JP4883473B2 - 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

  This invention has a hard coating layer with excellent high-temperature hardness and a further excellent high-temperature strength, and therefore, such as a hardened material of alloy tool steel or bearing steel that generates high heat and has a high load on the cutting edge. A hard coating layer is formed on the surface of a cutting tool base made of cubic boron nitride based ultra-high pressure sintered material that exhibits excellent chipping resistance even when used in heavy cutting of high hardness steel. The present invention relates to a cutting tool made of a surface-coated cubic boron nitride-based ultra-high pressure sintered material (hereinafter referred to as a coated cBN-based sintered tool).

  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). There are known coated cBN-based sintered tools formed by vapor-depositing a surface coating layer such as a layer, a composite nitride layer of Ti, Si and B (boron), and a composite nitride layer of Ti and Al. Is also used for cutting various steels and cast irons.

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, between a cathode electrode (evaporation source) made of metal Ti, a Ti—Al alloy or a Ti—Si—B alloy each having a predetermined composition and an anode electrode while being heated to 500 ° C., for example, A 90 A current was applied to generate an arc discharge, and at the same time, nitrogen gas was introduced into the apparatus as a reaction gas to form a reaction atmosphere of 2 Pa, for example, while a bias voltage of, for example, −100 V was applied to the tool base. Under certain conditions, a layer having a desired component composition such as a TiN layer, a (Ti, Al) N layer, or a (Ti, Si, B) N layer is deposited on the surface of the tool base. It is also known to be.
JP-A-8-119774 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. In addition, when used under heavy cutting conditions where a heavy load is applied to the cutting edge, chipping (small chipping) is likely to occur at the cutting edge, especially due to the lack of high-temperature strength 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) a composite nitride of Ti and Si that constitutes the hard coating layer _{([Ti 1-X Si X} ] N) layer, the value of the content X (atomic ratio) of Si, 0.02 to 0.1 It has excellent high-temperature strength and high-temperature hardness within the range, and it has the wear resistance required under normal cutting conditions, but it is more severe cutting conditions, that is, it generates high heat. At the same time, in heavy cutting of high hardness steel with a heavy load on the cutting edge, high temperature strength is not satisfactory and chipping is likely to occur.

(B) On the other hand, the titanium nitride (TiN) layer is suitable as a vapor deposition layer constituting a hard coating layer in terms of prevention of chipping because of its very high temperature strength. composite nitride _{[Ti 1-X Si X]} N ( provided that, X is 0.02 to 0.1 in atomic ratio) to poor high-temperature hardness as compared with the layer, in particular, heavy cutting machining hardened steel However, it cannot be said to have sufficient wear resistance under severe cutting conditions.

(C) the Si content of the (a) has excellent high-temperature hardness is 2-10 _{atomic% [Ti 1-X Si X} ] N ( where the X atomic ratio from 0.02 to 0.1 ) Layer (hereinafter referred to as thin layer A) and a titanium nitride (TiN) layer (hereinafter referred to as “thin layer A”) having a high temperature strength superior to that of the thin layer A, although the high temperature hardness is lower than that of the thin layer A. When the thin layer B is alternately laminated in a state where each layer has an average layer thickness of 0.01 to 0.3 μm, the hard coating layer of this alternately laminated structure has the excellent high temperature of the thin layer A. It must have both hardness and high temperature strength, and it must have both the high temperature strength of the thin layer B and excellent strength.
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) The lower layer of the hard coating layer is vapor-deposited and satisfies the composition formula: [Ti _1-X Si _X ] N (where X is an atomic ratio and indicates 0.02 to 0.1). A composite nitride layer of Ti 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 of the thin layer A and the thin layer B each having an average layer thickness of 0.01 to 0.3 μm alternately. It has an alternating laminated structure in which 10 layers are laminated,
The thin layer A is composed of a composite nitride layer of Ti and Si that satisfies the composition formula: [Ti _1-X Si _X ] N (where X represents an atomic ratio of 0.02 to 0.1),
The thin layer B includes a titanium nitride (TiN) 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.

