JP6198137B2 - Surface coated cutting tool - Google Patents

Description

  The present invention relates to a surface-coated cutting tool (hereinafter referred to as a coated tool) that exhibits excellent wear resistance over a long period of time. With this coated tool, even when cutting various steels and cast irons at high speeds and under intermittent cutting conditions where intermittent and impact loads are applied to the cutting edge, the hard coating layer has excellent peeling resistance. And chipping resistance.

Conventionally, generally on the surface of a substrate (hereinafter collectively referred to as a tool substrate) composed of a tungsten carbide (hereinafter referred to as WC) -based cemented carbide or titanium carbonitride (hereinafter referred to as TiCN) -based cermet. ,
(A) The lower layer is a Ti carbide (hereinafter referred to as TiC) layer, a nitride (hereinafter also referred to as TiN) layer, a carbonitride (hereinafter referred to as TiCN) layer, a carbon oxide (hereinafter referred to as TiCO). And a Ti compound layer composed of one or more of a carbonitride oxide (hereinafter referred to as TiCNO) layer,
(B) an aluminum oxide layer (hereinafter, referred to as an Al ₂ O ₃ layer) having an α-type crystal structure in a state where the upper layer is chemically vapor-deposited;
A coated tool in which the hard coating layer constituted by (a) and (b) is formed by vapor deposition is known.

However, the conventional coated tool as described above exhibits excellent wear resistance in continuous cutting of, for example, various steels and cast irons. However, when this is used for high-speed interrupted cutting, There was a problem that peeling and chipping were likely to occur and the tool life was shortened.
Therefore, various types of coating tools have been proposed in which the lower layer and the upper layer are improved in order to suppress peeling and chipping of the coating layer.

For example, in Patent Literature 1, a TiCN layer and an Al ₂ O ₃ layer are sequentially laminated in a coating layer, and when observed in a 100 μm ² region, the TiCN layer has an average particle width of 3 to 6 μm. The particle size distribution is composed of TiCN particles having a standard deviation σ and a mean particle width of 0.3 times or less, and the Al ₂ O ₃ layer has 10-30 area% of Al ₂ O ₃ giant particles having a particle size of _{3 to 6} μm. In addition, it is disclosed that excellent chipping resistance and chipping resistance can be obtained when Al ₂ O ₃ fine particles having a particle diameter of 0.3 to 1.5 μm are composed of 70 to 90 area%.

Further, in Patent Document 2, the coating layer includes one or several refractory layers, and at least one layer is a dense microcrystalline α-type Al ₂ O textured in the (104) direction. It has been disclosed that the _three layers exhibit excellent surface finish and exhibit greatly improved wear and toughness characteristics.

Patent Document 3 discloses a surface-coated cutting tool formed by vapor-depositing a hard coating layer in which a lower layer is a Ti compound layer and an upper layer is an α-type Al ₂ O ₃ layer, and Al ₂ directly above the lower layer. 30-70% of the O ₃ crystal grains consist of (11-20) oriented Al ₂ O ₃ crystal grains, and 45% or more of the total Al ₂ O ₃ crystal grains in the upper layer consist of (0001) oriented Al ₂ O ₃ crystals. More preferably, the outermost surface layer of the lower layer comprises an oxygen-containing TiCN layer containing 0.5 to 3 atomic% of oxygen only over a depth region up to 500 nm, Since the value of the ratio between the number of oxygen-containing TiCN grains in the surface layer and the number of Al ₂ O ₃ grains at the interface between the lower layer and the upper layer is 0.01 to 0.5, the hard coating layer Excellent peeling resistance and chipping resistance in cutting and high-speed interrupted cutting Rukoto have been disclosed.

Further, in Patent Document 4, in a surface-coated cutting tool in which a lower layer made of a Ti compound layer and an upper layer made of an Al ₂ O ₃ layer are formed on the surface of a tool base, an Al ₂ O ₃ crystal of the upper layer is formed. For the grains, measure the tilt angle formed by the normal of the (0001) plane, and identify the crystal grains as different crystal grains when the angle difference between the measured tilt angles from adjacent measurement points is 5 degrees or more, When determining the aspect ratio of individual crystal grains, crystal grains having an aspect ratio of less than 5 account for 10 to 50% by area ratio, crystal grains having an aspect ratio of 5 or more occupy 50 to 90% by area ratio, Further, when the average orientation difference in crystal grains of each crystal grain is obtained, the average crystal grain orientation difference of crystal grains having an aspect ratio of less than 5 is less than 5 degrees, while the aspect ratio is 5 or more. The average average grain orientation difference of grains is 5 degrees or more By indicating the hard coating layer to exert has excellent chipping resistance is disclosed a high speed interrupted cutting.

