JP7031532B2 - TiN-based sintered body and cutting tool made of TiN-based sintered body - Google Patents

Description

The present invention relates to a TiN-based sintered body in which a high toughness layer is formed on a surface layer portion, and a TiN-based sintered body using this TiN-based sintered body as a substrate and having excellent resistance to abnormal damage such as chipping and chipping. It relates to a cutting tool made of a surface-coated TiN-based sintered body and a cutting tool made of a surface-coated TiN-based sintered body.

Conventionally, as a cutting tool, a WC-based cemented carbide cutting tool, a TiCN-based cermet cutting tool, a TiC-based sintered alloy cutting tool, a TiN-based sintered alloy cutting tool, and the like are known.
Of these cutting tools, TiC-based sintered body cutting tools have excellent wear resistance, but their toughness is significantly inferior to other cutting tools, they are vulnerable to thermal impact, and they also have defects. Due to its ease of use, it is mainly used in high-speed finish cutting.
Further, the TiCN-based cermet cutting tool has a low affinity for steel and is excellent in wear resistance and finished surface roughness, but on the other hand, its toughness is not sufficient.
On the other hand, WC-based cemented carbide cutting tools have excellent toughness, but their wear resistance is not sufficient, and they use rare metals W and Co as alloy components. In order to reduce the cost, it is necessary to reduce the amount of W used and the amount of Co used.
Therefore, some proposals have been made conventionally in order to provide a tool material having excellent toughness and wear resistance.

For example, as for a TiN-based sintered alloy, as shown in Patent Document 1, in a sintered hard alloy for a cutting tool containing a hard phase and a metal for bonding, the alloy is a hard phase of 65 to 97% by weight. The hard phase is composed of a nitride and / or a carbon nitride having an oxygen content of 0.15% or less, and the hard phase is bonded to the hard phase. As the metal for cutting, a sintered hard alloy for cutting tools, which is an alloy of at least one of the iron group metals and one of the chromium group metals, has been proposed, and this sintered hard alloy is said to have toughness.
In Example 1 showing a specific example, 90% by weight of TiN as a hard phase component (the oxygen content in this is 0.05%) and 10% by weight of a (80:20) mixture of Ni and Mo. The sintered cemented carbide obtained by sintering the above in nitrogen under a pressure of 350 mmHg at about 1450 ° C. exhibits a hardness of about 1500 Vickers (load 3 kg) and a bending breakage strength of 80-90 kg / mm ² . Is described.

Further, for example, in Patent Document 2, 100 parts by weight of a sintered alloy raw material powder mainly composed of TiN consisting of 65 to 95% by weight of TiN, Mo and / or Mo ₂ C2 to 20% by weight, and 3 to 15% by weight of an iron group metal. On the other hand, the carbon powder was added and mixed at a ratio of 0.2 to 6.8 parts by weight with respect to 100 parts by weight of TiN to be blended in the raw material powder, and the TiN base-fired bond was molded and sintered. Gold has been proposed, and according to this TiN-based sintered alloy, carbon powder is deposited as TiC on the surface of TiN particles during firing, and the wettability of the TiN particles and the bonded metal (Ni, Co) is improved. In particular, it is said that the durability (frank wear, plastic deformation resistance) of the cutting tool is enhanced in high-speed continuous / intermittent cutting of cast iron.

Further, for example, in Patent Document 3, in a Ti-based cermet containing a hard component such as TiC, (Ti, Nb) C, TiCN or (Ti, Ta) CN, the surface of the Ti-based cermet extends from the surface of the cermet to the inside of the cermet within a range of 300 μm. A cermet having an excellent toughness, which forms a softened layer and has a hardness in the softened layer that is 5 to 20% lower than the hardness inside the cermet, has been proposed. Cutting tools having a coating layer made of carbides, nitrides, aluminum oxides, etc. are said to exhibit excellent chipping resistance and chipping resistance in intermittent cutting of alloy steel.

