JP7488752B2 - Carbide Tools - Google Patents

Description

The present invention relates to a tungsten carbide (hereinafter sometimes referred to as WC) based cemented carbide tool (hereinafter sometimes referred to as cemented carbide tool), particularly applicable to drilling tools for mining and civil engineering (rock drilling bit tips, gauge tips for mining and civil engineering button bits, etc.), cutting tools (drills, inserts, milling cutters, rotary cutting tools, etc.), and plastic processing tools (press dies, forging dies, rolling rolls for steel, etc.).

Cemented carbide tools use cemented carbide having a WC hard phase and a Co binder phase. The properties of this cemented carbide depend on the grain size of the WC grains and the Co content, and it is known that there is a trade-off between wear resistance and chipping resistance. Various proposals have been made to resolve this trade-off.

For example, Patent Document 1 describes a carbide tool in which, for WC particles contained in the hard phase at 9.5 mass% or more, 50-75% of particles are 4.5-7.5 μm and 15-40% are 1.5-4.5 μm (area ratios when the total WC is taken as 100%), the relationship (total WC area of 4.5-7.5 μm)/(total WC area of 1.5-4.5 μm)=2/1-5/1 is satisfied, and the area ratio of WC particles of 1 μm or less is 3% or less, and the carbide tool is said to have improved wear resistance without reducing chipping resistance.

Furthermore, for example, Patent Document 2 describes a cemented carbide tool having a surface layer mainly composed of M ₁₂ C type composite carbide, a structure gradient in which the average WC grain size in the surface layer is 0.3 to 0.7 times smaller than that in the inner layer, and a concentration gradient in which the binding metal in the surface layer moves to the inner side, and the cemented carbide tool is said to have excellent wear resistance and chipping resistance.

For example, Patent Document 3 describes a carbide tool that has a columnar tip body made of WC and Co, the tip portion along the axial direction of the tip body is formed so as to taper in diameter toward the tip side, the tip portion of the tip body is provided with multiple binder pools that are mainly composed of Co and have lengths of 5 to 25 μm, and the number of binder pools contained per unit area of the tip portion is smaller on the inside of the tip than near the outer surface of the tip portion, and the carbide tool is said to have excellent wear resistance and chipping resistance.

Japanese Patent Application Laid-Open No. 8-302441 JP 2006-188749 A JP 2014-214426 A

In recent years, there has been a demand for even greater wear resistance and chipping resistance in carbide tools. For example, with regard to drilling tools, there has been an increase in the number of cases where holes are drilled using high-power, high-frequency rock drills, and the load on drilling tools has tended to increase, so there is a demand for even greater durability, including wear resistance and chipping resistance. Also, for example, with regard to cutting tools, there is a demand for even greater resistance to abnormal damage, such as chipping resistance, chipping resistance, and peeling resistance, as well as durability, in order to achieve even higher speeds and more efficient cutting processes, and the same is true for plastic processing tools.

The present invention was made in consideration of the above circumstances and proposals, and aims to provide a carbide tool that has excellent wear resistance, chipping resistance, and durability.

The cemented carbide tool according to the embodiment of the present invention is
The composition contains 2.0 to 30.0 mass % Co, with the remainder consisting of WC and unavoidable impurities, and the area ratio of crystal grains having a face-centered cubic structure among the Co crystal grains forming the binder phase is such that the value (A) of a surface region up to a depth of 50 μm from the surface is 50.0 to 100.0 area %, the value (B) of an internal region extending beyond 50 μm from the surface is 30.0 to 90.0 area %, and A/B is 0.70 to 3.33.

Furthermore, the cemented carbide tool according to the embodiment may satisfy one or more of the following requirements.
(1) Contains _0.2 to 3.5 mass% _Cr3C2 and/or 0.2 to 3.7 mass% VC.
(2) The Ni content is 0.4 to 21.0 mass %.
(3) The internal region has a Vickers hardness of 1500 Hv or more.
(4) The fracture toughness value is 12.00 MPa·m ^1/2 or more.
(5) The chips are button bits for use in mining and civil engineering.

