JP2023028335A - WC-based cemented carbide - Google Patents

Abstract

To provide a WC-based cemented carbide suitable for a cutting tool in which the wear of a flank is suppressed in a milling process of steel and the like.SOLUTION: A WC-based cemented carbide contains Co of 5 mass% or more and 12 mass% or less, at least one of Ta and Nb of 1 mass% or more and 15 mass% or less in total, and Ti of 1 mass% or more and 10 mass% or less, with the balance being WC and inevitable impurities. The WC particles have an average particle size of 0.7 μm or more and 2.5 μm or less, and the WC particles have an integrated circularity of 0.480 or more and 0.520 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a WC-based cemented carbide.

WC-based cemented carbides such as WC--Ti--(Ta, Nb)--Co are used as tool materials for cutting steel because they are excellent in heat resistance and adhesion resistance. In order to improve the cutting performance of cutting tools using this WC-based cemented carbide, proposals have been made, for example, as described in Patent Document 1.

Japanese Patent Application Laid-Open No. 2004-330314

SUMMARY OF THE INVENTION It is an object of the present invention to provide a WC-based cemented carbide which is suitable for cutting tools in which flank wear is further suppressed in milling of steel or the like.

A WC-based cemented carbide according to an embodiment of the present invention is
5% by mass to 12% by mass of Co, 1% by mass to 15% by mass of at least one of Ta and Nb in total, 1% by mass to 10% by mass of Ti, and the balance being WC and The WC particles have an average particle size of 0.7 μm or more and 2.5 μm or less, and the cumulative circularity of the WC particles is 0.480 or more and 0.520 or less.

Further, the WC-based cemented carbide according to the embodiment of the present invention further includes
HRA may be 89.5 or more and 91.5 or less.

According to the above, it is possible to provide a WC-based cemented carbide suitable for a cutting tool in which wear of the flank is further suppressed in milling of steel or the like.

It is a structure|tissue observation photograph of an Example. It is a structure|tissue observation photograph of a comparative example. It is a figure which shows WC particle size (particle diameter) distribution of an Example and each of a comparative example. It is a figure which shows the WC integrated circularity of an Example and each of a comparative example.

The present inventors have found that when the WC-based cemented carbide of WC-Ti-(Ta, Nb)-Co system has a WC cumulative circularity within a predetermined range, the variation in toughness in the cemented carbide structure is small, and the steel It was found that flank wear is easily suppressed in milling such as.

Embodiments of the present invention are described in detail below.
In this specification, the WC constituting the WC-based cemented carbide is expressed as "WC" or "WC particles", but both expressions are not intended to clearly distinguish between WC and WC particles. do not have.

1. Composition The composition of the WC-based cemented carbide will be described.

(1) Co
Co is an element that forms a binder phase that binds WC particles, which are hard phases, carbide phases and complex carbide phases generated by addition of Ta, Nb, and Ti, and imparts high toughness to WC-based cemented carbide. If the Co content is too small, the toughness and strength of the WC-based cemented carbide are reduced, and the sinterability of the WC-based cemented carbide is deteriorated. and it becomes difficult to maintain strength. Furthermore, if the Co content is small, the range of sound structures in which no decarburized phase or free carbon precipitates becomes narrower, making it difficult to control carbon in mass production. On the other hand, if the Co content becomes too large, the hardness decreases.

Based on the above, the Co content is preferably 5% by mass or more and 12% by mass or less, more preferably 8% by mass or more and 10% by mass or less.

(2) Ta and Nb
Ta and Nb preferably contain either one or both. These elements are added as carbides to improve the heat resistance of the WC-based cemented carbide. The total content of Ta and Nb (content as metal, not as carbide) is preferably 1% by mass or more and 15% by mass or less. The reason for this is that if the content is 1% by mass or more, the aforementioned improvement in heat resistance is not observed, while if the content exceeds 15% by mass, the toughness and sinterability of the WC-based cemented carbide are lowered.
The total content of Ta and Nb is preferably 5% by mass or more and 10% by mass or less.

(3) Ti
Ti is added as a carbide to improve the heat resistance of the WC-based cemented carbide. On the other hand, if the Ti content becomes too large, the toughness and sinterability are lowered. Therefore, the content of Ti (content as a metal, not as a carbide) is preferably 1% by mass or more and 10% by mass or less, more preferably 2% by mass or more and 8% by mass or less.