JP 2012-144766 A JP-A-9-507528 JP 2013-63504 A JP 2013-111721 A

In recent years, the performance of cutting machines has been remarkably improved. On the other hand, there is a strong demand for labor saving and energy saving and further cost reduction for cutting. Along with this, cutting speed is further increased, and a high load tends to be applied to the cutting edge due to heavy cutting such as high cutting and high feed, and intermittent cutting. There is no problem when the above-described conventional coated tool is used for continuous cutting under normal conditions such as steel and cast iron. However, when a conventional coated tool is used under high-speed intermittent cutting conditions, the adhesion strength between the lower layer composed of the Ti compound layer and the upper layer composed of the Al ₂ O ₃ layer constituting the hard coating layer becomes insufficient. . Therefore, abnormal damage such as peeling and chipping between the upper layer and the lower layer occurs, and the tool life is reached in a relatively short time.

In view of the above, the present inventors have improved the adhesion between the lower layer made of the Ti compound layer and the upper layer made of the Al ₂ O ₃ layer from the viewpoints described above, and therefore, abnormal damage such as peeling and chipping has been improved. We conducted intensive research to prevent the occurrence and to increase the tool life. As a result, the following knowledge was obtained.
(1) In a coated tool in which a lower layer made of a Ti compound layer and an upper layer made of an Al ₂ O ₃ layer are coated, crack propagation in the film thickness direction is suppressed by atomizing the Al ₂ O _3. And found that the residual stress can be reduced. As a result, the peel resistance can be improved.
(2) Further, by atomizing the Al ₂ O _{3 in} the upper layer, the adhesion with the oxygen-containing TiCN layer formed between the lower layer and the upper layer is improved. As a result, the peel resistance is improved. I found it to improve.
(3) It has been found that by forming an intermediate layer comprising an oxygen-containing TiCN layer on the outermost surface of the lower layer, the C-axis orientation of the upper layer is increased, and the high temperature hardness and high temperature strength are improved.
(4) atomization of _Al 2 _{O 3} is, by increasing the HCl gas partial pressure during the formation of _Al 2 _{O 3,} occurs etched to induce new nucleation, resulting finely divided _Al 2 _{O 3} It was found that chemistry occurred.

  The present invention has been completed as a result of repeated research based on the aforementioned knowledge, and has the following characteristics.

“A surface-coated cutting tool comprising a tool base made of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet and a hard coating layer deposited on the surface of the tool base,
The hard coating layer has a lower layer formed on the surface of the tool base and an upper layer formed on the lower layer,
(A) The lower layer has a total average layer thickness of 3 to 20 μm, and is composed of two or more layers of TiC, TiN, TiCN, TiCO, and TiCNO, and at least one of them is composed of a TiCN layer. Consisting of a Ti compound layer,
(B) The outermost surface layer of the lower layer is a TiCN layer having a layer thickness of at least 500 nm or more, and the depth from the interface between the TiCN layer and the upper layer to a maximum thickness of 500 nm in the layer thickness direction of the TiCN layer. Oxygen is contained only in the region, and the average oxygen content contained in the depth region is 0.5 to 3 atoms of the total content of Ti, C, N, and O contained in the depth region. %
(C) The upper layer has an average layer thickness of 2 to 15 μm, and is composed of an Al ₂ O ₃ layer having an α-type crystal structure in the state of chemical vapor deposition. The individual crystals constituting the Al ₂ O ₃ layer When determining the aspect ratio of the grains, the crystal grains having the aspect ratio of less than 3 account for 60-90% of the entire upper layer in area ratio, and the average grain diameter of the grains having the aspect ratio of less than 3 is Included in the range of 0.1 to 1.0 μm,
(D) A crystal having a hexagonal crystal lattice existing in the measurement range of the cross-sectional polished surface of the Al ₂ O ₃ crystal grains of the entire upper layer using a field emission scanning electron microscope and an electron beam backscattering diffractometer When each particle is irradiated with an electron beam and the inclination angle formed by the normal of the (0001) plane, which is the crystal plane of the crystal grain, is measured with respect to the normal of the tool base surface, When the measured inclination angle within the range of 0 to 45 degrees is divided into pitches of 0.25 degrees, and the inclination angle number distribution graph is formed by counting the frequencies existing in each division, the inclination The sum of the frequencies existing in the tilt angle section of the Al ₂ O ₃ crystal grains having an angle in the range of 0 to 10 degrees is 60% or more of the entire frequencies in the tilt angle frequency distribution graph,
(E) Among the Al ₂ O ₃ crystal grains of the entire upper layer described in (c), the average orientation difference in crystal grains of crystal grains having an aspect ratio of less than 3 is less than 5 degrees. A surface-coated cutting tool. "