As a result of the above, it is possible to obtain a carbide tool with excellent wear resistance, chipping resistance, and toughness.

FIG. 2 is a schematic diagram of a side view of the gauge chip (ballistic type) of Example A. FIG. 2 is a schematic diagram of a side view of the button bit of Example A. FIG. 3 is a schematic diagram illustrating a gauge diameter of the button bit of FIG. 2. FIG. 2 is a schematic cross-sectional view of a rattler testing machine. FIG. 5 is a schematic side view of the rattler tester shown in FIG. 4 . FIG. 1 is a schematic diagram of a rotary cutting tool (rotary die cutter).

The inventors have conducted extensive research into carbide tools containing WC and Co, particularly into the distribution of the Co crystal structure. As a result, they have discovered that when the area ratio of Co crystal grains with a face-centered cubic structure in the area near the surface of the carbide tool, including the surface that contacts the rock or workpiece being cut, (A), and the area ratio in the area near the surface of the carbide tool, including the surface that contacts the rock or workpiece being cut, (B), are each a predetermined value and A/B is within a predetermined range, the carbide tool has excellent wear resistance, chipping resistance, and toughness.

Hereinafter, a cemented carbide tool according to one embodiment of the present invention will be described.
In this specification and claims, when a numerical range is expressed as "M to N" (where M and N are both numerical values), the range includes an upper limit value (N) and a lower limit value (M), and the upper limit value (N) and the lower limit value (M) have the same units.

<Composition>
First, the composition of the cemented carbide tool according to this embodiment will be described.

<<Co>>
The composition of the cemented carbide tool according to this embodiment contains 2.0 to 30.0 mass% Co, with the remainder being WC and unavoidable impurities. The reason for the Co content being in this range is that if the Co content is less than 2.0 mass%, densification during sintering is difficult to proceed and internal defects are likely to remain, resulting in a loss of uniformity as a structure and a decrease in the mechanical strength of the cemented carbide tool, while if it exceeds 30.0 mass%, the wear resistance of the cemented carbide tool decreases. When the cemented carbide tool is a drilling tool (drilling tip), the Co content is more preferably 3.0 to 10.0 mass%.

<<Other elements>>
The cemented carbide tool according to the present embodiment may contain one or more of Cr, V, Nb, Ta, Ti, Ni, Hf, and Zr. These elements may be added as carbides, composite carbides, nitrides, or carbonitrides. These elements will be described below.

Cr and V act to suppress the grain growth of WC during sintering, and in order to achieve this suppression, 0.2 to 3.5 mass % of Cr ₃ C ₂ and/or 0.2 to 3.7 mass % of VC may be added.

Depending on the application of the cemented carbide tool, Ni may be included as a substitute for Co, which forms a binder phase, in an amount of 20 to 70% of the Co content, i.e., 0.4 to 21.0 mass%.

Nb, Ta, and Ti improve the high-temperature hardness and creep strength of cemented carbide tools, and may be added in amounts of 0.2 to 3.0 mass % as carbides, etc., to ensure this improvement.

Zr and Hf improve high-temperature mechanical properties such as high-temperature toughness and high-temperature flexural strength, and to ensure this improvement, 0.2 to 3.0 mass % may be added as carbides, etc.

<<Inevitable Impurities>>
The cemented carbide tool according to this embodiment is permitted to contain 1.0 mass % or less of elements that are inevitably mixed in during the manufacturing process.

<Distribution of crystal structure of Co crystal grains>
In the cemented carbide tool according to this embodiment, it is preferable that the area ratio of Co crystal grains having a face-centered cubic structure (fcc crystal structure) is 50.0 to 100.0 area % in the surface region up to a depth of 50 μm from the surface, i.e., the deepest valley bottom (the part located most inside the cemented carbide tool body) of the cemented carbide tool body in contact with a surface layer such as a black skin or paint present on the surface, and the value (A) is 30.0 to 90.0 area % in the internal region having a depth of more than 50 μm from the surface, and the ratio A/B is 0.70 to 3.33.