Special Publication No. 49-1364 Japanese Unexamined Patent Publication No. 51-71809 Japanese Unexamined Patent Publication No. 54-117510

In recent years, there have been strong demands for labor saving, energy saving, high speed, high efficiency, and low cost in the technical field of cutting, and there are remarkable improvements in the performance of cutting equipment, but on the other hand, for cutting tools. The conditions of use are becoming more and more harsh, and there is a need to further improve tool performance, extend the life of tools, and develop materials that can meet such demands. It is desired.
As described above, the WC-based cemented carbide has excellent toughness, but its wear resistance is not sufficient, and since rare metals W and Co are used as alloy components. It is an expensive tool material, and in order to reduce the cost, it is an issue to reduce the amount of W used and the amount of Co used.
In addition, TiCN-based cermet has excellent hardness and wear resistance, but its toughness is not sufficient, so when it is used as a cutting tool, chipping, chipping, etc. are likely to occur, which is the cause of the tool. There is a problem that the life is short.
Therefore, as a material for a cutting tool, a cutting tool material that has both excellent toughness and hardness and exhibits excellent cutting performance over a long period of time without causing abnormal damage such as chipping and chipping is desired. ing.

From the above viewpoint, the present inventor has toughness comparable to that of WC-based cemented carbide, hardness and wear resistance comparable to those of TiCN-based cermet, and use of rare metals W and Co. As a result of diligent research on cutting tool materials that do not require, the following findings were obtained.

First, the present inventor investigated the cause of the short life of a cutting tool made of a conventional TiN-based sintered body. As a result, it has excellent hardness and wear resistance like the TiCN-based cermet. Since the toughness is not sufficient, it has been found that chipping, chipping, etc. generated on the surface of the TiN-based sintered body are the main factors leading to breakage.
Therefore, the present inventor formed a low Mo region on the surface layer of the TiN-based sintered body by optimizing the composition of the bonded phase and controlling the sintering conditions when producing the TiN-based sintered body. By reducing the micro-hardness (micro-Vickers hardness) in the low Mo region of the surface layer to the micro-hardness inside the TiN-based sintered body, the surface layer has excellent toughness and the inside is It has been found that a TiN-based sintered body having high hardness can be produced.
When this TiN-based sintered body having both toughness and hardness was used as a cutting tool for continuous cutting and intermittent cutting of carbon steel, alloy steel, etc., for example, it was made of a conventional WC-based cemented carbide. It has almost the same or better resistance to abnormal damage than cutting tools, and has almost the same wear resistance as conventional TiCN-based cermet cutting tools, and exhibits excellent cutting performance over long-term use. I found it.
Further, when a cutting tool made of a surface-coated TiN-based sintered body was produced by forming a hard coating layer on at least the cutting edge using the TiN-based sintered body as a substrate, the hard coating layer was not brittle and was hard-coated. It has been found that the adhesion strength between the layer and the substrate is excellent, abnormal damage such as chipping and chipping does not occur, and excellent cutting performance is exhibited over a long period of use.

The present invention has been made based on the above findings.
"(1) A TiN-based sintered body containing a TiN phase and a Mo _2C phase, the balance of which is a bonded phase.
(A) When observing the cross section of the sintered body, the average area ratio of the TiN phase in the sintered body is 70.0 to 91.5 area%, and the average area ratio of the Mo _2C phase is 3. 5 to 25.0 area%,
(B) The components of the bonded phase are Fe and Ni, the area ratio of the bonded phase is 5.0 to 15.0 area%, and the content ratio of Ni to the total content of Fe and Ni is 15. It is 0.0 to 35.0% by mass,
(C) A low Mo region is formed in a region from the surface of the sintered body to a depth of 50 to 300 μm toward the inside thereof, and the average Mo content in the low Mo region is the same as that of the sintered body. 30-80% of the average Mo content inside the sintered body at a depth of at least 500 μm from the surface .
(D) The average microhardness of the low Mo region is 70 to 90% of the average microhardness inside the sintered body at a depth of at least 500 μm from the surface of the sintered body. Base sintered body.
(2) A cutting tool made of a TiN-based sintered body, characterized in that the TiN-based sintered body according to (1) above is configured as at least a cutting edge.
(3) A surface-coated TiN-based sintered body cutting tool characterized in that a hard coating layer is formed on at least the cutting edge of the TiN-based sintered body cutting tool according to (2) above. "
It has the characteristics of.

