JP7748024B2 - sintered cermet - Google Patents

Description

The present invention relates to a sintered cermet body.

Cermet tools have superior resistance to reactivity with iron and high-temperature strength compared to cemented carbide tools. Therefore, cermet tools take advantage of these properties and are often used for finishing iron-based materials.

Various cermet tools have been proposed to date. For example, Patent Document 1 proposes a titanium carbonitride-based cermet cutting insert having a through hole for attachment to the tool body, in which the surface roughness of the inner surface of the through hole exceeds 0.2 μm in arithmetic mean roughness Ra at a cutoff value of 0.08 mm, while the surface roughness of the flank face and chip breaker of the insert is 0.2 μm or less in arithmetic mean roughness Ra at a cutoff value of 0.08 mm, and further the residual stress in the hard phase of the insert surface is 450 MPa or more in compressive strength.

JP 2011-088239 A

In recent years, demands for faster and more labor-efficient cutting have become even stricter, leading to a trend toward higher speeds and heavy cutting, such as high feed rates and large depths of cut. Under these harsh high-speed cutting conditions, tool life tends to be shorter than before.

In Patent Document 1, the surface of a cermet tool is wet-blasted to smooth the tool surface and impart a predetermined compressive residual stress to the insert surface, thereby improving the tool's fracture resistance to some extent. However, this is still not sufficient performance. Furthermore, the cermet cutting insert described in Patent Document 1 does not have improved wear resistance or plastic deformation resistance, making it difficult to extend the tool's life in high-speed cutting.

The present invention was made in consideration of the above circumstances, and aims to provide a sintered cermet that has excellent chipping resistance, wear resistance, and plastic deformation resistance, and can extend tool life.

The inventors conducted extensive research into extending the tool life of sintered cermets and discovered that a specific configuration of sintered cermets not only provides excellent fracture resistance, but also improves wear resistance and plastic deformation resistance, thereby extending the tool life of sintered cermets. This discovery led to the completion of the present invention.

That is, the gist of the present invention is as follows.
[1]
A sintered cermet comprising a hard phase and a binder phase,
the hard phase is a phase containing a carbonitride, a carbide, or a nitride containing at least one element selected from the group consisting of Ti, W, Mo, Cr, Ta, Nb, V, Hf, and Zr,
the binder phase is a phase containing at least one selected from the group consisting of Co, Ni, and Fe,
The content of the hard phase is 82% by mass or more and 93% by mass or less,
The content of the binder phase is 7% by mass or more and 18% by mass or less,
The hard phase is
(i) a first hard phase having a cubic crystal structure that exhibits a diffraction peak derived from the (422) plane at an angle of 123.5° or more and 125.0° or less in X-ray diffraction (XRD) measurement;
(ii) a second hard phase having a cubic crystal structure that exhibits a diffraction peak derived from the (422) plane at an angle of 121.0° or more and less than 123.5° in X-ray diffraction (XRD) measurement;
Including,
the residual stress of the second hard phase is −1000 MPa or more and −600 MPa or less,
The residual stress of the binder phase is −600 MPa or more and −200 MPa or less,
The thickness of the first hard phase enriched region is 0 μm or more and 1.0 μm or less,
A cermet sintered body having a surface binder phase ratio of 0.80 or more and 0.95 or less.
[2]
The cermet sintered body according to [1], wherein a surface nitrogen ratio is 0.42 or more and 0.50 or less.

The cermet sintered body of the present invention has excellent chipping resistance, wear resistance, and plastic deformation resistance, allowing for extended tool life.

1 is an example of a backscattered electron (BSE) observation image of a cross-sectional structure inside a sintered cermet body.

The following provides a detailed description of an embodiment of the present invention (hereinafter simply referred to as "the present embodiment"); however, the present invention is not limited to the present embodiment. Various modifications of the present invention are possible without departing from the spirit of the present invention. In the drawings, identical elements are designated by the same reference numerals, and redundant explanations will be omitted. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to those shown.

The cermet sintered body of the present embodiment includes a hard phase and a binder phase, the hard phase being a phase containing a carbonitride, carbide, or nitride containing at least one element selected from the group consisting of Ti, W, Mo, Cr, Ta, Nb, V, Hf, and Zr, the binder phase being a phase containing at least one element selected from the group consisting of Co, Ni, and Fe, the content of the hard phase being 82 mass% or more and 93 mass% or less, the content of the binder phase being 7 mass% or more and 18 mass% or less, and the hard phase having (i) a cubic crystal structure which shows a diffraction peak derived from the (422) plane at an angle of 123.5° or more and 125.0° or less in X-ray diffraction (hereinafter also referred to as "XRD") measurement. and (ii) a second hard phase having a cubic crystal structure that exhibits a diffraction peak derived from the (422) plane at an angle of 121.0° or more and less than 123.5° in XRD measurement, wherein the residual stress of the second hard phase is −1000 MPa or more and −600 MPa or less, the residual stress of the binder phase is −600 MPa or more and −200 MPa or less, the thickness of the first hard phase-enriched region calculated by the method below (hereinafter also simply referred to as “thickness of the first hard phase-enriched region”) is 0 μm or more and 1.0 μm or less, and the surface binder phase ratio calculated by the method below (hereinafter also simply referred to as “surface binder phase ratio”) is 0.80 or more and 0.95 or less.
(Method for calculating thickness of first hard phase enriched region)
In a backscattered electron (hereinafter also referred to as "BSE") observation image of a cross section perpendicular to the surface of the cermet sintered body, lines parallel to the surface of the cermet sintered body are drawn at 0.5 μm intervals from the surface of the cermet sintered body inward. When the length of the lines is taken as 100%, the shortest distance between the surface of the cermet sintered body and a line segment that crosses the first hard phase at a rate of less than 30% is defined as the thickness of the first hard phase-enriched region. In this case, the length of the lines is set to 20 μm or more.
(Method of calculating the surface bonded phase ratio)
In a cross section perpendicular to the surface of the cermet sintered body, the mass percentages of Co, Ni, and Fe are analyzed at a position 10 μm inward from the surface of the cermet sintered body (surface portion) and at a position 500 μm or more inward from the surface of the cermet sintered body (interior portion) using a scanning electron microscope (hereinafter also referred to as "SEM") equipped with an energy dispersive X-ray analyzer (hereinafter also referred to as "EDS"). The EDS analysis is performed by area analysis of a 10 μm × 10 μm region centered on the above analysis position. The surface binder phase ratio is determined by dividing the sum of the mass percentages of Co, Ni, and Fe in the surface portion by the sum of the mass percentages of Co, Ni, and Fe in the interior.

