JP2020094277A - Wc-based super hard alloy and coating cut tool using the same - Google Patents

Abstract

To provide a super hard alloy excellent in durability in high speed processing of a soft steel, and a coating cut tool.SOLUTION: There is provided a WC-based super hard alloy containing, by mass%, Co of 8.5% to 9.5%, Cr of 0.3% to 1.0%, Ta of 1.0% to 3.0% as metal elements, and the balance non-metal elements existing by dissolving or compounding with the metal elements, and inevitable impurities, and having an average particle diameter of WC particles with equivalent circular particle diameter of 0.4 μm or more of 1.0 μm to 2.0 μm, a ratio of a particle diameter D90 at an integrated value of area ratio of 90% in a particle size distribution of the average particle diameter and a particle diameter D10 at integrated value of 10%, D90/D10 of less than 3.2, in which a phase mainly containing Ta is dispersed in a structure, and an average equivalent circular particle diameter of the phase mainly containing Ta is 1.0 μm to 3.0 μm, and a coating cut tool having a hard coated film on a surface of the WC-based super hard alloy.SELECTED DRAWING: Figure 1

Description

The present invention relates to a WC-based cemented carbide and a coated cutting tool using the same.

Conventionally, in cutting of metallic materials, cutting tools coated with a ceramic hard coating with excellent wear resistance and oxidation resistance are widely used, with WC-based cemented carbide having high rigidity and high hardness as the base material. Has been done. In the situation where the load on cutting tools increases as the hardness and work efficiency of work materials increase, heat resistance and chipping resistance not only for hard coatings but also for cemented carbide as the base material Is required to improve. For example, in Patent Documents 1 and 2, it is proposed to improve the chipping resistance of the WC-Co-based cemented carbide to which chromium (Cr) and tantalum (Ta) are added in combination, by making the structure uniform. Has been done.

JP, 2017-88999, A JP, 2013-244588, A

In recent years, further cost reduction and shortening of delivery time have been required in the field of die processing, and also in cutting, high cutting speed and high efficiency using high feed conditions are being promoted.
However, according to the study by the inventors, even when using a conventionally proposed coated cutting tool based on cemented carbide, high-speed cutting of steel or the like, particularly in high-speed processing of mild steel, still chipping or plasticity It was confirmed that there was a problem that the tool life was not sufficient because of deformation.
Therefore, the present inventors have proposed a WC-based cemented carbide and a WC-based cemented carbide that do not cause chipping or plastic deformation as a base material even when high-speed cutting of steel or the like, particularly, high-speed processing of mild steel is performed. It was an issue to be solved to provide a coated cutting tool using.

Then, the present inventors, in the WC cemented carbide as the base material of the coated cutting tool, the content of Co constituting the binder phase, the content of Cr dissolved in the binder phase, and the binder phase. The content of Ta which forms a solid solution or is dispersed in the structure and constitutes the main component phase in a predetermined range is adjusted to a predetermined range. , The average particle size range, and the particle size (D10) for which the integrated value of the area ratio is 10% with respect to the particle size (D90) for which the integrated value of the area ratio in the particle size distribution of the equivalent circle diameter is 90%. The ratio of (D90/D10) to () and the main component phase of Ta are dispersed in the structure, thereby performing high-speed cutting of steel or the like, particularly high-speed processing of mild steel. It was found that the problems of chipping and plastic deformation that occur in the base material at that time can be solved.
Further, the inventors of the present invention further include a hard coating having a TiCN coating including a columnar structure on the surface of the base material and having a predetermined average width on the surface side and including it as a maximum thickness. By providing an Al ₂ O ₃ coating on the TiCN coating, a coated cutting tool having excellent chipping resistance and plastic deformation resistance can be obtained when performing high-speed machining of mild steel. I found it.

