Carbide alloys and cutting tools

Abstract

A first hard phase consisting of multiple tungsten carbide particles with a content of 75.0% to 97.0% by volume, a second hard phase consisting of at least one first compound selected from the group consisting of TiNbC, TiNbN, TiNbCN, TiTaC, TiTaN, TiTaCN, TiTaNbC, TiTaNbN, and TiTaNbCN with a content of 0.1% to 5.0% by volume, and a binding phase containing 50% or more by mass of cobalt with a content of 4.0% to 15.0% by volume. A cemented carbide alloy having the following characteristics: the total of the first hard phase, second hard phase, and binder phase of the cemented carbide alloy is 94% by volume or more; the standard deviation sd of the particle size distribution of tungsten carbide particles on a volume basis by Heywood diameter is 0.1 μm or more and 0.25 μm or less; the percentage of the second hard phase with a diameter of 0.2 μm or less relative to the total number of second hard phases is 1% or more and 10% or less; and the percentage of the second hard phase with a diameter of 0.8 μm or more relative to the total number of second hard phases is 1% or more and 10% or less.

Description

Technical Field

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

Background Art

[0002] Conventionally, a cemented carbide including a phase mainly composed of tungsten carbide (WC), a phase composed of carbides, nitrides, carbonitrides, etc. containing metal elements other than tungsten, and a bonding phase mainly composed of iron group elements has been used as a material for cutting tools (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The cemented carbide alloy of the present disclosure comprises a first hard phase, a second hard phase, and a binder phase, wherein the first hard phase consists of a plurality of tungsten carbide particles, the second hard phase consists of at least one first compound selected from the group consisting of TiNbC, TiNbN, TiNbCN, TiTaC, TiTaN, TiTaCN, TiTaNbC, TiTaNbN, and TiTaNbCN, the binder phase contains 50% by mass or more of cobalt, the total content of the first hard phase, the second hard phase, and the binder phase of the cemented carbide alloy is 94% by volume or more, and the content of the first hard phase of the cemented carbide alloy is 75.0% by volume or more. The cemented carbide alloy has a composition of 97.0% by volume or less, a content of the second hard phase of the cemented carbide alloy of 0.1% to 5.0% by volume, a content of the binder phase of the cemented carbide alloy of 4.0% to 15.0% by volume, a standard deviation sd of the volume-based particle size distribution of the Heywood diameter of the tungsten carbide particles of 0.1 μm to 0.25 μm, a percentage of the number of second hard phases with a diameter of 0.2 μm or less relative to the total number of second hard phases of 0.2 μm or less, and a percentage of the number of second hard phases with a diameter of 0.8 μm or more relative to the total number of second hard phases of 0.8 μm or more, which is 1% to 10%. [Brief explanation of the drawing]

[0005] [Figure 1] Figure 1 is a schematic diagram of a cutting tool (PCB drill) according to Embodiment 2. [Figure 2] Figure 2 is a schematic diagram of a cutting tool (exchangeable cutting tip) according to Embodiment 2. [Modes for carrying out the invention]

[0006] [Issues this disclosure aims to address] From a cost reduction perspective, there is a demand for cemented carbide alloys and cutting tools made from them that enable longer tool life, even when used as materials for cutting tools used for drilling holes in printed circuit boards and for intermittent machining of steel.

[0007] [Effects of this disclosure] According to this disclosure, it is possible to provide cemented carbide and cutting tools equipped therewith that enable longer tool life even when used as a material for cutting tools for drilling holes in printed circuit boards and for intermittent machining of steel.

[0008] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described. (1) The cemented carbide of the present disclosure comprises a first hard phase, a second hard phase, and a binder phase, wherein the first hard phase consists of a plurality of tungsten carbide particles, the second hard phase consists of at least one first compound selected from the group consisting of TiNbC, TiNbN, TiNbCN, TiTaC, TiTaN, TiTaCN, TiTaNbC, TiTaNbN, and TiTaNbCN, the binder phase contains 50% by mass or more of cobalt, the total content of the first hard phase, the second hard phase, and the binder phase of the cemented carbide is 94% by volume or more, and the content of the first hard phase of the cemented carbide is 75.0% by volume or less. The cemented carbide alloy has a composition of 97.0% or less by volume, a content of the second hard phase of the cemented carbide alloy of 0.1% to 5.0% by volume, a content of the binder phase of the cemented carbide alloy of 4.0% to 15.0% by volume, a standard deviation sd of the volume-based particle size distribution of the Heywood diameter of the tungsten carbide particles of 0.1 μm to 0.25 μm, a percentage of the number of second hard phases with a diameter of 0.2 μm or less relative to the total number of second hard phases of 0.2 μm or less, a percentage of the number of second hard phases with a diameter of 0.8 μm or more relative to the total number of second hard phases of 0.8 μm or more, a percentage of the number of second hard phases with a diameter of 0.8 μm or more relative to the total number of second hard phases of 0.2 μm or less, and is a cemented carbide alloy.

[0009] According to this disclosure, it is possible to provide cemented carbide and cutting tools equipped therewith that enable longer tool life, even when used as materials for cutting tools for drilling holes in printed circuit boards and for intermittent machining of steel. The reason for this is presumed to be as follows.

[0010] The cemented carbide alloy of this disclosure contains a first hard phase consisting of multiple tungsten carbide particles (hereinafter also referred to as "WC particles"), a second hard phase consisting of TiNbC or the like, and a binder phase, totaling 94 volume% or more. The content of the first hard phase is 75.0 volume% to 97.0 volume%, the content of the second hard phase is 0.1 volume% to 5.0 volume%, and the content of the binder phase is 4.0 volume% to 15.0 volume%. As a result, the cemented carbide alloy can have hardness and toughness suitable for cutting tools.

[0011] In the cemented carbide alloy of this disclosure, the standard deviation (sd) of the particle size distribution in the volume-based Heywood diameter distribution of tungsten carbide particles is 0.1 μm or more and 0.25 μm or less, indicating a narrow and sharp particle size distribution of tungsten carbide particles. As a result, the cemented carbide alloy can reduce defects by forming a homogeneous microstructure and possess excellent fracture toughness.

