sintered cermet

Abstract

To provide a cermet compact excellent in defect resistance, excellent also in wear resistance and resistance to plastic deformation, and capable of extending a tool life.SOLUTION: A cermet compact containing a hard phase and a binder phase, wherein the hard phase is a phase containing a carbonitride, carbide or nitride containing a specific component, the binder phase is a phase containing a specific component, and a hard phase content is 82 mass% or more and 93 mass% or less, the binder phase content is 7 mass% or more and 18 mass% or less, and the hard phase (i) contains the first hard phase and second hard phase having a cubic crystal structure exhibiting a specific diffraction peak in XRD measurement, wherein the residual stress of the second hard phase is -1000 MPa or more and -600 MPa or less, and the residual stress of the binder phase is -600 MPa or more and -200 MPa or less, wherein the thickness of the first hard phase-rich region is 0 μm or more and 1.0 μm or less, and the surface bonding phase ratio is 0.80 or more and 0.95 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a sintered cermet body. [Background technology]

[0002] Cermet tools have superior resistance to reactivity with iron and high-temperature strength compared to cemented carbide tools, and are therefore widely used in the finishing of iron-based materials.

[0003] 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 a 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 of the hard phase in the surface portion of the insert is 450 MPa or more in compressive stress. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2011-088239 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been an increasing demand for higher speeds and lower labor costs in cutting processes, which has led to a trend toward higher speed cutting and heavy cutting, such as high feed rates and large depths of cut. Under such severe high-speed cutting conditions, tool life tends to be shorter than before.

[0006] 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, but this is still not sufficient.In addition, the cermet cutting insert described in Patent Document 1 does not have improved wear resistance and plastic deformation resistance, making it difficult to extend the tool life in high-speed cutting.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sintered cermet that has excellent chipping resistance, wear resistance, and plastic deformation resistance, and that can extend tool life. [Means for solving the problem]

[0008] The present inventors have conducted extensive research into extending the tool life of sintered cermets, and have found that when a sintered cermet has a specific configuration, it is possible to provide excellent fracture resistance and improve wear resistance and plastic deformation resistance, thereby extending the tool life of the sintered cermet. This finding led to the completion of the present invention.

[0009] 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, carbide or nitride containing at least one 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 the surface nitrogen ratio is 0.42 or more and 0.50 or less. [Effects of the Invention]

[0010] The cermet sintered body of the present invention is excellent in chipping resistance, wear resistance, and plastic deformation resistance, and can extend the tool life. [Brief explanation of the drawings]

[0011] [Figure 1] This is an example of a backscattered electron (BSE) observation image of the cross-sectional structure inside a sintered cermet. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail, but the present invention is not limited to the following embodiment. The present invention can be modified in various ways without departing from the gist of the invention. In the drawings, the same elements are given the same reference numerals, and redundant explanations will be omitted. Furthermore, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown.

[0013] 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 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 selected from the group consisting of Co, Ni, and Fe, the content of the hard phase being 82% by mass or more and 93% by mass or less, the content of the binder phase being 7% by mass or more and 18% by 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 shows 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 following method (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 following method (hereinafter also simply referred to as "surface binder phase ratio") is 0.80 or more and 0.95 or less. (Method of 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 inward from the surface of the cermet sintered body at 0.5 μm intervals. When the length of the lines is taken as 100%, the shortest distance between the line segment that crosses the first hard phase at a rate of less than 30% and the surface of the cermet sintered body 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 for calculating the surface bonded phase ratio) In a cross section perpendicular to the surface of the sintered cermet, a scanning electron microscope (hereinafter also referred to as "SEM") equipped with an energy dispersive X-ray analyzer (hereinafter also referred to as "EDS") is used to analyze the mass percentages of Co, Ni, and Fe at a position 10 μm inward from the surface of the sintered cermet (surface region) and at a position 500 μm or more inward from the surface of the sintered cermet (interior region). The EDS analysis is performed by area analysis of a 10 μm x 10 μm region 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 region by the sum of the mass percentages of Co, Ni, and Fe in the interior region.

