JP6488106B2 - Surface-coated cutting tool with excellent chipping resistance in high-speed intermittent cutting - Google Patents

Description

  The present invention relates to a surface-coated cutting tool (hereinafter referred to as “coated tool”) that exhibits excellent chipping resistance in a hard coating layer in high-speed intermittent cutting where a high load acts on the cutting edge.

Conventionally, cutting is performed by coating a hard film made of carbide, nitride, carbonitride, or the like of at least one element selected from groups 4a, 5a, and 6a of the periodic table on the tool base surface. It is known to improve the wear resistance of tools.
Among the hard coatings, the α-type aluminum oxide layer is selected from groups 4a, 5a, and 6a in the periodic table from the viewpoints of excellent thermal stability, low reactivity, and high hardness. Further, a coated tool having an α-type aluminum oxide layer formed thereon is known as the outermost surface layer of a hard coating made of carbide, nitride, carbonitride, or the like of at least one element, but cutting conditions are severe. Accordingly, there is a need for a coated tool having cutting performance that can withstand it, and various improvements and proposals have been made for the α-type aluminum oxide layer that constitutes the outermost surface layer of the hard coating.

  For example, in Patent Document 1, at least an aluminum oxide layer is formed by a chemical vapor deposition method as a hard coating layer of a surface-coated cutting tool, and Ti oxide is dissolved or 30% by volume in the aluminum oxide layer. It has been proposed to improve the toughness, adhesion, and wear resistance of the surface-coated cutting tool by containing the following.

In Patent Document 2, the hard coating layer of the surface-coated cutting tool contains at least an Al ₂ O ₃ phase, a second phase composed of ZrO ₂ and / or HfO _2, and a third finely dispersed phase such as TiO _X. It has been proposed to improve the wear resistance of surface-coated cutting tools by forming a hard coating layer by chemical vapor deposition.

  Further, in Patent Document 3, the surface of the tool substrate is formed as a method for forming the α-type alumina layer by physical vapor deposition under a low temperature condition (1000 ° C. or less) so as not to cause deterioration and deformation of the characteristics of the tool substrate and the hard film. And nitrides, carbides, carbonitrides, borides, nitrogen oxides, charcoal containing Al and at least one element selected from the group consisting of 4a group, 5a group, 6a group and Si. After forming a hard film made of a nitride oxide by physical vapor deposition, an oxide-containing layer is formed by oxidizing the hard film, and physical vapor deposition is performed on the oxide-containing layer to form an outermost surface layer. It has been proposed to vapor-deposit an alumina layer mainly composed of an α-type crystal structure having excellent wear resistance and heat resistance.

  Furthermore, Patent Document 4 discloses a surface-coated cutting tool for coating an α-alumina-structured aluminum oxide layer having a film thickness of 0.05 to 5 μm and having a corundum type crystal structure on at least the outermost surface of a tool base. In the production method, the aluminum oxide layer is prepared by adding an alcohol (preferably an alcohol containing α-alumina particles having an average particle diameter of 10 to 300 nm) to an aluminum alkoxide, and further adding an acid (for example, dilute hydrochloric acid). A sol is produced by stirring at a low temperature of ℃ or less, and water is added to the sol so that the molar ratio of aluminum to water contained in the sol is 1:30 to 1: 150. A hard crystallization process is performed by heating and stirring at a temperature of 5 ° C., and the sol subjected to the high crystallization process is formed on the tool base surface or on the tool base surface. By coating on the outermost surface of the film, and subsequently repeating the drying process at 100 to 400 ° C. one or more times, and then performing a coating process by a sol-gel method in which a baking process is performed at a temperature range of 500 to 1000 ° C. It has been proposed to improve the wear resistance of the coated tool.

  In Patent Document 5, in a surface-coated cutting tool in which an aluminum oxide layer having an average layer thickness of 0.2 to 5 μm and high smoothness is formed on at least the outermost surface of a tool base by a sol-gel method, The aluminum layer is composed of a substrate and a spherical structure dispersed in the substrate, and the substrate is composed of an aluminum oxide crystal phase and an amorphous phase. The spherical structure is a kind of acicular crystal phase and plate-like crystal phase. Or it consists of an aggregate | assembly of 2 types and an amorphous phase, and the ratio of the area which the spherical structure | tissue which contains in the longitudinal cross-section of an aluminum oxide layer occupies 20-60 area%, and the radius of an approximate circle is 0.02-0. It has been proposed to improve the lubricity and wear resistance of the hard coating layer in high-speed heavy cutting such as cast iron and carbon steel by setting the thickness to 0.5 μm.

JP-A 61-195975 JP 2002-526654 A JP 2004-124246 A JP 2013-53344 A JP 2013-139076 A

  In the coated tool in which the aluminum oxide layer proposed in Patent Documents 1 and 2 is formed by chemical vapor deposition, in the cutting process under normal conditions due to the thermal stability and non-reactivity of the formed α-type aluminum oxide. It exhibits a certain degree of toughness and wear resistance, but for example, when it is used for cutting with high heat generation and intermittent and impact loads on the cutting edge, chipping and chipping are likely to occur. This has caused a problem that sufficient wear resistance cannot be exhibited over a long period of use.

