JP4883472B2 - Cutting tool made of surface-coated cubic boron nitride-based ultra-high pressure sintered material that exhibits excellent chipping resistance in hard cutting of hardened steel - Google Patents

Description

  The present invention provides a hard coating layer having a predetermined high-temperature strength, excellent high-temperature hardness and lubricity, and therefore, an alloy tool steel or bearing steel that generates high heat and at the same time places a high load on the cutting edge. Hard coating on the surface of the cutting tool base made of cubic boron nitride-based ultra-high pressure sintered material that exhibits excellent chipping resistance even when used for heavy cutting of hardened steel such as hardened materials The present invention relates to a cutting tool made of a surface-coated cubic boron nitride-based ultrahigh pressure sintered material (hereinafter referred to as a coated cBN-based sintered tool) in which a layer is formed.

  In general, a coated cBN-based sintered tool can be attached to a throwaway tip that is detachably attached to the tip of a cutting tool for turning various work materials such as steel and cast iron, and the throwaway tip can be detachably attached. There are known slow-away end mills that are attached and cut in the same manner as solid type end mills used for chamfering, grooving, and shoulder machining.

  In addition, as the coated cBN-based sintered tool, titanium nitride (TiN) is formed on the surface of a tool body made of various cubic boron nitride-based ultrahigh pressure sintered materials (hereinafter referred to as cBN-based sintered materials). A coated cBN-based firing layer formed by vapor deposition of a surface coating layer such as a composite nitride layer of Ti, Si and B (boron), a composite nitride layer of Ti and Al, and a composite nitride layer of Cr and Si It is also known that knotting tools are known, and these are used for cutting various steels and cast irons, for example.

Further, the above-mentioned coated cBN-based sintered tool is loaded with the above-mentioned tool base in an arc ion plating apparatus which is one type of physical vapor deposition apparatus schematically shown in FIG. For example, in a state heated to 500 ° C., a cathode electrode (evaporation source) made of metal Ti, Ti—Al alloy, Ti—Si—B alloy, Cr—Si alloy having a predetermined composition, and an anode electrode, During this time, for example, a current of 90 A is applied to generate arc discharge, and at the same time, nitrogen gas is introduced into the apparatus as a reaction gas to obtain a reaction atmosphere of, for example, 2 Pa, while the tool base has, for example, −100 V A desired component such as a TiN layer, a (Ti, Al) N layer, a (Ti, Si, B) N layer, or a (Cr, Si) N layer is formed on the surface of the tool base under a condition where a bias voltage is applied. It is also known that are prepared by depositing a layer of growth.
JP-A-7-300649 JP-A-8-119774 JP 2003-340603 A JP 2003-340605 A

  In recent years, the performance of cutting machines has been remarkable. On the other hand, there is a strong demand for labor saving and energy saving and further cost reduction for cutting work. In the conventional coated cBN-based sintered tool, there is no particular problem when this is used for normal cutting of various carbon steels, low alloy steels, and cast iron. However, when this is used for cutting of high hardness steel having a hardness of 50 or higher, such as hardened material of alloy tool steel or bearing steel, particularly with high heat generation. At the same time, when used under heavy cutting conditions where a heavy load is applied to the cutting edge, chipping (slight chipping) occurs at the cutting edge due to insufficient high-temperature strength and lubricity of the hard coating layer. As a result, the service life is reached in a relatively short time.

In view of the above, the inventor of the present invention has a coated cBN-based firing that exhibits excellent chipping resistance with a hard coating layer particularly in heavy cutting of high hardness steel such as a hardened material of alloy tool steel and bearing steel. As a result of research to develop a knot,
(a) composite nitride of Cr and Si constituting the hard layer _{([Cr 1-X Si X} ] N) layer, the value of the content X (atomic ratio) of Si, 0.02 to 0.1 Within the range of the above, it has excellent high-temperature hardness and lubricity with a predetermined high-temperature strength, and has the wear resistance required under normal cutting conditions, but more severe cutting conditions, At the same time as the generation of high heat, high-strength steel with heavy load on the cutting edge portion is not sufficiently satisfactory in high-temperature strength and lubricity, and chipping is likely to occur.

