JP2019171531A - Surface-coated cutting tool excellent in thermal crack resistance and chipping resistance - Google Patents

Abstract

The present invention provides a surface-coated cutting tool for rolling of stainless steel, in which a hard coating layer has both excellent heat crack resistance and chipping resistance and improves tool life. (A) The hard coating layer has a total average layer thickness of 0.5 to 7.0 μm, and has two layers of a lower layer and an upper layer, and (b) the average total thickness of the lower layer is 0.3 to 7.0 μm. 4.0 μm, a multilayer coating layer in which a TiN layer having a cubic single-phase structure and an AlTiN layer are alternately laminated from the surface side of the tool base, the AlTiN layer has a composition formula of AlxTi1-xN, and x (atomic ratio) has an average composition of 0. 40 ≦ x ≦ 0.70, each TiN layer and each AlTiN layer have an average layer thickness of 3 to 30 nm, (c) the upper layer has an average layer thickness of 0.2 to 3.0 μm, and a cubic phase structure. A mixed phase structure with the h-AlN hexagonal phase structure, the overall composition satisfies the composition formula AlzTi1-zN, z (atomic ratio) satisfies the average composition 0.40 ≦ z ≦ 0.70, and the upper layer is perpendicular to the tool substrate surface. In the cross section, the area ratio occupied by the hexagonal phase structure is 3 to 30%. [Selection diagram] Fig. 1

Description

The present invention relates to, for example, a surface-coated cutting tool (hereinafter referred to as a coated tool) in which a hard coating layer exhibits excellent heat cracking resistance and chipping resistance in a rolling process of stainless steel.

Conventionally, in a coated tool for turning, an Al-Ti composite nitride layer or the like as a hard coating layer on the surface of a tool base composed of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet, etc. A surface-coated cutting tool that exhibits excellent wear resistance, heat cracking resistance, or chipping resistance by forming a coating on the surface is known.

For example, in Patent Document 1, a chemical composition represented by (Al _x Ti _1-x ) (N _y C _1-y ) (however, 0.56 ≦ x ≦ 0.75, 0.6 ≦ on the surface of the tool base). A coating with excellent wear resistance, heat resistance and adhesion formed by an arc ion plating method comprising a wear resistant film having a thickness of 0.8 to 10 μm, comprising a TiAl (C, N) layer having y ≦ 1) Tools have been proposed.

  Further, for example, in Non-Patent Document 1, a titanium alloy or the like can be obtained by alternately laminating TiN layers and TiAlN layers at the nano level on the surface of a cemented carbide substrate and suppressing the progress of cracks at the interface of each layer. In the cutting of difficult-to-cut materials, a coated tool that exhibits excellent chipping resistance has been proposed.

Furthermore, in Patent Document 2, at least a hard coating layer having a composition composed of (Ti _y Al _x Me _1-xy ) N (where Me is Zr, Hf, V, Nb, Ta, Cr, A coating that is a component element selected from Mo, W, and Si, and has 0.55 ≦ x ≦ 0.80, 0.50 ≦ x / (x + y) ≦ 0.85, 0.7 ≦ x + y <1.0) Cubic TiN, cubic crystal, generated by spinodal decomposition of (Ti _y Al _x Me _1-xy ) N, held in a tool in an argon or nitrogen atmosphere at a temperature of 800-1100 ° C. for 5-240 minutes It has been proposed to improve the hardness, toughness and thermal stability of the hard coating layer by precipitation hardening of AlN and hexagonal AlN.

JP-A-8-209333 US Pat. No. 7,056,602

"Surface and Coatings Technology" 163-164 (2003) p. 681-688 "Deposition, characterisation and machining performance of multilayer PVD coatings on cemented cutting tools"

  In recent years, there has been a high demand for labor saving, energy saving, and cost reduction in cutting, and along with this, cutting tends to be faster and more efficient, especially stainless steel turning. In some cases, in addition to wear resistance, high heat cracking is required because of high temperatures during cutting, and the chip becomes a saw blade shape, causing minute vibrations and chipping. In addition, improvement of chipping resistance is demanded.

On the other hand, the coated cutting tool described in Patent Document 1 uses an AlTi (C, N) layer having excellent wear resistance, heat resistance, and adhesion as a hard coating layer. In machining, there was a problem that both heat crack resistance and chipping resistance were insufficient.
In the coated cutting tool described in Non-Patent Document 1, the nano-laminated multilayer film has excellent chipping resistance, but has insufficient heat cracking resistance.

