Method of Manufacturing Coated Cutting Tool and Coated Cutting Tool Made From

1. Field of the Invention

The present invention relates to a method for manufacturing a coated cutting tool to provide a hard coating layer comprising an aluminum oxide overlayer and having a uniform layer thickness even at high thicknesses, as well as excellent adhesion to other layers of the cutting tool, wherein the tool exhibits excellent chipping resistance for extended periods of time in both continuous and intermittent cutting.

2. Discussion of the Background

Hard-material-coated sintered carbide cutting tools made of a cemented tungsten carbide-based substrate (hereinafter, referred to as a cemented carbide substrate), the surface of which is coated with a hard coating layer comprising an Al.sub.2 O.sub.3 layer are known. For example, hard coating layers composed of an Al.sub.2 O.sub.3 layer and one, two or more of a titanium carbide (TiC) layer, a titanium nitride (TiN) layer, a titanium carbonitride (TiCN) layer, a titanium oxide (TiO.sub.2) layer, a titanium oxycarbide (TiCO) layer, a titanium oxynitride (TiNO) layer, and a titanium oxycarbonitride (TiCNO) layer deposited using chemical vapor deposition and/or physical vapor deposition to an average layer thickness of 3-20 microns are known.

Further, it is also known to form the Al.sub.2 O.sub.3 layer of the coated cemented carbide cutting tool using a reaction gas having the following composition in vol % (hereinafter referred to merely as %, unless otherwise specified): Aluminum trichloride (AlCl.sub.3): 1-20%; Carbon dioxide (CO.sub.2): 1-20% (optionally, carbon monoxide (CO) or hydrogen chloride (HCl): 1-30%) and Hydrogen: remainder, at a reaction temperature of 950.degree.-1100.degree. C. and an atmospheric pressure of 20-200 torr of hydrogen.

Recently, there has been a strong tendency towards providing automatic cutting operations and labor cost savings in factories. Accordingly it is required to prolong the usable life of coated tools. As one means for coping with this requirement, the thickness of the Al.sub.2 O.sub.3 layer has been increased to provide improved oxidation resistance, thermal stability and high hardness among the hard coating layers constituting the tool. However when the Al.sub.2 O.sub.3 layer is made thicker, relative to other parts of the hard coating layer, the layer thickness thereof is made locally uneven by the use of the above-noted conventional Al.sub.2 O.sub.3 layer forming methods. As a result, not only is the layer thickness highly variable among the flank face, the rake face, and the cutting edge of the insert but also the adhesion (interlayer adhesion) of the Al.sub.2 O.sub.3 layer with other constituting layers is lowered. Because of this, the cutting edge tends to chip when the tool is used in intermittent cutting of metals, such as steel or cast iron, and the usable life of the tool is spent in a relatively short period of time.

Accordingly, one object of the present invention is to provide a method for the preparation of an Al.sub.2 O.sub.3 layer in a coating layer of a coated cemented carbide cutting tool that reduces chipping and provides longer tool lifetime in both continuous and intermittent cutting of metals.

A further object of the present invention is to provide a method for the preparation of an Al.sub.2 O.sub.3 layer in a coating layer of a coated cemented carbide cutting tool that provides improved layer thickness consistency.

A further object of the present invention is to provide a method for the preparation of an Al.sub.2 O.sub.3 layer in a coating layer of a coated cemented carbide cutting tool that provides improved interlayer adhesion.

These and other objects of the present invention have been satisfied by the discovery of a method for preparing a coated cutting tool comprising:

coating a surface of a substrate with a hard coating layer comprising an aluminum oxide layer, using chemical vapor deposition, physical vapor deposition or both, wherein the aluminum oxide layer is formed from a reaction gas comprising aluminum trichloride and nitrogen oxides in an inert gas as carrier gas.

The present invention relates to a method for preparing a coated cutting tool comprising:

coating a surface of a substrate with a hard coating layer comprising an aluminum oxide layer, using chemical vapor deposition, physical vapor deposition or both, wherein the aluminum oxide layer is formed from a reaction gas comprising aluminum trichloride and nitrogen oxides in an inert gas as carrier gas.

The present inventors have made the following observations:

(A) In an Al.sub.2 O.sub.3 layer formed using a conventional hydrogen atmosphere, CO.sub.2 and hydrogen (H.sub.2) as components constituting the reaction gas, the components react with each other according to the following reaction formula (1).

The resultant H.sub.2 O reacts with AlCl.sub.3 according to the following reaction formula (2) so that Al.sub.2 O.sub.3 is created by the hydrolysis of AlCl.sub.3.

