Cemented carbide and cutting tool

Abstract

Provided is a cemented carbide comprising a first phase and a second phase, wherein the first phase is composed of a plurality of tungsten carbide particles, the content of the first phase in the cemented carbide is 65-85 vol%, the content of the second phase in the cemented carbide is 4-25 vol%, the second phase contains 50 mass% or more of cobalt, the second phase contains zirconium, the cobalt content MCo in the cemented carbide is 3-15 mass%, and a and b of the cemented carbide have a relationship of expression I: b<0.0485a+0.0001, where a is the percentage ((MZr / MCo)×100) of the zirconium content MZr mass% in the cemented carbide with respect to the cobalt content MCo mass% in the cemented carbide, a is more than 0 and 8 or less, and b is the area percentage of voids in a first region of a cross section of the cemented carbide, the first region being a region within 50 μm from the surface of the cemented carbide in the cross section.

Description

Cemented Carbide and Cutting Tools

[0001] The present disclosure relates to cemented carbides and cutting tools.

[0002] 2. Description of the Related Art Conventionally, cemented carbide alloys having a hard phase mainly composed of tungsten carbide (WC) and a binder phase mainly composed of an iron group element have been used as materials for cutting tools.

[0003] In Patent Documents 1 and 2, zirconium carbide (ZrC) is used as a raw material for the cemented carbide to improve the plastic deformation resistance and the wear resistance.

[0004] JP-A-2008-69420 JP-A-6-93367

[0005] The cemented carbide of the present disclosure is a cemented carbide comprising a first phase and a second phase, wherein the first phase is composed of a plurality of tungsten carbide particles, the content of the first phase in the cemented carbide is 65% by volume or more and 85% by volume or less, the content of the second phase in the cemented carbide is 4% by volume or more and 25% by volume or less, the second phase contains 50% by mass or more of cobalt, the second phase contains zirconium, and the cobalt content M of the cemented carbide is Ｃｏ is 3% by mass or more and 15% by mass or less, and a and b of the cemented carbide satisfy the relationship of the following formula I, b<0.0485a+0.0001 formula I, where a is the cobalt content M of the cemented carbide. Ｃｏ The zirconium content M of the cemented carbide in mass% Ｚｒ Percentage of mass (M Ｚｒ / M Ｃｏ ) × 100, wherein a is greater than 0 and equal to or less than 8, and b is the area percentage of voids in a first region of a cross section of the cemented carbide, the first region being a region in the cross section that is within 50 μm of the surface of the cemented carbide.

[0006] Fig. 1 is a diagram for explaining the cutting position of the cutting tool made of the cemented carbide of embodiment 1. Fig. 2 is a diagram for explaining another example of the cutting position of the cutting tool made of the cemented carbide of embodiment 1. Fig. 3 is a diagram for explaining the cobalt content M of the cemented carbide of each sample produced in the examples. Ｃｏ Zirconium content M of the cemented carbide in mass%Ｚｒ Percentage of mass (M Ｚｒ / M Ｃｏ ) × 100 and the area percentage of voids in the first region.

[0007] [Problem to be Solved by the Present Disclosure] In Patent Document 1 and Patent Document 2, ZrC is used to improve plastic deformation resistance and wear resistance. However, ZrC is partially oxidized before sintering, and this oxide is difficult to reduce, remaining as a gas during sintering, resulting in the presence of voids in the cemented carbide. For this reason, cemented carbide using ZrC as a raw material has problems such as many voids, reduced fracture resistance, and reduced tool life.

[0008] Therefore, an object of the present disclosure is to provide a cemented carbide that, when used as a tool material, can provide a cutting tool that has excellent wear resistance and fracture resistance and a long tool life, and to provide a cutting tool that has a long tool life.

[0009] [Effects of the Present Disclosure] According to the present disclosure, it is possible to provide a cemented carbide that, when used as a tool material, can provide a cutting tool that has excellent wear resistance and fracture resistance and a long tool life, as well as a cutting tool that has a long tool life.

[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. (1) The cemented carbide of the present disclosure is a cemented carbide comprising a first phase and a second phase, wherein the first phase is composed of a plurality of tungsten carbide particles, the content of the first phase in the cemented carbide is 65% by volume or more and 85% by volume or less, the content of the second phase in the cemented carbide is 4% by volume or more and 25% by volume or less, the second phase contains 50% by mass or more of cobalt, the second phase contains zirconium, and the cobalt content M of the cemented carbide is Ｃｏ is 3% by mass or more and 15% by mass or less, and a and b of the cemented carbide satisfy the relationship of the following formula I, b<0.0485a+0.0001 formula I, where a is the cobalt content M of the cemented carbide. Ｃｏ The zirconium content M of the cemented carbide in mass% Ｚｒ Percentage of mass (MＺｒ / M Ｃｏ ) × 100, wherein a is greater than 0 and equal to or less than 8, and b is the area percentage of voids in a first region of a cross section of the cemented carbide, the first region being a region in the cross section that is within 50 μm of the surface of the cemented carbide.

[0011] According to the present disclosure, it is possible to provide a cemented carbide that, when used as a tool material, can provide a cutting tool that has excellent wear resistance and fracture resistance and a long tool life, as well as a cutting tool having a long tool life.

[0012] (2) In the above (1), the a and the b may have the relationship of the following formula II: b≦0.0350a+0.0001 Formula II

[0013] This improves the balance between the improvement in hardness of the cemented carbide and the reduction in voids, and further improves the wear resistance and chipping resistance of a cutting tool incorporating the cemented carbide.

[0014] (3) In the above (1) or (2), the b may be 0.0001 or more.

[0015] (4) In any of the above (1) to (3), the a may be 0.0250 or more, thereby improving the plastic deformation resistance of the cemented carbide.

