JP2023134938A - Cemented carbide alloy for cutting tools, and cutting tool substrate including the alloy - Google Patents

Abstract

To provide a cemented carbide alloy for cutting tools that shows improved fracture resistance when used as a cutting tool, and a cutting tool substrate that includes the cemented carbide alloy for cutting tools.SOLUTION: A cemented carbide alloy for cutting tools is provided which contains at least one of Co and Ni in an amount of 4.0 mass% or more and less than 10.0 mass% in total, M (at least one selected from Ti, Ta, Nb, Zr, Hf, and V) in an amount of 4.0 mass% or more and less than 12.0 mass% in terms of MC, and Cr in an amount of less than 0.5 mass% in terms of Cr3C2, with the balance being WC and inevitable impurities. Main hard phases include the WC. Secondary hard phases include the MC. The secondary hard phases have an area ratio of 17% or more and less than 19%. The value determined by dividing the number of grain boundaries between the secondary hard phases by the number of secondary hard phase particles is 0.8 or more and 1.2 or less. There is also provided a cutting tool substrate including the alloy.SELECTED DRAWING: None

Description

The present invention relates to a cemented carbide for cutting tools and a cutting tool base (sometimes referred to as the base) using the cemented carbide for cutting tools.

Cemented carbide is hard and has toughness, so it is used as cutting tools. In order to meet the severe cutting conditions required of cutting tools, proposals have been made to improve cemented carbide and cutting tool bases using this cemented carbide.

For example, Patent Document 1 discloses that a hard phase mainly composed of tungsten carbide and a binder phase mainly composed of iron group elements are provided, the number of particles of the tungsten carbide is A, and contact with other tungsten carbide particles is provided. When the number of tungsten carbide particles with a score of 1 or less is B, a cemented carbide that satisfies B/A≦0.05 is described, and this cemented carbide is said to have excellent plastic deformation resistance. There is.

Furthermore, Patent Document 2 states that the amount of Co is 10 to 13% by mass, the ratio of the amount of Cr to the amount of Co is 2 to 8%, and the total amount of at least one of TaC and NbC is 0.2 to 0.5% by mass. The remainder consists of WC, the hardness is 88.6 to 89.5 HRA, and the ratio of the WC integrated particle size 80% diameter D ₈₀ and the integrated particle size 20% diameter D ₂₀ in the area ratio on the polished surface D ₈₀ /D ₂₀ is in the range of 2.0≦D ₈₀ /D ₂₀ ≦4.0, the above D ₈₀ is in the range of 4.0 to 7.0 μm, and the WC adhesion degree c is 0.36≦c≦ 0.43 is described, and this cemented carbide is said to have improved adhesion resistance when used in a cutting tool base.

In addition, Patent Document 3 describes Cr or/and Cr compound: 0 to 4% by mass (in terms of Cr), V or/and V compound: 0 to 4% by mass (in terms of V), and TaC: 0 to 2% by mass. mass%, TiC: 0 to 2 mass%, N or/and N compound: 0 to 1 mass% (in terms of N), Co: 0.1 to 10 mass%, remainder WC and inevitable impurities, Co average thickness : 0.06 to 30 nanometers (the Co average thickness (nm) is 0.58*A/(100-A)*R, A: Co (mass%), 2R: WC average particle size (nm)). A cemented carbide is described in which the density is increased by applying a gas as a pressure medium to a cemented carbide at a temperature of 900 to 1600°C during heating during sintering to achieve a pressure of 3 to 200 atm. It is said to have high toughness and high wear resistance.

Furthermore, Patent Document 4 describes a WC phase, a B1 type solid solution phase consisting of one or more carbides or carbonitrides of metals from groups 4, 5, and 6 of the periodic table other than WC, and one type of iron group metal. A cemented carbide with a binder phase consisting of the above is used as a base, and a surface region where the B1 type solid solution phase does not exist exists in a region with a depth of 5 to 100 μm from the surface of this base, and directly below the surface region. A cutting tool substrate is disclosed in which the average particle size of the B1 type solid solution phase is larger than the average particle size of the B1 type solid solution phase inside the substrate, and the cutting tool substrate has high temperature strength and thermal shock resistance. It is considered to be excellent.

