JP2008001918A - Wc-based cemented carbide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a WC-based cemented carbide having both excellent hardness and toughness. <P>SOLUTION: The WC-based cemented carbide is characterized in that: a binder phase is composed of 3 to 15 wt.% of at least one iron-group metal element; two or more elements among Cr, Ta, V, Ti and Zr are contained; Ta content is 0.005 to 0.06 wt.%; Cr content ranges from 0.03 to 0.2 in weight ratio to the binder phase; the balance has WC and inevitable impurities; and the average grain size of WC is made to ≤0.3μm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a WC-based cemented carbide having WC particles having an average particle size of 0.3 μm or less and having excellent hardness and toughness.

  Patent Documents 1 to 6 contain Cr and V in a metal binder phase containing Co and / or Ni in a cemented carbide, suppress grain growth of WC particles during firing, and contain fine WC particles. A cemented carbide has been proposed.

Japanese Examined Patent Publication No.59-56224 Japanese Patent Publication No. 4-50374 Japanese Patent Publication No. 7-76403 Japanese Patent No. 3008532 Japanese Patent Application No. 2005-54258 Japanese Patent No. 3762777

Patent Document 1 improves wear resistance and toughness without generating a third phase that reduces toughness due to the synergistic effect of Cr and V. Patent Document 2 improves the strength by adjusting the contents of vanadium carbide and chromium carbide and dissolving them in a metal binder phase. Patent Document 3 contains VC and Cr3C2, while suppressing the contents of TaC, NbC, and TiC to suppress the decrease in hardness and toughness. In Patent Document 4, composite carbide containing V and W is formed as a third phase at the grain boundary between the metal binder phase and the WC phase, and characteristics such as hardness and bending strength are improved. The above document contains V for the purpose of improving hardness and strength by the effect of suppressing grain growth of WC particles, and for the purpose of improving toughness by dissolving Cr in Co and / or Ni which are metal binder phases. . Patent Document 5 contains one or more of Cr, V, Ta, Nb, Zr, Hf, and Mo, and a Cr oxide having a size of 100 nm or less exists in the hard dispersed phase. Cr oxide is precipitated in the hard dispersed phase to improve toughness, fracture resistance and chipping resistance. However, it cannot be said that sufficient studies have been made on the contents of Cr, V, Ta, Nb, Zr, Hf and Mo. Patent Document 5 discloses a cemented carbide containing Ti, Cr, and Ta, and discloses that Ti is used to suppress grain growth of the hard phase.
Accordingly, the problem to be solved by the present invention is to provide a WC-based cemented carbide which is further improved in hardness and toughness and is excellent in both.

The WC-based cemented carbide of the present invention contains 3% to 15% by weight of at least one iron group metal element as a binder phase and contains two or more elements of Cr, Ta, V, Ti, and Zr elements. The Ta content is 0.005% to 0.06% by weight, the Cr content is 0.03 to 0.2 by weight ratio to the binder phase, the balance has WC and inevitable impurities, and the average of WC The WC-based cemented carbide is characterized by having a particle size of 0.3 μm or less. By adopting the above configuration, a WC-based cemented carbide having excellent hardness and toughness can be realized.
The Ti content of the WC-based cemented carbide of the present invention is preferably less than 0.005% by weight. The V content is preferably 0.02 to 0.1 by weight ratio to the binder phase.

  By this invention, the WC base cemented carbide which has the outstanding hardness and toughness was able to be provided. For example, when the cemented carbide of the present invention is applied to a processing tool or the like, excellent wear resistance and breakage resistance are exhibited.

