JP7494952B2 - Cemented carbide and cutting tools containing it as a substrate - Google Patents

Description

The present disclosure relates to a cemented carbide and a cutting tool including the same as a substrate. This application claims priority to Japanese Patent Application No. 2021-021597, filed on February 15, 2021. All contents of the Japanese patent application are incorporated herein by reference.

Conventionally, cemented carbide having a hard phase mainly composed of tungsten carbide (WC) and a binder phase mainly composed of iron group elements (e.g., Fe, Co, Ni) has been used as a material for cutting tools. The properties required for cutting tools include strength (e.g., flexural strength), toughness (e.g., fracture toughness), hardness (e.g., Vickers hardness), plastic deformation resistance, wear resistance, etc.

JP 2012-077352 A

The cemented carbide according to the present disclosure is
A cemented carbide comprising a first hard phase and a binder phase,
the first hard phase is made of tungsten carbide particles;
The binder phase contains nickel and a metal element M as constituent elements,
The metal element M includes at least one selected from the group consisting of chromium, molybdenum, vanadium, and iron,
The binder phase has stacking faults.

The cutting tool according to the present disclosure comprises the above-mentioned cemented carbide according to the present disclosure as a base material.

FIG. 1 is a photograph showing an STEM image of a cross section of the cemented carbide according to this embodiment. FIG. 2 is a photograph showing a diffraction grating image in the binder phase of the cemented carbide according to this embodiment. FIG. 3 is a photograph showing a diffraction grating image in the binder phase of the cemented carbide of the comparative example. FIG. 4 is a graph showing a temperature and pressure variation program (sintering program 1) in the method for producing a cemented carbide according to this embodiment. FIG. 5 is a graph showing a typical temperature and pressure variation program (sintering program 2) in a conventional method for producing cemented carbide.

[Problem that this disclosure aims to solve]
Since Co used in the binder phase is a scarce resource, in recent years, cemented carbide that does not contain Co in the binder phase has been developed. For example, JP 2012-077352 A (Patent Document 1) discloses a cemented carbide in which metal element ceramic particles containing tungsten carbide (WC) are dispersed, and the binder phase is composed of iron (Fe), aluminum (Al), boron (B), and inevitable impurities, and the content of B in the binder phase is 0.07 mass% or more and 0.28 mass% or less.

In recent years, the conditions under which cutting tools are used have become severe, as workpieces have become increasingly difficult to cut, shapes have become more complex, etc. For this reason, there is a demand for improved properties in the cemented carbide used as the base material for cutting tools, and in particular, cemented carbide with high toughness and high hardness is desired.
Furthermore, since Co is a scarce resource as described above, there is a demand for cemented carbide alloys with a reduced Co content.

The present disclosure has been made in consideration of the above circumstances, and aims to provide a cemented carbide alloy that has excellent toughness and hardness even with a low Co content, and a cutting tool that includes the same as a substrate.

[Effects of this disclosure]
According to the present disclosure, it is possible to provide a cemented carbide having excellent toughness and hardness even with a low Co content, and a cutting tool including the same as a substrate.

[Description of the embodiments of the present disclosure]
First, the contents of one embodiment of the present disclosure will be listed and described.
[1] A cemented carbide according to one embodiment of the present disclosure,
A cemented carbide comprising a first hard phase and a binder phase,
the first hard phase is made of tungsten carbide particles;
The binder phase contains nickel and a metal element M as constituent elements,
The metal element M includes at least one selected from the group consisting of chromium, molybdenum, vanadium, and iron,
The binder phase has stacking faults.

The above-mentioned cemented carbide contains the above-mentioned metal element M in the binder phase in addition to nickel, which allows the cemented carbide to have stacking faults in the binder phase. As a result, the above-mentioned cemented carbide can have a hardness equivalent to that of a conventional cemented carbide containing cobalt in the binder phase. In other words, the above-mentioned cemented carbide is a cemented carbide with excellent toughness and hardness.

[2] The content of the metal element M is preferably 25 wt % or more and 35 wt % or less with respect to the binder phase. By specifying it in this way, the cemented carbide alloy has even better toughness and hardness.

[3] The metal element M preferably contains molybdenum. This provides a cemented carbide with even greater toughness and hardness.

[4] The cemented carbide preferably further comprises a second hard phase made of a compound containing one or more metallic elements selected from the group 4, 5 and 6 elements of the periodic table excluding tungsten, and one or more non-metallic elements selected from the group consisting of carbon, nitrogen, oxygen and boron. By defining it in this way, when the cemented carbide is used as a material for a cutting tool, a balance between wear resistance and chipping resistance as a cutting tool can be ensured.

[5] The second hard phase is composed of particles of the compound,
The average particle size of the compound particles is preferably 0.05 μm or more and 2 μm or less. By specifying it in this way, when the cemented carbide is used as a material for a cutting tool, a balance between the wear resistance and chipping resistance of the cutting tool can be ensured.

[6] The average particle size of the tungsten carbide particles is preferably 0.1 μm or more and 10 μm or less. By specifying it in this way, the resulting cemented carbide has even greater toughness and hardness.

