JP6443207B2 - Cemented carbide and cutting tools - Google Patents

Description

  The present invention relates to a cemented carbide and a cutting tool. In particular, the present invention relates to a cemented carbide and a cutting tool that can effectively suppress flank wear and have excellent chipping resistance.

  2. Description of the Related Art Conventionally, as a cutting tool, a cemented carbide tool including a cemented carbide in which a WC particle is a main hard phase and bonded with a binder phase mainly composed of an iron group metal such as Co or Ni is used as a cutting tool. Yes. Typical performances required for cemented carbide tools include wear resistance and chipping resistance.

  When a work material is cut with a cutting tool, heat is generated due to deformation of the cut chips and friction with the work material and the chips, and the cutting edge surface of the cutting tool becomes hot during cutting. When the cemented carbide is heated, the hardness tends to decrease and the strength tends to decrease. Thus, wear and defects are likely to occur, and chemical wear also easily proceeds.

Therefore, in order to improve the wear resistance and heat resistance of the cemented carbide used as the base material for cutting tools, in addition to WC, TiC, TaC, NbC, etc. are added as the hard phase, or the cemented carbide base material. The surface is coated with TiC, TiN, TiCN, Al ₂ O ₃ or the like. (See Patent Documents 1 to 3.)

  Patent Documents 1 to 3 describe a technique for forming a de-β layer (a layer made of only WC-Co without a β phase) on the surface of a cemented carbide. In general, the de-β layer has a higher binder phase content than the inside of the cemented carbide and is soft, so it has excellent toughness. Therefore, by forming a de-β layer on the surface of the cemented carbide, it is possible to mitigate the impact during cutting and suppress the development of cracks, improving the impact resistance and fracture resistance of the cemented carbide. it can.

Japanese Patent Laid-Open No. 60-174876 JP 61-34103 A JP-A-8-225877

  In recent years, higher efficiency of cutting has been demanded, and machining under high load cutting conditions such as high speed, high feed, and high cutting has been increasing, and the temperature rise of the tool edge during cutting is remarkable. Therefore, the request | requirement with respect to the abrasion resistance of a cemented carbide tool and the improvement of a fracture resistance is increasing further.

  In a cemented carbide base material, when the cutting edge surface is locally heated at the time of cutting, the hardness and strength of the surface portion are reduced, so that chipping occurs due to impact at the time of cutting, and defects are likely to occur from that point. In addition, the flank that forms the cutting edge generates heat due to rubbing with the work material during cutting, and is easily deformed when pressed against the work material in a high temperature state, so the flank wear progresses quickly.

  The present invention has been made in view of the above circumstances, and one of its purposes is to provide a cemented carbide which can effectively suppress flank wear and has excellent chipping resistance. Another object is to provide a cutting tool including a substrate made of the above cemented carbide.

  The cemented carbide according to one aspect of the present invention is selected from a first hard phase composed of WC particles, at least one metal selected from Group 4, 5, and 6 elements of the periodic table, and C, N, O, and B. And a binder phase containing at least one iron group metal selected from Co, Ni, and Fe, and the content of the binder phase is A low β layer having a content of 4% by mass or more and 11% by mass or less and having a lower content of the second hard phase than the inside is formed on the surface, and the heat permeability of the low β layer is TEa, and the internal heat When the penetration rate is TEb, 1.02 <TEa / TEb <1.08 is satisfied.

  The cutting tool which concerns on 1 aspect of this invention is equipped with the base material which consists of a cemented carbide alloy which concerns on 1 aspect of the said invention.

  The cemented carbide can effectively suppress flank wear and has excellent chipping resistance. The cutting tool can exhibit excellent wear resistance and fracture resistance.

It is a figure which shows the optical microscope photograph of the cross section of the cemented carbide alloy which concerns on embodiment. It is a schematic perspective view of the blade-tip-exchange-type cutting tip which is an example of the cutting tool which concerns on embodiment of this invention. FIG. 3 is a partially enlarged schematic cross-sectional view in the vicinity of the cutting edge in the (II)-(II) cross section of the cutting edge replacement type cutting tip shown in FIG. It is a figure which shows the optical microscope photograph of the cross section of the conventional cemented carbide.

  The present inventors have a de-β layer (a layer that is substantially free of WC and a binder phase (iron group metal) without a solid solution (β phase) containing a compound such as TiC or TaC) on the surface. As a result of intensive studies on the relationship between thermal characteristics and cutting performance in cemented carbides to which TiC, TaC, NbC, etc. were added, the following findings were obtained.

  Although it depends on the literature, the thermal conductivity of WC, which is the main hard phase of cemented carbide, is said to be about 140 W / mK. On the other hand, the thermal conductivity of TiC, TaC, NbC, etc. added as a hard phase is as low as about 10-50 W / mK. The thermal conductivity of the iron group metal as the binder phase is about 100 W / mK for Co, 90 W / mK for Ni, and about 80 W / mK for Fe. The thermal conductivity of a general cemented carbide is about 50 to 80 W / mK, although it depends on the type, particle size, content, etc. of the compound particles constituting the hard phase.

  FIG. 4 is a view showing a micrograph (magnification 1000 times) of a cross section of a conventional cemented carbide having a de-β layer, and dark gray particles in the structure are β phase. In FIG. 4, the upper side of the paper is the surface side of the cemented carbide, the upper black part is the resin embedded with the cemented carbide, and the other part is the cemented carbide. As shown in FIG. 4, the deβ layer 110 is formed on the surface of the cemented carbide, and the β phase 101 is hardly present in the deβ layer 110. When examining the thermal characteristics of conventional cemented carbide, WC and iron group metal with high thermal conductivity exist in the de-β layer on the surface, and the hard phase has thermal conductivity in the hard phase. Since low TiC, TaC, NbC, etc. exist, the surface portion (deβ layer) has a relatively high thermal conductivity compared to the inside. In the conventional cemented carbide, part of the heat generated on the cutting edge surface during cutting tends to diffuse from the deβ layer on the surface, but the internal heat conductivity is low. Since heat conduction is hindered at the interface, heat is likely to be generated in the de-β layer, and the surface portion (particularly, the cutting edge portion) tends to be locally hot. Therefore, the conventional cemented carbide tends to easily wear on the surface portion, and further, defects due to the strength reduction of the surface portion, thermal cracks and defects due to local thermal expansion and thermal shock of the surface portion, etc. This problem is likely to occur.

The present inventors pay attention to the thermal permeability between the surface part and the inside of the cemented carbide, and reducing the ratio of the thermal permeability between the surface part and the interior can reduce the wear resistance and fracture resistance of the cemented carbide tool. It was found to be effective for improving the sex. Specifically, in the de-β layer on the surface part of the cemented carbide, by partially leaving the β phase without completely disappearing the β phase, while reducing the heat permeability ratio between the surface part and the inside, The function (impact resistance and fracture resistance) as a conventional de-β layer is ensured to some extent. Since such a cemented carbide has a small thermal permeability ratio between the surface portion and the inside, heat reflection is unlikely to occur at the interface between the surface portion and the inside, and heat can be effectively diffused from the surface portion to the inside. The temperature rise of the surface portion is small, and the surface portion is unlikely to become high temperature. As a result, wear and chipping due to high temperatures can be suppressed, and the wear resistance and chipping resistance of the tool are improved. The thermal permeability is an index (unit: J / (m ² s ^1/2 K)) indicating the ease of heat transfer between two substances in contact with each other. If the thermal permeability of the two substances is equal, Even if the thermal conductivity and specific heat are different, heat is diffused without reflection of heat at the interface between the two substances.

[Description of Embodiment of the Present Invention]
Embodiments of the present invention will be listed and described.

  (1) A cemented carbide according to an aspect of the present invention includes a first hard phase composed of WC particles, at least one metal selected from Group 4, 5, and 6 elements of the periodic table, C, N, O, and A second hard phase composed of a compound with at least one element selected from B, and a binder phase containing at least one iron group metal selected from Co, Ni and Fe. This cemented carbide has a binder phase content of 4 mass% or more and 11 mass% or less. In this cemented carbide, a low β layer having a lower content of the second hard phase than the inside is formed on the surface portion, and the thermal permeability of the low β layer is TEa, and the internal thermal permeability is TEb. In this case, 1.02 <TEa / TEb <1.08 is satisfied.