[0012] In the cemented carbide alloy of this disclosure, the percentage of the number of second hard phases with a diameter of 0.2 μm or less relative to the total number of second hard phases is between 1% and 10%, and the percentage of the number of second hard phases with a diameter of 0.8 μm or more relative to the total number of second hard phases is between 1% and 10%, and the grain size distribution of the second hard phase is narrow and sharp. In this cemented carbide alloy, the second hard phase easily fills the gaps between tungsten carbide particles, and the retention force of the tungsten carbide particles is improved by the second hard phase. As a result, when using a cutting tool made of this cemented carbide alloy, the shedding of tungsten carbide particles is suppressed. Therefore, in drilling holes in printed circuit boards and intermittent machining of steel using this cutting tool, the occurrence of breakage and chipping is suppressed, and tool life is improved. In this disclosure, the diameter of the second hard phase means the Heywood diameter of the multiple crystal grains constituting the second hard phase in the cross-section of the cemented carbide alloy.

[0013] (2) In (1) above, the volume average diameter mv of the tungsten carbide particles may be 0.2 μm or more and 0.65 μm or less. This further suppresses the shedding of tungsten carbide particles when using cutting tools made of cemented carbide. Also, if the volume average diameter mv of the tungsten carbide particles is 0.2 μm or more, the toughness of the cemented carbide is improved. If the volume average diameter mv of the tungsten carbide particles is 0.65 μm or less, the hardness of the cemented carbide is improved.

[0014] (3) In (1) or (2) above, the cemented carbide further comprises a third hard phase, the third hard phase consisting of at least one second compound selected from the group consisting of TiWNbC, TiWNbN, TiWNbCN, TiWTaC, TiWTaN, TiWTaCN, TiTaWNbC, TiTaWNbN, and TiTaWNbCN, and the content of the third hard phase in the cemented carbide may be 0.1 volume% or more and 5 volume% or less. When the content of the third hard phase in the cemented carbide is 0.1 volume% or more, the fracture toughness is improved. When the content of the third hard phase in the cemented carbide is 5 volume% or less, the strength is improved.

[0015] (4) In (3) above, the 50% cumulative particle size D50 of the third hard phase based on area (hereinafter also referred to as "D50 of the third hard phase") may be 0.1 μm or more and 3.0 μm or less. When the D50 of the third hard phase is 0.1 μm or more, fracture toughness is improved. When the D50 of the third hard phase is 3.0 μm or less, strength is improved.

[0016] (5) The cutting tool of this disclosure is a cutting tool having an edge made of any of the cemented carbide alloys described in (1) to (4) above. The cutting tool of this disclosure can have a long lifespan even when used for drilling holes in printed circuit boards and intermittent machining of steel.

[0017] [Details of the embodiments of this 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. Also, dimensional relationships such as length, width, thickness, depth, etc. have been appropriately changed for the clarity and simplification of the drawings and do not necessarily represent actual dimensional relationships.

[0018] In the present disclosure, the notation in the form of "A to B" means A or more and B or less. When there is no unit description for A and there is only a unit description for B, the units of A and B are the same.

[0019] When representing a compound or the like by a chemical formula in the present disclosure, when the atomic ratio is not particularly limited, it includes all conventionally known atomic ratios and should not necessarily be limited only to those within the stoichiometric range.

[0020] In the present disclosure, when one or more numerical values are described as the lower limit and upper limit of a numerical range, any combination of any one numerical value described as the lower limit and any one numerical value described as the upper limit is also disclosed.

[0021] In the present disclosure, "comprising", "including", "having", and their variants are open-ended terms. Open-ended terms may further include additional elements or may not include additional elements in addition to essential elements. The description of "consisting of" is a closed term. However, even a configuration expressed by a closed term may include additional elements that are normally accompanying impurities or are irrelevant to the target technology.

[0022] [Embodiment 1: Cemented Carbide] The cemented carbide of one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") includes a first hard phase, a second hard phase, and a binder phase. The first hard phase is composed of a plurality of tungsten carbide particles. The second hard phase is composed of at least one first compound selected from the group consisting of TiNbC, TiNbN, TiNbCN, TiTaC, TiTaN, TiTaCN, TiTaNbC, TiTaNbN, and TiTaNbCN. The binder phase contains 50% by mass or more of cobalt. The total content of the first hard phase, the second hard phase, and the binder phase of the cemented carbide is 94% by volume or more. The content of the first hard phase of the cemented carbide is 75.0% by volume or more and 97.0% by volume or less. The content of the second hard phase of the cemented carbide is 0.1% by volume or more and 5.0% by volume or less. The content of the binder phase of the cemented carbide is 4.0% by volume or more and 15.0% by volume or less. The standard deviation sd in the particle size distribution based on volume of the Heywood diameter of the tungsten carbide particles is 0.1 μm or more and 0.25 μm or less. The percentage of the number of the second hard phases having a diameter of 0.2 μm or less with respect to the total number of the second hard phases is 1% or more and 10% or less. The percentage of the number of the second hard phases having a diameter of 0.8 μm or more with respect to the total number of the second hard phases is 1% or more and 10% or less. It is a cemented carbide.

[0023] <Composition of Cemented Carbide> The cemented carbide of Embodiment 1 includes a first hard phase, a second hard phase, and a binder phase. The total content of the first hard phase, the second hard phase, and the binder phase of the cemented carbide is 94% by volume or more, may be 94% by volume or more and 100% by volume or less, may be 94.1% by volume or more and 99.7% by volume or less, may be 96.0% by volume or more and 99.0% by volume or less, or may be 97.0% by volume or more and 98.5% by volume or less.

[0024] The content of the first hard phase of the cemented carbide of Embodiment 1 is 75.0% by volume or more and 97.0% by volume or less, may be 76.0% by volume or more and 95.0% by volume or less, may be 80.0% by volume or more and 92.0% by volume or less, or may be 85.0% by volume or more and 90.0% by volume or less.

