KR101789230B1 - POWDER INJECTION MOLDING METHOD FOR FEBRICATING WC-Co STRUCTURE AND SYSTEM THEREOF - Google Patents

Abstract

A powder injection molding method is disclosed. The method comprises: an injection molding step of mixing a tungsten carbide (WC) powder and a cobalt (Co) powder at predetermined ratios, injecting additional carbon and injecting the powder together with the binder, heating the injection product to remove the binder And a sintering step of sintering the degreased product to produce a cemented carbide structure made of WC-Co. Here, the amount of additional carbon may be an amount set to reduce the? Phase on the surface structure of the cemented carbide structure to compensate for the amount of carbon loss in the degreasing and sintering steps.

Description

TECHNICAL FIELD [0001] The present invention relates to a powder injection molding method for manufacturing a cemented carbide structure,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder injection molding method and system for manufacturing a cemented carbide structure, and more particularly, to a powder injection molding method and system for manufacturing a cemented carbide structure by injection molding WC-Co powder.

Due to the development of technology, devices having more various structures and functions are being developed. Accordingly, efforts have been made to develop a technique for manufacturing a more complex shaped structure with a better material than in the past.

One of them is Powder Injection Molding (PIM) technology. Powder injection molding technology is a combination of Powder Metallurgy (PM) technology and injection molding technology. In the powder injection molding process, injection molding is performed by mixing a binder which is a main material of fine powder and flow, that is, a binder, followed by removing only the binder from the injection body and finally sintering only the powder. The structures thus fabricated can be used as parts of various machines and devices.

Powder injection molding can be roughly divided into Metal Injection Molding (MIM) and Ceramic Injection Molding (CIM). In addition, it shows great potential for the production of composite materials and intermetallic compounds, and the research and commercialization development among the new powder molding technology is being performed most intensively all over the world.

Particularly, in recent years, attempts have been made to produce a cemented carbide used as a cutting tool with a hard workable hard material by using a powder injection molding method which does not require a post-processing, but this method has various problems .

That is, the surface free energy of the particles due to the fine particles of the WC-Co-based cemented carbide is high, resulting in deterioration of fluidity and long-term degreasing. When degreasing and sintering are carried out, free carbon or (Co3W3C) phase is formed in the sintered body due to a change in the carbon content, and mechanical properties may be deteriorated. Also, there is a problem that the structure may be warped during the degreasing process

there was.

It is an object of the present invention to provide a powder injection molding method and system that can maintain mechanical properties by adding additional carbon.

According to an embodiment of the present invention, a powder injection molding method includes: an injection molding step of mixing a tungsten carbide (WC) powder and a cobalt (Co) powder at predetermined ratios, injecting additional carbon to be injected together with the binder, A sintering step of heating the resultant to remove the binder from the injection product, and a sintering step of sintering the degreased product to produce a cemented carbide structure made of WC-Co. Here, the amount of the additional carbon is an amount set to reduce the η phase on the surface structure of the cemented carbide structure to compensate for the amount of carbon loss in the degreasing and sintering steps.

Here, the amount of the additional carbon may be set to an amount within the range of 0.5 g to 5 g per 100 g.

Alternatively, the amount of the additional carbon may be one of 1.2 g, 1.5 g, or 1.8 g per 100 g.

The degreasing step may include a first degreasing step of raising the temperature of the debinding furnace into which the injection product is introduced to a first temperature and then maintaining the first temperature for a predetermined first time period, A second degassing step of maintaining the second temperature for a second predetermined time after the temperature of the degassing furnace is raised to a second temperature, a step of raising the degassing furnace to a third temperature, and maintaining the third temperature for a third predetermined time And a third degreasing step.

The first degreasing step may include raising the degreasing path to a first intermediate temperature lower than the first temperature and lowering the temperature from the first intermediate temperature to the first temperature, 2 < / RTI >

Wherein the second degreasing step is a step of raising the degreasing path from the first temperature to a second intermediate temperature lower than the second temperature to a third heating rate and from the second intermediate temperature to the second temperature, The temperature can be raised at the fourth heating rate lower than the speed.

