JPH06145876A - Cemented carbide and its production - Google Patents

Abstract

PURPOSE:To provide a slitter knife contg. fine-grained added substance and small in the generation of chipping or the like, to provide cemented carbide used therefor and to provide the producing method therefor. CONSTITUTION:This cemented carbide used for a slitter knife for a magnetic tape contains, by weight, 95 to 80% carbides constituted of 0.5 to 2.0% chromium carbide and the balance substantial tungsten carbide and 5 to 20% cobalt. The carbides contained in the cemented carbide is constituted of carbide powder preliminarily subjected to compounding treatment. Moreover, the average grain size of the tungsten carbide grains contained in the cemented carbide is regulated to <=1.0mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a WC-Co type cemented carbide, and more particularly to a cemented carbide used for a slitter knife for cutting a magnetic tape and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a knife made of carbon steel, high speed steel, cemented carbide, ceramics or the like has been used for cutting magnetic tape and the like. Among them, carbon steel and high speed steel have a large amount of wear on the cutting edge due to the hardness of the material, and cannot withstand long-term slitting. Ceramics are inferior to metal knives in terms of their material reliability. For these reasons, WC-Co based cemented carbide is now widely used for cutting magnetic tape.

Usually, in the cemented carbide used in such applications, in order to make the WC grain size finer, generally, fine grained WC and added carbides such as VC, TaC and C are used.
This has been dealt with by suppressing grain growth by adding r ₃ C ₂ or the like. For example, in Japanese Patent Laid-Open No. 61-12847, by adding V and Cr to a WC-Co alloy,
A cemented carbide having excellent wear resistance and high toughness has been proposed, which aims to suppress the grain growth of WC by the combined effect. Further, Japanese Patent Application Laid-Open No. 62-48413 proposes a cemented carbide having excellent characteristics of having HRa of 91 or more and bending strength of 350 kg / mm ² or more by adding vanadium carbide and zirconium nitride.

[0004]

However, in any of the above-mentioned cemented carbides, in order to make the grain size fine, additives are added to suppress grain growth. As described above, since a large amount of added carbide is used in the fine grain alloy, when it is used in a slitting knife, chipping and the like easily occur, which is an unavoidable drawback.

Therefore, a technical object of the present invention is to provide a slitter knife which contains fine-grained additives and which causes little chipping and the like, a cemented carbide used for the slitter knife, and a method for producing the same.

[0006]

As a result of studies to solve the above technical problems, the present inventors have found a cemented carbide for slitter knives having high strength and high hardness and a method for producing the same.

That is, according to the cemented carbide of the present invention,
0.5% to 2.% containing 0 wt.% Cobalt as binder phase.
It is characterized in that 0% by weight of chromium carbide and the balance comprises tungsten carbide as hard phase. Here, in the present invention, the average grain size of tungsten carbide in the cemented carbide is 1.
It is preferably 0 μm or less.

The reasons for limiting the chemical composition and the shape of the powder in the cemented carbide of the present invention will be described below.

In the present invention, the content of cobalt is 5 to 5
The reason why the content is limited to 20% by weight is that if the Co content is less than 5%, the cemented carbide is not sufficiently densified. On the other hand, if it exceeds 20%, the hardness as a cutting blade of a magnetic tape or the like becomes insufficient, and the wear resistance decreases.

Further, in the present invention, the amount of chromium carbide added is limited to 0.5 to 2.0% by weight because the amount added is less than 0.1%.
If it is less than 5% by weight, the desired grain growth suppressing effect cannot be obtained, while if it exceeds 2% by weight, the toughness of the cemented carbide is lowered.

Further, the cemented carbide of the present invention is characterized by using a carbide powder in which chromium carbide and tungsten carbide are previously compounded. Here, in the present invention, the carbide powder obtained by previously subjecting chromium carbide and tungsten carbide to the composite treatment is used because the alloy powder obtained by adding the chromium carbide powder to the mixed powder of tungsten carbide and cobalt alone and sintering the mixture is used. This is also because it was found that the composite-treated powder was superior in strength and hardness.

The composite powder of chromium carbide and tungsten carbide used in the present invention is prepared by mixing a predetermined amount of tungsten powder and chromium carbide powder or chromium oxide powder, and
By heating in a reducing atmosphere at 350 ° C to 1500 ° C, at least a part of the solidified carbide is obtained.

The method for producing a cemented carbide according to the present invention is such that a predetermined amount of fine tungsten carbide powder containing chromium carbide and cobalt powder are wet-mixed, sieved and dried, and then press-molded, and then in vacuum. Sintering is performed at 1350 ° C to 1450 ° C for 1 hour. After that, 1250 ° C to 1350 ° C, 100
By performing hot isostatic pressing (HIP) at 0 kg / cm ² , a high-strength and high-toughness cemented carbide is obtained.

