JP2008133508A - Hard metal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hard metal which has enhanced abrasion resistance and deformation resistance on the surface, while enhancing toughness thereof. <P>SOLUTION: The hard metal 1 comprises WC grains 2 and a binder phase 3 which combine the WC grains 2. When a cross-section structure of the hard metal 1 is observed, WC grains 2a which show polygonal shapes and roundness with curvature radiuses of 50 nm or more at the corners are contained in the inner part of the hard metal so as to occupy 50% or more of the area of the whole WC grains 2, and a mean length of neck growing parts 4 among WC grains 2 is longer in the surface part than in the inner part of the hard metal 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cemented carbide used for a cutting tool or the like.

  Conventionally, a cemented carbide widely used for metal cutting processing has a hexagonal shape, a hard phase mainly composed of angular WC particles having a polygonal shape such as a triangle or a quadrangle, and a Co or the like. A WC-Co alloy composed of a binder phase of an iron group metal, or a system in which a solid solution phase such as carbides, nitrides, carbonitrides of the fourth, fifth and sixth group metals of the periodic table is dispersed in the WC-Co system. Are known.

  These cemented carbides are mainly used for cutting cast iron, carbon steel, etc. as cutting tools, but recently, cutting of hard-to-cut materials such as stainless steel and small-diameter drilling of printed circuit boards has been further performed. The use for high-speed cutting and high-feed cutting has been promoted in order to improve efficiency.

  For example, in Patent Document 1, when a WC raw material on the low carbon side is used in the manufacture of cemented carbide, the shape of the WC particles in the sintered cemented carbide becomes relatively round, and cracks propagate. It has been disclosed that cracks tend to propagate through the periphery of the particles, so that the crack resistance is increased and the progress of cracks is suppressed. Patent Document 2 discloses that a cemented carbide excellent in toughness can be produced by controlling the mixing and firing conditions in the manufacturing process of cemented carbide to include a grain-grown WC particle phase at a predetermined ratio. Has been.

Furthermore, in Patent Document 3, voids are formed between the plate-like WC particles on the surface by increasing the ratio of the plate-like WC particles on the surface of the cemented carbide compared to the inside, and this void holds the lubricant and the like. It is described that the effect as a bearing material is exerted by this function, and that the adhesion of the coating layer is improved when the diamond layer is coated on the surface of the cemented carbide.
JP 2000-15514 A Japanese Patent Laid-Open No. 06-172912 JP 2000-119790 A

  However, in the cemented carbides of Patent Documents 1 and 2, the shape of the WC particles is rounded and the effect of suppressing crack growth is high, but the amount of crystallization WC is small and coalescence of WC particles accompanying grain growth is difficult to occur. For this reason, the wear resistance and deformation resistance of the cemented carbide are not sufficient. For example, when used as a cutting tool, there is a problem that the cutting edge shape is changed at an early stage and the processing accuracy is lowered. Further, the cemented carbide disclosed in Patent Document 3 has a problem that the surface has a lot of voids, resulting in poor wear resistance on the surface of the cemented carbide.

  Accordingly, an object of the present invention is to provide a cemented carbide having improved wear resistance and deformation resistance on the surface while enhancing the toughness of the cemented carbide.

  The cemented carbide of the present invention is a cemented carbide in which WC particles are bonded with a binder phase, and when the cross-sectional structure of the cemented carbide is observed, a polygonal shape and a radius of curvature of a corner portion are formed inside. WC particles exhibiting a roundness of 50 nm or more are contained in a ratio of 50 area% or more with respect to the entire WC particles, and the average length of the neck growth portion between the WC particles is larger than the surface of the inside of the cemented carbide. It is characterized by being long.

  Here, in the above configuration, the average particle diameter of the WC particles is 0.5 to 1.5 μm.

  In the above configuration, the ratio of WC particles having a particle size within ± 30% with respect to the average particle size is 80% by area or more with respect to the entire WC particles.

  Further, in the above configuration, the half width of the diffraction peak of the (101) plane in the X-ray diffraction measurement on the surface is larger than the half width of the diffraction peak of the (101) plane in the internal X-ray diffraction measurement. It is characterized by being narrow.

