Cermet sintered body, cermet tool and cutting tool

Abstract

A cermet sintered body according to the present disclosure comprises: a first hard phase mainly composed of TiCN; a second hard phase that is a composite carbonitride solid solution of Ti and at least one of the metals of Groups 4, 5, and 6 of the periodic table; and a binder phase containing W and at least one of Co and Ni. The average particle size of the second hard phase in an internal region and the average particle size of the second hard phase in a surface region are each 0.35-0.6 μm. The strength σ1 in the surface region and the strength σ2 in the internal region are each 2300 MPa or more, and the strength ratio of σ1 to σ2 is 0.8 or more.

Description

[Technical Field]

[0001] The present disclosure relates to a sintered cermet body, a cermet tool, and a cutting tool. [Background technology]

[0002] Cermet sintered bodies containing titanium (Ti) as the main component are widely used as substrates for components that require wear resistance, sliding properties, and chipping resistance, such as cutting tools, wear-resistant components, and sliding components. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3099834 Summary of the Invention

[0004] A cermet sintered body according to one embodiment of the present disclosure includes a first hard phase mainly composed of TiCN, a second hard phase which is a composite carbonitride solid solution of Ti and at least one metal selected from Groups 4, 5, and 6 of the periodic table, and a binder phase containing W and at least one of Co and Ni. 2in , and the average grain size of the secondary hard phase in the surface region, d 2sf are both 0.35 μm or more and 0.6 μm or less. The strength σ1 in the surface region and the strength σ2 in the internal region are both 2300 MPa or more, and the strength ratio of σ1 to σ2 (σ1 / σ2) is 0.8 or more. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a perspective view showing an example of a cermet tool according to an embodiment. [Figure 2] FIG. 2 is a side cross-sectional view showing an example of a cermet tool according to the embodiment. [Figure 3] FIG. 3 is a schematic diagram of a scanning electron microscope photograph of a cross section of a sintered cermet body. [Figure 4] FIG. 4 is a front view showing an example of a cutting tool according to an embodiment. [Figure 5] FIG. 5 is a graph showing the flexural strength in the surface region and the inner region for Sample No. 1, which is a comparative example, and Sample No. 3, which is an example. [Figure 6] FIG. 6 is a graph showing the thermal shock strength of Sample No. 1, which is a comparative example, and Sample No. 3, which is an example. DETAILED DESCRIPTION OF THE INVENTION

[0006] Hereinafter, modes for implementing the cermet sintered body, cermet tool, and cutting tool according to the present disclosure (hereinafter referred to as "embodiments") will be described in detail with reference to the drawings. Note that the cermet sintered body, cermet tool, and cutting tool according to the present disclosure are not limited to these embodiments. Furthermore, the respective embodiments can be appropriately combined within the scope of not causing any contradiction in the processing content. Furthermore, the same parts in the following respective embodiments will be given the same reference numerals, and redundant explanations will be omitted.

[0007] Furthermore, in the following embodiments, expressions such as "constant," "orthogonal," "perpendicular," or "parallel" may be used, but these expressions do not necessarily mean "constant," "orthogonal," "perpendicular," or "parallel" in the strict sense. In other words, the above expressions allow for deviations due to, for example, manufacturing precision, installation precision, etc.

[0008] Conventional sintered cermets have room for further improvement in terms of thermal shock resistance at the surface, and therefore, it is desired to provide a sintered cermet, a cermet tool, and a cutting tool having high thermal shock resistance at the surface.

[0009] <Cermet tools> Fig. 1 is a perspective view showing an example of a cermet tool according to an embodiment, Fig. 2 is a side cross-sectional view showing an example of a cermet tool according to an embodiment, and Fig. 3 is a schematic diagram of a scanning electron microscope photograph of a cross section of a cermet sintered body.

[0010] As shown in FIGS. 1 and 2, the cermet tool 1 according to the embodiment has a substrate 2 and a coating layer 3.

[0011] The base 2 has, for example, a hexahedral shape in which the upper and lower surfaces (surfaces intersecting with the Z axis shown in FIG. 1) are parallelogram-shaped.

