WO2022172730A1

WO2022172730A1 - Cemented carbide and cutting tool comprising same as base material

Info

Publication number: WO2022172730A1
Application number: PCT/JP2022/002228
Authority: WO
Inventors: 聡小野; 裕明後藤; 圭一津田
Original assignee: 住友電気工業株式会社
Priority date: 2021-02-15
Filing date: 2022-01-21
Publication date: 2022-08-18
Also published as: JPWO2022172730A1

Abstract

A cemented carbide comprising a first hard phase and a binding phase, wherein the first hard phase is formed of tungsten carbide particles, the binding phase includes nickel and a metal element M as constituent elements, the metal element M includes at least one element selected from the group consisting of chromium, molybdenum, vanadium, and iron, and the binding phase has a stacking fault.

Description

Cemented carbide and cutting tools containing it as a base material

The present disclosure relates to a cemented carbide and a cutting tool containing it as a base material. This application claims priority from Japanese Patent Application No. 2021-021597 filed on February 15, 2021. All the contents described in the Japanese patent application are incorporated herein by reference.

Conventionally, cemented carbide comprising 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. It is Properties required for cutting tools include strength (eg, transverse rupture strength), toughness (eg, fracture toughness), hardness (eg, Vickers hardness), plastic deformation resistance, wear resistance, and the like.

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 consists of tungsten carbide particles,
The binder phase contains nickel and a metal element M as constituent elements,
The metal element M contains at least one selected from the group consisting of chromium, molybdenum, vanadium and iron,
The binder phase has stacking faults.

A cutting tool according to the present disclosure includes the 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 Comparative Example. FIG. 4 is a graph showing a temperature and pressure variation program (sintering program 1) in the cemented carbide manufacturing method according to the present embodiment. FIG. 5 is a graph showing a general temperature and pressure variation program (sintering program 2) in a conventional cemented carbide manufacturing method.

[Problems to be Solved by the Present Disclosure]
Since Co used in the binder phase is a scarce resource, cemented carbides containing no Co in the binder phase have been developed in recent years. For example, in JP-A-2012-077352 (Patent Document 1), metal element ceramic particles containing tungsten carbide (WC) are dispersed, and the binding phase is iron (Fe), aluminum (Al), boron (B) and inevitable impurities, wherein the content of B in the binder phase is 0.07% by mass or more and 0.28% by mass or less. It is

In recent years, cutting tools have become more difficult to cut, and cutting tools have become more difficult to machine. Therefore, cemented carbides used as base materials for cutting tools are also required to have various properties improved, and in particular, cemented carbides having high toughness and high hardness are desired.
Further, as described above, Co is a scarce resource, so a cemented carbide with a reduced Co content is desired.

The present disclosure has been made in view of the above circumstances, and aims to provide a cemented carbide with excellent toughness and hardness even if the Co content is low, and a cutting tool containing it as a base material. .

[Effect of the present disclosure]
According to the present disclosure, it is possible to provide a cemented carbide with excellent toughness and hardness even with a low Co content, and a cutting tool containing the same as a base material.

[Description of Embodiments of the Present Disclosure]
First, the contents of one aspect of the present disclosure are listed and described.
[1] A cemented carbide according to an aspect of the present disclosure,
A cemented carbide comprising a first hard phase and a binder phase,
The first hard phase consists of tungsten carbide particles,
The binder phase contains nickel and a metal element M as constituent elements,
The metal element M contains at least one selected from the group consisting of chromium, molybdenum, vanadium and iron,
The binder phase has stacking faults.

By including the metal element M in the binder phase in addition to nickel, the cemented carbide can have stacking faults in the binder phase. As a result, the cemented carbide can have a hardness comparable to that of conventional cemented carbide containing cobalt in the binder phase. That is, the cemented carbide is a cemented carbide having 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 defining in this way, the cemented carbide can be further excellent in toughness and hardness.

[3] The metal element M preferably contains molybdenum. By defining in this way, the cemented carbide can be further excellent in toughness and hardness.

