WO2021193445A1

WO2021193445A1 - Surface-coated cutting tool

Info

Publication number: WO2021193445A1
Application number: PCT/JP2021/011434
Authority: WO
Inventors: 和宏引田; 英彰高島
Original assignee: 三菱マテリアル株式会社
Priority date: 2020-03-25
Filing date: 2021-03-19
Publication date: 2021-09-30
Also published as: JPWO2021193445A1

Abstract

A surface-coated cutting tool comprising a tool body and a coating layer on the tool body, wherein: the average thickness of the coating layer is 0.5-5.0 µm; the coating layer has a Ti-boride composite layer; and the Ti-boride composite layer has a crystalline phase and an amorphous phase, and has an average composition such that when expressed by the compositional formula TiBx, the atomic ratio x satisfies 1.5≤x≤3.0.

Description

Surface coating cutting tool

The present invention relates to a surface-coated cutting tool (hereinafter, may be referred to as a coated tool). This application claims priority based on Japanese Patent Application No. 2020-55010, which is a Japanese patent application filed on March 25, 2020. All the contents of the Japanese patent application are incorporated herein by reference.

Conventionally, a coated tool is known in which a cemented carbide or the like is used as a tool substrate and a coating layer is formed on the surface of the tool substrate by a vapor deposition method. Although this covering tool has wear resistance, various proposals have been made to further improve the wear resistance, and a coating layer containing boron has also been proposed.

For example, Patent Document 1 has a Ti borodate layer having an average layer thickness of 0.5 to 5 μm on the surface of a tool substrate, and the layer is configured as a composite structure of crystal grain structures having a plurality of average particle sizes. The composite structure has an average particle size of 300, which is composed of an aggregate of primary crystal grains having an average particle size of 10 to 15 nm and a secondary crystal grain having an average particle size of 20 to 70 nm, and an aggregate of the secondary crystal grains. A coating tool composed of tertiary crystal grains having a diameter of about 600 nm has been proposed. It is said that this coating tool can suppress the peeling of the soft coating layer due to welding in high-speed cutting of soft difficult-to-cut materials.

Further, for example, in Patent Document 2, the chemical bond between the element M (M is one or more elements selected from Ti, W, Zr, Hf, V, Nb, Ta, Mo, and Cr) and B. A coating tool having a boride phase, which is a region containing, and a carbide phase, which is a region containing a chemical bond between the elements M and C, has been proposed. It is said that this covering tool has better wear resistance than a covering tool having only _{TiB 2 as a coating layer.}

Japanese Unexamined Patent Publication No. 2012-139795 Japanese Unexamined Patent Publication No. 2017-166055

The high performance and automation of cutting equipment is remarkable, while cutting of materials called difficult-to-cut materials is required. For example, high-speed intermittent cutting of materials that are prone to welding during cutting, such as Ti-based alloys and austenitic stainless steel, is no exception.

The present invention has been made in view of the above circumstances and proposals, and in particular, excellent crack resistance and wear resistance can be used for a long period of time even when subjected to high-speed intermittent cutting of Ti-based alloys and austenitic stainless steels. The purpose is to provide a covering tool that can be used for a long time.

Here, the high-speed intermittent cutting process for Ti-based alloy refers to a process in which the cutting edge of a cutting tool repeats cutting and idling at a cutting speed faster than 70 m / min, and the high-speed intermittent cutting process for austenite stainless steel is 100 m / min. A process in which the cutting edge of a cutting tool repeats cutting and idling at a cutting speed faster than min.

The surface-coated cutting tool according to the embodiment of the present invention has a tool substrate and a coating layer on the tool substrate.
The average layer thickness of the coating layer is 0.5 to 5.0 μm.
The coating layer has a Ti boride layer and
The Ti boronized layer has an average composition in which the atomic ratio x satisfies 1.5 ≦ x ≦ 3.0 when the composition is represented by the composition formula: TiB _{x, and further, a crystal having a hexagonal structure.} It has a crystalline phase and an amorphous phase formed by grains.

Further, the surface coating cutting tool according to the embodiment may satisfy one or more of the following items (1) to (3).

