JP2002205207A - Cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated cemented carbide tool for milling cutter in which heat resisting cracking property and an impact strength are compatible. SOLUTION: A cutting tool has cemented carbide consisting of a hard phase containing WC and a binder phase containing Co and a covering phase formed on the surface of the cemented carbide and satisfies under-mentioned conditions. (1) 1-25%mass at least one kind selected from a group consisting of carbide (except WC) of periodic tables 4a, 5a, and 6a group metals, nitride, oxide, and a solid solution is contained as a hard phase. (2) A content of a coupling phase in cemented carbide is 5-15 mass%. (3) An average grain size of WC is at least 2 μm. (4) A value of an anti magnetic force Hc of cemented carbide is in a range of 140-180. (5) A value (4 πσ/Co) obtained by dividing a saturated magnetic amount 4 πσ of cemented carbide by mass% of Co contained in cemented carbide is 8-15. (6) A η phase is not contained in cemented carbide. (7) A coated layer contains Al.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cutting tool. In particular, it relates to a carbide tool for milling that has both heat crack resistance and wear resistance.

[0002]

2. Description of the Related Art In cemented carbide cutting tools, high-speed cutting and dry cutting have been promoted from the viewpoint of high efficiency of cutting lines and environmental measures, and under these cutting conditions, thermal cracking has occurred. Breakage is a major determinant of tool life. As a countermeasure against damage due to thermal cracking, a technique for improving the heat resistance by forming a coating layer having Al ₂ 0 ₃ layer on the cemented carbide surface has been proposed. Also, by defining the ratio of the saturation magnetic amount of the cemented carbide to the Co content and the coercive force Hc,
Techniques for improving the hardness and toughness of cemented carbide have also been proposed (Japanese Patent Publication No. 62-48751, Japanese Patent Laid-Open No. 4-202738,
JP-A-5-98385).

[0003]

However, under severe cutting conditions such as high-speed machining, no matter how much the heat resistance of the coating layer is improved, heat is generated and thermal cracking of the cemented carbide cannot be avoided. There's a problem. In other words, in a process in which heat is likely to be generated at the cutting edge of a tool such as a high-speed or dry process, it is important to improve the heat resistance of the cemented carbide itself as well as the heat resistance of the coating layer. Therefore,
Further improvements in hardness and heat resistance of cemented carbide have been demanded.

Accordingly, it is a primary object of the present invention to provide a cutting tool having both toughness and hardness, and in particular, to provide a coated cemented carbide tool for milling which can achieve both heat crack resistance and impact strength.

[0005]

SUMMARY OF THE INVENTION According to the present invention, the amount of carbon in a cemented carbide is adjusted to an appropriate amount so that the saturated magnetic amount of the cemented carbide is 4πσ.
Divided by the mass% of Co contained in the cemented carbide (4πσ / C
The above object is attained by stabilizing o) at a value lower than the normal good region of the tissue and maintaining the coercive force Hc at a lower value than usual.

That is, the cutting tool of the present invention is a cutting tool having a cemented carbide comprising a hard phase containing WC and a binder phase containing Co, and a coating layer formed on the surface of the cemented carbide,
It is characterized by satisfying the following conditions. As the hard phase, carbides of metals from groups 4a, 5a and 6a of the periodic table (WC
), At least one selected from the group consisting of nitrides, oxides, and solid solutions thereof, in an amount of 1 to 25% by mass. The content of the binder phase in the cemented carbide is 5 to 15% by mass. The average particle size of WC is 2 μm or more. The value of the coercive force Hc of the cemented carbide is in the range of 140 to 180. C contained in cemented carbide with saturation magnetic quantity of 4πσ of cemented carbide
The value (4πσ / Co) divided by the mass% of o is 8 or more and less than 15. Does not contain η phase in cemented carbide. The coating layer contains Al.

Hereinafter, the configuration of the present invention will be described in detail. (Chemical composition of cemented carbide) The cutting tool of the present invention comprises a cemented carbide and a coating layer formed on its surface. This cemented carbide is composed of a hard phase and a binder phase.

