JP2016030846A - Cemented carbide and cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cemented carbide having a good balance between wear resistance and defect resistance at a high level; and a cutting tool using the cemented carbide as a base material.SOLUTION: There is provided a cemented carbide 1A comprising a hard phase 10 mainly composed of tungsten carbide 100 and a bonded phase 20 mainly composed of iron group elements, wherein the tungsten carbide 100 contains polycrystalline tungsten carbide particles 101. In the cross-section structure, when the area of the hard phase 10 is defined as St and the area of the polycrystalline tungsten carbide particles is defined as Sp, the cemented carbide 1A preferably satisfies Sp/St≥0.5. In addition, in the cross-section structure, when the number of all hard phase particles constituting the hard phase 10 is defined as Nt and the number of the polycrystalline tungsten carbide particles 101 is defined as Np, the cemented carbide 1A preferably satisfies Np/Nt≥0.2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a cemented carbide and a cutting tool using the cemented carbide. In particular, the present invention relates to a cemented carbide having a good balance between wear resistance and fracture resistance, and a cutting tool using the cemented carbide.

  Hard materials called cemented carbides are used as materials for cutting tools and molds. A cemented carbide is a composite material including a hard phase mainly composed of tungsten carbide (WC) and a binder phase mainly composed of an iron group element.

  Conventionally, there has been a demand for a cemented carbide having a good balance between wear resistance and fracture resistance. For example, Patent Document 1 discloses a cemented carbide in which WC, which is a main component of a hard phase, is finely divided and the grain size distribution of WC is small. This cemented carbide has fine WC and a small deviation in particle size distribution, so that it has a good balance between wear resistance and fracture resistance. WC constituting such a conventional cemented carbide is considered to be a WC particle having a single crystal structure (hereinafter referred to as a single crystal WC particle) from the manufacturing method of the cemented carbide. For example, the cemented carbide 1J in FIG. 12 includes a hard phase 10 mainly composed of WC100 and a binder phase 20 mainly composed of an iron group element, and WC100 is all single crystal WC particles 105.

JP 2012-117100 A

  In the conventional cemented carbide as described above, both wear resistance and fracture resistance can be achieved at a certain level. However, in order to realize high-efficiency machining and long-life tools that can meet the stricter cutting conditions required in recent years, it is desired to achieve both higher levels of wear resistance and fracture resistance.

  The present invention has been made in view of the above circumstances, and one of the objects of the present invention is to provide a cemented carbide having a high level of balance between wear resistance and fracture resistance.

  A cemented carbide according to one embodiment of the present invention is a cemented carbide comprising a hard phase mainly composed of tungsten carbide and a binder phase mainly composed of an iron group element, wherein the tungsten carbide is polycrystalline. Contains tungsten carbide particles.

  According to the above cemented carbide, it is possible to provide a cemented carbide having a high level of balance between wear resistance and fracture resistance.

It is a mimetic diagram showing an example of organization of cemented carbide 1A concerning one mode of the present invention. It is a schematic diagram which shows an example of the structure | tissue of the cemented carbide 1B which concerns on 1 aspect of this invention. It is a mimetic diagram showing an example of organization of cemented carbide 1C concerning one mode of the present invention. It is a mimetic diagram showing an example of organization of cemented carbide 1D concerning one mode of the present invention. It is a schematic diagram which shows an example of the structure | tissue of the cemented carbide 1E which concerns on 1 aspect of this invention. It is a schematic diagram which shows an example of the structure | tissue of the cemented carbide 1F which concerns on 1 aspect of this invention. It is a schematic diagram which shows an example of the structure | tissue of the cemented carbide 1G which concerns on 1 aspect of this invention. It is a schematic diagram which shows an example of the structure | tissue of the cemented carbide 1H which concerns on 1 aspect of this invention. It is a schematic diagram which shows an example of the structure | tissue of the cemented carbide 1I which concerns on 1 aspect of this invention. 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 1 aspect of this invention. FIG. 11 is a partially enlarged schematic cross-sectional view in the vicinity of the blade edge in the (XI)-(XI) cross section of FIG. 10. It is a schematic diagram which shows an example of the typical structure | tissue of the conventional cemented carbide 1J.

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

  (1) A cemented carbide according to one embodiment of the present invention is a cemented carbide comprising a hard phase mainly composed of tungsten carbide and a binder phase mainly composed of an iron group element, wherein the tungsten carbide comprises Including polycrystalline tungsten carbide particles.

  When WC which is the main component of the hard phase includes polycrystalline WC particles composed of a plurality of single crystal WC particles, a cemented carbide having a high level of wear resistance and fracture resistance can be obtained. The reason for having a high level of wear resistance and fracture resistance is thought to be due to the grain boundaries present in the polycrystalline WC particles contained in the WC. It is considered that the crystal grain boundary acts as a resistance to deformation of the cemented carbide and a resistance to crack propagation. In particular, even when the average particle size of the polycrystalline WC particles is large to some extent, the reason for having a high level of wear resistance is considered to be that the polycrystalline WC particles are formed from a plurality of single crystal WC particles. Even if the average particle size of the polycrystalline WC particles is somewhat large, the average particle size of the single crystal WC particles forming the polycrystalline WC particles is somewhat small. Thereby, it is considered that the same improvement in wear resistance as in the case where the hard phase is composed of fine WC is obtained. Therefore, the cemented carbide according to one embodiment of the present invention has a high level of balance between wear resistance and fracture resistance.

  (2) As one form of the cemented carbide, in the cross-sectional structure, when the area of the hard phase is St and the area of the polycrystalline tungsten carbide particles is Sp, Sp / St ≧ 0.5 is satisfied. Is mentioned.

  In the cemented carbide satisfying Sp / St ≧ 0.5, the ratio of the area of the polycrystalline WC particles to the area of the hard phase is large, and as a result, the ratio of the polycrystalline WC particles in the hard phase becomes a predetermined amount or more. A higher level of wear resistance and fracture resistance can be realized.

  (3) As one form of the cemented carbide, in the cross-sectional structure, when the number of all hard phase particles constituting the hard phase is Nt and the number of the polycrystalline tungsten carbide particles is Np, Np / Nt Satisfying ≧ 0.2.

  In the cemented carbide satisfying Np / Nt ≧ 0.2, the ratio of the number of polycrystalline WC particles to the total number of hard phase particles is large, and as a result, the ratio of the polycrystalline WC particles in the hard phase becomes a predetermined amount or more. Thus, a higher level of wear resistance and fracture resistance can be realized.

  (4) As one form of the cemented carbide, the hard phase is a carbide of at least one element selected from the group consisting of Group 4, 5 and 6 elements of the periodic table and silicon (excluding tungsten carbide), It includes at least one of nitride and carbonitride.

  A cemented carbide containing at least one of carbide, nitride and carbonitride of at least one element selected from the above group as the hard phase is particularly excellent in wear resistance. This is considered because each of the above compounds is superior in hardness as compared with WC.

  (5) As one form of the said cemented carbide, it is mentioned that the average particle diameter of the said polycrystalline tungsten carbide particle is 2 micrometers or more.

  When the average particle size of the polycrystalline WC particles is 2 μm or more, the fracture resistance is further improved. This is presumably because the polycrystalline WC particles are large to some extent, so that the hard phase / bonding phase interface serving as a fracture path is reduced.