(1) The hexagonal crystal grains constituting the crystal phase have an average particle size of 2 to 30 nm, and the area ratio to the Ti boride layer is 50 to 95 area%.

(2) The nano-intention hardness of the Ti boride layer is 30 to 50 GPa.

(3) With respect to the hexagonal structure crystal grains constituting the crystal phase of the Ti borochrome layer, the peak intensities of the 001 diffraction line, the 100 diffraction line, and the 101 diffraction line in the X-ray diffraction are set to Ih (001), respectively. When Ih (100) and Ih (101) are set, 0.01 ≦ Ih (001) / {Ih (001) + Ih (100) + Ih (101)} ≦ 0.80 shall be satisfied.

According to the above, excellent crack resistance and wear resistance are exhibited over a long period of time, even when subjected to high-speed intermittent cutting of Ti-based alloys and austenitic stainless steels.

The present inventor has recognized the following matters regarding the covering tools described in Patent Documents 1 and 2.

(1) The covering tool described in Patent Document 1 enables high-speed cutting of soft difficult-to-cut materials such as Al-based alloys. However, in particular, sufficient consideration has not been given to high-speed intermittent cutting of materials such as Ti-based alloys and austenitic stainless steel, which are prone to welding during cutting.

(2) The covering tool described in Patent Document 2 suppresses the occurrence of welding during cutting of hard-to-cut materials such as Ti-based alloys and high-Si-containing Al—Si alloys, and has peeling resistance and abrasion resistance. However, further improvement in wear resistance is required.

Based on the above recognition, the present inventor diligently studied the Ti boride layer as a coating layer. As a result, we obtained a new finding that the wear resistance is improved when the Ti boride layer of the coating layer has a crystalline phase and an amorphous phase.

Hereinafter, the surface coating cutting tool according to the embodiment of the present invention will be described. When the numerical range is expressed as "A to B" (both A and B are numerical values) in the present specification and the claims, the range includes the numerical values of the upper limit (B) and the lower limit (A). The unit of the upper limit (B) and the lower limit (A) is the same. In addition, the numerical values include tolerances.

Average thickness of coating layer:
The coating layer has a Ti boride layer, and the average layer thickness thereof is preferably 0.5 to 5.0 μm. The reason is that if the average layer thickness is less than 0.5 μm, it is difficult to exhibit wear resistance for a long period of time, while if it exceeds 5.0 μm, chipping is likely to occur. A more preferable range of the average layer thickness is 1.0 to 2.5 μm.

Here, the average layer thickness of the coating layer is measured as follows. For example, using a focused ion beam device (FIB: Focused Ion Beam system), a cross section polisher device (CP: Cross section Policeher), or the like, the coating layer is placed in a vertical cross section at an arbitrary position (ignoring minute irregularities on the surface of the tool substrate). Then, when the surface of the tool substrate is treated as a flat surface, it is cut at a cross section in the direction perpendicular to this surface) to prepare a sample for observation. The vertical cross section can be obtained by observing a plurality of locations (for example, 5 locations) with a scanning electron microscope (SEM) and arithmetically averaging the obtained layer thickness.

Average composition of Ti boride layer:
The Ti boride layer preferably has an average composition in which the atomic ratio x satisfies 1.5 ≦ x ≦ 3.0 when the composition is represented by the composition formula: TiB _x. The reason is that when x is less than 1.5, adhesion wear is likely to proceed at the contact portion between the Ti boride layer and the work material such as Ti-based alloy, while when it exceeds 3.0, Ti boride is likely to proceed. This is because the crystal structure of the above is disturbed and the hardness is reduced. A more preferable range of x is 1.8 to 2.2.

The boron content is measured as follows.
Using an electron probe microanalyzer (EPMA), electron beams are applied to the surface of the coating layer or five points in the longitudinal section at an arbitrary position of the coating layer. The content of each element is quantified by analyzing the characteristic X-rays corresponding to the elements constituting the coating layer obtained from each location, and the results are arithmetically averaged.

