Cubic boron nitride sintered body cutting tool

Abstract

A cBN sintered material cutting tool is provided. The cBN cutting tool includes a cutting tool body, which is a sintered material including cBN grains and a binder phase, wherein the sintered material comprises: the cubic boron nitride grains in a range of 40 volume % or more and less than 60 volume %; and Al in a range from a lower limit of 2 mass % to an upper limit Y, satisfying a relationship, Y=0.1X+10, Y and X being an Al content in mass % and a content of the cubic boron nitride grains in volume %, respectively, the binder phase comprises: at least a Ti compound; Al.sub.2O.sub.3; and inevitable impurities, the Al.sub.2O.sub.3 includes fine Al.sub.2O.sub.3 grains with a diameter of 10 nm to 100 nm dispersedly formed in the binder phase, and there are 30 or more of the fine Al.sub.2O.sub.3 grains generated in an area of 1 m1 m in a cross section of the binder phase.

Claims

1. A cubic boron nitride sintered material cutting tool comprising: a cutting tool body, which is a sintered material including cubic boron nitride grains and a binder phase, wherein the sintered material comprises: the cubic boron nitride grains in a range of 40 volume % or more and less than 60 volume %; and Al in a range from a lower limit of 2 mass % to an upper limit Y, satisfying a relationship, Y=0.1X+10, Y and X being an Al content in mass% and a content of the cubic boron nitride grains in volume %, respectively, the binder phase comprises: at least a Ti compound; Al.sub.2O.sub.3; and inevitable impurities, the Al.sub.2O.sub.3 includes fine Al.sub.2O.sub.3 grains with a diameter of 10 nm to 100 nm evenly dispersed in the binder phase, and there are 30 or more of the fine Al.sub.2O.sub.3 grains generated in an area of 1 m1 m in a cross section of the binder phase.

2. The cubic boron nitride sintered material cutting tool according to claim 1, further comprising a hard coating layer deposited on a surface of the cutting tool body.

3. The cubic boron nitride sintered material cutting tool according to claim 2, wherein the hard coating layer includes at least a titanium nitride coating.

4. The cubic boron nitride sintered material cutting tool according to claim 3, wherein the hard coating layer is made of a single layer of the titanium nitride coating.

5. The cubic boron nitride sintered material cutting tool according to claim 3, wherein the hard coating layer is made of: a single layer of the titanium nitride coating; and a single layer of a titanium aluminum nitride coating.

6. The cubic boron nitride sintered material cutting tool according to claim 2, wherein a layer thickness of the hard coating layer is in a range of 1.0 m to 2.5 m.

7. The cubic boron nitride sintered material cutting tool according to claim 1, wherein there are 60 or more of the fine Al.sub.2O.sub.3 grains generated in the area of 1 m1 m in the cross section of the binder phase.

8. The cubic boron nitride sintered material cutting tool according to claim 1, wherein there are 90 or more of the fine A1.sub.2O.sub.3 grains generated in the area of 1 m1 m in the cross section of the binder phase.

9. The cubic boron nitride sintered material cutting tool according to claim 1, wherein the diameter of the fine Al.sub.2O.sub.3 grains dispersedly formed in the binder phase is in the range of 10 nm to 85 nm.

10. The cubic boron nitride sintered material cutting tool according to claim 1, wherein the diameter of the fine Al.sub.2O.sub.3 grains dispersedly formed in the binder phase is in the range of 10 nm to 60 nm.

11. The cubic boron nitride sintered material cutting tool according to claim 1, wherein a median diameter of the Al.sub.2O.sub.3 existing in the binder phase is in a range of 60 nm to 85 nm.

12. The cubic boron nitride sintered material cutting tool according to claim 1, wherein a median diameter of the Al.sub.2O.sub.3 existing in the binder phase is in a range of 60 nm to 70 nm.

13. The cubic boron nitride sintered material cutting tool according to claim 3, wherein a layer thickness of the hard coating layer is in a range of 1.0 m to 2.5 m.

14. The cubic boron nitride sintered material cutting tool according to claim 4, wherein a layer thickness of the hard coating layer is in a range of 1.0 m to 2.5 m.

15. The cubic boron nitride sintered material cutting tool according to claim 5, wherein a layer thickness of the hard coating layer is in a range of 1.0 m to 2.5 m.