[4] The cemented carbide is selected from the group consisting of one or more metal elements selected from Group 4 elements, Group 5 elements and Group 6 elements of the periodic table excluding tungsten, and carbon, nitrogen, oxygen and boron. It is preferable to further include a second hard phase composed of a compound containing one or more nonmetallic elements. By defining in this way, when the cemented carbide is used as a material for a cutting tool, it is possible to secure a balance between wear resistance and chipping resistance as the cutting tool.

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

[6] The average particle size of the tungsten carbide particles is preferably 0.1 μm or more and 10 μm or less. By defining in this way, the cemented carbide can be further excellent in toughness and hardness.

[7] A cutting tool according to an aspect of the present disclosure includes the cemented carbide according to any one of [1] to [6] above as a base material. The above-mentioned cutting tool can realize processing corresponding to severer cutting conditions, longer life, and the like by providing a base material made of a cemented carbide having excellent toughness and hardness.

[8] Preferably, the cutting tool further comprises a coating provided on the base material. By providing the coating on the surface of the base material, the wear resistance of the cutting tool can be improved. Therefore, the above-mentioned cutting tool can cope with severer cutting conditions and achieve a longer life.

[Details of the embodiment of the present disclosure]
An embodiment of the present disclosure (hereinafter referred to as "this embodiment") will be described below. However, this embodiment is not limited to this. As used herein, a notation of the form "X to Y" means the upper and lower limits of a range (ie, greater than or equal to X and less than or equal to Y). 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 constituent elements is not limited, such as "TiC", the chemical formula can be any conventionally known composition ratio (element ratio) shall include At this time, 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 an element name is described, it may mean the simple substance of that element, or it may mean a constituent element in a 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 consists of tungsten carbide particles,
The binder phase contains nickel and a metal element M as constituent elements,
The metal element M contains 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 consists of tungsten carbide (hereinafter sometimes referred to as "WC") particles. Here, the WC includes not only “pure WC (WC that does not contain any impurity elements, and WC in which impurity elements are below the detection limit)” but also “as long as the effect of the present disclosure is achieved, WC in which other impurity elements are intentionally or unavoidably included. The content ratio of impurities in the WC particles (if there are two or more elements constituting the impurities, the total content ratio of them) is 5% by mass or less (5 wt% or less) with respect to the total amount of the WC and the impurities. be.

(Average particle size of WC particles)
The average particle size of the WC particles in the cemented carbide is preferably 0.1 μm or more and 10 μm or less, more preferably 0.5 μm or more and 3 μm or less. When the average grain 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, a cutting tool containing the cemented carbide as a base material can suppress chipping or breakage due to mechanical and thermal impacts. In addition, since the cutting tool has improved crack propagation resistance, crack propagation is suppressed, and chipping or breakage can be suppressed. On the other hand, when the average grain size is 10 μm or less, the hardness of the cemented carbide tends to increase. Therefore, a cutting tool containing the above cemented carbide as a base material can suppress deformation during cutting, and can suppress wear or chipping.

Here, the average grain size of the WC particles in the cemented carbide is determined by mirror-finishing any surface or cross-section of the cemented carbide, photographing the processed surface with a microscope, and analyzing the photographed image. Desired. Specifically, the particle diameter of each WC particle (Heywood diameter: equivalent circle diameter with equal area) is calculated from the photographed image, and the average value is taken as the average particle diameter of the WC particles. The number of WC particles to be measured should be at least 100, preferably 200 or more. Further, in the same cemented carbide, it is preferable to perform the above image analysis in a plurality of fields of view and use the average value as the average grain size of the WC grains. The number of fields for image analysis is preferably 5 or more, more preferably 7 or more, still more preferably 10 or more, and even more preferably 20 or more. One field of view may be, for example, a 20 μm long by 20 μm wide square.

Examples of mirror-finishing methods include polishing with diamond paste, using a focused ion beam device (FIB device), using a cross-section polisher device (CP device), and combining these methods. 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, scanning transmission electron microscopes (STEM), and the like. Images taken with a microscope are taken into a computer and analyzed using image analysis software to obtain various information such as the average particle size. At this time, each of the WC particles constituting the first hard phase, the binder phase described later, and the second hard phase described later can be identified from the photographed image by the shade of color. Image analysis type particle size distribution software (“Mac-View” manufactured by Mountec Co., Ltd.) can be preferably used as the image analysis software.