The hard phase contains, in addition to WC, 1 to 25% by mass of at least one of carbides (excluding WC), nitrides, oxides, and solid solutions of metals of Groups 4a, 5a, and 6a of the periodic table. If the content of these hard phases is less than 1% by mass, the wear resistance of the cemented carbide itself will be significantly reduced, and if it exceeds 25%, the hardness and toughness will be sharply reduced.

On the other hand, the binder phase is usually mainly composed of cobalt (Co). The binder phase is desirably present in the alloy in a proportion of 5 to 15% by mass. If it is less than 5%, the toughness of the cemented carbide itself is significantly reduced, and chipping occurs in milling, so that good heat crack resistance cannot be expected. If it exceeds 15%, the hardness of the cemented carbide itself will be significantly reduced, and the heat resistance at the time of cutting will increase due to the reduced wear resistance in milling.

(Coercive force Hc and "saturated magnetic amount 4πσ / Co content") The coercive force Hc of the cemented carbide is set to 140 to 180, and the saturated magnetic amount
4πσ (G / cm ³ / g) and Co content ratio 4πσ / Co value of 8 to 15
And

In general, coercive force Hc is known as an index of the thickness of Co as a binder phase as one factor for evaluating the characteristics of a cemented carbide. This coercive force is contained in the cemented carbide
There is a large relationship between the size of the WC particles and the thickness of the Co phase. When the WC particles are large, the Co phase becomes thick and the coercive force decreases. Also, there is a relationship that when the WC particles are small, the thickness between the Co phases between the WC particles becomes thin, and the coercive force increases.

Further, conventionally, the ratio of the saturated magnetic quantity 4πσ of the cemented carbide itself to the Co content of the binder phase, that is, 4πσ
The value represented by (G / cm ³ / g) / Co (% by mass) is known as one factor for evaluating the characteristics of a cemented carbide. This saturation magnetic amount has a great relationship with the amount of carbon and the amount of Co contained in the cemented carbide. For example, if the carbon content is small, the hard phase W
In addition, there is a relationship in which the additive forms a solid solution in Co and the apparent amount of Co decreases, so that the saturation magnetic amount of the alloy decreases.

Generally, in a cemented carbide, 4πσ (G / cm
^If the ratio of ³ / g) / Co (% by mass) is less than 15, the η phase (Co ₂ W ₃ C, Co ₆ W ₆ C, Ni ₃ W ₃ C, Ni ₆ W ₆ C, Fe ₃ W
₃ C, Fe ₆ W ₆ C, etc., a low carbon content double carbide)
When it exceeds 0, it is known that the properties deteriorate due to the precipitation of free carbon in the alloy. Therefore, a cemented carbide having the above ratio in the range of about 15 to 20 is called a good range.

The coercive force Hc generally depends on the WC particle size and the amount of Co. The higher the WC is, the smaller the amount of Co is, and the higher the value is. Therefore, conventionally, when the value of 4πσ / Co is 8 or more and less than 15 lower than the normal good range, WC growth does not occur, and Hc is considered to be as high as 200 or more.

According to the present invention, the coercive force Hc is set lower than usual.
Limited to ~ 180, and stabilize the value of 4πσ (G / cm ³ / g) / Co (mass%) at 8 or more and less than 15 which is lower than the normal good range. This is based on the finding that by forming a layer, excellent heat crack resistance is exhibited.

The present inventors have found a method of keeping the coercive force within the range of 140 to 180 while keeping the value of 4πσ / Co at 8 to 15, and have excellent heat crack resistance in cemented carbide tools within this range. To show that That is, the excess carbon is dissolved in the Co phase at a high temperature and rapidly returned to room temperature, so that the value of 4πσ (G / cm ³ / g) / Co (% by mass) does not include the η phase even when the value is less than 15. Good tissue can be obtained. And, since a large amount of C is dissolved in Co, solid solution strengthening is caused, and performance excellent in thermal shock resistance can be exhibited.

