Cubic boron nitride sintered material cutting tool
11130713 · 2021-09-28
Assignee
Inventors
Cpc classification
C04B2235/781
CHEMISTRY; METALLURGY
B23B27/148
PERFORMING OPERATIONS; TRANSPORTING
C04B2235/72
CHEMISTRY; METALLURGY
B23B2224/32
PERFORMING OPERATIONS; TRANSPORTING
C04B2235/785
CHEMISTRY; METALLURGY
C04B2235/3869
CHEMISTRY; METALLURGY
C04B2235/3217
CHEMISTRY; METALLURGY
C04B2235/614
CHEMISTRY; METALLURGY
C04B2235/3873
CHEMISTRY; METALLURGY
C04B2235/5445
CHEMISTRY; METALLURGY
C04B2235/6581
CHEMISTRY; METALLURGY
C04B35/6263
CHEMISTRY; METALLURGY
C04B35/5831
CHEMISTRY; METALLURGY
International classification
C04B35/5831
CHEMISTRY; METALLURGY
Abstract
A cBN sintered material cutting tool includes a cutting tool body that is made of a sintered material including cubic boron nitride particles and a binder phase, in which: an average particle size of the cBN particles is 0.5 μm or less and a content ratio of the cBN particles in the sintered material is 35 vol % to 80 vol %; and the binder phase includes 1.0 vol % to 20 vol % of an Al compound, an average particle size of the Al compound present in the binder phase is 300 nm or less, and a value of a ratio (a value of S.sub.N/S.sub.O; area ratio) of a content S.sub.N of nitrogen (N) included in the Al compound to a content S.sub.O of oxygen (O) included in the Al compound is 1.1 to 5.
Claims
1. A cubic boron nitride sintered material cutting tool comprising a cutting tool body that is made of a sintered material including cubic boron nitride particles and a binder phase, wherein: (a) an average particle size of the cubic boron nitride particles is 0.5 μm or less and a content ratio of the cubic boron nitride particles in the sintered material is 35 vol % to 80 vol %; and (b) the binder phase includes 1.0 vol % to 20 vol % of an Al compound, an average particle size of the Al compound present in the binder phase is 300 nm or less, and a value of a ratio S.sub.N/S.sub.O as an area ratio of a content S.sub.N of nitrogen N included in the Al compound to a content S.sub.O of oxygen O included in the Al compound is 1.1 to 5.
2. The cubic boron nitride sintered material cutting tool according to claim 1, wherein a content ratio of the cubic boron nitride particles in the sintered material is 45 vol % to 80 vol %.
3. The cubic boron nitride sintered material cutting tool according to claim 1, wherein a content ratio of the cubic boron nitride particles in the sintered material is 70 vol % to 80 vol %.
4. The cubic boron nitride sintered material cutting tool according to claim 1, wherein an average particle size of the cubic boron nitride particles is 0.05 μm to 0.35 μm.
5. The cubic boron nitride sintered material cutting tool according to claim 1, wherein an average particle size of the Al compound present in the binder phase is 10 nm or more.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1)
(2)
(3)
DETAILED DESCRIPTION OF THE INVENTION
(4) As a part of an embodiment of the present invention, a configuration of the present invention will be described below.
(5) Average Particle Size of cBN Particles:
(6) An average particle size of cBN particles in a cBN sintered material of a cBN tool according to the present invention is 0.5 μm or less. The reason for this is that, by increasing an interface between cBN particles and a binder phase in the cBN sintered material, the toughness of the cBN sintered material is improved, and the fracturing resistance of the cBN tool is improved.
(7) In the present invention, fracturing or chipping that originates from surface unevenness of an edge tip occurring when cBN particles peel off from a tool surface during the use of the tool can be suppressed, and propagation of cracks from an interface between the cBN particles and the binder phase caused by stress applied to the edge tip during the use of the tool or propagation of cracks caused by the fracturing of the cBN particles can be suppressed. As a result, the fracturing resistance of the cBN tool can be improved.
(8) Accordingly, the average particle size of the cBN particles in the cBN sintered material of the cBN tool according to the present invention is in a range of 0.5 μm or less and preferably in a range of 0.05 to 0.35 μm.