In this case, since the reaction based on the formula (2) has a significantly higher reaction rate compared with the reaction based on the formula (1), H.sub.2 O created by the formula (1) is immediately reacted with AlCl.sub.3 existing in the reaction atmosphere. Therefore, almost all of the Al.sub.2 O.sub.3 is created in the gas phase and consequently the Al.sub.2 O.sub.3 layer is formed by the deposition of Al.sub.2 O.sub.3 nuclei onto the surface of substrate. Consequently, it is difficult to form Al.sub.2 O.sub.3 layers having a uniform layer thickness on the flank face, the rake face of a cutting portion and the cutting edge where the flank face intersects the rake face even if, for example, a cutting insert is placed in the flow of the reaction gas in any state. This difficulty is also increased since the Al.sub.2 O.sub.3 layers are affected by the flow of the reaction gas and the shape of the substrate. Thus there is great dispersion in the layer thickness.

(B) Based on observation (A) above, the present inventors concluded that when a layer is made by creating Al.sub.2 O.sub.3 nuclei adjacent and as close as possible to the surface, the layer thickness thereof can be made uniform. Thus, the inventors have developed an inert gas type reaction gas which permits such layer formation. The present method uses this reaction gas having the following composition by volume:

AlCl.sub.3 : 0.5-10%

Nitrogen oxides (hereinafter, shown by NO.sub.x): 1-30%

Inert gas as the carrier gas: remainder

When the inert gas type reaction gas mentioned above is used, NO.sub.x is dissolved at the surface of substrate according to the following reaction formula (a) and O created by the reaction according to the formula (a) is adsorbed to that surface, thus, the above O reacts with AlCl.sub.3 at that surface according to the following reaction formula (b).

Therefore, the layer is formed in a state where the Al.sub.2 O.sub.3 nuclei are mainly formed at the surface of the substrate, instead of in the gas phase, and the deposited layer is not significantly affected by the flow of the reaction gas and the shape of the substrate. As a result, the resultant deposited layer has a very small amount of local dispersion even if it is formed into a thick layer and further the adhesion of the layer to the substrate is enhanced. In addition, since the deposited layer is mainly composed of Al.sub.2 O.sub.3, that is, an aluminum oxide layer in which the content of the components constituting the reaction gas except Al and oxygen is 15% or less and preferably 10% or less, the deposited layer has oxidation resistance, thermal stability and high hardness similar to the characteristics provided with Al.sub.2 O.sub.3.

(C) TiCl.sub.4, ZrCl.sub.4 and HfCl.sub.4 gases additionally mixed with the reaction gas act as a catalyst for the reaction NO.sub.x .fwdarw.N.sub.2 +O (a)

Note, the aluminum oxide layer of the present invention is described herein as a crystalline/non-crystalline aluminum oxide compound layer in which the content of the components other than Al and O constituting the reaction gas is 15% or less.

The present invention relates to a method for preparing a coated tool by forming a hard coating layer comprising an aluminum oxide layer, preferably a hard coating layer having an average layer thickness of 3-20 microns and comprising the aluminum oxide layer and one, two or more of a TiC layer, a TiN layer, a TiCN layer, a TiO.sub.2 layer, a TiCO layer, a TiNO layer, and a TiCNO layer. The aluminum oxide layer is formed on the surface of a substrate using chemical vapor deposition and/or physical vapor deposition from a reaction gas comprising AlCl.sub.3 and NO.sub.x with an inert gas as carrier. The present method preferably forms the aluminum oxide layer constituting the hard coating layer as a relatively thick layer (compared to conventional Al.sub.2 O.sub.3 layers) using an inert gas-type reaction gas having the following composition:

AlCl.sub.3 : 0.5-10%

NO.sub.x : 1-30%

TiCl.sub.4 : 0-15%

N.sub.2 : 0-15%

H.sub.2 : 0-20%

with the proviso that when TiCl.sub.4 is present in the reaction gas, the volume ratio of Al.sub.2 O.sub.3 :TiCl.sub.4 is from 5 to 100; with the remainder of the reaction gas being an inert gas.

The present method provides a coated cutting tool in which the layer thickness of the Al.sub.2 O.sub.3 layer is more uniform and has enhanced adhesion to provide excellent chipping resistance.

When the amount of AlCl.sub.3 in the reaction gas is less than 0.5%, the formation of the aluminum oxide layer is slowed to a practically unacceptable level due to insufficient amounts of an Al source. When the amount exceeds 10%, since the Al source is excessively supplied, the crystallinity of the aluminum oxide layer (deposited layer) is lowered. Thus the amount is preferably set to 0.5-10%, more preferably to 2-7%.

When the amount of NO.sub.x in the reaction is less than 1%, the crystallinity of the deposited layer is lowered due to an insufficient supply of O relative to the amount of Al. When the amount of NO.sub.x exceeds 30%, there is too much dissolved O relative to the Al source, causing localized fluctuations in layer thickness due to the reaction:

Thus, the uniformity of the layer thickness is lowered. Accordingly, the amount is preferably set to 1-30%, more preferably to 5-20%.

