JP2015062980A - Hard material and cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hard material which can be an alternative of cemented carbide and has thermal shock resistance and to provide a cutting tool using the hard material.SOLUTION: A hard material includes a hard phase and a connection phase consisting essentially of iron group metal. The hard phase has a core constituted with at least one kind of carbide, nitride and carbonitride containing one or more elements selected from Si and period 4, 5, 6 elements in the periodic table excluding W, and a shell which is constituted with WC and is used for covering the core therewith, and the connection phase contains both of V and Cr. A cutting tool is provided with a cutting blade peripheral region which contains a cutting blade constituted with ridge line parts of both faces of a flank relief and a cutting face and the neighborhood of the cutting blade. At least the cutting blade peripheral region includes base material made of the hard material and hard cover with which the base material is covered and the hard material constituting the base material is covered with the shell without exposing the core on at least a part of the flank relief and the cutting face.

Description

  The present invention relates to a hard material suitable for cutting a metal material such as steel, cast iron, and sintered alloy, and a cutting tool using the hard material.

  Conventionally, as a hard material for cutting steel, cast iron, and sintered alloy, cemented carbide or a coated cemented carbide in which a hard coating of ceramics is provided on the surface thereof is known. Cemented carbide is excellent in strength and fracture toughness, and is also excellent in thermal conductivity, so it is suitable for cutting tools used for roughing and intermittent cutting of steel and cast iron.

  Tungsten, the main raw material for cemented carbides, is highly localized in the region, and there is concern about supply risks. Therefore, it is desirable to develop hard materials that can replace tungsten and reduce the amount of tungsten used. ing. Patent Document 1 discloses a hard material having a core-shell structure hard phase having a core made of at least one of Ti carbide and Ti carbonitride and a shell made of WC and covering the core. This hard material is manufactured by mixing raw material powder containing a hard phase and a binder phase containing an iron group metal, compressing it at a predetermined pressure to form a compact, and sintering the compact.

JP 2013-14792 A

  However, in order to form a heat conduction path by WC in a hard material and improve the thermal shock resistance of the hard material, it may not be sufficient to use only a hard phase having a core-shell structure as a raw material powder. For example, depending on the composition of the core and the coating thickness of the shell, WC may be dissolved during the sintering process, and a heat conduction path may not be formed.

  This invention is made | formed in view of the said situation, and one of the objectives of this invention is to provide the hard material provided with the thermal shock resistance which can substitute for a cemented carbide. Another object of the present invention is to provide a cutting tool having excellent thermal shock resistance.

  The hard material of the present invention is a hard material including a hard phase and a binder phase mainly composed of an iron group metal. The hard phase is a core composed of at least one of carbide, nitride, and carbonitride containing one or more elements selected from Group 4, 5 and 6 elements of the periodic table excluding W and Si; A shell made of WC and covering the core. The binder phase contains both V and Cr.

  The hard material of the present invention is excellent in thermal shock resistance.

It is a schematic diagram which shows an example of the structure | tissue of the hard material which concerns on embodiment. It is a schematic cross section which shows the cutting blade vicinity of the cutting tool which concerns on embodiment.

[Description of Embodiment of the Present Invention]
First, the contents of the embodiment of the present invention will be listed and described.

  (1) The hard material of the embodiment is a hard material including a hard phase and a binder phase mainly composed of an iron group metal. The hard phase is a core composed of at least one of carbide, nitride, and carbonitride containing one or more elements selected from Group 4, 5 and 6 elements of the periodic table excluding W and Si; A shell made of WC and covering the core. The binder phase contains both V and Cr.

  According to the hard material of the above-described embodiment, by containing V and Cr in the binder phase, it is possible to suppress the dissolution of WC in the liquid phase generated in the sintering process of the hard material. Therefore, it can be set as the sintered compact which combined the hard phase of the core-shell structure which covered the outer periphery of the core with the shell with the binder phase. Therefore, by using the shell as a heat conduction path, a hard material having high thermal conductivity can be obtained, and a hard material having excellent thermal shock resistance can be obtained.

