JP2012162753A - Cemented carbide and method of manufacturing the same, and micro drill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cemented carbide having high toughness and strength and having excellent chipping resistance and breaking resistance, to provide a method of manufacturing the same, and to provide a micro drill.SOLUTION: The cemented carbide has a hard phase mainly composed of WC particles and a bonded phase mainly composed of Co. Then, the hard phase is formed by a solid solution of Cr in the WC particles, and the average particle diameter of the WC particles is 0.5 μm or smaller. Furthermore, in the local structure of a Cr atom by an X-ray absorption spectrum method, the Cr atom is bonded to a W atom, and the ratio of (number of the W atoms/{number of the Cr atoms+number of Co atoms}) obtained by dividing the number of the W atoms present within 300 pm from the Cr atom by the sum of the number of the Cr atoms and the number of the Co atoms present within 300 pm from the Cr atom is 0.3 or larger.

Description

  The present invention relates to a cemented carbide, a manufacturing method thereof, and a micro drill. In particular, the present invention relates to a cemented carbide having high toughness and strength and excellent fracture resistance (chipping resistance) and fracture resistance.

  For example, raw material powders containing WC (tungsten carbide) powder (hard phase) and Co (cobalt) powder (binding phase) are mixed as materials for cutting tools such as micro drills and end mills for drilling printed circuit boards. Then, sintered cemented carbide is used (for example, see Patent Documents 1 to 7).

In the above-mentioned cemented carbide for cutting tools such as a micro drill, for example, it has been proposed to refine WC particles in order to extend the life. In order to refine the WC particles, as described in Patent Documents 1 to 3, VC (vanadium carbide), Cr ₃ C ₂ (chromium carbide), etc., as grain growth inhibitors that suppress the grain growth of WC particles. Addition of metal carbide of

  On the other hand, Patent Documents 4 to 7 use WC powder in which Cr is dissolved in WC particles as a raw material powder to refine the WC particles and improve the hardness, strength, toughness, etc. of the cemented carbide. It is described.

JP 2004-52110 A Japanese Examined Patent Publication No. 62-56224 Japanese Patent Publication No. 4-50374 Japanese Patent Laid-Open No. 2001-269809 JP-A-9-302437 JP-A-7-252555 JP 2004-238660 A

  For example, in micro drills for drilling printed circuit boards, the hardness, strength, and strength of the cemented carbide alloy used as the material are met to reduce the diameter, make the board difficult to process, and increase the processing efficiency (high-speed rotation and high-feed processing). There is a need for further improvement in toughness. However, conventional cemented carbides cannot sufficiently meet the requirements in terms of strength and toughness, and cannot be said to have sufficient fracture resistance (chipping resistance) and fracture resistance.

  The present invention has been made in view of the above circumstances, and one of its purposes is to provide a cemented carbide having high toughness and strength, excellent fracture resistance (chipping resistance) and fracture resistance, and a method for producing the same. It is to provide. Another object of the present invention is to provide a micro drill made of this cemented carbide.

  The present inventors use WC powder in which Cr is dissolved in WC particles as raw material powder, and by devising a manufacturing method (especially sintering and cooling conditions in the sintering process), the toughness and strength are high, It was found that a cemented carbide excellent in fracture resistance (chipping resistance) and fracture resistance can be obtained. The present invention is based on the above findings.

  The cemented carbide of the present invention includes a hard phase mainly composed of WC particles and a binder phase mainly composed of Co. The hard phase is a solid solution of Cr in the WC particles, and the average particle size of the WC particles is 0.5 μm or less. In addition, in the local structure of Cr atoms by X-ray absorption spectroscopy, the number of W atoms present within 300 pm from Cr atoms and Cr atoms bonded to W atoms is defined as Cr atoms present within 300 pm from Cr atoms. The ratio (number of W atoms / {number of Cr atoms + number of Co atoms}) divided by the sum of the number of and the number of Co atoms is 0.3 or more.