  Further, in the coated tool in which the aluminum oxide layer formed by physical vapor deposition proposed in Patent Document 3 is a hard coating layer, the high-temperature stability of the aluminum oxide layer is poor and the hardness is not sufficient. There was a problem of inferiority.

In the coated tool in which the aluminum oxide layer is formed by the sol-gel method proposed in Patent Documents 4 and 5, the hard coating layer is excellent in thermal stability and is made into α-Al ₂ O ₃ having high nonreactivity. Therefore, by adding water or hydrochloric acid to the sol and heating it, the hydrolysis / condensation polymerization reaction is promoted, and a sol in which dense Al-O bonds close to α-type with a close-packed structure are dispersed is formed. Α-Al ₂ O ₃ having high crystallinity was formed by using the film. And when this is used for high-speed continuous cutting of cast iron and steel, it exhibits a long life, but in high-speed intermittent cutting of steel that is subject to a large impact, the film structure is made up of spherical structures and needle-like / plate-like crystal grains. It is poor in uniformity, and it is easy to cause abnormal damage such as chipping, chipping, peeling, etc. due to the nonuniformity and cracks from the tip of needle-like crystal grains, etc. There was a problem that it was not possible to exhibit excellent wear resistance.

Therefore, the inventors of the present invention have intensively studied to form an aluminum oxide layer having excellent chipping resistance on the surface of the tool base by the sol-gel method. As a result, an alumina sol in which Ti oxide fine particles are added in advance to the alumina sol is used. By forming an α-type aluminum oxide layer by the conventional sol-gel method, the α-type aluminum oxide crystal grains to be formed have a relatively large particle size, and the shape thereof is made spherical and elliptical. Furthermore, the present inventors have found that the formation of fragile tissue formed by the conventional sol-gel method can be suppressed.
And, when the coated tool formed with such an aluminum oxide layer is subjected to high-speed intermittent cutting with high heat generation and intermittent / impact load acting on the cutting edge, chipping, chipping, etc. It has been found that it exhibits excellent wear resistance over a long period of use.

This invention has been made based on the above findings,
“(1) In a surface-coated cutting tool in which a hard coating layer is coated on the surface of a tool base made of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet,
(A) The outermost surface layer of the hard coating layer is composed of an α-type aluminum oxide layer having an average layer thickness of 0.2 to 5.0 μm,
(B) The average crystal grain size of the α-type aluminum oxide crystal grains constituting the α-type aluminum oxide layer is smaller than the average layer thickness of the α-type aluminum oxide layer and is 0.05 to 0.4 μm. Within the range of
(C) Observe the cross-section of the α-type aluminum oxide layer and approximate the cross-sectional shape of the α-type aluminum oxide crystal grains having an average crystal grain size in the range of 0.05 to 0.4 μm. When the curvature of the grains is obtained, α-type aluminum oxide crystal grains whose maximum value of the curvature of each crystal grain whose shape is approximated are 70 (μm) ⁻¹ or less are 60% of all crystal grains present in the observation field. A surface-coated cutting tool characterized by occupying at least area%.
(2) In a surface-coated cutting tool formed by coating a hard coating layer on the surface of a tool base made of a tungsten carbide-based cemented carbide,
A base surface hardened layer having an average layer thickness of 0.5 to 3.0 μm in the depth direction from the surface of the tool base is formed, and an average content of Co as a binder phase metal contained in the base surface hardened layer is The surface-coated cutting tool according to (1), which is less than 2.0% by mass.
(3) In a surface-coated cutting tool formed by coating a hard coating layer on the surface of a tool base composed of a titanium carbonitride-based cermet,
A base surface hardened layer having an average layer thickness of 0.5 to 3.0 μm in the depth direction from the surface of the tool base is formed, and the total average of Co and Ni as binder phase metals contained in the base surface hardened layer Content is less than 2.0 mass%, The surface-coated cutting tool as described in (1) characterized by the above-mentioned.
(4) The α-type aluminum oxide layer contains fine Ti oxide, and the content of Ti contained in the α-type aluminum oxide layer is the total metal contained in the α-type aluminum oxide layer. The surface-coated cutting tool according to any one of (1) to (3), which is 0.2 to 10 atomic% of the element.
(5) the α-type aluminum oxide layer of the pre-Ti oxide particles with a sol obtained by adding a sol - method for producing a surface-coated cutting tool having the constitution that you formed gel method (4) . "
It is characterized by.

  Hereinafter, the present invention will be described in detail.

  The coated tool of the present invention includes an α-type aluminum oxide layer having an average layer thickness of 0.2 to 5.0 μm formed as a hard coating layer by a sol-gel method. If it is less than 2 μm, sufficient wear resistance cannot be exhibited over a long period of use. On the other hand, if the average layer thickness exceeds 5.0 μm, chipping tends to occur. The layer thickness of the aluminum layer was determined to be 0.2 to 5.0 μm.