(9) Here, the average particle size of the cBN particles can be obtained as follows. A secondary electron image is obtained by observing a cross-sectional structure of the cBN sintered material with an SEM. A portion of the cBN particles in the obtained image is extracted by image processing as illustrated in
(10) In a case where the portion of the cBN particles in the image is extracted by image processing, in order to clearly determine the cBN particles and the binder phase, the image is displayed in monochrome (256 gradations with 0 as black and 255 as white), and is binarized using an image in which a ratio between a pixel value of the cBN particle portion and a pixel value of the binder phase portion is 2 or higher such that the cBN particles are displayed black.
(11) An average value is obtained from a region of about 0.5 μm×0.5 μm as a region for obtaining the pixel value of the cBN particle portion or the binder phase portion, and it is desirable that an average value obtained from at least three different regions of the same image is used as each contrast.
(12) After the binarization, cBN particles that appear to be in contact with each other are separated from each other using a treatment of separating a portion where cBN particles appear to be in contact with each other, for example, using watershed which is one image processing operation.
(13) A portion (black portion) corresponding to a cBN particle in the image obtained after the binarization is analyzed to obtain a maximum length thereof, the obtained maximum length is set as a maximum length of each particle, and the maximum length of each particle is set as a diameter of each particle. In the particle analysis for obtaining the maximum length, for example, Feret diameters are calculated from one cBN particle to obtain two lengths, a larger value among the obtained two lengths is defined as a maximum length, and this value is obtained as a diameter of each particle. Based on the volume of each particle that is calculated from the above diameter, a graph in which the vertical axis represents the volume percentage [%] and the horizontal axis represents the diameter [μm] is drawn. A value corresponding to a volume percentage of 50% is obtained as an average particle size of cBN particles in one image, and an average value of values that are obtained by processing at least three images in a secondary electron image obtained by observation using a SEM at a magnification of 20000 is obtained as an average particle size [μm] of cBN. During the particle analysis, a length (μm) per pixel is set using a scale value obtained using a SEM in advance. In a case where the average particle size of the cBN particles is 0.3 μm, a visual field region of about 5.0 μm×3.0 μm is desirable as an observation region used for the image processing.
(14) Content Ratio of cBN Particles in cBN Sintered Material:
(15) Typically, a cBN sintered material includes cBN particles and a binder phase component as hard components. In the present invention, in a case where a content ratio of the cBN particles is lower than 35 vol %, the amount of a hard material in the sintered material is small, and the hardness of the cBN tool is not sufficient. On the other hand, in a case where the content ratio of the cBN particles is 80 vol % or higher, a proportion of the binder phase in the sintered material is relatively low, and the effect of improving toughness obtained by the binder phase is not sufficient. Therefore, in order for the cBN sintered material according to the present invention to obtain a predetermined hardness and a predetermined toughness, the content ratio of the cBN particles in the cBN sintered material is in a range of 35 vol % to 80 vol %.
(16) It is more preferable that the content ratio of the cBN particles in the cBN sintered material is in a range of 45 vol % to 80 vol %. It is still more preferable that the content ratio of the cBN particles in the cBN sintered material is in a range of 70 vol % to 80 vol %.
(17) The content ratio of the cBN particles in the cBN sintered material is obtained by observing a cross-sectional structure of the cBN sintered material with a SEM to obtain a secondary electron image, extracting a portion of cBN particles in the obtained secondary electron image by image processing, calculating an area of the cBN particles by image analysis, obtaining a proportion of cBN particles in one image, processing at least three images to obtain values, and obtaining an average value of the values as the content ratio of the cBN particles. For example, in a case where the average particle size of the cBN particles is 0.3 μm, a visual field region of about 5.0 μm×3.0 μm is desirable as an observation region used for the image processing.