  The cemented carbide of the present invention suppresses the decrease in toughness and strength of cemented carbide due to cleavage of WC particles because Cr dissolves in the WC particles of the hard phase to obtain a solid solution strengthening action on the WC particles. The toughness and strength of the cemented carbide can be ensured. In the local structure of Cr atoms by X-ray absorption spectroscopy, since Cr atoms are bonded to W atoms, Cr atoms are substituted at the W atom sites, and Cr is dissolved in WC particles. I understand that. The ratio of the number of W atoms existing within 300 pm from the Cr atom divided by the sum of the number of Cr atoms existing within 300 pm from the Cr atom and the number of Co atoms (number of W atoms / {number of Cr atoms + number of Co atoms }) Is 0.3 or more, the ratio of Cr present in WC particles (hard phase) (existence probability) is higher than Cr present in Co (binding phase), and the effect of improving toughness and strength Is obtained. When this number of W atoms / {number of Cr atoms + number of Co atoms} is less than 0.3, the ratio of Cr present in the hard phase is low, so the effect of improving toughness and strength is small, and a sufficient effect is obtained. Absent. Furthermore, since the average particle diameter of the WC particles is 0.5 μm or less, the toughness and strength of the cemented carbide can be increased while maintaining high hardness.

  In the local structure of Cr atoms by the X-ray absorption spectroscopy described above, the number of W atoms existing within 300 pm from the Cr atom is the sum of the number of Cr atoms existing within 300 pm from the Cr atom and the number of Co atoms. The divided ratio (number of W atoms / {number of Cr atoms + number of Co atoms}) is preferably 0.5 or more.

  The number of W atoms / {number of Cr atoms + number of Co atoms} is 0.5 or more, so there is almost no Cr in Co (bonded phase) and most of Cr is present in WC particles (hard phase). is doing. That is, almost no Cr is eluted in Co (binding phase), and most of Cr is dissolved in WC particles (hard phase). Thereby, since the ratio of Cr existing in the hard phase becomes higher, the effect of improving toughness and strength is greater.

  As one form of the cemented carbide of the present invention, a form in which the content of Cr with respect to the WC particles in the hard phase is 0.5% by mass or more and 3.0% by mass or less.

  When the content of Cr with respect to the WC particles is less than 0.5% by mass, the solid solution amount of Cr with respect to the entire WC particles (hard phase) is small, and it is difficult to obtain a solid solution strengthening action with respect to the WC particles. On the other hand, if the Cr content exceeds 3.0% by mass, the solid solution amount of Cr in the entire WC particles (hard phase) is large, and the strength of the WC particles decreases. There is a risk of inviting.

  One form of the cemented carbide of the present invention is a form in which the content of the binder phase in the cemented carbide is 5% by mass or more and 20% by mass or less.

  When the content of the binder phase in the cemented carbide is less than 5% by mass, the ratio of the binder phase to the whole alloy is small, which may lead to a decrease in the toughness and strength of the cemented carbide, and the sinterability may decrease. On the other hand, when the content of the binder phase is more than 20% by mass, the proportion of the hard phase is relatively decreased, and the hardness of the cemented carbide may be lowered. The content of the hard phase in the cemented carbide may be 80% by mass or more and 95% by mass or less.

  One form of the cemented carbide of the present invention is a form containing 1.0% by mass or less of VC.

  By containing VC, grain growth of WC particles can be suppressed. However, if a large amount of metal carbide such as VC (more than 1% by mass) is contained, the toughness and strength of the cemented carbide may decrease due to the precipitation of metal carbide, so the VC content is 1.0% by mass or less. Preferably there is. When the cemented carbide of the present invention does not contain VC, it contains, for example, Co and Cr, and the balance consists of WC and inevitable impurities. In the case of containing VC, for example, Co, VC, and Cr are contained, and the balance is composed of WC and inevitable impurities.

