JP2012052237A - Cemented carbide, method for production thereof, and rotating tool using the cemented carbide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cemented carbide having high transverse strength with less variation, and to provide such a rotating tool with the use of the cemented carbide as to have excellent breakage resistance even when used for small diameter drilling or high-feed cutting.SOLUTION: The cemented carbide 1 has a structure such that the tungsten carbide particles 2 with an average particle size of 0.1-0.4 μm are combined by a binding phase 3 consisting mainly of 3-13 mass% cobalt. According to observation by a transmission electron microscope, the number of tungsten carbide particles 4 with the particle size of 0.05 μm or smaller is 10% or less based on the total number of the tungsten carbide particles 2, and the cemented carbide has coercivity of 34,000 to 56,000 A/m and a saturation magnetization rate of 1.35-1.65 μTmin terns of 1 mass% of cobalt. The filtrate prepared by pulverizing the cemented carbide, dissolving a pulverized powder passed through a screen of #20 mesh in a dilute hydrochloric acid (HCl:HO=1:1) of 50°C for 24 h and filtering, contains tungsten in an amount of 8-24 mass%, chrome in 3-6 mass% and vanadium in 0.6-1.5 mass% based on the total metal contents in the filtrate.

Description

  The present invention relates to a cemented carbide, a method for producing the same, and a rotary tool using the same.

  Conventionally, as a material for a printed circuit board drill, the particle size of tungsten carbide particles to which a grain growth inhibitor such as Cr (chromium) or V (vanadium) is added as described in Patent Document 1 is smaller than 1 μm. A so-called ultrafine cemented carbide is mainly used, and a drill having excellent fracture resistance and wear resistance and high hole position accuracy is used by taking advantage of high hardness and high strength.

  Further, in Patent Document 2, a cemented carbide excellent in toughness having high hardness and high bending strength is obtained by further reducing the average particle size of tungsten carbide particles to 0.1 μm or less and containing cobalt in an amount of 15% by mass or more. In addition, Patent Document 3 describes the bending strength by suppressing the generation of tungsten carbide particles (gigantic coal) having a particle diameter of 2 μm or more and a binder phase pool exceeding 1 μm. Patent Document 4 describes that submicron tungsten carbide particles produced by a high-temperature carbonization reaction and a particle size distribution without aggregation are described. The amount of grain growth inhibitor added can be reduced to 1% by mass or less using a narrow cobalt powder, and a cemented carbide with a low carbon content can be produced. There has been described.

  On the other hand, with respect to the drill for processing a printed circuit board, the diameter of the hole to be processed tends to be fined recently as the density of the printed circuit board is increased, and the drill diameter is also required to be reduced.

Japanese Patent Laid-Open No. 61-12847 Japanese Patent Laid-Open No. 7-157837 JP 2001-335876 A Japanese Patent Application Laid-Open No. 2001-515962

  However, as described in Patent Document 1 and Patent Document 2 described above, cemented carbide in which the particle size of tungsten carbide particles is atomized tends to increase the bending strength of the alloy, but tungsten carbide powder, cobalt powder As a result of agglomeration of raw material powders such as additive powders and other additives, the presence of tungsten carbide particles (giant coal) grown in the alloy and a binder phase pool are likely to occur, resulting in large variations in bending strength among products. As the drill diameter becomes smaller, the strength of the drill decreases, and there is something that breaks from the base of the drill before the tip of the drill wears out, resulting in stable drilling. There is a problem in that the number of machining operations is reduced and the tool life cannot be extended, leading to a reduction in tool cost.

  In addition, as described in Patent Document 3, although the variation in bending strength can be reduced simply by controlling the generation of giant coal and a binder phase pool, in order to cope with further reduction in the drill diameter, the bending strength is reduced. It was necessary to further improve the absolute value of the strength.

Furthermore, even in the cemented carbide described in Patent Document 4, the carbon content close to the formation of the η phase cannot be precisely controlled, and this cannot be inspected / determined. The characteristic variation was large.

