Cemented carbide and cutting tool

Abstract

A cemented carbide according to the present disclosure comprises a first hard phase that is composed of a plurality of tungsten carbide particles, and a binder phase that contains cobalt, wherein: the total amount of the first hard phase and the binder phase in the cemented carbide is 80.0 vol% or greater; the amount of the binder phase in the cemented carbide is 5.0-21.0 vol%; the cobalt content of the binder phase is 50 mass% or greater; the percentage ((H200 / H25) × 100) of the hardness H200 of the cemented carbide at 200°C with respect to the hardness H25 of the cemented carbide at 25°C is 85-100%; the ratio c / M of the specific heat c of the cemented carbide at 200°C with respect to the mass-based amount M of the binder phase in the cemented carbide is 0.028-0.042; the mass-based amount M of the binder phase in the cemented carbide is 3.0-13.0 mass%; and the units of the specific heat are J / g⋅K.

Description

Carbide alloys and cutting tools

[0001] This disclosure relates to cemented carbide and cutting tools.

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

[0003] Japanese Patent Publication No. 2004-131769

[0004] The cemented carbide alloy of this disclosure comprises a first hard phase consisting of a plurality of tungsten carbide particles and a cobalt-containing binder phase, wherein the total content of the first hard phase and the binder phase of the cemented carbide alloy is 80.0 volume% or more, the content of the binder phase of the cemented carbide alloy is 5.0 volume% or more and 21.0 volume% or less, the cobalt content of the binder phase is 50 mass% or more, and the hardness of the cemented carbide alloy at 25°C is H ２５ Hardness H at 200°C ２００ Percentage of (H ２００ / H ２５ The cemented carbide alloy is such that ) × 100 is 85% or more and 100% or less, the ratio c / M of the specific heat c of the cemented carbide alloy at 200°C to the mass-based content M of the bonding phase of the cemented carbide alloy is 0.028 or more and 0.042 or less, the mass-based content M of the bonding phase of the cemented carbide alloy is 3.0 mass% or more and 13.0 mass% or less, and the unit of the specific heat c is J / g·K.

[0005] Figure 1 is a schematic diagram of a cutting tool according to Embodiment 2.

[0006] [Problems this disclosure aims to solve] From the perspective of cost reduction, there is a need for cemented carbide alloys and cutting tools made therefrom that enable longer tool life, especially when used as materials for cutting tools used in the finishing of die 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, especially when used as a material for cutting tools for finishing die steel.

[0008] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. (1) The cemented carbide of the present disclosure is a cemented carbide comprising a first hard phase composed 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 of the cemented carbide is 80.0% by volume or more, the content of the binder phase of 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 hardness H of the cemented carbide at 25 °C ２５ with respect to the hardness H at 200 °C ２００ percentage of (H ２００ / H ２５ ) × 100 is 85% or more and 100% or less, and the ratio c / M of the specific heat c of the cemented carbide at 200 °C to the content M of the binder phase of the cemented carbide on a mass basis is 0.028 or more and 0.042 or less, and the content M of the binder phase of the cemented carbide on a mass basis is 3.0% by mass or more and 13.0% by mass or less, and the unit of the specific heat c is J / g·K, which is a cemented carbide.

[0009] According to the present disclosure, it is possible to provide a cemented carbide that enables the tool to have a long service life, particularly when used as a material for a cutting tool for finishing die steel. The reason is presumed as follows.

[0010] The cemented carbide of the present disclosure contains a first hard phase composed of tungsten carbide particles and a binder phase containing cobalt in a total amount of 80.0% by volume or more. The content of the binder phase of the cemented carbide is 5.0% by volume or more and 21.0% by volume or less, and the cobalt content of the binder phase is 50% by mass or more. Thereby, the cemented carbide can have hardness and toughness suitable for a cutting tool.

[0011] The percentage of the hardness H of the cemented carbide of the present disclosure at 25 °C ２５ with respect to the hardness H at 200 °C ２００ of (H ２００ / H ２５The value obtained by multiplying by 100 is 85% or more and 100% or less. Generally, the hardness of cemented carbide decreases at high temperatures. However, the cemented carbide of the present disclosure suppresses the decrease in hardness even at 200°C. Therefore, a cutting tool having a cutting edge made of the cemented carbide can have excellent wear resistance even in finish machining using a ball end mill for die steel, where the cutting edge temperature during machining is about 200°C.