2. Particle Shape of WC The particle shape of WC will be described.

(1) Average Particle Size The average particle size of WC is preferably 0.7 μm or more and 2.5 μm or less. When the WC average grain size is within this range, it is possible to obtain a cutting tool having an excellent balance between wear resistance and toughness in machining steel and the like.
Here, the grain size is the diameter of a circle that gives an area equal to the grain area of WC for 2000 or more WCs obtained by observing the cross section of the WC-based cemented carbide. In the graph plotting the diameters of the circles, the diameter when the cumulative frequency of the particle size distribution reaches 50% is taken as the average particle size.
More preferably, the average particle diameter is 0.8 μm or more and 2.0 μm or less.

(2) Accumulated Circularity The circularity of WC particles is given by 4πS/L ² where S is the area of each WC particle and L is the perimeter of 2000 or more WC particles. When the circularity of WC is close to 1, the shape becomes close to a perfect circle.
The cumulative circularity is calculated from the circularity and the particle size distribution. The particle size distribution is based on the number, and the WC particles are counted in order from the smallest particle size, and the particle size when the occupancy rate of the total number is N % is defined as the cumulative frequency N %. Then, the average circularity of all particles up to the cumulative frequency of N% is taken as the cumulative circularity of N%.
The cumulative circularity of the WC particle size distribution in the range of cumulative frequency of 10% or more and 90% or less is preferably 0.480 or more and 0.520 or less, and is preferably 0.490 or more and 0.510 or less. more preferred.
The reason for this is that when the cumulative circularity is within this range, the amount of WC having angular shapes such as triangles and squares is reduced. This is because flank wear is easily suppressed in milling of steel or the like.

For measurement of circularity and particle size distribution, an electron probe microanalyzer (for example, JEOL Ltd. JXA-8350F, hereinafter EPMA) equipped with a backscattered electron diffraction detector (for example, TSL Solutions OIM Co., Ltd., hereinafter referred to as EBSD) ) is used. Inverse pole figures are obtained by EBSD and individual grain boundaries are determined by considering regions with values of misorientation greater than 5° as separate grains. All the WC particles in the measurement area are processed in the same way to obtain the circularity and the particle size distribution.

Coarse WC grains that have grown grains during the sintering process become triangular or quadrangular, so the degree of circularity tends to be small. Considering this, the cumulative frequency and cumulative circularity of the WC particle size distribution are
When the cumulative frequency is 20%, the cumulative circularity is 0.500 or more and 0.510 or less,
When the cumulative frequency is 50%, the cumulative circularity is 0.495 or more and 0.505 or less,
When the cumulative frequency is 80%, it is more preferable that the cumulative circularity be 0.485 or more and 0.495 or less.

Further, as will be described later in the manufacturing method, in order to achieve the cumulative circularity, it is preferable to add coarse-grained WC raw material powder after mixing the raw material powders.

3. Others It is more preferable that the WC-based cemented carbide has an HRA of 89.5 or more and 91.5 or less. By setting the HRA within this range, hardness and toughness, which are in a trade-off relationship, can be balanced in the milling of steel or the like.

4. Manufacturing method The following can be shown as an example of the manufacturing method.
That is, the WC raw material powder having an average particle size of 4.0 to 6.0 μm, in particular, two types (fine particles and coarse particles) with different particle size distributions (average particle sizes) with a narrow particle size distribution width and single crystallization It is preferable to use WC raw material powder. When mixing the raw material powders, it is preferable that the fine-grained WC raw material powder and other raw material powders are mixed for a predetermined time, and then the coarse-grained WC raw material powder is added (post-added) and mixed.

By adding the coarse-grained WC raw material powder later, the coarse-grained WC raw material powder is not excessively pulverized, and the shape of the WC raw material powder can be easily maintained even after mixed sintering, and the accumulated circularity of the cemented carbide can be increased.
An attritor, a ball mill, or the like can be used for mixing. Sintering is preferably carried out under pressure at 1400 to 1480° for several hours.

Two types of WC raw material powders were used, one having an average particle size of 4.5 μm (30% by mass) and the other having an average particle size of 4.0 μm (70% by mass). Co raw material powder used had an average particle size of 1.5 μm. As the TaC raw material powder and the TiC raw material powder, powders having an average particle size of 1 μm were used.
These raw material powders were blended so as to have the composition shown in Table 1. The total mass of raw material powders was set to 200 kg, and wet mixing was performed using an attritor for mass production. During mixing, a very small amount of C powder and binder powder for molding were added to compensate for the carbon consumed during the sintering process.