(B) Hard coating layer constituting lower layer Ti component in Ti and Si composite nitride layer [Ti _1-X Si _X ] N contributes to improvement of high temperature strength, and Si component improves improvement of high temperature hardness from contributing to, Ti and Si composite nitride layer of constituting the lower layer of the hard coating layer _{[Ti 1-X Si X]} N ( provided that, X is atomic ratio, a 0.02 to 0.1 Is a layer having a predetermined high-temperature hardness and high-temperature strength, and basically plays a role of ensuring the wear resistance of the cutting edge during heavy cutting of high-hardness steel. 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 rapidly decreases due to the decrease of the Ti 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 progress of wear of the cutting edge portion during heavy cutting of high-hardness steel is rapid. The value of the Si content ratio X was determined to be 0.02 to 0.1 because the wear resistance could not be sufficiently ensured.
Moreover, if the average layer thickness of the lower layer is less than 1.5 μm, the excellent high-temperature hardness and high-temperature strength cannot be imparted to the hard coating layer over a long period of time, resulting in a short tool life, while the average layer When the thickness exceeds 6 μm, chipping is likely to occur. Therefore, the average layer thickness is 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 Ti and Si that constitutes the thin layer A of the top layer _{[Ti 1-X Si X]} N ( provided that, X is atomic ratio, shows a 0.02 to 0.1), the lower layer And has a predetermined high-temperature hardness and high-temperature strength, and has an 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 titanium nitride (TiN) layer is insufficient for the thin layer A in an upper layer having an alternately laminated structure in which the thin layer A and the thin layer B are alternately laminated by 2 to 10 layers. The main purpose is to supplement the properties (high temperature strength).
As already described, the thin layer A of the upper layer is a layer having excellent high temperature hardness and high temperature strength. However, under severe cutting conditions such as heavy cutting of high hardness steel, the high temperature strength is not sufficient. Since it cannot be said, chipping is likely to occur.
Therefore, as the thin layer B of the upper layer, titanium nitride (TiN) layers, which are superior to the thin layer A in terms of high-temperature strength, are alternately arranged with the thin layers A, thereby forming an alternate laminated structure. Thus, an upper layer having both the excellent high temperature hardness of the thin layer A and the excellent high temperature strength of the thin layer B 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 characteristics of the thin layer cannot be exhibited, and as a result, it is impossible to ensure excellent high-temperature hardness and higher-temperature strength in the upper layer, and the average thickness of each layer is 0. If the thickness exceeds 3 μm, the disadvantages of each thin layer, that is, if the thin layer A is insufficient in high-temperature strength, if it is thin layer B, the lack of high-temperature hardness will appear locally in the layer. Since chipping occurs and wear proceeds rapidly, 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 an alternate laminated structure in which the thin layer A and the thin layer B are alternately laminated by 2 to 10 layers has an excellent high temperature strength in addition to excellent high temperature hardness. It acts as if it is a single layer. However, if the average layer thickness of each of the thin layers A and B exceeds 0.3 μm, the high temperature strength of the thin layer A is insufficient or the high temperature of the thin layer B is high. Insufficient hardness appears locally in the layer, and the upper layer as a whole cannot exhibit good characteristics as a single layer, so the average layer thickness of each of the thin layer A and the thin layer B is increased. It was determined to be 0.01 to 0.3 μm.
By forming an upper layer composed of an alternately laminated structure in which two to 10 layers each having an average layer thickness of the thin layer A and the thin layer B within a range of 0.01 to 0.3 μm are formed on the surface of the lower layer, excellent Thus, a hard coating layer having both high-temperature hardness and superior high-temperature strength 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. Because sufficient high temperature hardness and high temperature strength required for processing cannot be imparted to the upper layer, causing a short tool life, while chipping tends to occur when the average layer thickness exceeds 3 μm. 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 Ti / Si composite nitride (TiSiN) layer. At that time, if the average layer thickness of the TiN layer or TiSiN 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 Ti and Si (TiSiN) layer may be 0.2 to 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 this invention, the hard coating layer is composed of an upper layer and a lower layer, and the upper layer of the hard coating layer is formed by alternately laminating the thin layer A and the thin layer B 2 to 10 layers alternately. It has not only excellent high-temperature hardness due to its structure, but also excellent high-temperature strength, so even in heavy cutting of high-hardness steel with high heat generation, the hard coating layer is excellent without chipping. It exhibits high wear resistance over a long period of time.