When the ratio of the area percentage to the area percentage of Co crystal grains having a face-centered cubic structure satisfies this range, the crack propagation resistance is improved, excellent wear resistance is maintained, and the chipping resistance is also improved.
When the cemented carbide tool is a drilling tool (drilling tip), it is preferable that the value (A) of the surface region is 60.0 to 97.0 area %, the value (B) of the inner region is 40.0 to 90.0 area %, and the A/B is 0.70 to 2.20.

Due to the properties of improved crack propagation resistance, excellent chipping resistance, and improved wear resistance, the carbide tool according to this embodiment is suitable, when used as a drilling tool, for example, for drilling hard rocks (e.g., granite) with a uniaxial compressive strength of 150 MPa or more, and as a drilling tool used with a high-pressure operating hammer.

The reason for this improved crack propagation resistance and excellent chipping resistance is unclear, but it is believed that the progression of cracks that occur on the surface of the tool during use from the surface to the inside is suppressed by the Co crystal grains with a face-centered cubic structure changing to a close-packed hexagonal structure (hcp crystal structure), giving the tool outstanding chipping resistance, and that the high strength of Co crystal grains with a close-packed hexagonal structure also improves wear resistance. In addition, while the close-packed hexagonal structure has three slip systems (1 face x 3 directions), the face-centered cubic structure has 12 slip systems (4 faces x 3 directions), so it is highly ductile, has distortion allowance, and has high impact resistance, giving the tool outstanding chipping resistance.

Here, the area ratio of Co crystal grains having a face-centered cubic structure (fcc crystal structure) is obtained by setting a plurality of observation fields (e.g., three fields) in a cross section perpendicular to the surface of the cemented carbide tool, measuring the depth from the deepest valley bottom (the part located most inside the cemented carbide tool body) of the cemented carbide tool body that contacts a surface layer such as a black skin or paint in each observation field, determining the area ratios in the surface region and the internal region, and calculating the average value.
Specifically, the following procedure, "Definition of grain boundaries of Co crystal grains and determination of crystal structure", is followed.

<Definition of grain boundaries of Co crystal grains and determination of crystal structure>
<<Definition of grain boundaries of Co crystal grains>>
The grain boundaries of the Co crystal are identified by crystal orientation measurement using electron backscatter diffraction. First, the surface perpendicular to the tool surface (longitudinal section) is mechanically polished using waterproof abrasive paper and diamond abrasive grains, and then the cross-sectional ion processing is performed using an ion milling device to prepare a measurement surface. Next, the crystal orientation is measured using an EBSD measurement device and analysis software. The EBSD measurement device has an electron beam acceleration voltage of 15 kV, a measurement field of view of 20 μm×30 μm, and a measurement point interval (Step Size) of the crystal orientation measurement of 0.05 μm. The data obtained by the EBSD measurement device is processed using analysis software.

<<Determination of the crystal structure of Co crystal grains>>
Here, the measured crystal orientation is measured discretely on the measurement surface, and the area up to the middle between adjacent measurement points is represented by the measurement results to obtain the orientation distribution of the entire measurement surface. The area represented by the measurement points (hereinafter sometimes referred to as a pixel) can be, for example, a regular hexagon.

If there is an angle difference of 5 degrees or more between the crystal orientations of adjacent pixels, or if only one of the adjacent pixels shows a face-centered cubic structure or a close-packed hexagonal structure, the side of the area where these pixels meet is considered to be a grain boundary. The area surrounded by the side considered to be a grain boundary is defined as one crystal grain. However, a single pixel that has an orientation difference of 5 degrees or more with all of its adjacent pixels, or that does not have any adjacent measurement points with a face-centered cubic structure, is not considered to be a crystal grain, and two or more connected pixels are treated as crystal grains. In this way, the grain boundaries are determined, the crystal grains are identified, and the area percentage occupied by the crystal grains is calculated for each crystal grain structure.