(Area ratio of first hard phase)
The cemented carbide according to the present embodiment preferably has an area ratio of the first hard phase of 85% or more and 96% or less with respect to any surface or any cross section of the cemented carbide. 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 contains the second hard phase, it will be described later). The area ratio of the first hard phase can be obtained, for example, by photographing an arbitrary processed surface of the cemented carbide with a microscope and analyzing the photographed image in the same manner as when obtaining the average grain size of the WC grains described above. Desired. That is, first, WC particles in a predetermined field of view are specified, and the sum of the areas of the WC particles specified 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. Moreover, in the same cemented carbide, it is preferable to perform the above image analysis in a plurality of fields of view (for example, 5 or more fields of view) and take the average value as the area ratio of the first hard phase. Image analysis type particle size distribution software (“Mac-View” manufactured by Mountec Co., Ltd.) can be preferably used for the image processing. The above-mentioned "predetermined field of view" may be the same as the field of view for determining the average particle size of the WC grains.

≪Bonded Phase≫
The binder phase binds the WC particles that form the first hard phase, the compounds that form the second hard phase described later, or the WC particles that form the first hard phase and the compound that forms the second hard phase. It is a phase that causes The content of the binder phase is preferably 4 wt % or more and 15 wt % or less based on the cemented carbide. The binder phase contains nickel (Ni) as constituent elements and a metal element M described later.

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. Say. The content of nickel and metal element M contained in the binder phase is preferably 80 wt % or more and 100 wt % or less, more preferably 90 wt % or more and 100 wt % or less.

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

The metal element M contains at least one selected from the group consisting of chromium (Cr), molybdenum (Mo), vanadium (V) and iron (Fe). More preferably, the metal element M contains molybdenum.

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

The content of nickel or metal element M contained in the binding phase can be measured by a titration method. That is, first, the atomic concentration of each element contained in the binding phase is obtained by a titration method. Here, the inventors consider that the atomic concentration measured by the titration method is the atomic concentration averaged over the entire bonding phase. Next, from the determined atomic concentration and the mass number of the corresponding element, the content ratio (wt%) of the element in the binder phase is determined.

(Area ratio of bonding phase)
The area ratio of the binder phase with respect to any surface or any cross section of the cemented carbide according to the present embodiment is preferably 4% or more and 15% or less, and more preferably 6% or more and 15% or less. . By setting the area ratio of the binder phase within the above range, the volume ratio of the first hard phase (a phase with higher hardness than the binder phase) in the cemented carbide is increased, and the cemented carbide as a whole can be The hardness can be increased and the adhesion strength between the first hard phase and the binder phase can be increased.

The area ratio of the binder phase can be calculated by the same method as the measurement of the area ratio of the first hard phase. That is, the bonded phases in a predetermined field of view are identified, and the sum of the areas of the bonded phases is calculated. Next, by dividing the sum of the calculated areas of the bonded phases by the area of the predetermined field of view, the area ratio of the bonded phases can be calculated. Moreover, in the same cemented carbide, it is preferable to perform the above image analysis in a plurality of fields of view (for example, 5 or more fields of view) and take the average value as the area ratio of the binder phase.

Examples of other elements that make up the binder phase include cobalt (Co) and copper (Cu). The above and other elements may be used alone, or may be used in combination. In addition, the binder phase may contain tungsten, carbon, and other unavoidable component elements of the first hard phase. The other elements that constitute the binder phase function as the binder phase (the WC particles that form the first hard phase, the compounds that form the second hard phase, or the WC particles that form the first hard phase). It is allowed to be included in the binding phase as long as the function of binding the compound constituting the second hard phase) is exhibited. In one aspect of the present embodiment, it can be understood that component elements other than the first hard phase and the later-described second hard phase are contained in the binder phase.

(stacking fault)
In the cemented carbide according to this embodiment, the binder phase has stacking faults. Here, "stacking fault" means a state in which the order of stacking is disturbed when the state of periodic stacking of two-dimensional atomic planes in a crystal is observed.