The TiN-based sintered body of the present invention has a TiN phase, a Mo ₂ C phase, and an Fe—Ni alloy phase as a bonded phase in a predetermined area ratio, and has a content ratio of Ni and Fe constituting the bonded phase. A low Mo region is formed in a region from the surface of the sintered body to a depth of 50 to 300 μm from the surface of the sintered body to a predetermined mass ratio, and the average microhardness in the region is the sintered body. Since the TiN-based sintered body has an excellent toughness on the surface layer because it is lower than the average micro-hardness inside, the inside of the sintered body has a high hardness, and the TiN-based sintered body as a whole has a high hardness. Has excellent toughness and hardness.

The TiN-based sintered body cutting tool made of the TiN-based sintered body of the present invention is used for continuous cutting and intermittent cutting of carbon steel, alloy steel, etc. by combining excellent toughness and hardness. Even in some cases, it exhibits chipping resistance and chipping resistance equal to or higher than those of WC-based superhard alloy cutting tools, and exhibits wear resistance equal to or higher than that of TiCN-based cermet cutting tools. ..

Further, in the surface-coated TiN-based sintered body cutting tool in which the cutting tool made of a TiN-based sintered body made of the TiN-based sintered body of the present invention is used as a base and a hard coating layer is coated on at least the cutting edge portion thereof, the cutting tool is made of a TiN-based sintered body. Since the surface layer portion of the sintered body has a low Mo region, brittleness of the hard coating layer due to diffusion of Mo is prevented, and further, the bonding strength between the substrate and the hard coating layer is enhanced, so that carbon steel and alloy steel are used. In continuous cutting and intermittent cutting, it exhibits excellent wear resistance without causing abnormal damage such as chipping, chipping, and peeling of the hard coating layer, and exhibits excellent cutting performance over a long period of use. ..

An example of a backscattered electron image observed with a scanning electron microscope (SEM) about the vertical cross section of the TiN-based sintered body of the present invention is shown.

In the present invention, the reason why each phase in the sintered structure of the TiN-based sintered body is set to a specific area ratio, the reason why the content ratio of Ni and Fe constituting the bonded phase is set to a specific mass ratio, and low Mo. The reason for defining the depth of the region, the minute hardness, etc. will be explained below.

TiN phase:
When observing the cross section of the TiN-based sintered body, if the average area ratio of the TiN phase to the TiN-based sintered body is less than 70.0 area%, the hardness of the sintered body is not sufficient, and as a result, the TiN-based sintered body is not sufficiently hard. The wear resistance of a sintered cutting tool (hereinafter referred to as "TiN-based cutting tool") is also reduced. On the other hand, when the TiN phase in the TiN-based sintered body exceeds 91.5 area%, fine voids (pores) are likely to be formed in the sintered structure, so that the toughness is lowered and the chipping resistance of the TiN-based cutting tool is reduced. It causes deterioration of sex and fracture resistance.
Therefore, the average area ratio of the TiN phase in the TiN-based sintered body is 70.0 to 91.5 area%.
Further, in the present invention, as shown in FIG. 1, an energy dispersive X-ray analyzer is provided for a cross section perpendicular to the surface of the TiN-based sintered body (hereinafter, such a surface is simply referred to as a “longitudinal cross section”). A vertical cross-section was observed with a scanning electron microscope (SEM) equipped with (EDS), and the amount of elements contained in the region (for example, a region of 40 μm × 50 μm) in the obtained secondary electron image was measured, and the TiN phase and Mo were measured. ₂ C phase and Fe—Ni phase are specified, the area ratio of each phase in the region is calculated, the area ratio is calculated in a plurality of regions of at least 5 regions or more, and the average value of these is calculated as the average value of each phase. Area%.
In the TiN-based sintered body of the present invention, the unavoidable impurity component inevitably mixed from the manufacturing process or the like is within a range that does not impair the object of the present invention (that is, the hardness and toughness of the TiN-based sintered body are maintained. A small amount of content (mixture) is allowed within the range that does not decrease).