  According to the above-mentioned cemented carbide, the low β layer having a lower content of the second hard phase than the inside is formed on the surface portion, and the heat permeability TEa of the low β layer on the surface portion and the internal heat permeability TEb (Thermal permeability ratio) satisfies 1.02 <TEa / TEb <1.08. Therefore, the cemented carbide has a small heat permeability ratio between the low β layer on the surface and the inside, so that heat generated on the surface of the cutting edge during cutting is easily diffused from the low β layer on the surface to the inside. Can effectively dissipate heat from the inside. Therefore, since the said cemented carbide can suppress that a surface part becomes high temperature locally and can suppress the fall of the hardness and intensity | strength of a surface part, abrasion resistance and a chipping resistance (chipping-proof) property improve. Furthermore, since the temperature rise at the surface portion is small and the temperature difference between the surface portion and the inside is small, the thermal shock resistance is also improved. Specifically, it is possible to suppress chipping from occurring on the surface portion due to an impact during cutting, and it is also possible to suppress defects starting from the chipping. Especially on the flank surface, the temperature rise due to scratching with the work material is suppressed, so it is difficult to become high temperature and deformation due to the pressing of the work material is difficult to occur, effectively suppressing flank wear. it can. Here, since the β phase (second hard phase component) is present in any degree in the layer formed on the surface portion, the conventional “substantially composed of WC of the first hard phase and metal of the binder phase”. Since it is different from “de-β layer”, it is called “low β layer”.

  When TEa / TEb ≦ 1.02, the content (content ratio) of the second hard phase in the low β layer on the surface portion is increased, so that the toughness of the surface portion (low β layer) is reduced. The functions of impact resistance and fracture resistance due to the β layer are not sufficiently exhibited. When TEa / TEb ≧ 1.08, the heat permeability ratio between the low β layer on the surface and the inside is increased, so that heat radiation from the surface to the inside is inhibited.

  When the content of the binder phase is 4% by mass or more, deterioration of sinterability during production is prevented, and the hard phase is firmly bonded by the binder phase, so that the strength is high and defects are not easily generated. Moreover, the toughness of a cemented carbide improves because content of a binder phase is 4 mass% or more. When the binder phase content is 11% by mass or less, it is possible to suppress a decrease in hardness of the cemented carbide due to a relative decrease in the hard phase, and it is possible to suppress a decrease in wear resistance and plastic deformation resistance.

  (2) As an example of the cemented carbide, there is an embodiment in which the maximum particle size of the second hard phase in the low β layer is less than 4 μm.

  When the maximum particle size of the second hard phase (β phase) is less than 4 μm in the low β layer on the surface, it is difficult to become a starting point of cracks due to impact during cutting, and chipping and chipping can be suppressed.

  (3) As an example of the cemented carbide, there is an embodiment in which the average particle size of the WC particles is 0.4 μm or more and 4.0 μm or less.

  When the average particle diameter of the WC particles is 0.4 μm or more, the toughness is high, and chipping and chipping due to mechanical and thermal impact can be suppressed. Further, since the crack propagation resistance is improved, the propagation of cracks is suppressed, and chipping and chipping can be suppressed. Since the average particle diameter of the WC particles is 4.0 μm or less, the hardness is high and deformation at the time of cutting is suppressed, so that wear and defects can be suppressed.

  (4) The cutting tool which concerns on 1 aspect of this invention is equipped with the base material which consists of a cemented carbide as described in any one of said (1)-(3).

  Since the cutting tool includes the cemented carbide having excellent wear resistance and fracture resistance (chipping resistance) on the base material, it can exhibit excellent wear resistance and fracture resistance, and has a long tool life. Specific examples of the cutting tool include a cutting edge replaceable cutting tip (throw away tip), a cutting tool, an end mill, a drill, a metal saw, a gear cutting tool, a reamer, and a tap.

  (5) As an example of the cutting tool, an aspect in which a coating film is provided on the surface of the base material can be given.

By providing a coating film on the surface of the substrate, the wear resistance of the tool can be improved, and the life can be further extended. Examples of the constituent material of the coating film include TiC, TiN, TiCN, Al ₂ O _{3 and the} like.

  (6) As an example of the cutting tool, an aspect in which the coating film is formed by a chemical vapor deposition method can be given.

  Since the coating film is formed by the chemical vapor deposition (CVD) method, a hard film having excellent adhesion to the substrate can be obtained.

[Details of the embodiment of the present invention]
Specific examples of the cemented carbide and the cutting tool according to the embodiment of the present invention will be described below. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to a claim are included.

<Cemented carbide>
The cemented carbide according to the embodiment includes a first hard phase composed of WC particles, at least one metal selected from Group 4, 5, and 6 elements of the periodic table, and at least 1 selected from C, N, O, and B. The composition comprises a second hard phase composed of a compound with a seed element, a binder phase containing at least one iron group metal selected from Co, Ni and Fe, and an unavoidable impurity. It does not specifically limit as a composition of a cemented carbide alloy, A well-known composition is also employable.

[First hard phase]
The cemented carbide has a first hard phase and a second hard phase as a hard phase, and contains WC particles of the first hard phase as a main component. In the cemented carbide, WC particles are contained in an amount of at least 50% by mass, for example, 70% by mass to 97% by mass. The content of WC particles is preferably 75% by mass or more, 80% by mass or more, 85% by mass or more, and 95% by mass or less.

(WC particles)
The average particle diameter of the WC particles constituting the first hard phase is preferably 0.4 μm or more and 4.0 μm or less. When the average particle diameter of the WC particles is 0.4 μm or more, the toughness is high, and chipping and chipping due to mechanical and thermal impact can be suppressed. Further, since the crack propagation resistance is improved, the propagation of cracks is suppressed, and chipping and chipping can be suppressed. Since the average particle diameter of the WC particles is 4.0 μm or less, the hardness is high and deformation at the time of cutting is suppressed, so that wear and defects can be suppressed. The average particle size of the WC particles is more preferably 1.0 μm or more and 2.0 μm or more, and further preferably 2.5 μm or more and 3.5 μm or less.

(Second hard phase)
The second hard phase is a compound (solid solution) of at least one metal selected from Group 4, 5, 6 elements of the periodic table and at least one element selected from C, N, O and B, excluding WC particles. Particles). Examples of the metal include Ti, Ta, Nb, Zr, V, and Cr. The compounds are mainly carbides, nitrides, carbonitrides, oxides, borides, and the like of the above metals, and the compounds include these solid solutions. Specific compounds include TiC, TaC, TiCN, NbC, ZrC, ZrN, TiN, TaN, TaCN, (Ta, Nb) C, VC, Cr ₃ C _{2 and the} like. In the cemented carbide, the second hard phase may be contained, for example, in the range of 1% by mass to 15% by mass.

[Binder Phase]
The binder phase preferably contains at least one iron group metal selected from Co, Ni and Fe as a main component, and substantially consists of the iron group metal. In addition to inevitable impurities, constituent elements (W, Ti, Ta, Nb, etc.) of WC constituting the hard phase and compounds of the second hard phase (TiC, TaC, NbC, etc.) are dissolved in the binder phase. Is acceptable.

  The content of the binder phase is preferably 4% by mass or more and 11% by mass or less. When the content of the binder phase is 4% by mass or more, deterioration of sinterability during production is prevented, and the hard phase is firmly bonded by the binder phase, so that the strength is high and defects are not easily generated. Moreover, the toughness of a cemented carbide improves because content of a binder phase is 4 mass% or more. When the binder phase content is 11% by mass or less, it is possible to suppress a decrease in hardness of the cemented carbide due to a relative decrease in the hard phase, and it is possible to suppress a decrease in wear resistance and plastic deformation resistance.

[Low β layer]
In the cemented carbide, a low β layer in which the content of the second hard phase is smaller than the inside is formed on the surface portion. Unlike the conventional “de-β layer”, the low β layer includes a β phase (a solid solution containing a compound of the second hard phase) to some extent. In the interior deeper than the low β layer, the composition of the cemented carbide, that is, the contents of the WC particles, the second hard phase, and the binder phase are substantially constant. The lower the content ratio (mass ratio) of the second hard phase in the low β layer is, the higher the heat permeability ratio between the low β layer and the inside is, and the content ratio of the second hard phase in the low β layer is The higher it is, the smaller the thermal permeability ratio between the low β layer and the inside. That is, the closer the content ratio of the second hard phase in the low β layer and the inside, the closer the heat permeability ratio between the low β layer and the inside approaches 1. The low β layer only needs to be formed on at least the cutting edge portion of the cemented carbide, and may be formed on the entire surface of the cemented carbide. The specific thickness of the low β layer is, for example, about 7 μm to 35 μm although it depends on the composition and manufacturing method of the cemented carbide. The thickness of the low β layer is preferably 10 μm or more and 30 μm or less. When the thickness of the low β layer is 10 μm or more, functions of impact resistance and fracture resistance are easily exhibited. On the other hand, if the low β layer is too thick, the hardness is lowered and the plastic deformation resistance is lowered. Therefore, the thickness of the low β layer is preferably 30 μm or less. The maximum particle size of the second hard phase in the low β layer is preferably less than 4.0 μm. When the maximum particle size of the second hard phase is less than 4.0 μm, it is difficult to become a starting point of a crack due to an impact at the time of cutting, and chipping and chipping can be suppressed. The maximum particle size of the second hard phase is more preferably 2.0 μm or less and 1.0 μm or less. Although the minimum of the maximum particle size of a 2nd hard phase is not specifically limited, For example, they are 0.1 micrometer or more and 0.4 micrometer or more.