Furthermore, the coated cutting tool described in Patent Document 2 has excellent heat cracking resistance under conditions where hexagonal AlN (h-AlN) precipitates in the stainless steel rolling process. In the chipping property and the wear resistance, there is a problem that the lifetime is reached due to the decrease.

Therefore, the present invention has an excellent thermal crack resistance and chipping resistance in addition to the wear resistance of the hard coating layer to the problem of the occurrence of thermal cracking and chipping of the hard coating layer, which is observed in the machining of the stainless steel. The object is to solve the problem by providing a coated tool that exhibits both properties.

  The inventors of the present invention have a coating tool for stainless steel milling, which has a thermal crack resistance and chipping resistance with excellent hard coating layer over a long period of use, and provides improved tool life. As a result of earnest research, the following knowledge was obtained.

That is, the inventors of the present invention have a nano-level thickness on the surface of the tool base in a limited condition on the surface of the tool base in a coated tool, particularly a coated tool for rolling stainless steel. Excellent wear resistance is ensured by forming a multilayer coating layer consisting of two or more layers of TiN layers and AlTiN layers composed of a cubic single-phase structure alternately in the desired stacking cycle as the lower layer. In addition, it was found that it has excellent chipping resistance, and, under limited conditions, as an upper layer on the lower layer, an AlTiN phase having a cubic structure and a predetermined cross section perpendicular to the tool base surface By coating and forming an AlTi composite nitride layer having a desired thickness consisting of a mixed phase (two-phase) structure with a h-AlN phase of a hexagonal structure having an area ratio of And has a hard coating layer obtained by laminating these coating layers together to provide wear resistance, chipping resistance, and thermal cracking. It has been found that all the characteristics of the sex can be exhibited at the same time.
The coated cutting tool having a hard coating layer formed by laminating the lower layer and the upper layer is excellent in wear resistance, chipping resistance, and heat cracking resistance especially in the machining of stainless steel and the like. The tool life is improved over long-term use.

The present invention has been made based on the above findings,
“(1) In a surface-coated cutting tool in which a hard coating layer is formed on the surface of a tool base made of a WC-based cemented carbide or TiCN-based cermet,
(A) The hard coating layer has two layers of a lower layer and an upper layer from the surface side of the tool base, and the total average layer thickness is 0.5 to 7.0 μm,
(B) The lower layer is a multilayer coating layer of two or more layers in which TiN layers and AlTiN layers are alternately stacked from the surface side of the tool base, and the AlTiN layer has a composition formula Al _x Ti _{1. -XN} , the Al content ratio x (where x is an atomic ratio) has an average composition satisfying 0.40 ≦ x ≦ 0.70 in any layer, and the TiN Both the layer and the AlTiN layer have a cubic single phase structure,
The average layer thickness of each TiN layer and each AlTiN layer is 3 to 30 nm, respectively, and the average total film thickness of the lower layer is 0.3 to 4.0 μm,
(C) The upper layer is a mixed phase structure composed of a cubic phase structure and a hexagonal phase structure,
As for the overall composition, when expressed by the composition formula Al _z Ti _1-z N, the Al content ratio z (where z is an atomic ratio) satisfies an average composition satisfying 0.40 ≦ z ≦ 0.70. Have
The hexagonal phase structure is composed of h-AlN, and the area ratio of the hexagonal phase structure to the sum of the cubic phase structure and the hexagonal phase structure in the cross section perpendicular to the tool base surface of the upper layer is 3 ~ 30%,
The surface coating cutting tool characterized by the average layer thickness being 0.2-3.0 micrometers. "
It is characterized by.
The “atomic ratio” here refers to the ratio of the number of atoms of Al and Ti when the total ratio of the number of atoms of Al and Ti, excluding N, is 1.00. .

  Next, the coated tool of the present invention will be described in detail.

