JP3103707B2 - Cermet for cutting tools - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cermet used for a cutting tool, and more particularly to a cermet for a cutting tool which does not deteriorate wear resistance and has excellent toughness.

[0002]

2. Description of the Related Art In recent years, a cermet 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 binder phase composed of an iron group metal. Cermet is being used.

[0003] As such a cermet, TiC has hitherto been used.
There are many TiCN-based cermets in which a nitride is added to a TiC-based cermet having a main component of TiC-based cermet as a mainstream.

Attempts have also been made to improve wear resistance or toughness by modifying the surface 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 (a seepage of a metal phase to the surface and a hard layer inside the surface layer) in the surface layer, and a tool that does not grind the surface. In order to obtain a uniform cermet up to the surface layer, we found that when cutting with
It is disclosed that the firing conditions are improved.

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 softening 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. 17-17176 discloses a hardened surface layer having a hardness distribution that continuously decreases from the surface toward the inside, and in which the surface hardness is 5 to 30% higher than the internal hardness. Cermets are disclosed, whereby a sintered hard alloy having excellent wear resistance and plastic deformation resistance is obtained.

[0008]

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

The cermet disclosed in Japanese Patent Publication Nos. 59-14534 and 59-15970 has a toughness due to the presence of a surface softening layer in which the surface hardness is 5 to 20% lower than the internal hardness. Can be improved, but there is a problem that wear resistance is deteriorated.

In the cermet disclosed in Japanese Patent Publication No. 17176/1984, the wear resistance can be improved by the presence of a hardened surface layer whose surface hardness is 5 to 30% higher than the internal hardness. However, there is a problem that toughness is reduced and fracture resistance is deteriorated.

As described above, in the conventional cermet, the wear resistance and the toughness are contradictory performances, and if the wear resistance is improved, the toughness is deteriorated, and if the toughness is improved, the wear resistance is deteriorated. Substantial improvement of the cermet was difficult.
That is, it was not possible to improve both the wear resistance and the toughness by any of the above methods.

[0012]

[Means for Solving the Problems] The present inventors have conducted various studies on the surface layer portion of the cermet sintered body and found that by adjusting the hardness and the location of the hardened layer and the softened layer,
The present inventors have found that both wear resistance and toughness can be improved, and have reached the present invention.

That is, in the cermet for a cutting tool according to the present invention, at least one main component selected from the group consisting of carbides, nitrides, carbonitrides, and composite compounds of Ti and a group 4a, 5a, 6a of the periodic table. Depth of 2 mm from the cermet surface in a cutting tool cermet comprising a hard phase composed of at least one of carbides, nitrides and carbonitrides, and a binder phase composed of at least one of iron group metals. A hardened layer having a hardness higher than the hardness x and a softened layer existing adjacent to a position deeper than the hardened layer and having a hardness lower than the hardness x, and a hardness x at a depth position of 2 mm from the surface. A boundary point between the hardened layer and the softened layer having a depth of 0.1 to 0.2 mm from the surface is present, and the lowest hardness peak position of the softened layer is from the boundary point. 0.3m Present in the following depth position, and with the hardened layer and the softened layer is characterized in that formed simultaneously by sintering.

In the present invention, x between the hardened layer and the softened layer
A boundary point having a hardness of 0.1 to 0.2 mm from the surface
The boundary point was 0.1 mm
If less than 0.2 mm, the effect of the hardened layer which affects the wear resistance is not sufficiently obtained. Conversely, if it is more than 0.2 mm, the hardness is high and the wear resistance is high, but the toughness is significantly reduced. . Here, the hardness of the hardened layer is desirably higher than the hardness x at a depth of 2 mm from the surface and equal to or less than 4x. This is because when the hardness of the hardened layer is higher than 4x, the toughness is significantly reduced.

The reason why the lowest hardness peak position of the softened layer is present at a depth of 0.3 mm or less from the boundary point is that if the distance is more than 0.3 mm, the plastic deformation resistance deteriorates. , Good cutting performance cannot be obtained. The depth position of the softened layer is determined by the hardness x which particularly defines the thickness of the softened layer.
Is preferably 0.1 to 0.3 mm from the boundary point. If the depth position where the hardness x is reached is less than 0.1 mm from the boundary point, the effect of improving toughness is small, and 0.
If the distance is more than 3 mm, the plastic deformation resistance tends to deteriorate. Here, the hardness of the softened layer needs to be lower than x, but is preferably 0.6x or more. This is because if the hardness is not less than x, the effect of improving toughness cannot be obtained, and if it is less than 0.6x, the plastic deformation resistance may be deteriorated.

