JP2009074121A - Wc-base hard metal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a WC-base hard metal having superior high-temperature strength. <P>SOLUTION: The WC-base hard metal comprises, by wt.%, 4% to 20% Co which shall be a binder phase, Zr and the balance WC with unavoidable impurities. The hard metal includes carboxide particles containing Zr and double-carbide particles containing Zr and W. When an average particle diameter of the carboxide particles containing Zr is expressed by d1 (μm), an average particle diameter of the double-carbide particles containing Zr and W by d2 (μm), and an average particle diameter of WC particles by D (μm), the particle diameters satisfy the expressions: (d1/D)≤2 and (d2/D)≤2. The hard metal has a deflective strength of 2.5 GPa or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a WC-based cemented carbide having excellent high temperature strength.

  Patent Documents 1 to 3 disclose a technique related to a tool using a cemented carbide containing Zr.

Japanese Patent No. 3235259 JP 2003-113437 A JP 2005-54258 A

  The problem to be solved by the present invention is to provide a WC-based cemented carbide having excellent high temperature strength.

  The WC-based cemented carbide according to the present invention comprises 4% to 20% by weight of Co as a binder phase, contains Zr, the remainder has WC and inevitable impurities, and the cemented carbide contains Zr. And a double carbide containing Zr and W, the average particle diameter of the carbonate containing Zr is d1 (μm), the average particle diameter of the double carbide containing Zr and W is d2 (μm), and the average particle of WC When the diameter is D (μm), the WC-based cemented carbide is characterized in that (d1 / D) ≦ 2, (d2 / D) ≦ 2, and the bending strength is 2.5 GPa or more. By adopting the above configuration, a WC-based cemented carbide having excellent high-temperature strength can be realized. The high temperature strength here refers to strength at about 800 ° C.

  By this invention, the WC base cemented carbide which has the outstanding high temperature strength was able to be provided.

