JPH0241570B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention provides a method for preventing blowholes from occurring in a cemented carbide.

(b) Conventional techniques and their problems During vacuum sintering of cemented carbide, blisters often occur due to blowholes as shown in Figure 1. This phenomenon tended to occur frequently in alloys containing a large amount of binder, which is a binder of various carbonitrides.
This type of blister can be small enough to be overlooked by the naked eye, or large enough to reach 10 to 15 mm. When this part was cut, there was a hole inside, which turned out to be a blowhole. Sintering conditions, gas components, etc. have been investigated, but no definitive solution has been found.

(c) Disclosure of the invention The present invention comprises powders of one or more carbides and nitrides of Groups A, A, and A of the Periodic Table, and 0.5 to 5% by weight of iron group metals and their oxides as binding metals. Furthermore, the method is characterized in that an amount of carbon is added that is at least an amount that can completely reduce the added iron group metal oxide. Hereinafter, as an example of the above-mentioned superhard metal, a case of a WC-Co-based superhard alloy (synonymous with cemented carbide in this application) will be explained in detail. There are various possible causes of blowholes, but the main cause is closely related to the physical properties of the binder Co. For example, during wet ball milling, WC, which is a brittle material, is pulverized, but The malleable metal Co is only flattened when beaten, but not pulverized, and oxygen is present on its surface.
It will be absorbed. This type of adsorbed oxygen, solid solution oxygen in Co, and carbon of the hard material WC react to form carbon monoxide gas. Before this gas escapes from inside the molded body, the surface of the molded body The temperature rises due to radiant heat, and a liquid phase emerges before entering the interior.
For this reason, they discovered that the surface becomes dense before sufficient gas can escape from the inside, leaving no escape route for the gas and creating a blowhole. In order to eliminate this cause, the first feature of the present invention is that gas is intentionally generated from inside, and the second feature is that carbon is added so that a liquid phase can be generated from the entire molded product at low temperatures. It has the characteristics of In other words, the melting point of Co alone is 1495℃, but the melting point of Co-C system is 1320℃.
The temperature drops to ℃. The third feature is that CoO is a brittle material, and during the process of being pulverized into fine particles during wet ball milling, it gets between the flat Co particles and prevents the Co particles from condensing, while at the same time C also gets mixed in between them. As a result, Co powder and C powder are dispersed and carbon monoxide is generated in each part. On the other hand, in the area where C and Co come into contact, the melting point drops to 1320°C, and a liquid phase is generated almost simultaneously on the surface and inside. In this case, the content of the iron group metal oxide is preferably 0.5 to 5% by weight, but the effect is even greater if it is in the range of 1 to 3%. That is, if it is less than 0.5% by weight, the mixing effect is so small that blowholes cannot be completely eliminated. Moreover, if it exceeds 5% by weight, the amount of gas generated from the compact becomes too large, the time required for degassing increases, and phenomena such as decarburization from the WC occur. In addition, it is necessary to add a sufficient amount of carbon to reduce the added CoO, and a range of 0.09% to 0.9% by weight is good, but if it is further increased to 0.16% to 0.5% by weight, blowholes may occur. can be made extremely small. Among iron group oxides, CoO, Co ₃ O ₄ ,
There are various types such as Co ₂ O ₃ and any of them can be used, but CoO has better stability. The same applies to Ni and Fe.

(d) Example 78% by weight of WC with a particle size of 3μ, Co powder 20.5%
wt% further CoO 1.35 wt%, graphite powder 0.15 wt%
Wet ball milling was carried out after blending in weight percent. A powder for pressing was prepared by adding 1.5% by weight of paraffin to this powder. Using this powder, molding, deparaffinization, and vacuum sintering are performed to create an inner diameter of 30φ, an outer diameter of 75φ,
A sintered body with a height of 60φ was produced, and no blowholes were found among the 50 pieces. In the same manner as above, a powder containing 2% by weight of Co2 without the addition of CoO or graphite was prepared, and the same procedure was performed.
A blowhole product was created. A cross-sectional view of these products is shown in FIG. A large cavity can be seen in the cross section.

(e) Effects of the invention The present invention provides headers, dies, guide rollers, etc.
In addition to WC-Co wear-resistant products, periodic table a,
It is effective in hard alloys made of carbides and nitrides of group a and a group elements and iron group metals. Among these wear-resistant parts, it is also effective when using alloys containing a large amount of iron group metals that require toughness, and when using coarse-grained powders that are prone to blowholes.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a cylindrical cemented carbide according to a conventional method, and 1 indicates a blowhole. 2 indicates a blistered portion.

Claims (1)

[Claims] 1. Carbide of groups a, a, a of the periodic table,
In a cemented carbide formed by sintering one or more types of nitride powder and iron group metal powder as a bonding metal, 0.5 to 5% by weight of an oxide of an iron group metal is added, and this is further reduced. Requires 0.09-0.9% carbon by weight
A method for preventing blowholes in cemented carbide, which is characterized by adding, mixing, and then sintering. 2. A method for preventing blowholes in cemented carbide, characterized in that the iron group metal oxide according to claim 1 is CoO.