  In the present invention, in order to achieve a WC-based cemented carbide having excellent hardness and toughness, the refinement of the microstructure of the cemented carbide was examined by using a fine raw material powder. This is because in a cemented carbide with a fine hard phase, the smaller the WC grain size, the higher the hardness. Therefore, in order to suppress the grain growth of WC, the relationship between the grain growth inhibitor and the amount of the binder phase was examined. As a result, it has been found that even when a small amount of Ta element is added, it effectively works to improve toughness, and the combined use of Cr and Ta has the effect of suppressing the growth of WC. There is a correlation between the Ta element and the element of the binder phase. In order to suppress the growth of WC, a small amount of the Ta element is added, and at the same time, the content of the binder phase element is specified in the present invention. The cemented carbide added with Cr and Ta is characterized by excellent heat resistance in addition to high toughness and high hardness. Since Cr and Ta are effective as a grain growth inhibitor, they are positively added in the present invention. However, sufficient consideration is required for the Ta content. The reason is that excessive Ta addition inevitably generates a precipitated phase. That is, during the liquid phase sintering, (WTa) C or TaC of a double carbide phase containing Ta is generated, and the hard phase may grow greatly. And even if the grain growth inhibitor, such as Cr, is added, it becomes difficult to suppress the grain growth and refine the precipitate phase containing Ta. Therefore, the present invention defines the Ta content from 0.005% to 0.06%. When the Ta content is less than 0.005%, high toughness, high hardness, and excellent heat resistance cannot be obtained, and the Ta addition effect does not appear. On the other hand, if added over 0.06%, a precipitated phase containing Ta is generated, making it difficult to refine the WC particles. Therefore, by adding a small amount of Ta element, Ta effectively works to improve the toughness, and when contained together with a grain growth inhibitor such as Cr, it is effective for atomizing WC particles, and has high toughness and high A cemented carbide with high hardness and excellent heat resistance can be obtained. Moreover, the knowledge that it was preferable to control Ta content so that it might become a specific relationship with respect to a binder phase was acquired. The present invention defines the relationship between the Ta content and Cr and the amount of binder phase as well as the average particle size of WC, which is a hard phase, and the amount of binder phase optimum for the average particle size of WC.

The WC-based cemented carbide of the present invention mainly uses the effect of Cr in order to suppress grain growth of WC particles. Cr content shall be a specific ratio with respect to the weight of the iron group metal element which is a binder phase. Specifically, the weight ratio of Cr with respect to the binder phase is specified to be 0.03 or more and 0.2 or less. If it is less than 0.03, the content is small and grain growth of WC cannot be sufficiently suppressed. On the other hand, if it exceeds 0.2, Cr is excessive, and a brittle phase such as a carbide of Cr is produced in a large amount in the cemented carbide, and this compound becomes a starting point of fracture, which tends to cause a decrease in strength.
The WC-based cemented carbide of the present invention is a sintered body having WC as a hard phase and an iron group metal element such as Co, Ni, or Fe as a binder phase. Here, the composition of the binder phase is preferably Co. In extreme terms, Co alone may be used. Alternatively, one part of Co may be replaced with another iron group element such as Ni. However, the content of the binder phase by the iron group element is specified to be 3% or more and 15% or less. In the case of multiple elements, the total content is assumed. If the content is less than 3%, the bending strength is lowered even if the Cr and Ta contents are appropriate. On the other hand, if the amount exceeds 15%, the amount of the binder phase is too large, which causes a disadvantage that the hardness decreases.
In the WC-based cemented carbide of the present invention, the average particle size of the hard phase is regulated to 0.3 μm or less. The reason for this is that when the thickness exceeds 0.3 μm, the wear resistance is reduced due to a decrease in hardness and the bending strength is decreased due to a decrease in strength. A more preferable average particle diameter is 0.1 μm or less.

On the other hand, in the WC-based cemented carbide of the present invention, it has been found that the phase containing the Ti element may react with carbon and grow grains, which becomes a defect. Therefore, the Ti content is preferably less than 0.005%, and Ti is not intentionally added. Therefore, it is most preferable not to contain Ti. This is because, as a result of examining Ti, particularly, the toughness is adversely affected. Considering the case where it is inevitably mixed, 0.003% or less is preferable, and 0.005% is preferably set as the upper limit. For example, a carbide phase containing Ti may be generated during liquid phase sintering, and the hard phase may grow greatly. And even if the precipitation phase containing these Ti contains Ta and Cr element of a grain growth inhibitor, grain growth advances. And a brittle phase produces | generates abundantly in a cemented carbide alloy, this compound becomes a starting point of a fracture | rupture, and tends to cause a toughness fall.
The fine cemented carbide of the present invention desirably contains V in a weight ratio of 0.02 to 0.1 with respect to the binder phase. Addition of V is preferable because grain growth can be more effectively suppressed and miniaturization can be stabilized. The fine-grain cemented carbide of the present invention is added with the aforementioned Cr as the main and V as the sub as a grain growth inhibitor. When the weight ratio is less than 0.02, the stability of the fine grain structure becomes insufficient, and the effect of adding V cannot be sufficiently obtained. On the other hand, if it exceeds 0.1, the wettability between the hard phase and the binder phase is deteriorated, and the fracture toughness tends to be lowered. A particularly preferred weight ratio is 0.02 or more and 0.06 or less. The content of each component in the WC-based cemented carbide of the present invention can be determined, for example, by inductively coupled plasma emission analysis (hereinafter referred to as ICP analysis).