In order to achieve a WC-based cemented carbide having excellent high-temperature strength, the present invention has studied the inclusion of Zr to improve the high-temperature strength of the cemented carbide, and includes a carbonate containing Zr and a double carbide containing Zr and W. It has been found that the high temperature strength is remarkably improved by the inclusion of. Furthermore, the knowledge that it was necessary to control the d1 value and the d2 value was obtained. Zr has been conventionally contained for the purpose of improving the high-temperature strength of the cemented carbide, but in the present invention, the presence or absence of a carbonate containing Zr and a double carbide containing Zr and W is specified, By prescribing the d2 value, the high temperature strength is further improved. At the same time, the bending strength at 25 ° C. at room temperature was also able to achieve 2.5 GPa or more.
The WC-based cemented carbide of the present invention is a sintered body having WC as a hard phase and iron group elements such as Co, Ni, Fe, etc. as a binder phase. The composition of the binder phase contains Co. The content of the binder phase is specified to be 4% or more and 20% or less. If it is less than 4%, even if the particle size of the carbonate containing Zr and the double carbide containing Zr and W is an appropriate amount, the bending strength is lowered. On the other hand, if it exceeds 20%, the amount of the binder phase is too large, which causes a disadvantage that the hardness is lowered. Further, a part of Co may be replaced with other iron group elements such as Ni.
In order to improve the high temperature strength of the WC-based cemented carbide of the present invention, a carbonate containing Zr (hereinafter referred to as a Zr-based carbonate) and a double carbide containing Zr and W (hereinafter referred to as a (ZrW) -based double carbide). It is necessary to contain it. As one of the strengthening mechanisms for high-temperature strength, the Zr element is converted into a Zr-based carbonate and (ZrW) -based double carbide and is effectively dispersed in the WC-based cemented carbide, thereby improving the high-temperature strength. In particular, the presence of dispersed Zr-based carbonates is effective in improving high-temperature strength and improving oxidation resistance. Zr compounds such as Zr-based carbonates and (ZrW) -based double carbides in the WC-based cemented carbide of the present invention are dispersed in the cemented carbide and have the effect of improving and strengthening the high temperature strength of the material, Moreover, the content has an appropriate range. That is, when the content of the Zr compound is too small, the effect of containing the Zr compound such as improvement of the high temperature strength and improvement of the bending strength at room temperature cannot be obtained. Moreover, when too much, inconveniences, such as the sinterability of a cemented carbide deteriorate, will arise. Therefore, there is an appropriate range for the content of the Zr compound. In the WC-based cemented carbide of the present invention, the range of the Zr element addition amount is preferably 0.1% to 5%.
Zr-based carbonates such as Zr (CO) are generated from an O element of a ZrC raw material powder containing O element and other raw material powders, and an O element attached by oxidation in a mixing step at the time of blending. For example, Zr-based carbonate is produced in the process in which the ZrC raw material powder containing the O element is dissolved and reprecipitated in the binder phase during the sintering of the alloy. Elements are contained in Zr-based carbonates. However, in the sintering process, the O content in Zr-based carbonates formed during sintering increases due to an increase in the O content of ZrC and other raw material powders, the amount of O mixed when mixing the raw material powders, etc. If it is too much, it becomes ZrO ₂ and the sinterability is significantly reduced. Therefore, the sintering condition is that a reducing gas such as CO or H ₂ is introduced into the sintering furnace under partial pressure control in the sintering process at 800 ° C. or higher, and the O content as the Zr-based carbonate is 30. The weight percentage was not exceeded. In addition, the atmosphere in the furnace was controlled so that the carbon amount became an appropriate value. In addition, (ZrW) -based double carbide such as (ZrW) C is considered to be derived from (ZrW) C of the raw material powder, or generated by dissolving and precipitating in the binder phase during the sintering process. It is considered that a part of the added Zr is dissolved in the binder phase or the WC phase. In addition, the binder phase and the WC phase may contain a small amount of each additive element such as Cr, V, and Hf and inevitable impurity elements.
In the present invention, in order to control the d1 and d2 values, a solid solution powder of (ZrW) C and a ZrC powder were used in combination. That is, the addition of the (ZrW) C solid solution powder alone cannot control the Zr-based carbonate content and d1 value. On the other hand, when Zr is added only to the ZrC powder, Zr-based carbonates and (ZrW) -based double carbides are formed in the cemented carbide, but this cannot control the d2 value. Accordingly, in the sintering process of the present invention, in order to obtain a Zr-based carbonate that is considered to be formed by dissolving a part of the binder phase in the binder phase and reprecipitating after the sintering, the ZrC powder is used in consideration of the binder phase content. Added. In addition, (ZrW) C solid solution powder was added as a raw material powder so that the cemented carbide contained the (ZrW) -based double carbide. Specifically, the weight ratio of (ZrW) C solid solution powder to ZrC powder was added in the range of 0.2-1.
In addition, the present invention includes a Zr-based carbonate and a (ZrW) -based double carbide, and in order to control these d1 and d2 values to be not more than twice the D value, the Zr content, the ZrC raw material powder and (ZrW) The operation of adding Zr with the C solid solution raw material powder, adjusting the content of Cr, V, etc. in accordance with the Zr content, the sintering temperature, and maintaining the constant temperature at a temperature lower than the sintering temperature were performed. As the Zr content increases, the d1 value inevitably increases. Therefore, about 5% to 10% of the binder phase content in which Zr is solid-solved in the binder phase during sintering is added as the ZrC raw material powder. Was set to be less than twice the D value. About (ZrW) type | system | group double carbide, it adjusted from the quantity produced | generated by containing ZrC raw material powder, and the quantity of the amount of (ZrW) C solid solution raw material powder. Furthermore, d2 value was also controlled. In addition, Cr, V and Zr added to suppress the grain growth of the WC particles are factors that reduce the sinterability of the cemented carbide. Therefore, the Cr content is mainly used because it has little influence on the sinterability. Was adjusted in consideration of the Zr content, and the D value was controlled. Furthermore, the average particle diameter at the time of the WC raw material powder was adjusted in consideration. Under sintering conditions, when the temperature is high, the grain growth of Zr becomes active. Therefore, when the Zr content is large, an intermediate holding of about 2 hours was set during sintering at 1290 ° C. And the sinterability which falls with Zr, Cr, and V content, especially the sinterability in the solid-phase sintering state of the cemented carbide improved. Further, as the Zr content increases, the d1 value and the d2 value increase with respect to the D value. Then, Zr-based carbonates and (ZrW) -based double carbides serve as starting points for destruction, causing a decrease in high temperature strength and room temperature strength. Therefore, the d1 value and d2 value of the WC-based cemented carbide of the present invention must be twice or less than the D value. On the other hand, in the conventional cemented carbide simply added Zr, since the presence of Zr-based carbonate has not been detected, it can be obtained by containing Zr-based carbonate and (ZrW) -based double carbide, The effect of improving the high temperature strength of the present invention cannot be obtained.
The WC-based cemented carbide of the present invention has a bending strength at room temperature of 2.5 GPa or more. The reason for this is that when the bending strength is less than 2.5 GPa, for example, when applied to a cutting tool, sufficient strength cannot be obtained, and satisfactory fracture resistance and wear resistance cannot be obtained in terms of performance. Because.