Hard coating layer;
The hard coating layer according to the present invention has a nano-level thickness from the tool substrate side, and two or more TiN layers and AlTiN layers composed of a cubic single-phase structure are alternately laminated at a desired lamination period. An AlTi composite that is a mixed phase (two-phase) structure of a lower layer that is a multilayer coating layer, an AlTiN phase that is a cubic structure, and an h-AlN phase that is a hexagonal structure having a predetermined area ratio in the longitudinal section of the coating layer And an upper layer which is a nitride layer.
If the total average total film thickness of the hard coating layer is less than 0.5 μm, the wear resistance cannot be exhibited over a long period of time, and if it exceeds 7.0 μm, abnormal damage such as film peeling and chipping is likely to occur. Therefore, the thickness is desirably 0.5 to 7.0 μm.
The hard coating layer having the lower layer and the upper layer according to the present invention is formed by using, for example, an ion plating method or a sputtering method, which is a kind of PVD method, and then subjected to specific conditions (temperature, time). , By performing heat treatment under cooling conditions), it can be obtained by causing fluctuations in the concentration distribution.
The average layer thickness of the lower layer and the upper layer, and the total average layer thickness of the hard coating layer, using a scanning electron microscope (SEM) or transmission electron microscope (TEM), for example, in the longitudinal section of the coating layer, It can be obtained as an average value of the layer thicknesses of five points in the observation visual field at a magnification of 5000 times.

Lower layer;
The lower layer formed on the tool base has a nano-level thickness from the surface side of the tool base, and a TiN layer composed of a cubic single-phase structure and an AlTiN layer are alternately stacked in a desired lamination cycle. And when the AlTiN layer is represented by the composition formula Al _x Ti _1-x N, the Al content ratio x (where x is an atomic ratio) is: Each layer has an average composition satisfying 0.40 ≦ x ≦ 0.70.
Moreover, the average layer thickness of each TiN layer and each AlTiN layer is 3-30 nm, respectively, and the average total film thickness of a lower layer is 0.3-4.0 micrometers.
(1) Composition of AlTiN layer When the Al content ratio x is less than 0.40, the hardness is not sufficient, so the wear resistance becomes insufficient. On the other hand, the hardness increases as the Al content ratio increases, If it exceeds 0.70, soft hexagonal AlN is generated and wear resistance becomes insufficient, so that a hard coating layer having high hardness and excellent wear resistance can be obtained. 0.40 or more, 0 Specified within a range of 70 or less.
(2) Film thickness of TiN layer and AlTiN layer The total film thickness of the TiN layer and AlTiN layer, that is, the total film thickness of the lower layer is less than 0.3 μm, and the wear resistance is insufficient. If the thickness exceeds 4.0 μm, abnormal damage such as peeling or chipping occurs, and therefore, it is defined as 0.3 to 4.0 μm.
Further, the unit layer thickness of each of the TiN layer and the AlTiN layer is less than 3 nm, the restraining effect on the crack progress at the interface is not sufficient, the crack progress cannot be suppressed, and the chipping resistance is insufficient. If the thickness exceeds 30 nm, the crystal grains in the TiN layer and the AlTiN layer become coarse, and as a result, sufficient wear resistance cannot be obtained.
(3) Laminated structure of TiN layer and AlTiN layer High wear resistance can be maintained for a long time by making the lower layer a nano-laminated layer composed of a cubic single-phase TiN layer and an AlTiN layer.
This is because, by sandwiching the AlTiN layer in the TiN layer that does not cause composition fluctuations even by heat treatment, the AlTiN layer suppresses the influence on the change in the component concentration due to heat or the like. It is considered that AlN hardly precipitates and can maintain a cubic structure.

