JP2001277008A - Cermet for cutting tool and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cermet for a cutting tool having excellent abrasion resistance and defective resistance in a region faster than conventional cutting speed. SOLUTION: The cermet for the cutting tool having excellent defective resistance against a crack due to thermal shock is provided by displaying excellent abrasion resistance as falling of particulates is hard to occur and a ratio of a core part to contribute to abrasion resistance is high in a hard phase in comparison with a cermet having a conventional particulate core part by making the particulates having more than one kind of the core parts of carbide, nitride and carbon nitride the hard phase of which is mainly periodic table 4a group metal are high nitrogen and making the core parts rough and improving adhesive strength between intermediate phases of each of the particulates.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cermet for a cutting tool which is required to have abrasion resistance and chipping resistance, particularly excellent in abrasion resistance and thermal shock resistance in a high-speed cutting region, and a method for producing the cermet.

[0002]

2. Description of the Related Art Some conventional cermets have been proposed as countermeasures against changes in cutting conditions. Specifically, inventions such as addition of nitrogen for the purpose of atomization, control of the amount of nitrogen in a cermet, control of a cored structure and composition, control of particle size, control of particle size distribution, and the like have been proposed.

[0003] Regarding the cored structure, for example, Japanese Patent Application Laid-Open No. 8-508
No. 066 contains (Ti, W, Ta, Nb) C and / or (Ti, W, Ta) C, TiCN, W and Co, and the nitrogen amount N / (C + N) in TiCN is 0.7. A nitrogen-rich cermet consisting of the above has been proposed. However, since the particle size is limited to 1.5 μm or less, the thermal shock resistance in a high-temperature region is poor, and the cutting performance under current high-speed cutting conditions is insufficient. Japanese Patent Application Laid-Open No. 9-1743
No. 06, Ti carbonitride and periodic table 4a,
A cermet having a hard phase composed of a group 5a, 6a carbide, nitride, or carbonitride and a binder phase containing an iron group metal and having an N / (C + N) ratio of 0.4 to 0.7, having a cored structure It has been proposed that non-core particles surrounded by the above particles or aggregates of fine particles of 1 μm or less were scattered. Here, as a condition for forming the agglomerated portion, the particle diameter of the Ti compound is 0.5 to 2 μm, so that the thermal shock resistance in a high-temperature region is inferior, and the cutting performance under current high-speed cutting conditions is insufficient. Was. Cermets characterized by a coarse-grained hard phase are disclosed in JP-B-61-411 and JP-B-61-22201.
No. 6 and both publications contain 1 μm or more of TiC of 7 μm or more.
It has been proposed to improve wear resistance by adding 〜30 vol%. Japanese Patent Application Laid-Open No. 61-12846 proposes a cermet containing particles having a particle size of 5 to 10 μm and having an average particle size of 3 to 8 μm. These are all Ti
The compound was for a low nitrogen cermet.

Further, Japanese Patent Application Laid-Open No. 5-186843 discloses that a finer matrix having an average particle size of a hard component of less than 1 μm has an average particle size of 2 to 8 for a core.
Hard component particles having a core / rim structure of 10 μm
A carbonitride sintered alloy containing 0% by volume and having a difference between the average particle diameter of the fine matrix particles and the core / rim structure particles of 1.5 μm or more has been proposed. Although effective in the cutting region as described, it is inferior in thermoplastic deformation and thermal shock resistance in a higher temperature region, and the tool performance under current high-speed cutting conditions is insufficient.

[0005] A cermet containing a hard phase having a core-rim structure has long been disclosed in US Pat.
No. 6 has been disclosed and various proposals have been made in Japan, and among them, patents focusing on the core have been proposed. For example, in Japanese Patent Application Laid-Open No. 10-287946, the ratio of particles having a core of 30% by area or more of the whole particles and particles having a core of less than 30% by area of the whole particles is limited to 0.3 to 0.8. However, there is a problem that a desired effect cannot be obtained in a region of cutting conditions where the influence of the absolute value of the particle size or the nitrogen content is large. JP-A-10-29897 discloses that the area of the black core has peaks in the range of 0.1 to 0.7 μm ² and 0.8 to 2.5 μm ² , but is limited by the claims. Since the core of the hard particles is relatively fine, the thermal shock resistance in a high-temperature region is inferior, and the cutting performance under current high-speed cutting conditions is insufficient.

[0006]

As described above, it is difficult for conventional cermets to improve both wear resistance and chipping resistance. Particularly, mechanical requirements in a high-temperature region that can cope with recent high-speed cutting are required. It has been difficult to simultaneously satisfy the required thermal characteristics.

