JPH10330875A - Cermet tools for cutting - Google Patents

Abstract

(57) [Problem] To provide a cutting tool excellent in both wear resistance and fracture resistance in cutting. A cermet tool for cutting which has a toughness almost continuously increased as it goes deeper from the surface and has a substantially constant hardness at a depth of 200 to 1000 μm or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cermet tool for cutting excellent in thermal shock resistance, fracture resistance and wear resistance, and more particularly to a cermet tool suitable for cutting steel.

[0002]

2. Description of the Related Art A cermet tool for a cutting tool is composed of a hard phase composed of carbides, nitrides and carbonitrides of elements of groups 4a, 5a and 6a of the periodic table and a hard phase composed of iron group metal. Cermet tools are common.

[0003] As a cermet constituting such a tool,
With the mainstream of TiC-based cermets containing TiC as the main component, TiCN-based cermets have been proposed in which additives are added to this system.

Attempts have been made to improve wear resistance or toughness by modifying the surface layer of these cermets.

As such a cermet having a modified surface, one disclosed in Japanese Patent Publication No. 34618/1985 is known. In the cermet disclosed in this publication, a conventional cermet has a non-uniform layer (exudation of a metal phase to the surface and a hard layer inside the surface layer) in the surface layer, and without grinding these surface layers, It has been found that when used as a tool, it has a drawback that the surface is brittle and thus tends to chip, so that it is disclosed that firing conditions are improved to obtain a uniform cermet up to the surface layer.

Further, Japanese Patent Publication No. 59-14534 and Japanese Patent Publication No. 59-15970 have a hardness distribution in which the hardness is continuously increased from the surface toward the inside, and the surface hardness is 5 times the internal hardness. A cermet having a surface hardened layer that is reduced by ２０20% is disclosed, whereby it is possible to have excellent toughness, and it is disclosed that it has excellent performance especially in heavy cutting such as intermittent turning and milling.

Further, Japanese Patent Publication No. 59-17176 discloses a surface-hardened surface layer having a hardness distribution that continuously decreases from the surface to the inside, and in which the surface hardness is 5 to 30% higher than the internal hardness. Cermets are disclosed,
It is disclosed that a sintered hard alloy having excellent wear resistance and plastic deformation resistance can be obtained by this.

[0008]

However, in the cermet disclosed in Japanese Patent Publication No. 60-34618, the firing conditions can be improved to provide a uniform structure up to the surface layer, and the fracture resistance can be improved. However, there is a problem that the fracture toughness is reduced.

Further, in the cermet disclosed in the above-mentioned JP-B-59-14534 and JP-B-59-15970, the toughness is increased by the presence of a surface softening layer whose surface hardness is lowered by 5 to 20% with respect to the inside. Although it can be improved, there is a problem that the wear resistance is deteriorated.

Further, in the cermet disclosed in the above-mentioned Japanese Patent Publication No. 59-17176, the wear resistance can be improved by the presence of a hardened layer whose surface hardness is 5 to 30% higher than the internal hardness. However, there is a problem that the fracture toughness is reduced and the fracture resistance is deteriorated.

As described above, in the conventional cermet, the hardness and the fracture toughness are inversely proportional physical properties. When the hardness is improved, the fracture toughness decreases, and when the fracture toughness is improved, the hardness decreases. Thus, substantial improvement of the cermet was difficult. That is, none of the above-mentioned methods could improve both the hardness and the fracture toughness, and could not improve both the wear resistance and the fracture resistance.

[0012]

Means for Solving the Problems The present inventors have conducted various studies on the sintering conditions for cermets and found that by controlling the atmosphere during firing, the degree of change in the fracture toughness value in the depth direction can be controlled well. In addition, the inventors have found that the fracture toughness is improved without lowering the hardness of the tool, and have reached the present invention.

That is, the present invention relates to carbides, nitrides of the 4a, 5a, and 6a groups, which contain at least one or more of Ti carbides, nitrides, carbonitrides, and composite compounds thereof and exclude Ti. In a cermet tool composed of a hard phase composed of any one or more of carbonitrides and a binder phase composed of at least one of iron group metals, a hardness H
The width of v is almost constant at 75 or less in a region of a depth of 200 μm to 1000 μm from the surface, while a depth of 1
To improve almost continuously over 000 μm,
In addition, the present invention provides a cutting cermet characterized in that the hardness Hv and the fracture toughness at a depth of 100 μm from the surface are maintained at high levels of 1400 or more and 7.5 or more, respectively. The fracture toughness value is 100
It is important that the ratio of the fracture toughness value between μm and 1000 μm is 1.1 or more.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail.

