WC-based cemented carbide

Abstract

This WC-based cemented carbide comprises: Co: 6.0-10.0 mass%; Cr: 0.1-1.0 mass%, with the ratio of Cr content (mass%) / Co content (mass%) being 0.10 or less; M: 0.5-10.0 mass% (where M is one or more selected from the group consisting of Ta, Nb, Ti, and Zr); and C: 4.5-7.5 mass%, with the balance being W and unavoidable impurities. The WC-based cemented carbide has a hard phase composed of a main hard phase and a sub hard phase, and a binder phase. Main components of the main hard phase, the sub hard phase, and the binder phase are a carbide of W, a carbide of M, and Co, respectively. The particle size at 50% cumulative frequency of the hard phase is 0.40-0.60 μm and the average particle size of the hard phase is 1.60-2.30 μm. The area ratio (%) occupied by the hard phase having a particle size of 3.30 μm or more is 1.0 or less. The particle size at 50% cumulative frequency of the binder phase is 0.20-0.80 μm.

Description

WC-based cemented carbide

[0001] The present invention relates to a WC-based cemented carbide. This application claims priority based on Japanese Patent Application No. 2024-166253, which is a Japanese patent application filed on September 25, 2024. All the matters described in the Japanese patent application are incorporated herein by reference.

[0002] WC-based cemented carbides are used, for example, as the substrate of cutting tools and as the substrate of surface-coated cutting tools (hereinafter sometimes referred to as coated tools). Here, the coated tool has a vapor deposition coating layer such as an Al ２ O ３ layer or a TiCN layer, and is used for cutting carbon steel, cast iron, alloy steel, etc.

[0003] In cutting operations where the cutting edge becomes hot, such as cutting various stainless steels, the cutting edge of the coated tool may undergo plastic deformation and reach the tool life prematurely. On the other hand, if the hardness of the substrate is increased to suppress this plastic deformation, the chipping resistance will decrease. Therefore, a substrate made of a WC-based cemented carbide that combines plastic deformation resistance and chipping resistance is required. For example, the following proposals have been made.

[0004] Patent Document 1 discloses a cemented carbide comprising a hard phase containing tungsten carbide particles and a binder phase mainly composed of an iron group element containing cobalt. When the number of the tungsten carbide particles is A and the number of the tungsten carbide particles having 1 or less contact points with other tungsten carbide particles is B, a WC-based cemented carbide satisfying B / A≤0.05 is described, and the alloy is said to have excellent plastic deformation resistance.

[0005] Further, Patent Document 2 discloses that the Co content is 10 to 13% by mass, the ratio of the Cr content to the Co content is 2 to 8%, at least one of TaC and NbC is contained in an amount of 0.2 to 0.5% by mass, the balance is composed of WC, the hardness is 88.6 to 89.5 HRA, and the ratio D ８０ of the cumulative grain size 80% diameter D ２０ to the cumulative grain size 20% diameter D ８０ is D ２０ / D ８０ / D ２０ is 2.0≤D ８０A WC-based cemented carbide alloy is described having a thickness of 4.0 to 4.86 μm and a WC adhesion degree c of 0.36 ≤ c ≤ 0.43, and this alloy is said to have excellent fracture resistance.

[0006] Patent No. 6256415 Patent No. 6774645

[0007] The present invention has been made in view of the above circumstances and proposals, and in particular aims to provide a WC-based cemented carbide that provides resistance to plastic deformation and fracture when used as a base material for cutting tools and coated tools (regardless of the shape of the cutting tool or coated tool).

[0008] A WC-based cemented carbide according to one embodiment of the present invention has a composition of Co: 6.0 to 10.0 mass%, Cr: 0.1 to 1.0 mass%, with a Cr content (mass%) / Co content (mass%) of 10.0 or less, M: 0.5 to 10.0 mass% (M is one or more selected from the group of Ta, Nb, Ti, Zr), C: 4.5 to 7.5 mass%, with the remainder being W and unavoidable impurities, and has a hard phase consisting of a main hard phase and a secondary hard phase and a binder phase, the main hard phase mainly contains carbides mainly composed of W, the secondary hard phase mainly contains carbides mainly composed of M, and the binder phase mainly consists of Co. The crystalline particles constituting the hard phase have a cumulative 50% particle size of 0.40 to 0.60 μm, an average particle size of 1.60 to 2.30 μm, and the area percentage of crystalline particles constituting the hard phase with a particle size of 3.30 μm or more is 1.0 or less. The crystalline particles constituting the binder phase have a cumulative 50% particle size of 0.20 to 0.80 μm.

[0009] The WC-based cemented carbide alloy may satisfy one or more of the following conditions (1) or (2).

