JP7587205B2 - Cutting Tools - Google Patents

Description

The present invention relates to a WC-based cemented carbide cutting tool (also called a "WC-based cemented carbide tool") and a surface-coated WC-based cemented carbide cutting tool (also called a "surface-coated WC-based cemented carbide tool") that exhibit excellent resistance to plastic deformation in continuous cutting (e.g., continuous turning) of alloy steels and the like (steel, stainless steel, Ni-based alloys, etc.).

WC-based cemented carbide has high hardness and toughness, and therefore WC-based cemented carbide tools and surface-coated WC-based cemented carbide tools using this alloy as a base exhibit excellent wear resistance and are known as cutting tools having a long life over long periods of use.
However, in recent years, various proposals have been made to further improve the cutting performance and tool life of WC-based cemented carbide tools depending on the type of work material, cutting conditions, etc.

For example, in Patent Document 1, it is proposed that in a cemented carbide alloy having a hard phase mainly composed of tungsten carbide and a binder phase mainly composed of an iron group element (including cobalt, the cobalt content of which is preferably 8% by mass or more in the cemented carbide alloy), when the number of tungsten carbide particles is A and the number of tungsten carbide particles having one or less contact points with other tungsten carbide particles is B, by satisfying B/A≦0.05, the plastic deformation resistance of the cemented carbide alloy is improved, and as a result, the life of a WC-based cemented carbide tool is extended in wet continuous cutting of carbon steel and stainless steel.

In Patent Document 2, in a WC-based carbide tool containing 10-13 mass% Co, 2-8% Cr to Co ratio, at least one of TaC and NbC in a range where the total amount of TaC and NbC is 0.2-0.5 mass%, and the remainder WC, and having a hardness of 88.6 HRA-89.5 HRA, it is proposed that the ratio D80/D20 of the WC cumulative grain size 80% diameter D80 to the cumulative grain size 20% diameter D20 in the area ratio on the polishing surface is set to a range of 2.0≦D80/D20≦4.0, D80 is set to a range of 4.0-7.0 μm, and the WC adhesion degree c is set to 0.36≦c≦0.43, thereby preventing adhesion of the workpiece and improving chipping resistance in cutting difficult-to-cut materials such as stainless steel.

In Patent Document 3, when the component composition of a WC-based cemented carbide is expressed as WC-x mass % Co-y mass % Cr ₃ C ₂ -z mass % VC, it satisfies 6≦x≦14, 0.4≦y≦0.8, 0≦z≦0.6, (y+z)≦0.1x in a WC-based cemented carbide tool, and when the WC-based cemented carbide has a WC-x mass % Co-y mass % Cr 3 C 2 -z mass % VC composition, it satisfies 6≦x≦14, 0.4≦y≦0.8, 0≦z≦0.6, and (y+z)≦0.1x. Also, when the WC-based cemented carbide has a WC adhesion degree C expressed as C=1−V _b ^α ·exp(0.391·L), the value of the binder phase volume fraction V _b of the WC-based cemented carbide in this formula satisfies 0.11≦V _b In addition, the value L of (standard deviation of particle size distribution of WC particles)/(average WC particle size) is within the range of 0.3≦L≦0.7, and further, the coefficient α satisfies the value of 0.3≦α≦0.55. In this way, a WC-based cemented carbide tool has been proposed which has improved toughness and enhanced chipping resistance without reducing hardness and rigidity in cutting Al alloys, carbon steels, etc.

In Patent Document 4, when the length of a WC-WC adhesive interface in a WC-based cemented carbide tool is L1 and the length of a WC-Co adhesive interface is L2,
R>(0.82-0.086×D)×(10/V)
It has been proposed that by satisfying the above formula, the heat plastic deformability and toughness of a WC-based cemented carbide tool can be improved in cutting a Ni-based heat-resistant alloy.
In addition, R = (L1) / ((L1) + (L2))
D: WC area average grain size (μm), in the range of 0.6≦D≦1.7.
Here, D refers to the grain size of WC when the area ratio of WC is 50%.
V: binder phase volume (vol%), in the range of 9≦V≦14.