(18) Content of Al Compound in Binder Phase of cBN Sintered Material:
(19) In a case where the content of the Al compound (for example, both Al.sub.2O.sub.3 and AlN, or Al.sub.2O.sub.3, AlN, and one or two or more selected from the group consisting of AlON, SiAlON, and AlB.sub.2) included in the binder phase of the cBN sintered material is lower than 1 vol %, a reaction between the cBN particles and the binder phase is small, an interfacial adhesion strength between the cBN and the binder phase is not sufficiently obtained, and thus the strength of the sintered material decreases. On the other hand, in a case where the content of the Al compound included in the binder phase of the cBN sintered material is higher than 20 vol %, the content of the Al compound included in the binder phase is excessively high. Therefore, the hardness of the sintered material decreases, and the fracturing resistance deteriorates.
(20) Accordingly, the content of the Al compound included in the binder phase of the cBN sintered material is 1 vol % to 20 vol %.
(21) The content of the Al compound in the binder phase of the cBN sintered material is the content ratio of the Al compound (phase) in the binder phase.
(22) Average Particle Size of Al Compound in Binder Phase:
(23) In a case where the average particle size of the Al compound (for example, both Al.sub.2O.sub.3 and AlN, or Al.sub.2O.sub.3, AlN, and one or two or more selected from the group consisting of AlON, SiAlON, and AlB.sub.2) present in the binder phase is more than 300 nm, the initiation or propagation of cracks from the Al compound particles in the binder phase is likely to occur, and thus the toughness of the cBN sintered material deteriorates.
(24) Accordingly, the average particle size of the Al compound present in the binder phase is 300 nm or less and preferably 150 nm or less.
(25) In a case where the particle size of the Al compound is less than 10 nm, the particle size exceeds a measurement limit. In addition, in a case where the particle size of the Al compound is less than 10 nm, there are adverse effects on the characteristics of the cBN sintered material. Therefore, in order to obtain the average particle size, a minimum value of the particle size of the Al compound measured in the present invention is set as 10 nm.
(26) In order to measure the average particle size of the Al compound, an Al mapping image is obtained by performing Auger electron spectroscopy (AES) on the cross-sectional structure of the cBN sintered material. A portion of the Al compound in the obtained image is extracted by image processing, maximum lengths of respective particles are obtained by image analysis, and an average particle size is calculated based on the maximum lengths. In the image analysis, for example, the maximum length can be obtained by obtaining Feret diameters of each particle.
(27) Al compound particles that appear to be in contact with each other are separated from each other using a treatment of separating a portion where Al compound particles appear to be in contact with each other, for example, using watershed which is one image processing operation.
(28) In order to calculate the average particle size of the Al compound, a maximum length of each particle is obtained from the Al mapping image as the diameter of each particle. Based on the volume of each particle that is calculated from the above diameter, a graph in which the vertical axis represents the volume percentage [%] and the horizontal axis represents the diameter [μm] is drawn. A value corresponding to a volume percentage of 50% is obtained as an average particle size of the Al compound in one image, and an average value of values that are obtained by processing at least three images in an Al mapping image obtained by AES at a magnification of 20000 is obtained as an average particle size [μm] of the Al compound. During the particle analysis, a length (μm) per pixel is set using a scale value obtained by AES in advance. A visual field region of about 5.0 μm×3.0 μm is desirable as an observation region used for the image processing.
(29) Ratio of Content S.sub.N of Nitrogen (N) Included in Al Compound to Content S.sub.O of Oxygen (O) Included in Al Compound (Value of S.sub.N/S.sub.O; Area Ratio):
(30) In a case where a ratio of a content S.sub.N of nitrogen (N) included in the Al compound to a content S.sub.O of oxygen (O) included in the Al compound (a value of S.sub.N/S.sub.O; an area ratio) is lower than 1.1, a proportion of an Al nitride inducing propagation of cracks in the binder phase is low, and cracks propagate linearly without propagating finely in the binder phase. As a result, the toughness of the cBN sintered material deteriorates. On the other hand, in a case where the value of S.sub.N/S.sub.O is higher than 5, the content of the Al compound in the cBN sintered material increases, and the fracturing resistance deteriorates due to a decrease in hardness.
(31) Accordingly, the ratio of the content S.sub.N of nitrogen (N) included in the Al compound to the content S.sub.O of oxygen (O) included in the Al compound (a value of S.sub.N/S.sub.O; an area ratio) is 1.1 to 5 and preferably 2 to 4.5.