Crystalline and amorphous phase of Ti boride layer:
The Ti boride layer preferably has a crystalline phase and an amorphous phase. The preferred reason is not clear, but the presence of the amorphous phase causes boron oxide to be generated on the scraped surface between the Ti boride layer and the Ti-based alloy as the work material during cutting. As a result, it is presumed that solid lubricity is imparted to the Ti boride layer and the wear resistance of the Ti boride layer is improved.

Further, the hexagonal crystal grains (hexagonal crystals) constituting the crystal phase are preferably microcrystal grains, and the average particle size is more preferably in the range of 2 to 30 nm. The reason is considered as follows. Since the fracture unit of the coating layer due to welding is a crystal unit, the fracture unit becomes smaller if it is a microcrystal, that is, if the crystal grain is small. As a result, wear of the Ti boride layer accompanied by fracture is suppressed, and the wear resistance of the same layer is improved.

The average particle size of the crystal grains constituting the crystal phase is obtained as follows. That is, the grain boundary is defined by performing an analysis using automatic crystal orientation mapping (ACOM: Automatic Crystal Orientation Mapping) -TEM by a transmission electron microscope (TEM: Transmission Electron Microscope). After that, the range closed by the grain boundary is defined as a crystal grain, and the maximum length of the crystal grain is defined as the particle size. For each of the five arbitrary crystal grains, determine the particle size, and use the arithmetic mean as the average particle size.

Here, the crystalline phase and the amorphous phase are distinguished from each other as follows. That is, a vertical cross section is observed using a TEM, and an image having a magnification such that a size of, for example, several nm can be identified on the observation surface is obtained. Then, FFT image conversion processing is performed on this image, and bright points corresponding to the lattice constants (for example, each bright point (including a circular shape) corresponding to the (001) plane of the hexagonal structure) are selected. Further, the inverse FFT conversion process is performed, and then the binarization process is performed. By this process, it is possible to emphasize the crystal structure of the lattice fringes / angles having the lattice constant selected as each bright point. The same processing is performed for each lattice constant to create an emphasized image corresponding to each lattice constant such as (001) surface-enhanced image and (100) surface-enhanced image. Then, each emphasized image is combined by performing OR combination for each of the above-mentioned emphasized images.

After that, by performing the expansion processing of the binarized image so that the grid spacing with the maximum grid constant is filled, an image in which the grid spacing with at least the maximum grid width is densely filled can be obtained. At this time, the filled portion is the crystalline phase, and the unfilled portion is the amorphous phase. The magnification is not particularly limited as long as the above lattice constant can be observed.

In addition, in two or more images different from the OR combination, it is a process of obtaining the logical sum of the pixels at the same position in all the pixels on the image and obtaining the image. Specifically, in a specific pixel, if any one image is a bright point, it is set as a bright point, and if it is a dark point in all images, that pixel is set as a dark point.

Using the above-mentioned method for distinguishing between the crystalline phase and the amorphous phase, the crystalline phase and the amorphous phase are discriminated from each of the five fields of view. In this way, the area ratio of the crystal phase in each field of view is obtained, and the arithmetic mean thereof is taken as the area ratio of the crystal phase. The area ratio of the crystal phase is more preferably 50 to 95 area%. The reason is as follows.

If the area ratio of the crystal phase is less than 50 area%, the hardness may decrease due to the small number of crystal phases in the Ti boride layer, and the performance as a coating layer may not be exhibited. On the other hand, when the area ratio of the crystal phase exceeds 95 area%, the abrasion resistance is lowered and the grain boundary fracture becomes dominant, and the crystal grains fall off at the grain boundary, resulting in inferior cutting performance. Sometimes. Here, it is considered that the reason why the wear resistance is lowered is that it becomes difficult for the Ti boride layer to form boron oxide during cutting.

Nano-intention hardness of Ti boride layer:
The Ti boride layer preferably has a nanointention hardness of 30 to 50 GPa. If the nano-intention hardness is within this range, the chipping resistance and wear resistance will be further improved. It is presumed that the reason is that when the nanointention hardness is in this range, the wear resistance is surely improved by having the Ti boride layer having a crystalline phase and an amorphous phase.