[0016] (5) In any of the above (1) to (4), the area percentage of the voids in a second region of a cross section of the cemented carbide may be 0.01% or more and 0.40% or less, wherein the second region is a region in the cross section whose distance from the surface of the cemented carbide to the interior of the cemented carbide exceeds 50 μm.

[0017] This further improves the chipping resistance of the cutting tool provided with the cemented carbide, and further improves the tool life.

[0018] (6) A cutting tool according to the present disclosure is a cutting tool including the cemented carbide according to any one of (1) to (5) above. According to the present disclosure, it is possible to provide a cutting tool having a long tool life.

[0019] [Details of the Embodiments of the Present Disclosure] Specific examples of the cemented carbide and cutting tool of the present disclosure will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference numerals represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been appropriately changed for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0020] In the present disclosure, the notation in the form of "A to B" means A or more and B or less, and when no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0021] In the present disclosure, when a compound or the like is represented by a chemical formula, unless the atomic ratio is particularly limited, it is intended to include any conventionally known atomic ratio, and should not necessarily be limited to only those within the stoichiometric range.

[0022] In the present disclosure, when one or more numerical values ​​are listed as the lower limit and the upper limit of a numerical range, the combination of any one numerical value listed as the lower limit and any one numerical value listed as the upper limit is also considered to be disclosed.

[0023] In this disclosure, "comprises," "includes," "has," and variations thereof are open-ended terms. Open-ended terms may or may not include additional elements in addition to the required elements. The term "consisting of" is closed-ended. However, even a configuration expressed in closed terms may include additional elements that are normally incidental impurities or unrelated to the subject technology.

[0024] [Embodiment 1: Cemented Carbide] A cemented carbide according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") is a cemented carbide including a first phase and a second phase, wherein the first phase is composed of a plurality of tungsten carbide particles, the content of the first phase in the cemented carbide is 65% by volume or more and 85% by volume or less, the content of the second phase in the cemented carbide is 4% by volume or more and 25% by volume or less, the second phase contains 50% by mass or more of cobalt, the second phase contains zirconium, and the cobalt content M Ｃｏis 3% by mass or more and 15% by mass or less, and a and b of the cemented carbide show the relationship of the following formula I, b<0.0485a+0.0001 I a is the cobalt content M of the cemented carbide Ｃｏ Zirconium content M of the cemented carbide in mass% Ｚｒ Percentage of mass (M Ｚｒ / M Ｃｏ ) × 100, a is greater than 0 and equal to or less than 8, and b is the area percentage of voids in a first region of a cross section of the cemented carbide, the first region being a region in the cross section that is within 50 μm of the surface of the cemented carbide.

[0025] When used as a tool material, the cemented carbide of the present disclosure can provide a cutting tool that has excellent wear resistance and fracture resistance and can have a long tool life. The reason for this is not clear, but is presumed to be as follows.

[0026] (i) The cemented carbide of the present disclosure contains 65% by volume or more and 85% by volume or less of a first phase consisting of a plurality of tungsten carbide particles (hereinafter also referred to as "WC particles"). The tungsten carbide particles have high hardness and high thermal conductivity. Therefore, the cemented carbide of the present disclosure also has high hardness and high thermal conductivity, and cutting tools including the cemented carbide can have excellent wear resistance.

[0027] (ii) The cobalt content M of the cemented carbide of the present disclosure Ｃｏ is 3% by mass or more and 15% by mass or less. Cobalt has high toughness. Therefore, the cemented carbide of the present disclosure also has high toughness, and a cutting tool including the cemented carbide can have excellent chipping resistance.

[0028] (iii) The second phase of the cemented carbide of the present disclosure contains zirconium. The solid solution of zirconium in the cobalt present in the second phase improves the high-temperature hardness of the cobalt. This improves the plastic deformation resistance of the cemented carbide of the present disclosure, and cutting tools incorporating the cemented carbide can have excellent wear resistance.

[0029] (iv) The cemented carbide of the present disclosure satisfies the relationship of the above formula I. According to this, the voids in the cemented carbide are sufficiently reduced, and a cutting tool including the cemented carbide can have excellent chipping resistance.

[0030] <Composition of Cemented Carbide> <Contents of First and Second Phases> The content of the first phase in the cemented carbide of embodiment 1 is 65% by volume or more and 85% by volume or less. When the content of the first phase in the cemented carbide is 80% by volume or more and 90% by volume or less, the hardness of the cemented carbide is further improved. When the content of the first phase in the cemented carbide is 70% by volume or more and 80% by volume or less, the toughness of the cemented carbide is further improved.

[0031] The cemented carbide of embodiment 1 has a second phase content of 4% by volume or more and 25% by volume or less. When the second phase content of the cemented carbide is 15% by volume or more and 25% by volume or less, the toughness of the cemented carbide is further improved. When the second phase content of the cemented carbide is 4% by volume or more and less than 15% by volume, the hardness of the cemented carbide is further improved.

[0032] The cemented carbide of Embodiment 1 includes a first phase and a second phase. The total content of the first and second phases in the cemented carbide of Embodiment 1 may be 74 vol% to 100 vol%, 80 vol% to 98 vol%, 85 vol% to 95 vol%, or 88 vol% to 92 vol%.

[0033] The cemented carbide of the first embodiment may be composed of a first phase and a second phase. In this case, the cemented carbide may contain inevitable impurities as long as the effects of the present disclosure are not impaired.