The WC-based cemented carbide of the present invention preferably contains 0.005% or more and 0.8% or less of Zr. Zr is considered to have little effect of suppressing grain growth and was hardly added to the cemented carbide. However, when added to a cemented carbide with an average particle size of the hard phase of 0.3 μm or less, it is effective for improving the strength, particularly at high temperatures. At this time, the content of Zr is controlled in accordance with the content of the iron group metal element as the binder phase, not just containing Zr. Specifically, when the binder phase is contained in an amount of 5% or more and 15% or less, the strength can be improved by adding Zr. When the Zr content is less than 0.005%, the content becomes an impurity level, and the effect of improving the strength is small. On the other hand, if the content exceeds 0.8%, the content of Zr in the entire cemented carbide becomes excessive, and carbides containing a large amount of Zr become the starting point of fracture, causing a decrease in strength.
In the present invention, at least one of periodic group 4a, 5a, 6a group metals and Al, Si is formed on the surface of the cemented carbide by sputtering, arc ion plating, chemical vapor deposition (hereinafter referred to as CVD), or the like. It is also effective to use a cemented carbide alloy coated with a hard film such as a film such as a compound of carbon, nitrogen, oxygen, boron or the like, a single layer such as an aluminum oxide film or a zirconium oxide film, or a multilayer film. By coating these hard coatings on the fine cemented carbide member of the present invention, the wear resistance, oxidation resistance, slidability, etc. of the surface can be further enhanced. In addition to the rotary tool and the cutting tool, the present invention can provide a remarkable effect when used for a small diameter tool having a blade diameter of 0.3 mm or less, particularly a small diameter drill or a router. The same excellent effect can be obtained even when applied to a processing tool such as a small wear-resistant tool, a push pin, a die, or a sliding material. The WC-based cemented carbide of the present invention will be specifically described based on the following examples.

(Example 1)
As raw material powders, WC powder having an average particle diameter of 0.4 μm, Co powder having an average particle diameter of 1.2 μm, Cr3C2 powder having an average particle diameter of 1.5 μm, TaC powder having an average particle diameter of 1.2 μm, A VC powder having an average particle size of 1.2 μm and a (W, Zr) C solid solution powder having an average particle size of 1.2 μm were prepared, and these powders were blended into the compositions shown in Table 1.