  When the binder phase contains V, WC dissolved in the liquid phase can be prevented from reprecipitation in the liquid phase during the sintering process. Further, since the binder phase contains Cr, the solubility of WC in the binder phase can be reduced during the sintering process. That is, by including both V and Cr in the binder phase, it is easy to maintain the WC coating even when the sintering conditions are high.

  (2) As a hard material of the embodiment, the binder phase may have a V content of 5% by mass or less based on the total binder phase.

  The more the content of V, the more the dissolution and reprecipitation can be suppressed, and the more effective the maintenance of the WC coating is. However, when the content is too large, V is likely to precipitate and causes embrittlement. Therefore, when the V content is 5% by mass or less with respect to the entire binder phase, the V content in the binder phase can be made appropriate, and embrittlement can be prevented.

  (3) As a hard material of the embodiment, the binder phase may have a Cr content of 10% by mass or less based on the total binder phase.

  The greater the Cr content, the lower the solubility of the WC in the binder phase, and the more effective the maintenance of the WC coating. However, too much Cr tends to precipitate and cause embrittlement. Therefore, when the Cr content is 10% by mass or less with respect to the entire binder phase, the Cr content in the binder phase can be made appropriate, and embrittlement can be prevented.

  (4) The cutting tool according to the embodiment includes a cutting edge peripheral region including a cutting edge constituted by ridges on both sides of the flank face and the rake face and the vicinity thereof. At least the peripheral region of the cutting edge includes a base material made of the hard material of the above-described embodiment and a hard coating that covers the base material. The hard material which comprises the said base material is covered with the said shell, without exposing the said core in at least one part of the said flank and rake face.

  When a base material is constituted by the hard material of the embodiment and the cutting tool is provided with a hard coating on the base material surface, at least a part of the base material in the peripheral region of the cutting edge, in particular, the flank and rake face of the cutting tool. Since the core to be formed is covered with a shell, a hard coating is formed on the shell of the WC. Therefore, the adhesion of the hard coating to the base material can be increased as compared with the case where the hard coating is formed on the base material from which the core is exposed. As a result, the life as a cutting tool can be extended. Since this cutting tool uses the hard material mentioned above, it is excellent in thermal shock resistance.

[Details of the embodiment of the present invention]
Details of the embodiment of the present invention will be described below. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to the claim are included.

[Hard material]
The hard material which concerns on embodiment is comprised with the sintered compact which couple | bonded the powder of the hard phase 10 with the binder phase 20, as the example shows in FIG.

《Hard phase》
The hard phase 10 has a core-shell structure in which the outer periphery of the core 11 is covered with a shell 12. The core 11 has a function that contributes mainly to the improvement of the wear resistance of the hard material by constituting the central portion of the hard phase of the core-shell structure and having sufficient hardness. The shell 12 covers the outer periphery of the core 11 and ensures the toughness of the hard material, and forms a heat conduction path with a high thermal conductivity in the hard material, so that mainly the fracture resistance and the thermal shock resistance of the hard material are formed. It has a function that contributes to improvement.

(core)
The material of the core is at least one of carbides, nitrides, and carbonitrides containing one or more elements selected from Group 4, 5 and 6 elements of the periodic table excluding W and Si. Specifically, TiC, TiN, TiCN, etc. are mentioned. By selecting these Ti-based compounds as the core material, the difference in linear expansion coefficient from the WC constituting the shell can be made relatively small, and cracks can occur in the shell due to the thermal history during the shell formation process and the hard material sintering process. It is easy to suppress the occurrence or partial peeling of the shell. Further, the core can be made of a material having higher hardness than WC. The hard phase core may be composed of the same material for all the hard phase cores, or may include a mixture of hard phases made of different materials.