[7] A cutting tool according to one embodiment of the present disclosure includes a substrate made of the cemented carbide described in any one of [1] to [6] above. By providing a substrate made of a cemented carbide having excellent toughness and hardness, the cutting tool can achieve machining that can handle more severe cutting conditions and can achieve a longer life.

[8] It is preferable that the cutting tool further comprises a coating provided on the substrate. By providing a coating on the surface of the substrate, the wear resistance, etc. of the cutting tool can be improved. Thus, the cutting tool can be adapted to even more severe cutting conditions and achieve even longer life, etc.

[Details of the embodiment of the present disclosure]
Hereinafter, one embodiment of the present disclosure (hereinafter, referred to as "the present embodiment") will be described. However, the present embodiment is not limited to this. In this specification, the notation in the form of "X to Y" means the upper and lower limits of the range (i.e., X or more and Y or less). When no unit is described for X and only a unit is described for Y, the unit of X and the unit of Y are the same. Furthermore, in this specification, when a compound is represented by a chemical formula in which the composition ratio of the constituent elements is not limited, such as "TiC", the chemical formula includes all conventionally known composition ratios (element ratios). In this case, the above chemical formula includes not only stoichiometric compositions but also non-stoichiometric compositions. For example, the chemical formula of "TiC" includes not only the stoichiometric composition "Ti ₁ C ₁ " but also non-stoichiometric compositions such as "Ti ₁ C _0.8 ". This also applies to the description of compounds other than "TiC". In this specification, when an element symbol or element name is described, it may mean the element itself, or it may mean the constituent element in the compound.

<Cemented carbide>
The cemented carbide of this embodiment is
A cemented carbide comprising a first hard phase and a binder phase,
the first hard phase is made of tungsten carbide particles;
The binder phase contains nickel and a metal element M as constituent elements,
The metal element M includes at least one selected from the group consisting of chromium, molybdenum, vanadium, and iron,
The binder phase has stacking faults.

<First hard phase>
The first hard phase is composed of tungsten carbide (hereinafter, sometimes referred to as "WC") particles. Here, WC includes not only "pure WC (including WC containing no impurity elements and WC containing impurity elements below the detection limit)" but also "WC containing other impurity elements intentionally or unavoidably contained therein, as long as the effect of the present disclosure is achieved." The content ratio of impurities in the WC particles (when there are two or more elements constituting the impurities, the total content ratio of the elements) is 5 mass % or less (5 wt % or less) with respect to the total amount of the WC and the impurities.

(Average grain size of WC grains)
The average particle size of the WC grains in the cemented carbide is preferably 0.1 μm or more and 10 μm or less, and more preferably 0.5 μm or more and 3 μm or less. When the average particle size of the WC grains in the cemented carbide is 0.1 μm or more, the toughness of the cemented carbide tends to be high. Therefore, the cutting tool including the cemented carbide as a substrate can suppress chipping or chipping due to mechanical and thermal shock. In addition, the crack propagation resistance of the cutting tool is improved, so that the propagation of cracks is suppressed and chipping or chipping can be suppressed. On the other hand, when the average particle size is 10 μm or less, the hardness of the cemented carbide tends to be high. Therefore, the cutting tool including the cemented carbide as a substrate can suppress deformation during cutting and suppress wear or chipping.

Here, the average particle size of the WC particles in the cemented carbide is determined by mirror-finishing any surface or any cross section of the cemented carbide, photographing the processed surface with a microscope, and performing image analysis on the photographed image. Specifically, the particle size (Heywood diameter: diameter equivalent to a circle of equal area) of each WC particle is calculated from the photographed image, and the average value is taken as the average particle size of the WC particles. The number of WC particles to be measured is at least 100 or more, and preferably 200 or more. In addition, it is preferable to perform the image analysis in multiple fields of view in the same cemented carbide, and to take the average value as the average particle size of the WC particles. The number of fields of view in which the image analysis is performed is preferably 5 or more, more preferably 7 or more, even more preferably 10 or more, and even more preferably 20 or more. One field of view may be, for example, a square of 20 μm in length and 20 μm in width.

Mirror finishing methods include, for example, polishing with diamond paste, using a focused ion beam device (FIB device), using a cross-section polisher device (CP device), and a combination of these. When photographing the processed surface with a metallurgical microscope, it is preferable to etch the processed surface with Murakami's reagent. Types of microscopes include metallurgical microscopes and scanning transmission electron microscopes (STEM). The images taken with the microscope are imported into a computer and analyzed using image analysis software to obtain various information such as the average grain size. At this time, the WC particles constituting the first hard phase, the bonding phase described later, and the second hard phase described later can be identified from the above photographed image by the shade of color. As the image analysis software, image analysis type grain size distribution software ("Mac-View" manufactured by Mountec Co., Ltd.) can be preferably used.

