JP7089743B2 - Hard materials and their manufacturing methods - Google Patents

Description

The present invention relates to a hard material in which a hard phase of a metal carbide and a bonded phase of an aluminum alloy are combined, and a method for producing the same.

WC-Co cemented carbide is a hard material that is hardened with tungsten carbide (WC) particles, which are hard particles, and metallic cobalt (Co). Since WC-Co cemented carbide is a material with an excellent balance between hardness and toughness, it is very widely used in the precision machining field such as cutting tools and mold materials.

However, Co used as a bonding phase of cemented carbide has a surface in which oxidation is easily promoted at a high temperature of 600 ° C. or higher. Due to the influence of this oxidation, cemented carbide has problems such as a decrease in strength and oxidation resistance at a high temperature of 600 ° C. or higher. In order to overcome this problem, that is, to maintain the strength at a high temperature of 600 ° C or higher and to produce a hard material having high temperature oxidation resistance, select a material of the bonded phase having excellent high temperature strength and high temperature oxidation resistance. It is a promising idea to combine it with hard particles such as WC.

Examples of the material of the bonded phase having excellent high-temperature strength and high-temperature oxidation resistance include alloys containing Al and intermetallic compounds. For example, Patent Document 1 describes that a cemented carbide having excellent high temperature oxidation resistance was obtained by combining an iron-aluminum (FeAl) alloy with WC as a bonding phase.

Since FeAl alloys show excellent yield strength at high temperatures around 600 ° C, hard materials using FeAl alloys for the bonding phase in this temperature range (hereinafter referred to as FeAl alloy hard materials) are machines with hardness, strength, toughness, etc. It has excellent characteristics. In addition, since nickel-aluminum (NiAl) alloy also exhibits excellent strength at high temperatures around 600 ° C like FeAl alloy, hard materials using NiAl alloy as the bonding phase in this temperature range (hereinafter referred to as NiAl alloy hard material) are also available. , Has excellent mechanical properties such as hardness, strength and toughness. From the above, FeAl alloy hard material and NiAl alloy hard material can be expected as hard materials having excellent high temperature characteristics around 600 ° C than WC-Co cemented carbide.

However, the mechanical properties of FeAl alloy hard materials and NiAl alloy hard materials at room temperature are slightly higher than those of WC-Co cemented carbide in terms of the volume ratio of the same bonded phase, but the strength and toughness are low. There is. Since mechanical properties such as strength and toughness at room temperature also affect mechanical properties at high temperatures, improving room temperature strength and toughness is an important issue for FeAl alloy sintered bodies and NiAl alloy hard materials.

In order to increase the strength and toughness of FeAl alloy hard materials and NiAl alloy hard materials at room temperature, it is convenient to increase the ratio of the bonded phase to the hard phase, but this method reduces the hardness at the cost. Therefore, a method of improving strength and toughness without reducing hardness is desirable.

The use of additives can be mentioned as a method for improving strength and toughness without reducing hardness. Boron (B) is one of the candidates for additives. In fact, Patent Document 2 reports a Co-free cemented carbide (FeAl alloy sintered body) having improved strength and toughness by dispersing B in a material.

According to Patent Document 2, the room temperature strength has been successfully improved by adding the B powder to the raw material powder such as WC. However, since the amount of B powder added to improve the room temperature strength is very small, there is a problem that uniform dispersion of B is difficult.

Nitrogen (N) is a candidate for additives other than B. The effect of N addition has been confirmed in titanium carbide (TiC) -based cermet, which is the same typical hard material as WC-Co cemented carbide. For example, in Non-Patent Document 2, cermet is formed by adding titanium nitride TiN to TiC and changing the hard phase from TiC to titanium carbonitride (TiCN) containing N to form a solid solution Ti (C, N). It has been reported that the improvement of toughness and the improvement of hardness by suppressing grain growth were confirmed.

For the addition of N to FeAl alloy hard materials and NiAl alloy hard materials, a method of exposing to nitrogen gas during sintering can be considered. However, this method cannot evenly diffuse N into the inside of the FeAl alloy hard material, and the effect is limited to the surface of the sintered body. Therefore, in order to maintain the cured surface layer, the processing of the sintered body is greatly restricted. Therefore, although this method can be applied to simple-shaped parts such as cutting tips, it is difficult to apply to complex-shaped parts such as drills and end mill tools that require precision machining. In order to eliminate the restrictions on the product shape, it was necessary to diffuse N evenly into the inside of the sintered body.

