CUTTING IMPLEMENT

In the present disclosure, a cutting implement includes a blade body including a base portion and a cutting edge portion connected to an end portion of the base portion. The base portion includes a first metal, and the cutting edge portion includes a second metal and hard particles having a hardness higher than the hardness of the second metal. The hard particles include first hard particles having a particle size of 20 μm or more and 50 μm or less.

TECHNICAL FIELD

The present disclosure relates to a cutting implement having excellent wear resistance.

BACKGROUND OF INVENTION

Traditionally, kitchen knives made of a material that contains a metal material as a main component have been used. Among these, in recent years, a kitchen knife made of stainless steel that contains nickel and chromium as components has been widely used. Patent Document 1 describes that titanium carbide particles and stainless steel particles having a high hardness are deposited on a leading end portion of a blade body made of stainless steel, and are simultaneously irradiated with a laser beam to be bonded to the blade body to form a bead, and the bead is ground and polished to make a cutting implement.

CITATION LIST

Patent Literature

Patent Document 1: JP 2007-524520 T

SUMMARY

In the present disclosure, a cutting implement includes a blade body that includes a base portion and a cutting edge portion connected to an end portion of the base portion. The base portion includes a first metal, and the cutting edge portion includes a second metal and hard particles having a hardness higher than the hardness of the second metal. The hard particles include first hard particles having a particle size of 20 μm or more and 50 μm or less and having an angular polyhedral shape.

In the present disclosure, another cutting implement includes a blade body that

includes a base portion and a cutting edge portion connected to an end portion of the base portion. The base portion includes a first metal, and the cutting edge portion includes a second metal and hard particles having a hardness higher than the hardness of the second metal. An interface portion having a crystal grain size larger than the crystal grain size of the cutting edge portion is provided between the base portion and the cutting edge portion.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a cutting implement according to an embodiment of the present disclosure will be described. Drawings used in the following description are schematic, and dimensional ratios and the like on the drawings do not always match the actual ones.

As illustrated inFIGS.1and2, a cutting implement1of the present disclosure includes a blade body1aand a handle1bconnected to the blade body1a. The shape and size of the blade body1aare set in accordance with the application of the cutting implement1. If the cutting implement1is a kitchen knife, examples of the shape of the blade body1ainclude shapes of a Japanese kitchen knife such as a kitchen knife for cutting fish and a santoku knife, a Western knife such as a butcher knife, or a Chinese knife. If the blade body1is for an application other than a kitchen knife such as a knife for a surgical instrument, the blade body1may have any shape as long as the shape is suited to its application.

The handle1bconnected to the blade body1ais to be gripped by a hand when a person uses the cutting implement1. As in the case of the blade body1a, the shape and size of the handle1bare set in accordance with the application of the cutting implement1.

The blade body1aand the handle1bmay be formed integrally or separately. The cutting implement1is not limited to including the handle1b, and may be composed of only the blade body1a. In the present embodiment, the blade body1aand the handle1bare separately formed. The blade body1ais partially inserted into the handle1b, and is fixed to the handle1bat the insertion portion. A part of the blade body1amay be welded to the handle1bmade of metal.

The handle1bincludes wood, resin, ceramic, or a metal material. As the metal material, a rust-resistant material such as a titanium-based or stainless-steel-based material may be used. As the resin, for example, an ABS resin (a copolymer of acrylonitrile, butadiene, and styrene) or a polypropylene resin may be used.

The blade body1aincludes a base portion3and a cutting edge portion2connected to the base portion3. The base portion3includes a first metal. As the first metal, for example, steel, synthetic steel, stainless steel, titanium alloy, or the like may be used. As the synthetic steel, for example, a material including chromium, molybdenum, vanadium, tungsten, cobalt, copper, combinations thereof, or the like may be used. As the stainless steel, chromium-nickel-based stainless steel or chromium-based stainless steel may be used. As the titanium alloy, for example, so-called 64 titanium, which is a titanium alloy including 6% of aluminum (Al) and 4% of vanadium (V), may be used. When the first metal is stainless steel, the corrosion resistance of the base portion3against rust or the like can be improved.

