Cemented Carbide and Cutting Tools

Abstract

The presently disclosed cemented carbide is a cemented carbide comprising a first hard phase consisting of a plurality of tungsten carbide particles and a binder phase containing cobalt, wherein the total content of the first hard phase and the binder phase in the cemented carbide is 80.0% by volume or more, the content of the binder phase in the cemented carbide is 5.0% by volume or more and 21.0% by volume or less, the cobalt content of the binder phase is 50% by mass or more, and the cemented carbide has a hardness H 25 Hardness H at 200℃ 200 Percentage of (H 200 / H 25 ) × 100 is 85% or more and 100% or less, a ratio c / M of the specific heat c of the cemented carbide at 200°C to the mass-based content M of the binder phase of the cemented carbide is 0.028 or more and 0.042 or less, the mass-based content M of the binder phase of the cemented carbide is 3.0 mass% or more and 13.0 mass% or less, and the unit of the specific heat c is J / g K.

Description

[Technical Field]

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

[0002] Conventionally, cemented carbide alloys comprising a plurality of tungsten carbide particles and a binder phase have been used as materials for cutting tools (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-131769 Summary of the Invention

[0004] The presently disclosed cemented carbide is a cemented carbide comprising a first hard phase consisting of a plurality of tungsten carbide particles and a binder phase containing cobalt, wherein the total content of the first hard phase and the binder phase in the cemented carbide is 80.0% by volume or more, the content of the binder phase in the cemented carbide is 5.0% by volume or more and 21.0% by volume or less, the cobalt content of the binder phase is 50% by mass or more, and the cemented carbide has a hardness H 25 Hardness H at 200℃ 200 Percentage of (H 200 / H 25 ) × 100 is 85% or more and 100% or less, a ratio c / M of the specific heat c of the cemented carbide at 200°C to the mass-based content M of the binder phase of the cemented carbide is 0.028 or more and 0.042 or less, the mass-based content M of the binder phase of the cemented carbide is 3.0 mass% or more and 13.0 mass% or less, and the unit of the specific heat c is J / g K. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a schematic diagram of a cutting tool according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0006] [Problem to be solved by this disclosure] From the viewpoint of cost reduction, there is a demand for cemented carbide alloys and cutting tools including such alloys that enable the tool life to be extended, particularly when used as materials for cutting tools for finishing die steel.

[0007] [Effects of this disclosure] According to the present disclosure, it is possible to provide a cemented carbide alloy and a cutting tool including the same that enable a longer tool life, particularly when used as a material for cutting tools for finishing die steel.

[0008] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. (1) The presently disclosed cemented carbide alloy comprises a first hard phase consisting of a plurality of tungsten carbide particles and a binder phase containing cobalt, wherein the total content of the first hard phase and the binder phase in the cemented carbide alloy is 80.0% by volume or more, the content of the binder phase in the cemented carbide alloy is 5.0% by volume or more and 21.0% by volume or less, the cobalt content of the binder phase is 50% by mass or more, and the cemented carbide has a hardness H 25 Hardness H at 200℃ 200 Percentage of (H 200 / H 25 ) × 100 is 85% or more and 100% or less, a ratio c / M of the specific heat c of the cemented carbide at 200°C to the mass-based content M of the binder phase of the cemented carbide is 0.028 or more and 0.042 or less, the mass-based content M of the binder phase of the cemented carbide is 3.0 mass% or more and 13.0 mass% or less, and the unit of the specific heat c is J / g K.

[0009] According to the present disclosure, it is possible to provide a cemented carbide that enables a longer tool life, particularly when used as a material for cutting tools for finishing die steels. The reason for this is presumed to be as follows.

[0010] The cemented carbide of the present disclosure contains a first hard phase consisting of tungsten carbide particles and a binder phase containing cobalt, totaling 80.0% by volume or more, with the binder phase content being 5.0% by volume or more and 21.0% by volume or less, and the binder phase containing cobalt being 50% by mass or more, thereby providing the cemented carbide with hardness and toughness suitable for cutting tools.

[0011] The hardness H of the cemented carbide of the present disclosure at 25°C 25 Hardness H at 200℃ 200 Percentage of (H 200 / H 25 ) × 100 is 85% or more and 100% or less. Normally, the hardness of cemented carbide decreases at high temperatures, but the cemented carbide of the present disclosure suppresses this decrease in hardness even at 200°C. Therefore, a cutting tool equipped with a cutting edge made of this cemented carbide can have excellent wear resistance even in finish machining using a die steel ball end mill, where the cutting edge temperature during machining reaches approximately 200°C.

