KR101245499B1 - Cemented carbide - Google Patents

Abstract

The present invention provides a cemented carbide having high hardness and excellent strength and toughness. The cemented carbide is a cemented carbide composed mainly of particles of WC, and a bonded phase composed mainly of Co _x W _y C _z , containing 0.2 to 0.9 mass% of Co and 0.2 to 1.5 mass of Cr, with the balance being W. And C binary compounds and impurities. The average particle size of the WC is 0.2 µm or more and 0.7 µm or less, and the standard deviation (σ) of the particle size of the WC is? Toughness can be improved by containing Co in the said range. By containing Co in the above range, the sinterability can be increased, the sintering temperature can be lowered, and by containing Cr, growth of the WC can be effectively suppressed, and the cemented carbide having a fine and uniform particle size can be formed. . When Cr exists as a metal component, the fall of the strength by presence of Cr carbide can be suppressed.

Description

Cemented carbide {CEMENTED CARBIDE}

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

As a constituent material of a member such as a glass lens mold used for a nozzle for high pressure water flow (water jet processing), a camera, and the like, a cemented carbide alloy mixed with WC (tungsten carbide) and Co (cobalt) and then sintered is used. (For example, patent documents 1-3).

Especially in the member, such as the said high pressure water flow nozzle, it is calculated | required which is excellent in abrasion resistance. In order to improve wear resistance, increasing the hardness is effective. As a method of increasing the hardness, the content of Co having a hardness lower than that of WC can be reduced or the WC can be made finer. In order to refine WC, as described in Patent Literatures 1 to 3, grain growth such as VC (vanadium carbide), Mo ₂ C (molybdenum carbide), Cr (chromium) carbides such as Cr ₃ C ₂ , etc. The addition of the metal carbide which has an inhibitory effect with respect to) is mentioned.

Patent Document 1: Japanese Patent Application Laid-Open No. 05-230588 Patent Document 2: Japanese Patent Application Laid-Open No. 09-025535 Patent Document 3: Japanese Patent Application Laid-Open No. 04-348873

In recent years, as a constituent material of the nozzle and the mold, a cemented carbide having a high hardness, excellent toughness and strength, and having a good balance of wear resistance and fracture resistance (chipping resistance) has been demanded. However, conventional cemented carbides cannot be said to have high hardness, high toughness and high strength sufficiently and well in balance.

As described in Patent Literatures 1 to 3, when metal carbide having a suppressive effect on grain growth is added as a raw material for miniaturization of WC in a cemented carbide, the metal carbide remains in the obtained cemented carbide or is reprecipitated, thereby reducing its strength. Deterioration is caused. Moreover, when the said metal carbide itself of a raw material is coarse, it is difficult to mix uniformly with the WC powder of a raw material, and the fluctuation | variation will arise in the suppression effect to the grain growth of WC. As a result, there exists a possibility that the coarse WC which grows and coarsens in a cemented carbide exists, or a coarse metal carbide exists in a cemented carbide. 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 the WC easily grows due to the Ostwald growth during sintering, so that the coarse WC There is a possibility of becoming a cemented carbide present. The presence of locally coarse WC results in a decrease in strength.

In addition, the lens die is excellent in wear resistance, and it is desired that a lens having a high surface quality can be obtained only by forming with the die. That is, a metal mold | die which can form the lens excellent in the surface property to the extent that it can be used as it is, without performing a separate grinding | polishing process etc. to the lens formed by the metal mold | die is desired. In order to respond to such a demand, it is desired that the WC in the cemented carbide constituting the mold is fine and homogeneous.

W ₂ C is present in the hard alloy described in Patent Document 1. Since W ₂ C is easier to grow than WC, coarse W ₂ C may exist in the cemented carbide. The presence of coarse particles in the cemented carbide leads to a decrease in strength and toughness and a deterioration in surface quality.

Since the sintered hard material of patent document 2 adds very little Co which is low hardness for the purpose of high hardness, it is low in strength and toughness. In addition, since Co is so small that W ₂ C is easy to precipitate and hardly sintered, it must be sintered at a very high temperature such as 1700 ° C. or higher for densification. Because such high temperature sintering, it is easy to precipitated W ₂ C is grown. For this reason, even if metal carbide is added as mentioned above, there exists a limit to the effect of suppressing grain growth. If coarse W ₂ C is present in the cemented carbide, it causes a decrease in strength and toughness and a deterioration in surface quality. Therefore, in this sintered hard material, high hardness, high toughness, and high strength are incompatible.