Upper layer;
The AlTi nitride layer formed as an upper layer with respect to the lower layer has an Al composition ratio z (provided that z is a composition formula Al _z Ti _1-z N). , Atomic ratio) has an average composition satisfying 0.40 ≦ z ≦ 0.70, and the AlTi nitride layer is obtained from a cubic phase structure and a hexagonal phase structure obtained by heat treatment. The hexagonal phase structure is a structure composed of h-AlN, and the hexagonal phase structure is a cubic phase structure and a hexagonal phase structure in a cross section perpendicular to the tool base surface of the upper layer. By setting the area ratio to the total area to be 3 to 30%, it has excellent thermal crack resistance.
That is, in the upper layer, high Al cubic AlTiN having excellent wear resistance and h-AlN having high thermal conductivity and h-AlN in the vicinity of the surface are formed due to fluctuations in Al concentration caused by heat treatment. This is because, in the high Al region containing, Al oxides that are chemically stable and excellent in welding resistance and lubricity are easily formed by heat during cutting.
In the overall composition, when the Al content ratio z is less than 0.40, the hardness is not sufficient and the wear resistance becomes insufficient. On the other hand, as the Al content ratio increases, the hardness increases, but z is If it exceeds 0.70, the amount of soft hexagonal AlN exceeds 30 area% and the wear resistance becomes insufficient. Therefore, z is specified in the above range.
Moreover, if the average layer thickness of the upper layer is less than 0.2 μm, the thermal crack resistance and wear resistance are insufficient, while if it exceeds 3.0 μm, abnormal damage such as peeling or chipping may occur. Defined as 0.2 μm to 3.0 μm.
As for the crystal structure, since the upper layer contains hexagonal h-AlN and high Al AlTiN, it is easy to form an Al oxide excellent in oxidation resistance, and has excellent lubricity and welding resistance. It is considered that the thermal crack resistance is improved. On the other hand, in the hexagonal single phase, the wear resistance is insufficient, the layer itself disappears due to initial wear, and the heat cracking effect cannot be exhibited, so the area ratio of the hexagonal structure to the entire structure is 3 to 3. 30%.

Method for forming a hard coating layer;
As described above, the hard coating layer formed by laminating the lower layer and the upper layer according to the present invention is first formed using an ion plating method or a sputtering method, which is a kind of PVD method, and then formed into a film. It can be obtained by performing heat treatment under specific conditions.
In the following, the lower layer and the upper layer are formed on the tool base using an arc ion plating (AIP) apparatus, and then heat treatment (temperature, time, cooling conditions) is performed under specific conditions. A method for producing a desired hard coating layer will be described.
1A and 1B are schematic views of an arc ion plating apparatus for forming a hard coating layer of the present invention.
The arc ion plating apparatus shown in FIGS. 1 (a) and 1 (b) is provided with a rotating table for mounting a substrate at the center of the apparatus, and sandwiches the rotating table, and a lower layer as a cathode electrode (evaporation source) on one side A Ti target for forming a TiN layer is disposed on the other side, a lower layer AlTiN layer having a predetermined composition as the cathode electrode, and an Al-Ti alloy target for forming an upper AlTiN layer are disposed on the other side, and a WC A tool base made of a base cemented carbide, a TiCN base cermet, or the like is placed on the rotary table so that the base itself can be rotated, and a bombard pretreatment for the tool base, the temperature of the tool base, and the N ₂ gas pressure Film formation can be performed by adjusting the bias voltage and arc current value during film formation and generating arc discharge in a nitrogen gas atmosphere.
First, the lower TiN layer deposition Ti target and the corresponding anode electrode, and the lower AlTiN layer deposition Al-Ti alloy target corresponding anode electrode and Between the TiN nanolayer and AlTiN nanolayer having a cubic single-phase structure as a lower layer, and forming a lower layer on the tool base surface. Only the arc discharge between the Ti target for forming the TiN layer of the lower layer, which is the cathode electrode, and the corresponding anode electrode is stopped, and the atmosphere in the apparatus is maintained in a nitrogen atmosphere, and the lower layer An arc discharge is generated between the AlTiN layer and the Al-Ti alloy target for forming the upper AlTiN layer and the anode electrode, and an AlTiN layer is formed as an upper layer on the lower layer. It is carried out by wearing.
Next, the tool base on which the lower layer and the upper layer are formed is subjected to heat treatment in a heat treatment furnace under predetermined heat treatment conditions (atmosphere, heating temperature, treatment time, cooling rate), so that excellent wear resistance and superiority are achieved. The lower layer is composed of a multilayer coating layer in which TiN layers and AlTiN layers each having a nano-level layer thickness are formed with a single-phase cubic structure, and a fluctuation in concentration distribution due to heat treatment. Due to the resulting mixed phase (two-phase) structure consisting of an AlTiN phase that is a cubic phase structure and an h-AlN phase that is a hexagonal structure, it is composed of an upper layer that exhibits excellent thermal crack resistance and wear resistance and resistance. A surface-coated cutting tool having a hard coating layer having both chipping properties can be obtained.

