JP2014221942A - Hard particles, hard material, cutting tool, method of producing hard particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide hard particles suitable as a raw material of a hard material having defect resistance, which can serve as an alternative for hard metals, and to provide a hard material and a cutting tool using the hard particles.SOLUTION: The hard particles include a core and a shell covering the core. The core is composed of at least one of carbides, nitrides and carbonitrides containing at least one element selected from Group 4, 5 and 6 elements other than W of the Periodic Table, and Si. The shell is composed of polycrystalline WC of an average crystal grain size of 20-50 nm. The hard particles can have a core coated with polycrystalline WC by: dissolving a tungstic acid compound and an organic acid in a basic aqueous solution to disperse cores in a precursor solution; subjecting the precursor solution having the cores dispersed to ultrasonic cavitation; and dry firing the cores in a state where surfaces thereof are coated with the precursor.

Description

  The present invention relates to a hard particle suitable as a raw material of a tool for cutting a metal material such as steel, cast iron, and sintered alloy, a manufacturing method thereof, a hard material using the hard particle, 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 made of at least one of Ti carbide and Ti carbonitride and a shell made of WC and covering the core.

JP 2013-14792 A

  In conventional hard materials, the hard phase (hard particles) of a specific core / shell structure is used to increase the thermal conductivity of the hard phase while ensuring sufficient wear resistance, especially the thermal shock resistance of hard materials. However, further improvement in fracture resistance is desired.

  The present invention has been made in view of the above circumstances, and one of the objects of the present invention is suitable as a raw material for a hard material having wear resistance, thermal shock resistance, and fracture resistance, which can replace cemented carbide. The object is to provide hard particles and a method for producing the same. Another object of the present invention is to provide a hard material and a cutting tool that are excellent in wear resistance, thermal shock resistance, and fracture resistance.

  The hard particle of the present invention is a hard particle having a core and a shell covering the core, and the core contains one or more elements selected from periodic table 4, 5, 6 elements other than W and Si. The shell is composed of at least one of carbide, nitride, and carbonitride contained therein, and the shell is composed of polycrystalline WC having an average crystal grain size of 20 nm to 50 nm.

The method for producing hard particles of the present invention includes the following steps.
(A) A preparatory step for preparing a precursor solution by dissolving a tungstic acid compound and an organic acid in a basic aqueous solution.
(B) The precursor solution is composed of 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. A dispersion step of dispersing the core to be dispersed.
(C) A coating step in which the precursor solution in which the core is dispersed is irradiated with ultrasonic cavitation to coat the precursor on the surface of the core.
(D) A drying and firing step in which the core coated with the precursor is dried and fired in an inert atmosphere to synthesize polycrystalline WC from the precursor.

  The hard particles of the present invention are excellent in wear resistance, thermal shock resistance, and fracture resistance, and can be suitably used as a raw material for cutting tools.

  Moreover, the manufacturing method of the hard particle of this invention can manufacture the hard particle which is excellent in abrasion resistance, thermal shock resistance, and fracture resistance with high productivity.

It is a schematic diagram which shows an example of the hard particle 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]
In cemented carbide, by reducing the WC grain size, the hardness that affects the wear resistance is improved, but the toughness that affects the fracture resistance tends to decrease. As a result of intensive studies by the present inventors, it has been found that by making WC polycrystalline, both hardness and toughness can be improved. The contents of the embodiments of the present invention will be listed and described below.

  (1) The hard particle of the embodiment is a hard particle including a core and a shell covering the core, and the core is one selected from periodic table 4, 5, 6 elements other than W and Si The shell is composed of at least one of carbides, nitrides, and carbonitrides containing the above elements, and the shell is composed of polycrystalline WC having an average crystal grain size of 20 nm to 50 nm.

  According to the hard particle | grains of above-described embodiment, both the hardness and toughness of a shell can be improved because the shell is comprised by the polycrystal WC. When the average crystal grain size of the polycrystalline WC is 20 nm or more, the thermal resistance of the crystal grain boundary can be reduced. 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 average crystal grain size of the polycrystalline WC is 50 nm or less, the hardness and toughness of the shell can be improved, and a hard material excellent in wear resistance and fracture resistance can be obtained.