The cutting cermet tool (hereinafter abbreviated as cermet tool) of the present invention can be obtained as follows. For example, a predetermined amount of TiCN, WC, T
Powders of aN, Mo2C, Ni, and Co are mixed and pulverized, a binder is added, and the mixture is molded at a predetermined pressure. This is 1500 ~
It is once held at a temperature of 1750 ° C. for 30 minutes to 1 hour in a nitrogen atmosphere or an atmosphere of a gas generated from a molded body. Thereafter, the cermet of the present invention can be obtained by exhausting the atmosphere gas while keeping the temperature constant and maintaining the atmosphere in a vacuum atmosphere for 30 minutes to 2 hours.

If the firing temperature is lower than 1500 ° C., a dense body cannot be obtained. If the firing temperature is higher than 1700 ° C., the sintering surface near the surface becomes rough, and the fracture toughness value decreases due to the evaporation of metal components, which is insufficient as a tool. Performance cannot be obtained.

If the atmosphere holding time is 30 minutes or less, the hardness is low, and the hardness in the deep region of 200 to 1000 μm in depth is not constant. If the atmosphere holding time is 1 hour or more, the property that the fracture toughness value becomes higher as the depth increases cannot be obtained.
Further, if the subsequent vacuum holding time is 30 minutes or less, the property that the fracture toughness value becomes higher as the depth becomes deeper is not obtained. Accuracy cannot be maintained.

It should be noted that those under these manufacturing conditions tend to be inferior in both abrasion resistance and chipping resistance as compared with those under the manufacturing conditions.

For the above reasons, the firing conditions of the cermet tool suitable in the present invention are as described above.

The cermet tool obtained as described above contains at least one or more of Ti carbides, nitrides, carbonitrides, and composite compounds thereof as main components,
Basically composed of a hard phase consisting of at least one of carbides, nitrides and carbonitrides of groups 4a, 5a, 6a excluding Ti and a binder phase consisting of at least one of iron group metals. In terms of its physical properties, the toughness increases almost continuously as it goes deeper than the surface, and the hardness is 200 to
It is characterized by exhibiting a substantially constant hardness at a depth of 1000 μm or more.

More specifically, the width of the hardness Hv is 200
In the region of μm to 1000 μm, the difference is substantially constant at 75 or less, while the fracture toughness value is characterized in that it increases almost continuously from the surface to the depth of 1000 μm. At this time, it is weight that the ratio of the fracture toughness value at a depth of 100 μm to 1000 μm is 1.1 or more. Here, if the toughness is not continuously improved toward the inside, the fracture resistance as a tool cannot be obtained, and the tool will be broken during wet cutting or intermittent cutting. On the other hand, if the hardness decreases with the improvement in fracture toughness, sufficient wear resistance as a tool cannot be obtained.

The cermet tool according to the present embodiment having such a configuration has excellent fracture resistance because the fracture toughness is continuously improved from the surface to the deep portion, and has almost the same hardness at both the deep portion and the surface portion. Also excellent in nature. In other words, it is an epoch-making cermet tool in which both hardness and fracture toughness are improved, thereby improving both wear resistance and fracture resistance.

When the hardness Hv at a depth of 100 μm from the surface is 1400 or less, or when the fracture toughness is 7.
When it was 5 or less, it was found that sufficient performance could not be exhibited even within the above numerical ranges of hardness and fracture toughness.

[0024]

Example 1 As raw material powder, TiCN: 57 wt%, W
C: 8 wt%, TaC: 7 wt%, Mo2C: 7 wt
%, NbC: 3 wt%, Ni: 9 wt%, Co: 9 wt%
% Was mixed and pulverized, and then molded at a pressure of 1.5 ton / cm 2.

Next, the compact was once held in a mixed atmosphere of nitrogen and gas generated from the compact at the temperature and time shown in Table 1 and then nitrogen and gas generated from the compact were maintained at the temperature and time shown in Table 1. After holding in the mixed atmosphere and exhausting the gas to make a vacuum atmosphere, the temperature and time shown in Table 1 were used to obtain a sintered body.

[0026]

[Table 1]

The characteristics were measured by inclining the sintered sample by 10 °, grinding the surface so that two corners of the rake face were cut, and preparing a Vickers hardness and an IF method under a load of 20 kg. The fracture toughness value was measured.

The measurement was performed at one of the two inclined ends of the cutout surface and at the center at a depth of 10 in each case.

In addition, cutting tests were performed under the following conditions.

