Cutting tool

Abstract

A cutting tool having a substrate comprising a first hard phase, a second hard phase, and a binder phase, wherein the first hard phase is a composite carbonitride containing 3.0 mass% or less of at least one selected from Zr, V, Nb, Ta, Mo, and W, less than 0.2 mass% of Cr, and 18.0-22.0 mass% in total of C and N, with the remainder comprising Ti and inevitable impurities, the second hard phase is a composite carbonitride containing 10.0-25.0 mass% of at least one selected from Zr, V, Nb, Ta, Mo, and W, more than 0.0 and less than 1.0 mass% of Cr (higher content than the first hard phase), and 15.0-20.0 mass% in total of C and N, with the remainder comprising Ti and inevitable impurities, the binder phaser contains less than 5.0 mass% in total of Ni and Fe, and 1.0-8.0% of Cr in terms of mass ratio with respect to the Co content, with the remainder comprising Co and inevitable impurities, and the Vickers hardness of the substrate monotonically decreases from the flank face toward the inside to 100 μm, with 1700-2100 Hv up to 40 μm and 1600-1780 Hv at a position of 600 μm inside.

Description

cutting tools

[0001] The present invention relates to a cutting tool made of a cermet substrate. This application claims priority from Japanese Patent Application No. 2024-54388, filed March 28, 2024. All disclosures contained in this application are incorporated herein by reference.

[0002] In addition to WC-based cemented carbides, cermets mainly composed of Ti carbides, nitrides, and carbonitrides are also used as cutting tool substrates. For example, there is a TiCN-based cermet, which has an iron group element as the main component of the binder phase, TiCN as the main component of the hard phase, and further contains carbides, nitrides, and carbonitrides of metals from groups 4, 5, and 6 of the periodic table.

[0003] Since the substrate of a cutting tool made of cermet is inferior in strength and toughness to the substrate made of WC-based cemented carbide, proposals have been made to adjust the hardness of the surface layer of the substrate in order to improve the wear resistance and chipping resistance.

[0004] For example, Patent Document 1 describes a cutting tool substrate made of cermet having a region with a Vickers hardness of 2000 or more within a depth of 50 μm from the surface, and the substrate is said to have excellent wear resistance and, in particular, durability even when used for cutting cast iron.

[0005] Furthermore, for example, Patent Document 2 describes a cutting tool substrate made of cermet, which has a region in which the binder phase decreases from the hardened surface to a depth of 30 to 200 μm inward, and has a region in which the Vickers hardness is 1800 or more in the region from the hardened surface to a depth of 30 μm inward, and which is said to have excellent wear resistance and chipping resistance, and to produce small finished surface roughness for the workpiece.

[0006] Patent No. 2628200 Patent No. 5644388

[0007] The present invention has been made in consideration of the above circumstances and proposals, and has an object to provide a cutting tool having a base made of cermet that has excellent wear resistance and fracture resistance, even during high-speed cutting, for example, at a cutting speed of 200 m / min or more, where the amount of heat generated at the cutting edge increases.

[0008] A cutting tool according to an embodiment of the present invention has a substrate made of cermet, wherein the substrate has a first hard phase, a second hard phase, and a binder phase, the first hard phase being a composite carbonitride containing 0.0 to 3.0 mass% in total of at least one element selected from the group consisting of Zr, V, Nb, Ta, Mo, and W, 0.0 to less than 0.2 mass% of Cr, 18.0 to 22.0 mass% in total of C and N, and the balance being Ti and unavoidable impurities, and the second hard phase being a composite carbonitride containing 10.0 to 25.0 mass% in total of at least one element selected from the group consisting of Zr, V, Nb, Ta, Mo, and W, more than 0.0 to less than 1.0 mass% of Cr (however, the Cr content of the second phase is higher than the Cr content of the first hard phase), 15.0 to 20.0 mass% in total of C and N, and the balance being Ti and unavoidable impurities, The binder phase contains a total of 0.0 to less than 5.0 mass% of Ni and Fe, 1.0 to 8.0% by mass of Cr relative to the Co content, and the remainder being Co and unavoidable impurities, and in a first region extending from the flank surface of the substrate to a depth of 100 μm into the substrate, the Vickers hardness monotonically decreases, in a second region extending from the flank surface to a depth of 40 μm into the substrate, the Vickers hardness is 1700 to 2100 Hv, and at a position 600 μm deep from the flank surface into the substrate, the Vickers hardness is 1600 to 1780 Hv.

[0009] The cutting tool may satisfy one or more of the following (1) to (3):

[0010] (1) The second hard phase further contains Ta and / or Nb, and W. (2) The steel further has a third hard phase which is a composite carbonitride containing a total of 25.0 to 45.0 mass% of at least one element selected from the group consisting of Zr, V, Nb, Ta, Mo, and W, 0.0 to less than 1.0 mass% of Cr (but less than the Cr content of the second hard phase), 10.0 to 17.0 mass% of C and N in total, and the balance being Ti (but less than the Ti content of the first hard phase) and unavoidable impurities. (3) The area ratio of the first hard phase is 10.0 to 30.0%, the area ratio of the second hard phase is 50.0 to 80.0%, and the area ratio of the third hard phase is 0.0 to 5.0%.