[0012] Typically, metals used in the binder phase of cemented carbide alloys tend to have a high specific heat at high temperatures, absorbing thermal energy and becoming resistant to temperature changes. In other words, the heat resistance of metals used in the binder phase improves at high temperatures. Meanwhile, the specific heat is affected by the binder phase content of the cemented carbide alloy. The ratio c / M, where c is the specific heat of the cemented carbide alloy at 200°C and M is the mass-based binder phase content of the cemented carbide alloy, is an index of heat resistance that is independent of the binder phase content of the cemented carbide alloy. When the ratio c / M is 0.028 or higher, the cemented carbide alloy has good heat resistance at 200°C. When the ratio c / M is 0.042 or lower, the cemented carbide alloy is not overheated and strength loss can be suppressed. Therefore, cutting tools equipped with cutting edges made of this cemented carbide alloy can have excellent heat resistance even during finish machining using a die steel ball end mill, where the cutting edge temperature during machining reaches approximately 200°C.

[0013] (2) In the above (1), the percentage (H 200 / H 25)×100 may be 90% or more and 100% or less, the ratio c / M may be 0.030 or more and 0.042 or less, and the cemented carbide may further include a second hard phase, and the second hard phase may be made of at least one first compound selected from the group consisting of TiNbC, TiNbN, and TiNbCN.

[0014] Percentage (H 200 / H 25 ) × 100 is 90% or more and 100% or less, the decrease in hardness of the cemented carbide at 200°C is further suppressed. Therefore, a cutting tool equipped with a cutting edge made of such a cemented carbide can have even better wear resistance in finish machining using a die steel ball end mill, in which the cutting edge temperature during machining reaches approximately 200°C.

[0015] When the cemented carbide contains a second hard phase consisting of at least one first compound selected from the group consisting of TiNbC, TiNbN, and TiNbCN, the heat resistance and hardness of the cemented carbide are further improved, and therefore, a cutting tool having a cutting edge made of the cemented carbide can have even better heat resistance and wear resistance.

[0016] (3) In the above (1) or (2), the median area of ​​the second hard phase in the cross section of the cemented carbide is 0.003 μm 2 More than 0.050μm 2 or less, and the coefficient of variation of the area of ​​the second hard phase may be 0.50 or more and 3.00 or less. This further improves the heat resistance of the cemented carbide and the balance between hardness and strength. Therefore, a cutting tool equipped with a cutting edge made of this cemented carbide can have even better heat resistance and wear resistance.

[0017] (4) In any of the above (1) to (3), the median area of ​​the tungsten carbide particles in the cross section of the cemented carbide is 0.080 μm 2 More than 0.150μm 2The coefficient of variation of the area of ​​the tungsten carbide particles may be 0.85 or more and 1.10 or less. This further improves the balance between hardness and strength of the cemented carbide. Therefore, a cutting tool equipped with a cutting edge made of the cemented carbide can have even better wear resistance.

[0018] (5) A cutting tool according to the present disclosure is a cutting tool having a cutting edge made of the cemented carbide according to any one of (1) to (4) above. The cutting tool according to the present disclosure can have a long life, especially when used for finishing die steel.

[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 "A to B" means greater than or equal to A and less than or equal to B, and when no unit is specified for A and only a unit is specified 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 this disclosure, when one or more numerical values ​​are listed as the lower limit and upper limit of a numerical range, the combination of any one numerical value listed in the lower limit and any one numerical value listed in the upper limit is also 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] The cemented carbide according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") is a cemented carbide comprising a first hard phase consisting of a plurality of tungsten carbide particles and a binder phase containing cobalt. The total content of the first hard phase and binder phase in the cemented carbide is 80.0% by volume or more. The content of the binder phase in the cemented carbide is 5.0% by volume or more and 21.0% by volume or less. The cobalt content of the binder phase is 50% by mass or more. The hardness H of the cemented carbide at 25°C 25 Hardness H at 200℃ 200 Percentage of (H 200 / H 25 ) × 100 is 85% or more and 100% or less. The ratio c / M of the specific heat c of the cemented carbide at 200°C to the mass-based binder phase content M of the cemented carbide is 0.028 or more and 0.042 or less. The mass-based binder phase content M of the cemented carbide is 3.0 mass% or more and 13.0 mass% or less. The unit of specific heat c is J / g K.

[0025] <Composition of cemented carbide> The cemented carbide of embodiment 1 comprises a first hard phase consisting of tungsten carbide particles and a binder phase containing cobalt. The total content of the first hard phase and binder phase in the cemented carbide is 80.0% by volume or more, and may be 82% by volume to 100% by volume, 82% by volume to 99% by volume, 92% by volume to 98% by volume, or 94% by volume to 97% by volume.

[0026] The content of the binder phase in the cemented carbide of embodiment 1 is 5.0 vol % or more and 21.0 vol % or less, and may be 7 vol % or more and 20 vol % or less, or may be 10 vol % or more and 18 vol % or less.

[0027] The cemented carbide of embodiment 1 may include a second hard phase in addition to the first hard phase and binder phase. The second hard phase is composed of at least one first compound selected from the group consisting of TiNbC, TiNbN, and TiNbCN. The content of the second hard phase in the cemented carbide may be more than 0% by volume and not more than 20% by volume, 1% by volume or more and not more than 18% by volume, 2% by volume or more and not more than 8% by volume, or 3% by volume or more and not more than 6% by volume.