[Heat permeability ratio between low β layer and inside (TEa / TEb)]
In the cemented carbide, the low β layer is formed on the surface, so that the heat permeability ratio between the low β layer on the surface and the inside is small, the heat permeability of the low β layer is TEa, and the internal heat When the penetration rate is TEb, 1.02 <TEa / TEb <1.08 is satisfied. Because the heat permeability ratio between the low β layer on the surface and the inside is small, the heat generated on the cutting edge surface during cutting is easily diffused from the low β layer on the surface to the inside, and heat can be effectively radiated from the surface to the inside. . When TEa / TEb ≦ 1.02, the content (content ratio) of the second hard phase in the low β layer on the surface portion is increased, so that the toughness of the surface portion (low β layer) is reduced. The functions of impact resistance and fracture resistance due to the β layer are not sufficiently exhibited. When TEa / TEb ≧ 1.08, the heat permeability ratio between the low β layer on the surface and the inside is increased, so that heat radiation from the surface to the inside is inhibited.

<Evaluation of cemented carbide>
<Evaluation of WC particles>
The evaluation of the WC particles in the cemented carbide is performed by mirror-finishing any surface or cross section of the cemented carbide and observing the processed surface with a microscope.

  Examples of the mirror finishing method include a method of polishing with diamond paste, a method using a focused ion beam (FIB) device, a method using a cross section polisher (CP) device, and a method combining these. .

  When the processed surface is observed with a metal microscope, it is preferable to etch the processed surface with Murakami's reagent. Various information such as an average particle diameter can be acquired by capturing an image obtained by microscopic observation into a computer and analyzing it using image analysis software. Examples of such software include image analysis type particle size distribution software (for example, “Mac-View” manufactured by Mountec Co., Ltd.).

  In addition, it is preferable to use a cutting edge portion as the observation surface. Examples of the microscopic observation method include observation at a magnification of 750 to 1500 times with a metal microscope and 3000 to 10,000 times with a scanning electron microscope (SEM).

  The particle diameter (Heywood diameter (equivalent area equivalent circle diameter)) of each WC particle is calculated from an image obtained by microscopic observation, and the average value is defined as the average particle diameter of the WC particles. The number of WC particles to be measured is at least 100 or more, preferably 200 or more.

<Evaluation of low β layer>
The thickness of the low β layer can be measured by mirror-processing a cross section of the cemented carbide perpendicular to the surface and observing the processed surface with an optical microscope. FIG. 1 is a view showing a micrograph (magnification 1000 times) of a cross section of an example of the cemented carbide according to the embodiment, and dark gray particles in the structure are β phase. In FIG. 1, the upper side of the paper is the surface side of the cemented carbide, the upper black part is the resin embedded with the cemented carbide, and the other part is the cemented carbide. As shown in FIG. 1, the low β layer 111 is formed on the surface of the cemented carbide, and a small amount of β phase 101 (indicated by a circle in the figure) remains in the low β layer 111. ing. Since the content (content ratio) of the β phase 101 is greatly different between the low β layer 111 and the interior 120, as shown in FIG. On the other hand, the interface with the low low β layer 111 region can be determined. When the vicinity of the surface of the cemented carbide cross section is observed, the region where the β phase abundance is relatively low is defined as the low β layer 111, and the thickness thereof is defined as the thickness of the low β layer. Specifically, a region where the abundance ratio (area ratio) of the β phase (second hard phase) relative to the inside is less than 50% is defined as the low β layer. Here, when measuring the abundance ratio of the β phase inside, it is preferable to measure a region sufficiently deeper than the low β layer and stable in composition, for example, the depth from the surface of the cemented carbide is One example is measuring a region in the range of 100 μm or more and 300 μm or less. The thickness of the low β layer is measured over 5 fields of view, and the average value is taken as the thickness of the low β layer. In addition, as a measurement location, it is preferable to use a cutting edge location.

  The maximum particle size of the β phase (second hard phase) in the low β layer is mirror-finished by cutting the cemented carbide perpendicular to the surface in the same way as measuring the thickness of the low β layer described above. And it can measure by observing this processed surface with an optical microscope. In the cross-sectional observation image of the surface of the cemented carbide as shown in FIG. 1, a 1 mm region is observed in the width direction of the low β layer (direction parallel to the surface, left-right direction in the figure). Then, by changing the observation location, observing a plurality of (at least 5 or more) regions, measuring the long diameters of all the second hard phases existing in each region, and determining the maximum value as the second hard in the low β layer The maximum particle size of the phase. When a plurality of second hard phases are aggregated, the major axis of the aggregated secondary particles is measured. It is preferable to use the cutting edge as the observation location.

<Evaluation of heat permeability>
Evaluation of the surface permeability (low β layer) and internal heat permeability of the cemented carbide is performed by measuring the retardation of the phase with a thermophysical microscope as follows. For the thermophysical microscope, for example, “Thermal Microscope TM3” manufactured by Bethel Co., Ltd. can be used.

(Preparation)
The cemented carbide is cut obliquely with respect to the surface. At this time, the length of the cut surface (the length of the hypotenuse) is cut to be three times the length of the cut surface when cut in the vertical direction (that is, the same as the thickness of the cemented carbide). To do. That is, when the thickness of the low β layer is A, cutting is performed so that the thickness (length along the cutting direction) of the low β layer on the cut surface is 3A. Thereafter, the cut surface is mirror-finished.

(Proofreading)
The processed surface and the reference sample are simultaneously subjected to Mo sputtering, and a calibration curve between the thermal permeability and the phase difference is obtained by a thermophysical microscope.

(Measurement condition)
Mapping measurement is performed on the low β layer and the internal 40 μm × 40 μm region on the processed surface with a detection light spot diameter of 3 μm and a measurement interval of 2 μm, and 21 × 21 points, for a total of 441 points. The average value measured 100 times per measurement point is calculated, and the remaining 80% measurement value excluding the measurement value of 10% from the maximum value and the measurement value of 10% from the minimum value among the data of all measurement points Is an average value of the heat penetration rate of the measurement region. The measurement area is changed, and the thermal permeability is measured for five different 40 μm square areas, and the average value of the five areas is defined as the low β layer and the internal thermal permeability of the cemented carbide.

<< Production method of cemented carbide >>
The cemented carbide according to the embodiment can be manufactured by the steps of preparation of raw material powder → mixing of raw material powder → drying → forming → sintering → cooling. Here, as a method of forming a low β layer by leaving a part of β phase (second hard phase component) on the surface portion of the cemented carbide, raw material powder size (particle size), sintering during sintering This is possible by controlling the temperature, atmosphere and pressure, the cooling rate during cooling, the atmosphere, and the like.

[Preparation process]
The preparation step is a step of preparing a WC powder serving as a first hard phase, a compound powder serving as a second hard phase, and an iron group metal powder serving as a binder phase as a raw material powder. Although the particle size of each powder is not specifically limited, For example, it is set as the range of 0.5 micrometer or more and 10 micrometers or less. In addition, the particle size of each powder is an average particle diameter (FSSS diameter) by a Fisher sub-sieve sizer (FSSS) method. In general, the smaller the particle size of the WC powder used as a raw material, the smaller the particle size of the WC particles in the cemented carbide finally obtained. The larger the particle size of the WC powder, the larger the particle size of the WC particles in the cemented carbide. The particle size increases. The particle size of the WC powder is, for example, 1.5 μm or more and 6.0 μm or less. Also, if the particle size of the second hard phase compound powder is large to some extent, the β phase tends to remain on the surface during sintering, and the larger the particle size, the more the β phase (second hard phase) in the low β layer on the surface. The size (maximum particle size) tends to increase. The particle size of the compound powder is, for example, 1.5 μm or more and 6.0 μm or less, preferably 5.0 μm or less, and further 3.0 μm or less.