Japanese Patent Application Publication No. 2016-20541 JP 2017-88999 Publication Japanese Patent Application Publication No. 7-305136 Japanese Patent Application Publication No. 2011-131318

The present invention was made in view of the above circumstances and proposals, and includes a cemented carbide for cutting tools that improves toughness when used as a cutting tool base, and a cutting tool using the cemented carbide for cutting tools. The purpose is to provide tool bases.

The cemented carbide for cutting tools according to the embodiment of the present invention is
A total of at least 4.0% by mass and less than 10.0% by mass of one or more of Co and Ni,
M (M is one or more selected from Ti, Ta, Nb, Zr, Hf, and V) is 4.0% by mass or more and less than 12.0% by mass as MC, and
Contains less than 0.5% by mass _of Cr as _Cr3C2 ,
The remainder consists of WC and unavoidable impurities,
The main hard phase has the WC,
The secondary hard phase has the MC,
The area ratio of the secondary hard phase is 17% or more and less than 19%,
The value obtained by dividing the number of sub-hard phase-sub-hard phase grain boundaries by the number of sub-hard phases is 0.8 or more and 1.2 or less.

A cutting tool base according to an embodiment of the present invention uses the above-mentioned cemented carbide for cutting tools.

The cemented carbide for cutting tools has excellent toughness, and the cutting tool base has improved toughness and thus has durability.

The present inventor conducted extensive research in order to obtain a cemented carbide that achieves the above object. As a result, if the composition is set to a specified value, the area ratio of the secondary hard phase is optimized, and the average value of the number of other secondary hard phases in contact with one secondary hard phase is within a specified range, then We obtained the knowledge that it is possible to achieve

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a description will be given of the cemented carbide for cutting tools of the present invention and a cutting tool base using the alloy, particularly an embodiment in which the cutting tool base is used as an insert.

In addition, in this specification and claims, when a numerical range is expressed using "M to N" (M and N are both numerical values), it is synonymous with "M or more and N or less", and that range shall include the numerical value of the upper limit (N) and lower limit (M), and when the unit is written only for the upper limit value (N), the unit of the lower limit value (M) is also the same unit as the upper limit value (N). .

1. Composition and structure of cemented carbide for cutting tools The composition and structure of the cemented carbide for cutting tools according to the present embodiment are as follows.

(1) Co and Ni
The total content of one or more of Co and Ni is preferably 4.0% by mass or more and less than 10.0% by mass.
The reason is that when this content is satisfied, the toughness is excellent when used as a cutting tool base.

Here, Co and Ni mainly exist in the bonding phase. The main components of the binder phase (having crystal grains having an FCC structure) are Co and Ni, that is, the total of Co and Ni accounts for 50 atomic % or more of all the components constituting the binder phase.

The binder phase may contain W and C, which are components of the hard phase, and other unavoidable impurities. Furthermore, the binder phase may contain one or more of Ti, Ta, Nb, Zr, Hf, and V whose content is defined by Cr and MC. When these elements exist in the binder phase, they are presumed to be in a solid solution state in the binder phase.
Note that a method for identifying the bonded phase will be described later.

(2)MC
It is preferable that M (M is one or more selected from Ti, Ta, Nb, Zr, Hf, and V) is contained in an amount of 4.0% by mass or more and less than 12.0% by mass as MC. If the M content is less than 4.0% by mass as MC, the oxidation resistance will not be sufficient and large wear will occur due to oxidation of the hard phase during cutting, leading to the end of the service life. In this case, since the toughness is insufficient and defects are likely to occur, it is preferable that M is contained in an amount of 4.0% by mass or more and less than 12.0% by mass as MC.

The content of these carbides, if present, is defined on the assumption that M (metal atom) and C are combined in a 1:1 ratio, but these carbides present in the alloy have a stoichiometric amount. The carbide is not limited to a carbide bonded in a theoretical atomic ratio, but includes a composite carbide in which M and C are bonded, and the crystal structure of this carbide is a cubic crystal structure.