The presence or absence of stacking faults can be determined by observing a diffraction grating image in the binder phase of the cemented carbide (for example, the portion surrounded by the dashed line in FIG. 1) with a transmission electron microscope (STEM). At this time, 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 diffraction points in the diffraction grating image as shown in FIG. 2, it can be determined that the binder phase has stacking faults. On the other hand, in the binder phase having no stacking faults, such streaks are not observed, and only diffraction spots are observed in the diffraction grating image (eg, FIG. 3). In this embodiment, the measurement conditions used when observing the diffraction grating image are as follows.
STEM measurement conditions Equipment: JEM-2100F (manufactured by JEOL Ltd.)
・STEM image observation, EDX analysis (STEM mode)
Accelerating voltage: 200 kV
Current amount: 0.3nA
Magnification: 300,000 times, diffraction image photography (TEM mode)
Accelerating voltage: 200 kV
Camera length: 100cm
Magnification: 300,000 times

≪Second hard phase≫
The cemented carbide according to the present embodiment may further have a second hard phase having a composition different from that of the first hard phase. The second hard phase includes "one or more metal elements selected from the group consisting of Group 4 elements, Group 5 elements and Group 6 elements of the periodic table excluding tungsten" and "carbon (C), nitrogen (N), oxygen (O) and one or more nonmetallic elements selected from the group consisting of boron (B)" (composite compound). Examples of Group 4 elements of the periodic table include titanium (Ti), zirconium (Zr), hafnium (Hf), and the like. Vanadium (V), niobium (Nb), tantalum (Ta), etc. are mentioned as a periodic table V group element. Chromium (Cr), molybdenum (Mo), etc. are mentioned as a periodic table 6-group element. Compounds are mainly carbides, nitrides, carbonitrides, oxides, borides, etc. of the above metal elements.

The second hard phase may consist of particles of the above 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 composed of one or more of the above compounds. Here, the term "compound phase or solid solution phase" indicates that the compounds that constitute 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, Mo2C, ZrC, and the like.

When the cemented carbide further has a second hard phase, the area ratio of the first hard phase is set as the area ratio of the first hard phase (tungsten carbide particles) and the second hard phase combined. 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 cross section of the cemented carbide is It 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 binder phase is 100%. The area ratio of the second hard phase can be calculated by the same method as the measurement of the area ratio of the first hard phase. That is, the "second hard phase" is specified in a predetermined field of view, and the sum of the areas of the "second hard phase" is calculated. Next, it is possible to calculate the area ratio of the second hard phase by dividing the calculated sum of the areas of the second hard phase by the area of the predetermined field of view. Moreover, in the same cemented carbide, it is preferable to perform the above image analysis in a plurality of fields of view (for example, 5 or more fields of view) and take the average value as the area ratio of the second hard phase.

The area ratio of the second hard phase to any surface or any cross section of the cemented carbide is preferably 1% or more and 10% or less, more preferably 2% or more and 5% or less. By keeping the area ratio of the second hard phase within this range, while maintaining the hardness of the cemented carbide, cracking due to thermal or mechanical impact is suppressed, oxidation resistance and reaction resistance with the work material are improved. can improve sexuality. In addition, when the area ratio of the second hard phase is larger than the upper limit, the strength of the cemented carbide tends to decrease and the toughness tends to decrease.

<<Manufacturing method of cemented carbide>>
The cemented carbide of this embodiment can typically be produced through the following steps: raw material powder preparation step mixing step molding step degreasing step sintering step heating and rapid cooling step cooling step. Each step will be described below.

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

(WC particles)
The WC grains used as the raw material are not particularly limited, and WC grains commonly used in the production of cemented carbide may be used. Commercially available products may be used as the WC particles. Commercially available WC particles include, for example, the “Uniform Grain Tungsten Carbide Powder” series manufactured by A.L.M.T.

The average particle size of the WC particles used as the raw material is preferably 0.3 μm or more and 10 μm or less, more preferably 0.3 μm or more and 5 μm or less. When the average grain size of the WC grains used as the raw material is 0.3 μm or more, the toughness tends to be high when made into a cemented carbide. Therefore, a cutting tool containing the cemented carbide as a base material can suppress chipping and breakage due to mechanical and thermal impacts. In addition, since the cutting tool has improved resistance to crack propagation, propagation of cracks is suppressed, and chipping and breakage can be suppressed. On the other hand, when the average grain size is 10 μm or less, the cemented carbide tends to have a high hardness. Therefore, a cutting tool containing the above cemented carbide as a base material can suppress deformation during cutting, and can 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. Commercially available products may be used as the nickel-containing particles.

