JP2002233902A - Coated cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated cutting tool capable of restraining a titanium carbonitride coat of a micro-columnar crystal structure from being separated by cracks generated in the columnar crystal grain boundary. SOLUTION: This coated cutting tool has a hard alloy base material and a hard coat formed on the surface thereof. The hard coat has the following constitution. A first layer is formed on the surface of the base material by a single layer or a plurality of layers made of titanium nitride, titanium carbide, titanium carbonate, titanium nitroxide, titanium carbonitride, and titanium boronitride. A second layer is formed right on the first layer by titanium carbonitroxide of a mixed crystal structure of a granular crystal and columnar crystal, in which the oxygen containing concentration in the coat satisfies 0.1 to 15% at the maximum value of atom %, and the average coat thickness is 0.2 or more and under 2.0 μm. A third layer is formed right on the second layer using titanium carbonitride of a columnar crystal structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated cutting tool having a hard coating on the surface of a substrate and a method for producing the same. In particular, under severe cutting conditions, the coating that increases the grain boundary strength of the columnar crystal structure of the hard coating and suppresses the growth of cracks while maintaining excellent wear resistance while improving peel resistance It relates to a cutting tool.

[0002]

2. Description of the Related Art In recent years, coated carbide tools have been used for high-speed cutting due to energy saving and labor saving, etc., and the environment in which they are used has become increasingly severe, and it is necessary to provide even more excellent wear resistance. . Therefore, a vertically elongated crystal structure that is effective in improving wear resistance (hereinafter, vertically elongated crystal is referred to as columnar crystal)
In order to increase the hardness of the titanium carbonitride having the above and to improve the wear resistance, there is a tendency to form fine columnar crystals.

In order to produce titanium carbonitride having fine columnar crystals, a lower layer of a titanium carbonitride layer having a columnar crystal structure using organic CN such as acetonitrile as disclosed in Japanese Patent Application Laid-Open No. It has been proposed to interpose a titanium oxycarbonitride layer having the same columnar crystal structure.
According to this publication, since titanium carbonitride is nucleated following the microstructure of titanium carbonitride, titanium carbonitride becomes relatively fine columnar crystals and contributes to improvement of wear resistance.

[0004]

However, the titanium carbonitride having a fine columnar crystal structure has a disadvantage that cracks are easily developed in the columnar crystal grain boundaries and the coating is peeled off. Titanium nitride, titanium oxynitride of granular crystal structure on hard alloy substrate,
At least titanium carbide, titanium carbonate, and titanium carbonitride
When one or more layers are coated, the coating surface becomes a cylindrical dome shape. Due to this dome-shaped effect, the columnar titanium carbonitride formed by the chemical vapor deposition method using organic CN such as acetonitrile tends to become a tapered columnar structure in which the structure expands toward the upper part in the growth direction. Therefore, as the film formation proceeds, fine voids are generated between the columnar crystals. These voids weaken the bonding force between the crystals, promote the development of cracks generated in the film during cutting, and reduce the peeling resistance.

When the titanium carbonitride having a columnar crystal structure has a tapered shape, the outermost surface has an uneven shape, and the titanium carbonitride having the same columnar crystal structure, which forms a nucleus and forms a film on the top, also has a tapered shape. Become. As a result, similarly to titanium carbonitride, titanium carbonitride forms fine voids in the columnar crystal grain boundaries, weakens the bonding strength of the grain boundaries, and reduces the peeling resistance.

On the other hand, JP-A-2-31202 (Patent No. 28761)
No. 30) and the like have proposed to improve the peeling resistance while maintaining the wear resistance by forming a mixed crystal structure of granular crystals and columnar crystals in order to prevent the propagation of cracks in the columnar crystal structure. In this technique, after the columnar crystals are generated, the pressure in the furnace is raised to a supersaturated state, and the granular crystals are precipitated at the columnar grain boundaries, whereby titanium oxycarbonitride has a mixed crystal structure of columnar crystals and granular crystals.

However, since the columnar crystal structure is first deposited, the crystal of titanium carbonitride becomes tapered, and the titanium carbonitride on the upper part also becomes tapered due to the influence, and eventually it can have excellent wear resistance. It does not lead to improving the peeling resistance of titanium carbonitride having a fine columnar crystal structure.

[0008] In addition, even if a titanium carbonitride layer having a mixed structure of granular crystals and columnar crystals is used in order to provide both wear resistance and peeling resistance, the wear resistance does not increase in recent high-speed cutting conditions. Obviously it is not as far as titanium carbonitride with a fine columnar crystal structure.

