JP7643106B2 - Cutting Tools - Google Patents

Description

The present invention relates to cutting tools using cemented carbide (WC-based sintered alloy).

Cemented carbide alloys are used as metal cutting tools because of their excellent mechanical strength and thermal fatigue resistance. The conditions under which these cutting tools are used are becoming more severe due to the increasing efficiency of cutting processes, and cutting tools are required to have even greater durability.

For this reason, various proposals have been made to improve the durability of the cemented carbide alloys used in cutting tools. Among these proposals is one that involves controlling the crystal grains of the binder phase in order to improve hardness, toughness, and breakage resistance.

For example, Patent Document 1 describes a cemented carbide whose Co crystal structure satisfies 0≦I(Co·hcp)/I(Co·fcc)≦0.1 (I(Co·hcp) is the X-ray diffraction intensity on the (101) plane of Co with the hcp structure, and I(Co·fcc) is the X-ray diffraction intensity on the (111) plane of Co with the fcc structure) and whose Co lattice constant is 3.570 or more, and which is said to have both toughness and strength, especially impact strength.

For example, Patent Document 2 describes a cemented carbide containing a hard phase consisting of at least one selected from WC, TiC, TiN, and TiCN, and a binder phase consisting of an iron-group metal, the binder phase being formed by electric current pressure sintering using binder phase powder having an average particle size at least three times that of the hard phase powder, the binder phase having a flat shape with an aspect ratio of 5 to 20 in a cross section of the hard alloy parallel to the pressure axis of a sintering device performing electric current pressure sintering, and a binder phase structure having a directional arrangement extending in a direction perpendicular to the pressure axis, and the cemented carbide is said to have high toughness and excellent hardness and strength.

For example, Patent Document 3 describes a fine-grained cemented carbide alloy in which the average grain size of WC is 0.8 μm or less, and the average grain size of the binder phase grains is 200 μm or less, and the cemented carbide alloy is said to have excellent resistance to breakage.

Patent No. 4537501 Patent No. 4177467 JP 2004-346370 A

According to the inventor's investigations, it was found that when the cemented carbide alloys described in Patent Documents 1 to 3 are used as cutting tools for hard-to-cut materials such as titanium alloys and stainless steel, they do not have sufficient resistance to plastic deformation or chipping.

The present invention was made in consideration of these circumstances, and aims to provide a cutting tool with excellent durability, with improved resistance to plastic deformation and chipping at the cutting edge, even when used to cut difficult-to-cut materials such as titanium alloys and stainless steel.

The inventors conducted extensive research to obtain a cutting tool that would achieve the above-mentioned objective. As a result, they discovered that if the cemented carbide constituting the cutting tool has a predetermined composition and a region having a predetermined proportion of a bonding phase composed of multiple crystals is present near the surface of the cutting tool, it is possible to obtain a cutting tool that has excellent durability and has resistance to plastic deformation and chipping at the cutting edge.

The present invention is based on this finding and is as follows.
"(1) 4.0 to 15.0 mass% of either Co or Ni,
0.5% by mass or less of Cr ₃ C ₂ ,
VC at 0.5% by mass or less,
Contains 12.0 mass% or less of any one or more of TaC, NbC, TiC, ZrC and HfC;
The balance is WC and unavoidable impurities;
The average grain size of the WC is 0.5 to 4.0 μm,
The ratio of measurement points in the bonding phase having a KAM value of less than 1 is 70% or more in a surface region from the surface to an interior region 10 μm away, and 60% or less in an interior region 15 to 25 μm away from the surface.
A cutting tool characterized by:
(2) The cutting tool according to (1) above, characterized in that the cutting edge has a surface coating layer.

The cutting tool of the present invention has excellent resistance to plastic deformation and chipping, and exhibits excellent durability even when used to cut difficult-to-cut materials such as titanium alloys and stainless steel.

FIG. 2 is a schematic diagram showing a measurement area of the KAM value. FIG. 2 is a schematic diagram illustrating a method for measuring a KAM value. 1 is a schematic diagram showing an example of the amount of plastic deformation on the flank of a cutting edge, in which the upper figure (the rake face) is a plan view and the lower figure (the flank on the cutting edge side) is a side view.