TiCl.sub.4 is an optional component of the reaction gas of the present method which can be used to accelerate the reaction of the formula (a) NO.sub.x .fwdarw.N.sub.2 +O. When the amount of TiCl.sub.4 is less than 0.01%, the progress of the reaction of the above formula (a) can be insufficient, thus causing the supply of O for the preparation of Al.sub.2 O.sub.3 to be insufficient. Under such conditions, the Al.sub.2 O.sub.3 cannot be formed at a practical speed and the thickness uniformity of the layer is damaged. When the amount of TiCl.sub.4 exceeds 1%, a large amount of Ti exists in the reaction atmosphere causing the crystallinity of the deposited layer to be lowered. Thus, the TiCl.sub.4 amount is preferably set to 0.01-1%, more preferably to 0.1-0.5%.

While H.sub.2 is an optional component of the reaction gas of the present method which activates the reaction atmosphere, when the amount of H.sub.2 is less than 0.5%, the reaction atmosphere can be difficult to activate to the desired high level. When the amount of H.sub.2 exceeds 20%, the layer thickness of the deposited layer is made uneven. Thus, the amount of H.sub.2 is preferably set to 0.5-20%, more preferably to 1-10%.

N.sub.2 has a stabilizing effect on the reaction of formula (a) above. This stabilization presumably is caused by suppressing the mutual bonding of created O. When the amount of N.sub.2 is less than 1%, this stabilization effect cannot be sufficiently maintained, while when the amount of N.sub.2 exceeds 15%, there is a tendency that the speed of formation of the deposited layer is lowered. Thus, the amount of N.sub.2 in the reaction is preferably set to 1-15%, more preferably to 4-10%.

When TiCl.sub.4 is used as an optional component of the reaction gas, the ratios by volume of AlCl.sub.3 :TiCl.sub.4 should be maintained to balance the crystallinity of the formed layer and the layer forming speed. When the volume ratio of AlCl.sub.3 :TiCl.sub.4 is less than 5, the resulting ratio of Ti source to Al source in the reaction atmosphere is excessively increased, thus lowering the crystallinity of the deposited layer and the required layer characteristics cannot be provided in the aluminum oxide layer. When the ratio of AlCl.sub.3 :TiCl.sub.4 exceeds 100, the ratio of Ti:Al in the reaction atmosphere is excessively decreased. This causes the NO.sub.x dissolving action carried out by Ti on the surface of the substrate to be greatly lowered, particularly at a reaction temperature equal to or less than 1000.degree. C. Further, the O source for production of Al.sub.2 O.sub.3 is then insufficient and the layer forming speed is lowered. Thus, when TiCl.sub.4 is present in the reaction gas, the ratio of AlCl.sub.3 :TiCl.sub.4 is set to 5-100, preferably to 10-100 and more preferably to 10-50.

The reaction temperature for the present process is preferably 850.degree.-1150.degree. C., more preferably 900.degree.-1100.degree. C. and the atmospheric pressure is preferably 20-200 torr, more preferably 40-100 torr. When the reaction temperature is less than 850.degree. C., the crystallinity of the deposited layer tends to be lowered, whereas when the temperature exceeds 1150.degree. C., the aluminum oxide layer is coarsened and wear resistance is lowered. In addition, when the atmospheric pressure is less than 20 torr, the reaction is slowed and the layer is not formed at a sufficiently desirable speed, whereas when the pressure exceeds 200 torr, the surface of the aluminum oxide layer is made irregular, causing the coating layer thickness to be uneven.

The average layer thickness of the hard coating layer is preferably set to 3-20 microns. When the layer thickness is less than 3 microns, the desired excellent wear resistance cannot be provided, whereas when the layer thickness exceeds 20 microns, the cutting edge is likely to break and chip.

The present method can be applied to other substrates besides cemented carbides, including, but not limited to Al.sub.2 O.sub.3, AlN, Si.sub.3 N.sub.4 or SiC based substrates and their combination type ceramics and TiC, TiN, TiCN based cermets which are stable under the conditions of the present method.

Further, the method can be used to provide a wide variety of coated cutting tools required for longer tool life, including but not limited to, cutting inserts, reamers, and end mills.

Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified.

The following powder materials were prepared: medium grain WC powder having an average grain size of 2.8 microns, rough grain WC powder having an average grain size of 4.9 microns, (Ti, W) C (TiC/WC in a 30/70 weight ratio) powder having an average grain size of 1.5 microns, (Ti, W) CN (TiC/TiN/WC in a 24/20/56 weight ratio) powder having an average grain size of 1.2 microns, (Ta, Nb) C (TaC/NbC in a 90/10 weight ratio) powder having an average grain size of 1.2 microns, and Co powder having an average grain size of 1.1 microns. These powder materials were blended to have the blended compositions shown in Table 1 and wet mixed in a ball mill for 72 hours and dried. Then, they were molded to green compacts having the shapes regulated by ISO/CNMG120408 (for cemented carbide substrates A-D) and ISO/SEEN42AFTN1 (for cemented carbide substrate E) by a press. The resultant green compacts were made into the cemented carbide substrates A-E by being subjected to vacuum sintering under the conditions also shown in Table 1, respectively.