The α-type aluminum oxide crystal grains constituting the α-type aluminum oxide layer have a spherical or ellipsoidal shape, the average crystal grain size is smaller than the average thickness of the aluminum oxide layer, and It is in the range of 05 to 0.4 μm.
When the shape of the α-type aluminum oxide crystal grains is not spherical or ellipsoidal, the occurrence of cracks cannot be suppressed when a high load acts on the cutting edge, and chipping resistance and chipping resistance I can't expect improvement.
In addition, when the average crystal grain size of the α-type aluminum oxide crystal grains is less than 0.05 μm, the wear resistance is not sufficient, while when the average crystal grain size exceeds 0.4 μm or the aluminum oxide layer When the thickness is larger than the average layer thickness, the surface roughness of the α-type aluminum oxide layer becomes rough, and chipping and defects are likely to occur.
Accordingly, the shape of the α-type aluminum oxide crystal grains is spherical or ellipsoidal, and the average crystal grain size is smaller than the average layer thickness of the aluminum oxide layer and is in the range of 0.05 to 0.4 μm. And

In addition, when the α-type aluminum oxide crystal grains of the present invention have a cross-sectional shape approximated by a circle or an ellipse, the circle curvature or the maximum curvature of the ellipse is 70 (μm). ^The aluminum oxide crystal grains that are ⁻¹ or less account for 60 area% or more of the total crystal grains.
Here, when the maximum ratio of the curvature of the α-type aluminum oxide crystal grains approximated to a circle or an ellipse is larger than 70 (μm) ⁻¹ , the ratio of the crystal grains in the α-type aluminum oxide layer is increased. Cracks are likely to occur at the tip of the crystal grains, and as a result, chipping resistance and chipping resistance are reduced.
Therefore, in the present invention, it is possible to increase the existence ratio of crystal grains having a maximum value of the curvature of a circle or an ellipse of α-type aluminum oxide crystal grains whose cross-sectional shape is approximated to a circle or an ellipse by 70 (μm) ⁻¹ or less. When such crystal grains occupy 60% by area or more of the total crystal grains, the frequency of occurrence of cracks is reduced even in cutting operations with high loads, and chipping resistance and chipping resistance The abnormal damage resistance such as is improved.
Therefore, in the present invention, when the cross-sectional shape of the α-type aluminum oxide crystal grains is approximated to a circle or an ellipse to obtain the curvature of the circle or the curvature of the ellipse, the maximum value of the curvature is 70 (μm) ⁻¹ or less. The occupation ratio of certain α-type aluminum oxide crystal grains was determined to be 60 area% or more of the total crystal grains present in the observation field.

In the present invention, the cross section of the α-type aluminum oxide layer is observed by TEM, and the cross-sectional shape of the α-type aluminum oxide crystal grains is approximated to a circle or an ellipse, thereby obtaining the maximum curvature and average crystal grain size of each crystal grain. It was.
As a method for circularly or elliptically approximating the cross-sectional shape of α-type aluminum oxide crystal grains, for example, a well-known method such as “method using multivariate linear least square method” is used. Approximate.
(Refer to Goro Sato, “Least-Square Method, Theory and Practice-Nonlinear Analysis of Observation Data”, or Goro Sato HP: http://www.geocities.jp/ikuro_kotaro/koramu/daenkinji.htm.)

For example, as shown in FIG. 1, the cross-sectional shape of an α-type aluminum oxide crystal grain is approximated by circle or ellipse from eight measurement points, and the circle or ellipse approximated by the circle or ellipse as shown in FIG. When the minor axis is 2b, the average particle diameter of the α-type aluminum oxide crystal grains can be obtained as (2a + 2b) / 2, and the curvature of the α-type aluminum oxide crystal grains is maximum at the end of the major axis. The maximum value k can be obtained by k = (a / b ² ).
In the case of a circle, a = b, the average particle diameter is 2a, and the maximum curvature k is k = 1 / b.

FIG. 3 shows four α-type aluminum oxide crystal grains obtained by TEM observation on the α-type aluminum oxide layer of the coated tool of the present invention. FIG. 4 shows these four α-type aluminum oxide layers. The crystal grains are approximated to a circle or an ellipse, and the respective values of the major axis 2a, minor axis 2b, grain size (a + b), and maximum curvature k measured for each crystal grain are shown.
As shown in FIG. 4, for the four α-type aluminum oxide crystal grains measured for the coated tool of the present invention, the average crystal grain diameter is in the range of 0.05 to 0.4 μm defined in the present invention, In addition, the maximum value of the curvature was 70 (μm) ⁻¹ or less in all cases.

Of course, the coated tool of the present invention can directly form the above-described α-type aluminum oxide layer on the surface of a tool base made of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet. Between the substrate surface and the α-type aluminum oxide layer, carbide, nitride, carbonitride, carbonate of at least one element selected from groups 4a, 5a, 6a, Al, Si of the periodic table After forming an under layer containing sapphire by physical vapor deposition (PVD method), chemical vapor deposition (CVD), or sol-gel method, the surface of the under layer hard coating is coated with the α-type aluminum oxide layer. It can also be formed.
Specific examples of the underlayer include Ti compound layers formed by chemical vapor deposition, such as TiN layers, TiCN layers, TiCO layers, TiCNO layers, and composite nitriding of Ti and Al formed by physical vapor deposition. A material layer, a composite nitride layer of Cr and Al, and the like. further,

  For example, in the formation of the base layer by physical vapor deposition (PVD), from the viewpoint of improving the adhesion with the α-type aluminum oxide layer, the base layer contains Al, and the base layer It is desirable to form a nitride layer (for example, a TiAlN layer, an AlCrN layer, etc.) in which the Al content in the metal component is 40 atomic% or more.