The present invention is based on the above findings,
“(1) In mass %, Co as a metal element is 8.5% or more and 9.5% or less, Cr is 0.3% or more and 1.0% or less, and Ta is 1.0% or more and 3.0% or less. And the balance is a WC-based cemented carbide composed of WC and a non-metallic element existing as a solid solution or a combination with the metal element and unavoidable impurities,
The average particle size of WC particles having a circle-equivalent particle size of 0.4 μm or more is 1.0 μm or more and 2.0 μm or less,
When D90/D10, which is the ratio of the particle size D90 at which the integrated value of the area ratio is 90% and the particle size D10 at which the integrated value of the area ratio is 10% in the particle size distribution of the average particle size, is less than 3.2. Yes,
A WC-based cemented carbide, wherein a phase containing Ta as a main component is dispersed in the structure.
(2) A coated cutting tool having a hard coating layer on the surface of the WC-based cemented carbide according to (1) as a base material.
(3) The hard coating layer includes at least a TiCN coating layer, the TiCN coating layer has a columnar structure having columnar particles, and the average width on the surface side of the columnar particles is 1.0 μm or less. The coated cutting tool according to (2), which is a coating layer having the thickest film thickness among them.
(4) The coated cutting tool according to (3), wherein the hard coating layer has an Al ₂ O ₃ coating layer on the TiCN coating layer. It is.

According to the present invention, it is possible to provide a WC cemented carbide base material having excellent durability and a coated cutting tool using the same in high-speed machining of mild steel.

1 is an electron micrograph (2,000 times) of a polished cross section of a WC cemented carbide base material of Example 1. 4 is an electron micrograph (2,000 times) of a polished cross section of a WC cemented carbide base material of Comparative Example 3.

The present inventors have specifically specified the composition and structure morphology of WC-based cemented carbide that can significantly improve the tool life in high-speed processing of steel, for example, high-speed processing of mild steel, and further the composition and structure of hard coatings. The present invention has been reached by the finding. The details will be described below.

[1] Composition of WC-based cemented carbide <Co content>
Co is a binder phase that holds the WC particles that are hard phases together, and is an element that imparts high toughness to the WC-based cemented carbide.
In the present invention, in high-speed processing of mild steel, in order to reproduce excellent durability, it is necessary to control the Co content within a narrow range, and the metal element content is 8.5 mass% or more and 9.5 mass% or more. Below (hereinafter, "mass %" is simply referred to as "%"), it is added.
If the Co content is less than 8.5%, the toughness of the cemented carbide is reduced. Further, the structure is likely to be non-uniform, and chipping is likely to occur during high-speed processing of mild steel. On the other hand, if the Co content exceeds 9.5%, the hardness and plastic deformation resistance are reduced even if the particle size distribution of WC particles described later is made uniform, so that the durability of the tool during high-speed machining of mild steel is reduced. Markedly reduced.
Therefore, the Co content is specified to be 8.5% or more and 9.5% or less.

<Cr content>
Cr is an element that forms a solid solution in Co and suppresses the grain growth of WC particles in the sintering process to make the structure uniform, and is added as a metal element at 0.3% or more and 1.0% or less. To do.
When the content of Cr is less than 0.3%, grain growth of WC particles is not suppressed, the particle size distribution of WC particles becomes non-uniform, and chipping easily occurs. In addition, since the WC particles have a non-uniform particle size distribution, the Co distribution also becomes non-uniform, and chipping easily occurs.
On the other hand, when the content of Cr exceeds 1.0%, coarse carbides mainly containing Cr are precipitated to reduce the toughness of the cemented carbide.
Therefore, the content of Cr is set to 0.3% or more and 1.0% or less. It is preferably 0.5% or more, and preferably 0.8% or less.