[Mixing process]
A mixing process is a process of mixing raw material powder and obtaining a mixture. As a mixing method, for example, an attritor or a ball mill can be used. Specifically, the raw material powders are blended at a predetermined ratio, and pulverized and mixed using a mixing device such as an attritor or a ball mill containing media (ground balls). Mixing may be performed in a solvent such as water, ethanol, acetone, or isopropyl alcohol.

  Here, when all the raw material powders are put together in the mixing device containing the media and pulverized and mixed for a long time, not only the WC powder but also the compound powder of the second hard phase is pulverized into fine particles. The β phase hardly remains on the surface during sintering. This is because the low β layer is formed by the dissolution and reprecipitation of the hard phase into the binder phase during sintering and the migration of the hard phase during dissolution and reprecipitation, similar to the deβ layer. If it is fine, dissolution is fast and complete dissolution, making it difficult for the β phase to remain on the surface.

  As the formation condition I for forming a predetermined low β layer, in the mixing step, not all the raw material powders are pulverized and mixed together from the start of mixing, but the pulverized and mixed time of the raw material compound powder is shortened. It is preferable to carry out in two or more stages. Specifically, a WC powder and an iron group powder, or only a WC powder is charged into a mixing device, and a first mixing stage in which pulverization and mixing is performed for a predetermined time, and then a compound powder or a compound powder and an iron group powder are charged. Then, it is divided into a second mixing stage in which pulverization and mixing are performed for a certain time. Thereby, the pulverization and mixing time of the compound powder is shortened, and the compound powder can be maintained in a coarse state. Since the compound powder is coarse, dissolution at the time of sintering is slow, and the powder is not completely dissolved at the time of sintering, and the β phase tends to remain on the surface portion. The mixing time in the first mixing stage is, for example, 3 hours to 24 hours, preferably 5 hours to 12 hours, and the mixing time in the second mixing stage is, for example, 0.25 hours to 5 hours, preferably For example, it may be 0.5 hours or more and 3 hours or less. By adjusting the mixing time in the second mixing stage, it is possible to adjust the size of the β phase in the low β layer, and the longer the mixing time, the coarser the compound powder and the agglomerated compound powder can be crushed. The size of the β phase is reduced. The mixing time in the second mixing stage is preferably adjusted according to the particle size (size) of the compound powder, and when coarse compound powder is used as a raw material, it is preferably set relatively long.

[Drying process]
A drying process is a process of drying the mixture obtained at the mixing process. As a drying method, a known method can be employed, and for example, spray drying can be used.

[Molding process]
The forming step is a step of forming a mixture into a predetermined shape to obtain a formed body. The molding conditions may be any general conditions and are not particularly limited. An example of the predetermined shape is a cutting tool shape.

[Sintering process]
A sintering process is a process of sintering a molded object and obtaining a sintered compact. As the formation condition II for forming a predetermined low β layer, in the sintering process, a first sintering stage in which the sintering temperature is maintained for a short time at a relatively high sintering temperature, and then the sintering temperature is lowered and further maintained for a certain period of time. The second sintering step is preferably performed separately. As a result, after starting sintering at a high sintering temperature, changing to a low sintering temperature suppresses dissolution / reprecipitation during sintering and slows the dissolution / reprecipitation speed. In this case, the β phase tends to remain. The sintering temperature in the first sintering stage is, for example, 1350 ° C. or more and 1500 ° C. or less, preferably 1400 ° C. or more and 1480 ° C. or less, and the holding time is, for example, 20 minutes or more and 80 minutes or less, preferably 30 minutes or more and 60 minutes or less. And so on. The sintering temperature in the second sintering stage is set, for example, 30 ° C. or more, preferably 40 ° C. or more and 50 ° C. or less lower than the sintering temperature in the first sintering stage, for example, 1300 ° C. or more and 1450 ° C. or less, preferably It is mentioned that it is 1350 degreeC or more and 1430 degrees C or less. The holding time in the second sintering stage is preferably shorter than the holding time in the first sintering stage, for example, 10 minutes or more and 60 minutes or less, preferably 40 minutes or less. By adjusting the sintering temperature or holding time in the first sintering stage, it is possible to adjust the size of the β phase in the low β layer, and the higher the sintering temperature or the longer the holding time, the β The phase size is reduced.

The atmosphere during sintering may be an N ₂ gas atmosphere or an inert gas atmosphere such as Ar. The degree of vacuum (pressure) during sintering is, for example, 10 kPa or less, preferably 5 kPa or less, and further 3 kPa or less.

[Cooling process]
The cooling step is a step of cooling the sintered body after completion of sintering. As the formation condition III for forming the predetermined low β layer, in the cooling step, it is preferable to cool at a relatively high cooling rate. Thereby, dissolution / reprecipitation is suppressed, and the β phase easily remains on the surface portion. The cooling rate is, for example, 10 ° C./min or more, preferably 30 ° C./min or more, and further 50 ° C./min or more. By adjusting the cooling rate, it is possible to adjust the size of the β phase in the low β layer, and the faster the cooling rate, the smaller the size of the β phase.

The atmosphere during cooling may be an N ₂ gas atmosphere or an inert gas atmosphere such as Ar. The degree of vacuum (pressure) during cooling is, for example, 100 kPa or less, 10 kPa or more, and further 50 kPa or more.

  It is possible to form a predetermined low β layer by satisfying at least one of the low β layer formation conditions I to III, but two or more of these conditions must be satisfied. It is preferable to satisfy all the conditions. In particular, it is preferable to satisfy both the formation conditions I and II. Further, from the viewpoint of forming a low β layer by denitrifying the surface portion during sintering, a nitrogen-containing compound such as nitride or carbonitride (eg, ZrN, TiN, TaN, TiCN, and the like) as the second hard phase It is preferable to contain a solid solution containing these compounds.

<Application>
The cemented carbide according to the above embodiment can suppress the surface portion from becoming locally high temperature, and can suppress the decrease in the hardness and strength of the surface portion, thereby improving wear resistance and chipping resistance (chipping resistance). To do. Furthermore, since the temperature rise at the surface portion is small and the temperature difference between the surface portion and the inside is small, the thermal shock resistance is also improved. Specifically, it is possible to suppress chipping from occurring on the surface portion due to an impact during cutting, and it is also possible to suppress defects starting from the chipping. Especially on the flank surface, the temperature rise due to scratching with the work material is suppressed, so it is difficult to become high temperature and deformation due to the pressing of the work material is difficult to occur, effectively suppressing flank wear. it can. Therefore, the cutting tool using the above cemented carbide as a base material exhibits excellent wear resistance and fracture resistance, and can extend the tool life.

"Cutting tools"
[Base material]
The cutting tool which concerns on embodiment is what is called a cemented carbide tool which equips a base material with the cemented carbide based on the said embodiment. Specific examples of the cutting tool include a cutting edge replaceable cutting tip (throw away tip), a cutting tool, an end mill, a drill, a metal saw, a gear cutting tool, a reamer, and a tap. In particular, it is preferable to provide the cemented carbide base material at least at the cutting edge.

[Coating film]
The cutting tool may include a coating film on the surface of the cemented carbide substrate. By providing a coating film on the surface of the substrate, the wear resistance of the tool can be improved, and the life can be further extended. The coating film may be formed on the entire surface of the cemented carbide base material, or only the blade edge part.

The coating film includes a compound (including a solid solution) of at least one metal selected from Group 4, 5, 6 elements, Al and Si, and at least one element selected from C, N, O, and B. It is preferable to have one or more layers. Specific examples of the compound constituting the coating film include TiC, TiN, TiCN, TiAlN, TiAlCN, TiSiN, and Al ₂ O ₃ . The coating film may have a single layer structure consisting of only one layer, or may have a multilayer structure in which two or more layers formed of different constituent materials are stacked. The thickness of the entire coating film is preferably, for example, 1 μm or more and 30 μm or less. When the thickness of the coating film is 1 μm or more, an improvement effect such as wear resistance can be sufficiently obtained. On the other hand, even if the thickness of the coating film exceeds 30 μm, no further effect is obtained, which is not economical.

  The coating film can be formed by a physical vapor deposition (PVD) method or a chemical vapor deposition (CVD) method. When the coating film is formed by the CVD method, it is easy to obtain a coating film having excellent adhesion to the substrate. Examples of the CVD method include a plasma CVD method.