The cemented carbide substrate B was held in an atmosphere of CH.sub.4 gas at a gas pressure of 100 torr at 1,400.degree. C. for one hour and then subjected to carburization while being gradually cooled. After the processing, a Co-enriched-zone having a maximum Co content of 15.9 wt% and a depth of 42 microns was formed on the surface of the substrate by removing carbon and Co attached to the surface of the cemented carbide substrate by acid and barrel grinding.

Each of the cemented carbide substrates A and D had a Co-enriched-zone having a maximum Co content of 9.1 wt% and a depth of 23 microns, whereas the remaining cemented carbide substrates C and E had no Co-enriched-zone formed thereon and had a uniform structure as a whole. Table 1 shows the internal hardness of cemented carbide substrates A-E. (Rockwell hardness: A scale). The edges of these cemented carbide substrates A-E were subjected to honing.

Next, reactions 1-15 of the present invention and conventional reactions 1-10 were performed and coated cemented carbide tools (hereinafter, coated cemented carbide tools corresponding to the respective methods are referred to as present coated cutting tools 1-15 and conventional coated cutting tools 1-10) were manufactured by forming hard coating layers having the compositions and target layer thicknesses (at the flank face) shown in Tables 4 and 5 using conventional chemical vapor deposition, under the conditions shown in Table 2 (1 -TiCN in Table 2 has a longitudinally-grown crystal structure as disclosed in Japanese Unexamined Patent Publication No. 6-8010 and p-TiCN in Table 2 has an ordinary grain-shaped crystal structure) and Table 3 (Al.sub.2 O.sub.3 (a) -(n) in Table 3 show aluminum oxide layers and Al.sub.2 O.sub.3 (o) shows an Al.sub.2 O.sub.3 layer, which are also applicable to Tables 4 and 5).

As to each of the aluminum oxide layers and the Al.sub.2 O.sub.3 layers (referred to collectively as Al.sub.2 O.sub.3 layers in Tables 6 and 7) constituting the hard coating layers of the various resultant coated cemented carbide tools, the maximum layer thickness of the cutting edge where a flank face intersected a rake face was measured and further the layer thicknesses on the flank face and the rake face which were located 1 mm inward from the cutting edge were measured. Tables 6 and 7 show the results of the measurements.

The layer thicknesses of the layers constituting the hard coating layer, other than the aluminum oxide layer and the Al.sub.2 O.sub.3 layer, had almost no local dispersion and exhibited almost the same values as the target layer thicknesses.

The elemental compositions of the aluminum oxide layer of the hard-material-coated cutting tools of the present invention and of the Al.sub.2 O.sub.3 layer of the conventional hard-material-coated cutting tools were analyzed using an EPMA. For those tools having an outermost layer composed of TiN, the analysis was carried out after the removal of the TiN using aqueous hydrogen peroxide. Measurement was carried out by irradiating, with a circular electron beam having a diameter of 1 mm, on the center of a flank face for tools having a shape according to ISO/CNMG120408 and on the center of a rake face for tools having a shape according to ISO/SEEN42AFTN1.

As a result, the present coated cutting tools 1-15 contained (in wt %) Al: 47.6-49.8%, O: 37.7-45.8%, Ti: 4.4-10.9%, and Cl: 0.015-0.21%. Likewise, the conventional coated cutting tools 1-10 contained Al: 52.8-53.0%, O: 47.0-47.2%, Ti: 0.01-0.02%, and Cl: less than measurable limit.

For the purpose of evaluating chipping resistance, present coated cutting tools 1-3 and conventional coated cutting tools 1 and 2 were subjected to an intermittent cutting test of ductile cast iron under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/FCD450

Cutting speed: 180 m/min.

Cutting depth: 2 mm

Feed rate: 0.3 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 4-6 and conventional coated cutting tools 3 and 4 were subjected to a dry intermittent cutting test of alloy steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/SCM440

Cutting speed: 180 m/min.

Cutting depth: 2 mm

Feed rate: 0.3 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 7-9 and conventional coated cutting tools 5 and 6 were subjected to a dry intermittent cutting test of carbon steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/S45C

Cutting speed: 180 m/min.

Cutting depth: 2 mm

Feed rate: 0.3 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 10-12 and conventional coated cutting tools 7 and 8 were subjected to a dry intermittent cutting test of cast iron under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/FC200

Cutting speed: 180 m/min.

Cutting depth: 2 mm

Feed rate: 0.3 mm/rev. Cutting time: 15 minutes

Present coated cutting tools 13-15 and conventional coated cutting tools 9 and 10 were subjected to a dry milling cutting test (intermittent cutting) of alloy steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/SNCM439 with a width of 100 mm and a length of 500 mm

Using condition: mounting of single tooth on cutter of 125 mm dia.

Rotation: 510 r.p.m.

Cutting speed: 200 m/min.

Cutting depth: 2 mm

Feed rate: 0.2 mm/tooth

Cutting time: 3 paths (cutting time/path: 5.3 minutes)

Tables 6 and 7 show the results of these measurements.