Here, regarding the nanoindentation hardness, the surface of the Ti boride layer is polished based on the nanoindentation test method (ISO14577), and a diamond Berkovich indenter is used, and the pushing load is 1.96 × 10 ^-3. It is carried out at N (200 mgf). In that case, the measurement is performed on at least 10 arbitrary points, and the arithmetic mean thereof is used as the measured value of hardness. In this measurement, the distance between the measurement points is 20 times or more the indentation depth at the time of the test.

Crystal orientation of the crystal phase of the Ti boride layer:
The hexagonal 011 diffraction line, 100 diffraction line, and 101 diffraction line by the X-ray diffraction method are measured as diffraction peaks by the (001) plane, the (100) plane, and the (101) plane, respectively. When the peak intensities are Ih (001), Ih (100), and Ih (101), respectively, 0.01 ≦ Ih (001) / {Ih (001) + Ih (100) + Ih (101)} ≦ It is more preferable to satisfy 0.80. When this relational expression is satisfied, the wear resistance is further improved.

Here, the measurement of the diffraction peak intensities of the (001) plane, the (100) plane, and the (101) plane of the hexagonal crystal is performed by 2θ / θ concentrated optics using Cu—Kα rays (wavelength λ: 0.15405 nm). The X-ray diffraction method of the system can be used.

The (001) plane of the hexagonal crystal may be expressed as the (0001) plane. Similarly, the (100) plane is the (10-10) plane, the (1-100) plane, the (01-10) plane, the (-1100) plane, the (-1010) plane, and the (0-110) plane. Will be done. Similarly, the (101) plane includes the (10-11) plane, the (1-101) plane, the (01-11) plane, the (-1101) plane, the (-1011) plane, and the (0-111) plane. May be represented. These are surface indices that are in an equivalent relationship with each other.

Other layers (lower layer):
In the present embodiment, in addition to the coating layer, it is composed of one or more layers of a carbide layer, a nitride layer, a nitride layer, a coal oxide layer and a carbonitride oxide layer of Ti, and is composed of 0.1. When a lower layer including a Ti compound (not limited to stoichiometric compound) layer having a total average layer thickness of ~ 2.0 μm is provided adjacent to the tool substrate, the effect of this layer is combined. Therefore, it is possible to exhibit even more excellent chipping resistance and heat-resistant crack resistance.

Here, if the total average layer thickness of the lower layer is less than 0.1 μm, the effect of the lower layer is not sufficiently exhibited, while if it exceeds 2.0 μm, the crystal grains of the lower layer tend to be coarsened and chipping occurs. It will be easier to do.

Tool base:
(1) Material As the tool base, any base material conventionally known as this type of tool base can be used as long as it does not hinder the achievement of the above-mentioned object. For example, cemented carbide (WC-based cemented carbide, WC, as well as those containing Co, or those containing carbides such as Ti, Ta, Nb), cermet (TiC). , TiN, TiCN, etc. as the main component), ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), or cBN sintered body is assumed, and any of these is preferable. ..

(2) Shape The shape of the tool base is not particularly limited as long as it is a shape used as a cutting tool, and the shape of the insert and the shape of the end mill can be exemplified.

Next, examples will be described, but the present invention is not limited to these examples.

As raw material powders, WC powder, VC powder, TaC powder, NbC powder, Cr ₃ C ₂ powder, and Co powder having an average particle size of 1 to 3 μm were prepared. These raw material powders were blended into the blending composition shown in Table 1, wet-mixed with a ball mill for 72 hours, and dried. Then, it was press-molded into a green compact at a pressure of 100 MPa. This green compact was sintered in a vacuum of 6 Pa under the condition of holding at a temperature of 1400 ° C. for 1 hour. After sintering, the cutting edge portion was subjected to a honing process of R: 0.03 to prepare tool bases 1 and 2 made of WC-based cemented carbide having an insert shape of ISO standard CNMG120408.