The factors that enable such cermet sintered bodies to have excellent fracture resistance, improved wear resistance and plastic deformation resistance, and extended tool life are not fully understood, but the inventors believe the factors are as follows. However, the factors are not limited to these. Specifically, when the hard phase content is 82% by mass or more, the cermet sintered body has improved hardness and excellent wear resistance and plastic deformation resistance. On the other hand, when the hard phase content is 93% by mass or less, the relative content of the binder phase increases, resulting in improved toughness and excellent fracture resistance. Furthermore, when the binder phase content is 7% by mass or more, the cermet sintered body has improved toughness and excellent fracture resistance. On the other hand, when the binder phase content is 18% by mass or less, the relative content of the hard phase increases, resulting in improved hardness and excellent wear resistance and plastic deformation resistance. Furthermore, when the residual stress of the second hard phase is -1000 MPa or more, embrittlement of the hard phase is suppressed, and the fracture resistance of the cermet sintered body is improved. On the other hand, when the residual stress of the second hard phase is -600 MPa or less, the toughness of the hard phase is improved, and the fracture resistance of the cermet sintered body is excellent. Furthermore, when the residual stress of the binder phase is -600 MPa or more, embrittlement of the binder phase is suppressed, and the fracture resistance of the cermet sintered body is improved. On the other hand, when the residual stress of the binder phase is -200 MPa or less, the toughness of the binder phase is improved, and the fracture resistance of the cermet sintered body is excellent. Furthermore, when the residual stress of the binder phase is -200 MPa or less, the binder phase is hardened, and the wear resistance of the cermet sintered body is improved. Furthermore, when the thickness of the first hard phase-enriched region is 1.0 μm or less, the wear resistance and plastic deformation resistance of the cermet sintered body are improved. Furthermore, when the surface binder phase ratio is 0.80 or more, the binder phase ratio increases relatively, resulting in the cermet sintered body having excellent fracture resistance. On the other hand, when the surface binder phase ratio is 0.95 or less, the hard phase ratio increases relatively, resulting in the cermet sintered body having excellent wear resistance and plastic deformation resistance. These effects combine to provide the cermet sintered body of this embodiment with excellent fracture resistance, improved wear resistance and plastic deformation resistance, and extended tool life.

In the cermet sintered body of this embodiment, the hard phase is a phase containing a carbonitride, carbide, or nitride containing at least one element selected from the group consisting of Ti, W, Mo, Cr, Ta, Nb, V, Hf, and Zr, preferably a phase containing a carbonitride or carbide containing at least one element selected from the group consisting of Ti, W, Mo, Cr, Ta, Nb, and Zr, and more preferably a phase containing a carbonitride containing at least one element selected from the group consisting of Ti, W, Mo, Nb, and Zr.

The specific composition of the hard phase is not particularly limited, but examples thereof include TiC, TiN, TiCN, WC, TaC, NbC, ZrC, _Mo2C , _Cr3C2 , VC, HfC, etc. Among these, TiCN, WC, TaC, NbC, ZrC, _Mo2C , and _Cr3C2 are preferred, _and TiCN _, WC, NbC, ZrC, and _Mo2C are more preferred.

In the cermet sintered body of this embodiment, the binder phase is a phase containing at least one element selected from the group consisting of Co, Ni, and Fe, preferably a phase containing at least one element selected from the group consisting of Co and Ni, and more preferably a phase consisting of Co and Ni.

In the cermet sintered body of this embodiment, the hard phase content is 82% by mass or more and 93% by mass or less. When the hard phase content is 82% by mass or more, the cermet sintered body has improved hardness and excellent wear resistance and plastic deformation resistance. On the other hand, when the hard phase content is 93% by mass or less, the binder phase content increases relatively, resulting in improved toughness and excellent chipping resistance. From the same perspective, the hard phase content is preferably 84% by mass or more and 90% by mass or less, and more preferably 85% by mass or more and 88% by mass or less.