[0025] The content of the second hard phase in the cemented carbide of Embodiment 1 is 0.1 volume% or more and 5.0 volume% or less, and may also be 0.2 volume% or more and 4.8 volume% or less, 0.5 volume% or more and 4.0 volume% or less, or 0.7 volume% or more and 3.0 volume% or less.

[0026] The binder phase content of the cemented carbide in Embodiment 1 is 4.0 volume% or more and 15.0 volume% or less, but may also be 4.2 volume% or more and 14.6 volume% or less, or 8.0 volume% or more and 14.0 volume% or less.

[0027] The cemented carbide of Embodiment 1 may further include a third hard phase in addition to the first hard phase, the second hard phase, and the binder phase. The third hard phase consists of at least one second compound selected from the group consisting of TiWNbC, TiWNbN, TiWNbCN, TiWTaC, TiWTaN, TiWTaCN, TiTaWNbC, TiTaWNbN, and TiTaWNbCN.

[0028] The content of the third hard phase in the cemented carbide of Embodiment 1 may be 0.1 volume% to 5 volume%, 0.2 volume% to 4.8 volume%, 0.4 volume% to 4.0 volume%, or 0.5 volume% to 3.5 volume%.

[0029] The cemented carbide of Embodiment 1 may consist of a first hard phase, a second hard phase, and a binder phase. To the extent that the effects of this disclosure are not impaired, the cemented carbide of Embodiment 1 may consist of a first hard phase, a second hard phase, a binder phase, and impurities. The cemented carbide of Embodiment 1 may consist of a first hard phase, a second hard phase, a binder phase, and a third hard phase. To the extent that the effects of this disclosure are not impaired, the cemented carbide of Embodiment 1 may consist of a first hard phase, a second hard phase, a binder phase, a third hard phase, and impurities.

[0030] Examples of the impurities mentioned above include iron (Fe), calcium (Ca), silicon (Si), and sulfur (S). The impurity content of the cemented carbide is acceptable as long as it does not impair the effects of this disclosure. For example, the impurity content of the cemented carbide may be 0% by mass or more and less than 0.1% by mass. The impurity content of the cemented carbide is measured by ICP emission spectrometry (Inductively Coupled Plasma Emission Spectroscopy). The measuring instrument can be the "ICPS-8100" (trademark) manufactured by Shimadzu Corporation.

[0031] The methods for measuring the content of the first hard phase, the second hard phase, the binder phase, and the third hard phase of cemented carbide are as follows. (A1) Cut out a section of the cemented carbide at an arbitrary location to expose the cross-section. Polish the cross-section to a mirror finish using a cross-section polisher (manufactured by JEOL Ltd.).

[0032] (B1) The mirror-finished surface of the cemented carbide is photographed with a scanning electron microscope (SEM) to obtain a backscattered electron image. The imaging area is set to the central part of the cross-section of the cemented carbide, i.e., a position that does not include parts with properties clearly different from the bulk portion, such as near the surface of the cemented carbide (a position where the entire imaging area is the bulk portion of the cemented carbide). The observation magnification is 5000x. The measurement conditions are an acceleration voltage of 3kV, a current of 2nA, and a working distance (WD) of 5mm.

[0033] (C1) The backscattered electron image obtained in (B1) above is imported into a computer and binarized using image analysis software (ImageJ ver.1.51J8). In the image after binarization, the first region consisting of the first hard phase and the second region consisting of the bonded phase, second hard phase, and third hard phase can be distinguished by the intensity of the colors. For example, in the image after binarization, the first region (first hard phase) is shown in black, and the second region (bonded phase, second hard phase, and third hard phase) is shown in white.

[0034] (D1) The imaging area described in (B1) above is analyzed using an energy-dispersive X-ray spectrometer (SEM-EDX) attached to a scanning electron microscope (instrument: Carl Zeiss). Elemental mapping images were obtained using the Gemini450™.

[0035] (E1) By superimposing the binarized image obtained in (C1) above with the elemental mapping image obtained in (D1) above, the regions where the first hard phase, second hard phase, binder phase, and third hard phase exist are identified on the binarized image.

[0036] In the binarized image, the regions shown in black, and the regions where tungsten (W) and carbon (C) are present in the elemental mapping image, correspond to the regions where the first hard phase is present.

[0037] In the binarized image, the region shown in white, where cobalt (Co) is present in the elemental mapping image, corresponds to the region where the bonding phase is present.

[0038] In the binarized image, the region shown in white, and in the elemental mapping image, the region where at least one first compound selected from the group consisting of TiNbC, TiNbN, TiNbCN, TiTaC, TiTaN, TiTaCN, TiTaNbC, TiTaNbN, and TiTaNbCN exists, corresponds to the region where the second hard phase exists.

[0039] In the binarized image, the region shown in white, where at least one second compound selected from the group consisting of TiWNbC, TiWNbN, TiWNbCN, TiWTaC, TiWTaN, TiWTaCN, TiTaWNbC, TiTaWNbN, and TiTaWNbCN is present, corresponds to the region where the third hard phase is present.

[0040] (F1) A rectangular measurement field of view of 24.9 μm × 18.8 μm is set in the binarized image. Using the image analysis software described above, the area percentages of the first hard phase, binding phase, second hard phase, and third hard phase are measured, with the total area of ​​the measurement field of view as the denominator.

[0041] (G1) The measurement described in (F1) above is performed in five distinct, non-overlapping measurement fields. In this disclosure, the average area percentage of the first hard phase in the five measurement fields corresponds to the content (volume %) of the first hard phase in the cemented carbide. The average area percentage of the second hard phase in the five measurement fields corresponds to the content (volume %) of the second hard phase in the cemented carbide. The average area percentage of the binder phase in the five measurement fields corresponds to the content (volume %) of the binder phase in the cemented carbide. The average area percentage of the third hard phase in the five measurement fields corresponds to the content (volume %) of the third hard phase in the cemented carbide.

[0042] It has been confirmed that, as long as the measurement is performed on the same sample, there is almost no variation in the measurement results even if the above measurement is performed multiple times by changing the selected area of ​​the measurement field.

