JP2828511B2 - Surface coated TiCN based cermet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is excellent in abrasion resistance and toughness, and has a high hardness of a base material at a cutting edge, and is particularly useful as a cutting tool for cast iron and has excellent smoothness of a machined surface of a work material. The present invention relates to a surface-coated TiCN-based cermet.

[0002]

2. Description of the Related Art Conventionally, WC-C has been used as a cutting sintered body.
A cemented carbide mainly containing o is mainly used, but recently, a cermet sintered body mainly containing carbides, nitrides, and carbonitrides of Ti has been used.

As such a cermet-based sintered body, T
The mainstream was a TiC-based cermet containing iC as a main component, an iron group metal as a binder phase, and carbides, nitrides, and carbonitrides of metals of groups 4a, 5a and 6a of the periodic table as hard phase components. . However, since such a TiC-based cermet sintered body is inferior in heat resistance and toughness, it has been proposed to further include a nitride such as TiN or a carbonitride in the above composition. This is intended to impart toughness to the sintered body due to the high toughness of TiN itself, and to improve thermal shock resistance and thermal plastic deformation due to high thermal conductivity.

Accordingly, TiC containing TiN has been conventionally used.
Various improvements have been made to the base cermet. For example, Japanese Patent Publication No. Sho 59-14534 discloses that nitrogen is introduced into a furnace at a temperature lower than the liquid crystal appearance temperature to form a softened layer having a high toughness on the surface of a sintered body.
No. 76, it is possible to form a hard layer having a specific hardness by firing in a Co reducing atmosphere. Further, according to Japanese Patent Publication No. 60-34618, when the temperature is lowered after firing,
It has been proposed to obtain a cermet having uniform characteristics inside the surface by forming an atmosphere.

[0005]

However, from the knowledge of wear resistance during high-speed cutting as a cutting tool for cast iron, JP-B-59-14534 and JP-B-60-34 are disclosed.
The cutting tool described in No. 618 has a low surface hardness,
Insufficient in performance. On the other hand, Japanese Patent Publication No. 59-17176 discloses a method of forming a hard layer on the surface, but the surface hardness is at most only Vickers hardness (Hv) up to 1800, and has a higher hardness. When forming the hard layer, M is contained in the hard forming component.
This cannot be achieved unless a large amount of o ₂ C and WC is contained, but such a composition containing a large amount of Mo, C, and WC results in substantially deteriorating other properties as a cutting tool.

[0006] Therefore, the applicant of the present invention, when preparing the TiCN-based cermet, first returned the atmosphere during firing to a vacuum more rapidly than the high nitrogen gas atmosphere, so that the surface portion of the cermet had a Vickers hardness of 2000 or more. It was proposed that by forming a layer, a cermet having excellent wear resistance and fracture resistance as a cutting tool for cast iron could be obtained.

However, such a TiCN-based cermet has a very low Ti content ratio on its surface and a large amount of W on its surface. In such a case, it has been found that there is a problem in that W and the like react with the work material, and the surface of the work material after cutting is roughened.

[0008]

Means for Solving the Problems As a result of repeated studies on the above problems, the present inventors have found that the surface of a TiCN-based cermet having a high Vickers hardness of 2000 or more on the surface of the cermet is proposed. By forming a Ti-containing hard film that is richer than the amount of Ti in the surface portion of the cermet, the reactivity with the work material can be significantly reduced while maintaining the excellent characteristics of the cermet, and further excellent cutting characteristics can be obtained. Was found to be.

That is, the surface-coated TiCN-based cermet according to the present invention comprises Ti carbide, nitride or carbonitride of 5%.
0 to 80% by weight, 1% of a carbide of Group 6a element of the periodic table
0 to 40% by weight.
60 to 95% by weight of a hard phase component having an atomic ratio represented by (carbon + nitrogen) in a range of 0.4 to 0.6, and 5 to 40% by weight of a binder phase component mainly composed of an iron group metal. And a Vickers hardness of 200 between 50 μm from the surface
On the surface of the TiCN-based cermet where a portion of 0 kg / mm ² or more exists, more T than the TiCN-based cermet.
It is characterized by being coated with a Ti-containing hard film containing i and having an average particle size of 0.4 μm or less and an iron group metal content of 100 ppm or less.

[0010] In the present invention, T
The iCN-based cermet contains 50 to 80% by weight, particularly 55 to 65% by weight of a carbide, nitride or carbonitride of Ti as a hard phase component, and a periodic table 6a such as W or Mo.
10 to 40% by weight, especially 15 to 3%
It is contained at a ratio of 0% by weight.