  (2) As hard particle | grains of embodiment, it is mentioned that the said core contains Ti.

  When the core contains Ti, the difference in coefficient of linear expansion from the WC constituting the shell can be made relatively small, and the shell may crack due to the thermal history in the shell formation process or the sintering process of the hard material. It can suppress peeling off partially. Further, the core can be made of a material having higher hardness than WC.

  (3) As the hard particles of the embodiment, the average particle diameter of the core is 0.5 μm or more and 5.0 μm or less.

  The toughness is improved when the average particle size of the core is 0.5 μm or more, and the hardness is improved when the average particle size is 5.0 μm or less. In addition, when a hard material is manufactured using the hard particles of the embodiment as a raw material, the effect of improving the thermal conductivity of the hard material is easily obtained.

  (4) As the hard particles of the embodiment, the average thickness of the shell is 50 nm or more and 300 nm or less.

  When the shell has an average thickness of 50 nm or more, the shell can be used as a heat conduction path, whereby a hard material with high thermal conductivity can be obtained and a hard material excellent in thermal shock resistance can be obtained. When the thickness of the shell is 300 nm or less, cracks are unlikely to occur in the shell, and it can be a hard material with high thermal conductivity, and can be a hard material excellent in wear resistance and thermal shock resistance.

  (5) The hard material of the embodiment is a hard material including a hard phase and a binder phase containing an iron group metal, and the hard phase includes the hard particles of the above-described embodiment.

  Since the hard material of the embodiment uses the hard particles of the embodiment described above as a raw material, it is excellent in wear resistance, thermal shock resistance, and fracture resistance.

  (6) The cutting tool of the embodiment includes a cutting edge peripheral region including a cutting edge constituted by ridge lines on both sides of the flank face and the rake face and the vicinity thereof. At least the cutting edge peripheral region includes a base material made of the hard material of the above-described embodiment and a hard coating covering 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 abrasion resistance, thermal shock resistance, and fracture resistance.

(7) The manufacturing method of the hard particle | grains of embodiment is equipped with the following processes.
(A) A preparatory step for preparing a precursor solution by dissolving a tungstic acid compound and an organic acid in a basic aqueous solution.
(B) The precursor solution is composed of 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. A dispersion step of dispersing the core to be dispersed.
(C) A coating step in which the precursor solution in which the core is dispersed is irradiated with ultrasonic cavitation to coat the precursor on the surface of the core.
(D) A drying and firing step in which the core coated with the precursor is dried and fired in an inert atmosphere to synthesize polycrystalline WC from the precursor.

  According to the method for producing hard particles of the above-described embodiment, hard particles having excellent wear resistance, thermal shock resistance, and fracture resistance can be produced with high productivity. By using ultrasonic cavitation in the coating step, the mechanochemical reaction field can be limited to the core surface, and the precursor can be efficiently coated on the core surface. More specifically, cavitation bubbles are generated in the aqueous solution by irradiating the precursor solution with ultrasonic cavitation, and the core is coated on the surface of the core by a strong impact force generated by the collapse of the cavitation bubbles. Can do. At this time, the average crystal grain size of the polycrystalline WC formed in the drying and firing step described later is adjusted by the W concentration in the precursor solution. When the W concentration is high, the particle size of the precursor to be coated increases, so that the average crystal particle size of the polycrystalline WC can be increased. On the other hand, when the W concentration is low, the particle size of the precursor to be coated becomes small, so that the average crystal particle size of the polycrystalline WC can be made small. In the drying and firing step, the precursor-coated core is dried, the precursor-coated particles are taken out, and the precursor-coated particles are subjected to a heat treatment, whereby the precursor can be converted into polycrystalline WC.

  (8) As a manufacturing method of the hard particle of embodiment, using ammonium paratungstate as said tungstic acid compound is mentioned.

  When ammonium paratungstate is used, the concentration of W in the precursor solution can be improved, so that W can be efficiently coated on the surface of the core.