[0012] One corner portion of the base 2 functions as a cutting edge portion. The cutting edge portion has a first surface and a second surface connected to the first surface. The first surface is, for example, the top surface of the base 2. The second surface is, for example, a side surface of the base 2. In the embodiment, the first surface functions as a "rake surface" that scoops up chips generated by cutting, and the second surface functions as a "flank surface." A cutting edge is located on at least a part of the ridge where the first surface and the second surface intersect, and the cermet tool 1 cuts the workpiece by bringing this cutting edge into contact with the workpiece.

[0013] A through-hole 21 that passes through the base 2 from top to bottom may be located in the center of the base 2. In this case, a screw 75 for attaching the cermet tool 1 to a holder 70 (described later) is inserted into the through-hole 21 (see FIG. 4).

[0014] The substrate 2 is made of a sintered cermet. The sintered cermet contains Ti (titanium), W (tungsten), and at least one of Co (cobalt) and Ni (nickel).

[0015] As shown in Fig. 3, the substrate 2, which is a sintered cermet, contains a hard phase 5 and a binder phase 6. Specifically, the substrate 2 is formed by binding the hard phase 5, which is a solid solution of TiCN and at least a portion of a carbide, nitride, or carbonitride of at least one metal other than Ti that is in Groups 4, 5, and 6 of the periodic table, with the binder phase 6. The binder phase 6 contains at least one of Co and Ni, and W.

[0016] The first hard phase is a hard phase containing TiCN as its main component. In the present disclosure, the term "main component" refers to, for example, 55% by mass or more of the hard phase when the entire hard phase of the constituent components is taken as 100% by mass.

[0017] Specifically, the first hard phase contains, as metal components, 80 wt % or more of Ti, and 1 wt % to 15 wt % in total of W and one or more metals selected from metals in Groups 4, 5, and 6 of the periodic table, with the remainder being Co and / or Ni.

[0018] The second hard phase is a hard phase consisting of a complex carbonitride solid solution of Ti and at least one metal selected from Groups 4, 5, and 6 of the periodic table. Specifically, the second hard phase contains 30 to 70% by weight of Ti, a total of 70 to 30% by weight of W and one or more metals selected from Groups 4, 5, and 6 of the periodic table, and a total of 0 to 3% by weight of Co and / or Ni binder phase metals.

[0019] As shown in Fig. 3, in an image of an arbitrary cross section of the cermet obtained by a scanning electron microscope (SEM), specifically, a backscattered electron image, the first hard phase 5a is observed to be relatively darker than the second hard phase 5b, and the second hard phase 5b is observed to be relatively grayish white than the first hard phase 5a. The second hard phase 5b may have a double-cored structure with the first hard phase 5a as the core and the second hard phase 5b as the periphery. However, it is not necessary that all of the second hard phases 5b have a cored structure.

[0020] Here, a region centered at a depth of 10 μm from the surface of the base 2 is defined as the base 2, in other words, the surface region of the cermet sintered body. The width of the surface region in the depth direction of the base 2 may be, for example, 20 μm. Furthermore, a region centered at any position 0.4 mm or deeper from the surface of the base 2 is defined as the internal region of the base 2. The width of the internal region in the depth direction of the base 2 may be, for example, 20 μm.

[0021] The substrate 2 according to the embodiment has an average grain size d 2in , and the average grain size d of the second hard phase 5b in the surface region 2sf The area ratio S of the second hard phase 5b to the entire hard phase in the inner region is 0.35 μm or more and 0.6 μm or less. 2in , and the area ratio S of the second hard phase 5b to the entire hard phase in the surface region 2sf are both 50 area % or more and 80 area % or less. In addition, the strength σ1 in the surface region and the strength σ2 in the internal region are both 2300 MPa or more, and the strength ratio (σ1 / σ2) of the strength σ1 in the surface region to the strength σ2 in the internal region is 0.8 or more.

[0022] This configuration increases the strength of the surface of the sintered cermet, reduces the increase in Young's modulus of the cermet surface, and improves the thermal shock resistance of the cermet surface. In particular, it is possible to improve the wear resistance and fracture resistance of the cermet even under conditions where severe thermal shock occurs, such as wet intermittent cutting.

