JP2015107546A - Coated cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated cutting tool exhibiting superior durability in, for example, cutting work of high-hardness material.SOLUTION: A coated cutting tool includes a substrate, an a-layer which is arranged on the substrate, has a nano-beam diffraction pattern indexed to crystalline structure of WC and is made of a carbide containing W and Ti, a b-layer which is arranged on the a-layer and is made of nitride or carbonitride having a content ratio of Al (atom%) of 60 to 75% and a content ratio of Ti (atom%) of 20% or more with respect to the net amount of metal (including metalloid) element and a c-layer which is arranged on the b-layer and is made of nitride or carbonitride of TiSi type in which the content ratio (atom%) of Ti is most with respect to the net amount of metal (including metalloid) element. Therein, film thickness of the a-layer is 1 to 10 nm and the crystalline structure of the b-layer is a face-centered cubic lattice structure.

Description

  The present invention relates to a coated cutting tool coated with a hard coating applied to a cutting process such as steel or cast iron.

  Conventionally, a coated cutting tool coated with a hard film has been applied for the purpose of improving the durability of the cutting tool. Among hard coatings, composite nitride coatings and carbonitride coatings (hereinafter referred to as TiSiN and TiSiCN) of Ti and Si have been applied to cutting of high-hardness steel because they have excellent wear resistance. Usually, TiSiN and TiSiCN are applied to a coated cutting tool that is coated with an intermediate film for improving the adhesion between the base material and TiSiN or TiSiCN because of its poor adhesion to the base material.

  For example, in Patent Document 1, the atomic percentage of only the metal component is directly above the substrate, Al: more than 40% and 75% or less, B, Si, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W One or more of the above, less than 10% of the remaining Ti, nitride, carbonitride, oxynitride, oxycarbonitride coated with TiSiN or TiSiCN directly on it A tool is disclosed. Further, in Patent Document 2, a nitride mainly composed of Ti is formed at a thickness of 0.1 μm to 1 μm immediately above a base material, and the atomic percentage of only the metal component is Al: more than 40% and 75% or less. N, B, Si, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W or less, and less than 10%, remaining nitride, carbonitride, oxynitride A coated cutting tool in which TiSiN or TiSiCN is coated directly on any of the oxycarbonitrides is disclosed.

JP 2000-334606 A JP 2000-326108 A

In recent years, the working environment of cutting tools has become more severe due to the higher hardness of workpieces and higher processing speeds. In particular, when cutting cold tool steel adjusted to a high hardness of 60 HRC or higher by heat treatment, peeling or wear of the hard coating tends to occur early. For this reason, even a coated cutting tool coated with TiSiN or TiSiCN through an intermediate film as described in Patent Documents 1 and 2 sometimes reaches the tool life early.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a coated cutting tool having excellent durability.

The present inventor has found a specific film structure exhibiting excellent durability in cutting of a hard material, and has reached the present invention.
That is, the present invention comprises a base material, an a layer made of a carbide containing W and Ti, disposed on the base material, the nanobeam diffraction pattern is indexed to the crystal structure of WC,
Al content ratio (atomic%) is 60% or more and 75% or less and Ti content ratio (atomic%) with respect to the total amount of metal (including semi-metals; the same shall apply hereinafter) disposed on the a layer. A layer b made of nitride or carbonitride having a Ti content of 20% or more, and a TiSi-based nitride disposed on the layer b and having the largest Ti content ratio (atomic%) with respect to the total amount of metal elements Or c layer made of carbonitride,
In the coated cutting tool, the layer a has a thickness of 1 nm to 10 nm, and the crystal structure of the layer b has a face-centered cubic lattice structure.
The thickness of the c layer is preferably 1 μm or more.

  According to the present invention, it is possible to significantly improve the durability of the coated cutting tool by suppressing the peeling and wear of the hard coating even in the cutting of cold hardened tool steel. In addition, for example, the durability of the coated cutting tool can be greatly improved even when a work material having a large amount of welding such as SUS is processed. Therefore, improvement in processing efficiency and reduction in processing cost can be realized.

It is the surface observation photograph of the tool blade edge | tip of this invention example 1 after the cutting test used in Example 2. FIG. It is the surface observation photograph of the tool blade edge | tip of this invention example 2 after the cutting test used in Example 2. FIG.

