KR950007331B1 - Hard metal of wc-ni system and process - Google Patents

Abstract

The WC-Ni hard alloy shows good corrosion resistance, non-magnetic property and high hardness by coating WC powders with silicon carbides. The method comprises (A) mixing silica colloid solution with WC powders for 10 to 40 minutes; (B) drying at 50 to 100 ≰C; (C) heating the mixed powders at 1400-1600≰C for 1 to 4 hours under argon gas atmosphere; (D) sintering at 1300-1600≰C at 10+˜10-5 torr for an half hour to 4 hours.

Description

WC-Ni cemented carbide and its manufacturing method

The present invention relates to a WC-Ni-based cemented carbide and a method of manufacturing the same.

More specifically, the WC-Ni-based cemented carbide, which can produce a non-magnetic alloy and a WC-Ni cemented carbide having excellent corrosion resistance, and can replace the non-binder metal of the WC-Co cemented carbide with Ni in Co And a WC-Ni-based cemented carbide prepared by the process.

The conventional cemented carbide has been mainly dominated by WC-Co cemented carbide since the development of Widia in 1926. WC-Co cemented carbide has excellent wear resistance, high temperature strength and toughness, and is used for cutting, tooling materials, various mold materials, and the like, and its use range is expanding.

However, Co, which is a binder metal of the WC-Co cemented carbide, is expensive in terms of price and unstable in supply and demand, and thus Co is becoming a strategic resource. For this reason, efforts have been made to replace Co with other binder metals, but have not been satisfactory in terms of mechanical properties.

The most suitable element to replace Co by adding other iron group metal elements is Ni, and Ni is currently used only in a limited range (for example, non-magnetic alloy). The study of WC-Ni cemented carbide was conducted in 1966 by Suzuki. Attempted for the first time, but did not achieve satisfactory results. In developing a WC-Ni cemented carbide alloy by replacing the binder metal with Ni in the tungsten carbide cemented carbide, the problem that occurs when the binder metal is replaced with Ni is a decrease in sinterability and mechanical properties.

The cause of the deterioration of the mechanical properties is the formation of coarse particles (composite carbides) generated during the particle growth process during sintering. In the process of forming a composite carbide phase in the sintering mechanism, WC and Ni react to form a composite carbide phase such as Ni ₅ W ₆ C, Ni ₃ W ₅ C ₂ and Ni ₃ W ₁₆ C ₆ due to the lack of carbon. This causes cracking when broken.

In addition, for WC, Ni has a lower solubility than Co. In liquid sintering, the binder metal should have a certain degree of solubility with the binder metal. The solubility in WC is 22% for Co, but only 12% for Ni.

As such, Ni has a lower solubility than Co, which also affects the deterioration of mechanical properties. Furthermore, since the liquid phase appearance temperature at the time of sintering is about 70 ° C. higher than that of WC-Co, side reactions are easily generated. Therefore, when Co is replaced with Ni, the mechanical properties deteriorate.

In addition, although a material similar to WC-Co alloy, such as WC-NI-Fe alloy, has been developed in mechanical properties, there is a problem in corrosion resistance or toughness, so it is used only in a limited range. This is in urgent need.

According to the current technology, the WC-Ni cemented carbide has the problems as described above, and also has specificity of use (for example, non-magnetic alloy and corrosion resistant alloy), but the present WC-Ni cemented carbide is used as a non-magnetic alloy. Because of its poor mechanical properties, its use is restricted to areas requiring wear resistance. Ni is inferior to Co in formability and sinterability compared to Co. If the carbon content of the WC is 5.9% by weight or less, it is nonmagnetic, so it is used in molding dies, for hot working, and because of its excellent corrosion resistance, it is used as a tough alloy with seawater resistance.

From the powder metallurgy point of view, WC-Ni alloys show a significant difference in hardness compared to WC-Co alloys when the starting materials of the WC powder are the same particle size. The difference in hardness value is that the finer the particle size of the WC (less than 1㎛), the hardness value of the WC-Co and WC-Ni is not a big difference, but the coarseness of the WC coarse, the greater the difference in hardness between the two.