[0023] The substrate 2 according to the embodiment has an average grain size d 1in , and the average grain size d of the first hard phase 5a in the surface region 1sf However, the average grain size d of the first hard phase 5a in the inner region may be 0.25 μm or more and 0.35 μm or less. 1in , and the average grain size d of the first hard phase 5a in the surface region 1sfThe area ratio S of the first hard phase 5a to the entire hard phase in the inner region may be 0.25 μm or more and 0.3 μm or less. 1in , and the area ratio S of the first hard phase 5a to the entire hard phase in the surface region 1sf The average grain size d of the first hard phase 5a in the surface region of the substrate 2 having such a structure may be 20 area % or more and 35 area % or less. 1sf and area ratio S 1sf is the average grain size d of the first hard phase 5a in the inner region. 1in and area ratio S 1in Therefore, the thermal shock resistance on the surface can be increased to the same extent as the thermal shock resistance inside.

[0024] The base 2 according to the embodiment may have a hardness H1 in the surface region and a hardness H2 in the internal region both of 1450 HV or more. In this case, the absolute value of the difference between the hardness H1 in the surface region and the hardness H2 in the internal region, |H1-H2|, may be 50 or less. In the base 2 having such a configuration, the hardness H1 in the surface region is approximately the same as the hardness H2 in the internal region, and therefore the thermal shock resistance in the surface can be increased to the same level as the thermal shock resistance in the internal region.

[0025] (Coating layer 3) The coating layer 3 is applied to the substrate 2 for the purpose of improving the abrasion resistance, heat resistance, etc. of the substrate 2. While FIG. 2 shows an example in which the coating layer 3 covers the entire surface of the substrate 2, the coating layer 3 does not necessarily have to cover the entire surface of the substrate 2. The coating layer 3 may be located on at least a portion of the surface of the substrate 2. When the coating layer 3 is located on the first surface of the substrate 2, in this case the top surface, the abrasion resistance and heat resistance of the first surface are high. When the coating layer 3 is located on the second surface of the substrate 2, in this case the side surface, the abrasion resistance and heat resistance of the second surface are high.

[0026] The coating layer 3 may be composed of, for example, at least one metal element selected from the group 4, 5, and 6 elements of the periodic table, aluminum (Al), and silicon (Si), and at least one nonmetal element selected from carbon (C), nitrogen (N), and oxygen (O). This configuration improves the oxidation resistance of the coating layer 3, further improving the wear resistance of the coating layer 3. The coating layer 3 may be a single layer. Alternatively, the cermet tool 1 may have a layered coating layer 3, i.e., two or more layers.

[0027] (Analysis method) The average particle size (d 1in , d 2in , d 1sf , d 2sf ) and area ratio (S 1in , S 2in , S 1sf , S 2sf ) can be obtained, for example, by the following procedure.

[0028] A cross section of the cermet sintered compact is photographed at 10,000x magnification using a scanning electron microscope (SEM) to obtain a backscattered electron image. The region including a position 10 μm deep from the surface of the cermet sintered compact is defined as the surface region, and the region including a position 400 μm deep from the surface of the cermet sintered compact is defined as the internal region. In each region, a line 10 μm long is drawn parallel to the surface of the cermet sintered compact, and the diameter of each phase, specifically the particle diameter, and the abundance ratio, specifically the area ratio, may be calculated from the length of the line segment intersecting the first hard phase and the length of the line segment intersecting the second hard phase.

[0029] Specifically, the average grain size of the first hard phase may be calculated by dividing the total length of the line segments crossing the first hard phase by the number of first hard phases crossed by the line. Similarly, the average grain size of the second hard phase may be calculated by dividing the total length of the line segments crossing the second hard phase by the number of second hard phases crossed by the line.

[0030] When calculating the average grain size of the first hard phase and the second hard phase, grains smaller than a specific value may be excluded from the calculation to avoid measurement variations. For example, 0.1 μm may be set as the specific value, and the first hard phases for which the line segments are 0.1 μm or more may be set as first measurement objects, and the average grain size of the first hard phases may be calculated by dividing the total length of the line segments in this first measurement object by the number of first measurement objects crossed by the line. Similarly, the second hard phases for which the line segments are 0.1 μm or more may be set as second measurement objects, and the average grain size of the second hard phases may be calculated by dividing the total length of the line segments in this second measurement object by the number of second measurement objects crossed by the line.