[0034] The cemented carbide of the first embodiment may contain other phases in addition to the first and second phases, as long as the effects of the present disclosure are not impaired. The other phases include carbides, nitrides, or carbonitrides containing at least one element selected from the group consisting of titanium (Ti), tantalum (Ta), niobium (Nb), hafnium (Hf), and molybdenum (Mo). Examples of the other phases include TiCN, TaC, NbC, HfC, and Mo. ２ C may be at least one selected from the group consisting of

[0035] The cemented carbide of embodiment 1 may be composed of a first phase, a second phase, and other phases. The content of the other phases in the cemented carbide of embodiment 1 is acceptable as long as the effects of the present disclosure are not impaired. For example, the content of the other phases in the cemented carbide may be more than 0 vol% and not more than 26 vol%. In this case, the cemented carbide may contain inevitable impurities as long as the effects of the present disclosure are not impaired.

[0036] The cemented carbide of embodiment 1 may contain inevitable impurities. Examples of inevitable impurities include iron (Fe), calcium (Ca), silicon (Si), and sulfur (S). The content of inevitable impurities in the cemented carbide is acceptable within a range that does not impair the effects of the present disclosure. For example, the content of inevitable impurities in the cemented carbide may be 0% by mass or more and less than 0.1% by mass. The content of inevitable impurities in the cemented carbide is measured by inductively coupled plasma (ICP) emission spectrometry.

[0037] In the present disclosure, the first phase content and the second phase content of a cemented carbide are measured by the following procedure.

[0038] (A1) A cemented carbide alloy is cut out at an arbitrary position to expose a cross section, which is then polished to a mirror finish using a cross section polisher (manufactured by JEOL Ltd.).

[0039] (B1) The mirror-finished surface of the cemented carbide is analyzed using an energy dispersive X-ray spectrometer (SEM-EDX) attached to a scanning electron microscope (apparatus: Carl Zeiss Gemini 450 (trademark)) to identify the elements contained in the cemented carbide.

[0040] (C1) A backscattered electron image is obtained by photographing the mirror-finished surface of the cemented carbide using a scanning electron microscope (SEM). The photographed area is set to the center of the cross section of the cemented carbide. The observation magnification is 5000x. The measurement conditions are an acceleration voltage of 10 kV, a current value of 2 nA, and a working distance (WD) of 10 mm.

[0041] (D1) The photographed region of (C1) above is analyzed using SEM-EDX to identify the distribution of the elements identified in (B1) above in the photographed region, and an element mapping image is obtained.

[0042] (E1) The backscattered electron image obtained in (C1) above is imported into a computer and binarized using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ). The binarization threshold varies depending on the contrast, so it is set for each image. In the binarized image, the first phase (tungsten carbide particles) is shown in white, and the second phase is shown in black.

[0043] (F1) By superimposing the elemental mapping image obtained in (D1) above on the binarized image obtained in (E1) above, the regions where the first and second phases exist are identified on the binarized image. The regions shown in white in the binarized image and where tungsten (W) and carbon (C) exist in the elemental mapping image correspond to the regions where the first phase exists. The regions shown in black in the binarized image and where cobalt (Co) exists in the elemental mapping image correspond to the regions where the second phase exists.

[0044] (G1) A rectangular measurement field of view of 24.9 μm × 18.8 μm is set in the image after the binarization process. Using the image analysis software, the area percentages of the first phase and the second phase are measured using the area of ​​the entire measurement field as the denominator.

[0045] (H1) The measurement of (G1) above is carried out in six different non-overlapping measurement fields. In the present disclosure, the average of the area percentages of the first phase in the six measurement fields corresponds to the content (volume %) of the first phase in the cemented carbide, and the average of the area percentages of the second phase in the six measurement fields corresponds to the content (volume %) of the second phase in the cemented carbide.

[0046] When the cemented carbide contains other phases in addition to the first and second phases, the contents of the other phases in the cemented carbide can be obtained by subtracting the contents (volume %) of the first phase and the second phase (volume %) measured by the above procedure from the total cemented carbide (100 volume %).

[0047] As long as measurements are made on the same sample, it has been confirmed that there is almost no variation in the measurement results even when the cut-out location of the cross section of the cemented carbide, the photographing area described in (C1) above, and the measurement field of view described in (G1) above are arbitrarily set and the first phase content and second phase content of the cemented carbide are measured multiple times according to the above procedure.

[0048] <Cobalt content of cemented carbide M Ｃｏ Cobalt content M of the cemented carbide of embodiment 1 Ｃｏ The cobalt content M of the cemented carbide is 3 mass % or more and 15 mass % or less. Ｃｏ When the cobalt content M of the cemented carbide is 10 mass % or more and 15 mass % or less, the toughness of the cemented carbide is further improved. Ｃｏ When the content of Si is 3 mass % or more and less than 10 mass %, the hardness of the cemented carbide is further improved.

[0049] Cobalt content of cemented carbide M Ｃｏ The method for measuring the cobalt content is as follows. Analysis is performed using SEM-EDX to obtain an elemental mapping image using the same method as the method for measuring the first phase content and the second phase content of the cemented carbide described above. Based on the elemental mapping image, the cobalt region in the cemented carbide is identified and the cobalt content is measured. The measurement is performed in six different, non-overlapping imaging regions. In the present disclosure, the average of the cobalt contents in the six imaging regions is determined as the cobalt content M of the cemented carbide. Ｃｏ The zirconium content M of the cemented carbide described below corresponds to Ｚｒ is measured in the same manner except that the region of zirconium is specified instead of cobalt.

[0050] As long as measurements were performed on the same sample, it was confirmed that there was almost no variation in the measurement results even when the cut-out location and photographed area of ​​the cross section of the cemented carbide were arbitrarily set and the cobalt content or zirconium content of the cemented carbide was measured multiple times according to the above procedure.

[0051] <First Phase> In the cemented carbide of the first embodiment, the first phase is composed of a plurality of tungsten carbide particles. Here, the tungsten carbide particles include not only "pure WC particles (including WC containing no unavoidable impurity elements and WC containing unavoidable impurity elements below the detection limit)" but also "WC particles containing unavoidable impurities therein, as long as the effects of the present disclosure are not impaired." Examples of unavoidable impurities include iron (Fe), molybdenum (Mo), and sulfur (S).

