JP2015188995A - Surface-coated cutting tool excellent in abnormal damage resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface-coated cutting tool which exhibits superior abnormal damage resistance in high-speed intermittent cutting.SOLUTION: In a surface-coated cutting tool in which a hard coating layer comprising a lower layer and an upper layer is formed by coating, (a) the lower layer is made of a Ti compound layer having a layer thickness of 3 to 15 μm and has one carbonitride layer, (b) the upper layer is made of a chemically deposited α type aluminum oxide layer having a layer thickness of 2 to 20 μm, (c) in a Ti carbonitride layer (hereinafter called as the thickest Ti carbonitride layer ) constituting the lower layer and having a layer thickness of 1.5 μm or more being the thickest layer among the lower layer, a crack origins layer in which fine vacancies having an average diameter of 25 to 200 nm exist with an average density of 3 or more and less than 20 pieces/μmis formed in a region of 1/3 to 2/3 of layer thickness of the thickest Ti carbonitride layer, with a thickness from 0.5 μm to a thickness of 1/3 of the thickest Ti thickest carbonitride layer, and (d) a stress relaxation layer in which cracks exist with an average density of 0.2 or more and less than 2 pieces/μm is formed from the crack origins layer to the lower layer of the base body side.

Description

  This invention has high heat generation, and in high-speed intermittent cutting such as sintered alloys in which a high load acts on the cutting blade, the hard coating layer exhibits excellent abnormal damage resistance, and excellent cutting performance over a long period of use. The present invention relates to a surface-coated cutting tool to be exhibited (hereinafter referred to as a coated tool).

  In general, for coated tools, throwaway inserts that can be used detachably attached to the tip of a cutting tool for turning and planing of various steel and cast iron, drilling of the work material, etc. Drills and miniature drills, and solid type end mills used for chamfering, grooving and shouldering of the work material, etc. A slow-away end mill tool that performs cutting work in the same manner as an end mill is known.

In order to prevent the occurrence of abnormal damage such as chipping, chipping, and peeling under high-speed and high-efficiency conditions such as interrupted cutting that involves high heat generation and a large mechanical / impact load on the cutting edge, various proposals have been made in the past. Has been made.
For example, as shown in Patent Document 1, in the coated tool, the first coating layer on the surface of the tool base is a layer formed by chemical vapor deposition in which tensile stress remains, cracks are introduced, and the average interval between the cracks is 10 to 100 μm, and the average crack length in the layer thickness direction is a fine crack having a layer thickness of −2 μm to a layer thickness of +5 μm, and is a group 4A metal carbide, nitride, carbonitride, carbonate, It consists of at least one single layer or multiple layers selected from carbonitride, boronitride, borocarbonitride, and alumina, and the second coating layer provided on the first coating layer has a periodicity. It consists of a carbide, nitride, carbonitride, carbonate, carbonitride, and at least one single layer or multiple layers selected from alumina, titanium aluminum nitride, titanium oxynitride, Physical vapor deposition with residual compressive stress A coated tool composed of a coated layer has been proposed. According to this coated tool, excellent adhesion strength to the tool substrate and a good balance of residual stress in the entire coating layer were obtained. It is said that it has wearability and at the same time can greatly improve fracture resistance.

  Further, as shown in Patent Document 2, on the surface of a tool metal base, a Ti compound layer having a granular crystal structure, a titanium carbonitride layer having a vertically long crystal structure, and an α type and / or a κ type having a granular crystal structure. In a coated tool coated with an aluminum oxide layer, the structure of the titanium carbonitride layer having a vertically grown crystal structure is observed along the side surface where the aluminum oxide layer is present by a scanning electron microscope with a right-angle polished cross section. There has been proposed a coated tool in which a fine pore dispersion zone is formed over a depth within the range of the average layer thickness of the titanium carbonitride layer having the vertically elongated crystal structure × 0.5) μm. The pore zone sufficiently absorbs the difference in thermal expansion between the titanium carbonitride layer and the aluminum oxide layer in the vertically grown crystal structure, so that no peeling occurs even under cutting conditions where heat generation is large. Has been.