[0012] Generally, the metal used for the binder phase of cemented carbide tends to have a large specific heat at high temperatures and is resistant to temperature changes due to the absorption of thermal energy. That is, the metal used for the binder phase has improved heat resistance at high temperatures. On the other hand, the specific heat is affected by the content of the binder phase of the cemented carbide. The ratio c / M of the specific heat c at ២០០°C of the cemented carbide to the content M of the binder phase of the cemented carbide based on mass is an index of heat resistance that does not depend on the content of the binder phase of the cemented carbide. When c / M is 0.028 or more, the heat resistance of the cemented carbide at 200°C is good. When c / M is 0.042 or less, it is not overheated and a decrease in strength can be suppressed. Therefore, a cutting tool having a cutting edge made of the cemented carbide can have excellent heat resistance even in finish machining using a ball end mill for die steel, where the cutting edge temperature during machining is about 200°C.

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

[0014] The percentage (H ２００ / H ２５ ) × 100 being 90% or more and 100% or less further suppresses the decrease in hardness of the cemented carbide at 200°C. Therefore, a cutting tool having a cutting edge made of the cemented carbide can have further excellent wear resistance in finish machining using a ball end mill for die steel, where the cutting edge temperature during machining is about 200°C.

[0015] When a 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. Therefore, a cutting tool equipped with a cutting edge made of this cemented carbide can have even better heat resistance and wear resistance.

[0016] (3) In (1) or (2) above, the median area of ​​the second hard phase in the cross-section of the cemented carbide is 0.003 μm ２ 0.050 μm or more ２ 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 the cemented carbide can have even better heat resistance and wear resistance.

[0017] (4) In any of (1) to (3) above, the median area of ​​the tungsten carbide particles in the cross-section of the cemented carbide is 0.080 μm ２ 0.150 μm or more ２ The 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 the hardness and strength of the cemented carbide. Therefore, a cutting tool equipped with a cutting edge made of this cemented carbide can have even better wear resistance.

[0018] (5) The cutting tool of this disclosure is a cutting tool having an cutting edge made of a cemented carbide as described in any of (1) to (4) above. The cutting tool of this disclosure can have a long life, especially when used for finishing die steel.

[0019] [Details of Embodiments of the Disclosure] Specific examples of cemented carbide and cutting tools of the Disclosure will be described below with reference to the drawings. In the drawings of the Disclosure, the same reference numerals indicate the same or equivalent part. In addition, dimensional relationships such as length, width, thickness, and depth have been modified as appropriate for clarity and simplification of the drawings and do not necessarily represent actual dimensional relationships.

[0020] In this disclosure, the notation "A to B" means A or greater and B or less. If no unit is specified for A, and only a unit is specified for B, then the unit for A and the unit for B are the same.

[0021] In this disclosure, when compounds and the like are represented by chemical formulas, unless otherwise specified, the atomic ratios should include all conventionally known atomic ratios and should not necessarily be limited to those within the stoichiometric range.

[0022] In this disclosure, if one or more numerical values ​​are listed as the lower limit and upper limit of a numerical range, any combination of any one numerical value listed as the lower limit and any one numerical value listed as the upper limit shall also be disclosed.

[0023] In this disclosure, “equipment,” “includes,” “possesses,” and variations thereof are open-ended terms. Open-ended terms may or may not include additional elements in addition to the essential elements. The statement “consists of” is a closed term. However, even a configuration expressed in closed terms may include additional elements that are usually incidental or irrelevant to the subject technology.

[0024] [Embodiment 1: Carbide Alloy] The carbide alloy of one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") is a carbide alloy 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 carbide alloy is 80.0 volume% or more. The content of the binder phase of the carbide alloy is 5.0 volume% or more and 21.0 volume% or less. The cobalt content of the binder phase is 50 mass% or more. Hardness of the carbide alloy at 25°C H ２５ Hardness H at 200°C ２００ Percentage of (H ２００ / H ２５ ) × 100 is between 85% and 100%. The ratio of the specific heat c of cemented carbide at 200°C to the mass-based content M of the bonding phase of cemented carbide, c / M, is between 0.028 and 0.042. The mass-based content M of the bonding phase of cemented carbide is between 3.0 mass% and 13.0 mass%. The unit of specific heat c is J / g·K.

[0025] <Composition of the 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 the binder phase of the cemented carbide is 80.0 volume% or more, and may be 82 volume% to 100 volume%, 82 volume% to 99 volume%, 92 volume% to 98 volume%, or 94 volume% to 97 volume%.