[0028] The cemented carbide of embodiment 1 may be composed of a first hard phase and a binder phase. The cemented carbide of embodiment 1 may be composed of a first hard phase, a binder phase, and impurities, provided that the effects of the present disclosure are not impaired. The cemented carbide of embodiment 1 may be composed of a first hard phase, a binder phase, and a second hard phase. The cemented carbide of embodiment 1 may be composed of a first hard phase, a binder phase, a second hard phase, and impurities, provided that the effects of the present disclosure are not impaired.

[0029] Examples of the impurities 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 the present 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 optical emission spectroscopy (Inductively Coupled Plasma Emission Spectroscopy). The measuring device that can be used is Shimadzu Corporation's "ICPS-8100" (trademark).

[0030] The methods for measuring the content of the first hard phase, the content of the binder phase, and the content of the second hard phase in the cemented carbide are as follows. (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.).

[0031] (B1) 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 the center of the cemented carbide cross section, that is, a position that does not include areas with properties that are clearly different from the bulk part, such as near the surface of the cemented carbide (a position where the photographed area is entirely the bulk part of the cemented carbide). The observation magnification is 5000x. The measurement conditions are an accelerating voltage of 3 kV, a current value of 2 nA, and a working distance (WD) of 5 mm.

[0032] (C1) The backscattered electron image obtained in (B1) above is imported into a computer and binarized using image analysis software (OpenCV, SciPy). In the binarized image, the first region consisting of the first hard phase and the second region consisting of the binder phase and the second hard phase can be distinguished by the shade of color. For example, in the binarized image, the first hard phase is shown as a black region, and the binder phase and the second hard phase are shown as white regions.

[0033] (D1) The photographed area in (B1) above is analyzed using an energy dispersive X-ray spectrometer (SEM-EDX) attached to a scanning electron microscope (apparatus: Carl Zeiss Gemini450 (trademark)) to obtain an elemental mapping image.

[0034] (E1) By superimposing the binarized image obtained in (C1) above on the element mapping image obtained in (D1) above, the regions where the first hard phase, binder phase, and second hard phase exist are identified on the binarized image. The regions shown in black in the binarized image and where tungsten (W) and carbon (C) exist in the element mapping image correspond to the regions where the first hard phase exists. The regions shown in white in the binarized image and where cobalt (Co) exists in the element mapping image correspond to the regions where the binder phase exists. The regions shown in white in the binarized image and where titanium (Ti) or niobium (Nb) exist in the element mapping image correspond to the regions where the second hard phase exists.

[0035] (F1) A rectangular measurement field of view of 24.9 μm × 18.8 μm is set in the image after binarization processing. Using the image analysis software, the area percentages of the first hard phase, binder phase, and second hard phase are measured using the area of ​​the entire measurement field as the denominator.

[0036] (G1) The measurement of (F1) above is carried out in five different non-overlapping measurement fields. In the present disclosure, the average of the area percentages 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 of the area percentages of the binder phase in the five measurement fields corresponds to the content (volume %) of the binder phase in the cemented carbide. The average of the area percentages of the second hard phase in the five measurement fields corresponds to the content (volume %) of the second hard phase in the cemented carbide.

[0037] 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 above measurement is performed multiple times by changing the selected location of the measurement field.

[0038] <1st hard phase> ≪Composition≫ In the cemented carbide of the first embodiment, the first hard phase is composed of a plurality of tungsten carbide particles (hereinafter also referred to as "WC particles"). The tungsten carbide particles include not only "pure WC particles (including WC containing no impurity elements and WC with impurity elements below the detection limit)" but also "WC particles containing impurities therein, as long as the effects of the present disclosure are not impaired." Examples of impurities include iron (Fe), molybdenum (Mo), and sulfur (S).

[0039] <Median area and coefficient of variation of area of ​​tungsten carbide particles> In the cross section of the cemented carbide of embodiment 1, the median area of ​​the tungsten carbide particles is 0.080 μm 2 More than 0.150μm 2 The median area of ​​the tungsten carbide particles is 0.085 μm or less, and the coefficient of variation of the area of ​​the tungsten carbide particles may be 0.85 or more and 1.10 or less. 2 More than 0.140μm2 It may be less than 0.100 μm, or 2 More than 0.125μm 2 The coefficient of variation of the area of ​​the tungsten carbide particles may be 0.90 or more and 1.06 or less, or 0.92 or more and 1.05 or less. The median area of ​​the tungsten carbide particles and the coefficient of variation of the area of ​​the tungsten carbide particles may be any combination of the above ranges.

[0040] In this disclosure, the median area of ​​tungsten carbide particles means the area where the cumulative frequency of the number-based areas of tungsten carbide particles is 50%. In this disclosure, the coefficient of variation of the area of ​​tungsten carbide particles is the value obtained by dividing the standard deviation of the area of ​​tungsten carbide particles by the average area of ​​tungsten carbide particles (standard deviation / average value). The average area of ​​tungsten carbide particles means the arithmetic average of the areas of tungsten carbide particles. The median area and coefficient of variation of the area of ​​the second hard phase described below have the same meanings.

