KR20130076451A

KR20130076451A - Method for producing high strength and high toughness cemented carbide material

Info

Publication number: KR20130076451A
Application number: KR1020110145044A
Authority: KR
Inventors: 김응주; 윤덕재; 박훈재; 이근안; 임성주
Original assignee: 한국생산기술연구원
Priority date: 2011-12-28
Filing date: 2011-12-28
Publication date: 2013-07-08

Abstract

Disclosed is a method for producing a high strength, high toughness cemented carbide material. The method of manufacturing a cemented carbide material according to the present invention comprises the steps of mixing tungsten carbide and cobalt to form granulated tungsten carbide-cobalt, mixing the granulated tungsten carbide-cobalt and cobalt and the mixed tungsten carbide- Sintering cobalt and cobalt.

Description

Method for Producing High Strength High Toughness Cemented Carbide Material

The present invention relates to a method for producing a high strength high toughness cemented carbide material, and more particularly, to a method for manufacturing a high strength high toughness cemented carbide material through microstructure control of tungsten carbide-cobalt.

Generally, cemented carbide is widely used as a mold material when forming metals such as cold forging. Here, cemented carbide is a kind of composite material having a structure in which tungsten carbide particles are randomly dispersed using cobalt as a matrix as a high hardness material.

Conventionally, tungsten carbide-cobalt (WC-Co) cemented carbide is added to at least one of Ni, Fe, Ni-Fe, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo to provide heat and wear resistance It is known as an improved cemented carbide.

The method for producing a high density cemented carbide disclosed in Korean Patent Laid-Open Publication No. 10-2009-0104414, which is a prior art document, is carried out by vacuum sintering a tungsten carbide powder (WC) or a very small amount of cobalt (Co) powder mixed with tungsten carbide and a metal binder. Carbide alloy manufacturing method to increase the relative density and hardness by hydrostatic molding.

However, the cemented carbide of the prior art has improved hardness and wear resistance due to the general properties of the material, but there is a limit of weak toughness. That is, the conventional cemented carbide has a high strength (Proof Stress) to the compressive load due to its structural characteristics, but has a weak problem in the tensile load and low toughness and impact resistance.

The method of manufacturing a cemented carbide sintered body for impact resistance and high compressive strength disclosed in Korean Patent No. 0178578, which is another prior art, has a higher cobalt concentration as the outer side of the average cobalt (Co) concentration of the cemented carbide sintered body, and the cobalt concentration toward the center thereof. It is described that by lowering it, it can contain both impact resistance and high compression strength. However, this prior document has a limit that can not satisfy the high strength and toughness of cemented carbide itself by controlling the concentration of cobalt by dividing the material into the outer and inner parts.

The present invention is to solve the above-described problems, to provide a method for producing a high strength high toughness cemented carbide material through the microstructure control of tungsten carbide-cobalt.

In order to achieve the above object, the present invention comprises the steps of mixing tungsten carbide and cobalt to form granulated tungsten carbide-cobalt, mixing the granulated tungsten carbide-cobalt and cobalt and the mixed tungsten It provides a method for producing a high strength, high toughness cemented carbide comprising the step of sintering carbide-cobalt and cobalt.

In addition, forming the granulated tungsten carbide-cobalt may include mixing the tungsten carbide and cobalt by milling in a wet atmosphere, and drying the mixed tungsten carbide and cobalt.

In addition, the forming of the granulated tungsten carbide cobalt may further comprise presintering the granulated tungsten carbide cobalt after the drying step.

In addition, the presintering temperature may be 1200 ℃ to 1370 ℃.

The sintering of the mixed tungsten carbide cobalt and cobalt may be performed by pressure sintering the mixed tungsten carbide cobalt and cobalt.

The sintering of the mixed tungsten carbide cobalt and cobalt may include pressurizing the mixed tungsten carbide cobalt and cobalt, presintering the pressurized tungsten carbide cobalt and cobalt, and the presintered tungsten. Hot isotropically pressing the carbide-cobalt and cobalt.