In the present embodiment, the first metal is a main component of the base portion3. Here, a “main component” means a component that accounts for 70 mass % or more of the total of 100 mass % of the components constituting the base portion3.

As illustrated inFIG.1, the base portion3includes an exposed portion30exposed from the handle1band a tang3E inserted in the handle1b. In the exposed portion30, an end portion3C and a back portion3A extend along a length direction (x-axis direction) of the exposed portion30. The exposed portion30narrows in width near a leading end in the length direction of the exposed portion30, and the end portion3C and the back portion3A are connected at the leading end of the exposed portion30. The cutting edge portion2is connected to the end portion3C of the exposed portion30along the end portion3C. The tang3E is narrower than the exposed portion30in a width direction (y-axis direction) and is inserted in the handle1b. In the present embodiment, the tang3E includes at least one hole portion3Ea, and a part of the handle1bis inserted into the hole portion3Ea so that the blade body1aand the handle1bare firmly fixed to each other. Note that the base portion3and the handle1bmay be integrated by welding.

As illustrated inFIG.3, the cutting edge portion2includes a second metal2aand a plurality of hard particles4. The second metal2amay be made of a material different from or the same as the material of the first metal. In the present embodiment, the second metal2ais made of a material different from the material of the first metal. This is advantageous in that a metal material suitable for the cutting edge portion2can be selected without being restricted by the material of the base portion3. As the material of the second metal2a, for example, stainless steel, nickel, titanium, nickel alloy, titanium alloy, or the like can be used, and further, nickel-chromium-iron alloy (for example, Inconel (registered trade mark)), nickel-silicon-boron alloy (for example, Colmonoy (registered trade mark)), or titanium-aluminum-vanadium alloy may be used.

When made of Inconel, the second metal2ahas a relatively high corrosion resistance, and can reduce thermal stress remaining in the cutting edge portion2when a laser is used in the manufacturing method.

When made of Ni-based Colmonoy, the second metal2acan suppress strength deterioration due to hardening and annealing of the cutting edge during manufacture of the cutting implement1. The Ni-based Colmonoy is preferably composed of 0.06 mass % or less of carbon, 0.8 mass % or less of iron, 2.4 to 3.0 mass % of silicon, 1.6 to 2.00 mass % of boron, 0.08 mass % or less of oxygen, and the balance of nickel with respect to the total amount of the Ni-based Colmonoy.

In the present embodiment, the second metal2aforms a metallic matrix as a main component of the cutting edge portion2, and the hard particles are present in this matrix. Here, a “main component” means a component that accounts for 50 mass % or more of the total of 100 mass % of the components constituting the cutting edge portion2. Since the second metal2ais the main component of the cutting edge portion2, the durability of the cutting edge portion2can be further improved.

The plurality of hard particles4included in the cutting edge portion2have a higher Vickers hardness than the Vickers hardness of the second metal2aincluded in the cutting edge portion2. Thus, the hardness of the entire cutting edge portion2can be increased, and the wear resistance of the cutting edge portion2can be improved. Since the hard particles4are made of a material harder than the second metal2a, the sharpness of the cutting edge portion2against an object is improved by the hard particles4coming into contact with the object during the use of the cutting implement1.

In the present embodiment, the hard particles4are made of a material that is harder than the second metal2aand also harder than the first metal. As described above, by using the hard particles4having a sufficient hardness, an effect of improving the sharpness and the wear resistance of the cutting edge portion2can be enhanced. The hard particles4may have, for example, a Vickers hardness of 1000 Hv or more and 4000 Hv or less. The Vickers hardnesses of the hard particles4, the first metal, and the second metal2acan be measured using a method according to JIS Z 2244 (ISO 6507-2, the same applies hereinafter).

The hard particles4are preferably exposed on a surface of the cutting edge portion2. In order for the hard particles4to be easily exposed on a surface of the cutting edge portion2even when the cutting edge portion2is polished, the hard particles4are preferably dispersed not only in a length direction (x-axis direction) and a width direction (y-axis direction) of the base portion3but also in a thickness direction (z-axis direction) of the base portion3inside the cutting edge portion2.