[0041] In the present disclosure, the method for measuring the median area of ​​tungsten carbide particles and the coefficient of variation of the area of ​​tungsten carbide particles in the cross section of a cemented carbide is as follows.

[0042] (A2) Using the same method as (A1) to (E1) for measuring the content of the first hard phase, the content of the binder phase, and the content of the second hard phase in the cemented carbide, the region where the first hard phase exists is identified in the image after the binarization process.

[0043] (B2) Prepare five binarized images in which the first hard phase region is identified, and set a rectangular measurement field of view of 40.3 μm in length and 30.2 μm in width in each image. Using image analysis software (ImageJ ver. 1.51J8), identify the outer edge of each tungsten carbide particle in the measurement field, and measure the area of ​​each tungsten carbide particle.

[0044] (C2) Based on all tungsten carbide particles in the five measurement fields, the median area of ​​the tungsten carbide particles and the coefficient of variation of the tungsten carbide particle areas are measured. In the present disclosure, the median area of ​​the tungsten carbide particles and the coefficient of variation of the tungsten carbide particle areas measured above correspond to the median area of ​​the tungsten carbide particles and the coefficient of variation of the tungsten carbide particle areas in the cross section of the cemented carbide.

[0045] 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 above measurement is performed multiple times by changing the selected location of the measurement field.

[0046] <Binded 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.

[0047] The method for measuring the cobalt content of the binder phase is as follows: An element mapping image and a binarized image are obtained by the same methods as (A1) to (E1) of the method for measuring the first hard phase content, binder phase content, and second hard phase content of the cemented carbide described above. The element mapping image and the binarized image are superimposed to identify the binder phase region in the element mapping image. A rectangular measurement field of view of 24.9 μm × 18.8 μm is set in the element mapping image. The cobalt content is measured in the binder phase region in the measurement field of view. The above measurement is performed in five different, non-overlapping measurement fields of view. In the present disclosure, the average of the cobalt contents in the binder phase region in the five measurement fields of view corresponds to the binder phase cobalt content.

[0048] 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 above measurement is performed multiple times by changing the selected location of the measurement field.

[0049] In the cemented carbide of embodiment 1, the binder phase may further contain at least one first element selected from the group consisting of silicon, germanium, rhenium, and ruthenium. This improves the deformation resistance of the binder phase. The binder phase may consist of cobalt and the first element.

[0050] In the cemented carbide of embodiment 1, the binder phase may contain, in addition to cobalt and the first element, at least one second element selected from the group consisting of iron, nickel, and chromium. The binder phase may consist of cobalt, the first element, and the second element.

[0051] <Second hard phase> ≪Composition≫ In embodiment 1, the second hard phase is composed of at least one first compound selected from the group consisting of TiNbC, TiNbN, and TiNbCN. In the present disclosure, each of TiNbC, TiNbN, and TiNbCN is not limited to a case where the ratio of the total number of Ti and Nb atoms to the total number of C and N atoms is 1:1, and may include any conventionally known ratio as long as it does not impair the effects of the present disclosure.

[0052] The second hard phase may contain metal elements such as tungsten (W), chromium (Cr), and cobalt (Co) within a range that does not impair the effects of the present disclosure. The total content of W, Cr, and Co in the second hard phase may be 0% by mass or more and less than 0.1% by mass. The contents of W, Cr, and Co in the second hard phase are measured by ICP optical emission spectroscopy.

[0053] The composition of the second hard phase was measured as follows. (A3) An arbitrary position of the cemented carbide is thinned using an ion slicer (device: IB09060CIS (trademark) manufactured by JEOL Ltd.) to prepare a sample with a thickness of 30 nm to 100 nm. The acceleration voltage of the ion slicer is 6 kV for thinning and 2 kV for finish processing.

[0054] (B3) The above sample is observed at 50,000x magnification using a scanning transmission electron microscope (STEM) (JFM-ARM300F (trademark) manufactured by JEOL Ltd.) to obtain a STEM-HAADF (HAADF: high-angle annular dark field) image. The imaging area for the STEM-HAADF image is set to the center of the sample, i.e., a position that does not include areas with properties clearly different from the bulk part, such as the vicinity of the surface of the cemented carbide (a position where the entire imaging area is the bulk part of the cemented carbide). The measurement condition is an acceleration voltage of 200 kV.

[0055] (C3) Next, elemental mapping analysis is performed on the STEM-HAADF image using EDX attached to the STEM to obtain an elemental mapping image. In the elemental mapping image, regions where titanium (Ti) and niobium (Nb) and one or both of carbon (C) and nitrogen (N) exist are identified as the second hard phase, and the composition of the second hard phase is identified.