The carbide of M, that is, MC, occupies 50% by mass or more of the main component of the secondary hard phase (having crystal grains having an FCC structure), that is, all the components constituting the secondary hard phase. In addition to MC, the sub-hard phase may contain WC and inevitable impurities contained in the hard phase.
Note that the method for identifying the secondary hard phase will be described later.

The secondary hard phase is preferably present in an area proportion of 17 area % or more and less than 19 area %. The reason for this is that if the secondary hard phase is less than 17 area %, the secondary hard phase is small and the high temperature hardness is insufficient, whereas if it is 19 area % or more, the toughness decreases.
Note that the measurement of the area ratio will be described later.

(3 _{) Cr3C2}
Cr may be contained in an amount of less than 0.5% by mass, calculated as the content of Cr ₃ C ₂ . That is, the inclusion of Cr is not essential (it may not be included).
Cr dissolves as Cr in the binder phase, suppresses the growth of WC contained in the main hard phase, makes the WC finer, makes the cemented carbide a fine-grained and uniform grain structure, increases toughness, and improves plastic deformation resistance. It has the ability to improve sex. This function is impaired when the Cr content exceeds 0.5% by mass in terms of Cr ₃ C ₂ , causing composite carbides of Cr and W to precipitate in the binder phase, reducing toughness and causing defects. It may become the starting point for the occurrence of.

(4) W.C.
WC is the main component of the main hard phase, that is, WC occupies 50% by mass or more of all components constituting the main hard phase. The main hard phase may contain a binder phase component, a subhard phase component, Cr, and unavoidable impurities that are inevitably mixed in during the manufacturing process. Furthermore, since the crystal structure of the main hard phase is an HCP structure, the crystal structure is different from that of the secondary hard phase.
The method for identifying the main hard phase will be described later.

(5) Unavoidable impurities As mentioned above, the main hard phase, secondary hard phase, and binder phase may contain impurities that are unavoidably (unintentionally) mixed in during the manufacturing process, and the amount of impurities is extremely large. It is preferably 0.3% by mass or less, based on 100% by mass of the entire hard alloy.

2. How to differentiate between the binder phase, secondary hard phase, and hard phase and measure the area ratio of the secondary hard phase After distinguishing the binder phase, secondary hard phase, and main hard phase, measure the area ratio of the secondary hard phase as follows. .
(1) Process any surface or cross section of the cemented carbide to make it smooth by removing minute irregularities so as not to interfere with EBSD measurement, and one field of view on the processed surface is, for example, 24 μm (vertical) x 72 μm. (Horizontal), the measurement point spacing is 100 nm, and multiple fields of view (for example, 5 fields of view) are measured using an energy dispersive Observation was performed using a field emission scanning electron microscope (SEM) equipped with an OIM Data Collection (manufactured by AMETEK) at an accelerating voltage of 15 kV, and the EBSD pattern and EDS data were simultaneously captured.

The size of the observation field and the number of phases to be observed may be the same in distinguishing the bonded phase, the sub-hard phase, and the hard phase.
For processing the surface or cross section, for example, a focused ion beam device (FIB device), a cross-section polisher device (CP device), or the like is used.

(2) Next, for example, OIM Analysis ver. manufactured by EDAX/TSL. Load the measurement data in 7.3.1, average the EDS count values obtained from each measurement point inside the crystal grain corresponding to each element for each crystal grain, and calculate the EDS measurement value for each element for each crystal grain. , the composition of each crystal grain is derived from the obtained measured values.

(3) Identify each phase according to the definition of each phase described above. That is, the crystal grains identified as WC from the EBSD pattern are defined as WC grains. Next, the average value of the detected Co and Ni EDS count values was calculated from all measurement points identified as the FCC phase, and the FCC phase was identified as having a Co and Ni EDS count value higher than the average value. The measured points are taken as the binder phase, and the remainder of the FCC phase is taken as the secondary hard phase.

