JPH11264003A - Cemented carbide sintered alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a cemented carbide sintered body provided with the part to be locked capable of engaged with a locking member and having required precision without requiring expensive equipment and while the generation of deterioration in the material can evaded by kneading cemented carbide powder and a caking agent to form a premolded body and thereafter executing sintering. SOLUTION: The member 3 to be locked after temporary sintering in which the part 4 to be locked is formed and a main body 1 in which an inserting hole 2 into which the member 3 to be locked is insertable is formed are separately formed, the member 3 to be locked is inserted into the inserting hole 2 without interposing a different material, thereafter normal sintering is executed at a sintering temp. higher than the temp. at the time of the temporary sintering, and they are integrally formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cemented carbide powder based on, for example, tungsten carbide, which is kneaded with a binder to form a preformed body, which is then sintered to allow a locking member to be engaged. TECHNICAL FIELD The present invention relates to a cemented carbide sintered body provided with various locked portions and used for, for example, a die for metal press working.

[0002]

2. Description of the Related Art The above-mentioned conventional cemented carbide sintered body will be described by taking a die for press working as an example. For example, FIG. For example, the material of the locked member 3A made of, for example, steel or the like, which can form the locked portion 4 such as a female screw in which a locking portion such as a male screw included in a locking member such as a bolt is formed so as to be freely locked, is prepared in advance. Have it ready. Separately from this, a pre-formed body of the main body 1 obtained by compacting a powder based on a super-hard material such as tungsten carbide, for example, in a vacuum at 600 to 700 ° C.
After temporary sintering at about the same temperature, after the sintered member 3A is sintered, a fitting hole 2 which can be fitted therein is pierced, and for example, 1370
The main sintering is performed in a vacuum or a non-oxidizing atmosphere at a temperature of ° C. Then, the material of the locked member 3A is fitted into the fitting hole 2 of the main body 1 after sintering, and brazed using a silver brazing or the like to form a pilot hole in the material of the locked member 3A. Then, the locked portion 4 is subjected to thread cutting (in some cases, a tubular material having a prepared hole is used in advance). Here, a steel material is used as a material having good workability of the locked portion 4,
In order to improve the brazing strength, for example, as shown in FIG. 3, a locked member 3A made of a high melting point metal material such as molybdenum is joined to the main body 1 during the main sintering of the main body 1. Is done. That is, the main body 1 after the preliminary sintering is perforated with the fitting hole 2 and the locked member 3A made of molybdenum or the like is fitted into the fitting hole 2 and the main body 1 is sintered to form the locked member. It binds 3A. The cemented carbide sintered body manufactured in this manner has a configuration in which the locked portion 4 is formed on the integrally formed main body. Conventionally, the reason for manufacturing a cemented carbide sintered body by such a manufacturing method is as follows.
This is because these cemented carbide sintered bodies are made of a material used for a metal machining tool or the like, and it is extremely difficult to machine the locked portion by a normal machining method.

[0003]

By the way, in the configuration based on the above-mentioned conventional manufacturing method, the locked member 3A
Although integrated into the main body 1, the locked member 3A attached by brazing is, for example, as shown in the structure photograph shown in FIG. 6, through a brazing material such as silver brazing. Since it is joined to the main body 1, there is a disadvantage that the joining strength is inferior. In addition, the brazing requires a separate step after the sintering of the main body 1, generally using a heating means different from that for sintering the main body, such as gas heating or high-frequency heating. On the other hand, when the locked member 3A formed of molybdenum or the like is diffusion-bonded to the main body 1, mutual diffusion of components occurs between the locked member 3A and the main body 1. In addition, there is a problem in that a diffusion layer is formed at the boundary portion, and abnormal tissue is generated to cause a deterioration in strength between the main body 1 and the locked portion 4. Further, since a high-melting point metal material (such as molybdenum) is inserted into the cemented carbide material and sintered, the metal material component is diffused during the main sintering to form an altered layer, and the deformation and strength of the main body 1 are increased. Deterioration may be caused. For example, FIG. 4 shows a microstructure of a boundary portion where a locked member 3A made of molybdenum is inserted into a main body 1 made of cemented carbide obtained by adding cobalt to tungsten carbide and sintered, and a brittle boundary layer is formed. Have been.
Murakami reagent was used as a corrosive liquid for the appearance of the tissue. In addition, high melting point metals (eg, molybdenum) that can withstand sintering temperatures
There is also a problem that the workability is poor, and it is difficult to machine a screw hole such as a thread for forming the locked portion 4. In order to solve this workability problem, the material of the locked portion 4 may be a steel material, but in this case, a brazing material is required between them. FIG. 6 shows a state where the boundary portions are joined using silver brazing (JIS BAg) as the brazing material.
Again, the metallographic structure of the steel material has not been revealed because Murakami's reagent is used to reveal the structure. As can be seen from these two structural photographs, in each case, an intermediate layer is formed between the main body 1 and the locked part 4, the material is not homogeneous, and there is a weak point at the boundary. I do. In order to cope with such a problem, the main body 1 is inserted without fitting the locked member.
Is pre-sintered (dewaxed) at a temperature of, for example, about 600 to 700 ° C., and the pre-sintered body is perforated, and the locked portion 4 is preliminarily formed by machining (for example, tapping). It is also conceivable that the main sintering is performed thereafter, but there is no need to embed the locked member, there is no risk of deterioration of the base material,
Although there is an advantage that deformation after sintering is small because no dissimilar material is inserted, the processing accuracy is poor, for example, screw threads are easily broken because the processing is such that powder is scraped off during processing. The problem remains. To cope with this, it is not impossible to form the locked portion 4 by subjecting the main body 1 after the main sintering to electric discharge machining.
It is not realistic because the cost is too high, the time required for machining is long, and the electric discharge machine is expensive.