  (6) As one form of the said cemented carbide alloy, it is mentioned that the average particle diameter of the several single crystal tungsten carbide particle which comprises the said polycrystalline tungsten carbide particle is 1 micrometer or less.

  It is expected that the wear resistance is further improved when the average particle size of the plurality of single crystal WC particles constituting the polycrystalline WC particles is 1 μm or less. This is presumably because the number of crystal grain boundaries serving as deformation resistance and fracture propagation resistance increases because the single crystal WC particles constituting the polycrystalline WC particles are small.

  (7) As one form of the said cemented carbide, it is mentioned that at least one of chromium and vanadium is included.

  Since the cemented carbide contains at least one of chromium (Cr) and vanadium (V), the WC particles can be prevented from being dissolved and reprecipitated in the manufacturing process of the cemented carbide, so that the polycrystalline WC particles can be easily maintained. Become.

  (8) The cutting tool which concerns on 1 aspect of this invention is a cutting tool using the cemented carbide as described in any one of said (1) to (7) as a base material.

  By using the cemented carbide according to one embodiment of the present invention as a base material, it is possible to provide a cutting tool having a good balance between wear resistance and fracture resistance.

  (9) As one form of the said cutting tool, providing the hard film coat | covered by at least one part of the surface of the said base material is mentioned.

  By forming the hard film on the base material, the wear resistance can be improved while maintaining the toughness of the base material. Moreover, it is expected that the finished surface state of the work material can be improved by forming a hard film on the base material.

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

<Cemented carbide>
"Overview"
The cemented carbide according to the embodiment of the present invention includes a hard phase mainly composed of WC and a binder phase mainly composed of an iron group element. Examples of the WC that is the main component of the hard phase include (1) polycrystalline WC particles composed of an aggregate of a plurality of single crystal particles, and (2) dispersed single crystal WC particles. One feature of the cemented carbide according to the embodiment of the present invention is that WC, which is the main component of the hard phase, includes polycrystalline WC particles. Hereafter, each component requirement is demonstrated with reference to FIGS. 1-9 as needed. In each figure, the cemented carbides 1A to 1I have a configuration in which particles of a hard phase 10 are dispersed in a matrix of a binder phase 20. For convenience of explanation, basically, polycrystalline WC particles, single crystal WC particles constituting one polycrystalline WC particle, and particles other than WC are illustrated in the same shape and the same particle size. Actually, there are various shapes and particle size distributions. In addition, when the illustrated particle size is different, such as the polycrystalline WC particles in FIGS. 2 and 7, it indicates that there are a plurality of peaks in the particle size distribution of the polycrystalline WC particles.

[Polycrystalline WC particles]
Polycrystalline WC particles refer to WC in which a plurality of single crystal WC particles are directly bonded with different crystal orientations. Hereinafter, in the cemented carbide according to the embodiment of the present invention, the single crystal WC particles constituting the polycrystalline WC particles are referred to as constituent single crystal WC particles. As shown in FIGS. 1 to 9, a crystal grain boundary 103 that is a boundary between crystal orientations is observed in the polycrystalline WC particles 101.

[Dispersed single crystal WC particles]
The dispersed polycrystalline WC particle is a WC constituting a hard phase, and means a single crystal WC particle dispersed in a cemented carbide without constituting a polycrystalline WC particle. The dispersed single crystal WC particles may include single crystal WC particles intentionally contained from the raw material stage and single crystal WC particles separated from the polycrystalline WC particles when the raw material powder is mixed. The dispersed single crystal WC particles include those in which a plurality of dispersed single crystal WC particles are three-dimensionally connected by necking or the like (not shown).

《Hard phase material and crystal structure》
The hard phase may be (1) a case where the hard phase is composed only of WC or (2) a case where the hard phase is composed of particles other than WC and WC. In either case, the WC includes polycrystalline WC particles.

[Hard phase is WC only]
(Only WC polycrystalline WC particles)
An example of a cemented carbide in which the hard phase is composed only of WC is cemented carbide 1A shown in FIG. In the cemented carbide 1A, the hard phase 10 is composed only of WC100, and all of the WC100 is polycrystalline WC particles 101. Here, when the particle size distribution of the polycrystalline WC particles 101 is obtained by observing the cross section of the cemented carbide 1A, the peak is single. In other words, the average particle diameter of the polycrystalline WC particles is almost equal to this peak.

  Another example of a cemented carbide in which WC is composed only of polycrystalline WC particles is cemented carbide 1B shown in FIG. The polycrystalline WC particles 101 in the cemented carbide 1B have a particle size distribution having a plurality of peaks. For example, when the particle size distribution of the polycrystalline WC particles 101 is obtained by observing the cross section of the cemented carbide 1B, there are two peaks of fine particles and coarse particles. That is, the cemented carbide 1B includes polycrystalline WC particles 101a that form a distribution including a fine-grained peak and polycrystalline WC particles 101b that form a distribution that includes a coarse-grained peak.

(WC is polycrystalline WC particles and dispersed single crystal WC particles)
The hard phase WC may include polycrystalline WC particles and dispersed single crystal WC particles. For example, in the cemented carbide 1C shown in FIG. 3, the hard phase 10 is composed of only WC100, but the WC100 is composed of polycrystalline WC particles 101 and dispersed single crystal WC particles 105. In the cemented carbide 1C, the average particle diameter βp of the polycrystalline WC particles 101 and the average particle diameter βm of the dispersed single crystal WC particles 105 are substantially the same. Of course, βp and βm may be different. Examples of such include a cemented carbide 1D shown in FIG. 4 and a cemented carbide 1E shown in FIG. In the cemented carbide 1D, βp is larger than βm. In the cemented carbide 1E, βp is smaller than βm.

  The polycrystalline WC particles may be composed of a plurality of polycrystalline WC particles having different average particle sizes α of the constituent single crystal WC particles. Examples of such a cemented carbide include cemented carbide 1F shown in FIG. 6 and cemented carbide 1G shown in FIG.

  The cemented carbide 1F has a single peak in the particle size distribution of the polycrystalline WC particles 101 itself, but there are two peaks when the particle size distribution of the constituent single crystal WC particles 102 in the polycrystalline WC particles 101 is measured. That is, the hard phase 10 of the cemented carbide 1F has a constituent single crystal of the polycrystalline WC particle 101c when the average particle diameter α of the constituent single crystal WC particles of the polycrystalline WC particle 101c and the polycrystalline WC particle 101d is compared. The average particle diameter α1 of the WC particles 102a is smaller than the average particle diameter α2 of the constituent single crystal WC particles 102b of the polycrystalline WC particles 101d. Furthermore, as in the cemented carbide 1G shown in FIG. 7, the particle size distribution of the polycrystalline WC particles 101 may have a plurality of peaks. The cemented carbide 1G shown in FIG. 7 has two peaks of fine particles and coarse particles when the particle size distribution of the polycrystalline WC particles 101 is obtained. That is, the cemented carbide 1G includes polycrystalline WC particles 101c that form a distribution including a peak on the coarse grain side and polycrystalline WC particles 101d that form a distribution that includes a peak on the fine grain side. The average particle diameter α1 of the constituent single crystal WC particles 102a of the polycrystalline WC particles 101c is smaller than the average particle diameter α2 of the constituent single crystal WC particles 102b of the polycrystalline WC particles 101d.