  When the surface of the WC-based cemented carbide of the present invention is coated with a physical vapor deposition method such as a sputtering method or an arc ion plating method, or a chemical vapor deposition (hereinafter referred to as CVD) method, the hardness and the like are further increased. This is preferable because of improved performance. Examples of the material to be coated include a film made of a compound of a periodic table 4a, 5a, 6a group metal and one or more of Al, Si, carbon, nitrogen, oxygen, boron, etc., an aluminum oxide film, a zirconium oxide film, etc. A hard film composed of a single layer or a multilayer film is effective. By coating these hard coatings on the cemented carbide member of the present invention, the surface wear resistance, oxidation resistance, slidability and the like can be improved. Since the WC-based cemented carbide of the present invention is excellent in terms of hardness and high-temperature strength, for example, it is widely used for rotating tools, turning tools, cutting tools, punching tools, etc., and the performance improvement effect Is obtained. The WC-based cemented carbide of the present invention will be specifically described based on the following examples.

Example 1
As raw material powders, average particle size: 0.4 μm, 1.0 μm, 1.5 μm, 2.5 μm, 3.5 μm, 4.5 μm WC powder, average particle size: 1.2 μm Co powder, average particle, respectively Diameter: 1.5 μm Ni powder, Average particle size: 1.5 μm Fe powder, Average particle size: 1.5 μm Cr3C2 powder, Average particle size: 1.2 μm VC powder, Average particle size: 1.5 μm HfC powder, average particle size: 2.0 μm TiC powder, average particle size: 1.5 μm TaC powder, average particle size: 0.4 μm (ZrW) C solid solution powder and 0.8 μm ZrC powder were prepared. . These powders were blended into a predetermined composition. The ZrC powder used contains about 1% by weight of O element. The blended powder was mixed with an attritor in alcohol for 12 hours, a molding resin was added and dried to prepare a mixed powder. Next, the 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 1400 ° C. for 30 minutes, in order to eliminate residual voids in the cemented carbide, they were pressurized with argon gas at 4.9 MPa for 30 minutes and cooled in the furnace. .
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. Composition analysis was performed using this test piece, and each content of Co, Ni, Zr, Cr, V, Ta, Hf, Ti, and the like was determined. Co and Ni, which are metal binder phases, were mirror-polished on the cross section of the cemented carbide, and then analyzed by a fluorescent X-ray analyzer (manufactured by Rigaku, ZSX-100E type), and the content thereof was quantitatively determined. For other metal elements, powder of finely pulverized cemented carbide is dissolved and ionized using H ₃ PO ₄ , HCl, HF, HNO ₃ and H ₂ SO ₄ , and inductively coupled plasma emission analysis (hereinafter referred to as “inductively coupled plasma emission spectrometry”) And ICP analysis), the type of each element was identified and its content was quantitatively determined. Table 1 shows the composition of each sample.