Patent Document 5 proposes a WC-Co based cemented carbide part for cutting tools, which has a composition consisting of, by weight %, Cr or/and Cr compounds: 0-4% (in terms of Cr), V or/and V compounds: 0-4% (in terms of V), TaC: 0-2%, TiC: 0-2%, N or/and N compounds: 0-1% (in terms of N), Co: 0.1-10%, WC and inevitable impurities: the remainder, and has a Co average thickness (CFP) of 0.06-30 nanometers, and is densified by applying a pressure of 3 atm to 200 atm using gas as a pressure medium in a part or the whole range of the temperature range of 900° C. to 1600° C. during heating during sintering, and it is said that the toughness of this WC-Co based cemented carbide part, preferably an ultrafine grain low Co cemented carbide part having an average WC grain size of 1 μm or less and a CFP in the range of 0.06-30 nm, can be improved.
where CFP is the average Co thickness (nm),
CFP=0.58*A/(100-A)*R
where A is Co (wt %), and 2R is the average grain size of WC (nm).

JP 2016-20541 A JP 2017-88999 A JP 2017-148895 A JP 2017-179433 A Japanese Patent Application Publication No. 7-305136

According to the conventional WC-based cemented carbide tools proposed in the above-mentioned Patent Documents 1 to 5, the cutting performance and tool characteristics of the WC-based cemented carbide tools are improved by controlling the number of contact points between WC-WC particles, the grain size of the WC, the degree of WC adhesion, or manufacturing conditions, etc.
However, when the conventional tools are used in continuous cutting of steel, alloy steel, stainless steel, and the like, particularly in continuous cutting under high load such as continuous turning, the plastic deformation resistance of the base body is insufficient, and the occurrence of tool deformation and the like cannot be sufficiently suppressed, resulting in a problem that the tool reaches the end of its life.

Therefore, the inventors of the present invention have conducted intensive research focusing on the morphology of the binder phase of WC-based cemented carbide alloys in order to develop a WC-based cemented carbide tool that exhibits excellent resistance to plastic deformation in continuous cutting processes under high loads, such as continuous turning of steel, alloy steel, stainless steel, etc., and have obtained the following findings.

That is, in the WC-based cemented carbide tools shown in Patent Documents 1 to 4, improvements were made mainly focusing on WC particles, and in the WC-based cemented carbide tool shown in Patent Document 5, improvements were made mainly focusing on CFP. However, the present inventors changed their viewpoint from that of the conventional techniques and conducted repeated research focusing on the morphology of the binder phase. As a result, by adjusting the sintering conditions for the binder phase particles (mainly Co particles) of a WC-based cemented carbide, it was found that when a predetermined number of binder phase particles of an appropriate size are present, that is, when a WC-based cemented carbide is observed with a scanning electron microscope (SEM) at a magnification of 500 times, and the area occupied by one binder phase particle at 10% cumulative particle area of the binder phase calculated by image analysis is defined as A10 (μm ² ), and the area occupied by one binder phase particle at 90% cumulative particle area is defined as A90 (μm ² ), it was found that A10 is 0.15 μm It has been found that, when the surface area of the WC-based cemented carbide substrate is ² or more and ^0.30 μm2 or less, and the A90/A10 ratio is 15.0 or more and 50.0 or less, the plastic deformation resistance is improved, and therefore, when a WC-based cemented carbide tool using such a WC-based cemented carbide substrate is used for continuous cutting of steel, alloy steel, stainless steel, etc., in particular for continuous turning of stainless steel, etc., the tool life can be extended.

Furthermore, the inventors have conducted extensive research into the maintenance and improvement of even better plastic deformation resistance in WC-based cemented carbide tools using the WC-based cemented carbide substrate, and have found that by increasing the ratio of Σ2 corresponding grain boundaries, which are grain boundaries that share lattice positions between WC crystal grains, i.e., WC corresponding grain boundaries, to the total WC/WC grain boundary length (hereinafter also referred to as the "Σ2 corresponding grain boundary ratio"), where the crystal arrangement is least disturbed compared to general grain boundaries (random grain boundaries) and the atomic bonds are strongest, it is possible to exhibit even better plastic deformation resistance in continuous cutting processes under high loads, such as continuous turning of the above-mentioned steel, alloy steel, stainless steel, etc., and to achieve even longer tool life.