(4) When adjacent measurement points are of the same phase and the difference in orientation obtained from each measurement point is 5 degrees or more, the boundary between the two measurement points is defined as an interface. do.
(5) To measure the area ratio of the accessory hard brain, select a field of view that includes at least 300 (preferably 300 to 1000) accessory hard phases, and sum the area of each accessory hard phase. , and calculate the ratio of this sum to the area of the observation visual field. The area ratio of the secondary hard phase is determined by averaging the calculated values over multiple fields of view.

(6) For each phase identified as the main hard phase, secondary hard phase, and binder phase in (3) above, EDS measurements were performed again, and the particles identified as the main hard phase contained 50 at% or more of WC. Confirm that MC accounts for 50% by mass or more in the particles identified as the secondary hard phase, and that the total of Co and Ni accounts for 50 atomic% or more in the particles identified as the binder phase. .

3. Measurement of the content of each element The content of W, Co, Ni, Ti, Ta, Nb, Zr, Hf, V, Cr, and C was measured on a mirror-finished surface (so as not to interfere with fluorescent X-ray measurement). It can be measured by performing fluorescent X-ray measurement on a surface that has been processed to be smooth by cutting away minute irregularities.

4. The value obtained by dividing the number of grain boundaries of the sub-hard phase-sub-hard phase by the number of sub-hard phases The value obtained by dividing the number of grain boundaries of the sub-hard phase-sub-hard phase by the number of sub-hard phases is 0.8 or more, 1. It is preferably 2 or less. The reason is that if this average value is less than 0.8, secondary hard phases will be scattered and the alloy will easily break under acceleration when a large load is applied, whereas if it exceeds 1.2, This is because the secondary hard phases coagulate and exist, resulting in a decrease in plastic deformation resistance. This average value is more preferably 1.0 or more and 1.2 or less.

Here, the value obtained by dividing the number of sub-hard phase-sub-hard phase grain boundaries by the number of sub-hard phases is measured using the same means as for measuring the area ratio described above and in the same observation field of view. Further, the sub-hard phase-sub-hard phase grain boundary refers to the boundary between the sub-hard phases where the sides that are the boundaries between adjacent pixels are in contact with each other. By using OIM Analysis to create a Partition containing only the secondary hard phase and extracting grain boundary information from this Partition, the number of grain boundaries between the secondary hard phase and the secondary hard phase can be obtained, and this can be By dividing by the number of particles of the phase, it is possible to obtain a value obtained by dividing the number of sub-hard phase-sub-hard phase grain boundaries by the number of sub-hard phases.

EXAMPLES A case in which the cemented carbide for cutting tools of the present invention is used as a cutting tool base will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

1. Production of Examples (1) Raw material powder and blending process First, as powders for sintering, WC powder, Co powder, Ni powder, Cr ₃ C ₂ powder, TiC powder, TaC powder, NbC powder, and ZrC shown in Table 1 were used as powders for sintering. Powder, HfC powder, and VC powder were prepared.

Among these powders, TiC powder, TaC powder, NbC powder, ZrC powder, HfC powder, and VC powder, which are raw materials for carbides contained in the sub-hard phase, were weighed out to a predetermined composition and then put into a ball mill. Mixing was carried out for 36 hours, followed by heat treatment at 1600° C. for 10 hours under vacuum, followed by crushing in a ball mill for 0.5 hours to produce a solid solution powder (see Table 1). In the following, the blending amount of the solid solution powder is shown as mass % when the sum of mass % of all base materials is 100 mass %).

Next, the obtained solid solution powder was combined with the WC powder, Co powder, Ni powder, and Cr ₃ C ₂ powder, and mixed using a ball mill at a rotation speed of 20 to 30 rpm for 30 to 40 hours under the conditions shown in Table 3. A molded body was produced by press molding at a pressure of 100 MPa.

(2) Sintering process The obtained molded body was sintered under the conditions shown in Table 3 to produce a sintered body. The temperature increase rate in Table 3 refers to the temperature increase rate from 1000° C. to the sintering temperature.