[Particles other than WC]
The hard phase may include particles other than WC (hereinafter referred to as other particles). This is because the wear resistance of the cemented carbide may be improved by containing other particles other than the WC particles. An example of a cemented carbide containing other particles in the hard phase is cemented carbide 1H shown in FIG. In the cemented carbide 1H, the hard phase 10 is composed of polycrystalline WC particles 101 and other particles 110. As another example of the cemented carbide containing other particles, as in the cemented carbide 1I shown in FIG. 9, the hard phase 10 is composed of polycrystalline WC particles 101, dispersed single crystal WC particles 105, and other particles. 110 is included.

  Examples of other particles include carbides (except WC), nitrides and carbonitrides of at least one element selected from the group consisting of Group 4, 5, 6 elements of the periodic table and silicon (Si). Can be mentioned. Examples of the periodic table elements 4, 5, and 6 include titanium (Ti), V, Cr, zirconium (Zr), niobium (Nb), tantalum (Ta), tungsten (W), and the like. Specific other particles include niobium carbide (NbC), tantalum carbide (TaC), titanium carbide (TiC), titanium nitride (TiN), titanium carbonitride (TiCN), zirconium carbonitride (ZrCN), and these Examples include composite carbonitrides.

<Ratio of hard phase>
The ratio of the hard phase includes the ratio of the hard phase in the cemented carbide, the ratio of polycrystalline WC particles in the hard phase, and the ratio of hard phases other than WC. The ratio of the polycrystalline WC particles includes a case where the ratio is defined by an area ratio and a case where the ratio is defined by the number of particles.

[Ratio of hard phase in cemented carbide]
The hard phase is preferably 75% by mass or more and 96% by mass or less, more preferably 80% by mass or more and 95% by mass or less of the total mass of the cemented carbide. This is because the cemented carbide can have sufficient toughness and can be made into a cemented carbide excellent in fracture resistance.

(Percentage of WC in the hard phase)
The hard phase is mainly composed of WC. A main component means containing WC in the ratio of 50 mass% or more in a hard phase. The lower limit of the WC content can be, for example, 70% by mass or more, 75% by mass or more, 80% by mass or more, and 85% by mass or more of the entire hard phase. On the other hand, the upper limit of the content of WC can be, for example, 98% by mass or less and 95% by mass or less of the entire hard phase.

(Ratio of polycrystalline WC particles in the hard phase)
The ratio of the above-mentioned polycrystalline WC particles using the area ratio as an index is such that in the cross-sectional structure of the cemented carbide, when the area of the hard phase is St and the area of the polycrystalline WC particles is Sp, Sp / St ≧ 0.5 It is preferable to satisfy. It can be said that the cemented carbide satisfying the above formula has a large ratio of the area of the polycrystalline WC particles to the area of the hard phase. Therefore, it can be said that the ratio of the polycrystalline WC particles in the hard phase is equal to or greater than a predetermined amount, and higher levels of wear resistance and fracture resistance can be realized. In particular, when the ratio of the area of the polycrystalline WC particles to the area of the hard phase represented by the above formula is 0.8 or more, and further 0.9 or more, a cemented carbide having excellent fracture resistance can be obtained.

  The ratio of the above-mentioned polycrystalline WC particles using the number of particles as an index is expressed as Np when the number of all hard phase particles constituting the hard phase is Nt and the number of polycrystalline WC particles is Np in the cross-sectional structure of the cemented carbide. /Nt≧0.17 is preferably satisfied, and Np / Nt ≧ 0.2 is more preferable. It can be said that the cemented carbide satisfying the above formula has a large ratio of the number of polycrystalline WC particles to the number of all hard phase particles. Therefore, it can be said that the ratio of the polycrystalline WC particles in the hard phase is equal to or greater than a predetermined amount, and higher levels of wear resistance and fracture resistance can be realized. In particular, when the value of the ratio of the number of polycrystalline WC particles to the number of all hard phase particles represented by the above formula is 0.4 or more, and further 0.5 or more, the carbide having excellent fracture resistance. Can be an alloy.

(Ratio of other particles in the hard phase)
When other particles are included in the hard phase, the ratio of the other particles with the area ratio as an index is 0 <Sa / St ≦ when the area of the other particles is Sa in the cross-sectional structure of the cemented carbide. It is preferable to satisfy 0.5. Although depending on the composition of other particles, it is expected that wear resistance and the like will be further improved by including other particles in the hard phase. The lower limit of the ratio of the area of other particles to the area of all hard phase particles represented by the above formula can be 0.01 or more, and further 0.1 or more. On the other hand, since the upper limit of the ratio of the area of other particles to the area of all the hard phase particles is 0.5 or less, the fracture resistance and thermal conductivity of the cemented carbide are reduced due to a relative decrease in WC. Can be suppressed. The upper limit of the ratio of the area of other particles to the area of all hard phase particles represented by the above formula can be 0.45 or less, and further 0.3 or less.

  When other particles are included in the hard phase, the ratio of the other particles in the entire hard phase preferably satisfies 0 <Na / Nt ≦ 0.7 or less when the number of other particles is Na. Although depending on the composition of the other particles, it is expected that the wear resistance of the cemented carbide will be further improved by including other particles in the hard phase. The lower limit of the ratio of the number of other particles to the number of all hard phase particles represented by the above formula can be 0.05 or more, further 0.1 or more, and particularly 0.2 or more. On the other hand, when the upper limit of the ratio of the number of other particles to the total number of hard phase particles is 0.7 or less, it is possible to suppress a relative decrease in the ratio of polycrystalline WC particles contained in WC. Thereby, the chipping resistance of a cemented carbide alloy and the fall of thermal conductivity by WC reducing relatively can be suppressed. The upper limit of the ratio of the number of other particles to the number of all hard phase particles represented by the above formula can be 0.65 or less, further 0.45 or less, and particularly 0.35 or less.

[Analysis method of hard phase]
The hard phase area, number, and composition can be identified by observing the section of the cemented carbide with an optical microscope, or analyzing the section of the cemented carbide with SEM (scanning electron microscope) and energy dispersive X-ray (EDS). It can be easily performed by performing image analysis using (EDS surface analysis). Details of the analysis method will be described in test examples described later.

[Average particle size of hard phase]
The average particle size β of all particles constituting the hard phase is preferably 2 μm or more, and more preferably 5 μm or more. This is because when β is increased, the interface between the hard phase and the binder phase is reduced, and a cemented carbide having excellent fracture resistance can be obtained.

  In particular, the average particle diameter βp of the polycrystalline WC particles is preferably 1 μm or more, more preferably 2 μm or more, and further preferably 5 μm or more. This is because βp can be increased by making βp to some extent, and a cemented carbide having excellent fracture resistance can be obtained.

  The average particle diameter α of the constituent single crystal WC particles is preferably 1 μm or less, more preferably 0.8 μm or less, further preferably 0.7 μm or less, and particularly preferably 0.5 μm or less. Preferably, it is most preferably 0.3 μm or less. If βp is the same, as α becomes smaller, there will be many crystal grain boundaries that act as deformation resistance and fracture propagation resistance in the polycrystalline WC particles, and the balance between wear resistance and fracture resistance is excellent. is there.

  βp is 1.4 times or more, 2 times or more, 5 times or more, 10 times or more, and 15 times or more of α. Because α becomes smaller than βp, there are many crystal grain boundaries that act as deformation resistance and fracture propagation resistance in the polycrystalline WC particles, and the balance between wear resistance and fracture resistance is excellent. .