(Area ratio of first hard phase)
In the cemented carbide according to the present embodiment, the area ratio of the first hard phase to any surface or any cross section of the cemented carbide is preferably 85% or more and 96% or less. In this case, the sum of the area ratio of the first hard phase and the area ratio of the binder phase described later is 100% (when the cemented carbide includes a second hard phase, the case will be described later). The area ratio of the first hard phase is obtained, for example, by photographing any processed surface of the cemented carbide with a microscope and analyzing the photographed image, in the same manner as when determining the average grain size of the WC grains described above. That is, first, WC grains in a predetermined field of view are identified, and the sum of the areas of the WC grains identified by image processing is calculated. Next, the area ratio of the first hard phase can be calculated by dividing the calculated sum of the areas of the WC grains by the area of the field of view. In addition, it is preferable to perform the image analysis in multiple fields of view (for example, 5 or more fields of view) in the same cemented carbide, and the average value is used as the area ratio of the first hard phase. For the image processing, an image analysis type grain size distribution software ("Mac-View" manufactured by Mountec Co., Ltd.) can be suitably used. The above-mentioned "predetermined visual field" may be the same as the visual field used when determining the average grain size of the WC grains described above.

Bonded Phase
The binder phase is a phase that bonds WC particles constituting the first hard phase together, compounds constituting the second hard phase described below, or WC particles constituting the first hard phase and compounds constituting the second hard phase together. The binder phase preferably has a content of 4 wt % or more and 15 wt % or less based on the cemented carbide. The binder phase contains nickel (Ni) and a metal element M described below as constituent elements.

In this embodiment, the main components of the binder phase are preferably nickel and the metal element M. "The main components of the binder phase are nickel and the metal element M" means that the content ratio of "nickel and the metal element M contained in the binder phase" to the binder phase is 50 wt% or more and 100 wt% or less. The content ratio of nickel and the metal element M contained in the binder phase is preferably 80 wt% or more and 100 wt% or less, and more preferably 90 wt% or more and 100 wt% or less.

The nickel content of the binder phase is preferably 65 wt% or more and 75 wt% or less, and more preferably 67 wt% or more and 73 wt% or less.

The metal element M includes at least one selected from the group consisting of chromium (Cr), molybdenum (Mo), vanadium (V) and iron (Fe). It is more preferable that the metal element M includes molybdenum.

The content of the metal element M is preferably 25 wt% or more and 35 wt% or less, and more preferably 27 wt% or more and 33 wt% or less, relative to the binder phase. Here, when the metal element M contains multiple metal elements, the total content of each metal element is the content of the metal element M.

The content of nickel or metal element M in the bonded phase can be measured by titration. That is, the atomic concentration of each element in the bonded phase is first determined by titration. Here, the inventors believe that the atomic concentration measured by titration is the average atomic concentration of the entire bonded phase. Next, the content (wt%) of the element in the bonded phase is determined from the determined atomic concentration and the mass number of the element corresponding to the determined atomic concentration.

(area ratio of bonding phase)
The area ratio of the binder phase to any surface or any cross section of the cemented carbide according to this embodiment is preferably 4% to 15%, more preferably 6% to 15%. By setting the area ratio of the binder phase within the above range, the volume ratio of the first hard phase (a phase harder than the binder phase) in the cemented carbide can be increased, thereby increasing the hardness of the entire cemented carbide at high temperatures and increasing the adhesive strength between the first hard phase and the binder phase.

The area ratio of the binder phase can be calculated in the same manner as in the measurement of the area ratio of the first hard phase. That is, the binder phase in a specified field of view is identified, and the sum of the areas of the binder phase is calculated. Next, the calculated sum of the areas of the binder phase is divided by the area of the specified field of view to calculate the area ratio of the binder phase. It is also preferable to perform the image analysis in multiple fields of view (e.g., five or more fields of view) for the same cemented carbide, and use the average value as the area ratio of the binder phase.

Examples of other elements constituting the bonding phase include cobalt (Co) and copper (Cu). The other elements may be used alone or in combination. The bonding phase may also contain tungsten, carbon, and other unavoidable components, which are components of the first hard phase. The other elements constituting the bonding phase are permitted to be included in the bonding phase within a range in which the function of the bonding phase (the function of bonding WC particles constituting the first hard phase, compounds constituting the second hard phase, or WC particles constituting the first hard phase and compounds constituting the second hard phase) is exerted. In one aspect of this embodiment, the component elements other than the first hard phase and the second hard phase described later can be understood to be included in the bonding phase.

(Stacking faults)
In the cemented carbide according to the present embodiment, the binder phase has stacking faults. Here, the term "stacking faults" refers to a state in which the order of stacking is disturbed when observing the periodic stacking state of two-dimensional atomic planes in a crystal.