[0056] 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 above measurement is performed multiple times by changing the selected location of the measurement field.

[0057] <Median area and coefficient of variation of the area of ​​the second hard phase> In the cross section of the cemented carbide of embodiment 1, the median area of ​​the second hard phase is 0.003 μm 2 More than 0.050μm 2 The median area of ​​the second hard phase is 0.010 μm or less, and the coefficient of variation of the area of ​​the second hard phase may be 0.50 or more and 3.00 or less. 2 More than 0.050μm 2 The coefficient of variation of the area of ​​the second hard phase may be 1.10 or more and 2.90 or less. The median value of the area of ​​the second hard phase and the coefficient of variation of the area of ​​the second hard phase may be an appropriate combination of the above ranges.

[0058] In the present disclosure, the median area and coefficient of variation of the area of ​​the second hard phase in the cross section of a cemented carbide are measured in the same manner as in the above-mentioned method for measuring the median area and coefficient of variation of the area of ​​tungsten carbide particles in the cross section of a cemented carbide, except that the region where the second hard phase exists is identified in the image after binarization processing, the area of ​​the second hard phase is measured, and the median area and coefficient of variation of the area of ​​the second hard phase are measured based on all the second hard phases in five measurement fields. As long as the measurement is performed on the same sample, it has been confirmed that there is almost no variation in the measurement results even if the above measurement is performed multiple times by changing the selected location of the measurement field.

[0059] <Hardness> Hardness H of the cemented carbide of embodiment 1 at 25 ° C. 25 Hardness H at 200℃ 200 Percentage of (H 200 / H 25 ) x 100 is between 85% and 100%. 200 / H 25 ) × 100 may be 87% or more and 100% or less, 90% or more and 100% or less, or 90% or more and 98% or less.

[0060] Hardness H of the cemented carbide of embodiment 1 at 25 ° C. 25 may be 12 GPa or more and 25 GPa or less, 13 GPa or more and 24 GPa or less, or 14 GPa or more and 23 GPa or less.

[0061] Hardness H of the cemented carbide of embodiment 1 at 200 ° C. 200 may be 10 GPa or more and 25 GPa or less, 11 GPa or more and 24 GPa or less, or 12 GPa or more and 23 GPa or less.

[0062] In this disclosure, the hardness H of the cemented carbide at 25 ° C. 25 and hardness H at 200°C 200is measured using a high-temperature micro Vickers hardness tester (HTM-1200 (trademark) manufactured by Intesco Co., Ltd.). First, the indenter temperature and the sample temperature are set to 25°C, and the hardness H of the sample made of cemented carbide at 25°C is measured. 25 Next, the indenter temperature and specimen temperature are set to 200°C, and the hardness H of the cemented carbide at 200°C is measured. 200 The temperature rise rate of the indenter and sample is 20°C / min. The measurement is carried out in a vacuum atmosphere. After reaching the set temperature, the set temperature is maintained for 5 minutes, and then the measurement is carried out. The measurement conditions are a load of 1000gf, maintained for 30 seconds. The hardness H is measured at 10 points on one sample. 25 and hardness H 200 In this disclosure, the hardness H 25 The average of these is the hardness H of the cemented carbide 25 In this disclosure, the hardness H 200 The average of these is the hardness H of the cemented carbide 200 This applies to:

[0063] As long as the measurement is performed on the same sample, it has been confirmed that there is almost no variation in the measurement results even if the above measurement is performed multiple times at different measurement locations.

[0064] <ratio c / M> The ratio c / M of the specific heat c (J / g K) of the cemented carbide at 200°C to the mass content M (mass%) of the binder phase of the cemented carbide of embodiment 1 is 0.028 or more and 0.042 or less, or may be 0.030 or more and 0.042 or less, or may be 0.032 or more and 0.040 or less.

[0065] The mass-based content M of the binder phase in the cemented carbide of embodiment 1 is 3.0 mass % or more and 13.0 mass % or less, or may be 3.5 mass % or more and 12.5 mass % or less, or may be 4.0 mass % or more and 12.0 mass % or less.

[0066] The method for measuring the mass-based binder phase content M of a cemented carbide is as follows: An element mapping image and a binarized image are obtained by the same methods as (A1) to (E1) of the above-mentioned method for measuring the first hard phase content, binder phase content, and second hard phase content of a cemented carbide. The element mapping image and the binarized image are superimposed to identify the region where the binder phase is present in the element mapping image. A rectangular measurement field of view of 24.9 μm × 18.8 μm is set in the element mapping image. The mass-based binder phase content relative to the entire measurement field of view is measured based on the element mapping image. The above measurement is performed in five different, non-overlapping measurement fields of view. In the present disclosure, the average of the mass-based binder phase contents in the five measurement fields of view corresponds to the mass-based binder phase content M of the cemented carbide.

[0067] As long as the measurement is performed on the same sample, it has been confirmed that there is almost no variation in the measurement results even if the above measurement is performed multiple times at different measurement locations.