Accordingly, an object of the present invention is to provide a cemented carbide sintered body in which a locked portion having the required accuracy is formed without requiring expensive equipment and avoiding deterioration of the material. The point is to provide.

[0005]

Means for Solving the Problems [Characteristic structure of the present invention] The characteristic structure of the cemented carbide sintered body of the present invention according to claim 1 is as follows.
The locked member after provisional sintering, in which the locked portion is formed, and a main body having an insertion hole into which the locked member can be inserted after temporary sintering are formed separately, The stop member is inserted into the insertion hole without any intervening dissimilar material, and then is main-sintered at a sintering temperature higher than the temporary sintering temperature to be integrally formed.

[0006] The characteristic configuration of the cemented carbide sintered body according to the present invention according to claim 2 is that, in the characteristic configuration of the invention according to the above-described claim 1, before the locked member is fitted into the fitting hole.
The pre-sintering is performed at a pre-sintering temperature higher than the pre-sintering temperature and lower than the sintering temperature, and then the pre-sintering is inserted into the fitting hole. The point is that the stop member is formed so as to be fittable.

According to a third aspect of the present invention, there is provided a cemented carbide sintered body according to the first or second aspect of the present invention, wherein the member to be locked is a locking member. The present invention is characterized in that a locked portion composed of a female screw is formed using a middle mold capable of forming the shape of a screw portion of a bolt.

[Function and Effect of Characteristic Configuration] The above-mentioned claim 1
According to the characteristic configuration of the cemented carbide sintered body according to the invention described in (1), the accuracy of forming the main body is good, and strength deterioration and distortion do not occur near the locked portion. That is, since the locked member is formed separately from the main body, when forming the locked portion on the locked member, no matter what means of forming the locked portion is selected. It does not affect the main body and there is no possibility of causing deformation of the main body. In addition, since the presintered body of both the main body and the locked member is sintered integrally without intervening dissimilar materials, an abnormal structure is generated at the boundary between the two to deteriorate the material. In addition, there is no deformation due to the occurrence of internal strain based on the difference in thermal expansion coefficient.
Further, by forming the locked member separately from the main body, it is possible to make the component mixing ratio and the particle size configuration of the powder different between the two, and to form the locked portion. The means for this purpose can be arbitrarily selected. In particular, it is also possible to use injection molding, which can be mass-produced at low cost, to form a common part for forming the preformed body of the locked member. For example,
In order to form the pre-molded body of the main body by injection molding, a large-sized one is required, and a plurality of locked parts must be formed at the same time. You will need it. On the other hand, when the preformed body of the locked member is formed by an injection molding method,
Since it is possible to use a small one and form a single locked portion, the preformed body can be easily formed.
Further, since the locked member is formed separately from the main body, for example, if the particle size of the cemented carbide material powder that forms the locked member and the main body according to respective required characteristics is different. It is also possible to make it. Further, by making the particle diameters of the two different as described above, it is also possible to adjust the amount of tightening of the locked member at the time of sintering by utilizing the fact that the shrinkage rate accompanying sintering differs depending on the particle diameter. Thus, the material properties of the boundary region can be suitably maintained.

