WO2010119795A1 - Cemented carbide - Google Patents

Abstract

Disclosed is a cemented carbide which has high hardness, excellent strength and excellent toughness. The cemented carbide has a hard phase that is mainly composed of WC particles and a binder phase that is mainly composed of CoxWyCz, and contains 0.2-0.9% by mass of Co and 0.2-1.5% by mass of Cr with the balance made up of a binary compound of W and C and impurities. The average particle size of WC particles is not less than 0.2 µm but not more than 0.7 µm, and the standard deviation s of the particle size of WC particles satisfies s = 0.25. By containing Co in an amount within the above-specified range, the toughness is improved. In addition, by containing Co in an amount within the above-specified range, sinterability is improved, thereby enabling a lower sintering temperature. By containing Cr, growth of WC particles is effectively suppressed, thereby providing a cemented carbide in which fine WC particles having a uniform particle size are present. Since Cr is present as a metal component, decrease in the strength due to the presence of Cr carbide can be suppressed.

Description

Cemented carbide

The present invention relates to a cemented carbide. In particular, the present invention relates to a cemented carbide excellent in toughness and strength while having high hardness.

WC (tungsten carbide) and Co (cobalt) were mixed and then sintered as a component material for components such as nozzles for high-pressure water flow processing (water jet processing), molds for glass lenses used in cameras, etc. Cemented carbide is used (for example, Patent Documents 1 to 3).

In the member such as the nozzle for high pressure water flow processing, it is particularly desired that the member has excellent wear resistance. In order to improve the wear resistance, it is effective to increase the hardness. Methods for increasing the hardness include reducing the Co content, which is lower than that of WC, or making WC fine. To make WC finer, as described in Patent Documents 1 to 3, against grain growth of Cr (chromium) carbides such as VC (vanadium carbide), Mo ₂ C (molybdenum carbide), Cr ₃ C ₂ And adding a metal carbide having an inhibitory effect.

Japanese Patent Laid-Open No. 05-230588 JP 09-025535 Japanese Patent Laid-Open No. 04-348873

Recently, as a constituent material for the nozzles and dies, it is a hard metal with a high balance of wear resistance and fracture resistance (chipping resistance) as a result of its high hardness and excellent toughness and strength. Is desired. However, it cannot be said that conventional cemented carbide has sufficient hardness and high toughness and high strength in a well-balanced manner.

As described in Patent Documents 1 to 3, when a metal carbide having an effect of suppressing grain growth is added as a raw material for the refinement of WC in the cemented carbide, the metal carbide is added to the obtained cemented carbide. Remains or reprecipitates, leading to a decrease in strength. In addition, if the metal carbide itself of the raw material is coarse, it is difficult to uniformly mix it with the WC powder of the raw material, resulting in variations in the effect of suppressing WC grain growth. As a result, there is a possibility that WC grown and coarsened in the cemented carbide alloy or coarse metal carbide tends to exist in the cemented carbide alloy. In order to sufficiently mix the WC powder of the raw material and the metal carbide, if the mixing time of the raw material is lengthened, the WC powder is excessively pulverized, and WC grows easily due to Ostwald growth during sintering. There is a risk of becoming a cemented carbide with WC present. The presence of locally coarse WC causes a decrease in strength.

Also, it is desired that the lens mold has a high surface quality only by forming with a mold in addition to being excellent in wear resistance. That is, there is a demand for a mold that can form a lens that is excellent in surface properties to such an extent that it can be used as it is without being subjected to a separate polishing process or the like. In order to meet such a demand, it is desired that WC in the cemented carbide constituting the mold is fine and homogeneous.

In the hard alloy described in Patent Document 1, W ₂ C is present. Since W ₂ C grows more easily than WC, coarse W ₂ C may be present in the cemented carbide. If coarse particles are present in the cemented carbide, the strength and toughness are lowered, and the surface quality is lowered.

The sintered hard material described in Patent Document 2 has low strength and toughness because it adds very low amount of Co for the purpose of increasing hardness. In addition, since there is too little Co, W ₂ C is likely to be precipitated and it is difficult to sinter, so it is necessary to sinter at a very high temperature of 1700 ° C. or higher for densification. Since sintering is performed at such a high temperature, the precipitated W ₂ C tends to grow. Therefore, even if metal carbide is added as described above, there is a limit to the effect of suppressing grain growth. If coarse W ₂ C is present in the cemented carbide, strength, toughness and surface quality are deteriorated. Therefore, this sintered hard material cannot achieve both high hardness, high toughness, and high strength.

The sintered body described in Patent Document 3 is intended to improve abrasive wear resistance, and has high hardness but low strength and toughness. In particular, the bending strength is low in a sintered body with little Co addition. Patent Document 3 only proposes to reduce the average particle size of WC, and does not discuss control of the particle size distribution. If the WC particle size variation in the sintered body is large, the Co thickness in the sintered body becomes non-uniform (locally thickens or thins), causing uneven wear and fractures. . In addition, when double carbides (dissimilar metal carbides) used as raw materials to precipitate grain growth are precipitated, the double carbides have poor wettability with a binder phase such as Co, leading to a decrease in strength. In addition, the deposited double carbide falls off, so that the wear easily proceeds. Therefore, this sintered body cannot achieve both high hardness, high toughness, and high strength.