  Accordingly, an object of the present invention is to provide a cemented carbide having a high bending strength that is stable and excellent in breakage resistance even when used for a small diameter drill or the like, and that uses this. Another object of the present invention is to provide a rotary tool having excellent breakage resistance even for small-diameter drilling and high-feed cutting.

  The present inventor controls the properties of the tungsten carbide raw material powder, cobalt raw material powder, and other additive raw material powders as well as the mixing / pulverizing conditions, firing conditions, and carbon content addition method of the cemented carbide, in response to the above problems. By doing so, a cemented carbide that does not contain ultrafine tungsten carbide particles in the cemented carbide, has a structure having fine and uniform tungsten carbide particles, and has a precisely controlled carbon content. It has been found that this makes it possible to produce a cemented carbide having excellent performance in hardness and bending strength and having a reliable performance with stable fracture resistance.

That is, the cemented carbide of the present invention bonds tungsten carbide particles having an average particle size of 0.5 μm or less with a binder phase mainly composed of 5 to 15% by mass of cobalt. The number of tungsten carbide particles having a particle size of 0.05 μm or less present in the structure of the cemented carbide is 10% or less with respect to the total number of tungsten carbide particles, and a coercive force of 34,000 to 56,000 A / m, the cemented carbide was pulverized at a saturation magnetic susceptibility of 1.35 to 1.65 μTm ³ / kg in terms of 1% by mass of cobalt, and the pulverized powder passed through # 20 mesh was diluted with dilute hydrochloric acid (HCl: H _In the filtrate which was dissolved in ₂ O = 1: 1) for 24 hours and filtered, tungsten was 8 to 24% by mass, chromium was 3 to 6% by mass and vanadium was 0% with respect to the total amount of metals in the filtrate. .6 to 1.5% by mass It contains by the ratio.

  Here, the number of tungsten carbide particles having a particle diameter of 0.5 μm or more present in the structure of the cemented carbide is 10% or less with respect to the total number of tungsten carbide particles. It is possible to obtain a cemented carbide with stable performance by suppressing variation.

  Further, in the cemented carbide, vanadium is contained in a total amount of 0.2 to 3% by mass in terms of carbide, and chromium is contained in a proportion of 0.2 to 3% by mass in terms of carbide. It is possible to improve the coercive force and breakage resistance by controlling the overall particle size and strengthening the binder phase.

  Furthermore, in the said filtrate, strengthening of a binder phase is carried out by containing chromium in the ratio of 3-6 mass% and vanadium in the ratio of 0.6-1.5 mass% with respect to the total amount of metals in a filtrate. It is possible to improve the overall bending strength of the illustrated cemented carbide.

In addition, the method for producing a cemented carbide according to the present invention includes a tungsten carbide (WC) powder having an average particle size of 0.05 to 0.4 μm and a vanadium carbide having an average particle size of 0.3 to 1.0 μm. (VC) 0.2-0.6% by mass of powder, 0.2-0.8% by mass of chromium carbide (Cr ₃ C ₂ ) powder having an average particle size of 0.3-2.0 μm, 0% of average particle size 2 to 0.6 μm of metallic cobalt (Co) in a ratio of 3 to 13% by mass, and an organic solvent and carbon powder are added so that the solid content ratio of the slurry is 60 to 80% by mass, A mixed powder was obtained by attritor pulverization for 10 to 20 hours using pulverized balls having an average diameter of 2 to 4 mm made of cemented carbide mainly composed of tungsten carbide particles having an average particle diameter of 0.1 to 0.4 μm as pulverization media. After that, the mixed powder was molded, and the vacuum was 0.1 to 5 Pa. 0-1380 After 0.2 to 2 hours under vacuum fired at a temperature of ° C., argon gas was introduced over 5 MPa 5 to 50 ° C. lower temperature than the vacuum baking temperature 0
. It is characterized by performing hot isostatic pressing for 5 to 2 hours and cooling to a temperature of 1000 ° C. or less at a cooling rate of 5 to 10 ° C./min.

