JP4975308B2 - Manufacturing method of fine cemented carbide for micro tool - Google Patents

Description

  The present invention relates to a fine cemented carbide for fine tools in which the average particle size of carbide particles such as WC is 0.8 μm or less and the Co content is 2 to 15% by mass, and a method for producing the same.

With the downsizing, high density, and high precision of electronic parts, automobile parts, etc., parts processing tools, jigs, and the parts themselves are rapidly becoming smaller and more precise. For this reason, these tools, jigs, and parts include, for example, highly reliable members that are long and thin but have high bending resistance, high hardness and wear resistance, high toughness and excellent chipping resistance. There is a strong demand.
In response to such demands, fine cemented carbides in which WC particles with a small average particle size are bonded with Co or the like are excellent in both wear resistance and strength, and therefore, small diameter end mills, small diameter drills, routers, various types Widely used in shear blades and sliding materials. The wear resistance mainly depends on the hardness (JISZ2245) of the fine-grained cemented carbide, and the strength mainly depends on the bending strength (JIS026).
The hardness of the fine cemented carbide shows a tendency to increase as the Co amount is small and the crystal grain size of the WC particles is small, and the bending strength is generally high as the Co amount is large and the crystal grain size of the WC particles is small. Become. For this reason, in order to suppress the grain growth of WC particles during sintering, a metal such as V, Cr, Ta or a compound such as a carbide, nitride, carbonitride, or the like is used as a grain growth inhibitor for WC. It is done to add. There exists patent document 1 as the specific example. In Patent Document 1, the total amount of V and Cr is obtained by adding V and Cr in a range in which a third phase that causes a reduction in the strength of the alloy does not occur, and performing HIP treatment in a 100 MPa Ar atmosphere after vacuum sintering. Is disclosed as a cemented carbide having essentially two WC particles and a binder phase, and having an average WC particle size of 0.7 μm or less. However, as will be described later, it is not sufficient to reduce the average particle diameter of WC particles to increase the bending strength. Rather, coarse carbide particles such as WC existing in the cemented carbide have a bending strength. Although the minimum value is determined and the bending strength is greatly reduced by the coarse carbide particles, Patent Document 1 examines only the average particle diameter, and regarding the coarse carbide particles contained in a small number, Not considering at all.
Patent Document 2 describes a toughness fine grain carbide in which the saturation magnetization and the coercive force of a cemented carbide material are maintained within a certain range, and there are 0 or more and 5 or less WC particles having a maximum diameter of 2 μm or more per 1 mm 2. It discloses that the alloy is tough and can avoid sudden fracture phenomena and is industrially significant. However, although Patent Document 4 describes that a huge WC particle induces a sudden destruction phenomenon, it is assumed that there is even one coarse carbide particle having a right angle portion and a span exceeding 4 μm. However, it has not been studied at all that the bending strength of the fine cemented carbide material is greatly reduced and its reliability is greatly reduced.
In addition, in Patent Document 3, in order to avoid mixing coarse WC powder in the raw material powder in the manufacturing process of the WC-based cemented carbide, “average particle diameter of WC: 0.7 μm or less and WC It is disclosed that mixed pulverization is performed using a ball for mixing and pulverizing made of a WC-based cemented carbide having a maximum particle size of 2.0 μm or less. However, this “WC-based cemented carbide” is a mixed powder composed of WC powder and Co powder having an average particle size of 0.7 μm and a maximum particle size of 2.0 μm. A ball for mixing and pulverization produced by a method of sintering after pressing into a spherical shape, that is, a WC-based cemented carbide having an average particle diameter of WC: 0.7 μm and a maximum particle diameter of WC: 2.0 μm As described above, a “mixing and pulverizing ball (mixing and pulverizing ball according to an embodiment of the present invention)” is merely “an average particle diameter of WC: 0.7 μm or less and a maximum particle diameter of WC: 2. It is an abbreviation of a cemented carbide produced using WC powder of “0 μm or less”, and does not indicate the average particle size and maximum particle size of WC after sintering. In addition, the fact that the WC grain size after sintering becomes larger than the grain size of the raw material powder is described on the right side of page 139 of Patent Document 1 as “WC particles cause grain growth by dissolution / precipitation reaction during sintering”. As is described, it is well known from that time, and it is clear that Patent Document 1 does not specifically examine the WC grain size after sintering. It is apparent that no consideration is given to the fact that the carbide particles of this type grow abnormally around the Co agglomerated part and coarse carbide particles such as WC having a particle size exceeding 4 μm are formed. That is, the mixing and pulverization method used in Patent Document 3 is a conventionally used attritor, ball mill, bead mill method, and the like, and at least several millimeters to several centimeters of a large pulverization medium (media) is collided or crushed. A WC powder and a Co powder are pulverized and mixed using a shearing force. However, since Co is soft as Hv250 and has extremely high ductility, Co is crushed into pieces during the mixing and pulverization described above, and is not uniformly dispersed in the WC powder. There is a big drawback. As a result, when the mixed powder of carbide particles such as WC and Co is molded and sintered, W solid-dissolved in Co at the sintering stage is reprecipitated in the Co agglomerated portion in the cooling process after sintering, and is coarse. There is a major drawback that WC particles and W2C crystal grains are formed and the bending strength is greatly reduced. As described above, Patent Document 3 discloses that even when fine WC powder or Co powder is used, carbide particles such as WC grow abnormally in Co agglomerated parts and the like, and coarse carbide particles having a particle diameter exceeding 4 μm are formed. Does not take into account. Furthermore, among the coarse carbide particles, in particular, it is completely considered that the carbide particles having an intersection angle of at least one corner within the range of 90 ± 5 degrees greatly reduce the bending strength of the fine cemented carbide. Not.
Patent Document 4 discloses that (i) the final particle size of tungsten carbide is determined under conditions for wet-kneading WC powder and Co powder, and (ii) in order to avoid grain growth in any part. It is necessary to obtain a uniform distribution of the growth inhibitor, and (iii) to obtain a uniformly distributed cobalt in order to avoid porous cobalt accumulation in the sintered material. In order to disclose that time is determined and to improve this, WC powder with well-defined narrow particle size distribution with round shape and final (sintered) particle size, and Cr, Ta, etc. A method for producing a WC-Co based cemented carbide using a Co alloy powder that is made of an alloy of a grain growth inhibitor and Co and that is sufficiently deagglomerated or easily deagglomerated in a round shape is disclosed. Moreover, the method of manufacturing the sintered compact of the WC-Co base cemented carbide whose average particle diameter of WC is 0.6-1.4 micrometers is disclosed using this manufacturing method. However, in Patent Document 4, it can be said that the kneading time is shortened to about one-tenth of the conventional method in Examples, but the WC powder and Co alloy powder are kneaded using the ball mill method. Therefore, as described above, contamination from the media and the case, contamination of the raw material powder through the gaps between the media, and collision and crushing between the media, the highly ductile Co particles are crushed in a single piece The problem of agglomeration has not been solved. Incidentally, the amount of the grain growth inhibitor such as Cr or Ta used in the cemented carbide is at most 10% by mass or less of Co, and is not so large as to significantly improve the ductility of Co grains. Patent Document 4 discloses that the average particle diameter of the sintered WC is 0.6 to 1.4 μm, but the coarse particles generated in the cemented carbide due to Co agglomeration and the like are disclosed. No consideration has been given to carbide particles such as WC.