For example, in case of WC-Co alloy, hardness is 90.5 when WC powder particles are 0.5 ~ 1㎛ or less, hardness is 89 when 2 ~ 3㎛, and hardness is 87.5 when about 6㎛ (above hardness is Rockwell hardness value) ). According to the present invention, however, coating the coarse WC powder with SiC yields a WC-Ni cemented carbide that is comparable to WC-Co in physical properties even with coarse powder. The sintered body of WC-Ni-based cemented carbide using WC powder coated with SiC has a higher hardness value than the sintered body of WC-Co cemented carbide.

As a result of earnest research to solve the above-mentioned problems of the prior art, the present inventors have found that Co can be replaced with Ni as a binder metal by using a WC powder coated with SiC.

The object of the present invention is to replace the binder metal with Ni to overcome the problems of price and supply and demand instability of Co, and the nonmagnetic magnetic alloy and WC, which are inherent in the WC-Ni-based cemented carbide, which are known to be known so far, It is to provide a WC-Ni-based cemented carbide and a method for producing these alloys excellent in acid resistance, corrosion resistance and thermal shock resistance compared to -Co alloy.

Another object of the present invention is to coat SiC on a WC powder to suppress the properties of coarse particles and to improve mechanical properties.

The object of the present invention is to form a SiC layer on the surface of the WC powder, to hydrolyze sodium silicate with water to obtain a colloidal solution of silica having a pH of 10.2 to 11.4, and put the WC powder into the clade solution and stirred, Carbon was added in an amount of 0.02 to 1 wt% based on the WC powder, followed by stirring, followed by drying at 50 to 100 ° C. to remove moisture, thereby obtaining a powder mixture, and the powder mixture at a temperature of 1400 ° C. to 1600 ° C. The reaction was carried out in an argon gas atmosphere for 1 to 4 hours to obtain a WC powder coated with 0.1 to 5% by weight of SiC on the WC powder. The SiC coated WC powder: 70 to 97% by weight and Ni: 3 to 30% by weight. The mixture was presintered in a vacuum or hydrogen atmosphere for 30 minutes to 3 hours at a temperature of 400 to 900 ° C., and thus the pre-sintered body was obtained at 1300 to 1600 ° C. at 10 ⁻² torr to 10 ⁻⁵ torr for 30 minutes. To 4 Method for producing a WC-Ni cemented carbide, characterized in that the main sintering for a while, in order to produce a WC-SiC-Ni cemented carbide, a SiC layer is formed on the surface of the WC powder to form a SiC coated WC powder instead of Co Method of preparing a cemented carbide material equivalent to or better than that of the WC-Co-based cemented carbide and mixed with 0.1 to 5% by weight of SiC WC powder: 70 to 97% by weight and Ni: 3 to 30% by weight It is achieved by WC-Ni-based cemented carbide.

Hereinafter, the present invention will be described in detail.

The absolute influence on the mechanical properties of WC cemented carbides is the growth of coarse particles of WC after sintering. Therefore, the suppression of grain growth of cemented carbide is the most important task in cemented carbide.

In the conventional method, in the case of WC-Co alloy, carbide growth of VC, TiC, TaC, Mo ₂ C was added as a particle growth inhibitor, and in the case of WC-Ni, VC, Cr ₂ C _3, etc. Was used to improve the mechanical properties.

In the present invention, however, the growth of the particles is suppressed by coating the WC powder with the particle growth inhibitor without inhibiting the growth of the particles, and by coating the WC powder with SiC having good reactivity with Ni, The addition of cheaper Ni in terms of price improves the problems of existing WC-Ni alloys.

When the cemented carbide is sintered, carbon is insufficient to produce a composite carbide of WC and binder metal. In WC-Co alloy, CoW ₃ C ( In the case of WC-Ni, Ni ₂ W ₄ C ( Phase) is generated. Although these composite carbides increase hardness, they have an absolute bad effect on toughness, and these composite carbides also affect coarse grain growth.

The problem to be improved in the present invention is to inhibit the interfacial reaction between WC and Ni, the growth of the composite carbide particles and the formation of coarse WC particles in the WC-Ni-based cemented carbide as described above.

In the present invention, in order to overcome the problems caused by replacing the binder metal with Ni (coarse particle growth, growth of complex carbide, processing), in the present invention, the WC powder is coated with WC powder with SiC having good reactivity with Ni. Therefore, the above problems, which are a problem in sintering, are improved, and the basic problems of the conventional WC-Ni cemented carbide are improved by coating the WC powder with Ni and SiC having good wettability. When SiC is coated on the WC powder, the interfacial reaction is smoothed, the growth of coarse particles is suppressed, and a high hardness value is obtained even when the binder metal is replaced with Co by Ni. In order to improve the wettability of WC and Ni, SiC having excellent Ni and wettability was coated on the WC to improve wettability between WC and Ni and to suppress formation of a composite carbide phase. Another noteworthy aspect of the present invention is the particle size of the WC powder.