The presence or absence of stacking faults can be determined by observing the diffraction grating image of the bonded phase of the cemented carbide (for example, the portion surrounded by the dashed line in FIG. 1) with a transmission electron microscope (STEM). In this case, a thin film sample processed using an ion slicer or the like may be used as the measurement sample. For example, when streaks are observed between the diffraction points in the diffraction grating image as shown in FIG. 2, the bonded phase can be determined to have stacking faults. On the other hand, in the bonded phase without stacking faults, such streaks are not observed, and only the diffraction points are observed in the diffraction grating image (for example, FIG. 3). In this embodiment, the measurement conditions used when observing the diffraction grating image are as follows.
STEM measurement conditions: JEM-2100F (manufactured by JEOL Ltd.)
・STEM image observation, EDX analysis (STEM mode)
Acceleration voltage: 200 kV
Current: 0.3nA
Magnification: 300,000 times, diffraction image shooting (TEM mode)
Acceleration voltage: 200 kV
Camera length: 100cm
Magnification: 300,000 times

<Second hard phase>
The cemented carbide according to this embodiment may further have a second hard phase having a different composition from the first hard phase. The second hard phase is preferably made of a compound (composite compound) containing "one or more metal elements selected from the group consisting of elements of Groups 4, 5, and 6 of the periodic table except tungsten" and "one or more nonmetal elements selected from the group consisting of carbon (C), nitrogen (N), oxygen (O), and boron (B)". Examples of elements of Group 4 of the periodic table include titanium (Ti), zirconium (Zr), and hafnium (Hf). Examples of elements of Group 5 of the periodic table include vanadium (V), niobium (Nb), and tantalum (Ta). Examples of elements of Group 6 of the periodic table include chromium (Cr), molybdenum (Mo), and the like. The compounds are mainly carbides, nitrides, carbonitrides, oxides, borides, and the like of the above-mentioned metal elements.

The second hard phase may be composed of particles of the above-mentioned compound. The average particle size of the particles is preferably 0.05 μm or more and 2 μm or less, more preferably 0.1 μm or more and 0.5 μm or less.

The second hard phase is a compound phase or solid solution phase consisting of one or more of the above compounds. Here, "compound phase or solid solution phase" indicates that the compounds constituting such a phase may form a solid solution, or may exist as individual compounds without forming a solid solution.

Specific examples of the second hard phase include TaC, NbC, TiC, HfC, Mo ₂ C, and ZrC.

When the cemented carbide further has a second hard phase, the area ratio of the first hard phase is set as the combined area ratio of the first hard phase (tungsten carbide particles) and the second hard phase. That is, when the cemented carbide further has a second hard phase, the sum of the area ratio of the first hard phase and the area ratio of the second hard phase with respect to any surface or any cross section of the cemented carbide is preferably 85% or more and 96% or less. In this case, the sum of the area ratio of the first hard phase, the area ratio of the second hard phase, and the area ratio of the bonding phase is 100%. The area ratio of the second hard phase can be calculated in the same manner as the measurement of the area ratio of the first hard phase. That is, the "second hard phase" in a specified field of view is identified, and the sum of the areas of the "second hard phase" is calculated. Next, the area ratio of the second hard phase can be calculated by dividing the calculated sum of the areas of the second hard phase by the area of the specified field of view. In addition, it is preferable to carry out the above image analysis in a plurality of fields (for example, five or more fields) for the same cemented carbide, and to use the average value as the area ratio of the second hard phase.

The area ratio of the second hard phase to any surface or cross section of the cemented carbide is preferably 1% or more and 10% or less, and more preferably 2% or more and 5% or less. By keeping the area ratio of the second hard phase within this range, it is possible to suppress the occurrence of cracks due to thermal or mechanical shock while maintaining the hardness of the cemented carbide, and to improve the oxidation resistance and reactivity resistance with the workpiece material. Note that if the area ratio of the second hard phase is greater than the upper limit, the strength of the cemented carbide decreases and the toughness tends to decrease.

<Method of manufacturing cemented carbide>
The cemented carbide of this embodiment can be typically manufactured through the steps of preparing raw material powders, mixing, molding, degreasing, sintering, heating and quenching, and cooling. Each step will be described below.

<Preparation process>
The preparation step is a step of preparing all raw material powders of materials constituting the cemented carbide. Examples of the raw material powders include WC particles that form the first hard phase, particles containing nickel that form the binder phase, and particles containing the metal element M. In addition, compound powders that form the second hard phase, grain growth inhibitors, etc. may be prepared as necessary.

(WC particles)
The WC particles as the raw material are not particularly limited, and WC particles that are normally used in the manufacture of cemented carbide may be used. The WC particles may be commercially available products. Examples of commercially available WC particles include the "Uniform Grain Tungsten Carbide Powder" series manufactured by A.L.M.T.C.

The average particle size of the WC grains as raw material is preferably 0.3 μm or more and 10 μm or less, and more preferably 0.3 μm or more and 5 μm or less. When the average particle size of the WC grains as raw material is 0.3 μm or more, the toughness tends to be high when the carbide alloy is made. Therefore, the cutting tool containing the carbide alloy as a base material can suppress chipping and chipping due to mechanical and thermal shock. In addition, the crack propagation resistance of the cutting tool is improved, so that the propagation of cracks is suppressed and chipping and chipping can be suppressed. On the other hand, when the average particle size is 10 μm or less, the hardness tends to be high when the carbide alloy is made. Therefore, the cutting tool containing the carbide alloy as a base material can suppress deformation during cutting and suppress wear and chipping.

(Particles containing nickel)
The particles containing nickel as a raw material (hereinafter, sometimes referred to as "nickel-containing particles") are preferably particles made of nickel metal. The nickel-containing particles may be commercially available products.