In the cermet sintered body of this embodiment, the binder phase content is 7% by mass or more and 18% by mass or less. When the binder phase content is 7% by mass or more, the cermet sintered body has improved toughness and excellent chipping resistance. On the other hand, when the binder phase content is 18% by mass or less, the hard phase content increases relatively, so the cermet sintered body has improved hardness and excellent wear resistance and plastic deformation resistance. From the same perspective, the binder phase content is preferably 10% by mass or more and 16% by mass or less, and more preferably 12% by mass or more and 15% by mass or less.

In this embodiment, the content ratios (mass %) of the hard phase and the binder phase are the values of the content ratios (mass %) relative to a total of 100 mass % of the carbonitride, carbide or nitride containing at least one element selected from the group consisting of Ti, W, Mo, Cr, Ta, Nb, V, Hf and Zr, and at least one element selected from the group consisting of Co, Ni and Fe.
In this embodiment, the hard phase and binder phase contents (mass%) can be measured by EDS analysis at a position 500 μm or more inward from the surface of the cermet sintered body. The EDS analysis is performed by area analysis of a 10 μm × 10 μm region centered on the above-mentioned analysis position. In this case, Ti was converted into carbonitride, and W, Mo, Cr, Ta, Nb, and Zr were converted into carbides, and the values were calculated as the contents (mass%) of each phase. Specifically, the hard phase and binder phase contents (mass%) can be measured by the method described in the Examples below.

In the cermet sintered body of this embodiment, the hard phase includes: (i) a first hard phase having a cubic crystal structure that exhibits a diffraction peak derived from the (422) plane at an angle of 123.5° or more and 125.0° or less in XRD measurement; and (ii) a second hard phase having a cubic crystal structure that exhibits a diffraction peak derived from the (422) plane at an angle of 121.0° or more and less than 123.5° in XRD measurement.

In this embodiment, the first hard phase and the second hard phase can be identified by a BSE observation image of the cross-sectional structure inside the cermet sintered body. Figure 1 is an example of a BSE observation image of the cross-sectional structure inside the cermet sintered body. In this BSE observation image, the areas with black contrast are the first hard phase (1), the areas with gray to white contrast are the second hard phase (6) (second hard phase a (2), another second hard phase b (3), and yet another second hard phase c (4)), and the elongated white areas between these hard phases are the binder phase (5).

In the cermet sintered body of this embodiment, the ratio of the first hard phase to the second hard phase is evaluated as follows. The integrated intensities of the two diffraction peaks resulting from each hard phase identified in the above-described XRD measurement of the hard phases are calculated. The ratio of the integrated intensity of the diffraction peak resulting from the (422) plane of the first hard phase to the integrated intensity of the diffraction peak resulting from the (422) plane of the second hard phase (first hard phase:second hard phase) is preferably 1.0:1.5 to 1.0:3.5, and more preferably 1.0:2.0 to 1.0:3.0.

The first hard phase is a phase containing a carbonitride, carbide, or nitride containing at least one element selected from the group consisting of Ti, W, Mo, Cr, Ta, Nb, V, Hf, and Zr. It is preferably a phase containing a carbonitride or carbide containing at least one element selected from the group consisting of Ti, W, Mo, Cr, Ta, Nb, and Zr, and more preferably a phase containing a carbonitride containing at least one element selected from the group consisting of Ti, W, Mo, Nb, and Zr.

The second hard phase is a phase containing a carbonitride, carbide, or nitride containing at least one element selected from the group consisting of Ti, W, Mo, Cr, Ta, Nb, V, Hf, and Zr. Preferably, the second hard phase is a phase containing a carbonitride or carbide containing at least one element selected from the group consisting of Ti, W, Mo, Cr, Ta, Nb, and Zr, and more preferably a phase containing a carbonitride containing at least one element selected from the group consisting of Ti, W, Mo, Nb, and Zr.

In the cermet sintered body of this embodiment, the residual stress of the second hard phase is -1000 MPa or more and -600 MPa or less. When the residual stress of the second hard phase is -1000 MPa or more, embrittlement of the hard phase is suppressed, and the fracture resistance of the cermet sintered body is improved. On the other hand, when the residual stress of the second hard phase is -600 MPa or less, the toughness of the hard phase is improved, and the cermet sintered body has excellent fracture resistance. From the same perspective, the residual stress of the second hard phase is preferably -950 MPa or more and -650 MPa or less, and more preferably -900 MPa or more and -700 MPa or less.

Residual stress refers to the internal stress (intrinsic strain) remaining in the hard phase and bonding phase. Generally, stress expressed as a "-" (negative) number is referred to as compressive stress, and stress expressed as a "+" (positive) number is referred to as tensile stress. In this embodiment, when expressing the magnitude of residual stress, the larger the "+" (positive) number, the greater the residual stress; and the larger the "-" (negative) number, the smaller the residual stress.

In this embodiment, the residual stress of the second hard phase can be measured by the sin ² ψ method using XRD. It is evaluated using the diffraction peak derived from the (422) plane of the second hard phase having a cubic crystal structure. This peak is present at a position of 121.0° or more and less than 123.5° in 2θ-θ measurement. Specifically, the residual stress of the second hard phase can be measured by the method described in the examples below.