  As an example of the cutting tool according to the embodiment, a blade-tip-exchangeable cutting tip is shown in FIG. The blade-tip-exchangeable cutting tip 1 shown in FIG. 2 has a substantially rhombic flat plate shape, a rake face 2 provided on the upper and lower surfaces of the substantially rhombus, and a flank 3 provided on each side surface intersecting the rake face 2. And the cutting edge (cutting edge) 4 provided in the intersection ridgeline part of the rake face 2 and the flank 3 and the attachment hole 5 in the center part. The cutting tip 1 is provided with a cutting edge 4 at each of the upper and lower ridge lines, and has a total of eight cutting edges 4. As shown in FIG. 3, the cutting tip 1 includes a cemented carbide base material 10 and a coating film 20 on the surface of the base material 10. This base material 10 is a cemented carbide according to the above-described embodiment, and a low β layer 11 is formed on a surface portion of the cemented carbide, and a heat permeability ratio (TEa / TEb) between the low β layer 11 and the inside 12 is formed. ) Satisfies more than 1.02 and less than 1.08. The cutting tip 1 is used, for example, attached to a holder (shank).

[Example]
A cutting tool (blade-tip-exchangeable cutting tip) provided with a base material made of cemented carbide was produced and evaluated.

<Example 1>
As raw material powders, a WC powder having a FSSS diameter of 3.8 μm, a TiC powder having a FSSS diameter of 2.5 μm, a TiCN powder, a TaC powder and an NbC powder, and a Co powder having a FSSS diameter of 2.5 μm were prepared. And the raw material was weighed so that each powder might become the composition shown below.
Raw material 1A ′: 1.0% by mass of TiC, 2.5% by mass of TiCN, 2.0% by mass of TaC, 1.0% by mass of NbC, 3.0% by mass of Co, and the balance Is the composition of WC.
Raw material 1B: 1.0% by mass of TiC, 2.5% by mass of TiCN, 2.0% by mass of TaC, 1.0% by mass of NbC, 5.0% by mass of Co, and the balance Composition of WC.

[Adjustment of cemented carbide]
Using the above raw materials, the production conditions were changed as follows, and sample Nos. Shown in Table 1 were used. 1-1-No. A cemented carbide base material of 1-5 blade tip exchange type cutting tips was produced.

The weighed raw materials were put into an attritor together with ethanol solvent and media, and mixed with the attritor to prepare a mixture. The mixing conditions were any of the following conditions.
Mixing condition M1a: Among the raw materials, WC powder and Co powder were charged, and after 9.5 hours of pulverization and mixing, the remaining TiC powder, TiCN powder, TaC powder and NbC powder were charged, and 0.5 hours Crushing and mixing.
Mixing condition M1b ′: All raw material powders are charged and pulverized and mixed for 10 hours.

After mixing, the mixture was spray dried and granulated. Subsequently, the mixture was press-molded at a pressure of 147 MPa (1500 kgf / cm ² ) to produce a molded body having a model number CNMG120408N-GU (manufactured by Sumitomo Electric Hardmetal Co., Ltd.).

Next, the compact was placed in a furnace where the degree of vacuum and temperature could be controlled, and the compact was sintered. The sintering conditions were any of the following conditions.
Sintering condition S1a: After holding at 1460 ° C. for 40 minutes in N ₂ gas atmosphere (furnace pressure 0.8 kPa), the temperature was lowered and held at 1410 ° C. for 20 minutes.
Sintering condition S1b ′: held at 1460 ° C. for 1 hour in N ₂ gas atmosphere (furnace pressure 0.2 kPa).
Sintering condition S1c: After holding at 1460 ° C. for 1 hour in N ₂ gas atmosphere (furnace pressure 0.8 kPa), the temperature was lowered and held at 1410 ° C. for 1 hour.

After the completion of sintering, it was cooled. The cooling conditions were any of the following conditions.
Cooling condition C1a: Cooling at 100 ° C./min in an Ar gas atmosphere (furnace pressure 80 kPa).
Cooling condition C1b ′: Cooling at 5 ° C./min in an Ar gas atmosphere (in-furnace pressure 4 kPa).

[Base material adjustment]
The cemented carbide obtained as described above was appropriately subjected to blade edge processing such as honing treatment, and sample No. 1-1-No. A base material made of cemented carbide of 1-5 blade-tip-exchangeable cutting tips (shape: CNMG120408N-GU) was completed.

[Characteristic evaluation of cemented carbide]
(Evaluation of WC particles)
The cutting edge part of the manufactured cemented carbide substrate (sample) is cut and mirror-finished with diamond paste, or part of the cut surface is ion milled with an argon ion beam using a CP device. An observation sample for a microscope was used.

  The processed surface of this observation sample was observed at a magnification of 5000 times using a field emission electron microscope (FE-SEM), and five fields of reflection electron images were taken. For each field of view, about 500 WC particles at the center of the field of view, the particle size (Heywood diameter) of each WC particle is obtained using image analysis type particle size distribution software ("Mac-View" manufactured by Mountec Co., Ltd.). The average particle diameter of WC particles in 5 fields of view was calculated. The results are shown in Table 1.

(Evaluation of low β layer)
The section of the cemented carbide substrate (sample) cut perpendicularly to the surface was mirror-finished, and the processed surface was observed with an optical microscope to measure the thickness of the low β layer. The magnification of the field of view of the microscope is, for example, 1000 times. Specifically, the cross section of the sample is observed in the thickness (depth) direction from the surface to the inside, and the content of the second hard phase (β phase) is small and the abundance ratio of the β phase is relatively low. Was the low β layer, and the thickness was the thickness of the low β layer. Here, the region where the β phase abundance ratio (area ratio) is less than 50% with respect to the inside of the cemented carbide substrate in the observation image is defined as the low β layer. The thickness of the low β layer was measured for five visual fields while changing the observation location, and the average value was taken as the thickness of the low β layer. The results are shown in Table 1.

(Evaluation of heat penetration rate)
The cutting edge portion of the manufactured cemented carbide substrate was cut in an oblique direction and mirror-finished using a diamond paste to obtain a sample for evaluating the thermal permeability. The cutting direction was cut obliquely with respect to the surface so that the length of the cut surface was three times the length of the cut surface when cut in the vertical direction. The processed surface of the sample for evaluation and the reference sample were simultaneously Mo-sputtered, and a calibration curve between the thermal permeability and the phase difference was obtained with a thermophysical microscope (“Thermal Microscope TM3” manufactured by Bethel Co., Ltd.). Then, mapping measurement is performed with respect to the low β layer on the processed surface and the internal 40 μm × 40 μm region at a detection light spot diameter of 3 μm and a measurement interval of 2 μm, and measurement of 21 × 21 points, a total of 441 points. The average value measured 100 times per measurement point is calculated, and the remaining 80% measurement value excluding the measurement value of 10% from the maximum value and the measurement value of 10% from the minimum value among the data of all measurement points Is an average value of the heat penetration rate of the measurement region. Change the measurement area, measure the thermal permeability of 5 different 40μm square areas, calculate the average value of the 5 areas, calculate the thermal permeability (TEa) of the low β layer of the sample and the internal The heat permeation rate (TEb) was determined, and the heat permeation rate ratio (TEa / TEb) was determined. The results are shown in Table 1.

[Formation of coating film]
TiN (0.3 μm), MT-TiCN (5.0 μm), and α-Al ₂ O ₃ (4.0 μm) are laminated in this order on the surface of the manufactured cemented carbide substrate using the CVD method. A coated film was formed (the value in parentheses indicates the thickness). In addition, “MT” of “MT-TiCN” indicates that it is formed by using MT (Moderate Temperature) -CVD method.

  As described above, the sample numbers shown in Table 1 were obtained. 1-1-No. A cutting edge type cutting tip of 1-5 was completed.

[Evaluation of cutting tools]
The wear resistance of each of the blade-tip-exchangeable cutting tips of each sample was evaluated. The cutting edge exchangeable cutting tip was attached to a holder of model number DCLNR2525 (manufactured by Sumitomo Electric Hardmetal Co., Ltd.), and a wear resistance test by steel turning was performed under the cutting conditions shown below.

(Cutting conditions)
Work material: SCM435
Cutting speed (V): 220 m / min
Feed amount (f): 0.3 mm / rev
Cutting depth (ap): 1.5 mm
Coolant: Wet (WET)

  In the evaluation, the flank wear width was appropriately measured, and the flank wear width was determined to be 0.2 mm or more, or the life was judged to be lost. The results are shown in Table 1.

  Sample No. 1 using raw material 1A ′ (Co: 3 mass%) 1-1 was lost in a short time. Sample No. In 1-1, it is presumed that the amount of Co serving as a binder phase is small and the sinterability is deteriorated, so that the strength is remarkably lowered and the life is shortened due to defects.

