TiN-based sintered body and cutting tool made of TiN-based sintered body

Abstract

Disclosed is a TiN-based sintered body and a cutting tool made of the TiN-based sintered body, which has 70 to 94 area % of a TiN phase, 1 to 25 area % of a Mo.sub.2C phase, and a remainder including a binder phase. The binder phase contains Fe and Ni whose total area ratio is 5 to 15 area %, and an amount of Ni to a total amount of Fe and Ni is 15 to 35 mass %. When an X-ray diffraction profile is measured in the cross section of the TiN-based sintered body, the diffraction peaks of TiN, Mo.sub.2C and Fe—Ni having an fcc structure are present, but the diffraction peaks of Fe—Ni having a bcc structure, a Fe.sub.3Mo.sub.3C phase, and a Fe.sub.3Mo.sub.3N phase are absent. The lattice constant of the TiN is 4.235 to 4.245 Å, and that of the Fe—Ni having an fcc structure is 3.58 to 3.62 Å.

Claims

1. A TiN-based sintered body comprising: a sintered structure containing; 70 to 94 area % of a TiN phase, 1 to 25 area % of a Mo.sub.2C phase, and a remainder being a binder phase, wherein (a) of the binder phase consists essentially of Fe and Ni, a total area ratio of Fe and Ni is 5 to 15 area %, and a content ratio of Ni with respect to a total amount of Fe and Ni is 15 to 35 mass %, (b) in a case where an X-ray diffraction profile is measured in a cross section of the TiN-based sintered body using an X-ray diffractometer, at least diffraction peaks of TiN, Mo.sub.2C, and Fe-Ni having an fcc structure are present, but diffraction peaks of Fe-Ni having a bcc structure, a Fe.sub.3Mo.sub.3C phase of a composite carbide, and a Fe.sub.3Mo.sub.3N phase of a composite nitride are not present, and (c) in a case where lattice constants of the TiN and the Fe-Ni having an fcc structure are determined from the X-ray diffraction profile in the cross section of the TiN-based sintered body measured using the X-ray diffractometer, the lattice constant of the TiN is 4.235 to 4.245 A, and the lattice constant of the Fe-Ni having an fcc structure is 3.58 to 3.62 Å.

2. A cutting tool made of a TiN-based sintered body, wherein at least a cutting edge of the cutting tool is formed of the TiN-based sintered body according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWING(S)

(1) The FIGURE shows examples of X-ray diffraction profiles measured in the cross sections of TiN-based sintered bodies, the upper graph shows the X-ray diffraction profile of an invention TiN-based sintered body 1, and the lower graph shows the X-ray diffraction profile of a comparative example TiN-based sintered body 12.

DETAILED DESCRIPTION OF THE INVENTION

(2) Hereinafter, a technical reason for determining the area ratio of each phase in the sintered structure of a TiN-based sintered body to a specific value, a technical reason for determining the content ratio of Ni and Fe forming a binder phase to a specific mass ratio, and a technical reason for determining the lattice constants of TiN and the binder phase to predetermined numerical value ranges will be described.

TiN Phase

(3) When the amount of a TiN phase in a TiN-based sintered body is less than 70 area %, the hardness of the sintered body is not sufficient, and as a result, the wear resistance of a cutting tool made of the TiN-based sintered body (hereinafter, referred to as “TiN-based cutting tool”) also degrades. On the other hand, when the TiN phase in the TiN-based sintered body exceeds 94 area %, fine voids (pores) are likely to be formed in the sintered microstructure, and thus the toughness degrades, and the chipping resistance and fracture resistance of the TiN-based cutting tool degrade.

(4) Therefore, the amount of the TiN phase in the TiN-based sintered body is set to 70 to 94 area %.

(5) In the present invention, the cross section of the TiN-based sintered body was observed with an electron scanning microscope (SEM) equipped with an energy dispersive X-ray analyzer (EDS), the amounts of elements contained in a region (for example, a 100 μm.sup.2 region) in the obtained secondary electron image were measured, the TiN phase, a Mo.sub.2C phase, and a Fe—Ni phase having an fcc structure were specified, the area ratio of each phase in the region was calculated, the area ratio was calculated in at least a plurality of regions, which is five or more regions, and the average value of the area ratio was regarded as the area percentage of each phase.