<Content of Ta>
Ta forms a solid solution in Co and suppresses the grain growth of WC particles to homogenize the structure. Further, since the phase having Ta as a main component is dispersed in the structure, the heat resistance can be improved, so that it is added as a metal element at 1.0% or more and 3.0% or less.
When the content of Ta is less than 1.0%, the particle size distribution of the WC particles becomes non-uniform, and the phase containing Ta as a main component dispersed in the structure is small and the heat resistance is lowered. On the other hand, when the content of Ta exceeds 3.0%, the amount of phases containing Ta as the main component becomes too large and the toughness of the cemented carbide is reduced.
Therefore, the content of Ta is set to 1.0% or more and 3.0% or less. It is preferably 2.5% or less, and more preferably 2.0% or less.

<Non-metal element and unavoidable impurities existing in solid solution or in combination with metal element>
The balance of the WC-based cemented carbide is WC which is the main component, non-metal elements which are present as a solid solution or combined with metal elements (Co, Cr, Ta) and unavoidable impurities.
The non-metal element which exists as a solid solution or a combination of metal elements is C, N, etc., and is present in an amount which is not confirmed as a free component by optical microscope observation.
In addition, Fe, Ni, Nb, Al and the like may be contained in trace amounts as raw material powders and inevitable impurities in the mixing and sintering processes.

[2] Microstructure of WC-based cemented carbide <Average particle size of WC particles>
The hardness and toughness of the WC-based cemented carbide have a trade-off relationship, and the toughness tends to decrease as the hardness increases, while the toughness tends to increase as the hardness decreases.
Then, if the Co content of the WC-based cemented carbide is the same, the hardness and toughness are almost determined by the average particle diameter of the WC particles.
The average particle diameter of the WC particles as used herein refers to the average particle diameter of the particle diameter corresponding to a circle (also referred to as “circular equivalent diameter”).
In addition, particularly for WC particles, when fine particles having a particle diameter corresponding to a circle of less than 0.4 μm are included, for example, in D90/D10 described later, it becomes impossible to accurately evaluate the uniformity of the structure. , And the average particle size of particles having a particle diameter corresponding to a circle of 0.4 μm or more.
In high-speed processing of mild steel, if the average particle size of WC particles becomes too fine, the toughness decreases and chipping occurs. On the other hand, if the average particle size of the WC particles becomes too coarse, the hardness decreases and the wear resistance decreases.
Therefore, in the present invention, the average particle size of WC particles having a circle-corresponding particle size of 0.4 μm or more is defined as 1.0 μm or more and 2.0 μm or less. It is preferably 1.2 μm or more, and more preferably 1.8 μm or less.
Then, specifically, the sample is mirror-polished to obtain an average circle-equivalent particle size of WC particles having a circle-equivalent particle size of 0.4 μm or more in a range of 60 μm in length×30 μm in width (1800 μm ² ). Therefore, the average particle size of the WC particles can be evaluated with high accuracy.
The average particle size of the WC particles can be measured using an EBSD (Electron Back Scatter Diffraction) method.
Since noise is included in the measurement of WC particles of less than 0.4 μm, as described above, by defining the particle size of the WC particles to be measured as the average particle diameter of the equivalent circle diameters of WC particles of 0.4 μm or more. evaluated. The area ratio of particles having an equivalent diameter of less than 0.4 μm to the whole is 5% or less.