Therefore, an object of the present invention is to provide a cemented carbide having a good balance of high hardness, high toughness, and high strength.

The inventors of the present invention have a specific composition and devise a raw material adjustment and manufacturing method, so that it has high hardness and excellent wear resistance, and has high toughness, high strength and excellent fracture resistance. I got the knowledge that The present invention is based on the above findings.

The cemented carbide of the present invention contains Co and Cr, and the balance is composed of a binary compound of W and C and impurities. The Co is contained in an amount of 0.2% by mass to 0.9% by mass with respect to the cemented carbide. Co exists in the state of Co _x W _y C _z . The Cr is contained in an amount of 0.2% by mass to 1.5% by mass with respect to the cemented carbide. The binary compound of W and C is mainly WC, the average grain size of WC in the cemented carbide is 0.2 μm or more and 0.7 μm or less, and the standard deviation σ of the grain size of WC satisfies σ ≦ 0.25. .

The cemented carbide of the present invention has a high hardness compared to metal Co (Co _x W _y C _z ) as the main binder phase and fine WC, so that it has high hardness and excellent wear resistance. In particular, the cemented carbide according to the present invention can effectively reduce the grain growth of WC to contain fine WC by containing Cr, thereby improving the hardness and improving the strength due to the presence of coarse WC. Reduction can be suppressed. Further, the cemented carbide of the present invention is easily sintered because it contains a Co component to such an extent that the periphery of WC can be sufficiently covered by the binder phase (mainly Co _x W _y C _z ). Therefore, in manufacturing the cemented carbide of the present invention, compared with Patent Documents 2 and 3, the sintering temperature can be lowered, so that local grain growth such as WC is suppressed, and the cemented carbide is incorporated in the cemented carbide. Coarse WC is difficult to exist. Furthermore, Cr in the cemented carbide of the present invention is present mainly as a metal component and hardly exists in the state of a compound such as carbide. For this reason, in the cemented carbide of the present invention, the strength of the metal carbide may be substantially reduced due to the metal carbide remaining or reprecipitating as in the case of using the metal carbide as a raw material in order to suppress grain growth. Absent. In addition, the cemented carbide of the present invention contains a Co component in the above specific range, so that an extreme decrease in toughness and strength like a cemented carbide with too little Co can be reduced, and the strength and toughness are also high. In addition, since the binder phase (mainly Co _x W _y C _z ) exists so as to cover the periphery of the fine and uniform WC as described above, the thickness of the binder phase is also uniform. Alloys are less prone to uneven wear and chipping, and are excellent in wear resistance and chipping resistance.

As described above, the cemented carbide of the present invention has a high balance of high hardness, high toughness, and high strength, and is excellent in both wear resistance and fracture resistance. In addition, the cemented carbide of the present invention, which has a low Co composition and Co exists in the state of Co _x W _y C _z , has a low decrease in hardness not only at room temperature but also at a high temperature, for example, 500 ° C. to 800 ° C. High hardness and excellent wear resistance in a wide range from room temperature to high temperature. Therefore, the cemented carbide of the present invention can be suitably used as a constituent material of, for example, a member that is desired to have excellent wear resistance, for example, a nozzle for high pressure water flow processing. The cemented carbide of the present invention has a fine and uniform WC and a uniform thickness of the binder phase (mainly Co _x W _y C _z ). That is, the cemented carbide of the present invention has a uniform structure and a relatively small amount of Co component. Therefore, in addition to wear resistance, a member that requires good finished surface quality such as mirror finish, such as a glass lens mold It can utilize suitably also for these constituent materials. And since the cemented carbide of the present invention has high toughness and high strength, even if grinding, wire machining, electric discharge machining, or the like is performed when manufacturing the nozzle or mold, etc., it accompanies these machining. Processing cracks and chipping can be reduced. Therefore, members such as the nozzle can be manufactured with high productivity. In addition, since the cemented carbide of the present invention has high strength and high toughness as described above, cracks and chipping hardly occur during use of the above-mentioned various members, and excellent fracture resistance. Hereinafter, the present invention will be described in detail.

<Cemented carbide>
"composition"
In the cemented carbide of the present invention, the hard phase is mainly composed of WC particles. Further, it is a WC—Co _x W _y C _z based cemented carbide whose binder phase is mainly composed of a Co compound (Co _x W _y C _z ). The balance excluding Co _x W _y C _z and Cr described later is composed of a binary compound of W and C and unavoidable impurities. Further, when V described later is included, the remainder excluding Co _x W _y C _z , Cr and V is composed of a binary compound of W and C and unavoidable impurities. Examples of binary compounds of W and C include WC and W ₂ C.