[0011] The cutting tool according to the embodiment, whose base is made of cermet, has excellent wear resistance and chipping resistance even under cutting conditions in which the amount of heat generated at the cutting edge increases during cutting, such as high-speed cutting.

[0012] Fig. 3 is a schematic diagram of an example of the structure of a substrate in a cutting tool having a substrate made of cermet according to an embodiment of the present invention. Fig. 4 is a schematic diagram of another example of the structure of a substrate in a cutting tool having a substrate made of cermet according to another embodiment of the present invention. Fig. 5 is a schematic diagram showing an example of a measurement surface when measuring Vickers hardness. Fig. 6 is a plan view of Fig. 3. Fig. 4 is an example of a graph (schematic diagram) showing the frequency and cumulative relative frequency distribution for the brightness of each pixel in 256 gradations, obtained by observing the structure of a cutting tool having a substrate made of cermet according to an embodiment of the present invention using an SEM.

[0013] In cutting processes such as high-speed cutting where the amount of heat generated at the cutting edge is high, cutting tools having a cermet substrate need to suppress abnormal damage such as thermal wear, oxidation wear, abrasive wear, and boundary damage.

[0014] The present inventors have found that if only a surface-hardened layer resulting from a decrease in the Co content of the binder phase is present on or near the surface of a cermet cutting tool substrate (hereinafter also referred to as substrate), the oxidation wear resistance during cutting is insufficient, and the abnormal damage described above cannot be sufficiently suppressed. Therefore, the present inventors have conducted further studies and have discovered the following 1) to 4) as measures for improving the durability of cermet substrates during cutting.

[0015] 1) To prevent the abnormal damage described above, it is preferable that a first hard phase, which is hard and has low oxidation resistance, and a second hard phase, which is soft and has high oxidation resistance, are dispersed in the substrate. Here, the first hard phase is a composite carbonitride containing Ti but not Cr, and the second hard phase is a composite carbonitride containing Ti and Cr. The composition of these composite carbonitrides is not limited to a stoichiometric composition.

[0016] 2) Furthermore, when a binder phase with high oxidation resistance is dispersed in the substrate, oxidation wear is further suppressed, and in order to obtain this binder phase with high oxidation resistance, it is preferable that the substrate contains Cr.

[0017] 3) In order to suppress abrasive wear, it is preferable that the hardness of the surface of the substrate and its vicinity is high. To achieve this, it is preferable that the above-mentioned first hard phase is increased on the surface of the substrate and its vicinity, and that the Vickers hardness be 1700 Hv or more in the region extending from the surface to a depth of 40 μm.

[0018] 4) In order to suppress abnormal damage such as boundary damage, it is necessary to specify the hardness of the substrate surface and its vicinity, and the hardness of the substrate interior, and to use a binder phase composition that improves toughness. The former is achieved by monotonically decreasing the Vickers hardness from the surface to 100 μm and by setting the Vickers hardness inside the substrate to a predetermined value, and the latter is achieved by not including Ni and Fe in the binder phase (the total content of Ni and Fe in the binder phase should be less than 5.0 mass %).

[0019] The present invention was derived based on these findings. A cermet cutting tool according to an embodiment of the present invention will be described in detail below. In this specification and claims, when a numerical range is expressed as "L to M" (where L and M are both numerical values), this is equivalent to "at least L and at most M," and the range includes an upper limit (M) and a lower limit (L). When a unit is specified for only the upper limit (M), the upper limit (M) and the lower limit (L) have the same unit. The average value is an arithmetic mean value. The cermet cutting tool referred to in the claims and this specification may or may not have a known coating layer on a substrate.

[0020] 1. Structure and Composition of the Substrate The cross-sectional structure of a substrate for a cermet cutting tool according to an embodiment of the present invention will be described. FIG. 1 is a schematic example of the cross-sectional structure of a substrate according to an embodiment of the present invention. As shown in FIG. 1, the substrate for a cermet cutting tool necessarily has a first hard phase (1), a second hard phase (2), and a binder phase (3). The first hard phase (1) may be present inside the second hard phase (2). FIG. 2 is a schematic example of the cross-sectional structure of a substrate for a cermet cutting tool according to another embodiment of the present invention. As shown in FIG. 2, the first hard phase (1) has a third hard phase (4) in addition to the second hard phase (2).

[0021] The structure of the substrate of the cermet cutting tool of the present invention is manufactured so that it contains only hard phases (first hard phase, second hard phase, third hard phase) and binder phase, but phases other than these (e.g., carbide phase, nitride phase) may be unintentionally generated partially during the manufacturing process.