The smaller the particle size of the powder, the better the sintered structure and the sintered body can be obtained. In general, cemented carbides exhibit relatively high hardness and toughness depending on the amount of binder metal.

In addition, it is the particle size of the raw material powder of WC that acts as a variable. The larger the particle size, the lower the hardness. In addition, the influence of the particle size of the powder also affects the molding pressure, sintering temperature, and sintering time. In the research papers and patents published so far, molded articles were manufactured using powder having a particle size of 1 μm or less. However, in the present invention, it is possible to produce a molded article from a powder having a particle size of 0.87 to 10 µm.

Hereinafter, the reason for limitation of the technical structure of this invention is demonstrated. If the pH of the colloidal solution of silica obtained by hydrolyzing the sodium silicate contained in the water glass is less than 10.2, it is weakly alkaline. On the other hand, if it exceeds 11.4, the hydrolysis of the waterglass does not occur properly. Therefore, the pH of the colloidal solution of silica was 10.2 to 11.4.

If the amount of carbon in the mixture of the colloidal solution and the WC powder is less than 0.02% by weight, the amount of carbon is insufficient so that silica is not carbonized, which adversely affects the properties (hardness, toughness, etc.) of the alloy. On the other hand, when it exceeds 1% by weight, the carbon becomes excessive and exists in the powder as free carbon, thereby deteriorating physical properties. Therefore, the amount of carbon in the WC powder was 0.02 to 1% by weight.

If the drying temperature of the powder mixture is less than 50 ° C., not only the moisture is not sufficiently removed but also the drying time is long, whereas if the drying temperature exceeds 100 ° C., the powder is oxidized. Therefore, the drying temperature of the powder mixture was 50 to 100 ° C.

When the reaction temperature in the argon gas atmosphere of the dried powder mixture is less than 1400 ° C., the carbonization reaction of SiO ₂ to SiC does not proceed smoothly. On the other hand, when the temperature exceeds 1600 ° C., reaction between Si and WC occurs rather than the reaction of the alloy. Physical properties deteriorate. Therefore, the reaction temperature was 1400 ℃ to 1600 ℃. In addition, if the reaction time of the dried powder mixture in the argon gas group is less than 1 hour, the carbonization reaction is insufficient, whereas if it exceeds 4 hours, the WC particles are coarsened to deteriorate the properties of the alloy. Therefore, the reaction time was 1 to 4 hours.

If the coating amount of SiC is less than 0.1% by weight, the effect of the present invention is insignificant, whereas if it is more than 5% by weight, the WC and Ni interfacial reactions are adversely affected, thereby lowering the mechanical properties of the alloy. Therefore, the coating amount of SiC was 0.1 to 5 weight%.

If the addition amount of the binder metal Ni to the SiC-coated WC powder is less than 3% by weight, it does not play a sufficient role as a binder, which causes problems in mixing, and requires high sintering temperature. Become vulnerable. On the other hand, if it exceeds 30% by weight, Ni powder is agglomerated when mixed, and it is present as pores during sintering, thereby lowering the mechanical properties of the alloy. Therefore, the amount of Ni was 3 to 30% by weight.

If the pre-sintering temperature is less than 400 ℃ gas or moisture adsorbed to the molded powder is not sufficiently removed, whereas if the pre-sintering temperature is higher than 900 ℃ carbonized particles become large, adversely affect the physical properties of the alloy. Therefore, presintering temperature was 400-900 degreeC. In addition, if the preliminary sintering time is less than 30 minutes, sufficient reaction does not occur, whereas if it exceeds 4 hours, the carbonized powder may be coarsened. Therefore, the preliminary sintering time was 30 minutes to 4 hours.