(3) Cutting process Following the sintering process, the sintered body was machined and ground to form the shape of CNMG432MM, and the cemented carbide cutting bases 1 to 10 of Examples shown in Table 4 (hereinafter referred to as Examples Tool bases 1 to 10) were manufactured.

2. Manufacture of Comparative Example In contrast, for comparison, cemented carbide cutting bases 1 to 8 (hereinafter referred to as Comparative Example Tool Bases 1 to 8) of Comparative Examples were manufactured in the following procedure.

(1) Raw material powder and blending process WC powder, Co powder, Ni powder, Cr ₃ C ₂ powder, TiC powder, TaC powder, NbC powder, ZrC powder, HfC powder, and VC powder were prepared as raw material powders.

Among these powders, TiC powder, TaC powder, NbC powder, ZrC powder, HfC powder, and VC powder, which are raw materials for carbides contained in the sub-hard phase, were weighed out to a predetermined composition and then put into a ball mill. Mixing was carried out for 36 hours, followed by heat treatment at 1600° C. for 10 hours under vacuum, followed by crushing in a ball mill for 0.5 hours to produce a solid solution powder (see Table 1). In the following, the blending amount of the solid solution powder is shown as mass % when the sum of mass % of all base materials is 100 mass %).

Next, these powders were mixed to have the composition shown in Table 2 to obtain a sintering powder. Using a ball mill, they were mixed under the conditions shown in Table 3, dried, and then press-molded at a pressure of 100 MPa. The body was created.

(2) Sintering process The obtained molded body was sintered under the conditions shown in Table 3 to produce a sintered body. Also in the comparative example process, the temperature increase rate in Table 3 refers to the temperature increase rate from 1000° C. to the sintering temperature.

(3) Cutting process Following the sintering process, the sintered body was machined and ground to the shape of CNMG432MM, thereby producing comparative tool bases 1 to 8 shown in Table 5.

The cross sections of the example tool bases 1 to 10 and the comparative example tool bases 1 to 8 prepared in this way were observed by the method described above to determine the content of the components, the area ratio of the secondary hard phase, the secondary hard phase - the secondary hard phase. The value obtained by dividing the number of grain boundaries by the number of secondary hard phases is calculated, and the results are shown in Table 4 (Example tool base) and Table 5 (Comparative example tool base).

Here, in measuring the area ratio of the sub-hard phase, the boundaries between adjacent EBSD pixels were regular hexagons.
In addition, in the example tool substrates 1 to 10 and the comparative example tool substrates 1 to 8, the contents of inevitable impurities were all within the above-mentioned preferred range.

The following cutting tests were conducted on Example tool bases 1 to 10 and Comparative example tool bases 1 to 8. After the cutting test, the amount of wear and wear state of the cutting edge was observed. Table 6 shows the results of this test.

Cutting test: Dry external turning of alloy steel Work material: JIS/SCM440 (HB290) round bar with 4 slits in the longitudinal direction Cutting speed: 95 m/min
Cut: 1.0mm
Feed: 0.2mm/rev
Cutting time: 5 minutes

According to the cutting test results shown in Table 6, all of the example tool bases exhibited excellent toughness without causing any fractures, whereas all of the comparative example tool bases exhibited excellent toughness. It can be seen that the tool life is short due to occurrence or wear.

Claims (2)

A total of at least 4.0% by mass and less than 10.0% by mass of one or more of Co and Ni,
M (M is one or more selected from Ti, Ta, Nb, Zr, Hf, and V) is 4.0% by mass or more and less than 12.0% by mass as MC, and
Contains less than 0.5% by mass _of Cr as _Cr3C2 ,
The remainder consists of WC and unavoidable impurities,
The main hard phase has the WC,
The secondary hard phase has the MC,
The area ratio of the secondary hard phase is 17% or more and less than 19%,
A cemented carbide for a cutting tool, characterized in that the value obtained by dividing the number of grain boundaries of the secondary hard phase-secondary hard phase by the number of secondary hard phases is 0.8 or more and 1.2 or less. A cutting tool base comprising the cemented carbide for cutting tools according to claim 1.