According to the characteristic configuration of the cemented carbide sintered body according to the second aspect of the invention, the continuity of the material in the boundary region between the main body and the locked member is enhanced. In other words, the locked member is contracted more than the temporarily sintered body by the preliminary sintering,
If this is inserted into the insertion hole and the main body is sintered together with the main body at a temperature higher than the pre-sintering temperature, the contraction of the main body is smaller than the contraction of the locked member after the pre-sintering during the main sintering. big,
At the time of the main sintering, the locked member fitted into the fitting hole is tightened from the peripheral wall of the fitting hole. As a result, sintering is performed while applying an inter-surface compressive force, and the sintering structure of the boundary region is continuous. Sex is enhanced. For example, when the contraction rate of the preformed body by the main sintering is 20%, if the locked member is contracted by about 5% by the presintering, the contraction rate of the main body is 20%. On the other hand, the contraction rate of the locked member after the preliminary sintering is about 15%, and a compressive force corresponding to this difference is exerted on the locked member from the peripheral wall portion of the fitting hole. . By this compressive force, the outer peripheral surface of the locked member and the inner wall surface of the fitting hole are securely joined and integrated, and the continuity of the crystal structure in the boundary region is improved.

According to the characteristic structure of the cemented carbide sintered body according to the third aspect of the present invention, the cemented carbide sintered body is provided with a high-precision internal thread as a locked portion.

In the above description, the term “sintered cemented carbide” refers not only to a carbide-metal-based sintered body obtained by mixing metallic cobalt with tungsten carbide, but also to a carbide according to a common name. The general term is used as a cemented carbide sintered body including a sintered body of only a compound which is generally regarded as a non-metal such as nitride, boride and the like.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of a cemented carbide sintered body according to the present invention will be described together with a method of manufacturing the same with reference to the drawings. FIG. 1 is an explanatory view showing a process of manufacturing a cemented carbide sintered body according to the present invention.

The cemented carbide sintered body described below is used for a metal pressing die, and has a locked portion 4 formed by a female screw for mounting on a press machine. 1 shows only the vicinity of the locked portion 4 of the die 10. The die 10 pierces the preformed body of the main body before sintering the locked member 3 formed by presintering the preformed body 6 in which the locked portion 4 is formed in advance. It is fitted into the fitted insertion hole 2 and both are sintered together, and thereafter are processed into a predetermined tool shape as required.

Raw materials for manufacturing the die 10 are prepared by adding a binder to cemented carbide powder in advance and kneading them. For example, as a cemented carbide powder, a particle size of 1.20 to 6.99 μm
m of tungsten carbide powder of 90 parts by weight.
A mixed metal powder obtained by mixing 10 parts by weight of a cobalt powder of 0 to 2.0 μm is wet-mixed in alcohol.
As a binder, a mixture of an organic binder (eg, polypropylene, stearic acid) and a wax (eg, paraffin wax, carnauba wax, etc.) is used. Then, 65 parts by weight of the binder is added to 1000 parts by weight of the mixed metal powder, and kneaded at, for example, 155 ° C. for 2 hours to form a small flake-shaped raw material compound.

On the other hand, a mold for molding the locked member 3 having the female screw as the locked portion 4 is separately prepared. The mold 7 is for injection molding, is configured to be assembled by combining a cylindrical outer mold 8 and a male thread-shaped middle mold 9, and is attached to an injection molding machine. Note that the illustrated mold is for showing a basic configuration, and is shown in a simplified manner.

The mold 7 is attached to an injection molding machine, and the raw material compound is pressed into the mold 7 at a temperature of, for example, 145 ° C. to form a preform 6. The preform 6 forming the locked member 3 is taken out of the mold 7.
Is removed from the injection molding machine, and the middle mold 9 is turned to remove it from the outer mold 8 and the preform 6, and then the preform 6 is taken out of the outer mold 8. The preform 6 is
After being removed from the mold 7, the temperature is gradually increased to, for example, 600 ° C. in a non-oxidizing reduced-pressure atmosphere to remove wax.
That is, the locked member 3 is formed by performing temporary sintering accompanied by heat treatment for removing most of the organic components in the preform 6. Thereafter, the locked member 3 is subsequently heated to, for example, 1150 ° C. under reduced pressure in a non-oxidizing atmosphere, and heated for 0.5 hour to perform preliminary sintering. At this stage, the locked member 3 has been contracted by about 5% from the state of the preformed body 6.

