Cubic boron nitride sintered material

Abstract

A cubic boron nitride sintered material comprises 30% by volume or more and 99.9% by volume or less of cubic boron nitride grains and 0.1% by volume or more and 70% by volume or less of a binder phase, the cubic boron nitride grain having a carbon content of 0.08% by mass or less, the cubic boron nitride sintered material being free of free carbon.

Claims

1. A cubic boron nitride sintered material comprising 30% by volume or more and 99.9% by volume or less of cubic boron nitride grains and 0.1% by volume or more and 70% by volume or less of a binder phase, the binder phase including: at least one selected from the group consisting of: a simple substance selected from the group consisting of a group 4 element, a group 5 element and a group 6 element of the periodic table, aluminum, silicon, cobalt and nickel; an alloy thereof; and an intermetallic compound thereof; at least one selected from the group consisting of: a compound consisting of at least one element selected from the group consisting of a group 4 element, a group 5 element and a group 6 element of the periodic table, aluminum, silicon, cobalt and nickel, and at least one element selected from the group consisting of nitrogen, carbon, boron and oxygen; and a solid solution derived from the compound; or at least one selected from the group consisting of a simple substance selected from the group consisting of a group 4 element, a group 5 element and a group 6 element of the periodic table, aluminum, silicon, cobalt and nickel, an alloy thereof, and an intermetallic compound thereof; and at least one selected from the group consisting of a compound consisting of at least one element selected from the group consisting of a group 4 element, a group 5 element and a group 6 element of the periodic table, aluminum, silicon, cobalt and nickel and at least one element selected from the group consisting of nitrogen, carbon, boron and oxygen, and a solid solution derived from the compound, the cubic boron nitride grain having a carbon content of 0.08% by mass or less, the cubic boron nitride sintered material being a cubic boron nitride sintered material free of free carbon, the cubic boron nitride grains having a calcium content of 0.02% by mass or more and 0.2% by mass or less, and wherein an interface between the cubic boron nitride grains has a carbon content equal to or smaller than that of the cubic boron nitride grains.

2. The cubic boron nitride sintered material according to claim 1, wherein the cubic boron nitride grains have a carbon content of 0.05% by mass or less.

3. The cubic boron nitride sintered material according to claim 1, wherein the cubic boron nitride grains have a carbon content of 0.035% by mass or less.

4. The cubic boron nitride sintered material according to claim 1, wherein the cubic boron nitride grains have a calcium content of 0.05% by mass or more and 0.17% by mass or less.

5. The cubic boron nitride sintered material according to claim 1, wherein the cubic boron nitride grains have a calcium content of 0.07% by mass or more and 0.15% by mass or less.

6. The cubic boron nitride sintered material according to claim 1, comprising 45% by volume or more and 95% by volume or less of the cubic boron nitride grains.

Description

EXAMPLES

(1) The present embodiment will be described more specifically with reference to examples. Note, however, that the present embodiment is not limited to these examples.

Example 1

(2) (Sample 1-1)

(3) 100 parts by mass of hexagonal boron nitride powder were blended with 10 parts by mass of LiCaBN.sub.2 serving as a catalyst, and the mixture was held at 5 GPa and 1450° C. for 30 minutes to obtain cubic boron nitride powder (cBN powder).

(4) The above cBN powder was subjected to heat treatment in an NH.sub.3 atmosphere (under the atmospheric pressure) at 700° C. for 3 hours.

(5) WC powder, Co powder and Al powder were prepared at a ratio in volume of 3:8:1. To the WC powder, the Co powder, and the Al powder, Zr powder was added and mixed so as to be 5% by mass of the total, heat-treated at 1200° C. for 30 minutes in a vacuum, and thereafter agitated and pulverized with a wet ball mill to obtain a binder powder. Note that Al.sub.2O.sub.3 shown in Table 1 is obtained as the Al reacts with oxygen that is contained in the powdery mixture while sintered.