  The average particle diameter of the core is 0.5 μm or more. If the particle size of the hard phase is small, the grain boundaries increase, and the thermal conductivity of the hard material decreases. Therefore, when the average particle size of the core is 0.5 μm or more, the effect of improving the thermal conductivity of the hard material is easily obtained. Moreover, the core particle of such a size is easy to manufacture. In particular, in consideration of increasing the thermal conductivity of the hard material, the average particle diameter is 1.5 μm or more, and further 2 μm or more. On the other hand, the upper limit of the average particle diameter of the core is about 7 μm. This is because if the average particle size of the core is 7 μm or less, a high-strength hard material can be easily obtained. This average particle size is calculated using the Fullman equation by taking a photograph with a scanning electron microscope (SEM) by polishing the cut surface of the hard material after sintering and then mirror polishing the surface. It is the value. In addition, since the average particle diameter (average particle diameter after sintering) in the hard material of the present embodiment is manufactured through a mixing method that does not use pulverization media as described later, the average of the core particles in the raw material powder The particle size is almost maintained.

(shell)
When the shell is made of WC, it is easy to form a WC skeleton network having excellent thermal conductivity in the hard material, and the thermal conductivity of the hard material can be increased. In addition, since the shell is WC, the wettability with the iron group metal is excellent. Therefore, when the iron group metal is used as the binder phase material, the sinterability is improved and a dense sintered body can be obtained. It can be a hard material with excellent chipping properties.

  The average thickness of the shell is about 0.01 μm or more and 2 μm or less. If the average thickness is 0.01 μm or more, the effect of increasing the thermal conductivity of the hard material by using the shell as a heat conduction path is easily obtained, and if it is 2 μm or less, the shell is difficult to crack, and the effect of increasing the thermal conductivity of the hard material Is easy to obtain. In order to make the effect of increasing the thermal conductivity of the hard material noticeable, the average thickness of the shell is 0.02 μm or more, particularly 0.04 μm or more. In order to suppress cracks in the shell more reliably, the average thickness of the shell is 1.5 μm or less, particularly 0.3 μm or less. This average thickness is measured by processing a focused ion beam (FIB) on a cutting surface of a hard material, taking a photograph with a transmission electron microscope (TEM), and taking a plurality of hard phase particles. This is done by averaging the thickness of the shell at 10 or more measurement points.

  Moreover, it is preferable that it is less than 3% of the average particle diameter of a core when the average thickness of the shell comprised by WC is shown by the ratio with the average particle diameter of a core. This is because when the ratio is less than 3%, the effect of increasing the thermal conductivity of the hard material is increased for the above-described reason.

  That is, a preferable condition for suppressing cracks in the shell is to make the volume content of the core in the composite particles having the core-shell structure larger than the volume content of the shell. If a shell having a thickness less than a certain ratio is formed according to the size of the core, it is easy to suppress the occurrence of cracks in the shell.

<< Binder Phase >>
The binder phase 20 is a material that bonds the particles of the hard phase, and includes an iron group metal, V, and Cr. As the iron group metal, at least one of Co and Ni is preferable since it has a hard phase and high wettability. When the binder phase is mainly composed of Co, the sinterability is particularly improved, the sintered body can be easily made dense, and the strength and fracture toughness can be improved. On the other hand, Ni is excellent in corrosion resistance.

  By containing V and Cr in the binder phase 20, it is possible to prevent WC from dissolving in the liquid phase generated in the sintering process of the hard material. Therefore, a sintered body in which the hard phase 10 having a core-shell structure in which the outer periphery of the core 11 is more reliably covered with the WC shell 12 is bonded with the bonding phase 20 can be obtained. Specifically, it is possible to obtain a hard phase in which the shell is coated over 30%, preferably 50% or more, further 70% or more, in particular, the entire circumference of the circumference of the core in the cross section of the hard phase.