[0022] (1) Hard Phase The first hard phase and the second hard phase are always present, but the third hard phase may or may not be present.

[0023] The first hard phase is a composite carbonitride containing 0.0 to 3.0 mass% in total of at least one element selected from the group consisting of Zr, V, Nb, Ta, Mo, and W, 0.0 to less than 0.2 mass% of Cr, 18.0 to 22.0 mass% in total of C and N, and the balance being Ti and unavoidable impurities. The Ti content of the first hard phase is more preferably 78.0 to 80.0 mass%. Here, "0.0 to 3.0 mass% in total of at least one element selected from the group consisting of Zr, V, Nb, Ta, Mo, and W" means that at least one of Zr, V, Nb, Ta, Mo, and W may or may not be present. When at least one element is present, the upper limit of the total content of at least one element selected from the group consisting of Zr, V, Nb, Ta, Mo, and W is 3.0 mass%. The same definition applies to the total content of the second hard phase and the third hard phase when they contain at least one element selected from the group consisting of Zr, V, Nb, Ta, Mo, and W. The first hard phase is a phase with excellent wear resistance.

[0024] The second hard phase is a complex carbonitride containing a total of 10.0 to 25.0 mass% of at least one element selected from the group consisting of Zr, V, Nb, Ta, Mo, and W, less than 1.0 mass% of Cr (but more than the Cr content of the first hard phase), a total of 15.0 to 20.0 mass% of C and N, and the balance being Ti and unavoidable impurities. The Ti content of the second hard phase is more preferably 60.0 mass% or more and less than 68.0 mass%. The second hard phase has excellent oxidation resistance.

[0025] The third hard phase is a complex carbonitride containing 25.0 to 45.0 mass% Zr, V, Nb, Ta, Mo, and W in total, 0.0 to less than 1.0 mass% Cr (but less than the Cr content of the second hard phase), 10.0 to 17.0 mass% C and N in total, and the balance being Ti (but less than the Ti content of the first hard phase) and unavoidable impurities. The Ti content of the third hard phase is more preferably 40.0 to 60.0 mass%. The third hard phase is a phase that has excellent fracture toughness and improves the chipping resistance of the tool.

[0026] The above-mentioned Zr, V, Nb, Ta, Mo and W contribute equally to improving hardness and chipping resistance (toughness), but among these, Ta and / or Nb, and W are particularly preferred.

[0027] The compositions of the first, second and third hard phases are such that the sum of the elements constituting the composite carbonitride of each hard phase is 100 mass %.

[0028] The area ratio of the first hard phase to any cross section or surface of the substrate is more preferably 10.0 to 30.0%, and even more preferably 15.0 to 25.0%. The area ratio of the second hard phase is more preferably 50.0 to 80.0%, and even more preferably 60.0 to 75.0%. The area ratio of the third hard phase is more preferably 0.0 to 5.0%, and even more preferably 0.0 to 3.0%. The method for identifying each hard phase will be described later.

[0029] (2) Binder Phase The binder phase has a composition containing a total of 0.0 to less than 5.0 mass% of Ni and Fe, 1.0 to 8.0% by mass of Cr relative to the Co content, and the remainder being Co and inevitable impurities. The inclusion of Cr in the binder phase improves the oxidation resistance of the substrate. If the Cr content in the binder phase is 1.0 to 8.0% by mass relative to the Co content in the binder phase, the oxidation resistance of the substrate of the cermet cutting tool is reliably improved. The binder phase may contain components contained in the first to third hard phases as examples of inevitable impurities.

[0030] The area ratio of the binder phase in the cross section or surface of the substrate (measured excluding the area near the surface because the area ratio of the binder phase near the surface is low) is more preferably 6.0 to 13.0%, and even more preferably 8.0 to 12.0%.

[0031] (3) Composition The composition of the entire substrate can be exemplified as follows: 1) Co: 10.0 to 15.0 mass%, Cr: 0.5 to 1.5 mass%, at least one of Zr, V, Nb, Ta, Mo, and W: 15.0 to 40.0 mass% in total, C: 5.0 to 10.0 mass%, N: 6.0 to 12.0 mass%, with the balance being Ti and inevitable impurities. 2) In addition to the composition of 1), further containing 7.0 to 25.0 mass% of W, and the Cr content is 0.5 to 1.0 mass%.

[0032] 2. Vickers Hardness In order to prevent abnormal damage such as abrasive wear and boundary damage, the flank surface of the cermet substrate preferably has a predetermined Vickers hardness. The Vickers hardness referred to in the claims and this specification is measured in accordance with JIS Z 2244:2009 under a load of 4.9 N (500 gf).

[0033] The Vickers hardness monotonically decreases in a first region from the flank surface of the substrate to a depth of 100 μm into the substrate, and in a second region from the flank surface to a depth of 40 μm into the substrate, the Vickers hardness is 1700 to 2100 Hv, and at a depth of 600 μm from the flank surface to the interior of the substrate, the Vickers hardness is 1600 to 1780 Hv.