Cemented carbide substrates A-E were prepared by the same method as used in Example 1. Next, reactions 16-30 of the present invention and conventional reactions 11-20 were performed and coated cemented carbide tools (hereinafter referred to as present coated cutting tools 16-30 and conventional coated cutting tools 11-20) were manufactured by forming hard coating layers having the compositions and target layer thicknesses (at the flank face) shown in Tables 9 and 10 using conventional chemical vapor deposition under the conditions shown in Table 2 and Table 8 (Al.sub.2 O.sub.3 (a)-(n) in Table 8 show aluminum oxide layers and Al.sub.2 O.sub.3 (o) shows an Al.sub.2 O.sub.3 layer, which are also applicable to Tables 9 and 10).

As to each of the aluminum oxide layers and the Al.sub.2 O.sub.3 layers (collectively referred to in Tables 11 and 12 as Al.sub.2 O.sub.3 layers) constituting the hard coating layers of the various resultant coated cutting tools, the maximum layer thickness of the cutting edge where a flank face intersected a rake face was measured and further the layer thicknesses on the flank face and the rake face which were located 1 mm inward from the cutting edge were measured. Tables 11 and 12 show the results of the measurements.

The layer thicknesses of the layers constituting the hard coating layer, other than the aluminum oxide layer and the Al.sub.2 O.sub.3 layer, had almost no local dispersion and exhibited almost the same values as target layer thicknesses.

The elemental composition of the aluminum oxide layer of the present coated cutting tools and that of the Al.sub.2 O.sub.3 layer of the conventional coated cutting tools were analyzed using an EPMA. Elemental analysis was carried out according to the same procedure used in Example 1.

As a result, present coated cutting tools 16-30 contained (in wt %) Al: 46.5-49.9%, O: 37.7-45.8%, Ti: 4.1-12.1%, and Cl: 0.019-0.23%. Likewise, conventional coated cutting tools 11-20 contained Al: 52.8-53.0%, O: 47.0-47.2%, Ti: 0.01-0.02%, and Cl: less than measurable limit.

For the purpose of evaluating chipping resistance, present coated cutting tools 16-18 and conventional coated cutting tools 11 and 12 were subjected to an intermittent cutting test of ductile cast iron under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/FCD450

Cutting speed: 180 m/min.

Cutting depth: 2.5 mm

Feed rate: 0.3 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 19-21 and conventional coated cutting tools 13 and 14 were subjected to a dry intermittent cutting test of alloy steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/SCM440

Cutting speed: 180 m/min.

Cutting depth: 2.5 mm

Feed rate: 0.3 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 22-24 and conventional coated cutting tools 15 and 16 were subjected to a dry intermittent cutting test of carbon steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/S45C

Cutting speed: 180 m/min.

Cutting depth: 2.5 mm

Feed rate: 0.3 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 25-27 and conventional coated cutting tools 17 and 18 were subjected to a dry intermittent cutting test of cast iron under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/FC200

Cutting speed: 180 m/min.

Cutting depth: 2.5 mm

Feed rate: 0.3 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 28-30 and conventional coated cutting tools 19 and 20 were subjected to a dry milling cutting test (intermittent cutting) of alloy steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/SCM440 with a width of 100 mm and a length of 500 mm

Using condition: mounting of single tooth on cutter of 125 mm dia.

Rotation: 510 r.p.m.

Cutting speed: 200 m/min.

Cutting depth: 2 mm

Feed rate: 0.2 mm/tooth

Cutting time: 3 paths (cutting time/path: 5.3 minutes)

Tables 11 and 12 show the results of these measurements.

Cemented carbide substrates A-E were prepared by the same method as used in Example 1. Next, reactions 31-44 of the present invention and conventional methods 21-30 were performed, and coated cemented carbide tools (hereinafter, referred to as present coated cutting tools 31-44 and conventional coating cutting tools 21-30) were manufactured by forming hard coating layers having the compositions and target layer thicknesses (at the flank face) shown in Tables 14 and 15 using conventional chemical vapor deposition, under the conditions shown in Table 2 and Table 13 (Al.sub.2 O.sub.3 (a)-(l) in Table 13 show aluminum oxide layers and Al.sub.2 O.sub.3 (m) shows an Al.sub.2 O.sub.3 layer, which are also applicable to Tables 14 and 15 likewise).

With respect to each of the aluminum oxide layers and the Al.sub.2 O.sub.3 layers (referred to collectively in Tables 16 and 17 as Al.sub.2 O.sub.3 layers) constituting the hard coating layers of the various resultant coated cutting tools, the maximum layer thickness of the cutting edge where a flank face intersected a rake face was measured and further the layer thicknesses on the flank face and the rake face which were located 1 mm inward from the cutting edge were measured. Tables 16 and 17 show the results of the measurements.

The layer thicknesses of the layers of the hard coated layer, other than the aluminum oxide layer and the Al.sub.2 O.sub.3 layer, had almost no local dispersion and exhibited almost the same values as target layer thicknesses.

The elemental composition of the aluminum oxide layer of the present coated cutting tools and that of the Al.sub.2 O.sub.3 layer of the conventional coated cutting tools were analyzed using an EPMA. Elemental analysis was carried out using the same procedure as in Example 1.

