JPH10324943A - Ultra-fine cemented carbide, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the cemented carbide which is high in hardness, high in strength and excellent in toughness by providing the cemented carbide having the composition of the bonded layer mainly consisting of VN, Cr2 N, TaN, ZrN and Co of the prescribed wt.%, and the balance WC, and specifying the mean grain size of WC particles and N content. SOLUTION: The WC-Co ultra-fine cemented carbide has the composition consisting of, by weight, 0.05-0.50% VN, 0.20-0.40% Cr2 N, 0.5-1.0% at least one kind of TaN and ZrN, 5-20% bonded layer mainly consisting of Co, and the balance WC with inevitable impurities. The mean grain size of WC particles is 1.0 μm. The content of nitrogen in the alloy is 0.10-0.20%. In manufacturing the alloy, the green compact of the raw powder is sintered in the atmosphere of nitrogen partial reassure of 600-760 Torr. In the temperature range from 1000-1200 deg.C in the temperature rise to 1200 deg.C in the middle of cooling through the prescribed holding temperature. The cemented carbide which is high in hardness, resistant in wear, and excellent in toughness can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine-grained cemented carbide and a method for producing the same, and more particularly to a cemented carbide having high hardness, excellent wear resistance and toughness containing fine tungsten carbide particles having an average particle size of 1.0 μm or less. The present invention relates to an alloy and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, cemented carbides mainly composed of tungsten carbide (WC) have been widely used as materials for cutting tools, wear-resistant tools and the like. Above all, the average particle size is 1.0μ
It is known that a cemented carbide mainly composed of WC particles of m or less has high hardness and high strength. For this reason, cemented carbide is used for various shearing swords, PCB drills, metal drills, end mills, and the like. On the other hand, higher efficiency is required in the market, and ultra-fine cemented carbide is indispensable to satisfy this requirement.

[0003] Here, the ultrafine-grained cemented carbide is produced by using fine WC powder as a starting material to suppress the grain growth in the sintering process, and to suppress the grain growth, various additives are added. Have been proposed.

For example, Japanese Patent Application Laid-Open No. 61-12847 (hereinafter referred to as “prior art 1”) discloses that a WC-Co alloy has
There is disclosed a method of suppressing the grain growth of WC and producing a fine-grain cemented carbide by adding Cr and Cr in combination.

Japanese Patent Laid-Open Publication No. Hei 6-81072 (hereinafter referred to as prior art 2) discloses a WC base material in which WC particles having an average particle size of 0.6 μm or less and a maximum particle size of 3.0 μm or less are dispersed. 2. The maximum grain size is 3 in the cemented carbide base.
A carbide or carbonitride particle of one of V, Cr, Ta, Nb and Ti, which is 0 μm or less, or a carbide of two or more of V, Cr, Ta, Nb and Ti, or A WC-based cemented carbide having a structure in which carbonitride particles are dispersed is disclosed.

[0006]

However, the method according to the prior art 1 requires a large amount of carbides of V and Cr, so that the resulting fine-grained cemented carbide is liable to cause chipping, etc. When used in an end mill for metal, etc., there is a problem that the tool is broken and the quality of the tool is not stable.

Further, in the fine-grain cemented carbide according to the prior art 2, the carbide or carbonitride particles of V, Cr, Ta, Nb and Ti in the fine WC may act as coarse particles, and toughness and hardness , There is a problem that it does not work to improve the strength.

As described above, any of the inventions according to the prior arts 1 and 2 is a method for suppressing the grain growth when sintering the cemented carbide. However, these methods alone are not enough to completely suppress the grain growth. Therefore, when used as cutting tools such as drills and end mills and shearing tools such as punching dies and slitters, the above-mentioned WC-based cemented carbide can reach a relatively short life due to chipping. The disadvantages have not been eliminated.