[0031] Alternatively, the area ratio of the first hard phase may be calculated as the ratio of the total length of the line segments crossing the first hard phase to the total length of the line segments crossing the second hard phase, where the sum of the total length of the line segments crossing the first hard phase and the total length of the line segments crossing the second hard phase is taken as 100%. Similarly, the area ratio of the second hard phase may be calculated as the ratio of the total length of the line segments crossing the second hard phase to the total length of the line segments crossing the first hard phase and the total length of the line segments crossing the second hard phase, where the sum of the total length of the line segments crossing the first hard phase and the total length of the line segments crossing the second hard phase is taken as 100%. In this case, the binder phase region is excluded. Preferably, the measurement is performed in three fields of view, and the results may be averaged. Alternatively, the measurement can be performed using a commercially available image analyzer.

[0032] (Manufacturing method) Next, a method for manufacturing the substrate 2, which is a sintered cermet body, will be described.

[0033] In the production of the cermet sintered body of the present disclosure, TiCN powder is used. This TiCN raw material powder may be one generally used in the production of cermets. The TiCN raw material powder may have already been subjected to a pulverization process. In addition, if the TiCN raw material powder has not been subjected to a pulverization process, it may be pulverized using a rotary mill and media.

[0034] When the raw powder of TiCN goes through the milling process, dislocations occur inside the raw powder of TiCN, and one or more metal elements from V, Nb, Ta, Cr, Mo, W, Co, and Ni move to the position of these dislocations.

[0035] It is advisable to use raw material powder of TiCN having such dislocations, carbides of the above metals, and Co or Ni as a binder phase as raw materials.

[0036] The raw material powder of TiCN having dislocations may be used, and the binder phase components such as Co and Ni may be 14% by mass or more and 22% by mass or less. When the binder phase components are in the above range, the cermet substrate has high toughness and high hardness.

[0037] As the component containing V, Nb, Ta, Cr, Mo, or W, it is preferable to use carbides of the respective metal elements.

[0038] The raw materials having the above-mentioned composition are mixed and then fired. The firing step may be, for example, the following steps. (a) A process of raising the temperature from room temperature to 1100°C in a vacuum (b) A step of holding the material in a vacuum at 1100°C for 1 to 2.5 hours. (c) A process of introducing N2 gas into the firing furnace at 1100°C, changing the pressure in the firing furnace to a pressure P1 of 5 Pa, and then raising the temperature from 1100°C to a temperature T1 of 1150-1300°C at a heating rate r1 of 0.1-2°C / min. (d) A step of maintaining the temperature at T1 for 0.5 to 2 hours (e) At temperature T1, the pressure in the firing furnace is changed to pressure P2, which is 300 to 2000 Pa higher than pressure P1, and then the temperature is increased from temperature T1 to temperature T2, which is 1300 to 1450°C, at a temperature increase rate r2 of 1 to 5°C / min. (f) a step of maintaining the temperature at T2 for 0.25 to 1.5 hours (g) A process of changing the pressure in the firing furnace to a pressure P3 of 30 to 1000 Pa, which is lower than the pressure P2, and then increasing the temperature from the temperature T2 to a temperature T3 of 1450 to 1600 ° C. at a temperature increase rate r3 of 2 to 10 ° C. / min. (h) maintaining the temperature at T3 for 1 hour Specifically, after 0.25 hours have passed, the pressure inside the firing furnace is gradually reduced from pressure P3 to 5 Pa for 0.25 hours, and then the pressure is maintained at 5 Pa for 0.5 hours. (i) A step of changing the atmosphere to an Ar gas atmosphere at a pressure P4 of 10,000 Pa to 80,000 Pa while decreasing the temperature from the temperature T3 to a temperature T4 of 100°C or less at a rate r4 of 10 to 50°C / min.

[0039] The cermet sintered body of the present disclosure can be produced by firing the molded body having the above-mentioned composition in the firing step described above.