Examples of the hard particles4include a cemented carbide alloy including tungsten carbide (WC), and a cermet including titanium carbide (TiC), titanium nitride (TiN), tantalum carbide (TaC), and vanadium carbide (VC). As the hard particles4, a plurality of materials such as tungsten carbide, titanium carbide, and the like may be mixed and used.

The hard particles4preferably include first hard particles41having an angular polyhedral shape (seeFIG.8B), whereby the wear resistance of the cutting edge portion2can be improved. Specifically, examples of the shape of the hard particles4include a polygonal shape such as a triangular shape, a quadrangular shape, and a trapezoidal shape in a cross-sectional view. However, as illustrated inFIG.5to be described later, the hard particles4having an angular irregular shape can also be used.FIG.5illustrates the shapes of the raw material powder of the hard particles4.

Preferably, the first hard particles41having an angular polyhedral shape and a particle size of 20 μm or more and 50 μm or less are included in the matrix of the second metal2aat an area ratio of 3% or more in cross section. The first hard particles41having such a relatively large particle size are susceptible to cracking. However, in the present disclosure, since the first hard particles41are present in the matrix of the second metal2a, the growth of cracks can be suppressed by the matrix, and thus the hard particles4having a relatively large particle size can be used. Here, when the particle size of the first hard particles41is 20 μm or more, the wear resistance is improved. On the other hand, when the particle size is 50 μm or less, the occurrence of cracks in the first hard particles41can be suppressed. In order to set the particle size of the first hard particles41as described above, for example, particles having a particle size of less than 20 μm and particles having a particle size of more than 50 μm may be screened out by using a sieve.

Note that the percentage of particles at an area ratio in a cross section is measured by calculating a region of hard particles by using the software “Image J”.

As described above, the hard particles4preferably include particles (first hard particles41) having a particle size (average particle size, the same applies hereinafter) of 20 μm or more and 50 μm or less. When the hard particles4include particles having a particle size of 20 μm or more, the wear resistance is improved. On the other hand, when the hard particles4include particles having a particle size of 50 μm or less, the occurrence of cracks in the hard particles4can be suppressed.

The hard particles4may include particles (second hard particles42to be described later) having a particle size of 2 μm or more and 10 μm or less. When such fine hard particles42are dispersed in the cutting edge portion, the strength of the cutting edge portion is improved and the wear resistance is also improved.

The hard particles4may include particles (third hard particles43to be described later) crystallized in a dendritic shape from the matrix of the second metal2a. The anchor effect of such dendritic particles can suppress degranulation of the hard particles43.

The hard particles4may be included in the cutting edge portion2in an amount of 10 mass % or more. In that case, the hard particles4having a particle size outside of the range of 20 μm or more and 50 μm or less may be included, but the hard particles4having a particle size of 20 μm or more and 50 μm or less are preferably included at an area ratio of 3% or more in a cross section as described above. Accordingly, the sharpness and the wear resistance of the cutting edge portion2can be further improved. The hard particles4may be included in the cutting edge portion2in an amount of 50 mass % or less. In that case, the productivity of the cutting edge portion2can be maintained at a high level. At this time, the content of the hard particles4having a particle size of 20 μm or more and 50 μm or less is preferably 32% or less as an area ratio in cross section.

Note that the content of the hard particles4can be obtained by observing a cross section (a cross section parallel to a yz plane) of the cutting edge portion2using an SEM and calculating a ratio of a total area of the hard particles4to an area of the entire cutting edge portion2as area percentage based on a photograph of the observed image.

A cross section of the blade body1a(a cross section parallel to a yz plane) will be described with reference toFIG.3. The cutting edge portion2includes a cutting edge2A and a pair of side surfaces2C disposed on both sides of the cutting edge2A and connected to the cutting edge2A. At least one of the plurality of hard particles4is exposed from the side surfaces2cof the cutting edge portion2. Accordingly, when an object is cut by using the cutting implement1, the hard particles4come into contact with the object. As a result, the sharpness of the cutting edge portion2is improved and the wear resistance of the cutting edge portion2can be improved.

In the present embodiment, at least one of the hard particles4is preferably exposed from the cutting edge2A. Accordingly, when an object is cut by using the cutting implement1, the hard particles4exposed from the cutting edge2A come into contact with the object, and the sharpness of the cutting edge2A can be improved.