(B) On the other hand, the chromium nitride (CrN) layer has a predetermined high-temperature strength and is excellent in lubricity, so that it is suitable as a vapor deposition layer constituting a hard coating layer from the viewpoint of preventing occurrence of chipping. And Si complex nitride [Cr _1-X Si _X ] N (wherein X is 0.02 to 0.1 in atomic ratio), the high temperature hardness is inferior. Under severe cutting conditions such as heavy cutting, it cannot be said to have sufficient wear resistance.

(C) above (a) Si content is 2 to 10 atomic% and is excellent high-temperature hardness of, lubricity and having a predetermined high-temperature strength _{[Cr 1-X Si X]} N ( provided that, X atomic ratio Has a high temperature strength and lubricity superior to those of the thin layer A, although the high-temperature hardness is lower than that of the thin layer A. When a chromium nitride (CrN) layer (hereinafter referred to as a thin layer B) is alternately laminated in a state where each layer has an average layer thickness of 0.01 to 0.3 μm, a hard coating layer having this alternately laminated structure Has the excellent high-temperature hardness and lubricity of the thin layer A, and combines the excellent high-temperature strength of the thin layer B with the superior lubricity.
The research results shown in (a) to (c) above were obtained.

This invention was made based on the above research results,
In the surface-coated cubic boron nitride-based ultra-high pressure sintered material cutting tool in which a hard coating layer is vapor-deposited on the surface of the insert made of ultra-high pressure sintered material containing 30 to 95% by mass of boron nitride,
(A) The hard coating layer consists of a lower layer having an average layer thickness of 1.5 to 6 μm and an upper layer having an average layer thickness of 0.3 to 3 μm,
(B) a lower layer of the hard coating layer was vapor deposited, the composition _{formula: [Cr 1-X Si X} ] N ( provided that, X is atomic ratio shows 0.02) satisfies A composite nitride layer of Cr and Si,
(C) The upper layer of the hard coating layer is formed by vapor deposition on the surface of the lower layer, and each layer has 2 to 10 layers each of a thin layer A and a thin layer B each having an average layer thickness of 0.01 to 0.3 μm. Having an alternate laminated structure of
The thin layer A is a composite nitride layer of Cr and Si that satisfies the composition formula: [Cr _1-X Si _X ] N (wherein X represents an atomic ratio of 0.02 to 0.1),
The thin layer B is a chromium nitride (CrN) layer,
A surface-coated cubic boron nitride-based ultra-high pressure sintered material cutting tool that exhibits excellent chipping resistance in heavy cutting of high-hardness steel by vapor deposition of a hard coating layer made of cBN-based sintering tool).

Next, the reason why the hard coating layer of the coated cBN-based sintered tool according to the present invention is numerically limited as described above will be described.
(A) Boron nitride (cBN) content When the boron nitride (cBN) content in the insert made of ultra high pressure sintered material is less than 30% by mass, the hardness of the cBN sintered material is reduced, and ultra high pressure sintering is performed. When performing heavy cutting of high-hardness steel using an insert made of binder material, it becomes impossible to provide the minimum required hardness and wear resistance is reduced, while boron nitride (cBN) content Is more than 95% by mass, it becomes difficult to ensure the adhesion strength between the cBN sintered material and the hard coating layer, and as a result, the hard coating layer is easily peeled off. Therefore, in this invention, the boron nitride (cBN) content Was determined to be 30 to 95% by mass.

Cr component in (b) a hard coating layer Cr and Si composite nitride layer of constituting the lower layer _{[Cr 1-X Si X]} N contributes to the improvement of retention and lubricity of predetermined high temperature strength, addition, Si Since the component contributes to the improvement of the high temperature hardness, the Cr and Si composite nitride layer [Cr _1-X Si _X ] N (where X is an atomic ratio, 0) constituting the lower layer of the hard coating layer. .02 to 0.1) is a layer having excellent high-temperature hardness and lubricity as well as predetermined high-temperature strength, and ensures the wear resistance of the cutting edge during heavy cutting of high-hardness steel. Basically play a role to do. However, when the Si content ratio X exceeds 10 atomic%, the high temperature hardness of the lower layer is increased and the wear resistance is improved, but the high temperature strength and lubricity are lowered by the decrease of the Cr content ratio. Therefore, chipping is likely to occur. On the other hand, when the Si content ratio X is less than 2 atomic%, the high-temperature hardness decreases, so that the wear of the cutting edge during heavy cutting of high-hardness steel progresses. The value of the Si content ratio X was determined to be 0.02 to 0.1 because it rapidly progressed and the wear resistance could not be sufficiently secured.
In addition, if the average thickness of the lower layer is less than 1.5 μm, the predetermined high-temperature strength possessed by itself and excellent high-temperature hardness and lubricity cannot be imparted to the hard coating layer over a long period of time, resulting in a short tool life. On the other hand, if the average layer thickness exceeds 6 μm, chipping is likely to occur. Therefore, the average layer thickness was set to 1.5 to 6 μm.
Note that a thin layer of titanium nitride (TiN) can be interposed between the base and the lower layer in order to ensure sufficient adhesion between the insert base made of the ultra-high pressure sintered material and the lower layer. The thin layer of TiN has little effect of improving the adhesion when the layer thickness is less than 0.01 μm, and on the other hand, even if the layer thickness exceeds 0.5 μm, further improvement in adhesion cannot be expected. The thickness of the TiN layer interposed between the substrate and the lower layer is preferably 0.01 μm or more and 0.5 μm or less.