The method for manufacturing a cemented carbide according to the present invention includes the following steps.
A mixing step in which a mixed powder is prepared by mixing and pulverizing raw material powder containing WC powder and Co powder in which Cr is dissolved in WC particles.
A sintering process in which the mixed powder is held at a sintering temperature of 1300 ° C. or more and 1370 ° C. or less for less than 60 minutes to be sintered, and then cooled to 1000 ° C. at a cooling rate of 50 ° C./min or more to produce a sintered body.

  A feature of the production method of the present invention is that WC powder in which Cr is dissolved in WC particles is used as a raw material powder, and there are sintering and cooling conditions in the sintering step. By setting the sintering temperature to a low temperature range of 1300 ° C or higher and 1370 ° C or lower, the activation of Cr dissolved in the WC particles (hard phase) is suppressed while the sintering proceeds sufficiently, and Cr is bound to Co (bonded) Elution in the phase) can be suppressed. By keeping the above-mentioned sintering temperature (holding time) shorter than 60 minutes, the liquid phase appearance time of Co (binding phase) is shortened and dissolved in WC particles (hard phase). Elution of Cr into Co (binding phase) can be suppressed. Moreover, grain growth of WC particles can be suppressed. The rapid cooling of the cooling rate to 1000 ° C at 50 ° C / min or more shortens the time until the Co (bonded phase) solidifies, and Cr dissolved in the WC particles (hard phase) becomes Co (bonded phase). Elution). When the sintering temperature is less than 1300 ° C., it is difficult to sufficiently advance the sintering. On the other hand, when the sintering temperature is higher than 1370 ° C. or the holding time is 60 minutes or more, Cr dissolved in the WC particles is easily eluted into Co or the WC particles are likely to grow. In addition, when the cooling rate is less than 50 ° C./min, Cr that is solid-solved in the WC particles tends to elute into Co.

  In the conventional manufacturing method, the sintering temperature was high temperature (above 1370 ° C.), the holding time was long (60 minutes or more), or the cooling rate was slow cooling (less than 50 ° C./min. For example, furnace cooling) By using WC powder, which dissolves Cr in WC particles, as raw material powder, Cr that dissolves in WC particles elutes into Co even though the WC particles can be refined. A sufficient reinforcing effect was not obtained.

  The above sintering temperature is preferably 1320 ° C. or higher and 1360 ° C. or lower. The holding time is preferably 10 minutes or longer and 30 minutes or shorter. Setting the holding time to 10 minutes or more makes it easier to suppress the dissolution of Cr, which dissolves in the WC particles, into the Co by setting the holding time to 30 minutes or less while allowing the sintering to proceed sufficiently. . Furthermore, the above cooling rate is preferably 70 ° C./min or higher up to 1000 ° C.

Sintering is performed, for example, in a sintering furnace in a vacuum atmosphere or an inert gas (eg, Ar, CO, N ₂ etc.) atmosphere, and cooling after sintering is performed by, for example, an inert gas for cooling (eg, This can be achieved by introducing Ar, CO, N ₂ etc.) into the sintering furnace. The cooling rate can be controlled by adjusting the temperature and flow rate of the cooling gas.

  In the production method of the present invention, it is preferable to include a HIP process for HIP processing the sintered body.

Defects (for example, pores) inside the sintered body (sintered cemented carbide) can be removed by HIP (hot isostatic pressing) processing, and a dense cemented carbide is obtained. Can do. The HIP conditions are preferably, for example, using an inert gas such as Ar or N ₂ as a pressure medium, temperature: 1370 ° C. or less, and pressure: 10 MPa to 100 MPa.

  As one form of the manufacturing method of this invention, the form whose average particle diameter of WC particle is 0.2 micrometer or more and 0.8 micrometer or less is mentioned.