Japanese Patent Laid-Open No. 5-177411 JP 2000-71108 A

In recent years, the performance of cutting devices has been remarkably improved. On the other hand, there is a strong demand for labor saving, energy saving, and cost reduction for cutting, and with this, cutting tends to be faster and more efficient.
And, when the above-mentioned conventional coated tool is used for normal cutting such as steel and cast iron, there is no particular problem. When subjected to high-speed and high-efficiency cutting such as intermittent cutting with mechanical and impact loads, abnormal damage such as chipping, chipping, and peeling is likely to occur, and this leads to tool life in a short time. There is a problem.

  That is, in the coated tool described in Patent Document 1, since the second coating layer is formed by physical vapor deposition, the adhesion between the first coating layer and the second coating layer cannot be said to be sufficient. In cutting, welding chipping or the like occurs, and delamination tends to occur.

  Further, the coated tool proposed in the above-mentioned Patent Document 2 absorbs the thermal expansion difference between the titanium carbonitride layer and the aluminum oxide layer of the vertically grown crystal structure by forming the microscopic void dispersion zone, so that the delamination Although the generation of cracks can be prevented, as shown in FIG. 2, the effect of suppressing the propagation of cracks in the layer thickness direction in intermittent machining is small, so the occurrence of abnormal damage due to the propagation of cracks is suppressed. I can't do it.

  From the above-mentioned viewpoint, the present inventor is a high-speed and high-efficiency cutting condition such as a sintered alloy, that is, a high-speed intermittent cutting condition that involves high heat generation and a large mechanical / impact load on the cutting edge. Even when it was conducted, intensive research was conducted to develop a coated tool in which the hard coating layer exhibits excellent abnormal damage resistance and also exhibits excellent wear resistance.

  As a result, at least one kind of Ti compound composed of a carbide, nitride, carbonitride, carbonate and carbonitride of Ti is formed on the surface of the substrate composed of a WC-based cemented carbide or a titanium carbonitride-based cermet. In a coated tool in which two or more kinds are vapor-deposited as a lower layer, and an aluminum oxide layer is vapor-deposited thereon as an upper layer, a part of the thickest Ti compound of the lower layers on the surface of the tool base is formed. When a crack starting layer having a high pore density is formed, and then the upper layer is deposited, wet blasting is applied from the upper layer surface to form a crack on the substrate side from the crack starting layer in the lower layer. It was found that the residual stress was relieved in the region.

  Furthermore, in the region where the residual stress in which cracks are formed from the crack starting layer to the substrate side (hereinafter referred to as “stress relaxation layer”), cracks generated in the upper layer due to a high load in high-speed intermittent cutting processing are observed. Even when propagation progresses to the lower layer side, the stress relaxation layer has an action to suppress further propagation progress of cracks, so that cracks are prevented from penetrating to the base, chipping, chipping, peeling, etc. It was found that the stress relaxation layer greatly contributes to the suppression of the occurrence of abnormal damage.

  That is, in a coated tool in which a lower layer and an upper layer are formed, a crack starting layer having a high hole density is formed in a part of the lower layer, and stress is generated between the crack starting layer and the substrate by wet blasting or the like. By forming a relaxation layer, high heat generation is generated, and in high-speed intermittent cutting such as sintered alloys where a large mechanical and impact load is applied to the cutting edge, it shows excellent abnormal damage resistance, and long-term It has been found that it exhibits excellent wear resistance over the use of.

This invention was made based on the above knowledge,
A surface-coated cutting tool in which a hard coating layer composed of a lower layer and an upper layer is coated on the surface of a substrate composed of a tungsten carbide-based cemented carbide or a titanium carbonitride-based cermet,
(A) The lower layer is composed of one or more Ti compounds of a Ti carbide layer, a nitride layer, a carbonitride layer, a carbonate layer, and a carbonitride layer having a total average layer thickness of 3 to 15 μm. And comprising at least one Ti carbonitride layer,
(B) The upper layer consists of an α-type aluminum oxide layer in a chemical vapor deposited state with an average layer thickness of 2 to 20 μm,
(C) Of the at least one Ti carbonitride layer constituting the lower layer, the Ti carbonitride layer having an average layer thickness of 1.5 μm or more is the thickest layer. of 1/3 from 2/3 of the area, the average diameter of fine pores of 25~200nm are three / [mu] m ² or more 20 / [mu] m crack origin layer present at less than ² average density, the from 0.5μm Formed with a thickness of 1/3 of the Ti carbonitride layer,
(D) In the lower layer on the substrate side from the crack starting layer, cracks exist at an average density of 0.2 / μm or more and less than 2 / μm per unit length when measured in a direction parallel to the substrate surface. A surface-coated cutting tool, wherein a stress relaxation layer is formed. "
It is characterized by.