[0043] <1st hard phase> ≪Composition of the First Hard Phase≫ In the cemented carbide of Embodiment 1, the first hard phase consists of a plurality of tungsten carbide particles. The tungsten carbide particles include not only "pure WC particles (WC containing no impurity elements whatsoever, and WC with impurity element content below the detection limit)" but also "WC particles containing impurities internally, as long as the effects of this disclosure are not impaired." Examples of impurities include iron (Fe), molybdenum (Mo), and sulfur (S).

[0044] ≪Standard deviation (sd) of the volume-based particle size distribution of tungsten carbide particles with Heywood diameter≫ In the cemented carbide of Embodiment 1, the standard deviation sd of the volume-based particle size distribution of tungsten carbide particles by Heywood diameter is 0.1 μm or more and 0.25 μm or less, but may also be 0.14 μm or more and 0.23 μm or less, 0.15 μm or more and 0.22 μm or less, or 0.18 μm or more and 0.20 μm or less.

[0045] ≪Volume-average diameter mv of tungsten carbide particles≫ In the cemented carbide of Embodiment 1, the volume-average diameter mv of the tungsten carbide particles may be 0.2 μm or more and 0.65 μm or less, 0.20 μm or more and 0.64 μm or less, 0.25 μm or more and 0.50 μm or less, or 0.30 μm or more and 0.40 μm or less.

[0046] In this disclosure, the standard deviation sd of the volume-based particle size distribution of tungsten carbide particles in cemented carbide, and the method for measuring the volume-average diameter mv of tungsten carbide particles are as follows.

[0047] (A2) Using the same method as (A1) to (E1) above for measuring the content of the first hard phase of the cemented carbide, the region where the first hard phase exists is identified in the binarized image.

[0048] (B2) Five binarized images were prepared in which the region of the first hard phase was identified, and a rectangular measurement field of view of 40.3 μm vertically × 30.2 μm horizontally was set in each image. Using image analysis software (Mountech's "Mac-View Version 5" trademark), the Heywood diameter (equivalent diameter of the projected area circle) of tungsten carbide particles in the measurement field of view was measured, and based on this, the standard deviation sd of the volume-based particle size distribution of Heywood diameter of tungsten carbide particles and the volume-average diameter mv of tungsten carbide particles in the measurement field of view were calculated. The Mac-View settings were non-spherical, detection sensitivity 20, and detection accuracy 0.7.

[0049] (C2) The average of the standard deviations sd in the volume-based particle size distribution of tungsten carbide particles based on Heywood diameter is calculated for the five measurement fields. In this disclosure, this average corresponds to the standard deviations sd in the volume-based particle size distribution of tungsten carbide particles based on Heywood diameter.

[0050] The average of the volume-average diameters mv of tungsten carbide particles in five measurement fields is calculated. In this disclosure, this average corresponds to the volume-average diameters mv of the tungsten carbide particles.

[0051] It has been confirmed that, as long as the measurement is performed on the same sample, there is almost no variation in the measurement results even if the above measurement is performed multiple times by changing the selected area of ​​the measurement field.

[0052] <Second hard phase> ≪Composition≫ In Embodiment 1, the second hard phase consists of at least one first compound selected from the group consisting of TiNbC, TiNbN, TiNbCN, TiTaC, TiTaN, TiTaCN, TiTaNbC, TiTaNbN, and TiTaNbCN. In the first compound, the ratio of the total number of Ti, Nb, and Ta atoms to the total number of C and N atoms is not limited to 1:1, and may include conventionally known ratios as long as they do not impair the effects of the present disclosure.

[0053] The second hard phase may contain metallic elements such as chromium (Cr), vanadium (V), and cobalt (Co) to the extent that it does not impair the effects of the present disclosure. The total content of Cr and Co in the second hard phase may be 0% by mass or more and less than 0.1% by mass. The content of Cr and Co in the second hard phase is measured by STEM-EDX.

[0054] ≪Grain size distribution of the second hard phase≫ In the cemented carbide of Embodiment 1, the percentage of the number of second hard phases with a diameter of 0.2 μm or less relative to the total number of second hard phases is 1% or more and 10% or less, and the percentage of the number of second hard phases with a diameter of 0.8 μm or more relative to the total number of second hard phases is 1% or more and 10% or less.

[0055] In the cemented carbide of Embodiment 1, the percentage of the number of second hard phases with a diameter of 0.2 μm or less relative to the total number of second hard phases may be 3% or more and 8% or 4% or more and 7% or less. In the cemented carbide of Embodiment 1, the percentage of the number of second hard phases with a diameter of 0.8 μm or more relative to the total number of second hard phases may be 3% or more and 8% or 5% or more and 7% or less. The percentage of the number of second hard phases with a diameter of 0.2 μm or less and the percentage of the number of second hard phases with a diameter of 0.8 μm or more can be combined as appropriate.

[0056] In this disclosure, the method for measuring the grain size distribution of the second hard phase in cemented carbide is as follows.

[0057] (A3) Cut out a section of the cemented carbide at an arbitrary location to expose the cross-section. Polish the cross-section to a mirror finish using a cross-section polisher (manufactured by JEOL Ltd.).

[0058] (B3) The mirror-finished surface of the cemented carbide is analyzed using SEM-EDX (instrument: Carl Zeiss Gemini 450™) to obtain an elemental mapping image. In the elemental mapping image, a second hard phase consisting of at least one first compound selected from the group consisting of TiNbC, TiNbN, TiNbCN, TiTaC, TiTaN, TiTaCN, TiTaNbC, TiTaNbN, and TiTaNbCN is identified.

[0059] (C3) In the elemental mapping image, an area of ​​20,000 μm² is visible. 2 Furthermore, set the measurement field of view such that the number of second hard phases is 500 or more.

[0060] (D3) The elemental mapping image is imported into a computer, and the measurement field is analyzed using microscope imaging software (LEICA Microsystems' "LAS X 2D Analysis" trademark) to measure the particle size distribution of the second hard phase based on the number of Heywood diameter particles. In the analysis, threshold adjustment is performed by a filter processing process pre-installed in the microscope imaging software. The filter processing conditions may be, for example, a color range of H0-357, S90-255, and I0-110.