  This is because when the Al content of the metal component in the underlayer is a nitride layer of 40 atomic% or more, an oxide with a high aluminum concentration is formed at the interface between the nitride layer and the α-type aluminum oxide layer. The reason is that this oxide has a function of firmly bonding the nitride film and the α-type aluminum oxide layer.

The α-type aluminum oxide layer constituting the hard coating layer of the coated tool of the present invention is, for example, α-type by a sol-gel method using a relatively high concentration of acid or adding Ti oxide fine particles to the sol. In the case where Ti oxide is used, a fine Ti oxide, for example, TiO ₂ is contained together with α-type aluminum oxide, and the content ratio of the Ti oxide is: It is contained in an amount of 0.2 to 10 atomic% with respect to all metal elements contained in the layer.

Here, the nucleation of α-type aluminum oxide formed when the content of Ti contained as fine Ti oxide is less than 0.2 atomic% with respect to the total metal elements contained in the layer There are few points and a uniform structure is not formed. On the other hand, when it exceeds 10 atomic%, brittle Al and Ti oxynitrides are formed in the layer, and chipping resistance and chipping resistance are lowered. Therefore, the content ratio of Ti with respect to all the metal elements contained in the layer is 0.2 to 10 atomic%.
In the case where an α-type aluminum oxide layer is formed by a sol-gel method in which Ti oxide fine particles are added to the sol, TiO ₂ is suitable as the Ti oxide fine particles to be added to the sol. The ratio of Ti is preferably 0.5 to 10 atomic% when the total metal elements contained in the sol are 100 atomic%.

The aluminum oxide main layer can exhibit its performance by directly forming a film on the tool base. However, when a cemented carbide containing titanium carbonitride is used as the base, it can be used in a nitrogen atmosphere. By firing, a large amount of at least one kind of highly wear-resistant carbonitride of Ti, Ta, Nb, and Zr is contained in the vicinity of the tool base surface to form a base surface hardened layer, and an aluminum oxide main layer and The adhesion strength with the tool base can be improved and the tool life can be extended. In addition, it is preferable that the hardness of the cemented carbide base body after this base-surface hardened layer formation is 2200 or more and 2800 or less in terms of Vickers hardness (Hv). At that time, Co in the vicinity of the substrate surface is relatively reduced by containing a large amount of carbonitride, and for example, 0.5 to 3.0 μm in the depth direction from the surface using a scanning electron microscope (SEM). When the content of Co as a binder phase metal is detected by quantitative analysis by wavelength dispersive X-ray spectroscopy in an analysis visual field range of 1 × 1 μm, the Co content is 2. If it is less than 0% by mass, carbonitrides that cause surface hardening of the substrate are sufficiently formed, and wear resistance is further improved.
If the average thickness of the substrate surface hardened layer is 0.5 μm or less, it will be worn away relatively quickly without exhibiting sufficient wear resistance, and if it is 3.0 μm or more, chipping is likely to occur.

  In addition, when the titanium carbonitride-based cermet is used as a substrate, the atmosphere when holding at the highest temperature and the highest temperature in the sintering process is a predetermined nitrogen atmosphere, and by reducing the pressure during holding or when lowering the temperature, The surface can be cured more than when the entire sintering process is performed in a nitrogen atmosphere at a constant pressure. This is because when the process up to holding at the maximum temperature is performed under a constant nitrogen pressure, carbonitrides with high hardness are uniformly dispersed inside the substrate. Is treated under a relatively high nitrogen pressure, and during treatment or when the temperature is lowered to a more reduced nitrogen atmosphere, only the very surface of the substrate is denitrified, resulting in a Ni or Co metal bonded phase. This is because dissolution of Ti and Nb and diffusion from the inside to the surface of the substrate become active, formation of carbonitrides such as Ti and Nb is promoted on the surface, and a substrate surface hardened layer is formed. In addition, it is preferable that the hardness of the cermet base | substrate after this base-surface hardened layer formation is 2000 or more and 2600 or less in Vickers hardness (Hv). In this case, similarly to the above-mentioned carbide substrate, Ni and Co in the vicinity of the substrate surface are relatively reduced. For example, 0.5 to 0.5 in the depth direction from the surface using a scanning electron microscope (SEM). When the cross section of 3.0 μm is observed and quantitative analysis is performed by wavelength dispersive X-ray spectroscopy in the analysis visual field region range of 1 × 1 μm, the total content of Ni and Co as binder phase metals is 2.0 mass. If it is less than%, carbonitrides that cause surface hardening of the substrate are sufficiently formed, and wear resistance is further improved.

The α-type aluminum oxide layer constituting the surface layer of the coated tool of the present invention can be formed, for example, by the sol-gel method shown below.
In the present invention, when the α-type aluminum oxide layer is formed by the sol-gel method, the sol-gel method in which Ti oxide fine particles are mainly added to the alumina sol will be described. As a method, a method of adding Ti oxide fine particles that have been surface-treated so that they can be uniformly dispersed in alumina sol, a method of adding Ti oxide fine particles as a slurry in which alcohol is uniformly dispersed, and adding a dispersant to alumina sol in advance Thereafter, various additions such as a method of adding the Ti oxide fine particles to the alumina sol are possible, but any addition method may be used.