  Furthermore, the rotary tool made of the above-described cemented carbide has excellent fracture resistance and wear resistance, and has high breakage resistance even when the diameter is reduced, and can process fine and highly accurate holes with a long life.

  According to the cemented carbide of the present invention, by controlling the properties of tungsten carbide raw material powder, cobalt raw material powder, other additive raw material powder, by controlling the mixing and grinding conditions of the cemented carbide, firing conditions, The cemented carbide does not contain very fine tungsten carbide particles, consists of fine and uniform tungsten carbide particles, and can be a cemented carbide with a precisely controlled carbon content, This makes it possible to produce a cemented carbide having excellent performance in hardness and bending strength, and having a reliable performance with stable breakage resistance.

  Further, according to the rotary tool of the present invention, since it is made of a cemented carbide alloy having fine and uniform tungsten carbide particles that do not contain extremely fine tungsten carbide particles, in a micro drill for drilling printed circuit boards, etc. In addition, it has stable breakage resistance and wear resistance, and exhibits excellent performance and reliability enabling long-life drilling.

It is a transmission-substituting electron micrograph for drawing which shows an example of the structure of an internal cross section about the cemented carbide of the present invention.

  The cemented carbide of the present invention will be described with reference to FIG. 1 which is a transmission electron micrograph inside the cemented carbide.

  According to FIG. 1, the cemented carbide 1 is mainly composed of 5 to 15% by weight of cobalt carbide particles 2 having an average particle size of 0.1 to 0.4 μm, in particular 0.2 to 0.3 μm. And a binder phase 3 containing 50% by mass or more of cobalt.

  According to the present invention, in the cemented carbide, the binder phase 3 is familiar with the tungsten carbide particles 2 and uses cobalt having good wettability, and its content is required to be 5 to 15% by mass as a drill. Is necessary for satisfying the required hardness and strength, but the content of cobalt constituting the binder phase 3 is particularly 6 to 10% by mass in terms of reducing the diameter and improving the position accuracy of the drill in order to prevent deformation of the drill. Furthermore, it is desirable that it is 6-8 mass%.

  Here, the average particle diameter of the tungsten carbide particles in the present invention is an average value obtained by measuring the area occupied by each tungsten carbide particle 2 in a transmission electron micrograph of the internal cross section of the cemented carbide 1 as shown in FIG. Is a value converted into a diameter when the tungsten carbide particles 2 are assumed to be spherical (circles in the photograph). According to the present invention, the average particle size of the tungsten carbide particles 2 is smaller than 0.1 μm. If the content ratio of the binder phase 3 for bonding between the tungsten carbide particles 2 is not set to 13% by mass or more, the toughness of the alloy is reduced or aggregates are easily generated in the structure. When the particle diameter is larger than 0.4 μm, the overall hardness and bending strength of the cemented carbide 1 are lowered, and the wear resistance of the tool and the breakage resistance of the drill are lowered.

Further, according to the present invention, the number of tungsten carbide particles 4 having a particle size of 0.05 μm or less present in the structure of the cemented carbide 1 is 10% or less, particularly 5% or less with respect to the total number of tungsten carbide particles. The ratio is a great feature, and when the impact is applied to the alloy during cutting, the tungsten carbide particles 4 having a particle size of 0.05 μm or less are present, so that the tungsten carbide has a very fine stress. Concentration on particles can prevent breakage in some cases, so that overall bending strength (average value of bending strength) can be increased and variation in bending strength can be reduced. Can do. That is, if the number of tungsten carbide particles 4 having a particle size of 0.05 μm or less is present in a ratio exceeding 10% with respect to the total number of tungsten carbide particles 2, the average value of the bending strength is reduced, or the bending strength is reduced. There is a risk of variations.