<WC particles D90/D10>
Here, D90/D10 refers to the ratio of the particle size D10 having an integrated area ratio of 10% to the particle size D90 having an integrated area ratio of 90% in the particle size distribution of the WC average particle size.
In the present invention, in addition to the control of the composition range described above, homogenization of the micro-level structure is important. As described above, the WC-based cemented carbide of the present invention is set to have a specific average grain size in order to secure a high level of hardness and toughness in high-speed cutting of mild steel. However, even if the average particle size is about the same, if the particle size distribution is wide, the micro-level structure becomes non-uniform and chipping easily occurs.
Therefore, in the present invention, as an index for evaluating the uniformity of WC particles on a micro level, the area ratio is integrated with respect to the particle size D90 at which the integrated value of the area ratio is 90% in the particle size distribution of the average particle size. The ratio of particle size D10 at which the value was 10%, that is, D90/D10 was used. If all particles have the same particle size, D90 and D10 have the same particle size, and the value of D90/D10 becomes the minimum value of 1. In a structure with a wide grain size distribution, the value of D90 with a large grain size increases, while the value of D10 with a small grain size decreases, so the value of D90/D10 exceeds 1 and increases. On the other hand, a small value of D90/D10 indicates that the grain size distribution is sharp and uniform.
However, as described above, considering extremely fine WC particles, since the number of fine WC particles is large, it is not possible to accurately evaluate the target WC particles of 1.0 μm or more and 2.0 μm or less, and according to D90/D10, Since the uniformity of the structure cannot be accurately evaluated, WC particles with a circle equivalent diameter of 0.4 μm or more are not taken into consideration without considering extremely fine WC particles with a circle equivalent particle size of less than 0.4 μm uniformly dispersed in the tissue. It was confirmed that the uniformity of the tissue can be accurately evaluated by evaluating the ratio of D10 to D90 of the particles. Then, the average particle size of the WC particles having a circle-equivalent particle size of 0.4 μm or more is set to 1.0 μm or more and 2.0 μm or less, and the particles in which the integrated value of the area ratio in the particle size distribution of the average particle size is 90% By defining D90/D10, which is the ratio of the diameter D90 and the particle size D10 when the integrated value of the area ratio is 10%, to be less than 3.2, the effect of suppressing the occurrence of chipping in the high-speed cutting of mild steel is sufficiently achieved. I found that I can demonstrate it.
Preferably, D90/D10 is set to 3.0 or less, and further, D90/D10 is set to 2.8 or less.

<WC coarse particles, aggregates (macro defects)>
In the above description, the case where WC particles or WC aggregates having a circle equivalent diameter of more than 10 μm are not generated has been described. However, WC particles or WC aggregates having a circle equivalent diameter of more than 10 μm are formed in a part of the tissue, and further, circles. In some cases, WC particles or WC aggregates (macro defects) having an equivalent diameter of more than 30 μm may be produced. Therefore, a method for measuring the average particle diameter when these coarse WC particles or WC aggregates are produced will be described below.
In particular, since chipping easily occurs when the number of macro defects increases, for WC particles or WC aggregates having a circle equivalent diameter of more than 30 μm, 8 or less in the range of 350,000 μm ² (500 μm×700 μm) in the structure observation with an optical microscope. It is preferable that the number be 5 or less, and in the case of WC particles or WC aggregates having an equivalent circle diameter of more than 10 μm, 8 or less.
After satisfying such conditions, a place having an average structure free from macro-defects and WC particles having an equivalent circle diameter of more than 10 μm and WC aggregates is selected and the average particle size is measured.
Specifically, the sample is mirror-polished to obtain circle-equivalent grains in the range of 1800 μm ² (60 μm in length×30 μm in width) free of macro defects and WC particles and WC aggregates having an equivalent circle diameter of more than 10 μm. The average particle size of the circles of WC particles having a diameter of 0.4 μm or more can be obtained, so that the average particle size of the WC particles can be evaluated with high accuracy.

<Ta phase structure (d90/d10)>
In the present invention, the phase containing Ta as a main component dispersed in the tissue can be confirmed by observation with an optical microscope. The phase containing Ta as a main component contains a large amount of W next to Ta, and is mainly present as carbides or carbonitrides. If the average particle size of the phase containing Ta as the main component dispersed in the structure is too small, the heat resistance of the cemented carbide decreases, while if it is too large, the toughness decreases.
Therefore, it is preferable that the phase mainly composed of Ta dispersed in the structure has an average particle diameter corresponding to a circle of 1.0 μm or more and 3.0 μm or more.
The phase containing Ta as a main component contains Ta as a metal element in an amount of 60 mass% or more and W in an amount of 1 to 30 mass %. In the particle size distribution of the phase containing Ta as the main component, d90/d10 is 6 when the particle size at an integrated value of area ratio of 90% is d90 and the particle size at an integrated value of area ratio of 10% is d10. It is preferably less than 0.0. Furthermore, d90/d10 is preferably 5.0 or less.