(C) Upper layer thin layer A
Composite nitride layer of Cr and Si constituting a thin layer A of the top layer _{[Cr 1-X Si X]} N ( provided that, X is atomic ratio, shows a 0.02 to 0.1), the lower layer The layer has substantially the same high-temperature hardness and lubricity as well as a predetermined high-temperature strength, and has the effect of ensuring the wear resistance of the cutting edge portion during heavy cutting of high-hardness steel.

(D) Upper layer thin layer B
The thin layer B made of a chromium nitride (CrN) layer compensates for the characteristics (high temperature strength and lubricity) that the thin layer A lacks in the upper layer made up of the alternately laminated structure of the thin layer A and the thin layer B. This is the main purpose.
As already described, the upper layer thin layer A is a layer having excellent high-temperature hardness and lubricity, but under severe cutting conditions such as heavy cutting of high-hardness steel, its high-temperature strength and lubricity are low. Since it is not sufficient, chipping is likely to occur.
Therefore, as a thin layer B of the upper layer, a chromium nitride (CrN) layer having excellent high-temperature strength as compared with the thin layer A and further excellent in lubricity is alternately arranged with the thin layer A, and alternately laminated. By constructing the structure, it compensates for the lack of high-temperature strength and lubricity of the adjacent thin layer A, so that the excellent high-temperature hardness and lubricity of the thin layer A, the excellent high-temperature strength of the thin layer B, An upper layer having better lubricity is formed.

(E) Upper layer thin layer A and thin layer B one layer average layer thickness, upper layer average layer thickness Upper layer thin layer A and thin layer B, each layer average layer thickness is less than 0.01 μm, respectively The excellent properties of the thin layer cannot be exhibited, and as a result, it is impossible to ensure excellent high-temperature hardness, high-temperature strength, and even better lubricity in the upper layer. If the average layer thickness exceeds 0.3 μm, the disadvantages of each thin layer, that is, if it is thin layer A, insufficient high-temperature strength and lubricity, and if thin layer B, insufficient high-temperature hardness is localized in the layer. Therefore, the chipping occurs and the wear progresses rapidly. Therefore, the average layer thickness of each layer was determined to be 0.01 to 0.3 μm.
That is, the thin layer B is provided in order to further improve the high temperature strength of the thin layer A, but the average layer thickness of each of the thin layer A and the thin layer B is 0.01 to 0.3 μm. If it is within the range, the upper layer composed of the alternately laminated structure of the thin layer A and the thin layer B is as if it is a single layer having more excellent lubricity in addition to excellent high temperature hardness and high temperature strength. However, if the average layer thickness of each of the thin layer A and the thin layer B exceeds 0.3 μm, the high temperature strength of the thin layer A is insufficient, the lubricity is insufficient, or the high temperature hardness of the thin layer B is insufficient. Appear locally in the layer, and the upper layer as a whole cannot exhibit good characteristics as a single layer, so that the average layer thickness of each of the thin layer A and the thin layer B is 0.01. It was set to -0.3 micrometer.
Excellent high-temperature hardness and high-temperature strength by forming an upper layer consisting of an alternately laminated structure in which the average layer thickness of the thin layers A and B is in the range of 0.01 to 0.3 μm on the lower layer surface. In addition, a hard coating layer having better lubricity can be obtained.
Further, when the average layer thickness of the upper layer (that is, the total layer thickness of the thin layers A and B constituting the alternate laminated structure) is less than 0.3 μm, heavy cutting of high hardness steel is performed. Sufficient high-temperature hardness, lubricity and high-temperature strength required for processing cannot be imparted to the upper layer, resulting in a short tool life. On the other hand, if the average layer thickness exceeds 3 μm, chipping occurs. Since it becomes easy, the average layer thickness was determined to be 0.3 to 3 μm.