[Co]
Co in the cemented carbide of the present invention exists in a state of a compound of Co and W called Co _x W _y C _z . As a result of analyzing the cemented carbide of the present invention by X-ray diffraction in the examples described below, the peak waveform of the component containing Co is obtained as a peak waveform of Co _x W _y C _z , and the peak waveform of metal Co depends on the detection limit. It was not obtained. Furthermore, if the Co _x W _y C _z Cr and V in is dissolved, Co _x W _y C _z peak waveform peak position is slightly deviated from the peak waveform of can be obtained. Therefore, when the cemented carbide is analyzed by X-ray diffraction, even if the peak waveform of Co _x W _y C _z is slightly shifted due to solid solution of Cr or V, the cemented carbide that cannot obtain the peak waveform of metal Co. Alloys are understood to be included within the scope of the present invention. According to the manufacturing method described later, substantially all of Co in the cemented carbide is present as Co _x W _y C _z and no metal Co is present (the peak waveform by X-ray diffraction of metal Co is obtained due to the detection limit. Can not be made). x, y, and z all take positive values and satisfy x + y> z.

The cemented carbide of the present invention can sufficiently generate Co _x W _y C _z by containing Co in an amount of 0.2% by mass or more with respect to the cemented carbide, can cover the periphery of WC, and is easily sintered. . Therefore, in producing the cemented carbide of the present invention, even if the sintering temperature is the same as that of ordinary cemented carbide, for example, under the same sintering conditions as that of ordinary reduced pressure sintering, a dense cemented carbide is obtained. It can be an alloy. When Co is less than 0.2% by mass, Co _x W _y C _z does not sufficiently cover the periphery of WC and is difficult to sinter, so the sintering temperature needs to be increased. By increasing the sintering temperature, grain growth of WC is promoted during sintering, and coarse WC is generated. In addition, the strength is reduced due to the presence of coarse particles. Moreover, when there is too little Co, toughness (for example, fracture toughness) will also fall extremely. The more Co, the better the toughness and the effect of being easily sintered, but if it exceeds 0.9% by mass, the WC grain growth is likely to occur, so the hardness (hardness from room temperature to high temperature) decreases, especially , The decrease in hardness at 600 ° C or higher is remarkable. In addition, the grain growth of WC also reduces the uniformity of the structure of the cemented carbide, resulting in a decrease in strength. By setting the Co content to 0.2 mass% or more and 0.9 mass% or less, Ostwald growth of WC due to an increase in the sintering temperature can be suppressed. As a result, the generation of coarse WC in the cemented carbide can be reduced, and a WC—Co _x W _y C _z based cemented carbide with a fine and uniform WC grain size can be obtained. In addition, the cemented carbide of the present invention has a fine structure and thus has excellent surface properties. In particular, by reducing the amount of Co component and making its presence state Co _x W _y C _z , even when used at high temperatures, Co is difficult to elute from the surface of the cemented carbide, and cemented carbide The mirror state of the surface of can be maintained for a long time. The Co content is more preferably 0.2% by mass or more and 0.6% by mass or less.

[Cr]
By containing 0.2% by mass or more of Cr with respect to the cemented carbide, the grain growth of WC is effectively suppressed, the generation of coarse WC is reduced, and fine and uniform size WC exists uniformly. The cemented carbide can be manufactured stably. Moreover, the oxidation resistance of a cemented carbide can be improved by containing Cr. As the amount of Cr increases, the effect of suppressing grain growth is enhanced. However, when there is too much Cr, it becomes easy to precipitate as Cr carbide, which causes a decrease in strength due to the presence of Cr carbide. Therefore, the cemented carbide of the present invention has a Cr content of 0.2 mass% or more and 1.5 mass% or less. A more preferable Cr content is 0.2 mass% or more and 0.9 mass% or less.

In addition to Cr, the cemented carbide of the present invention may further contain V. V, like Cr, has a high inhibitory effect on WC grain growth. By containing both Cr and V, the grain growth of WC can be more effectively suppressed. If the content of V is too large, the wettability between WC and W ₂ C and Co _x W _y C _z is deteriorated and it is difficult to sinter. For this reason, the strength of the cemented carbide decreases, or it becomes easy to precipitate as V carbide, which causes a decrease in strength due to the presence of V carbide. Therefore, the content of V is preferably 0.2% by mass or less (including 0% by mass) with respect to the cemented carbide.

It is preferable that substantially all of the Cr and the V are dissolved as a metal component in Co _x W _{y Cz} or WC. As a result of analyzing the cemented carbide of the present invention by X-ray diffraction in Examples to be described later, the peak waveform of Cr carbide and the peak waveform of V carbide are in a range that cannot be obtained due to the detection limit. From this, it is considered that Cr and V in the cemented carbide are dissolved in Co _x W _y C _z and WC. Accordingly, when a cemented carbide is analyzed by X-ray diffraction, a cemented carbide having a peak waveform deviated from the peak waveform of pure Co _x W _y C _z is interpreted as being included in the scope of the present invention. According to the manufacturing method to be described later, substantially all of Cr and V in the cemented carbide exist as a metal component dissolved in Co _x W _y C _z or WC, Cr and V simple metal, and It is possible to manufacture a cemented carbide that does not contain Cr carbide or V carbide (the peak waveform of X-ray diffraction of Cr carbide or V carbide cannot be obtained due to the detection limit).