Japanese Examined Patent Publication No. 62-56224 JP 2001-115229 A JP-A-8-38925 JP 2000-336437 A

  The inventors of the present application have examined the above-mentioned drawbacks of the prior art in detail, and the dispersion of the carbide particle powder such as WC and the binder phase forming particle powder such as Co, which is the raw material powder, is insufficient, When there is agglomeration, carbide particles such as WC grow abnormally and tend to be coarsened around the Co agglomerated part during sintering, and such abnormal growth is particularly noticeable in a fine cemented carbide having a small WC particle diameter. In particular, when coarse carbide particles having a right angle portion are formed, the bending strength is greatly reduced, and the reliability thereof is greatly reduced, and the present invention has been conceived.

The problem to be solved by the present invention is to provide a method for producing a fine cemented carbide for a micro tool that has high hardness, high toughness, high bending strength, and high reliability. As described above, a slurry obtained by mixing and pulverizing carbide particles such as WC and a binder phase forming component such as Co in order to avoid Co clumps and flat pieces generated during mixing and pulverization has an opening of 45 μm. It is a common practice to remove Co clumps and flat pieces through a (330 mesh) sieve. However, even when passing through a sieve having an opening of 45 μm, only Co having a size of approximately 40 μm or more can be removed, and Co agglomerated powder and flat powder having a size of less than 40 μm pass through. On the other hand, if the mesh is made finer, a large amount of Co solids and flat pieces remain on the sieve, the sieve is clogged, and the composition ratio of carbides such as WC and Co greatly deviates from the predetermined value. Disadvantages appear. For this reason, Co agglomerated powder and flat powder of less than 40 μm pass through the sieve, and these are mixed into the cemented carbide manufacturing powder after pulverizing and mixing the compounded powder such as carbide particles and Co powder. It is the current situation that it is tolerated to remain.

There are two methods for producing a fine cemented carbide for a micro tool of the present invention: WC powder , Co powder, and a metal such as V, Cr, Ta as a grain growth inhibitor, or their carbide, nitride, carbonitride powder. Alternatively , when pressurized energy is applied to a slurry composed of a mixed powder for producing a fine cemented carbide for a micro tool and a solvent containing three kinds and then conveyed through a flow path, the flow branches to at least two or more upstream of the flow path The first and second flow paths have an opening with a smaller inner diameter on the downstream side, and the slurry ejected from the opening is arranged to oppose each other, and the ejected slurry is mutually It collides so as to intersect at substantially one point, mixing, and a second step of pulverizing, recovered slurry after the collision, the third step, the micro tool fine cemented carbide for producing mixed powder prepared by drying Molding and sintering It is the manufacturing method of the fine-grain cemented carbide for micro tools characterized by the above-mentioned. By adopting this production method, hard particles such as WC and a binder phase forming component such as Co are more uniformly dispersed, there is no coarse region where a binder phase forming component such as Co is aggregated, and A mixed powder for manufacturing a fine cemented carbide for a micro tool substantially free of flat Co can be realized, and by using this, there is no coarse carbide particles having a right angle portion, high hardness, high toughness, A highly reliable fine cemented carbide for a micro tool having a high bending force can be produced.

  According to the present invention, it is possible to realize a highly reliable method for producing a fine cemented carbide for a micro tool which is free of coarse and easily broken carbide particles, has high hardness, high toughness, and high bending strength.