In such a hard phase component, if the amount of Ti is less than 50% by weight, the abrasion resistance is reduced, and
If it exceeds sinterability, the sinterability is undesirably reduced. In addition, the 6a
Group elements have the effect of suppressing grain growth and improving the wettability with the binder phase. However, if the content is less than 10% by weight, the above effects cannot be obtained, the hard phase becomes coarse, and the hardness and strength decrease. Also 4
If it exceeds 0% by weight, an unhealthy phase such as an η phase is generated and sintering becomes difficult.

In addition to the above, other hard phase components include Ta and Nb for the purpose of improving crater wear resistance, and nitrides, carbides and carbonitrides such as Zr, V and Hf for the purpose of improving plastic deformation resistance. Although it is possible to contain it in a ratio of 0.1 to 40% by weight in total, it is not preferable that the content exceeds 40% by weight because deterioration of abrasion resistance, generation of pores and voids tend to remarkably increase.

On the other hand, the binder phase is mainly composed of an iron group metal such as Fe, Co, and Ni, and may partially include a hard phase forming component.

The hard phase component is 60 to 9 as a whole of the sintered body.
5% by weight, the binder phase component comprising 5 to 40% by weight.

The feature of the composition in the present invention is that the atomic ratio represented by (nitrogen / carbon + nitrogen) in the hard phase component is in the range of 0.4 to 0.6, particularly 0.4 to 0.5. The point that is set. That is, if this atomic ratio is less than 0.4, improvement in toughness and wear resistance cannot be expected, and the object of the present invention is not achieved. If it exceeds 0.6, pores and voids are generated in the sintered body, and As the reliability decreases.

Further, as shown in FIG. 1, the cermet according to the present invention has a high hardness portion having a Vickers hardness of 2000 or more in a surface layer portion up to 50 μm from the surface. Such a high hardness portion of the surface layer portion is due to the fact that the bonding phase on the surface portion occurs and the amount of the Group 6a element in the surface layer portion increases, also from the manufacturing method described later. The presence of such a hard portion can greatly improve the plastic deformation resistance of the coated cermet base material.

In general, when a high hardness portion is present on the surface, chipping, chipping and the like are likely to occur due to a decrease in toughness. However, according to the present invention, the above-mentioned specific composition, particularly containing a large amount of nitrogen, Toughness is imparted, chipping,
It is an excellent base material with no defects or the like.

The TiCN-based cermet according to the present invention can maintain the effect of improving toughness and abrasion resistance by containing a large amount of nitrogen for a long period of time with the above structure, and has a high hardness portion on the surface. Therefore, it becomes possible to achieve a long life and high reliability as a base material for a surface-coated cast iron cutting tool.

According to the above-described cermet, when the cutting is performed using, for example, the structural alloy steel SCM435 as a work material due to the low Ti content in the surface layer, the iron group metal in the cermet or the hard phase in the hard phase is cut. W reacts with the work material and the finished surface may be roughened. Therefore, according to the present invention, the surface of the TiCN-based cermet is coated with a hard film containing Ti.

In order to suppress the reactivity between the cermet base material and the work material, the hard film should be a film in which the amount of Ti in the hard film is larger than the amount of Ti in the base material, particularly the amount of Ti in the surface layer. Thereby, the reactivity of the cermet with the work material can be suppressed. In addition, when forming a hard film on the cermet surface, the iron-group metal rich in the cermet surface diffuses into the hard film, which deteriorates the hardness of the hard film and the original properties of the film such as low reactivity with the work material. Let me do it. Therefore, in this hard film, it is necessary to control the amount of iron group metal contained in the film to 100 ppm or less, particularly 70 ppm or less.

Further, the grain size of the crystal constituting the hard film is:
This is a factor that affects the hardness and strength of the film. The smaller the crystal grain size, the harder the film, the higher the strength and the higher the toughness. Therefore, according to the present invention, the crystal grain size of this hard film is 0.4 μm
By controlling the thickness to 0.3 μm or less, the original function as a hard film can be exhibited, and at the same time, it is possible to prevent the falling off of the particles due to the breakage in the film and the peeling of the film.

Incidentally, as the Ti-containing hard film in which the amount of Ti is larger than the amount of Ti in the cermet base material, TiC, TiN,
TiCN and the like are preferable, and oxygen may be contained in these films in some cases.