If the dome effect of the granular crystal in the lower layer of titanium carbonitride makes the columnar crystal of titanium carbonitride tapered, a method of directly forming a titanium carbonitride film by smoothing a hard alloy substrate is also available. is there. However, the adhesion between the hard alloy substrate and the titanium carbonitride film is weak, and it cannot be an excellent cutting tool.

[0010] Accordingly, a main object of the present invention is to provide a coated cutting tool which suppresses peeling of titanium carbonitride due to cracks between tapered columnar crystal grains and has excellent peeling resistance, and a method of manufacturing the same. It is in.

[0011]

Means for Solving the Problems The inventor of the present invention has conducted research on the above problems, and has obtained the following findings to accomplish the present invention.

A: A reaction occurs in which a granular crystal and a columnar crystal of titanium oxycarbonitride are simultaneously precipitated on the upper layer of the titanium nitride of the granular crystal, so that the oxygen concentration and the film thickness of the titanium oxycarbonitride are within specified ranges. A film is formed. As a result, the film can be formed such that the granular crystals are preferentially buried in the concave portions generated in each step of the film forming reaction of titanium carbonitride and the flatness increases.

B: When the flatness of the surface of the titanium oxycarbonitride increases, the generation of columnar crystals having a high film-forming speed is prioritized, and at the same time, the crystals having a granular structure that precipitates have the effect that the surface has a dome shape. Are so fine that they are no longer shown.

C: The nucleation and film formation of titanium oxynitride on the smoothed upper layer of titanium oxycarbonitride have a dense columnar crystal grain boundary which grows directly above the titanium oxycarbonitride and have a strong grain boundary bonding force. Can be difficult to develop.

D: The columnar crystal of titanium carbonitride becomes finer and the mixed granular crystal becomes very fine, so that the titanium carbonitride in the upper layer becomes finer, and excellent wear resistance is maintained. It becomes possible to do.

That is, the present invention relates to a coated cutting tool comprising a hard alloy substrate and a hard coating formed on the surface thereof, wherein the hard coating has the following configuration. Formed on the surface of the base material, titanium nitride, titanium carbide,
A first layer comprising a single layer or a plurality of layers of titanium carbonate, titanium oxynitride, titanium carbonitride, and titanium boronitride. A titanium oxycarbonitride formed directly above the first layer and having a mixed crystal structure of granular crystals and columnar crystals. The oxygen concentration in the film satisfies 0.1% to 15% at the maximum of atomic%, and the average film A second layer having a thickness of 0.2 to 2.0 μm. A third layer made of titanium carbonitride having a columnar crystal structure and formed immediately above the second layer.

Here, it is preferable to further include at least one of the following structures.

(A) The film crystal structure of the first layer has a granular structure.

(B) The second layer has an average thickness of 0.3 μm to 1.5 μm.
At m, its oxygen content satisfies 1% to 6% with a maximum of atomic%.

(C) The crystal grains of the third layer in the vicinity of the edge line of the substrate have an aspect ratio of 6 or more.

(D) The average thickness of the third layer satisfies 2 to 20 μm.

(E) The hard coating comprises a fourth layer composed of one or more layers formed above the third layer. This fourth layer is made of a titanium compound and has a chemical formula of Ti (Cw'Nx'Oy'Bz ') {w' +
x ′ + y ′ + z ′ = 1, 0 ≦ w ′, x ′, y ′, z ′ ≦ 1}, and one or more selected from aluminum oxide, zirconium oxide and hafnium oxide. The average thickness of the hard coating is 2.5 to 30 μm.

(F) The base material is a cemented carbide or cermet.

(G) The surface roughness in the vicinity of the ridge of the cutting edge of the substrate is 0.2 to 1.3 μm in Rmax with respect to a reference length of 5 μm measured by a method of observing from the cross section of the substrate.

(H) The vicinity of the ridge of the cutting edge of the hard coating film is substantially constituted by a smooth surface having a surface roughness Rmax of 0.2 μm or less with respect to a reference length of 5 μm.

The above components will be described in detail.