(32) Method of Measuring Ratio of Content S.sub.N of Nitrogen (N) included in Al Compound to Content S.sub.O of Oxygen (O) included in Al Compound (Value of S.sub.N/S.sub.O; Area Ratio):
(33) In order to measure the ratio S.sub.N/S.sub.O of the content S.sub.N of nitrogen (N) included in the Al compound to the content S.sub.O of oxygen (O) included in the Al compound, a cross-sectional structure of the prepared cBN sintered material is observed using Auger electron spectroscopy (AES), and an Al mapping image, a nitrogen (N) mapping image, and an oxygen (O) mapping image are obtained. In each of the obtained images, a portion where the Al mapping image and nitrogen (N) overlap with each other and a portion where the Al mapping image and oxygen (O) overlap with each other are extracted by image processing as illustrated in
(34) Hereinafter, the cBN sintered material cutting tool according to the present invention will be described in detail based on Examples.
Examples
(35) During the manufacturing of a cBN sintered material according to Example, cBN particles having pre-treated surfaces were used as a cBN raw material.
(36) First, for example, an AlN film was formed on the cBN particle surfaces using an ALD method. During the film formation, a fluidized bed was charged with the cBN particles, the inside of the furnace was heated to about 350° C., and one cycle was repeated until a desired AlN film thickness was obtained, the cycle including an Ar+Al(CH.sub.3).sub.3 gas inflow step, an Ar gas purge step, an Ar+NH.sub.3 gas inflow step, and an Ar gas purge step. For example, by performing the film formation for 60 minutes, the AlN film having a thickness of about 10 nm was able to be coated and formed on the cBN particle surfaces.
(37) Next, the cBN particles having the surfaces on which the AlN film having the desired thickness was formed were heated in a vacuum at about 1000° C. such that impurity elements such as oxygen on the cBN surface were diffused into the AlN film and were captured in the AlN film.
(38) By performing the heat treatment as described above, the AlN film in which the impurity elements were captured were peeled off from the cBN surfaces due to ball mill mixing after the heat treatment. As a result, cBN particles having a high surface cleanliness from which the impurity components such as oxygen adsorbed on the cBN surfaces were removed were able to be obtained.
(39) As shown in Table 1, cBN particles in which the thickness of the AlN film was 10 nm and cBN particles in which the thickness of the AlN film was 35 nm were prepared, respectively, and were heated in a vacuum at about 1000° C. As a result, cBN powders with the AlN film were obtained. Regarding the cBN powder in which the thickness of the AlN film was 10 nm, a heat treatment at about 400° C. was performed in addition to the heat treatment at about 1000° C. As a result, cBN powders with the AlN film having different surface cleanlinesses were obtained.
(40) The cBN particle powder having an average particle size of 0.5 μm or less that was pre-treated as described above and TiN powder, TiC powder, Al powder, TiAl.sub.3 powder, Al.sub.2O.sub.3 powder, and Si.sub.3N.sub.4 powder having an average particle size in a range of 0.3 to 0.9 μm were prepared as base powders for forming a binder phase. Some base powders selected from the base powders and the cBN particle powder were blended such that a content ratio of the cBN particle powder was 35 to 80 vol % with respect to the total amount of the powders as 100 vol %, were mixed with each other in a wet process, and were dried.
(41) Next, this mixed powder was press-molded by hydraulic pressing into a green compact having a diameter of 50 mm and a thickness of 1.5 mm at a molding pressure of 1 MPa. Next, this green compact underwent a heat treatment by being held at a predetermined temperature in a range of 1000° C. to 1300° C. in a vacuum atmosphere under a pressure of 1 Pa for 30 to 60 minutes.
(42) Next, the green compact on which the above-described heat treatment was performed was superimposed on a support piece made of WC-based cemented carbide including 8 mass % of Co and a balance of WC and having a diameter of 50 mm and a thickness of 2 mm that was prepared separately. In this state, the green compact was charged into a typical ultra-high pressure sintering apparatus and was sintered under typical conditions of pressure: 3 to 10 GPa, for example, 5 GPa, temperature: 1400° C., and holding time: 30 minutes. As a result, cBN sintered materials 1 to 15 according to the present invention (hereinafter, also referred to as “sintered materials according to the present invention”) shown in Table 2 were prepared.