16. The cubic boron nitride sintered material cutting tool according to claim 1, wherein an average grain size of the cubic boron nitride grains is in a range of 0.5 m to 8.0 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows cBN extracted by image analysis of the secondary electron image obtained by SEM in a cross-section of the cBN sintered material.

(2) FIG. 2A shows the secondary electron image by AES in the cross-section of the cBN sintered material.

(3) FIG. 2B shows an Al elemental mapping image in the cross-section of the cBN sintered material.

(4) FIG. 2C shows an O (oxygen) elemental mapping image in the cross-section of the cBN sintered material.

(5) FIG. 2D shows an image that Al2O3 is extracted in the cross-section of the cBN sintered material.

(6) FIG. 3A shows a schematic plan view of the arc-ion plating apparatus 1 used in the deposition of the hard coating layer in the cutting tool of the present invention.

(7) FIG. 3B shows a schematic side view of the arc-ion plating apparatus 1 used in the deposition of the hard coating layer in the cutting tool of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(8) Embodiments of the present invention are explained below.

(9) The Content of cBN Grains in the cBN Sintered Material:

(10) Normally, the cBN sintered material is made of cBN grains as the hard phase component and binder phase component. The cBN sintered material, which constitutes the cutting tool body of the cBN sintered material cutting tool of the present invention, contains: at least one or more of Ti compounds selected from titanium nitride, titanium carbide, titanium carbonitride, titanium boride, titanium oxide, and a solid solution thereof; and Al.sub.2O.sub.3, as the binder phase component.

(11) If the content of cBN grains in the cBN sintered material were less than 40 volume %, hardness of the cBN sintered material tool would become insufficient due to the reduced amount of the hard material in the sintered material. Thus, fracturing resistance deteriorates when it is used as a cutting tool. On the other hand, if the content of cBN grains in the cBN sintered material were 60 volume % or more, the ratio of the binder phase in the sintered material would be relatively reduced. Thus, the toughness improving effect, which is contributed from the binder phase, cannot be obtained sufficiently. Therefore, it is preferable that the content of cBN grains in the cBN sintered material is set in the range from 40 volume % or more to less than 60 volume % in order to obtain the effect of the present invention more effectively.

(12) The content of cBN grains (volume %) in the cBN sintered material can be calculated based on the secondary electron image obtained by observing the cross-section structure of the cBN sintered material by the scanning electron microscopy (SEM). The parts corresponding to the cBN grains in the obtained secondary electron image can be extracted by image processing. After identifying the parts corresponding to the cBN grains, the value, which is the calculated area occupied by the cBN grains by image processing, is obtained. Then, by dividing the value by the image total area, the area ratio of the cBN grains can be calculated. Then, by regarding this area ratio as the volume %, the content of cBN grains (volume %) can be measured. In this measurement, the average value, which is obtained by processing at least 3 secondary electron images magnified 5,000 times with the scanning electron microscopy, is treated as the content of cBN grains (volume %). In the case where the average grain size of the cBN grains is about 3 m, it is preferable that the viewing area with the dimension of about 20 m20 m is used as the observing area for the image processing.

(13) The Average Grain Size of cBN Grains:

(14) The average grain size of the cBN grains, which are used for making the cutting tool of the present invention, is not particularly limited. However, it is preferable that the average grain size is in the range of 0.5 m to 8.0 m.

(15) In addition to the fracturing resistance improving effect due to including the hard cBN grains in the sintered material, the cBN sintered material can obtain even more excellent fracturing resistance by having the cBN grains with the average grain size of 0.5 m to 8.0 m being dispersed in the sintered material, since: not only fracturing and chipping, which are started from a start point with a convex-concave shape on the cutting edge formed by falling off of cBN grains on the tool surface during use of the tool, are suppressed; but cracking, which is formed by the stress applied on the cutting edge during use of the tool and extends from the interface between the cBN grain and the binder phase, or propagation of cracks, which extends with cracking of the cBN grain, are suppressed by the cBN grains dispersing in the sintered material and having the predetermined grain size.

(16) Therefore, it is preferable that the average grain size of the cBN grains used for making the cutting tool of the present invention is set to the range of 0.5 m to 8.0 m.