(6) After the heat treatment, the cBN powder and the binder powder were blended at a ratio in volume of 95:5 and uniformly mixed in a wet ball mill method using ethanol to obtain a powdery mixture. Subsequently, the powdery mixture was degassed in a vacuum at 900° C. to remove impurities such as moisture on the surface thereof.

(7) Subsequently, the powdery mixture was brought into contact with a WC-6% Co cemented carbide disc and a Co (cobalt) foil and thus introduced into a container made of Ta (tantalum), and the container was vacuumed and sealed. Using a belt-type ultrahigh-pressure and ultrahigh-temperature generator, the powdery mixture in the vacuumed and sealed container was held at 7 GPa and 1700° C. for 15 minutes and thus sintered to provide a cBN sintered material for sample 1-1.

(8) (Sample 1-2 to Sample 1-6)

(9) cBN sintered materials were produced in the same manner as in sample 1-1 except that the cBN powder was subjected to heat treatment under conditions indicated in table 1.

(10) (Sample 1-7 to Sample 1-12)

(11) cBN sintered materials were produced in the same manner as in sample 1-5 except that in producing the cBN powder, a holding time at 5 GPa and 1450° C. was changed to those indicated in table 1.

(12) (Sample 1-13)

(13) A cBN sintered material was produced in the same manner as in sample 1-5 except that in producing the binder powder, Cr powder was added instead of Zr powder.

(14) (Sample 1-14)

(15) A cBN sintered material was produced in the same manner as in sample 1-5 except that in producing the binder powder, Ni powder and Nb powder were added instead of Zr powder. The mass ratio of the Ni powder and the Nb powder was Ni:Nb=1:1.

(16) (Sample 1-15)

(17) A cBN sintered material was produced in the same manner as in sample 1-5 except that Zr powder was not added in producing the binder powder and ZrN powder was added in mixing the cBN powder and the binder powder. The ZrN powder was added in an amount of 5% by mass with respect to the amount of the binder.

(18) (Sample 1-16)

(19) A cBN sintered material was produced in the same manner as in sample 1-5 except that Zr powder was not added in producing the binder powder and CrN powder was added in mixing the cBN powder and the binder powder. The CrN powder was added in an amount of 5% by mass with respect to the amount of the binder.

(20) (Sample 1-17)

(21) A cBN sintered material was produced in the same manner as in sample 1-16 except that the powdery mixture was sintered with a pressure of 10 GPa applied.

(22) (Sample 1-18)

(23) A cBN sintered material was produced in the same manner as in sample 1-16, except that a ratio in volume of the cBN powder and the binder powder was set to 90:10 and the powdery mixture was sintered with a pressure of 6.5 GPa applied.

(24) (Sample 1-19)

(25) A cBN sintered material was produced in the same manner as in sample 1-16, except that a ratio in volume of the cBN powder and the binder powder was set to 90:10 and the powdery mixture was sintered with a pressure of 5.5 GPa applied.

(26) (Sample 1-20)

(27) A cBN sintered material was produced in the same manner as in sample 1-16, except that the powdery mixture was sintered with a pressure of 15 GPa applied.

(28) (Sample 1-21)

(29) A cBN sintered material was produced in the same manner as in sample 1-5 except that the cBN powder was not subjected to heat treatment.

(30) (Sample 1-22)

(31) A cBN sintered material was produced in the same manner as in sample 1-5 except that LiBN.sub.2 was used instead of LiCaBN.sub.2 in producing the cBN powder.

(32) (Sample 1-23)

(33) A cBN sintered material was produced in the same manner as in sample 1-5 except that the cBN powder was subjected to heat treatment at 900° C. for 10 hours.

(34) (Sample 1-24)

(35) A cBN sintered material was produced in the same manner as in sample 1-5 except that the binder powder was not used and the cBN powder was alone sintered, and in doing so, the WC-6% Co cemented carbide disc and the Co (cobalt) foil were not used.