The cermet for a cutting tool according to the present invention is obtained, for example, as follows. For example, a predetermined amount of TiC, W
After mixing and pulverizing each powder of C, Mo ₂ C, Ni and the like, molding is performed at a predetermined pressure, and this is used as a base material. Next, a mixed powder having a larger amount of metal such as Ni than the base material is pulverized in, for example, acetone to prepare a slurry, and the slurry is formed on a compact with a sintered body thickness of 0.1 to 0.3 mm. It is applied so that the layer becomes a tough softening layer after sintering. Next, a mixed powder having a smaller amount of metal than the base material composition is pulverized in, for example, acetone to prepare a slurry, and the slurry is formed into a softened layer after sintering. 0.
It is applied so as to have a thickness of 2 mm, and a layer to be a cured layer after sintering is prepared. The molded body on which each layer is formed in this manner is 1300
The cermet of the present invention can be obtained by firing in a vacuum atmosphere at １1600 ° C. for 0.5 to 3 hours.

[0017]

In the cermet for a cutting tool according to the present invention, a hardened layer having a higher hardness than the inside is provided at a depth of 0.1 to 0.2 mm from the surface of the cermet to improve wear resistance. The toughness deteriorated by the presence can be improved by the presence of the softened layer having the peak position at a depth of 0.3 mm or less from the boundary point, and both the wear resistance and the toughness can be improved.

[0018]

【Example】

Example 1 As raw material powder, TiCN: 55% by weight, WC: 10% by weight, Mo ₂ C: 10% by weight, NbC: 10% by weight, N
i: 10% by weight and Co: 5% by weight were mixed and pulverized, and then molded at a pressure of 1.5 ton / cm ² . Then T
iCN: 40% by weight, Mo ₂ C: 10% by weight, Ni: 5
0% by weight of the mixed powder was pulverized in acetone to prepare a slurry. This slurry was applied on the molded body so that the sintered body had a thickness of 0.1 mm, and a layer to be a softened layer after sintering was formed. Further, a powder of 100% by weight of TiC was pulverized in acetone in the same manner as above to prepare a slurry.
A layer to be a hardened layer after sintering was formed on the layer to be a softened layer after sintering such that the thickness of the sintered body was 0.2 mm. This compact was sintered in vacuum at 1475 ° C. for 1 hour.

When the hardness of the sintered body was measured at a micro Vickers hardness under a load of 200 g in a cross section perpendicular to the surface, the hardened layer was 0.2 mm from the surface. hardness 2600kg / mm ^2, 0.1mm from the cured layer has a softening layer, the hardness of the softened layer is 1450kg / mm ^2, the internal hardness of 2mm from the surface was 1650kg / mm ^2. That is, the hardness x at a depth of 2 mm from the surface of the sintered body is 1650 kg / m.
m ^2, and the hardened layer has a hardness of 1.58X, softened layer has a hardness of 0.88X, the position of the boundary point is 0.2mm from the surface, the lowest hardness of the softened layer Is located at a depth of 0.05 mm from the boundary point. FIG. 1 shows the hardness with respect to the distance from the surface of the product of the present invention.

As a comparative alloy, a comparative cermet (1) having the same composition as the above and having no softened layer and hardened layer, the peak position of the lowest hardness of the softened layer having the same composition and the same thickness of the hardened layer from the boundary point A comparative cermet (2) having a thickness of 0.5 mm and a comparative cermet (3) having the same composition and the same peak position of the lowest hardness of the softened layer as the above and having a cured surface layer thickness of 0.4 mm were prepared.

Using the above samples, a test was performed under the following cutting conditions, and the flank wear after cutting and the chipping ratio of the cutting edge were examined.

(Wear test) Work material SCM435 Cutting speed 250 m / min Cutting depth 2 mm Feed 0.3 mm / rev. Cutting time 15min (breakage test) Work material SCM435 (with 4 grooves) Cutting speed 100m / min Depth of cut 2mm Feed 0.3mm / rev. Cutting time 2 min The amount of wear was 0.24 mm for the cermet, but 0.30 m for the cermet of comparative cermet (1).
m, 0.36 mm for the comparative cermet (2) and 0.21 mm for the comparative cermet (3), and the comparative cermets (1) and (2) had a large amount of wear. In the defect test, the defect rate of the cermet was 25%, while the defect rate of the comparative cermet (1) was 32%, that of the comparative cermet (2) was 19%, and that of the comparative cermet (3) was 36%. Indicated.