Preparation of alumina sol:
First, an alcohol (eg, ethanol, 1-butanol) is added to an aluminum alkoxide (eg, aluminum secondary butoxide, aluminum isopropoxide), then an acid (eg, hydrochloric acid, nitric acid) is added, and a predetermined amount After adding Ti oxide fine particles having a size, an acid sol (for example, hydrochloric acid) of a predetermined concentration is further added, and then the alumina sol is prepared by stirring at a temperature range of 30 to 50 ° C. for 1 to 3 hours.

  The concentration of the acid to be added is preferably 0.5 to 4.0 N, and the amount of acid added to the alcohol is preferably 0.1 to 2 times (volume).

Alumina sol retention:
Next, the alumina sol is held at a temperature range of 30 to 50 ° C. for 12 hours or more for the purpose of waiting until the hydrolysis / condensation reaction occurring in the sol reaches an equilibrium state.

Drying and firing:
A tool base coated with a tool base or an underlayer (for example, a Ti compound layer) is immersed in the alumina sol prepared above, and then pulled up from the alumina sol at a rate of 0.5 mm / sec. A drying treatment is performed at ˜600 ° C. for 10 minutes, this immersion treatment and drying treatment are repeated until the required layer thickness is obtained, and then a firing treatment is carried out in a temperature range of 700 to 1100 ° C.

  By the above drying treatment, a dry gel of alumina containing finely divided Ti oxide is formed, and by a subsequent firing treatment, a predetermined amount (0.2 to 10 atomic% of all metal elements) of aluminum oxide phase is formed. An α-type aluminum oxide layer containing dispersed fine Ti oxide is formed.

  The film thickness of the α-type aluminum oxide layer depends on the number of times of immersion in the alumina sol, but if the average layer thickness of the α-type aluminum oxide layer formed by coating is less than 0.2 μm, the coated tool can be used over a long period of use. On the other hand, when the average layer thickness exceeds 5.0 μm, the α-type aluminum oxide layer is liable to be peeled off. The thickness is 0.2 to 5.0 μm.

  In addition, when the firing temperature is less than 700 ° C., the rate of formation of α-type aluminum oxide crystal grains is slow, and amorphous or γ-type aluminum oxide is generated. An effective α-type aluminum oxide layer having sufficient high-temperature hardness is not formed, and chipping resistance is not sufficient. On the other hand, when firing at a temperature exceeding 1100 ° C., cracking due to the difference in thermal expansion between the fine Ti oxide and the α-type aluminum oxide layer is likely to occur, so the firing temperature is set to 700 to 1100 ° C.

In the present invention, the concentration of the acid used as the catalyst is increased without using Ti oxide fine particles, so that the colloidal particles dispersed in the alumina sol are likely to be nucleation points of α-type aluminum oxide crystals. It can be formed in a large and dense shape. As a result, it does not easily aggregate due to local hydrolysis and condensation polymerization in the aluminum oxide film. A high α-type aluminum oxide layer can be formed. In addition, when the sol-gel method using an alumina sol in which Ti oxide fine particles are added in advance to an alumina sol is used for this structure, a large number of Ti oxides become the starting point of crystallization, and an aluminum oxide layer with higher structure uniformity is formed. In addition to being able to be formed, the lubricity of the Ti oxide is combined with a further extension of the tool life. In addition, the conventional sol-gel method exhibits excellent lubricity and wear resistance in high-speed heavy cutting of cast iron and carbon steel due to accelerated hydrolysis and condensation polymerization, especially cracks during high-speed intermittent cutting. However, according to the present invention, the α-type aluminum oxide crystal grains are spherical or ellipsoidal and relatively round with no corners. It becomes a crystal grain with a large grain size, and the formation of a fragile structure is also suppressed.
Therefore, the coated tool of the present invention absorbs the impact with the entire particle even when a high load such as intermittent impact is applied to the cutting edge during high-speed intermittent cutting, so that the generation of cracks is suppressed, chipping, chipping, etc. It is possible to exhibit excellent wear resistance over a long period of use without causing any abnormal damage.

The schematic diagram which carried out the circular approximation or the ellipse approximation of the cross-sectional shape of the alpha-type aluminum oxide crystal grain of this invention is shown. These show schematic explanatory drawings for calculating the crystal grain size and the maximum curvature k of α-type aluminum oxide crystal grains that are elliptically approximated. About the alpha type aluminum oxide layer of this invention coated tool, the alpha type aluminum oxide crystal grain of the four measurement points which performed TEM observation, and the maximum value of the curvature are shown. The major axis 2a, minor axis 2b, grain size (a + b), and maximum value k of curvature measured at four measurement points of the α-type aluminum oxide crystal grains of the coated tool of the present invention are shown.

  Next, the present invention will be specifically described with reference to examples.