<Vickers hardness>
The cemented carbide tool according to the present embodiment preferably has a Vickers hardness of 1400 Hv or more in an inner region thereof, as measured at a load of 490 N (50 kgf) by a method specified in ISO 6507 or ASTM E 385. When the Vickers hardness is 1500 Hv or more, the cemented carbide tool is even more excellent in wear resistance, fracture resistance, and toughness.
There is no particular restriction on the upper limit of the Vickers hardness, but in the manufacturing method of the embodiment described later, the upper limit is about 1550 Hv.

<Fracture toughness value>
The cemented carbide tool according to this embodiment preferably has a fracture toughness value (K _1c ) of 12.00 MPa·m ^1/2 or more. When the fracture toughness value is 12.00 MPa·m ^1/2 or more, the cemented carbide tool has even more excellent wear resistance, fracture resistance, and toughness.
Here, the fracture toughness value can be measured by known methods, such as the IF method in which the toughness value is calculated from the indentation and crack length measured by the method specified in JIS R1607, and in areas where a sufficient crack length cannot be obtained, the SEPB method or SEVNB method is used.
There is no particular restriction on the upper limit of fracture toughness, but in the manufacturing method of the examples described below, the upper limit is about 25.00 MPa·m ^1/2 .

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

Example A
Hereinafter, the present invention will be described using, as Example A, an example in which the cemented carbide tool is a drilling tip of a button bit (BB036A).

In order to obtain the button bit drilling tip shown in Figure 1, in each embodiment, six ballistic type (gauge tips) with a diameter of φ (T: diameter) of 10 mm and three ballistic type (face tips) with a diameter of φ (T: diameter) of 9 mm were manufactured by the following procedure.
That is, the product was manufactured through the steps of preparing the raw material powder, blending/mixing and press molding, sintering, pressure treatment, deburring, and re-sintering.

1. Raw Material Powder Preparation Step As raw material powders, WC powder and Co powder, each having an average particle size of 3.0 μm, and Cr ₃ C ₂ powder and VC powder, each having an average particle size of 0.1 to 3.0 μm, were prepared.

The prepared raw material powders were mixed according to the composition shown in Table 1, and paraffin wax was added. The mixture was mixed in a ball mill for 24 hours in a solvent containing 85% ethanol. The mixture was dried under reduced pressure and then pressed into a green compact with a compression ratio of 20%.
The blending ratio shown in Table 1 is the composition of the button bit drilling tip .

3. Sintering process The pressed powder compact was sintered in a vacuum of 20 Pa or less by maintaining the temperature in the range of 1350 to 1500°C for 60 minutes with a temperature increase rate of 4°C/min, and after sintering, it was cooled to 50°C at a cooling rate of 6°C/min using Ar gas.

4. Pressure treatment process (HIP treatment and S-HIP treatment)
Next, the temperature was raised to 1320° C. at a heating rate of 7° C./min, and the HIP treatment was performed by holding the temperature at 900 MPa for 60 minutes. Thereafter, the temperature was cooled to 50° C. at a cooling rate of 6° C./min.
In place of the HIP treatment, an S-HIP treatment was performed in which sintering and HIP treatment were performed simultaneously. The S-HIP treatment was performed by vacuum heating to 1350-1500°C with a temperature increase rate of 3°C/min, and then pressurizing in the reached temperature range at 5 MPa for 90 minutes in an Ar gas atmosphere. After that, the material was cooled to 50°C at a cooling rate of 3/min.