The fine cemented carbide for fine tools of the present invention is a fine cemented carbide for fine tools with an average particle size of carbide particles of 0.2 to 0.8 μm and an amount of Co of 2 to 15% by mass. When broken, at least one corner constituting a part of the contour of the carbide particles on the fracture surface intersects with each other within an angle range of 90 ± 5 degrees among the carbide particles on the fracture surface. There are carbide particles that are two-sided and have a right-angled corner that has a length of at least one of the two sides of 0.1 times or more of the carbide particles to which the corner belongs, and the right-angled corner It is a fine cemented carbide for fine tools, characterized in that the maximum value of the carbide particles having a particle size of 0.6 to 4 μm. By doing so, it is possible to realize a highly reliable fine cemented carbide for a micro tool having high hardness, high toughness, and high bending strength. Such a fine cemented carbide for fine tools is, for example, a fine tool fine particle in which a carbide raw material powder such as WC and a mixed powder of Co or the like are pulverized and mixed by a jet collision method described later to eliminate Co agglomeration of 20 μm or more. It is obtained by using cemented carbide powder and precisely controlling from molding to sintering. When other dispersion methods or Co agglomerated powder removal methods are used, the Co powders are made in accordance with the composition and manufacturing process of each cemented carbide so that the fine cemented carbide for micro tools of the present invention is produced. By increasing the dispersion of Co and optimizing the size of the Co agglomerated powder, the fine cemented carbide for micro tool of the present invention can be realized.
If the average particle size of the carbide particles is larger than 0.8 μm, the hardness of the fine cemented carbide is significantly lowered, and the wear resistance becomes insufficient. In addition, for example, when a small diameter tool having a blade diameter of 0.3 mm or less is made, there are disadvantages that the surface roughness when the tool tip is machined is deteriorated due to the large particle size and chipping is likely to occur at the tool tip. appear. On the other hand, when the average particle size of the carbide particles is less than 0.2 μm, the growth of the carbide particles is insufficient, so that once the cracks are generated in the sintered body, the progress is not suppressed, and the pores remain. Alternatively, there is a defect that sufficient toughness cannot be obtained in the fine cemented carbide because the sufficient adhesion strength between the carbide particles and Co cannot be obtained. Therefore, the average particle size of the carbide particles of the present invention is set to 0.2 to 0.8 μm or less.
Further, if the amount of Co exceeds 15% by mass of the total composition, the hardness of the fine cemented carbide is greatly reduced, and the raw Co powder is sufficient in the process of mixing and pulverizing the raw material for the fine cemented carbide. When it is difficult to disperse uniformly in the carbide particle powder such as WC and the compact of the mixed powder is sintered, the fine carbide powder dissolved in the binder phase in the sintering process is Re-precipitation occurs during the cooling process, and a defect that coarse carbide particles such as WC are formed appears. In addition, when the amount of Co is less than 2% by mass, there is a disadvantage that the absolute amount of Co is small and Co is difficult to be uniformly dispersed in a carbide particle powder such as WC. As a result, the toughness of the produced fine cemented carbide is greatly reduced, and the drawback that the bending strength is significantly reduced appears. Therefore, the Co content is set to 2 to 15% by mass of the total composition.
And, when broken by an external load, among the carbide particles on the fracture surface, at least one corner portion constituting a part of the contour of the carbide particle on the fracture surface has an angle of 90 ± 5 degrees with each other. There are carbide particles that are two-sided crossing within a range, and the length of at least one side of the two sides is a right-angled corner that is 0.1 times or more of the carbide particles to which the corner belongs. The fine cemented carbide for a micro tool is characterized in that the maximum value of the carbide particles having a right angle portion is 0.6 to 4 μm. By setting the maximum value of the carbide particles having a right-angled corner to 0.6 to 4 μm, it is possible to realize a highly reliable fine cemented carbide for a micro tool with high hardness, high toughness and high bending strength. . Carbide particles having only corners whose crossing angle between the two sides constituting the corners is outside the range of 90 ± 5 degrees are less likely to penetrate the crystal grains than carbide particles having right angle corners. The effect of hard alloy on bending resistance is small. Further, if the lengths of the two sides constituting the right angle portion are both less than 0.1 times the passing of the carbide particles to which the right angle portion belongs, the corner portions are not independently formed and are cleaved. Is not strong and does not significantly reduce the bending strength of the cemented carbide. This is because the carbide strength of the fine cemented carbide consists of two sides intersecting each other within an angle range of 90 ± 5 degrees, and the length of at least one of the two sides is a carbide to which the corner belongs. This is because it is mainly determined by carbide particles having a right angle portion that is 0.1 times or more of the particle passing (hereinafter referred to as right angle carbide particles). For this reason, even if the angle at which the two sides constituting the corner intersect is outside the range of 85 to 95 degrees, or the angle at which the two sides intersect is within the range of 85 to 95 degrees, the 2 When both of the sides are less than 0.1 times the passing of the carbide particles to which the corner belongs, it is not determined as a right angle corner.