[Binary compound of W and C]
In the cemented carbide of the present invention, the balance excluding Co _x W _y C _z , Cr, (V) is composed of a binary compound of W and C and inevitable impurities. Among the binary compounds of W and C, in particular, the content of WC is 97% by mass or more with respect to the cemented carbide. This WC exists in a granular form in the cemented carbide and functions as a hard phase. In particular, WC is fine and has a uniform size. Specifically, the average particle size of WC is 0.2 μm or more and 0.7 μm or less, and the standard deviation σ of the particle size is 0.25 or less. When the average particle size satisfies the above range and the standard deviation satisfies the above range, the hardness can be increased by fine WC, and the decrease in strength can be reduced by reducing the amount of coarse WC. If the average particle size is too small, such as less than 0.2 μm, cracks are likely to develop and the toughness is reduced, and if the average particle size is more than 0.7 μm, the hardness is reduced. A more preferable average particle size is 0.2 μm or more and 0.4 μm or less. The standard deviation σ is preferably small, and no lower limit is particularly set.

It is preferable that there is little coarse WC in the cemented carbide. Specifically, when the area ratio of WC having a particle size (particle diameter) of 1.0 μm or more is 5% or less with respect to the cemented carbide, the strength is reduced due to the presence of coarse WC as described above. Suppressing, it can become a high strength cemented carbide. The area ratio of the coarse WC is preferably smaller, and more preferably 4% or less.

Most of the W and C present in the cemented carbide is present in WC, and it is preferable that W ₂ C is small. As described above, since W ₂ C grows more easily than WC, it can be a cemented carbide containing coarse particles. Specifically, the volume ratio preferably satisfies W ₂ C / (WC + W ₂ C) ≦ 0.005 or less. The volume ratio of W ₂ C is preferably small and is not present, that is, it is desirable that the binary compound of W and C is only WC.

The average particle size of WC, the standard deviation of the particle size, and the area ratio of coarse WC can be obtained by using, for example, the EBSD method. The volume ratio of W ₂ C can be obtained by using X-ray diffraction. Details of these measurement methods will be described later.

[Characteristic]
The cemented carbide of the present invention has high hardness, high toughness, and high strength. Specifically, it is preferable that the HRA hardness is 94 to 96, the fracture toughness is 4 MPa · m ^1/2 or more, and the bending strength is 1 GPa or more. With HRA hardness of 94 or more, it has excellent wear resistance. When the HRA hardness is 96 or less, a decrease in toughness due to excessively high hardness can be reduced. In addition, since fracture toughness is 4 MPa · m ^1/2 or more and bending strength is 1 GPa or more, cracks and chipping during processing can be effectively suppressed and high hardness can be achieved in the production of various parts. In addition, it is possible to provide a member having excellent performance inherent in cemented carbide having high toughness and high strength.

<Manufacturing method>
Cemented carbide is generally manufactured by the process of raw material preparation-mixing and grinding of raw materials-drying-forming-sintering. The cemented carbide of the present invention is further subjected to HIP (hot isostatic pressing) after the above-mentioned sintering, as well as using specific raw materials and mixing / pulverizing under specific conditions.

[Raw material WC]
As the raw material WC powder, it is preferable to use a fine one so that the WC in the cemented carbide is likely to be in a fine state. Specifically, WC powder having an average particle size of 0.1 μm to 0.5 μm is preferable. Even if it is less than 0.1 μm or more than 0.5 μm, a cemented carbide having grain growth and coarse WC is easily formed.

Especially, if the raw material WC powder contains Cr, it is difficult to produce Cr carbide in the cemented carbide. When manufacturing a cemented carbide containing Cr and V, if WC powder containing Cr and V is used as a raw material, Cr carbide and V carbide are hardly generated in the cemented carbide. When the present inventors use Cr carbide or V carbide powder, metal Cr or metal V powder as a raw material, Cr carbide or V carbide remains, precipitates, or reprecipitates, resulting in a decrease in strength. , And got the knowledge. On the other hand, when the WC powder itself contains Cr and V, Cr carbide and V carbide are hardly precipitated or are not substantially formed, and Cr and V are uniformly present throughout the raw material (dispersion). Can). Therefore, knowledge that WC grain growth during sintering is uniformly suppressed throughout the entire cemented carbide, and that a cemented carbide with a structure in which fine and uniform WC exists uniformly can be manufactured stably. Got. In addition, it has been found that the cemented carbide in which WC powder itself contains Cr and V and thus Cr and V are dissolved in WC can be easily obtained. Furthermore, it becomes possible to avoid the difficulty of sintering by not using a compound such as VC which is difficult to be sintered as a raw material. Based on these findings, we propose to use WC powder containing Cr and V. Note that the content of Cr and V added in the raw material WC powder is substantially equal to the content in the cemented carbide.