[0068] The specific heat c of the cemented carbide at 200°C may be 0.095 J / g·K or more and 0.522 J / g·K or less, or 0.200 J / g·K or more and 0.330 J / g·K or less.

[0069] In the present disclosure, the specific heat c of cemented carbide at 200°C is measured using a simultaneous thermogravimetry / differential thermal analyzer ("STA 449 F3" (trademark) manufactured by Netsch Japan). The atmosphere during measurement is an Ar flow of 100 mL / min. Measurement is performed in 50°C steps.

[0070] <Method of manufacturing cemented carbide> The cemented carbide of embodiment 1 can be manufactured by carrying out the steps of preparing raw material powder, mixing, molding, sintering, HIP (Hot Isostatic Pressing), and reheat treatment in the above order. Each step will be described below.

[0071] <Preparation process> The preparation step is a step of preparing raw material powders of materials that constitute the cemented carbide. Examples of raw material powders include tungsten carbide powder (hereinafter also referred to as "WC powder") and Co powder. The WC powders used are "WC04NRP" (average particle size by the Fischer method: 0.45 μm to 0.49 μm) and "WC02NP" (equivalent particle size by the BET method: 0.10 μm to 0.13 μm), manufactured by A.L.M.T. Corporation, in a mass ratio of WC04NRP:WC02NP = 1:1. The average particle size of the Co powder is 5 μm.

[0072] Further examples of raw material powders that can be prepared include VC powder, Cr3C2 powder, TiO2 powder, Nb2O5 powder, TiN powder, Ni powder, Ru powder, Re powder, Si powder, and TiCN powder. 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. The average particle size of the raw material powder refers to the average particle size measured by the FSSS (Fisher Sub-Sieve Sizer) method. The average particle size is measured using a Fisher Scientific "Sub-Sieve Sizer Model 95" (trademark).

[0073] <Mixing process> The mixing step is a step of mixing the raw material powders prepared in the preparation step in a predetermined ratio to obtain a mixed powder. The mixing ratio of the raw material powders is appropriately adjusted depending on the target composition of the cemented carbide.

[0074] An attritor is used to mix the raw material powders. The mixing conditions are a rotation speed of 200 rpm, a ball diameter of φ3 mm, and a mixing time of 12 hours.

[0075] After the mixing step, the mixed powder may be granulated as necessary. Granulating the mixed powder makes it easier to fill the mixed powder into a die or mold during the molding step described below. A known granulation method can be applied to the granulation, and for example, a commercially available granulator such as a spray dryer can be used.

[0076] <Forming process> The forming process is a process of forming the mixed powder 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.

[0077] <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 sintering furnace and heated to 1380°C at a heating rate of 20°C / min under a vacuum or nitrogen atmosphere and held at 1380°C for 2 hours. Subsequently, the formed body is cooled to 1000°C at a cooling rate of -5°C / min. The above heating and cooling are repeated 5 sets. Subsequently, the formed body is cooled to 25°C at a cooling rate of -20°C / min to obtain a cemented carbide intermediate.

[0078] <HIP Process> The HIP process is a process of performing HIP on the cemented carbide intermediate. The conditions for HIP are holding at 200 MPa and 1300°C for 2 hours in an Ar atmosphere.

[0079] <Post-Heat Treatment Process> The post-heat treatment process is a process of performing heat treatment on the cemented carbide intermediate after the HIP process and then cooling it to obtain the cemented carbide of Embodiment 1. The post-heat treatment conditions are holding at 1100°C for 2 hours in a vacuum. The cooling conditions can use conventionally known conditions. <00,003,36>

[0080] <Features of the Manufacturing Method of the Cemented Carbide of Embodiment 1> In the manufacturing method of the cemented carbide of Embodiment 1, two types of WC powders with different particle sizes are used as the WC powder. Thereby, the cemented carbide structure is densified, and the hardness and heat resistance of the cemented carbide at 200°C are improved.

[0081] In the mixing process of the manufacturing method of the cemented carbide of Embodiment 1, the raw material powder is mixed for a long time using fine balls. Thereby, the pulverization of the raw material powder progresses, the sinterability of the cemented carbide is improved, and the hardness and heat resistance of the cemented carbide at 200°C are improved. <,

[0082] In the sintering step of the method for producing a cemented carbide according to the first embodiment, five sets of heating to 1380°C at a heating rate of 20°C / min, holding the temperature for two hours, and cooling to 1000°C at a cooling rate of -5°C / min are repeated. This results in rearrangement of the structure due to softening of the binder phase, improving the heat resistance of the cemented carbide at 200°C. In a conventional general sintering step, only one set of heating and cooling is performed. In this case, the heat resistance of the cemented carbide is insufficient because rearrangement of the structure due to softening of the binder phase does not occur.