[0034] The reason why such a Vickers hardness is preferable is as follows: If the Vickers hardness does not monotonically decrease in the first region from the flank to a depth of 100 μm into the base, the flank wear of the cutting tool is large; if the Vickers hardness in the second region from the flank to a depth of 40 μm into the base is less than 1700 Hv, the flank wear of the cutting tool is large; and if the Vickers hardness is 2100 Hv or more, the frequency of boundary damage increases. Furthermore, if the Vickers hardness at a depth of 600 μm from the flank is less than 1600, the flank wear of the cutting tool is large; and if it exceeds 1780 Hv, the cutting tool is prone to chipping during high-speed cutting.

[0035] In the claims and this specification, "the Vickers hardness monotonically decreases in a first region from the flank face to a depth of 100 μm into the base" means that the Vickers hardness (Hv) monotonically decreases at depth positions within the base at 10, 40, and 100 μm from the flank face, in other words, there is one or more positions where the Vickers hardness (Hv) decreases in the depth direction, and the hardness does not increase even at positions where it does not decrease; and "the Vickers hardness is 1700 to 2100 Hv in a second region from the flank face to a depth of 40 μm into the base" means that the Vickers hardness (Hv) is 1700 to 2100 Hv at both depth positions 10 and 40 μm from the flank face.

[0036] 4. Method for Measuring Vickers Hardness The method for measuring Vickers hardness will be described with reference to FIGS.

[0037] 1) Select the flank surface of the cutting tool to measure the hardness.

[0038] 2) As shown in Figure 3, a polished portion (12) is provided on a part of the surface (10) at an angle φ (an angle (11) between 5 degrees and 20 degrees that makes it easy to measure the hardness). The surface (10) provided with this polished portion (12) has an unpolished portion (13).

[0039] 3) A magnification of about 5 times is selected, and an observation field is set that includes a polished portion (12) and an unpolished portion (13), for example, 0.9 mm (vertical) × (0.9 to 1.2) mm (horizontal), in which a large number of hard phases can be visually recognized.

[0040] 4) As shown in Figure 3, within this observation field, observe the minute irregularities at the boundary between the polished portion (12) and the unpolished portion (13), and draw a line segment X connecting both ends of the minute irregularities within this field.

[0041] 5) A line segment S on the surface of the most recessed portion is drawn parallel to the line segment X and tangent to the point (the most recessed portion) of the minute irregularities that is the innermost part of the polished portion, and this line segment S is regarded as the reference position of the flank surface (hereinafter, no distinction will be made between the most recessed portion and the reference position of the flank surface). This line segment S on the most recessed portion does not intersect with any of the minute irregularities mentioned above except at the most recessed portion.

[0042] 6) On the polished portion (12), a line segment A parallel to the outermost surface line segment S is drawn at a position 10 / sinφμm away from the outermost surface line segment S, and the Vickers hardness (the measurement positions for this hardness correspond to a depth of (10 / sinφ)×sinφ=10μm from the outermost surface line segment B inside the base body of the cutting tool) is measured at seven measurement points a (only five points are shown in Figure 4) at intervals of 150 μm on the line segment A, and the maximum and minimum values ​​are discarded to determine the average value a of the five values. Note that Figure 4 shows the measurement positions for the Vickers hardness at these five points.

[0043] In a similar manner, a line segment B is drawn on the polished portion (12) at a position 40 / sinφμm away from the outermost surface line segment S, and a line segment C is drawn at a position 100 / sinφμm away. The centers of the indentations are measured at seven measurement points b and c (only five points are shown in Figure 4) at intervals of 150 μm on the lines B and C, respectively, to measure Vickers hardness (these hardness measurement positions correspond to depths of 40 and 100 μm from the outermost surface line segment B within the base body of the cutting tool). The maximum and minimum values ​​are discarded and the average values ​​b and c are calculated from the five values.

[0044] 8) The position on the polished portion (12) from the outermost surface line segment S that is 600 / sinφμm or more is defined as the internal region, and the average Vickers hardness in that region is used as the representative value of the hardness of the internal region. The hardness of the internal region is obtained by drawing a line segment D parallel to the outermost surface line segment S at a position on the polished portion (12) that is 600 / sinφμm or more away from the outermost surface line segment S, measuring the Vickers hardness at seven measurement points d (only five points are shown in Figure 4) at intervals of 150 μm, with the center of each indentation on the line segment D, and calculating the average value d from the five values ​​after discarding the maximum and minimum values. Note that Figure 4 shows the measurement positions of these five Vickers hardness points.