[Raw material Co]
As the raw material Co powder, it is preferable to use a fine powder of the same level as the WC powder so that it can be uniformly mixed with the fine WC powder. Specifically, Co powder having an average particle size of 0.2 μm or more and 0.6 μm or less is preferable. If it is less than 0.2 μm, Co will be re-agglomerated because it is too small, and Co will not be uniformly dispersed, making it difficult to sinter and increasing the sintering temperature due to difficulty in sintering. This promotes WC grain growth and makes it difficult to obtain a uniform particle size distribution. If it exceeds 0.6 μm, it is difficult to uniformly mix with the fine WC powder, and as described above, it becomes difficult to sinter due to the non-uniform presence of Co and causes a non-uniform particle size distribution.

[Raw material carbon]
In addition to the above-described Cr and V-containing WC powder and Co powder, the total amount of carbon (C) in the cemented carbide is adjusted by adding carbon powder as appropriate. By adjusting the total amount of carbon in the cemented carbide and manufacturing under the manufacturing conditions described later, substantially all of the Co powder can be made Co _x W _y C _z and the obtained cemented carbide Carbon in the alloy _tends to exist as WC, Co _x W _y C _z . When the total amount of carbon in the cemented carbide is too large, metal Co tends to exist. In addition, when the total amount of carbon in the cemented carbide is too large, the strength is lowered due to the presence of free carbon in the cemented carbide or precipitation of Cr carbide.

[Mixing / Crushing]
The above-mentioned raw material powder is prepared, and mixed and pulverized by a pulverizing / dispersing machine having rotating blades such as an attritor, a ball mill, and a bead mill. The mixing and grinding time is preferably 10 hours or more and 20 hours or less. In particular, the initial process from the start of mixing / pulverization to 5 hours is performed at high speed rotation (25 rpm or more), and the subsequent mixing / pulverization (hereinafter referred to as post-process) is performed at low speed (less than 25 rpm). It is preferable. In the initial step, the mixing and pulverization is generally completed, and in the subsequent step, dispersion is mainly performed. Thus, it is easy to achieve uniform mixing and dispersion by making the mixing and pulverization process multistage. If the entire mixing and pulverization process is performed at high speed, Co agglomerates, the dispersion state becomes poor, and WC tends to grow, resulting in a non-uniform structure. On the other hand, if the mixing and pulverization process is performed at a low speed, the pulverization and mixing are insufficient and the structure becomes non-uniform.

For the drying, molding, sintering, etc., conditions comparable to general conditions can be used. For example, the sintering conditions include sintering at a sintering temperature of 1450 to 1550 ° C. (vacuum sintering, Ar atmosphere sintering, CO atmosphere sintering, etc.). The cemented carbide of the present invention is blended in the above composition using fine WC powder and Co powder as raw materials as described above, and further mixed and pulverized under specific conditions as described above and dispersed appropriately. Yes. Therefore, since Co _x W _y C _z can sufficiently cover the WC, the sintering temperature can be made relatively low as described above. Since the sintering temperature is low, the grain growth of WC (W ₂ C) can be suppressed.

In manufacturing the cemented carbide of the present invention, HIP is performed after the sintering. Here, in general, a cemented carbide with a relatively small amount of Co does not sufficiently wrap around Co, so it is sintered at a high temperature to facilitate sintering (Patent Document 2: 1700 ° C or higher, patent (Reference 3: 1600 ° C or higher). On the other hand, in the manufacture of the cemented carbide of the present invention, as described above, the cemented carbide can be sufficiently sintered even at a low temperature, and a cemented carbide having a uniform structure can be obtained. Also, by performing HIP after sintering, the fine nests (pores) remaining in the sintered cemented carbide can be eliminated, and a dense cemented carbide can be obtained. In particular, by making the sintering temperature relatively low as described above, it is easy to manufacture a cemented carbide alloy having a uniform structure.

As described above, not using metal carbide to suppress grain growth, but using WC powder itself containing Cr and V, optimizing the Co content, and using fine Co powder And by manufacturing on the said manufacturing conditions, WC in a cemented carbide alloy can be made into fine and uniform particle size distribution, and the fall of the intensity | strength by presence of a coarse particle can be suppressed. Further, as described above, Co in the cemented carbide can be present as Co _x W _y C _z .

Since the cemented carbide of the present invention has a balance of high hardness, high toughness, and high strength, it is possible to achieve both excellent wear resistance and excellent fracture resistance.

It is a mapping image of sample No. 2 observed using the EBSD method. 4 is a graph showing the particle size distribution of WC in a cemented carbide of sample No. 2. It is a mapping image of sample No. 106 observed using the EBSD method. 4 is a graph showing the particle size distribution of WC in a cemented carbide of Sample No. 106.

(Test example)
Various raw material powders were prepared to prepare cemented carbide, and the composition, structure and mechanical properties of the obtained cemented carbide were examined. Moreover, a nozzle for high-pressure water flow processing was produced from this cemented carbide, and the life of the nozzle was examined.