  The characteristics of the cemented carbide 1 are the shape and composition of the tungsten carbide particles 2 (carbon content), the distribution of the binder phase 3 (thickness and presence of the binder phase pool) and the composition (the solid solution amount of carbon, tungsten and other metals). However, according to the present invention, in addition to the homogeneity of the alloy structure, the characteristics sensitively vary depending on the amount of carbon contained in the alloy, and the carbon content Paying attention to the fact that the hardness and strength are maximized when the η phase is as low as possible and the η phase is not precipitated, and that the variation in hardness and strength is caused by the variation in the carbon content. The suppression method was examined.

  As a result, it is possible to control the presence of extremely fine tungsten carbide particles, to suppress the variation in the carbon content in the alloy by uniformly adding carbon, and the carbon content in the alloy It has been found that there is a correlation with the solid solution amount of tungsten contained in a part other than the tungsten particles 2, that is, a part eluted with hydrochloric acid under a predetermined condition.

Therefore, according to the present invention, the coercive force of 34,000 to 56,000 A / m and the saturation magnetic susceptibility of 1.35 to 1.65 μTm ³ / kg in terms of 1% by mass of cobalt are controlled. And the ground powder through # 20 mesh was dissolved in dilute hydrochloric acid (HCl: H ₂ O = 1: 1) at 50 ° C. for 24 hours and filtered to obtain the total amount of metal in the filtrate. On the other hand, the amount of carbon contained in Alloy 1 is controlled by containing 8 to 24 mass% of tungsten, 3 to 6 mass% of chromium, and 0.6 to 1.5 mass% of vanadium. It is possible to manage the properties and characteristics of the alloy containing, and to manufacture a cemented carbide and a rotary tool with stable performance.

  Further, according to the present invention, by controlling the tungsten content in the filtrate within the above range, the plastic deformation and impact resistance of the portion other than the tungsten carbide particles in the alloy are reduced. It also has the effect of improving wear resistance and fracture resistance.

  Further, according to the present invention, in the transmission electron microscope observation of the cemented carbide, tungsten carbide particles 5 having a particle size of 0.5 μm or more present in the structure (not shown in FIG. 1 (not shown)). ) Is 10% or less, particularly 5% or less of the total number of tungsten carbide particles 2, which suppresses variations in bending strength and improves the fracture resistance of the tool and the fracture resistance of the drill. Desirable in terms.

  According to the present invention, the cemented carbide contains vanadium in a proportion of 0.2 to 3% by mass in terms of carbide and chromium in a proportion of 0.2 to 3% by mass in terms of carbide. Thus, the overall particle size (average particle size) of the tungsten carbide particles 2 can be effectively controlled, and the binder phase 3 is strengthened to improve the overall bending strength and to improve the fracture resistance and resistance. The breakability can be improved.

Further, according to the present invention, the cemented carbide 1 is pulverized, and the pulverized powder passing through # 20 mesh is dissolved in dilute hydrochloric acid (HCl: H ₂ O = 1: 1) at 50 ° C. for 24 hours and filtered. In the liquid, the binder phase 3 is strengthened by containing tungsten in an amount of 8 to 24% by mass, particularly 10 to 20% by mass, and further 12 to 18% by mass with respect to the total amount of metals in the filtrate. The overall bending strength of the cemented carbide 1 can be improved.

  Further, in the alloy composition, a VWC phase having a particle size smaller than the average particle size of the tungsten carbide particles 2 may be precipitated and dispersed between the tungsten carbide particles, and the tungsten carbide is precipitated and dispersed by the precipitation and dispersion of the VWC phase. The carbon content of the particles can be optimized.

  Further, the rotary tool made of the above-described cemented carbide 1 has excellent fracture resistance and wear resistance, and has high breakage resistance even when the diameter is reduced, and can process fine and highly accurate holes with a long life. .

(Production method)
In order to manufacture the cemented carbide 1 described above, first, for example, a tungsten carbide (WC) powder having an average particle size of 0.05 to 0.4 μm is 80 to 90% by mass and an average particle size is 0.3 to 1.0 μm. 0.2-0.6% by mass of vanadium carbide (VC) powder, 0.2-0.8% by mass of chromium carbide (Cr ₃ C ₂ ) powder having an average particle size of 0.3-2.0 μm, average particle 3 to 13% by mass of metallic cobalt (Co) having a diameter of 0.2 to 0.6 μm is mixed.