In the cermet sintered body of this embodiment, the residual stress of the binder phase is -600 MPa or more and -200 MPa or less. When the residual stress of the binder phase is -600 MPa or more, embrittlement of the binder phase is suppressed, and the fracture resistance of the cermet sintered body is improved. On the other hand, when the residual stress of the binder phase is -200 MPa or less, the toughness of the binder phase is improved, and the fracture resistance of the cermet sintered body is excellent. Furthermore, when the residual stress of the binder phase is -200 MPa or less, the binder phase hardens, and the wear resistance of the cermet sintered body is improved. From the same perspective, the residual stress of the binder phase is preferably -550 MPa or more and -250 MPa or less, and more preferably -500 MPa or more and -300 MPa or less.

In this embodiment, the residual stress of the binder phase can be measured by the sin ² ψ method using XRD. Among the diffraction peaks derived from the binder phase having a cubic crystal structure, the diffraction peak derived from the (311) plane is used for evaluation. This peak is present at a position between 89.5° and 93.0° in 2θ-θ measurement. Specifically, the residual stress of the binder phase can be measured by the method described in the Examples below.

In the cermet sintered body of this embodiment, the thickness of the first hard phase-enriched region is 0 μm or more and 1.0 μm or less. When the thickness of the first hard phase-enriched region is 1.0 μm or less, the wear resistance and plastic deformation resistance of the cermet sintered body are improved. From the same perspective, the thickness of the first hard phase-enriched region is preferably 0.5 μm or less, and more preferably 0 μm.

In this embodiment, the thickness of the first hard phase-enriched region is calculated using the following method. First, in a BSE observation image of a cross section perpendicular to the surface of the sintered cermet, lines parallel to the surface of the sintered cermet are drawn at 0.5 μm intervals from the surface of the sintered cermet inward. When the length of the lines is taken as 100%, the thickness of the first hard phase-enriched region is determined as the shortest distance between the surface of the sintered cermet and a line segment that crosses the first hard phase at a rate of less than 30%. In this case, the length of the line segment is set to 20 μm or more.

In the cermet sintered body of this embodiment, the surface binder phase ratio is 0.80 or more and 0.95 or less. When the surface binder phase ratio is 0.80 or more, the ratio of the binder phase increases relatively, and the cermet sintered body has excellent chipping resistance. On the other hand, when the surface binder phase ratio is 0.95 or less, the ratio of the hard phase increases relatively, and the cermet sintered body has excellent wear resistance and plastic deformation resistance. From the same perspective, the surface binder phase ratio is preferably 0.81 or more and 0.91 or less, and more preferably 0.83 or more and 0.88 or less.

In this embodiment, the surface binder phase ratio is calculated using the following method. First, EDS is used to analyze the mass percentages of Co, Ni, and Fe at a position 10 μm inward from the surface of the cermet sintered body (surface portion) and at a position 500 μm or more inward from the surface of the cermet sintered body (interior portion). The EDS analysis is performed by area analysis of a 10 μm x 10 μm area centered on the above analysis position. The surface binder phase ratio is calculated by dividing the sum of the mass percentages of Co, Ni, and Fe in the surface portion by the sum of the mass percentages of Co, Ni, and Fe in the interior.

In the cermet sintered body of this embodiment, the surface nitrogen ratio calculated by the following method (hereinafter also simply referred to as "surface nitrogen ratio") is preferably 0.42 or more and 0.50 or less.
(Calculation method for surface nitrogen ratio)
Using EDS, the mass percentages of N and C elements are analyzed at a position 10 μm inward from the surface of the cermet sintered body. The EDS analysis is performed by area analysis of a 10 μm × 10 μm area centered on the above analysis position. The ratio of N element to the total of N and C elements is defined as the surface nitrogen percentage.

In the cermet sintered body of this embodiment, a surface nitrogen ratio of 0.42 or more indicates that the body contains a certain amount of N element, which makes it difficult for the hard particles to react with the workpiece during cutting, suppressing the progression of reactive wear and tending to improve wear resistance. Furthermore, a surface nitrogen ratio of 0.42 or more tends to improve the machined surface of the workpiece. On the other hand, a surface nitrogen ratio of 0.50 or less suppresses the generation of voids due to denitrification during sintering, and the cermet sintered body tends to have excellent fracture resistance. From the same perspective, the surface nitrogen ratio is more preferably 0.43 or more and 0.48 or less, and even more preferably 0.44 or more and 0.46 or less.

Next, an example of a method for manufacturing the cermet sintered body of this embodiment will be described. Note that the method for manufacturing the cermet sintered body of this embodiment is not particularly limited as long as it can achieve the above-mentioned configuration.

The method for manufacturing the cermet sintered body of this embodiment includes, for example, the following steps 1 to 11.

Step 1 is a step of blending the raw material powders (blending step). Specific examples include, but are not limited to, blending 82 to 93 mass% of at least one powder selected from the group consisting of carbonitrides, carbides, and nitrides containing at least one element selected from the group consisting of Ti, W, Mo, Cr, Ta, Nb, V, Hf, and Zr, each having an average particle size of 0.5 to 4.0 μm, and 7 to 18 mass% of at least one powder selected from the group consisting of Co, Ni, and Fe, each having an average particle size of 0.5 to 3.0 μm (the total of these amounts being 100 mass%). Specific examples of the raw material powder include, but are not limited to, powders of TiC _0.5 N _0.5 , TiC _0.3 N _0.7 , WC, TaC, NbC, ZrC, Mo ₂ C, Cr ₃ C ₂ , VC, HfC, Co, Ni, and Fe.