[Sample Nos. 1-5]
As raw materials, WC powder having an average particle size of 0.5 μm, Co powder having an average particle size of 0.2 μm and 0.6 μm, and carbon powder were prepared. A WC powder containing 0.2 to 1.5 mass% Cr or 0.2 to 1.5 mass% Cr and 0.2 mass% V was prepared as the WC powder. The amount of Co powder added was adjusted so that the Co content was 0.2 to 0.9 mass% with respect to the total mass of the WC powder, Co powder, and carbon powder containing Cr and V. Furthermore, the amount of carbon powder added is adjusted so that the carbon content is plus 0.05% by mass or more and less than 0.1% by mass with respect to the theoretical carbon content of the cemented carbide of each composition to be manufactured, and the balance is WC powder. It was. Any of these raw material powders can be used commercially. Sample Nos. 1 and 2 used Co powder with an average particle size of 0.2 μm, and Samples Nos. 3 to 5 used Co powder with an average particle size of 0.6 μm.

The powdery paraffin (1% by mass with respect to the raw material powder) was added to the raw material powder, and mixing and pulverization were performed using an attritor or a ball mill as a pulverizing and dispersing machine. Both the attritor and the ball mill used cemented carbide balls with a diameter of 5 mm for the media. Table 1 shows the types of pulverizing and dispersing machines used, and the mixing and pulverizing time. In particular, in Sample Nos. 1 to 5, 5 hours from the start of mixing and pulverization were performed at high speed (25 r.p.m. or more), and the remaining time after 5 hours was performed at low speed (5 r.p.m.).

After the above mixing and pulverization, the raw material powder was granulated into granules using a granulation dryer and then dried. A predetermined amount of the obtained granulated powder is put into a rubber mold and subjected to isostatic pressing, and then the outer periphery of the obtained press body is machined to obtain a round bar having a diameter of 8 mm × length L: 80 mm. A material was prepared. The obtained round bar was placed in a sintering furnace, sintered by holding it in a vacuum at 1450 ° C. to 1550 ° C. for 1 hour, cooled from the above heating temperature, and then taken out from the sintering furnace. The obtained sintered body was subjected to HIP in an Ar atmosphere at 1320 ° C. and 1000 atmospheres (about 101 MPa) to obtain a cemented carbide.

The obtained cemented carbide is subjected to grinding and electric discharge machining, forming an outer peripheral shape, forming a tapered portion where water is introduced, and a through-hole extending in the longitudinal direction in the center of the cemented carbide ( A nozzle for high-pressure water flow processing was manufactured.

[Sample Nos. 101-106]
For comparison, samples using Cr ₃ C ₂ , VC, and Mo ₂ C as raw materials and samples not using Cr ₃ C ₂ , VC, and Mo ₂ C were prepared. Specifically, as a raw material, WC powder having an average particle size of 0.7 μm (containing no Cr or V), Co powder, Mo ₂ C powder, VC powder, Cr ₃ C ₂ powder (all average particle size: 0.7 ˜1.5 μm), and carbon powder were prepared. Adjust the amount of these raw material powders as appropriate, and go through the steps of mixing, crushing, granulation, drying, isostatic pressing, round bar material production, sintering, and HIP, as with sample Nos. 1-5. A cemented carbide was obtained. Samples Nos. 101 to 106 were mixed and pulverized at high speed (over 25 rpm) over the entire mixing and pulverization time. The sintering conditions and HIP conditions were the same as those of Sample Nos. 1 to 5 did. The obtained cemented carbide was processed in the same way as Sample Nos. 1 to 5, and a nozzle for high-pressure water flow processing was manufactured.

[Composition and structure]
Each cemented carbide obtained was subjected to ICP (inductively-coupled plasma) spectroscopic analysis and X-ray diffraction to examine the composition and structure. The results are shown in Table 1. The Co content of all the samples, the Cr and V contents in the sample Nos. 1 to 5, and the Cr, V, and Mo contents in the sample Nos. 101 to 106 are mass ratios relative to the cemented carbide. When only peak waveforms of WC, W ₂ C, and Co _x W _y C _z are obtained by X-ray diffraction, and the peak waveforms of Cr carbide and V carbide are not obtained due to the detection limit, Cr and V are WC, It is determined that it exists in a solid solution state in W ₂ C, Co _x W _y C _z . Further, when the peak waveform of WC is obtained by X-ray diffraction and the peak waveform of W ₂ C is not obtained due to the detection limit, it is determined that all binary compounds of W and C exist as WC. Furthermore, the peak waveform of Co _x W _y C _z (including the case where the peak waveform is slightly shifted from the peak waveform of pure Co _x W _y C _z due to solid solution such as Cr) is obtained by X-ray diffraction, If the peak waveform of metal Co cannot be obtained due to the detection limit, it is determined that Co exists as Co _x W _y C _z . The analysis of the composition of the cemented carbide can utilize Co titration in addition to the above ICP spectroscopic analysis. Moreover, the composition of the compounding raw material is substantially equal to the composition of the cemented carbide.