Mo2C Phase

(6) When the amount of the Mo2C phase in the TiN-based sintered body is less than 1 area %, the wettability between the TiN phase and a binder phase is insufficient, and voids are generated in the sintered microstructure. Therefore, the toughness degrades. On the other hand, when the amount of Mo.sub.2C phase exceeds 25 area %, a composite carbide such as a Fe.sub.3Mo.sub.3C phase and a composite nitride such as a Fe.sub.3Mo.sub.3N phase are likely to be formed, and the composite carbide and the composite nitride degrade the toughness. Therefore, the amount of the Mo.sub.2C phase in the TiN-based sintered body is determined to be 1 to 25 area %.

Binder Phase

(7) When the amount of the binder phase in the TiN-based sintered body is less than 5 area %, the amount of the binder phase is small, and thus the toughness of the TiN-based sintered body degrades. On the other hand, when the amount of the binder phase exceeds 15 area %, the amount of the TiN phase, which is a hard phase component, relatively decreases, and thus the hardness decreases, and as a result, the wear resistance of the TiN-based cutting tool also degrades.

(8) Therefore, the amount of the binder phase in the TiN-based sintered body is determined to be 5 to 15 area %.

(9) In addition, in the present invention, when the content ratio of Ni with respect to the total amount of Fe and Ni forming the binder phase (=Ni/(Fe+Ni)×100) is determined to be 15 to 35 mass %, it is possible to further enhance the toughness and hardness of the TiN-based sintered body.

(10) The reasons are as follows. In a case where the content ratio of Ni with respect to the total amount of Fe and Ni (=Ni/(Fe+Ni)×100) is less than 15 mass %, Ni forms solid solutions in Fe, but the effect of the solid solutions is not strong enough for strengthening of the binder phase, and thus the hardness of the binder phase is insufficient. In a case where the content ratio of Ni with respect to the total amount of Fe and Ni (=Ni/(Fe+Ni)×100) exceeds 35 mass %, an intermetallic compound FeNi.sub.3 is likely to be generated, and thus the toughness of the binder phase degrades.

(11) In a case where an X-ray diffraction profile is measured in the cross section of the TiN-based sintered body of the present invention using an X-ray diffractometer in a measurement range (2θ) of 25 to 115 degrees, as shown in FIG. 1, the presence of at least the diffraction peaks of TiN, Mo.sub.2C, and Fe—Ni having an fcc structure is confirmed, but the presence of the diffraction peaks of Fe—Ni having a bcc structure and Fe.sub.3Mo.sub.3C is not confirmed. The diffraction peaks were identified using JCPDS card, No. 00-088-1420 was used for TiN, No. 01-071-0242 was used for Mo.sub.2C, No. 98-063-2933 was used for Fe—Ni having an fcc structure, No. 00-087-0474 was used for Fe—Ni having a bcc structure, and No. 00-047-1191 (Fe.sub.3Mo.sub.3C), No. 01-089-7952 (Fe.sub.3Mo.sub.3N), No. 01-089-2579 (Fe.sub.3W.sub.3C) were used for the double carbide and the double nitride.

(12) From this fact, it is understood that, in the TiN-based sintered body of the present invention, a hetero-phase formed of a Fe—Ni phase having a bcc structure, a composite carbide such as a Fe.sub.3Mo.sub.3C phase, or a composite nitride such as a Fe.sub.3Mo.sub.3N phase, which degrades the toughness and hardness of the sintered body, is not formed.

(13) The X-ray diffraction measurement can be carried out using a Cu-Kα ray (λ=1.5418 Å) as a radiation source under the conditions of a scan step of 0.013 degrees and a measurement time per step of 0.48 sec/step.

(14) In addition, when an X-ray diffraction profile as shown in FIG. 1 is measured in the cross section of the TiN-based sintered body of the present invention in the same manner, and the lattice constants of TiN and Fe—Ni having an fcc structure are determined from the diffraction peaks thereof, the lattice constant of TiN is in a range of 4.235 to 4.245 Å, and the lattice constant of Fe—Ni having an fcc structure is in a range of 3.58 to 3.62 Å.