  According to the cemented carbide of the present invention, the WC particles are polygonal and the WC particles having a rounded curvature radius of 50 nm or more are included at a ratio of 50 area% or more with respect to the entire WC particles. In addition, since the average length of the neck growth portion between the WC particles is longer on the surface than the inside of the cemented carbide, the wear resistance and resistance on the surface of the cemented carbide are improved while improving the toughness of the entire cemented carbide. Deformability can be improved.

  Here, the average particle diameter of the WC particles is preferably 0.5 to 1.5 μm from the viewpoint of increasing the hardness of the cemented carbide.

  Further, the ratio of WC particles having a particle size within ± 30% with respect to the average particle size is present at a ratio of 80 area% or more with respect to the entire WC particles, thereby increasing the strength of the cemented carbide. It is desirable in that it can.

  Furthermore, the half width of the diffraction peak of the (101) plane in the X-ray diffraction measurement on the surface is narrower than the half width of the diffraction peak of the (101) plane in the internal X-ray diffraction measurement, It is desirable in that the wear resistance and deformation resistance on the surface of the cemented carbide can be further improved.

  The cemented carbide of the present invention will be described with reference to FIG. 1 which is a scanning electron micrograph of (a) surface and (b) inside.

  According to FIG. 1, the cemented carbide 1 is composed of a structure in which WC particles 2 are bonded by a bonding phase 3.

  According to the present invention, when the cross-sectional structure of the cemented carbide 1 is observed, WC particles (hereinafter abbreviated as round WC particles) 2a that are rounded and have a polygonal shape and a radius of curvature of 50 nm or more are formed inside. It is contained at a ratio of 50 area% or more with respect to the entire WC particles 2, and the average length of the neck growth portion 4 between the WC particles 2 is longer on the surface than the inside of the cemented carbide 1. To do. In FIG. 1, corners c of round WC particles 2a are indicated by solid arrows, and corners c of WC particles 2 other than round WC particles 2a are indicated by dotted arrows. Thereby, the wear resistance and the deformation resistance on the surface of the cemented carbide 1 can be enhanced while enhancing the toughness of the cemented carbide 1 as a whole.

  Here, in the present invention, the corner of the WC particle 2 is, as shown in FIG. 1, the smallest radius of curvature among the corners present in each WC particle 2 in the micrograph of the cross section of the cemented carbide. WC particles 2 having a small radius, that is, a rounded corner having a radius of curvature of 50 nm or more at the sharpest corner c (the tip of the arrow in FIG. 1) are defined as round WC particles 2a. At this time, the portion where the WC particle 2 forms the neck growth portion with the adjacent WC particle 2 is not regarded as a corner portion, and only the portion forming the corner portion alone is evaluated. Therefore, when calculating the content ratio of the round WC particles 2a, the WC particles 2 having no corners are omitted for estimation. In addition, since the neck growth part 4 has the effect | action which changes the propagation direction of a crack, it is thought that it is effective with respect to crack progress suppression. In addition, the neck growth portion 4 between the WC particles 2 is a WC particle 2 in which the WC particles 2 as shown in FIG. It refers to the length of the parts connected by. In the present invention, the inside of the cemented carbide 1 refers to a depth region of 300 μm or more from the surface of the cemented carbide 1.

  Further, the average particle diameter of the WC particles 2 is preferably 1.5 μm or less from the viewpoint of increasing the hardness of the cemented carbide 1. Here, in order to obtain the structure of the cemented carbide 1, it is desirable that the average particle diameter of the WC particles 2 is 0.5 μm or more in that stable supply of the WC raw material powder is possible. Therefore, in the present invention, it is desirable that the average particle diameter of the WC particles 2 is 0.5 to 1.5 μm.

  It is to be noted that the ratio of WC particles having a particle size within ± 30% with respect to the average particle size is present in a ratio of 80 area% or more with respect to the entire WC particles 2 to increase the strength of the cemented carbide 1. It is desirable in that it can.