The sintered compact of patent document 3 is high hardness but low in strength and toughness for the purpose of improving abrasion resistance. In particular, the resistance is low in the sintered compact with less Co addition. In addition, patent document 3 only proposes simply making the average particle diameter of WC small, and does not consider the control of particle size distribution. If the variation of the particle size of the WC in the sintered body is large, the thickness of Co in the sintered body becomes uneven (locally thickened or thinned), which causes uneven wear and defects. In addition, when complex carbides [different metal carbides] used in the raw materials are precipitated to suppress grain growth, the complex carbides have poor wettability with a bonding phase such as Co, leading to a decrease in strength. In addition, since the precipitated complex carbide falls off, wear is likely to proceed. Therefore, in this sintered compact, high hardness, high toughness, and high strength are incompatible.

Accordingly, 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 have found that cemented carbides having a specific composition and devising a method for adjusting and producing raw materials can provide a cemented carbide having high hardness, excellent wear resistance, high toughness, high strength and excellent fracture resistance. This invention is based on the said knowledge.

The cemented carbide of the present invention contains Co and Cr, with the balance being composed of W and C binary compounds and impurities. The said Co contains 0.2 mass% or more and 0.9 mass% or less with respect to the said cemented carbide. Co exists in the state of Co _x W _y C _z . The said Cr contains 0.2 mass% or more and 1.5 mass% or less with respect to the said cemented carbide. The binary compounds of W and C are mainly WC, and the average particle 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?

The cemented carbide of the present invention has a Co compound (Co _x W _y C _z ) that is harder than metal Co as a main bonding phase, has a fine WC, high hardness, and excellent wear resistance. In particular, the cemented carbide of the present invention can effectively inhibit grain growth of WC, thereby making it fine WC, and improve hardness, while suppressing a decrease in strength due to the presence of coarse WC. . In the cemented carbide of the present invention, since the Co component is contained to such an extent that it is possible to sufficiently cover the WC circumference by the bonding phase (mainly Co _x W _y C _z ), it is easy to sinter. For this reason, in manufacture of the cemented carbide of this invention, compared with patent documents 2 and 3, since sintering temperature can be made low, grain growth, such as local WC, is suppressed and coarse WC etc. are hard to exist in a cemented carbide. Lose. In the cemented carbide of the present invention, Cr is mainly present as a metal component and is hardly present in the form of a compound such as carbide. For this reason, in the cemented carbide of the present invention, as in the case where metal carbide is used as the raw material for suppressing grain growth, the reduction in strength due to residual or reprecipitation of metal carbide can not occur substantially. Further, the cemented carbide of the present invention can reduce the extreme deterioration of toughness and strength such as cemented carbide with too little Co by containing the Co component in the specific range, and the strength and toughness are also high. In addition, since the bonding phase (mainly Co _x W _y C _z ) exists so as to cover the circumference of the fine and uniform WC as described above, the thickness of the bonding phase is also uniform, so that the cemented carbide of the present invention may have uneven wear and defects. It is difficult and excellent in abrasion resistance and defect resistance.

As described above, the cemented carbide of the present invention has a good 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 is present in the state of Co _x W _y C _z , has a low hardness and high hardness not only at room temperature but also at a high temperature such as 500 ° C. to 800 ° C. Excellent wear resistance even in a wide range from room temperature to high temperature. Therefore, the cemented carbide of the present invention can be suitably used, for example, as a constituent material of a member which is desired to be excellent in wear resistance, such as a nozzle for high pressure water flow processing. In addition, the cemented carbide of the present invention has a fine and uniform WC and a uniform thickness of the bonding phase (mainly Co _x W _y C _z ). That is, since the cemented carbide of the present invention has a uniform structure and a relatively small Co component, the cemented carbide can be suitably used also as a member for which a good finish surface quality, such as mirror finish, is desired, in addition to wear resistance. have. In addition, since the cemented carbide of the present invention has high toughness and high strength, it is possible to reduce processing cracks and chipping associated with these processes even when grinding, wire machining, or electric discharge machining, etc., are performed during the manufacture of the nozzle, mold, and the like. have. For this reason, members, such as said nozzle, can be manufactured efficiently. 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 various members, and the fracture resistance is also excellent. Hereinafter, the present invention will be described in detail.

Cemented Carbide

"Furtherance"

In the cemented carbide of the present invention, the hard phase is mainly composed of particles of WC. In addition, the bonded phase is a WC-Co _x W _y C _z- based cemented carbide mainly composed of Co compounds (Co _x W _y C _z ). And the remainder except Co _x W _y C _z and Cr mentioned later is comprised by the binary compound of W and C, and an unavoidable impurity. In addition, when it mentions V mentioned later, remainder except Co _x W _y C _z , Cr, and V is comprised by the binary compound of W and C, and an unavoidable impurity. Examples of the binary compounds of W and C include WC and W ₂ C.