[0061] Based on the obtained particle size distribution of the second hard phase, the percentage of second hard phase particles with a diameter of 0.2 μm or less relative to the total number of second hard phase particles, and the percentage of second hard phase particles with a diameter of 0.8 μm or more relative to the total number of second hard phase particles are calculated.

[0062] It has been confirmed that, as long as the measurement is performed on the same sample, there is almost no variation in the measurement results even if the above measurement is performed multiple times by changing the selected area of ​​the measurement field.

[0063] In the cemented carbide of Embodiment 1, the second hard phase consists of a plurality of crystal grains. Examples of crystal grains include first compound particles made of one first compound selected from the group consisting of TiNbC, TiNbN, TiNbCN, TiTaC, TiTaN, TiTaCN, TiTaNbC, TiTaNbN, and TiTaNbCN, and first compound particles made of two or more first compounds. The second hard phase can also be described as consisting of a plurality of first compound particles. In this disclosure, the grain size distribution of the second hard phase is synonymous with the grain size distribution of the plurality of crystal grains constituting the second hard phase and the grain size distribution of the first compound particles.

[0064] <Binded phase> ≪Composition of the bonded phase≫ In the cemented carbide of Embodiment 1, the cobalt content of the binder phase is 50% by mass or more. This allows the cemented carbide to have excellent toughness. The cobalt content of the binder phase may be 80% by mass or more and 100% by mass or less, or 90% by mass or more and 100% by mass or less.

[0065] The method for measuring the cobalt content of the binder phase is as follows: An elemental mapping image and a binarized image are acquired using the same method as (A1) to (E1) of the method for measuring the content of the first hard phase of the cemented carbide described above. By superimposing the elemental mapping image and the binarized image, the region where the binder phase exists is identified 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 binder phase exists within the measurement field of view. The above measurement is performed in five different measurement fields that do not overlap with each other. In this disclosure, the average of the cobalt content in the region where the binder phase exists in the five measurement fields of view corresponds to the cobalt content of the binder phase.

[0066] It has been confirmed that, as long as the measurement is performed on the same sample, there is almost no variation in the measurement results even if the above measurement is performed multiple times by changing the selected area of ​​the measurement field.

[0067] In the cemented carbide of Embodiment 1, the bonding phase may further include a first element selected from the group consisting of iron (Fe), nickel (Ni), chromium (Cr), vanadium (V), titanium (Ti), niobium (Nb), and tantalum (Ta), to the extent that it does not impair the effects of the present disclosure. The bonding phase may consist of cobalt and the first element.

[0068] <Third hard phase> ≪Composition≫ In Embodiment 1, the third hard phase consists of at least one second compound selected from the group consisting of TiWNbC, TiWNbN, TiWNbCN, TiWTaC, TiWTaN, TiWTaCN, TiTaWNbC, TiTaWNbN, and TiTaWNbCN. In the second compound, the ratio of the total number of Ti, W, Nb, and Ta atoms to the total number of C and N atoms is not limited to 1:1, and may include conventionally known ratios as long as they do not impair the effects of the present disclosure.

[0069] The third hard phase may contain metallic elements such as chromium (Cr), vanadium (V), and cobalt (Co) to the extent that it does not impair the effects of this disclosure. The total content of Cr and Co in the third hard phase may be 0% by mass or more and less than 0.1% by mass. The content of Cr and Co in the third hard phase is measured by STEM-EDX.

[0070] ≪50% cumulative particle size D50 based on area of ​​the third hard phase≫ In the cemented carbide of Embodiment 1, the 50% cumulative grain size D50 of the third hard phase, based on area, is 0.1 μm or more and 3.0 μm or less, but may also be 0.2 μm or more and 2.8 μm or less, 0.4 μm or more and 2.2 μm or less, or 0.5 μm or more and 2.0 μm or less.

[0071] In this disclosure, the method for measuring the 50% cumulative grain size D50 of the third hard phase in cemented carbide based on area is as follows:

[0072] (A4) Cut out a section of the cemented carbide at an arbitrary location to expose the cross-section. Polish the cross-section to a mirror finish using a cross-section polisher (manufactured by JEOL Ltd.).

[0073] (B4) The mirror-finished surface of the cemented carbide is analyzed using SEM-EDX (instrument: Carl Zeiss Gemini 450™) to obtain an elemental mapping image. In the elemental mapping image, a third hard phase consisting of at least one second compound selected from the group consisting of TiWNbC, TiWNbN, TiWNbCN, TiWTaC, TiWTaN, TiWTaCN, TiTaWNbC, TiTaWNbN, and TiTaWNbCN is identified.

[0074] (C4) Prepare 10 elemental mapping images in which the third hard phase has been identified, and set a rectangular measurement field of view of 4.0 μm in height × 3.0 μm in width within each elemental mapping image.

[0075] (D4) The elemental mapping image is imported into a computer, and the measurement field is analyzed using microscope imaging software (LEICA Microsystems' "LAS X 2D Analysis" trademark) to measure the Heywood diameter (equivalent diameter of projected area circle) of the third hard phase in the measurement field.

[0076] (E4) Based on all third hard phases within the measurement field of view of 10, calculate the 50% cumulative particle size D50 of the third hard phase based on the area of ​​the Heywood diameter.

[0077] It has been confirmed that, as long as the measurement is performed on the same sample, there is almost no variation in the measurement results even if the above measurement is performed multiple times by changing the selected area of ​​the measurement field.

[0078] In the cemented carbide of Embodiment 1, the third hard phase consists of a plurality of crystal grains. Examples of crystal grains include second compound particles made of one second compound selected from the group consisting of TiWNbC, TiWNbN, TiWNbCN, TiWTaC, TiWTaN, TiWTaCN, TiTaWNbC, TiTaWNbN, and TiTaWNbCN, and second compound particles made of two or more types of second compounds. The third hard phase can also be described as consisting of a plurality of second compound particles. In this disclosure, the 50% cumulative particle size D50 based on the area of ​​the Heywood diameter of the third hard phase is synonymous with the 50% cumulative particle size D50 based on the area of ​​the plurality of crystal grains constituting the third hard phase, and the 50% cumulative particle size D50 based on the area of ​​the Heywood diameter of the second compound particles.