Step 2 is a mixing step in which the raw material powders blended in Step 1 are mixed together with a solvent using a wet ball mill. Here, the mixing time for the raw material powders is preferably 10 to 40 hours.

Step 3 is the step of drying the powder mixed in Step 2 (drying step). Here, the drying temperature is preferably 100°C or less.

Step 4 is a molding step (molding step) in which the mixed powder dried in step 3 is molded into a predetermined shape. Specifically, in the molding step, it is preferable to press and mold the mixed powder using, for example, a mold having a predetermined tool shape. Furthermore, in the molding step, adding paraffin, for example, tends to improve moldability.

Step 5 is a step (first heating step) in which the molded body obtained in step 4 is heated from room temperature to a predetermined temperature (ultimate temperature) in a vacuum atmosphere. The ultimate temperature in the first heating step is the starting temperature of the second heating step, and is preferably 1300 to 1440°C, for example. In the first heating step, the pressure is preferably 70 Pa or less.

Step 6 is a step (second heating step) in which the molded body is heated to a predetermined temperature (ultimate temperature) in an _N2 gas atmosphere after Step 5. The starting temperature of the second heating step is preferably 1300 to 1440°C, for example. The ultimate temperature of the second heating step is the temperature of the sintering step, and is preferably 1450 to 1550°C. In the second heating step, the pressure is preferably 133 to 6650 Pa.

Step 7 is a sintering step (after Step 6) in which the compact is sintered by holding it at a predetermined temperature in a _N2 gas atmosphere. The sintering temperature is preferably 1450 to 1550°C, and more preferably 1480 to 1550°C. In the sintering step, the pressure is preferably 70 to 600 Pa. The sintering time is preferably 30 to 120 minutes.

Step 8: The cermet sintered body obtained in Step 7 is cooled to a predetermined temperature in a vacuum atmosphere (first cooling step). Here, the first cooling start temperature is the sintering temperature, and is preferably 1450 to 1550°C, for example. The first cooling end temperature is preferably 1300 to 1350°C, for example. In the first cooling step, the cooling rate is preferably 20°C/min or less, and more preferably 3 to 15°C/min. In the first cooling step, the pressure is preferably 133 Pa or less.

Step 9, after Step 8, is a step (second cooling step) in which the cermet sintered body is cooled to room temperature in an inert gas atmosphere. Here, the second cooling start temperature is the first cooling end temperature, and is preferably, for example, 1300 to 1350°C. The second cooling end temperature is room temperature. In the second cooling step, the pressure is preferably 133 to 300,000 Pa. Specific examples of the inert gas atmosphere in the second cooling step include, but are not limited to, He, Ne, and Ar gas atmospheres.

Step 10, after step 9, is the honing process, in which the cutting edge of the sintered cermet is honed. Here, the desired honing shape is achieved.

Step 11 is a blasting step (after step 10) in which particles of a shot material such as alumina (Al ₂ O ₃ ) are collided with the surface of the sintered cermet. Here, the blasting method is preferably a dry method. In the blasting step, the average particle size of the shot material particles is preferably 100 to 150 μm. In the blasting step, the projection angle (when formed into the shape of a tool, the inclination angle from the normal to the rake face of the tool) is preferably 30 to 60 degrees. In the blasting step, the projection speed is preferably 70 to 150 m/sec, and more preferably 70 to 130 m/sec.

The average particle size of the raw material powder used in step 1 can be measured using the Fisher Sub-Sieve Sizer (FSSS) method described in American Society for Testing and Materials (ASTM) standard B330.

The steps in the manufacturing method of the cermet sintered body of this embodiment have the following significance:

In step 1 (blending step), the blending ratio of each raw material powder can be adjusted to achieve the desired composition of the sintered cermet.

In step 2 (mixing step), a mixture can be obtained in which raw material powders of a predetermined composition are uniformly mixed. Furthermore, the particle size of the raw material powder can be adjusted, allowing for the structure and particle size of the sintered body to be controlled.

In step 3 (drying step), the solvent is evaporated from the mixture to obtain a mixed powder.

In step 4 (molding step), a molded body of the desired tool shape is obtained from the mixed powder. Adding paraffin improves moldability.

Step 5 (first heating step) promotes degassing before and immediately after the liquid phase appears, and also improves the sinterability in the following step 7 (sintering step).

In step 6 (second heating step), the temperature can be raised to the sintering temperature while suppressing denitrification from the compact. By combining this step 6 (second heating step) with the following step 7 (sintering step), the proportion of surface bonded phase can be reduced.

In step 7 (sintering step), the compact is sintered by holding it at a predetermined temperature to obtain a sintered cermet and reduce the proportion of surface binder phase.

In step 8 (first cooling step), a first hard phase-enriched region can be formed. The surface nitrogen ratio can also be adjusted.

In step 9 (second cooling step), the cermet sintered body can be cooled to room temperature.

In step 10 (honing step), the cutting edge of the tool-shaped cermet sintered body is given a predetermined honing shape.

In step 11 (blasting step), compressive residual stress can be imparted to the second hard phase and the binder phase. As a blasting method, dry blasting can impart higher compressive residual stress than wet blasting. On the other hand, wet blasting tends to have a stronger grinding force on the sintered body surface than dry blasting.