  The particle size of the WC particles in the hard phase of the cemented carbide finally obtained varies depending on the particle size of the WC particles constituting the WC powder used for the raw material powder and the mixing and pulverizing conditions in the mixing step. In the production method of the present invention, the WC particles of the WC powder may be fine so that a cemented carbide with a fine WC particle in the hard phase (average particle size: 0.5 μm or less) can be stably obtained. preferable. Specifically, it is preferable to use WC powder having an average particle diameter of WC particles of 0.2 μm or more and 0.8 μm or less. When the average particle diameter of the WC particles is less than 0.2 μm, the WC particles are likely to aggregate when mixed in the mixing step, which may cause the WC particles to become coarse and non-uniform. Further, when the average particle diameter of the WC particles is more than 0.8 μm, the WC particles are not sufficiently pulverized in the mixing step, and there is a possibility that the WC particles become coarse and non-uniform.

  On the other hand, as the Co powder used as the raw material powder, it is preferable to use, for example, one having an average particle size of 0.5 μm or more and 3.0 μm or less so as to be easily mixed with fine WC powder. When the average particle size of the Co powder is less than 0.5 μm, the Co powder tends to aggregate when mixed in the mixing step, and the Co powder is not uniformly dispersed, which may cause a decrease in sinterability. On the other hand, when the average particle size of the Co powder is more than 3.0 μm, it is difficult to uniformly mix with the fine WC powder, which may cause a decrease in sinterability. In order to improve the sinterability in a low temperature region and in a short time, the average particle size of the Co powder is preferably 2.0 μm or less.

  In the mixing step described above, the mixing and pulverization of the raw material powder can be realized by using a pulverizing and dispersing machine having a rotating blade 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 mixing and pulverization (hereinafter referred to as a pre-process) for 5 hours from the start of mixing and pulverization at a high speed, and to perform subsequent mixing and pulverization (hereinafter referred to as a post-process) at a low speed. In the previous step, the rough mixing and grinding are completed, and in the subsequent step, dispersion is mainly promoted. Thus, it is easy to realize uniform mixing, pulverization and dispersion by changing the mixing and pulverization conditions in multiple stages. Here, when the mixing and pulverization is performed at a high speed over the whole, the raw material powder is agglomerated, and there is a possibility that the dispersed state of the mixed powder becomes non-uniform. On the other hand, when the mixing and pulverization is performed at a low speed over the whole, mixing and pulverization of the raw material powder is insufficient, and there is a possibility that the mixed state and the pulverized state of the mixed powder are not uniform.

  As one form of the manufacturing method of this invention, the form whose content of Cr with respect to WC particle is 0.5 mass% or more and 3.0 mass% or less is mentioned.

  In the production method of the present invention, a WC powder that dissolves Cr in WC particles is used as a raw material powder, and the production method is devised to suppress the dissolution of Cr dissolved in WC particles into Co during production. Thus, in the cemented carbide finally obtained, one of the aims is to obtain a solid solution strengthening action on the WC particles by the solid solution of Cr in the hard phase WC particles. If the Cr content in the WC particles is less than 0.5% by mass, the solid solution amount of Cr in the WC particles is small, and it is difficult to obtain a solid solution strengthening action on the WC particles. On the other hand, if the Cr content is more than 3.0% by mass, the solid solution amount of Cr in the WC particles is large, and the strength of the WC particles is decreased, which may cause a decrease in the toughness and strength of the cemented carbide. . Here, when Cr that dissolves in WC particles is not eluted in Co, the Cr content in the WC particles of the WC powder is the Cr content in the WC particles in the hard phase of the cemented carbide finally obtained. Is substantially equal to the quantity.

  The micro drill of the present invention is characterized by comprising the above-described cemented carbide of the present invention.