Further, as shown in the X-ray diffraction pattern on the surface (a) and inside (b) of the cemented carbide 1 in FIG. 3, the half value of the diffraction peak on the (101) plane in the X-ray diffraction measurement on the surface (a). The width w _s is narrower than the half-value width w _i of the diffraction peak of the (101) plane in the X-ray diffraction measurement in the interior (b), thereby reducing the wear resistance and deformation resistance on the surface of the cemented carbide 1. It is desirable in that it can be further increased.

(Production method)
In order to manufacture the above-described cemented carbide, first, for example, 80 to 90% by mass of WC powder having an average particle size of 0.5 to 1.5 μm, TaC powder having an average particle size of 0.1 to 2 μm, Cr ₃ C ₂ powder, VC powder, TiC powder, NbC powder, ZrC powder, MoC powder, 0.5 to 5 mass% in a total amount of HfC powder, average particle diameter of iron group metals of 0.5 to 1 [mu] m 5 to 15 wt% Further, if desired, metal W (tungsten) powder or carbon black (C) is mixed.

  Here, in this invention, the high temperature carbonization WC powder carbonized at 1750 degreeC or more at the time of manufacture is used as WC powder. As a result, the WC particles contained in the cemented carbide after firing do not cause partial abrupt grain growth, and the entire WC particles grow relatively uniformly. For this reason, the particle diameters of the WC particles are uniform over the entire cemented carbide as compared with the conventional case.

  Moreover, since the shape of the WC particles 2 gradually grows into a triangular or quadrangular polygonal shape, the cemented carbide 1 containing the WC particles 2 having the above-described shape is obtained by firing under predetermined conditions described later. be able to.

  In the present invention, the high-temperature carbonized WC powder is used, and the average length of the neck growth portion in the cemented carbide can be made a structure in which the surface is longer than the inside by the manufacturing method described later. . That is, by firing at a relatively low temperature for a short time, the difference in heat capacity applied between the surface and the inside of the cemented carbide is increased. Moreover, since the high-temperature carbonized WC powder is used, the sintered body can be densified without grain growth inside the cemented carbide. Thereby, the grain growth degree of the WC particles 2 on the surface and inside of the cemented carbide 1 can be changed. As a result, the wear resistance and deformation resistance on the surface of the cemented carbide can be improved. The high-temperature carbonized WC powder can be produced with an average particle size of 0.5 μm or more, and when it exceeds 1.5 μm, the hardness of the cemented carbide decreases.

  Further, at the time of the mixing, it is preferable to add a solvent such as water or methanol and perform attritor pulverization.

  Next, the mixture powder is molded into a predetermined shape by a known molding method such as press molding, casting molding, extrusion molding, cold isostatic pressing, etc., and then the temperature is increased at a rate of 5 to 10 ° C./min. After heating, the above-mentioned cemented carbide can be obtained by firing at 1350 to 1380 ° C. for 0.2 to 0.5 hours in a vacuum atmosphere.

  Here, among the above steps, when the firing temperature is lower than 1350 ° C., the sinterability of the cemented carbide decreases, and conversely, when the firing temperature is higher than 1380 ° C., the surface structure of the cemented carbide of the present invention is obtained. I can't. If the firing time is shorter than 0.2 hours, the cemented carbide cannot be densified, and if the firing time is longer than 0.5 hours, the surface structure of the cemented carbide cannot be obtained.

  In addition, since the cemented carbide of the present invention described above has high toughness and high hardness and high strength, it can be suitably used as a cutting tool.

Further, the cutting tool of the present invention has a group of carbides, nitrides, carbonitrides, TiAlN, TiZrN, diamond, and Al ₂ O ₃ of periodic table groups 4, 5 and 6 metals on the surface of the cemented carbide described above. A single layer or a plurality of layers of at least one coating layer selected from the above may be used.