[0014] The factors that enable such a cermet sintered body to have excellent fracture resistance, improved wear resistance and plastic deformation resistance, and extended tool life are not fully understood, but the present inventors believe that the factors are as follows. However, the factors are not limited to these. That is, 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, so the cermet sintered body has 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 hard phase content increases relatively, so the cermet sintered body has 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. On the other hand, 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. On the other hand, 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 ratio of the binder phase increases relatively, and the cermet sintered body has excellent fracture 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. 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.

[0015] In the cermet sintered body of the present embodiment, the hard phase is a phase containing a carbonitride, carbide or nitride containing at least one 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 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 selected from the group consisting of Ti, W, Mo, Nb and Zr.

[0016] 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.

[0017] In the cermet sintered body of this embodiment, the binder phase is a phase containing at least one selected from the group consisting of Co, Ni, and Fe, preferably a phase containing at least one selected from the group consisting of Co and Ni, and more preferably a phase consisting of Co and Ni.

[0018] In the cermet sintered body of this embodiment, the content of the hard phase is 82% by mass or more and 93% by mass or less. When the content of the hard phase 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 content of the hard phase is 93% by mass or less, the content of the binder phase relatively increases, so the cermet sintered body has improved toughness and excellent fracture resistance. From the same viewpoint, the content of the hard phase 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.

[0019] 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 fracture resistance. On the other hand, when the binder phase content is 18% by mass or less, the content of the hard phase relatively increases, so the cermet sintered body has improved hardness and excellent wear resistance and plastic deformation resistance. From the same viewpoint, 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.

[0020] In this embodiment, the content ratios (mass%) of the hard phase and the binder phase are the content ratios (mass%) relative to a total of 100 mass% of the carbonitride, carbide or nitride containing at least one selected from the group consisting of Ti, W, Mo, Cr, Ta, Nb, V, Hf and Zr, and at least one 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 content (mass%) of each phase was calculated. Specifically, the hard phase and binder phase contents (mass%) can be measured by the method described in the Examples below.

[0021] 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.

[0022] 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. Fig. 1 is an example of a BSE observation image of the cross-sectional structure inside the cermet sintered body. In the BSE observation image, the part with black contrast is the first hard phase (1), the part with gray to white contrast is 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 part between these hard phases is the binder phase (5).

[0023] 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 intensity of two diffraction peaks derived from each hard phase identified in the above-mentioned XRD measurement of the hard phases is calculated. 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) is preferably 1.0:1.5 to 1.0:3.5, and more preferably 1.0:2.0 to 1.0:3.0.

[0024] The first hard phase is a phase containing a carbonitride, carbide or nitride containing at least one 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 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 selected from the group consisting of Ti, W, Mo, Nb and Zr.

[0025] The second hard phase is a phase containing a carbonitride, carbide or nitride containing at least one 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 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 selected from the group consisting of Ti, W, Mo, Nb and Zr.

[0026] 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 viewpoint, 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.

[0027] Residual stress is an internal stress (intrinsic strain) remaining in the hard phase and the bonding phase, and generally, stress represented by a "-" (minus) numerical value is called compressive stress, and stress represented by a "+" (plus) numerical value is called tensile stress. In this embodiment, when expressing the magnitude of residual stress, the larger the "+" (plus) numerical value, the larger the residual stress, and the larger the "-" (minus) numerical value, the smaller the residual stress.

[0028] In this embodiment, the residual stress of the second hard phase is measured by sin 2 It can be measured by the ψ method. It is evaluated using the diffraction peak derived from the (422) plane of the second hard phase having a cubic crystal structure. In 2θ-θ measurement, the peak exists at a position of 121.0° or more and less than 123.5°. Specifically, the residual stress of the second hard phase can be measured by the method described in the examples below.