(36) (Sample 1-25)

(37) A cBN sintered material was produced in the same manner as in sample 1-5 except that the binder powder was not used and the cBN powder was alone sintered, and in doing so, the WC-6% Co cemented carbide disc and the Co (cobalt) foil were replaced with an Al plate.

(38) (Sample 1-26)

(39) A cBN sintered material was produced in the same manner as in sample 1-5 except that in mixing the cBN powder and the binder powder together, a general, anionic dispersant (“SN Dispersant 5023” (trademark) manufactured by SAN NOPCO LIMITED) was added and mixed in an amount of 2% by mass with respect to the mass of the powdery mixture.

(40) (Sample 1-27)

(41) Sample 1-27 was basically produced in the same manner as sample 1-5. It is different from sample 1-5, as follows:

(42) The binder powder was obtained by mixing Co powder, Al powder and Cr powder at a weight ratio of Co powder:Al powder:Cr powder=7.5:1:0.5.

(43) The cBN powder and the binder powder were blended at a ratio in volume of cBN powder:binder powder=90:10 and uniformly mixed in a wet ball mill method using ethanol to obtain a powdery mixture. Subsequently, the powdery mixture was degassed in a vacuum at 900° C. to remove impurities such as moisture on the surface thereof.

(44) The powdery mixture was sintered without using the WC-6% Co cemented carbide disc to obtain a cBN sintered material for sample 1-27. When the powdery mixture was sintered, Co, Al and Cr in the binder powder each form a solid solution and thus form a CoCrAl alloy.

(45) (Sample 1-28)

(46) A cBN sintered material was produced in the same manner as in sample 1-5 except that in mixing the binder powder and the cBN powder, an organic matter of dodecanamine (CH.sub.3(CH.sub.2).sub.11NH.sub.2) was added at a weight ratio of 0.05%.

(47) <Evaluation>

(48) (Composition of cBN Sintered Material)

(49) The ratio in volume between the cBN grains and the binder phase in the cBN sintered material was measured. How it was specifically measured will not be described as it is identical to that described in an embodiment for implementing the present invention, as has been described above. A result is shown in table 1 at the “cBN grains (vol %)” and “binder phase (vol %)” columns.

(50) In sample 1-1 to sample 1-16, sample 1-18 to sample 1-23, and sample 1-25, a ratio in volume of the cBN powder and the binder powder in the powdery mixture and a ratio in volume of the cBN grains and the binder phase in the cubic boron nitride sintered material were different. It is believed that this is because the powdery mixture is sintered in contact with the WC-6% Co cemented carbide disc, and accordingly, while the powdery mixture is sintered, the cemented carbide component flows into the powdery mixture, and in the resultant cBN sintered material, that cemented carbide component is present as a binder phase.

(51) (Composition of Binder Phase)

(52) The composition of the binder phase in the cBN sintered material was determined. How it was specifically determined will not be described as it is identical to that described in an embodiment for implementing the present invention, as has been described above. A result is shown in Table 1 at the “binder phase” column at the “composition” sub column.

(53) (Carbon Content)

(54) The carbon content of the cBN grains in the cBN sintered material was measured with a carbon analyzer. How it was specifically measured will not be described as it is identical to that described in an embodiment for implementing the present invention, as has been described above. A result is indicated in Table 1 at the “cBN grain's carbon content” column.

(55) (Calcium Content)

(56) The calcium content of the cBN grains in the cBN sintered material was measured through an ICP analysis. How it was specifically measured will not be described as it is identical to that described in an embodiment for implementing the present invention, as has been described above. A result is indicated in Table 1 at the “cBN grain's Ca content” column.

(57) (Free Carbon Concentration)

(58) The free carbon concentration in the cBN sintered material was measured. How it was specifically measured will not be described as it is identical to that described in an embodiment for implementing the present invention, as has been described above. A result is indicated in table 1 at the “free carbon” column. In the table, “none” indicates that the free carbon concentration is equal to or lower than the detection limit and free carbon is thus absent.