(15) Here, when the lattice constant of TiN is less than 4.235 Å, Ti or N is released from the crystal lattice of TiN having an fcc structure, and an increase in defects in TiN particles degrades the toughness. In addition, when the lattice constant of TiN exceeds 4.245 Å, C is contained in the crystal lattice of TiN, and thus the toughness of TiN particles is impaired.

(16) Therefore, the lattice constant of TiN needs to be in a range of 4.235 to 4.245 Å.

(17) In addition, when the lattice constant of Fe—Ni having an fcc structure, which forms the binder phase, is less than 3.58 Å, the amount of C contained in the binder phase is small, and thus Fe.sub.3Mo.sub.3C is likely to be generated, and the toughness of the TiN-based sintered body degrades. On the other hand, when the lattice constant of Fe—Ni having an fcc structure exceeds 3.62 Å, a hetero-phase of iron carbide such as cementite is likely to be generated, and the toughness degrades.

(18) Therefore, the lattice constant of Fe—Ni having an fcc structure, which forms the binder phase, needs to be in a range of 3.58 to 3.62 Å.

(19) Regarding the measurement of the lattice constant, the lattice constants can be respectively obtained from the value of 2θ where the diffraction peak of the (200) plane of TiN appears and the value of the 2θ where the diffraction peak of the (111) plane of Fe—Ni having an fcc structure appears by calculation based on Bragg's equation: 2d sin θ=nλ (where d is the lattice spacing, θ is the Bragg angle, 2θ is the diffraction angle, λ is the wavelength of the incident X-ray, and n is an integer).

Production of TiN-Based Sintered Body of Present Invention

(20) In the production of the TiN-based sintered body of the present invention, in order to obtain the component composition and the like of each phase described above, first, it is preferable to use, as raw material powders, raw material powders containing components of TiN: 55 to 92 mass %, Mo.sub.2C: 1 to 40 mass %, Fe: 5 to 18 mass %, and Ni: 1 to 5 mass % and having a composition satisfying a relationship in which the mass percentage of Ni with respect to the total amount of Ni and Fe (=Ni×100/(Fe+Ni)) is 15 to 35 mass %.

(21) In addition, the raw material powders satisfying the above-described condition are mixed together with a ball mill, and the mixed powders are press-formed to produce a green compact.

(22) Then, the green compact is sintered in a temperature range of 1350° C. to 1450° C. for 30 to 120 minutes under the flow of a gas mixture having a hydrogen concentration of 1% to 3% and having a nitrogen concentration of 97% to 99% (nitrogen-diluted hydrogen atmosphere). After that, the atmosphere is switched to a vacuum atmosphere of 10.sup.−1 Pa, and the green compact is cooled to 1200° C. while being heated with a heater at a rate of 10° C./minute. Furthermore, the heating with the heater is stopped at 1200° C., and the green compact is naturally cooled to room temperature. As a result, the TiN-based sintered body of the present invention that is excellent in terms of both toughness and hardness can be produced.

(23) The reason for sintering the green compact in the nitrogen-diluted hydrogen atmosphere is that, when the wettability between the TiN powder and Fe, which is the major component of the binder phase, is enhanced, the sinterability is enhanced at the same time.

(24) In addition, after that, the TiN-based sintered body is machined into a predetermined shape, whereby a cutting tool made of the TiN-based sintered body that is excellent in terms of abnormal damage resistance against chipping and fracturing and wear resistance and exhibits excellent cutting performance over long-term use can be produced.

(25) Next, examples of the present invention will be specifically described.

EXAMPLES

(26) As powders for producing TiN-based sintered bodies, TiN powder having an average grain size of 10 μm, Mo.sub.2C powder having an average grain size of 2 μm, Fe powder having an average grain size of 2 μm, and Ni powder having an average grain size of 1 μm were prepared, blended together to obtain blending ratios shown in Table 1, and blended together such that the amount of the Fe powder blended and the amount of the Ni powder blended satisfied blending percentages shown in Table 1, thereby preparing raw material powders 1 to 8. The average grain size mentioned herein means the median diameter (d50).