On the other hand, in order to form the main body 1, the mixed metal powder is wet-mixed in alcohol, and the powder to which paraffin wax has been added is compacted by a press molding machine.
A dewaxing process is performed in the same manner as in the preform 6 to form a preform of the main body 1. Taking the shrinkage allowance during sintering into consideration at a predetermined position of the preformed body of the main body 1, the size of the locked member 3 after sintering is reduced by an amount corresponding to the interference (for example, tungsten carbide 90). %, In the case of a cemented carbide of 10% cobalt, 0.1 to 0.2 mm). In the case of a hard alloy, since the shrinkage is about 21%, the inner diameter is equal to the locked member 3.
(The inner diameter is 100/79 of the size obtained by subtracting 0.2 mm from the outer diameter of the above). The locked member 3 is fitted into each of the fitting holes 2 and charged into a heating furnace maintained in a non-oxidizing atmosphere.
For example, the die 10 is manufactured by holding at a temperature of 1370 ° C. for 60 minutes and performing sintering.

The most distinctive feature of the sintered body manufactured in the above process is that there is no metallographic boundary layer around the locked portion 4. In particular, when the main body 1 and the locked member 3 are both made of the same mixed metal powder, the two are completely continuous, and the boundary is not clear. If there is a difference in particle size between the two, only regions having different particle sizes are formed (see FIG. 2).

Therefore, the cemented carbide sintered body thus formed is characterized in that the locked portion has the required accuracy, there is no unevenness in strength, and the deformation with time can be prevented.

[Other Embodiments] Regardless of the description of the above embodiment, the following aspects are included in the present invention. <1> Temporary sintering may be performed during the dewaxing process. Therefore, after the main body 1 and the locked member 3 are both pre-sintered, the fitting hole 2 is formed in the main body 1 and the fitting hole 2 is formed.
The locked member 3 after the above-mentioned temporary sintering may be fitted into the second member, and both may be sintered together. Further, the pre-sintered locked member 3 may be fitted into the fitting hole 2 after the main body 1 is pre-sintered, and both may be sintered together. Since the sintering process is a liquid phase reaction and does not depend on the sintering time, the bonding strength between the two members may be heated for the time required for soaking.

<2> In the above embodiment, 115
Although the example of pre-sintering at 0 ° C. has been described, the pre-sintering temperature is to be determined according to the composition and the like of the mixed metal powder to be sintered, and is not fixed. Further, the holding time should be adjusted according to the required degree of sintering.

<3> The sintering temperature, 1370 ° C., is merely an example, and should be selected according to the composition and particle size composition of the mixed metal powder. In the case of tungsten carbide-cobalt mixed metal powder, Although it depends on the particle size of tungsten and the blending amount of cobalt, a range of about 1320 to 1420 ° C. is preferably used.

<4> The fitting hole 2 does not penetrate the main body 1 and may be a hole with a bottom. Further, the locked portion 4 composed of a female screw
Alternatively, it may be formed with a bottom having a screw stop that does not penetrate the locked member 3. That is, the shapes of the locked member 3 and the locked portion 4 can be arbitrarily selected.

<5> The preliminary sintering temperature or the degreasing temperature may be about 600 ° C. in order to completely remove the wax inside, but if the molding is to be performed thereafter, it may be 600 ° C.
The molded body is pre-sintered within a temperature range of -700 ° C. By this temporary sintering, the temporary sintered body is given a strength of about black ink. That is, machining becomes possible. <6> The cemented carbide powder is composed of tungsten carbide powder and cobalt powder in a weight ratio of 15 to tungsten carbide powder.
% Or less is preferable, but at least 5%
It is more preferred that they are blended. The other metal powder to be added to the tungsten carbide is tungsten carbide / titanium (commonly known as double carbide: for example, WC 70% -T
iC 30%), titanium carbide, molybdenum carbide, chromium carbide, vanadium carbide, tantalum carbide and the like. Further, the cemented carbide powder may be made of a cermet containing titanium carbide as a main component (for example, TiC-Ni) as a base material.

[0025]

EXAMPLES Examples of cemented carbide sintered bodies according to the present invention will be described below. As a cemented carbide powder, a mixed metal powder obtained by mixing a tungsten carbide powder and a cobalt powder as shown in the following table was sintered to produce a cemented carbide sintered body sample.