(59) (Carbon Content in Grain Boundaries Between Cubic Boron Nitride Grains)

(60) In the cBN sintered material, a carbon content in grain boundaries between the cBN grains and a carbon content in the cBN grains were measured to determine a relationship in magnitude therebetween. How it was specifically measured and determined will not be described as it is identical to that described in the “Carbon content in grain boundaries between cubic boron nitride grains” section according to an embodiment for implementing the present invention, as has been described above. A result is indicated in table 1 at the “carbon content determined” column. In the table, “equal” means that at seven or more of ten points, an amount of carbon at an interface between cBN grains is equal to or less than a maximum value in a range in which line scan is performed, and the carbon content at the interface between the cBN grains is equal to or smaller than that in the cBN grains. In the table, “intra-grain<interface” means that at six or less of ten points, an amount of carbon at an interface between cBN grains is equal to or less than a maximum value in a range in which line scan is performed, and the carbon content at the interface between the cBN grains is larger than that in the cBN grains.

(61) (Cutting Test)

(62) The cBN sintered material of each sample produced was used as a cutting edge to produce a cutting tool (with a substrate having a shape: CNGA120408, and cutting-edge treatment: T01215). Using this, a cutting test was performed undercutting conditions indicated below: The following cutting conditions correspond to high-efficiency machining for high-strength hardened steel. Cutting speed: 200 m/min Feed rate: 0.1 mm/rev Depth of cut: 0.1 mm Coolant: (Dry) Cutting method: continuous end face cutting Lathe: LB400 (manufactured by Okuma Corporation) Workpiece: cylindrical sintered part (“Hardened Sintered Alloy D-40” manufactured by Sumitomo Electric Industries, Ltd.)

(63) Evaluation Method: The cutting edge was observed every 0.5 km and flank wear was measured in amount to draw a graph showing how flank wear varies in amount with a cutting distance. A line indicating an amount of wear of 200 μm is drawn in the graph, and a cutting distance at an intersection of the line and the graph showing how wear varies in amount is read as a tool life. A result is indicated in table 1 at the “tool life” column.