[3] Coated cutting tool based on WC-based cemented carbide <Formation of hard coating layer>
By coating a hard coating on the above-mentioned cutting tool using WC-based cemented carbide as a base material by a physical vapor deposition method or a chemical vapor deposition method, a coated cutting tool having further excellent durability can be obtained.
In a coated cutting tool applied to high-speed machining of mild steel, at least a TiCN coating is used as a hard coating, and the TiCN coating has a columnar structure, and the average width on the surface side of the columnar particles is 1 μm or less, and the thickness of the TiCN coating is the maximum thickness. Preferably. In particular, by making the TiCN coating having a fine grain structure the maximum thickness, the coating breakage is easily suppressed.
Further, in order to exert the effect of the TiCN film, it is preferable that the film thickness is 5.0 μm or more. On the other hand, if the film thickness becomes too thick, film peeling easily occurs, so it is 8.0 μm or less. Preferably.
Further, it is preferable to provide an Al ₂ O ₃ film having excellent heat resistance and wear resistance on the upper layer of the TiCN film, and the film thickness thereof is preferably 1.0 μm or more and 4.0 μm or less.
By applying the coated cutting tool of the present invention to which such a coating structure is applied to milling of mild steel having an HRC of 40 or less, particularly excellent durability can be exhibited, which is preferable. Further, it is preferable to use at a cutting speed of 200 m/min. preferable.

[4] Method for Producing WC-Based Cemented Carbide An example of the method for producing a WC-based cemented carbide having a microstructure according to the present invention will be shown below, but the production method of the present invention is limited to the following method. There is nothing.
<Mixing process of raw material powder>
Since it is effective to suppress over-pulverization of the WC raw material powder, in the raw material powder mixing step, it is preferable that the raw material powders other than the WC raw material powder are first mixed and then the WC raw material powder is added and mixed. ..
As an example of the mixing conditions, when an attritor is used, the mixing of the WC raw material powder is preferably 0.5 to 5 hours. The mixing of the raw material powders other than the WC raw material powder is preferably 2 to 5 times the mixing time of the WC raw material powder. In addition, the rotation speed of the attritor is preferably 80 to 200 rpm in order to make the structure uniform and suppress over-milling.
Also, if the WC raw material powder used has a low carbonization temperature and is formed by agglomeration of fine powder, the WC particles are over-crushed in the mixing step and the structure becomes non-uniform. The WC raw material powder is preferably a high temperature carbonized raw material carbonized at 1900°C to 2200°C.
On the other hand, even in the case of a WC raw material powder having a high carbonization temperature during the production of the raw material powder and little agglomeration of the fine powder, when the average particle diameter is 5 μm or more, the particle size distribution is widened by pulverization and the structure becomes non-uniform, In that case, it is preferable to use a powder of WC raw material having an average particle size of 2.0 μm or more and 4.0 μm or less as measured by the Fischer method and having less aggregation of fine powder.
<Sintered body manufacturing process>
In the sintering step, a WC-based cemented carbide having excellent characteristics can be obtained by maintaining the sintering temperature in the range of 1350° C. or higher and 1450° C. or lower for about 1 hour.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following Examples.