[0007]

According to the present invention, as a result of various studies to solve these problems, one or more of carbides, nitrides, carbonitrides and mutual solid solutions of Group 4a metals in the periodic table are mainly obtained. The atomic ratio of the amount of nitrogen to the amount of carbon in the particles having a core of 0.4 ≦ nitrogen / (nitrogen + carbon) ≦ 0.95, and the structure of the sintered body has a particle diameter of the core. Is 3 μm or more, the core area of the particles is 3% by area or more of the total hard phase, and
The core area of the particles of 2 μm or more is 10% by area of the total hard phase
It has been clarified that the cermet characterized as above has both excellent wear resistance and chipping resistance. Furthermore, particles having a core particle size of 3 μm or more have a core area of 10% by area or more of the entire hard phase core having a cored structure, and particles having a core area of 2 μm or more have a core area of a cored structure. It has been clarified that the high-temperature characteristics are further improved when the area is 30% by area or more of the hard phase core. in addition,
It has been clarified that the particles having a core of 0.5 μm or less shorten the mean free path of the binder phase and improve the thermal shock resistance.

[0008] In addition, the above-mentioned particles having one or more cores of carbides, nitrides, carbonitrides, and mutual solid solutions of mainly Group 4a metals in the periodic table have a core having a distribution width of 3 µm or more. Therefore, it has both strength and hardness required in a high temperature region. Furthermore, periodic rate table 4
The average particle diameter of the particles having at least one core of a group a metal carbide, nitride, carbonitride and mutual solid solution is represented by A, mainly periodic table 5a, group 6a metal carbide, nitride, carbonitride When the average particle diameter of the particles having a core portion made of one or more kinds of mutual solid solutions is B, the strength and fracture resistance are improved by forming a sintered body structure in which B / A ≦ 0.5. Things. These cermets have an average particle size of 6 μm
As mentioned above, titanium nitrocarbide powder satisfying 0.4 ≦ nitrogen / (nitrogen + carbon) ≦ 0.95 was blended as a raw material and could not be obtained conventionally by sintering under high temperature and high nitrogen atmosphere. Cermet has been realized.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a conventional high nitrogen cermet, the sinterability decreases with an increase in the amount of nitrogen. Therefore, the grain size and the sintering conditions have been adjusted to make the structure finer and sintered. If the particles are not atomized, the strength of the sintered body after sintering is reduced. Therefore, when used as a cutting tool, the desired strength cannot be obtained under the conventional sintering conditions. As a result of conducting various tests focusing on the improvement of high-temperature characteristics required for high-speed cutting, the present invention has formed a coarse-grained and high-nitrogen core that could not be obtained under conventional sintering conditions. Thus, a sintered body having the hard phase obtained is obtained. In order to increase the nitrogen content of particles having at least one core selected from the group consisting of carbides, nitrides and carbonitrides of Group 4a metals in the periodic table, finer particles are more desirable in terms of sinterability. The purpose of coarse graining is to improve the thermal shock resistance at high temperatures, because it has been found that the effect is extremely high on the cutting performance in extremely high-speed cutting. In addition, the toughness was improved as compared with the low nitrogen alloy due to the high nitrogen. Further, as the amount of nitrogen increases, the reactivity with metals and oxygen decreases, so that the chemical wear resistance is also improved as compared with conventional cermets.

In the present invention, it has been clarified that the particle has a cored structure, and the size of the core greatly affects the cutting performance.
Particles having at least one core of a group a metal carbide, nitride, carbonitride and mutual solid solution have a nitrogen / (nitrogen + carbon) atomic ratio of 0.4 to 0.95. The structure of the sintered body is such that the core area of particles having a core particle size of 3 μm or more is 3% by area or more of the total hard phase, and the core area of particles having a core particle size of 2 μm or more is 10% of the total hard phase. If the area% or more, the desired effect is recognized, and the sintered body which does not satisfy the above-mentioned limitation has poor cutting performance in a high-speed region in which attention is particularly paid. This is because compared to the conventional cermet having a fine-grained core portion, particles are less likely to fall off, and the ratio of the core portion that contributes to abrasion resistance among the hard phases is high, so that excellent wear resistance is exhibited, and individual particles It is considered that the improved adhesive strength between the intermediate phases has excellent fracture resistance against cracks due to thermal shock. If the nitrogen content of the core is less than 0.4, the high-temperature characteristics deteriorate, and if the nitrogen content is 0.95 or more, the desired wear resistance cannot be obtained, so the content is limited to 0.4 or more and 0.95 or less. 0.7 or less is preferable,
0.5 or more and 0.64 or less are more preferable. Further, the core area of particles having a core particle size of 3 μm or more is 10% by area or more of the entire hard phase core having a cored structure and the core area of particles having a core particle size of 2 μm or more is a cored structure. 30 of all hard phase core
In a sintered body that satisfies the above condition with the proportion of particles having a coarse core so that the area ratio becomes not less than the area%, the thermal shock cracking is improved because the coarse particles delay the development of thermal shock cracks. .