If the temperature of the sintering is less than 1300 ° C, sufficient liquid phase sintering effect is not obtained because the liquid phase of Ni, a binder metal, is not produced. On the other hand, if the temperature exceeds 1600 ° C, gas is generated inside the sintered body due to oversintering, and swelling phenomenon occurs. This adversely affects the physical properties of the sintered compact. Therefore, the temperature of main sintering was 1300-1600 degreeC. In addition to the cost when the sintering atmosphere of vibration also is less than 10 ^-2 torr to get up a reaction with the sintered body and the degree of vacuum is low, the atmospheric gas is sintered under an adverse effect, on the other hand, if exceeding 10 ^-5 torr to create and maintain this degree of vacuum For many it is uneconomical. Therefore, the vacuum degree of the main sintering atmosphere was 10 ^-2 to 10 ^-5 torr.

If the time of the main sintering is less than 30 minutes, the binder metal formed in the liquid phase sufficiently flows and there is not enough time to spread evenly among the particles, so that the sintering effect is small. Physical properties deteriorate. Therefore, the time for main sintering was 30 minutes to 4 hours.

Hereinafter, a method of manufacturing the WC-Ni-based cemented carbide of the present invention will be described in detail with reference to Examples.

EXAMPLE

1) Raw material powder

a. SiC

The reason for coating SiC on WC is as follows.

① It is chemically and thermally stable at high temperature.

② When Ni is used in place of Co, SiC has good reactivity with Ni, especially wettability.

③ SiC reacts better than WC when coated, so there is no problem in thermodynamics.

WC powder

① WC uses powder whose particle size is 0.87 ~ 10㎛. If the particle size is finer than 0.87㎛, it is difficult to coat, and if coarse powder of 10㎛ or more is used, the mechanical properties are poor.

② WC powder used in the present invention is manufactured by Daeseok Jung Mining Co., Ltd.

③ The amount of WC is adjusted to 70-97% by weight.

c. Ni powder

① Ni is cheaper than conventional Co, and there is no supply and demand problem like Co, so it is very advantageous to replace the binder metal from Ni to Co.

2) cloth of powder

Sodium silicate (water glass) was used to make a colloidal solution of silica through the reactions of the following formulas (1) and (2). Sodium silicate is easy to purchase and inexpensive. Since sodium silicate is hydrolyzed with water, adding sodium silicate to an appropriate amount of water gives a colloidal solution of silica.

Scheme 1

_{NaO · 2SiO 2 + 5H 2 O} → Na + + OH - + Si (OH) 2 ... … … … … … … … … … (One)

Scheme 2

Si (OH) ₂ → SiO ₂ + H ₂ O... … … … … … … … … … … … … … … … … … … … (2)

WC powder was added to the mixture and initially stirred with ultrasonic waves to obtain a homogeneous dispersion, followed by stirring using a magneticster. The stirring time is 10 to 40 minutes, preferably 25 to 35 minutes. After 10-20 minutes of stirring, carbon was inserted and stirred. Carbon may use either activated carbon or carbon black. After the stirring was terminated, the suspension of silica and carbon mixed in the WC powder was washed with a gradient method or precipitated by a natural precipitation method, and then water was discarded.

It is then dried at 50-100 ° C. to remove moisture. The dried powder is reacted for 1 to 4 hours at 1400 ~ 1600 ° C to make SiC raw ingredients so that SiC is coated on the WC powder. At this time, the atmosphere uses argon gas atmosphere.

The chemical reaction formula is as follows.

Scheme 3

SiO ₂ (s) + 3 C (s) = SiC (s) + 2 CO (g)

Thus, after coating SiC on the WC powder, the state of the powder was analyzed by XRD, and it was found that the powder of SiC-coated state also had high oxidation by using TGA (differential weight gravimetric method or oxidation degree measuring method). The amount of water glass is only 15% after washing, so this problem should be taken into account when adding.

3) sintering of powder

As in 2), 3-30% by weight of Ni was added to the WC powder coated with SiC. If the content of Ni is less than 3% by weight, homogeneous mixing is difficult when mixing and the sintering temperature must be raised, so it is economically unsuitable. In addition, when the Ni content is 30% by weight or more, the Ni powder aggregates to facilitate formation of the binder pool, which is left as pores during sintering.

In addition, when the amount of the binder metal is 30% by weight or more, it becomes an inappropriate form as a cemented carbide. Therefore, it is preferable to add 3-30 weight% of Ni. Presintering was carried out in a hydrogen or vacuum atmosphere, and presintering in a hydrogen atmosphere was carried out between 400-900 ° C. for 30 minutes to 4 hours. For example, for degassing and removing impurities, the mixture was first reacted at 400 ° C. for 2 hours and then presintered at 900 ° C. for 30 minutes to 4 hours. In the case of using a vacuum atmosphere, it was presintered in the same manner as the hydrogen atmosphere.