Example 1 shows a specific method for producing a WC-based cemented carbide base material, and shows the relationship between the component composition and the structure and physical property values of the obtained WC-based cemented carbide base material.
The average particle size of the WC raw material powder to be used, the mixing method, and the mixing ratio of the respective raw material powders were changed for each sample to prepare WC-based cemented carbide base materials as examples of the present invention and comparative examples. (See Table 1 and Table 2.)
First, in Inventive Examples 1, 2, 4, and 5, as the WC raw material powder, WC raw material powder carbonized at a high temperature of about 2000° C. in which aggregation of fine-grained powder is small is used in principle. In Example 3, a carbonization temperature of less than 2000° C. was used, but WC raw material powder with less aggregation and large average particle size was used.
Next, in Inventive Examples 1 to 5, WC powder (average particle size 2.5 to 8.6 μm), Co powder (average particle size 1.2 μm), Cr ₃ C ₂ powder (average particle size 1.0 μm). ), TaC powder (average particle size 1.5 μm) and carbon powder are prepared, and 2% by mass of paraffin wax and ethyl alcohol (water content less than 10%) relative to the total mass of all the raw material powders, and WC powder Other than the above, all other raw material powders were charged into a small-sized attritor, the rotation speed was set to 192 rpm and mixed for 4 hours, then the WC powder was charged and further mixed for 1 hour to prepare a WC mixed slurry.
The average particle size of the powder is a representative value measured by the Fisher method.
Then, the WC mixed slurry was dried by a stationary dryer to obtain granulated powder by a pan granulator. With the obtained granulated powder, a molded body for a base material of a milling insert (WDNT140520-B, a shape in which a breaker was arranged) was molded. After heating and holding at a sintering temperature of 1400° C. for 60 minutes, the mixture was forcibly cooled from the sintering temperature with nitrogen gas to prepare a sintered body made of a WC-based cemented carbide having a medium carbon composition.
On the other hand, Comparative Example 1 uses, as the WC raw material powder, a WC raw material powder carbonized at a high temperature of about 2000° C., in which agglomeration of fine powder is less, but does not include Ta-containing powder, and In Comparative Examples 2 to 3, although the WC raw material powder is carbonized at a high temperature, a WC-based cemented carbide is sintered by using a WC raw material powder having a large grain size and using the same manufacturing method as the example of the present invention. The body was made.
Further, in Comparative Example 4, although the WC raw material powder was carbonized at a high temperature, one having a large particle size was used, and all the raw material powders including the WC powder were charged at the same time and mixed for 3 hours. Using, a sintered body made of WC-based cemented carbide was prepared.
Further, in Comparative Example 5, as the WC raw material powder, the WC raw material powder having an average particle diameter of 2.5 μm is used as in the case of the inventive example 2, but the raw materials other than the WC raw material powder are the same as in the inventive examples 1 to 5. After mixing for a long time, the WC raw material powder is added and further mixing is not performed. Like Comparative Example 4, all the raw material powders including the WC powder are added at the same time, and after mixing for several hours, the WC-based cemented carbide is added. A sintered body made of an alloy was prepared.
Table 1 shows the WC raw material powder used for the production of each sample and the mixing method thereof.

Next, the structure of the sample obtained by subjecting the produced sintered body to mirror finishing was observed with EPMA (JXA-8530F manufactured by JEOL). Then, an EBSD (Electron Back Scatter Diffraction) method was used to measure the cross-sectional area of each WC particle in the range of 30 μm×60 μm, and the particle diameter corresponding to a circle was determined from the value. This is measured at three locations, and for WC particles having a circle-equivalent particle size of 0.4 μm or more, the average particle size and the integrated value of the area ratio in the particle size distribution of the average particle size are 90%. The particle diameter D90, the particle diameter D10 at which the integrated value of the area ratio is 10%, and the ratio of the particle diameter D10 to the particle diameter D90, D90/D10, were obtained and shown in Table 2.
The area ratio of particles having a circle-equivalent diameter of less than 0.4 μm, which was not included in the calculation due to the presence of noise, was about 1 to 2%.
Next, Table 3 shows the physical property values (coercive force (Hc), saturation magnetization (4πσ), hardness (HRA)) of the produced WC cemented carbide.
Conventional examples 1 and 2 are commercially available inserts of the same shape which are applied to milling mild steel.