Here, the configuration of the present invention described above will be described in detail.
(A) Lower layer:
The Ti compound layer (eg, TiC layer, TiN layer, TiCN layer, TiCO layer and TiCNO layer) constituting the lower layer basically exists as a lower layer of the Al ₂ O ₃ layer, and has an excellent high temperature. Depending on the strength, the hard coating layer is given high temperature strength. In addition, the Ti compound layer is in close contact with both the tool base surface and the upper layer composed of the Al ₂ O ₃ layer, and has an effect of maintaining the adhesion of the hard coating layer to the tool base. However, when the total average layer thickness of the Ti compound layer is less than 3 μm, the above-described action cannot be sufficiently exhibited. On the other hand, when the total average layer thickness of the Ti compound layer exceeds 20 μm, high-speed heavy cutting and high-speed intermittent cutting accompanied by high heat generation are likely to cause thermoplastic deformation, which causes uneven wear. From the above, the total average layer thickness of the Ti compound layer was determined to be 3 to 20 μm.

(B) The outermost surface layer of the lower layer:
The outermost surface layer of the lower layer in the present invention is formed, for example, as follows.
That is, first, using a normal chemical vapor deposition apparatus, various Ti compound layers consisting of one or more of TiC layer, TiN layer, TiCN layer, TiCO layer and TiCNO layer are formed by vapor deposition (in addition, Of course, it is possible to form only the TiCN layer by vapor deposition). Then, using the same chemical vapor deposition equipment,
Reaction gas composition (volume%): TiCl ₄ 2 to 10%, CH ₃ CN 0.5 to 1.0%, N ₂ 25 to 60%, balance H ₂ ,
Reaction atmosphere temperature: 800 to 900 ° C.
Reaction atmosphere pressure: 6 to 10 kPa,
The TiCN containing oxygen (hereinafter referred to as oxygen-containing TiCN) layer is formed as the outermost surface layer of the lower layer by chemical vapor deposition under the conditions described above.
At this time, during 5 to 30 minutes before the end of the deposition time required to obtain the predetermined layer thickness, the chemical vapor deposition is performed by adding CO gas so as to be 1 to 5% by volume with respect to the total reaction gas amount. The average oxygen content of 0.5 to 3 atomic% of the total content of Ti, C, N, and O contained in the depth region only in the depth region up to a maximum of 500 nm in the layer thickness direction An oxygen-containing TiCN layer containing the oxygen is formed by vapor deposition.

The outermost surface layer of the lower layer composed of the oxygen-containing TiCN layer is formed as a layer thickness of at least 500 nm or more, for example, in order to form preferable Al ₂ O ₃ crystal grains thereon (see (c) below). Furthermore, the total content of Ti, C, N, and O contained in the depth region only from the interface between the oxygen-containing TiCN layer and the upper layer to a depth region up to 500 nm in the layer thickness direction. 0.5 to 3 atomic% of oxygen is contained, and oxygen is contained only in a depth region up to a maximum of 500 nm.
Here, the reason why the depth region of the oxygen-containing TiCN layer is limited as described above is that when oxygen is contained in a region deeper than 500 nm, the structure of the TiCN outermost surface changes from a columnar structure to a granular structure. This is because the inclination angle number distribution of the Al ₂ O ₃ crystal grains immediately above the outermost surface layer of the lower layer cannot be made desired.
However, if the average oxygen content up to a depth region of 500 nm is less than 0.5 atomic%, it is not only possible to improve the adhesion strength between the upper layer and the lower layer TiCN, but also Al ₂ directly above the outermost surface layer of the lower layer. The tilt angle number distribution of the O ₃ crystal grains cannot be satisfied. On the other hand, when the average oxygen content in this depth region exceeds 3 atomic%, in the upper layer Al ₂ O ₃ immediately above the interface, (0001) oriented Al ₂ O ₃ crystal grains (note that (0001) oriented Al ₂ O _The area ratio of the _three crystal grains will be described later.) Is less than 60% by area with respect to the total area of Al ₂ O _{3 in} the entire upper layer, and the high temperature strength of the upper layer is lowered.
Here, the average oxygen content is determined from titanium (Ti) and carbon in the depth region up to 500 nm in the thickness direction of the TiCN layer from the interface between the TiCN layer and the upper layer constituting the outermost surface layer of the lower layer. The oxygen (O) content in the total content of (C), nitrogen (N) and oxygen (O) is expressed in atomic% (= O / (Ti + C + N + O) × 100).

