JP2628200B2 - TiCN-based cermet and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improvement of a TiCN-based cermet which is excellent in wear resistance and toughness, has a good burnt surface, and is particularly useful as a cutting tool for cast iron.

(Prior art)

Conventionally, cemented carbide mainly composed of WC-Co has been mainly used as a sintered body for cutting, but recently, a cermet sintered body mainly composed of carbides, nitrides and carbonitrides of Ti. Is used.

Such a cermet-based sintered body includes TiC as a main component, an iron group metal as a binder phase, and
The mainstream was a TiC-based cermet to which carbides, nitrides, and carbonitrides of a, Va, and VIa group metals were added 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 vapor composition. This is intended to impart toughness to the sintered body due to richness of TiN itself and to improve thermal shock resistance and thermal plastic deformation due to high thermal conductivity.

On the other hand, cermets originally have a drawback in that metal is leached on the surface in the production process and a hard layer exists immediately below the surface, which easily causes a defect in cutting performance.

Therefore, various improvements have been made to the TiC-based cermet containing TiN. For example, Japanese Patent Publication No. 59
In -14534, nitrogen is introduced into the furnace at a temperature below the liquid phase appearance temperature to form a softened layer with high toughness on the surface of the sintered body.In Japanese Patent Publication No. 59-17176, firing in a CO reducing atmosphere is required. According to JP-B-60-34618, it is possible to obtain a cermet having uniform mechanical properties both inside and outside the surface by forming a CO atmosphere at the time of cooling after firing according to Japanese Patent Publication No. 34618/1985. Has been proposed.

[Problems to be solved by the invention]

However, from the knowledge of wear resistance during high-speed cutting as a cutting tool for cast iron, Japanese Patent Publication Nos.
The cutting tool described in 0-34618 is insufficient in performance due to low surface hardness. On the other hand, Japanese Patent Publication No. 59-17176 discloses a method for forming a hard layer on the surface, but the surface hardness is at most 1800 Vickers hardness (Hv).
Kg / mm ² not been only achieved until, in forming the hard layer having a higher hardness, Mo ₂ C in the hard-forming component
However, plasticity containing a large amount of Mo, C, and WC results in substantially deteriorating other characteristics as a cutting tool.

Therefore, conventionally, without deteriorating other characteristics,
At present, cutting tools for cast iron having excellent wear resistance have not been developed.

[Object of the invention]

The present invention has as its main object to solve the above problems, and specifically, provides a TiCN-based cermet excellent in flank wear resistance and crater wear resistance, particularly for a cutting tool of cast iron, and a method for producing the same. It is in.

[Means for solving the problem]

The present inventors have repeatedly studied the above problems, and found that Ti is 50 to 80% by weight as a carbide, nitride or carbonitride and 10 to 10% by weight as a group VIa metal of the periodic table as a carbide. 40% by weight and nitrogen / (carbon +
Nitrogen) in a TiCN-based cermet comprising 70 to 90% by weight of a hard phase component having an atomic ratio in the range of 0.4 to 0.6 and 10 to 30% by weight of a binder phase component mainly composed of an iron group metal; TiCN-based cermets, which have a hard part with a Vickers hardness of 2,000 or more in the surface layer from the surface to a depth of 50 μm, where the amount of the binder phase is smaller than the inner part, have excellent flank resistance when used as a cutting tool for cast iron. It has been found that abrasion resistance and claimer wear resistance are achieved.

The TiC-based cermet contains Ti at a ratio of 50 to 80% by weight as a carbide, nitride or carbonitride, and a metal of Group VIa of the periodic table at a ratio of 10 to 40% by weight as a carbide. 70 to 90% by weight of a hard phase component having an atomic ratio represented by / (carbon + nitrogen) in the range of 0.4 to 0.6
And 10 to 30% by weight of a binder phase component mainly composed of an iron group metal
After placing the molded body consisting of in a vacuum furnace, the temperature is increased, and nitrogen gas is introduced at a pressure of 70 torr or more into the furnace before the sintering maximum temperature is reached at or above the liquid phase appearance temperature due to the iron group metal, It has been found that the furnace can be easily and stably manufactured by returning the inside of the furnace to a vacuum and firing after reaching the maximum sintering temperature, and the present invention has been accomplished.

 Hereinafter, the present invention will be described in detail.

The TiCN-based cermet of the present invention contains 50 to 80% by weight, particularly 55 to 65% by weight, of Ti as a hard phase component as a carbide, nitride or carbonitride, and contains a Group VIa element of the periodic table such as W or Mo as a carbide. 10 to 40% by weight, especially 15 to 30% by weight.

In such a hard phase component, if the amount of Ti is less than 50% by weight, the abrasion resistance decreases, and if it exceeds 80% by weight, the sinterability decreases, which is not preferable. Further, the Group VIa element has an effect of suppressing grain growth and improving wettability with a binder phase. However, if it is less than 10% by weight, the above effect cannot be obtained, and the hard phase becomes coarse, and the hardness and strength are reduced. descend. On the other hand, if it exceeds 40% by weight, an unhealthy phase such as an η phase is generated and sintering becomes difficult.