[Co]

Co in the cemented carbide of the present invention exists in the state of a compound of Co and W such as Co _x W _y C _z . As a result of analyzing the cemented carbide of the present invention in the following examples by X-ray diffraction, the peak waveform of the Co-containing component can obtain the peak waveform of Co _x W _y C _{z, and} the peak waveform of the metal Co is It was not obtained by the limit of detection. In addition, it is considered Co _x W _y C _z is Cr or V in this case, which is employed (固溶), the peak waveform from the peak waveform of the Co _x W _y C _z is the peak position just off the jindago obtained. Therefore, when the cemented carbide is analyzed by X-ray diffraction, even when the peak waveform of Co _x W _y C _z is slightly deviated by the solid solution of Cr or V, the cemented carbide cannot be obtained. It is interpreted as being included in the scope of the invention. According to the production method described later, substantially all of Co in the cemented carbide is present as Co _x W _y C _z , and metal Co is not present (a peak waveform by X-ray diffraction of metal Co is not obtained due to the detection limit. Cemented carbide can be produced. x, y, z all take a positive value and satisfy x + y> z.

The cemented carbide of the present invention sufficiently contains Co _x W _y C _z by containing Co by 0.2 mass% or more relative to the cemented carbide, can cover the WC, and is easy to sinter. For this reason, in producing the cemented carbide of the present invention, it is possible to produce a dense cemented carbide even if the sintering temperature is sintered under the same sintering conditions as those of ordinary cemented carbide, for example, the same as that of ordinary vacuum sintering. If Co is less than 0.2 mass%, the sintering temperature must be increased because Co _x W _y C _z is not sufficiently covered around WC and sintered poorly. Due to the high temperature of the sintering temperature, grain growth of WC is promoted at the time of sintering, and coarse WC is generated. Then, a decrease in strength due to the presence of coarse particles is caused. In addition, when Co is too small, toughness (for example, fracture toughness) also decreases extremely. The more Co, the better the toughness and the easier the sintering. However, if the content of Co exceeds 0.9% by mass, the grain growth of WC tends to occur. Therefore, the hardness (hardness from room temperature to high temperature) is lowered, and especially high temperature of 600 ° C or higher The decrease in hardness at the station is remarkable. In addition, since the uniformity of the structure of the cemented carbide also decreases due to grain growth of WC, a decrease in strength is also caused. By making Co content into 0.2 mass% or more and 0.9 mass% or less, the Ostwald growth of WC by the high temperature of sintering temperature can be suppressed. As a result, the generation of coarse WC in the cemented carbide can be reduced, and the grain size of the WC can be made to be fine and uniform to the WC-Co _x W _y C _z- based cemented carbide. Moreover, since the cemented carbide of the present invention has a fine structure, it is excellent in surface properties. In particular, by reducing the component of Co and making the presence state Co _x W _y C _z , even when used at a high temperature, Co is hardly eluted from the surface of the cemented carbide, and the mirror surface state of the cemented carbide surface can be maintained for a long time. As for content of Co, 0.2 mass% or more and 0.6 mass% or less are more preferable.

[Cr]

By containing 0.2 mass% or more of Cr with respect to the cemented carbide, the grain growth of the WC can be effectively suppressed to reduce the occurrence of coarse WC, and the cemented carbide with the uniformity of fine and uniform sized WC can be stably produced. In addition, by containing Cr, the oxidation resistance of the cemented carbide can be improved. The more Cr, the higher the effect of suppressing grain growth. However, when there is too much Cr, it will become easy to precipitate as Cr carbide, and it will become a factor of the strength fall by presence of Cr carbide. Therefore, the cemented carbide of the present invention has a Cr content of not less than 0.2 mass% and not greater than 1.5 mass%. More preferable content of Cr is 0.2 mass% or more and 0.9 mass% or less.

In addition, the cemented carbide of the present invention may contain V in addition to Cr. Like Cr, V also has a high inhibitory effect on grain growth of WC. By containing both Cr and V, grain growth of WC can be suppressed more effectively. When the content of V is too high, the wetting of WC and W ₂ C with _x W _y C _z is no Co is not good, no longer it is well sintered. For this reason, the strength of the cemented carbide is reduced, or is easily precipitated as V carbide, which causes a decrease in strength due to the presence of V carbide. For this reason, as for content of V, 0.2 mass% or less (including 0 mass%) is preferable with respect to a cemented carbide.

It is preferable that substantially all of Cr and said V are solid-solution in Co _x W _y C _z or WC, and exist as a metal component. As a result of analyzing the cemented carbide of the present invention by the X-ray diffraction in Examples described later, the peak waveform of Cr carbide and the peak waveform of V carbide are in a range not obtained by 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 or WC. Therefore, when the cemented carbide is analyzed by X-ray diffraction, the cemented carbide having a peak waveform deviating 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 production method described later, substantially all of Cr and V in the cemented carbide are present as a metal component dissolved in Co _x W _y C _z or WC, and a single metal of Cr or V, Cr carbide and A cemented carbide can be produced in which no V carbide is present (where the peak waveform of X-ray diffraction of Cr carbide or V carbide is not obtained due to the detection limit).