[0040] Thereafter, a coating layer 3 may be provided as necessary. The coating layer 3 may be a so-called hard film, and may be formed by, for example, a PVD method or a CVD method. The coating film may be a single layer or a multilayer film.

[0041] <Cutting tools> Next, the configuration of a cutting tool including the above-described cermet tool 1 will be described with reference to Fig. 4. Fig. 4 is a front view showing an example of a cutting tool according to an embodiment.

[0042] As shown in FIG. 4, a cutting tool 100 according to the embodiment includes a cermet tool 1 and a holder 70 for fixing the cermet tool 1.

[0043] The holder 70 is a rod-shaped member extending from a first end to a second end. For example, the first end is the upper end in FIG. 4, and the second end is the lower end in FIG. 7. The holder 70 is made of, for example, steel or cast iron. Of these materials, it is particularly preferable to use steel, which has high toughness.

[0044] The holder 70 has a pocket 73 at the end on the first end side. The pocket 73 is a portion where the cermet tool 1 is attached, and has a seating surface that intersects with the rotation direction of the workpiece and a constraint side surface that is inclined relative to the seating surface. A screw hole is provided in the seating surface to thread into a screw 75, which will be described later.

[0045] The cermet tool 1 is positioned in a pocket 73 of the holder 70 and attached to the holder 70 by a screw 75. That is, the screw 75 is inserted into the through hole 21 of the cermet tool 1, and the tip of the screw 75 is inserted into a screw hole formed in the seating surface of the pocket 73 to screw the threaded portions together. In this way, the cermet tool 1 is attached to the holder 70 so that the cutting edge portion protrudes outward from the holder 70.

[0046] In the embodiment, a cutting tool used for so-called turning is exemplified. Examples of turning include internal diameter machining, external diameter machining, and grooving. The cutting tool is not limited to that used for turning. For example, the cermet tool 1 may be used as a cutting tool used for turning. Examples of cutting tools used for turning include milling cutters such as flat milling cutters, face milling cutters, side milling cutters, and groove milling cutters, and end mills such as single-blade end mills, multi-blade end mills, tapered-blade end mills, and ball end mills. [Example]

[0047] Examples of the present disclosure will be specifically described below, but the present disclosure is not limited to the examples shown below.

[0048] Samples No. 3 and No. 4, which are cermet sintered bodies, were produced by the above-mentioned manufacturing method. Samples No. 3 and No. 4 are examples of the present disclosure. Samples No. 1 and No. 2 are conventional cermet sintered bodies and are comparative examples.

[0049] The average grain size and area ratio of the first hard phase and the second hard phase were calculated for the surface region and the internal region of each of Samples No. 1 to No. 4 using the analytical method described above. In this calculation, the lower limit of the measurement object was set to 0.1 μm as described above. The results are shown in Table 1.

[0050] [Table 1]

[0051] The average grain size of the primary hard phase in sample No. 1 was 0.22 μm in the surface region and 0.31 μm in the internal region. The average grain size of the primary hard phase in sample No. 2 was 0.29 μm in the internal region. The average grain size of the primary hard phase in sample No. 3 was 0.29 μm in the surface region and 0.3 μm in the internal region. The average grain size of the primary hard phase in sample No. 4 was 0.26 μm in the surface region and 0.34 μm in the internal region.

[0052] The area ratio of the first hard phase in sample No. 1 was 12 area% in the surface region and 36.8 area% in the internal region. The area ratio of the first hard phase in sample No. 2 was 0 area% in the surface region and 4.3 area% in the internal region. The area ratio of the first hard phase in sample No. 3 was 28.7 area% in the surface region and 30.1 area% in the internal region. The area ratio of the first hard phase in sample No. 4 was 19 area% in the surface region and 51 area% in the internal region.

[0053] The ratio of the average grain size of the primary hard phase in the surface region to the average grain size of the primary hard phase in the internal region was 0.7 for sample No. 1, 0.95 for sample No. 3, and 0.76 for sample No. 4. The ratio is calculated as the average grain size on the surface / average grain size on the internal region.