[0045] 4. Method for Confirming Composition The method for analyzing the non-metallic components of the substrate is as follows: First, the substrate is pulverized into powder, and then carbon is quantitatively analyzed by non-dispersive infrared analysis, nitrogen by thermal conductivity analysis, and oxygen contained in the raw material powder as an impurity or taken in by oxidation of the raw material powder (oxygen as an unavoidable impurity) by infrared absorption analysis to determine the mass % contained in the substrate.

[0046] Next, the substrate is cut so that any cross section can be obtained that ensures an observation surface of 5 mm x 5 mm for the metal components in the substrate, and the substrate is ground 1 mm in the depth direction and further mirror-polished, and then the cross section is analyzed by X-ray fluorescence analysis (XRF). The mass % of each metal element in the substrate is determined by multiplying the obtained value expressed as mass % for each metal element by the value obtained by subtracting the value expressed as mass % of the total content of the above-mentioned analysis results of carbon, nitrogen, and oxygen from 100%.

[0047] To illustrate this calculation, when the total mass percent of carbon, nitrogen, and oxygen is 20 mass percent, and the Ti content analyzed by XRF is 80 mass percent, the Ti content in the substrate of the cutting tool is 80 x (100 - 20) = 64 (mass%).

[0048] 5. Identification and Area Ratio of Each Phase Identification of each phase is performed using a scanning electron microscope (SEM) and an electron probe microanalyzer (EPMA). First, an arbitrary observation field of the substrate (preferably having a size of 18 μm (vertical) × 24 μm (horizontal) or more, and containing at least 15 or more of each phase) is mirror-polished so as not to interfere with SEM observation and EPMA composition analysis.

[0049] Next, the mirror-polished cross section is observed using an SEM to obtain a backscattered electron image consisting of pixels with a brightness of 256 levels (black is 0, white is 255). Figure 5 shows a histogram in which the horizontal axis represents brightness and the vertical axis represents the number of pixels with that brightness. The solid line represents the frequency of pixel occurrence (frequency), and the dashed line represents the cumulative relative frequency (cumulative relative frequency). Using this graph, the phases are distinguished by setting thresholds as follows: Here, the spacing between each pixel can be, for example, 20 nm in both the vertical and horizontal directions.

[0050] Identification and area ratio of the phase considered to be the first hard phase This will be explained below with reference to Figure 5. Each pixel included in the range from brightness A, which is closest to black (greater than 0), to brightness D (referred to as left threshold D), which is midway between brightness B, which corresponds to a cumulative relative frequency of 5.0%, and brightness C, which corresponds to the maximum frequency, is considered to belong to the first hard phase. The area ratio of the first hard phase is calculated by dividing the number of these pixels by the total number of pixels in the entire observation field. Just to be sure, EPMA analysis is performed at the positions of these pixels to confirm that the composition of the first hard phase described above is satisfied.

[0051] Identification and area ratio of the phase regarded as the second hard phase Each pixel included between the brightness F value (referred to as the right threshold F) that is intermediate between the brightness located immediately to the right of the left threshold D and the brightness E corresponding to a cumulative relative frequency of 97.0% is regarded as belonging to the second hard phase. The area ratio of the second hard phase is calculated by dividing the number of these pixels by the total number of pixels. Just to be sure, EPMA analysis is performed at the positions of these pixels to confirm that the composition of the second hard phase described above is satisfied.

[0052] Identification and area ratio of the phase treated as the third hard phase Pixels with brightness on the white side (right side) of the right threshold F are considered to belong to the third hard phase or binder phase. The number of these pixels is divided by the total number of pixels to find the area ratio of the third hard phase or binder phase. Just to be sure, EPMA analysis is performed at the positions of these pixels to confirm that the composition of the third hard phase described above is satisfied.

[0053] Since there is almost no difference in brightness between the third hard phase and the binder phase in SEM images, it is difficult to distinguish between the third hard phase and the binder phase based on brightness alone. Therefore, EPMA analysis is used to confirm whether it is the third hard phase or the binder phase. The third hard phase and the binder phase are distinguished based on whether they satisfy the aforementioned third hard phase components and whether they contain Co as the main component.

[0054] 3. Manufacturing Method An example of a method for manufacturing the cermet cutting tool according to this embodiment will be described.

[0055] 1) Raw material powder: TiCN, MCN (where M is two or more of Zr, V, Nb, Ta, Mo, and W), Cr, with a Fischer particle size of 0.8 to 3.0 μm. ３ C ２ Furthermore, one or more carbides of Ti, Zr, V, Nb, Ta, Cr, Mo, and W (which may be composite carbides), W, Co, and Ni are prepared as required.

[0056] By using TiCN powder, a first hard phase that does not dissolve Cr after sintering is formed. ０．７５ Nb ０．１０ Mo ０．０５ W ０．１０ By using a composite carbide powder such as CN, the melting point of the hard phase in the substrate of the cermet cutting tool is lowered, and after sintering, Cr is added to the hard phase. ３ C ２ The derived Cr is Cr ３ C ２ Instead, it exists as a solid solution as Cr, forming a second hard phase.