[0079] <Manufacturing method for cemented carbide> The cemented carbide of Embodiment 1 can be manufactured by performing the following steps in the order described above: preparation of raw material powder, mixing, molding, sintering, and HIP (Heat Injection Processing). Each step will be described below.

[0080] <Preparation process> The preparation process involves preparing the raw materials for the cemented carbide alloy. Examples of raw materials include metallic tungsten powder (hereinafter also referred to as "W powder"), carbon powder (hereinafter also referred to as "C powder"), Co powder (average particle size 1 μm), TaC powder (average particle size 1 μm), TiO2 powder, and Nb2O5 powder.

[0081] First, tungsten carbide powder is prepared using the following procedure. W powder, C powder, and TiO2 powder are strongly mixed using a dry attritor, and then weakly mixed using a wet ball mill to obtain a mixed powder. If Nb2O5 powder is used as a raw material, the Nb2O5 powder is also mixed at the same time. The mixing conditions for the dry attritor are: carbide media diameter: 3 mm, rotation speed: 40 rpm, mixing time: 1 hour. The mixing conditions for the wet ball mill are: carbide media diameter: 6 mm, rotation speed: 30 rpm, mixing time: 6 hours.

[0082] The mixed powder is placed in a batch furnace and heated at 1500°C for 2 hours under a vacuum atmosphere. After heating, the mixed powder is crushed in a dry ball mill to obtain tungsten carbide powder. The conditions for the dry ball mill are: carbide media diameter: 6 mm, rotation speed: 5 rpm, crushing time: 2 hours.

[0083] If TiO2 powder is used as a raw material and Nb2O5 powder is not used, the resulting tungsten carbide powder is Ti-added tungsten carbide powder. If both TiO2 powder and Nb2O5 powder are used as raw materials, the resulting tungsten carbide powder is TiNb-added tungsten carbide powder, which contains both Ti and Nb.

[0084] Further raw material powders such as Ni powder, VC powder, and Cr3C2 powder can be prepared. Commercially available raw material powders can be used. The average particle size of these raw material powders is not particularly limited and can be, for example, 0.5 μm to 2 μm.

[0085] The average particle size of the raw material powder means the average particle size measured by the FSSS (Fisher Sub-Sieve Sizer) method. The average particle size is measured using the "Sub-Sieve Sizer model 95" (trademark) manufactured by Fisher Scientific.

[0086] <Mixing process> The mixing process is a process of mixing the raw materials (including WC powder) prepared in the preparation process at a predetermined ratio to obtain a mixture. The mixing ratio of the raw materials is appropriately adjusted according to the target composition of the cemented carbide.

[0087] A ball mill is used for mixing the raw materials. The mixing conditions are a rotation speed of 66 rpm, a ball diameter of φ6 mm, and a mixing time of 24 hours.

[0088] After the mixing process, the mixture may be granulated as necessary. By granulating the mixture, it is easier to fill the mixture into the die or mold during the subsequent forming process. For granulation, known granulation methods can be applied, for example, commercially available granulators such as spray dryers can be used.

[0089] <Forming process> The forming process is a process of forming the mixture obtained in the mixing process into the shape of a cutting tool to obtain a formed body. The forming method and forming conditions in the forming process may adopt general methods and conditions and are not particularly limited.

[0090] <Sintering process> The sintering process is a process of sintering the formed body obtained in the forming process to obtain a cemented carbide intermediate. The formed body is placed in a furnace and heated to 1250°C at a heating rate of 5°C / min in an Ar atmosphere and a pressure of 6.7 kPa, or in a N2 atmosphere and a pressure of 30 kPa or 6.7 kPa, and held at 1250°C for 2 hours. Subsequently, it is heated to 1350°C at a heating rate of 5°C / min and held at 1350°C for 2 hours. Subsequently, the formed body is cooled to 25°C at a cooling rate of -50°C / min to obtain a cemented carbide intermediate.

[0091] <HIP process> In the HIP process, the cemented carbide intermediate is subjected to HIP. The HIP conditions are an Ar atmosphere, 200 MPa, and holding at 1100°C for 2 hours. After that, it is cooled to obtain the cemented carbide of Embodiment 1. Conventional known cooling conditions can be used.

[0092] <Characteristics of the manufacturing method for cemented carbide in Embodiment 1> In the manufacturing method of cemented carbide according to Embodiment 1, Ti-added tungsten carbide powder or TiNb-added tungsten carbide powder is used. With this, during cemented carbide manufacturing, Ti, or Ti and Nb react uniformly, and the second hard phase containing Ti, or the second hard phase containing Ti and Nb, tends to grow uniformly, resulting in a sharper grain size distribution of the second hard phase. In conventional general cemented carbide manufacturing methods, Ti-added tungsten carbide powder or TiNb-added tungsten carbide powder is not used, so it is not possible to achieve a grain size distribution of the second hard phase such that the percentage of the second hard phase with a diameter of 0.2 μm or less relative to the total number of second hard phases is 1% to 10%, and the percentage of the second hard phase with a diameter of 0.8 μm or more relative to the total number of second hard phases is 1% to 10%.

[0093] In the mixing step of the cemented carbide manufacturing method of Embodiment 1, the raw materials are mixed using a low-speed ball mill. This tends to result in a sharper particle size distribution of WC particles. Conventional general mixing conditions include, for example, using an attritor with a rotation speed of 100 rpm, a ball diameter of φ6 mm, and a mixing time of 6 hours. With these conditions, it is not possible to achieve a standard deviation sd of 0.10 μm or more and 0.25 μm or less in the volume-based particle size distribution of WC particles with a Heywood diameter.

[0094] In the sintering step of the cemented carbide manufacturing method of Embodiment 1, the material is heated to 1250°C at a heating rate of 5°C / min and held at 1250°C for 2 hours. Subsequently, it is heated to 1350°C at a heating rate of 5°C / min and held at 1350°C for 2 hours. By performing sintering in two stages, grain growth of the second hard phase is suppressed, and the grain size distribution of the second hard phase containing Ti and Nb tends to become sharper. Furthermore, sintering at a low temperature for a long period of time, such as holding at 1350°C for 2 hours, suppresses grain growth of WC particles, and makes it easier to maintain a sharp grain size distribution of WC particles.