(A) As a raw material powder, fine WC powder having an average particle diameter of 0.8 μm, medium WC powder having an average particle diameter of 2 to 3 μm, and TiCN powder, ZrC powder, TaC powder each having an average particle diameter of 1 to 3 μm, After preparing NbC powder, Cr ₃ C ₂ powder and Co powder, these raw material powders were blended in the prescribed blending composition shown in Table 1, added with wax, ball mill mixed in acetone for 24 hours, and dried under reduced pressure , Pressed into a green compact of a predetermined shape at a pressure of 98 MPa, this green compact was vacuum-sintered at a temperature of 1400 ° C. for 1 hour in a vacuum of 5 Pa, and after sintering, the cutting edge portion R: A tool base A, B, C, D, E, F, G, H, I made of WC base cemented carbide having an insert shape specified in ISO / CNMG120408 by honing to 0.05 mm. (Tool substrate A, It was prepared C, D, E, F, G, H, a) that I.
However, after holding at 1400 ° C. for 1 hour, cooling to 1320 ° C. is performed for 40 minutes in a nitrogen atmosphere of 3.3 kPa for the carbide substrate F, and in a nitrogen atmosphere of 1 kPa for the carbide substrate G. The substrate surface is cured by cooling for 40 minutes in a nitrogen atmosphere of 2 kPa for carbide substrate H and for 120 minutes in a nitrogen atmosphere of 3.3 kPa for carbide substrate I. did.

(B) Next, a lower layer was formed on the tool bases A to I.
In forming the lower layer, the tool bases A and B are charged into a chemical vapor deposition apparatus, and the TiN layer, TiCN layer, TiCO layer, TiCNO having a granular crystal structure are formed using the film formation conditions shown in Table 2. An underlayer was formed in advance with a Ti compound layer comprising a layer and a TiCN layer having a vertically grown crystal structure (hereinafter referred to as 1-TiCN) with a film configuration shown in Table 5. On the other hand, the tool base C is inserted into an arc ion plating apparatus which is a kind of physical vapor deposition apparatus, and an underlayer composed of Ti _0.5 Al _0.5 N layers having the film thicknesses shown in Table 5 is formed in advance. did.
Further, the tool base D was similarly inserted into an arc ion plating apparatus, and an underlayer composed of an Al _0.7 Cr _0.3 N layer having a thickness shown in Table 5 was formed in advance.
On the other hand, for the tool bases E, F, G, H, and I, the base layer was not particularly formed.

(C) On the other hand, an alumina sol for coating the α-type aluminum oxide layer as the outermost surface layer of the hard coating layer by a sol-gel method was prepared as follows.
After adding a predetermined amount of ethanol shown in Table 3 and a specific and predetermined amount of Ti oxide fine particles shown in Table 3 to aluminum secondary butoxide, which is an alkoxide of a predetermined amount of aluminum shown in Table 3, 30 ~ Stirring was performed at 50 ° C., and hydrochloric acid to which a predetermined amount of water was added was added dropwise over 1 hour.

(D) As shown in Table 3, stirring is continued for 1 hour or more while being kept at 30 to 50 ° C. in a thermostatic bath, and further, the hydrolysis / condensation polymerization reaction in the sol is stabilized at 20 ° C. An alumina sol was prepared by holding for a predetermined time.
The final solution composition is in molar ratio
(Aluminum secondary butoxide): (water): (ethanol): (hydrochloric acid)
= 1: (80 to 120): 20: (0.5 to 4.0)
Adjustments were made to

(E) Next, the tool bases A to I (the lower layers were formed on some tool bases) were immersed in the alumina sol.

(F) Next, the tool bases A to I are pulled up from the alumina sol at a pulling rate of 0.5 mm / sec, dried at 500 ° C. for 10 minutes, and further dipped, lifted and dried. The coating tools 1 to 15 of the present invention shown in Tables 5 and 6 (referred to as the present invention tools 1 to 15) are performed by performing a firing treatment under the conditions shown in FIG. ) Was manufactured. In addition, about the tool bases E, F, G, H, and I in which the formation of the underlayer was not particularly performed, a cross section of 0.5 to 3.0 μm in the depth direction from the surface using a scanning electron microscope (SEM). Observation was performed, and the quantitative analysis of the binder phase metal and the measurement of the thickness of the hardened surface layer were performed by wavelength dispersion X-ray spectroscopy in the analysis visual field region of 1 × 1 μm. The results are shown in Table 5.

When the average layer thickness of the α-type aluminum oxide layer was measured with a transmission electron microscope for the present invention tools 1 to 15 above, the average value was substantially the same as the target layer thickness (average value of five locations). showed that.

Further, the α-type aluminum oxide layers of the above-described tools 1 to 15 of the present invention were observed in five views within the observation field range of layer thickness × 1 μm, and the cross-sectional shape of each α-type aluminum oxide crystal grain in the observation field range Was approximated to a circle or an ellipse, and the maximum value k of the approximate circle curvature or ellipse curvature was obtained.
In addition, the area ratio which occupies in the observation visual field of the alpha type aluminum oxide crystal grain whose maximum value of the calculated | required curvature k is 70 (micrometer) <^-1> or less was calculated | required.
Further, for each α-type aluminum oxide crystal grain, the cross-sectional shape is approximated to a circle or an ellipse, and the major axis 2a and the minor axis 2b are measured to obtain the grain size (a + b) of each individual crystal grain. The average crystal grain size was determined by averaging the grain sizes of the crystal grains.