(43) The heat treatment was performed on the green compact mainly in order to remove a solvent during the wet mixing.
(44) In addition, in the preparation steps, it is preferable that the oxidation of the base powders is prevented in the steps until the ultra-high pressure sintering. Specifically, it is preferable that the base powders were handled in a non-oxidation protective atmosphere.
(45) For comparison, cBN particle powder having an average particle size of 0.5 μm or less that was pre-treated as shown in Table 1, cBN particle powder having an average particle size of about 1.5 μm or less that was prepared under conditions other than the conditions defined in the present invention, TiN powder, TiC powder, Al powder, TiAl.sub.3 powder, Al.sub.2O.sub.3 powder, AlN powder, and Si.sub.3N.sub.4 powder having an average particle size in a range of 0.3 to 0.9 μm that were base powders for forming a binder phase, cBN particle powder having an average particle size of 0.5 μm or less that was not heated, and TiN powder, TiC powder, Al powder, TiAl.sub.3 powder, Al.sub.2O.sub.3 powder, AlN powder, and Si.sub.3N.sub.4 powder having an average particle size in a range of 0.3 to 0.9 μm that were base powders for forming a binder phase were prepared. Some base powders selected from the base powders and the cBN particle powder were blended such that a content ratio of the cBN particle powder was 21 to 85 vol % with respect to the total amount of the powders as 100 vol %, were mixed with each other in a wet process, and were dried.
(46) Next, a green compact was prepared under the same conditions as those of the sintered materials 1 to 15 according to the present invention and was heated. This green compact was sintered under an ultrahigh pressure at a high temperature under the same conditions as those of sintered materials 1 to 15 according to the present invention. As a result, cBN sintered materials according to Comparative Examples (hereinafter, referred to as “comparative sintered materials”) 1 to 11 shown in Table 3 were prepared.
(47) The comparative sintered materials 1 to 5 were cBN sintered materials in which base powders that were not heated were used. The comparative sintered materials 6 and 11 were cBN sintered materials in which the cBN content was outside of the condition defined in the present invention. The comparative sintered materials 7 and 9 were cBN sintered materials in which the proportion of Al or the Al compound in the base powders was adjusted such that the content of the Al compound in the cBN sintered materials was outside of the condition defined in the present invention. The comparative sintered material 8 was a cBN sintered material in which the cBN particle size was outside of the condition defined in the present invention. The comparative sintered material 10 is a cBN sintered material in which the proportion of MN in the base powders was increased such that the ratio S.sub.N/S.sub.O of the content S.sub.N of nitrogen (N) included in the Al compound of the binder phase of the cBN sintered material to the content S.sub.O of oxygen (O) included in the Al compound of the binder phase of the cBN sintered material was outside of the condition defined in the present invention.
(48) TABLE-US-00001 TABLE 1 Pre-Treatment Conditions of cBN Base Powder Heat Treatment Conditions of cBN Particles Thickness of AIN with AIN Film Film formed on cBN Heat Treatment Heat Treatment Particles using ALD Temperature Time Kind (nm) (° C.) (min) A 10 1000 60 B 35 C 10 400
(49) Regarding each of the sintered materials 1 to 15 according to the present invention and the comparative sintered materials 1 to 11, a cross-section thereof was polished, and an Al mapping image, a nitrogen (N) mapping image, and an oxygen (O) mapping image are obtained using Auger electron spectroscopy (AES) to measure the content ratio of Al in the binder phase of the cBN sintered material, the average particle size of the Al compound in the binder phase, and the ratio S.sub.N/S.sub.O (area ratio) of the content S.sub.N of nitrogen (N) in the Al compound to the content S.sub.O of oxygen (O) in the Al compound.
(50) Tables 2 and 3 shows the results.
(51) The binder phase composition of the cBN sintered material was measured by X-ray diffraction (XRD) analysis.