In the cermet sintered body of this embodiment, the method for forming the two hard phases, the first hard phase and the second hard phase, is not particularly limited. For example, the first hard phase and the second hard phase can be obtained in the above-described manufacturing method by using, as the raw material powder consisting of carbonitride, carbide, or nitride, a powder of Ti carbonitride, carbide, or nitride and a powder of carbonitride, carbide, or nitride containing at least one element selected from the group consisting of W, Mo, Cr, Ta, Nb, V, Hf, and Zr. Furthermore, increasing the blending ratio of Ti carbonitride, carbide, or nitride powder tends to increase the integrated intensity of the diffraction peak derived from the (422) plane of the first hard phase, as determined by XRD measurement.

One method for controlling the thickness of the first hard phase-enriched region within the desired range is to adjust the starting temperature of the second heating step (the temperature reached in the first heating step) in the above-mentioned manufacturing method. Specifically, if the starting temperature of the second heating step is increased within the starting temperature range of the second heating step described above (1300 to 1440°C), the thickness of the first hard phase-enriched region tends to decrease.

Methods for controlling the surface bonded phase proportion within the desired range include using a dry rather than wet blasting method in the above-mentioned manufacturing method, and adjusting the starting temperature of the second heating step (the temperature reached in the first heating step), adjusting the cooling rate of the first cooling step, or adjusting the sintering temperature of the sintering step. Specifically, if a dry rather than wet blasting method is used, and the starting temperature of the second heating step is lowered, the cooling rate of the first cooling step is slowed, or the sintering temperature of the sintering step is increased, the surface bonded phase proportion tends to decrease.

One method for controlling the residual stress of the second hard phase within the desired range is to use a dry blasting method instead of a wet blasting method in the above-mentioned manufacturing method and adjust the projection speed during the blasting process. Specifically, if a dry blasting method instead of a wet blasting method is used and the projection speed during the blasting process is increased, the residual stress in the second hard phase tends to be reduced.

One method for controlling the residual stress of the binder phase within the desired range is to use a dry blasting method rather than a wet blasting method in the above-mentioned manufacturing method and adjust the projection speed during the blasting process. Specifically, if a dry blasting method rather than a wet blasting method is used and the projection speed during the blasting process is increased, the residual stress in the second hard phase tends to be reduced.

One method for controlling the surface nitrogen ratio within the desired range in the above-mentioned manufacturing method is to use a dry blasting process rather than a wet blasting process, and adjust the starting temperature of the second heating process (the temperature reached in the first heating process), the cooling rate of the first cooling process, or the sintering temperature of the sintering process. Specifically, if a dry blasting process rather than a wet blasting process is used, and the starting temperature of the second heating process is lowered, the cooling rate of the first cooling process is slowed, or the sintering temperature of the sintering process is increased, the surface nitrogen ratio tends to decrease.

The cermet sintered body of this embodiment may further be coated on its surface with a hard film by conventional physical vapor deposition or chemical vapor deposition methods.

The cermet sintered body of this embodiment can be used, for example, as an indexable cutting insert for milling or turning, a drill, an end mill, etc., without any particular limitation.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

Example 1
[Production of sintered cermet]
As raw material powders, commercially available TiC _0.5 N _0.5 powder with an average particle size of 2.0 μm, TiC _0.3 N _0.7 powder with an average particle size of 2.0 μm, WC powder with an average particle size of 1.5 μm, TaC powder with an average particle size of 1.5 μm, NbC powder with an average particle size of 1.5 μm, ZrC powder with an average particle size of 1.5 μm, Mo ₂ C powder with an average particle size of 1.5 μm, Cr ₃ C ₂ powder with an average particle size of 1.5 μm, Co powder with an average particle size of 1.0 μm, Ni powder with an average particle size of 1.0 μm were prepared. The average particle size of the raw material powders was measured by the Fisher method (Fisher Sub-Sieve Sizer (FSSS)) according to the American Society for Testing and Materials (ASTM) standard B330.

The prepared raw material powders were weighed out to obtain the composition shown in Table 1 below. Each weighed raw material powder was placed in a stainless steel pot together with an acetone solvent and cemented carbide balls, and mixed and pulverized in a wet ball mill. The mixing and pulverization time in the wet ball mill was 15 hours.

After mixing and grinding using a wet ball mill, the mixture was dried at 60°C to evaporate the acetone solvent and obtain a mixed powder.

3.0% by mass of paraffin was added to the resulting mixed powder, which was then press-molded at a pressure of 100 MPa using a mold that would result in an insert shape of TNMG160404 after sintering, to obtain a compact of the mixed powder.

The obtained molded body was heated in a vacuum atmosphere from room temperature to the starting temperature of the second heating step shown in Table 2 (first heating step). Furthermore, the pressure during the first heating step was set to 50 Pa.

Thereafter, the molded body was heated in an _N gas atmosphere from the starting temperature of the second heating step shown in Table 2 to the temperature of the sintering step shown in Table 2 (second heating step). In the second heating step, the pressure was 600 Pa.

Thereafter, the compact was sintered in an _N2 gas atmosphere at a temperature shown in Table 2 (sintering step). In the sintering step, the pressure was 270 Pa and the sintering time was 60 minutes.

The obtained sintered cermet body was cooled in a vacuum atmosphere from the sintering temperature shown in Table 2 to 1350°C (first cooling step). In the first cooling step, the cooling rate was as shown in Table 2, and the pressure was 90 Pa.