  After mirror-polishing the cross section of the test piece, the crystal grain boundaries are clarified by etching with Murakami reagent for 0.5 minutes and aqua regia for 0.5 minutes, and various particles and Zr-containing compounds are measured. It was. The apparatus used for the analysis is a field emission electron probe microanalyzer (manufactured by JEOL, JXA-8500F, hereinafter referred to as FE-EPMA). By this analysis, the presence or absence of Zr (CO) as an example of a Zr-based carbonate and (ZrW) C as an example of a (ZrW) -based double carbide was identified. First, using FE-EPMA, a surface analysis of 20 fields of view was performed at a magnification of 5k. Next, the particles containing Zr were analyzed, and Zr (CO) and (ZrW) C were identified. A sample in which the presence of Zr (CO) was confirmed in one or more fields of view by FE-EPMA analysis was judged to contain a Zr-based carbonate. Similarly, the sample in which the presence of (ZrW) C was confirmed was judged to contain (ZrW) -based double carbide. Table 2 shows the analysis results of Invention Examples 2, 16, and 17, Comparative Examples 25 and 26, and Conventional Example 30. Here, the conventional example 30 used the commercially available cutting tool.

As shown in Table 2, two types of phases were observed in Inventive Example 2, Compound No. 2-1 was Zr (CO), and Compound No. 2-2 was (ZrW) C. In distinguishing between the two compound phases, the feature of Zr (CO) is that it contains Zr, O and C. Compound No. 2-1 contains Zr, O and C, but Compound No. 2-2 did not contain O. On the other hand, the feature of (ZrW) C is that it is a double carbide not containing O but containing Zr and W. Compound No. 2-1 contains W but is not (ZrW) C because it also contains O at the same time. Compound No. 2-2 contained Zr, W, and C and did not contain O, so was determined to be (ZrW) C. Further, (ZrW) C may contain other elements such as Co, V and Ta as in Compound No. 16-2 of Invention Example 16 and Compound No. 17-2 of Invention Example 17 ( The property as a ZrW) -based double carbide is not impaired, and conversely, the property may be improved. On the other hand, Comparative Example 25 was confirmed to contain only Zr (CO) of Compound No. 25-1, and did not contain (ZrW) C. In Conventional Example 30, one type of phase of Compound No. 30-1 was observed, which was (ZrW) C. Moreover, Zr (CO) was not contained.
The d1 value and the d2 value are obtained by magnifying and copying an image photographed at a magnification of 10 k with respect to a sample determined to contain each compound phase, and using this image analysis software (Image-ProPlus Version 4.0 for Windows, Media Cybernetics) (Company, Windows is a registered trademark). Similarly, the D value was determined by observing 5 visual fields at a magnification of 10 k. Table 1 shows the D value, d1 value, d2 value, and their ratios.
The bending strength of the test piece at room temperature and high temperature was determined by a three-point bending test using a Metal Testing Machine (manufactured by Shimadzu Corporation, EHF-ED20 type) under the conditions of a span of 20 mm and a cross bed speed of 1 mm / min. . The room temperature condition was measured in the air at room temperature of 25 ° C. The high temperature condition was measured in a constant temperature furnace maintained at 800 ° C. in an Ar atmosphere. The number of each test was 5 points, and the average value was obtained. The hardness of the test piece was determined using a Rockwell hardness tester (manufactured by Mitutoyo, model HR-523) under the conditions of A scale and a load of 249.2N. Table 3 shows the bending strength and hardness of each sample at room temperature and high temperature.