Method for producing a high strength high toughness cemented carbide material of the present invention for solving the above problems has the following effects.

First, tungsten carbide and cobalt are mixed to form granulated tungsten carbide-cobalt, and the granulated tungsten carbide-cobalt and cobalt are mixed and sintered to form a cluster structure, thereby improving the toughness of the cemented carbide material. Can be.

Second, in controlling the microstructure of tungsten carbide-cobalt, by mixing tungsten carbide and cobalt to granulate tungsten carbide-cobalt, it is possible to reduce the cost of manufacturing high-strength high toughness cemented carbide material by simplifying the microstructure control process. have.

1 is a microstructure photograph of a cemented carbide material according to an embodiment of the present invention using an optical microscope;
FIG. 2 is a microstructure diagram of FIG.
3 is a view schematically showing the microstructure of the cemented carbide material of FIG.
Figure 4 is a flow chart showing a method for producing granulated tungsten carbide cobalt in accordance with an embodiment of the present invention;
FIG. 5 shows granulated tungsten carbide-cobalt prepared according to FIG. 2; FIG.
6 is a flow chart showing a method of manufacturing a cemented carbide material according to an embodiment of the present invention; And
7 is a table of experimental results comparing the strength and toughness of a conventional cemented carbide material and a cemented carbide material according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In describing the present embodiment, the same designations and the same reference numerals are used for the same components, and further description thereof will be omitted.

1 is a microstructure diagram of a cemented carbide material according to an embodiment of the present invention using an optical microscope, FIG. 2 is a microstructure diagram of FIG. 1, and FIG. 3 is a microstructure of the cemented carbide material of FIG. It is a figure which shows a structure schematically.

With reference to Figures 1 to 3 will be described the microstructure of the cemented carbide material according to an embodiment of the present invention.

In the cemented carbide material according to the present invention, tungsten carbide-cobalt (WC-Co) forms a cluster structure using cobalt as a matrix. As shown in FIG. 2, a tungsten carbide cluster (WC-Co Cluster) structure refers to an aggregate in which tungsten carbide-cobalt (WC-Co) is collected.

Conventionally, in order to increase the strength of the cemented carbide material, the particles of tungsten carbide (WC), which are cemented carbide particles, are made small and the weight of cobalt (Co) is reduced. In this case, the strength increases but the toughness decreases. On the other hand, in order to increase the toughness of the cemented carbide, there was a problem that the strength is lowered when the tungsten carbide particles are increased.

The cemented carbide material having the cluster structure according to the present invention has the same composition as the conventional tungsten carbide-cobalt (WC-Co), but by first granulating the tungsten carbide-cobalt to reduce the weight of cobalt between the small particles of tungsten carbide strength Allow to increase

Next, granulated tungsten carbide-cobalt forms a cluster structure using cobalt as a matrix, thereby improving toughness. That is, when a crack occurs in the cemented carbide material, the cluster structure increases the mean free path between the clusters, thereby preventing propagation of the cracks, and consequently, the toughness of the cemented carbide material may be improved.

A method of granulating tungsten carbide-cobalt in a method of manufacturing a cemented carbide material according to an embodiment of the present invention will be described with reference to FIG. 4.

First, in the step of preparing tungsten carbide and cobalt generally has a size of 200 ~ 700 nm of tungsten carbide, cobalt is prepared to have a powder having a size of 1 ㎛ or less. However, tungsten carbide is not limited to nano size, but may have a size up to 5 μm.

In addition, cobalt has a weight of 5 to 15% based on tungsten carbide.

Next, in the step of mixing tungsten carbide and cobalt consists of milling and mixing.

Milling consists of a commonly used Attrition Mill. The attrition mill may mix the tungsten carbide and cobalt and at the same time increase the surface energy of the tungsten carbide so that cobalt may be easily coupled to the periphery of the tungsten carbide.