  According to the study by the present inventors, it has been found that it is important to reduce the cutting resistance during the cutting process in order to increase the durability of the tool in the cutting process of the high hardness steel. Then, it was confirmed that the cutting resistance during cutting was reduced while securing excellent wear resistance by forming a TiSi-based nitride or carbonitride on a hard film having a specific composition. Specifically, it is confirmed that the tool life is improved by forming TiSi-based nitride or carbonitride on nitride or carbonitride containing Al and Ti with increased Al content. did. And it is important to improve the adhesion between the base material and the nitride or carbonitride containing Al and Ti, and this is the result of finding a specific film structure that can further enhance the durability of the tool. The invention has been reached. Hereinafter, the configuration requirements of the present invention will be described.

In the present invention, the a layer disposed on the substrate is made of a carbide containing W and Ti in which the nanobeam diffraction pattern is indexed to the crystal structure of WC. The a layer directly above the base material has a nanobeam diffraction pattern indexed to the crystal structure of WC, and is a carbide containing tungsten (W), so the affinity with the cemented carbide, which is the base material, is increased and adhesion is increased. It is considered that the property is excellent. In addition, since the a layer contains titanium (Ti), the adhesiveness of the b layer disposed on the base material and the a layer is further increased, and the crystal structure of the hard coating of the b layer immediately above the a layer Tends to have a face-centered cubic lattice (fcc; hereinafter simply abbreviated as “fcc”) structure, and the durability of the coated cutting tool tends to be improved. The a layer preferably has a Ti content ratio (atomic%) of 10% to 25% with respect to the total amount of metal elements.
Moreover, even if a layer becomes too thin or too thick, it is unpreferable for improving adhesiveness with a base material. Therefore, the film thickness of the layer a is in the range of 1 nm to 10 nm. About the minimum of the film thickness of a layer, Preferably it is 2 nm or more, Furthermore, 3 nm or more is preferable. The upper limit of the thickness of the a layer is preferably 7 nm or less. Furthermore, it is preferable that it is 6 nm or less.

  The a layer of the present invention may contain a film component and a base material component in addition to W and Ti. The a layer of the present invention may contain Co on the substrate side and Al and N on the hard coating side in a diffused manner. However, the a layer has a nanobeam diffraction pattern indexed to the crystal structure of WC and tungsten (W ) And titanium (Ti), the effect of the present invention can be exhibited. The a layer can be confirmed by cross-sectional observation, composition analysis, and nanobeam diffraction pattern of the tool edge by observation with a transmission electron microscope.

The b layer is made of a nitride or carbonitride having an Al content ratio (atomic%) of 60% to 75% and a Ti content ratio (atomic%) of 20% or more with respect to the total amount of metal elements.
Nitride or carbonitride containing Al and Ti is a film type excellent in heat resistance and wear resistance. The b layer has an Al content ratio (atomic%) of 60% or more with respect to the total amount of metal elements, so that welding to the cutting edge of the cutting tool is easily suppressed during processing, and cutting resistance during processing is reduced. It tends to decrease. When the Al content in the b layer is less than 60%, the cutting resistance during processing increases and the heat resistance of the coating tends to decrease. Further, when the Al content of the b layer is more than 75%, the crystal structure of a fragile hexagonal close-packed (hcp; hereinafter sometimes abbreviated as “hcp”) structure is likely to be mainly used, and the coated cutting The durability of the tool tends to decrease.
The b layer is preferably provided immediately above the a layer, so that the adhesion between the base material and the b layer is enhanced, and the effect of reducing cutting resistance during processing is effectively exhibited.

  In order to change the crystal structure of the b layer to the fcc structure, the Ti content ratio (atomic%) is set to 20% or more with respect to the total amount of metal elements. When Ti of the b layer is less than 20%, the wear resistance is lowered and it is difficult to obtain an fcc structure capable of realizing excellent durability as a coated cutting tool. In order to realize more excellent durability in cutting of hard steel, the b layer preferably has a total content ratio (atomic%) of Al and Ti of 90% or more.