The present invention has been made based on the above findings,
"(1) In a cutting tool made of WC-based cemented carbide having a substrate made of WC-based cemented carbide,
The composition of the WC-based cemented carbide is as follows: Co is 6.0 to 14.0 mass % and Cr ₃ C ₂ is 0.1 to 1.4 mass % as binder phase forming components, and the remainder is WC and inevitable impurities;
A WC- based cemented carbide cutting tool characterized in that, when the particle size distribution of the binder phase in a cross section of a substrate of the WC-based cemented carbide is analyzed, the area occupied by one binder phase particle at 10% of the cumulative particle area is defined as A10 ( ^μm2 ), and the area occupied by one binder phase particle at 90% of the cumulative particle area is defined as A90 ( ^μm2 ), A10 is 0.15 ^μm2 or more and 0.30 ^μm2 or less, and A90/A10 is 15.0 or more and 50.0 or less.
(2) The WC-based cemented carbide cutting tool according to (1), further comprising at least one selected from the group consisting of TaC, NbC, TiC and ZrC in a total amount of 4.0 mass% or less.
(3) A WC-based cemented carbide cutting tool according to (1) or (2), characterized in that the average grain size of WC in the WC-based cemented carbide is 0.2 μm or more and 4.0 μm or less, and the presence ratio of Σ2 correspondence grain boundaries of WC to all WC/WC grain boundaries (Σ2 correspondence grain boundary ratio) is 15% or more.
(4) A surface-coated WC-based cemented carbide cutting tool, characterized in that a hard coating layer is formed on at least the cutting edge of the WC-based cemented carbide cutting tool according to any one of (1) to (3).
The present invention is characterized by the following:
The contents of _Cr3C2 , TaC, NbC, TiC and ZrC in (1 ₎ to (4) above are the amounts of Cr, Ta, Nb, Ti and Zr measured on a cross section of the WC-based cemented carbide, all of which are calculated as carbide equivalents.
In addition, in this specification, when a numerical range is indicated using the symbol "to" it means that the numerical range includes the lower and upper limits.

The WC-based cemented carbide tool and surface-coated WC-based cemented carbide cutting tool according to the present invention have a particular composition range for the components of the WC-based cemented carbide constituting the base, namely Co, _Cr3C2 , and _/ or TaC, NbC, TiC, and ZrC, and when the particle size distribution of the binder phase is analyzed and the area occupied by one binder phase particle at 10% cumulative particle area is defined as A10 ( ^μm2 ) and the area occupied by one binder phase particle at 90% cumulative particle area is defined as A90 ( ^μm2 ), ^A10 is 0.15 ^μm2 or more and 0.30 μm2 or less, and A90/A10 is 15.0 or more and 50.0 or less, thereby exhibiting the remarkable effects of improved plastic deformation resistance and a long cutting life.
Furthermore, by setting the average grain size of WC in the WC-based cemented carbide to 0.2 μm or more and 4.0 μm or less, and increasing the presence ratio of WC Σ2 corresponding grain boundaries to all WC/WC grain boundaries (Σ2 corresponding grain boundary ratio) to 15% or more, or even to 25% or more, the plastic deformation resistance is further improved.
Therefore, the WC-based cemented carbide tool and the surface-coated WC-based cemented carbide tool of the present invention have excellent resistance to plastic deformation in continuous cutting, particularly continuous turning, of steel, alloy steel, stainless steel, and the like. In addition, when the Σ2 corresponding grain boundary ratio is increased, they also have the effect of suppressing chipping, thereby extending the tool life.

The present invention will be described in detail below.

1. WC-based cemented carbide Co:
Co is contained as a main component forming the binder phase of WC-based cemented carbide. If the Co content is less than 6.0 mass %, sufficient toughness is not maintained in high-efficiency machining of steel, alloy steel, stainless steel, etc. On the other hand, if the Co content exceeds 14.0 mass %, the steel sheet will rapidly soften, and the desired hardness required for a cutting tool will not be obtained, resulting in significant deformation and wear. Therefore, the Co content in the WC-based cemented carbide is set to 6.0 to 14.0 mass %.
The binder phase may contain W and C, which are components of the hard phase, and other unavoidable impurities.
The binder phase may contain at least one of Cr, Ta, Nb, Ti and Zr. When these elements are present in the binder phase, they are in the form of a solid solution in the binder phase. It is estimated that there is.
The mass % of Co can be determined by mirror-finishing any surface or cross section of the cemented carbide and subjecting the machined surface to fluorescent X-ray diffraction measurement.