The cermet sintered body was then cooled from the first cooling temperature of 1,350°C to room temperature in an Ar gas atmosphere (second cooling process). The pressure during the second cooling process was 100,000 Pa.

Then, the cutting edge of the sintered cermet was subjected to a round honing process using a SiC brush (honing process).

Thereafter, a blasting process was carried out in which alumina ( _Al2O3 ) particles were used as shot material and collided with the surface of _the sintered cermet. The blasting method was as shown in Table 2. In the blasting process, the average particle size of the shot material particles was 120 μm, and the projection angle was 45 degrees. The projection speed was as shown in Table 2.

In this manner, invention products 1 to 16 and comparison products 1 to 13 were produced.

The cermet sintered bodies of Invention Products 1 to 16 and Comparative Products 1 to 13 were observed with an EDS-equipped SEM at a position 500 μm inward from the surface of the cermet sintered body in a cross section perpendicular to the surface of the cermet sintered body, and the compositions of the hard phase and binder phase were identified.
The hard phase and binder phase contents (mass%) of the cermet sintered bodies of Invention Products 1 to 16 and Comparative Products 1 to 13 were measured using EDS at a position 500 μm inward from the surface of the cermet sintered body in a cross section perpendicular to the surface of the cermet sintered body. The EDS analysis was performed using an area analysis of a 10 μm x 10 μm region centered on the above analysis position. Ti was considered to be a carbonitride, and W, Mo, Cr, Ta, Nb, and Zr were considered to be carbides, and the converted values were used to calculate the content (mass%) of each phase. The results are shown in Table 3.

XRD measurements were performed on the cermet sintered bodies of Invention Products 1 to 16 and Comparative Products 1 to 13, confirming that they contain a first hard phase having a cubic crystal structure that exhibits a diffraction peak derived from the (422) plane at an angle of 123.5° to 125.0°, and a second hard phase having a cubic crystal structure that exhibits a diffraction peak derived from the (422) plane at an angle of 121.0° to less than 123.5°. For Invention Products 1 to 16, the ratio of the integrated intensity of the diffraction peak derived from the (422) plane of the first hard phase to the integrated intensity of the diffraction peak derived from the (422) plane of the second hard phase (first hard phase:second hard phase) was within the range of 1.0:2.0 to 1.0:2.7. Specifically, the above XRD measurements were performed using the following method. X-ray diffraction using a 2θ/θ focusing optical system with Cu-Kα radiation was performed using a Rigaku Corporation X-ray diffractometer (product name: RINT TTRIII) under the following conditions to measure the peak intensity of each of the above plane indices. The measurement conditions were: output: 50 kV, 250 mA, incident-side Soller slit: 5°, divergence vertical slit: 2/3°, divergence vertical limiting slit: 5 mm, scattering slit 2/3°, receiving-side Soller slit: 5°, receiving slit: 0.3 mm, BENT monochromator, receiving monochromator slit: 0.8 mm, sampling width: 0.01°, scan speed: 4°/min, 2θ measurement range: 20° to 140°.

The first and second hard phases were identified using BSE observation images of the cross-sectional structure inside the sintered cermet.

For the cermet sintered bodies of Invention Products 1 to 16 and Comparative Products 1 to 13, the residual stress of the second hard phase was measured by the sin ² ψ method using XRD. Evaluation was performed using the diffraction peak derived from the (422) plane of the second hard phase having a cubic crystal structure. In 2θ-θ measurement, this peak was present at a position between 121.0° and 123.5°. The results are shown in Table 4.

The residual stress of the binder phase of the cermet sintered bodies of Invention Products 1 to 16 and Comparative Products 1 to 13 was measured by the sin ² ψ method using XRD. Among the diffraction peaks derived from the binder phase having a cubic crystal structure, the diffraction peak derived from the (311) plane was used for evaluation. In 2θ-θ measurement, this peak was present at a position between 89.5° and 93.0°. The results are shown in Table 4.

For the cermet sintered bodies of Invention Products 1 to 16 and Comparative Products 1 to 13, the thickness of the first hard phase-enriched region was calculated using the following method. First, in the BSE observation image of a cross section perpendicular to the surface of the cermet sintered body, lines parallel to the surface of the cermet sintered body were drawn at 0.5 μm intervals from the surface of the cermet sintered body inward. When the length of the line was taken as 100%, the thickness of the first hard phase-enriched region was determined as the shortest distance between the surface of the cermet sintered body and the line segment where the proportion of the line segment crossing the first hard phase was less than 30%. The length of the line segment was set to 20 μm. The results are shown in Table 4.

The surface binder phase proportion for the cermet sintered bodies of Invention Products 1-16 and Comparative Products 1-13 was calculated using the following method. First, the mass percentages of Co, Ni, and Fe were analyzed using EDS at a position 10 μm inward from the surface of the cermet sintered body (surface region) and at a position 500 μm or more inward from the surface of the cermet sintered body (interior region). The EDS analysis was performed by area analysis of a 10 μm x 10 μm region centered on the above analysis position. The surface binder phase proportion was calculated by dividing the sum of the mass percentages of Co, Ni, and Fe in the surface region by the sum of the mass percentages of Co, Ni, and Fe in the interior region. The results are shown in Table 4.