[0054] The average grain size of the secondary hard phase in sample No. 1 was 0.95 μm in the surface region and 0.48 μm in the internal region. The average grain size of the secondary hard phase in sample No. 2 was 0.91 μm in the surface region and 0.85 μm in the internal region. The average grain size of the secondary hard phase in sample No. 3 was 0.41 μm in the surface region and 0.51 μm in the internal region. The average grain size of the secondary hard phase in sample No. 4 was 0.36 μm in the surface region and 0.58 μm in the internal region.

[0055] The area ratio of the second hard phase in sample No. 1 was 88 area% in the surface region and 63.2 area% in the internal region. The area ratio of the second hard phase in sample No. 2 was 100 area% in the surface region and 95.7 area% in the internal region. The area ratio of the second hard phase in sample No. 3 was 71.3 area% in the surface region and 69.9 area% in the internal region. The area ratio of the second hard phase in sample No. 4 was 81 area% in the surface region and 49 area% in the internal region.

[0056] The ratio of the average grain size of the second hard phase in the surface region to the average grain size of the second hard phase in the internal region was 1.98 for sample No. 1, 1.07 for sample No. 2, 0.8 for sample No. 3, and 0.62 for sample No. 4.

[0057] The average grain size of the entire hard phase, including the first and second hard phases, was 0.64 μm in the surface region and 0.39 μm in the internal region for sample No. 1, 0.91 μm in the surface region and 0.85 μm in the internal region for sample No. 2, 0.36 μm in the surface region and 0.42 μm in the internal region for sample No. 3, and 0.34 μm in the surface region and 0.46 μm in the internal region for sample No. 4.

[0058] In this way, in the samples No. 3 and No. 4 of the examples, the average grain size d 2in , and the average grain size of the secondary hard phase in the surface region, d 2sf In addition, in the sample No. 3 of the example, the area ratio S of the second hard phase to the entire hard phase in the inner region is 0.35 μm or more and 0.6 μm or less. 2in , and the area ratio S of the second hard phase to the entire hard phase in the surface region 2sf However, in all cases, the area percentage is between 50% and 80%.

[0059] In addition, in the samples No. 3 and No. 4, which are examples, the average grain size d 1in , and the average grain size of the primary hard phase in the surface region, d 1sfIn addition, in the sample No. 3 of the example, the area ratio S of the first hard phase to the entire hard phase in the inner region is 0.25 μm or more and 0.35 μm or less. 1in , and the area ratio S of the first hard phase to the entire hard phase in the surface region 1sf However, in all cases, the area percentage is between 20% and 35%.

[0060] These results show that the second hard phase in the surface region of Example Samples No. 3 and No. 4 is finer than that of Comparative Examples Samples No. 1 and No. 2. Furthermore, it is also shown that the difference in particle size between the hard phase, specifically the first hard phase and the second hard phase, between the surface region and the internal region is smaller in Example Samples No. 3 and No. 4 than that of Comparative Examples Samples No. 1 and No. 2.

[0061] Measurements of thermal conductivity, Young's modulus, thermal expansion coefficient, hardness, and flexural strength were carried out for Samples No. 1 to No. 4. The results are shown in Table 2.

[0062] [Table 2]

[0063] The thermal conductivity (λ) can be determined in accordance with JIS R 1611. The Young's modulus (E) can be determined in accordance with ISO 14577. The thermal expansion coefficient (α) can be determined in accordance with JIS R 1618. The hardness can be determined in accordance with JIS R 1610. The flexural strength can be determined in accordance with JIS R 1601. Strength test pieces were prepared as follows and used for flexural strength tests of the surface and internal regions. For the internal strength test piece (dimensions: 4 mm x 5 mm x 40 mm), each surface of the rectangular sintered body was ground off by 0.5 mm. For the surface strength test piece (dimensions: 4 mm x 5 mm x 40 mm), each surface except the tensile surface of the rectangular sintered body was ground off by 0.5 to 1 mm. Furthermore, in order to make the surface of the tool the same shape, the tension surface of each strength test piece was subjected to blasting treatment and polished to a few μm to 10 μm, and test pieces of 3 mm * 4 mm * 40 mm were prepared.

