11 to 18 (hereinafter referred to as Comparative Examples 11 to 18) shown in Table 6 were manufactured.
In the manufacturing process, as shown in Tables 2 and 4, the blending composition (mass%), mixing conditions, or sintering conditions were changed with respect to the examples. The unavoidable impurities were 0.3% by mass or less as an outside number when the entire cutting tool made of WC-based cemented carbide was taken as 100% by mass.

Subsequently, with respect to the cross sections of the WC-based cemented carbide cutting tools of Examples 1 to 10 and Comparative Examples 11 to 18, the contents of Co, Cr, Ta, Nb, Ti, and Zr, which are the components thereof, are set to 10 by EPMA. Point measurement was performed. The average value was taken as the content of each component. The results are shown in Tables 5 and 6.
The contents of Cr, Ta, Nb, Ti, and Zr were calculated by converting them into carbides.

Next, the cross sections of the WC-based cemented carbide cutting tools of Examples 1 to 10 and Comparative Examples Tools 11 to 18 were observed by the SEM equipped with EBSD by the method described above, and the WC-WC interface length L1 was observed. Then, the WC- (bonded phase + γ phase) interface length L2 was measured, and the WC-WC interface length ratio (R value) was calculated. Moreover, the WC area average particle diameter D (μm) was determined. The results are shown in Tables 5 and 6.

Further, regarding the bonded phase area ratio V (%), in the cross section of the WC-based cemented carbide cutting tool of Examples 1 to 10 and Comparative Examples 11 to 18, a field of view containing 300 or more WC particles per field of view. In, three visual fields are selected, an observation image is taken using an FE-SEM (field emission scanning electron microscope), binarized by image processing, the WC particle + γ phase and the bound phase are separated, and the bound phase is separated. The area ratio of was calculated. The results are shown in Tables 5 and 6.

Regarding the particle size of the γ phase, the area of each γ phase was measured in the vertical cross section of the WC-based cemented carbide cutting tool of Examples 1 to 10 and Comparative Examples 11 to 18 by the method described above, and γ was measured. The average particle size of the phase was calculated. The results are shown in Tables 5 and 6.

Furthermore, the theoretical volume fraction (Vγ) of the γ phase is as described above, and the results are shown in Tables 5 and 6.

Next, with respect to Examples 1 to 10 and Comparative Examples 11 to 18, the following wet continuous cutting test was performed with the tip of the tool steel cutting tool screwed with a fixing jig.

Work material: JIS / SUS304 (HB170) round bar Cutting speed: 100 m / min
Notch: 2.0 mm
Feed: 0.7mm / rev
Cutting time: 5 minutes Wet water-soluble cutting oil is used

The amount of plastic deformation of the flank of the cutting edge after the wet continuous cutting test was measured, and the state of wear of the cutting edge was observed. The amount of plastic deformation of the flank surface of the cutting edge (10) is determined by scooping the flank surface (8) on the main cutting edge side of the tool with the flank surface (8) on the main cutting edge side at a position sufficiently distant from the cutting edge (9). A line segment (11) is drawn on the ridge line where the surfaces (12) intersect, and the same line segment is extended in the direction of the cutting edge portion, and the distance between the extended line segment and the ridge line of the cutting edge portion (vertical direction of the extended line segment). ) Was measured and used as the flank plastic deformation amount (10) of the cutting edge. Further, when the flank plastic deformation amount was 0.04 mm or more, the worn state was defined as the cutting edge deformation (see FIG. 2).
Table 7 shows the measurement results.

Further, a coating layer having an average layer thickness shown in Table 8 was formed on the cutting edge surfaces of Examples 1 to 4 and Comparative Examples 11 to 14 by a PVD method or a CVD method, and Examples 21 to 24 and Comparative Examples 31 to 31 to were formed. 34 was made.

For Examples 21 to 24 and Comparative Examples 31 to 34, the wet continuous cutting test shown below was carried out, the flank plastic deformation amount of the cutting edge was measured in the same manner, and the wear state of the cutting edge was observed.

Cutting conditions:
Work material: JIS / SUS304 (HB170) round bar Cutting speed: 150 m / min
Notch: 2.0 mm
Feed: 0.7mm / rev
Cutting time: 5 minutes Wet water-soluble cutting oil used Table 9 shows the results of the cutting test.

According to the test results shown in Tables 7 and 9, it can be seen that all of the examples exhibit excellent chipping resistance and plastic deformation resistance without causing chipping.
On the other hand, all of the comparative examples were inferior in chipping resistance and plastic deformation resistance, and reached the end of their life in a short time.

The disclosed embodiment is merely an example in all respects and is not restrictive. The scope of the present invention is indicated by the scope of claims rather than the embodiment described above, and is intended to include meaning equivalent to the scope of claims and all modifications within the scope.

1 WC particle 2 WC-WC interface 3 Bonded phase (hcp)
4 Bonding phase (fcc)
5 γ phase 6 WC-bonded phase (hcp) interface 7 WC- (bonded phase (fcc) + γ phase) interface 8 Main cutting edge side flank surface 9 Cutting edge 10 Spacing amount of flank surface 11 Intersection of flank surface and rake face Line segment 12 rake face that extends the ridgeline

Claims

1) Co: 8.0 to 14.0% by mass,
Cr 3 C 2 : 0.1 to 1.4% by mass,
One or more selected from TaC, NbC, TiC and ZrC: 0.6 to 4.0% by mass
Including
The rest are WC and unavoidable impurities,
2) The interface length between WC particles is L1,
The interface length between the WC particles and the bound phase or γ phase is L2,
The area ratio of the bonded phase is V (%),
The average particle size of WC particles is D (μm),
The theoretical volume fraction of the γ phase is Vγ,
When the WC-WC interface length ratio is R, respectively,
R = (L1) / ((L1) + (L2)),
R ≧ (0.76-0.059 × D) × (10 / V) -Vγ × 0.06,
1.0 ≤ D ≤ 4.0
A WC-based cemented carbide cutting tool characterized by satisfying.
The WC-based cemented carbide cutting tool according to claim 1, wherein the average particle size of the γ phase is 0.2 to 4.0 μm.
The WC-based cemented carbide cutting tool according to claim 1 or 2, wherein a coating layer is formed on the cutting edge.