[0052] <Average particle size of tungsten carbide particles> In the cemented carbide of embodiment 1, the average particle size of the tungsten carbide particles may be 1 μm or more and 6 μm or less. When the average particle size of the tungsten carbide particles is 3 μm or more, cutting tools using the cemented carbide are less likely to experience shedding wear during use. When the average particle size of the tungsten carbide particles is less than 3 μm, the cemented carbide has excellent transverse rupture strength, and the chipping resistance of cutting tools using the cemented carbide is further improved.

[0053] In the cemented carbide of the first embodiment, the ratio d10 / d90 of the cumulative 10% particle diameter d10 from the small diameter side to the cumulative 90% particle diameter d90 from the small diameter side in the cumulative particle size distribution based on the number of tungsten carbide particles may be 0.2 or more and 0.3 or less. When d10 / d90 is 0.2 or more, the transverse rupture strength of the cemented carbide is likely to be improved.

[0054] In the present disclosure, the average particle size and d90 / d10 of tungsten carbide particles are measured by the following procedure: (A2) Six binarized images are obtained using the same method as the method for measuring the first phase content and second phase content of the cemented carbide described above.

[0055] (B2) A rectangular measurement field of view measuring 25.3 μm in height and 17.6 μm in width was set in each of the six binarized images obtained. Using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ), the circle-equivalent diameter (Heywood diameter: diameter equivalent to a circle with equal area) of each of the tungsten carbide particles (first phase) in the six measurement fields was measured.

[0056] (C2) Calculate the number-based arithmetic mean value of the equivalent circle diameter and d90 / d10 based on all tungsten carbide particles in the six measurement fields, excluding tungsten carbide particles with an equivalent circle diameter of 0.22 μm or less. In the present disclosure, the arithmetic mean value and d90 / d10 correspond to the average particle size and d90 / d10 of the tungsten carbide particles, respectively.

[0057] The reason for excluding tungsten carbide particles having an equivalent circle diameter of 0.22 μm or less when calculating the average particle size is that measurements by the present inventors confirmed that particles having an equivalent circle diameter of 0.22 μm or less often correspond to noise that is erroneously detected as tungsten carbide particles in image analysis.

[0058] As far as the applicant has measured, it has been confirmed that, as long as measurements are made on the same sample, even if the above measurement is performed multiple times by changing the selected location of the measurement field, there is little variation in the measurement results, and that setting the measurement field arbitrarily will not be arbitrary.

[0059] <Second Phase> In the cemented carbide of embodiment 1, the second phase contains 50 mass% or more of cobalt. This allows the cemented carbide to have excellent toughness. The cobalt content of the second phase may be 50 mass% or more but less than 100 mass%, 60 mass% or more but 90 mass% or less, or 70 mass% or more but 80 mass% or less.

[0060] The method for measuring the cobalt content of the second phase is as follows: An elemental mapping image and a binarized image are obtained using the same method as the method for measuring the first phase content and second phase content of the cemented carbide described above. The elemental mapping image and the binarized image are superimposed to identify the region where the second phase exists in the elemental mapping image. A rectangular measurement field of view of 24.9 μm × 18.8 μm is set in the elemental mapping image. The cobalt content is measured in the region where the second phase exists in the measurement field of view. The above measurement is performed in six different, non-overlapping measurement fields of view. In the present disclosure, the average of the cobalt contents in the region where the second phase exists in the six measurement fields of view corresponds to the cobalt content of the second phase.

[0061] As long as measurements were performed on the same sample, it was confirmed that there was almost no variation in the measurement results even when the cut-out location of the cross section of the cemented carbide, the photographed area, and the above-mentioned measurement field of view were arbitrarily set and the cobalt content of the second phase was measured multiple times according to the above-mentioned procedure.

[0062] In the cemented carbide of embodiment 1, the second phase comprises zirconium.

[0063] The presence of zirconium in the second phase can be confirmed by the following procedure. An elemental mapping image and a binarized image are obtained using the same method as the method for measuring the content of the first phase and the content of the second phase in the cemented carbide described above. The elemental mapping image and the binarized image are superimposed to identify the region in which the second phase exists in the elemental mapping image. If zirconium is present in the region in which the second phase exists in the elemental mapping, it is confirmed that the second phase contains zirconium.

[0064] The second phase of the cemented carbide of embodiment 1 includes cobalt and zirconium. The second phase of the cemented carbide of embodiment 1 may consist of cobalt and zirconium. In this case, the cemented carbide may contain inevitable impurities as long as the effects of the present disclosure are not impaired.

[0065] As long as the effects of the present disclosure are not impaired, the second phase of the cemented carbide of Embodiment 1 may contain, in addition to cobalt and zirconium, at least one first element selected from the group consisting of iron (Fe), nickel (Ni), and chromium (Cr). The second phase of the cemented carbide of Embodiment 1 may consist of cobalt, zirconium, and the first element. In this case, the second phase may contain inevitable impurities as long as the effects of the present disclosure are not impaired. Examples of inevitable impurities include manganese (Mn), magnesium (Mg), calcium (Ca), molybdenum (Mo), sulfur (S), and aluminum (Al).

[0066] <Cobalt content of cemented carbide M Ｃｏ , zirconium content M Ｚｒand Area Percentage of Pores in First Region> The values ​​a and b of the cemented carbide of embodiment 1 satisfy the relationship of the following formula I: b<0.0485a+0.0001 Formula I

[0067] In formula I, a is the cobalt content M of the cemented carbide. Ｃｏ Zirconium content M of the cemented carbide in mass% Ｚｒ Percentage of mass (M Ｚｒ / M Ｃｏ ) x 100.

