JP2008290890A - Method of molding cemented carbide integrally with metallic material and integrally molded member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of molding a hard-to-work carbide base material represented by tungsten carbide (WC) and having high molting point and high hardness integrally with a metallic material and an integrally molded member thereby. <P>SOLUTION: Low sintering temperature, low pressurizing force and high densification speed in powder metallurgy are attained by micronizing crystal grains of the carbide base material. The densification of a compression-molded body comprising the hardly workable carbide-based material such as tungsten carbide (WC) which is compression-molded on the surface of the metallic base material is performed at a temperature lower than that of a conventional one by 500°C or more by using the superplasticity phenomenon caused by the micronization of the crystal grains. As a result, the metal carbide-metal integrated molded material having high accuracy is manufactured without causing the plastic deformation in the base material side. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for integrally forming a metal carbide on a metal material, and more particularly, by low-temperature sintering using a superplastic phenomenon between a metal material and a hard-working carbide material having a high melting point and high hardness. It relates to integral molding technology.

Cemented carbide, which is a metal carbide obtained by adding a binder such as cobalt or nickel to a hard metal carbide powder and sintering it, is wear resistant due to its extremely hard properties such as cutting and mold forming. Is widely used as a cemented carbide tool, in particular, tungsten carbide (WC) is widely used as a typical cemented carbide. However, since tungsten itself is a rare metal, it is not preferable in terms of cost and element strategy to make the entire tool with tungsten carbide (WC). Therefore, conventionally, tungsten carbide (WC) has been used only for portions where wear resistance is actually required, rather than making the entire tool with tungsten carbide (WC). In this conventional method, a member made of cemented carbide prepared in advance according to the shape of the joining surface of the metal member is prepared for a desired metal member as a base material, and then both are joined afterwards. Thus, a tool in which a cemented carbide alloy and a metal base material are integrated is manufactured, and the joining of both is performed by brazing or diffusion bonding. Japanese Patent Application Laid-Open No. 2004-231476 (Patent Document 1) describes a mold used for press-molding an optical element made of glass in a mold surface portion mainly composed of tungsten carbide (WC) and a mother made of nickel chromium molybdenum steel. Disclosed is a method of integrally joining a material part with a brazing material.
JP 2004-231476 A

  The present invention has been made in view of the above prior art, and the present invention integrates a hard-working carbide-based material having a high melting point and high hardness represented by tungsten carbide (WC) with a metal material. An object of the present invention is to provide a method for molding the molded article and an integral molded member thereof.

  As a result of intensive studies on a method of integrally forming a carbide-based material and another metal base material, the inventors have made a subsequent analysis of a metal carbide and a metal base material that have been formed in advance so that the joint surfaces are aligned. Apart from the conventional idea of joining to a metal base, the idea of integrally forming metal carbide directly on the metal base material was obtained. Here, a cemented carbide, which is a metal carbide, generally obtains a bulk body by powder metallurgy technology, but because of its high sintering temperature, the cemented carbide is directly formed by powder metallurgy technology against other metal materials. It is difficult. This is because if the sintering temperature of the carbide-based material is close to the melting point of the metal that is the base material, the base material side is easily deformed during the sintering process, resulting in problems in the molding accuracy of the product. Because. In this regard, the present inventors have made it possible to reduce the sintering temperature and the applied pressure of the carbide-based material during pressure sintering by refining the crystal grains of the carbide-based material used for powder metallurgy. The present inventors have found that low stress and high densification rate can be realized, and have reached the present invention. That is, according to the present invention, it is possible to sinter carbide-based materials such as tungsten carbide (WC) in the service temperature range of the metal material that is the base material, and without causing plastic deformation on the base material side. It becomes possible to manufacture a metal carbide-metal integrally molded product with high accuracy.

  In addition, the inventors of the present invention have a structure that cannot be easily realized by the conventional method of joining a part made of a carbide-based material and a metal base material separately prepared in advance by the above-described novel method of the present invention. The present inventors have found that it is possible to easily produce a metal carbide-metal integrated member having the following, and have reached the present invention.

  As described above, according to the present invention, a method of integrally forming a hard-working carbide-based material and a metal material and an integrally formed member thereof are provided.

  Hereinafter, the present invention will be described with embodiments, but the present invention is not limited to the embodiments described below. First, the novel manufacturing method of the metal carbide-metal integral molded member of this invention is demonstrated below.