[0029] 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 is hardened, and the wear resistance of the cermet sintered body is improved. From the same viewpoint, 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.

[0030] In this embodiment, the residual stress of the binder phase is measured by using XRD. 2 It can be measured by the ψ method. Among the diffraction peaks originating from the binder phase having a cubic crystal structure, the diffraction peak originating from the (311) plane is used for evaluation. This peak is present at a position of 89.5° to 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.

[0031] 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 viewpoint, the thickness of the first hard phase-enriched region is preferably 0.5 μm or less, and more preferably 0 μm.

[0032] In this embodiment, the thickness of the first hard phase-enriched region is calculated by the following method. First, in a BSE observation image of a cross section perpendicular to the surface of the cermet sintered body, line segments parallel to the surface of the cermet sintered body are drawn inward from the surface of the cermet sintered body at 0.5 μm intervals. When the length of the line segments is taken as 100%, the thickness of the first hard phase-enriched region is determined as 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%. In this case, the length of the line segments is set to 20 μm or more.

[0033] 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 relatively increases, and the cermet sintered body has excellent fracture resistance. On the other hand, when the surface binder phase ratio is 0.95 or less, the ratio of the hard phase relatively increases, and the cermet sintered body has excellent wear resistance and plastic deformation resistance. From the same viewpoint, 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.

[0034] In this embodiment, the surface binder phase ratio is calculated by 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 × 10 μm region 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.

[0035] 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 sintered cermet. The EDS analysis is performed by area 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 elements is taken as the surface nitrogen percentage.

[0036] In the cermet sintered body of this embodiment, a surface nitrogen ratio of 0.42 or more indicates that the cermet contains a certain amount of N element, which makes it difficult for the hard particles to react with the workpiece during cutting, suppresses the progression of reactive wear, and tends 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.

[0037] Next, an example of a method for producing the cermet sintered body of this embodiment will be described. Note that the method for producing the cermet sintered body of this embodiment is not particularly limited as long as it can achieve the above-mentioned configuration.

[0038] The method for producing the cermet sintered body of this embodiment includes, for example, the following steps 1 to 11.

[0039] 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, or nitrides containing at least one selected from the group consisting of Ti, W, Mo, Cr, Ta, Nb, V, Hf, and Zr, with 7 to 18 mass% of at least one powder selected from the group consisting of Co, Ni, and Fe, with an average particle size of 0.5 to 3.0 μm (the total of these amounts is 100 mass%). Specific examples of the raw material powder include, but are not limited to, TiC 0.5 N 0.5 , TiC 0.3 N 0.7 , WC, TaC, NbC, ZrC, Mo2C, Cr3C2, VC, HfC, Co, Ni and Fe powders.

[0040] Step 2 is a step (mixing step) of mixing the raw material powders blended in step 1 together with a solvent using a wet ball mill. Here, the mixing time of the raw material powders is preferably 10 to 40 hours.

[0041] Step 3 is a step (drying step) of drying the powder mixed in step 2. Here, the drying temperature is preferably 100° C. or lower.

[0042] Step 4 is a step (molding step) of molding the mixed powder dried in step 3 into a predetermined shape. Specifically, in the molding step, it is preferable to press and mold the mixed powder using a mold having a predetermined tool shape. Furthermore, in the molding step, for example, adding paraffin tends to improve moldability.

[0043] 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, for example, 1300 to 1440° C. In the first heating step, the pressure is preferably 70 Pa or less.

[0044] Step 6 is a step (second heating step) of heating the compact 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.

[0045] Step 7 is a sintering step (after Step 6) in which the compact is sintered by holding it at a predetermined temperature in an 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.

[0046] Step 8: A step of cooling the cermet sintered body obtained in Step 7 to a predetermined temperature in a vacuum atmosphere (first cooling step). Here, the first cooling start temperature is the sintering temperature, and is preferably, for example, 1450 to 1550°C. The first cooling end temperature is preferably, for example, 1300 to 1350°C. 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.