[0026]

[Table 1]

The mixed metal powder of each of the above formulations was suspended in alcohol and mixed with stirring. As the binder, paraffin wax, carnauba wax, polypropylene,
Using a wax binder composed of a mixture of stearic acid, 65 parts by weight per 1000 parts by weight of the mixed metal powder of each of the above-mentioned compositions was added to the mixed metal powder of each of the above-mentioned compositions and kneaded. This kneading was performed for 2 hours while heating to 155 ° C., and three types of small flake-shaped cemented carbide raw material compounds were produced.

The sample of the member to be locked is attached to an injection molding machine with a mold having a structure as shown in FIG. 1, and the above-mentioned compounds are injected and molded under a temperature condition of 145 ° C. The body is gradually heated to 600 ° C. in a heating furnace under a reduced-pressure hydrogen atmosphere as a non-oxidizing atmosphere,
Dewaxing treatment is applied, then the furnace temperature is raised,
Preliminary sintering was performed while maintaining the temperature at 1150 ° C. for 0.5 hour, and the furnace was cooled. The pre-sintered cylindrical locked member with screw holes was shrunk by about 5% from the dimension after injection molding.

The sample of the main body is molded by pressing the raw material compound by a press molding machine, subjected to a dewaxing treatment in the same manner as the above-mentioned locked member, and is then locked to the preformed body after the dewaxing treatment. 0.2m from outer diameter after complete sintering of member
A fitting hole having an inner diameter (for example, in the case of document No. 2, an inner diameter of 1000/814 of a size obtained by subtracting 0.2 mm from the outer diameter) in consideration of a shrinkage allowance was cut and drilled. Thereafter, the locked member was fitted into the fitting hole, the two were united, and heated in a heating furnace maintained at 1370 ° C. for 60 minutes to perform main sintering.

The hardness as a mechanical property and the shrinkage after the main sintering of each sample after the main sintering under the above conditions were examined. The results shown in the following table were obtained.

[Table 2]

After the main sintering, the peripheral section of the insertion hole of the sintered body was observed with a microscope. As can be seen from the microstructure of Sample No. 1 shown in FIG. 2, a boundary layer was formed. However, only the boundary due to the difference in the particle diameter on both sides of the boundary is observed, but there is no difference in microscopic structure. Sample Nos. 2 and 3 also showed no significant difference in microscopic structure. In particular, for Sample No. 2, there was no difference in the particle size between the main body and the locked portion. The border is much more blurred than it is.

[Brief description of the drawings]

FIG. 1 is a process explanatory view showing an example of a cemented carbide sintered body of the present invention together with an example of a manufacturing process.

FIG. 2 is a photograph of a cross-sectional metal structure showing a boundary portion of an example of a cemented carbide sintered body in an example.

FIG. 3 is a process explanatory view of an example of forming a locked portion of a conventional die made of cemented carbide.

FIG. 4 is a photograph of a sectional structure of a cemented carbide sintered body manufactured by sintering according to a conventional method.

FIG. 5 is a process explanatory diagram showing an example of a process of forming a locked portion of a conventional cemented carbide sintered body.

FIG. 6 is a photograph of a cross-sectional structure of a cemented carbide sintered body manufactured by a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main body 2 Fitting hole 3 Locked member 4 Locked part 5 Fitting part 6 Preformed body 9 Medium size

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[Procedure amendment]

[Submission date] March 18, 1998

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[Procedure amendment 2]

[Document name to be amended] Drawing

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[Correction method] Change

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[Document name to be amended] Drawing

[Correction target item name] Fig. 6

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Claims (3)

[Claims] 1. A cemented carbide alloy having a locked portion to which a locking member can be engaged by kneading a cemented carbide powder with a binder to form a preform and then sintering the preformed body. A body, in which a locked member after provisional sintering in which the locked portion is formed, and a main body having an insertion hole into which the locked member can be fitted after temporary sintering are formed separately. In addition, after the locked member is fitted into the fitting hole without interposing a dissimilar material, the cemented carbide is formed by sintering integrally at a sintering temperature higher than the temperature of the temporary sintering. Sintered body. 2. The locked member is pre-sintered at a pre-sintering temperature higher than the pre-sintering temperature and lower than the sintering temperature prior to being inserted into the insertion hole. The cemented carbide sintered body according to claim 1, wherein the sintered hole is inserted later into the insertion hole, and the insertion hole is formed so that the locked member after the preliminary sintering can be inserted. 3. The locked member, wherein a locked portion made of a female screw is formed using a middle mold capable of forming a threaded shape of a bolt as the locking member. 3. The method for producing a cemented carbide sintered body according to item 2.