  The metal carbide-metal integral molded member of the present invention is manufactured by applying so-called powder metallurgy technology. As shown in FIG. 1, a metal mold 12 designed according to a desired shape of a metal carbide layer is disposed on a metal member 10 serving as a base material, and is formed between the metal mold 12 and the metal member 10. After filling the gap 14 with a hard carbide-based material powder 14 and applying a predetermined stress S to the powder 14 for compression molding, the powder 14 is baked while maintaining the pressure at a high temperature by spark plasma sintering or hot pressing. Conclude. Generally, the temperature required to sinter metal carbide typified by tungsten carbide (WC) may reach the melting point of a general-purpose metal material such as iron used for the metal member 12, and at such a high temperature. When sintered, the metal member 10 may be deformed by the action of the stress S. The risk of this deformation becomes excessive when the joint surface between the metal member 10 and the metal carbide has a complicated shape. In this regard, in the present invention, the metal carbide powder used for powder metallurgy is refined to achieve sintering within the service temperature range of the metal member 10.

  The present inventors consider that a superplastic phenomenon occurs by refining the powder particles of the carbide-based material, and this superplastic phenomenon enables sintering at a lower temperature and accompanying integral molding. Here, the superplastic phenomenon is that a huge deformation is obtained by sliding between fine crystal grains, and this superplastic characteristic is improved by controlling the refinement of crystal grains or grain boundary characteristics. Can do. That is, the present invention makes it possible to densify a carbide-based material at a sintering temperature of 1000 to 1400 ° C., which is significantly lower than before, by utilizing the superplastic phenomenon. Highly integrated molding is realized. In the present invention, the average particle size of the powder particles of the carbide material used for powder metallurgy is preferably 100 nm or less, and more preferably about 20 to 40 nm. The carbide-based material used for the metal carbide-metal integral molded member of the present invention is not limited to tungsten carbide (WC), but is a transition metal typified by titanium carbide (TiC) and vanadium carbide (VC). Can be used.

  According to the present invention, a superplastic phenomenon can be used to lower the sintering temperature, pressurize the stress, and increase the densification rate during pressure sintering of the cemented carbide. Therefore, it can be integrally formed without deforming the metal member as the base material. Further, by adding metal particles such as cobalt as a sintering aid, the sintering temperature can be further lowered and the toughness can be improved.

  In addition, according to the present invention, a metal carbide-metal integrated member having a structure that could not be easily realized by the conventional method can be easily manufactured. For example, when manufacturing the metal carbide-metal integrated member having the structure shown in FIG. 1 described above by a conventional method, that is, a method of joining a part made of a cemented carbide and a metal base material separately prepared in advance, Although the manufacturing process is complicated as compared with the method of the present invention, for example, precise control is required so that the joint surfaces of the two are matched, the manufacturing itself is possible. However, for example, when it is intended to form a metal carbide layer on the inner wall N in order to improve the wear resistance of the inner wall N of the cylindrical metal base material 20 as shown in FIG. Its production by law is extremely difficult. This point will be described in detail with reference to FIG. 2B. When a metal carbide layer is formed on the inner wall N of the metal base material 20 by a conventional method, a metal is separated from the cylindrical metal base material 20. After preparing the thin-walled cylindrical member 22 of carbide in advance, the method of subsequently press-fitting the thin-walled cylindrical member 22 into the metal base material 20 or the thermal expansion coefficient of the metal base material 20 and the thin-walled cylindrical member 22 It is possible to envisage a method of filling by using the difference. However, it is obvious that it is difficult to sinter and form a brittle carbide-based material into a thin-walled cylinder, and that it is necessary to further press-fit or heat-fill the process. Thus, the method as described above is not realistic. The same applies to the case of forming a cemented carbide layer on the outer wall of the metal base material 20. In this regard, according to the method of the present invention, it is possible to apply a powder metallurgy technique if it is possible to make a mold even if it is a fairly complicated shape such as the shape shown in FIG. Since the metal carbide-metal integral molded member can be easily manufactured and the sintering temperature at that time is within the service life range of the base metal, high-precision parts can be manufactured in large quantities. From the above-mentioned points, it will be understood that the method for producing a metal carbide-metal integral molded member of the present invention is much more advantageous in terms of productivity and production cost than the conventional method.

  Hereinafter, the metal carbide-metal integral molded member of the present invention will be described more specifically using examples, but the present invention is not limited to the examples described later.

Example 1
The sintering behavior of the WC powder having an average particle diameter of several tens of nm and the commercially available WC powder (average particle diameter of 800 nm) was compared and verified. FIG. 3 shows the relationship between the sintering time, sintering temperature, and displacement (mm) due to shrinkage when performing discharge plasma sintering by applying a pressure of 50 MPa to the WC powder and raising the temperature at 50 ° C./min. “X” indicates the sintering behavior of a commercially available WC powder (800 nm), and “Y” indicates the WC obtained by pulverizing a commercially available WC powder with a planetary ball mill (450 rpm, 15 hours). The sintering behavior of nanocrystal grain powder (average grain size of 100 nm or less) is shown. As shown in FIG. 3, since the displacement due to the shrinkage of the nanocrystalline powder (Y) reaches almost 1200 ° C., it can be seen that densification is completed at around 1200 ° C. . On the other hand, densification of the commercially available powder (X) is finally completed at around 1750 ° C. From this result, it was shown that the sintering temperature in powder metallurgy can be lowered by 500 ° C. or more by refining metal carbide.