[0095] The inventors have discovered, through diligent research, that the cemented carbide described herein can be realized by adopting the manufacturing process described above.

[0096] [Embodiment 2: Cutting Tools] A cutting tool in one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 2") includes a cutting edge made of cemented carbide as in Embodiment 1. In the present disclosure, "cutting edge" means the portion involved in cutting. More specifically, "cutting edge" means the region enclosed by the cutting edge ridge and a hypothetical plane at a distance of 0.5 mm or 2 mm from the cutting edge ridge to the cemented carbide side.

[0097] Examples of cutting tools include cutting tools, drills, end mills, replaceable cutting inserts for milling, replaceable cutting inserts for turning, metal saws, gear cutting tools, reamers, or taps. The cutting tool 10 of Embodiment 2 can exhibit particularly excellent effects in the case of PCB drills as shown in Figure 1 and replaceable cutting inserts as shown in Figure 2. The cutting edge 11 of the cutting tool 10 shown in Figures 1 and 2 is made of the cemented carbide of Embodiment 1.

[0098] In the cutting tool of Embodiment 2, the cemented carbide of Embodiment 1 may constitute the entire tool or a part of it. Here, "constituting a part" refers to a configuration in which the cemented carbide of Embodiment 1 is brazed to a predetermined position on any base material to form the cutting edge.

[0099] The cutting tool of Embodiment 2 may further include a hard coating that covers at least a portion of the surface of a substrate made of cemented carbide. For example, diamond-like carbon or diamond can be used as the hard coating.

[0100] The cutting tool of Embodiment 2 can be obtained by shaping the cemented carbide of Embodiment 1 into a desired shape. [Examples]

[0101] This embodiment will be described in more detail by reference to examples. However, this embodiment is not limited by these examples.

[0102] <Preparation process> As raw materials, we prepared metallic tungsten powder (hereinafter also referred to as "W powder"), carbon powder (hereinafter also referred to as "C powder"), Co powder (average particle size 1 μm), TaC powder, TiO2 powder, Nb2O5 powder, Ni powder, VC powder, and Cr3C2 powder. The average particle size of the TaC powder, TiO2 powder, Nb2O5 powder, Ni powder, VC powder, and Cr3C2 powder is 1 μm.

[0103] First, tungsten carbide powder was prepared using the following procedure. W powder, C powder, and TiO2 powder were strongly mixed using a dry attritor, and then weakly mixed using a wet ball mill to obtain a mixed powder. When Nb2O5 powder was used as a raw material, the Nb2O5 powder was also mixed at the same time. The amounts of TiO2 powder and Nb2O5 powder in the mixed powder were adjusted to the ratios shown in Table 1. Samples 1-5 were prepared by mixing only W powder and C powder. The amounts of W powder and C powder in the mixed powder were adjusted so that W powder:C powder = 14:1 (mass ratio). The mixing conditions for the dry attritor were: carbide media diameter: 3 mm, rotation speed: 40 rpm, mixing time: 1 hour. The mixing conditions for the wet ball mill were: carbide media diameter: 6 mm, rotation speed: 30 rpm, mixing time: 6 hours.

[0104] The mixed powder was placed in a batch furnace and heated at 1500°C for 2 hours under a vacuum atmosphere. After heating, the mixed powder was crushed in a dry ball mill to obtain tungsten carbide powder. The conditions for the dry ball mill were: carbide media diameter: 6 mm, rotation speed: 5 rpm, crushing time: 2 hours.

[0105] <Mixing process> The raw materials were mixed in the proportions listed in Table 1. The proportions (mass%) of each raw material listed in Table 1 represent the proportion when the total raw materials are considered as 100% by mass. In Table 1, "remaining" indicates that the proportion of WC powder is the value obtained by subtracting the total proportion of the other raw materials from 100% by mass of the total raw materials. The mixing conditions were either A or B below. Condition B is the conventional general mixing condition. A: Use a ball mill. The mixing conditions are: rotation speed 66 rpm, ball diameter φ6 mm, and mixing time 24 hours. B: Use an attritor. The mixing conditions are: rotation speed 100 rpm, ball diameter φ6 mm, and mixing time 6 hours.

[0106] [Table 1]

[0107] <Forming process> By pressing the mixed powder, we obtained molded bodies in the shape of a round bar and molded bodies in the shape of an interchangeable cutting tip (model number: CNMG120408N-SU).

[0108] <Sintering process> The formed body was placed in a furnace and heated to the temperature described in the "First-stage temperature / time" column of Table 2 at the heating rate described in the "Heating rate" column of Table 2 under the conditions described in the "atmosphere / pressure" column of "Sintering" in Table 2 (where "Ar-6.7 kPa" means an argon atmosphere and a pressure of 6.7 kPa; "N2-30 kPa" means a N2 atmosphere and a pressure of 30 kPa; "N2-6.7 kPa" means a N2 atmosphere and a pressure of 6.7 kPa), and held at that temperature for the time described in the "First-stage temperature / time" column. Then, it was heated to the temperature described in the "Second-stage temperature / time" column of Table 2 at the heating rate described in the "Heating rate" column of Table 2 and held at that temperature for the time described in the "Second-stage temperature / time" column. For the samples described as "-" in the "First-stage temperature / time" column, sintering was not performed under the first-stage conditions, and only sintering under the second-stage conditions was carried out. Subsequently, the formed body was cooled to 25 °C at the cooling rate described in the "Cooling rate" column of Table 2 to obtain a cemented carbide intermediate body.

[0109]

Table 2

[0110] <HIP process> The cemented carbide intermediate body was subjected to HIP under the conditions described in the "HIP" column of Table 3. Then, it was cooled to obtain a cemented carbide.