As the hard phase component, in addition to the above, Ta, Nb for the purpose of improving crater wear resistance, and Zr, V, Hf, etc., for the purpose of improving plastic deformation resistance, are used as nitrides, carbides, and carbonitrides. Although it is possible to include it in a proportion of about 40% by weight,
If it exceeds 40% by weight, deterioration of wear resistance, generation of pores and voids tends to increase remarkably, which is not preferable.

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 comprises 70 to 90% by weight and the binder phase component comprises 10 to 30% by weight in the whole sintered body.

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 from 0.4 to 0.4.
0.6, especially in the range of 0.4 to 0.5. That is, if the atomic ratio is less than 0.4, improvement in toughness and wear resistance cannot be expected, and the object of the present invention cannot be achieved. If the atomic ratio exceeds 0.6, pores and voids are generated in the sintered body, and the reliability as a tool is increased. Is reduced.

Further, as shown in FIG. 1, the cermet of the present invention has a Vickers hardness of 2000 on the surface layer from the surface to a depth of 50 μm.
The hard part having the above-described high hardness exists. The presence of such a hard portion can greatly improve the wear resistance of the cermet.

Normally, when a high-hardness layer is present on the surface, chipping, cracking, and the like are likely to occur due to a decrease in toughness, but according to the present invention, the specific composition described above, in particular, by including a large amount of nitrogen, the toughness is reduced. This gives an excellent sintered body free from chipping and cracking.

With such a configuration, the cermet of the present invention can maintain the effect of improving toughness, abrasion resistance, and heat resistance by containing a large amount of nitrogen for a long period of time, and has a hard portion having high hardness on the surface. This makes it possible to extend the life of the cutting tool for cast iron and achieve high reliability. Moreover, it is possible to commercialize the sintered body without performing a polishing step or the like on the sintered body after sintering.

According to the method for producing a TiCN-based cermet of the present invention, the proportion of Ti as a carbide, nitride or carbonitride is 50 to 80% by weight, and the Group VIa element of the periodic table is 10 to 40% by weight as a carbide. And 70 to 90% by weight of a hard phase component having an atomic ratio of nitrogen / (carbon + nitrogen) in the range of 0.4 to 0.6, and 10 to 30% by weight of a binder phase component
To produce a molded body comprising:

Specifically, TiC, TiN, TiCN, etc. are used as raw material powders.
As a VIa-group system, WC, Mo ₂ C, MoC, or the like, or a composite carbide thereof, using a composite carbonitride, after blending so as to have the above composition, known molding means, for example, press molding,
It is formed by extrusion molding, casting molding, injection molding, cold isostatic molding, or the like.

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

The obtained compact is placed in a vacuum furnace and transferred to firing.

The firing is performed at a firing temperature of 1400 to 1700 ° C. According to the present invention, the firing is first performed by heating in a vacuum furnace of 0.5 Torr or less, and nitrogen at a predetermined time of 70 Torr or more, particularly 100 to 200 Torr. Introduce gas.

The nitrogen gas is introduced at a temperature higher than the temperature at which the liquid phase of the iron group metal appears in the temperature raising process, particularly when the theoretical density ratio is about 5% or more higher than the initial compact. That is,
Above the liquid phase appearance temperature, a film is formed on the surface of the molded body by the liquid phase. By introducing nitrogen gas after the formation of the film, the nitrogen gas is trapped in the voids existing in the molded body and is prevented from remaining, and nitrogen due to thermal decomposition of nitrides such as TiN contained in the molded body. Generation of gas can be suppressed, and as a result, pores and voids can be prevented from remaining in the sintered body.

However, when the time of introduction of nitrogen gas reaches the maximum sintering temperature, especially around the point where the theoretical density ratio exceeds 90%, substantially,
The effect of suppressing the decomposition of nitride cannot be obtained, and the surface of the sintered body becomes rough.

After the temperature in the furnace reaches the maximum sintering temperature,
After holding for a predetermined time, the pressure is immediately returned to the vacuum, and the firing is continued.

This means that if the pressure is further increased after reaching the maximum sintering temperature, the surface of the sintered body contains coarse metal and almost no metal,
A brittle nitride layer is generated, causing roughening of the burnt surface and significantly reducing the toughness of the surface.

The pressure of the introduced nitrogen gas needs to be a pressure that can sufficiently suppress the thermal decomposition of the nitride, but this nitrogen gas pressure is lower than the hardness of the hard portion formed on the surface of the sintered body. It has a significant effect. This is because a pressure is generated between the inside of the compact and the atmosphere in the furnace after the introduction of the nitrogen gas. When the pressure is suddenly returned to vacuum, the bonding metal near the surface of the molded body moves inside, and the hardness increases near the surface layer due to a decrease in the amount of the bonding phase relative to the inside. At the same time, it is considered that the toughness is improved due to the spheroidization of crystals near the surface in the structure and the inclusion of a large amount of Group VIa elements.