  Hereinafter, the present invention will be described in detail.

Lower layer (Ti compound layer):
In the present invention, as the lower layer of the hard coating layer, one or more Ti compound layers of Ti carbide layer, nitride layer, carbonitride layer, carbonate layer and carbonitride layer are chemically vapor-deposited. And at least one of them is formed of a Ti carbonitride layer.
The lower Ti compound layer itself has high-temperature strength, and the presence of the Ti compound layer makes the hard coating layer have high-temperature strength, and it is strong against both the tool base and the upper layer made of aluminum oxide. It adheres and has the effect | action which contributes to the adhesive improvement with respect to the tool base | substrate of a hard coating layer.
When the total thickness of the lower layer is less than 3 μm, the above-mentioned effect cannot be fully exerted. On the other hand, when the total average thickness exceeds 20 μm, chipping, chipping, peeling, etc. are generated. Therefore, the total average layer thickness is preferably 3 to 20 μm.
In the present invention, at least one of the lower layers is formed of a Ti carbonitride layer. As will be described later, this has an average layer thickness of 1.5 μm or more. This is because it is necessary to form a crack starting layer having micropores with a predetermined diameter at a predetermined density in a partial region of the Ti carbonitride layer.

In the present invention, after forming the lower layer having the crack starting layer by chemical vapor deposition, an upper layer is formed thereon, and then post-treatment such as shot blasting is performed to move the crack starting layer from the crack starting layer to the substrate side. The residual stress of the lower layer is reduced by actively forming cracks and forming a stress relaxation layer.
In FIG. 1, a crack starting layer is formed in the lower layer (TiCN layer) formed on the substrate, and there are cracks positively introduced from the crack starting layer toward the substrate by post-treatment such as shot blasting. The longitudinal cross-sectional schematic diagram of the hard coating layer to perform is shown.

In the crack starting layer in the present invention, for example, when the lower layer is formed by chemical vapor deposition, the average thickness of the Ti carbonitride layer of the at least one Ti carbonitride layer constituting the lower layer is the thickest of the Ti carbonitride layer. By performing chemical vapor deposition shown below in the region of 1/3 to 2/3 of the layer thickness, it has a predetermined average diameter and a predetermined pore density, and from 0.5 μm to 1 of the Ti carbonitride layer. A crack starting layer having a thickness of / 3 can be formed.
Deposition conditions for forming the crack origin layer:
Reaction gas composition (volume%):
TiCl ₄ : 1 to 5%, N ₂ : 2 to 15%, CH ₃ CN: 6 to 15%, H ₂ : remainder Reaction atmosphere temperature: 860 to 900 ° C
Reaction atmosphere pressure: 20-66.6 kPa
By vapor deposition under the above-mentioned vapor deposition conditions, the average layer thickness has a predetermined average diameter and a predetermined pore density in a region of 1/3 to 2/3 of the thickness of the Ti carbonitride layer having the largest average thickness. A crack starting layer having a thickness of 1/3 of the Ti carbonitride layer can be formed from 0.5 μm.
The deposition of the Ti carbonitride layer in the region where the crack starting layer is not formed is, for example,
Reaction gas composition (volume%):
TiCl ₄ : 1 to 5%, N ₂ : 2 to 20%, CH ₃ CN: 0.5 to 4%, H ₂ : remainder Reaction atmosphere temperature: 860 to 1000 ° C
Reaction atmosphere pressure: 5 to 13.3 kPa
Vapor deposition is performed under the conditions.
In other words, in order to form the crack starting layer, it is necessary to increase the composition ratio of CH ₃ CN as a reaction gas component and to form a film under a condition in which the reaction atmosphere pressure is increased.