[0111]

Table 3

[0112] [Evaluation of cemented carbide] <Content ratio of the first hard phase, content ratio of the binder phase, content ratio of the second hard phase, and content ratio of the third hard phase of the cemented carbide> The content ratio (volume %) of the first hard phase, content ratio (volume %) of the binder phase, content ratio (volume %) of the second hard phase, and content ratio (volume %) of the third hard phase of the cemented carbide of each sample were measured by the method described in Embodiment 1. The results are shown in Table 4.

[0113]

Table 4

[0114] <Standard deviation (sd) of the volume-based particle size distribution of tungsten carbide particles in terms of Heywood diameter, volume-average diameter (mv) of tungsten carbide particles, composition of the second hard phase, and particle size distribution of the second hard phase> For each cemented carbide sample, the standard deviation sd of the volume-based particle size distribution of tungsten carbide particles (Heywood diameter), the volume-average diameter mv of tungsten carbide particles, the composition of the second hard phase, and the particle size distribution of the second hard phase were measured using the method described in Embodiment 1. The results are shown in Table 5. In Table 5, the column "Diameter 0.2 μm or less" shows the percentage of the number of second hard phase particles with a diameter of 0.2 μm or less relative to the total number of second hard phase particles. In Table 5, the column "Diameter 0.8 μm or more" shows the percentage of the number of second hard phase particles with a diameter of 0.8 μm or more relative to the total number of second hard phase particles.

[0115] [Table 5]

[0116] <Cobalt content of the binder phase, composition of the third hard phase, and 50% cumulative particle size D50 of the third hard phase based on area> For each cemented carbide sample, the cobalt content of the binder phase, the composition of the third hard phase, and the 50% cumulative particle size D50 of the third hard phase based on area were measured using the method described in Embodiment 1. The results are shown in Table 6.

[0117] [Table 6]

[0118] [Cutting Test 1] Round bars made of cemented carbide for each sample were processed to create printed circuit board (PCB) drills with a cutting diameter of φ0.12 mm. Using the PCB drills, commercially available printed circuit boards for semiconductor packages were drilled under the conditions of a rotational speed of 120 krpm, a feed rate of 2.0 m / min, and a withdrawal speed of 20 m / min. The drilling process was performed with 10 PCB drills, and the fracture rate up to 5000 hits was calculated as ((number of PCB drills that fractured (drills) / 10 (drills)) × 100). The results are shown in the "Fracture Rate" column of "Cutting Test 1" in Table 7. A lower fracture rate indicates better fracture resistance of the cutting tool in the initial stages of cutting and a longer tool life.

[0119] [Cutting Test 2] Turning was performed on a notched round bar made of SCM435 using replaceable cutting tips (model number: CNMG120408N-GU) made of cemented carbide for each sample. The machining conditions were a cutting speed of vc 100 m / min, a feed rate of f 0.1 mm / rev, a depth of cut of ap 1.0 mm, and dry machining, performed for 1 minute. The above turning was performed with 10 replaceable cutting tips, and the chipping rate ((number of chipped replaceable cutting tips (pieces) / 10 (pieces)) × 100) was calculated. The results are shown in the "Chipping Rate" column of "Cutting Test 2" in Table 7. A lower chipping rate indicates better chipping resistance in the initial stages of cutting and a longer tool life. Note that the above machining conditions correspond to intermittent machining of steel.

[0120] [Table 7]

[0121] The cemented carbide alloys and cutting tools of Samples 1 to 10 correspond to the examples. The cemented carbide alloys and cutting tools of Samples 1-1 to 1-6 correspond to the comparative examples. It was confirmed that the cutting tools of Samples 1 to 10 had a longer tool life in cutting tests 1 and 2 than the cutting tools of Samples 1-1 to 1-6.

[0122] As described above, embodiments and examples of this disclosure have been explained, but it is also intended from the outset that the configurations of each of the above embodiments and examples may be combined as appropriate or modified in various ways. The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the embodiments and examples described above, and all modifications within the scope of the claims are intended to be included in the meaning of equivalents and within the scope. [Explanation of Symbols]

[0123] 10 cutting tools, 11 cutting edges.

Claims

1. A cemented carbide comprising a first hard phase, a second hard phase, and a binder phase, The first hard phase consists of a plurality of tungsten carbide particles. The second hard phase consists of at least one first compound selected from the group consisting of TiNbC, TiNbN, TiNbCN, TiTaC, TiTaN, TiTaCN, TiTaNbC, TiTaNbN, and TiTaNbCN. The aforementioned bonding phase contains 50% by mass or more of cobalt, The total content of the first hard phase, the second hard phase, and the binder phase of the cemented carbide is 94% by volume or more. The content of the first hard phase in the cemented carbide is 75.0% by volume or more and 97.0% by volume or less. The content of the second hard phase in the cemented carbide is 0.1% by volume or more and 5.0% by volume or less. The content of the binder phase in the cemented carbide is 4.0 volume% or more and 15.0 volume% or less. The standard deviation (sd) of the volume-based particle size distribution of the Heywood diameter of the tungsten carbide particles is 0.1 μm or more and 0.25 μm or less. The percentage of the number of second hard phases with a diameter of 0.2 μm or less relative to the total number of second hard phases is 1% or more and 10% or less. A cemented carbide alloy in which the percentage of the number of second hard phases with a diameter of 0.8 μm or more relative to the total number of the second hard phases is 1% or more and 10% or less.

2. The cemented carbide according to claim 1, wherein the volume-average diameter mv of the tungsten carbide particles is 0.2 μm or more and 0.65 μm or less.

3. The cemented carbide further comprises a third hard phase, The third hard phase consists of at least one second compound selected from the group consisting of TiWNbC, TiWNbN, TiWNbCN, TiWTaC, TiWTaN, TiWTaCN, TiTaWNbC, TiTaWNbN, and TiTaWNbCN. The cemented carbide alloy according to claim 1 or claim 2, wherein the content of the third hard phase in the cemented carbide alloy is 0.1 volume% or more and 5 volume% or less.

4. The cemented carbide according to claim 3, wherein the 50% cumulative particle size D50 of the third hard phase, based on area, is 0.1 μm or more and 3.0 μm or less.

5. A cutting tool comprising a cutting edge made of cemented carbide as described in claim 1 or claim 2.

Images