Hereinafter, a cutting tool according to an embodiment of the present invention will be described, particularly when used as an insert.
In the specification and claims, when a numerical range is expressed using "M to N" (where M and N are both numerical values), the range is intended to include the upper limit (N) and lower limit (M) numerical values.

1. Composition The composition of the cutting tool of the present embodiment is
One or both of Co and Ni are 4.0 to 15.0 mass%;
0.5% by mass or less of Cr ₃ C ₂ ,
VC at 0.5% by mass or less,
Contains 12.0 mass% or less of any one or more of TaC, NbC, TiC, ZrC and HfC;
The balance consists of WC and unavoidable impurities.
The following explains each in order.

(1) Co and Ni
The content of either one or both of Co and Ni is preferably 4.0 to 15.0 mass %. The reason is that if it is less than 4.0 mass %, chipping resistance and fracture resistance are insufficient, while if it is 15.0 mass % or more, plastic deformation resistance and wear resistance are insufficient.
Co and Ni are mainly present in the binder phase, and either one or both of Co and Ni account for 50 mass % or more of the main components of the binder phase, that is, all the components forming the binder phase.

The binder phase may contain one or more of Cr, Ta, Nb, Ti, Zr, Hf, and V. When these elements are present in the binder phase, they are presumed to be in a solid solution state in the binder phase. Furthermore, the binder phase may contain W and C, which are components of the hard phase, and other unavoidable impurities.

( ₂ ) _Cr3C2
In order to improve the plastic deformation resistance of the cutting tool, it is preferable to contain Cr (although the inclusion of Cr is not essential). The content of Cr is preferably 0.5 mass% or less calculated _{as Cr3C2} with respect to the entire cutting tool.

(3) Virtual Currency
In order to improve the plastic deformation resistance of the cutting tool, it is preferable to contain V (although the inclusion of V is not essential). The content of V is preferably 0.5 mass % or less, calculated as VC, based on the entire cutting tool.

(4) TaC, NbC, TiC, ZrC and HfC
Any one or more of TaC, NbC, TiC, ZrC and HfC form a γ phase. The γ phase does not have to exist, but when it does exist, it is preferable that the content ratio of one or more of the compounds represented by MC is up to 12.0 mass% based on the entire cutting tool, assuming that the carbide is a carbide in which M (metal atom) and C are bonded in a 1:1 ratio. The reason is that if it exceeds 12.0 mass%, the wear resistance of the cutting tool becomes insufficient, and aggregates are easily generated inside the cutting tool, which becomes the starting point of chipping.

(5) World Cup
WC is the main component of the hard phase. The hard phase may contain unavoidable impurities that are inevitably mixed in during the manufacturing process.

The average grain size of WC is preferably 0.5 to 4.0 μm. This is because if it is less than 0.5 μm, slippage occurs between the hard phases, resulting in insufficient resistance to plastic deformation and chipping, while if it exceeds 4.0 μm, sufficient wear resistance cannot be obtained. The average grain size of WC is more preferably 1.0 to 3.0 μm.

The average grain size of WC was determined by observing at pixel size, determining the area of at least 4,000 hard phases by image analysis, and averaging the diameters of circles equal to the areas.

Specifically, for example, one field of view is 30 μm x 70 μm, pixel size is 40 nm x 40 nm, and when a cross-section of a region from the surface of the cutting tool (described later) to a depth of 30 μm is observed, the number of WC particles and the number of bonding phases in the region are each 4000 or more, and each observation field of view includes 60 to 70 μm of the cutting tool surface. For example, multiple fields of view (5 or more) are observed at a magnification of 1000 times.

(6) Inevitable Impurities As described above, the hard phase and the binder phase may contain impurities that are inevitably mixed in during the manufacturing process. The amount of impurities is preferably 0.3% by mass or less, with the total mass of the cutting tool being 100% by mass.

