JP2014029001A - Cermet, method for manufacturing the cermet, and cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cermet excellent in terms of the balance of abrasion resistance and defect resistance and a method for manufacturing the same.SOLUTION: The cermet comprises: a hard phase layer including at least one type of compound selected from the group consisting of carbides, carbonitrides, composite carbides, and composite carbonitrides of metals selected from the group consisting of Group 4, 5, and 6 metals of the periodic table; a binder layer including an iron group metal as a main component; and inevitable impurities. Within the surface region of the cermet over a depth of 10 μm from the surface toward interior thereof, furthermore, a soft surface layer having a hardness distribution of a continuously waxing hardness profile along the depth direction and having a surface hardness lesser than the internal hardness of the internal region by 2-10% is formed. The soft surface layer, furthermore, comprises a core portion consisting of a Ti compound and peripheral tissues surrounding the former. The peripheral tissues consist of a composite carbonitride solid-solution including at least Ti and W.

Description

  The present invention relates to a cermet, a cermet manufacturing method, and a cutting tool. In particular, the present invention relates to a cermet having an excellent balance between wear resistance and fracture resistance.

  Conventionally, cermets that use titanium carbide (TiC) or titanium carbonitride (TiCN) as the main hard phase as the base material for cutting tools and are bonded with iron group elements such as cobalt (Co) or nickel (Ni) have been used. (For example, refer to Patent Documents 1 to 6 and Non-Patent Document 1). Cutting tools based on cermet are 1) superior in wear resistance compared to cutting tools based on cemented carbide with tungsten carbide (WC) as the main hard phase. 2) Finishing in steel processing. There are advantages such as high quality surface, 3) high-speed cutting, 4) light weight, and 5) abundant and inexpensive raw materials.

  In the cermet used for the base material of the cutting tool, from the viewpoint of reducing the manufacturing cost, the surface of the cermet obtained by sintering is not polished and the surface state of the cermet (after sintering) An unpolished product (M-class product) that is used as it is (surface state) is known. For example, in an unpolished (M-class) cutting tip, the cutting edge is generally subjected to a cutting edge treatment such as honing, and the cutting edge processing amount is generally about 80 μm on the rake face and about 50 μm on the flank face. .

  In Patent Documents 1 and 2, a softened surface layer having a hardness distribution that continuously increases from the cermet surface to the maximum depth of 300 μm toward the inside, and the surface hardness is 5 to 20% lower than the internal hardness. Cermets having the following are described: In these Patent Documents 1 and 2, by sintering in a nitrogen atmosphere, the hard phase component in the surface layer is nitrided, it becomes difficult for the hard phase particles to form a bridge, and the internal binder phase is drawn out to the surface layer. Thus, it is described that a softened surface layer is formed.

  Patent Documents 3 and 4 describe cermets in which the surface and the internal structure of the cermet are uniform, that is, the hardness is substantially constant from the cermet surface to the inside. Patent Document 3 describes that in the cooling step, the CO gas partial pressure in the atmosphere is controlled to suppress the seepage of the binder phase to the surface and to uniformly disperse the binder phase. . On the other hand, Patent Document 4 describes cooling in the cooling step from the sintering temperature to 1200 ° C. at a cooling rate of 50 ° C./min or more.

  Patent Documents 5 and 6 describe cermets having a high hardness layer on the cermet surface. Specifically, Patent Document 5 has a hardness distribution that continuously decreases from the cermet surface to the maximum depth of 1 mm toward the inside, and the surface hardness is 5 to 30% of the internal hardness. Cermets with a high cured surface are described. Patent Document 5 describes that a hardened surface layer is formed by heating to a temperature lower than the temperature at which a liquid phase appears in a carburizing gas atmosphere such as CO, and subsequently vacuum sintering. On the other hand, in Patent Document 6, in the temperature raising step, nitrogen gas having a pressure of 70 Torr or more is introduced into the furnace before reaching the maximum sintering temperature and reaching the vacuum after reaching the maximum sintering temperature. Describes that a portion having a Vickers hardness of 2000 or more is formed in the surface layer portion from the cermet surface to 50 μm.