[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 particles]
The hard particles 10 according to the embodiment have a core-shell structure as shown in FIG. The core 11 constitutes the central portion of the hard particle 10 having a core-shell structure, and has a function that contributes mainly to improvement of the wear resistance of the hard material by 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 compounds as the core material, hard particles having excellent wear resistance can be obtained. In the powder made of hard particles, the cores of all hard particles may be made of the same material, or hard particles of cores made of different materials may be mixed.

  The average particle size of the core is preferably 0.5 μm or more and 5.0 μm or less. The average particle size of the core contributes particularly to hardness and toughness. Considering the balance between the two, it is preferably 1.0 μm or more and 4.0 μm or less, more preferably 1.5 μm or more and 3.0 μm or less. This average particle size is determined by applying a full-man formula to a hard material manufactured using hard particles as a raw material, cutting the surface of the cut surface after mirror polishing, and taking a photograph with a scanning electron microscope (SEM). Is a value calculated using. In addition, the average particle diameter of the core in the hard material manufactured using the hard particles of the embodiment as a raw material (average particle diameter after sintering) is preferably manufactured through a mixing method that does not use pulverization media as described later. In that case, the average particle diameter of the core in the raw material powder is substantially maintained.

"shell"
Since the shell is composed of polycrystalline WC, the shell can be composed of an aggregate of a plurality of minute single crystals, so that both hardness and toughness can be improved. The average crystal grain size of the polycrystalline WC is preferably 20 nm or more and 50 nm or less. The average crystal grain size of the polycrystalline WC is obtained by processing a focused ion beam (FIB) on a cutting surface of a hard material manufactured using hard particles as a raw material, and using a transmission electron microscope (TEM). This is a value calculated using the Fullman equation after taking a picture.

  The average thickness of the shell is preferably 50 nm or more and 300 nm or less. In particular, in order to make the effect of increasing the thermal conductivity of a hard material produced using hard particles as a raw material, it is preferably 100 nm or more, more preferably 200 nm or more. This average thickness is a value obtained by performing FIB processing on the cut surface of the hard material, taking a photograph with a TEM, and calculating the thickness of the shell at 10 or more measurement points in a plurality of hard particles using the Fullman equation. .

[Method for producing hard particles]
The method for producing hard particles includes a preparation step, a dispersion step, a coating step, and a drying and firing step. Each step will be described in detail.

<< Preparation process >>
In the preparation step, a tungstic acid compound and an organic acid are dissolved in a basic aqueous solution to prepare a precursor solution. As the tungstic acid compound, for example, ammonium paratungstate, aluminum tungstate, sodium tungstate, or the like can be used. Among these, ammonium paratungstate is preferable in that the concentration of W in the precursor solution can be improved. Examples of organic acids that can be used include formic acid, maleic acid, fumaric acid, acetic acid, citric acid, and oxalic acid. Examples of the basic aqueous solution include an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide which is a strong base, or an alkaline earth metal hydroxide such as an aqueous ammonia solution or calcium hydroxide which is a weak base. An aqueous solution of a substance or an aqueous solution of a metal hydroxide other than the above can be used.

  By changing the W concentration in the precursor solution, the average crystal grain size of the polycrystalline WC constituting the shell can be changed. That is, when the tungstic acid compound is dissolved so as to increase the W concentration, the average crystal grain size of the polycrystalline WC increases. Forming a WC shell having an average crystal grain size of 20 nm or more and 50 nm or less by containing a tungstic acid compound so that the W concentration in the precursor solution is 6.5 mass% or more and 10.0 mass% or less. Can do. This W concentration can be easily determined from the blending ratio of the raw materials used, but can also be directly measured from the precursor solution by plasma emission analysis (ICP-AES). The mixing ratio of the tungstic acid compound and the organic acid is preferably 1: 2 to 1: 3 in terms of molar ratio.

<< Dispersing process >>
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 other than W and Si, in the precursor solution Disperse the powder. In addition to core powders such as TiC and TiCN, various powders having different W solid solution amounts can be selected from commercially available core powders in which W is solid solution.