The average particle diameter of the nickel-containing particles is preferably 0.5 μm or more and 10 μm or less, 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 the raw material are preferably molybdenum metal particles, chromium metal particles, vanadium metal particles, or iron metal particles. Commercially available particles may be used as the particles containing the metal element M.

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

(Compound constituent powder)
The compound-constituting powder is not particularly limited, and a compound-constituting powder that is usually used as a raw material for the second hard phase in the production of cemented carbide may be used. Examples of such compound constituent powders include TaC, TiC, NbC, Cr ₃ C ₂ , ZrC and TiN.

One of the conditions for uniformly dispersing the second hard phase with a uniform grain size in the cemented carbide is to use a powder with fine grains and a uniform grain size as the compound-constituting powder. By doing so, the second hard phase can be made fine and dispersed in the sintering step, which will be described later. The average particle size of the compound-constituting powder is, for example, in the range of 0.5 μm or more and 3 μm or less. The smaller the average particle size of the compound-constituting powder used as the raw material, the smaller the average particle size of the second hard phase in the finally obtained cemented carbide. The larger the average particle size of the compound-constituting powder used as the raw material, the larger the average particle size of the second hard phase in the finally obtained cemented carbide. The compound-constituting powder can be obtained by pulverizing/classifying a commercially available product so as to obtain a fine particle having a uniform particle size.

<Mixing process>
The mixing step is a step of mixing each raw material powder prepared in the preparation step. A mixed powder in which each raw material powder is mixed is obtained by the mixing step. The mass ratio of the raw material powders (for example, WC particles, nickel-containing particles, metal element M-containing particles, etc.) when mixed is the area ratio of the first hard phase, the area ratio of the second hard phase, and the The ratio corresponds to the area ratio of the bonding phase. A known device can be used for the device used in the mixing step. For example, attritors, rolling ball mills, Karman mixers, bead mills and the like can be used. An example of mixing conditions when using an attritor is rotation speed: 100 m/min or more and 400 m/min or less, and mixing time: 1.5 hours or more and 25 hours or less. The mixing conditions for the attritor may be either wet mixing or dry mixing. Mixing may also be performed in a solvent such as water, ethanol, acetone, or isopropyl alcohol. Mixing may be performed with a binder such as polyethylene glycol, paraffin wax, and the like.

After the mixing process, the mixed powder may be granulated as needed. By granulating the mixed powder, it is easy to fill the mixed powder into a die or mold during the molding process 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 step is a step of molding the mixed powder obtained in the mixing step into a predetermined shape to obtain a compact. General methods and conditions may be adopted for the molding method and molding conditions in the molding step, and are not particularly limited. Examples of the predetermined shape include cutting tool shapes (for example, the shape of indexable cutting inserts: CNMG120408, etc.).

<Degreasing process>
The degreasing step is a step of removing a binder (such as paraffin wax) in the molded body obtained in the molding step, and is a step of performing heat treatment under the following conditions.

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

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

The treatment time in the degreasing step is preferably 30 minutes or more and 120 minutes or less, more preferably 60 minutes or more and 90 minutes or less.

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

<Sintering process>
The sintering step is a step of sintering the molded body obtained through the degreasing 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 30 minutes or more and 120 minutes or less, more preferably 50 minutes or more and 90 minutes or less.

The atmosphere during sintering is not particularly limited, and may be an _N2 gas atmosphere or an inert gas atmosphere such as Ar.

Also, 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. Although the lower limit is not particularly limited, it may 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 volatilization of Ni and the like from the surface of the compact during sintering.

In addition, the sintering process may perform a sintering HIP (sintering HIP) process which can pressurize at the time of sintering. HIP conditions include, for example, N ₂ gas atmosphere, inert gas atmosphere such as Ar, temperature: 1300° C. or higher and 1350° C. or lower, pressure: 5 MPa or higher and 200 MPa or lower.