From the results shown in Table 3, Examples 1 to 19 of the present invention had high bending strength, and showed strengths of 2.5 GPa to 2.9 GPa at 25 ° C. at room temperature and 1.6 GPa to 2.1 GPa at 800 ° C. at high temperature. . Further, in Example 2 of the present invention containing Co and Ni, and Example 4 of the present invention containing Co, Ni and Fe, compared to Example 2 containing Co in the binder phase, the room temperature was about 2.7 GPa. It showed strength, high temperature strength of about 1.8 GPa, and hardness of about HRA 90.3. From this result, the binder phase in the cemented carbide of the present invention may contain iron group elements such as Ni and Fe in addition to Co. Inventive Examples 9 to 14 having different Zr contents were able to obtain the effect of containing Zr-based carbonates and (ZrW) -based double carbides, and a high bending strength of 1.6 GPa or more was obtained at high temperatures. Invention Examples 15 to 19 containing Cr, V, Ta, Hf, and Ti also showed the same high high temperature bending strength. From this, even if it contained a small amount of the additive element, the effect of improving the high temperature bending strength was observed. Further, Invention Examples 20 and 21, which are fine cemented carbides having a D value of 1.0 μm or less, showed a high high temperature bending strength of 2.9 GPa or more.
However, Comparative Example 22 with a small amount of binder phase contains Zr (CO), (ZrW) C, and even if the d1, d2 value and Zr content are within the specified range of the present invention, they are as low as 1.9 GPa. Only room temperature strength and low high temperature strength of 0.9 GPa were shown. Comparative Example 23 having more Co content than the specified range of the present invention contains Zr (CO), (ZrW) C, and has a large amount of binder phase even if the d1 and d2 values are within the specified range of the present invention. Therefore, the hardness decreased. Therefore, the amount of the binder phase in the cemented carbide of the present invention needs to be 4% or more and 20% or less. The comparative example 24 which does not contain Zr (CO) and (ZrW) C did not obtain the inclusion effect of both compounds, and showed only a low bending strength of 0.9 GPa at a high temperature. Moreover, even if the binder phase content is within the range specified in the present invention, Comparative Examples 25 and 27 containing only Zr (CO) cannot obtain the effect of containing the (ZrW) -based double carbide, and are 1. Only low bending strength of 0 GPa or less was exhibited. As shown in Comparative Example 26 of Table 2, even if Zr (CO) and (ZrW) C are contained, if the (d1 / D) value is larger than 2, coarse particles of Zr (CO) are formed. The room temperature and high-temperature bending strength were 1.0 GPa or less as a starting point of destruction. Comparative Examples 28 and 29 having a (d1 / D) value exceeding 2 exhibited only a low high temperature bending resistance of 1.9 GPa or less.

(Example 2)
In order to specifically explain the high temperature strength of the WC-based cemented carbide of the present invention, a turning insert was created and subjected to a comparative study. Here, Invention Examples 31 to 35 and Comparative Examples 36 to 41 were produced. Each sample used a material selected from the samples in Table 1. Therefore, the content of each element in each sample, the presence / absence of Zr (CO) and (ZrW) C, d1 value, d2 value, D value, bending strength, and hardness are determined according to the JIS test piece and sample preparation method. Are the same as the measured values in Table 1, Table 2, and Table 3. The sample numbers in Table 1 corresponding to each sample are also shown in Table 4.