Mo ₂ C phase:
When observing the vertical cross section of the TiN-based sintered body, when the average area ratio of the Mo ₂ C phase in the TiN-based sintered body is less than 3.5 area%, TiN is particularly high in the low Mo region of the TiN-based sintered body. Wetness between the phase and the bonded phase is insufficient, voids are formed in the sintered structure, and the toughness tends to decrease. On the other hand, when the average area ratio of the Mo ₂ C phase exceeds 25.0 area%, Fe ₃ Mo ₃ Since double carbides such as C phase and double nitrides such as Fe ₃ Mo ₃ N phase are likely to be generated, which causes a decrease in toughness, the average area ratio of Mo ₂ C phase in the TiN-based sintered body is 3.5. ~ 25.0 Area%.

Average Mo content in the low Mo region:
The vertical cross section of the TiN-based sintered body of the present invention was observed in a vertical cross section with a scanning electron microscope (SEM) equipped with an energy-dispersed X-ray analyzer (EDS), and from the surface of the TiN-based sintered body to the inside thereof. When the Mo content is measured toward the inside, the Mo content is in the depth range of 50 to 300 μm toward the inside of the TiN-based sintered body as compared with the Mo content inside the TiN-based sintered body. A region having a small low Mo content (specifically, a region having an average Mo content of 30 to 80% of the average Mo content inside the sintered body at a depth of at least 500 μm from the surface of the TiN-based sintered body is defined as a region. The existence of the "low Mo region" can be confirmed, and the presence of this low Mo region improves the toughness of the TiN-based sintered body.
Here, when the average Mo content in the low Mo region is less than 30% of the average Mo content inside the TiN-based sintered body, the wettability of the TiN particles and the bonded phase is lowered, and the wettability of the TiN particles and the bonded phase is lowered into the low Mo region. It creates voids and reduces toughness. On the other hand, when the average Mo content in the low Mo region exceeds 80% of the average Mo content inside the TiN-based sintered body, the effect of reducing the hardness due to the reduction in the Mo content is reduced, and thus the surface surface. When used as a cutting tool due to insufficient toughness, chipping and chipping are likely to occur.
Therefore, the average Mo content in the low Mo region is 30 to 80% of the average Mo content inside the sintered body at a depth of at least 500 μm from the surface of the TiN-based sintered body .

Low Mo region thickness:
When the low Mo region having an average Mo content of 30 to 80% of the average Mo content inside the TiN-based sintered body has a shallow depth of less than 50 μm from the surface of the sintered body, the TiN-based sintered body is fired. If the effect of improving the toughness of the body cannot be fully exerted, while the depth exceeds 300 μm from the surface of the sintered body and the low Mo region extends to the inside of the sintered body, TiN-based sintering is performed. Due to the decrease in hardness of the whole body, plastic deformation is likely to occur when used as a cutting tool.
Therefore, the low Mo region is formed in a range of 300 μm or less at a depth of 50 μm or more from the surface of the TiN-based sintered body toward the inside thereof.

Micro-hardness in the low Mo region:
When the micro-hardness of the TiN-based sintered body including the low Mo region is measured from the surface of the sintered body toward the inside thereof, the average micro-hardness in the low Mo region is the surface of the sintered body. Below 70% of the average microhardness inside the sintered body at a depth of at least 500 μm , the low Mo region is prone to plastic deformation, while exceeding 90% of the average microhardness inside the sintered body. When it becomes hard, the effect of improving the toughness of the TiN-based sintered body is not sufficiently exhibited.
Therefore, the average microhardness in the low Mo region is 70 to 90% of the average microhardness inside the sintered body at a depth of at least 500 μm from the surface of the sintered body.