_{Cr3C2 :
Cr3C2} dissolves as Cr in Co, which forms the main binder phase, and suppresses the growth of the WC phase, which forms the hard phase, to refine the grain size of the WC phase, to make the WC-based cemented carbide into _a fine-grained and uniform-grained structure, and to improve toughness. However, this effect is insufficient when _{the Cr3C2} content is less than 0.1 mass%, while when the content exceeds 10% relative to the Co content, a composite carbide of Cr and W precipitates, which reduces toughness and becomes the starting point for chipping.
In the present invention, since the upper limit of the Co content is 14.0 mass %, the upper limit of Cr ₃ C ₂ is set to 1.4 mass %, which is 10% of the upper limit of the Co content.
Therefore, the Cr ₃ C ₂ content in the WC-based cemented carbide is set to 0.1 to 1.4 mass %.

TaC, NbC, TiC, ZrC:
The WC-based cemented carbide of the present invention may further contain, as its components, at least one selected from the group consisting of TaC, NbC, TiC and ZrC in a total amount of 4.0 mass % or less.
Ta, Nb, Ti, and Zr all have the effect of increasing hardness by dissolving in Co, which forms the main binder phase. However, when the total content of these elements calculated as carbides exceeds 4.0 mass %, The precipitation of carbides reduces toughness and becomes the starting point for the generation of defects.
Therefore, when at least one selected from TaC, NbC, TiC and ZrC is contained as a component in the WC-based cemented carbide, the total content of the elements is set to 4.0 mass% or less. desirable.
The above-mentioned contents of Cr ₃ C ₂ , TaC, NbC, TiC and ZrC are the amounts of Cr, Ta, Nb, Ti and Zr measured by EPMA for the WC-based cemented carbide alloy, all calculated as carbides. This is the numerical value.

W.C.:
WC is contained as a main hard phase forming component of the WC-based cemented carbide. The hard phase may contain inevitable impurities that are inevitably mixed in during the manufacturing process.

(1) Average particle size:
If the average grain size of WC is less than 0.2 μm, slippage between hard phases during cutting is likely to occur, resulting in insufficient resistance to plastic deformation and chipping. On the other hand, if the average grain size exceeds 4.0 μm, sufficient wear resistance cannot be obtained. Therefore, it is preferable to select the grain size from the range of 0.2 μm or more and 4.0 μm or less.
The average grain size of WC is determined by mirror-finishing any surface or cross section of the cemented carbide, observing the machined surface by electron backscatter diffraction (EBSD), determining the area of at least 300 hard phases by image analysis, and calculating the diameter of a circle equal to the area and averaging it.
For the mirror finishing, for example, a focused ion beam device (FIB device), a cross section polisher device (CP device), or the like is used.

(2) Σ2 corresponding grain boundary ratio:
The present inventors have conducted extensive research to impart excellent plastic deformation resistance to cemented carbide, and have discovered that by increasing the ratio of the Σ2 correspondence grain boundary length, which has the least crystal arrangement disorder and the strongest atomic bonds compared to general grain boundaries (random grain boundaries), to the total WC/WC grain boundary length, i.e., the Σ2 correspondence grain boundary ratio, it is possible to obtain excellent wear resistance and plastic deformation resistance depending on the application.
If the Σ2 corresponding grain boundary ratio is less than 15%, the ratio of the WC/WC grain boundary having high grain boundary strength becomes insufficient and the fracture resistance is not satisfied, so it is specified to be 15% or more.More preferably, it is 25% or more.
The Σ2 coincidence grain boundary ratio can be measured, for example, by using the SEM-EBSD method. That is, by observing a plurality of fields of view with a pixel size of 0.1 μm×0.1 μm in a field of view of 24 μm×72 μm in an SEM so that the number of WCs is 1000 or more, and by defining a grain boundary having an orientation relationship in which the (0001) planes of adjacent WCs are rotated 90° around the axis of the [0001] direction or the [1-210] direction, as the Σ2 coincidence grain boundary, the ratio of the Σ2 coincidence grain boundary length to the total WC/WC grain boundary length can be calculated.
However, according to Brandon's conditional formula, the Σ2 corresponding grain boundary is defined as including an angle range of within 10.6° in both directions from the above-mentioned 90° orientation relationship, so the (0001) planes of adjacent WCs have an orientation relationship of 79.4° or more and 100.6° or less with the [0001] direction or the [1-210] direction as the axis, and therefore the Σ2 corresponding grain boundary is defined as one.