  In Non-Patent Document 1, a layer composed only of a hard phase and a binder phase of carbonitride particles having no surrounding structure is formed on the cermet surface by sintering in a denitrification atmosphere such as a vacuum, It is described that a cermet having a softened surface layer having a surface hardness of 2 to 13% lower than the hardness and a thickness of 2.0 to 7.5 μm can be obtained.

JP 54-117510 A JP 54-150411 A JP 54-101704 A JP 63-57732 A JP-A-54-139815 JP-A-2-93036

Edited by Satoshi Suzuki, “Cemented carbides and sintered hard materials”, Maruzen Co., Ltd., February 1986, p.352,353

  In cermets, it is known that hardness (wear resistance) and toughness (breakage resistance) are contradictory properties. Recently, improvement in cutting performance and tool life of cutting tools has been strongly demanded, and a cermet used as a base material for cutting tools is required to have an excellent balance between wear resistance and fracture resistance. However, conventional cermets have room for improvement in terms of a balance between wear resistance and fracture resistance.

  As a result of intensive studies by the present inventors, when a cermet having a uniform surface and internal hardness as described in Patent Documents 3 and 4 is used as a base material of a cutting tool, the wear resistance and fracture resistance are improved. It turned out to be insufficient in terms of balance. Moreover, in the cermet whose surface hardness is high as compared with the internal hardness as described in Patent Documents 5 and 6, the wear resistance is excellent, but since the toughness of the surface portion is low, in terms of fracture resistance I found it inferior.

  On the other hand, Patent Documents 1 and 2 propose a cermet having a softened surface layer for the purpose of imparting toughness. However, in these Documents 1 and 2, the thickness of the softened surface layer is at least 40 μm (for example, patent (See Table 2 of Document 1) and the comparative example is also 20 μm. And when a cermet having a softened surface layer as described in Patent Documents 1 and 2 is used for a cutting tool, although it has excellent fracture resistance, the thickness of the softened surface layer with low hardness is large, so that the wear resistance is insufficient. I found out that

  Further, in Non-Patent Document 1, although the thickness of the softened surface layer is 3 μm at the minimum, the softened surface layer is constituted only by the hard phase and the binder phase of carbonitride particles having no surrounding structure. Therefore, since the thermal conductivity in the vicinity of the cermet surface is low, a cermet having a softened surface layer as described in Non-Patent Document 1 is used for a cutting tool due to insufficient thermal shock resistance, which is one of the disadvantages of cermet. It was found to be inferior in fracture resistance. In particular, this tendency is remarkable in a cutting environment using cutting oil.

  Therefore, the development of a cermet for a cutting tool that has an excellent balance between wear resistance and fracture resistance is awaited.

  This invention is made | formed in view of the said situation, and one of the objectives is to provide the cermet which is excellent in the balance of abrasion resistance and fracture resistance, and its manufacturing method. Another object of the present invention is to provide a cutting tool comprising a substrate made of this cermet.

<Cermet>
The cermet of the present invention includes a hard phase containing at least one compound selected from the group consisting of carbides, carbonitrides, composite carbides, and composite carbonitrides of metals selected from Groups 4, 5, and 6 of the periodic table; It consists of a binder phase mainly composed of a group metal and unavoidable impurities. And, in the surface region from the cermet surface to the depth up to 10 μm, it has a hardness distribution in which the hardness increases continuously in the depth direction, and the surface hardness with respect to the internal hardness in the inner region A softened surface layer of 2 to 10% lower. The softening surface layer includes hard phase particles having a core portion made of a Ti compound and a surrounding structure surrounding the core, and the surrounding structure is made of a composite carbonitride solid solution containing at least Ti and W.

  According to the cermet of the present invention, the above-described specific softened surface layer is formed, so that the balance between wear resistance and fracture resistance is excellent. Therefore, when used for a cutting tool, an improvement in cutting performance and tool life can be expected. Here, the softened surface layer is a portion having a hardness distribution in which the hardness continuously increases in the depth direction from the surface toward the inside. In the present invention, the softened surface layer is directed from the surface toward the inside. Existing in the surface area up to a depth of 10 μm, and the surface hardness is 2 to 10% lower than the internal hardness. That is, in the cermet of the present invention, the thickness of the softened surface layer is 10 μm or less, and the decreasing rate (softening rate) of the surface hardness with respect to the internal hardness is 2 to 10%. Further, in the present invention, the internal region is a portion having a substantially constant hardness distribution in the depth direction from the softened surface layer toward the inside, and the change in hardness is within 1% over a section of 5 μm. If so, the hardness is substantially constant. The thickness of the softened surface layer is preferably at least 5 μm.