The b layer is selected from 4a group, 5a group and 6a group metal elements of the periodic table and Si and B as long as the fcc structure crystal structure is maintained in consideration of the contents of Al and Ti. The total of one or more elements can be contained in an atomic ratio of 10% or less with respect to the total amount of metal elements. Moreover, if b layer is a nitride or carbonitride, you may contain nonmetallic elements, such as oxygen, in a part of membrane | film | coat. The b layer is more preferably a nitride that tends to have excellent heat resistance. The b layer is preferable because it contains W and tends to exhibit excellent durability not only in high-hardness steel but also in cutting of high-carbon steel and Ni-base superalloys. The content ratio (atomic%) of W is particularly preferably 2% or more and 7% or less with respect to the total amount of metal elements.
In the present invention, the fcc structure means that the peak intensity corresponding to the fcc structure shows the maximum intensity in electron beam diffraction or X-ray diffraction. In the present invention, the b layer may contain an hcp structure as part of the film structure. The film thickness of the b layer is preferably 1 μm to 5 μm. About the minimum of the film thickness of b layer, More preferably, it is 1.5 micrometers or more. About the upper limit of the film thickness of b layer, More preferably, it is 3 micrometers or less.

In wet processing of high hardness steel, it is effective to provide a hard film having a high residual compressive stress as a protective film because the hard film is easily peeled off by heating and cooling cycles. In the present invention, a c layer made of TiSi nitride or carbonitride having the largest Ti content ratio (atomic%) with respect to the total amount of metal elements is disposed on the b layer. In order to impart high wear resistance to the c layer, the Ti content (atomic%) is preferably 55% or more with respect to the total amount of metal elements. Moreover, in order to give a high residual compressive stress to the hard coating, the Si content ratio (atomic%) is preferably 10% or more. The c layer is a film type having a high residual compressive stress with excellent thermal shock resistance. By providing the c layer, the wear of the b layer is suppressed, and the cutting resistance continuously decreases even in the cutting of high-hardness steel. Tool damage tends to be suppressed.
In order to further improve the wear resistance after applying a high residual compressive stress to the c layer, the c layer has a Ti content ratio (atomic%) of 60% to 85% with respect to the total amount of metal elements. The content ratio (atomic%) is preferably 15% or more and 40% or less.

If the c layer becomes too thin, the wear resistance tends to decrease. Also, if the c layer becomes too thick, film peeling tends to occur. Therefore, the film thickness of the c layer is preferably 0.3 μm to 5 μm. About the minimum of the film thickness of c layer, More preferably, it is 0.5 micrometer or more. The upper limit of the thickness of the c layer is more preferably 3 μm or less, and further preferably 2.5 μm or less. In addition, the c layer has a total of one or more elements selected from Group 4a, Group 5a, Group 6a of the periodic table and Al, B, and 10% of the total amount of the metal elements. It can be contained in the following atomic ratio.
If c layer is nitride or carbonitride, you may contain nonmetallic elements, such as oxygen, in a part of membrane | film | coat. The c layer is more preferably a nitride that tends to have excellent heat resistance. In order to enhance the adhesion, it is preferable to provide the c layer immediately above the b layer, but an interlaminate film composed of the composition of the b layer and the c layer may be provided.

In the cutting of high-hardness steel, it is preferable that the c layer that is a protective film has a certain thickness or more. The coated cutting tool of the present invention is preferable because the film thickness of the c layer is 1 μm or more, so that excellent durability can be exhibited even when cutting a hard tool steel having high hardness. For example, even when high speed machining at a cutting speed of 200 m / min or more is performed, excellent durability can be exhibited. Furthermore, even when the cutting speed is 250 m / min or more, excellent durability can be exhibited, which is preferable. Since this invention can exhibit the outstanding tool performance by applying to cutting of cold tool steel of 55HRC or more, it is preferred. Furthermore, it can be preferably applied to cutting of cold tool steel of 60HRC or more. Since the time required for cutting can be shortened by increasing the cutting speed, an effect that the manufacturing efficiency of the mold is improved can be expected.
The cutting speed in the present invention is the speed of the work surface (blade edge). That is, in the case of a blade-tip replaceable tool, the speed is the speed of the outermost edge of the insert when the insert tip is set, and in the case of a turning tool such as a drill or end mill, the speed of the outer peripheral edge.