In the coated cBN-based sintered tool of the present invention, a slightly different interference color may be generated depending on the thickness of the coating layer on the outermost surface, and the tool appearance may be uneven. In such a case, unevenness of the appearance of the tool can be prevented by thickly depositing a titanium nitride (TiN) layer or a composite nitride of Cr and Si (CrSiN) layer. At that time, if the average layer thickness of the TiN layer or CrSiN layer is less than 0.2 μm, uneven appearance cannot be prevented, and if the average layer thickness is up to 2 μm, uneven appearance can be sufficiently prevented. The average layer thickness of the titanium (TiN) layer or the composite nitride of Cr and Si (CrSiN) layer may be 0.2-2 μm.
In addition, the surface roughness of the coated cBN-based sintered tool base of the present invention is desirably 0.05 to 1.0 in terms of Ra. If the surface roughness Ra is 0.05 or more, an improvement in adhesion strength between the substrate and the hard coating layer due to the anchor effect can be expected. On the other hand, if Ra exceeds 1.0, the finished surface of the work material This is because the accuracy is adversely affected.

  In the coated cBN-based sintered tool of the present invention, the hard coating layer is composed of an upper layer and a lower layer, and the upper layer of the hard coating layer has an excellent laminated structure of thin layers A and thin layers B. Because it has not only high-temperature strength but also excellent lubricity, even in heavy cutting of high-hardness steel with high heat generation, there is no chipping in the hard coating layer, and excellent wear resistance is provided for a long time. It is demonstrated over the long term.

  Next, the coated cBN-based sintered tool of the present invention will be specifically described with reference to examples.

As raw material powders, cubic boron nitride (cBN) powder, titanium carbide (TiC) powder, titanium nitride (TiN) powder, titanium carbonitride (TiCN) powder each having an average particle size in the range of 0.5 to 4 μm , Tungsten carbide (WC) powder, Al powder, Co powder, Ti ₃ Al powder that is an intermetallic compound powder of Ti and Al, TiAl powder, and TiAl ₃ powder, and a composite metal nitride having a composition formula: Ti ₂ AlN Prepare powder, TiB ₂ powder, aluminum nitride (AlN) powder, aluminum boride (AlB ₂ ) powder, aluminum oxide (Al ₂ O ₃ ) powder, and blend these raw material powders into the composition shown in Table 1, After wet mixing with a ball mill for 80 hours and drying, a green compact having a diameter of 50 mm × thickness of 1.5 mm was preliminarily formed at a pressure of 120 MPa. Then, the green compact is sintered in a vacuum atmosphere at a pressure of 1 Pa at a predetermined temperature within a range of 900 to 1300 ° C. for 60 minutes to obtain a presintered body for a cutting blade piece. This pre-sintered body is overlaid with a separately prepared WC-based cemented carbide support piece having dimensions of Co: 8% by mass, WC: remaining composition, and diameter: 50 mm × thickness: 2 mm. In an ordinary ultra high pressure sintering apparatus, the normal pressure is 5 GPa, the temperature is 1200 ° C. within a predetermined temperature range of 1200 to 1400 ° C., and the holding time is 0.8 hours. After sintering, the upper and lower surfaces are polished with a diamond grindstone and divided into a regular triangle shape with a side of 3 mm by a wire electric discharge machine, and Co: 5% by mass, TaC: 5% by mass, WC: remaining composition And CIS standard SNGA12041 shape (thickness: 4 The brazing part (corner part) of the WC-based cemented carbide chip main body having a 76 mm × one side length: 12.7 mm regular triangle) is 30% by mass, Cu: 30%, Zn: 28%, Ni: After brazing using a brazing material of Ag alloy having a composition of 2%, Ag: remaining, and processing the outer periphery to a predetermined dimension, the cutting edge is subjected to a honing process of width: 0.15 mm, angle: 25 ° Further, the tool bases A to H having the chip shape of ISO standard SNGA120212 were manufactured by finishing polishing.