  As described above, the cutting edge processing is performed in the cutting tool, but when the softening surface layer is 20 μm or more as in the prior art, the softening surface layer remains on the surface of the cutting edge even after the cutting edge processing is performed. Even if there is a part from which the metal is removed, the range is limited to an extremely narrow range, and as a result, there is a limit in improving the wear resistance. On the other hand, when the softened surface layer is 10 μm or less as in the present invention, the wear resistance is greatly improved by removing the softened surface layer on the surface of the blade edge by performing the blade edge treatment.

  In addition, the softening surface layer contains so-called cored hard phase particles that have a surrounding structure composed of a composite carbonitride solid solution containing Ti and W around the Ti compound, so that the thermal conductivity near the cermet surface is increased. Since the thermal shock resistance can be improved, the fracture resistance is improved.

Specific examples of the compound constituting the hard phase include Ti compounds such as TiC and TiCN, and Ti containing at least one metal selected from Groups 4, 5, and 6 of the periodic table excluding Ti and Ti. Examples of the compound include composite carbide (TiWC) and composite carbonitride (TiWCN) containing Ti and W. Other examples of the metal compound selected from Groups 4, 5, and 6 of the periodic table excluding Ti include TaC, NbC, WC, Mo ₂ C, ZrC, Cr ₃ C ₂ , and VC. In the present invention, the Ti compound is the main component of the hard phase (mass ratio is 50% or more of the entire hard phase, and the Ti compound is the most in the hard phase), and the hard phase is 75% by mass with respect to the entire cermet. % Or more and 95% by mass or less is desirable.

  The peripheral structure is substantially composed of a composite carbonitride solid solution containing at least Ti and W. Furthermore, you may contain the at least 1 sort (s) of metal element selected from periodic table group 4,5,6 (however, except Ti and W). As a specific composition of the surrounding tissue, for example, (Ti, W) (C, N), (Ti, W, Nb) (C, N), (Ti, W, V) (C, N), ( (Ti, W, Zr) (C, N), (Ti, W, Mo) (C, N), (Ti, W, Nb, V) (C, N), (Ti, W, Nb, Zr) ( C, N), (Ti, W, Nb, Mo) (C, N), (Ti, W, V, Zr) (C, N), (Ti, W, V, Mo) (C, N), (Ti, W, Zr, Mo) (C, N), (Ti, W, Nb, V, Zr) (C, N), (Ti, W, Nb, V, Mo) (C, N), ( Ti, W, Nb, V, Zr, Mo) (C, N).

  On the other hand, examples of the iron group metal constituting the binder phase include Co and Ni. In the present invention, it is desirable that the iron group metal is the main component of the binder phase (by mass ratio, 65% or more of the whole binder phase, and the iron group metal is the most in the binder phase).

  As one form of the cermet of this invention, it is mentioned that the nitrogen content in a hard phase is 4 mass% or more and 7 mass% or less.

  According to this configuration, when the amount of nitrogen contained in the hard phase is 4% by mass or more, the degree of softening of the pole surface is increased, and the fracture resistance can be improved. Moreover, when the nitrogen content in the hard phase is 7% by mass or less, it is possible to suppress a decrease in wear resistance due to an excessively high softening rate. The amount of nitrogen contained in the hard phase is substantially determined by, for example, the amount of nitrogen contained in the hard phase component in the raw material. As a hard phase, in addition to metal carbonitrides and composite carbonitrides selected from Groups 4, 5, and 6 of the periodic table, at least one compound of the above metal nitrides and composite nitrides is added. However, this compound may be contained in the hard phase. Examples of such compounds include TiN, TaN, and ZrN.

  One form of the cermet of the present invention is that the Vickers hardness Hv in the inner region is 15.0 GPa or more and less than 18.0 GPa.

  According to this configuration, when the internal hardness satisfies the above range, it is easy to realize a cermet having an excellent balance between wear resistance and fracture resistance.

<Method for producing cermet>
The cermet is generally manufactured through a process of preparation of raw material powder → mixing / molding → sintering.