[0083] In the HIP step of the method for producing a cemented carbide according to embodiment 1, low-temperature, high-pressure HIP is performed. This densifies the structure of the cemented carbide and improves the hardness of the cemented carbide at 200°C. In conventional methods for producing cemented carbide, HIP is often not performed to reduce costs, or even when HIP is performed, the pressure is low (e.g., 10 MPa), resulting in insufficient hardness of the cemented carbide at 200°C.

[0084] The method for producing a cemented carbide according to the first embodiment includes a reheat treatment step. The reheat treatment step can remove impurities from the structure of the cemented carbide intermediate after the HIP step. This improves the hardness of the cemented carbide at 200°C. In conventional methods for producing cemented carbide, the reheat treatment step is not performed, and therefore the hardness of the cemented carbide at 200°C is insufficient.

[0085] The inventors have found, as a result of extensive research, that the cemented carbide of the present disclosure can be realized by employing the above manufacturing process.

[0086] [Embodiment 2: Cutting Tool] A cutting tool according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 2") includes a cutting edge made of the cemented carbide of Embodiment 1. In this disclosure, the cutting edge refers to the portion involved in cutting. More specifically, the cutting edge refers to the region surrounded by the cutting edge ridge and an imaginary plane that is 0.5 mm or 2 mm away from the cutting edge ridge toward the cemented carbide.

[0087] Examples of cutting tools include cutting tools, drills, end mills, indexable cutting inserts for milling, indexable cutting inserts for turning, metal saws, gear cutting tools, reamers, taps, etc. As shown in Fig. 1, the cutting tool 10 of the second embodiment can exhibit excellent effects, particularly in the case of an end mill. The cutting edge 11 of the cutting tool 10 shown in Fig. 1 is made of the cemented carbide of the first embodiment.

[0088] In the cutting tool of Embodiment 2, the cemented carbide of Embodiment 1 may constitute the entire tool or may constitute a part of the tool. Here, "constitute a part" refers to a mode in which the cemented carbide of Embodiment 1 is brazed to a predetermined position of any substrate to form a cutting edge, etc.

[0089] 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. The hard film may be made of, for example, diamond-like carbon or diamond.

[0090] The cutting tool of the second embodiment can be obtained by forming the cemented carbide of the first embodiment into a desired shape. [Example]

[0091] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0092] [Preparation of cemented carbide] Each sample of cemented carbide was prepared according to the following procedure. <Preparation process> The raw material powders were prepared in the proportions shown in Table 1: "WC04NRP" (average particle size 0.45 μm to 0.49 μm by the Fischer method) and "WC02NP" (equivalent particle size 0.10 μm to 0.13 μm by the BET method) manufactured by A.L.M.T. Corporation, Co powder (manufactured by Kojundo Chemical, average particle size 5 μm), VC powder, Cr3C2 powder, TiO2 powder, Nb2O5 powder, TiN powder, Ni powder, Ru powder, Re powder, Si powder, Ge powder, and TiCN powder. The proportions (mass %) of each raw material powder listed in Table 1 are the proportions when the total amount of raw material powder is taken as 100 mass %. The average particle size of the raw material powders other than WC powder and Co powder is 1 μm.

[0093] [Table 1]

[0094] <Mixing process> In the mixing process, each raw material powder was mixed under the following conditions A or B. The conditions used for each sample are shown in Table 2. Condition B is a conventional general mixing condition. A: An attritor is used. The mixing conditions are a rotation speed of 200 rpm, a ball diameter of φ3 mm, and a mixing time of 12 hours. B: An attritor was used. The mixing conditions were a rotation speed of 100 rpm, a ball diameter of 6 mm, and a mixing time of 6 hours.

[0095] <Forming process> The mixed powder was pressed to obtain a round bar-shaped compact.

[0096] <Sintering process> Place the green compact in a sintering furnace, and under the conditions described in the "atmosphere" column of "sintering" in Table 2 (where "vac" means vacuum and "N2" means nitrogen atmosphere), heat it at a heating rate of 20 °C / min to the temperature described in the "temperature" column of Table 2, and hold it at that temperature for the time described in the "time" column. Subsequently, cool the green compact to 1000 °C at the cooling rate described in the "cooling rate" column of Table 2. Repeat the above heating and cooling for the number of times described in the "set number" column of Table 2. Subsequently, cool the green compact to 25 °C at a cooling rate of -20 °C / min to obtain a cemented carbide intermediate. The notation that the "set number" of sample 102 is "0" indicates that the green compact was heated in vacuum at a heating rate of 20 °C / min to 1400 °C, held at 1400 °C for 1 hour, and then cooled to 25 °C at a cooling rate of -20 °C / min.

[0097] [Table 2]

[0098] <HIP process> Perform HIP on the cemented carbide intermediate under the conditions described in the "HIP" column of Table 3.

[0099] <Post heat treatment process> For samples marked "yes" in the "post heat treatment" column of Table 3, perform heat treatment on the cemented carbide intermediate after the HIP process, hold it in vacuum at 1100 °C for 2 hours, and then cool it to obtain a cemented carbide. For samples marked "no", no post heat treatment was performed.