  Here, according to the present invention, among the raw material powders, it is important to control the average particle size of the tungsten carbide powder, the chromium carbide powder, the vanadium carbide powder, and the metallic cobalt powder within the above range. When the average particle size deviates from the above range, the sintered body cannot be densified at the firing temperature, and the above-described cemented carbide structure cannot be achieved when the firing temperature described later exceeds 1380 ° C.

  Next, at the time of the above mixing, an organic solvent such as methanol and carbon powder are added so that the solid content ratio of the slurry is 60 to 80% by mass, an appropriate dispersant is added, and an average particle size of 0 as a grinding medium is added. After homogenizing the mixed powder by grinding attritor for 10 to 20 hours using grinding balls made of cemented carbide mainly composed of tungsten carbide particles of 1 to 0.4 μm and having an average diameter of 2 to 4 mm, mixing An organic binder is added to the powder to obtain a mixed powder for molding.

  According to the present invention, together with the raw material composition, during the mixing, it is possible to control the state of the slurry (solid content ratio), adding the carbon powder in advance as a slurry rather than as a powder, and controlling the grinding media and mixing conditions This is important, and the structure of the cemented carbide 1 can be made to have the above-described uniform grain size tungsten carbide particles without causing excessive pulverization or particle aggregation.

  Next, the mixture powder is molded into a predetermined shape by a known molding method such as press molding, casting molding, extrusion molding, cold isostatic pressing, and then in a vacuum of 0.1 to 5 Pa, 1320 After vacuum baking at a temperature of ˜1380 ° C. for 0.2 to 2 hours, argon gas is introduced at 5 MPa or more, and hot isostatic pressing is performed at a temperature 5 to 50 ° C. lower than the vacuum baking temperature for 0.5 to 2 hours. The cemented carbide of the present invention can be manufactured by cooling to a temperature of 1000 ° C. or lower at a cooling rate of 5 to 10 ° C./min.

Here, among the above firing conditions, if the firing temperature is lower than 1320 ° C., the alloy cannot be densified, resulting in a decrease in strength, and the number of extremely fine tungsten carbide particles having a particle size of 0.05 μm or less is 10 If the firing temperature exceeds 1380 ° C., tungsten carbide particles grow and the hardness and strength decrease. When the difference between the hot isostatic press firing temperature and the vacuum firing temperature is less than 5 ° C., the number of ultrafine tungsten carbide particles having a particle size of 0.05 μm or less is 10% or more, or the particle size is 0.00. If the number of coarse tungsten carbide particles of 5 μm or more is 10% or more, conversely, if this temperature difference is larger than 50 ° C., the number of extremely fine tungsten carbide particles having a particle size of 0.05 μm or less in the alloy. Is generated more than 10%, and voids are easily generated, causing a decrease in strength.

  In addition, the above-described cemented carbide of the present invention has high hardness, high strength, and excellent deformation resistance, and has high reliability mechanical properties, so it is suitable for molds, wear-resistant members, high-temperature structural materials, etc. In particular, it can be suitably used as a cutting tool, and further as a drill for processing printed circuit boards.

Furthermore, the cutting tool of the present invention has a carbide, nitride, carbonitride, carbonitride, especially (Ti _a M _b ) of the periodic table Nos. 4a, 5a, and 6a metals on the surface of the cemented carbide described above. C _x N _y O _z (however, at least one selected from the group of M: Al, Zr, Cr, Si, 0 <a ≦ 1, 0 ≦ b <1, a + b = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1), at least one coating layer selected from the group of diamond, cBN, and Al 2 O 3 may be formed as a single layer or a plurality of layers.

  In order to form the coating layer on the cemented carbide, the surface of the cemented carbide is polished and washed as desired, and then formed using a conventionally known thin film forming method such as PVD or CVD. . The thickness of the coating layer is preferably 0.1 to 20 μm.