The method for producing a cermet according to the present invention includes, as a raw material powder, at least one compound selected from a metal carbide, carbonitride, composite carbide, and composite carbonitride selected from Groups 4, 5, and 6 of the periodic table. And the iron group metal powder are mixed, formed, sintered, and then sintered. The method includes the following steps.
(1) A preparatory step of preparing a Ti compound powder and a W compound powder and the iron group metal powder as the raw material powder.
(2) A mixing step in which the raw material powder is mixed to obtain a mixture.
(3) A molding step for obtaining a molded body obtained by molding the mixture.
(4) A sintering step in which the molded body is sintered to obtain a sintered body.
The sintering process includes a temperature raising process and a cooling process.
(4a) In the temperature raising step, the molded body is heated to the liquid phase appearance temperature at which the liquid phase appears, and then the sintering is completed in which the sintering is completed from the liquid phase appearance temperature in a nitrogen atmosphere of 100 Pa to 1000 Pa. Raise to temperature.
(4b) In the cooling step, cooling is performed at a cooling rate of 10 ° C./min to 30 ° C./min in a CO gas atmosphere of 1 kPa to 50 kPa.

  According to the cermet manufacturing method of the present invention, the above-described cermet of the present invention can be manufactured. In the cermet manufacturing method of the present invention, the temperature raising condition and the cooling condition in the sintering step are set as the specific conditions described above. Specifically, in the temperature raising step, the temperature is raised from a liquid phase appearance temperature to a sintering completion temperature in a nitrogen atmosphere at a predetermined pressure. If the pressure of the nitrogen atmosphere is too low, or the atmosphere is a vacuum or an inert gas (such as Ar), a denitrification phenomenon occurs in the temperature raising step. As a result, in the subsequent cooling step, the carbonization phenomenon of the hard phase existing in the vicinity of the surface is less likely to occur due to the CO gas atmosphere, so there is a possibility that the extreme surface softening phenomenon does not occur, that is, the softened surface layer is not formed. On the other hand, if the pressure of the nitrogen atmosphere in the temperature raising step is too high, excessive denitrification may occur in the subsequent cooling step, which may cause the leaching of the binder phase to the surface and the accompanying hardening of the extreme surface. There is.

In addition, by sintering at a temperature higher than the liquid phase appearance temperature in a nitrogen atmosphere at a predetermined pressure as described above, a part of the Ti compound and a part of the W compound are contained in the liquid phase. After dissolution, the composite carbonitride solid solution containing Ti and W is precipitated as a surrounding structure around the Ti compound, thereby forming cored hard phase particles having a surrounding structure. Examples of the W compound include W carbide, nitride, carbonitride and the like. In addition, powders of at least one metal compound (eg, carbide, nitride, carbonitride) selected from Groups 4, 5, and 6 of the periodic table (excluding Ti and W), such as TaC, Powders such as NbC, Mo ₂ C, ZrC, Cr ₃ C ₂ and VC may be added to the raw material powder.

  The liquid phase appearance temperature in the temperature raising step is, for example, 1200 ° C. or more and 1300 ° C. or less, and the sintering completion temperature is preferably 1400 ° C. or more and 1600 ° C. or less. If the sintering temperature is too high, the compound particles constituting the hard phase grow and coarse particles increase in the cermet, which may reduce the wear resistance and fracture resistance. On the other hand, if the sintering temperature is too low, wetting between the hard phase and the binder phase is insufficient, and fine pores are generated in the cermet, which may reduce wear resistance and fracture resistance. Furthermore, in the temperature raising step, it is preferable to have a holding step of holding the sintering completion temperature for a certain period of time in a nitrogen atmosphere of 100 Pa or more and 1000 Pa or less after the temperature is raised to the sintering completion temperature. The sintering holding time at this time is, for example, 30 minutes or more and 1.5 hours or less.

  The temperature rise to the liquid phase appearance temperature may be nitrogen, vacuum or an inert gas (eg, Ar). Further, the rate of temperature rise to the liquid phase appearance temperature is, for example, 1 ° C./min or more and 10 ° C./min or less. The rate of temperature rise from the liquid phase appearance temperature to the sintering completion temperature is preferably 1 ° C / min to 5 ° C / min. By increasing the temperature at such a low rate, densification of the cermet Can be achieved.