Meanwhile, the first intermediate temperature is 200 ° C, the first temperature is 260 ° C, the second intermediate temperature is 420 ° C, the second temperature is 480 ° C, the third temperature is 900 ° C,

Wherein the first heating rate and the third heating rate are respectively 3 ° C per minute and the second heating rate and the fourth heating rate are 1 ° C per minute,

The first and second temperature holding periods are respectively 6 hours,

In the third degreasing step, the temperature is raised from 480 ° C to 900 ° C at a rate of temperature increase of 4.5 ° C per minute. When the temperature reaches 900 ° C, the temperature of 900 ° C can be maintained for 1 hour.

In addition, the cobalt powder is contained in an amount of 10%. In the degreasing step in which the degreasing step is performed, hydrogen and nitrogen are charged at a mixing ratio of 1: 1 to 200 ml per minute, and hydrogen gas is not introduced into the degreasing furnace .

Meanwhile, a powder injection molding system according to an embodiment of the present invention may include a mixing apparatus for mixing tungsten carbide (WC) powder and cobalt (Co) powder, which have been charged to predetermined proportions, together with additional carbon and a binder, An injection device for injecting the mixed product, a degreasing device for heating the injection product, and removing the binder from the injection product, when the injection product is injected from the injection device, And sintering the resultant to produce a cemented carbide structure made of WC-Co. Here, the amount of the additional carbon may be an amount set to reduce the η phase on the surface structure of the cemented carbide structure to compensate for the amount of carbon loss during the degreasing and sintering process.

The amount of the additional carbon may be one of 1.2 g, 1.5 g, and 1.8 g per 100 g.

The degreasing step may include a first degreasing step of raising the temperature to a first temperature and keeping the first temperature for a first predetermined time after the injection product is introduced, A second degreasing step of maintaining the temperature for a predetermined second time, a third degreasing step of raising the temperature to a third temperature, and then maintaining the third temperature for a predetermined third time.

Here, the degreasing process may change the heating rate at least once during the first degreasing process and the second degreasing process.

According to various embodiments of the present invention as described above, degradation of mechanical characteristics due to carbon loss can be prevented.

1 is a view showing a configuration of a powder injection molding system according to an embodiment of the present invention;
FIG. 2 is a flowchart for explaining a powder injection molding method according to an embodiment of the present invention;
3 is a graph showing the result of measurement of the degree of magnetic saturation when additional carbon is added according to an embodiment of the present invention,
FIG. 4 is a graph showing carbon content results when additional carbon is added according to an embodiment of the present invention. FIG.
5 is a graph showing the results of measurement of hardness when additional carbon is added according to an embodiment of the present invention,
FIG. 6 is a graph showing the results of the anti-pullout test when additional carbon is added according to an embodiment of the present invention,
7 is a photograph showing the surface state of the cemented carbide structure when additional carbon is added according to an embodiment of the present invention,
FIG. 8 is a flowchart specifically illustrating a three-stage degreasing step in the powder injection molding method according to another embodiment of the present invention. FIG.
9 is a graph for explaining the temperature and time of the three-stage degreasing process,
FIG. 10 is a view for explaining the deformed state of the injection product in the case where the injection product is degreased in the conventional manner and the case where the product is degreased in the three-stage degreasing process,
11 is a view showing an example of experimental conditions for each step of the powder injection molding method according to various embodiments of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing a configuration of a powder injection molding system according to an embodiment of the present invention. 1, the powder injection molding system includes a mixing apparatus 10, an injection apparatus 20, a degreasing furnace 30, and a sintering apparatus 40. [

The powder injection molding method in the present powder injection molding system can be roughly classified into a feedstock manufacturing process, an injection molding process, a degreasing process, and a sintering process for producing raw materials for injection molding.

The mixing device (10) mixes the metal powder as a raw material with a binder. The result of the mixing becomes a feedstock of various forms. The feedstock is prepared by kneading the raw metal powder and the organic binder to uniformly apply the organic binder to the raw metal powder. The feedstock can be made into pellets to facilitate injection of the material during injection molding. At this time, a binder system mainly based on a plastic-wax mixed component is used as an organic binder. Specifically, wax (Paraffin wax; PW) may be used as a binder, and polyethylene (PE), polypropylene (PP) and stearic acid (SA) may be used as a binder. It has excellent fluidity in the molten state of the polymer. When a small amount of additive is used, it has good wettability to many metal particles and has many advantageous features such as being easily released from a mold and the like.