5. Deburring Step Next, any one of the following deburring processes (1) to (3) was performed as necessary.

(1) Barrel polishing Equipment: Vibration barrel polishing machine Capacity: 20 liters Frequency: 60 Hz
Polishing media: Diatomaceous earth

(2) Profile polishing: Abrasive grain: #200 diamond abrasive grain; Circumferential speed: 1000 m/min
Stroke count: 90 times/min
Cutting depth: 0.1 mm

(3) Sandblasting Air pressure 0.3 to 0.2 MPa
Blast gun Φ19mm
Alumina diameter 425-300μm (FA46)
Processing time per unit area: 3 to 6 s/ ^cm2

6. Resintering Step In a vacuum of 1 Pa or less, the temperature was raised to 1100° C. at a rate of 5° C./min, and the product was held for 60 minutes for resintering, and then cooled to 50° C. at a rate of 15° C./min.

From each of the ballistic-type chips thus obtained in Examples 1 to 7, one chip was randomly selected, and the area ratio of crystal grains having a face-centered cubic structure was determined by the method described above. The results are shown in Table 2. Here, the EBSD device used was a Carl Zeiss Ultra 55 scanning electron microscope, OIM Data Collection by EDAX/TSL, and the analysis software used was OIM Data Analysis ver. 7.3 by EDAX/TSL. The Vickers hardness was measured by the method described above, and the fracture toughness value was measured by the IF method.

In contrast, for Comparative Examples 1 to 7, six ballistic type (gauge chips) with a diameter of 10 mm and three ballistic type (face chips) with a diameter of 9 mm, each of which had the same shape as the Examples, were produced using the same raw material powder as the Examples, and following the same manufacturing process as the Examples, except that no resintering step was performed. The area ratio of crystal grains with a face-centered cubic structure was determined in the same way as in the Examples. The results are shown in Table 2.

The ballistic type tips of Examples 1 to 7 and Comparative Examples 1 to 7 were attached to the head of a button bit having a gauge diameter G of 47.0 mm as shown in Figure 3 , with six tips having a tip diameter T of 10 mm as gauge tips and three tips having a tip diameter T of 9 mm as face tips, and the following drilling test was performed.

1. Specifications of the drilling test equipment (drilling equipment) Impact pressure: 20 MPa
Impact frequency: 93Hz
Thrust: 8MPa
Rotation pressure 7.5MPa

2. Drilling length (per drilling): 4m
Drilling diameter: 45 mm
Rock mass - axial compressive strength 210MPa

3. Re-polishing is carried out after 10 drillings (a total of 40m drilling) are completed.

The following evaluations were then carried out, and the results are shown in Table 3.
(1) After completing five drillings (a total of 20 m), the shape of the drilling tip was observed.
(2) Using a gauge diameter measuring jig, when the gauge diameter G of the button bit became less than 44 mm, it was visually observed for wear or the presence or absence of loss (either partial or complete loss) along a length of 1/3 or more of the tip diameter. When loss occurred in three or more of the nine tips, regardless of whether they were gauge tips or face tips, it was determined that the tip had reached the end of its life, and the total drilling length (meters) until the tip reached the end of its life was measured.

As is clear from Table 3, the drilling tips of Examples 1 to 7 did not develop any abnormalities immediately after drilling 20 m, had a long total cutting length, and all demonstrated excellent wear resistance, chipping resistance, and toughness. On the other hand, the drilling tips of Comparative Examples 1 to 7 had chipping in some of the tips immediately after drilling 20 m, had a short total drilling length, and suffered early chipping and wear.

Example B
As Example B below, a cubic test piece with a side length of 10 mm was prepared, and the rattler test shown in Figs. 4 and 5 was carried out to evaluate the wear resistance, fracture resistance, and toughness of the test piece.
The test specimens were manufactured through the steps of preparing the raw material powder, blending, mixing and press molding, sintering, pressure treatment, polishing and re-sintering.

1. Raw Material Powder Preparation Step As raw material powders, WC powder and Co powder, each having an average particle size of 1.0 μm, and Cr ₃ C ₂ powder and VC powder, each having an average particle size of 0.1 to 3.0 μm, were prepared.