(C) Al ₂ O ₃ crystal grains in the upper layer:
After the oxygen-containing TiCN layer (b) is deposited on the outermost surface layer of the lower layer, the upper Al ₂ O ₃ layer is formed under the following conditions.
That is, the surface of the oxygen-containing TiCN layer formed in (b) is
Reaction gas composition (volume%): CO 3 to 10%, CO ₂ 3 to 10%, balance H ₂ ,
Atmospheric temperature: 950 to 1000 ° C.
Atmospheric pressure: 5-15 kPa,
After processing under conditions of processing time: 1-5 min,
<Al ₂ O ₃ initial growth>
Reaction gas composition (volume%): AlCl ₃ 1-3%, CO ₂ 1-5%, HCl 0.3-1.0%, balance H ₂
Atmospheric temperature: 950 to 1000 ° C.
Atmospheric pressure: 5-15 kPa,
Processing time: After vapor deposition under conditions of 5 to 30 min,
<Al ₂ O ₃ upper layer formation>
Reaction gas composition (volume%): AlCl ₃ 1.5-5.0%, CO ₂ 2-8%, HCl 3-8%, H ₂ S 0.5-1.0%, balance H ₂
Reaction atmosphere temperature: 950 to 1000 ° C.
Reaction atmosphere pressure: 5 to 15 kPa,
Processing time: (until the target upper layer thickness is reached)
Thus, an upper layer made of fine granular Al ₂ O ₃ crystal grains having a (0001) -oriented α-type crystal structure having a predetermined tilt angle number distribution is formed. At this time, by setting the HCl gas partial pressure relatively high compared to other reaction gases when forming the Al ₂ O ₃ upper layer, the crystal grain surface is etched to form secondary nuclei during film formation. By inducing, the crystal grains constituting the Al ₂ O ₃ layer are miniaturized.
If the thickness of the entire upper layer is less than 2 μm, excellent high-temperature strength and high-temperature hardness cannot be exhibited over a long period of use, while if it exceeds 15 μm, chipping tends to occur. Therefore, the layer thickness of the upper layer was determined to be 2 to 15 μm.
Further, when the fine granular Al ₂ O ₃ crystal grains having an α-type crystal structure constituting the upper layer were analyzed in detail, the degree of granularity was such that crystal grains having an aspect ratio of less than 3 were found throughout the upper layer. On the other hand, the area ratio is preferably 60 to 90%, and the degree of refinement is preferably in the range of 0.1 to 1.0 μm in average particle size.
The reason is that when the area ratio is less than 3 and the area ratio is less than 60% of the entire upper layer, the proportion of crystal grains having an aspect ratio of 3 or more is relatively increased, and the effect of suppressing crack propagation is reduced. Therefore, it is not preferable. On the other hand, when the area ratio is less than 3 and the area ratio exceeds 90% of the entire upper layer, the ratio of (0001) oriented Al ₂ O ₃ crystal grains decreases, resulting in a decrease in high-temperature strength and high-temperature hardness. Therefore, it is not preferable. Therefore, the crystal grain having an aspect ratio of less than 3 is determined to be 60 to 90% by area ratio with respect to the entire upper layer. Further, if the average grain size of the crystal grains having an aspect ratio of less than 3 is less than 0.1 μm, it is impossible to ensure wear resistance over a long period of use, while if the average grain size exceeds 1.0 μm, The effect of suppressing crack propagation is reduced by coarsening. Therefore, the grain size of the crystal grains having an aspect ratio of less than 3 is determined to be 0.1 to 1.0 μm. Note that the grain size of the crystal grains can be controlled by adjusting the deposition conditions.

(D) Tilt angle number distribution of (0001) plane-oriented Al ₂ O ₃ crystal grains in the upper layer:
The inclination angle (see FIG. 2) formed by the normal of the (0001) plane, which is the crystal plane of the Al ₂ O ₃ crystal grains having the hexagonal crystal lattice of the upper layer, with respect to the normal of the tool base surface is as follows: It can be measured by the procedure.
First, a tool cross-section polishing surface perpendicular to the surface-coated tool base of this embodiment is prepared (see FIG. 1). Next, using the Al ₂ O ₃ crystal grains of (c) formed immediately above the outermost surface layer of the lower layer (immediately above the interface between the upper layer and the lower layer), using a field emission scanning electron microscope, Each crystal grain having a hexagonal crystal lattice existing within the measurement range of the tool cross-section polished surface is irradiated with an electron beam to obtain data relating to the orientation of the Al ₂ O ₃ crystal grains. And based on this data, when the inclination angle (see FIG. 2) formed by the normal of the (0001) plane which is the crystal plane of the crystal grain is measured with respect to the normal of the tool base surface, the measurement The measured inclination angle within the range of 0 to 45 degrees of the inclination angles is divided for each pitch of 0.25 degrees, and the inclination angle number distribution graph is formed by counting the frequencies existing in each division. Then, the sum of the frequencies of the inclination angle is present in the tilt angle sections of Al ₂ O ₃ grains in the range of 0 degrees, measuring the area percentage of the total power in the inclination angle frequency distribution graph.
The inclination angle formed by the normal line of the (0001) plane of the Al ₂ O ₃ crystal grains obtained by the above-described procedure is the ratio of the CO ₂ gas amount and the H ₂ S gas amount to the AlCl ₃ gas amount in the vapor deposition conditions. By relatively increasing the value, it is possible to obtain a value in which the power ratio existing in the tilt angle section of 0 to 10 degrees in the tilt angle distribution graph is 60% or more of the entire power. (0001) oriented Al ₂ O ₃ crystal grains, that is, Al ₂ O ₃ crystal grains present in the tilt angle section with the tilt angle of 0 to 10 degrees formed by the normal line of the (0001) plane, are shown in the tilt angle number distribution graph. When it is less than 60% of the entire frequency, the high temperature strength and the high temperature hardness are lowered.
Therefore, with respect to the Al ₂ O ₃ crystal grains of the upper layer immediately above the interface between the upper layer and the lower layer, the inclination angle of the normal line of the (0001) plane of the Al ₂ O ₃ crystal grains with respect to the normal line of the tool base surface Is defined as 60% or more of the total frequency in the gradient angle distribution graph.