Japanese Unexamined Patent Publication No. 07-003357 Japanese Unexamined Patent Publication No. 2012-77352

D.E. Alman et al., Wear of iron-aluminide intermetallic-based alloys and composites by hard particles, Wear 2001, Vol. 251 p.875-884 Yuji Katsumura et al., Characteristics of recent TiN cermets, Precision Machinery 1980 Vol. 46, p.553-559

The present invention has been made in view of the above-mentioned problems, and provides a heat-resistant hard material having excellent hardness and toughness at room temperature by uniformly diffusing B and N to the inside, and a method for producing the same. That is the subject.

In order to achieve the above problems, the hard material of the present invention has a hard phase containing at least one of (1) group 4, group 5 and group 6 metal alloys, and (2) a ratio of aluminum (Al). A hard material that combines a bonded phase containing at least one of an iron-aluminum alloy having a proportion of 20 atomic% or more and 50 atomic% or less and a nickel-aluminum alloy having an aluminum (Al) ratio of 20 atomic% or more and 50 atomic% or less. It is characterized in that boron (B) and nitrogen (N) are solidly dissolved in the bonded phase.
In this hard material, boron (B) and nitrogen (N) are preferably derived from hexagonal boron nitride (h-BN).
The method for producing a hard material of the present invention is a method for producing the hard material, which is a step of adding hexagonal boron nitride powder (h-BN) to a raw material powder and mixing and / or pulverizing the mixture to obtain a mixed powder. It is characterized by including a step of sintering the mixed powder.

According to the present invention, a heat-resistant hard material having excellent mechanical properties such as hardness and toughness (strength) at room temperature by having a bonded phase of FeAl alloy or NiAl alloy in which B and N are uniformly dissolved to the inside. The material can be obtained.

It is a photograph which shows the appearance of a sample after an oxidation resistance test.

Hereinafter, the present invention will be described in detail.
The rigid material of the present invention is characterized in that boron (B) and nitrogen (N) are dissolved in the bonded phase, and B and N are preferably derived from hexagonal boron nitride (h-BN). That is, it is produced by adding h-BN to a composite material in which metal carbides are bonded with an alloy containing Al, and utilizing the reaction between h-BN and FeAl alloy or NiAl alloy at the time of sintering. h-BN, known as a solid lubricant, is easy to disperse uniformly in powders and reacts with FeAl or NiAl alloys at high temperatures above 1100 ° C. By this reaction, even if the amount of h-BN added is very small, B and N can be homogeneously dispersed in the hard material after sintering. B mainly dissolves homogeneously in FeAl alloy or NiAl alloy. An important point of the present invention is to uniformly disperse the B and N components in the hard material by the reaction of h-BN and FeAl alloy or NiAl alloy. It is conceivable to use B powder as the B source and N contained in the metal powder as the N source, but it is difficult to uniformly diffuse the B powder into the hard material because the addition amount is very small. In addition, most of N contained in the metal powder is desorbed at the initial stage of sintering, and only an uncertain amount remains in the hard material, so that it is difficult to control it as an N source. On the other hand, h-BN reacts with FeAl alloy or NiAl alloy at a temperature 50 ° C to 200 ° C lower than the temperature at which the hard material becomes densified, so that the target amount of B component and N component can be added to the hard material. It can be dispersed uniformly and hardly desorbs the N component. h-BN is known as a thermally stable compound and is used as a member for molten metal of cast iron. Therefore, even if h-BN is added, it is assumed that h-BN remains as a simple substance in the hard material, so it was thought that it would not lead to improvement in characteristics. The finding that it reacts was obtained, and the present invention was completed.

In the hard material of the present invention, when the total amount of iron and nickel in the bonded phase is 100% by weight, the content of B is preferably 0.03% by weight or more and 0.6% by weight or less, and more preferably 0.1% by weight or more and 0.3% by weight or less. preferable.

In the hard material of the present invention, when the total amount of iron and nickel in the bonded phase is 100% by weight, the content of N is preferably 0.1% by weight or more and 1.0% by weight or less, and more preferably 0.4% by weight or more and 0.8% by weight or less. preferable.