Further, by shortening the mean free path of the binder phase with particles having a core of 0.5 μm or less, the thermal shock resistance is improved, but the core area is more than 5% by area of the total hard phase. In the case of a sintered body, the characteristics in a high-temperature region are deteriorated.
It was limited to 5 area%. This limits that 50% or more of the particles having a core of 0.5 μm or less are in contact with the binder phase. In addition, the particle size distribution of the size of the core is limited to 3 μm or more, because the desired performance with respect to the fluctuation of cutting stress and the load due to thermal shock cannot be obtained if it is less than 3 μm, but is more preferably 5 to 10 μm. .

The average particle diameter of particles having at least one core of carbides, nitrides, carbonitrides and mutual solid solutions of group 4a metals is mainly represented by A, and the periodicity tables 5a and 6a are mainly used.
When the average particle diameter of particles having a core portion made of one or more of group III metal carbides, nitrides, and carbonitrides is B, and when B / A is larger than 0.5, heat-resistant plastic deformation at high temperatures Was inferior, so it was limited to 0.5 or less.

In order to obtain the cermet for a cutting tool of the present invention, it is natural that the raw material powder is high in nitrogen, but desired characteristics can be obtained by further mixing the raw material powder having an average particle diameter of 6 μm or more. Was clarified in this case. Even if a raw material powder having an average particle diameter smaller than 6 μm is used, a sintered body having a coarse core can be obtained by shortening the mixing time and the sintering time. In short conditions, the dispersion is poor because of poor dispersion, and the cutting performance of wear resistance and fracture resistance is large.In the condition of short sintering time, the strength tends to decrease due to the fact that defects are likely to remain, and the variation in tool life related to fracture is extremely small. The average particle size is 6μ
Although the use of TiCN powder of m or more as a raw material is limited, it is preferable to use coarser TiCN powder of 8 μm or more. The sintering was performed in a high-temperature and high-nitrogen atmosphere to obtain a sintered body having a high nitrogen and a coarse core of 3 μm or more.

[0014]

EXAMPLE W which is commercially available and has an average particle size of 1-2 μm
C, (W, Ti) C complex carbide (weight ratio WC / Ti
C = 70/30), TaC, Mo ₂ C, ZrC, Co,
Ni and TiC and Ti with an average particle size of 10 μm as inventions
N, TiCN (TiC / TiN = 40 / 60- by weight ratio)
50/50), Ti with an average particle size of 1.5 μm
C, TiN, TiCN (TiC / TiN = 40 by weight ratio)
/ 60 to 50/50) were weighed to the composition shown in Table 1, charged into a stainless steel pot together with an acetone solvent and a cemented carbide ball, and mixed for 20 hours. The obtained mixed powder was subjected to SPMN1 described in JIS-B4120.
It was press-formed at a pressure of 196 MPa using a 20308 shape mold. The obtained powder compact was subjected to an atmospheric pressure of 0.
Temperature 1773-18 in a nitrogen stream of 13-2.6 kPa
Sintering was carried out under the conditions of 73K and a holding time of 1 hour to obtain inventive products 1 to 6 and comparative products 1 to 6.

[0015]

[Table 1] Composition of sintered body Compounding amount: mass%, invention product sintering temperature: 1873K, comparative product sintering temperature: 1773K

The cermet chips of the present invention products 1 to 6 and comparative products 1 to 6 thus obtained were cut, the cross section on the flank side was ground, and then wrapped from the surface to 0.2 mm inside with 1 μm diamond paste. Processing was performed. The processed surface was observed with an optical microscope at a magnification of 1500 times, and the image analysis device was used to measure the area% of the core part of the particle having a core part of 3 μm or more and the core part of the particle having a core part of 2 μm or more in five visual fields and averaged. The value was determined. The N and C contents of the core were measured by WDS. The sintered body obtained under the conditions of Table 1 was ground on the upper and lower surfaces with a # 230 diamond grindstone, and further subjected to a honing process of 0.15 × −30 ° on the ridge of the cutting edge, and then cut under the following conditions. A comparative evaluation of the flank wear amount was performed by a test. Table 2 shows the results.