The position of the Ti carbonitride layer forming the crack starting layer is determined to be a region of 1/3 to 2/3 of the thickness of the Ti carbonitride layer having the largest average layer thickness. It is because the excessive fall of the intensity | strength of the existing Ti carbonitride layer is prevented.
Further, the thickness of the crack starting layer is determined from 0.5 μm to 1/3 of the Ti carbonitride layer. When the thickness is below 0.5 μm, a crack starting layer having a desired pore diameter is formed. When the thickness exceeds 1/3 of the Ti carbonitride layer, the strength of the Ti carbonitride layer decreases, causing in-layer fracture, resulting in an extremely long tool life. This is because it is reduced.

  In the crack starting layer formed as described above, if the average diameter of the formed micropores is less than 25 nm, a desired crack is formed from the crack starting layer toward the substrate even if post-treatment by wet blasting is performed. Since the effect is small, sufficient stress relaxation of the lower layer cannot be achieved. On the other hand, when the average diameter of the micropores exceeds 200 nm, the strength of the Ti carbonitride layer itself in which the crack initiation layer exists is lowered. Therefore, the average diameter of the minute holes is set to 25 to 200 nm.

The diameter of the micropores in the crack starting layer is obtained by directly measuring the diameter and density of the pores with a scanning electron microscope after setting the vertical cross section of the hard coating layer including the crack starting layer as a polished surface. Can do.
In addition, the average diameter of the minute holes is obtained by measuring the diameters of the minute holes at a plurality of positions and averaging them.

In the crack starting layer, the surface of the substrate was observed in the longitudinal section, and when the density of micropores per unit area was determined for an arbitrary 10 μm ² in the crack starting layer, the average density of micropores was 3 / If it is less than μm ² , sufficient stress relaxation of the lower layer cannot be achieved. On the other hand, if the average density of microvoids is 20 / μm ² or more, Ti carbonitride in which a crack initiation layer is present Since the strength of the physical layer itself is lowered, the density of the micropores is determined to be 3 / μm ² or more and less than 20 / μm ² .

The density of micropores in the crack starting layer is obtained by directly measuring the diameter and density of the pores with a scanning electron microscope after setting the vertical cross section of the hard coating layer including the crack starting layer as a polished surface. Can do.
In addition, the average density of micropores is obtained by measuring the density of micropores at a plurality of locations and averaging them.

After forming a Ti carbonitride layer having a crack starting layer having the desired average diameter and average density, and further forming an upper layer thereon, the crack starting point is applied by wet blasting or the like from the surface of the upper layer. A stress relaxation layer having cracks with an average density of 0.2 / μm or more and less than 2 / μm in the layer thickness direction is formed from the layer to the lower layer on the substrate side.
When the average density of cracks in the stress relaxation layer is less than 0.2 / μm, sufficient stress relaxation in the lower layer cannot be achieved, while the average density of cracks is 2 / μm or more. In this case, since the strength of the lower layer itself was lowered, the average density of cracks was determined to be not less than 0.2 / μm and less than 2 / μm.
In this case, cracks having an average density of less than 0.2 / μm are formed in the lower layer or the upper layer located above the stress relaxation layer.

  The density of cracks in the stress relaxation layer is determined by making the longitudinal section of the hard coating layer including the stress relaxation layer a polished surface, etching, observing with an optical microscope, and longitudinally cutting a reference line extending in a direction parallel to the substrate surface. It can be determined by measuring the number of cracks, and the average density of cracks is obtained by averaging the measured values at a plurality of locations.

And the stress relaxation layer which has such an average crack density can be formed by performing a wet blast process, for example.
However, since the ease of formation of cracks in the stress relaxation layer naturally changes depending on the layer thickness of the upper layer and the entire layer thickness of the lower layer, in the stress relaxation layer, a desired crack formed from the crack origin layer to the substrate side is desired. The wet blasting conditions need to be adjusted according to the crack average density.