The bonded phase of the hard material of the present invention comprises at least one of an iron-aluminum (FeAl) alloy and a nickel-aluminum (NiAl) alloy. The FeAl alloy has an Al content of 20 atomic% or more and 50 atomic% or less. The NiAl alloy has an Al content of 20 atomic% or more and 50 atomic% or less. The composition of the FeAl alloy and NiAl alloy used as the bonding phase is such that Al is 20 atomic% or more and 50 atomic% or less, and the rest is Fe or Ni. By having a bonded phase having this alloy composition, a hard material having excellent fracture toughness, strength and oxidation resistance from room temperature to around 600 ° C. can be obtained. In particular, it is preferable that the aluminum alloy constituting the bonded phase is at least one of a FeAl-based intermetallic compound and a NiAl-based intermetallic compound. FeAl-based intermetallic compound that does not contain a solid solution, that is, B2 type FeAl intermetallic compound, D03 type Fe ₃ Al intermetallic compound, and NiAl-based intermetallic compound that does not contain a solid solution, that is, B2 type NiAl intermetallic compound, L1 ₂ When composed of a type of Ni ₃ Al intermetallic compound, it is possible to prepare a hard material having a good balance between oxidation resistance, fracture toughness and strength. If the proportion of Al in the alloy is less than 20 atomic%, the oxidation resistance of the hard material decreases. On the other hand, when the ratio of Al is larger than 50 atomic%, the fracture toughness and strength of the bonded phase are lowered, the hard material becomes brittle, and the strength and toughness are lowered.

In the hard material of the present invention, the hard phase is a group 4 metal carbide such as titanium carbide (TiC), zirconium carbide (ZrC), hafnium carbide (HfC), a group 5 metal carbide such as niobide (NbC), and carbide. Contains at least one of Group 6 metal carbides such as molybdenum (Mo ₂ C) and tungsten carbide (WC). Due to the characteristics of the present invention, there is no problem even if any of the carbides is used for the hard phase, and the content of B or N that produces a significant difference of the present invention is not affected. However, in a sintering method other than the method using pressure sintering, for example, in a sintering method under vacuum using liquid phase sintering, the hard phase has wettability with a FeAl alloy or a NiAl alloy as a bonded phase. It is preferable to contain WC having excellent WC in an amount of 50% by volume or more when the total volume of the hard phase is 100% by volume. When pressure sintering is used, it is preferable to use TiC, which is lightweight and has relatively good wettability with FeAl alloy or NiAl alloy, as the hard phase in addition to WC. As for the volume of the hard phase, if an image obtained from a scanning electron microscope or the like is used, shading appears depending on the magnitude of the molar mass of the compound, so that the type of hard material can be easily identified and the volume fraction can be obtained. When it is difficult to distinguish by shading, it is possible to confirm the target element and specify the type of hard material by using energy dispersive X-ray spectroscopy in combination.

The hard material of the present invention can be produced through a step of obtaining a mixed powder and a sintering step of sintering the obtained mixed powder. In the step of obtaining a mixed powder, h-BN is added to the raw material powder, mixed and / or ground. Specifically, h-BN powder is added in addition to the alloy powder containing Al and the raw material powder such as the carbide hard powder, and mixed and / or pulverized to prepare a mixed powder. B in h-BN reacts with FeAl alloy or NiAl alloy in the sintering process and dissolves in solid solution. The content of B when the total amount of Fe and Ni is 100% by weight can be detected and evaluated by a wavelength dispersive X-ray spectroscope. On the other hand, a part of the N component in h-BN evaporates, but the rest dissolves in the FeAl alloy or NiAl alloy. The content of N when the total amount of Fe and Ni is 100% by weight can be measured by using a nitrogen analyzer using the inert gas melting-heat conductivity method.

In the sintering step, the mixed powder is sintered. The hard material of the present invention is filled with a mixed powder mixed with raw materials in a vacuum of 100 Pa or less and sintered at a temperature of 1150 ° C. or more and 1300 ° C. or less under a pressure of 10 MPa or more and 200 MPa or less, or the above. It can be produced by subjecting a molded product of a mixed powder to sintering without pressure at a temperature of 1350 ° C. or higher and 1600 ° C. or lower. Specifically, in the former case, the mixed powder is filled in a mold and sintered using pressure sintering such as energization pulse sintering or hot pressing under a vacuum of 100 Pa or less. In the latter, the mixed powder is filled in a mold, pressure-molded, and then sintered in a vacuum of 100 Pa or less (hereinafter referred to as vacuum sintering). In the case of energization pulse sintering, if the radiation thermometer is adjusted to the mold and the displayed temperature is regarded as the sintering temperature, densification is possible in the range of 1150 ° C or higher and 1300 ° C or lower. Generally, it is possible to produce a denser alloy sintered body by using pressure sintering than by vacuum sintering. However, in the case of a hard material in which WC is not contained in the hard phase at a volume fraction of 25% or more, it is difficult to densify by ordinary vacuum sintering. Further, in both vacuum sintering and pressure sintering, a process such as adding an inert gas such as argon to cool the temperature may be performed in the temperature lowering process.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