<Heating and rapid cooling process>
The heating and quenching step is a step of repeatedly heating and quenching the sintered compact after completion of sintering (see FIG. 4). The present inventors believe that the heating and quenching step facilitates the generation of stacking faults in the binder phase.

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

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

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

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

The temperature drop rate during rapid cooling in the heating and rapid cooling step is preferably 10°C/minute or more and 20°C/minute or less, more preferably 12°C/minute or more and 17°C/minute or less.

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

The number of repetitions of heating and quenching in the heating and quenching step is preferably 3 or more, and more preferably 3 or more and 5 or less from the viewpoint of production cycle time.

The atmosphere in the heating and quenching step is not particularly limited, and may be an N ₂ gas atmosphere or an inert gas atmosphere such as Ar.

The pressure in the heating and rapid cooling step is preferably 100 kPa or more and 490 kPa or less, 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 rapid cooling step to room temperature. The cooling step is not particularly limited. The cooling rate is, for example, cooling at a temperature drop rate of 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/min. The atmosphere at the time of cooling is not particularly limited, and may be an N ₂ gas atmosphere or an inert gas atmosphere such as Ar. The pressure during cooling is not particularly limited, and may be increased or reduced. The pressure at the time of pressurization is, for example, 400 kPa or more and 500 kPa or less. Further, the pressure during the decompression is, for example, 100 kPa or less, preferably 10 kPa or more and 50 kPa or less. In one aspect of the present embodiment, the cooling step includes cooling the sintered body to room temperature in an Ar gas atmosphere.

≪Cutting tools, wear-resistant tools and grinding tools≫
Since the cemented carbide of this embodiment has excellent toughness and hardness as described above, it can be used as a base material for cutting tools, wear-resistant tools and grinding tools. That is, the cutting tool of this embodiment contains the cemented carbide as a base material. Further, the wear-resistant tool and grinding tool of the present embodiment contain the cemented carbide as a base material.

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, drills, end mills, indexable cutting inserts for milling, indexable cutting inserts for turning, metal saws, gear cutting tools, reamers and taps. Examples of wear-resistant tools include dies, scribers, scribing wheels, and dressers. Furthermore, as a grinding tool, for example, a grinding wheel can be exemplified.

The cemented carbide of this embodiment may constitute the entirety of these tools. The cemented carbide may form part of these tools. Here, "constituting a part" indicates, for example, in the case of a cutting tool, a cutting edge portion formed by brazing the cemented carbide of the present embodiment at a predetermined position of an arbitrary base material.

<Coating>
The cutting tool according to this embodiment may further include a coating provided on the substrate. The wear-resistant tool and grinding tool according to this embodiment may further include a coating provided on the substrate. The composition of the coating is one or more metals 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). Examples include compounds of the element with one or more nonmetallic 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 this embodiment, the film may be a single metal. In addition, cubic boron nitride (cBN), diamond-like carbon, and the like are also suitable as the coating composition. Such coatings can be formed by vapor phase methods such as chemical vapor deposition (CVD) methods and physical vapor deposition (PVD) methods. When the coating is formed by the CVD method, it is easy to obtain a coating with excellent adhesion to the substrate. The CVD method includes, for example, a thermal CVD method. When the film is formed by the PVD method, compressive residual stress is imparted, and the toughness of cutting tools and the like is likely to be increased.

The coating in the cutting tool according to the present embodiment is preferably provided on the cutting edge portion of the base material and its vicinity. The coating may be provided on the entire surface of the substrate. Also, 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 may be 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.

≪Fabrication of Cemented Carbide≫
<Preparation of raw material powder: preparation process>
Powders having the compositions shown in Table 1 were prepared as raw material powders. Raw material powders used as the first hard phase, the second hard phase, or the binder phase in Table 1 had the following average particle sizes.
Average particle size WC of each raw material powder: 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 particle size 3 μm
V: average particle size 3 μm
Fe: average particle size 3 μm

<Mixing of Raw Material Powders: Mixing Process>
Each of the prepared raw material powders was added at the mixing ratio shown in Table 1 and mixed using an attritor to prepare a mixed powder. Mixing conditions are shown below. After mixing, the resulting slurry was dried in the atmosphere to obtain a mixed powder.
Attritor mixing condition ball: Cemented carbide, diameter 3.5 mm
Dispersion medium: ethanol Rotational speed of stirrer: 100 rpm
Processing time: 12 hours

<Production of molded body: molding process>
The mixed powder thus obtained was press-molded to produce a molded body having a model number CNMG120408 (manufactured by Sumitomo Electric Hardmetal Co., Ltd.) (indexable cutting tip).