[0010] (1) The length of the interface in which the main hard phase contacts the secondary hard phase is 6.0% or less of the total interface length. (2) The Rockwell hardness (HRA) is 89.0 to 90.4.

[0011] The WC-based cemented carbide according to the above embodiment provides excellent resistance to plastic deformation and chipping when used as a base material for cutting tools and coated tools.

[0012] The inventors of the present invention have diligently studied WC-based cemented carbide alloys that provide excellent resistance to plastic deformation and fracture when used as a base material for cutting tools and coated tools, and have obtained the following findings that form the basis for the present invention.

[0013] (a) The main hard phase (a phase mainly containing carbides with W as the main component) and the secondary hard phase (a phase mainly containing carbides with M, i.e., one or more selected from the group of Ta, Nb, Ti, and Zr as the main component) are both included in WC-based cemented carbide, but their functions are not necessarily the same in terms of improving the durability of cutting tools.

[0014] (b) In other words, when the secondary hard phase is included in the WC-based cemented carbide, the properties of element M improve resistance to welding, oxidation, and wear when cutting steel and stainless steel. On the other hand, the main hard phase does not have the properties to improve these resistances to welding, oxidation, and wear.

[0015] (c) On the other hand, in terms of improving resistance to plastic deformation and fracture as a cutting tool, the main hard phase and the secondary hard phase are considered to play almost equivalent roles, and by controlling the grain size distribution of these together, the resistance to plastic deformation and fracture of WC-based cemented carbide can be improved.

[0016] (d) In view of (b) and (c) above, it is desirable that the area ratio of the main hard phase and the secondary hard phase, which is determined solely by the composition, be within a specific range.

[0017] (e) In order to obtain a WC-based cemented carbide alloy that has a good balance of resistance to plastic deformation and resistance to fracture, it is preferable that a certain proportion of relatively large crystal grains are present in the main hard phase and the secondary hard phase. However, if the grain size of the crystal grains constituting the main hard phase and the secondary hard phase becomes too large, the fracture resistance will decrease, so it is necessary to appropriately control this grain size.

[0018] The following describes in detail the WC-based cemented carbide according to embodiments of the present invention. In this specification and the claims, when a numerical range is expressed as "A to B" (where A and B are both numerical values), the range includes an upper limit (B) and a lower limit (A), and when a unit is specified only for the upper limit (B), the units of the upper limit (B) and the lower limit (A) are the same. Furthermore, matters described as "defined" apply to all such matters described in this specification and the claims.

[0019] 1. Composition The composition of the WC-based cemented carbide is as follows: Co: 6.0 to 10.0 mass%, Cr: 0.1 to 1.0 mass%, Cr content (mass%) / Co content (mass%) ratio of 0.10 or less, M: 0.5 to 10.0 mass% (M is one or more selected from the group of Ta, Nb, Ti, Zr), C: 4.5 to 7.5 mass%, with the remainder being W and unavoidable impurities. The following describes each component.

[0020] (1) Co When the Co content is 6.0 to 10.0 mass%, the WC-based cemented carbide exhibits excellent resistance to plastic deformation and fracture when used as a base material for cutting tools and coated tools. Co is mainly present in the bonding phase and is the main component of the bonding phase (accounting for 50 atomic percent or more of all components contained in the bonding phase). The bonding phase is composed of crystalline grains having an hcp structure or an fcc structure. A Co content of 7.0 to 9.6 mass% is more preferable.

[0021] (2) Cr Cr dissolves in Co, the main component of the binding phase, and inhibits the growth of W carbides, which mainly form the main hard phase, thereby refining the W carbides. This effect is insufficient when the Cr content is less than 0.1 mass%. On the other hand, if the Cr content exceeds 1.0 mass% or exceeds 10% relative to the Co content, composite carbides of Cr and W precipitate, reducing toughness, and these composite carbides become the starting point for defect formation. Therefore, the ratio of Cr content (mass%) / Co content (mass%) should be 0.10 or less.

[0022] (3) M (M is one or more selected from the group Ta, Nb, Ti, Zr) M is present in an amount of 0.5 to 10.0 mass%. M has the function of increasing the hardness of the WC-based cemented carbide by solid dissolving in Co, which is the main component of the bonding phase. In addition, M forms carbides (not limited to stoichiometric composition) and is mainly contained in the secondary hard phase in which these carbides are the main component (mainly contained means that carbides in which M is the main component account for 50 atomic percent or more of all components contained in the secondary hard phase). If the M content is less than 0.5 mass%, the resistance to welding and oxidation of the WC-based cemented carbide according to this embodiment decreases, and the wear resistance decreases. On the other hand, if the M content exceeds 10.0 mass%, it reduces the toughness of the WC-based cemented carbide, and carbides containing M become the starting point for chipping.