Mixing of the raw metal powder and the organic binder is considered to be a very important element technology because it can greatly affect the subsequent processes. The most important point should be that they should be mixed as uniformly as possible and that the formation of agglomerates of particles should not cause pores due to air mixing during uneven mixing and mixing processes. It is known that, when kneaded, pressurization facilitates the transition of the powder-like polymer to the preliminary state, and therefore it is easy to obtain uniform mixing.

On the other hand, when the mixing is completed by the mixing device 10, the mixed product, that is, the feedstock, is injected into the injection device 20. The injection apparatus 20 includes a mold having a shape corresponding to a structure to be manufactured. Accordingly, the introduced mixed result is subjected to temperature and / or pressure and is compressed into a shape corresponding to the mold. Thereby generating an injection result. The injection apparatus 20 may be implemented as a hydraulic vertical injection molding apparatus (Ministar VMP Hydraulic).

In this case, the powder is put into the mixing apparatus 10 in a predetermined mixing ratio. For example, tungsten carbide (WC) powder and cobalt (Co) powder can be mixed and mixed.

Here, the cobalt powder may occupy only 10% of the mixing ratio. However, these numerical values are not limited and can be appropriately changed depending on the shape and mechanical characteristics of the structure to be manufactured. That is, the cobalt ratio can be increased to 20 to 30% or more.

On the other hand, carbon deposition can be reduced during degreasing and sintering.

That is, WC forms a process point at Co and 1320, and WC is employed in Co solution at about 35 at.%. The WC-Co cemented carbide is a sintering technique that uniformly mixes the WC of a certain crystal with a predetermined Co so that there is no growth of pores and coarse WC, a perfect WC in which free carbon or η phase does not precipitate, and a uniformly distributed Co alloy phase Technology. The lower the Co content, the narrower the area where only two phases exist without WC and η phase in the WC and Co liquid phase, and the narrower the Co content is, the narrower it is. When WC / Co-based alloys are in an appropriate range of carbon, they are in the (WC +) sound phase region, but when carbon is insufficient, a bicomparate phase of W ₂ C or η phase (Co ₃ W ₃ C) tends to form, Free carbon is produced. In WC-10wt.% Co alloy, the range of WC in which the two phase region appears is 6.04 ~ 6.22wt.% C, the width is about 0.18wt.%, And the stoichiometric carbon composition of WC is 6.12wt.% . These free carbon and η phases inhibit the strength of the cemented carbide, especially the η phase, which results in a reduction in the amount of Co acting as an effective binder since it makes Co and bicarbonate, so the effect on mechanical properties is much greater than free carbon. The η phase has a composition of η ₁ (M ₆ C, Co ₃ W ₃ C) and η ₂ (M ₁₂ C, Co ₆ W ₆ C) as a composite of W, Co and C. The η phase appears when the amount of C is insufficient. However, in recent studies, the η phase is not generated only when the amount of C is lower than the theoretical value, but it may occur even in the presence of free carbon. Here, free carbon means an aggregate of carbon only, not a precipitated compound when the carbon content is increased.

On the other hand, in the binder removal process which takes the most time in the powder injection molding process, a large amount of carbon is lost in the decarburization process during the hot degreasing process, so that the carbon content in the specimen after sintering may be somewhat low. If the carbon content is lowered, mechanical properties such as anticipated hardness, abrasion resistance, abrasion resistance, corrosion resistance, and the like may not be obtained. On the other hand, when the carbon content is increased by adjusting the mixing ratio in consideration of this, free carbon is formed as described above, which makes it difficult to secure a healthy phase. Therefore, it is necessary to appropriately compensate for the loss of carbon in the subsequent process after injection.

According to an embodiment of the present invention, additional carbon is injected to perform injection molding in consideration of this point. The amount of additional carbon added may be an amount that is set to reduce the η phase on the surface structure of the cemented carbide structure to compensate for the amount of carbon loss in the subsequent process after injection molding, i.e., the degreasing and sintering steps.

Specifically, the amount of additional carbon can be set within the range of 0.5 to 5 g per 100 g. According to the experiment, the amount of additional carbon can be set to one of 1.2 g, 1.5 g, or 1.8 g. Specific experimental conditions and methods will be described later.

On the other hand, the injection result produced by the injection apparatus 20 is a portion including a binder. The degreasing furnace 30 means that the binder is removed from the injection product.