The value of the coercive force Hc is set to 140 to 180 because if the value of the coercive force is less than 140, the WC becomes coarse, the Co phase between the WCs becomes thick, and cracks easily propagate through the Co phase. It is. Conversely, when Hc exceeds 180, the WC becomes finer and the C
o This is because the phase becomes thin, and the cracks easily propagate through the grain boundaries of Co and W, so that improvement in heat crack resistance cannot be expected.

The value of 4πσ (G / cm ³ / g) / Co (% by mass) should be 8 or more and 15
The reason for setting the value to less than 8 is that if the value is less than 8, even if a large amount of carbon is dissolved as a solid solution, the η phase is precipitated and the heat crack resistance deteriorates. On the other hand, if it is 15 or more, deterioration of heat crack resistance is observed due to precipitation of free carbon.

(Addition of Cr) It is desired to further improve the heat crack resistance by adding a small amount of Cr to the cemented carbide.
The ratio of the Cr content% by mass to the Co content% is 0.03-0.20
Is desirable. If this ratio is less than 0.03, solid solution strengthening of the Co phase by Cr is not promoted, and the desired improvement in heat crack resistance cannot be expected. In addition, Cr content% by mass / Co content% by mass is 0.20%.
Exceeds the limit, Cr reacts with the carbon in the cemented carbide to form Cr ₇
Precipitate as C _3, because can not be expected to improve the thermal cracking resistance of interest.

(Addition of Ni) Further, a small amount of Ni is added to the cemented carbide.
, It is desired to further improve the heat crack resistance. The ratio of Ni content% by mass to Co content% is 0.03
~ 0.10 is desirable. If this ratio is less than 0.03, the solid solution strengthening of the Co phase by Ni is not promoted, and the desired improvement in heat crack resistance cannot be expected. Also, as the amount of Ni added increases,
Since the solid solution amount of W in the binder phase Co increases, solid solution strengthening of the Co phase is desired, but Ni content mass% / Co content mass%
If it exceeds 0.10, WC becomes coarse and the heat crack resistance deteriorates.

(Crystal Structure of Co) The lattice constant of the Co phase is 3.580.
It is desirable that it be Å or more. As described above, in order to improve the heat crack resistance of the cemented carbide according to the present invention, it is important to form a solid solution of a carbon-based third element in Co. In order to obtain Co, the lattice constant of Co is desirably 3.580 ° or more.

Furthermore, it is desirable that the crystal structure of Co as the binder phase satisfies the following equation. 0 ≦ I (Co: hcp)) / I (Co: fcc) ≦ 0.2where I (Co: hcp) is the X-ray diffraction intensity on the (101) plane of Co of the hcp structure, and I (Co: fcc) Is the X-ray diffraction intensity on the (111) plane of Co having the fcc structure.

If the value of I (Co: hcp) / I (Co: fcc) exceeds 0.2, the proportion of Co in the fragile hcp structure increases and the toughness becomes insufficient. Therefore, when a cutting tool is used, cracks due to impact or heat are likely to occur, and it is important to suppress the cracking to 0.2 or less.

(Coating Layer) The cutting tool of the present invention preferably has at least one coating layer containing Al. The coating layer containing Al may be a single layer or a multilayer, and may be TiN, TiC, Si
It may be laminated with a hard coating such as C. As the Al-containing coating layer, a TiAl (CxNy) film (x + y = 1, 0 ≦ x ≦ 1) is preferable. If a TiAl (CxNy) film (x + y = 1, 0 ≦ x ≦ 1) is coated on a cemented carbide, it has excellent heat resistance, so it will further improve heat crack resistance and wear resistance. be able to.

In addition, as the Al-containing coating layer, Al _20
Three membranes are preferred. Al ₂ O ₃ is particularly excellent in heat resistance,
Heat crack resistance can be improved.

The preferable total thickness of the coating layer is about 0.1 to 30 μm.