  Since the microdrill of the present invention is made of the above-described cemented carbide of the present invention having high toughness and strength, it is excellent in fracture resistance (chipping resistance) and fracture resistance. When the cemented carbide of the present invention is processed into, for example, a microdrill, cleaving of WC particles hardly occurs even if grinding processing or other processing (eg, wire processing, electric discharge processing, etc.) is performed. , Cracks, and breakage are unlikely to occur. When the microdrill of the present invention is used for cutting (drilling), cleaving of WC particles hardly occurs during cutting, and chipping and breakage during cutting can be reduced. In addition, the micro drill of the present invention can increase the residual stress due to grinding during drilling due to improved strength of the WC particles in the cemented carbide, making it difficult to break, and increasing the number of HITs (longer life). it can. Furthermore, the micro drill of the present invention has an average particle diameter of WC particles in the cemented carbide of 0.5 μm or less, and can realize highly accurate and stable cutting (drilling). The micro drill of the present invention has a diameter (drill diameter) of φ0.5 mm or less, for example.

  The cemented carbide of the present invention has high toughness and strength by dissolving Cr in WC particles and having a specific structure (average particle diameter of WC particles, local structure of Cr atoms by X-ray absorption spectroscopy). , Excellent in chipping resistance (chipping resistance) and breakage resistance. Moreover, the manufacturing method of the cemented carbide alloy of this invention can manufacture the above-mentioned cemented carbide alloy of this invention. Furthermore, the microdrill of the present invention is made of the above-mentioned cemented carbide of the present invention, is less likely to cause chipping and breakage, and is excellent in chipping resistance and breakage resistance.

It is the spectrum which carried out the Fourier transform of each EXAFS vibration of the cemented carbide of sample No.1-1, 1-4, 1-36.

[Example 1]
A WC powder in which Cr was dissolved in WC particles was prepared, and this was used as a raw material powder to produce a cemented carbide. The resulting cemented carbide was analyzed. Moreover, a micro drill for drilling a printed circuit board was produced from the cemented carbide and the drill cutting performance was evaluated.

<Cemented carbide>
(Sample Nos. 1-1 to 1-27)
Prepare WC powder (average particle size: 0.5μm), Co powder (average particle size: 0.7μm) and VC powder (average particle size: 1.0μm) in which Cr is dissolved in WC particles. Powder was prepared. Here, a WC powder having a Cr content of 1.0% by mass with respect to the WC particles was prepared. The raw material powder was blended so that the Co powder was 7% by mass, the VC powder was 0.3% by mass, and the balance was WC powder. Any of various powders can use commercially available powders.

(Sample Nos. 1-28 to 1-33)
WC powder, Co powder and VC powder were blended in the same proportions as in Sample Nos. 1-1 to 1-27 described above except that the average particle diameter of WC particles of the prepared WC powder was 1.0 μm. Raw material powder was prepared.

(Sample Nos. 1-34 to 1-39)
WC powder (pure WC powder, average particle size: 0.5 μm), Co powder (average particle size: 0.7 μm), VC powder (average particle size: 1.0 μm) and Cr ₃ C ₂ powder that do not dissolve Cr in WC particles (Average particle size: 1.0 μm) was prepared, and a raw material powder containing these powders was prepared. Here, the raw material powder was blended so as to be Co powder: 7% by mass, VC powder: 0.3% by mass, Cr ₃ C ₂ powder: 0.9% by mass, and the balance: WC powder.

  The raw material powder of each sample was mixed and pulverized to prepare a mixed powder. Here, 2% by mass of powdered paraffin was added to the raw material powder, and wet mixed and pulverized using a bead mill. For the media of the bead mill, balls made of cemented carbide with a diameter of 2 mm were used. Further, the mixing and pulverization was performed for a total of 10 hours, from the start to 5 hours by high speed rotation (1000 r.p.m.), and for the remaining time by low speed rotation (500 r.p.m.).

  The mixed powder of each sample was dried by spray drying and then molded using a molding apparatus. And after arrange | positioning the molded object of the mixed powder of each sample in a sintering furnace, and sintering each in a vacuum atmosphere on the conditions of sintering temperature: 1320 degreeC-1400 degreeC and holding time: 10 minutes-60 minutes, A cooling gas was introduced into the sintering furnace, and each was cooled at a cooling rate of 70 ° C./min to 30 ° C./min to produce sintered bodies (hard metal) of each sample. Tables 1 and 2 show the sintering conditions (sintering temperature and holding time) and cooling conditions (cooling rate) for each sample, respectively. The cooling rate is a cooling rate up to at least 1000 ° C. Here, Ar was used as the cooling gas, and the cooling rate was controlled by adjusting the flow rate of the cooling gas introduced into the sintering furnace.