<Degreasing of Molded Body: Degreasing Process>
The compact thus obtained was placed in a sintering furnace and degreased under the following conditions.
Temperature during treatment: 500°C
Pressure during treatment: 250 kPa
Processing time: 60 minutes Atmosphere during processing: Ar gas

<Sintering compact: sintering process>
After the degreasing step, the molded body was sintered for 60 minutes in an Ar gas atmosphere (0.5 kPa) under the sintering program shown in Table 2 under the maximum sintering temperature (Tmax).

<Heat and rapid cooling of compact: heating and rapid cooling process>
The samples corresponding to sintering program 1 (FIG. 4) in Table 2 were subjected to heating and rapid cooling under the following conditions after the sintering process. On the other hand, the samples corresponding to sintering program 2 (FIG. 5) in Table 2 were not heated and quenched after the sintering process.
Atmosphere during treatment conditions for heating and rapid cooling process: Pressure during Ar gas treatment: 200 kPa
Temperature during heating: 600°C
Heating rate during heating: 15°C/min Holding time during heating: 10 minutes Temperature during rapid cooling: 200°C
Heating rate during rapid cooling: 15°C/min Holding time during rapid cooling: 10 minutes Number of repetitions of heating and rapid cooling: 3 times

<Cooling of compact: cooling process>
After completion of the heating and quenching process, it was cooled to room temperature in an Ar gas atmosphere. At this time, the temperature was cooled at a rate of temperature decrease of 2°C/min. From the above, sample no. 1 to 13 cemented carbide and sample no. Cemented carbides of 101 to 107 were produced. Sample no. Cemented carbides 1 to 13 correspond to the examples. Sample no. Cemented carbides 101-103 correspond to comparative examples. Sample no. Cemented carbides 104-107 correspond to reference examples.

<<Observation of sample>>
<Calculation of Average Particle Size of Tungsten Carbide Particles>
Sample no. 1 to 13 and sample no. Cemented carbides No. 101 to 107 were cut and the cut surface was mirror-finished. Thereafter, the mirror-finished cut surfaces were subjected to ion milling using an argon ion beam, and these cross sections were used as microscopic observation samples.

The processed surface of this observation sample was photographed with a scanning transmission electron microscope (STEM) (manufactured by JEOL Ltd.) at a magnification of about 2000 times. For each sample, 10 fields of view were taken for each of the outer side of the processed surface and the center of the processed surface.

For each sample, for 300 or more tungsten carbide particles per field of view, image analysis type particle size distribution software ("Mac-View" manufactured by Mountech Co., Ltd.) is used to determine the particle size (Heywood diameter) of each particle. , the average particle size of the tungsten carbide particles after sintering in a total of 10 fields of view was calculated. As a result, it was found that the average particle size of the tungsten carbide particles after sintering was substantially equal to the average particle size of the WC particles used as the raw material.

<Calculation of Area Ratios of First Hard Phase, Second Hard Phase, and Bonding Phase>
Using image analysis type particle size distribution software (“Mac-View” manufactured by Mountec Co., Ltd.), the area ratio of the first hard phase, the second hard phase and the binder phase on the processed surface of each sample was determined. As a result, the area ratios of the first hard phase, the second hard phase, and the binder phase correspond to the mixing ratios of the raw material powders corresponding to the first hard phase, the second hard phase, and the binder phase (Table 1). I found out.

<Composition analysis of bonded phase>
The binder phase on the processed surface of each sample was analyzed by a titration method to determine the composition of the binder phase. As a result, it was found that the composition of the binder phase corresponds to the raw composition of the binder phase shown in Table 1.