(64) TABLE-US-00001 TABLE 1 conditions for synthesizing cBN conditions for cBN sintered material powder heat treatment cBN grains cutting sam- holding of cBN powder cBN binder phase carbon Ca carbon test ple time temp. time grains vol compo- content content free content tool life Nos. catalyst min. ° C. hrs vol % % sition mass % mass % carbon determined (km) 1-1  LiCaBN.sub.2 30 700 1 90 10 WC, Co, 0.08 0.1 none equal 3.3 Al.sub.2O.sub.3, Zr 1-2  LiCaBN.sub.2 30 900 1 90 10 WC, Co, 0.001 0.1 none equal 3.2 Al.sub.2O.sub.3, Zr 1-3  LiCaBN.sub.2 30 700 2 90 10 WC, Co, 0.05 0.1 none equal 3.7 Al.sub.2O.sub.3, Zr 1-4  LiCaBN.sub.2 30 900 2 90 10 WC, Co, 0.005 0.1 none equal 3.5 Al.sub.2O.sub.3, Zr 1-5  LiCaBN.sub.2 30 700 3 90 10 WC, Co, 0.035 0.1 none equal 4 Al.sub.2O3, Zr 1-6  LiCaBN.sub.2 30 900 3 90 10 WC, Co, 0.008 0.1 none equal 3.8 Al.sub.2O.sub.3, Zr 1-7  LiCaBN.sub.2 60 700 3 90 10 WC, Co, 0.035 0.2 none equal 3.1 Al.sub.2O.sub.3, Zr 1-8  LiCaBN.sub.2 5 700 3 90 10 WC, Co, 0.035 0.02 none equal 3.2 Al.sub.2O.sub.3, Zr 1-9  LiCaBN.sub.2 50 700 3 90 10 WC, Co, 0.035 0.17 none equal 3.5 Al.sub.2O.sub.3, Zr 1-10 LiCaBN.sub.2 10 700 3 90 10 WC, Co, 0.035 0.05 none equal 3.7 Al.sub.2O.sub.3, Zr 1-11 LiCaBN.sub.2 40 700 3 90 10 WC, Co, 0.035 0.15 none equal 3.9 Al.sub.2O.sub.3, Zr 1-12 LiCaBN.sub.2 20 700 3 90 10 WC, Co, 0.035 0.07 none equal 3.8 Al.sub.2O.sub.3, Zr 1-13 LiCaBN.sub.2 30 700 3 90 10 WC, Co, 0.035 0.1 none equal 4.1 Al.sub.2O.sub.3, Cr 1-14 LiCaBN.sub.2 30 700 3 90 10 WC, Co, 0.035 0.1 none equal 3.9 Al.sub.2O.sub.3, Ni, Nb 1-15 LiCaBN.sub.2 30 700 3 90 10 WC, Co, 0.035 0.1 none equal 3.9 Al.sub.2O.sub.3, ZrN 1-16 LiCaBN.sub.2 30 700 3 90 10 WC, Co, 0.035 0.1 none equal 3.9 Al.sub.2O.sub.3, CrN 1-17 LiCaBN.sub.2 30 700 3 95 5 WC, Co, 0.035 0.1 none equal 4 Al.sub.2O.sub.3, CrN 1-18 LiCaBN.sub.2 30 700 3 85 15 WC, Co, 0.035 0.1 none equal 3.7 Al.sub.2O.sub.3, CrN 1-19 LiCaBN.sub.2 30 700 3 80 20 WC, Co, 0.035 0.1 none equal 3.5 Al.sub.2O.sub.3, CrN 1-20 LiCaBN.sub.2 30 700 3 99 1 WC, Co, 0.035 0.1 none equal 4.1 Al.sub.2O.sub.3, CrN 1-21 LiCaBN.sub.2 30 — — 90 10 WC, Co, 0.1 0.1 none equal 1.5 Al.sub.2O.sub.3, Zr 1-22 LiBN.sub.2 30 700 3 90 10 WC, Co, 0.035 <0.001 none equal 3 Al.sub.2O.sub.3, Zr 1-23 LiCaBN.sub.2 30 900 10 90 10 WC, Co, <0.001 0.1 none equal 4 Al.sub.2O.sub.3, Zr 1-24 LiCaBN.sub.2 30 700 3 100 0 — 0.035 0.1 none equal 1.5 1-25 LiCaBN.sub.2 30 700 3 98 2 Al.sub.2O.sub.3 0.035 0.1 none equal 3.1 1-26 LiCaBN.sub.2 30 700 3 90 10 WC, Co, 0.035 0.1 0.1% intra-grain < 1.2 Al.sub.2O.sub.3, Zr binder interface phase 1-27 LiCaBN.sub.2 30 700 3 90 10 CoAlCr 0.035 0.1 none equal 3.9 1-28 LiCaBN.sub.2 30 700 3 90 10 WC, Co, 0.035 0.1 none intra-grain < 3.0 Al.sub.2O.sub.3, Zr interface

(65) <Discussions>

(66) The cBN sintered materials of sample 1-1 to sample 1-20, sample 1-22, sample 1-23, sample 1-25, sample 1-27, and sample 1-28 correspond to examples.

(67) The cBN sintered material of sample 1-21 corresponds to a comparative example as it comprises cBN grains having a carbon content exceeding 0.08% by mass.

(68) The cBN sintered material of sample 1-24 corresponds to a comparative example as it is composed of 100% by volume of cBN grains and does not comprise a binder phase.

(69) The cBN sintered material of sample 1-26 corresponds to a comparative example as it contains 0.1% of free carbon. Note that the free carbon was present in the binder phase.