In sample Nos. 1 to 5 made using WC powder containing Cr and V as raw materials, Cr carbide and V carbide are X-ray diffracted in the cemented carbide except sample No. 4 as shown in Table 1. It can be said that Cr carbide and V carbide are not present. In sample No. 4, Cr ₃ C ₂ was only slightly detected. One of the reasons why Cr ₃ C ₂ was slightly detected in Sample No. 4 is considered to be that it was precipitated without being completely dissolved in the binder phase or the like by containing V in addition to Cr. On the other hand, Sample Nos. 102 to 104,106 produced using carbide powder such as Cr ₃ C ₂ powder as raw materials were detected as Cr carbide (Cr ₃ C ₂ ), V carbide (VC), and Mo carbide (Mo ₂ C). It can be said that carbide exists. Therefore, it can be said that by using WC powder containing Cr or V as a raw material, Cr or the like can be prevented from being present in the carbide state in the cemented carbide. In addition, it is considered that Cr of sample Nos. 1 to 3 and 5 and most of Cr and V of sample No. 4 are dissolved in Co _x W _y C _z or WC. In Samples Nos. 1 to 5, the values of x, y, and z of Co _x W _y C _z changed due to different carbon contents in the cemented carbide.

In all of sample Nos. 1-5, Co was not detected by X-ray diffraction, so the Co component in the cemented carbide of sample Nos. 1-5 was Co _x W _y C _z It can be said that it exists. Furthermore, in all of sample Nos. 1 to 4, W ₂ C is not detected by X-ray diffraction, and considering the detection limit of X-ray diffraction, the volume ratio is W ₂ C / (WC + W ₂ C) ≦ 0.005 it is conceivable that. Sample No.5, since the carbon content in the cemented carbide by an amount of carbon powder in formulation set smaller than that of the sample No.3 was a low alloy, but W ₂ C is detected slightly W ₂ C / (WC + W ₂ C) is considered to be 0.01 or less.

[WC grain size]
The obtained cemented carbide was subjected to structure observation, and the average particle size of WC, the standard deviation σ of the particle size, and the area ratio of WC having a particle size (particle size) of 1.0 μm or more were determined. The results are shown in Table 2. Tissue observation was performed as follows. Each cemented carbide was arbitrarily cut to take a cross section, and after grinding this cross section, buffing up to # 3000 was performed. The polished surface was observed using an EBSD (Electron Back-Scatter Diffraction) method by FESEM (Field Emission Scanning Electron Microscope) at a magnification of about 5000 times. Observation was performed for each field by selecting an arbitrary plurality of fields (here, one field: three fields at 180 μm ² ) on the polished surface. All WC crystal grains present in each field of view were color-coded (mapped) for each crystal orientation so that the crystal grain size could be grasped visually. Image analysis is performed on the obtained mapping image, and the equivalent circle diameter of each area is obtained for all WCs existing in the three fields of view, and the equivalent circle diameter is defined as the WC grain size (diameter). The average grain size of all WC is the average grain size of the cemented carbide. A commercially available EBSD apparatus can be used for the measurement of the particle size. Also, the standard deviation of the grain size is obtained for all WCs present in the three fields of view, and this standard deviation is defined as the standard deviation σ of the cemented carbide. Further, for all WCs present in the three visual fields, the total area S1.0WC of the WC having a particle size of 1.0 μm or more is obtained, and the area ratio R (%) = (S1.0WC) with respect to the total area S _f of the three visual fields / Sf) × 100, and this ratio R is defined as the area ratio R of WC in the cemented carbide.

As representative of the prepared samples, FIGS. 1 to 4 show mapping images observed using the EBSD method and sample size distributions of WC for sample No. 2 and sample No. 106. FIG. 1 is a mapping image of sample No. 2, FIG. 2 is a particle size distribution of sample No. 2, FIG. 3 is a mapping image of sample No. 106, and FIG. 4 is a particle size distribution of sample No. 106. Although shown in gray scale in FIGS. 1 and 3, each WC is actually provided with red to blue to green. 1 and 3, each of the white to gray blocks is WC, the black block in FIG. 1 is Co _x W _y C _z , and the black block in FIG. 3 is metallic Co.

As shown in Table 2, in all of sample Nos. 1 to 5, the WC has a mean particle size of 0.2 to 0.7 μm, and the standard deviation σ of the WC particle size is 0.25 or less. Variation is small and uniform. In particular, all of sample Nos. 1 to 5 have few coarse WC of 1.0 μm or more. Also from FIG. 1, it can be seen that all the WC in the cemented carbide has a fine and uniform size. Furthermore, in the cemented carbide shown in FIG. 1, it can be seen that fine Co _x W _y C _z is uniformly dispersed in the cemented carbide.

On the other hand, as shown in FIG. 3, sample No. 106 has coarse WC particles locally even when Cr ₃ C ₂ is used as a raw material. This is supported by the graph in FIG. Further, in Sample No. 106, Co is locally solidified as shown in FIG. 3, and the thickness of Co in the cemented carbide is not uniform.

In addition, when the structure of sample No. 105 was observed, there were many nests (pores).

[Mechanical properties]
About each obtained cemented carbide, HRA hardness, fracture toughness (KIC), and bending strength were measured. The results are shown in Table 2. HRA hardness and bending strength were measured using a commercially available apparatus at room temperature. Fracture toughness (KIC) was measured using a commercially available apparatus capable of measurement based on the Vickers method.