The prepared raw material powders were mixed according to the composition shown in Table 4, and paraffin wax was added. The mixture was mixed in a ball mill for 24 hours in a solvent containing 85% ethanol, dried under reduced pressure, and then pressed into a green compact with a compression ratio of 20%.
The blending ratios shown in Table 4 represent the compositions of the test pieces.

3. Sintering process The pressed powder compact was sintered in a vacuum of 20 Pa or less by maintaining the temperature in the range of 1350 to 1500°C for 60 minutes with a temperature increase rate of 4°C/min, and after sintering, it was cooled to 50°C at a cooling rate of 6°C/min using Ar gas.

4. Pressure treatment process (HIP treatment and S-HIP treatment)
Next, the temperature was raised to 1320° C. at a heating rate of 7° C./min, and the HIP treatment was performed by holding the temperature at 900 MPa for 60 minutes. Thereafter, the temperature was cooled to 50° C. at a cooling rate of 6° C./min.
In place of the HIP treatment, an S-HIP treatment was performed in which sintering and HIP treatment were performed simultaneously. The S-HIP treatment was performed by vacuum heating to 1350-1500°C with a temperature increase rate of 3°C/min, and then pressurizing in the reached temperature range at 5 MPa for 90 minutes in an Ar gas atmosphere. After that, the material was cooled to 50°C at a cooling rate of 3/min.

5. Polishing Step Using a surface grinder, six faces of the test piece were polished with a #140 grinding wheel.

6. Resintering Step In a vacuum of 1 Pa or less, the temperature was raised to 1100° C. at a rate of 5° C./min, and the product was held for 60 minutes for resintering, and then cooled to 50° C. at a rate of 15° C./min.

The surface area ratio of Co crystal grains having a face-centered cubic structure was determined for the test pieces of Examples 11 to 15 obtained in this manner, in the same manner as Example A. The results are shown in Table 5.

In contrast, Comparative Examples 11 to 15 were produced using the same raw material powder as in the Examples, and following the same manufacturing process as in the Examples, except that they did not include a resintering process, and the area ratio of Co crystal grains having a face-centered cubic structure was calculated in the same way as in the Examples. The results are shown in Table 5.

Rattler Test For each of the test pieces of Examples 11 to 15 and Comparative Examples 11 to 15, the defect rate was evaluated using a ratler tester shown in a cross-sectional schematic diagram in FIG. 4 and in a side schematic diagram in FIG .

The conditions for the Rattler test were as follows:
Dimensions of the container for the rattra test: Inner diameter φ110mm
Length: 200mm
Ball: φ20mm alumina ball (total mass 480g)
Container rotation speed: 250 rpm
Test duration: 180 minutes

The mass of the test piece before and after the test was compared to determine the following defect rate, and the wear resistance, defect resistance, and toughness of the test piece were evaluated. The results are shown in Table 6.
Defective rate (%) = (mass before test - mass after test) / (mass before test) x 100

As is clear from Table 6, the test pieces of Examples 11 to 15 had a small defect rate (%) after testing, and all of them can be said to have excellent wear resistance, defect resistance, and toughness. On the other hand, the test pieces of Comparative Examples 11 to 15 had a high defect rate (%), and it is clear that they had inferior wear resistance, defect resistance, and toughness.

Example C
Hereinafter, as Example C, a case where the cemented carbide tool is a rotary cutting tool (rotary die cutter) as shown in FIG. 6 will be described as an example.
The rotary cutting tool was manufactured through a process of preparing the raw material powder, blending and pressing, sintering, pressure treatment, re-sintering, and polishing.

1. Raw Material Powder Preparation Step As raw material powders, WC powder and Co powder, each having an average particle size of 1.0 μm, and Cr ₃ C ₂ powder and VC powder, each having an average particle size of 0.1 to 3.0 μm, were prepared.

The prepared raw material powders were mixed according to the composition shown in Table 7, and paraffin wax was added. The mixture was mixed in a solvent containing 85% ethanol for 24 hours using a ball mill. The mixture was dried under reduced pressure and then pressed into a green compact with a compression ratio of 20%.
The blending ratios shown in Table 7 represent the composition of the rotary cutting tool.