[0068] a is greater than 0 and less than or equal to 8. When a is greater than 0, the high-temperature hardness of cobalt is improved. When a is greater than 8, zirconium, which is insoluble in cobalt, precipitates, reducing the fracture resistance of cutting tools equipped with cemented carbide. From the viewpoint of improving fracture resistance, a is less than or equal to 8. a may be greater than or equal to 0.0250, greater than or equal to 0.0250 and less than or equal to 8, greater than or equal to 1.5 and less than or equal to 7.1, or greater than or equal to 2.0 and less than or equal to 7.1.

[0069] b is the area percentage of voids in a first region of a cross section of the cemented carbide, the first region being a region in the cross section that is within 50 μm of the surface of the cemented carbide, and b may be 0.0001 or more and 0.40 or less, 0.05 or more and 0.30 or less, 0.06 or more and 0.20 or less, or 0.08 or more and 0.18 or less.

[0070] The a and b of the cemented carbide of embodiment 1 may satisfy the relationship of the following formula II: b≦0.0350a+0.0001 Formula II

[0071] In the present disclosure, the area percentage of voids in a first region of a cross section of a cemented carbide is measured by the following procedure.

[0072] (A2) The cemented carbide is cut in a direction normal to the surface to expose a cross section, which is then mirror-polished using a cross-section polisher (manufactured by JEOL Ltd.).

[0073] When the cemented carbide is formed into the shape of a cutting tool, the cutting position is determined in consideration of the actual usage conditions of the cutting tool. Figures 1 and 2 are diagrams for explaining the cutting position of a cutting tool 1 made of cemented carbide according to embodiment 1. In cutting tool 1, the upper and lower surfaces form a rake face 11, and the four side surfaces (and the arc surfaces connecting these) form a flank face 12. The boundary between the rake face 11 and the flank face 12 functions as a cutting edge 13 region.

[0074] When the cutting tool 1 is used to cut a workpiece with the cutting edge 13 of the corner portion (the portion with an apex angle that forms an arc), the cutting is performed so that a cross section that includes a line L1 that bisects the corner portion and is along a normal to the surface of the cutting tool is exposed, as shown in Fig. 1. On the other hand, when the cutting tool 1 is used to cut a workpiece with the cutting edge 13 of the straight portion (the portion that forms a straight line), the cutting is performed so that a cross section that includes a line L2 that is perpendicular to the cutting edge 13 of the straight portion and is along a normal to the surface of the cutting tool is exposed, as shown in Fig. 2.

[0075] (B2) The mirror-finished surface of the cemented carbide is analyzed using an energy dispersive X-ray spectrometer (SEM-EDX) attached to a scanning electron microscope (apparatus: Carl Zeiss Gemini 450 (trademark)) to identify the elements contained in the cemented carbide.

[0076] (C2) The mirror-finished surface of the cemented carbide is photographed with a scanning electron microscope (SEM) to obtain a backscattered electron image. The photographed area is set to include the surface of the cemented carbide. The observation magnification is 5000x. The measurement conditions are an acceleration voltage of 10 kV, a current value of 2 nA, and a working distance (WD) of 10 mm.

[0077] (D2) The photographed region of (C2) above is analyzed using SEM-EDX to identify the distribution of the elements identified in (B2) above in the photographed region, and an element mapping image is obtained.

[0078] (E2) The backscattered electron image obtained in (C2) above is imported into a computer and binarized using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ). The binarization threshold varies depending on the contrast, so it is set for each image. In the binarized image, the first phase (tungsten carbide particles) is shown in white, and the voids and second phase are shown in black.

[0079] (F2) By superimposing the element mapping image obtained in (D2) above on the binarized image obtained in (E2) above, void regions are identified on the binarized image. Regions shown in black in the binarized image and where no elements are present in the element mapping image correspond to void regions.

[0080] (G2) In the image after the binarization process, a first region between the surface of the cemented carbide and a virtual line L that is 50 μm from the surface to the inside of the cemented carbide is identified. A rectangular measurement field of view of 24.9 μm × 18.8 μm is set within the first region. Using the image analysis software, the area percentage of voids is measured using the area of ​​the entire measurement field as the denominator.

[0081] (H2) The measurement of (G2) is carried out in six different non-overlapping measurement fields set within the first region. In the present disclosure, the average of the area percentages of voids in the six measurement fields corresponds to the area percentage of voids in the first region of the cross section of the cemented carbide.

[0082] As long as measurements are made on the same sample, it has been confirmed that there is almost no variation in the measurement results, even if the cut-out location of the cemented carbide cross section, the photographing area described in (C2) above, and the measurement field of view described in (G2) above are arbitrarily set within the above ranges, and the area percentage of voids in the first region of the cemented carbide cross section is measured multiple times according to the above procedure.

[0083] <Area percentage of voids in the second region of the cemented carbide> The area percentage of voids in the second region of the cross section of the cemented carbide of embodiment 1 may be 0.01% or more and 0.40% or less. The second region is a region in the cross section where the distance from the surface of the cemented carbide to the interior of the cemented carbide exceeds 50 μm. When the area percentage of voids in the second region is 0.40% or less, the chipping resistance of a cutting tool including the cemented carbide is further improved. The area percentage of voids in the second region may be 0.01% or more and 0.20% or less.

[0084] In the present disclosure, the area percentage of voids in the second region of the cross section of a cemented carbide is measured by the same method as the above-mentioned method for measuring the area percentage of voids in the first region of the cross section of a cemented carbide, except that the measurement field is set within the second region at a distance of more than 50 μm from the surface of the cemented carbide to the interior of the cemented carbide.