The degreasing furnace 30 is heated to a specific temperature to remove the binder from the injection product. Here, the degreasing path 30 is subjected to a two-stage degreasing step or a three-stage degreasing step. The second stage degreasing step is an operation in which the debinding furnace 30 is heated so as to sequentially pass through two temperature holding sections. The third stage degreasing step is a stage in which the debinding furnace 30 has three And the temperature is raised so as to sequentially pass the temperature maintaining period. An embodiment in which the three-stage degreasing step is performed will be described later.

When the degreasing process is performed through the degreasing furnace 30, the sintering process can be performed in the sintering apparatus 40. That is, when the solid powder is injected into a mold and pressurized appropriately, the mixture is heated at a temperature close to the melting point of the material, It becomes a lump. This process is called sintering. The sintering apparatus 40 is provided with the result of the degreasing and is heated to produce a complete single structure 50.

For example, as the sintering apparatus 40, a batt-shaped sintering furnace using a super-cantilever as a heating element may be used. A plate made of carbon can be used for sintering, and cooling of the sintered body can be gradually cooled by the roOH method.

In the system of Fig. 1, various types of structures can be manufactured. As an example, a cemented carbide structure can be produced. Cemented carbides are alloys obtained by sintering nine kinds of transition metal carbides belonging to groups IV, V and VI of the periodic table using iron family metals (Co, Ni, Fe). The cemented carbide is excellent not only in room temperature hardness and high temperature hardness but also in mechanical properties such as strength and abrasion resistance. Many kinds of cemented carbides can be produced by combining these carbides and metal binders. However, since the mechanical properties of WC-Co alloys are the most excellent, the alloy system is usually called cemented carbide. Cemented carbide is widely used as a cutting tool material, and is widely used as a material for abrasion resistance, impact resistance tools, and high-temperature and high-pressure parts.

Since cemented carbides have intermediate properties between high hardness ceramic materials and high-speed high-speed steel materials, they have high hardness and resistance at room temperature as well as high temperature, and are excellent in abrasion resistance, impact resistance and corrosion resistance. And wear resistant parts. Recently, the use range of mold materials for generating ultra-high pressure has been expanded

In the system of FIG. 1, a WC-Co super-competitive structure can be manufactured by injection molding a mixture of tungsten carbide (WC) powder and cobalt (Co) powder as an example of a cemented carbide.

2 is a flowchart illustrating a powder injection molding method according to an embodiment of the present invention. Referring to FIG. 2, first, tungsten carbide powder and cobalt powder are mixed with a binder, and additional carbon is injected to perform injection molding (S210). The amount of additional carbon added can be determined in consideration of the amount of carbon loss as described above. The amount of additional carbon can be determined experimentally as an optimal value. Experimental methods and conditions for this will be described later.

When injection molding is performed to obtain an injection result, defatting is performed (S220).

Accordingly, when the binder is removed, a sintering process is performed (S230).

The degreasing and sintering process and the operation of the apparatus have been described in detail in the description of FIG. 1, and a duplicate description thereof will be omitted.

As noted above, additional carbon can be added to maintain mechanical properties. The amount of additional carbon can be determined experimentally. An example of a specific experiment is as follows. That is, after a plurality of specimens were produced by injecting different amounts of additional carbon into the mixing device 10, the magnetic saturation, the carbon content, the hardness, the resistance characteristic, and the generation of the η phase were confirmed for each specimen, The optimum amount of additional carbon can be determined.

In this experimental example, the self-saturation test for the sintered body was carried out using SJ-2000C equipment, and the CS analysis was performed for carbon content analysis. For the CS analysis, the specimens were crushed and weighed at 0.2 g, and then subjected to three times per each specimen. The results were averaged three times. The method for analyzing the characteristics of sintered specimens was conducted according to the Korean Industrial Standards. First, to confirm the microstructure of the sintered specimen, the specimens were polished to 1 ㎛ and then etched with Murakami solution (10 g of K3Fe (CN) 6, 10 g of NaOH, 200 ml of distilled water) for several seconds and observed through an optical microscope. The microstructure of each sintered body was observed using a field emission scanning electron microscope (FE-SEM, Phillips Co., XL30 SFEG).