2. Structure of the binder phase As shown in FIG. 1, the ratio of measurement points in the binder phase having a KAM value of less than 1 is preferably 70% or more in the surface region (O) of the cutting tool extending from the surface of the cutting tool to the interior at a distance of 10 μm, and less than 60% in the interior region (I) of the cutting tool extending from 15 to 25 μm from the surface.
Here, the KAM value is also called the local orientation difference average value.

By having the KAM value in the binder phase take such values in each region away from the surface of the cutting tool, the chipping resistance and plastic deformation resistance are improved.

Here, the KAM value is measured as follows:

(1) Definition of grain boundaries Using an electron beam backscattering analyzer, an observation field of view is set in a longitudinal section (described later) from the surface of the cutting tool toward the inside, for example, 100 μm wide and the region to be measured (region 10 μm away from the surface, 15 to 25 μm away from the surface), and measurements are taken at 40 nm intervals. The observation field is 5 or more. In the observation field, the measurement points (pixels) are present discretely, but the region up to the middle between adjacent measurement points (a regular hexagon can be exemplified) is represented by the measurement results of the measurement points. When there is an orientation difference of 5 degrees or more between adjacent measurement points among these measurement points, the region up to the middle is defined as the grain boundary.

However, if a measurement point has an orientation difference of 5 degrees or more from all of its adjacent measurement points, or if it exists alone with no adjacent measurement points, it is not treated as a crystal grain; instead, a measurement point is treated as a group of two or more measurement points that are connected.

(2) Measurement of KAM Value Then, the average value of the orientation difference between two adjacent pixels in a crystal grain is calculated and defined as the KAM (Kernel Average Misorientation) value.
Generally, when expressing the KAM value at pixel i by a formula, if the measurement area is divided into a regular hexagon and analyzed, it can be expressed as the average of the orientation differences between up to six measurement points surrounding the point of interest (the measurement point of interest, pixel) by the following formula 1. In addition, m in [Formula 1] represents the number of pixels adjacent to the measurement point i in the same crystal grain, and α _k,i represents the orientation difference between pixel i and adjacent pixel k. In other words, when expressing the KAM value at the attention point U shown in Figure 2 by a formula, the pixels to be measured are 6 points 1 to 6, so it can be obtained by the following [Formula 2], and the KAM value at the attention point V is the pixels to be measured are 2 points 1 and 2, so it can be obtained by the following [Formula 3].

In the claims and specification, the surface of a cutting tool refers to a line connecting the deepest valley and the second deepest valley on the cutting tool surface in a longitudinal section when observed at a magnification of 100 to 200 times and with a field of view of 500 to 1000 μm horizontal by 400 to 800 μm vertical. For example, being 10 μm away from the surface of a cutting tool means being 10 μm away from the perpendicular line of this line toward the inside of the tool.

When the cutting tool is an insert, a longitudinal section is a section perpendicular to the surface of the cutting tool when the surface is treated as a horizontal plane, ignoring any unevenness on the surface, and this perpendicular direction does not necessarily coincide with the direction of the perpendicular line mentioned above. Also, when the cutting tool has a central axis, such as a drill, the longitudinal section is a section perpendicular to this axis.

3. Surface Coating Layer The cutting tool of the present embodiment can achieve the above-mentioned object as it is, but a surface coating layer may be provided on the surface of the cutting tool including the cutting edge. By providing a surface coating layer, the above-mentioned object can be achieved more reliably. There are no particular restrictions on the surface coating layer, and any known surface coating layer can be used as appropriate.

Next, the present invention will be specifically explained using examples, but the present invention is not limited to these examples.

1. Blending with raw material powder First, as powders for sintering, WC powder with an average particle size (d50) of 0.5 to 4.0 μm, and Co powder, Ni powder, Cr ₃ C ₂ powder, TaC powder, NbC powder, TiC powder, ZrC powder, HfC powder, and VC powder with an average particle size (d50) of 1.0 to 4.0 μm shown in Table 1 were prepared.

2. Preparation of a green body Next, these powders were mixed to obtain the composition shown in Table 1 to prepare a powder for sintering, which was then wet-mixed in a ball mill for 72 hours and dried using a spray dryer. After that, the powder was pressed at a pressure of 100 MPa to obtain the shape of the ANSI designation CNMG432MS to prepare a green body.