The sintering was carried out at 1300 ° C to 1600 ° C for 30 minutes to 4 hours in the range of 10 ^-1 torr to 10 ^-5 torr.

When the degree of vacuum was high, the metal was evaporated, so it was carried out at 10 ⁻⁵ torr or less. In addition, the sintering temperature is about 70 ℃ higher than that of WC-Co alloy, so that WC-Ni is 30-100 ℃ higher when WC-Co and WC-Ni have the same composition. Sintered (for example, 1400 degreeC-1450 degreeC for WC-15Ni, 1425 degreeC-1500 degreeC for WC-10Ni).

After the measurement test of T.R.S, which is generally performed on cemented carbides, the fracture cross section is observed. That is, it is divided into coarse WC particles (composite carbide phase), binder metal pool, pores, and the like.

When the WC powder is coated with SiC and coated, the composite carbide phase is suppressed and the growth of coarse particles is controlled. It was confirmed that the composite carbide did not grow in the X-ray diffraction pattern. The growth of coarse particles can also be confirmed by SEM or optical microscope.

In the case of wettability between WC and Ni, which is the most problematic in the conventional WC-Ni cemented carbide, the wettability between WC and Ni is improved by coating the chemically and thermally stable SiC on the WC, thus replacing the binder metal with Co to Ni. It is possible to do Also, when the binder metal is conventionally replaced with Ni in Co, the toughness can be obtained similarly, but the hardness value is remarkably large.

However, in the present invention, this problem can be overcome by coating SiC on the WC powder, and the WC-Ni-based cemented carbide alloy can be manufactured better than the WC-Co alloy.

According to the present invention, Co, a binder metal of cemented carbide, can be replaced with Ni, and even a WC powder having a coarse particle size can be combined with the unique properties of the raw powder through the complexing and encapsulation of the powder and the powder itself. Gives high functionality to

4) Experiment to confirm the effect of the present invention

a. Comparison of WC-Ni and WC-SiC-Ni Composite Carbide Phases and Inhibition Methods A colloidal solution of silica with a pH of 11.1 was obtained by adding hydrolysis to 9.77 g of water glass in 100 ml of distilled water. 100 g of 2.39 µm WC powder was added thereto and stirred for 15 minutes, followed by addition of 0.19 g of carbon black, followed by stirring for 30 minutes.

After leaving the powder compound to stand still, the water went away. In this powder mixture dryer, it dried at the temperature of about 80 degreeC, and water was removed. The dried powder mixture was reacted in an argon gas atmosphere at 1500 ° C. for 3 hours to cover 3% by weight of SiC, and then 15% by weight of Ni, a binder metal, was added to WC-3SiC-15Ni (3% by weight of WC powder). 15% by weight of Ni coated with SiC) to obtain a powder mixture of the present invention, which was pre-sintered in a hydrogen atmosphere at 400 ° C. for 2 hours and at 900 ° C. for 30 minutes at 10 ⁻⁴ torr. The sintered compact (carbide alloy) of this invention was obtained by carrying out main sintering for 2 hours at the atmospheric cloud temperature of 1500 degreeC. In addition, a WC-15Ni powder mixture not coated with SiC was also prepared and reacted at 1450 ° C. for 3 hours to obtain a sintered body.

Here, the reason of the sintering treatment with the relatively high sintering temperature and the long sintering time is Ni ₂ W ₂ C (known as the composite carbide phase in the WC-Ni cemented carbide) To facilitate the generation of phase). this The phase is a weak phase caused by lack of carbon in the sintered body. The phase increases the hardness, but the toughness decreases. If the cross section is examined when fractured, it can be seen that the crack originates in this part.

Two specimens of WC-15Ni and WC-3SiC-15Ni of the present invention were analyzed by X-ray and the phase change was examined. It was confirmed that a compact sintered body can be obtained compared to 15Ni. The composite carbide phase is also suppressed when a WC-SiC-Ni alloy is produced by coating SiC on a WC powder having a particle size different from the above-mentioned WC powder. This is the result obtained by observing with X-ray.