Using a granulated powder of the materials shown in Table 1, a CNMG type test piece press for cutting having an inscribed circle of 12.4 mm and a thickness of 4.8 mm was produced. Each pressed body was sintered under the same conditions as the sample shown in Table 1 to produce a sintered body. Each sintered body was ground to the same size, and a TiN, Ti (CN), and Al2O3 hard coating was coated on the substrate using a CVD film forming apparatus. Cutting was performed under the following test condition 1 using each sample. For the cutting performance, the cutting time until the maximum flank wear width of the cutting specimen reached 0.4 mm was determined as the tool life. The results are shown in Table 4.
(Test condition 1)
Work material: Carbon steel S53C, diameter 300mm
Cutting method: Turning Cutting speed: 220m / min
Cutting depth: 2mm
Feed amount: 0.4mm per rotation
From Table 4, Examples 31 to 35 of the present invention all showed a tool life of 55 minutes or more. This is because the inventive examples 31 and 32 were prepared using the materials of the inventive examples 1 and 2 in which the Co content was changed in the samples shown in Table 1, and the inventive examples 33 to 35 were It is because it created from the material of this invention example 11 and 12 which changed Zr content, and the material of this invention example 17 containing Ta. From the above results, the cutting tool produced using the WC-based cemented carbide of the present invention has fracture resistance and wear resistance due to excellent high-temperature strength, and was able to improve the tool life in cutting. . On the other hand, Comparative Examples 36 to 41 all showed only a tool life of 25 minutes or less. This is because the Co contents in Comparative Examples 36 and 37 were prepared using Comparative Examples 22 and 23, which are materials outside the scope of the present invention. Further, Comparative Example 38 was prepared using Comparative Example 24 containing no Zr-based carbonate and (ZrW) -based double carbide, and Comparative Example 39 was prepared using Comparative Example 25 containing only Zr-based carbonate. This is because Example 40 was prepared using Comparative Example 26 having a large (d1 / D) value exceeding 2 and Comparative Example 41 was prepared using the material of Comparative Example 27 containing only Zr-based carbonate.

(Example 3)
In order to explain the high temperature strength of the WC-based cemented carbide of the present invention, a drilling test using a small diameter drill was conducted. Small-diameter drills have a narrow cutting edge diameter and can easily compare the performance difference of fine-grain cemented carbide. Further, at the time of drilling, the cutting edge of the drill becomes about 800 ° C. or higher. The decrease in strength at high temperature causes the cutting edge of the drill to be deformed, and this deformation causes breakage of the drill. Therefore, high temperature strength can be compared by measuring the number of breaks. In the samples shown in Table 1, small-diameter drills were prepared using the materials of Invention Examples 20 and 21, Comparative Examples 28 and 29 having a D value of 1.0 μm or less, and these were used as Invention Examples 42 and 43 and Comparative Examples. 44 and 45. The mixed powder of each material was extrusion molded at a pressure of 25 MPa to produce a round bar molded body having a diameter of 4.7 mm. Each round bar sintered body obtained from this round bar molded body is polished and processed into 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. did. Using these small diameter drills, drilling was performed under the following test condition 2. In order to measure the quality of breakage resistance, which is an index of high-temperature strength, 20 drills were used for each condition, and when the work material hit 6000, the number of broken drills was measured to determine the breakage resistance. evaluated. The results are shown in Table 5.

(Test condition 2)
Work material: Glass epoxy copper-clad 4-layer laminate with a thickness of 1.6 mm, 2 layers Stacking speed: 160,000 revolutions per minute Feeding amount: 19 μm / rotation From Table 5, any of Examples 42 and 43 of the present invention Although the number of breaks was 0, Comparative Examples 44 and 45 both showed a very large number of breaks of 7 or more. From the above results, the cutting tool produced using the WC-based cemented carbide of the present invention has excellent fracture resistance due to high temperature strength, and improves the tool life using a fine cemented carbide such as a small diameter drill. I was able to.

Claims (1)

The WC-based cemented carbide contains 4% to 20% by weight of Co as a binder phase, contains Zr, the balance has WC and inevitable impurities, the cemented carbide includes a carbonate containing Zr, and Zr And a double carbide containing Zr, the average particle size of the carbonate containing Zr is d1 (μm), the average particle size of the double carbide containing Zr and W is d2 (μm), and the average particle size of WC is D A WC-based cemented carbide characterized by (d1 / D) ≦ 2, (d2 / D) ≦ 2, and the bending strength is 2.5 GPa or more when (μm).