(70) <Discussions>

(71) It has been confirmed that the cBN sintered materials of the examples (i.e., sample 1-1 to sample 1-20, sample 1-22, sample 1-23, sample 1-25, sample 1-27, and sample 1-28) have a longer tool life than the cBN sintered materials of the comparative examples (sample 1-21, sample 1-24, and sample 1-26).

Example 2

(72) (Sample 2-1)

(73) A cBN powder was obtained in the same manner as in sample 1-1. The cBN powder was subjected to heat treatment in an NH.sub.3 atmosphere (under the atmospheric pressure) at 700° C. for 1 hour.

(74) Titanium (Ti) powder, aluminum (Al) powder, and TiN powder were mixed at a mass ratio of 37:22:41 and heat-treated in an argon atmosphere at 1500° C. for 60 minutes to obtain a single-phase compound having a composition of Ti.sub.2AlN. The single-phase compound was agitated and pulverized in a wet ball mill to obtain Ti.sub.2AlN powder having a particle diameter (D50) of 0.5 μm.

(75) The cBN powder, Ti.sub.2AlN powder, and TiN powder were mixed in a ball mill to obtain a powdery mixture. The cBN powder, the Ti.sub.2AlN powder and the TiN powder were mixed together at a ratio adjusted such that a ratio of the cBN powder in the powdery mixture was 70% by volume, and a mass ratio of the Ti.sub.2AlN powder and the TiN powder was set to 1:1.

(76) Subsequently, the powdery mixture was brought into contact with a WC-6% Co cemented carbide disc and a Co (cobalt) foil and thus introduced into a container made of Ta (tantalum), and the container was vacuumed and sealed. Using a belt-type ultrahigh-pressure and ultrahigh-temperature generator, the powdery mixture in the vacuumed and sealed container was held at 6.5 GPa and 1500° C. for 15 minutes and thus sintered to obtain a cBN sintered material for sample 2-1.

(77) (Sample 2-2 to Sample 2-6)

(78) cBN sintered materials were produced in the same manner as in sample 2-1 except that the cBN powder was subjected to heat treatment under conditions indicated in table 2.

(79) (Sample 2-7 to Sample 2-12>

(80) cBN sintered materials were produced in the same manner as in sample 2-5 except that in producing the cBN powder, a holding time at 5 GPa and 1450° C. was changed to those indicated in table 2.

(81) (Sample 2-13)

(82) A cBN sintered material was produced in the same manner as in sample 2-5 except that TiNbCN powder was used instead of TiN powder. The TiNbCN powder was produced through the following procedure:

(83) TiO.sub.2 powder, Nb.sub.2O.sub.5 powder, and carbon powder were mixed at a ratio in mass of 57.19:16.79:26.02 and heat-treated at 2150° C. for 60 minutes in a nitrogen atmosphere to obtain a single-phase compound having a composition of TiNbCN.

(84) The single-phase compound was agitated and pulverized in a wet ball mill to obtain TiNbCN powder having a particle diameter (D50) of 0.5 μm.

(85) (Sample 2-14)

(86) A cBN sintered material was produced in the same manner as in sample 2-5 except that TiZrCN powder was used instead of TiN powder. The TiZrCN powder was produced through the following procedure:

(87) TiO.sub.2 powder, ZrO.sub.2 powder, and carbon powder were mixed at a ratio in mass of 58.35:15.88:25.77 and heat-treated at 2150° C. for 60 minutes in a nitrogen atmosphere to obtain a single-phase compound having a composition of TiZrCN. The single-phase compound was agitated and pulverized in a wet ball mill to obtain TiZrCN powder having a particle diameter (D50) of 0.5 μm.

(88) (Sample 2-15)

(89) A cBN sintered material was produced in the same manner as in sample 2-5 except that TiHfCN powder was used instead of TiN powder. The TiHfCN powder was produced through the following procedure:

(90) TiO.sub.2 powder, HfO.sub.2 powder, and carbon powder were mixed at a ratio in mass of 52.45:24.38:23.17 and heat-treated at 2150° C. for 60 minutes in a nitrogen atmosphere to obtain a single-phase compound having a composition of TiHfCN. The single-phase compound was agitated and pulverized in a wet ball mill to obtain TiHfCN powder having a particle diameter (D50) of 0.5 μm.