(17) The average grain size of the cBN grains can be obtained based on the secondary electron image obtained by observing the cross-section structure of the produced cBN sintered material by SEM. First, the parts corresponding to the cBN grains within the obtained image are extracted by binarization in the image processing as shown in FIG. 1. After identifying the parts corresponding to the cBN grains, the maximum length of each cBN grain is obtained by image processing, and it is regarded as the diameter of each cBN grain. Then, a graph is drawn by defining the vertical axis as the cumulative volume ratio (volume %) and the horizontal axis as the diameter (m), based on the volume of each grain obtained by calculation from the diameter; and the diameter, in which the cumulative volume ratio is the value of 50 volume %, is regarded as the average grain size of the cBN grains. In this measurement, the average value, which is obtained by processing at least 3 secondary electron images magnified 5,000 times with the SEM, is treated as the average grain size cBN grains (m). In the case where the average grain size of the cBN grains is about 3 m, it is preferable that the viewing area with the dimension of about 20 m20 m is used as the observing area for the image processing.

(18) Al Content in the cBN Sintered Material:

(19) If the Al content in the cBN sintered material were less than 2 mass %, the amount of Al.sub.2O.sub.3 generated in the binder phase would be reduced; and the crack extension would not be suppressed sufficiently. Thus, the toughness improving effect of the cBN sintered material cannot be obtained sufficiently. On the other hand, if the Al content Y in the cBN sintered material exceeded the value, Y=0.1X+10 when Y is the Al content (mass %) and X is the content of cBN grains (volume %), the amounts of AlN and Al.sub.2O.sub.3 formed in the binder phase increase. Furthermore, because of growth of these AlN and Al.sub.2O.sub.3 grains being proceeded to be coarse grains, toughness of the cBN sintered material deteriorates.

(20) Therefore, it is preferable that the Al content in the cBN sintered material is set to the range from the lower limit of 2 mass % to the upper limit Y satisfying the relationship, Y=0.1X+10, when Y is the Al content (mass %) and X is the content of cBN grains (volume %).

(21) The above-described Al content means the total content of Al contained in the all of Al, Al.sub.2O.sub.3, and TiAl used in the crushing process of the raw material powders for the binder phase formation.

(22) The Measurement Method of the Al Content in the cBN Sintered Material:

(23) Qualitative and quantitative analysis of the cBN sintered material is performed by using Electron Probe Micro Analyser (EPMA). The Al content (mass %) in the cBN sintered material is obtained by ZAF matrix correction method on the detected elements in the qualitative analysis.

(24) The Grain Size of the Al.sub.2O.sub.3 Grain in the Binder Phase and the Number per Unit Area:

(25) If the grain size of the Al.sub.2O.sub.3 grain in the binder phase were the diameter of less than 10 nm, it would be possible that toughness of the cBN sintered material deteriorates since contamination of impurities, such as oxygen, water, and the like, increases. On the other hand, if the grain size of the Al.sub.2O.sub.3 grain in the binder phase were the diameter exceeding 100 nm, it would be possible that crack extension is not suppressed sufficiently since the number of the Al.sub.2O.sub.3 grains is reduced relatively. In addition, if the number of the Al.sub.2O.sub.3 grains in the region of 1 m1 m in the cross-section of the binder phase were less than 30, crack extension would not be suppressed sufficiently.

(26) Therefore, the size of the Al.sub.2O.sub.3 grains in the binder phase is set to the diameter range of 10 nm to 100 nm; and the number of the Al.sub.2O.sub.3 grains in the region of 1 m1 m in the cross-section of the binder phase is set to 30 or more.

(27) A preferable diameter range of the fine Al.sub.2O.sub.3 grains dispersedly formed in the binder phase is 10 nm to 85 nm.

(28) A more preferable diameter range of the fine Al.sub.2O.sub.3 grains dispersedly formed in the binder phase is 10 nm to 60 nm.

(29) A preferable median diameter range of the Al.sub.2O.sub.3 existing in the binder phase is the diameter of 60 nm to 85 nm.

(30) A more preferable median diameter range of the Al.sub.2O.sub.3 existing in the binder phase is the diameter of 60 nm to 70 nm.

(31) A preferable number of the fine Al.sub.2O.sub.3 grains in the region of 1 m1 m in the cross-section of the binder phase is 60 or more.

(32) A more preferable number of the fine Al.sub.2O.sub.3 grains in the region of 1 m1 m in the cross-section of the binder phase is 90 or more.

(33) The upper limit of the number of the fine Al.sub.2O.sub.3 grains in the region of 1 m1 m in the cross-section of the binder phase is 200 taking the cost-effectiveness into consideration. A more preferable upper limit of the fine Al.sub.2O.sub.3 grains is 150. An even more preferable upper limit of the fine Al.sub.2O.sub.3 grains is 130.