(1) Changes in N amount of WC-FeAl, WC-NiAl, TiC-FeAl hard materials prepared by adding h-BN As raw material powder, WC powder (average particle size 2.0 μm, manufactured by Nippon Shinkinzoku Co., Ltd.), TiC powder (average particle size 1.7 μm manufactured by Nippon Shinkinzoku Co., Ltd.), Fe powder (particle size 3-5 μm manufactured by High Purity Science Laboratory Co., Ltd.), Al powder (average particle size 10 μm or particle size 3-5 μm) High Purity Science Laboratory Co., Ltd.) and h-BN powder (average particle size 2 μm, AP-20S, manufactured by MARUKA) were prepared. First, the amount of N contained in the raw material powder was measured by an analyzer (TC-436, manufactured by Leco Co., Ltd.) using an inert gas melting-thermal conductivity method. The results are shown in Table 1. Significant amounts of N were detected in the raw material powders in two types, Fe powder and h-BN powder, and the other powders were out of the detection range.

After clarifying the amount of N contained in the raw material powder, put the prescribed amount of WC powder, TiC powder, Fe powder, Al powder, and Ni powder in a 420 ml stainless steel pot, and add 900 g of carbide balls with a diameter of 9.3 mm and 100 ml of acetone. It was added and mixed with a wet ball mill for 72 hours. Then, the slurry was dried using an evaporator to obtain a mixed powder. Al powder was added to this mixed powder, and dry mixing was performed using a grinder. The obtained mixed powder and a predetermined amount of h-BN powder were dry-mixed using a mortar, and after mixing, the powder was placed in a graphite mold and sintered with a current-carrying pulse sintering device. The pressurization was 40 MPa, and the maximum temperature (sintering temperature) was changed in the range of 1150 ° C to 1260 ° C for each sample after checking the shrinkage amount. As a general tendency, the sintering temperature decreases as the addition ratio of h-BN increases and the ratio of Al in the alloy-bonded phase increases. As shown in Table 2, the composition of the FeAl alloy or NiAl alloy, which is the bonding phase of the hard material produced this time, is abbreviated as four compositions of Fe _0.33 Al _0.67 , Fe _0.5 Al _0.5 , Fe _0.7 Al _0.3 , and Ni _0.7 Al _0.3 . Let be F3A7, Fe5A5, F7A3, and N7A3, respectively.

In order to investigate the amount of N contained in the sintered hard material, the obtained sintered body is surface-ground, then a part is cut out and crushed, and the debris is melted by an inert gas-analysis using the thermal conductivity method. The N content was measured by an apparatus (TC-436, manufactured by Leco Co., Ltd.). The surface of the sample other than the part used for measuring the amount of nitrogen was mirror-finished by polishing. After measuring the apparent density of this sample by the Archimedes method, a diamond indenter was driven into the mirror surface, and the Vickers hardness was measured based on JIS Z 2244 and the fracture toughness was measured by the IF method. The fracture toughness value K _IC was obtained from the following equation (1) proposed by Shetty et al.
(Number 1)
K _IC = 1.39 × (H _v・ P / C) ^0.5 (1)
Here, H _v indicates the Vickers hardness (GPa), P indicates the indentation load (N), and C indicates the average crack length (μm). Tables 3 to 5 show the types of hard particles in each hard material, the composition of the bonded phase, the volume ratio of the bonded phase, the B content, the ratio of Al in the alloy bonded phase, the volume ratio of the bonded phase in the hard material, and the hard material. B content in, ratio of B to Fe or Ni component of bound phase, N content in hard material (measured / theoretical), ratio of N to Fe or Ni component of bound phase, sintered samples The apparent density, relative density, Vickers hardness, and fracture toughness value of are shown. The relative density indicates a value obtained by dividing the apparent density by the theoretical density, but when determining the theoretical density, it is assumed that the hard phase and the bonded phase do not react, and the alloy is based on the composition of the bonded phase. It includes the theoretical calculation process of the bound phase. For this reason, the relative density is a useful index for assessing the density of a sample, but it contains some errors, and it is clearly stated that the relative density may exceed 100% depending on the sample. back.