The present coated cutting tools 31-44 contained (in wt %) Al: 46.6-47.8%, O: 35.5-42.8%, Ti: 6.5-14.3%, and Cl: 0.11-0.46%. Likewise, conventional coated cutting tools 21-30 contained Al: 52.8-53.0%, O: 47.0-47.2%, Ti: 0.01-0.02%, and Cl: less than measurable limit.

For the purpose of evaluating chipping resistance, present coated cutting tools 31-36 and conventional coated cutting tools 21 and 22 were subjected to an intermittent cutting test of mild steel under the following conditions to measure the flank face wear.

Cutting material: square piece of mild steel

Cutting speed: 220 m/min.

Cutting depth: 1.5 mm

Feed rate: 0.18 mm/rev.

Cutting time: 20 minutes

Present coated cutting tools 37-38 and conventional coated cutting tools 23 and 24 were subjected to a dry intermittent cutting test of ductile cast iron under the following conditions to measure the flank face wear.

Cutting material: square piece of JIS/FCD450

Cutting speed: 150 m/min.

Cutting depth: 2 mm

Feed rate: 0.3 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 39 and 40 and conventional coated cutting tools 25 and 26 were subjected to a dry intermittent cutting test of alloy steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/SNC/N439

Cutting speed: 150 m/min.

Cutting depth: 2 mm

Feed rate: 0.3 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 41 and 42 and conventional coated cutting tools 27 and 28 were subjected to a dry intermittent cutting test of carbon steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/S45C

Cutting speed: 150 m/min.

Cutting depth: 2 mm

Feed rate: 0.3 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 43 and 44 and conventional coated cutting tools 29 and 30 were subjected to a dry milling cutting test (intermittent cutting) of mild steel under the following conditions to measure flank face wear.

Cutting material: square piece of mild steel with a width of 100 mm and a length of 500 mm

Using condition: mounting of single tooth on cutter of 125 mm dia.

Rotation: 600 r.p.m.

Cutting speed: 280 m/min.

Cutting depth: 2 mm

Feed rate: 0.24 mm/tooth

Cutting time: 7 paths (cutting time/path: 3.6 minutes) Tables 16 and 17 show the result of these measurements.

Cemented carbide substrates A-E were prepared by the same method as used in Example 1. Next, reactions 46-60 (45 lacked) of the present invention and conventional reactions 31-40 were performed, and coated cemented carbide tools (hereinafter, referred to as present coated cutting tools 46-60 and conventional coated cutting tools 31-40) were manufactured by forming hard coating layers having the compositions and target layer thicknesses (at the flank face) shown in Tables 19 and 20 using conventional chemical vapor deposition, under the conditions shown in Table 2 and Table 18 (Al.sub.2 O.sub.3 (a)-(l) in Table 18 show aluminum oxide layers and Al.sub.2 O.sub.3 (m) shows an Al.sub.2 O.sub.3 layer, which are also applicable to Tables 19 and 20 likewise).

As to each of the aluminum oxide layers and the Al.sub.2 O.sub.3 layers (collectively referred to in Tables 21 and 22 as Al.sub.2 O.sub.3 layers) constituting the hard coating layers of the various resultant coated cutting tools, the maximum layer thickness of the cutting edge where a flank face intersected a rake face was measured and further the layer thicknesses on the flank face and the rake face which were located 1 mm inward from the cutting edge were measured. Tables 21 and 22 show the result of the measurements.

The layer thicknesses of the layers constituting the hard coating layer, other than the aluminum oxide layer and the Al.sub.2 O.sub.3 layer, had almost no local dispersion and exhibited almost the same values as target layer thicknesses.

The elemental composition of the aluminum oxide layer of the present coated cutting tools and that of the Al.sub.2 O.sub.3 layer of the conventional coated cutting tools were analyzed using an EPMA. Elemental analysis was carried out based on the same procedure as used in Example 1.

Present coated cutting tools 46-60 contained (in wt %) Al: 44.3-47.9%, O: 35.1-42.7%, Ti: 5.9-14.7%, and Cl: 0.14-0.41%. Likewise, conventional coated cutting tools 31-40 contained Al: 52.8-53.0%, 0: 47.0-47.2%, Ti: 0.01-0.02%, and Cl: less than measurable limit.

For the purpose of evaluating chipping resistance, present coated cutting tools 46-48 and conventional coated cutting tools 31 and 32 were subjected to an intermittent cutting test of ductile cast iron under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/FCD450

Cutting speed: 180 m/min.

Cutting depth: 3 mm

Feed rate: 0.2 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 49-51 and conventional coated cutting tools 33 and 34 were subjected to a dry intermittent cutting test of alloy steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/SNCM439

Cutting speed: 180 m/min.

Cutting depth: 3 mm

Feed rate: 0.2 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 52-54 and conventional coated cutting tools 35 and 36 were subjected to a dry intermittent cutting test of carbon steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/S30C

Cutting speed: 180 n/min.