[W and C Binary Compounds]

In the cemented carbide of the present invention, the balance excluding Co _x W _y C _z , Cr, (V) is composed of binary compounds of W and C and unavoidable 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 as a grain in a cemented carbide and functions as a hard phase. In particular, WC is particulate and uniform in size. Specifically, the average particle size of the 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 the small coarse WC. If the average particle size is too small, less than 0.2 µm, cracks tend to develop, leading to a decrease in toughness, and when the average particle size exceeds 0.7 µm, a decrease in hardness is caused. More preferable average particle size is 0.2 micrometer or more and 0.4 micrometer or less. The smaller the standard deviation σ is, the lower the limit is not particularly set.

Less coarse WC in the cemented carbide is desirable. Specifically, if the area ratio of WC having a particle size (particle size) of 1.0 µm or more is 5% or less with respect to the cemented carbide, as described above, the decrease in strength due to the presence of coarse WC is suppressed, resulting in a high strength cemented carbide. Can be. The smaller the area ratio of the coarse WC is, the more preferable is 4% or less.

W and C are present in the cemented carbide, and the majority is present in the WC, W ₂ C is preferably small. As described above, since W ₂ C is more easily grained than WC, it may be a cemented carbide containing coarse particles. Specifically, it is preferable to satisfy W ₂ C / (WC + W ₂ C) ≦ 0.005 by volume ratio. The volume ratio of the W ₂ C is preferably not present the smaller preferably, and, that is, only a WC two won a compound of W and C.

The average particle size of the above-mentioned WC, the standard deviation of the particle size, and the area ratio of the coarse WC can be obtained by using the EBSD method, for example. The volume ratio of W ₂ C can be obtained by using X-ray diffraction. The detail of this measuring method is mentioned later.

[characteristic]

The cemented carbide of the present invention is high hardness, high toughness and high strength. Specifically, the HRA hardness is preferably 94 or more and 96 or less, fracture toughness of 4 MPa · m ^1/2 or more, and break strength of 1 GPa or more. If HRA hardness is 94 or more, it is excellent in abrasion resistance. By setting the HRA hardness to 96 or less, the decrease in toughness due to excessive high hardness can be reduced. In addition, when the fracture toughness is 4 MPa · m ^1/2 or more and the cut strength is 1 GPa or more, in the manufacture of various members, cracks and chipping during processing can be effectively suppressed, and not only high hardness but also high The member which has the outstanding outstanding performance of the cemented carbide which is toughness and high strength can be provided.

<Manufacturing Method>

The cemented carbide is generally produced by the same process as the preparation of the raw material, the mixing, grinding, drying, forming and burning of the raw material. The cemented carbide of the present invention is further subjected to HIP (hot hydrostatic sintering) after the sintering, using a specific raw material and mixing and grinding under specific conditions.

[Raw material WC]

As the WC powder of the raw material, it is preferable to use a fine one so that the WC in the cemented carbide tends to be in a fine state. Specifically, WC powders having an average particle size of 0.1 µm or more and 0.5 µm or less are preferable. Even if it is less than 0.1 micrometer or more than 0.5 micrometer, it is easy to form a cemented carbide and coarse WC exists.

In particular, when the Cr-containing WC powder is used, Cr carbide is hardly formed in the cemented carbide. When producing a cemented carbide containing Cr and V, Cr carbide and V carbide are hardly produced in the cemented carbide when WC powders containing Cr and V are used as raw materials. The present inventors have found that when Cr powder or V carbide powder, metal Cr or metal V powder is used as a raw material, Cr carbide and V carbide remain or are precipitated and reprecipitated, resulting in a decrease in strength. On the other hand, when Cr or V is contained in the WC powder itself, Cr carbide or V carbide is difficult to precipitate or is not substantially produced, and Cr or V is uniformly present (dispersed) throughout the raw material. Can be. For this reason, the knowledge that grain growth of WC at the time of sintering is suppressed uniformly over the whole cemented carbide, and the cemented carbide of the structure in which WC with a fine and uniform particle size exist uniformly can be manufactured stably is obtained. Moreover, since WC powder itself contains Cr or V, the knowledge that a cemented carbide in which Cr or V was dissolved in WC is easy to be obtained is obtained. In addition, by not using a compound which does not sinter well, such as VC, as a raw material, it can prevent that it does not sinter well. Based on this knowledge, it is proposed to use WC powder containing Cr or V. In addition, content of Cr and V contained and added in WC powder of a raw material is substantially the same as content in a cemented carbide.