Regarding the inhibitory effect of the composite carbide, it was confirmed that the formation of the composite carbide phase was suppressed by coating SiC on the WC. It was confirmed that SiC was excellent in reactivity with Ni, and especially wettability. In addition, since abnormal grain growth acts as a source of defects in fracture, it can be seen that the suppression of the formation of the composite carbide phase increases the toughness and improves the mechanical properties.

b. Microstructure observation (suppression of coarse particle growth)

In order to observe the structure after sintering, it was observed using an optical microscope or a scanning electron microscope. In order to observe the coating treatment effect of SiC on WC, WC-Ni alloy and WC-SiC-Ni alloy were compared and observed.

The particle size was measured using an image analyzer (phase analyzer). In the case of the conventional WC-Ni alloy, it was observed that coarse particles grow much, and uniform in the sintered body sintered using a powder coated with SiC on the WC powder (hereinafter referred to as WC-SiC-Ni). Particle growth was observed and no coarse particles were observed. Since this was different depending on the amount (wt%) of added SiC, the amount of SiC added was suitably in the range of 0.1 to 5 wt%.

In order to measure the exact particle size, the particle size of the WC-SiC-Ni alloy and the conventional WC-Ni alloy was measured using an image analyzer. These alloys and powder mixtures of the same composition were sintered at 1425 ° C. for 1 hour, and the microstructures were measured with a phase analyzer.

As a result, in the case of WC-Ni alloy, the raw material powder was 3.94 mu m and the particle size after sintering was 4.38 mu m. However, WC-1SiC-15Ni (1% SiC coated on the WC powder) was 4.29 µm.

Therefore, it can be seen that WC-1SiC-Ni has an effect of suppressing grain growth. In addition, the grain size and area of the WC-20Ni alloy and WC-1SiC-20Ni alloy were sintered at 1400 ° C. for 1 hour. The WC-20Ni alloy was 17.11 μm 2 and the WC-1SiC-20Ni alloy was 15.57 μm 2. In the case of the WC-20Ni alloy, the particle size ranged from 1.48 µm to 27.29 µm, whereas the WC-1SiC-20Ni alloy ranged from 2.16 µm to 14.89 µm.

In other words, the WC-20Ni alloy has a wide particle size distribution, but the WC-1SiC-20Ni alloy has a narrow particle size distribution. This shows that the growth of the particles was suppressed. This experimental value was analyzed using an image analyzer.

c. Comparison of Pore between WC-Ni Alloy and WC-SiC-Ni Alloy

Conventional WC-Ni-based cemented carbide is inferior in formability and sinterability to WC-Co. This is because the sintering temperature of the WC-Ni cemented carbide is about 70 ° C higher than that of WC-Co. Therefore, side reactions can easily occur. In addition, when the particle size is large, more pores are generated. This is a problem in the reaction and this problem is solved by coating SiC on the WC powder.

The WC powders were coated with WC powders of 6.46 μm and 2.39 μm with SiC amounts of 0 to 2% by weight. The coated powder was added with 10% by weight and 15% by weight of Ni, respectively, to form a powder mixture of WC-SiC-10Ni and WC-SiC-15Ni.

Pre-sintering was performed for 2 hours at 400 ° C. and 30 minutes at 900 ° C. in a furnace in a hydrogen atmosphere, and sintered for 1 hour at 1475 ° C. and 1425 ° C., respectively, in a furnace in a vacuum atmosphere. In order to observe the pore was observed 50 times using an optical microscope.

SiC was coated with 6.46 μm WC powder by 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, and 2%, respectively, to observe the pores of the WC-SiC-Ni alloy. . Large and many pores were observed in the WC-Ni alloy without SiC coating, but the pores decreased with increasing the amount of SiC coating, and a dense sintered compact having almost no pores was obtained at 1%. When more than 1.2%, the pores again existed little by little.

WC-SiC-Ni alloys coated with SiC by 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.5% and 2%, respectively, were used with a 2.39㎛ WC powder. In the case of 0.6%, a dense sintered compact having almost no pores was obtained.

As described above, the amount of pores was not related to the amount of binder metal added, and the pore amount was changed depending on the particle size of the starting material, WC powder.

d. Particle Size and Shape Comparison between WC-Ni and WC-SiC-Ni

The size of grain growth was measured by sintering the WC-Ni-based and WC-SiC-Ni-based specimens. After sintering, the specimens were first polished 100, 200, 300, 400, 600, 800, 1000, 1200 times with specimen SiC polishing cloth, and polished in the order of 4㎛, 1㎛, / ㎛ using diamond paste. .