[0085] As long as measurements are made on the same sample, it has been confirmed that there is almost no variation in the measurement results even when the cut-out location of the cemented carbide cross section, the photographing area described in (C2) above, and the measurement field of view described in (G2) above are arbitrarily set within the above ranges, and the area percentage of voids in the second region of the cemented carbide cross section is measured multiple times according to the above procedure.

[0086] <Method for manufacturing cemented carbide> The cemented carbide of embodiment 1 can be manufactured by, for example, carrying out a raw material powder preparation step, a mixing step, a pressing step, a sintering step, and a cooling step in the above order. Each step will be described below.

[0087] <<Step of Preparing Raw Material Powders>> In the step of preparing raw material powders, raw material powders of the cemented carbide are prepared. As the raw material powders, tungsten carbide powder (hereinafter also referred to as "WC powder"), which is a raw material for the first phase, cobalt powder (hereinafter also referred to as "Co powder"), which is a raw material for the second phase, and zirconium carbide powder (hereinafter also referred to as "ZrC powder") are prepared.

[0088] As the tungsten carbide powder, WC powder having a fine and uniform particle size is prepared, specifically, WC powder having an average particle size of 1.5 μm to 6.0 μm and a d10 / d90 ratio of 0.2 or more.

[0089] As the cobalt powder, a Co powder having a fine and uniform particle size is prepared, specifically, a Co powder having an average particle size of 0.5 μm to 3.0 μm and a d10 / d90 ratio of 0.2 or more.

[0090] The zirconium carbide powder has an average particle size of 1.8 μm or more and 2.5 μm or less.

[0091] In the present disclosure, the average particle size of each raw material powder is measured by the Fisher Sub-Sieve Sizer (FSSS) method. The measuring device used for the FSSS method is a "Sub-Sieve Sizer Model 95" (trademark) manufactured by Fisher Scientific.

[0092] In the present disclosure, the d10 / d90 of the raw material powder means the ratio of the cumulative 10% particle diameter d10 from the smaller diameter side to the cumulative 90% particle diameter d90 from the smaller diameter side in the volume-based cumulative particle size distribution of the raw material powder. The particle size distribution of the WC powder is measured using a particle size distribution analyzer manufactured by Microtrac (product name: MT3300EX).

[0093] As raw material powders, titanium carbide (TiC) powder, titanium nitride (TiN) powder, tantalum carbide (TaC) powder, niobium carbide (NbN) powder, which are raw materials for other phases, and chromium carbide (Cr ３ C ２ ) powder may be prepared. The average particle size of the raw material powder of the other phase may be 0.5 μm or more and 2.0 μm or less. The raw material powder of the other phase may be commercially available.

[0094] In the mixing step, the raw material powders prepared in the preparation step are mixed to obtain a mixed powder. The content of each raw material powder in the mixed powder is appropriately adjusted taking into consideration the content of each component, such as the first phase and second phase, of the cemented carbide.

[0095] An attritor is used for mixing. First, the raw material powders other than the Co powder are charged into the attritor and mixed for 3 to 6 hours (hereinafter also referred to as "first mixing"). Next, the Co powder is additionally charged into the attritor and mixed for 3 to 6 hours (hereinafter also referred to as "second mixing") to obtain a mixed powder.

[0096] <Pressing Step> The pressing step is a step in which the mixed powder obtained in the mixing step is press-molded into a predetermined shape to obtain a molded body. The pressing pressure is 1.0 to 2.0 t / cm ２ The pressing method can be a general method, and the shape of the compact can be, for example, the shape of a cutting tool.

[0097] <Sintering Step> In the sintering step, the compact obtained in the molding step is sintered to obtain a cemented carbide. First, the compact is placed in a sintering furnace, heated to a sintering temperature of 1410 to 1460°C, and held at the sintering temperature for 30 to 60 minutes. While holding at the sintering temperature, argon (Ar) is introduced into the sintering furnace to set the pressure inside the sintering furnace to 140 to 500 kPa. In this way, the compact is sintered to obtain a cemented carbide.

[0098] <Cooling Step> The cooling step is a step of cooling the cemented carbide after sintering is completed. The cooling step is a step of cooling the cemented carbide after sintering is completed. The cooling conditions may be general conditions and are not particularly limited.

[0099] <Features of the cemented carbide manufacturing method of embodiment 1> In the raw material powder preparation step, WC powder and Co powder with fine and uniform particle sizes are prepared. Therefore, the Co powder is finely and uniformly dispersed in the mixed powder of WC powder and Co powder. Even if voids occur during sintering of a compact of the mixed powder, the presence of Co in the vicinity of the voids facilitates the flow of Co into the voids, thereby reducing the voids. To finely and uniformly disperse the Co powder in the mixed powder, the particle size of the WC powder must also be fine and uniform. The step of preparing WC powder and Co powder with fine and uniform particle sizes to facilitate the flow of Co into the voids was newly discovered by the present inventors and has not been performed in the past.

[0100] The mixing process uses an attritor with strong crushing power. This allows the Co powder to be uniformly and finely dispersed in the mixed powder. However, Co is a ductile and malleable raw material, and re-agglomerates over long mixing times. To prevent Co re-agglomeration, the mixing time must be long enough to prevent Co from re-agglomerating. On the other hand, WC agglomerates in the raw powder, and to break down these agglomerates, it must be mixed for a longer time than Co. In the mixing process, raw powders containing WC powder other than Co powder are mixed for 3 to 6 hours (first mixing), and then Co powder is added and mixed for 3 to 6 hours (two-stage mixing). This sufficiently breaks down WC agglomerates, and Co is uniformly and finely dispersed in the mixed powder without re-agglomerating. In conventional methods for manufacturing cemented carbide, two-stage mixing was not performed because it required long mixing times and increased production costs.