3. Sintering process The pressed powder compact was sintered in a vacuum of 20 Pa or less by maintaining the temperature in the range of 1350 to 1500°C for 60 minutes with a temperature increase rate of 4°C/min, and after sintering, it was cooled to 50°C at a cooling rate of 6°C/min using Ar gas.

4. Pressure treatment process (HIP treatment)
Next, the temperature was raised to 1320° C. at a heating rate of 7° C./min, and the HIP treatment was performed by holding the temperature at 900 MPa for 60 minutes. Thereafter, the temperature was cooled to 50° C. at a cooling rate of 6° C./min.

5. Resintering Step In a vacuum of 1 Pa or less, the temperature was raised to 1100° C. at a rate of 5° C./min, and the product was held for 60 minutes for resintering, and then cooled to 50° C. at a rate of 15° C./min.

6. Polishing Step The following polishing process was carried out so that the finished surface roughness (Rz) was 0.8 μm.
Processing machine: Cylindrical grinding machine and machining center Grindstone size: #140 (rough processing) to #1000 (finishing processing)

The area ratio of crystal grains having a face-centered cubic structure was determined for the rotary cutting tools of Examples 21 to 23 obtained in this way using the same method as in Example A. The results are shown in Table 8.

In contrast, Comparative Examples 21 to 23 were produced using the same raw material powder as in the Examples, and following the same manufacturing process as in the Examples, except that the resintering process was not performed. The area ratio of crystal grains having a face-centered cubic structure was calculated in the same way as in the Examples. The results are shown in Table 8.

Evaluation of durability A rotary cutting tool as shown in FIG.
Rotational speed: 600 rpm
Pressing pressure 1.5MPa
Blade tip protrusion amount 1.5μm
The condition of the cutting edge was visually checked every 100,000 rotations, and the cumulative number of rotations up to the point where chipping was observed was taken as the number of rotations until the end of the tool life. The results are shown in Table 9. In Table 9, the term "tool life" refers to the number of rotations until the end of the tool life.

As is clear from Table 9, the cumulative rotation numbers of Examples 21 to 23 are high, and all of them can be said to have excellent wear resistance, fracture resistance, and toughness. On the other hand, the test pieces of Comparative Examples 21 to 23 have low cumulative rotation numbers, and it is clear that they have inferior wear resistance, fracture resistance, and toughness.

1. Ballistic type tip (gauge tip)
2. Ballistic tip type (face tip)
3 Button bit 4 Rattler tester container 5 Obstacle plate 6 Test piece 7 Alumina ball 8 Die cut roll 9 Anvil roll 10 Blade tip 11 Bearer T Tip diameter G of ballistic type tip Gauge diameter R of button bit Rotation direction

Claims (6)

A cemented carbide tool having a composition containing 2.0 to 30.0 mass % Co with the remainder consisting of WC and unavoidable impurities, characterized in that, with respect to the area ratio of crystal grains having a face-centered cubic structure among Co crystal grains forming a binder phase, a value (A) of a surface region up to a depth of 50 μm from the surface is 50.0 to 100.0 area %, a value (B) of an internal region beyond 50 μm from the surface is 30.0 to 90.0 area %, and A/B is 0.70 to 3.33. 2. The carbide tool according to claim 1 _, characterized in that it contains 0.2 to 3.5 mass % of _Cr3C2 and/or 0.2 to 3.7 mass % of VC. The carbide tool according to claim 1 or 2, characterized in that it contains 0.4 to 21.0 mass % Ni. The carbide tool according to any one of claims 1 to 3, characterized in that the Vickers hardness of the inner region is 1500 Hv or more. The cemented carbide tool according to any one of claims 1 to 4, characterized in that it has a fracture toughness value of 12.00 Mpam ^1/2 or more. The carbide tool according to any one of claims 1 to 5, characterized in that the carbide tool is a tip for a button bit for mining and civil engineering.

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