[0023] (4) C is contained in order to form carbides and is found exclusively in the main hard phase and the secondary hard phase. If its content is between 4.5% by mass and 7.5% by mass, an appropriate amount of carbides will be formed in the main hard phase and the secondary hard phase.

[0024] (5) W W constitutes carbides mainly composed of W, which are contained in the hard phase as carbides. That is, W accounts for 50 atomic percent or more of all components contained in the main hard phase. W exists in the hard phase as carbides (mostly WC, but may include W carbides not limited to stoichiometric composition) in the main hard phase. Here, carbides mainly composed of W include both carbides of W alone and composite carbides of the main component W and other metals.

[0025] (6) Unavoidable impurities Raw materials may contain unintended impurities, and unintended impurities may be introduced during the manufacturing process. These impurities are called unavoidable impurities. The presence of unavoidable impurities does not affect the physical properties of the WC-based cemented carbide according to this embodiment. Preferably, the content of unavoidable impurities is 0.3% by mass or less when the total mass of the WC-based cemented carbide is considered to be 100% by mass.

[0026] 2. Structure WC-based cemented carbide has a main hard phase, a secondary hard phase, and a binder phase. In addition to these three phases, it may unintentionally contain free carbon, the η phase (i.e., a composite carbide phase of Co and W), the W oxide phase, the M oxide phase, and a composite oxide phase of W and M. In the claims and specification, the hard phase consists of a main hard phase and a secondary hard phase. Each phase will be described below. In the claims and specification, each phase including the hard phase is composed of one or more crystalline grains, and the grain size of these crystalline grains is defined by the equivalent diameter of a circle (the diameter of a circle having an area equal to the area of ​​each phase).

[0027] (1) Main hard phase The main hard phase mainly contains carbides (not limited to stoichiometric composition) with W as the main component, and may also contain components of the bonding phase, components of the secondary hard phase, Cr, and unavoidable impurities. The main hard phase is composed of crystalline grains having an hcp structure. The method for identifying the main hard phase will be described later.

[0028] (2) Sub-hard phase The sub-hard phase mainly contains carbides (not limited to stoichiometric composition) with M as the main component, and may also contain components of the bonding phase, components of the main hard phase, Cr, and unavoidable impurities. The sub-hard phase is composed of crystalline grains having an fcc structure. The method for identifying the sub-hard phase will be described later.

[0029] (3) The bonded phase is mainly composed of Co, and may also contain W and C, which are components of the main hard phase, M, which is included in the secondary hard phase, and unavoidable impurities. If these components other than Co are present, they are thought to exist in the bonded phase as solid solutions. The bonded phase is composed of crystalline grains having an hcp structure or an fcc structure. The method for identifying the bonded phase will be described later.

[0030] 3. Average grain size and area ratio of each phase (1) Hard phase As already mentioned, from the perspective of improving plastic deformation resistance and fracture resistance, the main hard phase and the secondary hard phase can be considered almost equivalent, and by controlling their grain size distribution, the plastic deformation resistance and fracture resistance of WC-based cemented carbide can be improved.

[0031] To determine the cumulative 50% particle size and average particle size of the crystalline particles constituting the hard phase, the particle sizes of at least 300, preferably 300 to 1000, crystalline particles in the hard phase are measured.

[0032] (1-1) The cumulative 50% number particle size of the crystal particles constituting the 50% number particle size of the hard phase is preferably 0.40 to 0.60 μm. The particle size of the crystal particles constituting the fine hard phase that contributes to the plastic deformation resistance is expressed by the cumulative 50% number particle size of the crystal particles constituting the hard phase, and when this particle size is within the above range, good plastic deformation resistance is shown. When the cumulative 50% number particle size of the crystal particles constituting the hard phase is less than 0.40 μm, the defect resistance of the WC-based cemented carbide decreases, and when it exceeds 0.60 μm, the plastic deformation resistance of the WC-based cemented carbide is insufficient. The cumulative 50% number particle size of the crystal particles constituting the hard phase is more preferably 0.45 to 0.55 μm. The definition of the cumulative 50% number particle size will be described later.

[0033] (1-2) The average particle size of the crystal particles constituting the hard phase is preferably 1.60 to 2.30 μm. When the average particle size of the crystal particles constituting the hard phase is less than 1.60 μm, the defect resistance of the WC-based cemented carbide decreases, and when it exceeds 2.30 μm, the plastic deformation resistance of the WC-based cemented carbide is insufficient. The average particle size of the crystal particles constituting the hard phase is more preferably 1.70 to 1.95 μm. Here, the average particle size is the arithmetic mean of the particle sizes (equivalent circle diameters) of the crystal particles constituting each hard phase.