Inevitable impurities:
As described above, the hard phase and binder phase may contain impurities that are inevitably mixed in during the manufacturing process, and the amount of such impurities is preferably 0.3 mass % or less based on the total amount of the cemented carbide.

Particle size distribution of the bonded phase:
In the present invention, in a WC-based cemented carbide, the binder phase particles are distributed in a coarse and fine mixed grain form, so that the degree of WC/WC adhesion is greatly increased in the regions other than the coarse binder phase, thereby obtaining a structure with excellent resistance to plastic deformation.
Specifically, the particle size distribution of the binder phase in a WC-based cemented carbide was analyzed, and the area occupied by one binder phase particle at 10% of the cumulative particle area was defined as A10, and the area occupied by one binder phase particle at 90% of the cumulative particle area was defined as A90. When A10 was 0.15 ^μm2 or more and 0.30 ^μm2 or less, and A90/A10 was 15.0 or more and 50.0 or less, the skeletal structure of WC was firmly constructed, and the effect of improving the resistance to plastic deformation was obtained.
In contrast, when A10 is less than 0.15 ^μm2 , a large amount of fine binder phase is present and a coarse binder phase is insufficient, so that the plastic deformation resistance is insufficient. On the other hand, when A10 exceeds 0.30 ^μm2 , the WC aggregate structure is insufficient, so that the plastic deformation resistance is deteriorated.
Furthermore, when A90/A10 is less than 15.0, the number of coarse Co grains is insufficient, the grain size distribution of the binder phase is narrow, and a homogeneous structure is formed, improving the fracture resistance. However, the WC skeleton structure is disrupted, making it difficult to exhibit sufficient plastic deformation resistance. On the other hand, when A90/A10 exceeds 50.0, cavities are easily generated, deteriorating the plastic deformation resistance.
The binder phase can be extracted from the SEM image using, for example, image analysis software ImageJ. The areas of the extracted binder phase particles are accumulated starting from the particle with the smallest area, and the area occupied by one binder phase particle at 10% of the accumulated particle area is determined as A10, and the area occupied by one binder phase particle at 90% of the accumulated particle area is determined as A90.
In the present invention, each binder phase region divided by WC in a cross-sectional image of a WC-based cemented carbide is referred to as a binder phase particle.

2. Cutting Tool The WC-based cemented carbide tool and the surface-coated WC-based cemented carbide tool according to the present invention can be produced, for example, by the following steps.
First, a raw material powder consisting of a coarse-grained WC powder, a fine-grained WC powder, a coarse-grained Co powder, a fine-grained Co powder, and _{a Cr3C2} powder having a predetermined average particle size, and further containing one or more types of powder selected from the group consisting of TaC powder, NbC powder, TiC powder, and ZrC powder, as necessary, are blended and mixed to obtain a mixed powder having a composition specified in the cemented carbide of the present invention.
In particular, the WC powder is subjected to press molding, heat treatment, and crushing processes multiple times before being mixed with other raw material powders, thereby increasing the Σ2 corresponding grain boundary ratio in the WC powder, and then can be mixed with other raw material powders, thereby making it possible to obtain a cutting tool with excellent resistance to plastic deformation.
The pretreated WC powder can be mixed with other raw material powders using a media-less mixer such as an ultrasonic homogenizer or a cyclone mixer, for example, so that the powders can be blended and mixed without applying a large crushing force, thereby preventing the disappearance of the Σ2 grain boundaries of WC formed during carbonization and pretreatment.
Next, the mixed powder is molded to produce a powder compact. In the sintering process of the powder compact, as solid phase sintering progresses, it becomes difficult for Σ2 grain boundaries to be formed during the subsequent liquid phase sintering. Therefore, in the temperature range in which solid phase sintering progresses (1000°C to 1350°C), the heating rate is increased to 40°C/min or more to suppress solid phase sintering, and the main sintering is performed at 1350°C to 1450°C in a vacuum atmosphere for 10 to 80 minutes. This prevents the Σ2 grain boundaries formed in the fine-grained WC from being burned away by dissolution and reprecipitation, and a WC sintered body in which the Σ2 grain boundary ratio is maintained at 15% or more, or even 25% or more, can be obtained.