Moreover, in order to produce a printed circuit board processing drill using the above-mentioned cemented carbide, a rod-like molded body is produced using the above-mentioned raw material and the mixed powder for molding, fired in accordance with the above-described firing method, and then sintered. It can produce by processing to a desired drill shape.
Further, the above-described coating film may be formed on at least a part of the drill.

The ratio (mass%, in the table) of tungsten carbide (WC) powder, metal cobalt (Co) powder, vanadium carbide (VC) powder and chromium carbide (Cr ₃ C ₂ ) powder having the average particle size shown in Table 1 is shown in Table 1. In addition, methanol in which the carbon powder shown in Table 1 is dissolved is added so that the solid content ratio of the slurry is the ratio shown in Table 1, and the average particle diameter of tungsten carbide particles is used as a grinding medium. Add a 3mm diameter ball of 0.3μm ultra-fine cemented carbide, grind and mix attritor for the time shown in Table 1, dry, and then press-mold into a round bar shape, 500 ℃ above the firing temperature The temperature was raised from a low temperature at a rate of 10 ° C./min, and vacuum firing and hot isostatic press firing (Sinter HIP) were performed under the conditions shown in Table 1 to produce a cemented carbide.

In Table 1, ΔT (° C.) indicates the temperature difference between vacuum firing and hot isostatic press firing, and the cooling rate indicates the cooling rate until cooling to 1000 ° C. or less after hot isostatic press firing. . Further, as a method for adding the carbon raw material, Table 1 shows either (a) addition as a solution in which carbon powder is preliminarily dissolved in methanol, or (b) preparation with other raw material powder as carbon powder.

  With respect to five arbitrary cross sections of the obtained cemented carbide, a reflection electron image at a magnification of 100,000 as shown in FIG. 1 was observed with a transmission electron microscope, and tungsten carbide particles were observed in an arbitrary region of 1 μm × 1.5 μm. The particle size was measured, and the abundance ratio was calculated by measuring the average particle size, the number of tungsten carbide particles having a particle size of 0.05 μm or less, and the number of tungsten carbide particles having a particle size of 0.5 μm or more. Furthermore, the coercive force and the saturation magnetic susceptibility of the cemented carbide were measured and converted to the saturation magnetic susceptibility per 1% by mass of cobalt. The results are shown in Table 2.

In addition, a hydrochloric acid (HCl: H ₂ O = 1: 1) solution was added to 1 g of pulverized powder obtained by pulverizing the above cemented carbide and passing through a # 20 mesh, and a solution obtained by stirring and stirring for 24 hours at 50 ° C. Filtered. Dilute hydrochloric acid (HCl: H ₂ O = 1: 1) solution was added to this solution to make a constant volume of 50 ml, and the content and content ratio of each metal containing tungsten in the filtrate were measured by ICP method for this filtrate. . The results are shown in Table 2.

Further, the cemented carbide was processed into a two-edged drill shape, a printed circuit board drilling test was performed under the following conditions, and the number of processed holes until the sample broke was measured. In addition, Table 2 shows the number of samples and the number of processed holes being the minimum.
<Conditions>
Work material: FR4 / 6-layer plate, 1.6 mm thick, 3-ply drill shape: φ0.15 mm undercut type Rotation speed: 120 kr. p. m.
Feeding speed: 2.4 m / min.

  From the results shown in Tables 1 and 2, the sample Nos. 1 and 2 in which the average particle sizes of the metallic cobalt powder, chromium carbide powder, and vanadium carbide powder raw material deviate from the predetermined range. 5. Sample No. 5 in which the solid content ratio and pulverization time in the slurry deviate from the predetermined range. 6. Sample No. with vacuum firing temperature exceeding 1380 ° C. 7. Sample No. 1 subjected to hot isostatic press firing at the same temperature as the vacuum firing temperature. 8 and Sample No. 8 in which the temperature difference (ΔT) between the vacuum firing temperature and the hot isostatic press firing temperature exceeds 50 ° C. In No. 9, the abundance ratio of fine particles of 0.05 μm exceeded 10%, the tungsten content in the filtrate exceeded the predetermined range, the average value of the bending strength was low, and the variation was large.