As is clear from Table 2, Examples 1 to 5 of the present invention having predetermined component compositions and manufactured under the manufacturing conditions described in Table 1 have the desired average particle size and sharpness in the WC phase structure. It had a uniform particle size distribution (D90/D10 value). As shown in Table 3, Examples 1 to 5 of the present invention had a hardness of 90.0 to 91.0 HRA, a coercive force of 180 to 220 (Oe), and a saturation magnetization of 11 to 12.
In Examples 1 to 5 of the present invention, the phase containing Ta as the main component having an average particle diameter corresponding to a circle of 1.0 μm or more and 3.0 μm or less is dispersed in the structure, and the composition of the phase containing Ta as the main component is , Ta was 60 to 80% by mass, and W was 10 to 30% by mass. In addition, in Example 1 of the present invention, in the particle size distribution of the phase containing Ta as a main component, the particle size at which the integrated value of the area ratio is 90% is d90, and the particle size at which the integrated value of the area ratio is 10% is d10. In that case, d90 was 6.0 to 8.0 μm, d10 was 1.5 to 2.0 μm, and d90/d10 was 4.6 to 5.2.
Inventive Examples 1, 2, 4, and 5 are presumed to have obtained a uniform structure by mixing using a WC raw material powder having an average particle size of about 2-3 μm that has been subjected to high temperature carbonization so as not to be over-ground. It Inventive Example 3 does not use the WC raw material powder that has been subjected to the high temperature carbonization treatment, but by using the raw material powder having a large average particle diameter and mixing so as not to over-pulverize, the same as other inventive examples. It is estimated that a uniform structure was obtained.
On the other hand, in Comparative Examples 2 and 3 using the WC raw material powder having an average particle size subjected to high temperature carbonization of about 5.0 to 6.0 μm, in the WC phase structure, the D90/D10 value was high and the particle size distribution was large. The hardness value was rather low because of the wide structure. Further, in Comparative Examples 4 and 5, the over-pulverization of the WC raw material powder progressed, so that the average particle size became small, while many coarse defects having an average particle size of more than 10.0 μm also occurred. Stable characteristics could not be obtained.
As FIGS. 1 and 2, photographs of microstructure observations of Example 1 of the present invention and Comparative Example 3 by an electron microscope are shown. From FIG. 1, it can be confirmed that the structure of Inventive Example 1 is a uniform structure composed of WC particles having a uniform particle size. On the other hand, from FIG. 2, it can be confirmed that the structure of Comparative Example 3 is a mixed-grain structure in which coarse particles are present in many fine WC particles.

In Example 2, the invention samples 1 to 3 having hard coatings formed on the invention samples 1 to 3 and the comparative examples 2 to 4 and the conventional examples 1 and 2 have the same hardness as the invention sample tools 1 to 3. A cutting evaluation test in high-speed machining of mild steel was carried out on the comparative example tools 2 to 4 having the film formed thereon and the conventional example tools 1 and 2.
The insert for cutting test was coated with a hard coating by chemical vapor deposition.
First, the surface side of columnar particles having a columnar structure was coated with 6.0 μm of TiCN having an average width of 0.5 μm to 0.7 μm, and 3.0 μm of Al ₂ O ₃ was coated thereon. After coating the hard coating, a wet blast treatment was performed.
In addition, it was confirmed that the comparative tools 2 to 4 and the conventional tools 1 and 2 have the same coating structure as the produced tools 1 to 3 of the present invention, and the residual compressive stress is about the same.
The cutting conditions are shown below, and the results of the cutting test are shown in Table 4. The tool life of the cutting test insert is the machining time until the maximum wear width of the flank exceeds 0.3 mm, or when chipping occurs and the width exceeds 0.3 mm ( min).
(Conditions) Dry processing/Tool: Tool for high speed/high feed/Cutter Model number: ASRT5063R-4
・Insert model number: WDNT140520-B
・Number of blades: 1
・Work Material: SCM440 (32HRC)
・Cutting method: Dry milling ・Incision: axial direction, 1.0 mm, radial direction, 43 mm
・Cutting speed: 250m/min
・One blade feed: 1.5 mm/blade ・Projection: 100 mm

Inventive Example Tools 1 to 3 exhibited stable wear forms and had the longest tool life.
Since the comparative tools 2 and 3 had a large D90/D10, chipping occurred and the tool life was reached early.
The comparative tool 4 had a small average grain size and chipping occurred to reach the tool life early.
Since the conventional tool 1 has a high Co content and does not contain Ta, the phase containing Ta as the main component is not dispersed in the structure, and the heat resistance is lower than that of the inventive examples. Tool life has shortened.
The conventional tool 2 has a large amount of Co and is plastically deformed to reach the tool life early.