  In addition to the temperature raising step described above, in the cooling step, cooling is performed at a predetermined cooling rate in a CO gas atmosphere at a predetermined pressure. If the pressure in this CO gas atmosphere is too low, the carbonization of the hard phase existing near the surface is difficult to occur, so the necking of the particles constituting the hard phase does not occur on the extreme surface, and the extreme surface softening phenomenon occurs. There is a possibility that no softened surface layer is formed. On the other hand, if the pressure of the CO gas atmosphere in the cooling process is too high, free carbon appears near the surface, wear resistance and fracture resistance decrease, and free carbon particles become defects of origin of fracture and yield strength May decrease. Here, when the above-mentioned nitride or composite nitride is included in the hard phase, such a compound can easily take in carbon in the CO gas atmosphere, and the degree of softening of the extreme surface can be increased.

  In addition, if the cooling rate is too low, the softened region may be softened not only to the pole surface but also to the inside, that is, the thickness of the softened surface layer may be increased, while if the cooling rate is too high, the pole surface may be softened. There is a possibility that the phenomenon does not occur, the hardness of the surface and the inside becomes uniform, and the softened surface layer is not formed. In the cooling step, it is preferable to cool from the sintering completion temperature to at least 1000 ° C. at a cooling rate of 10 ° C./min to 30 ° C./min.

<Cutting tools>
The cutting tool of the present invention includes a base material composed of the cermet of the present invention described above.

  As described above, the cermet of the present invention has an excellent balance between wear resistance and fracture resistance, and can be suitably used as a base material for cutting tools. And the cutting tool of this invention which used the cermet of this invention for the base material improves cutting performance and tool life compared with the conventional cutting tool. Specific examples of the cutting tool include a cutting tip, a cutting tool, an end mill, and a drill.

  In the above-described cutting tool of the present invention, the surface of the base material may be coated with a hard film. This hard film is preferably coated at least on the cutting edge and in the vicinity thereof (specifically, a region where cutting acts and a region where chips are in contact), and may be coated on the entire surface of the substrate. The hard film may be a single layer or multiple layers, and the total thickness is preferably 1 to 20 μm. The hard film can be formed by a chemical vapor deposition method (CVD method) such as a thermal CVD method or a physical vapor deposition method (PVD method) such as a cathode arc ion plating method.

The hard film includes at least one element selected from the metal elements of Groups 4, 5, and 6 of the periodic table, aluminum (Al), silicon (Si), and boron (B), carbon, nitrogen, oxygen, and boron. What consists of a compound with the at least 1 sort (s) of element chosen from these is preferable. Specific film types include TiCN, Al ₂ O ₃ , TiAlN, TiN, and AlCrN.

  The cermet of the present invention is excellent in the balance between wear resistance and fracture resistance because a specific softened surface layer is formed. Moreover, the manufacturing method of the cermet of this invention can manufacture the above-mentioned cermet of this invention. Furthermore, the cutting tool of the present invention is provided with a base material composed of the cermet of the present invention described above, so that the balance between wear resistance and fracture resistance is excellent, and cutting performance and tool life are improved.

It is a figure which shows hardness distribution of the depth direction toward the inside from the surface in the cermet of each sample of Test Example 1. FIG.

[Test Example 1]
The cermet of the present invention was produced, the obtained cermet was analyzed, a cutting tool using the cermet as a base material was produced, and the cutting performance was evaluated.

<Cermet>
As raw material powders, powders of the compounds constituting the hard phase shown below and iron group metal powders constituting the binder phase were prepared.
(Compound) TiCN (Ti: C: N molar ratio is 1: 0.5: 0.5), TiC, TiN, TaC, TaN, NbC, WC, Mo ₂ C, ZrC, ZrN
(Iron group metals) Co, Ni
And each powder was mix | blended so that it might become a composition shown in Table 1 from these powders, and the raw material powder was prepared. In this example, raw material powders having two types of compositions shown in Table 1 were prepared. The amount of nitrogen contained in the hard phase component in composition I shown in Table 1 was 6.1% by mass, and the amount of nitrogen contained in the hard phase component in composition II was 6.5% by mass.