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

[0027] The cemented carbide of Embodiment 1 may contain a second hard phase in addition to the first hard phase and the binder phase. The second hard phase consists 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 greater than 0 vol% and 20 vol% or less, 1 vol% to 18 vol% or less, 2 vol% to 8 vol% or less, or 3 vol% to 6 vol% or less.

[0028] The cemented carbide of Embodiment 1 may consist of a first 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 binder phase and impurities. The cemented carbide of Embodiment 1 may consist of a first hard phase, a binder phase and a second 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 binder phase, a second hard phase and impurities.

[0029] 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.

[0030] The method for measuring the content of the first hard phase, the binder phase, and the second hard phase of cemented carbide is as follows: (A1) Cut out a section of 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.).

[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 imaging area is set to the central part of the cross-section of the cemented carbide, that is, 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.

[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 image after binarization, the first region consisting of the first hard phase and the second region consisting of the bonded phase and the second hard phase can be distinguished by the intensity of the colors. For example, in the image after binarization, the first hard phase is shown as a black region, and the bonded phase and the second hard phase are shown as white regions.

[0033] (D1) The imaging area described in (B1) above is analyzed using an energy-dispersive X-ray spectrometer (SEM-EDX) attached to the scanning electron microscope (instrument: Carl Zeiss Gemini 450™) to obtain an elemental mapping image.

[0034] (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, the bonded phase, and the second hard phase exist are identified on the binarized image. Regions shown in black in the binarized image and where tungsten (W) and carbon (C) exist in the elemental mapping image correspond to the regions where the first hard phase exists. Regions shown in white in the binarized image and where cobalt (Co) exists in the elemental mapping image correspond to the regions where the bonded phase exists. Regions shown in white in the binarized image and where titanium (Ti) or niobium (Nb) exists in the elemental 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 binarized image. Using the image analysis software described above, the area percentages of the first hard phase, the binding phase, and the second hard phase are measured, with the total area of ​​the measurement field of view as the denominator.

[0036] (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 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 second hard phase in the five measurement fields corresponds to the content (volume %) of the second hard phase in the cemented carbide.

[0037] 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.

[0038] <First Hard Phase> <Composition> In the cemented carbide of Embodiment 1, the first hard phase consists of a plurality of tungsten carbide particles (hereinafter also referred to as "WC particles"). The tungsten carbide particles include not only "pure WC particles (WC that do not contain any impurity elements, and WC in which the content of impurity elements is below the detection limit)" but also "WC particles that contain impurities internally, as long as the effects of this disclosure are not impaired." Examples of impurities include iron (Fe), molybdenum (Mo), and sulfur (S).

[0039] <<Median Area and Coefficient of Variation of Tungsten Carbide Particle Area>> In the cross-section of the cemented carbide alloy of Embodiment 1, the median area of ​​the tungsten carbide particles is 0.080 μm ２ 0.150 μm or more ２ The following conditions apply, and the coefficient of variation of the area of ​​the tungsten carbide particles may be between 0.85 and 1.10. The median area of ​​the tungsten carbide particles is 0.085 μm. ２ 0.140 μm or more ２ The following is also acceptable, or 0.100 μm ２ 0.125 μm or more ２ The following are also acceptable: 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 a combination of the above ranges as appropriate.

[0040] In this disclosure, the median area of ​​tungsten carbide particles refers to the area where the cumulative frequency of tungsten carbide particle areas, based on the number of particles, reaches 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 mean area of ​​tungsten carbide particles (standard deviation / mean). The mean area of ​​tungsten carbide particles refers to the arithmetic mean of the area of ​​tungsten carbide particles. The median area and coefficient of variation of the area of ​​the second hard phase described later have the same meaning.

[0041] In this 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 the 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 binder phase, and the second hard phase of the cemented carbide described above, the region where the first hard phase exists is identified in the binarized image.

[0043] (B2) Prepare five binarized images in which the region of the first hard phase is identified, and set a rectangular measurement field of view of 40.3 μm vertically × 30.2 μm horizontally in each image. Use image analysis software (ImageJ ver. 1.51J8) to identify the outer edge of each tungsten carbide particle in the measurement field of view 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 area are measured. In this disclosure, the median area of ​​the tungsten carbide particles and the coefficient of variation of the tungsten carbide particle area measured above correspond to the median area of ​​the tungsten carbide particles and the coefficient of variation of the tungsten carbide particle area in the cross-section of the cemented carbide.