To determine the hardness of the sintered WC-10wt% Co cemented carbide, the specimens were cut with a diamond wheel cutting equipment, and their cross-section was polished down to 1 μm and the microhardness was measured. The hardness meter (Akashi Co., (HM-112)) micro-Vickers hardness tester was used. The load was 1 kgf and the holding time was 10 seconds. The density was measured using the Archimedes method. The transverse rupture strength test was commissioned by a test evaluation company to confirm the results.

All the sintering processes in this study were carried out in a vacuum atmosphere. The sintering temperature was varied from 1320 to 1500 and sintered. The characteristics of each specimen with different amounts were investigated in terms of carbon content.

First, experiments were conducted on the formation and disappearance of η phase and free carbon by adding additional carbon to WC-10% Co in a wide range. The experimental conditions are as follows.

- Carbon addition amount: WC-10% Co + 0, 1, 2, 3, 4, 5% (weight ratio)

- Specimen preparation conditions

Ⓐ Mixing conditions: [metal powder + organic binder + added carbon] Twin-edged extruder, 160 ^o C, 60 rpm, 1 hour

Ⓑ Injection process: injection temperature 160oC, mold temperature 60oC, injection pressure 58MPa

Ⓒ Degreasing process: solvent degreasing -> 3 step hot degreasing

Ⓓ Sintering process: Vacuum atmosphere, 1380 ^o C / 1hr

- amount of η phase and free carbon: area occupied by η phase and free carbon phase in total area

The results of the measurements with different carbon additions for the two specimens are summarized in the following table.

Carbon
Addition amount
(%) Psalm 1 Psalm 2 η phase Free carbon Vickers hardness
(Hv) η phase Free carbon Vickers hardness
(Hv) 0 9.5% 0% 1940 9.8% 0% 1950 One 5.4% 0% 2002 5.5% 0% 1995 2 0.1% 0% 2130 0% 0% 2135 3 0% 2.8% 2120 0% 3.0% 2110 4 0% 5.2% 2005 0% 5.0% 1997

According to the above experiment, when 2% of carbon was added, the η phase and free carbon were most suppressed and the hardness value was evaluated to be the highest.

FIG. 3 is a graph showing one of the experimental results of the experiment of injecting the additional carbon. FIG. 3 shows the result of measurement of the degree of self-saturation of the specimen to which carbon was not additionally added and the specimen to which the amount of carbon was added from 1.2 g to 1.8 g. According to FIG. 3, the results are shown in the range of 110 gauss, which is less than 150 ~ 160 gauss, in which the WC-10% Co composition shows a healthy phase in the specimen without carbon. These low magnetic saturation values were attributed to the fact that the phase of the ternary composite carbide phase was present due to the low carbon content of Co and the presence of the ternary composite carbide phase. As a result of observing the specimens after surface polishing with optical microscope, Respectively. The carbon contents of the specimens were investigated using a carbon analyzer. To obtain the exact carbon content, three specimens were analyzed for each specimen and the mean values for the three specimens were taken.

4 is a graph showing the results of the carbon content investigation. According to Fig. 7, the results were obtained in the range of 4.8 to 4.9 wt%, which is less than the theoretical carbon content of 5.517 wt%. The reason for the low carbon content is that the carbon content is low due to decarburization as a result of degreasing and releasing to hydrogen for a long time in order to make the specimen free from defects during the hot degreasing process of the specimen. The porosity of the specimen after addition of carbon was found to be in the range of 140gauss for 1.2g added sample and 150gauss for 1.5g carbon added specimen. Also, the specimen with 1.8 g of carbon was found to have a magnetic saturation value higher than 160 gauss. As a result of the carbon content analysis, it was confirmed that the carbon content gradually increased according to the amount of carbon added.

FIG. 5 is a graph showing the hardness characteristics of the test results.

According to FIG. 5, it was confirmed that the hardness value of the specimen to which the carbon was added was higher than that of the specimen to which the carbon was not added. The average hardness value of the specimen without carbon was 1940 Hv, while the specimen with 1.2 g carbon added with 2010Hv and 1.5 g showed 2080 Hv and 1.800 g, respectively, at 2100 Hv. . The higher the sintering temperature, the lower the hardness value. This is because the microstructure grows and the hardness of the specimen is lowered.

Fig. 6 shows changes in the results of the anti-pullout test depending on the amount of carbon added.