[0034] The reason for specifying the average particle size in addition to the cumulative 50% number particle size regarding the size of the crystal particles constituting the hard phase is as follows. The cumulative 50% number particle size is an index for evaluating the plastic deformation resistance, but if the particle size of the crystal particles constituting the hard phase is too small, the defect resistance of the WC-based cemented carbide decreases. Therefore, it is necessary to contain a predetermined amount of crystal particles constituting a hard phase of a certain size. The index indicating that a predetermined amount of crystal particles constituting a hard phase of a certain size is contained is the average particle size of the crystal particles constituting the hard phase.

[0035] (1-3) Crystal particles with a particle size of 3.30 μm or more that constitute the area ratio hard phase significantly reduce the defect resistance of the WC-based cemented carbide. Therefore, the area ratio occupied by the hard phase with a particle size of 3.30 μm or more is controlled to 1.0% or less. That is, when this area ratio exceeds 1.0%, the defect resistance of the WC-based cemented carbide is insufficient. Here, the lower limit of this area ratio may be 0.0%, but if it is manufactured according to an example of the manufacturing method described later, about 0.1% will be the lower limit value.

[0036] (1-4) Area ratio of the secondary hard phase in the hard phase The area ratio of the secondary hard phase in the hard phase, that is, (area of the secondary hard phase) / (area of the primary hard phase + area of the secondary hard phase) × 100 (%) is preferably 5.0 to 25.0%. The reason is as follows. When it is less than 5.0%, the welding resistance and oxidation resistance of the WC-based cemented carbide decrease, and the wear resistance decreases. On the other hand, when it exceeds 25.0% by mass, the toughness of the WC-based cemented carbide decreases, and the carbide containing M becomes the starting point of defect generation. Since the area ratio is solely determined by the composition of the WC-based cemented carbide, within the above-described composition range, it will be 5.0 to 25.0%.

[0037] (2) Bonding phase If the hard phase is not sufficiently dispersed in the WC-based cemented carbide structure, an agglomeration part of the hard phase will occur, which will reduce the defect resistance of the WC-based cemented carbide. When there is an agglomeration part of the hard phase, especially the bonding phase existing between the primary hard phases becomes finer. The degree of dispersion of the hard phase can be known from the cumulative 50% number particle size in the bonding phase. Therefore, the value of the cumulative particle number 50% in the bonding phase is defined as an index of this degree of dispersion.

[0038] That is, the cumulative 50% number particle size of the bonding phase is preferably 0.20 to 0.80 μm. The reason is as follows. When it is less than 0.20 μm, the primary hard phase is not sufficiently dispersed, and the defect resistance of the WC-based cemented carbide will not decrease. When it exceeds or equal to 0.80 μm, the bonding phase penetrates between the primary hard phase particles, and the strength of the WC-based cemented carbide is insufficient, so plastic deformation is likely to occur. The cumulative 50% number particle size of the bonding phase is more preferably 0.30 to 0.65 μm.

[0039] 3. Interface ratio It is more preferable that the length of the interface where the main hard phase contacts the secondary hard phase is 6.0% or less of the total interface length. The reason for this is as follows: The interface between the main hard phase, which is composed of crystalline grains with an hcp structure, and the secondary hard phase, which is composed of crystalline grains with an fcc structure, has low interfacial strength due to differences in crystal structure and mismatch between particles caused by segregation of elements molten in the binder phase. As a result, the interface is easily fractured by the load during cutting, which easily causes plastic deformation of the cutting edge.

[0040] Therefore, it is preferable to suppress the length of the interface where the main hard phase contacts the secondary hard phase in order to improve resistance to plastic deformation. If the ratio of the length of the interface where the main hard phase contacts the secondary hard phase to the total interface length exceeds 6.0%, the resistance to plastic deformation decreases. The lower limit of this ratio of interface length may be 0.0%, but if manufactured according to an example of the manufacturing method described later, the lower limit will be around 1.0%.

[0041] The total interface length is the sum of the lengths of the following six types of interfaces: the sum of the lengths of the interfaces between the main hard phase and the main hard phase, the sum of the lengths of the interfaces between the main hard phase and the secondary hard phase, the sum of the lengths of the interfaces between the secondary hard phase and the secondary hard phase, the sum of the lengths of the interfaces between the main hard phase and the binder phase, the sum of the lengths of the interfaces between the secondary hard phase and the binder phase, and the sum of the lengths of the interfaces between the binder phase and the binder phase. The ratio of the length of the interface where the hard phase is in contact with the secondary hard phase to the total interface length is calculated as follows: (sum of the lengths of the interfaces where the hard phase is in contact with the secondary hard phase) / (total interface length) × 100. The identification of each phase and the measurement method of the interface lengths will be described later.