[0045] 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.

[0046] <Bonding Phase> In the cemented carbide of Embodiment 1, the cobalt content of the bonding phase is 50% by mass or more. This allows the cemented carbide to have excellent toughness. The cobalt content of the bonding 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 elemental mapping image and a binarized image are acquired in the same manner as (A1) to (E1) of the above-described methods for measuring the content of the first hard phase, the binder phase, and the second hard phase of the cemented carbide. 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.

[0048] 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.

[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 can consist of cobalt and the first element.

[0050] In the cemented carbide of Embodiment 1, the binder phase may include, 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 consists of at least one first compound selected from the group consisting of TiNbC, TiNbN, and TiNbCN. In this disclosure, each of TiNbC, TiNbN, and TiNbCN is not limited to the 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 conventionally known ratios as long as they do not impair the effects of this disclosure.

[0052] The second hard phase may contain metallic elements such as tungsten (W), chromium (Cr), and cobalt (Co) to the extent that it does not impair the effects of this 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 content of W, Cr, and Co in the second hard phase is measured by ICP emission spectrometry.

[0053] The method for measuring the composition of the second hard phase is as follows: (A3) A sample with a thickness of 30 nm to 100 nm is prepared by thinning an ion slicer (device: IB09060CIS™ manufactured by JEOL Ltd.) at an arbitrary position on the cemented carbide. The acceleration voltage of the ion slicer is 6 kV for thinning and 2 kV for finishing.

[0054] (B3) The above sample is observed at 50,000x magnification using a scanning transmission electron microscope (STEM) (JFM-ARM300F™ manufactured by JEOL Ltd.) to obtain a STEM-HAADF (HAADF: high-angle angular dark field) image. The imaging area for the STEM-HAADF image is set to the central part of the sample, that is, a position that does not include parts with properties clearly different from the bulk portion, such as the vicinity of the surface of the cemented carbide (a position where the entire imaging area is the bulk portion 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 the EDX attached to the STEM to obtain an elemental mapping image. In the elemental mapping image, the region containing titanium (Ti) and niobium (Nb), and one or both of carbon (C) and nitrogen (N) is identified as the second hard phase, and the composition of the second hard phase is determined.

[0056] 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.

[0057] <Median area and coefficient of variation 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 0.050 μm or more ２The following conditions apply, and the coefficient of variation of the area of ​​the second hard phase may be between 0.50 and 3.00. The median area of ​​the second hard phase is 0.010 μm². ２ 0.050 μm or more ２ The following is also acceptable: The coefficient of variation of the area of ​​the second hard phase may be between 1.10 and 2.90. The median area of ​​the second hard phase and the coefficient of variation of the area of ​​the second hard phase may be a combination of the above ranges as appropriate.

[0058] In this disclosure, the median area of ​​the second hard phase and the coefficient of variation of the area of ​​the second hard phase in the cross-section of the cemented carbide are measured in the same manner as the above-described 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 the cemented carbide, except that the region where the second hard phase exists is identified in the image after binarization, the area of ​​the second hard phase is measured, and the median area of ​​the second hard phase and the coefficient of variation of the area of ​​the second hard phase are measured based on all of the second hard phase in the five measurement fields. 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 location of the measurement field.

[0059] <Hardness> Hardness H of the cemented carbide of Embodiment 1 at 25°C ２５ Hardness H at 200°C ２００ Percentage of (H ２００ / H ２５ ) × 100 is between 85% and 100%. Percentage (H 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 The glucose level may be between 12 GPa and 25 GPa, between 13 GPa and 24 GPa, or between 14 GPa and 23 GPa.

[0061] Hardness H of the cemented carbide of Embodiment 1 at 200°C ２００ The pressure may be between 10 GPa and 25 GPa, between 11 GPa and 24 GPa, or between 12 GPa and 23 GPa.