(27) Next, the raw material powders 1 to 8 were loaded into a ball mill and mixed together to produce mixed powders 1 to 8. The mixed powders 1 to 8 were dried and then press-formed at a pressure of 100 to 500 MPa, thereby producing green compacts 1 to 8.

(28) Next, these green compacts 1 to 8 were sintered under the conditions shown in Table 2, the atmosphere was switched to a vacuum atmosphere of 10.sup.−1 Pa, and the green compacts were cooled to 1200° C. while being heated with a heater at a rate of 10° C./min. Furthermore, the heating with the heater was stopped at 1200° C., and the green compacts were naturally cooled to room temperature, thereby producing TiN-based sintered bodies of the present invention (hereinafter referred to as “prevent invention sintered bodies”) 1 to 8 shown in Table 3.

(29) For comparison, a variety of powders each having an average grain size equivalent to those for present invention tools were blended together to obtain blending composition shown in Table 4, thereby preparing raw material powders 11 to 18. Next, the raw material powders 11 to 18 were loaded into the ball mill and mixed together to produce mixed powders 11 to 18. The mixed powders 11 to 18 were dried and then press-formed at a pressure of 100 to 500 MPa to produce green compacts 11 to 18.

(30) Next, these green compacts 11 to 18 were sintered under the conditions shown in Table 2 and Table 5 and then cooled to room temperature, thereby producing sintered bodies of comparative examples shown in Table 6 (hereinafter, referred to as “comparative example sintered bodies”) 11 to 18.

(31) For reference, a WC-based cemented carbide sintered body was produced by the following method.

(32) As raw material powders, WC powder and Co powder each having an average grain size of 0.5 to 1 μm were prepared. These raw material powders were blended together at a ratio of WC: 90 mass % and Co: 10 mass %, wet-mixed for 24 hours in the ball mill, and dried. After that, the mixture was press-formed to a green compact at a pressure of 100 MPa, and the green compact was sintered in a vacuum of 6 Pa under the conditions of a temperature of 1400° C. and a retention time of one hour, thereby forming the WC-based cemented carbide sintered body (hereinafter, simply referred to as “cemented carbide”).

(33) A WC-based cemented carbide sintered body 21 (hereinafter, referred to as “reference example sintered body 21”) having a component composition of WC: 84 area % and Co: 16 area % was produced by the above-described method.

(34) For additional reference, a TiCN-based cermet sintered body was produced by the following method.

(35) As raw material powders, TiCN powder, Mo.sub.2C powder, Co powder, and Ni powder each having an average grain size of 0.5 to 3 μm were prepared. These raw material powders were blended together at a ratio of TiCN: 75 mass %, Mo.sub.2C: 10 mass %, Co: 7.5 mass %, and Ni: 7.5 mass %, wet-mixed for 24 hours in the ball mill, and dried. After that, the mixture was press-formed to a green compact at a pressure of 200 MPa, and the green compact was sintered in a vacuum of 6 Pa under the conditions of a temperature of 1450° C. and a retention time of one hour, thereby forming a TiCN-based cermet sintered body (hereinafter, simply referred to as “cermet”).

(36) A TiCN-based cermet sintered body 22 (hereinafter, referred to as “reference example sintered body 22”) having a component composition of TiMoCN: 90 area % and Co+Ni: 10 area % was produced by the above-described method.

(37) Next, the cross sections of the present invention sintered bodies 1 to 8 and the comparative example sintered bodies 11 to 18 were observed with an electron scanning microscope (SEM) equipped with an energy dispersive X-ray analyzer (EDS), the amounts of elements contained in a measurement region (for example, a 100 μm×100 pm measurement region) in the obtained secondary electron image were measured. A TiN phase, a Mo.sub.2C phase, and a Fe—Ni phase having an fcc structure were specified, and the area ratio of each phase in the measurement region was calculated. The area ratio were calculated in five measurement regions, and the average value of these calculation values was obtained as the area percentage of each phase in the sintered microstructure.

(38) In addition, regarding the Fe—Ni phase having an fcc structure, the Ni content and the Fe content in the phase were measured at 10 points on the Fe—Ni phase using an Auger electron spectrometer, and the content ratio of Ni with respect to the total amount of Fe and Ni (=Ni×100/(Fe+Ni)) was obtained from the average value of the obtained calculation values in terms of the mass percentage.