  In the coated tool according to the present invention, as described above, the lower layer of the hard coating layer is a lower layer formed by alternately laminating TiN nanolayers and AlTiN nanolayers each having a cubic phase single phase structure, and the upper layer. Is a mixed phase (two-phase) structure consisting of an AlTiN phase which is a cubic phase structure and an h-AlN phase which is a hexagonal structure, thereby having excellent wear resistance, chipping resistance and thermal crack resistance. In particular, a surface-coated cutting tool having both of the above-mentioned characteristics, particularly in a coated tool for rolling stainless steel, improves tool life over a long period of use.

It is the schematic which shows the arc ion plating (AIP) apparatus used in order to form the hard coating layer of this invention coated tool, (a) is a schematic plan view, (b) shows a schematic front view.

Next, the coated tool of the present invention will be specifically described with reference to examples.
As a specific description, a coated tool using a WC-based cemented carbide or TiCN-based cermet as a tool substrate will be described, but the same applies to a coated tool using a cubic boron nitride sintered body as a tool substrate.

Production of a tool substrate;
As raw material powders, Co powder, TaC powder, NbC powder, Cr ₃ C ₂ powder and WC powder, all having an average particle diameter of 0.5 to 5 μm, are prepared, and these raw material powders are blended as shown in Table 1. Blended into the composition, added with wax, wet mixed in a ball mill for 72 hours, dried under reduced pressure, then press molded at a pressure of 100 MPa, sintered these compacts, and processed to a predetermined size. Thus, tool bases A and B made of WC-base cemented carbide having an insert shape of ISO standard SEEN1203AFEN were manufactured.

Moreover, as raw material powder, all have an average particle diameter of 0.5 to 5 μm, TiCN (TiC / TiN = 50/50 in mass ratio) powder, NbC powder, Mo ₂ C powder, WC powder, Co powder and Ni powder is prepared, these raw material powders are blended in the blending composition shown in Table 2, further added with wax, wet mixed in a ball mill for 72 hours, dried under reduced pressure, and then press molded at a pressure of 100 MPa. The green compact was sintered and processed so as to have a predetermined size, to produce tool bases C and D made of TiCN-based cermet having an ISO standard SEEN1203AFEN insert shape.

Film formation process;
The tool base was subjected to film formation and heat treatment using an AIP apparatus (arc ion plating apparatus) shown in FIG. 1 to produce a coated tool of the present invention.
(A) Each of the tool bases A, B, C, and D is ultrasonically washed in acetone and dried, and is predetermined in the radial direction from the central axis on the rotary table in the AIP apparatus shown in FIG. A Ti target (cathode electrode) for forming a lower TiN layer is disposed on one side of the position opposite to the rotary table with the rotary table interposed therebetween, and the lower layer of the lower layer is disposed on the other side. An Al—N alloy target (cathode electrode) for forming an AlTiN layer and an upper layer of AlTiN is disposed.
(B) Next, the inside of the AIP apparatus is evacuated and the inside of the apparatus is heated to 500 ° C. with a heater while maintaining a vacuum of 10 ⁻² Pa or less, and then set to an Ar gas atmosphere of 0.5 to 2.0 Pa. Then, a DC bias voltage of −400 to −1000 V is applied to the tool base that rotates while rotating on the rotary table, and bombard cleaning is performed for 5 to 30 minutes.
(C) Next, nitrogen gas is introduced into the AIP apparatus as a reaction gas, and the pressure of the nitrogen gas is set to a predetermined reaction atmosphere within the range of 2.0 to 10.0 Pa shown in Table 3, The tool base that rotates at the number of revolutions shown in Table 3 while rotating on the rotary table while maintaining the temperature in the apparatus shown in FIG. A DC bias voltage is applied, and the cathode electrode shown in Table 3 corresponds to an Al—Ti alloy target for forming the lower layer and the corresponding anode electrode, and also corresponds to a Ti target for forming the lower layer. A predetermined current in the range of 90 to 140 A shown in Table 3 is caused to flow between each anode electrode and the anode electrode to generate arc discharge, and the target average composition shown in Table 7 is formed on the surface of the tool base. And target level Forming a lower layer formed by alternately stacking a TiN nano layer and AlTiN nanolayers having layer thickness.
(D) Next, the arc discharge between the Ti target for forming the lower layer, which is the cathode electrode, and the anode electrode is stopped, and the pressure of nitrogen gas in the apparatus is shown in Table 3 while maintaining the temperature in the apparatus. A predetermined direct current within a range of −30 to −100 V shown in Table 3 with respect to a tool base which is adjusted to a predetermined reaction atmosphere within a range of 0.0 to 10.0 Pa and rotates while rotating on a rotary table. A bias voltage is applied, and a predetermined current in the range of 90 to 140 A shown in Table 3 is passed between the Al—Ti alloy target for forming the upper layer, which is the cathode electrode shown in Table 3, and the anode electrode. Arc discharge is generated, and an upper layer having a target average composition and a target average layer thickness in the entire upper layer shown in Table 7 is formed on the surface of the tool base.
(E) Next, the obtained coated tool is subjected to heat treatment under the conditions shown in Table 5 to produce the present coated tools (hereinafter referred to as “the present tool”) 1 to 12 shown in Table 7. did.
The layer thicknesses of the TiN nanolayer and the AlTiN nanolayer obtained by the alternate lamination are adjusted by relatively adjusting the arc current value flowing between the independent target and the anode electrode, respectively. Can be changed as appropriate.