[0062] In this disclosure, the hardness H of cemented carbide at 25°C ２５ and hardness H at 200°C ２００ The hardness is measured using a high-temperature micro-Vickers hardness tester (Intesco "HTM-1200" trademark). First, the indenter temperature and sample temperature are set to 25°C, and the hardness H of the cemented carbide sample at 25°C is measured. ２５ Next, the indenter temperature and sample temperature are set to 200°C to measure the hardness H of the cemented carbide at 200°C. ２００ The hardness H is measured at 10 locations on each sample. The heating rate of the indenter and sample is 20°C / min. The measurement is performed in a vacuum atmosphere. After reaching the set temperature, the set temperature is maintained for 5 minutes before measurement. The measurement conditions are a load of 1000 gf held for 30 seconds. For each sample, the hardness H is measured at 10 locations. ２５ and hardness H ２００ The hardness H of 10 locations is measured. ２５ The average hardness of cemented carbide is H ２５ This applies to the following. In this disclosure, the hardness H of 10 locations ２００ The average hardness of cemented carbide is H ２００ This applies.

[0063] As long as the measurements are 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 with 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-based content M (mass%) of the bonding phase of the cemented carbide in Embodiment 1 is 0.028 or more and 0.042 or less, and may be 0.030 or more and 0.042 or less, or 0.032 or more and 0.040 or less.

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

[0066] The method for measuring the mass-based content M of the binder phase in a cemented carbide is as follows: An elemental mapping image and a binarized image are acquired in the same manner as (A1) to (E1) of the above-described methods for measuring the content of the first hard phase, the binder phase, and the second hard phase of the cemented carbide. 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. Based on the elemental mapping image, the mass-based content of the binder phase relative to the entire measurement field is measured. The above measurement is performed in five different measurement fields that do not overlap with each other. In this disclosure, the average of the mass-based content of the binder phase in the five measurement fields corresponds to the mass-based content M of the binder phase in the cemented carbide.

[0067] As long as the measurements are 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 with different measurement locations.

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

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

[0070] <Method for Manufacturing Carbide Alloys> The carbide alloy of Embodiment 1 can be manufactured by performing the following steps in the order described above: preparation of raw material powder, mixing, molding, sintering, HIP (Hot Isostatic Pressing) process, and reheat treatment process. Each step will be described below.

[0071] <Preparation Process> The preparation process involves preparing the raw material powders for the cemented carbide. Examples of raw material powders include tungsten carbide powder (hereinafter also referred to as "WC powder") and Co powder. For the WC powder, Allied Material's "WC04NRP" (average particle size 0.45 μm to 0.49 μm by Fischer method) and "WC02NP" (converted particle size 0.10 μm to 0.13 μm by BET method) are used in a mass ratio of WC04NRP:WC02NP = 1:1. The average particle size of the Co powder is 5 μm.

[0072] As raw material powders, further, VC powder, Cr ３ C ２ Powder, TiO ２ powder, Nb ２ O ５ Powders such as TiN powder, Ni powder, Ru powder, Re powder, Si powder, and TiCN 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. The average particle size of the raw material powder refers to the average particle size measured by the FSSS (Fisher Sub-Sievee Sizer) method. This average particle size is measured using the "Sub-Sievee Sizer Model 95" (trademark) manufactured by Fisher Scientific.

[0073] <Mixing Process> The mixing process involves mixing the raw material powders prepared in the preparation process in predetermined proportions to obtain a mixed powder. The mixing ratio of each raw material powder is adjusted as appropriate according to the desired 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 process, the mixed powder may be granulated as needed. Granulating the mixed powder makes it easier to fill the die or mold with the mixed powder during the molding process described later. Known granulation methods can be applied to granulation, and commercially available granulators such as spray dryers can be used.

[0076] <Molding Process> The molding process is a process in which the mixed powder obtained in the mixing process is molded into the shape of a cutting tool to obtain a molded body. The molding method and molding conditions in the molding process can be general methods and conditions and are not particularly limited.

[0077] <Sintering Process> The sintering process is a process in which the molded body obtained in the molding process is sintered to obtain a cemented carbide intermediate. The molded 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 molded body is cooled to 1000°C at a cooling rate of -5°C / min. The above heating and cooling process is repeated 5 times. Subsequently, the molded 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 in which heat treatment (HIP) is performed on cemented carbide intermediates. The HIP conditions are an Ar atmosphere, 200 MPa, and holding at 1300°C for 2 hours.

[0079] <Reheat Treatment Process> The reheat treatment process involves heat-treating the cemented carbide intermediate after the HIP process, followed by cooling to obtain the cemented carbide of Embodiment 1. The reheat treatment conditions are holding at 1100°C for 2 hours in a vacuum. Conventional known cooling conditions can be used.