In order to form the a layer of the present invention, it is preferable to perform Ti bombardment using a cathode having a magnetic field configuration in which a coil magnet is provided on the outer periphery of the target to confine the arc spot inside the target. By using such a cathode and bombarding with Ti, which is an element species that easily forms carbides, the oxide on the substrate surface is removed and cleaned, and the bombarded Ti ions are converted into WC on the substrate surface. And the nanobeam diffraction pattern is indexed to the crystal structure of WC, and carbides containing W and Ti are easily formed.
Further, when the negative bias voltage applied to the base material during Ti bombardment and the current applied to the target are low, carbides containing W and Ti are hardly formed. Therefore, the negative bias voltage applied to the substrate is preferably −1000 V to −700 V. Further, the current supplied to the target is preferably 80A to 150A.
Bombarding may be carried out while introducing argon gas, nitrogen gas, hydrogen gas, hydrocarbon-based gas, etc., but the substrate is formed by carrying out the furnace atmosphere under a vacuum of 1.0 × 10 ⁻² Pa or less. It is preferable because the surface is cleaned and a diffusion layer is easily formed.

  The coated cutting tool of the present invention is preferable because it is particularly effective when applied to a tool such as a radius end mill or a square end mill that mainly uses an outer peripheral blade.

A square end mill made of a WC-based cemented carbide was used as a base material, and a coated cutting tool was produced by coating a hard film under each condition, and the characteristics were evaluated. An arc ion plating film forming apparatus was used for forming the hard film. A bias power source was connected to the base material installed in the vacuum vessel, and a negative DC bias voltage was applied to the base material to coat the hard film.
Table 1 shows cathodes and bias conditions used for film formation. In order to cover the b layer and the c layer of the present invention, permanent magnets were provided on the outer periphery and the back surface of the target, and cathodes having an average magnetic flux density of 20.2 mT (hereinafter referred to as C1 and C2) were used. In the metal bombardment process of the example of the present invention, a cathode (hereinafter referred to as C3) provided with a coil magnet on the outer periphery of the target was used.

In Invention Examples 1 to 4 and Comparative Examples 1 and 5, after fixing the base material to a pipe-shaped jig in a vacuum vessel and performing heat degassing in a vacuum of about 500 ° C. and 1 × 10 ⁻³ Pa Cleaning with Ar plasma was performed. And it vacuum-evacuated so that it might become 8 * 10 < ^-3 > Pa or less, The arc current of 150 A was supplied to C3, and Ti bombarding process was implemented for 4 minutes. Thereafter, nitrogen gas was introduced, and electric power was applied to C1 to coat the nitride b layer. Subsequently, power was supplied to C2 to produce a coated cutting tool coated with a nitride c layer.
In Comparative Examples 2 and 3, a target was not provided on C2, and after Ti bombarding, power was applied to C1 to coat a single-layer nitride film.
In Comparative Example 4, after the surface of the base material was cleaned with Ar plasma, Ti bombarding was not performed and the nitride film was coated. Thereafter, power was applied to C1 and C2 to coat the a layer and the b layer, respectively.

Using an electronic probe microanalyzer device (model number: JXA-8500F) manufactured by JEOL Ltd., the coating compositions of the b layer and the c layer were measured by the attached wavelength dispersion type electron probe microanalysis (WDS-EPMA). The analysis of the coating composition was performed by processing a coated cutting tool for analysis and observing a cross section. Each layer was subjected to an acceleration voltage of 10 kV, an irradiation current of 5 × 10 ⁻⁸ A, an acquisition time of 10 seconds, and an analysis region diameter of 0.5 μm at 5 points. The measurement was performed by determining the composition from the average.

  A coated cutting tool for analysis was processed and TEM analysis was performed. As the apparatus, a field emission transmission electron microscope (model number: JEM-2010F type) manufactured by JEOL Ltd. was used. From the limited field diffraction pattern, it was confirmed that the b layers of Invention Examples 1 to 4 and Comparative Examples 1 to 5 had the peak intensity corresponding to the fcc structure and the fcc structure. Further, the peak intensity corresponding to the hcp structure was slightly confirmed.