[0047] Step 9 is a step (second cooling step) of cooling the cermet sintered body to room temperature in an inert gas atmosphere after step 8. Here, the second cooling start temperature is the first cooling end temperature, and is preferably set to, for example, 1300 to 1350°C. The second cooling end temperature is room temperature. In the second cooling step, the pressure is preferably set to 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.

[0048] Step 10 is a step (honing step) of honing the cutting edge of the cermet sintered body after step 9. Here, the cutting edge is adjusted to a desired honing shape.

[0049] Step 11 is a step (blasting step) that follows step 10 and involves impacting the surface of the sintered cermet with particles of alumina (Al2O3) or other shot material. 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.

[0050] The average particle size of the raw material powder used in step 1 can be measured by the Fisher method (Fisher Sub-Sieve Sizer (FSSS)) described in the American Society for Testing and Materials (ASTM) standard B330.

[0051] Each step in the method for producing the cermet sintered body of this embodiment has the following significance.

[0052] In step 1 (blending step), the blending ratio of each raw material powder can be adjusted to obtain a desired composition of the cermet sintered body.

[0053] In step 2 (mixing step), a mixture can be obtained by uniformly mixing raw material powders of a predetermined composition. In addition, the particle size of the raw material powder can be adjusted, and the texture and particle size of the sintered body can be controlled.

[0054] In step 3 (drying step), the solvent is evaporated from the mixture to obtain a mixed powder.

[0055] In step 4 (molding step), a molded body having a predetermined tool shape is obtained from the mixed powder. Adding paraffin improves moldability.

[0056] Step 5 (first temperature-raising step) promotes degassing before the appearance of the liquid phase and immediately after the appearance of the liquid phase, and can also improve the sinterability in the following step 7 (sintering step).

[0057] 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 the surface binder phase can be reduced.

[0058] In step 7 (sintering step), the compact is sintered by holding it at a predetermined temperature to obtain a sintered cermet, and the proportion of the surface binder phase can be reduced.

[0059] In step 8 (first cooling step), a first hard phase enriched region can be formed, and the surface nitrogen ratio can be adjusted.

[0060] In step 9 (second cooling step), the cermet sintered body can be cooled to room temperature.

[0061] In step 10 (honing step), the cutting edge of the tool-shaped cermet sintered body can be provided with a predetermined honing shape.

[0062] 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 a 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.

[0063] 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, but for example, the first hard phase and the second hard phase can be obtained by using a powder of Ti carbonitride, carbide, or nitride and a powder of carbonitride, carbide, or nitride containing at least one selected from the group consisting of W, Mo, Cr, Ta, Nb, V, Hf, and Zr as raw material powders composed of carbonitride, carbide, or nitride. Furthermore, increasing the blending ratio of the powder of Ti carbonitride, carbide, or nitride tends to increase the integrated intensity of the diffraction peak derived from the (422) plane of the first hard phase identified by XRD measurement.

[0064] As a method for controlling the thickness of the first hard phase-enriched region within a desired range, there is a method for adjusting the start temperature of the second heating step (the temperature reached in the first heating step) in the above-mentioned manufacturing method. Specifically, when the start temperature of the second heating step is increased within the above-mentioned range of the start temperature of the second heating step (1300 to 1440°C), the thickness of the first hard phase-enriched region tends to decrease.

[0065] A method for controlling the surface binder phase ratio within a desired range in the above-described manufacturing method includes adopting a dry blasting process instead of a wet blasting process, and adjusting the starting temperature of the second heating process (the temperature reached in the first heating process), adjusting the cooling rate of the first cooling process, or adjusting the sintering temperature of the sintering process. Specifically, adopting a dry blasting process instead of a wet blasting process, lowering the starting temperature of the second heating process, slowing the cooling rate of the first cooling process, or raising the sintering temperature of the sintering process tends to reduce the surface binder phase ratio.