[0042] 4. Rockwell Hardness WC-based cemented carbide is more preferably Rockwell hardness (HRA) between 89.0 and 90.4. Satisfying this range of Rockwell hardness more reliably improves resistance to plastic deformation. Rockwell hardness (HRA) is measured according to ISO 3738-1:1982 and ISO 3738-2:1988.

[0043] 5. Measurement Method Next, we will explain the measurement method.

[0044] 5-1. Composition Measurement The content of each component, Co, Ti, Nb, Ta, Zr, W, and C, in the WC-based cemented carbide is measured using an electron beam microanalyzer (EPMA). The content is measured after the WC-based cemented carbide is processed into the base shape of a cutting tool or coated tool (hereinafter referred to as the base), and the cross section of the base (any cross section if there is no coating layer; in the case of a coated tool with a coating layer, the interface between the coating layer and the base is considered a straight line, and the cross section is perpendicular to this straight line) is processed using, for example, a focused ion beam (FIB) device to remove fine irregularities so as not to interfere with EPMA measurement.

[0045] Because the surface of the substrate may be affected by sintering and other factors, resulting in a composition that does not match the composition inside the substrate, three or more observation fields, each measuring 100 μm (length) x 100 μm (width), are set up in a region at least 500 μm inward from the surface of the substrate (with one side of one adjacent observation field parallel to one side of the other observation field, and the distance between them being at least 10 μm). Each observation field is irradiated with an electron beam, and the components and their amounts are measured from the resulting characteristic X-rays. The arithmetic mean of each component is then calculated and used as the average content of each component.

[0046] 5-2. Method for Identifying the Binder Phase, Hard Phase, and Sub-Hard Phase, and Measurement of the Particle Size at 50% Cumulative Number and Average Particle Size The binder phase, sub-hard phase, and hard phase are identified as follows, and the average particle size is measured. The particle size at 50% cumulative number is determined by the following procedure. That is, a graph is created with the circular equivalent particle size of the crystal grains constituting the target phase (hard phase, binder phase) on the horizontal axis and the cumulative number ratio of the target crystal grains corresponding to each circular equivalent particle size on the horizontal axis ((cumulative number of target crystal grains up to each particle size) / (total number of target crystal grains) × 100) on the vertical axis. The circular equivalent diameter when the cumulative number ratio reaches 50% is defined as the particle size of the crystal grain at 50% cumulative number.

[0047] (1) The cross-section of the substrate is processed to be smooth by removing any fine irregularities so as not to interfere with electron backscatter diffraction (EBSD) measurements. Multiple fields of view (for example, 5 fields of view (where one side of one adjacent observation area is parallel to one side of the other observation area, with a distance of 10 μm or more)) are set in a region that is 500 μm or more inland from the surface of the substrate, with each field of view measuring, for example, 24 μm (vertical) × 72 μm (horizontal)). Each field of view is observed with an energy-dispersive X-ray spectrometer (EDS) and EBSD measuring device (for example, AMETEK OIM Data Collection) equipped with a field emission scanning electron microscope (SEM: observation magnification 3000x) at an acceleration voltage of 15 kV and a measurement point spacing of 0.1 μm (the number of measurement points is as described in (5) below), and the EBSD pattern and EDS data are acquired simultaneously.

[0048] The number of crystal grains observed when identifying the crystal grains of the main hard phase, secondary hard phase, and phase-bonded phase is arbitrary.

[0049] (2) Next, the measurement data is analyzed using software for analyzing EBSD measurement results, for example, OIM Analysis ver. 7.3.1 from AMETEK. For each crystal grain constituting each phase, the EDS count values ​​obtained from each measurement point inside the crystal grain corresponding to each element are averaged to obtain the elemental EDS measurement value for each crystal grain, and the composition of each crystal grain is determined from the obtained measurement values.

[0050] (3) Identify which phase each crystal particle belongs to according to the definition of crystal particles described above. Specifically, the aggregate of crystal particles identified as having an hcp structure from the EBSD pattern and mainly containing W carbides is defined as the main hard phase. Particles with Co as the main component and having an hcp crystal structure or an fcc crystal structure are defined as the binding phase. Phases that are not the main hard phase and have an hcp crystal structure are defined as the secondary hard phase. However, it is not possible to distinguish whether a phase identified as having an fcc crystal structure is the binding phase or the secondary hard phase. Therefore, the aggregate of crystal particles whose total EDS count values ​​for Ti, Nb, Ta, or Zr obtained by EDS measurement are 100 or more is defined as the secondary hard phase, and the aggregate of the remaining crystal particles identified as having an fcc crystal structure is defined as the binding phase.

[0051] (4) In EBSD measurement, if the difference in crystal orientation between adjacent measurement points is within 5 degrees, those measurement points are judged to belong to the same crystal grain. If the difference in crystal orientation between adjacent measurement points exceeds 5 degrees, the boundary (midpoint) between those measurement points is considered the interface of the crystal grain.