3. Sintering Next, the powder compacts were subjected to a sintering process in which they were held at a predetermined temperature for a predetermined time. In this example, the conditions shown in Table 2 were used, that is, the compacts were heated to a holding temperature range of 1350 to 1450°C in a vacuum atmosphere of 0.1 Pa or less, and held at the holding temperature for 60 to 120 minutes.

4. First blasting treatment (dry blasting treatment)
The abrasive grains used were granulated cemented carbide powder (the same granulated powder as that used in producing the cemented carbide alloy), and the treatment was carried out under the conditions shown in Table 2. The conditions shown in Table 2 were roughly as follows:
Abrasive grain size: diameter 100-200 μm
Blasting pressure: 0.35-0.40MPa
Projection time: 15 to 20 seconds Projection angle: 35 to 55 degrees to the normal line of the cutting tool surface
The normal line to the cutting tool surface refers to the normal line to the cutting tool surface when the cutting tool surface is treated as a horizontal plane, ignoring any irregularities on the cutting tool surface, and does not necessarily coincide with the perpendicular line described above.

5. Heat Treatment The samples were held in a vacuum atmosphere of 0.1 Pa or less at 700 to 1000° C. for 5 to 50 hours as shown in Table 2.

6. Second blasting treatment (wet blasting treatment)
The blasting liquid was water containing Al ₂ O ₃ abrasive grains, and the treatment was carried out under the conditions shown in Table 2. The conditions shown in Table 2 were roughly as follows.
Media (abrasive grain) size: 170-500 (mesh)
Media concentration: 15 to 60% by mass
Blasting pressure: 0.10-0.15MPa
Projection time: 6 to 60 seconds Projection angle: 35 to 55 degrees to the normal line of the cutting tool surface
The normal line to the cutting tool surface refers to the normal line to the cutting tool surface when the cutting tool surface is treated as a horizontal plane, ignoring any irregularities on the cutting tool surface, and does not necessarily coincide with the perpendicular line described above.

These processes were repeated so that each of steps 4 to 6 was performed twice.

7. Post-treatment Next, machining and grinding were carried out to shape the CNMG432MS, and cutting tools 1 to 10 shown in Table 3 (hereinafter referred to as Examples 1 to 10) were produced.

For comparison, cutting tools 1' to 7' of comparative examples (hereinafter referred to as Comparative Examples 1' to 7') were manufactured.
The manufacturing process is one in which the first blasting process, heat treatment process, and second blasting process are omitted from the manufacturing processes of Examples 1 to 10 (in Table 2, the conditions for each process are marked with "-"), or one in which the first blasting process or heat treatment process shown in Table 2 was carried out outside the manufacturing conditions described above.

That is, the powder for sintering, which was blended according to the blending composition shown in Table 1, was wet mixed in a ball mill for 72 hours, dried by a spray dryer, and then pressed under a pressure of 100 MPa to produce a green compact having the shape of CNMG432MS. The green compact was then sintered under the conditions shown in Table 2, namely, a heating temperature of 1350° C. to 1450° C., a heating holding time of 60 to 120 minutes, and a vacuum atmosphere of 0.1 Pa or less. The first blasting treatment was performed under the conditions of a blasting pressure of 0.10 to 0.20 MPa, a projection time of 15 to 20 seconds, and a projection angle of 35 to 55 degrees relative to the normal line of the tool surface. The heat treatment step was performed under the conditions of a heating temperature of 400 to 850° C., a heating holding time of 10 to 50 hours, and a vacuum atmosphere of 0.1 Pa or less. The second blasting treatment was performed under the conditions of a media (abrasive grains): Al ₂ O The blasting was performed under the conditions of ₃ abrasive grains, media size: 230 to 500 (mesh), blast pressure: 0.10 to 0.15 MPa, projection time: 6 to 60 seconds, projection angle: 35 to 55 degrees relative to the normal to the tool surface, and the resultant was machined and ground to produce comparative example tools 1' to 7' shown in Table 4, which have a CNMG432MS insert shape.