[0100] [Table 3]

[0101] [Evaluation of cemented carbide] <Content ratio of the first hard phase, content ratio of the binder phase, and content ratio of the second hard phase of the cemented carbide> The content (volume %) of the first hard phase, the content (volume %) of the binder phase, and the content (volume %) of the second hard phase of each sample of cemented carbide were measured by the method described in embodiment 1. The results are shown in Table 4. In Table 4, it was confirmed that cemented carbide having a total content of the first hard phase, the binder phase, and the second hard phase of less than 100 volume % further contained a phase based on VC or Cr3C2 (e.g., a (Cr,W,V)C phase) and / or a TiCN phase.

[0102] [Table 4]

[0103] <Median area and coefficient of variation of area of ​​tungsten carbide particles, cobalt content of binder phase, composition of secondary hard phase, median area, and coefficient of variation of area> For each sample of cemented carbide, the median area and coefficient of variation of the tungsten carbide particles, the cobalt content of the binder phase, the composition of the second hard phase, and the median area and coefficient of variation of the second hard phase were measured by the method described in embodiment 1. The results are shown in Table 5. The cobalt content of the cemented carbide was calculated from the cobalt content of the binder phase. The results are shown in Table 4.

[0104] [Table 5]

[0105] <Hardness> The hardness H of each cemented carbide sample at 25°C 25 and hardness H at 200°C 200 is measured by the method of embodiment 1, and the percentage (H 200 / H 25 ) × 100 was calculated. The results are shown in Table 6.

[0106] <c m> For each sample of cemented carbide, the mass content M of the binder phase and the specific heat c at 200°C were measured by the method described in embodiment 1, and the ratio c / M was calculated. The results are shown in Table 6.

[0107] [Table 6]

[0108] [Cutting test] Each cemented carbide round bar was machined to create a ball end mill with a cutting diameter of 6 mm. The ball end mill was used to machine the side of a workpiece made of SKD51. The machining conditions were a cutting speed Vc of 150 m / min, a feed rate fz of 0.02 mm / tooth, an axial depth of cut ap of 0.1 mm, and a radial depth of cut ae of 0.1 mm, all in dry conditions. The cutting length was measured until the flank wear of the cutting tool reached 100 μm. A cutting length of 30 m or more was considered to be a long tool life. Longer cutting lengths indicate longer tool life. The results are shown in the "Cutting Length" column of the "Cutting Test" section in Table 6. The above machining conditions apply to the finish machining of die steel.

[0109] [Consideration] The cemented carbide alloys and cutting tools of Samples 1 to 12 correspond to Examples. It was confirmed that these cutting tools had long tool lives. The cemented carbide alloys and cutting tools of Samples 101 to 109 correspond to Comparative Examples. These cutting tools had insufficient tool lives.

[0110] Although the embodiments and examples of the present disclosure have been described above, it is originally intended 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 embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims. [Explanation of symbols]

[0111] 10 Cutting tools, 11 Cutting edges.< / c>

Claims

1. A cemented carbide comprising a first hard phase consisting of a plurality of tungsten carbide particles and a binder phase containing cobalt, The total content of the first hard phase and the binder phase of the cemented carbide is 80.0% by volume or more, The content of the binder phase in the cemented carbide is 5.0 vol% or more and 21.0 vol% or less, the cobalt content of the binder phase is 50% by mass or more; The hardness H of the cemented carbide at 25°C ２５ Hardness H at 200 ° C. ２００ Percentage of (H ２００ / H ２５ ) × 100 is equal to or greater than 85% and equal to or less than 100%, a ratio c / M of the specific heat c of the cemented carbide at 200°C to the mass content M of the binder phase of the cemented carbide is 0.028 or more and 0.042 or less, The mass-based content M of the binder phase of the cemented carbide is 3.0 mass% or more and 13.0 mass% or less, The cemented carbide, wherein the unit of the specific heat c is J / g·K.

2. The percentage (H ２００ / H ２５ ) × 100 is 90% or more and 100% or less, the ratio c / M is equal to or greater than 0.030 and equal to or less than 0.042, The cemented carbide further comprises a second hard phase, 2. The cemented carbide according to claim 1, wherein the second hard phase comprises at least one first compound selected from the group consisting of TiNbC, TiNbN, and TiNbCN.

3. In the cross section of the cemented carbide, the median area of ​​the second hard phase is 0.003 μm ２ 0.050 μm or more ２ is as follows: The cemented carbide according to claim 2, wherein the coefficient of variation of the area of ​​the second hard phase is 0.50 or more and 3.00 or less.

4. In the cross section of the cemented carbide, the median area of ​​the tungsten carbide particles is 0.080 μm ２ 0.150 μm or more ２ is as follows:

4. The cemented carbide according to claim 1, wherein the coefficient of variation of the area of ​​the tungsten carbide particles is 0.85 or more and 1.10 or less.

5. A cutting tool having a cutting edge made of the cemented carbide according to claim 1 or 2.

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