(Cutting edge treatment) In the cutting tool of the present invention, the cutting edge treatment is performed by negative land processing, the processing width when viewed from the rake face is 0.03 to 0.20 mm, and the negative land angle is 15
Preferably, the size is about 30 °. If the width of the negative land as viewed from the rake face is less than 0.03 mm or the angle of the negative land is less than 15 °, the strength of the cutting edge is significantly reduced, and chipping occurs during cutting. Also, if the negative land processing width exceeds 0.20 mm or the negative land angle exceeds 30 °,
The amount of heat generated during cutting is significantly increased, which is not preferable.

(Production method) The cemented carbide of the cutting tool of the present invention
Perform sintering at about 1400 ° C or press the raw material powder in a block shape, intermediate sinter at about 700 ° C, mold the intermediate sintered body into a predetermined tool shape, and sinter at about 1400 ° C. Obtained by cooling. Preferred sintering temperature is 1380-14
50 ° C. In the cooling process after sintering, it is important to perform rapid cooling from a temperature of 1200 ° C. to 1300 ° C. using an inert gas such as Ar and N ₂ and a refrigerant such as oil and water. At that time, the cooling speed is controlled by changing the cooling gas pressure, the refrigerant temperature, etc., thereby controlling the value of the coercive force Hc and the ratio of the saturation magnetic amount and the Co amount (4πσ / Co). Can be. A preferred cooling rate is 15 ° C./sec or more.

The coating film is formed by a plasma CVD method, a thermal CVD method,
CVD (chemical vapor deposition) such as photo-excited CVD, vacuum deposition,
It can be obtained by using a known film forming technique called a PVD method (physical vapor deposition method) such as ion plating and sputtering.

[0030]

Embodiments of the present invention will be described below. (Example 1) Commercially available WC powder (average particle size 6.6 μm), TiC powder (average particle size 1 μm), TaC (average particle size 2 μm), Cr ₃ C ₂ (average particle size 2 μm)
m) and Co powder (average particle size: 1.2 μm) were blended in the composition shown in Table 1, wet-mixed with an attritor, and dried to obtain a raw powder.

[0031]

[Table 1]

This powder was press-molded at a pressure of 1 ton / cm ² , sintered at 1380 ° C. for 60 minutes in a vacuum, and quenched from 1250 ° C. Quenching was performed by cooling under pressure and oil cooling in N ₂ gas, to prepare a sample shown in Table 2 by changing the applied pressure of N ₂ gas. The cooling rate of chip Nos. 2, 3, and 4 is 5 ° C./sec or more.

With respect to the obtained sintered body, the coercive force Hc was measured, and the crystal structure of Co by X-ray diffraction (I (Co: hcp) / I (Co: fc
After measuring c)) and the lattice constant, the sintered body of the same lot was processed and formed into a throw-away tip shape for milling.

[0034]

[Table 2]

The surface of each carbide tip is coated with a 4 μm-thick TiAlN film by the PVD method, and the edge is processed by negative land processing (processing width as viewed from the rake face side: 0.10 m)
m, negative land angle: 20 °) to obtain a cutting insert for cutting.

Cutting was performed using these indexable inserts, and the thermal crack resistance of the cutting edge was compared. Table 3 shows the cutting conditions.

[0037]

[Table 3]

In the cutting, high-speed wet milling was performed in order to accelerate damage caused by thermal cracking of the cemented carbide. Table 4 shows the results of cutting the work material by 600 mm. In order to evaluate the heat crack resistance, the chip was driven in by lapping from the rake face side, and the depth of the heat crack, the crack length on the flank side, and the number of heat cracks were observed.

[0039]

[Table 4]

Looking at the above results, the chip of the present invention (chip
It can be seen that Nos. 2, 3, and 4) have excellent heat crack resistance.