Further, the present inventors have variously changed the thickness of a layer to be a softened layer or a hardened layer after sintering with the same composition as described above,
An experiment was conducted in which the depth position of the boundary point from the surface and the peak position of the lowest hardness of the softened layer were changed, and the wear amount and the chipping rate of the cutting edge were examined. The results are shown in Table 1. Table 1
In the above, the comparative cermet (1) was added to sample No. 1,
The comparative cermet (2) was described in sample No. 8, and the comparative cermet (3) was described in sample No. 6. The flank wear and chipping rate were set to 100% with respect to the amount of wear and chipping rate of the comparative cermet (1). The ratio to this is described.

[0024]

[Table 1]

From Table 1, it can be seen that the cermet of the present invention has a small wear amount, a small chipping ratio of the cutting edge, and is excellent in wear resistance and chipping resistance.

Example 2 65% by weight of TiC, 10% by weight of WC, 10% by weight of Mo ₂ C, and 15% by weight of Ni were mixed as raw material powders.
After pulverization, molding was performed at a pressure of 1.5 ton / cm ² . Then, TiC: 45% by weight, Mo ₂ C: 5% by weight,
A mixed powder of Ni: 50% by weight was pulverized in acetone to prepare a slurry. This slurry was applied on the molded body so that the thickness of the sintered body was 0.1 mm, and a layer to be a softened layer after sintering was formed. Further, TiC: 97% by weight, C
o: 3% by weight of the mixed powder was pulverized in acetone in the same manner as described above to prepare a slurry, and the slurry was formed such that the sintered body had a thickness of 0.2 mm on a layer to be a softened layer after sintering. Then, a layer to be a hardened layer after sintering was formed. This molded product is 1450
Sintered in vacuum at ℃ for 1 hour.

When the hardness of the sintered body was measured at a micro Vickers hardness under a load of 200 g in a cross section perpendicular to the surface, the hardened layer was 0.2 mm from the surface. The hardness was 2500 kg / mm ² , and 0.1 mm from the hardened layer was the softened layer. The hardness of the softened layer was 1400 kg / mm ² , and the internal hardness 2 mm from the surface was 1600 kg / mm ² . That is, the hardness x at a depth of 2 mm from the surface of the sintered body is 1600 kg / m.
m ^2, and the hardened layer has a hardness of 1.56X, softened layer has a hardness of 0.875X, the position of the boundary point is 0.2mm from the surface, the lowest hardness of the softened layer Is located at a depth of 0.05 mm from the boundary point.

As a comparative alloy, a cermet having the same composition as the above-mentioned inside having no tough layer and no hardened surface was prepared.

Using the above-mentioned sample, a test was conducted under the same cutting conditions as in Example 1 to examine the flank wear after cutting and the chipping ratio of the cutting edge.

The amount of wear was 0.28 mm with the cermet.
On the other hand, in the comparative cermet, the wear amount was as large as 0.40 mm. In the defect test, the cermet showed a defect rate of 30%, while the comparative cermet showed a defect rate of 40%.

[0031]

As described in detail above, the cermet for a cutting tool according to the present invention has a hardened layer having a hardness higher than x at a depth of 2 mm from the surface and a hardened layer adjacent to a deeper position than the hardened layer. Having a softened layer having a hardness lower than the hardness x,
A boundary point having a hardness of x between the hardened layer and the softened layer exists at a depth position between 0.1 and 0.2 mm from the surface, and a peak position of the lowest hardness of the softened layer is 0 from the boundary point. 0.3 mm or less, so that a hardened layer having a higher hardness than the inside is provided to improve wear resistance, and the toughness deteriorated by the presence of the hardened layer is reduced by a toughened softened layer having a lower toughness than the inner hardness. , And both wear resistance and toughness can be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing hardness against distance from a surface of a cermet for a cutting tool according to the present invention.

Claims (1)

(57) [Claims] 1. A main component of at least one of Ti carbides, nitrides, carbonitrides and composite compounds thereof, and carbides, nitrides and carbonitrides of groups 4a, 5a and 6a of the periodic table. A cermet for a cutting tool comprising a hard phase composed of at least one of the following, and a binder phase composed of at least one of the iron group metals, having a hardness higher than the hardness x at a depth of 2 mm from the surface. A layer and a softened layer present adjacent to a position deeper than the hardened layer and having a hardness lower than the hardness x, and the hardened layer and the softened layer having a hardness x at a depth of 2 mm from the cermet surface. The boundary point between
The softened layer is located at a depth between 0.2 mm and the peak position of the lowest hardness of the softened layer is 0.
A cermet for a cutting tool, wherein the cermet is present at a depth of 3 mm or less and wherein the hardened layer and the softened layer are simultaneously formed by firing.