A method for manufacturing the cutting implement1will be described with reference toFIG.4. The cutting implement1includes: a step of preparing the base portion3including the first metal; a step of preparing a metal powder2a1constituting the second metal and the hard particles4; a step of forming a build-up portion6for forming the cutting edge portion2including the second metal as a main component and the plurality of hard particles4by spraying the metal powder2a1and the hard particles4to the end portion3C of the base portion3and baking the metal powder2a1; and a step of polishing the build-up portion6or polishing the build-up portion6and the base portion3. The steps will be described in order below.

First, the base portion3including the first metal is prepared. The base portion3has a shape as illustrated inFIGS.4A and4B. The hardness of the base portion3can be increased by pressing a plate of stainless steel or another material, punching out a predetermined blade shape, and then performing quenching.

On the other hand, separately from the preparation of the base portion3, metal powder constituting the second metal and raw material powder forming the hard particles4are prepared.FIG.5illustrates the shapes of tungsten carbide (WC) powder as an example of the raw material powder forming the hard particles4. As illustrated in theFIG.5, the raw material powder of the hard particles4preferably includes ground products that have been ground to have a particle size of 20 μm or more and 50 μm or less and to have angular surfaces.

As illustrated inFIG.4A, while a powder-particle mixture5of the metal powder2a1and the hard particles4is sprayed onto the end portion3C of the base portion3, the metal powder2a1is baked onto the end portion3C. Accordingly, the build-up portion6for forming the cutting edge portion2including the second metal2aand the plurality of hard particles4is formed.

The metal powder2a1is preferably melted and baked by laser. That is, a cladding technique using laser is preferably used. Specifically, as illustrated inFIG.4A, the powder-particle mixture5(cladding material) including the metal powder2a1is supplied onto the end portion3C while the vicinity of the end portion3of the base portion3is irradiated with a laser beam7indicated by the arrows. In this state, the base portion3is moved relative to the irradiation position of the laser beam7along a length direction (x direction illustrated inFIG.1) of the base portion3. Accordingly, the powder-particle mixture5, which is a material constituting the cutting edge portion2, can be melted and metallically bonded over the entire length of the end portion3C. As described above, the powder-particle mixture5is irradiated with the laser beam7(two laser beams in the present embodiment), whereby the powder-particle mixture5is melted and the build-up portion6is formed on the end portion3C of the base portion3. Thus, the base portion3is less likely to be melted, and a molten pool is suppressed. Preferably, an inert gas is blown to the end portion3C from outside of the powder-particle mixture5. This makes it easier for the powder-particle mixture5to be hit by the laser beam7. An example of the inert gas is argon gas.

As illustrated inFIG.4B, a width W of the end portion3C of the base portion3is preferably 0.3 mm or more and 1.0 mm or less, but is not particularly limited because the width W varies depending on the size of the cutting implement or the like.

When the powder-particle mixture5is irradiated with the laser beam7, the powder-particle mixture5excluding the hard particles4is melted and adheres to the end portion3C. On the other hand, the hard particles4have a high melting point, and thus are not likely to be melted by the laser beam7. Therefore, when the powder-particle mixture5is melted, the build-up portion6in which the plurality of hard particles4are dispersed can be obtained at the cutting edge portion2. As will be described later, the hard particles4are partially solid-dissolved into the matrix during a build-up process, and the hard particles4are crystallized from the matrix, which has become a supersaturated solid solution.

FIG.6is an SEM photograph showing an example of the build-up portion6formed on the end portion3C of the base portion3as described above.

The cutting edge portion2is formed on the end portion3C of the base portion3by polishing a part of the build-up portion6. Only the build-up portion6may be polished, or a part of the base portion3may be polished in addition to the build-up portion6. Polishing can be performed by using a polishing stone having a surface coated with, for example, aluminum oxide (Al2O3), silicon carbide (SiC) or diamond, mixed particles of silicon carbide (SiC) or diamond. Polishing may be performed in a plurality of steps.

FIG.7is an SEM photograph showing the cutting edge2A of the cutting edge portion2made as described above. As is apparent from the drawing, the hard particles4are exposed at the leading end and both side surfaces of the cutting edge2A. Thus, when an object is cut, the hard particles4come into contact with the object, whereby the sharpness of the cutting edge portion2with respect to the object is improved.