(A) Next, each of the tool bases A to H is ultrasonically cleaned in acetone and dried, and then in a radial direction from the central axis on the rotary table in the arc ion plating apparatus shown in FIG. Are mounted along the outer periphery at a predetermined distance, and the upper layer thin layer B forming Cr is used as the cathode electrode (evaporation source) on one side and the cathode electrode (evaporation source) on the other side. The upper layer thin layer A and the lower layer forming Cr—Si alloy having a component composition corresponding to the target composition shown in FIG.
(B) First, while the inside of the apparatus is evacuated and kept at a vacuum of 0.1 Pa or less, the inside of the apparatus is heated to 500 ° C. with a heater, and then Ar gas is introduced to create an atmosphere of 0.7 Pa. A DC bias voltage of −200 V is applied to the tool base that rotates while rotating on the table, and the tool base surface is bombarded with argon ions.
(C) Nitrogen gas is introduced as a reaction gas into the apparatus to form a reaction atmosphere of 3 Pa, a DC bias voltage of −100 V is applied to the tool base rotating while rotating on the rotary table, and the thin layer A current of 100 A is passed between the A and Cr-Si alloy for forming the lower layer and the anode electrode to generate an arc discharge, so that the target composition and target layer thickness shown in Table 2 ( (Cr, Si) N layer is deposited as a lower layer of the hard coating layer,
(D) Next, the flow rate of nitrogen gas as a reaction gas introduced into the apparatus is adjusted to obtain a reaction atmosphere of 2 Pa, and within a range of −10 to −100 V on the tool base that rotates while rotating on the rotary table. In a state where a predetermined DC bias voltage is applied, a predetermined current in the range of 50 to 200 A is passed between the cathode electrode and the anode electrode of the thin layer B forming Cr to generate arc discharge, A thin layer B having a predetermined layer thickness is formed on the surface of the tool base, and after the thin layer B is formed, the arc discharge is stopped. Instead, the cathode and anode of the thin layer A and Cr-Si alloy for forming the lower layer Similarly, a predetermined current in the range of 50 to 200 A is passed between the electrodes to generate arc discharge to form a thin layer A having a predetermined thickness. Then, the arc discharge is stopped and the thin layer B forming Cr is again formed. With cathode electrode The formation of the thin layer B by arc discharge between the node electrodes and the formation of the thin layer A by arc discharge between the cathode electrode and the anode electrode of the Cr-Si alloy for forming the thin layer A and the lower layer are alternately repeated. On the surface of the tool base, the total layer thickness shown in Table 2 is also formed on the upper layer composed of alternating layers of the thin layer A and the thin layer B having the target composition shown in Table 2 along the layer thickness direction. The coated cBN-based sintered tools 1 to 8 of the present invention were manufactured by vapor deposition with (average layer thickness).

For comparison purposes, each of the above tool bases A to H is ultrasonically cleaned in acetone and dried, and then charged into the ordinary arc ion plating apparatus shown in FIG. As the (evaporation source), a Cr—Si alloy having a component composition corresponding to the target composition shown in Table 3 was mounted, and first, the heater was evacuated and kept at a vacuum of 0.1 Pa or less. After heating the inside of the apparatus to 500 ° C., Ar gas is introduced to make an atmosphere of 0.7 Pa, and a DC bias voltage of −200 V is applied to the tool base that rotates while rotating on the table. The tool substrate surface is bombarded with argon ions, and then nitrogen gas is introduced into the apparatus as a reaction gas to form a reaction atmosphere of 3 Pa, and a via applied to the tool substrate. Lower the voltage to -100 V, the cause arcing between the cathode electrode and the anode electrode of Cr-Si alloy, on each surface of the tool substrate A~H with a target composition and are shown in Table 3 Conventionally coated cBN-based sintered tools 1 to 8 were respectively produced by vapor-depositing a hard coating layer composed of a target layer thickness (Cr, Si) N layer.