On the other hand, when broken by an external load, among the carbide particles on the fracture surface, at least one corner portion constituting a part of the contour of the carbide particle on the fracture surface is 90 ± 5 degrees relative to each other. Although there are right-angle carbide particles that have two sides intersecting within the range of the angle and the length of at least one of the two sides is 0.1 times or more of the carbide particles to which the corner belongs, If the maximum value of the right-angle carbide particles exceeds 4 μm, it becomes easier to cleave in the plane having the right-angled corners, and the maximum value of the right-angle carbide particles exceeds 4 μm. , Cracks penetrate through the crystal grains and breakage easily proceeds, and the bending strength is remarkably reduced. On the other hand, when the maximum value of the right-angle carbide particles is less than 0.6 μm, the carbide particles are not sufficiently grown by firing, the fine cemented carbide is not sufficiently dense, and locally If cracks occur, the progress cannot be prevented by the carbide particles, so that a sufficient bending force cannot be obtained in the fine cemented carbide and a defect appears.
The above effect is particularly prominent when the right-angle carbide particles have a hexagonal crystal structure, and are particularly WC particles. This is presumably because the hexagonal carbide particles such as WC are easily broken in the plane including the [0001] axis.
The intersection angle of the corners of the carbide particles is obtained by photographing the fractured surface with a scanning electron microscope (hereinafter referred to as SEM) at a magnification of 5 k, and in each carbide particle, at least one corner (including a concave corner) is included. )) Was measured only when the distance to the carbide particles belonging to the corner portion was 0.1 times or more. The crossing angle is calculated by drawing a straight line in parallel to each side forming the corner to be measured, enlarging and copying this 1.75 times, translating so that the above-mentioned straight line touches each side, and then translating 2 The angle at which the straight lines intersect was defined as the intersection angle. Then, only those having a measured crossing angle of at least one corner within a range of 90 ± 5 degrees were defined as right-angle carbide particles. Further, the carbide particles observed on the fracture surface may be composed of a composite of a plurality of carbide particles. In that case, the intersection angle of at least one corner of at least one carbide particle constituting the composite Is a right-angle carbide particle if the angle is within the range of 90 ± 5 degrees, and the size of the crystal grains is measured by observing the entire complex and measuring the passing of the complex. Whether or not the carbide particles are composed of a composite of a plurality of carbide particles is determined by whether or not they are surrounded by a grain boundary having the same width as the other crystal grain boundaries. When there are multiple cracks or grain boundaries that appear in the composite, even at one location, there are only cracks or grain boundaries that are much narrower than other grain boundaries, and the cleavage planes are continuous. If the location is present, it is determined as one complex. In addition, the fracture surface that is broken by an external load refers to, for example, a fracture surface that is broken when the bending strength is evaluated. When the specimen to be cut is not uniform in the longitudinal direction (direction substantially perpendicular to the face to be cut) or the surface roughness is different, the sample is processed by centerless or surface grinding so that the cross section becomes a circle or a rectangular parallelepiped. After processing the sample so that it has a uniform shape in the direction and substantially the same surface roughness, the bending strength is evaluated by a three-point bending method, and the maximum particle size of the carbide particles on the fractured surface is measured. . As for the shape of the sample to be cut, for example, the cross-sectional shape is preferably 2 mmΦ and the span is preferably 20 mm, but the cross-section may be 2 mmΦ or less and the span may be 20 mm or less.
The fine cemented carbide for a micro tool of the present invention has a higher bending strength and a higher reliability that the maximum value of the carbide particles having a right angle corner is in the range of 0.6 to 2 μm. A fine cemented carbide for a micro tool is preferably obtained.
In addition, the production method of the present invention contains WC powder, Co powder, and a metal such as V, Cr, Ta as a grain growth inhibitor, or two or three kinds of carbide, nitride, carbonitride powder thereof. A first step of branching at least two or more upstream on the upstream side of the flow path when a pressurized energy is applied to a slurry composed of a mixed powder for producing a fine cemented carbide for a micro tool and a solvent and conveyed by the flow path; The flow path branched into two or more has an opening with a reduced inner diameter on the downstream side, and the slurry ejected from the opening is arranged so as to oppose each other, so that the ejected slurry intersects with each other at substantially one point. A second step of colliding, mixing, and crushing (hereinafter, the first step and the second step are collectively referred to as jet collision), and a third step of collecting and drying the slurry after the collision For micro tools made by Forming a particle cemented carbide for producing mixed powder, a method for producing a fine cemented carbide for small tools, characterized by sintering. By adopting this production method, hard particles such as WC and a binder phase forming component such as Co are more uniformly dispersed, there is no coarse region where a binder phase forming component such as Co is aggregated, and It is possible to realize a mixed powder for manufacturing fine cemented carbide for micro tools that is substantially free of flat Co. By using this, it is possible to achieve high hardness, high toughness, high bending strength, and high reliability for micro tools. A fine cemented carbide can be produced. This is because, by producing a mixed powder for producing a fine cemented carbide for a micro tool by jet collision, at least a carbide particle powder such as WC and a Co powder are mixed better, and the Co powder is more uniformly dispersed. , Flat Co is not formed, and by using this mixed powder, since there is no large Co accumulation in the molded body, abnormal growth of carbide particles such as WC during sintering is suppressed, high hardness, high toughness, This is because a fine cemented carbide for a micro tool with high bending strength and high reliability can be manufactured. In addition, it is preferable to mix and pulverize the slurry by the above jet collision method and then pass it through a sieve having an opening of 20 μm or less because Co agglomeration can be further removed.