(E) In-grain average orientation difference of crystal grains having an upper layer aspect ratio of less than 3:
First, using a field emission scanning electron microscope and an electron beam backscatter diffractometer, each crystal grain having a hexagonal crystal lattice existing within the measurement range of the cross-sectional polished surface is irradiated with an electron beam, and the method of the tool base surface When the inclination angle formed by the normal line of the (0001) plane which is the crystal plane of the crystal grain is measured with respect to the line, and there is an orientation difference of 5 ° or more between adjacent pixels, the boundary between adjacent pixels is determined. Assuming that it is a crystal grain boundary, a range surrounded by crystal grain boundaries and not divided by other crystal grain boundaries is defined as one crystal grain. Here, one pixel means a crystal in an image when an image observed when the sample is irradiated with an electron beam is analyzed with analysis software using a field emission scanning electron microscope and an electron beam backscatter diffraction device. It is the smallest unit constituting a grain image.
Then, an orientation difference is calculated between a certain pixel in the crystal grain and all other pixels in the crystal grain, and an average of the difference is defined as an intra-grain average orientation difference. These measurements were performed between the Al ₂ O ₃ crystal grains observed using an electron beam backscattering diffractometer.
The average grain orientation difference of the grains having an aspect ratio of less than 3 in the present invention is less than 5 degrees, that is, excellent by selectively (0001) orientation of a grain structure having a low aspect ratio. Creates wear resistance.

According to the coated tool of the present invention, the hard coating layer has a lower layer formed on the surface of the tool base and an upper layer formed on the lower layer, and (a) the lower layer is 3 to 20 μm. A total average layer thickness of TiC, TiN, TiCN, TiCO, and TiCNO, at least one of which is a Ti compound layer composed of a TiCN layer, and (b) a lower layer The outermost surface layer is composed of a TiCN layer having a layer thickness of at least 500 nm, and oxygen is contained only in a depth region up to 500 nm in the thickness direction of the TiCN layer from the interface between the TiCN layer and the upper layer. The average oxygen content contained in the depth region is 0.5 to 3 atomic% of the total content of Ti, C, N, and O contained in the depth region, and (c) the upper layer Has an average layer thickness of 2-15 μm and is chemically vapor-deposited Consists the Al ₂ O ₃ layer having a α-type crystal structure in the state, if the determined aspect ratio of individual crystal grains constituting the the Al ₂ O ₃ layer, crystal grains the aspect ratio is less than 3 area The average grain size of the crystal grains that occupy 60-90% of the entire upper layer and the aspect ratio is less than 3 is included in the range of 0.1 to 1.0 μm, and (d) the entire upper layer For Al ₂ O ₃ crystal grains, a field emission scanning electron microscope and an electron beam backscatter diffraction apparatus were used to irradiate each crystal grain having a hexagonal crystal lattice existing within the measurement range of the cross-sectional polished surface with an electron beam. When the inclination angle formed by the normal line of the (0001) plane, which is the crystal plane of the crystal grain, is measured with respect to the normal line of the tool base surface, it is within the range of 0 to 45 degrees of the measurement inclination angle. In addition to dividing the measured inclination angle at 0.25 degree pitch, When expressed in formed by aggregating the frequencies present in the classification inclination angle frequency distribution graph, the frequency of the inclination angle is present in the tilt angle sections of Al ₂ O ₃ grains in the range of 0 degrees The total is 60% or more of the whole frequency in the tilt angle number distribution graph, and (e) a crystal having an aspect ratio of less than 3 among the Al ₂ O ₃ crystal grains of the entire upper layer described in (c) above By having a configuration unique to the present invention in which the average orientation difference within a crystal grain of each grain is less than 5 degrees, there is an effect unique to the present invention of improving peeling resistance and wear resistance. For this reason, excellent high-temperature strength and high temperature can be achieved even when cutting various steels and cast irons at high speeds, high-speed heavy cutting conditions where high loads / impact loads are applied to the cutting edge, and high-speed intermittent cutting conditions. It exhibits hardness and exhibits excellent cutting performance over a long period of use without the occurrence of peeling or chipping of the hard coating layer.