<Simultaneous Formation of Columnar Crystals and Granular Crystals in Titanium Carbonitride Oxide (Second Layer)> To simultaneously form columnar crystals and granular crystals of titanium carbonitride oxide as the second layer, first,
A TiCN reaction using an organic CN-based gas having a columnar crystal structure and a TiCO reaction having a granular crystal structure proceed simultaneously. And
The active O and N atoms generated in the reaction process are caused to undergo solid solution reactions, respectively, to form columnar crystal TiCNO and granular crystal TiCNO.
Are generated simultaneously.

The reason why the granular crystals precipitate in the concave portions on the film surface during the TiCNO film formation process is that the reaction gas moves on the film surface during the film formation process, and the organic CN having a relatively fast reaction is formed on the convex portions.
This is because columnar crystals using the system gas are precipitated, and the amount of the organic CN-based gas decreases by the time the reaction gas reaches the concave portion, so that the generation of granular crystals becomes dominant.

As a result, the granular crystals fill the recesses and the film surface becomes flat. As the surface becomes flat, columnar crystals using an organic CN-based gas, which reacts relatively quickly, are not affected by the surface shape effect and are preferentially formed. At the same time, the generation of granular crystals is reduced, the granular structure is refined, and the tapered growth of columnar crystals in the second layer due to the dome shape of the first layer is suppressed.

<Regulation of Oxygen Concentration in Titanium Carbonitride (Second Layer)> The reason for defining the oxygen concentration in the titanium oxycarbonitride film is that when the maximum value of oxygen atom% is less than 0.1 atm%, the columnar crystal effect is not obtained. It appears strongly, and columnar crystals do not sufficiently precipitate in the recesses.
When the content exceeds 15 atm%, the precipitation of granular crystals increases, and TiCN (third layer) having a columnar crystal structure formed on the upper portion grows in a tapered shape. A more preferred range is 1 to 6 atm%.

<Film thickness regulation of titanium carbonitride (second layer)>
The reason for defining the thickness of titanium carbonitride is that the thickness is 0.
If it is less than 2 μm, the titanium carbonitride is not sufficiently flattened because it is affected by the granular crystals in the lower layer.On the other hand, if it exceeds 2.0 μm, the flattening of the titanium carbonitride is saturated and there is no point in further laminating is there. A more preferred range is 0.3 to 1.5 μm.

<Arrangement of First and Second Layers> If the titanium oxycarbonitride layer (second layer), which is a mixture of columnar crystals and granular crystals, is coated directly on the granular crystal layer (first layer), This is because the adhesion of the hard coating to the substrate can be further increased, and the peeling resistance as a cutting tool can be improved.

<Definition of Aspect Ratio of Titanium Carbonitride (Third Layer)> First, the aspect ratio will be described. As shown in FIG. 1, the upper and lower positions corresponding to the thickness D of 70% of the film thickness A are determined based on the center line of the film thickness A of the columnar crystal TiCN in the fracture surface of the tool, and the horizontal direction at each position is determined. The upper-side particle size B and the lower-side particle size C are determined. And D / {(B + C) / 2}
Is the aspect ratio. The reason for specifying the aspect ratio is that if the aspect ratio of the crystal grains of titanium carbonitride having a columnar crystal structure in the vicinity of the ridgeline of the cutting edge of the hard alloy base material is 6 or more, the cutting performance is increased and it is desirable.

<Average Film Thickness of Titanium Carbonitride (Third Layer)> If the average thickness of titanium carbonitride is 2.0 μm or less, excellent abrasion resistance cannot be exhibited. The average film thickness of the third layer was set to 2.0 to 20 μm because the property deteriorated.

<Formation of Fourth Layer> The outer layer of the third layer is made of a titanium compound with a chemical formula of Ti (Cw'Nx'Oy'Bz ') {w' + x '+ y' + z'≤1,0.
≤w ', x', y ', z'≤1}, cutting tool with improved wear resistance by coating at least one kind of single layer or multilayer film selected from aluminum oxide, zirconium oxide, hafnium oxide Is preferred. If the average thickness of the entire hard coating at that time is 2.0 to 30 μm, the balance between wear resistance and crater resistance is improved, and excellent performance can be exhibited over a long period of time.

<Substrate Material> If the substrate is a cemented carbide or cermet, excellent performance can be exhibited. As the cemented carbide, those composed of a hard phase mainly composed of WC and a binder phase mainly composed of Co are generally used. The cermet and the like TiC group, Cr ₃ C ₂ group, Al ₂ O ₃ group cermet.

<Substrate Surface Roughness> The surface roughness of the coated cutting tool near the ridge of the cutting edge of the substrate is 0.2 to 1.3 μm in Rmax with respect to a reference length of 5 μm measured from the cross section of the substrate.
If so, the cutting performance further increases, which is desirable.