Sample No. 1 using raw material 1B (Co: 5 mass%) 1-2-No. No. 1-5 contains a certain amount of Co as a binder phase and has sufficient strength, so that it was able to be cut without breaking until the flank wear width was 0.2 mm or more. Among them, sample No. 1 satisfying 1.02 <TEa / TEb <1.08. 1-2-No. Since 1-4 has a lifetime of 20 minutes or more, it can be seen that flank wear is effectively suppressed and wear resistance is excellent. This is because, by satisfying TEa / TEb <1.08, the heat permeability ratio between the low β layer and the inside is small, so the heat generated on the cutting edge surface during cutting is effective from the low β layer on the surface to the inside. Therefore, it is presumed that the surface portion is prevented from locally becoming high temperature and wear resistance is improved. In particular, sample No. 1 satisfying TEa / TEb <1.07. 1-2, no. 1-3 has a lifetime of 25 minutes or more and is excellent in wear resistance. Sample No. In the 1-2 cemented carbide substrate, the low β layer and the internal heat permeability (actually measured values) were as follows: low β layer: 14786 (J / (m ² s ^1/2 K), internal: 14120 (J / (M ² s ^1/2 K).

  In contrast, the sample No. TEa / TEb ≧ 1.08. 1-5 has a fast flank wear and a short life. This is presumably because the heat permeability ratio is large, so that heat is not easily diffused from the low β layer in the surface portion, the surface portion becomes locally hot, and the wear resistance is lowered. The reason for the increase in the thermal permeability ratio is that the β phase cannot remain on the surface part and the β phase contained in the surface part is small (close to the de-β layer), so the low β layer heat penetration to the inside This is thought to be due to the higher rate.

<Example 2>
As raw material powders, four types of WC powders having FSSS diameters of 4.7 μm, 3.8 μm, 1.2 μm, and 6.3 μm were prepared. The WC powder of each particle size was designated as WC powder 1 (4.7 μm), WC powder 2 (3.8 μm), WC powder 3 (1.2 μm), and WC powder 4 (6.3 μm) (the values in parentheses are Indicates particle size). Further, TiC powder, ZrC powder, and ZrN powder having a FSSS diameter of 2.5 μm, and Co powder and Ni powder having a FSSS diameter of 2.5 μm were prepared. And the raw material was weighed so that each powder might become the composition shown below.
Raw material 2A ₁ : 1.0% by mass of TiC, 3.0% by mass of ZrC, 0.6% by mass of ZrN, 9.0% by mass of Co, 1.0% by mass of Ni, and the balance Is the composition of WC. However, WC powder 1 (4.7 μm) is used.
Raw material 2B ′: 1.0% by mass of TiC, 3.0% by mass of ZrC, 0.6% by mass of ZrN, 11.8% by mass of Co, 1.2% by mass of Ni, and the balance Is the composition of WC. However, WC powder 1 (4.7 μm) is used.
Raw material 2A ₂ : Same composition as raw material 2A ₁ except that WC powder 2 (3.8 μm) is used.
Raw material 2A ₃ : Same composition as raw material 2A ₁ except that WC powder 3 (1.2 μm) is used.
Raw material 2A ₄ : Same composition as raw material 2A ₁ except that WC powder 4 (6.3 μm) is used.

[Adjustment of cemented carbide]
Using the above raw materials, the production conditions were changed as follows, and sample Nos. Shown in Table 2 were used. 2-1. A cemented carbide base material of 2-8 blade-tip-exchangeable cutting tips was produced.

The weighed raw materials were put into an attritor together with ethanol solvent and media, and mixed with the attritor to prepare a mixture. The mixing conditions were any of the following conditions.
Mixing condition M2a: WC powder, Co powder and Ni powder among the raw materials were added and mixed for 9 hours, then the remaining TiC powder, ZrC powder and ZrN powder were added and mixed for 0.5 hour. .
Mixing condition M2b: WC powder, Co powder and Ni powder among the raw materials were added and pulverized and mixed for 7 hours, then the remaining TiC powder, ZrC powder and ZrN powder were added and pulverized and mixed for 2.5 hours. .
Mixing condition M2c ′: pulverization and mixing for 9.5 hours with all raw material powders added.

After mixing, the mixture was spray dried and granulated. Next, the mixture was press-molded at a pressure of 147 MPa (1500 kgf / cm ² ) to produce a compact having a model number CNMG120212N-GU (manufactured by Sumitomo Electric Hardmetal Co., Ltd.).

Next, the compact was placed in a furnace where the degree of vacuum and temperature could be controlled, and the compact was sintered. The sintering conditions were any of the following conditions.
Sintering condition S2a: After holding at 1400 ° C. for 30 minutes in an Ar gas atmosphere (furnace pressure 1 kPa), the temperature was lowered and held at 1360 ° C. for 20 minutes.
Sintering condition S2b: After holding at 1400 ° C. for 40 minutes in an Ar gas atmosphere (furnace pressure 1 kPa), the temperature was lowered and held at 1350 ° C. for 10 minutes.
Sintering condition S2c ′: held at 1400 ° C. for 50 minutes in an Ar gas atmosphere (furnace pressure 1 kPa).

After the completion of sintering, it was cooled. The cooling conditions were any of the following conditions.
Cooling condition C2a: Cooling at 110 ° C./min in an Ar gas atmosphere (furnace pressure 100 kPa).
Cooling condition C2b: Cooling at 90 ° C./min in an Ar gas atmosphere (furnace pressure 70 kPa).
Cooling condition C2c ′: Cooling at 3 ° C./min in an Ar gas atmosphere (furnace pressure 10 kPa).

[Base material adjustment]
The cemented carbide obtained as described above was appropriately subjected to blade edge processing such as honing treatment, and sample Nos. Shown in Table 2 were obtained. 2-1. A cemented carbide base material (shape: CNMG120212N-GU) of 2-8 blade-tip-exchangeable cutting tips was completed.

[Evaluation of cemented carbide]
About the produced cemented carbide base material (sample), the characteristics of the cemented carbide were evaluated in the same manner as in Example 1. Table 2 shows the average particle diameter of the WC particles, the thickness of the low β layer, and the thermal permeability ratio (TEa / TEb) between the thermal permeability (TEa) of the low β layer and the internal thermal permeability (TEb). Show.

[Formation of coating film]
TiN (0.3 μm), MT-TiCN (3.0 μm), and α-Al ₂ O ₃ (3.0 μm) are laminated in this order on the surface of the manufactured cemented carbide substrate using the CVD method. A coated film was formed (the value in parentheses indicates the thickness).

  As described above, the sample numbers shown in Table 2 were obtained. 2-1. A 2-8 cutting edge replacement type cutting tip was completed.

[Evaluation of cutting tools]
The chipping resistance of the cutting edge exchangeable cutting tip of each sample was evaluated. The cutting edge exchangeable cutting tip was attached to a holder of model number DCLNR2525 (manufactured by Sumitomo Electric Hardmetal Co., Ltd.), and a fracture resistance test by steel turning was performed under the following cutting conditions.

(Cutting conditions)
Work Material: SCM435 (φ150 ~ 180mm round bar, 4 groove material)
Cutting speed (V): 110 m / min
Feed amount (f): 0.25 mm / rev
Cutting depth (ap): 1.6 mm
Coolant: Wet (WET)

  In the evaluation, cutting was performed for 5 minutes under the above conditions, and the ratio of the cutting edge to the defective cutting edge among all 10 cutting edge-exchangeable cutting tips (defect rate: number of defects / 10) was examined. The results are shown in Table 2.

  Sample No. 2 using raw material 2B ′ (Co: 11.8 mass%, Ni: 1.2 mass%) was used. 2-5 has a high defect rate. Sample No. In No. 2-5, since the total amount of Co and Ni serving as the binder phase is large and the hardness is lowered, it is presumed that plastic deformation occurred during cutting and defects frequently occurred.

Sample No. 1 satisfying 1.02 <TEa / TEb <1.08. 2-1. 2-3 and Sample No. 2-6-No. No. 2-8 has a defect rate of 50% or less and is excellent in defect resistance. This is because, by satisfying TEa / TEb <1.08, the heat permeability ratio between the low β layer and the inside is small, so the heat generated on the cutting edge surface during cutting is effective from the low β layer on the surface to the inside. Therefore, it is presumed that the strength of the surface portion is hardly lowered and the fracture resistance is improved. In addition, from the comparison of these samples, the sample No. 1 in which the average particle diameter of the WC particles is in the range of 0.4 μm to 4 μm. 2-1. 2-3 and no. Sample No. 2-6 has a defect rate of 30% or less and is out of range. 2-7, No. 2 Excellent fracture resistance compared to 2-8. This is a sample No. In No. 2-7, since the particle size of the WC particles in the cemented carbide is small, the crack propagation resistance is inferior, and defects due to mechanical and thermal shock during cutting are likely to occur. In No. 2-8, since the particle diameter of the WC particles in the cemented carbide is large, it is presumed that the hardness is lowered and defects are likely to occur due to deformation during cutting. Sample No. 2 using the same raw material 2A ₁ was used. 2-1. From the comparison of 2-3, it can be seen that the fracture resistance is further improved by satisfying TEa / TEb <1.07.