  Depending on conditions such as the composition of the hard phase, the coating thickness of the shell, and the sintering temperature, WC is dissolved in the liquid phase of the binder phase in the sintering process, and the core-shell structure cannot be sufficiently maintained. May be exposed from the shell 12. Therefore, the heat conduction path by the shell cannot be formed, and the thermal conductivity of the hard material is likely to be lowered. By containing V in the binder phase, it is possible to suppress reprecipitation of WC dissolved in the liquid phase in the liquid phase during the sintering process. By containing Cr in the binder phase, the solubility of WC in the binder phase can be reduced during the sintering process.

  The V content may be 1% by mass or more and 10% by mass or less based on the entire binder phase. When the V content is 1% by mass or more, dissolution / reprecipitation of the WC can be suppressed, and it is easy to maintain the WC covered by the outer periphery of the core, and further 2% by mass or more, particularly 5% by mass or more. There are some. The greater the V content, the more effective the maintenance of the WC coating. However, if too much V is likely to precipitate and cause embrittlement, the content is 10% by mass or less, and further 5% by mass or less. .

  The Cr content is 2% by mass or more and 15% by mass or less with respect to the entire binder phase. When the Cr content is 2% by mass or more, the solubility of the WC in the binder phase can be reduced, and it is easy to maintain the WC covered by the outer periphery of the core, and further 5% by mass or more, particularly 10% by mass or more. It is mentioned that. The higher the Cr content, the more effective the maintenance of the WC coating. However, if too much Cr is likely to precipitate and cause embrittlement, it is 15% by mass or less, and further 10% by mass or less. .

  The content ratio of V and Cr may be V: Cr = 0.5: 1.5 to 1.5: 0.5 by mass ratio. In particular, when the V content is more than 2% by mass and 5% by mass or less, and the Cr content is 2% by mass or more and 10% by mass or less, when the content ratio of V and Cr is the above ratio, It can suppress effectively that WC melt | dissolves in the liquid phase of a binder phase. Furthermore, it is mentioned that V: Cr = 0.8: 1.2 to 1.2: 0.8, especially V: Cr = 1: 1.

  Each content of V and Cr in the binder phase can be measured with respect to a hard material (sintered body) with an electron probe microanalyzer (EPMA).

  In addition, constituent elements of the hard phase such as W, Ru, and C may be dissolved in the binder phase. In particular, a large amount of at least one of W and Ru is preferable because the binder phase is strengthened by solid solution and the toughness of the hard material can be improved.

  The binder phase may be contained in an amount of 3% by mass or more and 20% by mass or less based on the entire hard material. As the binder phase content increases, the toughness and sinterability of the hard material tend to increase, and when the content is small, the strength and toughness tend to decrease.

《Other hard phases》
The hard material may contain another hard phase (second hard phase) as necessary in addition to the hard phase of the above-described embodiment. As the second hard phase, a compound of at least one metal element selected from Group 4, 5, 6 elements of the periodic table and at least one element of C and N, that is, carbide, nitride, and carbon of the above metal element At least one kind of nitride can be used. When at least one of TaC and NbC is included, the resistance to steel can be improved, and when at least one of ZrC, ZrCN, and ZrN is included, the strength of the hard material at high temperature can be improved.

[Method of manufacturing hard material]
The hard material of this embodiment is typically manufactured through the steps of preparation of raw material powder → mixing → molding → sintering.

<< Preparation process >>
In the preparation step, a hard phase powder and a binder phase powder are prepared. In order to obtain a core-shell structured hard phase powder, first, as a powder composed of core particles, carbides, nitrides containing one or more elements selected from Group 4, 5, 6 elements except Si and Si, And a core powder composed of at least one kind of carbonitride. Next, each particle of the prepared core powder is coated with WC serving as a shell. For the formation of the shell, a liquid phase method such as a sol-gel method can be used in addition to a vapor phase growth method such as a CVD method and a PVD method. By forming the shell by a vapor deposition method, a dense shell can be formed relatively easily.