Cutting depth: 3 mm

Feed rate: 0.2 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 55-57 and conventional coated cutting tools 37 and 38 were subjected to a dry intermittent cutting test of cast iron under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/FC300

Cutting speed: 180 m/min.

Cutting depth: 3 mm

Feed rate: 0.2 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 58-60 and conventional coated cutting tools 39 and 40 were subjected to a dry milling cutting test (intermittent cutting) of alloy steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/SNCM439 with a width of 100 mm and a length of 500 mm

Using condition: mounting of single tooth on cutter of 125 mm dia.

Rotation: 510 r.p.m.

Cutting speed: 200 m/min.

Cutting depth: 2 mm

Feed rate: 0.2 mm/tooth

Cutting time: 3 paths (cutting time/path: 5.3 minutes) Tables 21 and, 22 show the results of these measurements.

Cemented carbide substrates A-E were prepared by the same method as used i n Example 1. Reactions 61-75 of the present invention and conventional methods 41-50 performed and coated cemented carbide tools (hereinafter, referred to as present coated cutting tools 61-75 and conventional coated cutting tools 41-50) were manufactured by forming hard coating layers having the compositions and target layer thicknesses (at the flank face) shown in Tables 24 and 25 using conventional chemical vapor deposition, under the conditions shown in Table 2 and Table 23 (Al.sub.2 O3 (a)-(m) in Table 23 show aluminum oxide layers and Al.sub.2 O.sub.3 (n) shows an Al.sub.2 O.sub.3 layer, which is also applicable to Tables 24 and 25 likewise).

As to each of the aluminum oxide layers and the Al.sub.2 O.sub.3 layers (collectively referred to in Tables 26 and 27 as Al.sub.2 O.sub.3 layers) constituting the hard coated layers of the various resultant coated cutting tools, the maximum layer thickness of the cutting edge where a flank face intersected a rake face was measured and further the layer thicknesses on the flank face and the rake face which were located 1 mm inward from the cutting edge were measured. Tables 26 and 27 show the results of the measurements.

The layer thicknesses of the layers constituting the hard coating layer, other than the aluminum oxide layer and the Al.sub.2 O.sub.3 layer, had almost no local dispersion and exhibited almost the same values as target layer thicknesses.

The elemental composition of the aluminum oxide layer of the present coated cutting tools and that of the Al.sub.2 O.sub.3 layer of the conventional coated cutting tools were analyzed using an EPMA. Elemental analysis was carried out based on the same procedure as Example 1.

Present coated cutting tools 61-75 contained (in wt %) Al: 52.8-53.1%, O: 46.5-46.9%, and Cl: 0.13-0.36%. Likewise, conventional coated cutting tools 41-50 contained Al: 52.8-53.0%, O: 47.0-47.2%, Ti: 0.01-0.02%, and Cl: less than measurable limit.

For the purpose of evaluating chipping resistance, present coated cutting tools 61-63 and conventional coated cutting tools 41 and 42 were subjected to an intermittent cutting test of ductile cast iron under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/FCD450

Cutting speed: 200 m/min.

Cutting depth: 1.5 mm

Feed rate: 0.35 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 64-66 and conventional coated cutting tools 43 and 44 were subjected to a dry intermittent cutting test of alloy steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/SCM440

Cutting speed: 200 m/min.

Cutting depth: 1.5 mm

Feed rate: 0.35 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 67-69 and conventional coated cutting tools 45 and 46 were subjected to a dry intermittent cutting test of carbon steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/S45C

Cutting speed: 200 m/min.

Cutting depth: 1.5 mm

Feed rate: 0.35 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 70-72 and conventional coated cutting tools 47 and 48 were subjected to a dry intermittent cutting test of cast iron under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/FC200

Cutting speed: 200 m/min.

Cutting depth: 1.5 mm

Feed rate: 0.35 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 73-75 and conventional coated cutting tools 49 and 50 were subjected to a dry milling cutting test (intermittent cutting) of alloy steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/SNCM439 with a width of 100 mm and a length of 500 mm

Using condition: mounting of single tooth on cutter of 125 mm dia.

Rotation: 380 r.p.m.

Cutting speed: 150 m/min.

Cutting depth: 2 mm

Feed rate: 0.25 mm/tooth

Cutting time: 2 paths (cutting time/path: 5.5 minutes) Tables 26 and 27 show the results of these measurements.

Cemented carbide substrates A-E were prepared by the same method as used in Example 1. Reactions 76-85 of the present invention and conventional reactions 51-60 were performed and coated cemented carbide tools (hereinafter, referred to as the present coated cutting tools 76-85 and conventional coated cutting tools 51-60) were manufactured by forming hard coating layers having the compositions and target layer thicknesses (at the flank face) shown in Tables 29 and 30 using conventional chemical vapor deposition device, under the conditions shown in Table 2 and Table 28 (Al.sub.2 O.sub.3 (a)-(i) in Table 28 show aluminum oxide layers and Al.sub.2 O.sub.3 (j) shows an Al.sub.2 O.sub.3 layer, which are also applicable to Tables 29 and 30).