On the other hand, milling may be made by ball milling. In ball milling, the ball is made of tungsten carbide or steel, and the size of the ball is several tens of mm.

Since the ball may be crushed in the mixing process, the ball is preferably made of tungsten carbide (WC).

The mixing method is dry mixing and wet mixing. Dry mixing does not require a drying step to be described later, but the process is simple, but powdered tungsten carbide and cobalt have a small size, and thus the powder is mixed due to the van der Waals force acting between the powders. Disturbs. However, in the wet mixing method, the fluid is present between the powders so that the van der Waals forces described above are not applied, and the powder is mixed more efficiently.

Here, water, ethanol or nucleic acid is added as a mixing aid for wet mixing. Then, paraffin wax is added as a molding aid in the mixing process.

Finally, drying the mixed powder in a wet atmosphere evaporates the mixing aid added for wet mixing. Since the mixed powder has a risk of ignition, a general method of drying is to use a spray dryer.

The spray dryer is a method of spraying a liquid or paste-like material into the hot air by a droplet sprayer to obtain a drying of about 30 to 50 μm. Drying time may vary depending on the amount of powder, mixing aid or molding aid.

In addition, the method of using a water bath can also be chosen as a method of drying.

In addition, the step of pre-sintering to maintain the formation of granulated tungsten carbide-cobalt may optionally further comprise.

The presintering is performed in a vacuum atmosphere or hydrogen atmosphere.

The presintering temperature is preferably in the range of 1200 ° C to 1380 ° C. In order to maintain the granulated state of tungsten carbide and cobalt, the pre-sintering temperature is more preferably in the range of 1250 ° C to 1340 ° C.

Accordingly, it is possible to obtain granulated tungsten carbide-cobalt as shown in FIG.

Referring to Figure 6 describes a method of manufacturing a cemented carbide material according to an embodiment of the present invention.

First, granulated tungsten carbide-cobalt and cobalt are prepared. Here, cobalt is similar in size to cobalt in the step of granulating the tungsten carbide-cobalt.

Next, the cobalt may have a weight of 10 to 25 based on the tungsten carbide-cobalt in the step of mixing the granulated tungsten carbide-cobalt and cobalt.

The step of mixing the granulated tungsten carbide-cobalt and cobalt is different from the step of mixing the tungsten carbide-cobalt and cobalt, and is mixed through a stirrer without mixing by milling.

In addition, the agitator (Mixer) may be a commonly used turbo mixer (Turbular Mixer).

In addition, the mixing step may be made of dry mixing and wet mixing, detailed description has already been described above, it will be omitted.

Next, the manufacturing method for obtaining a high strength high toughness cemented carbide material according to an embodiment of the present invention by sintering the mixed tungsten carbide-cobalt and cobalt is a step of pressure sintering the mixed tungsten carbide-cobalt and cobalt It may be made of.

The pressure sintering step generally uses a graphite mold made of a graphite material that can withstand a higher temperature and pressure than a metal mold.

Accordingly, the cemented carbide material may be obtained by hot sintering the mixed tungsten carbide-cobalt and cobalt in the graphite mold.

On the other hand, unlike the embodiment of the present invention consisting of the pressure sintering step, the step of sintering the mixed tungsten carbide-cobalt and cobalt is the step of pressing the mixed tungsten carbide-cobalt and cobalt, the pressurized tungsten Pre-sintering carbide-cobalt and cobalt; and hot isotropically pressing the pre-sintered tungsten carbide-cobalt and cobalt.

Pressing the mixed tungsten carbide-cobalt and cobalt is performed by cold forming. The mixed tungsten carbide-cobalt and cobalt are pressurized at room temperature to determine the appearance of the cemented carbide material according to the method of using the cemented carbide material.

The step of pre-sintering the pressurized tungsten carbide-cobalt and cobalt is as described above, a detailed description thereof will be omitted.