[Measurement method of average particle diameter]
The average particle diameter β (μm) of each particle constituting the hard phase is obtained by analyzing the cross section of the cemented carbide and calculating the average value of the horizontal ferret diameter and the vertical feret diameter in the cross sectional image. Specifically, for each particle identified by the above-described image analysis or the like, the ferret diameter in the horizontal direction and the ferret diameter in the vertical direction are measured for each of at least 100 particles in the cross-sectional image. Then, the average value of both ferret diameters of each hard phase particle is added together and divided by the number of measured particles is the average particle diameter β of the hard phase particles. The average particle size βp of the polycrystalline WC particles, the average particle size α of the constituent single crystal WC particles, and the average particle size βm of the dispersed single crystal WC particles are also determined from the same image analysis. A detailed image analysis method will be described in Test Example 1 described later. The average particle size of each particle of the hard phase in the cemented carbide is different from the average particle size of the raw material powder described later in the measuring method.

<< Binder Phase >>
The binder phase is mainly composed of an iron group element. A main component means containing an iron group element in the ratio of 50 mass% or more of the whole binder phase. Typical examples of the iron group element constituting the binder phase include nickel (Ni), cobalt (Co), iron (Fe), and the like. These may be used alone or in combination. Moreover, the binder phase may contain W, carbon (C), which are components of the hard phase, and other inevitable components.

  The binder phase may include at least one of Cr and V. When these elements are present in the binder phase, it is considered that they are present in a solid solution state in the binder phase.

  The content of the binder phase is preferably 4% by mass or more and 25% by mass or less, more preferably 5% by mass or more and 20% by mass or less of the entire cemented carbide. Since the lower limit of the content of the binder phase is 4% by mass or more, and further 5% by mass or more, the deterioration of sinterability during production is prevented, and the hard phase is firmly bonded by the binder phase. Is high and is less prone to defects. Moreover, the toughness of a cemented carbide improves because the minimum of content of a binder phase is 4 mass% or more, Furthermore, 5 mass% or more. On the other hand, when the upper limit of the binder phase content is 25% by mass or less, further 20% by mass or less, particularly 15% by mass or less, the hardness of the cemented carbide decreases due to the relative reduction of the hard phase. It is possible to suppress the decrease in wear resistance and plastic deformation resistance.

《Action ・ Effect》
[1] The cemented carbide according to the embodiment described above is composed only of dispersed single-crystal WC particles because the WC particles, which are the main components of the hard-phase particles constituting the hard phase, include polycrystalline WC particles. Compared to conventional cemented carbide (see FIG. 12), the balance between wear resistance and fracture resistance is good.

  [2] When the particle size distribution of each particle of the hard phase has a plurality of peaks, further improvement in wear resistance and fracture resistance is expected. For example, as in the cemented carbide shown in FIGS. 2 and 7, the polycrystalline WC particles are composed of fine polycrystalline WC particles and coarse polycrystalline WC particles, or as shown in FIGS. In addition, when the average particle size of the dispersed single crystal WC particles and the average particle size of the polycrystalline WC particles are different, an effect of improving wear resistance and fracture resistance due to the presence of fine and coarse hard phases can be expected.

  [3] For example, when the hard phase particles contain other particles, such as the cemented carbide 1H shown in FIG. 8, depending on the composition of the other particles, the wear resistance and fracture resistance may be further improved. It is thought that there is.

<Manufacturing method of cemented carbide>
"Overview"
The cemented carbide according to the above-described embodiment of the present invention can be manufactured by a method for manufacturing a cemented carbide comprising a raw material powder preparation step, a mixing step, and a mixed powder forming / sintering step. One of the features of this production method is (1) using polycrystalline WC powder containing polycrystalline WC particles, and (2) devising the conditions of the raw material powder mixing step and the mixed powder sintering step. . Hereinafter, each process will be described.

《Preparation process of raw material powder》
In the raw material powder preparation step, all raw material powders of materials constituting the cemented carbide are prepared. As preparation objects, polycrystalline WC powder and binder phase powder are essential, and single crystal WC powder and hard phase powder other than WC are included as necessary. This single crystal WC powder is intentionally mixed with the polycrystalline WC powder as a raw material powder to become dispersed single crystal particles after sintering, or used as a raw material for the polycrystalline WC powder to be described later. What becomes single crystal WC particles is included. Commercially available powders can be used other than the polycrystalline WC powder. For example, the polycrystalline WC powder is preferably obtained by the following production method.

[Method for producing polycrystalline WC powder]
The polycrystalline WC powder can be produced by a single crystal WC powder preparation step, a single crystal WC powder forming / sintering step, and a pulverization step. A polycrystalline WC powder having a desired average particle size (particle size distribution) can be obtained by a classification step. Hereinafter, each process will be described.

(Preparation process of single crystal WC powder)
In the single crystal WC powder preparation step, a single crystal WC powder as a raw material for the polycrystalline WC particles is prepared. The average particle size of the single crystal WC powder is preferably 0.3 μm or more and 1 μm or less. By setting the average particle size to 0.3 μm or more, it is possible to obtain a powder that is easy to handle. By setting the average particle size to 1.0 μm or less, it is easy to obtain a cemented carbide having excellent wear resistance. The average particle size of the single crystal WC powder is preferably the same as the average particle size α of the constituent single crystal WC particles of the polycrystalline WC particles to be produced. This is because the average particle diameter α of the constituent single crystal WC particles in the polycrystalline WC particles is substantially equal to the average particle diameter of the single crystal WC particles constituting the single crystal WC powder as the raw material.

(Molding and sintering process of single crystal WC powder)
In the molding / sintering step of the single crystal WC powder, a known method such as a spark-plasma sintering method can be used. Thereby, a bulk WC sintered body containing polycrystalline WC particles can be obtained. In the case of the electric current pressure sintering method, it is preferable to carry out under conditions of load: 25 MPa to 150 MPa, maximum temperature: 1600 ° C. to 2000 ° C., maximum temperature holding time: 5 minutes to 60 minutes, atmosphere: vacuum. . This is because the single crystal WC particles can be sufficiently bonded to each other. More preferably, the conditions are load: 50 MPa to 100 MPa, maximum temperature: 1750 ° C. to 1950 ° C., and maximum temperature holding time: 10 minutes to 30 minutes. If it is an electric current pressure sintering method, shaping | molding and sintering can be performed simultaneously. This molding / sintering is carried out by subjecting the single crystal WC powder to CIP (cold isostatic pressing), and then sintering the resulting WC compact, in addition to the current pressure sintering method. May be. Conditions for CIP molding and main sintering are not particularly limited, and conditions within a range where an ideal specific gravity (15.6) of WC can be obtained can be appropriately selected. As an example, CIP molding pressure: 400 MPa, maximum temperature during main sintering: 1800 ° C., holding time: 30 minutes, atmosphere: vacuum.

(Crushing process)
In the pulverization step, the bulk WC sintered body obtained in the sintering step is pulverized into a pulverized powder. The pulverization is not particularly limited as long as it can pulverize a bulk WC sintered body. Specifically, crushing by hammering can be mentioned. If necessary, the pulverized powder may be further pulverized by a known method such as a jet mill to obtain a finer pulverized powder.