<Surface Roughness of Hard Coating> The surface roughness of the hard coating film of the coated cutting tool near the edge of the cutting edge is substantially composed of a smooth surface having a Rmax of 0.2 μm or less from the cross section of the base material. This is because the cutting performance is further improved if it is performed.

<Production Method> The hard alloy substrate in the cutting tool of the present invention can be produced by a known sintering method. The hard coating can be formed by a chemical vapor deposition method (CVD method). Thermal CVD, plasma CVD,
An optical CVD method and the like can be mentioned. The first layer, the third layer, and the fourth layer may be formed by these CVD methods under known conditions. The control of the film thickness is adjusted by the film forming time. The titanium carbonitride (second layer) having a flat upper portion and a mixed crystal structure of columnar crystals and granular crystals is preferably formed by a thermal CVD method under the following conditions.

Reaction gas composition (% by volume) TiCl ₄ : 0.4 to 4.0% CH ₃ CN: 0.1 to 2.0% CO: 1.0 to 3.0% N ₂ : 3.0 to 35% CH ₄ : 0.1 to 0.5% HCl: 0.1 to 0.5 % Ar: 0.5~10% H _2: remainder atmosphere temperature: eight hundred and twenty to eight hundred eighty ° C. ambient pressure: 53~267hPa (40~200torr)

[0041]

Embodiments of the present invention will be described below. (Test Example 1) The raw material powder shown in Table 1 was used as a hard alloy base material, and the mixture was blended in the composition shown in Table 1, and the mixture was mixed with a ball mill.
After wet mixing for 2 hours and drying, the mixture was press-molded into a compact having a breaker shape in the form of ISO • CNMG120408, and sintered in a vacuum atmosphere under the conditions shown in Table 1 to produce a substrate. After that, the surface of the base material is subjected to flat polishing and cutting edge honing, and the surface roughness of the base material is adjusted by brush polishing to the values shown in Tables 4 and 5, and then, using a chemical vapor deposition device (thermal CVD), Table 2, Three
A hard coating was formed under the conditions shown in Table 4 to obtain coated cutting tools shown in Tables 4, 5, and 6. The hard coating of Table 4 has a three-layer structure of first to third layers, and the hard coatings of Tables 5 and 6 have a laminated structure of first to fourth layers, and the fourth layer is a single layer or It has multiple layers. "Total average film thickness" in Tables 4 and 6 refers to the thickness of the entire hard coating.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

[Table 5]

[0047]

[Table 6]

Next, the titanium carbonitride layer in the obtained coated cutting tool was subjected to SIMS (Secondary Ion Mass Spectros
Copy) was used for line analysis, and the maximum atm% of the contained oxygen was calculated. As for the structure of the titanium carbonitride, a mixed crystal structure of granular crystals and columnar crystals was confirmed on the film fracture surface of the coated cutting tool using a transmission electron microscope. The aspect ratio is
As shown in FIG. 1, it was determined by D / {(B + C) / 2}. The surface roughness of the substrate was determined by Rmax with respect to a reference length of 5 μm in a cross section near the edge of the cutting edge.

With respect to the various coated cutting tools obtained from the results, abrasion resistance test was performed under the following conditions 1 to determine the flank wear amount, and peel resistance test was performed under the following conditions 2
A cutting test was performed to determine the time until a defect. The results are shown in Tables 4 and 6.

(Condition 1) Work material: SCM435 round bar Cutting speed: 150m / min Feed: 0.3mm / rev Depth of cut: 1.8mm Cutting time: 40min Cutting oil: not used

(Condition 2) Work material: SCM415 Grooved round bar Cutting speed: 400 m / min Feed: 0.3 mm / rev Cutting depth: 1.5 mm Cutting oil: not used

As is evident from Tables 4 and 6, it is clear that when the machining is performed using the coated cutting tool of the present invention, it has not only excellent wear resistance but also excellent peeling resistance. Was.

(Test Example 2) Among the coated cutting tools with a chip breaker obtained in Test Example 1 above, the hard coating near the ridge of the cutting edge was wrapped with diamond powder having an average particle size of 4 μm for the invention products 1 to 21. The surface roughness of the hard coating was adjusted. The surface roughness was measured by observing the cross section of the hard coating and measuring the surface roughness Rmax with respect to the reference length of 5 μm. Then, a cutting test was performed under the above two cutting conditions by adjusting the hard coating having a surface roughness of 0.2 μm or less and the hard coating having a surface roughness of more than 0.2 μm.