It is a schematic diagram of the cross section perpendicular | vertical to the tool base | substrate surface in the surface coating tool of embodiment of this invention. In the surface-coated tool of the embodiment of the present invention, it is a diagram showing an inclination angle formed by the normal of the tool base surface and the normal of the (0001) plane which is the crystal plane of the Al ₂ O ₃ crystal grains of the upper layer, (A) shows an inclination angle of 0 degrees, and (b) shows an inclination angle of 45 degrees. In the surface-coated tool according to the embodiment of the present invention, the inclination angle number distribution graph of the inclination angle formed by the normal line of the tool base surface and the normal line of the (0001) plane which is the crystal plane of the Al ₂ O ₃ crystal grains of the upper layer It is.

  Embodiment of the coated tool of this invention is described concretely based on an Example. In particular, each layer constituting the hard coating layer of the coated tool of the present invention will be described in detail.

As raw material powders, WC powder, TiC powder, ZrC powder, TaC powder, NbC powder, Cr ₃ C ₂ powder, TiN powder, and Co powder all having an average particle diameter of 1 to 3 μm are prepared. Then, blended into the composition shown in Table 1, added with wax, ball mill mixed in acetone for 24 hours, dried under reduced pressure, and then press-molded into a green compact of a predetermined shape at a pressure of 98 MPa. WC based cemented carbide tool having an ISO standard CNMG120408 insert shape after being sintered in a vacuum of 5 Pa at a predetermined temperature in the range of 1370 to 1470 ° C. for 1 hour. Substrates A to E were produced.

Further, as raw material powders, TiCN (TiC / TiN = 50/50 by mass ratio) powder, ZrC powder, TaC powder, NbC powder, Mo ₂ C powder, WC powder each having an average particle diameter of 0.5 to 2 μm. Co powder and Ni powder are prepared, these raw material powders are blended in the blending composition shown in Table 2, wet mixed by a ball mill for 24 hours, dried, and then pressed into a compact at a pressure of 98 MPa, This green compact was sintered in a nitrogen atmosphere of 1.3 kPa at a temperature of 1500 ° C. for 1 hour, and after sintering, a tool base a to TiCN-based cermet having an insert shape of ISO standard CNMG120212 was obtained. e was produced.

Subsequently, each of the tool bases A to E and the tool bases a to e was charged into a normal chemical vapor deposition apparatus, and the inventive coated tools 1 to 13 were manufactured according to the following procedure.
(A) First, under the conditions shown in Table 3, a Ti compound layer as a lower layer having a target layer thickness shown in Table 7 was formed by vapor deposition.
(B) Next, under the conditions shown in Table 4, the oxygen-containing TiCN layer as the outermost surface layer of the lower layer (ie, 0.5 to 3 atoms only in the depth region from the surface of the layer to 500 nm) % (Containing oxygen of O / (Ti + C + N + O) × 100) was formed with the target layer thickness shown in Table 7.
(C) Next, under the conditions shown in Table 5, the uppermost TiCN layer of the lower layer was subjected to oxidation treatment (lower surface treatment) with a mixed gas of CO and CO ₂ .
(D) Next, although the initial growth of Al ₂ O ₃ was carried out under the initial growth conditions shown in Table 6, vapor deposition under the upper layer formation conditions shown in Table 6 was also performed. By carrying out until it becomes, this invention coated tool 1-13 was manufactured, respectively.

  For comparison purposes, the step (b) of the inventive coated tools 1 to 13 is not performed, and / or the conditions of the step (d) are performed under the upper layer forming conditions shown in Table 6, so that Comparative coated tools 1 to 13 shown in FIG.

  Next, for the inventive coated tools 1 to 13 and comparative coated tools 1 to 13, with respect to the TiCN layer constituting the outermost surface layer of the lower layer, the average oxygen content in the depth region up to 500 nm in the layer thickness direction of this TiCN layer The amount (= O / (Ti + C + N + O) × 100), and the average oxygen content (= O / (Ti + C + N + O) × 100) in a depth region exceeding 500 nm were determined by cross-sectional polishing of the coated tool using an Auger electron spectrometer. The surface is irradiated with an electron beam having a diameter of 10 nm from the outermost surface of the lower Ti carbonitride layer to a distance corresponding to the thickness of the Ti carbide layer, and the intensity of the Auger peaks of Ti, C, N, and O is measured. The ratio of the Auger peak intensity of O was calculated from the sum of the peak intensities.