  For the purpose of comparison, the target average shown in Table 8 is formed by vapor-depositing the lower layer and the upper layer on the tool bases A, B, C, and D under the conditions shown in Table 4. The lower layer and the upper layer were formed by vapor deposition with the composition and target average layer thickness, and then the obtained coated tool was subjected to heat treatment under the conditions shown in Table 6 to thereby cover the comparative examples shown in Table 8. Tools (hereinafter referred to as “comparative example tools”) 1 to 12 were produced.

About this invention tools 1-12 produced above and comparative example tools 1-12, the vertical section with respect to the tool base surface of a lower layer and an upper layer is a scanning electron microscope (SEM), a transmission electron microscope (TEM), By cross-sectional measurement using energy dispersive X-ray spectroscopy (EDS), the average Al content ratio (atomic ratio) x in the AlTiN layer in the lower layer, the average Al content ratio (atomic ratio) z in the entire upper layer, and The maximum value and the minimum value of the Al content ratio (atomic ratio) of the cubic phase in the upper layer were measured, and the average layer thickness of the lower layer and the upper layer was measured.
Further, for the upper layer, it is confirmed whether or not a h-AlN phase having a hexagonal crystal structure is present, and if present, the generation area ratio is measured by using an electron beam backscattering diffractometer (EBSD). did.
More specifically, it is as follows.
For the measurement of the average Al content ratio (atomic ratio) x in the AlTiN layer in the lower layer and the average Al content ratio (atomic ratio) z in the entire upper layer, transmission electrons that are optimal for the composition analysis of a minute region Using an energy dispersive X-ray spectroscopy (EDS) attached to a microscope (TEM), area analysis is performed in an area including a scale more than half of the film thickness at any five points in the cross section of the lower layer and the upper layer. The Al content ratio was measured, and this value was averaged to obtain the average Al content ratios x and z.
As for the maximum and minimum values of the cubic phase Al content (atomic ratio) in the upper layer, the energy dispersive X-ray spectroscopy (EDS) attached to the transmission electron microscope (TEM) is used. It is also possible to measure using an EDS attached to a scanning electron microscope (SEM), and in the cross section of the upper layer, an area analysis of 3 × 3 nm is performed on any 10 points, and the Al content ratio is measured. The maximum value and the minimum value can be obtained.
Moreover, the layer thickness of the lower layer and the upper layer is measured by measuring the layer thickness at any five points in the film cross section separated by 5 μm or more using a transmission electron microscope (TEM), and averaging this value. The average layer thickness of the lower layer and the upper layer was calculated.
Regarding the detection of the hexagonal phase, electron beam diffraction by TEM was used to measure hexagonal crystals in a circle with a diameter of 0.8 (film thickness of each layer) × 0.8 at any five locations in each of the lower layer and the upper layer. Judgment was made based on the presence or absence.
When a hexagonal phase was present, the area ratio was calculated as an average value of five locations using an electron beam backscattering diffractometer (EBSD).
That is, the area ratio of the h-AlN phase is measured by using an electron beam backscatter diffractometer (EBSD) in a state where the vertical section of the lower layer and the upper layer perpendicular to the tool base surface is a polished surface. Each crystal grain is set in an electron microscope (SEM) column, and an electron beam with an acceleration voltage of 15 kV is applied to the polished surface at an incident angle of 70 degrees with an irradiation current of 1 nA within the measurement range of the polished surface. The electron beam backscatter diffraction image was measured at an interval of 0.01 μm / step over the tool substrate in the horizontal direction with a length of 50 μm and in the normal direction, less than the thickness of the AlTiN layer. By analyzing the crystal structure, h-AlN crystal grains having a hexagonal crystal structure and other crystal grains having a face-centered cubic structure of NaCl type are identified, and the hexagonal crystal accounts for the total number of pixels of these crystal structures. H-AlN structure of structure By determining the ratio of the number of pixels corresponding to the crystal grains, the generation area ratio (area%) of the h-AlN phase can be determined.
Tables 7 and 8 show the values measured above.
In Tables 7 and 8, the number of times n is the total number of TiN layers and AlTiN layers.