  The fine cemented carbide for a micro tool of the present invention contains 1 to 10% by mass of Cr, 1 to 5% by mass of Ta, and 1 to 4% by mass of V in Co which mainly forms a binder phase. Thus, the heat resistance, plastic deformation and wear resistance of the binder phase are increased, and a fine cemented carbide material for fine tools having excellent durability characteristics is obtained, which is preferable. When the contents of Cr, Ta and V in Co are less than 1% by mass, the effect of containing Cr, Ta and V is small. When the Cr content in Co exceeds 10% by mass, a part of Cr precipitates and the bending strength of the entire member tends to decrease. Further, when the Ta content in Co exceeds 5% by mass, a part of Ta is precipitated to form spotted crystals, and the bending strength of the entire member tends to decrease. Further, when the V content in Co exceeds 4% by mass, a part of V is precipitated around the WC, and the bending strength of the entire member tends to be lowered. The amount of Cr, Ta, and V dissolved in Co is determined by finely pulverizing a fine cemented carbide material and electrolyzing it with an electrolytic solution composed of a mixture of 5% ammonium citrate and 0.5% sodium chloride. It is determined by high frequency inductively coupled plasma emission analysis (hereinafter referred to as ICP-AES).

The fine cemented carbide for micro tools of the present invention has inherently contradictory properties such as wear resistance, chipping resistance and chipping resistance when used for small diameter tools with a narrow practical part and a maximum diameter of 3.2 mm or less. The long and practical parts are made of fine cemented carbide for micro tools with high hardness and high toughness, both of which have excellent surface roughness and processing accuracy at the tip of the member. The portion can be processed with high accuracy and reliability, which is preferable. Such a small diameter member having a long and narrow practical part includes, for example, a small diameter cutting tool such as a small diameter drill, a small diameter end mill, and a small diameter router, and is particularly preferable because excellent cutting edge and chipping resistance and chipping resistance can be obtained. It is also particularly useful for wear-resistant tools having a small diameter, push pins, punches, sliding rod portions of fuel injection nozzles, and the like. The practical part refers to a blade part, a punch tip, a nozzle tip, and the like, and refers to a part to which an actual action such as a load, a frictional force, and a gripping force is applied. The maximum diameter is 3.2 mm or less and the cross section is 3.2 mmΦ. The cross-sectional shape is not necessarily circular.
Further, on the surface of the fine cemented carbide for a micro tool of the present invention, carbide, nitride, oxide, boride, and a composite thereof composed of at least one of group 4a, 5a, and 6a elements, Al, and Si. It is more preferable to coat one or more compounds and a hard film made of a carbon film such as diamond or DLC, since further excellent wear resistance can be obtained.

First, 15.4 kg of raw material powder in which WC having an average particle size of 0.6 μm, 1.4 μm of Co, 1.5 μm of Cr3C2, 1.2 μm of TaC, and 1.5 μm of VC powder are blended in predetermined amounts. And 13 denatured alcohol were mixed and pulverized with an attritor for 5 hours to prepare a slurry in which the concentration of the raw material powder in the slurry (hereinafter referred to as the slurry concentration) was 60% by mass. Then, for the purpose of further improving the dispersion of Co, after applying energy of 180 MPa to the slurry and branching into two flow paths in the middle, the slurry is released from the openings narrower than the diameter of each flow path. The mixed powder in the slurry was further mixed and pulverized by repeating four times of jetting collisions in which the jets collide and collide with each other at substantially one point. And after passing this slurry through a sieve with an opening of 20 μm, this was dried under reduced pressure to prepare a raw material powder mixed powder for producing fine cemented carbide for fine tools of Invention Examples 1 to 19. Although the same raw material powder and the same production conditions are used, only the number of jet collisions is changed to 1, 2, 3, and 5 times to produce the fine cemented carbide for fine tools of Examples 20 to 23 of the present invention. Raw material powder mixed powder was prepared. The amount of Co remaining on the sieve after the slurry after jetting was passed through the sieve having an opening of 20 μm was 10% or less of the total amount of Co blended. The raw material powder mixed powder thus prepared was added with an extrusion molding wax and a solvent and kneaded for 1 hour, and then an elongated molded body having a diameter of 2.8 mm was prepared and dewaxed by an extrusion molding machine. After these dewaxed products were held at a firing temperature of 1400-1450 ° C. for 1 hour in a vacuum atmosphere of 1.3 to 13.2 Pa, then the pressure was changed to a pressurized atmosphere of 4.9 MPa and held for 30 minutes By cooling to 1000 ° C. at a cooling rate of 5 ° C./minute, a fine cemented carbide for micro tools of Invention Examples 1 to 23, which is a long sintered body having a diameter of 2.2 mm and a length of 110 mm, is produced. did. The production conditions of these inventive examples 1 to 23 are summarized in Table 1. In addition, Table 2 summarizes the results of ICP analysis of the Co amount of the produced fine cemented carbide for fine tools, Cr, Ta, and V amount in Co. Invention Examples 1 to 15 and 20 to 23 having a Co content of 8 mass% were sintered at 1450 ° C., and Invention Examples 16 to 19 having a Co content of 2, 5, 12, and 15 mass% were 1500 respectively. 1475, 1425, and sintered at 1400 ° C.
Further, for comparison, the Co amount is 1% by mass and the sintering temperature is different from 1525 ° C., but the other compositions and production conditions are the same as those in Comparative Examples 24 to 19 of the present invention examples 16 to 19, and Co. Comparative Example 25 in which the amount of 16% by mass and the compact containing no Cr3C2, TaC, or VC powder is different from the sintering temperature of 1375 ° C., but the other production conditions are the same as those of Invention Examples 16-19. Was made. For comparison, the raw material powder blended in the same composition as the present invention example 20 with Co amount of 8% by mass, Cr amount in Co, same Ta amount, same V amount as 4, 2, 2% by mass, respectively, After mixing and pulverizing under the same attritor conditions to prepare a slurry, it is only passed through a sieve with a mesh opening of 45 μm, and it is directly dried under reduced pressure without mixing by the jet mixing method. An alloy raw material powder mixed powder was prepared. Then, by using this mixed powder, molding, dewaxing, and sintering were performed under the same conditions as in Invention Example 20, thereby producing Comparative Example 26, which is a fine cemented carbide having the same shape as in Invention Example 20. In addition, after pulverizing the same composition as Comparative Example 26 under the same attritor conditions, this slurry was passed through a sieve having an opening of 20 μm, but 30% or more of Co did not pass through the sieve, so in Comparative Example 26, the opening was 45 μm. Only through the sieve. For comparison, a blended powder having a Co content of 16% by mass and containing no Cr3C2, TaC, or VC powder was mixed and ground under the same attritor conditions as in Comparative Example 26, and then passed through a sieve having an opening of 45 μm. The raw material powder mixed powder for producing a fine cemented carbide was prepared by directly drying under reduced pressure without performing mixing by jet mixing, and using this, molding and dewaxing were performed under the same conditions as in Comparative Example 26. The comparative example 27 which is a fine grain cemented carbide alloy of the same shape as this invention example 1 was produced by sintering. Table 1 shows the production conditions of the fine cemented carbides of Comparative Examples 24 to 28, and Table 2 shows the results of ICP analysis of Co amount, Cr, Ta, and V amount in Co.