As is well known, wet blasting is a process of injecting a polishing liquid, which is a liquid (generally water) containing an injection abrasive, onto a workpiece to give compressive residual stress. Or the surface polishing process. As a spray abrasive for such wet blasting, the material is alumina, silicon carbide, zirconia, resin, glass, etc. It can be used in various ways, and the average particle size is preferably about 1 to 500 μm, more preferably about 10 to 250 μm.
As the wet blasting condition, for example, when alumina is used as the medium, the polishing liquid is adjusted by adding the medium so that it is in the range of 15 to 60% by weight when mixed with the liquid (water). It is desirable that the pressure of the compressed air supplied to the gun, that is, the injection pressure is 0.05 to 0.5 MPa, preferably 0.1 to 0.3 MPa.

Upper layer (α-type aluminum oxide layer):
In the state of chemical vapor deposition, the α-type aluminum oxide layer generally has excellent high-temperature hardness and chemical stability and contributes to improving the wear resistance of the hard coating layer. However, if the average layer thickness is less than 2 μm, The hard coating layer cannot exhibit sufficient wear resistance over a long period of use. On the other hand, if the thickness exceeds the average layer thickness of 20 μm, chipping, defects, and abnormal damage to the release layer are likely to occur. Therefore, the upper limit of the average layer thickness is 20 μm.

  In the coated tool of the present invention, a crack starting layer having a predetermined average pore diameter and average density is formed in a part of the lower layer, and stress relaxation having a predetermined crack average density is formed from the crack starting layer to the substrate side. Due to the formation of the layer, high-temperature heat generation occurs, and high-speed intermittent machining such as sintered alloys in which a high load acts on the cutting blade can be used for a long time without causing abnormal damage such as chipping, chipping, and peeling. It exhibits excellent wear resistance throughout its use.

It is a schematic diagram which shows the state of the crack in the hard coating layer of this invention coated tool. It is a schematic diagram which shows the state of the crack in the hard coating layer of the conventional coating tool.

Next, the coated tool of the present invention will be specifically described with reference to examples.
Here, a case where a tungsten carbide-based cemented carbide is used as the substrate will be described, but the same applies to the case where the substrate is a titanium carbonitride-based cermet.

  Prepare WC powder, TaC powder, NbC powder, and Co powder each having an average particle diameter of 1 to 3 μm as raw material powders, blend these raw material powders with the blending composition shown in Table 1, and add wax. The mixture was ball milled in acetone for 24 hours, dried under reduced pressure, and then pressed into a green compact having a predetermined shape at a pressure of 98 MPa. The green compact was subjected to a predetermined pressure within a range of 1370 to 1470 ° C. in a vacuum of 5 Pa. Made of WC-base cemented carbide with insert shape specified in ISO / CNMG120408 by performing vacuum sintering under temperature holding condition for 1 hour, and then performing honing of R: 0.02mm on the cutting edge after sintering A tool substrate A was manufactured.

Next, the tool substrate A is charged into a normal chemical vapor deposition apparatus,
First, Table 2 (l-TiCN in Table 2 indicates the conditions for forming a TiCN layer having a vertically grown crystal structure described in JP-A-6-8010, and other than that, a normal granular crystal structure is shown. The lower layer made of the Ti compound layer having the target layer thickness shown in Table 5 was formed by vapor deposition under the conditions shown in FIG.
Here, in forming the Ti carbonitride layer as the lower layer, for a specific Ti carbonitride layer (the “layer in which the crack initiation layer is formed” in Table 5), the layer thickness of the layer is 1 A crack starting layer having a thickness shown in Table 5 was formed under the conditions shown in Table 3 over a range of / 3 to 2/3.
Next, an upper layer made of an α-type aluminum oxide layer was formed by vapor deposition with a predetermined target layer thickness shown in Table 5 under the conditions shown in Table 2.
Next, the surface of the upper layer is subjected to wet blasting under the conditions shown in Table 4 to form the stress relaxation layer shown in Table 5, and at the same time, by forming cracks of a predetermined density in the stress relaxation layer. And this invention coated tool 1-10 was produced.