Cutting test condition 1 (wear test) Work material: S48C Cutting speed: 240 m / min Cutting depth: 1.5 mm Feed: 0.32 mm / rev. Cutting oil: not used (dry cutting) Cutting time: 20 min

Cutting test condition 2 (breakage test) Work material SNCM439 Cutting speed 240 m / min Cutting depth 1 mm Feed 0.2 mm / rev. Cutting oil: WET (Water soluble) 5 sec. Cutting-5 sec. End of test 3 times for each sample

[0019]

[Table 2] Test results * 1 Comparative product 5 contained many defects due to low temperature at the time of sintering, and the desired performance was not obtained.

[0020]

As is clear from the above results, the core area of the hard phase having high nitrogen and having a coarse core of 3 μm or more as in Invention products 1 to 6 has a core area of 3% of the total hard phase. Area% or more, and a cermet in which the core area of the hard phase having a coarse core of 2 μm or more is included in 10% or more of the total hard phase,
Excellent wear resistance due to the higher ratio of the core which contributes to the abrasion resistance among hard phases compared to the conventional cermet having a fine core as shown in Comparative Products 1 to 6, which hardly causes the particles to fall off. In addition, it shows excellent fracture resistance against cracks due to thermal shock due to the improved adhesive strength between the intermediate phases of the individual particles.

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Claims (7)

[Claims] The present invention is characterized in that one or more Ti compounds of carbides, nitrides, and carbonitrides of Ti are used as main components.
70 to 97% by weight of a hard phase containing at least one of carbides, nitrides and carbonitrides of Group 6a metal and at least one of these solid solutions
And a titanium carbonitride-based alloy consisting of a binder phase composed of at least one of iron group metals and unavoidable impurities, wherein the hard phase is mainly composed of carbides, nitrides, carbonitrides and mutual solid solutions of group 4a metals in the periodic table. Particles having at least one kind of core, particles having a core mainly composed of at least one of carbides, nitrides, carbonitrides and mutual solid solutions of Group 6a metals, and 4a of the periodicity table In a cermet comprising single-phase particles of at least one of carbides, nitrides, carbonitrides and mutual solid solutions of 5a and 6a, carbides, nitrides, carbonitrides and mutual solid solutions of metals belonging to Group 4a of the periodic table are mainly used. The atomic ratio of the amount of nitrogen to the amount of carbon in the particles having at least one of the following cores is 0.4 ≦ nitrogen / (nitrogen + carbon) ≦ 0.95, and the structure of the sintered body has a core particle size of 3 μm. The core area of the above particles is A cermet for a cutting tool, wherein the core area of particles having a surface area of 3% or more and 2μm or more is 10% or more of the total hard phase. 2. Particles having a core of at least one of carbides, nitrides, carbonitrides and mutual solid solutions of the above-mentioned Group 4a metals of the periodic table, wherein the particle diameter of the core is 3 μm or more. The core area of the particles having a core area of at least 10% by area of the entire hard phase core having a cored structure and the core area of the particles having a particle size of at least 2 μm should be at least 30% by area of the entire hard phase core having a cored structure. The cermet for a cutting tool according to claim 1, wherein 3. The particles having one or more cores of carbides, nitrides, carbonitrides, and mutual solid solutions of the above-mentioned metals of Group 4a, mainly having a core particle diameter of 0.5 μm or less. 2. The cermet for a cutting tool according to claim 1, wherein the core area of the particles is 2 to 5 area% of the total hard phase. 4. The particles having one or more cores of carbides, nitrides, carbonitrides and their mutual solid solutions of the above-mentioned metals of Group 4a mainly having a core particle diameter of 0.5 μm or less. 4. A cermet for a cutting tool according to claim 1, wherein at least 50% of the particles are in contact with the binder phase. 5. A particle having one or more cores of carbides, nitrides, carbonitrides and mutual solid solutions of the above-mentioned metals of Group 4a mainly having a distribution width of 3 μm or more. Claims 1 and 2 characterized by having
Cermets for cutting tools according to items 3 and 4 6. An average particle diameter of particles having one or more cores of carbides, nitrides, carbonitrides and mutual solid solutions of group 4a metals mainly represented by A in the periodic table 4a.
a, when the average particle diameter of particles having a core portion composed of one or more of carbides, nitrides, and carbonitrides of Group 6a metals is B,
The cermet for a cutting tool according to claim 1, 2, 3, 4, or 5, wherein B / A ≤ 0.5 is satisfied. 7. The method according to claim 1, wherein a titanium carbonitride powder having an average particle diameter of 6 μm or more and 0.4 ≦ nitrogen / (nitrogen + carbon) ≦ 0.95 is blended as a raw material. PROCESS FOR PRODUCING CERMET FOR CUTTING TOOLS