(39) Table 3 and Table 6 show these values.

(40) In addition, the X-ray diffraction profiles in the cross sections of the present invention sintered bodies 1 to 8 and the comparative example sintered bodies 11 to 18 were measured using an X-ray diffractometer in a measurement range (2θ) of 25 to 115 degrees, and a phase present in the sintered microstructure of each sintered body was confirmed.

(41) The X-ray diffraction measurement was carried out using a Cu-Kα ray (λ=1.5418 Å) as a radiation source under the conditions of a scan step of 0.013 degrees and a measurement time per step of 0.48 sec/step. In addition, regarding the presence or absence of a peak, first, peaks were extracted from the obtained XRD profile using a commercially available XRD analysis software. Subsequently, from the individual extracted peaks, a peak having a count 3% or more higher than the background count around the peak was selected. For the selected peak, a peak was determined to be present, and, for other peaks, a peak was determined to be not present.

(42) In addition, from the diffraction peaks of TiN and Fe—Ni having an fcc structure in the X-ray diffraction profiles measured in the cross sections of the present invention sintered bodies 1 to 8 and the comparative example sintered bodies 11 to 18, the lattice constants of TiN and Fe—Ni having an fcc structure were obtained.

(43) The lattice constants were respectively obtained from the value of 20 where the diffraction peak of the (200) plane of TiN appeared and the value of the 20 where the diffraction peak of the (111) plane of Fe—Ni having an fcc structure appeared by calculation based on Bragg's equation: 2d sin θ=nλ (where d is the lattice spacing, θ is the Bragg angle, 2θ is the diffraction angle, λ is the wavelength of the incident X-ray, and n is an integer).

(44) λ is 1.5418 Å as described above.

(45) Table 3 and Table 6 show phases present in the sintered microstructures and the lattice constants of TiN and Fe—Ni having an fcc structure.

(46) Next, for the present invention sintered bodies 1 to 8, the comparative example sintered bodies 11 to 18, and the reference example sintered bodies 21 and 22, the Vickers hardness HV (N/mm.sup.2) was measured with a test force of 10 kg, and the average value of values measured at five points was obtained as the Vickers hardness HV (N/mm.sup.2) of each sintered body.

(47) In addition, as the index of the toughness of each sintered body, the length of an indentation (the length of the maximum diagonal line of the indentation) formed during the measurement of the Vickers hardness was measured, and the length of a crack (the length of the maximum crack) extended from the indentation was measured. The fracture toughness value (MPa.Math.m.sup.0.5) was obtained from Niihara et al.'s equation (refer to K. Niihara, R. Morena, and D. P. H Hasselman's “Evaluation of KIc of brittle solids by the indentation method with low crack-to-indent ratios”, J Mater Sci Lett, 1, 13 (1982)), and the values obtained from five points were averaged to obtain the fracture toughness value of each sintered body.

(48) It can be said that the more the average Vickers hardness (HV) increases, the more the hardness increases, and the more the fracture toughness increases, the more the toughness increases, in each sintered body.

(49) Table 3 and Table 6 show these values.

(50) According to Table 3 and Table 6, it is found that the present invention sintered bodies 1 to 8 had hardness that was almost comparable to the hardness of the reference example sintered body 22 (TiCN-based cermet sintered body) and toughness that was almost comparable to the toughness of the reference example sintered body 21 (WC-based cemented carbide sintered body).

(51) TABLE-US-00001 TABLE 1 Blending composition (mass %) Blending ratio Type of raw of Ni powder material TiN Mo.sub.2C Fe Ni (mass %) powder powder powder powder powder Ni × 100/(Fe + Ni) 1 85.0 4.0 8.7 2.3 20.9 2 83.0 4.0 10.0 3.0 23.1 3 58.5 35.3 5.0 1.2 19.4 4 59.5 21.5 15.2 3.8 20.0 5 91.2 1.6 5.8 1.4 19.4 6 83.0 4.0 8.5 4.5 34.6 7 83.0 4.0 11.0 2.0 15.4 8 75.0 12.0 9.0 4.0 30.8