As shown in Table 2, all of sample Nos. 1-5 have a better balance of hardness (HRA hardness), toughness (fracture toughness), and strength (bending strength) than sample Nos. 101-106. Yes. In particular, sample Nos. 1 to 3 all have high hardness of 94-96 HRA, high toughness with fracture toughness of 4 MPa · m ^1/2 or higher, and high strength with a bending strength of 1 GPa or higher. It is. Sample No. 4 in which Cr ₃ C ₂ was slightly detected had slightly smaller toughness and strength than Sample Nos. 1 to 3, but WC was fine and relatively high in hardness. Sample No. 5, in which W ₂ C was slightly detected, had a slightly smaller hardness than samples No. 1 to 3, but had relatively large WC, and thus had high toughness and high strength. Samples Nos. 1 and 2 have less Co than Samples Nos. 3 to 5, so that dissolution of W into Co and reprecipitation of WC during sintering were suppressed. High hardness.

On the other hand, Sample No. 101, which did not use Cr ₃ C ₂ or the like, has particularly low hardness due to the presence of large WC having a particle size of 1.0 μm or more. Sample No. 102 in which Cr ₃ C ₂ was present in the cemented carbide has particularly low toughness and strength. Samples Nos. 103 and 104 have many WCs having a particle size of 1.0 μm or more, but they have high hardness due to the presence of VC or Mo ₂ C having a hardness higher than WC, but have low toughness and strength. Sample No. 105 has low toughness and strength as a whole alloy although the amount of Co is too small, so that dissolution of W into Co during sintering and reprecipitation of WC are suppressed and WC is fine. Sample No. 106 has particularly low hardness due to too much Co.

Furthermore, Vickers hardness Hv (GPa) of the cemented carbide of sample No. 2 was measured in the temperature range from room temperature (20 ° C.) to 800 ° C. As a result, it was 24.6 GPa at room temperature, the degree of hardness decrease was small even at 600 ° C. or higher, and it was about 15 GPa even at 800 ° C. Further, when the surface of the cemented carbide exposed to the temperature range of 600 ° C. or higher was observed, no Co elution was observed and the surface properties were excellent. Therefore, the cemented carbides of Sample Nos. 1 to 5 can maintain high hardness even at high temperatures and have excellent surface properties. It is expected that the material can be suitably used as a constituent material of a member for which quality is desired, for example, a glass lens mold.

[Nozzle life]
Using the prepared nozzle, the lifetime was examined as follows. The results are shown in Table 2. Use a # 120 garnet as the abrasive and cut the steel plate at a water pressure of 300 MPa. The diameter of the nozzle through-hole is measured at regular intervals, and the change in diameter due to wear is examined. The steel plate is cut until the initial diameter of the through hole is increased by 0.1 mm, that is, until the diameter of the through hole is 0.6 mm, and the time when the diameter becomes 0.6 mm is evaluated as the life. did.

As shown in Table 2, all of sample Nos. 1 to 5 have a very long life compared to sample Nos. 101 to 106. In particular, Sample Nos. 1 to 3 in which Cr carbide and W ₂ C were not detected have a very long life. On the other hand, Samples Nos. 101, 105, and 106 having low hardness were inferior in wear resistance. In sample Nos. 102 to 104 in which metal carbide was present, chipping occurred during the life test.

Note that the above-described embodiment can be appropriately changed without departing from the gist of the present invention, and is not limited to the above-described configuration. For example, the composition of the cemented carbide, the average particle diameter of the raw material powder, and the like can be changed as appropriate.

The cemented carbide of the present invention can be suitably used as a constituent material for various wear-resistant parts that are desired to have excellent wear resistance, such as high-pressure water-flow nozzles and dies (punches and dies). Further, the cemented carbide of the present invention can be suitably used as a constituent material of a glass lens mold for a camera or the like, which is excellent in surface properties and requires formation of a high-quality member.

Claims (6)

Co is contained in an amount of 0.2% by mass or more and 0.9% by mass or less, Cr is contained by 0.2% by mass or more and 1.5% by mass or less, and the balance is composed of binary compounds of W and C and impurities.
The Co exists in the state of Co _x W _y C _z ,
Among the binary compounds of W and C, the average particle size of WC is 0.2 μm or more and 0.7 μm or less,
Cemented carbide characterized in that standard deviation σ of grain size of WC is σ ≦ 0.25. 2. The cemented carbide according to claim 1, wherein an area ratio of WC having a particle size of 1.0 μm or more is 5% or less with respect to the cemented carbide. The binary compound of W and C is mainly WC,
_3. The cemented carbide according to claim 1, wherein, when W ₂ C is contained, the volume ratio is W ₂ C / (WC + W ₂ C) ≦ 0.005 or less. 4. The cemented carbide according to claim 1, wherein the cemented carbide has an HRA hardness of 94 to 96, a fracture toughness (KIC) of 4 MPa · m ^1/2 or more, and a bending strength of 1 GPa or more. The cemented carbide described in 1. The cemented carbide according to any one of claims 1 to 4, further comprising 0.2 mass% or less of V. The cemented carbide according to any one of claims 1 to 5, wherein Cr carbide and V carbide are not detected by X-ray diffraction.

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