  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 In the brazed part (corner part) of the WC-based cemented carbide chip body having a 76 mm × one side length: 12.7 mm regular triangle), 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, by performing finish polishing, tool bases A to G each having a chip shape of ISO standard SNGA12041 were manufactured.

(A) Next, each of the tool bases A to G is ultrasonically cleaned in acetone and dried, and then in the 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 away from each other, and as the cathode electrode (evaporation source) on one side, Ti for forming the upper layer B is used as the cathode electrode (evaporation source) on the other side. The upper layer thin layer A having a component composition corresponding to the target composition shown in FIG. 2 and the lower layer forming Ti—Si alloy are opposed to each other with the rotary table interposed therebetween,
(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 caused to flow between A and the Ti-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 ( Ti, 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 within a range of 50 to 200 A is passed between the cathode and anode electrodes of the Ti for forming the thin layer B 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, a cathode electrode and an anode of the Ti-Si alloy for forming the thin layer A and the lower layer Similarly, a predetermined current in the range of 50 to 200 A is passed between the electrodes to generate an arc discharge to form a thin layer A having a predetermined layer thickness. Then, the arc discharge is stopped and the Ti for forming the thin layer B 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 Ti-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 7 of the present invention were manufactured by vapor deposition with (average layer thickness).

For comparison purposes, each of the tool bases A to G described above is ultrasonically cleaned in acetone and dried, and then charged into a normal arc ion plating apparatus shown in FIG. As the (evaporation source), a Ti—Si alloy having a component composition corresponding to the target composition shown in Table 3 was attached, 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 Ti-Si alloy, on each surface of the tool substrate A~G with a target composition and are shown in Table 3 Conventionally coated cBN-based sintered tools 1 to 7 were manufactured by vapor-depositing a hard coating layer composed of a (Ti, Si) N layer having a target layer thickness.

Next, according to the present invention, the coated cBN-based sintered tools 1 to 7 and the conventional coated cBN-based sintered tools are screwed to the tip of the tool steel tool with a fixing jig. For cBN based sintered tools 1-7 ,
Work material: JIS / SCM415 quenching material (hardness: HRC60) round bar,
Cutting speed: 180 m / min. ,
Cutting depth: 0.4mm,
Feed: 0.16 mm / rev. ,
Cutting time: 20 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 quenching material (hardness: HRC61), 4 longitudinally spaced round bars with equal intervals in the length direction,
Cutting speed: 140 m / min. ,
Cutting depth: 0.45 mm,
Feed: 0.12 mm / rev. ,
Cutting time: 20 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: 150 m / min. ,
Cutting depth: 0.2mm,
Feed: 0.35 mm / rev. ,
Cutting time: 15 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 7 and the conventional coated cBN-based sintered tools 1 to 9 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 Table 2-4, the present invention coated cBN-based sintered tool are both hard coating layer, and a further thin layer A of 0.01~0.3μm average layer thickness is respectively thin layer B the average layer thickness (total layer thickness) 0.3 to 3 m upper layer with alternating multilayer structure obtained by stacking the 2-10 layers alternately, consists of a lower layer having an average layer thickness of 1.5～6Myuemu, the Since the upper layer has excellent high-temperature strength and predetermined high-temperature hardness, and the lower layer has predetermined high-temperature strength and high-temperature hardness, high-hardness steel such as alloy tool steel and hardened material of bearing steel Even with heavy cutting with high heat generation, excellent wear resistance is exhibited without occurrence of chipping. On the other hand, the conventional coated cBN-based sintering in which the hard coating layer is composed of a single (Ti, Si) N layer The tool is relatively chipped because of the high temperature strength of the hard coating layer. Time it is clear that through use 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) The lower layer of the hard coating layer is vapor-deposited and satisfies the composition formula: [Ti _1-X Si _X ] N (where X is an atomic ratio and indicates 0.02 to 0.1). A composite nitride layer of Ti 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 of the thin layer A and the thin layer B each having an average layer thickness of 0.01 to 0.3 μm alternately. It has an alternating laminated structure in which 10 layers are laminated,
The thin layer A is composed of a composite nitride layer of Ti and Si that satisfies the composition formula: [Ti _1-X Si _X ] N (where X represents an atomic ratio of 0.02 to 0.1),
The thin layer B includes a titanium nitride (TiN) 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