Bonded phase:
When the average area ratio of the bonded phase to the TiN-based sintered body is less than 5.0 area%, the toughness of the TiN-based sintered body decreases due to the small amount of the bonded phase, while the average area of the bonded phase. When the ratio exceeds 15.0 area%, the amount of the TiN phase, which is a hard phase component, is relatively reduced, so that the hardness is lowered, and as a result, the wear resistance of the TiN-based cutting tool is also lowered.
Therefore, the average area ratio of the bonded phase to the TiN-based sintered body is 5.0 to 15.0 area%.

Further, in the present invention, TiN is set to 15.0 to 35.0% by mass by setting the Ni content ratio (= Ni / (Fe + Ni) × 100) to the total content of Fe and Ni constituting the bonded phase. The toughness and hardness of the base sintered body can be further increased.
This is because when the content ratio of Ni to the total content of Fe and Ni (= Ni / (Fe + Ni) × 100) is less than 15.0% by mass, Ni dissolves in Fe, but the bonded phase is formed. Since the effect of strengthening the solid solution is not exhibited, the hardness of the bonded phase is insufficient, and the Ni content ratio (= Ni / (Fe + Ni) × 100) to the total content of Fe and Ni is 35.0% by mass. If it exceeds, the intermetallic compound FeNi ₃ is likely to be generated, and the toughness of the bonded phase is lowered.

Fabrication of TiN-based sintered body, cutting tool made of TiN-based sintered body, and cutting tool made of surface-coated TiN-based sintered body of the present invention:
In order to obtain the component composition of each of the above phases when producing the TiN-based sintered body of the present invention, first, as the raw material powder thereof, TiN: 55 to 92% by mass, Mo ₂ C: 1 to 40% by mass. %, Fe: 5 to 18% by mass, Ni: 1 to 4.5% by mass, and the mass% of Ni with respect to the total amount of Ni and Fe (= Ni × 100 / (Fe + Ni)) is 15.0 to It is preferable to use a raw material powder having a component and composition satisfying the relationship of 35.0% by mass.
Then, the raw material powder satisfying the above conditions is mixed by, for example, a ball mill using a WC-based cemented carbide as a mixed medium, and the mixed powder is press-molded to prepare a powder compact.
Then, the powder compact was baked in a temperature range of 1350 to 1450 ° C. for 30 to 150 minutes while flowing a mixed gas having a hydrogen concentration of 1 to 3% and a nitrogen concentration of 97 to 99% (nitrogen diluted hydrogen atmosphere). After that, the atmosphere is switched to Ar gas atmosphere, and the temperature range from the sintering temperature to about 1200 ° C. (for example, 1180 to 1220 ° C.) is about 1 ° C./min (for example, 0.5 to 1.5 ° C./min). The TiN-based sintered body of the present invention having excellent toughness and hardness in which a low Mo region is formed on the surface layer of the TiN-based sintered body by slowly cooling at a cooling rate and then naturally cooling to room temperature. Can be made.
The reason why the powder compact is sintered in a nitrogen-diluted hydrogen atmosphere is to improve the wettability between the TiN powder and Fe, which is a component of most of the bonded phase, and at the same time to improve the sinterability.
Further, after that, by machining into a predetermined shape, a cutting tool made of a TiN-based sintered body, which has excellent resistance to abnormal damage such as chipping and chipping and wear resistance, and exhibits excellent cutting performance over a long period of use, is produced. Can be made.
Further, on at least the cutting tool of the cutting tool made of the TiN-based sintered body, a carbide such as Ti—Al or Al—Cr, a nitride, a carbonitride _, or a hard film such as _Al2O3 is applied to PVD, CVD. A cutting tool made of a surface-coated TiN-based sintered body can be manufactured by forming a coating by a film forming method such as.
When manufacturing a cutting tool made of a surface-coated TiN-based sintered body, the type of hard film and the film forming method may be a film type and a film forming method already well known to those skilled in the art, and are particularly limited. It's not something to do.