In the examples, powders other than the WC powder having an average particle size of 4.5 μm were first mixed for 4.5 hours, and then the WC powder having an average particle size of 4.5 μm was post-added and mixed for another 2 hours.
In the comparative example, the same raw material powders as in the example were prepared, and all the raw material powders were put into an attritor at the same time and mixed for 6 hours.
After mixing, in both Examples and Comparative Examples, the mixture was dried with a spray dryer to prepare granulated powders of each composition, and press molding was performed to form inserts. Thereafter, sintering was performed at 1400° C. for 1 hour to produce a medium-carbon WC-based cemented carbide in which no decarburized phase and free carbon precipitated. Table 1 shows the compositions and the like of the WC-based cemented carbides according to Examples and Comparative Examples.

As is clear from Table 1, it was confirmed that the Example and the Comparative Example have almost the same HRA value and therefore have the same hardness, and also have almost the same coercive force and saturation magnetization.

The prepared WC-based cemented carbide was mirror-finished, and its structure was observed using EPMA (JXA-8530F manufactured by JEOL). FIG. 1 shows a structure observation photograph of this example (magnification: 3000 times, scale length: 10 μm), and FIG. 2 shows a structure observation photograph of a comparative example (magnification: 3000 times, scale length: 10 μm).

Using EBSD (Electron Back Scatter Diffraction) and image analysis software, 2000 WC particles were measured to determine the circle-equivalent particle size distribution and cumulative circularity of the WC particles. FIG. 3 shows the particle size distribution of WC particles, and FIG. 4 shows the measurement results of cumulative circularity.

As shown in Table 1, the average particle size obtained from FIG. 3 was almost the same between this example and the comparative example. On the other hand, as shown in FIG. 4, the integrated circularity of the present embodiment is in the range of 0.480 to 0.520, and the comparative example is in the range of 0.465 to 0.490. It was confirmed that the accumulated circularity was larger than that of the comparative example.

Next, the crack length was measured in order to evaluate the variation in toughness in the WC-based cemented carbide. That is, on the mirror-polished surface of the WC-based cemented carbide, under the following conditions, a Vickers indenter was linearly pressed into 10 places so that the center interval of each indentation was 3 to 4 mm, and each of the four corners of the indentation was pressed. The length of cracks (L1 to L4) was measured.
The crack length measurement results are shown in Table 2 for Examples and Table 3 for Comparative Examples.

(Conditions for pressing the Vickers indenter)
Test machine used: AVK type manufactured by Akashi Seisakusho Pushing force: 50 kgf (approximately 490 N)
Push holding time: 15 seconds

The maximum value, minimum value, average value, standard deviation, and
The difference between the maximum and minimum values of the total crack lengths (L1 to L4) in each indentation,
and
Table 4 shows the difference between the maximum and minimum crack lengths (L1 to L4) in each indentation, the average value of this difference, and the difference between the maximum and minimum values of this difference.

As is clear from Table 4, the standard deviation, the difference between the maximum value and the minimum value in the total value of the crack lengths (L1 to L4), and the maximum value among the crack lengths (L1 to L4) In all of the difference between the value and the minimum value, the average value of this difference, and the difference between the maximum value and the minimum value of this difference, the example has a smaller value, and the variation in crack length is small, that is, , it can be said that the variation in toughness is small.

Subsequently, for the WC-based cemented carbides of Examples and Comparative Examples, AlTiN-coated inserts having an average thickness of about 4 μm were produced by the PVD method (referred to as an example tool and a comparative example tool, respectively). Cutting evaluation was performed under the following conditions. The test was performed three times under the same conditions, and the maximum flank wear width after cutting and its variation were evaluated. Table 5 shows the results of cutting evaluation.

(Conditions for cutting evaluation)
・Cutter model number: ASRT5063R-4
・Insert model number: WDNW140520
・Number of blades: 1
・Cutting method: Plane processing ・Work material: S50C (220HB)
・Incision: axial direction, 1 mm, radial direction, 42 mm
・Cutting speed: 180m/min
・Feed amount per blade: 1.5mm/blade ・Protrusion amount: 100mm
・Cutting length: 37m

As is clear from Table 5, the tool of this embodiment has a smaller maximum flank wear width and a difference between the maximum and minimum values than the comparative example tool. Therefore, it can be said that the WC-based cemented carbides of Examples have more stable toughness than the WC-based cemented carbides of Comparative Examples, and the maximum flank wear width and variation are improved.

Claims (2)

5% by mass to 12% by mass of Co, 1% by mass to 15% by mass of at least one of Ta and Nb in total, 1% by mass to 10% by mass of Ti, and the balance being WC and It consists of unavoidable impurities, the WC particles have an average particle diameter of 0.7 μm or more and 2.5 μm or less, and the WC particles have an accumulated circularity of 0.480 or more and 0.520 or less. WC-based cemented carbide. 2. The WC-based cemented carbide according to claim 1, wherein HRA is 89.5 or more and 91.5 or less.

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