The average particle size of the nickel-containing particles is preferably 0.5 μm or more and 10 μm or less, and more preferably 0.5 μm or more and 5 μm or less.

(Particles containing metal element M)
The particles containing the metal element M as a raw material are preferably particles made of molybdenum metal, particles made of chromium metal, particles made of vanadium metal, or particles made of iron metal. The particles containing the metal element M may be commercially available products.

The average particle size of the particles containing the metal element M is preferably 0.5 μm or more and 10 μm or less, and more preferably 0.5 μm or more and 5 μm or less.

(Compound composition powder)
The compound constituent powder is not particularly limited, and may be any compound constituent powder that is commonly used as a raw material for the second hard phase in the production of cemented carbide. Examples of such compound constituent powder include TaC, TiC, _NbC , _Cr3C2 , ZrC, TiN, etc.

One of the conditions for uniformly dispersing the second hard phase with a uniform grain size in the cemented carbide is to use a compound powder with a fine grain size and a uniform grain size. By doing so, the second hard phase can be finely dispersed in the sintering process described later. The average grain size of the compound powder can be set to, for example, 0.5 μm or more and 3 μm or less. The smaller the average grain size of the compound powder used as the raw material, the smaller the average grain size of the second hard phase in the cemented carbide obtained in the end. The larger the average grain size of the compound powder used as the raw material, the larger the average grain size of the second hard phase in the cemented carbide obtained in the end. The compound powder with a fine grain size and a uniform grain size can be obtained by crushing/classifying a commercially available product.

<Mixing step>
The mixing step is a step of mixing the raw material powders prepared in the preparation step. The mixing step produces a mixed powder in which the raw material powders are mixed. The mass ratio of the raw material powders (e.g., WC particles, particles containing nickel, particles containing the metal element M, etc.) when mixed corresponds to the area ratio of the first hard phase, the area ratio of the second hard phase, and the area ratio of the binder phase described above. A known device can be used for the mixing step. For example, an attritor, a rolling ball mill, a Karman mixer, a bead mill, etc. can be used. An example of the mixing conditions when an attritor is used is a rotation speed of 100 m/min to 400 m/min, and a mixing time of 1.5 hours to 25 hours. The mixing conditions using an attritor may be wet mixing or dry mixing. The mixing may be performed in a solvent such as water, ethanol, acetone, isopropyl alcohol, etc. The mixing may be performed together with a binder such as polyethylene glycol or paraffin wax.

After the mixing step, the mixed powder may be granulated as necessary. Granulating the mixed powder makes it easier to fill the mixed powder into a die or mold during the molding step described below. A known granulation method can be applied for granulation, and for example, a commercially available granulator such as a spray dryer can be used.

<Molding process>
The molding process is a process of molding the mixed powder obtained in the mixing process into a predetermined shape to obtain a molded body. The molding method and molding conditions in the molding process are not particularly limited, and general methods and conditions may be adopted. The predetermined shape may be, for example, a cutting tool shape (for example, the shape of an indexable cutting tip: CNMG120408, etc.).

<Degreasing process>
The degreasing step is a step for removing the binder (e.g., paraffin wax, etc.) in the molded body obtained in the molding step, and is a step for carrying out a heat treatment under the following conditions.

The processing temperature in the degreasing process is preferably 300°C or higher and 1000°C or lower, and more preferably 400°C or higher and 800°C or lower.

The pressure during the degreasing process is preferably 110 kPa or more and 500 kPa or less, and more preferably 200 kPa or more and 400 kPa or less.

The processing time for the degreasing process is preferably 30 minutes or more and 120 minutes or less, and more preferably 60 minutes or more and 90 minutes or less.

The atmosphere in the degreasing step is not particularly limited, and examples thereof include an _N2 gas atmosphere or an inert gas atmosphere such as Ar.

<Sintering process>
The sintering step is a step of sintering the compact obtained through the debinding step to obtain a sintered body. The sintering temperature is preferably 1300° C. or higher and 1600° C. or lower, and more preferably 1350° C. or higher and 1500° C. or lower.

The sintering time is preferably from 30 to 120 minutes, and more preferably from 50 to 90 minutes.

The atmosphere during sintering is not particularly limited, and examples thereof include an _N2 gas atmosphere or an inert gas atmosphere such as Ar.

The degree of vacuum (pressure) during sintering is preferably 10 kPa or less, more preferably 5 kPa or less, and even more preferably 3 kPa or less. There is no particular lower limit, but it can be, for example, 0.5 kPa or more. By setting the pressure during sintering to 0.5 kPa or more, it is possible to suppress the volatilization of Ni and the like from the surface of the molded body during sintering.

The sintering step may be a sintering HIP (sinter-hip) process that can apply pressure during sintering. The HIP conditions are, for example, in an _N2 gas atmosphere or an inert gas atmosphere such as Ar, at a temperature of 1300°C to 1350°C, and at a pressure of 5 MPa to 200 MPa.