(52) TABLE-US-00002 TABLE 2 Sintering conditions Sintering Sintering Hydrogen Nitrogen Sintering temperature time concentration concentration conditions (°C) (minute) (%) (%) 1 1400 60 2 98 2 1450 30 1 99 3 1350 120 3 97 4 1400 90 3 97

(53) TABLE-US-00003 TABLE 3 X-ray diffraction profile Type of Lattice constant (Å) present Fe—Ni Fracture invention Type of Component composition of sintered body (area %) having Vickers toughness sintered sintering Binder phase Phase detected from fcc hardness value body conditions TiN Mo.sub.2C Fe + Ni Ni × 100/(Fe + Ni) diffraction peak TiN structure (HV) (MPa .Math. m.sup.0.5) 1 1 89.7 2.5 7.8 20.9 TiN, Mo.sub.2C, 4.241 3.605 1585 11.5 Fe—Ni (fcc) 2 2 88.2 2.5 9.3 23.1 TiN, Mo.sub.2C, 4.238 3.588 1509 12.3 Fe—Ni (fcc) 3 3 70.0 25.0 5.0 20.0 TiN, Mo.sub.2C, 4.242 3.602 1627 10.2 Fe—Ni (fcc) 4 4 70.0 15.0 15.0 20.0 TiN, Mo.sub.2C, 4.245 3.606 1420 13.6 Fe—Ni (fcc) 5 1 94.0 1.0 5.0 20.0 TiN, Mo.sub.2C, 4.243 3.615 1650 9.5 Fe—Ni (fcc) 6 2 88.3 2.5 9.2 34.6 TiN, Mo.sub.2C, 4.235 3.580 1522 12.1 Fe—Ni (fcc) 7 3 88.1 2.5 9.4 15.4 TiN, Mo.sub.2C, 4.236 3.620 1493 12.6 Fe—Ni (fcc) 8 4 82.7 7.8 9.5 30.8 TiN, Mo.sub.2C, 4.240 3.584 1475 13.1 Fe—Ni (fcc)

(54) TABLE-US-00004 TABLE 4 Blending composition (mass %) Blending ratio Type of raw of Ni powder material TiN Mo.sub.2C Fe Ni (mass %) powder powder powder powder powder Ni × 100/(Fe + Ni) 11 85.0 4.0 6.5 4.5 40.9 12 87.0 0.0 10.0 3.0 23.1 13 52.0 40.0 6.0 2.0 25.0 14 70.0 2.0 20.0 8.0 28.6 15 94.0 2.0 3.0 1.0 25.0 16 83.0 4.0 9.5 3.5 26.9 17 83.0 4.0 12.0 1.0 7.7 18 80.0 10.0 8.0 2.0 20.0

(55) TABLE-US-00005 TABLE 5 Sintering conditions Sintering Sintering Hydrogen Nitrogen Sintering temperature time concentration concentration conditions (° C.) (minute) (%) (%) 11 1400 60 0 100 12 1500 60 2 98 13 1300 120 3 97 14 1400 90 10 90

(56) TABLE-US-00006 TABLE 6 X-ray diffraction profile Type of Lattice constant (Å) comparative Component composition of sintered body (area %) Fe—Ni Fracture example Type of Binder phase having Vickers toughness sintered sintering Ni × 100/ Phase detected from fcc hardness value body conditions TiN Mo.sub.2C Fe + Ni (Fe + Ni) diffraction peak TiN structure (HV) (MPa .Math. m.sup.0.5) 11 1 89.9 2.5 7.6 40.9 TiN, Mo.sub.2C, 4.238 3.550 1561 7.2 Fe—Ni (fcc), FeNi.sub.3 12 2 90.9 0.0 9.1 23.1 TiN, Fe-Ni(fcc, bcc) 4.236 3.592 1357 10.3 13 3 64.2 29.2 6.6 25.0 TiN, Mo.sub.2C, 4.251 3.614 1430 9.5 Fr—Ni (fcc), Fe.sub.3Mo.sub.3N 14 4 77.9 1.3 20.8 28.6 TiN, Mo.sub.2C, 4.242 3.603 1237 14.2 Fe—Ni (fcc, bcc) 15 13 96.1 1.2 2.7 25.0 TiN, Mo.sub.2C, 4.239 3.593 1573 6.1 Fe—Ni (fcc, bcc) 16 12 88.2 2.5 9.2 26.9 TiN, MO.sub.2C, 4.229 3.597 1334 11.1 Fe—Ni (fcc, bcc), Fe.sub.3Mo.sub.3C 17 14 88.1 2.5 9.4 7.7 TiN, MO.sub.2C, 4.231 3.625 1486 8.7 Fe—Ni (fcc, bcc), Fe.sub.3Mo.sub.3C 18 11 86.3 6.4 7.3 20.0 TiN, MO.sub.2C, 4.242 3.584 1394 9.6 Fe—Ni (fcc, bcc), Fe.sub.3C Reference example sintered body 21 1532 12.0 Reference example sintered body 22 1617 9.3