For example, in the case of the CVD method, the core powder is put into a container, and after the container is evacuated, a predetermined gas is introduced into the container while rotating the container, and the core powder is held at a predetermined temperature. A WC shell is formed on the surface of each particle. By rotating the container, a shell can be uniformly formed on each particle of the core powder. Examples of the gas introduced into the container include tungsten fluoride (for example, WF ₆ gas) and methane (CH ₄ ) or acetonitrile (CH ₃ CN) as a source gas, and hydrogen or argon gas as a carrier gas. In particular, it is preferable to use CH ₃ CN gas because it is easier to form a WC that is chemically more stable and has a higher thermal conductivity than brittle W ₂ C, and in particular, a WC with high crystallinity can be formed. The film forming temperature is preferably about 700 to 1100 ° C. When a WC film is formed in this temperature range, the crystallinity of the WC increases, phonon scattering accompanying crystal defects in the WC can be suppressed, and the shell can have high thermal conductivity. In addition, when the film is formed in this temperature range, the adhesion between the core and the shell becomes high, and the thermal conductivity of the shell due to the WC peeling and the solid solution of the WC with the Ti element in the sintering process is accompanied. Since a fall can be suppressed, it is preferable.

  On the other hand, in the case of the PVD method, for example, the following method may be mentioned. First, core powder is put in a container, and after vacuuming the container, tungsten is sputter-deposited on the core powder using a tungsten target while rotating the container. Next, the obtained tungsten-coated core powder is carbonized at a temperature of about 1700 to 2000 ° C. to form WC on each particle surface of the core powder.

  In order to obtain a binder phase powder, a powder containing iron group metal as a main component and uniformly dispersing both V and Cr is prepared. For example, a metal powder containing iron group metal as a main component and a carbide powder containing both V and Cr are blended at a predetermined composition ratio and pulverized and mixed with a ball mill to uniformly disperse V and Cr. To do. In addition, it is also possible to use a technique such as coating V and Cr on metal powder containing iron group metal as a main component, or pulverizing an alloy body in which V and Cr are dissolved in metal powder.

《Mixing process》
Each raw material powder mentioned above is mixed as uniformly as possible by a suitable mixing means to obtain a mixed powder. In this mixing step, it is important to mix the raw material powder so as not to damage the core-shell structure of the hard phase. That is, in this mixing step, the mixing means is selected so that the shell does not crack or peel off. Specifically, for example, the raw material powder is mixed with an organic solvent such as ethanol or acetone to form a slurry, and the slurry is mixed without pulverizing media while being irradiated with ultrasonic waves. According to this mixing method, the raw material powder can be mixed without substantially pulverizing the raw material powder and without damaging the shell.

  When the raw material powder is mixed to obtain a mixed powder, usually, a binder is added to the mixed powder, and the mixture is spray-dried using a drying means such as a spray dryer and granulated. Examples of the binder include paraffin wax and polyethylene glycol. As for content of this binder, about 1 mass% or more and 4 mass% or less are mentioned with respect to the sum total of the said raw material powder and a binder.

<Molding process>
Molding of the mixed powder obtained in the mixing step is performed by filling the mold with the mixed powder and molding it into a predetermined shape with a predetermined pressure. Examples of the molding method include a dry pressure molding method, a cold isostatic pressing method, an injection molding method, and an extrusion molding method. The molding pressure is preferably about 0.5 ton / cm ² (about 50 MPa) or more and about 2.0 ton / cm ² (about 200 MPa) or less. Moreover, the shape of a molded object selects the appropriate shape which does not become an excessively complicated shape according to the shape of the product calculated | required. The final product shape may be appropriately machined after calcination or sintering as necessary.

<< Sintering process >>
It is preferable to perform the sintering of the compact by holding the compact for a predetermined time in a temperature range where a liquid phase is generated. As for sintering temperature, 1300 degreeC or more and about 1600 degrees C or less are mentioned. If the sintering temperature is too high, particles constituting the hard phase tend to grow. The holding time is preferably about 0.5 to 2.0 hours, particularly preferably about 1.0 to 1.5 hours. The atmosphere during heating is preferably an inert gas atmosphere such as nitrogen or argon or a vacuum (about 0.1 Pa or more and 0.5 Pa or less).