[0052] (5) The particle size of the crystalline grains constituting each phase is determined by calculating the area of ​​at least 300 (preferably 300 to 1000) of each phase, calculating the diameter of a circle equal to that area, and determining the particle size of 50% of the cumulative number of particles of the hard phase and the binder phase, as well as the average particle size of the hard phase, according to the definition above.

[0053] (6) Determine the area ratio of the main hard phase and sub-hard phase with an equivalent circular diameter of 3.30 μm or more in each of the aforementioned fields of view, and calculate their arithmetic mean.

[0054] (7) For confirmation purposes, it is preferable to perform EDS measurements again on each of the phases identified as the main hard phase, secondary hard phase, and binder phase in (3)-(4) above, and to confirm that the crystalline particles identified as being contained in the main hard phase mainly contain carbides with W as the main component, the crystalline particles identified as being contained in the secondary hard phase mainly contain carbides with M as the main component, and the crystalline particles identified as being contained in the binder phase mainly contain Co.

[0055] 5-3. Phase Interface Lengths In each of the fields of view described above, the total phase interface lengths of the defined main hard phase, secondary hard phase, and binder phase, and the length of the phase interface where the main hard phase is in contact with the secondary hard binder phase are determined. The interface lengths are calculated using the crystal orientation data obtained from the EDS and EBSD measurements described in (1)-(4) above with analysis software (for example, OIM Analysis ver. 7.3.1 from AMETEK). Then, the ratio of the length of the phase interface where the main hard phase is in contact with the secondary hard phase to the total interface length is calculated.

[0056] 6. Manufacturing Method An example of a manufacturing method is described below. The manufacturing method involves preparing the specified raw material powder, followed by (1) a mixing step, (2) a molding step, (3) a sintering step, (4) a finishing step, and, if necessary, (5) a coating step, in that order. These steps are explained in order below.

[0057] (1) Mixing process In the WC-based cemented carbide according to this embodiment, it is preferable to thoroughly disperse the main hard raw material and the secondary hard raw material, which have been processed by crushing fine particles. It is recommended to perform the following three mixing steps: a pre-mixing step, a first mixing step, and a second mixing step.

[0058] 1) Pre-mixing step: In the pre-mixing step, a predetermined amount of secondary hard raw material powder, a predetermined amount of binding phase raw material powder, and a predetermined amount of Cr ３ C ２ The powders are mixed to prepare a pre-mixed powder. The mixing ratios of these powders are all equal to the ratio of the raw materials used in the cemented carbide to be manufactured. The pre-mixing is done using an attritor, for example, at a rotation speed of 60-100 mins. －１ Mix at (rpm), with 300-600 kg of cemented carbide balls, for 5-7 hours. Divide the resulting pre-mixed powder into first mixed raw material powder and second mixed raw material powder.

[0059] 2) First Mixing Step In the first mixing step, WC powder is added to the first mixed raw material powder so that it matches the composition of the WC-based cemented carbide to be manufactured, and these are mixed to prepare the mixed powder after the first mixing step. Mixing is performed using an attritor, for example, at a rotation speed of 30 to 90 mins. －１ Mix 150-400 kg of carbide balls for 4-7 hours.

[0060] 3) Second Mixing Step In the second mixing step, the mixed powder obtained in the first mixing step, the second mixed raw material powder, and the WC powder are mixed to obtain the composition of the WC-based cemented carbide to be manufactured. The proportion of the mixed powder obtained in the first mixing step in the second mixed raw material powder shall be 10 to 60% by mass. Mixing shall be performed using an attritor, for example, at a rotation speed of 30 to 90 mins. －１ Mix 150-400 kg of carbide balls for 4-7 hours.

[0061] (2) Molding Process The raw material powder that has gone through the mixing process is molded into a substrate of a predetermined shape (an insert shape of CNMG120408 can be exemplified, but is not limited to this). Molding can be done by press molding at a pressure of, for example, 100 MPa.

[0062] (3) Sintering process: The molded raw material is sintered. Sintering is performed at a maximum holding temperature of 1370 to 1430°C, 10 －１The material is held in a vacuum atmosphere below Pa for 50 to 100 minutes, and then rapidly cooled from the maximum holding temperature to 1100°C to 1200°C at a cooling rate of 35 to 50°C / min. Slow cooling promotes grain growth of hard phase particles, causing them to coarseen; therefore, rapid cooling suppresses the generation of coarse hard phase particles due to abnormal grain growth of the hard phase.

[0063] (4) Finishing process The molded body that has undergone the sintering process is subjected to grinding to form a predetermined shape (an insert shape of CNMG120408 as defined in ISO standard 1832:2017 can be an example, but it is not limited to this and may be a shape such as a drill, milling cutter, or end mill).