[0057] 2) Blending and Mixing These raw material powders are mixed, for example, in the following mixture: MCN: 20 to 50 mass % Cr ３ C ２: 0.5 to 1.5 mass % Co: 10.0 to 17.0 mass % TiCN: balance

[0058] Then, in ethyl alcohol, first, Cr ３ C ２ A preliminary crushing step is carried out in which the chisel is mixed in an attritor for 6 to 20 hours, after which paraffin and the remaining raw material powder are added and mixed in an attritor for 9 to 13 hours to form a slurry.

[0059] Cr ３ C ２ By mixing only the attritor in advance, Cr ３ C ２ There is little aggregation of Cr ３ C ２ Since it is possible to finely grind Cr into the binder phase and hard phase in the substrate of the cermet cutting tool, ３ C ２ The derived Cr is Cr ３ C ２ Instead, it exists as a solid solution as Cr, which promotes the formation of the second hard phase. The obtained slurry is spray-dried with a spray dryer to obtain a granulated powder.

[0060] 3) Molding, Sintering, and Post-Treatment The granulated powder is press-molded into a desired cutting tool shape to obtain a molded body, which is then sintered.

[0061] The sintering process includes the following steps, in order: a first heating step in which the molded body is heated from room temperature to a first heating temperature of 500 to 950°C under reduced pressure; a second heating step in which the molded body is heated from the first heating temperature of 500 to 950°C to a second heating temperature of 1000 to 1250°C in a nitrogen atmosphere at a pressure of 1 Torr or more; a third heating step in which the molded body is heated from the second heating temperature of 1000 to 1250°C to a third heating temperature of 1280 to 1410°C in a vacuum; a first holding step in which the molded body is held at the third heating temperature of 1280 to 1410°C; a fourth heating step in which the molded body is heated from a fourth heating temperature of 1280 to 1410°C to a fourth heating temperature of 1430 to 1600°C in a nitrogen atmosphere at a pressure of 5 Torr or more; a second holding step in which the molded body is held at the fourth heating temperature for 180 minutes or more in a nitrogen atmosphere at a pressure lower than that of the fourth heating step; and a cooling step in which the molded body is cooled to room temperature.

[0062] The sintering process adjusts the amount of nitrogen in the interior and surface of the substrate of the cermet cutting tool, thereby achieving a desired hardness distribution. After sintering, the molded body is cooled and then subjected to honing as a post-treatment.

[0063] 4) Deposition of Coating Layer A coating layer is formed as needed. There are no restrictions on the composition, average thickness, layer structure, or deposition method of the coating layer, and known coating layers can be used. Here, known coating layers are not particularly limited, but examples include one or more of a Ti carbide layer, nitride layer, carbonitride layer, carbonate layer, and carbonitride oxide layer, a Ti and Al composite nitride layer or composite carbonitride layer, and an aluminum oxide layer. Note that the composition of each of the aforementioned layers is not limited to a stoichiometric composition.

[0064] The above description includes the following additional features: (Additional Note 1) A cutting tool including a cermet substrate, wherein the cermet substrate has a first hard phase, a second hard phase, and a binder phase, and the first hard phase is a complex carbonitride containing 0.0 to 3.0 mass% in total of at least one element selected from the group consisting of Zr, V, Nb, Ta, Mo, and W, 0.0 to less than 0.2 mass% of Cr, 18.0 to 22.0 mass% in total of C and N, and the balance being Ti and unavoidable impurities; the second hard phase is a complex carbonitride containing 10.0 to 25.0 mass% in total of at least one selected from the group consisting of Zr, V, Nb, Ta, Mo, and W, more than 0.0 and less than 1.0 mass% of Cr (however, the Cr content of the second hard phase is higher than the Cr content of the first hard phase), 15.0 to 20.0 mass% in total of C and N, and the balance being Ti and unavoidable impurities; the binder phase contains 0.0 to less than 5.0 mass% in total of Ni and Fe, 1.0 to 8.0% by mass of Cr relative to the content of Co, and the balance being Co and unavoidable impurities; a Vickers hardness of 1700 to 2100 Hv in a first region extending from the flank face of the substrate to a depth of 100 μm into the substrate, a Vickers hardness of 1700 to 2100 Hv in a second region extending from the flank face to a depth of 40 μm into the substrate, and a Vickers hardness of 1600 to 1780 Hv at a depth of 600 μm from the flank face into the substrate. (Appendix 2) The cutting tool according to Appendices 1, wherein the second hard phase further contains Ta and / or Nb, and W. (Appendix 3) The cutting tool according to Appendices 1 or 2, characterized in that it further has a third hard phase which is a composite carbonitride containing 25.0 to 45.0 mass% in total of at least one selected from the group consisting of Zr, V, Nb, Ta, Mo, and W, 0.0 to but less than 1.0 mass% of Cr (but less than the Cr content of the second hard phase), 10.0 to 17.0 mass% in total of C and N, and the balance being Ti (but less than the Ti content of the first hard phase) and unavoidable impurities. (Appendix 4) The cutting tool according to any of Appendices 1 to 3, characterized in that the area ratio of the first hard phase is 10.0 to 30.0%, the area ratio of the second hard phase is 50.0 to 80.0%, and the area ratio of the third hard phase is 0.0 to 5.0%.(Appendix 5) The cutting tool according to any one of Appendices 1 to 4, wherein the area ratio of the binder phase in the entire cross section or surface of the base is 6.0 to 13.0%. (Appendix 6) The cutting tool according to any one of Appendices 1 to 5, wherein the composition of the base is 9.0 to 15.0 mass% Co, 0.1 to 1.5 mass% Cr, 10.0 to 40.0 mass% in total of at least one of Zr, V, Nb, Ta, Mo, and W, 5.0 to 10.0 mass% C, 5.5 to 12.0 mass% N, and the balance being Ti and unavoidable impurities.