The theoretical value of the N content of the hard material of the present invention is calculated from the sum of N derived from h-BN powder and N derived from Fe powder. From the results in Table 4, it was found that the measured value of the N content was lower than the theoretical value in the experimental example containing Fe in the bound phase. In the experimental example (Comparative Example 1 and Example 1 to Example 4) in which the volume fraction of the bound phase containing Fe was 35%, the measured value was one-fifth or less of the theoretical value. It is considered that this is because the theoretical value was obtained on the assumption that N derived from Fe powder remained inside the sample, but most of the added N did not actually remain in the sample and was desorbed during sintering. In general, N contained in Fe powder has a weak covalent bond and is considered to be easily desorbed during heating. On the other hand, N derived from h-BN has a strong covalent bond and is considered not to be easily desorbed by heating. In fact, in Comparative Example 11 and Examples 21 to 23 in which N7A3 containing no N component is used as the binding phase, the measured values and the theoretical values are almost the same. From the above, it is considered that most of the N contained in the Fe metal powder is desorbed during sintering, and the N derived from h-BN is dissolved in the FeAl alloy.

(2) Effect of the composition of the bonded phase and the ratio of the volume ratio of the bonded phase on the mechanical properties of the WC-FeAl hard material to which h-BN was added From the results in Tables 3 to 5, the composition of the FeAl alloy bonded phase is F7A3. In the case of F5A5 (see Comparative Examples 1 to 17), changes in Vickers hardness and fracture toughness were clearly observed depending on the amount of B and N, and the optimum values existed for the amount of B and N. The optimum value of the amount of h-BN added that maximizes Vickers hardness or breaking toughness is at least 0.03% by weight or more and 0.6% by weight or less in terms of the weight of component B when Fe is 100% by weight. It was found that it exists in the range of at least 0.1% by weight or more and 1% by weight or less in terms of the weight of the N component when Fe is 100% by weight. Therefore, it can be clearly said that the addition of h-BN that satisfies the same range improves the characteristics as compared with the system without h-BN addition.

On the other hand, when the composition of the FeAl alloy bonded phase was F3A7, the effect of improving the Vickers hardness by increasing the amount of B and N was hardly seen, and no clear tendency was seen in the fracture toughness (Comparative Example 5). Refer to Comparative Example 10). From this, it was found that whether the dispersion of B and N components contributes to the improvement of the characteristics of the WC-FeAl hard material depends on the composition of the FeAl alloy bonded phase. When the proportion of Al is greater than 50 atomic%, it may form the intermetallic compound FeAl ₂ , which may inhibit the effect of h-BN addition. From this, in the present invention, the ratio of Al in the bonded phase of the FeAl alloy is 50 atomic% or less.

The volume fraction of the bound phase in this experimental example is 15%, 25%, or 35%, but the changes in Vickers hardness and fracture toughness due to changes in the amount of B and N can be clearly seen at any volume fraction. There were optimum values for the B and N quantities. That is, the change in the volume fraction of the bonded phase means the change in the volume fraction of WC, which is a hard phase, but by changing the ratio of WC, the mechanical properties of the WC-FeAl hard material by adding h-BN are improved. The effect of was not lost. This suggests that h-BN basically does not react with WC, which is a hard phase.

(3) Effect of difference in hard particles of hard material with h-BN on mechanical properties Even when using TiC-FeAl hard material in which the hard phase is changed from WC to TiC, the results in Tables 3 to 5 are obtained. Changes in Vickers hardness and fracture toughness due to changes in the amount of B and N were clearly seen, and optimum values existed for the amount of B and N (see Comparative Examples 10 and 18 to 20). TiC may react with h-BN in the sintering process, but the optimum values for the B and N amounts that improve mechanical properties are based on the weight of the alloy components excluding Al, that is, the weight of Fe in this case. As far as we can see, there is no large fluctuation, suggesting that the reaction between TiC and h-BN during sintering does not occur or is slight, and that the reaction between h-BN and FeAl alloy is prioritized. ..

(4) Effect of difference in bonded phase of hard material with h-BN on mechanical properties From the results in Tables 3 to 5, WC-NiAl hard with the bonded phase changed from FeAl alloy to NiAl alloy (N7A3). Even when used as a material, changes in Vickers hardness and fracture toughness were basically clearly observed depending on the amount of B and N, and optimum values existed for the amount of B and N (Comparative Example 11 and Examples 21 to 23). See). As in the case of Fe, the optimum values of the amount of B and the amount of N, which maximize the mechanical properties, did not change significantly when the weight of Ni was used as the reference value. From this, it was suggested that h-BN and NiAl also reacted, and the characteristics were improved by the same mechanism as in the case of the bonded phase of FeAl alloy.