As a result, it was confirmed that the wear width of the flank was reduced by about 20% under the cutting condition 1, and the life was extended by 20 to 40% under the cutting condition 2, and the performance was improved.

[0055]

As described in detail above, according to the method for producing a coated cutting tool of the present invention, the titanium carbonitride oxide layer has a mixed crystal structure of granular crystals and columnar crystals, and the concentration of oxygen contained in the mixed crystal has a specific range. This makes it possible to produce titanium carbonitride having a smooth surface. As a result, in the coated cutting tool of the present invention, the on-column crystals of the titanium carbonitride layer grow more directly, rather than in a tapered shape, and the grain boundary strength increases, making it difficult to crack.
Excellent peel resistance can be provided without deteriorating wear resistance.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a method of calculating an aspect ratio.

[Explanation of symbols]

 1 grain

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideki Moriguchi 1-1-1, Koyo-Kita, Itami-shi, Itami-shi, Hyogo Sumitomo Electric Industries, Ltd. Itami Works (72) Inventor Kazuhiro Watanabe 776, Naie, Naie-cho, Sorachi-gun, Hokkaido F-term (reference) in Hokkaido Sumiden Seimitsu Co., Ltd.

Claims (10)

[Claims] 1. A coated cutting tool comprising a hard alloy substrate and a hard coating formed on the surface thereof, wherein the hard coating has the following configuration. Formed on the surface of the base material, titanium nitride, titanium carbide,
A first layer comprising a single layer or a plurality of layers of titanium carbonate, titanium oxynitride, titanium carbonitride, and titanium boronitride. A titanium oxycarbonitride formed directly above the first layer and having a mixed crystal structure of granular crystals and columnar crystals. The oxygen concentration in the film satisfies 0.1% to 15% at the maximum of atomic%, and the average film A second layer having a thickness of 0.2 to 2.0 μm. A third layer made of titanium carbonitride having a columnar crystal structure and formed immediately above the second layer. 2. The coated cutting tool according to claim 1, wherein the film crystal structure of the first layer has a granular crystal structure. 3. An average film thickness of the second layer is 0.3 μm to 1.5 μm.
3. The coated cutting tool according to claim 1, wherein the oxygen content concentration satisfies 1% to 6% at a maximum value of atomic%. 4. The coated cutting tool according to claim 1, wherein crystal grains of the third layer in the vicinity of the edge line of the base material have an aspect ratio of 6 or more. 5. The coated cutting tool according to claim 1, wherein the average thickness of the third layer satisfies 2 to 20 μm. 6. The hard coating comprises a fourth layer composed of a single layer or a plurality of layers formed above the third layer, wherein the fourth layer is made of a titanium compound and has a chemical formula of Ti (Cw'Nx'Oy). 'B
z ') It is composed of at least one selected from {w' + x '+ y' + z '= 1,0≤w', x ', y', z'≤1}, aluminum oxide, zirconium oxide and hafnium oxide, and is hard. The coated cutting tool according to any one of claims 1 to 5, wherein the entire coating has an average thickness of 2.5 to 30 µm. 7. The coated cutting tool according to claim 1, wherein the substrate is a cemented carbide or a cermet. 8. The surface roughness of the base near the ridge of the cutting edge is 0.2 to 1.3 μm in Rmax with respect to a reference length of 5 μm measured by a method of observing from the cross section of the base. A coated cutting tool according to any one of claims 1 to 7. 9. The hard coating film according to claim 1, wherein the vicinity of the ridge of the cutting edge is substantially constituted by a smooth surface having a surface roughness Rmax of 0.2 μm or less with respect to a reference length of 5 μm. 1-8
A coated cutting tool according to any one of the above. 10. A coating comprising at least one of titanium nitride, titanium carbide, titanium carbonate, titanium oxynitride, titanium carbonitride, and titanium boronitride having a granular crystal structure on the surface of a hard alloy substrate by a chemical vapor deposition method. A step of forming a titanium carbonitride layer having a mixed crystal structure of granular crystals and columnar crystals by causing a reaction in which granular crystals and columnar crystals of titanium carbonitride are simultaneously precipitated by a chemical vapor deposition method, Forming a titanium carbonitride layer having a columnar crystal structure by a chemical vapor deposition method.