Raw Material Co

As the Co powder of the raw material, it is preferable to use a fine fine as the WC powder so as to be easily mixed with the fine WC powder uniformly. Specifically, Co powder having an average particle size of 0.2 µm or more and 0.6 µm or less is preferable. If the thickness is less than 0.2 µm, the Co is too small to easily reaggregate and the Co is not uniformly dispersed and the sintering temperature is increased due to the high temperature of the sintering temperature accompanying the poor sintering or poor sintering. It is difficult to obtain a particle size distribution. If it exceeds 0.6 µm, it becomes difficult to mix uniformly with the fine WC powder, and as described above, Co is not uniformly sintered, resulting in non-sintering or non-uniformity of the particle size distribution.

[Raw carbon]

In addition to the above-mentioned Cr and V-containing WC powder and Co powder, carbon powder is appropriately added to adjust the total amount of carbon (C) in the cemented carbide. By adjusting the total amount of carbon in the cemented carbide and producing it under the production conditions described below, substantially all of the Co powder can be made Co _x W _y C _z , and the carbon in the cemented carbide obtained is WC, Co _x W _y C _z It is easy to exist as. If the total amount of carbon in the cemented carbide is too large, the metal Co tends to exist. In addition, when the total amount of carbon in the cemented carbide is too large, the carbon is present in the cemented carbide as free carbon or precipitation of Cr carbide or the like causes a decrease in strength.

[Mixing and grinding]

The powder used as a raw material mentioned above is prepared, and it mixes and grinds by the grinding | dispersing disperser which has rotary 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, it is preferable to perform the initial process from the start of mixing and grinding to 5 hours at high speed (25 rpm or more), and to carry out subsequent mixing and grinding (hereinafter referred to as subsequent step) at low speed (less than 25 rpm). Do. In the initial step, the mixing and grinding are substantially completed, and in the subsequent step, dispersion is mainly performed. By making the mixing and grinding step into multiple stages as described above, it is easy to realize uniform mixing and dispersion. Performing at high speed rotation throughout the mixing and pulverizing process results in cohesion of Co, resulting in poor dispersion, and easy growth of WC, resulting in uneven structure. On the other hand, when it is performed at low speed rotation throughout the mixing and grinding | pulverization process, grinding | pulverization and mixing are inadequate, and nonuniformity of a structure will be caused.

As for the drying, molding, sintering, and the like, conditions similar to those of general conditions can be used. For example, sintering conditions can be sintered under reduced pressure (vacuum sintering, Ar atmosphere sintering, CO atmosphere sintering, etc.) at a sintering temperature of 1450 ° C to 1550 ° C. As described above, the cemented carbide of the present invention is blended into the raw material by using the finely divided WC powder and Co powder in the above-described composition, and further mixed and pulverized under specific conditions as described above to disperse them properly. For this reason, it can be relatively low, as the sintering temperature of the above, since the periphery of the WC Co _x W _y C _z to fully cover. The sintering temperature is low, and the grain growth of WC (W ₂ C) can be suppressed.

In the manufacture of the cemented carbide of the present invention, HIP is performed after the sintering. In general, in a cemented carbide having relatively low Co, Co cannot be sufficiently enclosed around the WC, so that it is sintered at high temperature in order to be easily sintered (Patent Document 2: 1700 ° C or higher, Patent Document 3: 1600 ° C or higher). It becomes necessary. On the other hand, in the manufacture of the cemented carbide of the present invention, as described above, the cemented carbide is easily sintered even at low temperatures, and a uniform cemented carbide is obtained. Further, by performing HIP after sintering, fine pores (pores) remaining in the cemented carbide after sintering can be eliminated, and a fine cemented carbide can be made. In particular, by making the sintering temperature relatively low as described above, it is easy to produce a cemented carbide having a uniform structure.

As described above, without using a metal carbide to suppress grain growth, the one containing Cr or V in the WC powder itself is used, the content of Co is optimized, and the fine Co powder is used. By manufacturing, WC in a cemented carbide can be made fine and uniform particle size distribution, and the fall of the strength by presence of coarse particle can be suppressed. 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 high hardness, high toughness and high strength in a good balance, excellent wear resistance and excellent fracture resistance can be achieved.

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

(Test example)

Various raw powders were prepared to prepare cemented carbide, and the composition, structure, and mechanical properties of the cemented carbide were examined. Moreover, the nozzle for high pressure water flow processing was produced from this cemented carbide, and the lifetime of the nozzle was investigated.