[0009] Therefore, the technical problem of the present invention is that a 1.0 μm
m, containing fine tungsten carbide particles
An object of the present invention is to provide a fine-grained cemented carbide having high hardness, high strength and excellent toughness, and a method for producing the same.

[0010]

Means for Solving the Problems From the above-mentioned viewpoints, the present inventors have conducted intensive studies in order to produce a WC-based cemented carbide having high strength. By controlling the atmosphere for sintering fine-grained cemented carbide by using a grain growth inhibitor containing nitrogen in it, and leaving nitrogen in the alloy, the fineness is less than 1.0 μm. The present inventors have found that a cemented carbide having high hardness, high strength and excellent toughness containing tungsten carbide particles can be obtained, and the present invention has been accomplished.

That is, in the present invention, VN is set to 0.05 to 0.
And 50 wt%, 0.5 at least one of 0.20 to 0.40 wt% and TaN and ZrN the Cr ₂ N
1.0% by weight and a Co-based binder phase of 5%.
A WC-Co-based fine-grain cemented carbide having a composition consisting of -20% by weight, a nitrogen content of 0.10-0.20% by weight, and the balance consisting of WC and unavoidable impurities, wherein the average of WC in said alloy is It is characterized by a particle size of 1.0 μm or less, high hardness, high strength and excellent toughness.

In the present invention, the fine-grain cemented carbide is characterized in that the nitrogen content in the alloy is 0.10 to 0.20% by weight.

Further, the present invention relates to a method for producing the above-mentioned fine-grained cemented carbide by powder metallurgy. The process up to 1200 ° C. in the middle of cooling after passing through a predetermined holding temperature is performed at a nitrogen partial pressure of 600 to 760.
It is characterized by sintering under control in a nitrogen atmosphere of Torr.

Here, the reason why the composition and the sintering conditions are limited as described above in the present invention will be described.

First, Co will be described.

The reason why the content of Co is limited to 5 to 20% by weight in the present invention is that if the content of Co is less than 5%, the cemented carbide cannot be sufficiently densified. If it exceeds 20%,
This is because when used as a cutting tool typified by a pit, a drill, an end mill and the like and a wear-resistant tool typified by a shearing tool such as a punching die and a slitter, the hardness is insufficient and the wear resistance is reduced.

Next, the amount of VN added will be described.

V forms a solid solution together with Cr in the binder phase to form WC
Has the effect of suppressing grain growth. In the present invention, the content is limited to 0.05 to 0.50% by weight.
If it is less than 0.05% by weight, the desired grain growth effect cannot be obtained even if it is added in combination with Cr. On the other hand, if it exceeds 0.50% by weight, the third phase may be contained in the alloy depending on the cooling rate after sintering. This causes the toughness to decrease, resulting in a decrease in toughness.

Next, the amount of Cr ₂ N added will be described.

Cr forms a solid solution with V in the binder phase to form WC
Has the effect of suppressing grain growth. In the present invention, the content is limited to 0.2 to 0.40% by weight.
If it is less than 0.2% by weight, the desired grain growth effect cannot be obtained even if it is added in combination with Cr. On the other hand, if it exceeds 0.40% by weight, the third phase may be contained in the alloy depending on the cooling rate after sintering. This causes the toughness to decrease, resulting in a decrease in toughness.

Next, the amount of TaN added will be described.

Ta is partially dissolved in the binder phase together with V and Cr, and has an effect of suppressing the grain growth of WC. In the present invention, the content is limited to 0.5 to 1.0% by weight. If the content is less than 0.5% by weight, a desired grain growth effect cannot be obtained, while if it exceeds 1.0% by weight. This is because the strength and hardness of the material after sintering are reduced.

Next, the amount of ZrN added will be described.

Zr has a high strength at high temperatures and has an effect of improving the plastic deformation resistance. In the present invention, the content is limited to 0.5 to 1.0% by weight,
If it is less than the above, the effect at the desired high temperature cannot be expected. on the other hand.
If the content exceeds 1.0% by weight, the strength and hardness of the sintered material are reduced.