(52) In addition, regarding the average particle size of the cBN particles and the content ratio of the cBN particles in the cBN sintered material, the cross-sectional structure of the cBN sintered material was observed with a SEM to obtain a secondary electron image. A portion of the cBN particles in the obtained image was binarized and extracted by image processing as illustrated in
(53) In a case where the average particle size of the cBN particles is 0.3 μm, a visual field region of about 5.0 μm×3.0 μm is desirable as an observation region used for the image processing.
(54) TABLE-US-00002 TABLE 2 cBN Binder Phase Kind of Content Average Particle Value of Pre-Treatment (Calculated Average Content of Al Size of Al Sn/Sq of cBN Base Value) Particle size Compound Composition of Binder Phase Compound (Area Kind Powder (vol %) (μm) (vol %) (XRD Peak) (nm) Ratio) Sintered 1 B 35 0.21 8 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3 163 3.7 Material 2 A 78 0.09 5 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3 11 3.9 according to 3 A 80 0.41 4 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3 26 4.5 Present 4 C 73 0.47 1 TiCN, TiB.sub.2, AlN, Al.sub.2O.sub.3, AlON 11 1.5 Invention 5 C 42 0.23 6 TiC, TiB.sub.2, AIN, A1.sub.2O.sub.3 86 2.1 6 A 54 0.05 16 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3, WC 248 4.2 7 A 57 0.12 7 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3 96 3.6 8 A 63 0.50 9 TiC, TiB.sub.2, AlN, Al.sub.2O.sub.3 13 3.9 9 A 59 0.43 20 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3 300 4.7 10 A 56 0.16 18 TiN, TiCN, TiC, TiB.sub.2, AlN, Al.sub.2O.sub.3 182 5.0 11 C 57 0.31 14 TiC, TiB.sub.2, AlN, Al.sub.2O.sub.3, SiAlON 101 1.9 12 C 52 0.25 7 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3, WC 92 1.5 13 C 47 0.07 17 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3, AlON 221 2.2 14 B 58 0.36 10 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3 99 3.4 15 C 63 0.27 12 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3, AlON 131 1.1
(55) TABLE-US-00003 TABLE 3 cBN Binder Phase Kind of Content Average Particle Value of Pre-Treatment (Calculated Average Content of Al Size of Sn/So of cBN Base Value) Particle size Compound Al Compound (Area Kind Powder (vol %) (μm) (vol %) XRD Peak of Al Compound (nm) Ratio) Comparative 1 — 43 0.14 0.4 TiC, TiB.sub.2, AlN, Al.sub.2O.sub.3 34 1.02 Sintered 2 — 39 0.07 12 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3, WC 253 1.04 Material 3 — 46 0.25 20 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3 520 1.9 4 — 53 0.33 16 TiC, TiB.sub.2, AlN, Al.sub.2O.sub.3, SiAlON 116 1.03 5 — 71 0.41 6 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3, AlON 94 1.02 6 B 21 0.14 7 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3 105 3.8 7 A 35 0.11 40 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3 264 4.8 8 B 64 1.50 11 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3 112 3.7 9 A 66 0.30 0.4 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3 44 1.2 10 B 58 0.13 9 TIN, TiB.sub.2, AlN, Al.sub.2O.sub.3, WC 102 10.1 11 C 85 0.38 3 TiN, TiB.sub.2, AlN, Al.sub.2O.sub.3 109 3.9
(56) Next, upper and lower surfaces of each of the sintered materials 1 to 15 according to the present invention and the comparative sintered materials 1 to 11 were polished using a diamond grindstone, and were split using a wire-electrical discharge machining device. Further, the split portions of the sintered material were brazed to brazing portions (corner portions) of an insert body made of WC-based cemented carbide including 5 mass % of Co, 5 mass % of TaC, and a balance of WC and having a shape according to ISO CNGA 120408 using a brazing material of an Ag alloy including 26 mass % of Cu, 5 mass % of Ti, and a balance of Ag. Further, the upper and lower surfaces and the outer periphery were polished and horned. As a result, cBN sintered material cutting tools 1 to 15 according to the present invention (hereinafter, also referred to as “tools according to the present invention”) and cBN sintered material cutting tools 1 to 11 according to Comparative Examples (hereinafter, referred to as “comparative tools”) having an insert shape according to ISO CNGA 120408 were prepared.