Next, an embodiment of the present invention will be specifically described.

As powders for producing a TiN-based sintered body, TiN powder having an average particle size of 10 μm, Mo ₂ C powder having an average particle size of 2 μm, Fe powder having an average particle size of 2 μm, and Ni powder having an average particle size of 1 μm were prepared. Raw material powders 1 to 8 were prepared by blending so as to have the blending ratio shown in Table 1 and blending the Fe powder and Ni powder so as to have the blending ratio shown in Table 1. The average particle size referred to here means the median diameter (d50).

Next, the raw material powders 1 to 8 are filled in a ball mill and mixed to prepare mixed powders 1 to 8, and the mixed powders 1 to 8 are dried and then press-molded at a pressure of 100 to 500 MPa. Powder compacts 1 to 8 were produced.

Next, as shown in Table 2, the powder compacts 1 to 8 were sintered in a nitrogen-diluted hydrogen atmosphere flow in a temperature range of 1350 to 1450 ° C. for 30 to 120 minutes, and then switched to an Ar gas atmosphere. Sintering is performed under the condition that the sinter is slowly cooled from the sintering temperature to a temperature range of about 1200 ° C. at a rate of about 1 ° C./min, and then naturally cooled to room temperature (cooling in the atmosphere outside the sintering furnace). The TiN-based sintered bodies of the present invention (hereinafter referred to as "sintered bodies of the present invention") 1 to 8 shown in Table 3 were produced.

For comparison, various powders having the same average particle size as the powder for producing the sintered body of the present invention are blended so as to have the same blending composition as shown in Table 4, and raw material powders 11 to 18 are prepared, and then the raw materials are prepared. The powders 11 to 18 are filled in a ball mill and mixed to prepare a mixed powder 11 to 18, and the mixed powders 11 to 18 are dried and then press-molded at a pressure of 100 to 500 MPa to obtain a powder compact 11 ~ 18 was prepared.
Next, by sintering the powder compacts 11 to 18 under the conditions shown in Tables 2 and 5, the sintered body of the comparative example shown in Table 6 (hereinafter referred to as “comparative example sintered body”) 1 ~ 8 was prepared.

For reference, a WC-based cemented carbide sintered body was produced by the following method.
As raw material powders, WC powder and Co powder, both of which have an average particle size of 0.5 to 1 μm, are prepared, and these raw material powders are mixed in a ratio of WC: 90% by mass and Co: 10% by mass with a ball mill. After wet mixing for 24 hours and drying, it is press-molded into a green compact at a pressure of 100 MPa, and this green compact is sintered in a vacuum of 6 Pa under the conditions of a temperature of 1400 ° C. and a holding time of 1 hour. A hard alloy sintered body (hereinafter, simply referred to as “cemented carbide”) was formed.
By the above method, a WC-based cemented carbide sintered body 1 (hereinafter referred to as “reference example sintered body 1”) having a component composition of WC: 84 area% and Co: 16 area% was produced.

For further reference, a TiCN-based cermet sintered body was produced by the following method.
As the raw material powder, TiCN powder, Mo ₂ C powder, Co powder and Ni powder having an average particle size of 0.5 to 3 μm are prepared, and these raw material powders are used as TiCN: 75% by mass and Mo ₂ C: 10. It was blended in a ratio of mass%, Co: 7.5% by mass, Ni: 7.5% by mass, wet-mixed with a ball mill for 24 hours, dried, and then press-molded into a green compact at a pressure of 200 MPa, and this pressure was obtained. The powder was sintered in a vacuum of 6 Pa at a temperature of 1450 ° C. and a holding time of 1 hour to form a TiCN-based cermet sintered body (hereinafter, simply referred to as “cermet”).
By the above method, a TiCN-based cermet sintered body 2 (hereinafter referred to as “reference example sintered body 2”) having a component composition of TiMoCN: 90 area% and Co + Ni: 10 area% was produced.