The WC-based carbide tool and surface-coated WC-based carbide tool of the present invention will be specifically described using examples.

<WC-based carbide tool of the present invention>
(a) Raw powder First, as powders for sintering, coarse WC powder with an average particle size (d50) of 10.0 to 15.0 μm on a volume basis, fine WC powder with an average particle size (d50) of 0.5 to 1.0 μm, coarse Co powder with an average particle size (d50) of 3.0 to 4.0 μm, fine Co powder with an average particle size (d50) of 0.5 to 1.5 μm, Cr ₃ C ₂ powder with an average particle size (d50) of 1.0 to 3.0 μm, and, as necessary, TaC powder, NbC powder, TiC powder, and ZrC powder, each with an average particle size (d50) of 1.0 to 3.0 μm, were prepared (see Table 2).
In particular, for the coarse-grained WC powder and fine-grained WC powder used to manufacture the tool base of the present invention, WC raw material powder types A to D in Table 1 were used, and as a preparatory step before mixing with other carbide powders, the coarse-grained WC powder and the fine-grained WC powder were each subjected to press molding-heat treatment-crushing treatment multiple times in accordance with the following procedure, thereby obtaining coarse-grained WC raw material powder and fine-grained WC raw material powder with excellent crystallinity and an increased Σ2 corresponding grain boundary ratio, and these were combined and used as the raw material.
1) The raw material WC powder is press-molded into spheres having a particle size of 1 mm to 3 mm, and heat-treated at 1300° C. to 1400° C. in an argon atmosphere at 10 Pa to 100 Pa for 30 minutes to 90 minutes.
2) The powder obtained by the heat treatment is subjected to a crushing treatment in a mortar for 3 minutes or more and 10 minutes or less.
3) Steps 1) and 2) were repeated at least two times and at most ten times to obtain WC powder having an increased Σ2 corresponding grain boundary ratio.
That is, first, in step 1), the coarse-grained WC particles and the fine-grained WC particles, which were separate, are pressed into contact with each other and then heat-treated to bond the coarse-grained WC particles and the fine-grained WC particles to each other, forming corresponding grain boundaries and random grain boundaries at their interfaces. Next, in step 2), random grain boundaries with low grain boundary strength and grain boundaries with high Σ values are preferentially destroyed by a crushing process, leaving Σ2 corresponding grain boundaries with high grain boundary strength. Then, in step 3), steps 1) and 2) are repeated multiple times to produce coarse-grained WC powder and fine-grained WC powder with a high ratio of Σ2 corresponding grain boundaries.

(b) Mixing process (media-less mixing process)
Next, in (a), coarse-grained WC powder with an average grain size (d50) of 10.0 to 15.0 μm and an average grain size (d50) of 0.5 to 1.0 μm with an increased Σ2 corresponding grain boundary ratio were used. The fine WC powder, the coarse Co powder having an average particle size (d50) of 3.0 to 4.0 μm, the fine Co powder having an average particle size (d50) of 0.5 to 1.5 μm, and the average particle size (d50) 1.0 to 3.0 μm _{Cr3C The two} powders are mixed together to obtain a predetermined composition, or, if necessary, further mixed with TaC powder, NbC powder, TiC powder, etc., each having an average particle size (d50) in the range of 1.0 to 3.0 μm. The WC powder and the ZrC powder are mixed to obtain a powder for sintering so as to have a predetermined composition. In particular, in order to prevent the Σ2 corresponding grain boundary formed by the pretreatment of the WC powder from being destroyed, a media-less sintering process is used. The mixture was wet mixed for 8 hours at a rotation speed of 50 rpm using an attritor mixer, dried, and then pressed at a pressure of 100 MPa to produce a green compact (see Table 2).