InFIGS.6and7, the materials used are as follows.Base portion3: Stainless steelBuild-up portion6(cutting edge portion2): Ni alloyHard particles4Composition: Ceramic including tungsten carbide as a main componentMesh particle size: 45 μmContent in the build-up portion6: 30 mass %

FIG.8Ais an SEM photograph showing the build-up portion6formed in the same manner as the build-up portion6illustrated inFIG.6, andFIG.8Bis an enlarged SEM photograph of the portion A inFIG.8A.FIG.9is an enlarged SEM photograph of the portion B inFIG.8B.FIG.8BandFIG.9illustrate that three types of first, second, and third hard particles41,42, and43having different shapes are present in the build-up portion6.

The first hard particles41have a particle size of 20 μm or more and 50 μm or less, and have an angular polyhedral shape. The first hard particles41retain the shape of the raw material powder of the hard particles (WC) to some extent. The presence of the first hard particles41being coarse in size as described above improves the wear resistance of the cutting edge portion2.

As illustrated inFIG.8B, in the vicinity of the first hard particles41, a large number of needle-shaped hard particles411are precipitated from the peripheries of the first hard particles41, whereby the concentration of the hard particles in the matrix of the second metal2abecomes high (that is, the surface area of the hard particles becomes large). With the presence of the needle-shaped hard particles411, the anchor effect of the first hard particles41being coarse in size is exerted, and degranulation of the hard particles41can be suppressed, thereby enabling long-term use.
The first hard particles41are formed in such a manner that the hard particles4having a raw material powder size are not melted while being processed and are present as is in the build-up portion.

The second hard particles42are fine hard particles having a particle size of 2 μm or more and 3 μm or less. When the second hard particles42which are fine in size as described above, are dispersed in the matrix of the second metal2a, the strength of the cutting edge portion2is improved and the wear resistance is improved. The second hard particles42are assumed to have been obtained in such a manner that the raw material powder is ground to be fine and dispersed. The second hard particles42are formed by grinding hard particles having a raw material powder size while being processed.

The third hard particles43are illustrated inFIG.9which is an enlarged view of the portion B inFIG.8B. That is, the third hard particles43are the hard particles4partially crystallized in a dendritic shape from the matrix of the second metal2a. This is presumably due to a part of the raw material powder of the hard particles4being solid-dissolved into the matrix of the second metal2aduring the build-up process and being crystallized in a dendritic shape from the matrix when the matrix which became a supersaturated solid solution was cooled. When the third hard particles43are crystallized in a dendritic shape, an anchor effect can be expected, and degranulation of the third hard particles43can be suppressed.

In the present embodiment, the first, second, and third hard particles41,42, and43are present in the build-up portion6. This is presumed because the raw material powder of the hard particles4has a relatively large particle size, the hard particles are likely to be ground, and the energy during the processing locally has enough power to melt the hard particles. Not all the three types of hard particles41,42, and43need to be present in one build-up portion6, but at least one type out of the hard particles41,42, and43needs to be present.

FIG.10is an SEM photograph (magnification: 2000 times) for showing in detail the structure of a boundary region between the base portion3and the build-up portion6. The SEM photograph P2is an enlarged view of the portion A of the SEM photograph P1and is shown by connecting a plurality of SEM photographs (magnification: 2000 times).

As is apparent fromFIG.10, an interface portion8, which has a crystal grain size larger than the crystal grain size of the cutting edge portion2, is formed between the base portion3and the build-up portion6. Preferably, the crystal grains of the interface portion8have an average crystal grain size of 1.2 times or more and an area ratio of the crystal grains of 2 times or more as compared with the crystal grains of the cutting edge portion2. The crystal grain size can be calculated by using image analysis software. In the analysis, the area per crystal is calculated by dividing the total area of crystals by the number of the crystals, and the diameter of a crystal is calculated as the crystal grain size based on the area per crystal under the assumption that the crystal is circular.