The blended powder was pulverized and mixed in an alcohol using an attritor for 12 hours, and a molding resin was added and dried to prepare a mixed powder. This mixed powder was press-molded at a pressure of 100 MPa to obtain a molded body for a JIS bending test piece (JIS-B-4053). After these compacts were sintered in a vacuum atmosphere at 1380 ° C. for 30 minutes, they were pressurized with argon gas at 4.9 MPa for 30 minutes and cooled in the furnace. As the sintering conditions, in order to control the amount of C to an appropriate value, conditions in which the temperature profile, the degree of vacuum, the atmospheric gas composition, etc. were optimized were used. The sintered body obtained from the molded body for JIS test pieces was ground with a diamond grindstone to produce JIS bending strength test pieces having dimensions of 4 mm × 8 mm × 24 mm. From these test pieces, the contents of Co, Cr, Ta, Ti, V, and Zr were measured. Co, which is a metallic binder phase, was mirror-polished on the cross section of the cemented carbide and then analyzed with a fluorescent X-ray analyzer (manufactured by Rigaku, ZSX-100E) to quantitatively determine its content. Cr, Ta, Ti, V, and Zr contained in the metal binder phase are obtained by dissolving finely pulverized cemented carbide with H3PO4, HCl, HF, HNO3, and H2SO4, and ionizing them. By ICP analysis, the type of each element was identified and the content was quantitatively determined. The analysis results are also shown in Table 1.
Further, Invention Example 19 having the same composition as Invention Example 3 in Table 1 and 1 part of Co substituted with Ni, and Invention Example 20 using pre-mixed material powders were prepared. Invention Example 19 was prepared under the same conditions as in the Invention Example except that Ni powder and Co powder having an average particle diameter of 1 μm were used. Invention Example 20 was prepared under the same conditions as in the above-described Invention Example except that the material powder having the composition shown in Table 1 was previously mixed. Furthermore, the comparative example 30 from which the average particle diameter of WC differs, and the comparative example 31 which does not give the pressurization process after sintering were produced. In Comparative Example 30, WC powder having an average particle size of 1.0 μm, Co raw material powder having an average particle size of 1 μm, Cr3C2 powder having an average particle size of 1.5 μm, and TaC powder having an average particle size of 1.2 μm are prepared. These powders were blended in the composition shown in Table 1. In Comparative Example 31, material powder having the composition shown in Table 1 was prepared and blended, and the sintering temperature was set to 1480 ° C., which is 100 ° C. higher than the conditions of the present invention example, and was sintered.

  Next, the average particle diameter, bending strength, and hardness of WC were measured using a JIS bending strength test piece. The average grain size of WC is obtained by clarifying the grain boundaries of cemented carbide by mirror polishing the section of cemented carbide and then etching 0.5 minutes with Murakami reagent and 0.5 minutes with aqua regia. , An enlarged copy of an image taken at a magnification of 10 k with a scanning electron microscope (manufactured by Hitachi, Ltd., S-4200, hereinafter referred to as SEM), and this is image analysis software (Image-Pro Plus Version 4.0 for Windows, Media) (Cybernetics, Windows is a registered trademark). In the bending strength test, ten bending strengths were measured for each sample, and an average value (GPa) of the ten bending strengths was obtained. The measurement results are shown in Table 2.

As shown in Table 2, Examples 1 to 20 of the present invention in which an iron group metal is used as a binder phase, a small amount of Ta is contained, and a predetermined amount of Cr is contained in the binder phase have an average WC particle size of 0.3 μm. It was as follows, showing high bending strength and high hardness, and was excellent in both. Further, it is considered that a uniform fine grain structure was obtained with little variation in bending strength. In particular, the inventive examples 14 to 18 containing V were found to have excellent bending strength and high hardness.
By comparing Invention Examples 1 to 4 and Comparative Examples 21 to 24, it can be seen that the content of the binder phase affects the bending strength. When the content of the binder phase was less than 3%, the bending strength was lowered even when the content of Cr and Ta was appropriate. On the other hand, if it exceeds 15%, the amount of the binder phase is too large, and thus the hardness is lowered.
By comparing Invention Example 3, Invention Examples 5 and 6, and Comparative Examples 25 to 27, the influence of the Ta content can be understood. By adding a small amount of Ta element, Ta effectively works to improve toughness, and when contained together with a grain growth inhibitor such as Cr, it is effective for atomizing WC particles, and has high bending strength and high resistance. A cemented carbide with high hardness was obtained. However, in Comparative Example 25 of less than 0.005%, satisfactory bending strength could not be obtained, and the Ta addition effect did not appear. In Comparative Examples 26 and 27 exceeding 0.06%, a precipitated phase containing Ta was generated, and it was difficult to refine the WC particles.
By comparing Invention Example 3 and Invention Examples 7 to 10 and Comparative Examples 28 and 29, the influence of Cr content on the bending strength can be understood. In the example of the present invention, WC can be uniformly atomized by adding an appropriate amount of Cr. However, Comparative Example 28 having a Cr content ratio of less than 0.03 has a small content and could not sufficiently suppress the grain growth of WC. In Comparative Example 29 in which the Cr content ratio exceeds 0.2, Cr is excessive, and a brittle phase such as a carbide of Cr is produced in a large amount in the cemented carbide. Power decreased. In Comparative Examples 28 and 29, the variation in the bending strength was large, so it is considered that the Cr content contributes to the suppression of grain growth of WC.
By comparing Invention Example 3 and Invention Examples 11 to 13, the effect of the presence or absence of Ti can be understood. Invention Example 3 containing no Ti is most preferred. This is because the Ti content adversely affects the bending strength. Therefore, 0.003% or less is preferable, and 0.005% is preferably set as the upper limit. By comparing Inventive Examples 3 and 19, when the binder phase was only Co, a cemented carbide having superior characteristics was obtained. By comparing Invention Examples 3 and 20, it was found that a powder in which material powders were mixed in advance could also be used. By comparing Inventive Example 3 and Comparative Example 30, by using finer powder as the raw material powder, a finer WC can be obtained, and a cemented carbide having both high bending strength and high hardness can be obtained. I understood. By comparing Inventive Example 3 and Comparative Example 31, a cemented carbide having excellent characteristics was obtained by sintering using an argon gas after sintering.