  After 3-5% by mass of paraffin is added to the prepared raw material powder as a molding aid, each raw material powder is charged into a stainless steel container together with an alcohol or acetone solvent and a WC-based cemented carbide ball and pulverized. And mixing (wet) was performed. After adding a small amount of paraffin to each mixture obtained after pulverization, mixing and drying, press molding is performed using a mold at a pressure of 98 MPa to produce a chip-shaped molded product of ISO model number CNMG120408 (with breaker). did.

  Each obtained molded body was heated to 450 ° C. to remove paraffin, and then sintered under the sintering conditions shown in Table 2. Specifically, the temperature is raised to 1200 ° C. (liquid phase appearance temperature) in a 5 Pa vacuum atmosphere, and then to 1500 ° C. (sintering completion temperature) under the temperature raising process conditions (atmosphere and pressure) shown in Table 2. After raising the temperature, it was held for 60 minutes under the conditions (atmosphere and pressure) of the holding step shown in Table 2. Then, it cooled to 1000 degreeC on the conditions (atmosphere, pressure, cooling rate) of the cooling process shown in Table 2, Then, nitrogen gas was introduce | transduced and pressure-cooled in 300 kPaG (gauge pressure) nitrogen atmosphere. In this example, for the sintering conditions A, C to F, after the temperature was raised in the temperature raising step, the state was maintained, but for the sintering condition B, the temperature was raised in the temperature raising step, Once the vacuum was evacuated to a 5 Pa vacuum atmosphere, nitrogen gas was introduced to maintain a 660 Pa nitrogen atmosphere.

  Sintered materials (cermets) of Samples 1 to 8 shown in Table 3 were manufactured using the raw material powders of Compositions I and II shown in Table 1 and sintered under the sintering conditions A to F shown in Table 2. About each obtained sample, hardness distribution was measured in the depth direction toward the inside from the surface (baked skin surface). The result is shown in FIG. In this example, a cross section passing through the approximate center of each sample was taken, and Vickers hardness (Hv) was measured in the depth direction from an arbitrary point on the surface near the center of each sample toward the inside. Specifically, the hardness distribution up to a depth of 160 μm was measured every 1 μm in the region from the surface to a depth of 10 μm and every 5 μm in the inner region beyond that. The measurement was performed at three different points on the sample surface, and the average value was taken.

And from the results of the obtained hardness distribution, the thickness (μm), surface hardness (GPa), internal hardness (GPa), softening rate (softening surface layer of sample 7) %). The results are also shown in Table 3. The softened surface layer is a region having a hardness equal to or lower than the internal hardness shown below in a portion having a hardness distribution in which the hardness continuously increases in the depth direction from the surface toward the inside, and the cured surface layer On the contrary, it is a portion having a hardness distribution where the hardness is lowered. That is, the softened (cured) surface layer refers to a portion whose hardness continuously changes in the depth direction from the surface. In this example, for samples 1 to 4 and 6 to 8, the thickness of the softened (cured) surface layer was determined as the depth (distance) from the surface to the internal region where the hardness is substantially constant. For sample 5, the thickness of the softened surface layer was determined as the depth (distance) from the surface to the point of the same hardness as the internal hardness. Note that if the change in hardness was within 1% over a 5 μm section, it was determined that the hardness was substantially constant. Further, the surface hardness was determined as the hardness at a point having a depth of 0 μm. For the internal hardness, the hardness of an internal region having a substantially constant hardness distribution in the depth direction was obtained. The softening rate was calculated from the surface hardness and internal hardness according to the following formula.
(Formula): [(Internal hardness−Surface hardness) / Internal hardness] × 100

  Sample 6 had a substantially constant hardness in the depth direction from the surface toward the inside, and no softened surface layer was formed. In Sample 7, a cured surface layer having a higher surface hardness than the internal hardness was formed.

  For samples 1, 2 and 5, the cross-sectional structure of the softened surface layer was observed with a scanning electron microscope (SEM). As a result, in samples 1 and 2, in the softened surface layer, a core portion made of a Ti compound (TiCN or TiC) and a composite carbonitride solid solution containing Ti and W (eg, (Ti, W) (C, N)) Core-phase hard phase particles having a surrounding structure consisting of: were observed in the binder phase. On the other hand, in Sample 5, the softened surface layer was composed only of the non-core structure hard phase particles having no surrounding structure and the binder phase, and no core structure hard phase particles were observed.