  In this sintering process, since hard particles that are substantially free of damage such as cracking and peeling are used in the shell from the raw material powder stage, the shell serves as a barrier to prevent the liquid phase from contacting the core, Interdiffusion between constituent elements between the core and the liquid phase is suppressed. Moreover, since both V and Cr are uniformly dispersed in the binder phase, dissolution of WC in the liquid phase is suppressed. Cr in the binder phase reduces the solubility of WC in the binder phase, and even if WC is dissolved by V in the binder phase, the dissolved WC is re-recovered in places other than where it was dissolved in the liquid phase or on the shell. In order to suppress the precipitation, most of the hard phases are maintained in a state where the outer periphery of the core is covered with the shell. More than 30% of the circumference of the core in the cross section of the hard phase, preferably 50% or more, more than 70%, especially 60% or more of the hard phase covered by the shell over the entire circumference of the entire hard phase Further, it is preferably 70% or more, particularly preferably 80% or more. In particular, of the entire hard phase, the ratio of the number of hard particles covered with the WC shell over the entire circumference of the core in the cross section of the hard phase is 20% or more, further 30% or more, particularly 50% or more. It is preferable. Further, in the entire hard phase, the ratio of the number of hard particles in which 70% or more of the peripheral length of the core in the cross section of the hard phase is exposed from the shell is 40% or less, further 30% or less, particularly 20% or less. Is preferred. This ratio can be performed by observing the cross section of the sintered body by SEM. At that time, an SEM image is acquired and observed so that about 100 hard particles are included in the visual field of the cross section.

  Further, in the sintering step, when the molded body heated by holding the sintering temperature for a predetermined time is cooled, it is preferably cooled in an inert gas atmosphere such as vacuum or argon.

〔Cutting tools〕
The manufactured cutting tool using the hard material includes, for example, as shown in FIG. 2, a base material 110 and a hard coating 120 that covers the base material 110. In FIG. 2, the upper surface of the cutting tool is a rake face, the left slope is a flank face, and the ridge lines on both sides are cutting edges.

<Area around cutting edge>
In the cutting tool of the embodiment, the entire base material is made of the hard material of the above-described embodiment, and the entire surface of the base material 110 is covered with the hard coating 120. However, the portion formed of the hard material of the embodiment may be at least a region related to cutting, that is, a peripheral region of the cutting blade including the cutting blade and the vicinity thereof, and the formation region of the hard coating 120 is the same. The peripheral region of the cutting edge includes a region where flank wear and crater wear are likely to occur, and a region where chips come into contact. By using the base material 110 made of the hard material of the embodiment in the peripheral region of the cutting edge, it is possible to obtain a cutting tool having excellent fracture resistance in addition to wear resistance and thermal shock resistance. In particular, in the hard material constituting the base material 110, the core is not exposed by being covered with the shell. Therefore, the hard coating 120 described below is formed on the WC constituting the shell instead of the core. The adhesion of the coating 120 to the substrate 110 can be enhanced. This is considered to be because the hard coating 120 is not formed on partially different materials (TiC, TiCN, WC) but on a uniform material (WC). In particular, when the hard coating 120 is formed by the PVD method, the fact that the core of the constituent material of the hard coating 120 is easily formed on the WC is considered to contribute to the improvement of the adhesion. On the other hand, cutting edge processing may be performed with a cutting tool. In that case, the cutting edge processing region may damage the shell and expose the core. However, even in that case, the core is covered with the shell without exposing at least a part of the flank face and the rake face which are not the blade edge processing region. Therefore, the adhesiveness of the hard coating 120 to the base material 110 is sufficiently high as compared with the case where the ratio of hard particles with damaged shells is high over the entire coating region of the base material 110.