[0080] <Features of the manufacturing method of cemented carbide in Embodiment 1> In the manufacturing method of cemented carbide in Embodiment 1, two types of WC powder with different particle sizes are used as WC powder. This densifies the structure of the cemented carbide, improving the hardness and heat resistance of the cemented carbide at 200°C.

[0081] In the mixing step of the cemented carbide manufacturing method of Embodiment 1, the raw material powder is mixed for a long time using fine balls. This promotes the disintegration of the raw material powder, improves the sinterability of the cemented carbide, and enhances the hardness and heat resistance of the cemented carbide at 200°C.

[0082] In the sintering process of the cemented carbide manufacturing method of Embodiment 1, heating to 1380°C at a heating rate of 20°C / min and holding for 2 hours, followed by cooling to 1000°C at a cooling rate of -5°C / min, is repeated five times. This causes rearrangement of the microstructure due to softening of the binder phase, improving the heat resistance of the cemented carbide at 200°C. In conventional general sintering processes, heating and cooling were performed only once. In this case, rearrangement of the microstructure due to softening of the binder phase did not occur, resulting in insufficient heat resistance of the cemented carbide.

[0083] In the HIP process of the cemented carbide manufacturing method of Embodiment 1, low-temperature, high-pressure HIP is performed. This densifies the cemented carbide structure and improves the hardness of the cemented carbide at 200°C. In conventional general cemented carbide manufacturing methods, HIP is often omitted from the perspective of cost reduction, or even when HIP is performed, it is at a low pressure (e.g., 10 MPa), resulting in insufficient hardness of the cemented carbide at 200°C.

[0084] The manufacturing method for cemented carbide according to Embodiment 1 includes a reheat treatment step. The reheat treatment step removes impurities from the intermediate structure of the cemented carbide after the HIP (High-Intensity Pressing) step. This improves the hardness of the cemented carbide at 200°C. In conventional general cemented carbide manufacturing methods, the reheat treatment step is not performed, resulting in insufficient hardness of the cemented carbide at 200°C.

[0085] The inventors have discovered, through diligent research, that the cemented carbide described herein can be realized by adopting the manufacturing process described above.

[0086] [Embodiment 2: Cutting Tool] The cutting tool of 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, the cutting edge means the part that is involved in cutting. More specifically, the cutting edge means the region enclosed by the cutting edge ridge and a hypothetical plane whose distance from the cutting edge ridge to the cemented carbide side is 0.5 mm or 2 mm.

[0087] Examples of cutting tools include cutting tools, drills, end mills, replaceable cutting tips for milling, replaceable cutting tips for turning, metal saws, gear cutting tools, reamers, or taps. As shown in Figure 1, the cutting tool 10 of Embodiment 2 can exhibit particularly excellent effects in the case of an end mill. The cutting edge 11 of the cutting tool 10 shown in Figure 1 is made of the cemented carbide alloy of Embodiment 1.

[0088] 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.

[0089] 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.

[0090] The cutting tool of Embodiment 2 can be obtained by shaping the cemented carbide of Embodiment 1 into a desired shape.

[0091] This embodiment will be described in more detail by reference to examples. However, this embodiment is not limited by these examples.

[0092] [Preparation of cemented carbide] Cemented carbide was prepared for each sample using the following procedure. <Preparation Steps> As raw material powders, Allied Material's "WC04NRP" (average particle size 0.45 μm to 0.49 μm by Fischer method) and "WC02NP" (converted particle size 0.10 μm to 0.13 μm by BET method) were used, along with Co powder (High Purity Chemicals, average particle size 5 μm), VC powder, and Cr ３ C ２ Powder, TiO ２ powder, Nb ２ O ５Powders, TiN powder, Ni powder, Ru powder, Re powder, Si powder, Ge powder, and TiCN powder were prepared in the proportions listed in Table 1. The proportions (mass%) of each raw material powder listed in Table 1 are the proportions when the total amount of raw material powder is considered to be 100% by mass. The average particle size of the raw material powders, except for WC powder and Co powder, is 1 μm.

[0093]

[0094] <Mixing Process> In the mixing process, each raw material powder was mixed under either condition A or B below. The conditions used for each sample are shown in Table 2. Condition B is the 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 is used. The mixing conditions are a rotation speed of 100 rpm, a ball diameter of φ6 mm, and a mixing time of 6 hours.

[0095] <Molding Process> A round bar-shaped molded body was obtained by pressing the mixed powder.