Further, for the inventive tools 1 to 15, the longitudinal section of the α-type aluminum oxide layer is observed with a transmission electron microscope (TEM) in the field of view of the layer thickness × 1 μm, and the attached energy dispersion type Elemental analysis in the visual field range was performed with a spectroscopic device, and the content of Ti contained as fine Ti oxide in the α-type aluminum oxide layer was measured.
Table 6 shows the results.

[Comparative Example 1]
For comparison, a coated tool of a comparative example was manufactured by the following manufacturing method.

(A) First, the solution composition of each component in the reaction raw material is a molar ratio,
(Aluminum secondary butoxide): (water): (ethanol): (hydrochloric acid)
= 1: (80 to 120): 20: (0.5 to 4.0)
The alumina sol was prepared under the conditions shown in Table 4.
(B) Next, the tool bases A to I (however, in some cases, a Ti compound layer by chemical vapor deposition shown in Table 5, a Ti _0.5 Al _0.5 N layer or Al _0.7 by physical vapor deposition) The above-mentioned alumina sol was applied to the surface of the (Cr _0.3 N layer formed).
(C) Next, the coated alumina sol is dried under the same conditions as in Example 1, and after repeating the coating and drying until a predetermined layer thickness is obtained, the firing treatment is performed under the conditions shown in Table 4. The coated tools 1-15 of the comparative examples shown in Tables 5 and 7 (referred to as comparative tools 1-15) were produced.

The comparative tools 1 to 15 were also subjected to cross-sectional TEM observation, and the average layer thickness of the α-type aluminum oxide layer, the average crystal grain size of the α-type aluminum oxide crystal grains, and the maximum value k of the curvature were 70 (μm) ^{− The} area ratio occupied by α-type aluminum oxide crystal grains of ¹ or less was determined.
Table 7 shows the results.

  Next, the above-mentioned inventive tools 1 to 15 and comparative tools 1 to 15 were subjected to a SUS304 dry high-speed intermittent cutting test under the following conditions.

Work material: SUS304 lengthwise equidistantly 4 vertical grooved round bars,
Cutting speed: 130 m / min. ,
Incision: 1.1mm,
Feed: 0.22 mm / rev. ,
Cutting time: 5 minutes
The dry high-speed intermittent cutting test under the conditions (normal cutting speed is 100 m / min.), The subsequent wear state of each tool was observed, and the amount of flank wear was measured.

  These results are shown in Table 8.

TiCN (mass ratio TiC / TiN = 50/50) powder, Mo ₂ C powder, NbC powder, TaC powder, WC powder, Co powder, and raw material powder, all having an average particle diameter of 0.5 to 2 μm, and Ni powders were prepared, blended into the prescribed composition shown in Table 9, wet mixed for 24 hours with a ball mill, dried, and then pressed into a green compact at a pressure of 98 MPa. .Sintered in a nitrogen atmosphere of 3 kPa at a temperature of 1540 ° C. for 1 hour, and after sintering, the cutting edge part is subjected to a honing process of R: 0.07 mm to form an ISO standard / CNMG120212 chip shape. Tool bases J to R made of TiCN base cermet (referred to as tool bases J to R) were produced. However, for the tool base O, in a nitrogen atmosphere of 1.3 kPa, the rate of temperature rise was 2 ° C./min, the temperature was raised from room temperature to 1540 ° C. and held for 30 minutes, then a vacuum of 13 Pa was applied, and further at 1540 ° C. After holding for 30 minutes, the temperature was lowered to cure the surface. For the tool base P, the temperature was always increased and held at 1540 ° C. for 60 minutes in a vacuum of 13 Pa. For the tool base Q, the temperature was raised from room temperature to 1540 ° C. in a nitrogen atmosphere of 1.3 kPa for 30 minutes. , A vacuum of 13 Pa, and further held at 1540 ° C. for 5 minutes, and the tool substrate R was heated from room temperature to 1540 ° C. in a nitrogen atmosphere of 1.3 kPa and held for 30 minutes, and then a vacuum of 13 Pa was further obtained. After holding at 1540 ° C. for 90 minutes, the temperature was lowered to cure the surface.

Next, the above-mentioned tool bases J to R (however, for some, the lower layer shown in Table 10 (Ti compound layer by chemical vapor deposition, Ti _0.5 Al _0.5 N layer by physical vapor deposition or Al _0.7 Cr) _The above-mentioned alumina sol was applied to the surface of _0.3 N layer formed) The tool bases N, O, P, Q, and R in which the underlayer was not particularly formed in the same manner as in Example 1 Cross-sectional observation of 0.5 to 3.0 μm in the depth direction from the surface using a scanning electron microscope (SEM), and bonded phase metal by wavelength dispersive X-ray spectroscopy in the analysis visual field region range of 1 × 1 μm Table 10 shows the results of quantitative analysis and measurement of the thickness of the surface hardened layer.

  Next, the coated alumina sol was dried under the same conditions as in Example 1, and after repeating the coating and drying until a predetermined layer thickness was obtained, a firing treatment was performed under the conditions shown in Table 3. The coated tools 16 to 30 of the present invention (referred to as the present invention tools 16 to 30) shown in FIG.