  Finally, the sintered body of each sample was subjected to HIP treatment under the conditions of pressure medium: Ar, temperature: 1370 ° C., and pressure: 10 MPa to produce a cemented carbide of each sample.

The microstructure of each sample of the cemented carbide was observed, and the average particle size of the WC particles in the cemented carbide was determined. The results are shown in Tables 1 and 2. Tissue observation was performed as follows. The cemented carbide of each sample was cut at an arbitrary position, this cross section was ground, and then further buffed (# 3000). The polished cross section was observed at a magnification of about 10000 times by FE-SEM (Field Emission Scanning Electron Microscope) using an EBSD (Electron Back-Scatter Diffraction) method. Tissue observation was performed for each field by selecting an arbitrary plurality of fields (here, one field: 100 μm ² for a total of three fields) with respect to the polished cross section. For each field of view, all the WC particles existing in the field of view were classified by color (mapping) according to crystal orientation so that the grain boundaries could be visually grasped. Image analysis was performed on the obtained mapping image of each visual field, and the diameter of a circle equal to the area was determined from each area of all WC particles present in the visual field in each visual field, and the average value was defined as the average particle diameter. . A commercially available FE-SEM / EBSD apparatus can be used for the measurement of the average particle diameter.

  X-ray absorption fine structure (XAFS) analysis was performed on the cemented carbide of each sample by X-ray absorption spectroscopy, and the local structure of Cr atoms in the cemented carbide was investigated. Specifically, the XAFS (Extend X-ray Absorption Fine Structure) analysis is mainly performed, and the resulting EXAFS vibration is Fourier transformed to obtain local structures around Cr atoms (proximity atomic species, Information on distance between atoms was obtained.

  Here, as an example, FIG. 1 shows a spectrum obtained by Fourier transforming each EXAFS vibration of the cemented carbides of Sample Nos. 1-1, 1-4, and 1-36. The vertical axis of the spectrum shown in FIG. 1 is an arbitrary unit (a.u .: arbitrary unit), and the horizontal axis is the distance (pm) from the Cr atom. In FIG. 1, the spectrum of sample No. 1-1 is indicated by a thick solid line, the spectrum of sample No. 1-4 is indicated by a thin solid line, the spectrum of sample No. 1-36 is indicated by a broken line, and the spectrum of each sample is shown together. . For the cemented carbide of each sample, the atomic species around the Cr atoms were identified from the obtained information. The result is also shown in FIG. 1 together with the spectrum.

  For example, in the spectrum of sample No. 1-1 shown in FIG. 1, O and C exist as the nearest atoms. Here, since the cross section of the sintered body is the object of analysis, Cr—C bonds due to W site substitution in the WC particles and Cr—O bonds due to oxidation have been detected. Cr and Co are present as the second neighboring atoms, Cr—Cr bond and Cr—Co bond are present, and W is present as the third neighboring atom and the Cr—W bond is detected. The Cr—Cr bond and the Cr—Co bond appear when Cr is present in the bonded phase or when it is present in the WC particle and at the interface between the WC particle and the bonded phase.

  Then, for the cemented carbide of each sample, the peak in the obtained spectrum is analyzed, the coordination number of each atom of W atom, Cr atom and Co atom is calculated, W atom number / {Cr atom number + Co atom Number}. The results are shown in Tables 1 and 2 (item “W / {Cr + Co}” in the table). Here, in the local structure of Cr atoms by X-ray absorption spectroscopy, the number of W atoms, Cr atoms, and Co atoms existing within 300 pm from all Cr atoms in the analysis target range is examined. By averaging, the number of W atoms / {number of Cr atoms + number of Co atoms} was obtained. In other words, the number of W atoms / {number of Cr atoms + number of Co atoms} shown in Tables 1 and 2 is not obtained in relation to a specific one Cr atom.