In Example 3, the present invention example tools 2, 4, 5 having hard coatings formed on the present invention examples 2, 4, 5 and the same hard as the present invention example tools 2, 4, 5 in Comparative Example 1 and Conventional Example 1 With respect to the comparative example tool 1 and the conventional example tool 1 on which the film was formed, a cutting evaluation test was performed on the mild steel at high speed machining under the condition of long protrusion from Example 2.
The cutting test insert was coated with the same hard coating as in Example 2 by the chemical vapor deposition method. First, TiCN having a columnar structure and having an average width on the surface side of the columnar particles of 0.5 μm to 0.7 μm was coated to 6.0 μm, and 3.0 μm of Al ₂ O ₃ was coated thereon. After coating the hard coating, a wet blast treatment was performed.
The cutting conditions are shown below, and the results of the cutting test are shown in Table 5. The tool life of the cutting test insert is the machining time until the maximum wear width of the flank exceeds 0.3 mm, or when chipping occurs and the width exceeds 0.3 mm ( min).
(Conditions) Dry processing/Tool: Tool for high speed/high feed/Cutter Model number: ASRT5063R-4
・Insert model number: WDNT140520-B
・Number of blades: 1
・Work Material: SCM440 (32HRC)
・Cutting method: Dry milling ・Incision: axial direction, 1.0 mm, radial direction, 43 mm
・Cutting speed: 250m/min
・Single blade feed: 1.5 mm/blade ・Projection: 200 mm

Inventive Example Tools 2, 4, and 5 all showed excellent tool life. In particular, the tool sample 5 of the present invention having a low Ta content tends to have stable tool damage.
Since the tool of Comparative Example 1 did not contain Ta, the tool life was shorter than that of the inventive tools 2, 4, and 5.
The conventional example 1 tool has a large amount of Co and reaches the tool life early.

The WC-based cemented carbide according to the present invention and the coated cutting tool using the same as the base material are easily resistant to chipping and plastic deformation when subjected to cutting of steel or the like, especially when high-speed processing of mild steel is performed. Therefore, it is extremely useful.

Claims (4)

% By mass, containing Co as a metal element in an amount of 8.5% to 9.5%, Cr in an amount of 0.3% to 1.0%, and Ta in an amount of 1.0% to 3.0%, The balance is a WC-based cemented carbide composed of WC and a non-metallic element existing in solid solution or in combination with the metal element and unavoidable impurities,
The average particle size of WC particles having a circle-equivalent particle size of 0.4 μm or more is 1.0 μm or more and 2.0 μm or less,
When D90/D10, which is the ratio of the particle size D90 at which the integrated value of the area ratio is 90% and the particle size D10 at which the integrated value of the area ratio is 10% in the particle size distribution of the average particle size, is less than 3.2. Yes,
A WC-based cemented carbide, wherein a phase containing Ta as a main component is dispersed in the structure. A coated cutting tool comprising the WC-based cemented carbide according to claim 1 as a base material and having a hard coating layer on its surface. The hard coating layer includes at least a TiCN coating layer, the TiCN coating layer has a columnar structure having columnar particles, and the average width on the surface side of the columnar particles is 1.0 μm or less. The coated cutting tool according to claim 2, which is a coating layer having the thickest film thickness. The coated cutting tool according to claim 3, wherein the hard coating layer has an Al ₂ O ₃ coating layer on the TiCN coating layer.