Corrosion is not required for pore observation, but for tissue observation, the specimen is kept in FeCl ₂ for 10 seconds and corroded for 2-5 minutes in Murakami solution (component: K ₃ Fe (CN) ₆ 10g and NaOHg in distilled water). I was.

Observing the shape of the particles in the WC-SiC-Ni alloy structure and the WC-Ni alloy structure, it can be seen that the shape is different. In the sintered structure of WC-Ni, the carbide phase, which is a typical form of WC-Co cemented carbide, shows a triangular template. That is, the corners are angled. It is estimated that the grain growth during sintering has triangular particles because the base surface grows.

However, in the case of WC-SiC-Ni-based alloy sintered by coating SiC on the WC powder, grain growth is suppressed by the SiC coating on the WC powder, and the grain shape is angular and the octagonal shape (nearly spherical). ), Indicating that grain growth was suppressed.

Apart from the phenomenological considerations, the particle size of the WC-1SiC-10Ni alloy and WC-10Ni alloy was analyzed using an image analyzer. WC-10Ni alloys were in the range of 2.01 ~ 31.45㎛ and WC-1SiC-10Ni alloys were in the range of 2.62 ~ 18㎛.

The average particle size of SiC-coated WC-SiC-Ni-based alloys showed uniform values and was suppressed to about 0.5 μm compared to the uncoated WC-Ni-based alloys. As a result of the particle size measurement, in the case of WC-15Ni, the range of particle size distribution ranged from 1.29 μm to 16.12 μm and the range of particle size of WC-1SiC-15Ni ranged from 1.99 μm to 12.31 μm. This indicates that the effect of the SiC coating on the average particle size was about 1.3 μm.

e. Hardness of Sintered Product

In the production of WC-Co-based cemented carbide, which is widely used commercially, there is also a method of obtaining complete densities by removing residual pores by hot isotropic pressing (HIP). Specimens were prepared according to the present invention and Vickers hardness was measured to compare the effect of coating and SiC of SiC.

Comparative Example 1 is cited in a catalog of Toshiba Dangaloy, Japan. This is intended to be compared directly with what is actually available on the market, Comparative Example 2 is not coated with SiC, the present invention is coated with SiC.

In the present invention, when the particle size was 2.39 μm, the coating amount of SiC was adjusted to 0.6 μm, and when the particle size was 6.46 μm, the SiC was coated by 1 wt%.

TABLE 1

In the present invention, in order to improve the hardness value, which was a problem when replacing the binder metal from Co to Ni in the WC-Co cemented carbide, SiC was coated on the WC powder to prepare a cemented carbide which was superior to the conventional WC-Ni cemented carbide. A cemented carbide that is superior to the Co-based cemented carbide can be obtained and is equivalent to or better than that of the sintering agent subjected to hot isostatic pressure treatment.

Claims (2)

WC-Ni-based cemented carbide, characterized in that consisting of 0.1 to 5% by weight of the coated WC powder: 70 to 97% by weight and Ni: 3 to 30% by weight. Sodium silicate was hydrolyzed to form a SiC layer on the surface of the WC powder to obtain a colloidal solution of silica having a pH of 10.2 to 11.4. The WC powder was added to the colloidal solution and stirred, and carbon was 0.02 to 1 weight based on the WC powder. After adding and stirring in an amount of%, the mixture was dried at a temperature of 50 to 100 ° C. to remove moisture to obtain a powder mixture, and the powder mixture was reacted in an argon gas atmosphere at a temperature of 1400 ° C. to 1600 ° C. for 1 to 4 hours. Thus, to obtain a WC powder coated with 0.1 to 5% by weight of SiC on the WC powder, the SiC coated WC powder: 70 to 97% by weight and Ni: 3 to 30% by weight were mixed at a temperature of 400 to 900 ° C. Presintering in a vacuum or hydrogen atmosphere for 30 minutes to 4 hours, and the presintered body thus obtained is main sintered at 1300 to 1600 ° C and 10 ^-2 torr to 10 ^-5 torr for 30 minutes to 4 hours. WC-Ni-based cemented carbide production method, characterized in that consisting of.