In addition, in order to determine the oxygen content inevitably contained in the TiCN layer, on the surface of the tool base made of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet separately,
Reaction gas composition (volume%): TiCl ₄ 2 to 10%, CH ₃ CN 0.5 to 1.0%, N ₂ 25 to 60%, balance H ₂ ,
Reaction atmosphere temperature: 800 to 900 ° C.
Reaction atmosphere pressure: 6 to 10 kPa,
The TiCN (hereinafter referred to as inevitable oxygen-containing TiCN) layer that does not intentionally contain oxygen was formed with a layer thickness of 3 μm or more by chemical vapor deposition under the following conditions. The oxygen content inevitably contained in the region deeper than 100 nm in the layer thickness direction from the surface of the inevitable oxygen-containing TiCN layer is Ti, C, N, contained in the depth region using an Auger electron spectrometer. The inevitable oxygen content obtained from the ratio of the total content of O and determined within the accuracy range of the Auger electron spectroscopic analyzer was determined to be 0.5 atomic%.

A value obtained by subtracting the inevitable oxygen content from the above-mentioned average oxygen content was determined as the average oxygen content of the TiCN layer constituting the outermost surface layer of the lower layer.
Tables 7 and 8 show these values.

Next, the Al ₂ O ₃ top layer of the hard coating layer, Al ₂ O ₃ crystal grains (0001) plane of a frequency distribution of inclination angle normal forms, field emission scanning electron microscope and an electron by the following steps It measured using the backscattering diffraction image apparatus.
First, cross-sectional polishing of 0.3 μm in the depth direction of the upper layer from the interface between the lower layer and the upper layer of the inventive coated tools 1 to 13 and comparative coated tools 1 to 13 and 50 μm in the direction parallel to the tool base surface. The surface measurement range (0.3 μm × 50 μm) was set in the column of a field emission scanning electron microscope. Next, each crystal grain having a hexagonal crystal lattice existing in the measurement range of each of the cross-sectional polished surfaces is irradiated with an electron beam with an acceleration voltage of 15 kV at an incident angle of 70 degrees on the cross-sectional polished surface with an irradiation current of 1 nA. And the measurement area of 0.3 × 50 μm at an interval of 0.1 μm / step at the crystal plane of the crystal grain with respect to the normal of the tool base surface. The inclination angle formed by the normal line of a certain (0001) plane was measured. In addition, the measured inclination angles within the range of 0 to 45 degrees of the measured inclination angles (hereinafter referred to as “measurement inclination angles”) are divided into pitches of 0.25 degrees and exist in each division. This is represented by an inclination angle frequency distribution graph obtained by summing up the frequencies. FIG. 3 shows an inclination angle number distribution graph of the coated tool 10 of the present invention. Then, the inclination angle is determined and the area percentage of the total power in the total inclination angle frequency distribution graph of the power present in the Al ₂ O ₃ grains of the tilt angle sections is in the range of 0 degrees.
In addition, the aspect ratio is calculated by measuring the orientation difference (rotation angle) between individual crystal lattices by measuring using the field emission scanning electron microscope and electron backscatter diffraction image apparatus described above. Measured from the difference in Euler angles of the lattice, when the orientation difference (rotation angle) between the crystal lattices of adjacent measurement points is 5 degrees or more, the boundary between the measurement points adjacent to each other is a grain boundary, A range surrounded by crystal grain boundaries and not divided by other crystal grain boundaries is specified as the same crystal grain, and for each of the specified crystal grains, the direction perpendicular to the tool base surface direction is the long axis, and the tool base The direction parallel to the surface direction was taken as the short axis, the length of the long axis and the short axis were determined, and the aspect ratio was determined from these ratios. The area ratio of the crystal grains having an aspect ratio of less than 3 is obtained by measuring the mirror-polished cross-section with an electron beam backscattering diffractometer at an observation magnification of 2,000 times in the horizontal direction: 50 μm × vertical direction: upper layer film. It calculated by measuring the area | region equivalent to thickness.
Further, the average grain size of the individual crystal grains constituting the Al ₂ O ₃ layer having an aspect ratio of less than ₃ draws a straight line parallel to the tool base surface direction on the crystal grains constituting the Al ₂ O ₃ layer, It calculated | required from the average of the measured value of the length of ten line segments divided by a grain boundary.
Tables 7 and 8 show these values.

  Furthermore, the crystal orientation of each crystal grain having an aspect ratio of less than 3 constituting the upper layer is analyzed from the longitudinal section direction using an electron beam backscattering diffraction apparatus, and the average orientation difference in the crystal grain is 0 degree or more and 1 degree. Less than, 1 degree or more, less than 2 degree, 2 degree or more, less than 3 degree, 3 degree or more, less than 4 degree,... From the mapping diagram, it was confirmed that the average orientation difference within each crystal grain was less than 5 degrees.

  Moreover, when the thickness of each structural layer of the hard coating layer of this invention coated tool 1-13 and comparative coating tool 1-13 was measured using the scanning electron microscope (longitudinal section measurement), all are target layer thickness. The average layer thickness (average value of 5-point measurement) was substantially the same.