<Stacking faults in binder phase>
The presence or absence of stacking faults was determined by observing the diffraction grating image of the bonding phase on the processed surface of each sample with an STEM. Measurement conditions are shown below. When streaks were observed between diffraction points in the diffraction grating image, the binder phase of the sample was determined to have stacking faults. Table 3 shows the results.
STEM measurement conditions Equipment: JEM-2100F (manufactured by JEOL Ltd.)
・STEM image observation, EDX analysis (STEM mode)
Accelerating voltage: 200 kV
Current amount: 0.3nA
Magnification: 300,000 times, diffraction image photography (TEM mode)
Accelerating 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. Table 3 shows the results.
Load: 1kgf
Holding time: 10s

<Measurement of transverse rupture strength>
The transverse rupture strength of each sample was measured under the following conditions. Table 3 shows the results.
Specimen size: 4mm x 8mm x 30mm
Distance between lower fulcrums: 20 mm
Load speed: 3.5mm/min

≪Cutting test≫
A hard film was formed on the surface of each sample by an ion plating method, which is a kind of known PVD method, to prepare a cutting tool for a cutting test. A TiAlN film having a thickness of 4.8 μm was used as the hard film. Below, sample no. A cutting tool using the cemented carbide of No. 1 as a base material is referred to as "Sample No. 1 cutting tool" or the like. Sample no. The same applies to samples other than No. 1.

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

<Cutting test 2: Fracture resistance test>
Sample No. prepared as described above. 1 to 13 and sample no. Using cutting tools Nos. 101 to 107, the cutting time (minutes) until chipping occurred on the cutting edge was measured under the following cutting conditions. Table 3 shows the results. As the cutting time is longer, the cutting tool can be evaluated to have excellent chipping resistance.
Fracture resistance test conditions Work material: SCM435 groove material (number of grooves: 4)
Cutting speed: 200m/min
Feed rate: 0.3mm/rev
Cutting depth: 2mm
Cutting oil: Yes

From the results in Table 3, sample No. Cutting tools 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 conventional cemented carbides containing cobalt in the binder phase (Sample Nos. 104-107). On the other hand, sample no. Cutting tools 101 to 103 (comparative examples) had a cutting time of 52 minutes or less in cutting test 1.

From the results in Table 3, sample No. Cutting tools 1 to 13 (Examples) had a cutting time of 2.9 minutes or longer in Cutting Test 2, which was a good result. This result is comparable to conventional cemented carbides containing cobalt in the binder phase (Sample Nos. 104-107). On the other hand, sample no. Cutting tools 101 to 103 (comparative examples) had a cutting time of 2.0 minutes or less in cutting test 2.

From the above results, sample No. Cemented carbides of 1 to 13 (Examples) are sample Nos. It was found to be superior to the cemented carbides of 101 to 103 (comparative examples) in hardness and toughness.

Although the embodiments and examples of the present invention have been described above, it is planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

The embodiments and examples disclosed this time are illustrative in all respects and should be considered not restrictive. The scope of the present invention is indicated by the scope of the claims rather than the above-described embodiments and examples, and is intended to include meanings equivalent to the scope of the claims and all modifications within the scope.

Claims

A cemented carbide comprising a first hard phase and a binder phase,
The first hard phase consists of tungsten carbide particles,
The binder phase contains nickel and a metal element M as constituent elements,
The metal element M contains at least one selected from the group consisting of chromium, molybdenum, vanadium and iron,
The cemented carbide, wherein the binder phase has stacking faults.
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 contains molybdenum.
One or more metal elements selected from periodic table group 4 elements, group 5 elements and group 6 elements excluding tungsten, and one or more non-metal elements selected from the group consisting of carbon, nitrogen, oxygen and boron Cemented carbide according to any one of claims 1 to 3, further comprising a second hard phase consisting of a compound comprising:
The second hard phase consists of particles of the compound,
5. The cemented carbide according to claim 4, wherein the particles of said compound have an average particle size of 0.05 [mu]m or more and 2 [mu]m or less.
The cemented carbide according to any one of claims 1 to 5, wherein the tungsten carbide particles have an average particle size of 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 base material.
The cutting tool according to claim 7, further comprising a coating provided on the base material.