  From the results in Tables 1 and 2, the cemented carbides of Sample Nos. 1-1, 1-2, 1-4, 1-5, 1-10, 1-11, 1-13, and 1-14 In the local structure of Cr atoms by X-ray absorption spectroscopy, the number of W atoms within 300pm / {Cr atoms + Co atoms } Was 0.3 or more. Moreover, in the cemented carbides of these samples, it was found from the information on the local structure of Cr atoms that Cr atoms were substituted at the W atom sites and the Cr atoms were bonded to the W atoms. From the above, the cemented carbides of Sample Nos. 1-1, 1-2, 1-4, 1-5, 1-10, 1-11, 1-13, 1-14 satisfy the requirements of the present invention. It is the product of the present invention that satisfies. The cemented carbides of these samples have a number of W atoms / {number of Cr atoms + number of Co atoms} of 0.3 or more, so WC particles (hard phase) with respect to Cr present in Co (binding phase) The ratio of Cr present in the inside is high. This is presumed that Cr dissolved in the WC particles of the WC powder used as the raw material powder was prevented from eluting into the Co of the binder phase, and Cr was dissolved in the WC particles of the hard phase. . Among these samples, the cemented carbides of Sample Nos. 1-1, 1-2, 1-4, 1-5, 1-10, 1-11 have the number of W atoms / {number of Cr atoms + number of Co atoms}. It is 0.5 or more, and Cr dissolved in the WC particles of the WC powder used as the raw material powder is hardly eluted in the binder phase Co, and most of the Cr is dissolved in the hard phase WC particles. Presumed to be. In particular, the cemented carbides of Sample Nos. 1-1, 1-2, 1-4, and 1-5 have a number of W atoms / {number of Cr atoms + number of Co atoms} of 0.8 or more, and the WC used for the raw material powder It is considered that Cr dissolved in the WC particles of the powder is not substantially eluted in the Co of the binder phase, and the Cr content dissolved in the WC particles of the WC powder and dissolved in the WC particles of the hard phase It is considered that the Cr content is substantially equal.

  On the other hand, among sample Nos. 1-1 to 1-27, in the sintering and cooling conditions, the sintering temperature was 1400 ° C., the holding time was 60 minutes, and the cooling rate was 30 ° C./min. Cemented carbide has a W atom count / {Cr atom count + Co atom count} of less than 0.3, and the ratio of Cr present in WC particles (hard phase) to Cr present in Co (binding phase) Is low. This is considered to be caused by the dissolution of Cr, which is solid-solved in the WC particles of the WC powder used as the raw material powder, into the binder phase Co. Therefore, the Cr content in the WC particles in the hard phase is also reduced. Presumed to be.

  In addition, the cemented carbides of Sample Nos. 1-28 to 1-33 in which the average particle size of the WC powder of the WC powder used as the raw material powder is 1 μm, the average particle size of the WC particles in the hard phase is more than 0.5 μm. there were.

  Furthermore, the cemented carbide of Sample Nos. 1-34 to 1-39 using WC powder that does not dissolve Cr in WC particles as the raw material powder has zero W atoms / {Cr atoms + Co atoms}. It is presumed that Cr exists only in Co (binding phase) and Cr does not exist in WC particles (hard phase).

<Micro drill>
Each of the cemented carbides of Sample Nos. 1-1 to 1-39 was ground to produce a plurality of micro drills having a drill diameter of 0.1 mm. And about the micro drill of each sample, various cutting tests (following tests AC) were done, and cutting performance was evaluated. The conditions and evaluation methods for each test are shown below. The results of each test are shown in Tables 3 and 4.