(Example 2) Using the tip No. 2 shown in Example 1, the cutting edge processing was performed while changing the negative land processing width and the negative land angle. After the edge treatment, a coating layer of 4 μm was coated. The coating layers were formed in various laminated structures by the CVD method or the PVD method, respectively. Table 5 shows each chip. In Table 5, “film composition” indicates that the composition of the lowermost layer is on the left and the composition of the upper layer is sequentially toward the right.

[0042]

[Table 5] Using the above-mentioned insert, the same cutting as in Example 1 (see Table 3 for cutting conditions) was performed, and the heat crack resistance of the cutting edge was compared. The work material is a round bar material with a diameter of 30 mm and four grooves.

Table 6 shows the results of cutting the work material by 600 mm.
In order to evaluate the heat crack resistance, the chip was driven in by lapping from the rake face side, and the depth of the heat crack, the crack length on the flank side, and the number of heat cracks were observed.

[0044]

[Table 6]

From the above results, it was found that Al having excellent heat resistance was formed on the coating layer.
CVD coating product containing a ₂ 0 ₃ film found to have excellent thermal crack resistance. If the processing width of the negative land is small (Chip No. 11) or the angle of the negative land is small (Chip No. 12), chipping tends to occur, and conversely, the processing width of the negative land is large (Chip No. 16) or the angle of the negative land is large (Chip No. 16). When chip No. 15) and high-speed cutting, heat is easily generated,
It can be seen that thermal cracks easily occur. Therefore, it can be seen that the products of the present invention (chips Nos. 13 and 14) have excellent heat crack resistance.

[0046]

As described above, the cutting tool of the present invention exhibits excellent heat crack resistance. Therefore, heat cracking is greatly improved in the cutting field where heat cracks are considered to be the main tool determinant of tool life, such as high-speed cutting and dry cutting, and tool life can be extended. Milling tool can be provided.

Claims (8)

[Claims] 1. A cutting tool having a cemented carbide comprising a hard phase containing WC and a binder phase containing Co, and a coating layer formed on the surface of the cemented carbide, and satisfying the following conditions. Features cutting tools. As the hard phase, carbides of metals from groups 4a, 5a and 6a of the periodic table (WC
), At least one selected from the group consisting of nitrides, oxides, and solid solutions thereof, in an amount of 1 to 25% by mass. The content of the binder phase in the cemented carbide is 5 to 15% by mass. The average particle size of WC is 2 μm or more. The value of the coercive force Hc of the cemented carbide is in the range of 140 to 180. C contained in cemented carbide with saturation magnetic quantity of 4πσ of cemented carbide
The value (4πσ / Co) divided by the mass% of o is 8 or more and less than 15. Does not contain η phase in cemented carbide. The coating layer contains Al. 2. The cutting tool according to claim 1, further comprising Cr in the binder phase, wherein (Cr content mass%) / (Co content mass%) is 0.03 to 0.20. 3. The cutting tool according to claim 1, further comprising Ni in a binder phase, wherein a value of (Ni content mass%) / (Co content mass%) is 0.03 to 0.10. 4. The lattice constant of the fcc phase of Co as the binder phase is 3.5
The cutting tool according to any one of claims 1 to 3, wherein the cutting tool is at least 80 mm. 5. The cutting tool according to claim 1, wherein the crystal structure of Co as the binder phase satisfies the following expression. 0 ≦ I (Co: hcp) / I (Co: fcc) ≦ 0.2where I (Co: hcp) is the X-ray diffraction intensity of the (101) plane of Co of the hcp structure, and I (Co: fcc) is 7 is an X-ray diffraction intensity on the (111) plane of Co having an fcc structure. 6. The coating layer is a TiAl (CxNy) film (x + y = 1, x
2. The cutting tool according to claim 1, wherein 0 to 1). 7. The cutting tool according to claim 1, wherein the coating layer includes an Al ₂ O ₃ film. 8. The cutting edge processing of the cemented carbide is performed by negative land processing, and the processing width when viewed from the rake face side is reduced.
2. The cutting tool according to claim 1, wherein the cutting tool has a negative land angle of 15 to 30 degrees.