Further, the same raw material powder as described above was blended into the blending composition shown in Table 1. The mixture was wet-mixed with a ball mill for 72 hours, dried, and then press-molded into a green compact at a pressure of 100 MPa. This green compact was sintered in a vacuum of 6 Pa at a temperature of 1400 ° C. for 1 hour to prepare a round bar sintered body for forming a cemented carbide substrate having a diameter of 4 mm. Furthermore, a tool made of WC-based cemented carbide having a 4-flute square shape with a cutting edge diameter x length of 2 mm x 4 mm and a twist angle of 40 degrees by grinding from the above-mentioned round bar sintered body. Substrate (end mill shape) 3 to 4 were manufactured.

Subsequently, these tool bases 1 to 4 were formed into a lower layer (provided only for some tool bases) and a coating layer by the following procedures (a) to (d).

(A) Each of the tool substrates 1 to 4 is ultrasonically cleaned in acetone, and in a dry state, the outer circumference is located at a position radially separated from the central axis on the rotary table in the high-power pulse sputtering apparatus. It was attached along the part. On the other hand, in the high-power pulse sputtering apparatus, a Ti target and a Ti and boron sintered body target were arranged at four locations facing each other across the rotary table.

(B) The inside of the device was heated to 500 ° C. with a heater while the inside of the device was exhausted and kept in a vacuum of 0.1 Pa or less. Then, a DC bias voltage of −200 V was applied to the tool substrate that revolves while rotating on the rotary table. Then, argon (hereinafter referred to as Ar) gas was introduced into the apparatus as a reaction gas to create an atmosphere of 2.0 Pa. Further, Ar ions were excited by passing a current of 40 A through the tungsten filament provided in the apparatus, and the tool substrate was subjected to Ar bombard treatment for 1 hour.

(C) Ar gas and nitrogen gas are introduced into the apparatus as reaction gases to create a reaction atmosphere of 0.6 Pa, and high-power pulse sputtering is performed on the Ti target under the predetermined pulse sputtering conditions shown in Table 2. rice field. As a result, a TiN layer having an average layer thickness shown in Table 3 was formed on the surface of the tool substrate as a lower layer of the coating layer. However, not all tool substrates have a lower layer.

(D) Subsequently, of the gases introduced into the device, the nitrogen gas was closed and switched to Ar gas, the atmosphere inside the device was set to 0.5 Pa, the nitrogen gas was sufficiently discharged, and the atmosphere inside the device was only Ar gas. bottom. After that, high-power pulse sputtering was performed on the sintered target composed of Ti and boron under the predetermined pulse sputtering conditions shown in Table 2 for a time corresponding to the layer thickness, and the coated inserts 1 to 13 shown in Table 3 were subjected to. Examples coated end mills 14 to 26 (hereinafter, collectively referred to as Examples 1 to 26) were manufactured.

Further, for the purpose of comparison, the lower layer and the covering layer are formed on the tool substrates 1 to 4 according to the procedures (a) to (d) above under the conditions shown in Table 4, and the comparative covering tools shown in Table 5 are formed. Comparative coated inserts 1 to 7 and comparative coated end mills 11 to 17 (8 to 10 are missing numbers, hereinafter collectively referred to as Comparative Examples 1 to 7 and 11 to 17) were manufactured. However, not all tool substrates have a lower layer.

In Table 1, "-" indicates that it is not contained.

In Table 2, when the examples are a and b and the tool base symbols ^* are α and β, the tool base α is used in Example a and the tool base β is used in Example b (a, b, α and β are numbers). ), And "-" indicates that the corresponding processing has not been performed.

In Table 3, when the examples are a and b and the tool base symbols ^* are α and β, the tool base α is used in Example a and the tool base β is used in Example b (a, b, α and β are numbers). ), And the intensity ratio ^** is the value of Ih {001} / {Ih {001} + Ih {100} + Ih {101}}, and "-" indicates that it does not exist.

In Table 4, when the comparative examples are a and b and the tool base symbols ^* are α and β, the tool base α is used for the comparative example a and the tool base β is used for the comparative example b (a, b, α and β are numbers). ), And "-" indicates that the corresponding processing has not been performed.

In Table 5, when the comparative examples are a and b and the tool base symbols ^* are α and β, the tool base α is used for the comparative example a and the tool base β is used for the comparative example b (a, b, α and β are numbers). ), And the intensity ratio ^** is the value of Ih {001} / {Ih {001} + Ih {100} + Ih {101}}, and "-" indicates that it does not exist.