(Classification process)
In the classification step, only powder having a predetermined particle size distribution is extracted from the pulverized powder that has passed through the pulverization step. By the classification step, a polycrystalline WC powder having a desired average particle size and particle size distribution can be obtained. For the classification step, a known method such as manual sieving or classification with a classifier can be applied. In particular, it is preferable to remove the single crystal WC powder mixed in the powder that has undergone the pulverization step.

[Average particle size of raw material powder]
The average particle size of each powder of the raw material powder (including the single crystal WC powder that is the raw material of the polycrystalline WC powder) is different from the average particle size of the hard phase in the cemented carbide. Specifically, the average particle diameter of each powder is an average particle diameter (FSSS diameter) obtained by the Fischer sub-sieve sizer (FSSS) method. However, there is not much difference between the average particle diameters obtained for the ferret diameter and the FSSS diameter.

《Mixing process》
In the mixing step, the raw material powder prepared in the raw material powder preparation step is mixed. By this mixing step, a mixed powder in which each raw material powder is mixed is manufactured. Mixing may be wet or dry. The mixing process is a milder condition than the conventional cemented carbide manufacturing process so that the polycrystalline WC particles can be prevented from being scattered to the single crystal WC particles due to the impact generated in the raw material powder mixing process. To do.

  In the mixing step, known devices such as an ultrasonic homogenizer, a rolling ball mill, and a V-type mixer can be used. As an example of mild conditions using these devices, in the case of mixing by ultrasonic waves, it is possible to lower the energization voltage than before. When mixing with a rolling ball mill, (1) lowering the peripheral speed than before, (2) shortening the mixing time, (3) not using mixing media, and the like. In the case of mixing with a V-type mixer, the same may be mentioned. By doing in this way, it can prevent as much as possible that the ratio of a single crystal WC particle increases by the influence of the impact which generate | occur | produces in the case of a mixing process, and the polycrystalline WC particle disperses. Examples of mild conditions when using a rolling ball mill include peripheral speed: 15 m / min to 60 m / min, time: 0.5 hours to 2.0 hours, and the like.

  After the raw material powder mixing step, the mixed powder may be granulated as necessary. By granulating each particle, it is easy to fill the mixed raw material powder into a die, a mold, or the like during the molding / sintering step of the mixed powder described later. For granulation, a known granulation method can be applied. For example, a commercially available granulator such as a spray dryer can be used.

<Molded powder molding and sintering process>
In the mixed powder forming / sintering step, the mixed powder is formed into a predetermined shape, and the formed body is sintered. Specific methods include a method of simultaneously forming and sintering a mixed powder, such as an electric pressure sintering method, and press-molding the mixed powder to produce a pressed body, and then sintering the pressed body. There is a way to do it. In the case of the electric current pressure sintering method, it is preferably performed under the conditions of load: 5 MPa to 20 MPa, maximum temperature: 1150 ° C. to 1450 ° C., maximum temperature holding time: 5 minutes to 60 minutes, atmosphere: vacuum. . This is because a dense cemented carbide can be sintered. More preferably, the conditions are a load of 5 MPa to 10 MPa, a maximum temperature of 1200 ° C. to 1300 ° C., and a maximum temperature holding time of 5 minutes to 15 minutes. When the molding step and the sintering step are separated, the pressing conditions in the molding step include a load: 50 MPa or more and 200 MPa or less a. As the sintering conditions for the pressed body, it is preferable to carry out the maximum temperature: 1300 ° C. to 1600 ° C., the maximum temperature holding time: 30 minutes to 120 minutes, and the atmosphere: vacuum. Note that the above atmosphere is not limited to a vacuum. The atmosphere may be a normal pressure (atmospheric pressure) state, a pressurized state, or an inert gas atmosphere. Specific examples of the inert gas include nitrogen, argon, and helium.

《Action ・ Effect》
According to the above-described method for manufacturing a cemented carbide, a cemented carbide including polycrystalline WC particles as hard phase particles can be efficiently manufactured.

<Cutting tools>
"Base material"
A cutting tool according to an embodiment of the present invention is a cutting tool using a cemented carbide as a base material. One of the features of the cutting tool according to the embodiment of the present invention is that the cemented carbide according to the above-described embodiment of the present invention is used as a base material. Thereby, it is possible to provide a cutting tool having a good balance between wear resistance and fracture resistance.

  The shape of the cutting tool is not particularly limited. Examples of the shape of the cutting tool include a bite, a ball mill, an end mill, a drill, and a reamer. In particular, for cutting tools and the like, a cutting edge-exchangeable cutting tip can be cited.

《Hard film》
The cutting tool according to the embodiment of the present invention may include a hard film on the base material. The composition of the hard film includes carbides, nitrides, oxides, borides, and solid solutions of one or more elements selected from the metals in Groups 4, 5, and 6 of the periodic table, aluminum (Al), and Si. Can be mentioned. For example, Ti (C, N), Al ₂ O ₃ , (Ti, Al) N, TiN, TiC, (Al, Cr) N, and the like can be given. In addition, cubic boron nitride (cBN), diamond-like carbon, and the like are also suitable as the composition of the hard film. Such a hard film can be formed by a vapor phase method such as a chemical vapor deposition (CVD) method or a physical vapor deposition (PVD) method. When the hard film is formed by the CVD method, it is easy to obtain a hard film having excellent adhesion to the base material. Examples of the CVD method include a thermal CVD method.

  It is preferable that the hard film is coated on a portion serving as a cutting edge in the base material and the vicinity thereof, and may be coated on the entire surface of the base material. By forming the hard film on the base material, the wear resistance can be improved while maintaining the toughness of the base material. In addition, by forming a hard film on the base material, chipping hardly occurs at the cutting edge of the base material, and it is expected that the finished surface of the work material can be made favorable.

  The hard film may be a single layer or multiple layers. The total thickness of the hard film is preferably 1 μm or more and 20 μm or less.

<Example of cutting tool>
As an example of the cutting tool according to the embodiment of the present invention, a blade-tip-exchangeable cutting tip is shown in FIG. The blade-tip-exchangeable cutting tip C has a substantially rhombus shape, and includes a cemented carbide base material 50 and a hard film 60 coated on the surface of the base material 50, as shown in FIG. The base material 50 is a cemented carbide according to the embodiment of the present invention described above. As shown in FIG. 10, the cutting edge exchange type cutting tip C has a rake face 51, a flank face 52, a cutting edge (cutting edge) 53, and an attachment hole 54. For example, in the case of a cutting tool, such a blade-tip-exchangeable cutting tip C is used by being fixed to an appropriate shank.

<Test Example 1>
In Test Example 1, a cemented carbide in which the WC constituting the hard phase includes polycrystalline WC particles and a conventional cemented carbide not including polycrystalline WC particles are produced, and a cutting tool using these as a base material is used. The cutting performance was investigated. The average particle diameter written together with the raw material powder is the average particle diameter determined by the FSSS method, the average particle diameter of the hard phase particles in the cemented carbide and the average particle diameter of the constituent single crystal WC particles are the feret diameter. It is considered that there is no significant difference between the average particle diameter obtained by the FSSS method and the feret diameter. The same applies to other test examples described later.