According to the present invention, it has been confirmed that it is necessary to set the nitrogen gas pressure to 70 Torr or more in order to form a hard portion having a Vickers hardness of 2,000 or more.

 Hereinafter, the present invention will be described with reference to the following examples.

〔Example〕

As raw material powder, Ti (CN), TiN,
Using TiC, WC, Mo ₂ C, NbC, NbN, VC, Ni and Co, after mixing to the composition shown in Table 1, pulverizing with a vibration mill, press-forming the binder-added one into TNGA332 chip shape, After debinding at 300 ° C., firing was performed according to the specifications shown in Table 1. The first
After the nitrogen gas was introduced under the firing conditions in the table, the maximum sintering temperature was maintained for 5 minutes, and the vacuum was immediately returned.

The obtained sintered body was quantitatively analyzed for carbon and nitrogen in the hard phase, and the N / (C + N) atomic ratio was determined. Further, the maximum surface roughness (Rmax) of the burnt skin surface was examined.

For each sample, polish the sample at an angle of about 20 °,
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 measured.
The maximum hardness is shown in Table 2.

In addition, a wear resistance test was performed on each sample under the following conditions.
The flank wear (mm) and crater wear (mm) were measured.

Wear test conditions Work material FC25 Cutting speed 150m / min Depth of cut 2mm Feed 0.3mm / rev Cutting time 10 minutes In Table 1, Sample Nos. 2, 4, and 7 showed a hardness distribution from the surface to 1 mm.

As is clear from the results in Table 1, the N / (C + N) ratio was 0.
The sample of No. 8 below 4 has roughness on the surface of the sintered body and has poor wear resistance. Conversely, a sample of No. 9 having a ratio of more than 0.5 cannot obtain a good sintered body and has poor wear resistance. Conversely, a sample of No. 9 having a ratio of more than 0.6 failed to obtain a good sintered body, and could not perform a wear resistance test. No. 7 and No. 10 samples in which the N ₂ pressure to be introduced was less than 70 Torr did not achieve Vickers hardness of 2000, and the results of the wear resistance test were poor.

Further, N ₂ gas introduction period is lower than the liquid phase emergence temperature T ₁ N
With o.12, a good sintered body was not obtained, and the maximum sintering temperature T ₂
After reaching, the surface became rough.

On the other hand, all of the products Nos. 1 to 6 of the present invention formed a hard portion having a Vickers hardness of 2000 or more, and exhibited excellent wear resistance to cutting of cast iron. Further, it was confirmed that the content of the binder phase in the hard portion formed in the surface layer portion of the cermet of the present invention was smaller than the content of the binder phase in the cermet, that is, in the central portion.

〔The invention's effect〕

As described above in detail, the cermet of the present invention contains a predetermined amount of nitrogen, and a hard portion having a high hardness of Vickers hardness of 2000 or more is formed on the surface portion, so that the surface has extremely excellent wear resistance. In particular, it shows excellent cutting characteristics as a cutting tool for cast iron, and can achieve a longer tool life.

[Brief description of the drawings]

FIG. 1 is a view showing a hardness distribution from the surface of the cermet sintered body to 0.2 mm from the surface, wherein Nos. 2 and 4 indicate the products of the present invention and No. 7 indicates comparative products.

Claims (2)

(57) [Claims] (1) Ti is contained in a proportion of 50 to 80% by weight as a carbide, nitride or carbonitride, and a Group VIa metal of the periodic table in a proportion of 10 to 40% by weight as a carbide.
TiCN group consisting of 70 to 90% by weight of a hard phase component having an atomic ratio of (carbon + nitrogen) in the range of 0.4 to 0.6 and 10 to 30% by weight of a binder phase component mainly composed of an iron group metal. A TiCN-based cermet characterized in that a cermet has a hard part having a Vickers hardness of 2,000 or more in a surface layer part having a depth of 50 μm from the surface, in which the amount of a binder phase is smaller than that in an inner part. (2) Ti is contained in a proportion of 50 to 80% by weight as a carbide, nitride or carbonitride, and a Group VIa metal of the periodic table in a proportion of 10 to 40% by weight as a carbide.
A molded article comprising 70 to 90% by weight of a hard phase component having an atomic ratio of (carbon + nitrogen) in the range of 0.4 to 0.6 and 10 to 30% by weight of a binder phase component mainly composed of an iron group metal. After placing in a vacuum furnace, the temperature was raised, and nitrogen gas having a pressure of 70 torr or more was introduced into the furnace before reaching the maximum sintering temperature above the liquid phase appearance temperature due to the iron group metal, A method for producing a TiCN-based cermet, wherein the temperature in the furnace is returned to a vacuum after the temperature is reached and the furnace is fired.