According to Fig. 6, it was also found that the resistance value of the specimen to which carbon was added was increased according to the addition amount. The η phase degrades the mechanical properties of the cemented carbide. It is confirmed that the specimen with no carbon added in both the hardness and the anti - force has lower results than the carbonized specimen. Also, it was confirmed that as the sintering temperature increases, the microstructure grows, which affects the hardness and the resistance characteristic.

FIG. 7 is a photograph of the result of observing the microstructure of the specimen surface by an optical microscope after polishing the specimen after finishing the final sintering of the specimen produced with different amounts of carbon added.

7, (a) and (b) show that no carbon was added, and (c) added with 1.2g, (d) added with 1.5g and (e) added with 1.8g. As the carbon content of the specimen increased, the η phase decreased and the carbon content of the specimen increased.

According to the above experiment, it can be seen that the mechanical properties are changed variously by adding about 0.5 to 5 g of carbon. Accordingly, it is possible to experimentally determine the amount of carbon to be experimentally measured so as to obtain desired mechanical properties, and then to input into the mixing apparatus 10 to produce a cemented carbide structure.

Meanwhile, according to another embodiment of the present invention, the degreasing process may be performed through a three-stage degreasing process. This embodiment may be applied with the above-described embodiment, that is, the embodiment in which the additional carbon is added, or separately from the three-stage degreasing process.

That is, in the embodiment of performing the three-stage degreasing step, the tungsten carbide powder and the cobalt powder are first mixed with the binder and then injected. The mixing and injection steps may be performed using the mixing apparatus 10 and the injection apparatus 20 in the system of FIG. Since a detailed description thereof has been described above, redundant description will be omitted.

After the injection is completed, a three-stage degreasing step is performed on the injection-molded article. Specifically, degreasing is performed while raising the degreasing path 30 to sequentially pass three temperature holding periods. The control of the degreasing path 30 may be performed automatically by a control device (not shown) provided separately, or may be manually controlled by an administrator while monitoring the temperature and time of the degreasing path 30.

After degreasing, the sintering step of sintering the degreased product to produce a cemented carbide structure made of WC-Co can be performed. Thus, it is possible to obtain a cemented carbide structure while preventing deformation such as warping or distortion of the structure.

FIG. 8 is a flowchart for explaining the three-stage degreasing process in more detail.

Referring to FIG. 8, when the injection result is input to the degreasing path 30, the degreasing path is heated (S810). Accordingly, if it is determined that the temperature has been increased to the first temperature (S815), the first temperature is maintained at the first temperature without further increasing the temperature (S820).

If the first time has elapsed while the first temperature is maintained (S825), the degassing furnace is again heated (S830). Thereafter, if it is determined that the temperature has been increased to the second temperature (S835), the second temperature is maintained (S840). If it is determined that the state maintained at the second temperature is continued for the second time (S845), the degassing furnace is again heated (S850). Accordingly, when the third temperature is reached (S855), the third temperature is maintained (S860). Thus, it is possible to carry out the degreasing process of three stages.

The three-stage degreasing process described above may be manually controlled by the manager as described above, but may be automatically controlled by the controller. That is, the controller senses the temperature inside the degreasing furnace 30 using a temperature sensor provided separately. If it is determined that the first, second, and third temperatures have reached, the control unit stops heating the degreasing bath 30 and maintains the temperature . Thereafter, using the timer provided separately, if it is determined that the temperature holding period has elapsed, the degassing furnace 30 is controlled to raise the temperature again.

9 is a graph for more specifically explaining the three-stage degreasing process.

Referring to FIG. 9, the first temperature maintaining period 1 is formed at 260 占 폚, the second temperature maintaining period 2 is 480 占 폚, and the third temperature maintaining period 3 is at 900 占 폚.

Here, according to one embodiment, the heating rate in the heating zone for reaching each temperature holding period can be set to a constant value of 3 to 5 per minute.

Alternatively, according to another embodiment, the heating rate for each heating zone may be different. Fig. 9 shows a case in which the heating rate is different.

According to FIG. 9, the temperature is increased from room temperature to 200 ° C at a rate of 3 ° C per minute, and the temperature is increased from 200 ° C to 260 ° C by 1 ° C per minute, followed by degreasing at 260 ° C for 6 hours. That is, the first degreasing step is performed.