[0064] (5) Coating step A predetermined coating layer is formed by known means. Forming the coating layer is not essential.

[0065] The above description includes the following characteristics: (Note 1) It contains Co: 6.0 to 10.0 mass%, Cr: 0.1 to 1.0 mass%, with a ratio of Cr content (mass%) to Co content (mass%) of 0.10 or less, M: 0.5 to 10.0 mass% (M is one or more selected from the group of Ta, Nb, Ti, Zr), C: 4.5 to 7.5 mass%, with the remainder being W and unavoidable impurities, and has a hard phase and a binder phase consisting of a main hard phase and a secondary hard phase, the main hard phase mainly contains carbides mainly composed of W, the secondary hard phase mainly contains carbides mainly composed of M, the binder phase is mainly composed of Co, and the crystalline particles constituting the hard phase have a cumulative 50% particle size of 0.40 to 0.60 μm and an average particle size of 1.60 to 2.30 μm. A WC-based cemented carbide characterized in that the area percentage of crystalline particles constituting the hard phase, having a particle size of 3.30 μm or more, is 1.0 or less, and the crystalline particles constituting the binder phase have a cumulative 50% particle size of 0.20 to 0.80 μm. (Note 2) The WC-based cemented carbide described in Note 1, characterized in that the area percentage of the secondary hard phase to the hard phase is 5.0 to 25.0%. (Note 3) The WC-based cemented carbide described in Note 1 or 2, characterized in that the length of the interface in contact between the main hard phase and the secondary hard phase is 6.0% or less of the total interface length. (Note 4) The WC-based cemented carbide described in any of Notes 1 to 3, characterized in that the Rockwell hardness (HRA) is 89.0 or more and 90.4 or less.

[0066] The present invention will be specifically described by examples when the WC-based cemented carbide of the present invention is used as the base material for a coated tool, but the present invention is not limited to these examples.

[0067] 1. Manufacturing of the Examples (1) Raw Material Powders As raw material powders, WC powder with an average particle size of 3.6 μm, Co powder with an average particle size of 0.9 μm, and Cr powder with an average particle size of 0.5 μm ３ C ２The following powders were mixed according to the formulations shown in Table 1, A1 to A9: TiC powder with an average particle size of 1.1 μm, TaC powder with an average particle size of 0.6 μm, NbC powder with an average particle size of 0.9 μm, ZrC powder with an average particle size of 1.4 μm, (Ta,Nb)C powder containing Ta and Nb in a mass ratio of 9:1 with an average particle size of 1.5 μm, and (Ti,W)C powder containing Ti and W in a mass ratio of 1:1 with an average particle size of 1.0 μm. Here, the average particle size of the raw material powders is the Fischer diameter measured by the air permeability method using a Fischer subsieve sizer.

[0068] (2) Mixing, Molding, Sintering, and Finishing Processes As described above, the mixing process (pre-mixing, first mixing, and second mixing), molding process, sintering process, and finishing process were carried out in order. In the mixing process, WC powder in the proportions shown in Table 1 was mixed using the first and second mixing processes shown in Table 3, and the resulting powder was press-molded at a pressure of 100 MPa to form an insert shape of CNMG120408. Subsequently, sintering was carried out at the holding temperatures shown in Table 3, and grinding was performed as a finishing process to form an insert of CNMG120408 shape. The results of the analysis of this insert using the method described above are shown in Table 4.

[0069] 2. For manufacturing comparison of the comparative examples, the compound powders were mixed according to the compound compositions shown in B1 to B6 of Table 2. Subsequently, the mixing process (pre-mixing process, first mixing process, second mixing process), molding process, sintering process, and finishing process were carried out sequentially. In the mixing process, the compound powders in the proportions shown in Table 2 were mixed in the first and second mixing processes shown in Table 3 (in Table 3, comparative example processes where the first mixing process is shown as "-" only had the second mixing process and no first mixing process). After the mixing process was completed, the mixed powder was press-molded at a pressure of 100 MPa to form an insert shape of CNMG120408. Subsequently, sintering was performed at the holding temperature shown in Table 3, and grinding was performed as a finishing process to form an insert shape of CNMG120408. The results of the analysis of this insert using the method described above are shown in Table 5.

[0070] 3. Formation of the coating layer Subsequently, the coating layer shown in Table 6 is formed by chemical vapor deposition (the coating layer consists of TiN, TiCN, and Al in order from the substrate surface).２ O ３ A coating consisting of four layers of TiN was formed to obtain Example coating tools 1 to 9 (hereinafter referred to as Example 1 to 9) and Comparative Example coating tools 1 to 7 (hereinafter referred to as Comparative Example 1 to 7).

[0071]

[0072]

[0073] In Tables 1 and 2, "-" indicates that the ingredient was not included.