<Heating and quenching process>
The heating and quenching process is a process in which heating and quenching are repeatedly performed on the sintered body after sintering is completed (see FIG. 4). The present inventors believe that performing the heating and quenching process makes it easier for stacking faults to occur in the binder phase.

The temperature during heating in the heating and quenching process is preferably 500°C or higher and 700°C or lower, and more preferably 550°C or higher and 650°C or lower.

The heating rate during heating in the heating and quenching process is preferably 10°C/min or more and 20°C/min or less, and more preferably 12°C/min or more and 17°C/min or less.

The holding time during heating in the heating and rapid cooling process is preferably 5 minutes or more and 15 minutes or less, and more preferably 7 minutes or more and 13 minutes or less.

The temperature during quenching in the heating and quenching process is preferably 100°C or higher and 300°C or lower, and more preferably 150°C or higher and 250°C or lower.

The cooling rate during rapid cooling in the heating and rapid cooling process is preferably 10°C/min or more and 20°C/min or less, and more preferably 12°C/min or more and 17°C/min or less.

The holding time during quenching in the heating and quenching process is preferably 5 minutes or more and 15 minutes or less, and more preferably 7 minutes or more and 13 minutes or less.

It is preferable that the heating and quenching steps are repeated three or more times in the heating and quenching process, and from the viewpoint of the production cycle time, it is more preferable that the number of repetitions be between three and five.

The atmosphere in the heating and quenching step is not particularly limited, and examples thereof include an _N2 gas atmosphere or an inert gas atmosphere such as Ar.

The pressure during the heating and quenching process is preferably 100 kPa or more and 490 kPa or less, and more preferably 190 kPa or more and 390 kPa or less.

<Cooling process>
The cooling step is a step of cooling the sintered body after the heating and quenching step to room temperature. The cooling step is not particularly limited. For example, the cooling rate may be 2°C/min or more. Here, "the temperature drop rate is 2°C/min" means that the temperature drops at a rate of 2°C per minute. The atmosphere during cooling is not particularly limited, and may be an _N2 gas atmosphere or an inert gas atmosphere such as Ar. The pressure during cooling is not particularly limited, and may be pressurized or reduced. For example, the pressure during pressurization may be 400 kPa or more and 500 kPa or less. In addition, the pressure during reduction may be 100 kPa or less, preferably 10 kPa or more and 50 kPa or less. In one aspect of this embodiment, the cooling step may be cooling the sintered body to room temperature in an Ar gas atmosphere.

<Cutting tools, wear-resistant tools and grinding tools>
As described above, the cemented carbide of this embodiment has excellent toughness and hardness, and can therefore be used as a substrate for cutting tools, wear-resistant tools, and grinding tools. That is, the cutting tool of this embodiment contains the above-mentioned cemented carbide as a substrate. Also, the wear-resistant tool and grinding tool of this embodiment contain the above-mentioned cemented carbide as a substrate.

The cemented carbide of this embodiment can be widely applied to conventionally known cutting tools, wear-resistant tools, and grinding tools. Examples of such tools include the following. Examples of cutting tools include cutting tools, such as cutting bits, drills, end mills, indexable cutting tips for milling, indexable cutting tips for turning, metal saws, gear cutting tools, reamers, or taps. Examples of wear-resistant tools include dies, scribers, scribing wheels, or dressers. Examples of grinding tools include grinding wheels.

The cemented carbide of this embodiment may constitute the entirety of these tools. The cemented carbide may constitute a part of these tools. Here, "constitute a part" refers to, for example, in the case of a cutting tool, brazing the cemented carbide of this embodiment to a predetermined position of any substrate to form a cutting edge.

<Coating>
The cutting tool according to the present embodiment may further include a coating provided on the substrate. The wear-resistant tool and the grinding tool according to the present embodiment may further include a coating provided on the substrate. The composition of the coating may include a compound of one or more metal elements selected from the group consisting of metal elements of Group 4 of the periodic table, metal elements of Group 5 of the periodic table, metal elements of Group 6 of the periodic table, aluminum (Al) and silicon (Si) and one or more nonmetal elements selected from the group consisting of nitrogen (N), oxygen (O), carbon (C) and boron (B). Examples of the compound include TiCN, Al ₂ O ₃ , TiAlN, TiN, TiC, AlCrN, and the like. In the present embodiment, the coating may be a simple metal. Other suitable compositions for the coating include cubic boron nitride (cBN), diamond-like carbon, and the like. Such a coating may be formed by a gas phase method such as a chemical vapor deposition (CVD) method or a physical vapor deposition (PVD) method. When the coating is formed by a CVD method, it is easy to obtain a coating having excellent adhesion to the substrate. Examples of the CVD method include a thermal CVD method. When the coating is formed by a PVD method, compressive residual stress is imparted, and it is easy to increase the toughness of a cutting tool or the like.

The coating in the cutting tool according to this embodiment is preferably provided on the cutting edge of the substrate and in its vicinity. The coating may be provided on the entire surface of the substrate. The coating may be a single layer or multiple layers. The thickness of the coating may be 1 μm or more and 20 μm or less, or 1.5 μm or more and 15 μm or less.