For the inventive tools 16-30, as in Example 1, the average thickness and curvature of the α-type aluminum oxide crystal grains in which the average layer thickness and cross-sectional shape of the α-type aluminum oxide layer are circular or elliptical approximated. The area ratio occupied by α-type aluminum oxide crystal grains having a maximum value k of 70 (μm) ⁻¹ or less, and the content of Ti contained in the α-type aluminum oxide layer were determined.
Table 11 shows the results.

[Comparative Example 2]
Using the same tool bases J to R used in Example 2, the same sol-gel method as in Example 2 was performed under the same conditions as in Example 1, and further, coating and drying were represented. After repeating until the predetermined layer thickness shown in FIG. 12 is reached, firing treatment is performed under the conditions shown in Table 4 to obtain the coated tools 16 to 30 of the comparative examples shown in Tables 10 and 12 (referred to as comparative example tools 16 to 30). Manufactured.

The average layer thickness of the α-type aluminum oxide layer, the average crystal grain size of the α-type aluminum oxide crystal grains, and the maximum value k of the curvature k obtained for the comparative tools 16 to 30 are 70 (μm) ⁻¹ or less α Table 12 shows the area ratio of the aluminum oxide crystal grains of the mold.

Next, a dry high-speed intermittent cutting test was performed on the above-described inventive tools 16 to 30 and comparative tools 16 to 30 under the following conditions.
Work material: JIS / SCM432 lengthwise equidistant 4 round bars with vertical grooves,
Cutting speed: 220 m / min,
Cutting depth: 0.8 mm,
Feed: 0.35 mm / rev,
Cutting time: After 5 minutes cutting test (normal cutting speed is 180 m / min.), Observe the wear state of each tool, measure the flank wear amount, and damage the hard coating layer Was observed.
These results are shown in Table 13.

From the results shown in Tables 6 to 8 and Tables 11 to 13, the α-type aluminum oxide layer formed as a surface layer of the coated tools 1 to 30 of the present invention is formed from α-type aluminum oxide crystal grains. Is a relatively large particle size, and the shape thereof can be spheroidized and ellipsoidal, and further, the formation of fragile tissue can be suppressed. When used in high-speed interrupted cutting, it exhibits excellent wear resistance over a long period of use without causing abnormal damage such as chipping, chipping or peeling.

On the other hand, the coated tools 1 to 30 of the comparative examples are those in which the average particle diameter of the α-type aluminum oxide crystal grains is out of the numerical range defined in the present invention, or, among the crystal grains, the maximum value of curvature. The area ratio occupied by crystal grains of 70 (μm) ⁻¹ or less is outside the numerical range defined in the present invention, and abnormal damage such as chipping and chipping occurs when used for high-speed intermittent cutting. It is clear that the tool life is reached in a short time.

The coated tool according to the present invention can be used not only as an insert-shaped tool described as an example but also with a drill, an end mill, etc. The above effect is great.

Claims (5)

In a surface-coated cutting tool formed by coating a hard coating layer on the surface of a tool base made of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet,
(A) The outermost surface layer of the hard coating layer is composed of an α-type aluminum oxide layer having an average layer thickness of 0.2 to 5.0 μm,
(B) The average crystal grain size of the α-type aluminum oxide crystal grains constituting the α-type aluminum oxide layer is smaller than the average layer thickness of the α-type aluminum oxide layer and is 0.05 to 0.4 μm. Within the range of
(C) Observe the cross-section of the α-type aluminum oxide layer and approximate the cross-sectional shape of the α-type aluminum oxide crystal grains having an average crystal grain size in the range of 0.05 to 0.4 μm. When the curvature of the grains is obtained, α-type aluminum oxide crystal grains whose maximum value of the curvature of each crystal grain whose shape is approximated are 70 (μm) ⁻¹ or less are 60% of all crystal grains present in the observation field. A surface-coated cutting tool characterized by occupying at least area%. In a surface-coated cutting tool formed by coating a hard coating layer on the surface of a tool substrate made of a tungsten carbide-based cemented carbide,
A base surface hardened layer having an average layer thickness of 0.5 to 3.0 μm in the depth direction from the surface of the tool base is formed, and an average content of Co as a binder phase metal contained in the base surface hardened layer is The surface-coated cutting tool according to claim 1, wherein the surface-coated cutting tool is less than 2.0% by mass. In a surface-coated cutting tool formed by coating a hard coating layer on the surface of a tool base made of titanium carbonitride-based cermet,
A base surface hardened layer having an average layer thickness of 0.5 to 3.0 μm in the depth direction from the surface of the tool base is formed, and the total average of Co and Ni as binder phase metals contained in the base surface hardened layer Content is less than 2.0 mass%, The surface-coated cutting tool of Claim 1 characterized by the above-mentioned.   The α-type aluminum oxide layer contains fine Ti oxide, and the content of Ti contained in the α-type aluminum oxide layer is 0% of the total metal elements contained in the α-type aluminum oxide layer. The surface-coated cutting tool according to claim 1, wherein the surface-coated cutting tool is 2 to 10 atomic%. The α-type aluminum oxide layer of the pre-Ti oxide sol using a sol obtained by adding fine particles - method for producing a surface-coated cutting tool according to claim 4, characterized that you formed gel method.