《Hard coating》
The cutting tool preferably includes a hard coating 120 in at least the peripheral region of the cutting edge of the substrate 110. By providing the hard coating, higher wear resistance can be obtained.

The material of the hard coating 120 is selected from the group consisting of one or more elements selected from the group consisting of metals of Group 4, 5, 6 of the periodic table, Al, Si and B, and carbon, nitrogen, oxygen and boron. It is preferable to use a compound composed of a compound with one or more elements. Specific examples include TiCN, Al ₂ O ₃ , TiAlN, TiN, and AlCrN. The film structure of the hard coating 120 may be a single layer or multiple layers. The total thickness of the hard coating 120 is preferably about 1 μm to 20 μm. As a method for forming the hard coating 120, any of CVD methods such as a thermal CVD method and PVD methods such as a cathode arc ion plating method can be used.

  In addition, although the cutting tool which has the hard coating 120 is shown in FIG. 2, the cutting tool which does not have this coating | cover and is comprised only with the base material 110 may be used.

[Test Example 1]
Prepare a TiC _0.5 N _0.5 powder with an average particle size of 3 μm as the core powder, charge the powder into a stainless steel container and evacuate it, then heat the container to 1000 ° C. while rotating the container. Then, WF ₆ gas and CH ₃ CN, H ₂ , Ar gas are flown, and WC (shell) with an average thickness of 0.08 μm is applied to each particle (core) of TiC _0.5 N _0.5 powder under a pressure of 6 kPa. A hard phase powder was produced by coating. The average thickness of the shell of the coating powder was about 2.7% of the average particle diameter of the core. The average thickness of the shell can be measured by TEM.

  As a binder phase powder, a powder containing Co as a main component and uniformly dispersing both V and Cr is prepared. This binder phase powder was prepared by blending a metal powder containing Co as a main component and a carbide powder containing both V and Cr in the proportions shown in Table 1, and pulverizing and mixing them with a ball mill.

  The hard phase powder and the binder phase powder were blended at a mass ratio of 85:15 and mixed so as not to break the shell of the hard particles. Specifically, the raw material powder was mixed in ethanol using ultrasonic waves without using a grinding medium.

These mixed powders are granulated using camphor and ethanol, and press-molded at a pressure of 1 ton / cm ² (about 98 MPa) to obtain a molded body.

  The compact was sintered under vacuum at a maximum temperature of 1410 ° C. and held for 1 hour to obtain a sintered body. It can be confirmed by EPMA that the composition of the sintered body is almost the same as the composition of the raw material powder.

  After cutting the obtained sintered body (hard material) and mirror-finishing the cut surface, the observation magnification is 5000 times so that about 100 hard particles (89 to 108 in this test example) are included in the visual field. The SEM image was acquired by observing the coated state of WC. In the SEM image, WC as a shell can be observed as a white structure with high luminance, and TiCN as a core can be observed as a black structure with low luminance. Note that a composite carbide such as (Ti, W) CN and a bonded phase such as Co are observed as a structure having a luminance intermediate between WC and TiCN. Based on the distribution of WC and TiCN observed in this way, the hard phase in which the WC is completely covered by WC is “completely coated”, and the hard phase in which 70% or more of the circumference of TiCN is exposed from the WC coating. The phases were classified as “uncoated” and the other hard phases were classified as “partially coated”, and the number of these hard phases was examined from all the hard particles in the field of view. Furthermore, as a comprehensive judgment of the covering state, a hard material in which the uncoated hard phase accounts for 50% or more of the whole is “C (defect)”, and a hard material in which the uncoated hard phase is less than 10% of the whole is “A”. (Excellent) ”and other hard materials were determined as“ B (good) ”. The results are shown in Table 1.