In the following examples of the present invention, the case where the tungsten carbide and the chromium carbide are compounded is described, but the chromium carbide is reduced with the chromium oxide,
Even when the carbon is replaced with carbon sufficient for carbonization, it is of course possible to produce the compounded carbide powder as in the example.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. (Example 1) As raw material powders, fine W powder having an average particle diameter of 0.8 µm, chromium carbide powder having an average particle diameter of 1.3 µm, and carbon black were mixed in the compounding compositions of Samples A to D shown in Table 1 below. Carbonization was performed in a reducing atmosphere at 1500 ° C. for 30 minutes to obtain a composite-treated carbide powder.

[0016]

[Table 1] The properties of the carbide powders obtained from the blended compositions of Samples A to D in Table 1 above are shown in Table 2 below. The sample numbers in Table 2 below correspond to the sample numbers in Table 1 above. In the table, TC is the total carbon content, FC is the free carbon content, and CC is the combined carbon content (CC = TC-FC).

[0017]

[Table 2] Then, after blending to have the composition shown in Table 3 below,
Mixing was performed for 12 hours by wet mixing in alcohol. still,
The composite-treated powders used in Samples 1 to 4 shown in Table 3 are Samples A to D, respectively.

[0018]

[Table 3] After mixing, it was dried under reduced pressure and press-molded at a pressure of 1000 kg / cm ² . Then, after vacuum sintering at 1400 ° C for 1 hour, 13
Hot isostatic pressing (HIP) was performed under an argon atmosphere at 50 ° C. and 1000 kg / cm ² for 1 hour.

As a comparative alloy, the average grain size is 0.8 μm.
Fine WC powder and Co powder, and chromium carbide powder with an average particle size of 1.3 μm are mixed in alcohol,
Preparation and sintering were performed in the same manner as in No. 4. The sintered bodies according to the examples and the comparative examples were ground with a diamond grindstone to obtain 4 mm × 8 mm × 25
mm JIS resistance pieces were manufactured, and the bending strength (TRS) and Rockwell hardness (HRa) of these specimens were measured, and the grain size of the cemented carbide was measured by a scanning electron microscope (S
The average particle size was measured by observing with EM). The results are shown in Table 4 below.

[0020]

[Table 4] Next, cemented carbide 2 according to the embodiment of the present invention shown in Table 4
And a cemented carbide 6 according to a comparative example were used to slit a magnetic tape (normal tape) under the conditions shown in Table 5 below. 1 and 2 are SEM photographs of the metal structure in the worn and chipped state of the knife as seen from the outer peripheral direction. As is clear from FIGS. 1 and 2, chipping was not observed in the cemented carbides according to the examples of the present invention, but chipping occurred in the cemented carbides according to the comparative examples.

[0021]

[Table 5] From the above, it was found that the cemented carbide according to the example of the present invention had better hardness and toughness than the cemented carbide according to the comparative example.

[0022]

As described above, although the cemented carbide of the present invention contains a trace amount of carbide, it has higher strength and higher hardness than conventional cemented carbides. When used for slitter knives such as tape, chipping is less likely to occur and excellent cutting performance is demonstrated.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph showing a metal structure of a cemented carbide according to an example of the present invention in a worn / chipping state.

FIG. 2 is a scanning electron micrograph showing a metal structure of a cemented carbide according to a conventional example in a worn / chipping state.

Claims (6)

[Claims] 1. A carbide containing 0.5 to 2.0% by weight of chromium carbide with the balance of chromium carbide consisting essentially of tungsten carbide.
A cemented carbide containing 5 to 80% by weight and 5 to 20% by weight of cobalt. 2. The cemented carbide according to claim 1, wherein the tungsten carbide particles in the cemented carbide have an average particle size of 1.0.
A cemented carbide having a thickness of less than μm. 3. The cemented carbide according to claim 1, wherein the carbide is composed of a carbide powder which has been subjected to a complexing treatment in advance. 4. A slitter knife for a magnetic tape, comprising the cemented carbide according to any one of claims 1 to 3. 5. A method for producing by a powder metallurgical method by mixing a powder of carbide, which comprises 0.5 to 2.0% by weight of chromium carbide with the balance of chromium carbide substantially consisting of tungsten carbide, and cobalt powder. Cemented carbide characterized in that the tungsten carbide particles have an average particle size of 1.0 μm or less. 6. The method for producing a cemented carbide according to claim 5, wherein the carbide powder is preliminarily compounded.