(5) High-temperature oxidation resistance evaluation of WC-FeAl hard material to which h-BN was added The oxidation resistance test of the hard material of the present invention and commercially available WC-Co (K10 type) was carried out. Samples having the compositions of Example 6 and Example 14 were prepared, cut into a disk shape having a diameter of 14 mm and a thickness of about 3 mm, and the weight increase due to oxidation of each sample after holding at 600 ° C. for 24 hours in the air was measured. FIG. 1 shows the appearance of the sample after the oxidation resistance test, and Table 6 shows the result of weight increase due to oxidation per unit surface area of each hard material.

From FIG. 1, it can be seen that the surface of the sample after the oxidation resistance test of the commercially available WC-Co (K10 type) is cracked and scattered. This means that oxygen diffused not only to the surface of the sample but also to the inside, causing volume expansion due to oxidation. From this, it can be said that it is difficult to use WC-Co at 600 ° C for a long time. On the other hand, in both Examples 6 and 14, brown coloring due to the oxidation of iron was observed after holding at 600 ° C. in the air for 24 hours, but the shape was maintained. It is considered that this is because the surface protective film such as aluminum oxide is formed from FeAl to suppress the diffusion of oxygen to the inside of the sample. As a result, as shown in Table 6, the weight increase due to oxidation in both Examples 6 and 14 is smaller than that in WC-Co, and it can be seen that the oxidation is suppressed. From the above results, it can be said that the hard material of the present invention is a hard material having better heat resistance than WC-Co in the temperature range around 600 ° C.

The heat-resistant alloy sintered body of the present invention has excellent heat resistance as compared with the WC-Co cemented carbide, and further has a bonded phase of FeAl alloy or NiAl alloy in which boron and nitrogen are uniformly dispersed to the inside. Since it is a sintered body with excellent mechanical properties such as hardness and toughness at room temperature and high temperature around 600 ° C throughout the material, it can be used as a material for cutting tools and molds exposed to high temperature environments of 600 ° C or higher. It can be suitably used. Further, since a heat-resistant alloy sintered body having high characteristics can be produced by using a production process similar to that of WC-Co cemented carbide, it can be expected to be widely used as a substitute material for WC-Co.

Claims (6)

(1) A hard phase containing at least one of Group 4, Group 5, and Group 6 metal carbides,
(2) A bonded phase containing at least one of an iron-aluminum alloy having an aluminum ratio of 20 atomic% or more and 50 atomic% or less and a nickel-aluminum alloy having an aluminum ratio of 20 atomic% or more and 50 atomic% or less. It is a composite hard material
Boron and nitrogen are dissolved in the bonded phase ,
When the total amount of iron and nickel in the bonded phase is 100% by weight, the boron content is 0.03% by weight or more and 0.6% by weight or less.
A hard material having a nitrogen content of 0.1% by weight or more and 1.02% by weight or less when the total amount of iron and nickel in the bonded phase is 100% by weight . The hard material according to claim 1, wherein the aluminum alloy constituting the bonded phase is at least one of a FeAl-based intermetallic compound and a NiAl-based intermetallic compound. The hard material according to claim 1 or 2 , wherein the hard phase contains 50% by volume or more of tungsten carbide when the total volume of the hard phase is 100% by volume. The hard material according to any one of claims 1 to 3 , wherein the hard phase contains 50% by volume or more of titanium carbide when the total volume of the hard phase is 100% by volume. The method for producing a hard material according to any one of claims 1 to 4 , wherein a hexagonal boron nitride powder is added to a raw material powder, and the mixture is mixed and / or pulverized to obtain a mixed powder.
A method for producing a hard material, which comprises a step of sintering the mixed powder. When sintering the mixed powder, in a vacuum of 100 Pa or less, the mixed powder mixed with the raw materials is filled in a mold and sintered at a temperature of 1150 ° C or more and 1300 ° C or less under a pressure of 10 MPa or more and 200 MPa or less. The method for producing a hard material according to claim 5 , wherein the molded body of the mixed powder is sintered without pressure at a temperature of 1350 ° C. or higher and 1600 ° C. or lower.

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