Then, the temperature is raised again to 420 ° C. at a rate of 3 ° C. per minute, and the rate of heating is decreased from 420 ° C. to 480 ° C. at a rate of 1 ° C. per minute, followed by degassing at 480 ° C. for 6 hours. That is, the second degreasing step is performed. Then, the temperature is raised up to 900 ° C without adjusting the temperature raising rate, and then degreased at 900 ° C for about 1 hour. The rate of temperature rise is maintained at 4.5 ° C per minute up to 900 ° C. The third degreasing step may correspond to pre-sintering.

Fig. 10 is a view showing an effect of preventing deformation due to such three-stage degreasing. In FIG. 10, the specimen 100 positioned in the middle represents the injection product itself, and the specimen 110 located on the upper side represents the result of degreasing by a conventional method. It can be seen that degreasing using the conventional method causes the structure to warp to one side. And the specimen 120 located on the lower side shows the result of the three-stage degreasing process according to an embodiment of the present invention. According to this, it can be seen that the shape is not deformed, but only the size is reduced compared to the injection result due to degreasing. It can be seen that the structure was not deformed and the degreasing was performed as it is.

Meanwhile, during the three-stage degreasing process according to FIG. 6, the atmosphere in the degreasing furnace 30 was used at a rate of 200 ml per minute at a mixing ratio of 1: 1 of hydrogen and nitrogen. In order to prevent a large amount of decarburization, no hydrogen gas was introduced into the degreasing bath 30 after 600 hours.

The embodiment shown in Fig. 8 may be applied together with the embodiment described in Figs. 1 and 2 as described above, or may be applied separately. That is, it is possible to implement a three-stage degreasing process while adding additional carbon.

11 is a diagram showing an experimental process for evaluating the characteristics of a cemented carbide structure manufactured by various embodiments of the present invention and an example of specific experimental conditions thereof.

According to Fig. 11, the mixing process is carried out twice at a speed of 60 rpm at 160 DEG C using a twin-blade extruder, in which carbon can be added by a set amount of 0 to 1.8 g.

In addition, the injection process may be performed at an injection temperature of about 160 캜 and a injection pressure of 58 MPa. For the experiment, the injection product, i.e., the injection specimen, injected from the injection apparatus 20 can be injected into a TRS test specimen for transverse rupture strength (TRS) characterization. The size of the injection body can be made to be 54 mm x 8 mm x 3 mm. In order to prevent the occurrence of defects in the injection body due to quenching while the feedstock in the slurry state is filled in the mold, Gt; 60 < / RTI >

The degreasing process may be solvent degreasing or hot degreasing. In case of solvent degreasing, n-hexane is used as a solvent at 60 ° C. for 24 hours. In case of hot degreasing, degreasing is performed at 260 ° C. and 480 ° C. for 6 hours for 2 hours, followed by degreasing at 900 ° C. .

In the sintering process, it is found that the sintering is performed at a sintering temperature of 1350 to 1500 ° C for 1 hour at a heating rate of 10 ° C per minute, and the conditions are a nitrogen and hydrogen mixed gas atmosphere.

In the foregoing, experimental conditions and methods have been described using concrete numerical values. However, it goes without saying that such experiment conditions and methods may be arbitrarily changed at a level that can be easily changed by those skilled in the art. It is also apparent that the spirit of the present invention is not limited to these numerical values and can be changed to numerical values not described in this specification.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be construed as limiting the scope of the invention as defined by the appended claims. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

10: mixing device 20: injection device
30: degreasing furnace 40: sintering apparatus

Claims (10)