  The conditions of each test were as follows. The work material was made by stacking five copper clad laminates (CCL: Copper Clad Laminate) with a thickness of 0.4 mm, the rotation speed was 30000 rpm, the feed speed Was 10 μm / rev.

The evaluation method for each test was as follows.
Test A: Presence / absence of chipping when drilling 5000HIT.
Test B: Number of breaks in 10 when drilling 15000 HIT was performed on 10 micro drills.
Test C: Average number of HITs (number of drilling operations) before breaking when drilling 5 micro drills.

  From the results in Tables 3 and 4, the micro drills of Sample Nos. 1-1, 1-2, 1-4, 1-5, 1-10, 1-11, 1-13, 1-14 There was no chipping, the number of breaks in test B was 3 or less out of 10, and the average number of HITs in test C was 18000 HIT or more. For this reason, the micro drills of these samples have high toughness and strength, and are excellent in fracture resistance (chipping resistance) and breakage resistance. In particular, the micro drills of sample Nos. 1-1, 1-2, 1-4, 1-5, 1-10, and 1-11 have less than 2 of 10 breaks in test B, and the average of test C The number of HITs is 19000 HIT or more, chipping and breakage hardly occur, and excellent chipping resistance (chipping resistance) and breakage resistance. On the other hand, the micro-drills of the remaining samples were inferior in terms of fracture resistance (chipping resistance) or breakage resistance.

  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 material for a cutting tool represented by, for example, a micro drill or an end mill. Moreover, the manufacturing method of the cemented carbide of this invention can be utilized for manufacture of the toughness and high intensity | strength super-fine-grain cemented carbide alloy. Furthermore, the micro drill of the present invention can be used, for example, for drilling a printed circuit board.

Claims (10)

A cemented carbide comprising a hard phase mainly composed of WC particles and a binder phase mainly composed of Co,
The hard phase is a solid solution of Cr in the WC particles, the average particle size of the WC particles is 0.5 μm or less,
In the local structure of Cr atoms by X-ray absorption spectroscopy, the number of W atoms present within 300 pm from Cr atoms, and the number of W atoms existing within 300 pm from Cr atoms is the number of W atoms present within 300 pm from Cr atoms. A cemented carbide characterized in that the ratio (number of W atoms / {number of Cr atoms + number of Co atoms}) divided by the sum of the number of atoms and the number of Co atoms is 0.3 or more.   The ratio of the number of W atoms existing within 300 pm from the Cr atom divided by the sum of the number of Cr atoms existing within 300 pm from the Cr atom and the number of Co atoms (number of W atoms / {number of Cr atoms + number of Co atoms }) Is 0.5 or more, The cemented carbide according to claim 1.   The cemented carbide according to claim 1 or 2, wherein a content of the Cr with respect to the WC particles in the hard phase is 0.5 mass% or more and 3.0 mass% or less.   The cemented carbide according to any one of claims 1 to 3, wherein a content of the binder phase in the cemented carbide is 5 mass% or more and 20 mass% or less.   The cemented carbide according to any one of claims 1 to 4, further comprising 1.0% by mass or less of VC. A mixing step of mixing and pulverizing a raw material powder containing WC powder and Co powder in which Cr is dissolved in WC particles to produce a mixed powder;
A sintering process in which the mixed powder is sintered at a sintering temperature of 1300 ° C. or more and 1370 ° C. or less for less than 60 minutes and then cooled to 1000 ° C. at a cooling rate of 50 ° C./min or more to produce a sintered body. When,
A method for producing a cemented carbide comprising:   The method for producing a cemented carbide according to claim 6, further comprising a HIP step of performing a HIP treatment on the sintered body.   The method for producing a cemented carbide according to claim 6 or 7, wherein an average particle size of the WC particles is 0.2 µm or more and 0.8 µm or less.   The method for producing a cemented carbide according to any one of claims 6 to 8, wherein a content of the Cr with respect to the WC particles is 0.5 mass% or more and 3.0 mass% or less.   A microdrill comprising the cemented carbide according to any one of claims 1 to 5.

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