[0101] In the pressing step, the mixed powder is pressed into a predetermined shape to obtain a compact. This densifies the compact, disposing Co in the vicinity of voids in the compact, which facilitates the flow of Co into the voids during sintering, reducing the voids. The pressing pressure for the compact is 1.0 to 2.0 t / cm. ２ The pressing pressure is 1.0 t / cm ２ Since the pressing pressure is 2.0 t / cm or more, the densification of the compact is promoted. ２ In conventional methods for producing cemented carbide, a pressing step using a pressing pressure in the above range has not been carried out.

[0102] In the above sintering process, the sintering temperature is 1410 to 1460°C. Because the sintering temperature is 1410°C or higher, the movement of Co during sintering is promoted, and Co easily flows into voids. Because the sintering temperature is 1460°C or lower, abnormal grain growth of WC is suppressed, and a decrease in the chipping resistance of the cemented carbide is suppressed. Furthermore, when maintaining the sintering temperature, Ar is introduced into the sintering furnace, and sintering is performed under pressure. This allows voids in the sintered body to be pushed out to the outside of the sintered body, reducing the voids. The above sintering conditions were not adopted in conventional cemented carbide manufacturing methods.

[0103] The present inventors have found that the cemented carbide described in embodiment 1 can be obtained by a manufacturing method including all of the above-mentioned raw material powder preparation step, mixing step, pressing step, and sintering step. Conventional cemented carbide manufacturing methods have not performed all of the above-mentioned raw material powder preparation step, mixing step, pressing step, and sintering step.

[0104] [Embodiment 2: Cutting Tool] The cutting tool of embodiment 2 includes the cemented carbide of embodiment 1. The cutting tool of embodiment 2 can include a cutting edge made of at least the cemented carbide of embodiment 1. In the present disclosure, the cutting edge refers to the portion involved in cutting, and in the cemented carbide, refers to the cutting edge ridge and the region of the cemented carbide that is within 0.5 mm of the cutting edge ridge toward the cemented carbide.

[0105] Examples of cutting tools include cutting tools, drills, end mills, indexable cutting tips for milling, indexable cutting tips for turning, metal saws, gear cutting tools, reamers, taps, and the like.

[0106] The cemented carbide of the second embodiment may constitute the entire tool or a part of the tool. Here, "constitute a part" refers to a mode in which the cemented carbide of the second embodiment is brazed to a predetermined position of any substrate to form a cutting edge.

[0107] The cutting tool of the second embodiment may further include a hard film that covers at least a part of the surface of the substrate made of cemented carbide. Examples of the hard film include diamond-like carbon, diamond, and Al. ２ O ３ Alternatively, a film made of TiCN can be used.The hard film may be a CVD film formed by chemical vapor deposition (CVD).

[0108] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0109] <Preparation Step> Powders having the compositions shown in the "Raw Powder" column of Table 1 were prepared as raw material powders. A plurality of WC powders and Co powders with different average particle sizes and particle size distributions were prepared. The average particle sizes and d10 / d90 of the WC powders and Co powders are as shown in Table 1.

[0110] The titanium carbide (TiC) powder has an average particle size of 1.5 μm, the titanium nitride (TiN) powder has an average particle size of 2.0 μm, the tantalum carbide (TaC) powder has an average particle size of 1.0 μm, the niobium carbide (NbC) powder has an average particle size of 1.1 μm, and the zirconium carbide (ZrC) powder has an average particle size of 2.2 μm.

[0111] <Mixing Step> A mixed powder was obtained by mixing the raw material powders in the proportions shown in the "mass %" column of "raw material powder" in Table 1. "mass %" in Table 1 indicates the percentage of the mass of each raw material powder with respect to the total mass of the raw material powders.

[0112] Mixing was performed using an attritor. First, the raw material powders other than the Co powder were charged into the attritor and mixed for the time shown in the "First Mixing" column of Table 2. Next, the Co powder was additionally charged into the attritor and mixed for the time shown in the "Second Mixing" column of Table 2 to obtain a mixed powder. For samples marked with "-" in the "First Mixing" column, all raw material powders were charged into the attritor at the same time and mixed for the time shown in the "Second Mixing" column to obtain a mixed powder.

[0113] <<Pressing Step>> This is a step in which the mixed powder obtained in the mixing step is press-molded into an insert shape (CNMG120408N-GU) to obtain a molded body. The pressing pressure is as shown in Table 2.

[0114] <Sintering Step> The compact was placed in a sintering furnace, heated to the sintering temperature shown in the "Temperature" column under "Sintering" in Table 2, and held at the sintering temperature for the time shown in the "Holding Time" column. When holding at the sintering temperature, argon (Ar) was introduced into the sintering furnace, and the pressure inside the sintering furnace was adjusted to the pressure shown in the "Ar Pressure" column.

[0115] <Cooling Step> After the sintering was completed, the mixture was slowly cooled in an argon (Ar) gas atmosphere to obtain a cemented carbide.

[0116]

[0117]

[0118] <Evaluation of Cemented Carbide> <Composition of Cemented Carbide> For each sample of cemented carbide, the first phase content, second phase content, cobalt content M Ｃｏ , zirconium content M Ｚｒ The specific measurement method is as described in embodiment 1. The results are shown in Table 3.

[0119] The cobalt content of the second phase of each cemented carbide sample was measured. Furthermore, it was confirmed whether the second phase contained Zr. The specific measurement method was as described in embodiment 1. The results are shown in Table 3.

[0120] <<Area Percentage of Pores in First Region and Second Region of Cemented Carbide>> For each sample of cemented carbide, the area percentage of voids in the first region and the second region in the cross section of the cemented carbide (referred to as "porosity" in the table) was measured. The specific measurement method was as described in embodiment 1. The results are shown in Table 4.