(91) (Sample 2-16)

(92) A cBN sintered material was produced in the same manner as in sample 2-5 except that TiCrCN powder was used instead of TiN powder. The TiCrCN powder was produced through the following procedure:

(93) TiO.sub.2 powder, Cr.sub.2O.sub.3 powder and carbon powder were mixed at a ratio in mass of 62.64:10.52:26.84 and heat-treated at 2150° C. for 60 minutes in a nitrogen atmosphere to obtain a single-phase compound having a composition of TiCrCN. The single-phase compound was agitated and pulverized in a wet ball mill to obtain TiCrCN powder having a particle diameter (D50) of 0.5 μm.

(94) (Samples 2-17 to Sample 2-20, and Sample 2-24)

(95) CBN sintered materials were produced in the same manner as in sample 2-5, except that a ratio in volume of the cBN powder and the binder powder was adjusted to allow each cBN sintered material to have a cBN grain content indicated in table 2.

(96) (Sample 2-21)

(97) A cBN sintered material was produced in the same manner as in sample 2-5, except that a ratio in volume of the cBN powder and the binder powder was adjusted to allow the cBN sintered material to have a cBN grain content indicated in table 2 and the cBN powder was not subjected to heat treatment.

(98) (Sample 2-22)

(99) A cBN sintered material was produced in the same manner as in sample 2-5, except that a ratio in volume of the cBN powder and the binder powder was adjusted to allow the cBN sintered material to have a cBN grain content indicated in table 2 and LiBN.sub.2 was used instead of LiCaBN.sub.2 in producing the cBN powder.

(100) (Sample 2-23)

(101) A cBN sintered material was produced in the same manner as in sample 2-5, except that a ratio in volume of the cBN powder and the binder powder was adjusted to allow the cBN sintered material to have a cBN grain content indicated in table 2 and the cBN powder was subjected to heat treatment at 900° C. for 10 hours.

(102) <Evaluation>

(103) (Composition of cBN Sintered Material, Composition of Binder Phase, Carbon Content of cBN Grains, Calcium Content of cBN Grains, and Confirmation of Presence/Absence of Free Carbon)

(104) Each produced cBN sintered material had measured its own composition, the binder phase's composition, the cBN grains' carbon and calcium contents, and the free carbon's concentration. How they were specifically measured will not be described as it is identical to that described in an embodiment for implementing the present invention, as has been described above. A result is shown in Table 2.

(105) (Cutting Test)

(106) The cBN sintered material of each sample produced was used to produce a cutting tool having a cutting edge composed of the cBN sintered material (with a substrate having a shape: DNGA150412, and a cutting-edge treatment: S01225). Using this, a cutting test was performed under cutting conditions indicated below: The following cutting conditions correspond to high-efficiency machining for high-strength hardened steel. Cutting speed: 200 m/min Feed rate: 0.2 mm/rev Depth of cut: 0.2 mm Coolant: (Dry) Cutting method: interrupted cutting Lathe: LB400 (manufactured by Okuma Corporation) Workpiece: Hardened steel (SCM415 carburized-quenched and having a hardness of 60 HRC, with a circumference having five grooves each in the form of the letter V in cross section)

(107) Evaluation Method: The cutting edge was observed every 0.5 km and flank wear was measured in amount to draw a graph showing how flank wear varies in amount with a cutting distance. A line indicating an amount of wear of 200 μm is drawn in the graph, and a cutting distance at an intersection of the line and the graph showing how wear varies in amount is read as a tool life. A result is indicated in table 2 at the “tool life” column.