  The types and amounts of elements constituting the fine cemented carbide were quantitatively analyzed by fluorescent X-ray analysis (hereinafter referred to as XRF). In addition, the average grain size of the carbide particles of the fine cemented carbide is obtained by mirror-polishing the cross section of the fine cemented carbide and then etching for 0.5 minutes with Murakami reagent and 0.5 minutes with aqua regia. Then, an average region where coarse carbide crystal grains are not observed is photographed with a scanning electron microscope (manufactured by Hitachi, S-4200, hereinafter referred to as SEM) at a magnification of 10 k, and this is imaged. It calculated by analyzing with analysis software (Image-Pro Plus Version4.0 for Windows, Windows is a registered trademark). The results are collectively shown in the column of carbide particle average particle diameter (μm) in Table 2.

  Three long-edged two-blade small-diameter drills each having a shank diameter of 2.0 mm and a cutting edge diameter of 0.1 mm were produced using the long fine-grained cemented carbide for a micro tool produced in the present invention example and the comparative example. Using this, four glass epoxy plates with a high glass transition temperature of 0.2 mm thickness on both sides with 5 μm Cu were stacked, and a drilling test was conducted at a rotational speed of 280000 rpm and a feed of 6 μm / rotation. went. This cutting condition is an evaluation condition in which the cutting edge temperature tends to be higher because cutting is performed at a higher speed. The number of holes drilled until wear of 5% on the outer diameter of the outer peripheral blade or the smaller number of holes drilled until breakage was measured, and the average of the three holes was defined as the drilling life. Then, using each of the three small-diameter drill shank parts evaluated above, the fracture strength of the fine cemented carbide constituting the small-diameter drill was measured, and the fracture surface fractured by the fracture surface fractured by the external load was measured with SEM. The shape and the maximum particle size of the carbide particles observed near the fracture base point were determined (see, for example, Journal of the Japan Institute of Metals, Vol. 33, 1969, pages 504-50). The measurement results of the drilling life of each small-diameter drill produced from the inventive examples and comparative examples, and the difference between the maximum bending strength and the minimum bending strength of the fine cemented carbide for micro tools, Table 2 also shows the measurement results of the average particle diameter of the carbide particles, the maximum value of the delivery of the right-angle carbide particles, and the maximum value of the delivery of the non-right-angle carbide particles observed on the fracture surface.