<< Sample preparation >>
[Preparation of polycrystalline WC powder]
As a starting material, a single crystal WC powder having an average particle size of 1.0 μm was prepared (preparation step of a single crystal WC powder). This WC powder was sintered by an electric pressure sintering method under the conditions of load: 50 MPa, maximum temperature: 1800 ° C., and maximum temperature holding time: 10 minutes to obtain a bulk WC sintered body (single Crystal WC powder forming / sintering process). The obtained bulk WC sintered body was pulverized to obtain a pulverized powder (pulverization step). This pulverized powder was classified by a commercially available classifier to obtain a polycrystalline WC powder having an average particle size of 5.0 μm (classifying step). This WC powder was embedded in a resin and used as a sample for observation. The cross section of the observation sample was subjected to cross section milling with an ion milling apparatus, and the cross section of the cross section milled cross section of the observation sample was observed with a scanning electron microscope. As a result, all the WC particles contained in the sample were polycrystalline WC particles, and the average particle size of the constituent single crystal WC particles was 1.0 μm. That is, in this polycrystalline WC powder, the average particle size of the single crystal WC powder used as a raw material was generally maintained. In Test Example 1, this polycrystalline WC powder was used.

[Preparation of single crystal WC powder]
As a comparative object, in order to produce a cemented carbide in which the hard phase WC is composed only of dispersed single crystal WC particles, commercially available single crystal WC powders having average particle diameters of 1 μm and 5 μm were prepared.

[Production of cemented carbide]
As the raw material powder, the above-mentioned polycrystalline WC powder, single crystal WC powder, Cr ₃ C ₂ powder (average particle size 1.0 μm), and Co powder (average particle size 1.5 μm) were prepared (preparation step of raw material powder) ). And each powder is mix | blended by the mixing | blending ratio shown in Table 1, and after adding ethanol, each mixing powder is wet-mixed on the conditions of ultrasonic output: 300microampere and irradiation time: 15 minutes with the commercially available ultrasonic homogenizer. To obtain a mixed powder (mixing step). Each mixed powder was sintered under vacuum by an electric pressure sintering method under the conditions of load: 5 MPa, maximum temperature: 1280 ° C., maximum temperature holding time: 5 minutes, and three types of cemented carbide were obtained. (Mixed powder molding and sintering process). Hereinafter, as the WC powder, a sample 1-1 using only the above polycrystalline WC powder, a sample 1-1 using only a single crystal WC powder having an average particle size of 1 μm, and an average particle size of 5 μm are used. A sample using only single crystal WC powder is designated as Sample 1-12.

《Analysis of hard phase particles》
Each of the above samples was cut and the cross section was mirror-finished, and then the processed layer of the cross section was removed by argon (Ar) ion beam processing. This cross section was photographed with SEM to obtain a reflected electron image. Further, EDS surface analysis was performed on the same field of view as the reflected electron image. Hereinafter, imaging by SEM and EDS surface analysis will be described in detail.

[SEM image]
Reflected electron images were acquired at an observation magnification of 1500 to 10,000 so that 100 or more hard phase particles were included in the visual field.

[EDS surface analysis]
An element predicted to appear in advance from the blend composition was selected as an analysis target, and an EDS surface analysis was performed within the same field of view as the reflected electron image to obtain a composition distribution image. Here, W, Cr, and Co were selected as elements to be analyzed from the composition of the raw material powder used for each sample. When the raw material powder contains TiC or TaC, Ti or Ta is added to the analysis target. Although light elements such as C and nitrogen (N) may be included in the analysis target, it is often difficult to identify light elements with the energy resolution of EDS, and they were not selected in this test example.

[Classification of hard phase particles]
Comparing the acquired backscattered electron image and composition distribution image, the hard phase in which only the W distribution is observed is WC, and the hard phase in which the distribution of other elements (such as Ti and Ta) is observed is other than WC Classified. In each sample of this test example, since distribution of only W was observed in the hard phase in any sample, all the hard phases were classified as “WC”.

[Classification of WC]
The contrast and brightness of the acquired backscattered electron image were adjusted to produce a channeling contrast image (also referred to as a crystalline contrast image) according to the difference in crystal orientation. From this channeling contrast image, WC was classified into polycrystalline WC particles and dispersed single crystal WC particles. In the channeling contrast image, it is easy to classify the polycrystalline WC particles from the dispersed single crystal WC particles because the polycrystalline WC particles can confirm the state in which a plurality of constituent single crystal WC particles are bonded via the crystal grain boundary. is there. As described above, WC bonded by necking was classified into dispersed single crystal WC particles.

  As a result of the analysis as described above, in Sample 1-1, almost all the hard phases were composed of polycrystalline WC particles. Therefore, the average particle diameter β of the hard phase particles constituting the hard phase is the average particle diameter βp of the polycrystalline WC particles. In Sample 1-1, βp was 5 μm, the average particle size α of the constituent single crystal WC particles was 1 μm, and each particle size distribution had a single peak. Thus, it can be seen that βp and α are substantially maintained as those of the polycrystalline WC powder used for the raw material powder. On the other hand, in Sample 1-11 and Sample 1-12, all the particles constituting the hard phase were composed of dispersed single crystal WC particles. Therefore, the average particle diameter β of the particles constituting the hard phase is equal to the average particle diameter βm of the dispersed single crystal WC particles. Samples 1-11 and 1-12 had βm of 1 μm and 5 μm, respectively, and had a single particle size distribution peak. In Samples 1-11 and 1-12, it can be seen that βm substantially maintains the average particle diameter of the single crystal WC powder used as the raw material powder.

《Cutting test》
Using each of the above samples as a base material, surface grinding of the seating surface was performed with a # 200 diamond grindstone, and the cutting edge treatment was further performed to produce a SNGN120408-shaped cutting tool. And the abrasion resistance and fracture resistance of the cutting tool produced with each sample were each evaluated. Table 2 shows the conditions of the wear resistance test and fracture resistance test, and Table 3 shows the results of these tests.

  As shown in Table 3, Sample 1-11 is excellent in wear resistance because the particles constituting the hard phase are relatively small, but has low fracture resistance. In Sample 1-12, since the hard phase particles are relatively large, the fracture resistance is excellent, but the wear resistance is low. On the other hand, in Sample 1-1, although the average particle diameter of the hard phase particles is relatively large at 5 μm, the wear resistance is comparable to that of Sample 1-11. In addition, Sample 1-1 has the same fracture resistance as Sample 1-12 in which the average particle size of the hard phase particles is relatively small. Thus, it can be seen that a cutting tool using a cemented carbide containing a hard WC containing polycrystalline WC particles as a base material has an excellent balance between fracture resistance and wear resistance.

<Test Example 2>
In Test Example 2, the influence of the number of polycrystalline WC particles in the WC constituting the hard phase was examined.

<< Sample preparation >>
[Preparation of polycrystalline WC powder]
A polycrystalline WC powder having an average particle diameter β of 3.5 μm and a single particle size distribution peak as in Test Example 1 except that a single crystal WC powder having an average particle diameter of 0.8 μm as a starting material was used. Was made. When this polycrystalline WC powder was observed in the same manner as in Test Example 1, all of the polycrystalline WC powder was composed of polycrystalline WC particles, and the average particle size α of the constituent single crystal WC particles was 0.8 μm. In Test Example 2, this polycrystalline WC powder was used.

[Preparation of single crystal WC powder]
In order to adjust the ratio of the hard-phase polycrystalline WC particles, single crystal WC powder having an average particle size of 0.8 μm was prepared.