<Coating process>
In the coating step, the precursor solution in which the core is dispersed is irradiated with ultrasonic cavitation to coat the surface of the core with the precursor. This precursor is presumed to be a state in which a tungstic acid compound and an organic acid are subjected to a condensation reaction. A commercially available ultrasonic irradiator can be used for the ultrasonic cavitation. The output of the ultrasonic wave to be irradiated is not particularly limited and can be changed as appropriate. For example, the coating process can be performed with an output of 300 μA. By adjusting the ultrasonic irradiation time, the thickness of the precursor coated on the surface of the core can be changed. By setting the irradiation time to 5 min to 60 min, a WC shell having an average thickness of 50 nm to 300 nm can be formed.

<< dry firing process >>
The core coated with the precursor is dried and fired in an inert atmosphere to synthesize polycrystalline WC from the precursor. The core coated with the precursor can be spray-dried using a drying means such as a spray dryer. The dried coating precursor is baked in an inert gas atmosphere such as argon to change the precursor to polycrystalline WC. The firing temperature is preferably 1000 ° C. or higher and 1400 ° C. or lower. By setting the firing temperature to 1000 ° C. or higher, conversion of the precursor to polycrystalline WC becomes easy, and by setting it to 1400 ° C. or lower, the solid phase reaction between the coating and the core can be suppressed. The firing time is not particularly limited. As an example, the precursor can be sufficiently converted into polycrystalline WC in a firing time of 0.5 hours or more and 4 hours or less.

[Hard material]
A hard material can be obtained by using, as a raw material powder, a hard phase powder containing a powder made of hard particles produced. The hard material is composed of a sintered body in which a hard phase powder is bonded with a binder phase.

《Other hard phase powder》
The hard phase powder may be only the hard particle powder of the above-described embodiment, but other hard phase powder may be added as necessary. Other hard phase powders include compounds 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, carbides, nitrides of the above metal elements, and At least one kind of carbonitride 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.

<< Binder Phase >>
The binder phase is a material that binds the hard particles, and is preferably an iron group metal. In particular, at least one of Co and Ni is preferable because of high wettability with hard particles. When the binder phase is mainly composed of Co, the sinterability is 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. Moreover, the constituent elements of hard particles such as W, Cr, Ru, and C may be dissolved in the binder phase. In particular, a large amount of at least one solid solution of W, Cr, 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 is preferably contained in an amount of 3% by mass to 20% by mass with respect to 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.

[Method of manufacturing hard material]
The manufacturing method of a hard material includes a mixing step, a forming step, and a sintering step. Each step will be described in detail.

《Mixing process》
A hard phase powder and a binder phase powder are prepared as raw material powders, and each raw material powder is mixed as uniformly as possible by an appropriate mixing means to obtain a mixed powder. In the mixing step, it is important to mix the raw material powder so as not to damage the core-shell structure of the hard particles. That is, in this mixing step, a mixing means is selected that does not cause cracks or peeling in the shell. 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. The use of a mixing method using a grinding medium having a small impact force such as a bead mill in which the diameter of the medium is reduced may be expected even when the hard particles are provided with a coating layer of a binder phase.

  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 1-4 mass% is preferable 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 50 to 200 MPa. 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. The sintering temperature is preferably about 1300 ° C to 1600 ° C. 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, vacuum (about 0.1 to 0.5 Pa), or a reduced-pressure hydrogen atmosphere.

  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, even if a part of the shell surface is dissolved in the liquid phase, it only re-deposits on the shell. As a result, the shell is maintained as WC without the element contained in the core being dissolved and becoming a solid solution with low thermal conductivity. Even if some shells of hard particles are cracked or peeled off, such hard particles are only a part, so most of the hard particle shells should be solid solutions with low thermal conductivity such as TiWC and TiWCN. Instead, the WC is maintained. In the entire powder composed of the hard particles of the embodiment, the proportion of particles in which cracks and peeling are not recognized in the shell is preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more. This ratio is obtained by calculating (number of hard particles in which cracks and peeling are not recognized in the shell / total number of hard particles) × 100 by observing the cross section of the sintered body by SEM or TEM. At that time, observation with a plurality of visual fields is performed as necessary so that the total number of hard particles is 30 or more.