Next, for the various coated tools of the present invention coated tools 1-13 and comparative coated tools 1-13, all are screwed to the tip of the tool steel tool with a fixing jig,
Work material: JIS / SCM440 lengthwise equidistant 4 flutes,
Cutting speed: 400 m / min,
Cutting depth: 2mm,
Feed: 0.4mm / rev,
Cutting time: 5 minutes
Dry high-speed intermittent cutting test (normal cutting speed is 300 m / min, respectively)
Work material: JIS / SNCM439 round bar,
Cutting speed: 120 m / min,
Incision: 1.5mm,
Feed: 1.0mm / rev,
Cutting time: 3 minutes
Dry high feed cutting test of nickel chrome molybdenum alloy steel under the conditions (cutting condition B) (normal cutting speed and feed rate are 250 m / min and 0.3 mm / rev., Respectively),
Work material: JIS / FC300 longitudinally equidistantly 4 vertical grooves,
Cutting speed: 400 m / min,
Incision: 2.5mm,
Feed: 0.4 mm / rev. ,
Cutting time: 5 minutes
A dry high-speed high-cut cutting test of cast iron under the above conditions (referred to as cutting condition C) (normal cutting speed and cutting amount are 350 m / min and 1.5 mm, respectively),
In each cutting test, the flank wear width of the cutting edge was measured.
Table 9 shows the measurement results.

From the results shown in Table 9, all of the coated tools 1 to 13 of the present invention were excellent in suppressing the propagation of cracks in the film thickness direction by achieving atomization of Al ₂ O _{3 in} the upper layer. Exfoliation resistance and chipping resistance were exhibited.
On the other hand, it is clear that the comparative coated tools 1 to 13 reach the service life in a relatively short time due to the occurrence of peeling of the hard coating layer and the occurrence of chipping in high-speed heavy cutting and high-speed intermittent cutting. .

As described above, the coated tool of the present invention is not limited to continuous cutting and intermittent cutting under normal conditions such as various types of steel and cast iron, but also high-speed heavy load in which a heavy load, intermittent / impact load acts on the cutting blade. Even under severe cutting conditions such as cutting and high-speed interrupted cutting, the hard coating layer does not peel and chipping occurs, and it exhibits excellent cutting performance over a long period of use. In addition, it is possible to sufficiently satisfy the labor-saving and energy-saving of the cutting process and the cost reduction.

Claims (1)

A surface-coated cutting tool comprising a tool base composed of a tungsten carbide-based cemented carbide or a titanium carbonitride-based cermet, and a hard coating layer deposited on the surface of the tool base,
The hard coating layer has a lower layer formed on the surface of the tool base and an upper layer formed on the lower layer,
(A) The lower layer has a total average layer thickness of 3 to 20 μm, and is composed of two or more layers of TiC, TiN, TiCN, TiCO, and TiCNO, and at least one of them is composed of a TiCN layer. Consisting of a Ti compound layer,
(B) The outermost surface layer of the lower layer is a TiCN layer having a layer thickness of at least 500 nm or more, and the depth from the interface between the TiCN layer and the upper layer to a maximum thickness of 500 nm in the layer thickness direction of the TiCN layer. Oxygen is contained only in the region, and the average oxygen content contained in the depth region is 0.5 to 3 atoms of the total content of Ti, C, N, and O contained in the depth region. %
(C) The upper layer has an average layer thickness of 2 to 15 μm, and is composed of an Al ₂ O ₃ layer having an α-type crystal structure in the state of chemical vapor deposition. The individual crystals constituting the Al ₂ O ₃ layer When determining the aspect ratio of the grains, the crystal grains having the aspect ratio of less than 3 account for 60-90% of the entire upper layer in area ratio, and the average grain diameter of the grains having the aspect ratio of less than 3 is Included in the range of 0.1 to 1.0 μm,
(D) A crystal having a hexagonal crystal lattice existing in the measurement range of the cross-sectional polished surface of the Al ₂ O ₃ crystal grains of the entire upper layer using a field emission scanning electron microscope and an electron beam backscattering diffractometer When each particle is irradiated with an electron beam and the inclination angle formed by the normal of the (0001) plane, which is the crystal plane of the crystal grain, is measured with respect to the normal of the tool base surface, When the measured inclination angle within the range of 0 to 45 degrees is divided into pitches of 0.25 degrees, and the inclination angle number distribution graph is formed by counting the frequencies existing in each division, the inclination The sum of the frequencies existing in the tilt angle section of the Al ₂ O ₃ crystal grains having an angle in the range of 0 to 10 degrees is 60% or more of the entire frequencies in the tilt angle frequency distribution graph,
(E) Among the Al ₂ O ₃ crystal grains of the entire upper layer described in (c), the average orientation difference in crystal grains of crystal grains having an aspect ratio of less than 3 is less than 5 degrees. A surface-coated cutting tool.