[Production of cemented carbide]
Each of the above WC powders, TaC powder (average particle size 1.0 μm), NbC powder (average particle size 1.0 μm), TiC powder (1.2 μm), ZrCN powder (average particle size 0.8 μm), Cr ₃ C ₂ powder (average particle size 1.0 μm), VC powder (average particle size 0.5 μm), Co powder (average particle size 1.5 μm), Ni powder (average particle size 2.0 μm) and Fe powder (average particle size) (Diameter 1.3 μm) was prepared (preparation step of raw material powder). And each powder was mix | blended with the mixing | blending ratio shown in Table 4, each was filled with the stainless steel pot with ethanol and a cemented carbide ball (ball diameter 1.5mm), with a commercially available rolling ball mill, peripheral speed: 60 m / min, Mixing was performed under the conditions of time: 2 hours to prepare 16 kinds of mixed powders (mixing step).

These mixed powders were added with camphor and ethanol, granulated, and press-molded with a load of 1 ton / cm ² (about 98 MPa) (mixed powder forming step). Thereafter, the molded body of the mixed powder thus formed was sintered under vacuum under the conditions of maximum temperature: 1400 ° C. and maximum temperature holding time: 1 hour, and sample 2-1 to sample 2-12, sample 2- 21 to obtain a cemented carbide of sample 2-24 (pressed body sintering step).

《Analysis of hard phase》
For each of these samples, the hard phase was observed in the same manner as in Test Example 1, the particles constituting the hard phase were classified, and the average particle diameter of each particle was examined. The results are shown in Table 5. Together, (1) Sp / St, which is the ratio of the area Sp of the polycrystalline WC particles to the area St of the hard phase, (2) Sm / St, which is the ratio of the area Sm of the dispersed single crystal WC particles to St, (3 ) Sa / St, which is the ratio of the area Sa of other particles to St, was examined. The results are shown in Table 6.

  In addition, (4) Np / Nt which is the ratio of the number Np of polycrystalline WC particles to the number Nt of all hard phase particles constituting the hard phase, and (5) the ratio of the number Nm of dispersed single crystal WC particles to Nt. Nm / Nt, (6) Na / Nt, which is the ratio of the number Na of other particles to Nt, was examined. The results are shown in Table 7.

《Cutting test》
A SNGN120408-shaped cutting tool was produced in the same manner as in Test Example 1, and a cutting test was performed under the conditions shown in Table 8 to evaluate the wear resistance and fracture resistance. The evaluation results are shown in Table 9.

  From Table 9, Sample 2-1 to Sample 2-9, in which WC, which is the main component of the hard phase, contains polycrystalline WC particles, Sample 2-1 where WC, which is the main component of the hard phase, does not contain polycrystalline WC particles, Thus, it can be seen that wear resistance and fracture resistance are provided at a high level in a well-balanced manner as compared with Sample 2-24. For example, in Sample 2-1 to Sample 2-5 and Sample 2-21 in which the hard phase is only WC, the wear resistance is comparable. On the other hand, Sample 2-1 to Sample 2-5 containing polycrystalline WC particles have higher fracture resistance than Sample 2-21 not containing polycrystalline WC particles. Therefore, it can be said that the inclusion of polycrystalline WC particles is excellent in the balance between wear resistance and fracture resistance.

  In Sample 2-1, only the polycrystalline WC powder containing no single crystal WC particles was used as the hard phase powder, but dispersed single crystal WC particles were observed in the hard phase (see Tables 6 and 7). ). Further, dispersed single crystal WC particles were also observed in Sample 2-6 to Sample 2-12 using only polycrystalline WC powder as the WC powder. Here, in Sample 2-9, the value of Sm / St in Table 6 is 0.00, and from the value of the area ratio, it seems that the dispersed single crystal WC particles are not included. This is because the effective number of each value of the area ratio is 3 digits. As is clear from the number ratio values shown in Table 7, a small amount of dispersed single crystal WC particles were also observed in Sample 2-9.

Most of the dispersed single crystal WC particles observed in Sample 2-1 and Sample 2-6 to Sample 2-12 are considered to be those in which the constituent single crystal WC particles of the polycrystalline WC particles are separated by a mixing process or the like. . Further, when comparing the sample 2-1 and the sample 2-9 having relatively close blending compositions, the ratio of the number of dispersed single crystal WC particles is smaller in the sample 2-9 blended with Cr ₃ C ₂ and VC ( (See Table 7). This is presumed that Sample 2-9 contained Cr and V, which had an effect of suppressing grain growth, so that the single-crystal WC particles were suppressed from being dissolved and reprecipitated in the sintering step of the mixed powder compact. Is done. Therefore, in the sample 2-9, the content ratio of the polycrystalline WC particles is larger than those in the sample 2-1 to the sample 2-3, and as a result, it is considered that the result of the most excellent fracture resistance in this test example was obtained. It is done.

  Comparing Sample 2-1 to Sample 2-5, it can be seen that Sp / St is 0.8 or more, so that the fracture resistance can be improved while maintaining the wear resistance (Tables 6 and 9). In particular, it can be seen that in the sample 2-2 and the sample 2-1, in which Sp / St is 0.9 or more, the improvement of the fracture resistance is large.

  When Sample 2-1 to Sample 2-5 are compared, it can be seen that when Np / Nt is 0.17 or more, particularly 0.2 or more, the chipping resistance is improved in the above cutting test (Table). 7 and Table 9). Further, it can be seen that in the sample 2-2 in which Np / Nt is 0.4 or more and the sample 2-1 in which Np / Nt is 0.8 or more, the fracture resistance is greatly improved.

  Comparing Sample 2-6 to Sample 2-8 and Sample 2-21, even if the hard phase contains a certain amount of other particles, by including polycrystalline WC particles, wear resistance and fracture resistance It can be seen that the sexuality is well-balanced at a high level. Further, comparing Sample 2-6 to Sample 2-8 and Sample 2-22 to Sample 2-24, it can be seen that the wear resistance tends to be improved by including other particles.

It can be seen that the cemented carbides of Samples 2-10 to 2-12 containing Ni and Fe, which are iron-based elements other than Co, are excellent in fracture resistance as in the other samples. Therefore, the following effects are expected.
(1) Even when Ni and Fe, which are iron-based elements other than Co, are contained as a binder phase, by including polycrystalline WC particles, wear resistance and resistance to resistance are higher than when polycrystal WC particles are not included. A cemented carbide with a good balance of deficiency can be obtained.
(2) Even if Ni or Fe which is inferior in fracture resistance compared to Co is used, a cemented carbide having excellent fracture resistance can be produced.
(3) A cemented carbide can be stably manufactured by providing a certain fracture resistance even when Fe, which is supplied more stably than Co and Ni, is used.

<Test Example 3>
In Test Example 3, the influence of the difference in the average particle diameter of the polycrystalline WC particles was examined.

<< Sample preparation >>
[Preparation of polycrystalline WC powder 1]
A WC sintered body was produced in the same manner as in Test Example 1 except that a single crystal WC powder having an average particle size of 0.3 μm as a starting material was used. Polycrystalline WC powders of 0.0 μm, 2.0 μm, and 5.0 μm were prepared. All the polycrystalline WC powders consisted of only polycrystalline WC particles and had a single particle size distribution peak. The average particle size α of the constituent single crystal WC particles constituting each polycrystalline WC powder was all 0.3 μm, and the peak of the particle size distribution was single.