Next, with respect to the sintered bodies 1 to 8 of the present invention and the comparative examples sintered bodies 1 to 8, the vertical cross section of the sintered body is measured by a scanning electron microscope (SEM) equipped with an energy dispersive X-ray analyzer (EDS). The vertical cross section was observed, the amount of contained elements in the measurement region (for example, the measurement region of 40 μm × 50 μm) in the obtained secondary electron image was measured, and the TiN phase, Mo _2C phase and Fe—Ni alloy phase were identified. The area ratio of each phase to the measurement area was calculated, the area ratio was calculated in the five measurement areas, and the average value of these calculated values was obtained as the area% of each phase in the sintered structure.
For the Fe—Ni alloy phase, the Ni content and Fe content in the phase were measured at 10 points on the Fe—Ni alloy phase using an Auger electron spectroscope, and the calculated values were obtained. The content ratio of Ni to the total content of Fe and Ni (= Ni × 100 / (Fe + Ni)) was determined as% by mass from the average value.
Tables 3 and 6 show these values.

Further, for the sintered bodies 1 to 8 of the present invention, the sintered bodies 1 to 8 of the comparative examples, and the sintered bodies 1 and 2 of the reference examples, a scanning electron microscope (SEM) equipped with an energy dispersive X-ray analyzer (EDS) is provided. The vertical cross section was observed in the above, the Mo content was measured, and the depth range of the low Mo region was determined based on the Mo content.
That is, the average value of the amount of Mo measured at five points near the center of the cross section of the vertical cross-section observation region (inside the sintered body at a depth of at least 500 μm from the surface of the sintered body) is the average Mo inside the sintered body. It was determined as the content. Further, a line segment having a length of 100 μm parallel to the surface of the sintered body is drawn every 10 μm from the surface of the sintered body to a position of 500 μm, and the amount of Mo is measured on the same line segment by an energy dispersive X-ray analyzer (EDS). The region where the average value of Mo amount on the line segment is 30 to 80% of the Mo amount inside the sintered body is determined as the low Mo region, and the depth range in which the low Mo region exists is determined. Identified.
Tables 3 and 6 show the average Mo content inside the sintered body and the depth range of the low Mo region from the surface of the sintered body obtained above.

Then, the vertical cross sections of the sintered bodies 1 to 8 of the present invention, the sintered bodies 1 to 8 of the comparative examples, and the sintered bodies 1 and 2 of the reference examples are subjected to a micro-hardness test (nano-indentation hardness test). The average value of the micro-hardness measured at 5 points in the low Mo region was obtained as the average micro-hardness, and the micro-hardness measured at 5 points inside the sintered body at a depth of at least 500 μm from the surface of the sintered body. The average value was determined as the average microhardness, and the ratio (%) of the average microhardness in the low Mo region to the average microhardness inside the sintered body was determined.
In the micro-hardness test, the micro-hardness HV (N / mm ² ) was measured every 10 μm over a range of 500 μm from the surface of the sintered body to the inside under the condition of a load of 10 g, and within the low Mo region. The average value of the measured values at the five points in the above is defined as the average microhardness, and the average value of the measured values at the five locations inside the sintered body at a depth of at least 500 μm from the surface of the sintered body is defined as the average microhardness. By dividing the average microhardness of the Mo region by the average microhardness inside the sintered body, the low Mo region with respect to the average microhardness inside the sintered body at a depth of at least 500 μm from the surface of the sintered body. The ratio (%) of the average microhardness of was calculated.
Of the sintered bodies 1 to 8 of the comparative examples and the sintered bodies 1 and 2 of the reference examples, those in which the low Mo region is not formed have an average fine hardness ratio of about 100 (%). Become.

Next, the insert shape of the ISO standard SEEN1203AFSN is obtained by grinding the sintered bodies 1 to 8 of the present invention, the sintered bodies 1 to 8 of the comparative examples, and the sintered bodies 1 and 2 of the reference examples produced above. Cutting tools made of the sintered body of the present invention (hereinafter referred to as "tools of the present invention") 1 to 8, comparative examples Cutting tools made of sintered bodies (hereinafter referred to as "comparative example tools") 1 to 8 and reference examples Cutting tools made of sintered body (hereinafter referred to as "reference example tools") 1 and 2 were manufactured.