  Next, the cutting tool which used the cermet of the samples 1-8 manufactured similarly was used for the base material. Specifically, each sample was subjected to a surface polishing treatment, and then a cutting edge was formed by brushing to form an R honing having a rake face / flank ratio of 1.5 to 2.0 on each sample. And about each obtained cutting tip, the cutting test (all are turning) shown in Table 4 was done, and cutting performance (abrasion resistance and fracture resistance) was evaluated. The results are shown in Table 5.

  From the results of Table 5, samples 1 and 2 whose softened surface layer has a thickness of 10 μm or less and a softening rate of 2 to 10% and the softened surface layer includes cored hard phase particles are flank wear amount Vb Is 0.12 (mm) or less, and the number of impacts to breakage is 2500 (times) or more, and it has an excellent balance between wear resistance and fracture resistance, enabling stable cutting over a long period of time. In contrast, Samples 3, 4, and 8 having a softened surface layer thickness of 20 μm or more are inferior in wear resistance, although they are excellent in fracture resistance. Sample 5 in which the core phase hard phase particles do not exist in the softened surface layer has a softened surface layer thickness of 10 μm or less, but has a high softening rate of 12.5% and is inferior in wear resistance. Moreover, although the softening rate is as high as 12.5%, the chipping resistance is insufficient. Wear resistance is also insufficient. The sample 6 having a constant hardness from the surface to the inside and the sample 7 having a higher surface hardness than the internal hardness are excellent in wear resistance but inferior in fracture resistance.

  The above-described embodiment can be appropriately changed without departing from the gist of the present invention, and is not limited to the above-described configuration. For example, the composition and manufacturing conditions of the cermet can be changed as appropriate.

  The cermet of this invention can be utilized suitably for the base material of a cutting tool. The method for producing cermet of the present invention can be suitably used for producing cermet. The cutting tool of the present invention can be suitably used for turning, milling, particularly steel cutting.

Claims (6)

A hard phase containing at least one compound of a carbide, carbonitride, composite carbide, and composite carbonitride of a metal selected from Groups 4, 5, and 6 of the periodic table, and an iron group metal as a main component A cermet consisting of a binder phase and inevitable impurities,
It has a hardness distribution where the hardness increases continuously in the depth direction in the surface area from the cermet surface to the depth of 10 μm, and the surface hardness is 2 with respect to the internal hardness in the inner area. ~ 10% lower softening surface layer is formed,
The softening surface layer includes hard phase particles having a core portion made of a compound of Ti and a surrounding structure surrounding the core portion,
The surrounding structure is a cermet made of a composite carbonitride solid solution containing at least Ti and W.   The cermet according to claim 1, wherein the nitrogen content in the hard phase is 4 mass% or more and 7 mass% or less.   The cermet according to claim 1 or 2, wherein a Vickers hardness Hv in the inner region is 15.0 GPa or more and less than 18.0 GPa. As raw material powders, powders of at least one compound of metal carbides, carbonitrides, composite carbides, and composite carbonitrides selected from Groups 4, 5, and 6 of the periodic table, and iron group metal powders A method for producing a cermet which is mixed and molded and then sintered.
As a raw material powder, a preparation step of preparing a powder of a compound of Ti and a compound of W, and a powder of the iron group metal,
A mixing step of mixing the raw material powders to obtain a mixture;
A molding step of obtaining a molded body obtained by molding the mixture;
A sintering step of obtaining a sintered body by sintering the molded body,
The sintering step includes a temperature raising step and a cooling step,
In the temperature raising step, the molded body is heated to a liquid phase appearance temperature at which a liquid phase appears, and then from a liquid phase appearance temperature to a sintering completion temperature at which sintering is completed in a nitrogen atmosphere of 100 Pa to 1000 Pa. Raise the temperature,
In the cooling step, a cermet manufacturing method in which cooling is performed at a cooling rate of 10 ° C./min to 30 ° C./min in a CO gas atmosphere of 1 kPa to 50 kPa.   The cutting tool which provides the base material which consists of a cermet of any one of Claims 1-4.   The cutting tool according to claim 5, wherein a hard film is coated on a surface of the base material.

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