It is assumed that the crystal grains are coarsened in the interface portion8as described above because the base portion3is heated by the irradiation of the laser beam7, and thus the cooling rate becomes lower toward the vicinity of the boundary between the base portion3and the build-up portion6than in the interior of the build-up portion6after the build-up process. A length L of the interface portion8is preferably about 10 μm or more and 200 μm or less with respect to the entire length of the build-up portion6.

FIG.11is an enlarged SEM photograph showing the interface portion8. Composition analysis was performed by energy dispersive X-ray spectroscopy (SEM) on a region (1) of the build-up portion6, a region (2) of the interface portion8, and a region (3) of the base portion3illustrated in the drawing. The results are shown in Table 1.

TABLE 1RegionFeNiCrWSi(1)20.754.83.418.4—(2)52.725.79.59.8—(3)82.6—14.6—0.6
It can be seen from Table 1 that, in the region (2) of the interface portion8, iron (Fe) mainly dispersed from the base portion3forms a Ni—Fe alloy phase.
In the present embodiment, preferably, after the build-up portion6is formed by the laser beam7, heat treatment such as annealing of the cutting edge, which is performed in a normal manufacturing process for a cutting tool, is not performed, or a mild heat treatment is performed. This is because the interface portion8may disappear, resulting in a uniform structure, and the hardness in the interface portion8to be described later may not decrease. Therefore, the heat treatment such as annealing is preferably performed before the build-up portion6is formed by the laser beam7.

As illustrated inFIGS.12A and12B, a Vickers hardness distribution from the build-up portion6to the base portion3was measured. Specifically, first, the base portion3and the build-up portion6were cut in a direction perpendicular to the x-axis direction illustrated inFIG.1and parallel to a cutting edge direction (y-axis direction) of the cutting edge portion2. In the cross section of the cut portion, Vickers hardnesses were measured from a leading end of the build-up portion6toward the base portion3. The measurement was performed by a method according to JIS Z 2244. The measurement conditions are as follows.Test force: 5 kgMeasurement pitch: 200 μm

The measurement result of the Vickers hardness distribution is illustrated inFIG.12B. InFIGS.12A and12B, the arrow S indicates the position of the interface portion8which is a vicinity of the boundary between the build-up portion6and the base portion3. The Vickers hardness at the position of the arrow S was 412 HV, which was the lowest hardness. The length L (seeFIG.10) of the interface portion8in this example was 70 μm.

Since the hardness of the interface portion8is low as described above, the toughness of the boundary region between the cutting edge portion and the base portion3in the cutting implement1is high. As a result, when the cutting implement1is used or the like, the interface portion8serves as a so-called buffer against an impact applied to the cutting implement1, and thus cracking or breakage of the cutting edge portion2can be reduced, which is advantageous in increasing the life of the cutting implement1. In order to achieve such an effect, the Vickers hardness of the interface portion8is suitably 400 HV or more and 450 HV or less.

FIG.13is an enlarged SEM photograph showing a surface of the cutting edge portion2in which the hard particles4having an angular surface are present in the matrix in the second metal2a.FIG.13illustrates a state in which an indentation P for Vickers hardness measurement is formed in the surface of the cutting edge portion2. The indentation P for Vickers hardness measurement refers to a depression obtained by pressing a rigid body (indenter) (not illustrated) of diamond into a surface of a target portion (here, the cutting edge portion2). Since the indenter has a shape of an inverted regular quadrangular pyramid, the indentation P formed has a substantially square shape. Here, the test force which is the load for pressing the indenter was 5 kg.

As illustrated inFIG.13, a crack9was generated in the hard particles4when the indenter was pushed in.FIG.14is an enlarged SEM photograph showing the portion A ofFIG.13, that is, a region where the crack9was generated. As illustrated inFIG.14, the crack9propagates from an end portion of the indentation P and stops at the matrix of the second metal2a. This is assumed because the second metal2ahas a low hardness and a high toughness.

As illustrated inFIG.15, even when the indenter for the Vickers hardness measurement was pressed against nickel (Ni) as the second metal2ato form an indentation P′, no crack was observed.

The embodiment of the present disclosure has been described above, but the cutting implement according to the present disclosure is not limited thereto, and various changes and improvements can be made within the range set forth in the present disclosure.

REFERENCE SIGNS