  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 of the embodiment preferably includes the 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 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 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]
A sample of core-shell structured hard particles whose shell is composed of polycrystalline WC is manufactured, a hard material containing the hard particles in the raw material powder is manufactured, and the hard particles, the hard material, and the cutting tool are evaluated. Sample No. 1 to Sample No. 17 is manufactured by the procedure shown below, and sample No. No. 18 was manufactured by forming a shell by a CVD method at a high temperature of about 1000 ° C.

<< Preparation process >>
Ammonium paratungstate as a tungstic acid compound and anhydrous citric acid as an organic acid were prepared, and these were dissolved in an aqueous ammonia solution to prepare a precursor solution. The ammonium paratungstate was contained so as to have a W concentration shown in Table 1 with respect to the precursor solution, and the mixing ratio of ammonium paratungstate and anhydrous citric acid was 1: 2 molar ratio.

<< Dispersing process >>
A hard powder of TiC _0.5 N _{0.5 serving} as a core of hard particles is prepared, and these are mixed and dispersed in the precursor solution. The hard powder of TiC _0.5 N _0.5 is obtained by carbonitriding Ti powder having an average particle size described in Table 1 prepared by an atomizing method, or by classifying commercially available TiCN powder in Table 1. Those having the average particle size described can be used.

<Coating process>
With respect to the precursor solution in which the hard powder is dispersed, an ultrasonic irradiator (US-600T manufactured by Nippon Seiki Seisakusho Co., Ltd.) is used, the output of the ultrasonic wave to be irradiated is 300 μA, and the ultrasonic wave is irradiated with the irradiation time shown in Table 1. Cavitation was irradiated.

<< dry firing process >>
The core coated with the precursor was spray-dried using a drying means such as a spray dryer, and these were fired in a firing furnace in an argon atmosphere at 1150 ° C. for 0.5 hours. By this firing, WC is synthesized from the precursor, and a composite powder composed of hard particles having a core-shell structure is obtained.

《Mixing process》
The composite powder having the core-shell structure is mixed with 12.5% by volume of Co powder as a binder phase and 7.5% by volume of additive powders such as TaNbC and Cr ₃ C ₂ to form hard particles. Mixed so as not to break the shell. Specifically, the raw material powder was mixed in ethanol using ultrasonic waves without using a grinding medium.

<Molding process>
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.

<< Sintering process >>
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 (Electron Probe Micro Analyzer) that the composition of the sintered body substantially matches the composition of the raw material powder. Moreover, it can confirm by TEM observation after FIB processing that the average particle diameter of the shell in a sintered compact does not change before sintering.

  The obtained sintered body is subjected to surface grinding of the seating surface with a # 200 diamond grindstone and subjected to blade edge processing to obtain a base material having a shape of SNMG120408 (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 tool, cutting test was performed on a SK5 groove-free work material at a cutting speed of 200 m / min, a feed rate of 0.3 mm / rev, a cutting depth of 1.5 mm, a cutting time of 5 minutes, and a flank. The amount of wear (mm) was measured to evaluate the wear resistance. The test results are shown in Table 2.

  In addition, using a tool of the same shape, a cutting test was performed on four slotted workpieces made of SCM435 using a cutting speed of 240 m / min, a feed rate of 0.2 mm / rev, a cutting depth of 1.5 mm, and wet conditions. The fracture resistance was evaluated by measuring the number of times until the tool was damaged. The test results are shown in Table 2.

  Further, using a tool having the same shape, milling a groove-free work material made of SCM435 using a cutting speed of 220 m / min, a feed rate of 0.15 mm / rev, a cutting depth of 2.0 mm, a cutting time of 5 minutes, and wet conditions. A cutting test was conducted, and the thermal shock resistance was evaluated by measuring the number of cracks introduced into the hard material (base material) of the tool. The number of cracks was measured by observing the SEM composition image of the substrate. The test results are shown in Table 2.