  In contrast, the sample No. TEa / TEb ≧ 1.08. 2-4 has a high defect rate and inferior defect resistance. This is presumed that since the heat permeability ratio is large, the strength of the surface portion is lowered locally due to high temperature, and defects starting from chipping frequently occur due to impact during cutting. The reason for the increase in the thermal permeability ratio is that the β phase cannot remain on the surface part and the β phase contained in the surface part is small (close to the de-β layer), so the low β layer heat penetration to the inside This is thought to be due to the higher rate.

<Example 3>
As raw material powders, a WC powder having a FSSS diameter of 4.7 μm, a TiC powder having a FSSS diameter of 2.5 μm, a TiCN powder, a TaC powder and an NbC powder, and a Co powder having a FSSS diameter of 2.5 μm were prepared. And the raw material was weighed so that each powder might become the composition shown below. The total amount of TiC and TiCN was 1.5% by mass.
Raw material 3A: composition of 1.5% by mass of TiC, 3.0% by mass of TaC, 1.5% by mass of NbC, 7.5% by mass of Co and the balance of WC.
Raw material 3B: 1.2% by mass of TiC, 0.3% by mass of TiCN, 3.0% by mass of TaC, 1.5% by mass of NbC, 7.5% by mass of Co, and the balance Composition of WC.
Raw material 3C: 0.5% by mass of TiC, 1.0% by mass of TiCN, 3.0% by mass of TaC, 1.5% by mass of NbC, 7.5% by mass of Co, and the balance Composition of WC.

[Adjustment of cemented carbide]
Using the above raw materials, the production conditions were changed as follows, and sample Nos. Shown in Table 3 were used. 3-1. A cemented carbide base material of 3-4 blade-tip-exchangeable cutting tips was produced.

The weighed raw materials were put into a ball mill together with ethanol solvent and media, and mixed by a ball mill to prepare a mixture. The mixing conditions were as shown below.
Mixing condition M3a: WC powder and Co powder among the raw materials were added and pulverized and mixed for 11 hours, then the remaining TiC powder, TiCN powder, TaC powder and NbC powder were added and pulverized and mixed for 1 hour.

After mixing, the mixture was spray dried and granulated. Subsequently, the mixture was press-molded at a pressure of 147 MPa (1500 kgf / cm ² ) to produce a molded body having a model number CNMG120408N-GU (manufactured by Sumitomo Electric Hardmetal Co., Ltd.).

Next, the compact was placed in a furnace where the degree of vacuum and temperature could be controlled, and the compact was sintered. The sintering conditions were any of the following conditions.
Sintering condition S3a ′: held at 1420 ° C. for 1.5 hours in N ₂ gas atmosphere (furnace pressure 30 kPa).
Sintering condition S3b: After holding at 1420 ° C. for 1 hour in an Ar gas atmosphere (furnace pressure 2 kPa), the temperature was lowered and held at 1380 ° C. for 0.5 hour.

After the completion of sintering, it was cooled. The cooling conditions were any of the following conditions.
Cooling condition C3a: Cooling at 10 ° C./min in Ar gas atmosphere (furnace pressure 10 kPa).
Cooling condition C3b: Cooling at 100 ° C./min in an Ar gas atmosphere (furnace pressure 80 kPa).

[Base material adjustment]
The cemented carbide obtained as described above was appropriately subjected to cutting edge processing such as honing processing, and sample Nos. Shown in Table 3 were obtained. 3-1. A cemented carbide base material (shape: CNMG120408N-GU) of a 3-4 cutting edge exchange type cutting tip was completed.

[Evaluation of cemented carbide]
About the produced cemented carbide base material (sample), the characteristics of the cemented carbide were evaluated in the same manner as in Example 1. Table 3 shows the average particle diameter of the WC particles, the thickness of the low β layer, and the thermal permeability ratio (TEa / TEb) between the thermal permeability (TEa) of the low β layer and the internal thermal permeability (TEb). Show.

[Formation of coating film]
TiN (0.2 μm), MT-TiCN (5.0 μm), and α-Al ₂ O ₃ (5.0 μm) are laminated in this order on the surface of the manufactured cemented carbide substrate using the CVD method. A coated film was formed (the value in parentheses indicates the thickness).

  As described above, the sample Nos. Shown in Table 3 were used. 3-1. A 3-4 cutting edge replacement type cutting tip was completed.

[Evaluation of cutting tools]
The chipping resistance of the cutting edge exchangeable cutting tip of each sample was evaluated. The cutting edge exchangeable cutting tip was attached to a holder of model number DCLNR2525 (manufactured by Sumitomo Electric Hardmetal Co., Ltd.), and a fracture resistance test by steel turning was performed under the following cutting conditions.

(Cutting conditions)
Work material: SCr420 (φ150-180mm round bar, 1 groove material)
Cutting speed (V): 190 m / min
Feed amount (f): 0.23 mm / rev
Cutting depth (ap): 3.0 mm
Coolant: Wet (WET)

  In the evaluation, the time until loss was measured. The results are shown in Table 3.

Sample No. 3 using a raw material 3A not containing a nitrogen-containing compound (eg, TiCN) such as nitride or carbonitride as the second hard phase. 3-1 was lost in a short time. Sample No. Since 3-1 is TEa / TEb ≦ 1.02 and the thermal permeability of the low β layer and the inside is substantially the same, it is considered that a large amount of β phase remains on the surface portion. This is the sample No. In 3-1, since the raw material does not contain a nitrogen-containing compound, a low β layer was formed by denitrifying the surface portion by performing sintering in an N ₂ atmosphere, but the β phase hardly disappeared, This is probably because many β phases remained on the surface. Therefore, sample no. In 3-1, since the surface portion (low β layer) contains a large amount of β phase, it is presumed that the toughness of the surface portion is reduced and defects are easily generated, and impact resistance and defect resistance are reduced.

  In contrast, Sample No. 1 satisfying 1.02 <TEa / TEb <1.08. 3-2-No. 3-4 shows that the time to defect is 15 minutes or more and is excellent in defect resistance. This is because, by satisfying TEa / TEb <1.08, the heat permeability ratio between the low β layer and the inside is small, so the heat generated on the cutting edge surface during cutting is effective from the low β layer on the surface to the inside. Therefore, it is presumed that the strength of the surface portion is hardly lowered and the fracture resistance is improved. Sample No. 3-2-No. 3-4 is 1.02 <TEa / TEb. From the comparison with 3-1, it is considered that a large amount of β phase does not remain on the surface portion. Therefore, sample no. 3-2-No. In 3-4, the toughness of the surface portion is high, and the impact during cutting was effectively absorbed by the low β layer, so that the functions of impact resistance and fracture resistance by the low β layer are sufficiently exhibited. Presumed.

<Example 4>
As raw material powders, a WC powder having a FSSS diameter of 3.8 μm, a NbC powder having a FSSS diameter of 2.5 μm or 6.0 μm, a ZrC powder and a ZrN powder, and a Co powder having a FSSS diameter of 2.5 μm were prepared. And the raw material was weighed so that each powder might become the composition shown below.
Raw material 4A: 3.5% by mass of NbC, 3.0% by mass of ZrC, 0.5% by mass of ZrN, 10.0% by mass of Co, and the balance of WC. However, NbC powder, ZrC powder, and ZrN powder having a FSSS diameter of 2.5 μm are used.
Raw material 4B: Same composition as raw material 4A, except that NbC powder, ZrC powder and ZrN powder with a FSSS diameter of 6.0 μm are used.

[Adjustment of cemented carbide]
Using the above raw materials, the production conditions were changed as follows, and sample Nos. Shown in Table 4 were used. 4-1. A base material made of cemented carbide of 4-6 cutting edge exchange type cutting tip was produced.