[0074]

[0075] In Table 3, "-" indicates that the first mixing step was not performed. "1 / min" refers to the SI unit "min －１ This refers to "[...]."

[0076] In each example, the area ratio of the secondary hard phase to the hard phase was 5.0 to 25.0%.

[0077] The area ratio of the secondary hard phase to the hard phase was 26.1% for Comparative Example 1, which had a different composition, while the other comparative examples ranged from 5.0% to 25.0%.

[0078] In Tables 4 and 5, "-" indicates that the component in question was not present. Furthermore, it was confirmed that in all examples and comparative examples, the content of unavoidable impurities was 0.3% by mass or less relative to 100% by mass of the entire WC-based cemented carbide.

[0079]

[0080] Next, cutting tests under the following cutting conditions 1 and 2 were performed on Examples 1 to 9 and Comparative Examples 1 to 7 for 15 minutes each. Every minute after the start of the cutting test, the presence or absence of chipping and delamination due to plastic deformation was visually observed, and the flank wear width was measured. When the flank wear width exceeded 0.2 mm, the flank wear width at the time elapsed since the start of the test (measurement time) when it exceeded 0.2 mm and the flank wear width at the previous measurement time were linearly approximated to determine the time elapsed since the start of the test that resulted in a flank wear width of 0.2 mm (time until the end of service life). The results are shown in Tables 7 and 8, respectively.

[0081] For Examples 1-9 and Comparative Examples 1-7, intermittent machining as shown in cutting condition 3 was performed 10,000 times with the maximum number of impacts. For tools that chipped before reaching 10,000 impacts, the number of impacts at which chipping occurred was measured. The results are shown in Table 9.

[0082] Cutting conditions 1 Workpiece material: SUS304 round bar with outer diameter of 100 mm Cutting speed: 150 m / sec Depth of cut: 1.5 mm Feed rate per revolution: 0.3 mm Wet cutting

[0083] Cutting conditions 2 Workpiece material: SUS630 round bar with outer diameter of 100 mm Cutting speed: 120 m / sec Depth of cut: 2.0 mm Feed rate per revolution: 0.15 mm Wet cutting

[0084] Cutting conditions 3 Workpiece material: Intermittent machining of the end face of a workpiece with four groove slits made of SUS316 Cutting speed: 120 m / sec Depth of cut: 2.0 mm Feed per revolution: 0.25 mm Wet cutting The number of impacts was counted as one impact per slit out of the total number of impacts that could be machined.

[0085]

[0086]

[0087]

[0088] As is clear from Tables 7 and 8, all of the examples showed excellent cutting performance with minimal flank wear width and plastic deformation, and no chipping or delamination due to plastic deformation. In contrast, all of the comparative examples experienced at least one of either chipping or delamination due to plastic deformation before the end of the cutting test time (15 minutes), and reached the end of their service life with a flank wear width of 0.2 mm.

[0089] Furthermore, as is clear from Table 9, all of the examples were able to undergo processing up to 10,000 impact cycles, the maximum number of cycles, without any defects. In contrast, all of the comparative examples developed defects before reaching 10,000 cycles.

[0090] The embodiments disclosed herein are illustrative in all respects and are not restrictive. The scope of the present invention is indicated by the claims rather than by the embodiments described herein, and all modifications within the scope of the claims are intended to be included in the meaning of equivalents and within the scope of the claims.

Claims

1. The material contains Co: 6.0 to 10.0 mass%, Cr: 0.1 to 1.0 mass%, with a ratio of Cr content (mass%) to Co content (mass%) of 0.10 or less, M: 0.5 to 10.0 mass% (M is one or more selected from the group of Ta, Nb, Ti, Zr), C: 4.5 to 7.5 mass%, with the remainder being W and unavoidable impurities, and has a hard phase consisting of a main hard phase and a secondary hard phase, the main hard phase mainly containing carbides with W as the main component, the secondary hard phase mainly containing carbides with M as the main component, the binding phase mainly containing Co, and the crystalline particles constituting the hard phase have a cumulative 50% particle size of 0.40 to 0.60 μm and an average particle size of 1.60 to 2.30 μm. A WC-based cemented carbide characterized in that the area percentage occupyed by crystalline particles constituting the hard phase, which have a particle size of 3.30 μm or more, is 1.0 or less, and the crystalline particles constituting the binder phase have a cumulative 50% particle size of 0.20 to 0.80 μm.

2. The WC-based cemented carbide according to claim 1, characterized in that the length of the interface in which the main hard phase contacts the secondary hard phase is 6.0% or less of the total interface length.

3. The WC-based cemented carbide according to claim 1 or 2, characterized in that its Rockwell hardness (HRA) is 89.0 or more and 90.4 or less.

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