Next, the amount of N added will be described.

The reason why the content of N bonded to V and Cr is limited to 0.10 to 0.20% by weight is that when the content is less than 0.10% by weight, the amount of N bonded to V and Cr is reduced. , The desired grain growth effect cannot be obtained even with the addition of a composite, while if it exceeds 0.20% by weight, it precipitates as a third phase in the metallurgical content of the sintered body and causes a decrease in toughness. is there.

Finally, the sintering conditions in the manufacturing method of the present invention will be described.

From a temperature of 1000 to 1200 ° C. (preferably 1100 to 1200 ° C.) in the course of raising the temperature to 1200 ° C. in the middle of cooling through a predetermined holding temperature, a nitrogen partial pressure of 600 to 760 T
orr (preferably 650 to 750 Torr) is controlled under a nitrogen atmosphere.
Introducing nitrogen gas from a temperature of 00 ° C or less does not compensate for denitrification or has no economic effect. 1200 ° C
If it is introduced beyond the limit, denitrification starts and nitrogen cannot be controlled. The reason for limiting the nitrogen partial pressure to 600 to 760 Torr is that if the partial pressure is less than 600 Torr, the decomposition of nitrogen is promoted and the nitrogen content does not reach the predetermined amount. Also, 76
If the pressure exceeds 0 Torr, pores may remain and the alloy does not exhibit the desired properties.

[0029]

Embodiments of the present invention will be described below.

(First Embodiment) As raw material powders, WC powder having an average particle diameter of 0.6 μm, Co powder having an average particle diameter of 1.4 μm, VN powder having an average particle diameter of 1.0 μm, and Cr ₂ N having an average particle diameter of 1.5 μm were used.
The powder was mixed with a 1.5 μm TaN powder having the composition shown in Table 1 below, mixed with a wet ball mill in alcohol, and dried under reduced pressure.

The obtained mixed powder was pressed into a green compact at a pressure of 1 ton / cm ² , and this compact was sintered under the conditions shown in Table 1 below.

After that, the obtained sintered body was kept at 1350 ° C. at 1,000 atm for 1 hour to perform HIP. These sintered bodies are ground with a diamond grindstone and are 4 mm long and 8 m wide.
A JIS bending test piece having a length of 25 mm and a length of 25 mm was prepared, and the bending force by three-point bending was measured. The hardness was measured with a Rockwell hardness tester. The average particle size of WC in the alloy was determined by performing image processing on the SEM observation results. The comparative cemented carbide was adjusted in the same manner. The properties of each alloy are shown in Table 2 below.

[0033]

[Table 1]

[0034]

[Table 2]

(Second Embodiment) The WC-Co-based fine-grain cemented carbide 3 and the comparative cemented carbide 3 of the present invention obtained in the first embodiment are cut into a two-flute end mill having a diameter of 10 mm. Using these end mills, the work material is SKD61
(HRC61), and a dry cutting test of steel was performed under the conditions of a cutting speed of 130 mm / min and a cutting depth of 10 mm. Flank wear: With the life standard of 0.25 mm, the cutting length up to the life was determined, and the ratio of the cutting length of the present end mill to the cutting length of the comparative end mill was evaluated.
The results are shown in Table 3 below.

[0036]

[Table 3]

From the results shown in Table 3 above, it was found that the end mill of the present invention exhibited superior cutting performance as compared with the comparative end mill.

(Third Embodiment) As raw material powders, WC powder having an average particle diameter of 0.6 μm, Co powder of 1.4 μm, VN powder of 1.0 μm, and Cr ₂ N of 1.5 μm were used.
The powder was mixed with ZrN powder of 2.3 μm in the composition shown in Table 4 below, mixed with a wet mixing ball mill in alcohol, and dried under reduced pressure. 1 ton / cm of the obtained mixed powder
^A green compact was press-molded at a pressure of ² and this compact was sintered under the conditions shown in Table 4 below.