(57) Next, a grinding process was carried out on the present invention sintered bodies 1 to 8, the comparative example sintered bodies 11 to 18, and the reference example sintered bodies 21 and 22 produced above, thereby producing cutting tools made of the present invention sintered bodies (hereinafter, referred to as “present invention tools”) 1 to 8, cutting tools made of the comparative example sintered bodies (hereinafter, referred to as “comparative example tools”) 11 to 18, and cutting tools made of the reference example sintered bodies (hereinafter referred to as “reference example tools”) 21 and 22 each having an insert shape of ISO standard SEEN 1203AFSN.

(58) A wet-type milling cutting process test of alloy steel, which will be described below, was carried out in a state in which each of the present invention tools 1 to 8, the comparative example tools 11 to 18, and the reference example tools 21 and 22 was screwed to the tip portion of a cutter made of tool steel with a fixing jig, the wear width of flank face of the cutting edge was measured, and the wear state of the cutting edge was observed.

Cutting Conditions

(59) Work material: JIS SCM440 block,

(60) Cutting speed: 150 m/min,

(61) Cutting depth: 1.0 mm,

(62) Feed: 0.38 mm/rev,

(63) Cutting time: 11 minutes,

(64) Table 7 shows the results of the cutting test.

(65) TABLE-US-00007 TABLE 7 Wear state Wear width of of cutting Type flank face (mm) edge Present 1 0.10 No invention abnormality tool 2 0.12 No abnormality 3 0.09 No abnormality 4 0.18 No abnormality 5 0.08 Mild chipping.sup.(Note) 6 0.11 No abnormality 7 0.13 No abnormality 8 0.14 No abnormality Comparative 11 0.25 Chipping example 12 *5 Fracturing tool 13 *9 Normal wear 14 *7 Heat crack 15 *3 Fracturing 16 *3 Fracturing 17 *4 Fracturing 18 *5 Fracturing Reference 21 0.19 No example abnormality tool 22 0.14 Chipping (Note) The mild chipping in the present invention tool 5 was damage that did not affect the tool service life and did not cause any problems even when the present invention tool was further used for cutting after the present test. *indicates the cutting time (minutes) elapsed until the service life ended.

(66) As shown in Table 7, the present invention tools 1 to 8 of the present invention did not allow the occurrence of an abnormal damage such as fracturing, chipping, or the like that was serious enough to affect the cutting service lives, showed excellent wear resistance that was almost comparable to the wear resistance of the reference example tool 21, and exhibited excellent cutting performance over long-term use.

(67) However, the comparative example tools 11 to 18 and the reference example tool 22 did not have sufficient toughness, and thus the tool service lives were short due to the occurrence of abnormal damage such as chipping and fracturing.

INDUSTRIAL APPLICABILITY

(68) The TiN-based sintered body of the present invention is excellent in terms of both hardness and toughness and thus can be applied not only to cutting tools but also to tough members and wear-resistant members in a variety of technical fields. Particularly, in the case of being used as a cutting tool, the TiN-based sintered body exhibits excellent wear resistance and excellent abnormal resistance. Therefore, the cutting tool exhibits excellent cutting performance over long-term use and is capable of sufficiently satisfying the labor-saving, energy-saving, and furthermore, cost reduction of cutting processes.