[Preparation 2 of polycrystalline WC powder]
Polycrystalline WC having average particle diameters of 1.0 μm, 2.0 μm, and 5.0 μm in the same manner as in preparation of polycrystalline WC powder 1 except that WC powder having an average particle diameter of 0.5 μm was used as a starting material. All the polycrystalline WC powders from which the powders were made consisted of only polycrystalline WC particles and had a single particle size distribution peak. The average particle size α of the constituent single crystal WC particles constituting each polycrystalline WC powder was all 0.5 μm, and the particle size distribution had a single peak.

[Preparation 3 of polycrystalline WC powder]
Polycrystalline WC having average particle diameters of 1.0 μm, 2.0 μm, and 5.0 μm in the same manner as in preparation of polycrystalline WC powder 1 except that WC powder having an average particle diameter of 0.7 μm was used as a starting material. A powder was prepared. All the polycrystalline WC powders consisted of only polycrystalline WC particles and had a single particle size distribution peak. The average particle size α of the constituent single crystal WC particles constituting each polycrystalline WC powder was 0.7 μm, and the particle size distribution had a single peak.

[Preparation of single crystal WC powder]
Six types of commercially available single crystal WC powder were prepared. Each single crystal WC powder had an average particle size of 0.3 μm, 0.5 μm, 0.7 μm, 1.0 μm, 2.0 μm, 5.0 μm, and a single particle size distribution peak.

[Production of cemented carbide]
These WC powder and Co powder (average particle size 1.5 μm) were prepared (preparation step of raw material powder), and blended in a mass ratio of WC: Co = 92.5: 7.5, respectively, Similarly, 15 types of mixed powders were prepared (mixing step). These mixed raw material powders were respectively sintered by an electric pressure sintering apparatus under the same conditions as in Test Example 1 to obtain 15 types of cemented carbides of Sample 3-1 to Sample 3-15 (mixed powder). Molding and sintering process).

<Observation of hard phase>
For each of these samples, the hard phase was observed in the same manner as in Test Example 1. As a result, the hard phases of Sample 3-1 to Sample 3-9 were all composed of polycrystalline WC particles. On the other hand, the hard phases of Sample 3-10 to Sample 3-15 were all composed of single crystal WC particles. Therefore, β of each sample is equal to βp or βm. Table 10 shows β of each sample. For Sample 3-1 to Sample 3-9 in which the hard phase is polycrystalline WC particles, α is also shown.

《Cutting test》
A SNGN120408-shaped cutting tool was produced from each sample in the same manner as in Test Example 1, and a cutting test was performed under the same conditions as in Test Example 2 to evaluate wear resistance and fracture resistance. Table 10 shows the evaluation results.

  From Table 10, comparing Sample 3-1 to Sample 3-3 with the same βp, it can be seen that the smaller the α, the better the wear resistance. On the other hand, there is no significant difference in the fracture resistance depending on the magnitude of α. The same can be said by comparing Sample 3-4 to Sample 3-6 and Sample 3-7 to Sample 3-9 that have the same βp. In particular, it can be seen that Samples 3-1, 3-2, 3-4, 3-5, 3-7, 3-8 having α of 0.5 μm or less are excellent in wear resistance. On the other hand, when Sample 3-1 to Sample 3-9 are compared, it can be seen that the larger the β is, the more the fracture resistance tends to be improved. In particular, it can be seen that Samples 3-4 to 3-9 having βp of 2.0 μm or more have excellent fracture resistance. Furthermore, Samples 3-4, 3-5, 3-7, and 3-8, in which α is 0.5 μm or less and βp is 2.0 μm or more, are extremely balanced in wear resistance and fracture resistance. It turns out that it is excellent. In particular, Sample 3-7, in which βp is about 16.7 times α, has the highest wear resistance and fracture resistance.

  When sample 3-1 and sample 3-10 are compared, sample 3-1 has the same α as β of sample 3-10, and has equivalent wear resistance. Comparing sample 3-1 and sample 3-13, it can be seen that sample 3-1 has the same β and has substantially the same defect resistance. From each sample, the same can be said for α and β of polycrystalline WC particles. Thus, it turns out that it can be set as the cemented carbide alloy which has a fracture balance and abrasion resistance with a high level and sufficient balance because a hard phase contains a polycrystalline WC particle.

<Test Example 4>
In Test Example 4, the cutting performance of a cutting tool coated with a hard film was examined.

<< Sample preparation and cutting test >>
In the same manner as in Test Example 1, base materials having the SNGN120408 (the flank and rake face were not ground) were prepared from Sample 1-1 and Sample 1-11. And the hard coating which consists of TiAlN was coat | covered by the well-known PVD method so that it might become the average thickness of 5 micrometers on the surface of each base material. Hereinafter, a sample obtained by coating a cutting tool using Sample 1-1 as a base material is referred to as Sample 4-1, and a sample obtained by coating a cutting tool using Sample 1-11 as a base material as Sample 4-11. Using these samples, cutting tests were performed under the conditions shown in Table 11 below, and the cutting performance of both samples was evaluated. The results are shown in Table 12.

  From Table 12, it can be seen that Sample 4-1 containing polycrystalline WC particles is superior in fracture resistance to Sample 4-11 not containing polycrystalline WC particles, and has a good balance between wear resistance and fracture resistance.

  Since the cemented carbide of the present invention has a good balance between wear resistance and fracture resistance, it can be suitably used as a base material for a cutting tool or a material for a mold.

1A-1J Cemented carbide 10 Hard phase 100 Tungsten carbide (WC)
101, 101a, 101b, 101c, 101d polycrystalline WC particles
102, 102a, 102b Constituent single crystal WC particles (single crystal WC particles)
103 Grain boundary 105 Dispersed single crystal WC particles (single crystal WC particles)
110 Particles other than WC (other particles)
20 Binder Phase C Cutting Edge Replaceable Cutting Tip (Cutting Tool)
50 Base Material (Cemented Carbide) 51 Rake Face 52 Flank Face 53 Cutting Edge (Cutting Edge) 54 Mounting Hole 60 Hard Film

Claims (9)

A cemented carbide comprising a hard phase mainly composed of tungsten carbide and a binder phase mainly composed of an iron group element,
A cemented carbide in which the tungsten carbide includes polycrystalline tungsten carbide particles.   The cemented carbide according to claim 1, wherein, in the cross-sectional structure of the cemented carbide, when the area of the hard phase is St and the area of the polycrystalline tungsten carbide particles is Sp, Sp / St ≧ 0.5 is satisfied.   In the cross-sectional structure of the cemented carbide, Np / Nt ≧ 0.2 is satisfied, where Nt is the number of particles constituting the hard phase and Np is the number of polycrystalline tungsten carbide particles. 2. The cemented carbide according to 2.   The hard phase includes at least one of carbide (except for tungsten carbide), nitride, and carbonitride of at least one element selected from the group consisting of Group 4, 5 and 6 elements of the periodic table and silicon. The cemented carbide according to any one of claims 1 to 3.   The cemented carbide according to claim 1, wherein the polycrystalline tungsten carbide particles have an average particle size of 2 μm or more.   The cemented carbide according to any one of claims 1 to 5, wherein an average particle diameter of the plurality of single crystal tungsten carbide particles constituting the polycrystalline tungsten carbide particles is 1 µm or less.   The cemented carbide according to any one of claims 1 to 6, comprising at least one of chromium and vanadium.   A cutting tool using the cemented carbide according to any one of claims 1 to 7 as a base material.   The cutting tool according to claim 8, comprising a hard film coated on at least a part of the surface of the base material.

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