Further, for the purpose of comparison, the tool base A is charged into a normal chemical vapor deposition apparatus,
First, under the conditions shown in Table 2, a lower layer made of a Ti compound layer having a target layer thickness shown in Table 6 is formed by vapor deposition.
Next, under the conditions shown in Table 3, for a specific Ti carbonitride layer (“layer in which the crack initiation layer is formed” in Table 6), 1/3 to 2/3 of the layer thickness of the layer Over the region, a crack starting layer having a thickness shown in Table 6 is formed under the conditions shown in Table 3,
Next, an upper layer composed of an α-type aluminum oxide layer is formed by vapor deposition with a predetermined target layer thickness shown in Table 6 under the conditions shown in Table 2.
Next, the surface of the upper layer is subjected to wet blasting under the conditions shown in Table 4, thereby forming the stress relaxation layer shown in Table 6, and simultaneously forming cracks of a predetermined density in the stress relaxation layer. Comparative example coated tools 1 to 4 were produced.

Furthermore, for the purpose of comparison, the tool substrate A is charged into a normal chemical vapor deposition apparatus,
First, under the conditions shown in Table 2, a lower layer made of a Ti compound layer having a target layer thickness shown in Table 6 is formed by vapor deposition.
Next, an upper layer composed of an α-type aluminum oxide layer is formed by vapor deposition with a predetermined target layer thickness shown in Table 6 under the conditions shown in Table 2.
Next, wet blasting was performed on the surface of the upper layer under the conditions shown in Table 4 to produce Comparative Example-coated tools 5 to 8 shown in Table 6.

Further, for reference, the tool substrate A is charged into a normal chemical vapor deposition apparatus,
First, under the conditions shown in Table 2, a lower layer made of a Ti compound layer having a target layer thickness shown in Table 6 is formed by vapor deposition.
Next, by depositing an upper layer made of an α-type aluminum oxide layer with a predetermined target layer thickness shown in Table 6 under the conditions shown in Table 2, the reference example coating tools 9 and 10 shown in Table 6 are formed. Was made.

Next, with respect to the inventive tools 1 to 10, the comparative tools 1 to 8 and the reference tools 9 and 10, the average diameter and average density of micropores in the crack starting layer of the lower layer were measured, and further the stress relaxation layer The average density of cracks was measured. For reference, the average density of cracks formed on the upper layer surface was also measured.
That is, the diameter and density of the micropores in the crack starting layer are measured directly with a scanning electron microscope after the longitudinal section of the hard coating layer including the crack starting layer is a polished surface. Can be determined by
In addition, since there are almost no cracks in the normal Ti carbonitride layer and vacancies appear significantly in the crack starting layer, the most substrate of the Ti carbonitride layer into which the crack starting layer is introduced The position in the film thickness direction of the vacancy observed in a portion close to the distance from is the start point of the crack starting layer, and similarly, the position of the vacancy located farthest away is the end point.
Next, as a result of observation over a range of 100 μm in a direction parallel to the base in the longitudinal section of the hard coating layer, a hole closest to the base is formed among the fine holes formed by providing the crack starting layer. The voids that are not present in the region of 1/3 of the Ti carbonitride layer thickness from the lowermost surface of the Ti carbonitride layer and are also the most distant from the substrate are the substrate side from the uppermost surface of the Ti carbonitride layer The distance to the substrate of the hole closest to the substrate side is a, and the distance to the substrate of the hole farthest from the substrate is not present in the region of 1/3 of the Ti carbonitride layer thickness in the direction It was confirmed that b-a was 0.5 μm or more when b was used. The diameter of the minute holes is measured from an image of a scanning electron microscope. If the holes are distorted, it is treated as an ellipse, and the actual diameter of the minute holes is determined by a weighted average of the major and minor radii. Asked.
The average diameter of the micropores is obtained by measuring the diameters of the micropores at a plurality of locations and averaging them. The average density of the micropores is the density of the micropores at a plurality of locations. Measured and averaged.
In addition, the density of cracks in the stress relaxation layer and the density of cracks formed on the surface of the upper layer were determined by etching the optical cross-section of the hard coating layer including the stress relaxation layer and the upper layer surface after polishing. In the region of 0.5 μm below the crack starting layer, among the cracks formed in the stress relaxation layer, the number of cracks that vertically cut the reference line extending in the direction parallel to the substrate surface is measured. The average density of cracks can be obtained by averaging the measured values with a reference length of 100 μm in a direction parallel to the substrate at a plurality of locations. Moreover, the average density of the crack formed in the upper layer surface can be calculated | required by measuring the number of the cracks currently formed in the upper layer surface in several places, and averaging it.