[0066] One method for controlling the residual stress of the second hard phase within a desired range is to use a dry blasting method instead of a wet blasting method and adjust the projection speed in the blasting process in the above-mentioned manufacturing method. Specifically, if a dry blasting method instead of a wet blasting method is used and the projection speed in the blasting process is increased, the residual stress in the second hard phase tends to be reduced.

[0067] One method for controlling the residual stress of the binder phase within a desired range is to use a dry blasting method instead of a wet blasting method and adjust the projection speed in the blasting process in the above-mentioned manufacturing method. Specifically, if a dry blasting method instead of a wet blasting method is used and the projection speed in the blasting process is increased, the residual stress in the second hard phase tends to be reduced.

[0068] Methods for controlling the surface nitrogen ratio within a desired range include using a dry method instead of a wet method for the blasting process in the above-mentioned manufacturing method, and adjusting the starting temperature of the second heating process (the temperature reached in the first heating process), adjusting the cooling rate of the first cooling process, or adjusting the sintering temperature of the sintering process. Specifically, if a dry method instead of a wet method is used for the blasting process, 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.

[0069] The surface of the cermet sintered body of this embodiment may further be coated with a hard film by a conventional physical vapor deposition method or chemical vapor deposition method.

[0070] 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, and the like, without being particularly limited thereto. [Example]

[0071] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0072] Example 1 [Manufacturing of sintered cermet] As raw material powder, commercially available TiC with an average particle size of 2.0 μm was used. 0.5 N 0.5 TiC powder, average particle size 2.0 μm 0.3 N 0.7 The following powders were prepared: 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, MoC powder with an average particle size of 1.5 μm, CrC powder with an average particle size of 1.5 μm, Co powder with an average particle size of 1.0 μm, and Ni powder with an average particle size of 1.0 μm. The average particle sizes of the raw powders were measured using a Fisher Sub-Sieve Sizer (FSSS) according to the American Society for Testing and Materials (ASTM) standard B330.

[0073] The prepared raw material powders were weighed out to obtain the composition shown in Table 1 below, and the weighed raw material powders were 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.

[0074] 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.

[0075] After adding 3.0 mass % of paraffin to the obtained mixed powder, the mixture was press-molded at a pressure of 100 MPa using a mold that would give the insert shape TNMG160404 after sintering, to obtain a compact of the mixed powder.

[0076] 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). In the first heating step, the pressure was set to 50 Pa.

[0077] Thereafter, the molded body was heated in an N2 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.

[0078] 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.

[0079] The obtained cermet sintered 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.

[0080] Thereafter, the cermet sintered body was cooled from the first cooling temperature of 1350°C to room temperature in an Ar gas atmosphere (second cooling step). The pressure in the second cooling step was set to 100,000 Pa.

[0081] Thereafter, the cutting edge of the sintered cermet was subjected to a round honing treatment using a SiC brush (honing process).

[0082] Thereafter, a blasting process was carried out in which alumina (Al2O3) particles were used as shot material to collide 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.

[0083] In this manner, invention products 1 to 16 and comparison products 1 to 13 were produced.

[0084] [Table 1]

[0085] [Table 2]

[0086] The cermet sintered bodies of invention products 1 to 16 and comparison products 1 to 13 were observed using an SEM equipped with 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, 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 1-16 and Comparative Products 1-13 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 on a 10 μm x 10 μm area 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.

[0087] [Table 3]

[0088] XRD measurements were performed on the cermet sintered bodies of Invention Products 1 to 16 and Comparative Products 1 to 13, and it was confirmed that they contained 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°. In 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. The above XRD measurements were specifically performed using the following method. X-ray diffraction was performed using a RINT TTRIII (Rigaku Corporation) X-ray diffractometer with Cu-Kα radiation and a 2θ / θ focusing optical system under the following conditions to measure the peak intensities of the above plane indices: 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°.