The weighed raw materials were put into an attritor together with ethanol solvent and media, and mixed with the attritor to prepare a mixture. The mixing conditions were any of the following conditions.
Mixing condition M4a: WC powder and Co powder among raw materials were added and pulverized and mixed for 8 hours, and then the remaining NbC powder, ZrC powder and ZrN powder were added and pulverized and mixed for 1 hour.
Mixing condition M4b: WC powder and Co powder among the raw materials were added and pulverized and mixed for 5 hours, and then the remaining NbC powder, ZrC powder and ZrN powder were added and pulverized and mixed for 4 hours.
Mixing condition M4c: Among the raw materials, WC powder and Co powder were charged and pulverized and mixed for 8.7 hours, then the remaining NbC powder, ZrC powder and ZrN powder were charged, and pulverized and mixed for 0.3 hour.
Mixing condition M4d: WC powder and Co powder among the raw materials were added and pulverized and mixed for 8.85 hours, and then the remaining NbC powder, ZrC powder and ZrN powder were added and pulverized and mixed for 0.15 hours.

After mixing, the mixture was spray dried and granulated. Next, the mixture was press-molded at a pressure of 147 MPa (1500 kgf / cm ² ) to produce a compact having a model number CNMG120212N-GU (manufactured by Sumitomo Electric Hardmetal Co., Ltd.).

Next, the compact was placed in a furnace where the degree of vacuum and temperature could be controlled, and the compact was sintered. The sintering conditions were any of the following conditions.
Sintering condition S4a: After holding at 1400 ° C. for 30 minutes in an Ar gas atmosphere (furnace pressure 1 kPa), the temperature was lowered and held at 1360 ° C. for 20 minutes.
Sintering condition S4b: After holding at 1400 ° C. for 40 minutes in an Ar gas atmosphere (furnace pressure 1 kPa), the temperature was lowered and held at 1350 ° C. for 10 minutes.
Sintering condition S4c ′: held at 1400 ° C. for 50 minutes in an Ar gas atmosphere (furnace pressure 1 kPa).

After the completion of sintering, it was cooled. The cooling conditions were any of the following conditions.
Cooling condition C4a: Cooling at 110 ° C./min in an Ar gas atmosphere (internal pressure of 100 kPa).
Cooling condition C4b: Cooling at 90 ° C./min in Ar gas atmosphere (furnace pressure 70 kPa).
Cooling condition C4c ′: Cooling at 3 ° C./min in an Ar gas atmosphere (furnace pressure 10 kPa).

[Base material adjustment]
The cemented carbide obtained as described above was appropriately subjected to blade edge processing such as honing treatment, and sample Nos. Shown in Table 4 were obtained. 4-1. A cemented carbide base material (shape: CNMG120412N-GU) of a 4-6 cutting edge exchange type cutting tip was completed.

[Evaluation of cemented carbide]
About the produced cemented carbide base material (sample), the characteristics of the cemented carbide were evaluated in the same manner as in Example 1. Table 4 shows the average particle diameter of the WC particles, the thickness of the low β layer, and the thermal permeability ratio (TEa / TEb) between the thermal permeability (TEa) of the low β layer and the internal thermal permeability (TEb). Show.

(Evaluation of maximum particle size of β phase in low β layer)
Furthermore, in this example, the maximum particle size of the β phase (second hard phase) in the low β layer was measured. Specifically, in the cross-sectional observation image used for measuring the thickness of the low β layer, an area of 1 mm is observed in the width direction of the low β layer, and the major axis of all β phases existing in the area is measured. . And it measured about five area | regions which changed the observation location, and made the longest diameter of the largest beta phase among all the beta phases which existed in each area | region into the largest particle diameter of the beta phase in a low beta layer. The results are shown in Table 4.

[Formation of coating film]
TiN (0.3 μm), MT-TiCN (3.0 μm), and α-Al ₂ O ₃ (3.0 μm) are laminated in this order on the surface of the manufactured cemented carbide substrate using the CVD method. A coated film was formed (the value in parentheses indicates the thickness).

  As described above, the sample numbers shown in Table 4 were obtained. 4-1. 4-6 cutting edge exchange type cutting tips were completed.

[Evaluation of cutting tools]
The chipping resistance of the cutting edge exchangeable cutting tip of each sample was evaluated. The cutting edge exchangeable cutting tip was attached to a holder of model number DCLNR2525 (manufactured by Sumitomo Electric Hardmetal Co., Ltd.), and a fracture resistance test by steel turning was performed under the following cutting conditions.

(Cutting conditions)
Work Material: SCM435 (φ150 ~ 180mm round bar, 4 groove material)
Cutting speed (V): 55 m / min
Feed amount (f): 0.25 mm / rev
Cutting depth (ap): 1.0 mm
Coolant: None

  In the evaluation, cutting was performed for 2 minutes under the above-mentioned conditions, and the ratio of chipping of the cutting edge among all ten cutting edge-exchangeable cutting tips (defect rate: number of defects / 10) was examined. The results are shown in Table 4.

  Sample No. 4-1. 4-6 all have the same composition (Co: 10% by mass), TEa / TEb is about the same (1.050 to 1.055), and the average particle diameter of the WC particles is about the same (3. 3 μm to 3.4 μm). Among these samples, the sample No. 1 in which the maximum particle size of the β phase (second hard phase) in the low β layer is less than 4 μm. 4-1. Sample No. 4-4 has a large maximum particle size of the β phase. 4-5, No. 4 Compared to 4-6, the defect rate is greatly reduced, indicating that the defect resistance is superior. This is because the β-phase size in the surface portion (low β layer) is small because the maximum particle size of the β phase in the low β layer is less than 4 μm, and the β phase is the origin of cracks due to impact during intermittent cutting. This is presumed to have improved fracture resistance. In particular, the maximum particle size of the β phase in the low β layer is 2 μm or less, and the size of the β phase is sufficiently small. 4-1, No. 1 4-2 has a defect rate of 10% or less. 4-3, no. Compared to 4-4, the fracture resistance is further improved. On the other hand, sample No. 4-5, No. 4 In No. 4-6, since the size of the β phase in the low β layer is large, it is presumed that cracks are easily generated due to impact during intermittent cutting, and defects are likely to occur.

  Sample No. 4-5, No. 4 In 4-6, the reason why the size (maximum particle size) of the β phase in the low β layer has increased is that the pulverization and mixing time relative to the size of the compound powder (NbC powder, ZrC powder and ZrN powder) used as the raw material is short. This is considered to be because the coarse compound powder and the agglomerated compound powder were not sufficiently pulverized and a large amount of coarse β phase and agglomerated β phase remained in the low β layer. In contrast, sample no. 4-1, No. 1 In 4-2, it is considered that the coarse compound powder and the agglomerated compound powder were sufficiently pulverized by increasing the pulverization and mixing time, and the size of the β phase in the low β layer was sufficiently reduced. Sample No. 4-3, no. In No. 4-4, since the pulverization and mixing time is slightly short, it is considered that a slightly larger β phase and an agglomerated β phase remained.

  The cemented carbide according to the embodiment of the present invention can be suitably used for a base material of a cutting tool, for example. The cutting tool which concerns on the embodiment of this invention can be utilized suitably for the cutting process of steel materials, for example.

1 Cutting edge exchangeable cutting tip (cutting tool)
2 Rake face 3 Flank face 4 Cutting edge (cutting edge)
5 Mounting hole 10 Base material (Cemented carbide)
11 Low β layer (surface portion) 12 Inner 20 Coating film 110 De-β layer 111 Low β layer 120 Inside 101 β phase

Claims (6)

A first hard phase consisting of WC particles, and at least one metal selected from the periodic table 4,5,6 group element, a compound of at least one element selected from C, N, O, and B a second hard phase, C o, at least one has a binder phase containing iron group metal, and in the content of the previous SL binder phase 4 wt% to 11 wt% selected from Ni and Fe having an interior and a surface portion Ru Oh,
The internal and low β layer is formed containing a small amount of the second hard phase than in the surface portion,
In the cross section, a region where the area ratio of the second hard phase to the inside is less than 50% is the low β layer,
A cemented carbide that satisfies 1.02 <TEa / TEb <1.08, where TEa is the thermal permeability of the low β layer and TEb is the internal thermal permeability.   The cemented carbide according to claim 1, wherein the maximum particle size of the second hard phase in the low β layer is less than 4 µm.   The cemented carbide according to claim 1 or 2, wherein an average particle size of the WC particles is 0.4 µm or more and 4.0 µm or less.   A cutting tool provided with the base material which consists of the cemented carbide of any one of Claims 1-3.   The cutting tool according to claim 4, wherein a coating film is provided on the surface of the base material.   The cutting tool according to claim 5, wherein the coating film is formed by a chemical vapor deposition method.