Thereafter, the obtained sintered body was maintained at 1350 ° C. at 1,000 atm for 1 hour, and HIP was performed. These sintered bodies were ground with a diamond grindstone to prepare JIS folded test specimens of 4 mm in length, 8 mm in width, and 25 mm in length, and the bending strength by three-point bending was measured. The hardness was measured with a Rockwell hardness tester. The average particle size of WC in the alloy was determined by performing image processing on the SEM observation results. The comparative cemented carbide was adjusted in the same manner. The properties of these alloys are shown in Table 5 below.

[0040]

[Table 4]

[0041]

[Table 5]

(Fourth Embodiment) The WC-Co-based fine-grain cemented carbide 2 of the present invention obtained in the third embodiment 2 and the comparative cemented carbide 6 are cut into a two-blade end mill having a diameter of 10 mm. Work material: SKD61 using these end mills
(HRC61), a cutting speed of 130 mm / min, a cutting depth: 10 mm, a dry cutting test of steel was performed. Then, the cutting length until the end of the life was determined based on the life of the flank wear: 0.25 mm, and the ratio of the cutting length of the end mill of the present invention to the cutting length of the comparative end mill was evaluated. The results are shown in Table 6 below.

[0043]

[Table 6]

[0044]

As described above, according to the present invention,
By using a grain growth inhibitor containing nitrogen in an alloy containing Co as a binder phase and sintering a fine-grained cemented carbide, the atmosphere is controlled to allow nitrogen to remain in the alloy.
It is possible to provide a fine-grain cemented carbide with high hardness, high strength and excellent toughness containing fine tungsten carbide particles having a particle size of 0 μm or less.

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[Procedure amendment]

[Submission date] July 1, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0002

[Correction method] Change

[Correction contents]

[0002]

2. Description of the Related Art Conventionally, cemented carbides mainly composed of tungsten carbide (WC) have been widely used as materials for cutting tools, wear-resistant tools and the like. Above all, the average particle size is 1.0μ
It is known that a cemented carbide mainly composed of WC particles of m or less has high hardness and high strength. For this reason, cemented carbide is used for various shearing blades , PCB drills, metal drills, end mills, and the like. On the other hand, higher efficiency is required in the market, and ultra-fine cemented carbide is indispensable to satisfy this requirement.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

Furthermore, in the present invention, the fine cemented carbide described above a method for producing the powder metallurgy, when sintering of pressed bodies of the raw material powder of the composition, of course raised from 1000 to 1200 ° C. The process up to 1200 ° C. in the middle of cooling after passing through a predetermined holding temperature is performed at a nitrogen partial pressure of 600 to 760.
It is characterized by sintering under control in a nitrogen atmosphere of Torr.

Claims (3)

[Claims] 1. The method according to claim 1, wherein said VN is 0.05 to 0.50% by weight and
The r ₂ N and 80.20 to 0.40 wt%, TaN and Z
0.5 to 1.0% by weight of at least one of rN
And a WC having a composition consisting of 5 to 20% by weight of a binder phase containing Co as a main component and the balance being WC and unavoidable impurities.
-A Co-based fine-grained cemented carbide, wherein the average particle size of the WC particles in the alloy is 1.0 µm or less, and the alloy is high in hardness, excellent in strength and excellent in toughness. 2. The fine-grain cemented carbide according to claim 1,
A fine-grain cemented carbide, characterized in that the alloy has a nitrogen content of 0.10 to 0.20% by weight. 3. A method for producing a fine-grained cemented carbide according to claim 1 or 2 by powder metallurgy, the method comprising:
The process from 00 to 1200 ° C. to 1200 ° C. in the middle of cooling through a predetermined holding temperature is performed under a nitrogen partial pressure of 600 to 760 Torr.
A method for producing a fine-grained cemented carbide, characterized in that sintering is performed while controlling in a nitrogen atmosphere of r.