[Samples No. 1 to 5]

As raw materials, WC powder having an average particle size of 0.5 mu m, Co powder and carbon powder having an average particle size of 0.2 mu m and 0.6 mu m were prepared. The WC powder was prepared with 0.2 to 1.5 mass% of Cr or 0.2 to 1.5 mass% of Cr and 0.2 mass% of V as the WC powder. The addition amount of Co powder was adjusted so that content of Co might be 0.2-0.9 mass% with respect to the total mass of the said WC powder, Co powder, and carbon powder containing Cr and V. In addition, the content of carbon adjusted the addition amount of carbon powder so that it might become plus 0.05 mass% or more and less than 0.1 mass% with respect to the theoretical carbon amount of the cemented carbide of each composition manufactured, and made remainder WC powder. As these raw material powders, all commercially available ones can be used. In addition, Co powder with an average particle diameter of 0.2 micrometer was used for sample No. 1, 2, and Co powder with an average particle diameter of 0.6 micrometer was used for samples No. 3-5.

Powdery paraffin (1 mass% relative to the raw material powder) was added to the raw material powder, and mixed and pulverized using an attritor or a ball mill as a pulverizing disperser. Both the attritor and the ball mill used a cemented carbide ball having a diameter of 5 mm as a medium. In Table 1, the type and mixing and grinding time of the used pulverizing disperser are shown. In particular, in Sample Nos. 1 to 5, five hours were performed at high speed (25 rpm or more) from the start of mixing and grinding, and the remaining time after 5 hours was performed at low speed (5 rpm).

After the mixing and grinding, the raw material powder was granulated into granules using a granulation dryer and then dried. After the obtained granulated powder was poured into the rubber mold only in a predetermined amount, hydrostatic pressing was performed, and the outer periphery of the obtained press body was machined to produce a round rod having a diameter of 8 mm x length (L): 80 mm. The obtained round bar was placed in a sintering furnace, sintered by holding at 1450 ° C to 1550 ° C for 1 hour in vacuum, cooled from the heating temperature, and then taken out of the sintering furnace. HIP was performed to the obtained sintered compact in Ar atmosphere of 1320 degreeC and 1000 atmospheres (about 101 MPa), and the cemented carbide was obtained.

The obtained cemented carbide is subjected to grinding and discharging, forming an outer circumferential shape, forming a tapered portion at the point where water is introduced, and a through hole (diameter φ0.5 mm) extending in the longitudinal direction in the center of the cemented carbide. Was formed and the nozzle for high pressure water flow was produced.

[Samples No. 101 to 106]

For the purpose of comparison, a sample was prepared, Cr ₃ C _2, VC, a sample which does not use the Mo ₂ C with a _{Cr 3 C 2, VC, Mo} 2 C in the raw material. Specifically, as a raw material, WC powder (without Cr or V) having an average particle size of 0.7 µm, Co powder, Mo ₂ C powder, VC powder, Cr ₃ C ₂ Powders (all average particle sizes: 0.7 µm to 1.5 µm) and carbon powders were prepared. The addition amount of these raw material powders was suitably adjusted, and the cemented carbide was obtained through the process similar to sample Nos. In Sample Nos. 101 to 106, mixing and grinding were performed at high speed (25 rpm or more) over the entire time of mixing and grinding, and sintering conditions and HIP conditions were the same as those of Samples No. 1 to 5. The obtained cemented carbide was subjected to the same processing as Sample Nos. 1 to 5 to produce a nozzle for high pressure water flow.

[Composition and Organization]

Each obtained cemented carbide was subjected to inductively-coupled plasma (ICP) spectroscopy and X-ray diffraction to investigate composition and structure. The results are shown in Table 1. Content of Co of all the samples, content of Cr and V in sample Nos. 1-5, and content of Cr, V, Mo in sample Nos. 101-106 are mass ratio with respect to cemented carbide. When only the 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 by the detection limit, Cr and V are WC, W ₂ C, Co _x and _y C _z is determined to exist in the solid solution state. In addition, when the peak waveform of WC is obtained by X-ray diffraction and the peak waveform of W ₂ C is not obtained by the detection limit, it is determined that both W and C binary compounds exist as WC. Further, by X-ray diffraction, a peak waveform of Co _x W _y C _z (including a case where the peak waveform slightly deviates from the peak waveform of pure Co _x W _y C _z by solid solution such as Cr) is obtained, and the metal If the peak waveform of Co is not obtained by the detection limit, Co is judged to exist as Co _x W _y C _z . In addition, Co titration etc. can be used for the analysis of the composition of a cemented carbide, in addition to the said ICP spectroscopic analysis. The composition of the blended raw material is substantially the same as that of the cemented carbide.