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

<Production of cemented carbide>
<Preparation of raw material powder: Preparation process>
As raw material powders, powders having the compositions shown in Table 1 were prepared. The raw material powders used as the first hard phase, second hard phase, and binder phase in Table 1 had the following average particle sizes.
Average particle size of each raw material powder WC: Average particle size 4 μm
TaC: average particle size 2 μm
NbC: average particle size 2 μm
TiC: average particle size 2 μm
Co: average particle size 3 μm
Ni: average particle size 3 μm
Mo: average particle size 3 μm
Cr: average grain size 3 μm
V: average particle size 3 μm
Fe: average particle size 3 μm

<Mixing of raw material powders: Mixing process>
The raw material powders prepared were added in the blending ratios shown in Table 1 and mixed using an attritor to produce a mixed powder. The mixing conditions are shown below. After mixing, the resulting slurry was dried in the air to obtain a mixed powder.
Mixing conditions for the attritor: Ball made of cemented carbide, diameter 3.5 mm
Dispersion medium: Ethanol Stirrer rotation speed: 100 rpm
Processing time: 12 hours

<Preparation of Molded Body: Molding Process>
The resulting mixed powder was press-molded to produce a molded body having the shape of model number CNMG120408 (manufactured by Sumitomo Electric Hardmetal Corp.) (replaceable cutting tip).

<Degreasing of molded body: degreasing process>
The obtained green body was placed in a sintering furnace and degreased under the following conditions.
Processing temperature: 500°C
Processing pressure: 250 kPa
Treatment time: 60 minutes Treatment atmosphere: Ar gas

<Sintering of Molded Body: Sintering Process>
The compact after the debinding step was sintered for 60 minutes in an Ar gas atmosphere (0.5 kPa) at the maximum sintering temperature (Tmax) according to the sintering program shown in Table 2.

<Heating and quenching of molded body: heating and quenching process>
For the samples corresponding to sintering program 1 (FIG. 4) in Table 2, heating and quenching were performed under the following conditions after the sintering process. On the other hand, for the samples corresponding to sintering program 2 (FIG. 5) in Table 2, heating and quenching were not performed after the sintering process.
Conditions for the heating and quenching process: Atmosphere during treatment: Ar gas Pressure during treatment: 200 kPa
Heating temperature: 600℃
Heating rate during heating: 15°C/min. Holding time during heating: 10 minutes. Temperature during rapid cooling: 200°C.
Heating rate during quenching: 15° C./min. Holding time during quenching: 10 min. Number of times heating and quenching were repeated: 3 times.

<Cooling of Molded Body: Cooling Step>
After the heating and quenching step was completed, the samples were cooled to room temperature in an Ar gas atmosphere. At this time, the cooling rate was 2°C/min. As described above, cemented carbide samples No. 1 to 13 and cemented carbide samples No. 101 to 107 were produced. The cemented carbide samples No. 1 to 13 correspond to examples. The cemented carbide samples No. 101 to 103 correspond to comparative examples. The cemented carbide samples No. 104 to 107 correspond to reference examples.

<Sample Observation>
<Calculation of the average particle size of tungsten carbide particles>
The prepared cemented carbide samples No. 1 to 13 and No. 101 to 107 were cut and the cut surfaces were mirror-finished. The mirror-finished cut surfaces were then subjected to ion milling with an argon ion beam, and these cross sections were used as microscope observation samples.

The processed surface of the observation sample was photographed at a magnification of about 2000 times using a scanning transmission electron microscope (STEM) (manufactured by JEOL Ltd.). This photographing was performed for each sample in 10 fields of view on the outside of the processed surface and in the center of the processed surface.

For each sample, the particle size (Heywood diameter) of each particle was determined for more than 300 tungsten carbide particles per visual field using image analysis particle size distribution software (Mac-View, manufactured by Mountec Co., Ltd.), and the average particle size of the tungsten carbide particles after sintering was calculated for a total of 10 visual fields. As a result, it was found that the average particle size of the tungsten carbide particles after sintering was almost equal to the average particle size of the WC particles used as the raw material.

<Calculation of area ratio of first hard phase, second hard phase, and binder phase>
The area ratios of the first hard phase, the second hard phase, and the binder phase on the machined surface of each of the above samples were determined using image analysis particle size distribution software (Mac-View manufactured by Mountech Co., Ltd.). As a result, it was found that the area ratios of the first hard phase, the second hard phase, and the binder phase corresponded to the blending ratios of the raw material powders corresponding to the first hard phase, the second hard phase, and the binder phase (Table 1).

<Composition analysis of binder phase>
The binder phase on the machined surface of each of the samples was analyzed by titration to determine the composition of the binder phase, which was found to correspond to the raw material composition of the binder phase shown in Table 1.