(34) Measurement methods of the grain size; the median diameter; and the number per unit area of the Al.sub.2O.sub.3 grains in the binder phase:

(35) The grain size and the number per unit area of the Al.sub.2O.sub.3 grains in the binder phase are measured: by observing the binder phase structure of the cBN sintered material by Auger Electron Spectroscopy (AES); and by obtaining the elemental mapping image of the elements Al and O (refer FIGS. 2A, 2B, 2C, and 2D). Then, the parts, in which these obtained Al mapping image and O (oxygen) mapping image are overlapped, are identified by image analysis; and the Al.sub.2O.sub.3 grains are extracted by image processing (FIG. 2D). After extracting the parts corresponding to the Al.sub.2O.sub.3 grains, the maximum length of each Al.sub.2O.sub.3 grain is obtained by image analysis. When referring to the grain size of the each Al.sub.2O.sub.3 grain (the grain size of the Al.sub.2O.sub.3 grain), the obtained maximum length of the Al.sub.2O.sub.3 grain is regarded as the diameter of the Al.sub.2O.sub.3 grain. When referring to the average grain size of multi Al.sub.2O.sub.3 grains (the median grain diameter of the Al.sub.2O.sub.3 grains), the obtained maximum length of each Al.sub.2O.sub.3 grain is regarded as the diameter of the each Al.sub.2O.sub.3 grain; and the graph, the vertical and horizontal axes of which are the cumulative volume ratio (volume %) and the diameter (nm), respectively, is drawn based on volumes of the each Al.sub.2O.sub.3 grain obtained from calculation from the diameter. Then, the diameter with the cumulative volume ratio of 50 volume % is regarded as the median diameter of the subjected multi Al.sub.2O.sub.3 grains. In this measurement, the value and the average value, which are obtained by processing at least 3 secondary electron images magnified 5,000 times with SEM, are treated as the grain size of the Al.sub.2O.sub.3 grain (nm); and the median diameter of the Al.sub.2O.sub.3 grains (nm). In addition, from the elemental mapping images subjected to image analysis, the number of the Al.sub.2O.sub.3 grains, which have the diameter of 10 nm to 100 nm within the area of 1 m1 m in the cross section of the binder phase, is calculated.

(36) A hard coating layer may be deposited on the surface of the cutting tool body of the cBN cutting tool of the present invention.

(37) The hard coating layer may include at least a titanium nitride coating.

(38) The hard coating layer may be made of a single layer of a titanium nitride coating.

(39) The hard coating layer may be made of a single layer of a titanium nitride coating and a single layer of a titanium aluminum nitride coating.

(40) The layer thickness of the hard coating layer may be in the range of 1.0 m to 2.5 m.

(41) The cBN sintered material cutting tool of the present invention is specifically explained based on Examples below.

EXAMPLES

(42) As the raw material powders for the binder phase formation, the Ti compound powder (for example, the TiN powder; the TiC powder; the TiCN powder; the TiAl powder; and the like); and the fine Al.sub.2O.sub.3 grains having the grain size less than 100 nm (the fine Al.sub.2O.sub.3 powder includes the ultra-fine Al.sub.2O.sub.3 powder having the average grain size of 5 nm to 15 nm) or the Al powder and the Al.sub.2O.sub.3 powder having the grain size exceeding 100 nm were prepared. Next, the above-mentioned raw material powders were blended in the blending compositions shown in Table 1; and filled in the pot, which had the cemented carbide lining, with the cemented carbide balls made of tungsten carbide; and acetone for example. In addition, the amine-based or carboxylic acid-based dispersant was added in order to stimulate dispersion of the fine and ultra-fine Al.sub.2O.sub.3 grains if it was needed. Then, after putting a lid, the raw material powders were crushed by performing crushing and mixing for the rotating ball mill treating times shown in Table 2 by using the rotating ball mill.

(43) Next, the cBN content after sintering was adjusted at 40 volume % or more and less than 60 volume % by adding the cBN powder having the average grain size of 0.5 m to 8.0 m in the mass % shown in Table 2; and 24-hour mixing was performed by the rotating ball mill.