(108) TABLE-US-00002 TABLE 2 conditions for synthesizing cBN conditions cBN sintered material powder for heat treatment cBN grains holding of cBN powder cBN carbon Ca cutting test sample time temperature time grains binder phase content content free tool life Nos. catalyst min. ° C. hours vol % vol % composition mass % mass % carbon (km) 2-1  LiCaBN.sub.2 30 700 1 70 30 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.08 0.1 none 3.3 2-2  LiCaBN.sub.2 30 900 1 70 30 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.001 0.1 none 3.2 2-3  LiCaBN.sub.2 30 700 2 70 30 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.08 0.1 none 3.7 2-4  LiCaBN.sub.2 30 900 2 70 30 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.005 0.1 none 3.5 2-5  LiCaBN.sub.2 30 700 3 70 30 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.04 0.1 none 4 2-6  LiCaBN.sub.2 30 900 3 70 30 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.008 0.1 none 3.8 2-7  LiCaBN.sub.2 60 700 3 70 30 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.04 0.2 none 3.1 2-8  LiCaBN.sub.2 5 700 3 70 30 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.04 0.02 none 3.2 2-9  LiCaBN.sub.2 50 700 3 70 30 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.04 0.17 none 3.5 2-10 LiCaBN.sub.2 10 700 3 70 30 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.04 0.05 none 3.7 2-11 LiCaBN.sub.2 40 700 3 70 30 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.04 0.15 none 3.9 2-12 LiCaBN.sub.2 20 700 3 70 30 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.04 0.07 none 3.8 2-13 LiCaBN.sub.2 30 700 3 70 30 TiNbCN,AlN,Al.sub.2O.sub.3, 0.04 0.1 none 4.1 TiB.sub.2 2-14 LiCaBN.sub.2 30 700 3 70 30 TiZrCN,AlN,Al.sub.2O.sub.3, 0.04 0.1 none 3.9 TiB.sub.2 2-15 LiCaBN.sub.2 30 700 3 70 30 TiHfCN,AlN,Al.sub.2O.sub.3, 0.04 0.1 none 3.9 TiB.sub.2 2-16 LiCaBN.sub.2 30 700 3 70 30 TiCrCN,AlN,Al.sub.2O.sub.3, 0.04 0.1 none 3.9 TiB.sub.2 2-17 LiCaBN.sub.2 30 700 3 75 25 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.04 0.1 none 4 2-18 LiCaBN.sub.2 30 700 3 60 40 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.04 0.1 none 3.7 2-19 LiCaBN.sub.2 30 700 3 50 50 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.04 0.1 none 3.5 2-20 LiCaBN.sub.2 30 700 3 40 60 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.04 0.1 none 3.3 2-21 LiCaBN.sub.2 30 — — 90 10 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.1 0.1 none 1.5 2-22 LiBN.sub.2 700 3 90 10 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.04 <0.001 none 3 2-23 LiCaBN.sub.2 30 900 10 90 10 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 <0.001 0.1 none 4 2-24 LiCaBN.sub.2 30 700 3 25 75 TiN,AlN,Al.sub.2O.sub.3,TiB.sub.2 0.04 0.1 none 1.5

(109) The cBN sintered materials of sample 2-1 to sample 2-20, sample 2-22 and sample 2-23 correspond to examples.

(110) Sample 2-21 corresponds to a comparative example as it comprises cBN grains having a carbon content exceeding 0.08% by mass.

(111) The cBN sintered material of sample 2-24 corresponds to a comparative example as it has a cBN grain content of 25% by volume.

(112) <Discussions>

(113) It has been confirmed that the cBN sintered materials of the examples (i.e., sample 2-1 to sample 2-20, sample 2-22, and sample 2-23) have a longer tool life than the cBN sintered materials of the comparative examples (sample 2-21 and sample 2-24).

(114) While embodiments and examples of the present disclosure have been described as above, it is also planned from the beginning that the configurations of the above-described embodiments and examples are appropriately combined and variously modified.

(115) The embodiments and examples disclosed herein are illustrative in any respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the above-described embodiments and examples, and is intended to include any modifications within the scope and meaning equivalent to the claims.