From Table 2, the average particle diameters of carbide particles such as WC forming the fine cemented carbide are 0.1 μm and 0.9 μm, and the right-angle carbide particles observed in the fracture surface fractured at the time of bending strength measurement are passed. In Comparative Examples 24 and 25 in which the maximum values of 0.5 and 4.1 μm are the difference between the maximum value and the minimum value of the bending strength are 2905 and 3009 MPa, and the drilling life is 1710 and 1620 holes On the other hand, Examples 1 to 5 of the present invention in which the average particle diameter of the carbide particles is 0.6 to 4.0 μm, and the maximum value of the right-angle carbide particles observed in the fracture surface is 0.6 to 4.0 μm. The bending strength difference is as small as 923 to 1950 MPa, the drilling life is 3430 holes or more, which is twice as long as that of Comparative Examples 24 and 25, and is extremely excellent. Further, from Table 2, with respect to Comparative Examples 24 and 25 in which the amount of Co of the fine cemented carbide is 1 to 16% by mass, the amount of Co is 2 to 15% by mass and the right-angle carbide particles observed in the fracture surface In Examples 16-19 of the present invention in which the maximum value of the handing over is in the range of 0.9-3.1 μm and 0.6-4.0 μm, the difference in bending strength is as small as 937-1421 MPa, and the drilling life is 4620 More than the hole and 2.8 times longer than those of Comparative Examples 24 and 25, which was remarkably excellent.
In addition, Comparative Example 26, in which the slurry was mixed and pulverized using the attritor method, only passed through a sieve having an opening of 45 μm, and not mixed and pulverized by jet mixing, had a composition of Co amount, Cr, Ta, and V. Although the average particle diameter of the carbide particles is 0.5 μm, which is the same as that of Example 20 of the present invention, the maximum value of the right-angle carbide particles observed on the fracture surface is as large as 4.2 μm, and the difference in bending strength is large. It is 3072 MPa and the drilling life is 1570 holes. On the other hand, Example 20 of the present invention has a small bending resistance difference 1862, and the drilling life is 3560, which is 2.2 times longer than that of Comparative Example 26, and is extremely excellent.
In addition, the amount of Co is 16% by mass, which is outside the scope of the present invention, and uses mixed powder that does not contain Cr3C2, TaC, VC powder, and after mixing and grinding for 8 hours under the same attritor conditions as in Invention Examples 1-15 1375 ° C., after molding and dewaxing under the same conditions as in Examples 1 to 15 of the present invention, using the mixed powder produced without passing through sieving with an opening of 45 μm and mixing and pulverization by jet mixing. In Comparative Example 27 produced by sintering with the above, the average particle size of the carbide particles constituting the sintered body is 0.7 μm, and the maximum value of the right-angled carbide particles observed on the fracture surface is 7.1 μm. Met. 1 and 2 show an SEM photograph of the fracture surface of Comparative Example 27 and a schematic diagram thereof. 1 and 2, there are four coarse carbide particles (a) to (d), of which (a) and (b) corner portions (a) to (d) form each corner portion. Since the crossing angle of the two sides is in the range of 90 ± 5 °, and at least one side of the two sides forming each corner is 0.1 times or more of the passing of the carbide particles to which the corner belongs, (a ) And (b) are right-angle carbide particles. Among these, one side of the corners of (B) and (C) is curved outward at a position slightly advanced from the corner, but the intersection angle of the two tangents forming each corner is 90 ± 5 degrees. It is within the range and is a right angle corner. On the other hand, the corner (e) of the crystal grain (c) has an intersecting angle in the range of 90 ± 5 °, but the two adjacent corners (concave) constituting the corner (e). Therefore, the crystal particle (c) is not a right-angle carbide particle. Further, each corner of the crystal particle (d) is not a right-angle carbide particle because the intersection angle between the two sides constituting the crystal particle (d) is outside the range of 90 ± 5 °. Further, as shown in FIG. 2, each particle is passed between 7.1 μm and 4.5 μm for the particles (a) and (b). Therefore, the maximum value of the right-angle carbide particles observed on the fracture surface of Comparative Example 27 was set to 7.1 μm. The difference in bending strength of Comparative Example 27 is as large as 6931 MPa, and the drilling life is as small as 0.46 times that of 740 holes and Comparative Example 25, which is inferior. This shows how much the maximum value of the right-angle carbide particle passing observed in the fracture surface has a great influence. Accordingly, the carbide particles constituting the fine cemented carbide for a micro tool of the present invention have an average particle size of 0.2 to 0.8 μm, a Co content of 2 to 15% by mass, and perpendicular carbide particles observed in the fracture surface. The maximum value of the handing over was set to 0.6 to 4.0 μm. The reason for this is that in Comparative Example 24, the amount of Co constituting the fine cemented carbide for a micro tool is less than 2% by mass, and the carbide particles grow so that the average particle size of the carbide particles is less than 0.2 μm. Is not sufficient and the fine cemented carbide is not sufficiently dense, so that sufficient bending strength cannot be obtained for the entire fine cemented carbide, and the maximum delivery of right-angle carbide particles observed in the fracture surface This is because, since the value is less than 0.6 μm, once a crack is generated in the fine-grained cemented carbide, its progress cannot be suppressed, and sufficient bending strength cannot be obtained. On the other hand, in Comparative Example 25, the amount of Co exceeds 15% by mass and the average particle size of the carbide particles grows greatly exceeding 0.8 μm, so the hardness of the fine cemented carbide decreases and wear resistance decreases. As the amount of Co becomes insufficient, Co agglomerates are easily formed, and carbide particles tend to grow abnormally around this agglomerated part. This is because the maximum value is larger than 4.0 μm, and since it becomes easy to break with this as a base point, a material having an extremely small bending force appears, that is, a difference in bending force is increased. In Comparative Example 26, although the average particle diameter of the carbide particles is 0.5 μm and the Co amount is 8 mass% within the scope of the present invention, the maximum value of the right-angle carbide particles observed on the fracture surface is 4 .2 μm, which is large beyond the scope of the present invention, so that it became easy to break with the coarse right-angle carbide particles as the starting point, so that the bending force is extremely small, the difference in bending force increases, This is because the drill is easily broken at the initial stage when measuring the drilling life. Further, in Comparative Example 27, although the average particle diameter of the carbide particles is 0.7 μm, the Co content is 16% by mass, which is large outside the scope of the present invention, and the right-angle carbide particles observed on the fracture surface are passed. The maximum value is 7.1 μm, which is much larger than the range of the present invention. Therefore, the fracture is caused by the coarse carbide particles as a base point, and the bending strength is extremely small, and the bending strength difference is large. This is because the drill easily breaks at the very initial stage when measuring the drilling life. In Comparative Examples 26 and 27, the reason why coarse carbide particles were formed was that the slurry was passed through a sieve having an opening of 45 μm after mixing and pulverization by an attritor in the production process of Comparative Examples 26 and 27. Since no collision is used, the dispersion between the hard carbide particles such as WC and the Co powder in the slurry is insufficient and Co agglomerates remain, and flat pieces are formed. Since the following Co agglomerated powder and flat pieces could not be removed, carbide hard particle forming elements such as W were once dissolved in the Co agglomerated parts and flat pieces in the process of sintering the compact produced from this slurry. This is because the carbide particles such as WC grew abnormally at the stage of reprecipitation, and large carbide particles exceeding 4 μm were formed during the sintering. This abnormal growth is conspicuous in Comparative Example 27 in which the Co content is 16% by mass, and it shows that it appears more remarkably as the Co content increases. In addition, even if the coarse carbide particles observed in the fracture surface fractured at the time of measuring the bending strength, the shape is the above-mentioned right-angle carbide particles, that is, the intersection angle of at least one corner is 90 ± 5 degrees. In the case of non-orthogonal carbide particles instead of the carbide particles in the range of 1, as shown in Examples 1, 6, and 11 of the present invention in Table 2, the bending strength is exceeded even when the maximum value of the passing exceeds 4 μm. The difference is smaller than 2000 MPa and the drilling life is as long as 3400 holes or longer. Therefore, in order to obtain an excellent fine cemented carbide for fine tools having a small difference in bending strength and a long drilling life, it is important to set the maximum diameter of the right-angle carbide particles to 0.6 to 4 μm.
From the above, the fine cemented carbide for fine tools of the present invention is a fine cemented carbide for fine tools having an average particle size of carbide particles of 0.2 to 0.8 μm and an amount of Co of 2 to 15% by mass, When broken by an external load, among the carbide particles on the fracture surface, at least one corner portion constituting a part of the contour of the carbide particle on the fracture surface is within an angle range of 90 ± 5 degrees from each other. And there are carbide particles having a right-angled corner that is at least 0.1 times the length of the carbide particles to which the corner belongs, and the length of at least one of the two sides is It was set as the fine cemented carbide alloy for micro tools characterized by the maximum value of the delivery of the carbide particle which has a right angle part being 0.6-4 micrometers. Further, according to the method for producing a fine cemented carbide for a micro tool of the present invention, pressure energy is applied to a slurry comprising a mixed powder for producing a fine cemented carbide for a micro tool and a solvent containing at least both WC powder and Co powder. In addition, when transported by a flow path, the first step that branches into at least two or more upstream on the flow path, and the flow path branched into two or more has an opening with a smaller inner diameter on the downstream side, The slurry ejected from the opening is arranged so as to oppose each other, and the ejected slurry collides so that they intersect each other at approximately one point, and is mixed and pulverized, and the slurry after the collision is recovered and dried. The method for producing a fine cemented carbide for a micro tool is characterized in that the mixed powder for producing a fine cemented carbide for a micro tool produced by the third step is formed and sintered.