(44) After performing wet-mixing by the rotating ball mill and drying, the mixed material was subjected to press-molding under the pressure of 120 MPa to obtain the green compacts having the dimension of: 50 mm of the diameter; and 15 mm of the thickness. Then, these green compacts were sintered under the condition: under the vacuum atmosphere with the pressure of 110.sup.4 Pa or less; and at the temperature range of 900 C. to 1300 C., to be preliminary sintered materials. It is preferable that the processes from crushing to molding are performed under the inert atmosphere. These preliminary sintered materials were inserted into the ultra-high pressure and temperature sintering apparatus, in the state where the preliminary sintered material was stacked to the separately-prepared supporting piece made of the WC-based cemented carbide alloy having the composition of 8 mass % of Co and the WC balance; and the dimension of the diameter of 50 mm and the thickness of 2 mm. Then, they were subjected to ultra-high pressure sintering in the condition: under the pressure of 5 GPa, at the temperature of 1200 C. to 1400 C.; and the retention time of 30 minutes to produce the cBN sintered materials 1 to 8 of the present invention (hereinafter, referred as Examples 1 to 8 of the present invention).

(45) Nucleation and uniform dispersion of the fine Al.sub.2O.sub.3 grains were stimulated, by adding the ultra-fine Al.sub.2O.sub.3 powder having the average grain size of 5 nm to 15 nm at 0.1 mass % to 2 mass % during crushing of the raw material powers for the binder phase formation in the present invention. Accordingly, the fine Al.sub.2O.sub.3 grains having the diameter of 10 nm to 100 nm obtained the dispersed distribution in the binder phase shown in FIGS. 2B to 2D.

(46) For comparison, comparative cBN sintered materials 1 to 7 (hereinafter, referred as Comparative Examples 1 to 7) were produced. In making Comparative Examples 1 to 7, raw material powders were blended in the blending compositions shown in Table 1 in either the method as in Examples of the present invention; or the method where the ultra-fine or fine Al.sub.2O.sub.3 grains were not added. Then, the mixed materials were crushed and mixed for the rotating ball mill treatment times shown in Table 2. Then, the cBN powders shown in Table 2 were added; and ultra-high pressure sintering was performed under the predetermined condition.

(47) TABLE-US-00001 TABLE 1 Blending composition (mass %) Fine Ultra-fine Al.sub.2O.sub.3 Al.sub.2O.sub.3 Type TiN TiC TiCN TiAl Al Al.sub.2O.sub.3 grains grains Raw 1 95.2 2.5 1.5 0.8 material 2 85.1 10.0 2.9 2.0 powder 3 92.0 5.5 1.8 0.7 4 92.8 5.5 1.1 0.5 0.1 5 85.1 2.5 1.3 0.5 6 90.8 5.0 2.7 1.5 7 94.5 4.0 1.1 0.4 8 87.9 7.0 4.2 0.9 9 82.4 12.0 5.6 10 84.0 10.0 6.0 11 98.2 1.0 0.8 12 97.5 1.5 1.0 13 89.6 7.0 3.4 14 74.5 18.0 7.5 15 76.2 18.0 5.8

(48) TABLE-US-00002 TABLE 2 Raw cBN powder material Ball mill Relative additive powder type treatment amount to the (refer Table time total powder Type 1) (hr) (mass %) Cubic boron Example 1 1 96 35.6 nitride based Example 2 2 120 38.9 ultra-high Example 3 3 120 44.1 pressure Example 4 4 120 53.2 sintered Example 5 5 120 37.6 materials Example 6 6 96 36.6 Example 7 7 96 44.9 Example 8 8 96 54.1 Comparative 9 48 28.8 Example 1 Comparative 10 48 64.9 Example 2 Comparative 11 96 27.7 Example 3 Comparative 12 72 43.5 Example 4 Comparative 13 24 44.6 Example 5 Comparative 14 96 49 Example 6 Comparative 15 72 56.5 Example 7

(49) In the above-described Examples 1 to 8 of the present invention and Comparative Examples 1 to 7, the Al content in the cBN sintered material; the median diameter of the Al.sub.2O.sub.3 grains in the binder phase; the number of the fine Al.sub.2O.sub.3 grains having the diameter of 10 nm to 100 nm per unit area; and the cBN content in the cBN sintered material, were measured. Results of these measurements are shown in Table 3.

(50) When binder phase structures of Examples 1 to 8 of the present invention and Comparative Examples 1 to 7 were analyzed by using the X-ray diffractometer, existence of the diffraction peaks of TiN, TiB.sub.2, and AlN was confirmed. However, the existence of the diffraction peak of the AlB.sub.2 was not confirmed. Thus, there was no AlB.sub.2 in the binder phase.