This hard film has a thickness of 1 to 10 on the surface of the cermet.
It is desirable to coat with a thickness of μm. If the thickness is less than 1 μm, the effect of suppressing the reactivity with the work material is small, and the surface of the work material is roughened. Is easy to peel off during use due to the thermal expansion difference.

According to the method for producing a surface-coated TiCN-based cermet according to the present invention, first, when producing a base material, a composition of Ti carbide, nitride or carbonitride of 50% is used.
From 80% by weight to 10% of carbides of Group 6a elements of the periodic table.
A hard phase component having an atomic ratio of (nitrogen / carbon + nitrogen) in the range of 0.4 to 0.6 and a binder phase component of 5 to 40% by weight.
To 40% by weight.

Specifically, TiC, Ti
N, TiCN, etc., and WC, Mo
_{After using 2} C, MoC, etc., or their composite carbides and composite carbonitrides to prepare the above composition,
Molding is performed by known molding means, for example, press molding, extrusion molding, casting molding, injection molding, cold isostatic molding, or the like.

At this time, as described above, Ta, Nb, Z
Naturally, it is also possible to use a combination of carbides, nitrides, and carbonitrides such as r, V, and Hf. When TiC is used as the Ti-based material, sinterability is reduced, and partial grain growth may occur. Therefore, a combination with Ti (CN) or TiN is more preferable.

Next, the compact is fired. Firing is 1
According to the present invention, in order to form a high hardness portion on the cermet surface portion, first, the material is heated in a vacuum furnace of 0.5 Torr or less, and is heated for a predetermined time. 70 Torr or more, especially 100-2
Nitrogen gas at a pressure of 00 Torr is introduced.

This nitrogen gas is introduced at a temperature higher than the liquid phase appearance temperature of the iron group metal in the heating process. That is, by introducing nitrogen gas at a temperature higher than the liquid phase appearance temperature, generation of nitrogen gas due to thermal decomposition of nitrides such as TiN contained in the compact is suppressed, and as a result, pores and voids are introduced into the sintered compact. Can be prevented from remaining. However, when the introduction time of the nitrogen gas reaches the maximum sintering temperature, the effect of suppressing the decomposition of the nitride is not obtained, and the surface of the sintered body is roughened.

After the temperature in the furnace reaches the maximum sintering temperature, the nitrogen gas is maintained for a predetermined time and then immediately returned to a vacuum to continue firing. If the pressure is further increased after reaching the maximum sintering temperature, a brittle nitride layer is formed on the surface of the sintered body, causing the surface of the burnt surface to be roughened and significantly reducing the toughness of the surface.

The pressure of the nitrogen gas to be introduced needs to be a pressure capable of sufficiently suppressing the thermal decomposition of the nitride, and the pressure of the nitrogen gas is set to a value for the improvement layer formed on the surface of the sintered body. It greatly affects hardness. This causes a pressure between the inside of the compact and the atmosphere in the furnace after the introduction of nitrogen gas. If the pressure is rapidly returned to vacuum, the hardness increases due to a decrease in the amount of the binder phase in the vicinity of the surface relative to the inside.
Further, it is considered that the toughness is improved by making the crystal near the surface spherical in the structure and by containing a large amount of the Group 6a element. In order to form a hard portion having a Vickers hardness of 2000 or more, the nitrogen gas pressure is set to 70T.
It is necessary to set it to orr or more.

The cermet prepared as described above is used as a base material, and a coating mainly composed of a Ti compound having low reactivity with the work material is used for the purpose of improving the surface finish of the work material particularly during cutting. A Ti compound film is formed, which is substantially higher than the Ti content near the cermet surface layer. In addition, this coating contains substantially no iron group metal of 100 ppm or less, and the average particle size of the coating needs to be 0.4 μm or less in order to maintain the strength of the coating. Specifically, a chemical vapor deposition method (CVD method) such as thermal CVD, plasma CVD, or laser CVD, a physical vapor deposition method (PDV method) such as sputtering or ion plating, or a gas phase impregnation method is used. However, in order to control the particle size of the hard film to 0.4 μm or less based on the present invention, ion plating, plasma CVD, and sputtering are preferable.

Further, the amount of the iron group metal mixed into the hard film is 1
When the concentration is limited to not more than 00 ppm and the film adhesion strength is taken into consideration, ion plating, plasma CVD and the like are desirable. In particular, according to the ion plating method, the crystal grain size of the film is low due to the low film formation temperature. Since the growth rate is low and the diffusion of the iron group metal from the base material is suppressed, the incorporation into the film can be prevented. Further, in film formation, it is necessary to consider that parts made of iron group metal should be eliminated as much as possible in facilities and the like in the reaction furnace.