[0089] The first hard phase and the second hard phase were identified by a BSE observation image of the cross-sectional structure inside the sintered cermet body.

[0090] For the cermet sintered bodies of invention products 1 to 16 and comparison products 1 to 13, the residual stress of the second hard phase was measured by XRD using sin 2 Measurement was performed using the ψ method. 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, the peak was present at a position of 121.0° or more and less than 123.5°. The results are shown in Table 4.

[0091] For the cermet sintered bodies of invention products 1 to 16 and comparison products 1 to 13, the residual stress in the binder phase was measured using XRD. 2Measurement was performed using the ψ method. Among the diffraction peaks originating from the binder phase having a cubic crystal structure, the diffraction peak originating from the (311) plane was used for evaluation. This peak was present at a position between 89.5° and 93.0° in 2θ-θ measurement. The results are shown in Table 4.

[0092] 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 shortest distance between the surface of the cermet sintered body and the line segment that crossed the first hard phase at a rate of less than 30% was taken as the thickness of the first hard phase-enriched region. In this case, the length of the line segment was 20 μm. The results are shown in Table 4.

[0093] The surface binder phase proportions of the cermet sintered compacts of Invention Products 1 to 16 and Comparative Products 1 to 13 were 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 compact (surface region) and at a position 500 μm or more inward from the surface of the cermet sintered compact (interior region). The EDS analysis was performed by area analysis of a 10 μm × 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.

[0094] The surface nitrogen ratio of the cermet sintered compacts of invention products 1 to 16 and comparison products 1 to 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 compact. The EDS analysis was performed on a 10 μm × 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.

[0095] [Table 4]

[0096] Using the obtained sintered cermets of invention products 1 to 16 and comparison products 1 to 13, cutting tests 1 and 2 were carried out. Cutting test 1 was a test to evaluate chipping resistance, and cutting test 2 was a test to evaluate wear resistance and plastic deformation resistance. The results of cutting tests 1 and 2 are shown in Table 5.

[0097] [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: 0.15mm / 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.

[0098] [Cutting test 2] Work material: S45C, Workpiece shape: round bar, Cutting speed: 250m / min, Cutting depth: 1.0 mm, Feed: 0.20mm / rev. Coolant: Wet, Insert: TNMG160404, Evaluation items: The tool life was determined as the time 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.

[0099] [Table 5]

[0100] Regarding the number of impacts until the tool life in Cutting Test 1, 20,000 or more were evaluated as A, 15,000 or more but less than 20,000 as B, and less than 15,000 as C. Furthermore, regarding the processing time until the tool life in Cutting Test 2, 30 minutes or more were evaluated as A, 25 minutes or more but less than 30 minutes as B, and less than 25 minutes as C. This evaluation was ranked as (excellent) A > B > C (poor), with the higher the A, the better the cutting performance.

[0101] From the results in Table 5, it was found that all of the cermet sintered compacts of the invention were rated B or higher in both cutting tests 1 and 2, demonstrating excellent fracture resistance, as well as excellent wear resistance and plastic deformation resistance. On the other hand, the comparative cermet sintered compacts were rated C in at least one of cutting tests 1 and 2, demonstrating inferior performance in at least one of fracture resistance, wear resistance, and plastic deformation resistance. From the above, it was found that the cermet sintered compacts of the invention have superior cutting performance and a longer tool life than the comparative cermet sintered compacts. 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 poor cutting performance and short tool life of the cermet sintered compact of Comparative Example 11 in Cutting Test 2. 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. [Industrial Applicability]

[0102] The cermet sintered body of the present invention has excellent chipping resistance, wear resistance, and plastic deformation resistance, and can extend the tool life compared to conventional tools, so it has high industrial applicability. [Explanation of symbols]

[0103] 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

1. 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.

2. 2. The cermet sintered body according to claim 1, wherein a surface nitrogen ratio is 0.42 or more and 0.50 or less.

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