  On the other hand, in accordance with the present invention, the sample powder No. 1 in which the properties of the raw material powder (particularly the average particle size), the mixing of the raw material mixed powder, the pulverization conditions, and the firing conditions were controlled within a predetermined range. 1-4, the average particle size of tungsten carbide particles is in the range of 0.1 to 0.4 μm, and the proportion of fine particles of 0.05 μm or less and coarse particles of 0.5 μm or more are both 10% or less. And a uniform structure, and the tungsten content in the filtrate was in the range of 8 to 24% by mass. These samples show excellent breakage resistance with a minimum number of processed holes of 4000 or more in a drilling test on a drill having a small diameter of 0.15 mmφ with small variations in magnetic properties and mechanical properties. there were.

DESCRIPTION OF SYMBOLS 1 Hard alloy 2 Solid solution phase 3 WC phase 4 Bonded phase 6 De-β region 7 Inside 8 High hardness region

Claims (5)

In a cemented carbide in which tungsten carbide particles having an average particle size of 0.1 to 0.4 μm are bonded with a binder phase mainly composed of 5 to 15% by mass of cobalt, grains existing in the structure of the cemented carbide The number of tungsten carbide particles having a diameter of 0.05 μm or less is a ratio of 10% or less with respect to the total number of tungsten carbide particles, and the coercive force is 34,000 to 56,000 A / m, in terms of 1% by mass of cobalt. The cemented carbide was pulverized with a saturation magnetic susceptibility of 1.35 to 1.65 μTm ³ / kg, and the pulverized powder that passed through # 20 mesh was diluted in dilute hydrochloric acid (HCl: H ₂ O = 1: 1) at 50 ° C. In the filtrate dissolved and filtered for 24 hours, tungsten is 8 to 24% by mass, chromium is 3 to 6% by mass, and vanadium is 0.6 to 1.5% by mass with respect to the total amount of metal in the filtrate. Carbide characterized by containing in proportion alloy.   The super-hard alloy according to claim 1, wherein the number of tungsten carbide particles having a particle size of 0.5 µm or more present in the structure of the cemented carbide is 10% or less with respect to the total number of tungsten carbide particles. Hard alloy.   3. The cemented carbide according to claim 1, wherein vanadium is contained in a proportion of 0.2 to 3% by mass in terms of carbide, and chromium is contained in a proportion of 0.2 to 3% by mass in terms of carbide. 80-90% by mass of tungsten carbide (WC) powder having an average particle size of 0.05-0.4 μm, and 0.2-0.6% by mass of vanadium carbide (VC) powder having an average particle size of 0.3-1.0 μm. %, 0.2 to 0.8 mass% of chromium carbide (Cr ₃ C ₂ ) powder having an average particle size of 0.3 to 2.0 μm, and metallic cobalt (Co) having an average particle size of 0.2 to 0.6 μm. 3 to 13% by mass, and an organic solvent and carbon powder are added so that the solid content ratio of the slurry is 60 to 80% by mass, and the average particle size is 0.1 to 0.4 μm as the grinding media. After a mixed powder was obtained by pulverizing for at least 10 to 20 hours using a pulverized ball made of a cemented carbide mainly composed of tungsten carbide particles of 10 to 20 hours, the mixed powder was molded, and 0.1 to 0.2 to 2 hours at a temperature of 1320 to 1380 ° C. in a 5 Pa vacuum After vacuum firing, argon gas is introduced at 5 MPa or more, hot isostatic pressing is performed at a temperature 5 to 50 ° C. lower than the vacuum firing temperature for 0.5 to 2 hours, and a cooling rate of 5 to 10 ° C./min. And cooling to a temperature of 1000 ° C. or less.   A rotary tool comprising the cemented carbide according to any one of claims 1 to 3.