The surface nitrogen ratio for the cermet sintered bodies of Invention Products 1-16 and Comparative Products 1-13 was calculated using the following method. Using EDS, the mass percentages of N and C elements were analyzed at a position 10 μm inward from the surface of the cermet sintered body. The EDS analysis was performed as a surface analysis of a 10 μm x 10 μm area centered on the above analysis position. The ratio of N element to the total of N and C element was taken as the surface nitrogen ratio. The results are shown in Table 4.

Cutting Test 1 and Cutting Test 2 were conducted using the resulting sintered cermets of Invention Products 1-16 and Comparative Products 1-13. Cutting Test 1 evaluated chipping resistance, while Cutting Test 2 evaluated wear resistance and plastic deformation resistance. The results of Cutting Tests 1 and 2 are shown in Table 5.

[Cutting test 1]
Work material: SCM415,
Workpiece shape: Round bar with two equally spaced grooves on the side,
Cutting speed: 200m/min,
Cutting depth: 1.0 mm,
Feed: 0.15 mm/rev.
Coolant: Wet,
Insert: TNMG160404,
Evaluation items: The tool life was determined when the cutting edge of the tool was chipped, and the number of impacts until the tool life was reached was measured.

[Cutting test 2]
Work material: S45C,
Workpiece shape: round bar,
Cutting speed: 250m/min,
Cutting depth: 1.0 mm,
Feed: 0.20 mm/rev.
Coolant: Wet,
Insert: TNMG160404,
Evaluation items: The tool life was determined to be when the cutting edge of the tool was chipped or when the wear width of the flank of the tool reached 0.2 mm, and the machining time until the tool life was reached was measured.

In Cutting Test 1, the number of impacts until the end of tool life was evaluated as A for 20,000 or more, B for 15,000 to less than 20,000, and C for less than 15,000. Furthermore, in Cutting Test 2, the processing time until the end of tool life was evaluated as A for 30 minutes or more, B for 25 to less than 30 minutes, and C for less than 25 minutes. This evaluation is ranked as A (excellent) > B > C (poor), with the higher the A rating, the better the cutting performance.

From the results in Table 5, it was found that all of the cermet sintered bodies of the invention were rated B or higher in both cutting tests 1 and 2, and were excellent in fracture resistance, wear resistance, and plastic deformation resistance. On the other hand, the comparative cermet sintered bodies were rated C in at least one of cutting tests 1 and 2, and were inferior in at least one of fracture resistance, wear resistance, and plastic deformation resistance. From the above, it was found that the cermet sintered bodies of the invention were superior in cutting performance and had a longer tool life than the comparative cermet sintered bodies.
It is considered that the proportion of the surface binder phase in the cermet sintered compact of Comparative Example 11 was increased because a large amount of the surface was removed, which resulted in the cermet sintered compact of Comparative Example 11 exhibiting poor cutting performance in Cutting Test 2 and shortening the tool life.
When the temperature of the second heating step, the temperature of the sintering step, and the cooling rate of the first cooling step were adjusted so that the proportion of the surface bonding phase was smaller than that of Comparative Product 11, the sintered body was severely deformed, and the desired tool shape could not be obtained, making it impossible to evaluate the cutting performance.

The cermet sintered body of the present invention has excellent chipping resistance, wear resistance, and plastic deformation resistance, and can extend tool life compared to conventional products, making it highly applicable industrially.

1: First hard phase, 2: Second hard phase a, 3: Another second hard phase b, 4: Yet another second hard phase c, 5: Binder phase, 6: Second hard phase

Claims (2)

A cermet sintered body comprising a hard phase and a binder phase,
The hard phase is a phase containing at least one selected from the group consisting of TiCN, WC , TaC, NbC, ZrC, _Mo2C and _{Cr3C2 ,}
the binder phase is a phase consisting of Co and Ni,
The content of the hard phase is 82% by mass or more and 93% by mass or less,
The content of the binder phase is 7% by mass or more and 18% by mass or less,
the TiCN content is 49.3 mass% or more and 60.0 mass% or less, the WC content is 20.0 mass% or more and 30.0 mass% or less, the Co content is 3.7 mass% or more and 9.5 mass% or less, the Ni content is 3.3 mass% or more and 8.5 mass% or less, and the total content of the TaC, NbC, ZrC, Mo2C _{, and} Cr3C2 _is the balance (wherein the total content of TiCN, WC, TaC, NbC, ZrC, Mo2C , Cr3C2 _, Co _, and Ni is 100.0 mass%) _;
The hard phase is
(i) a first hard phase having a cubic crystal structure that exhibits a diffraction peak derived from the (422) plane at an angle of 123.5° or more and 125.0° or less in X-ray diffraction (XRD) measurement;
(ii) a second hard phase having a cubic crystal structure that exhibits a diffraction peak derived from the (422) plane at an angle of 121.0° or more and less than 123.5° in X-ray diffraction (XRD) measurement;
Including,
the residual stress of the second hard phase is −1000 MPa or more and −600 MPa or less,
The residual stress of the binder phase is −600 MPa or more and −200 MPa or less,
The thickness of the first hard phase enriched region is 0 μm or more and 1.0 μm or less,
A cermet sintered body having a surface binder phase ratio of 0.80 or more and 0.95 or less. The cermet sintered body according to claim 1, wherein the surface nitrogen ratio is 0.42 or more and 0.50 or less.