(57) Next, each of the various cutting tools was screwed and fixed to a tip portion of an insert holder of tool steel using a fixing jig. In this state, regarding each of the cutting tools 1 to 15 according to the present invention and the comparative tools 1 to 11, an intermittent cutting test was performed under the following cutting conditions.
(58) Work material: a round bar made of carbolized steel (hardness: HRC 61) according to JIS SCr420 with eight longitudinal grooves formed at equal intervals in the longitudinal direction
(59) Cutting speed: 200 m/min
(60) Depth of cut: 0.10 mm
(61) Feed rate: 0.10 mm/rev
(62) Condition: dry
(63) The number of times of intermittent cutting was counted until chipping or fracturing occurs on an edge tip of the cutting tool, and was evaluated for tool life. The edge tip was observed every 500 times of intermittent cutting to determine whether or not fracturing occurred on the edge tip.
(64) Table 4 shows the test results.
(65) TABLE-US-00004 TABLE 4 Tool Life Tool Life (Number of Times of (Number of Times of Kind Intermittent Cutting) Kind Intermittent Cutting) Tool 1 according to Present invention Chipping (2,000) Comparative Tool 1 Fracturing (500) Tool 2 according to Present invention Chipping (14,000) Comparative Tool 2 Fracturing (500) Tool 3 according to Present invention Chipping (15,000) Comparative Tool 3 Fracturing (1,000) Tool 4 according to Present invention Chipping (14,000) Comparative Tool 4 Fracturing (1,000) Tool 5 according to Present invention Chipping (5,000) Comparative Tool 5 Chipping (1,500) Tool 6 according to Present invention Chipping (5,000) Comparative Tool 6 Fracturing (500) Tool 7 according to Present invention Chipping (7,000) Comparative Tool 7 Fracturing (500) Tool 8 according to Present invention Chipping (8,000) Comparative Tool 8 Fracturing (1,000) Tool 9 according to Present invention Chipping (7,500) Comparative Tool 9 Fracturing (1,000) Tool 10 according to Present invention Chipping (8,500) Comparative Tool 10 Fracturing (500) Tool 11 according to Present invention Chipping (8,000) Comparative Tool 11 Fracturing (500) Tool 12 according to Present invention Chipping (8,000) Tool 13 according to Present invention Chipping (7,500) Tool 14 according to Present invention Chipping (8,500) Tool 15 according to Present invention Chipping (8,500)
(66) Based on the results shown in Table 4, the following was found. In the cBN sintered material according to the present invention, the average particle size of the cBN particles was 0.5 μm, the content ratio of the cBN particles in the cBN sintered material was 35 vol % to 80 vol %, the binder phase included 1.0 vol % to 20 vol % of the Al compound, the average particle size of the Al compound present in the binder phase was 300 nm or less, and the value of S.sub.N/S.sub.O (area ratio) was 1.1 to 5. Therefore, the initiation or propagation of cracks from the Al compound particles was less likely to occur, a local and excessive reaction between the cBN particles and the binder phase in the sintered material was suppressed, and the amount of an oxide was small. Therefore, the interfacial adhesion strength between the cBN particles and the binder phase was improved, and the toughness was excellent.
(67) Accordingly, in each of the tools 1 to 15 according to the present invention, the tool life was long during cutting of high hardness steel where the edge tip was at a high temperature and under a high load, only chipping occurred and critical fracturing did not occur on the edge tip, and excellent toughness and fracturing resistance were exhibited.
(68) On the other hand, it is clear that, in each of comparative cutting tools 1 to 11, the cBN sintered material did not satisfy the conditions defined in the present invention, and thus critical fracturing occurred within a relatively short period of time such that the tool life ended.
INDUSTRIAL APPLICABILITY
(69) As described above, the cBN tool according to the present invention has excellent fracturing resistance, and thus is applicable not only to cutting of high hardness steel but also to cutting under various cutting conditions. The cBN tool according to the present invention can satisfactorily cope with the improvement of the performance of cutting apparatuses, power saving and energy saving during cutting, and a reduction in costs.