Further, the thicknesses of the constituent layers of the hard coating layers of the inventive tools 1 to 10, the comparative example tools 1 to 8, and the reference example tools 9 and 10 were measured using a SEM (scanning electron microscope) (longitudinal section measurement). ), All showed an average layer thickness (average value of five-point measurement) substantially the same as the target layer thickness.
Tables 5 and 6 show the values obtained above.

Next, the present invention tools 1 to 10, the comparative example tools 1 to 8 and the reference example tools 9 and 10 are all screwed to the tip of the tool steel tool with a fixing jig,
Work material: JIS P2044 sintered alloy in the longitudinal direction, two equally spaced round bars,
Cutting speed: 330 m / min,
Incision: 2 mm,
Feed: 0.1 mm / rev,
Maximum value of the number of impacts: A dry high-speed intermittent cutting test was performed on the gear end face made of a sintered alloy under the condition of 5000 times, and the flank wear width of the cutting edge was measured.
Table 7 shows the results.
FIG. 1 shows a schematic diagram of a crack generated in the hard coating layer of the tool of the present invention after completion of the cutting test, and FIG. 2 shows the hard coating layer of a comparative tool after the cutting test. The schematic diagram of the generated crack is shown.

From the results shown in Tables 5 to 7, in the coated tool of the present invention, a crack starting layer having a predetermined average pore diameter and average density is formed in a part of the lower layer, and from the crack starting layer to the substrate side. In addition, since a stress relaxation layer having a predetermined crack average density is formed, chipping, chipping, delamination, etc., even in high-speed intermittent cutting processing such as sintered alloys with high heat generation and high load acting on the cutting edge It exhibits excellent wear resistance over long-term use without causing abnormal damage.
On the other hand, among the comparative tools 1 to 4 in which the average pore diameter and density outside the scope of the present invention were formed, the comparative tools 1 and 2 had no effect of stress relaxation because the crack average density was low, and the time was short. Chipping and chipping occurred in Comparative Tool 3 because the average diameter of the microvoids was too large, and chipping and chipping occurred due to the lower strength of the lower layer itself. Since the average density was too large, chipping and chipping occurred, and all of the comparative tools 1 to 4 reached the tool life before finishing the predetermined cutting due to the occurrence of abnormal damage.
Further, although the wet blast treatment was performed, the crack starting layer was not formed, and as a result, the stress relaxation layer was not formed. However, abnormal damage during cutting could not be suppressed, and the life was reached due to chipping and chipping.
Further, the reference tools 9 and 10 which are conventional tools are not subjected to stress relaxation of the film, and abnormal damage progresses rapidly from the initial stage of cutting due to the tensile stress remaining in the film, and cutting becomes impossible early. .

Claims (1)

A surface-coated cutting tool in which a hard coating layer composed of a lower layer and an upper layer is formed on the surface of a substrate composed of a tungsten carbide-based cemented carbide or a titanium carbonitride-based cermet,
(A) The lower layer is composed of one or more Ti compounds of a Ti carbide layer, a nitride layer, a carbonitride layer, a carbonate layer, and a carbonitride layer having a total average layer thickness of 3 to 15 μm. And comprising at least one Ti carbonitride layer,
(B) The upper layer consists of an α-type aluminum oxide layer in a chemical vapor deposited state with an average layer thickness of 2 to 20 μm,
(C) The average thickness of the at least one Ti carbonitride layer constituting the lower layer is the largest, and the Ti carbonitride layer having a layer thickness of 1.5 μm or more has a layer thickness of the layer. In the region of 1/3 to 2/3, the crack starting layer having micropores having an average diameter of 25 to 200 nm with an average density of 3 / μm ² or more and less than 20 / μm ² is 0.5 μm to the Ti Formed with a thickness of 1/3 of the carbonitride layer,
(D) A stress relaxation layer in which cracks exist at an average density of 0.2 / μm or more and less than 2 / μm when measured in the direction parallel to the substrate surface from the crack starting layer to the lower layer on the substrate side A surface-coated cutting tool characterized in that is formed.