  As shown in Table 2, the sample No. 1 in which the average crystal grain size of the polycrystalline WC constituting the shell is 20 nm or more and 50 nm or less. 1 to Sample No. No. 13 has a well-balanced expression of wear resistance, fracture resistance, and thermal shock resistance. Sample No. whose polycrystalline WC has an average crystal grain size of less than 20 nm 14 and sample no. Although No. 16 is excellent in abrasion resistance and fracture resistance, it is considered that the thermal shock resistance is lowered due to the thermal resistance of the crystal grain boundary. On the other hand, the sample No. 1 in which the average crystal grain size of the polycrystalline WC is more than 50 nm. 15 and Sample No. No. 17 is excellent in thermal shock resistance, but wear resistance is reduced. In addition, the sample No. 1 in which the shell was formed by the CVD method was used. In No. 18, polycrystalline WC is formed in a columnar shape with a short axis of 100 nm and a long axis of 300 nm, and wear resistance and fracture resistance are lowered.

  Only the average particle diameter of WC is different (the average particle diameter of the core and the thickness of the shell are the same). 1 to Sample No. 4 indicates that the smaller the average crystal grain size of the polycrystalline WC, the better the fracture resistance. That is, in the case of polycrystal, it is considered that both hardness and toughness can be improved by atomization. However, if the average crystal grain size of the polycrystalline WC is too small as less than 20 nm, the thermal shock resistance is lowered.

  Moreover, as shown in Table 1, by containing a tungstic acid compound (here, ammonium paratungstate) so that the W concentration is 6.5% by mass or more and 10% by mass or less with respect to the precursor solution. It can be seen that the average crystal grain size of the polycrystalline WC is 20 nm or more and 50 nm or less. In the coating step, it is understood that the average thickness of the shell is 50 nm or more and 300 nm or less by irradiating ultrasonic cavitation for 5 minutes or more and 60 minutes or less.

  The hard particles of the present invention are expected to be used as an alternative raw material for conventional cemented carbide. In particular, since the hard particles do not easily react with steel, when used as a sintered body, the hard particles can be suitably used as a cutting tool for steel processing. Moreover, the manufacturing method of the hard particle | grains of this invention can be utilized for the manufacture field | area etc. of a cutting tool.

10 Hard particles (hard phase)
11 Core 12 Shell 20 Bonded phase 110 Base material 120 Hard coating

Claims (8)

Hard particles comprising a core and a shell covering the core,
The core is composed of at least one of a carbide, a nitride, and a carbonitride containing one or more elements selected from Group 4, 5 and 6 elements of the periodic table excluding W and Si,
The shell is a hard particle composed of polycrystalline WC having an average crystal grain size of 20 nm to 50 nm.   The hard particle according to claim 1, wherein the core contains Ti.   3. The hard particle according to claim 1, wherein an average particle diameter of the core is 0.5 μm or more and 5.0 μm or less.   The hard particles according to any one of claims 1 to 3, wherein the shell has an average thickness of 50 nm to 300 nm. A hard material comprising a hard phase and a binder phase containing an iron group metal,
The said hard phase is a hard material containing the hard particle as described in any one of Claims 1-4. 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 claim 5;
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. A method for producing hard particles that forms a shell on the outside of a core,
A preparation step of preparing a precursor solution by dissolving a tungstic acid compound and an organic acid in a basic aqueous solution;
The precursor solution is composed of at least one of carbides, nitrides, and carbonitrides containing one or more elements selected from Si, periodic group 4, 5, 6 elements and Si, excluding W. A dispersion step of dispersing the core;
A coating step of irradiating the precursor solution in which the core is dispersed with ultrasonic cavitation to coat the precursor on the surface of the core;
A method for producing hard particles, comprising: drying a core coated with the precursor, firing in an inert atmosphere, and synthesizing polycrystalline WC from the precursor.   The method for producing hard particles according to claim 7, wherein ammonium paratungstate is used as the tungstic acid compound.

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