[0096] <Sintering Process> The molded body is placed in the sintering furnace and under the conditions described in the "Atmosphere" column of "Sintering" in Table 2 ("vac" means vacuum, and "N" means vacuum). ２ ) means a nitrogen atmosphere.), the molded body was heated at a heating rate of 20°C / min to the temperature indicated in the "Temperature" column of Table 2, and held at that temperature for the time indicated in the "Time" column. Subsequently, the molded body was cooled to 1000°C at the cooling rate indicated in the "Cooling Rate" column of Table 2. The above heating and cooling was repeated the number of times indicated in the "Number of Sets" column of Table 2. Subsequently, the molded body was cooled to 25°C at a cooling rate of -20°C / min to obtain a cemented carbide intermediate. The notation "0" for the "Number of Sets" of sample 102 indicates that the molded body was heated to 1400°C in a vacuum at a heating rate of 20°C / min, held at 1400°C for 1 hour, and then cooled to 25°C at a cooling rate of -20°C / min.

[0097]

[0098] <HIP Process> The cemented carbide intermediate was subjected to HIP under the conditions described in the "HIP" column of Table 3.

[0099] <Reheat Treatment Process> For samples marked "Yes" in the "Reheat Treatment" column of Table 3, the cemented carbide intermediate after the HIP process was heat-treated, held at 1100°C for 2 hours in a vacuum, and then cooled to obtain the cemented carbide. For samples marked "No," no reheat treatment was performed.

[0100]

[0101] [Evaluation of cemented carbide] <Content of first hard phase, content of binder phase, and content of second hard phase of cemented carbide> The content of the first hard phase (volume %), the content of the binder phase (volume %), and the content of the second hard phase (volume %) of each cemented carbide sample were measured using the method described in Embodiment 1. The results are shown in Table 4. In Table 4, cemented carbide in which the sum of the contents of the first hard phase, binder phase, and second hard phase is less than 100 volume percent is VC or Cr ３ C ２ It was confirmed that the system further includes a phase based on (e.g., (Cr,W,V)C phase) and / or a TiCN phase.

[0102]

[0103] <Median area and coefficient of variation of tungsten carbide particles, cobalt content of the binder phase, composition of the second hard phase, median area, and coefficient of variation of area> For each cemented carbide sample, the median area and coefficient of variation of tungsten carbide particles, the cobalt content of the binder phase, the composition of the second hard phase, the median area and coefficient of variation of area of ​​the second hard phase were measured using 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]

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

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

[0107]

[0108] [Cutting Test] Round bars made of cemented carbide for each sample were machined to create ball end mills with a cutting edge diameter of φ6 mm. Side machining of a workpiece made of SKD51 was performed using the ball end mills. The machining conditions were: cutting speed Vc 150 m / min, feed per tooth fz 0.02 mm / tooth, depth of cut (axial) ap 0.1 mm, depth of cut (radial) ae 0.1 mm, and dry cutting. The cutting length until the flank wear of the cutting tool reached 100 μm was measured. A cutting length of 30 m or more is considered to indicate a long tool life. A longer cutting length indicates a longer tool life. The results are shown in the "Cutting Length" column of "Cutting Test" in Table 6. Note that the above machining conditions correspond to the finishing of die steel.

[0109] [Discussion] Samples 1 to 12, consisting of cemented carbide alloys and cutting tools, correspond to the examples. These cutting tools were confirmed to have a long tool life. Samples 101 to 109, consisting of cemented carbide alloys and cutting tools, correspond to the comparative examples. These cutting tools had an insufficient tool life.

[0110] While embodiments and examples of this disclosure have been described above, it is intended from the outset that the configurations of each of the embodiments and examples described above may be combined or modified in various ways as appropriate. 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 equivalences.

[0111] 10 Cutting tool, 11 Cutting edge.

Claims

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

2. The aforementioned percentage (H ２００ / H ２５ The cemented carbide according to claim 1, wherein the ratio c / M is 90% or more and 100% or less, the cemented carbide further comprises a second hard phase, and 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 μm². ２ 0.050 μm or more ２ 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 value of the area of the tungsten carbide particles is 0.080 μm ２ or more and 0.150 μm ２ or less, and the coefficient of variation of the area of the tungsten carbide particles is 0.85 or more and 1.10 or less. The cemented carbide according to any one of claims 1 to 3 5. A cutting tool comprising a cutting edge made of cemented carbide as described in any one of claims 1 to 4.

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