Next, the following cutting tests 1 and 2 were performed on Examples 1 to 26 and Comparative Examples 1 to 17, and the results are shown in Tables 6 and 7.

In both Examples 1 to 13 and Comparative Examples 1 to 7, a dry high-speed intermittent cutting test (cutting test 1) is performed under the following conditions in a state where the tip of the tool steel cutting tool is screwed with a fixing jig. Was carried out.

Cutting test 1
Work material: JIS / SUS316L, round bar with 4 vertical grooves at equal intervals in the length direction Cutting speed: 180 m / min
Notch: 2 mm
Feed: 0.2 mm / rev
Cutting time: 10 minutes

After the cutting test was completed, the flank wear width was measured and the presence or absence of chipping was observed. However, if chipping occurred before the cutting time expired, cutting was stopped and the time from the start of cutting was measured.
Table 6 shows the test results.

In Table 6, the cutting time (minutes) to reach the life of the comparative example indicates the cutting time (minutes) to reach the life due to the occurrence of chipping.

Next, with respect to Examples 14 to 26 and Comparative Examples 11 to 17, a wet high-speed intermittent cutting test (cutting test 2) was carried out in side surface machining with an end mill under the following conditions.

Cutting test 2
Work material: Ti-based alloy (mass%, Ti-6% Al-4% V alloy) block material (width 100 mm x length 250 mm)
Cutting speed: 130m / min
Rotation speed: 20690min ^-1
Notch: 2.0 mm
Feed: 0.05 mm / rev
End mill blade outer diameter: 2 mm

The cutting length was cut to 150 m (cutting time was about 144 minutes), the flank wear width was measured, and the presence or absence of chipping was observed. However, if chipping occurred before the cutting length reached 150 m, the cutting was stopped and the time from the start of cutting was measured.
Table 7 shows the test results.

In Table 7, the cutting time (minutes) to reach the life of the comparative example indicates the cutting time (minutes) to reach the life due to the occurrence of chipping.

From the results shown in Tables 6 to 7, the examples in which the coating layer using the Ti borocarbonate layer has a crystalline phase and an amorphous phase are welded to various Ti-based alloys and coating tools such as austenite stainless steel. Demonstrates excellent welding resistance and abrasion resistance in high-speed intermittent cutting of highly resistant materials.
On the other hand, in the comparative example, it is clear that the cutting edge portion wears quickly in the high-speed intermittent cutting of the highly weldable material, and the service life is reached in a relatively short time.

The disclosed embodiment is merely an example in all respects and is not restrictive. The scope of the present invention is indicated by the scope of claims rather than the embodiment described above, and is intended to include meaning equivalent to the scope of claims and all modifications within the scope.

Claims

A surface-coated cutting tool having a tool substrate and a coating layer on the tool substrate.
The average layer thickness of the coating layer is 0.5 to 5.0 μm.
The coating layer has a Ti boride layer and
The Ti boronized layer has an average composition in which the atomic ratio x satisfies 1.5 ≦ x ≦ 3.0 when the composition is represented by the composition formula: TiB x, and further, a crystal having a hexagonal structure. It has a crystalline phase and an amorphous phase formed by grains.
A surface coating cutting tool characterized by that.
The first aspect of claim 1 is that the hexagonal crystal grains constituting the crystal phase have an average particle size of 2 to 30 nm and an area ratio of 50 to 95 area% in the Ti boride layer. Described surface coating cutting tools.
The surface coating cutting tool according to claim 1 or 2, wherein the nano-intention hardness of the Ti boride layer is 30 to 50 GPa.
Regarding the crystal grains having a hexagonal structure constituting the crystal phase of the Ti boronized layer, the peak intensities of the 001 diffraction line, the 100 diffraction line, and the 101 diffraction line in the X-ray diffraction are set to Ih (001) and Ih (100), respectively. ), Ih (101), claims 1 to 3 satisfying 0.01 ≦ Ih (001) / {Ih (001) + Ih (100) + Ih (101)} ≦ 0.80. The surface coating cutting tool described in any of.