In samples Nos. 1 to 5 produced using WC powders containing Cr or V as the raw materials, except for sample No. 4 as shown in Table 1, Cr carbides and V carbides in the cemented carbide were subjected to X-ray diffraction. It is not detected and it can be said that Cr carbide and V carbide do not exist. Sample No. 4 also merely detects Cr ₃ C ₂ slightly. In Sample No. 4, one of the reasons why Cr ₃ C ₂ was slightly detected is considered to be that V is further contained in Cr and precipitated without solid solution in a bonding phase or the like. On the other hand, Sample Nos. 102 to 104 and 106 prepared by using carbide powder such as Cr ₃ C ₂ powder as the raw material are Cr carbide (Cr ₃ C ₂ ), V carbide (VC), and Mo carbide (Mo ₂ C). It can be said that it is detected and carbide exists. Therefore, by using WC powder containing Cr or V as a raw material, it can be said that Cr etc. do not exist in a carbide state in a 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. The values of x, y and z of Co _x W _y C _z in Sample Nos. 1 to 5 were different because the content of carbon in the cemented carbide was different.

In addition, since the metal Co was not detected by X-ray diffraction in all of samples No. 1-5, the Co component in the cemented carbide of samples No. 1-5 is said to exist in the state of Co _x W _y C _z . Can be. Further, in all samples No. 1 to 4, W ₂ C was not detected by X-ray diffraction, and considering the detection limit of X-ray diffraction, W ₂ C / (WC + W ₂ C) ≦ 0.005 in volume ratio. It is considered to be. Sample No. 5 had a small amount of carbon in the cemented carbide by setting the amount of carbon powder added at the time of blending less than sample No. 3. Thus, W ₂ C was slightly detected, but W ₂ C / (WC + W ₂ C) is considered to be 0.01 or less.

[WC particle size]

About each obtained cemented carbide, the structure was observed and the area ratio of WC whose average particle size, standard deviation ((sigma)) of particle size, and particle size (particle size) is 1.0 micrometer or more was calculated | required. 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 the cross section, buff polishing up to # 3000 was performed. The polished surface was observed at a magnification of about 5000 times using the EBSD (Electron Back-Scatter Diffraction) method by the Field Emission Scanning Electron Microscope (FESEM). Observation was performed for every visual field by selecting arbitrary several visual fields (here, 1 visual field: 180 micrometer <^2> and 3 visual field) with respect to the polished surface. All the WC crystal grains present in each field of view were color-coded (mapping) for each crystal orientation to visually grasp the grain size. The image analysis is performed on the obtained mapping, and the circular equivalent diameter of each area is calculated | required about all WC which exists in three visual fields, and this circular equivalent diameter is made into the particle size (diameter) of WC, and it exists in all three visual fields. The mean particle size of the WC is the mean particle size of the cemented carbide. A commercially available EBSD device can be used for measuring the particle size. In addition, the standard deviation of particle size is calculated | required about all WC which exists in three visual fields, and this standard deviation is made into the standard deviation ((sigma)) of a cemented carbide. Further, for all WCs present in the three fields of view, 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 (%) to the total area (S _f ) of the three fields of view is (S1. 0 WC / S _f ) × 100 is obtained, and this ratio R is defined as the area ratio R of the WC in the cemented carbide.

Representative samples produced are shown in FIGS. 1 to 4 of mapping images observed using EBSD method and sample particle size distribution of WC. 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. FIG. In FIG. 1 and FIG. 3, although shown in gray scale, red, blue, and green are respectively coat | covered with each WC. In Figs. 1 and 3, each chunk of white to gray is WC, the black chunk in Fig. 1 is Co _x W _y C _z and the black chunk in Fig. 3 is Metal Co.

As shown in Table 2, all samples Nos. 1 to 5 had fine grains in the range of WC of average particle size: 0.2 µm to 0.7 µm, and standard deviation (?) Of the particle size of WC was 0.25 or less, and the variation in particle size. Is small and uniform. In particular, samples No. 1 to 5 all have a coarse WC of 1.0 µm or more. In addition, it can be seen from FIG. 1 that the WCs in the cemented carbide are all fine and uniform in size. 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.

In contrast, as shown in FIG. 3, even when Cr ₃ C ₂ is used as the raw material, coarse WC particles are present locally. This is also supported by the graph of FIG. As shown in Fig. 3, sample No. 106 was locally hardened by Co, and the thickness of Co in the cemented carbide was uneven.

Moreover, when the structure observation of sample No. 105 was performed, many holes (pores) existed.

[Mechanical Properties]

For each of the obtained cemented carbides, HRA hardness, fracture toughness (KIC), and tensile strength were measured. The results are shown in Table 2. HRA hardness and cut strength were measured at room temperature using a commercially available apparatus. Fracture toughness (KIC) was measured using a commercially available apparatus capable of measuring based on the Vickers method.