WC powder having the carbonization temperature and average particle size shown in Table 1, Co powder having an average particle size of 0.6 μm, TaC powder having an average particle size of 1.5 μm, Cr ₃ C ₂ powder having an average particle size of 1.3 μm, and average particle size A 1.5 μm VC powder and a TiC powder having an average particle size of 2.0 μm are added at a ratio shown in Table 1, water is used as a solvent, a cemented carbide with a media diameter of 4 mm and a WC particle average particle size of 0.3 μm is used as a medium. Balls were added and mixed with a vibration mill for 24 hours to prepare a mixed powder. After that, 1.6% by mass of paraffin wax was added as an organic binder, the mold was press-molded, and fired under the conditions shown in Table 1 to obtain SPMN120408. A cutting tool-shaped cemented carbide was produced.

  As shown in FIG. 1, a 10,000 times magnified backscattered electron image is observed with respect to five arbitrary cross sections of the obtained cemented carbide with three parts (at the same depth from the surface) of an arbitrary area of 11 μm × 8 μm. The shape of WC particles (average particle diameter of WC particles, ratio of round particles having a radius of curvature of 50 nm or more with respect to corner portions of WC particles) was calculated for three consecutive positions. The results are shown in Table 2. Moreover, the cutting performance of the tool was evaluated under the following conditions. 1 shows the sample No. of the above example. 4 shows organizational photographs.

<Conditions>
Work Material: Grooved Alloy Steel (SCM440) Four Grooved Tool Shape: SPMN120408
Cutting speed: 150 m / min
Feed rate: 0.3 mm / rev.
Cutting depth: 2mm
Cutting state: Dry evaluation item: Wear width of cutting edge at the time of impact 1000 times, and the number of impact until the tool life

  From the results of Tables 1 and 2, the sample No. In No. 7, the length of the neck part in the inside and the inside of the cemented carbide alloy became the same, and the wear resistance and deformation resistance in the tool cutting edge were insufficient. In addition, Sample No. In No. 8, the ratio of round particles decreased, and chipping occurred at the tool cutting edge. Furthermore, sample No. 1 with a firing time shorter than 0.2 hours was used. In No. 9, the cemented carbide alloy was insufficiently densified, the length of neck growth on the surface and inside was the same, and the wear resistance of the tool cutting edge was insufficient. In addition, as a raw material WC powder, sample No. 1 using a WC powder having a carbonization temperature of 1500 ° C. as in the prior art. In No. 10, the average length of neck growth on the surface and inside of the cemented carbide was the same, and the deformation resistance was insufficient in cutting characteristics.

  On the other hand, according to the present invention, sample No. 1 manufactured under predetermined firing conditions using WC powder carbonized at 1750 ° C. or higher as a raw material. 1 to 6, the ratio of particles with rounded corners is higher than 50% by volume in the WC particles, and the average length of the neck portion on the surface is longer than that of the inside, and has excellent fracture resistance and wear resistance. And deformation resistance.

It is a scanning electron micrograph in an example of the cemented carbide of this invention in the cross section of (a) surface and (b) inside. It is the figure which wrote the neck growth part in the scanning electron micrograph of FIG. It is the X-ray diffraction pattern in the (a) surface and (b) inside of the cemented carbide of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cemented carbide 2 WC particle 2a Round WC particle 3 Bonding phase 4 Neck growth part c Half value of diffraction peak of (101) plane in X-ray diffraction measurement of corner part w _s cemented carbide surface located at both ends of diagonal L Width w _i Half width of diffraction peak of (101) plane in X-ray diffraction measurement inside cemented carbide

Claims (4)

A cemented carbide in which WC particles are bonded with a binder phase, and when a cross-sectional structure of the cemented carbide is observed, a WC particle having a polygonal shape and a rounded curvature radius of 50 nm or more inside. Is included at a ratio of 50 area% or more with respect to the entire WC particles, and the average length of the neck growth portion between the WC particles is longer on the surface than the inside of the cemented carbide. Hard alloy. The cemented carbide according to claim 1, wherein an average particle size of the WC particles is 0.5 to 1.5 µm. The cemented carbide according to claim 2, wherein the ratio of WC particles having a particle size within ± 30% of the average particle size is 80% by area or more with respect to the whole WC particles. . The half width of the diffraction peak of the (101) plane in the X-ray diffraction measurement on the surface is narrower than the half width of the diffraction peak of the (101) plane in the internal X-ray diffraction measurement. The cemented carbide according to any one of claims 1 to 3.