(Wear test 1) Work material S50C Cutting speed 250 m / min Cutting depth 2 mm feed 0.2 mm / tooth state Dry cutting time 20.5 minutes (Wear test 2) Work material SKD11 Cutting speed 120 m / min Cutting depth 2 mm feed 0.2mm / tooth state Dry cutting time 4.25 minutes (breakage test) Work material SCM440 Cutting speed 100m / min Condition Dry cutting time Increase feed by 0.5 / tooth if there is no chipping after cutting by 40 mm at each feed. Table 1 shows the results of these tests and the results of characteristic measurement of the observation results of the sintered state and surface state.

The term "constant" in the column of hardness distribution in Table 1 means that the width of the hardness Hv in the region of 200 μm to 1000 μm in depth is almost constant at 75 or less. In the column of fracture toughness, “internal height” means that the fracture toughness value is set to a depth of 1000 from the surface so that the ratio of the fracture toughness value at a depth of 100 μm to 1000 μm is 1.1 or more.
It means that it increases almost continuously over μm.

Hereinafter, test results of this embodiment will be described.

As shown in Table 1, the sample No. In No. 1, the hardness distribution was “constant” and the fracture toughness was “internal high”. However, the hardness Hv at a depth of 100 μm from the surface is 1
Since it was less than 400, the wear width was 0.2 mm
As described above, there was a problem in the abrasion resistance, and the defective feed was as small as 0.3. This is because the firing temperature is 1400 °
This is considered to be due to the low sintering.

The sample No. In No. 7, the atmosphere holding time was too short, 0.25 hours, and as a result, the hardness was lower in the deeper part, the wear width was 0.2 mm or more, and the chipped feed was as small as 0.3. On the other hand, the sample No. 8
In the case of, the atmosphere holding time was too long, 2.0 hours, and the fracture toughness was almost the same level between the surface portion and the deep portion. As a result, the abrasion width was 0.2 mm or more, and the defective feed was even smaller.

Further, the sample No. In No. 9, the vacuum holding time was too short, 0.25 hours, and the fracture toughness was almost the same level between the surface portion and the deep portion. As a result, the wear width was relatively small, but the feed loss was considerably small at 0.25. On the other hand, the sample No. 10 is good in both hardness distribution and gradient of fracture toughness, and has a depth of 100 from the surface.
The hardness Hv at μm was 1400 or more, and the fracture toughness value was as large as 7.5 or more. However, since the vacuum holding time was too long, 3 hours, the surface was deformed. As a result, the wear width was 0.2 m without surface polishing.
m or more, the missing feed was relatively small. In addition, this sample No. No. 10 falls within the scope of the present invention because surface polishing increases the number of processing steps but provides good surface cutting performance.

Sample No. Sample No. 11 is a sample No. 10
Although the hardness distribution and the gradient of fracture toughness were both good, the calcination temperature was too high and the fracture toughness value at 100 μm from the surface was low, less than 7.5.
It was very small, 2 mm, and the wear width was also large.

On the other hand, the sample No. Each of Nos. 2 to 6 was prepared within the range of the above sintering conditions, had good hardness distribution and gradient of fracture toughness, had a hardness Hv at a depth of 100 μm from the surface of 1400 or more, and had a fracture toughness value of not less than 1400. Was also as large as 7.5 or more. Furthermore, it is densely sintered and has a good surface condition. As a result, the wear width in S50C is less than 0.15 mm, and the SKD1
The wear width in No. 1 was as small as less than 0.20, while the defective feed was as large as 0.5 mm or more.

[0038]

As described in detail above, the cermet tool of the present invention has a toughness almost continuously increasing as the physical properties go deeper than the surface, and has a substantially constant hardness at a depth of 200 to 1000 μm or more. It is characterized by exhibiting hardness, and since it has high toughness and hardness, both wear resistance and chipping resistance in cutting work are improved.

As a result, a high performance with a good finish can be obtained.
In addition, it has an extremely excellent effect that a long-life and economical cutting tool can be obtained.

Claims (1)

[Claims] 1. A group consisting of carbides, nitrides, and carbonitrides of the 4a, 5a, and 6a groups containing at least one or more of Ti carbides, nitrides, carbonitrides, and composite compounds thereof and excluding Ti. In a cermet tool composed of a hard phase composed of any one or more of them and a binder phase composed of at least one of iron group metals, a depth of 200 μm from the surface
The width of the hardness Hv in the range of m to 1000 μm is 75 or less, and the fracture toughness increases almost continuously from the surface to the depth of 1000 μm.
A cermet tool for cutting, wherein the hardness Hv and the fracture toughness value in μm are 1400 or more and 7.5 or more, respectively.