  About the tool blade edge | tip part, the cut surface at the time of cut | disconnecting in a surface perpendicular | vertical to a film surface was analyzed by TEM. The composition of the a layer was analyzed at a beam diameter of 1 nm using the attached UTW type Si (Li) semiconductor detector. Nanobeam diffraction was performed with a camera length of 50 cm and a beam diameter of 2 nm or less. From the EDS spectrum analysis and the nanobeam diffraction pattern, the substrate, a layer, and b layer were confirmed. From the EDS spectrum analysis results, it was confirmed that the layer a of the present invention example contained the largest amount of W in the metal element content ratio (atomic%), and then contained a large amount of Ti. The content ratio (atomic%) of W was about 80% with the content ratio (atomic%) of the metal element. The Ti content ratio (atomic%) was about 15%. In addition to W and Ti, Al and N, which are hard film components, were contained. Further, Co, which is a base material component, was also slightly contained. The layer a of the present invention example could be indexed to the crystal structure of the WC nanobeam diffraction pattern. From the EDS spectrum analysis and the nanobeam diffraction pattern, it was confirmed that the layer a of the example of the present invention was indexed to the crystal structure of WC and was a carbide containing tungsten (W) and titanium (Ti). The results of physical property evaluation of each sample are shown in Table 2.

A cutting test was performed using the manufactured coated cutting tool. Table 2 shows the cutting test results. Cutting conditions are as follows.
Tool: Square end mill (CEPR6080)
φ8 × 6 blades (Hitachi Tool Co., Ltd.)
Base material: WC (bal.)-Co (8 mass%)-TaC (0.25 mass%)-Cr ₃ C ₂ (0.9 mass%), WC average particle diameter 0.6 μm, hardness 93.4HRA Cemented carbide cutting method: Side cutting Work material: SKD11 (60HRC)
Cutting depth: axial direction, 9 mm, radial direction, 0.16 mm
Cutting speed: 150 m / min
Single blade feed rate: 0.06mm / tooth
Cutting oil: Air blow Cutting distance: 10m

Since the c example which has high residual compressive stress was provided as the protective film in the example of the present invention, it was confirmed that the tool damage was reduced even in the cutting of high hardness steel.
In Comparative Example 1, since the Al content in the b layer was small, the resistance during cutting was larger than that of the inventive example, and the maximum wear width of the tool edge was increased.
In Comparative Examples 2 and 3, since the c layer having a high residual compressive stress is not provided as a protective coating, it is confirmed that the maximum wear width of the tool edge is larger in cutting of hard steel than in the present invention. did.
In Comparative Example 4, since the adhesion between the base material and the b layer was not sufficient, the maximum wear width of the tool blade edge was increased.
Since the comparative example 5 provided AlCrN which cannot give a high residual compressive stress as a protective film, the maximum wear width of the tool edge became large.

The inventive examples 1 and 2 evaluated in Example 1 were evaluated by increasing the cutting speed. Cutting conditions are as follows. The test results are shown in Table 3.
Tool: Square end mill (CEPR6080)
φ8 × 6 blades (Hitachi Tool Co., Ltd.)
Base material: WC (bal.)-Co (8 mass%)-TaC (0.25 mass%)-Cr ₃ C ₂ (0.9 mass%), WC average particle diameter 0.6 μm, hardness 93.4HRA Cemented carbide cutting method: Side cutting Work material: SKD11 (60HRC)
Cutting depth: axial direction, 9 mm, radial direction, 0.16 mm
Cutting speed: 250 m / min
Single blade feed rate: 0.06mm / tooth
Cutting oil: Air blow Cutting distance: 1.25m

  1 and 2 show observation photographs of the tool edge after the cutting test. It is confirmed that the present invention example 2 in which the film thickness of the c layer is 1 μm or more suppresses the maximum wear width of the tool edge than the present invention example 1, and is more effective for cutting at a higher speed. It was.

Claims (2)

A substrate;
An a layer of carbide comprising W and Ti disposed on the substrate, the nanobeam diffraction pattern being indexed to the crystal structure of WC, and
The Al content ratio (atomic%) is 60% to 75% and the Ti content ratio (atomic%) is 20% or more with respect to the total amount of metal (including metalloid) elements disposed on the a layer. A layer b made of nitride or carbonitride that is
A c layer made of TiSi-based nitride or carbonitride having the highest Ti content ratio (atomic%) with respect to the total amount of metal (including metalloid) elements disposed on the b layer. ,
A coated cutting tool in which the thickness of the a layer is 1 nm to 10 nm, and the crystal structure of the b layer is a face-centered cubic lattice structure. The coated cutting tool according to claim 1, wherein the film thickness of the c layer is 1 μm or more.