(c) Sintering step 1) Heating step; (see Table 4 "Inventive step")
Next, in the temperature increasing step from 1000° C. to the sintering temperature of 1350° C., which is the solid-phase sintering temperature, the temperature increase rate was increased to 40° C./min or more to suppress solid-phase sintering.
That is, during liquid phase sintering after heating in the liquid phase temperature region, new Σ2 corresponding grain boundaries are also formed. However, in the temperature region before the liquid phase appears, when WC bonds with each other through solid phase diffusion and necking is strongly formed, the Σ2 corresponding grain boundaries that would normally be formed during liquid phase sintering decrease. Therefore, the heating rate is increased in the temperature region of 1000°C to 1350°C where solid phase diffusion progresses.
2) Sintering process; (see Table 4 "Inventive process")
Next, in the sintering process, the temperature was raised to 1350°C or higher, and then the sintering was performed at 1350°C to 1450°C for 10 to 80 minutes under a vacuum of 0.1 Pa or less, thereby preventing the dissolution and disappearance of the Σ2 corresponding grain boundaries formed in the coarse-grained WC and fine-grained WC due to reprecipitation, and a WC-based cemented carbide sintered body was obtained.

Next, the WC-based cemented carbide sintered body was machined and ground to the shape of CNMG432MM to produce cemented carbide substrates 1 to 10 shown in Table 5 (hereinafter referred to as inventive tool substrates 1 to 10).

≪Comparative example WC-based carbide tool≫
For comparison, comparative cemented carbide substrates 1 to 8 (hereinafter referred to as comparative tool substrates 1 to 8) were prepared.
First, as the raw material powder, in addition to the WC raw material powder types A to D in Table 1 described above, raw material powders of the WC raw material powder types E to H shown in Table 1 were used.
The manufacturing process is as follows: First, coarse WC powder having an average particle size (d50) of 10.0 to 18.0 μm or fine WC powder having an average particle size (d50) of 0.5 to 1.5 μm is mixed in the proportions shown in Table 3. WC powder, coarse Co powder having an average particle size (d50) of 3.0 to 4.0 μm or fine Co powder having an average particle size (d50) of 0.5 to 1.5 μm, and fine Co powder having an average particle size (d50) of 1. 0-3.0 μm _{Cr3C The two} powders are mixed together to obtain a predetermined composition, or, if necessary, further mixed with TaC powder, NbC powder, TiC powder, etc., each having an average particle size (d50) in the range of 1.0 to 3.0 μm. The powder and ZrC powder were mixed together to obtain a predetermined composition to prepare a powder for sintering. The powder was then wet-mixed for 8 hours at a rotation speed of 50 rpm using a media-less attritor mixer. After drying, the powder was sintered under a pressure of 100 MPa. The mixture was pressed at a pressure of 1000 to prepare a green compact.
Next, a sintering process was carried out under the solid phase sintering conditions and liquid phase sintering conditions of Comparative Processes 1' to 8' shown in Table 4, which are different from the manufacturing conditions of the tool base bodies 1 to 10 of the present invention. After obtaining the WC-based cemented carbide sintered body, the WC-based cemented carbide sintered body was machined and ground to have a shape of CNMG432MM, to obtain comparative tool base bodies 1 to 8 shown in Table 6. It was made.

For the cross sections of the cemented carbide of the tool bases 1 to 10 of the present invention and the comparative tool bases 1 to 8, the contents of each of the elements Cr, Ti, Ta, Nb and Zr were measured at 10 points using an electron microanalyzer (EPMA), and the average values were taken as the contents of each element.
The contents of the elements Cr, Ti, Ta, Nb, and Zr were calculated by converting them into carbides. Tables 5 and 6 show the average contents of each element.

Next, the cross sections of the WC-based cemented carbide of the present invention tools 1 to 10 and the comparative example tools 1 to 8 were observed at a magnification of 200 to 500 times using a scanning electron microscope (SEM), and SEM images were obtained with an image size of 120 × 96 mm and a pixel count of 1280 × 1024 pixels. These were then processed using image analysis software ImageJ to measure the area of each binder phase within one observation field. The areas of each binder phase particle were accumulated starting from the particle with the smallest area, and the area occupied by one binder phase particle when the accumulated area exceeded 10% of the total binder phase area was determined as A10, and the area occupied by one binder phase particle when the accumulated area exceeded 90% of the total binder phase area was determined as A90.
Next, the obtained A90 is divided by A10 to obtain A90/A10.
The number of binder phases is measured by counting each individual binder phase divided by WC grains as one binder phase.
In order to include a sufficient number of binding phases in the image, the observation was performed at a magnification of 200 to 500 times, and the observation magnification was selected so that the number of binding phases measured after image processing was in the range of 5,000 to 15,000.