(51) TABLE-US-00003 TABLE 3 In the sintered material structure median Number of Al.sub.2O.sub.3 having the Raw material Al diameter diameter of 10 nm to cBN powder type content of Al.sub.2O.sub.3 100 nm per unit area content Type (refer Table 1) (mass %) (nm) (Number/m.sup.2) (volume %) Cubic boron Example 1 1 2.1 70 45 40.4 nitride based Example 2 2 5.9 68 130 40.8 ultra-high Example 3 3 3 60 95 50 pressure Example 4 4 2.1 60 63 59.8 sintered Example 5 5 2.1 60 63 40.4 material Example 6 6 4 100 65 40.9 Example 7 7 2 70 35 50 Example 8 8 4 85 44 59.8 Comparative 9 7 490 10 30.3 Example1 Comparative 10 3.1 390 9 70.2 Example 2 Comparative 11 1 70 22 30.5 Example 3 Comparative 12 1 280 6 50 Example 4 Comparative 13 4.1 530 5 49.9 Example 5 Comparative 14 9.1 200 15 50.9 Example 6 Comparative 15 7 400 12 60.7 Example 7

(52) Next, the top and bottom surfaces of the sintered materials of the Examples 1 to 8 of the present invention and Comparative Examples 1 to 7 were polished by using the diamond grindstone; and each of the sintered materials were split into the equilateral triangle shape having the side of 3 mm by the wire-electrical discharge machine. Then, each of them was brazed on the brazing part (the corner part) of the chip main body made of WC-based cemented carbide alloy, which had the composition of 5 mass % of Co, 5 mass % of TaC and the WC balance; and the shape of CNGA120408 in ISO Standard (rhombic shape having the thickness of 4.76 mm and the side of 12.7 mm), by using the brazing material made of Ag alloy having the composition of 25 mass % of Cu, 5 mass % of Ti, 2.5 mass % of Ni, and the Ag balance. Finally, by performing final polishing, the cutting tools 1 to 8 of the present invention and the comparative cutting tools 1 to 7 having the insert shape of CNGA120408 in ISO Standard were produced.

(53) To the cutting tools 2, 4, 6 and 8 of the present invention, the hard coating layers shown in Table 4 were formed in the layer thickness shown in Table 4 to coat the outermost surfaces thereof by the physical vapor deposition apparatus shown in FIGS. 3A and 3B. Accordingly, the surface coated cutting tools 2, 4, 6 and 8 of the present invention (hereinafter, referred as the coated cutting tools of the present invention) were produced.

(54) The above-described physical vapor deposition apparatus (the arc ion plating apparatus 1) had the rotation table 2 rotating in the middle of the chamber. On the rotation table 2, multiple rotating shafts, each of which extended in the vertical direction, were provided (4 shafts in the example shown in the drawings). Multiple cemented carbide bodies 3 were held by the each of the rotating shafts in the state that they were skewered with the each of the rotating shafts. The rotation 2 rotated, and the multiple rotating shafts provided on the rotation table 2 rotated at the same time. Below the rotation table 2, the bias electric power supply was provided.

(55) In the chamber, a pair of the metal Ti or TiAl alloy targets 9 (cathode electrodes) were provided in such a way that the rotation table 2 was sandwiched from the left and right. Behind the each of the metal Ti or TiAl alloy targets 9 from the rotation table 2, the multiple magnetic force generating sources 8 (permanent magnets) were provided. The each of the metal Ti or TiAl alloy targets 9 were connected to the arc electric power supply 6. The side of the arc electric power supply 6 not connected to the metal Ti or TiAl alloy targets 9 was connected to the anode electrode 5. A pair of the anode electrodes 5 was provided in the chamber in such a way that they sandwiched the rotation table 2 from the left and right.

(56) The heater 7 was provided in the chamber and on the side where the metal Ti or TiAl alloy targets 9 were not provided, in such a way that the heater 7 faced the side surface of the rotation table.

(57) In the upper part of the chamber, the reaction gas inlet 10 was provided. In the lower part of the chamber, the exhaust gas outlet 11 was provided.