Next, with the tools 1 to 12 of the present invention and the comparative tools 1 to 12 both screwed to the tip of the tool steel tool with a fixing jig, the following cutting test was carried out, and cutting was performed. The flank wear width of the blade and the density of generated thermal cracks (number / mm ² ) were measured.
For the flank wear amount, the maximum wear amount including chipping was measured.
In addition, the generation density of thermal cracks is the number of thermal cracks generated on the rake face,
It was calculated by dividing by the area surrounded by 1-blade feed.
Here, the notch is the thickness for removing the work material, and the one-blade feed is the amount obtained by dividing the distance the table advances when the cutter makes one revolution by the number of blades.
<Cutting condition 1>
Work material: Block material of JIS / SUS304 Cutting speed: 250 m / min,
Cutting depth: 2.0mm,
Single blade feed amount: 0.20 mm / tooth,
Cutting time: Dry high-speed milling cutting test of stainless steel under the condition of 10 minutes <Cutting condition 2>
Work material: JIS / SUS304
Cutting speed: 150 m / min,
Cutting depth: 2.5mm,
Single blade feed amount: 0.20 mm / tooth,
Cutting time: 10 minutes,
The results are shown in Tables 9 and 10 for the center cut wet high speed cutting test of stainless steel under the following conditions.

According to the results of Tables 9 and 10, the inventive tools 1 to 12 have less thermal crack generation density especially on the rake face than the comparative tools 1 to 12. Therefore, the occurrence of abnormal damage such as chipping and chipping due to thermal cracks can be suppressed, and at the same time, the wear resistance is excellent and the progress of flank wear can be suppressed.
As a result, excellent cutting performance can be exhibited over a long period of use.

  In addition to wear resistance, the surface-coated cutting tool of the present invention achieves both heat cracking resistance and chipping resistance, which has been a problem in conventional stainless steel turning, and has excellent cutting performance over a long period of time. Since it exhibits the performance, it can sufficiently satisfy the demand for higher performance of the cutting device, labor saving and energy saving of the cutting work, and further cost reduction.

Claims (1)

In a surface-coated cutting tool in which a hard coating layer is formed on the surface of a tool base made of a WC-based cemented carbide or TiCN-based cermet,
(A) The hard coating layer has two layers of a lower layer and an upper layer from the surface side of the tool base, and the total average layer thickness is 0.5 to 7.0 μm,
(B) The lower layer is a multilayer coating layer of two or more layers in which TiN layers and AlTiN layers are alternately stacked from the surface side of the tool base, and the AlTiN layer has a composition formula Al _x Ti _{1. -XN} , the Al content ratio x (where x is an atomic ratio) has an average composition satisfying 0.40 ≦ x ≦ 0.70 in any layer, and the TiN Both the layer and the AlTiN layer have a cubic single phase structure,
The average layer thickness of each TiN layer and each AlTiN layer is 3 to 30 nm, respectively, and the average total film thickness of the lower layer is 0.3 to 4.0 μm,
(C) The upper layer is a mixed phase structure composed of a cubic phase structure and a hexagonal phase structure,
As for the overall composition, when expressed by the composition formula Al _z Ti _1-z N, the Al content ratio z (where z is an atomic ratio) satisfies an average composition satisfying 0.40 ≦ z ≦ 0.70. Have
The hexagonal phase structure is composed of h-AlN, and the area ratio of the hexagonal phase structure to the sum of the cubic phase structure and the hexagonal phase structure in the cross section perpendicular to the tool base surface of the upper layer is 3 ~ 30%,
The surface coating cutting tool characterized by the average layer thickness being 0.2-3.0 micrometers.

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