[0064] In addition, the thermal shock strength (R 1c ) was calculated. Thermal shock strength R 1c is R 1c = (λσ) / Eα. Also, "ΔHV20" shown in Table 2 is the absolute value |H1-H2| of the difference between the hardness H1 in the surface region and the hardness H2 in the internal region. "HV20" refers to the hardness measured with a test force of 20 kgf.

[0065] In the example sample No. 3, the flexural strength σ1 in the surface region was 2449 MPa, and the flexural strength σ2 in the internal region was 2512 MPa. In addition, the strength ratio (σ1 / σ2) of the flexural strength σ1 to the flexural strength σ2 in the sample No. 3 was 0.97. Note that the flexural strength σ1 is the surface strength, and the flexural strength σ2 is the internal strength.

[0066] In addition, sample No. 4, which is an example, had a flexural strength σ1 in the surface region of 2450 MPa and a flexural strength σ2 in the inner region of 2350 MPa. In addition, sample No. 4 had a strength ratio (σ1 / σ2) of flexural strength σ1 to flexural strength σ2 of 1.04.

[0067] Thus, in the example samples No. 3 and No. 4, the flexural strength σ1 in the surface region and the flexural strength σ2 in the internal region are both 2300 MPa or more, and the strength ratio of flexural strength σ1 to flexural strength σ2 (σ1 / σ2) is 0.8 or more. From these results, it can be seen that the strength in the internal region of the example samples No. 3 and No. 4 is relatively high, and the strength in the surface region is as high as the strength in the internal region.

[0068] In addition, sample No. 3, which is an example, had a hardness H1 in the surface region of 1531 HV20, a hardness H2 in the inner region of 1495 HV20, and ΔHV20 of 36 HV.

[0069] Thus, in sample No. 3, which is an example, the hardness H1 in the surface region and the hardness H2 in the internal region are both 1450 HV or more, and the absolute value of the difference between hardness H1 and hardness H2, |H1-H2|, is less than or equal to 50. From these results, it can be seen that in sample No. 3, which is an example, the hardness in the surface region is approximately the same as the hardness in the internal region.

[0070] In addition, Sample No. 4, which is an example, had a hardness H1 in the surface region of 1560 HV20, a hardness H2 in the inner region of 1450 HV20, and ΔHV20 of 110 HV.

[0071] Furthermore, sample No. 3, an example, had a thermal shock strength of 9783 in the surface region and 10105 in the internal region. Sample No. 4, an example, had a thermal shock strength of 9795 in the surface region and 9549 in the internal region. On the other hand, sample No. 1, a comparative example, had a thermal shock strength of 5922 in the surface region and 10309 in the internal region. Sample No. 2, a comparative example, had a thermal shock strength of 7970 in the surface region and 8274 in the internal region. As such, it can be seen that samples No. 3 and No. 4, which are examples, have improved thermal shock strength in the surface region compared to samples No. 1 and No. 2, which are comparative examples.

[0072] Further, a fracture resistance test was carried out on each of Samples No. 1 to No. 4. The fracture resistance test conditions were as follows.

[0073] <Fracture resistance test (turning)> Work material: S45C (25mm wide grooves x 4) Cutting speed: 250m / min Feed: 0.25mm / rev Cutting depth: 0.5 mm Cutting condition: Wet Evaluation method: Number of impacts until fracture

[0074] As shown in Table 2, the number of impacts until fracture occurred was 8,464 for sample No. 1 (comparison example) and 9,141 for sample No. 2, while it was 11,040 for sample No. 3 (example) and 10,070 for sample No. 4 (embodiment). These results show that sample Nos. 3 and 4 (example) have improved fracture resistance compared to sample Nos. 1 and 2 (comparison example).

[0075] Fig. 5 is a graph showing the flexural strength in the surface region and the internal region of Sample No. 1 (Comparative Example) and Sample No. 3 (Example). In Fig. 5, the vertical axis shows the strength ratio when the flexural strength in the internal region is set to 100%. Fig. 6 is a graph showing the thermal shock strength of Sample No. 1 (Comparative Example) and Sample No. 3 (Example). In Fig. 6, the vertical axis shows the strength ratio when the thermal shock strength in the surface region of Sample No. 1 is set to 100%.