(58) TABLE-US-00004 TABLE 4 Hard coating layer type (Number in parenthesizes indicates Type the average layer thickness in m) The coated cutting tool 2 of the TiN (1.0) present invention The coated cutting tool 4 of the present invention The coated cutting tool 6 of the TiN (1.0)TiAlN (1.5) present invention The coated cutting tool 8 of the present invention

(59) Next, in the state where each of the above-described cutting tools was screwed on the tip part of the insert holder of tool steel with the jig to be fixed, continuous cutting tests were performed on: the cutting tools 1 to 8 of the present invention; the coated cutting tools 2, 4, 6 and 8 of the present invention; and the comparative cutting tools 1 to 7, in the cutting conditions 1 and 2 shown below.

(60) [Cutting Condition 1]

(61) Work: Round rod of JIS.SCr420 carbolized steel (hardness: HRC61)

(62) Cutting speed: 220 m/min

(63) Cutting depth: 0.2 mm

(64) Feed: 0.15 mm/rev.

(65) The tool life was defined as the cutting time until the cutting edge of the cutting tool was fractured.

(66) [Cutting Condition 2]

(67) Work: JIS.Math.SCr420 carbolized steel (hardness: HRC61) having one slit having the width of 10 mm in the longitudinal direction

(68) Cutting speed: 150 m/min

(69) Cutting depth: 0.2 mm

(70) Feed: 0.2 mm/rev.

(71) The tool life was defined as the cutting time until the cutting edge of the cutting tool was fractured.

(72) Results of the cutting tests in the cutting conditions 1 and 2 are shown in Table 5.

(73) TABLE-US-00005 TABLE 5 Cutting Cutting condition condition 1 2 Tool life Tool life Type (sec) (sec) The cutting tool 1 of the present invention 595 159 The cutting tool 2 of the present invention 700 180 The cutting tool 3 of the present invention 690 177 The cutting tool 4 of the present invention 650 170 The cutting tool 5 of the present invention 650 170 The cutting tool 6 of the present invention 660 172 The cutting tool 7 of the present invention 550 150 The cutting tool 8 of the present invention 555 152 The coated cutting tool 2 of the present 710 185 invention The coated cutting tool 4 of the present 660 175 invention The coated cutting tool 6 of the present 690 182 invention The coated cutting tool 8 of the present 585 162 invention The comparative cutting tool 1 315 48 The comparative cutting tool 2 330 52 The comparative cutting tool 3 400 110 The comparative cutting tool 4 320 50 The comparative cutting tool 5 200 30 The comparative cutting tool 6 390 80 The comparative cutting tool 7 360 60

(74) Based on the results shown in Table 5, it was demonstrated that fracturing and chipping were less likely to occur in cutting of the high hardness steel in the cutting tools 1 to 8 of the present invention; and the coated cutting tools 2, 4, 6, and 8; and they exhibited excellent cutting performance for a long-term usage. It was because: the fine Al.sub.2O.sub.3 grains having the diameter of 10 nm to 100 nm as the median diameter were dispersedly formed in the binder phase (existed in an uniformly dispersed state); and there were 30 or more of the fine Al.sub.2O.sub.3 grains generated in the area of 1 m1 m in the cross section of the binder phase in the cutting tools 1 to 8 of the present invention; and the coated cutting tools 2, 4, 6, and 8. In addition, the cutting performance was further improved by depositing the hard coating layer on the surfaces of the cutting tool bodies in the coated cutting tools of the present invention without deteriorating the above-described characteristics.

(75) Contrary to that, clearly any one of the comparative cutting tools 1 to 7 reached to the tool life in a relatively short time in the cutting work of the high hardness steel since Al.sub.2O.sub.3 in the binder phase did not have the characteristics of the cutting tools of the present invention.

INDUSTRIAL APPLICABILITY

(76) As described above, the cBN cutting tool of the present invention has the excellent chipping resistance and fracturing resistance. Thus, it can be utilized not only to cutting of the high hardness steel, but to cutting under varieties of conditions. Therefore, the present invention is satisfactory applicable to: high-performance cutting work apparatuses; and power-saving, energy-saving; and reduction of costs in cutting work.

REFERENCE SIGNS LIST

(77) 1: Arc ion plating apparatus

(78) 2: Rotation table

(79) 3: Cemented carbide body

(80) 4: Bias electric power supply

(81) 5: Anode electrode

(82) 6: Arc electric power supply

(83) 7: Heater

(84) 8: Magnetic force generating source (permanent magnet)

(85) 9: Metal Ti or TiAl alloy target (cathode electrode)

(86) 10: Reaction gas inlet

(87) 11: Exhaust gas outlet