As shown in Table 2, all of the samples No. 1 to 5 have a good balance of hardness (HRA hardness), toughness (breaking toughness) and strength (break strength) as compared with samples No. 101 to 106. In particular, all of the samples No. 1-3 were HRA hardness 94-96, high hardness, fracture toughness of 4 MPa * m ^1/2 or more, high toughness, and breaking strength of 1 GPa or more, and high strength. Sample No. 4 in which Cr ₃ C ₂ was slightly detected, although the toughness and strength were slightly smaller than Sample Nos. 1 to 3, WC was fine and relatively high in hardness. Sample No. 5 in which W ₂ C was slightly detected has a slightly smaller hardness compared to Samples Nos. 1 to 3, but it has high toughness and high strength due to the presence of relatively large WC. In addition, samples No. 1 and 2 had less Co than samples Nos. 3 to 5, and dissolution of W into Co and reprecipitation of WC during sintering were suppressed, so that WC became fine particles and high hardness.

Meanwhile, Cr ₃ C ₂ In sample No. 101 without using a back or the like, many large WCs having a particle size of 1.0 µm or more exist, and the hardness is particularly low. Sample No. 102 in which Cr ₃ C ₂ was present in the cemented carbide was particularly low in toughness and strength. Sample Nos. 103 and 104 had many large WCs having a particle size of 1.0 µm or more. However, VC and Mo ₂ C, which had higher hardness than WC, existed, and thus the hardness was high, while the toughness and strength were low. Sample No. 105 has too little Co, so that dissolution of Co in sintering Co and reprecipitation of WC are suppressed, and WC is fine, but the toughness and strength of the alloy are low. Sample No. 106 has too much Co, and the hardness is particularly low.

Moreover, about the cemented carbide of sample No. 2, Vickers hardness Hv (GPa) was measured about the temperature range from room temperature (20 degreeC) to 800 degreeC. As a result, it was 24.6 GPa at room temperature, the degree of hardness fall was small at 600 degreeC or more, and it had about 15 GPa even at 800 degreeC. Moreover, when the surface of the cemented carbide exposed to the said temperature range of 600 degreeC or more was observed, Elution of Co was not seen but the surface property was excellent. As a result, the cemented carbides of Sample Nos. 1 to 5 can maintain high hardness even in a high temperature range and are excellent in surface properties, and therefore are also used in a high temperature range, and have a desired finish surface quality, for example, a mold for glass lenses. It is expected that it can be used suitably for the constituent material of.

[Nozzle Life]

Using the produced nozzle, life was investigated as follows. The results are shown in Table 2. Using a garnet of # 120 in the abrasive grains, the iron plate is cut at a water pressure of 300 MPa. The diameter of the through-hole of the nozzle is measured at regular intervals, and the change of the diameter due to abrasion is investigated. The steel sheet is cut until the diameter of the initial through hole increases by 0.1 mm, that is, until the diameter of the through hole reaches 0.6 mm, and the time at which the diameter φ reaches 0.6 mm is used. It was evaluated as.

As shown in Table 2, all of the samples No. 1 to 5 have a very long life compared to the samples No. 101 to 106. In particular, in samples Nos. 1 to 3 in which Cr carbide and W ₂ C were not detected, the service life is very long. On the other hand, samples No. 101, 105, and 106 having low hardness were inferior in wear resistance. In samples Nos. 102 to 104 where metal carbides were present, distortion occurred during the life test.

In addition, embodiment mentioned above can be suitably changed without deviating from the summary of this invention, and is not limited to the structure mentioned above. For example, the composition of the cemented carbide, the average particle diameter of the raw material powder, and the like can be appropriately changed.

The cemented carbide of the present invention can be suitably used for a variety of wear-resistant parts, such as nozzles for high-pressure water flow processing, molds (punches and dies), and the like that are excellent in wear resistance. In addition, the cemented carbide of the present invention can be suitably used for a constituent material of a mold for glass lenses such as a camera, which is excellent in surface properties and in which a high quality member is desired to be formed.

Claims (6)

It contains 0.2 mass% or more and 0.9 mass% or less of Co, Cr 0.2 mass% or more and 1.5 mass% or less, and remainder contains the binary compounds and impurities of W and C,
Co is present in the state of Co _x W _y C _z (where x, y, z> 0, x + y> 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 the standard deviation (σ) of the particle size of the WC is σ≤0.25. 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 method according to claim 1, wherein the binary compound of W and C comprises WC or WC and W ₂ C, W ₂ C, W ₂ C / (WC + W ₂ C) ≤ by volume ratio Cemented carbide, characterized in that less than 0.005. The cemented carbide according to claim 1, wherein the cemented carbide has a HRA hardness of 94 or more and 96 or less, fracture toughness (KIC) of 4 MPa · m ^1/2 or more, and a breakdown force of 1 GPa or more. The cemented carbide according to claim 1, further comprising 0.2% by mass or less of V. The cemented carbide according to claim 1, wherein Cr carbide and V carbide are not detected by X-ray diffraction.

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