An injection molding step of mixing the tungsten carbide (WC) powder and the cobalt (Co) powder at predetermined ratios, injecting additional carbon and injecting the powder together with the binder;
A degreasing step of heating the result of the injection to remove the binder from the injection product;
And sintering the degreased product to produce a cemented carbide structure made of WC-Co,
The amount of additional carbon is an amount set to reduce the η phase and the free carbon on the surface structure of the cemented carbide structure to compensate for the amount of carbon loss in the degreasing and sintering step,
Wherein the amount of the additional carbon is set to an amount exceeding 1 g and less than 5 g per 100 g. delete delete The method according to claim 1,
In the degreasing step,
A first degreasing step of raising the temperature of the debinding furnace into which the injection product is introduced to a first temperature and then maintaining the first temperature for a predetermined first time;
A second degreasing step of raising the degreasing path to a second temperature and then maintaining the second temperature for a second predetermined time;
And a third degreasing step of raising the degreasing path to a third temperature and maintaining the third temperature for a predetermined third time period. 5. The method of claim 4,
The first degreasing step may include:
Raising the temperature of the degreasing furnace to a first intermediate temperature lower than the first temperature at a first temperature raising rate and raising a temperature from the first intermediate temperature to the first temperature to a second temperature raising rate lower than the first raising rate,
The second degreasing step may include:
The degassing furnace is heated from the first temperature to a second intermediate temperature lower than the second temperature to a third heating rate, and from the second intermediate temperature to the second temperature, a fourth heating rate And the temperature of the powder injection molding is raised. An injection molding step of mixing the tungsten carbide (WC) powder and the cobalt (Co) powder at predetermined ratios, injecting additional carbon and injecting the powder together with the binder;
A degreasing step of heating the result of the injection to remove the binder from the injection product;
And sintering the degreased product to produce a cemented carbide structure made of WC-Co,
The amount of additional carbon is an amount set to reduce the? Phase on the surface structure of the cemented carbide structure to compensate for the amount of carbon loss in the degreasing and sintering step,
In the degreasing step,
A first degreasing step of raising the temperature of the debinding furnace into which the injection product is introduced to a first temperature and then maintaining the first temperature for a predetermined first time;
A second degreasing step of raising the degreasing path to a second temperature and then maintaining the second temperature for a second predetermined time;
And a third degreasing step of raising the degreasing path to a third temperature and then maintaining the third temperature for a predetermined third time,
The first degreasing step may include:
Raising the temperature of the degreasing furnace to a first intermediate temperature lower than the first temperature at a first temperature raising rate and raising a temperature from the first intermediate temperature to the first temperature to a second temperature raising rate lower than the first raising rate,
The second degreasing step may include:
The degassing furnace is heated from the first temperature to a second intermediate temperature lower than the second temperature to a third heating rate, and from the second intermediate temperature to the second temperature, a fourth heating rate , ≪ / RTI >
Wherein the first intermediate temperature is 200 占 폚, the first temperature is 260 占 폚, the second intermediate temperature is 420 占 폚, the second temperature is 480 占 폚, the third temperature is 900 占 폚,
Wherein the first heating rate and the third heating rate are respectively 3 ° C per minute and the second heating rate and the fourth heating rate are 1 ° C per minute,
The first and second temperature holding periods are respectively 6 hours,
The third degreasing step may include:
The temperature is raised from 480 ° C to 900 ° C at a rate of temperature increase of 4.5 ° C per minute, and when the temperature reaches 900 ° C, the temperature is kept at 900 ° C for 1 hour. 7. The method according to any one of claims 1 to 6,
The cobalt powder contained 10%
Wherein the degreasing step is performed in a degassing furnace in which hydrogen and nitrogen are mixed at a mixing ratio of 1 to 200 ml per minute and hydrogen gas is not introduced into the degreasing furnace at a temperature of 600 ° C or more. A mixing device for mixing the tungsten carbide (WC) powder and the cobalt (Co) powder, which have been charged to a predetermined ratio, together with the additional carbon and the binder;
An injection device for injecting the mixed product in the mixing device;
A degreasing furnace for heating the injection product to remove the binder from the injection product when the injection product is injected from the injection device;
And sintering the sintered product to produce a cemented carbide structure made of WC-Co when the degreased product is introduced into the degreasing furnace,
The amount of the additional carbon is an amount set to reduce the η phase and the free carbon on the surface structure of the cemented carbide structure by supplementing the amount of carbon loss in the degreasing and sintering process,
Wherein said additional carbon amount is set to an amount of more than 1 g per 100 g and less than 5 g. 9. The method of claim 8,
Wherein said additional carbon amount is one of 1.2 g, 1.5 g, or 1.8 g per 100 g. 9. The method of claim 8,
In the degreasing furnace,
A first degassing step of raising the temperature to a first temperature and keeping the first temperature for a first predetermined time after the injection result is input, a second degassing step of raising the temperature to a second temperature, A third degreasing step of raising the temperature to a third temperature and maintaining the third temperature for a predetermined third time,
Wherein the temperature raising rate is changed at least once during the first degreasing process and the second degreasing process.

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