<Stacking faults in the binder phase>
The diffraction grating image of the binder phase on the processed surface of each of the above samples was observed by STEM to determine the presence or absence of stacking faults. The measurement conditions are shown below. If streaks were observed between diffraction points in the diffraction grating image, the binder phase of the sample was determined to have stacking faults. The results are shown in Table 3.
STEM measurement conditions: JEM-2100F (manufactured by JEOL Ltd.)
・STEM image observation, EDX analysis (STEM mode)
Acceleration voltage: 200 kV
Current: 0.3nA
Magnification: 300,000 times, diffraction image shooting (TEM mode)
Acceleration voltage: 200 kV
Camera length: 100cm
Magnification: 300,000 times

<Measurement of Vickers hardness>
The Vickers hardness of each sample was measured under the following conditions. The results are shown in Table 3.
Load: 1 kgf
Holding time: 10 s

<Measurement of transverse strength>
The transverse strength of each sample was measured under the following conditions. The results are shown in Table 3.
Test piece size: 4mm x 8mm x 30mm
Distance between lower supports: 20 mm
Loading speed: 3.5 mm/min

<Cutting test>
A hard film was formed on the surface of each sample by ion plating, which is a type of known PVD method, to prepare a cutting tool for cutting tests. The hard film was a TiAlN film with a thickness of 4.8 μm. Hereinafter, the cutting tool using the cemented carbide of sample No. 1 as the substrate will be referred to as "cutting tool of sample No. 1", etc. The same applies to samples other than sample No. 1.

<Cutting test 1: Wear resistance test>
Using the cutting tools of Samples No. 1 to 13 and Samples No. 101 to 107 prepared as described above, the cutting time (min) until the flank wear amount Vb reached 0.2 mm was measured under the following cutting conditions. The results are shown in Table 3. The longer the cutting time, the more excellent the wear resistance of the cutting tool can be evaluated.
Wear resistance test conditions Workpiece: S50C round bar Cutting speed: 250 m/min
Feed rate: 0.15 mm/rev
Depth of cut: 1mm
Cutting oil: Yes

<Cutting test 2: Fracture resistance test>
Using the cutting tools of Samples No. 1 to 13 and Samples No. 101 to 107 prepared as described above, the cutting time (min) until chipping occurred on the cutting edge was measured under the following cutting conditions. The results are shown in Table 3. The longer the cutting time, the more excellent the chipping resistance of the cutting tool can be evaluated.
Conditions for fracture resistance test Workpiece: SCM435 groove material (number of grooves: 4)
Cutting speed: 200 m/min
Feed rate: 0.3 mm/rev
Depth of cut: 2mm
Cutting oil: Yes

From the results in Table 3, the cutting tools of Samples 1 to 13 (Examples) had a cutting time of 55 minutes or more in Cutting Test 1, which was a good result. This result is comparable to that of conventional cemented carbide alloys (Samples 104 to 107) that contain cobalt in the binder phase. On the other hand, the cutting tools of Samples 101 to 103 (Comparative Examples) had a cutting time of 52 minutes or less in Cutting Test 1.

From the results in Table 3, the cutting tools of Samples 1 to 13 (Examples) had a cutting time of 2.9 minutes or more in Cutting Test 2, which was a good result. This result is comparable to that of conventional cemented carbide alloys (Samples 104 to 107) that contain cobalt in the binder phase. On the other hand, the cutting tools of Samples 101 to 103 (Comparative Examples) had a cutting time of 2.0 minutes or less in Cutting Test 2.

From the above results, it was found that the cemented carbide samples No. 1 to 13 (Examples) were superior in hardness and toughness to the cemented carbide samples No. 101 to 103 (Comparative Examples).

Although the embodiments and examples of the present invention have been described above, it has been planned from the outset that the configurations of the above-mentioned embodiments and examples may be appropriately combined.

The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is indicated by the claims, not by the embodiments and examples described above, and is intended to include all modifications within the scope of the claims and meanings equivalent thereto.

Claims (8)

A cemented carbide comprising a first hard phase and a binder phase,
the first hard phase is made of tungsten carbide particles;
The binder phase contains nickel and a metal element M as constituent elements,
The metal element M includes at least one selected from the group consisting of chromium, molybdenum, vanadium, and iron,
The binder phase has stacking faults,
The binder phase has a content of 4 wt % or more and 15 wt % or less based on the cemented carbide,
The content ratio of the nickel and the metal element M contained in the binder phase is 90 wt % or more and 100 wt % or less . The cemented carbide according to claim 1, wherein the content of the metal element M is 25 wt% or more and 35 wt% or less with respect to the binder phase. The cemented carbide according to claim 1 or 2, wherein the metal element M includes molybdenum. The cemented carbide according to any one of claims 1 to 3, further comprising a second hard phase made of a compound containing one or more metal elements selected from the group 4, 5 and 6 elements of the periodic table excluding tungsten, and one or more nonmetallic elements selected from the group consisting of carbon, nitrogen, oxygen and boron. the second hard phase is composed of particles of the compound,
The cemented carbide according to claim 4, wherein the average particle size of the compound particles is 0.05 μm or more and 2 μm or less. The cemented carbide according to any one of claims 1 to 5, wherein the average particle size of the tungsten carbide particles is 0.1 μm or more and 10 μm or less. A cutting tool comprising the cemented carbide according to any one of claims 1 to 6 as a substrate. The cutting tool according to claim 7, further comprising a coating provided on the substrate.

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