(Example 2)
The mixed powder shown in Table 1 was extruded at a pressure of 25 MPa to produce a round bar molded body having a diameter of 4.7 mm. Each of the round bar sintered bodies obtained from this round bar molded body was polished, and a small diameter drill having a total length of 38.1 mm, a shank diameter of 3.175 mm, a cutting edge diameter of 0.25 mm, and a groove length of 5.5 mm was obtained. Produced. Using these small diameter drills, a drilling test was conducted. The evaluation method evaluated the wear resistance by measuring the amount of reduction in the diameter of the edge of a small-diameter drill after processing after hitting 5000 holes. Also, in order to measure the strength, 20 drills were used for each condition, and the number of broken drills was measured when the work material hit 6000 with a feed rate of 19 μm / rotation, Sex was evaluated. These evaluation results are shown in Table 3.

(Test conditions)
Work material: Two glass epoxy copper-clad 4-layer laminates with a plate thickness of 1.6 mm Rotating speed: 160,000 rotations per minute Feed rate during evaluation of wear resistance: 13 μm / rotation breakage evaluation Feeding time: 19 μm / rotation WC average particle diameter, Co, Cr, Ta, Ti, V, Zr analysis values, bending strength, hardness of each small-diameter drill shown in Table 3 are materials for firing conditions, etc. Since the conditions were the same as those of the JIS bent specimen, the JIS bent specimen numbers shown in Tables 1 and 2 were regarded as the same as the same. Therefore, according to the sample numbers in Table 1, the present invention examples 32 to 51 and comparative examples 52 to 62 were used. From the results in Table 3, Invention Examples 32 to 51 showed excellent wear resistance and breakage resistance. Invention Examples 45 to 48 containing Zr were excellent in strength at a high temperature of the cutting edge temperature at the time of cutting. The present invention example in which a predetermined amount of an iron group metal is used as a binder phase and contains a very small amount of Ta and a predetermined amount of Cr with respect to the binder phase is less likely to break, and is further excellent in breakage resistance and toughness. It turned out to be a thing. This result was because there was almost no coarse WC in the small diameter drill. Therefore, the cutting tool made of the cemented carbide of the present invention has excellent wear resistance and breakage resistance, and has a long tool life. I was able to improve.

Claims (3)

The WC-based cemented carbide contains 3% to 15% by weight of at least one iron group metal element as a binder phase, and contains two or more elements of Cr, Ta, V, Ti, and Zr elements. The content is 0.005% to 0.06% by weight, the Cr content is 0.03 to 0.2 by weight ratio to the binder phase, the balance has WC and inevitable impurities, and the average particle size of WC is A WC-based cemented carbide characterized by being 0.3 μm or less. The WC-based cemented carbide according to claim 1, wherein the WC-based cemented carbide has a Ti content of less than 0.005% by weight. The WC-base cemented carbide according to claim 1, wherein the WC-base cemented carbide has a V content of 0.02 to 0.1 in terms of weight ratio to the binder phase.