For the cutting tools of Examples 1 to 10 and Comparative Examples 1' to 7', the component composition and average grain size of WC were determined based on the above-mentioned observation field, and the results are shown in Tables 3 and 4. It was confirmed that the content ratio of unavoidable impurities was within the above-mentioned preferable range.

Next, a hard coating layer with the average thickness shown in Table 5 was formed on the surfaces of Examples 1 to 10 and Comparative Examples 1' to 7' by CVD.

The following cutting tests were conducted on Examples 1 to 10 and Comparative Examples 1' to 7' to measure the amount of plastic deformation on the flank of the cutting edge and to observe the state of wear on the cutting edge.

In the following cutting tests, the following was used as the amount of plastic deformation on the flank of the cutting edge. In other words, the undeformed cutting edge ridge before cutting was used as the reference, and the amount of deformation caused by the cutting edge ridge being pressed in by cutting was used as the amount of plastic deformation on the flank of the cutting edge.

Specifically, as shown in Fig. 3, for the flank (12) of the main cutting edge of the tool, a line was drawn on the ridge where the flank (12) on the cutting edge (13) side and the rake face (11) intersect at a position sufficiently away from the cutting edge, and the line was extended in the direction of the cutting edge, and the distance between the extended line (15) and the ridge of the cutting edge (perpendicular to the extended line) was measured at the farthest point, which was defined as the amount of plastic deformation (14) of the flank of the cutting edge. In addition, the wear state of the cutting edge was observed after the cutting time was completed.
Table 6 shows the results of the cutting tests.

Wet external diameter turning of Ti-6Al-4V alloy round bar (diameter 200 mm)
Work material: Ti-6Al-4V alloy Cutting speed: 70m/min
Cut: 1.0 mm
Feed: 0.16 mm/rev
Cutting time: 5 minutes

Further, the following cutting test was carried out on the above-mentioned Inventions 1 to 4 and Comparative Examples 1' to 4' not having the above-mentioned coating layer, and the amount of plastic deformation on the flank of the cutting edge was measured, and the state of wear of the cutting edge was observed.
Table 7 shows the results of the cutting tests.

Wet external diameter turning of JIS/SUS304 round bar (diameter 200 mm)
Work material: JIS/SUS304
Cutting speed: 50m/min,
Cut: 1.0 mm,
Feed: 0.11 mm/rev.
Cutting time: 5 minutes,
Uses wet water-soluble cutting oil.

According to the test results shown in Tables 6 and 7, all of the Examples exhibit excellent resistance to plastic deformation without causing severe chipping that would affect the tool's life. In contrast, the Comparative Examples showed significant plastic deformation of the tool at a given cutting time, with some samples suffering from chipping at the cutting edge. In other words, the Examples have high resistance to plastic deformation and chipping, since the proportion of measurement points in the binder phase with a KAM value of less than 1 is 70% or more in the surface region up to 10 μm from the surface, and 70% or less in the internal region 15 to 25 μm from the surface.

1 to 6: crystal grain number 11: rake face 12: cutting edge side flank 13: cutting edge 14: amount of composition deformation of flank face 15: line segment O extending the ridge where the flank face and the rake face intersect; surface region I of the cutting tool; internal region B of the cutting tool; grain boundary P: measurement point (pixel)
U: Attention point V: Attention point

Claims (2)

One or both of Co and Ni are 4.0 to 15.0 mass%;
0.5% by mass or less of Cr ₃ C ₂ ,
VC at 0.5% by mass or less,
Contains 12.0 mass% or less of any one or more of TaC, NbC, TiC, ZrC and HfC;
The balance is WC and unavoidable impurities;
The average grain size of the WC is 0.5 to 4.0 μm,
The ratio of measurement points in the bonding phase having a KAM value of less than 1 is 70% or more in a surface region up to a distance of 10 μm from the surface, and 60% or less in an inner region 15 to 25 μm away from the surface.
A cutting tool characterized by: The cutting tool according to claim 1, characterized in that the cutting edge has a surface coating layer.

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