[0065] Next, the cermet cutting tool of the present invention will be specifically described with reference to an example in which it is applied to an insert.

[0066] TiCN, (Ti) having a Fischer particle size of 0.7 to 2.3 μm as shown in Table 1 ０．７５ Nb ０．１０ Mo ０．０５ W ０．１０ ) CN, (Ti ０．７５ Ta ０．１０ Mo ０．０５ W ０．１０ ) CN, (Ti ０．７７ Mo ０．０８ W ０．１５ ) CN, (Ti ０．９０ W ０．１０ ) CN, (Ti ０．７５ Nb ０．１５ W ０．１０ ) CN, (Ti ０．７７ Mo ０．０８ W ０．１５ ) CN, (Ti ０．７７ Nb ０．１０ Cr ０．０３ W ０．１０ ) CN, Cr ３ C ２ , VC, W, NbC, ZrC, Co and Ni powders were prepared so as to obtain the composition shown in Table 1. Then, Cr, ３ C ２ The mixture was mixed in an attritor for 6 hours, and then paraffin and the remaining raw material powders were added and mixed in an attritor for 11 hours to form a slurry. The slurry was dried in a spray dryer, and the blended composition was then press-molded into a green compact to produce green compacts for the Examples and Comparative Examples.

[0067] The compact was then sintered. The thermal history for both the Example and Comparative Examples was as follows, except that the pressure atmospheres in the first and second holding steps were different. In the first heating step, the compact was heated from room temperature to 600°C under reduced pressure. In the second heating step, the compact was heated to 1200°C in a nitrogen atmosphere at 3.0 Torr. In the third heating step, the compact was heated to a third heating temperature of 1400°C in a vacuum. In the first holding step, the compact was held at this temperature for 30 minutes in a nitrogen atmosphere at 2.0 Torr. In the fourth heating step, the compact was heated to 1490°C in a nitrogen atmosphere at 0.5 Torr or 10.0 Torr. In the second holding step, the compact was held at this temperature for 210 minutes in a nitrogen atmosphere at 0.5 Torr or 1.0 Torr. (The atmospheric pressures in the fourth heating step and second holding step are listed in Table 2.) The compact was then cooled to room temperature.

[0068] Next, the produced sintered body was subjected to honing to produce Examples 1 to 11 and Comparative Examples 1 to 6 shown in Tables 3 to 6, each having an insert shape of CNMG120408 (with breaker).

[0069] The area ratio of each hard phase and the analysis results of the binder phase are shown in Tables 3 to 6. The area ratio and binder phase were measured as described above.

[0070] The backscattered electron images by SEM were taken under conditions of an acceleration voltage of 10 kV, a probe current of 30 nA, and a magnification of 5000 times. The measurement conditions for EPMA were as follows. Point analysis (to analyze the composition of each phase): An observation field of 9 μm in length and 12 μm in width was set, with an acceleration voltage of 8 kV, a probe current of 20 nA, a set beam diameter of Φ0 μm, and a counting time of 300 sec. Area analysis (to analyze the area ratio of the bonding phase): An observation field of 18 μm in length and 24 μm in width was set, with a magnification of 5000 times, an acceleration voltage of 10 kV, a probe current of 30 nA, a pixel interval of 0.1 μm, and a counting time of 30 msec for each point. The analyzing crystal used for each element in both point analysis and area analysis was CK. α : LDE2H, NK α :LDE1H, TiK α : LIFH, CoL α :TAPH, W.M. α :TAP was used.

[0071]

[0072] In Table 1, the values ​​listed above the names of the raw material powders are Fischer particle sizes, and "-" indicates that no powder was blended.

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079] Table 7 shows the "Vickers hardness (Hv) at each distance from the outermost surface line segment", that is, the "Vickers hardness (Hv) at each distance from the surface of the substrate" measured according to the Vickers hardness measurement method described above.