[0121] <<Formula I and Formula II>> Cobalt content M of each sample cemented carbide Ｃｏ , zirconium content M Ｚｒ Based on the area percentage b of voids in the first region, it was confirmed whether each sample satisfied the relationships of the following formulas I and II: b<0.0485a+0.0001 Formula I b≦0.0350a+0.0001 Formula II The results are shown in Table 4. In the "Formula I" column, "Yes" indicates that the relationship of formula I is satisfied, and "No" indicates that the relationship of formula I is not satisfied. In the "Formula II" column, "Yes" indicates that the relationship of formula II is satisfied, and "No" indicates that the relationship of formula II is not satisfied.

[0122] The cobalt content M of the cemented carbide of Sample 1, Sample 2, Sample 1-1, and Sample 1-2 Ｃｏ Zirconium content M of the cemented carbide in mass% Ｚｒ Percentage of mass (M Ｚｒ / M Ｃｏ3 shows a graph showing the relationship between the area percentage of voids in the first region and the area ratio (M Ｚｒ / M Ｃｏ ) × 100, and the vertical axis b is the area percentage of voids in the first region.

[0123] <Average particle size and d90 / d10 of tungsten carbide particles> For each sample of cemented carbide, the average particle size and d90 / d10 of the tungsten carbide particles were measured by the method described in embodiment 1. For samples 1 to 6, the average particle size of the tungsten carbide particles was 1 μm or more and 6 μm or less, and the d10 / d90 was 0.2 or more and 0.3 or less.

[0124]

[0125]

[0126] <Cutting Test 1> Turning was performed under the following conditions using a cutting tool (tool model number: CNMG120408N-GU (manufactured by Sumitomo Electric Hardmetal Corporation)) for each sample, and the average wear volume Vb (mm) on the flank side of the cutting tool after 15 minutes of cutting was measured. The smaller the average wear volume Vb (mm), the better the wear resistance and the longer the tool life. In Cutting Test 1, when the average wear volume Vb (mm) is 0.25 mm or less, it is judged that the wear resistance is excellent and the tool life is long. The results are shown in the "Cutting Test 1" column in Table 4.

[0127] ≪Cutting conditions≫ Work material: S45C Processing: Round bar outer diameter turning Cutting speed: 280 m / min Feed rate: 0.25 mm / rev Depth of cut: 1.5 mm Cutting fluid: Water-soluble cutting oil

[0128] <Cutting Test 2> A cutting tool (tool model number: CNMG120408N-GU (manufactured by Sumitomo Electric Hardmetal Corporation)) for each sample was prepared. Turning was performed using 20 corners of the cutting tool under the following conditions, and the percentage of the number of corners that broke within 20 seconds (hereinafter also referred to as the "breakage rate (%)") was measured. A smaller breakage rate indicates better fracture resistance and a longer tool life. In Cutting Test 2, a breakage rate of 5% or less was considered to be a long tool life. The results are shown in the "Cutting Test 2" column in Table 4.

[0129] <Cutting conditions> Workpiece: SCM435 (grooved round bar) Processing: Intermittent outer diameter processing of grooved round bar Cutting speed: 150 m / min Feed rate: 0.20 mm / rev Depth of cut: 2.0 mm Cutting fluid: None

[0130] In this example, if the average wear amount Vb is 0.25 mm or less in Cutting Test 1 and the breakage rate is 5% or less in Cutting Test 2, the cutting tool is judged to have excellent wear resistance and chipping resistance and a long tool life.

[0131] <Discussion> The cemented carbide alloys and cutting tools of Samples 1 to 6 correspond to Examples. It was confirmed that these cutting tools have excellent wear resistance and chipping resistance, and have long tool life.

[0132] The cemented carbide and cutting tool of Sample 1-1 correspond to comparative examples. The cutting tool of Sample 1-1 had poor fracture resistance.

[0133] Although the embodiments and examples of the present disclosure have been described above, it is intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0134] 1 Cutting tool, 11 Rake face, 12 Flank face, 13 Cutting edge

Claims

1. A cemented carbide alloy having a first phase and a second phase, wherein the first phase is composed of a plurality of tungsten carbide particles, the content of the first phase in the cemented carbide alloy is 65% by volume or more and 85% by volume or less, the content of the second phase in the cemented carbide alloy is 4% by volume or more and 25% by volume or less, the second phase contains 50% by mass or more of cobalt, the second phase contains zirconium, and the cobalt content M of the cemented carbide Ｃｏ is 3% by mass or more and 15% by mass or less, and a and b of the cemented carbide satisfy the relationship of the following formula I, b<0.0485a+0.0001 formula I, where a is the cobalt content M of the cemented carbide. Ｃｏ The zirconium content M of the cemented carbide in mass% Ｚｒ Percentage of mass (M Ｚｒ / M Ｃｏ ) × 100, wherein a is greater than 0 and equal to or less than 8, and b is the area percentage of voids in a first region of a cross section of the cemented carbide, the first region being a region in the cross section that is within 50 μm of the surface of the cemented carbide.

2. The cemented carbide according to claim 1, wherein a and b satisfy the relationship of the following formula II: b≦0.0350a+0.0001 Formula II.

3. The cemented carbide according to claim 1 or 2, wherein b is 0.0001 or more.

4. A cemented carbide according to any one of claims 1 to 3, wherein a is 0.0250 or more.

5. The cemented carbide according to any one of claims 1 to 4, wherein the area percentage of the voids in a second region of a cross section of the cemented carbide is 0.01% or more and 0.40% or less, and the second region is a region in the cross section whose distance from the surface of the cemented carbide to the interior of the cemented carbide exceeds 50 μm.

6. A cutting tool comprising the cemented carbide according to any one of claims 1 to 5.

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