[0076] As shown in Figure 5, Sample No. 3, an example, has a smaller difference between the flexural strength in the surface region and the flexural strength in the internal region than Comparative Sample No. 1. Furthermore, as shown in Figure 6, Sample No. 3, an example, has improved thermal shock strength in the surface region than Comparative Sample No. 1. Specifically, it can be seen that the thermal shock strength in the surface region of Sample No. 3, an example, is approximately 1.65 times higher than that of Comparative Sample No. 1.

[0077] As described above, the cermet sintered body according to the embodiment (for example, the substrate 2) includes a first hard phase (for example, the first hard phase 5a) containing TiCN as a main component, a second hard phase (for example, the second hard phase 5b) which is a composite carbonitride solid solution of Ti and at least one of metals in Groups 4, 5, and 6 of the periodic table, and a binder phase (for example, the binder phase 6) containing W and at least one of Co and Ni. The average grain size d of the second hard phase in the inner region 2in , and the average grain size of the secondary hard phase in the surface region, d 2sfare both 0.35 μm or more and 0.6 μm or less. The strength σ1 in the surface region and the strength σ2 in the internal region are both 2300 MPa or more, and the strength ratio of σ1 to σ2 (σ1 / σ2) is 0.8 or more.

[0078] Therefore, the cermet sintered body according to the embodiment can improve the thermal shock resistance on the surface.

[0079] 1 is merely an example and does not limit the shape of the cermet tool according to the present disclosure. The cermet tool according to the present disclosure may have, for example, a rod-shaped main body having a rotation axis and extending from a first end to a second end, a cutting edge located at the first end of the main body, and a groove extending spirally from the cutting edge toward the second end of the main body.

[0080] Further, although an example in which the cermet sintered body is used as a tool has been described here, the use of the cermet sintered body according to the present disclosure is not limited to tools.

[0081] Further advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. [Explanation of symbols]

[0082] 1 Cermet tools 2 Base 3 Covering layer 5 Hard phase 5a 1st hard phase 5b Second hard phase 6 Bonded phase 21 Through hole 70 Holder 73 Pocket 75 screws 100 cutting tools

Claims

1. A sintered cermet body, a first hard phase containing TiCN as a main component and 80% by weight or more of Ti; a second hard phase which is a composite carbonitride solid solution of at least one metal of Groups 4, 5 and 6 of the periodic table and Ti, containing 30% by weight or more and 70% by weight or less of Ti; a binder phase containing at least one of Co and Ni and W; Including, Average grain size d of the second hard phase in the inner region ２ｉｎ , and the average grain size d of the second hard phase in the surface region ２ｓｆ are all 0.35 μm or more and 0.6 μm or less, The strength σ1 in the surface region and the strength σ2 in the internal region are both 2300 MPa or more, and the strength ratio of σ1 to σ2 (σ1 / σ2) is 0.8 or more; the first hard phase in the inner region has an average grain size d 1in and the first hard phase in the surface region has an average grain size d 1sf of 0.25 μm or more and 0.35 μm or less; an area ratio S 1in of the first hard phase to all the hard phases in the internal region and an area ratio S 1sf of the first hard phase to all the hard phases in the surface region each being 20 area % or more and 35 area % or less.

2. The area ratio S of the second hard phase to the entire hard phase of the internal region ２ｉｎ , and the area ratio S of the second hard phase to the entire hard phase in the surface region ２ｓｆ The cermet sintered body according to claim 1, wherein each of the above is 50 area % or more and 80 area % or less.

3. The hardness H1 in the surface region and the hardness H2 in the inner region are both 1450 HV or more, 2. The cermet sintered body according to claim 1, wherein the absolute value |H1-H2| of the difference between H1 and H2 is 50 or less.

4. The cermet sintered body according to any one of claims 1 to 3, one or more coating layers located on at least a portion of the surface of the cermet sintered body and comprising at least one metal element selected from Groups 4, 5, and 6 of the periodic table, Al, and Si, and at least one nonmetal element selected from C, N, and O; A cermet tool comprising:

5. a holder extending from a first end to a second end and having a pocket on the side of the first end; A cutting tool comprising: the cermet tool according to claim 4 located in the pocket.

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