As to each of the aluminum oxide layers and the Al.sub.2 O.sub.3 layers (collectively referred to in Tables 31 and 32 as Al.sub.2 O.sub.3 layers) constituting the hard coating layers of the various resultant coated cutting tools, the maximum layer thickness of the cutting edge where a flank face intersected a rake face was measured and further the layer thicknesses on the flank face and the rake face which were located 1 mm inward from the cutting edge were measured. Tables 31 and 32 show the results of the measurements.

The layer thicknesses of the layers constituting the hard coating layer, other than the aluminum oxide layer and the Al.sub.2 O.sub.3 layer, had almost no local dispersion and exhibited almost the same values as target layer thicknesses.

The elemental composition constituting the aluminum oxide layer of the present coated cutting tools and that of the Al.sub.2 O.sub.3 layer of the conventional coated cutting tools were analyzed using an EPMA. Elemental analysis was carried out based on the same procedure used in Example 1.

Present coated cutting tools 76-85 contained (in wt %) Al: 52.9-53.1%, O: 46.4-46.7%, and Cl: 0.45-0.47%. Likewise, the conventional coated cutting tools 51-60 contained Al: 52.8-53.0%, O: 47.0-47.2%, Ti: 0.01-0.02%, and Cl: less than measurable limit.

For the purpose of evaluating chipping resistance, present coated cutting tools 76 and 77 and conventional coated cutting tools 51 and 52 were subjected to an intermittent cutting test of ductile cast iron under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/FCD450

Cutting speed: 200 m/min.

Cutting depth: 1.5 mm

Feed rate: 0.3 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 78 and 79 and conventional coated cutting tools 53 and 54 were subjected to a dry intermittent cutting test of alloy steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/SCM440

Cutting speed: 200 m/min.

Cutting depth: 1.5 mm

Feed rate: 0.3 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 80 and 81 and conventional coated cutting tools 55 and 56 were subjected to a dry intermittent cutting test of carbon steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/S45C

Cutting speed: 200 m/min.

Cutting depth: 1.5 mm

Feed rate: 0.3 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools 82 and 83 and conventional coated cutting tools 57 and 58 were subjected to a dry intermittent cutting test of cast iron under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/FC200

Cutting speed: 200 m/min.

Cutting depth: 1.5 mm

Feed rate: 0.3 mm/rev.

Cutting time: 15 minutes

Present coated cutting tools of the present invention 84 and 85 and conventional coated cutting tools 59 and 60 were subjected to a dry milling cutting test (intermittent cutting) of alloy steel under the following conditions to measure flank face wear.

Cutting material: square piece of JIS/SNCM439 with a width of 100 mm and a length of 500 mm

Using condition: mounting of single tooth on cutter of 125 mm dia.

Rotation: 380 r.p.m.

Cutting speed: 150 m/min.

Cutting depth: 2 mm

Feed rate: 0.2 mm/tooth

Cutting time: 2 paths (cutting time/path: 7 minutes)

Tables 31 and 32 show the result of these measurements.

It is apparent from the above results that the coated cutting tools made by the method of the present invention, in which the aluminum oxide layer constituting the hard coating layers is formed using the inert gas type reaction gas, have only very small amounts of local layer thickness dispersion in the aluminum oxide layer among the hard coating layers constituting the tools, even if the layer is relatively thick and the layer thicknesses of the flank face and the rake face of a cutting portion and the cutting edge where the flank face intersects the rake face are made uniform, whereas the conventional coated cutting tools made by the conventional method using a reaction gas in hydrogen for the formation of the Al.sub.2 O.sub.3 layer have a great amount of dispersion of the layer thicknesses in a flank face, a rake face, and a cutting edge. Thus the present coated cutting tools exhibited excellent chipping resistance in the intermittent cutting of steel and cast iron as compared with that of the conventional coated cutting tools.

As described above, according to the method of the present invention, coated cutting tools in which the aluminum oxide layer constituting the hard coating layer has an increased thickness, give a very small amount of local dispersion in the layer thickness. Consequently, the above aluminum oxide layer of the present invention coated cutting tools has the same characteristics as those of the Al.sub.2 O.sub.3 layer. Additionally, the present tools exhibit excellent chipping resistance not only in continuous cutting but also in intermittent cutting of metals, such as steel and cast iron, and achieve an excellent cutting performance over extended periods of time. Therefore, the present invention provides a useful industrial advantage by contributing to automatic cutting operation and labor cost saving in factories.

This application is based on Japanese Patent Applications 08-002292 (filed Jan. 10, 1996); 08-068114 (filed Mar. 25, 1996); 08-091025 (filed Apr. 12, 1996); 08-092423 (filed Apr. 15, 1996); 08-093966 (filed Apr. 16, 1996); 08-304335 (filed Nov. 15, 1996); and 08-304336 (filed Nov. 15, 1996), all filed with the Japanese Patent Office, the entire contents of each of which are hereby incorporated by reference.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.