The above-mentioned tools 1 to 10 of the present invention and comparative tools 1 to 8 were subjected to the following wet continuous turning test while each tool was screwed to the tip of a tool steel bit using a fixing jig.
Workpiece: JIS SUS304 (HB170) round bar,
Cutting speed: 120m/min,
Cut: 1.8 mm,
Feed: 0.6 mm/rev.
Cutting time: 5 minutes,
Uses wet water-soluble cutting oil.
After the above-mentioned wet continuous cutting test, the amount of flank plastic deformation of the cutting edge was measured, and the wear state of the cutting edge was observed. The amount of flank plastic deformation of the cutting edge was measured by drawing a line segment on the ridge where the flank of the main cutting edge side and the rake face intersect at a position sufficiently distant from the cutting edge, extending the line segment toward the cutting edge portion, and measuring the part where the distance between the extended line segment and the ridge line of the cutting edge portion (perpendicular to the extended line segment) was the furthest, and was taken as the amount of flank plastic deformation of the cutting edge. When the amount of flank plastic deformation was 0.04 mm or more, the wear state was taken as cutting edge deformation.
Table 7 shows the results of this test.

In addition, hard coating layers having average thicknesses shown in Table 8 were formed by PVD or CVD on the cutting edge surfaces of the tools 1 to 4 of the present invention and the tools 1 to 4 of the comparative examples to produce surface-coated WC-based cemented carbide cutting tools of the present invention (hereinafter referred to as "coated tools of the present invention") 1 to 4 and comparative surface-coated WC-based cemented carbide cutting tools (hereinafter referred to as "coated tools of the comparative examples") 1 to 4.
For each of the above-mentioned coated tools, the following wet continuous cutting test was carried out to measure the amount of plastic deformation on the flank of the cutting edge and to observe the state of wear of the cutting edge.
Cutting conditions:
Workpiece: JIS SUS304 (HB170) round bar,
Cutting speed: 180m/min,
Cut: 2.1 mm,
Feed: 0.5 mm/rev.
Cutting time: 4 minutes,
Uses wet water-soluble cutting oil.
Table 9 shows the results of the cutting tests.

The test results shown in Tables 7 and 9 show that the tools of the present invention and the coated tools of the present invention exhibit excellent resistance to plastic deformation without chipping, whereas the comparative example tools and the comparative example coated tools have a short tool life due to chipping or plastic deformation.

As described above, the tool and the coated tool of the present invention exhibit excellent effects over long periods of use in heavy-duty continuous cutting, such as continuous turning of alloy steel, stainless steel, etc., and greatly contribute to extending the tool life.

Claims (4)

In a WC-based cemented carbide cutting tool having a WC-based cemented carbide substrate,
The composition of the WC-based cemented carbide is as follows: Co is 6.0 to 14.0 mass % and Cr ₃ C ₂ is 0.1 to 1.4 mass % as binder phase forming components, and the remainder is WC and inevitable impurities;
A WC- based cemented carbide cutting tool characterized in that, when the particle size distribution of the binder phase in a cross section of a substrate of the WC-based cemented carbide is analyzed, the area occupied by one binder phase particle at 10% of the cumulative particle area is defined as A10 ( ^μm2 ), and the area occupied by one binder phase particle at 90% of the cumulative particle area is defined as A90 ( ^μm2 ), A10 is 0.15 ^μm2 or more and 0.30 ^μm2 or less, and A90/A10 is 15.0 or more and 50.0 or less. The WC-based cemented carbide cutting tool according to claim 1, characterized in that the WC-based cemented carbide further contains at least one selected from TaC, NbC, TiC and ZrC in a total amount of 4.0 mass% or less. The WC-based cemented carbide cutting tool according to claim 1 or 2, characterized in that the average grain size of WC in the WC-based cemented carbide is 0.2 μm or more and 4.0 μm or less, and the ratio of WC Σ2 corresponding grain boundaries to the total WC/WC grain boundaries (Σ2 corresponding grain boundary ratio) is 15% or more. 4. A surface-coated WC-based cemented carbide cutting tool according to claim 1, further comprising a hard coating layer formed on at least a cutting edge of the WC-based cemented carbide cutting tool.