Next, the present invention examples 1 to 5 in which the amount of Cr contained in Co is different from 0 to 11% by mass of Co will be compared. In both cases, the amount of Ta and V in Co and Co is the same as 8, 3, and 2% by mass, respectively, but the amount of Cr contained in Co is 0% by mass. While the life is 3430 holes, the drilling life of the present invention example 2 in which the Cr content in Co is 1% by mass is 1.5 times as long as 5180 holes, and the Cr content is 11% by mass. The drilling life of Invention Example 5 is 3460 holes, whereas the drilling life of Invention Example 4 having the same Cr content of 10% by mass is 5390 holes, which is 1.5 times as great. Therefore, in the present invention, the amount of Cr contained in Co is preferably 1 to 10% by mass. The reason for this is that if the amount of Cr contained in Co is less than 1% by mass, carbide particles tend to grow abnormally during sintering, and the maximum diameter of right-angle carbide particles observed in the fracture surface tends to increase. This is because the bending strength of the fine cemented carbide decreases. On the other hand, if the amount of Cr contained in Co exceeds 10% by mass with respect to Co, Cr is likely to precipitate from Co, and this precipitate reduces the bending strength of the fine cemented carbide. is there.
Next, the present invention examples 6 to 10 in which the amount of Ta contained in Co is different from 0 to 6% by mass of Co will be compared. In both cases, the amount of Ta in Co and the amount of Ta contained in Co is 0% by mass although the amount of Cr and V in Co is the same as 8, 5, and 2% by mass, respectively. While the life is 3590 holes, the drilling life of the present invention example 7 in which the Ta content in Co is 1% by mass is 1.5 times as long as 5390 holes, and the same Ta content is 6% by mass. The drilling life of Invention Example 10 is 3480 holes, whereas the drilling life of Invention Example 9 having the same Ta content of 5% by mass is 5270 holes, which is 1.5 times as great. Therefore, in the present invention, the amount of Ta contained in Co is preferably 1 to 5% by mass. The reason for this is that if the amount of Ta contained in Co is less than 1% by mass, carbide particles such as WC tend to grow abnormally during sintering, and the maximum size of the right-angle carbide particle crystal grains observed in the fracture surface This is because the diameter increases and the bending strength of the fine cemented carbide decreases. On the other hand, when the amount of Ta contained in Co exceeds 5% by mass with respect to Co, Ta precipitates out of Co and makes it easy to form spot crystals, and the spot crystals cause the bending strength of the fine cemented carbide. It is because it falls.
Next, the present invention examples 11 to 15 in which the amount of V contained in Co is different from 0 to 5% by mass of Co will be compared. In both cases, the amount of Cr and Ta in Co and Co is the same as 8, 4, and 2% by mass, respectively, but the amount of V contained in Co is 0% by mass. Whereas the life is 3440 holes, the drilling life of Example 12 of the present invention in which the V content in Co is 1% by mass is 1.5 times as large as 5270 holes, and the same V content is 5% by mass. The drilling life of Inventive Example 15 is 3450 holes, whereas the drilling life of Inventive Example 14 in which the V content is 4 mass% is 5250 holes, which is 1.5 times as great. Therefore, in the present invention, the amount of V contained in Co is preferably 1 to 4% by mass. The reason for this is that if the amount of V contained in Co is less than 1% by mass, the crystal grains of carbide particles tend to grow abnormally during sintering, and the maximum value of the right-angle carbide particles observed on the fracture surface is maximum. This is because the bending strength of the fine cemented carbide decreases. On the other hand, when the amount of V contained in Co exceeds 4% by mass, V precipitates in the vicinity of the interface between carbide particles such as WC and Co, and the strength between the carbide particles and Co increases. This is because the bending strength of the fine cemented carbide decreases.

FIG. 1 shows a scanning electron micrograph of the fracture surface of Comparative Example 27. FIG. 2 shows a schematic diagram of FIG.

Claims (1)

For the production of fine cemented carbide for micro tools containing WC powder , Co powder and metals such as V, Cr, Ta, etc., or carbides, nitrides, carbonitride powders thereof, as a grain growth inhibitor . A first step of branching at least two or more on the upstream side of the flow channel when the pressurized energy is applied to the slurry composed of the mixed powder and the solvent and conveyed by the flow channel, and the flow channel branched into the two or more Has an opening having a smaller inner diameter on the downstream side, and the slurry ejected from the opening is arranged to oppose each other, and the ejected slurry collides so as to intersect at approximately one point, and is mixed and pulverized. and second step, recovering a slurry after the collision, drying the third step, forming a microloads tool fine cemented carbide for producing mixed powder prepared by the, fine for small tools, which comprises sintering How to make cemented carbide Law.