Hot isostatic pressing in the step of hot isostatic pressing of the pre-sintered tungsten carbide-cobalt and cobalt is carried out by inserting a cemented carbide material into a mold and heating and injecting an inert gas such as vacuum or argon at the same time. It is a method of promoting densification by applying a uniform pressure to the. Through such densification, it is possible to remove the pores of the cemented carbide material.

In the hot isotropic pressing step, the hot isotropic pressing temperature is in the range of 1200 ° C. to 1300 ° C., and the pressure is 200 MPa or less. In addition, the pressure is preferably 100 MPa or less.

Accordingly, it is possible to obtain a cemented carbide material according to an embodiment of the present invention. Since the tungsten carbide-cobalt has a cluster structure in the cobalt matrix, it has high strength as well as high toughness.

In addition, the method of granulation of tungsten carbide-cobalt is mixed before sintering tungsten carbide and cobalt, so that the microstructure control process of the cemented carbide material is simple, thereby obtaining a high strength, high toughness cemented carbide material having low manufacturing cost.

7 is a table of experimental results comparing the strength and toughness of a conventional cemented carbide material and a cemented carbide material according to an embodiment of the present invention.

Coarse WC having a size of 6 μm of tungsten carbide (WC), UF WC having a size of 0.5 μm of tungsten carbide (WC), and clustered UF WC having a cluster structure of 0.5 μm of tungsten carbide (WC) were compared.

The weight of cobalt in the Coarse WC, UF WC and Clustered UF WC is 20%. In addition, the Coarse WC, UF WC, and Clustered UF WC were tested by cutting the following specimen to make a test specimen of 200 g and the strength (Hardness) and Fracture Toughness test to be described later.

First, the Coarse WC, UF WC and Clustered UF WC were subjected to a strength test under a load of 1 kg.

Next, the values representing fracture toughness are converted to K _1C .

As described above, the cemented carbide material Coarse WC and UF WC according to the prior art can be seen that the strength and toughness is a trade-off relationship according to the size of tungsten carbide.

In the clustered UF WC according to an embodiment of the present invention, the strength is somewhat lower than the UF WC but higher than the Coarse WC, and the toughness is slightly lower than the Coarse WC but higher than the UF WC.

Accordingly, it can be seen that the cemented carbide material according to the embodiment of the present invention is superior in strength to Coarse WC and excellent in toughness than UF WC.

It will be apparent to those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or scope of the invention as defined in the appended claims. It is obvious to them. Therefore, the above-described embodiments are to be considered as illustrative rather than restrictive, and the present invention is not limited to the above description, but may be modified within the scope of the appended claims and equivalents thereof.

Claims

Mixing tungsten carbide and cobalt to form granulated tungsten carbide-cobalt;
Mixing the granulated tungsten carbide-cobalt and cobalt; And
Sintering the mixed tungsten carbide-cobalt and cobalt;
Method for producing a high strength high toughness cemented carbide material comprising a.

The method of claim 1,
Forming the granulated tungsten carbide cobalt,
Mixing the tungsten carbide and cobalt by milling in a wet atmosphere; And
Drying the mixed tungsten carbide and cobalt;
Method of producing a high strength high toughness cemented carbide material comprising a.

The method of claim 2,
Forming the granulated tungsten carbide cobalt is
After the drying step further comprises the step of pre-sintering the granulated tungsten carbide-cobalt.

The method of claim 3,
The presintering temperature is a method of producing a high strength high toughness cemented carbide material, characterized in that 1200 ℃ to 1370 ℃.

The method of claim 1,
Sintering the mixed tungsten carbide cobalt and cobalt is
Method of producing a high strength high toughness cemented carbide material comprising the step of sintering the mixed tungsten carbide-cobalt and cobalt.

The method of claim 1,
Sintering the mixed tungsten carbide cobalt and cobalt is
Pressurizing the mixed tungsten carbide-cobalt and cobalt;
Presintering the pressurized tungsten carbide-cobalt and cobalt; And
And hot isotropically pressing the pre-sintered tungsten carbide-cobalt and cobalt.