  Further, FIG. 4 shows a sintered body obtained by spark plasma sintering (1100 ° C., 50 MPa, 3 minutes) of the above-mentioned WC nanocrystal grain powder (average particle size of 100 nm or less), and FIG. And (b) shows the SEM photograph and TEM photograph of a sintered compact, respectively. As shown in FIG. 4, despite the low sintering temperature of 1100 ° C., the WC sintered body of this example is a densified alloy having a fine grain structure of 100 nm or less. It was done. From the results described above, the effectiveness of the method of manufacturing the cemented carbide-metal integrally formed member of the present invention was proved.

(Example 2)
Commercially available WC powder (average particle size 800 nm) was pulverized on a planetary ball mill (450 rpm, 50 hours) to obtain a WC fine powder composed of nanoparticles having an average particle size of several tens of nm. The obtained WC fine powder was filled in a cylindrical shape on the inner wall of a stainless steel cylindrical mold as a base material. FIG. 5 is a diagram showing a jig configuration used in this example. As shown in FIG. 5, an inner shaft 32 made of graphite having an outer diameter of 16 mm is disposed in a cylindrical mold 30 made of stainless steel (SUS303) having an inner diameter of 20 mm. Filled. The filled WC fine powder 34 was pressed from above and below with a graphite cylinder 36 to apply a stress of 100 MPa to the WC fine powder 34, and then discharge plasma sintering was performed using an SPS apparatus. The sintering temperature was 1100 ° C. and the sintering time was 5 minutes. As a result, the WC layer having a thickness of 2 mm was successfully formed integrally with the inner wall of the cylindrical mold having an inner diameter of 20 mm. FIG. 6 shows a stainless steel cylindrical mold 30 in which a WC layer 40 is integrally formed on the inner wall.

(Example 3)
10 wt% cobalt powder was added as a sintering aid to commercially available WC powder (average particle size 100 nm), and a mixed powder was obtained by ball mill mixing. Using this mixed powder, discharge plasma sintering was performed using the same jig as in Example 2 and using the SPS apparatus under the same sintering conditions. As a result, as in Example 2, the WC layer having a thickness of 2 mm was successfully formed integrally with the inner wall of the cylindrical mold having an inner diameter of 20 mm.

  As described above, according to the present invention, a method of integrally forming a hard-working carbide-based material and a metal material and an integrally formed member thereof are provided. By the method of the present invention, it is expected that various types of wear-resistant members using carbide materials are manufactured with high quality and low cost.

The figure explaining the manufacturing method of this invention. The figure explaining the problem in the conventional method. The figure which compared the sintering behavior of normal WC powder and refined WC powder. The figure which shows the sintered compact of WC obtained by the manufacturing method of this invention. The figure which shows the jig | tool structure used for the present Example. The figure which shows the cylindrical metal mold | die made from stainless steel by which the layer of WC was integrally molded by the inner wall.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Metal member, 12 ... Mold, 14 ... Metal carbide powder, 20 ... Cylindrical metal base material, 22 ... Thin metal cylindrical member of metal carbide, 30 ... Stainless steel cylindrical die, 32 ... Graphite center axis 34 ... WC fine powder, 36 ... Cylindrical cylinder, 40 ... WC layer

Claims (8)

  A method of integrally molding a metal carbide on the surface of the metal base material by sintering a compression-molded body formed by compression-molding a fine powder of a carbide-based material on the surface of the metal base material, the carbide system The method is characterized in that the average particle size of the fine powder of the material is 100 nm or less.   A wear-resistant layer made of metal carbide is formed on the inner wall surface of the metal base material by sintering a cylindrical compression molded body formed by compressing a fine powder of a carbide material on the inner wall surface of the cylindrical metal base material. A method of molding integrally, wherein an average particle size of the fine powder of the carbide material is 100 nm or less.   The method according to claim 1, wherein the carbide-based material is a transition metal carbide.   4. The method according to claim 3, wherein the transition metal carbide is at least one transition metal carbide selected from the group consisting of tungsten carbide (WC), titanium carbide (TiC), and vanadium carbide (VC).   The method of any one of Claims 1-4 whose sintering temperature which sinters the said compression molding body is 1000-1400 degreeC.   A metal member comprising a cylindrical wear-resistant layer made of a metal carbide on an inner wall surface of the metal member.   The metal member according to claim 6, wherein the metal carbide is a transition metal carbide.   8. The method according to claim 7, wherein the transition metal carbide is at least one transition metal carbide selected from the group consisting of tungsten carbide (WC), titanium carbide (TiC), and vanadium carbide (VC).

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