[0080] As is clear from Tables 1 to 7, Example 1 and Comparative Example 1 are compacts with the same blending composition, but because the atmospheric pressure in the first holding step was different, the Vickers hardness at 10 μm and 40 μm from the substrate surface did not decrease monotonically; Comparative Example 2 had a Vickers hardness of less than 1600 (Hv) at 600 μm from the substrate surface; Comparative Example 3 did not contain Cr in the second hard phase; Comparative Example 4 had a total content of Zr, Nb, Ta, V, W, and Mo exceeding 25% by mass; Comparative Example 5 had a total content of C and N in the second hard phase of less than 15.0% by mass, a total content of Ni and Fe in the binder phase of more than 5.0% by mass, and a Cr content relative to the Co content in the binder phase of more than 8.0%; In Comparative Example 6, the total content of Ni and Fe in the binder phase exceeded 5%, and the Vickers hardness at a depth of 10 μm from the flank surface toward the inside of the substrate exceeded 2100 Hv, and the Vickers hardness at a depth of 600 μm exceeded 1780 Hv.

[0081] Next, a wear resistance test was carried out on each sample under the following conditions, and the flank wear width was measured after 20 minutes.

[0082] <Cutting conditions for wear resistance test> Workpiece: SNCM439 Cutting speed: 250 m / min Depth of cut: 0.5 mm Rotational feed: 0.1 mm / rev Coolant: Water-soluble

[0083] Further, a fracture resistance test was carried out on each sample under the following conditions, and it was confirmed whether or not fracture occurred in the cutting tool after one minute of machining.

[0084] <Cutting conditions for fracture resistance test> Workpiece: SCM440 Workpiece shape: Round bar with four equally spaced grooves on the outer surface Cutting speed: 200 m / min Depth of cut: 1.0 mm Rotational feed: 0.1 mm / rev Coolant: None

[0085]

[0086] As is clear from Table 8 of the wear resistance test and fracture resistance test described above, the Examples all had a small wear width on the flank face and were durable, and no fractures occurred on the cutting edge in the fracture resistance evaluation. On the other hand, the Comparative Examples had a large wear width on the flank face and were either poor in durability or suffered fractures on the cutting edge in the fracture resistance evaluation.

[0087] The above-disclosed embodiments are merely illustrative in all respects and are not restrictive. The scope of the present invention is defined by the claims, not by the above-disclosed embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0088] 1 First hard phase 2 Second hard phase 3 Binder phase 4 Third hard phase 10 Flank face (substrate surface) 11 Angle φ 12 Polished portion 13 Unpolished portion X Line segment X S Outermost surface line segment A Line segment A B Line segment B C Line segment C D Line segment D a to d Vickers hardness measurement points (indentations)

Claims

1. A cutting tool including a cermet substrate, wherein the cermet substrate has a first hard phase, a second hard phase, and a binder phase, and the first hard phase is a complex carbonitride containing 0.0 to 3.0 mass% in total of at least one element selected from the group consisting of Zr, V, Nb, Ta, Mo, and W, 0.0 to less than 0.2 mass% of Cr, 18.0 to 22.0 mass% in total of C and N, and the balance being Ti and unavoidable impurities; the second hard phase is a complex carbonitride containing 10.0 to 25.0 mass% in total of at least one selected from the group consisting of Zr, V, Nb, Ta, Mo, and W, more than 0.0 and less than 1.0 mass% of Cr (however, the Cr content of the second hard phase is higher than the Cr content of the first hard phase), 15.0 to 20.0 mass% in total of C and N, and the balance being Ti and unavoidable impurities; the binder phase contains 0.0 to less than 5.0 mass% in total of Ni and Fe, 1.0 to 8.0% by mass of Cr relative to the content of Co, and the balance being Co and unavoidable impurities; a Vickers hardness monotonically decreasing in a first region extending from the flank surface of the base to a depth of 100 μm inside the base, a Vickers hardness of 1700 to 2100 Hv in a second region extending from the flank surface to a depth of 40 μm inside the base, and a Vickers hardness of 1600 to 1780 Hv at a depth of 600 μm from the flank surface inside the base.

2. The cutting tool according to claim 1, wherein the second hard phase further contains Ta and / or Nb, and W.

3. A cutting tool according to claim 1 or 2, further comprising a third hard phase which is a composite carbonitride containing 25.0 to 45.0 mass% in total of at least one element selected from the group consisting of Zr, V, Nb, Ta, Mo, and W, 0.0 to less than 1.0 mass% of Cr (but less than the Cr content of the second hard phase), 10.0 to 17.0 mass% in total of C and N, and the balance being Ti (but less than the Ti content of the first hard phase) and unavoidable impurities.

4. A cutting tool according to claim 1 or 2, characterized in that the area ratio of the first hard phase is 10.0 to 30.0%, the area ratio of the second hard phase is 50.0 to 80.0%, and the area ratio of the third hard phase is 0.0 to 5.0%.

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