The alloy steel shown below, in which the tools 1 to 8 of the present invention, the tools 1 to 8 of the comparative examples, and the tools 1 and 2 of the reference examples are all screwed to the tip of the tool steel cutter with a fixing jig. Wet front milling test was carried out, the flank wear width of the cutting edge was measured, and the wear state of the cutting edge was observed.
Cutting conditions:
Work material: JIS / SCM440 block material,
Cutting speed: 180 m / min,
Notch: 0.9 mm,
Feed: 0.3 mm / rev,
Cutting time: 15 minutes,
Table 7 shows the results of the cutting test.

Further, a hard coating layer having an average layer thickness shown in Table 8 is coated on the cutting edge surfaces of the tools 1 to 8 of the present invention, tools 1 to 8 of comparative examples and tools 1 and 2 of reference examples by the PVD method or the CVD method. , The covering tools 1 to 8 of the present invention, the covering tools 1 to 8 of the comparative examples, and the covering tools 1 and 2 of the reference examples were manufactured.
The wet face milling cutting test shown below was carried out for each of the above-mentioned coated tools, the flank wear width of the cutting edge was measured, and the wear state of the cutting edge was observed.
Cutting conditions:
Work material: JIS / SCM440 block material,
Cutting speed: 220 m / min,
Notch: 1.0 mm,
Feed: 0.3 mm / rev,
Cutting time: 10 minutes,
Table 9 shows the results of the cutting test.

As shown in Tables 7 and 9, the tools 1 to 8 of the present invention and the covering tools 1 to 8 of the present invention have abnormal damages such as chipping and chipping, respectively, like the reference example tool 1 and the reference example covering tool 1. Demonstrated excellent cutting performance over a long period of use without causing any problems.
However, since the toughness of Comparative Examples Tools 1 to 8 and Reference Example Tools 2 and Comparative Examples Covered Tools 1 to 8 and Reference Example Covered Tools 2 are not sufficient, the tool life is shortened due to abnormal damage such as chipping and chipping. It was short-lived.

Since the TiN-based sintered body of the present invention has excellent hardness and toughness, it can be applied not only as a cutting tool but also as a tough member and an abrasion resistant member in various technical fields. When used as a tool, it exhibits excellent wear resistance and abnormal damage resistance, so it exhibits excellent cutting performance over a long period of use, and is sufficient for labor saving, energy saving, and cost reduction in cutting. It is something that can respond to satisfaction.

Claims (3)

A TiN-based sintered body containing a TiN phase and a Mo _2C phase, the balance of which is a bonded phase.
(A) When observing the cross section of the sintered body, the average area ratio of the TiN phase in the sintered body is 70.0 to 91.5 area%, and the average area ratio of the Mo _2C phase is 3. 5 to 25.0 area%,
(B) The components of the bonded phase are Fe and Ni, the area ratio of the bonded phase is 5.0 to 15.0 area%, and the content ratio of Ni to the total content of Fe and Ni is 15. It is 0.0 to 35.0% by mass,
(C) A low Mo region is formed in a region from the surface of the sintered body to a depth of 50 to 300 μm toward the inside thereof, and the average Mo content in the low Mo region is the same as that of the sintered body. 30-80% of the average Mo content inside the sintered body at a depth of at least 500 μm from the surface .
(D) The average microhardness of the low Mo region is 70 to 90% of the average microhardness inside the sintered body at a depth of at least 500 μm from the surface of the sintered body. Base sintered body. A cutting tool made of a TiN-based sintered body according to claim 1, wherein the TiN-based sintered body is configured as at least a cutting edge. A surface-coated TiN-based sintered body cutting tool, characterized in that a hard coating layer is formed on at least the cutting edge of the TiN-based sintered body cutting tool according to claim 2.

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