  Further, the above-mentioned hard material is subjected to surface grinding of the bearing surface with a # 200 diamond grindstone and subjected to cutting edge processing to obtain a base material having a shape of SNGN120408 (the flank and rake face are not ground). When this base material was observed by SEM or TEM, the core-shell structured composite particles in which cracks and peeling occurred in the shell were substantially absent in the flank face and rake face area where the blade edge treatment was not performed. Furthermore, the surface of this base material was coated with a TiAlN film (hard coating) to an average thickness of 5 μm by a known PVD method to obtain a cutting tool.

  Using this cutting tool, a milling cutting test was performed on an S50C grooveless work material at a cutting speed of 200 m / min, a feed rate of 0.2 mm / rev, a cutting depth of 2.0 mm, and a cutting time of 5 minutes under wet conditions. The thermal shock resistance was evaluated by measuring the number of cracks generated in the hard material (base material) of the cutting tool. The number of cracks was measured by observing the SEM composition image of the substrate surface (flank and rake face). The results are shown in Table 1.

  As shown in Table 1, sample Nos. 1 and 2 containing both V and Cr in the binder phase. 1 to Sample No. It can be seen that the 16 hard materials have a ratio of the uncoated hard phase of less than 50% of the total, and can stably maintain the WC coating. Among them, sample No. 1 in which the Cr content is 10% by mass or more with respect to the whole binder phase and the V content is 2% by mass or more with respect to the whole binder phase. The hard materials of 7, 8, 11, 12, 15, 16 have a ratio of uncoated hard phase of less than 10%, and it can be expected that a heat conduction path by WC can be stably formed. In particular, Sample No. No. 2 having a Cr content of 10% by mass or more with respect to the entire binder phase and a V content of 5% by mass or more with respect to the entire binder phase. The hard materials of 11, 12, 15, and 16 have a ratio of the hard phase of the complete coating of 50% or more, and it can be expected that the WC coating can be stably maintained and the heat conduction path can be stably formed.

  In addition, as shown in the evaluation results of thermal shock resistance in Table 1, the sample No. 1 containing both V and Cr in the binder phase was used. 1 to Sample No. The hard material of No. 16 has a sample No. 1 containing neither V nor Cr in the binder phase. 101, sample No. 101 containing only V or Cr in the binder phase. 102-Sample No. It can be seen that the number of hot cracks is smaller than that of 106, and the thermal shock resistance is excellent. Sample No. 1 to Sample No. No. 16 in which the V content exceeds 5% with respect to the entire binder phase or the Cr content exceeds 10% by mass with respect to the entire binder phase. It can be seen that the hard materials of 4, 8, 12 to 16 are excellent in maintaining the WC coating but tend to slightly increase the number of hot cracks. This is considered to be due to the fact that the content of V and Cr in the binder phase is increased, so that Co is solid solution hardened, the toughness is lowered, and the thermal crack resistance is slightly lowered.

  The hard material of the present invention is expected to be used as an alternative raw material for conventional cemented carbide. In particular, since this hard material does not easily react with steel, when it is made into a sintered body, it can be suitably used as a cutting tool for steel processing.

10 Hard phase 11 Core 12 Shell 20 Bonded phase 110 Base material 120 Hard coating

Claims (4)

A hard material comprising a hard phase and a binder phase mainly composed of an iron group metal,
The hard phase is
A core composed of at least one of carbides, nitrides, and carbonitrides containing one or more elements selected from periodic table 4, 5, 6 elements and Si, excluding W;
A shell made of WC and covering the core;
The binder phase is a hard material containing both V and Cr.   The hard material according to claim 1, wherein the binder phase has a V content of 5% by mass or less based on the total binder phase.   The hard material according to claim 1, wherein the binder phase has a Cr content of 10% by mass or less based on the total binder phase. A cutting tool comprising a cutting edge peripheral region including a cutting edge composed of ridges on both sides of the flank and rake face and the vicinity thereof,
At least the peripheral area of the cutting edge is
A substrate made of the hard material according to any one of claims 1 to 3,
A hard coating covering the substrate,
The hard material which comprises the said base material is the cutting tool with which the said core is covered with the said shell, without exposing in at least one part of the said flank and rake face.

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