[0033]

EXAMPLES As raw material powder, Ti (CN), TiN, TiC, WC, Mo ₂ C, Nb having an average particle size of 1 to 1.5 μm
Using C, NbN, VC, Ni, and Co, the mixture was blended into the composition shown in Table 1, and then pulverized with a vibration mill. The binder-added product was press-formed into a shape for a TNGA332 chip.
After removing the binder at 00 ° C., firing was performed according to the specifications shown in Table 1.
After the nitrogen gas was introduced under the firing conditions in Table 1, the maximum sintering temperature was maintained after 5 minutes, and the vacuum was immediately returned.

The obtained sintered body was quantitatively analyzed for carbon and nitrogen in the hard phase to determine the (N / C + N) atomic ratio. Each sample was polished at an angle of about 5 °, the Vickers hardness was measured in a direction perpendicular to the polished surface while changing the distance (depth) from the surface, and the hardness distribution was observed.

As the hard film, a TiN, TiCN, TiCNO film was formed by ion plating at a base material temperature of 300 to 700 ° C. so as to have a thickness of 3 μm. The average grain size of the crystals in the film was measured by SEM, and the content of iron group metal in the film was measured by ICP analysis.

Each sample was subjected to an abrasion resistance test under the following conditions, the flank wear amount (mm) was measured, and the number of non-deleted corners was examined by a defect test. The results are shown in Table 2.

(Abrasion test conditions) Work material SCM435 Cutting speed 250 m / min Cutting depth 2 mm Feeding 0.3 mm / rev Cutting time 10 min

(Fracture test) Work material SCM435 (with 4 grooves) Cutting speed 100 m / min Cutting depth 2 mm Feeding 0.3 mm / rev Cutting time 1 min

The evaluation of the finished surface is performed by a method of expressing the finished surface state of the work material by Rmax using a surface roughness meter. If the value is 10 s or more, x is less than 10 s. O was evaluated.

[0040]

[Table 1]

[0041]

[Table 2]

In Table 1, for samples Nos. 1, 2, and 6 (Comparative Examples), the hardness distribution from the surface to 0.2 mm is shown in FIG.

As is clear from the results in Table 1, (N / C
Sample No. 7 using a cermet having a (+ N) ratio of less than 0.4 as a base material has a rough surface on the sintered body and has poor wear resistance. Conversely, in sample No. 11 having a ratio exceeding 0.6, a good sintered body could not be obtained, and a wear resistance test could not be performed.
Sample No. 6, in which the N ₂ pressure to be introduced was low and a hard film was formed on the surface of a cermet in which a hard layer having a Vickers hardness of 2,000 or more was not formed, was markedly abnormally worn in the middle of cutting, and could not be cut. .

On the other hand, based on the product of the present invention, the product of the present invention in which a Ti-containing hard film composed of a microstructure is formed on the surface of a cermet having a portion having a Vickers hardness of 2000 or more on the surface portion is excellent. The surface condition of the work material was very good while exhibiting wear resistance and chipping resistance.

[0045]

As described in detail above, the surface coating T of the present invention
iCN-based cermets are extremely excellent in wear resistance of the surface, exhibit excellent cutting characteristics especially as cutting tools for cast iron, and have excellent surface smoothness after cutting of the work material. Life can be extended.

[Brief description of the drawings]

FIG. 1 is a diagram showing a hardness distribution from the surface of a cermet base material to 0.2 mm from the surface of the cermet base material.

Claims (1)

(57) [Claims] 1. A titanium carbide, nitride or carbonitride of 50 to 80% by weight and a carbide of a Group 6a element of the periodic table in a ratio of 10 to 40% by weight, and (Nitrogen / carbon + The atomic ratio represented by nitrogen) is 0.4 to 0.6
And a binder phase component mainly composed of an iron group metal in an amount of 60 to 95% by weight, and a Vickers hardness of 2 to 50 μm from the surface.
The surface of the TiCN-based cermet where a portion of 000 kg / mm ² or more is present contains more Ti than the TiCN-based cermet, the average particle diameter is 0.4 μm or less, and the content of iron group metal is 100 ppm or less. A surface-coated TiCN-based cermet characterized by being coated with a hard film.