Next, the above-mentioned various coated cBN-based sintered tools are screwed to the tip of the tool steel tool with a fixing jig, and the present coated cBN-based sintered tools 1 to 8 and the conventional coated For cBN-based sintered tools 1-8 ,
Work material: JIS / SCM415 (hardness: HRC60) round bar,
Cutting speed: 160 m / min. ,
Cutting depth: 0.42mm,
Feed: 0.17 mm / rev. ,
Cutting time: 25 minutes,
Dry continuous high-cutting cutting test of alloy tool steel under the above conditions (referred to as cutting condition A) (normal cutting is 0.2 mm),
Work material: JIS / SUJ2 (Hardness: HRC61) lengthwise equidistant four round grooved round bars,
Cutting speed: 155 m / min. ,
Cutting depth: 0.42mm,
Feed: 0.14 mm / rev. ,
Cutting time: 15 minutes,
Dry interrupted high cutting test of bearing steel under the conditions (cutting condition B) (normal cutting 0.2 mm),
Work material: JIS · SKD11 hardened material (hardness: HRC63) round bar,
Cutting speed: 160 m / min. ,
Cutting depth: 0.18mm,
Feed: 0.38 mm / rev. ,
Cutting time: 12 minutes,
Dry continuous high-feed cutting test of die steel under the conditions (cutting condition C) (normal feed is 0.15 mm / rev.)
In each cutting test, the flank wear width of the cutting edge was measured. The measurement results are shown in Table 4.

As a result, the composition of the hard coating layers of the present coated cBN-based sintered tools 1 to 8 and the conventional coated cBN-based sintered tools 1 to 8 are analyzed by energy dispersive X-ray analysis using a transmission electron microscope. As a result of measurement, each showed substantially the same composition as the target composition.

  Moreover, when the cross-sectional measurement was carried out using the transmission electron microscope, the average layer thickness of the structure layer of said hard coating layer showed all the average value (average value of five places) substantially the same as target layer thickness. .

From the results shown in Tables 2 to 4, the coated cBN-based sintered tool of the present invention has a hard coating layer, each of a thin layer A and a thin layer B each having an average layer thickness of 0.01 to 0.3 μm. It consists of an upper layer having an average layer thickness (total layer thickness) of 0.3 to 3 μm having an alternating laminated structure of 2 to 10 layers, and a lower layer having an average layer thickness of 1.5 to 6 μm, and the upper layer is excellent High temperature strength and lubricity, and the lower layer has a predetermined high temperature strength and excellent high temperature hardness and lubricity, so high heat of high hardness steel such as hardened alloy tool steel and bearing steel. The conventional coated cBN-based sintered tool in which the hard coating layer is composed of a single (Cr, Si) N layer, while exhibiting excellent wear resistance without occurrence of chipping even in heavy cutting with generation, In particular, chipping occurs due to insufficient high-temperature strength and lubricity of the hard coating layer. It is clear that lead to comparatively short time service life.

  As described above, the coated cBN-based sintered tool of the present invention is excellent not only for cutting under normal cutting conditions such as various steels and cast iron, but particularly for heavy cutting with high heat generation of high hardness steel. It exhibits excellent chipping resistance and exhibits excellent wear resistance and cutting performance over a long period of time. Therefore, it is possible to improve the performance of cutting equipment, reduce the labor and energy of cutting, and reduce costs. It can respond satisfactorily.

The arc ion plating apparatus used for forming the hard coating layer which comprises the coated cBN group sintered tool of this invention is shown, (a) is a schematic plan view, (b) is a schematic front view. It is a schematic explanatory drawing of a normal arc ion plating apparatus.

Claims (1)

In the surface-coated cubic boron nitride-based ultra-high pressure sintered material cutting tool in which a hard coating layer is vapor-deposited on the surface of the insert made of ultra-high pressure sintered material containing 30 to 95% by mass of boron nitride,
(A) The hard coating layer consists of a lower layer having an average layer thickness of 1.5 to 6 μm and an upper layer having an average layer thickness of 0.3 to 3 μm,
(B) a lower layer of the hard coating layer was vapor deposited, the composition _{formula: [Cr 1-X Si X} ] N ( provided that, X is atomic ratio shows 0.02) satisfies A composite nitride layer of Cr and Si,
(C) The upper layer of the hard coating layer is formed by vapor deposition on the surface of the lower layer, and each layer has 2 to 10 layers each of a thin layer A and a thin layer B each having an average layer thickness of 0.01 to 0.3 μm. Having an alternate laminated structure of
The thin layer A is a composite nitride layer of Cr and Si that satisfies the composition formula: [Cr _1-X Si _X ] N (wherein X represents an atomic ratio of 0.02 to 0.1),
The thin layer B is a chromium nitride (CrN) layer,
A surface-coated cubic boron nitride-based ultrahigh pressure sintered material cutting tool that exhibits excellent chipping resistance in heavy cutting of high-hardness steel with a hard coating layer made of